Abstract: This application describes techniques for optical multiplexing and demultiplexing in optical communication systems based on polarization multiplexing of different signal channels.

Abstract: A method is provided for predicting an installed performance parameter of an optical fiber cable. The method includes obtaining a measurement indicative of a value of the performance parameter at a first moment in time. A measurement indicative of a value of the performance parameter at a second moment in time may then be obtained. A first correlation may then be determined between the measurement at the first moment in time and the measurement at the second moment in time. A value of the performance parameter at the second moment in time may then be estimated based upon the measurement at the first moment in time in combination with the first correlation, the first correlation being based upon observations of a manner in which the performance parameter varies over time for at least a second optical fiber.

Abstract: Various embodiments of the present invention are directed to compact systems for generating polarization-entangled photons. In one embodiment of the present invention, a non-degenerate, polarization-entangled photon source comprises a half-wave plate that outputs both a first pump beam and a second pump beam, and a first beam displacer that directs the first pump beam into a first transmission channel and the second pump beam into a second transmission channel. A down-conversion device converts the first pump beam into first signal and idler photons and converts the second pump beam into second signal and idler photons. A second beam displacer directs both the first signal and idler photons and the second signal and idler photons into a single transmission channel. A dichroic mirror directs the first and second signal photons to a first fiber optic coupler and the first and second idler photons to a second fiber optic coupler.

Abstract: A Quantum Dense Coding System. The system includes a source, a transmitter and a receiver. The source is capable of down-converting a pump photon into a signal photon and an idler photon and outputting probability amplitudes, the signal photon and the idler photon, wherein the signal photon and the idler photon have an equal probability of outputting to a transmission channel and a reception channel. The transmitter is capable of receiving probability amplitudes, signal photons and idler photons from the transmission channel; and selectively changing vertical and horizontal phases of probability amplitudes of signal photons and idler photons; and outputting probability amplitudes, signal photons and idler photons. The receiver is capable of receiving probability amplitudes, signal photons and idler photons from the reception channel and the transmitter; and identifying vertical and horizontal phase changes created by the transmitter. A method for the system is also described.

Abstract: An apparatus, a polarization diversity receiver and a method of receiving a received optical signal. In one embodiment, the apparatus includes: (1) an optical device configured to separate in-phase and quadrature components of a received optical signal, to transmit the in-phase components to a first optical output thereof and to transmit the quadrature components to a second optical output thereof, (2) a first polarization splitter coupled to receive light at the first optical output and (3) a second polarization splitter coupled to receive light at the second optical output.

Abstract: In the invention, an input light including a signal light and a noise light within a signal wavelength band of the signal light is divided into a first component with a polarization parallel to a polarization direction of the signal light and a second component with a polarization orthogonal to the polarization direction of the first component. The first component is supplied into a first arm and the second component into a second arm. The optical phase of the second component in the second arm is shifted so that the optical phase of the second component in the second arm relatively differs by ? from the optical phase of the first component in the first arm. The first component output from the first arm and the second component output from the second arm are combined to make the noise lights included in the first and second components interfere with each other.

Abstract: A method and system enables measurement of polarization dependent loss (PDL) in an optical communications system including a plurality of cascaded optical components. An optical signal having a predetermined initial polarization state is launched into the optical communications system. A polarization state of the signal is detected at a selected detection point downstream of the launch point. The PDE is evaluated using the predetermined initial polarization state and the detected polarization state.

Abstract: An optical communication system and method may be configured to operate with optical signals having reduced channel spacing. The system may transmit optical signals on a plurality of optical channels with a pair-wise orthogonal relationship such that a first subset of channels has a first polarization state and a second subset of channels has a second polarization state. The channels may be spaced such that there is no overlap of modulation sidebands associated with channels in each of the polarization states. When receiving the optical signals, the orthogonal channels adjacent to a selected channel of interest may be nulled.

Abstract: A system parametrically down-converts a photon into a pair of first and second quantum-entangled photons. A transmitter is coupled to receive the first photon and includes an irreversible collapse event device for collapsing the quantum-entangled state of each photon in the pair. The collapse is caused by attempting to detect the first photon at the transmitter. Because of quantum-entanglement, collapse of the first photon collapses the second photon of the pair. The transmitter can also be used to not cause the collapse. A receiver includes polarization detectors to detect whether the transmitter has collapsed or left uncollapsed the quantum-entangled state of the photon pair. Causing or not causing the collapse can be used for communication. Every down-converted photon can be used for communication, even though few of the photons actually leave the source and reach the transmitter. This allows communication with a minimal number of transmitted photons.

Abstract: Methods and systems for PMD compensation in an optical communication system are implemented by transmitting multiple optical signals through a common optical conduit to an optical compensator that adjustably rotates the polarization states of the multiple optical signals and transmits the rotated optical signals to an optical receiver. The receiver, upon sensing an excessive error condition, commands the optical compensator to change the polarization state of rotation, which changes the PMD profile of the received optical signals.

Abstract: A polarization scrambler has a polarization state rotating unit rotating the polarization state of a signal light, and a rotation speed controlling unit controlling the rotation speed of the polarization state in the polarization state rotating unit on the basis of the speed and scheme of modulation of the signal light, and the value of polarization mode dispersion of a transmission path on which the signal light is to be transmitted. Degradation of the transmission quality due to PMD is more mitigated than the known techniques.

Abstract: An optical communication method and apparatus are provided, the apparatus including polarization controllers, and drive circuitry for driving the polarization controllers at a plurality of frequencies such that the penalties from PMD, PDL and PDG are mitigated.

Abstract: A method is provided for predicting an installed performance parameter of an optical fiber cable. The method includes obtaining a measurement indicative of a value of the performance parameter at a first moment in time. A measurement indicative of a value of the performance parameter at a second moment in time may then be obtained. A first correlation may then be determined between the measurement at the first moment in time and the measurement at the second moment in time. A value of the performance parameter at the second moment in time may then be estimated based upon the measurement at the first moment in time in combination with the first correlation, the first correlation being based upon observations of a manner in which the performance parameter varies over time for at least a second optical fiber.

Abstract: An optical signal multiplexer/demultiplexer using an orthogonal pseudorandom (PRN) coding scheme for optical mode modulation to produce a plurality of independent optical signals that may be combined into one multiplex signal for transmission over an optical fiber to the receiving end, where the multiplex signal may be demultiplexed by relying on the orthogonal properties of the PRN code to isolate each independent optical signal from the transmitted multiplex signal. In channels subject to mode modulation distortion, one of the signal components may be used as a pilot signal to obtain a correction for channel mode modulation distortion. The PRN optical signal multiplexer/demultiplexer is particularly useful with polarization mode modulation.

Abstract: The present invention relates to a multiple access space laser communications optical system. According to the present invention, multiple optical signals containing a number of channels are simultaneously received and demultiplexed at a multiple access communication device. Separate communication signals may be multiplexed by the multiple access communication device, and transmitted through the same or a different telescope optical assembly used to receive communication signals. Double-pass reflection is used to selectively polarize signals and to ensure that signals are substantial normal to optical bandpass filters, to avoid large shifts in the wavelengths transmitted by the optical bandpass filters. The system is capable of providing discrete communications with a number of communication endpoints, regardless of where the communication endpoints are located within the field of view of the telescope optical assembly.

Abstract: An exemplary optical hybrid includes a 50/50 un-polarized beam splitter, a folding prism, a beam shifter, a spacer and a phase shifter such that from an input S-beam (signal) and an L-beam (reference), four outputs, S+L, S?L, S+jL, S?jL, are produced. The phase difference of S and L at the four output ports is phi_0, phi_0+90-degrees, phi_0+180-degree, phi_0+270-degree, where the phase difference between S and L at the S+L port is an arbitrary number phi_0 and the phase difference between S and L at the other output ports, S?L, S+jL, S?jL, is 90, 180 and 270, respectively, shifted from phi_0.

Abstract: Disclosed is an apparatus for monitoring an optical signal-to-noise ratio in a WDM optical network. The apparatus includes an orthogonal polarization component module for receiving an optical signal and outputting it after removing a signal component thereof at a specific frequency band; and calculation means for measuring both average signal and noise component intensity of the optical signal outputted from the orthogonal polarization component module. By removing a signal component at a specific frequency bandwidth and passing only a noise component through, it is possible to easily measure the noise intensity within a signal bandwidth that cannot be measured in general. A frequency band is set within a signal bandwidth, and the signal intensity is minimized at the set frequency band, so that it is possible to measure the optical signal-to-noise ratio even for a signal whose amplified spontaneous emission noise spectrum is not flat, irrespective of the signal pattern length.

Abstract: Tunable PMD emulators and compensators for producing different PMD profiles with an adjustable average DGD value.

Abstract: A monitoring system is described that is comprised of a processing system and a database system. The database system is configured to store identities for a plurality of channels in the communication network. The processing system identifies an error on a first channel of the plurality of channels. The processing system identifies a second channel of the plurality of channels that is adjacent to the first channel based on the database system and determines if an error occurs on the second channel. The processing system identifies a third channel of the plurality of channels based on database system and determines if an error occurs on the third channel. The processing system identifies polarization-mode dispersion based on determining the error occurs on the second channel and determining the error does not occur on the third channel.

Abstract: A system and method for reducing polarization dependent loss in optical circuits is disclosed. The system includes a first optical device having an output, and a polarization controller optically coupled to the first optical device for adjusting a polarization state of the output of the first optical device. The system further includes a second optical device optically coupled to the polarization controller. Adjusting the polarization state of the output of the first optical device alters a total polarization-dependent loss for the cascaded device system. A series of fiber optic loops can be used to adjust the output of the first optical device. A PDL measuring device can be inserted after the second optical device to provide feedback to the polarization controller, so that the controller may be tuned to adjust the polarization to a desired state.

Abstract: A multi-wavelength optical signal copropagates through a fiber-optic communication link with a continuous-wave ancillary wavelength having an unknown state of polarization (SOP), which is scrambled periodically in time. The instantaneous value of polarization dependent loss (PDL) in the ancillary wavelength is monitored in real time, and is used as an error signal to adjust at least one polarization controller. Polarization scrambling is performed by periodically changing the SOP with time, such that the polarization-scrambled optical signal covers approximately an entire Poincaré sphere surface, preferably uniformly, during each time period. At an optical node between fibers, an adjustable PDL compensator contains two ordered pairs each consisting of one polarization controller and one optical element introducing fixed PDL.

Abstract: The present invention provides a WDM optical communication system, comprising input means and output means for an optical signal, an optical fibre path connecting signal-transmissively said input and output means, wherein the optical signal is amplified by means of Raman amplification and said optical fibre path comprises at least one Raman amplifier, further comprising WDM means for coupling at least two polarized pump radiation wavelengths with wavelengths less than the signal radiation wavelength into said Raman amplifier, wherein one pump radiation wavelength has a selected different polarization with respect to the polarization of the other pump radiation wavelengths.

Abstract: A PMD emulator configured by connecting in this order: an input-side optical fiber 71 for receiving light to be measured; a first polarization rotating portion 73 including M DGD sections 76 (M is an integer equal to or more than 2) concatenated by (M?1) polarization rotators 80, one DGD section being arranged at each end of said first polarization rotating portion; an arbitrary-arbitrary polarization controller 75 for changing any state of polarization into any other state of polarization, a second PMD rotating portion 74 configured in the same way as the first polarization rotating portion 73 an output-side optical fiber for outputting the light to be measured.

Abstract: It is disclosed that a method and apparatus that automatically monitors each channel's optical signal-to-noise ration (OSNR) using optical filter and polarization extinction method in wavelength division multiplexing (WDM) scheme-based optical transmission systems. OSNR is simply measured using optical filter by comparing amplified spontaneous emission (ASE) over the signal band, of which bandwidth has changed, while leaving signal intensity intact, with that original signal and, OSNR measurement is allowable over a wider range of OSNR by minimizing the ratio of signal to ASE over the signal band using polarization extinction method.

Abstract: An apparatus for measuring a set of frequency-resolved states of polarization (SOP) of an optical signal includes a local oscillator (LO), a polarization scrambler, a coupler for mixing the polarization-scrambled signal with the optical signal to produce a heterodyned signal with a radio frequency (RF) component, and an analyzer for passing a fixed polarization component and resolving the polarization and frequency from the RF component. The apparatus is used for measuring, monitoring or compensating the polarization mode dispersion (PMD) in a working channel of an optical telecommunication system. A method for measuring frequency-resolved SOP of an optical signal includes tuning and polarization-scrambling a local oscillator (LO), mixing the scrambled LO with the optical signal, and resolving the RF signal in frequency and polarization. The method is applied to measure and monitor PMD in a working optical channel, and to dynamically compensate for the PMD.

Abstract: This invention provides a technique for realizing low-cost optical signal waveform monitoring with improved realtimeness to be applied to signal quality monitoring in an actual optical transmission system, and a technique for stably controlling an optical transmitter/receiver and various compensators by means of this waveform monitoring. Opening/closing of a optical gate is controlled by means of a clock signal synchronized with an optical signal input from a photocoupler and having a period equal to the bit interval of data or N (N: a positive integer) times longer than the bit interval to allow each pulse of the optical signal for one bit of data to pass through the optical gate for only part of the time width of the gate. A photoelectric conversion element to which the optical signal transmitted through the optical gate for only part of the time width obtains an average light intensity of the input optical signal. Information on this average light intensity is output to a monitoring output section.

Abstract: A system for optical communication forms a family of orthogonal optical codes modulated by a data stream. The orthogonal codes are formed by creating a stream of evenly spaced-apart pulses using a pulse spreader circuit and modulating the pulses in amplitude and/or phase to form a family of orthogonal optical code words, each representing a symbol. A spreader calibration circuit is used to ensure accurate timing and modulation. Each code word is further modulated by a predetermined number of data bits. The data modulation scheme splits a code word into H and V components, and further processes the components prior to modulation with data, followed by recombining with a polarization beam combiner. The data-modulated code word is then sent, along with others to receiver. The received signal is detected and demodulated with the help of a symbol synchronization unit which establishes the beginning and end of the code words.

Abstract: Optical devices with folded optical paths to reduce size of optical devices and optical elements in the optical devices. The folded optical paths operate by manipulating optical polarization of light. Exemplary optical switches and variable optical attenuators are described.

Abstract: A transmitter subsystem generates an optical signal which contains multiple subbands of information. The subbands have different polarization. For example, in one approach, two or more optical transmitters generate optical signals which have different polarization. An optical combiner optically combines the optical signals into a composite optical signal for transmission across an optical fiber. In another aspect, each optical transmitter generates an optical signal containing both a lower optical sideband and an upper optical sideband (i.e., a double sideband optical signal). An optical filter selects the upper optical sideband of one optical signal and the lower optical sideband of another optical signal to produce a composite optical signal.

Abstract: A method and apparatus for transferring information of an optical information-bearing signal from a first wavelength to a second wavelength. The method is implemented in an all-optical wavelength converter circuit which includes a laser diode in communication with a polarization controller. An information-bearing signal having a first wavelength is input to the circuit. A polarization controller adjusts the polarization of the information-bearing signal. The laser diode receives the polarization-adjusted information-bearing signal and generates a converted information-bearing signal by transferring the information of the polarization-adjusted information-bearing signal from the first wavelength to the second wavelength. The polarization controller receives the converted information-bearing signal from the laser diode, and polarizes the converted information-bearing signal.

Abstract: An operation unit of a PMD compensation module includes a PBS (polarization beam splitter), a compensating part and a combiner. The PBS separates an optical input into a first polarized signal and a second polarized signal. The compensating part includes a fixed prism and a movable prism. The first polarized signal outputted from the PBS travels through the fixed prism and the movable prism in series. The light path of the first polarized signal in the movable prism is elongated or shortened according to a position of the movable prism. A continuously variable delay can thus be applied between the first and second polarized signals. The combiner recombines the first polarized signal received from the compensating part and the second polarized signal received from the PBS into an optical output signal.

Abstract: The present invention provides an optical system for decoding, switching, demultiplexing, and routing of optical encoded data symbols, including: a plurality of optical paths having first and second terminals; a splitting mechanism for directing the encoded data symbols to each of the first terminals; a plurality of decoding devices for producing decoded signals in response to the encoded data symbols; and each of the optical paths includes, between the first and second terminals, at least one of the decoding devices to produce one of the decoded signals at one of the second terminals in response to one of the encoded data symbols.

Abstract: A optical polarization encoding device (16) provides wavelength dependent processing of polychromatic optical signals without prior separation into narrow wavelength bands. Embodiments of the encoding device include a wavelength dependent tunable optical switch (400, 500) and a wavelength tunable optical level controller (600). An encoded signal is processed, (e.g., rerouted or attenuated), as a function of wavelength using polarization dependent devices (18). Desired states of polarization are imparted to optical signals to either direct selected wavelengths to selected output ports (optical switch), or to adjust the level of selected channels or wavelengths (level controller). Desired polarizations are achieved simultaneously at all wavelengths contained within the incoming signal by independently varying the birefringence and/or crystallographic orientation of each variable element within the stack.

Abstract: A method and apparatus for transmitting information using the phenomenon of quantum entanglement. Two streams of quantum-entangled particles are emitted from a source. Performing a measurement on one of the streams results in the observable destruction of interference on the other stream. Information is transmitted by modulating the performance of the measurement on the first stream, and received by observing the presence or absence of interference in the second stream.

Abstract: In an optical transmission system, a first modulated signal with a first transmission bit rate is generated at the transmitting end by modulating a first carrier signal with the first data signal, using a nonreturn to zero coding, and a second modulated signal with a second transmission bit rate is generated by modulating a second carrier signal with the second data signal, using a return to zero coding. The first and second modulated signal are polarized orthogonally with respect to one another and combined to form an optical multiplex signal and transmitted. At the receiving end, the optical multiplex signal is conducted via a polarization control element to a polarization splitter which splits the optical multiplex signal into the first and second modulated signal.

Abstract: To generate light with the degree of polarization zeroed and the spread of an optical spectrum suppressed even with temporal overlapping between optical pulses each of which is polarized orthogonally to the succeeding pulse, a polarization scrambler includes an optical pulse generator that generates optical pulses with an intensity waveform repetition period T/2 and an electrical field repetition period T in which the same intensity waveform is repeated every repetition period T/2 and in which phase is inverted every repetition period T/2, and an orthogonal polarization delay unit which receives each of the optical pulses, separates the optical pulse into two optical pulses with orthogonal states of polarization, and relatively shifts the temporal position of one of the two optical pulses from that of the other optical pulse by (2n?1)T/4 (n is a natural number) to generate light in which each pulse is polarized orthogonally to a succeeding pulse.

Abstract: Optical transmitter/receivers for use in a DWDM systems are provided. Transmission of data signals in a quadrature-return-to-zero (QRZ) format achieves a data transmission rate equal to eight times a base data rate, i.e., 80 Gbps over a 100 GHz channel if the base data rate is 10 Gbps, with high non-linear performance by setting the polarization state of the data bands such that non-linear effects induced by PMD are reduced. Additionally, a transmitter achieves a transmission data rate equal to 16 times the base data rate by sharpening the QRZ pulses and interleaving pulse-sharpened QRZ data signals in the time domain, further doubling the data rate. Using counterpropagation in the transmitter, carrier signals and data signals traverse the same length of fiber, reducing fringing effects in the transmitter. Related techniques enhance reception and detection of data at high data rates. A local pulse-sharpened carrier is mixed with a QRZ data signal at a detector reducing amplification noise by a factor of two.

Abstract: In accordance with the invention, an optical fiber communication system is provided with a tunable linearly chirped Bragg grating in high birefringence fiber for reduction of polarization mode dispersion without increasing chromatic dispersion. A first embodiment using a single grating can be tuned for optimal PMD compensation, optimal chromatic compensation or optimal simultaneous compensation. Alternative embodiments using a plurality of gratings permit simultaneous compensation of both PMD and chromatic dispersion.

Abstract: A system for optical communication send optical signals over a plurality of wavelength channels. Each wavelength channel comprises a number of orthogonal subchannel frequencies which are spaced apart from one another by a predetermined amount. Each of the subchannel frequencies is modulated with data from a data stream. The data modulation scheme splits a subchannel frequency code into H and V components, and further processes the components prior to modulation with data. The various data-modulated subchannels are then combined into a single channel for transmission. The received signals are detected and demodulated with the help of a symbol timing recovery module which establishes the beginning and end of each symbol. A polarization mode distortion compensation module at the receiver is used to mitigate the effects to polarization more distortion in the fiber.

Abstract: An optical monitor that generates a signal indicative of at least two optical properties of an input optical signal. The monitor utilizes a polarization dependent beam splitter having a signal input port, a mixing signal input, a first output port and a second output port. The signal input port receives an input optical signal having first and second orthogonal polarization components. The mixing signal input receives an optical mixing signal having a first and second polarization component parallel to the first and second polarization components of the optical input signal, respectively. The polarization dependent beam splitter generates first and second output signals on the first and second output ports, respectively. The output signals are the sum of the like polarization components of the input optical signal and the optical mixing signal.

Abstract: Wavelength interleaving cross-connects pass a first optical signal including a first set of optical frequencies in a first direction and a second optical signal including a second set of optical frequencies in a second direction. In one embodiment, the first optical signal, when input to a first input/output (I/O) port, is routed from the first I/O port to a third I/O port. The first optical signal, when input to a fourth I/O port, is routed from the fourth port to a second I/O port. The second optical signal, when input to the second I/O port, is routed from the second I/O port to the third I/O port. The second optical signal, when input to the fourth I/O port, is routed from the fourth I/O port to the first I/O port. Thus, by coupling an optical device (e.g., amplifier, filter) between the third port and the fourth port, the optical device can be used for bi-directional communications thereby reducing the number of devices required for a bi-directional optical network architecture.

Abstract: A system for reducing the influence of polarization mode dispersion (PMD) in high speed fiber optical transmission channels. A signal is forward error correction (FEC) encoded according to an FEC code that defines a specified error tolerance per codeword. The invention then effectively randomizes the input polarization of the signal before transmission, in order to reduce the likelihood that PMD will distort one or more codewords beyond the allowed error tolerance. The invention will thereby increase the PMD-limited transmission distance in an optical transmission system.

Abstract: An exemplary polarization controller includes a first optical element having a first optical axis and configured to receive light having a first phase, a second optical element having a second optical axis and configured to emit the light having a second phase, and a third element having a third optical axis. At least a portion of the third element is interstitial to the first element and the second element. The exemplary controller also includes at least two drivers, both of which can operate in accordance with an exemplary method of present invention.

Abstract: To generate light with the degree of polarization zeroed and the spread of an optical spectrum suppressed even with temporal overlapping between optical pulses each of which is polarized orthogonally to the succeeding pulse, a polarization scrambler includes an optical pulse generator that generates optical pulses with an intensity waveform repetition T/2 and an electrical field repetition period T in which the same intensity waveform is repeated every repetition period T/2 and in which phase is inverted every repetition period T/2, and an orthogonal polarization delay unit which receives each of the optical pulses, separates the optical pulse into two optical pulses with orthogonal states of polarization, and relatively shifts the temporal position of one of the two optical pulses from that of the other optical pulse by (2n?1)T/4 (n is a natural number) to generate light in which each pulse is polarized orthogonally to a succeeding pulse.

Abstract: A method of detecting polarization mode dispersion (PMD) indicative parameters of an optical fiber link comprising at least one transmission channel in which is transmitted a first wideband optical signal with a bandwidth divided into sub-bands. For each sub-band is produced a second reference optical signal with which to find a third optical signal by superposition. For each of the third signals are calculated first parameters considered indicative of the PMD thereof, and with the first parameters of all the sub-bands are calculated second parameters considered indicative of the PMD of the first wideband signal. The method can be used as part of a PMD compensation method for a transmission system employing the parameters calculated for feedback piloting of a PMD compensator.

Abstract: A system and method for multi-channel PMD/PDL/PDG mitigation, the system including polarization scramblers adapted to vary the state of polarization of an optical signal propagated through the system to effectively vary the polarization mode dispersion experienced by the signal during each burst-error-correcting-period of the forward error correction used in the system.

Abstract: An all-optical 3R regenerator (AO3R) and a method for using the AO3R to retime, reshape and retransmit an optical signal are described herein. The AO3R includes a polarizer that receives an input optical signal which is of unknown, potentially varying phase and outputs a stable polarized input optical signal. The AO3R also includes a first interferometer (e.g., interferometric converter module) that retimes and reshapes the polarized input optical signal and transmits the retimed and reshaped polarized input optical signal as a polarized output optical signal. The first interferometer is able to retime the polarized input optical signal with the aid of a laser and a clock recovery mechanism.

Abstract: A waveguide type variable optical attenuator has: a substrate; two optical circuits that are in parallel formed on the substrate, each of the optical circuits including two couplers that conduct the branching and coupling of light and are connected to the input port and output port of light and two waveguides through which the two couplers are connected; a polarization maintaining fiber one end of which is connected to the output port of one of the two optical circuits and the other end of which is connected to the input port of the other of the two optical circuits while being twisted 90°; and a heater that is provided around neighboring waveguides of the two optical circuits such that the neighboring waveguides share heat to be generated by the heater.

Abstract: To generate light with the degree of polarization zeroed and the spread of an optical spectrum suppressed even with temporal overlapping between optical pulses each of which is polarized orthogonally to the succeeding pulse, a polarization scrambler includes an optical pulse generator that generates optical pulses with an intensity waveform repetition period T/2 and an electrical field repetition period T in which the same intensity waveform is repeated every repetition period T/2 and in which phase is inverted every repetition period T/2, and an orthogonal polarization delay unit which receives each of the optical pulses, separates the optical pulse into two optical pulses with orthogonal states of polarization, and relatively shifts the temporal position of one of the two optical pulses from that of the other optical pulse by (2n?1)T/4 (n is a natural number) to generate light in which each pulse is polarized orthogonally to a succeeding pulse.

Abstract: A re-generator of an optical clock signal has at least a mode-locked semiconductor laser outputting a re-generated optical clock signal from at least one end face of the mode-locked semiconductor laser, with inputted light signals having different polarized wave states respectively at both end faces of the mode-locked semiconductor laser; wherein the re-generator has a light splitter to split the light signal into two kinds of elements with respective polarized waves different by a right angle, and to emit one of the elements split from the light signal, to one of both end faces of the mode-locked semiconductor laser; and a rotator to input the other elements split from the light signal, to rotate the other elements by a right angle, and to lead the rotated element to the other end face of the mode-locked semiconductor laser.