Monolithic Mode-locked Semiconductor Lasers Research Articles

Temperature-dependent phase noise properties of a two-section GaSb-based mode-locked laser emitting at 2 μ m

The temperature-dependent phase noise properties of a monolithic two-section mode-locked semiconductor laser are first investigated. This is performed on a GaSb-based quantum well laser emitting at ∼2 μm. Stable mode locking operation with a fundamental repetition frequency of ∼13.3 GHz is achieved on this laser up to 60 °C. At a fixed temperature, there is no monotonous dependence of integrated jitter on the bias condition. For a given gain current or absorber voltage, there exists a corresponding optimal absorber voltage or gain current, respectively, that minimizes the integrated jitter. More important, the phase noise properties improve obviously at elevated temperatures with the lowest achievable jitter reducing obviously from 3.15 ps at 20 °C to 1.39 ps at 60 °C (100 kHz–1 GHz). We consider that the reason is reduced amplified spontaneous emission noise at high temperatures. This is confirmed by the extracted peak-to-valley ratio of the involved laser modes. We believe that this study provides an important insight into the carrier behaviors and noise performance of mode-locked semiconductor lasers, which is meaningful to their applications especially at high temperatures.

Comparison of the noise performance of 10 GHz repetition rate quantum-dot and quantum well monolithic mode-locked semiconductor lasers

Mode-locked lasers are commonly used in carrier-wave signal generation systems because of their excellent phase noise performance. Owing to the importance of this key parameter, this study presents a like-for-like comparison of the noise performance of the passive mode-locked regime of two devices fabricated with different material gain systems, one quantum well and the other quantum dot (QD), both with a monolithic all-active two-section mode-locked structure. Two important factors are identified as having a significant effect on the noise performance, the RF linewidth of the first harmonic and the shape of the noise pedestals, both depending on the passive mode-locked bias conditions. Nevertheless, the dominant contribution of the RF linewidth to the phase noise, which is significantly narrower for the QD laser, makes this material more suitable for optical generation of low-noise millimetre-wave carrier frequencies.

1-GHz Monolithically Integrated Hybrid Mode-Locked InP Laser

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.

Numerical Study of Dynamical Regimes in a Monolithic Passively Mode-Locked Semiconductor Laser

Bifurcation mechanisms of the development and break up of different operation regimes in a passively mode-locked monolithic semiconductor laser are studied by solving numerically partial differential equations for amplitudes of two counterpropagating waves and carrier densities in gain and absorber sections. It is shown that mode-locking regimes with different repetition rates can be multistable for a wide range of laser parameters and that the harmonic mode-locking regime with two counterpropagating pulses in the cavity can exhibit a period-doubling bifurcation leading to different amplitudes and separations of the pulses. The effect of linewidth enhancement factors in gain and absorber sections on the laser dynamics is discussed.

Fundamental and Subharmonic Hybrid Mode-Locking of a High-Power (220 mW) Monolithic Semiconductor Laser

We report on the generation of stable optical pulses at 1.55- mum wavelength via fundamental and subharmonic hybrid mode-locking of a high-power electrically pumped semiconductor diode laser with a slab-coupled optical waveguide structure. The highest average power measured in mode-locked operation was 220 mW. This is the highest power reported for a hybrid mode-locked monolithic semiconductor laser. We also measure the phase (or timing) noise during fundamental and subharmonic operation and our measurements show good agreement with theory.

Suppression of Q-switching instabilities in broadened-waveguide monolithic mode-locked laser diodes

It is predicted theoretically that broadening the optical confinement layer in monolithic mode-locked semiconductor lasers may suppress Q-switching instability, by increasing the carrier transport time, and lead to emission of shorter, more stable optical pulses.

Experimental investigations on the suppression of Q switching in monolithic 40GHz mode-locked semiconductor lasers

Inherent Q switching as a source of intracavity pulse energy modulations, i.e., unwanted amplitude noise, is still a challenging task in order to fabricate monolithic mode-locked semiconductor lasers in view of different commercial applications. In this letter, the results of experimental investigations on the influence of the quantum well number on the occurrence and suppression of Q switching in 40GHz mode-locked multiple quantum well lasers are presented. Improved mode-locked lasers emit short optical pulses (⩽1.6ps) with very low amplitude noise (1%–2%) and timing jitter (50–100fs).

Q-switching instability in a mode-locked semiconductor laser

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.

Dispersion-tolerant multiple WDM channel millimeter-wave signal generation using a single monolithic mode-locked semiconductor laser

This work presents a scheme by which multiple wavelength-division-multiplexed millimeter-wave (mm-wave) signals in the range of 30 GHz can be generated from a single monolithic semiconductor laser for applications in optically fed mm-wave networks or fiber radio networks. The mm-wave signals are generated using dual optical modes separated by a mm-wave frequency, obtained from spectrum slicing the output from a stable multimode hybrid mode-locked semiconductor laser. In this scheme, self-heterodyne detection at a high-speed photodetector achieves the photonic upconversion of low-data-rate signals to mm-wave frequencies without the need for electronic mixing. Experimental results show the generation of up to 14 WDM channels using a single laser. The phase noise of electrical signals generated by photonic upconversion of these signals is less than -94 dBc/Hz at 100-kHz offset frequency across the wavelengths. Also presented is the transmission of 155-Mb/s binary-phase-shift-keyed data signals at 30-GHz frequency over 10 km of single-mode fiber at different wavelengths using dual-mode signals. The results confirm that a bit-error rate of 10/sup -9/ can be easily achieved. The dispersion tolerance of the dual-mode signals is evaluated using simulation and an analytical model and compared with other mm-wave signal generation techniques.

High-performance 10 GHz all-active monolithic modelocked semiconductor lasers

Using a novel design strategy for the epitaxial structure for monolithic modelocked semiconductor lasers, lasers capable of producing <2 ps pulses at 10 GHz with very low high-frequency jitter have been fabricated in a single growth step.

Solid-State Repetition-Rate Tunable Semiconductor Colliding-Pulse Mode-Locked Laser

A monolithic mode-locked semiconductor laser with the capability of tuning its repetition rate while passively mode-locked through solid-state means is reported. Over 200 MHz of tuning is demonstrated with variations in the applied dc bias. Dynamic tuning is demonstrated by applying an ac signal to one section showing a tuning bandwidth over a hundred megahertz. Pulse parameters and timing jitter are also presented for passive and hybrid mode-locking operation.

Low-Jitter and High-Power 40-GHz All-Active Mode-Locked Lasers

A novel design strategy for the epitaxial structure of monolithic mode-locked semiconductor lasers is presented. Using an all-active design, we fabricate 40-GHz lasers generating 2.8-ps almost chirp-free pulses with record low high-frequency jitter and more than 7-mW fiber coupled output power.

Monolithic and multi-GigaHertz mode-locked semiconductor lasers: Constructions, experiments, models and applications

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.

Recent works on monolithic mode-locked semiconductor laser diodes

Recent works on monolithic mode-locked semiconductor laser diodes

All-optical WDM-to-TDM conversion with total capacity of 33 Gb/s for WDM network links

We demonstrate all-optical WDM-to-TDM conversion in a switching node with a total throughput of 33 Gb/s. This is the highest throughput ever reported using a low timing jitter monolithic mode-locked semiconductor laser and a nonlinear optical loop mirror. The NOLM serves as an N/spl times/1 wavelength converter and the node has a unified output wavelength at 1554 nm. Wavelength-to-time-domain conversion using the node is simulated by inputting two data channels each at 1 Gb/s. This scheme is proposed to serve as an interface between independent high capacity WDM networks to avoid the limitations imposed by the optical bandwidth and unequal gain of EDFAs in optical networking and to minimize the deleterious effect of fiber nonlinearities during transmissions. The switching node for multiwavelength operation based on the wavelength dependence of the switching characteristics of the NOLM is also evaluated.

Continuously tunable optoelectronic millimetre-wavetransmitter using monolithic mode-locked semiconductor laser

The authors demonstrate a continuously tunable optoelectronic transmitter which uses a monolithic mode-locked semiconductor laser. Millimetre-wave subcarrier frequencies up to 300 GHz can be generated by photomixing a microwave subcarrier frequency with the selected harmonics of the mode-locked frequency, using an electro-optic modulator. A subcarrier frequency which can be tuned continuously from DC to 43 GHz is achieved experimentally.

Extremely low-amplitude modulation in a subharmonically hybrid mode-locked monolithic semiconductor laser

Negligibly small amplitude modulation and sufficiently low timing jitter are achieved simultaneously in a passively mode-locked monolithic semiconductor laser stabilized by applying an electrical signal at the second subharmonic of the pulse repetition frequency. Nearly transform-limited 33 GHz pulse trains with 0.56 ps timing jitter and -23 dBc amplitude modulation are obtained with 23 dBm driving signals at 16.5 GHz. Detailed investigations are carried out on the dependence of the amplitude modulation and timing jitter on RF driving power for the second- and third-order subharmonic cases. The excellent amplitude modulation property of the second subharmonic case with the specific laser used in this work is ascribed to the frequency response characteristics of the device.

Optical transmission of narrowband millimeter-wave signals

We describe experimentally and theoretically three techniques used to transmit narrowband millimeter-wave (MM-wave) analog signals over optical fiber: 1) narrowband MM-wave optical transmitters based on resonant modulation of monolithic semiconductor lasers, 2) feedforward optical modulation, and 3) a passively mode-locked laser operating in an optoelectronic phase-locked loop. The resonant modulation response at the cavity round-trip frequency is fully characterized for multiple-contact lasers under various bias conditions. Issues such as modulation efficiency, passband bandwidth, noise, and intermodulation distortion are addressed. A system implementation of resonant modulation is presented in which two simultaneous 2.5-Mb/s BPSK channels centered at a subcarrier frequency of 41 GHz is transmitted over 400 m of single-mode fiber. Simple microstrip matching circuits are fabricated at 41 GHz to couple the MM-wave signals into the laser. Resonant modulation of single-contact lasers is also reported. Next, implementation of a tunable MM-wave (30-300 GHz) optical transmitter based on feedforward optical modulation is presented, and the fundamental performance of this technique investigated in terms of noise and dynamic range. Feedforward modulation is used to transmit 300-Mb/s data at 39 GHz over 2.2 km of single-mode fiber. Finally, a passively mode-locked monolithic semiconductor laser operating in an optoelectronic phase-locked loop is implemented as a narrowband MM-wave optical transmitter at 46 GHz. The phase-locked loop bandwidth, MM-wave tracking capability, and fundamental limit to the stability of the MM-wave subcarrier is established. The relative merits of the three techniques are discussed and compared. The MM-wave subcarrier transmission results presented here represent the highest reported to date.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Pulse buildup in passively mode-locked monolithic quantum-well semiconductor lasers

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.

Comparison of timing jitter in external and monolithic cavity mode-locked semiconductor lasers

A comprehensive timing jitter comparison is made for mode-locked semiconductor lasers using active, passive, and hybrid mode-locking techniques in both external and monolithic cavity configurations. Active mode locking gives the lowest residual rms timing jitter of 65 fs (150 Hz-50 MHz), followed by the hybrid and passive mode-locking techniques. It is found that monolithic cavity devices with all active waveguides have higher timing jitter levels than the comparable external cavity case.