Abstract: A waveguide structure formed with a three-dimensional (3D) photonic crystal is disclosed. The 3D photonic crystal comprises a periodic array of voids formed in a solid substrate. The voids are arranged to create a complete photonic bandgap. The voids maybe formed using a technique called “surface transformation,” which involves forming holes in the substrate surface, and annealing the substrate to initiate migration of the substrate near the surface to form voids in the substrate. A channel capable of transmitting radiation corresponding to the complete bandgap is formed in the 3D photonic crystal, thus forming the waveguide. The waveguide may be formed by interfacing two 3D photonic crystal regions, with at least one of the regions having a channel formed therein. The bandgap wavelength can be chosen by arranging the periodic array of voids to have a lattice constant a fraction of the bandgap wavelength.

Abstract: A photonic device designed with an intermittent absorption profile along a waveguide. The absorption profile is divided into low-absorption and high-absorption segments that are distributed axially in order to decrease the maximum local temperature in the device. The distribution of low-absorption segments can be controlled through techniques such as proton implantation or selective-area quantum well intermixing. The lengths of low-absorption and high-absorption segments can be adjusted to optimize heat dissipation along the device length.

Abstract: In one version, the present invention provides an optical switching device including a splitting device having a first terminal for receiving an input signal and second and third terminals, and an optical loop associated with the second and third terminals and having first and second non-linear elements and first and second directing devices. One of the first and second non-linear elements may receive an activating signal from a third directing device and, in response to the activating signal, cause the optical loop to producing first and second output signals at the first and second directing devices, respectively. In another version, the present invention provides an optical gating device. The present invention also provides an optical switching device that may include two optical gating devices and an optical toggle device.

Abstract: This application describes examples and implementations of optical devices and techniques based on use of whispering gallery mode (WGM) optical resonators that have nonlinear optical materials in multiple sectors where nonlinear coefficients of two adjacent sectors are oppositely poled.

Abstract: The present invention relates to a method for regenerating an optical signal suitable for WDM (wavelength division multiplexing). In this method, an optical signal is supplied to an optical waveguide structure (e.g., optical fiber) for providing a nonlinear effect. As a result, the optical signal undergoes chirp induced by the nonlinear effect. Then, an output optical signal output from the optical waveguide structure is supplied to an optical filter to thereby remove a small-chirp component from the output optical signal. By removing the small-chirp component from the output optical signal in the form of pulse, intensity fluctuations or accumulated noise especially at a top portion and/or a low-power portion of the pulse can be removed. Accordingly, the optical signal can be regenerated independently of the bit rate, pulse shape, etc. of the optical signal.

Abstract: The present invention concerns an optical guide (100) comprising an amplifier medium including: a core (10) in a main matrix of a transparent material, the main matrix containing particules (1, 2), each particule being formed of a submicronic matrix distinct from the main matrix and doped by an active metal element, an external guiding cladding (11) in contact with the core (10). The size of the particules (1, 2) is smaller than 20 nm. The present invention also concerns a method for producing this guide.

Abstract: In one embodiment of the present invention, a method includes introducing an optical signal into a first arm and a second arm of an optical device; self-phase modulating the optical signal propagating in the first arm; and outputting a high intensity portion of the optical signal spatially separated from a low intensity portion of the optical signal. In such manner, optical signals input into the optical device may be restored via cleaning and shaping.

Abstract: A photonic crystal structure includes a microcavity (point defect). The photonic crystal structure (or just the microcavity) is doped with materials that exhibit electro-magnetic induced transparency (EIT) so as to increase the non-linear properties of the photonic crystal.

Abstract: A device for bending a laser beam is provided. The device includes a beam deflection device that produces the beam having a selected number of addressable points. A soliton forming mechanism is positioned at the output of the beam deflection device so it receives the beam and increases the number of addressable points by a certain magnitude.

Abstract: The present invention is to a method of adapting optical rare-earth-doped waveguide (10) having a plurality of transverse propagation modes, such that in use, signal gains of non-fundamental modes of the waveguide are attenuated relative to a signal gain of a fundamental mode of the waveguide. The waveguide (10) has a light-guiding region (45) defined by a refractive index-modifying dopant, such as Ge, which has a thermal diffusion coefficient at temperature T in the waveguide greater than a thermal diffusion coefficient of the rare-earth dopant at temperature T. The method comprises heating the waveguide (10) at the temperature T such that a concentration profile of the refractive index-modifying dopant becomes broader than a concentration profile of the rare-earth dopant.

Abstract: A nonlinear optical chromophore having the formula D-?-A, wherein ? is a ? bridge including a thiophene ring having oxygen atoms bonded directly to the 3 and 4 positions of the thiophene ring, D is a donor, and A is an acceptor.

Abstract: The invention relates to an optical device. The optical device comprises a waveguide core and a nanocomposite material optically coupled to the waveguide core. The nanocomposite material includes a plurality of quantum dots. The nanocomposite material has a nonlinear index of refraction ? that is at least 10?9 cm2/W when irradiated with an activation light having a wavelength ? between approximately 3×10?5 cm and 2×10?4 cm.

Abstract: Among other things, the present invention provides optical attenuators and modulators, especially variable optical attenuators and modulators, and materials and methods for their fabrication. In particular, the invention provides optical attenuators and modulators that preferably are comprised of a second-order nonlinear optical polymer. Desirably the attenuators and modulators comprise at least one grating, and even more preferably, comprise at least two gratings. Optimally any such grating is contained within a waveguide layer.

Abstract: According to the present invention, an improved waveguide device utilizes an advantageously designed optically functional cladding region and an associated modulation controller to address design challenges in applications requiring modulation, attenuation, control, switching, etc. of optical signals. In accordance with one embodiment of the present invention, an electrooptic modulator is provided comprising an optical waveguide, a cladding optically coupled to the optical waveguide, an optically functional cladding region defined in at least a portion of the cladding, and a modulation controller configured to provide a modulating control signal to the optically functional cladding region. The modulation controller is configured to generate an electric field in the optically functional region in response to a biased modulating RF control signal.

Abstract: A highly nonlinear optical fiber includes a core, a cladding surrounding the core, and a coating covering the cladding. A bending loss at a wavelength of 1550 nanometers with a bending diameter of 20 millimeters is equal to or less than 0.01 dB/m. A nonlinear coefficient at the wavelength of 1550 nanometers is equal to or more than 10 W?1km?1. A cut-off wavelength is equal to or less than 1530 nanometers. A zero dispersion wavelength is in a range between 1400 nanometers and 1650 nanometers. A diameter of the coating is 125 micrometers with a tolerance of ±5 percent.

Abstract: Distributed fiber optic chemical and physical sensors provide a relatively highly uniform response over the length of the fiber by, for example, varying such properties as the core/cladding index of refraction ratio to compensate for the non-linearity in sensitivity due to the loss of higher order modes in multi-mode fibers. The variation of the ratio changes the absorption coefficient of the fiber and can be used to compensate for any non-linearity in response. Other techniques for compensation also are disclosed.

Abstract: A method of simultaneously specifying the wavelength dispersion and nonlinear coefficient of an optical fiber. Pulsed probe light and pulsed pump light are first caused to enter an optical fiber to be measured. Then, the power oscillation of the back-scattered light of the probe light or idler light generated within the optical fiber is measured. Next, the instantaneous frequency of the measured power oscillation is obtained, and the dependency of the instantaneous frequency relative to the power oscillation of the pump light in a longitudinal direction of the optical fiber is obtained. Thereafter, a rate of change in the longitudinal direction between phase-mismatching conditions and nonlinear coefficient of the optical fiber is obtained from the dependency of the instantaneous frequency. And based on the rate of change, the longitudinal wavelength-dispersion distribution and longitudinal nonlinear-coefficient distribution of thee optical fiber are simultaneously specified.

Abstract: A photosensitive resist layer is formed on one surface of a single-polarized ferroelectric substance having nonlinear optical effects. The resist layer has properties such that, when light is irradiated to the resist layer, only exposed areas of the resist layer or only unexposed areas of the resist layer become soluble in a developing solvent. The resist layer is then exposed to near-field light in a periodic pattern with a device, which receives exposure light and produces the near-field light in the periodic pattern. The resist layer is then developed to form a periodic pattern. A periodic electrode is then formed on the one surface of the ferroelectric substance by utilizing the periodic pattern of the resist layer as a mask, the periodic electrode being formed at positions corresponding to opening areas of the mask.

Abstract: A device for transmitting information between at least two units mobile relative to each other comprises a light guide having a light-guiding medium, the optical properties of which can be changed by external electromagnetic fields. The light guided in this light guide is modulated by electromagnetic fields emitted by a movable probe.

Abstract: A two-dimensional photonic crystal resonator apparatus in which the power of light coupled out of the apparatus in one direction is greater than the power of light coupled out of the apparatus in the opposite direction The apparatus has a photonic crystal slab waveguide structure having a waveguide and a resonator in the vicinity of the waveguide such that light propagated through the waveguide is extracted from the waveguide through the resonator and is coupled out of the plane of the apparatus. The apparatus has upper and lower cladding layers on the photonic crystal slab waveguide structure having different indices of refraction, and the power of light coupled out of the apparatus in the direction of the cladding layer having the higher index of refraction is greater than the power of the light coupled out of the apparatus in the direction of the cladding layer having the lower index of refraction.

Abstract: This invention pertains to a hollow core photonic band gap chalcogenide optical glass fiber and to a fabrication method for making the fiber. The fiber, which is 80-1000 microns in outside diameter, is characterized by a solid glass circumferential region and a structured region disposed centrally within the solid region, the structured region includes a hollow core of 1 micron to several hundreds of microns in diameter surrounded by a plurality of parallel hollow capillaries extending parallel to the core, the core being centrally and longitudinally located within the fiber. Ratio of open space to glass in the structured region is 30-99%. The fabrication method includes the steps of providing a mold, placing chalcogenide micro-tubes around the mold, stacking chalcogenide micro-canes around the stacked micro-tubes, fusing the micro-tubes and the micro-canes to form a preform, removing the mold and drawing the preform to obtain the fiber.

Abstract: An optical AND logic gate includes a summing gate having first and second inputs for receiving first and second optical signals, and a threshold device. The gate produces an output corresponding to the AND product of the first and second optical signals. In another version the AND gate includes first and second inputs for receiving first and second optical signals, and an optical loop for producing an output corresponding to the AND product of the first and second optical signals. In an alternative versions a NAND gate is provided by applying an optical logic NOT on an AND gate.

Abstract: An electro-optic system in accordance with an embodiment of the present invention comprises a high glass transition temperature (Tg?about 210° C.) polymer matrix featuring aromatic groups on the backbone repeating unit, which hosts a guest, high hyperpolarizability organic NLO chromophore. Electro-optic systems according to embodiments of the present invention exhibit relatively high electro optical activity and low optical loss, and may exhibit optical stability at temperatures exceeding 70° C. Guest-host polymer systems in accordance with embodiments of the present invention may be formed into unique and appropriate shapes such as waveguides.

Abstract: An optical wavelength conversion device including a micro-structured optical waveguide, which includes sections with a non-linear material having an index of refraction which changes as a non-linear function of light intensity. The optical waveguide includes a light guiding core region, and is dimensioned for providing spatial overlap between the sections filled with the non-linear material and light propagating within the waveguide. First and second optical light sources may also be included, the second light source having an intensity sufficient to change the refractive index of the non-linear material sufficiently to encode or modulate the light from the first light source through the effect of leaking light from the first light source inside the guiding core to the outside of the guiding core.

Abstract: An apparatus and method for nonlinear frequency mixing of light waves relying on a nonlinear material having a nonlinear coefficient d and a waveguide fabricated in the nonlinear material. The waveguide is equipped with a quasi-phase-matching (QPM) grating extending along the length of the waveguide and endowed with an asymmetry of the nonlinear coefficient d along the width of the waveguide. The transverse asymmetry is chosen to establish a mode overlap for nonlinear frequency mixing between different transverse width modes of light. The transverse asymmetry can be odd or else neither odd nor even so as to establish mode overlap for frequency mixing between even transverse width modes and odd transverse width modes. The QPM grating can have single or multiple grating stripes that can be staggered, interleaved, angled and otherwise altered to achieve the transverse asymmetry establishing a mode overlap for frequency mixing between even transverse width modes and odd transverse width modes.

Abstract: The invention relates to an optical device. The optical device comprises a waveguide core and a nanocomposite material optically coupled to the waveguide core. The nanocomposite material includes a plurality of quantum dots. The nanocomposite material has a nonlinear index of refraction ? that is at least 10?9 cm2/W when irradiated with an activation light having a wavelength ? between approximately 3×10?5 cm and 2×10?4 cm.

Abstract: The present invention comprises an optical fiber have a small effective area and a positive dispersion suitable for use in the reshaping and regeneration of optical signals. The optical fiber according to the present invention has an effective area between about 10 ?m2 and 16 ?2, and a total dispersion between about 4 ps/nm/km and 8 ps/nm/km. Also disclosed is a method of making the inventive fiber wherein a high core relative refractive index can be achieved.

Abstract: A method of inducing a periodic variation of nonlinearity in a sample of ferroelectric material, comprises applying an electrically insulting mask to surface of the sample, applying an electric field across the sample to produce domain inversion in the sample, and removing the electric field when non-inverted regions of the sample remain only in the vicinity of the surface of the sample beneath parts of the surface covered by the mask. This method can be used to engineer accurate domain periods of submicron dimensions or larger which are confined to a surface region of the ferroelectric material, so that the poled material can be used to fabricate planar waveguide devices for nonlinear optical applications. In particular, the submicron periods can be exploited in the fabrication of one and two-dimensional photonic band gap devices.

Abstract: Disclosed are a functional material and a functional device, each of which is capable of changing a wavelength of a transmission electromagnetic wave such as transmission light or a transmission sound wave such as a transmission ultrasonic wave through the device on the basis of a signal supplied from external. Each of the functional material and the functional device includes a periodic structure having a periodicity with a unit cycle on the order of a wavelength of an electromagnetic wave or a sound wave, and means for disturbing the periodicity which is inserted in at least one portion of the periodic structure, wherein a wavelength of the electromagnetic wave or sound wave passing through the periodic structure by controlling the means on a signal supplied from external.

Abstract: An apparatus and associated method for controlling the propagation constant of a region of focusing propagation constant in an optical waveguide. The method comprising positioning an electrode of a prescribed electrode shape proximate the waveguide. A region of focusing propagation constant is projected into the waveguides that corresponds, in shape, to the prescribed electrode shape by applying a voltage to the shaped electrode. The propagation constant of the region of focusing propagation constant is controlled by varying the voltage. Light of certain wavelengths passing through the region of focusing propagation constant has a variable focal length.

Abstract: A photonic crystal comprising a waveguide made of material. The waveguide has a periodic set of holes. The material proximate to at least one of the holes in the periodic set of holes exhibits an index of refraction that has been modified by the application of laser energy relative to the material proximate to other holes in the periodic set of holes.

Abstract: Crystalline non-linear optical films for nonlinear-optics applications are provided. One such crystalline non-linear optical film includes a substrate and an alignment layer material disposed on said substrate. The alignment layer includes elongated polymeric molecules aligned in a substantially uniaxial direction. Further, at least one non-linear optical material is disposed on the alignment layer.

Abstract: An optical device comprises a cavity resonator and an intracavity ridge waveguide. The ridge waveguide includes a monolithically integrated intersubband core region and a nonlinear mixing region (NMR). In response to external pumping energy the core region generates laser light at a first frequency and in a first transverse mode. In response to the laser light the NMR generates parametric light at a second frequency and in a second transverse mode. For phase matching the effective-refractive-index-versus-ridge-width characteristics of the modes of the laser and the parametric light intersect one another at a phase matching width and so that, at greater widths, the effective refractive index of the mode of the higher frequency light is less than that of the lower frequency light. For true phase matching the width of the ridge is made to be essentially equal to the phase matching width.

Abstract: The specification describes dispersion compensators that are adjustable based on selection of mode propagation properties of two or more modes. The fundamental device structure comprises two or more sections of optical fiber that support the fundamental mode as well as well as one or more higher-order-modes (HOM). The HOM fibers are connected to each other by means of a spatial mode-converter (MC) that is switchable. The MC may be fabricated with, for example, long-period fiber-gratings (LPG), coupled waveguide devices, free-space phase-retardation elements, micro-electro-mechanical devices, or acousto-optic couplers. The MC is assembled such that it transforms any incoming spatial mode into one of any other guided modes in the HOM fiber. Switching is achieved by strain, temperature, the electro-optic or nonlinear optic effect, or any other physical effect that changes the refractive index of the optical material used to construct the MC.

Abstract: A photonic switch according to the present invention may be formed using one of a selected group of non-linear optical materials. Each of the materials within this group has a refractive index that demonstrates a substantial peak as a function of wavelength, where the peak occurs at a wavelength distinct from the wavelength of the input signal. A method of producing a photonic switch according to the present invention includes fabricating source and drain waveguides using micro-molding or micro-contact printing processes, or MIMIC (micro-molding in capillaries) of a UV-curable polymer. If desired, a gate waveguide may also be formed in part by these processes. The photonic switch also includes a photonic crystal formed from non-linear optical material, which may be formed, for example, using a block copolymer and nanoparticle composite in a MIMIC or ?fluidics process. Such a process may employ a functionalized mold material to align the blocks.

Abstract: An optical fiber transmission line including first, second and third optical fibers connected together so that light travels through the transmission line from the first optical fiber, then through the second optical fiber and then through the third optical fiber. The first, second and third optical fibers have first, second and third characteristic values, respectively. The second characteristic value is larger than the first characteristic value and the third characteristic value. The characteristic value of a respective optical fiber being a nonlinear refractive index of the optical fiber divided by an effective cross section of the optical fiber. Pump light is supplied to the transmission line so that Raman amplification occurs in the transmission line as an optical signal travels through the transmission line.

Abstract: The invention provides an optical wavelength multiplex transmission method wherein a band in the proximity of a zero dispersion wavelength of an optical fiber is used and optical signals are disposed at efficient channel spacings taking an influence of the band, the wavelength dispersion and the four wave mixing into consideration to realize an optical communication system of an increased capacity which is not influenced by crosstalk by FWM. When optical signals of a plurality of channels having different wavelengths are to be multiplexed and transmitted using an optical fiber, a four wave mixing suppressing guard band of a predetermined bandwidth including the zero-dispersion wavelength ?0 of the optical fiber is set, and signal light waves of the plurality of channels to be multiplexed are arranged on one of the shorter wavelength side and the longer wavelength side outside the guard band.

Abstract: A waveguide device is provided comprising an optical waveguide core and a cladding optically coupled to the optical waveguide core. The cladding comprises an optically functional region defining a refractive index that is configured to vary in response to a control signal applied to the optically functional region. The refractive index of the optically functional region is lower than the refractive index of the optical waveguide core. In accordance with one embodiment of the present invention, the optically functional region may be characterized as a Kerr Effect medium.

Abstract: The invention provides an optical switch that consumes a less power, excels in a high-speed response, and possesses a structure suitable for a miniaturization and multi-channel switching. The optical switch switches a plurality of input signals to a plurality of output positions, in which a laminated structure that has a nonlinear optical layer and a buffer layer laminated in the same number as that of input parts intersects an optical path between the input parts and output parts. By providing the laminated structure using the nonlinear optical thin films, the invention achieves a small matrix optical switch excellent in a high-speed response and suitable for switching a large-capacity of information.

Abstract: A broadband optical spectrum generating apparatus 20 includes a ultrashort pulsed fiber laser 22 that generates pulsed light having a pulse width in the unit of picosecond to femtosecond, and broadband optical spectrum-generating optical fibers 24 that are connected with the ultrashort pulse fiber laser 22 via a lens 26 and have characteristics of normal dispersion, that is, a nonlinear coefficient of not less than 10 [W?1 km?1] and a magnitude of wavelength dispersion of not greater than a value 0 [ps/km/nm] with regard to a wavelength of the pulsed light. The resulting output is super continuum that is widely broadened to a wavelength band of 1400 nm to 1750 nm and is chirped to a linear characteristic.

Abstract: Disclosed is an optical recording medium comprising a recording layer. The recording layer contains: a charge generation material generating an electron and a hole by light irradiation; a charge transport material transporting one of the electron and the hole; a charge trap which traps the transported one of the electron and the hole to separate the electron and the hole; and a non-linear optical material which changes optical properties of the recording layer in accordance with electric field formed by the electron and the hole being separated from each other. The non-linear optical material has an asymmetrical carbon atom and a cyclic group. Or, it is a cyclic-group-containing constituent having: an inversion symmetric pi-electron system; at least one of an electron donating group and an electron accepting group which are bonded to the inversion symmetric ?-electron system; and an asymmetrical carbon atom.

Abstract: An optical pulse generator comprises a comb-like dispersion profiled fiber formed into an optical loop mirror. The fiber may comprise three or more segments of fiber having alternating highly dispersive and highly nonlinear characteristics. The optical loop mirror construction splits an input pulse into two portions that propagate through the CDPF in opposite directions. The pulse portions are re-combined, and a compressed pulse with reduced noise is produced.

Abstract: A method for determining at least one parameter of a periodic spin function ?(z) with period p, to be applied to an optical fiber along its length z during a drawing process. At least one parameter is selected so that (I) where ?1 is about 0.05 and y1 is the first of the three components y1(z), y2(z), y3(z) of a periodic function y(z) of period p such that (II) where LB is an expected beat length of said optical fiber and ?(z) is the derivative of the spin function ?(z) with respect to the length z. The method is effective for substantially reducing the PMD of optical fibers drawn when applying a spin function.

Abstract: An optical memory having an input port for receiving an input optical signal to be stored in the optical memory is disclosed. A portion of the optical signal is coupled to a storage loop for storing optical signals by a coupler that transfers a portion of the input optical signal to the storage loop. An optical signal stored in the storage loop is output by coupling a portion of that optical signal to a first external optical waveguide. The storage loop includes a semiconductor optical amplifier for amplifying the signals stored in the storage loop to compensate for losses incurred by those signals in traversing the storage loop. A plurality of such optical memories can be combined to form a larger memory that includes a reconditioning circuit that resets the amplitude of the optical signals to a value that depends on the amplitude of the optical signals.

Abstract: Techniques, devices, and systems for generating tunable dispersions to control or compensate for dispersions in optical signals by using wave-guiding grating elements with nonlinear group delays.

Abstract: The present invention relates to an optical waveguide type grating element and others in structure for decreasing absolute values of chromatic dispersion occurring in selective reflection of each of signal channels in a reflection band. The optical waveguide type grating element is provided with an optical waveguide in which signal light containing a plurality of signal channels spaced at a channel spacing ?i propagates, and a grating which is an index modulation formed over a predetermined range of the optical waveguide. Particularly, the optical waveguide type grating element has a transmittance of ?20 dB or less for each of the signal channels in the reflection band, and has a reflectance of ?20 dB or less for each of signal channels outside the reflection band. Furthermore, a deviation of a group delay time of each of the signal channels in the reflection band, which is caused by reflection in the grating, is 10 ps or less in a wavelength range of (?CH??i×0.375/2) or more but (?CH+?i×0.

Abstract: Optical systems and methods for optical wavelength conversion are provided. One such exemplary optical system includes a waveguide located in a substrate at least partially of a non-linear optical material, the waveguide structured to receive a continuous-wave optical signal. Also included is a grating located at least partially in the non-linear optical material section of the waveguide. The grating has a period “d,” and the waveguide produces a photonic bandgap when a forward propagating state of photonic energy of the continuous wave signal is separated from a backward propagating state of photonic energy of the continuous wave optical signal by a wavenumber (kz) equal to (2?/d), at a first photonic energy level in the waveguide.

Abstract: A fiber Bragg grating may be written at an arbitrary wavelength without extensive recalibration or reconfiguration of the writing equipment in some embodiments. A pair of writing beams may be used to expose the fiber. The crossing angles of the writing beams may be adjusted.

Abstract: A microfabrication process for preparing articles in which a precursor article that includes (a) a substrate, (b) a first polymer layer overlying the substrate, (c) a second polymer layer overlying the first polymer layer, (d) a metal hardmask layer overlying the second polymer layer, and (e) a photodefinable layer overlying the metal hardmask layer is subjected to photolithographic imaging, developing, and plasma etching steps to form an article that includes the substrate and portions of the first polymer layer arranged in a pattern corresponding to the pattern of the photomask used for photolithographic imaging.

Abstract: An optical pulse code recognition device and an optical distributor recognize multiple bits of a 1 Tbps packet signal as they are, all at one time. A serial signal light emitted from an optical fiber is collimated by a lens and applied onto a mask having a mask pattern. A thin film optical switch increases its optical transmittance when irradiated with a control light, allowing the collimated signal light to transmit through it. When the control light is applied, the transmitted collimated signal light is converted into a parallel signal. The mask pattern has multiple transmission portions allowing one bit of signal light to transmit through and an equal number of non-transmitting portions to block the light, and whether or not a bit pattern of the signal light and the mask pattern match each other is found by detecting a maximum or minimum value of light intensity with a photodetector.