Opto-Electronic Oscillator Using Suppressed Phase Modulation

NASA’s Jet Propulsion Laboratory, Pasadena, California

Monday, October 01 2007 The proposed system (see figure) would include two subsystems: a phase modulation OEO and a modulation- suppression noise-reduction subsystem. Each subsystem would contain an asymmetric Mach-Zehnder (AMZ) phase demodulator, which would be a combination of an AMZ interferometer with voltage-controlled phase tuning in one arm, and a photodiode at either or both of two optical output ports. The length differential between the two arms is approximately matched to one half of the wavelength of the radio-frequency (RF) modulation signal, typically 1.5 cm for an X-band (10-GHz) modulation signal. With appropriate choice of delays and of phase shifts (ϕ1, ϕ2, ϕ3), the AMZ in the modulation-suppression noisereduction system would couple almost all of the optical power to a termination at one of its output ports, denoted the bright port and labeled “B” in the figure. The small remaining portion of the optical power, in the form a suppressed-carrier signal, would be coupled to a lownoise photodiode at the other port, denoted the dark port and labeled “D” in the figure. This arrangement would afford high sensitivity, at the photodiode output, to input phase modulation.

Sideband amplitude would also be reduced before detection by use of a phase “un-modulator” — a second phase modulator, at the output end of the fiber-optic delay line, that would exert an approximation of the reverse of the effect of the phase modulator at the input end of the line. Thus, both the carrier and the sideband components of the optical signal arriving at the low-noise photodiode in the AMZ phase demodulator in the modulation-suppression noise-reduction subsystem would be suppressed, thereby helping to prevent overload of the low-noise photodiode as optical power is increased. (Prevention of overload is necessary for preservation of sensitivity because low-noise photodiodes saturate at low optical power levels.)

This work was done by G. John Dick and Nan Yu of Caltech for NASA’s Jet Propulsion Laboratory. For further information, contact This e-mail address is being protected from spambots. You need JavaScript enabled to view it .