Mode-locked Semiconductor Laser Diode Research Articles

Synchronous mode-locking in passively mode-locked semiconductor laser diodes using optical short pulses repeated at subharmonics of the cavity round-trip frequency

Synchronous mode-locking was achieved in passively mode-locked semiconductor lasers using optical pulses with repetition rates at subharmonics of the cavity round-trip frequency. Stable and continuous mode-locked pulses at 8.5 GHz were generated when the repetition rate of the control optical pulses was 4.25 GHz (2nd subharmonic). The timing jitter of the mode-locked pulses was reduced to 1 ps. The relationship between repetition rates of the control pulses and the realization of stable and continuous mode-locking was examined.

Terahertz-rate optical pulse generation from a passively mode-locked semiconductor laser diode

We report what is to our knowledge the first demonstration of terahertz-rate optical pulse generation by harmonic passive mode locking in a distributed-Bragg-reflector laser diode. Along with the fundamental repetition rate of 38.8 GHz, we observed 400-GHz, 800-GHz, and 1.54-THz harmonics, depending on the bias condition of gain section. The pulse envelope for 1.54-THz pulses was in good agreement with a calculation from the Fourier transformation of the optical spectrum, indicating that the output pulses are transform limited.

All laser diode compression of 5 GHz picosecond pulses using cross-phase modulation in optical fibre

5 GHz pulses from a mode-locked semiconductor laser diode have been compressed from 10.5 to 4.6 ps by means of crossphase modulation using a separate optically amplified mode-locked laser diode. By tuning the laser wavelengths symmetrically about the 1.55 μm dispersion zero of an 11km length of fibre, the effect of group velocity dispersion is minimised, ensuring that the fibre is used efficiently. The spectral broadening induced by the cross-phase modulation enables pulse compression in a dispersive fibre.

Repetition frequency stabilisation of passively mode-locked semiconductor lasers

The repetition frequency of an external cavity mode-locked GaAs semiconductor diode laser has been stabilised by voltage controlled electrical feedback. The phase noise has been reduced by 40 dB at 1 kHz offset from the carrier and timing jitter reduced from more than 30 ps to 4 ps. This technique can be used to stabilise millimetre-wave mode-locked lasers.

Hybrid soliton pulse source with fibre external cavity and Bragg reflector

The first results of an actively mode-locked semiconductor laser diode using a fibre external cavity with integrated Bragg reflector are reported. The device produces transform limited pulses of 18-5ps FWHM at a repetition rate of 2-37GHz. High peak power of 49 mW in the output fibre is achieved.

Optical clock distribution using a mode-locked semiconductor laser diode system

An experiment in which a high-power mode-locked femtosecond semiconductor laser system was used as a source of extremely low jitter intense optical pulses in the distribution of a clock to 1024 ports via optical fibers is described. The total accumulated dynamic clock jitter between any two ports, which contains both correlated and uncorrelated sources, was measured to be less than 12 ps. This laser system produced a train of 460-fs optical pulses with over 70 W of peak power at 302 MHz. These results represent the largest fanout with the minimum timing jitter for an optically distributed clocking network.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Amplification of mode-locked semiconductor diode laser pulses in erbium-doped fibre amplifier

Amplification of picosecond pulses from an actively modelocked semiconductor diode laser in an erbium-doped fibre amplifier pumped at 532 nm is demonstrated. Peak emission was centred on 1.536µm and a saturated amplifier gain of 13dB yielded less than 10ps pulses with a peak power of 0.58 W at 600 MHz. Optimisation of the mode-locked oscillator allowed amplified peak pulse powers greater than 3W to be generated.

Picosecond pulse generation from a synchronously pumped mode-locked semiconductor laser diode

A semiconductor laser diode was mode locked in an external cavity when synchronously pumped with 90-ps current pulses. Transform-limited optical pulses with a 10-ps pulse width and a peak power of 160 mW were produced. Operating characteristics of such a system are described.

Introductory remarks

The first day of this Discussion Meeting is mainly devoted to ultra-short laser sources and the methods of measurement of picosecond and subpicosecond pulses of radiation over the electromagnetic spectrum from X-rays to the infrared. The last decade has seen dramatic advances in the understanding of the complex physical and chemical processes occurring in mode-locked lasers and in the interactions, linear and nonlinear, with matter of the ultra-short light pulses so produced. The flashlamp-pumped frequency-tunable dye laser has played a key role in these advances. It provided the shortest and most controllable pulses for the development of time-resolving instruments and, later, was an experimental model for the detailed measurements that eventually led to the elucidation of the mechanisms by which ultra-short pulses evolve in a mode-locked laser from the initial fluorescence intensity fluctuations (see Bradley &amp; New (1974) for references). These new concepts, in turn, were applied to the development of mode-locked continuous wave (c.w.) dye lasers and, more recently, to mode-locked semiconductor diode lasers. Both of these types of c.w. lasers will be discussed in some of the following papers.