JPH0795159A - Optical transmitter - Google Patents

Abstract

PURPOSE:To provide the optical transmitter in which a wavelength of an output light is stable independently of a secular change in a light source and an output light intensity and the wavelength is easily set. CONSTITUTION:The optical transmitter provided with a light source drive section 52 controlling the intensity of an output light of a light source 51 and connected to the light source 51 whose emitting light wavelength depends on temperature, a temperature detection section 53 detecting the temperature of the light source 51 and a temperature control section 54 controlling the temperature is provided with a wavelength control section 57 detecting a deviation of an emitting light center wavelength based on the luminous intensity of the wavelength of the part of the output light and feeding back a temperature reference value to the control section 54 based on the deviation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical transmitter using laser light, and in particular, the wavelength of the output light is stable regardless of the change with time of the light source and the output light intensity, and the setting of the wavelength is easy. The present invention relates to an optical transmitter.

[0002]

2. Description of the Related Art FIG. 6 shows a configuration example of a conventional optical transmitter.
A laser diode is used as the light source. The laser diode 1 has a property that the emission wavelength depends on temperature. The configuration of FIG. 6 is a configuration for stabilizing the intensity and wavelength of the output light 2.

That is, the output light 2, 3 of the laser diode 1
Of the output light 3 is incident on the monitor diode 4, and the intensity of the output light 3 is detected by the monitor diode 4. The detected current 5 is compared with a predetermined reference value in the laser drive circuit 6. The error obtained by the comparison is amplified and becomes the laser drive current 7. The laser drive current 7 drives the laser diode 1. Thereby, the intensity of the output light 2 of the laser diode 1 is kept constant.

At the same time, the thermistor 8 is mounted on the package 14 in which the laser diode 1 is housed, and the resistance value of the thermistor 8 is compared with a predetermined reference value in the temperature detecting circuit 9. The temperature inside the package 14 is detected by this comparison. The temperature detection signal 10 obtained by the comparison is input to the Peltier drive circuit 11. In the Peltier drive circuit 11, the current of the Peltier element 13 is controlled so that there is no difference between the detected temperature and the set temperature reference value 12. As a result, the temperature inside the package 14 is kept constant, and as a result, the wavelengths of the output lights 2 and 3 of the laser diode 1 are kept stable.

[0005]

If the conventional circuit as described above is used and the temperature is kept constant at the set temperature and the drive current is kept constant, the light source emits light at a constant wavelength. However, when the light source deteriorates due to aging, it emits light at a wavelength different from the initially set wavelength even if the temperature is kept the same.

Even if the temperature of the light source is kept constant,
When the output light intensity is changed, the emission wavelength also changes.

Therefore, an object of the present invention is to solve the above problems and provide an optical transmitter in which the wavelength of the output light is stable regardless of the change of the light source with time and the intensity of the output light, and the wavelength can be easily set. It is in.

[0008]

In order to achieve the above object, the present invention is to connect a light source drive section for controlling the intensity of output light of the light source to a light source whose emission wavelength depends on temperature and to control the temperature of the light source. In an optical transmitter provided with a temperature detection unit for detecting and a temperature control unit for controlling the temperature, the deviation of the emission center wavelength is detected from the intensity of light of a part of the wavelength of the output light, and the temperature based on this deviation is detected. A wavelength controller for returning the reference value to the temperature controller is provided.

The wavelength control unit detects the intensity of light on the short wavelength side and the intensity of light on the long wavelength side of the emission center wavelength of the output light, and from the comparison of these light intensities, the emission center of the output light is detected. The wavelength may be detected, and the detected emission center wavelength may be compared with an arbitrarily set reference wavelength to detect the deviation.

The wavelength control unit separates the light on the short wavelength side of the emission center wavelength and the light on the long wavelength side from the output light, and detects the intensity of the separated light. It may have a light intensity detection section for controlling the light intensity and a light emission wavelength detection circuit for detecting the emission center wavelength by comparing the light intensities on the short and long wavelength sides.

The light separating section may be composed of an optical separator for separating the light on the short wavelength side of the emission center wavelength from the output light and an optical separator for separating the light on the long wavelength side.

The light splitting unit splits a part of the output light from the light, and a splitting unit splits the split light into a short wavelength side and a long wavelength side of the emission center wavelength. May consist of

The light separating section may be composed of a planar optical circuit board formed by integrating optical elements such as a wavelength separator on a single substrate.

Further, a light source driving section for controlling the intensity of the output light of the light source is connected to a light source whose emission wavelength depends on temperature, and a temperature detecting section for detecting the temperature of the light source and a temperature control section for controlling the temperature. In the provided optical transmitter, it has a light splitting unit for splitting light of a part of the wavelength of the output light, detects the shift of the emission center wavelength from the intensity of the split light, and sets the temperature reference value based on this shift. A wavelength control unit for feeding back to the temperature control unit is provided, and a separation wavelength changing unit for changing the separation wavelength is additionally provided in the light separation unit.

The separation wavelength changing means may change the separation wavelength by changing the temperature of the light separating section.

[0016]

With the above structure, the wavelength controller detects the intensity of light having a partial wavelength of the output light, detects the deviation of the emission center wavelength from this intensity, and controls the temperature reference value based on this deviation to the temperature control value. To return to the department. The temperature control unit controls the temperature so that the detected temperature of the light source approaches the temperature reference value.

When the wavelength of the light source is about to change due to a change over time, the wavelength control unit changes the temperature reference value according to the change in the wavelength. The direction of change of the temperature reference value is, of course, the direction of returning the wavelength of the light source to the original wavelength. As a result, the light source will continue to output light at the initially set wavelength.

The spectral characteristic of the output light has a finite wavelength band including the emission central wavelength, and forms a skirt on both sides of the central wavelength having the strongest intensity, which is substantially symmetrical to the outside and weakens toward the outside. The light splitting unit splits light of a part of the wavelength from the output light. That is, the light corresponding to somewhere in the foot is separated. Since the light intensity detection unit detects the intensity of the separated light, if the wavelength of the output light changes, the intensity of the separated light also changes.

The light separating section separates the output light into the light on the short wavelength side and the light on the long wavelength side of the emission center wavelength, and the light intensity detecting section detects the intensities of the light on the short wavelength side and the long wavelength side. By doing so, both sides of the skirt can be detected. The emission center wavelength of the output light can be detected by comparing the light intensities on both sides. When the detected emission center wavelength is compared with the arbitrarily set reference wavelength, the magnitude of the change in the wavelength of the output light appears as a difference. If the temperature reference value is changed and fed back to the temperature control unit so that the difference becomes small, the wavelength of the output light becomes stable.

The light separating section can be composed of a wavelength separator integrated on a planar optical circuit board. In this wavelength separator, the separation wavelength changes depending on the temperature. That is, when the separation wavelength changing means changes the temperature of the light separation section, the separation wavelength changes.
When the separation wavelength changes, the wavelength used for detection in the detection of the skirt changes, so that a detection result that the output light itself is relatively changed can be obtained even if the output light itself is not changed. Since the wavelength control section feeds back the temperature reference value to the temperature control section based on the detected wavelength, the output light changes according to the temperature change given by the separation wavelength changing means.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

As shown in FIG. 1, a package 14 accommodates a laser diode 1, which is a light source 51, a monitor diode 4, a thermistor 8, and a Peltier element 13. The monitor diode 4 and the laser drive circuit 6 constitute a light source drive section 52 that controls the intensity of the output light of the light source 51. The thermistor 8 and the temperature detection circuit 9 constitute a temperature detection unit 53 that detects the temperature 51 of the light source. The Peltier element 13 and the Peltier drive circuit 11 constitute a temperature control unit 54 that controls the temperature.

A wavelength demultiplexer 15 and a wavelength demultiplexer 16 for demultiplexing the output light 2 of the light source 51 are provided. In this embodiment, the output light 2 is made incident on the wavelength demultiplexer 15, its passing light 24 is made incident on the wavelength demultiplexer 16, and its passing light 25 is taken out as an optical transmitter output light 25 to separate each wavelength. The separated lights 17 and 18 of the containers 15 and 16 enter the light intensity detectors 19 and 20, respectively. The wavelength separators 15 and 16 form a light separating unit 55, and the light intensity detectors 19 and 20 form a light intensity detecting unit 56.
Separated light intensity detection signals 21, 2 of the light intensity detectors 19, 20
2 are input to the optical wavelength detection circuit 23, respectively. The reference wavelength value 26 is also input to the light wavelength detection circuit 23. The reference wavelength value 26 can be set to a desired light wavelength in advance. The output of the light wavelength detection circuit 23 is input to the temperature controller 54. Light separation unit 55, light intensity detection unit 5
6 and the light wavelength detection circuit 23 constitute a wavelength control unit 57 for feeding back the temperature reference value to the temperature control unit 54 based on the detection wavelength of the output light.

The characteristics of the wavelength demultiplexers 15 and 16 will be described with reference to FIG. The wavelength separator 15 has a separation characteristic 31 and a passage characteristic 32. That is, the separation characteristic 31 is 100 on the shorter wavelength side than the emission center wavelength of the laser diode 2.
%, The pass ratio drops sharply in the vicinity of the short wavelength side of the emission center wavelength, and becomes 0% at a wavelength longer than the emission center wavelength. The pass characteristic 32 shows a pass ratio of 0% on the short wavelength side of the emission center wavelength, the pass ratio sharply rises in the vicinity of the short wavelength side of the emission center wavelength, and becomes 100% at the long and short wavelengths of the emission center wavelength. Become. Here, the passing ratio is a ratio of the output light 2 passing in the direction of the passing light 24, and the remaining light is separated in the direction of the separated light 17. Therefore, the separation characteristic 31 and the passage characteristic 32 are complementary characteristics.

The wavelength separator 16 has a separation characteristic 33 and a passage characteristic 34. That is, the separation characteristic 33 shows a passing ratio of 100% on the long wavelength side of the emission center wavelength of the laser diode 2, the passing ratio drops sharply in the vicinity of the long wavelength side of the emission center wavelength, and at a wavelength shorter than the emission center wavelength. The pass rate is 0%. The pass characteristic 34 shows a pass ratio of 0% on the long wavelength side of the emission center wavelength, the pass ratio rises sharply in the vicinity of the long wavelength side of the emission center wavelength, and becomes 100% at the short wavelength of the emission center wavelength. Become. Separation characteristics 33
The wavelength at which the pass characteristic 34 and the pass characteristic 34 intersect and the wavelength at which the separation characteristic 31 and the pass characteristic 32 intersect are located symmetrically with respect to the emission center wavelength, and the curves of the respective characteristics are also symmetrical. Has been formed.

The wavelength separators 15 and 16 are integrally formed on the planar optical circuit board 35 as shown in FIG. The planar optical circuit board 35 is housed in an optical circuit package 38. In the optical circuit package 38, an optical fiber 36 that guides the output light 2 to the planar optical circuit board 35 and a passing light 25.
An optical fiber 37 for taking out from the flat optical circuit board 35 is inserted. On the planar optical circuit board 35, other waveguides 62 and 63 that are close to the waveguide 61 that connects between the optical fibers
Two are provided. These waveguides 62 and 63 are
The wavelength separators 15 and 16 are formed and the separated lights 17 and 18 are guided in the portions close to the waveguide 61, respectively. The light intensity detectors 19 and 20 are housed in the optical circuit package 38 and are coupled to the waveguides 62 and 63 at one side of the planar optical circuit board 35.

A heater 41 is provided so as to cover the wavelength separators 15 and 16. The heater 41 is the heater control circuit 4
An electric current is supplied from No. 4 through the heater electrodes 42 and 43. Heater 41 and heater control circuit 44
Is a wavelength control unit 5 that changes the separation wavelength of the light separation unit 55.
Make up 7.

Next, the operation of the embodiment will be described.

The power spectrum of the laser diode 1 at the time of light emission is substantially symmetrical with respect to the light emission center wavelength, and forms a short wavelength side, a long wavelength side and a skirt of the light emission center wavelength. One wavelength demultiplexer 15 that constitutes the optical demultiplexer 55
Separates the light corresponding to the skirt on the short wavelength side of the emission center wavelength from the output light 2 as the separated light 17, and the other wavelength separator 1
6 separates the light corresponding to the skirt on the long wavelength side of the emission center wavelength from the transmitted light 24 as the separated light 18. The light intensity detectors 19 and 20 that form the light intensity detection unit 56 detect the power at the foot. When the laser diode 1 emits light at a desired center wavelength, the powers at the bases are equal to each other.

When the output light 2 deviates from the desired center wavelength, the powers detected by the light intensity detectors 19 and 20 are not equal. By comparing these detected values, the approximate value of the center wavelength of the output light 2 can be detected. The light wavelength detection circuit 23 determines the approximate value of the center wavelength of the output light 2 by comparing the separated light intensity detection signals 21 and 22. Further, the approximate value of the center wavelength is compared with the reference wavelength value 26 to detect an error. The temperature reference value output 12 based on the error detection is fed back to the temperature control unit 54. The Peltier drive circuit 11 performs temperature control using the temperature reference value output instead of the set temperature reference value 12 in FIG. As a result, the center wavelength of the output light 2 returns to the desired center wavelength and stabilizes.

Next, the setting of the center wavelength will be described.

The passing / separating wavelengths of the wavelength separators 15 and 16 change depending on the temperature. When the current flowing from the heater control circuit 44 to the heater 41 is increased or decreased, the wavelength demultiplexers 15 and 16 are separated.
Changes almost in the same way, and the wavelengths of the separated lights 17 and 18 change due to the change of the separated wavelength. While the center wavelength of the output light 2 is constant, when the wavelengths of the separated lights 17 and 18 change, the light intensity detection unit 56 detects power at positions where the skirts are not symmetrical. Since the temperature control is performed based on this power difference, the center wavelength of the output light 2 changes.

Next, another embodiment of the present invention will be described. Figure 4
In FIG. 1, the light source 51 and the light source driving unit 5 described in FIG.
2, temperature detector 53, temperature controller 54, light intensity detector 5
6 is provided, the light separating section 55 has a different configuration. The output light 2 of the laser diode 1 is branched by the optical branching device 27 at the same ratio in all wavelengths. The branched light 28 is separated by the wavelength separator 29 with the central wavelength as a boundary. Separated light 1
The processing of 7 and 18 is the same as that of the example of FIG.

The optical branching device 27 and the wavelength demultiplexer 29 are integrated and formed on a planar optical circuit board 35 as shown in FIG. 5, the configuration of the optical circuit package 38 is the same as that of FIG. 3, but the waveguide pattern of the planar optical circuit board 35 is different. The optical branching device 27 includes a waveguide 64 that is adjacent to a waveguide 61 that connects the optical fibers 36 and 37.
And the wavelength demultiplexer 29 is formed by the waveguide 65 adjacent to the waveguide 64. The heater 41 is provided so as to cover the wavelength separator 29.

[0035]

The present invention exhibits the following excellent effects.

(1) Even if the wavelength of the output light changes due to the aging of the light source, the wavelength of the output light is changed in a direction of canceling it by the temperature control, so that the wavelength of the output light eventually becomes constant. Therefore, the optical transmitter can be used regardless of the change with time of the light source, and the life of the optical transmitter is extended.

(2) The wavelength of the output light becomes stable regardless of the output light intensity, and the range of the light intensity used by the optical transmitter is expanded.

[Brief description of drawings]

FIG. 1 is a circuit diagram of an optical transmitter showing an embodiment of the present invention.

FIG. 2 is a graph showing a separation characteristic and a passage characteristic of the wavelength separator used in the present invention.

FIG. 3 is a configuration diagram of an optical circuit package used in the present invention.

FIG. 4 is a circuit diagram of an optical transmitter showing another embodiment of the present invention.

FIG. 5 is a configuration diagram of an optical circuit package showing another embodiment of the present invention.

FIG. 6 is a circuit diagram of a conventional optical transmitter.

[Explanation of symbols]

 51 light source 52 light source drive section 53 temperature detection section 54 temperature control section 55 light separation section 56 light intensity detection section 57 wavelength control section

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical indication location H04B 10/28 10/26 (72) Inventor Norifumi Kobayashi 5-1-1 Hidakacho, Hitachi City, Ibaraki Prefecture No. 1 within Hitachi Cable's Optro System Research Laboratory

Claims (8)

[Claims] 1. A light source driving unit for controlling the intensity of output light of the light source is connected to a light source whose emission wavelength depends on temperature, and a temperature detecting unit for detecting the temperature of the light source and a temperature control unit for controlling the temperature. In the provided optical transmitter, a wavelength control unit is provided for detecting the deviation of the emission center wavelength from the intensity of light of a part of the wavelength of the output light and feeding back a temperature reference value based on this deviation to the temperature control unit. An optical transmitter characterized in that 2. The wavelength control unit detects the intensity of light on the short wavelength side and the intensity of light on the long wavelength side of the emission center wavelength of the output light, and compares the intensity of these lights to determine the output light 2. The optical transmitter according to claim 1, wherein an emission center wavelength is detected, and the detected emission center wavelength is compared with an arbitrarily set reference wavelength to detect the shift. 3. The wavelength control section separates the light on the short wavelength side of the emission center wavelength from the output light and the light on the long wavelength side, and the intensity of the separated light. 3. The optical transmitter according to claim 2, further comprising: a light intensity detecting section for detecting each and a light emission wavelength detecting circuit for detecting a light emission center wavelength by comparing the intensities of light on the short and long wavelength sides. 4. The light splitting section comprises an optical splitter that splits light on the short wavelength side of the emission center wavelength from the output light and an optical splitter that splits light on the long wavelength side. The optical transmitter according to claim 3. 5. The light splitting unit splits a part of the light from the output light, and a light splitting unit splits the split light into a short wavelength side and a long wavelength side of an emission center wavelength. The optical transmitter according to claim 3, wherein the optical transmitter comprises: 6. The optical transmission according to claim 3, wherein the light splitting portion is composed of a planar optical circuit substrate formed by integrating optical elements such as a wavelength splitter on one substrate. vessel. 7. A light source driving section for controlling the intensity of output light of the light source is connected to a light source whose emission wavelength depends on temperature, and a temperature detecting section for detecting the temperature of the light source and a temperature control section for controlling the temperature. In the provided optical transmitter, it has a light splitting unit for splitting light of a part of the wavelength of the output light, detects the shift of the emission center wavelength from the intensity of the split light, and sets the temperature reference value based on this shift. An optical transmitter characterized in that a wavelength control section for returning to the temperature control section is provided, and further, a separation wavelength changing means for changing the separation wavelength is provided in the optical separation section. 8. The optical transmitter according to claim 7, wherein the separation wavelength changing means changes the separation wavelength by changing the temperature of the light separating section.