Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Frequency of cyclic current or voltage
Patent
1982-12-20
1985-04-16
Sikes, William L.
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Frequency of cyclic current or voltage
324 77K, 350 9614, G02B 5174
Patent
active
045112061
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to an integrated optical spectrum analyzer for analysis of the spectral content of an electric signal.
The advantage of using optical signal processing is that it affords the possibility of detecting within a very short time (<1 .mu.s) the occurrence of a large number of simultaneous signal frequencies, which at the present state of the art is impossible with purely electronic methods. Moreover, optical spectrum analysers can be made very small and light.
Such spectrum analysers that exploit acousto-optic effects have been known for some years. One such analyser makes use of an acousto-optically controlled deflection of a collimated light field. The deflected light passes a transformation lens which focuses the light on to a diode matrix. As a rule, the latter is positioned in a plane in which the light from a source is guided (optical waveguide) and in which the lenses are waveguide lenses, preferably so-called geodesical lenses. The acousto-optical deflection is accomplished by means of a surface acoustic wave from a surface acoustic converter. A complete spectrum analyser of this kind may have the dimensions 15.times.50 mm.
A major disadvantage of this prior art analyser is that the geodesic lenses are difficult and costly to produce. A common method of producing them is by diamond turning in a lathe. Hitherto, it has not been possible to produce them with the aid of photolithographic technology which is used for the production of the component otherwise. This, in turn, means that the precision-demanding alignment of the optical components will be difficult.
A further disadvantage of the known spectrum analysers is that they have both a constant analysis time (T) and a constant bandwidth (B).
SUMMARY OF THE INVENTION
The object of the present invention is therefore to provide an integrated optical spectrum analyser which lacks both separate collimation lens and transformation lens but nevertheless performs these functions and which, moreover, does indeed have a fixed product of time and bandwidth (T.times.B) but in which the analysis time or band width can be selected.
The present invention solves these problems. The integrated optical spectrum analyser comprises an optical radiation source connected to an optical waveguide. This waveguide is provided with an electro-optical deflector which, in turn, is furnished with an electrode matrix and is connected via electronic control circuits to the signal which is to be analysed. The spectrum analyser according to the invention also consists of a detection matrix connected to the waveguide.
The present invention is characterized in that the electrode matrix comprises a plurality of electrodes located in line, the electrodes having different widths and different spaces between them and of equal or different lengths. They are arranged with their longitudinal direction largely coinciding with the direction of the optical radiation incident from the radiation source and entering towards the deflector, the direction thus being largely at a right angle to the line. Further, the diode matrix is arranged after the electro-optical deflector, viewed in the propagation direction of the optical radiation. The elements of the detection matrix is then arranged to be disposed along a focal line, which is determined in position and direction by the parameters of the electrode configuration. A certain point in this focal line then corresponds to a given frequency of the signal to be analysed.
It has proved advantageous to allow the width of the electrodes, for example, as well as the spaces between them to vary quadratically along the line. This gives a lens effect on the part of the deflector appropriate to the purpose. It nevertheless presupposes that each electrode in the electrode matrix is supplied with a separate electrical signal voltage which is generated by the said electronic control circuits.
The source of radiation may be a laser diode which may be integrated in a waveguide or comprise an additional waveguide or an optical fiber
REFERENCES:
patent: 3997687 (1976-12-01), Phillips
patent: 4274049 (1981-06-01), Stoll
patent: 4403825 (1983-09-01), Tangonan et al.
patent: 4418980 (1983-12-01), Keil et al.
patent: 4440468 (1984-04-01), Auracher et al.
Thylen et al., IEEE J. on Quantum Electronics, vol. QE-18, No. 3, Mar. 1982, "Lensless Integrated Optics Spectrum Analyzer", pp. 381-385.
Thylen et al., Applied Optics, vol. 20, No. 10, May 15, 1981, "Electrooptic Approach to an Integrated Optics Spectrum Analyzer", pp. 1825-1832.
Takizawa, Optics Communications, vol. 37, No. 5, Jun. 1981, "Fresnel Light Modulator with an Array of Channel Waveguides", pp. 345-348.
Wright et al., Electronics Letters, vol. 10, No. 24, Nov. 28, 1974, "High Speed Electrooptic Analogue Digital Conversion", pp. 508-509.
DeBarros et al., Electronics Letters, vol. 7, No. 10, May 20, 1971, "Nanosecond Baseband Optical-Diffraction Modulator", pp. 267-269.
Arvidsson Gunnar
Stensland Leif
Thylen Lars
Gonzalez Frank
Institutet for Optisk Forskning
Sikes William L.
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