Patent GB-1198085-A (GB)
Title: Optical Parametric Device
Inventor: ANDERSON DEAN BROWN
IPC: H01L31/00
Filed: 1967-09-26
Abstract: 1,198,085. Optical parametric amplifiers. NORTH AMERICAN ROCKWELL CORP. 26 Sept., 1967 [28 Dec., 1966], No. 43811/67. Heading H3B. [Also in Division G2] An optical parametric device comprises a dielectric wavebinding structure of rectangular cross-section capable of simultaneously supporting waves at a plurality of parametrically related frequencies wherein the dielectric exhibits a non-linear electric susceptibility and effects parametric interaction. The wavebinding structure may be a waveguide or a tuned cavity. In Fig. 4 a dielectric travelling-wave waveguide comprises a substrate 41 (which may be a dielectric, a semi-conductor or a metal), and a dielectric ribbon 43, having a larger refractive index than a dielectric layer 42 lying between the ribbon and the substrate. By plotting a Brillouin diagram of the relationship between frequency and propagation constant for several modes it is possible to determine three or four frequencies, in different modes, which have the same phase velocity and are parametrically related. A list of dielectric materials having a non-linear electric polarization susceptibility so as to provide parametric interaction is given in the Specification. In a preferred embodiment ribbon 43 consists of gallium arsenide oriented so that its (100) direction is along arrow 44 and its (110) direction is along arrow 45. A beam of pumping light having its electric field component polarized in a direction lying in the (110) plane is directed along the waveguide in a selected mode, and a signal beam is introduced into the waveguide in a different mode but with the same phase velocity. An output can be extracted either at the signal or at the idler frequency. Tn a four-frequency device the output may be at any one of three different frequencies, one of which is the signal frequency w 1  and the others being related to the signal and pump (wp) frequencies by the relationship Fig. 10 shows a tunable travelling-wave waveguide parametric device comprising a semi-conductor dielectric material. As in the previous arrangement a ribbon extends from one surface of the body, but here body 73 consists of N-type material and the upper part 74 of the ribbon is of P-type material (or vice versa). Between these regions is a PN-junction region which when properly biased forms a depletion layer 75. The refractive index of the depletion layer differs from that of the adjacent P- and N-regions and acts as a waveguide, the dimensions of which can be controlled by means of a bias voltage applied between, electrodes 76, 77. As a result different sets of frequencies having the same phase velocity can be selected. As shown, pump source 81 is a laser, polarized light from which is focused and deflected on to the waveguide by a lens 82 and dichroic mirror 83. If necessary the pumping light is converted to the correct mode for parametric operation by a mode converting dielectric film on lens 82. The input signal is transmitted through the dichroic mirror 83, and the desired output frequency is selected by filter 88. The ends of the waveguide preferably have antireflective coatings 18, 19. Discrete circuit parametric operation. The arrangement shown in Fig. 10 may be modified so that the semi-conductor body acts as a resonant cavity resonant at the parametrically related frequencies, instead of as a travelling- wave device. The antireflective coatings are replaced by optical band-pass filters capable of reflecting light at some frequencies and transmitting other frequencies. The filters may also introduce different degrees of phase shift when reflecting light at different frequencies if this is necessary to obtain simultaneous resonance at the selected frequencies. Alternatively this may be achieved by using the dispersive properties of the dielectric material forming the waveguide. Tn this arrangement the pumping light may be introduced at the output end of the resonant cavity. Carrier-injection pumping. Instead of using an external source, pumping light may be obtained by forward biasing the PN-junction 75 to cause carrier injection giving rise to recombination radiation. Operation may be controlled by modulating the bias. The device may be placed in a microwave cavity and a microwave signal may form an input or output of the device.