JP2016146399A - Wavelength tunable surface-emitting laser - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wavelength tunable surface-emitting laser capable of changing the oscillating laser light over a wide wavelength band, while suppressing generation of internal stress in a lower DBR layer.SOLUTION: A wavelength tunable surface-emitting laser has a fixed substrate 2, a lower DBR layer 3, a lower contact layer 4, an active layer 5, an upper contact layer 6, deposited sequentially on the upper surface of the fixed substrate 2, and an upper DBR layer arranged oppositely to the upper side of the fixed substrate 2, and displaceably in the vertical direction for the fixed substrate 2. The lower DBR layer 3 is formed by laminating a plurality of low refractive index layer composed of an oxide, and a plurality of high refractive index layer having a refractive index higher than that of the low refractive index layer alternatively. In the lower DBR layer 3, opening holes 33 formed entirely in a vertical direction and opening upward are arranged while being dispersed over the whole area of the lower DBR area 3.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a wavelength tunable surface emitting laser.

In general, a surface emitting semiconductor laser includes a distributed Bragg reflection layer (DBR layer) on each of an upper portion and a lower portion of an active layer, and resonates light between a pair of DBR layers in the normal direction of the active layer. It is configured to oscillate laser light.
Among surface emitting lasers, various types of wavelength tunable surface emitting lasers (VCSELs) that can change the wavelength of light to be oscillated have been developed. A variable wavelength surface emitting laser disclosed in Patent Document 1 includes a lower stacked portion in which a lower DBR layer is disposed below an active layer, and an upper portion disposed to face the upper side of the lower stacked portion with a gap interposed therebetween. And an upper mirror part provided with a DBR layer. And it is comprised so that the cavity length between an upper DBR layer and a lower DBR layer can be changed by comprising so that an upper mirror part can be moved up and down with respect to a lower laminated part. Thereby, it is possible to change the wavelength of the light to be resonated between the upper DBR layer and the lower DBR layer, and to output while changing the wavelength of the laser light to be oscillated.

  Such a wavelength tunable surface emitting laser is considered to be used as a light source of a wavelength scanning light source type optical tomographic image display system (SS-OCT), for example, as disclosed in Patent Document 1. . In this case, in order to improve the resolution in the depth direction by OCT, it is desired to widen the wavelength band of the laser beam to be oscillated. In various applications such as gas sensing and optical device evaluation, not limited to OCT, the wavelength band of the laser light oscillated by the wavelength tunable surface emitting laser may be expanded, that is, high-intensity laser light may be emitted. There is a demand for expanding the wavelength band that can be achieved.

  However, in the wavelength tunable surface emitting laser, in order to widen the wavelength band of the laser light, it is necessary to widen the reflection wavelength band (wavelength band capable of obtaining a high reflectance) of the upper DBR layer and the lower DBR layer. The lower DBR layer is difficult to expand the reflection wavelength band from the viewpoint of manufacturing. That is, since the lower DBR layer is formed on the semiconductor substrate together with the active layer and the like, the material of the lower DBR layer is restricted. Therefore, it is difficult to expand the reflection wavelength band of the lower DBR layer by the conventional film forming method.

In addition, as a method for forming the DBR layer, the difference in refractive index between the high refractive index layer and the low refractive index layer can be increased by using the low refractive index layer as an oxide layer, thereby expanding the reflection wavelength band. It is being considered. In manufacturing such an oxide DBR layer, for example, a layer made of gallium arsenide (GaAs) and a layer made of aluminum arsenic (AlAs) are alternately formed (crystal growth), and an active layer or the like is formed thereon. There is a method of forming a DBR layer formed by stacking an aluminum oxide (Al _x O _y ) layer and a gallium arsenide layer by oxidizing the aluminum arsenic layer after the formation. As a method for forming such a DBR layer, a method is disclosed in which an AlAs layer in an untreated DBR layer is oxidized by supplying an oxidizing gas (water vapor) from its end face to form an Al _x O _y layer. (Non-Patent Document 1).

JP 2007-278868 A

Kenichi Iga, Fumio Koyama “Fundamentals and Applications of Surface-Emitting Lasers”, Kyoritsu Shuppan, June 25, 1999, p. 105-p. 108

  However, AlAs to be made into a low refractive index layer by the subsequent oxidation treatment is sequentially oxidized from the end face, but if the whole layer cannot be oxidized, an oxidized region and a non-oxidized region are formed. As a result, stress is generated at the boundary between the two. As a result, in some cases, it may cause a problem such as a crack occurring in the lower DBR layer starting from the boundary.

  The present invention has been made in view of such a background, and provides a wavelength tunable surface emitting laser capable of changing an oscillating laser beam over a wide wavelength band while suppressing generation of internal stress in a lower DBR layer. It is something to try.

One embodiment of the present invention includes a fixed substrate;
A lower DBR layer, a lower contact layer, an active layer, and an upper contact layer sequentially formed on the upper surface of the fixed substrate;
An upper DBR layer disposed on the upper side of the fixed substrate and disposed so as to be vertically displaced with respect to the fixed substrate;
The lower DBR layer is formed by alternately laminating a plurality of low refractive index layers made of oxide and a plurality of high refractive index layers having a higher refractive index than the low refractive index layer,
The wavelength tunable surface emitting laser, wherein the lower DBR layer is formed with a plurality of apertures formed in the entire vertical direction and open upward, distributed over the entire area of the lower DBR layer. It is in.

  In the wavelength tunable surface emitting laser, the low refractive index layer in the lower DBR layer is an oxide layer. Thereby, the refractive index difference between the high refractive index layer and the low refractive index layer can be easily increased. As a result, it is possible to obtain a wavelength tunable surface emitting laser that can broaden the reflection wavelength band of the lower DBR layer and can change the oscillating laser light over a wide wavelength band.

  In the wavelength tunable surface emitting laser, the aperture holes are distributed over the entire area of the lower DBR layer. Therefore, in forming the lower DBR layer, the low refractive index layer can be reliably oxidized over the entire spreading direction.

  That is, the oxidation treatment of the low refractive index layer can be performed after the lower DBR layer before oxidation, the lower contact layer, the active layer, and the upper contact layer are formed on the fixed substrate. Here, since the opening hole opened upward is formed in the lower DBR layer, the oxidizing gas (for example, water vapor) can be supplied to each low refractive index layer before oxidation through the opening hole. And since the opening hole is distributed and arranged over the whole area of the spreading direction of the lower DBR layer, the low refractive index layer can be easily oxidized reliably over the whole spreading direction. As a result, it is possible to prevent a state in which an oxidized portion and an unoxidized portion exist in the low refractive index layer, and to prevent internal stress from being generated. Therefore, it is possible to prevent problems such as a crack starting from the boundary portion between the oxidized portion and the unoxidized portion in the lower DBR layer.

  As described above, according to the present invention, it is possible to provide a wavelength tunable surface emitting laser capable of changing the oscillating laser light over a wide wavelength band while suppressing the generation of internal stress in the lower DBR layer.

FIG. 3 is a cross-sectional explanatory view of a wavelength tunable surface emitting laser according to the first embodiment. FIG. 3 is an explanatory plan view of the movable substrate in the first embodiment. FIG. 3 is an enlarged cross-sectional explanatory view of a lower DBR layer in the first embodiment. FIG. 3 is a cross-sectional explanatory diagram of a part of a wavelength tunable surface emitting laser around a fixed substrate in the first embodiment. FIG. 3 is an explanatory plan view of the arrangement of opening holes as viewed from the upper contact layer side in the first embodiment. FIG. 3 is a cross-sectional explanatory view of a film formation substrate in the first embodiment. FIG. 3 is a cross-sectional explanatory view of an unoxidized substrate in the first embodiment. FIG. 4 is a cross-sectional explanatory diagram of a part of a wavelength tunable surface emitting laser around a fixed substrate in Comparative Example 1; Plane description of arrangement of opening holes as seen from the upper contact layer side in Comparative Example 1

(Embodiment 1)
An embodiment of a wavelength tunable surface emitting laser will be described with reference to FIGS.
As shown in FIG. 1, the wavelength tunable surface emitting laser 1 includes a fixed substrate 2, a lower DBR layer 3, a lower contact layer 4, an active layer 5, and an upper contact layer 6 that are sequentially formed on the upper surface of the fixed substrate 2. And an upper DBR layer 7 disposed so as to be opposed to the upper side of the fixed substrate 2 and to be displaced in the vertical direction with respect to the fixed substrate 2.

As shown in FIG. 3, the lower DBR layer 3 is formed by alternately laminating a plurality of low refractive index layers 31 made of an oxide and a plurality of high refractive index layers 32 having a higher refractive index than the low refractive index layer 31. Become.
As shown in FIGS. 4 and 5, in the lower DBR layer 3, opening holes 33 that are formed in the entire vertical direction and open upward are distributed over the entire area of the lower DBR layer 3 in the spreading direction.

In the present specification, the upper and lower are expressions for convenience, and the side on which the active layer 5 and the like are laminated with respect to the fixed substrate 2 will be referred to as the upper side, and the opposite side will be described as the lower side.
In the present embodiment, the lower contact layer 4 is an n contact layer, and the upper contact layer 6 is a p contact layer. However, the polarities of the lower contact layer 4 and the upper contact layer 6 can be reversed.

  The lower DBR layer 3 is formed by laminating a plurality of pairs of low refractive index layers 31 and high refractive index layers 32, for example, preferably by laminating 2 pairs to 8 pairs. However, in the present embodiment, the number of stacked layers of the low refractive index layer 31 and the high refractive index layer 32 is 6 pairs.

The low refractive index layer 31 is made of, for example, aluminum oxide (Al _x O _y ) or an alloy of aluminum oxide (Al _x O _y ) and gallium arsenide (GaAs), and the high refractive index layer 32 is made of, for example, gallium arsenide ( GaAs). The low refractive index layer 31 and the high refractive index layer 32 are each configured to have an optical thickness of about ¼ of the wavelength of the laser beam to be oscillated.

Similarly to the lower DBR layer 3, the upper DBR layer 7 is also formed by laminating a plurality of pairs of low refractive index layers and high refractive index layers.
As shown in FIG. 1, the upper DBR layer 7 is provided on a movable substrate 11 disposed so as to be displaceable in the vertical direction with respect to the fixed substrate 2. In the present embodiment, the upper DBR layer 7 is provided on the lower surface of the movable substrate 11. An AR layer (antireflection film) 12 is formed on the upper surface of the movable substrate 11.

  The movable substrate 11 is made of, for example, Si (silicon), and as shown in FIGS. 1 and 2, as shown in FIGS. 1 and 2, the outer peripheral portion 111 fixed to the fixed substrate 2 via the spacer 13, and the vertical direction inside the outer peripheral portion 111. And a vibrating portion 112 that vibrates. The vibration part 112 and the outer peripheral part 111 are partially connected by a plurality of hinge parts 113. In addition, the upper DBR layer 7 and the AR layer 12 are disposed in the vibration unit 112. FIG. 2 is a plan view of the movable substrate 11 provided with the upper DBR layer 7 as viewed from below.

A handle substrate 15 is disposed above the movable substrate 11 via an insulating layer 14. The insulating layer 14 is made of, for example, SiO ₂ (silicon oxide), and the handle substrate 15 is made of, for example, Si. The handle substrate 15 has an opening at a position above the upper DBR layer 7. A voltage source 16 is connected between the movable substrate 11 and the handle substrate 15. The voltage of the voltage source 16 is set to such an extent that the vibrating part 112 can be displaced up and down by electrostatic attraction. As described above, the upper DBR layer 7 vibrates up and down with respect to the active layer 5 and the lower DBR layer 3 by a micro electro mechanical system (MEMS) constituted by the handle substrate 15, the movable substrate 11, and the voltage source 16. It is configured.

  A current source 17 is connected between the fixed substrate 2 and the upper contact layer 6. Then, by injecting current from the current source 17 into the active layer 5, laser oscillation occurs in the cavity between the upper DBR layer 7 and the lower DBR layer 3 at a wavelength that is equal to an integral fraction of the cavity length. This laser beam is output upward from the central opening of the handle substrate 15.

  Here, since the wavelength tunable surface emitting laser 1 has the above-described configuration, the lower DBR layer 3 disposed vertically opposite to the lower contact layer 4, the active layer 5, and the upper contact layer 6. The cavity length between the upper DBR layer 7 can be varied. That is, by changing the voltage applied between the handle substrate 15 and the movable substrate 11, the position of the vibration part 112 is changed in the vertical direction by electrostatic attraction. Thereby, the position of the upper DBR layer 7 with respect to the lower DBR layer 7 is changed, and the cavity length is changed. As a result, the wavelength of the light that resonates between the lower DBR layer 3 and the upper DBR layer 7 can be varied, and the wavelength of the laser light to be oscillated can be changed.

  In the present embodiment, the lower DBR layer 3, the lower contact layer 4, the active layer 5, and the upper contact layer 6 are formed over the entire upper surface of the fixed substrate 2. That is, the lower contact layer 4, the active layer 5, and the upper contact layer 6 are formed over the entire surface of the lower DBR layer 7. Therefore, as described above, as shown in FIGS. 4 and 5, the opening 33 formed in the lower DBR layer 7 is also continuously formed in the lower contact layer 4, the active layer 5, and the upper contact layer 6. Has been. That is, the opening hole 33 is formed so as to penetrate through the entire laminate in the thickness direction including the lower DBR layer 3, the lower contact layer 4, the active layer 5, and the upper contact layer 6.

  As shown in FIG. 5, the opening holes 33 are uniformly formed over the entire spreading direction of the fixed substrate 2 (lower DBR layer 3). That is, the plurality of opening holes 33 are arranged at equal intervals. However, the arrangement of the plurality of opening holes 33 is preferably equidistant, but is not necessarily limited thereto.

  As shown in FIGS. 4 and 5, the stacked portion including the lower contact layer 4, the active layer 5, and the upper contact layer 6 has a columnar portion 8 ( Mesa structure part) is formed. An aperture 81 made of an oxide is formed in a part of the columnar portion 8 in an annular shape from the outer peripheral surface toward the center side.

The aperture 81 is formed between the active layer 5 and the upper contact layer 6. Further, a non-oxidized conductive non-oxidized portion 811 is formed on the inner peripheral side of the annular aperture 81. The aperture 81 is made of, for example, an alloy of aluminum oxide (Al _x O _y ) and gallium arsenide (GaAs). The non-oxidized portion 811 is made of Al _y Ga _1-y As (y is about 0.6 to 0.99).

An annular groove 83 is formed around the columnar portion 8 by a depth from the upper contact layer 6 to the lower contact layer 4.
In the present embodiment, the columnar portion 8 has a substantially cylindrical shape, and the aperture 81 is formed in a substantially annular shape. A large number of the opening holes 33 are distributed in the spreading direction of the fixed substrate 2 in a region different from the portion where the columnar portions 8 are formed.

  When the diameter of the columnar portion 8 is Lm, the inner diameter of the aperture 81 is Dm, and the distance from an arbitrary point in the lower DBR layer 3 to the nearest opening hole 33 or the edge 35 of the lower DBR layer 3 is Lx, Lx / (Lm−Dm) ≦ 5 is satisfied. That is, the opening holes 33 are dispersedly arranged in consideration of the mutual distance and the positional relationship with the edge 35 so that this condition is satisfied. More preferably, Lx / (Lm−Dm) ≦ 2.5 is satisfied.

Here, the distance Lx is the closest among the plurality of opening holes 33 and the edge 35 of the lower DBR layer 3 from the point arbitrarily selected in the lower DBR layer 3 when viewed from the normal direction of the lower DBR layer 3. It means the distance to the part. Therefore, as the configuration of the lower DBR layer 3 that satisfies the above conditions, the opening holes 33 are dispersedly arranged so that Lx / (Lm−Dm) ≦ 5 is satisfied regardless of which point on the lower DBR layer 3 is selected. It is the structure which was made.
Further, when the shape of the columnar portion 8 is not a cylindrical shape, the “diameter Lm of the columnar portion” means an inscribed circle of the outer shape of the columnar portion 8. Similarly, when the shape of the inner peripheral contour of the aperture 81 is not circular, the “inner diameter Dm of the aperture” means an inscribed circle of the aperture 81.

Next, a manufacturing method of the wavelength tunable surface emitting laser 1 of the present embodiment will be described.
First, as shown in FIG. 6, the lower DBR layer 3 in the state before the oxidation treatment is formed on the upper surface of the fixed substrate 2 made of, for example, GaAs. The lower DBR layer 3 in the state before the oxidation treatment is the lower DBR layer 3 in a state before the low refractive index layer 31 is oxidized, and is hereinafter referred to as “unoxidized DBR layer 30” as appropriate. That is, for example, the unoxidized DBR layer 30 is formed on the upper surface of the fixed substrate 2 by alternately forming (crystal growth) layers made of aluminum arsenic (AlAs) and layers made of gallium arsenide (GaAs). . For the layer made of AlAs (the layer to be the low refractive index layer 31), Al _x Ga _1-x As in which Ga is doped into AlAs can be used (x is about 0.8 to 1.0).

Next, a lower contact layer 4 made of, for example, n-doped gallium arsenide and an active layer 5 made of, for example, gallium arsenide and indium gallium arsenide are sequentially formed. Next, an aperture precursor layer 810 for forming the aperture 81 is formed. Here, the aperture precursor layer 810 means a layer that is partially made into the aperture 81 by being partially oxidized in a later step. As the aperture precursor layer 810, for example, Al _y Ga _1-y As can be used.

Next, the upper contact layer 6 made of, for example, p-doped gallium arsenide is formed.
The substrate obtained as described above (FIG. 6) is referred to as a film formation substrate 101 for convenience.
In the present embodiment, the lower DBR layer 3, the lower contact layer 4, the active layer 5, the aperture precursor layer 810, and the upper contact layer 6 in a state before the oxidation treatment are formed over the entire surface of the fixed substrate 2.

  Next, as shown in FIG. 7, the upper contact layer 6, the aperture precursor layer 810, the active layer 5, and the lower contact layer 4 are partially removed by etching to form an annular groove 83, and the inner side thereof The columnar portion 8 is formed on the substrate. Further, a large number of opening holes 33 are formed by etching so as to penetrate from the upper contact layer 6 to the lower DBR layer 3. The substrate in this state is referred to as an unoxidized substrate 102 for convenience.

  Next, the non-oxidized substrate 102 is placed in a predetermined oxidizing atmosphere (for example, a water vapor atmosphere at about 450 ° C.) for a predetermined time, whereby a part of the low refractive index layer 31 and the aperture precursor layer 810 of the non-oxidized DBR layer 30 is formed. Oxidize. The low-refractive index layer 31 of the unoxidized DBR layer 30 is the low-refractive index layer 31 before the oxidation treatment, and this is also simply referred to as the low-refractive index layer 31 as appropriate.

  Oxidizing gas (water vapor) is fed into the low refractive index layer 31 and the aperture precursor layer 810 through the opening hole 33. That is, water vapor contacts the edges of the low refractive index layer 31 and the aperture precursor layer 810 exposed on the inner surface of the opening hole 33, and oxidation proceeds in the spreading direction of the low refractive index layer 31 and the aperture precursor layer 810. . Similarly, water vapor enters from the groove 83, and oxidation proceeds from the edges of the low refractive index layer 31 and the aperture precursor layer 810. Note that water vapor contacts the edge of the low-refractive index layer 31 and the aperture precursor layer 810 also from the end surface of the unoxidized substrate 102, and oxidation proceeds inward as well.

  Here, regarding the aperture precursor layer 810, it is important that the oxidation range in the columnar portion 8 is accurately performed. That is, as shown in FIG. 4, the aperture precursor layer 810 in the columnar portion 8 is oxidized from the outer peripheral surface of the columnar portion 8 to a predetermined region to form an aperture 81 without oxidizing the region inside it. The non-oxidized portion 811 needs to be left. That is, the inner diameter of the aperture 81 is, for example, 5 to 10 μm, and the inner portion is a non-oxidized portion 811. Note that, in the aperture precursor layer 810 other than the columnar portion 8, an oxidized portion 812 is partially formed, and an unoxidized portion 813 remains.

On the other hand, the entire low refractive index layer 31 is oxidized. That is, an unoxidized region is not left in the low refractive index layer 31.
Note that, at the boundary portion between the oxidized portion 812 and the non-oxidized portion 813 formed by oxidizing a part of the aperture precursor layer 810, the thickness of the layer is as thin as several tens of nanometers. There is no such internal stress.

In order to obtain such a state, the arrangement density of the opening holes 33, the diameter of the columnar portion 8, the oxidation rates of the aperture precursor layer 810 and the low refractive index layer 31, and the like are appropriately adjusted.
Specifically, in the present embodiment, in order to make the oxidation rates of the aperture precursor layer 810 and the low refractive index layer 31 different, the compositions of both are adjusted as appropriate. Specifically, the aperture precursor layer 810 is composed of Al _y Ga _1-y As, the low refractive index layer 31 is AlAs or Al _x Ga _1-x As, and x is about 0.8 to 1.0, y is appropriately adjusted between about 0.6 and 0.99.

However, since there is a limit to the adjustment of the composition and film thickness of the aperture precursor layer 810 and the low refractive index layer 31, the aperture 81 is formed by forming the opening holes 33 at appropriate intervals as described above. And lower DBR layer 3 can be appropriately oxidized. That is, when the aperture precursor layer 810 and the low refractive index layer 31 are oxidized at a time, the opening hole 33 is appropriately disposed so that the inner diameter of the aperture 81 can be ensured to an appropriate size. Form at intervals. As the conditions, “the diameter Lm of the columnar portion 8”, “the inner diameter Dm of the aperture 81”, and “the distance from an arbitrary point in the lower DBR layer 3 to the nearest opening hole 33 or the edge 35 of the lower DBR layer 3” The relationship with “Lx” is Lx / (Lm−Dm) ≦ 5. Thereby, when the aperture precursor layer 810 is oxidized until the aperture 81 has an appropriate size, the low refractive index layer 31 can be surely oxidized throughout.
More preferably, by setting Lx / (Lm−Dm) ≦ 2.5, the entire low refractive index layer 31 can be more reliably oxidized.

  On the other hand, the smaller the distance Lx, the faster the entire low refractive index layer 31 can be oxidized, and it is easier to more reliably prevent the state without the unoxidized portion. In consideration of adhesion, the formation density of the opening holes 33 in the lower DBR layer 3 is preferably, for example, 30% or less in terms of area ratio.

  The wavelength tunable surface emitting laser 1 of the present embodiment can be used as a light source of a wavelength scanning light source type optical tomographic image display system (SS-OCT). The laser light oscillated by the wavelength tunable surface emitting laser 1 of the present embodiment can be infrared laser light, and can be configured to scan the wavelength between 980 and 1200 nm, for example.

Next, the effect of this embodiment is demonstrated.
In the wavelength tunable surface emitting laser 1, the low refractive index layer 31 in the lower DBR layer 3 is an oxide layer. Thereby, the refractive index difference between the high refractive index layer 32 and the low refractive index layer 31 can be easily increased. In the present embodiment, for example, the refractive index of the high refractive index layer 32 can be about 3.5, and the refractive index of the low refractive index layer 31 can be about 1.5 to 1.7. As a result, the reflection wavelength band of the lower DBR layer 3 can be expanded, and it is possible to obtain the wavelength tunable surface emitting laser 1 that can change the oscillating laser light over a wide wavelength band.

  In the wavelength tunable surface emitting laser 1, the opening holes 33 are distributed over the entire area of the lower DBR layer 3 in the spreading direction. Therefore, when the lower DBR layer 3 is formed, the low refractive index layer 31 can be reliably oxidized over the entire spreading direction.

  That is, the oxidation treatment of the low refractive index layer 31 is performed after forming the lower DBR layer 3, the lower contact layer 4, the active layer 5, and the upper contact layer 6 before oxidation on the fixed substrate 2. it can. Here, since the opening hole 33 opened upward is formed in the lower DBR layer 3, the oxidizing gas (water vapor) can be supplied to each low refractive index layer 31 before oxidation through the opening hole 33. Since the opening holes 33 are distributed over the entire area of the lower DBR layer 3 in the spreading direction, the low refractive index layer 31 can be reliably oxidized over the entire spreading direction. As a result, it is possible to prevent the low refractive index layer 31 from being formed with an oxidized portion and an unoxidized portion, and to prevent internal stress from being generated. Therefore, the lower DBR layer 3 can be prevented from having a defect such as a crack starting from a boundary portion between the oxidized portion and the unoxidized portion.

  Further, a columnar portion 8 is formed in the laminated portion including the lower contact layer 4, the active layer 5, and the upper contact layer 6, and an aperture 81 is formed in a part of the columnar portion 8. Thereby, the current flowing between the lower contact layer 4 and the upper contact layer 6 can be narrowed down and the transverse mode of light can be suppressed, and single mode laser light can be efficiently oscillated. In such a structure, by adopting a structure in which the opening hole 33 is formed in the lower DBR layer 31, the oxidation of the aperture 81 and the oxidation of the low refractive index layer 31 in the lower DBR layer 3 can be easily performed in one step. Become.

  In particular, in relation to the diameter Lm of the columnar portion 8 and the inner diameter Dm of the aperture 81, the distance Lx from any point in the lower DBR layer 3 to the nearest opening hole 33 or the edge 35 of the lower DBR layer 3 is Lx / Satisfies (Lm−Dm) ≦ 5. Thereby, the aperture 81 can be accurately formed, and the entire low refractive index layer 31 in the lower DBR layer 3 can be more reliably oxidized.

  That is, in view of the function of the aperture 81, it is necessary to leave a non-oxidized portion (conductive portion) in an appropriate size inside the aperture 81. That is, the size of the inner diameter Dm of the aperture 81 has an appropriate size (for example, 5 to 10 μm) for emitting a single mode laser beam from the non-oxidized portion 811 inside the aperture 81, and there are design restrictions. Therefore, when the oxidation of the aperture 81 and the oxidation of the low-refractive index layer 31 are performed in one process, the low refraction is surely reduced when the aperture 81 is oxidized until the inner diameter of the aperture 81 becomes an appropriate size. It is necessary to reliably oxidize the entire rate layer 31. The oxidation rate of the aperture 81 and the oxidation rate of the low refractive index layer 31 can be adjusted to some extent by adjusting the material, but there are limitations from the viewpoint of the film formation state and the like. Therefore, by setting Lx / (Lm−Dm) ≦ 5, the entire low refractive index layer 31 can be surely oxidized when the inner diameter Dm of the aperture 81 becomes an appropriate size. Therefore, the aperture 81 and the low refractive index layer 31 can be more reliably formed at a time, and the production efficiency of the wavelength tunable surface emitting laser 1 can be improved.

  As described above, according to the present embodiment, it is possible to provide a wavelength tunable surface emitting laser capable of changing the oscillating laser light over a wide wavelength band while suppressing the generation of internal stress in the lower DBR layer. .

In addition, this invention is not limited to the said embodiment, In the range which does not deviate from the summary, it is possible to apply to various embodiment.
For example, in the stacked body of the fixed substrate 2, the lower DBR layer 3, the lower contact layer 4, the active layer 5, and the upper contact layer 6, other layers may be interposed between the respective layers as long as the functions thereof are not impaired. . An optical film may be formed on the upper surface of the upper contact layer 6.

The wavelength-tunable surface emitting laser is not limited to the OCT light source, and can be used in various applications such as gas sensing and optical device evaluation.
The vertical displacement of the upper DBR layer relative to the fixed substrate is not limited to the mechanism shown in the embodiment, and various mechanisms can be employed. Further, the upper DBR layer can be formed on the upper surface of the movable substrate, or the movable substrate itself may constitute the upper DBR layer.
Moreover, the groove part around a columnar part may be connected with the opening hole.

(Comparative Example 1)
This comparative example is an example in which no opening hole is provided in the lower DBR layer 3 as shown in FIGS.
However, the groove portion 830 around the columnar portion 8 is continuously formed up to the lower DBR layer 3.

  The laminated body 9 of the fixed substrate 2, the lower DBR layer 3 (unoxidized DBR layer 30), the lower contact layer 4, the active layer 5, the aperture 81 (aperture precursor layer 810), and the upper contact layer 6 having such a configuration is implemented. When the oxidation process is performed by the same method as that of the first embodiment, the unoxidized portion 39 remains in the lower DBR layer 3. That is, when the lower DBR layer 3 is oxidized together with the oxidation of the aperture 81 in the columnar portion 8, the oxidation progresses from the outer peripheral edge of the groove 83 and the stacked body 9 in both the aperture 81 and the lower DBR layer 3. In this case, in order to leave the non-oxidized portion 811 with an appropriate size inside the aperture 81, the oxidation process is stopped halfway. At this stage, the oxidation of the lower DBR layer 3 is also stopped. At this time, if a state in which the entire lower DBR layer 3 is oxidized is not obtained, the boundary portion 38 between the oxidized portion 34 and the non-oxidized portion 39 becomes lower DBR layer 3 (low refractive index) as shown in FIG. The rate layer 31) is formed.

  As described above, by adjusting the materials of the aperture precursor layer 810 and the unoxidized DBR layer 30 and the like, it is possible to make a difference in oxidation rate to some extent, but there is a limit to this. Therefore, in the above configuration, when the aperture 81 having the appropriate inner diameter and the lower DBR layer 3 are oxidized in the same process, the boundary portion 38 is easily formed. As a result, an internal stress is generated in the boundary portion 38, which may cause a crack or the like.

  On the other hand, by providing the opening hole 33 in the lower DBR layer 3 as in the wavelength tunable surface emitting laser 1 according to the first embodiment, the above-described problems can be prevented.

DESCRIPTION OF SYMBOLS 1 Wavelength-variable surface emitting laser 2 Fixed substrate 3 Lower DBR layer 31 Low refractive index layer 32 High refractive index layer 33 Open hole 4 Lower contact layer 5 Active layer 6 Upper contact layer 7 Upper DBR layer

Claims (3)

A fixed substrate;
A lower DBR layer, a lower contact layer, an active layer, and an upper contact layer sequentially formed on the upper surface of the fixed substrate;
An upper DBR layer disposed on the upper side of the fixed substrate and disposed so as to be vertically displaced with respect to the fixed substrate;
The lower DBR layer is formed by alternately laminating a plurality of low refractive index layers made of oxide and a plurality of high refractive index layers having a higher refractive index than the low refractive index layer,
The wavelength tunable surface emitting laser, wherein the lower DBR layer is formed with a plurality of apertures formed in the entire vertical direction and open upward, distributed over the entire area of the lower DBR layer. .   In the laminated portion composed of the lower contact layer, the active layer, and the upper contact layer, a columnar portion that is erected in a state of being separated from other portions in the spreading direction is formed. 2. The wavelength tunable surface emitting laser according to claim 1, wherein an aperture made of an oxide is formed in an annular shape from the outer peripheral surface toward the center.   The diameter of the columnar portion is Lm, the inner diameter of the aperture is Dm, and the distance from an arbitrary point in the spreading direction of the lower DBR layer to the nearest opening hole or the edge of the nearest lower DBR layer is Lx. 3. The tunable surface emitting laser according to claim 2, wherein Lx / (Lm−Dm) ≦ 5 is satisfied.

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