Ehsan Sooudi

Injection-Locking Properties of InAs/InP-Based Mode-Locked Quantum-Dash Lasers at 21 GHz

We report optical injection-locking in 21-GHz single-section and two-section InAs/InP 1.5-μm quantum-dash mode-locked lasers. Two distinct mode-locked regimes were observed and successfully locked to the optically injected light. The single-section laser only operates as a self-mode-locked laser while the two-section laser could operate as both a self-mode-locked laser and saturable-absorber dominated mode-locked laser. The continuous-wave (CW) injection-locked self-mode-locked laser shows wide tuning of the mode-locked frequency (≈270 MHz) within the locking range. The CW injection-locked saturable-absorber dominated mode-locked laser demonstrates wide optical spectrum, and 5.5 × reduction in the time-bandwidth product of the pulses. Using dual-mode injection, strong reduction of timing jitter ( ≈235 fs) is possible leading to the generation of a wide coherent frequency comb. Coherence between all the modes and the master laser is confirmed by measuring the RF beat note of each mode with a narrow linewidth laser.

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

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.

Observation of Harmonic-Mode-Locking in a Mode-Locked InAs/InP-Based Quantum-Dash Laser With CW Optical Injection

We report tunable harmonic mode-locking in continuous-wave (CW) optically injected InAs/InP quantum-dash lasers emitting at 1.56 μm. The frequency of generated microwave pulses is twice the lasers self-mode-locked frequency. Autocorrelation traces show Gaussian pulses with low time-bandwidth product ( ≈0.6). Mapping of the dynamics shows that this coherent microwave oscillation (MWO) region has maximum locking range ≈600 MHz (≈5 pm). Measurement of the optical linewidth of each individual mode at this regime shows strong narrowing relative to free running values by two orders of magnitude. The RF linewidth of the generated signal is ≈160 kHz confirming the coherence among the optical modes and low timing jitter.

Practical and cost-effective high-fidelity optical carrier dissemination using coherent communication techniques

We report a unidirectional frequency dissemination scheme for high-fidelity optical carriers deployable over telecommunication networks. For the first time, a 10 Gb/s Binary Phase Shift Keying (BPSK) signal from an ultra-narrow linewidth laser was transmitted through a field-installed optical fibre with round-trip length of 124 km between Cork City and town of Clonakilty, without inline optical amplification. At the receiver, using coherent communication techniques and optical injection-locking the carrier was recovered with noise suppression. The beat signal between the original carrier at the transmitter and recovered carrier at the receiver shows a linewidth of 2.8 kHz. Long term stability measurements revealed fractional instabilities (True Allan deviation) of 3.3 × 10(-14) for 1 s averaging time, prior to phase noise cancellation.

A unidirectional scheme for high-fidelity optical-carrier dissemination using phase-modulation, homodyne coherent-detection, and frequency entrainment

We report for the first time an ultra-stable optical-carrier dissemination technique for transmission over a 20 km unidirectional fibre link. The optical-linewidth of the recovered carrier matches closely that of the original carrier.

All optical passive stabilization of a two-section InAs/InP based quantum-dash mode-locked laser with simultaneous CW injection-locking and selective optical feedback

We demonstrate narrow pulses with low RF linewidth from two-section InP quantum-dash mode-locked lasers. Simultaneous CW injection-locking and selective optical feedback lead to ≃50 times RF linewidth and 1.5 times time-bandwidth product reduction.

Scaling and tuning properties of microwave generation in CW injection locked InP-based mode-locked quantum dash lasers

A comparative study of frequency tunable microwave generation using CW injection locked InP based quantum dash mode-locked lasers is presented. Devices with different repetition rates and active region structures are analyzed.

Stabilization of self-mode-locked quantum dash lasers by symmetric dual-loop optical feedback

We have stabilized self mode-locked quantum dash lasers emitting at 1550nm, reducing pulse train RF linewidth by 100x, using optical feedback from dual fiber loops.

Optimum stabilization of self-mode-locked quantum dash lasers using dual loop optical feedback

We have experimentally investigated the RF linewidth and timing jitter in self-mode-locked two-section quantum dash lasers emitting at ∼1.55 µm and operating at ∼21 GHz repetition rate, subjected to single and dual loop optical feedback into the gain section, over a wide range of feedback delay. Various feedback conditions are investigated and optimum levels determined for narrowest linewidth and reduced timing jitter for both single and dual-loop configurations. We demonstrate that dual-loop feedback with the shorter feedback cavity tuned to be fully resonant, followed by fine tuning of the phase of the longer feedback cavity, gives stable narrow RF spectra across the widest delay range, 10 – 50× better than single-loop feedback. In addition, for dual-loop configurations, under fully resonant conditions, phase noise is reduced to 295 fs [10 kHz – 100 MHz], the RF linewidth narrows to < 1 kHz, with more than 30 dB fundamental side-mode suppression. We show that dual-loop optical feedback with separate fine tuning of both external cavities is far superior to single-loop feedback, with increased system tolerance against phase delay mismatch, making it a robust and cost-effective technique for developing practical, reliable and low-noise mode-locked lasers, optoelectronic oscillators and pulsed photonic circuits.

A novel symmetric dual loop feedback scheme insensitive to phase tuning using self-mode-locked two-section quantum dash laser

We demonstrate a symmetric dual loop feedback scheme, insensitive to delay phase tuning, for a self-mode-locked quantum dash laser emitting at ∼ 1.55 µm and operating at ∼ 21 GHz repetition rate. These lasers are subjected to single and dual loop optical feedback into the gain section. Various feedback conditions are studied and optimum levels determined for narrowest linewidth and reduced timing jitter for both single and symmetric dual loop configurations. We demonstrate that symmetric dual loop with the inner cavity fully resonant and the outer one slightly offset, produces narrowed RF spectra across the widest delay range. In general, symmetric dual loop feedback is far more effective than single loop feedback in reducing RF linewidth and timing jitter, across a much wider range of delay phase. Resonant conditions for dual loop feedback are nearly independent of delay, making it ideal for practical applications where robustness and tolerance to misalignment are essential.