Leland Stanford Junior University

William P Risk

Gordon S Kino

Butrus Thomas Khuri-Yakub

Herbert J Shaw

Robert C Youngquist

Brian L Heffner

An acoustic wave is propagated colinearly with the optical signals in an optical fiber to cause coupling of an optical signal in one propagation mode of the optical fiber to the other propagation mode in the optical fiber. The acoustic wave is selected to have an acoustic wave length which is shorter in the direction of optical propagation than the optical beat length between the two propagation modes of the fiber. In order to cause phase-matching between the two optical propagation modes, a periodic structure is used to cause the acoustic wave to contact the optical fiber at periodic locations so that the coupling between the two propagation modes is periodically enabled and disabled. The periodic contact of the acoustic wave with the optical fiber has the effect of adding a spatial propagation constant. The periodicity of the periodic structure is selected so that the spatial propagation constant of the periodic structure is equal to the mismatch in the propagation constants of the two optical propagation modes and the acoustic wave. The present invention thereby provides a means of obtaining greater shifts in the optical frequency while using a colinearly propagating acoustic wave.

Acousto-optic fiber-optic frequency shifter using periodic contact with

A fiber optic amplitude modulator couples light between two orthogonal polarization codes of a birefringent fiber. Dynamic coupling is caused by applying synchronized acoustic surface waves to the birefringent fiber in a direction normal to the fiber axis. A static biasing force is applied across the fiber to statically couple apparoximately 50% of the light input to one polarization mode into the other polarization mode. The additional force caused by the acoustic waves causes the fraction of coupled power to vary about the coupling caused by the static force.

Optical fiber acousto-optic amplitude modulator

An acousto-optic frequency shifter having a long interaction region is used as an optical analyzer. A variable frequency signal generator is used to drive an acoustic transducer to launch an acoustic wave in contact with an optical fiber. The acoustic frequency is varied over a known range to generate acoustic waves having known wavelengths. An optical signal having an unknown optical wavelength is introduced into one end of the optical fiber in a first polarization mode. The effect of the acoustic wave on the optical signal is to cause coupling of the optical signal from the first polarization mode to a second orthogonal polarization mode. The amount of the coupling is dependent upon the phase-matching between the acoustic wavelength and the optical beat length. The coupling between the polarization modes is maximum when the acoustic wavelength is equal to the optical beat length. The intensity of the optical signal coupled to the second polarization mode can be measured to determine the optical wavelength corresponding to the acoustic wavelength when the maximum intensity occurs.

Fiber optic apparatus and method for spectrum analysis and filtering

A Bragg cell device for use as a tap in optical systems. In one embodiment an acoustic transducer is secured to a surface of an acoustic transmission medium, which is adjustably secured in hertzian contact with a surface of a waveguide. Bulk acoustic waves at frequencies above about 1 GHz are transmitted from the transducer through the transmission medium into the waveguide along a propagation path wherein the acoustic wavefronts intersect a light path in the waveguide at an angle which satisfies Bragg conditions, producing deflection of light out of the light path. Preferably, the transmission medium is also an optical conductor and is oriented upon the waveguide to receive the deflected light and transmit it to a polished optical window on the transmission medium. A grating transducer is secured on the transmission medium to detect acoustic signals reflected in the transmission medium. During position adjustment of the transmission medium and the waveguide, proper positioning is confirmed by a detected decrease in reflected acoustic signals, indicating the signals are entering the waveguide. In another embodiment, a grating transducer is deposited directly on a surface of a waveguide in a configuration to launch acoustic waves into the waveguide at an angle necessary to produce deflection of light from optical paths in the waveguide. When the waveguide comprises an optical fiber, the grating transducer conforms to the curvature of the fiber surface, thereby focusing acoustic signals from the transducer onto the fiber core.

Acousto-optic bragg cell

A fiber optic frequency shifter comprises an optical fiber having two propagation modes and an acoustic transducer for generating an acoustic wave. The transducer is positioned relative to the fiber to cause the wave fronts of the acoustic wave to acoustically contact the fiber at an angle of incidence which is less than 90.degree. greater than 0.degree.. Preferably, the wavelength of the acoustic wave is substantially equal to the beat length of the fiber times the sine of the angle of incidence.

Growing community of inventors

Palo Alto, CA, United States of America

William P Risk