No abstract

Modal noise, which can cause severe distortion in signals transmitted by fiber optics, is an interference effect that is made more severe by the narrow spectral width of single-mode lasers. The linearity of these devices may be totally obscured after the optical signal has passed through the connectors and fiber lengths of a practical signal system. Dithering the laser's operating point by means of a high-frequency current (>2 GHz) has been found greatly to reduce modal noise.

No abstract

The report describes a wideband linear response fiber optic transmission link designed to telemeter signals from a system being irradiated in a space /radiation simulator.The environment is severe: the transmitter must withstand an x -ray pulse delivering 109 rad(Si) /sec (surface dose rate), beams of 300 -1000 Kell electrons, hard vacuum, and liquid nitrogen temperatures without degradation or even momentary upset. Radiation hardness is achieved by a combination of circuit design and high -Z shielding, including an optical fiber shield made of non -conducting lead -loaded polyethylene. Special heat conducting and insulating measures are employed to maintain temperature.The transmitter measures 15 x 8.5 x 9.5 cm and operates on self-contained batteries. Signal bandwidth is greater than 10 KHz to 400 MHz with approximately 35 dB of dynamic range. Signal inputs ranging from one millivolt to several volts are accommodated; four single -or double -ended inputs are provided, with remote selection. The single -fiber coupled remote control also allows adjusting input attenuation, power and calibrator control, and verification of transmitter function.The single -mode laser used as the high frequency optical source is microwave dither-biasedl to reduce modal noise.2

My name is Jonathan Vanderwall and I am by profession an electronics engineer at the Army's Harry Diamond Laboratories in Adelphi, Maryland, although I have worked in electrooptics for the past 15 years. About five years ago, Clive Sinclair put out the first really cheap computer, and I have had a Sinclair computer of the latest type on my desk ever since. Then, three years ago, Don Small published his program, "Small Optical Design and Analysis," (SODA -I) and gave the listing away to interested parties. I discarded the optics program that I had been working on, and began to translate SODA -I for my Timex -Sinclair 2068. Later, I recruited a colleague, Walter Hattery, who also likes the idea of inexpensive computation for scientific purposes, and we have been doing the final debugging and testing for about the last year, not, I rush to add, on taxpayers' time.Let me briefly describe the program as we now offer it, and afterwards say why we think there is a place for this program in the scientific community, particularly in electro-optics. SODA supports first -order layout, third -order surface contributions, solves for bending and scaling, achromatism by Conrady's (D -d) method, and exact ray tracing.This version, expanded from Small's original, accommodates 30 surfaces, of which any 16 may be aspheric, decentered, or tilted, in any combination.The exact -trace routines may be accessed to trace single rays, to trace saggital and tangential ray fans, and to trace a grid of rays through your system.Various output forms are supported, including tabular data, television -resolution ray intercept plots, wavefront error plots, wavefront error over the exit pupil, and plots of field curvature and distortion.In other words, this program offers an extraordinarily full range of features and runs on a dirt -cheap microcomputer.Further, it is incredibly easy to use. This is the great virtue of SODA as Don Small originally wrote it; I believe that I and my co-writer, Walter Hattery, have succeeded in retaining and improving this ease while tranlating the original, at the same time providing certain useful enhancements. Our version is thus better than Small's partly because the graphics on the Sinclair 2068 machines are far better than those of the TRS -80, and partly because we had more than twice the free RAM available to him.Thus we were able to add some convenience features and some file -handling features not previously available. Also, we rewrote the bending routine to allow bending more than two surfaces at once.As in the original, necessary inputs are prompted, and changes are always easily made.You will never have to leave the program and use an editor to alter your lens file. I have been checking the accuracy of SODA against GENII -PC, for something more than ayear.The computational accuracy of the Sinclair is just in excess of nine figures, and I think a good case can be made that if you can't do it with 9 figures, you can't do it at all.One known potential problem is that the entrance pupil is located by paraxial ...