Mode-locked Semiconductor Laser Diode Research Articles

Optoelectronic mixer with a photoconductive switch for 1550 nm wavelengths

We demonstrate an optoelectronic mixer based on an ultrafast InGaAs photoconductive switch and its use in an innovative heterodyne detection system for Radio over Fibre transmission. The advantage of the proposed switch is its relatively flat response curve in a wide frequency range up to 67 GHz. Two mixing schemes are presented through I-Q modulated data-stream down-conversion. The data can modulate either the electrical signal or the optical signal. In case the electrical signal is modulated, a mode-locked semiconductor laser diode is used as an optical local oscillator at the self-oscillating frequency of 24.5 GHz. The InP based quantum-dash mode-locked laser emitting in the 1570 nm wavelength range is stabilized by a feedback loop and shows a low phase noise in order to increase the mixing performances of the detection apparatus. In a second experiment, the photoconductive switch is combined with a continuous wave laser to demonstrate the feasibility of down converting an optically provided data-stream with an electrical local oscillator.

9-kW peak power and 150-fs duration blue-violet optical pulses generated by GaInN master oscillator power amplifier.

Blue-violet optical pulses of 9-kW peak power and 150-fs duration were obtained from a GaInN master oscillator power amplifier system using a nonlinear dispersion compensator. Seed pulses from a dispersion-compensated GaInN mode-locked semiconductor laser diode were stretched to 3-ps duration using a nonlinear dispersion compensator with a spatial light modulator that added second-order phase dispersion to an optimized nonlinear phase dispersion compensating the higher-order dispersion of the optical pulses. The stretched phase-optimized pulses were efficiently amplified to 3.0 nJ by a GaInN semiconductor optical amplifier. The amplified pulses were subsequently compressed using a linear pulse compressor, yielding 1.4-nJ femtosecond pulses. The obtained results show the highest peak-power ever reported for an electrically-pumped semiconductor gain medium.

140-fs duration and 60-W peak power blue-violet optical pulses generated by a dispersion-compensated GaInN mode-locked semiconductor laser diode using a nonlinear pulse compressor.

Blue-violet optical pulses of 140-fs duration and 60-W peak power were obtained from a dispersion-compensated GaInN mode-locked semiconductor laser diode using a nonlinear pulse compression technique. Wavelength-dependent group velocity dispersion expressed by third-order phase dispersion was applied to the optical pulses using a pulse compressor with a spatial light modulator. The obtained optical pulses had the shortest duration ever obtained for a mode-locked semiconductor laser diode using edge-emitting type devices.

Numerical Simulation of Nonlinear Optical Effects in Frequency-Modulation Mode-Locked Semiconductor Laser Diodes

The nonlinear optical effects in frequency-modulation mode-locked semiconductor laser diodes have been examined. The numerical simulation carried out in the frequency domain showed that the asymmetric nonlinear optical gain, which causes mode instability in mode-locked lasers, can be compensated for by an additional phase modulator. The stabilization of multimode oscillation was experimentally confirmed by applying phase modulation to the grating coupled laser diode.

Numerical Simulation of Nonlinear Optical Effects in Frequency-Modulation Mode-Locked Semiconductor Laser Diodes

The nonlinear optical effects in frequency-modulation mode-locked semiconductor laser diodes have been examined. The numerical simulation carried out in the frequency domain showed that the asymmetric nonlinear optical gain, which causes mode instability in mode-locked lasers, can be compensated for by an additional phase modulator. The stabilization of multimode oscillation was experimentally confirmed by applying phase modulation to the grating coupled laser diode.

Coherent spectral bandwidth combining by optical pulse injection locking in quantum dot modelocked semiconductor diode lasers

An optical pulse injection locking technique is employed to generate shorter pulses from a passively modelocked quantum dot laser. The optical pulse injection locking enables the coherent addition of phase-locked longitudinal mode groups from two separate modelocked lasers without the use of stabilisation control loops, thus increasing the spectral bandwidth output resulting in optical pulses with shorter temporal duration.

External-Cavity Mode-Locked Quantum-Dot Laser Diodes for Low Repetition Rate, Sub-Picosecond Pulse Generation

This paper presents an investigation of the mode-locking performance of a two-section external-cavity mode-locked InGaAs quantum-dot laser diode, focusing on repetition rate, pulse duration and pulse energy. The lowest repetition rate to-date of any passively mode-locked semiconductor laser diode is demonstrated (310 MHz) and a restriction on the pulse energy (at 0.4 pJ) for the shortest pulse durations is identified. Fundamental mode-locking from 310 MHz to 1.1 GHz was investigated, and harmonic mode-locking was achieved up to a repetition rate of 4.4 GHz. Fourier transform limited subpicosecond pulse generation was realized through implementation of an intra-cavity glass etalon, and pulse durations from 930 fs to 8.3 ps were demonstrated for a repetition rate of 1 GHz. For all investigations, mode-locking with the shortest pulse durations yielded constant pulse energies of ~0.4 pJ, revealing an independence of the pulse energy on all the mode-locking parameters investigated (cavity configuration, driving conditions, pulse duration, repetition rate, and output power).

10 and 20 Gb/s all-optical RZ to NRZ modulation format and wavelength converter based on nonlinear optical loop mirror

We present experimental and theoretical results on all-optical 10 and 20 Gb/s RZ to NRZ modulation format and wavelength converter based on a nonlinear optical loop mirror (NOLM). A vector model of converter was developed and the shape of converted pulses was found analytically for particular choice of polarization states. In the experiment, non-zero dispersion shifted fiber with a length 1200 m was used as a nonlinear medium. Pulses from a 10 GHz mode-locked semiconductor laser diode were modulated to form pseudorandom RZ signal and eventually time division multiplexed to 20 Gb/s. RZ pulses were subsequently converted to NRZ signal. The performance of the converter was evaluated experimentally using the data communication analyzer and bit error ratio tester.

Integrated chirp compensation in a monolithic passively mode-locked semiconductor diode laser

We present traveling wave numerical simulations of passively mode-locked diode lasers that incorporate chirp compensation monolithically using a Fabry–Pérot interferometer, which provides a negative group delay. Numerical results show pulse compression of up to 65%. Time-frequency domain study of the pulses reveal a significant reduction in chirp across the pulse. Limitations of this simple linear chirp compensation scheme are examined.

High-quality photonic sampling streams from a semiconductor diode ring laser

We report on the development of an ultralow-noise, external-cavity, actively mode-locked semiconductor diode laser for application in next-generation photonic sampling systems. A summary of harmonically mode-locked noise characteristics in a 65-MHz ring cavity is presented through the range of pulse repetition frequencies between 130 MHz and 8.3 GHz (2nd-128th harmonic). Important implications regarding the use of gain-versus-loss modulation as the active modelocking mechanisms are discussed. We also report what are, to our knowledge, the lowest noise characteristics achieved to date for a semiconductor diode laser operating at 10 GHz. Individually optimized results of 0.12% rms amplitude noise (10 Hz-10 MHz), and 43 fs rms residual phase jitter (10 Hz-10 MHz) provide a theoretical resolution of 8.6 bits in a 10-GSPS optical analog-to-digital converter. We have also achieved dispersion-compensated pulsewidths; as short as 1.2 ps, and shown successful operation of a novel phase-locked-loop capable of reducing the rms; residual phase noise by as much as 91% within its response bandwidth. Finally, the first measurements of residual phase noise out to the Nyquist frequency (5 GHz) are presented, providing an upper bound on the rms residual phase jitter of 121 fs (10 Hz-5 GHz).

60 channel WDM transmitter using multiwavelength modelocked semiconductor laser

The simultaneous generation of 60 discrete wavelengths, with a 75 GHz interwavelength spacing, from a modelocked semiconductor diode laser is reported. The individual wavelengths are emitted as mutually synchronised 898 MHz return-to-zero pulse trains. Optical spectra and temporal diagnostics are provided.

10-GHz ultralow-noise optical sampling stream from a semiconductor diode ring laser

We report, what is to our knowledge, the lowest-noise pulsetrain produced to date with an actively mode-locked external-cavity semiconductor diode laser. Operating characteristics at 10 GHz include dispersion-compensated pulsewidths as short as 1.2 ps, amplitude noise as low as 0.12% rms, and residual phase noise as low as 43-fs rms. Potential application of such a laser in a next-generation optical analog-to-digital converter would theoretically provide as much as 8.6 bits of resolution, while sampling a 5-GHz waveform at the Nyquist frequency.

Joint time-frequency measurements of modelocked semiconductor diode lasers and dynamics using frequency-resolved optical gating

Joint time-frequency ultrafast measurements using frequency-resolved optical gating (FROG) have been used to provide a fundamental understanding of: (1) ultrashort pulse propagation in semiconductor optical amplifiers; (2) the modelocking dynamics in external cavity semiconductor diode lasers; and (3) correlated multiple-wavelength generation from mode locked semiconductor lasers. The pulse shaping and chirping effects measured by FROG are shown to be attributed to intracavity gain and saturable absorbing dynamics, as well as group velocity dispersion. In addition, the intracavity gain dynamics show a regime of transient unsaturated gain, which can be exploited to allow phase-correlated multiple-wavelength modelocked operation from a single-stripe external-cavity semiconductor diode laser. In this case, FROG techniques are used to understand the underlying mechanisms involved in the phase correlation process.

Demonstration of phase correlation in multiwavelength mode-locked semiconductor diode lasers

Wideband spectral phase correlation is demonstrated from a multiwavelength mode-locked semiconductor laser. By use of frequency-resolved optical gating techniques, significant phase correlation was observed between multiple intracavity oscillating wavelengths, with wavelength separations of ~1 nm . The resultant temporal characteristics show a substantial modulation owing to the spectral coupling induced by intracavity-generated four-wave mixing. This result may lead to novel methods for directly generating ultrafast subpicosecond optical pulse sequences with spectrally tailored amplitude and phase characteristics from actively mode-locked semiconductor lasers.

Efficient optoelectronic mixing at Ka-band using a mode-locked laser

The authors present optoelectronic mixing of data signals with a carrier signal in a mode-locked semiconductor laser diode. A long Fabry-Perot (FP) laser at 1.5 μm, which is monolithically integrated with an electro-absorption modulator, is mode-locked at 19.3 GHz through loss modulation. The gain section of the mode-locked laser is modulated by S-band signals. Modulation sidebands are observed in the optical domain as a result of mixing between the mode-locking and S-band communication signals. Optical up-conversion loss of 2.7 and 1.4 dB is measured for the LSB and USB. The measured spurious-free dynamic range is as high as 89 dB.Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> 3/.

Highly Stabilized Mode-Locked Semiconductor Diode Lasers.

Monolithic and external-cavity mode-locked diode lasers (Mode-Locked Laser Diodes: MLLDs) are highly stabilized by means of electrical or optical signal injection incorporating a compact device module packaging. These MLLDs have potential applications in ultrahigh-speed optical communication and optical measurement systems. The MLLDs developed fully satisfy the requirements in a light source for the optical time division multiplexing (OTDM) communication scheme at 100 Gb/s rate. Instead of electrical hybrid mode-locking, subharmonic optical pulse injection can stabilize the MLLD operating at over 100 GHz. This technology will be useful for the generation of millimeter and sub-millimeter electromagnetic waves with optoelectronic conversion. Another notable feature of highly stable MLLDs is to provide pump and probe optical measurements with a simple system excluding mechanical optical-delay, that is to say the optical sampling. This optical sampling enables to observe 100 Gb/s rate optical data eye-pattern as well as precise temporalresponse of optical materials.

Generation of synchronized subterahertz optical pulse trains by repetition-frequency multiplication of a subharmonic synchronous mode-locked semiconductor laser diode using fiber dispersion

We describe the generation of a synchronized, low-jitter, subterahertz optical pulse train by repetition-frequency multiplication of a subharmonic synchronous mode-locked semiconductor laser diode using the group-velocity dispersion (GVD) of optical fiber. A 49-196 GHz optical pulse train was generated with low intensity fluctuation and with low timing jitter, by adjusting fiber length in accordance with the mode-locking frequency and the fiber's GVD.

Recent works on monolithic mode-locked semiconductor laser diodes

Recent works on monolithic mode-locked semiconductor laser diodes

Intracavity gain and absorption dynamics of hybrid modelocked semiconductor lasers using multiple quantum well saturable absorbers

Time resolved intracavity gain, saturable absorption dynamics, intracavity intensity pulse profiles, and their corresponding spectrograms, were measured in an external cavity hybrid mode-locked semiconductor diode laser. These measurements were performed to obtain fundamental information of the mode-locking dynamics and to determine their role in the pulse shaping and chirping dynamics. The results of these experiments show that the integrating nonlinearity associated with gain depletion, coupled with group velocity dispersion, leads to asymmetric intensity pulse profiles with predominantly cubic temporal phase, while saturable absorption coupled with group velocity dispersion tends to linearize the chirp. Exploitation of these dynamics may allow researchers to generate optical pulses with higher peak intensities than previously reported.

Improvements in mode-locked semiconductor diode lasers using monolithically integrated passive waveguides made by quantum-well intermixing

By using the technique of quantum-well intermixing (QWI), monolithically integrated passive, and active waveguides can be fabricated. It is shown that mode-locked extended cavity semiconductor lasers with integrated low-loss passive waveguides display superior performance to devices in which the entire waveguide is active: the threshold current is a factor of 3-5 lower, the pulsewidth is reduced from 10.2 ps in the all active laser to 3.5 ps in the extended cavity device and there is a decrease in the free-running jitter level from 15 to 6 ps (10 kHz-10 MHz).