JP3761528B2 - Optical transmission device and optical transmission method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical transmission device used for optical transmission, and particularly to an optical transmission device and an optical transmission method used for ultrahigh-speed wavelength division multiplexing transmission.
[0002]
[Prior art]
Conventionally, to increase the transmission capacity in optical transmission, there are a direction to increase the number of wavelength multiplexing and a direction to increase the transmission speed. However, the two are in conflict with limited wavelength resources. That is, since the occupied band per wave increases in proportion to the transmission speed, the number of wavelength multiplexing decreases. Therefore, in order to further increase the transmission capacity in a limited wavelength resource, it is necessary to improve the frequency utilization efficiency.
[0003]
An optical duobinary modulation system has been proposed as an optical modulation system with a compact modulation spectrum (see, for example, Patent Document 1).
Since this optical duobinary modulation method only occupies the spectrum width of the band of the signal to be transmitted, it is a very excellent modulation method from the viewpoint of frequency utilization efficiency. Further, since the output optical signal is also a binary signal, consistency with a conventional receiver can be ensured. Furthermore, it has an excellent resistance to chromatic dispersion of optical fibers.
[0004]
In ultra-high-speed transmission, resistance to nonlinear phenomena in optical fibers is important. For example, in order to obtain the same optical signal-to-noise ratio when the repeater interval and transmission distance of the optical amplifier are the same, in the 40 Gbps system, approximately four times as much optical power as that in the 10 Gbps system is input to the optical fiber. There is a need to. However, the non-linear tolerance of the optical duobinary modulation system is very poor and is not suitable for ultra-high speed transmission.
[0005]
As a modulation method having excellent nonlinear tolerance, a carrier suppression RZ (CS-RZ) modulation method (for example, see Non-Patent Document 2), an alternating chirp RZ (AC-RZ) modulation method (for example, Non-Patent Document 3). In addition, a carrier suppression RZ (DPCS-RZ) modulation method using a differential phase (see, for example, Non-Patent Document 4) has been proposed. Since the DPCS-RZ modulation system has a feature that the optical phase is inverted between adjacent mark bits, the nonlinear proof stress is excellent.
[0006]
However, in any method, since the occupied band of the optical spectrum is wide, it is difficult to realize high frequency utilization efficiency.
[Non-Patent Document 1]
K. Yonenaga et al., Electron. Lett. Vol. 31, No. 4, 1995, p. 302-304
[Non-Patent Document 2]
Y.Miyamoto et al., OAA'99, post-deadline paper PDP-4, 1999
[Non-Patent Document 3]
R. Ohhira et al., OFC'2001, WM2, 2000
[Non-Patent Document 4]
Ito et al., Study of carrierless RZ modulation using differential phase, 40Gbit / s optical transmission technology workshop OCS 40G-6-9, June 20, 2002, p.35-38
[0007]
[Problems to be solved by the invention]
As described above, the conventional optical transmission apparatus has a problem that the optical duobinary modulation method is not suitable for ultrahigh-speed transmission because the nonlinear resistance in the optical fiber is remarkably inferior. In addition, the modulation method with excellent nonlinear tolerance has a problem that it is not suitable for high-density multiplexing because the occupied band of the optical spectrum is wide.
[0008]
It is an object of the present invention to provide an optical transmission apparatus that has a narrow modulation spectrum occupancy band and is excellent in nonlinear tolerance.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, an optical carrier generator for generating an optical signal having two carrier components having a frequency interval equal to the clock frequency of a data signal in the NRZ code format to be transmitted, and an input Code conversion means for code-converting the received data signal into an NRZI code, phase modulation means for phase-modulating the optical signal input from the optical carrier generation unit with a signal code-converted by the code conversion means, and the phase From an optical signal output from the modulation means, a Mach-Zehnder interferometer that suppresses a carrier frequency component of the optical signal generated by the optical carrier generator, and an optical signal output from the Mach-Zehnder interferometer An optical transmission device comprising a band optical filter that passes the frequency bands of the two carriers is provided.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Prior to the description of the embodiments, the principle of the present invention will be described with reference to the drawings. FIG. 13A shows the optical spectrum of the DPCS-RZ system. The DPCS-RZ system has excellent nonlinear tolerance, but occupies at least twice the bandwidth of the bit rate (B), so there is a problem in terms of higher density, that is, frequency utilization efficiency when applied to wavelength multiplexing transmission. It was.
[0011]
As shown in FIG. 13B, the optical spectrum of FIG. 13A can be separated into two components of the upper and lower sidebands across the carrier frequency f0, and further, these two components in time series. Found that they do not occur at the same time.
[0012]
Therefore, as shown in FIG. 14 (a), DPCS-RZ modulation is simultaneously applied to two optical carrier components having carrier frequencies f1 and f2 (the difference between the carrier frequencies matches the bit rate). Only the broken line portion including f1-f2 is extracted by the optical filter from the cross-hatched portion where the two overlap each other.
[0013]
As a result, it is possible to obtain an optical transmission apparatus that has a characteristic that it is excellent in the nonlinear tolerance of the DPCS-RZ system while narrowing the band equivalent to optical duobinary modulation as the occupied band of the modulation spectrum.
[0014]
(First embodiment)
An optical transmission apparatus according to a first embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram for explaining the configuration of the optical transmission apparatus according to the first embodiment of the present invention.
In FIG. 1, the optical transmission device 1 includes an optical carrier generation unit 100, a signal input terminal 101, a code conversion unit 102, an optical phase modulator 103, a Mach-Zehnder interferometer 104, and an optical filter 105.
[0015]
The optical carrier generation unit 100 includes semiconductor lasers 111 and 112 and an optical multiplexer 120. The semiconductor laser 111 oscillates at the optical frequency f1. The semiconductor laser 112 oscillates at an optical frequency f2 different from f0. These two oscillated laser beams are input to the optical multiplexer 120.
[0016]
The optical multiplexer 120 combines the two laser beams input from the semiconductor lasers 111 and 112 and outputs the combined laser beam to the optical phase modulator 103. In the following embodiments, a semiconductor laser is used. However, the present invention is not limited to this, and a laser using a gas may be used.
[0017]
The difference between the optical carrier frequencies output from the semiconductor lasers 111 and 112 by a control signal from a control circuit (not shown) is set to match the clock frequency of the data signal to be transmitted.
[0018]
An NRZ (Non-Return to Zero) signal that is a data signal to be transmitted is input to the code conversion unit 102 via the signal input terminal 101.
The code conversion unit 102 converts the NRZ signal input from the signal input terminal 101 into an NRZI (Non-Return to Zero Inverse) signal and outputs the signal to the optical phase modulator 103.
[0019]
The optical phase modulator 103 modulates the phase of the combined laser beam input from the optical multiplexer 120 in the optical carrier generation unit 100 with the NRZI signal input from the code conversion unit 102 and performs Mach-Zehnder interference. Output to total 104.
[0020]
The FSR (Free Spectrum Range) of the Mach-Zehnder interferometer 104 substantially matches the frequency difference frequency difference between the two laser beams (optical carriers) output from the optical carrier generator 100, and this transmission characteristic is the optical carrier generation. The optical carrier component (both two carrier components) output from the unit 100 is adjusted to be suppressed.
[0021]
The Mach-Zehnder interferometer 104 suppresses the optical carrier component output from the optical carrier generator 100 from the phase-modulated signal input from the optical phase modulator 103 and outputs the suppressed signal to the narrowband optical filter 105.
[0022]
The transmission center frequency of the narrow-band optical filter 105 is set to coincide with the center of the two laser light (optical carrier) frequencies output from the optical carrier generating unit 100. The narrow-band optical filter 105 limits the band of light input from the Mach-Zehnder interferometer 104 so as to suppress other frequency bands through a band between two optical carrier frequencies, and outputs the light to the optical transmission line. As a band limitation at this time, the band may be limited by an optical filter having a full width at half maximum (FWHM) of about the bit rate or more.
[0023]
Next, the operation of the thus configured optical transmission apparatus according to the first embodiment of the present invention will be described with reference to FIGS. 2 to 5 showing output optical spectra and optical waveforms in the respective units. 2-5 (a) shows an optical spectrum, and FIGS. 2-5 (b) show optical waveforms.
[0024]
FIG. 2 is a diagram illustrating an output signal of the optical carrier generation unit 100.
In this embodiment, the transmission rate is set to 40 [Gbps], and the difference in optical carrier frequency is set to 40 [GHz] as shown in FIG.
As an optical waveform, a sine wave signal of 40 [GHz] appears as a beat component of two optical carrier frequencies.
FIG. 3 is a diagram illustrating an optical signal output from the optical phase modulator 103.
Since phase modulation is performed by the optical phase modulator 103, the optical spectrum is remarkably broadened as shown in FIG. 3A, and the optical spectrum width at a point 20 [dB] lower than the peak is about 100 [GHz]. ].
[0025]
There is no change in the optical waveform from FIG.
FIG. 4 is a diagram illustrating an optical signal output from the Mach-Zehnder interferometer 104.
As shown in FIG. 4A, the optical carrier component from the optical carrier generation unit 100 is suppressed by the Mach-Zehnder interferometer 104 in the optical spectrum. In the optical spectrum, the phase modulation component received by the optical phase modulator 103 is converted into an intensity modulation component.
[0026]
As a result, the optical waveform appears in a form in which the NRZ signal input from the signal input terminal 101 is converted into the optical RZ signal as shown in FIG.
If this is the case, the optical spectrum remains largely spread, and the spectrum utilization efficiency is lowered.
FIG. 5 is a diagram illustrating an optical signal output from the narrowband optical filter 105.
In the present embodiment, a 3 [dB] bandwidth and a 40 [GHz] third order Gaussian filter are used as the narrow band optical filter.
As a result of the band limitation of the optical spectrum by the narrow band optical filter 105, the band is greatly limited as shown in FIG. 5A (about 40 GHz with 20 dB down).
However, as shown in FIG. 5B, a good eye opening is obtained as the optical waveform.
Next, the nonlinear proof strength of the optical transmission apparatus according to the first embodiment of the present invention will be described with reference to FIG. For comparison, the conventional Duobinary method and NRZ method are also shown in FIG.
[0027]
As a transmission line, four spans of SMF (Single Mode Fiber) 80 [km] are assumed, and fiber dispersion and dispersion slope are compensated 100% in each optical repeater.
[0028]
The horizontal axis of FIG. 6 shows the input power to the SMF of each span, and the vertical axis shows the eye opening degree deterioration.
As shown in FIG. 6, the method of the present invention is superior to the other two methods against the nonlinear effect in the transmission line, despite the narrow optical spectrum width compared to the conventional Duobinary method and NRZ method. It can be seen that
[0029]
As described above, since the optical transmission apparatus of the present invention has a narrow spectrum width comparable to the transmission speed, it is possible to realize excellent frequency utilization efficiency in the high-density wavelength multiplexing system.
[0030]
In addition, since the non-linear proof stress has characteristics superior to those of the conventional narrow spectrum modulation method, it is possible to obtain good reception sensitivity in long-distance transmission.
Further, an optical multiplexer can be used in place of the narrow band filter 105 at the time of wavelength multiplexing transmission.
(Second Embodiment)
An optical transmission apparatus according to the second embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 7 is a diagram for explaining the configuration of the optical transmission apparatus 1 according to the second embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the same part as FIG. 1, and the description is abbreviate | omitted.
FIG. 7 is different from FIG. 1 in the configuration in the optical carrier generation unit 100.
In FIG. 7, the optical carrier generation unit 100 includes a semiconductor laser 111, a signal input terminal 701, a frequency divider 702, a modulation voltage adjustment unit 703, an optical phase modulator 704, and an optical filter 705. The semiconductor laser 111 oscillates at the optical frequency f1.
[0031]
A clock signal of the data signal to be transmitted is input to the frequency divider 702 via the signal input terminal 701.
The frequency divider 702 divides the clock input from the signal input terminal 701 into two and outputs the divided clock to the modulation voltage adjustment unit 703.
The modulation voltage adjustment unit 703 adjusts the voltage applied to the optical phase modulator 704 so that the optical carrier component output from the semiconductor laser 111 in the light output from the optical phase modulator 704 is minimized. . At this time, the minimum is the best, but it is not necessarily the minimum, and may be substantially the minimum as long as the effect of the present invention can be obtained.
[0032]
The semiconductor laser 111 outputs laser light to the optical phase modulator 704.
The optical phase modulator 704 modulates the phase of the laser light input from the semiconductor laser 111 according to the applied voltage value applied from the modulation voltage adjustment unit 703 and outputs the result to the optical filter 705.
[0033]
FIG. 8 shows the input / output light spectrum of the optical filter 705.
When the optical phase modulator 103 performs phase modulation so that the carrier component is minimized with respect to the laser light (oscillated at the optical frequency f1) input from the semiconductor laser 111, a large harmonic as shown in FIG. Wave components are generated.
[0034]
Therefore, the optical filter 705 suppresses the harmonic component of the output light phase-modulated by the optical phase modulator 704 as shown in FIG. Thus, two optical carrier signals having a frequency interval corresponding to the clock frequency of the data signal to be transmitted can be obtained. Note that there is no problem because the carriers at the center and both ends in the figure are suppressed by 50 [dB] or more with respect to the main carrier component.
[0035]
By configuring the optical carrier generation unit 100 in this way, two optical carrier signals can be obtained with one semiconductor laser, and the apparatus can be made smaller. Also, the frequency interval of the optical carrier can be varied according to the input data signal.
[0036]
In the description using FIG. 7 described above, the clock signal of the data signal to be transmitted is input from the outside of the optical carrier generation unit 100. Instead of this, a configuration may be adopted in which the clock component of the data signal to be transmitted is extracted from the data signal to be transmitted.
[0037]
Even if the optical carrier generation unit 100 is configured as described above, the same effects as those of the first embodiment can be obtained.
(Third embodiment)
An optical transmission apparatus according to the third embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 9 is a diagram for explaining the configuration of the optical transmission apparatus 1 according to the third embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the same part as FIG. 1, and the description is abbreviate | omitted.
FIG. 9 is different from FIG. 7 in the configuration in the optical carrier generation unit 100. In FIG. 7, phase modulation is performed in the optical carrier generation unit 100, but in FIG. 9, intensity modulation is performed in the optical carrier generation unit 100.
[0038]
In FIG. 9, the optical carrier generation unit 100 includes a semiconductor laser 111, a signal input terminal 701, a frequency divider 702, a modulation voltage adjustment unit 703, an intensity modulator 902, and a bias control unit 901.
[0039]
A clock signal of the data signal to be transmitted is input to the frequency divider 702 via the signal input terminal 701.
The modulation voltage adjustment unit 703 outputs to the Mach-Zehnder type intensity modulator 902 so that the optical carrier component output from the semiconductor laser 111 in the light output from the Mach-Zehnder type intensity modulator 902 is minimized. Adjust the modulation signal. At this time, the minimum is the best, but it is not necessarily the minimum, and may be substantially the minimum as long as the effect of the present invention can be obtained.
[0040]
The Mach-Zehnder type intensity modulator 902 modulates the intensity of the laser light input from the semiconductor laser 111 in accordance with the modulation signal applied from the modulation voltage adjustment unit 703 and outputs the intensity to the optical phase modulator 103.
[0041]
The bias control unit 901 applies a bias voltage to the Mach-Zehnder type intensity modulator 902 so as to optimize the operating point of the Mach-Zehnder type intensity modulator 902.
Next, the bias voltage applied from the bias control unit 901 to the Mach-Zehnder type intensity modulator 902 will be described with reference to FIGS. 10 and 11.
The transmission characteristics with respect to the modulation voltage of the Mach-Zehnder type intensity modulator 902 are as shown in FIG.
The horizontal axis indicates the magnitude of the voltage of the modulation signal applied to the electrode of the Mach-Zehnder type intensity modulator 902 from the modulation voltage adjusting unit 703, and the vertical axis indicates the optical power output from the Mach-Zehnder type intensity modulator 902. Indicates the size.
[0042]
FIG. 11A is a diagram illustrating a modulation signal output from the modulation voltage adjustment unit 703.
FIGS. 11B, 11C, and 11D are diagrams from a Mach-Zehnder type intensity modulator 902 when a DC bias is set at each point A, B, and C shown in FIG. It is a figure which shows the optical waveform output.
[0043]
In the present embodiment, the bias voltage applied from the bias control unit 901 to the Mach-Zehnder type intensity modulator 902 sets a DC bias at the point A or B shown in FIG.
[0044]
Here, the modulation voltage adjustment unit 703 performs adjustment so that the amplitude (peak-to-peak) of the modulation signal applied to the Mach-Zehnder type intensity modulator 902 is twice the half-wave voltage.
[0045]
As shown in FIGS. 11B and 11C, if the operating point of the Mach-Zehnder type intensity modulator 902 is set to a voltage at which the transmission characteristic is minimum (bias: A) or maximum (bias: B), It can be seen that an optical pulse train having an original clock frequency, that is, an optical carrier having a frequency interval corresponding to the clock frequency, is generated using the clock signal divided by two by the frequency divider 702 (FIGS. 11B and 11C). ). At this time, the minimum or minimum is the best, but it is not necessarily the minimum / maximum. If the optical pulse train having the original clock frequency can be obtained using the clock signal divided by two by the frequency divider 702, It may be approximately minimum / approximately maximum.
[0046]
Further, in the case of the Mach-Zehnder type intensity modulator, since the harmonic component is smaller than that of the optical phase modulator, it is not necessary to suppress the harmonic component by the optical filter 705 necessary in FIG. Therefore, cost reduction and loss reduction can be realized.
[0047]
In the above embodiment, the single-electrode Mach-Zehnder type intensity modulator is used as the intensity modulator, but a two-electrode type Mach-Zehnder modulator may be used. In this case, since the amplitude of the modulation signal applied to the two-electrode Mach-Zehnder modulator can be halved, the modulation voltage adjustment unit 703 does not require a high-output amplifier, and can further reduce the cost and size. Further, since the chirp of the modulator output light pulse can be reduced, the optical spectrum spread can be suppressed.
[0048]
(Fourth embodiment)
An optical transmission apparatus according to the fourth embodiment of the present invention will be described in detail with reference to the drawings. This embodiment is an optical transmission apparatus in which the third embodiment is applied to wavelength multiplexing transmission.
[0049]
FIG. 12 is a diagram for explaining the configuration of the optical transmission apparatus 2 according to the fourth embodiment of the present invention. In addition, the same code | symbol is attached | subjected to FIG. 9 and an identical part, and the description is abbreviate | omitted. 12 includes n (n is a natural number) optical transmission units 1201 having a configuration in which the optical filter 105 is removed from the optical transmission device 1 illustrated in FIG. The semiconductor lasers 111 in the n optical transmitters 1201 oscillate at different optical frequencies.
[0050]
Each optical transmitter 1201 outputs an optical signal having the optical spectrum and optical waveform shown in FIG. However, the center frequencies of the optical spectrum are different from each other in each optical transmitter 1201.
[0051]
The optical signal output from each optical transmission unit 1201 is input to each input port of the optical multiplexer 1202. The transmission characteristic from each input port to the output port of the optical multiplexer 1202 has an optical filtering characteristic that suppresses interference with adjacent channels. The transmission center frequency of this optical filtering characteristic substantially matches the oscillation frequency of the semiconductor laser 111 mounted in each optical transmission unit 1201.
[0052]
As described above, in the wavelength division multiplexing method, the narrow-band optical filter 105 necessary for each optical transmission device can be omitted by narrowing the optical spectrum based on the transmission wavelength characteristics of the optical multiplexer. The cost of the entire apparatus can be reduced.
[0053]
Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.
[0054]
【The invention's effect】
As described above, according to the present invention, it is possible to realize an optical transmitter that has a very narrow modulation spectrum and is resistant to nonlinear effects in the transmission path, and therefore, high-density wavelength multiplexing is possible even in an ultrahigh-speed transmission system. Therefore, the limited wavelength resources can be effectively used, and the total cost of the system can be reduced.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an optical transmission apparatus according to a first embodiment of the present invention.
FIG. 2 is a diagram showing an output from an optical carrier generation unit in the first embodiment of the present invention.
FIG. 3 is a diagram showing an optical signal output from the optical phase modulator 103 according to the first embodiment of the present invention.
FIG. 4 is a diagram showing an optical signal output from a Mach-Zehnder interferometer 104 according to the first embodiment of the present invention.
FIG. 5 is a diagram showing an optical signal output from the narrowband optical filter 105 according to the first embodiment of the present invention.
FIG. 6 is a diagram for explaining the non-linear proof strength of the optical transmission apparatus according to the first embodiment of the present invention.
FIG. 7 is a diagram showing a configuration of an optical transmission apparatus according to a second embodiment of the present invention.
FIG. 8 is a diagram illustrating an optical carrier generation unit according to a second embodiment of the present invention.
FIG. 9 is a diagram showing a configuration of an optical transmission apparatus according to a third embodiment of the present invention.
FIG. 10 is a diagram showing transmission characteristics with respect to an applied voltage and a modulation voltage of a Mach-Zehnder optical intensity modulator.
FIG. 11 is a diagram illustrating an optical carrier generation unit according to a third embodiment of the present invention.
FIG. 12 is a diagram showing a configuration of an optical transmission apparatus according to a fourth embodiment of the present invention.
FIG. 13 illustrates an optical spectrum in the DPCS-RZ modulation method.
FIG. 14 is a diagram for explaining the principle of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1, 2 ... Optical transmitter, 100 ... Optical carrier generator, 101, 701 ... Signal input terminal, 102 ... Code converter, 103, 704 ... Optical phase modulator, 104 ... Mach-Zehnder interferometer, 105, 705 ... Optical narrow band filter, 111, 112 ... Semiconductor laser, 120 ... Optical multiplexer, 702 ... Frequency divider, 703 ... Modulation voltage adjustment unit, 901 ... Bias control unit, 902 ... Mach-Zehnder light intensity modulator, 1201 ... Optical transmission unit, 1202... Optical multiplexer.

Claims (8)

An optical carrier generator for generating an optical signal having two carrier components at a frequency interval equal to the clock frequency of the data signal in the NRZ code format to be transmitted;
Code conversion means for code-converting the input data signal into an NRZI code;
Phase modulation means for phase-modulating the optical signal input from the optical carrier generator with the signal code-converted by the code conversion means;
A Mach-Zehnder interferometer that suppresses the carrier frequency component of the optical signal generated by the optical carrier generation unit from the optical signal output from the phase modulation unit,
An optical transmission apparatus comprising: a band optical filter that passes the frequency band of the two carriers from an optical signal output from the Mach-Zehnder interferometer. The optical carrier generator is
A plurality of lasers having different optical frequencies;
The optical transmission device according to claim 1, further comprising: an optical multiplexing unit configured to multiplex light from the plurality of lasers. The optical carrier generator is
A light source that generates an optical signal having one carrier component;
Frequency dividing means for dividing the clock frequency component of the data signal by two;
A light source side phase modulation unit that is controlled by the input control signal and phase-modulates an optical signal input from the light source by a signal divided by two by the frequency dividing unit;
Control for outputting the control signal that substantially minimizes the carrier frequency component of the optical signal generated by the optical carrier generator included in the optical signal output from the light source side phase modulation means to the light source side phase modulation means Means,
The optical transmission device according to claim 1, further comprising: an optical filter that suppresses harmonic components from the optical signal input from the light source side phase modulation means. The optical carrier generator is
A light source that generates an optical signal having one carrier component;
Frequency dividing means for dividing the clock frequency component of the data signal by two;
Mach-Zehnder type intensity modulation means for intensity-modulating the optical signal from the light source by a signal divided by two by the frequency dividing means,
Bias control means for controlling the bias voltage applied to the Mach-Zehnder type intensity modulation means,
This bias control means
The voltage corresponding to the DC component of the signal frequency-divided by 2 from the frequency dividing means is controlled so as to correspond to the substantially minimum or substantially maximum light transmission characteristic of the Mach-Zehnder type intensity modulating means. Item 5. The optical transmission device according to Item 1. 5. The optical transmitter according to claim 4, wherein the Mach-Zehnder type intensity modulation means is a two-electrode type Mach-Zehnder intensity modulator. The optical transmission device according to claim 1, wherein the band optical filter is an optical multiplexer. The optical transmission device according to claim 4, further comprising clock extraction means for extracting a clock frequency component of the data signal from the data signal. An optical carrier generation unit generates an optical signal having two carrier components having a frequency interval equal to the clock frequency of the data signal in the NRZ code format to be transmitted,
Code conversion means converts the input data signal into an NRZI code,
The phase modulation means modulates the phase of the optical signal output from the optical carrier generator with the signal converted by the code conversion means,
The Mach-Zehnder interferometer suppresses the carrier frequency component of the optical signal generated by the optical carrier generator from the optical signal input from the phase modulation unit,
An optical transmission method characterized by passing a frequency band of the two carriers from an optical signal output from the Mach-Zehnder interferometer by a band optical filter.

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