Optical waveguides – Having particular optical characteristic modifying chemical... – Of waveguide core
Reexamination Certificate
2000-12-08
2003-03-04
Bovernick, Rodney (Department: 2874)
Optical waveguides
Having particular optical characteristic modifying chemical...
Of waveguide core
C385S040000, C385S041000, C385S125000, C385S141000
Reexamination Certificate
active
06529676
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to optical communications system having waveguides or waveguide devices with tunable properties.
2. Discussion of the Related Art
As the prevalence of optical communications systems has increased, numerous techniques for modifying and/or controlling propagation of light through waveguides have been developed. Such techniques have included incorporation of photosensitive materials into the core of single mode optical fibers, to allow formation of periodic refractive index modulations. Such modulations enabled fiber Bragg gratings (FBG) as well as long period gratings (LPG), which have become widely used for a variety of applications, including reflection of selected frequency bands and gain flattening. Continued research led to so-called microstructured fiber, in which the fiber contains axially oriented elements—typically capillary air holes—that provide a variety of useful properties such as photonic crystal characteristics, supercontinuum generation, and soliton generation. (See, e.g., B. J. Eggleton et al., “Cladding-Mode-Resonances in Air-Silica Microstructure Optical Fibers,”
Journal of Lightwave Technology
, Vol. 18, No. 8 (2000);.J. C. Knight et al., “Anomalous Dispersion in Photonic Crystal Fiber,”
IEEE Photonics Technology Letters
, Vol. 12, No. 7 (2000); J. Ranka et al., “Visible continuum generation in air-silica microstructure optical fibers with anomalous dispersion at 800 nm,”
Optics Letters
, Vol. 25, No. 1 (2000); and U.S. Pat. Nos. 5,907,652 and 6,097,870.) Such microstructured fiber also allows adjustment of effective refractive index profiles to attain, for example, decoupling of interior cladding modes from the influence of the material surrounding the fiber. Combinations of microstructured fiber with in-fiber gratings have also shown interesting results. (See, e.g., B. J. Eggleton et al., “Grating Resonances in Air-Silica Microstructured Optical Fibers,”
Optics Letters
, Vol. 24, No. 21, 1460 (1999); P. S. Westbrook et al., “Cladding-Mode Resonances in Hybrid Polymer-Silica Microstructured Optical Fiber Gratings,”
IEEE Phot. Tech. Lett
., Vol. 12, No. 5, 495 (2000).)
More recent efforts have focused on attaining real-time tunability of the properties of gratings and/or microstructured fiber. For example, in J. A. Rogers et al., “Temperature stabilised operation of tunable fibre grating devices that use distributed on-fiber thin film heaters,”
Electronics Letters
, Vol. 35, No. 23, 2052 (1999), the authors describe a technique for thermally tuning the properties of fiber Bragg gratings or long period gratings. Specifically, a thin-film resistive heater is formed on the exterior of the fiber, and electrical control is used to tune and stabilize the grating properties. In Jeong et al., “Electrically Controllable Long-Period Liquid Crystal Fiber Gratings,”
IEEE Phot. Tech. Lett
., Vol. 12, No. 5, 519 (2000), the authors describe a fiber having a liquid crystal-filled core. A combed electrode, i.e., an electrode having periodic gaps, is used to selectively align the liquid crystals at the periodic distance of the electrode. The result is essentially a long period grating capable of being turned on and off (see
FIG. 2
of the paper). In another approach, reflected in K. Takizawa et al., “Polarization-independent optical fiber modulator by use of polymer-dispersed liquid crystals,”
Applied Optics
, Vol. 37, No. 15, 3181 (1998), a ferrule, which has polymer-dispersed liquid crystals therein, is placed between two fibers to provide adjustable modulation of a propagating signal.
A variety of references report use of a second material either within a microstructured fiber or surrounding a fiber, where the second material is capable of undergoing a bulk refractive index change in response to external stimuli, e.g., heat. For example, in U.S. Pat. No. 6,058,226 to Starodubov, a fiber with a LPG therein is surrounded by a second material that undergoes a bulk index change in response to applied or encountered external stimuli. The resulting changes in the bulk refractive index of this second material alters the propagation and coupling of the core/cladding modes. U.S. Pat. No. 5,361,320 to Liu et al. discloses a fiber having a liquid crystal core or cladding, similar to what is disclosed in Jeong et al.,
supra
. Liu discloses adjusting the orientation of all the liquid crystals, by electrical control, to provide a bulk index change in the material, this change altering the properties of the fiber core or cladding. In A. A. Abramov et al., “Electrically Tunable Efficient Broad-Band Fiber Filter,”
IEEE Phot. Tech. Lett
., Vol. 11, No. 4, 445 (1999), a microstructured fiber having a long period grating formed-therein is imbibed with, or surrounded by, a polymer having a temperature-sensitive-index of refraction. A resistive heating film is formed on the exterior of the fiber, and allows tuning of the bulk refractive index of the polymer. By changing the index of the polymer, the properties of the LPG, e.g., the resonance wavelength, can be controlled. Co-assigned U.S. Pat. No. 6,111,999 to Espindola et al. uses a similar approach. Specifically, a fiber having a grating written therein is provided with one or more variable refractive index regions. These regions contain a material having an adjustable bulk refractive index, such that adjusting the index of the regions provides a desired change in the properties of the grating.
While these numerous approaches to tunable and/or microstructured fiber and fiber gratings exist, further improvements and enhancements are always desired.
SUMMARY OF THE INVENTION
The invention provides a unique waveguide structure in which the waveguide contains individual scattering elements that are capable of being tuned to provide local refractive index variations, e.g., on a micron scale—which is on the order of wavelengths typically used for communication system. (Micron scale indicates that the individual elements provide tunable local index changes covering a distance of 0.1 to 10 &mgr;m.) For example, for a system containing a source that launches one or more wavelengths into the waveguide, the scattering elements will have a size typically ranging from 0.1 to 10 times such wavelengths, typically 0.3 to 3 times such wavelengths. (Generally, the tunable local index changes are made on a length scale that provides the maximum scattering effect at the signal system's wavelength of interest.)
According to the invention, the waveguide contains a core region, a cladding region, and a solid or liquid material having the tunable scattering elements dispersed therein, where the material is disposed within the core and/or cladding regions, and/or on the exterior of the cladding region. Useful scattering elements include, for example, liquid crystals dispersed in a polymer (polymer-dispersed liquid crystals—PDLC) or electrophoretic particles dispersed in a liquid medium. (As used herein, a material having tunable scattering elements dispersed therein indicates, for example, any mixture, dispersion, suspension, solution, etc. that provides a material with distinct tunable elements or regions that provide local variation in refractive index.)
As noted above, several groups have explored the use in waveguides of materials capable of having their refractive index varied by external controls. However, these approaches, reflected for example in U.S. Pat. No. 6,058,226, U.S. Pat. No. 5,361,320, A. A. Abrambv et al.,
supra
, and U.S. Pat. No. 6,111,999, rely on changing the bulk refractive index of the entire region of the waveguide in which the material is located. By contrast, the invention uses individual scattering elements that provide tunable local variations in the refractive index, such that the nature of the waveguide's scattering cross-section can be adjusted. For example, it is possible to tune the scattering elements such that their refractive index (as encountered by propagating light) is substantially matched to the surrounding material in which th
Eggleton Benjamin John
Mach Peter
Rogers John A.
Westbrook Paul Stephen
Wiltzius Pierre
Bovernick Rodney
Gurey Stephen M.
Lucent Technologies - Inc.
Rahll Jerry T
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