Abstract: A multiwavelength transmitter comprises several laser sources (1) each configured to generate light of a different wavelength and a first array waveguide grating (2) arranged to direct light from each of the laser sources (1) into a first waveguide. The transmitter further comprises several electroabsorption modulators (7) each arranged to modulate light at one of the wavelengths with a respective data signal and a second array waveguide grating (6) arranged to direct each of said different wavelengths of light from the first waveguide to a respective one of the modulators (7). The optical modulators (7) are reflective optical modulators and the second array waveguide grating (6) is arranged to direct the modulated light reflected from each of the optical modulators (7) back into the first waveguide. An optical circulator (5) is provided in the first waveguide to couple modulated light from the second array waveguide grating (6) into an output waveguide.

Abstract: A wavelength routing system includes a plurality of nodes (1, 2, 3, 4) and an array waveguide grating (40) having a routing property and optically connected to the plurality of nodes. Each of the nodes has a plurality of light sources (TLS) outputting lights at different wavelengths to the array waveguide grating, respectively, and a wavelength demultiplexer (125, 225, 325, 425) having a periodic property, demultiplexing a light output from the array waveguide grating, and outputting demultiplexed lights. The wavelength demultiplexer is set a channel period which is different from that of the array waveguide, and which is more than or equal to a number of output ports of the wavelength demultiplexer.

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 provides a remodulating channel selector for a wavelength division multiplexed optical communication system. The remodulating selector receives a WDM input signal, selects a particular optical channel from the WDM signal and places the information from the selected signal onto a newly-generated optical output signal. The wavelength of the output optical signal can be the same as or different from one of the optical channels which comprises the WDM input signal. When used in a WDM optical communication system with remodulators at the transmission input, the remodulating selectors provide complete control over the interfaces with optical transmitters and receivers, permitting use with a broad range of optical equipment.

Abstract: A network of global coverage, scalable to hundreds of petabits per second, comprises bufferless switch units each of dimension n×n, n>1, arranged in a matrix of ? columns and ? rows, ?>1, interconnecting a maximum of ?×n edge nodes. Each edge node has ? upstream channels to ? switch units in ? different columns and ? downstream channels from ? switch units in ? different rows. All upstream channels to a switch unit are time-locked to the switch unit, thus enabling coherent switching at the switch unit. The switch units are preferably fast-switching optical nodes. Alternatively, the switch units may comprise fast-switching optical nodes each of dimension m×m, arranged in a first ?×? matrix, and latent space switches each of dimension n×n, n>1, arranged in a second ?×? matrix, ?>1, where ?×m=?×n. An edge node time locks to each optical node and each latent space switch to which it connects.

Abstract: An optical device for rearranging wavelength channels in an optical network is disclosed. The optical device has a wavelength selective coupler having one input port and a plurality of output ports coupled to a plurality of input ports of an optical grating demultiplexor such as an arrayed waveguide grating. The wavelength channels in each of the input ports are dispersed by the demultiplexor and are directed to a plurality of output ports of the optical grating demultiplexor. As a result, at least one wavelength channel at each of the input ports of the optical grating demultiplexor is coupled into a common output port. The optical device is useful in passive optical networks wherein a same demultiplexor is used for simultaneous multiplexing and demultiplexing of wavelength channels.

Abstract: Consistent with the present disclosure, a coherent detector is provided that includes an optical hybrid that supplies optical signals including local oscillator light to a balanced detector. The amount of imbalance or “balance error” in the balanced detector is identified by comparing an output of the balanced detector and an output of a photodiode that receives a portion of an input optical signal provided to the optical hybrid. Based on the balance error, electrical signals generated by the balanced detector or the power of optical signals passing through (or output from) the optical hybrid circuit can be adjusted so that the balance error is minimized or reduced to zero. As a result, imbalance associated with the balanced detector is corrected so that unwanted currents and/or related electrical signals are cancelled out or substantially cancelled out.

Abstract: An optical hybrid circuit includes a MMI coupler including a pair of input channels provided at positions symmetrical with respect to a center position in a widthwise direction thereof, a pair of first output channels outputting a pair of first optical signals having an in-phase relationship, and a pair of second output channels neighboring with each other outputting a pair of second optical signals having an in-phase relationship. The MMI coupler converts QPSK signal light or DQPSK signal light into the pair of first optical signals and the pair of second optical signals having an in-phase relationship. The optical hybrid circuit includes a 2:2 optical coupler connected to the first or the second output channels. The 2:2 optical coupler converts the pair of first optical signals or the pair of second optical signals into a pair of third optical signals having a quadrature phase relationship with the pair of first or second optical signals.

Abstract: The present disclosure provides optical communication systems and methods that utilize, on top or in place of the conventional framework: (1) optical amplifiers that are provided with extended bandwidth coverage, such as Extended Band Erbium-Doped Fiber Amplifiers (EDFAs), combination of Raman amplifiers and EDFAs, Split-Band C+L EDFAs, etc.

Abstract: The present invention provides a system, apparatus and method to provide for amplification at various points along one or more optical paths of a photonic integrated circuit. According to various embodiments of the invention, the photonic integrated circuit includes a plurality of optical devices having associated characteristics which may have lead to optical signal degradation. One or more optical amplifiers provided along one or more optical paths of the photonic integrated circuit compensate for such signal degradation, resulting in a highly configurable photonic integrated circuit. The various optical devices of the photonic integrated circuit may be provided on a single substrate.

Abstract: An apparatus includes one or more optical de-interleavers. Each optical de-interleaver includes an optical component having a first pair of optical input and output ports and a second pair of optical input and output ports and a 1×2 optical coupler. Each optical output port of the optical component is optically connected to a corresponding optical port of the 1×2 optical coupler. The optical component is constructed to operate as a first optical filter for light propagating between the optical ports of the first pair and is constructed to operate as a second optical filter for light propagating between the optical ports of the second pair. The first and second optical filters have substantially regularly spaced and interleaved passbands.

Abstract: This invention provides a fiber optic rotary joint (20) for enabling the transmission of digital optical signals across the interface between facing surfaces (26, 29) of a rotor and a stator (21, 22), comprising: a plurality of light sources (42A, 42B, 42C, . . .

Abstract: An optical transceiver capable of narrowing an extra space for an external optical fiber is disclosed. The optical transceiver of an embodiment provides an optical receptacle with a port, to which the external optical fiber is to be inserted, headed for a direction in diagonal to the longitudinal axis of the optical transceiver. In another embodiment, the optical transceiver provides an optical receptacle capable of turning the port thereof.

Abstract: Embodiments of a system that includes an array of chip modules (CMs) is described. In this system, a given CM in the array includes a semiconductor die that is configured to communicate data signals with one or more adjacent CMs through electromagnetic proximity communication using proximity connectors. Note that the proximity connectors are proximate to a surface of the semiconductor die. Moreover, the given CM is configured to communicate optical signals with other CMs through an optical signal path using optical communication, and the optical signals are encoded using wavelength-division multiplexing (WDM).

Abstract: The present disclosure is directed to a light source distributor for use in an injection-locked WDM-PON (wavelength division multiplexed-passive optical network). The light source distributor receives an A band and a B band injection optical signals through a single optical terminal from an injection light source for outputting both the A band and the B band injection optical signals; transmits the A band injection optical signal to a first optical multiplexer/demultiplexer of a central office and the B band injection signal to a second optical multiplexer/demultiplexer of a remote node; transmits a wavelength-locked A band optical signal received from the first optical multiplexer/demultiplexer to the second optical multiplexer/demultiplexer; and transmits a wavelength-locked B band optical signal received from the second optical multiplexer/demultiplexer to the first optical multiplexer/demultiplexer.

Abstract: In general, optical communication systems and methods may generate higher-level nmQAM from nQAM signals using one or more delay line interferometers (DLIs) arranged in various configurations. The nQAM signals may be generated by a lower-level modulator, such as a BPSK modulator, QPSK modulator or lower-level QAM modulator, with binary driving signals. Different parameters of the DLIs, such as free spectral range (FSR), phase shift, and amplitude imbalance, may be selected to accomplish the desired higher-level nmQAM depending upon the nQAM signal.

Abstract: An optical communicating apparatus that is connected to another optical communicating apparatus by a two-core optical transmission path includes: a one-core optical transmission path that passes an optical signal transmitted from an optical transmitter/receiver performing one-core bilateral communication and an optical signal transmitted to the optical transmitter/receiver in an opposite direction; a transmitting unit that transmits the optical signal transmitted from the optical transmitter/receiver through the one-core optical transmission path, to the other optical communicating apparatus through a first core of the two-core optical transmission path; and a receiving unit that receives the optical signal transmitted from the other communicating apparatus through a second core of the two-core optical transmission path, and passes the received optical signal to the one-core optical transmission path.

Abstract: A simple optical waveband multiplexer/demultiplexer operable to separate a wavelength-division multiplexed light beam WDM consisting of a plurality of wavebands WB each including a plurality of optical channels, into a predetermined plurality of wavebands WB, and output the separated plurality of wavebands WB from a plurality of output ports, wherein the wavelength-division multiplexed light beam WDM is transmitted through two array waveguides each capable of performing a demultiplexing function with a resolution corresponding to wavelengths of the optical channels, and a characteristic of sequentially shifting the output ports by one position with shifting of input ports by one position, whereby the wavelength-division multiplexed light beam WDM is separated into a plurality of wavebands WB each including the mutually different optical channels selected from the optical channels included in the wavelength-division multiplexed light beam WDM, and the separated wavebands WB are outputted from the plurality of

Abstract: An optical transmission apparatus includes an optical transmitter that outputs a signal light corresponding to a wavelength of a WDM light, a multiplexer that multiplexes lights input to the plurality of input ports, and that outputs a light generated through the multiplexing from the one or more output port, an optical amplifier that amplifies the light output from the multiplexer; and an amplified spontaneous emission (ASE) transmitter that inputs branching off part of the light output from the optical amplifier by a splitter and multiplexes, with the signal light, ASE in a wavelength band corresponding to an unused wavelength adjacent to the signal light included in the branched-off light.

Abstract: In an example embodiment, lightwave device for use in a dispersion compensator, includes a light coupler configured to direct light toward a grating structure. The light coupler includes a first strip including a first material and a second strip attached to the first strip. The second strip includes a second material, and the second material has an expansion coefficient different than the first material. The first and second strips form a deformable reflector. A thermoelectric unit is coupled to the light coupler and is configured to adjust a shape of the deformable reflector based on a temperature of the thermoelectric unit. A support member is connected to the light coupler and is configured to position the deformable reflector so to receive light for transmission to the grating structure. Another embodiment provides a dispersion compensator using the lightwave device.

Abstract: A method and apparatus for enabling multiple optical line termination (OLT) devices to share a feeder fiber are disclosed. For example, the optical network comprises a plurality of optical line termination (OLT) devices, where each OLT device having a transceiver for sending and receiving optical signals. The optical network further comprises a wave division multiplexer (WDM) combiner, coupled to the plurality of OLT devices, for combining optical signals received from the plurality of OLT devices. The optical network further comprises an optical extender box comprising at least one hybrid SOA-Raman amplifier, wherein the optical extender box is coupled to the WDM combiner via a first standard single mode fiber section. Finally, the optical network further comprises at least one optical splitter coupled to the optical extender box via a second standard single mode fiber section.

Abstract: A protected light source for generating seed light for at least two wavelength division multiplexed passive optical networks (WDM-PONs). The protected light source includes an optical coupler having N?2 input ports and M?2 output ports, each output port being optically connected to supply seed light to a respective set of one or more WDM-PONs. A respective multi-wavelength light source (MWLS) is optically coupled to supply seed light to each input port of the optical coupler. A controller unit controls operation of each multi-wavelength light source (MWLS).

Abstract: An optical waveguide-type wavelength domain switch includes a waveguide-type multi/demultiplexing device laminate comprising three or more laminated waveguide-type multi/demultiplexing devices, a lens system positioned on a demultiplex side of the waveguide-type multi/demultiplexing device laminate, and a reflective optical phase-modulating cell positioned on an opposite side of the waveguide-type multi/demultiplexing device laminate to the lens system.

Abstract: A multiport passive optical signal sharing device enabling optical signals received by each of a first plurality of ports of the device to be transmitted to all of the ports of a second plurality of ports of the device. The device includes a first coupling mechanism adapted to combine signals received by each port of the first plurality of ports of said device into a first optical signal, the first optical signal being transmitted over a bi-directional optical link. The device further includes a second coupling mechanism and guide for redirecting the first optical signal in a form of a second optical signal into the bi-directional optical link, in the opposite direction from that of the first optical signal, the first coupling mechanism being adapted to duplicate the second optical signal on each port of the second plurality of ports of the device.

Abstract: A planar lightwave circuit (PLC) includes a substrate, a tunable filter, a demultiplexer (DEMUX), and an optical processor each disposed on the substrate. The tunable filter is configured to filter at least one of a bandwidth or a wavelength of a Wavelength Division Multiplexed (WDM) optical input signal. The DEMUX is connected to the tunable filter and configured to receive a filtered WDM optical input signal at an input and to supply one of a plurality of channels of the filtered WDM input signal at a respective one of a plurality of outputs. Each of the plurality of channels corresponds to one of a plurality of wavelengths of the filtered WDM input signal. The optical processor includes a bit-delay interferometer communicating with a respective one of the plurality of outputs of the DEMUX. The optical processor is configured to receive one of the plurality of channels from the DEMUX and output a plurality of demodulated optical signal components.

Abstract: In an optical switch, fibers in a fiber array are arranged in a row. When a region where lights input into or output from the fibers in the fiber array intersect is taken as an intersecting position C, and an axis parallel to the fibers in the fiber array and passing through the intersecting position C is taken as a Z axis, then a distance ? between a core of a desired fiber among the fibers and an optical axis of a corresponding one of the lenses varies depending on a distance S of the desired fiber from the Z axis.

Abstract: An optical network node for an n-channel dense wavelength division multiplexing (DWDM) optical communications network, includes an add path for adding an n-channel wavelength multiplex onto the network. The add path has an n-channel signal combiner for combining the n signal channels. An optical amplifier amplifies an output of the signal combiner. A multichannel wavelength selective filter with variable-per-channel attenuation filters out noise from the amplifier on a channel which carries no content to be added to the network, and controls amplitude of signals in channels to be added to the network. An add coupler couples the add path to the network.

Abstract: A communication system includes a transmitter, a receiver device, and a control circuit. The transmitter transmits an optical signal. The receiver device receives the optical signal. The control circuit reduces a power consumption of the receiver device based on an accumulated chromatic dispersion of the received optical signal. The receiver device includes a receiver, an analog/digital converter, and a digital signal processor. The receiver extracts a signal indicating a complex amplitude of the optical signal. The analog/digital converter converts the signal indicating the complex amplitude into a digital signal. The digital signal processor digitally-processes the digital signal.

Abstract: An optical apparatus including input ports receiving WDM light, an output port, a first wavelength dividing unit that divides the lights input from the input ports into divided lights with different wavelengths, an optical signal processing unit that reflects the divided lights respectively to the first wavelength dividing unit, thereby light from one of the input ports is directed to the output port, for respective wavelength of the divided lights, a light source outputting a monitor light, a first coupler branching the monitor light to the monitor lights to the input ports, a second coupler branching the monitor lights output from the output port and outputs branched output monitor light, a second wavelength dividing unit that divides the branched monitoring lights into divided lights with different wavelengths, and a monitoring unit monitoring the divided lights from the second wavelength dividing unit.

Abstract: The optical transmitter includes a light source; a signal processor; an optical modulator that modulates output light from the light source in accordance with a transmitting signal subjected to digital signal processing in the signal processor and outputs the modulated light as a light signal to a transmission path; and a control circuit that controls a carrier-wave frequency of the light signal output from the optical modulator, the signal processor including a mapping circuit that maps the transmitting signal to electric-field information according to a modulating scheme, and a phase rotating circuit that provides a phase rotation having a constant cycle to an electric-field phase of the electric-field information to which the mapping circuit maps the transmitting signal, the control circuit controlling the cycle of the phase rotation that the phase rotating circuit provides and thereby controlling the carrier-wave frequency of the light signal output from the optical modulator.

Abstract: A dense wavelength-division-multiplexing (DWDM) system, comprising a plurality of laser transmitters, a wavelength division multiplexer (WDM) optically coupled to the laser transmitters and to an output optical transmission media, a coupler optically coupled to the output optical transmission media, an interferometric filter optically coupled to the coupler but not directly to the output optical transmission media, and a light reflector optically coupled to the interferometric filter and not directly to the output optical transmission media.

Abstract: The invention pertains to optical fiber transmission systems, and is particularly relevant to transmission of high volume of data and voice traffic among different locations. In particular, the improvement teaches the use of a single optical transport system for both metropolitan area transport and long haul transport of data and voice traffic.

Abstract: A wavelength selective switch utilizing aperture-shared optics and functionally distinct planes of operation that enables high fiber port counts, such as 1×41, and multiplicative expansion, such as to 1×83 or 1×145, by utilizing elements optimized for performance in one of the functionally distinct planes of operation without affecting the other plane.

Abstract: Apparatus and methods for using a tunable optical source in safety curtain applications provide for enhanced operation of the safety curtain. In an embodiment, a safety curtain includes a transmit unit and a receive unit to operate as the safety curtain, where a single tunable light source generates different wavelengths of light and a single detector is used to detect the generated light.

Abstract: In a wavelength selecting switch, light output from an input port of an input/output optical system is angularly dispersed according to a wavelength thereof, with a spectral element. Then the lights of respective wavelengths are collected by a light collecting optical system and reflected with a corresponding reflecting mirror of a mirror section. The reflected light corresponding to the angle of the reflecting mirror, is input to an output port at an output destination of the input/output optical system. The respective output ports of the input/output optical system each have a lens coupled to an end face of an optical fiber, and the lens has a structure where a focal length of a first region corresponding to inside a variable range of attenuation is different from a focal length of a second region corresponding to outside the variable range.

Abstract: In today's reconfigurable optical add/drop multiplexer (ROADM) based optical node, transponders associated with the ROADMs' add/drop ports are dedicated to a given network node interface. Dedicated transponders reduce the flexibility to route around network failures. Example embodiments of the invention includes an optical node and corresponding method for routing optical signals within an optical node. The optical node may include at least two ROADMs to transmit respective wavelength division multiplexed (WDM) signals onto at least two inter-node network paths and at least one add/drop module including add ports to direct add wavelengths received from tributary network paths to each of the ROADMs via intra-node network paths to allow the wavelengths to be available to be added to the inter-node network paths.

Abstract: Provided are a network node which has a wavelength switching cross-connection function and can thus interconnect paths of a wavelength-division-multiplexed optical signal and convert wavelengths, and an operating method of the network node. Accordingly, it is possible to provide a multi-degree cross-connection system having a simple structure at lower cost by allowing transmission of optical signals supposed not to be added/dropped at a network node without converting them into electrical signals and performing O/E conversion or E/O conversion only on optical signals supposed to be added/dropped at a network node. In addition, it is possible to increase the expandability of networks by regenerating degraded signals and which can effectively utilize bandwidths by grooming low-speed electrical digital hierarchy signals and transmitting them as high-speed optical signals.

Abstract: A method for providing multi-wavelength switching. The method comprising receiving a plurality of signals through at least one input port, and separating the plurality of said signals into at least one wavelength signal set based on wavelengths, wherein a first wavelength signal set of said at least one wavelength signal sets corresponds to a first wavelength. The method further comprises providing a plurality of output lanes to at least one output port, and determining if two signals from said first wavelength signal set traveling on said first wavelength are scheduled output from an output port during an overlapping time period through said plurality of output lanes.

Abstract: A WDM optical transmission system includes a plurality of optical nodes optically coupled by a transmission line, a processor that is operative to calculate an amount of adjustment of a reception level capable of increasing an optical signal-to-noise ratio for each channel of the WDM light reaching the optical node positioned at a receiving end of the unit section based on information on amplification operation of the WDM light in at least one optical-amplification repeating node disposed on the optical transmission line in the unit section, and to adjust a power level corresponding to each channel of the WDM light transmitted on the transmission line from the optical node positioned at a transmission end of the unit section in accordance with a calculation result of the calculation.

Abstract: Consistent with the present disclosure, an optical communication system, such as a passive optical network (PON), is provided that includes an optical line terminal (OLT) and a plurality of optical network units (ONUs). The OLT includes a plurality of photonic integrated circuits that have both optical transmitters and receivers provided therein. Accordingly, the OLT may have fewer components and a simpler, more reliable and cost-effective design than a conventional OLT including discrete components. In addition, various ONU configurations are provided that also have a simple design and fewer components. Thus, ONUs consistent with the present disclosure may also have reduced costs.

Abstract: A method for amplifying a burst optical signal, a burst optical amplifier and system, and a communications system are provided according to embodiments of the present invention. The method includes: combining an auxiliary light and a signal light into a mixed light and outputting the mixed light, where the auxiliary light is a non-burst light, the signal light is a burst light, and power of the auxiliary light is set to be independent from power of the signal light; generating a pump light; and combining the pump light with the mixed light and inputting the combined light into a gain medium, so as to obtain an amplified mixed light. Present invention has the following advantages: reducing the delay time of enabling the burst optical amplifier, improving the transient response speed of the burst optical amplifier, and preventing the generation of a surge phenomenon, so as to prevent the generation of signal distortion.

Abstract: Consistent with the present disclosure, an optical communication system, such as a passive optical network (PON), is provided that includes an optical line terminal (OLT) and a plurality of optical network units (ONUs). The OLT includes a plurality of photonic integrated circuits that have both optical transmitters and receivers provided therein. Accordingly, the OLT may have fewer components and a simpler, more reliable and cost-effective design than a conventional OLT including discrete components. In addition, various ONU configurations are provided that also have a simple design and fewer components. Thus, ONUs consistent with the present disclosure may also have reduced costs.

Abstract: The power level of a wavelength division multiplexed optical signal is detected by a detection unit. When the power level of the optical signal detected by the detection unit is equal to or lower than a first threshold, the coupling direction of an attenuation unit for controlling the coupling direction for the ports of the optical signal is controlled in the direction orthogonal to the array direction of the ports. When the power level of the optical signal exceeds a second threshold, the coupling direction of the attenuation unit is controlled in the array direction of the ports.

Abstract: A method, system, and computer program product for implementing stream processing are provided. The system includes an application framework and applications containing dataflow graphs managed by the application framework running on a first network. The system also includes at least one circuit switch in the first network having a configuration that is controlled by the application framework, a plurality of processing nodes interconnected by the first network over one of wireline and wireless links, and a second network for providing at least one of control and additional data transfer over the first network. The application framework reconfigures circuit switches in response to monitoring aspects of the applications and the first network.

Abstract: A hermetically packaged, MEMS array-based ROADM module is disclosed. The enclosure sidewalls and a top lid are made of Kovar, and the base is made of alumina ceramic AuSn-soldered to the enclosure sidewalls. The MEMS array is attached to the ceramic base. The optics are passively pre-aligned using a removable template and epoxied to an optical bench. The optical bench is actively aligned as a whole and attached to the ceramic base. A plurality of electrical feedthrough contact pins extend from the bottom of the ceramic base for connecting the MEMS to a connector on a printed circuit board. In one embodiment of the invention, the ceramic base extends beyond the footprint of the sidewalls of the enclosure of the module, for mounting additional electronic components, for example MEMS driver circuitry chips, directly to the ceramic base of the enclosure.

Abstract: A reconfigurable optical add drop multiplexer core device includes a light distributor, a light combiner, and first and second sets of add and drop ports. The light distributor is configured to receive an optical signal along a primary input of the reconfigurable optical add drop multiplexer core device and to distribute the received optical signal along a plurality of subtending outputs. The light combiner is configured to receive optical signals along a plurality of subtending inputs, to combine the received optical signals into a combined signal, and to output the combined signal. The add and drop ports in the first set function as add and drop ports, respectively, and the add and drop ports in the second set function as both add and drop ports, respectively, and as express ports connectable to another reconfigurable optical add drop multiplexer core device.

Abstract: The invention generally relates, in one aspect, to an interferometer system. The interferometer system includes a splitter/combiner element (SCE), a first bi-directional optical path, and a second bi-directional optical path.

Abstract: An optical switch including a first reversible optical circulator and a second reversible optical circulator is provided. Each of the first reversible optical circulator and the second reversible optical circulator respectively has four I/O ports, wherein the four I/O ports are respectively a first terminal, a second terminal, a third terminal, and a fourth terminal, the four terminals sequentially transmit an optical signal in a forward circulation or a backward circulation according to a control signal, and an open end is formed between the first terminal and the adjacent fourth terminal. The open ends of the first reversible optical circulator and the second reversible optical circulator are coupled with each other.

Abstract: A tunable filter is provided.

Abstract: An optical transmission system includes a plurality of optical nodes that transmits wavelength multiplexing light including a plurality of signal light components having different wavelengths, wherein each of the optical nodes includes superimposed signal light generation circuit which superimposes a low frequency signal having a common frequency on a corresponding signal light component included in the wavelength multiplexing light; low frequency signal extraction circuit which extracts a low frequency signal having a frequency of a given range from a corresponding signal light component; and pass-through node number measurement circuit which measures, for each of the signal light components, a pass-through node number based on the frequency of the low frequency signal extracted by the low frequency signal extraction circuit, the pass-through node number being the number of optical nodes through which the signal light component has passed before being transmitted to a specific optical node.