JP2001308792A - Optical communication device, optical transmitter and optical receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize an optical communication device capable of realizing a stable operation by keeping high dispersion resistance stable in a large power range of incident light, facilitating the design of an optical transmission system and speeding up the introduction of the optical transmission system, and to realize an optical transmitter and an optical receiver composing it. SOLUTION: The device is provided with an optical transmitter consisting of an optical duo binary signal generating means for generating optical duo binary signals and an optical modulation means for returning the optical duo binary signal to zero by adding an alternated optical retardation to it to transform it into a carrier suppression optical duo binary signal returned to zero and then transmitting it, an optical transmission medium for transmitting the carrier suppression optical duo binary signal returned to zero, and an optical receiver consisting of a band dividing means for receiving the carrier suppression optical duo binary signal returned to zero and then for dividing and outputting two optical duo binary components in the spectrum component, and an optical receiving means for receiving either or both of two optical duo binary components.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical communication device for minimizing deterioration of transmission quality caused by chromatic dispersion of a transmission medium such as an optical fiber or an interaction between the chromatic dispersion and a nonlinear optical effect. Further, the present invention relates to an optical transmitter and an optical receiver constituting the optical communication device.

[0002]

2. Description of the Related Art In optical signal transmission, there is a problem of chromatic dispersion of an optical fiber as a transmission medium or deterioration of transmission quality caused by waveform deterioration due to an interaction between the chromatic dispersion and a nonlinear optical effect. This occurs because the group velocity dispersion of the optical fiber acts on the bandwidth of the optical signal, causing the optical pulse waveform to collapse and causing interference with adjacent time slots.

In order to suppress the deterioration due to the group velocity dispersion, for example, an optical duobinary transmission system using an optical communication device shown in FIG. 16 has been proposed (Japanese Patent Laid-Open No. 9-2367).
No. 81).

In FIG. 16, a binary data signal (binary signal) is input to a code conversion circuit 71 and converted into a ternary duobinary signal. The duobinary signal is branched into two, one of which is inverted in phase by an inverting circuit 72 and band-limited by amplitude adjusting circuits 73-1 and 73-2.
The two-electrode type Mach-Zehnder type light intensity modulator 74 whose transmittance is biased to the minimum is push-pull driven. The continuous light output from the continuous light source 75 is intensity-modulated in accordance with the duo-binary signal whose phase is inverted, converted into an optical duo-binary signal, and transmitted to the optical transmission medium 3. The optical duobinary signal transmitted via the optical transmission medium 3 is directly detected by an optical detection circuit 81, and the detected signal is identified and reproduced by an identification circuit 82, and the phase is inverted by an inversion circuit 83. The signal is restored.

[0005] It has been reported that such an optical duobinary transmission system can obtain a high resistance to chromatic dispersion of an optical fiber (K. Yonnaga et al., Electron.
Lett., Vol. 31, pp. 302-304, 1995).

[0006]

However, in the conventional configuration, there is a problem that the dispersion tolerance decreases when the power of light incident on the optical fiber transmission line is increased. FIG. 17 shows computer simulation results of the dispersion tolerance of the optical duobinary transmission system and the transmission system using the general NRZ and RZ code formats. Here, the local variance is +2 ps / n
A contour line of 1 dB of eye opening deterioration when 100 km of a single mode fiber of 100 m / km is transmitted for two spans through one optical amplifier is shown. In addition, the dispersion proof stress when the present invention described later is used is also shown.

In FIG. 17, when the incident light power is 0 dBm, the NRZ code format has about twice the dispersion tolerance as compared with the RZ code format, and the optical duobinary transmission system has about four times the dispersion tolerance as compared with the NRZ code format. It has a dispersion tolerance and shows the dispersion tolerance as predicted from the bandwidth of each. The optimum dispersion value at this time is almost 0 ps / nm.

However, when the optical power incident on the optical fiber transmission line is increased, the dispersion tolerance of the optical duobinary transmission system is reduced, and the total dispersion, which is the optimum point in the low optical power region, is close to 0 ps / nm. Significantly deteriorated. And
The eye opening deterioration exceeds 1 dB when the incident light power exceeds 5 dBm.

On the other hand, in the NRZ / RZ code format, the optimum dispersion value shifts to the positive dispersion side as the incident light power increases, and 0 ps / nm, which is the optimum point at low light power (0 dBm), is the dispersion tolerance margin. At the end, the dispersion tolerance margin disappears sharply as the incident light power is further increased. This is because frequency chirp is additionally added to the optical signal due to the nonlinear optical effect in the optical fiber. Also, the dispersion tolerance itself is very small, from 1/4 to 1/8 of that of the optical duobinary transmission system, so that the system design becomes strict and optimization when introducing the system becomes difficult.

Thus, the optical duobinary transmission method,
In the transmission system using the NRZ / RZ code format, the optimum point of dispersion tolerance varies in a wide range of incident light power. This complicates the design of the optical transmission system and hinders quick introduction and stable operation. That is, in designing an optical transmission system, it is necessary to consider an optimum dispersion value that varies depending on the incident light power, and the design becomes complicated.

When an optical transmission system is introduced, a dispersion value of an optical fiber transmission line is measured by a dispersion measuring device, and an optimum dispersion value (generally 0 ps / nm) is obtained. To shift) and start the system. In the measurement of the dispersion value, only information on the dispersion value of the optical fiber can be obtained, so that it is difficult to follow the deviation of the above-mentioned optimum dispersion value that differs for each transmission method. In other words, the dynamic range of the incident light power that can be used in the conventional method is small. Therefore, in the optical transmission system using the conventional method, it becomes a factor that limits the bit rate and the transmission distance.

Also, an optical duobinary transmission system, NRZ
-In any of the transmission systems using the RZ code format,
When the incident light power is increased, the dispersion proof stress rapidly deteriorates. This is a problem that hinders stable operation of the optical transmission system.

The present invention provides an optical communication device which stably maintains a high dispersion tolerance over a wide range of incident optical power, facilitates the design of an optical transmission system, speeds up the introduction of the optical transmission system, and realizes stable operation. An object of the present invention is to provide an optical transmitter and an optical receiver to be configured.

[0014]

An optical communication apparatus according to the present invention comprises:
An optical duobinary signal generating means for generating an optical duobinary signal; and an optical modulating means for converting the optical duobinary signal into an RZ by adding an alternating phase difference, converting the optical duobinary signal into a carrier suppressed RZ-converted optical duobinary signal, and transmitting the resulting signal. Optical transmitter, an optical transmission medium for transmitting a carrier-suppressed RZ-converted optical duobinary signal, and a carrier-suppressed RZ-converted optical duobinary signal, dividing and outputting two optical duobinary components in the spectrum component Band dividing means,
An optical receiver configured to receive one or both of the two optical duobinary components.

Thus, the carrier-suppressed RZ-converted optical duobinary signal transmitted through an optical transmission medium such as an optical fiber is expressed by R
By taking the form of a Z pulse, it is possible to minimize waveform deterioration due to nonlinear optical effects in the optical fiber. In addition, the band dividing means of the optical receiver divides the two optical duobinary components of the carrier suppressed RZ-converted optical duobinary signal and individually extracts and receives them. The components are affected by the chromatic dispersion of the optical transmission medium. Therefore, waveform deterioration due to chromatic dispersion of the optical transmission medium can be suppressed to almost 1/4.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) FIG. 1 shows a first embodiment of an optical communication apparatus (optical transmitter and optical receiver) according to the present invention.

In the figure, an optical communication apparatus according to the present invention comprises: an optical transmitter 1 for converting an optical duobinary signal into a carrier-suppressed RZ-converted optical duobinary signal;
The optical receiver 2 is configured to receive the carrier-suppressed RZ-converted optical duobinary signal transmitted through the optical network through a band division.

The optical transmitter 1 is provided with an optical duobinary signal generating means 70 for generating an optical duobinary signal as in the prior art.
And an optical modulating means 10 for adding the alternating phase difference to the generated optical duobinary signal to RZ and converting it into a carrier suppressed RZ-converted optical duobinary signal.

As the optical transmission medium 3, a dispersion optical fiber (DSF) or a silica-based optical fiber such as a 1.3 μm band single mode fiber is used. Note that an optical fiber amplifier (optical repeater) may be included.

The optical receiver 2 receives the transmitted carrier suppression R
Band splitting means 20 for separating two optical duobinary components in the spectral component of the Z-converted optical duobinary signal;
The optical duobinary component comprises one or both of the optical duobinary components. Band dividing means 20
Use an optical band-pass filter composed of a dielectric multilayer film, a Mach-Zehnder interferometer type optical filter formed on an optical fiber or an optical waveguide, an arrayed waveguide diffraction grating type filter (AWG), etc. Can be. The optical receiving means 80 includes an optical detection circuit 81, an identification circuit 83, and an inversion circuit 83 as shown in FIG. 16, and performs photoelectric conversion, identification reproduction, and phase inversion on the band-divided optical duobinary component to obtain the original. Restore the binary data signal. In addition,
The inverting circuit 83 may not be necessary in some cases due to the configuration of the code conversion circuit of the optical duobinary signal generating means 70 of the optical transmitter 1.

FIG. 2 shows a configuration example of the optical transmitter 1. 2A shows a first configuration example of the optical transmitter 1, and FIG. 2B shows a second configuration example of the optical transmitter 1 described later. In FIG. 2A, the optical duobinary signal generation means 70 includes a code conversion circuit 71, a phase inversion circuit 72, and an amplitude adjustment circuit 73-.
1, 73-2, two-electrode type Mach-Zehnder optical modulator 7
4. A continuous light source 75, which converts an input binary data signal (binary signal) into a ternary duobinary signal by a code conversion circuit 71 in the same manner as in the conventional configuration, and further converts a Mach-Zehnder optical modulator 74. An optical duobinary signal is generated by push-pull driving. Light modulation means 1
Reference numeral 0 denotes a two-electrode type Mach-Zehnder optical modulator 11, which is push-pulled by a clock signal (for example, a sine wave) CLK having a frequency half the bit rate of the optical duobinary signal generated by the optical duobinary signal generating means 70. By driving, a carrier-suppressed RZ-converted optical duobinary signal is generated.

The operation of this embodiment will be described below with reference to FIGS. The optical duobinary signal generation means 70 generates an optical duobinary signal having about half the band as compared with a normal NRZ code. Optical waveform (eye pattern) obtained by computer simulation
FIG. 3A shows the optical spectrum at that time.

This optical duobinary signal is converted to light modulation means 1
0 (Mach-Zehnder type optical modulator 11), and is modulated by push-pull driving with a synchronized clock signal (CLK) to be converted into a carrier-suppressed RZ signal (carrier-suppressed RZ optical duobinary signal). You. At this time, the drive point is set to a voltage at which the transmittance at the time of non-modulation is minimum,
The frequency of the clock signal to be driven is set to half the bit rate of the optical duobinary signal generated in the preceding stage. Also,
The drive amplitude is 1 of Vπ of the Mach-Zehnder optical modulator 11.
Up to three times. The Mach-Zehnder optical modulator 11 driven in this manner has a gate characteristic having a function of converting the phase into an alternating phase RZ. This is schematically shown in FIG.

FIG. 4A shows an optical duobinary signal output from the optical duobinary signal generating means 70 at the preceding stage.
The push-pull drive gate phase of the Mach-Zehnder optical modulator 11 is set as shown in FIG. By this operation, an RZ signal having a phase difference between bits shown in FIG. 4C is obtained. This is the waveform of the carrier suppressed RZ-converted optical duobinary signal.

Here, the Mach-Zehnder type optical modulator 11
Is push-pull driven by a clock signal having a frequency half the bit rate of the input optical duobinary signal. Due to the folding characteristics of this optical modulator, the obtained RZ pulse has a repetition frequency of the bit rate of the input optical duobinary signal. Matches. The optical waveform (eye pattern) and optical spectrum obtained at this time are shown in FIG. This is a case where the drive voltage of the Mach-Zehnder optical modulator 11 is a sine wave having an amplitude (peak-to-peak) that is exactly twice Vπ of the modulator. Duty ratio is about 2/3
Has been converted to a light pulse. By converting the optical duobinary signal into the RZ as described above, it is possible to obtain strong resistance to the nonlinear optical effect in the optical transmission medium 3.
This optical spectrum is composed of two optical duobinary components with the carrier component suppressed.

The carrier suppression R transmitted through the optical transmission medium 3
The z-converted optical duobinary signal is input to the band dividing means 20 of the optical receiver 2, and one of the two optical duobinary components is selected. The optical waveform (eye pattern) and optical spectrum obtained at this time are shown in FIG. By this band division, the optical waveform becomes substantially equal to the NRZ signal. By such processing, waveform deterioration due to group velocity dispersion of the optical fiber can be limited to only one of the two optical duobinary components after transmission. By this effect, as shown in FIG. 17, for both high incident light power, a wide dispersion tolerance and a high tolerance for the nonlinear optical effect in which the optimum dispersion value is maintained near zero at all dispersion values are compatible. Can be. If the transmitted carrier-suppressed RZ-converted optical duobinary signal is received without band division, the group velocity dispersion of the optical fiber is affected as the entire band of the two duobinary components. I do.

(Second Configuration Example of Optical Transmitter 1) The optical transmitter 1 shown in FIG. 1 has a continuous light source 75 as shown in FIG.
Is input to the optical modulator 10 (Mach-Zehnder optical modulator 11) for first performing the alternating phase RZ conversion, and is input to the Mach-Zehnder optical modulator 74 for converting the output light into an optical duobinary signal. It is good also as a structure which performs. That is, the Mach-Zehnder optical modulator 11 of the preceding stage is push-pull driven by the clock signal (CLK), and the Mach-Zehnder optical modulator 74 of the succeeding stage is driven by the amplitude adjusting circuit 73-.
Push-pull driving is performed with the duobinary signal output from the 1, 73-2.

In the case of this configuration, the continuous light source 7
5 and light modulating means 10 (Mach-Zehnder type light modulator 11)
Instead, a two-mode oscillation mode-locked laser can be used. Thereby, the number of components is reduced, and a simpler optical transmitter 1 can be configured.

(Second Embodiment) FIG. 5 shows an optical communication device (optical transmitter) according to a second embodiment of the present invention. The configurations of the optical transmitter and the optical receiver of this embodiment are the same as those of the first embodiment shown in FIG. 1, but drive the optical modulator 10 (Mach-Zehnder optical modulator 11) of the optical transmitter 1. The frequency of the clock signal (CLK) is different.

In the first embodiment, the frequency of the clock signal (CLK) for driving the Mach-Zehnder optical modulator 11 constituting the optical modulator 10 is the optical duobinary signal generated by the optical duobinary signal generator 70. Of the bit rate. The frequency difference between the two optical duobinary components of the carrier-suppressed RZ-converted optical duobinary signal thus generated is NHz when the bit rate of the optical duobinary signal is Nbit / s as shown in FIG.
Becomes

Generally, when the bit rate of the optical duobinary signal is Nbit / s, the frequency of the clock signal for push-pull driving the Mach-Zehnder optical modulator 11 is mN / 2 Hz (m is a positive integer). It may be. The second embodiment shows a case where the Mach-Zehnder optical modulator 11 is driven by push-pull using a clock signal (m = 2) having the same frequency as the bit rate of the optical duobinary signal. Thus, as shown in FIG. 6B, the frequency difference between the two optical duobinary components of the generated carrier-suppressed RZ-converted optical duobinary signal is twice (2 times) that of the first embodiment.
NHz). Accordingly, when each optical duobinary component is extracted by the band division unit 20 of the optical receiver 2, a margin for the center frequency and the transmission width of the optical filter is increased, and stable operation is facilitated.

(Third Embodiment) FIG. 7 shows a third embodiment of the optical communication apparatus (optical receiver) of the present invention. The configuration of the optical transmitter according to this embodiment is the same as that of the first embodiment or the second embodiment, but the configuration of the optical receiver is different.

The optical receiver 2 of this embodiment is characterized in that it comprises an optical receiving means 80a for receiving the two optical duobinary components band-divided by the band dividing means 20. The optical receiving means 80a includes two optical detection circuits 81-1 and 81-
2. It is composed of an addition circuit 84, an identification circuit 82, and an inversion circuit 83. The two optical detection circuits 81-1 and 81-2 are:
For example, PIN type photodiodes are used and have the same output polarity. The electric signal is added by the adding circuit 84 and input to the identification circuit 82.

The operation of this embodiment will be described with reference to FIG. Carrier suppression RZ transmitted from optical transmitter 1
The converted optical duobinary signal is received by the optical receiver 2 via the optical transmission medium 3, divided into two optical duobinary components by the band dividing means 20, and separated and output. The two optical duobinary components are separated by an optical detection circuit 81-
At 81-2, they are independently converted into electric signals.
Here, the output amplitudes of the optical detection circuits 81-1 and 81-2 are V1 and V2, respectively. The adding circuit 84 adds the two electric signals, and the amplitude of the added signal becomes V1 + V
2 can be increased. As a result, the input amplitude to the identification circuit 82 increases, the operation margin increases, and a stable operation can be realized.

(Fourth Embodiment) FIG. 9 shows an optical communication apparatus (optical receiver) according to a fourth embodiment of the present invention. The configuration of the optical transmitter according to this embodiment is the same as that of the first embodiment or the second embodiment, but the configuration of the optical receiver is different.

The optical receiver 2 of this embodiment is characterized in that it comprises an optical receiving means 80b for receiving two optical duobinary components band-divided by the band dividing means 20. The optical receiving means 80b includes two optical detection circuits 81-1 and 81-
2, a subtraction circuit 85, an identification circuit 82, and an inversion circuit 83. The two optical detection circuits 81-1 and 81-2 are:
For example, PIN type photodiodes are used and have different output polarities. The electric signal is subtracted by the subtraction circuit 85 and input to the identification circuit 82.

Here, the operation of this embodiment will be described with reference to FIG. The carrier-suppressed RZ-converted optical duobinary signal transmitted from the optical transmitter 1 is received by the optical receiver 2 via the optical transmission medium 3 and is divided into two optical duobinary components by the band dividing means 20 and separated from each other. And output. The two optical duobinary components are independently converted into electric signals by the optical detection circuits 81-1 and 81-2. Here, the output amplitudes of the optical detection circuits 81-1 and 81-2 are V1 and V2, respectively. However, the polarities of the two electric signals are opposite, one of which has a positive polarity (a positive potential when light is incident) and the other has a negative polarity (a negative potential when light is incident). The subtraction circuit 85 subtracts the two electric signals, so that the amplitude of the subtraction signal is V1−
V2, which can be increased. As a result, the input amplitude to the identification circuit 82 increases, the operation margin increases, and a stable operation can be realized.

(Fifth Embodiment) FIG. 11 shows an optical communication device (optical receiver) according to a fifth embodiment of the present invention. The configuration of the optical transmitter according to this embodiment is the same as that of the first embodiment or the second embodiment, but the configuration of the optical receiver is different.

The optical receiver 2 of this embodiment includes optical receiving means 80-1 and 80-2 for receiving two optical duobinary components divided in band by the band dividing means 20 in parallel. It is characterized in that the other is used as a standby system. Each of the optical receiving means 80-1 and 80-2 is constituted by an optical detection circuit, an identification circuit, and an inversion circuit.

The operation of each light receiving means of the present embodiment is the first operation.
This is the same as the optical receiver 2 of the embodiment. Band splitting means 2
By receiving each of the two optical duobinary components band-divided by 0 in each of the optical receiving means 80-1 and 80-2, even if one of the optical receiving means fails, the other optical receiving means can continue receiving. , Can increase the stability and reliability of the system.

(Sixth Embodiment) FIG. 12 shows an optical communication device (optical receiver) according to a sixth embodiment of the present invention. The configuration of the optical transmitter according to this embodiment is the same as that of the first embodiment or the second embodiment, but the configuration of the optical receiver is different.

The optical receiver 2 according to the present embodiment is characterized in that the two optical duobinary components divided by the band dividing means 20 are monitored and the band dividing means 20 is controlled.
The two optical duobinary components that have been band-divided by the band dividing unit 20 are partially branched by the optical branching units 21-1 and 21-2, respectively, and the optical power monitoring circuits 22-1 and 22-22.
The optical power is measured at 2 and input to the control circuit 23. The control circuit 23 is configured to control the band dividing means 20 so that the sum of the two optical powers is maximum and the difference is minimum. The band dividing means 20 uses a Mach-Zehnder interferometer type optical filter formed on an optical fiber or an optical waveguide. As the light branching units 21-1 and 21-2, an optical fiber coupler or a light beam splitter using a partially reflecting mirror is used. Optical power monitor circuits 22-1 and 22-2
2-2 is a unit for measuring optical power using a photoelectric conversion circuit or the like.

The optical receiving means 80c is configured to receive only one of two band-divided optical duobinary components as in the first embodiment, and is configured to receive two optical duobinary components as in the third and fourth embodiments. A configuration in which each duobinary component is converted into an electric signal and added and subtracted for identification, as in the fifth embodiment, two optical duobinary components are each converted into an electric signal and used as a working system and a standby system. Either may be used.

When an array waveguide diffraction grating type filter (AWG) is used as the band splitting means 20, the band splitting means is set so that the sum of the optical powers of the two band-divided optical duobinary components is maximized. 20. This is because, since the frequency interval (grid interval) at which the AWG is demultiplexed is fixed, it is impossible to control so that the difference between the optical powers of the two optical duobinary components is minimized. Therefore, when the AWG having a Grigg interval that matches the bit rate of the carrier-suppressed RZ-converted optical duobinary signal is used, the optical power of only one of the two optical duobinary components is monitored, and the value is maximized. May be controlled so that

(Seventh Embodiment) FIG. 13 shows a seventh embodiment of the optical communication apparatus of the present invention. The present embodiment is characterized in that a plurality of sets of the optical transmitter 1 and the optical receiver 2 of the present invention described above are provided for each transmission wavelength, and the carrier-suppressed RZ-converted optical duobinary signal of a plurality of wavelengths is wavelength-multiplexed and transmitted. I do. Thereby, the transmission capacity can be increased.

Each of the optical transmitters 1-1 to 1-n is composed of an optical duobinary signal generating means 70 and an optical modulating means 10 and has carrier suppression RZs of different wavelengths.
Generates a modified optical duobinary signal. The carrier-suppressed RZ-converted optical duobinary signal of each wavelength is multiplexed by the optical multiplexing means 4, transmitted through the optical transmission medium 3, and separated into the carrier-suppressed RZ-converted optical duobinary signal of each wavelength by the optical demultiplexing means 5. The waves are received by the corresponding optical receivers 2-1 to 2-n. The optical receivers 2-1 to 2-n include a band splitting unit 2
0 and the light receiving means 80c.

The optical receiving means 80c is configured to receive only one of the two optical duobinary components that are band-divided as in the first embodiment, and two optical duobinary components as in the third and fourth embodiments. Each of the components is converted into an electric signal and added and subtracted for identification. As in the fifth embodiment, the two optical duobinary components are each converted into an electric signal and used as a working system and a standby system. Good.

(Eighth Embodiment) FIG. 14 shows an eighth embodiment of the optical communication apparatus (optical transmitter) of the present invention. The optical transmitter 1 according to the present embodiment includes an optical band limiting unit 12 that suppresses an extra harmonic component generated when generating a carrier suppressed RZ-converted optical duobinary signal. The optical receiver 2 has any one of the configurations of the embodiments described above.

The effect of the present embodiment will be described with reference to FIG. In the optical modulator 10 of the optical transmitter 1, FIG.
As shown in (a), a harmonic component is generated when the carrier-suppressed RZ optical duobinary signal is generated. As the transmission band of the optical band limiting means 12 is adapted to the bandwidth of the carrier-suppressed RZ-converted optical duobinary signal as shown in FIG. Components can be effectively suppressed. As a result, it is possible to improve the band use efficiency in wavelength multiplexing.

In the wavelength division multiplexing transmission system according to the seventh embodiment, an array waveguide diffraction grating type filter (AWG) is used as the optical multiplexing means 4, and the transmission bandwidth is set to the optical band limiting means 12 of the present embodiment. By setting the same,
The harmonic components of the carrier suppressed RZ-converted optical duobinary signal of each wavelength can be suppressed collectively.

[0051]

As described above, in the optical communication apparatus according to the present invention, the carrier-suppressed RZ-converted optical duobinary signal for transmitting an optical transmission medium such as an optical fiber takes the form of an RZ pulse, and a nonlinear signal in the optical fiber. Waveform deterioration due to the optical effect can be minimized.

Also, by dividing the two optical duobinary components of the carrier-suppressed RZ-converted optical duobinary signal by the band dividing means of the optical receiver and extracting and receiving each individually, almost half of the optical duobinary signal is obtained. The band component close to the signal is affected by the chromatic dispersion of the optical transmission medium. Therefore, the waveform deterioration due to the chromatic dispersion of the optical transmission medium is reduced by almost 1 /
4 can be suppressed.

Further, as shown in FIG. 17, according to the present invention, a system having both the widest dispersion tolerance and the characteristic that the optimum value does not fluctuate with the fluctuation of the optical power at the incident light power at the practical level is constructed. Can be. That is, the optical communication apparatus of the present invention (optical transmitter and optical receiver)
Has strong characteristics against degradation of transmission quality due to the interaction between the nonlinear optical effect and chromatic dispersion of the optical transmission medium. Thereby, the conventional optical duobinary, NR
As compared with an optical communication device using a signal system such as Z or RZ, an optical transmission system having a longer distance, a larger capacity, and higher reliability can be quickly constructed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a configuration example of an optical transmitter 1.

FIG. 3 is a view for explaining the operation of the first embodiment;

FIG. 4 is a diagram illustrating the principle of generating a carrier-suppressed RZ-converted optical duobinary signal.

FIG. 5 is a diagram showing a second embodiment of the present invention.

FIG. 6 is a view for explaining a difference between the effects of the first embodiment and the second embodiment.

FIG. 7 is a diagram showing a third embodiment of the present invention.

FIG. 8 is a view for explaining the operation of the third embodiment.

FIG. 9 is a diagram showing a fourth embodiment of the present invention.

FIG. 10 is a view for explaining the operation of the fourth embodiment.

FIG. 11 is a diagram showing a fifth embodiment of the present invention.

FIG. 12 is a diagram showing a sixth embodiment of the present invention.

FIG. 13 is a view showing a seventh embodiment of the present invention.

FIG. 14 is a diagram showing an eighth embodiment of the present invention.

FIG. 15 is a view for explaining effects of the eighth embodiment.

FIG. 16 is a diagram showing a configuration of a conventional optical communication device using an optical duobinary transmission system.

FIG. 17 is a diagram showing a computer simulation result of dispersion proof stress.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 optical transmitter 2 optical receiver 3 optical transmission medium 4 optical multiplexing means 5 optical demultiplexing means 10 optical modulation means 11 Mach-Zehnder type optical modulator 12 optical band limiting means 20 band dividing means 21 optical branching means 22 optical power monitoring circuit 23 Control circuit 70 Optical duobinary signal generation means 71 Code conversion circuit 72 Inversion circuit 73 Amplitude adjustment circuit 74 Mach-Zehnder type optical modulator 75 Continuous light source 80 Light reception means 81 Optical detection circuit 82 Identification circuit 83 Inversion circuit 84 Addition circuit 85 Subtraction circuit

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04B 10/06 10/00 H04L 25/497 (72) Inventor Kazushige Yonaga 2-3 Otemachi, Chiyoda-ku, Tokyo No. 1 Inside Nippon Telegraph and Telephone Corporation (72) Inventor Noriyoshi Sato 2-3-1 Otemachi, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation (72) Inventor Hiroshi Toba Otemachi, Chiyoda-ku, Tokyo F-term (reference) in Nippon Telegraph and Telephone Co., Ltd. 3-1, 5K002 AA02 AA03 BA05 CA01 CA14 DA02 DA06 FA01 5K029 AA01 CC04 DD05 GG03 GG07 HH01

Claims (12)

[Claims] An optical duo-binary signal generating means for generating an optical duo-binary signal;
An optical modulation means for converting the signal into a Z-converted signal and converting it into a carrier-suppressed RZ-converted optical duobinary signal and transmitting the converted signal. 2. A carrier-suppressed RZ-converted optical duobinary signal transmitted from the optical transmitter according to claim 1,
An optical receiver comprising: a band splitter that splits and outputs two optical duobinary components in the spectrum component; and an optical receiver that receives one or both of the two optical duobinary components. vessel. 3. An optical duo-binary signal generating means for generating an optical duo-binary signal, and RZ by adding an alternating phase difference to the optical duo-binary signal to perform carrier suppression RZ.
An optical transmitter comprising optical modulation means for converting and transmitting the carrier-suppressed RZ-converted optical duobinary signal; and an optical transmission medium for transmitting the carrier-suppressed RZ-converted optical duobinary signal. A band splitting means for inputting, splitting and outputting two optical duobinary components in the spectrum component, and an optical receiver comprising optical receiving means for receiving one or both of the two optical duobinary components; An optical communication device comprising: 4. Carrier suppression R of transmission wavelengths different from each other
A plurality of optical transmitters according to claim 3 for generating a z-converted optical duo-binary signal; an optical multiplexing unit configured to multiplex and transmit the carrier-suppressed RZ-converted optical duo-binary signals of the plurality of wavelengths; An optical transmission medium that wavelength-multiplexes and transmits a carrier-suppressed RZ-converted optical duobinary signal of a wavelength, and a carrier-suppressed RZ-converted optical duobinary signal of a plurality of wavelengths transmitted through the optical transmission medium are input and separated into respective wavelengths. An optical communication device comprising: an optical demultiplexing unit that oscillates; and a plurality of optical receivers according to claim 3 that respectively receive a carrier-suppressed RZ-converted optical duobinary signal of each wavelength. 5. The optical transmitter according to claim 1, or the optical transmitter of the optical communication device according to claim 3, wherein the optical modulation unit sets a bit rate of the optical duobinary signal to Nbit / s. Then, a phase difference alternated at a frequency of mN / 2 Hz (m is a positive integer) is added to the optical duobinary signal, and the optical duobinary signal is converted into a carrier suppressed RZ-converted optical duobinary signal as an RZ pulse having a repetition frequency of mNHz. An optical transmitter, characterized in that: 6. The optical transmitter according to claim 1, or an optical transmitter of an optical communication apparatus according to claim 3, wherein a harmonic of a carrier-suppressed RZ-converted optical duobinary signal output from the optical modulation unit. An optical transmitter comprising an optical band limiting means for suppressing a wave component. 7. An optical communication apparatus according to claim 4, wherein said optical multiplexing means has a configuration including the function of the optical band limiting means according to claim 6. 8. The optical receiver according to claim 2, wherein the optical receiving unit is a photoelectric conversion unit having the same output polarity. An optical receiver, wherein each optical duobinary component is converted into an electric signal, and the electric signals are added and discriminated and reproduced. 9. The optical receiver according to claim 2, or the optical receiver of the optical communication device according to claim 3, wherein the optical receiving means is a photoelectric conversion means having output polarities different from each other. An optical receiver, wherein each of the optical duobinary components is converted into an electric signal, and the electric signal is subtracted and discriminated and reproduced. 10. The optical receiver according to claim 2, or the optical receiver of the optical communication device according to claim 3, wherein the optical receiving unit individually receives the two optical duobinary components. An optical receiver characterized in that one of them is a redundant system. 11. The optical receiver according to claim 2, or the optical receiver of the optical communication device according to claim 3, wherein the optical receiving unit is configured to control an optical power of one of the two optical duobinary components. , And controlling the band dividing means so that the optical power is maximized. 12. The optical receiver according to claim 2, or the optical receiver of the optical communication device according to claim 3, wherein the optical receiving means controls each optical power of the two optical duobinary components. An optical receiver which monitors and controls the band dividing means so that the sum of the two optical powers is maximum and the difference is minimum or zero.