Surface emitting laser, laser device, detection device, and mobile object

Abstract

To provide a surface emitting laser, a laser device, a detection device, and a mobile object in which an oxidized region of an oxidized constriction layer can be easily manufactured.SOLUTION: A surface emitting laser includes: a first resonator including an active layer; a first reflector and a second reflector facing each other with the active layer interposed therebetween; a second resonator provided in the first reflector; an oxidation constriction layer provided in the second reflector and having a non-oxidized region and an oxidized region surrounding the non-oxidized region in a plane perpendicular to an emission direction of light; and an electrode pair connected to a power supply device and capable of injecting a current into the active layer. When a period in which the current is injected into the active layer by the power supply device is a current injection period, and a period in which a current value injected into the active layer after the current injection period is lower than a current value in the current injection period is a current decrease period, a laser oscillation is not performed in the current injection period, and a laser oscillation is performed in the current decrease period.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a surface-emitting laser, a laser device, a detection device, and a moving object. [Background technology]

[0002] Surface-emitting lasers are used in distance measuring devices, etc. Surface-emitting lasers that generate short pulses of light with small tailing are known to satisfy laser safety standards for human eyes.

[0003] The period during which current is injected into the active layer is referred to as the current injection period, and the period after the current injection period during which the value of the current injected into the active layer is lower than the current value during the current injection period is referred to as the current injection period. In a surface-emitting laser having an oxidized constriction layer, laser oscillation does not occur during the current injection period, but occurs during the current reduction period, thereby reducing the tailing of short-pulse light. Patent Document 1 describes that in order to achieve laser oscillation during the current reduction period, the oxidized region of the oxidized constriction layer is made thinner. Summary of the Invention [Problem to be solved by the invention]

[0004] However, thinning the oxidized region of the oxidized constriction layer can be difficult in manufacturing.

[0005] An object of the present invention is to provide a surface-emitting laser, a laser device, a detection device, and a moving body in which the oxidized region of the oxidized constriction layer can be easily manufactured. [Means for solving the problem]

[0006] According to one aspect of the disclosed technique, a surface-emitting laser includes a first resonator including an active layer, a first reflecting mirror and a second reflecting mirror opposing each other with the active layer sandwiched therebetween, a second resonator provided within the first reflecting mirror, an oxidized constriction layer provided within the second reflecting mirror, the oxidized constriction layer having a non-oxidized region and an oxidized region surrounding the non-oxidized region in a plane perpendicular to a light emission direction, and an electrode pair connected to a power supply device and capable of injecting a current into the active layer, wherein a period during which the current is injected into the active layer by the power supply device is defined as a current injection period, and a period after the current injection period during which the value of the current injected into the active layer is lower than the current value during the current injection period is defined as a current reduction period, and the surface-emitting laser does not oscillate during the current injection period but oscillates during the current reduction period.

[0007] According to another aspect of the disclosed technique, a surface-emitting laser includes a first resonator including an active layer, a first reflecting mirror and a second reflecting mirror opposed to each other with the active layer interposed therebetween, a second resonator provided within the first reflecting mirror, an oxidized constriction layer provided within the second reflecting mirror and having a non-oxidized region and an oxidized region surrounding the non-oxidized region in a plane perpendicular to a light emission direction, and an electrode pair connected to a power supply device and capable of injecting a current into the active layer, wherein the thickness of the layer with the largest Al composition in the non-oxidized region is 35 nm or less, the thickness of the oxidized region at a position 3 μm from an end of the boundary between the oxidized region and the non-oxidized region is two times or less the thickness of the layer, and the area of ​​the region surrounded by the end of the boundary between the oxidized region and the non-oxidized region in the plane perpendicular to the light emission direction is 120 μm. 2 The following is the result. [Effects of the Invention]

[0008] According to the disclosed technology, it is possible to provide a surface-emitting laser, a laser device, a detection device, and a moving body in which the oxidized region of the oxidized constriction layer can be easily manufactured. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view showing a surface-emitting laser according to a first embodiment of the present invention. [Figure 2]FIG. 2 is a cross-sectional view of a main part of the surface-emitting laser according to the first embodiment of the present invention. [Figure 3] FIG. 3 is a cross-sectional view of a surface-emitting laser according to a reference example. [Figure 4] 4(a) to 4(c) are diagrams showing the measurement results of the reference example. [Figure 5] 5(a) and 5(b) are diagrams showing the equivalent refractive index and the electric field intensity distribution. [Figure 6] FIG. 6(a) is a graph showing the carrier density N, the threshold carrier density Nth, and the optical output with respect to time, and FIG. 6(b) is a graph showing the optical confinement factor Γr with respect to time. [Figure 7] 7(a) and 7(b) are enlarged views of FIGS. 6(a) and 6(b), respectively. [Figure 8] FIG. 8 is a diagram showing the thickness of the oxidized region relative to the oscillation wavelength. [Figure 9] FIG. 9 is a diagram showing the optical confinement factor Γr versus the diameter of the oxidized aperture. [Figure 10] FIG. 10 is a diagram showing the optical confinement factor Γr versus the position of the second resonator. [Figure 11] FIG. 11 is a diagram showing a laser device according to a second embodiment of the present invention. [Figure 12] FIG. 12 is a diagram showing the relationship between the duty ratio and the peak output of the optical pulse when the pulse current width is 2.5 ns. [Figure 13] FIG. 13 is a diagram showing a distance measuring device according to a third embodiment of the present invention. [Figure 14] FIG. 14 is a diagram showing an automobile as an example of a moving body according to the fourth embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following embodiments are examples for embodying the technical ideas of the invention, and the present invention is not limited to the described configurations and numerical values. In each drawing, the same components are given the same reference numerals, and duplicated explanations may be omitted as appropriate. The size, positional relationship, etc. of each component shown in each drawing may be exaggerated to facilitate understanding of the invention.

[0011] (First embodiment) First, a first embodiment will be described. The first embodiment relates to a surface-emitting laser. Fig. 1 is a cross-sectional view showing a surface-emitting laser according to the first embodiment of the present invention.

[0012] The surface-emitting laser 100 according to the first embodiment is, for example, a vertical cavity surface-emitting laser (VCSEL) that employs oxide confinement. The surface-emitting laser 100 includes a substrate 10, a first reflecting mirror 20, a first resonator 30, a second reflecting mirror 40, an upper electrode 50, and a lower electrode 52.

[0013] Light is emitted in a direction perpendicular to the surface of the substrate 10. The light emission direction is perpendicular to the surface of the substrate 10 and is also called the vertical direction. A plane parallel to the surface of the substrate 10 is a plane perpendicular to the light emission direction, and a direction parallel to a plane parallel to the surface of the substrate 10 is also called the planar direction or horizontal direction.

[0014] The substrate 10 is a semiconductor substrate, such as an n-type GaAs substrate. The first reflecting mirror 20 is provided on the substrate 10 and is, for example, a distributed Bragg reflector (DBR) formed by stacking a plurality of n-type semiconductor films.

[0015] The first reflecting mirror 20 includes a lower laminated film 21, an upper laminated film 22, and a second resonator 24. The lower laminated film 21 and the upper laminated film 22 sandwich the second resonator 24 in the vertical direction. The optical thickness T2 of the second resonator 24 is an integer multiple of the wavelength λ of the laser light, for example, λ corresponding to one wavelength. This causes the light to resonate within the second resonator 24, increasing the light intensity. Note that the wavelength λ is a value in a vacuum, and the optical thickness is the value obtained by multiplying the physical thickness of a material by the refractive index of the material.

[0016] The first cavity 30 is provided on the first reflecting mirror 20 and includes spacer layers 31 and 32 and an active layer 34. The spacer layers 31 and 32 sandwich the active layer 34 in the vertical direction. The active layer 34 includes, for example, a plurality of quantum well layers and barrier layers.

[0017] The optical thickness T1 of the first resonator 30 is an integer multiple of the wavelength λ, e.g., λ, which causes light to resonate and oscillate within the first resonator 30. When the active layer 34 is located at a position corresponding to an antinode of the electric field in the standing wave, the light emission efficiency is maximized.

[0018] The second reflecting mirror 40 is provided on the first resonator 30. The first reflecting mirror 20 and the second reflecting mirror 40 face each other in the vertical direction, sandwiching the first resonator 30 therebetween. The second reflecting mirror 40 is, for example, a distributed Bragg reflector formed by stacking multiple p-type semiconductor films. The second reflecting mirror 40 includes a lower stacked film 41, an upper stacked film 42, and an oxide constriction layer 44. The lower stacked film 41 and the upper stacked film 42 sandwich the oxide constriction layer 44 in the vertical direction. In other words, the oxide constriction layer 44 is provided midway along the second reflecting mirror 40.

[0019] The oxidized constriction layer 44 determines the range of current flowing in the vertical direction. The oxidized constriction layer 44 is provided in the second reflecting mirror 40, and has, in the surface direction, a non-oxidized region 49 and an oxidized region 48 surrounding the non-oxidized region 49. The oxidized region 48 has a lower refractive index than the non-oxidized region 49.

[0020] The first resonator 30 and the second reflecting mirror 40 are provided on a mesa 54 provided on the first reflecting mirror 20. The entire first resonator 30 and the second reflecting mirror 40 do not have to have a mesa structure, as long as at least the oxidized constriction layer 44 has a side surface that allows oxidation to proceed. For example, only the second reflecting mirror 40 may have a mesa structure. Alternatively, a part of the first resonator 30 and the second reflecting mirror 40 may have a mesa structure.

[0021] The upper electrode 50 contacts the upper surface of the second reflecting mirror 40. The lower electrode 52 contacts the lower surface of the substrate 10. The pair of the upper electrode 50 and the lower electrode 52 is one example of an electrode pair. However, the position of the electrodes is not limited to this, and may be in any position that allows current to be injected into the active layer 34. An intra-cavity structure may be employed in which the electrodes are placed directly on the spacer layers 31 and 32, rather than via the first reflecting mirror 20 and the second reflecting mirror 40.

[0022] 2 is a cross-sectional view of the main parts of the surface-emitting laser according to the first embodiment of the present invention, which mainly shows the first reflecting mirror 20, the first resonator 30, and the second reflecting mirror 40 in an enlarged scale.

[0023] The first reflecting mirror 20 includes a plurality of first high-refractive index layers 25 and a plurality of first low-refractive index layers 26 that are alternately stacked. The refractive index of the first low-refractive index layers 26 is lower than the refractive index of the first high-refractive index layers 25. The first high-refractive index layers 25 are made of, for example, n-type Al 0.5 Ga 0.5 The first low refractive index layer 26 is, for example, an n-type Al 0.9 Ga 0.1 This is the As layer.

[0024] The second reflecting mirror 40 includes a plurality of second high-refractive index layers 45 and a plurality of second low-refractive index layers 46 that are alternately stacked. The refractive index of the second low-refractive index layers 46 is lower than the refractive index of the second high-refractive index layers 45. The second high-refractive index layers 45 are made of, for example, p-type Al 0.5 Ga 0.5 The second low refractive index layer 46 is, for example, a p-type Al 0.9 Ga 0.1 It is an As layer. The lower laminated film 41 as shown in FIG.

[0025] The first high refractive index layer 25, the first low refractive index layer 26, the second high refractive index layer 45, and the second low refractive index layer 46 are made of Al. X Ga 1-X When the layers are As, the X values ​​of the first high-refractive-index layer 25 and the second high-refractive-index layer 45 are smaller than the X values ​​of the first low-refractive-index layer 26 and the second low-refractive-index layer 46. The thicknesses of the first high-refractive-index layer 25, the first low-refractive-index layer 26, the second high-refractive-index layer 45, and the second low-refractive-index layer 46 are each approximately λ / 4. As a result, the first reflecting mirror 20 and the second reflecting mirror 40 Bragg-reflect light of wavelength λ.

[0026] The second cavity 24 is a high refractive index layer 25a, and is made of the same material as the other first high refractive index layers 25. The optical thickness T2 of the second cavity 24 is an integer multiple of λ, and is therefore thicker than the other first high refractive index layers 25.

[0027] The oxidized confinement layer 44, which is an oxidized confinement structure, includes an oxidized region 48 and a non-oxidized region 49 in a plane perpendicular to the light emission direction. The oxidized region 48 has a ring-shaped planar shape and surrounds the non-oxidized region 49. The region surrounded by the oxidized region 48 when viewed from the vertical direction is an oxidized aperture 55. The planar shape of the oxidized aperture 55 can be set arbitrarily, for example, to a circle.

[0028] The non-oxidized region 49 includes a first layer 64 and two second layers 65. The two second layers 65 sandwich the first layer in the vertical direction. The first layer 64 is, for example, a p-type AlAs layer, and the second layers 65 are, for example, p-type AlAs layers. x Ga 1-x As layer (0.70≦x≦0.90), for example, p-type Al 0.85 Ga 0.15 It is an As layer. At least one of the second layers 65 does not have to be provided. The first layer 64 of the non-oxidized region 49 is preferably disposed at a node position of the electric field of the standing wave in the oxidized constricting layer 44. The node position of the electric field of the standing wave is, for example, a position at an optical thickness of λ / 4 from the active layer side of the oxidized constricting layer 44. In the first embodiment, the first layer 64 is disposed at a position at an optical thickness of λ / 4 from the boundary between the oxidized constricting layer 44 and the spacer layer 32.

[0029] The oxidized region 48 is, for example, aluminum oxide (AlO x The refractive index of the oxidized region 48 is lower than that of the non-oxidized region 49. For example, the refractive index of aluminum oxide is 1.65, the refractive index of an AlAs layer is 2.96, and the refractive index of an AlAs layer is 2.96. 0.85 Ga 0.15 The refractive index of As is 3.04, which causes light to be focused on the non-oxidized region 49.

[0030] The oxidized region 48 has an outer region 62 and an inner region 60. When viewed in the vertical direction, the inner region 60 is annular and surrounds the oxidized opening 55. The outer region 62 is annular and surrounds the inner region 60. At a boundary 61 between the inner region 60 and the outer region 62, the thickness of the inner region 60 and the thickness of the outer region 62 are the same, and the upper and lower surfaces of the oxidized region 48 are approximately parallel to the surface direction. The outer region 62 gradually becomes thicker as it moves outward in the horizontal direction, and the inner region 60 gradually becomes thinner as it moves inward in the horizontal direction.

[0031] The total optical thickness of the oxidized constriction layer 44 and the pair of second low refractive index layers 46 sandwiching the oxidized constriction layer 44 is T3. The thickness of the non-oxidized region 49 in the oxidized aperture 55 is T4. The thickness of the first layer 64 is T5.

[0032] The oxidized opening 55 has a horizontal length of L1. The oxidized region 48 has a horizontal length of L3. The oxidized region 48 has a thickness of T6 at a distance L2 from the tip 63 of the boundary between the oxidized region 48 and the non-oxidized region 49. Note that thicknesses T4, T5, and T6 are all physical thicknesses.

[0033] The length L1 is set so that the area of ​​the oxidized opening 55, which is the area surrounded by the tip 63, is 120 μm 2 The dimensions are as follows: Distance L2 is 3 μm; Length L3 is, for example, 8 μm or more and 11 μm or less.

[0034] The optical thickness T3 is, for example, about 3λ / 4. The thickness T4 is, for example, 110 nm or less. The thickness T5 is, for example, 30 nm or less. The thickness T6 is, for example, twice the thickness T5 or less. The oxidized region 48 may be provided outward from the second layer 65 in the vertical direction.

[0035] The oxidized region 48 is formed, for example, by oxidizing the first layer 64 and the second layer 65. For example, the oxidized region 48 can be formed by oxidizing the first layer 64 and the second layer 65 in a high-temperature steam environment. Because AlAs in the first layer 64 is easily oxidized, oxidation of the first layer 64 progresses from the side surface of the mesa 54. The second layer 65 is less susceptible to oxidation than the first layer 64. For this reason, the cross-sectional shape of the oxidized region 48 is as shown in FIG. 2. Note that even if the same first layer 64 and second layer 65 are oxidized, the structure of the oxidized confinement layer obtained from the first layer 64 and the second layer 65 may differ depending on the oxidation conditions.

[0036] The effects of the first embodiment will be described in comparison with a reference example. Fig. 3 is a cross-sectional view of a surface-emitting laser according to the reference example. As shown in Fig. 3, in the surface-emitting laser 110 of the reference example, the second resonator 24 is not provided within the first reflecting mirror 20. The other configurations are the same as those of the first embodiment shown in Fig. 1.

[0037] 4(a) to 4(c) are diagrams showing the measurement results of the reference example. The measurement method is the same as that in Patent Document 1. The horizontal axis represents time, and the vertical axis represents the current flowing between the upper electrode 50 and the lower electrode 52, and the output.

[0038] Figure 4(a) shows the measurement results when the pulse current width is approximately 0.8 ns, Figure 4(b) shows the measurement results when the pulse current width is 1.3 ns, and Figure 4(c) shows the measurement results when the pulse current width is 2.5 ns. The magnitude of the bias current and the amplitude of the pulse current are the same in the measurements of Figures 4(a) to 4(c).

[0039] As shown in Figures 4(a) to 4(c), in the reference example, no optical output is generated while the pulse current is being injected, and an optical pulse is output immediately after the injection of the pulse current is reduced. In addition, there is almost no tail light (i.e., trailing tail) after the optical pulse is output. If the optical output is due to gain switching, the timing at which the optical pulse is generated does not change even if the pulse current width is changed. In contrast, in the reference example, the optical pulse is output as a result of the reduction in the injection of the pulse current. Therefore, it can be said that the optical output in the reference example is not due to ordinary gain switching that utilizes the relaxation oscillation phenomenon.

[0040] Laser safety standards for human eyes are classified into eye-safe classes and are specified by IEC.60825-1Ed.3 (the equivalent domestic standard, JIS C 6802). In order for distance measurement devices to be used in a variety of environments, it is desirable for them to meet the Class 1 standards, which do not require safety measures or warnings. One of the standards for Class 1 specifies an upper limit on average power.

[0041] In the case of pulsed light, the peak value, pulse width, and duty ratio are converted into average power and compared with the standard value. The shorter the pulse width of the light pulse, the higher the allowable peak value. In the reference example, the pulse width can be made smaller, so the peak value can be made higher. If pulsed light has tailing, it is a disadvantage from the perspective of eye safety because it is unnecessary energy. In the reference example, tailing can be suppressed, so it is advantageous from the perspective of eye safety.

[0042] In the reference example, the contents described in Patent Document 1 will be briefly explained regarding the reason why an optical pulse is output in response to a decrease in the injection of pulse current, the reason why the pulse width can be reduced, and the reason why tailing can be suppressed.

[0043] 5(a) and 5(b) are diagrams showing the equivalent refractive index and electric field strength distribution. The horizontal axis represents the radius r from the center 66 of the oxidized opening 55, with the center 66 of the oxidized opening 55 in FIG. 2 being set as 0. The point where the radius r is r1 corresponds to the tip 63. In other words, the region where the radius r is r1 or less corresponds to the oxidized opening 55, and the region where the radius r is r1 or more corresponds to the oxidized region 48. The vertical axis represents the equivalent refractive index and electric field strength within the oxidized constriction layer 44.

[0044] 5(a) shows the equivalent refractive index and electric field strength during a period when no current is injected into the active layer 34. As shown in FIG. 5(a), the equivalent refractive index of the oxidized region 48 is n0. The equivalent refractive index of the oxidized opening 55 is n1. The difference Δn between the equivalent refractive index n1 of the oxidized opening 55 and the equivalent refractive index n0 of the oxidized region 48 is large. As a result, the electric field strength within the oxidized opening 55 becomes high, and when the radius r is equal to or greater than r1, the electric field strength drops sharply.

[0045] 5(b) shows the equivalent refractive index and electric field strength during the period when current is injected into the active layer 34. As shown in FIG. 5(b), the equivalent refractive index of the oxidized region 48 is n0, which is the same as that in FIG. 5(a). The equivalent refractive index of the oxidized aperture 55 is n2, which is lower than the equivalent refractive index n1 in FIG. 5(a). This is because when current is injected, the carrier density in the oxidized aperture 55 increases, and the equivalent refractive index decreases due to the carrier plasma effect.

[0046] The difference Δn between the equivalent refractive index n2 of the oxidized opening 55 and the equivalent refractive index n0 of the oxidized region 48 is smaller than Δn in Fig. 5(a). Therefore, the electric field strength in the oxidized opening 55 is lower than in Fig. 5(a), and the electric field strength where the radius r is equal to or greater than r1 is higher than in Fig. 5(a).

[0047] In this way, the light confinement is smaller during the period when a current is injected into the active layer 34 than during the period when a current is not injected into the active layer 34. In the oxidized confinement layer 44, light is confined in the oxidized opening 55, and thus in the active layer 34, light is also confined in the region corresponding to the oxidized opening 55.

[0048] The graph shows the results of a simulation of the carrier density N, threshold carrier density Nth, photon density S, and optical confinement factor Γr in the lateral direction against time. The threshold carrier density Nth is the carrier density at which laser light oscillates, and laser light oscillates when N≧Nth. The optical confinement factor Γr indicates the proportion of light intensity within the oxidized opening 55 in the light intensity distribution. The details of the simulation are the same as those in Patent Document 1.

[0049] Fig. 6(a) shows the carrier density N, threshold carrier density Nth, and optical output power versus time, and Fig. 6(b) shows the optical confinement factor Γr versus time. Fig. 7(a) and Fig. 7(b) are enlarged views of Fig. 6(a) and Fig. 6(b), respectively.

[0050] The period up to time t1 is a period P1 in which no current flows. The period between times t2 and t3 is a current injection period P2 in which current is injected into the active layer 34. The period after time t2 is a period P3 in which no current flows. Within period P3, the period after current injection period P2 in which the value of the current injected into the active layer 34 is lower than the current value in current injection period P2 is a current reduction period P4.

[0051] As shown in Figures 6(a) and 6(b), in period P1, the carrier density N is low and the threshold carrier density Nth is greater than the carrier density N. As a result, stimulated emission is unlikely to occur, and laser oscillation does not occur. Because the carrier density N is small, the carrier plasma effect does not occur, as shown in Figure 5(a), and the optical confinement factor Γr is large.

[0052] During period P2, current is injected, and carrier density N increases. Accordingly, as shown in FIG. 5(b), the carrier plasma effect reduces the equivalent refractive index at oxidized aperture 55. This reduces the optical confinement factor Γr. As Γr decreases, threshold carrier density Nt increases. Even though carrier density N increases, threshold carrier density Nth also increases. Therefore, carrier density N is smaller than threshold carrier density Nth, and stimulated emission is unlikely to occur, resulting in no laser oscillation.

[0053] In period P3, no current flows, so the carrier density N decreases. The carrier plasma effect does not occur, so the optical confinement factor Γr increases.

[0054] As shown in Figures 7(a) and 7(b), at time t2, when the current injection starts to decrease, the carrier density N starts to decrease over the carrier lifetime. At the same time, the lateral optical confinement factor Γ r also begins to rise. If the confinement factor Γr increases before the carrier density N completely decays, the threshold carrier density Nth decreases. Because the rate at which the threshold carrier density Nth decreases is faster than the rate at which the carrier density N decreases, N>Nth at time t3 during the process of the carrier density N decreasing.

[0055] After time t3, the photon density S first increases due to spontaneous emission, and once the photon density S has increased to a certain extent, stimulated emission becomes dominant and the photon density S increases rapidly. When stimulated emission occurs, the carrier density N decreases rapidly, and at time t4, N <Nthとなる。

[0056] After time t4, the photon density S drops sharply. In this way, laser oscillation does not occur during period P2, and an optical pulse is output during period P4, triggered by the cessation of pulse current injection. This allows the pulse width to be narrowed. Furthermore, because the photon density S drops sharply after time t4, tailing can be suppressed.

[0057] To achieve this operation, it is important that the lateral optical confinement coefficient is small during period P2, as shown in Figure 5(b). In a surface-emitting laser, the equivalent refractive index of the oxidized region 48 is smaller than that of the non-oxidized region 49, so if the propagation direction of the laser light is the vertical direction, lateral optical confinement is achieved. Here, the thinner the oxidized region 48 of the oxidized confinement layer 44, the smaller the difference in equivalent refractive index between the oxidized region 48 and the non-oxidized region 49, and the smaller the lateral optical confinement coefficient Γr. Therefore, to reduce the lateral optical confinement coefficient during period P2, it is preferable that the oxidized region 48 of the oxidized confinement layer 44 is thin.

[0058] Therefore, using the fabricated surface-emitting lasers with different oscillation wavelengths, we estimated the thickness of the first layer 64 that would not oscillate in period P2 but would oscillate stably in period P4. Figure 8 is a diagram showing the thickness of the first layer versus the oscillation wavelength. The dots represent the estimated oscillation wavelength of the surface-emitting laser and the thickness of the first layer 64, the thick lines connect the dots, and the dashed straight lines represent the relationship between the oscillation wavelength and the thickness of the first layer 64 estimated from the dots.

[0059] As shown in Figure 8, when the oscillation wavelength becomes shorter, stable laser oscillation is not achieved unless the first layer 64 is thinned. When the oscillation wavelength is about 940 nm, the thickness of the first layer 64 that stabilizes oscillation is about 34 nm. When the oscillation wavelength is about 780 nm, the thickness of the first layer 64 that stabilizes oscillation is about 25 nm.

[0060] From the dashed line, it is believed that when the oscillation wavelength is approximately 670 nm, the thickness of the first layer 64 that stably oscillates is approximately 20 nm or less. This is because, even when the thickness of the oxidized region 48 is the same, as the oscillation wavelength becomes shorter, the proportion of the first layer 64 per wavelength of the standing wave generated in the vertical direction increases, and the optical confinement factor Γr increases. For this reason, it is believed that as the oscillation wavelength becomes shorter, the thickness of the first layer 64 that stably oscillates becomes smaller.

[0061] However, it is difficult to form a thin oxidized region 48. For example, when oxidizing the first layer 64 and the second layer 65 from the side surface of the mesa 54, it is difficult to form the oxidized region 48 in a desired shape (e.g., aspect ratio) and to control the thickness of the oxidized region 48. If the oxidized region 48 becomes too thin, a tunnel current will flow through the oxidized region 48, impairing the function of the oxidized confinement layer 44 as a current confinement layer.

[0062] In the first embodiment and the reference example, a simulation was performed to determine the lateral optical confinement factor Γr relative to the diameter (corresponding to the length L1) of the oxidized opening 55. The structure used in the simulation is as follows.

[0063] The oscillation wavelength is about 670 nm. The substrate 10 is an n-type GaAs substrate. In the first reflecting mirror 20, the first high refractive index layer 25 is an n-type Al 0.5 Ga 0.5 The first low refractive index layer 26 is an n-type Al layer. 0.9 Ga 0.1 The first high-refractive-index layer 25 and the first low-refractive-index layer 26 are arranged in pairs of 72. The second resonator 24 is the high-refractive-index layer 25a of the predetermined pair counted from the first resonator 30. The optical thickness T2 is one wavelength.

[0064] In the first resonator 30, the spacer layers 31 and 32 are undoped AlInP layers. The active layer 34 is a multi-quantum well (MQW) having a GaInP layer and an AlGaInP layer. The optical thickness T1 is one wavelength.

[0065] In the second reflecting mirror 40, the second high refractive index layer 45 is made of p-type Al 0.5 Ga 0.5 The second low refractive index layer 46 is a p-type Al layer. 0.9 Ga 0.1 The number of pairs of the second high refractive index layers 45 and the second low refractive index layers 46 is 44.

[0066] The oxidized constriction layer 44 is provided on the first pair of second low refractive index layers 46 from the first resonator 30 side. The first layer 64 is a p-type AlAs layer and is located at the antinode of the electric field in the standing wave. The thickness T5 is, for example, 25 nm. The optical thickness T3 is 3λ / 4. The thickness T6 of the oxidized region 48 is less than twice the thickness T5 of the first layer 64.

[0067] In the reference example, the second resonator 24 is not provided, and the first high refractive index layer 25 having an optical thickness of λ / 4 is provided.

[0068] 9 is a diagram showing the optical confinement factor Γr versus the diameter of the oxidized aperture. The horizontal axis is the diameter of the oxidized aperture 55, and the vertical axis is the optical confinement factor Γr when no current is injected. In the reference example, the second resonator 23 is not provided. The second and third pairs show that the second resonator 23 is provided in the high refractive index layer 25a of the second pair (corresponding to FIG. 2) and the third pair from the first resonator 30 side.

[0069] 9, the optical confinement factor Γr decreases as the diameter of the oxidized opening 55 decreases. When compared at the same diameter of the oxidized opening 55, the optical confinement factor Γr is smaller in the first embodiment than in the reference example.

[0070] In this way, by providing the second resonator 24 within the first reflecting mirror 20, the optical confinement factor Γr can be reduced. Therefore, even if the oxidized region 48 is thick, laser oscillation does not occur during period P2, and stable laser oscillation can be achieved during period P4. For example, even if the oscillation wavelength is approximately 670 nm, stable laser oscillation can be achieved when the thickness T6 of the oxidized region 48 is 25 nm. This allows the oxidized region 48 to be formed with good reproducibility.

[0071] FIG. 10 is a diagram showing the optical confinement factor Γr versus the position of the second resonator. The horizontal axis shows the position of the second resonator 23 from the first resonator 30 side using pairs. The vertical axis is the optical confinement factor Γr when current is injected. The diameter of the oxidized aperture was set to 5 μm. The solid line extending in the horizontal direction indicates a reference example.

[0072] 10, Γr decreases as the number of pairs increases up to the fourth pair of the second resonator 23. From the fifth pair onwards, Γr remains almost constant.

[0073] The reason why the optical confinement factor Γr is reduced by providing the second resonator 24 can be considered as follows: In the reference example, the lateral width of the region where the light intensity is high in the first reflecting mirror 20 is smaller than the lateral width of the region where the light intensity is high in the first resonator 30, and the lateral width of the region where the light intensity is high gradually decreases with increasing distance from the first resonator 30.

[0074] In the first embodiment, by providing the second resonator 24 in the first reflecting mirror 20, light resonates again in the second resonator 23. This increases the light intensity between the first resonator 30 and the second resonator 23. Therefore, when the second resonator 23 is provided, the light spreads more widely in the lateral direction in the first resonator 30. When the second resonator 24 is provided at a position farther away from the first resonator 30, the second resonator 24 has less influence on the first resonator 30, and the optical confinement factor Γr remains constant.

[0075] The second resonator 24 is a high-refractive index layer 25a in which the optical thickness T2 of one of the first high-refractive index layers 25 in the first reflecting mirror 20 is an integer multiple of the wavelength λ. This allows the second resonator 24 to be formed by changing the thickness of one of the first high-refractive index layers 25. The optical thickness T2 of the high-refractive index layer 25a is preferably one wavelength λ. This allows the resonance of the second resonator 24 to be increased. Therefore, the light in the first resonator 30 is more likely to spread laterally, allowing the optical confinement factor Γr to be smaller.

[0076] In this embodiment, the optical thickness of the semiconductor layer being A times the wavelength λ (A is a positive integer) does not necessarily mean that the optical thickness of the semiconductor layer is strictly Aλ. The optical thickness of the semiconductor layer is allowed to have an error to the extent that the function of the semiconductor layer can be obtained. For example, the optical thickness of the semiconductor layer may be 0.995 Aλ or more and 1.005 Aλ or less.

[0077] The high refractive index layer 25a is the first high refractive index layer 25 that is at least second from the first cavity 30 in the first reflecting mirror 20. This allows the optical confinement factor Γr to be small, as shown in FIG. 9 . The high refractive index layer 25a is preferably at least third from the first cavity 30, more preferably at least fourth. The high refractive index layer 25a is preferably at most tenth from the first cavity 30, more preferably at most eighth.

[0078] To set the optical thickness T3 to 3λ / 4 and to thin the oxidized region 48, the thickness T4 of the non-oxidized region 49 is preferably 110 nm or less. The thickness T5 of the first layer 64 is preferably 35 nm or less, more preferably 30 nm or less, and even more preferably 25 nm or less. To form the oxidized region 48 with good reproducibility, the thickness T4 is preferably 80 nm or more. The thickness T5 of the first layer 64 is preferably 10 nm or more. Although an AlAs layer has been described as the first layer 64, the first layer 64 is the layer with the highest Al composition among the layers of the non-oxidized region 49.

[0079] From the viewpoint of reducing the optical confinement factor Γr, the thickness T6 of the oxidized region 48 is preferably equal to or less than twice the thickness T5 of the first layer 64, and more preferably equal to or less than 1.5 times.

[0080] In order to reduce the optical confinement factor Γr, the area of ​​the oxidized opening 55 is set to 120 μm 2 Preferably less than 50 μm 2 From the viewpoint of increasing the optical output, the area of ​​the oxidized opening 55 is preferably 5 μm or less. 2 More than 10 μm is preferable. 2 The above is preferable.

[0081] As shown in FIGS. 6(a) and 7(a), the surface-emitting laser 100 outputs an optical pulse having a time width shorter than the current injection period P2. The time width of the optical pulse is, for example, 0.5 times or less, or 0.1 times or less, of the period P2. The optical pulse width is, for example, 1 ns or less, 500 ps or less, 110 ps or less, or 100 ps or less. The optical pulse width is, for example, 10 ps or more. The optical pulse width is defined as 1 / e of the peak value. 2 This is the time width.

[0082] (Second embodiment) Next, a second embodiment will be described. The second embodiment relates to a laser device. Fig. 11 is a diagram showing a laser device according to the second embodiment of the present invention.

[0083] The laser device 300 according to the second embodiment includes the surface-emitting laser 100 according to the first embodiment, and a power supply device 301 connected to the upper electrode 50 and the lower electrode 52 of the surface-emitting laser 100. The power supply device 301 injects a current into the surface-emitting laser 100.

[0084] The duty ratio of the current injected from the power supply device 301 is preferably 0.5% or less. In other words, the current injection period and the current reduction period are repeated multiple times, and the ratio of the current injection period to the current reduction period is preferably 0.5% or less. The duty ratio is the ratio of the time during which a current pulse is injected within a unit time. If the pulse current width is t [s] and the repetition frequency of the pulse current is f [Hz], the duty ratio corresponds to f × t (%).

[0085] FIG. 12 is a diagram showing the relationship between the duty ratio and the peak output of the optical pulse when the pulse current width is 2.5 ns.

[0086] As shown in Figure 12, when the duty ratio exceeds 0.5%, the optical peak output tends to decrease. The following model is thought to explain this. First, as the duty ratio increases, the amount of heat generated in the current confinement region (non-oxidized region 49) by the injected pulse current increases. This causes a temperature difference between the center of the current confinement region, where the current is concentrated, and the peripheral region. As a result, the refractive index in the center of the current confinement region increases due to the thermal lens effect, and the lateral optical confinement factor increases.

[0087] When the lateral optical confinement factor increases due to the thermal lens effect, the influence of refractive index changes caused by the carrier plasma effect resulting from increases and decreases in the pulse current is reduced. This reduces the likelihood of an optical pulse being output immediately after the injection of the pulse current is stopped. On the other hand, if the duty ratio is 0.5% or less, the influence of refractive index changes due to the thermal lens effect is sufficiently small, and the refractive index changes resulting from the confinement structure become dominant, so the peak output is expected to remain almost constant.

[0088] (Third embodiment) Next, a third embodiment will be described. The third embodiment relates to a distance measurement device. Fig. 13 is a diagram showing a distance measurement device according to the third embodiment of the present invention. The distance measurement device is an example of a detection device.

[0089] The distance measurement device 400 according to the third embodiment is a distance measurement device using a TOF (Time of Flight) method. The distance measurement device 400 includes a light emitting element 410, a light receiving element 420, and a drive circuit 430. The light emitting element 410 emits an emitted light beam (irradiated light 411) toward a distance measurement object 450. The light receiving element 420 receives reflected light 421 from the distance measurement object 450. The drive circuit 430 drives the light emitting element 410 and measures the round-trip distance to the distance measurement object 450 by detecting the time difference between the emission timing of the emitted light beam and the reception timing of the reflected light 421 by the light receiving element 420.

[0090] The light emitting element 410 includes the surface emitting laser 100 according to the first embodiment. The light emitting element 410 may include a plurality of surface emitting lasers 100 according to the first embodiment arranged in an array. The pulse repetition frequency is, for example, in the range from several kHz to several tens of MHz.

[0091] The light receiving element 420 is, for example, a photodiode (PD), an avalanche photodiode (APD), or a single-photon avalanche diode (SPAD). The light receiving element 420 may include a plurality of light receiving elements arranged in an array. The light receiving element 420 is an example of a detection unit.

[0092] In distance measurement using the TOF method, it is important to separate the signal from the object being measured from noise. When measuring an object that is farther away or has lower reflectivity, it is preferable to use a more sensitive light-receiving element to obtain the signal from the object. However, using a more sensitive light-receiving element increases the possibility of false detection of background light noise or shot noise. In order to separate the signal from noise, it is possible to raise the threshold of the received light signal, but if the peak output of the emitted light beam is not increased accordingly, it will become difficult to receive the signal light from the object being measured. However, the output of the emitted light beam is subject to restrictions imposed by laser safety standards.

[0093] The surface-emitting laser 100 according to the first embodiment can output optical pulses with a pulse width of about 100 ps. This is about 1 / 10 of the optical pulse width of several ns output by conventional surface-emitting lasers. According to the third embodiment, the shorter the pulse width of the optical pulse, the higher the peak output power allowed by safety standards. Therefore, it is possible to achieve both high accuracy and long distances while satisfying eye safety.

[0094] (Fourth embodiment) Next, a fourth embodiment will be described. The fourth embodiment relates to a moving body. Fig. 14 is a diagram showing an automobile as an example of a moving body according to the fourth embodiment of the present invention.

[0095] The distance measurement device 400 described in the fourth embodiment is provided above the front surface (for example, above the windshield) of an automobile 500, which is an example of a moving body according to the fourth embodiment. The distance measurement device 400 measures the distance to an object 502 around the automobile 500. The measurement result of the distance measurement device 400 is input to a control unit of the automobile 500, and the control unit controls the operation of the moving body based on the measurement result. Alternatively, the control unit may display a warning on a display unit provided inside the automobile 500 to a driver 501 of the automobile 500 based on the measurement result of the distance measurement device 400.

[0096] As described above, in the fourth embodiment, by providing the distance measurement device 400 in the automobile 500, the position of the object 502 in the vicinity of the automobile 500 can be recognized with high accuracy. The mounting position of the distance measurement device 400 is not limited to the upper front of the automobile 500, but it may be mounted on the side or rear. Also, in this example, the distance measurement device 400 is provided in the automobile 500, but the distance measurement device 400 may also be provided in an aircraft or a ship. Furthermore, it may also be provided in a mobile object that moves autonomously without a driver, such as a drone or a robot.

[0097] The above describes in detail preferred embodiments, but the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the claims.

[0098] The above-disclosed embodiments include, for example, the following aspects. (1) a second resonator provided within the first reflecting mirror; an oxidation constriction layer provided within the second reflecting mirror, the oxidation constriction layer having a non-oxidized region and an oxidized region surrounding the non-oxidized region in a plane perpendicular to a light emission direction; and an electrode pair connected to a power supply device and capable of injecting a current into the active layer, wherein a period during which the current is injected into the active layer by the power supply device is defined as a current injection period, and a period after the current injection period during which the value of the current injected into the active layer is lower than the current value during the current injection period is defined as a current reduction period, and the surface-emitting laser does not oscillate during the current injection period but oscillates during the current reduction period. (2) The surface-emitting laser according to (1), wherein the first reflecting mirror has a plurality of first high-refractive index layers and a plurality of first low-refractive index layers that are alternately stacked, and the second resonator is a high-refractive index layer in which one of the first high-refractive index layers in the first reflecting mirror has a thickness that is an integer multiple of the wavelength of the light. (3) The surface-emitting laser according to (2), wherein the high-refractive index layer is a first high-refractive index layer that is at least second and at most tenth from the first cavity in the first reflecting mirror. (4) The surface-emitting laser according to (2) or (3), wherein the thickness of the high refractive index layer is equal to the wavelength. (5) The thickness of the layer with the largest Al composition in the non-oxidized region is 35 nm or less, the thickness of the oxidized region at a position 3 μm from the tip of the boundary between the oxidized region and the non-oxidized region is 2 times or less the thickness of the layer, and the area of ​​the region surrounded by the tip of the boundary between the oxidized region and the non-oxidized region in a plane perpendicular to the light emission direction is 120 μm 2 A surface-emitting laser according to any one of (1) to (4), which is: (6) a first resonator including an active layer, a first reflecting mirror and a second reflecting mirror opposed to each other with the active layer interposed therebetween, a second resonator provided within the first reflecting mirror, an oxidation constriction layer provided within the second reflecting mirror and having a non-oxidized region and an oxidation region surrounding the non-oxidized region in a plane perpendicular to the light emission direction, and an electrode pair connected to a power supply device and capable of injecting a current into the active layer, wherein the thickness of the layer with the largest Al composition in the non-oxidized region is 35 nm or less, the thickness of the oxidized region at a position 3 μm from the tip of the boundary between the oxidized region and the non-oxidized region is two times or less the thickness of the layer, and the area of ​​the region surrounded by the tip of the boundary between the oxidized region and the non-oxidized region in the plane perpendicular to the light emission direction is 120 μm 2 Below is the Surface-emitting laser. (7) A surface-emitting laser according to any one of (1) to (6), a power supply device connected to the electrode pair and configured to inject a current into the surface-emitting laser; A laser device comprising: (8) The laser device according to (7), a detection unit that detects light emitted from the surface-emitting laser and reflected by an object; A detection device comprising: (9) The detection device according to (8), which detects the distance to the object based on a signal from the detection unit. (10) A moving body equipped with the detection device according to (8) or (9). [Explanation of symbols]

[0099] 20 1st reflector 24 Second resonator 25 First high refractive index layer 25a High refractive index layer 26 First low refractive index layer 30 1st resonator 34 Active layer 40 Second reflector 44 Oxidized constriction layer 48 Oxidation Region 49 Non-oxidized area 50 Upper electrode 52 Lower electrode 100 Surface-emitting laser 300 Laser Device 301 Power Supply 400 Distance Measuring Device 500 Automobiles (mobile vehicles) [Prior art documents] [Patent documents]

[0100] [Patent Document 1] Japanese Patent Publication No. 2023-20850

Claims

1. a first cavity including an active layer; a first reflecting mirror and a second reflecting mirror that face each other with the active layer interposed therebetween; a second resonator provided within the first reflector; an oxidation constriction layer provided in the second reflecting mirror, the oxidation constriction layer having a non-oxidized region and an oxidation region surrounding the non-oxidized region in a plane perpendicular to the light emission direction; a pair of electrodes connected to a power supply and capable of injecting a current into the active layer; Equipped with a period during which the current is injected into the active layer by the power supply device is defined as a current injection period, and a period after the current injection period during which the value of the current injected into the active layer is lower than the current value during the current injection period is defined as a current reduction period, Laser oscillation does not occur during the current injection period, and laser oscillation occurs during the current reduction period. Surface-emitting laser.

2. the first reflecting mirror has a plurality of first high refractive index layers and a plurality of first low refractive index layers, each having a refractive index lower than that of the first high refractive index layers, which are alternately stacked; 2. The surface-emitting laser according to claim 1, wherein the second resonator is a high-refractive index layer having a thickness of one of the first high-refractive index layers of the first reflector that is an integer multiple of the wavelength of the light.

3. 3. The surface-emitting laser according to claim 2, wherein the high-refractive index layer is a first high-refractive index layer of the first reflecting mirror that is at least second and at most tenth from the first resonator.

4. 4. The surface-emitting laser according to claim 2, wherein the thickness of the high-refractive-index layer is equal to the wavelength.

5. the thickness of the layer with the highest Al composition in the non-oxidized region is 35 nm or less; the thickness of the oxidized region at a position 3 μm from the tip of the boundary between the oxidized region and the non-oxidized region is not more than twice the thickness of the layer; The area of ​​the region surrounded by the tip of the boundary between the oxidized region and the non-oxidized region in the plane perpendicular to the light emission direction is 120 μm ２ 4. The surface-emitting laser according to claim 1, wherein:

6. a first cavity including an active layer; a first reflecting mirror and a second reflecting mirror that face each other with the active layer interposed therebetween; a second resonator provided within the first reflector; an oxidation constriction layer provided in the second reflecting mirror, the oxidation constriction layer having a non-oxidized region and an oxidation region surrounding the non-oxidized region in a plane perpendicular to the light emission direction; a pair of electrodes connected to a power supply and capable of injecting a current into the active layer; Equipped with the thickness of the layer with the highest Al composition in the non-oxidized region is 35 nm or less; the thickness of the oxidized region at a position 3 μm from the tip of the boundary between the oxidized region and the non-oxidized region is equal to or less than twice the thickness of the layer; The area of ​​the region surrounded by the tip of the boundary between the oxidized region and the non-oxidized region in the plane perpendicular to the light emission direction is 120 μm ２ Below is the Surface-emitting laser.

7. A surface-emitting laser according to any one of claims 1 to 3; a power supply device connected to the electrode pair and configured to inject a current into the surface-emitting laser; A laser device comprising:

8. The laser device according to claim 7; a detection unit that detects light emitted from the surface-emitting laser and reflected by an object; A detection device comprising:

9. The detection device according to claim 8 , wherein the distance to the object is detected based on a signal from the detection unit.

10. A moving object comprising the detection device according to claim 8.

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