Optical: systems and elements – Optical amplifier – Particular active medium
Patent
1998-02-13
2000-01-11
Moskowitz, Nelson
Optical: systems and elements
Optical amplifier
Particular active medium
359337, 372 45, 372 50, 257 17, H01S 319
Patent
active
060142502
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD OF THE INVENTION
The present invention relates to the field of optical systems including optical fibers and more particularly to the field of laser amplifiers in such optical systems as well as to methods of forming such laser amplifiers.
DESCRIPTION OF RELATED ART
Semi-Conductor Laser Amplifiers (SCLA) are expected to be important components in future optical systems. One important reason for this is their ability to amplify signals in the optical domain without converting them to the electrical domain. This gives flexibility regarding bit rates and code formats. Another reason is their small physical dimensions and suitability for integration (can for example be used as gating switch elements in optical switch matrices). A simple SCLA can consist of an anti reflection coated semiconductor laser.
However there exists a problem in these devices, which has to do with the polarization sensitivity of SCLAs. At the output of an ordinary single mode fiber the state of polarization (SOP) is fluctuating randomly due to temperature variations and mechanical disturbances despite the fact that the laser source has a well defined SOP. The simplest form of the SCLA does not have a polarization independent amplification. This means that it is incompatible with ordinary fibers if constant signal levels are required. This is a major drawback.
However there exist some designs for polarization independent laser amplifiers. One simply consists of making the waveguide of the laser amplifier more square. This makes the TE- and TM-modes of the light more equal. One problem with this approach is however that a smaller line width and thicker layer thickness than in conventional laser fabrication has to be used, which will lower the yield drastically in for example a laser amplifier gate switch matrix. Another problem with the laser amplifiers of this type is that they may saturate when amplifying strong input signals and thus do not work linearly under these circumstances.
Another approach for polarization independent laser amplifiers, which is more compatible with standard laser fabrication, make use of structures with two strained quantum well types, one with compressive strain and one with tensile strain. The strain results when the well layers have compositions that by themselves do not give lattice constants that are matched to the substrate of the amplifier. The compressive wells contribute to the TE-gain and the tensile wells contribute mostly to the TM-gain (they however contribute slightly to the TE-gain as well). Another advantage of this approach compared with the previous one is that the polarization dependency in the solitary SCLA can be tailored to compensate the polarization dependent losses in the rest of the chip (e. g. in the passive interconnecting waveguides or in waveguide crossovers and y-junctions).
This approach does however have one problem. This is the small wavelength operation region that is obtained. This is due to the fact that the different kinds of strained quantum wells have different wavelength dependencies, which limits the effectiveness of the amplifier to a small wavelength region and a system with such amplifiers will therefore be limited to a small variety of laser sources.
Another problem with these limitations of the amplifier with layers having strain is that it is difficult to amplify signals with the same gain if they have different wavelengths.
It therefore exists a need within the field of a laser amplifier, which has a polarization independent behaviour over a large wavelength region and which at the same time does not saturate when strong signals are used.
In the article "Effects of nonuniform well width on compressively strained multiple quantum well lasers", D Teng et al, Appl. Phys. Lett., Vol 60 (1992), p 2729-2731 a quantum well laser is described, which has compressive wells, the width of which have been varied. In the article, which is directed to a laser source and not a laser amplifier, the authors note that the varied widths in compressively strained w
REFERENCES:
patent: 4839899 (1989-06-01), Burnham et al.
patent: 5274656 (1993-12-01), Yoshida
patent: 5363392 (1994-11-01), Kasukawa et al.
patent: 5406574 (1995-04-01), Rennie et al.
D. Teng et al., "Effects of Non-Uniform Well Width on Compressively Strained Multiple Quantum Well Lasers," Applied Phys. Letter, vol. 60, pp. 2729-2731, 1992.
Newkirk, et al, IEEE Phootnics Technology Letters, vol. 5, #4, pp. 406-408; Abst. Only Herewith, Apr. 1993.
Magari et al, IEEE S.Q.E., vol. 30, #3, pp. 695-702; Abst.Only Herewith, Mar. 1994.
Kasukawa et al, Jap. Jour. App. Phys., p. 1, vol. 31, No. 5A, pp. 1365-1371, May 1992.
Kasukawa et al, App. Phys. Lett., vol. 59, #20, pp. 2486-2488; abst. only herewith, Nov. 11, 1991.
Moskowitz Nelson
Telefonaktiebolaget LM Ericsson
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