Self-assembled InAs/InP quantum dots and quantum dashes: Material structures and devices

Phase noise of the period-one (P1) nonlinear dynamical oscillation in an optically injected semiconductor laser is numerically investigated. The P1 dynamics causes the laser output intensity to oscillate at a widely tunable frequency for photonic microwave generation, although the intrinsic spontaneous emission in the laser inevitably degrades the microwave signal and manifests as the oscillation phase noise. To characterize the phase noise, the P1 microwave linewidth is first numerically examined through the rate equations with a Langevin term. The P1 microwave linewidth is found to vary with the injection parameters. It is nearly minimized when the microwave power maximizes. Owing to the laser nonlinearities, the P1 microwave linewidth can even be smaller than the free-running optical linewidth. By adding an optical feedback to the laser, the P1 microwave linewidth is found to reduce as the feedback strength and feedback delay increase, in which an inverse-square dependency is followed asymptotically. By modification to a dual-loop feedback, noisy side peaks around the central P1 frequency are effectively suppressed through the Vernier effect. The dual-loop feedback maintains a low phase noise variance over a wide tuning range of the P1 frequency, while allowing long delay times for significant P1 microwave linewidth narrowing.

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Phase noise characteristics of microwave signals generated by semiconductor laser dynamics

In this contribution we experimentally demonstrate the change and improvement of dynamical properties of a passively mode-locked semiconductor laser subject to optical feedback from two external cavities by coupling the feedback pulses back into the gain segment. Hereby, we tune the full delay-phase of the pulse-to-pulse period of both external cavities separately and demonstrate the change of the repetition rate, timing jitter, multi-pulse formation and side-band suppression for the first time for such a dual feedback configuration. In addition, we thereby confirm modeling predictions by achieving both a good qualitative and quantitative agreement of experimental and simulated results. Our findings suggest a path towards the realization of side-band free all-optical photonic oscillators based on mode-locked lasers.

Experimental demonstration of change of dynamical properties of a passively mode-locked semiconductor laser subject to dual optical feedback by dual full delay-range tuning.

Period-one (P1) oscillations in semiconductor lasers are applicable in photonic millimeter-wave (mm-wave) generation. P1 oscillation can be invoked by optically injecting a laser, where the phase noise can be suppressed by modulation. To increase the frequency range of mm-wave generation, cascaded injection is investigated for enhancing the P1 oscillation harmonics. Relative to the optical frequency of the injection from a master laser, P1 oscillation at frequency f0 is induced in a primary slave laser which, in turn, injects a secondary slave laser for enhancing the harmonic at 2f0. Experimentally, photonic mm-wave generation at 2f0=72 GHz is demonstrated using P1 oscillations at f0=36 GHz. Subharmonic locking by modulation at f0/4=9 GHz can suppress the output phase noise to −87 dBc/Hz at 10 kHz offset. The mm-wave power can be strengthened by the coherent addition from the master laser. The mm-wave frequency can be tuned by varying the operating conditions of the lasers. Extension to higher frequencies is possible using the approach of cascaded injection.

Cascaded injection of semiconductor lasers in period-one oscillations for millimeter-wave generation.

We present the first integrated linear extended-cavity passively mode-locked (PML) semiconductor laser in which the operating mode can be switched electrically between two configurations. The first configuration is where the saturable absorber (SA) is located next to the output coupler, the so-called anti-colliding pulse mode-locking (ACPML) scheme. The second is where the SA is next to the high reflectance mirror, the self-colliding pulse mode-locking (SCPML) scheme. The 7.5-GHz PML was used to demonstrate experimentally the theoretical prediction that placing the SA next to the output coupler leads to a significant improvement in the laser stability and quality of the optical pulses. The experimental results show that the ACPML scheme allows for more deeply saturated SA due to the increase of optical power in the SA. The measurements of the RF spectra and autocorrelation traces confirm the superiority of the ACPML design in terms of pulse stability and width over the SCPML design for a wide range of operating conditions. The linewidth of the beat tone at the repetition rate was reduced by more than 60 times, the measured minimal autocorrelation width improved from 22 to 7.5 ps and a 3 dB increase in average output power was achieved.

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Integrated Extended-Cavity 1.5-μm Semiconductor Laser Switchable Between Self- and Anti-Colliding Pulse Passive Mode-Locking Configuration

We introduce a novel scheme for the simultaneous reduction of time-bandwidth product (TBP) and RF linewidth of quantum-dash two-section mode-locked lasers using optical injection-locking and filtered optical feedback. The optical injection-locked laser, double-locked with optical feedback showed 2× TBP reduction and RF linewidth reduction by two orders of magnitude. This stabilization technique is implemented in an all-optical arrangement without optical/electrical conversion which is ideal for high-repetition-rate devices and photonic integration.

L. Lelarge

Papers

A Novel Scheme for Two-Level Stabilization of Semiconductor Mode-Locked Lasers Using Simultaneous Optical Injection and Optical Feedback