Recent works on monolithic mode-locked semiconductor laser diodes

We report a novel monolithic multi-wavelength mode-locked semiconductor laser design based on arrayed waveguide grating (AWG) for the first time. 19.6 ps pulses at a repetition rate of 2.9 GHz are obtained.

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.

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.

A compact and economical terahertz time-domain spectroscopy system can be constructed by using a monolithic mode-locked laser diode (MLLD) as the light source and by employing an off-the-shelf optical delay unit (ODU). The sub-picosecond pulses emitted by the MLLD promise a system bandwidth of up to 2 THz. However, mechanical inaccuracy and wobble of the ODU often cause the delay axis of the detected terahertz signal to be non-linear. In this work, we show how the optical signal from the MLLD can be used in a Mach-Zehnder interferometer to generate a low-frequency reference signal that allows us to correct the delay axis with femtosecond-accuracy.

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.

Frequency up/down conversion of optically transmitted RF signals may be useful for a number of microwave-over-fibre applications. In the earlier works [1-2], we have proposed to perform such conversion by means of operating passively Q-switched (self-pulsing) or passively mode locked semiconductor laser diodes (LDs) as integrated optoelectronic frequency mixers, i.e. as a local oscillator and a mixing element integrated within one device. Theoretical calculation proved the feasibility of RF frequency conversion due to parametric effects in such LDs. The calculations considered the input signal applied to a laser as either an electrical signal (optoelectronic scheme) or an RF modulated optical signal (all-optical scheme), the frequency-converted output being in the form of a modulated stream of optical pulses, convenient for further transmission, with an electrical signal as a by-product. In [3], optoelectronic up-conversion has been performed using self-pulsating lasers with subcarrier modulation in optical communications in view. The results of both [1-2] and [3] experimentally demonstrate the feasibility of frequency mixing in GHz range using self-pulsing lasers, but little study has been performed so far of the mixing efficiency, and the spectral properties of the device have been only studied theoretically [2] for the case of mode locked extended-cavity lasers. Here, we investigate, in more detail, the issue of the efficiency of the optoelectronic frequency conversion in dependency of frequency (in different frequency ranges) and intensity of the modulation signal for monolithic cavity Q-switched and mode locked lasers.

We present a detailed investigation of the radio-frequency (RF) linewidth and noise performance of a 10-GHz packaged monolithic two-section quantum-dot mode-locked laser diode. Record low 500-Hz RF linewidths are reported under passive mode-locking operation, and the single sideband phase noise spectra and associated timing jitter performance under both passive and hybrid mode-locking is investigated.

In this work, we present an analytical model that links the complex terahertz spectrum acquired with a terahertz time-domain spectroscopy (THz-TDS) system to the complex optical spectrum from a monolithic mode-locked laser diode (MLLD) and the transfer function of the terahertz channel. It also gives the relationship between the optical intensity autocorrelation and the terahertz spectrum. This model greatly improves the understanding of THz-TDS with ultra-high repetition rate lasers and enables the design of lasers with optimized optical spectra.

We demonstrate an optoelectronic mixer based on an ultrafast InGaAs photoconductive switch and a mode-locked semiconductor laser diode. The advantage of the switch is its relatively flat response curve in a wide frequency range of 1–67 GHz. The InP based quantum-dash mode-locked laser emitting in the 1550 nm wavelength range, serves as the source of the local oscillator frequency of 24.5 GHz. The proposed scheme is taking advantage of the low-linewidth of the pulsed laser source and can be used as a heterodyne mixer at the receiver side of a Radio-over-fiber network's wireless link. We show the mixing performance through I-Q modulated data-stream downconversion and its improvement when the phase noise of the laser is reduced thanks to an optical feedback loop.

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.

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.

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.

Heterodyne autocorrelation measurement of 1.55 /spl mu/m optical pulses from an actively mode-locked external cavity diode laser is performed before and after transmission through an optical fiber. In heterodyne autocorrelation, optical spectrum is resolved electronically. This method is suitable for measurement of optical pulses with a spectral width of less than 100 GHz, and it gives not only the pulse width and chirp of the pulses, but also it is useful for determining the dispersion and optical Kerr constant of an optical fiber. Analytical formalism for deducing these quantities is given for Gaussian pulses. Principal measurement is performed using a mode-locked diode laser. Dispersion is measured for a conventional-dispersion fiber of 35 km. Also, self-phase modulation (SPM) is measured for a dispersion-shifted fiber of 15.83 km.