Wideband heterodyne receiver provides detection and demodulation of incident frequency modulated laser signal; search and acquisition circuitry to align two stations; tracking circuitry to maintain spatial alignment; and laser frequency monitor to frequency lock the transmit and local oscillator lasers

Arams, F. R.

Dinardo, A.

Kanischak, G.

Lange, R.

Peyton, B.

English

NASA Technical Reports Server

August 1973 
•	 NASA TECH BRIEF 
Goddard Space Flight Center 
B73-10223 
H 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
High-Sensitivity Receiver for CO2 Laser Communications 
The problem: 
A wideband heterodyne receiver for a two-way 
satellite-to-ground CO2 laser communication link must 
provide the following: 
(1) detection and demodulation of the incident fre-
quency modulated (FM) laser signal, 
(2) search and acquisition circuitry to align the two 
stations, 
(3) tracking circuitry to maintain spatial alignment, 
and 
(4) a laser frequency monitor to frequency lock the 
transmit and local oscillator (LO) lasers. 
The solution: 
These objectives are satisfied by a wideband, 
10.6-Aim heterodyne receiver which includes a cooled
PV-HgCdTe photomixer, a spatial search and signal 
acquisition channel, a conical scanner for spatial tracking, 
and an automatic frequency-control (AFC) channel to 
maintain a fixed laser-frequency offset. 
How it's done: 
The front end of the infrared receiver uses a 
PV-HgC die photomixer and a low-noise IF pre-
amplifier. Heterodyne measurements were carried out 
using two single-frequency stabilized lasers having an 
IF offset which was adjustable between 5 and 45 MHz. 
Measurements on a HgCdTe photomixer, interfaced 
with the matched low noise ('-'l.S dB noise factor) 
wideband amplifier in a variable temperature cooler, 
resulted in a measured noise equivalent power (NEP) 
•
Cooler 
r---i Infrared Pointing
Nutator Mixer Signal	 Optics 
I- __________	 NEP 
III II	
Voltage Bit 
I ____________________ II 
I Nutator Reference 
Driver I	 i Driver I L_.J
Oscillator 
L2 Laser J 
fAFC Error Voltage
L Tracking	 Voltages
ACQ	 ACQ	 Video 
Confirm	 Encounter	 Output 
Pulse	 Pulse	 (1 to 6 MHz) 
High Sensitivity Receiver
(continued overleaf) 
This document was prepared under the sponsorship of the National
	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free from privately owned rights. 
https://ntrs.nasa.gov/search.jsp?R=19730000223 2020-03-17T07:12:04+00:00Z
of less than 10-19 W/Hz, over the 15- to 40-MHz IF 
band for mixer temperatures from 85 to 115 K. The 
measured 3-dB cutoff frequency of the photomixer 
was greater than 240 MHz over the 77 to 130 K tem-
perature range, and the combined laser local oscillator 
and dc bias power was less than 8 mW. 
The receiver, as shown in the figure, has the fol-
lowing features: 
Detection and demodulation - An unusually wide-
band photomixer and discriminator (12-MHz linear 
bandwidth centered at 30 MHz) are provided to 
detect and demodulate the receivedFM laser signal. 
The unequalized receiver group delay of ± 47 
nanoseconds has been reduced to ± 5 nanoseconds 
using a specially designed delay equalizer. 
2. Spatial acquisition - To obtain maximum sensitivity 
during spatial acquisition, a narrowband acquisition 
channel with a matched filter was developed and 
tested. Measurement of the probability of encounter 
versus the video channel signal-to-noise ratio (S/N) 
resulted in a 100-percent probability of acquisition 
IF S/N as low as —24 dB. 
ci Spatial tracking - A conically scanned receive 
beam is used to generate spatial tracking error 
voltages when the two stations are not aligned. The 
error voltages position the receiver optics to main-
tain station alignment.
4. Frequency tracking - A wideband discriminator is 
used to generate an AFC error voltage over the 
24-to 36-MHz IF frequency band. The AFC error 
voltage maintains a fixed frequency offset between 
the incoming signal and LO laser. 
Note: 
No further documentation is available. Specific ques-
tions, however, may be directed to: 
Technology Utilization Officer 
Goddard Space Flight Center 
Code 207;l 
Greenbelt, Maryland 20771 
Reference: B73-10223 
Patent status: 
NASA has decided not to apply for a patent. 
Source: B. Peyton, A. DiNardo,
G. Kanishchak, R. Lange, 
and F.R. Arams of

Cutler Hammer Corp.
under contract to

Goddard Space Flight Center 
(GSC-1 1455)
S 
. 
B73-10223	 Category 02, 03


High-sensitivity receiver for CO2 laser communications

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