Abstract: A control unit of a bias control circuit performs a loop process that fixes a second bias voltage and iterates a process of recording a pair of a first candidate bias voltage and a second candidate bias voltage that are a first bias voltage when optical power of a multi-level QAM signal output by an optical modulator is controlled so that the optical power converges to a value in the vicinity of the maximum value or the minimum value before and after a third bias voltage is increased or decreased by a half-wave voltage while changing the second bias voltage within a predetermined range. The control unit calculates the difference between the first candidate bias voltage and the second candidate bias voltage for each of a plurality of recorded pairs and determines a value between first candidate bias voltage and the second candidate bias voltage of a pair selected on the basis of the calculated difference as the value of the first bias voltage.

Abstract: A transmission quality estimation system includes, three or more nodes and a transmission quality estimation device configured to estimate, transmission quality. A multi-core fiber having a plurality of cores, the multi-core fiber being used in at least a partial segment of a connection between the nodes. A node of the nodes includes a core connection unit configured to drop, add or relay light transmitted from, to or to each of to the plurality of cores of the multi-core fiber. The transmission quality estimation device includes an estimation unit configured to estimate transmission quality between the nodes on the basis of a transmission quality measurement light dropped by the core connection unit.

Abstract: A communication system which includes: three or more nodes; a multi-core fiber having a plurality of cores, the multi-core fiber being used in at least a partial segment of a connection between the nodes; a detection signal output unit configured to output a fault detection signal transmitted by the core provided in the multi-core fiber configured to connect together the nodes; and a fault detection unit configured to determine whether a fault has occurred between the nodes on the basis of a detection result of the fault detection signal.

Abstract: Accommodation design for wavelength and sub-? paths in a communication network is performed. If sub-? path accommodation is possible according to search for a wavelength path present in a single-hop logical route, the accommodation in the wavelength path is executed. If sub-? path accommodation is possible according to search for a wavelength path present in a multi-hop logical route, a logical route is selected based on the wavelength path and the sub-? path is accommodated in the wavelength path. Additionally, each physical route suitable for the sub-? path accommodation is searched for. If the route can accommodate a wavelength path set in a single-hop logical route by available wavelength allocation, the sub-? path is accommodated in the wavelength path. Furthermore, routes in consideration of overlapping of nodes, pipelines, and links and operation rate are selected based on information about the start and end nodes of each of redundant routes.

Abstract: A communication system includes three or more nodes and a multi-core fiber having a plurality of cores, the multi-core fiber being used in at least a partial segment of the connection between the nodes is provided. One node of the nodes is connected to the multi-core fiber and includes a connector configured to add and drop a signal to and from an allocated core exclusively allocated from among the cores as a communication path between the one node and another node of the nodes and/or configured to relay a signal transmitted through another core of the cores allocated for communication between other nodes in the multi-core fiber connected to the one node, and a relative positional relationship between a connection position of the allocated core in which a signal is added or dropped in the connector and a connection position of another core in which a signal is relayed in the connector is the same for all of the nodes connected to the multi-core fiber.

Abstract: A communication system includes three or more nodes, and a multi-core fiber having a plurality of cores, the multi-core fiber being used in at least a partial segment of a connection between the nodes, wherein each of nodes includes: a fault information transmitting device configured to transmit fault information indicating that a fault has occurred in a communication path between one node and another node of the nodes when it is detected that it is not possible to perform communication between the one node and the another node; and a fault location specifying device configured to specify a section between nodes in which a fault has occurred on the basis of the fault information received from the fault information transmitting device provided in each of the nodes.

Abstract: A nitride semiconductor ultraviolet light-emitting element 1 comprises a sapphire substrate 10 and an element structure part 20 formed on a main surface 101 of the substrate 10. In the substrate 10, in a first portion 110 extending from the main surface 101 by a first distance, a sectional area of a cross section parallel to the main surface 101 continuously increases with distance from the main surface 101, and in a second portion 120 extending from a side opposite to the main surface 101 by a second distance, a sectional area of a cross section parallel to the main surface 101 continuously increases with distance from the side opposite to the main surface 101. The sum of the first distance and the second distance is equal to or less than the thickness of the substrate 10.

Abstract: An optical receiver includes: a first calculation unit that obtains a log likelihood ratio for each M-dimension (M is a natural number), based on a received signal; and a second calculation unit that obtains a log likelihood ratio of an N dimensional symbol (N is a natural number), based on the log likelihood ratio for each M-dimension.

Abstract: To prevent degradation of electrical characteristics caused by a resin filled between electrodes in an ultraviolet light-emitting operation, the present invention provides a base 10 that comprises an insulating base material 11 and two or more metal films 12 and 13 that are formed on one side of the insulating base material 11 and electrically separated from each other. The two or more metal films are formed to include an upper surface and a side wall surface that are covered by gold or a platinum group metal, to be capable of mounting thereon one or more nitride semiconductor light-emitting elements and the like, and to have, as a whole, a predetermined planar view shape including two or more electrode pads.

Abstract: A nitride semiconductor light emitting element comprises a sapphire substrate, and a light emitting element structure portion that has a plurality of nitride semiconductor layers formed on the sapphire substrate. The nitride semiconductor light emitting element is a back-surface-emitting type nitride semiconductor light emitting element that outputs light from the light emitting element structure portion to an outside of the element through the sapphire substrate. The nitride semiconductor light emitting element is divided into a chip whose planarly-viewed shape is a square or a rectangle. A thickness of the sapphire substrate is 0.45 to 1 times an average length of sides of the planarly-viewed shape of the chip.

Abstract: To prevent degradation of electrical characteristics caused by a resin filled between electrodes in an ultraviolet light-emitting operation, there is provided a nitride semiconductor wafer having ultraviolet light-emitting elements on a substrate 12, each element including a semiconductor laminated portion 21 constituted by an n-type AlGaN layer 16, an active layer 17 composed of an AlGaN layer, and p-type AlGaN layers 19 and 20, an n-electrode 23, a p-electrode 22, a protective insulating film 24, first and second plated electrodes 25 and 26, and a fluororesin film 27. The p-electrode is formed on an upper surface of the p-type AlGaN layer in the first region R1 and the n-electrode is formed on an upper surface of the n-type AlGaN layer in the second region R2. The protective insulating film has openings for exposing at least parts of the n-electrode and the p-electrode.

Abstract: A manufacturing method of a nitride semiconductor ultraviolet light-emitting element having a peak emission wavelength of 285 nm or shorter comprises a first step of forming an n-type semiconductor layer composed of an n-type AlXGa1-XN-based semiconductor (1?X?0.5) on an upper surface of an underlying portion including a sapphire substrate, a second step of forming, above the n-type semiconductor layer, an active layer that includes a light-emitting layer composed of an AlYGa1-YN-based semiconductor (X>Y>0) and that is composed of an AlGaN-based semiconductor as a whole, and a third step of forming a p-type semiconductor layer composed of a p-type AlZGa1-ZN-based semiconductor (1?Z>Y) above the active layer. In the manufacturing method, a growth temperature at the second step is higher than 1200° C. and equal to or higher than a growth temperature at the first step.

Abstract: A nitride semiconductor ultraviolet light emitting device 1 is configured such that a nitride semiconductor ultraviolet light emitting element 10 is mounted on a base 30 by flip-chip mounting and sealed with an amorphous fluororesin whose terminal functional group is perfluoroalkyl group. The nitride semiconductor ultraviolet light emitting element 10 includes a sapphire substrate 11, a semiconductor laminated portion 12 of an AlGaN-based semiconductor laminated on a front surface of the sapphire substrate 11, an n electrode 13, a p electrode 14 and a back surface covering layer 15 which is formed on a back surface of the sapphire substrate 11 and transmits ultraviolet light.

Abstract: An optical transmitter includes: an optical modulator including an MZ interferometer, a drive signal input electrode, and a phase difference adjustment bias electrode; a drive amplifier; a phase difference adjustment bias voltage generator; a dithering unit that applies dithering of a predetermined frequency to an amplitude of a drive signal or to a half-wave voltage of the MZ interferometer; a controller unit that changes a phase difference adjustment bias voltage based on a modulation component of the frequency that is superimposed onto modulated light that is output from the optical modulator, to thereby bias the MZ interferometer to a null point; and a synchronous detection circuit that synchronously detects the modulation component of the frequency that is superimposed onto the modulated light. The controller unit changes the phase difference adjustment bias voltage such that a result of synchronous detection by the synchronous detection circuit becomes maximized or minimized.

Abstract: A nitride semiconductor ultraviolet light-emitting element comprises an underlying portion that includes a substrate that is composed of sapphire and has a surface inclined to a (0001) surface so as to form a multi-step terrace, and an AlN layer formed on a surface of the substrate, and a light-emitting portion that is formed on a surface of the underlying portion and includes an active layer having an AlGaN based semiconductor layer. At least the AlN layer of the underlying portion, the active layer of the light-emitting portion, and each layer between the AlN layer and the active layer are formed by step flow growth in which a side surface of a multi-step terrace grows so as to achieve two-dimensional growth. The active layer has a quantum well structure including at least a well layer composed of AlGaN. The average roughness of a 25 ?m by 25 ?m region on a surface of the active layer is a thickness of the well layer or more and 10 nm or less.

Abstract: Provided is an ultraviolet light emitting device that prevents peeled off of a non-bonding amorphous fluororesin and has high quality and high reliability.

Abstract: A nitride semiconductor ultraviolet light-emitting element 1 comprises a sapphire substrate 10 and an element structure part 20 formed on a main surface 101 of the substrate 10. In the substrate 10, in a first portion 110 extending from the main surface 101 by a first distance, a sectional area of a cross section parallel to the main surface 101 continuously increases with distance from the main surface 101, and in a second portion 120 extending from a side opposite to the main surface 101 by a second distance, a sectional area of a cross section parallel to the main surface 101 continuously increases with distance from the side opposite to the main surface 101. The sum of the first distance and the second distance is equal to or less than the thickness of the substrate 10.

Abstract: A communication system includes three or more nodes and a multi-core fiber having a plurality of cores and being used in at least a partial segment of the connection between the nodes. One node of the nodes is connected to the multi-core fiber and includes a connector configured to add and drop a signal to and from an allocated core exclusively allocated for communication between the one node and another node of the nodes and/or configured to relay a signal transmitted through another core allocated to communication between the other nodes in multi-core fibers connected to the one node.

Abstract: A communication system which includes: three or more nodes; a multi-core fiber having a plurality of cores, the multi-core fiber being used in at least a partial segment of a connection between the nodes; a detection signal output unit configured to output a fault detection signal transmitted by the core provided in the multi-core fiber configured to connect together the nodes; and a fault detection unit configured to determine whether a fault has occurred between the nodes on the basis of a detection result of the fault detection signal.

Abstract: An optical amplification system includes: three or more nodes; a multi-core fiber having a plurality of cores, the multi-core fiber being used in at least a partial segment of the connection between the nodes; an amplification light input unit configured to input amplification light to a core of the plurality of cores of the multi-core fiber; an amplification unit configured to amplify communication light transmitted through at least one core of the plurality of cores of the multi-core fiber using the amplification light, the amplification unit being provided in the nodes or between the nodes; and an amplification light coupling unit configured to couple the amplification light input by the amplification light input unit to the amplification unit.