Optical waveguides – With optical coupler – Switch
Reexamination Certificate
1999-10-29
2001-11-13
Phan, James (Department: 2872)
Optical waveguides
With optical coupler
Switch
C385S015000, C385S016000
Reexamination Certificate
active
06317532
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for reducing coupling loss via a geometrical optimization in free-space micro-machined optical switches, and more particularly, to a method and apparatus for reducing data loss caused by light beam divergence and the associated differences between the radius of an optical light beam and the radius of a mirror of a free-space micro-machined optical switch.
2. Description of the Art
Due to very rapid increases in core-transport network demand (e.g., in the bit rates of individual services and in the number of wavelength channels being built into Wavelength Division Multiplexing (WDM) transport systems), fiber-optic switches with large port-count have quickly emerged as perhaps the most important, yet unrealized, technological need in future high-capacity light-wave networks. These fiber-optic network elements will be chiefly used for network restoration to begin with, with substantial provisioning value likely emerging thereafter.
The optical switching technologies advanced so far offer the potential advantages of bit-rate transparency, low power consumption, small volume, and low cost. Nevertheless, the requirements in port count (on the order of 512×512) and in loss budget represent deep challenges that have not yet been met by any current photonic switching technology. Although conventional mechanical switches can achieve high optical quality, they are large in size and mass, and are thus relatively slow in switching speed. On the other hand, guided-wave solid-state switches, though compact, generally have high loss and high crosstalk. The inherent disadvantages of these technologies thus appear to limit their expandability to the port counts mentioned above.
By contrast, free-space micro-machined optical-switching technology holds particular appeal in this application because it combines the advantages of free-space interconnection (i.e., low loss and high optical quality) with those of monolithic integrated optics, namely, compactness. Various small-scale (2×2) micro-machined switches utilizing sliding micro-mirrors have been demonstrated. In addition, collimating optics and rotating micro-mirrors have also been proposed as a means of achieving high-density optical switches. Given the fertility that the field of micro-optical systems is beginning to show, and the considerable variety of switching devices that has already emerged, it is likely that diverse applications will be best suited to diverse switching technologies. However, for the application of restoration and provisioning in core-transport light-wave networks, free-space micro-machined optical switches (FS-MOS) with free-rotating hinged micro-mirrors are particularly attractive. Attractive because such applications do not require frequent switching, but do require very high reliability even for switch mirrors that remain in one switching state for extended periods on the order of years. Furthermore, the sub-millisecond switching times exhibited by FS-MOS devices are well-matched to the needs of restoration and provisioning in core-transport light-wave communications networks.
However, like other optical cross-connect technologies, free-space micro-machined optical switches face the substantial challenge of achieving increased port-count while living within a specified loss budget that will in practice be fixed by adjacent transponders. Studies of scaling and loss in these devices have thus far been purely empirical, and thus neither the fundamental limits nor the means of approaching them are understood.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides the theoretically and experimentally investigated fundamental loss mechanisms in free-space micro-machined optical cross-connects showing the existence of geometrical loss minima. The physical investigation of the geometrical loss minima focuses on measuring insertion loss of a 16×16 free-space micro-machined optical cross-connect having a switch-mirror radius of 150 &mgr;m. The investigation reveals that even in the face of diffraction, mirror-aperturing and mirror-curvature, an insertion loss of only 2.9 dB can be achieved.
Theory then suggests that by exploiting these geometric loss minima it is possible to achieve 1024-port (512×512) multistage switches with only 6 dB of loss. This would make possible the sort of large-scale cross-connects that appear to be needed in core WDM network applications.
The present invention, including its features and advantages, will become more apparent from the following detailed description with reference to the accompanying drawings.
REFERENCES:
patent: 5208880 (1993-05-01), Riza et al.
patent: 5933478 (1999-08-01), Ozaki et al.
patent: 5960132 (1999-09-01), Lin
L.Y.Lin, E.L. Goldstein, J.M. Simmons, R.W. Tkach “High-Density Micromachined Polygon Optical Crossconnects Exploiting Network Connection-Symmetry” IEEE Photonics Technology Letters, vol. 10, No. 10, Oct. 1998, pp. 1425-1427.
L.Y. Lin, E.L. Goldstein, R.W. Tkach “Free-Space Micromachined Optical Switches with Submillisecond Switching Time for Large-Scale Optical Crossconnects” IEEE Photonics Technology Letters, vol. 10, No. 4, Apr. 1998, pp. 525-527.
Goldstein Evan Lee
Lin Lih Yuan
Tkach Robert William
AT&T Corp.
Kenyon & Kenyon
Phan James
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