Resonant waveguide-grating filters and sensors and methods for making and using same Number:7,167,615 from the United States Patent and Trademark Office (PTO) owispatent Waveguide grating devices. One includes at least one waveguide having an end, the end having an endface; and a waveguide grating fabricated on the endface, the waveguide grating having at least one waveguide layer and at least one grating layer. The waveguide layer is a separate waveguide from the waveguide on which the waveguide grating is fabricated. Systems for spectral filtering. One, which utilizes a guided-mode resonance effect in a waveguide, includes at least one waveguide having a proximal end and a distal end having an endface; and a waveguide grating fabricated on the end of the waveguide and having a plurality of variable parameters such as permittivity of the grating layer(s) and permittivity of the waveguide layer(s). Methods of forming waveguide grating devices, and methods of detecting one or more parameters of a medium using a waveguide grating device are also disclosed.<H waveguide, Resonant, Resonant, wavegu, 7167615.html, Patent, pto, 7167615

Title: Resonant waveguide-grating filters and sensors and methods for making and using same

Abstract: Waveguide grating devices. One includes at least one waveguide having an end, the end having an endface; and a waveguide grating fabricated on the endface, the waveguide grating having at least one waveguide layer and at least one grating layer. The waveguide layer is a separate waveguide from the waveguide on which the waveguide grating is fabricated. Systems for spectral filtering. One, which utilizes a guided-mode resonance effect in a waveguide, includes at least one waveguide having a proximal end and a distal end having an endface; and a waveguide grating fabricated on the end of the waveguide and having a plurality of variable parameters such as permittivity of the grating layer(s) and permittivity of the waveguide layer(s). Methods of forming waveguide grating devices, and methods of detecting one or more parameters of a medium using a waveguide grating device are also disclosed.

Patent Number: 7,167,615 Issued on 01/23/2007 to Wawro, et al.

Inventors: Wawro; Debra D. (Arlington, TX), Tibuleac; Sorin (Norcross, GA), Magnusson; Robert (Arlington, TX)
Assignee: Board of Regents, The University of Texas System (Austin, TX)

Appl. No.: 09/707,435

Filed: November 6, 2000

Current U.S. Class: 385/37 ; 385/12; 385/38

Current International Class: G02B 6/34 (20060101)

Field of Search: 385/37,38,12

References Cited [Referenced By]

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4533247	August 1985	Epworth
4753529	June 1988	Layton
5216680	June 1993	Magnusson et al.
5291574	March 1994	Levenson et al.
5325386	June 1994	Jewell et al.
5331654	July 1994	Jewell et al.
5343542	August 1994	Kash et al.
5442169	August 1995	Kunz
5598300	January 1997	Magnusson et al.
5633527	May 1997	Lear
5812571	September 1998	Peters
5863449	January 1999	Grabbe
5891747	April 1999	Farah
5978401	November 1999	Morgan
6035089	March 2000	Grann et al.
6055262	April 2000	Cox et al.
6096127	August 2000	Dimos et al.
6191890	February 2001	Baets et al.
6212312	April 2001	Grann et al.
6488414	December 2002	Dawes et al.

Foreign Patent Documents


WO 97/47997	Dec., 1997	WO

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Primary Examiner: Glick; Edward J.
Assistant Examiner: Kao; Chih-Cheng Glen
Attorney, Agent or Firm: Fulbright & Jaworski L.L.P.

Parent Case Text

This application claims priority to provisional patent application Ser. No. 60/163,705 filed Nov. 5, 1999, the entire text of which is specifically incorporated by reference herein without disclaimer. This application also claims priority to provisional patent application Ser. No. 60/164,089 filed Nov. 6, 1999, the entire text of which is specifically incorporated by reference herein without disclaimer.

Claims

What is claimed is:

1. A waveguide grating device, comprising: at least one fiber having an end, the end having an endface; and a guided-mode resonance waveguide grating fabricated on the endface of the at least one fiber, the guided-mode resonance waveguide grating having at least one waveguide layer and at least one grating layer.

2. The device of claim 1, wherein the at least one grating layer comprises a dielectric material.

3. The device of claim 1, wherein the at least one grating layer comprises a polymer.

4. The device of claim 1, wherein the at least one waveguide layer comprises a dielectric material.

5. The device of claim 1, wherein the at least one waveguide layer comprises a polymer.

6. The device of claim 1, wherein the at least one grating layer and the at least one waveguide layer comprise the same layer.

7. The device of claim 1, wherein the at least one grating layer and the at least one waveguide layer comprise different layers in contact with each other.

8. The device of claim 7, wherein the guided-mode resonance waveguide grating further comprises at least a third layer in contact with the at least one waveguide layer, the at least one grating layer, or both the at least one waveguide layer and the at least one grating layer.

9. The device of claim 8, wherein the at least third layer comprises a dielectric material.

10. The device of claim 8, wherein the at least third layer comprises a metal.

11. The device of claim 7, wherein the guided-mode resonance waveguide grating further comprises a third layer in contact with the at least one grating layer.

12. A system comprising: a waveguide grating device, comprising: at least one fiber having a proximal end and a distal end having an endface; and a guided-mode resonance waveguide grating fabricated on the endface of the at least one fiber, the guided-mode resonance waveguide grating having at least one waveguide layer and at least one grating layer, the waveguide grating also having a plurality of parameters including at least one permittivity of the at least one grating layer, permittivity of the at least one waveguide layer, periodic structure of the at least one grating layer, grating fill factor of the at least one grating layer, thickness of the at least one waveguide layer, and thickness of the at least one grating layer.

13. The system of claim 12, further comprising: a source coupled to the proximal end of the at least one fiber for propagating a signal therethrough; wherein after the signal is propagated, it contacts the guided-mode resonance waveguide grating and is reflected from the waveguide grating in whole or in part, or transmitted through the waveguide grating in whole in or in part, depending at least partially upon the plurality of variable parameters.

14. The system of claim 13, wherein the source is a laser.

15. The system of claim 13, wherein the source is a continuous wave source.

16. The system of claim 12, further comprising a photodetector operationally coupled to the at least one fiber.

17. The system of claim 16, wherein the photodetector comprises silicon.

18. The system of claim 12, wherein the at least one grating layer comprises a dielectric material.

19. The system of claim 12, wherein the at least one grating layer comprises a polymer.

20. The system of claim 12, wherein the at least one waveguide layer comprises a dielectric material.

21. The system of claim 12, wherein the at least one waveguide layer comprises a polymer.

22. The system of claim 12, wherein the at least one grating layer and the at least one waveguide layer comprise the same layer.

23. The system of claim 12, wherein the at least one grating layer and the at least one waveguide layer comprise different layers in contact with each other.

24. The system of claim 23, wherein the guided-mode resonance waveguide grating further comprises a third layer in contact with the at least one waveguide layer.

25. The system of claim 23, wherein the guided-mode resonance waveguide grating further comprises a third layer in contact with the at least one grating layer.

26. The system of claim 12, wherein the guided-mode resonance waveguide grating is configured for use as a biosensor.

27. The system of claim 12, wherein the guided-mode resonance waveguide grating is configured for use as an electrochemical sensor.

28. The system of claim 12, wherein the guided-mode resonance waveguide grating is configured for use as an optical sensor.

29. The system of claim 12, wherein the permittivity of the at least one waveguide layer and one of the permittivities of the at least one permittivity of the at least one grating layer are the same.

30. The system of claim 12, wherein the permittivity of the at least one waveguide layer and one of the permittivities of the at least one permittivity of the at least one grating layer are different.

31. A method of forming a waveguide grating device, comprising: providing at least one fiber having an end, the end having an endface; fabricating a guided-mode resonance waveguide grating on the endface of the fiber to form the waveguide grating device, the guided-mode resonance waveguide grating including at least one waveguide layer and at least one grating layer.

32. The method of claim 31, further comprising cleaving the end to form the endface of the at least one fiber.

33. The method of claim 31, wherein the at least one waveguide layer comprises polymer.

34. The method of claim 33, wherein the fabricating comprises dipping the endface of the at least one fiber into a polymer.

35. The method of claim 34, further comprising patterning the at least one waveguide layer.

36. The method of claim 35, wherein the patterning comprises holographic interferometry.

37. The method of claim 35, wherein the patterning comprises photolithography.

38. The method of claim 33, wherein the fabricating comprises spin coating the endface of the at least one fiber with a polymer.

39. The method of claim 31, wherein the at least one grating layer comprises dielectric material.

40. The method of claim 39, further comprising etching the at least one grating layer.

41. The method of claim 31, wherein the at least one waveguide layer is adjacent the at least one grating layer, and the fabricating comprises depositing the at least one waveguide layer on the endface of the at least one fiber by sputtering and coating the at least one waveguide layer with the at least one grating layer.

42. The method of claim 31, wherein the fabricating comprises depositing the at least one waveguide layer on the endface of the at least one fiber by thermal evaporation.

43. The method of claim 31, wherein the fabricating comprises depositing the at least one waveguide layer on the endface of the at least one fiber by electron-beam evaporation.

44. The method of claim 31, wherein the fabricating comprises depositing the at least one waveguide layer on the endface of the at least one fiber by liquid phase epitaxy.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the field of optical filters and sensors. More particularly, it concerns the use of the guided-mode resonance effect occurring through the use of waveguide gratings attached to the endfaces of waveguides such as optical fibers in fields such as optical sensing and communications.

2. Description of Related Art

Resonance anomalies occurring in waveguide gratings (WGGs) have been the subject of current interest for spectral filtering applications [Magnusson and Wang, 1992; Wang and Magnusson, 1993; Wang and Magnusson, 1994; Shin et al., 1998; Tibuleac and Magnusson, 1997; Tibuleac, et al., 2000; Wawro, et al., 2000; Avrutsky, et al., 1989; Boye and Kostuk, 1999; and Rosenblatt, et al., 1997]. Guided-mode resonances (GMRs) occurring in subwavelength WGGs admitting only zero-order propagating diffraction orders yield spectral filters with unique properties such as peak reflectances approaching 100%, narrow linewidths, and low sidebands. Filter characteristics, such as center wavelength, linewidth and sideband behavior, are defined by the waveguide-grating parameters, such as grating period, grating profile, refractive indices, layer thicknesses, and grating fill factor.

Changes in any parameters of the diffractive structure can result in a responsive shift of the reflected or transmitted wavelength band. In general, for spectral filtering applications, the most stable GMR structure is sought to prevent an unwanted resonance shift due to small parameter fluctuations. However, for spectroscopic sensing applications, it is desirable to enhance the resonance instability to create a device that will respond to very small parameter changes. This type of device can be utilized, for example, to detect very small changes in the refractive index or thickness of a media being evaluated in biomedical, industrial or environmental sensing applications. Implementation of the guided-mode resonance effect for optical sensing using planar waveguide grating structures and free-space propagating incident waves has been proposed in previous publications [Wang and Magnusson, 1993; Shin et al., 1998].

Experimental fabrication of waveguide gratings utilizing the GMR effect has primarily been restricted to planar WGGs with an incident beam that is propagating in free space. Experimental results for 1-D grating GMR filters incorporate single layer and multilayer reflection filter designs, including a TM polarization reflection filter utilizing the Brewster effect [Magnusson, et al., 1998]. Double layer GMR filter efficiencies as high as 98.5% have been reported by Liu, et al. for TE incident polarization [Liu, et al., 1998]. GMR crossed grating structures (2-D grating filters) have been experimentally fabricated by Peng and Morris [Peng and Morris, 1996], with a reported filter efficiency of 60%. Norton et al. [Norton, et al., 1998] investigated the dependence of lineshape and tunability in central wavelength and resonant angle position on grating parameters.

Chen [Chen, 1988] reports a theoretical design incorporating a diffraction grating on an optical fiber endface that is used to excite higher order modes in multimode optical fibers. Wang et al. [Wang, et al., 1995] reports a fiber optic proximity sensor design incorporating a diffraction grating on a fiber endface. However, the diffraction gratings reported in these two references do not have waveguide properties, and, consequently, do not exhibit the GMR effect.

A biosensor is an analytical device that integrates an immobilized biologically sensitive material (analyte), such as enzyme, antibody, DNA, cells, or organic molecules, with an electrochemical, piezoelectric, optical or acoustic transducer to convert a biochemical response into a signal for measurement, interpretation, or control. Electrochemical and optical sensors are most widely used. Optical biosensors can provide fast, accurate, and safe analyte detection. Current fiber-optic sensor technology applies fluorescence, total internal reflection, intensity reflection, and surface-plasmon resonances.

The surface plasmon resonance (SPR) effect, is a widely used optical detection method that is highly sensitive to changes in the optical properties (refractive index, monolayer thickness) at the sensor surface. The term surface plasmon (SP) refers to an electromagnetic field charge-density oscillation that can occur at the surface of a conductor. An SP mode can be resonantly excited by parallel-polarized (TM) incident light. Conventional surface plasmon sensors include a prism or diffraction grating for phase matching of the incident and SP waves; commercial systems employ bulk optical components. Fiber-optic SPR sensors have been reported; in these a metal sleeve is deposited on the side of the fiber to which the analyte is contacted. A drawback of the SPR technology is the inherently large linewidth; typically .DELTA..lamda..about.50 nm. Therefore, a sensor utilizing the GMR effect that would provide smaller linewidths would exhibit a significant resolution dynamic-range advantage over SPR sensors.

SUMMARY OF THE INVENTION

In one respect, the invention is a waveguide grating device. The device includes at least one waveguide that has an end, and the end has an endface. As used herein, "waveguide" means any device possessing a structure capable of confining optical energy. As used herein, "endface" means a face on the end of a waveguide that may be oriented at any angle with respect to a wave being propagated through the waveguide. The device also includes a waveguide grating fabricated on the endface of the at least one waveguide. The waveguide grating has at least one waveguide layer and at least one grating layer. As used herein, "grating layer" includes any suitable layer possessing a grating. The gratings on the present grating layers include surface-relief type gratings (e.g., those in which the amplitude of the grating may be modulated) and volume gratings (e.g., those in which the refractive index of the grating may be modulated). The periodicity of the gratings of the present grating layers may be varied and/or their modulation depth (amplitude or index) may be varied. The grating may be nonuniform. As used herein, "waveguide layer" includes any suitable layer possessing a structure capable of confining optical energy. Throughout the present disclosure, including the claims, waveguide layers are distinct from the waveguides on which they are fabricated. The at least one waveguide layer and the at least one grating layer may be the same layer.

In other respects, the at least one waveguide may be a fiber. The at least one waveguide may possess any suitable shape, including elliptical. The shape may be rectangular. The at least one waveguide may be a channel waveguide. The at least one waveguide may be cylindrical in shape. The at least one waveguide may be a slab waveguide. The at least one waveguide may be a ridge waveguide. The at least one grating layer may include a dielectric material. The at least one grating layer may include a glass. The at least one grating layer may include a polymer. The at least one grating layer may include a solid or liquid crystalline material. The at least one grating layer may include a semiconductor material. The at least one grating layer may include a photorefractive material. The at least one waveguide layer may include a dielectric material. The at least one waveguide layer may include a glass. The at least one waveguide layer may include a polymer. The at least one waveguide layer may include a solid or liquid crystalline material. The at least one waveguide layer may include a semiconductor material. The at least one waveguide layer may include a photorefractive material. The at least one grating layer and the at least one waveguide layer may be the same layer. The at least one grating layer and the at least one waveguide layer may be different layers in contact with each other. The waveguide grating may also include at least a third layer in contact with the at least one waveguide layer, the at least one grating layer, or both the at least one waveguide layer and the at least one grating layer. The at least third layer may be a buffer layer, which may be formed from any material suitable for forming either the at least one waveguide layer or the at least one grating layer, and which may be formed using the same techniques that may be used to form either the at least one waveguide layer or the at least one grating layer.

As a buffer layer, the at least third layer may be made of a dielectric and may serve to shape the spectral reflection of the waveguide grating, such as to lower the sidebands, shift the resonance to a desired wavelength, or narrow or widen the linewidth of the GMR. The buffer layer may serve as neither a waveguide layer nor a grating layer. The at least third layer may also be formed of metal, which in some embodiments, may serve a buffer layer intermediate two layers of the waveguide grating that do not otherwise attach well to one another. In other embodiments, the at least third layer (made from either a dielectric or a metal, for example), may be the layer of the waveguide grating in contact with a substance to be sensed/evaluated. In some cases, the substance to be sensed may not attach itself efficiently to dielectric materials composing, at least in part, the waveguide grating. The use of a third layer that is thin may facilitate the attachment of substances being sensed. In still other embodiments, such as biomedical applications, an organic substance being sensed may attach itself only to other organic substances, and not to dielectric or metallic layers of the waveguide grating. In such situations, the use of a third layer (metallic, for example) may be used to which another (fourth) organic layer could be attached. The organic substance being sensed could then attach itself to such a fourth organic layer. The at least third layer may be distinct from both the at least one waveguide and grating layers. The waveguide grating may also include at least a third layer in contact with the at least one grating layer, and may include an arbitrarily large number of layers, each of which may be either additional waveguide layers, additional grating layers, or additional buffer layers.

In another respect, the invention is a system for spectral filtering and the system utilizes a guided-mode resonance effect in a waveguide. The guided-mode resonance effect is described below in greater detail. The system includes a waveguide grating device. The waveguide grating device includes at least one waveguide that has a proximal end and a distal end. The distal end of the at least one waveguide has an endface. The device also has a waveguide grating fabricated on the endface of the at least one waveguide. The waveguide grating has at least one waveguide layer and at least one grating layer. The waveguide grating also has a plurality of variable parameters. The plurality of variable parameters includes at least one permittivity of the at least one grating layer, the permittivity of the at least one waveguide layer, the periodic structure of the at least one grating layer, the grating fill factor of the at least one grating layer, the thickness of the at least one waveguide layer, and the thickness of the at least one grating layer. The at least one waveguide layer and the at least one grating layer may be the same layer. Also, the permittivity of the at least one waveguide layer and one of the permittivities of the at least one permittivity of the at least one grating layer may be the same.

In other respects, the system may also include a source coupled to the proximal end of the at least one waveguide for propagating a signal through the at least one waveguide. After the signal is propagated, it contacts the waveguide grating and is reflected from the waveguide grating in whole or in part, or transmitted through the waveguide grating in whole in or in part, depending at least partially upon the plurality of variable parameters. The source may be a broadband source. The source may be a white light. The source may be a light emitting diode. The source may be a laser. The source may be a continuous wave source. The source may be a pulsed source. The source may be polarized. The source may be unpolarized. The source may be an incoherent light source. The source may be a coherent light source. The source may have wavelengths ranging from the ultraviolet to microwave range (on the order of 100 nm to the order of tens of centimeters).

In still other respects, the system may also include a photodetector operationally coupled to the at least one waveguide. As used herein, if a first device is "operationally coupled" to a second device, one or more mediums or devices may separate the first and second devices such that the first and second devices are not in physical contact with each other. The photodetector may include silicon. The photodetector may include germanium. The photodetector may include indium gallium arsenide. Silicon, germanium, and indium gallium arsenide are examples of semiconductor detectors that may serve as photodetectors operationally coupled to waveguides of the present devices. Semiconductor detectors are power detectors commonly used in the detection of continuous wave sources ranging from about 160 nm to about 1800 nm wavelengths (e.g., visible range to infrared). The photodetector may include a pyroelectric material. The photodetector may include the human eye.

In other respects, the at least one waveguide may be a fiber. The at least one waveguide may be rectangular in shape. The at least one waveguide may be a channel waveguide. The at least one waveguide may be cylindrical in shape. The at least one waveguide may be a slab waveguide. The at least one waveguide may be a ridge waveguide. The at least one grating layer may include a dielectric material. The at least one grating layer may include a glass. The at least one grating layer may include a polymer. The at least one grating layer may include a liquid or solid crystalline material. The at least one grating layer may include a semiconductor material. The at least one grating layer may include a photorefractive material. The at least one waveguide layer may include a dielectric material. The at least one waveguide layer may include a glass. The at least one waveguide layer may include a polymer. The at least one waveguide layer may include a liquid or solid crystalline material. The at least one waveguide layer may include a semiconductor material. The at least one waveguide layer may include a photorefractive material. The at least one grating layer and the at least one waveguide layer may be the same layer. The at least one grating layer and the at least one waveguide layer may be different layers in contact with each other. The waveguide grating may also include a third layer in contact with the at least one waveguide layer. The third layer may be a buffer layer, which may be formed from any material suitable for forming either the at least one waveguide layer or the at least one grating layer, and which may be formed using the same techniques that may be used to form either the at least one waveguide layer or the at least one grating layer. The third layer may be distinct from both the at least one waveguide and grating layers. The plurality of variable parameters may include the thickness of the third layer. The waveguide grating may also include a third layer in contact with the at least one grating layer, and may include an arbitrarily large number of layers, each of which may be either additional waveguide layers, additional grating layers, or additional buffer layers.

In still other respects, the system may include a sensor operationally coupled to the waveguide grating device. The sensor may be an electrochemical sensor. The sensor may be an optical sensor. The sensor may be a surface plasmon sensor. The sensor may be a fluorescence sensor. The sensor may be an evanescent wave sensor.

In another respect, the invention is a waveguide grating device that includes at least one waveguide through which a signal having at least one wavelength may be propagated. The at least one waveguide has an end, and the end has an endface. The device also includes a waveguide grating fabricated on the endface of the at least one waveguide. The waveguide grating has at least one waveguide layer and at least one grating layer. The waveguide grating also has a plurality of variable parameters. The plurality of variable parameters includes at least one permittivity of the at least one grating layer, the permittivity of the at least one waveguide layer, the periodic structure of the at least one grating layer, the grating fill factor of the at least one grating layer, the thickness of the at least one waveguide layer, and the thickness of the at least one grating layer. The periodic structure of the at least one grating layer has a period less than the at least one wavelength of the signal. The at least one waveguide layer and the at least one grating layer may be the same layer. Also, the permittivity of the at least one waveguide layer and one of the permittivities of the at least one permittivity of the at least one grating layer may be the same.

In another respect, the invention is a waveguide grating device that includes at least a first waveguide having a first end. The first end has a first endface. The waveguide grating device also includes a first waveguide grating fabricated on the first endface. The first waveguide grating has at least a first waveguide layer and at least a first grating layer. The at least first waveguide layer and the at least first grating layer may be the same layer. The waveguide grating device also includes at least a second waveguide having a second end. The second end has a second endface. The waveguide grating device also includes a second waveguide grating fabricated on the second endface. The second waveguide grating has at least a second waveguide layer and at least a second grating layer. The at least second waveguide layer and the at least second grating layer may be the same layer.

In other respects, the at least first and second waveguides may be fibers.

In another respect, the invention is a method of forming a waveguide grating device that includes providing at least one waveguide that has an end, and the end has an endface; and fabricating a waveguide grating on the endface of the at least one waveguide to form the waveguide grating device.

In other respects, the method may also include cleaving the end to form the endface of the at least one waveguide. The method may also include polishing the end to form the endface of the at least one waveguide.

In still other respects, the waveguide grating may include at least one layer of polymer. The fabricating may include dipping the endface of the at least one waveguide into the polymer. The method may also include heating the at least one layer of polymer. The method may also include patterning the at least one layer of polymer. The patterning may include holographic interferometry, photolithography, electron-beam lithography, laser-beam lithography, or contact printing the at least one layer of polymer to form a grating. The fabricating may include spin coating the endface of the at least one waveguide with a polymer.

In still other respects, the waveguide grating may include at least one layer of photosensitive glass or at least one layer of dielectric. The method may also include etching the at least one layer of dielectric to form a grating.

In other respects, the waveguide grating may include at least a first layer and at least a second layer adjacent the at least first layer. The fabricating may include depositing the at least first layer on the endface of the at least one waveguide by sputtering and coating the at least first layer with the at least second layer. The fabricating may also include depositing the at least first layer on the endface of the at least one waveguide by thermal evaporation. The fabricating may include depositing the at least first layer on the endface of the at least one waveguide by electron-beam evaporation. The fabricating may also include depositing the at least first layer on the endface of the at least one waveguide by molecular beam epitaxy. The fabricating may also include depositing the at least first layer on the endface of the at least one waveguide by metal-organic chemical vapor deposition. The fabricating may include depositing the at least first layer on the endface of the at least one waveguide by chemical vapor deposition. The fabricating may include depositing the at least first layer on the endface of the at least one waveguide by liquid phase epitaxy.

In another respect, the invention is a method of detecting at least one parameter of a medium. As used herein, "medium" means material under investigation in solid, liquid, plasma, or gas form. The method includes providing a waveguide grating device. The device includes at least one waveguide that has an end, and the end has an endface. The device also includes a waveguide grating fabricated on the endface of the at least one waveguide. The waveguide grating has at least one waveguide layer and at least one grating layer. The at least one waveguide layer and the at least one grating layer may be the same layer. The method also includes contacting the waveguide grating with a medium, propagating a signal having at least one signal attribute through the at least one waveguide such that the signal contacts the waveguide grating and the at least one signal attribute is modified, and comparing the modified signal attribute to a known signal attribute to detect the at least one parameter of the medium. As used herein, "signal attribute" means power of a reflected or transmitted wave at a specific wavelength, a specific spectral range, or a specific polarization.

In other respects, the at least one signal attribute may be the spectral content of the signal. The at least one signal attribute may be the intensity of the signal. The at least one signal attribute may be the polarization of the signal. The at least one parameter of the medium may be the presence or absence of a substance. The at least one parameter of the medium may also be the quantity of a substance. The at least one parameter of the medium may be the refractive index of the medium. The at least one parameter of the medium may be the thickness of the medium. The medium may include a first parameter and a second parameter, and the comparing may include comparing the modified signal attribute to a known signal attribute to detect both the first and second parameters.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawings form part of the present specification and are included to further demonstrate certain aspects of the present invention. The invention may be better understood by reference to one or more of these drawings in combination with the detailed description of specific embodiments presented herein.

FIGS. 1 and 2. An embodiment of one of the present devices useful as a reflection filter designed for an ionic self assembled polymer waveguide layer having a thickness d.sub.2 and a photoresist grating layer having a thickness d.sub.1 recorded on the top surface. TE polarization at normal incidence, n.sub.C=1.0, n.sub.1H=1.632, n.sub.1L=1.0, n.sub.2=1.8, n.sub.S=1.45, d.sub.1=200 nm, d.sub.2=280 nm, .LAMBDA.=515 nm, fill factor f=0.5. As depicted, f.LAMBDA. is the width of the high-index region of the grating layer.

FIG. 3. Transmission measurement at normal incidence performed with a broadband source using an embodiment of one of the present devices that has separate waveguide and grating layers.

FIGS. 4 and 5. Calculated TE and TM-polarization spectral response (FIG. 4) of an embodiment of one of the present devices that is useful as a filter and has separate waveguide and grating layers (FIG. 5) with the following parameters: .LAMBDA.0.51 .mu.m, d.sub.1=0.4 .mu.m, d.sub.2=0.18 .mu.m, n.sub.H=1.63, n.sub.L=1.0, n.sub.2=1.9, and n.sub.S=1.45.

FIGS. 6 and 7. Calculated (FIG. 6) and measured (FIG. 7) spectral shift of one embodiment of the present waveguide gratings on a planar substrate, before and after immersion in water. Physical parameters are as follows: grating period .LAMBDA.=510 nm, fill factor f=0.5, n.sub.2=2.0, d.sub.2=200 nm, d.sub.1=300 nm, n.sub.H=1.62, n.sub.L=1.0 (air) and n.sub.L=1.33 (water), TE polarization.

FIG. 8. Test setup used to obtain transmission measurements for the present devices used as sensors.

FIG. 9. Schematic of a test setup to measure properties of light (spectrum, polarization, and/or power) from the present waveguide gratings.

FIG. 10. Single beam holographic setup using ultraviolet laser to record grating pattern on optical fiber endfaces coated with photosensitive polymer.

FIG. 11. Raw transmission data measured for an embodiment of one of the present devices having separate waveguide and grating layers that are fabricated using Si3N4 and photoresist, with the following parameters: grating period .LAMBDA.=510 nm, thickness of the photoresist grating layer, d.sub.1=300 nm, thickness of the waveguide layer (Si3N4), d.sub.2=200 nm, low refractive index of the grating layer, which is the same as the refractive index of the cover region (n.sub.C of air), n.sub.L=10.0, high refractive index of the grating layer, n.sub.H=1.62, refractive index of the waveguide layer (Si3N4), n.sub.2=1.85, refractive index of the substrate (silica optical fiber), n.sub.F=1.45.

FIGS. 12 and 13. Thickness sensing in water. TE polarization spectral response of an embodiment of the present devices useful as fiber endface reflection filter (FIG. 13). The peak wavelength shifts from 749.6 nm to 751.5 nm and 754.1 nm, as 20 nm and 40 nm of material are added, respectively. The physical parameters of the waveguide grating are as follows (FIG. 12): grating period, .LAMBDA.=454 nm, thickness, d=371 nm, refractive indices of the grating layer, n=2.55 (ZnSe) and n=1.33 (water). The refractive index of the material to be detected is n=1.4.

FIGS. 14 and 15. Refractive index sensing in liquid. TE polarization spectral response of an embodiment of the present devices useful as fiber endface reflection filter (FIG. 15). The peak wavelength shifts from 749.6 nm to 752.2 nm and 754.8 nm, as the refractive index of the detected liquid varies from 1.33 to 1.34 and 1.35, respectively. The physical parameters of the waveguide grating are as follows (FIG. 14): grating period, .LAMBDA.=454 mm, thickness, d=371 nm, refractive indices of the grating layer, n=2.55 (ZnSe) and n=1.33-1.35 (liquid being detected).

FIGS. 16 and 17. Thickness sensing in air. TE polarization spectral response of an embodiment of the present devices useful as fiber endface reflection filter (FIG. 17). The peak wavelength shifts from 1.554 .mu.m to 1.564 .mu.m and 1.575 .mu.m, as 20 nm and 40 nm of material are added, respectively. The physical parameters of the waveguide grating are as follows (FIG. 16): grating period, .LAMBDA.=0.907 nm, thickness, d=1.1 .mu.m, refractive indices of the grating layer, n=3.2 (Silicon) and n=1.0 (air). The refractive index of the material to be detected is n=1.4.

FIGS. 18 and 19. Thickness sensing in air. TE polarization spectral response of an embodiment of the present devices useful as fiber endface reflection filter (FIG. 19). Approximately 1 nm shift for 10 nm of adhered material (n=1.4). The physical parameters of the waveguide grating are as follows (FIG. 18): grating period .LAMBDA.=0.349 .mu.m, f=0.5, d.sub.1=0.12 .mu.m, d.sub.2=0.15 .mu.m, n.sub.H,1=1.45 (SiO.sub.2), n.sub.2=2.0 (HfO.sub.2), n.sub.L,1=n.sub.C=1.0, n.sub.S=1.45.

FIGS. 20 and 21. Refractive index sensing in water. Approximately 3.1 nm shift for 0.01 change in refractive index (FIG. 21). The peak wavelength shifts from 807.4 nm to 810.1 nm and 813.3 nm, as the refractive index of the detected liquid varies from 1.34 to 1.35 and 1.36, respectively. Linewidth=0.8 nm. The physical parameters of the waveguide grating are as follows (FIG. 20): grating period .LAMBDA.=0.530 .mu.m, f=0.5, d=0.470 .mu.m, n.sub.H=2.0 (Si.sub.3N.sub.4), n.sub.S=1.45, n.sub.L=n.sub.C=1.34, 1.35, and 1.36.

FIG. 22. Plot of peak wavelength shift for large dynamic range sensing. Response is linear and sensitivity is retained for a refractive index range from 1.3 to 1.7. Corresponds to structure described in FIG. 20.

FIG. 23. Scanning electron micrograph of 800 nm period photoresist grating recorded on a multimode fiber endface 800 times magnification.

FIG. 24 (see Appendix). Flow chart of a genetic algorithm using rigorous coupled-wave analysis for merit function evaluation [77]. The program uses the library PGAPACK [110] to perform specific genetic algorithm operations such as mutation, crossover, selection, ranking, and generation of new chromosomes.

FIG. 25 (see Appendix). Crossover and mutation operations illustrated for chromosomes composed of 6 genes encoded as real numbers. In the 3 types of crossover operations shown here genes of the parent chromosomes (white and grey) are exchanged to yield new chromosomes. In the mutation operation, one or more genes are randomly changed from one value to another.

FIGS. 26A and 26B (see Appendix). Example of a diffractive structure consisting of two gratings in two separate layers, with physical parameters shown in FIG. 26A and corresponding chromosome represented in FIG. 26B. The chromosome is a candidate solution in the optimization process. A set of chromosomes forms a population. The total population of chromosomes at a given iteration is called a generation. In this case, the parameters to be optimized are the grating period .LAMBDA., the thicknesses d.sub.1, d.sub.2, refractive indices, n.sub.L,1, n.sub.H,1, n.sub.L,2, n.sub.H,2, and relative positions of the high-refractive index materials within a grating period, x.sub.L,1, x.sub.H,1, x.sub.L,2, and x.sub.H,2.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Disclosed herein is a new GMR device that includes a waveguide having an end that has an endface and a waveguide grating fabricated on the endface. As defined above, waveguides include fibers such as optical, single-mode, multi-mode, polarization-maintaining, graded-index, step-index, nonlinear core (either with or without embedded electrodes), polymer, phototonic crystal waveguides and fibers, glass, crystal-core, and chalcogenide fibers; waveguides with shapes such as rectangular, elliptical and cylindrical; slab waveguides and ridge waveguides. The waveguide grating is made up of at least one waveguide layer and at least one grating layer, and the grating and waveguide layers may be the same layer. The layers, if separate, may be arranged in any suitable fashion with respect to each other and the waveguide. A source may propagate an incident signal, such as a broad-spectrum signal, through the waveguide, the waveguide may guide the signal to the waveguide grating, and the waveguide grating, depending on its design, may filter the signal to reflect or transmit a desired spectral band of the signal. Used as a filter, characteristics such as center wavelength (the wavelength at which a peak or a notch is exhibited in the spectrum of the reflected or transmitted wave), linewidth (the width of the spectral peak or notch) and sideband (reflectance or transmittance in the spectral region outside the peak or notch spectral region) are defined by certain waveguide-grating parameters, such as the periodic structure of the grating layer(s), the refractive indices of the layer(s) forming the waveguide grating, the thicknesses of those layers, and the fill factor of the grating layer(s). The present waveguide grating devices provide a new class of diffractive optical elements as a result of the GMR spectral filters resulting therefrom. Potential applications for the present devices include use as spectral filters for use in fiber optic systems (such as communications), as sensors for high resolution chemical or biochemical sensing, and as integrated polarized reflectors for fiber lasers.

The phrase guided-mode resonance (GMR) refers to a rapid variation in the diffraction efficiency spectrum of waveguide gratings generally, and those described herein. A resonance occurs when an incident wave from a propagated signal that may include more than one wave is phase matched to a leaky guided mode allowed by a waveguide grating. Phase matching may be accomplished through a diffraction grating, which is inherently polarization sensitive. Resonances occurring in subwavelength waveguide gratings (i.e., waveguide gratings having a grating layer(s) with a period, .LAMBDA., less than the wavelength, .lamda., of the input wave admitting only zero-order propagating diffraction orders, where .LAMBDA.<.lamda./n.sub.s, .lamda./n.sub.c where .lamda./n.sub.s and .lamda./n.sub.c are the wavelengths in the substrate and cover regions respectively, [ie. regions of propagation of the incident and emerging waves]; .LAMBDA. is the wavelength in vacuum, and n.sub.s and n.sub.c are the refractive indices of the substrate and cover regions, respectively) allow complete energy exchange between the forward and backward propagating zero-order waves. In this case, all higher order diffracted waves are evanescent. In fact, when these evanescent waves correspond to waveguide modes supportable by the WGG, the resonance occurs.

Considering a single layer WGG, for a resonance to occur, the average refractive index of the grating layer, n.sub.av, is required to be higher than the refractive index of the surrounding cover and it is required to be higher than the refractive index of the substrate. For a multi-layer structure, one of the layers in the stack needs to meet this requirement. The average refractive index of the grating layer may be calculated using the following equation: n.sub.av=[n.sub.L.sup.2+f(n.sub.H.sup.2-n.sub.L.sup.2)].sup.1/2

where n.sub.H and n.sub.L are the refractive indices of the high and low-refractive index regions of the grating layer, and f is the fill factor of the grating layer (i.e. the fraction of the grating period occupied by the high-refractive index material). The efficient energy exchange occurs within small ranges of at least one physical parameter of the device, such as the angle of incidence of the input wave or signal, wavelength, thickness of the layers utilized, period of the grating layer(s), and the refractive indices of the grating and waveguide layers and surrounding adjacent media n.sub.f and n.sub.c.

Integration of resonant WGGs with thin-film coatings may provide low sidebands surrounding the resonance regime, achieving high-quality near ideal filter properties. Such filters are disclosed in U.S. Pat. No. 5,598,300 to Magnusson and S. S. Wang (1997) (hereinafter the '300 patent), which is hereby expressly incorporated herein by reference in its entirety. Generic GMR filters and their many applications are described in U.S. Pat. No. 5,216,680 issued to R. Magnusson and S. S. Wang.

Modeling of the Present Waveguide Grating Devices

Rigorous coupled wave analysis (RCWA) [Gaylord and Moharam, 1985; Moharam, et al., 1995a; and Moharam, et al., 1995b], all three of which are expressly incorporated herein by reference, is a numerical tool that may be used to accurately model the present waveguide grating devices based on the use of certain known parameters of the waveguide grating. "Modeling," as used herein, means to determine the spectral characteristics, i.e., the fraction of the incident wave power that is reflected and transmitted through a waveguide grating device at any wavelength of interest. This includes determining the GMR spectral locations, shape, and width of GMR peaks or notches, and reflectance and transmittance in the sidebands (i.e. outside the resonance region). For a rigorous analysis and development of these theories see Magnusson and Wang U.S. Pat. No. 5,216,680, which is hereby expressly incorporated herein by reference in its entirety, and [Wang and Magnusson, 1995], which is also hereby expres