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Gain Switching

Definition: a technique for generating short optical pulses in a laser by modulating the laser gain

German: Verstärkungsschalten

Categories: lasers, light pulses

How to cite the article; suggest additional literature

Gain switching is a method for pulse generation by quickly modulating the laser gain via the pump power. If a high pump power is suddenly applied to a laser, laser emission sets in only with a certain delay, as it starts with weak fluorescence light, which first needs to be amplified in a number of resonator round trips. Therefore, some amount of energy can be stored in the gain medium, which is subsequently extracted in the form of a short pulse. The pulse obtained can be shorter than the pump pulse and also shorter than the upper-state lifetime; the dynamics are essentially as in the phenomenon of spiking, where the pump power is applied for a short enough time to generate only a first spike.

The higher the pump pulse energy, the shorter is the pulse build-up time, and consequently the required pump pulse duration. The pulse build-up time of a gain-switched laser can be increased by using a longer laser resonator, but this also increases the output pulse duration.

The pump power may be completely switched off between the pulses, or may be kept at a level just below the laser threshold.

gain switching
Figure 1: Simulated power evolution for gain switching of a solid-state laser. The pump energy is so high that the laser pulse is emitted at the end of the pump pulse. For a higher pump energy, the laser pulse would start too early, and a second pulse may be emitted.

Gain switching can be applied to various types of lasers:

An interesting approach to the generation of energetic nanosecond pulses is to combine a gain-switched laser diode with a fiber amplifier or an optical parametric amplifier. In this way, pulses with microjoule or millijoule energies can be generated. This method provides a high flexibility in terms of pulse duration, shape and repetition rate.

Bibliography

[1]P.-T. Ho et al., “Picosecond pulse generation with a cw GaAlAs laser diode”, Appl. Phys. Lett. 33 (3), 241 (1978)
[2]H. Ito et al., “Picosecond optical pulse generation from an r.f. modulated AlGaAs double heterostructure diode laser”, Electron. Lett. 15, 738 (1979)
[3]C. Lin et al., “Simple picosecond pulse generation scheme for injection lasers”, Electron. Lett. 16, 600 (1980)
[4]J. AuYeung, “Picosecond optical pulse generation at gigahertz rates by direct modulation of a semiconductor laser”, Appl. Phys. Lett. 38, 308 (1981)
[5]T. Sogawa et al., “Observation of a short optical pulse (< 1.3 ps) from a gain switched quantum well laser”, Appl. Phys. Lett. 53, 1580 (1988)
[6]P. Paulus et al., “Generation and optimum control of picosecond optical pulses from gain-switched semiconductor lasers”, IEEE J. Quantum Electron. 24 (8), 1519 (1988)
[7]J. J. Zayhowski et al., “Gain-switched pulsed operation of microchip lasers”, Opt. Lett. 14 (23), 1318 (1989)
[8]K. Iwatsuki et al., “Generation of transform limited gain-switched DFB-LD pulses < 6ps with linear fibre compression and spectral window”, Electron. Lett. 27 (21), 1981 (1991)
[9]M. Jinno, “Correlated and uncorrelated timing jitter in a gain-switched laser diodes”, IEEE Photon. Technol. Lett. 5 (10), 1140 (1993)
[10]L. Chusseau and C. Kazmierski, “Optimum linear pulse compression of a gain-switched 1.5 μm DFB laser”, IEEE Photon. Technol. Lett. 6 (1), 24 (1994)
[11]N. Stelmakh et al., “Generation of high-energy (0.3 μJ) short pulse (< 400 ps) from a gain-switched laser diode stack with sub-ns electrical pump pulses”, IEEE J. Sel. Top. Quantum Electron. 3 (2), 245 (1997)
[12]A. Fragemann et al., “Optical parametric amplification of a gain-switched picosecond laser diode”, Opt. Express 13 (17), 6482 (2005)
[13]P. Dupriez et al., “High average power, high repetition rate, picosecond pulsed fiber master oscillator power amplifier source seeded by a gain-switched laser diode at 1060 nm”, IEEE Photon. Technol. Lett. 18 (9), 1013 (2006)
[14]P. M. Anandarajah et al., “System-performance analysis of optimized gain-switched pulse source employed in 40- and 80-Gb/s OTDM systems”, J. Lightwave Technol. 25 (6), 1495 (2007)
[15]Y. Wang et al., “1 MHz repetition rate single-frequency gain-switched Nd:YAG microchip laser”, Laser Phys. Lett. 4 (8), 580 (2007)

(Suggest additional literature!)

See also: pulse generation, pulses, spiking, mode locking, Q switching, nanosecond lasers
and other articles in the categories lasers, light pulses

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