JPH1155224A - Wave-length multiplexing communication equipment, optical communication method and system therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the equipment low in cost simple in configuration and low in fault rate by using each of two kinds of light different wavelength beams emitted by a distributed feedback laser with no phase shift in a diffraction grating in vertical mode oscillation discharges as light signals among the plural light signals in the equipment for multiplexing and transmitting the plural light signals of different wavelengths. SOLUTION: The light of the wavelength λ1 is selected by a wavelength filter 41 and is modulated by a modulator 31 in the light beams of wavelength λ1 and λ2 , which are outputted from one terminal of the two mode DBF laser 10 by an example showing a second WDM transmitter. A filter 42 selects only λ2 from light outputted from the other terminal of the two mode DBF 10 and a modulator 32 individually modulats light. The outputs of λ1 and λ2 , on which the signals are loaded, are inputted to a synthesizer through an optical fiber and are synthesized. Then, they are connected to the fiber and are transmitted. Since light emitted from both sides of the laser are used, a demultiplexer is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength multiplexing optical communication apparatus, a wavelength multiplexing optical communication method, and a system. More specifically, the present invention uses a DFB laser that oscillates at two stable wavelengths and reduces the number of elements to half the number of channels, thereby simplifying the configuration, reducing the size and cost, and improving the reliability. The present invention relates to a multiplex optical communication device, a wavelength multiplex optical communication method, and a system.

[0002]

2. Description of the Related Art Wavelength division multiplexing optical communication is a technology for transmitting light in a plurality of wavelength bands in a superimposed manner, and is attracting attention as a technology capable of dramatically increasing the information capacity that can be transmitted through a limited optical fiber. Have been. A conventionally proposed light source for wavelength division multiplexing communication is a distributed feedback laser (DFB-LD: Distribute) that oscillates in a single longitudinal mode.
d FeedBack Laser Diode (d FeedBack Laser Diode) element is used. That is, the number of DFB-LD elements equal to the number of channels of the wavelength division multiplexing optical communication is used. These DFB-LD elements have oscillation wavelengths corresponding to the respective channels. And these are DFB-LD
The device is prepared as a single device for each wavelength, or is an array type monolithic (mono) device.
lithic).

FIG. 6 is a schematic explanatory view of such a DFB laser oscillating in a single longitudinal mode. That is, FIG. 1A is a schematic longitudinal sectional view of a DFB laser, and FIG. 1B is a schematic diagram of the oscillation wavelength characteristics of the laser. D
The FB laser 100 emits In on the n-type InP layer 111.
GaAsP active layer (active layer) 11
2. The band gap (bandga) is higher than that of the active layer 112.
p) Large InGaAsP optical waveguide layer (guiding)
layer 113 has been grown. Further, the phase at the center of the resonator is further shifted by 波長 wavelength
Gratings with 4 shifts 118
117 are formed. On this, the p-InP layer 114 is formed.
Is grown to form a pn junction. Anti-reflection (AR: Anti-Reflection)
n) A coat 116 is formed.

A DFB laser has a Bragg wavelength (λ
It oscillates near _Bragg ). Assuming that the period of the diffraction grating 117 is Λ and the effective refractive index of the laser waveguide is n _eff , Br
The agg wavelength (λ _Bragg ) is represented by the following equation. λ _Bragg = 2n _eff Λ (1) A so-called λ / 4 shift DFB laser in which an AR coat 116 is applied to both ends to suppress reflection and a λ / 4 phase shift is provided to the diffraction grating 117 at the center of the laser resonator is shown in FIG. 6 (b)
As shown in, the stop band (Stopband)
Oscillate at the Bragg wavelength at the center of Here, the “stop band” is a technical term indicating a wavelength band in which the reflection coefficient of Bragg reflection by the diffraction grating 117 is maximized.

[0005] If a plurality of λ / 4 shift DFB laser elements that oscillate at different wavelengths are prepared by changing the period of the diffraction grating, a WDM transmitter that oscillates at multiple wavelengths can be constructed. it can.

FIG. 7 is a schematic diagram showing a basic configuration of a WDM system using such a DFB laser. That is, in FIG. 1A, λ having a constant wavelength interval
A plurality of DFB lasers 10 each oscillating at a wavelength of _{1 to} λ _N
.. Are directly modulated, and their outputs are combined by a multiplexer 150 and transmitted through one optical fiber 200. On the receiving side, the transmitted signal is
The signal is amplified by 0, and separated by the splitter 400 for each original wavelength.
The light receiving elements 20, 20, such as APD and PIN-PD,
Return to electrical signals with.

In the example shown in FIG.
External modulators 30, 30,... Are provided. When an external modulator is used in this manner, lasers 10, 10,...
Can be DC-driven, and the output light is 10 Gbp
Modulation can be performed at a high speed of s (gigabits per second) or more.

On the other hand, recently, a light source using a fiber ring light source or an arrayed waveguide grating (AWG: Array-Wa
The development of a light source using Vegetable Gratings is also active. References that disclose these light sources include, for example, Miyazaki et al., IEICE, IEICE Technical Report 0CS-96-45, 0PE96-95, LQE9
6-96, p-49, 1996-10 and the like.

FIG. 8A is a schematic diagram showing a schematic configuration of a fiber ring light source, and FIG. 8B is a schematic diagram showing a schematic configuration of a light source using an arrayed waveguide grating. Both are Erbium-doped fiber amplifiers (EDF
A) is a light source using A), and a plurality of wavelengths corresponding to each channel are selected using the Fabry-Perot optical filter 500 and the arrayed waveguide gratings 601 and 602.

[0010]

However, the transmitters for WDM as described above have complicated configurations, are not easily miniaturized, and have room for improvement in reliability.
Further, there is a problem that the manufacturing cost is high. That is, the transmitter using the DFB laser 100 that oscillates in a single longitudinal mode as described with reference to FIGS. 6 and 7 as a light source has a problem that the structure is complicated and the manufacturing cost is high. That is, in these transmission units, the number of DFBs equal to the number of optical communication channels, that is, the number of wavelength bands
A laser 100 is used. Therefore, there is a problem that the structure of the transmitter is complicated and large, and the manufacturing cost is high.

Here, the manufacturing yield Y (array) of an array-type element in which n elements are integrated will be described. When the yield of each DFB element is Y (Y ≦ 1), the following equation is used. expressed. Y (array) = Y ⁿ (2) For example, when Y = 0.9, if n = 5, Y (arr)
ay) = 0.69, but when the number of elements is doubled and n = 10, the yield is extremely reduced to Y (array) = 0.35. The conventional transmitter has a disadvantage that the yield decreases as the number of channels increases. Moreover, it is extremely difficult to actually manufacture a DFB laser with a high yield.

When a large number of DFB lasers are used, the probability that any one of them will fail increases, and the failure rate of the light source increases. When an optical communication system fails, not only the user but also a wide range of problems are caused, so improving the reliability of the system is a very important issue. On the other hand, since the fiber ring light source shown in FIG. 8A and the transmitter using the arrayed waveguide grating described in FIG. 8B both use a fiber amplifier for the light source part, their dimensions are extremely large. Becomes Also,
Since the fiber amplifier requires a dedicated high-output pump laser light source, there is a problem that power consumption is large and the price is high.

Further, when a fiber ring light source is used, if the pump light source or the fiber amplifier fails, all wavelength channels of the multiplexed optical communication are interrupted, causing a serious problem.

The present invention has been made in view of such a point. That is, an object of the present invention is to provide a wavelength division multiplexing optical communication apparatus, a wavelength division multiplexing optical communication method, and a system which have a simple configuration, a low failure rate, and a low manufacturing cost.

[0015]

That is, a wavelength multiplexing optical communication device according to the present invention is a wavelength multiplexing optical communication device for multiplexing and transmitting a plurality of optical signals having different wavelengths from each other. A distributed feedback laser having no phase shift and emitting two types of light having different wavelengths by longitudinal mode oscillation, wherein each of the two types of light is used as one of the plurality of optical signals. By using a laser that oscillates at two wavelengths, the number of laser elements can be reduced by half.

The plurality of optical signals have a constant wavelength interval, and the wavelength interval of the two types of light is equal to an integral multiple of the wavelength interval of the plurality of optical signals. Thereby, the laser can be efficiently arranged.

Further, when light is input to the distributed feedback laser to excite the light so as to output two kinds of light having different wavelengths, optical signals can be directly modulated.

Further, by providing a laser power source, a demultiplexer and a modulator, a small and highly reliable transmitter can be constructed.

Furthermore, by utilizing the light emitted from both end faces of the distributed feedback laser, the extraction efficiency is improved, and a small transmitter can be constructed.

The wavelength multiplexing optical communication method according to the present invention is a wavelength multiplexing optical communication method for multiplexing a plurality of optical signals having different wavelengths and transmitting the multiplexed optical signals. Each of the two types of light emitted from a distributed feedback laser that emits two types of light having different wavelengths by oscillation is used as one of the plurality of optical signals. Be composed.

Further, while applying a voltage near the threshold value to the distributed feedback laser, the pumping light is incident on the distributed feedback laser to cause photoexcitation to emit two kinds of light having different wavelengths. Each of the lights may be used as one of the plurality of optical signals.

A wavelength division multiplexing optical communication system according to the present invention is configured to include any one of the above-described devices, or is configured to use any one of the above-described methods. It has the advantages of high performance and low manufacturing cost.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention utilizes a DFB laser that oscillates in a stable longitudinal mode at two wavelengths simultaneously.
This is to reduce the number of elements of the DM device by half. That is,
Whereas in the prior art, a single element that oscillates at one wavelength is used, the present invention uses a DFB element that oscillates at two wavelengths, thereby simplifying the configuration and improving the reliability. This is to improve the manufacturing yield by halving n in equation (2).

FIG. 1 is a schematic diagram showing a configuration of a transmitting section of a wavelength division multiplexing communication system according to the present invention. That is, in the transmission unit TX shown in FIG.
Lasers 10A, 10B, 10C,... Are arranged. The lasers 10A, 10B, 10C,... Stably oscillate in longitudinal mode in two wavelength regions. When such a two-mode DFB laser is directly modulated, that is, its drive current is modulated, two wavelength channels receive the same modulation. Therefore, the output light is supplied to the duplexer 401.
, And is modulated by the modulator 31. Output light from each modulator 31 is multiplexed by a multiplexer 101 and transmitted to one fiber 200. Fiber 20
The wavelength multiplexed signal transmitted to 0 is received by, for example, a receiving unit as shown in FIG. 7, and demodulated into an electric signal for use.

Here, the demultiplexer 401 may be arranged so as to multiplex all the output lights from the respective lasers before demultiplexing.

On the other hand, in a system in which the same signal is distributed to two wavelength channels from the beginning, the demultiplexer 40
1 is unnecessary, and the modulator 31 can be common to each laser. Or lasers 10A, 10B, 10
.. May be directly modulated.

FIG. 2 is an explanatory diagram showing an example of the DFB lasers 10A, 10B, 10C,... Used in the present invention. That is, FIG. 1A is a schematic vertical cross-sectional view, and FIG. 1B is a schematic view of the oscillation wavelength characteristics of the laser. The DFB laser 10 is a DFB laser 1 shown in FIG.
It does not have a phase shift like 00. That is, DFB
The laser 10 has InGaAs on the n-type InP layer 11.
A P active layer 12 and an InGaAsP optical waveguide layer 13 having a larger band gap than the active layer 12 are sequentially grown.
Further, a diffraction grating 17 is formed thereon. A p-InP layer 14 is grown on this, forming a pn junction. AR coats 16 are formed on both end faces of the laser.

The DFB laser 10 having the uniform diffraction grating 17 without such a phase shift oscillates in longitudinal mode in two wavelength bands as shown in FIG. The wavelength interval Δλ between the longitudinal modes is determined by the width of the stop band. The width of the stop band is an adjustable parameter because it depends on the coupling coefficient κ and the resonator length L. If the end face reflectance is sufficiently suppressed by the AR coating, stable two-mode oscillation can be obtained. If κL is large and the effect of spatial hole burning in the axial direction is large, two-mode oscillation is most stable. As described above, realizing two-mode oscillation is much easier than stably oscillating in a single longitudinal mode as shown in FIG.

In the present invention, since the two-mode oscillation characteristics of the DFB laser are used, the realization is easy and the yield is high. Further, by forming a structure of the phase shift 117 as shown in FIG. 6A, it is easier to manufacture a uniform diffraction grating as shown in FIG. Much higher. In addition to halving the number of elements, the yield is improved from the above viewpoint.

Here, returning to FIG. 1 again, FIG. 1B shows the lasers 10A, 10B, 10
It is the schematic which illustrates the relationship of the oscillation wavelength of C, ....
Here, the figure shows a DFB when the intervals of the set wavelengths of a plurality of lights used in the WDM system are equal.
This describes a method for setting the laser oscillation wavelength.
That is, in the present invention, as shown in FIG.
The wavelength interval Δλ between the two longitudinal modes is adjusted to be twice the set wavelength interval of WDM. By shifting the Bragg wavelength of the laser 10B by Δλ / 2 with respect to the DFB laser 10A, four oscillation wavelengths λ _{1 to} λ ₄ can be obtained at _one time. Further, by shifting the Bragg wavelength of the laser 10C by 3 △ λ / 2 with respect to the DFB laser 10B, λ ₅ and λ ₆
Can be obtained. The Bragg wavelength of the laser 10D is
Returning to the beginning, the laser 10C is shifted by Δλ / 2. Hereinafter, similarly, the Bragg wavelength of each laser is set.

As another example, the wavelength interval Δλ between two longitudinal modes of the laser may be adjusted to be three times the set wavelength interval of WDM. In this case, the Bragg wavelengths of the DFB lasers 10A, 10B and 10C are sequentially shifted by △ λ / 3 to set them.
Six wavelengths λ _{1 to} λ ₆ are obtained. The next laser 10D
Is shifted by 4 △ λ / 3 with respect to the laser 10C. Hereinafter, it is preferable to set the Bragg wavelength of each laser in the same manner.

Similarly, the wavelength interval Δλ of each longitudinal mode of the laser may be set so as to be four times, five times... The interval of the set wavelength channel of WDM.

As described above, in the present invention,
By setting the wavelength interval Δλ of the two modes of each laser so as to be an integral multiple of the wavelength channel interval of the WDM system, it is possible to obtain predetermined oscillation wavelengths.

Next, a modification of the present invention will be described.
FIG. 3 is a schematic configuration diagram illustrating a second WDM transmitter according to the present invention. That is, in the example shown in FIG. 3A, the light having the wavelength λ ₁ is selected by the wavelength filter 41 from the light having the wavelengths λ ₁ and λ ₂ output from one end of the two-mode DFB laser 10. Modulated by the modulator 31. On the other hand, from the light output from the other end of the laser 10, only λ ₂ is selected by the filter 42 and is separately modulated by the modulator 32. Thereafter, the outputs of λ ₁ and λ ₂ on which the signals are loaded are input to a multiplexer (not shown) via an optical fiber, multiplexed, coupled to the fiber, and transmitted.

In the example shown in FIG. 3B,
The arrangement of the filter and the modulator is reversed. That is, the wavelengths λ ₁ emitted from the end faces on both sides of the laser 10 respectively.
And λ ₂ are first modulated by modulators 31 and 32, respectively, and then wavelength-separated by filters 41 and 42 and output.

As shown in these examples, according to the present invention, since the light emitted from both sides of the laser is used, the duplexer as shown in FIG. 1 is not required. The duplexer is required to have a predetermined size in order to require a waveguide for spatially splitting light. However, according to the present invention, such a duplexer becomes unnecessary, so that the transmitter can be downsized.

Further, according to the present invention, the light use efficiency of the two-mode DFB laser 10 can be improved. That is, conventionally, light emitted from the back surface of the DFB laser has not been used. However, according to the present invention, light emitted from such a back surface can also be used, so that the light use efficiency can be improved.

Next, a third WDM device according to the present invention will be described. FIG. 4 is a schematic configuration diagram showing a third WDM device according to the present invention. That is, the two-mode DFB laser as described above can be used as an element that converts the wavelength of input light and outputs light of two types of wavelengths. That is, the DFB laser 10 oscillating in the two-wavelength longitudinal mode is biased near the threshold. Then, oscillation occurs due to slight optical excitation (optical pumping), and oscillation occurs in two unique longitudinal modes λ ₂ and λ ₃ . Here, if the input light is light having energy higher than the band gap of the active layer of the laser, optical pumping of the laser can be caused. That is, an optical output having wavelengths of λ ₂ and λ ₃ can be obtained with an input of λ ₁ . Such a two-mode DFB laser 10
Can be used as an optical repeater / branch device in a WDM system, for example. That is, when the laser 10 is arranged at a predetermined node of the WDM system, the light of the wavelength λ ₁ is input from the transmitter and the lights of the wavelengths λ ₂ and λ ₃ are output. Therefore, the same signal can be distributed to a plurality of receivers.

Further, the device shown in the figure can also perform direct modulation from an optical signal to an optical signal. That is,
If the input light is modulated, the output light is modulated accordingly. Therefore, it is possible to directly modulate another light based on the optical signal without modulating the electric signal.

FIG. 5 is a schematic block diagram showing a fourth WDM apparatus according to the present invention. That is, W illustrated in FIG.
The DM transmitter uses the above-described characteristics of the DFB laser. Here, the transmission unit TX includes two-mode DFB lasers 10a, 10b, 10c,. Each laser is biased near the threshold. Then, the light is oscillated by a slight optical excitation (optical pump) λ ₀ , and emits two unique longitudinal mode oscillation lights.
That is, by inputting λ ₀ , an optical output of each wavelength of λ ₁ , λ ₂ ,... Is obtained. In this case, the lasers 10a, 1
0b, 10c,... Have the same wavelength λ ₀ having energy higher than the band gap of the active layer.
Just input the light. That is, with the same light source,
The effect that all lasers can be excited is also obtained.

Each of the lasers 10a, 10b, 10c,
The wavelength of the excitation light input to... May be different for each laser as long as it has energy larger than the band gap of the active layer.

[0042]

The present invention is embodied in the form described above, and has the following effects.

First, according to the present invention, the DFB laser 2
Since the mode oscillation characteristic is used, the realization is easy and the yield is high. In addition, it is easier to produce a uniform diffraction grating and the yield is much higher than to make a conventional phase shift structure. In addition to halving the number of elements, there is an effect that the yield is improved from the above viewpoint.

Further, according to the present invention, since the light emitted from both sides of the laser is used, no duplexer is required. The duplexer is required to have a predetermined size in order to require a waveguide for spatially splitting light. However, according to the present invention, such a duplexer becomes unnecessary, so that the transmitter can be downsized.

Further, according to the present invention, a two-mode DFB
The utilization efficiency of laser light can be improved. That is, conventionally, light emitted from the back surface of the DFB laser has not been used. However, according to the present invention, light emitted from such a back surface can also be used, so that the light use efficiency can be improved.

According to the present invention, a two-mode DFB laser can be used as an optical repeater / branch device in, for example, a WDM system. That is, when the laser 10 is arranged at a predetermined node of the WDM system, the light of the wavelength λ ₁ is input from the transmitter and the wavelengths λ ₂ and λ
Outputs ₃ lights respectively. Therefore, the same signal can be distributed to a plurality of receivers.

Further, according to the present invention, direct modulation from an optical signal to an optical signal can be performed by optically exciting the DFB laser. That is, if the input light is modulated, the output light is modulated accordingly. Therefore, it is possible to directly modulate another light based on the optical signal without modulating the electric signal.

According to the present invention, the DF which is photoexcited
By using the B laser as a light source, there is also obtained an effect that all lasers can be excited by the same light source.

As described above, according to the present invention, it is possible to provide an apparatus, method and system for wavelength division multiplexing optical communication having a simple configuration, high performance and high reliability, and low manufacturing cost. The industrial benefits are enormous.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a transmitter for wavelength division multiplexing optical communication according to the present invention. That is, FIG. 2A is a schematic diagram illustrating the configuration, and FIG. 2B is a schematic diagram illustrating the relationship between the wavelengths of the laser.

FIG. 2 is a schematic diagram illustrating a two-mode DFB laser used in the present invention. That is, FIG. 3A is a longitudinal sectional view, and FIG. 3B is a schematic diagram showing oscillation characteristics.

FIG. 3 is a schematic diagram illustrating a second WDM transmitter according to the present invention. That is, FIG. 1A shows a schematic configuration thereof, and FIG. 1B shows a modification thereof.

FIG. 4 is a schematic diagram illustrating a third WDM transmitter according to the present invention.

FIG. 5 is a schematic configuration diagram illustrating a fourth WDM device according to the present invention.

FIG. 6 is a schematic diagram illustrating a DFB laser that oscillates in a single longitudinal mode. That is, FIG. 3A is a longitudinal sectional view, and FIG. 3B is a schematic diagram showing oscillation characteristics.

FIG. 7 is a schematic diagram illustrating a transmitter for conventional wavelength division multiplexing optical communication.

FIG. 8A is a schematic diagram showing a schematic configuration of a fiber ring light source, and FIG. 8B is a schematic diagram showing a schematic configuration of a light source using an arrayed waveguide grating.

[Explanation of symbols]

10, 10A, 10B, 10C, 2-mode DFB
Laser 11, 111 n-InP 12, 112 InGaAsP active layer 13, 113 InGaAsP waveguide layer 14, 114 p-InP 16, 116 AR coat 17, 117 Diffraction grating 20 APD, PIN-PD 30, 31, 32 Modulator 41 , 42 filter 100 single mode DFB laser 118 λ / 4 phase shift 150 multiplexer 200 optical fiber 300 optical amplifier 400, 401 duplexer

Claims (11)

[Claims] 1. A wavelength division multiplexing optical communication device for multiplexing and transmitting a plurality of optical signals having different wavelengths from each other, wherein the diffraction grating has no phase shift and two types of light having different wavelengths due to longitudinal mode oscillation. A wavelength division multiplexing optical communication device comprising: a distributed feedback laser that emits light; and wherein each of the two types of light is used as one of the plurality of optical signals. 2. The optical signal according to claim 1, wherein each of the plurality of optical signals has a constant wavelength interval, and a wavelength interval of the two types of light is equal to an integral multiple of the wavelength interval of the plurality of optical signals. The device according to claim 1. 3. The distributed feedback laser further comprises: means for applying a voltage near a threshold to the distributed feedback laser; and optical input means for optically exciting the distributed feedback laser. 3. The apparatus according to claim 1, wherein said distributed feedback laser is optically pumped by inputting light by said light input means to output two kinds of light having different wavelengths. 4. A power supply for applying driving power to the distributed feedback laser, and a demultiplexer for demultiplexing one of the two types of light emitted from the distributed feedback laser. The apparatus according to claim 1, further comprising: a modulator that modulates each of the split lights. 5. A first modulator for modulating light emitted from one end face of the distributed feedback laser, and a light modulated by the first modulator being demultiplexed to produce the two types of light. A first demultiplexer that extracts one of the two components; a second modulator that modulates light emitted from the other end face of the distributed feedback laser; and a second modulator that is modulated by the second modulator. The apparatus according to claim 1, further comprising a second demultiplexer that demultiplexes light and extracts one of the two types of light. 6. A first demultiplexer for demultiplexing light emitted from one end face of the distributed feedback laser to extract one of the two types of light, and the first demultiplexer. The first modulating the light extracted by the waver
A second splitter that splits the light emitted from the other end face of the distributed feedback laser and extracts one of the two types of light, and the second splitter. The second modulates the light extracted by the waver
The modulator according to claim 1 or 2, further comprising a modulator. 7. A wavelength-division multiplexing optical communication method for multiplexing and transmitting a plurality of optical signals having different wavelengths from each other, wherein the diffraction grating has no phase shift and transmits two types of light having different wavelengths by longitudinal mode oscillation. A wavelength-division multiplexing optical communication method, wherein each of the two types of light emitted from the emitted distributed feedback laser is used as one of the plurality of optical signals. 8. A wavelength division multiplexing optical communication method for multiplexing and transmitting a plurality of optical signals having different wavelengths from each other, wherein the diffraction grating does not have a phase shift, and two types of light having different wavelengths are generated by longitudinal mode oscillation. While applying a voltage near the threshold to the emitting distributed feedback laser, the pumping light is injected to cause photoexcitation to emit two types of light having different wavelengths, and each of the emitted two types of light is emitted. Is used as any one of the plurality of optical signals. 9. A wavelength-division multiplexing optical communication method for multiplexing and transmitting a plurality of optical signals having different wavelengths from each other, wherein two types of light having different wavelengths due to longitudinal mode oscillation without a phase shift in a diffraction grating. Either one of the two types of light emitted from one end face of the distributed feedback laser to be emitted is modulated and used as the optical signal, and emitted from the other end face of the distributed feedback laser. A wavelength multiplexing optical communication method, wherein one of the two types of light is modulated and used as the optical signal. 10. A wavelength division multiplexing optical communication system comprising any one of the devices according to claim 1. 11. A wavelength division multiplexing optical communication system using any one of the methods according to claim 7.