Abstract: A method for imprinting a plurality of slanted Bragg gratings into a photosensitive optical fiber by exposure of said fiber to a pattern of light shaped in space and/or time and of suitable wavelenth is presented. According to the invention a basic slanted Bragg grating of a determined period is imprinted into said fiber, while, simultanously, a periodic apodisation function is applied to said single slanted Bragg grating. In its preferred embodiment the imprinting light pattern is generated by a phase mask from a UV laser, the phase mask being dithered during the imprinting.

Abstract: A method for writing a Bragg grating in a waveguide comprises the steps of placing the waveguide in a writing position in which the waveguide extends essentially along one axis; generating a beam of ultraviolet radiation; executing a first and a second scan with the said beam along the waveguide through a phase mask, in such a way as to generate interference fringes capable of modifying the refractive index along the said waveguide in a predetermined way; moving the phase mask, during the first or the second scan, with an oscillatory motion about one of its equilibrium positions and along a direction lying at an angle of less than 90° to the axis of the said waveguide, in such a way as to produce, in this scan, an essentially zero envelope of the refractive index; and varying the intensity of the energy of the ultraviolet radiation in a controlled way along the waveguide during the first and the second scan, for example by controlling the scanning velocity.

Abstract: A holographic recording medium comprising an amorphous host material which undergoes a phase change from a first to a second thermodynamic phase in response to a temperature rise above a predetermined transition temperature; a plurality of photo-sensitive molecular units embedded in the host material and which can be orientated in response to illumination from a light source; whereby said molecular units may be so orientated when said host material is at a temperature equal to or above said transition temperature but retain a substantially fixed orientation at temperatures below said transition temperature.

Abstract: The present relates to a method of changing the index of refraction of a optical fiber waveguide having a photosensitive core region fiber. The method includes providing a laser beam having a wavelength that will interact with the photosensitive core to change the index of refraction of the photosensitive core. The method uses a shadow mask and a lens. The lens is positioned to direct the portion of the laser beam passing through and the opening in the shadow mask onto the photosensitive core region of the optical waveguide fiber.

Abstract: The optical article of the invention, e.g., holographic recording medium or polymeric waveguide, is formed by mixing a matrix precursor and a photoactive monomer, and curing the mixture to form the matrix in situ. The reaction by which the matrix precursor is polymerized during the cure is independent from the reaction by which the photoactive monomer is polymerized during writing of data. In addition, the matrix polymer and the polymer resulting from polymerization of the photoactive monomer are compatible with each other. Use of a matrix precursor and photoactive monomer that polymerize by independent reactions substantially prevents cross-reaction between the photoactive monomer and the matrix precursor during the cure and inhibition of subsequent monomer polymerization. Use of a matrix precursor and photoactive monomer that result in compatible polymers substantially avoids phase separation. And in situ formation allows fabrication of articles with desirable thicknesses.

Abstract: There are disclosed the following three types of optical recording film: (1) an optical recording film comprising a gel having a network structure of an inorganic substance and a polymer which is from a photopolymerizable compound (A) and present in the network structure in the gel, said gel containing an optical recording-induced difference in the network structure. (2) an optical recording film, which consists essentially of a porous gel having a network structure of an inorganic substance, the porous gel containing recording-induced porosity differences in the network structure. (3) an optical recording film which consists essentially of a porous gel having a network structure of an inorganic substance or a gel obtained by densification of the porous gel, the porous gel or the gel having a recording-induced concavo-convex form on the surface thereof.

Abstract: Optical code division multiple access (OCDMA) coder:decoder gratings have been fabricated. The modulated refractive index profile that makes up the OCDMA coder:decoder grating incorporates changes in polarity between OCDMA chips by discrete phase shifts, thereby to provide bipolar coding through phase modulation. (In another embodiment quadrupolar coding is achieved). For NRZ modulation, each grating section is either in phase with, or has a predetermined phase shift relative to, the preceding grating section, depending on whether the OCDMA signature has a change in polarity between chips. RZ modulation is also possible. Results are presented from specific examples of bipolar OCDMA with NRZ modulation, which show higher data rates (10 Gbit/s), shorter chip-lengths (6.4ps) and far longer code sequences (63 bits) than previously demonstrated. Other embodiments relate to optical packet switching, for example using the Internet Protocol (IP) or Asynchronous Transfer Mode (ATM).

Abstract: Advantageous methodologies are disclosed for embedding periodic patterns in optical waveguide elements such as optical fibers. Polarization independence in an elongated waist region of a coupler can be established by measuring polarization characteristics during fusion and elongation, and controlling the heating and stretching to impart a cross-sectional shape, such as a hybrid dumbbell-ellipsoid produces a polarization insensitive drop wavelength. Alternatively, or additionally, polarization dependence can be minimized by angular deformation of the elements along its light transmissive axis. In addition, an element of relatively low photosensitivity is held in an hydrogen or deuterium environment pressurized to about 1000 to 5000 psi. While the environment is pressurized, a scanning UV beam is transmitted through a photomask and impinges on the coupler waist. In writing the grating, the in-diffused gas is constantly replenished, enabling the grating to grow.

Abstract: The optical article of the invention, e.g., holographic recording medium or polymeric waveguide, is formed by mixing a matrix precursor and a photoactive monomer, and curing the mixture to form the matrix in situ. The reaction by which the matrix precursor is polymerized during the cure is independent from the reaction by which the photoactive monomer is polymerized during writing of data. In addition, the matrix polymer and the polymer resulting from polymerization of the photoactive monomer are compatible with each other. Use of a matrix precursor and photoactive monomer that polymerize by independent reactions substantially prevents cross-reaction between the photoactive monomer and the matrix precursor during the cure and inhibition of subsequent monomer polymerization. Use of a matrix precursor and photoactive monomer that result in compatible polymers substantially avoids phase separation. And in situ formation allows fabrication of articles with desirable thicknesses.

Abstract: The present invention provides a manufacturing method capable of obtaining minute structures. In order to achieve this, as shown in FIG. 1, a process target material (108) is exposed and the shape thereof is changed by relatively shifting a laser beam or electronic beam (101) against such process target material (108) and simultaneously repeating irradiation in an intermittent manner. Here, a plurality of minute convex or concave shapes are formed on the process target material (108) by employing a branching element (103) for branching a single beam (108) into a plurality of beams (106, 107); a parallel element (104) for converting said plurality of beams into beams which respectively advance in parallel; and a condensing element (105) for condensing the plurality of beams to the process target material (108) and generating a plurality of minute spots thereon.

Abstract: A method for manufacturing an optical waveguide refractive index grating having a desired grating pitch A. The method includes the step of providing a photosensitive waveguide and a writing beam of actinic radiation, the writing beam having an intensity. The waveguide is translated relative to the writing beam at a velocity v(t). The intensity of the writing beam is modulated as a function of time at a frequency f(t), wherein 1 v ⁡ ( t ) f ⁡ ( t ) ≈ Λ .

Abstract: A method of fabricating a grating in a planar optical device by fabricating a surface grating or by photoinscription. For surface gratings, a method comprises providing a substrate material that includes a substrate layer, a first core layer, a second core layer, and a first photoresist layer. An exposure of a grating and a plurality of alignment marks is formed onto the substrate material. The second core layer is etched to form the grating in the second core layer. A second photoresist layer is deposited on the substrate material that remains after the first etching. An exposure of a waveguide pattern is formed in the first core layer. The first core layer is etched to define a first waveguide in the first core layer, where the first waveguide includes a first portion having the surface grating. For photoinscription, the fabrication method comprises providing a substrate material that includes a substrate layer, a core layer, and a first photoresist layer.

Abstract: An optical recording method suited for recording a very small object or movement of a living organism such as a microorganism, which comprises irradiating an informative object set on or above a recording layer comprising a photosensitive material capable of undergoing a storable and detectable photochemical reaction, preferably a polymer material containing a photoreactive component capable of photoisomerization and having in the repeating unit thereof at least one group selected from a urethane group, a urea group, an amide group, a carboxyl group and a hydroxyl group, and recording a distribution of an optical near field generated from the informative object being irradiated on the photosensitive material as a photoreacting quantity of the photosensitive material.

Abstract: A method of manufacturing a grating in an optical waveguide that includes a core and a cladding covering the core. The method includes the steps of providing the optical waveguide and scanning a laser beam along an optical axis of the optical waveguide to form modulation of refractive index of radiation in the core. The core is made of a material having the refractive index that is changeable by irradiation of radiation. In addition, on the step of scanning, in the core, the irradiation range of the laser beam is controlled and the laser beam is scanned a plurality of times. Therefore, predetermined distribution of irradiation amount is obtained in a direction of the optical axis of the grating.

Abstract: A polymer material is exposed to radiation of a type that changes some aspect of the polymer's radiation passing properties. The radiation that caused the property change is then contained by the material. The property change can be self-focusing or self-trapping light can be used. In that case, the same light that causes the photopolymerization is contained by the change in index of refraction that is caused by the polymerization.

Abstract: There is disclosed a method of constructing photosensitive waveguides on silicon wafers through the utilization of a Plasma Enhanced Vapor Deposition (PECVD) system. The deposition is utilized to vary the refractive index of resulting structures when they have been subject to Ultra Violet (UV) post processing.

Abstract: A process for forming a refractive-index-patterned film for use in optical device manufacturing. The process includes forming a photosensitive lead-silicate-containing film on a substrate (e.g., a silicon, quartz or glass substrate) using, for example, a conventional and inexpensive sol-gel process. A predetermined portion of the lead-silicate-containing film is subsequently exposed to ultra-violet (UV) light through a patterned mask (e.g., a patterned amplitude mask, patterned phase mask or patterned gray scale mask). The UV exposure modifies the refractive index of the predetermined portion, thereby forming a refractive-index-patterned lead-silicate-containing film suitable for use in optical device manufacturing. The use of a photosensitive lead-silicate-containing film enables a relatively large refractive index modification upon exposure to UV light.

Abstract: The present invention relates to compositions useful for optically recording or storing data by stimulating a composition having a refraction modulating composition, where a stimulated region of the composition represents one kind of data and a non-stimulated region of the composition represents another kind of data. The present invention also relates to methods of optically recording data utilizing the compositions of the present invention, as well as to optical data storage devices and optical data storage elements which utilize the optical data storage compositions of the invention.

Abstract: A method of making a three-dimensional refractive index structure in a photosensitive material using photo-patterning. The wavelengths at which a photosensitive material exhibits a change in refractive index upon exposure to optical radiation is first determined and then a portion of the surface of the photosensitive material is optically irradiated at a wavelength at which the photosensitive material exhibits a change in refractive index using a designed illumination system to produce a three-dimensional refractive index structure. The illumination system can be a micro-lenslet array, a macroscopic refractive lens array, or a binary optic phase mask. The method is a single-step, direct-write procedure to produce a designed refractive index structure.

Abstract: The present invention relates to a fiber grating formed on an optical component for processing optical signals and a method of forming the grating. After the sheath (2) of an optical fiber (3) is partially removed, the surface of the bare optical fiber (1) at an area where the sheath (2) is removed is covered by a resin film (7) having a thinness at which ultraviolet light permeability not hindering formation of gratings. Thereafter, by irradiating ultraviolet light (ultraviolet coherent light) via a phase mask (9), a grating where the refractive index of the core (4) of the bare optical fiber 81) cyclically changes in the beam axis is formed. The resin film (7) is made of, for example, an organic material having heat resistance, which is not dissolved by ultraviolet ray irradiation, such as polyimide resin, polyamideimide resin, etc. The thickness of the resin film (7) is 10 &mgr;m or less to ensure that ultraviolet light sufficiently permeates and the convergence of interference light is not lowered.

Abstract: A process for forming a pattern which comprises irradiating with light a film of a poly(arylenevinylene) polymer represented by the following formula (I) —(Ar—CR1=CR2)n—  (I) wherein Ar is a substituted or unsubstituted divalent aromatic hydrocarbon group or a substituted or unsubstituted divalent heterocyclic ring group, and the aromatic hydrocarbon group and the heterocyclic ring group may be a fused ring, R1, R2 independently of each other, are H, CN, alkyl, alkoxy are substituted or unsubstituted aromatic hydrocarbon groups or substituted or unsubstituted aromatic heterocycles, which may both be fused rings, and n is an integer of 2 or more. It is preferred that either R1 or R2 is H and more preferred that both R1 and R2 are H.

Abstract: The photonic crystal material has a 3-D periodic structure with a periodicity that varies on a length scale comparable to the wavelength of electromagnetic radiation. The 3-D periodic structure is produced by irradiating photosensitive material with electromagnetic radiation such that interference between radiation propagating in different directions within the sample gives rise to a 3-D periodic variation in intensity within the sample. Thereafter the irradiated material is developed to remove the less or more irradiated regions of the material to produce a structure having 3-D periodicity in the refractive index of the composite material. 3-D photonic material is particularly suited to use as low-loss waveguides and as a control with lasers to limit the number of modes into which a laser may emit radiation.

Abstract: Disclosed a device for fabricating a polarization insensitive long-period fiber grating which includes: a ultraviolet laser for irradiating a ultraviolet laser beam; a ultraviolet polarizer for converting a polarization status of the ultraviolet laser beam into a linear polarization status in parallel along the longitudinal direction of a fiber; a lens for adjusting a focus of the ultraviolet laser beam from the ultraviolet polarizer; an amplitude mask for selectively passing the ultraviolet laser beam from the lens; and, a mount for holding both ends of the fiber so that the outer circumferential surface of the fiber can be exposed to the ultraviolet laser beam from the amplitude mask.

Abstract: The invention provides a method and apparatus that precisely and efficiently improves the optical properties of an optical fiber grating. Preferably hydrogen loading processing, grating formation processing that forms a grating part by irradiation with ultraviolet light at a predetermined period, and preferably dehydrogenation, adjusting the optical properties by a suitable combination of uniform ultraviolet irradiation processing that irradiates the grating part as a whole with ultraviolet light and heat trimming processing, and finally heat aging is carried out.

Abstract: The invention provides organic optical waveguide devices which employ perfluoropolymeric materials having low optical loss and low birefringence. An optical element has a substrate; a patterned, light transmissive perfluoropolymer core composition; and a light reflecting cladding composition on the pattern of the core. Writing of high-efficiency waveguide gratings is also disclosed.

Abstract: There are disclosed the following three types of optical recording film:

Abstract: The present invention relates to an optical fiber grating element having structure enabling more precise design and fabrication, a production method thereof, and an optical fiber filter including the same. The optical fiber grating element according to the present invention comprises a multi-mode optical fiber having a first core region of a refractive index n1, a second core of a refractive index n2 provided on a periphery of the first core region, and a cladding region of a refractive index n3 provided on a periphery of the second core region, and having a cutoff wavelength regarding to LP02-mode light on the longer wavelength side than a wavelength band in use. A long-period grating for selectively coupling the fundamental LP01-mode light of a predetermined wavelength in the wavelength band I use to LP0m (m≧2)-mode light is provided in a predetermined region of the first core region.

Abstract: An apodised refractive index grating is recorded in a photosensitive optical fibre by forming first and second component interference patterns with different pitches, that are recorded in the grating such as to result in apodisation. The component patterns (16, 17) are spatially in phase in a central region and move progressively out of phase towards the ends of the patterns. The patterns may be recorded sequentially or concurrently. The fibre may be stretched one or cyclically.

Abstract: The invention provides organic optical waveguide devices which employ perfluoropolymeric materials having low optical loss and low birefringence. An optical element has a substrate; a patterned, light transmissive perfluoropolymer core composition; and a light reflecting cladding composition on the pattern of the core. Writing of high-efficiency waveguide gratings is also disclosed.

Abstract: An optical structure is fabricated by forming an active layer including a photodefinable material on a substrate or on another underlying layer, forming an upper layer above the active layer, and then patterning the active layer by selective application of radiation through the upper layer. The upper layer is substantially transparent to radiation of the type required to activate the photodefinable material in the active layer.

Abstract: Disclosed is a long-period optical fiber grating according to the present invention. The long-period optical fiber grating includes a plurality of sections. The sections have a different grating periodicity. The distribution of the grating periodicity is asymmetric around a central reference section. Also, the sections have their lengths twice, or longer, as the respective grating periodicity.

Abstract: A method for a method including the steps of: irradiating ultra short pulse laser rays having a pulse width not more than 30 pico-seconds to at least one of a core section and a clad section of an optical wave-guide device to modify a refractive index of the core section and the clad section.

Abstract: During the process of writing a grating, the fiber is placed in a support which has a surface cut-out such as a V-shaped groove. The side walls of this groove form an angle (&agr;) of 60° with respect to the direction of propagation of the radiation arriving from the source. The aforesaid surfaces have characteristics of high reflectivity with respect to the aforesaid radiation. Consequently, during the writing process, the core of the fiber is subjected to the action of a plurality of radiation fronts converging on the core. The first radiation front corresponds to the radiation arriving from the source and two other radiation fronts are obtained from this radiation by the effect of the reflection from the walls of the surface cut-out of the support. The preferred application is to the making of long-period gratings.

Abstract: Disclosed is an apparatus and method for fabricating a multi-period optical fiber grating. The apparatus includes an optical light source; a movable optical fiber having a first part of the optical fiber and at least a second part of the optical fiber bent from the first part of the optical fiber and arranged substantially parallel with the first part of the optical fiber; and a multi-period amplitude mask including a first sector having a predetermined on-off ratio corresponding to the first part of the optical fiber and at least a second sector disposed substantially parallel with the first sector and having an on-off ratio different from the predetermined on-off ratio, wherein the mask position on top of the fiber is translated in relation to the light source so that the gratings of differing periods can be formed along the exposed optical fiber member.

Abstract: A method is disclosed wherein optical structures such as Bragg gratings can be written into planar waveguides disposed on a substrate. By employing the method of this invention, a polarization insensitive device can be made. Such relatively thin planar waveguides disposed on a substrate are inherently polarization sensitive and the structure itself is birefringent. By writing structures in the waveguides or by simply writing a refractive index change in the waveguide by limiting the beam width at the waveguide layer to less than or equal to the thickness of the waveguiding layers on the substrate, in combination with conventional wider beam writing techniques, polarization sensitivity can be lessened or obviated.

Abstract: An apparatus for fabricating a long-period fiber grating, including a laser source, a first lens for adjusting the focal point of laser generated by the laser source, a dispersing portion for dispersing laser passed through the first lens so that the size of a beam of the laser is broadened, a second lens for collimating the dispersed laser, and a composite amplitude mask for periodically transmitting laser collimated by the second lens, to an optical fiber, wherein the refractive index of the core of the optical fiber is periodically changed by laser which has passed through the composite amplitude mask. The coupling bandwidth of a long-period fiber grating can be controlled by adjusting the size of a laser beam which reaches an optical fiber. The wavelength where coupling occurs is controlled by adjusting the rotation angle of two amplitude masks, so that a desired light transmission spectrum is easily created.

Abstract: A polymer material is exposed to radiation of a type that changes some aspect of the polymer's radiation passing properties. The radiation that caused the property change is then contained by the material. The property change can be self-focusing or self-trapping light can be used. In that case, the same light that causes the photopolymerization is contained by the change in index of refraction that is caused by the polymerization.

Abstract: The present invention is a process for manufacturing an optical fiber Bragg grating, which in a preferred embodiment includes the steps of: (a) removing at least a portion of a removable coating on an optical fiber element in at least one predetermined section to sufficiently expose the optical fiber in the section for a subsequent treatment by a source of optical radiation; (b) fixing the at least one section with respect to the source of optical radiation; (c) directing optical radiation from the source into the optical fiber to produce at least one Bragg grating in the at least one section; and (d) covering the at least one section. The present invention also extends to an apparatus for carrying out the process steps described above, which includes means for coating removal, means for fiber immobilization, means for writing a Bragg grating, and means for packaging.

Abstract: An improved photorecording medium suitable for use in holographic storage systems contains a glassy hybrid inorganic-organic, three dimensional matrix, in which is distributed a photoimageable system comprising one or more photoactive, organic monomers. The medium is fabricated by providing a precursor of the hybrid inorganic-organic matrix, mixing the matrix precursor with the photoimageable system, and curing the matrix precursor to form the matrix in situ. The matrix and photoimageable system exhibit independent chemistries, such that the step of matrix formation does not substantially affect the photoimageable system. The hybrid matrix precursor is typically an oligomer derived from a compound represented by RnM(OR′)4−n, where M is a metallic element having a valence of three or higher, such as silicon, titanium, germanium, zirconium, vanadium, or aluminum, R is an alkyl or aryl, R′ is a lower alkyl, and n ranges from 1 to 2.

Abstract: Optical components have a material-distribution gradient due to nanometer-size particles embedded in a solid matrix. The components are manufactured by forming a dispersion of nanometer-size particles in a liquid, curable matrix material, causing the particles to migrate in the matrix material on the basis of a potential difference to form a distribution gradient, and subsequently curing the matrix material, retaining the distribution gradient. The method is suitable for use in the manufacture of optical lenses with a refractive index gradient.

Abstract: A length of oxynitride optical fiber is exposed to actinic radiation that is modulated by an interference technique to form a pattern of refractive index variations that functions as a reflective grating.

Abstract: A method of fabricating an integrated circuit using photolithography and an antireflective coating. An antireflective coating is formed on a substrate wherein the antireflective coating is electrically polarizable. A photoresist coating is formed on the antireflective coating on a side opposite from the substrate and the photoresist is exposed to activating radiation. The antireflective coating is subjected to an applied electric field at substantially the same time as the photoresist is exposed to activating radiation. The radiation absorption coefficient of said antireflective coating is increased and the refractive index of said antireflective coating is changed to be substantially equal to the refractive index of said photoresist coating.

Abstract: The present invention is directed to a method of enhancing the photosensitivity of an optical waveguide and an optical waveguide having persistent UV photosensitivity following out diffusion of a loading gas such as H2 or D2. The optical waveguide is loaded with a gas such as H2 or D2 to form an associated baseline refractive index. At least a portion of the loaded optical waveguide is exposed to UV radiation to induce a change in the baseline refractive index and the waveguide is annealed to diffuse the gas from the loaded optical waveguide and to stabilize the change in refractive index. Following annealing the optical waveguide retains a UV photosensitivity sufficient to produce significant refractive index changes relative to the induced change in baseline refractive index. The method of the present invention is particularly well suited for designing and fabricating grating devices, tuning grating strength and wavelength, and for providing accurate spatial control of waveguide photosensitivity.

Abstract: A photorefractive composite comprises a charge transport matrix and an electrooptic dye having an aliphatic group of four or more carbon atoms.

Abstract: An apparatus for manufacturing a long-period fiber grating and a two-band long-period fiber grating manufacturing apparatus using the same are provided. The apparatus includes a light source for generating the UV laser light, a mirror for reflecting the UV laser light generated in the light source at a predetermined angle and changing the traveling path thereof, a lens for focusing the laser light whose traveling path is changed by the mirror, a dispersing unit for dispersing the laser light passed through the lens, and an amplitude mask positioned between the dispersing unit and the optical fiber, and having a transmission region in which the dispersed laser light is periodically transmitted to the optical fiber. The bandwidth of a long-period fiber grating can be adjusted by adjusting the size of a laser beam irradiated into an optical fiber. Also, amplitude masks can be easily manufactured at low cost and damage threshold power thereof is high.

Abstract: A method of forming a resist pattern comprising the steps of depositing a resist on a semiconductor substrate, performing a first exposure on the resist using a reticle with a certain pattern formed on it as a mask to change the degree of polymerization at the exposed area in the resist, causing diffusion of a silicon compound to silylate selectively a part of the surface of the resist, performing a second exposure on the resist so that light passing through the silylated area and the unsilylated area become inverse in phase, and developing the resist for forming a micropattern on the resist.

Abstract: An anti-reflective coating and method of forming the anti-reflective coating are described wherein the anti-reflective coating is part of a silicon nitride layer formed on a semiconductor integrated circuit substrate. The anti-reflective coating is formed under the photoresist layer for greater effectiveness but does not disrupt the process flow since the anti-reflective coating is part of the silicon nitride layer. A first silicon nitride layer is formed having an index of refraction of about 2.1. A second silicon nitride layer having an index of refraction of about 1.9 and a second thickness is formed on the first silicon nitride layer. A layer of photoresist is then formed on the second silicon nitride layer. The second thickness is chosen to be equal to the wavelength of the light used to expose the layer of photoresist divided by the quantity of 4 multiplied by 1.9. The second silicon nitride layer acts as an effective anti-reflective layer.

Abstract: A method for creating nonuniform grating strengths within fiber optic includes exposing photosensitive fiber optic material to an optical source for various periods of time through a mask. As the fiber optic material is exposed, the grating strength of the fiber changes. By linearly exposing the fiber optic material to different durations of optical energy, nonuniform grating strengths are created within the fiber, thereby creating a fiber optic section having asymmetric grating strengths.

Abstract: Optical plates which have columnar features approximately in the direction of light propagation which are capable of total internal reflection, a controllable numeric aperture (NA) at input and output surfaces, rotational azimuthal averaging and translation of the object plane from a back surface of the plate to a front surface of the plate and are optical equivalent of a FOFP. These plates are made from a composition of irradiation sensitive glass which has been etched in either the columnar features or the surrounding features. If the surrounding features have been etched, the etched areas are filled with either a low melt glass or plastic or a light blocking material such as a black composition material. If the columnar features have been etched the etched areas are filled with a low melt glass or plastic.

Abstract: A method and an apparatus to photoinduce a grating or other type of modulated refractive index change in a photosensitive optical medium such as optical fiber. The resulting grating has a variable and controllable intensity profile and average value of the index change. The modulated refractive index change is photoimprinted in the medium in a series of writing steps, each comprising exposing a segment of the medium to a writing beam for a predetermined exposure time. To change the modulation intensity from step to step, the angle of incidence of the writing beam is dithered for an appropriate fraction of the exposure time at each step. This allows to control the amount of incident light on the medium for each step. If the exposure time is the same for each writing step, the average value of the index change may be kept constant avoiding undesired structure in the grating frequency response.