JP4239507B2 - Light emitting module - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a light emitting module.
[0002]
[Prior art]
The light emitting module is used, for example, in a wavelength division multiplexing (WDM) transmission system using a plurality of wavelength components. In the WDM system of the 1.55 μm band, the wavelength interval between adjacent grids is about 0.8 nm (100 GHz). In order to realize this wavelength interval, it is necessary to control the emission wavelength of light from the light emitting module within a range of ± 0.03 nm with respect to the grid wavelength.
[0003]
Many of currently used light emitting modules have a semiconductor light emitting element, a photodetector, and a temperature regulator. The wavelength of the laser light slightly emitted from the light reflecting surface of the semiconductor light emitting element is monitored by a photodetector, the temperature of the semiconductor light emitting element is adjusted based on the monitoring result, and the wavelength of the laser light is controlled. Here, in order to detect the wavelength fluctuation with high accuracy, an optical element having a wavelength dependency (for example, an etalon) is provided between the semiconductor light emitting element and the photodetector, and the laser light component having a specific wavelength is monitored. Is done.
[0004]
[Problems to be solved by the invention]
As a result of investigations by the present inventors, it has been found that the light emitting module having the above-described configuration has the following problems.
[0005]
In a light emitting module using an etalon, the wavelength of light emitted from the light emitting module is controlled as follows. FIG. 4 is a schematic diagram showing the relationship between the wavelength of light output from the semiconductor light emitting element and the output current of the photodetector. As shown in FIG. 4, the waveform W of the output current of the photodetector periodically changes as the wavelength λ increases. Here, it is assumed that the grid wavelength used in the WDM system is λ ₀ . Further, the current value of the output current output from the photodetector when light having the wavelength λ ₀ enters the photodetector is assumed to be I ₀ . At this time, the grid wavelength λ ₀ is also locked by locking (controlling) the output current to the current value I ₀ .
[0006]
However, unless the output current of the photodetector has a sufficient differential term with respect to the wavelength λ, it is impossible to lock the wavelength by the wavelength control circuit. That is, the area near the maximum and minimum of the waveform W becomes a dead zone, and only the wavelength of the portion excluding the dead zone can be set. For this reason, it is necessary to adjust the position of the photodetector or the optical element having wavelength dependency to an appropriate position. Also, if the interval between the set wavelengths is shortened or the wave number of the set wavelengths is increased, it will be difficult to adjust the position of the photodetector or wavelength-dependent optical element to an appropriate position while avoiding the dead zone region. Become.
[0007]
The present invention has been made in view of the above points, and an object thereof is to provide a light emitting module capable of easily adjusting the position of a photodetector or an optical element having wavelength dependency.
[0008]
[Means for Solving the Problems]
A light emitting module according to the present invention includes a semiconductor light emitting element having an end face from which light is emitted, and first and second lights that are disposed at a predetermined interval and monitor the wavelength of light of the semiconductor light emitting element. A detector, a lens optically coupled to the end face, collimating the light from the semiconductor light emitting element, receiving the light from the lens and directing the branched light toward the optical fiber and the first and second photodetectors And an optical element that is disposed between the first and second photodetectors and the optical branching device and has wavelength dependency.
[0009]
In the light emitting module according to the present invention, the first and second photodetectors for monitoring the wavelength of the light of the semiconductor light emitting element are arranged with a predetermined interval. The optical element having the position can be easily adjusted. In addition, an optical system for wavelength monitoring is disposed in front of the semiconductor light emitting element in the light emission direction to the optical fiber, and the light emission direction to the optical fiber is behind the semiconductor light emitting element in the light emission direction. Since there is no need to provide the wavelength monitoring optical system on the side, the light emitting module can be miniaturized.
[0010]
Moreover, it is preferable to further include a third photodetector for monitoring the light emission power of the semiconductor light emitting element, and the optical branching device further generates branched light directed to the third photodetector. When configured in this manner, the light emitted to the optical fiber is the same as the light for monitoring the light emission power, and the tracking error due to the positional deviation of the lens that collimates the light from the semiconductor light emitting element can be canceled.
[0011]
The optical filter preferably further includes an optical filter that receives the branched light directed toward the optical fiber and selectively transmits light of a predetermined wavelength, and the optical filter is preferably bonded to or in contact with the optical branching device. When configured in this way, position adjustment of individual elements for adjusting the optical axis can be omitted. In addition, the light emitting module can be downsized.
[0012]
The predetermined interval is preferably set to 1/8 or more and 3/8 or less of the peak distance of the interference fringes formed by the optical element.
[0013]
Further, the predetermined interval is preferably set so that the dead zone region where the change of the output current with respect to the wavelength becomes minimum and maximum in the first and second photodetectors is shifted.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, preferred embodiments of a light emitting module according to the present invention will be described in detail with reference to the drawings. In the present embodiment, the light emitting module of the present invention is applied to a semiconductor laser module, but the present invention is not limited to such an embodiment.
[0015]
FIG. 1 is a schematic configuration diagram showing a semiconductor laser module 1 of the present embodiment. Referring to FIG. 1, the semiconductor laser module 1 includes a semiconductor laser module main part 10 housed in a housing 3. The housing 3 includes a main body (not shown) that houses the main part of the light emitting module, a cylindrical part (not shown) that guides the optical fiber 12 to the main part 10 of the semiconductor laser module, and a plurality of lead pins (not shown). Is provided.
[0016]
The semiconductor laser module main part 10 has a thermoelectric cooler 21 as temperature adjusting means. As this thermoelectric cooler 21, for example, a temperature control element using the Peltier effect can be used. On the thermoelectric cooler 21, a semiconductor light emitting element 31, a collimator lens 32, an optical branching device 33, an etalon 34 as an optical element having wavelength dependency, photodetectors 35a, 35b, 35c and an optical filter 36 are directly provided. Mounted indirectly or indirectly.
[0017]
The semiconductor light emitting element 31 has a pair of end surfaces 31a and 31b and an active layer (light emitting layer) provided between the pair of end surfaces 31a and 31b. The pair of end faces 31a and 31b constitute an optical resonator. One end face is called a light emitting face 31a, and the other end face is called a light reflecting face 31b. Since the light reflectance of the light emitting surface 31a is lower than the light reflectance of the light reflecting surface 31b, laser oscillation light can be extracted from the light emitting surface 31a. The light exit surface 31 a is optically coupled to the collimator lens 32, and light emitted from the light exit surface 31 a enters the collimator lens 32. As the semiconductor light emitting element 31, for example, a distributed feedback type (DFB) or Fabry-Perot type semiconductor laser element can be used. In the following description, the semiconductor light emitting element 31 is a semiconductor laser element that emits laser light.
[0018]
The collimator lens 32 is optically coupled to the light emitting surface 31 a of the semiconductor light emitting element 31. The light emitted from the light emitting surface 31a is divergent light, and is collimated by passing through the collimator lens 32 to become parallel light. The parallel light transmitted through the collimator lens 32 is output to the light branching device 33.
[0019]
The light branching device 33 is optically coupled to the collimator lens 32. The optical branching device 33 receives the parallel light transmitted through the collimator lens 32, branches light toward the photodetectors 35a and 35b, branched light toward the photodetector 35c, and branched light toward the optical fiber 12. And generate An example of the optical branching device 33 is an optical beam splitter. The collimator lens 32 and the light branching device 33 may be bonded.
[0020]
The optical filter 36 is optically coupled to the optical branching device 33, and is optically coupled to the light emitting surface 31 a of the semiconductor light emitting element 31 via the collimator lens 32 and the optical branching device 33. The optical filter 36 receives branched light from the optical branching device 33 toward the optical fiber 12 and selectively transmits light having a predetermined wavelength. The optical filter 36 is desirably bonded or in contact with the optical branching device 33.
[0021]
The light having a predetermined wavelength that has passed through the optical filter 36 is collected by the lens 37 and enters the optical fiber 12. The optical fiber 12 passes through a collimator lens 32, an optical branching device 33, an optical filter 36, and a lens 37 disposed so as to be optically coupled between the optical fiber 12 and the light emitting surface 31 a of the semiconductor light emitting element 31. Therefore, light will enter.
[0022]
The etalon 34 is disposed between the optical branching device 33 and the photodetectors 35 a and 35 b so as to be optically coupled thereto, and the semiconductor light emitting element 31 is interposed via the collimator lens 32 and the optical branching device 33. It is optically coupled to the light reflecting surface 31b. In the etalon 34, the light incident surface 34a and the light emitting surface 34b are relatively inclined at a minute angle. Here, the angle is set to a range in which the light incident on the etalon 34 can cause multiple interference between the light incident surface 34a and the light emitting surface 34b. Specifically, the angle is preferably 0.01 degrees or more and 0.1 degrees or less. Since the light incident surface 34a and the light emitting surface 34b are inclined with respect to each other, the distance between the surfaces 34a and 34b changes along the inclination direction. Therefore, the transmission wavelength of the etalon changes along the inclination direction. The etalon 34 may have a multilayer reflective film on the light incident surface 34a and the light emitting surface 34b. The reflectance of the light incident surface 34a and the light emitting surface 34b is adjusted by the multilayer reflective film. The etalon 34 is desirably adhered or in contact with the optical branching device 33.
[0023]
The photodetectors 35a and 35b are arranged at a predetermined interval in the inclination direction of the etalon 34 so that each can receive light emitted from the light emitting surface 34b of the etalon 34. This predetermined interval is desirably set to / 8 or more and 3/8 or less of the peak distance d of the interference fringes (light intensity distribution) formed by the etalon 34. In this embodiment, this predetermined interval is shown in FIG. Thus, it is set to d / 4. Thereby, as shown in FIG. 3, in the photodetectors 35a and 35b, the dead zone region where the change of the output current with respect to the received light wavelength becomes minimum and maximum is shifted. In FIG. 3, a curve W1 indicates the output characteristic of the photodetector 35a, and a curve W2 indicates the output characteristic of the photodetector 35b.
[0024]
Signals from the photodetectors 35 a and 35 b are sent to the wavelength stabilization circuit 40. The wavelength stabilization circuit 40 selects a signal from one of the photodetector 35a and the photodetector 35b, and generates a signal for adjusting the temperature of the semiconductor light emitting element 31 based on the selected signal. The thermoelectric cooler 21 receives a signal for adjusting the temperature of the semiconductor light emitting element 31 from the wavelength stabilizing circuit 40 and changes the temperature of the semiconductor light emitting element 31 in response to the signal.
[0025]
More specifically, the lock wavelength is set in the semiconductor laser module main part 10 and the wavelength stabilization circuit 40. The oscillation wavelength of the semiconductor light emitting element 31 varies from the lock wavelength. In response to this change, the photocurrents of the photodetectors 35a and 35b change. In response to the current change, the wavelength stabilization circuit 40 generates an electrical signal for changing the temperature of the thermoelectric cooler 21 so that the temperature of the semiconductor light emitting element 31 changes in a direction to cancel the change.
[0026]
The difference between the characteristic curve W1 and the characteristic curve W2 is characterized by a phase difference Δλ. When the characteristics of the photodetector 35a are substantially the same as the characteristics of the photodetector 35b, the characteristic curve W1 is the same as the characteristic curve W2 except for the phase difference Δλ. The periodicity of the characteristic curve is defined by the etalon, the phase of the characteristic curve is defined by the position of the photodetector with respect to the etalon, and the amplitude of the characteristic curve is defined by the intensity of the signal provided by the photodetector.
[0027]
The semiconductor laser module 1 can expand the wavelength range in which wavelength locking is possible by selecting signals from the photodetectors 35a and 35b. For example, the vicinity of the maximum and minimum of the characteristic curve W1 is a region where the lock wavelength cannot be arranged. However, wavelength locking is possible in this region using the characteristic curve W2. In order to maintain the oscillation wavelength of the semiconductor light emitting device 31 at the lock wavelength, the thermoelectric cooler 21 adjusts the temperature of the semiconductor light emitting device 31.
[0028]
The photodetector 35c is arranged so as to receive the branched light generated by the optical branching device 33. The light detector 35c is for monitoring the light emission power of the semiconductor light emitting element 31, and outputs a signal corresponding to the intensity of the received parallel light.
[0029]
A signal from the photodetector 35 c is sent to the power control circuit 50. The power control circuit 50 generates a drive signal for the semiconductor light emitting element 31 in response to the signal from the photodetector 35 c and the input signal 51. The power control circuit 50 is connected to the semiconductor light emitting element 31 via a signal line. The semiconductor light emitting element 31 is driven by a power adjusted drive signal.
[0030]
The photodetectors 35a, 35b, and 35c may be, for example, InGaAs-pin type photodiodes that use an InGaAs semiconductor layer formed on an InP substrate as a light receiving window. The intervals between the photodetectors 35a and 35b may be fixed by being incorporated in a monolithic or hybrid.
[0031]
Next, the assembly procedure of the main part 10 of the semiconductor laser module will be briefly described. First, the semiconductor light emitting element 31 is mounted, and the position of the collimator lens 32 is adjusted. After the optical branching device 33 is arranged, the monitor system is aligned by adjusting the positions of the photodetectors 35a, 35b, and 35c, and the optical output system is aligned by adjusting the position of the lens 37.
[0032]
As described above, in the semiconductor laser module 1 according to this embodiment, the photodetectors 35a and 35b for monitoring the wavelength of light of the semiconductor light emitting element 31 are arranged with a predetermined interval (d / 4). Therefore, the position adjustment of the photodetectors 35a and 35b or the etalon 34 can be easily performed. In addition, an optical system for wavelength monitoring is disposed on the front side (light emission surface 31a side) of the semiconductor light emitting element 31 in the light emission direction to the optical fiber 12, so that the light to the optical fiber 12 is transmitted. Since there is no need to dispose the wavelength monitoring optical system behind the semiconductor light emitting element 31 (on the light reflecting surface 31b side) in the emission direction, the semiconductor laser module 1 can be miniaturized.
[0033]
Further, in the present embodiment, a light detector 35c for monitoring the light emission power of the semiconductor light emitting element 31 is further provided, and the light branching device 33 further generates branched light directed toward the light detector 35c. Thereby, the light emitted to the optical fiber 12 and the light for monitoring the light emission power become the same, and the tracking error due to the misalignment of the collimator lens 32 can be canceled.
[0034]
In the present embodiment, the optical filter 36 further includes an optical filter 36 that receives the branched light directed toward the optical fiber 12 and selectively transmits light having a predetermined wavelength. The optical filter 36 is bonded to or in contact with the optical branching device 33. Yes. Thereby, position adjustment of each element for adjusting the optical axis can be omitted. In addition, the semiconductor laser module 1 can be downsized.
[0035]
While the principles of the invention have been illustrated and described in preferred embodiments, those skilled in the art will recognize that the invention can be modified in arrangement and detail without departing from such principles. For example, the configuration is not limited to the specific semiconductor laser module shown in the present embodiment. We therefore claim all modifications and changes that come within the scope and spirit of the following claims.
[0036]
【The invention's effect】
As described above in detail, according to the present invention, it is possible to provide a light emitting module capable of easily adjusting the position of a photodetector or an optical element having wavelength dependency. Further, according to the present invention, the light emitting module can be downsized.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a semiconductor laser module of an embodiment.
FIG. 2 is a diagram showing interference fringes (light intensity distribution) formed by an etalon 34;
FIG. 3 is a diagram showing a change in output current with respect to a received light wavelength in a photodetector for wavelength monitoring.
FIG. 4 is a diagram showing the relationship between the wavelength of light output from a semiconductor light emitting element and the output current of a photodetector.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Semiconductor laser module, 10 ... Main part of light emitting module, 12 ... Optical fiber, 31 ... Semiconductor light emitting element, 31a ... Light emission surface, 31b ... Light reflection surface, 32 ... Collimator lens, 33 ... Optical branching device, 34 ... Etalon , 35a ... photodetector, 35b ... photodetector, 35c ... photodetector, 36 ... optical filter, 37 ... lens, 40 ... wavelength stabilization circuit, 50 ... power control circuit.

Claims (3)

A semiconductor light emitting device having an end face from which light is emitted;
First and second photodetectors arranged at a predetermined interval for monitoring the wavelength of light of the semiconductor light emitting element;
A third photodetector for monitoring the light emission power of the semiconductor light emitting element;
A lens that is optically coupled to the end face and collimates light from the semiconductor light emitting element;
The light from the lens is received and branched into a branched light directed toward the optical fiber and a branched light directed toward the first and second photodetectors, and the branched light directed toward the optical fiber is further supplied to the optical fiber. An optical branching device that branches into a branched light directed toward the third optical detector and a branched light directed toward the third photodetector ;
A light-emitting module comprising: an optical element that is disposed between the first and second photodetectors and the optical branching device and has wavelength dependency.   2. The light emitting module according to claim 1, wherein the predetermined interval is set to 1/8 or more and 3/8 or less of a peak distance of interference fringes formed by the optical element.   2. The light emitting device according to claim 1, wherein the predetermined interval is set so that a dead zone region in which a change in output current with respect to a wavelength becomes minimum and maximum in the first and second photodetectors is shifted. module.

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