The Furukawa Electric Co., Ltd.

Hijiri Nimura

Haruki Ogoshi

Shu Namiki

Osamu Aso

Masaru Fukushima

Kouki Sato

Akira Fujisaki

Haruki Ohgoshi

Masateru Tadakuma

Masahito Morimoto

Kazunori Nakamura

A wavelength converter using difference frequency generation (DFG) is disclosed. In one embodiment, the wavelength converter comprises (a) a first optical filter configured to filter out one or more lightwaves requiring wavelength conversion from wavelength-division multiplexed (WDM) lightwaves, and (b) a broadband multi-channel simultaneous wavelength conversion portion comprising a pump source that generates pump light for use in the process of the DFG, a first optical combiner for combining said pump light with said filtered lightwaves, a high non-linear medium configured to generate wavelength converted lightwaves from said filtered lightwaves using the DFG, and a second optical filter for filtering said wavelength converted from said filtered lightwaves.

Wavelength converter and wavelength division multiplexing transmission method using the same

Solely lightwaves required to be wavelength converted are filtered out from the input broadband WDM lightwaves and are wavelength converted by use of FWM. Not only the broadband simultaneous wavelength conversion that is studied by many researchers, but also more flexible, sub-band wavelength conversion is realized. Frequency interval of the input WDM lightwaves is broadened or reduced in comparison of the frequency interval of the WDM lightwaves inputted to the wavelength converter. The frequency interval variation techniques using the wavelength converter, it can be realized to transfer from a transmission line less influenced by inter-channel crosstalk due to FWM to the different transmission lines strongly influenced by inter-channel crosstalk due to FWM, and vice versa.

Wavelength converter and wavelength division multiplexing transmission method using same

A method of manufacturing an optical filter that can restrain the wavelength dependence of the gain of an optical amplifier. The input signal light power, output power of pump light source (,), and the output signal light power of an optical amplifier (,) are set to the power values used for optical communication systems, and the total power of the simulation input light of a plurality of wavelengths (&lgr;1, &lgr;2, . . . &lgr;n) from light sources (,) and an input light (probe light) from light sources (,) are set equal to the total power of the input signals of a plurality of wavelengths used in wavelength division multiplex transmission systems. In this condition, the input light are multiplexed and are launched into optical amplifier (,), and the amount of attenuation is variably adjusted so that the output power from optical amplifier (,) in correspondence to the probe light will be within the range determined by the maximum and minimum of the output power corresponding to the simulation input light to determine the attenuation amount corresponding to the wavelength of the probe light. The above operation is repeated upon varying the wavelength of the probe light, and loss spectrum of the optical filter is set to the loss spectrum of the attenuation amounts in one-to-one correspondence with the respective wavelengths.

Optical filter, manufacturing method thereof, and optical amplifier equipped with said optical filter

A method of manufacturing an optical filter that can restrain the wavelength dependence of the gain of an optical amplifier. The input signal light power, output power of pump light source (8), and the output signal light power of an optical amplifier (4) are set to the power values used for optical communication systems, and the total power of the simulation input light of a plurality of wavelengths (.lambda.1, .lambda.2, . . . .lambda.n) from light sources (1a) and an input light (probe light) from light sources (1m) are set equal to the total power of the input signals of a plurality of wavelengths used in wavelength division multiplex transmission systems. In this condition, the input light are multiplexed and are launched into optical amplifier (4), and the amount of attenuation from light source (1m) to the input end (14) of optical amplifier (4) is variably adjusted so that the output power from optical amplifier (4) in correspondence to the probe light will be within the range determined by the maximum and minimum of the output power corresponding to the simulation input light to determine the attenuation amount corresponding to the wavelength of the probe light. The above operation is repeated upon varying the wavelength of the probe light, and loss spectrum of the optical filter is set to the loss spectrum of the attenuation amounts in one-to-one correspondence with the respective wavelengths.

Optical filter, manufacturing method thereof and optical amplifier

There is provided an optical telecommunications method that can externally modulate a plane of polarization without producing any null point. According to the invention, in an optical telecommunications system for externally modulating the plane of polarization of the light being transmitted through an optical fiber for the transmission of a polarized wave signal by externally applying a signal to modify the state of polarization, the source of light for the transmission of a polarized wave signal is a fiber ring laser.

Optical telecommunications system

There is provided a method for optical telecommunications with which an optical signal modulated for the plane of polarization can be received for certain without lowering the threshold level and being affected by noises so that any optical telecommunications can be identified without fail. With the method, an optical signal is modulated by continuous pulses a at the transmitting side before transmission and a predetermined number (n) of pulses a are extracted within a given period of time in synchronism at the receiving side so that the presence of a modulated optical signal is acknowledged only when the number of pulses a received within the given period of time is smaller than the predetermined number (n) but greater than another predetermined number (m) (n.gtoreq.m). This method may be so modified that the absence of a modulated optical signal is acknowledged even when the above defined number of pulses are received if k or more than k (k.gtoreq.1) noise signals b are found between any successive two of the received pulses.

Method for optical communications

There is provided a method of identifying a particular optical cable out of a plurality of similar optical cables in a simple, quick and accurate manner without requiring any significant additional cost. For identifying a particular optical cable C2 out of a plurality of optical cables C1 through C3 by means of a means for transmitting optical signals 11, a signal receiving/detecting means 13 and a signal applying device 16 and by utilizing the fluctuation in the level of optical signal due to the photoelastic effect that appears when external signals are applied to a cable carrying an optical signal, external signals are applied to the outer peripheral surface of each of the optical cable at a plurality of spots to boost the level of fluctuation of optical signal so that the particular optical cable can be identified without fail. Thus, the method of the present invention can be used to identify a particular optical cable out of a plurality of similar optical cables in an accurate and reliable manner by using a simple means of applying external signals.

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Tokyo, Japan

Hijiri Nimura