Laterally coupled dual-grating distributed feedback lasers for generating mode-beat terahertz signals.

We present a laterally coupled dual wavelength 1.56/1.57-µm AlGaInAs/InP DFB laser, which, by introducing two different grating periods on each sidewall, emits two longitudinal modes simultaneously within the same cavity at a frequency separation of 0.82 THz. The beating signal is stabilized by nonlinear four-wave mixing in an electro-absorption modulator (EAM), located within a monolithically integrated resonant cavity. A stable 0.82-THz beating signal was observed over a wide range of bias parameters in terms of drive currents and bias to the DFB and EAM sections.

Mode-locking and frequency mixing at THz pulse repetition rates in a sampled-grating DBR mode-locked laser.

We report a sampled grating distributed Bragg reflector (SGDBR) laser with two different gratings which mode-lock independently at respective pulse repetition frequencies of 640 and 700 GHz. The device operates in distinct regimes depending on the bias conditions, with stable pulse trains observed at 640 GHz, 700 GHz, the mean repetition frequency of 666 GHz, and the sum frequency of 1.34 THz (due to nonlinear mixing). Performance is consistent and highly reproducible with exceptional stability observed over wide ranges of drive bias conditions. Furthermore, a monolithically integrated semiconductor optical amplifier is used to amplify the pulse trains, providing an average output power of 46 mW at 666 GHz.

Mode locking at terahertz frequencies using a distributed Bragg reflector laser with a sampled grating.

We present a highly reproducible method of producing terahertz (THz) optical pulses using a class of mode-locked AlGaInAs/InP laser operating in the 1.55 µm wavelength range. The device uses a sample grating distributed Bragg reflector to provide strong frequency selectivity at the mode-locked frequency while the distributed reflectors relax the fabrication tolerances and ensure the cavity can self adjust to being an integral number of mode-locked periods in length. The measured devices provide nearly transform-limited pulse trains at 640 GHz or 1.28 THz with a high degree of controllability and operate with consistent performance over a wide range of drive conditions. Being low cost and compact sources of THz radiation, these lasers will open up many applications, including systems for high-speed optical communication and THz imaging.

Narrow linewidth laterally coupled 1.55 µm AlGaInAs/InP distributed feedback lasers integrated with a curved tapered semiconductor optical amplifier.

We present a laterally coupled 1.55 µm AlGaInAs/InP distributed feedback laser monolithically integrated with a curved tapered optical amplifier, providing an output power of 210 mW with single transverse and longitudinal mode operation exhibiting a record low linewidth of 64 kHz.

490 fs pulse generation from a passive C-band AlGaInAs/InP quantum well mode-locked laser.

We report femtosecond pulses from a passive C-band two-section AlGaInAs/InP mode-locked laser with a monolithically integrated passive waveguide made by quantum well intermixing. Without any external pulse compression, Lorentzian pulses are generated at a repetition frequency of ~38 GHz with 490 fs pulse duration, which is, to the best of our knowledge, the shortest pulse from any directly electrically pumped quantum well semiconductor mode-locked laser. The mode-locking range is relatively large and the ultranarrow pulse width is very stable over a broad range of driving conditions.

High power (130 mW) 40 GHz 1.55 µm mode-locked distributed Bragg reflector lasers with integrated optical amplifiers.

High output power 40 GHz 1.55 µm passively mode-locked surface-etched distributed Bragg reflector (DBR) lasers with monolithically integrated semiconductor optical amplifiers are reported. These are based on an optimized AlGaInAs/InP epitaxial structure with a three quantum well active layer and an optical trap layer. The device produces near transform limited Gaussian pulses with a pulse duration of 3.3 ps. An average output power during mode-locked operation of 130 mW was achieved with a corresponding peak power of >1 W.

High frequency optoelectronic oscillators based on the optical feedback of semiconductor mode-locked laser diodes.

Optical self seeding feedback techniques can be used to improve the noise characteristics of passively mode-locked laser diodes. External cavities such as fiber optic cables can increase the memory of the phase and subsequently improve the timing jitter. In this work, an improved optical feedback architecture is proposed using an optical fiber loop delay as a cavity extension of the mode-locked laser. We investigate the effect of the noise reduction as a function of the loop length and feedback power. The well known composite cavity technique is also implemented for suppressing supermode noise artifacts presented due to harmonic mode locking effects. Using this method, we achieve a record low radio frequency linewidth of 192 Hz for any high frequency (>1 GHz) passively mode-locked laser to date (to the best of the authors' knowledge), making it promising for the development of high frequency optoelectronic oscillators.

CWDM source based on AlGaInAs/InP monolithically integrated DFB laser array.

The monolithic integration of four 1.5 µm range AlGaInAs/InP distributed feedback lasers with a 4×1 multimode-interference optical combiner, a curved semiconductor optical amplifier, and an electro-absorption modulator using relatively simple technologies--sidewall grating and quantum well intermixing--has been demonstrated. The four channels span the wavelength range of 1530 to 1566 nm with a channel spacing of 12 nm. The epitaxial structure was designed to produce a far-field pattern as small as 21.2°×25.1°, producing a coupling efficiency with an angled-end single-mode fiber at twice that of a conventional device design.

Fast saturable absorption and 10 GHz wavelength conversion in Al-quaternary multiple quantum wells.

We measured the absorption recovery times in reverse biased AlInGaAs multiple quantum well material designed to emit at around 1.5 µm wavelength. Absorption recovery times as low as 2.5 ps were found at -4V bias, with values below 5 ps consistently found for biases above 3 V. The short absorption recovery times obtained under reverse bias were confirmed by using cross-absorption modulation in the material to demonstrate wavelength conversion of a 10 GHz pulse train, showing both up and down conversion of the incident pulses.

Low divergence angle and low jitter 40 GHz AlGaInAs/InP 1.55 µm mode-locked lasers.

We demonstrate a novel (to the best of our knowledge) 40 GHz passively mode-locked AlGaInAs/InP 1.55 µm laser with a low divergence angle (12.7°×26.3°), timing jitter of 1.2 ps (10 kHz-100 MHz), and a radio frequency linewidth of 25 kHz.

10 GHz AlGaInAs/InP 1.55 µm passively mode-locked laser with low divergence angle and timing jitter.

We present a 10 GHz 1.55 µm all-active passively mode-locked laser based on a novel AlGaInAs/InP epitaxial structure with a three-quantum-well active layer and a passive far-field reduction layer. The device generated 1.06 ps pulses with a state-of-the-art timing jitter value of 194 fs (4-80 MHz), and a radio-frequency linewidth of 2 kHz, while demonstrating a low divergence angle (14.7° × 27.3°) with a twofold butt coupling efficiency to a flat cleaved single mode fiber, compared to the conventional five-quantum-well MLLs.

160 GHz harmonic mode-locked AlGaInAs 1.55 µm strained quantum-well compound-cavity laser.

We characterized the reflectivity and the modal discrimination of intracavity reflectors (ICRs) with different numbers of slots and presented harmonic mode-locking operation of a monolithic semiconductor laser comprising a compound cavity formed by a single deeply etched slot ICR fabricated from 1.55 µm AlGaInAs strained quantum well material. Gaussian pulses were generated at a 161.8 GHz repetition rate with a pulse duration of 1.67 ps and a time-bandwidth product of 0.81.