JP3545673B2 - Optical communication device, optical transmitter and optical receiver - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical communication apparatus 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]
[Prior 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 interaction between the optical fiber and a nonlinear optical effect. This is caused by the fact that the group velocity dispersion of the optical fiber acts on the bandwidth of the optical signal, thereby distorting the optical pulse waveform and causing interference with adjacent time slots.
[0003]
In order to suppress the deterioration due to the group velocity dispersion, for example, an optical duobinary transmission method using an optical communication device shown in FIG. 16 has been proposed (Japanese Patent Laid-Open No. 9-236781).
[0004]
In FIG. 16, a binary data signal (binary signal) is input to a code conversion circuit 71 and converted into a ternary duobinary signal. This duobinary signal is branched into two, one of which is phase-inverted by an inverting circuit 72, band-limited by amplitude adjusting circuits 73-1 and 73-2, and a two-electrode type Mach-Zehnder light whose bias is minimized. The intensity modulator 74 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 discriminated and reproduced by an identification circuit 82, and the phase is inverted by an inversion circuit 83, so that binary data is obtained. The signal is restored.
[0005]
It has been reported that in such an optical duobinary transmission system, high resistance to chromatic dispersion of an optical fiber can be obtained (K. Yonnega et al., Electron. Lett., Vol. 31, pp. 302-). 304, 1995).
[0006]
[Problems to be solved by the invention]
However, in the conventional configuration, there is a problem that the dispersion tolerance decreases when the incident light power to 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 general NRZ and RZ code formats. Here, a contour line of 1 dB of eye opening deterioration when 100 km of a single mode fiber having a local dispersion of +2 ps / nm / km is transmitted for two spans via one optical amplifier is shown. In addition, the dispersion resistance when the present invention described later is used is also shown.
[0007]
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. And the dispersion tolerance as predicted from the respective bandwidths. The optimum dispersion value at this time is almost 0 ps / nm.
[0008]
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 was the optimum point in the low optical power region, is significantly degraded near 0 ps / nm. I do. The eye opening deterioration exceeds 1 dB when the incident light power exceeds 5 dBm.
[0009]
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 was the optimum point at low light power (0 dBm), is the end of the dispersion tolerance margin. The dispersion tolerance margin sharply disappears when the incident light power is further increased. This is because the 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.
[0010]
As described above, in the optical duobinary transmission system and the transmission system using the NRZ / RZ code format, the optimum point of the dispersion tolerance fluctuates in a wide incident light power range. This complicates the design of the optical transmission system and hinders quick introduction and stable operation. That is, in the design of the 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.
[0011]
When an optical transmission system is introduced, the dispersion value of an optical fiber transmission line is measured by a dispersion measuring device, and the dispersion value becomes an optimum dispersion value (generally 0 ps / nm, which is slightly shifted if a transmission signal is chirped). Set up 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.
[0012]
In both the optical duobinary transmission method and the transmission method using the NRZ / RZ code format, when the incident light power is increased, the dispersion tolerance is rapidly deteriorated. This is a problem that hinders stable operation of the optical transmission system.
[0013]
The present invention provides an optical communication device that 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 an optical transmission system, and realizes stable operation, and an optical device that constitutes the optical communication device. It is an object to provide a transmitter and an optical receiver.
[0014]
[Means for Solving the Problems]
An optical communication apparatus according to the present invention comprises: an optical duobinary signal generating means for generating an optical duobinary signal; RZ by adding an alternating phase difference to the optical duobinary signal; and converting the optical duobinary signal into a carrier suppressed RZ-converted optical duobinary signal. An optical transmitter comprising an optical modulating means for transmitting, an optical transmission medium for transmitting a carrier suppressed RZ optical duobinary signal, and a carrier suppressed RZ optical duobinary signal, and two lights in the spectrum components thereof are inputted. It comprises a band splitting means for splitting and outputting a duobinary component and an optical receiver comprising an optical receiving means for receiving one or both of two optical duobinary components.
[0015]
As a result, the carrier-suppressed RZ-converted optical duobinary signal transmitted through an optical transmission medium such as an optical fiber takes the form of an RZ pulse, and waveform deterioration due to the nonlinear optical effect in the optical fiber can be minimized. Also, the band splitting means of the optical receiver splits 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]
BEST MODE FOR CARRYING OUT THE INVENTION
(1st Embodiment)
FIG. 1 shows a first embodiment of the optical communication device (optical transmitter, optical receiver) of the present invention.
[0017]
In the figure, an optical communication apparatus according to the present invention includes an optical transmitter 1 for converting an optical duobinary signal into a carrier suppressed RZ-converted optical duobinary signal and transmitting the converted signal, and a carrier suppressed RZ-converted signal transmitted via an optical transmission medium 3. It is configured by an optical receiver 2 that receives an optical duobinary signal by band division.
[0018]
The optical transmitter 1 includes an optical duo-binary signal generating means 70 for generating an optical duo-binary signal as in the related art, an RZ by adding an alternating phase difference to the generated optical duo-binary signal, and carrier-suppressed RZ-converted optical duo. The light modulation unit 10 converts the light into a binary signal.
[0019]
As the optical transmission medium 3, a silica-based optical fiber such as a dispersion-shifted fiber (DSF) or a 1.3 μm band single mode fiber is used. Note that an optical fiber amplifier (optical repeater) may be included.
[0020]
The optical receiver 2 receives band splitting means 20 for separating two optical duobinary components in the spectral component of the transmitted carrier suppressed RZ-converted optical duobinary signal, and receives one or both of the two optical duobinary components. The light receiving unit 80 is used. The band splitting means 20 includes an optical band-pass filter composed of a dielectric multilayer film or the like, a Mach-Zehnder interferometer type optical filter formed on an optical fiber or an optical waveguide, and an arrayed waveguide grating filter (AWG) Etc. can be used. 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. Note that 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.
[0021]
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, an optical duobinary signal generation means 70 includes a code conversion circuit 71, a phase inversion circuit 72, amplitude adjustment circuits 73-1 and 73-2, a two-electrode Mach-Zehnder optical modulator 74, a continuous light A binary data signal (binary signal), which is composed of a light source 75 and is input as in the conventional configuration, is converted into a ternary duobinary signal by a code conversion circuit 71, and a Mach-Zehnder optical modulator 74 is further driven by push-pull. This generates an optical duobinary signal. The optical modulating means 10 comprises a two-electrode type Mach-Zehnder optical modulator 11, and 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. To generate a carrier-suppressed RZ optical duobinary signal.
[0022]
Hereinafter, the operation of the present embodiment will be described with reference to FIGS. The optical duobinary signal generating means 70 generates an optical duobinary signal having about half the band as compared with a normal NRZ code. FIG. 3A shows an optical waveform (eye pattern) obtained by computer simulation and an optical spectrum at that time.
[0023]
This optical duobinary signal is input to the optical modulation means 10 (Mach-Zehnder type optical modulator 11), and is modulated by push-pull driving with a synchronized clock signal (CLK), so that the carrier-suppressed RZ signal (carrier-suppressed RZ signal) is obtained. Optical duobinary signal). At this time, the drive point is set to a voltage at which the transmittance at the time of non-modulation is the minimum, and the frequency of the clock signal to be driven is set to half the bit rate of the optical duobinary signal generated in the previous stage. The driving amplitude is set to be 1 to 3 times Vπ of the Mach-Zehnder optical modulator 11. 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 situation is schematically shown in FIG.
[0024]
FIG. 4A shows an optical duo-binary signal output from the optical duo-binary signal generating means 70 in the preceding stage. The Mach-Zehnder type optical modulation is performed in accordance with the phase of the optical duo-binary signal as shown in FIG. The gate phase of the push-pull drive of the detector 11 is set. 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 optical duobinary signal.
[0025]
Here, the Mach-Zehnder optical modulator 11 is push-pull driven by a clock signal having a frequency half the bit rate of the input optical duobinary signal, and the obtained RZ pulse has a repetition frequency due to the folding characteristics of the optical modulator. Coincides with the bit rate of the input optical duobinary signal. The light waveform (eye pattern) and light spectrum obtained at this time are shown in FIG. This is a case where the driving 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. It is converted into an optical pulse having a duty ratio of about 2/3. 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.
[0026]
The carrier-suppressed RZ-converted optical duobinary signal transmitted through the optical transmission medium 3 is input to the band dividing means 20 of the optical receiver 2, and one of the two optical duobinary components is selected. The light waveform (eye pattern) and light spectrum obtained at this time are shown in FIG. By this band division, the optical waveform becomes almost 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 a high incident light power, a wide dispersion tolerance and a high tolerance to a nonlinear optical effect in which an optimum dispersion value is maintained near zero at all dispersion values are compatible. Can be. If the transmitted carrier-suppressed RZ 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.
[0027]
(Second configuration example of optical transmitter 1)
As shown in FIG. 2B, the optical transmitter 1 shown in FIG. 1 is an optical modulator 10 (Mach-Zehnder optical modulator 11) for performing continuous phase RZ conversion on continuous light output from a continuous light source 75 first. ) May be input to a Mach-Zehnder optical modulator 74 that converts the output light into an optical duobinary signal. That is, the Mach-Zehnder optical modulator 11 in the preceding stage is push-pull driven by the clock signal (CLK), and the Mach-Zehnder optical modulator 74 in the subsequent stage is pushed by the duobinary signal output from the amplitude adjusting circuits 73-1 and 73-2. Pull drive.
[0028]
In the case of this configuration, a two-mode oscillation mode-locked laser can be used instead of the continuous light source 75 and the light modulator 10 (Mach-Zehnder optical modulator 11). Thereby, the number of components is reduced, and a simpler optical transmitter 1 can be configured.
[0029]
(Second embodiment)
FIG. 5 shows a second embodiment of the optical communication device (optical transmitter) 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 generated clock signal (CLK) is different.
[0030]
In the first embodiment, the frequency of the clock signal (CLK) that drives the Mach-Zehnder optical modulator 11 that constitutes the optical modulator 10 is determined by the bit rate of the optical duobinary signal generated by the optical duobinary signal generator 70. And half. 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. It becomes.
[0031]
Generally, when the bit rate of the optical duobinary signal is N bit / s, the frequency of the clock signal for push-pull driving the Mach-Zehnder optical modulator 11 may be mN / 2 Hz (m is a positive integer). . The second embodiment shows a case where the Mach-Zehnder optical modulator 11 is push-pull driven by 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 NHz) as compared with the first embodiment. can do. Therefore, when each optical duobinary component is extracted by the band dividing means 20 of the optical receiver 2, a margin for the center frequency and the transmission width of the optical filter is increased, and the stable operation is facilitated.
[0032]
(Third embodiment)
FIG. 7 shows a third embodiment of the optical communication device (optical receiver) of the present invention. The configuration of the optical transmitter of the present embodiment is the same as that of the first embodiment or the second embodiment, but the configuration of the optical receiver is different.
[0033]
The optical receiver 2 of the present embodiment is characterized by including an optical receiving unit 80a that receives two optical duobinary components band-divided by the band dividing unit 20. The light receiving means 80a includes two light detection circuits 81-1 and 81-2, an addition circuit 84, an identification circuit 82, and an inversion circuit 83. The two photodetector circuits 81-1 and 81-2 use, for example, PIN type photodiodes and have the same output polarity. The electric signal is added by the adding circuit 84 and input to the identification circuit 82.
[0034]
The operation of the present 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. Is output. The two optical duobinary components are independently converted into electrical 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. The adding circuit 84 adds the two electric signals to increase the amplitude of the added signal as V1 + V2. As a result, the input amplitude to the identification circuit 82 increases, the operation margin increases, and a stable operation can be realized.
[0035]
(Fourth embodiment)
FIG. 9 shows a fourth embodiment of the optical communication device (optical receiver) of the present invention. The configuration of the optical transmitter of the present embodiment is the same as that of the first embodiment or the second embodiment, but the configuration of the optical receiver is different.
[0036]
The optical receiver 2 of the present embodiment includes an optical receiving unit 80b that receives two optical duobinary components that have been band-divided by the band dividing unit 20. The light receiving means 80b includes two light detection circuits 81-1 and 81-2, a subtraction circuit 85, an identification circuit 82, and an inversion circuit 83. The two photodetector circuits 81-1 and 81-2 use, for example, PIN type photodiodes and have different output polarities. In this configuration, the electric signal is subtracted by the subtraction circuit 85 and input to the identification circuit 82.
[0037]
Here, the operation of the present 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. Is output. The two optical duobinary components are independently converted into electrical 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 enters) and the other has a negative polarity (a negative potential when light enters). In the subtraction circuit 85, by subtracting the two electric signals, the amplitude of the subtraction signal can be increased to V1−V2. As a result, the input amplitude to the identification circuit 82 increases, the operation margin increases, and a stable operation can be realized.
[0038]
(Fifth embodiment)
FIG. 11 shows a fifth embodiment of the optical communication device (optical receiver) of the present invention. The configuration of the optical transmitter of the present embodiment is the same as that of the first embodiment or the second embodiment, but the configuration of the optical receiver is different.
[0039]
The optical receiver 2 of the present embodiment includes optical receiving units 80-1 and 80-2 that receive two optical duobinary components divided in band by the band dividing unit 20 in parallel, one of which is a working system and the other is a standby system. It is characterized by being used as a 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.
[0040]
The operation of each optical receiving unit of the present embodiment is the same as that of the optical receiver 2 of the first embodiment. The two optical duobinary components that have been band-divided by the band division unit 20 are respectively received by the optical reception units 80-1 and 80-2, so that even if one of the units fails, reception is continued by the other optical reception unit. And increase the stability and reliability of the system.
[0041]
(Sixth embodiment)
FIG. 12 shows a sixth embodiment of the optical communication device (optical receiver) of the present invention. The configuration of the optical transmitter of the present embodiment is the same as that of the first embodiment or the second embodiment, but the configuration of the optical receiver is different.
[0042]
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 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 is monitored by the optical power monitoring circuits 22-1 and 22-2. The measured value is 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 means 21-1, 21-2, an optical fiber coupler or a light beam splitter using a partially reflecting mirror is used. The optical power monitor circuits 22-1 and 22-2 are means for measuring optical power using a photoelectric conversion circuit or the like.
[0043]
Note that the optical receiving unit 80c is configured to receive only one of the two optical duobinary components that are band-divided as in the first embodiment, and that the two optical duobinary components are used as in the third and fourth embodiments. May be converted into an electric signal, and added and subtracted for identification. As in the fifth embodiment, two optical duobinary components may be respectively converted into electric signals and used as a working system and a standby system. .
[0044]
When an array waveguide diffraction grating filter (AWG) is used as the band dividing unit 20, the band dividing unit 20 is controlled so that the sum of the optical powers of the two band-divided optical duobinary components is maximized. Configuration. 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 becomes the maximum. May be controlled so that
[0045]
(Seventh embodiment)
FIG. 13 shows a seventh embodiment of the optical communication device 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 wavelength-division multiplex transmission of a carrier-suppressed RZ optical duobinary signal of a plurality of wavelengths is provided. I do. Thereby, the transmission capacity can be increased.
[0046]
Each of the optical transmitters 1-1 to 1-n includes an optical duobinary signal generation unit 70 and an optical modulation unit 10, and generates carrier suppressed RZ-converted optical duobinary signals having different wavelengths. The carrier-suppressed RZ-converted optical duobinary signal of each wavelength is multiplexed by the optical multiplexing unit 4, transmitted through the optical transmission medium 3, and separated by the optical demultiplexing unit 5 into the carrier-suppressed RZ-converted optical duobinary signal. The waves are received by the corresponding optical receivers 2-1 to 2-n. Each of the optical receivers 2-1 to 2-n includes a band dividing unit 20 and an optical receiving unit 80c.
[0047]
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 is configured to receive two optical duobinary components as in the third and fourth embodiments, respectively. Any of a configuration in which the optical duobinary component is converted into an electrical signal and added and subtracted for identification, and a configuration in which two optical duobinary components are respectively converted into electrical signals and used as a working system and a standby system as in the fifth embodiment may be used.
[0048]
(Eighth embodiment)
FIG. 14 shows an eighth embodiment of the optical communication device (optical transmitter) of the present invention. The optical transmitter 1 according to the present embodiment is characterized by including an optical band limiting unit 12 that suppresses excess harmonic components 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.
[0049]
The effect of the present embodiment will be described with reference to FIG. In the optical modulator 10 of the optical transmitter 1, a harmonic component is generated when generating the carrier-suppressed RZ-converted optical duobinary signal as shown in FIG. As the transmission band of the optical band limiting means 12, the one adapted to the bandwidth of the carrier-suppressed RZ-converted optical duobinary signal as shown in FIG. The components can be effectively suppressed. As a result, it is possible to improve band use efficiency in wavelength multiplexing.
[0050]
In the wavelength division multiplexing transmission system of the seventh embodiment, an array waveguide diffraction grating type filter (AWG) is used as the optical multiplexing means 4 and its transmission bandwidth is set to be equal to that of the optical band limiting means 12 of the present embodiment. By doing so, it is possible to collectively suppress the harmonic components of the carrier-suppressed RZ-converted optical duobinary signal of each wavelength.
[0051]
【The invention's effect】
As described above, in the optical communication device according to the present invention, the carrier suppressed RZ-converted optical duobinary signal transmitted through an optical transmission medium such as an optical fiber takes the form of an RZ pulse, and the waveform degradation due to the nonlinear optical effect in the optical fiber. Can be minimized.
[0052]
In addition, 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, the optical duobinary signal is almost half of the optical duobinary signal. The band component is 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.
[0053]
Further, as shown in FIG. 17, the present invention makes it possible to configure a system having the widest dispersion tolerance and the characteristic that the optimum value does not change with respect to the fluctuation of the optical power at the incident light power at the practical level. In other words, the optical communication device (optical transmitter and optical receiver) of the present invention can have strong characteristics against degradation of transmission quality due to the interaction between the nonlinear optical effect and the chromatic dispersion of the optical transmission medium. This makes it possible to quickly build a longer-distance, larger-capacity, and more reliable optical transmission system as compared to an optical communication device using a conventional signal system such as optical duobinary, NRZ, or RZ.
[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 view for explaining 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 the 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 diagram illustrating 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 diagram 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 strength.
[Explanation of symbols]
1 Optical transmitter
2 Optical receiver
3 Optical transmission media
4 Optical multiplexing means
5 Optical demultiplexing means
10 Light modulation means
11 Mach-Zehnder optical modulator
12 Optical band limiting means
20 Band splitting means
21 Optical branching means
22 Optical power monitor circuit
23 Control circuit
70 Optical duobinary signal generation means
71 Code conversion circuit
72 Inverting circuit
73 Amplitude adjustment circuit
74 Mach-Zehnder optical modulator
75 continuous light source
80 Optical receiving means
81 Optical Detection Circuit
82 Identification Circuit
83 Inverting circuit
84 Addition circuit
85 Subtraction circuit

Claims (10)

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 optical duobinary signal, and transmitting the same. Optical transmitter,
A band splitting means for receiving the carrier-suppressed RZ-converted optical duobinary signal and dividing and outputting two optical duobinary components in the spectrum component; and a light receiving one or both of the two optical duobinary components. An optical communication device comprising: an optical receiver configured by receiving means. A plurality of optical transmitters according to claim 1, which generate carrier-suppressed RZ-converted optical duobinary signals having different transmission wavelengths;
Optical multiplexing means for multiplexing and transmitting the carrier-suppressed RZ-converted optical duobinary signals of the plurality of wavelengths;
Optical demultiplexing means for receiving the carrier-suppressed RZ optical duobinary signal of a plurality of wavelengths transmitted from the optical multiplexing means, and demultiplexing each of the wavelengths;
An optical communication device comprising: a plurality of optical receivers according to claim 1, each receiving a carrier-suppressed RZ-converted optical duobinary signal of each wavelength. The optical transmitter of the optical communication device according to claim 1 or 2,
When the bit rate of the optical duobinary signal is Nbit / s, the optical modulation means adds a phase difference alternated at a frequency of mN / 2 Hz (m is a positive integer) to the optical duobinary signal, An optical transmitter characterized in that it is configured to convert into a carrier-suppressed RZ-converted optical duobinary signal that is converted into an mNHz RZ pulse. The optical transmitter of the optical communication device according to claim 1 or 2,
An optical transmitter comprising: an optical band limiting unit that suppresses a harmonic component of a carrier-suppressed RZ-converted optical duobinary signal output from the optical modulation unit. The optical communication device according to claim 2,
The optical communication apparatus according to claim 1, wherein the optical multiplexing means has a function of an optical band limiting means for suppressing a harmonic component of the carrier-suppressed RZ optical duobinary signal output from the optical modulation means . The optical receiver of the optical communication device according to claim 1 or 2,
The light receiving means converts the two optical duobinary components into electric signals by photoelectric conversion means having the same output polarity, adds the electric signals, and performs discrimination reproduction. Receiver. The optical receiver of the optical communication device according to claim 1 or 2,
The light receiving means converts the two optical duobinary components into electric signals by photoelectric conversion means having mutually different output polarities, and subtracts the electric signals to perform identification reproduction. Receiver. The optical receiver of the optical communication device according to claim 1 or 2,
The optical receiver, wherein the optical receiving means is configured to individually receive the two optical duobinary components, and one of them is a redundant system. The optical receiver of the optical communication device according to claim 1 or 2,
The optical receiver according to claim 1, wherein the optical receiving unit monitors one optical power of the two optical duobinary components and controls the band dividing unit so that the optical power becomes maximum. The optical receiver of the optical communication device according to claim 1 or 2,
The optical receiving unit monitors each optical power of the two optical duobinary components, and controls the band dividing unit such that the sum of the two optical powers is maximum and the difference is minimum or zero. An optical receiver having a configuration.

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