Two-section semiconductor optical amplifier

Reexamination Certificate

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Reexamination Certificate

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06186631

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to optical amplifiers, and in particular, to a two-section semiconductor optical amplifier with increased output power and a relatively wide dynamic range, and a process for manufacturing the same.
DESCRIPTION OF RELATED ART
The increasing complexity of high density wave division multiplex (WDM) and time division multiplex (TDM) networks, requires a significant number of optical amplifiers to compensate for losses in multiplexing, splitting, switching, or wavelength converting. Optical amplifiers in conjunction with integrated or hybrid power monitors may be used as optical power equalizers for receiving a relatively wide range of input power and delivering substantially constant power for devices with a relatively narrow dynamic range, such as an optical N×N switch or an all-optical wavelength converter.
Conventional single section semiconductor optical amplifiers (SOAs) have been widely used to meet these needs. The use of SOAs is advantageous in that they are less expensive and smaller in overall size than fiber amplifiers. Undesirably, however, the gain saturation of SOAs limit both the output power level and dynamic range of the input signal. Furthermore, as shown in the waveform in
FIG. 1
, for a conventional single section SOA having an output power of 1.5 dBm, an input power of 6.2 dBm, and an injection current of 106 mA, the signal pulses are distorted by gain saturation. Specifically, the beginning photons of the pulses experience a higher (unsaturated) gain than later photons.
It is therefore desirable to develop a semiconductor optical amplifier that has an increased saturation output power, while reducing the effects of gain saturation over a relatively wide input dynamic range.
SUMMARY OF THE INVENTION
The present invention is directed to a unitary two-section semiconductor optical amplifier including a first active region, a second active region, and a passive region integrally connected between the first and second active regions to minimize optical loss therebetween. The gain in the first active region may be increased so that an input power level to the second active region remains substantially constant over a predetermined range of first input power levels.
In addition, the invention is directed to a method of fabricating the unitary two-section semiconductor optical amplifier described above by epitaxial growth deposition of the semiconductor and later removal of a portion of the semiconductor to define a passive region. Initially, at least one passive waveguide layer is grown to form a wafer. An etch stop layer, at least one quantum well layer, and a cladding layer are then grown on top of the at least one passive waveguide layer, in that order. Then, a photoresist waveguide mask is applied to define the first and second active regions separate from one another. Thereafter, a portion of the cladding and at least one quantum well layer are etched away to define the passive region interposed between the first and second active regions.
Alternatively, the unitary two-section semiconductor optical amplifier in accordance with the present invention may be fabricated using selective area growth techniques. Initially, at least one passive waveguide layer is deposited to form a wafer. At least one quantum well layer is then grown on top of the at least one passive waveguide layer to define the first active region, and at least one quantum well layer is grown on top of said at least one passive waveguide layer to define a second active region separate from the first active region. Thereafter, a cladding layer is grown on top of the at least one quantum well layers defining the first and second active regions.


REFERENCES:
patent: 5175643 (1992-12-01), Andrews
patent: 5457569 (1995-10-01), Liou et al.
patent: 5930031 (1999-07-01), Zhou et al.
patent: 6040938 (2000-03-01), Ducellier
Marcenac, D.D. et al.,Bandwidth enhancement of wavelength conversion via cross-gain modulation by semiconductor optical amplifier cascade, Electronics Letters, Aug. 17th, 1995, vol. 31, No. 17, pp. 1442-1443.
Castro, J.C.S. et al.,Improved Signal to Noise Ratio in Gain-Levered Laser, Electronics Letters, Jul. 1995, vol. 31, pp. 1156-1157.

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