Abstract: An optical signal of an optical transmission part is brought into a high-speed polarization scrambling state by a polarization scrambling part, and transmitted to en optical fiber transmission line as the optical signal from the optical transmitter. The optical signal passing through the optical fiber transmission line is inputted to an optical receiver. The optical signal inputted to the optical receiver is converted into an electric signal by a polarization dependent photoelectric detection part. The converted electric signal is inputted to a digital signal processing part having a polarization scrambling cancel part of canceling the polarization scrambling state by a digital signal processing operation. At the digital signal processing part, the polarization scrambling state of the electric signal is canceled, and a data signal is outputted.

Abstract: A polarization multiplexing transmitter which generates polarization-multiplexed signals which are arbitrarily polarization-scrambled at high speed, without adding a polarization modulator and a polarization scrambler. In the transmitter, an orthogonally polarized signal generator includes two optical modulators which modulate the electric fields of optical signals and generate two optical signals with mutually orthogonal polarized waves. The transmitter includes electric field mappers which convert two data strings into electric field signals, polarization mappers which give different polarized waves to the two signals, polarization rotators which rotate the polarized waves of the signals uniformly, a polarization multiplexer which multiplexes the two polarization-rotated signals, a polarization demultiplexer which demultiplexes the multiplexed signal into polarized wave components of optical signals generated by the orthogonally polarized signal generator, and a driver.

Abstract: The present invention relates to an optical modulator that generates quaternary amplitude modulated light without inter-symbol-interference by splitting input light into three optical paths, generating a continuous wave signal in a first optical path, generating binary phase modulated lights using a single drive MZ type optical phase modulator in second and third optical paths, and interfering them at in-phase and at field amplitude 1:a:b.

Abstract: A problem to be solved in an optical communication system for carrying out bidirectional transmission between communication nodes by wavelength-division-multiplexed optical signals is that a plurality of optical add-drop multiplexers installed in the communication nodes are required for each transmission direction, and therefore, the communication cost is increased. An optical circulator or an optical coupler is arranged at an input/output port of the optical add-drop multiplexer and the wavelength-division-multiplexed optical signals are assembled for each transmission direction, whereby optical signals transmitted bidirectionally can be handled by one optical add-drop multiplexer.

Abstract: The waveform deterioration detection range is broadened and multi bit rates can be handled. A chromatic dispersion compensator (or polarization mode dispersion compensator) (102) receives a waveform-deteriorated NRZ optical signal entered through an input fiber (101) and compensates it. On the other hand, an optical detector (106) receives part of output light and a sampling circuit (A/D converter) (107) performs asynchronous sampling of received waveform intensity. A control circuit (110) calculates the nth even moment (n is 4 or more) from an obtained waveform amplitude histogram and performs control to minimize its value.

Abstract: It is provided an optical field transmitter comprising a light source, a DA converter and an optical field modulator. The optical field transmitter modulates an information signal into an optical field signal. The information signal includes one of multilevel signals arranged irregularly on a complex plane and multilevel signals arranged by combining mutually different numbers of phase values in at least two amplitude values. The optical field transmitter further comprises a phase pre-accumulation circuit for outputting phase pre-accumulation complex information obtained by previously accumulating a phase component of the information signal at predetermined time intervals. The DA converter converts the information signal including the output phase pre-accumulation complex information into an analog signal, and inputs the converted analog signal to the optical field modulator.

Abstract: A signal speed converting apparatus to be connected to a WDM transmission end office, comprising a first interface connected to a first optical line group, a plurality of second interfaces connected to a second optical line group, and a speed converter. The first interface has a first framer for terminating a frame in a first format received from the first optical line group and outputting an information signal extracted from the received frames as a serial signal train or parallel signal trains. The speed converter converts the output signal from the first framer into transmission signal trains each including interleaved communication frame by cyclically distributing the output signal from the first framer to a plurality of internal lines. Each of the second interfaces has a second framer for converting the communication frame received from one of the internal lines into information frame in a second format to be transmitted to the second optical line group.

Abstract: An optical field receiver comprises an optical brancher that branches a received optical multilevel signal into first and second optical signals; an optical delayed detector that performs delayed detection on the first optical signal by a delayed detector with a delay time of T/2 (where T is equal to a symbol time) and a phase difference of 90 degrees; a balanced optical receiver that converts the optical signal outputted from the first delay detector to an electric signal; and an optical intensity receiver that converts the second optical signal to an electric signal; and an electric field calculating part that generates, from the output signals of the first and second optical receivers, first and second reproduced signals indicative of the phase angle and amplitude value of the received symbol represented by the complex signal in each symbol time T.

Abstract: Part of an inputted optical add signal 118 is reflected by a mirror 117, and is thereby inputted into an optical wavelength multiplexer 105 in the reverse direction so that the optical add signal is returned to paths 115-1 through 115-16 corresponding to wavelengths ?1 through ?16. If the returned optical add signal is an optical add signal having a correct wavelength, the optical signal enters its corresponding backward direction optical detector 113-16. Accordingly, it is possible to check whether or not a wavelength of the optical add signal is correct.

Abstract: Heretofore, it was necessary to individually locate an optical switch, an optical switch control circuit, and the like, before and after an optical transceiver that performs optical protection. As a result, costs and the space for implementation increase, and a delay in services is also caused, which were the problems. For the purpose of solving the above problems, the present invention provides a simple optical protection method used in an optical add-drop multiplexer. Add switches 105-1 through 105-N and drop switches 103-1 through 103-N for optical signals corresponding to each wavelength in an optical add-drop multiplexer 100 are made controllable independently of one another. Add switches and drop switches of the active-side and backup-side optical add-drop multiplexers are switched by optical switch control circuits 106-1 through 106-N respectively to make a detour around a failure so that the optical protection is achieved.

Abstract: The present invention relates to an optical modulator that generates quaternary amplitude modulated light without inter-symbol-interference by splitting input light into three optical paths, generating a continuous wave signal in a first optical path, generating binary phase modulated lights using a single drive MZ type optical phase modulator in second and third optical paths, and interfering them at in-phase and at field amplitude 1:a:b.

Abstract: An optical balanced receiver including an optical coupler for combining input optical information signal and optical reference signal and outputting two optical interfering signals whose phases are opposite to each other, two photodetectors for receiving the two optical interfering signals and outputting detection signals as electrical signals having the amplitudes corresponding to the interference intensities of the received optical interfering signals, a balance compensation type difference device for compensating an intensity fluctuation component added to a difference signal of the two detection signals due to the difference in amplitude and/or delay between the detection signals output from the two photodetectors in accordance with an input control signal, and outputting the compensated difference signal of the two detection signals, and a control circuit for outputting the control signal to the balance compensation type difference device.

Abstract: An electric field waveform of an optical signal is precisely measured with high time resolution. Particularly, determination of inter-symbol interference has been difficult. Output light from the laser source is divided into first and second portions. The first portion is modulated by an optical modulator. The second portion is delayed by a delay line for the same quantity of delay as that of the first portion. The first and second portions are fed to a phase diversity circuit to configure a homodyne interferometer. An optical input sampling oscilloscope stabilizes a variable optical phase shifter to set an optical phase at a particular point of time to a fixed value using a pattern sync signal as a reference. An optical input sampling oscilloscope repeatedly averages optical waveforms and a CPU conducts three-dimensional display of the optical electric field waveform from which noise has been removed.

Abstract: Provided is a pre-equalized optical transmitter, comprises: a laser source; a duo-binary pre-coder circuit; a pre-equalization circuit for applying an inverse function of chromatic dispersion; at least two D/A converters; and an optical field modulator comprising at least two input terminals for an electric signal.

Abstract: An optical field receiver comprises an optical branching circuit for branching a received optical multilevel signal into first and second optical signals, a first optical delayed demodulator for performing delayed demodulation on the first optical signal at a delay time T (T=symbol time), a second optical delayed demodulator for performing delayed demodulation on the second optical signal at the delay time T with an optical phase difference deviating from the first optical delayed demodulator by 90°, first and second optical receivers for converting each of the delayed demodulation signals representing x and y components of complex signals output from the first and second delayed demodulators into first and second electrical signals, and a field processing unit fort generating a first reconstructed signal representing an inter-symbol phase difference or a phase angle of a received symbol from the first and second electrical signals for each symbol time T.

Abstract: A signal speed converting apparatus to be connected to a WDM transmission end office, comprising a first interface connected to a first optical line group, a plurality of second interfaces connected to a second optical line group, and a speed converter. The first interface has a first framer for terminating a frame in a first format received from the first optical line group and outputting an information signal extracted from the received frames as a serial signal train or parallel signal trains. The speed converter converts the output signal from the first framer into transmission signal trains each including interleaved communication frame by cyclically distributing the output signal from the first framer to a plurality of internal lines. Each of the second interfaces has a second framer for converting the communication frame received from one of the internal lines into information frame in a second format to be transmitted to the second optical line group.

Abstract: In a quaternary phase modulator including two phase modulators disposed in parallel and a phase adjuster that adjusts a phase difference when the outputs of the two phase modulators are combined, there are provided a second light source that introduces light propagated in a backward direction, a first controller that controls the bias of the two phase modulators so that the intensity of the backward light is a minimum on the input side of the quaternary phase modulator, and a second controller that controls the bias of the phase adjuster so that a result monitored by a photodiode having a bandwidth not exceeding the bit rate on the output side of the quaternary phase modulator is a minimum, the first controller being implemented after the second controller is implemented.

Abstract: Optical transmission equipment, capable of electrically adjusting the delay difference between a plurality of digital signal paths to be connected to a multilevel optical modulation unit or demodulation unit, having multiplexing circuits connected to the digital signal paths and a delay adjustment unit inserted in one of the digital signal paths to adjust delay of N-bit-parallel low-speed digital signals with the timing unit of a bit period of a high-speed serial digital signal to be outputted from multiplexing circuit.

Abstract: In the bias stabilization control using average optical power of signal light, there is a case where a control algorithm (maximum control or minimum control) changes depending on the amplitude of clock voltage, or it becomes out of control. In an optical modulation device for performing CSRZ optical modulation on outgoing light from an optical source, control light inputted from a control light input path is inputted into an LN-MZ optical modulator having traveling-wave type modulating electrodes from a direction opposite to signal light, and the average optical power is detected by a photodetector. A bias-voltage Vb is so generated that this optical power may be minimized, and is applied to a bias input terminal, whereby automatic bias stabilization control is performed.

Abstract: In the bias stabilization control using average optical power of signal light, there is a case where a control algorithm (maximum control or minimum control) changes depending on the amplitude of clock voltage, or it becomes out of control. In an optical modulation device for performing CSRZ optical modulation on outgoing light from an optical source, control light inputted from a control light input path is inputted into an LN-MZ optical modulator having traveling-wave type modulating electrodes from a direction opposite to signal light, and the average optical power is detected by a photodetector. A bias-voltage Vb is so generated that this optical power may be minimized, and is applied to a bias input terminal, whereby automatic bias stabilization control is performed.