Recent research on fibers with very small or very large birefringence for polarization-dependent applications is reviewed. The nature of random coupling between normal modes of polarization is analyzed and discussed in connection with various applications.

Polarization in optical fibers

The feasibility of maintaining a single-mode optical fiber interferometer in quadrature is demonstrated using a servo driven piezoelectrically stretched coiled fiber. The controller has a range of ~10(-5)-1000 rad with a stress voltage coefficient of ~27pi rad/V.

Elimination of drift in a single-mode optical fiber interferometer using a piezoelectrically stretched coiled fiber

We review the current status of guided-wave optical communication devices. The operation and presently demonstrated performance characteristics of waveguides switches, modulators, filters, and polarization transforming devices are discussed. Emphasis is given to recent developments with very high speed modulators and polarization insensitive devices.

Guided-wave devices for optical communication

The state of polarization at the output end of a long nominally circular single‐mode optical fiber is stabilized by an active control system. It contains a polarimeter and two electromagnetic fiber squeezers which introduce variable amounts of stress birefringence directly into the fiber, compensating for the effects of changing intrinsic fiber birefringence.

Polarization stabilization on single‐mode fiber

The polarization properties of single-mode optical fibers are easily modified by environmental factors. While this can be exploited in a number of fiber sensor devices, it can be troublesome in applications where a stable output polarization-state is required. Fibers with both low and high birefringence have been developed to enhance or diminish their environmental sensitivity, and recent progress in each area is reviewed. Low-birefringence fibers are described which are made by spinning the preform during the draw. In addition, developments in high-birefringence fibers which maintain a polarization state over long lengths are summarized. The effect on performance of external factors such as bends, transverse pressure, and twists is analyzed. Consideration is also given to polarization mode-dispersion as a potential limiting factor in ultrahigh bandwidth systems.

Development of low- and high-birefringence optical fibers

Crosstalk in optical waveguide switches/modulators caused by having two polarizations simultaneously present is studied in this work. This situation is expected to arise when fiber optical transmission lines are coupled to integrated optical circuits. Modulator/switch performance is found to be strongly affected by having two propagating polarizations. Conditions on device design are found that minimize the polarization sensitivity of switches/modulators, making them suitable for use with fiber optic transmission lines.

Performance limitations imposed on optical waveguide switches and modulators by polarization

The combination of two different types of electrodes in integrated optical switches is shown to permit polarization-insensitive operation. The ability to process arbitrarily polarized light is critical to the use of integrated optical devices with glass fiber transmission lines, due to the rapid changes in polarization state of light propagating in the fibers. We examine the performance of a Δβ reversal switch which uses two different types of electrodes and show that polarization-insensitive operation is readily achievable.

Polarization-insensitive integrated-optical switches: a new electrode design

In Ref. 1 I present a numerical example that illustrates how variations in video pre-amp characteristics impact the clutter-rejection performance of a scanning IR surveillance sensor. It has been pointed out to me that the correct interpretation of this example is that performance improvements against structured backgrounds are obtained with increasing video cut-on frequency, not with increasing video bandwidth, as originally claimed.

Infrared surveillance. 2: Continuous-time signal processors; erratum.

A new procedure is presented for calculating the performance of scanning background-limited IR sensors with adaptive threshold signal-processing logic. The IR background scene is presumably specified as a radiance map of arbitrary (but deterministic) structure. The nonstationary statistical nature of the photocurrent is taken into account by combining some results from optical communications theory with a formalism for the threshold-crossing statistics of nonstationary noises. The present work is extended in a companion paper in which various simplifying approximations and illustrative numerical examples are presented. The theory developed in these two papers is applicable to design studies for IR passive surveillance devices.

Infrared surveillance. 1:Statistical model

A number of infrared passive surveillance receivers are analyzed with the theory developed in a previous paper. The specific problem of interest is the detection of low-contrast point source targets against high-contrast structured backgrounds. A new and promising approach to signal processing is proposed for minimizing background-induced false alarms while retaining maximum target detection sensitivity. We show that time-delay and integration detector technology may afford us excess detector sensitivity that we can intentionally sacrifice in the interest of enhanced performance against structured scenes.

Richard A. Steinberg

Papers

Performance limitations imposed on optical waveguide switches and modulators by polarization

Polarization-insensitive integrated-optical switches: a new electrode design

Infrared surveillance. 2: Continuous-time signal processors; erratum.

Infrared surveillance. 1:Statistical model

Infrared surveillance. 2: Continuous-time signal processors