AWG optical demultiplexers: from design to...

The Development of Excellence of the Telecommunication Research Team in

Relation to International Cooperation - CZ.1.07/2.3.00/20.0217

AWG optical demultiplexers:

from design to chip

Dana Seyringer

Research Centre for Microtechnology

Vorarlberg University of Applied Sciences, Austria

Telecommunication

Educational Seminar

The Development of Excellence of the Telecommunication Research Team in

Relation to International Cooperation - CZ.1.07/2.3.00/20.0217

Where Can I Switch It On?

We live in a computerworld!!!

We live in a computerworld!!!

Fiber Optics Communication

What is Fiber Optics?

Fiber Optics = Fiber + Optics

Fiber: a very thin plastic or glass strand

Optics: light

In essence: light guided in an optical fiber

Point-to-point

optical communication

Point-to-point

optical communication

An optical system increases strongly the bandwidth (the speed of network).

How To Expand Network Capacity?

To expand the capacity of transmitted data in the point-to-point optical

system, multiple optical signals can be multiplexed together on a

single fiber simply by adding optical multiplexers/demultiplexers.

SM-fiber core is cca. 9 µm thick!

SM-fiber core is cca. 9 µm thick!

WDM is the process by which multiple wavelengths carrying the various

data are simultaneously combined (multiplexed) in a single optical fiber,

and then after the data was transmitted, they are separated (demultiplexed)

again at the receiving end of the fiber.

WDM: Wavelength Division Multiplexing

Optical fiber

www.lightriver.com

l1 l2 l3

l1

l2

l3

l1

l2

l3

http://www.lightriver.com/

Optical MUX/DeMUX Technologies

There are four basic MUX/DeMUX technologies:

• Thin Film Filters (TFF),

• Fiber Bragg Gratings (FBG),

• Arrayed Waveguide Grating (AWG)

• Free-Space Diffraction Gratings (FSDG)

There are four basic MUX/DeMUX technologies:

• Thin Film Filters (TFF),

• Fiber Bragg Gratings (FBG),

• Arrayed Waveguide Grating (AWG)

• Free-Space Diffraction Gratings (FSDG)

Wavelength filtering:

1. Serially: where individual elements are used to multiplex (or demultiplex)

wavelengths on one-by-one basis: TFF & FBG

• TFFs Only for low channel counts (up to 16) due to size and insertion losses.

• FBGs Only for low channel counts (up to 16) due to size and insertion

losses.

2. Parallely: where all wavelengths are demultiplexed at the same time with the

same optical demultiplexer:

• AWGs & FSDG (for high channel counts).

top viewtop view

Arrayed Waveguide Gratings (AWG)

focus line with focus points

lc

lc: input design parameter

Modern SM fibers have losses cca 0.2 dB/km in the 3rd window!Modern SM fibers have losses cca 0.2 dB/km in the 3rd window!

Optical losses in the fibers depend on the specific transmission wavelength.

lc: Input Design Parameter

lc = 1.55 µm

Different AWGs

Based on applications the AWGs can be divided according to:

Number of channels: N = 4, 8, 16, 32, 64 (standard); N = 128, 256, … (on request)

Channel spacing: df = 100 GHZ (0.8 nm), 50 GHz (0.4 nm) (standard)

df = 25 GHz (0.2 nm), 12.5 GHz (0.1 nm), 10 GHz (0.08 nm) (on request)

l1 l2 l3 l4 l5 l6 l7 l8

l2

l4

l3

l5l6

l8

l7

Optical

demultiplexer

l1

lc = 1.55 µm100 GHz

lc, N, df: input design parameters

ITU Grid

ITU Grid:

Standards developed by the

ITU (International

Telecommunications

Union)

The center operating

wavelength of the C-band

lies at a wavelength of

1550.12 nm (193.4 THz).

Different AWGs

Based on applications the AWGs can be divided according to:

Signal shape:

Gaussian: features very low insertion loss.

Flat-top: suffers far higher insertion losses but features much better detection conditions.

Colourless: 100 GHz or 50 GHz channel spacing and 8 (or 16) output channels

From a technological point of view:

Low-index contrast AWGs (silica based waveguide devices) with a typical refractive index

difference of 0.75%:

• advantage - very low coupling losses between input/output waveguides and optical fibers.

• disadvantage – device size.

High-index contrast AWGs (Silicon On Insulator (SOI)) with a refractive index contrast 58 %:

• advantage - much smaller size (can be easily implemented on-chip).

• disadvantage - much higher coupling losses compared to silica AWGs.

Different AWGs

Low-index contrast AWGs High-index contrast AWGs

waveguide size, nc, ncl, lc, N, df: input design parameters

waveguide

waveguide

How to Design AWG? Apollo Photonics design tool

Geometrical

parameters

Output: simulated AWG

transmission characteristics

lc = 1.55 µm100 GHz

Transmission parameters (IL, AX, ILu, …) are calculated from simulated or measured

transmission characteristics.

Transmission parameters (IL, AX, ILu, …) are calculated from simulated or measured

transmission characteristics.

AWG request:Number of channels: N = 8Channel spacing: df =100 GHzITU Wavelengths: lc = 1.55 µmPrice (per channel)

Transmission parameters:• Insertion loss, IL• Channel crosstalk, AX• Insertion loss uniformity, ILu• Packaged/on chip• ….



AWG design

waveguide size, nc, ncl, lc, N, df: input design parameters

How to Design AWG? Insertion loss (pILu)





8-Channel, 100 GHz AWG: Geometrical Parameters

Geometrical parameters:

• coupler length (Lf)

• waveguide length increment (dL)

• minimum waveguide separation in PA (dd)

• minimum waveguide separation at I/O (dx)Geometrical

parameters

AWG request:Number of channels: N = 8Channel spacing: df =100 GHzITU Wavelengths: lc = 1.55 µm

Transmission parameters:•Insertion loss, IL 0 dB•Channel crosstalk, AX = 30 dB•Insertion Loss uniformity, Lu = 0.5 dB

AWG request:Number of channels: N = 8Channel spacing: df =100 GHzITU Wavelengths: lc = 1.55 µm

Transmission parameters:•Insertion loss, IL 0 dB•Channel crosstalk, AX = 30 dB•Insertion Loss uniformity, Lu = 0.5 dB

„AWG-parameters“ Tool

M. Bielik and M. Kytka

8-Channel, 100 GHz AWG at 1 Wavelength

top viewtop view

top viewtop view

8-Channel, 100 GHz AWG at 8 Demultiplexing Wavelengths

Ph

ased

arr

ay

Output coupler

Output

waveguide

AWG Simulation in the Whole Wavelength Range

sideviewsideview

Optiwave

simulation

top viewtop viewP

hased

arr

ay

Output couplerOutput

waveguide

Cross-section of theoutput waveguidesCross-section of theoutput waveguides

Optical power calculated in eachoutput waveguide

Optical power calculated in eachoutput waveguide

----TE

----TM

----TE

----TM

8-channel 100 GHz AWG Transmission Characteristics

The output from the simulation are the transmission characteristics forTE and TM palarization. They describe the optical properties of the

designed AWG.

The output from the simulation are the transmission characteristics forTE and TM palarization. They describe the optical properties of the

designed AWG.

Transmission parameters arecalculated fromsimulated/meas

uredtransmission

characteristics. They describe

the AWGs functionality andare also used in

the design ofoptical

networks.

Transmission parameters arecalculated fromsimulated/meas

uredtransmission

characteristics. They describe

the AWGs functionality andare also used in

the design ofoptical

networks.

AWG Transmission Parameters

Patrick Schmid: AWG-Analyzer software tool

AWG Mask Layout

When the AWG designs are ready for the fabrication the next step is their export in

GDSII format. From all single GDSII files the whole mask layout will be

generated and sent to the mask house for the fabrication.

When the AWG designs are ready for the fabrication the next step is their export in

GDSII format. From all single GDSII files the whole mask layout will be

generated and sent to the mask house for the fabrication.

Whole maskWhole mask Device stampsDevice stamps

Mask design rule: no T chip connections!!!Mask design rule: no T chip connections!!!

AWG Fabrication

Final Structure

Cross-sectional

view shows cross-

section of 4 output

waveguides.

Fabricated Wafer with Various AWGs

AWG MeasurementILC Bratislava

Measured Transmission CharacteristicsCoupling

losses

AWG

losses

8-channel, 100 GHz AWG

Simulated transmission

characteristics

Mesured transmission

characteristics

2 cm x 1.7 cm

Design Verification

Parameter AWG-Parameters tool:

input design parameters

AWG-Analyzer tool:

simulation

AWG-Analyzer tool:

measurement

Number of ch. Num = 8 Nr. Channels = 8 Nr. Channels = 8

AWG central wavelength Lambda = 1550.012 nm lc = 1549.00 nm lc = 1547.50 nm

Channel spacing df = 100 GHz Ch. Sp. = 100 GHz Ch. Sp. = 100 GHz

Insertion loss IL = -2.624 dB IL = -6.438 dB

Insertion loss uniformity Lu = 0.712248 dB ILu = 0.520 dB ILu = 0.694 dB

Adjacent channel crosstalk Cr = - 29.338942 dB AX = -42.024 dB AX = -32.476 dB

Non-adj. channel crosstalk nAX = -46.413 dB nAX = -46.308 dB

Background crosstalk BX = -54.571 dB BX = -54.793 dB

Transmission Parameters

20-ch, 200 GHz AWG

Chip 02 Chip 03

Chip 04 Chip 05Chip 01

Design (fabrication) stability

Design (fabrication) stability

Insertion loss 2.594 dB

Insertion loss uniformity 0.490 dB

Adjacent crosstalk 40.804 dB

Non-adjacent crosstalk 41.724 dB

layout


Size: 4.5 cm x 3 cm

Parameter AWG-Parameters tool:

input design parameters

AWG-Analyzer tool:

simulation

AWG-Analyzer tool:

measurement

Number of channels Num = 40 Nr. Channels = 40 Nr. Channels = 40

AWG central

wavelength

lc = 1550.043 nm lc ~ 1550.12 nm lc ~ 1548.35 nm

Channel Spacing df = 100 GHz Ch. Spacing ~ 100 GHz Ch. Spacing ~ 100 GHz

Peak insertion loss Depends on technology pIL = -1.502 dB pIL = -4.145 dB

Insertion loss Depends on technol. IL = -2.833 dB IL = -5.964 dB

Peak insertion loss

uniformity

Lu = 0.982 dB pILu = 0.873 dB pILu = 0.754 dB

Insertion loss

uniformity

ILu = 0.923 dB ILu = 0.785 dB

Adj. channel crosstalk Cr = -31.4 dB AX = -30.395 dB AX = -30.280 dB

Non-Adj. channel

crosstalk

Depends on technology nAX = -37.703 dB nAX = -40.664 dB

Background crosstalk Depends on technology BX = -65.197 dB BX = -67.653 dB

40-channel, 100 GHz AWG: Transmission Paramenters

?Design

Foundry (Fabrication)Measurement

DesignFoundry (Fabrication)

Measurement


Simulation

Measurement

PDL < 7dB

PDW = 0.2nm

PDL< 0.7dB

PDW = 0.02nm

64-channel, 50 GHz AWG. PDL & PDW

Simulation

Measurement


8-ch, 100 GHz AWG8-ch, 100 GHz AWG


256-Ch, 25 GHz Narrow Channel Spacing AWG



13 cm x 10 cm

256-Ch, 25 GHz Narrow Channel Spacing AWG

Optimized 256-Ch, 25 GHz Narrow Channel Spacing AWG

128-Ch., 10 GHz, Narrow Channel Spacing AWG2 months computing time

Background crosstalk

Non-Uniformity

ILu = 1.7 dB

BX = -65 dB

8-channel, 100 GHz Colourless AWG

The condition for cyclic or colourless AWGs is

that the FSR should equal N times the

channel spacing, where N is the number of

output channels.

FSR = 8 x 100 GHz = 800 GHz.

AWG Design: 8-channel, 100 GHz Colourless AWG

Transmission characteristics: 8-ch., 100 GHz Colourless AWG

AWG Temperature Dependence

Since the refractive indices are temperature dependent, they cause wavelength

shift by temperature fluctuations.

Since the refractive indices are temperature dependent, they cause wavelength

shift by temperature fluctuations.

SOLUTION?SOLUTION?

Temperature stabilization: AWG is packaged with the heater that keeps the chip at

constant temperature (usually 75oC).

Temperature stabilization: AWG is packaged with the heater that keeps the chip at

constant temperature (usually 75oC).

AWG athermal design: the AWG structure is composed of two parts: SiO2 + polymers.

The refractive index of the polymers has opposite temperature dependence im

comparison to SiO2.

AWG athermal design: the AWG structure is composed of two parts: SiO2 + polymers.

The refractive index of the polymers has opposite temperature dependence im

comparison to SiO2.

AWG Packaging

Datasheet

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AWG optical demultiplexers: from design to...

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