JPH11234246A - Optical transmission system and optical transmitter to be used for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-reliability wavelength multiplex optical transmission system. SOLUTION: This optical transmission system is formed by providing plural optical transmitters 1 and an optical transmission line for the multiplex transmission of beams having mutually different wavelengths transmitted from the plural optical transmitters 1 and the optical transmitter 1 is provided with an external resonant laser diode 10 equipped with a semiconductor device 6 and a fiber grating 2 for extracting only the light of a predetermined set wavelength out of laser beams emitted from the semiconductor device 6 while selectively reflecting it, thermistor 7 for detecting the temperature around the laser diode 10 and wavelength control means for controlling a Peltier element 8 through a control circuit 9 based on the detected temperature of the thermistor 7 and controlling the temperature of the fiber grating so that control can be performed for providing wavelengths within a range not exceeding the predetermined allowable range at all the time from the said set wavelength corresponding to the wavelength of light reflected by the fiber grating 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength division multiplexing optical transmission system for multiplexing and transmitting light of a plurality of different wavelengths, and an optical transmitter used in the optical transmission system.

[0002]

2. Description of the Related Art In the field of optical communication, a wavelength division multiplexing transmission system for multiplexing and transmitting light having a plurality of different wavelengths is used. FIG. 1 shows an example of a wavelength division multiplexing system. As shown in FIG. 1, the system includes a plurality of optical transmitters 1 (1a1 to 1aN) that emit light having different wavelengths (λ1, λ2,. It has an optical coupler 12 for multiplexing outgoing light of different wavelengths and an optical fiber 3 as an optical transmission line, and multiplexes the light of different wavelengths multiplexed by the optical coupler 12 through the optical fiber 3. Has become.

[0003] In addition, a WDM
(Wavelength Division Multi
iplex) Multiple receivers 5a1 through 5a1
5aN is provided, and of the wavelength division multiplexed transmission light obtained by multiplex transmission of the optical fiber 3, light of different wavelengths (λ1, λ2,.
Each of the receivers 5a is separated by the M filter 4 and taken out.
1 to 5aN. In addition,
As shown in FIG. 5, the WDM filter 4 has a band (filter band) for each separation wavelength. Generally, each of the optical transmitters 1a1 to 1a is assigned to each filter band.
The optical transmission system is configured so that the wavelength of each optical signal from aN enters.

[0004] The optical transmitter 1 is, for example, as shown in FIG.
And a thermistor 7, a control circuit 9, and a Peltier element 8. As is well known, the laser diode 10 excites the semiconductor element 6 by injecting electrons or light into the semiconductor element 6, so that when electrons and holes flow out to the junction of the semiconductor element, the laser diode 10 uses a pn junction. , Which emits coherent light, and the wavelength of light emitted from the laser diode 10 is
May fluctuate depending on the ambient temperature.

Accordingly, in the optical transmitter 1 shown in FIG. 1, the ambient temperature of the laser diode 10 is detected by the thermistor 7, and when the detected temperature deviates from a predetermined reference value, the control circuit 9 controls the Peltier device. By controlling the direction and intensity of the voltage applied to 8,
The semiconductor element 6 constituting the laser diode 10 is heated or cooled by the Peltier element 8 to compensate for the deviation from the reference value of the detected temperature, thereby keeping the temperature of the laser diode 10 constant. ing. By such feedback control, the wavelength of the light transmitted from the optical transmitter 1 is kept constant, and as shown in FIG. 5, the wavelength of the signal light does not deviate from the filter band of the WDM filter 4. I have.

When the center wavelength of the laser diode 10 fluctuates due to aging of the laser diode 10 or the like, the reference value is changed and the ambient temperature of the laser diode 10 is arbitrarily changed. The center wavelength of the diode 10 is returned to the wavelength before the change.

[0007]

However, in the optical transmission system as described above, the optical transmitter 1 heats the semiconductor element 6 of the laser diode 10 by the Peltier element 8 when managing the wavelength of the light to be transmitted. Since the temperature of the laser diode 10 is controlled by cooling or cooling, a load is applied to the laser diode 10 due to heating or cooling of the laser diode 10, and the life of the laser diode 10 is shortened. As a result, there is a problem that the reliability of the optical transmitter 1 is reduced, and the construction of a highly reliable optical transmission system is hindered.

The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide a highly reliable wavelength division multiplexing optical transmission system and an optical transmitter used in the optical transmission system. It is in.

[0009]

In order to achieve the above-mentioned object, the present invention has the following structure to solve the problem. That is, the first invention of the optical transmission system includes a semiconductor element and a fiber grating that selectively reflects and extracts only light having a predetermined set wavelength out of laser light emitted from the semiconductor element. A plurality of optical transmitters having an external resonance type laser diode, and an optical transmission line for multiplexing light of different wavelengths transmitted from the plurality of optical transmitters, wherein the optical transmitter has A configuration provided with wavelength control means for controlling the wavelength of light reflected by the fiber grating so that the wavelength of light reflected by the fiber grating always falls within a range not exceeding a predetermined allowable range from the corresponding set wavelength. It is a means to solve the problem.

The second invention of the optical transmission system is as follows.
In addition to the configuration of the first aspect, the wavelength control means may include:
This is a means for solving the problem by having a configuration as a temperature control means for controlling the wavelength of light reflected by the fiber grating by controlling the temperature of the fiber grating.

Further, in the third aspect of the optical transmission system, in addition to the configuration of the first or second aspect, the wavelength control means controls a stress applied to the fiber grating to thereby control the fiber grating. This is a means for solving the problem by having a configuration as a stress control means for controlling the wavelength of the reflected light.

Furthermore, an optical transmitter according to the present invention is an optical transmitter used in an optical transmission system, wherein the wavelength control means according to the first aspect of the optical transmission system or the wavelength control means according to the second aspect of the optical transmission system. The present invention is a means for solving the problem by having a configuration having a wavelength control means constituted by a temperature control means or a wavelength control means constituted by a stress control means of the third invention of the optical transmission system.

In the present invention having the above-described configuration, the plurality of optical transmitters used in the optical transmission system selectively select only a light having a predetermined set wavelength from a semiconductor element and laser light emitted from the semiconductor element. An external resonance type laser diode provided with a fiber grating to be reflected and taken out, and in the optical transmitter, the wavelength of light reflected by the fiber grating always exceeds a predetermined allowable range from the corresponding set wavelength. Since the wavelength control means for controlling the wavelength of the reflected light of the fiber grating is provided so as to have a wavelength within the range which is not within the range, the wavelength of the reflected light of the fiber grating is controlled by the wavelength control means, and the temperature of the semiconductor element of the laser diode is increased. The application of a load by the control is suppressed.

Therefore, an optical transmission system using an optical transmitter for controlling the wavelength of light emitted from the laser diode by controlling the temperature of the semiconductor element of the laser diode, and controlling the emission wavelength of the optical transmitter. On the contrary, the life of the laser diode can be extended, and the reliability of the optical transmission system can be increased.

The wavelength control of the reflected light from the fiber grating can be easily and accurately performed by controlling the temperature of the fiber grating or controlling the stress applied to the fiber grating. The transmission wavelength of the optical transmitter can be accurately controlled by accurately controlling the reflected light wavelength of the fiber grating in accordance with the reception wavelength of each of the plurality of optical receivers provided in the transmission system. The reliability of the system can be increased, and the above-mentioned problem is solved.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. In the description of the present embodiment, the same reference numerals are given to the same parts as those in the conventional example, and the overlapping description will be omitted. First optical transmission system according to the present invention
The embodiment has the block configuration shown in FIG. 1 similarly to the conventional optical transmission system, and the feature of this embodiment different from the conventional example is that a plurality of optical systems used in the optical transmission system are used. That is, the transmitter 1 is configured as shown in FIG.

That is, the characteristic of the optical transmission system of this embodiment is that, as shown in FIG. 2, the laser diode 10 of the optical transmitter 1 is connected to the semiconductor element 6 and the semiconductor element 6.
Laser diode 1 having a fiber grating 2 for selectively reflecting and extracting only light of a predetermined set wavelength from laser light emitted from the laser beam 1
0, a wavelength control for controlling the wavelength of the reflected light of the fiber grating 2 so that the wavelength of the light reflected by the fiber grating 2 is always within a range not exceeding a predetermined allowable range from the corresponding set wavelength. That is, a means is provided.

Specifically, in this embodiment, as shown in FIG. 2, the optical transmitter 1 includes a laser diode 10 having a semiconductor element 6 and a fiber grating 2, a thermistor 7, a Peltier element 8, , A control circuit 9, and the wavelength control means is constituted by the thermistor 7, the Peltier element 8, and the control circuit 9.

As is well known, since the wavelength of light reflected by the fiber grating changes by 0.01 nm per 1 ° C., the ambient temperature of the fiber grating 2 is detected by the thermistor 7 and the detected temperature is set to a predetermined reference value. By applying a voltage to the Peltier element 8 by the control circuit 9 so that the temperature becomes equal to the temperature, control is performed so that the ambient temperature of the fiber grating 2 is constant. The wavelength control means controls the wavelength of the light reflected by the fiber grating 2 by controlling the temperature of the grating 2.

The present embodiment is configured as described above. In this embodiment, a plurality of optical transmitters 1 used in an optical transmission system are connected to an external resonance type having a semiconductor element 6 and a fiber grating 2. In order to control the wavelength of the light transmitted from the optical transmitter 1 by controlling the temperature of the fiber grating 2, the temperature of the semiconductor element 6 constituting the laser diode 10 is controlled. Unlike a conventional optical transmission system provided with a transmitter 1, a laser diode 10
Almost no load is applied to the semiconductor element 6, and the life of the laser diode 10 can be extended.

Further, it is easy to control the wavelength of the reflected light from the fiber grating 2 by controlling the temperature of the fiber grating 2, and it is possible to control the wavelength of the reflected light from the fiber grating 2 very accurately. The transmission wavelength of the transmitter 1 can be easily and accurately controlled, and the transmission wavelength of the optical transmitter 1 can accurately correspond to the wavelength band of the WDM filter 4 provided in the optical transmission system. it can. Therefore, according to the present embodiment, it is possible to accurately control the wavelength of the signal light to be wavelength-multiplexed, and to construct an excellent optical transmission system with high long-term reliability.

Next, the second embodiment of the optical transmission system according to the present invention will be described.
An embodiment will be described. The optical transmission system according to the present embodiment is also configured in substantially the same manner as the optical transmission system according to the first embodiment, and this embodiment is different from the first embodiment in that As shown in FIG. 3, the plurality of optical transmitters 1 provided in the first embodiment have a configuration in which a piezoelectric element 25 is provided instead of the thermistor 7 and the Peltier element 8 of the optical transmitter 1 used in the first embodiment. And the wavelength control means is provided by the fiber grating 2
The stress control means controls the wavelength of light reflected by the fiber grating 2 by controlling the stress applied to the fiber grating 2.

As is well known, if the stress applied to the fiber grating 2 changes by 30 μm per cm, the wavelength of the light reflected by the fiber grating 2 changes by about 3 nm. The stress applied to the fiber grating 2 by the piezoelectric element 25 is proportional to the voltage applied to the piezoelectric element 25. Accordingly, by controlling the voltage applied to the piezoelectric element 25 by the control circuit 9, the present embodiment can be easily and similarly to the first embodiment.
The wavelength of the light reflected by the fiber grating 2 can be accurately controlled, and the same effects as in the first embodiment can be obtained.

The present invention is not limited to the above-described embodiment, but can adopt various embodiments. For example,
In the second embodiment, the piezoelectric element 25 is provided in the optical transmitter 1 to control the stress applied to the fiber grating 2, and the stress control means for controlling the stress applied to the fiber grating 2 includes the piezoelectric element 25. However, instead of the piezoelectric element 25, for example, a control means for mechanically controlling stress in the fiber axis direction of the fiber grating, such as a mechanical actuator, is provided,
The stress control means may be formed by the control means, and the stress control means may constitute a wavelength control means for controlling the wavelength of the reflected light of the fiber grating 2.

Further, the optical transmitter 1 used in the optical transmission system according to the present invention is characterized in that the wavelength control means for controlling the reflected light wavelength of the fiber grating 2 includes a temperature control means for controlling the temperature of the fiber grating 2 and a fiber grating. 2 may be provided with both stress control means for controlling the stress applied to the second member.

Further, according to the optical transmission system of the present invention, of the plurality of optical transmitters 1 provided in the optical transmission system, the temperature control means for controlling the temperature of the fiber grating 2 provided in the optical transmitter 1 reflects the reflection of the fiber grating 2. One or more optical transmitters 1 constituting the wavelength control means for controlling the optical wavelength are provided, and the remaining optical transmitters 1 are constituted by the stress control means for controlling the stress applied to the fiber grating 2. The optical transmitter 1 may be used.

Further, the optical transmission system of the present invention includes the optical transmitter 1 shown in FIGS. 2 and 3, the semiconductor device 6, the fiber grating 2, and the reflected light wavelength control means of the fiber grating 2 as described above. And a plurality of optical transmitters 1 each having the following configuration, and an optical transmission line that multiplexes and transmits light having different wavelengths transmitted from these optical transmitters 1. For example, it does not always have the block configuration as shown in FIG. 1, and the detailed configuration is not particularly limited.

[0028]

According to the present invention, a plurality of optical transmitters used in an optical transmission system are selected from a semiconductor device and only a laser beam emitted from the semiconductor device having a predetermined wavelength. A fiber grating having an external resonance type laser diode provided with a fiber grating for optically reflecting and taking out, and the optical transmitter always has a predetermined tolerance from the set wavelength corresponding to the wavelength of light reflected by the fiber grating. Since the wavelength control means for controlling the reflected light wavelength of the fiber grating is provided so as to have a wavelength within the range not exceeding the range, by controlling the reflected light wavelength of the fiber grating by the wavelength control means, Light transmitted from an optical transmitter without applying a load due to temperature control to the semiconductor element of the laser diode It is possible to control the wavelength.

Therefore, a conventional optical transmission using an optical transmitter that controls the wavelength of light emitted from the laser diode by controlling the temperature of the semiconductor element of the laser diode and controls the emission wavelength of the optical transmitter. Unlike the system, the life of the laser diode can be extended, and the reliability of the optical transmission system can be increased.

The reflected light wavelength of the fiber grating can be easily and accurately controlled by controlling the temperature of the fiber grating or controlling the stress applied to the fiber grating. By using the wavelength control means as a temperature control means for controlling the temperature of the fiber grating or as a stress control means for controlling the stress applied to the fiber grating, the reception wavelength of each of the plurality of light receiving units provided in the optical transmission system can be adjusted. Accordingly, it is possible to accurately control the wavelength of the reflected light from the fiber grating and accurately control the emission wavelength of the optical transmitter, thereby increasing the reliability of the optical transmission system.

[Brief description of the drawings]

FIG. 1 is a configuration diagram illustrating an example of an optical transmission system that multiplexes and transmits light of different wavelengths transmitted from a plurality of optical transmitters.

FIG. 2 is a block diagram showing an optical transmitter used in the first embodiment of the optical transmission system according to the present invention.

FIG. 3 is a block diagram showing an optical transmitter used in a second embodiment of the optical transmission system according to the present invention.

FIG. 4 is a block diagram illustrating an optical transmitter used in a conventional optical transmission system.

FIG. 5 is an explanatory diagram showing a relationship between a wavelength of an optical signal transmitted from an optical transmitter and a filter band of a WDM filter in the wavelength division multiplexing optical transmission system as shown in FIG.

[Explanation of symbols]

 1, 1a1 to 1aN Optical transmitter 2 Fiber grating 3 Optical fiber 4 WDM filter 6 Semiconductor 7 Thermistor 8 Peltier element 9 Control circuit 10 Laser diode 25 Piezoelectric element

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI H04B 10/14 H04B 9/00 S 10/06 10/04 // G02B 6/00 306

Claims (4)

[Claims] 1. An external resonance type laser diode comprising a semiconductor element and a fiber grating which selectively reflects and extracts only light having a predetermined wavelength among laser lights emitted from the semiconductor element. A plurality of optical transmitters, and an optical transmission line that multiplexes and transmits light of different wavelengths transmitted from the plurality of optical transmitters, wherein the optical transmitter has a wavelength of light reflected by the fiber grating. A wavelength control means for controlling the wavelength of the reflected light of the fiber grating so that the wavelength is always within a predetermined allowable range from the corresponding set wavelength. 2. The optical transmission system according to claim 1, wherein the wavelength control means is a temperature control means for controlling the temperature of the fiber grating to control the wavelength of the light reflected by the fiber grating. 3. The wavelength control means according to claim 1, wherein said wavelength control means controls stress applied to said fiber grating to control the wavelength of light reflected by said fiber grating. Optical transmission system. 4. An optical transmitter for use in an optical transmission system, wherein the wavelength control means comprises the wavelength control means according to claim 1 or the temperature control means according to claim 2, or the stress control according to claim 3. An optical transmitter comprising wavelength control means constituted by the means.