Interferometer apparatus using electro-optic material with feedback

• US 4,196,396 A
• Filed: 05/03/1978
• Issued: 04/01/1980
• Est. Priority Date: 10/15/1976
• Status: Expired due to Term

• Current Assignee: Bell Telephone Laboratories, Inc. (Nokia Corporation)
• Original Assignee: Bell Telephone Laboratories, Inc. (Nokia Corporation)
• Inventors: Smith, Peter W.
• Primary Examiner(s): Moskowitz, Nelson
• Application Number:
  US05/902,733
• Time in Patent Office: 699 Days
• Field of Search: 332/7.51, 356/106 S, 356/112, 331/94.5 C, 330/4.3, 330/4.5
• US Class Current: 359/336
• CPC Class Codes: G02F 1/21 by interference

Abstract

A nonlinear interferometer apparatus is disclosed wherein a Fabry-Perot cavity is substantially filled with an electro-optic material having terminals to which a potential can be applied. A single frequency, single mode, linearly polarized source of optical radiation is coupled into the cavity and a beam splitter at the output of the cavity deflects a portion of the optical energy coming from the cavity. This deflected portion of output optical energy is incident on a photodetector whose output is amplified and connected to the terminals of the electro-optic material. The resulting device exhibits differential gain, and can function as an optical switch, limiter or optical memory element. With sufficient amplification of the detector output, an optical quantizer is provided. By properly adjusting the cavity length and providing a substantially constant optical signal to the input end of the cavity, an amplified replica of an amplitude modulated optical signal applied to the photodetector appears at the output end of the cavity.

Claims

1. An amplitude-sensitive interferometer device comprising an interferometer cavity having two ends one of which is arranged to receive a single frequency linearly polarized single mode of input optical energy having a changing amplitude and the other of which is arranged to provide output optical energy whose amplitude is related to the amplitude of said input optical energy by a predetermined relationship, an electro-optic medium having terminals and positioned within said cavity so as to interact with optical energy present in said cavity, and photodetector means responsive to the optical energy in said cavity for coupling a voltage to the terminals of said electro-optic medium whose magnitude is a function of the intensity of the optical energy in said cavity, said two ends of said cavity are positioned such that the predetermined transmission through said cavity with zero voltage across said terminals at said single frequency is substantially equal to the minimum transmission obtainable for said cavity, whereby said predetermined relationship between the input optical energy amplitude and output optical energy amplitude is a bistable one in that two different output energy amplitudes are possible over a range of input optical energy amplitudes.

2. An amplitude-sensitive interferometer device comprising an interferometer cavity having two ends one of which is arranged to receive a single frequency linearly polarized single mode of input optical energy having a changing amplitude and the other of which is arranged to provide output optical energy whose amplitude is related to the amplitude of said input optical energy by a predetermined relationship, an electro-optic medium having terminals and positioned within said cavity so as to interact with optical energy present in said cavity, and photodetector means responsive to the optical energy in said cavity for coupling a voltage to the terminals of said electro-optic medium whose magnitude is a function of the intensity of the optical energy in said cavity, said two ends of said cavity being positioned such that a predetermined loss occurs through said cavity at said frequency with zero voltage across said terminals, said photodetector means includes an amplitude means having sufficient gain so as to cause a phase shift in said interferometer cavity equal to a plural number of π

radians in response to the maximum amplitude of said input optical energy.

3. An amplitude-sensitive interferometer apparatus comprising a Fabry-Perot cavity having two parallel highly reflective surfaces one of which is arranged to receive a single frequency linearly polarized single mode of input optical energy having a changing amplitude and the other of which is arranged to provide output optical energy whose amplitude is related to the amplitude of said input optical energy by a predetermined relationship, an electro-optic medium having terminals and positioned within said cavity so as to interact with optical energy present in said cavity, said electro-optic medium substantially filling said cavity, beam splitter means positioned so as to deflect a portion of said output optical energy, and photodetector means responsive to the deflected optical energy from said beam splitter means for coupling a voltage to the terminals of said electro-optic medium whose magnitude is a function of the intensity of said output optical energy, said two reflective surfaces being positioned such that a predetermined transmission substantially equal to minimum transmission for said cavity occurs through said cavity at said frequency with zero voltage across said terminals, whereby said predetermined relationship betweenn the input optical energy amplitude and output optical energy amplitude is a bistable one in that at least two different output energy amplitudes are possible over a range of input optical energy amplitudes.

4. An amplitude-sensitive interferometer apparatus as defined in claim 3 wherein said photodetector means includes a solar cell having its output connected to an electronic amplifier.

5. An amplitude-sensitive interferometer apparatus as defined in claim 3 wherein said photodetector means includes an amplifier means having sufficient gain so as to cause a phase shift in said interferometer cavity equal to a plural number of π

radians in response to the maximum amplitude of said input optical energy.

6. Apparatus for amplifying an input modulated optical signal comprising an interferometer cavity having two ends, an electro-optic medium having terminals and positioned within said cavity so as to interact with optical energy in said cavity, a source of single frequency linearly polarized single mode of optical energy having its output radiation coupled to one of said two ends of said cavity, a photodetector means for developing an output voltage in response to radiation impinging on its photosensitive surface, means for coupling said output voltage to the terminals of said electro-optic medium, and means for coupling said input signal and some of said optical energy in said cavity to the photosensitive surface of said photodetector means, the ends of said cavity being adjusted such that the cavity presents a low transmission factor in response to zero voltage at said terminals of said electro-optic medium and presents a near maximum transmission factor for a small increase in said voltage, and the amplitude of output radiation from said source of single frequency linearly polarized single mode of optical energy is selected such that the cavity presents a low transmission factor when said input modulated optical signal has zero amplitude.

7. Apparatus as defined in claim 6 wherein said means for coupling said input signal and some of said optical energy in said cavity includes at least one beam splitter means.