An all-fiber-optic frequency shifter is demonstrated that uses mode coupling between the LP(01) and LP(11) modes by a traveling acoustic flexural wave guided along the optical fiber. The input and output leads of this frequency shifter are single-mode fibers. Unity mode-conversion efficiency for cw operation is achieved at 8-MHz frequency shift with about 0.25 W of electrical input power. Carrier and image sideband suppression of 15 and 35 dB, respectively, are demonstrated.

All-fiber acousto-optic frequency shifter

A thin, large, high-definition television screen employs optical waveguides. Light (32) flows through waveguides (28) arranged, in parallel, across a substrate (64). Light from a source (44) is coupled into the waveguides using a Graded Index (GRIN) microlens array (56). Taps (37) direct light out and make it visible at different locations along the length of the waveguides. Long interaction length (8) taps with deflectors (10) are introduced which enable many waveguides to be placed side-by-side and still maintain high screen resolutions. Polymers, both electro-optic and non-electro-optic, are used in one embodiment as a waveguide building material. However, acousto-optic, thermo-optic (86) and magneto-optic effects may also be used with other materials such as glass and silicon dioxide. This display can be economically produced by forming a flexible waveguide ribbon (62) which integrates multiple waveguides (1), intensity modulators (40) and taps (38) into a single unit. Waveguide manufacturing techniques based on thermo-poling, photolocking, extruding, preform fiber-drawing, and laser milling are also discussed.

Optical waveguide display system

A technique for creating patterns of material deposited on a surface involves forming a self-assembled monolayer in a pattern on the surface and depositing, via chemical vapor deposition or via sol-gel processing, a material on the surface in a pattern complementary to the self-assembled monolayer pattern. The material can be a metal, metal oxide, or the like. The surface can be contoured, including trenches or holes, the trenches or holes remaining free of self-assembled monolayer while the remainder of the surface is coated. When exposed to deposition conditions, metal or metal oxide is deposited in the trenches or holes, and remaining portions of the article surface remain free of deposition. The technique finds particular use in creation of conductive metal pathways selectively within holes passing from one side of a substrate to another.

Self-assembled monolayer directed patterning of surfaces

An apparatus utilizes a two-mode optical waveguide with a non-circular core to provide stable spatial intensity patterns in both propagation modes for light propagating therein. The light has a wavelength, and the non-circular core has cross-sectional dimensions selected such that (1) the waveguide propagates light at that wavelength in a fundamental mode and a higher order mode, and (2) substantially all of the light in the higher order mode propagates in only a single, stable intensity pattern. Embodiments of the invention include, for example, modal couplers, frequency shifters, mode selectors and interferometers. One of the interferometer embodiments may be used as a strain gauge.

Apparatus using two-mode optical waveguide with non-circular core

The evolution of optical interferometers into extreme resolution large dynamic range sensors implemented in a guided wave form is discussed. The design and performance of fibre optic interferometric sensors optimised for specific periodic and quasi-steady-state measurands such as rotation, magnetic field, temperature, etc., are described.

https://iopscience.iop.org/article/10.1088/0022-3735/18/12/001/pdf

Monomode optical fibre interferometers for precision measurement

Single-sideband frequency shifting has been accomplished using traveling acoustic waves to couple the orthogonal polarizations of birefringent fiber. The light coupled from one polarization to the other is shifted in frequency by the frequency of the acoustic wave. An upper sideband is produced in one polarization, a lower sideband in the other. Both surface and bulk acoustic waves have been used. Sideband suppression of better than 30 dB and carriersuppression of better than 20 dB below the desired sideband have been achieved.

Acousto-optic frequency shifting in birefringent fiber

A fiber-optic single-sideband frequency shifter has been demonstrated that uses a surface acoustic wave incident upon an optical fiber at an angle to produce phase-matched polarization coupling. Coupling efficiencies as high as 95% at 4.4 MHz have been obtained using 25 W of input power (electrical). A tuning range of 290 kHz was achieved. Sideband suppressions of 40 dB and carrier suppressions as high as 25 dB have been observed.

Fiber-optic frequency shifter using a surface acoustic wave incident at an oblique angle

The two principal polarizations of birefringent optical fiber can be coupled by subjecting the fiber to stress that is spatially periodic along the length of the fiber. If the stress is temporally varied by using an acoustic wave, the coupling varies accordingly, and optical power can be transferred between polarizations dynamically. When an output polarizer is used to pass only one of the principal polarizations, this transfer of power is seen as a modulation of the intensity of the light passed by the polarizer. By using a surface acoustic-wave device, modulation depths up to 70% have been obtained. The bandwidth of such a device is limited only by the bandwidth of the transducers. A bandwidth of 4 MHz centered at 4.5 MHz has been obtained with the device reported here.

Acousto-optic polarization coupler and intensity modulator for birefringent fiber.

Light can be coupled between the two principal polarizations of birefringent fiber by using a traveling acoustic wave to produce a spatially periodic stress in the fiber. For a fixed acoustic frequency, maximum coupling occurs when the input optical wavelength is such that the beat length of the fiber equals the acoustic wavelength. By changing the acoustic frequency, the wavelength at which peak coupling occurs can be tuned. A prototype device has a passband 5 nm wide with a peak optical wavelength that can be tuned from 570 to 630 nm by changing the acoustic frequency from 2.85 to 2.55 MHz.

Tunable optical filter in fiber-optic form.

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.

William P. Risk

Papers

Acousto-optic frequency shifting in birefringent fiber

Fiber-optic frequency shifter using a surface acoustic wave incident at an oblique angle

Acousto-optic polarization coupler and intensity modulator for birefringent fiber.

Tunable optical filter in fiber-optic form.

Optical fiber acousto-optic amplitude modulator