Mode-locked External-cavity Semiconductor Laser Research Articles

High-Spatial-Resolution Brillouin Optical Correlation Domain Analysis Using Short-Pulse Optical Sources

High-spatial-resolution distributed optical fiber sensing based on Brillouin optical correlation domain analysis (BOCDA) using short-pulse optical sources is demonstrated. Short optical pulses phase-modulated with a pseudo random bit stream (PRBS) are used for pump and Stokes probe lights for the correlation-domain measurement of distributions of local Brillouin frequency shift (BFS). Because the excitation of acoustic wave is tightly confined in short length along the fiber owing to the short pulse duration, spatial resolution of the measurement is improved as compared with the case using not-return-to-zero pulses. In this experiment, BFS variation in a 2 mm standard single-mode fiber section is clearly detected by the use of an external cavity mode-locked semiconductor laser emitting 3 ps pulses as the light source. Spatial resolution shorter than 1 mm is obtained. Scanning of measurement location is achieved electrically by changing the clock speed of the PRBS, which is an advantage of the proposed scheme over the high-spatial-resolution BOCDA using amplified spontaneous emission as a light source. Theoretical estimation of Brillouin gain that the short-pulse Stokes probe light acquires is presented.

Actively mode-locked diode laser with a mode spacing stability of

We have studied mode spacing stability in an actively mode-locked external-cavity semiconductor laser. It has been shown that, in the case of mode spacing pulling to the frequency of a highly stable external microwave signal produced by a hydrogen standard (stability of over an averaging period ), this configuration ensures a mode spacing stability of .

Self-optimizing femtosecond semiconductor laser.

A self-optimizing approach to intra-cavity spectral shaping of external cavity mode-locked semiconductor lasers using edge-emitting multi-section diodes is presented. An evolutionary algorithm generates spectrally resolved phase- and amplitude masks that lead to the utilization of a large part of the net gain spectrum for mode-locked operation. Using these masks as a spectral amplitude and phase filter, a bandwidth of the optical intensity spectrum of 3.7 THz is achieved and Fourier-limited pulses of 216 fs duration are generated after further external compression.

Experimental Study of the Timing Jitter of a Passively Mode-Locked External-Cavity Semiconductor Laser Subject to Repetition Rate Transitions and Optical Feedback

We experimentally investigate the timing jitter (TJ) of a passively mode-locked external-cavity diode laser. Variation of the gain current and the absorber reverse bias voltage allows transitions from fundamental mode-locking up to seventh harmonic mode-locking. Hereby, a reduction of the TJ as a function of the harmonic mode-locking order is found. Furthermore, the application of optical feedback results in an additional reduction of TJ for almost the whole investigated operation range. In particular, the reduction increases with harmonic mode-locking order. The highest observed reduction of TJ amounts to a factor of 10 as compared with the free-running case which corresponds to a repetition-rate linewidth reduction by a factor of 100.

A passively mode-locked external-cavity semiconductor laser emitting 60-fs pulses

A compact source of 60-fs pulses is demonstrated, based on a semiconductor laser that is mode-locked using a saturable absorber mirror in an external cavity.

Optimization of Ultrashort Pulse Generation in Passively Mode-Locked Vertical External-Cavity Semiconductor Lasers

We present a genetic algorithm based method to optimize the gain medium design of a passively mode-locked vertical external-cavity surface-emitting laser (VECSEL) for ultrashort pulse generation. Beginning with a given standard VECSEL design, we show that a simple modification to the DBR within the active mirror can significantly reduce both the duration and the chirp of the generated pulse. We demonstrate, using realistic numerical simulations, that the full-width at half-maximum of the pulse can be reduced by more than a factor of two. The required design changes come at the cost of increased sensitivity to perturbations in the active chip growth. Methods of counteracting this trend are presented.

Intracavity dispersion effect on timing jitter of ultralow noise mode-locked semiconductor based external-cavity laser

We report the generation of optical pulse trains with 380 as of residual timing jitter (1 Hz-1 MHz) from a mode-locked external-cavity semiconductor laser, through a combination of optimizing the intracavity dispersion and utilizing a high-power, low-noise InGaAsP quantum-well slab-coupled optical waveguide amplifier gain medium. This is, to our knowledge, the lowest residual timing jitter reported to date from an actively mode-locked laser.

Synchronized Mode-Locked Semiconductor Lasers and Applications in Coherent Communications

The general features and characteristics of two different external-cavity mode-locked semiconductor lasers (MSLs) were studied. Coherent optical frequency combs and short pulses from the MSLs were used to develop a synchronized MSL system. Exploiting the synchronized MSLs as a phase-locked transmitter and a local oscillator, various heterodyne and homodyne coherent detection techniques were experimentally demonstrated. The experimental results have shown that the phase-coherent optical frequency combs and short pulses from the synchronized MSLs are very promising optical sources for many future coherent photonic systems, especially for spectrally phase-encoded optical code-division multiple access (SPE-OCDMA).

High-Power Hybrid Mode-Locked External Cavity Semiconductor Laser Using Tapered Amplifier with Large Tunability

We report on hybrid mode-locked laser operation of a tapered semiconductor amplifier in an external ring cavity, generating pulses as short as 0.5 ps at 88.1 MHz with an average power of 60 mW. The mode locking is achieved through a combination of a multiple quantum well saturable absorber (>10% modulation depth) and an RF current modulation. This designed laser has 20 nm tuning bandwidth in continuous wave and 10 nm tuning bandwidth in mode locking around 786 nm center wavelength at constant temperature.

Analysis of Timing Jitter in External-Cavity Mode-Locked Semiconductor Lasers

We develop a comprehensive theoretical description of passive mode-locking in external-cavity mode-locked semiconductor lasers based on a fully distributed time-domain approach. The model accounts for the dispersion of both gain and refractive index, nonlinear gain saturation from ultrafast processes, self-phase modulation, and spontaneous emission noise. Fluctuations of the mode-locked pulses are characterized from the fully distributed model using direct integration of noise-skirts in the phase-noise spectrum and the soliton perturbations introduced by Haus. We implement the model in order to investigate the performance of a MQW buried heterostructure laser. Results from numerical simulations show that the optimum driving conditions for achieving the shortest pulses with minimum timing jitter occur for large reverse bias in the absorber section at an optimum optical bandwidth limited by Gordon-Haus jitter.

Pulse properties of external-cavity mode-locked semiconductor lasers

The performance of an external-cavity mode-locked semiconductor laser is investigated both theoretically and experimentally. The optimization analysis focuses on the regimes of stable mode locking and the generation of sub-picosecond optical pulses. We demonstrate stable output pulses down to one picosecond duration with more than 30 dB trailing pulse suppression. The limiting factors to the device performance are investigated on the basis of a fully-distributed time-domain model.We find that ultrafast gain dynamics effectively reduce the pulse-shaping strength and inhibit the generation of femtosecond optical pulses.

10 GHz passively mode-locked external-cavity semiconductor laser with 1.4W average output power

We present a 10GHz passively mode-locked vertical external-cavity surface-emitting semiconductor laser (VECSEL) with 1.4W average output power in 6.1ps pulses. The output features a very good pulse quality with a time–bandwidth product of 0.42 in a nearly diffraction-limited beam. This demonstrates that passively mode-locked VECSELs are suitable for generating high powers in high-repetition-rate pulse trains.

21-W picosecond passively mode-locked external-cavity semiconductor laser

We demonstrate an optically pumped passively mode-locked external-cavity semiconductor laser generating 4.7-ps pulses at 957 nm with as much as 2.1 W of average output power and a 4-GHz repetition rate. Compared with earlier results, the chirp of the pulses has been greatly reduced by use of an intracavity etalon. Apart from restricting the bandwidth, the etalon also helps optimize wavelength-dependent gain parameters and dispersion.

Noise in fundamental and harmonic modelocked semiconductor lasers: Experiments and simulations

Electric-field correlation measurements of fundamental and harmonic modelocked external cavity semiconductor lasers are presented. Based on these results, an empirical model of a harmonic modelocked pulsetrain is constructed. Using this model, the equivalence between the time-interleaved pulsetrains picture and the supermode picture of a harmonic modelocked pulsetrain is shown. Simulations based on the model are presented showing the key characteristics of modelocked pulsetrains in radio frequency (RF) and optical domains. The fundamental relationship between longitudinal mode linewidth and RF phase-noise corner frequency is delineated. The generated results point to fundamental limitations in timing jitter in modelocked lasers.

Toward a photonic arbitrary waveform generator using a modelocked external cavity semiconductor laser

We propose an architecture for photonic arbitrary waveform generation where the phase-locked longitudinal modes of a 12.4-GHz fundamentally modelocked external cavity semiconductor laser are individually modulated. We report photonic synthesis of microwave tones at 37.2 GHz (limited by photodetector bandwidth) with linewidth < 100 Hz and dynamic range 50 dB at 100-Hz resolution bandwidth. We show photonically synthesized 12.4-GHz sine waves with superimposed sinusoidal and pulsed RF modulations, demonstrating the potential for photonic arbitrary waveform generation with the proposed architecture.

Performance of External Cavity Mode-Locked Semiconductor Lasers Employing Reverse Biased Saturable Absorbers

We have experimentally investigated the performance of external cavity mode-locked semiconductor lasers employing reverse biased saturable absorbers. We have measured the magnitude of trailing pulses when varying the chip length and studied the pulse quality when changing the driving conditions. The observed behavior is explained and we conclude on the optimum operating parameters

Ultrashort pulse generation by intracavity spectral shaping and phase compensation of external-cavity modelocked semiconductor lasers

Intracavity spectral shaping and external chirp compensation techniques were employed to generate nearly transform-limited optical pulses with a temporal duration of 250 fs from an external-cavity modelocked semiconductor laser. It was also demonstrated that intracavity spectral shaping techniques can be used for artificially tailoring the chirp of the output pulses.

Pulsed injection locking dynamics of passively mode-locked external-cavity semiconductor laser systems for all-optical clock recovery

The performance characteristics of a pulse injection locked, passively mode-locked (PML) external-cavity semiconductor laser system for all-optical clock recovery are investigated in detail. It is important to characterize the clock recovery dynamics to understand the fundamental capabilities and limitations of the clock recovery system. It is experimentally shown that these devices offer robust clock recovery with low phase and amplitude noise, low injected data power requirements, large frequency locking bandwidth, large phase tracking bandwidth, short lockup time, long dephasing time and immunity to bit-pattern-effects. Harmonic clock generation and subharmonic clock generation are demonstrated for data-rate conversion applications.

Intracavity spectral shaping in external cavity mode-locked semiconductor diode lasers

Intracavity spectral shaping techniques have been employed to artificially shape and broaden the optical spectrum of external cavity mode-locked semiconductor lasers. Using an intracavity spectrometer and intensity Fourier-plane filtering, active mode-locked output spectra with a multiplicity of independently tunable wavelengths have been generated, while an adjustable intracavity etalon has been employed to generate an 18-nm spectral width. Furthermore, hybrid mode-locking with a multiple-quantum-well (MQW) saturable absorber combined with the intracavity etalon, followed by dispersion compensation has led to the generation of optical pulses of 330 fs in duration.

Highly sensitive and compact cross-correlator for measurement of picosecond pulse transmission characteristics at 1550 nm using two-photon absorption in Si avalanche photodiode

A highly sensitive and compact cross-correlator in which an Si avalanche photodiode (APD) is used as a two-photon absorber is described, which was developed for the measurement of picosecond-pulse transmission characteristics at 1550 nm. A 10 GHz, 1.7 ps pulse under test is generated from an external-cavity modelocked semiconductor laser, and is transmitted through an 80 km long dispersion-shifted fibre. A 200 fs sampling pulse is obtained from the pulse under test by pulse compression. An Si APD is used as a two-photon absorber for the cross-correlation measurement of the transmitted pulse waveform. The asymmetric pulse-waveform distortion stemming from the dispersion slope is clearly detected by the system.