Coherent light generators – Particular beam control device – Optical output stabilization
Patent
1992-04-21
1994-02-01
Scott, Jr., Leon
Coherent light generators
Particular beam control device
Optical output stabilization
372 19, 372 28, 372 98, 372 9, H01S 313
Patent
active
052837963
ABSTRACT:
Frequency modulated radar transmitters with a repetitive linear increase in frequency with time, referred to as "frequency chirps", are required for many radar applications. The present invention provides a simple way of obtaining such a chirped frequency modulation for a laser radar transmitter or the like. The principle is to translate an optical wedge in the direction of its wedge gradient at constant velocity across the optical path of a laser resonator. The resulting increase or decrease in the effective optical length of the resonator causes frequency chips. In a first embodiment of the present invention, a rotating phase plate on the face of a rotating wheel with the added phase varying linearly with angular position around the wheel is placed within a laser's resonator cavity to tune the optical pathlength of the cavity and thereby the longitudinal mode of the resonator to produce the chirp. This embodiment can be used in either a reflective or a transmissive mode. In a second embodiment of the present invention, the outer peripheral rim of a spiral wheel having a spirally increasing or decreasing radius is used, whereby the rim functions as a mirror, is disposed within the laser resonator. Rotating the wheel changes the optical pathlength of the resonator and causes the longitudinal modes of the resonator to tune so as to generate the required chirp sequence. Lastly, various systems are proposed for eliminating various types of errors in the system as well as for generating both up-chirps and down-chirps sequentially and/or simultaneously.
REFERENCES:
patent: 4088898 (1978-05-01), Stitch
patent: 4314210 (1982-02-01), Everett
patent: 4977562 (1990-12-01), Welch et al.
Denson-Low Wanda K.
Hughes Aircraft Company
Jr. Leon Scott
Streeter William J.
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