JPS62190887A - Semiconductor laser - Google Patents

Abstract

PURPOSE:To reduce an irregularity in incident light intensity to a photodetector disposed at the rear of a light emitting element according to the position of the photodetector by disposing the distance of a light emitting position at the end of a semiconductor laser and the outermost layer surface of the electrode nearest to the emitting position to 10mum or shorter. CONSTITUTION:A distance from an active layer 10 to a boundary 13 between crystal electrodes is increased at an electrode outermost layer 11 of the side fusion-bonded to the same heat sink 2, and a distance from a light emitting unit position 101 to the surface 21 of the heat sink 1 is 10mum or longer. The formation of a thick electrode layer by a normal depositing method is not so practical, and a thick gold layer of 3mum or larger is adapted by the plating. In case of h=10mum, the width of the irregularity in the incident light quantity to the photodetector having 200mum of photodetecting diameter is approx. 1.3:1 in calculation, and in case of h=15mum, it becomes approx. 1.1:1 in calculation. Even if the increase in the irregularity due o the displacement from the approximate value occurring in the actual case is considered, the irregularity in the incident light quantity is largely improved as compared with the case of h 5mum.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to semiconductor lasers.

[Traditional technology]

Semiconductor lasers are usually made by forming a multilayer structure including a so-called active layer, which is a light emitting part, on a substrate such as GaAs or InP by liquid phase epitaxial growth or other growth methods, and then polishing the structure to a thickness of about 100 to 150 mm. A common manufacturing method is to form ohmic electrodes on the p-side and n-side and fuse either side to a heat sink. The distance from the active layer to the crystal surface in the above-mentioned multilayer structure is usually 4 to 6, considering various constraints on crystal growth.
It is designed to resemble scales. In addition, the thickness of both electrodes is usually about 1 to 2 μs. It is well known that the recombination of injected carriers in the active layer is accompanied by heat generation, and the temperature increase in the active layer is This has a significant effect on the various characteristics and reliability of the semiconductor laser. Therefore, when it is assumed that the semiconductor laser will be operated in an environment with a relatively high ambient temperature, the electrodes closer to the active layer, that is, the substrate side, The so-called upside down mount (up-9i
It is usually used in a de-down-mounted state. When a semiconductor laser is used as a light source for an optical fiber, a so-called module is used in which an optical fiber optically coupled to the semiconductor laser and a monitor light receiving element optically coupled to the semiconductor laser are combined in one case. It is usually used in the form When the oscillation wavelength of the semiconductor laser is in the so-called long wavelength region of 14 m or more, a germanium photodiode is used as the above-mentioned light receiving element.
It is a well-known fact that GePD (GePD) is commonly used, but due to the physical cancerous nature of Ge, which is the material, it has a large dark current, and therefore it is difficult to increase the light receiving diameter, and it is usually It is designed to have a value of about 〇-. As described above, the conceptual diagram of the module is shown in FIG. There is. The heat sink 2 usually has a size of 0.5 to 11 squares to facilitate handling during the assembly process or to ensure positional accuracy.The length in the optical cavity direction of the semiconductor laser I is 0.5 square. 2 to 0
．． It is designed to be about 3+sm. On the other hand, the light receiving element is normally housed in a hermetically sealed case 5 and receives light from the rear light emitting portion 101 of the semiconductor laser through a window 51 made of a material such as glass. Under the circumstances described above, the distance from the light emitting portion 101 on the rear end face 16 of the semiconductor laser 1 to the light receiving surface B1 of the light receiving element 6 is approximately 1.5 to 2 cm.

[Problem that the invention seeks to solve]

1- When the conventional semiconductor laser described above is used by being fused to a heat sink in an upside-down manner, the following problems may occur. On the side to which the heat sink semiconductor laser is fused, Sn, AnSn, etc., which usually serve as a fusion agent, are formed by vapor deposition or the like, and the semiconductor laser is brought into contact with this surface and heated.

At this time, the fusing agent on the surface of the heat sink is melted and then solidified again, so that it usually becomes mirror-like. In that case, it is known that a component of the light emitted from the semiconductor laser that is reflected on the heat sink surface causes an interference effect.

Now, if this is shown schematically in Fig. 2, the rear end surface 1
A light ray 31 that forms an angle θ above the horizontal direction from 01 and a light ray 32 that forms an angle 0 below the horizontal direction and is reflected on the heat sink surface 22 is reflected due to a phase delay due to the difference in optical path length between the two. A phase difference equal to the sum of the phase delay −π is generated. If the radiation deflection in the direction perpendicular to the active layer 10 of the semiconductor laser 1 is approximated by a Gaussian distribution, then the electric field strength distribution E at a sufficiently far distance is)... (1) expressed in form. However, j is an imaginary unit.

is the wavelength of the emitted light in vacuum, h is the emission site 101
, that is, the distance of the active layer 10 from the heat sink surface 21. Therefore, the light intensity distribution p at a sufficiently far distance can be expressed as tree-E-E. However, the coefficients are omitted here.

Let us calculate the light intensity distribution in the direction perpendicular to the active layer lO at the rear of the semiconductor laser based on equation (2). As shown in Figure 4, the distance from the rear end face lG is Z, and the heat sink surface 2
Let the height from 1 be X. Light emitting part 101 on the rear end face
Since we are considering a position that is sufficiently far away, the light emitting region 101 and its mirror image 201 in FIG. 2 are approximated to those on the heat sink surface 21. When 0 in the figure is sufficiently small, the approximate equation X=Z θ (3) holds true, and using this, equation (2) becomes as follows.

When this is calculated, a curve as shown in FIG. 5 is obtained. Next, a specific calculation example of the above equation (4) will be shown using a typical example. Enter now. InGaAsp oscillates at =1.3μ
/InP double hetero semiconductor laser, the thickness of the active layer IO is usually designed to be about o,tIL11, and the vertical radiation angle of the emitted light is about 35° at full width at half maximum, so 0O=20'' Assuming the parameters mentioned above, that is, Z = 2 mm, h = 5-, the fifth
The parts in the figure where the light intensity is the lowest (x=0, x2,
X4- ) (7) Spacing approx. 280 Jul f
do. As mentioned above, if a light-receiving element with a light-receiving layer of φ200 mm is used for monitoring, it is expected from Figure 5 that the amount of incident light will vary greatly depending on the position where it is installed, and the ratio between the maximum and minimum is calculated. The ratio is approximately 2:1. In reality, the maximum value of the light intensity shown in FIG. 5 may vary even more between adjacent ones due to deviations in the approximation conditions mentioned above, non-uniform reflectance of the heat sink surface 21, etc. Variations in the monitor current value of the light receiving element caused by such reasons not only result in an absolute shortage of the monitor current value, but also greatly restrict the design and manufacture of the above-mentioned APC circuits using this, and have a large impact on the yield. Since this may be a factor, it is necessary to keep it as small as possible.

[Means for solving problems]

The semiconductor laser of the present invention is characterized in that the distance between the light emitting site on the end face of the semiconductor laser and the surface of the outermost layer of the electrode closest to the light emitting site is 10 μs or more.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

The first [Δ is a schematic diagram showing an embodiment of the semiconductor laser of the present invention.

This embodiment has the same crystal structural dimensions as the conventional semiconductor laser 1 shown in FIG. The outermost electrode layer 11 (T
f, the detailed multilayer structure of the polar metal is omitted) is thickened, and the distance between the light emitting portion 101 and the surface 21 of the heat sink 1 is 10 − or more.

The position (X2
, Xa −) (7) The spacing is Z-2+++e, h
-1011j is about 110μ, roughly h=154m
Then, it becomes about 90-, and the larger h becomes, the smaller the interval becomes.

It is not very practical to form a thick electrode layer as shown in FIG. 1 by a normal vapor deposition method, and formation by plating is particularly suitable for forming a thick gold layer of 3 μs or more.

When h=10-, the width of the variation in the amount of light incident on the light receiving element of φ200 IJJl is calculated to be approximately 1.3:l, h-
In the case of ts tiles, it is calculated to be approximately 1.1:1, and even if we take into account the increased variation due to the deviation from the approximation that occurs in the actual case, the variation in the amount of incident light is greatly improved compared to the case where h = 5 g. Ru. Therefore, there is no need to set the dynamic range of the APC circuit using the current from the light receiving element excessively, which is a very advantageous condition in terms of design. Although GePD has been described as a light-receiving element, development is also progressing on compound-based light-receiving elements that have features such as low dark current and a wavelength range that allows floor light reception. These are more expensive than GePDs, so in order to reduce the cost of the module, it is desirable to reduce the light-receiving area of the light-receiving element used, and at this time, reducing the variation caused by the position of the light-receiving element described above is an essential requirement. be.

〔Effect of the invention〕

As explained above, the present invention makes the distance between the light emitting part of the semiconductor laser and the heat sink surface as large as 10 μs, and reduces the repetition period of the spatial distribution of light intensity caused by reflection on the heat sink surface. This has the effect of reducing variations in the intensity of light incident on the light receiving element installed at the rear of the element, which occurs depending on the position of the light receiving element.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing a state in which an embodiment of the semiconductor laser of the present invention is fused to a heat sink, and FIG. 2 is a schematic diagram showing a state in which a semiconductor laser having a conventional electrode structure is fused to a heat sink. , Fig. 3 is a conceptual diagram of a module that integrates a laser, a light receiving element, and an optical fiber, Fig. 4 is a conceptual diagram showing the light intensity distribution behind a semiconductor laser fused to a heat sink, and Fig. 5 is a conceptual diagram of a module that integrates a laser, a light receiving element, and an optical fiber. FIG. 3 is a diagram showing a light intensity distribution in the coordinate system shown in FIG. 1... Semiconductor laser, 2... Heat sink, 10... Active layer, 11...
... Electrode, 13 ... Crystal electrode interface, 21 ... Heat sink surface, 101 ... Light emitting site.

Claims (1)

[Claims] 1. A semiconductor laser characterized in that the distance between a light emitting site on an end face of the semiconductor laser and a surface of an outermost layer of an electrode closest to the light emitting site is 10 μm or more.