Showing papers on "Phase conjugation published in 1977"

Amplified reflection, phase conjugation, and oscillation in degenerate four-wave mixing

Abstract: A number of new optical effects that result from degenerate four-wave mixing in transparent optical media are proposed and analyzed. The applications are relevant to time-reversed (phase-conjugated) propagation as well as to a new mode of parametric oscillation.

Experimental test of an infrared phase conjugation adaptive array

Abstract: Results of an experimental program to investigate the properties of an infrared phase conjugation adapative array are described. Both linear and planar adaptive arrays of up to 7 elements using a new integrated frequency phase control technique at 10.6 μm are discussed. The results presented include correction for atmospheric turbulence at ranges of 1, 6, and 9.5 km. Beam broadening induced by turbulence is reduced to the array diffraction limit and target irradiance fluctuations are decreased by a factor of ≈ 20 in strong turbulence. Received irradiance fluctuations are reduced by ≈ 50 db out to 2 kHz. Beam pointing, scanning, and automatic target acquistion and tracking are demonstrated over the 1 mrad array field of view.

Phase conjugation method and apparatus for an active retrodirective antenna array

Abstract: An active retrodirective antenna array wherein a reference array element is used to generate a phase reference which is replicated at succeeding elements of the array. Each element of the array is associated with a phase regeneration circuit and the phase conjugation circuitry of an adjacent element. In one implementation, the phase reference circuit operates on the input signal at the reference element, a voltage controlled oscillator (VCO) output signal and the input pilot signal at the next array element received from a transmission line. By proper filtering and mixing, a phase component may be produced to which the VCO may be locked to produce the phase conjugate of the pilot signal at the next array element plus a transmission line delay. The same phase conjugation process occurs at the next element where the proper phase reference is regenerated by mixing samples of the input pilot and transmitted signal. In another implementation, particularly suited for large arrays in space, two different input pilot frequencies are employed. Their difference is the phase reference of the system, and a local oscillator is used in obtaining this difference, which is in the IF range. The two pilot frequencies are selected in accordance with particular criteria to insure proper phase addition and elimination of local oscillator components. Appropriate mixing and filtering is performed to achieve phase conjugation and phase reference replication.

Nonlinear Optical Phase Conjugation For Laser Systems

Abstract: This paper deals with certain nonlinear effects that,can directly generate a wavefront which is the phase conjugate of the incident field. These phenomena can be exploited in pulsed laser systems to remove aberrations in the optical train as well as aberrations arising from turbulence in the atmosphere. We discuss our measurements of the effectiveness of this conjugation process using a ruby laser and stimulated Brillouin scattering in a CS2 waveguide device. Measurements are made of the divergence angle of the beam after correction as a function of interaction length. The application of conjugate processes realizable in SBS, SRS, parametric down conversion, and four-wave mixing is considered for typical CO2 laser systems. System gain, backscatter limitations and parasitic oscillation are discussed for typical pulsed amplifier systems. Amplified spontaneous emission and unwanted glint returns from optical defects appear to be the most serious limitations.