Optics: measuring and testing – By particle light scattering – With photocell detection
Patent
1997-01-17
1998-10-06
Turner, Samuel A.
Optics: measuring and testing
By particle light scattering
With photocell detection
385 27, 25022727, G01B 902
Patent
active
058185844
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to optical waveguide interferometers, which may be used as optical splitters, which involve more than two waveguides and to a method of making the same.
BACKGROUND OF THE INVENTION
Optical waveguide interferometers, which may be used as optical splitters, are composed of two or more optical waveguide couplers which couple more than two waveguides. In order to make them, more than one of the output ports of a first coupler are connected to the input ports of the following coupler with waveguides of prescribed lengths such as to create an optical interferometer. The control of the coupler properties and the phase shift between two successive couplers is used to adjust the output transmission properties of the interferometer, such as to produce essentially wavelength insensitive responses.
The present invention is an improvement to the invention disclosed in U.S. Pat. No. 5,119,453, which describes a wavelength flattened 2.times.2 splitter made on the basis of a Mach-Zehnder interferometer structure. In said U.S. Patent the splitter was made by concatenating two 2.times.2 waveguide couplers of predetermined wavelength response and by inducing a phase shift between the waveguides connecting the two couplers so that the wavelength response of the first coupler compensates the wavelength dependency of the second coupler. The invention in U.S. Pat. No. 5,119,453 is useful to make 2.times.2 spitters, but does not permit the fabrication of 1.times.N splitters other than concatenating 2.times.2 couplers in a tree arrangement. It was surprisingly found in accordance with the present invention that, under certain conditions, the principle described in U.S. Pat. No. 5,119,453 of compensating the wavelength dependency of a first coupler with a second coupler can be extended to couplers involving more than 2 waveguides, thus allowing manufacture of a 1.times.N splitter which is much more compact than any such splitter produced previously.
SUMMARY OF THE INVENTION
The present invention is directed to a waveguide interferometer made by concatenating 2 or more N.times.N couplers, thereby creating a structure which has wavelength properties different from the individual couplers. In particular, this structure can produce a 1.times.N splitter which has a reduced wavelength sensitivity. To create this interferometer, the N output ports of a first coupler are connected to the N input ports of a second coupler. The wavelength properties of each coupler and the phase differences induced to the signals in each of the waveguides connecting the couplers must be properly chosen, just like in the case of the above mentioned Mach-Zehnder interferometer disclosed in U.S. Pat. No. 5,119,453. The special condition to realize this device will be made clear in the following description of the invention.
One object of this invention is the fabrication of a waveguide interferometer composed of two or more waveguide couplers having more than two waveguides, wherein the couplers are placed in series, the output waveguides of the first coupler being linked to the input waveguides of the second coupler and so on.
Another object of this invention is to provide this waveguide interferometer with a low wavelength sensitivity which is created by selecting the couplers of the interferometer and the phase shifts in the interferometer such that the wavelength dependencies of the couplers compensate each other.
A further object of this invention is to fabricate the above mentioned interferometer using single-mode optical fibers.
A still further object is for the waveguide interferometer to be composed of two N.times.N couplers made by placing N-1 fibers around a central fiber, the optical length of the central fiber between the couplers being different from the optical lengths of the outer fibers, such structure having low wavelength sensitivity.
Still another object of this invention is to provide a fabrication method for realizing and tuning such waveguide interferometer.
Other objects and advantages
REFERENCES:
patent: 5119453 (1992-06-01), Gonthier et al.
patent: 5351325 (1994-09-01), Miller et al.
Gonthier Fran.cedilla.ois
Lacroix Suzanne
Framatome Connectors Canada Inc.
Turner Samuel A.
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