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

2. Outline Motivation Device fabrication Wafer and device structure DBR optimization Material characterization and QWI results Device characterization Conclusions

3. Motivations OCDMA RZ source Optical sampling Terahertz Generation

4. 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

5. Device Structure  CH1-4 = 734-740 nm L slot = 180 nm L DBR-eff =55 μm L MLLD-eff = 4280 μm W MMI =30 μm L s-bend =1200 μm EAM output tilt angle=10˚

6. 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

7. AlGaInAs/InP material characterisation Fast recovery times < 3ps Internal loss is ~15/cm Input Pulse recovery time λ converted

8. Quantum Well Intermixing results

9. L-I characteristics of the four channels and SOA

10. Four channels simultaneous measurement Channels tuned in wavelength and frequency to allow visibility of all 4 channels

11. Mode locking range for the mode-locked DBR laser

12. Peak wavelength, pulse repetition frequency, pulse width and TBP tuning by DBR section (b) (a) (c) (d) (a) pulse repetition frequency F r, (b) Emission peak wavelength W P, (c) TBPs vs. I DBR, (d) Pulse width P w I gain = 120 (black), 180 (red), and 240 mA (green), while V SA = -3.0 V, I SOA = 200 mA and all other sections are left floating.

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

14. The shortest pulse and its corresponding optical spectrum, RF signal, and SSB noise Frequency=10 GHz; W P = 1561.3 nm, Δλ=1.27 nm;  =3.84, Δt = 2.49 ps; TBP = 0.389; Timing jitter=6ps (100 kHz- 100 MHz)

15. Pulse Stabilisation using Synchronous Mode Locking Optical attenuator compressor Pritel (10 GHz active fibre MLL) EDFA Pulse compressor Polarization controller OSA ESA + SHG Autocorrelator Circulator

16. Injected Signal Characteristics Injected Pulse Injected Spectrum

17. 2 Channel Synchronisation Timing jitter=0.3ps(100 Hz-100 MHz) ~100 MHz Locking Range

18. 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 (sech 2 ) Synchronization of the mode-locked laser array by using injection mode- locked technique

19. 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’EP/E065112/1