Kokusai Denshin Denwa Kabushiki Kaisha

Kdd Submarine Cable Systems, Inc.

Other

Kddi Corporation

Takayuki Miyakawa

Shigeyuki Akiba

Hidenori Taga

Shu Yamamoto

Masatoshi Suzuki

Noboru Edagawa

Noriyuki Takeda

Yasuyuki Nagao

In a Raman gain measuring method according to the invention, a CW (continuous wave) probe light is input into a Raman amplifying medium. A Raman pumping light being binary-intensity-modulated at a modulation factor is generated. The Raman pumping light is input into the Raman amplifying medium. Two index values regarding to AC component and DC component are extracted from the probe light having propagated through the Raman amplifying medium. The Raman gain of the Raman amplifying medium is determined from the two index values and the modulation factor.

Raman gain measuring method and apparatus

An optical fiber ( ) with a large effective core area and a large chromatic dispersion value is disposed on an input side of signal light, and an optical fiber ( ) with a small effective core area and a small chromatic dispersion value or a chromatic dispersion value of negative polarity is disposed on an output side of the signal light. A pumping light source ( ) generates pumping light of 1450 nm to cause Raman amplification of 1550 nm in the optical fiber ( ). The output light from the pumping light source ( ) enters the optical fiber ( ) from the back through a WDM optical coupler ( ). Provided that y&equals;(Pin&minus;&agr;)/(Pp&middot;10 Log L) where input power of the optical fiber ( ) (i.e. output power of an optical transmitter ( )) is Pin, a total loss of the optical fibers ( and ) is &agr;, pumping power for Raman amplification is Pp, and a total length of the optical fibers ( and ) is L, the relation between ratio x (0&lE;x&lE;1) of the optical fiber ( ) and y is expressed as y&equals;6.63&times;10 x&minus;0.077. Here, the satisfactory x value is in a range from &plus;0.2 to &minus;0.2 of the y value.

Optical transmission line

The object of this invention is to improve SNR in the Raman amplification. An optical fiber ( ) consists of a dispersion shift fiber in which a zero dispersion wavelength is shifted to the 1.55 &mgr;m band, and an optical fiber ( ) consists of a single mode optical fiber having the effective core area of 100 &mgr;m which is larger than that of the optical fiber ( ). An optical coupler is disposed at the optical signal emission end of the optical fiber ( ). A laser diode ( ) outputs the laser light of 1455 nm as a Raman pumping light source. The output light from the laser diode ( ) is introduced into the optical fiber ( ) from the back, namely in the opposite direction to that of the optical signal propagation. The ratio of the Raman gain coefficient of the optical fiber ( ) to that of the optical fiber ( ) should be 1/1.08 or less, preferably 1/1.1 or less.

Raman amplifier

The present invention is directed towards an optical ADM apparatus provided with a narrow band-pass filter which is capable of minimizing declination of the transmission characteristics. An optical transmission prohibiting element composed of an optical isolator and a fiber grating is connected in series to the downstream of a fiber grating interposed between two optical circulators. The drop light is reflected by the fiber grating and released from an output optical fiber of the optical circulator. A leak component of the drop light having passed through the fiber grating appears on the side of the isolator and runs across the isolator to the other fiber grating. Most of the leak component is however reflected by the fiber grating while its small portion enters the optical circulator via the fiber grating. The small portion of the leak component is as small as negligible and will hardly interfere with the add light. The optical transmission prohibiting element may be an optical circulator.

Optical add-drop multiplexer

An optical add/drop multiplexing scheme capable of reducing the degradation of the transmission characteristic due to the beat noises caused by the interference of the fiber grating leakage components. An optical add/drop multiplexing device is formed by a high speed polarization scrambler for entering signal lights with a data modulation at a high speed bit rate applied thereto, and scrambling polarization states of entered signal lights at high speed, and an optical add/drop element for receiving the signal lights with the polarization states scrambled by the high speed polarization scrambler, and carrying out an add/drop multiplexing operation for signal lights in a specific wavelength among received signal lights. The high speed polarization scrambler scrambles the polarization states of the entered signal lights so as to lower a probability for having worst polarization states of signal lights and interference lights, by scrambling the polarization states of the entered signal lights into every possible polarization states at nearly equal probabilities.

Method and device for optical add/drop multiplexing using high speed

Wavelength multiplexed optical signals which are input into a first optical amplifier from an optical transmission terminal device over an optical fiber are differently amplified in respective wavelengths due to unevenness of gain of the optical amplifiers and then output. By providing M-transmission optical filters having an M-type transmission characteristic to cancel gain deviation of the optical amplifiers in respective wavelengths, a flat gain characteristic can be achieved even after the optical signals are transmitted via a plurality of optical amplifiers and a plurality of M-transmission optical filters. Also, by removing ASE in a wavelength range of 1.53 .mu.m which prevents signal amplification in a wavelength range of 1.55 .mu.m, the wavelength multiplexed optical signals which are sufficiently amplified can be transmitted to an optical reception terminal device over the optical fiber.

An object of the present invention is to provide an optical add-drop multiplexer capable of giving improved characteristics with a simple, inexpensive arrangement which needs not a corresponding number of optical bandpass filters to the wavelength components of a light signal to be carried. The wavelength components .lambda.1 to .lambda.n of an input n-wave signal is received by an input optical fiber and transmitted through an optical circulator and an optical fiber to an optical bandpass filter which allows a specific wavelength .lambda.1 to pass but rejects the other wavelengths .lambda.2 to .lambda.n. While the rejected wavelengths .lambda.2 to .lambda.n are returned back to the optical fiber, the specific wavelength .lambda.1 runs through another optical fiber and another optical circulator and then is dropped from an output optical fiber. Meanwhile, another signal component of the wavelength .lambda.1 is added and introduced from another input optical fiber through the another optical circulator and the another optical fiber to the optical bandpass filter. Upon the added wavelength .lambda.1 having passed the optical bandpass filter and entering the optical fiber, it is mixed with the rejected wavelengths .lambda.2 to .lambda.n. A resultant sum signal of the full wavelengths .lambda.1 to .lambda.n is passed through the optical circulator and transmitted from an output optical fiber.

Growing community of inventors

Saitama, Japan

Takayuki Miyakawa