Mode-locked Distributed Bragg Reflector Research Articles

Multi-Frequency Doppler Velocimetry Based on a Mode-Locked Distributed Bragg Reflector Laser

A differential multi-frequency laser Doppler velocimetry is demonstrated, utilizing the synchronized multimode of a mode-locked distributed Bragg reflector laser. This scheme enables the simultaneous detection of multiple Doppler frequency shifts. Multiple differential Doppler shifts of 0.6 Hz, 1.3 Hz, and 1.9 Hz are obtained, with an average speed of 3.677 mm/s and a standard deviation of 0.122 mm/s, demonstrating a cross-referenced velocity measurement capability. The measurement results are also compared with the dual-frequency laser Doppler velocimetry scheme using electro-optical modulation.

Photonic Integrated Circuits Based on Quantum well Intermixing Techniques

The passive sections of a monolithic device must have a wider bandgap than the active regions to reduce losses due to direct interband absorption. Such bandgap engineering is usually realized by complicated regrown butt-joint or selective-area growth techniques. We, however, have developed a simple, flexible and low-cost alternative technique – quantum well intermixing (QWI) – to increase the bandgap in selected areas of an integrated device post-growth. To verify the QWI process, we have fabricated the following demonstrators: a 40 GHz semiconductor mode-locked laser producing pulses as short as 490 fs; a 10 GHz passively mode-locked extended cavity laser integrated with surface-etched distributed Bragg reflector (DBR) which can be tuned in both wavelength and pulse repetition rate; four 10 GHz 1.55 μm AlGaInAs/InP mode-locked surfaced-etched DBR lasers integrated combiner, a semiconductor optical amplifier and modulator where the four channels can be operated separately or simultaneously; a CWDM source with 12 nm wavelength separation based on an AlGaInAs/InP integrated distributed feedback laser array; and a 1.55μm DFB laser monolithically integrated with power amplifier array. In all these applications, QWI has the advantage of eliminating crystal regrowth and the associated stringent tolerance requirements that are required in traditional integration schemes.

High-Power AlGaInAs Mode-Locked DBR Laser With Integrated Tapered Optical Amplifier

We demonstrate a high output power passively mode-locked distributed Bragg reflector laser with integrated tapered semiconductor optical amplifier, operating at 1.5 μm. These devices are based on an optimized low-optical-confinement AlGaInAs/InP epitaxial material with a three quantum wells active region and a passive far-field reduction layer. The device generates nearly transform-limited pulses with minimum pulse duration of 4.3 ps at 40-GHz repetition rate. An average output power of 200 mW with a corresponding output peak power of >;1.2 W is achieved.

Ultrashort Q-switched pulses from a passively mode-locked distributed Bragg reflector semiconductor laser

A compact semiconductor mode-locked laser (MLL) is presented that demonstrates strong passive Q-switched mode-locking over a wide range of drive conditions. The Q-switched frequency is tunable between 1 and 4 GHz for mode-locked pulses widths around 3.5 ps. The maximum ratio of peak to average power of the pulse-train is >120, greatly exceeding that of similarly sized passively MLLs.

Generation of Tunable Carrier-Suppressed Optical Pulses From a Mode-Locked DBR Laser Diode Operating With Two Carrier-Wavelengths

We proposed a method to generate pulsewidth-tunable carrier-suppressed (CS) optical pulsetrain from a mode-locked distributed Bragg reflector (DBR) laser diode (LD) operating with two carrier wavelengths. Our new method made it possible to generate the CS pulsetrains with widely tunable duty ratios of both more and less than 0.5 from a single chip of semiconductor device. With theoretical explanation and suggestion on the operation principle, we experimentally demonstrated the tunable CS pulse generation using a monolithic 40-GHz actively mode-locked DBR LD integrated with an electroabsorption modulator. Wide tunability in the pulsewidth from 3 to 16 ps was successfully achieved retaining almost chirp-free conditions. We also succeeded in the asymmetric pulse generation with different rise and fall times by fine tuning of the operating conditions.

Monolithic 40-GHz Mode-Locked MQW DBR Lasers for High-Speed Optical Communication Systems

The state-of-the-art of the development and fabrication of advanced 1.55-mum/40-GHz pulse laser modules with a monolithic InP-based mode-locked distributed Bragg reflector (DBR) MQW laser chip inside is reported, with respect to the future applications in high-speed optical communications. We emphasize the latest improvements for hybrid mode-locked devices, which integrate a saturable absorber or an electroabsorption modulator. We further illustrate different technical approaches that enable meeting predetermined frequencies and wavelengths, and which are at the same time promising with respect to high fabrication yields

Generation of carrier-suppressed broad pulses from modelocked DBR laser operating with two carrier wavelengths

A method is presented to generate a carrier-suppressed (CS) optical pulse train from a modelocked distributed Bragg reflector laser diode operating with two carrier wavelengths. Generation of 40 GHz CS broad pulse trains at 40 GHz was successfully achieved with tunable pulse width from 10.3 to 15.9 ps.

Modelocked distributed Bragg reflector laser

The fabrication and performance of a modelocked distributed Bragg reflector laser is described. The laser has a threshold current of 60 mA and differential efficiency of 0.05 mW/mA when coupled into a singlemode fibre. Modelocked pulses with 7 ps pulsewidth, with a time-bandwidth (ΔtΔν) product of ~0.7 at ~5 GHz, have been obtained.

Tuning characteristics of monolithic passively mode-locked distributed Bragg reflector semiconductor lasers

Tuning characteristics of multicontact passively mode-locked distributed Bragg reflector (DBR) semiconductor lasers are investigated in terms of center wavelengths and pulse repetition frequencies. It is shown that the center wavelength of the pulses can be tuned over a wide range by changing the refractive index of the Bragg reflector section either by means of carrier injection or by thermal effects while maintaining the pulses to be nearly transform-limited. Tuning of the pulse repetition rates is realized by using four different approaches, i.e., current injection to a passive phase-control section, varying of the reverse bias to the absorber, varying of the injection current to the gain region, and thermal effects. Injecting current into the phase-control region results in a tuning range of more than 400 MHz while maintaining the pulses at transform-limited condition. Varying the reverse bias voltage to the absorber is shown to be an alternative to achieve large repetition rate tuning, by which a tuning range of 600 MHz is obtained. By combining these tuning schemes, a total tuning range of more than 1 GHz is realized.

Frequency-tunable millimetre-wave signal generation using a monolithic passively mode-locked semiconductor laser

Repetition frequency tuning characteristics of a monolithic passively mode-locked distributed Bragg reflector semiconductor laser are investigated. By injecting current at a passive phase control section, a tuning range of 400 MHz is achieved while keeping the pulse characteristics nearly unchanged. Varying the absorber reverse bias offers an alternative to tune the frequency. By combining these techniques, a total tuning range of 1 GHz is realised.

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.

Generation of wavelength-tunable transform-limited pulses from a monolithic passively mode-locked distributed Bragg reflector semiconductor laser

Generation of wavelength tunable transform-limited picosecond pulses from a monolithic passively mode-locked distributed Bragg reflector (DBR) laser is demonstrated for the first time. A wide tuning range of 12 nm is realized by changing the refractive index of the passive DBR region through a thin-film heater embedded on the DBR section without causing significant changes in pulse characteristics. >

500 GHz optical short pulse generation from a monolithic passively mode-locked distributed Bragg reflector laser diode

A 500 GHz optical short pulse train was generated from a passively mode-locked distributed Bragg reflector laser diode (DBR-LD). The repetition frequency was thirteen times the fundamental round trip frequency in the LD, and harmonic mode-locking occurred. The pulse duration was 700 fs and the time-bandwidth product was 0.51, very close to the transform-limited value of a Gaussian waveform, 0.44. To our knowledge, this is the first report on the harmonic mode locking of a monolithic passively mode-locked laser diode.

Transform-limited optical short-pulse generation at high repetition rate over 40 GHz from a monolithic passive mode-locked DBR laser diode

The fabrication of monolithic InP-based passively mode-locked distributed-Bragg-reflector (DBR) laser is reported. An optical short-pulse train with a duration of 3.5 ps was generated at a repetition rate of over 40 GHz. The time-bandwidth product was 0.43, and it was very close to the transform-limited value of a Gaussian waveform. Peak power of 60 mW has been achieved. This laser is promising as an optical source for a high-bit-rate soliton transmission system.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>