JP3277905B2 - Wavelength selective laser device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a wavelength tunable (selective)
The present invention relates to a transmission light source, particularly to a wavelength selection laser device that outputs a laser beam having an arbitrary wavelength.

[0002]

2. Description of the Related Art In the optical communication market involving the wavelength selective laser device of the present invention, in response to a demand for a rapid increase in the capacity of a communication line due to a rapid increase in the Internet and the like, a conventional time-division transmission method (TDM. Divided Mu
It is not possible to cope with the increase in the operating speed of the L.Tx.
-Wavelength Divided Multi
plexer) has been used to greatly increase the communication line capacity per fiber.

In this D-WDM system, different signals are transmitted by transmission light sources of respective wavelengths, and the ITU-T also defines absolute wavelengths of transmission light sources and their intervals. Initially, communication capacity was secured by wavelength multiplexing of 16 wavelengths, but recently, 64 wavelengths, 80 wavelengths, 96 wavelengths, and 128 wavelengths have been secured.
There is an increasing tendency to increase the degree of multiplexing of wavelengths and wavelengths, and reduce the wavelength spacing to secure communication capacity.

On the other hand, in the D-WDM system, since the transmission light sources, which are one of the factors affecting the reliability of the system, operate independently of each other, the system as a whole is more computationally expensive than the conventional system. The reliability must be reduced.

For this reason, there has been a situation in which a measure for improving the reliability of the entire system, such as providing a spare transmission light source for the transmission panel of each wavelength, must be taken. That is, the probability that the transmission light source itself becomes inoperable is generally small as compared with the life of the system.
Since one system has a large number of transmission light sources and each transmits an independent signal, it is necessary to actually take measures such as providing spare transmission light sources by the number of transmission light sources.

In such a situation, when a transmission light source of a certain wavelength in the system malfunctions, a wavelength tunable (selective) transmission light source capable of backing up the wavelength has been strongly desired.

As a specific wavelength variable transmission light source, for example, as shown in FIG. 3, an FP-LD (Fabry-Pe
rot LD) 31, an external diffraction grating 33, and an optical coupling lens 32, and a wavelength tunable in which the wavelength of light emitted through the spherical fiber 38 is variable by adjusting the angle of the external diffraction grating 33. There is an example of configuring a transmission light source.

[0008]

However, in such a configuration, it is necessary to configure a very precise optical system from the FP-LD 31 to the external diffraction grating 33, and in that case, a wavelength requirement for the optical system is required. It is necessary to perform precise angle adjustment control according to the above, and it is necessary that the precise optical system must operate stably for a long time, but in reality it is movable to select the wavelength There is a drawback that the stability of optical coupling is not compatible, that is, there is no long-term fluctuation between the angle adjustment mechanism of the external diffraction grating and the optical system.

Therefore, for example, with respect to the angle adjustment of the external diffraction grating, it is possible to add a function of monitoring the oscillating wavelength and performing a minute angle adjustment in consideration of the variation over time.

However, when used in an actual system, it is necessary to switch to a transmission light source having a wavelength required as a backup in a short time. In addition to adjusting the angle of the external diffraction grating, the oscillation wavelength is monitored. Then, it is difficult to realize a stable operation within a desired time in order to add a fine adjustment.

Furthermore, there is a problem in that the device has a function of monitoring the oscillation wavelength and must be equipped with a feedback circuit, which leads to an increase in the size of the device.

An object of the present invention is to provide an optical system having excellent stability,
The structure is simple, miniaturization and integration are possible,
It is still another object of the present invention to provide a wavelength selection laser device capable of arbitrarily selecting a wavelength.

[0013]

To achieve the above object, according to an aspect of, the wavelength selective laser device according to the present invention comprises a composite optical waveguide having a semiconductor optical amplifier device, the semiconductor light up
The drive current is increased while controlling the operating temperature of the width element,
A wavelength selection laser device for driving while substantially fixing a wavelength for obtaining a maximum gain , wherein the composite optical waveguide includes an optical demultiplexer formed on the optical waveguide between an optical input end and an optical output end. , a diffraction grating, possess an optical multiplexer, the optical demultiplexer before
One terminal connected to the optical input terminal and multiple optical waveguides
Having different terminals and diffracted on the plurality of optical waveguides respectively.
Diffraction gratings with different periods are formed, and the optical multiplexer is
Ends connected to a plurality of optical waveguides connected via a diffraction grating
A semiconductor and another terminal connected to the optical output terminal, the semiconductor
An optical amplifier is optically coupled to the optical input end, and a semiconductor optical
The optical output of the amplifying element is input to all the multiple diffraction gratings simultaneously.
Only the wavelengths that match the diffraction period of the diffraction grating are diffracted.
To be fed back to the semiconductor optical amplifier
The is <br/> which forms an external cavity laser having a wavelength selectivity.

Further, a semiconductor optical amplifier, a semiconductor optical amplifier is optically coupled to the optical output end of the composite optical waveguide, in which suppressing the variation between the laser beam output wavelength, to enable lasing of high purity is there.

[0015]

Further, the semiconductor optical amplifier has a semiconductor optical amplifier, and the semiconductor optical amplifier is optically coupled on the optical waveguide of the composite optical waveguide, and selectively amplifies only a specific wavelength.

Further, the semiconductor optical amplifier is operated (ON) at a wavelength corresponding to a selected wavelength, and is deactivated (OFF) at other wavelengths. It is to let.

The diffraction gratings formed on the plurality of optical waveguides of the composite optical waveguide have different diffraction periods and effective diffraction efficiencies, and are standardized by the ITU-T in a 1.55-um band D-WDM system. It is configured to select the respective wavelengths.

[0019]

(Embodiment 1) FIG. 1 shows a configuration diagram of a first embodiment of a wavelength selective laser device according to the present invention. The wavelength selective laser device according to the present invention has an optical demultiplexer 13 formed by an optical waveguide. The optical demultiplexer 13
A single optical input / output terminal is formed between an optical input terminal 12 and an optical output terminal 16, and each optical waveguide forms diffraction gratings 14 a to 14 e and passes through an optical multiplexer 15. The composite optical waveguide 111 is formed by being guided to the optical output end 16.

In the composite optical waveguide 111, the semiconductor optical amplifier 11 is optically coupled to the optical input terminal 12 and the semiconductor optical amplifier 17 is optically coupled to the optical output terminal 16. Light output is extracted.
The diffraction gratings 14a to 14e formed on the plurality of optical waveguides of the composite optical waveguide 111 have different diffraction periods and effective diffraction efficiencies, and have a D-WD of 1.55 μm band.
The M system is configured to select a wavelength standardized by ITU-T.

In this embodiment, the semiconductor optical amplifying element 11 has the 1520 normally required in a D-WDM system.
InGaAs capable of laser oscillation in the vicinity of 近 傍 1620 nm
The active layer structure is formed using a material system such as P, and a non-reflective coating is formed on the end face on the optical waveguide side to obtain an appropriate light output, and a high-reflection coating is formed on the other end face to form a resonator. It has been subjected.

Since the gain of the semiconductor optical amplifier 11 is different depending on the drive current and the operating temperature, the wavelength at which the maximum gain is obtained by increasing the drive current and increasing the gain of the semiconductor optical amplifier 11 while controlling the temperature. Can be driven almost fixed.

Since the maximum gain wavelength changes by 0.3 to 0.5 nm / ° C. depending on the temperature in accordance with the change in the refractive index of the active layer, the semiconductor optical amplifier 11 has a temperature change of 30 ° C. to 40 ° C. , An adjustment range of about 9 to 20 nm can be secured, and the wavelength giving the maximum gain can be freely selected in this range.

The optical output of the semiconductor optical amplifying element 11 optically coupled to the optical input end 12 of the composite optical waveguide 111 is applied to each of the diffraction gratings 14a to 14e via an optical demultiplexer 13 formed on the waveguide. Is entered. Diffraction gratings 14a to 14e
In this case, only the frequency (wavelength) suitable for the period is diffracted and input again to the semiconductor optical amplifier 11, so that the semiconductor optical amplifier and the diffraction gratings 14a to 14e can oscillate at different wavelengths. A plurality of laser devices will be configured.

With an increase in the drive current of the semiconductor optical amplifier,
The gain between each of the diffraction gratings 14a to 14e increases, and finally the laser oscillation occurs when the wavelength of the maximum gain reaches the threshold gain. After the laser oscillation, the increase in the drive current of the semiconductor optical amplifier is consumed by the increase in the laser light output and does not affect the gain. Therefore, the laser light of the oscillated wavelength increases with the increase of the drive current, and the laser oscillation at another wavelength Will not cause.

Therefore, the oscillation wavelength of the laser device can be selected by selecting the wavelength giving the maximum gain of the semiconductor optical amplifier by controlling the operating temperature and increasing the current application.

Each of the optical waveguides on which the diffraction gratings 14a to 14e are formed is thereafter passed through the optical multiplexer 13 to the semiconductor optical amplifier 1
The optical coupling unit 7 corrects a loss caused by demultiplexing / combining and a light output difference caused by an effective diffraction efficiency of the diffraction gratings 14a to 14e having different wavelengths.

In this manner, by setting the maximum gain wavelength of the semiconductor optical amplifier 11 to an arbitrary wavelength to be selected, it is possible to configure a wavelength selective laser device capable of selecting an arbitrary wavelength. Become.

In the above embodiment, the semiconductor optical amplifier 11 and the composite optical waveguide 111 are optically coupled independently of each other, but they may be formed on the composite optical waveguide 111. Further, in the present embodiment, the interval of the wavelength to be selected was not discussed, but by selecting the operating temperature,
The semiconductor optical amplifying element 1 is selected so that an arbitrary wavelength can be selected.
It is necessary to set the wavelength interval in consideration of the gain dependency on one wavelength and the gain difference between the wavelength giving the maximum gain and other wavelengths.

At this time, if it is necessary to construct a wavelength selection laser device for selecting a maximum of n wavelengths, k
If k wavelength-selective laser devices of m + 1, km + 2,..., km + k are used to effectively configure n wavelength-selective lasers, the required wavelength interval is maintained and a sufficient gain difference between wavelengths is maintained. It is possible to configure a wavelength selection laser device having the same. Incorporating a spot size conversion structure advantageous for optical coupling between the semiconductor optical amplifier and the semiconductor optical amplifier does not affect the essence of the present invention.

(Embodiment 2) FIG. 2 shows a configuration of a wavelength selection laser device as a second embodiment of the present invention. 2, in the second embodiment, as in the first embodiment, the wavelength selective laser device has an optical demultiplexer 23 formed by a plurality of optical waveguides.

The optical demultiplexer 23 is formed by an optical waveguide, and has an optical demultiplexer 23 between a single optical input / output end 22 and a single optical output end 26. Each of the optical waveguides is guided to the semiconductor optical amplifier array 127 optically coupled via the diffraction gratings 24a to 24e, and then guided to the optical output end via the optical multiplexer 25.
One. The diffraction gratings 24a to 24e formed on the plurality of optical waveguides of the composite optical waveguide 121 have different diffraction periods and effective diffraction efficiencies, respectively.
-The WDM system is configured to select a wavelength standardized by ITU-T.

In the second embodiment of the present invention, the external cavity laser formed by the semiconductor optical amplifier 21 and the diffraction gratings 24a to 24e is connected to a semiconductor optical amplifier 127 optically coupled on each optical waveguide. Is characterized in that only specific wavelengths are selectively amplified,
A wavelength selection laser device is configured via the optical multiplexer 25.

The semiconductor optical amplifier 127 can control the wavelength for giving gain and its wavelength bandwidth depending on its composition and structure. Therefore, as described in the first embodiment of the present invention, if the wavelength interval selectable by one wavelength selection laser device is set in consideration of the wavelength band of the semiconductor optical amplifier and the semiconductor optical amplifier, the selection can be made. By operating the semiconductor optical amplifier corresponding to the wavelength to be operated (ON) and deactivating (OFF) the other semiconductor optical amplifiers, a wavelength selective laser device configured to oscillate only the wavelength of the selected wavelength with higher purity. be able to.

At this time, as shown in the first embodiment, a semiconductor optical amplifier array in which the gain wavelength of each semiconductor optical amplifier is controlled by the composition and structure may be used. It is also possible to adopt a configuration in which the gain wavelength is controlled by controlling the temperature of the semiconductor optical amplifier having the structure.

As described above, also in the embodiment of the present invention, the fact that the spot size conversion structure capable of greatly relaxing the tolerance of the optical coupling is incorporated in the portion requiring the optical coupling determines the essence of the present invention. Not something.

[0037]

As described above, according to the present invention, a semiconductor optical amplifying device optically coupled to a composite optical waveguide, together with a diffraction grating formed on the optical waveguide of the composite optical waveguide, has an external resonance having wavelength selectivity. Therefore, according to the present invention, lasers oscillating at different wavelengths can be configured by a plurality of optical waveguides having a semiconductor optical amplifier and a diffraction grating, and the stability of the optical system can be improved. It is excellent, has a simple structure, can be miniaturized, and can be integrated, and can obtain a laser light output of an arbitrary wavelength according to demand.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a wavelength selection laser device according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a wavelength selective laser device according to a second embodiment of the present invention.

FIG. 3 is a diagram showing a conventional wavelength selection laser device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Semiconductor optical amplifier 12 Optical input terminal 13 Optical demultiplexer 14a-14e Diffraction grating 15 Optical multiplexer 16 Optical output terminal 17 Semiconductor optical amplifier 18 Spherical fiber 21 Semiconductor optical amplifier 22 Optical input terminal 23 Optical demultiplexer 24a -24e Diffraction grating 25 Optical multiplexer 26 Optical output end 32 Optical coupling lens 33 External diffraction grating 38 Spherical fiber 111 Composite optical waveguide 121 Composite optical waveguide

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-199487 (JP, A) JP-A-9-260753 (JP, A) JP-A-8-97516 (JP, A) JP-A-4-975 81724 (JP, A) JP-A-63-160391 (JP, A) JP-A-5-343792 (JP, A) IEEE Photonics Technology Letters, 5 [8], 908-910 Electronics Letters, 28 [25] (58) Fields investigated (Int. Cl. ⁷ , DB name) H01S 5/00-5/50 G02B 6/12 G02B 6/293

Claims (5)

(57) [Claims] 1. A semiconductor optical amplification device comprising : a composite optical waveguide; and a semiconductor optical amplification device.
Increase the dynamic current and fix the wavelength for maximum gain almost fixed
A wavelength selecting laser device to be driven , wherein the composite optical waveguide comprises: an optical demultiplexer formed on an optical waveguide between an optical input end and an optical output end; a diffraction grating; and an optical multiplexer. Yes, and the optical demultiplexer is connected to the optical input end one
A terminal and another terminal connected to the plurality of optical waveguides;
Diffraction gratings with different diffraction periods on a number of optical waveguides
And the optical multiplexer is connected through the diffraction grating.
Connecting to a plurality of optical waveguides and connecting to the optical output end
The semiconductor optical amplification element has a light input port.
Optically coupled to the power end, the optical output of the semiconductor optical amplifier
Input to all diffraction gratings at the same time
Only the wavelengths that match the
A wavelength-selective laser device characterized in that an external cavity laser having wavelength selectivity is formed by being configured to feed back to a laser. Has a 2. A semiconductor optical amplifier, a semiconductor optical amplifier is optically coupled to the optical output end of the composite optical waveguide, in which suppressing the variation between the laser beam output wavelength, to enable lasing of high purity 2. The wavelength selection laser device according to claim 1, wherein: 3. The semiconductor optical amplifier according to claim 1, further comprising a semiconductor optical amplifier, wherein the semiconductor optical amplifier is optically coupled on the optical waveguide of the composite optical waveguide and selectively amplifies only a specific wavelength. Wavelength selection laser device. 4. The semiconductor optical amplifier operates at a wavelength corresponding to a selected wavelength (ON) and deactivates the other wavelengths (OFF), thereby oscillating only the selected wavelength at higher purity. The wavelength selection laser device according to claim 3 , wherein the wavelength selection laser device is operated. 5. A diffraction grating formed on a plurality of optical waveguides of a composite optical waveguide has different diffraction periods and effective diffraction efficiencies.
The wavelength selection laser device according to claim 1, wherein the wavelength selection laser device is configured to select a wavelength standardized by UT.