Glass manufacturing – Processes – Forming product or preform from molten glass
Patent
1991-01-22
1992-07-07
Jones, W. Gary
Glass manufacturing
Processes
Forming product or preform from molten glass
20415715, 20415741, 264 14, 264 15, 65111, 65 311, 65 301, C03B 3700
Patent
active
051279282
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention concerns improvements in or relating to methods for the manufacture of waveguide mixers. It concerns thus the manufacture of waveguides, in particular but not exclusively waveguides implemented using optical quality fibre. Mixers have application for second harmonic generation and for three wave mixing for frequency up conversion and or down conversion.
BACKGROUND
Frequency-mixing of optical waves has traditionally been achieved using crystals with non-inversion symmetric lattices. In the case of three-wave mixing, two waves of frequency .omega..sub.1, .omega..sub.2 are mixed to produce another optical wave at either the sum or the difference frequency .omega..sub.3 =.omega..sub.1 .+-..omega..sub.2. The efficiency of the process is governed by two conditions: initiates the frequency-mixing process; and three waves must be matched in order to ensure that the waves propagate in-phase inside the crystal, a condition which is commonly referred to as phase-matching.
It has recently been shown that efficient frequency-mixing, in particular second-harmonic generation (whereby a pump-wave at frequency .omega. is converted into a second-harmonic at frequency 2.omega.), may be obtained in spatially-prepared optical fibre waveguides (Osterberg, U. and Margulis, W.: "Dye-laser pumped by Nd: Yag laser pulses frequency-doubled in a glass optical fibre", Opt. Lett., 1986, 11, p 516; Farries, M. C. et al: "Second-harmonic generation in an optical fibre by self-written-grating", Electron. Lett. 1987, 23, p 322; Stolen, R. H. and Tom, H. W. K: "Self-Organisation phase-matched harmonic generation in optical fibres", Opt. Lett., 1987, 12, p 585). The fibres are usually prepared by exciting them simultaneously with intense radiation at two different wavelengths, a fundamental and the second harmonic, e.g. 532 nm and 1.064 .mu.m. This process has been shown to produce a permanent spatially-periodic second-order susceptibility (.chi..sup.(2)) in the fibre. The efficiency of of this process has been up to 10% for an input peak power of 1 kw (Farries M. C. "Efficient second-harmonic generation in an optical fibre", Proc. Colloquium on Non-Linear Optical Waveguides, London IEE 1988).
It is believed that the second-order susceptibility arises from the orientation of multi-photon-excited defect centres under the influence of a self-induced internal dc-field. The internal field is generated by a third-order nonlinear process involving both the exciting radiations at 1.064 .mu.m and at 532 nm.
Recently, it has been shown that a much greater second-order susceptibility may be produced in a fibre by applying a large (>100 V/.mu.m) external dc electric-field across the fibre at the same time as defects are being excited by intense blue light propagating in the core in a guided mode (Bergot, M. V. et al: "Generation of permanent optically-induced second-order non-linearities in optical fibres by poling"), Opt. Lett., 1988, 13, p. 592). The increase in x(.sup.2) is due to the much larger electric field inside the fibre. However, in this reported experiment, second-harmonic conversion efficiency was very low, since no phase-matching between applied infra-red wavelength waves was achieved.
A degree of phase-matching has since been demonstrated using a non-periodic second-order non-linearity (Fermann, M. E. et al: "Frequency-doubling by modal phase-matching in poled optical fibres", Electron. Lett. 24, 1988, p. 894). Here phase-matching has been achieved by exploiting the phase velocity difference which occurs between the pump in the lowest-order guided mode and the second-harmonic in a higher-order guided mode. This technique has the disadvantage that is is extremely sensitive to the small changes in fibre parameters along the length.
DISCLOSURE OF INVENTION
This invention provides a technique for producing a periodic nonlinear susceptibility in a waveguide which allows phase-matching for frequency-mixing to be obtained between different guided modes inside the waveguide. As a result efficient f
REFERENCES:
patent: 4950042 (1990-08-01), Gaylor et al.
Fermann, Frequency-Doubling by Modal Phase Matching in Poled Optical Fibres, Electronics Letters, vol. 24, No. 14, Jul. 1988, pp. 894-895.
Stolen, Self-organized phase-matched harmonic generation in optical fibers, Optics Letters, vol. 12, No. 8, Aug. 1987, pp. 585-587.
Farries, Second-Harmonic Generation in an Optical Fibre, Electronics Letters, vol. 23, No. 7, Mar. 1987, pp. 322-324.
Osterberg, Dye laser pumped by Nd:YAG laser pulses frequency doubled in optical fiber, Optics Letters, vol. 11, No. 8, Aug. 1986, pp. 516-518.
Mizrahi, Direct test of a model efficient second-harmonic generator, Applied Physics Letters, vol. 53, No. 7, Aug. 1988, pp. 557-558.
Optics Letters, vol. 13, No. 7, Jul. 1988, M.-V. Bergot et al: "Generation of permanent optically induced second-order nonlinearities in optical fibers by poling", pp. 592-594.
Optics Letters, vol. 13, No. 11, Nov. 1988, L. J. Poyntz-Wright, M. E. Fermann, and P. St. J. Russell: "Non-linear transmission and color-center dynamics in germanosilicate fibers at 420-540 nm", pp. 1023-1025.
Farries Mark
Fermann Martin
Li Luksun
Payne David
Bruckner John J.
GEC--Marconi Limited
Jones W. Gary
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