Optical frequency generator

Details Optical frequency generator Optical frequency generator

1997-10-20

1999-12-28

Lee, John D.

Optical: systems and elements

Optical frequency converter

G02F 135

Patent

active

060089318

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention relates to an optical frequency generator including a reference light source, a frequency transmitter, an optical comb generator for generating a plurality of optical frequencies, and electronic controls.
2. The State of the Art
An optical frequency generator of this kind is known from U.S. Pat. No. 5,233,462. In the known optical frequency generator, the light output of a laser functioning as an intensive monochromatic reference light source is fed to an optical comb generator provided with a plurality of optical parametric oscillators. The optical parametric oscillators arrayed in parallel are tuned relative to each other such that the so-called signal and idler beams of individual ones of the optical parametric oscillators form a coarse frequency comb with large frequency spacings. One of the two output beams, e.g. the signal beam, of each optical parametric oscillator is fed to an associated electro-optical modulator of the comb generator, the modulator being fed with a frequency from a microwave transmitter acting as a frequency transmitter and capable of generating a plurality of side bands to the center frequency of the input signal beam, the frequency spacing of the side bands corresponding to the supplied microwave frequency.
While, because of the optical parametric process at a constant frequency of the reference light source, the tuning range of the known optical frequency generator is relatively wide, it is extremely complex in terms of equipment, owing to the requisite number of optical parametric oscillators, electro-optical modulators as well as the requirement for precise control of the frequency division ratio of each optical parametric oscillator. Furthermore, to operate the optical parametric oscillators, a highly intensive reference light source is mandatory. Moreover, before the unknown frequency of an light source can be determined it is necessary to take advance measurements with a wavelength meter.
In one application, the known frequency generator is used as an optical frequency measuring device. In this context, it is possible to measure the unknown frequency of the frequency component of the test light, provided the frequency of the frequency component of the reference light source, the division ratio of the optical parametric oscillators and the frequency of the microwaves fed to the electro-optical modulators are known exactly. To this end, the beat signal or frequency between the unknown frequency and the next adjacent sideband of an optical parametric oscillator are measured following a relatively coarse measurement of the wavelength of the test light. The exact position of the sideband and, with it, the absolute frequency may be determined by varying the frequency of the microwaves fed to the electro-optical modulators and by measuring any change in the beat frequency correlated to the order of the sideband.


OBJECT OF THE INVENTION

It is a task of the invention to provide an optical frequency generator of the kind referred to supra which makes it possible to generate a frequency comb with precisely determinable frequency lines with relatively simple equipment.


BRIEF SUMMARY OF THE INVENTION

In accordance with the invention, the task is accomplished by a is comb generator is provided with a light source which may be frequency modulated by an output signal of a frequency transmitter adjustable in its frequency by an electronic control circuit and by an optically non-linear component acted upon by the light source whereby a plurality of sidebands may be generated with frequency spacings corresponding to a multiple of the frequency of the input signal output by the frequency transmitter and by the fact that the light output of the comb generator may be superposed by the light output of the reference light source in a superheterodyne unit to generate a control signal.
By superheterodyning the light output of the comb generator with the very narrow-banded light output of a reference light source which for re

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IEEE Journal of Quantum Electronics vol. 29, No.10, Oct. 1, 1993, pp. 2693-2701.
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IEEE Photonics TechnologyLetters, vol. 6, No. 3, Mar. 1, 1994, pp. 365-368.
IEEE Photonic TechnologyLetters, vol. 5, No. 6, Jun. 1, 1993, pp. 721-725.

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