Abstract: A modular optical router/switch construction system and method are described. In one aspect of the present invention, the modules provided are basic 1×N optical components and/or pass-through 1×N optical components, both of which have input/output (I/O) ports which are capable of detachably interconnecting. Pass-through 1×N optical components are like the basic 1×N optical components but include extra ports so that input light may “pass through” the component. In another aspect of the present invention, a bi-directional optical component capable of modular construction is provided. The bi-directional optical component has the same I/O ports as the basic 1×N optical component, but the bi-directional I/O ports are built to engage a duplex optical link (i.e., a link comprised of two optical fibers with signals going in two opposite directions).

Abstract: A system for switching optical energy from a plurality of input waveguides to a plurality of output waveguides, while balancing power in the output waveguides, and a method for its use. The system is based on an optical switch matrix that includes, for each input waveguide and for each output waveguide, one or more attenuators that divert an adjustable portion of the optical energy, that enters via that input waveguide, to that output waveguide. Preferably, each input waveguide is coupled to each output waveguide via a pair of 2×2 mach-Zehnder interferometers, a first of which has an idle input port and a second of which has an idle output port. The system also includes a feedback mechanism that taps fixed portions of the power in either the input waveguides or the output waveguides, and adjusts the attenuators accordingly.

Abstract: A method of aligning optical components is described. The system utilizes a highly transmissive sensor positioned in the optical path of an optical signal to determine the precise position of the optical signal. A feedback loop uses output from the highly transmissive sensor to readjust elements that maintains the optical signal in a desired position. The current system is particularly suitable for use in an optical cross switch.

Abstract: The present invention is directed to an optical switch for switching the light from one of a plurality of inputs to one of a plurality of outputs. The switch contains at least two moveable mirrors constructed using MEM technology and a servo mechanism connected to the moveable mirrors to be used in mirror, input and output alignment. These switches are useful in applications such as fiber-fiber switches and optical disk drives. The switches may be combined with other optical equipment including stationary mirrors and lenses, such as focusing lenses, to optimize optical transmission.

Abstract: An optical device is provided, including two dual-fiber collimators, two single-fiber collimators, two filters connected respectively to the two dual collimators, and two mirrors. The two dual-fiber collimators are interconnected by coupling an optical fiber thereof to each other. One mirror is fixed in position, and the other mirror is mounted on a mechanism capable of moving up and down so as to switch an optical path.

Abstract: A method and apparatus for optical switching is described wherein a first optical input/output port and plurality of second optical input/output ports are coupled using an optical guiding assembly. An optical signal may thereby be movably directed between the first input/output port and a selected one of the second optical input/output ports. The optical guiding assembly includes a optical micro-element assembly and an actuator assembly which moveably directs the microlens assembly to a predetermined position corresponding to the selected one of the input/output ports. The actuator assembly includes a comb drive and the optical micro-element assembly includes an etched lens, a ball lens, a mirror, or the like.

Abstract: A non-linear optical loop mirror for processing optical signals comprises an optical fiber, a bi-directional amplifier, and a coupler. The optical fiber has a signal input and a signal output. At least a portion of the optical fiber includes a dispersion compensating fiber. At least a portion of the optical fiber forms a loop. The dispersion compensating fiber has an absolute magnitude of dispersion of at least 20 ps/nm-km for at least a portion of wavelengths in the optical signals. The bi-directional amplifier is coupled to the optical fiber. The coupler is coupled to a first portion of the optical fiber and a second portion of the optical fiber to form a fiber loop.

Abstract: A wavelength multiplex optical communication module is provided. This module consists of first to third optical waveguides on a substrate, the first waveguide coupled to the second waveguide, with a light emitting device disposed on the end of the first waveguide opposite the coupler. A wavelength filter is located at one end of the substrate in conjunction with ends of the second and third waveguide for passing a wavelength of light to a detector while reflecting a different wavelength to the third waveguide. By virtue of this construction, the communication module can realize various functions such as transmission or reception of signal light with a plurality of wavelengths. That is, light with a specific wavelength can be sent, or other specific light in the input light can be received or transferred to another site.

Abstract: This invention provides a novel wavelength-separating-routing (WSR) apparatus that uses a diffraction grating to separate a multi-wavelength optical signal by wavelength into multiple spectral channels, which are focused onto an array of corresponding channel micromirrors. The channel micromirrors are individually controllable and continuously pivotable to reflect the spectral channels into selected output ports. As such, the inventive WSR apparatus is capable of routing the spectral channels on a channel-by-channel basis and coupling any spectral channel into any one of the output ports. The WSR apparatus of the invention may further employ a polarization diversity scheme, whereby polarization-sensitive effects become inconsequential and insertion loss is minimized. The WSR apparatus of the invention may additionally be equipped with servo-control and channel equalization capabilities.

Abstract: A programmable electro-optically controlled optical delay device providing multiple optical outputs. The optical delay device provides multiple output ports where the optical propagation delay increases at each port. An incident optical beam is propagated within electro-optically active material within the device, so that the propagation delay at each output port may be varied according to an applied voltage. In an optical beam steering system, the present invention provides true-time delay for multiple optical beams, allowing the beams radiated by the beam steering system to be time-coincident. The present invention provides for one or two dimensional beam steering.

Abstract: The present invention is directed to an economical approach for compensating for the dispersion of optical signals having different wavelengths. In accordance with the present invention, photonic crystals (K1-Kn) are positioned on a common optical waveguide (2). In this context, each photonic crystal (K1-Kn) is tuned to reflect or deflect the signals of one wavelength and to transmit the signals of other wavelengths, unattenuated. The specific arrangement of the photonic crystals (K1-Kn) on the waveguide (2) and the specific arrangement of the deflecting elements in the photonic crystal are defined, in the process, as a function of the dispersion to be compensated for between the individual wavelengths. The approach of the present invention makes it possible to assemble permanently set or controllable photonic dispersion compensators of a high quality, which are approximately 1000 times shorter than conventional diffraction gratings.

Abstract: A photonic crystal drop filter apparatus and a method for tuning a photonic crystal drop filter. The photonic crystal drop filter has a photonic crystal having first waveguide for transmitting light having a frequency within a bandgap of the photonic crystal, and a second waveguide. The second waveguide is connected to the first waveguide by a resonant cavity for extracting at least one wavelength of the light transmitted by the first waveguide and redirecting the extracted light to the second waveguide. A tuning device is included in the apparatus to tune the wavelength of the extracted light over a full range of wavelengths. The apparatus is particularly suitable as an extraction device for optical communications systems such as a WDM communications system wherein it is necessary to extract one or more carrier signals from a plurality of carrier signals.

Abstract: A luminescent material, such as phosphor, is radiated by energy propagated from the side of an optical fiber, causing the luminescent material to emit visible light. The luminescent material can be of: a coincidentally-excited type, requiring the absorption of two wavelengths of radiation to emit visible light; memory-type, requiring absorption of one wavelength of charging radiation and absorption of another wavelength of controlling radiation to emit visible light; and quenchable type, requiring absorption of one wavelength of radiation to emit visible light and absorption of another wavelength of radiation to stop, i.e. quench, the emission of visible light. Two side-emitting optical fibers can be used, with each optical fiber providing one of the needed radiation wavelengths. One embodiment of the invention involves a matrix of optical fibers forming an optical display panel made using coincidentally-excited phosphors.

Abstract: Optical package and module designs use multiple-port (e.g. six-port) optical packages to create compact DWDM modules, add/drop packages, heat dissipation packages, optical amplifier filters, and the like.

Abstract: In a triangular-sectioned prism 11 having a first plane 11a opposite an end face of an optical fiber 12, a second plane 11b opposite a light receiving element 13 and a third plane 11c which reflects received light 21 incident thereon from the optical fiber 12 toward the second plane 11b and transmits transmission light 22 emitted from a light emitting element toward the first plane 11a, a cylindrical member 32 of a refractive index larger than that of the prism 11 is embedded in that area of the prism 11 which is opposite the end face of the optical fiber 12. The cylindrical member 32 effectively suppresses the leakage therefrom of light, providing increased optical coupling efficiency as compared with that achievable by use of a mere prism structure.

Abstract: The present invention relates to a fiber grating filter optical waveguide device, comprising an optical fiber with an optical filter, both consisting essentially of silica, whereby said optical filter has an area with a grating region, wherein said area with a grating region is covered with a layer comprising a material having a refractive index which is the same or higher than the refractive index of the material of the optical fiber. The variation of the physic-chemical nature of said material allows to match the changes in the refractive index of the optical fiber of the optical filter when specific requirements for a high transmission spectrum of the filter are required.

Abstract: Optical device for compensating chromatic dispersion, comprising a variable-pitch Bragg grating having a predetermined reflection wavelength and a predetermined chirping factor, and a substrate, in which the said grating is fitted into a central longitudinal groove, and which can be elongated in such a way as to cause a change in the said predetermined chirping factor.

Abstract: An external mode size transformer includes a waveguide having an input section, an output section, and a tapered section disposed between the input and output sections. The cross sections between the input and output sections of the waveguide can vary smoothly throughout the length of the waveguide, similar to a waveguide shaped like a boat hull. By positioning the external mode size transformer between optical devices, coupling between optical devices is substantially improved compared to that of direct coupling. For example, by positioning the external mode size transformer between a laser and an optical fiber, laser to fiber coupling is significantly improved compared to that of direct coupling between these optical devices. The present invention can include a manufacturing method that employs multiple masks with predetermined shapes to fabricate the sections of the waveguide within a planar substrate via an exemplary ion exchange process.

Abstract: According to this invention, there are provided a wavelength correction method and apparatus which can easily correct the wavelength characteristics of an optical element such as an arrayed waveguide diffraction grating in a slab waveguide or another waveguide, and a wavelength check method and apparatus which check the quality of a waveguide. A center wavelength &lgr;0 of light having a predetermined wavelength &lgr;, emitted from a light source, is obtained at the initial position of an input-side slab waveguide which is cut into a first input-side waveguide component and a second input-side waveguide component. When a light component having a first wavelength &lgr;s on the short wavelength side and a light component having a second wavelength &lgr;1 on the long wavelength side, centered on a desired wavelength &lgr;g, are sequentially output from the light source, the amount of each light component is measured while the relative position of the input-side slab waveguide is changed.

Abstract: The present invention's optical cable is provided with optical fibers, a forming pipe for housing the optical fibers, a sheath provided around the forming pipe, and at least one pair of rip cords embedded in the sheath. The forming pipe is formed of a plurality of tapes so that it is dividable along its longitudinal direction. When dividing the optical cable, the rip cords are pulled to tear open the sheath, and the already split forming pipe is divided while staying adhered to the respective parts of the sheath. As a result, the division of the sheath and the forming pipe is carried out in one stroke, so that the optical fibers inside the forming pipe can be exposed easily and quickly.

Abstract: The present invention includes an optical fiber cable configuration comprising fibers that are grouped into buffer tubes or buffer cells, containing fiber bundles or ribbon stacks, using a lightweight fabric-type composite tape material to serve as a light-weight strength member and protective low-thermal-expansion sheath. A plurality of the buffer tubes or buffer cells of various shapes are then positioned upon another piece of composite tape material. Gel or foamy glue is placed on the tape and is used to secure the buffer tubes to the tape. A triangular or trapezoidal stack is then formed by rolling the tape to enclose the buffer tubes and excess gel serves to fill in gaps. Multiple stacks may then be stranded to form a larger super-cable structure that uses a piece of composite tape material along with the rolling process, as described above, to support the individual stacks.

Abstract: An optical-path-superposing-and-separating unit superposes optical paths of two inputted signal lights with each other, and then separate them. A non-linear waveguide is arranged in an area where the optical paths are superposed with each other. First and second optical waveguide are connected to the optical path superposing-and-separating unit. The second optical waveguide has a longer optical path than the first optical waveguide. A control light is introduced to the non-linear waveguide. An interference separator distributes the inputted two signal lights depending on a phase difference therebetween. Third and fourth optical waveguides connect the optical-path-superposing-and-separating unit to the interference separator.

Abstract: Disclosed is a dispersion controlled optical waveguide fiber, and telecommunication systems using such a waveguide fiber, in which the end to end total dispersion and total dispersion slope is controlled by varying the refractive index profile along the fiber length. The waveguide fiber includes length portions each of which is characterized by total dispersion having a magnitude and sign and total dispersion slope having a magnitude and sign. The magnitudes and signs of total dispersion and total dispersion slope of respective length portions are chosen to provide for the optical waveguide fiber a desired end to end total dispersion and total dispersion slope. An advantage is achieved in the present invention by designing the refractive index profiles of the length portions to have total dispersion and total dispersion slope of opposite sign.

Abstract: The present invention relates to a glass article for use as an optical waveguide fiber and more particularly to an optical waveguide fiber, the core of which is doped with a chalcogenide element to significantly increase the refractive index of the core. The subject of this invention is novel doped silica core compositions wherein a portion of the oxygen in the silica is replaced with either sulfur, selenium or tellurium using plasma enhanced chemical vapor deposition (PECVD). These compositions are designed to have higher refractive indices than silica, low coefficients of expansion, high optical transparency, and appropriate viscosity and softening points to make them ideal candidates for use as optical waveguide fibers.

Abstract: An optical waveguide fiber having a relatively large effective area which exhibits low attenuation, low PMD and low microbending sensitivity. A step-index refractive index profile is advantageously used.

Abstract: A thermoplastic resin coated optical fiber having an outer diameter of 0.9 mm is formed by providing a coating layer around a reinforcing resin coated optical fiber having an outer diameter of 0.25 mm, and has a flexural rigidity of 5.5 to 7.5 N·mm2. The coating layer comprises a thermoplastic resin having a bending elastic modulus of 200 to 350 MPa and the thermoplastic resin is a polyester elastomer. When optical fiber cords are connected to each other or when an optical fiber is exposed to low temperatures, loss is prevented from increasing and superior transmission characteristics are exhibited.

Abstract: A method for fabricating a three-dimensional tapered optical waveguide and a three-dimensional tapered optical waveguide are shown and described. The fabrication method takes advantage of RIE lag to create a shaped trench in a lower cladding layer that has one end that is wider and deeper and than the opposite end. After the trench is filled with core material, a second RIE process is carried out which takes advantage of reverse RIE lag to etch the core material at a faster rate at the shallower and narrower end and at a slower rate at the wider and deeper end. The result is shaped core of a three-dimensional tapered optical waveguide that is wider and deeper at one end and tapers towards a shallower and narrower end for improved optical signal transmission.

Abstract: An apparatus for storing fiber optic cable including an add-on structure for holding fiber optic cable connectors that includes clips that are integral with the structure. In one example, the clips include two opposing prongs integrally connected to a panel of the structure. The add-on structure can be removably attached to a carrier of the apparatus that is used for storing fiber optic cable in a communications system such as a router. The connectors that terminate fiber optic cable legs stored in the carrier are secured to the clips of the add-on structure so as to prevent damage to the cable legs during the shipment of the carrier and cable legs. The add-on structures can also be used to secure the connectors in repair operations involving the cable legs and/or for shipping the panel and plurality of clips with connectors inserted therein to a use location.

Abstract: A fiber optic telecommunications frame is provided including panels having front and rear termination locations, the panels positioned on left and right sides of the frame. The frame includes vertical access for the rear cables. The frame further includes left and right vertical cable guides for the front patch cables. The frame further includes cable storage spools for the patch cables. The frame includes a horizontal passage linking the left and right panels and the cable guides. A portion of the frame defines splice tray holders and a central passage from the splice tray holders to the rear sides of the left and right panels. From a front of each panel, access to a rear of the panel is provided by the hinged panels. Alternatively, the panels can form connector modules with front termination locations and rear connection locations for connecting to the rear cables. The modules can house couplers, such as splitters, combiners, and wave division multiplexers.

Abstract: An optical device including dynamic channel equalization is provided. In an exemplary multiplexer or line amplifier configuration the device includes a plurality of separate optical paths, each of which receiving a separate group of optical signals. Each group of optical signals is provided to an associated variable optical attenuator. Separate inputs of an optical combiner are each coupled to an output of an associated one of the variable optical attenuators. The optical combiner has an output providing the separate groups of optical signals in an aggregated form on an aggregate optical signal path. An optical performance monitor is coupled to the aggregate optical signal path, and is configured to detect an optical signal power of each of the separate groups. The monitor supplies a feedback signal to corresponding ones of the variable optical attenuators for adjusting a respective attenuation associated with each of the attenuators in dependence of the detected optical signal powers.

Abstract: An adhesive composition for bonding optical parts comprising (A) 3 to 60 wt % of an epoxysilane or a hydrolysis/polycondensation product thereof, (B) 5 to 90 wt % of a bisphenol type epoxy resin having a viscosity of 2,000 to 5,000 mPa·s, (C) 5 to 35 wt % of a novolak type epoxy resin, 3 to 30 wt % of a curing agent which is an amine, and water and an alcohol in an amount of 0 to 0.75 time the total number of mols of the hydrolyzable groups or atoms of the epoxysilane. This composition has excellent moisture resistance and heat resistance, suppresses the formation of bubbles during curing, is free from such a defect as opaqueness caused by bubbles and can be used for the assembly and bonding of optical parts.

Abstract: A fiber scope and cleaning tool including a hand-held housing having a magnification and viewing system. A fiber inlet through the housing is used to insert a fiber into the viewing system. A fiber cleaning mechanism, including a strip of cleaning fabric spooled between rollers, is associated with the housing for cleaning the fiber.

Abstract: An apparatus marks files within a content archive. The content archive contains a database that has a plurality of content files. The content archive also contains a plurality of entries or records. Each of the entries corresponds to a distinct one of the plurality of content files. Each of the entries also includes a played field that is automatically set when the corresponding content file has been played. The content archive also includes a writing module that is configured to record a new content file to the content archive and, if insufficient space is available, to overwrite a content file for which the played fields are set. According to one aspect, the plurality of entries also includes an entry corresponding to an overwritten content file previously contained within the database that is no longer contained within the database. The database may contain references to content no longer in the database.

Abstract: Browsing of digital video data is performed using a fast forward or fast reverse play mode. The digital video is analyzed and processed to produce a content-based variable-rate video playback sequence for fast browsing. To create the playback sequence, each shot in a video is sped-up at a relatively slow rate at the beginning of the shot by selecting many frames and then the speedup rate is increased as the shot progresses by selecting progressively fewer frames. This method and apparatus of variable-rate frame selection can be used to add and index to a video, play an original video in fast forward/backward mode or to create a new video—a fast forward playback video summary.

Abstract: Television programs are tuned by a television tuner using a method involving establishing a communications link between a user of a television tuner and database of television schedule information, the database located a site remote from the user. The user communicates program selection criteria to the site remote from the user. A database of television schedule information is searched based on the program selection criteria and program identification data is derived from the database, the program identification data corresponding to television programs meeting the program selection criteria. The program identification data is transmitted over the communications link to a television tuner controller.

Abstract: The present invention is directed to a video recorder having user extended and automatically extended time slots. An embodiment of the present invention includes a set top box having an internal storage device, such as a hard drive where broadcasts are transferred from a broadcast input source to the storage device. The set top box is connected to an output device such as a television, which displays a graphical user interface (GUI) and an interactive program guide (IPG). The user has the option to extend a chosen time slot, in which a show is scheduled to be transferred to the storage device. The time slot may be extended before the show, after the show, or both.

Abstract: A video object is recorded on an optical disc. The video object is composed of at least one video object unit, and each video object unit contains control information and video data and has a presentation time of one second or shorter. The control information relates to display control and copying control for the video object unit.

Abstract: An information storage medium includes: a video zone for recording audio/video information including video information and audio information associated with the video information; an audio zone for recording audio information; first navigation information for a video player which can reproduce the audio/video information; second navigation information for an audio player which can reproduce the audio information in the video zone and the audio information in the audio zone; and third navigation information for a compatible player which can reproduce both the audio/video information and the audio information. The first navigation information, the second navigation information and the third navigation information are recorded separately from each other.

Abstract: To distribute data for an information processing device, and if an improper electronic device connection is made, to inform the user of this fact and have him make the correct connection. If a correct connection is made, image part 61 is displayed on a display device, such as a television receiver. When an incorrect electronic device connection is made, data part 62 is displayed on the screen of the image display device together with image part 61. Option data area 62a of data part 62 notifies the user by a caption that an improper connection has been made. Data for the information processing device to perform various processing is recorded in basic data area 62b. Data consisting of image part 61 and data part 62 is thus input to the image processing device, and if correct connections are made, then in accordance with the data of basic data area 62b, the data that is input is processed so that only image part 61 is displayed on the image display device.

Abstract: Real time information, such as a digital video signal, is supplied and simultaneously received, converted into/from blocks of information in channel's signals and read/written from/onto a disc-like record carrier. Read/write-scheduling algorithms are used for reading/writing blocks of information recorded in fixed sized fragment areas on the record carrier. Typically one writing action and a plurality of readings actions are used in one read/write cycle of either a fixed duration or of a variable duration. The invention provides for reading and writing of edited files and re-ordering of read actions in a read/write cycle.

Abstract: An apparatus for providing thermal energy comprising a housing defining a first interior space and a second interior space; at least one electric heating element positioned within the first interior space; and an air circulator positioned within the second interior space and adjacent the first interior space, the air circulator receiving intake air from a first flow path and generating exhaust air along a second flow path, the second flow path substantially orthogonal to the first flow path such that the exhaust air flows through the at least one heating element.

Abstract: A camera frame assembly has a frame. A lens mount has one or more hooks that grip the frame. A backer dogs the hooks against the frame. In camera recycling, the hooks are first undogged to provide access. The hooks are then released from the camera frame. Following the releasing, the lens mount is separated from the camera frame. The backer can include a baffle that defines an exposure opening aligned with the optical axis of the lens module.

Abstract: A camera and method for image capture at less than a nominal minimum focus distance provide for initiating image capture through a variable aperture at a first aperture size, collecting a predetermined amount of ambient scene light during image capture, initiating closing of the variable aperture, and illuminating a flash unit during closing of the variable aperture at a predetermined restricted second aperture size.

Abstract: A viewfinder assembly mounting system includes a mounting hole formed at least in one of a camera body and a base barrel in a direction of an optical axis, a viewfinder assembly provided with a guide hole corresponding to the mounting hole of the base barrel; and a guide member inserted and coupled to the mounting hole and the guide hole in the direction of the optical axis. The guide member is either a strobe guide member or a viewfinder lens guide member for respectively guiding a motion of the strobe and the viewfinder lens in a direction of an optical axis by synchronizing with the barrel.

Abstract: A rangefinder apparatus includes an autofocus data generator for forming an image of light from an object at a distance to be determined by rangefinding onto a pair of line sensors. Each line sensor includes light detecting elements, and generates AF data for computing a correlation value according to signals produced by the light detecting elements; an AF data acquirer for acquiring the AF data from a pair of sensor areas used for rangefinding, within the pair of line sensors. A correlation value computer determines a pair of window areas for selecting the AF data to be used for computing the correlation value within the pair of sensor areas, and successively computes correlation values while shifting the pair of window areas; an interpolater for detecting correlation extreme values among the correlation values computed by the correlation value computer, and interpolating the correlation extreme values detected to compute interpolated correlation extreme values.

Abstract: A disclosed photographing apparatus has a LCD display, a select member, and a controller. The display displays information about a photographic condition, in arbitrary display form using a dot-matrix. The select member selects one display mode among a plurality of display modes. In each mode of the plurality of display modes, display forms are different to each other, standard information required for photographing is displayed common to every display mode, and at least one information inherent to each display mode is displayed. The controller controls the display to display the display mode selected by the selector, and at a time of starting the camera, to display a display mode which has been displayed when the camera was previously switched off.

Abstract: An optical signaling header technique applicable to optical networks wherein packet routing information is embedded in the same channel or wavelength as the data payload so that both the header and data payload propagate through network elements with the same path and the associated delays. The technique effects survivability and security of the optical networks by encompassing conventional electronic security with an optical security layer by generating replicated versions of the input data payload at the input node, and the transmission of each of the replicated versions over a corresponding one of the plurality of links. Moreover, each of the links is composed of multiple wavelengths to propagate optical signals or optical packets, and each of the replicated versions of the data payload may be propagated over a selected one of the wavelengths in each corresponding one of the plurality of links.

Abstract: Systems and methods are described for reverse digitized communications. A method includes: providing at least one optical fiber from at least one member selected from the group consisting of a headend and a hub, a minifibernode coupled to said at least one optical fiber, and an electrical conductor coupled to said minifibernode; transforming a forward optical signal from said at least one optical fiber to a forward analog electrical signal on said electrical conductor at said minifibernode; and transforming a reverse analog electrical signal on said electrical conductor to a reverse digital optical signal at said minifibernode. The systems and methods provide advantages because the need for muxnode units is eliminated, the cost of the node units is reduced, the amount of optical fiber is reduced and the reverse bandwidth is increased.

Abstract: The present invention is a decoder for decoding a signal. The decoder includes a discriminator and a threshold generator. The discriminator receives the signal and generates an output voltage equal to a first voltage if the signal is less than a threshold level that is input to the discriminator and equal to a second voltage if the signal is greater than the threshold level. The threshold level depends on the output from the discriminator in a preceding time interval that depends on the impulse response of a transmission link through which the input signal has passed. The threshold generator implements a low-pass analog filter that receives the output voltage during each of the clock periods and generates therefrom a filtered output signal.

Abstract: An optical receiving circuit 1 is composed of a preamplifier circuit 2, an output differential amplifier 3 and a mean value holding circuit 4. The optical receiving circuit 1 is connected to a photodetector 5 for receiving an input optical signal and outputting current. For the preamplifier circuit 2, a transimpedance type circuit may also be used. The preamplifier circuit 2 comprises a feedback resistor 21 and a resistor for detecting output voltage 22, the transimpedance gain is 55 dB &OHgr; and 3 dB bandwidth when the photodetector 5 the capacity of which is 0.2 pF is connected to its output is 8 GHz. The output differential amplifier 3 discriminates and regenerates data by regulating reference voltage Vref between the high level and the low level of the amplitude of an input signal. The mean value holding circuit 4 includes a sample-hold circuit 41 and capacity 42 for holding the mean value of voltage output from the preamplifier circuit 2.