Ford Aerospace & Communications Corporation

USA As Represented by Secretary of the Navy

United States of America As Represented by the Secretary of the Air Force

Carl J Buczek

Ronald E Belek

Vito F Pizzurro

James G Myers

Hoyt A Bostick

A dual-beam amplitude-modulated laser transmitter/receiver suitable for laser-radar applications is scalable to high powers because there is no active modulator element that the laser beam passes through. The transceiver comprises a laser source with two separate independent laser optical cavities. Each laser cavity is similar, but each operates at its own frequency. Signals from the two cavities are superimposed at a combining beam splitter to form two transmitter output beams with each combined beam intensity modulated at the laser difference frequency. The output consists of two beams separated in elevation and with equal beam powers from each laser cavity the intensity modulation is 100%. Each beam has its own homodyne detector and separate local oscillator. Thus, each beam path is considered to be a distinct homodyne transceiver. If the frequency of one of the laser sources is changed in time, an AM/FM/CW output suitable for absolute range measurements and fine doppler is generated. The laser transmitter does not require internal or external modulators such as acousto-optic or electro-optic cells. Thus, it is not limited by the modulator characteristics.

Infrared coherent optical sensor

A polarization insensitive mirror (3) comprises a single homogeneous coating (1) coated onto a typically metallic reflective surface (2). The mirror (3) is substantially insensitive to polarization of incident radiation (4) over a wide range of angles of incidence (A). The coating (1) has an index of refraction (n) greater than 2.4, is substantially transmissive to the incident radiation (4), and has a thickness (t) substantially equal to L.sub.0 /2n, where L.sub.0 is the wavelength of the incident radiation (4) in freespace. Germanium makes a good coating (1). The reflective surface (2) is typically gold or silver. Increasing slightly the thickness (t) of the coating (1) increases the range of incident angles (A) over which the mirror (3) exhibits minimized phase differentials (B). Graphs (FIGS. 3-8) are presented comparing the reflectivity, phase differential (B), and average reflectivity of mirrors (3) fabricated according to the teachings of the present invention with those of the prior art.

Polarization insensitive mirror

An improved detector array for scan receiver applications whereby each contiguous element of the array is connected to a summing port with its adjacent element.

Detector array

A laser radar transmitter (2) has, associated with a single active lasing region (11) and preferably in the same laser cavity (1) therewith, an amplitude modulator (21) and a frequency modulator (25), which may simultaneously place continuous AM and continuous FM on a single output beam (7). Amplitude modulator (21) is preferably an EO crystal having a high EO coefficient, low loss, and field-induced birefringence. Frequency modulator (25) is preferably an EO crystal having a high EO coefficient, low loss, and a field-induced index change. Applying a d.c. driving voltage to the AM crystal (21) and an a.c. driving voltage to the FM crystal (25) produces an output beam (7) having FM. Applying an a.c. driving voltage to the AM crystal (21) produces an output beam (7) having AM, independently of whether FM is added by means of applying an a.c. driving voltage to the FM crystal (25).

Combined AM/FM laser radar transmitter

An optical sensor has a gain medium situated at a first location and defines one end of a resonating optical cavity. An optical fiber couples electromagnetic radiation to a predetermined point at a second location where it is directed toward a reflective surface. The physical condition to be sensed causes the reflective surface to move with respect to the end of the optical fiber. This movement essentially changes the length of the cavity in which the electromagnetic energy is resonating causing a corresponding change in the axial mode difference frequency within the cavity. A small portion of electromagnetic energy is coupled out of the cavity at the first location to a photodetector. Finally, the photodetector creates an electrical signal which varies as the change in the axial mode difference frequency, thus indicating the change in the physical condition.

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Encinitas, CA, United States of America

Carl J Buczek