JP2003060574A - Optical transmitter system, wavelength division multiplexer and method for dispersion compensation of wavelength division multiplexing transmission system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical transmission system capable of housing transmitters having different frequency chirps and optical transmission powers or the like at respective transmission wavelengths in a wavelength division multiplexing(WDM) optical transmission system. SOLUTION: The optical transmission system comprises a plurality of optical transmitters 61 to 6n for transmitting optical pulses having different wavelengths, a wavelength division multiplexer 8, a transmitting unit (optical fiber) 10, a wavelength demultiplexer 13, and a plurality of optical receivers 141 to 14n . Frequency chirp compensators 71 to 7n each for compensating for a deviation of a frequency chirp amount of the optical pulse transmitted from the plurality of the transmitters 61 to 6n are disposed between at least one of the plurality of the transmitters 61 to 6n and the multiplexer 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmission system, and more particularly to an optical transmission system for wavelength division multiplexing.

[0002]

2. Description of the Related Art In recent years, optical transmission systems have been developed aiming at large capacity and long span. In order to increase the capacity, wavelength multiplexing (WDM; Wax) that increases the bit rate and transmits multiple optical signals with different wavelengths using a single optical fiber.
velength Division Multiplexing) methods are being studied. The lengthening of the span can be realized by introducing an optical amplifier for compensating the propagation loss of the fiber. In this case, the optical amplifier is used as a post amplifier for increasing the transmission power output, a preamplifier for increasing the reception power sensitivity, or an in-line amplifier for the repeater. As an optical amplifier, one having a characteristic capable of collectively amplifying light in a wide wavelength range has been developed. By combining such an optical amplifier with a wide wavelength range with the WDM method, low cost, large capacity, and long distance transmission can be realized with a simple configuration.

However, when the optical amplifier is introduced to increase the optical input level to the fiber, the influence of the nonlinear effect of the optical fiber on the optical pulse cannot be ignored. One of them is the self-phase modulation (SPM) in which the phase is modulated by the Kerr effect, which is one of the nonlinear optical effects, at the rising and falling edges of the signal light pulse, that is, the wavelength (frequency) shifts. modul
ation) is known to occur. Self-phase modulation (SP
The wavelength shift due to (M) shifts to the short wavelength side (blue shift) at the rising portion of the signal light pulse, and shifts to the long wavelength side at the falling portion of the signal pulse.
(Red shift) Therefore, even if the wavelength width of the optical pulse before transmission is narrow, the wavelength width is widened by self-phase modulation (SPM) during transmission.

The spread of the wavelength width of the optical pulse due to self-phase modulation (SPM) is caused by the chromatic dispersion (CD) of the optical fiber.
associated with ispersion) and causes a large waveform change after transmission. That is, when an optical pulse with a wide wavelength width is transmitted through a normal dispersion fiber (dispersion value is negative), the pulse width increases, and when transmitted through an abnormal dispersion fiber (dispersion value is positive), the pulse width is compressed and the waveform changes. To do.

Further, during wavelength division multiplexing (WDM) transmission, cross phase modulation (XPM) causes mutual interference between an optical signal having a certain wavelength and another optical signal having a different wavelength, resulting in signal light. It is known that a pulse has a wavelength (frequency) shift. The wavelength (frequency) shift due to cross-phase modulation (XPM) depends on the bit phase and polarization direction of overlapping optical pulses, so it occurs randomly inside the pulses, and waveform deterioration and arrival are associated with chromatic dispersion (CD). A time lag (timing jitter) occurs.

Conventionally, in order to reduce the waveform distortion of an optical pulse after fiber transmission, Japanese Patent Laid-Open No. 7-74699 discloses a self-phase modulation effect (SPM) in relay transmission using an optical amplifier.
There is disclosed a dispersion compensating method in consideration of the influence of. This method is a method of reducing waveform deterioration and timing jitter due to the nonlinear effect by making the dispersion value after the point where the nonlinear effect such as self-phase modulation (SPM) occurs zero. Further, Japanese Patent Application Laid-Open No. 9-23187 discloses an optical transmission system that compensates the first-order dispersion and the second-order dispersion of an optical fiber transmission line over a wide wavelength band during wavelength-multiplexed transmission.

[0007]

The optical pulses generated at the transmitter typically include frequency chirp.
The frequency chirp is represented by a chirp coefficient defined by the α parameter, and an optical pulse having a frequency chirp with a positive α parameter has its pulse width compressed during normal dispersion fiber transmission and has its pulse width increased during abnormal dispersion fiber transmission. The chirp coefficient differs depending on the type of transmitter. For example, as a typical transmitter, a certain type of transmitter that uses an electroabsorption type semiconductor modulator has a frequency chirp amount α of the emitted optical pulse of about 0.9. On the other hand, another type of transmitter using a Mach-Zehnder type lithium niobate modulator has an emitted optical pulse frequency chirp amount α of about −0.2. Therefore, when the normal dispersion fiber is used as the transmission line, the pulse width of the optical pulse from the transmitter using the electro-absorption semiconductor modulator is compressed, and the optical pulse from the transmitter using the Mach-Zehnder type lithium niobate modulator is compressed. The pulse increases in pulse width.

Further, with the increase in communication traffic accompanying the spread of the Internet in recent years, optical transmitters accommodated in wavelength division multiplexing (WDM) devices have been diversified, and in the future, IP routers, transponders, cross-connects, etc. Such,
It is essential to accommodate various optical transmitters with heterogeneous optical interfaces. At this time, different optical transmitters use different modulation methods, and therefore different frequency chirps are included in the optical pulse.

However, in the conventional optical transmission systems such as the above-mentioned JP-A-7-74699 and JP-A-9-23187, the optical pulse from the optical transmitter contains the same frequency chirp for each wavelength. , Dispersion compensation is performed on the assumption that the waveform distortion due to frequency chirp is equal for each wavelength, and the frequency chirp included in the optical pulse from the optical transmitter differs for each wavelength of wavelength division multiplexing (WDM). Is not considered. When such a conventional optical transmission system accommodates an optical transmitter having different frequency chirp characteristics for each wavelength, there is a possibility that transmission cannot be performed by simply connecting. In that case, the dispersion compensation of the entire transmission line must be reviewed and replaced, which may affect the entire traffic being operated.

An object of the present invention is to provide an optical transmission system for wavelength division multiplexing (WDM), which can accommodate transmitters having different frequency chirps or optical transmission powers for each transmission wavelength. is there.

[0011]

In order to achieve the above object, the present invention provides the following optical transmission system.

That is, a plurality of optical transmitters for respectively emitting optical pulses having different wavelengths, a wavelength multiplexing unit for multiplexing the optical pulses emitted from the optical transmitters, and multiplexing by the wavelength multiplexing unit. The optical pulse transmitted by the transmission unit, a wavelength separation unit for separating the optical pulse transmitted by the transmission unit for each wavelength, and a plurality of lights for receiving the optical pulses separated by the wavelength separation unit for each wavelength A receiver, and between at least one of the plurality of optical transmitters and the wavelength multiplexing unit, a deviation of the frequency chirp amount of the optical pulse emitted from each of the plurality of optical transmitters. The optical transmission system is characterized in that a frequency chirp compensation unit for compensation is arranged.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described.

The configuration of the optical transmission system of this embodiment will be described with reference to FIG. The optical transmission system of FIG. 2 has n optical transmitters 6 _{1 to} 6 _n , a wavelength multiplexing unit 8, and an optical fiber 1.
0, an optical separation unit 13, and optical receivers 14 _{1 to} 14 _n . From the optical transmitters 6 _{1 to} 6 _n , signal light pulses each having a predetermined wavelength are emitted. The wavelength multiplexing unit 8
The signal light pulses of n kinds of wavelengths emitted from the optical transmitters 6 _{1 to} 6 _n are wavelength-multiplexed. The multiplexed signal is transmitted by the optical fiber 10, separated again by the wavelength separation unit 13 for each wavelength, and received by the light receiving units 14 _{1 to} 14 _n .

In the present embodiment, as the optical transmitters 6 _{1 to} 6 _n , a plurality of types such as a transmitter using an electroabsorption type semiconductor modulator and a transmitter using a Mach-Zehnder type lithium niobate modulator are used. It is composed of a transmitter. Therefore, the frequency chirp amount of the optical pulse emitted by the optical transmitters 6 _{1 to} 6 _n is different for each transmitter.

Deviation compensators 7 _{1 to} 7 _n are arranged between the optical transmitters 6 _{1 to} 6 _n and the wavelength multiplexing unit 8, respectively. The deviation compensators 7 _{1 to} 7 _n are frequency chirp compensators 16 for compensating the deviation of the frequency chirp and the deviation of the light intensity for the optical pulses of n kinds of wavelengths emitted from the optical transmitters 6 _{1 to} 6 _n. And a light intensity adjuster 17 for adjusting the light intensity. As the frequency chirp compensator 16, a dispersion compensating fiber that can obtain a desired frequency chirp compensation amount by setting a desired length or a device using a grating such as a fiber Bragg grating (FBG). Etc. can be used. As the light intensity adjuster 17, for example, a variable attenuation optical attenuator can be used.

Further, in order to compensate for the deterioration of the optical pulse due to the wavelength dispersion of the optical fiber 10 and the self-phase modulation effect (SPM) during the transmission of the optical fiber 10, it is provided between the optical fiber 10 and the wavelength multiplexer 8. Is provided with a dispersion compensator 15a and a post amplifier 9, and the dispersion compensator 1 is provided in the middle of the optical fiber 10.
5b and the in-line amplifier 11 are arranged, and the optical fiber 1
A dispersion compensator 15c and a preamplifier 12 are arranged between 0 and the wavelength separation unit 13. As the post-amplifier 9, the in-line amplifier 11, and the pre-amplifier 12, a band-equivalent optical amplifier in which the wavelength dependence of loss (gain) can be ignored can be used. For example, as the post-amplifier 9, a post-amplifier 9 including an erbium-doped fiber 20 and a backward pumping light source 22 as shown in FIG. 3 is used. As the in-line amplifier 11 and the pre-amplifier 12, the erbium-doped fiber 20, the forward pumping light source 21, and the backward pumping light source 22 are arranged before and after the dispersion compensators 15b and 15c as shown in FIG. Can be used.

Next, a method of determining the amount of frequency chirp compensation of the frequency chirp compensator 16 of the deviation compensators 7 _{1 to} 7 _n will be described. In the present embodiment, the simulation shown in FIG. 9 is performed to create a graph as shown in FIG. 5, and the compensation amount of the frequency chirp of the frequency chirp compensator 16 of the deviation compensators 7 _{1 to} 7 _n is determined.

In the simulation method of FIG. 9, the simulation is performed assuming the system of FIG. 10 which is a simplified version of the optical transmission system of FIG. The system of FIG. 10 includes optical transmitters 6 _{1 to} 6 6.
_The optical pulse emitted from the i-th optical transmitter 6 _i of _n is subjected to frequency chirp compensation by the frequency chirp compensator 16 and then subjected to phase modulation and wavelength dispersion when transmitted through the optical fiber 10, This is the system received by the i-th receiver 14 _i . In the system of FIG. 10, the shape of the transmitted waveform is calculated. In the actual optical fiber 10,
Phase modulation and chromatic dispersion act simultaneously, and it is necessary to perform a complicated simulation depending on the type of optical fiber. In this system, phase modulation and chromatic dispersion act on the optical pulse separately in the optical fiber 10. By treating as, the relationship between the phase modulation amount, the dispersion value, and the waveform deterioration amount can be drawn in a more general graph as shown in FIG. As described above, the phase modulation and the wavelength dispersion are generally described as acting separately so that the influence of various parameters such as the type of the optical fiber and the loss coefficient is referred to as the phase modulation. By converting into two parameters of chromatic dispersion, it becomes possible to handle in the graph of FIG. As a method of calculating the shape of the transmitted waveform, various well-known methods can be used. Here, a method of solving a differential equation called SSFM (split step Fourier method) is used. Since this SSFM is a well-known method, detailed description of the solution is omitted.

First, the outline of the simulation method of FIG. 9 will be described. In this simulation method, in the system shown in FIG. 10, when the frequency chirp compensation amount of the frequency chirp compensator 16 is set to a certain value, the optical pulse emitted from the optical transmitter 6 _i is transmitted through the optical fiber 10. The amount of waveform deterioration is calculated, and it is checked whether the amount of waveform deterioration is within a predetermined range, here 1 dB or less. This simulation is performed using the chromatic dispersion value of the optical fiber 10 and the optical fiber 1.
The phase modulation amount due to the non-linear optical effect of 0 is repeatedly changed while changing the amount within a predetermined range, and a graph as shown in FIG. 5 is drawn. This is performed for all the optical transmitters 6 _{1 to} 6 _n . In FIG. 5, only _two optical transmitters 6 ₁ and 6 ₂ are shown. In FIG. 5, if the areas where the deterioration amount is 1 dB or less overlap for all of the optical transmitters 6 _{1 to} 6 _n , by using the optical fiber 10 having the dispersion value and the phase modulation amount of the overlapping areas, Optical pulses with different frequency chirps emitted from the respective optical transmitters 6 _{1 to} 6 _n are transmitted with almost the same transmission characteristics (that is, a waveform deterioration amount of 1 dB or less). Further, if the area of the region 5 where the deterioration amount is 1 dB or less overlaps between the optical transmitters 6 _{1 to} 6 _n is large, the optical fiber 1
There is a large margin for fluctuations in the variance value of 0. Therefore, in the present embodiment, in the above simulation, the regions where the deterioration amount is 1 dB or less are the optical transmitters 6 _{1 to} 6 _n.
The frequency chirp compensation amount of each deviation compensator 7 _{1 to} 7 _n is calculated so that the area of the overlapping portion 5 becomes maximum, and this is set as the compensation amount of the deviation compensator 7 _{1 to} 7 _n .

Specifically, the simulation method of FIG. 9 will be described. First, the output power of the i-th (initial value i = 1) optical transmitter 6 _i , the waveform shape (extinction ratio, etc.), and the frequency chirp amount α are set (step 91). The output power is a predetermined value within a range that can be emitted by the optical transmitter 6 _i , and the waveform shape (extinction ratio, etc.) and the frequency chirp amount α
Is a characteristic value of the optical transmitter 6 _i . Next, the chirp compensation amount of the frequency chirp compensator 16 is set to a predetermined initial value, and the waveform after the waveform determined in step 91 has passed through the frequency chirp compensator 16 is calculated. Next, the phase modulation amount Φ due to the nonlinear effect of the transmission line (optical fiber 10)
Is set to the initial value 0.1 (radian), and the chromatic dispersion amount is set to the initial value -15
It is set to 00 ps / nm (steps 93 and 94). In step 91, the waveform that has passed through the frequency chirp compensator 16 is
The received waveform distorted under the influence of the phase modulation and chromatic dispersion in steps 93 and 94 is calculated by the SSFM. If the deterioration amount of the received waveform is 1 dB or less, transmission is possible, and if it is 1 dB or more, transmission is not possible (step 95). , Fill in the graph in FIG.

Returning to step 93, the phase modulation amount Φ is set to 0.1
It is changed in 0.1 (radian) steps in the range of up to 10 (radian), and the chromatic dispersion amount is -1500 ps / nm to +150 in step 94.
It is changed in the range of 0 ps / nm by about 100 ps / nm step (step 96). The received waveform is calculated in step 95 for the phase modulation amount Φ and the chromatic dispersion amount that are changed,
Obtain the amount of deterioration of the received waveform. If the amount of deterioration is 1 dB or less, it is possible to transmit, and if it is 1 dB or more, it is not possible to transmit and enter it in the graph of FIG. After repeating this in the range of phase modulation amount Φ0.1 to 10 (radian) and the wavelength dispersion amount of -1500ps / nm to + 1500ps / nm, the deterioration amount entered in Fig. 5 is 1dB or less. A borderline is drawn between the possible range and the non-transmittable range where the degradation exceeds 1 dB, and the transmittable range (dispersion strength)
Determine.

Next, returning to step 92, the chirp compensation amount of the frequency chirp compensator 16 is changed within a predetermined range, and steps 93 to 97 are repeated.

For the next transmitter 6 _{i + 1} , step 9
1 to 98 are repeated to create the graph of FIG. This is sequentially repeated up to the _nth transmitter 6 _n .

FIG. 5 created by the above steps
At all transmitters 6₁~ 6 _nOf transmission range
Frequency chirp compensation amount that maximizes the common area
The transmitter 6₁~ 6_nDecide for each.

The phase modulation amount Φ of the optical fiber 10 is
It is defined by the equation (1).

Φ = γ · P _in · N · Z _eff (1)

In the equation (1), γ is a nonlinear parameter, which is defined by the following equation (2). P _in the light pulse peak power, N represents the number of transmission spans. Z _eff
Is an effective distance defined by the following equation (3).

Γ = n ₂ · ω ₀ / c / A _eff (2)

Z _eff = (1−exp (−β · Z)) / β (3)

N ₂ is a nonlinear refractive index, A _eff is an effective cross-sectional area of the optical fiber, ω ₀ is an angular frequency, c is the speed of light, β is a loss propagation distance of a transmission line, and Z is a transmission distance. ₂ =
2.6 × 10-20 m ^{2 /} W, β = 0.22 dB / km
_Therefore , Z _eff = about 20 km. Therefore, the phase modulation amount Φ = 1rad is, for example, A _eff = 5
A 5 μm ² NZ-DSF (dispersion shift fiber) is used as an optical amplifier output power = + 3.5 dBm / ch (peak power: +
This is equivalent to the case of 6 span transmission at 6.5 dBm / ch).

In the example of FIG. 5, the optical transmitter ₆₁ is an optical transmitter using a frequency chirp amount alpha = -0.2 MZ lithium niobate modulator (LN-MZ modulator),
Optical transmitter 6 ₂ is a transmitter using a frequency chirp amount alpha = 0.9 electro-absorption semiconductor modulator (EA modulator).
These optical transmitters 6 ₁ and 6 ₂ perform the transmission range (dispersion by the simulation of FIG. 9 described above when the frequency chirp compensation is not performed, that is, when the frequency chirp compensation amount by the frequency chirp compensator 16 in step 92 is zero. The yield strength is calculated as shown in Fig. 1. That is, the phase modulation amount Φ by the optical fiber 10 is almost zero (= 0.
In the area of 1 rad), the transmission range of the optical transmitter ₆₁ (dispersion tolerance) 4, whereas it is approximately -800 + 1000 ps / nm, the transmission range (dispersion tolerance of the optical transmitter 6 ₂₎ 3 Is -1050 to +
It is about 250 ps / nm. Further, when the phase modulation amount Φ by the optical fiber 10 is near ₁ rad, the transmittable range (dispersion proof) 2 of the optical transmitter 6 _{1 and} the transmittable range (dispersion proof) ₁ of the optical transmitter 6 ₂ are almost the same range. It is about -150 to +300 ps / nm. Therefore, as shown in FIG. 1, when the frequency chirp compensation amount is zero, in the region where the phase modulation amount Φ is 0 to 1, that is, in the region corresponding to 1 to 6 span transmission, the optical transmitter 6 ₁ and the optical transmitter 6 ₁ are connected. to indicate different transmission characteristics due to the difference in frequency chirp characteristic of the transmitter 6 _2, the width of both the common part 5 is small, a small margin for such dispersion fluctuations of the transmission line (optical fiber 10).

On the other hand, as shown in FIG. 5, the optical transmitter 6 ₁
The difference in frequency chirp characteristics between the optical transmitter 6 ₂ and the optical transmitter 6 ₂ is compensated by the frequency chirp compensator 16, and the chirp compensation amount for the optical transmitter 6 ₁ is set to −600 ps / nm.
_When the chirp compensation amount for ₂ is 0 ps / nm,
In the region where the phase modulation amount Φ is 0 to 1, that is, in the region of 1 to 6 span transmission under the above conditions, the transmittable range (dispersion strength) 3 of the optical transmitter 6 ₁ shifts to the plus side of the dispersion value, transmission range of the optical transmitter 6 ₂ overlaps with (dispersion tolerance) 4. As a result, in the region where the phase modulation amount Φ is 0 to 1, the optical transmitters 6 ₁ and 6 ₂ having different chirp characteristics show almost the same transmission characteristics. Further, since the common portion 5 of the transmittable range is large, the margin for dispersion fluctuation of the transmission line (optical fiber 19) is large.

In addition, in the optical transmission system of the present embodiment, the deviation compensators 7 _{1 to} 7 _n include, in addition to the frequency chirp compensator 16, an optical intensity adjuster for setting the optical intensity to a desired value. 17 are included. The light intensity adjuster 17 controls the intensities of the optical pulses emitted from the optical transmitters 6 _{1 to} 6 _n to be the same preset intensity at the time of entering the wavelength multiplexing unit 8. Specifically, in the wavelength multiplexing unit 8, the light intensity detectors 8a are arranged at the connection portions for taking in the optical pulses from the optical transmitters 6 _{1 to} 6 _n, respectively. Each deviation compensator 7 _{1 to} 7 _n
Feedback control is performed on the light intensity adjuster 17 to adjust the intensity to a preset intensity.

As described above, the optical transmission system of the present embodiment
Optical transmitter 6₁~ 6_nFrequency chirp characteristics for each
Deviation compensator 7₁
~ 7 _nCan be compensated by. Therefore, between wavelengths
Since the frequency chirp and the optical power of can be equalized,
The transmission characteristics when transmitting the optical fiber 10 are almost the same between wavelengths.
Can be equal. As a result, the dispersion compensator 15
Dispersion compensation by a, 15b and 15c and each optical amplifier
Amplification by 9, 11, 12 is performed by each optical transmitter 6₁~ 6_nOr
These optical pulses contain the same frequency chirp for each wavelength.
Rarely, waveform distortion due to frequency chirp is equivalent for each wavelength
It is assumed that the light intensity is the same at each wavelength.
be able to. Therefore, each optical amplifier 9, 11, 12
Band equalization type in which the wavelength dependence of loss (gain) can be ignored
Using the optical amplifier, the dispersion compensators 15a, 15b, 15c
Dispersion flat transmission in which the wavelength dependence of the dispersion value can be ignored
The optical amplifiers 9, 11, 12 and
Dispersion compensators 15a, 15b, 15c are commonly used for each wavelength.
Can be used to perform dispersion compensation for each wavelength at once.
It

As described above, the dispersion compensators 15a, 15b and 15c can perform the dispersion compensation and the optical amplifiers 9, 11 and 12 can perform the optical amplification in common for each wavelength, and therefore, the dispersion compensators 15a, 15b and 15c. The amount of dispersion compensation and the arrangement thereof, and the optical amplification factors of the optical amplifiers 9, 11, and 12 and the arrangement thereof can have known configurations for reducing the waveform distortion of the optical pulse due to the conventional nonlinear optical effect. .

As described above, the optical transmission system according to the present embodiment is an optical transmitter for wavelength division multiplexing (WDM), and various optical transmitters having different frequency chirp amount and optical transmission power for each transmission wavelength. The deviation compensators 7 _{1 to} 7 _{n can} absorb the deviation of the frequency chirp amount of the optical pulse for each wavelength and transmit the light with substantially the same transmission characteristics. Moreover, the deviation compensators 7 _1-
Since the frequency chirp compensator 16 of 7 _n is set,
The optical fiber 10 has a large margin for fluctuations in dispersion, and stable transmission can be performed with the same transmission characteristics.

In the above-described embodiment, the transmission range of the optical transmitters 6 _{1 to} 6 _n is determined by the simulation method of FIG. 9 when the phase modulation amount Φ of the optical fiber 10 is in the range of 0.1 to 10 rad. Although the method of determining the frequency chirp compensation amount that maximizes the common part 5 has been described, the present invention is not limited to this method. In a general optical transmission system, since the number of transmission spans and the output power of the optical amplifier are known, the phase modulation amount Φ can be almost determined based on the above equation (1). Therefore, the simulation of FIG. 9 is performed within the range of the phase modulation amount Φ calculated based on the equation (1), and the frequency chirp compensation of the frequency chirp compensator 16 is performed so that the width of the dispersion proof strength of the most common portion 5 becomes large. The amount can be determined.

As a simpler method of determining the amount of frequency chirp compensation, a predetermined amount of frequency chirp is set at the time when the optical pulses emitted from the optical transmitters 6 _{1 to} 6 _n enter the wavelength multiplexing unit 8. It is also possible to determine the frequency chirp compensation amount of the frequency chirp compensator 16 so that

Further, in the present embodiment, the optical transmitter ₆ 1
6 _n and the wavelength multiplexer 8 between the deviation compensators 7 ₁ to
Although 7 _n are arranged, the deviation compensator may be arranged between at least one of the optical transmitters 6 _{1 to} 6 _n and the wavelength multiplexing unit 8. For example, when only one of the optical transmitters 6 _{1 to} 6 _n has a different amount of frequency chirp from the other optical transmitters, wavelength multiplexing with an optical transmitter having a different amount of frequency chirp is performed. By arranging at least a deviation compensator with the section 8, deviation compensation of the frequency chirp amount can be performed.

As the configuration of the deviation compensators 7 _{1 to} 7 _n , in addition to the configuration of FIG. 6, a variable amplification amount optical amplifier can be used as the light intensity adjuster 17 as shown in FIG. Also, FIG.
Like Raman amplification pump as light intensity adjuster 17
It is also possible to use LD. Also in the case of the deviation compensators 7 _{1 to} 7 _n in FIGS. 7 and 8, the frequency chirp compensator 16
In addition to the dispersion compensating fiber, a device using a grating such as a fiber Bragg grating (FBG) can be used.

In the above-described embodiment, the frequency chirp compensation amount is determined based on the simulation method of FIG. 9, and the frequency chirp compensator 16 is preset to the value. However, the present invention is not limited to this. However, the setting method is not limited to this. For example, a variable dispersion compensator such as FBG is used as the frequency chirp compensator 16, and the computer is caused to automatically perform the simulation of FIG. 9 and the determination of the frequency chirp compensation amount, and the result is output to the variable dispersion compensator. The variable dispersion compensator may be configured to automatically set the frequency chirp compensation amount.

[0043]

As described above, according to the present invention,
It is possible to provide an optical transmission system for wavelength division multiplexing (WDM) that can accommodate transmitters having different frequency chirps or optical transmission powers for each transmission wavelength.

[Brief description of drawings]

FIG. 1 shows an optical transmission system according to an embodiment of the present invention.
Deviation compensator 7₁, 7 _TwoThe frequency chirp compensation amount of
Optical transmitter 6₁, 6_TwoTransmission range (inferior
Of the phase modulation amount Φ of the optical fiber 10
The graph shown by the correlation with the variance value.

FIG. 2 is a block diagram showing a configuration of an optical transmission system according to an embodiment of the present invention.

3 is a block diagram showing a configuration of a post amplifier 9 of the optical transmission system of FIG.

4 is an in-line amplifier 11 of the optical transmission system of FIG.
3 is a block diagram showing the configuration of a preamplifier 12; FIG.

[5] In the optical transmission system of an embodiment of the present invention, the frequency chirp compensation amount of the deviation compensator 7 ₁ -600
When ps / nm is set and the deviation chirp compensation amount of the deviation compensator 7 ₂ is set to zero, the transmittable range (deterioration amount of 1 dB or less) of the optical transmitters 6 ₁ and 6 ₂ is defined as the phase modulation amount Φ of the optical fiber 10. The graph shown by the correlation with the variance value.

6 is a block diagram showing a configuration of deviation compensators 7 _{1 to} 7 _n of the transmission system of FIG.

7 is a block diagram showing another configuration of deviation compensators 7 _{1 to} 7 _n of the transmission system of FIG.

8 is a block diagram showing still another configuration of deviation compensators 7 _{1 to} 7 _n of the transmission system of FIG.

FIG. 9 is a flowchart showing a simulation method for obtaining a transmittable range when the compensation amount of the frequency chirp compensator 16 of the deviation compensators 7 _{1 to} 7 _n of the optical transmission system according to the embodiment of the present invention is changed.

10 is a block diagram showing a system in which the simulation method of FIG. 9 performs a simulation.

[Explanation of symbols]

1 ... Transmittable range (dispersion tolerance) of the output of the optical transmitter 6 ₂ (α = 0.9) when the phase modulation amount is 1, 2 ... Output of the optical transmitter 6 ₁ (α = -0.2) when the phase modulation amount is 1 Transmission range (dispersion proof strength) of the optical transmitter 6 ₂ (α = 0.
9) Output transmittable range (dispersion strength), 4 ... Optical transmitter 6 ₁ (α =-when phase modulation amount is near zero)
0.2) Output transmittable range (dispersion proof strength), 5 ... Common part, 6 ₁ , 6 ₂ , ..., 6 _n ... Optical transmitter, 7 ₁ , 7 ₂ , ..., 7 _n ... Frequency chirp compensator, 8 ... wavelength multiplexer, 9 ... post-amplifier, 10 ... optical fiber 11 ... line amplifier, 12 ... preamplifier 13 ... wavelength separator _{14 1, 14 2, ···,} 14 n ... optical receiver 15a, 15b , 15c ... Dispersion compensator 16 ... Frequency chirp compensator, 17 ... Light intensity adjuster 20 ... Erbium-doped fiber 21 ... Forward pumping light source 22 ... Backward pumping light source

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04B 10/18 H04B 9/00 E H04J 14/00 14/02 (72) Inventor Keisho Kusano Totsuka Ward, Yokohama City, Kanagawa Prefecture 216 Totsuka Town, Hitachi Ltd., Communications Business Department (72) Inventor Hitoshi Asamizu 216 Totsuka, Totsuka-ku, Yokohama, Kanagawa Prefecture 216 Totsukacho F-Term (Reference) in the Communications Division, Hitachi, Ltd. 2H079 AA02 AA12 AA13 BA01 CA04 DA03 DA16 EA05 EA07 5F072 MM20 PP07 QQ07 YY17 5K002 AA01 AA03 BA05 CA01 CA09 CA13 FA01

Claims (5)

[Claims] 1. A plurality of optical transmitters for respectively emitting optical pulses having different wavelengths, a wavelength multiplexing unit for multiplexing the optical pulses emitted from the optical transmitters, and multiplexing by the wavelength multiplexing unit. A transmission unit that transmits the generated optical pulse,
A wavelength demultiplexing unit that demultiplexes the optical pulses transmitted by the transmission unit for each wavelength; and a plurality of optical receivers that receive the optical pulses demultiplexed by the wavelength demultiplexing unit for each wavelength, Between at least one of the transmitters and the wavelength multiplexing unit, a frequency chirp compensating unit for compensating the deviation of the frequency chirp amount of the optical pulse emitted from each of the plurality of optical transmitters is arranged. An optical transmission system characterized in that 2. The optical transmission system according to claim 1, wherein the frequency chirp compensating unit has a predetermined amount of waveform deterioration after the optical pulses emitted from the plurality of optical transmitters are transmitted through the transmitting unit. An optical transmission system, which compensates for a frequency chirp amount that is equal to or less than a specified value. 3. The optical transmission system according to claim 1, wherein light emitted from each of the plurality of optical transmitters is provided between at least one of the plurality of optical transmitters and the wavelength multiplexing unit. An optical transmission system characterized in that a light intensity adjusting unit for compensating for deviations in light intensity of pulses is arranged. 4. A plurality of connecting sections for connecting a plurality of optical transmitters, and an emitting section for wavelength-multiplexing and emitting the optical pulses respectively emitted from the plurality of optical transmitters. A wavelength chirp compensating unit for compensating a deviation in frequency chirp amount of the optical pulses emitted from each of the plurality of optical transmitters is provided in at least one of the connecting portions of the wavelengths. Multiplexer. 5. A dispersion compensation method for a wavelength division multiplex transmission system, wherein the frequency chirp amount contained in optical pulses of different wavelengths emitted from a plurality of optical transmitters is transmitted through a transmission line. After compensating up to the frequency chirp amount where the waveform deterioration amount of is less than or equal to a predetermined value,
A dispersion compensating method for a wavelength division multiplexing transmission system, characterized in that wavelength division multiplexing is performed and transmission is performed through a transmission line.