1550 nm Tunable Lasers and VCSEL Arrays for WDM applications

Transcription

1 1550 nm Tunable Lasers and VCSEL Arrays for WDM applications L. A. Coldren UC-Santa Barbara Increase bandwidth without increasing data rate/electronics' performance Parallel protection channels in one medium (cost/size/weight/robustness) Wavelength selective routing (very fast, efficient, and remote routing) Outstanding leverage in commercial marketplace (but it isn't addressing important issues) Need small, fast, efficient, chip-scale O/E components

2 Report Documentation Page Form Approved OMB No Public reporting burden for the collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for Information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington VA Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to a penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. 1. REPORT DATE 18 APR REPORT TYPE N/A 3. DATES COVERED - 4. TITLE AND SUBTITLE 1550 nm Tunable Lasers and VCSEL Arrays for WDM Applications 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) 5d. PROJECT NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) University of California, Santa Barbara 8. PERFORMING ORGANIZATION REPORT NUMBER 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR S ACRONYM(S) 12. DISTRIBUTION/AVAILABILITY STATEMENT Approved for public release, distribution unlimited 11. SPONSOR/MONITOR S REPORT NUMBER(S) 13. SUPPLEMENTARY NOTES DARPA/MTO, WDM for Military Platforms Workshop held in McLean, VA on April 18-19, 2000, The original document contains color images. 14. ABSTRACT 15. SUBJECT TERMS 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF ABSTRACT UU a. REPORT unclassified b. ABSTRACT unclassified c. THIS PAGE unclassified 18. NUMBER OF PAGES 24 19a. NAME OF RESPONSIBLE PERSON Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std Z39-18

3 Outline (1550 nm InP-based hardware) SGDBR Widely-tunable Lasers/Laser-Modulators/Laser-Amplifiers -- Needed: Compact/efficient wavelength converter/sgdbr Compact/efficient wavelength router Integration/packaging 1550nm VCSELs -- Needed: Higher performance/better manufacturability WDM arrays/coupling optics Amplifiers/wavelength converters

4 SGDBR Laser Front Mirror Improved Sampled Grating DBR Widely-Tunable 1.55µm Lasers Larry A. Coldren, University of California Santa Barbara Back Mirror Gain Phase Objective Improved widely tunable SGDBR laser Increase tuning range to greater than 60nm Develop integrated wavelength monitor for tuning control Develop integrated modulator & amplifier designs Approach Dry etch gratings through windows in SiNx mask for improved regrowth Employ a thick low bandgap waveguide to increase index tuning efficiency Taper the active passive junctions to eliminate spurious reflections Employ a buried heterostructure design for improved carrier confinement Accomplishments Demonstrated continuous tuning range of 72 nm for buried device Developed integrated wavelength monitor Integrated the tunable laser with an electroabsorption modulator capable of 22dB extinction over a 47nm tuning range Integrated a SOA with a gain of 8.5dB and a 6mW saturation power together with the SGDBR Transferred technology to Agility Communications

5 Introduction SGDBR Lasers Periodically sampling the gratings in the mirrors yields multiple reflection peaks. The laser wavelength is controlled by aligning reflection peaks in the front and back mirrors. Reflection Coefficient Front M irror Gain Phase Control Back M irror p - InP 1.4Q W aveguide n - InP Intensity (dbm) Stop Etch Layer Offset Quantum W els Sam pling Period Wavelength (nm)

6 72 nm Quasi-Continuous Tuning Range Laser Wavelength(nm) nm Laser Wavelength(nm) Front Mirror Tuning Current (ma) Front Mirror Tuning Current (ma) GHz channels, > 35 db SMSR, 2 mw peak power Tuning range limited by available gain from MQW.

7 Integrated SGDBR and SOA Device Structure Gain Back Mirror Phase Amplifier Front Mirror Buried Ridge Stripe (BRS( BRS) InGaAs Contact Layer Ti/Pt/Au Contact Grating Bursts Curved Passive Output Guide (R~10-4 ) SiNx n-inp Waveguide: : 1.4 µm InGaAsP Active Region: Six 1% Compressively Strained QWs p-inp Waveguide Implanted Region Quantum Wells

8 Integrated Amplifier Characteristics Output Power (mw) db Gain Compression Point 25 ma, 3.8 db 50 ma, 7.1 db 150 ma, 8.7 db Transparency Relative Intensity (dbm) / nm (5 GHz) 45 db Input Power (mw) Wavelength (nm) 6 mw peak output power (1 mw min), 8.5 db gain. <10 GHz wavelength shift with 45 db power variation.

9 SGDBR Lasers With Integrated Electro-Absorption Modulators Extinction Ratio is Greater Than 22 db over the entire 40 nm tuning range of the laser for a 250 µm long modulator. Gain Back Mirror Extinction (db) Voltage (V) EAM Front Mirror Extinction (db) V -1.0 V -2.0 V -3.0 V -4.0 V Phase -40 Implanted Section Wavelength (nm)

10 Wavelength Converter types Input Optical signal Output Optical Signal All-optical λ-converter: -Uses interferometric branches - Signal remains optical - Design more complex - Physically large device Opto-Electronic λ-converter: - Optical signal is converted to an electrical signal, then retransmitted - Large tunability and conversion range - Much smaller device - very flexible Jennifer Dolan 4/11/00

11 Perspective view of O/E/O wavelength converter. Pre-Amp lifier Bias Tu ne -1 Bias Tu ne -2 H + SOA Ab so rb e r H + DBR DBR Current Cond itio ning Elem en t n p Gai n φ SOA-1 EA M SOA-2 SGDBR Tune-1 S. I. Acti ve Bias Phase SG DB R Tu ne -2 SOA Bias -1 SOA Bias -2 (Much simpler versions are possible by eliminating optional elements such as gratings and preamp in receiver section or an SOA in the transmitter section.)

12 Optical Switching/Routing Wavelength Routing Element (possibly remote) Header extraction/insertion Wavelength converters Integration of processing elements and packet switching system on a chip using wavelength routing techniques.

13 Integrated optical crossbar switch A 1 A 5 A n > > DET SGDBR DET SGDBR DET SGDBR λ f λ k λq Slab- Waveguide Beam-Expansion/ Interference Section InP Substrate > > > > > > 1-D O/E/O widely-tunable wavelength converter array with a compact AWG. A 32 x 32 switch should fit on a 1 cm 2 chip, assuming 250 µm input & output waveguide spacings. B 1 B n

14 Surface-normal wavelength converter. V in p u t n-ing aala s p-ing aa s D etector n-top DBR n-ing aa la s Active Active Active n-ing aa la s p n p n p n n - Bottom D BR n-inp -su b stra te ou tpu t InP-based VCSEL with multiple-active-regions and series photodetector => PNA

15 MAR VCSEL Fully-epitaxial, lattice-matched to InP 45 period n-type AlGaInAs/AlInAs DBR R=99.8% Esaki-junctions 2-λ cavity QW active regions n-inp substrate 35 period n-type AlGaInAs/AlInAs DBR R=98.4% Good quality DBRs Total thickness of epitaxial layers ~ 20 µm

16 MAR VCSEL Results Power (mw) D=25µm D=50µm D=100µm Current (ma) J th as low as 570 A/cm 2 η d > 60 % (d = 50µm) P out > 15 mw V th ~ 3 V (3hν = 2.4eV) R d 100 Ω (d = 25µm) λ 1.55 µm 7 I = 2I th 6 Voltage (V) I = 1.1I th Current (ma) λ

17 Sb-Based DBR VCL with Underetched Active Region Ti/Pt/Au AlGaAsSb DBR SiO 2 + SiN InAlGaAs QW AlGaAsSb DBR AuGe/Ni/Au Etched Pillar VCL VCL with Underetched Active Region Light Output [mw] Pulsed: 300ns, 1kHz 15 o C 25µm: J th =1.2kA/cm 2 ηd =7.6% 50µm: J th =1.3kA/cm 2 ηd =8.2% µm: J th =3.1kA/cm 2 ηd=4.4% Current [ma] Output Power [mw] Pulsed: 300ns, 1kHz 15 o C 15µm Underetched: J th =1.6kA/cm 2 ηd=8.0% 25µm Etched Pillar 15µm Etched Pillar Current [ma]

18 New VCSEL Results Light [mw] Current [ma] 0C 5C 10C 13C 17C 20C 25C 30C 35C 40C 45C 50C 55C Voltage [V] Current [ma] η d ~ 7%, J th ~ 800A/cm 2 Voltage reduced by 50%!! CW lasing being tested

19 Thermally Managed Long Wavelength VCSEL Au contacts Tunnel diode Oxide aperture AlInGaAs QWs n-inp n-inp AlAsSb/AlGaAsSb DBR InP Substrate Intracavity-contacted all-epitaxial device with no mirror doping and InP heat spreaders

20 Tapered Oxide Apertures in AlInAs on InP Tapered Oxide 30 minutes at 500 C AlInAs (λ/4) AlInGaAs (λ/4)??????????????????????????????????? AlInGaAs (λ/4) Layer thickness not to scale. Oxidant Supply Layer Oxidation Layer The presence of the oxidant supply layer accelerated the lateral oxidation rate of the neighboring?????? layer by a factor of 4 relative to identical AlInAs layers elsewhere in the structure. 1 hour at 500 C Vertical oxidation of?????? (oxidation downward from the oxidant supply layer) resulted in a taper.

21 BOTTOM-EMITTING PIE-VCSEL Light Intensity (dbm) Wavelength (nm)

22 Coupling of WDM VCSEL Array to Fiber VCSEL Chip λ 1 λ 2 Fiber λ 3 λ n Coupling of several VCSELs to the same point by offset integrated microlenses. Nearly lossless coupling possible for multimode fiber for angles within its NA.

23 Coupling of WDM VCSEL Array to Fiber 2-D WDM VCSEL Array with µlenses CGH Fiber Driver Circuit Use of computer generated hologram (or simple grating in one dimension) to provide spectral separation for matching to single mode fiber

24 Outline (1550 nm InP-based hardware) SGDBR Widely-tunable Lasers/Laser-Modulators/Laser-Amplifiers -- Needed: Compact/efficient wavelength converter/sgdbr Compact/efficient wavelength router Integration/packaging 1550nm VCSELs -- Needed: Higher performance/better manufacturability WDM arrays/coupling optics Amplifiers/wavelength converters

25 1550 nm Tunable Lasers and VCSEL Arrays for WDM applications L. A. Coldren UC-Santa Barbara Increase bandwidth without increasing data rate/electronics' performance Parallel protection channels in one medium (cost/size/weight/robustness) Wavelength selective routing (very fast, efficient, and remote routing) Outstanding leverage in commercial marketplace (but it isn't addressing important issues) Need small, fast, efficient, chip-scale O/E components