http://www.wiretechworld.com/the-future-of-optical-fibres/

EE 443/CS 543 Optical Fiber Communications

Dr. Donald EstreichFall Semester

1

Lecture 19

Passive OpticalComponents

2

Summary of Lecture 18

1. Many factors can give rise to splice and connector loss: end gaps, non-concentric alignment, NA mismatch,, core mismatch, non-coaxiality, poor finish or dirt on end of fiber strands.

2. Two types of fiber splicing are used: fusion splicing and mechanical splicing3. Fusion splicing is welding of two fibers together with careful alignment

and use of an electric arc for heating.4. Fusion splicing equipment is available for field and laboratory use.5. Mechanical splicing commonly uses a V-groove for alignment of the fibers

and then a lid is tightly fastened to mechanically grip the fibers.6. Cleaving the ends of the fiber is a critical step in obtaining a good splice.7. Evaluation of splice quality: Use optical time domain reflectometry. This

is a measurement technique analogous to radar where a narrow lightpulse is sent down the fiber and a sensitive detector measures thereflected signals of the fiber under test.

3

Summary of Lecture 18 (continued)

8. In OTDR, connectors show typically show a reflection spike followed by astep down equal to the loss of the connector and splices show only astep down equal to the loss (no reflected pulse).

9. Many OFC connectors are available – connectors are for convenience andquick connect/disconnect and consist of a ferrule, a connector body,and a latching or coupling mechanism to hold the connection overtime without failure.

10. The most common types of connectors are the FC, ST, SC, LC and the MTPconnectors. While many others exist, these have been the most widely used.

11. Some connectors use fibers with an angled physical contact (APC) for mating to its companion connector.

4

Access, Metro and Long-Haul Network Connection

https://www.itu.int/ITU-T/2001-2004/com15/otn/definitions.html

• SONET/SDH • DWDM, CWDM• Optical Ethernet • Resilient Packet Ring • A-PON, B-PON, G-PON, and E-PON

Metro CoreLONG-HAUL

OPTICAL

NETWORK

Many connectionsare needed and theymust be switchableto deliver data as required

5

The Optical Network Node

An optical node is a multifunctional component – it performs send, receive &resend, and redirection of signals. Therefore, it performs both the routingoperation and the switching operation.

When several signals are simultaneously involved in multiplexed format, thenthe optical node becomes transmission system dependent. This is because different optical multiplexing techniques (e.g., time division multiplexing and wavelength division multiplexing) can be involved. It serves as a router by directingan input signal to a specified output port – often called a wavelength router. If the node changes the wavelength of the incoming signal it then functions as a wavelength converting router.

From Section 15.2.2, page 974, of John M. Senior, Optical Fiber Communications,: Principles

and Practice, 3rd edition, Pearson, 2009.

6

Four Functions of the Optical Node

Optical WavelengthDemultiplexer

12

1

2

12

1

2

Optical WavelengthMultiplexer

123

1Drop

234

4Add

Optical Add/DropMultiplexer

Optical 22Switch

12

34

13

24

From Figure 15.4, page 975, of John M. Senior, Optical Fiber Communications,: Principles

and Practice, 3rd edition, Pearson, 2009.

7

From Figure 15.4, page 975, of John M. Senior, Optical Fiber Communications,: Principles

and Practice, 3rd edition, Pearson, 2009.

Reconfigurable Optical Add/Drop Multiplexer

Optical Switch

DroppedChannels

AddedChannels

1 2 N 1 2 N

MU

X

DeM

UX

N components

ROADM

Combing an N-to-1 MUX, with a 1-to-N DeMUX and N N Optical Switch makes a ROADM.

8

Concept of the Cross Connect Switch

INP

UTS

1

1

OUTPUTS

2

3

32switches

9

Optical Cross Connect (OXC)

https://commons.wikimedia.org/wiki/File:Optical_Cross_Connect,_OXC.png

The OXC is for complex mesh topologies with large numbers of optical nodes.

10

We have covered sources and detectors and optical fibers.

Next: How we implement the other components neededto create large networks.

One way is to use optical integrated circuits.

https://cdn.comsol.com/wordpress/2017/09/Photonic-integrated-circuit_schematic.png

Optical Integrated Circuits

11

Introducing Lithium Niobate (LiNbO3)

Lithium Niobate is a salt consisting of niobium, lithium and oxygen.It is used for numerous applications:

optical waveguidesmobile phonespiezoelectric sensorsnon-linear optical devices

https://en.Wikipedia.org/wiki/Lithium_niobate

Phys. Rev. B 101, 214311 (2020) -Laser polarization dependence of strong-field ionization in lithium niobate (aps.org)

12https://www.sciencedirect.com/science/article/pii/S2352847818300923

Lithium Niobate (LiNbO3) Crystal Cuts

Lithium niobate (LiNbO3, LN) crystal is a multi-functional material with favorable piezoelectric, nonlinear optical and electro-optic properties.

Polarization:

13

Lithium niobate has proven suitable for manufacture ofspatial switches,phase modulators,amplitude modulators, dispersion compensation devices, polarization scramblers, tunable filters and resonatorswavelength-selective optical add/drop

multiplexers and cross-connects

Lithium Niobate: The Silicon of Photonics!

14Lithium Niobate for M/NEMS Resonators | SpringerLink

Lithium Niobate Resonator

Equivalent Circuit

15

Lithium niobate (LiNbO3) on insulator (LNOI) is a material

platform for integrated photonics due to single crystal

LiNbO3 film’s wide transparent window, high refractive index, and high second-order nonlinearity.

Integrated lithium niobate photonics – Yang Li's Group (yligroup.com)

Lithium Niobate on Insulator for Photonic Integrated Circuits

16

Lithium Niobate Index of Refraction

5% Mg-doped

1% Mg-doped

17

https://picmagazine.net/article/105021/Thinking_Beyond_Conventional_Silicon_Photonics/feature

Photonic Integrated Circuit Waveguide Structures

18

Strip Waveguide StructuresPlanar and Strip Waveguide Structures

Titanium doped or proton bombarded

https://slideplayer.com/slide/6245103/

Propagation loss in Ti-doped LNbO3 is less than 0.2 dB/cm

19

Passive Y-Junction Beam Splitter

The fiber optic splitter is one of the most important

passive devices in the optical fiber link.

https://www.researchgate.net/figure/The-two-dimensional-Y-junction-dielectric-waveguide-used-in-the-analysis-The-main_fig12_3240569

W

W/2

W/2

n2

n2

n1

20http://www.satellitebyfibre.co.uk/contents/en-uk/d111.html

The heart of a Passive Optical Network is the optical splitter.

Passive Optical Network Splitter

1-to-16 Splitter

21

For the GPON, the optical splitter is essentially the heart of the network. The splitter allows a single port on the optical line terminal (OLT) to serve many optical network terminals (ONT).

Gigabit Passive Optical Network (GPON)

http://www.fiberlogs.fomsn.com/go4fiber/fiber-optic-news/what-is-gigabit-passive-optical-networks-gpon/

Point-to-Multipoint Network

22

PONPassive Optical Network: A point-to-multipoint, passive fiber network architecture in which a single fiber utilizes optical splitters to serve multiple premises.----------------------------------APONATM PON: The first type of PON standard, based on ATM (Asynchronous Transfer Mode) which is a protocol in telecom networkingBPONBroadband PON: Coming after APON, BPON supports WDM, higher upstream bandwidth, and a standard management interface that enabled shared vendor networksGPONGigabit PON: Based on the previous PON types, GPON supports higher data rates and increased security, and has been deployed around the world by major telecom operators.EPONEthernet PON: EPON is part of IEEE standard Ethernet for 1/1 Gbit/s, 10/1 Gbit/s, and 10/10 Gbit/s. With over 40 million installed EPON ports, it is the most widely deployed PON technology worldwide. Cable operators are utilizing EPON for business services as part of the DOCSIS initiative.10G-PONXG-PON: Is a new standard from 2010 that enables the delivery of 10Gbit/s speeds using PON network architecture. As the next generation of GPON, devices operate on the same network as GPON devices.

http://www.m2optics.com/blog/bid/52030/Passive-Optical-Networks-PON-Commonly-Used-Terms-Definitions

Passive Optical Networks

23

An optical fiber coupler is a device that distributes light from a main fiber toone or more branch fibers.

Two types of optical fiber couplers:

A. Core interaction – core to core interaction either directly or through lenses or gratings

B. Surface interaction – through itssurface normal to its core axis by converting guided core modes to both cladding or refracted modes

From: Senior, Optical Fiber Communications, 3rd ed., 2009; Section 5.6, Fig. 5.26, p. 257

Optical Fiber Couplers

24

Splitter

Combiner

Coupler

Optical Fiber Coupler Types and Functions

From: Senior, Optical Fiber Communications, 3rd ed., 2009; Section 5.6, Fig. 5.27, p. 258

25

Optical Fiber Coupler Types and Functions

From: Senior, Optical Fiber Communications, 3rd ed., 2009; Section 5.6, Fig. 5.27, p. 258

WavelengthMultiplexer

WavelengthDemultiplexer

Star Coupler

26

https://www.brainkart.com/article/Fiber-couplers_13622/

https://www.fiber-mart.com/news/fiber-optic-couplers-and-splitters-tutorial-a-922.html

Optical Fiber Fused Biconical Taper Coupler

Four-port (or 2 2)

27

Reducing the Cladding Thickness of Core-to-Core Spacing

28

Coupling Between Closely Spaced Optical Waveguides

21 0

22 0

coupling coefficient

( ) ( )cos

( ) ( )sin

P z P z Cz

P z P z Cz

C

=

=

=

From: Saleh & Teich, Fundamentals of Photonics, J. Wiley & Sons, Inc.; Section 7.4B

Light scattering is thephysical mechanismleading to coupling

Planar waveguides

z

2 ( )P z

1( )P z

Transfer length

29From: Saleh & Teich, Fundamentals of Photonics, J. Wiley & Sons, Inc.; Section 7.4B

0

21 0

22 0

coupling coefficient

( ) ( )cos

( ) ( )sin

transfer distance2

L

P z P z Cz

P z P z Cz

C

C

=

=

=

= =

3-dB couplerSwitch

Optical Couplers Operating as a Switch or a 3-dB Coupler

1P

3P

4P

2P

30

Optical Fiber Fused Biconical Taper Coupler

From: Senior, Optical Fiber Communications, 3rd ed., 2009; Section 5.6, p. 261-262

10

10

10

1

3 4

1

4

2

1

Excess loss 10 log (dB)

Insertion loss 10 log (dB)

Crosstalk 10 log (dB)

P

P P

P

P

P

P

= +

=

=

3

3 4

Split ratio 100%P

P P

= +

This is actuallya four-port

device

Refer to EE 443 Handout:

“Directional Couplers”

31

Optical Fiber Fused Biconical Taper 8 x 8 Star Coupler

32

https://www.fs.com/uk/how-do-different-fiber-optic-couplers-work-aid-405.html

Forming an Optical Fiber Fused Biconical Taper 4 x 4 Star Coupler

pull

33https://slideplayer.com/slide/8540576/

8 x 8 Bi-Directional Star Coupler Using 3-dB Couplers

34

Electro-Optic Effects

https://en.wikipedia.org/wiki/Electro-optic_effect

An electro-optic effect is a change in the optical properties of a material in

response to an electric field that varies slowly compared with the

frequency of light.

a) Change of the absorption

• Electroabsorption: general change of the absorption constants

b) Change of the refractive index and permittivity

• Pockels effect (or linear electro-optic effect): change in the refractive index

linearly proportional to the electric field. Only certain crystalline solids show the

Pockels effect, as it requires lack of inversion symmetry

• Kerr effect (or quadratic electro-optic effect, QEO effect): change in the

refractive index proportional to the square of the electric field. All materials

display the Kerr effect, with varying magnitudes, but it is generally much weaker

than the Pockels effect

35

Certain materials change their optical properties when subjected to an

electric field E. This is caused by forces that distort the positions,

orientations or shapes of the molecular structure of the material.

The electro-optic effect is the change in the refractive index of the

Material from the application of a DC or slowly varying electric field.

An applied electric field to an anisotropic electro-optic material modifies

Its refractive index and thus its effect of polarized light.

E

n(E)

n

Pockels medium

E

n(E)

n

Kerr medium

From: B.E.A. Saleh and M.C. Teich, Fundamentals of Photonics, Wiley & Sons, Inc. 1991.

Electro-Optic Effect (continued)

36

Electro-Optic Effect (continued)

From: B.E.A. Saleh and M.C. Teich, Fundamentals of Photonics, Wiley & Sons, Inc. 1991.

The change in the refractive index is typically very small. However,

its effect upon an optical wave propagating a distance much greater

than a wavelength can be very significant. Suppose the refractive

index increases by only 10-5, then an optical wave traveling 105

wavelengths will experience an added phase shift of 2 radians.

Materials which exhibit electro-optic effect can be modified by

deliberately applying a DC or slowly varying electric field by way of

electrodes placed strategically on the material’s surface. The next

slide presents an example.

37

(a) A lens of material whose index of refraction can be varied thus

varying its focal length.

(b) A prism whose bean bending ability is controllable can function

as a scanning device.

(c) Light transmitted through a transparent plate of controllable

refractive index undergoes a controllable phase shift – it can

be used as a phase modulator.

(d) An anisotropic crystal with variable refractive index can be used

as a controllable wave retarder – used to change the polarization

of the light beam – polarizer.

(e) A wave retarder placed between two crossed polarizers gives rise

to transmitted light whose intensity is dependent upon the phase

retardation allows for a device whose transmittance is voltage

controllable – thereby making an optical intensity modulator or

a switch.

Some Applications of EO Devices

From: B.E.A. Saleh and M.C. Teich, Fundamentals of Photonics, Wiley & Sons, Inc. 1991.

38

Electro-Optic Effect (continued)

Taylor’s series expansion:

https://slideplayer.com/slide/6245103/

633 21 1

2 2( )n E n r n sE E= − − −

6331

2( )n E n r n E= −

21

2( )n E n sE= −

39

Pockels Effect

Schematic diagram of the operation of a modulator based

on the electro-optic effect. In this configuration, the voltage is

applied parallel to the direction of light propagation.

https://pe2bz.philpem.me.uk/Lights/-%20Laser/Info-999-LaserCourse/C04-M07-ElectroOptic+AcoustoOpticDevices/mod04_07.htm

When the

correct voltage

is applied to

the device, the

direction of the

polarization is

rotated by 90° .

V = 0; no light.Otherwise,light passes.

V

T = T0 sin2(p Dn L/)

40From: B.E.A. Saleh and M.C. Teich, Fundamentals of Photonics, Wiley & Sons, Inc. 1991; p. 701

Longitudinal, Transverse & Traveling-Wave Modulators

(a) Longitudinal Modulator (b) Transverse Modulator (c) Traveling-Wave Modulator

Section 18.1 of Saleh & Teich; pp. 696-712

41

Phase Modulators

When a beam of light traverses a Pockels cell of length L with an electric

field E is applied, it exhibits a phase shift (wavelength 0)

We can write the phase as

where

The electric field is applied across the cell with voltage V over distance d.

Hence, E = V /d .

Traveling Wave:

0

0

2 ( )( )

n E Ln E k L

= =

630

0

3r n LV

d

− = =

0

0

2 nL

=

From: B.E.A. Saleh and M.C. Teich, Fundamentals of Photonics, Wiley & Sons, Inc. 1991;. Sect. 18.1B

Section 18.1 of Saleh & Teich; pp. 696-712

0 0( , ) exp ;V

t L A j tV

= − − +

0

633

dV

L r n

=

V

L

d

42

Phase Modulators (continued)

From: B.E.A. Saleh and M.C. Teich, Fundamentals of Photonics, Wiley & Sons, Inc. 1991;. Sect. 18.1B

Section 18.1 of Saleh & Teich; pp. 696-712

V

V

00

633

where

V

V

dV

L r n

= −

=

The parameter V is known as the half-wave voltage, and it is the applied voltage at which the phase shift changes by radians. Note that this is a linear relationship between optical phase shift and applied voltage.

The electric field may be applied either perpendicular (transverse) to the direction of light propagation or parallel (longitudinal) to that direction.

43

Phase Modulators (Traveling Wave Effect)

From: B.E.A. Saleh and M.C. Teich, Fundamentals of Photonics, Wiley & Sons, Inc. 1991;. Sect. 18.1B

Section 18.1 of Saleh & Teich; pp. 696-712

How fast a phase modulator can be operated depends upon the capacitanceof the device and the transit time of the light through the modulator. If the

electric field E(t) varies significantly over the transit time T of the light, thenthe traveling optical wave will be subjected to different electric fields during itstravel through the device. A traveling wave electrode structure which matches the velocity of the light is one solution to this issue.

Practical phase modulators operate from hundreds of megahertz to several gigahertz. A commonly used material for such modulators is lithium niobate(LiNbO3). An optical waveguide for defining the path if the light signal is todope the LiNbO3 with titanium (to increase the refractive index). Another wayto form the waveguide is to use proton ion bombardment.

See the next slide for an illustration of this.

44

Integrated-Optical Phase Modulator (Using E-O Effect)

From: B.E.A. Saleh and M.C. Teich, Fundamentals of Photonics, Wiley & Sons, Inc. 1991; p. 702

Section 18.1 of Saleh & Teich; pp. 696-712Section 18.1 of Saleh & Teich; pp. 696-712

Such modulators have been operatedat speeds in excess of100 GHz.

+V

+V

45From: B.E.A. Saleh and M.C. Teich, Fundamentals of Photonics, Wiley & Sons, Inc. 1991; p. 704Section 18.1 of Saleh & Teich; pp. 696-712

Integrated-Optical Intensity Modulator (IM) For Switching

46

The Kerr electro-optic effect, or DC Kerr effect, occurs when a slowly

varying external electric field is applied (e.g., a voltage between two

electrodes) across the sample material, the sample becomes

birefringent. Thus, the material exhibits different indices of refraction

for light polarized parallel to or perpendicular to the applied field. The

difference in index of refraction, n, is given by

where is the wavelength of the light, K is the Kerr constant, and E is

the strength of the electric field. This difference in index of refraction

causes the material to act like a waveplate when light is incident on it

in a direction perpendicular to the electric field. If the material is

placed between two "crossed" (perpendicular) linear polarizers, no

light will be transmitted when the electric field is turned off, while

nearly all the light will be transmitted at some optimum value of the

electric field.

2n KE =

https://en.wikipedia.org/wiki/Kerr_effect

Kerr Electro-Optic Effect

47

Laser Source

50/50 Beam Splitter

Mirror

Mirror

Phase Shifter

Outputs

Mach-Zehnder Interferometer

Mach – Zehnder Interferometer | PhysicsOpenLab

Combiner

48From: B.E.A. Saleh and M.C. Teich, Fundamentals of Photonics, Wiley & Sons, Inc. 1991; p. 703

A Phase Modulator Within a Mach-Zehnder Interferometer

Section 18.1 of Saleh & Teich; pp. 696-712

Transmittance: 02( ) cos2 2

VT V

V

= −

( )T V

V

49

X-Cut LiNbO3 Intensity Modulator

https://www.semanticscholar.org/paper/Mode-switch-based-on-Mach-Zehnder-interferometer-in-Zhang-

Chen/4b3cf7d891196b5d7e5257250981c7c13777babe

https://www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=3918

50https://www.slideshare.net/SureshJat5/external-modulators

Driving an Integrated-Optical Mach-Zehnder Modulator

51

Modulation Characteristic of an External Intensity ModulatorShowing output light-wave signal from input electrical signal

From: Papen & Blahut, Lightwave Communications, Cambridge University Press,2019

V

2cos2

V

V

Figure 7.18 (p. 328)

Input electrical signal

Output light-wavepowerNonlinear

Operation

52From: Papen & Blahut, Lightwave Communications, Cambridge University Press,2019

Operating Equations for a Balanced Intensity Modulator

( ) ( )

+= −

= −

=

1 2( ) ( )/2

1 2

1 2

( )cos ( ( ) ( ))/2

When ( ) ( ), the device operates as

a balanced modulator with response,

( ) ( )cos

2

j t tout

in

out

in

s tt t

s

t t

s t V t

s V

e

phase amplitude

53Lithium Niobate Electro-Optic Modulators, Fiber-Coupled (thorlabs.com)

Lithium Niobate Electro-Optical Modulators

• 10 GHz, 20 GHz, or 40 GHz Lithium Niobate (LiNbO3) Modulators

• Fiber-Coupled, High-Speed Modulation

• Intensity, Phase, or IQ

• X-Cut or Z-Cut Devices

LN81S-FC 10 GHz Intensity Modulator, X-Cut

LN27S-FC 40 GHz

Phase Modulator with

Polarizer, Z-Cut LNLVL-IM-Z Low Vπ 40 GHz

Intensity Modulator, Z-Cut

54From: B.E.A. Saleh and M.C. Teich, Fundamentals of Photonics, Wiley & Sons, Inc. 1991; p. 706Section 18.1 of Saleh & Teich; pp. 696-712

An Electro-Optic Prism & An Electro-Optic Double Prism

3 31 1

2 2

Vn n n

dr rE = = − −=

Rotate EOP by 90

Selects anx y array

Vy

Vx

55

Schematic arrangement principle and transmission spectra of the... | Download Scientific Diagram (researchgate.net)

Transmission Spectra of a Fabry-Pérot Interferometer

r r

Free spectral range

Center wavelength

56Fabry-Perot Interferometer (gsu.edu)

The net phase change is zero for two adjacent rays, so the condition

represents an intensity maximum.

Fabry-Pérot Interferometer (FPI)

57

RP Photonics Encyclopedia - acousto-optic modulators, AOM, Bragg cells, diffraction efficiency, traveling wave, sound, RF driver,

applications (rp-photonics.com)

An acousto-optic modulator (AOM) is a device which can be used for controlling the

power of a laser beam with an electrical drive signal. It is based on the acousto-optic

effect, i.e. the modification of the refractive index of some crystal or glass material by the

oscillating mechanical strain of a sound wave (photoelastic effect).

Acoustic-Optic Modulator (AOM)

Refer to Figure 11.16In Senior on page 626.

58Isomet Acousto-optics.

Acoustic-Optic Modulator (AOM)or Bragg Cell

inc2 B

/a av f =

( )sin2

2

B B

B

a

n

f

nv

= =

=

B

~

f

Refer to Figure 11.16In Senior on page 626.

59

Launching Surface Acoustic Waves on Piezoelectric Material

Difference between 1 Port SAW Resonator,2 Port SAW Resonator (rfwireless-world.com)

60Filed by TriQuint Semiconductor, Inc.

61

https://medium.com/@stangarfield/100-questions-answers-on-collaboration-communities-5ceed474dca9

62

Atomic Origin of Optical Nonlinearity

• Simple harmonic oscillator model (linear)

Electronic charge

Atomic nucleus

Restoring force

Linear polarization: parabolic potential

Lorentz-Drude

2nd order nonlinearity: Pockels media

3rd order nonlinearity: Kerr media

2nd order nonlinearity is absent in crystals

with centro-symmetry!

Induced dipole moment

Charge density Electron charge

Displacement

PED += 0

F = kx F = kx + k2x2 F = kx + k3x3

22

2 b

d r drm m r eE

dt dt + + =

eP n e r=

Damping Restoring Driving

Juejun Hu, MSEG 667 Nanophotonics: Materials and Devices, hujuejun@udel.edu