Abstract: A free-space optical communication device includes an optical fiber bundle and one or more processors. The optical fiber bundle includes a central fiber connected to a first photodetector, and a plurality of surrounding fibers, each surrounding fiber connected to a corresponding second photodetector. The one or more processors are in communication with the first photodetector and each second photodetector. The one or more processors are also configured to receive a current or voltage generated at the first photodetector and each second photodetector and to determine a pointing accuracy of a beam received at the optical fiber bundle based on the current or voltage generated at the second photodetectors.

Abstract: A monolithic fiber-lens array includes a number of optical fibers integrated into a fiber block and multiple lens elements integrated into a lens block. The fiber block is coupled to the lens block via a transparent adhesive layer, and the tips of the optical fibers are aligned with respective focal points of the lens elements.

Abstract: A recessed portion in a semiconductor substrate and a method of forming the same are provided. The method comprises: forming a mask on the semiconductor substrate; forming a protection layer on a top surface of the mask and on at least one sidewall of the mask, and on at least one surface of the semiconductor substrate exposed by the mask; performing a first etching process to remove the protection layer on the top surface of the mask and on a bottom surface of the semiconductor substrate exposed by the mask; and performing a second etching process to remove the remaining protection layer and to etch the semiconductor substrate to form the recessed portion. In this way, a recessed portion with relatively smooth and vertical sidewalls can be realized.

Abstract: There is provided an intermittent connection type optical fiber ribbon in which at least a part of a plurality of optical fibers that are arranged to be in parallel come into contact with each other, and between a part or the entirety of the optical fibers, a connection portion at which the adjacent optical fibers are connected to each other with an adhesive resin, and a non-connection portion at which the adjacent optical fibers are not connected to each other with the adhesive resin, are intermittently provided in the longitudinal direction, in which an outer diameter dimension of the optical fiber is equal to or less than 0.22 mm, and an inter-center distance of the adjacent optical fibers is 0.20±0.02 mm, and in which at least a part of the outer periphery of the optical fiber has no adhesive resin attached thereto.

Abstract: A ferrule-to-lens latch mechanism includes a cover movable with respect to a housing of an optical assembly between an open position in which a cavity defined by the housing is visible and a closed position in which the cavity is covered by the cover. A lens is positioned in the cavity and has one or more guide pins which are visible when the cover is in the open position prior to mating a ferrule to the lens. A spring clip coupled to the housing and positioned in the cavity is configured to allow insertion and removal of the ferrule from the cavity when the cover is in the open position and may bias the ferrule against the lens when the ferrule is mated to the lens. When the ferrule is mated to the lens, the cover may cooperate with the spring clip to inhibit removal of the ferrule.

Abstract: A fiber optic voltage conditioner, and method therefor, generally relate to voltage conditioning. In such a fiber optic voltage conditioner, there is a laser, and an optical circulator is coupled to receive a light signal from the laser. A controller is coupled to the laser and is configured to generate first control information for wavelength-drift control of the laser. A data acquisition module is coupled to the controller and is configured to generate second control information for the controller for adjustment of the first control information. A photodetector is coupled to the optical circulator to receive a returned optical signal and is coupled to the data acquisition module to provide an analog output signal thereto. The photodetector is configured to generate the analog output signal responsive to the returned optical signal. The data acquisition module is configured to generate the second control information using the analog output signal.

Abstract: A compact method for forming strong hermetic bonds and seals. Such bonds are made simply and with no intervening adhesives, by directly melting a thermoplastic polymer against or between two surfaces of thermoset materials.

Abstract: An optical fiber assembly includes a ferrule body with a plurality of optical fibers and an end of each optical fiber positioned adjacent the front face of the ferrule body. A beam-expanding element is positioned adjacent the front face of the ferrule body including a lens array aligned with the optical fibers. The lens array is spaced from the optical fibers by a predetermined distance to form a gap with an index-matched medium within the gap. A method of manufacturing the optical fiber assembly is also provided.

Abstract: Described is an optical fiber system for delivering ultrashort pulses with minimal distortions due to nonlinearity. The system is based on delivering the optical pulses in a higher order mode (HOM) of a few-moded fiber. The fiber is designed so that the dispersion for the HOM is very large. This results in a dispersion length LD for the delivery fiber that is exceptionally small, preferably less than the non-linear length LNL. Under these conditions the system may be designed so the optical pulses experience minimum non-linear impairment, and short pulse/high peak power levels are reproduced at the output of the delivery fiber.

Abstract: An anisotropic conductive film, containing a resin film; and conductive particles aligned into a monolayer within the resin film adjacent to or on one plane of the resin film with respect to a thickness direction of the resin film, wherein a distance between the one plane of the resin film and a center of the conductive particle is 9 ?m or less based on 10-point average.

Abstract: Fiber optic connection assemblies for rearranging sets of fiber optic signals arranged in one parallel optical configuration into one or more different parallel optical configurations are disclosed. In one arrangement, two (2) data transmission pairs are connected between one multi-fiber connector from each of two connector sets in a first parallel optical configuration using a common set of fiber positions for each multi-fiber connector. Another two (2) data transmission pairs are connected to the common set of fiber positions of a multi-fiber connector from the first connector set, but are connected to other fiber positions of the multi-fiber connectors of the second connector set, using fiber positions that are not used by the other two (2) data transmission pairs. In this manner, cabling complexity can be reduced with increased signal density within fiber optic cables having a multi-fiber configuration.

Abstract: A dual optical path rotary joint provides a low friction coupling of optical fiber connections for optogenetic research and other applications. Two optical paths are provided through the rotary joint which are rotation-insensitive. The ends of the rotary joint rotate with respect to a common housing, which may be provided with ball-bearings or other suitable low-friction rotational mounts in which a first rotating component and a second rotating component are secured. The first and second rotating components are not mechanically linked in rotation, and their rotation is only synchronized by magnets disposed on the first rotating component and the second rotating component. A pair of optical fibers is coupled to the first rotating component and another pair of optical fiber is coupled to the second rotating component. A pair of isolated optical paths links the pairs of fibers, which are directed between the first and second rotating components by reflection.

Abstract: A method of coupling optical fiber to a tubular includes positioning at least one optical fiber at least partially within an annular cavity defined between a tubular and an elongated member and radially compressing the elongated member against the tubular.

Abstract: A method of creating a region of index change in a photopolymer includes providing a photopolymer having a photosensitivity to light of a particular wavelength and creating a region of index change in the photopolymer by applying direct write lithography to expose the photopolymer of the region to light that includes the particular wavelength.

Abstract: The thermal processing device includes a stage, a continuous wave electromagnetic radiation source, a series of lenses, a translation mechanism, a detection module, a three-dimensional auto-focus, and a computer system. The stage is configured to receive a substrate thereon. The continuous wave electromagnetic radiation source is disposed adjacent the stage, and is configured to emit continuous wave electromagnetic radiation along a path towards the substrate. The series of lenses is disposed between the continuous wave electromagnetic radiation source and the stage, and are configured to condense the continuous wave electromagnetic radiation into a line of continuous wave electromagnetic radiation on a surface of the substrate. The translation mechanism is configured to translate the stage and the line of continuous wave electromagnetic radiation relative to one another. The detection module is positioned within the path, and is configured to detect continuous wave electromagnetic radiation.

Abstract: An optical coupling device includes an optical fiber holder configured to hold an optical fiber, a wavelength conversion member including a phosphor and an optical characteristic matching member and a wavelength conversion member holder configured to hold the wavelength conversion member. The optical coupling device includes a first region which is formed on an end face of the optical fiber and an end face of the wavelength conversion member, which are optically coupled, when bonding the optical fiber holder and the wavelength conversion member holder, and in which foreign bodies that shield the laser beam are removed from an optical axis of the optical fiber and an optical axis of the wavelength conversion member and a second region which is formed outside the first region when bonding the optical fiber holder and the wavelength conversion member holder, and in which the foreign bodies removed from the first region flow.

Abstract: An novel fiber pump signal combiner is disclosed in which a fiber bundle array is coupled to a double-clad fiber with a taper section that is formed by etching a tapered outer surface into the cladding of a fiber rod to produce a high quality tapered outer surface free of defects with an inner core that has a constant diameter.

Abstract: An optical engine for providing a point-to-point optical communications link between a first computing device and a second computing device. The optical engine includes a modulated hybrid micro-ring laser formed on a substrate and configured to generate an optical signal traveling parallel to the plane of the substrate. The optical engine further includes a waveguide, also formed in a plane parallel to the plane of the substrate, that is configured to guide the optical signal from the modulated ring laser to a defined region, a waveguide coupler at the defined region configured for coupling the optical signal into a multi-core optical fiber, and a multi-core optical fiber at the defined region that is configured to receive and transport the optical signal to the second computing device.

Abstract: In one exemplary embodiment, an optical coupler of a fiber optic system can include a light-source input cavity packaged in an outer casing. The cavity can receive an optical signal from a light source. An optical collimator packaged in the outer casing such that a receiving end of the optical collimator can receive the light source from the light-source input cavity. The optical collimator can include at least one beam forming stage. The optical collimator can generate a collimated beam output from the optical signal. An optical cavity can receive the collimated beam output of the optical collimator. The optical cavity can be coaxially included in a receiving optical fiber coupled with the outer casing coupled with optical cavity. The optical cavity can receive the collimated beam output of the optical collimator and input the collimated beam into the receiving optical fiber.

Abstract: An optical connection structure which permits easy and automatic alignment between the optical axes of optical fibers and the optical axes of cores of an optical waveguide, and a production method which ensures that an optical waveguide for the optical connection structure can be efficiently produced with higher dimensional accuracy are provided. An over-cladding layer of the optical waveguide includes an extension portion provided in a longitudinal end portion thereof, and optical fiber fixing grooves are provided in the extension portion as extending along extension lines of cores coaxially with the cores and each having opposite ends, one of which is open in an end face of the extension portion and the other of which is closed. Optical fibers are fitted and fixed in the respective optical fiber fixing grooves. The over-cladding layer further includes a boundary portion (6) provided between the other closed ends of the optical fiber fixing grooves and the cores.

Abstract: An optical transmission module has an optical transmission path in which optical transmission is performed between a first circuit board and a second circuit board disposed opposite the first circuit board. The optical transmission path has a folded structure having a bending radius. A circumferential portion drawn by the bending radius is provided substantially perpendicular to board surfaces of the first circuit board and the second circuit board.

Abstract: A method of creating a region of index change in a photopolymer includes providing a photopolymer having a photosensitivity to light of a particular wavelength and creating a region of index change in the photopolymer by applying direct write lithography to expose the photopolymer of the region to light that includes the particular wavelength.

Abstract: A combined optical and electrical flexible wiring includes a first film substrate, a plurality of conductors aligned parallel on a surface of the first film substrate, an optical fiber provided on the surface of the first film substrate and aligned parallel to the plural conductors, a second film substrate with which the plural conductors and the optical fiber are covered in such a manner as to include an exposed portion, a resin mount provided over the exposed portion in such a manner as to cover the plural conductors and the optical fiber, the resin mount being formed with a light inlet or outlet groove including a mirror surface therein, an optical-electrical conversion component formed on a surface of the resin mount, and a wiring pattern formed on the surface of the resin mount.

Abstract: Provided is a ferrule which includes a positioning mechanism configured to position an optical fiber having a predetermined outer diameter, and a recess configured for an adhesive to be disposed therein and having a first inner wall from which a front end of the optical fiber portion positioned by the positioning mechanism is protrudable, and a second inner wall opposite to the first inner wall. A distance between the first inner wall and the second inner wall is less than or equal to four times the outer diameter of the optical fiber.

Abstract: An embodiment of the invention relates to an optical resonator. The optical resonator includes an input optical waveguide and a closed loop coupled to the input optical waveguide. The closed loop is adapted to receive light from the input optical waveguide, wherein the closed loop includes at least one hole formed within a portion of the closed loop.

Abstract: An optical transmitter includes three or more emission optical fibers that are three-dimensionally arranged, a single reception optical fiber, and an optical path converting component to optically couple the emission optical fibers to the reception optical fiber. The optical path converting component includes optical transmission portions that are optically coupled to the three or more emission optical fibers one to one, respectively, and optically coupled commonly to the single reception optical fiber. Entry ends of the optical transmission portions are aligned with exit ends of the three or more emission optical fibers, respectively. Exit ends of the optical transmission portions are aligned, as a whole, with an entry end of the single reception optical fiber. The exit ends of the optical transmission portions are arranged substantially parallel to one another and in closer proximity to one another than the entry ends of the optical transmission portions.

Abstract: Embodiments of the present invention provide a plastic fiber coupler. The plastic fiber coupler includes a bundle of plastic optical fibers (POFs) arranged in a ring-shape; and an optical mixing tube attached to a cross-section of the bundle of POFs. In one embodiment, a cross-section of the optical mixing tube may be coated with a reflective film forming a reflective type plastic fiber coupler; in another embodiment, the optical mixing tube is attached to a second bundle of plastic optical fibers forming a transmissive type plastic fiber coupler.

Abstract: In accordance with a method of producing a ferrule with an optical fiber, a reinforcing pipe is adhered to a single-core fiber to form an adhesive portion that protrudes and tapers from a pipe end surface portion of the reinforcing pipe toward a front end of the single-core fiber. The single-core fiber includes an optical fiber and a coating. The coating is stripped from the front end of the single-core fiber to provide an exposed optical fiber portion and a coated optical fiber portion. The coated optical fiber portion has a coating end surface portion. The single-core-fiber is inserted in a ferrule provided with a first tapered hole and a second tapered hole until the coating end surface portion abuts against the first tapered hole and until the pipe end surface portion abuts against the second tapered hole. Thereafter, the single-core fiber is secured in the ferrule.

Abstract: An optical connector includes a fiber-support block configured to couple cores of a plurality of optical fibers, and a lens-support block including a contact surface provided with a plurality of openings, the contact surface contacted to a contact surface of the fiber-support block, the cores of the optical fibers projecting from the contact surface of the fiber-support block insertable into the respective openings, the lens-support block having pairs of collimate lenses and convex lenses in the respective openings, each of the collimate lenses and a corresponding one of the convex lenses being spaced apart from each other in an optical-axis direction, the collimate lenses being movable in the optical-axis direction and being pressed by elastically deformable members, respectively, in the optical-axis direction and toward the contact surface of the fiber-support block.

Abstract: An optical module includes an emitter-side mounting substrate, a receiver-side mounting substrate and an external waveguide substrate. The mounting substrate is provided with a waveguide having a core and a pair of fitting recesses. The external waveguide substrate is provided with an external waveguide having a core, a pair of fitting tabs and a lap joint portion. As the fitting tabs are fitted into the respective fitting recesses, the mounting substrate) and the external waveguide substrate are joined together, the two cores are aligned with each other, and the lap joint portion is positioned to overlap the mounting substrate.

Abstract: According to one embodiment, an optical rotary joint comprises a first collimator arrangement for coupling-on first light-waveguides, and a second collimator arrangement for coupling-on second light-waveguides, with the latter being rotatably supported relative to the first collimator arrangement about a rotation axis. A Dove prism is provided between the first and second collimator arrangements as a derotating element. The first and second collimator arrangements have at least one micro-lens array on which light-waveguides with associated ferrules are disposed. In order to avoid tensile forces from arising in the arrangement, or as a result of individual ferrules becoming interconnected by an applied adhesive, trenches, barriers, or also coatings are provided between the individual ferrules.

Abstract: An optical hybrid circuit includes a multimode interference coupler; a first 2:2 optical coupler; a second 2:2 optical coupler; a third 2:2 optical coupler; and a phase controlling region. The first 2:2 optical coupler, the second 2:2 optical coupler, and the third 2:2 optical coupler are coupled to one of the pair of first output channels, the pair of second output channels, the pair of third output channels, and the pair of fourth output channels of the multimode interference coupler. The phase controlling region is provided in one or both of each pair of at least two pairs of output channels from among three pairs of output channels to which the first 2:2 optical coupler, the second 2:2 optical coupler, and the third 2:2 optical coupler are coupled, respectively.

Abstract: The present invention relates to an optical module having a structure for reducing adverse contingencies such as increased number of fusion splicing points, drops in output, and higher costs associated with a greater number of optical components. The optical module comprises an amplification optical fiber, a transmission optical fiber, and a fusion splicing structure that fusion-splices the amplification optical fiber to the transmission optical fiber, in a state where a cover layer is removed at the tip portions, including the end faces, of these optical fibers. The fusion splicing structure includes a pumping light removing resin that covers directly the tip portions of the amplification optical fiber and the transmission optical fiber from which the cover layer is removed. The pumping light removing resin has a higher refractive index than a first cladding of the amplification optical fiber.

Abstract: An optical adapter that is arranged to connect two or more optical devices that have different connector layouts, the optical adapter comprising a material through which a plurality of waveguides is formed, the waveguides defining a first connector configuration at one end or face of the material and a second connector configuration at another, or same end or face of the material.

Abstract: An optical connector comprises a sleeve with a flange provided at one end face of a hollow cylinder, a collimator lens, which is press-fitted into or fitted by insertion into the sleeve to be thereafter adhered and fixed to the sleeve, and an optical fiber, which is fusion-bonded at the end face of the collimator lens on the opposite side to the flange side in such a state that the collimator lens is fixed into the sleeve, wherein the end face of the flange is machined to a plane perpendicular to an optical axis, and the collimator lens has a focal position at the end face on the opposite side to the flange side.

Abstract: A fiber-optic coupler packaging including an internal encapsulation for encapsulating a fiber-optic coupler, the refraction index of the internal encapsulation is smaller than the refraction index of the fiber-optic coupler, and an external encapsulation, for encapsulating the internal encapsulation, the refraction index of the external encapsulation is greater than the refraction index of the internal encapsulation, the internal encapsulation and the external encapsulation are substantially transparent to the range of wavelengths of the light traveling inside the fiber-optic coupler.

Abstract: The present invention relates to an optical interconnection structure and a method for manufacturing the same. The present invention provides an optical interconnection structure comprising: a substrate on which a hole penetrating through a predetermined region is formed; and an optical guide member fixed to the inside of the hole of the substrate, wherein the optical guide member and the substrate are fixed by metal oxide. The present invention provides the optical interconnection structure that can facilitate the optical interconnection between the active optoelectronic devices that transmit/receive the optical signals and the optical waveguide, making it possible to enhance heat dissipation efficiency and improve operation speed.

Abstract: Embodiments of the present invention provide a plastic fiber coupler. The plastic fiber coupler includes a bundle of plastic optical fibers (POFs) arranged in a ring-shape; and an optical mixing tube attached to a cross-section of the bundle of POFs. In one embodiment, a cross-section of the optical mixing tube may be coated with a reflective film forming a reflective type plastic fiber coupler; in another embodiment, the optical mixing tube is attached to a second bundle of plastic optical fibers forming a transmissive type plastic fiber coupler.

Abstract: The present invention provides a semiconductor laser module in which a coupling efficiency does not easily vary even though a displacement amount varies by the effect of welding. The semiconductor laser module comprises: a semiconductor laser element 2 for emitting a laser light whose cross-sectional shape at an emission end face is elliptical; an optical fiber 3 arranged to receive the laser light from the semiconductor laser element 2; a package 4 for housing the semiconductor laser element 2 and the optical fiber 3; a first fastening means 117 for fastening the optical fiber 3 to the package 4; and a second fastening means 7 for fastening the semiconductor laser element 2 to the package 4, wherein the semiconductor laser element 2 and the optical fiber 3 are fastened such that a minor axis of the elliptical shape of the laser light becomes parallel to a line connecting both ends of the optical fiber 3, said both ends being restricted by the first fastening means 117.

Abstract: An optical cable module is mainly provided with: an optical waveguide (10), a light-receiving element (11) and a supporting substrate (14) at its end portion of the light releasing side. The end portion of the optical waveguide (10) is fixed in its relative positional relationship with the light-receiving element (11). The end face of the optical waveguide (10) is not made perpendicular to the light axis (X-axis), and is diagonally cut so as to form an optical path conversion mirror (10D). Assuming that a light ray (indicated by a solid line in the Figure) that passes through the center of the light-axis cross section of a core (10A), and is reflected by the optical path conversion mirror (10D), and then reaches a light-receiving face at a light axis reflection position, the center of the light-receiving element (11) is placed with a gap from the light axis reflection position, in the optical cable module (1).

Abstract: A light input/output terminal module 100 comprises a jacket tube 110 and a flange 120. A glass portion 20 of the optical fiber is inserted in the center portion thereof. To efficiently remove the leaked light in a cladding 22 to the jacket tube 110, the jacket tube 110 is made of silica glass or the same material as that of the cladding 22. The jacket tube 110 is fixed by fusion splicing or adhesion to the cladding so as to integrally unify the jacket tube 110 and the cladding 22. The beam diameter at the fiber end portion is enlarged by an optical component which fusion bonds the tip end of the optical fiber to the coreless fiber so that the optical power density at the light input/output terminal module is reduced.

Abstract: A method for producing an optical fiber element provided with several optical fibers disposed in a matrix, including: a) placing and maintaining the several optical fibers in grooves formed in a mould plate, said grooves being in different planes, b) injecting a hardenable material adhering to the several optical fibers, c) solidifying the hardenable material to maintain the several optical fibers in a position set by the grooves, and d) removing at least the mould plate.

Abstract: Optical fiber lasers and components for optical fiber laser. An optical fiber laser can comprise a fiber laser cavity having a wavelength of operation at which the cavity provides output light, the cavity including optical fiber that guides light having the wavelength of operation, the fiber having first and second lengths, the first length having a core having a V-number at the wavelength of operation and a numerical aperture, the second length having a core that is multimode at the wavelength of operation and that has a V-number that is greater than the V-number of the core of the first length optical fiber at the wavelength of operation and a numerical aperture that is less than the numerical aperture of the core of the first length of optical fiber. At least one of the lengths comprises an active material that can provide light having the wavelength of operation via stimulated emission responsive to the optical fiber receiving pump light.

Abstract: Provided are a photoelectric conversion module for direct optical interconnection and a method of manufacturing the same, wherein an optical element array is bonded to a side surface of an IC board having a semiconductor chip mounted thereon and an optical waveguide array is bonded to one end of the optical element array having the other end bonded to the IC board to be optically connected to the optical element array, thereby improving the efficiency of optical coupling between optical elements and optical waveguides, and wherein since the optical coupling between the optical elements and the optical waveguides is realized on the same plane between the optical waveguides having the same array as the optical elements, multi-channel optical coupling can be facilitated to enable easy implementation of an optical design.

Abstract: A method for producing an optical fiber element provided with several optical fibers disposed in a matrix, including: a) placing and maintaining the several optical fibers in grooves formed in a mould plate, said grooves being in different planes, b) injecting a hardenable material adhering to the several optical fibers, c) solidifying the hardenable material to maintain the several optical fibers in a position set by the grooves, and d) removing at least the mould plate to p.

Abstract: An optical fiber structure includes a first fiber array and a second fiber array, which are placed one on the other. For example, the first fiber array includes a substrate having four V-shaped grooves and four first optical fibers, the output ends of which are linearly arranged and fixed to the substrate, and the second fiber array includes a substrate having four V-shaped grooves and four second optical fibers, the output ends of which are linearly arranged and fixed to the substrate. The first optical fiber is a multimode fiber having a core and a cladding, and the core diameter is 60 ?m and the outer diameter of the fiber is 80 ?m. The second optical fiber is a multimode fiber having a core and a cladding, and the core diameter is 105 ?m and the outer diameter of the fiber is 125 ?m.

Abstract: A rod lens is used for fitting in an endoscopes. The rod lens has a rod-shaped body which is made at least in a section of a flexible, transparent solid piece of plastic material.

Abstract: An optical fiber mounting waveguide device and a method for fabricating the same, which provide a low optical connection loss and a high productivity. An under cladding layer (3u), a core (4), and an over cladding layer (3o) are sequentially formed on a substrate (8) to constitute an optical fiber mounting waveguide device (1). An optical fiber mounting groove (2) for mounting an optical fiber (6) is formed on the optical fiber mounting waveguide device (1). An end surface (3a) of the over cladding layer (3o) faces to the optical fiber mounting groove (2). The core (4) and the under cladding layer (3u) are projected toward the optical fiber mounting groove (2) with respect to the end surface (3a) of the over cladding layer (3o).

Abstract: An integrated optical-amplification module includes a housing member, a first input optical terminal configured to receive an optical signal, a second input, optical terminal that can receive a pump light, and an output optical terminal that can output a combined optical signal comprising at least a portion of the optical signal and a portion of the pump light. The integrated optical-amplification module also includes an optical combiner fixedly installed relative to the housing member. The optical combiner can receive the pump light and the optical signal and an optical prism fixedly installed relative to the housing member. The optical combiner can merge the pump light and the optical signal to form the combined optical signal. The optical prism can direct at least a portion of the optical signal through free space to the optical combiner.

Abstract: A ferrule includes a recess formed on an obliquely polished surface to house a protrusion formed on an obliquely polished surface of another ferrule, so as to avoid an angular change at an interface between end surfaces of the pair of obliquely polished end surfaces of the ferrules facing each other.