Two substantially identical optical fiber interferometers, preferably packaged together and exposed to the same parameter to be measured, wherein an increase of the field quantity to be measured causes an increase of the delay time difference of one interferometer and a decrease of the delay time difference of the other interferometer. Demodulator means is connected to the outputs of the interferometers to demodulate the phase-modulated signals from each of the interferometers, and electronic differencing means is connected to receive the demodulated signals from the demodulator means to difference one of the signals from the other to enhance the measured signals relative to the laser-induced noise signals.

In apparatus useful in immunoassay of a fluid, light is directed to an optical sensor wherein the light is transmitted to a replaceable optical device that is responsive to index of refraction in a sensing region thereof that is exposed to the fluid. One portion of the light is transmitted via a reference path to a first detector. Another portion of the light is transmitted via a sensing path that includes the sensing region to another detector. A ratioing device receives an output from each detector and provides a signal responsive to the ratio of the outputs. The replaceable optical device typically comprises a pair of channel waveguides in directional coupling arrangement, or a pair of channel waveguides in an interferometer arrangement, or a ridge waveguide having a serpentine path.

A device for reading sensors in fiber optics which includes an integrated optics interferometer wherein the interference signal is slaved to a set-point value by means of a negative feedback signal. The measurement for reading the sensors is provided from the negative-feedback generated signal. In one of the disclosed embodiments generated delays of a value greater than an optical wavelength are measured by coupling the interferometer to a counting-up/counting-down system for interference fringe jumps.

A gyroscope is based upon the integration of an optical resonant cavity and a photodiode to detect minute perturbations due to angular forces. A Fabry-Perot cavity is created from two parallel semitransparent mirrors used in conjunction with a monochromatic light source. One mirror is fixed while the other is allowed to rotate with respect to the first mirror. A resonant cavity is thereby formed on either side of the axis. The gap between the mirrors is set so that light transmission through the mirrors is optimized. Rotation of the mirror from this position causes the distance between the mirrors to be altered and the light transmission on either side of the rotational axis to be change. Photodiodes on these sides sense this change as a change in photo-generated current, enabling the amount of change in rotation to be calculated. The photo-currents can be differentially amplified for sensitivity.

In an optical switching arrangement comprising a laser, an electrooptical phase modulator formed as a two-arm interferometer, and a second two-arm interferometer as a multistable element, the second interferometer is formed with interferometer arms having optical pathlength differences of the order of magnitude of 10.sup.4 times the wavelength of the light from the laser and has at least one signal output arranged parallel to a further output; the further output is connected to a photodiode the output voltage of which is amplified and then used to control the current supply of the laser. The wavelength of the light emitted by the laser is variable by changing the control voltage of the modulator or the bias voltage of the current supply of the laser so that the output signal alternates between two stable interference signals.