Vellayan Ramaswamy - Lincroft NJ
Robert D. Standley - Shrewsbury NJ
Bell Telephone Laboratories, Incorporated - Murray Hill NJ
Optical signal processing devices, primarily intended for use in integrated optical communication systems, include 3 dB coupled strip guide directional couplers. Each coupler is formed in a body of electrooptic material and includes electrodes bracketing at least one of the guides in the coupled region. Each coupler is fabricated so as to be overcoupled (i. e. , greater than 3 dB coupling) when the coupling is synchronous. Voltage bias, supplied to the electrodes of each coupler, produces sufficient asynchronism to independently adjust each coupler to the desired 3 dB coupling condition. Permutation switches are produced by including a switchable phase shifter between two couplers. Channel drop filters are produced by including reflection gratings between two couplers. Differential phase detectors, for a pulse code modulation system, are produced by including a selected path length difference between the two strip guides connecting two couplers. A photolithographic technique for producing the required electrodes in precise registry with the strip guide couplers (typically characterized by 3 micrometer spacings) includes the use of the primary strip guide mask and a secondary mask to produce a photolithographic mask for defining the electrodes.