Mixing interferometer used as a communications link

Details Mixing interferometer used as a communications link Mixing interferometer used as a communications link

1989-06-16

1992-09-01

Coles, Sr., Edward L.

Optical: systems and elements

Deflection using a moving element

Using a periodically moving element

359161, H04B 1012

Patent

active

051444682

ABSTRACT:
An interferometer, such as a fiberoptic Mach-Zehnder type, is equipped at a transmission end of the system with a phase modulator driven by a data-input signal to be transmitted; and at a reception end with another phase modulator driven by a large reference signal. Nonlinear dependence of output intensity on these signals yields an intensity component that is the product of the signals at the modulators; and in turn an electrical output-signal component at frequency equal to the difference between the data- and reference-signal frequencies. A servocontrolled phase bias holds the system near a minimum in overall light level, where nonlinearity is prominent while intensity-related noise is minimized. The reference source and the bias are at the receiver end of the system, providing advantages: (1) the reference signal can be tuned manually or dynamically to optimize reproduction of the input signal, (2) the detector output can be mixed back up to the original data-input frequency using the same reference for mixing up as used optically for mixing down--eliminating frequency error and drift, and excess phase noise; and (3) only the modulators and purely optical elements need operate near the data frequency, which may be very high, while the detector and its amplifier run at the difference frequency.

REFERENCES:
patent: 3752992 (1973-08-01), Fluhr
patent: 4748686 (1988-05-01), Glomb
patent: 4755016 (1988-07-01), DeLoach
patent: 4868898 (1989-09-01), Gilden
patent: 4893352 (1990-01-01), Welford

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