Electro-optical system is placed on a satellite to effect communications between two remote stations. The system employs an essentially passive, retrodirective, laser beam modulator-reflector

Minott, P. O.

English

NASA Technical Reports Server

November 1965	 Brief 65-10333 
NASA TECH BRIEF 
NASA Tech Briefs are issued by the Technology Utilization Division to summarize specific 
technical innovations derived from the space program. Copies are available to the public from 
the Clearinghouse for Federal Scientific and Technical information, Springfield, Virginia, 22151. 
Communication System Uses Modulated Laser Beam 
Spherical Mirror	 Interferometer Plates 
Piezoelectric Crystal 
Photomultiplier 
I/I	
'Unmodtjlatodulated Laser Beam 
Modulated Laser Beam 
/ 
I/f	 Modulated Laser Beam 
Transmitting Station	 Receiving Station 7 - 
The problem: To develop a laser-beam system for 
communicating between two remote stations via 
satellite. 
The solution: An electro-optical system employing 
an essentially passive, retrodirective, laser beam 
modulator-reflector aboard the satellite. 
How it's done: The modulator-reflector consists of 
a catadioptric lens (combining a spherical mirror and 
a refractor which corrects for mirror aberration), 
closely spaced curved interferometer plates mounted in 
the focal surface of the lens, and a piezoelectric 
crystal. The spacing between the interferometer plates
is made to vary by applying a signal voltage to the 
piezoelectric crystal. When an unmodulated laser 
beam parallel to the optical axis of the lens system 
strikes the surface of the spherical mirror, the beam 
is reflected to the focal surface where it is modulated 
by the optical interference patterns generated between 
the interferometer plates. The modulated beam passes 
to the spherical mirror from which it is reflected in a 
direction parallel to, but opposite in sense to, that 
of the original unmodulated beam. 
In operation, a modulated laser beam from a 
ground station is directed to a receiver on the 
(continued overleaf) 
This document was prepared under the sponsorship of the National 
Aeronautics and Space Administration. Neither the United States 
Government nor any person acting on behalf of the United States
Government assumes any liability resulting from the use of the 
information contained in this document, or warrants that such use 
will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19650000331 2020-03-11T17:21:10+00:00Z
satellite. This receiver, consisting of a photoniultiplier, 
converts the laser signal to an electrical signal which 
is used to drive the piezoelectric crystal in the modu-
lator-reflector at the modulation rate. An unmodu-
lated laser beam from another ground station (the 
receiving station) is directed to the modulator 
reflector aboard the satellite where it acquires the 
modulation (information signal) being transferred by 
the information-carrying beam to the piezoelectric 
crystal and interferometer plates. The modulated 
laser beam from these plates is retrodirected by 
multiple reflection in the optical system to the receiv-
ing station. 
Notes: 
I. The spacing between the interferometer plates can 
be varied by other means instead of using an 
electrically driven piezoelectric crystal.
2. A parabolic mirror could be used, instead of a 
spherical mirror, to locus the beam on the inter-
ferometer. 
3. The laser beam retrodirective modulator-reflector 
could have application in a line-of-sight Com-
munication system in situations where weight or 
power limitations are critical. 
4. Inquiries concerning this invention may be directed 
to:
Technology Utilization Officer 
Goddard Space Flight Center 
Greenbelt, Maryland, 20771 
Reference: B65-10333 
Patent status: NASA encourages the immediate 
commercial use of this invention. Inquiries about 
obtaining rights for its commercial use may be made 
to NASA, Code AGP, Washington, D.C., 20546. 
Source: Peter 0. Minott 
(GSFC-377) 
Brief 65-10333	 Categories 0 1., 02


Communication system uses modulated laser beam

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