Apparatus for producing a time standard including a source of radiation, two fibers of different length to transmit the radiation, and means to produce a signal representative of the difference in propagation time through the fibers that is constant despite temperature changes.

A direction finding apparatus and method for an RF signal are described which provide a variable time delay in fiber optic cables. A tunable transmitter launches optical emissions of several wavelengths into a plurality of fiber optic cables. Since the waveguide material of each cable exhibits anomalous dispersion of the optical emissions, large changes in group refractive index are provided as a function of the different wavelengths of the optical emissions. As a consequence, only small changes in the different wavelengths of the optical emissions produce large changes in the time delay of the different wavelengths of the optical emissions within a fixed length of the optical fiber cables. This apparatus and method produce sensitive angle of arrival determinations for RF signals.

A spectroscopic system that processes spatially dispersed electromagnetic emissions at a number of wavelengths from a test material. The spectroscopic system includes a converter that generates an electrical signal that is proportional to the intensity of electromagnetic radiation received by the converter. An optical delay circuit is coupled to an input of the converter. The optical delay circuit selectively delays application to the converter of electromagnetic emissions from the test material for at least one wavelength of electromagnetic emissions. A data processing circuit is coupled to an output of the converter. The data processing circuit records the value of the electrical signal from the converter over time so as to measure, contemporaneously, the intensity of electromagnetic emissions at each wavelength as a function of time.

An optical waveguide having a detour is disposed at either or both of the light-receiving and light-emitting ends of a dispersion optical system in a spectroscope. Even though light being propagated through the optical waveguide has specified polarizing characteristics, the light is depolarized by passing through the optical waveguide and many times reflecting therein. Accordingly, unpolarized light not affected by the polarization selectivity of the dispersion optical system or the like can be emitted from the spectroscope.

A number of high frequency signal sources such as a number of receiving annas have their information content extracted by an optoelectronic synchronous sampling system. A laser provides pulses of proper frequency and duration and feeds them to a fiberoptic bundle. In one embodiment the fibers are lengthened to be simultaneously actuated. Otherwise, each of the fibers in the bundle has a different length so that light emanating from their distal ends appears as a delayed series of actuating light pulses. Phase shifters, pressure or electric field effects, can effect delay and consequent beamforming. Optoelectronic switches are disposed adjacent the distal ends so that the delayed series of actuating pulses actuates the switches in a synchronous sequence to synchronously sample the high frequency signals received by each of the antennas. Interconnected analog-to-digtal and processing circuitry conditions the synchronously received samples for further use. The discrete delays assured by the different lengths of the optical fibers and the optoelectronic switches enable responsive synchronous sampling of the number of high frequency sources to extract their information content. There is no EMI or RFI, neither does it generate them. This can effectively operate in a high noise environment.