Optical waveguides – Accessories – Attenuator
Reexamination Certificate
2000-08-02
2002-08-13
Sanghavi, Hemang (Department: 2874)
Optical waveguides
Accessories
Attenuator
Reexamination Certificate
active
06434318
ABSTRACT:
BACKGROUND
1. Field of the Invention
The invention relates generally to optical communications, and more specifically to a variable attenuator for removing optical energy from a waveguide in a controllable manner.
2. Description of the Prior Art
The telecommunication industry is making increasing use of optical communication systems for high-bandwidth transmission of voice, video, and data signals. In optical communication systems, it is frequently necessary or desirable to precisely adjust optical signal levels entering various system components. Adjustment of optical signal levels is typically achieved by incorporating variable optical attenuators into the optical circuits. In one example, a variable optical attenuator may be employed to equalize power levels among separate channels of optical circuits implementing wavelength division multiplexing (WDM). Variable optical attenuators may also be employed to avoid exposing optical detectors to excessive signal levels, which may damage the detectors and cause them to become inoperative.
Various references in the prior art disclose attenuators for use in optical circuits. Examples of such attenuators include those described in U.S. Pat. No. 4,762,383 to Yamashita et al. (“Two Dimensional Light Beam Deflectors Utilizing Thermo-optical Effect and Method of Using Same”); U.S. Pat No. 5,881,199 to Li (“Optical Branching Device Integrated with Tunable Attenuators for System Gain/Loss Equalization”), and; U.S. Pat. No. 5,966,493 to Wagoner et al. (“Fiber Optic Attenuators and Attenuation Systems”). The attenuators described in the foregoing references, as well as other prior art attenuators, are known to suffer from operationally significant problems or limitations. These problems include sensitivity to ambient temperature, high power consumption, limited or no adjustability, the occurrence of cross-talk between adjacent channels, high coupling losses, bulkiness and slow responsiveness.
Thus, there is a need in the optical communications art for a variable optical attenuator which overcomes the problems associated with prior art devices.
SUMMARY
In accordance with an embodiment of the invention, a variable optical attenuator is provided having at least one elongated core, a cladding surrounding the core, and a controllable thermal source and a heat sink arranged on opposite sides of the core and defining therebetween a first or vertical axis oriented transversely to the longitudinal axis of the core. The core and cladding collectively form a conventional waveguide structure, which normally confines optical energy propagating along the longitudinal axis of the core by virtue of the difference in refractive indices between the core and cladding. The core and cladding materials are preferably selected such that their thermo-optic coefficients (i.e., dn/dT, where n is the local refractive index and T is temperature) are closely matched within the ambient temperature range of interest. Matching the thermo-optic coefficients of the core and cladding ensures that the waveguide confinement (a function of the difference between the refractive indices of the core and cladding) is substantially invariant with respect to ambient temperature, thereby obviating the need to provide heating or cooling of the waveguide package.
When attenuation of the optical energy propagating along the core is desired, a control signal is applied to the thermal source, which in turn causes a temperature gradient to be developed along the first (vertical) axis extending between the thermal source and the heat sink. The temperature gradient results in a “tilted” or asymmetric refractive index profile within the core wherein the refractive index of the core increases along the first axis from the proximal core-cladding boundary (the boundary nearer to the thermal source) to the distal core-cladding boundary (the boundary more remote from the thermal source). Extraction of optical energy from the waveguide occurs when the local refractive index at the higher-temperature areas of the core (those adjacent the proximal boundary) is depressed below that of the local refractive index of the cladding immediately adjacent to the distal core-cladding boundary. This condition causes at least a portion of the optical energy propagating along the core to be transversely deflected in the direction away from the thermal source (i.e., toward the heat sink). The amount of optical energy extracted from the waveguide is controlled by adjusting the signal (for example, a voltage) applied to the thermal source.
The invention further encompasses an attenuation system, incorporating a variable optical attenuator of the foregoing description, in which a control circuit applies a variable signal to the thermal source in accordance with a desired degree of channel attenuation and with feedback information obtained by monitoring the power level of optical energy traveling through the core. The attenuator and attenuation system of the present invention may be advantageously employed in any number of optical circuit applications where it is necessary or desirable to control optical power transmission within individual optical channels.
REFERENCES:
patent: 3801185 (1974-04-01), Ramaswamy et al.
patent: 3809696 (1974-05-01), Porret et al.
patent: 3809732 (1974-05-01), Chandross et al.
patent: 3953620 (1976-04-01), Chandross et al.
patent: 3993485 (1976-11-01), Chandross et al.
patent: 4648687 (1987-03-01), Yoshida et al.
patent: 4712854 (1987-12-01), Mikami et al.
patent: 5009483 (1991-04-01), Rockwell, III
patent: 5045847 (1991-09-01), Tarui et al.
patent: 5106181 (1992-04-01), Rockwell, III
patent: 5159699 (1992-10-01), de Monts
patent: 5402514 (1995-03-01), Booth et al.
patent: 5544268 (1996-08-01), Bischel et al.
patent: 5874187 (1999-02-01), Colvin et al.
patent: 5932397 (1999-08-01), Mustacich
patent: 5966493 (1999-10-01), Wagoner et al.
patent: 6035083 (2000-03-01), Brennan, III et al.
patent: 6122416 (2000-09-01), Ooba et al.
patent: 6208798 (2001-03-01), Morozov et al.
patent: 6229949 (2001-05-01), Ido et al.
patent: 6236774 (2001-05-01), Lackritz et al.
patent: 6282361 (2001-08-01), Nishimura et al.
patent: 0 412 675 (1991-02-01), None
patent: 0 616 234 (1994-09-01), None
patent: 0 642 052 (1995-03-01), None
patent: 0 689 094 (1995-12-01), None
patent: 0 981 064 (2000-02-01), None
patent: 0987580 (2000-03-01), None
patent: 2 191 603 (1987-12-01), None
patent: WO 92/00185 (1992-01-01), None
patent: WO 98/45759 (1998-10-01), None
“Variable Optical Attenuator Based on a Cutoff Modulator with Tapered Waveguides in Polymers” by Lee et al, IEEE Journal of Lightwave Technology, vol. 17, No. 12.*
P.R. Ashley and E.A. Sornsin, “Doped optical claddings for waveguide devices with electrooptical polymers”, IEEE Photonics Technology Letters, vol. 4, No. 9, Sep. 1992, pp. 1026-1028.
B.L. Booth et al., “Polyguide™ polymeric technology for optical interconnect circuits and components”, SPIE, vol. 3005, pp. 238-251.
W.S. Colburn and K.A. Haines, “Volume hologram formation in photopolymer materials”, Applied Optics, vol. 10, No. 7, Jul. 1971, pp. 1636-1641.
J.E. Marchegiano et al., “Polyguide™ technology for passive optical interconnects”. SPIE, vol. 2690, pp. 361-368.
G.B. McKenna, Chapter 10: Glass formation and glassy behavior, vol. 2: Polymer Properties, C. Booth and C. Price (vol. eds.), Comprehensive Polymer Science: the synthesis, characterization, reactions & applications of polymers, Sir Geoffrey Allen and J.C. Bevington (chairman and deputy chairman of the ed. board), Pergamon Press, Oxford (1989).
Robert H. Wopshall, “MB16. Dry photopolymer film for recording holograms”, abstract of presentation, 1971 Spring Meeting, Journal of the Optical Society of America, vol. 61, 1971, p. 649.
Joshi, et al., “Three Dimensional Optical Circuitry Using Two-Photon-Assisted Polymerization,” Applied Physics Letters, Jan. 11, 1999, vol. 74, No. 2, pp. 170-172.
F.R. Akkari et al., “Thermo-optic mode extinction modulation in polymeric waveguide structures”, Journal of Non-Crystalline Solids, vol.187, 1995, pp. 4
Bischel William K.
Kowalczyk Tony C.
Gemfire Corporation
Haynes Beffel & Wolfeld
Katz Charles B.
Knauss Scott A
Sanghavi Hemang
LandOfFree
Device and method for variable attenuation of an optical... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Device and method for variable attenuation of an optical..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Device and method for variable attenuation of an optical... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2960276