JP3389474B2 - Optical transmission method and optical transmission system - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to time division multiplexing (TD).
M) technology and wavelength division multiplexing (WDM) technology are combined to achieve ultra-high speed
The present invention relates to an optical transmission method and an optical transmission system for performing large-capacity optical communication.

[0002]

2. Description of the Related Art Currently, a transmission experiment of 400 Gbit / s with a single wavelength using TDM technology has been reported (S. Kawanis).
hi et al., "400 Gbit / s TDM Transmission of 0.98ps P
ulsesOver 40 km Employing Dispersion Slope Compens
ation ", In Proc. Optical Fiber Communication (OFC) '
96, PD-24, 1996). Also, using WDM technology, 1.1Tb
Transmission capacity exceeding it / s has been reported (H. Onaka et
al., "1.1 Tbit / s WDMTransmission Over a 150 km 1.3
μm Zero-Dispersion Single-Mode Fiber ", InProc. OF
C'96, PD-19, 1996). In order to increase the capacity in the future, it is considered necessary to use the TDM technology and the WDM technology together.

However, at the time of ultra-high speed and large capacity, T
The DM technology and the WDM technology have the following problems, respectively. When performing TDM transmission, the influence of wavelength dispersion of the optical fiber becomes a problem. Here, it is the average chromatic dispersion value that affects the TDM transmission quality, and the transmission quality deteriorates as the average chromatic dispersion value increases. There is a trade-off relationship between the extremely high bit rate and the limitation of the transmission distance due to the average wavelength dispersion, and the required regenerative repeat interval becomes shorter in inverse proportion to the square of the beat rate. Therefore, a technique for equalizing the average chromatic dispersion is required, and for example, a technique for incorporating a measurement system and a compensation system into a transmission system to realize automatic equalization has been reported (Reference 1: M. Tomizawa. et al., "Aut
omaticdispersion equalization for installation of
high-speed optical transmission system ", OFC'97, T
uT-2, 1997).

On the other hand, WDM using dispersion-shifted fiber
When performing transmission, the non-linear optical effect of the optical fiber, particularly the influence of four-wave mixing (FWM) becomes a problem. This FW
The generation efficiency of M strongly depends on chromatic dispersion. here,
WDM transmission quality is affected by the local chromatic dispersion near the fiber entrance end, and the transmission quality deteriorates as the local chromatic dispersion value decreases. The wavelength multiplexing number and transmission distance limit are
After all, there is a trade-off relationship.

[0005]

In order to increase the capacity by using the TDM technology and the WDM technology together, it is necessary to perform control for mitigating the influence of chromatic dispersion, and to realize this economically. Is desirable to be automatically controlled.

The present invention alleviates the wavelength dispersion limitation in TDM transmission and the nonlinear optical effect limitation in WDM transmission at the same time, and assigns wavelengths to a plurality of signal channels in order to enable optical communication of ultrahigh speed and large capacity. An object of the present invention is to provide an optimized optical transmission method and optical transmission system.

[0007]

The optical transmission method of the present invention comprises:
When assigning multiple signal channels to different wavelengths, assign the signal channel with the highest bit rate to the average zero-dispersion wavelength of the optical fiber, and order each wavelength away from the average zero-dispersion wavelength sequentially from the signal channel with the highest bit rate. (Claim 1). As a result, it is possible to reduce the influence of chromatic dispersion on a high bit rate signal channel, and it is possible to realize a large capacity by TDM transmission.

Further, signal channels are prohibited from being allocated to the local zero-dispersion wavelength near the incident end of the optical fiber and the wavelength in the vicinity thereof (claim 1). This allows WD
It is possible to reduce the nonlinear optical effect in M transmission, particularly the influence of FWM, and it is possible to realize a large capacity by increasing the number of wavelength division multiplexing.

Further, the optical transmission system of the present invention measures the average zero-dispersion wavelength and the local zero-dispersion wavelength of the optical fiber when the system is introduced, and automatically controls the signal channel assigned to each wavelength (claims 2, 3). ).

[0010]

FIG. 1 shows a wavelength allocation algorithm according to the optical transmission method of the present invention. FIG. 2 shows the operation process of the wavelength allocation algorithm.

First, the bit rate of each signal channel input in M parallel is manually registered in the database or is automatically recognized and registered. When the bit rate of each signal channel is registered, the local zero-dispersion wavelength near the incident end of the optical fiber is measured, and then the average zero-dispersion wavelength is measured. Here, when the local zero-dispersion wavelength and the average zero-dispersion wavelength are equal to or close to each other, the variable dispersion compensator on the receiving side is driven to shift the average zero-dispersion wavelength, and the average zero-dispersion wavelength is measured again. . When the local zero-dispersion wavelength and the average zero-dispersion wavelength are different, each signal channel is assigned to a different wavelength.

Wavelength allocation of each signal channel is performed as follows. First of all, refer to the database, N available
The wavelength of the wave is recognized, and the bit rate of each signal channel input in M parallel is recognized (N> M). continue,
A signal channel having a maximum bit rate (40 Gbit / s in FIG. 2) is assigned to the measured mean zero dispersion wavelength. Next, from the wavelengths that symmetrically deviate from the mean zero-dispersion wavelength to the high-wavelength side and low-wavelength side in order, except for the wavelengths near the local zero-dispersion wavelength (within several nm), from the high-speed signal channel in order. Assign to. In the case of a multi-relay system, allocation is performed so as to avoid the vicinity of all local zero-dispersion wavelengths.

The average zero-dispersion wavelength of the optical fiber may be measured by a known phase difference method or a known method of measuring chromatic dispersion by the PM-AM conversion effect of the measuring light (Reference 1). The local zero dispersion wavelength is measured by an optical pulse tester (OTD).
R) for measuring the dispersion of the zero dispersion wavelength of the optical fiber in the longitudinal direction (Reference 2: M. Ohashi and MT).
ateda, "Novel technique for measuring chromatic dis
persion distribution in singlemode fibers ", Electr
on. Lett., vol.29, no.5, pp.426-428, 1993), or a known method for measuring the average zero-dispersion wavelength (local zero-dispersion wavelength) only near the incident end of the optical fiber (Reference 3). : M.Tomizawa, "Me
asurement of local aerodispertion wavelength at th
e input side of dispertion managed optical fiber
s ", J. Lightwave Technol., vol.15, no.8, Special is
sue on applications of photosensitivity and quadra
tic nonlinearity of glass, 1997).

Here, the method of measuring the local zero-dispersion wavelength according to Document 3 will be described with reference to the flowchart of FIG. First, the CW light whose intensity modulation of the incident light is set to 0 is subjected to phase modulation and is incident. In this state, the wavelength at which the fiber output intensity modulation is minimized is measured. However, the power of the incident light shall be +10 dBm or less. Next, intensity modulation is applied to the incident light, and the wavelength at which the fiber output intensity modulation is minimized in this state is measured at each power. The local zero-dispersion wavelength is obtained by fitting the variation amount Δλ (P ₀ ) due to the optical power of the minimum intensity modulation wavelength to the equation (1).

[0015]

[Equation 1]

In the case of a multi-repeater system using an optical amplifier, the local zero-dispersion wavelength near each incident end can be measured by changing the incident power of each optical repeater one by one. it can.

In order to obtain the minimum intensity modulation wavelength in the flowchart of FIG. 3, the wavelength is swept and measured while communicating between the transmitter and the receiver. This algorithm is shown as a sequence in FIG. 4 (reference 1). The solid arrow indicates the control light λcont, and the broken arrow indicates the measurement light λmea.

First, the receiver side notifies the transmitter side that it enters the measurement mode. The transmitter responds with an ACK and transmits the CW light subjected to the phase modulation. Also, the wavelength value is written in the control light and sent to the receiver. The receiver measures the intensity modulated component and sends a command to the next wavelength.
In the following, the intensity modulation component is measured for all the sweepable wavelengths in sequence, and the wavelength at which the measured value becomes the minimum is calculated.
This sequence is S2, S4 of the flowchart of FIG.
Then it is common.

(First Embodiment of Optical Transmission System) FIG. 5
1 shows a first embodiment of an optical transmission system of the present invention.
In the figure, each signal channel input in M parallel is M
Intensity modulators 12-1 to 12-12 via the xN switch 11
The light having wavelengths λ1 to λN input to −N and output from the laser light sources 13-1 to 13-N is modulated. The light modulated by each intensity modulator is combined by the star coupler 14 and 2 × 1
Is output to the optical fiber 1 via the optical switch 15, the post amplifier 16, and the optical coupler 17. In addition, the measurement light source 18
Is the wavelength λme for measuring the chromatic dispersion of the optical fiber 1.
The light of a is transmitted through the 2 × 1 optical switch 15 to the optical fiber 1
Send to. The controller 19 controls the switch 11, the optical switch 15, and the measurement light source 18, and further transmits the control light of the wavelength λcont used for communication with the receiving side via the optical coupler 17, and outputs the control light input from the down line. To receive.

The wavelength division multiplexed light input from the optical fiber 1 is an optical coupler 21, a preamplifier 22, and a variable dispersion compensator 2.
The light of each wavelength is input to the wavelength filters 26-1 to 26-N via the 3, 2 × 1 optical switch 24 and the star coupler 25, and the light of each wavelength is converted into each signal channel by the light receivers 27-1 to 27-N. , M × N switches 28 to output in parallel to a predetermined output port. The measurement processing circuit 29 receives the light of the wavelength λmea via the optical switch 24 and measures the intensity modulation component at each wavelength and each power. The controller 30 controls the variable dispersion compensator 23, the optical switch 24, the switch 28, and the measurement processing circuit 29, and further controls the control light of the wavelength λcont used for communication with the transmission side.
1 to receive the control light and transmit the control light to the transmission side via the downlink.

In the optical transmission system of the present invention, the controllers 19 and 30 control the switches 11 and 28 to allocate each signal channel to a predetermined wavelength according to the above-mentioned wavelength allocation method. Therefore, the measurement light source 18 and the measurement processing circuit 2
The average zero-dispersion wavelength and the local zero-dispersion wavelength of the optical fiber 1 are measured according to the above-mentioned algorithm using the controller 9 and the controllers 19 and 30.

The switches 11 and 28 can be compatible with bit rate flexible coaxial matrix switches. It is also possible to use an optical switch. In this case, if the electric / optical converter and the optical / electrical converter are arranged before and after the optical switch, or if the electric / optical converter is arranged only on the input side and the intensity modulator 12 is the optical modulator. Good.

The 2 × 1 optical switches 15 and 24 are switches for switching between the measurement mode and the normal data transmission mode. This optical switch is unnecessary if the configuration is such that chromatic dispersion is monitored during data transmission.
The output light of No. 8 may be connected to the star coupler 14 and the output of the star coupler 25 may be connected to the measurement processing circuit 29. However, in this case, it is necessary to have a control function that does not output from a light source other than the measurement light source in the measurement performed when the system is installed.

(Second Embodiment of Optical Transmission System) FIG. 6
2 shows a second embodiment of the optical transmission system of the present invention.
The feature of this embodiment is that, on the transmission side, variable wavelength laser light sources 41-1 to 41-M are used in place of the laser light sources 13-1 to 13-N in the first embodiment, and a large M × N switch is used. 11 is unnecessary. On the receiving side, the wavelength filter 2
Variable wavelength filters 51-1 to 51-1 instead of 6-1 to 26-N
51-M, eliminating the need for large M × N switches 28. Further, in place of the measurement light source 18 on the transmission side, one of the variable wavelength laser light sources 41-1 to 41-N is used as a representative light source, and the bias of the intensity modulator of the representative light source is set via the electric switch 42 during measurement. Gives signals to control the points. The receiver on the receiving side corresponding to this is the representative receiver,
The output is sent to the measurement processing circuit 29 via the electric switch 52.
To enter. Other configurations and wavelength allocation algorithms are the same as those in the first embodiment.

That is, when the measurement mode is entered, the electric switches 42 and 52 are activated on both the transmitting side and the receiving side.
On the transmission side, phase-modulated CW light is output by adjusting the bias point of the intensity modulator of the representative light source (Reference 1).
In the normal data transmission mode, a midpoint between the maximum transmittance and the minimum transmittance is selected as the bias point, and a large extinction ratio is obtained by vibrating with a large amplitude. On the other hand, in the measurement mode, the bias point is set to the maximum transmittance, and the quasi-phase modulated light is obtained by vibrating the bias point slightly around the bias point. The output of other lasers other than the representative light source is stopped.

The measurement processing circuit 29 on the receiving side measures the intensity modulation component from the output of the representative photodetector, and measures the local zero-dispersion wavelength and the average zero-dispersion wavelength. The controllers 19 and 30 are
The wavelength of the variable wavelength laser light source connected to the intensity modulator to which the signal channel of the maximum bit rate is input and the wavelength of the corresponding variable wavelength filter are set to the average zero dispersion wavelength (see FIG. 6).
Then set it to λ ₂ ). The wavelength of the remaining variable wavelength laser light source and the wavelength of the variable wavelength filter are adjusted according to the above wavelength allocation algorithm.

[0027]

As described above, in the optical transmission method of the present invention, the fastest signal channel is assigned to the average zero-dispersion wavelength of the optical fiber, and as the distance from the average zero-dispersion wavelength increases, the higher-speed signal channel starts in order. By allocating, the chromatic dispersion limitation of TDM transmission can be relaxed and the capacity of the optical transmission system can be increased.

Further, the non-linear optical effect limitation of WDM transmission is relaxed by prohibiting the allocation to the local zero dispersion wavelength near the incident end of the optical fiber and the wavelength in the vicinity thereof,
It is possible to increase the capacity of the optical transmission system.

Further, in the optical transmission system of the present invention, when the system is introduced, the average zero-dispersion wavelength and the local zero-dispersion wavelength of the optical fiber are measured, and the wavelengths are automatically assigned to the signal channels. A series of introduction costs such as labor costs can be reduced.

[Brief description of drawings]

FIG. 1 is a flowchart showing a wavelength allocation algorithm according to the optical transmission method of the present invention.

FIG. 2 is a schematic diagram showing an operation process of a wavelength allocation algorithm.

FIG. 3 is a flowchart illustrating a known method of measuring a local zero dispersion wavelength.

FIG. 4 is a diagram illustrating an algorithm for obtaining a minimum intensity modulation wavelength.

FIG. 5 is a block diagram showing a first embodiment of an optical transmission system of the present invention.

FIG. 6 is a block diagram showing a second embodiment of the optical transmission system of the present invention.

[Explanation of symbols]

1 optical fiber 11,28 M × N switch 12 Intensity modulator 13 Laser light source 14,25 star coupler 15,24 2 × 1 optical switch 16 post amplifier 17 Optical coupler 18 Measuring light source 19,30 controller 21 Optical coupler 22 Preamplifier 23 Variable dispersion compensator 26 wavelength filters 27 Light receiver 29 Measurement processing circuit 41 Variable wavelength laser light source 42,52 electric switch 51 Variable wavelength filter

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kazuo Hagimoto 3-19-2 Nishishinjuku, Shinjuku-ku, Tokyo Nihon Telegraph and Telephone Corporation (56) References JP-A-6-216845 (JP, A) Kaihei 4-219704 (JP, A) JP 61-206334 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H04B 10/00-10/28 H04J 14/00- 14/08 JISST file (JOIS)

Claims (4)

(57) [Claims] 1. An optical transmission method for allocating a plurality of signal channels to different wavelengths and wavelength-multiplexing and transmitting an optical fiber, wherein the maximum bit among the plurality of signal channels is at the average zero dispersion wavelength of the optical fiber. A signal channel having a rate is assigned, in order from a wavelength close to the mean zero dispersion wavelength of the optical fiber, signal channels other than the signal channel having the maximum bit rate of the plurality of signal channels are arranged in order of increasing bit rate. An optical transmission method, characterized in that the allocation and the allocation of signal channels to the local zero-dispersion wavelength near the incident end of the optical fiber and the wavelength in the vicinity thereof are prohibited. 2. A plurality of optical transmitting means for respectively modulating and outputting light of different wavelengths, and a plurality of signal channels each having a predetermined bit rate are input, and each signal channel is input to any one of the plurality of optical transmitting means. Switch means for allocating wavelengths as a modulated signal, wavelength multiplexing means for multiplexing the signal light output from the plurality of optical transmission means and transmitting to an optical fiber, wavelength input from the optical fiber Wavelength demultiplexing means for demultiplexing the multiplexed light into signal light of each wavelength, a plurality of light receiving means for converting the signal light of each wavelength demultiplexed by the wavelength demultiplexing means into a signal channel of an electric signal, and the plurality of Receiving side switching means for connecting each signal channel output from the optical receiving means to an output port corresponding to each bit rate, and an average chromatic dispersion value and incidence of the optical fiber. Measuring light transmitting means for transmitting the measuring light for measuring the local chromatic dispersion value near the edge and transmitting and receiving a control signal related to the measuring light with the receiving side, and receiving the measuring light and transmitting and receiving the control signal Then, a measurement processing means for measuring an average chromatic dispersion value and a local chromatic dispersion value of the optical fiber, and an average chromatic dispersion value and a local chromatic dispersion value of the optical fiber measured by the measurement light transmitting means and the measurement processing means. 3. An optical transmission system comprising: a control means for controlling each switch means so as to allocate each signal channel and wavelength according to the wavelength allocation algorithm of claim 1. 3. A plurality of optical transmission means for inputting each signal channel having a predetermined bit rate as a modulation signal, modulating light of a wavelength set according to the bit rate of each signal channel, and outputting the modulated light. Wavelength multiplexing means for multiplexing the signal light output from the plurality of optical transmission means and transmitting to the optical fiber, and when demultiplexing into the signal light of each wavelength of the wavelength multiplexed light input from the optical fiber, Wavelength demultiplexing means for setting the wavelength to be demultiplexed so as to be connected to the optical receiving means corresponding to each bit rate, and the signal light of each wavelength demultiplexed by the wavelength demultiplexing means is converted into a signal channel of an electric signal. Then, an average chromatic dispersion value of the optical fiber and a local chromatic dispersion near the incident end are output from a plurality of optical receiving means for outputting to an output port corresponding to each bit rate and one of the plurality of optical transmitting means. Measuring light transmitting means for transmitting measuring light for measuring, and transmitting and receiving a control signal relating to the measuring light to and from a receiving side; and receiving the measuring light by one of the plurality of light receiving means, Measurement processing means for transmitting and receiving a signal and measuring an average chromatic dispersion value and a local chromatic dispersion value of the optical fiber, and an average chromatic dispersion value and a local area of the optical fiber measured by the measurement light transmitting means and the measurement processing means. Based on the chromatic dispersion value, each signal channel and wavelength are allocated according to the wavelength allocation algorithm of claim 1,
An optical transmission system comprising: a control means for controlling the wavelengths of the plurality of optical transmission means and the wavelength of the wavelength separation means. 4. The optical transmission system according to claim 2 or 3, wherein when the measured average chromatic dispersion value and the local chromatic dispersion value of the optical fiber are equal to or close to each other, the optical fiber is provided to the receiving side. An optical transmission system comprising a variable dispersion compensator for shifting the average chromatic dispersion value of.