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Optical Parametric Generators

Author: the photonics expert Dr. Rüdiger Paschotta (RP)

Acronym: OPG

Definition: light sources based on parametric amplifiers with no signal or idler input

More general term: light sources

Categories: article belongs to category nonlinear optics nonlinear optics, article belongs to category photonic devices photonic devices, non-laser light sources

DOI: 10.61835/0pm Cite the article: BibTex plain text HTML Link to this page LinkedIn

A parametric generator is an optical parametric amplifier with fairly high gain (many tens of decibels), so that a substantial output power is generated even without any input signal. The physical origin of this emission is parametric fluorescence, amplified to high levels. This phenomenon is similar to amplified spontaneous emission (ASE) in a laser amplifier; in both cases, quantum fluctuations of the vacuum (→ vacuum noise) are amplified to macroscopic power levels.

Figure 1: Schematic of an optical parametric generator.

High enough gain for parametric generation can only be achieved by pumping with intense laser pulses. Typical OPG setups are based on nanosecond pump pulses from a Q-switched laser, but it is also possible to operate OPGs with femtosecond or picosecond (ultrashort) pulses from a mode-locked laser. (Note that the parametric gain builds up and decays as fast as the pump pulse.) In most cases, ultrashort pulses first need to be amplified (e.g. in a regenerative amplifier), but by combining certain high-power mode-locked lasers with highly nonlinear crystals it is possible to use the laser pulses directly [4].

Compared with an optical parametric oscillator, the setup of a parametric generator is simpler because it does not need a resonator. The wavelengths of the signal and idler can simply be tuned by influencing the phase-matching conditions, e.g. by varying the crystal temperature or rotating the crystal (for critical phase matching). It is convenient that there is no need to keep a resonator synchronized or well aligned. On the other hand, a parametric generator gives less control over the properties of the pulses than would be possible with a synchronously pumped optical parametric oscillator, which can also have a much lower threshold pump power. Also, the required high optical intensities in OPG setups sometimes enforce operation close to the optical damage threshold of the nonlinear material.

It is possible to lower the threshold and significantly decrease the linewidth by injection seeding a parametric generator with some signal light, e.g. from a laser diode. However, the device should then actually be seen as a parametric amplifier.

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Bibliography

[1]	D. A. Kleinman, “Theory of optical parametric noise”, Phys. Rev. 174 (3), 1027 (1968); https://doi.org/10.1103/PhysRev.174.1027
[2]	A. Piskarskas, “Optical parametric generators: tunable, powerful, ultrafast”, Opt. Photon. News 7 (7), 25 (1997); https://doi.org/10.1364/OPN.8.7.000024
[3]	A. Galvanauskas et al., “Fiber-laser-based femtosecond parametric generator in bulk periodically poled LiNbO₃”, Opt. Lett. 22 (2), 105 (1997); https://doi.org/10.1364/OL.22.000105
[4]	T. Südmeyer et al., “Novel ultrafast parametric systems: high repetition rate single-pass OPG and fiber-feedback OPO”, J. Phys. D: Appl. Phys. 34 (16), 2433 (2001); https://doi.org/10.1088/0022-3727/34/16/307
[5]	B. Köhler et al., “A 9.5-W 82-MHz-repetition-rate picosecond optical parametric generator with cw diode laser injection seeding”, Appl. Phys. B 75, 31 (2002); https://doi.org/10.1007/s00340-002-0942-4
[6]	S. V. Marchese et al., “Room temperature femtosecond optical parametric generation in MgO-doped stoichiometric LiTaO₃”, Appl. Phys. B 81 (8), 1049 (2005); https://doi.org/10.1007/s00340-005-1964-5
[7]	E. Innerhofer et al., “Analysis of nonlinear wavelength conversion system for a red–green–blue laser projection source”, J. Opt. Soc. Am. B 23 (2), 265 (2006); https://doi.org/10.1364/JOSAB.23.000265

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Suppliers

The RP Photonics Buyer's Guide contains five suppliers for optical parametric generators. Among them:

Covesion

The large nonlinear coefficient of PPLN and broad transparency range allows researchers and OEM’s to efficiently generate mid-IR wavelengths from a variety of visible and near-IR wavelengths.

Utilizing our knowledge and experience in poling techniques, Covesion can offer a variety of free space bulk crystal solutions for single pass OPG to generate mid-IR wavelengths from visible and near-IR pump lasers for applications such as mid-IR spectroscopy.

Our custom capabilities include:

multiple grating, chirped or fan-out designs
tailored AR coatings
custom grating periods and apertures
broad mid-IR coverage
compatibility with both CW and pulsed lasers

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