JP2002064241A - Optical transmitter and optical transmission system - Google Patents

Abstract

(57) [Summary] The present invention provides an optical transmission device capable of extending the transmission distance at low cost compared to the conventional one. SOLUTION: The present invention has a light source and a driving unit of the light source, wherein the light source has a multimode oscillation whose signal light has a wavelength of not less than 1.24 μm and a transmission speed of 1G.
An optical transmitter, which is a semiconductor laser device capable of transmitting light at a bit rate of not less than bit / s and having a wavelength interval between adjacent modes of the multimode oscillation signal light of 0.5 nm or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical signal transmitting device and an optical transmission system using a semiconductor laser device.

[0002]

2. Description of the Related Art Semiconductor lasers used as transmission light sources for optical communication are mainly composed of a semiconductor laser device having a Fabry-Perot type resonator (hereinafter abbreviated as a Fabry-Perot laser: hereinafter abbreviated as an FP laser) and a DFB. (Dist
laser (Returned Feedback: distributed feedback) laser. The FP laser has a feature of low cost because a cavity structure is formed using the cleavage planes at both ends of the semiconductor as a reflecting mirror. However, in general, the cavity length, that is, the interval between the reflecting mirrors on both end faces is longer than the oscillation wavelength of the laser, so that there are a plurality of optical modes, and so-called multi-mode oscillation in which a plurality of laser beams oscillates. Therefore, in a high-speed modulation operation, the transmission distance of an optical fiber is limited mainly by mode distribution noise. This fact, for example, IEEE J
own of Quantum electron
ics, Vol. QE-18, no. 5, pp. 84
9-855, 1982.

FIG. 1 shows a calculation result on a relationship between a transmission wavelength and a transmission distance in consideration of mode distribution noise. The lower region of each of the curves A, B, and C shown in FIG. 1 is a region where the corresponding wavelength can be propagated. That is, FIG. 1 shows more specifically, in this example, when the FP laser is driven at the following transmission speed, the dispersion Δλ _RMS (Ha
If Spectrum width / root m
5 shows the transmission possible distance of the optical fiber when the wavelength is 2.5 nm and 4 nm, respectively. The oscillation spectrum dispersion Δλ _RMS is a dispersion value when the wavelength dependence of each spectrum intensity oscillating in multiple modes is approximated by a Gaussian distribution. Curve A shows that the transmission speed is 2.5
When Gbit / s and Δλ _RMS are 2.5 nm, curve B shows a transmission rate of 2.5 Gbit / s and Δλ _RMS is 4 nm, and curve C shows a transmission rate of 10 Gbit / s and Δλ.
_This shows each characteristic when the _RMS is 2.5 nm. In FIG. 1, the zero-dispersion wavelength of the optical fiber is 1.31 μm.
And As described above, in FIG. 1, the lower region of each curve is a transmittable range, and it can be seen from FIG. 1 that the maximum transmission distance strongly depends on the oscillation wavelength. The relationship between the transmission wavelength and the transmission distance shown in FIG. 1 naturally depends on the transmission speed. For example, IEEE, JO
URNAL OF QUANTUM ELECTRON
ICS, Vol. , QE-18, No. 5, MAY, 1
982, pp. 849-855.

On the other hand, in actual optical transmission, the zero dispersion of an actually laid optical fiber is from 1.29 μm to 1.3.
It varies in the range of 3 μm. For this reason, the practical transmission distance range is illustrated in FIG. 2, and the range in which transmission is possible is more dependent on the oscillation wavelength than in the case of FIG. 1 under simple conditions. FIG. 2 is a diagram showing the relationship between the transmission wavelength and the transmission distance as in FIG. The horizontal axis indicates the wavelength, and the vertical axis indicates the transmission distance. Curve a shows the relationship when the zero dispersion of the optical fiber is 1.29 μm, and curve b shows the relationship when the zero dispersion of the optical fiber is 1.31 μm.
m, and the curve c shows the relationship when the zero dispersion of the optical fiber is 1.33 μm. For each curve, as in the case of FIG. Is shown. In this example, the transmission speed is 2.5
This is an example when Gbit / s and Δλ _RMS are 4 nm. When a large number of optical fibers having variations in zero dispersion are used in an optical transmission system, the area where optical transmission is possible in the entire section is within the range of zero dispersion of the optical fibers, and transmission is possible with all optical fibers. This area is a transmittable range in the optical transmission system. Therefore, in this example, only the shaded area in FIG. 2 is the area that can be transmitted. Therefore, the maximum transmission distance is a very limited distance.

[0005]

The transmission characteristics as described above are particularly disadvantageous especially in a transmission module without a Peltier cooling element which is characterized by low cost and small size. That is, in the FP laser, the oscillation wavelength of the semiconductor laser changes at a maximum of 0.55 nm / ° C. due to a change in the environmental temperature. Therefore, from 0 ° C., which is an example of actual use conditions, to 8 ° C.
In the range of 0 ° C., the oscillation wavelength changes by 47 nm. further,
At present, the variation range of the oscillation wavelength due to the manufacturing variation of the FP laser is about 15 nm, so the oscillation wavelength variation range of the FP laser must be 62 nm. That is,
The change of the oscillation wavelength due to the change of the environmental temperature, 47n
In addition to m, the variation range of the oscillation wavelength due to the manufacturing variation of the FP laser, about 15 nm, must be further considered. Therefore, as shown in FIG. 2, the maximum transmission distance by the FP laser remains at about 2.8 km. In order to extend the transmission distance with the FP laser, it is necessary to reduce the dispersion of the oscillation spectrum.

FIG. 3 shows the oscillation spectrum width dependence of the transmission distance calculated based on the method of obtaining the transmission distance shown in FIG. As in FIG. 2, each characteristic assumes that the zero dispersion of the optical fiber is 1.29 to 1.33 μm, and that the FP laser is 0 to 8 μm.
It is a rough characteristic in the fluctuation range of 0 degreeC. Further, the transmission speed is various driving conditions in the range of 622 Mbit / s to 10 Gbit / s. For example, as shown in the figure, transmission over 10 km requires oscillation spectrum dispersion of 1.2 nm or less.

In order to perform optical communication over a longer distance, a DFB laser that can perform single mode oscillation and is not affected by mode distribution noise is used. Since the DFB laser has a diffraction grating provided along the optical waveguide of the laser, laser oscillation can be performed in a single mode. However, it requires advanced technology to manufacture the diffraction grating, and the phase of the diffraction grating whose one cycle is about 200 nm to 240 nm cannot be controlled by the laser end face.
In principle, there is a stochastic laser that oscillates in two modes instead of a single mode. Therefore, the yield of the single mode is low, and the cost is higher than that of the FP laser.
Furthermore, the operation of the DFB laser becomes unstable when the light emitted by the DFB laser returns, and therefore requires an optical isolator to prevent this. Generally, an optical isolator is much more expensive than a semiconductor laser itself, and there is a problem that the cost of an optical module using a DFB laser as a light source is increased.

An object of the present invention is to use a semiconductor laser device, which is a light source for optical communication, to ensure long-distance transmission at a low cost and for optical transmission using an optical fiber. An object of the present invention is to provide a useful optical signal transmission device and an optical transmission system.

[0009]

According to a first aspect of the present invention, there is provided a light source and a driving unit for the light source.
The signal light is multi-mode oscillation having a wavelength of 1.24 μm or more, the transmission speed is 1 Gbit / s or more, and the wavelength interval between adjacent modes of the multi-mode oscillation signal light is 0.5 nm or less. An optical transmission device characterized by being a semiconductor laser device capable of performing certain functions.

In the present invention, in order to provide an apparatus at low cost,
A multimode oscillation semiconductor laser device is used. The wavelength interval of the multimode oscillation mode is 0.5n
It is important to make it less than m. As described later, by setting the wavelength interval of the multi-mode oscillation mode to 0.5 nm or less, the dispersion width of the oscillation spectrum can be reduced. As a result, signal light having a wavelength of 1.24 μm or more, which is used for optical communication,
At a transmission speed of Gbit / s or more, the transmission distance of light can be made longer.

A second main aspect of the present invention has a light source and a driving unit for the light source, and the light source is a Fabry-Perot (F
a semiconductor laser device having an (abry-Perot) type resonator, wherein the semiconductor laser device has a multimode oscillation whose signal light has a wavelength of 1.24 μm or more, and a transmission speed of 1 Gbit / s or more, and An optical transmission device characterized in that the wavelength interval between adjacent modes of the multi-mode oscillation signal light can be 0.5 nm or less.

In particular, the present invention provides a Fabry-Perot resonator semiconductor laser device in which the wavelength spacing between adjacent modes of the multi-mode oscillation signal light is 0.5 nm or less. Useful. That is, the Fabry-Perot resonator is manufactured very inexpensively from its structure, which is particularly useful in practical use. That is, the reflection surface of the resonator can be formed by cleavage.

A semiconductor laser device useful in the present invention has a Fabry-Perot resonator and an active region having a multiple quantum well structure, and the active region of the Fabry-Perot resonator depends on the length of the resonator. A semiconductor laser device having a short length, wherein the signal light from the semiconductor laser device is a multi-mode oscillation having a wavelength of 1.24 μm or more, the transmission speed is 1 Gbit / s or more, and It can be said that the wavelength interval between adjacent modes of the signal light is 0.5 nm or less.

An example of a typical and practical structure for realizing a structure in which the length of the active region is shorter than the length of the resonator of the Fabry-Perot type resonator is a structure commonly called a butt joint. That is, this structure comprises a light emitting portion, a first optical waveguide crystallographically bonded to the light emitting portion, and a second optical crystallographically bonded to the light emitting end face of the first optical waveguide. Has a structure having at least the optical waveguide described above. It is useful that the first and second optical waveguides have a configuration in which the optical waveguide is guided by the cladding region.

Another example of this structure includes a light emitting portion, a first optical waveguide that is crystallographically joined to the light emitting portion, and a crystallographically disposed light emitting end face of the first optical waveguide. At least a bonded second optical waveguide is provided, and at least the first and second optical waveguides have a structure in which the film thickness decreases continuously toward the emission end face. It is also possible to use a plurality of such butt joints in the second optical waveguide. That is, still another example is a light emitting unit,
A beam spot converter that forms the butt joint with the light emitting unit, wherein the thickness of the optical waveguide of the beam spot converter is continuously reduced toward the emission end face, and It has one or more butt joints inside the optical waveguide.

In the various structures in which the film thickness of the second optical waveguide is continuously reduced toward the emission end face, the beam spot of the laser light is enlarged, and the coupling efficiency with the optical fiber from the emission portion is improved. I can do it.

The two reflecting surfaces of the Fabry-Perot resonator are sufficient to be realized with a customary Fabry-Perot resonator. Typically, the semiconductor laser device is formed on a predetermined surface of a semiconductor laminate constituting the semiconductor laser device. Secondly, at least one of the two reflecting surfaces of the Fabry-Perot resonator is used as the semiconductor laser device. This is an embodiment in which the semiconductor laser device is formed so as to be spaced apart from the surface of the semiconductor laminate constituting the semiconductor laser device. The second mode is what is usually called an external resonator.

The Fabry-Perot resonator preferably has a resonator length of 500 μm or more, especially 600 μm or more, which is practical. The length of the active region is 400 μm.
m or less, which is practical. Further, the length of the active region is about 300 μm to 400 μm,
It is preferable from the viewpoint of high output. From the viewpoint of the relaxation oscillation frequency, the length of the active region is from 100 μm to 200 μm.
It is preferably about μm. In these cases, it goes without saying that regardless of the length of the active region, the length of the active region must be shorter than the length of the resonator of the Fabry-Perot resonator.

The semiconductor laser device of the present invention can be constituted by using a semiconductor material provided for a general semiconductor laser device for optical communication, particularly, a compound semiconductor material, especially, a group III-V compound semiconductor material. A semiconductor laser using an InP-based compound semiconductor material is typical as a material suitable for the current optical fiber. The multiple quantum well structure is any one of a multiple quantum well structure including In, Ga, As, and P, and a multiple quantum well structure including In, Ga, Al, and As. Is a typical example. That is, InGaAs is formed in the active region of the semiconductor laser.
sP or InGaAlAs is frequently used.

Here, it is sufficient for the multiple quantum well structure itself to use an ordinary structure.

Further, it is advantageous to have a p-type semiconductor layer among the plurality of semiconductor layers constituting the multiple quantum well structure. Part of the multiple quantum well structure, in particular, a structure in which the barrier layer is doped with p-type doping is known as p-type modulation doping. This structure has a narrow gain spectrum.
Therefore, the present invention employing this structure can further reduce the dispersion Δλ _{RMS of the} oscillation spectrum.

A third main aspect of the present invention comprises a light source, a driving section of the light source, and an optical fiber optically connected to the light source, wherein the light source has a signal light having a wavelength of 1.
A semiconductor laser device which has a multi-mode oscillation of 24 μm or more, has a transmission speed of 1 Gbit / s or more, and has a wavelength interval of adjacent modes of the multi-mode oscillation signal light of 0.5 nm or less. An optical transmission system characterized by the following. At present, a typical optical fiber for optical communication has a zero dispersion value of about 1.29 μm to about 1.55 μm. According to the present invention, it is possible to realize optical transmission over a longer distance than before using such an optical fiber for optical communication. Further, in this embodiment, even if an inexpensive pin photodetector is used, it is possible to sufficiently realize an optical communication system.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION The gist of the present invention is summarized in the following points. First, in order to enable high-speed transmission and long-distance transmission, the semiconductor laser device is set to multi-mode oscillation,
In addition, it is to reduce the wavelength interval δλ of the adjacent modes. In this case, as a point to be basically noted for high-speed transmission, it is necessary to sufficiently increase the relaxation oscillation frequency of the semiconductor laser device and sufficiently increase the optical response in high-speed transmission. The present invention can provide an inexpensive device by using a multimode oscillation semiconductor laser device.

Under these conditions, for the first time, 1 Gbit /
In high-speed transmission of s or more, while ensuring good optical response, while responding to transmission wavelengths of 1.24 μm or more used in optical communication, and variations in zero dispersion of optical fibers,
Optical transmission over longer distances is now possible. Currently, the installed optical fibers are from 1.29 μm to 1.29 μm.
Although it has a dispersion of zero dispersion up to 33 μm, the present invention can sufficiently cope with such a situation.

The above features of the present invention can be exemplified by the following means as technically representative means.
A first aspect is that while maintaining the length of the active region in the resonator at a predetermined length, and connecting the active region to the second region,
And a resonator length longer than the length of the active region is ensured. This makes it possible to reduce the wavelength interval δλ of the adjacent modes. Further, by using a multiple quantum well structure in the active region of the semiconductor laser, the length of the active region in the resonator can be secured to a predetermined length, and as a result, the reduction of the relaxation oscillation frequency is suppressed. . The use of the multiple quantum well structure makes it possible to suppress a decrease in the relaxation oscillation frequency particularly at a high temperature. Thus, using the semiconductor laser device, high-speed transmission can be performed in a device temperature range of 0 to 80 degrees Celsius. FIG. 10 shows an example of a waveform in multi-mode oscillation. In the drawing, the wavelength interval δλ of adjacent modes is illustrated.

The transmission distance (L) of light is represented by a transmission wavelength (λ),
It is a function of the transmission speed (v) and the dispersion width (Δλ _RMS ) of the oscillation spectrum of the light source. That is, it can be represented by the following equation.

L = f (λ, v, Δλ _RMS ) In particular, it is important that the light transmission distance (L) contributes to the dispersion width (Δλ _RMS ) of the oscillation spectrum of the multimode oscillation light source. .

Although the transmission distance generally depends on the wavelength and transmission speed for transmission, the transmission distance increases as the dispersion width (Δλ _RMS ) of the oscillation spectrum of the light source decreases. The inventors of the present application have found that the dispersion width (Δλ _RMS ) of the oscillation spectrum of the light source of the multimode oscillation depends on the wavelength interval (δλ) of the oscillation spectrum of the multimode oscillation. That is, it has been found that when the wavelength interval (δλ) of the oscillation spectrum of the multi-mode oscillation decreases, the dispersion width (Δλ _RMS ) of the oscillation spectrum decreases. In order to increase the transmission distance, it is the is important to reduce the dispersion width of an oscillation spectrum of the light source (Δλ _{RM S).}

Naturally, the relationship between the dispersion width (Δλ _RMS ) of the oscillation spectrum of the light source of the multi-mode oscillation and the wavelength interval (δλ) of the oscillation spectrum itself also depends on the transmission speed. That is, the relationship between the dispersion width of the oscillation spectrum (Δλ _RMS ) and the wavelength interval of the oscillation spectrum (δλ) uses the transmission speed as a parameter. Therefore, when the relationship between the transmission speed (v) and the transmission distance (L) is examined using the wavelength interval (δλ) of the oscillation spectrum of multimode oscillation as a parameter, for example, when the wavelength interval (δλ) is 0.5 nm or less, Light can be transmitted at a transmission speed of 1 Gbit / s or more. The specific relationship between the transmission speed (v) and the transmission distance (L) using the wavelength interval (δλ) of the oscillation spectrum of multimode oscillation as a parameter is illustrated in FIG. 9 described later.

The relationship between the transmission speed (v) and the transmission distance (L) is from the currently laid 1.29 μm to 1.3.
This was sufficient for an optical fiber having a dispersion of zero dispersion up to 3 μm. Then, under the conditions, for example, a transmission distance of 30 km could be secured at a transmission speed of 1 Gbit / s. This transmission distance, 30 km, is the limit distance of the loss of the optical fiber when receiving with currently used pin silicon diodes. In constructing an optical communication system, it is extremely important to ensure the consistency with the light receiver. From this viewpoint, the fact that the transmission speed is 1 Gbit / s or more and the transmission distance is 30 Km is a very great practical advantage of the present invention. Note that such a relationship is ensured when the ambient temperature of the semiconductor laser device as the light source ranges from 0 degrees Celsius to 80 degrees Celsius.

Making the relaxation oscillation frequency of the semiconductor laser device sufficiently large and making the optical response in high-speed transmission sufficient are prerequisite technologies for achieving a transmission speed of 1 Gbit / s or more.

Heretofore, with an inexpensive FP laser device, a transmission speed of 1 Gbit / s or more and a transmission distance of 30 km could not be secured. The optical transmission in which the transmission speed and the transmission distance are secured is the first one realized by the present invention.

Next, an example of an optical transmission apparatus as a typical example of the present invention will be described. Next, the basic matter of the present invention summarized above will be described in detail based on the results of various experiments using the representative apparatus.

FIG. 4 is a schematic diagram of a first embodiment of the optical communication transmitting apparatus according to the present invention. In FIG. 4, reference numeral 1 denotes 1.
A semiconductor laser that oscillates in a multi-mode of 3 μm band and has an interval of 0.39 nm between adjacent wavelengths, 2 is a laser driving circuit that operates at 2.5 Gbit / s, 6 is a temperature sensor for measuring the temperature of the semiconductor laser, Reference numeral 3 denotes a temperature compensation circuit, 4 denotes a monitor photodiode, and 7 denotes a lens for optically coupling the semiconductor laser and the optical fiber of 8. The temperature compensation circuit 3 adjusts the driving conditions of the semiconductor laser 1 using the temperature of the semiconductor laser obtained by the temperature sensor 6,
The information is transmitted to the laser drive circuit 2. The monitoring photodiode 4 is a photodiode for monitoring the light output from the rear of the semiconductor laser 1, and the driving current is adjusted by the laser drive circuit 2 so that the average light output in front of the semiconductor laser is constant.

In the present invention, it is important that the characteristics of the semiconductor laser device 1, particularly the adjacent wavelength of the multi-mode oscillation, be 0.5 nm or less. In this example, specifically, for example, a Fabry-Perot type semiconductor laser device was used, and the wavelength interval δλ between adjacent wavelengths of multimode oscillation was set to 0.39 nm.

FIG. 5 is a sectional view of the center of the semiconductor laser 1 parallel to the optical axis direction. In FIG. 5, reference numeral 21 denotes InG
A multiple quantum well active layer made of an aAsP semiconductor, 22 is an optical waveguide layer made of an InGaAsP semiconductor. The optical waveguide layer has an InP upper cladding layer 27 and an InP lower cladding layer 26 around which the band gap is higher than the light energy of the laser light so that the laser light from the active layer 21 is not absorbed.
It is set so that the refractive index becomes larger.

Next, the configuration of the present invention will be described in accordance with the manufacturing steps with reference to FIGS. 14A to 14D. It goes without saying that the matters relating to the present invention, which are described in accordance with the steps, can be applied to embodiments other than the present example relating to the present invention.

In the crystal growth, first, a multiple quantum well (MQ)
W) An active layer was grown, and thereafter, the active layer portion was masked with an insulator, and an optical waveguide layer connected to the active layer region was grown.
First, an n-type (100) In is formed by a usual MOCVD method.
An n-type InP substrate-side cladding layer (thickness: 0.1 μm) 25, an active layer region 21, and an insulating film 90 are formed on a P substrate 25. Here, the active layer region 21 includes a first optical confinement layer (composition wavelength: 1.05 μm, 50 nm thick) 33, M
QW active layer (oscillation wavelength: 1.3 μm) and second optical confinement layer (composition wavelength: 1.05 μm, 50 nm thick) 34
Having. An example of the strained MQW active layer is InGaAsP
(6 nm thick) as well layer 31 and InGaAsP (composition wavelength 1.10 μm, 10 nm thick) as barrier layer 32
The period of the QW active layer is nine. FIG. 6 illustrates a configuration of the multiple quantum well structure. In this example, the thickness is 70
A light confinement layer 33 of nm is provided so that light is efficiently confined in the quantum well layer. The light confinement layers 33 and 34 are not necessarily required in principle, but are practically used for light confinement. In addition, although it is not necessarily required in principle above and below the quantum well structure, it is often used practically.

In the present invention, a semiconductor laser device practically uses an active layer region having a quantum well structure, an active layer region having a multiple quantum well structure, or an active layer region having a strained multiple quantum well structure. Conventional structures are sufficient for these structures. The same applies to other embodiments.

The well layer of the multiple quantum well structure has a thickness of about 3n.
The thickness in the range of about 7 nm to about 7 nm and the thickness of the barrier layer in the range of about 6 nm to about 12 nm are frequently used. The stacking of the multiple quantum well structure generally uses a range of about 12 to 3 periods. The selection of well layers and barrier layers is also sufficient according to customary methods. Of course, the selection of the thickness and material of the well layer and barrier layer
Needless to say, it is set according to various characteristics required for the device.

The semiconductor laser used in the present invention is InP
A typical example is a semiconductor laser using a compound semiconductor material. The active region of the semiconductor laser is InGaAsP
Alternatively, InGaAlAs is frequently used. If necessary, for example, InGaP, InGaAs, InAlA
III-V compound semiconductor materials such as s, GaAsP, and GaAsP can be used. As the well layer in the active layer region of the semiconductor laser device, InGaAs, InGa
AsP, InGaAlAs, and the like are frequently used. In addition, as the barrier layer, InGaAsP, InGaP, InG
aAlAs, InAlAs and the like are frequently used. And
In this case, the composition of the active layer region has a composition wavelength of 1.2.
The range of 1.68 μm to μm is frequently used for optical communication.

Next, an insulator layer (for example, a SiN layer) 90 is formed on a region corresponding to the active layer region of the MQW layer. A SiN pattern 90 having a desired shape is formed with an opening in a region where an additional optical waveguide according to the present invention is formed. Thus, the MQW layer in the mask opening is removed by etching using the pattern region of the insulator layer as a region to be masked (FIG. 14B).

Further, the composition wavelength of the InGaAsP optical waveguide layer (But Joint) portion is 1.10 μm by the well-known MOCVD selective growth using the pattern region of the insulator layer 90 as a region to be masked.
m, thickness 300 nm) 22 (FIG. 14C).

Thereafter, the insulating film 90 is once removed, and a normal BH type (Buried Heterostructure) is used.
ure type) In order to form a laser structure, a striped insulating film 91 as shown in FIG. 15 is formed. FIG.
5 is a cross-sectional view of the optical resonator on a plane intersecting the direction of travel of the laser light. Using the region of the insulating film 91 as a mask region, the active layer region 21 and the cladding layer 2 on the n-type substrate side are formed.
6 is removed by etching. Thus, FIG.
Then, the mesa stripes of the laminate indicated by reference numerals 26 and 21 are formed. Next, a p-type InP layer 45 and an n-type InP layer 46 are formed on both sides of the mesa stripe.
Each of these layers is a so-called buried layer. The buried layer always requires a plurality of p-type and n-type layers, but generally a pn junction is provided in the buried layer region in order to prevent leakage current. In this case, a plurality of p
In some cases, it may have n conveniences. The buried layer region is naturally provided on both sides of the optical waveguide layer 22.

Next, the insulator layer used as a mask in the above step is removed, and on the semiconductor laminate thus prepared,
A p-InP layer (thickness: 4 μm) as the second cladding layer 27
m) is replaced by a conventional MOCVD method (Metal-Organ
ic Chemical Vapor Deposit
(Ion Method) (FIG. 14)
D).

Thus, a so-called BH type light confinement region is formed.

This embodiment shows an example of a so-called buried type (BH type) semiconductor laser device in which the light emitting section is buried with a semiconductor material. The BH type semiconductor laser device of this example has good control of the transverse mode of laser oscillation.

After that, the SiO ₂ mask is removed and LD
A contact layer 48 and a p-type electrode 35 were formed immediately above the portion. Furthermore, after the n-type electrode 36 is formed on the back surface of the substrate, both end faces are cleaved. In the present invention, the pair of electrodes 35 and 36 are provided not in the entire surface of the semiconductor laminate but in a region corresponding to the active layer region. When the electrode 35 is formed, a so-called contact layer 48 is generally formed below the electrode 35. This contact layer 48 is a layer for forming an ohmic junction with the upper electrode 35. Since this contact layer is not a main part of the present invention, it is omitted from the basic explanatory view of the present invention in FIG.

On the cleavage plane of the crystal, reflection films 23 and 24 made of a usual dielectric are provided.

FIG. 7 is a cross-sectional view of the semiconductor laser device thus manufactured, taken along a plane intersecting the direction of travel of the laser beam. In FIG. 7, reference numeral 41 denotes an active layer region having a multiple quantum well structure; 42, a lower cladding layer on the substrate side;
Is a second upper cladding layer.
The buried layers in this example are a p-InP layer 45 and an n-InP layer 4.
6, and three layers of a p-InP layer 47.
A -np junction is formed. Therefore, the buried layer region has an effect of reducing a leak current from the active layer region.

Next, the basic matters of the present invention will be described in detail based on the results of various experiments using the above light source.

First, the first viewpoint will be described. That is, in the multi-mode oscillation of the semiconductor laser device, there are problems of the wavelength interval δλ between the oscillation modes and the dispersion width Δλ _RMS of the oscillation spectrum. That is, as δλ decreases, Δλ _RMS decreases.

The cavity length of the semiconductor laser of this embodiment, that is, La + Lb is 600 μm in the example of FIG.
The active layer length La is 200 μm.

In general, the wavelength interval δλ between adjacent modes of an FP laser oscillating in a multimode is represented by λ ₀ ² / (2n _r L). Where λ ₀ is the oscillation center wavelength of the semiconductor laser,
n _r is the effective refractive index of the optical waveguide in consideration of dispersion. L
Is the resonator length, which is La + Lb here. In this embodiment, λ ₀ = 1.31 μm, n _r = 3.7, L = 600 μm
Therefore, the wavelength interval δλ is 0.39 nm.

[0055] FIG. 8 is a diagram illustrating an example of a correlation between the wavelength interval δλ between adjacent modes of the obtained oscillation spectrum width [Delta] [lambda] _{R MS} and a multimode Experiments using semiconductor laser device. In FIG. 8, the horizontal axis represents the wavelength interval δλ, the vertical axis represents the oscillation spectrum width Δλ _{RMS , and the} parameter is the transmission rate. Since the wavelength interval δλ can be converted to the length of the resonator, this value is shown on the horizontal axis at the top of the figure. Examples of the reflectance of the reflection surface of the semiconductor laser device and the ratio of the active layer length to the resonator length used in this experiment are as follows, for example. The reflectance of the front surface is 30%, the reflectance of the rear surface is 90%, and the ratio of active layer length / resonator length is 0.33. Other semiconductor laser devices having other reflectivities and active layer lengths / resonator lengths generally show similar characteristics. If the reflectivity is different, the threshold current density of the semiconductor laser, the lifetime of internal photons, etc. change, but it can be seen that the oscillation spectrum width does not depend much on those parameters. Further, this oscillation spectrum dispersion showed a substantially constant value almost independent of the driving current. FIG.
In the measurement, the bias current was 0.9 times the threshold current, and the drive current was 4 times the threshold current density.

In each curve of FIG. 8, the area indicated by the dotted line is a characteristic when the active layer length and the resonator length are the same. On the other hand, the region indicated by the solid line is a characteristic in the case where the active layer length characteristic of the present invention is shorter than the resonator length. So, for example,
In the characteristic of 1 Gbit / s, by applying the present invention,
This is the first realization of the characteristic that the wavelength interval δλ is 0.5 nm or less. Such characteristics cannot be realized in a typical semiconductor laser device in which the active layer length and the resonator length are the same.

From FIG. 8, it is understood that the smaller the wavelength interval δλ, the smaller the oscillation spectrum width Δλ _RMS .

A series of these experimental results show that the characteristic that the dispersion width Δλ _{RMS of the} oscillation spectrum becomes smaller as the wavelength interval between the multimodes becomes smaller is the same in any multimode oscillation semiconductor laser device. It was confirmed that.

So far, the conditions on the light source side, that is, the oscillation conditions of the semiconductor laser device have been studied. on the other hand,
Consider the viewpoint of optical transmission by optical fiber. That is, to conclude briefly, the dispersion width Δλ of the oscillation spectrum
_{As the RMS} decreases, the transmission distance increases.

The results of a series of experiments are summarized below. From the relationship between the transmission speed and the oscillation spectrum dispersion width Δλ _RMS , when the transmission speed is 1 Gbit / s or more due to the effect of reducing the oscillation spectrum dispersion width Δλ _RMS. It has been shown that transmission distances longer than this can be achieved.

FIG. 9 is a diagram showing the relationship between the maximum transmittable distance and the transmission speed based on the results obtained in the experiment. The horizontal axis is the transmission speed, the vertical axis is the transmission distance, and the parameter is the wavelength interval δλ. This result indicates that the zero dispersion of the optical fiber is 1.29μ.
This is a case where it is assumed that the distance corresponds to m to 1.33 μm. The semiconductor laser device was measured in a temperature range of 0 ° C to 80 ° C. In each curve of FIG. 9, the area indicated by the dotted line is a characteristic when the active layer length and the resonator length are the same.
On the other hand, the region indicated by the solid line is a characteristic in the case where the active layer length characteristic of the present invention is shorter than the resonator length. Therefore, by using the present invention, for example, when the wavelength interval δλ is 1.
In the characteristic of 0 nm, the transmission speed is 2.7 at 5 Gbit / s.
Km can be obtained. Further, a predetermined transmission distance can be secured even at a higher transmission speed, for example, 6 Gbit / s or 10 Gbit / s. Also, the wavelength interval δλ
Is 0.5 nm, a transmission speed of 1 Gbit / s can provide a transmission distance of 22 km. Further, with this characteristic, a longer transmission distance can be obtained in a region where the transmission speed is high, which has not been realized until now. Also, the wavelength interval δλ is 0.4n
With a characteristic of m, a transmission distance of 42 Km can be obtained in a characteristic of a transmission speed of 0.8 Gbit / s. Further, with this characteristic, a longer transmission distance can be obtained in a region where the transmission speed is high, which has not been realized until now. For example, if the transmission speed is 1 Gbi
At t / s, a transmission distance of 34 km can be obtained. On the other hand, at 10 Gbit / s, a transmission distance of 2.7 km can be obtained. By applying the present invention to make the wavelength interval δλ smaller, the transmission speed becomes 10G.
A predetermined transmission distance can be ensured even at a bit rate of more than bit / s, for example, 20 Gbit / s. Such a transmission distance cannot be ensured at a high transmission speed as seen in this example.

Therefore, it can be said that the improvement of the characteristics according to the present invention according to FIG. 9 is achieved by the following transmission method. That is, it has a light source, a driving part of the light source, and an optical fiber optically connected to the light source, and the light source has a signal light having a wavelength of 1.
It is a multi-mode oscillation of 24 μm or more, and the wavelength interval (δλ) of adjacent modes of the signal light of the multi-mode oscillation is at least 1.0 nm or less, and the relationship between the transmission speed and the δλ is the transmission speed Is 5Gbit /
In the case of s, δλ is 1.0 nm and the transmission rate is 1 Gbit /
In the case of s, δλ is 0.5 nm and the transmission rate is 0.8
In the case of Gbit / s, with respect to a straight line connecting each characteristic point when δλ is 0.4 nm and a characteristic line connecting δλ to 1.0 nm with this straight line, the range where the above δλ is small and the transmission speed is large is set. The optical transmission system is characterized in that optical transmission is performed to the optical fiber. In other words, in FIG. 9, line A (line A is indicated by a dashed line)
And δλ are to set the transmission conditions in a range connecting the solid line of the characteristic line of 1.0 nm and a range above the connected line.

Assuming that a low-cost pin-type photodiode receiver is used as the receiver, the reception limit sensitivity is about -18 dBm. Since the loss of the optical fiber is 0.6 dB / km and the optical output input to the optical fiber by the semiconductor laser is about 0 dBm, (0 dB
m − (− 18 dBm)) ÷ 0.6 dB / km, and the maximum transmission distance due to the loss limit is 30 km. The photodiode receiver is InGaAs or InGaAlAs
Are frequently used.

From the results shown in FIG. 9, it can be understood that the oscillation spectral dispersion increases at any transmission speed due to the increase in the transmission speed, but the shorter the adjacent mode interval δλ, the longer the transmission distance. . As described above, the present invention has a practically usable transmission distance even at a transmission speed of 1 Gbit / s or more, at which the transmission distance could hardly be secured until now.

Here, high-speed transmission, in particular, 1 Gbi
It is necessary to refer to the high-speed operation of t / s or more and the optical response of the semiconductor laser device. This is a second aspect of the present invention. The considerations so far have been based on the premise that the semiconductor laser device can operate at a desired high speed. However, in reality, apart from the transmission characteristics of the optical fiber, it is necessary to ensure high-speed operation of the semiconductor laser device itself.

In order to obtain a good optical response waveform at 1 Gbit / s or more, the relaxation oscillation frequency of the semiconductor laser needs to be two to three times the driving speed. Here, the relaxation oscillation frequency refers to a frequency having an oscillatory transient response characteristic that occurs in an optical output response when a current is injected into a semiconductor laser. This relaxation oscillation frequency decreases with an increase in the length La of the active layer.

In general, when the optical resonator length is increased, the adjacent mode interval Δλ of the multi-mode oscillation is reduced.
Accordingly, when the length of the resonator is a semiconductor laser in which the entire length of the resonator is an active layer, that is, in Lb = 0, if the length of the resonator is increased and the interval between adjacent modes Δλ is reduced, the relaxation oscillation frequency is reduced. Therefore, it is necessary to make the resonator length longer than the length of the active layer. The fact that the dispersion of the oscillation spectrum depends not on the length of the active layer but on the adjacent mode interval δλ has been experimentally verified as shown by the diamond in FIG. However, since a certain length of the active layer is required to obtain an optical output, the relaxation oscillation frequency is desirably about 2 to 3 times the driving speed.

In the transmitting apparatus for optical communication according to the present embodiment, the interval between adjacent wavelengths of the semiconductor laser oscillating in the multi-mode is set to 0.1.
Reflecting the narrowness of 4 nm, the dispersion of the oscillation spectrum during operation at 2.5 Gbit / s was as extremely small as 1.2 nm. The wavelength at which the dispersion becomes 0 is 1.3.
The transmission distance when using an optical fiber of 15 μm was 17 km when the operating temperature range of the semiconductor laser was 0 to 80 ° C. This transmission distance limit almost coincides with the calculation result in consideration of the mode dispersion noise. This result confirms that transmission of 10 km is possible even with the currently installed optical fiber having a zero dispersion of 1.29 μm to 1.33 μm. As described above, according to the present invention, it is possible to perform transmission 3.6 times the conventional transmission distance.

Although an InGaAsP semiconductor is used for the active layer of the semiconductor laser in this embodiment, an InGaAlAs multiple quantum well active layer on an InP semiconductor substrate may be used.

FIG. 11 is a schematic diagram of a second embodiment in which the present invention is applied to a transmission device for optical communication. The difference from the first embodiment is that a light emitting surface itself uses a condensing semiconductor laser device. Other structures are the same as those in the first embodiment.
A detailed description thereof will be omitted.

The feature of this embodiment is, specifically, that the optical waveguide layer 28 connected to the active layer region of the semiconductor laser 1 has a tapered vertical width narrower toward the light emitting portion. . Therefore, the light beam expands in the waveguide layer and can be coupled to the optical fiber without a lens. Therefore, the cost of the optical transmission module can be reduced. The structure itself, referred to as the joint butt structure, is sufficient to be formed in a customary manner.

The present invention relates to the following two joints:
It is useful when applied to an optical semiconductor device having a butt structure.

The first is the example shown in the second embodiment.
That is, it comprises a light emitting portion, a first optical waveguide crystallographically joined to the light emitting portion, and a second optical waveguide crystallographically joined to the exit end face side of the first optical waveguide. An optical semiconductor device having at least a waveguide, wherein at least the thickness of the first and second optical waveguides decreases continuously toward the emission end face.

The second example has a light emitting section, a beam spot converter section forming a butt joint with the light emitting section, and the film thickness of the optical waveguide of the beam spot converter section is directed toward the emission end face. An optical semiconductor device characterized by having one or more butt joints inside the optical waveguide of the beam spot converter section.

The method in which the film thickness of the optical waveguide is continuously reduced toward the emission end face is such that the loss at the beam spot conversion portion is small, and the selective growth technique by metal organic chemical vapor deposition (MOCVD) is used. There is a feature that integration with an optical element such as a semiconductor laser device is easy. In this film thickness tapered beam spot converter, the light propagating in the core of the optical waveguide spreads to the outside of the core without being confined in the core due to the decrease in the core film thickness, and the beam spot diameter at the emission end face is reduced. It is enlarged. As a result, the divergence angle of the laser light from the emission end face is reduced, and the function of improving the coupling efficiency with an optical fiber or the like is provided.

The principle of film thickness taper formation by MOCVD selective growth is based on the fact that the organic metal material used for growth is diffused in the lateral direction on the mask near the dielectric mask and the growth rate of the mask opening region is increased. ing. Because of this,
The film thickness distribution around the dielectric mask by the selective growth has an exponential distribution shape. Therefore, when the film thickness obtained under normal MOCVD growth conditions is 1 near the dielectric mask, it is 1 / at a position infinitely distant from the dielectric mask.
It is about 3. The principle of the formation of the film thickness taper is already known. That is, when the thickness of the optical waveguide 22 is tapered as in the example of FIG. 13D, the area of the mask made of a dielectric for crystal growth can be reduced from the inside of the optical waveguide toward the emission surface. good. The degree of taper in the film thickness of the optical waveguide 22 is controlled by the degree of the decrease or the like.

This example will be specifically described. In the SiN mask opening, an InGaAsP thickness tapered optical waveguide layer 6 whose thickness is continuously reduced is formed. The thickness of the tapered optical waveguide layer at a position 150 μm from the first butt joint is about 150 nm, and the composition wavelength is about 1.07 μm.
m.

As in Example 1, in the crystal growth, a multiple quantum well active layer was first grown, and then the active layer was masked with an insulator to grow an optical waveguide layer. Tapered optical waveguide layer 6
The procedure is basically the same as that of the above embodiment, except for the shape of the mask for forming the mask. The configuration of the present invention will be described according to the manufacturing process with reference to FIGS. 13A to 13D.

In crystal growth, first, a multiple quantum well (MQ
W) An active layer was grown, and thereafter, the active layer portion was masked with an insulator, and an optical waveguide layer connected to the active layer region was grown.
First, an n-type (100) In is formed by a usual MOCVD method.
An n-type InP substrate-side cladding layer (thickness: 0.1 μm) 25, an active layer region 21, and an insulating film 90 are formed on a P substrate 25. Here, the active layer region 21 has a first optical confinement layer, an MQW active layer (with an oscillation wavelength of 1.3 μm), and a second optical confinement layer. In the example of the strained MQW active layer, InGaAsP (6 nm thick) is
A strained MQW active layer using GaAsP (having a composition wavelength of 1.10 μm and a thickness of 10 nm) as a barrier layer 32, and its period is nine. In the present invention, a semiconductor laser device practically uses an active layer region having a quantum well structure, an active layer region having a multiple quantum well structure, or an active layer region having a strained multiple quantum well structure. Conventional structures are sufficient for these structures. The same applies to other embodiments.

The well layer of the multiple quantum well structure has a thickness of about 3n.
The thickness in the range of about 7 nm to about 7 nm and the thickness of the barrier layer in the range of about 6 nm to about 12 nm are frequently used. The stacking of the multiple quantum well structure generally uses a range of about 12 to 3 periods.

Next, an insulator layer (for example, a SiN layer) 90 is formed on a region corresponding to the active layer region of the MQW layer. A SiN pattern 90 having a desired shape is formed with an opening in a region where an additional optical waveguide according to the present invention is formed. Thus, the MQW layer at the mask opening is removed by etching, using the pattern region of the insulator layer as a masked region (FIG. 13B).

Further, the composition wavelength of the InGaAsP optical waveguide layer (But Joint: Butt Joint) portion is 1.10 μm by the well-known MOCVD selective growth using the pattern region of the insulator layer 90 as a region to be masked.
m, thickness 300 nm) 22 (FIG. 13C).

Thereafter, the insulating film 90 is once removed, and a normal BH type (Buried Heterostructure) is used.
Example 1 for forming a laser structure
As in the case of (1), a striped insulating film is formed. Using the region of the insulating film 91 as a mask region, the active layer region 21 and the cladding layer 26 on the n-type substrate side are removed by etching. Thus, a mesa stripe is formed. Next, a p-type InP layer 45 and an n-type InP layer 46 are formed on both sides of the mesa stripe. Each of these layers is a so-called buried layer.

Next, the insulator layer used as a mask in the above step is removed, and the thus prepared semiconductor laminate is
A p-InP layer (thickness: 4 μm) as the second cladding layer 27
m) is replaced by a conventional MOCVD method (Metal-Organ
ic Chemical Vapor Deposit
(Ion Method) for crystal growth (FIG. 13)
D).

After that, the SiO ₂ mask is removed, and the LD
A contact layer 48 and a p-type electrode 35 were formed immediately above the portion. Furthermore, after the n-type electrode 36 is formed on the back surface of the substrate, both end faces are cleaved. In the present invention, the pair of electrodes 35 and 36 are provided not in the entire surface of the semiconductor laminate but in a region corresponding to the active layer region. When the electrode 35 is formed, a so-called contact layer 48 is generally formed below the electrode 35.

In the present embodiment, a structure in which La = 300 μm and Lb = 400 μm is used using 10 multiple quantum well layers. Therefore, the adjacent wavelength interval δλ of the multimode was 0.34 nm. In this example, the oscillation spectrum dispersion during operation at 1 Gbit / s was as small as 0.87 nm. 13 illustrates a configuration example of the optical communication device according to the present embodiment of FIG.
The difference from the example of FIG. 4 is that the lens 7 is omitted because the configuration of the light source itself is different. The other points are basically the same as those in the example of FIG. 4, and the detailed description thereof will be omitted.

In this example, the drive circuit operates at 1 Gb / s, and the transmission distance of the optical fiber at this time is 3 which is the loss limit.
Transmission of 0 km, which is three times that of conventional transmission, has become possible.

In this embodiment, the transmitting apparatus using the semiconductor laser in which the multiple quantum well active layer is not doped has been described. However, p-type modulation in which a p-type dopant is introduced only into the barrier layer of the multiple quantum well active layer is described. Needless to say, the same effect can be obtained even with a doped structure.

Next, an example of the present invention using an external resonator will be described. FIG. 16 is a schematic explanatory view showing an example of a semiconductor laser device using an external resonator. In this example, the portion having the active region has the structure of a general semiconductor laser device. That is, a first cladding layer 26 on a semiconductor substrate, for example, an InP substrate 25, a multiple quantum well active layer 21 as an active region,
A second cladding layer 27 is formed. After cleaving the end face of such a semiconductor laminate, the dielectric reflection film 23 is disposed on one cleavage surface and the dielectric low reflection film 24b is disposed on the other. Reference numeral 35 denotes an upper first electrode, and reference numeral 36 denotes a lower second electrode. A lens 53 and a semi-reflective mirror 54 are arranged facing the low reflection film 24b. In this example, the dielectric reflecting mirror 23 and the semi-reflecting mirror 54 form the reflecting surface of the resonator, and form a Fabry-Perot resonator. The laser light is taken out of the resonator from the semi-reflective mirror 54 side. Therefore, in this example, the length in the longitudinal direction of the resonator of the active region incorporated in the semiconductor laminate is La, and the distance between the low reflection film 24b and the semi-reflection mirror (half mirror) 54 is Lb. I do.

According to the present embodiment, it is also possible to provide an optical transmitter capable of reducing the cost and extending the transmission distance.

[0091]

According to the present invention, it is possible to provide an optical transmission device which can operate at a high speed of 1 Gb / s or more and which can be used for optical communication in which transmission over an optical fiber has a longer distance. In addition, the present invention can be provided at low cost.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a relationship between a transmission wavelength and a transmission distance in an optical fiber.

FIG. 2 is a diagram illustrating an example of a relationship between a transmission wavelength and a transmission distance in an optical fiber having a plurality of zero dispersion wavelengths.

FIG. 3 is a diagram illustrating an example of a relationship between an oscillation spectrum dispersion width of a semiconductor laser and a transmission distance;

FIG. 4 is a configuration diagram illustrating an example of an optical communication device according to the present invention.

FIG. 5 is a cross-sectional view taken along a plane parallel to a light traveling direction of an example of a semiconductor laser device according to the present invention.

FIG. 6 is a diagram showing an example of a multiple quantum well structure.

FIG. 7 is a cross-sectional view of a semiconductor laser device according to an embodiment of the present invention, taken along a plane intersecting the light traveling direction.

FIG. 8 is a diagram illustrating a relationship between a wavelength interval of a multi-mode oscillation mode and a dispersion width of an oscillation spectrum.

FIG. 9 is a diagram illustrating an example of a relationship between a transmission speed and a transmission distance in optical transmission using an optical fiber.

FIG. 10 is a diagram showing an example of a multi-mode oscillation waveform.

FIG. 11 is a cross-sectional view of another example of the semiconductor laser device according to the present invention, taken along a plane parallel to a light traveling direction.

FIG. 12 is a configuration example showing another example of the optical communication device of the present invention.

FIG. 13 is a sectional view showing a semiconductor laser device according to the present invention in the order of manufacturing steps.

FIG. 14 is a sectional view showing the semiconductor laser device according to the present invention in another manufacturing process order;

FIG. 15 is a cross-sectional view taken along a plane parallel to a light traveling direction during a manufacturing process of the example of the semiconductor laser device according to the present invention.

FIG. 16 is a cross-sectional view taken along a plane parallel to a light traveling direction of an example of a semiconductor laser device according to the present invention.

[Explanation of symbols]

1: semiconductor laser, 1 ': semiconductor laser with mode expander, 2: laser drive circuit, 3: temperature compensation circuit, 4: light receiver, 5: resistance, 6: temperature sensor, 7: lens, 8: optical fiber, 21, 41: multiple quantum well active layer, 22: semiconductor waveguide layer, 23, 24b: dielectric reflector, 25: semiconductor substrate, 26: first cladding layer, 27: second cladding layer, 28: taper Semiconductor waveguide layer, 31: well layer, 32: barrier layer, 33: light confinement layer, 35: first electrode, 36: second electrode, 42: first cladding layer, 4
3: a second cladding layer, 44: another second cladding layer,
45: p-InP buried layer, 46: first buried layer, 47: second buried layer, 48: contact layer, 4
9: p-InP substrate, 50: first electrode, 51: second electrode, 52: insulating film, 53: lens, 54: semi-reflective mirror,
90: Insulating film, 91: Striped insulating film.

Claims (10)

[Claims] 1. A light source comprising: a light source; and a driving unit for the light source, wherein the light source is a multi-mode oscillator whose signal light has a wavelength of 1.24 μm or more, and has a transmission speed of 1 Gbit / s or more, and An optical transmission device, which is a semiconductor laser device that enables a wavelength interval between adjacent modes of the multi-mode oscillation signal light to be 0.5 nm or less. 2. A semiconductor laser device having a light source and a driving unit for the light source, wherein the light source has a Fabry-Perot type resonator, and the semiconductor laser device has a signal light having a wavelength of 1.24 μm or more. Multi-mode oscillation, a transmission speed of 1 Gbit / s or more, and a wavelength interval between adjacent modes included in the multi-mode oscillation signal light can be 0.5 nm or less. Optical transmitter. 3. A Fabry-Perot resonator comprising a Fabry-Perot resonator and an active region having a multiple quantum well structure. A semiconductor laser device in which the length of the active region is shorter than the length of the semiconductor laser device, and the signal light from the semiconductor laser device is multi-mode oscillation having a wavelength of 1.24 μm or more;
In addition, the transmission speed is 1 Gbit / s or more, and the wavelength interval between adjacent modes included in the multi-mode oscillation signal light can be 0.5 nm or less. 4. The semiconductor laser device according to claim 2, wherein the two reflection surfaces of the Fabry-Perot resonator are formed on predetermined surfaces of a semiconductor laminate constituting the semiconductor laser device. 4. The optical transmission device according to claim 3. 5. The semiconductor laser device according to claim 1, wherein at least one of the two reflecting surfaces of the Fabry-Perot resonator is formed apart from the surface of the semiconductor laminate constituting the semiconductor laser device. 4. The optical transmission device according to any one of items 2 to 3. 6. The optical transmission device according to claim 2, wherein the Fabry-Perot resonator has a resonator length of 500 μm or more. 7. The optical transmission device according to claim 2, wherein a length of said active region is 400 μm or less. 8. The multiple quantum well structure according to claim 3, wherein the multiple quantum well structure is any one of a multiple quantum well structure including an InP-based compound semiconductor material. The optical transmission device according to claim 1. 9. A light source comprising: a light source; a driving unit of the light source; and an optical transmission line optically connected to the light source, wherein the light source is a multi-mode oscillator whose signal light has a wavelength of 1.24 μm or more. And a semiconductor laser device having a transmission speed of 1 Gbit / s or more, and a wavelength interval between adjacent modes of the multimode oscillation signal light of 0.5 nm or less. Optical transmission system. 10. A light source, a driving unit of the light source, and an optical fiber optically connected to the light source, wherein the light source is a multi-mode oscillation whose signal light has a wavelength of 1.24 μm or more; In addition, the wavelength interval between adjacent modes of the multi-mode oscillation signal light is at least 1.0 nm.
The relationship between the transmission speed and the wavelength interval between adjacent modes of the multi-mode oscillation signal light is as follows. When the transmission speed is 5 Gbit / s, the wavelength interval between adjacent modes is 1.0 nm, when the transmission rate is 1 Gbit / s, the wavelength interval between the adjacent modes is 0.5 nm, and when the transmission rate is 0.8 Gbit / s, the wavelength interval between the adjacent modes is 0. In contrast to a straight line connecting each characteristic point at 4 nm and a characteristic line having a wavelength interval of 1.0 nm between the adjacent modes connected to the straight line, the wavelength interval between the adjacent modes is small and transmission is performed. An optical transmission system, wherein a speed is set in a large range to enable optical transmission to the optical fiber.