JP3510995B2 - Optical transmission method and optical transmission device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmission method and an optical transmission device for performing one wavelength or wavelength division multiplexing, and particularly to a technique effective when applied to an optical transmission device for modulating an optical signal using a partial response code. It is about.

[0002]

2. Description of the Related Art Conventionally, in an optical fiber communication system, various modulation codes for improving the tolerance against the waveform distortion due to the wavelength dispersion of the optical fiber and reducing the waveform distortion due to the optical nonlinear effect in the optical fiber transmission line have been used. Proposed.

For example, as a technique for improving the chromatic dispersion tolerance, reference 1 (K.Yonenaga et al. "Dispersion-
tolerant optical transmission system using duobina
ry transmitter and binary receiver ", J. Lightwave T
echnol. LT-15, (8), pp.1530-1537, (1997)) uses a duobinary signal, which is one of the ternary partial response codes, as a modulation signal.
ull) type Mach-Zehnder (MZ) intensity modulator (hereinafter,
An optical duobinary modulation means for modulation by means of a MZ intensity modulator) is disclosed.

As shown in FIG. 22, the transmitter of the conventional optical transmission device using the optical duobinary modulation means has a binary NRZ (non return to ze) synchronized with the system clock source 2.
ro) It has a duobinary encoding means 6 which inputs the binary NRZ signal from the digital signal source 5 and outputs an electric duobinary code. As shown in FIG. 23 (a),
Binary NR generated by the binary NRZ digital signal source 5
The Z signal P3 is an electric partial response encoding means 6
In the logic inverting circuit 62 of FIG.
After being logically inverted to the RZ signal P4, it is encoded by the precoder 61 composed of an exclusive OR circuit (EX-OR) 63 and a 1-bit delay circuit (that is, a 1-time-slot delay device for data of the transmission rate B) 64. After the conversion, the differential converter 65 outputs a difference between the binary NRZ precoder output signal P5a as shown in FIG. 23 (c) and the 1-bit delayed precoder output signal P5b as shown in FIG. 23 (d). Output. 23. The binary NRZ precoder output signal P5a and the 1-bit delayed precoder output signal P5b are amplified by an amplifier circuit 66, and then input to a low pass filter (LPF) 67 having a 3 dB band of B / 4.
A three-valued complementary duobinary signal P6 as shown in (e) is obtained. The logical equivalent circuit of the low pass filter (LPF) 67 is a 1-bit delay circuit 67A and an adder 6
It is equivalent to a precoder composed of 7B.

In the optical modulator 7, the push-pull (push-p
(f) by the MZ intensity modulator 71 having the (ull) configuration.
The single mode optical signal P1 output from the continuous wave (CW) laser light source 42 as shown in FIG. 24 is modulated according to the ternary complementary duobinary signal P6, and the optical duobinary signal as shown in FIG. Converted to P7.

[0006] Document 1 discloses that the chromatic dispersion tolerance can be doubled as compared with the conventional NRZ signal by using the configuration shown in FIG.

Reference 2 (A. Matsuura et al. "High-
speed transmission system basedon optical modified
duobinary signals ". Electron. Lett. Vol.35, No.9, p
p.1-2,1999) discloses an optical partial response modulation means in the case of using a modified duobinary signal which is one of ternary partial response codes as a modulation signal, and similarly, a conventional NRZ code. The chromatic dispersion tolerance is doubled as compared with the above.

On the other hand, in order to reduce the influence of waveform distortion due to the nonlinear effect, RZ (return t) with a constant pulse width is used.
It is effective to use a zero signal. Reference 3 (K.Sa
to et al. "Frequency Range Extension of actively m
ode-locked lasers integrated with electroabsorptio
n modulators using chirped grating "J.of selectedto
pics in quantum electronics vol.3, No.2,1997, pp.250
-255) technology using a mode-locked laser, Reference 4
(M.Suzuki, et al. New application of sinusoidal dr
iven InGaAsP electroabsorption modulator to in-lin
e optical gatewith ASE noise resuction effect, JL
ightwave Technol., 1992, vol.10, pp.1912-1928), a technique using an absorption type semiconductor modulator, and reference 5 a technique using a gain switch of a semiconductor laser (K. Iwatsuki et al. Ge.
neration of transform limited gain-switched DFB-LD
pulses <6ps with linear fiber compression and spec
tral window, Electronics Letters vol.27, pp1981-198
2, 1991) is disclosed. None of the above-mentioned Documents 3 to 5 discloses the data conversion code of the RZ pulse train.

On the other hand, as a means for generating a pulse train by a 2-mode beat, reference 6 (D. Wake et al. "Optical genera
tion of millimeter-wave signals for fiber-radio sy
stems using a dual-mode DFB semiconductor laser ", I
EEE Trna. Microwave Theory Tech., Vol.43, pp.2270-22
76, 1995), a technique for generating two-mode beat pulse signals by synchronizing two single longitudinal mode lasers, Reference 7
(Kenshi Sato et al., 2 of 60 GHz mode-locked semiconductor laser
Mode operation, 1999 IEICE Electronics Society Conference C-4-8), a technique for generating a two-mode beat pulse signal using a semiconductor mode-locked laser, Reference 8 (Y. Miyamoto et al. "320 Gbit / s"). (8x
40Gbit / s) WDM transmission over 367km with 120km re
pearter spacing using carrier-suppressed reterntoz
ero format ", Electron. Lett., Vol.35, No.23, pp.204
1-2042, 1999) discloses a technique for generating a bimodal beat pulse signal using an LN modulator. Documents 6 and 7 do not show the use of a baseband signal as a modulation signal. Further, Document 8 discloses that an NRZ signal synchronized with the beat frequency B is used.

[0010]

However, in the above-mentioned conventional technique, when a binary optical partial response modulation signal such as an optical duobinary signal or an optical modified duobinary signal is used, the input binary NRZ signal is The same sign continuity occurs in the optical modulation signal depending on the pattern, and the pulse width of the optical modulation signal is not constant. Therefore, when the optical input power in the optical fiber becomes high,
Due to the interaction between the self-phase modulation effect and the chromatic dispersion, the waveform distortion becomes remarkable, and there is a problem that the tolerance characteristic for the chromatic dispersion is deteriorated in the case of a high in-fiber input.

When wavelength dispersion equalization of an optical fiber transmission line is performed, generally, a dispersion medium having a dispersion opposite to that of the transmission line is arranged inside the receiver or inside the optical amplification repeater, and the total dispersion D is zero (0 ), Dispersion compensation is easy. This is a condition that is easy to measure even when measuring the dispersion of the optical fiber transmission line. However, in the conventional binary optical partial response modulation signal, the optimum total dispersion value D generally shifts to the abnormal dispersion (D> 0) region. Therefore, if dispersion compensation is simply performed with D = 0 and dispersion compensation is performed, the optimum value of dispersion compensation is deviated, which causes a large intersymbol interference due to wavelength dispersion in the receiving device, resulting in deterioration of reception sensitivity. was there.

Further, in the conventional binary optical partial response modulation signal, the initial intersymbol interference of the modulation waveform is caused by the conventional NR.
Since it is larger than the Z signal, there is a problem that the receiving sensitivity is likely to deteriorate in the same binary receiving circuit as the NRZ signal.

On the contrary, when a conventional optical pulse train having a constant pulse width is modulated with a partial response code for the purpose of improving the waveform deterioration due to the optical nonlinear effect and suppressing the intersymbol interference of the initial modulation waveform, the partial response signal causes There is a problem that the chromatic dispersion tolerance is significantly impaired.

On the other hand, in the conventional RZ modulation method (references 4, 5, and 6), the optical phases of all the pulses are in-phase, as shown in FIG. In the Fourier transform, as shown in FIG. 25 (e), a mode of the clock component occurs at a position separated by the transmission speed B on both sides of the carrier component with the carrier f ₀ as the center. When these three modes are modulated with normal NRZ code,
Each mode is modulated by the NRZ signal having a bandwidth of 2B, and the total bandwidth becomes 4B as shown in FIG.

That is, since the occupied bandwidth of the optical modulation spectrum of the pulse train is as wide as 3B to 4B (B is the transmission speed) or more, it is easily affected by chromatic dispersion and dispersion slope, and the transmission distance is limited when the transmission speed is increased. Easy to be affected. Further, when considering a wavelength multiplexing system, if the occupied band of the optical modulation spectrum is wide, the number of wavelength channels that can be multiplexed in a certain optical amplification band of the optical amplifier used in the wavelength multiplexing system is small, and the frequency utilization efficiency is reduced. descend.
Therefore, there is a problem that the total transmission capacity of the wavelength division multiplexing system is reduced.

Further, the technique of generating the two-mode beat pulse signal of the above-mentioned document 7 has a problem that it is difficult to realize optical frequency synchronization of two longitudinal modes and lacks stability. Although a bimodal beat pulse signal is disclosed in Document 8 as well, the modulated data signals are all conventional N
Only the RZ code is disclosed, and in each case, a bright line spectrum occurs in the optical spectrum at an interval equal to the transmission rate B. As a result, the input in the optical fiber is a threshold for stimulated Brillouin scattering (1.
If the wavelength exceeds 5 m and exceeds several mW, the light is back-scattered to the input side, and the input power in the fiber that can be input from the transmitter to the optical fiber transmission line is significantly limited. To solve this problem, an additional circuit for expanding the line width of the optical carrier signal has been conventionally required.

An object of the present invention is to provide a technique capable of expanding wavelength tolerance, simplifying dispersion compensation, and relaxing the input power limitation in a fiber in an optical transmission device using a partial response code.

The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

[0019]

Among the inventions disclosed in the present application, a brief description will be given to the outline of typical ones.
It is as follows.

(1) An optical transmission method of modulating a longitudinal mode optical signal based on a partial response signal and outputting the modulated signal, wherein a single mode optical signal is modulated by using a clock signal from a system clock source as an input, Interval is n × B
(N is a natural number, B is a transmission speed), two vertical mode pulsed optical signals are generated, and a binary NRZ signal from a digital signal source synchronized with the system clock source is code-converted to generate a partial response signal. Then, a binary RZ modulation signal obtained by modulating the pulsed optical signals in the two longitudinal modes based on the partial response signal is output.

(2) An optical transmission method of modulating a longitudinal mode optical signal based on a partial response signal and outputting the modulated signal, wherein a single mode optical signal is modulated by using a clock signal from a system clock source as an input, and a frequency is generated. Interval is n × B
(N is a natural number, B is a transmission speed), two vertical mode pulsed optical signals are generated, and a binary NRZ signal from a digital signal source synchronized with the system clock source is code-converted to generate a partial response signal. Then, based on the partial response signal, a binary RZ-modulated signal obtained by modulating the pulse light signals in the two longitudinal modes is generated, and the generated harmonic binary component of the generated binary RZ-modulated signal is removed and then output.

(3) In the optical transmission method of (1) or (2), a duobinary signal is used as the partial response signal.

(4) In the optical transmission method of (1) or (2), a modified duobinary signal is used as the partial response signal.

(5) A system clock source for generating a clock signal, a binary NRZ digital signal source for generating a binary NRZ digital signal in synchronization with the clock signal,
An electrical partial response encoding means for generating an electrical partial response signal by inputting the binary NRZ digital signal, an optical transmitter having an optical modulator means for modulating an optical signal based on the electrical partial response signal, and the optical transmission. In an optical transmission device including an optical reception unit that receives an optical signal transmitted from a transmission unit, the optical transmission unit has two longitudinal modes separated by an optical frequency interval n × B (n is a natural number, B is a transmission speed). Bi-mode beat light pulse generation means for generating a pulsed light signal, and binary NRZ of transmission speed B
Pulsed light source driving means for generating a signal for driving the two-mode beat light pulse generating means from a clock signal synchronized with an input signal.

(6) In the optical transmission device of (5) above,
An MZ intensity modulator is used as the two-mode beat light pulse generating means.

(7) In the optical transmission device of (5) above,
A two-mode oscillation mode-locked laser is used as the two-mode beat light pulse generating means.

(8) In the optical transmission device of (5) above,
The two-mode beat light pulse generation means has an optical filter for removing harmonic components of the two longitudinal mode light pulse signals.

(9) In the optical transmission device of (8) above,
A large number of the generated signals are wavelength-multiplexed using an array grating filter for wavelength multiplexing as the optical filter means.

(10) In the optical transmission device of (8) or (9), a push-pull is further used as the two-mode beat optical pulse generating means, and the amplitude is the push-pull MZ intensity modulator. It is driven by a frequency clock signal of nB / 2 equal to the half-wave voltage of.

(11) A system clock source for generating a clock signal, and a binary NR in synchronization with the clock signal.
A binary NRZ digital signal source for generating a Z digital signal, an electrical partial response encoding means for generating an electrical partial response signal by inputting the binary NRZ digital signal, and an optical signal modulated based on the electrical partial response signal. In an optical transmission device including an optical transmission unit having an optical modulation unit that performs, and an optical reception unit that receives an optical signal transmitted from the optical transmission unit, the optical transmission unit includes:
Two-mode beat optical pulse generating means for generating two longitudinal mode pulse optical signals separated by an optical frequency interval n × B (n is a natural number, B is a transmission rate), and a binary NR of the transmission rate B
A pulse light source driving means for generating a signal for driving the two-mode beat optical pulse generating means from a clock signal synchronized with the Z input signal, and an optical filter means for removing a harmonic component of the optical signal modulated by the optical modulating means. It is equipped with.

Hereinafter, the present invention will be described in detail with reference to the drawings together with the embodiments (embodiments).

In all the drawings for explaining the embodiments, parts having the same function are designated by the same reference numerals and their repeated description will be omitted.

[0033]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a block diagram showing a schematic configuration of an optical transmission apparatus of the present invention. 1 is an optical transmitter, 2 is a system clock source, 3 is a pulse light source driving means, and 4 is a two-mode beat. Pulse generation means, 5 is a binary NRZ digital signal source, 6 is an electrical partial response encoding means, 7 is an optical modulation means, 8 is an optical filter means, and 9 is an optical receiving section.

The optical transmission apparatus of the present invention, as shown in FIG. 1, includes an optical transmitter 1 for transmitting an optical signal modulated by using an electrical partial response code, and an optical signal transmitted from the optical transmitter 1. It is composed of a light receiving unit 9 for receiving.

Pulse light source driving means 3 of the optical transmitter 1
Receives a clock signal of the binary NRZ digital signal source 5 synchronized with the system clock source 2 and generates and outputs a driving clock signal for driving the 2-mode beat pulse generating means 4. The two-mode beat pulse generation means 4 receives the drive clock signal as an input and generates two longitudinal mode optical signals separated by a transmission speed B to generate the binary NRZ signal.
A two-mode beat pulse optical signal having a repetition frequency n × B (n is a natural number, B is a transmission speed) synchronized with the binary NRZ signal generated by the digital signal source 5 is output.

The electrical partial response encoding means 6 converts the binary NRZ signal generated by the binary NRZ digital signal source 5 into an electrical partial response signal. In the optical modulator 7, the two-mode beat pulse optical signal input from the two-mode beat pulse generator 4 is
2 according to the electric partial response signal
A value light modulated signal is generated.

The optical filter means 8 removes only the harmonic component when a harmonic is generated in the optical modulation spectrum of the two-mode beat optical pulse train signal. The optical filter means 8 may also have a wavelength multiplexing function.

The configuration and operation of the optical transmitter 1 shown in FIG. 1 will be specifically described below.

(Embodiment 1) FIG. 2 is a block diagram showing a schematic configuration of an optical transmission unit in an optical transmission apparatus of Embodiment 1 according to the present invention, 2 is a system clock source, 3 is a pulse light source driving means, 31 Is a 1/2 (1/2) frequency divider, 32
Is a drive circuit, 4 is a 2-mode beat pulse generating means, 41
Is Mach-Zehnder (MZ) intensity modulator, 42 is continuous oscillation
(CW) laser light source, 5 is a binary NRZ digital signal source, 6
Is an electric partial response encoding means, 61 is a precoder, 62 is a logical inversion circuit, 63 is an exclusive OR circuit (EX-OR), 64 is a 1-bit delay circuit, 65 is a differential converter, 66 is an amplifier circuit, 67 is a low-pass filter (L
PF), 67A is a 1-bit delay circuit, 67B is an adder,
Reference numeral 7 is an optical modulator, 71 is a Mach-Zehnder (MZ) intensity modulator, 8 is an optical filter, 81 is an optical amplifier, and 82 is an optical bandpass filter. Further, P1 is a single-mode optical signal, P2 is a 2-mode beat pulse optical signal, and P3 is a binary N.
RZ signal, P4 is an inverted NRZ signal, P5 is a binary NRZ precoder differential output signal, P6 is an electrical duobinary signal, and P7 and P8 are binary RZ modulated signals (optical duobinary signals).

3 to 6 are diagrams for explaining the operation of the optical transmission section of the optical transmission device of the first embodiment.

The operation of the optical transmitter of the first embodiment shown in FIG. 2 will be described below with reference to FIGS. 3 to 6. Example 1
In the optical transmission section, the duobinary code is used as the electrical partial response code, the MZ intensity modulator 41 is used as the two-mode beat pulse generating means 4, and the frequency interval between the two longitudinal modes is equal to the transmission rate B.

First, the clock signal of frequency B (B is equal to the transmission rate) generated by the system clock source 2 is input to the 1/2 frequency dividing circuit 31 of the pulse light source driving means 3.
The 1/2 frequency dividing circuit 31 generates a 1/2 frequency divided signal having a frequency f / 2. The 1/2 frequency-divided signal is amplified to a half-wave voltage Vp of the MZ intensity modulator in the drive circuit 32 and then differentially output to the 2-mode beat pulse generation means 4.

In the two-mode beat pulse generation means 4, the continuous oscillation (CW) laser light source 42 is used, as shown in FIG.
Optical carrier frequency f as shown in (a) and FIG. 3 (b)
The single-mode optical signal P1 of _0, the MZ intensity modulator 41 DC biased push-pull (push-pull) adapted transmission characteristic becomes zero, is the differential output from the pulsed light source driving means 3 A two-mode beat pulse optical signal P2 is generated, which is modulated in accordance with the ½ frequency-divided signal and has a frequency interval B apart as shown in FIGS. 3 (c), 3 (d), and 3 (e). To do.

Here, FIG. 3 (c) is a time waveform of the two-mode beat pulse optical signal P2, and FIG. 3 (d) is FIG. 3 (c).
The direct detection waveform of Fig. 3 (e) is an optical spectrum. As shown in FIG. 3C, the two-mode beat pulse optical signal P2 is an optical pulse train having a repetition frequency B in which the optical phase is inverted by π for each bit. When this signal is Fourier-transformed, as shown in FIG. 3 (e), two longitudinal modes a and b whose frequency difference is equal to the transmission rate B are detected at the optical frequency f ₀ −.
B / 2, and the optical frequency f ₀ + B / 2.

On the other hand, the electrical partial response encoding means 6 is a binary NR synchronized with the system clock source 2.
A duobinary encoding circuit that inputs a binary NRZ signal from the Z digital signal source 5 and outputs an electric duobinary code is configured. Binary NRZ input from the binary NRZ digital signal source 5 as shown in FIG.
The signal P3 is logically inverted by the logical inversion circuit 62 as the inverted NRZ signal P4 shown in FIG. 4 (g), and then the exclusive OR circuit (EX-OR) 63 and the 1-bit delay circuit (that is, the transmission speed B Data is converted into a binary NRZ precoder output signal from the precoder 61. After being code-converted by the precoder 61, a difference between the binary NRZ precoder output signal P5a shown in FIG. 4 (h) and the precoder output signal P5b delayed by 1 bit shown in FIG. 4 (i) is obtained by the differential converter 65. Output. The binary NRZ precoder differential output signal P5 output from the differential converter 65 is amplified by an amplifier circuit 66, and then input to a low pass filter (LPF) 67 having a 3 dB band of B / 4. A ternary complementary electrical duobinary signal P6 as shown in FIG. 4 (j) is obtained. The logical equivalent circuit of the low pass filter (LPF) 67 is
It is equivalent to a precoder composed of a 1-bit delay circuit 67A and an adder 67B, and is equivalent to a sum of the binary NRZ precoder output signal P5a and a binary NRZ precoder output signal P5b obtained by delaying the binary NRZ precoder output signal P5a by 1 bit. I know there is.

In the light modulation means 7, the push-pull (push-p
null mode MZ intensity modulator 71 modulates the two-mode beat pulse optical signal P2 in accordance with the three-valued complementary electrical duobinary signal P6 into a binary RZ-modulated signal P7 shown in FIG. To be converted.

Since the two longitudinal modes generated by the two-mode beat pulse generating means 4 are duobinary-modulated by the optical modulating means 7, the optical frequency f ₀ -B / 2 and the optical frequency of FIG. The emission line spectrum of f ₀ + B / 2 disappears, and two duobinary signal spectra of bandwidth B occur around the optical frequencies f ₀ -B / 2 and f ₀ + B / 2 as shown in FIG. 5 (m). , 2B for the entire signal band
Becomes When this signal is viewed again in the time domain, the two optical duobinary signals interfere with each other, resulting in an RZ waveform as shown in FIG. 5 (k).

In the conventional optical pulse signal as shown in FIGS. 25 and 26, unlike the first embodiment, the optical phases of all the pulses are the same. Therefore, in the conventional Fourier transform of the optical pulse train signal, a mode of the clock component occurs at a position separated by the transmission speed B on both sides of the carrier component around the carrier f ₀ as shown in FIG. This 3
When one mode was modulated with a normal NRZ code, each mode was modulated with an NRZ signal with a bandwidth of 2B, resulting in a total bandwidth of 4B.

That is, the occupied band of the RZ signal light modulation spectrum generated by the optical transmitter of the first embodiment is the conventional R band.
The signal band can be halved as compared with the Z code.

As can be seen from FIG. 5 (k), the time waveform of the binary RZ modulation signal P7 is an RZ signal in which the electric field intensity (light intensity) becomes 0 for each time slot. In the first embodiment, since each of the two longitudinal modes a and b shown in FIG. 3E is subjected to optical duobinary modulation, the emission line spectra of the optical frequencies f ₀ -B / 2 and f ₀ + B / 2. Disappears and there is no bright line spectrum with high spectral density in the light modulation spectrum. As a result, at the same average input power in the optical fiber, the influence of stimulated Brillouin scattering can be reduced to 3 dB because the spectral density is 1/2 of that of the conventional optical duobinary code.

In the case of using the MZ intensity modulator, in order to obtain the output power of the MZ intensity modulator 71, if the modulation degree is set to about 100% and each drive amplitude is made equal to the half-wave voltage, the MZ intensity modulation is performed. Due to the non-linearity of the response characteristics of the device, harmonics may occur in the two-mode beat pulse optical signal P2 as shown in FIGS. 6 (b) and 6 (c). In that case, an optical bandpass filter 82 having a transmission characteristic centered on the optical frequency f ₀ is used as shown in FIG.
The harmonic components are removed as shown in FIG. At this time, an optical amplifier 81 is arranged at the output of the optical modulation means 7 to amplify it, and then the output port of the optical modulation means 7, or the output port of the two-mode beat pulse generation means 4 and the input port of the optical modulation means 7. The optical bandpass filter 82 may be inserted in either or both of the two.

FIG. 7 and FIG. 8 are diagrams for explaining the operation and effect of the optical transmission apparatus of the first embodiment, and show the fiber input power dependence of the chromatic dispersion tolerance that allows 1 dB of eye opening deterioration of the optical modulation signal. The results of computer simulation are shown in comparison with the conventional optical duobinary code. The transmission fiber used in the simulation is shown in Fig. 7.
As shown in Fig. 2, 200k obtained by directly amplifying and amplifying 100km of dispersion-shifted fiber (DSF) with 1.55μm zero dispersion
m fiber transmission path was used, and the condition was set to perform dispersion compensation with the dispersion compensation fiber DCF in each section. The power P ₀ of each repeater 10 was changed at the same time. The transmission speed is 40G
The line loss is 0.2 dB / km, and the dispersion value is +2 ps / nm / km.

FIG. 8 shows the dependence of the chromatic dispersion tolerance on the repeater power output when the total dispersion amount of the optical transmission line (DSF) and the dispersion compensating fiber (DCF) is changed by changing the DCF on the horizontal axis. 8A shows the case of the binary RZ modulated signal P7 of the first embodiment, FIG. 8B shows the case of the conventional NRZ signal, and FIG. 8C shows the case of the conventional RZ signal. ) Indicates the case of a conventional optical duobinary signal. Figure 8
As can be seen from the above, the fiber input power P ₀ is 0 dBm
Under the condition that the degree of optical nonlinearity is negligible, FIG.
The chromatic dispersion tolerance of the binary RZ modulation signal in (a) is 12
8 ps / nm, which is equivalent to the conventional NRZ code (135 ps / nm) of FIG. 8 (b), about twice that of the conventional RZ code (55 ps / nm) of FIG. 8 (c), and FIG. ) 1 of conventional optical duobinary code (460 ps / nm)
A wavelength dispersion tolerance of about / 4 can be realized.

Further, the power P ₀ of the fiber input to the repeater 10 at which the optical nonlinear effect in the optical fiber becomes noticeable is 8
In the region of dBm or more, the wide dispersion tolerance of the duobinary code deteriorates rapidly as shown in FIG. 8, and the optimum dispersion compensation value shifts to the abnormal dispersion region. The fiber input power Pd (indicated by a circle in the figure) that allows a penalty of 1 dB in the zero-dispersion region where dispersion compensation is easy to perform is 6.2 dBm in the conventional NRZ code of FIG. The RZ code is severely limited to 8.2 dBm and the conventional optical duobinary signal shown in FIG. 8D is strictly limited to 5.8 dBm.
On the other hand, the binary RZ modulation signal P7 of the first embodiment shown in FIG. 8 (a) is +12 dBm or more, and the tolerance of the fiber input power Pd is expanded.

The binary RZ modulation code of the first embodiment is
As shown in FIG. 8A, the power P ₀ of the repeater 10 is 8
The dispersion tolerance does not change significantly up to about dBm,
Since the shift does not occur in the abnormal dispersion region where the optimum dispersion compensation value is D> 0, the dispersion compensation design becomes easy.

Consider, for example, the case of performing dispersion compensation design of a system that outputs high output repeater power up to 8 dBm. In the conventional code, it is necessary to design the dispersion compensation amount under the condition that the optimum total dispersion amount is D ≠ 0. At this time, the optimum D changes depending on the loss condition of each transmission line and the dispersion value. It is difficult to measure and determine this value with a conventional dispersion measuring instrument.

On the other hand, the binary RZ modulation signal P7 of the first embodiment.
If the dispersion compensation amount is used, the dispersion compensation amount may be designed so that the total dispersion amount D = 0 in the region where the optical nonlinear effect does not occur at the repeater power of 0 dBm or less. That is, the dispersion amount of the transmission line (DSF in this case) is measured with the conventional dispersion measuring device, and the DCF
The DCF dispersion amount may be determined so that the total dispersion amount including D becomes 0. As a result, the fiber input power Pd that allows a penalty of 1 dB is expanded to +8 dBm or more, and at the same time, a wide dispersion tolerance of 100 ps / nm or more is obtained, and an optical repeater transmission system with high repeater power that does not reduce the SN ratio of the entire system. Can be realized with an easy dispersion compensation design.

As described above, according to the first embodiment, a single-mode optical signal is modulated into a two-mode beat pulse optical signal having a frequency interval B and then modulated with an electric duobinary signal to obtain a wavelength. It is possible to provide an optical transmission device that has a wide dispersion tolerance, is easily designed for dispersion compensation, and relaxes the limitation on the input power in the fiber.

(Embodiment 2) FIG. 9 is a block diagram showing a schematic structure of an optical transmission section in an optical transmission apparatus of Embodiment 2 according to the present invention, in which 33 is a drive circuit and 43 is a mode-locked laser. In the optical transmission section of the second embodiment, the first embodiment
3 is that a mode-locked laser 43 is used as the two-mode beat pulse generation means 4.

Pulse light source driving means 3 in the second embodiment
Then, the clock signal from the system clock source 2 of frequency B (B is equal to the transmission rate) is input, and the drive circuit 33 amplifies the clock signal of frequency B up to the synchronization voltage Vs of the mode-locked laser.

In the two-mode beat pulse generating means 4, the mode-locked laser 43 is mode-synchronized with the frequency B of the clock signal to generate a two-mode beat pulse optical signal P2 having a frequency interval of B.

On the other hand, the electrical partial response coding means 6 is a binary NR synchronized with the system clock source 2.
A binary NRZ signal P3 from the Z digital signal source 5 is used as an input to configure a duobinary encoding circuit that outputs an electric duobinary code. The ternary complementary electric duo is formed by the same procedure as in the first embodiment. Since the binary code P6 is generated, its detailed description is omitted.

In the light modulation means 7, the push-pull (push-p
The two-mode beat pulse optical signal P2 output from the mode-locked laser 43 is converted into the ternary complementary electric duo-binary signal P by the MZ intensity modulator 71 having a null structure.
6 and is converted into a binary RZ modulation signal P7.

Also in the second embodiment, as in the first embodiment, a harmonic component may be generated in the two-mode beat pulse optical signal P2. In that case, as shown in FIG. 6D, an optical bandpass filter 82 having a transmission characteristic centered on the optical frequency f ₀ is used, and high frequency components are removed as shown in FIG. 6E. At this time, an optical amplifier 81 is arranged at the output of the optical modulation means 7 to amplify it, and then the output port of the optical modulation means 7, or the output port of the two-mode beat pulse generation means 4 and the input port of the optical modulation means 7. The optical bandpass filter may be inserted in either or both of the two.

As described above, according to the second embodiment, the mode-locked laser modulates the two-mode beat pulse optical signal having the frequency interval B and then the duobinary signal to obtain the chromatic dispersion tolerance. It is possible to provide an optical transmission device that is wide and easily designed for dispersion compensation, and that limits the input power in the fiber.

Further, as in the second embodiment, by using the mode-locked laser 43 in the two-mode beat pulse generating means 4, the MZ intensity modulator is reduced to one as compared with the first embodiment.
It is possible to reduce the insertion loss of the MZ intensity modulator and improve the optical SN ratio of the transmission signal.

(Embodiment 3) FIG. 10 is a diagram showing a schematic configuration of an optical transmission unit in an optical transmission apparatus of Embodiment 3 according to the present invention.

The optical transmitter of the third embodiment differs from that of the first embodiment in that the two-mode beat pulse generating means 4 is used.
The mode-locked laser 43 is used for the sub-harmonic mode synchronization in which the optical pulse repetition frequency B is mode-locked by using the frequency division signal of 1 / m (m is a natural number) of the optical pulse repetition frequency B.

In the pulse light source driving means 3 of FIG. 7, the clock signal from the system clock source 2 having the frequency B (B is equal to the transmission rate) is input, and first the 1/2 frequency dividing circuit 3 is inputted.
At 1, the signal is converted into a 1/2 frequency-divided signal of frequency f / 2.
The 1/2 frequency-divided signal is amplified by the drive circuit 33 to the synchronization voltage Vs of the mode-locked laser.

Electric partial response encoding means 6
Composes a duobinary encoding circuit which receives the binary NRZ signal from the binary NRZ digital signal source 5 synchronized with the system clock source 2 and outputs an electrical duobinary code.

Also in the third embodiment, the ternary complementary electric duobinary signal P6 is processed by the same procedure as in the first embodiment.
Is generated, a detailed description thereof will be omitted.

The light modulator 7 has a push-pull (push-p)
The 2-mode beat pulse optical signal P2 is modulated according to the ternary complementary electrical duobinary signal P6 by the MZ intensity modulator 71 having the (ull) configuration and converted into a binary RZ modulation signal P7.

In the third embodiment as well, similar to the first embodiment, a harmonic component may be generated in the two-mode beat pulse optical signal P2. In that case, the high frequency component is removed by using the optical bandpass filter 82 having a transmission characteristic centered on the optical frequency f ₀ . At this time, an optical amplifier 81 is arranged at the output of the optical modulation means 7 to amplify it, and then the output port of the optical modulation means 7, or the output port of the two-mode beat pulse generation means 4 and the input port of the optical modulation means 7. The optical bandpass filter may be inserted in either or both of the two.

As described above, according to the third embodiment, a mode-locked laser modulates a two-mode beat pulse optical signal having a frequency interval B and then an electrical duobinary signal to obtain chromatic dispersion tolerance. It is possible to provide an optical transmission device that has a wide range, a dispersion compensation design is easy, and restrictions on the input power in the fiber are relaxed.

Further, as in the third embodiment, the frequency-divided signal generated by the 1/2 frequency dividing circuit 31 is used to repeatedly perform mode-locking of the frequency B to lower the drive frequency of the mode-locked laser. Therefore, the drive circuit of the two-mode beat pulse generating means 4 can be easily realized.

(Embodiment 4) FIG. 11 is a diagram showing a schematic configuration of an optical transmission section in an optical transmission apparatus of Embodiment 4 according to the present invention, and 68 is a multiplier.

The optical transmitter of the fourth embodiment is the same as the optical transmitter 2 shown in FIG.
The feature is that the mode beat pulse generation means 4 and the optical modulation means 7 are simultaneously realized by one MZ intensity modulator, and excessive insertion loss such as waveguide loss in each portion can be reduced.

12 to 14 are diagrams for explaining the operation of the optical transmitter of the fourth embodiment.

The operation of the optical transmitter of the fourth embodiment will be described below with reference to FIGS. 11 to 14.

In the pulse light source driving means 3, the frequency B (B
Is equal to the transmission speed) from the system clock source 2 as an input, and a 1/2 frequency dividing circuit 31 first generates a 1/2 frequency dividing signal of frequency f / 2. The ½ frequency-divided signal is amplified in the drive circuit 32 and then differentially output as the ½ frequency-divided signal P9 as shown in FIG.

On the other hand, the electrical partial response encoding means 6 is a binary NR synchronized with the system clock source 2.
A duobinary encoding circuit that receives the binary NRZ signal P3 from the Z digital signal source 5 and outputs an electric duobinary code is configured. First, the binary NRZ signal P3 as shown in FIG.
After being logically inverted to the inverted NRZ signal P4 shown in 2 (c), an exclusive OR circuit (EX-OR) 63 and a 1-bit delay circuit (that is, a 1-time-slot delay device for data at the transmission rate B) 64 Binary N by configured precoder 61
The RZ precoder output signal is code-converted. After the code conversion by the precoder 61, the differential converter 65 outputs the binary NRZ precoder output signal P5a shown in FIG. 12D and the 1-bit delayed binary N shown in FIG. 12E.
The RZ precoder output signal P5b is differentially output. The binary NRZ precode differential output signal P5 differentially output from the differential converter 65 is amplified by the amplifier circuit 66, and then 3
Low-pass filter (LPF) 6 whose dB band is B / 4
13 is input to obtain a three-valued complementary electric duobinary signal P6 as shown in FIG. The logical equivalent circuit of the all-device low pass filter (LPF) 67 is equivalent to a precoder composed of a 1-bit delay circuit 67A and an adder 67B. In the multiplier 68, the electric duobinary signal P6 is output from the pulse light source driving unit 3 by 1
It is mixed with the 1/2 frequency-divided signal P9 and converted into a ternary duobinary RZ electric signal P10 as shown in FIG.

FIG. 13 (h) shows a ternary duobinary RZ.
It is an output waveform of the electric signal P10. It can be seen that the ternary duobinary RZ electric signal P10 has a waveform obtained by multiplying the waveform of the 1/2 frequency-divided signal P9 from the pulse light source driving means 3 and the waveform of the electric duobinary signal P6. FIG. 13 (i) is a baseband spectrum of the ternary duobinary RZ electric signal P10. 1
/ 2 divided signal P9 is B / of the frequency in the baseband
It becomes a subcarrier of 2 and is a baseband signal spectrum which is modulated by the electric duobinary signal P6.

The three-value duobinary RZ electric signal P1
0 is input as a differential output to the MZ intensity modulator 71 having a push-pull configuration that is DC biased so that the transmission characteristic becomes 0, and the continuous transmission (CW) as shown in FIG. ) The optical carrier frequency from the laser light source 42 is f ₀
Of the single mode optical signal P1 of the binary R shown in FIG.
The Z-modulated signal P11 is converted.

FIG. 14 (l) shows the signal waveform of the binary RZ modulation signal P11, FIG. 14 (m) shows the direct detection waveform of FIG. 14 (l), and FIG. 14 (n) shows the spectrum of the binary RZ modulation signal P11. is there. As can be seen from FIG. 14 (l), the time waveform is an RZ signal in which the electric field intensity (light intensity) becomes 0 for each time slot. Further, since the carrier bright line spectrum shown in FIG. 14 (n) is modulated by the ternary duobinary RZ electric signal P10, the bright line spectrum disappears, and the light modulation spectrum has no bright line spectrum with high spectral density. As a result, the effect of stimulated Brillouin scattering can be reduced to 3 dB because the spectral density is 1/2 as compared with the conventional optical duobinary code at the same average optical fiber input power.

Also in the fourth embodiment, a harmonic component may be generated as in the first embodiment. In that case,
The harmonic component is removed by using the optical bandpass filter 82 having a transmission characteristic centered on the optical frequency f ₀ . At this time, an optical amplifier 81 may be arranged at the output of the optical modulation means 7 for amplification, and then the optical bandpass filter may be inserted into the output port of the optical modulation means 7.

As described above, according to the fourth embodiment, the single-mode optical signal P1 is mixed with the 1/2 frequency-divided signal P9 generated from the clock signal having the frequency interval B and the electric duobinary signal P6. By modulating in accordance with the ternary duobinary electric signal P10, it is possible to provide an optical transmission device having a wide chromatic dispersion tolerance, easy dispersion compensation design, and relaxing the restriction of the input power in the fiber.

(Embodiment 5) FIG. 15 is a block diagram showing a schematic structure of an optical transmission section in an optical transmission apparatus of Embodiment 5 according to the present invention. 11 is a wavelength division multiplexing filter, 11A, 1
1B, 11C and 11n are input ports, and 12 is an output port.

In the optical transmitter of the fifth embodiment, the wavelength multiplexing filter 1 is used as an optical bandpass filter for removing unnecessary harmonic components generated in the two-mode beat pulse generating means 4.
1 is used so that the removed harmonic component does not cause crosstalk of other wavelength ports. As the wavelength multiplex filter 11, for example, an array grating filter may be used. Further, as the two-mode beat pulse generating means 4, the MZ intensity modulator 4 described in the first embodiment is used.
1 may be used, and the above-described Embodiments 2 to 3 may be used.
It may be a means that uses the mode-locked laser 43 described above. In addition, a duobinary signal or a modified duobinary signal may be used as the partial response code.

FIG. 16 is a diagram for explaining the operation of the optical transmitter of the fifth embodiment.

In the optical transmission apparatus of the fifth embodiment, there are a plurality (n) of the first optical transmission section 1A to the nth optical transmission section 1n, and as shown in FIG. Each optical carrier frequency up to the nth optical transmitter 1n is set to f ₀ to f _n . The binary RZ modulated signal generated by each optical transmitter according to the procedure described in the first to fourth embodiments is connected to the wavelength multiplexing filter 11 having n input ports. The transmission characteristics of the wavelength multiplex filter 11 from each input port to the output port 12 are such that, as shown in FIG. 16 (b), the center of the transmission pass band is such that each optical carrier frequency coincides with f ₀ to f _n , and The cutoff characteristic of the optical bandpass filter can be configured to remove only harmonic signal components. The wavelength multiplexing filter 1
1, for example, when an array lattice filter is used,
If the free spectral range (FSR) of the array grating filter is set sufficiently wider than the entire optical signal band of the wavelength-multiplexed signal to be multiplexed as compared with the multiplexed signal band B0, the removed harmonic signal component will cross the other wavelength channels. It can be configured so that it does not cause talk, and wavelength multiplexing is possible.

(Embodiment 6) FIG. 17 is a diagram showing a schematic structure of an optical transmission section in an optical transmission apparatus of an embodiment 6 according to the present invention, in which 69A is a 1: 2 (1: 2) bit interleave separation circuit, 69B is a 2 to 1 (2: 1) bit interleave multiplex circuit.

18 to 21 are diagrams for explaining the operation of the optical transmitter of the sixth embodiment.

The operation of the optical transmitter of the sixth embodiment will be described below with reference to FIGS. 17 to 21. In the sixth embodiment, a modified duobinary signal is used as the partial response code, and MZ is used as the two-mode beat pulse generating means 4.
It is assumed that the intensity modulator 41 is used and the frequency interval between the two longitudinal modes is equal to the transmission rate B.

First, in the pulse light source driving means 3, the clock signal from the system clock source 2 having the frequency B (B is equal to the transmission rate) is input, and first the 1/2 frequency dividing circuit 3 is inputted.
At 1, the frequency-divided signal of frequency f / 2 is generated.
The generated 1/2 frequency-divided signal is amplified by the drive circuit 32 up to the half-wave voltage Vp of the MZ intensity modulator and differentially output.

Next, in the two-mode beat pulse generating means 4, the single-mode optical signal P1 from the continuous wave (CW) laser light source 42 as shown in FIG. DC-biased push-pul
18 (c), 18 (d) and 18 (e), which are modulated by the 1/2 frequency-divided signal differentially output from the pulse light source driving means 3 by the MZ intensity modulator 41 having the configuration l). A two-mode beat pulse optical signal P2 having a frequency interval of B is generated.

Here, FIG. 18C shows the output waveform of the two-mode beat pulse optical signal P2, and FIG. 18D shows FIG.
18C is the direct detection waveform, and FIG. 18E is the optical spectrum of FIG. 18C. Two vertical modes a and b,
It occurs at optical frequencies f ₀ −B / 2 and f ₀ + B / 2. Therefore, it can be seen that the frequency difference between the two longitudinal modes is equal to the transmission rate B.

On the other hand, the electrical partial response encoding means 6 is a binary NR synchronized with the system clock source 2.
A modified duobinary code circuit that receives the binary NRZ signal P3 from the Z digital signal source 5 and outputs an electrically modified duobinary code is configured. First, FIG. 19 (f)
The binary NRZ signal P3 shown in FIG. 19 is input to the 1: 2 bit interleave separation circuit 69A, and is input to FIGS.
Two binary NRs with data rate B / 2 as shown in (h)
Z-bit interleave separation signals P12a and P12b are separated. The 1: 2 bit interleave separation circuit 69
The two binary NRZ bit interleave separation signals P12a and P12b separated by A are the exclusive logic loop circuits (EX-OR) 63A and 63B and the 1-bit delay circuit (that is, data of transmission speed B / 2). 1 time slot delay device) 64A, 64B precoder 61
As a result, a binary NRZ bit interleaved precoder output signal P13 as shown in FIGS. 19 (i) and 19 (j) is obtained.
After being code-converted to a and P13b, they are input to the 2: 1 bit interleave multiplexing circuit 69B and multiplexed to the binary NRZ modified duobinary precode output signal P14 at the data rate B as shown in FIG. 19 (k). . The binary NRZ
The modified duobinary precode output signal P14 is differentially output by the differential converter 65. The differential converter 65
The binary NRZ precode differential output signal differentially output by the amplifier is amplified by the amplifier circuit 66 and then has a 3 dB band of B / 4.
And a bandpass filter (BPF) with a center frequency of B / 4
67 ', and a ternary complementary electrically modified duobinary signal P15 as shown in FIG. 19 (l) is obtained. The logical equivalent circuit of the band pass filter 67 'is a 2-bit delay circuit (2-time slot delay device with transmission speed B).
67C, a logic inverting circuit 67D, and an adder 67B.

In the light modulation means 7, the push-pull (push-p
20. The MZ intensity modulator 71 having the (ull) configuration modulates the two-mode beat pulse optical signal P2 according to the three-valued complementary electrically modified duobinary signal P15, and FIG.
It is converted into a binary RZ modulation signal P16 as shown in (m).

Here, FIG. 20 (m) is the signal waveform of the binary RZ modulated signal P16, FIG. 20 (n) is the direct detection waveform of FIG. 20 (m), and FIG. 20 (o) is FIG. 20 (m). Is a light modulation spectrum of. As can be seen from FIG. 20 (m), the time waveform shows that the electric field intensity (light intensity) is 0 for each time slot.
Is an RZ signal. In addition, 2 in FIG.
Since each of the two longitudinal modes a and b undergoes modified optical duobinary modulation, the emission line spectra at optical frequencies f ₀ -B / 2 and f ₀ + B / 2 disappear, and the optical modulation spectrum has a high emission line spectrum. There is no. As a result, the influence of stimulated Brillouin scattering can be reduced to 6 dB because the spectral density is 1/4 that of the conventional optical duobinary code.

Also in the sixth embodiment, a harmonic component may be generated as in the first embodiment. In that case,
The harmonic component is removed by using the optical bandpass filter 82 having a transmission characteristic centered on the optical frequency f ₀ . At this time, an optical amplifier 81 is arranged at the output of the optical modulation means 7 to amplify it, and then the output port of the optical modulation means 7, or the output port of the two-mode beat pulse generation means 4 and the input port of the optical modulation means 7. The optical bandpass filter may be inserted in either or both of the two.

As described above, according to the sixth embodiment, the single-mode optical signal is modulated into the two-mode beat pulse optical signal having the frequency interval B, and then the modified duobinary signal to obtain the wavelength. It is possible to provide an optical transmission device that has a wide dispersion tolerance, is easily designed for dispersion compensation, and relaxes the limitation on the input power in the fiber.

Further, as in the sixth embodiment, by modulating with the modified duobinary signal, the first to fourth embodiments can be performed.
Compared with, the effect of stimulated Brillouin scattering can be further mitigated.

Although the present invention has been specifically described based on the above embodiments, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention. Of course.

[0104]

As described above, according to the present invention,
As a modulated optical carrier, one conventional longitudinal mode CW
Instead of the optical signal, the frequency interval n × B (n is a natural number, B
By using two longitudinal mode optical signals (two-mode beat pulse optical signals) separated by a transmission speed), the initial code interference of the optical modulation waveform can be improved as compared with the ordinary optical partial response signal and the sensitivity can be increased.

Further, a means for optical transmission can be provided without significantly degrading the chromatic dispersion tolerance characteristic when the optical input power in the fiber is high, and the design of equalization of chromatic dispersion of the optical fiber transmission line can be facilitated.

The input power limitation in the optical fiber due to stimulated Brillouin scattering in the optical fiber transmission line is
It can be relaxed compared to the conventional optical duobinary code.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an optical transmission device according to the present invention.

FIG. 2 is a diagram showing a schematic configuration of an optical transmission unit in the optical transmission device according to the first embodiment of the present invention.

FIG. 3 is a diagram for explaining the operation of the optical transmitter of the first embodiment.

FIG. 4 is a diagram for explaining the operation of the optical transmitter of the first embodiment.

FIG. 5 is a diagram for explaining the operation of the optical transmitter of the first embodiment.

FIG. 6 is a diagram for explaining the operation of the optical transmitter of the first embodiment.

FIG. 7 is a diagram for explaining the function and effect of the optical transmitter of the first embodiment.

FIG. 8 is a diagram for explaining the function and effect of the optical transmitter of the first embodiment.

FIG. 9 is a diagram showing a schematic configuration of an optical transmission unit in an optical transmission device according to a second embodiment of the present invention.

FIG. 10 is a diagram showing a schematic configuration of an optical transmission unit in an optical transmission device according to a third embodiment of the present invention.

FIG. 11 is a diagram showing a schematic configuration of an optical transmission unit in an optical transmission device according to a fourth embodiment of the present invention.

FIG. 12 is a diagram for explaining the operation of the optical transmitter of the fourth embodiment.

FIG. 13 is a diagram for explaining the operation of the optical transmitter of the fourth embodiment.

FIG. 14 is a diagram for explaining the operation of the optical transmitter of the fourth embodiment.

FIG. 15 is a diagram showing a schematic configuration of an optical transmission unit in an optical transmission device according to a fifth embodiment of the present invention.

FIG. 16 is a diagram for explaining the operation of the optical transmitter of the fifth embodiment.

FIG. 17 is a diagram showing a schematic configuration of an optical transmission section in an optical transmission device of Example 6 according to the present invention.

FIG. 18 is a diagram for explaining the operation of the optical transmitter of the sixth embodiment.

FIG. 19 is a diagram for explaining the operation of the optical transmitter of the sixth embodiment.

FIG. 20 is a diagram for explaining the operation of the optical transmitter of the sixth embodiment.

FIG. 21 is a diagram for explaining the operation of the optical transmitter of the sixth embodiment.

FIG. 22 is a diagram showing a schematic configuration of an optical transmission unit in a conventional optical transmission device.

FIG. 23 is a diagram for explaining the operation of the conventional optical transmitter.

FIG. 24 is a diagram for explaining the operation of the conventional optical transmitter.

FIG. 25 is a diagram for explaining the operation of the conventional optical transmitter.

FIG. 26 is a diagram for explaining the operation of the conventional optical transmitter.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical transmission part, 2 ... System clock source, 3 ... Pulse light source drive means, 31 ... 1/2 (1/2) frequency dividing circuit, 3
2, 33 ... Driving circuit, 4 ... 2-mode beat pulse generating means, 41 ... Mach-Zehnder (MZ) intensity modulator, 42 ... Continuous oscillation (CW) laser light source, 43 ... Mode-locked laser, 5
... binary NRZ digital signal source, 6 ... electrical partial response encoding means, 61 ... precoder, 62 ... logical inversion circuit, 63, 63A, 63B ... exclusive OR circuit (EX
-OR), 64, 64A, 64B ... 1-bit delay circuit,
65 ... Differential converter, 66 ... Amplification circuit, 67 ... Low pass filter (LPF), 67 '... Band pass filter (BP)
F), 67A ... 1-bit delay circuit, 67B ... Adder, 6
7C ... 2-bit delay circuit, 67D ... Logic inversion circuit, 68
... multiplier, 69A ... 1 to 2 (1: 2) bit interleave separation circuit, 69B ... 2 to 1 (2: 1) bit interleave multiplexing circuit, 7 ... optical modulation means, 71 ... Mach-Zehnder
(MZ) intensity modulator, 8 ... Optical filter means, 81 ... Optical amplifier, 82 ... Optical bandpass filter, 9 ... Optical receiving unit, 10
... Repeater, 11 ... Wavelength multiplex filter, 12 ... Output port, P1 ... Single mode optical signal, P2 ... Bimode beat pulse optical signal, P3 ... Binary NRZ signal, P4 ... Inversion NRZ
Signal, P5 ... Binary NRZ precoder differential output signal, P5
a ... Binary NRZ precoder output signal, P5b ... 1-bit delayed binary NRZ precoder output signal, P6 ... Electric duobinary signal, P7, P8 ... Binary RZ modulation signal (optical duobinary signal), P9 ... 1 / 2 divided signal, P
10 ... 3-valued duobinary RZ electric signal, P11 ... 2-valued RZ modulation signal (optical duobinary signal), P12a, P
12b ... Binary NRZ bit interleaved separation signal, P1
3a, P13b ... Binary NRZ bit interleaved precoder output signal, P14 ... Binary NRZ modified duobinary precode output signal, P15 ... Electrically modified duobinary signal, P16, P17 ... Binary RZ modulated signal (optical modified duobinary signal ).

Front page continuation (51) Int.Cl. ⁷ identification code FI H04B 10/152 H04B 9/00 M 10/18 H04L 25/02 303 25/49 25/497 (72) Inventor Kenji Sato Chiyoda-ku, Tokyo Large 2-3-1 Machi, Nippon Telegraph and Telephone Corporation (72) Inventor Hiroshi Toba 2-3-1, Otemachi, Chiyoda-ku, Tokyo Inside Nippon Telegraph and Telephone Corporation (72) Inventor Akihiko Matsuura Major, Chiyoda-ku, Tokyo 2-3-1, Machi, Nippon Telegraph and Telephone Corporation (56) Reference JP-A-9-236781 (JP, A) JP-A-11-234213 (JP, A) JP-A-10-332939 (JP, A) ) JP-A-2-215242 (JP, A) JP-A-11-337894 (JP, A) JP-A-11-109428 (JP, A) JP-A-10-335753 (JP, A) JP-A-11- 17274 (JP, A) JP 11-354868 (JP, A) JP 2000-56279 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H04B 10/00-10 / 28 H04J 14/00-14/08 H04L 25/02 303 H04L 25/49 H04 L 25/497 JISC file (JOIS)

Claims (11)

(57) [Claims] 1. An optical transmission method for modulating a longitudinal mode optical signal based on a partial response signal and outputting the modulated optical signal, wherein a single mode optical signal is modulated by using a clock signal from a system clock source as an input, and a frequency interval is set. Is n × B (n
Is a natural number, B is a transmission speed), and two vertical mode pulsed light signals are generated, and the binary NRZ signal from the digital signal source synchronized with the system clock source is code-converted to generate a partial response signal, An optical transmission method comprising outputting a binary RZ modulated signal obtained by modulating the pulsed optical signals of the two longitudinal modes based on the partial response signal. 2. An optical transmission method for modulating a longitudinal mode optical signal based on a partial response signal and outputting the modulated optical signal, wherein a single mode optical signal is modulated by using a clock signal from a system clock source as an input, and a frequency interval is set. Is n × B (n
Is a natural number, B is a transmission speed), and two vertical mode pulsed light signals are generated, and the binary NRZ signal from the digital signal source synchronized with the system clock source is code-converted to generate a partial response signal, A binary RZ modulation signal obtained by modulating the pulsed optical signals of the two longitudinal modes based on the partial response signal is generated, and a harmonic component of the generated binary RZ modulation signal is removed and then output. Optical transmission method. 3. The optical transmission method according to claim 1, wherein a duobinary signal is used as the partial response signal. 4. The optical transmission method according to claim 1 or 2, wherein a modified duobinary signal is used as the partial response signal. 5. A system clock source for generating a clock signal, a binary NRZ digital signal source for generating a binary NRZ digital signal in synchronization with the clock signal, and an electrical partial response with the binary NRZ digital signal as an input. An electrical partial response encoding means for generating a signal, an optical transmitter having an optical modulator for modulating an optical signal based on the electrical partial response signal, and an optical receiver for receiving an optical signal transmitted from the optical transmitter. In the optical transmission device consisting of two parts, the optical transmission parts are separated by an optical frequency interval n × B (n is a natural number, B is a transmission speed).
Two-mode beat light pulse generation means for generating two longitudinal mode pulse light signals, and a pulse for generating a signal for driving the two-mode beat light pulse generation means from a clock signal synchronized with a binary NRZ input signal of transmission speed B An optical transmission device comprising a light source driving means. 6. The optical transmission device according to claim 5, wherein a Mach-Zehnder (MZ) intensity modulator is used as the two-mode beat optical pulse generation means. 7. The optical transmission device according to claim 5, wherein a two-mode oscillation mode-locked laser is used as the two-mode beat light pulse generating means. 8. The optical transmission device according to claim 5, wherein the two-mode beat optical pulse generating means has an optical filter for removing harmonic components of the two longitudinal mode optical pulse signals. Optical transmission equipment. 9. The optical transmission device according to claim 8, wherein a plurality of generated signals are wavelength-multiplexed by using a wavelength multiplexing array grating filter as the optical filter means. 10. The optical transmission device according to claim 8 or 9, wherein a push-pull is further used as the two-mode beat optical pulse generating means, and an amplitude of the push-pull MZ intensity modulator is used. An optical transmission device characterized by being driven by a frequency clock signal of n × B / 2 equal to a half wavelength voltage. 11. A system clock source for generating a clock signal, a binary NRZ digital signal source for generating a binary NRZ digital signal in synchronization with the clock signal, and an electrical partial response with the binary NRZ digital signal as an input. An electrical partial response encoding means for generating a signal, and an optical transmitter having an optical modulating means for modulating an optical signal based on the electrical partial response signal,
In an optical transmission device including an optical receiving unit that receives an optical signal transmitted from the optical transmitting unit, the optical transmitting unit includes two optical frequency units separated by an optical frequency interval n × B (n is a natural number, B is a transmission speed). A 2-mode beat light pulse generating means for generating a pulse light signal in the longitudinal mode, and a pulse light source for generating a signal for driving the 2-mode beat light pulse generating means from a clock signal synchronized with a binary NRZ input signal of a transmission speed B. An optical transmission device comprising: a driving unit and an optical filter unit for removing a harmonic component of an optical signal modulated by the optical modulation unit.