Gain-switched Semiconductor Laser Research Articles

Design of low-timing-jitter, stable picosecond optical-pulse source using an uncooled gain-switched Fabry-Perot semiconductor laser with external continuous-wave light injection

This paper presents the design of a low-timing-jitter, stable picosecond optical-pulse source, which is based on a low-cost, uncooled Fabry–Perot (FP) semiconductor laser in the gain-switching operation. The wavelength of the designed laser can be tuned from 1538 to 1554 nm under the condition of external continuous-wave (CW) light injection. The relationship between injection light power and timing jitter or between injection light power and pulse width of this gain-switched laser is studied experimentally. Our results show that the optical pulses with widths about 28 and 19 ps at the repetition frequencies of 2.5 and 5 GHz, respectively, are produced by an uncooled gain-switched FP semiconductor laser with timing jitter ≤600 fs, when the injection power and wavelength of an external CW light are appropriately chosen. The use of a 500-m dispersion-compensation fiber can easily compress the optical pulses from 26 to 7.7 ps. Moreover, the stability of an uncooled gain-switched FP laser is experimentally investigated, and a stable optical-pulse train at 5 GHz can be feasibly produced over 7 h of continuously working. © 2011 Wiley Periodicals, Inc. Microwave Opt Technol Lett, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26176

Time resolved chirp measurements of gain switched semiconductor laser using a polarization based optical differentiator

We present a novel implementation of the "phase reconstruction using optical ultra fast differentiation" (PROUD) technique and apply it to characterize the time resolved chirp of a gain switched semiconductor laser. The optical temporal differentiator is a fiber based polarization interferometer. The method provides a fast and simple recovery of the instantaneous frequency from two temporal intensity measurements, obtained by changing the spectral response of the interferometer. Pulses with different shapes and durations of hundreds of picoseconds are fully characterized in amplitude and phase. The technique is validated by comparing the measured pulse spectra with the reconstructed spectra obtained from the intensity and the recovered phase.

Ultrawideband Pulse Generation Based on Overshooting Effect in Gain-Switched Semiconductor Laser

We demonstrate an alternative procedure to achieve ultrawideband (UWB) radio-frequency (RF) doublet impulses. It is based on the overshooting effect appearing by biasing a semiconductor laser close to the threshold with a large-amplitude signal. Specifically, with an optical bandpass filter and an electrical low-pass filter, we easily obtain doublet-like impulses whose RF spectrum meets the UWB regulations. Furthermore, we have been able to propagate such signals through an optical fiber link of 118-km length. Though the technique is not flexible in terms of waveform generation, our method constitutes a reliable, easy, and low-cost alternative for RF UWB impulse generation.

Generation of Fiber Tunable High-power Picosecond Laser Pulse

A fiber tunable high-power picosecond laser system has been for the first time demonstrated. A gain switch semiconductor laser diode was introduced as seed source, and a multi-stage single mode Yb-doped fiber amplifier was combined with a single mode double-clad Yb-doped fiber amplifier to construct the amplification system. High stability and good beam quality pulses with 1MHz tunable repetition rate, 3W average power, 90ps pulse duration, and central wavelength tunable from 1053 nm to 1073 nm were generated. The completely fiber integrated approach has the potential to be scaled to significantly higher average powers.

Aeronautical use of semiconductor lasers for short optical pulses

In this paper, we investigate the feasible schemes to generate periodic optical pulses of width between several picoseconds (ps) and tens ps. Gain-switched semiconductor laser diodes are shown to be more suitable for avionics applications than mode-locked laser diodes. In the experiment, we use a low-cost Fabry-Perot laser diode to generate short optical pulse streams. A simple optical injection-locking scheme is then used to reduce the timing jitter and frequency chirp in such laser diodes, which in turn can improve the transmission performance of the generated optical pulses. It is expected that the use of gain-switched semiconductor lasers can meet the requirement of high-speed airborne communication networks or ground supporting systems at airports. Moreover, we discuss the possibility of using the pulsed semiconductor lasers to generate millimetre-wave (mm-wave) signals for future applications to airborne high-resolution, mm-wave radars.

Addendum to: Picosecond pulse generation for visible semiconductor laser operating at 650‐NM wavelength with the use of the gain‐switching technique

AbstractOriginally published Microwave Opt Technol Lett 35: 65–67, 2002. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 35: 342–342, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10584

Spectral technique for measuring the pulse-width jitter of a gain-switched laser

We report the experimental investigation of the harmonic number dependence of the noise power spectrum of a train of Gaussian pulses from a gain-switched semiconductor laser. In particular, we examined the dependence under the condition of τω>1, where τ is the pulse-width and ω is the angular frequency. We demonstrated that: (a) the spectral noise function is fully described by a fourth order polynomial, (b) the pulse-width jitter is 5 ps, and (c) there is significant correlation between the different types of jitter (amplitude, timing, and width).

A Novel Method for Eliminating Chirp and Compressing Pulses from Gain-Switched Distributed-Feedback Bragg Semiconductor Laser

A novel method is proposed that simultaneously eliminates chirp and compresses pulses from gain-switched distributed-feedback Bragg (G-S DFB) semiconductor laser employing chirped fiber Bragg grating (FBG) with narrow bandwidth. It is demonstrated that with this method, only the central frequency of the FBG is slightly shifted from the central frequency of the G-S DFB laser; the nearly transform-limited narrow pulse with symmetrical waveform can be obtained.

A Novel Method for Eliminating Chirp and Compressing Pulses from Gain-Switched Distributed-Feedback Bragg Semiconductor Laser

A novel method is proposed that simultaneously eliminates chirp and compresses pulses from gain-switched distributed-feedback Bragg (G-S DFB) semiconductor laser employing chirped fiber Bragg grating (FBG) with narrow bandwidth. It is demonstrated that with this method, only the central frequency of the FBG is slightly shifted from the central frequency of the G-S DFB laser; the nearly transform-limited narrow pulse with symmetrical waveform can be obtained.

Jitter dynamics of a gain switched semiconductor laser under self-feedback and external optical injection

We investigate the jitter dynamics of a gain switched laser diode (LD) under the influence of strong optical injection due either to multiple reflections from an external cavity mirror, or from another LD. A numerical technique that considers both the spontaneous emission noise and multiple reflections from external optical components is implemented. At all times, the LD exhibits multi-longitudinal mode operation with a Gaussian-shaped spectral line profile that is centered around a fixed dominant output wavelength. We separately consider three (strong) optical injection conditions: 1) coherent self-feedback; 2) incoherent self-feedback; and 3) coherent, external continuous-wave (CW) optical injection. Incoherent self-feedback results in a reduction, by an order of magnitude, in both the intensity and timing jitter (0.5 ps), while maintaining the average peak power and pulsewidth. Eye pattern results show an opening of at least 90 %, which represents an improvement by a factor of two over the same LD that operates without optical injection. The external CW injection condition approaches that of incoherent self-feedback only at high external injection. Coherent self-feedback does not produce any significant change in the LD performance.

Influence of Nonlinear Gain Saturation on the Time-Bandwidth Product of Optical Pulse from a Gain-Switched Semiconductor Laser

It is found numerically that the time-bandwidth product (TBP) of optical pulse from a gain-switched semiconductor laser operating under a sufficient gain saturation condition increases monotonously with increasing modulation amplitude. This enhancement of the TBP becomes remarkable for longer-wavelength semiconductor lasers (1.3, 1.55 μm) having large value of the gain compression factor e (∼ 10−23 m3), making the pulse chirp estimation using the TBP difficult.

Generation of 20-fs optical pulses from a gain-switched laser diode by a four-stage soliton compression technique

7.5-ps optical pulses generated from a gain-switched semiconductor laser at 2 GHz are successfully compressed down to 20 fs using a four-stage fiber soliton pulse compressor consisting of standard single-mode transmission, Er-doped, dispersion-decreasing, and dispersion-flattened fibers, respectively. We have experimentally confirmed that the soliton self-frequency shift plays an important role in obtaining such high compression in very short fibers, and also in minimizing the inherent undesirable pedestal component.

Limit of optical pulsewidth in the gain-switched DFB semiconductor laser

We investigate the minimum optical pulsewidth that is obtainable in the gain-switched distributed-feedback semiconductor laser. The minimum obtainable optical pulsewidth is determined by either the period doubling or the saturation of modulation efficiency. The shift of the resonance frequency to the lower frequency side with increase of the modulation current brings about these phenomena. It is predicted theoretically that the minimum obtainable pulsewidth is about 0.2 times the period of the small-signal resonance. The minimum pulsewidth after compression with a dispersion compensating fiber is also discussed. Experimental measurements are in good agreement with the theory.

Complete characterization of ultrashort pulse sources at 1550 nm

This paper reviews the use of frequency-resolved optical gating (FROG) to characterize mode-locked lasers producing ultrashort pulses suitable for high-capacity optical communications systems at wavelengths around 1550 nm, Second harmonic generation (SHG) FROG is used to characterize pulses from a passively mode-locked erbium-doped fiber laser, and both single-mode and dual-mode gain-switched semiconductor lasers. The compression of gain-switched pulses in dispersion compensating fiber is also studied using SHG-FROG, allowing optimal compression conditions to be determined without a priori assumptions about pulse characteristics. We also describe a fiber-based FROG geometry exploiting cross-phase modulation and show that it is ideally suited to pulse characterization at optical communications wavelengths. This technique has been used to characterize picosecond pulses with energy as low as 24 pJ, giving results in excellent agreement with SHG-FROG characterization, and without any temporal ambiguity in the retrieved pulse.

Wavelength switching of picosecond pulses in a self-seeded Fabry-Perot semiconductor laser with external fiber Bragg grating cavities by optical injection

All-optical wavelength switching of single-mode picosecond pulses was demonstrated in an optically gain-switched Fabry-Perot semiconductor laser with self-seeding from two uniform fiber Bragg gratings (FBGs) or a linearly chirped FBG by injecting optical pulse trains with a peak power of /spl sim/1.0 mW at GHz repetition rates. Sidemode suppression ratio (SMSR) better than 17 dB was achieved in both wavelengths in the former case. Wavelength switching among three successive laser cavity modes was achieved in the latter case. A SMSR better than 15 dB was obtained at all three wavelengths. This laser has potential applications in remote optically controlled fiber sensors, such as temperature sensors.

THEORETICAL AND EXPERIMENTAL STUDY ON COMPRESSION OF CHIRPED OPTICAL PULSES UTILIZING DISPERSION-COMPENSATION AND HIGH-ORDER SOLITON EFFECT

In this paper,we study theoretically and experimentally the compression of chirped optical pulses in dispersion-compensation fiber and dispersion-shifted fiber utilizing single mode rate equation of semiconductor laser and nonlinear Schrdinger (NLS) equation.In experiment,the 53.8ps pulses generated by a gain-switched DFB semiconductor laser diode with 2.5GHz repetition rate were compressed to 12ps in a length of dispersion-compensation fiber.Then,the 12ps pulses were compressed to 2.5 or 2.1ps due to high-order soliton effect in dispersion-shifted fiber.Experimental results agree with theoretical results.

Generator of ultrashort optical pulses for time division multiplexing

The performance of a device based on modified injection-locking techniques is studied by means of numerical simulations. The device incorporates master and slave configurations, each one with a DFB laser and an electroabsorption modulator (EAM). This arrangement allows the generation of high peak power, narrow optical pulses according to a periodic or pseudorandom bit stream provided by a current signal generator. The device is able to considerably increase the modulation bandwidth of free-running gain-switched semiconductor lasers using multiplexing in the time domain. Opportunities for integration in small packages or single chips are discussed.

Wavelength-tunable nearly transform-limited pulsegeneration by external injection-seeding of again-switched Fabry-Perot laser

The authors report the generation of wavelength-tunable, nearly transform-limited pulses by external CW injection seeding and fibre compression of a gain-switched Fabry-Perot semiconductor laser. Nearly transform-limited, ~ 6 ps pulses with a time-bandwidth product of ~ 0.6 have been obtained over a tuning range of ~ 10 nm.

Harmonic generation limitations in gain-switched semiconductor lasers due to distributed microwave effects

A large-signal, time domain semiconductor laser model that incorporates propagation effects within the cavity and a microwave circuit simulator are used to investigate distributed microwave effects on gain-switching performance. It is shown that the position of the feed point to the top electrode can have a significant influence on the harmonic content of the generated pulses, which is an important consideration in microwave/millimeter-wave signal generation schemes.

Nonlinear spatio-temporal dynamics due to transverse-mode competition in gain-switched microcavity semiconductor lasers

We show through numerical simulations that transverse-mode competition induced by spatial hole-burning in gain-switched vertical-cavity surface-emitting lasers gives rise to rich nonlinear dynamics, including period doubling, optical chaos, and anti-phase oscillations. The spatio-temporal nature of gain switching is explored over a wide range of modulation currents and modulation frequencies.