ucsb cs-wdm quarterly report 6/16/2003 n66001 …...ucsb cs-wdm quarterly report 6/16/2003...

UCSB CS-WDM Quarterly Report 6/16/2003

N66001-02-C-8026

DARPA CS-WDM Quarterly Report

Award Number N66001-02-C-8026 “On-Chip Integration of Advanced Wavelength and Switching

Functions for Wavelength-Agile Analog/Digital Optical Networks” Report Date June 12, 2003 Principal Investigator Daniel J. Blumenthal Room 5163, Engineering I University of California Santa Barbara, CA 93106 Tel: (805) 893-4168 Fax: (805) 893-5705 Email: [email protected] Report Distribution [email protected] [email protected] [email protected] [email protected]

Table of Contents Executive Summary........................................................................................................................................ 2 1. Program Management Plan ................................................................................................................... 3

1.1. Program Plan Progress Summary ................................................................................................ 3 1.2. Task I: All Optical Tunable Wavelength Converter.................................................................... 6

1.2.1. Single-Stage Integrated Widely Tunable Sampled-Grating DBR Tunable Laser and SOA Based Mach Zehnder Wavelength Converter ....................................................................................... 6 1.2.2. Digital and Analog Performance Measurements .................................................................... 7 1.2.3. Next Generation AOWC....................................................................................................... 10 1.2.4. Novel Photocurrent-Assisted EAM Wavelength Converter with Optical Monitoring ......... 12

1.3. Task II: Filter/Mux/Router ........................................................................................................ 13 1.3.1. TIR and Disc Micro-resonator Filters Compatible with InP Planar Integration Platform .... 13 1.3.2. Low Loss TIR Mirrors and Waveguides for InP Planar Integration Platform...................... 15

1.4. Task III: OEOIC-WC ................................................................................................................ 17 1.4.1. Directly Modulated SGDBR Wavelength Converters .......................................................... 17 1.4.2. Integrated External Modulator Wavelength Converters ....................................................... 19

1.5. Wafer Processing Subcontract (Agility Communications)........................................................ 20 2. Publications......................................................................................................................................... 20 3. Programmatic Interactions and Collaborations ................................................................................... 21

3.1. Test Facility: MIT Lincoln Labs ............................................................................................... 21 3.2. Architecture Study: MIT ........................................................................................................... 21

4. Patents ................................................................................................................................................. 21 5. Appendix A: Program Management Plan for Baseline Period............................................................ 22 6. Appendix B: Budget Summary for FY02 ........................................................................................... 23


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Executive Summary The scope of this program is to develop and demonstrate chip-scale integrated wavelength

conversion and routing functions on a common substrate. The wavelength converters and routers developed will be photonic integrated circuits on InP substrates. The wavelength converters and routers will be compatible with both analog and digital transmission requirements. Issues involved in integration will be studied. Three classes of device will be investigated. The program is organized and managed by sub-area according to these three classes of device:

• Sub-area I (AOWC): In-plane SOA interferometric wavelength converter.

• Sub-area II (Filter/Mux/Router): Wavelength router and multiplexers based on filter and interferometric technologies.

• Sub-area III (OEIC-WC): Optoelectronic integrated wavelength converter with monitoring function capabilities.

Significant Achievements: In this quarter, the following significant achievements were made. A new result mentioned in item 5 is demonstration of an EAM based AOWC that can serve as both the first stage of the dual stage converter and provides the signal monitoring function.

Sub-Area I 1. Completed first phase of analog measurements of widely tunable monolithically

integrated SOA based AOWC chip at MIT-LL test facilities. Demonstrated SFDR >85 dB/(Hz)2/3 at 10mW input power and RIN of -135dB/Hz over varying input wavelengths (15nm range).

2. Characterization of 50nm input (62 lambdas 100GHz spacing) 22nm output (27 lambdas 100GHz spacing) tuning range for of widely tunable monolithically integrated SOA based AOWC chip. Digital testing of BER = 10-9 at 2.5 Gbps.

3. Completed digital network testbed characterization of widely tunable monolithically integrated SOA based AOWC chip at BOSSNET facility at MIT-LL.

4. New mask designed for improved performance and electrical signal monitoring capability for widely tunable monolithically integrated SOA based AOWC chip.

5. Novel demonstration of a new EAM based WC with electrical monitoring capability that can serve as the front end for the dual stage converter.

Sub-Area II

6. Fabricated and demonstrated light guiding in TIR InP structures compatible with planar integration process and ridge waveguides.

7. Fabricated first ring resonator filters compatible with planar InP integration process.

Sub-Area III 8. Fabricated first directly-driven OEIC-WC.

9. Demonstrated error free wavelength conversion and signal monitoring at 2.5 Gbps for > 15 nm tuning range.

10. Demonstrated SFDR > 90 (dB/Hz)2/3 over wide bias range.


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1. Program Management Plan A program management plan for the baseline period is included as an Appendix in the form

of Microsoft Project Gantt Chart identifying major tasks, milestones of the major tasks and their completion dates. A graphical representation of the budget for the first spending increment (FY02) is also included as an appendix to this quarterly report to the distribution list in the form of an excel graph showing the (1) monthly planned, committed and most recent actual spending, (2) cumulative spending (planned, committed and actual), and (3) cumulative total of money received from the government.

1.1. Program Plan Progress Summary The status of CS-WDM program milestones that this project meets and the project major

milestones status are shown in Table 2 and Table 3 respectively. In Table 3 the target performance values are shown in bold. Actual performance values in (italics). Table 3 summarizes progress in each research sub-area with respect to the project plan shown in Appendix A. The completed tasks are indicated with gray shading.

Table 1. June 2003 status for DARPA CS-WDM program milestones.

Institution: UCSB

Proposal Title: Integrated Optical Wavelength

Converters and Routers for Robust Wavelength-Agile

Analog/Digital Optical Networks

PI: Daniel J. Blumenthal DARPA'S 12 MONTH MILESTONES

Task Description 12-Month Milestones Measurement Metrics

2 W

DM

Pr

oces

sing

Fu

nctio

ns

4 Pr

otoc

ol

Inde

pend

ent C

hann

els

1 G

b/s

digi

tal d

ata

tran

smis

sio

n

< 50

ms

switc

hing

sp

eed

Ana

log

link

perf

orm

anc

e: S

FDR

115

bB

-Hz^

2/3;

N

F 6

dB

In-Plane SOA-IWC

Delivery of operational single-stage SOA-IWC with integrated

tunable laser to DARPA designated government or

FFRDC test facility

32 wavelengths in C-band separated by 100 GHz, 0.1 mW output per channel, RIN < 150dB/Hz for SGDBR and 10-20dB less with 1st generation SOA-IWC, 2.5 GHz conversion bandwidth, 1 s

switching speed between converted wavelengths

X XX

2.5 Gbps BER 10-9

X >85 dB/Hz2/3

Wavelength Router

Mux/Demux

Demonstrate InP single disk resonator filter; static and

dynamically tunable versions

C-band operation; 3dB Filter bandwidth < 1nm; 30nm free spectral range (FSR); filter loss < 2.0dB; fiber-to-fiber loss < 10 dB; polarization

sensitivity: single polarization; 1 s center wavelength tuning speed;

X

Wavelength Router

Mux/Demux

Demonstrated strongly confined InP waveguide and TIR mirror C-band operation; loss per TIR mirror < 2dB; X

OEIC

Delivery of direct-modulation OEIC-WC chip-on-carrier to

DARPA designated government or FFRDC test facility

32 wavelengths in C-band separated by 100 GHz, 1.0 mW output per channel, RIN < -150dB/Hz

using saturated post SOA , 2.5 GHz conversion bandwidth, 1ms switching speed between

wavelengths

X 2.5 Gbps

Eye Diagram

X X X 92.3dB/Hz2/3


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Table 2. Project milestone measurement metric goals. Dark shaded boxes are complete. Partially completed targets are indicated with status and current performance.

NANANANA

< 2/ mirror(Not

Measured Yet)

NA

100 GHz(Not

Measured Yet)

C-Band(Not Measured Yet)

TIR

RRF

< -150(Not Measured

Yet)

NA

< -150(-135

Achieved)

RIN (dB/Hz)

1.0(Not Measured

Yet)

1.0(Not Measured

Yet)

1.0 (Not Measured

Yet)

τswitch (ms)

2.5 GHz(2.5 Gbps

eye diagram)

<1nm 3dB(Not

Measured Yet)

2.5 GHz(BER 10-9 @

2.5 Gbps; 5.0

Achieved)

BW

1.0(Not

Measured Yet)

NA

0.1(0.5

Achieved)

Pout (mW)

TBD(Not

Measured Yet)

NA100 GHz

32 (C-Band)(C-band: 15nm

output range = 18 λs)

OEIC

< 10(Not

Measured Yet)

30(Not

Measured Yet)

100 GHz(Not

Measured Yet)


WR-M/D

TBD(Not

Measured Yet)

NA100 GHz

32 (C-Band)(L-Band: 50nm input

= 62 λs; 22nm output = 27 λs)

AOWC

Loss/ Gain (dB)

FSR (nm)

λ Resolution/Channel

Spacing

# λs

NANANANA

< 2/ mirror(Not

Measured Yet)

NA

100 GHz(Not

Measured Yet)


TIR

RRF

< -150(Not Measured

Yet)

NA

< -150(-135

Achieved)

RIN (dB/Hz)

1.0(Not Measured

Yet)

1.0(Not Measured

Yet)

1.0 (Not Measured

Yet)

τswitch (ms)

2.5 GHz(2.5 Gbps

eye diagram)

<1nm 3dB(Not

Measured Yet)

2.5 GHz(BER 10-9 @

2.5 Gbps; 5.0

Achieved)

BW

1.0(Not

Measured Yet)

NA

0.1(0.5

Achieved)

Pout (mW)

TBD(Not

Measured Yet)

NA100 GHz

32 (C-Band)(C-band: 15nm

output range = 18 λs)

OEIC

< 10(Not

Measured Yet)

30(Not

Measured Yet)

100 GHz(Not

Measured Yet)


WR-M/D

TBD(Not

Measured Yet)

NA100 GHz

32 (C-Band)(L-Band: 50nm input

= 62 λs; 22nm output = 27 λs)

AOWC

Loss/ Gain (dB)

FSR (nm)

λ Resolution/Channel

Spacing

# λs

Table 3. Summary of status of tasks and milestones.

Sub-Task Description Due Date Status

Widely Tunable AOWC

Development of growth and processing technologies to fabricate integrated MZI-WC with tunable laser using offset quantum well design for active/passive waveguide fabrication

1/31/03 Completed 12/5/02

Widely Tunable AOWC

Report details of integration process and process characterization

2/3/03 Completed 2/3/03

Widely Tunable AOWC

Mask fabrication, device processing and mounting

4/21/03 Completed 3/15/03

Widely Tunable AOWC

Digital characterization 9/1/03 Completed 5/1/03

Widely Tunable AOWC

Analog characterization 9/1/03 Initial testing completed 6/1/03. New devices will be tested to try to meet program goals by end of July.

Task I

EAM AOWC with signal monitoring

Initial demonstration Not specified

Completed 4/25/03

Task II

InP Ring Resonator: Coupled Disk Design

Development of growth and processing technologies to fabricate disk resonator filter compatible with in-Plane SOA-WC

9/20/02 Completed 12/1/02


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Mask fabrication, device processing, mounting and AR coating

12/13/02 Completed 12/13/02


Fabricate and test small resonators 3/25/03 Completed: Disk Filter Completed, redesigned as TIR based filter based

InP Ring Resonator: TIR Design

Designed and fabricated first generation structures for wavelength selective devices

6/17/03 In Progress

InP Ring Resonator Filter

Analog and Digital Performance Evaluation

8/29/03 Not Started

InP TIR Mirror Development of growth and processing technologies to fabricate strongly guiding waveguides and mirrors

9/20/02 Completed 12/1/02

InP TIR Mirror Mask fabrication, device processing 1/31/03 Completed 12/1/02

InP TIR Mirror Fabricate and test TIR mirrors 3/31/03 Completed 4/25/03

InP TIR Mirror Fabricate and test multiple TIR mirrors with integrated InP waveguides on a single chip

8/29/03 In Progress

InP TIR Mirror Demonstrate TIR mirrors with integrated waveguides on single chip as platform for next generation AOWC devices

8/29/03 Not Started

Task: Directly Modulated OEIC-WC

Develop growth and processing technologies to fabricate integrated PICs with tunable laser

12/13/02 Completed 11/2/02

Task: Directly Modulated OEIC-WC

Device fabrication and basic characterization of directly modulated OEIC wavelength converter

5/2/03 Completed 5/30/03

Task: Design PD/EAM with no Interface Electronics

Study and assess alternative SOA and detector designs for the directly modulated

12/13/02 Completed 12/10/02


Study and evaluate saturable absorber and gain levered direct modulated devices

12/31/02 Completed 10/15/02

Task III


Design and simulate various embodiments of PD/EAM modulated wavelength converters

8/29/03 First generation completed 5/30/03. Second gen. will be done by 7/30/03


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1.2. Task I: All Optical Tunable Wavelength Converter

1.2.1. Single-Stage Integrated Widely Tunable Sampled-Grating DBR Tunable Laser and SOA Based Mach Zehnder Wavelength Converter

We have successfully fabricated the first batch of fully operational tunable wavelength converters and conducted digital performance characterization and preliminary analog testing. Comprehensive characterization was conducted on two device types: S-bend Mach-Zehnder Interferometer (MZI-AOWC) and MMI-MZI-AOWC. The main difference in performance between these two device types was higher output power of the MZI-AOWC device (up to 5dBm).

The tunable AOWC chip, wire-bonded on a sub-mount, is shown in Figure 1. The lasers and devices fabricated currently operate in the L-band region, with 50 nm input and 22 nm output tuning range (Figure 2). The next generation device currently in fabrication will operate in the C-band. The maximum device power coupled in fiber is 5dBm and is limited by absorption losses of the waveguide (1.435Q), grating depth in the mirrors, length of device passive sections, coupling loss. The gain of the active region is additionally influenced by thermal crosstalk between the active region of the laser and the input semiconductor optical amplifier SOA.

Figure 1. The first generation of the integrated sampled grating DBR laser and a MZI wavelength converter

soldered and wire bonded on a sub-mount

Static and dynamic testing has been conducted. Due to relatively low SGDBR output power, the SOAs of the MZI are not operating in saturation for large bias currents which reduces the attainable electrical and optical extinction due to large cross gain modulation effects. Therefore, the static extinction varies between 28 and 10 dB, depending of the SOA bias points (Figure 2).


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Figure 2. AOWC tuning range and Mach-Zehnder electrical control extinction map

1.2.2. Digital and Analog Performance Measurements Dynamic digital operation at 2.5 Gbps was demonstrated and is summarized in Figure 3.

Wavelength conversion was error free over 50nm of input signal range and 22nm of output signal conversion range. Figure 3a shows wavelength conversion from several wavelengths in this range onto one fixed SGDBR. The eyes are clearly open, and reduction in extinction is noticed as we move towards the edge of the gain spectrum of the SOA (1585nm). On the lower side, we were limited by the available C-band filters, so we believe that the actual input signal wavelength span could be as high as 60nm. Figure 3b shown eye diagrams for wavelength conversion from one fixed input wavelength onto several different SGDBR wavelengths (22nm range). Carrier dynamics in the SOA of the MZI limits the current speed of operation to 5 GB/s.

Figure 3. Eye diagrams at 2.5GB/s - a) Fixed SGDBR wavelength - b) Fixed input wavelength

During this quarter, we have completed digital characterization of the first version of integrated WC devices. Overlapped spectra showing 22 nm tuning range and a typical electrical transfer curve are shown in Figure 4a and Figure 4b respectively. Figure 4c represents BER results for wavelength conversion from 4 different input wavelengths to a known output wavelength. Figure 5 shows BER results for the case of various output wavelengths and one fixed input wavelength. Overall, for both cases, 1.6dB maximum power penalty was measured for 50nm in and 22 nm out wavelength conversion range.


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Figure 4. Spectra and BER results for different input wavelengths

Figure 5. BER results for various output wavelengths and MZI input power vs. SGDBR wavelength

To characterize the SFDR, two RF tones at 1.00GHz and 1.0001GHz were combined and used to directly modulate an Agility EML. The output power of the Agility laser was 10mW. The signal was then wavelength converted, detected, and the resulting signal and 3rd order IMD terms measured using an electrical spectrum analyzer. The particular device used in these characterizations had 4dBm output power. A typical plot of the SFDR is shown in Figure 6 for conversion from 1561nm to 1550nm. Similar SFDR measurements were taken over a range of RF tone spacing to characterize ∆f dependence. As seen in the Figure 6, the SFDR remained >85dB. The SFDR can be improved by using a low-noise receiver. Current measurements were limited by a noise floor of -130dBm. Future characterization includes measuring SFDR vs. wavelength, SOA bias, and input optical power.


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Figure 6. Measured SFDR and its frequency dependence.

RIN characterization of the device was also performed, using a HP 71401C lightwave signal analyzer. Measurements were performed as a function of input wavelength. As seen in Figure 7, the RIN values obtained were between -130 and -140dB/Hz. We believe the RIN value is currently limited by SGDBR output power. This has a two-fold effect on reducing RIN. First, laser RIN is inversely proportional to the laser output power. Secondly, driving the SOAs into saturation will reduce the amount of ASE seen at the output as laser RIN.

Figure 7. RIN measurements of single stage tunable AOWC.

Transmission performance of the WC was evaluated by sending data over a 600km loop through BOSSNET. Data from the Agility laser was converted and sent over the network. A BER of 10-9 was achieved in this experiment. A network testbed demonstration was also made with the wavelength converter mid-span between two 600km loops through BOSSNET. The diagrams below (Figure 8 and Figure 9) show the principle of operation and the system layout. 2.5 Gb/s data was sent using the Agility EML over a 600km loop through BOSSNET at 1560nm. The data was then converted to 1550nm and sent over the same 600km loop before being tapped and detected. Eye diagrams at each stage are shown below, which exhibit the added noise through the network and partial signal regeneration by the WC. End-to-end performance is


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limited by the achievable extinction ratio of the WC, and should see improvement in the next generation of devices.

Figure 8. Schematic of WC over BOSSNET.

λin=1560nm

EDFABPF

BPFBPF

Attenuator

EDFA

Device

PDBER

Error Rate

Optically Pre-Amp Receiver

50:50

70

30

90

10

ClockRecovery

PC

λc=1550nm

To BOSSNET

From BOSSNETBPF

EDFA

EML

Dat

a G

en.

λin=1560nm

EDFAEDFABPF

BPFBPFBPFBPF

Attenuator

EDFAEDFA

Device

PDBER

Error Rate

Optically Pre-Amp Receiver

50:50

70

30

90

10

90

10

ClockRecovery

PCPC

λc=1550nm

To BOSSNET

From BOSSNETBPF

EDFAEDFA

EMLEML

Dat

a G

en.

Figure 9. Experimental setup for digital performance characterization of AOWC on BOSSNET.

1.2.3. Next Generation AOWC

A new, low-loss epitaxial structure was designed in collaboration with our subcontractor Agility communications. We have also redesigned the wavelength converter in order to improve its performance and are currently working on a new mask set. Our goals are to fabricate the new set of improved devices, with lower loss waveguides, improved laser mirror design, higher electrical and optical extinction for high SOA current densities, and lower carrier lifetimes for higher speed operation.


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Some of the major limitations in performance of the first generation of devices are a consequence of relative low input power into the Mach-Zehnder interferometer, and the need to control the phase of the light by changing the bias currents of the SOAs in the branches of the interferometer. The generation 2 device (Gen-2) shown in Figure 10 removes these constraints on operation of the wavelength converter.

Figure 10. Generation 2 device layout and Mask layout - Gen-2 AOWC devices

There are several key changes to the design that have been implemented in the Gen-2 device including

1) Independent phase electrodes in the branches of the MZI

2) Longer SOAs in the MZI

3) Dual output waveguide with signal monitoring capability

4) Output SOAs after the SGDBR laser

5) Differential input waveguides

The ability to control the phase in the interferometer independently (1) and longer SOAs (2) will lead to higher extinction since the arms of the interferometer will be balanced. Ultimately, this will lead to higher output power of the device. This will also be affected by the lower loss waveguide that we are using to fabricate the new set of devices. The output SOAs after the SGDBR laser (4) will help increase the level of saturation of the SOAs in the MZI, which will help decrease the carrier lifetime to some extent, and also further reduce the RIN and improve the SFDR of the device. Introduction of the dual output waveguides (3) at the end of the interferometer will allow for light evacuation from the chip at all times, plus it will provide us with an option to do electrical signal monitoring without sacrificing the device performance. Finally, having two functional input waveguides and SOAs will provide for redundancy and also enable additional device characterization by using a differential excitation to the interferometer, such as RZ wavelength conversion. The Gen-2 device mask has been designed (Figure 10) and is currently being fabricated. Our expectations are that we will have the first samples fabricated in July 2003 in time to be measured for the July CS-WDM review.


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1.2.4. Novel Photocurrent-Assisted EAM Wavelength Converter with Optical Monitoring We have successfully demonstrated a novel Photocurrent-Assisted Wavelength Conversion

(PAWC) with electrical monitoring capability using a traveling-wave electroabsorption modulator (TW-EAM). We believe this approach may be a good choice for the first stage of the 2-stage AOWC for Phase II of this project (to be integrated with the tunable SOA-MZI) in that it has potentially lower power dissipation, low polarization sensitivity and signal monitoring functions. As shown in Figure 11, the PAWC utilizes the photocurrent generated by the pump signal at λ1 to change the absorption of the CW probe at λ2 in the latter part of the active waveguide. This photocurrent signal goes through the TW-EAM and then is processed further by outside electronics that provide electrical monitoring capability. This work differs from other reported works using EAM as a wavelength converter in that the PAWC dose not require saturation of the device and hence can potentially reduce the required pump power and avoid the speed limitation caused by internal electric field screening due to strong excitation in the quantum wells.

Figure 11. Schematic drawing of PAWC using a TW-EAM

A 2.5Gb/s NRZ wavelength conversion experiment was carried out. The pump signal is at 1545.8 nm with 13 dBm average power and the CW probe signal is at 1555.2 nm with 1 dBm average power. Two kinds of termination, open and 50 Ohm are used to show that microwave properties do play an critical role in PAWC, which is not expected if the conversion is caused solely by saturation. The eye diagrams are shown in Figure 12.

Figure 12. Electrical and optical eye diagrams of new EAM based AOWC


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BER measurements (Figure 13) were carried out for the converted optical signal and the detected electrical signal. The optical power penalty for the open termination is 0.5 dB and 1.5 dB for the 50 Ohm termination. The difference is mainly caused by the extinction ratio of the optical eyes. The extinction ratio measured from the optical eye on the scope is 10.9 dB and 7.5 dB for the open termination and the 50 Ohm termination, which also indicates that saturation also contributes about 4~5dB to the extinction ratio. BER for the electrical signal are too low to be measured at normal operating power level at this time.

(a) (b)

Figure 13. Bit-error-rate curves. (a) Optical; (b) Electrical; Square: 1545 nm back-to-back; triangle: open termination; circle: 50 Ohm termination.

1.3. Task II: Filter/Mux/Router This sub-area addresses the process compatible design and fabrication of optical filters and

TIR mirrors and waveguides for the AWOC chip-scale project. The results of this research will be used in the AOWC in Phase II of this project.

1.3.1. TIR and Disc Micro-resonator Filters Compatible with InP Planar Integration Platform

A new TIR based design for the filter was reported in the last quarter. This quarter we have completed the required growth and basic fabrication and have started testing of the optical filters and TIR mirrors. The TIR based filter structures shown in Figure 14 are at the stage of pre-metallization fabrication. The process was designed to be compatible with the AOWC planar platform. The MOCVD grown base wafer has active quantum wells (QW) for optical gain everywhere. In order to define passive waveguides on the chip, the active part containing QWs is etched away. To achieve this, areas where the QW’s needed are protected using a PR mask, and selective wet etching is used to etch the QW’s elsewhere. A 2 µm thick p-InP and a thin p-InGaAs cap layers are grown on top of the patterned wafer. In the optical microscope pictures shown in Figure 14 the active QW areas appear as small rectangles under the waveguide arms of the micro-resonator cavity. These are the areas containing QW active material. After the regrowth, the waveguide and micro-resonator patterns are defined using a SiN mask and the chip is dry-etched for the appropriate amount to form single mode waveguides. Figure 14a shows the picture of the device after this step. Next, a SiO2 lift-off mask is used to define small openings at


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the position of the mirrors while keeping the SiN mask for self-alignment of the mirrors and the waveguides. These areas then further etched using the same dry-etch recipe to form the mirrors. The picture on Figure 14b shows the device after this step.

Input Waveguide

Output WaveguideDeep Etch

MirrorsActive QW’s

Resonator cavity

a b

Figure 14. 2-waveguide coupler traveling wave micro-resonator filters a) after WG etch b) after deep mirror etch.

Figure 15 shows examples of both ring based and TIR mirror based device structures on the chip after the deep-etching step. On the micro-disc and micro-ring devices a deep etch is used to etch the whole circumference of the resonators to enhance optical confinement. We are currently in the process of measuring the optical filtering characteristics of the devices in Figure 14 and Figure 15 and plan to have these results for the July 2003 PI meeting.

a b c

Figure 15. Traveling wave micro-resonator band-stop filters fabricated a) Micro-disk b) Micro-ring

c) 3-waveguide coupler mirror cavity.


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1.3.2. Low Loss TIR Mirrors and Waveguides for InP Planar Integration Platform In this work we investigate techniques to increase the density of PIC circuits in our InP

integration platform in order to reduce the area of chip-scale AOWCs, filters and mux/demuxes. Our approach is to fabricate large angle bending by total internal reflective (TIR) mirrors. This approach has the potential to be low cost. We focus on a compatible process that can be integrated with our existing InGaAs/InP Chip-scale WDM devices.

Figure 16 illustrates the basic TIR mirror structure that we have demonstrated and are establishing a platform compatible process for. Normally, a waveguide with a large angle bending will be optically lossy. However, if a smooth mirror intercepts at the corner of the two waveguides, light traveling in the incoming waveguide is going to be totally internal reflected to the outgoing waveguide because of the high refractive index change at the air/semiconductor interface. Low loss TIR mirrors depend on high quality mirrors so the challenge in this work is twofold (i) to produce low loss TIR mirrors and (ii) make the process compatible with the AOWC chip scale circuit so that these mirrors may be employed for certain functions. Our current goal is for 0.5dB loss per mirror.

Figure 16. TIR mirror with standard process InP waveguides for dense chip-scale integration.

Our first approach to fabricate the TIR mirror uses a Focus Ion Beam (FIB) etching technique. Our FEI FIB provides nanometer-scale resolution with gallium Liquid Metal Ion Source (LMIS). A focused ion beam creates unique imaging mechanisms unavailable with electron beams. The electro-optics ensures controlled high current density beam profiles for precise ion milling and deposition while maintaining high-resolution imaging capabilities. Compared to conventional dry etching, FIB etching does not require a lithographic mask and the beam can be positioned to the part to be etched and to modify the device structure on the screen in real time yielding a –“what you see is what you get” etch process. The FIB can be used to etch structures from scratch in InP or to clean up a mirror after standard lithographic processing. The FIB process flow for TIR mirrors is shown in Figure 17.


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Wafer Structure:

InGaAs 100nm

InP 2um

InGsAsP 320nm

InP Substrate

Lithography SiOx deposition

SiOx etching Dry Etching FIB Milling

Figure 17. Process flow for FIB TIR mirrors.

The SEM pictures in Figure 18 were taken before and after FIB etching. By adjusting the parameters such as beam current, beam dwell time, beam overlap, smooth TIR mirror can be achieved. The FIB etching technique still needs to be improved. To obtain a smooth etched sidewall, the beam current needs to be very low. However, a low beam current leads to slow etch rate, which limits the throughput to ion-milling the micron-sized mirrors. Also, we find that the etching residue re-deposition could be observed under ultra-high resolution, possibly Ga droplets deposition on the sidewall. There may be other issues like the ion damage to be characterized.

(a) (b)

Figure 18. InP TIR mirrors (a) before FIB processing, and (b) after FIB processing.

We are currently optimizing the TIR fabrication by FIB and have started mirror loss testing. Initial results were achieved by etching rib loaded waveguides with the TIR mirrors and launching light into the waveguides and observing the waveguides at the output using a CCD camera. The very first results are encouraging and are shown in Figure 19.


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Finished FIB-polished TIR mirror(2-step FIB milling at 5000 and 500 pA)

Figure 19. Fabricated TIR and input and output waveguides.

1.4. Task III: OEOIC-WC

1.4.1. Directly Modulated SGDBR Wavelength Converters In this quarter, the first generation directly modulated OEIC wavelength converters

introduced in the last quarter has been characterized. The devices have been AR-coated, mounted and wire-bound to an AlN-carrier substrate for heat-sinking and proper RF monitor probing. Figure 20 shows the resulting optical AC gain performance. The gain peaks at about –10dB, and the bandwidth is above 3GHz at higher bias currents.

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Figure 20. Figure 1: Small signal optical AC gain as a function of frequency for different gain section bias currents and conversion from 1547nm to 1545 nm.

The spurious-free dynamic range (SFDR) of the device has also been characterized. The SFDR was measured at 0.5 GHz using two tones separated by 1 MHz. To reduce any intermixing components between the two tones at the input, the two tones were modulated to two separate optical sources, coupled together and tuned to a wavelength offset of 60GHz around 1555 nm, well above the detector bandwidth to avoid coherence effects. Figure 21 shows the measured


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SFDR: 92.3dBHz2/3, at 55mA bias to the gain section, while converting from 1555nm to 1545 nm. Figure 3 shows the SFDR-performance for different gain section bias currents.

The wavelength tuning range of the SGDBR laser was compromised due to a defective mirror design. Nevertheless, 2.5 Gb/s wavelength conversion were conducted from 1547nm to an output wavelength of 1545nm, 1550nm, 1552nm, and 1560nm. In all cases, error-free conversion was obtained. Figure 22 shows the detected eye diagram at 1545nm. Signal monitoring was achieved by connecting the gain section to a 50Ω serial resistance and an RF coplanar line for RF probing. Error-free signal monitor at 2.5 Gb/s was obtained. Figure 23 shows the detected monitor eye diagram. Future plans include further characterization of the signal monitor performance.

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Figure 23. Detected and filtered eye-diagram at 2.5 Gb/s for conversion from 1547nm to 1545nm.

Figure 24. Detected and filtered eye-diagram at 2.5 Gb/s for monitor signal taken over the directly-

modulated SGDBR gain section.

In summary, the first generation OEIC directly modulated embodiment provides about the expected level of performance for the quality of the devices fabricated. Simple improvements in contact resistance should result in the ability to significantly increase the preamplifier gain to provide more photocurrent and reduce overall insertion loss from the -10 dB level observed to near zero net insertion loss. The SFDR and modulation bandwidth should also improve directly as the improvement in laser output which will result from the corrected mirror design as well as the improved contacts.

The design of the first integrated externally modulated OEIC-WC has been completed and fabrication begun. Results from both Mach-Zehnder and EAM external modulators are expected within the next month. Simulations suggest that improved speed and SFDR should result.

1.4.2. Integrated External Modulator Wavelength Converters A first generation mask has been designed and is in house where wavelength conversion is

achieved using the signal from a photodetector to drive an external integrated Electro absorption modulator (EAM). Processing is currently underway and should be completed within the next several weeks. In addition, a dual EAM scheme is being examined for increased linearity and better chirp performance, and a Mach Zehnder based device is under examination for low drive voltage, more efficient power handling capability, and chirp design.


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1.5. Wafer Processing Subcontract (Agility Communications) Agility has continued to support this program in its role as a subcontractor supplying 1) base

epitaxial structures, 2) MOCVD regrowth and 3) facet coating. Such services allow the UCSB program to take full advantage of Agility’s high level of control on these critical growth and process steps.

Figure 25 shows the historical summary and plan for base epitaxial structure deliveries. Deliveries are now proceeding regularly and on time. In May, the supplied base epitaxial layers included a 3rd new design: an epitaxial structure on a Fe-Doped semi-insulating substrate.

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Figure 25. Historical and planned base epitaxial layer deliveries

2. Publications The following publications have resulted to-date from this research project: [1] "Monolithically Integrated Mach-Zehnder Interferometer Wavelength Converter and Widely-Tunable

Laser in InP:, Milan L. Mašanović, Vikrant Lal, Jonathon S. Barton, Erik J. Skogen, Larry A. Coldren and Daniel J. Blumenthal, IEEE Photonics Technology Letters, August 2003.

[2] "Widely-tunable chip-scale transmitters and wavelength converters", Larry Coldren, Topical Meeting on Integrated Photonics Research (IPR), Talk IMB-1, Washington, June 16, 2003.

[3] “InP Laterally Tapered Wide-bandwidth Optical Power Splitter,” Xuejin Yan, Marcelo Davanco, Milan Masanovic, Wenbin Zhao, Daniel J. Blumenthal, CLEO, Maryland. June 4, 2003. CWP7 (Wednesday, CW pp 66 - 68).

[4] “Demonstration of Monolithically-Integrated InP Widely-Tunable Laser and SOA-MZI Wavelength Converter,” Milan L. Mašanović, Erik J.Skogen, Jonathon S. Barton, Vikrant Lal, Daniel J. Blumenthal and Larry A. Coldren, paper WB2.2, Fifteenth International Conference on Indium Phosphide and Related Materials, May 2003., Santa Barbara, CA.


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[5] “Multimode Interference-Based 2-Stage 1x2 Light Splitter for Compact Photonic Integrated Circuits,” Milan L. Mašanović, Erik J. Skogen, Jonathon S. Barton, Joseph Sullivan, Daniel J. Blumenthal and Larry A. Coldren, IEEE Photonics Technology Letters, vol. 15, no 5., pp 706-8, May 2003.

[6] “Cascaded Multimode Interference-Based 1x2 Light Splitter for Photonic Integrated Circuits,” M. Masanovic, E. Skogen, Barton, J. Sullivan, D. J. Blumenthal, and L. Coldren, Topical Meeting on Integrated Photonics Research (IPR), Vancouver, Canada, Paper IThA5, Jul 14-17, 2002.

[7] “Integrated Devices for Wavelength-Agile All-Optical Networks,” D. J. Blumenthal, Topical Meeting on Integrated Photonics Research (IPR), Vancouver, Canada, Paper IWB1, July 14-17, 2002 (Plenary Paper)

3. Programmatic Interactions and Collaborations

3.1. Test Facility: MIT Lincoln Labs • The results of a visit to MIT-LL for 7 days are described in the body of this status

report. Two students visited MIT-LL from UCSB for 7 days and helped perform detailed measurements on AOWC devices that were brought with them.

3.2. Architecture Study: MIT • We met with Vincent Chan in April 2003 and discussed the system wide and

architectural impact issues for this work.

4. Patents None to date.


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5. Appendix A: Program Management Plan for Baseline Period


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6. Appendix B: Budget Summary for FY02 TOTAL

$0.00

$200,000.00

$400,000.00

$600,000.00

$800,000.00

$1,000,000.00

$1,200,000.00

July

AugSep

tOct Nov

DecJa

nFeb Mar Apr

MayJu

ne July

AugSep

t

Target RateExpendedBalanceExpended + Committed*

1st Increment($458,972.00)

2nd Increment($633,816.00)

ucsb cs-wdm quarterly report 6/16/2003 n66001 …...ucsb cs-wdm quarterly report 6/16/2003...

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