Coherent light generators – Particular active media – Semiconductor
Reexamination Certificate
1998-04-29
2001-10-30
Davie, James W. (Department: 2881)
Coherent light generators
Particular active media
Semiconductor
C372S026000, C385S014000, C385S131000
Reexamination Certificate
active
06310902
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to modulators such as included in electroabsorption modulated lasers (EML), and in particular to a structure and method of fabricating such modulators for analog applications.
BACKGROUND OF THE INVENTION
Electroabsorption modulated lasers (EMLs) are known in the art primarily for digital applications. Such lasers typically include a multi-quantum well laser and a modulator formed in a body of InP. (See, eg, Johnson, et al., “High Speed Integrated Electroabsorption Modulators” SPIE Proceedings, Vol. 30-38, pp. 30-38 (Feb. 1997) and Aoki, et al., “Novel Structure MQW Electroabsorption Modulator IDFB Laser . . . ” Electronics Letters, vol. 27, pp. 2138-2140 (Nov. 1991), which are incorporated by reference herein). The transfer function of such lasers, which is the light output as a function of voltage across the modulator, tends to be highly nonlinear. In particular, a sharp transfer function is exhibited, which is suitable for digital applications. However, analog applications normally require a linear transfer function.
In order to produce a more linear transfer function, it has been proposed to apply a predistortion to the input RF signal to the laser. This solution tends to be expensive and complex.
It is desirable, therefore, to provide a modulator which exhibits a fairly linear transfer function without the need for external circuitry.
SUMMARY OF THE INVENTION
The invention in one aspect is a modulator which includes a waveguide region of semiconductor material having a graded band gap along a direction selected from a path of light propagation through the modulator and a path perpendicular to the path of light propagation. In accordance with another aspect, the invention is an electroabsorption modulated laser including a laser and modulator formed on a substrate and having a waveguide region of semiconductor material, wherein the portion of the region defining the modulator has a graded band gap along a direction selected from a path of light propagation through the modulator and a path perpendicular to the path of light propogation. In accordance with a further aspect, the invention is a method for forming a modulator comprising selectively growing a layer of semiconductor material on a substrate wherein a mask is used to define the area of growth, and the width of the mask is varied in a direction selected from a path of light propogation through the modulator and a path perpendicular to the path of light propagation.
REFERENCES:
patent: 4875750 (1989-10-01), Spaeth et al.
patent: 6150667 (2000-11-01), Ishizaka et al.
“High-Speed Integrated Electroabsorption Modulators”, John E. Johnson et al., Proceedings of SPIE, High-Speed Semiconductor Lasers for Communication, Feb. 10-11, 1997, San Jose, California, vol. 3038, pp. 30-38.
“Novel Structure MQW Electroabsorption Modulator/DFB-Laser Integrated Device Fabricated By Selective Area MOCVD Growth”, M. Aoki et al., Electronics Letters, Nov. 7, 1991, vol. 27, No. 23, pp. 2138-2140.
Bylsma Richard Bendicks
Ketelsen Leonard Jan-Peter
Sputz Sharon Kay
Agere Systems Optoelectronics Guardian Corp.
Birnbaum Lester H.
Davie James W.
LandOfFree
Modulator for analog applications does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Modulator for analog applications, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Modulator for analog applications will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2615101