Hybrid Mode-locked Semiconductor Research Articles

Modelocked semiconductor laser system with pulse picking for variable repetition rate

The generation of picosecond pulses from a hybrid modelocked semiconductor master oscillator power amplifier system with a repetition rate as low as 340 kHz is presented. The fundamental repetition rate of the external cavity laser was 348 MHz and is reduced by an integrated ultrafast semiconductor pulse picker element which picks and amplifies only every 2nth pulse. The central wavelength was around 850 nm.

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.

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.

Coherent pulse detection and multi-channel coherent detection based on a single balanced homodyne receiver

The performance of coherent pulse detection (CPD) and multichannel coherent detection (MCCD) based on a single dual-balanced homodyne receiver was experimentally demonstrated using a gratingcoupled hybridly mode-locked semiconductor laser. Compared with direct detection, a high coherent gain of over 10 dB, as well as an SNR improvement of over 5 dB, was obtained in both detection schemes. Our experimental results have confirmed that the coherent detection processes in CPD and MCCD are nearly the same based on a square-root LO power dependence. Nevertheless, the MCCD scheme has shown an advantage in a path-length error over the CPD scheme, revealing 2~3 dB improvement in sensitivities.

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.

Amplitude noise of subharmonically hybrid mode-locked pulses generated from a monolithic semiconductor laser

Broad-band amplitude noise (100 MHz to 20 GHz) of 40 GHz pulses generated by a subharmonically hybrid mode-locked (SHML) monolithic semiconductor laser is investigated. Experiments show that the amplitude noise can only be suppressed at some certain subharmonic numbers, while the phase noise can be suppressed by subharmonic hybrid mode-locking under many subharmonic numbers.

325 nm bandwidth supercontinuum generation at 10 Gbit/s using dispersion-flattened and non-decreasing normal dispersion fibre with pulse compression technique

325 nm bandwidth (at 20 dB) supercontinuum generation at 10 Gbit/s using dispersion-flattened uniform normal dispersion fibre along with a pulse compression technique is experimentally demonstrated with a pumped 3.8 ps, 1552 nm hybrid modelocked semiconductor laser. Application to a 50 nm wavelength tunable source is also demonstrated.

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.

Ultrafast semiconductor laser-diode-seeded Cr:LiSAF regenerative amplifier system

An ultrafast, hybrid mode-locked semiconductor laser-diode system has been used to seed a flash-lamp-pumped Cr:LiSAF regenerative amplifier system, producing subpicosecond pulses with millijoule output pulse energy. This system has the potential to eliminate argon-ion-pumped-based, ultrafast laser systems.

Locking characteristics of a subharmonically hybrid mode-locked multisection semiconductor laser

Locking characteristics of a subharmonically hybrid mode-locked (SH-ML) semiconductor laser are investigated experimentally. The locking bandwidths under the second- and third-order SH-ML operation, as well as under fundamental hybrid mode-locking (FH-ML) condition, are characterized with a variety of microwave power and reverse bias voltage applied to the saturable absorber of the laser. Unique locking characteristics are observed for the third-order SH-ML where the locking bandwidth increases with increasing reverse bias, which is opposite to the FH-ML case. This leads to a locking bandwidth of 56 MHz, 2.3 times broader than that for the FH-ML under the shortest pulse condition.

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.

On the locking range of hybridly mode-locked semiconductor lasers

We theoretically investigate the locking range of hybridly mode-locked semiconductor lasers with a DBR section as a reflector. The DBR coupling constant and length are crucial in determining the locking range. At constant pulse width, the tuning range of the repetition frequency can be increased by a factor of 3 by using a strongly coupled, long DBR rather than a short and weakly coupled DBR. For a 30 GHz cavity and a pulse width of 5 ps, a locking range of 2.5% is predicted after optimization. We explain the increase in the locking range as a consequence of the dispersion inherent to a DBR. In addition, the pulses are found to be asymmetric, depending on the DBR parameters.

Subharmonic hybrid mode-locking of a monolithic semiconductor laser

Performance of a subharmonically hybrid mode-locked (SH-ML) monolithic semiconductor laser is investigated. A 33-GHz passively mode-locked distributed Bragg reflector semiconductor laser is stabilized by the injection of an electrical signal with a subharmonic frequency of the laser cavity resonance. Systematic measurements on the phase noise, timing jitter, amplitude modulation, and locking bandwidth are performed for the second- and third-order SH-ML conditions, and the results are compared with the fundamental hybrid mode-locking (FH-ML) case. Low timing jitter of less than 0.6 ps, comparable to that under the FH-ML case, is achieved for the both SH-ML cases. The amplitude modulation imposed by the subharmonic driving frequencies is found to be very small (<-24 dBc) for the second-order SH-ML because of the sufficiently low modulation response of the laser at 16.5 GHz. The third-order SH-ML is found to exhibit a very unique locking characteristics, leading to a maximum locking bandwidth of 56 MHz that is even larger than that for the FH-ML case.

Optically-fed millimetre-wave (37 GHz) transmission system incorporating a hybrid mode-locked semiconductor laser

The authors demonstrate, for the first time, millimetre-wave transmission systems incorporating a hybrid mode-locked semiconductor laser that are suitable for optically-fed wireless communication systems. Error free transmission at data rates up to 500 Mbit/s at 37 GHz over a wireless distance of 1 m is demonstrated. In addition, the system is capable of delivering up to 200 Mbit/s of BPSK modulated millimetre-wave signals over 10 km of standard optical fibre.

200-fs optical pulse generation and intracavity pulse evolution in a hybrid mode-locked semiconductor diode-laser/amplifier system

Optical pulses of 200 fs with 165 W of peak power have been generated from an AlGaAs semiconductor diode-laser system. These pulses represent, to our knowledge, both the shortest and most intense ever generated from an all-semiconductor injection diode-laser system. The intracavity pulse evolution in the external cavity is also investigated experimentally. The findings show that the large nonlinearities associated with gain depletion and saturable absorption cause appreciable spectral and temporal modification of the mode-locked optical pulse as it oscillates in the laser cavity.

Generation of subpicosecond high-power optical pulses from a hybrid mode-locked semiconductor laser

Ultrashort optical pulses 0.46 psec in duration with over 70 W of peak power are generated from an all-semiconductor laser-diode system. These results represent to our knowledge both the shortest and most-intense optical pulses generated from an all-semiconductor laser system.