Beam steered laser IFF system

A communications system for selectively communicating between an inquisitor and a plurality of possible respondents comprising:

• signal generator means located at a transmission site for generating and transmitting an inquiry signal;
• control means for selectively steering the inquiry signal to one of a plurality of receiving sites;
• coder means for encoding an inquiry message and modulating a first portion of the inquiry signal with the message;
• and,
• passive receiver means at a receiving site for receiving said inquiry signal and reflecting a portion of said inquiry signal back to said transmission site, said receiver means being a fixedly mounted, non-steerable normally passive receiver for receiving said inquiry signal regardless of the direction from which said inquiry signal is received and for transmitting energy contained in said received inquiry signal back toward said transmission site with said energy being transmitted only in the opposite direction from that in which said inquiry signal was received, said receiver only being activated when an inquiry signal is received which is a properly encoded inquiry signal transmitted by the signal generator means, said receiver further responding to receipt of the properly encoded inquiry signal to modulate a second and subsequent portion of the inquiry signal with a reply message which is transmitted back to the inquiry site, the passive receiver otherwise not responding to the receipt of any message but rather absorbing any energy contained in the inquiry signal, and said coder means receiving said reflected signal and decoding said reply message to determine if the reply message is a proper response to the inquiry message.

A method of friend-or-foe identification (IFF) comprising:

• generating and transmitting a laser beam by an interrogator means carried on a first platform;
• selectively steering the transmitted laser beam toward one of a plurality of second platforms;
• encoding an IFF interrogation message and modulating a first portion of the transmitted laser beam with the message;
• receiving said laser beam by a normally passive, non-steerable reflector means fixedly mounted on one of said second platforms, said reflector means including a reflector for receiving said transmitted laser beam regardless of the direction from which said transmitted laser beam is received;
• and,
• reflecting said laser beam back toward said first platform including activating said reflector with the received beam, energy contained in a received laser beam being transmitted back toward said first platform only in the opposite direction from that in which said transmitted laser beam was received, the reflector responding only to a properly encoded IFF message contained in said received laser beam by modulating a second portion of said reflected laser beam with a response message, the reflector means otherwise remaining passive if it receives a message other than a properly encoded IFF message and absorbing any energy contained in said laser beam.

A method of selectively communicating between an inquisitor and a respondent comprising:

• generating and transmitting an inquiry signal by a signal generator means located at a transmission site;
• selectively steering the inquiry signal to one of a plurality of receiving sites;
• encoding an inquiry message and modulating a first portion of the inquiry signal with the encoded message;
• and,
• receiving said transmitted inquiry signal at the selected receiving site and responding thereto by reflecting a portion of said inquiry signal back to said transmission site, responding to receipt of said inquiry signal including activating a normally passive, fixedly mounted, nonsteerable receiver means for modulating the reflected signal with an encoded reply message only upon receipt of the encoded message, said non-steerable receiver means being capable of receiving said inquiry signal regardless of the direction from which said inquiry signal is transmitted and replying thereto by transmitting energy contained in said received inquiry signal back toward said transmission site with said energy being transmitted only in the opposite direction from that in which said inquiry signal was received;
• receiving said reflected signal at said transmission site;
• decoding said reply message:
• and,
• determining if the reply message is a proper response to the inquiry message.

A system of friend-or-foe identification comprising:

• interrogator means carried on a first platform for generating and transmitting a laser beam containing energy;
• control means for selectively steering the transmitted laser beam toward a second platform;
• coding means for encoding an interrogation message and modulating a portion of the transmitted beam with the message;
• and,
• passive retro-reflector means receiving transmitted laser energy, said passive retro-reflector means normally absorbing any received laser energy and becoming activated only upon receipt of a properly encoded interrogation message regardless of the direction from which said transmitted laser beam is received, said passive retro-reflector means thereupon coding a second portion of the transmitted laser beam with a response message which is reflected back to the first platform with energy contained in said reflected laser beam being transmitted only in the opposite direction from that in which said transmitted laser beam was received, said passive retro-reflector means including a fixedly mounted, non-steerable comer cube reflector having total internal reflectance, energy absorbing means for absorbing laser energy, and positioning means for positioning the energy absorbing means against an inner end surface of said reflector whereby the coded message portion of the transmitted laser beam causes the absorbing means to vibrate against the positioning means rather than absorbing the energy in the received laser beam, vibration of the absorbing means modulating the second portion of the laser beam to code the response message and said coding means decoding said modulated second portion of said reflected laser beam to determine if said response message corresponds to a predetermined response which identifies the second platform as a "friend".