Optical transversal fiber with reflective taps

Details Optical transversal fiber with reflective taps Optical transversal fiber with reflective taps

1985-10-25

1988-06-07

Buczinski, Stephen C.

35016222, G02B 634, G02B 518

Patent

active

H00004740

ABSTRACT:
A method and means for forming an optical transversal filter and the optical transversal filter itself. The optical transversal filter comprises an optical fiber with a plurality of short reflective phase gratings disposed therein, with each reflective phase grating comprising a periodic variation of the refractive index of the optical fiber. These reflective phase gratings are disposed at predetermined positions along the length of the optical fiber and each reflective phase grating has a predetermined reflectance in order to reflect a predetermined relative amplitude of the light propagating in a first direction within the optical fiber to thereby counterpropagate back along the optical fiber. Modulated light source means are provided for directing light into one end of the optical fiber, and means for detecting light are provided to detect the light reflected by the plurality of reflective phase gratings. The predetermined positions of the plurality of reflective phase gratings and the individual reflectances of the plurality of reflective phase gratings are set in order that the light reflected by each of the reflective phase gratings is summed in light detecting means to yield a desired transversal filter function. The reflective phase gratings are written into the optical fiber core by means of two short counterpropagating coherent light pulses. The precise locations of these reflective phase gratings are determined by changing the optical length that either the forward-propagating or the counterpropagating pulse must traverse, thereby changing the location where these two pulses overlap in the optical fiber.

REFERENCES:
D. K. W. Lam and B. K. Garside, Publication, Applied Optics, vol. 20, No. 3, Feb. 1, 1981, pp. 440-445, "Characterization of Single-Mode Optical Fiber Filters".
B. S. Kawasaki et al., Optics Letters, vol. 3, No. 2, Aug. 1978, pp. 646-649, "Narrow-Band Bragg Reflectors in Optical Fibers".
Zhong-Yi Yin et al., Applied Optics, vol. 22, No. 24, Dec. 15, 1983, "Photo-Induced Grating Filters in GeO.sub.2 Thin-Film Waveguides."
K. O. Hill et al., Appl. Physics. Lett. 32(10), May 15, 1978, pp. 647-649, Photosensitivity in Optical Fiber Waveguides: Application to Reflection Filter Fabrication.

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