Electrical transmission or interconnection systems – Nonlinear reactor systems – Parametrons
Patent
1989-10-02
1991-05-07
Lee, John D.
Electrical transmission or interconnection systems
Nonlinear reactor systems
Parametrons
307427, 307430, 350 9615, 350 9629, G02F 137
Patent
active
050131150
DESCRIPTION:
BRIEF SUMMARY
This invention relates to methods of optical frequency mixing of particular but not exclusive application to optical frequency mixing in silica optical fibres for example to provide optical frequency doubling.
Frequency mixing has been recently observed in phosphorous doped single-mode fibres by several workers (Osterberg U and Margulis W. Opts Letts 11, pp 516-518, 1986, Farries M C et al, Electronics Letts, 23, pp 322-324, 1987, Stolen R and Tom H W K, 12,585, 1987). Since silica exhibits a centre of inversion and thus lacks an electric dipole allowed second order nonlinearity, X.sup.(2), it has been postulated that the non-linear interaction is due to the electric quadrupole and magnetic dipole moment (Payne D P, Electronics Letts, 23 (23), pp 1215-1216, 5th Nov. 1987). This process is self-phasematched, and as such there is little choice in the selection of particular interacting modes.
Phasematching has been discussed by Terhune R W and Weinberger D A, (JOSA-B, 4(5), May 1987) and dc-field-induced second-harmonic generation discussed by Weinberger D A and Terhune R W (CLEO, Session TUHH3, pp 78-79, Baltimore, Apr. 27 May 1, 1987,) where phasematching is achieved by proper design of the fibre. Efficient nonlinear devices may also be fabricated by incorporating high X.sup.(3) media as the core of a hollow fibre and using a periodic electrode grating structure opposite a continuous electrode for phase matching (Kashyap R, in Proc of SPIE Symposium on "Molecular and Polymeric Optoelectronic Materials: Fundamentals and Applications", San Diego, Calif., Volume 682, pp 170-178, 21-22 August 1986). The centre of asymmetry is induced by the electric field and phasematching is achieved by the spatial periodicity of the field.
The second-harmonic power from a fibre of length 1, with a third order nonlinearity of X.sup.(3) and for an applied spatially-periodic static electric field amplitude of E.sub.o, is given by Kashyap R, in Proc of SPIE Symposium on "Molecular and Polymeric Optoelectronic Materials: Fundamentals and Applications", San Diego, Calif., Volume 682, pp 170-178, 21-22 August 1986 as ##EQU1## where, P(.omega.) is the power in the fundamental mode, .DELTA..beta. is the phase mismatch and I is the overlap integral between the static field, the transverse fundamental and second harmonic mode fields.
The effective second order nonlinearity is then given by X.sup.(3) E.sub.o. For phase matching the spatially periodic static field pitch equals 21.sub.c, where 1.sub.c is the effective coherence length as a result of the mismatch between the phase velocities of the fundamental and second harmonic guided modes. In general, the static field need not be uniform. Additionally, the selection rules for the mode interactions are governed by symmetry of the modes and sign of the fields. For non-uniform static fields, the forbidden interactions in the linearly polarised modes (LP) approximation are no longer valid and virtually all mode interactions thus have a finite overlap integral. The strength of the interaction will also depend on the square of the Fourier coefficient of the spatial harmonic of the field which will generally be less than 1.
A polarisation insensitive optical frequency mixer for generating a harmonic of a light signal comprises an optical waveguide and a pair of interdigitated electrodes located on one side of the waveguide for producing within the waveguide a spatially periodic electric field having a reversal every half period the period being selected to phasematch the interacting frequencies each with its own mode with the light signal and the electrode dimensions being selected to provide that the electric field within the optical waveguide and are substantially equal in two mutually orthogonal directions transverse the waveguide.
The invention finds particular application in the generation of second harmonic optical signals and without prejudice to the generality of modes of operation of the invention its use will be described in terms of optical frequency doubling. In use, the interdigi
REFERENCES:
patent: 4684215 (1987-08-01), Shaw et al.
Proceedings of SPIE--The International Society for Optical Engineering: Molecular and Polymeric Optoelectronic Materials: Fundamentals and Applications, 21st-22nd Aug. 1986, San Diego, Calif., vol. 682, pp. 170-178, SPIE, Bellingham, Wash. U.S., R. Kashyap.
IEEE Journal of Quantum Electronics, vol. QE-9, No. 9, Sep. 1973, pp. 919-933; A. Yariv: "Coupled-Mode Theory for Guided-Wave Optics".
Payne--"Second-Harmonic Generation In Single-Mode Optical Fibers," Elec. Letter, 5th Nov. 87, vol. 23, No. 23, pp. 1215-1216.
Osterberg et al.--"Experimental Studies On Efficient Frequency Doubling In Glass Optical Fibers," Optics Letters, Jan. 87, vol. 12, No. 1, pp. 57-59.
Terhune et al.--"Second-Harmonic Generation In Fibers," J. Opt. Soc. Am. B, May 87, vol. 4, No. 5, pp. 661-674.
Levine et al.--"Phase-Matched Second Harmonic Generation In A Liquid-Filled Waveguide", Appl. Phys. Letters, Apr. 1975, vol. 26, No. 7, pp. 375-377.
Marcuse, "Optimal Electrode Design for Integrated Optics Modulators," IEEE J of QU. Elec., vol. QE-18, No. 3, Mar. 1982, pp. 393-398.
British Telecommunications public limited company
Lee John D.
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