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: 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: 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: 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: It was difficult to detect a wavelength error. Further, a wavelength error of an optical add signal is accompanied by a calculation error of the number of wavelengths of a wavelength division multiplexing signal, which causes a set value of an optical signal level to become abnormal, resulting in the degradation of the optical signal. According to the present invention, 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 (in FIG. 1, ?16), 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: 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: An object of the present invention is to prevent an interruption circuit of an optical amplifier from malfunctioning due to Raman pump wave. A typical mode of the present invention is characterized in that an pump wave elimination filter is inserted before an input-light detector and a reflected-light detector which constitute the optical amplifier. This permits only a signal component to be detected, enabling interruption operation, while eliminating a remaining component of Raman pump wave transmitted from for example a downstream of an optical fiber transmission line. In addition, a judgment threshold value for the interruption operation is changed according to ON/OFF condition of the pump wave. Or the Raman pump wave itself is used for detecting output's open.

Abstract: With the normal modulation method, it is difficult to construct a Hilbert transform device because it is complicated. To solve the problem, a single sideband modulated optical pulse train is generated by driving a Mach-Zehnder optical modulator for optical pulse generation with a laser source's sine wave clock signals that have been rendered 90 degrees out of phase from each other. The generated pulse train is applied to an optical modulator, modulated with an NRZ (nonreturn-to-zero) data signal, and filtered by a narrow-band optical filter to obtain one of two sidebands.

Abstract: A transponder which may form part of communication device such as an optical transmitters device includes an optical receiver for receiving a high speed optical information signal and for converting the high speed optical information signal to an electrical signal, a demultiplexing circuit for separating the electrical signal into a plurality of low speed information signals, a plurality of optical transmitters each of which converts one of the low speed electrical signals into an optical signal of mutually different wavelengths, and a propagation delay difference compensating circuit. The propagation delay difference compensating circuit is provided between the demultiplexing circuit and the plurality of optical transmitters and compensates mutual propagation delay differences of each of the optical signals outputted from the optical transmitters.

Abstract: Objects of the present invention are to reduce the number of optical filters, and to improve crosstalk characteristics of periodic optical filters. WDM signals are converted into vestigial-side-band signals collectively using a periodic optical filter. As an example, light signals having odd number wavelengths (wavelengths &lgr;1, &lgr;3, &lgr;5) and light signals having even number wavelengths (wavelengths &lgr;2, &lgr;4, &lgr;6) are wavelength-multiplexed in the first optical wavelength multiplexer, and are then filtered by a periodic narrow band-pass optical filter to convert the light signals into vestigial-side-band (VSB) signals. Then, the vestigial-side-band signals are combined by the second optical wavelength multiplexer. Such an interleave configuration enables suppression of crosstalk caused by adjacent channels.

Abstract: An object of the present invention is to prevent an interruption circuit of an optical amplifier from malfunctioning due to Raman pump wave. A typical mode of the present invention is characterized in that an pump wave elimination filter is inserted before an input-light detector and a reflected-light detector which constitute the optical amplifier. This permits only a signal component to be detected, enabling interruption operation, while eliminating a remaining component of Raman pump wave transmitted from for example a downstream of an optical fiber transmission line. In addition, a judgment threshold value for the interruption operation is changed according to ON/OFF condition of the pump wave. Or the Raman pump wave itself is used for detecting output's open.

Abstract: The present invention offers a polarization mode dispersion compensator and a compensation method for polarization mode dispersion having simple constitution and being strong against external disturbances. The polarization mode dispersion compensator, a representative example of the present invention, is provided with a compensation circuit for polarization mode dispersion, a degree of polarization measuring circuit, and a control circuit. An optical signal is input to the compensation circuit for polarization mode dispersion through an optical fiber, and after the process of compensation for polarization mode dispersion, it is output to an optical fiber. An optical coupler divides a part of the optical signal passing through the optical fiber. The degree of polarization measuring circuit finds the degree of polarization of the divided optical signal.

Abstract: With the normal modulation method, it is difficult to construct a Hilbert transform device because it is complicated. To solve the problem, the present invention generates a single sideband modulated optical pulse train by driving a Mach-Zehnder optical modulator for optical pulse generation with a laser source's sine wave clock signals rendered 90 degrees out of phase from each other. The generated pulse train is entered into an optical modulator, modulated with an NRZ (nonreturn-to-zero) data signal, and filtered by a narrow-band optical filter to obtain one of two sidebands.

Abstract: A transponder which may form part of communication device such as an optical transmitters device includes an optical receiver for receiving a high speed optical information signal and for converting the high speed optical information signal to an electrical signal, a demultiplexing circuit for separating the electrical signal into a plurality of low speed information signals, a plurality of optical transmitters each of which converts one of the low speed electrical signals into an optical signal of mutually different wavelengths, and a propagation delay difference compensating circuit. The propagation delay difference compensating circuit is provided between the demultiplexing circuit and the plurality of optical transmitters and compensates mutual propagation delay differences of each of the optical signals outputted from the optical transmitters.

Abstract: A method for enabling a pump laser to be added on by means of an optical fiber Raman amplifier and reducing signal degradation to be caused by a gain change to occur after and in the pump laser source add-on process. The above method is achieved as follows. Add-on ports 114-1 and 114-2 are provided in a wavelenth multiplexer 110 so as to enable new wavelength pump laser sources to be added on. When an add-on pump laser source 112 is turned on, the output intensity of each of the pre-installed Raman pump lasers 111-1 and 111-2 changes, thereby the intensity of each signal laser in each pre-installed band is kept unchanged before and after the add-on. The output intensity of each pump laser source that increases/decreases the output, for example, during the add-on is changed linearly with time, thereby the transient gain changes in the pre-installed bands are prevented.

Abstract: The technical problem disclosed concerns increase of transmission distance between inter-site transmission parts when a circuit speed is increased, and simplification of an intra-site circuit. The means to resolve the problem is as follows. An intra-site circuit connecting an intra-site information communications device 140-1 and a wavelength division multiplexing optical transmission device 147 is demultiplexed into plural low speed wavelength division multiplexing signals by a transponder 100 according to this invention, and transmitted to an inter-site optical fiber circuit 144. The signals are again multiplexed into a high-speed optical signal by a transponder 110 in a wavelength division multiplexing optical transmission device 148 on the receiving side, and transmitted to an intra-site optical fiber circuit 143-1.

Abstract: A method for enabling a pump laser to be added on by means of an optical fiber Raman amplifier and reducing signal degradation to be caused by a gain change to occur after and in the pump laser source add-on process.

Abstract: An optical transmission system in which influences of worsening of the waveform by SPM are canceled by setting an amount of compensation of a dispersion compensator at about 50% of a total amount of dispersion of an optical fiber transmission line so that received waveform is almost not varied, even if light intensity is varied. In the case where a plurality of dispersion compensators are used, the number of compensators is optimized by setting arrangement interval in the neighborhood of a receiving end at a small value. Further, in a transmission line, in which amounts of dispersion of optical fibers have positive and negative fluctuations, the smallest transmission distance of a transmission system is increased by effecting dispersion compensation so that an expected value of the total amount of dispersion of the transmission line is abnormal dispersion.

Abstract: An optical transmission system in which influences of worsening of the waveform by SPM are cancelled by setting an amount of compensation of a dispersion compensator at about 50% of a total amount of dispersion of an optical fiber transmission line so that received waveform is almost not varied, even if light intensity is varied. In the case where a plurality of dispersion compensators are used, the number of compensators is optimized by setting arrangement interval in the neighborhood of a receiving end at a small value. Further, in a transmission line, in which amounts of dispersion of optical fibers have positive and negative fluctuations, the smallest transmission distance of a transmission system is increased by effecting dispersion compensation so that an expected value of the total amount of dispersion of the transmission line is abnormal dispersion.

Abstract: In an optical transmission system, SPM influences on the degradation of wave forms are canceled by setting an amount of compensation of a dispersion compensator at about 50% of the total amount of dispersion of an optical fiber transmission line so that a received wave form is substantially not varied, even if light intensity is varied. When a plurality of dispersion compensator are used, the number of compensators is optimized by setting the arrangement interval in the vicinity of the receiving end to a small value. Further, in a transmission line, in which amounts of dispersion of optical fibers have positive and negative fluctuations, the smallest transmission distance of a transmission system is increased by effecting dispersion compensation so that an expected value of the total amount of dispersion of the transmission line is abnormal dispersion.