Mode locked laser array monolithically integrated with SOA and EA modulatorL. Hou, M. Haji, A. E. Kelly, J. M. Arnold, A. C. Bryce

Outline

• Motivation• Device fabrication• Wafer and device structure• DBR optimization• Material characterization and QWI results• Device characterization• Conclusions

Motivations

• OCDMA• RZ source • Optical sampling• Terahertz Generation

Device features

• AlGaInAs/InP material

• Planarisation using Hydrogen Silsesquioxane (HSQ)

• Surface-etched DBR:• Require only a single epitaxial growth step• Simultaneously fabricated with the ridge waveguide• Al-containing active layers can be used without the risk

of oxidization

• Using QWI to fabricate the passive sections• Phase section , DBR section, S-bend, and MMI• Postgrowth tuning of the QW band edge• Simple, flexible and low-cost alternative compared with

the selective etching and re-grow process

Device Structure

L CH1-4 = 734-740 nm

Lslot = 180 nm

LDBR-eff =55 μm

LMLLD-eff = 4280 μm

WMMI =30 μm

Ls-bend=1200 μm

EAM output tilt angle=10˚

Optimisation of DBR gratings

• Simultaneous etching of waveguide mesa and grating

• RIE lag effects

• 3rd order gratings investigated with CAMFR software

• Low-loss and efficient DBRs are obtainable for narrow slots

• Slot width of 180 nm is selected as a trade-off between reduced losses and fabrication

AlGaInAs/InP material characterisation

Fast recovery times < 3psInternal loss is ~15/cm

Input Pulse recovery time

λ converted

Quantum Well Intermixing results

L-I characteristics of the four channels and SOA

Four channels simultaneous measurement

• Channels tuned in wavelength and frequency to allow visibility of all 4 channels

Mode locking range for the mode-locked DBR laser

Peak wavelength, pulse repetition frequency, pulse width and TBP tuning by DBR section

(b)

(a) (c)

(d)

(a) pulse repetition frequency Fr, (b) Emission peak wavelength WP, (c) TBPs vs. IDBR,(d) Pulse width Pw

Igain = 120 (black), 180 (red), and 240 mA (green), while VSA= -3.0 V, ISOA = 200 mA and all other sections are left floating.

Peak wavelength, pulse repetition frequency, pulse width and TBP tuning by phase section

The shortest pulse and its corresponding optical spectrum , RF signal, and SSB noise

Frequency=10 GHz;

WP = 1561.3 nm, Δλ=1.27 nm;

=3.84, Δt = 2.49 ps;

TBP = 0.389;

Timing jitter=6ps (100 kHz-100 MHz)

Pulse Stabilisation using Synchronous Mode Locking

Optical attenuator compressor

Pritel(10 GHz active fibre MLL)

EDFA

Pulse compressor

Polarization controller

OSAESA+ SHG Autocorrelator

Circulator

Injected Signal Characteristics

Injected Pulse

Injected Spectrum

2 Channel Synchronisation

Timing jitter=0.3ps(100 Hz-100 MHz)

~100 MHz Locking Range

Conclusions

Mode-Locked Laser Array Monolithically Integrated with SOA and EA Modulator :

• Surface etched DBR mode locked laser• QWI for the postgrowth tuning of the QW band edge• Each channel can tune the peak wavelength, pulse repetition rate, and

pulse width by using DBR, phase section or SA section • Minimum pulse width of 2.49 ps with 3 dB optical spectral bandwidth of

1.27 nm and TBP of 0.389 (sech2)• Synchronization of the mode-locked laser array by using injection mode-

locked technique

Acknowledgements

• P. Stolarz for his automated LabView measurements system• R. Dylewicz for input to grating designs• The technical staff of JWNC at the University of Glasgow• This work was funded via EPSRC EP/E065112/1 ‘High Power,

High Frequency Mode-locked Semiconductor Lasers’