Fail-safe acousto-optic T-couplers for optical communication networks

Claim 1

A fail-safe optical T-coupler for coupling a local terminal having at least one light source and at least one photodetector to a segmented optical data bus, said coupler comprising: an optically transparent acousto-optic cell; first and second collimating lenses for coupling adjacent segments of said data bus to opposite ends of said acousto-optic cell, said lenses defining a generally linear optical axis for said coupler, and said data bus segments being coupled to said acousto-optic cell symmetrically with respect to said optical axis, thereby providing a fail-safe path for transmitting remotely injected light from one to another of said data bus segments; means for coupling relatively high power bulk acoustic waves into said acousto-optic cell when said terminal is operating in a transmit mode, thereby creating an ultrasonic grating within said cell along an acoustic axis; said light source and a first of said data bus segments being coupled to said acousto-optic cell symmetrically with respect to said acoustic axis, whereby a relatively high percentage of locally injected light is Bragg reflected from said light source to a least said first data bus segment when said terminal is operating in said transmit mode; said photodetector being optically coupled to acousto-optic cell; and means for redirecting a relatively low percentage of said remotely injected light to said photodetector when said terminal is operating in a receive mode, said means for redirecting including means for coupling lower power bulk acoustic waves into said acousto-optic cell when said terminal is operating in said receive mode, thereby creating a relatively weak ultrasonic grating within said cell for Bragg reflecting remotely injected light from at least one of said data bus segments to said photodetector when said terminal is operating in said receive mode: said coupler being characterized in that said Bragg reflection of said remotely and locally injected light occurs from ultrasonic gratings created along different acostic axes, said light source and said first data bus segment are coupled to said acousto-optic cell symmetrically with respect to a first of said acoustic axes, whereby locally injected light is Bragg reflected from said light source to at least said first data bus segment when said terminal is operating in said transmit mode, and said one data bus segment and said photodetector are coupled to said acousto-optic cell symmetrically with respect to a second of said acoustic axes, whereby remotely injected light is Bragg reflected from at least said one data bus segment to said photodetector when said terminal is operating in said receive mode.