Arrayed Waveguide Grating Based Monolithic Multi-wavelength Mode-locked Semiconductor Laser

Progress in technology, theory and applications of high-frequency mode-locked diode lasers is reviewed. We present a systematic overview of a wealth of experimental and theoretical results and approaches reported recently in the field of physics, technology and applications of monolithic mode-locked laser diodes.

Monolithic mode-locked semiconductor lasers are attractive sources of short optical pulses with advantages over more conventional sources in compactness, robustness, performance stability, power consumption, and cost savings. The use of quantum well intermixing (QWI) to integrate passive sections and surface etched distributed Bragg reflectors (DBR) into monolithic laser cavity will be described. The performance of the devices will be presented.

We investigate conditions for optically coherent injection locking of a monolithic mode-locked semiconductor laser. An interferometric technique is used to quantify the relationship between modal detuning, pulse shape, and optical spectrum.

Recent works on monolithic mode-locked semiconductor laser diodes

The buildup of pulses in a passively mode-locked monolithic semiconductor laser is investigated experimentally and theoretically. A simple model, based on competition between the fundamental and higher order mode-locking ‘‘supermodes,’’ gives a time constant for the buildup in good agreement with the experimental values, which are on the order of 3.5 ns. The theory shows that to minimize the pulse buildup time, the photon life time and the width of the gain spectrum should be minimized, and the gain and the gain modulation, should be maximized.

We demonstrate GHz repetition-rate, monolithic mode-locked lasers, with a short-term, free-running phase noise performance rivalling actively stabilized lasers at a fraction of the system complexity. These lasers are robust and quick to assemble.

Active mode-locking of a broadly tunable monolithic semiconductor laser based on a grating assisted vertical coupler filter resulted in 10 - 12 ps pulses at a repetition rate of 15.8 GHz. Mode-locking was achieved at discrete wavelengths from 1544.5 nm to 1564.7 nm.

Low-noise, high-repetition-rate mode-locked solid-state lasers are attractive for precision measurement and microwave generation, but the best lasers in terms of noise performance still consist of complex, bulky optical setups, which limits their range of applications. In this Letter, we present an approach for producing highly stable pulse trains with a record-low residual integrated offset frequency phase noise of 14 mrad at 1 GHz fundamental repetition rate using a monolithic mode-locked solid-state laser. The compact monolithic design simplifies implementation of the laser by fixing the cavity parameters and operates using just 265 mW of 980 nm pump light.

We investigate the effect of carrier transport on active and passive resonantly enhanced modulation of monolithic quantum-well semiconductor lasers. While the ultimate frequency at which narrow-band resonant modulation can be achieved may be severely affected by carrier transport, no such limitation is predicted for passive model coupling.

High performance, inexpensive light sources are needed for the advancement of wavelength division multiplexed (WDM) photonic access networks. In this paper, the unique features of multiwavelength modelocked semiconductor lasers are demonstrated with an emphasis on possible integration into access networks. An evaluation of multiwavelength passive, active, and hybrid modelocking reveals that hybrid modelocking is optimum for the suppression of mode partition noise as well as coherence tailoring in multiwavelength lasers. Low-distortion propagation of 10 channeltimes5 GHz multiwavelength pulses through multimode fiber is achieved. Intracavity gain flattening enables the simultaneous generation of 6 GHz pulse trains into 168 parallel wavelength channels for a 1 THz aggregate pulse rate from a single laser source. This work conveys the potential for semiconductor laser modelocking to produce multiple telecommunications wavelengths for data transmission and auxiliary functions in photonic networking

We suggest semianalytic estimates for the Q-switching instability boundary of the continuous-wave (cw) mode-locking regime domain for a ring-cavity semiconductor laser. We use a differential delay laser model that allows us to assume large gain and loss in the cavity, which is a typical situation for this class of lasers. The Q-switching instability boundary is obtained as a Neimark-Sacker bifurcation curve of a map describing the transformation of pulse parameters after a round trip in the cavity. We study the dependence of this boundary on laser parameters and show that our theoretical results are in qualitative agreement with the experimental data obtained with a passively mode-locked monolithic semiconductor laser.

Tunable 12×10 GHz mode-locked semiconductor fiber laser incorporating a Mach-Zehnder interferometer filter

This letter demonstrates a 1-GHz hybrid mode-locked monolithic semiconductor laser fabricated on indium phosphide. Its operating regimes are explored and optical pulses as short as 36 ps were measured. The linear cavity is 41 mm long with integrated active quantum well and passive waveguide structures. To our knowledge, this is the lowest reported repetition rate for a monolithically integrated mode-locked semiconductor laser. We further describe optimization steps of the saturable absorber reverse bias, driving RF frequency, and the semiconductor optical amplifier gain current for minimal output pulsewidth.

A review is presented, based on our experimental and theoretical works, of mode-locked monolithic semiconductor lasers with optical pulse train output stabilized by the subharmonic electrical injection and their performance in the millimeter wave photonic application. The following issues are emphasized: (1) the novel method of pulse train stabilization and its mechanism, (2) the application of a mode-locked semiconductor laser as an optical mm-wave oscillator and (3) the unique functionality in the compact optical mm-wave transmitter applications.

In conventional active mode locking [1], a periodic gain/loss or phase modulation can produce a coherent train of optical pulses, provided that it is synchronized to the natural laser repetition rate to within a few percent of frequency detuning. Here, we present a novel regime, where the repetition frequency of a mode-locked semiconductor laser can be tuned continuously and significantly, both above and below the repetition rate imposed by the cavity dimensions. This is achieved by inducing a strong spatiotemporal gain/loss modulation along the entire laser cavity, with the injected microwaves generating a frequency-dependent modulation standing wave. In Fig. 1(a), we display the optical pulse (blue) and modulation wave (red) in the co-propagating reference frame. For high modulation frequencies (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{f}_{\text {mod }}&gt;\mathrm{f}_{\text {rep }, 0}$</tex>, top), there is a positive delay between the peak of the optical and the modulation wave, meaning that the leading edge of the optical pulse is amplified and its trailing edge is attenuated. This pulse pulling effect increases the group velocity of the optical pulse, while the opposite occurs for low modulation frequencies (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\mathrm{f}_{\text{mod}}&lt;\mathrm{f}_{\text{rep}, 0}$</tex>, bottom), where the group velocity is reduced. This way, for any arbitrary modulation frequency, the repetition rate of the periodic intracavity waveform is adjusted to be synchronized to the external modulation frequency, producing a continuously tunable frequency comb.