GB1254617A - Optical parametric device - Google Patents

Abstract

1,254,617. Optical parametric devices. NORTH AMERICAN ROCKWELL CORP. 9 Dec., 1969, No. 60095/69. Heading H3B. An optical parametric device comprises a waveguide formed of a plurality of layers of dielectric material, one or more of which exhibits a non-linear susceptibility. In operation, the signal, pump and output frequencies #s, #p and #i must all be propagated with the same phase velocity, and this is effected by a suitable choice of layer thickness and refractive index, i.e. a suitable refractive index profile. Fig. 5 relates to a three layer waveguide having a central layer of thickness D and refractive index 3À5, while the outer layers are of thickness D/2 and refractive index 4À0. An effective frequency 2#D/#. is plotted against the inverse of phase velocity (i.e. the effective refractive index) C/Vp, where #. is the light wavelength in free space, and C is the velocity of light in vacuo. Solid curves represent TE n modes, and dotted curves TM n modes, n being the mode order 1-8 shown adjacent the curves. For the line 50 of constant phase velocity, it is seen that suitable #s, #i and up are available corresponding to a signal in the TE 1 mode, a pump in the TM 3 mode and an output in the TE 3 mode. Such frequencies, where #i and #p have the same order but one is TE and the other TM are stated to be the most satisfactory. Other refractive index profiles are described, Figs. 3-8 (not shown). To ensure that light entering the waveguide is of a suitable mode, a structure shaped as in Fig. 10 or 11 may be used, wherein the layered waveguide has a tapered end 65 or 75, and is mounted on an insulating substrate 61 or 71. A wider choice of refractive index profiles and hence operating frequencies may be obtained by using birefringent dielectrics since they exhibit two refractive indices, or by using materials whose refractive indices may be varied by applied magnetic or electric fields or heat. Broadband operation may be achieved if the line of constant phase velocity meets the curves near a point of inflection, Figs. 6, 7 (not shown). Materials referred to are: for the substrate, single crystal sapphire, chrysoberyl, BeO or MgO, and for the dielectric, single crystal GaP, GaAs, Ge, CaCl 3 or cinnabar (i.e. α-HgS). Polycrystalline materials may be used. The width of the waveguide is not critical but should exceed ten times the thickness. At ratios less than this the refractive index profile depends more on the cross-sectional area than the thickness.