JP2002141601A - Semiconductor laser module - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser module in which monitor light can be monitored accurately even in the case of a high output semiconductor laser element where the intensity of monitor light is high. SOLUTION: The semiconductor laser module 1 comprises a semiconductor laser element 7 having one end delivering an output light and the other end delivering a monitor light, an optical fiber 12 passing the output light from the semiconductor laser element, and a light receiving element 9 receiving the monitor light from the semiconductor laser element. Means for attenuating the intensity of light impinging on the light receiving element 9 below an allowable level is disposed between the semiconductor laser element 7 and the light receiving element 9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a semiconductor laser module.

[0002]

2. Description of the Related Art A semiconductor laser module includes, for example, a semiconductor laser element for emitting output light in an infrared region used in optical communication, a photodiode for monitoring monitor light of the semiconductor laser element, a lens, a thermo module, and the like. A device that is housed in a package and transmits the output light of the semiconductor laser device to the outside via an optical fiber is known (see JP-A-6-318762). And
The semiconductor laser device has an optical output portion having a low-reflectance dielectric film formed at one end, and a monitor light output portion having a high-reflectance dielectric film formed at the other end, based on monitor light. The output light intensity is automatically controlled.

At this time, it is known that the intensity of the monitor light is determined by the intensity of the output light and the reflectance of the dielectric film of the light output section or the monitor light output section. In particular,
The intensity PPD (mW) of the monitor light is expressed by P
When LD (mW), the high reflectance of the dielectric film is RHR, and the low reflectance is RAR, it is given by the following equation. PPD = PLD. [(1-RHR) / (1-RAR)]. (RAR / RHR) ^1/2 Normally, in a semiconductor laser device, the intensity P of monitor light
PD (mW) is as small as about 1% of the output light intensity PLD (mW). For this reason, the photodiode has an anti-reflection film formed on the light receiving surface thereof in order to prevent a decrease in light receiving sensitivity, so that monitor light can be received without leakage.

[0004]

Incidentally, in recent years, dense wavelength division multiplexing (DWDM) has been recently developed.
With the progress of optical communication using the iplexing transmission method, there is an increasing demand for higher output semiconductor laser modules for use in optical amplifiers utilizing erbium-doped fibers, Raman scattering, and the like. For this reason, in a semiconductor laser device, an increase in output light is an urgent issue. For example, it is necessary to increase the cavity length or to lower the reflectance RAR of the dielectric film on the output side of output light. Have been done.

However, as the output light of the semiconductor laser device increases, the intensity of the monitor light inevitably increases accordingly. On the other hand, the allowable light receiving intensity of a photodiode is usually limited to about several mW due to the spatial electric field effect. For this reason, the semiconductor laser module
If the intensity of the monitor light incident on the photodiode exceeds the permissible received light intensity due to the high output, there is a problem that the monitor light cannot be accurately monitored due to saturation of the received light intensity.

The present invention has been made in view of the above points, and provides a semiconductor laser module that is a high-power semiconductor laser element and that can accurately monitor monitor light even when the intensity of monitor light is large. The purpose is to:

[0007]

Means for Solving the Problems To achieve the above object, the inventor of the present invention has decided to positively reduce the intensity of monitor light incident on a light receiving element based on a concept opposite to that of the prior art. Things. That is, in the present invention, in order to achieve the above object, a semiconductor laser device that outputs output light from one end and monitor light from the other end, an optical fiber into which output light of the semiconductor laser device enters, and the semiconductor laser device In the semiconductor laser module provided with the light receiving element to which the monitor light is incident, attenuating means for limiting the light intensity incident on the light receiving element to an allowable light receiving intensity or less is arranged between the semiconductor laser element and the light receiving element. That is the configuration.

Preferably, the attenuating means is a light intensity attenuating film formed on a light receiving surface of the light receiving element. Preferably, the attenuation film is a dielectric film having a plurality of layers. More preferably, a fiber Bragg grating is formed on the optical fiber.

Preferably, the light output of the semiconductor laser device is controlled based on monitor light from the light receiving device. As described above, it is preferable that the attenuation means be an attenuation film in order to reduce the size of the semiconductor laser module.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a semiconductor laser module according to the present invention will be described below in detail with reference to FIGS. As shown in FIG. 1, the semiconductor laser module 1 includes a package 2, a thermo module 3, a base 4, a semiconductor laser element 7, a photodiode 9, a lens holder 10, an optical fiber 12, an optical isolator 14, and a control device 16. I have.

The package 2 has a bottom plate 2a to be described later that is made of Cu.
-W-based alloy, the peripheral wall 2b is formed from an Fe-Ni-based alloy or the like, and as shown in FIG. 1, the thermo module 3, the base 4, the semiconductor laser element 7, the photodiode 9, the lens holder 10, the optical isolator 14, etc. Is stored.
The package 2 has a bottom plate 2a, a peripheral wall 2b, and a lid 2c, and the lid 2c is attached to an upper portion of the peripheral wall 2b. In the package 2, a flange 2d is provided on the peripheral wall 2b, and the optical fiber 12 is supported on the flange 2d via a sleeve 2e.

As shown in FIG. 1, the thermo module 3 is a Peltier device which is mounted on the bottom plate 2a and cools the heat generated by the operation of the semiconductor laser device 7 to control the temperature to a predetermined temperature. Are located. The thermo module 3 is based on a temperature measured by a thermistor (not shown) arranged near the semiconductor laser device 7,
The temperature of the semiconductor laser element 7 is controlled by adjusting the current value.

The base 4 is formed in a plate shape from, for example, a copper-tungsten alloy, and as shown in FIG. 1, a ferrule 12a to be described later is supported on the flange 2d side of the package 2, and a lens holder to be described later is mounted on the other side. 10, the first chip carrier 5 and the second chip carrier 8 are supported adjacent to each other. The semiconductor laser device 7 is an existing ridge waveguide type device, and is provided on a first chip carrier 5 via a heat sink 6 as shown in FIG. Here, the first chip carrier 5 and the second chip carrier 8 are made of Cu-W based alloy, and the heat sink 6 is made of
Each is formed from aluminum nitride. The semiconductor laser element 7 has an Al surface on the lens holder 10 side.
A reflectance of 5% made of 2O3 and a reflectance of 98% in which a low-reflection dielectric film is formed on the rear surface of the photodiode 9 side by alternately forming silica (SiO2) and amorphous silicon (a-Si) three layers each in a total of six layers. Are provided respectively, and a resonator structure is formed between both surfaces. The semiconductor laser element 7 emits high-power laser light mainly used in optical communication, exceeding 300 mW, toward the lens holder 10 from the front surface, and emits monitor light to the photodiode 9 from the rear surface. Here, the high reflection dielectric film is
Assuming that the oscillation wavelength of the semiconductor laser element 7 is λ (nm) and the refractive index of the dielectric film is n, SiO 2 and amorphous silicon are each laminated to a thickness of λ / 4 n (nm).

The photodiode 9 is a light receiving element composed of a carrier type photodiode. As shown in FIG.
It is provided on the inclined surface of the second chip carrier 8 and monitors monitor light emitted from the rear surface of the semiconductor laser device 7.
As shown in FIG. 2, the photodiode 9 has an amorphous silicon layer 9b and silica (SiO2) on the front surface on the light receiving side.
The reflection attenuation film 9a having a two-layer structure composed of the layer 9c is
An n + layer 9f is formed on the p − substrate 9d formed on the lower side of the ring-shaped anode 9e by ion implantation. At this time, the amorphous silicon layer 9b forms a layer having a high refractive index, and the silica layer 9c forms a layer having a low refractive index, and the reflection attenuation film 9a can exhibit high attenuation characteristics by this combination. On the other hand, in the photodiode 9, a cathode 9h is formed on the lower surface of the p− substrate 9d via the P + layer 9g over the front surface. Here, the reflection attenuation film 9a is formed, for example, by plasma CVD (chemical vapor deposition).
por deposition).

Here, in FIG. 2, hatching is omitted in order to make each component of the photodiode 9 easy to see. The lens holder 10, as shown in FIG.
It is provided above and supports the lens 10a. Lens 1
Reference numeral 0a denotes a collimation lens for making the output light of the semiconductor laser element 7 parallel.

The optical fiber 12 has a ferrule 12a attached to the end on the lens holder 10 side, and a fiber Bragg grating 12b formed in a core (not shown). As shown in FIG. 1, the optical isolator 14 is formed in a cylindrical shape, and is supported at the front of the ferrule 12a.

The control device 16 is a controller that automatically controls the light output of the semiconductor laser element 7 based on monitor light emitted from the rear surface of the semiconductor laser element 7 monitored by the photodiode 9. The semiconductor laser module 1 configured as described above is assembled as follows.

First, the temperature control element 3 is attached to the bottom plate 2a of the package 2 and leads (not shown) are attached to the package 2
Is connected with solder. Next, the base 4 is mounted on the temperature control element 3. Next, the first chip carrier 5 is fixed to the base 4 with solder. The first chip carrier 5 has a semiconductor laser element 7 fixed in advance via a heat sink 6 by soldering, and the semiconductor laser element 7 is fixed by wire bonding.
Is electrically connected to

Thereafter, the second chip carrier 8 is fixed to the base 4 by soldering. The photodiode 9 is fixed to the second chip carrier 8 in advance by soldering, and is electrically connected to the photodiode 9 by wire bonding. Next, the lens holder 10 is soldered to the base 4 adjacent to the first chip carrier 5.

Next, the optical isolator 14 is opposed to the lens holder 10, and the output light of the semiconductor laser element 7 is aligned via the lens 10a so as to be located at the center of the optical isolator 14, and the front of the ferrule 12a is Fix by welding. Thereafter, the electrodes of the first chip carrier 5 and the second chip carrier 8 are connected to the leads (not shown) of the package 2 by gold wires (not shown) (wire bonding).

Then, the cover 2a is attached to the upper part of the peripheral wall 2b, and the assembly of the semiconductor laser module 1 is completed. As described above, the semiconductor laser module 1 has the reflection attenuation film 9 on the front surface where the monitor light of the photodiode 9 is incident.
a is formed. Therefore, in the semiconductor laser module 1, even if an excessive monitor light exceeding the allowable light receiving intensity is output from the semiconductor laser element 7, the monitor light is attenuated by the reflection attenuation film 9a and enters. For this reason, in the semiconductor laser module 1, the photodiode 9 can appropriately receive the monitor light with the received light intensity equal to or less than the allowable light receiving intensity and can monitor the monitor light accurately. Therefore, the semiconductor laser module 1 can appropriately and automatically control the optical output of the semiconductor laser element 7 by the control device 16.

Example 1 and Comparative Example 1 A semiconductor laser module 1 was manufactured using a photodiode 9 having a reflection attenuation film 9a having an allowable light receiving intensity of 2.4 mW and a light receiving intensity of 2.4 mW or less. , The intensity P (mW) of the output light with respect to the input current I (mA) to the semiconductor laser element 7 and the monitor current IP (m
FIG. 3 shows the results of evaluating the output characteristics for A).

For comparison, the allowable light receiving intensity is 2.4 mW,
A semiconductor laser module 1 using a photodiode 9 having a reflection attenuation film 9a having a received light intensity exceeding 2.4 mW is formed.
FIG. 4 shows the results of evaluating the same output characteristics. Here, the semiconductor laser module 1 has a reflectance obtained by changing the number of pairs of the output light of the semiconductor laser element 7 and the amorphous silicon layer 9 b and the silica layer 9 c formed on the semiconductor laser element 7, and the reflectance of the second chip carrier 8. By varying the angle of the inclined surface and the distance between the semiconductor laser element 7 and the photodiode 9, the intensity of the monitor light received by the photodiode 9 can be made smaller or smaller than 2.4 mW. Can be set to

Here, the received light intensity P of the photodiode 9
PDin is obtained as follows from the reflectance RPD of the reflection attenuation film 9a and the intensity PPD of the monitor light reaching the front surface of the photodiode 9. In the following equation, S is the probability of receiving monitor light on the front surface of the photodiode 9, and η is the monitor efficiency. PPDin = (1-RPD) × PPD = (1-RPD) × (η ⁻¹ × IP)
= S × IP In the first embodiment, the photodiode 9 has a reflection attenuation film 9a.
As described above, the oscillation wavelength of the semiconductor laser device 7 is changed to λ by the amorphous silicon layer 9b and the silica layer 9c.
(Nm), and when the refractive index of the dielectric film is n, two layers were formed to have a thickness of λ / 4n (nm). At this time, the reflectance R PD of the reflection attenuation film 9a was 78%.
On the other hand, in Comparative Example 1, the reflection attenuation film 9 having a reflectance R PD of 1% was used.
The photodiode 9 having a was used.

As is apparent from FIG. 3, when the light receiving intensity PPDin of the photodiode 9 is smaller than the allowable light receiving intensity, the semiconductor laser module 1 does not saturate the light receiving intensity of the photodiode 9 and thus monitors the monitor current. IP
(MA) is stable. However, in the semiconductor laser module 1, when the light receiving intensity PPDin of the photodiode 9 is larger than the allowable light receiving intensity, the light receiving intensity of the photodiode 9 is saturated. Therefore, in the semiconductor laser module shown in FIG. 4, the monitor current IP (mA) is bent near the input current I = 240 (mA), and the monitor light cannot be monitored accurately.

The semiconductor laser module according to the present invention
The gist of the present invention is to form a reflection attenuating film 9a on the photodiode 9 to make the light receiving intensity equal to or less than the allowable light receiving intensity. Therefore, the semiconductor laser module of the present invention is not limited to the above-described embodiment, but may be any module using a semiconductor laser element having a high output and an increased output of monitor light emitted from the rear surface. Similar effects can be exerted. For example, the semiconductor laser module of the present invention may use an InP-based semiconductor laser element or photodiode regardless of the material system constituting the semiconductor laser element or photodiode.

On the other hand, in the light receiving element, the total number of the SiO2 layer and the amorphous silicon layer may be an even number or an odd number, and the SiNx layer may be used instead of the SiO2 layer. Further, the light receiving element may be of a can type instead of a carrier type.

[0028]

According to the first aspect of the present invention, it is possible to provide a semiconductor laser module which is a high-output semiconductor laser element and can monitor monitor light accurately even if the intensity of monitor light is large. . According to the second to fifth aspects, the semiconductor laser module can be downsized.

[Brief description of the drawings]

FIG. 1 is a sectional front view showing a schematic configuration of a semiconductor laser module of the present invention.

FIG. 2 is a sectional view of a photodiode used in the semiconductor laser module of FIG.

FIG. 3 shows an embodiment of a semiconductor laser module according to the present invention, in which an output light intensity P (mW) with respect to an input current I (mA) to a semiconductor laser element and an output relating to a monitor current IP (mA) at that time. It is a characteristic evaluation figure.

FIG. 4 shows a comparative example of the semiconductor laser module of the present invention, in which the output light intensity P (mW) with respect to the input current I (mA) to the semiconductor laser element and the output relating to the monitor current IP (mA) at that time. It is a characteristic evaluation figure.

[Explanation of symbols]

 Reference Signs List 1 semiconductor laser module 2 package 3 thermo module 4 base 5 first chip carrier 6 heat sink 7 semiconductor laser element 8 second chip carrier 9 photodiode (light receiving element) 9a attenuation film 10 lens holder 10a lens 12 optical fiber 12b fiber Bragg grating 14 Optical isolator 16 Control device 16

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H037 AA01 BA03 CA00 2H050 AC84 AD00 5F049 MA02 PA10 SZ03 TA03 5F073 AA83 AB27 AB28 AB30 BA01 CA12 FA02 FA06 FA11 FA25 FA27 5F089 AA10 AB03 AC10 CA15

Claims (5)

[Claims] 1. A semiconductor laser device for outputting output light from one end and monitor light from the other end, an optical fiber on which output light of the semiconductor laser device enters, and a light receiving device on which monitor light of the semiconductor laser device enters. A semiconductor laser module comprising: a semiconductor laser module, wherein attenuating means for limiting light intensity incident on the light receiving element to an allowable light receiving intensity or less is arranged between the semiconductor laser element and the light receiving element. Laser module. 2. The semiconductor laser module according to claim 1, wherein said attenuation means is a light intensity attenuation film formed on a light receiving surface of said light receiving element. 3. The attenuating film is a dielectric film having a plurality of layers.
The semiconductor laser module according to claim 2. 4. The semiconductor laser module according to claim 1, wherein a fiber Bragg grating is formed on said optical fiber. 5. The semiconductor laser module according to claim 1, wherein an optical output of said semiconductor laser element is controlled based on monitor light in said light receiving element.