Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Reexamination Certificate
1998-03-10
2001-08-14
Pascal, Leslie (Department: 2633)
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
C359S199200, C359S199200
Reexamination Certificate
active
06275317
ABSTRACT:
TECHNICAL FIELD
The present invention relates to optical communications and, more particularly, to wavelength division multiplexing (WDM) transmitters having a hybrid integrated wavelength selectable laser source and optical amplifier/modulator.
BACKGROUND OF THE INVENTION
It is well known in the art that wavelength division multiplexing (WDM) affords multiple channel communications over a single optical fiber link, thereby increasing transmission capacity without the need for higher speed components. For switching or networking applications, wavelength division multiplexing, moreover, permits optical routing of signals at different wavelengths to different destinations or stations.
Optical transmitters, however, used in wavelength division multiplexing must critically generate light at controlled wavelengths, either fixed or dynamically selectable. Such transmitters must restrict the wavelengths to preselected spaced values so that the optical signals do not interfere with each other. As such, wavelength division multiplexing systems benefit importantly from highly stable, wavelength selectable optical transmitters and, more particularly, from those producing modulated light with low chirp, i.e., low uncontrolled wavelength shifts.
Among the first attempts to provide such stable wavelength selectable transmitters were those using discrete fixed frequency lasers. An array of lasers, for example, comprising distributed Bragg reflector (DBR) lasers, is each integrated with an electroabsorption modulator, followed by an optical combiner and amplifier so as to provide multiple wavelength division channels over a single fiber link. An example of this approach is shown in the article by M. G. Young et al., entitled “A 16×1 WDM Transmitter With Integrated DBR Lasers and Electroabsorption Modulators,” Paper No. IWA3,
Technical Digest of
1993
Topical Meeting on Integrated Photonics Research,
Palm Springs (1993) pp. 414-17. Unfortunately, such an approach requires a modulator for each laser, thereby requiring a complex electrical packaging to drive each modulator separately.
An alternative to the above approach has recently been developed wherein the cost and complexity make it more attractive for communication systems having a large number of optical channels, such as for local area networks and “fiber to the home” applications. This latter alternative monolithically integrates on a single substrate individually actuable lasers with an optical combiner. The output of the combiner containing the different wavelengths advantageously passes through only a single optical modulator, which is also likewise integrated on the same substrate. Of course, in this latter case, each wavelength is modulated on a time division basis with separate signals. See, U.S. Pat. No. 5,394,489, entitled “Wavelength Division Multiplexed Optical Communication Transmitters,” which is incorporated herein by reference and commonly assigned.
Although optical transmitters based on the above latter approach perform acceptably, the material compatibility imposed by the monolithical integration may compromise the performance of the optical devices. Furthermore, and more importantly, such optical transmitters are substantially prone to having high chirp because of unwanted optical feedback. The extensive time resolved spectra (TRS) testing required and cost associated therewith to ensure that the chirp requirements are met make this approach unattractive for most optical communication systems.
SUMMARY OF THE INVENTION
In accordance with the principles of the invention, a hybrid integrated optical transmitter comprising a wavelength selectable laser (WSL) source coupled to an optical amplifier/modulator via an optical combiner has been realized. Disposed between the optical combiner and the optical amplifier/modulator is an “optical isolator.” The optical isolator preferably includes at least a Faraday rotator and half-wave plate. Optical isolation may be achieved by the egressing radiation from, and back reflections incident on the laser, being at two mutually exclusive orthogonal polarization states or by the unwanted back reflections being totally extinguished.
More specifically, a Faraday rotator, either solely or in combination with a single polarizer and/or half-wave plate is used to selectively rotate and pass polarized light egressing from the wavelength selectable laser source. Unwanted reflections, although not necessarily totally extinguished, are at least orthogonally polarized. Advantageously, the laser(s) is unresponsive or substantially insensitive to the orthogonally polarized light, and hence any unwanted back reflections do not affect the operating characteristics of the laser(s). Optical isolation may be further improved, however, with the use of an additional polarizer positioned in front of the Faraday rotator to totally extinguish the orthogonally polarized back reflections. Furthermore, a latching Faraday rotator is preferred. In this manner, permanent magnets are not needed to maintain the Faraday rotator in its saturated state, and, as such, substantially reduces cost, size and complexity of the transmitter package.
In one embodiment, the wavelength selectable laser source is integrated on a single substrate with an optical combiner that directs the radiation to the optical amplifier/modulator integrated on a second substrate. Alternatively, the laser source and optical combiner may be integrated on different substrates. Regardless of the configuration, these optical components are assembled, and then aligned with respect to each other on an optical platform so as to afford ease of manufacturability and separate optimization control over the optical components. The wavelength selectable laser source includes single tunable lasers, multiple frequency lasers (MFLs), or laser array structures, such as distributed Bragg reflector (DBR) laser arrays, and distributed feedback (DFB) laser arrays.
Moreover, the laser source may be temperature regulated and/or use feedback control to compensate for environmental variations, such as temperature variations or performance degradations.
REFERENCES:
patent: 4210923 (1980-07-01), North et al.
patent: 4904036 (1990-02-01), Blonder
patent: 4989935 (1991-02-01), Stein
patent: 5134671 (1992-07-01), Koren et al.
patent: 5288659 (1994-02-01), Koch et al.
patent: 5373385 (1994-12-01), Darcie et al.
patent: 5394489 (1995-02-01), Koch
patent: 5444725 (1995-08-01), Zirngibl
patent: 5479544 (1995-12-01), Ono et al.
patent: 5568303 (1996-10-01), Liedenbaum et al.
patent: 5574742 (1996-11-01), Ben-Michael et al.
patent: 5576881 (1996-11-01), Doerr et al.
patent: 5608570 (1997-03-01), Brandle, Jr. et al.
patent: 5642447 (1997-06-01), Pan et al.
Kurt E. Petersen, “Silicon as a Mechanical Material,” Proceedings Of The IEEE, vol. 70, No. 5, May 1982, pp. 420-457.
Y. Seiwa et al., “High Power CW Operation over 400 mW On Five-Stripe Phase-Locked Laser Arrays Assembled By New Junction Down Mounting,” J. Appl. Phys. 61(1), Jan. 1, 1987, pp. 440-442.
C. Dragone, “Efficient N x N Star Couplers Using Fourier Optics,” Journal Of Lightwave Technology, vol. 7, No. 3, Mar. 1989, pp. 479-489.
U. Koren et al., “Wavelength Division Multiplexing Light Source With Integrated Quantum Well Tunable Lasers And Optical Amplifiers,” Appl. Phys. Lett. 54(21) May 22, 1989, pp. 2056-2058.
Takeuchi et al., “Low-Loss Single-Mode GaAs/A1GaAs Miniature Optical Waveguides with Straight and Bending Structures,” Journal Of Lightwave Technology, vol. 7, No. 7, Jul. 1989, pp. 1044-1054.
Ippen et al., “Additive Pulse Mode Locking,” J. Opt. Soc. Am. B/vol. 6, No. 9, Sep. 1989, pp. 1736-1745.
Zirngibl et al., “Digitally Tunable Laser Based on the Integration of a Waveguide Grating Multiplexer and an Optical Amplifier,” IEEE Photonics Technology Letters, vol. 6, No. 4, Apr. 1994, pp. 516-518.
J.M. Verdiell et al., “8-Wavelength DBR Laser Array Fabricated with a Single-Step Bragg Grating Printing Technique,” IEEE Photonics Technology Letters, vol. 5, No. 6, Jun. 1993, pp. 619-621.
Zirngibl et al., “Digit
Doerr Christopher Richard
Johnson John Evan
Joyner Charles H.
Ketelsen Leonard Jan-Peter
Koren Uziel
Agere Systems Optoelectronics Guardian Corp.
De La Rosa J.
Pascal Leslie
Singh Dalzid
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