Abstract: Rhomb beam splitters are used to implement various optical demodulators, in particular PSK and DPSK demodulators. The parallel beam-splitting and reflective surfaces of the rhomb structure produce reflection and transmission beams that exit the beam splitter parallel to one another and with a relative phase shift determined by the distance between the surfaces. These features afford the advantages of low cost, compactness, easily tunable, and temperature-insensitive optical structures for constructing a variety of optical demodulators.

Abstract: An object of the present invention is to provide a film having a high brightness and a natural metal-effect, and also having excellent formability, causing no delamination and maintaining the metal-effect after forming. Another object is to provide a molded body having less environmental burden, excellent in recycling efficiency and giving no electromagnetic interference. A laminated film including a structure where each 30 layers or more of a layer composed of a resin A (A layer) and a layer composed of a resin B (B layer) are alternately laminated, wherein a relative reflectance in a wavelength range of 400 nm to 1000 nm is 30% or more, tensile stresses at 100% elongation in a longitudinal direction and a width direction of the film are 3 MPa or more and 90 MPa or less in a tensile test at 150° C., and the number of layers with a layer-pair thickness of 10 nm or more and less than 220 nm is more than the number of layers with a layer-pair thickness of 220 nm or more and 320 nm or less.

Abstract: The main object of the present invention is a method for obtaining a flexible Bragg mirror (1?) from a photonic crystal consisting of a rigid porous multilayer (1), the method comprising filling with a polymer the pores of the porous multilayer (1) to provide it with mechanical stability.

Abstract: Various embodiments of the invention relate to methods and systems for generating the color white in displays created from interferometric modulators and more specifically, to the generation of the color white through the use of reflected light at two wavelengths. In one embodiment, a display device displays the color white. The color white is generated by reflecting light from two pluralities of interferometric modulator types. The first modulator type reflects colored light at a specific wavelength. The second modulator type reflects colored light selected to be at a wavelength complementary to the first. The combined light reflected from the two types appears white in the display.

Abstract: A method of manufacturing a multi-layer panel having a curved reflective and/or transmitting facing layer that includes the steps of increasing and/or decreasing pressure on a side of a thin membrane to form a pressure differential across the thin membrane that causes the thin membrane to deform to a required shape; applying a first layer of material to an outer surface of the thin membrane while the thin membrane is maintained in the required shape by the increase and/or decrease in pressure, and allowing the first layer of material to cure for a pre-determined time.

Abstract: A microscope includes optics configured to direct beams onto an object including a reflective material, a detector configured to receive a field spectrum formed by beams reflected by the object, and a calculator configured to reconstruct an image of the object from the field spectrum detected by the detector.

Abstract: Methods of fabricating a static interferometric image device and static interferometric image device formed by the same are disclosed. In one embodiment, a method includes providing a substrate. A plurality of liquid layers are formed over the substrate by an inkjet process such that the layers are lateral to one another. The liquid layers contain a solidifiable material or particles. Then, the plurality of liquid layers are solidified to form a plurality of solid layers. In some embodiments, the substrate includes pre-defined cavities, and the liquid layers are formed in the cavities. In other embodiments, the substrate includes a substantially planar, stepped, or continuously transitioning surface, and the liquid layers are formed on the surface. The inkjet process provides optical fillers or spacers for defining interferometric gaps between absorbers and reflectors in the display device, based at least partially on an image that the display device is designed to display.

Abstract: For the use in illumination systems and projection exposure apparatuses for UV or EUV lithography, a reflective optical element is provided for a operating wavelength in the ultraviolet to extreme ultraviolet wavelength ranges. The reflective optical element includes a substrate and a reflective surface on the substrate. The multilayer system has layers of at least two alternating materials having different real parts of the refractive index at the operating wavelength. Radiation in the operating wavelength of a certain incident angle bandwidth distribution can impinge on the reflective optical element. The reflective surface includes one or more first portions, in which the layers have alternating materials of a first period thickness. The reflective surface includes one or more additional portions, in which the layers of alternating materials have a first period thickness and at least one additional period thickness.

Abstract: An optical filter includes a first substrate, a second substrate, a first reflecting film disposed on a first opposed surface of the first substrate, a second reflecting film disposed on a second opposed surface of the second substrate, a first electrode provided to the first substrate at a peripheral position of the first reflecting film in a plan view, and a second electrode provided to the second substrate and opposed to the first electrode. At least one of the first opposed surface and the second opposed surface is provided with a step section, and an initial gap between the first reflecting film and the second reflecting film is smaller than an initial gap between the first electrode and the second electrode, to thereby allow control of the gap between the reflecting films with good accuracy.

Abstract: An image screen includes a transparent substrate, a metal film, and an optical reflective stack layer. The metal film is disposed on a first surface of the transparent substrate, having a thickness and a set of material characteristic constants being predetermined. The optical reflective stack layer is disposed over the metal layer. The metal film and the optical reflective stack layer function together to selectively reflect a light with a portion of wavelength. In addition, according to the need, a diffusion micro-structure layer can be disposed on a second surface of the transparent substrate. Further for example, another reflective layer or optical absorbing layer can be further disposed on another surface of the optical reflective stack layer. The reflective layer can be, for example, a metal film.

Abstract: A rhomb beam splitter, rather than a conventional cube, is used in combination with a mirror reflecting both the reflected and transmitted beams to obtain a delay-line interferometer demodulator with a substantially common path. This significantly reduces the sensitivity of the device to environmental changes and also greatly simplifies the manufacture process. A polarization-insensitive coating or a wave plate, a thermal phase tuner with a micro-heater, and two compensator plates are used in the paths of the beams to balance the optical path lengths and to compensate for polarization and environmental effects.

Abstract: Certain example embodiments relate to an improved secondary reflector panel with a heat-treatable coating. Certain example embodiments related to method of making a secondary reflector panel where a reflective coating is disposed onto a glass substrate. A portion of the reflective coating is removed and a frit material is disposed over the reflective coating. An elevated temperature is applied to the glass substrate, the coating, and the frit material where the frit is cured and the glass substrate is formed as desired.

Abstract: A method for compensating an image produced by image means for implementing image information takes account of ambient illumination. Luminance of external background illumination around the image means is measured. The measured luminance of the background illumination is compared with preset tristimulus values and a reflectance factor of the image means, a comparison result is computed, and a control signal is generated to compensate luminance and chroma of an image. Luminance and chroma of the image means are compensated in response to the control signal.

Abstract: A system and method for uniform light generation in projection display systems. An illumination source comprises a light source to produce colored light, and a scrolling optics unit optically coupled to the light source, the scrolling optics unit configured to create lines of colored light from the colored light, and to scroll the lines of colored light along a direction orthogonal to a light path of the illumination source. The scrolling optics unit comprises a single light shaping diffuser to transform the colored light into the lines of colored light, an optical filter positioned in the light path after the light shaping diffuser, and a scrolling optics element positioned in the light path after the optical filter. The single light shaping diffuser is capable of simultaneously transforming colored light into lines of colored light having substantially uniform intensity to provide uniform illumination.

Abstract: A half mirror has a shape on a substrate and excels in appearance and design and is fabricated by a method. The method includes forming an organic film by applying, onto a transparent substrate or film, a primer composition containing an addition-polymerizable compound having three or more reactive groups, an addition-polymerizable compound having an acidic group, and an addition-polymerizable compound having a hydrophilic functional group, and polymerizing the primer composition. The method includes turning the acidic group into a metal (M1) salt by treating the organic film with an aqueous solution containing metal (M1) ions, and turning the metal (M1) salt into a metal (M2) salt by treating the organic film with a metal (M2) ion aqueous solution containing metal (M2) ions that are lower in ionization tendency than metal (M1) ions, and (d) reducing metal (M2) ions to form a metal film on a surface of the organic film.

Abstract: An interference filter includes: a first substrate; a second substrate that faces one side of the first substrate and is bonded to the first substrate; a first reflection film formed on the side of the first substrate that faces the second substrate; and a second reflection film provided on the second substrate and faces the first reflection film, the first substrate including a first gap formation region in which the first reflection film is disposed and which is not contact with the second substrate, and wherein the first substrate and the second substrate are adhesively bonded to each other with the adhesive applied into the adhesive grooves with the first bonding region and the second bonding region bonded to each other.

Abstract: An omnidirectional structural color (OSC) having a non-periodic layered structure. The OSC can include a multilayer stack that has an outer surface and at least two layers. The at least two layers can include at least one first index of refraction material layer A1 and at least one second index of refraction material layer B1. The at least A1 and B1 can be alternately stacked on top of each other with each layer having a predefined thickness dA1 and dB1, respectively. The dA1 is not generally equal to the dB1 such that the multilayer stack has a non-periodic layered structure.

Abstract: It is an object to prevent deterioration of reflectance of a reflection layer composed of silver or a silver alloy, resulting from heat-caused migration of silver. The reflector for projection type display apparatuses which display image light beams emitted and reflected by a light source, modulated for light intensity by a display device and magnified by a projection lens, wherein the reflector is provided, on the reflection surface side, with a reflection layer composed at least of silver or a silver alloy, and a layer comprising inorganic particles and a binder composed of a silicon compound; and a light source and image display device which use the reflector.

Abstract: A reflective optical element and an EUV lithography appliance containing one such element are provided, the appliance displaying a low propensity to contamination. The reflective optical element has a protective layer system consisting of at least one layer. The optical characteristics of the protective layer system are between those of a spacer and an absorber, or correspond to those of a spacer. The selection of a material with the smallest possible imaginary part and a real part which is as close to 1 as possible in terms of the refractive index leads to a plateau-type reflectivity course according to the thickness of the protective layer system between two thicknesses d1 and d2. The thickness of the protective layer system is selected in such a way that it is less than d2.

Abstract: Multilayer-film reflective mirrors are disclosed that exhibit desired optical characteristics and resistance to reflective-surface degradation. An exemplary multilayer-film mirror includes a base and a multilayer film on the base. The multilayer film is made of first and second layers alternatingly laminated at a prescribed period length. The surface of the multilayer film has an irregular surface profile, relative to the surface profile of the base. The multilayer film reflects incident extreme ultraviolet (EUV) light. A third layer, situated on and covering the surface of the multilayer film, is formed of a substance having substantially the same refractive index to EUV light as the refractive index of a vacuum. The third layer has a surface profile substantially the same as the surface contour of the base. The third layer is covered with a protective layer.

Abstract: A multilayer mirror is constructed and arranged to reflect radiation haying a wavelength in the range of 2-8 nm. The multilayer mirror has alternating layers selected from the group consisting of: Cr and Sc layers, Cr and C layers, C and B4C layers, U and B4C layers, Th and B4C layers, C and B9C layers, La and B9C layers, U and B9C layers, Th and B9C layers, La and B layers, C and B layers. U and B layers, and Th and B layers.

Abstract: A method for removing at least one reflective layer (4a, 4b) from an optical element (1) for EUV lithography, wherein the optical element (1) has a substrate (2) and an interlayer (6) between the substrate (2) and the at least one reflective layer (4a, 4b). The method includes etching away the at least one reflective layer (4a, 4b) as far as the interlayer (6) with an etching gas (7), wherein the material of the interlayer (6) does not react with the etching gas (7), and wherein, after the etching away, the interlayer (6) has a surface roughness of less than 0.5 nm rms, preferably of less than 0.2 nm rms, and more preferably of less than 0.1 nm rms. Also, an optical element (1) for reflecting radiation in the EUV wavelength range includes a substrate (2), at least one reflective layer (4a, 4b), and an interlayer (6) arranged between the substrate (2) and the at least one reflective layer (4a, 4b).

Abstract: A cavity ring-down spectroscopy (CRDS) mirror is constructed to resist migration of a maximum reflectance peak during use where the CRDS mirror may become accreted with contamination that would otherwise cause the maximum reflectance peak to migrate. The mirror includes a mirror stack disposed on a mirror substrate and a plurality of alternating laminates including a first film with a first index of refraction and a second film with a second index of refraction. Each film is a one-quarter wavelength thickness of a given light energy that is to illuminate the mirror. A subsequent laminate is disposed on the plurality of alternating laminates. The subsequent laminate includes a quarter wavelength thickness first film and a second film with a wavelength thickness in a range from greater than 1.5 quarter wavelength and less than 2 quarter wavelength.

Abstract: Taught herein is an integragted narrow bandpass filter array and a method of its fabrication. The filter array is a Fabry-Perot type of filter array, wherein the pass band changes with the thickness of the spacer layer. The integrated filter array comprises a substrate, a lower mirror stack, a spacer array, and an upper mirror stack. The spacer array is an array of varied thicknesses formed using a combinatorial deposition technique. The spacer array is used to control the pass band of each mini-size narrow bandpass filter and realizes the integration of narrow bandpass filters with different pass bands on a single substrate. The merit of this technique lies in its fabrication efficiency and finished product rate which are much higher than for conventional methods. The filter array is completely matched with detector arrays and functional in most of the important optical ranges.

Abstract: Disclosed is a multilayer structure wherein a first layer of a first material having an outer surface and a refracted index between 2 and 4 extends across an outer surface of a second layer having a refractive index between 1 and 3. The multilayer stack has a reflective band of less than 200 nanometers when viewed from angles between 0° and 80° and can be used to reflect a narrow range of electromagnetic radiation in the ultraviolet, visible and infrared spectrum ranges. In some instances, the reflection band of the multilayer structure is less than 100 nanometers. In addition, the multilayer structure can have a quantity defined as a range to mid-range ratio percentage of less than 2%.

Abstract: A article includes a substrate and a metal dielectric reflective film. The metal dielectric reflective film is formed on the substrate, the metal dielectric reflective film includes a dielectric multiple layer and a metal layer. The dielectric multiple layer includes a first layer, a second layer, a third layer, and a fourth layer arranged in the order written and stacked one on another. The first and third layers comprised of a low refractive index material, the second and fourth layers comprised of a high refractive index material. The metal layer is disposed on the fourth layer.

Abstract: The present invention provides an optical laminated polyester film which can exhibit a good adhesion to a light diffusion plate, a prism layer and a hard coat layer as well as an excellent antistatic property without deterioration in transparency. The present invention relates to an optical biaxially oriented polyester film comprising a polyester film, a coating layer comprising a cationic polymer which is formed on one surface of the polyester film, and a layer formed on the other surface of the polyester film which is obtained by applying thereonto a coating agent comprising a polyurethane comprising a diol component having a polycarbonate structure, and a heat-crosslinking agent.

Abstract: An asymmetric mirror is composed of a dielectric substrate [500] and a coating [502] on the dielectric substrate. Within an operational wavelength range ??, the mirror has a transmission symmetry ?T=0% and a reflection asymmetry ?R>10%, where the reflection asymmetry ?R varies by less than 5% within the operational wavelength range ??. In addition, the wavelength range ?? is substantially broad, i.e., satisfies ??/?max>10%. The coating [502] is a metamaterial having structural features smaller than the smallest operational wavelength, e.g., a nano-structured metamaterial such as a photonic crystal or a disordered nano-composite of a metal and a dielectric. In a preferred embodiment, the coating [502] is semi-continuous with a filling factor p between 70% and 75%. The dielectric may be, for example, air, vacuum, an electro-optic polymer, an optical gain material, an electro-active material, or a semiconductor.

Abstract: A method for manufacturing optical elements (5), comprising the steps of providing (100) an optical sheet (1); coating (103) a reflective layer (4) on the optical sheet (1); and forming (102) a first set of tracks (3), each having a first width, across the optical sheet (1) to divide the optical sheet into a plurality of optical elements (5).

Abstract: An optical recognition device is provided. The optical recognition device includes a transparent substrate, a patterned infrared reflective film formed thereon, and an infrared anti-reflective film sheltering a gap in a recognition pattern of the patterned infrared reflective film, wherein the patterned infrared reflective film reflects the recognition pattern by reflection of infrared light and transmission of visible light. The invention also provides a display incorporating the optical recognition device.

Abstract: Retroreflective elements and articles that include such elements. The retroreflective elements (100) include a solid spherical core (110) having an outer surface. A first complete concentric optical interference layer (112) overlays the outer surface of the core providing a first interface between the core and the first optical interference layer, and a second complete concentric optical interference layer (122) overlays the first optical interference layer to provide a second interface between the first optical interference layer and the second optical interference layer. In some embodiments, a third complete concentric optical interference layer overlays the second optical interference layer to provide a third interface between the second optical interference layer and the third optical interference layer.

Abstract: Various embodiments are disclosed that are related to an optic with a dichroic coating. In one embodiment, sn optic comprises a wedge-shaped light guide having opposing first and second faces and a turning film bonded to the wedge-shaped light guide. The turning film comprises a plurality of facets oblique to the first face of the wedge-shaped light guide and supports a dichroic coating.

Abstract: An optical system has an optical component with a curved surface and zero optical power. The optical system is configured so that the optical component is the first optical structure encountered by radiation entering the optical system from externally thereof. According to a different aspect, a method is provided for making an optical system that has an optical component with a surface, where the optical component is the first optical structure encountered by radiation entering the optical system from externally thereof. The method includes configuring the surface to be curved, and configuring the optical component to have zero optical power.

Abstract: A wavelength dispersion compensation device includes an etalon 100 having a slab shape. Reflective films are formed on each side of the etalon 100. The reflective films respectively have predetermined reflectance. Reflectance of one of the reflective films differs according to a light incident angle by using a portion of light within a wavelength range to be used with which a filter characteristic in which transmittance rapidly changes is obtained.

Abstract: A cool light source includes a reflector having a band-reject reflective coating and an underlying absorptive coating. The cool light source also includes a window with a band-pass transmission function that is substantially complimentary to the band-reject reflective coating.

Abstract: A dichroic mirror includes a substrate, a first film stack, and a second film stack. The first film stack is deposed on the substrate and has a structure represented by a first formula: (2HL)n. The second film stack is deposed on the first film stack and has a structure represented by a second formula: (0.325H0.65L0.325H)m. ‘2HL’ and ‘0.325H0.65L0.325H’ respectively represent a double-layer sub-structure of the first film stack and a sandwiched sub-structure of the second film stack, and ‘n’ and ‘m’, which are integers, respectively represent the number of repetitions of the double-layer sub-structures and sandwiched sub-structures ‘H’ and ‘L’ respectively represent a high refractive index layer and a low refractive index layer, both of which have a height equal to ¼ of the reference wavelength of the dichroic mirror, and ‘2’, ‘0.325’ and ‘0.65’ are height coefficients.

Abstract: Micromirrors and micromirror arrays described herein are useful, for example in maskless photolithography systems and methods and projection display devices and methods. According to one aspect, the micromirrors comprise a polymer structural layer and a reflective dielectric multilayer for selective reflection and/or redirection of incoming electromagnetic radiation. According to another aspect, incorporation of a reflective dielectric multilayer allows for use of polymer structural materials in micromirrors and prevents damage to such polymer materials due to excessive heating from absorption of electromagnetic radiation, as the reflective dielectric multilayers are highly reflective and minimize heating of the micromirror components. According to yet a further aspect, top down fabrication methods are described herein for making a micromirror comprising a polymer structural layer and a reflective dielectric multilayer.

Abstract: A very low energy-absorption coating and related methods for use with high power CO2 lasers includes at least a thin layer of ThF4 (16) used as a water/moisture barrier, in combination with BaF2 (14), for various optical elements. When used in connection with a ZnSe substrate (12) or any other suitable material (such as for a focusing lens), the coating (10) extends the useful life by helping prevent moisture adsorption that otherwise may occur within 2-3 days of contact with air. The coating (10) may comprise (1) a BaF2 layer (14) of approximately optical quarter wave thickness, (2) a thin 200-300 Angstrom layer of ThF4 (16) used as a water barrier (3) a thin 1000-2000 Angstrom layer of ZnSe (18), and (4) an optional ZnSe layer (20) of optical half wave thickness. Among other applications, the coating (10) provides very low energy absorption for a 10.6 um CO2 laser at a value<0.15%, and provides longer lifetimes as compared to conventional coated lenses without the combination of BaF2 (14) and ThF4 (16).

Abstract: A multilayer reflective film coated substrate includes a multilayer under film comprised of Mo/Si alternately-layered films and a multilayer reflective film comprised of Mo/Si alternately-layered films for reflecting exposure light. The multilayer under film and the multilayer reflective film are formed on a substrate in this order. Given that a cycle length of the multilayer under film is d bottom (unit:nm) and a cycle length of the multilayer reflective film is d top (unit:nm), a relationship of a formula (1) is satisfied when d bottom>d top, the formula (1) given by (n+0.15)×d top?d bottom?(n+0.9)×d top where n is a natural number equal to or greater than 1.

Abstract: [Problem] In case of producing a plastic film-inserted laminated glass by forming an infrared rays reflection functioning film on a transparent plastic film and then by interposing the plastic film between intermediate films, an adhesion between the plastic film and the intermediate film is not good thereby causing such a problem that a peeling occurs upon collision. [Solving Means] A silane coupling film is formed on a surface where no infrared rays reflection film is formed, of a plastic film, and a hard coat layer is formed between the plastic film and the infrared rays reflection film.

Abstract: A plurality of optically isotropic, parallel dielectric plates of uniform thickness, mutually separated by gaps having a uniform width. The plates are connected by spacers located in the gaps. The gaps are either filled with a gas or evacuated. The plate thickness is on the order of one-half of the wavelength of incident radiation traveling within the medium filling the gaps. Each plate is composed of a transparent material characterized by its index of refraction. The stack of plates should include at least fifteen plates. This abstract is provided to comply with the rules requiring an abstract, and is intended to allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. 37 CFR §1.72(b).

Abstract: Plasmon-enable devices such as ultra-small resonant devices produce electromagnetic radiation at frequencies in excess of microwave frequencies when induced to resonate by a passing electron beam. The resonant devices are surrounded by one or more depressed anodes to recover energy from the passing electron beam as/after the beam couples its energy into the ultra-small resonant devices.

Abstract: An improved low-glare motor-vehicle mirror is realized by providing it with a multilayer coating comprising the following layers, in the order of their deposition: a transparent metallic layer; a first dielectric layer; a second dielectric layer with a lower refractive index than that of the first dielectric layer, and a metallic reflecting layer.

Abstract: An optical device, such as an interference mirror of the type which can be incorporated into ring laser gyros. One embodiment is an interference mirror having at least one layer formed from a matrix of material consisting of ZrO2 and about 2-15 weight percent of Al2O3.

Abstract: Example embodiments relate to a reflective structure, a display apparatus including the reflective structure, and a method of manufacturing the reflective structure and the display apparatus. A reflective structure according to example embodiments may include a plurality of nanoparticles of non-uniform size, which are arranged on a substrate, or an uneven element having a surface contour that resembles a plurality of nanoparticles; and a reflective layer covering the plurality of nanoparticles or the uneven element. The reflective layer may have a random/variable height.

Abstract: End reflectors, flat panel lens that may utilize the end reflector, and methods are provided. The end reflector for a flat panel lens may include a first grating having a first set of parallel planes. The first set of parallel planes may be of layers of alternating refractive indexes disposed at a first angle with a central plane of the flat panel lens. The end reflector may also include a second grating having a second set of parallel planes. The second set of parallel planes may be of layers of alternating refractive indexes of alternating refractive indexes disposed at a second angle with the central plane. The second angle may be equivalent to the first angle reflected about the central plane.

Abstract: An areal security element for security papers, documents of value and the like, with at least two different areal security features (20, 22) disposed one above the other, which each are recognizable upon viewing the security element from opposite sides, wherein the first security feature (20) has a thin-layer element (42) provided with an areal diffraction structure (46) with color shift effect, which contains a first reflection layer (40) with a first color effect, the second security feature (22) has a second reflection layer (44) provided with an areal diffraction structure (46) for producing a diffractive image, which shows a second color effect different from the first color effect, and wherein the thin-layer element (42) of the first security feature (20) and the reflection layer (44) of the second security feature (22) are provided with the same areal diffraction structure (46).

Abstract: Multilayer films are provided that exhibit a colored appearance when viewed at an oblique angle as a result of one or more reflection bands in the visible region of the spectrum. The films however provide no substantial reflection bands in either the visible or near infrared regions for light normally incident on the film. The films can be made to shift from clear at normal incidence to an arbitrary designed color at an oblique angle without necessarily becoming cyan.

Abstract: A method of reflecting impinging electromagnetic radiation by using engineered surfaces of alternating layers of materials having different indices of refraction is described. These layers can be fabrication or applied onto the surfaces of macro-scale objects. Also, a method of limiting the heating within the interior of an object being impinged upon by electromagnetic radiation is described.

Abstract: An image projection system includes a light source for generating a light beam, a reflective housing, and an invisible-light reflector. The reflective housing includes an opening and forms an accommodating space for accommodating the light source so that the light beam can emit from the opening along an optical path. The invisible-light reflector, whose normal is arranged to form an acute angle with the optical path, is installed at a reflecting position intersecting with the optical path outside the opening of the reflective housing. The invisible light of the light beam will be reflected back to the accommodating space by the invisible-light reflector without any destruction caused by the invisible light.