Abstract: An optical communication assembly includes a demultiplexer coupled to an input fiber, a multiplexer coupled to an output fiber and a plurality of optical fibers. Each optical fiber is coupled to one or both of the demultiplexer and multiplexer. A plurality of attenuators are each coupled to an optical fiber in the pluality of optical fibers.

Abstract: An acousto-optic filter includes an optical fiber with a longitudinal axis, a core and a cladding in a surrounding relationship to the core. The optical fiber has multiple cladding modes. At least one acoustic wave generator is included and made of a sufficiently high frequency piezoelectric material to produce a longitudinal acoustic wave. An acoustic wave propagation member has proximal and distal ends. The distal end is coupled to the optical fiber and the proximal end is coupled to the acoustic wave generator. The acoustic wave propagation member propagates the longitudinal acoustic wave from the proximal to the distal ends and excites the longitudinal acoustic wave in the optical fiber.

Abstract: An acousto-optic filter has a non-birefringent single mode optical fiber with a longitudinal axis, a core and a cladding in a surrounding relationship to the core. The optical fiber has multiple cladding modes and a single core mode that is guided along the core. An acoustic wave propagation member has a proximal end and a distal end coupled to the optical fiber. The acoustic wave propagation member propagates an acoustic wave from the proximal to the distal end and launches a flexural wave in the optical fiber. At least one acoustic wave generator is coupled to the proximal end of the acoustic wave propagation member.

Abstract: An optical communication assembly has an optical cross connect coupled to a first, a second, a third and a fourth set of optical fibers. A first demultiplexer is coupled to a first input fiber and the first set of optical fibers and a second demultiplexer is coupled to a second input fiber and the second set of optical fibers. A first multiplexer is coupled to a first output fiber and the third set of optical fibers. A second multiplexer is coupled to a second output fiber and the fourth set of optical fibers. A first set of attenuators is coupled to the third set of optical fibers and a second set of attenuators coupled to the fourth set of optical fibers.

Abstract: The optical loss filter according to the present invention is configured such that a first long-period grating and a second long-period grating are formed in cascade on a unitary optical fiber having a core region and a cladding region. A coating layer surrounding a part of the cladding region is provided between the first and second long-period gratings. The optical loss filter can be made smaller, and can easily realize a desirable loss characteristic.

Abstract: This invention relates to an optical transmission line having a structure that reduces dispersion with respect to signal light in a 1.55-&mgr;m band. Each transmission unit includes a dispersion-shifted optical fiber as a transmission medium and a mode removing unit for reducing the optical power of high-order modes excluding a fundamental mode of light signals propagating through the dispersion-shifted optical fiber. The dispersion-shifted optical fiber has an incident terminal on which the light signals are incident and an exit terminal from which the light signals are emitted, and has a cutoff wavelength longer than the wavelength of the light signals at a fiber length of 2 m. The mode removing unit has a structure for reducing the optical power of high-order modes to 1/10 or less, preferably 1/40 or less, of the optical power of the fundamental mode so as to satisfy the single-mode condition in relation to fiber length.

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

Abstract: This invention relates to optical fiber systems where light is launched into and propagated in the fundamental mode of graded-index multimode fiber. Generally, it is not possible to launch light exclusively into the fundamental mode of graded-index multimode fiber by butt-coupling the multimode fiber to an arbitrary fiber carrying light from a source; several other modes may be launched. By inserting a length of a special singlemode fiber between an arbitrary fiber carrying light from a source and the graded-index multimode fiber, light can be launched exclusively into the fundamental mode of the graded-index multimode fiber. The special singlemode fiber has a modal pattern that matches the fundamental Gaussian modal pattern of the graded-index multimode fiber, which permits launching of the light into only the fundamental mode of the multimode fiber. Several applications for propagation in the fundamental mode of graded-index multimode fiber arises.

Abstract: The invention relates broadly to a fiber optic sensor device, advantageously, a refractive index measurement device. A light emitting member transmits light, preferably coherent light, to a light splitter. The light splitter splits the light into a first portion that is transmitted to a first fiber optic coupler having an input optical fiber member and an optical fiber member having a waist region. A first output optical fiber member emerges from the first fiber optic coupler waist region. The light splitter is positioned to insert light into the first fiber optic coupler input optical fiber member. A reference fiber optic coupler includes an input optical fiber member and an optical fiber member having a waist region. The reference fiber optic coupler is enclosed in a potting medium stable reference of constant refractive index. A reference output optical fiber member emerges from the reference fiber optic coupler waist region.

Abstract: An electromagnetic field frequency filter which includes a bus waveguide that carries a signal having a plurality of frequencies, including a desired frequency, and a drop waveguide. A resonator-system is coupled to the bus and drop waveguides via directional couplers and transfers the desired frequency from the bus waveguide to the drop waveguide while allowing transmission of the remaining frequencies in the bus waveguide. The input signal in the bus waveguide is coupled from the bus waveguide to the resonator-system by a first directional coupler. The resonator-system includes two sub-elements each comprising at least one resonator. The first directional coupler splits the input signal into two preferably equal parts and directs each part into a resonator sub-element. The desired frequency is transferred to the drop waveguide by a second directional coupler. The non-desired frequencies are returned to the bus waveguide, in the forward direction, by the first directional coupler.

Abstract: An optical waveguide supporting a plurality of modes including an annulus which attenuates a desired mode to a lesser degree than any other mode in the plurality of modes. In one embodiment, the annulus is disposed in the core of the waveguide. In another embodiment, the annulus is concentric about the core. In another embodiment, the annulus has a predetermined width and radius. In yet another embodiment the optical waveguide includes an annulus that is disposed at a radial position corresponding to a region in the core in which the desired mode has substantially no energy. In yet another embodiment the desired mode includes the LP02 mode. In another embodiment, the annulus includes a scattering material. In still another embodiment, the annulus includes a conductive dopant material. Another embodiment includes a sharp change of refractive index within the core. Still other embodiments include disposing a region of increased refractive index in the core of the waveguide to attenuate undesired modes.

Abstract: In accordance with the invention, an optical waveguide comprising a longitudinally extending core housing an optical grating and a cladding layer peripherally surrounding the core, is provided with an outer surface of the cladding layer having one or more perturbations. Each perturbation has a height with respect to the core that varies by at least 0.1 times a Bragg wavelength of the grating over the surface of the perturbation and covers an extent of the outer surface whose linear dimensions are less than 1 cm. The perturbations suppress cladding mode spectra and reduce short wavelength cladding mode loss.

Abstract: The invention relates to apparatus and methods for transforming a spatial mode of an optical signal. The apparatus includes an optical phase element for imparting a predetermined spatially selective phase delay to the optical signal, and a mask in optical communication with the optical phase element. The mask, in one embodiment, includes an optically attenuating region disposed in a predetermined spatial pattern. In one aspect of the invention, the optical signal is transformed from a first spatial mode to a second spatial mode. In another aspect of the invention, the mask includes an absorbing material arranged in a predetermined spatial pattern. In yet another aspect of the invention, the mask includes a scattering material arranged in a predetermined spatial pattern. The invention also relates to a method for transforming a spatial mode of an optical signal. The method includes the step of receiving the optical signal having a first spatial mode with an intensity distribution and a phase.

Abstract: A method of improving modal bandwidth in computer networks using multimode optical fiber and single mode sources is disclosed in which the optical signal from a center of the optical fiber is prevented from reaching the detector. This is accomplished according to a number of different techniques including the use of opaque spots on the fiber media/fiber couplers or the use of dark-cored fiber couplers. These configurations prevent pulse splitting that occurs in single mode source/multimode fiber systems by preventing light from the multimode fiber's center from interfering with the detector. When this is achieved, the detector is insulated from the effects of pulse splitting, supporting increased data rates by increasing the modal bandwidth.

Abstract: A Mach-Zehnder device includes a delay element in one arm which delays propagation of light at a first wavelength relative to propagation of light at a second wavelength. The delay element may be made up of a grating having a period which causes coupling of the first wavelength from a first mode into a second mode. In another aspect, the invention includes a second grating positioned downstream from the first grating and having a period which causes coupling of the portion of light from the second propagation mode back into the first propagation mode. Also disclosed is an optical waveguide in which light at a wavelength &lgr; can propagate in at least a first and a second mode. The waveguide has an effective index of refraction n1 with respect to the first propagation mode of &lgr;, and an effective index of refraction n2 with respect to the second propagation mode. A grating formed in said waveguide and having a period approximately equal to(&lgr;/2)(n1−n2).

Abstract: An optical add/drop multiplexer includes a mode converter. A first mode coupler is coupled to an input of the mode converter. A second mode coupler is coupled to an output of the mode converter. The mode converter includes an optical fiber with multiple cladding modes and a single core mode guided along a core. An acoustic wave propagation member is coupled to the optical fiber. The acoustic wave propagation member propagates an acoustic wave from its proximal to its distal end. At least one acoustic wave generator is coupled to the proximal end of the acoustic wave propagation member.

Abstract: A photonic integrated circuit (PIC) device comprising two or more vertically stacked asymmetric waveguides is provided. A photo-detector PIC device comprises a coupling waveguide for providing low-coupling loss with an external optical fiber and for guiding primarily a first mode of light, a second waveguide vertically coupled to the first waveguide for guiding primarily a second mode of light having an effective index of refraction different from the first mode, and a photo-detector vertically coupled to the second waveguide. Light received at the coupling waveguide is moved into the second waveguide via a lateral taper in the second waveguide. The photo-detector PIC device may further comprise a third waveguide having an optical amplifier therein and positioned between the coupling waveguide and the second waveguide.

Abstract: An optical waveguide supporting a plurality of modes including an absorbing annulus which attenuates a desired mode to a lesser degree than any other mode in the plurality of modes. In one embodiment, the absorbing annulus is disposed in the core of the waveguide. In another embodiment, the annulus is concentric about the core. In another embodiment, the annulus has a predetermined width and radius. In yet another embodiment the desired mode includes the LP02 mode.

Abstract: A twin coupler system couples a multimode pump power signal from a pump fiber to an optical information carrying double-clad signal fiber. The twin coupler system includes first and second optical couplers and a mode scrambler. The first optical coupler couples the pump fiber to the optical signal fiber to transfer outer modes of the pump power signal from the pump fiber into the optical signal fiber. The mode scrambler scrambles the modes of the pump power signal remaining in the pump fiber beyond the first optical coupler. The second optical coupler couples the pump fiber to the optical signal fiber to transfer outer modes of the scrambled pump power signal from the pump fiber into the optical signal fiber.

Abstract: The present invention is directed to a generally small mode field diameter (“MFD”) optical fiber having a core bounded by a cladding, a cleaved end, and an expanded mode field diameter. The expanded mode field diameter is formed by thermally diffusing one or more dopants in the core of the small mode field diameter optical fiber using a highly localized heat source. The resulting adiabatic taper has an expanded mode field diameter that is optimized for connection to another optical fiber having a larger mode field diameter. The adiabatic taper is formed in the smaller mode field diameter optical fiber by aligning and abutting the cleaved ends of two fibers having different mode field diameter's to form a splice seam. The splice seam is offset a predetermined distance from the center of the region heated by a heat source to splice the fibers and expand the mode field diameters. As the mode field diameters expand, the splice loss across the splice is monitored.

Abstract: Systems and methods for suppressing cladding modes at the signal wavelength in an optical fiber system utilizing an optical amplifier without perturbing the pump wavelength. An outer cladding of the gain fiber is removed providing a short section of a single mode fiber that does not guide the higher order modes, thus attenuating the higher order modes. Therefore, this system eliminates unwanted noise. In an embodiment, the modes are filtered at the end of the gain section of the optical fiber before splicing to an input fiber. Hydro florate etching can be utilized to remove the outer cladding. The resulting fiber maintains fundamental mode propagation and no mode mixing occurs while losing the higher order modes eliminating the noise.

Abstract: A single-ended long period grating optical device is presented. The single-ended optical device comprises an optical waveguide having at least one core mode and a plurality of cladding modes. At least one long period grating couples light from the core mode to the cladding modes. A reflector is positioned in an operable relationship to the long period grating, and the reflector reflects a signal. A mode stripper is positioned after the long period grating and removes the cladding modes from a transmitted signal and the reflected signal.

Abstract: An acousto-optic filter has a non-birefringent single mode optical fiber with a longitudinal axis, a core and a cladding in a surrounding relationship to the core. The optical fiber has multiple cladding modes and a single core mode that is guided along the core. An acoustic wave propagation member has a proximal end and a distal end coupled to the optical fiber. The acoustic wave propagation member propagates an acoustic wave from the proximal to the distal end and launches a flexural wave in the optical fiber. At least one acoustic wave generator is coupled to the proximal end of the acoustic wave propagation member.

Abstract: An acousto-optic filter has a non-birefringent single mode optical fiber with a longitudinal axis, a core and a cladding in a surrounding relationship to the core. The optical fiber has multiple cladding modes and a single core mode that is guided along the core. An acoustic wave propagation member has a proximal end and a distal end coupled to the optical fiber. The acoustic wave propagation member propagates an acoustic wave from the proximal to the distal end and launches a flexural wave in the optical fiber. At least one acoustic wave generator is coupled to the proximal end of the acoustic wave propagation member.

Abstract: An irreversible optical device using an optical frequency shift. The invention provides an irreversible phase shifter including frequency shifters. An irreversible interferometer is also provided which includes the irreversible phase shifter. The invention also provides an irreversible interferometer using a twin-mode optical fiber. In addition to the twin-mode optical fiber, this irreversible interferometer includes mode/frequency shifters and LP11 mode strippers. The irreversible interferometer exhibits a light transmissivity varying in accordance with the advancing direction of light, so that it can have the same functions as conventional optical isolators or circulators. In accordance with the invention, it is possible to configure a comb filter by incorporating passive mode couplers to the irreversible interferometer. It is also possible to vary the transmissivity and transmitting direction of light or to shift the comb position of the comb filter from a wavelength range, using electrical signals.

Abstract: An acousto-optic filter has a non-birefringent single mode optical fiber with a longitudinal axis, a core and a cladding in a surrounding relationship to the core. The optical fiber has multiple cladding modes and a single core mode that is guided along the core. An acoustic wave propagation member has a proximal end and a distal end coupled to the optical fiber. The acoustic wave propagation member propagates an acoustic wave from the proximal to the distal end and launches a flexural wave in the optical fiber. At least one acoustic wave generator is coupled to the proximal end of the acoustic wave propagation member.

Abstract: A single-mode fiber laser (66) that provides increased power. The fiber laser (66) includes a fiber ribbon (30) having a plurality of parallel waveguides (10). Each waveguide (10) includes a rectangular shaped core (12) that has a relatively thin dimension in one direction and a relatively wide dimension in an orthogonal direction. A step-index cladding (14, 16) is provided in the thin direction to limit the propagation of light in the core (12) to a single mode in that direction. Mode filters (18, 20) are provided adjacent the ends of the core (12) in the thickness direction and the various propagation modes in the core (12) enter the mode filters (18, 20). The mode filters (18, 20) guide the desirable single-mode back into the core (12) and reject the other modes away from the core (12). Light absorbing layers (22, 24) are provided adjacent the mode filters (18, 20) and opposite the core (12) to absorb the undesirable propagation modes of light.

Abstract: The polarizer is formed on a silicon rib waveguide (4) having an upper face and two side faces, and comprises a section of the silicon rib waveguide (4) with a buffer layer (6) and a light absorbing layer (7) on either the upper face of the rib or at least one side face of the rib. The buffer layer (6) has a refractive index similar to that of the waveguide (4) such that light traveling along the waveguide (4) and incident upon the respective face thereof passes into the buffer layer (6) and then into the light absorbing layer (7) so either the TM (transverse magnetic) or TE (transverse electric) mode of the light traveling along the waveguide is attenuated.

Abstract: A method for improving modal bandwidth in computer networks using multimode optical fiber and single mode sources is disclosed in which the optical signal from a center of the optical fiber is blocked from reaching detector. This is accomplished according to a number of different techniques including the use of opaque spots on the fiber media/fiber couplers or the use of dark-cored fiber couplers. These configurations prevent pulse splitting that occurs in single mode source/multimode fiber systems by preventing light from the multimode fiber's center from interfering with the detector. When this is achieved, the detector is insulated from the effects of any pulse splitting, supporting data rates of greater than one GBPS by increasing the modal bandwidth.

Abstract: The present invention is a tunable optic fiber bandpass filter using flexural acoustic waves that includes an optic fiber; a first silica horn; a first acoustic transducer; a first signal generator; a first acoustic absorber; a core blocker; a second acoustic absorber; a second silica horn; a second acoustic transducer; and a second signal generator.

Abstract: A semiconductor optical device, a fiber optical amplifier and an optical transmission system are disclosed. The semiconductor optical device is excellent in the stability of the coupling efficiency and the splitting ratio of a Y-branch. Both the fiber optical amplifier and the optical transmission system operate in a stable manner over a long period of time even if an optical waveguide is employed which is operative in a multi-mode in the transverse direction. The semiconductor optical device has an optical waveguide, a mode filter for transmitting therethrough light of a fundamental mode and blocking the propagation of light of a higher-order mode. The mode filter is provided in at least a part of the optical waveguide. The width of the mode filter is larger than that of the optical waveguide.

Abstract: A semiconductor TE/TM mode converter comprises a semiconductor waveguide layer including a compressive-strained first region and a tensile-strained second region, and a diffraction grating formed on the first region. The first region and second region are reversed-biased and forward-biased, respectively. TE mode light incident on the facet of the first region generates TM mode light outgoing from the facet of the second region. The diffraction grating in the first region has selective reflectance against TM mode light and reflects the TM mode light toward the second region, to lower the lasing threshold of TM mode light and raise the conversion efficiency.

Abstract: A method and apparatus for coupling high intensity light into a low melting temperature optical fiber which uses a high temperature, low NA optical fiber as a spatial filter between a source of high intensity light and a low melting temperature, low NA optical fiber. In an alternate embodiment, the spatial filter is composed of a fused bundle of optical fibers. The source of light may be a high intensity arc lamp or may be a high NA, high melting temperature optical fiber transmitting light from a remote light source.

Abstract: An optical waveguide amplifier is formed to include an adiabatic region disposed between an input single mode waveguide and a large area, multimode gain region. The utilization of the adiabatic region allows for a single mode signal to be supported and provides for a larger gain area to be formed, thus providing a larger gain and higher output power than conventional prior art waveguide amplifier arrangements.

Abstract: This invention relates to an all-fiber acousto-optic tunable wavelength filter which is useful in optical communications or optical fiber sensor systems. The present invention provides an all-fiber acousto-optic tunable filter, comprising: a length of optical fiber for propagating optical waves; a first mode converting means for selectively converting a core mode of the optical wave propagating in said optical fiber into a cladding mode by means of acoustic wave, depending on the wavelength of the optical wave; and a mode selecting means for selecting one or more mode among the core modes and cladding modes. In the embodiment of the invention, the mode selecting means may be configured to be a length of optical fiber whose jacket is partially stripped and a flexural acoustic wave generator to which electrical signal with a plurality of frequency components is applied. According to the invention, the wavelength filters provides a wide tuning range and can electrically control its filtering feature.

Abstract: A fiber optic system in accordance with the present invention includes an optical fiber, a coupling device, and a system for generating a pump signal. The optical fiber has a birefringence which preserves polarization and has a first polarization mode which is substantially perpendicular to a second polarization mode. The coupling device couples an input signal with an input wavelength into the optical fiber so that the input signal propagates in the first polarization mode in the optical fiber. The system for generating a pump signal generates a pump signal with a pump wavelength which is within a range of 50 nanometers (nm) to 300 nm less than the input wavelength and which has a first amount of pump power which is enough power to switch the input signal, but not enough to create higher order solitons. The coupling device also couples the pump signal into the optical fiber so that the pump signal propagates in the first polarization mode in the optical fiber.

Abstract: An optical waveguide device comprises: a waveguide substrate with a waveguide created therein; optical fibers optically linked to the waveguide at both end surfaces of the waveguide; and a double-refraction means provided at the one end surface for splitting an incident light into normal and abnormal lights. A rutile plate stuck to an end surface of the waveguide is used as an actual double-refraction means for arbitrarily selecting an incident light hitting the waveguide and splitting the incident light into normal and abnormal components. By providing rutile plate having a double-refraction effect such as the rutile plate on the end surface of the waveguide, a difference in phase between optical paths is resulted in due to polarization of the incident light, making separation into TE and TM modes possible. By optically linking lights split and radiated in the rutile plate to the incident end surface of the waveguide, any arbitrary polarization light can be applied to the waveguide.

Abstract: A monolithically integrated vertical twin-waveguide structure reduces the sensitivity of the device performance characteristics due to the laser cavity length and variations in the layer structure. This is achieved by the introduction of an absorption or loss layer between the active and passive regions. This layer eliminates the propagation of the even mode, while having minimal effect on the odd mode. The threshold current densities and differential efficiencies of the devices are unaffected by the loss layer. A coupling efficiency of 45% from the laser to the external passive waveguide is obtained.

Abstract: Two new techniques for the separation of orthogonally polarized light or ht of 2 arbitrary wavelengths by use of a waveguide optical device, based on either 1) simultaneous crossed and barred 1-by-1 off-center self-imaging, or 2) out-of-phase self-imaging. Simultaneous crossed and barred 1-by-1 off-center self-imaging utilizes a waveguide optical polarization splitter having an input waveguide containing TE and TM, a multimode interference region, aligned so that TE and TM refractive indices are very different, and with the length set so that the polarization with the lower refractive index is bar self-imaged while the other polarization is cross self-imaged, an output waveguide containing polarization with higher refractive index, and another output waveguide containing the other polarization. Both of these methods may also be used to separate light of 2 arbitrary wavelengths.

Abstract: An optical mode filter, that is, an optical component in which the basic mode can propagate undamped as much as possible but which in higher modes are strongly damped. The optical mode filter, is an integrated optical wave guide formed by, a higher-refracting or an absorbent material disposed near a flat wave guide core. Two buffer layers are located opposite the wave guide core, and one is formed with a thinned region to function as a filter for higher modes being transmitted through the wave guide core.

Abstract: The optical waveguide system comprises a mode discriminating coupler and reflective mode coupling means. These components can be combined in a variety of ways to perform a variety of functions. Among them are drop multiplex devices, add multiplex devices, add/drop multiplex devices, and power combiners. The device combinations can have low loss as well as high reliability, the latter due to the robust structure of the devices.

Abstract: A waveguide layer is formed on a transparent substrate disposed to cross an optical axis perpendicularly, and on the waveguide layer, a concentric circular grating coupler is disposed so that the optical axis passes the center. A light beam radiated from a semiconductor laser passes through the transparent substrate and enters the waveguide layer. Light beams enter the respective positions of the grating coupler are excited and move from the periphery to the center, and the light beams pass through the center and become waveguide light beams. The waveguide light beam is the reverse wave of the waveguide light beam inputted at the transmittance position. Therefore, the radiant beam radiated from the grating coupler also becomes a reverse wave inputted at the irradiating position, and is accurately fed back to the semiconductor laser. The laser wavelength is locked since the radiant beam has wavelength selectivity.

Abstract: A method is provided for reducing the polarization shift between different modes of an optical signal propagating in an optical grating having a plurality of waveguides extending in a common plane. The method includes the step of imparting curvature to the optical grating along a line that traverses the plurality of waveguides in a direction that is substantially perpendicular to the direction in which the optical signal propagates. The curvature varies in a nonuniform manner along the line to which it is imparted. The curvature may vary in a substantially linear manner along this line, which in some cases may define a symmetry axis of the grating. Sufficient curvature may be imparted to substantially eliminate the polarization shift. The curvature may be imparted by flexing the optical grating at two contact points respectively located near a longest and shortest of the plurality of waveguides.

Abstract: An apparatus for selecting waveguide modes in optical fibers is disclosed, which comprises an optical fiber having of a core and a cladding sheathing the core. The optical fiber has a selected portion of the cladding removed and forms a recessed space in the cladding while preserving a predetermined thickness of the cladding remaining covering the core. The optical fiber is selected for allowing the transmission of light having multiple waveguide modes with radial and azimuthal electric field components. The apparatus further comprises a birefringent material filled in the recessed space. The birefringent material has the first and second refractive indices and the first refractive index is larger than the core index of the optical fiber, while the second refractive index is smaller than the cladding index of the optical fiber.

Abstract: A waveguide device comprising a cladding layer having a refractive index n.sub.cl, a first waveguide having a refractive index n.sub.g (n.sub.g >n.sub.cl) formed on said cladding layer, and a second waveguide having a refractive index n.sub.cp (n.sub.cp >n.sub.g) formed on said first waveguide, wherein the sectional shape of said second waveguide has a tapered structure in which a layer thickness of said second waveguide reduces as the distance from the end face of the waveguide increases, and a tapering angle .THETA. in said tapered structure satisfies the following conditions:.THETA..sub.a ={90.degree.-arcsin (n.sub.eff /n.sub.cp)}/2 (1).THETA.<2.0 .THETA..sub.a (2)wherein n.sub.eff represents an effective refractive index of said first waveguide. This waveguide device has a high resistance against the deviation in the positions of the light exit face of an LD or an optical fiber and the light entrance face of a waveguide and thus enables an optical coupling at a high efficiency.

Abstract: An optical waveguide circuit comprises a mode splitter and an input guide (1/4/6.1) and first and second output guides (6.2/2, 6.3/3), and a mode converter (5) incorporated in the input guide for converting a fraction of an optical signal (I.sub.i), entering via the input waveguide, of a first propagation mode into a second propagation mode having mutually different order. The mode converter (5) has a first waveguiding section (5.1) and a second waveguiding section (5.2), which adjoin each other via a single discontinuity (7). The first and second sections (5.1 and 5.2) have propagation modalities, as a result of which, at the discontinuity, a coupling can take place between two propagation modes of different order, whereas the extent (x) of discontinuity determines the fraction of conversion for obtaining a desired splitting ratio in emitting signals (I.sub.o1, I.sub.o2).

Abstract: A mode splitter and the magneto-optical pick-up device including the mode splitter are provided. The mode splitter includes a tapered waveguide portion whose thickness gradually becomes thin so that a light of at least one mode can be cut off. An emission position of a light wave can be varied depending on its mode. In this mode splitter, the emission position of the light wave of each mode can be adjusted by changing a thickness of the tapered waveguide, thereby improving the degree of freedom in designing the device.

Abstract: When a laser beam enters into a grating coupler at a right angle, a guided wave with a wave mode corresponding to an incident angle can be generated. Although the guided wave is a light beam in single mode, the waveguide mode is deflected by passing through a step-wise structure and is converted into several guided waves having several modes. When the guided waves are radiated from a straight output grating coupler, the radiant angle is dependent upon the waveguide mode, so beams are radiated in different directions according to their respective waveguide modes. Therefore, a guided wave in zero-order mode outputs a radiant beam having a larger radiant angle, while a guided wave in first-order mode outputs a radiant beam having a smaller radiant angle.

Abstract: A light-receiving module includes: a pigtail optical fiber including a core portion for transmitting an optical signal and a cladding portion covering a side face of the core portion; an optical connector provided at a first end of the pigtail optical fiber for optically connecting a transmitting optical fiber with the end of the pigtail optical fiber; a light-receiving device having a light-receiving face for receiving the optical signal propagating through the core portion and for converting the optical signal into an electric signal; an optical coupling system for converging the optical signal emitted from a second end of the pigtail optical fiber onto the light-receiving face of the light-receiving device; and means for preventing light propagating through the cladding portion from reaching the light-receiving face of the light-receiving device so that the optical signal propagating through the core portion does not interfere with the light propagating through the cladding portion on the light-receiving f

Abstract: Side planes of input and output waveguides are exposed in a waveguide type optical device by etching. The exposed side planes are covered with deposited metal films. A TM mode light is propagated through the input and output waveguides without being badly affected by the metal films, but a TM mode light is absorbed by the metal films.