Laser light could be generated within light pipe itself, thereby eliminating coupling losses. Theoretical calculations have shown feasibility of light-pipe laser propagating in circularly-polarized TE mode. It is predicted that fiber-optic distributed-feedback laser would have gain on order of 25 dB

Elachi, C.

Evans, G. A.

Yeh, Y. C. M.

English

NASA Technical Reports Server

June 1975	 B75-10127 
NASA TECH BRIEF 
V	 NASA Pasadena Office
	
A 
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 relatingtto the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Laser Action Generated Within a Light Pipe: A Concept 
.
The problem: 
In optical communications systems currently under 
development, fiber optics (light pipes) are used to 
conduct laser beams. When a laser beam is coupled to 
the light pipe, there is a signal loss at the interface. 
The solution: 
The laser light could be generated within the light 
pipe itself, thereby eliminating coupling losses. 
How it's done: 
The light pipe is made to act as a distributed-
feedback laser, which would be incorporated in the 
beginning of the optical transmission line. In such a
system, distributed reflections at periodic sites 
replaces end reflection as the method of reinforcing 
the light signal. The light pipe is doped with active 
material, and could be micromachined to have 
periodic variations in its index of refraction as shown 
in the figure. The pipe has what are essentially Bragg 
gratings that generate a feedback wave which leads to 
self oscillation. 
Theoretical calculations have shown the feasibility 
of a light-pipe laser propagating in the circularly-
polarized TE mode. It is predicted that a fiber-optic 
distributed-feedback laser would have a gain on the 
order of 25 dB. However, the fiber optic design and 
the laser frequency would have to be chosen to 
optimize performance. 
Periodic 
Notches to 
Act as Bragg 
Scattering Depth of Notch 
Sites Depends on 
Diameter of Fiber 
and Laser Wavelength 
Period 
of Grating
Light Pipe
Light Pipe Grated To Act as a Laser
(continued overieof) 
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=19750000127 2020-03-19T20:24:05+00:00Z
Note: 
Requests for further information may be directed 
to:
Technology Utilization Officer 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91103 
Reference: TSP75- 10127
Patent status: 
This invention is owned by NASA, and a patent 
application has been filed. Inquiries concerning non-
exclusive or exclusive license for its commercial 
development should be addressed to: 
Patent Counsel 
NASA Pasadena Office 
4800 Oak Grove Drive 
Pasadena, California 91403 
Source: Charles Elachi, Gary A. Evans,

and Cavour Yeh of

Caltech/JPL
under contract to

NASA Pasadena Office 
(NPO-13531) 
Categories: 03 (Physical Sciences) 
B75-10127
	
02 (Electronics Systems)


Laser action generated within a light pipe: A concept

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