JP2001109024A - Wavelength control method for optical soliton signal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the center wavelength of an optical soliton signal from being shifted to a longer wavelength-side due to the deviation of a self-Raman wavelength when a transmission bit rate is increased in an optical soliton transmission system. SOLUTION: In the optical soliton transmission transmitting an optical soliton signal by using an optical fiber, the center wavelength of the optical soliton signal is shifted to a shorter wavelength-side or the longer wavelength-side by positioning the wavelength of the Raman gain peak of a Raman amplifier at the side of a wavelength shorter or longer than the center wavelength of the optical soliton signal. The center wavelength of the optical soliton signal is shifted to the shorter wavelength-side by an amount equivalent to an amount in which the center wavelength of the optical soliton signal in propagating through the optical fiber is shifted to the longer wave-length-side by the deviation of the self-Raman wavelength to the longer wavelength-side by positioning the wavelength of the Raman gain peak of the Raman amplifier at the side of the wavelength shorter than the center wavelength of the optical soliton signal. Thus, the center wavelength of the optical soliton signal is shifted to a wavelength separatable from the wavelength of ASE noise.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an optical soliton transmission system used for optical communication.

[0002]

2. Description of the Related Art The optical soliton transmission system is a system for transmitting an optical soliton signal through an optical fiber. The optical soliton signal has a property that the center wavelength shifts to a higher gain during propagation of the optical fiber. The shift of the center wavelength (self-Raman wavelength shift) is caused by the self-Raman gain generated by the optical soliton signal itself, and the center wavelength shifts to a longer wavelength side. Here, the shift of the center wavelength is also caused by an external gain.

[0003] In recent years, in the optical soliton transmission system, the transmission bit rate of the optical soliton signal has been improved in order to increase the transmission capacity. For this purpose, an optical TDM (Time Division Division) that divides and multiplexes the optical soliton signal temporally. Multiple
xing) system has been attempted.

[0004]

However, as the transmission bit rate of the optical soliton signal is increased, the spectral width of the optical soliton signal is increased, and the center wavelength of the optical soliton signal is transmitted due to a self-Raman wavelength shift during propagation in the optical fiber. There is a problem that the wavelength shifts to the longer wavelength side in proportion to the distance, and the wavelength shifts out of the wavelength band in which transmission is possible. Further, it is difficult to separate the center wavelength of the optical soliton signal from the wavelength of the spontaneous emission optical noise (ASE noise) generated from the optical amplifier, and the S / N of the transmitted optical soliton signal deteriorates. Further, the ASE noise is accumulated when the Raman amplifiers are connected in multiple stages, and the SASE of the optical soliton signal is accumulated.
/ N was further deteriorated.

[0005]

SUMMARY OF THE INVENTION The present invention adjusts the Raman gain peak wavelength of a Raman amplifier to reduce the center wavelength of an optical soliton signal shifted to a longer wavelength side by a self-Raman wavelength shift during propagation in an optical fiber. Side so that the center wavelength can be maintained within a predetermined band that can be transmitted even when the transmission bit rate of optical soliton transmission increases, and the center wavelength and the wavelength of ASE noise are reliably separated and removed. By doing, the S / S of the optical soliton signal
It is an object of the present invention to provide a wavelength control method of an optical soliton signal capable of improving N.

A first invention of the present application relates to an optical soliton transmission for transmitting an optical soliton signal by an optical fiber,
The center wavelength of the optical soliton signal is shifted to the short wavelength side or the long wavelength side by positioning the Raman gain peak wavelength of the Raman amplifier on the shorter wavelength side or the longer wavelength side than the central wavelength of the optical soliton signal. This is a wavelength control method for an optical soliton signal.

In the second invention of the present application, the center wavelength of the optical soliton signal propagating in the optical fiber is adjusted by positioning the Raman gain peak wavelength of the Raman amplifier on the shorter wavelength side than the center wavelength of the optical soliton signal. This is a wavelength control method of an optical soliton signal that is shifted to a shorter wavelength side by an amount shifted to a longer wavelength side due to a Raman wavelength shift.

In a third aspect of the present invention, the center wavelength of the optical soliton signal is shifted to a wavelength separable from the wavelength of the ASE noise by the first or second wavelength control method of the optical soliton signal. This is a wavelength control method for an optical soliton signal.

[0009]

(Embodiment 1) FIG. 1 shows a principle diagram of an optical soliton transmission system. In this transmission system, an optical soliton signal is transmitted to a Raman amplification optical fiber 2 by a transmission optical fiber 1, and excitation light from an excitation light source (semiconductor laser) 3 is transmitted through an optical coupler 4 to the Raman amplification optical fiber 2.
The optical soliton signal is amplified in the Raman amplification optical fiber 2.

FIG. 2 shows the spectrum of the optical soliton signal, the self-Raman gain spectrum of the optical soliton signal, the gain spectrum of the Raman-amplified optical fiber, and the total gain spectrum received by the optical soliton signal. The gain spectrum of the Raman amplification optical fiber has a Lorentz distribution, and the pump light wavelength (Raman gain peak wavelength λpmax) at which the peak gain Xpmax is obtained is shifted to the longer wavelength side by Raman shift + Δλ from the pump light source wavelength λp. Therefore, if the Raman gain peak wavelength λpmax is adjusted by changing the excitation light source wavelength λp, the peak gain Xpmax can be realized on the shorter wavelength side or the longer wavelength side than the center wavelength λs of the optical soliton signal.

Therefore, in the first embodiment, the optical dispersion characteristics of the transmission optical fiber 1 of FIG. 1, the center wavelength λs of the optical soliton signal transmitted by the optical fiber 1, and the gain spectrum of the Raman amplification optical fiber 2 (FIG. 2) , Raman gain peak wavelength λ
Pmax and the like are designed so as to have the relationship shown in FIG. 2, and the total gain spectrum (FIG. 2) received by the optical soliton signal is a band centered on the center wavelength λs of the optical soliton signal. After the wavelength dependence of the gain of the Raman amplifier cancels each other and becomes flat with respect to the wavelength, the difference between the pumping light wavelength λp and the center wavelength λs of the optical soliton signal becomes the pumping light wavelength λp and the Raman gain. By adjusting the pumping light source wavelength λp so as to be larger than the peak wavelength λpmax and realizing the peak gain Xpmax on the shorter wavelength side than the center wavelength λs of the optical soliton signal, it is shifted to the longer wavelength side by the self-Raman wavelength shift. The center wavelength λs of the shifted or shifted optical soliton signal is shifted to the shorter wavelength side.

At this time, since the optical soliton signal has a self-shaping effect, it propagates while maintaining its own pulse waveform shape. As shown in FIG. 3, the center wavelength λs of the optical soliton signal at the start point and the end point of one relay span is substantially the same. However, it is also possible to design so that the center wavelength λs of the optical soliton signal becomes a desired wavelength in a plurality of relay spans.

(Embodiment 2) A second embodiment of the wavelength control method for an optical soliton signal according to the present invention will be described below. In the wavelength control method shown in this embodiment, the center wavelength of the optical soliton signal is controlled to a wavelength that can be separated from the wavelength of the ASE noise, and the ASE noise separated from the optical soliton signal can be removed by a band-elimination filter. The ASE noise due to Raman gain / EDFA has a noise band (λa to λb in FIG. 4) as shown by hatching in FIG. 4 depending on the relay transmission distance, but this ASE noise is different from the optical soliton signal, Since no shift occurs, by controlling the center wavelength of the optical soliton signal, the optical soliton signal and the ASE noise can be wavelength-separated at a certain point (for example, point Z in FIG. 4) where the relay point exists.

Therefore, in the second embodiment, the Raman amplification optical fiber 2 is applied by the wavelength control method described in the first embodiment.
Is shifted to a longer wavelength side than the center wavelength λs of the optical soliton signal to shift the center wavelength λs of the optical soliton signal to the longer wavelength side to separate the ASE noise from the ASE noise. The ASE noise separated from the center wavelength λs of the soliton signal is removed by the band elimination filter 5 inserted in the Raman amplification optical fiber 2 as shown in FIG.
Only the signal of (1) is made to propagate further. As shown in FIG. 6, when the Raman amplification optical fiber 2 is multi-stage relayed, the accumulation of ASE noise is prevented by inserting the band elimination filter 5 into all or a part of each Raman amplification optical fiber 2. Can also.

[0015]

According to the first invention of the present application, the Raman gain peak wavelength of the Raman amplifier is located on the short wavelength side or the long wavelength side with respect to the center wavelength of the optical soliton signal.
Since the center wavelength of the optical soliton signal is shifted to the short wavelength side or the long wavelength side, the following effects are obtained. (1) The center wavelength of the optical soliton signal can be arbitrarily shifted to the short wavelength side or the long wavelength side. (2) Since the limitation on the transmission bit rate of the optical soliton signal due to the self-Raman wavelength shift is eliminated, the transmission bit rate can be improved and the transmission capacity can be increased.

In the second invention of the present application, the center wavelength of the optical soliton signal propagating in the optical fiber is adjusted by positioning the Raman gain peak wavelength of the Raman amplifier on the shorter wavelength side than the center wavelength of the optical soliton signal. Since the wavelength is shifted to the short wavelength side by the shift to the long wavelength side due to the Raman wavelength shift, the following effects are obtained. (1) Since the limitation on the transmission bit rate of the optical soliton signal caused by the self-Raman wavelength shift is eliminated, the transmission bit rate can be improved and the transmission capacity can be increased. (2) The center wavelength of the optical soliton signal can be controlled over the entire transmission path.

The third invention of the present application shifts the center wavelength of the optical soliton signal to a wavelength separable from the wavelength of the ASE noise, and has the following effects. (1) The ASE noise can be removed only by adding a band rejection filter or the like, so that the deterioration of the S / N of the optical soliton signal can be easily and effectively prevented. (2) Accumulation of ASE noise in the multistage relay system can be easily and effectively prevented.

[Brief description of the drawings]

FIG. 1 is a principle diagram of an optical soliton transmission system.

FIG. 2 is an explanatory diagram showing spectra of an optical soliton signal, a self-Raman gain of the signal, a total gain received by the signal, and a gain of a Raman-amplified optical fiber.

FIG. 3 is an explanatory diagram showing an example of a change in the center wavelength of an optical soliton signal in one relay span.

FIG. 4 shows a second method of controlling the wavelength of an optical soliton signal according to the present invention.
FIG.

FIG. 5 shows a second method of controlling the wavelength of an optical soliton signal according to the present invention.
Explanatory drawing which shows an example of a specific structure which implement | achieves embodiment.

FIG. 6 shows a second method of controlling the wavelength of an optical soliton signal according to the present invention.
Explanatory drawing which shows the other example of the specific structure which implements the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transmission optical fiber 2 Raman amplification optical fiber 3 Pump light source 4 Optical coupler 5 Band elimination filter

Continued on the front page F term (reference) 2K002 AA02 AB30 AB32 BA01 CA15 DA10 EB15 HA23 HA25 5F072 AB07 AK06 HH05 KK11 QQ07 QQ20 YY17 5K002 AA06 BA04 BA05 BA13 CA02 CA05 CA13 DA05 DA31 FA01 FA02

Claims (3)

[Claims] In an optical soliton transmission for transmitting an optical soliton signal through an optical fiber, an optical signal is obtained by positioning a Raman gain peak wavelength of a Raman amplifier on a shorter wavelength side or a longer wavelength side than a center wavelength of the optical soliton signal. A wavelength control method for an optical soliton signal, characterized in that a center wavelength of a soliton signal is shifted to a short wavelength side or a long wavelength side. 2. The method for controlling the wavelength of an optical soliton signal according to claim 1, wherein the Raman gain peak wavelength of the Raman amplifier is positioned on the shorter wavelength side than the center wavelength of the optical soliton signal, so that the light transmitted through the optical fiber is controlled. A method for controlling the wavelength of an optical soliton signal, characterized in that the center wavelength of the soliton signal is shifted to the shorter wavelength side by the shift to the longer wavelength side due to the self-Raman wavelength shift. 3. The optical soliton signal according to claim 1 or 2, wherein the center wavelength of the optical soliton signal is shifted to a wavelength separable from the wavelength of the ASE noise. Wavelength control method.