JP3691828B2 - Semiconductor laser element - Google Patents

Description

  The present invention relates to a semiconductor laser device having a quantum well structure.

  Conventionally, quantum well semiconductor laser elements have been widely used as light sources for optical communications, and the structure of a quantum well semiconductor laser element having a typical buried waveguide of this type is shown in FIG.

  In the figure, a quantum well layer 7 is formed in the central portion of an N-type InP substrate 1, and constriction layers 8 are formed on the left and right sides of the quantum well layer 7. The quantum well layer 7 is formed by laminating a light confinement layer (GRIN-SCH region) 3, an active layer 4, a light confinement layer 5, and a P-type clad layer 6 made of InP in this order on the N-type clad layer 2. The optical confinement layers 3 and 5 are four types of GaInAsP layers having different compositions, that is, four types of band gap wavelengths λg of 1.05, 1.10, 1.20 and 1.30 μm and a thickness of 300 mm each. A layer of GaInAsP is stacked to change the refractive index in a stepped manner, thereby confining the light in the active layer 4 from above and below.

  The active layer 4 has a well layer made of GaInAsP having a band gap wavelength λg of 1.55 μm and a thickness of 65 mm and a barrier layer made of GaInAsP having a band gap wavelength λg of 1.30 μm and a thickness of 80 mm. 5 MQW active layers.

  When manufacturing a semiconductor laser device having this quantum well structure, the N-type cladding layer 2, the optical confinement layer 3, the active layer 4, the optical confinement layer 5, and the P-type cladding layer 6 are formed over the entire upper surface of the InP substrate 1. After that, the left and right sides of the quantum well are removed by etching so as to form a mesa stripe shape, leaving a width L of the quantum well of about 2 μm, and the P-type InP layer 9 and the N-type InP are formed in the removed portion. The layer 10 is buried by re-growing to form the constriction layer 8, and a P-type clad layer 11 made of InP is formed on the upper side where the active layer 4 and the constriction layer 8 are formed. The side electrode 12 is produced by forming the P-side electrode 13 on the upper surface side.

  When driving this type of semiconductor laser element, a positive power supply voltage is applied to the P-side electrode 13 and a negative power supply voltage is connected to the N-side electrode 12. Since the current flowing from the P-side electrode 13 to the N-side electrode 12 does not flow to the constriction layer 8, it flows in a concentrated manner in the quantum well layer 7, thereby exciting the active layer 4 and exciting the active layer 4. The light source light is emitted from one end face of the active layer 4 (usually, reflection films having different reflectivities are formed on both end sides of the active layer 4, and the power of the light excited in the active layer 4 has a reflectivity. When the smaller threshold value is exceeded, the light source light is emitted from the end face side).

Japanese Patent Laid-Open No. 3-153091 JP-A-4-151877 JP-A-63-152194 JP-A-55-157281 JP-A-60-239080

  However, when manufacturing this type of semiconductor laser device, it is unavoidable that the cross-sectional shape of the active layer 4 is rectangular, and therefore, the divergence angle of the beam emitted from the active layer 4 in the vertical direction is It becomes larger than the beam divergence angle in the horizontal direction (parallel direction) of the active layer 4. For example, in the conventional semiconductor laser, the vertical beam divergence angle of the active layer 4 is 36 °, the horizontal beam divergence angle of the active layer 4 is about 25 °, and the vertical beam divergence angle is about 25 °. Since it becomes large, the cross-sectional shape of the beam emitted from the active layer 4 becomes elliptical, and there is a problem that when light is introduced from the semiconductor laser element into the optical fiber of the circular core, the light coupling efficiency is deteriorated.

  The present invention has been made to solve the above-described conventional problems, and an object of the present invention is to provide a semiconductor laser device capable of increasing the coupling efficiency to an optical fiber by making the spread pattern of a beam emitted from an active layer substantially circular. Is to provide.

In order to achieve the above object, the present invention is configured as follows. That is, the first invention is a sandwich an active layer comprising a plurality of _{Ga 1-X In X As 1} -Y P Y well layer and a multiple quantum well composed of a barrier layer on an InP substrate, the active layer from upper and lower sides In an embedded semiconductor laser device having an optical confinement layer sandwiched in a shape, each of the optical confinement layers sandwiching the active layer vertically is made up of a plurality of types of layers arranged so that the band gap wavelength becomes shorter in order from the center of the active layer The optical confinement layer formed and sandwiching the active layer is thinner than the active layer, and the total thickness of the active layer and the optical confinement layer is 1000 mm or more and 2000 mm or less. .

  According to a second aspect of the present invention, the semiconductor laser element is used for an excitation light source and is optically coupled to an optical fiber after having the configuration of the first aspect of the present invention.

  Further, the third invention is characterized by having the configuration of the second invention and the excitation wavelength in the 1.48 μm band.

In the present invention configured as described above, the total thickness of the active layer and the light confinement layers above and below it is reduced to 2000 mm or less , and the light confinement layer sandwiching the active layer is thinner than the active layer. The light confinement coefficient decreases, and the energy of light excited in the active layer oozes out from the active layer to the cladding layer outside the light confinement layer. As a result of this oozing amount maximizing at the middle part of the width of the quantum well, the light emitting surface taking into account the oozing area on the cladding layer side becomes almost circular, and this makes the vertical direction of the emitted light The beam divergence angles in the horizontal direction are substantially equal, and a beam having a mode pattern close to a circle is output as light source light.

As described above, according to the present invention, the total thickness of the active layer of the quantum well and the optical confinement layers on both upper and lower sides of the active layer is 2000 mm or less , and the thickness of the optical confinement layer sandwiching the active layer is smaller than that of the active layer. Since the total is thin, the light confinement factor is small, and the amount of light that is confined and activated in the active layer increases to the cladding layer. In comparison, a significant light oozing effect of the light confinement layer can be obtained. The total thickness of the active layer and the optical confinement layers on both upper and lower sides of the active layer is 2000 mm or less , and the thickness of the optical confinement layer sandwiching the active layer is smaller than that of the active layer. The output beam can be output as a circular mode pattern beam by reducing the vertical divergence angle in the vertical direction so that the vertical and horizontal divergence angles are almost the same, greatly increasing the coupling efficiency to the optical fiber. Can do.

In particular, when a high-power beam for an excitation light source is emitted, if the sum of the thicknesses of the active layer and the light confinement layers on both the upper and lower sides of the active layer is large, the beam pattern of the emitted beam becomes an elliptic pattern. As in the present invention, the total thickness of the active layer and the light confinement layers on both upper and lower sides of the active layer is reduced to 2000 mm or less , and the thickness of the light confinement layer sandwiching the active layer is smaller than that of the active layer. As a result, a good circular mode beam pattern can be obtained even in a high-power emission beam for an excitation light source.

  Embodiments of the present invention will be described below with reference to the drawings. In addition, the same code | symbol is attached | subjected to the part same as a prior art example, and the duplication description is abbreviate | omitted. FIG. 1 shows an embodiment of a semiconductor laser device according to the present invention. The semiconductor laser device of this embodiment also has a quantum well structure as in the conventional example, and has a quantum well layer 7 and a constriction layer 8. Each layer formed on the InP substrate 1 is formed by vapor phase growth by MO-CVD (Metal-Organic Chemical Vapor Deposition). The quantum well layer 7 in this embodiment is formed by laminating the N-type cladding layer 2, the optical confinement layer 23, the active layer 24, the optical confinement layer 25, and the P-type cladding layer 6 on the InP substrate 1 as in the conventional example. However, the characteristic feature of this embodiment is that the total thickness of the optical confinement layers 23 and 25 and the active layer 24 is 2000 mm or less.

  When the semiconductor laser is operated at an excitation band wavelength of 1.48 μm band for the excitation light source, the beam power as the excitation light source is larger than the beam power for communication, and the 1.48 μm band excitation band for the excitation light source. In order to operate at a wavelength, the total thickness of the active layer and the upper and lower optical confinement layers needs to be thick, and the above-mentioned sum that is automatically determined to operate at the excitation band wavelength of 1.48 μm band for this excitation light source. The lower limit of thickness is 1000 angstroms (Å).

  The optical confinement layer 23 is composed of two types of GaInAsP having bandgap wavelengths λg of 1.20 μm and 1.30 μm and different thicknesses of 200 mm, and the optical confinement layer 25 has the same configuration. ing. Similarly to the conventional example, the active layer 24 is composed of a GaInAsP well layer with a band gap wavelength λg of 1.55 μm and a layer thickness of 65 mm, and a GaInAsP barrier layer with a band gap wavelength of 1.30 μm and a layer thickness of 80 mm, The number of wells is 5. In this embodiment, the optical confinement layer 23 has a thickness of 400 mm, the active layer 24 has a thickness of 645 mm, and the optical confinement layer 25 has a thickness of 400 mm. The total thickness of 25 is 1445 mm, which is thinner than the conventional 3045 mm.

  When the semiconductor laser device of this embodiment is driven, the current flowing between the electrodes 12 and 13 is concentrated in the quantum well layer 7 to excite the light confined in the active layer 24 and increase the light energy in the active layer 24. However, at this time, the optical confinement coefficient is reduced by reducing the thickness of the optical confinement layers 23 and 25, and as a result, the light confined in the active layer 25 and activated to the cladding layers 2 and 6. The oozing out increases. The soaking of light into the cladding layers 2 and 6 is the largest at the central portion of the width L of the quantum well, and the amount of soaking gradually decreases toward both ends. The cross-sectional shape of the light emission including the 6 exudation portions is almost a circle, so that the spread angle of the beam emitted from the active layer 24 and the exudation portion of the light is substantially the same in the vertical direction and the horizontal direction. It becomes an angle and is output as light of a substantially circular mode pattern.

  The present inventor fabricated the semiconductor laser device of this example and measured the divergence angle of the emitted beam to obtain the measurement result of FIG. According to this, when the radiation power is 50 mW, the vertical spread angle is 25.0 ° ((b) in the figure) and the horizontal spread angle is 25.4 ° ((a) in the figure). It was possible to create a radiation beam pattern that was almost a perfect circle.

  FIG. 3 shows the output characteristics of an apparatus in which an optical fiber is coupled to a laser diode having a resonator length of 1 mm by AR-HR coating of the semiconductor laser element of this embodiment to form a module. According to this, when the driving current is 1 A, a high output that can be used for an excitation light source of 128 mW is obtained as the end light output of the optical fiber, and the coupling efficiency between the semiconductor laser element and the optical fiber at this time is 70 %Met. The excitation band wavelength of the semiconductor laser at this time is 1.48 μm band when the emission wavelength is calculated from the thickness of the well layer and barrier layer of the active layer and the band gap wavelength of each layer. When the coupling efficiency between the semiconductor laser device of the conventional example and the optical fiber was examined in the same manner, the coupling efficiency was about 50%, and this example improved the coupling efficiency by about 20% compared to the conventional example. I was able to.

  In addition, this invention is not limited to the said Example, Various aspects can be taken. For example, in the above embodiment, the total thickness of the light confinement layers 23 and 25 and the active layer 24 is 1445 mm, but the total thickness may be 2000 mm or less. The present inventor examined the relationship between the sum of the thicknesses of the light confinement layers 23 and 25 and the active layer 24 and the divergence angle of the outgoing beam due to the oozing of the light into the cladding layer, and found that the thickness of the sum was 2000 mm. In the case of exceeding the above, the amount of light bleed out almost disappeared, and the beam emission pattern was almost elliptical, and the characteristics of the coupling efficiency with the optical fiber could not be improved. As it became below, the oozing of light gradually increased, and the shape of the outgoing beam pattern was changed from an ellipse to a circle, and it was confirmed that the coupling efficiency to the optical fiber could be improved.

  In the above embodiment, the thickness of the active layer 24 is set to the same thickness as that of the conventional example, and the thickness of the light confinement layers 23 and 25 is reduced, so that the total thickness of the active layer 24 and the light confinement layers 23 and 25 is reduced. However, in this embodiment, the thickness of the light confinement layers 23 and 25 is made thinner than that of the active layer 24. Of course, the thickness of the active layer 24 may be reduced together with the light confinement layers 23 and 25.

1 is a cross-sectional configuration diagram of an embodiment of a semiconductor laser device according to the present invention. It is a graph of the beam divergence angle of the semiconductor laser element of the same Example. It is an output characteristic graph in the module incorporating the semiconductor laser element of the same Example. It is sectional drawing of the semiconductor laser element of the conventional quantum well structure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 InP board | substrate 2 N type clad layer 6,11 P type clad layer 7 Quantum well layer 8 Narrowing layer 9 P type InP layer 10 N type InP layer 23,25 Optical confinement layer 24 Active layer

Claims (3)

An active layer comprising a plurality of _{Ga 1-X In X As 1} -Y P Y well layer and a multiple quantum well composed of a barrier layer on an InP substrate, and an optical confinement layers sandwiching the active layer from upper and lower sides in a sandwich In each of the embedded semiconductor laser elements, the optical confinement layers sandwiching the active layer above and below are formed by a plurality of types of layers arranged so that the band gap wavelength becomes shorter from the center of the active layer, and sandwich the active layer. A semiconductor laser device, wherein the thickness of the light confinement layer is thinner than that of the active layer, and the sum of the thicknesses of the active layer and the light confinement layer is 1000 to 2000 mm. 2. The semiconductor laser device according to claim 1, wherein the semiconductor laser device is used for an excitation light source and is optically coupled to an optical fiber. The semiconductor laser device according to claim 2, wherein an excitation wavelength is in a 1.48 μm band.

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