Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2002-02-27
2003-09-16
Ben, Loha (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C349S198000, C356S454000
Reexamination Certificate
active
06621614
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to etalons in which the reflectivity of the etalon varies according to spatial location.
2. Description of the Related Art
As the result of recent advances in technology and an ever-increasing demand for communications bandwidth, there is increasing.interest in optical communications systems, especially fiber optic communications systems. This is because optical fiber is a transmission medium that is well-suited to meet the demand for bandwidth. Optical fiber has a bandwidth which is inherently broader than its electrical counterparts. At the same time, advances in technology have increased the performance, increased the reliability and reduced the cost of the components used in fiber optic systems. In addition, there is a growing installed base of laid fiber and infrastructure to support and service the fiber.
Despite this progress, optical communications is still in many respects very different from its electrical counterparts. Optical communications is inherently optical and relies on the manipulation of lightwave signals. As a result, many of the basic components used in fiber optic systems are unique to the optical domain: lasers, electro-optic and electro-absorptive modulators, photodetectors, lenses, beam splitters, gratings, waveguides, couplers, and wavelength filters to name a few.
Etalons are one basic type of optical component. An etalon basically includes a pair of parallel surfaces, each with a predetermined reflectivity, and a plano-plano cavity between the two surfaces. Light which enters the etalon circulates within the etalon cavity . The resulting interference between multiply reflected waves causes interesting behavior. This behavior can potentially be used for a number of useful applications. For example, etalons have been suggested for use as wavelength filters. They potentially can also be used for dispersion compensation.
A simple etalon only has a few degrees of freedom. The reflectivity of the surface(s) and the free spectral range (determined by the optical length of the cavity) are two major ones. It would be desirable to have etalons in which one or more of these degrees of freedom can be adjusted. The adjustments can be used to compensate for variations in manufacturing and/or to tune the performance of the etalon. Adjustability would also permit the same etalon to be used under a variety of conditions. For example, if a change in a fiber optic system required a corresponding change in the reflectivity of the etalon, it is usually more advantageous to have an etalon with an adjustable reflectivity rather than requiring the replacement of a fixed reflectivity etalon with another fixed reflectivity etalon.
Conventionally, reflective surfaces for etalons are produced by depositing thin layers of dielectric materials onto an optically flat surface, with the thickness and material composition of the layers determining the reflectivity. Conventional processes are capable of yielding dielectric layers of a fairly uniform and predetermined thickness across the surface. As a result, the reflectivity of an etalon's surfaces can be fairly well controlled. However, in such an approach, the layers deposited are uniform across the entire surface and, therefore, the reflectivity is also the same across the entire surface. In order to achieve a reflectivity which varies by location, the layers must be varied in some fashion. However, it can be difficult to do this with repeatable accuracy on an optical surface while also maintaining the optical smoothness of the surface quality.
Thus, there is a need for etalons with variable parameters, such as surface reflectivity.
SUMMARY OF THE INVENTION
The present invention overcomes the limitations of the prior art by providing an etalon in which the reflectivity of a first surface (i.e., the partially reflective surface) varies with position. Thus, this reflectivity can in effect be adjusted by varying the point at which an optical beam is incident upon the etalon. At one point of incidence, the optical beam experiences one reflectivity. At a different point of incidence, the optical beam experiences a different reflectivity.
In one implementation, the etalon includes a transparent body having a first surface and a second surface that are substantially plane-parallel. A second dielectric reflective coating with a reflectivity of substantially 100% is disposed upon the second surface. A first dielectric reflective coating is disposed upon the first surface. The reflectivity of the first reflective coating varies according to location on the first surface. In one embodiment, the first reflective coating includes a top layer of varying physical thickness. For example, the top layer may exhibit a thickness variation of approximately a quarter wave of optical thickness (i.e., from zero to a quarter wave, or from a quarter wave to a half wave, etc.).
Another aspect of the invention concerns the manner for varying the point of incidence of an optical beam on the etalon. In most implementations, the optical beam is received through an input port and directed to the etalon. In one class of devices, the input port and/or etalon are translated with respect to each other, thus varying the point of incidence. In another class of devices, the input port and etalon are in fixed locations relative to each other. However, a beam displacer located in the optical path between the input port and the etalon is used to vary the point of incidence.
In one example, the beam displacer includes a second transparent body having parallel input and output surfaces. The optical beam enters the second transparent body through the input surface and exits the second transparent body through the output surface. Because the two surfaces are parallel, the optical beam exits the body in the same direction as it entered but laterally displaced by some amount. The second transparent body can be rotated about an axis perpendicular to the direction of propagation of the optical beam. Rotating the second transparent body about the axis changes the amount of lateral displacement, thus changing the point of incidence of the optical beam on the etalon.
Another aspect of the invention concerns the manufacture of such etalons. In one approach, the first reflective coating is created (at least in part) by depositing a top layer of uniform thickness and then removing different thicknesses of the top layer at different locations. The remaining top layer has a varying thickness. For example, the uniform top layer may be covered by a layer of photoresist that has a varying thickness. The photoresist layer and top layer are then etched in a uniform etching process. In areas where the photoresist is thick, less of the top layer will be removed. In areas where the photoresist is thin, more of the top layer will be removed. In an alternate approach, the first reflective coating is created by depositing a top layer of varying thickness.
REFERENCES:
patent: 4395769 (1983-07-01), Damen et al.
patent: 5557468 (1996-09-01), Ip
patent: 5828689 (1998-10-01), Epworth
patent: 6115121 (2000-09-01), Erskine
patent: 0 426 357 (1996-04-01), None
patent: 0 997 751 (2000-05-01), None
Cimini, L.J., Jr., et al., “Optical Equalization for High-Bit-Rate Fiber-Optic Communications,”IEEE Photonics Technology Letters, vol. 2, No. 3 (Mar. 1990), pp. 200-202.
Cimini, Leonard J., Jr., et al., “Optical Equalization to Combat the Effects of Laser Chirp and Fiber Dispersion,”Journal of Lightwave Technology, vol. 8, No. 5 (May 1990), pp. 649-659.
French, P.M.W., et al., “Tunable Group Velocity Dispersion Interferometer for Intracavity and Extracavity Applications,”Optics Communications, vol. 57, No. 4 (Mar. 15, 1986), pp. 263-268.
Garthe, D., et al., “Low-loss dispersion equaliser operable over the entire erbium window,”Electronics Letters, vol. 32 (1996), pp. 371-373.
Gnauck, A.H., et al., “8-Gb/s-130 km Transmission Experiment Using Er-Doped Fiber Preamplifier and Optical Dispersion Equalization,”IEEE Transact
Arista Networks, Inc.
Ben Loha
Choi William
Fenwick & West LLP
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