JPS6366436B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an integrated multi-wavelength light source in which output intensity deviation of a plurality of lights having mutually different wavelengths is small.

[Technical background of the invention and its problems]

Wavelength multiplexing technology plays a major role in making effective use of optical fibers and constructing optical communication systems that are highly flexible and flexible. In this optical wavelength multiplexing communication system, as illustrated in _{FIG .} The optical signals are multiplexed and transmitted via an optical fiber cable 4, and the optical signals are separated into wavelengths λ ₁ and λ ₂ by a demultiplexer 5 and received by optical receivers 6 and 7, respectively. . Therefore, it is possible to simultaneously perform two systems of optical signal communication using two lights of different wavelengths as signal propagation media. When performing such wavelength multiplexed communication, it is desired to multiplex a large amount of light by making the wavelength interval of the light as narrow as possible, for example, about 10 Å, from the viewpoint of communication efficiency.

Now, when changing the emission wavelength of a semiconductor light emitting device used as a light source, it has conventionally been generally done by changing its composition. For example, AlGaAs
In the case of a system semiconductor laser, as shown in Figure 2,
By changing the composition ratio of Al and Ga by about 1%, the band gap can be changed by about 0.01 eV, which can give a change in wavelength of about 70 Å. However, it is difficult to integrate multiple semiconductor lasers with different compositions and different emission wavelengths on the same substrate, especially to form these semiconductor lasers in close proximity.
It is extremely difficult to manufacture.

On the other hand, there is a semiconductor laser in which a diffraction grating is formed on a substrate with a uniform composition and the emission wavelength is varied by changing the lattice constant. This semiconductor laser uses so-called DFB (distributed feedback) and DBR.
(distributed blurred reflection) technology, for example, as shown in FIG. 3, an uneven diffraction grating 10 is formed near the laser active layer 9 of a semiconductor laser 8 to construct a distributed optical resonator. It has a structure. The emission wavelength of a semiconductor laser having such a structure is determined only by the size of the unevenness of the diffraction grating 10 without depending on its composition, and has the advantage of high wavelength accuracy. Therefore, it is considered suitable as an integrated wavelength multiplexed light source.

However, when considering the oscillation mechanism, there is a problem in that there is a large deviation in the emission output intensity of each simultaneously integrated semiconductor laser. That is, as shown in FIG. 4a, the gain characteristics of a GaAlAs semiconductor laser having a p-type active layer are shown using the minority carrier (electron) concentration n injected into the active layer as a parameter.
Its center gain increases in proportion to the injected carrier. At this time, when the semiconductor laser oscillates, the gain needs to exceed various losses such as free carrier absorption, scattering loss, and reflection loss. The gain coefficient that gives the oscillation value in a general GaAlAs semiconductor is about 300 cm ^-1 , and as is clear from the characteristics shown in Figure 4a, when the injection carrier is 2.0 × 10 ¹⁸ cm ^-3 , the gain coefficient of about 100 Å Laser oscillation light can be obtained within the range. Therefore, it is possible to form a light source that multiplexes approximately 10 waves of light with a wavelength interval of 10 Å. However, there is a problem in that the oscillation threshold current values for each wavelength obtained in this manner are different as shown in FIG. 4b, and that when driven with the same current value, there is an output intensity deviation. That is, when the wavelengths are λ ₁ , λ ₂ to _{λ 10} from the short wavelength side,
There is a problem in that the output intensity at the wavelengths λ ₅ and λ ₆ near the center is high, and the output intensity is low at the wavelengths at both ends.

On the other hand, various types of optical multiplexers for multiplexing the thus obtained lights of different wavelengths have been developed. However, when an optical multiplexer is integrated with the plurality of integrated semiconductor lasers to achieve miniaturization, various problems arise, such as the need to equalize insertion loss. FIG. 5 shows an optical waveguide type optical multiplexer in which an optical waveguide 12 is formed by diffusing Ti on a LiNbO ₃ crystal substrate 11, and the waveguide dimensions are approximately 5 to 10 μm and the waveguide thickness is 2 to 3 μm. It has a structure in which the waveguide spacing is about 500 μm, and the overall size is about 1 cm square. However, in such a small integrated multiplexer, radiation of propagating light due to waveguide bending has not been a problem in conventional multiplexers constructed using individual components. Losses become a big problem. This means that the optical propagation losses between the plurality of input ports and the output ports are different.

When trying to obtain a compact wavelength-multiplexing integrated light source that is integrated in this way, there are problems with the output intensity deviation of the light of different wavelengths output by multiple semiconductor lasers, as described above, and the input of the multiplexer. There were problems such as differences in optical propagation loss between output ports. For this reason, there was a problem in its practicality as a wavelength multiplexed light source used in wavelength multiplexed communications.

[Purpose of the invention]

The present invention has been made in consideration of these circumstances, and its purpose is to achieve practicality in a compact form that suppresses the deviation in output light intensity of lights of different wavelengths that are wavelength-multiplexed and output. The objective of the present invention is to provide a multi-wavelength integrated light source with high performance.

[Summary of the invention]

The present invention provides that the deviation in the output light intensity of a plurality of semiconductor lasers whose emission wavelengths are different by changing the distribution constant of the diffraction grating and the difference in optical propagation loss between ports of an optical multiplexer depend on the structure thereof. The semiconductor laser that outputs light at a wavelength with high output light intensity is optically coupled to the input port of the optical multiplexer, which has a large loss, and conversely, the semiconductor laser that outputs light with low output light intensity is optically coupled. By optically coupling the input ports of the multiplexer with low loss, and by optically coupling the multiple semiconductor lasers and the input ports of the multiplexer in correspondence with each other, each of the multiplexed outputs can be This is designed to suppress the output deviation of wavelength light.

〔Effect of the invention〕

Therefore, according to the present invention, the output intensity deviation of lights of different wavelengths can be effectively canceled by using the loss difference between the ports of the multiplexer, and thereby the intensity deviation of the combined output can be easily suppressed. By doing so, it is possible to achieve miniaturization and integration. Therefore, it is extremely effective as a light source device in wavelength multiplexed communication, and its practical advantages are enormous.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 6 is a schematic configuration diagram showing the first embodiment, and 21 is a plurality of semiconductor lasers 22a, 22b--
A first substrate 22n is formed, and 23 is a second substrate formed with an optical multiplexer consisting of an optical waveguide. Semiconductor lasers 22a, 22b to 22n
They have a structure in which they are formed with the same composition on, for example, a GaAlAs substrate 21, are provided with a DBR type diffraction grating 24, and are simultaneously integrated with different emission wavelengths. Each of these semiconductor lasers 22a, 22
The emission wavelength interval from b to 22n is set to 10 Å by changing the distribution constant of the DBR type diffraction grating 24. Note that these semiconductor lasers 22
a, 22b to 22n are arranged close to each other in parallel with the light oscillation directions aligned.

On the other hand, the optical multiplexer 23 is its substrate.
The optical waveguide 25 is formed by diffusing Ti on a LiNbO ₃ crystal, and has a structure as shown in FIG. 5 above. This optical multiplexer 23 inputs the lights of different wavelengths outputted from each of the semiconductor lasers 22a, 22b to 22n through its input ports, multiplexes them, and outputs them from its output port. It is something.

Therefore, each semiconductor laser 22a, 22b-2
Optical coupling between 2n and each input port of the multiplexer 23 is performed as follows. Now, assuming that the wavelengths of the 10 waves of light are λ ₁ , λ ₂ to _{λ 10} from the shortest wavelength side, these are ranked in descending order of light intensity. On the other hand, for the optical multiplexer 23, the ranking is set in order from the input port side having the characteristic of large optical propagation loss. Then, according to these orders, the semiconductor lasers 22a, 22b to 22n and the input ports are associated with each other and optically coupled. That is, in this case, semiconductor lasers that output light with wavelengths λ ₅ and λ ₆ are provided facing the outermost input ports of the optical multiplexer 23, respectively. Inside, semiconductor lasers that output light with wavelengths λ ₄ and λ ₇ and semiconductor lasers that output light with wavelengths λ ₃ and λ ₈ are arranged facing the input port in this order. Therefore, the innermost input port has the wavelength λ ₁ ,
Semiconductor lasers that output light with a wavelength of λ ₁₀ will be placed facing each other. Incidentally, each semiconductor laser 2 like this
The emission wavelength setting of 2a, 22b to 22n is determined by variably setting the distribution constant of the DBR type diffraction grating 24, as described above. Furthermore, here, an example is shown in which the semiconductor lasers 22a to 22n and the optical multiplexer 23 are formed on separate substrates, and placed close to each other to perform the above-mentioned optical coupling. Of course, it is also possible to simultaneously integrate and form them on the same substrate.

Thus, according to the multi-wavelength integrated light source configured in this way, the light having different wavelengths outputted from each of the semiconductor lasers 22a, 22b to 22n with output intensity deviation is transmitted to input ports having different loss characteristics. The signals are inputted from each other and multiplexed. Moreover, a large loss is caused to wavelength light with high output intensity. Therefore, the light intensity of each wavelength in the multiplexed output is averaged, and the intensity deviation is effectively suppressed.

Therefore, it is very useful as an integrated light source in wavelength multiplexed communications. Moreover, it can be easily miniaturized through integration, and has many practical advantages.

By the way, there is a concept that in order to equalize the output intensity of each semiconductor laser, it is sufficient to change the applied current to the semiconductor laser or change the temperature. However, since the dimensions of the integrated light source as described above are very small,
It is extremely difficult to perform the above control for each individual semiconductor laser. Furthermore, even if such control were possible, the control mechanism would be extremely complicated, and for example, a change in current value would also appear as a change in temperature. Therefore, in order to perform such control, a certain degree of ingenuity is required, and the merits of the multi-wavelength integrated light source, which is integrated and miniaturized, are lost. Therefore, as mentioned above, the optical coupling relationship between the semiconductor laser and the input port of the multiplexer is
It can be said that determining the output intensity in correspondence with the loss characteristics of the input port has an extremely large advantage.

Now, FIG. 7 is a diagram showing another embodiment of the present invention, and shows an example in which the multiplexer 26 is constructed using a diffraction grating 27. In this case, the farther the input port is from the output port, the more times it passes through the diffraction grating 27, and as a result, the loss increases. Optical coupling may be effected by arranging it to face the input port farther from the output port.

Needless to say, even in this case, the same effects as in the above-mentioned embodiment can be achieved.

As described above, according to the present invention, it is possible to oscillate and output light having different wavelengths from a plurality of simultaneously integrated semiconductor lasers, and to combine and multiplex the light while suppressing intensity deviation and output the light. Moreover, it can be integrated into a small size and its structure is simple. Therefore, it has great practical effects as a light source used in wavelength division multiplexing communications.

Note that the present invention is not limited to the above embodiments. For example, the wavelength interval and the number of wavelengths of a plurality of lights may be determined according to specifications. Further, a semiconductor laser can be constructed using a DFB type diffraction grating instead of a DBR type diffraction grating. In short, the present invention can be implemented with various modifications without departing from the gist thereof.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of a wavelength division multiplexing communication system, Figure 2
The figure shows the change in bandgap depending on the composition of an AlGaAs semiconductor laser, Figure 3 shows the structure of a DFB semiconductor laser, and Figure 4 a and b show AlGaAs semiconductor lasers.
A diagram showing gain characteristics and output intensity of a semiconductor laser,
Figure 5 is a diagram showing an example of an optical waveguide type multiplexer, Figure 6
The figure is a schematic block diagram showing one embodiment of the present invention, and FIG. 7 is a block diagram showing another embodiment of the present invention. 22a, 22b to 22n... semiconductor laser, 23
...Optical multiplexer, 24... DBR type diffraction grating, 25... Half waveguide, 26... Optical multiplexer, 27... Diffraction grating.

Claims (1)

[Scope of Claims] 1. n semiconductor lasers of the same composition formed by simultaneous integration on a substrate with different oscillation wavelengths, and respective outputs from each of the semiconductor lasers integrated on the substrate. The multiplexer is equipped with a multiplexer for multiplexing the light beams having different oscillation wavelengths, and the multiplexer has n light beams each having a different oscillation wavelength outputted from each of the semiconductor lasers. It has an input port and an output port that multiplexes and outputs the input light, and the n semiconductor lasers and the input port have a high optical propagation loss between the semiconductor laser with high output light intensity and the output port. A multi-wavelength integrated light source characterized by being arranged to optically couple input ports in sequence. 2. The substrate on which the semiconductor laser is integrated and the substrate on which the optical multiplexer is integrated are the same substrate, and optical coupling between the semiconductor laser and the optical multiplexer is performed via an optical waveguide formed on the substrate. 2. A multi-wavelength integrated light source according to claim 1. 3. The substrate on which the semiconductor laser is integrated and the substrate on which the optical multiplexer is integrated are two separate substrates that are placed close to each other, and the optical coupling between the semiconductor laser and the optical multiplexer is performed by the two separate substrates. 2. The multi-wavelength integrated light source according to claim 1, wherein the multi-wavelength integrated light source is transmitted through an optical propagation path formed between optical input/output ports arranged oppositely on the substrate. 4. The multi-wavelength integrated light source according to claim 1, wherein the optical multiplexer has a structure in which a diffraction grating is formed on a substrate. 5. The multi-wavelength integrated device according to claim 1, wherein the optical multiplexer has a structure in which an optical waveguide is formed by selectively diffusing Ti on a LiNbO ₃ crystal substrate.