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The Technology of Selective Area Growth and How its Simulation Makes Photonic Integrated Circuit Possible. Muhammad A. Alam and Roosevelt E. People Silicon Lab, Agere Systems. Outline Introduction: why is PIC difficult ? SAG and its Simulation How Agere designs PIC Circuits

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slide1

The Technology of Selective Area Growth and How its Simulation Makes Photonic Integrated Circuit Possible

Muhammad A. Alam and Roosevelt E. People

Silicon Lab, Agere Systems

Outline

Introduction: why is PIC difficult ?

SAG and its Simulation

How Agere designs PIC Circuits

PIC for short-haul systems

Conclusions

slide2

Collaborators

  • S. Sputz, Eric Issacs, Y. Vandenberg, K. Evans-Lutterodt
  • J. Johnson, L. Ketelsen, and J. Eng
  • M. Hybertsen, Kent Smith, M. Pinto
  • L. Gruezke and L. Reynolds
slide3

Long distance vs. local area network

long-distance

metro

LAN

Wide Area Network : high performance circuits (part 1)

Local Area Network: lower performance but also

lower cost (part II)

introduction a simple optical communication system
Introduction: A Simple Optical Communication System

Receiver

Transmitter

Laser Modulator Coupler

Amplifier

Detector Amplifier

data in

data out

introduction silicon vs iii v integration
Introduction: silicon vs. III-V Integration

GaAs H-MESFET Chips (1996)

~ 1 million Transistors

~ 4 level of metals

Silicon DSP Chip:

~ 10 million Transistors

~ 5/6 level of metals

When devices are the same, high integration is possible

when devices are dissimilar, integration becomes difficult

slide6

PIC issue 1: Integration of Dissimilar Devices (e.g. EML)

Top View

x

z

Laser

Modulator

Side

View

y

z

How to make devices of different thicknesses on the same wafer ?

slide7

PIC issue 2: Optical Interconnect (e.g. EML)

Coupling (D)

Mode Shift ( dD)

Radiation Loss ( L/D )

FCA

( L )

How to make a low loss optical interconnect ?

slide8

glass WG

glass WG

glass WG

InP laser

PIC issue 3: Coupling to Fiber

poor

Simple Coupling

InP laser

Good but costly

and lossy

Lens Coupling

InP laser

5 mm

Integrated and

excellent

Expanded-Beam

Coupling

30mm

How to ensure good coupling between PIC and the fiber ?

(L. Ketelsen)

how to solve these three problems

isolators

Laser array

Amplifer/modulator

fiber

Ball lens

in V-grove

p-i-n- Monitor

diode

Planar lightwave

circuit

How to Solve these Three Problems

(~ 1992/1993),

(Tom Koch, U. Koren ...)

(~1999/2000),

(L. Ketelsen, J. Johnson ...)

traditional interconnect integration issue 2
Traditional Interconnect Integration (Issue 2)

Multiple Step Etch

Shadow Deposition

Photo-Resist

sag basics a schematic diagram of a mocvd reactor
SAG Basics: A Schematic Diagram of a MOCVD Reactor

H2

Carrier Gas + AsH3 + PH3

TMIn

TMGa

SiH4

Stagnant Layer

Heater

Wafer

slide14

The Empirical Approach to SAG

A team of about ten people trying to see -

a. did we get the correct thickness variation

b. did we get the right composition variation (index) ?

slide15

Model: Simulation of SAG MOCVD

Dj Dnj(r)=0, kjnj(0)=J(0)

Dj ~ T(3/2) [(mjmH)/(mj+mH) ]s P

P = pressure, D = diffusion coefficient

mH=masses

sag model simulation of gas dynamics in boundary layer
SAG Model: Simulation of Gas Dynamics in Boundary Layer

x

z

Ga Flow Pattern

D/k=180 um

In Flow Pattern

D/k = 25 um

properties of the composite films
Properties of the Composite Films

Enhancement Factor:

E In (x,y) = n In (x,y,0) / n In (x0,y0,0)

Thickness Enhancement:

E Q (x,y) = E In (x,y) (1-s0) + E Ga (x,y)s0

Composition

1 - s(x,y) = ( E In (x,y)/E Q (x,y) ) (1-s0)

Q0 = In(1-s0)Ga(s0)As(1-t0)P(t0)

Q=In(1-s)Ga(s)As(1-t)P(t)

basics experimental techniques
Basics: Experimental Techniques

WYCO

Micro-Xray

Micro-PL

Thickness

Bandgap

Strain

E. Issacs, J. Vandenberg,

K. Lutterodt

R. Scotti, S. Sputz

S. Sputz

experimental verification
Experimental Verification

Thickness In, Bandgap Ga ; Thickness, bandgap, and strain has same profile

a puzzle
A Puzzle

( 30 mm )

Laser

x

z

Alley

300 mm

T. Siegrist, J. Vandenberg,

T. Pernell, and S. Sputz

Intuition: Bandgap follows thickness in the laser section

Puzzle: It does the opposite in the alley

Process vs. characterization

slide21

Puzzle Resolved

Thickness (nm)

Line Cut

Expt

Wavelength (nm)

Sim.

  • Explanation:
  • In decay 25 um; Ga decay 180 um
  • Expander is Ga rich
  • Intrinsic property, not a material
  • problem

Strain(%)

design process an example for wsl

Rectangular

Laser

  • Hammerhead

Relative Thickness

  • Final Design

Distance (micron)

Design Process: An Example for WSL

Laser array

fiber

slide25

Isolator modulator

amplifier

fiber

p-i-n- Monitor

diode

Design: Mask design for the XBAM

Lens no longer necessary

self-aligned, reduced cost

slide26

Design: Mask design for the XBAM

prev best

Ultra-short oxide masks, impossible without a simulator

slide27

Design: Mask design for the Tunable Laser Project

Isolator modulator

amplifier

fiber

p-i-n- Monitor

diode

Laser array

slide28

Design: Mask design for the Tunable Laser Project

Side view

Top view

mask layer

- first use of two level SAG - 26 parameter optimization

- OFC best new product award

slide30

where do we stand now on long-haul device integration ?

1. Simulation tools available on the web. Automatically evaluates designs and tells one if how closely the objectives can be made.

2. All the designers know how to use it, and since 1997 all the PIC designs are based on it.

3. Instead of months, design of PIC integration now takes only days.

4. All optical processing for > 40G circuits will also be completely integrated from the very beginning - this in contrast to our competitors

“…. SAG modeling has become so remarkably accurate and predictive that we will no longer use characterization as a means for verifying SAG processing step ... “

slide31

Long distance vs. local area network

fiber

transceiver

long-distance

metro

LAN

ethernet and fiber-Channel

- direct modulation

- very low cost (detector/transmitter)

- short distances (amplifier-less)

small footprint lasers packing density and radiation loss
Small footprint lasers, Packing Density and Radiation Loss

Minimum inter-device spacing is 300 micron (NTT, 1996)!

slide33

Small footprint lasers: Radiation Loss and Redesign

1. Main contribution to radiation is

from the transition region.

2. Rectangular to special mask profile

slide34

Lateral taper

Small footprint lasers: after fabrication

Quantum well active

Underlying thick waveguide

Blocking structure

Laser Facet

20:1 lateral active taper

Underlying thick waveguide

Expander Facet

No active, thinned

waveguide

slide35

expanded beam laser

standard laser

Small footprint lasers: coupled power 3x times greater

XBL Far Field ~16x9 degrees

  • Coupled power is ~3x greater
  • Narrow far field provides increased coupling
  • power and increased alignment tolerance

FP Far Field: ~30x30 degrees

slide36

Small footprint lasers: increased packing density

Prev. “theory” limit

- 50 percent more devices with 3x higher

performance - a win/win situation

- Part of Agere’s new Transceiver chip-set,

by far the best in the industry

- J. Eng did laser design

pic of a self aligned transponder for lan

fiber

transceiver

PIC of a Self-aligned Transponder for LAN

I/O Port

Laser

Detector

Transceiver

Oxide Mask

In Distribution

pic for coarse wdm transceiver for lan
PIC for coarse-WDM Transceiver for LAN

fiber

transceiver

Direct modulation must be below 20 GHz

EML or external modulation too expensive

Multiple wavelength is a solution

- 8-10 colors over a multi-mode/

single- mode fiber

lan cwdm solution multiple wavelength vcsel array
LAN-CWDM Solution: Multiple Wavelength VCSEL Array

Mirror

QW

Mirror

l1

l1

l2

l3

Simultaneous matching of Cavity Mode and Gain Peak is difficult !

lan cwdm vcsel design of cavity and matching
LAN-CWDM VCSEL: Design of Cavity and Matching

Top SCH

Bottom SCH

Mirror

Z-axis (um)

SAG allows perfect matching of cavity and

emission modes for all wavelengths !

conclusions
Conclusions
  • Photonic Integrated Circuits are becoming integral part of modern communication systems, and SAG-MOCVD has been an enabling process technique to fabricate these PIC.
  • The 3D SAG model has been remarkably successful in designing these PIC, and has reduced design cycle time from months to days.
  • As part of a tool suite (laser simulation for QW and Bragg-grating design, beam propagation for waveguide design, etc. ), makes PIC design less of a trial-an-error process.