Technologies for Photonic Integrated Circuits

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Technologies for Photonic Integrated Circuits
Larry A. Coldren Fred Kavli Professor of
Optoelectronics and Sensors ECE and Materials
Departments
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Motivation for Photonic Integration

• Role of photonic integrated circuits
• Reduce cost, size, power consumption
• Improve functionality, performance, and
  reliability of optical networks
• Enable new functionalitiese.g., high BW OPLLs
• Demonstrated components
• Tunable transmitters/receivers
• Tunable transceivers/wavelength converters
• WDM transmitters/receivers
• Optical routers on chip
• Ultimate goal - simplest technological platform
  to enable integration of many different
  (optimized) functions on the same chip
• For a new PIC, only mask set changes
• Processes are fixed, although different ones may
  be selected

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Coldren-OIDA, November 7, Baltimore
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PIC Platform Requirements

• Passive waveguide
• Low loss
• High index tuning/absorption efficiency
• Strong optical guiding
• Weak optical guiding

• Active waveguide
• Optical gain/photocurrent
• Efficient electrical pumping
• Large optical confinement
• Small optical confinement

Low reflection space efficient
transitions Polarization insensitivity
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Coldren-OIDA, November 7, Baltimore
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Overview of Existing Technologies

• Offset quantum well
• Dual quantum well
• Butt-joint growth
• Selective area growth
• Twin waveguide
• Quantum well intermixing

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Coldren-OIDA, November 7, Baltimore
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Integrated SGDBR-MZ (ILMZ) modulator Optical
Duobinary Modulation (offset QW)
JDSU
ILMZ
200km

• Improved transmission compared to NRZ
• Three-level encoding 1, 0, -1
• Require well-behaved modulation response
• Push-pull InP modulator can support this format
• 250 km _at_ 10 Gb/s demonstrated

Coldren-OIDA, November 7, Baltimore
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Mach-Zehnder Wavelength Converter(Dual QW)
DQW

• Traveling wave Mach-Zehnder
• Series push-pull configuration for increased
  bandwidth
• Increased bias complexity

MZ-WC Bias Circuit
Figures courtesy of Anna Tauke-Pedretti
Coldren-OIDA, November 7, Baltimore
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Mach-Zehnder Wavelength Converter(Dual QW)

• Transmitter Performance
• 30 GHz Bandwidth
• 40 Gb/s error free operation
• Low/negative chirp

DQW

• Wavelength conversion
• Error free 40 Gb/s operation
• 2.5 dB power penalty over 30 nm

10 Gb/s Eyes
0 km
25 km
50 km
Figures courtesy of Anna Tauke-Pedretti
Coldren-OIDA, November 7, Baltimore
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Flexible Integration Platform

• High performance integration platform
• Multiple band-edges using quantum well
  intermixing
• Very efficient modulators, high gain active
  regions, low loss passive regions
• Extra low loss passive regions reduce modal
  interaction with p-doped layers
• Simple Offset QW blanket regrowth High Sat
  Power SOAs
• Simple UTC blanket regrowth Very high speed
  detectors

1 dB/mm
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Coldren-OIDA, November 7, Baltimore
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Centered Offset QW Comparison

• QWs placed in center of optical mode
• 7-10 QWs
• Maximize confinement factor
• Maximize gain
• Minimize device length
• Reduce saturation power
• Increased nonlinearity
• QWs placed outside of waveguide
• 5-7 QWs
• Reduce confinement factor
• Reduce gain
• Increase device length
• Increase saturation power
• Linear response over wider input power range

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Coldren-OIDA, November 7, Baltimore
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Linear SOAs using Low-Confinement Offset QW

• Regrow o-MQWs on thin InP layer above intermixed
  c-MQW regions
• LC-OQWs interact only with mode tail
• 3-5 QWs
• Minimize confinement factor
• Low gain
• Increase saturation power
• Increased linearity
• PSAT gt 20dBm theoretically possible

(INTERMIXED)
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Coldren-OIDA, November 7, Baltimore
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Centered QW LC-OQW SOA

• Dual section SOA gain
• c-MQW G 12.6 o-MQW G 2.6
• GMAX 22.7dB PSAT 18.6dBm
• GMAX 28.2dB PSAT 18.2dBm

J(c-MQW) 15 kA/cm2 J(o-MQW) 6 kA/cm2
J.Raring et al., ISLC (2006)
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Coldren-OIDA, November 7, Baltimore
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Quantum-Well Intermixing (QWI) Plus Regrowths

• Only blanket regrowths

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Coldren-OIDA, November 7, Baltimore
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QWI Transceiver
QWI
Figures courtesy of James W. Raring
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Centered QW UTC Photodiode
40 Gb/s NRZ OEIC Wavelength Conversion with UTC
Detectors
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Coldren-OIDA, November 7, Baltimore
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PIC Summary

• Integration platforms have evolved from simple
  offset QW for increased functionality and
  performance
• Dual QWimproved modulators
• Quantum-well intermixing (QWI)multiple band
  edges within guide
• QWI offset gain and absorbershigh sat. SOAs
  and Detectors
• Quantum well intermixing provides a platform to
  realize these functions
• Multiple bandgap
• Low loss
• Easy addition of extra active epi layersstill a
  platform technology
• Single-chip photonic transmitters, receivers,
  transceivers, wavelength converters, and routers
  demonstrated

Coldren-OIDA, November 7, Baltimore
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Toward 40 Gb/s VCSELs

• Tapered oxide apertures for near zero optical
  scattering loss and low C
• - hd 0.7 down to 0.6 mm
• Careful bandgap engineering and modulated doping
  for low R and low optical absorption loss
• Bottom emitting for compatibility with flip-chip
  bonding
• 35 Gb/s error-free operation demonstrated