An apparatus is provided for use in determining the distance and velocity of a distant object. The apparatus employs a low energy optical radiation source that emits identical external and internal radiation signals whose wavelengths are swept. The wavelength sweep is induced by varying the magnitude of an electrical input supplied to the optical radiation source. An external ranging system employs common optical means, including polarizing means, to direct the external signal towards a distant object, and to receive a portion of that signal which reflects off of the object. First optical heterodyne means are provided to mix the reflected external signal and a local oscillator signal derived from the external optical radiation signal, to produce an output signal. Means are provided to determine representative values of the frequency of that output signal. An internal processing system directs the internal signal into an optical delay means of a known length. Upon exiting the optical delay means, the delayed internal signal is received by a second optical heterodyne means and mixed therein with a local oscillator signal derived from the internal optical radiation signal. Means are provided to determine a representative value of the frequency of the output signal from the second optical heterodyne means. Additional means are provided to determine the central frequency of the external and internal optical radiation signals. Finally, processor means utilize the representative frequency values derived from the external ranging system and internal processing system, and the central frequency value, to calculate the distance and velocity of the distant object.
A signal processing circuit for a reference signal occurring in a heterodyne interferometer and a measured signal. The underlying frequency modulation of the radiation source of the heterodyne interferometer results in phase jumps in both signals. Signal filtering of both the reference signal and the measured signal with a gate signal removes from both signals those signal components that have the same phase sign. Further simplification of the signal processing results from signal interpolation by band pass filters and signal down-mixing into a lower frequency range below the heterodyne frequency. The input signals processed by the circuit can be further processed by a conventional phase comparator.
The distance between two objects, such as aircraft, helicopters and other vehicles, can be determined by transmitting from a first object through atmosphere a first frequency which is absorbed by atmosphere and a second frequency which is not absorbed by atmosphere, receiving at a second distant object the first and second frequencies, and determining from the received first and second frequencies the distance between the first and second objects. In preferred methods and apparatus, the first frequency is a frequency characteristic of atmospheric oxygen absorption (e.g., 760 nm wavelength), and the frequency transmission comprises emitting a laser light beam while modulating its frequency through a frequency range which is greater than a frequency range characteristic of atmospheric oxygen absorption (e.g., 750 nm-770 nm wavelength) and includes a second frequency which is not absorbed by atmosphere.
A three-dimensional optical scanning vision system capable of producing high-resolution images in real-time includes an optical source for producing a source light beam. The source light beam is directed to a beam splitter which splits it into a local oscillator beam and a signal beam. The local oscillator beam is directed toward a photodetector, while the signal light beam is directed toward a target. Light reflected from the target is received by the beam splitter and directed toward a retroreflector which returns the beam to the beam splitter interface. Quarter wave plates and the retroreflector insure that the return light beam and the local oscillator beam are collimated and have the same polarization state. Mixing of the local oscillator beam and the return light beam occurs at the beam splitter interface, thus providing coherent optical detection by the photodetector. The photodetector thus provides an output signal providing a high degree of information about the target. The system also includes scanner optics to scan the signal light beam across the target. A processor is also included for outputting a three-dimensional image of the target, and for controlling the scanner optics.
A system and a method for obtaining object data with a direct detection technique which employs radiation are disclosed. A set of radiation pulses are transmitted to an object area. A mechanical scan of the object area for returning pulses reflected off an object can be carried out for each pulse, so that each pulse is reflected onto a particular position of a light-sensitive array dependent upon the object distance and/or other data pertaining to the object. Alternatively, the scanning relative to each returning reflected pulse can be conducted by electrically scanning a radiation-sensitive array which comprises a CCD array having pixels. The scanning takes place relative to each pulse so that each returning reflected pulse strikes one or more pixels on the array so that the resulting signal reside at a position depending upon certain object data. The relationship between the generation of the pulses and the scanning can be changed as desired in order to seek objects at different ranges from the system or to improve accuracy of the object data.
A laser apparatus and method that provide for suppression of source spontaneous emission (SSE) and amplified spontaneous emission (ASE) light in laser output with minimal intracavity loss. The apparatus comprises a gain medium emitting a light beam, a wavelength element positioned in the light beam, and a non-reciprocal pickoff positioned in the light beam between the gain medium and wavelength element. The non-reciprocal pickoff may comprise a polarization-dependent beam splitter and a non-reciprocal polarization rotator positioned in the light beam before the wavelength selection element. The non-reciprocal pickoff may further comprise a reciprocal polarization rotator positioned in the light beam after the polarization-dependent beam splitter. The method may comprise emitting a light beam from a gain medium outward along an optical path, allowing the outward light beam to interact with a tunable element, returning a spectrally cleaned light beam along the optical path to the gain medium from the tunable element, and non-reciprocally picking off a portion of the returning, spectrally cleaned light beam from the optical path and directing the portion along an output path.
