review article recent approaches for broadening the

Review ArticleRecent Approaches for Broadening the Spectral Bandwidth inResonant Cavity Optoelectronic Devices

Gun Wu Ju1 Byung Hoon Na2 Yong-Hwa Park2 Young Min Song3 and Yong Tak Lee14

1School of Information and Communications Gwangju Institute of Science and Technology Gwangju 500-712 Republic of Korea2Imaging Device Lab Samsung Advanced Institute of Technology Suwon-si 443-803 Republic of Korea3Department of Electronics Engineering Pusan National University Busan 609-735 Republic of Korea4Advanced Photonics Research Institute Gwangju Institute of Science and Technology Gwangju 500-712 Republic of Korea

Correspondence should be addressed to Young Min Song ysongpusanackr and Yong Tak Lee ytleegistackr

Received 9 May 2015 Accepted 1 September 2015

Academic Editor Rosa Lukaszew

Copyright copy 2015 GunWu Ju et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Resonant cavity optoelectronic devices such as vertical cavity surface emitting lasers (VCSELs) resonant cavity enhancedphotodetectors (RCEPDs) and electroabsorption modulators (EAMs) show improved performance over their predecessors byplacing the active device structure inside a resonant cavity The effect of the optical cavity which allows wavelength selectivity andenhancement of the optical field due to resonance allows the devices to be made thinner and therefore faster while simultaneouslyincreasing the quantum efficiency at the resonant wavelengths However the narrow spectral bandwidth significantly reducesoperating tolerances which leads to severe problems in applications such as optical communication imaging and biosensingRecently in order to overcome such drawbacks andor to accomplishmultiple functionalities several approaches for broadening thespectral bandwidth in resonant cavity optoelectronic devices have been extensively studied This paper reviews the recent progressin techniques for wide spectral bandwidth that include a coupled microcavity asymmetric tandem quantum wells and high indexcontrast distributed Bragg-reflectors This review will describe design guidelines for specific devices together with experimentalconsiderations in practical applications

1 Introduction

Multilayer thin film growth and coatings have been inves-tigated for many years as distributed Bragg-reflector (DBR)or Fabry-Perot cavities to produce resonant enhancementin numerous optoelectronic devices such as light emittingdiodes [1] photodetectors [2] low-threshold lasers [3 4] andmodulators [5] Recently to achieve multiple functionalitiesit is necessary to optimize parameters related to performancesuch as the spectral bandwidth angular bandwidth wave-length selectivity and polarization In particular the widespectral bandwidth characteristic of optoelectronic devicesallows high manufacturing tolerance wide angular proper-ties and robust operation Several studies have demonstratedthese characteristics using microcavity structures asymmet-ric tandem quantum wells and high index contrast DBRstructures

In wavelength division multiplexed (WDM) systems itis desirable to have wavelength selective photodetectors withlow channel crosstalk at the channel spacing (lt4 nm) [6ndash8]The resonant cavity enhanced photodetector (RCEPD) bene-fits fromwavelength selectivity and a large increase of the res-onant optical field introduced by the Fabry-Perot cavityThinabsorption layers are inserted into a resonant cavity sand-wiched by two mirrors forming a Fabry-Perot cavity Thisresults in an increased optical field and therefore faster speedwhile simultaneously increasing the quantum efficiency atthe resonant wavelength [9] Narrow spectral bandwidth canbe achieved by adopting a high-119876 cavity design in the con-ventional single-cavity RCEPD structure or by employing anarrow-band Fabry-Perot filter However it is very importantto have a flat-topped passbandwhen the channel-aligning tol-erance between the transmitter and the receiver is consideredand thereby the system performance will not be sensitive

Hindawi Publishing CorporationAdvances in Condensed Matter PhysicsVolume 2015 Article ID 605170 11 pageshttpdxdoiorg1011552015605170

2 Advances in Condensed Matter Physics

to wavelength fluctuation in the transmitter or the resonantcontrol in the receiver [10] During the past two decadesnumerous theoretical and experimental methods have beenreported to address this crucial need [10ndash13] The conceptunderlying the designed structures was realizing a low losscavity for coupling with different mirrors such as compoundsemiconductors dielectric materials and Au metals

Another application using a coupled cavity is an elec-troabsorption modulator (EAM) used as an optical shutterin a three-dimensional (3D) image capturing system basedon time of flight This is a simple and inexpensive methodto realize a 3D image with a small system The basic 3Dimaging system consists of an active illumination light sourceas an optical transmitter and a demodulator and a detectoras a receiver The modulated light source travels towardthe object and the light reflected from the object reachesthe detector A 3D image of an object can be realizedby extracting distance information from the phase delaybetween the illuminated light and reflected light which isachieved using a large area optical shutter To obtain highresolution depth image information it is thus essential thatthe large area optical shutter has high performance suchas high modulation depth [14] and high-speed modulationwhich can increase the resolution depth [15] High-speedmodulation is obtained by utilizing the electroabsorptionmechanism of a multilayer structure which has an opticalresonance cavity and light absorption in quantum wells Theoptical shutter is positioned in front of a standard highresolution complementarymetal oxide semiconductor imagesensor The optical shutter modulates the incoming infraredimage to acquire the depth image [16] Despite advancesto improve the modulation speed and modulation depththis approach still suffers from relatively narrow spectralbandwidth due to the high quality factor of the Fabry-Perotcavity The narrow spectral bandwidth is also problematicsince the modulation depth degrades significantly as theemission wavelength of the light source used in the timeof flight based 3D imaging system varies according to tem-perature Moreover a narrow spectral bandwidth reducesthe manufacturing tolerance of the 3D imaging system andthe operating temperature range since the bandgap of asemiconductor material changes as the temperature changesThus in order to improve the operational reliability of 3Dimaging systems the EAM should be capable of operatingover a wide spectral bandwidth with high modulation depth

High index contrast DBR structures are used in a widerange of applications such as vertical cavity surface emittinglasers (VCSELs) filtering and wavelength division mul-tiplexing The reflectivity and spectral bandwidth directlydepend on the refractive index contrast between the highand low index materials Moreover a higher index contrastguarantees higher tolerance during the fabrication process ofthe DBRs because the deposition rate dramatically affects thequality of the optical reflective wavelength and highly tol-erant DBRs are required for low-cost fabrication Holonyakand coworkers have established a technique involving wetoxidation of AlAs [17ndash19] and have shown that AlAs can beoxidized without considerably affecting the GaAsAlAs DBRsystem Since the refractive index of oxidizedAlAs is low (15)

the combination of oxidized AlAs and GaAs shows favorableproperties of broad spectral bandwidth [19] Recently it wasshown that oblique-angle deposition (OAD) of materials forexample SiO

2 TiO2 ITO and amorphous silicon (a-Si) can

be used to fabricate DBR structures with optical propertiesthat can be controlled by the oblique angle [20ndash22] By con-trolling the angle of deposition and thereby the layer porosityand refractive index OAD allows easy fabrication of a DBRcomposed of a singlematerial chosen for its optical propertiesinwhich each layer has a different refractive index that is indi-vidually tuned to a specific desired value A novel subwave-length high index contrast grating (HCG) as a surface-normalbroadband reflector was later proposed by Chang-Hasnain[23 24] An HCG has been shown to replace conventionalDBRs for VCSELs and offers desirable attributes includinglithographically defined polarization [25] and wavelength[26] a large aperture while maintaining a single transversemode [25 27] and a large fabrication tolerance [28]

Here we summarize recent approaches to achieve widespectral bandwidth using a coupled microcavity asymmetrictandem quantum wells and high index contrast distributedBragg-reflector and assess the trends in this field We firstaddress two light absorption optoelectronic devices RCEPDsand EAMs using a coupled cavity structure for wide responseand transmittance respectively Next absorption couplingusing quantumwells of different thickness called asymmetrictandem quantum wells in an EAM for wide transmittancechange is described Finally wide spectral bandwidth usingoblique-angle deposition and high index contrast gratingtechniques is discussed

2 Flat Top Response of RCEPD

WDM is a key technology for increasing the transmissioncapacity of optical fiber communication systems [29 30]A high-speed and high-gain demultiplexing receiver is acrucial part of these systems A monolithic multiple wave-length demultiplexing device with a narrow interchannelwavelength spacing and low crosstalk between channels isessential for effective use of the available bandwidth

Since 1991 the RCEPD which is constructed by insertingan absorption layer into an integrated Fabry-Perot resonantcavity has been established as a promising device for WDMapplications because of its wavelength selectivity as well asits high-speed response In particular monolithic integrationof VCSEL and RCEPD can reduce alignment time lowerpackaging cost and provide design flexibility (Figure 1(a))[31 32] The problem of misalignment of the cavity-modewavelength of the emitter and RCEPD however significantlyaffects the system performance [30 33ndash35] As shown inFigure 1(b) misaligned operating wavelengths between theVCSEL and RCEPD can be changed by etching the top mostlayer of RCEPD [33 36] However the conventional RCEPDspectral response shapes are triangular which affects thesensitivity of system performance because of the extremelynarrow spectra of the VCSELs (Figure 1(c)) As shown inFigure 1(d) there is also a tradeoff between the quantumefficiency and the interchannel crosstalk parameter in theconventional RCEPD [37] To solve this issue low loss

Advances in Condensed Matter Physics 3

VCSEL RCE-PD

Solder

MMF MMFFiber block

sim2120583m sim75120583m

SI GaAs-substrate

(a)

VCSEL Heat

RCEPD

8482nm27 ∘C

8500nm528 ∘C

Tuning Heat

8482nm27 ∘C

8491nm27 ∘C

8500nm40 ∘C

(b)

After heatWO tuning

Before heat

minus60

minus45

minus30

minus60

minus45

minus30

VCSE

L op

tical

pow

er (d

Bm)

845 850 855 860840Wavelength (nm)

00

02

04

00

02

04

RCEP

D re

spon

sivity

(AW

)

840 845 850 855 860

(c)

842nm

847nm 851nm855nm

850 860840

Wavelength (nm)

000

005

010

015

020

025

030

035

040

045

050

REPD

resp

onsiv

ity (A

W)

00

02

04

06

08

10

VCSE

L op

tical

out

put (

norm

aliz

ed)

(d)

Figure 1 (a)The VCSEL array and RCEPD array are separately passive aligned with planar waveguides such as multimode fiber (MMF) [33](b) Schematic diagram of cavity-mode wavelength alignment by using cavity-mode tuning of RCEPD chips [33] and (c) the related spectrawithout alignment (d) The measured responsivity and CW lasing spectra of four elements from two RCEPD and VCSEL arrays in closeproximity to each other [34]

cavity is added to the top mirror and optically coupled inseries with the absorptive cavity of the conventional singleresonant cavity design [10 11 38] This flat top response withsharp edges reduces the interchannel crosstalk and improvesthe accuracy and stability of the system although lasingwavelength is changed

When two or more Fabry-Perot cavities are placed inseries a double-peak transmittance curve can be obtainedwhich has a more promising response shape This multiplehalf-wave cavities structures with three mirrors can be madeof quarter-wave stacks of semiconductor compounds ordielectric materials A theoretical analysis of the quantumefficiency of an InGaAsGaAsRCEPDwas presented by usingthis microcavity in place of the top DBR (Figure 2) Thequantum efficiency can amount to 100 with a sufficientlylarge quantity of bottom mirror pairs in a conventionalRCEPD (gray curve) On the other hand the flat-toppedquantum efficiency spectrum has been obtained in a coupledcavity RCEPD (black curve) This response can be explainedin consideration of phase conditions in the resonator Theelectromagnetic field between the mirrors almost does not

depend on wavelength when the slope of the phase change iszero on the wavelengthWhen the thickness of coupled cavityis thicker than quarter-wave resonant thickness the phasechange for the wavelength is zero As a result the reflectivityshows the flatness near the resonance wavelength [13]

The location of the absorption layer affects the responsecurve Two cavities have the same optical lengths as integraltimes of half resonant wavelength When the absorptionlayer is on the coupled cavity the quantum efficiency curveis hollow and much deeper for the top-illuminated device(Figure 3) Because the light from the top of the device issignificantly absorbed there is no coupling effect of electricfields by the coupled cavity Therefore the coupled cavity isplaced above the absorption cavity for a flat-topped response

3 Wide Spectral BandwidthElectroabsorption Modulator

Surface-normal EAMs based on the quantum confined Starkeffect are prime candidates for applications such as three-dimensional (3D) imaging systems [16 39]The development


QWSubstrate

N pair

405 pairs

High n

Low n

(a)

405 pairs

Active layer

Coupled cavity

QWSubstrate

High n

Low n

p pair

q pair

(b)

0

20

40

60

80

100

Qua

ntum

effici

ency

(120578a (

))

980 985970 975 990 995965

Wavelength (120582 (nm))

(c)

Figure 2 (a)The RCEPD structure with conventional RCEPD (b) RCEPD with coupled cavity and (c) calculated quantum efficiency of twoRCEPDs Grey curves illustrate results of calculation of conventional RCEPDs where119873 = 8 (solid curve) and119873 = 3 (dashed curve) Blackcurves illustrate results of calculation of RCEPD with coupled cavity where 119901 = 21 119902 = 45 (solid curve) and 119901 = 15 119902 = 15 (dashed curve)[13]

Top DBR

Bottom DBR

Middle DBR

Active layer

Coupled cavity

QWSubstrate

High n

Low n

(a)

Active layer

Coupled cavity

QWSubstrate

High n

Low n

(b)

1290 1295 1300 1305 1310

Wavelength (nm)

minus10

0

10

20

30

40

50

60

70

80

90

Qua

ntum

effici

ency

()

Active layer above the cavityActive layer below the cavity

(c)

Figure 3 (a)The RCEPD structure with the active layer above the cavity (b) RCEPD structure with the active layer below the cavity and (c)the calculated quantum efficiency of the two structures [12]

of an optical shutter using an EAM to obtain high resolutiondepth information in a time of flight based 3D imagingsystem was recently reported as shown in Figure 4 [16 40]Despite improving the modulation speed and depth EAMsstill have relatively narrow spectral bandwidth produced bythe Fabry-Perot cavity A narrow spectral bandwidth reducesthe manufacturing tolerance of the 3D imaging system and

the operating temperature range because the bandgap andrefractive index of a semiconductor material change as afunction of the temperature Thus the EAM should beable to operate over a wide spectral bandwidth with highmodulation depth in order to improve the reliability of 3Dimaging systems A thick absorption region results in widespectral bandwidth of the EAM but this results in a high


850nmGlass lid

p-pad

Polyimide

n-pad

GaAs sub

p-DBRi-MQWn-DBRn-InGaP

(a)

Active

p-top DBR

n-bottom DBR

AlGaAs (high n)AlGaAs (low n)GaAs

(b)

Active

p-top DBR


p-cavity

p-middle DBR

n-bottom DBR

(c)

Figure 4 (a) Top view image and cross-sectional schematic of 850 nm EAM [40] and (b) designed single-cavity and (c) coupled microcavityEAM structures

Max = 65

Min = 14

0V

ΔT = 51

0

01

02

03

04

05

06

07

08

09

1

Tran

smitt

ance

880820 850 860 870830 840

Wavelength (nm)

4nm

minus3Vminus5V

minus7Vminus93Vminus10V

(a)

minus0V (731)minus5V (713)minus10V (683)minus15V (599)minus20V (425)minus22V (324)

minus24V (254)minus25V (237)minus26V (236)minus27V (241)minus28V (260)

8nm

ΔT 495

0

10

20

30

40

50

60

70

80

90

100

Tran

smitt

ance

()

820 880810 850 860 870830 890840

Wavelength (nm)

Voff 731

Von 236

(b)

Figure 5 (a) Transmittance measurement for characterization of transmittance variation of the EAM for single-cavity structure [16] and (b)coupled microcavity structure [40]

operating voltage To solve this issue a coupled Fabry-Perotcavity structure used in band-pass filters [41ndash43] allows therealization of a rectangular transmittance band leading toa broad and flat spectrum for high transmittance And themeasured transmittances of the EAM for single-cavity andcoupledmicrocavity structures are shown in Figures 5(a) and

5(b) respectively Under zero bias the spectral bandwidth ofthe coupled microcavity is about 8 nm which is two timeswider than that of the single-cavity structure Furthermorethe transmittance change for the coupledmicrocavity EAM iscomparable with that of the single-cavity structure Howeverto achieve 50 transmittance change in coupled microcavity


Transmittance change ()

12

10

8

6

4

2

0

Num

ber o

f DBR

pai

rs (a

u)

835 840 845 850 855 860 865

Wavelength (nm)

0 10 20 30 40 50ltminus10 gt60

(a)

Transmittance change ()0 10 20 30 40 50ltminus10 gt60

0

2

4

6

8

10

12

Num

ber o

f DBR

pai

rs (a

u)

840 845 850 855 860 865835

Wavelength (nm)

(b)

A B

0V120583m81V120583m

minus20

minus10

0

10

20

30

40

50

60

70

80

90

100

Tran

smitt

ance

()

840 845 850 855 860 865835

Wavelength (nm)

minus20

minus10

0

10

20

30

40

50

60

70

80

90

100

Tran

smitt

ance

chan

ge (

)

(c)

A B

0V120583m81V120583m

minus20

minus10

0

10

20

30

40

50

60

70

80

90

100

Tran

smitt

ance

()

840 845 850 855 860 865835

Wavelength (nm)

minus20

minus10

0

10

20

30

40

50

60

70

80

90

100

Tran

smitt

ance

chan

ge (

)

(d)

Figure 6 Contour plots of the calculated transmittance change as a function of the number of pairs of DBR for a 7-120582 SC structure with (a)8 nm thick SQWs and (b) 885 nm ATQWs The transmittance and transmittance change at the dashed line AB of the (c) 8 nm thick SQWsand the (d) 885 nm ATQWs The insets of (a) and (b) schematically illustrate a SC structure with 8 nm thick SQWs and 885 nm ATQWsrespectively [61]

structure the pairs ofQWs are increased which result in highoperating voltage There is a tradeoff between transmittancecontrast and operating voltage in EAM structure

Another approach to broaden the spectral bandwidth is touse asymmetric tandem quantum wells (ATQWs) Whereasthe above techniques use coupling of the electric field in aDBR structure under zero bias ATQWs use coupling of lightabsorption in the active region under reverse bias Figure 6shows the contour plots and transmittance changes as afunction of DBR pairs for a 7-120582 single-cavity (SC) structureof 8 nm thick single quantum wells (SQWs) and 885 nmthick ATQWs The transmittance of the EAM decreasesunder reverse bias because of absorption of the quantum

well As shown in Figure 6(d) there are two absorptionresonances transmittance peaks under bias with ATQWs Itis noteworthy that the quantumwells with different thicknessabsorb broad wavelength As a result the spectral bandwidthof the transmittance change for a single cavity with ATQWswas improved in comparison with the single-cavity structurewith SQWs

4 Wide Stop Band of DBR

Normally DBRs consist of low index layers alternating withhigh index layers The semiconductor DBRs are grown bymolecular beam epitaxy or metal organic chemical vapor


(a) (b)

Figure 7 (a) SEM image of 5-period a-Sia-Si DBR fabricated on Si substrate The yellow line is an enlarged cross-sectional TEM image andan image of an a-Si DBR is shown in (b) [46]

deposition equipment for single crystal quality For highreflectivity semiconductor DBR pairsmust be repeatedmanytimes in excess of 20 pairs because of the low index contrastof the semiconductor DBR Thickness control is thus animportant parameter because it can change the spectral stopband and reflectivity To address this dielectric materialswith high index contrast are used for a wide stop band ofreflectivity These dielectric DBRs demonstrate a wide stopband with high reflectivity using relatively few layers

Figure 7 shows a-Si layers deposited on a Si substrateby an e-beam evaporator using inclined sample holders fortilted angle evaporationThe refractive index of the depositedfilm decreases as the oblique angle increases in the OADprocess [44 45] First a low index layer was deposited witha tilted angle The nanocolumnar layers have a separatepattern as shown in a cross-sectional scanning electronmicroscope (SEM) image The interface between the low andhigh index layers is relatively good in terms of distinguishingthe interface as seen in the TEM image hence the refractiveindex of the layers was decreased in a controllable manner

For comparison the reflectivity values ofDBRswith othergeneral material systems were calculated and the results areshown in Figure 8(a)The spectral bandwidth and reflectivityof a dielectric SiO

2TiO2DBR (Δ119899 = 10) are broader and

higher than those of a semiconductor GaAsAlAs DBR (Δ119899 =048) In an a-Sia-Si DBR (Δ119899 = 165) structure almost 100reflectivity was observed in a wavelength range from 1400 nmto 1800 nm and good agreement between the calculatedand measured results was observed Figure 8(b) shows thereflectivity spectra of fabricated a-Sia-Si DBRs as a functionof the number of periods A three-period a-Sia-Si DBR wassufficient to ensure high reflectivity that exceeded 97

The reflective property of the 210158401015840 full-wafer a-Sia-SiDBR with five periods was investigated experimentally [46]The relative reflectivity mapping was measured at a centerwavelength of 1550 nm (Figure 9(a)) There is only a smallvariation in the measured relative reflectivity with relatively

uniform reflectivity over the full-wafer The measured reflec-tivity of each position is marked in Figure 9(b) by spec-trophotometry measurement There was little difference inthe measured reflectivity of each position A wide stop band(800 nm) with only a five-period a-Sia-Si DBR was achievedexperimentally Therefore a-Sia-Si DBR is practical andinnovative for cost-effective optical components capable ofhigh levels of reflection

Recent innovations of one-dimensional and high-con-trast gratings (HCG) as a surface-normal broadband reflectorwere reported This grating provides a high contrast in therefractive indices for the gratingmedium and its surroundingmaterials This HCG can replace conventional DBRs forVCSELs as shown in Figure 10 [26 28 45 47ndash52] tunableVCSELs [47 53ndash55] and high-119876 optical resonators [56] Alsoby removing the quantum wells and turning the device suchthat it is totally passive all-pass filters can be constructed asphase tuners [57] These tunable devices can be further fab-ricated via large scale photonic integration By replacing theDBR with HCG the manufacturing cost can be reduced dueto thinner epitaxial layers and the microelectromechanicalstructure (MEMS) footprint also can be reduced leading toa more compact structure and higher integration capability

The design parameters for the structure include theindices of refraction of the high and low index materialsgrating period thickness and duty cycle [25 58ndash60] Whenthe period of the grating becomes smaller than the incidentwavelength which is known as a subwavelength gratingonly the zeroth diffraction order exists in the reflectedand transmitted waves and all the higher diffraction ordersare evanescent modes [58] This subwavelength grating willbasically operate as a simple mirror When the reflectiveindex of grating material has high contrast to surroundingsthe high and broad reflectivity are possible [59] The broadreflectivity can be optimized for one E-field orientation asshown in Figure 11This characteristic of polarization controlcan be designed with simple HCG structure


1009080706050403020100

Refle

ctan

ce (

)

1000 1200 1400 1600 1800 2000 2200 2400

Wavelength (nm)

Calculated result

GaAsAlAsa-Sia-SiSiO2TiO2

(a)

1009080706050403020100

Refle

ctan

ce (

)

1000 1200 1400 1600 1800 2000 2200 2400

Wavelength (nm)

High index contrast (HIC)a-Sia-Si DBRMeasured result120582center 1550nm

2 pair3 pair

4 pair5 pair

(b)

Figure 8 (a) Calculated reflectivity spectra of GaAsAlAs SiO2TiO2 and a-Sia-Si DBRs as a function of wavelength (b) Measured

reflectivity spectra of 2- 3- 4- and 5-period a-Sia-Si DBRs as a function of wavelength The center wavelength of every DBR was 1550 nm[46]

(V)

1500

1413

1325

1237

1150

1063

0976

0887

0800

Median 1477

(0063)

(a)1009080706050403020100

Refle

ctan

ce (

)

1000 1200 1400 1600 1800 2000 2200 2400

Wavelength (nm)

High index contrast (HIC)5-period a-Sia-Si DBRMeasured result120582center 1550nm

(b)

ABC

DE

Avge 1485

Std Dev 4235

Figure 9 (a) The relative reflectance mapping image of a 210158401015840 full-wafer DBR fabricated on a Si substrate The letters AndashE represent eachposition for measuring the reflectivity (b) The measured reflectivity of all positions of the DBR fabricated on a 210158401015840 Si wafer as a function ofwavelength [46]

Suspended HCG mirror

Sacrificial layer

M-pair p-DBRs Etchedsacrificial

layer

34 pairs of bottom n-DBRActive region

Figure 10 Schematic of a typical 850 nm design consisting of anHCG-based top mirror a 54-120582 air gap a 120582-cavity containing anactive region and a conventional semiconductor-based bottom 119899-DBR mirror Here119872 = 2 or 4 [47]

5 Summary

Recently developed techniques for wide spectral bandwidththat make it possible to realize multiple functionalities arereviewed The flat-topped response of a RCEPD with acoupled cavity can reduce the channel crosstalk and is notsensitive to wavelength fluctuation in the transmitter or res-onant control in the receiver in a WDM system Meanwhilean EAM with a coupled cavity as an optical shutter shows awide transmittance spectrum without a bias state MoreoverATQWs that consist of quantum wells with different thick-ness coupling light absorption under reverse bias result ina wide transmittance change These two structures help theEAM in 3D imaging systems which require operation withhigh reliability over a wide temperature range To increasethe reflectivity over a wide wavelength range the use ofhigh index contrast materials in tandem with oblique-angle


x

y

z

TM

a

t

Λ

(a)

x

y

z

a

t

Λ

TE

(b)

1

08

06

04

02

0

Refle

ctiv

ity

07 08 09 1

Wavelength (120583m)

995

TM

TE

(c)

TM

TE

1

08

06

04

02

0

Refle

ctiv

ity

07 08 09 1


995

(d)

Figure 11 Schematic of (a) TM-polarized (Λ = 380 nm 119886 = 130 nm and 119905 = 235 nm) and (b) TE-polarized (Λ = 620 nm 119886 = 400 nm and119905 = 140 nm) HCG Red arrows show the light propagation directions The black arrows show the E-field polarization directions Calculatedreflectivity spectra for surface-normal incident plane waves with E-field along the 119909 (blue) and 119910 (red) directions for (c) TM- and (d) TE-HCG The TM-HCG has a very high reflectivity for E-field aligned in the 119909 direction but significantly lower reflectivity for the 119910 directionThe opposite is true for TE-HCGThis enables polarization selection in HCG-VCSELs [25]

deposition which is independent of size features and sub-strate will provide an interesting new method that mayachieve improved performance in practical applications suchas light emitting diodes VCSELs and photovoltaics Alsoby replacing the DBR with HCG manufacturing costs canbe reduced due to thinner epitaxial layers and the MEMSfootprint can be reduced leading to amore compact structureandhigher integration capability Furthermore anHCGcouldbe a key component for producing devices that requireparticularly pure polarization characteristics The reviewedapproaches and design guidelines for wide spectral band-width in resonant cavity optoelectronic devices can be readilymerged with a variety of other optoelectronic devices

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work was partly supported by the Center for Inte-grated Smart Sensors funded by the Ministry of Science

ICT amp Future Planning as Global Frontier Project (CISS-2013M3A6A6073718) and by Basic Science Research Programthrough the National Research Foundation of Korea (NRF)funded by the Ministry of Science ICT amp Future Planning(2014R1A1A1005945) and by BK21PLUS Creative HumanResource Development Program for IT Convergence

References

[1] T Jeong H H Lee S-H Park J H Baek and J KLee ldquoInGaNAlGaN ultraviolet light-emitting diode with aTi3O5Al2O3distributed Bragg reflectorrdquo Japanese Journal of

Applied Physics vol 47 no 12 pp 8811ndash8814 2008[2] B Temelkuran E Ozbay J P Kavanaugh G Tuttle and K

M Ho ldquoResonant cavity enhanced detectors embedded inphotonic crystalsrdquo Applied Physics Letters vol 72 no 19 pp2376ndash2378 1998

[3] M Loncar T Yoshie A Scherer P Gogna and Y Qiu ldquoLow-threshold photonic crystal laserrdquoApplied Physics Letters vol 81no 15 pp 2680ndash2682 2002

[4] Y M Song K S Chang B H Na J S Yu and Y T Lee ldquoLowthermal resistance high-speed 980 nm asymmetric intracavity-contacted oxide-aperture VCSELsrdquo Physica Status Solidi (A)vol 206 no 7 pp 1631ndash1635 2009


[5] P R Villeneuve D S Abrams S Fan and J D JoannopoulosldquoSingle-modewaveguidemicrocavity for fast optical switchingrdquoOptics Letters vol 21 no 24 pp 2017ndash2019 1996

[6] A Sharkawy S Shi and D W Prather ldquoMultichannel wave-length division multiplexing with photonic crystalsrdquo AppliedOptics vol 40 no 14 pp 2247ndash2252 2001

[7] G T Paloczi J Scheuer and A Yariv ldquoCompact microring-based wavelength-selective inline optical reflectorrdquo IEEE Pho-tonics Technology Letters vol 17 no 2 pp 390ndash392 2005

[8] S T Chu B E Little W Pan T Kaneko S Sato and YKokubun ldquoAn eight-channel add-drop filter using verticallycoupled microring resonators over a cross gridrdquo IEEE PhotonicsTechnology Letters vol 11 no 6 pp 691ndash693 1999

[9] M S Unlu and S Strite ldquoResonant cavity enhanced photonicdevicesrdquo Journal of Applied Physics vol 78 no 2 pp 607ndash6391995

[10] S Y Hu E R Hegblom and L A Coldren ldquoCoupled-cavity resonant photodetectors for high-performance wave-length demultiplexing applicationsrdquoApplied Physics Letters vol71 no 2 pp 178ndash180 1997

[11] C-H Chen K Tetz and Y Fainman ldquoResonant-cavity-enhanced p-i-n photodiode with a broad quantum-efficiencyspectrum by use of an anomalous-dispersion mirrorrdquo AppliedOptics vol 44 no 29 pp 6131ndash6140 2005

[12] Y Zhong Z Pan L Li Y Huang and X Ren ldquoPropositionof a nearly rectangular response resonant cavity enhanced(RCE) photodetectorrdquo in Semiconductor Optoelectronic DeviceManufacturing and Applications vol 4602 of Proceedings ofSPIE pp 74ndash78 Nanjing China November 2001

[13] S V Gryshchenko A A Dyomin and V V Lysak ldquoTheoreticalstudy of the quantum efficiency of InGaAsGaAs resonant cav-ity enhanced photodetectorsrdquo inProceedings of the InternationalWorkshop on Optoelectronic Physics and Technology (OPT rsquo07)pp 20ndash22 IEEE Kharkov Ukraine June 2007

[14] R Lange and P Seitz ldquoSolid-state time-of-flight range camerardquoIEEE Journal of Quantum Electronics vol 37 no 3 pp 390ndash3972001

[15] S Gokturk H Yalcin and C Bamji ldquoA time-of-flight depthsensor-system description issues and solutionsrdquo in Proceedingsof the Conference on Computer Vision and Pattern RecognitionWorkshop p 35 Washington DC USA June 2004

[16] Y-H Park Y-C Cho J-W You et al ldquoMicro-optical systembased 3D imaging for full HD depth image capturingrdquo inMOEMS and Miniaturized Systems XI vol 8252 of Proceedingsof SPIE San Francisco Calif USA January 2012

[17] J M Dallesasse N Holonyak Jr A R Sugg T A Richardand N El-Zein ldquoHydrolyzation oxidation of AlxGa1-xAs-AlAs-GaAs quantumwell heterostructures and superlatticesrdquoAppliedPhysics Letters vol 57 no 26 pp 2844ndash2846 1990

[18] A R Sugg N Holonyak Jr J E Baker F A Kish andJ M Dallesasse ldquoNative oxide stabilization of AlAs-GaAsheterostructuresrdquo Applied Physics Letters vol 58 no 11 pp1199ndash1201 1991

[19] G W Pickrell J H Epple K L Chang K C Hsieh and KY Cheng ldquoImprovement of wet-oxidized Al

119909Ga1minus119909

As (119909 sim 1)through the use of AlAsGaAs digital alloysrdquo Applied PhysicsLetters vol 76 no 18 pp 2544ndash2546 2000

[20] M J Brett and M M Hawkeye ldquoMaterials science newmaterials at a glancerdquo Science vol 319 no 5867 pp 1192ndash11932008

[21] J-Q Xi M F Schubert J K Kim et al ldquoOptical thin-filmmaterials with low refractive index for broadband eliminationof Fresnel reflectionrdquoNature Photonics vol 1 no 3 pp 176ndash1792007

[22] J K Kim T Gessmann E F Schubert et al ldquoGaInN light-emitting diode with conductive omnidirectional reflector hav-ing a low-refractive-index indium-tin oxide layerrdquo AppliedPhysics Letters vol 88 no 1 Article ID 013501 2006

[23] C F R Mateus M C Y Huang Y Deng A R Neureuther andC J Chang-Hasnain ldquoUltrabroadband mirror using low-indexcladded subwavelength gratingrdquo IEEE Photonics TechnologyLetters vol 16 no 2 pp 518ndash520 2004

[24] C F R Mateus M C Y Huang L Chen C J Chang-Hasnainand Y Suzuki ldquoBroad-band mirror (112-162 120583m) using asubwavelength gratingrdquo IEEE Photonics Technology Letters vol16 no 7 pp 1676ndash1678 2004

[25] C J Chang-Hasnain Y Zhou M C Y Huang and C ChaseldquoHigh-contrast grating VCSELsrdquo IEEE Journal on SelectedTopics in Quantum Electronics vol 15 no 3 pp 869ndash878 2009

[26] V Karagodsky B Pesala C Chase W Hofmann F Koyamaand C J Chang-Hasnain ldquoMonolithically integrated multi-wavelength VCSEL arrays using high-contrast gratingsrdquo OpticsExpress vol 18 no 2 pp 694ndash699 2010

[27] C Chase Y Rao W Hofmann and C J Chang-Hasnain ldquo1550nm high contrast grating VCSELrdquoOptics Express vol 18 no 15pp 15461ndash15466 2010

[28] Y Zhou M C Y Huang and C J Chang-Hasnain ldquoLargefabrication tolerance for VCSELs using high-contrast gratingrdquoIEEE Photonics Technology Letters vol 20 no 6 pp 434ndash4362008

[29] C A Brackett ldquoDense wavelength division multiplexing net-works Principles and applicationsrdquo IEEE Journal on SelectedAreas in Communications vol 8 no 6 pp 948ndash964 1990

[30] A Alduino Y Zhou S Luong C PHains and J Cheng ldquoWave-length multiplexing and demultiplexing using multiwavelengthVCSEL and resonance-enhanced photodetector arraysrdquo IEEEPhotonics Technology Letters vol 10 no 9 pp 1310ndash1312 1998

[31] Y M Song B K Jeong B H Na K S Chang J S Yu andY T Lee ldquoHigh-speed characteristics of vertical cavity surfaceemitting lasers and resonant-cavity-enhanced photodetectorsbased on intracavity-contacted structurerdquo Applied Optics vol48 no 25 pp F11ndashF17 2009

[32] B K Jeong Y M Song V V Lysak and Y T Lee ldquoLargearea InGaAsGaAs resonant cavity enhanced photodetector forsensor applicationrdquo Journal of Optoelectronics and AdvancedMaterials vol 10 no 10 pp 2547ndash2554 2008

[33] I-S Chung and Y T Lee ldquoA method to tune the cavity-modewavelength of resonant cavity-enhanced photodetectors forbidirectional optical interconnectsrdquo IEEE Photonics TechnologyLetters vol 18 no 1 pp 46ndash48 2006

[34] S O Luong G GOrtiz Y Zhou et al ldquoMonolithic wavelength-graded VCSEL and resonance-enhanced photodetector arraysfor parallel optical interconnectsrdquo IEEE Photonics TechnologyLetters vol 10 no 5 pp 642ndash644 1998

[35] Y Zhou J Cheng and A A Allerman ldquoHigh-speedwavelength-division multiplexing and demultiplexing usingmonolithic quasi-planar VCSEL and resonant photodetectorarrays with strained InGaAs quantum wellsrdquo IEEE PhotonicsTechnology Letters vol 12 no 2 pp 122ndash124 2000

[36] Y M Song K S Chang B H Na J S Yu and Y T LeeldquoPrecise etch-depth control of microlens-integrated intracavity


contacted vertical-cavity surface-emitting lasers by in-situ laserreflectometry and reflectivity modelingrdquo Thin Solid Films vol517 no 19 pp 5773ndash5778 2009

[37] K Kishino M S Unlu J-I Chyi J Reed L Arsenault andHMorkoc ldquoResonant cavity-enhanced (RCE) photodetectorsrdquoIEEE Journal of Quantum Electronics vol 27 no 8 pp 2025ndash2034 1991

[38] M Gokkavas G Ulu O Dosunmu R P Mirin andM S UnluldquoResonant cavity enhanced photodiodes with a broadenedspectral peakrdquo in Proceedings of the 14th Annual Meeting of theIEEE Lasers and Electro-Optics Society (LEOS rsquo01) vol 2 pp768ndash769 IEEE San Diego Calif USA November 2001

[39] B H Na GW Ju H J Choi Y C Cho Y H Park and Y T LeeldquoLarge aperture asymmetric Fabry Perot modulator based onasymmetric tandem quantum well for low voltage operationrdquoOptics Express vol 20 no 6 pp 6003ndash6009 2012

[40] S H Lee C Y Park J-W You H Yoon Y-C Cho and Y-H Park ldquo850 nm IR transmissive electro-absorptionmodulatorusing GaAs micromachiningrdquo Sensors and Actuators A Physi-cal vol 197 pp 47ndash52 2013

[41] S A Alboon andRG Lindquist ldquoFlat top liquid crystal tunablefilter using coupled Fabry-Perot cavitiesrdquoOptics Express vol 16no 1 pp 231ndash236 2008

[42] A A M Saleh and J Stone ldquoTwo-stage Fabry-Perot filters asdemultiplexers in optical FDMA LANrsquosrdquo Journal of LightwaveTechnology vol 7 no 2 pp 323ndash330 1989

[43] E Dorjgotov A Bhowmik and P Bos ldquoDesign of a widebandwidth switchable mirror based on a liquid crystal etalonrdquoJournal of Applied Physics vol 105 no 10 Article ID 1049062009

[44] Y Zhong Y C Shin C M Kim et al ldquoOptical and electricalproperties of indium tin oxide thin films with tilted and spiralmicrostructures prepared by oblique angle depositionrdquo Journalof Materials Research vol 23 no 9 pp 2500ndash2505 2008

[45] K Robbie and M J Brett ldquoSculptured thin films and glancingangle deposition growth mechanics and applicationsrdquo Journalof Vacuum Science and Technology A Vacuum Surfaces andFilms vol 15 no 3 pp 1460ndash1465 1997

[46] S J Jang Y M Song C I Yeo C Y Park and Y T Lee ldquoHighlytolerant a-Si distributed Bragg reflector fabricated by obliqueangle depositionrdquo Optical Materials Express vol 1 no 3 pp451ndash457 2011

[47] M C Y Huang Y Zhou and C J Chang-Hasnain ldquoA surface-emitting laser incorporating a high-index-contrast subwave-length gratingrdquoNature Photonics vol 1 no 2 pp 119ndash122 2007

[48] C Chase Y Zhou and C J Chang-Hasnain ldquoSize effect of highcontrast gratings in VCSELsrdquo Optics Express vol 17 no 26 pp24002ndash24007 2009

[49] W Hofmann C Chase M Muller et al ldquoLong-wavelengthhigh-contrast grating vertical-cavity surface-emitting laserrdquoIEEE Photonics Journal vol 2 no 3 pp 415ndash422 2010

[50] P Gilet N Olivier P Grosse et al ldquoHigh-index-contrast sub-wavelength grating VCSELrdquo inVertical-Cavity Surface-EmittingLasers XIV vol 7615 of Proceedings of SPIE p 76150J SanFrancisco Calif USA January 2010

[51] S Boutami B Benbakir J-L Leclercq and P ViktorovitchldquoCompact and polarization controlled 155 120583m vertical-cavitysurface-emitting laser using single-layer photonic crystal mir-rorrdquoApplied Physics Letters vol 91 no 7 Article ID 071105 2007

[52] S Boutami B Benbakir X Letartre J L Leclercq P Regrenyand P Viktorovitch ldquoUltimate vertical Fabry-Perot cavity based

on single-layer photonic crystal mirrorsrdquoOptics Express vol 15no 19 pp 12443ndash12449 2007

[53] I-S Chung J Moslashrk P Gilet and A Chelnokov ldquoSubwave-length grating-mirror VCSEL with a thin oxide gaprdquo IEEEPhotonics Technology Letters vol 20 no 2 pp 105ndash107 2008

[54] M C Y Huang Y Zhou and C J Chang-Hasnain ldquoAnanoelectromechanical tunable laserrdquo Nature Photonics vol 2no 3 pp 180ndash184 2008

[55] I-S Chung V Iakovlev A Sirbu et al ldquoBroadband MEMS-tunable high-index-contrast subwavelength grating long-wavelength VCSELrdquo IEEE Journal of Quantum Electronics vol46 no 9 pp 1245ndash1253 2010

[56] Y Zhou M C Y Huang C Chase et al ldquoHigh-index-contrastgrating (HCG) and Its applications in optoelectronic devicesrdquoIEEE Journal on Selected Topics in Quantum Electronics vol 15no 5 pp 1485ndash1499 2009

[57] W Yang T Sun Y Rao et al ldquoHigh speed optical phased arrayusing high contrast grating all-pass filtersrdquo Optics Express vol22 no 17 pp 20038ndash20044 2014

[58] C J Chang-Hasnain ldquoHigh-contrast gratings as a new platformfor integrated optoelectronicsrdquo Semiconductor Science andTech-nology vol 26 no 1 Article ID 014043 2011

[59] C J Chang-Hasnain and W Yang ldquoHigh-contrast gratings forintegrated optoelectronicsrdquo Advances in Optics and Photonicsvol 4 no 3 pp 379ndash440 2012

[60] C Chang-Hasnain and W Yang ldquoIntegrated optics using highcontrast gratingsrdquo in Photonics D L Andrews Ed chapter 2pp 57ndash105 John Wiley amp Sons 2015

[61] B H Na G W Ju H J Choi et al ldquoWide spectral bandwidthelectro-absorption modulator using coupled micro-cavity withasymmetric tandem quantum wellrdquo Optics Express vol 20 no17 pp 19511ndash19519 2012

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

High Energy PhysicsAdvances in

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


FluidsJournal of

Atomic and Molecular Physics

Journal of



Advances in Condensed Matter Physics

OpticsInternational Journal of



AstronomyAdvances in

International Journal of


Superconductivity


Statistical MechanicsInternational Journal of


GravityJournal of


AstrophysicsJournal of


Physics Research International


Solid State PhysicsJournal of

Computational Methods in Physics

Journal of



Soft MatterJournal of

Hindawi Publishing Corporationhttpwwwhindawicom

AerodynamicsJournal of

Volume 2014


PhotonicsJournal of


Journal of

Biophysics


ThermodynamicsJournal of


to wavelength fluctuation in the transmitter or the resonantcontrol in the receiver [10] During the past two decadesnumerous theoretical and experimental methods have beenreported to address this crucial need [10ndash13] The conceptunderlying the designed structures was realizing a low losscavity for coupling with different mirrors such as compoundsemiconductors dielectric materials and Au metals

Another application using a coupled cavity is an elec-troabsorption modulator (EAM) used as an optical shutterin a three-dimensional (3D) image capturing system basedon time of flight This is a simple and inexpensive methodto realize a 3D image with a small system The basic 3Dimaging system consists of an active illumination light sourceas an optical transmitter and a demodulator and a detectoras a receiver The modulated light source travels towardthe object and the light reflected from the object reachesthe detector A 3D image of an object can be realizedby extracting distance information from the phase delaybetween the illuminated light and reflected light which isachieved using a large area optical shutter To obtain highresolution depth image information it is thus essential thatthe large area optical shutter has high performance suchas high modulation depth [14] and high-speed modulationwhich can increase the resolution depth [15] High-speedmodulation is obtained by utilizing the electroabsorptionmechanism of a multilayer structure which has an opticalresonance cavity and light absorption in quantum wells Theoptical shutter is positioned in front of a standard highresolution complementarymetal oxide semiconductor imagesensor The optical shutter modulates the incoming infraredimage to acquire the depth image [16] Despite advancesto improve the modulation speed and modulation depththis approach still suffers from relatively narrow spectralbandwidth due to the high quality factor of the Fabry-Perotcavity The narrow spectral bandwidth is also problematicsince the modulation depth degrades significantly as theemission wavelength of the light source used in the timeof flight based 3D imaging system varies according to tem-perature Moreover a narrow spectral bandwidth reducesthe manufacturing tolerance of the 3D imaging system andthe operating temperature range since the bandgap of asemiconductor material changes as the temperature changesThus in order to improve the operational reliability of 3Dimaging systems the EAM should be capable of operatingover a wide spectral bandwidth with high modulation depth

High index contrast DBR structures are used in a widerange of applications such as vertical cavity surface emittinglasers (VCSELs) filtering and wavelength division mul-tiplexing The reflectivity and spectral bandwidth directlydepend on the refractive index contrast between the highand low index materials Moreover a higher index contrastguarantees higher tolerance during the fabrication process ofthe DBRs because the deposition rate dramatically affects thequality of the optical reflective wavelength and highly tol-erant DBRs are required for low-cost fabrication Holonyakand coworkers have established a technique involving wetoxidation of AlAs [17ndash19] and have shown that AlAs can beoxidized without considerably affecting the GaAsAlAs DBRsystem Since the refractive index of oxidizedAlAs is low (15)

the combination of oxidized AlAs and GaAs shows favorableproperties of broad spectral bandwidth [19] Recently it wasshown that oblique-angle deposition (OAD) of materials forexample SiO

2 TiO2 ITO and amorphous silicon (a-Si) can

be used to fabricate DBR structures with optical propertiesthat can be controlled by the oblique angle [20ndash22] By con-trolling the angle of deposition and thereby the layer porosityand refractive index OAD allows easy fabrication of a DBRcomposed of a singlematerial chosen for its optical propertiesinwhich each layer has a different refractive index that is indi-vidually tuned to a specific desired value A novel subwave-length high index contrast grating (HCG) as a surface-normalbroadband reflector was later proposed by Chang-Hasnain[23 24] An HCG has been shown to replace conventionalDBRs for VCSELs and offers desirable attributes includinglithographically defined polarization [25] and wavelength[26] a large aperture while maintaining a single transversemode [25 27] and a large fabrication tolerance [28]

Here we summarize recent approaches to achieve widespectral bandwidth using a coupled microcavity asymmetrictandem quantum wells and high index contrast distributedBragg-reflector and assess the trends in this field We firstaddress two light absorption optoelectronic devices RCEPDsand EAMs using a coupled cavity structure for wide responseand transmittance respectively Next absorption couplingusing quantumwells of different thickness called asymmetrictandem quantum wells in an EAM for wide transmittancechange is described Finally wide spectral bandwidth usingoblique-angle deposition and high index contrast gratingtechniques is discussed

2 Flat Top Response of RCEPD

WDM is a key technology for increasing the transmissioncapacity of optical fiber communication systems [29 30]A high-speed and high-gain demultiplexing receiver is acrucial part of these systems A monolithic multiple wave-length demultiplexing device with a narrow interchannelwavelength spacing and low crosstalk between channels isessential for effective use of the available bandwidth

Since 1991 the RCEPD which is constructed by insertingan absorption layer into an integrated Fabry-Perot resonantcavity has been established as a promising device for WDMapplications because of its wavelength selectivity as well asits high-speed response In particular monolithic integrationof VCSEL and RCEPD can reduce alignment time lowerpackaging cost and provide design flexibility (Figure 1(a))[31 32] The problem of misalignment of the cavity-modewavelength of the emitter and RCEPD however significantlyaffects the system performance [30 33ndash35] As shown inFigure 1(b) misaligned operating wavelengths between theVCSEL and RCEPD can be changed by etching the top mostlayer of RCEPD [33 36] However the conventional RCEPDspectral response shapes are triangular which affects thesensitivity of system performance because of the extremelynarrow spectra of the VCSELs (Figure 1(c)) As shown inFigure 1(d) there is also a tradeoff between the quantumefficiency and the interchannel crosstalk parameter in theconventional RCEPD [37] To solve this issue low loss


VCSEL RCE-PD

Solder

MMF MMFFiber block

sim2120583m sim75120583m

SI GaAs-substrate

(a)

VCSEL Heat

RCEPD

8482nm27 ∘C

8500nm528 ∘C

Tuning Heat

8482nm27 ∘C

8491nm27 ∘C

8500nm40 ∘C

(b)

After heatWO tuning

Before heat

minus60

minus45

minus30

minus60

minus45

minus30

VCSE

L op

tical

pow

er (d

Bm)

845 850 855 860840Wavelength (nm)

00

02

04

00

02

04

RCEP

D re

spon

sivity

(AW

)

840 845 850 855 860

(c)

842nm

847nm 851nm855nm

850 860840

Wavelength (nm)

000

005

010

015

020

025

030

035

040

045

050

REPD

resp

onsiv

ity (A

W)

00

02

04

06

08

10

VCSE

L op

tical

out

put (

norm

aliz

ed)

(d)









QWSubstrate

N pair

405 pairs

High n

Low n

(a)

405 pairs

Active layer

Coupled cavity

QWSubstrate

High n

Low n

p pair

q pair

(b)

0

20

40

60

80

100

Qua

ntum

effici

ency

(120578a (

))

980 985970 975 990 995965


(c)


Top DBR

Bottom DBR

Middle DBR

Active layer

Coupled cavity

QWSubstrate

High n

Low n

(a)

Active layer

Coupled cavity

QWSubstrate

High n

Low n

(b)

1290 1295 1300 1305 1310

Wavelength (nm)

minus10

0

10

20

30

40

50

60

70

80

90

Qua

ntum

effici

ency

()


(c)





850nmGlass lid

p-pad

Polyimide

n-pad

GaAs sub


(a)

Active

p-top DBR

n-bottom DBR


(b)

Active

p-top DBR


p-cavity

p-middle DBR

n-bottom DBR

(c)


Max = 65

Min = 14

0V

ΔT = 51

0

01

02

03

04

05

06

07

08

09

1

Tran

smitt

ance

880820 850 860 870830 840

Wavelength (nm)

4nm

minus3Vminus5V


(a)



8nm

ΔT 495

0

10

20

30

40

50

60

70

80

90

100

Tran

smitt

ance

()

820 880810 850 860 870830 890840

Wavelength (nm)

Voff 731

Von 236

(b)






12

10

8

6

4

2

0

Num

ber o

f DBR

pai

rs (a

u)

835 840 845 850 855 860 865

Wavelength (nm)

0 10 20 30 40 50ltminus10 gt60

(a)


0

2

4

6

8

10

12

Num

ber o

f DBR

pai

rs (a

u)

840 845 850 855 860 865835

Wavelength (nm)

(b)

A B

0V120583m81V120583m

minus20

minus10

0

10

20

30

40

50

60

70

80

90

100

Tran

smitt

ance

()

840 845 850 855 860 865835

Wavelength (nm)

minus20

minus10

0

10

20

30

40

50

60

70

80

90

100

Tran

smitt

ance

chan

ge (

)

(c)

A B

0V120583m81V120583m

minus20

minus10

0

10

20

30

40

50

60

70

80

90

100

Tran

smitt

ance

()

840 845 850 855 860 865835

Wavelength (nm)

minus20

minus10

0

10

20

30

40

50

60

70

80

90

100

Tran

smitt

ance

chan

ge (

)

(d)








(a) (b)












1009080706050403020100

Refle

ctan

ce (

)

1000 1200 1400 1600 1800 2000 2200 2400

Wavelength (nm)

Calculated result


(a)

1009080706050403020100

Refle

ctan

ce (

)

1000 1200 1400 1600 1800 2000 2200 2400

Wavelength (nm)


2 pair3 pair

4 pair5 pair

(b)



(V)

1500

1413

1325

1237

1150

1063

0976

0887

0800

Median 1477

(0063)

(a)1009080706050403020100

Refle

ctan

ce (

)

1000 1200 1400 1600 1800 2000 2200 2400

Wavelength (nm)


(b)

ABC

DE

Avge 1485

Std Dev 4235



Sacrificial layer


layer



5 Summary



x

y

z

TM

a

t

Λ

(a)

x

y

z

a

t

Λ

TE

(b)

1

08

06

04

02

0

Refle

ctiv

ity

07 08 09 1


995

TM

TE

(c)

TM

TE

1

08

06

04

02

0

Refle

ctiv

ity

07 08 09 1


995

(d)





Acknowledgments



References






















119909Ga1minus119909




















































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




VCSEL RCE-PD

Solder

MMF MMFFiber block

sim2120583m sim75120583m

SI GaAs-substrate

(a)

VCSEL Heat

RCEPD

8482nm27 ∘C

8500nm528 ∘C

Tuning Heat

8482nm27 ∘C

8491nm27 ∘C

8500nm40 ∘C

(b)

After heatWO tuning

Before heat

minus60

minus45

minus30

minus60

minus45

minus30

VCSE

L op

tical

pow

er (d

Bm)

845 850 855 860840Wavelength (nm)

00

02

04

00

02

04

RCEP

D re

spon

sivity

(AW

)

840 845 850 855 860

(c)

842nm

847nm 851nm855nm

850 860840

Wavelength (nm)

000

005

010

015

020

025

030

035

040

045

050

REPD

resp

onsiv

ity (A

W)

00

02

04

06

08

10

VCSE

L op

tical

out

put (

norm

aliz

ed)

(d)









QWSubstrate

N pair

405 pairs

High n

Low n

(a)

405 pairs

Active layer

Coupled cavity

QWSubstrate

High n

Low n

p pair

q pair

(b)

0

20

40

60

80

100

Qua

ntum

effici

ency

(120578a (

))

980 985970 975 990 995965


(c)


Top DBR

Bottom DBR

Middle DBR

Active layer

Coupled cavity

QWSubstrate

High n

Low n

(a)

Active layer

Coupled cavity

QWSubstrate

High n

Low n

(b)

1290 1295 1300 1305 1310

Wavelength (nm)

minus10

0

10

20

30

40

50

60

70

80

90

Qua

ntum

effici

ency

()


(c)





850nmGlass lid

p-pad

Polyimide

n-pad

GaAs sub


(a)

Active

p-top DBR

n-bottom DBR


(b)

Active

p-top DBR


p-cavity

p-middle DBR

n-bottom DBR

(c)


Max = 65

Min = 14

0V

ΔT = 51

0

01

02

03

04

05

06

07

08

09

1

Tran

smitt

ance

880820 850 860 870830 840

Wavelength (nm)

4nm

minus3Vminus5V


(a)



8nm

ΔT 495

0

10

20

30

40

50

60

70

80

90

100

Tran

smitt

ance

()

820 880810 850 860 870830 890840

Wavelength (nm)

Voff 731

Von 236

(b)






12

10

8

6

4

2

0

Num

ber o

f DBR

pai

rs (a

u)

835 840 845 850 855 860 865

Wavelength (nm)

0 10 20 30 40 50ltminus10 gt60

(a)


0

2

4

6

8

10

12

Num

ber o

f DBR

pai

rs (a

u)

840 845 850 855 860 865835

Wavelength (nm)

(b)

A B

0V120583m81V120583m

minus20

minus10

0

10

20

30

40

50

60

70

80

90

100

Tran

smitt

ance

()

840 845 850 855 860 865835

Wavelength (nm)

minus20

minus10

0

10

20

30

40

50

60

70

80

90

100

Tran

smitt

ance

chan

ge (

)

(c)

A B

0V120583m81V120583m

minus20

minus10

0

10

20

30

40

50

60

70

80

90

100

Tran

smitt

ance

()

840 845 850 855 860 865835

Wavelength (nm)

minus20

minus10

0

10

20

30

40

50

60

70

80

90

100

Tran

smitt

ance

chan

ge (

)

(d)








(a) (b)












1009080706050403020100

Refle

ctan

ce (

)

1000 1200 1400 1600 1800 2000 2200 2400

Wavelength (nm)

Calculated result


(a)

1009080706050403020100

Refle

ctan

ce (

)

1000 1200 1400 1600 1800 2000 2200 2400

Wavelength (nm)


2 pair3 pair

4 pair5 pair

(b)



(V)

1500

1413

1325

1237

1150

1063

0976

0887

0800

Median 1477

(0063)

(a)1009080706050403020100

Refle

ctan

ce (

)

1000 1200 1400 1600 1800 2000 2200 2400

Wavelength (nm)


(b)

ABC

DE

Avge 1485

Std Dev 4235



Sacrificial layer


layer



5 Summary



x

y

z

TM

a

t

Λ

(a)

x

y

z

a

t

Λ

TE

(b)

1

08

06

04

02

0

Refle

ctiv

ity

07 08 09 1


995

TM

TE

(c)

TM

TE

1

08

06

04

02

0

Refle

ctiv

ity

07 08 09 1


995

(d)





Acknowledgments



References






















119909Ga1minus119909




















































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




QWSubstrate

N pair

405 pairs

High n

Low n

(a)

405 pairs

Active layer

Coupled cavity

QWSubstrate

High n

Low n

p pair

q pair

(b)

0

20

40

60

80

100

Qua

ntum

effici

ency

(120578a (

))

980 985970 975 990 995965


(c)


Top DBR

Bottom DBR

Middle DBR

Active layer

Coupled cavity

QWSubstrate

High n

Low n

(a)

Active layer

Coupled cavity

QWSubstrate

High n

Low n

(b)

1290 1295 1300 1305 1310

Wavelength (nm)

minus10

0

10

20

30

40

50

60

70

80

90

Qua

ntum

effici

ency

()


(c)





850nmGlass lid

p-pad

Polyimide

n-pad

GaAs sub


(a)

Active

p-top DBR

n-bottom DBR


(b)

Active

p-top DBR


p-cavity

p-middle DBR

n-bottom DBR

(c)


Max = 65

Min = 14

0V

ΔT = 51

0

01

02

03

04

05

06

07

08

09

1

Tran

smitt

ance

880820 850 860 870830 840

Wavelength (nm)

4nm

minus3Vminus5V


(a)



8nm

ΔT 495

0

10

20

30

40

50

60

70

80

90

100

Tran

smitt

ance

()

820 880810 850 860 870830 890840

Wavelength (nm)

Voff 731

Von 236

(b)






12

10

8

6

4

2

0

Num

ber o

f DBR

pai

rs (a

u)

835 840 845 850 855 860 865

Wavelength (nm)

0 10 20 30 40 50ltminus10 gt60

(a)


0

2

4

6

8

10

12

Num

ber o

f DBR

pai

rs (a

u)

840 845 850 855 860 865835

Wavelength (nm)

(b)

A B

0V120583m81V120583m

minus20

minus10

0

10

20

30

40

50

60

70

80

90

100

Tran

smitt

ance

()

840 845 850 855 860 865835

Wavelength (nm)

minus20

minus10

0

10

20

30

40

50

60

70

80

90

100

Tran

smitt

ance

chan

ge (

)

(c)

A B

0V120583m81V120583m

minus20

minus10

0

10

20

30

40

50

60

70

80

90

100

Tran

smitt

ance

()

840 845 850 855 860 865835

Wavelength (nm)

minus20

minus10

0

10

20

30

40

50

60

70

80

90

100

Tran

smitt

ance

chan

ge (

)

(d)








(a) (b)












1009080706050403020100

Refle

ctan

ce (

)

1000 1200 1400 1600 1800 2000 2200 2400

Wavelength (nm)

Calculated result


(a)

1009080706050403020100

Refle

ctan

ce (

)

1000 1200 1400 1600 1800 2000 2200 2400

Wavelength (nm)


2 pair3 pair

4 pair5 pair

(b)



(V)

1500

1413

1325

1237

1150

1063

0976

0887

0800

Median 1477

(0063)

(a)1009080706050403020100

Refle

ctan

ce (

)

1000 1200 1400 1600 1800 2000 2200 2400

Wavelength (nm)


(b)

ABC

DE

Avge 1485

Std Dev 4235



Sacrificial layer


layer



5 Summary



x

y

z

TM

a

t

Λ

(a)

x

y

z

a

t

Λ

TE

(b)

1

08

06

04

02

0

Refle

ctiv

ity

07 08 09 1


995

TM

TE

(c)

TM

TE

1

08

06

04

02

0

Refle

ctiv

ity

07 08 09 1


995

(d)





Acknowledgments



References






















119909Ga1minus119909




















































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




850nmGlass lid

p-pad

Polyimide

n-pad

GaAs sub


(a)

Active

p-top DBR

n-bottom DBR


(b)

Active

p-top DBR


p-cavity

p-middle DBR

n-bottom DBR

(c)


Max = 65

Min = 14

0V

ΔT = 51

0

01

02

03

04

05

06

07

08

09

1

Tran

smitt

ance

880820 850 860 870830 840

Wavelength (nm)

4nm

minus3Vminus5V


(a)



8nm

ΔT 495

0

10

20

30

40

50

60

70

80

90

100

Tran

smitt

ance

()

820 880810 850 860 870830 890840

Wavelength (nm)

Voff 731

Von 236

(b)






12

10

8

6

4

2

0

Num

ber o

f DBR

pai

rs (a

u)

835 840 845 850 855 860 865

Wavelength (nm)

0 10 20 30 40 50ltminus10 gt60

(a)


0

2

4

6

8

10

12

Num

ber o

f DBR

pai

rs (a

u)

840 845 850 855 860 865835

Wavelength (nm)

(b)

A B

0V120583m81V120583m

minus20

minus10

0

10

20

30

40

50

60

70

80

90

100

Tran

smitt

ance

()

840 845 850 855 860 865835

Wavelength (nm)

minus20

minus10

0

10

20

30

40

50

60

70

80

90

100

Tran

smitt

ance

chan

ge (

)

(c)

A B

0V120583m81V120583m

minus20

minus10

0

10

20

30

40

50

60

70

80

90

100

Tran

smitt

ance

()

840 845 850 855 860 865835

Wavelength (nm)

minus20

minus10

0

10

20

30

40

50

60

70

80

90

100

Tran

smitt

ance

chan

ge (

)

(d)








(a) (b)












1009080706050403020100

Refle

ctan

ce (

)

1000 1200 1400 1600 1800 2000 2200 2400

Wavelength (nm)

Calculated result


(a)

1009080706050403020100

Refle

ctan

ce (

)

1000 1200 1400 1600 1800 2000 2200 2400

Wavelength (nm)


2 pair3 pair

4 pair5 pair

(b)



(V)

1500

1413

1325

1237

1150

1063

0976

0887

0800

Median 1477

(0063)

(a)1009080706050403020100

Refle

ctan

ce (

)

1000 1200 1400 1600 1800 2000 2200 2400

Wavelength (nm)


(b)

ABC

DE

Avge 1485

Std Dev 4235



Sacrificial layer


layer



5 Summary



x

y

z

TM

a

t

Λ

(a)

x

y

z

a

t

Λ

TE

(b)

1

08

06

04

02

0

Refle

ctiv

ity

07 08 09 1


995

TM

TE

(c)

TM

TE

1

08

06

04

02

0

Refle

ctiv

ity

07 08 09 1


995

(d)





Acknowledgments



References






















119909Ga1minus119909




















































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics





12

10

8

6

4

2

0

Num

ber o

f DBR

pai

rs (a

u)

835 840 845 850 855 860 865

Wavelength (nm)

0 10 20 30 40 50ltminus10 gt60

(a)


0

2

4

6

8

10

12

Num

ber o

f DBR

pai

rs (a

u)

840 845 850 855 860 865835

Wavelength (nm)

(b)

A B

0V120583m81V120583m

minus20

minus10

0

10

20

30

40

50

60

70

80

90

100

Tran

smitt

ance

()

840 845 850 855 860 865835

Wavelength (nm)

minus20

minus10

0

10

20

30

40

50

60

70

80

90

100

Tran

smitt

ance

chan

ge (

)

(c)

A B

0V120583m81V120583m

minus20

minus10

0

10

20

30

40

50

60

70

80

90

100

Tran

smitt

ance

()

840 845 850 855 860 865835

Wavelength (nm)

minus20

minus10

0

10

20

30

40

50

60

70

80

90

100

Tran

smitt

ance

chan

ge (

)

(d)








(a) (b)












1009080706050403020100

Refle

ctan

ce (

)

1000 1200 1400 1600 1800 2000 2200 2400

Wavelength (nm)

Calculated result


(a)

1009080706050403020100

Refle

ctan

ce (

)

1000 1200 1400 1600 1800 2000 2200 2400

Wavelength (nm)


2 pair3 pair

4 pair5 pair

(b)



(V)

1500

1413

1325

1237

1150

1063

0976

0887

0800

Median 1477

(0063)

(a)1009080706050403020100

Refle

ctan

ce (

)

1000 1200 1400 1600 1800 2000 2200 2400

Wavelength (nm)


(b)

ABC

DE

Avge 1485

Std Dev 4235



Sacrificial layer


layer



5 Summary



x

y

z

TM

a

t

Λ

(a)

x

y

z

a

t

Λ

TE

(b)

1

08

06

04

02

0

Refle

ctiv

ity

07 08 09 1


995

TM

TE

(c)

TM

TE

1

08

06

04

02

0

Refle

ctiv

ity

07 08 09 1


995

(d)





Acknowledgments



References






















119909Ga1minus119909




















































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




(a) (b)












1009080706050403020100

Refle

ctan

ce (

)

1000 1200 1400 1600 1800 2000 2200 2400

Wavelength (nm)

Calculated result


(a)

1009080706050403020100

Refle

ctan

ce (

)

1000 1200 1400 1600 1800 2000 2200 2400

Wavelength (nm)


2 pair3 pair

4 pair5 pair

(b)



(V)

1500

1413

1325

1237

1150

1063

0976

0887

0800

Median 1477

(0063)

(a)1009080706050403020100

Refle

ctan

ce (

)

1000 1200 1400 1600 1800 2000 2200 2400

Wavelength (nm)


(b)

ABC

DE

Avge 1485

Std Dev 4235



Sacrificial layer


layer



5 Summary



x

y

z

TM

a

t

Λ

(a)

x

y

z

a

t

Λ

TE

(b)

1

08

06

04

02

0

Refle

ctiv

ity

07 08 09 1


995

TM

TE

(c)

TM

TE

1

08

06

04

02

0

Refle

ctiv

ity

07 08 09 1


995

(d)





Acknowledgments



References






















119909Ga1minus119909




















































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




1009080706050403020100

Refle

ctan

ce (

)

1000 1200 1400 1600 1800 2000 2200 2400

Wavelength (nm)

Calculated result


(a)

1009080706050403020100

Refle

ctan

ce (

)

1000 1200 1400 1600 1800 2000 2200 2400

Wavelength (nm)


2 pair3 pair

4 pair5 pair

(b)



(V)

1500

1413

1325

1237

1150

1063

0976

0887

0800

Median 1477

(0063)

(a)1009080706050403020100

Refle

ctan

ce (

)

1000 1200 1400 1600 1800 2000 2200 2400

Wavelength (nm)


(b)

ABC

DE

Avge 1485

Std Dev 4235



Sacrificial layer


layer



5 Summary



x

y

z

TM

a

t

Λ

(a)

x

y

z

a

t

Λ

TE

(b)

1

08

06

04

02

0

Refle

ctiv

ity

07 08 09 1


995

TM

TE

(c)

TM

TE

1

08

06

04

02

0

Refle

ctiv

ity

07 08 09 1


995

(d)





Acknowledgments



References






















119909Ga1minus119909




















































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




x

y

z

TM

a

t

Λ

(a)

x

y

z

a

t

Λ

TE

(b)

1

08

06

04

02

0

Refle

ctiv

ity

07 08 09 1


995

TM

TE

(c)

TM

TE

1

08

06

04

02

0

Refle

ctiv

ity

07 08 09 1


995

(d)





Acknowledgments



References






















119909Ga1minus119909




















































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics



















119909Ga1minus119909




















































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics




































FluidsJournal of


Journal of










Superconductivity




GravityJournal of








Journal of






Volume 2014


PhotonicsJournal of


Journal of

Biophysics



review article recent approaches for broadening the

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