Optical waveguides – Having nonlinear property
Reexamination Certificate
1999-02-12
2003-06-17
Lee, John D. (Department: 2874)
Optical waveguides
Having nonlinear property
C385S002000, C385S005000, C385S008000, C385S042000
Reexamination Certificate
active
06580859
ABSTRACT:
TECHNICAL FIELD
The present invention relates in general to nonlinear integrated and fiber optics and more specifically to completely optical switches and optical transistors and may be used in both fiberoptic and air-path optical communications, in optical logical schemes and in other fields, where all optical switching, amplification, control and modulation of optical radiation are needed.
BACKGROUND ART
Methods for switching are known in optical bistable devices with opposite-directional coupled waves, in particular, in Fabry-Perot resonators with a cubic-nonlinear medium (Felber F. S., Marburger J. H.,
Appl. Phys. Lett
., 28, 731, 1976; Marburger J. H., Felber F. S.,
Phys. Rev., A
17, 335, 1878), and also in systems with a distributed coupling of waves (Winful H. G., Marburger J. H., Garmire E.,
Appl. Phys. Lett
., 35, 379,1979; Winful H. G., Marburger J. H.,
Appl. Phys. Lett
., 36, 613,1980).
Extensive opportunities for the creation of an optical switching, modulating and amplifying information signal are provided by a different class of systems with so-called unidirectional distributively coupled waves (UDCWs), if these waves propagate in a nonlinear medium. The methods and devices for optical switching, amplifying and modulating optical radiation based on the self-switching of the UDCWs was described for the first time in the papers: A. A. Maier, “The method of signal switching in tunnel coupled optical waveguides”, USSR Patent No. 1152397 (September 1982, publ. 1998). [Byull. Izobret. (46), 300 (1988)]; A. A. Maier, “Optical transistors and bistable elements on the basis of nonlinear transmission of light in systems with unidirectional coupled waves”, Kvantovaya Elektron. 9, pp.2296-2302 (1982). [Sov. J. Quantum Electron., v.12, 1490 (1982)]; A. A. Maier, “On self-switching of light in a directional coupler”, Kvantovaya Elektron. 11, pp.157-162 (1984). [Sov. J. Quantum Electron. v.11, p.101 (1984)]; A. A. Maier, “Self-switching of light in integrated optics”, Izv. Acad. Nauk SSSR, ser. Fis., v.48, 1441-1446 (1984). Later these methods and devices were extensively developed in the whole world.
In particular, in the known method for all-optical switching of radiation in tunnel-coupled optical waveguides A. A. Maier, “The method of signal switching in tunnel-coupled optical waveguides”, USSR Patent No. 1152397 (September 1982); Byull. Izobret. (46), 300 (1988)], a signal optical radiation with a variable small power and a pump optical radiation with a power more than threshold value are fed into cubic-nonlinear tunnel-coupled optical waveguides.
A method for switching and modulating UDCWs (P. Li. Kam Wa, P. N. Robson, J. S. Roberts, M. A. Pate, J. P. R. David, <<All-optical switching between modes of a GaAs/GaAlAs multiple quantum well waveguide)>>,
Appl.Phys.Lett
. v.52, No. 24, 2013-2014, 1988.) is also known. The method consists of switching and modulating waves, propagating as different waveguide modes in a nonlinear-optical waveguide made on the basis of a layered semiconductor multiple quantum well (MQW) structure with alternating layers. The switching and modulating are achieved by changing the power transmission coefficient from one wave to another by changing the power at the input of the optical waveguide. Wavelengths are chosen to be close to an exiton resonance wavelength &lgr;
r
to provide for a maximum cubic-nonlinear coefficient of the waveguide.
With this method and device it is very difficult to fit the exiton resonance wavelength to the wavelength of pump optical radiation and/or signal optical radiation accurately. So it is very difficult to achieve a maximum nonlinear-optical coefficient, and therefore to decrease the threshold and critical powers of pump optical radiation to a sufficient degree. Besides, it is not possible to adjust (control, regulate) values of threshold and critical powers in order to chose a predetermined regime of operation of the device. The impossibility to adjust the values of threshold and critical powers leads to high demands on the stability in time of the pump optical radiation source, because even a small variation of pump optical radiation power can cause accidental radiation switching, i.e. in this case the probability of an accidental error in switching and modulation at the output is high. Besides, the method has the following significant shortcoming. If the exiton resonance wavelength is close to the wavelength of the pump and/or signal optical radiation then a large loss of the optical radiations takes place. In order to carry out the method a nonlinear-optical waveguide made on the basis of a nonlinear-optic semiconductor MQW wafer structure is used. Micro-objectives are placed at the input and output of the nonlinear-optical waveguide. Besides the shortcomings mentioned above, the device also has loss at the input and output due to shortcomings of collimating optics at the input and output, which ignore the shape (form) of the profile (section) of the nonlinear-optical waveguide. The complexity of placing and mounting the micro-objectives relative to the nonlinear-optical waveguide, and the large size of the device are also shortcomings of the method and the device.
One prior-art switching device (R. Jin, C. L. Chuang, H. M. Gibbs, S. W. Kohh, J. N. Polky, G. A. Pubans “Picosecond all-optical switching in single-mode GaAs/AlGaAs strip-loaded nonlinear directional coupler”,
Appl. Phys. Lett
., 53 [19], 1977, pp.1791-1792) also comprises nonlinear TCOWs, made on the basis of a layered nonliner-optic semiconductor MQW structure with alternate layers GaAs/AlGaAs. The wavelength of the input optical radiation is chosen close to the exiton resonance wavelength to provide a large cubic-nonlinear coefficient of the waveguides. Using this device it is possible to implement the method for switching, modulating, amplifying and controlling, consisting in feeding (launching) optical radiation into nonlinear TCOWs, switching coupled waves in the nonlinear-optical waveguides and separating coupled waves in neighboring optical waveguides at the output of the device.
It is also very difficult in this device and method to adjust the threshold and critical power. Besides, in the device the transmission of radiation through the nonlinear TCOWs is only 1%, this being due to the maximum of absorption at the exiton resonance wavelength. The small transmission and the impossibility to adjust the threshold and critical power; and the mode of operation restricts the field of using the device.
Besides the shortcomings mentioned above, this switching device has optical power losses because of defects of the collimating optics placed at the input and output of the device.
The low efficiency of the focusing and collimating elements at the input and output of the known devices is due to difficulties in precisely positioning and mounting the focusing and collimating elements (objectives) relative to the nonlinear-optical waveguides. Besides, the focusing and collimating elements in the known device do not take into account the asymmetry of the cross section of the nonlinear-optical waveguide(s).
Known methods for feeding light into an optical waveguide (for example, Inventor's Certificate SU No. 1238569, 1984) do not provide possibility to control and check the efficiency of feeding optical radiation into the optical waveguide. This method does not provide for mounting focusing and collimating optical elements relative to the nonlinear-optical waveguide with precision, satisfying the high requirements in respect to the efficiency of feeding radiation into and/or feeding radiation out of the nonlinear-optical waveguide. This method cannot be used for mounting a semiconductor laser or laser module relative to the nonlinear-optical waveguide or nonlinear TCOWs either.
Uniting (joining) the aforesaid devices into a single chip is of great interest for devices processing optical signals, for example, for logical optical schemes, for optical computing devices and optical communicati
Cleomen Ltd.
Collard & Roe P.C.
Lee John D.
Song Sarah U
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