Surface-emitting laser, laser device, detection device and moving body

Abstract

To provide a surface-emitting laser capable of achieving both high pulse output and short pulse width, a laser device, a detection device, and a moving body.SOLUTION: The surface-emitting laser includes: multiple active layers; a resonator including a tunnel junction between the multiple active layers; multiple reflectors facing each other across the resonator; and a first electrode pair connected to a first power supply so as to inject a current into the active layer. Defining the period during which the current is injected by the power supply as a current injection period, and defining a period after the current injection period in which the current value injected into the resonator is lower than the current value during the current injection period as a current decreasing period, no laser oscillates during the current injection period and the laser oscillates during the current decreasing period.SELECTED DRAWING: Figure 18

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] In many applications, a large pulse output of the laser is desirable, and a multi-junction structure has been proposed as a structure for improving the output (Non-Patent Document 5).

[0003] Meanwhile, applications requiring both high pulse output and short pulse width are expanding. One example is the TOF (Time of Flight) sensor. For TOF sensors, a laser light source with high pulse output and short pulse width is useful to achieve high accuracy and long distances while satisfying eye-safety standards. This is because the average power, which is one of the eye-safety standards, is a value converted from peak output, pulse width, and duty ratio, and the shorter the pulse width of the optical pulse, the higher the allowable peak output.

[0004] Gain switching, Q switching, and mode locking are some of the methods for achieving pulses shorter than 1 ns. Gain switching is a method for achieving pulse widths of 100 ps or less by utilizing the relaxation oscillation phenomenon. Since it can be achieved simply by controlling the pulse current, it has a simpler configuration than Q switching or mode locking. Summary of the Invention [Problem to be solved by the invention]

[0005] The inventors have discovered that even if gain switching is applied to a conventional surface-emitting laser having a multi-junction structure, variations in the oscillation characteristics from the multiple well layers occur, making it difficult to achieve both a high pulse output and a short pulse width.

[0006] An object of the present invention is to provide a surface-emitting laser, a laser device, a detection device, and a moving object that can achieve both a high pulse output and a short pulse width. [Means for solving the problem]

[0007] According to one aspect of the disclosed technique, a surface-emitting laser includes a resonator including a plurality of active layers and tunnel junctions between the plurality of active layers, a plurality of reflecting mirrors facing each other across the resonator, and a first electrode pair connected to a first power supply device and capable of injecting a current into the active layer, 1st By power supply Pulse Current is injected attitude The period during which the current is injected is the current injection period, and the period after the current injection period is the The injection of the pulse current is stopped. A period during which the current value injected into the resonator is lower than the current value during the current injection period is defined as a current decrease period, and laser oscillation does not occur during the current injection period but does occur during the current decrease period. [Effects of the Invention]

[0008] According to the disclosed technology, it is possible to achieve both a high pulse output and a short pulse width. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a band diagram showing a tunnel junction. [Figure 2] FIG. 1 is a band diagram showing a tunnel junction used to connect multiple active layers. [Figure 3] FIG. 2 is a cross-sectional view showing a surface-emitting laser according to a first reference example. [Figure 4] FIG. 3 is a cross-sectional view showing an oxidized constriction layer and its vicinity in a first reference example. [Figure 5] FIG. 10 is a cross-sectional view showing an oxidized constriction layer and its vicinity in a second reference example. [Figure 6] FIG. 1 is an equivalent circuit diagram showing a circuit used for actual measurements. [Figure 7] FIG. 10 is a diagram showing the results of actual measurements for the second reference example. [Figure 8] FIG. 10 is a diagram showing the results of actual measurements for the first reference example. [Figure 9] 10A and 10B are diagrams illustrating differences in distribution of electric field intensity and transmission refractive index depending on the structure. [Figure 10] 10A and 10B are diagrams showing changes in the distribution of electric field intensity and transmission refractive index over time. [Figure 11] FIG. 10 is a diagram showing simulation results for the carrier density and threshold carrier density in the second reference example. [Figure 12] FIG. 10 is a diagram showing a simulation result of the optical output in the second reference example. [Figure 13] FIG. 10 is a diagram showing an example of a function used in a simulation for the first reference example. [Figure 14] FIG. 10 is a diagram showing a simulation result of the optical output in the first reference example. [Figure 15] FIG. 10 is a diagram showing simulation results of the carrier density, threshold carrier density, photon density, and lateral optical confinement factor in the first reference example. [Figure 16] FIG. 16 is an enlarged view of a part of FIG. 15. [Figure 17] 10A and 10B are diagrams illustrating examples of actual measurement results and simulation results of an optical pulse. [Figure 18] 1 is a cross-sectional view showing a surface-emitting laser according to a first embodiment. [Figure 19] FIG. 10 is a diagram showing the relationship between the current confinement area and the peak optical output. [Figure 20] 1A and 1B are a cross-sectional view and a top view showing a surface-emitting laser according to a second embodiment. [Figure 21] FIG. 10 is a cross-sectional view showing a surface-emitting laser according to a third embodiment. [Figure 22A] FIG. 10 is a top view showing a surface-emitting laser according to a fourth embodiment. [Figure 22B] FIG. 10 is a cross-sectional view showing a surface-emitting laser according to a fourth embodiment. [Figure 23] FIG. 10 is a cross-sectional view showing a surface-emitting laser according to a fifth embodiment. [Figure 24]FIG. 10 is a cross-sectional view showing a surface-emitting laser according to a sixth embodiment. [Figure 25] FIG. 10 is a cross-sectional view showing a surface-emitting laser according to a seventh embodiment. [Figure 26] FIG. 13 is a cross-sectional view showing a surface-emitting laser according to an eighth embodiment. [Figure 27] FIG. 13 is a diagram illustrating a laser device according to a ninth embodiment. [Figure 28] FIG. 10 is a diagram illustrating the relationship between the duty ratio and the peak output of an optical pulse. [Figure 29] FIG. 22 is a diagram showing a distance measurement device according to a tenth embodiment. [Figure 30] FIG. 22 is a diagram showing a moving body according to an eleventh embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0010] First, we will explain the multi-junction structure. A multi-junction structure has multiple active layers connected via tunnel junctions. The tunnel junction consists of a heavily doped pn junction. When a reverse bias is applied to this pn junction and the conduction band energy on the n-type semiconductor side becomes lower than the valence band energy of the p-type semiconductor, as shown in Figure 1, electrons can tunnel from the valence band of the p-type semiconductor layer through the depletion layer to the conductor in the n-type semiconductor layer. At this time, holes are generated in the p-type semiconductor due to the tunneling of electrons. Therefore, electrons can be supplied to the n-type semiconductor side and holes to the p-type semiconductor side via this tunnel junction.

[0011] Furthermore, as shown in Figure 2, using tunnel junctions to connect multiple active layers allows the number of well layers to be increased without reducing the carrier injection efficiency into the well layers, enabling high-efficiency, high-power operation. Simply increasing the number of well layers without using tunnel junctions makes it difficult to sufficiently inject carriers, especially holes, into well layers far from the injection side. Therefore, it is difficult to achieve a uniform carrier density between well layers close to the injection side and well layers far from the injection side, making it impossible to improve power output. On the other hand, using tunnel junctions allows electrons and holes to be generated and used for injection, enabling uniform carrier injection even when the number of well layers is increased.

[0012] Furthermore, due to the continuity of the current, the same number of electrons as those supplied from the power source are generated at the tunnel junction, so that one electron undergoes radiative recombination multiple times in each active layer via the tunnel junction. This improves the so-called slope efficiency in proportion to the number of well layers. As a result, high output power can be obtained.

[0013] However, the inventors have found through their investigations that when attempting to obtain laser light with a short pulse width from a surface-emitting laser having a multi-junction structure, the following problem occurs.

[0014] Gain switching operation utilizes the relaxation oscillation phenomenon caused by the interaction between the electron system in the active layer and the photon system in the resonator, which occurs immediately after the application of a drive current pulse, to output short pulses. This is a transient phenomenon until the pulse reaches a steady-state output. For this reason, gain switching operation is fundamentally unstable, and the oscillation characteristics are easily affected by variations in various structural and characteristic factors. In other words, to obtain high-output short pulses with a multi-junction structure, it is desirable for each active layer to exhibit the same oscillation characteristics and be synchronized in time, but achieving the same oscillation characteristics is difficult.

[0015] Specifically, the main factors that determine the oscillation characteristics of the active layer are the gain constant, transparent carrier density, active layer volume, injection efficiency, etc., but it is difficult to obtain the same oscillation characteristics for multiple active layers provided in a resonator.

[0016] For example, since the active layer volume is determined by the injection current spreading, differences in the distance from the oxide confinement structure affect the injection current spreading and the active layer volume. Differences in the active layer volume result in differences in the carrier density when a drive current pulse is applied to the device, resulting in differences in the active layer gain. Variations in the well layer thickness and the amount of strain in the strained quantum well also result in similar variations in the oscillation characteristics.

[0017] Furthermore, because the tunnel junctions in surface-emitting lasers are composed of thin films, variations in the impurity concentration profile can cause variations in the electrical characteristics of the tunnel junctions, such as their resistance, and thus variations in the carrier injection rate into the active layer. Therefore, variations in the impurity concentration profile can result in differences in the number of carriers and carrier density at a given time among multiple well layers. Under such circumstances, when the well layer that first reaches the oscillation threshold gain begins to oscillate, the number of photons in the cavity rapidly increases, causing other well layers to also begin oscillating. At this time, differences in carrier density result in differences in stimulated emission rates, which affect the pulse width, and differences in the number of carriers result in differences in pulse output, which affects the output power. In particular, variations in the injection current during current pulse application affect the variations in the number of carriers accumulated in each active layer, which manifests as variations in pulse output during oscillation, significantly affecting the output power characteristics. Furthermore, variations in the electrical characteristics of the tunnel junctions are more likely to become apparent in surface-emitting laser elements, which have a smaller current injection area than edge-emitting lasers. As described above, it is difficult for conventional gain-switched surface-emitting lasers to efficiently achieve high output power.

[0018] (Reference example) Next, a reference example related to the present disclosure will be described. In this specification and drawings, components having substantially the same functional configurations may be denoted by the same reference numerals to avoid redundant description.

[0019] First, a first reference example will be described. The first reference example relates to a surface-emitting laser. Fig. 3 is a cross-sectional view showing a surface-emitting laser according to the first reference example.

[0020] The surface-emitting laser 100 according to the first reference example is, for example, a vertical cavity surface-emitting laser (VCSEL) that employs oxide confinement. The surface-emitting laser 100 includes an n-type GaAs substrate 110, an n-type distributed Bragg reflector (DBR) 120, an active layer 130, a p-type DBR 140, an oxide confinement layer 150, an upper electrode 160, and a lower electrode 170.

[0021] In the first reference example, light is emitted in a direction perpendicular to the surface of the n-type GaAs substrate 110. Hereinafter, the direction perpendicular to the surface of the n-type GaAs substrate 110 may be referred to as the vertical direction, and the direction parallel to the surface of the n-type GaAs substrate 110 may be referred to as the horizontal direction or in-plane direction.

[0022] The n-type DBR 120 is on an n-type GaAs substrate 110. The n-type DBR 120 is, for example, a semiconductor multilayer film reflector formed by stacking multiple n-type semiconductor films. For example, the n-type DBR 120 is made of Al 0.95 Ga 0.05 As film and Al 0.15 Ga 0.85 The active layer 130 is located on the n-type DBR 120. The active layer 130 includes, for example, multiple quantum well layers and barrier layers. The active layer 130 is included in the resonator. The p-type DBR 140 is located on the active layer 130. The p-type DBR 140 is a semiconductor multilayer film reflector configured by stacking, for example, multiple p-type semiconductor films. For example, the p-type DBR 140 is made of Al 0.95 Ga 0.05 As film and Al 0.15 Ga 0.85The resonator further includes a spacer layer (not shown) between the n-type DBR 120 and the active layer 130, and a spacer layer (not shown) between the active layer 130 and the p-type DBR 140.

[0023] The upper electrode 160 is formed in a ring shape in a plan view and contacts the upper surface of the p-type DBR 140. The lower electrode 170 contacts the lower surface of the n-type GaAs substrate 110. The pair of upper electrode 160 and lower electrode 170 is an 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. For example, an intra-cavity structure may be used in which the electrodes are placed directly on the spacer layer of the resonator rather than via a DBR.

[0024] The p-type DBR 140 includes, for example, an oxidized constriction layer 150. The oxidized constriction layer 150 contains Al. The oxidized constriction layer 150 includes an oxidized region 151 and a non-oxidized region 152 in a plane perpendicular to the light emission direction. The oxidized region 151 has an annular planar shape and surrounds the non-oxidized region 152. The non-oxidized region 152 is made up of a p-type AlAs layer 155 and two p-type AlAs layers 156 that sandwich the p-type AlAs layer 155 in the vertical direction. 0.85 Ga 0.15 The oxidized region 151 is made of AlO x The refractive index of the oxidized region 151 is lower than that of the non-oxidized region 152. For example, the refractive index of the oxidized region 151 is 1.65, the refractive index of the p-type AlAs layer 155 is 2.96, and the refractive index of the p-type AlAs layer 155 is 2.96. 0.85 Ga 0.15 The refractive index of the As layer 156 is 3.04. In plan view, the inner portion of the inner edge of the oxidized region 151 of the mesa 180 is an example of a high refractive index region, and the outer portion of the inner edge of the oxidized region 151 of the mesa 180 is an example of a low refractive index region. 0.85 Ga 0.15 Instead of the As layer 156, p-type Al x Ga 1-xAn As layer (0.70≦x≦0.90) may be provided. In this embodiment, the p-type DBR 140, the active layer 130, and the n-type DBR 120 form a mesa 180. However, in the first reference example in which a current confinement region is formed by oxidation confinement, it is sufficient that at least the oxidized confinement layer 150 and the semiconductor layers located above the oxidized confinement layer 150 are formed in a mesa shape. Furthermore, by forming at least the active layer to be included in the mesa, it is possible to prevent light generated in the active layer from leaking laterally.

[0025] Here, a detailed description will be given of the oxidized constriction layer 150. Fig. 4 is a cross-sectional view showing the oxidized constriction layer and its vicinity in the first reference example.

[0026] As shown in FIG. 4 , the oxidized region 151 has an annular outer region 153 and an annular inner region 154 in plan view. The outer region 153 is exposed on the side surface of the mesa 180. The outer region 153 is a region whose thickness changes so that the surface contact surface is located outside the oxidized region 151 in cross-sectional view. The inner region 154 is a region whose thickness changes so that the surface contact surface is located inside the oxidized region 151 in cross-sectional view. The inner region 154 is located inside the outer region 153. The thickness of the inner region 154 is the same as the thickness of the outer region 153 at the boundary with the outer region 153 and becomes thinner toward the center of the mesa 180. The inner region 154 has a tapered shape in cross-sectional view, gradually thickening from the inner edge toward the boundary with the outer region 153. The non-oxidized region 152 is located inside the outer region 153. Portions of the non-oxidized region 152 vertically sandwich the inner region 154. Another part of the non-oxidized region 152 is located inside the inner edge of the inner region 154 in plan view. For example, the thickness of the non-oxidized region 152 is 35 nm or less. The thickness of the outer region 153 may be greater than the thickness of the non-oxidized region 152. In the present disclosure, the thickness of the non-oxidized region 152 refers to the thickness of the portion closer to the center of the mesa 180 than the inner edge of the oxidized region 151 (the inner edge of the inner region 154). For example, the distance from the side surface of the mesa 180 to the inner edge of the oxidized region 151 is in the range of approximately 8 μm to 11 μm.

[0027] The oxidized region 151 is, for example, a p-type AlAs layer and a p-type Al 0.85 Ga0.15 For example, the p-type AlAs layer and the p-type AlAs layer are formed by oxidation confinement of the As layer under high-temperature water vapor conditions. 0.85 Ga 0.15 The oxidation treatment of the As layer can form the oxidized region 151. 0.85 Ga 0.15 Even if the As layer is oxidized, depending on the oxidation conditions, the p-type AlAs layer and the p-type Al 0.85 Ga 0.15 The structure of the oxidized constriction layer obtained from the As layer may differ. Therefore, the layer that becomes the oxidized constriction layer 150 by oxidation, such as a p-type AlAs layer and a p-type Al 0.85 Ga 0.15 Even if the structure of the As layer before oxidation is the same, depending on the oxidation conditions, an oxidized constriction layer 150 having an oxidized region 151 and a non-oxidized region 152 may not be obtained.

[0028] Here, the effects of the first reference example will be described in comparison with the second reference example. Fig. 5 is a cross-sectional view showing the oxidized constriction layer and its vicinity in the second reference example.

[0029] In the second reference example, the oxidized constriction layer 150 has an oxidized region 251 and a non-oxidized region 252 instead of the oxidized region 151 and the non-oxidized region 152. The oxidized region 251 has an annular planar shape and surrounds the non-oxidized region 252. The non-oxidized region 252 is formed by a p-type AlAs layer 255 and two p-type AlAs layers sandwiching the p-type AlAs layer 255 in the vertical direction. 0.85 Ga 0.15The oxidized region 251 is composed of an As layer 256. In plan view, the oxidized region 251 has an annular outer region 253 and an annular inner region 254. The outer region 253 is exposed on the side surface of the mesa 180. The thickness of the outer region 253 is constant in the in-plane direction. The inner region 254 is located inside the outer region 253. The thickness of the inner region 254 is the same as that of the outer region 253 at the boundary with the outer region 253 and becomes thinner as it approaches the center of the mesa 180. In cross-sectional view, the inner region 254 has a tapered shape that gradually becomes thicker from the inner edge toward the boundary with the outer region 253. The non-oxidized region 252 is located inside the outer region 253. Part of the non-oxidized region 252 sandwiches the inner region 254 in the vertical direction. Another part of the non-oxidized region 252 is located inside the inner edge of the inner region 254 in plan view. For example, the distance from the side surface of the mesa 180 to the inner edge of the oxidized region 251 is in the range of approximately 8 μm to 11 μm. The thickness of the oxidized region 251 and the non-oxidized region 252 is equal to the thickness of the oxidized constriction layer 150.

[0030] First, the measurement results for Reference Examples 1 and 2 will be described. Fig. 6 is an equivalent circuit diagram showing the circuit used for the measurement.

[0031] In this circuit, a resistor 12 for monitoring current is connected in series to a surface-emitting laser 11 corresponding to the first or second reference example. A voltmeter 13 is connected in parallel to the resistor 12. The light output from the surface-emitting laser 11 is received by a wideband high-speed photodiode and converted into a voltage signal, which is then observed by an oscilloscope.

[0032] FIG. 7 shows the measurement results for the second reference example. FIG. 7(a) shows the measurement results when the pulse width is approximately 2 ns, FIG. 7(b) shows the measurement results when the pulse width is approximately 9 ns, and FIG. 7(c) shows the measurement results when the pulse width is approximately 17 ns. The magnitude of the bias current and the amplitude of the pulse current are the same in the measurements of FIGS. 7(a) to 7(c). FIG. 7 shows the current flowing through resistor 12 and the optical output measured by the high-speed photodiode. The current flowing through resistor 12 can be calculated using voltmeter 13.

[0033] As shown in Figure 7, in the second reference example, an optical pulse is output immediately after the injection of the pulse current, regardless of the pulse width. After that, an equilibrium state is reached, and a constant tail light is output until the injection of the pulse current is stopped. The leading optical pulse is due to relaxation oscillation, a typical gain-switching drive. Changing the pulse width does not change the timing of the optical pulse generation. This is because the optical pulse generated by relaxation oscillation occurs immediately after the carrier density in the laser resonator exceeds the threshold carrier density. To suppress the output of the tail light, it is possible to stop the current injection immediately after the optical pulse is output. However, because the time width of the optical pulse due to relaxation oscillation is 100 ps or less, it is difficult to stop the current injection within 100 ps immediately after the optical pulse is output when the current magnitude is large, such as 10 A or more.

[0034] FIG. 8 shows the measurement results for the first reference example. FIG. 8(a) shows the measurement results when the pulse width is approximately 0.8 ns, FIG. 8(b) shows the measurement results when the pulse width is 1.3 ns, and FIG. 8(c) shows the measurement results when the pulse 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 FIGS. 8(a) to 8(c). FIG. 8 shows the current flowing through resistor 12 and the optical output measured by the high-speed photodiode. The current flowing through resistor 12 can be calculated using voltmeter 13.

[0035] As shown in Figure 8, in the first 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, almost no tail light is observed 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 first 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 first reference example is not due to normal gain switching that utilizes the relaxation oscillation phenomenon.

[0036] As described above, the mechanism and manner of light output are clearly different between the first and second reference examples. This difference will be explained as follows.

[0037] In a surface-emitting laser, laser light propagates through the cavity perpendicular to the oxidized confining layer. Therefore, the thicker the oxidized confining layer, the longer the equivalent waveguide length, which depends on the refractive index difference, and the greater the lateral optical confinement effect. When a DBR including an oxidized confining layer is considered an equivalent waveguide structure, the electric field intensity distribution of the laser light is concentrated near the center when the equivalent refractive index difference is large, as shown in FIG. 9(a). In contrast, when the equivalent refractive index difference is small, as shown in FIG. 9(b), the electric field intensity distribution of the laser light extends to the surrounding oxidized region. Comparing the first and second reference examples, in the first reference example, the oxidized confining layer 150 includes the inner region 154, resulting in a smaller equivalent refractive index difference. Therefore, in the second reference example, the electric field intensity distribution of the laser light is concentrated near the center, as shown in FIG. 9(a), whereas in the first reference example, the electric field intensity distribution of the laser light extends to the oxidized region 151, as shown in FIG. 9(b).

[0038] Here, the lateral optical confinement coefficient is defined as the ratio of the "integral strength of the electric field in a region of the same radius as the current passing region" to the "integral strength of the electric field in a lateral cross section passing through the center of the surface-emitting laser element," and is given by equation (1), where a corresponds to the radius of the current passing region, and Φ represents the direction of rotation around the axis of rotation perpendicular to the substrate.

[0039]

number

[0040] Next, we will explain the model of what happens when the injection of the pulse current is stopped. When the pulse current is being injected, the oxide confinement layer concentrates the current path near the center of the mesa, creating a high carrier density. At this time, in the non-oxidized region with high carrier density, the carrier plasma effect occurs, which reduces the refractive index. The carrier plasma effect is a phenomenon in which the refractive index decreases in proportion to the free carrier density. For example, according to the reference "Kobayashi, Soichi, et al. "Direct frequency modulation in AlGaAs semiconductor lasers," IEEE Transactions on Microwave Theory and Techniques 30.4 (1982): 428-441," the amount of change in refractive index is expressed by equation (2), where N is the carrier density.

[0041]

number

[0042] Figure 10 shows the schematic diagrams of the equivalent refractive index and electric field intensity distribution during the period when the pulse current is injected (Fig. 10(a)) and during the period when the pulse current injection is stopped and the current decreases (Fig. 10(b)). During the period when the pulse current is injected, the carrier plasma effect acts to cancel the equivalent refractive index difference (n1 - n0) caused by the oxidized confinement layer, resulting in an equivalent refractive index difference of (n2 - n0). When the pulse current injection is decreased in this state, the carrier plasma effect disappears, and the equivalent refractive index difference returns to (n1 - n0). As a result, photons that had spread to the periphery of the mesa are concentrated in the center of the mesa, and the photon density in the non-oxidized region increases. In other words, the lateral optical confinement changes to a strong state. When the pulse current injection is stopped, the carriers accumulated in the resonator decrease over the carrier lifetime. However, if the lateral optical confinement becomes strong before the carrier density completely decays, stimulated emission begins, and the accumulated carriers are suddenly consumed, resulting in the output of an optical pulse. The period during which the pulse current is injected is an example of a current injection period, and the period during which the injection of the pulse current is stopped and the current is reduced is an example of a current reduction period.

[0043] The results of verifying the above model through simulation are shown below. The rate equations for carrier density and photon density are shown in equations (3) and (4).

[0044]

number

[0045]

number

[0046] Here, the contents of each letter in the formulas (3) and (4) are as follows: N: Carrier density [1 / cm 3 ] S: Photon density [1 / cm 3 ] i(t): injection current [A] e: elementary charge [C] V: Resonator volume [cm3 ] τ n (N): Carrier lifetime [s] v g : Group velocity [cm / s] g(N,S): Gain [1 / cm] Gamma a : Optical confinement factor τ p : Photon lifetime [s] β: spontaneous emission coupling coefficient g0: Gain coefficient [1 / cm] ε: Gain suppression coefficient N tr : transparent carrier density [1 / cm 3 ] η i : Current injection efficiency α m : Resonator mirror loss [1 / cm] h: Planck's constant [Js] ν: frequency of light [1 / s]

[0047] The gain g(N, S) is expressed by equation (5).

[0048]

number

[0049] Optical confinement factor Γ a is the lateral optical confinement factor Γ as shown in equation (6). r and the longitudinal optical confinement factor Γ z It is defined as the product of

[0050]

number

[0051] Threshold carrier density N th is expressed by equation (7).

[0052]

number

[0053] Threshold current I th and threshold carrier density N th There is a relationship between them as shown in equation (8).

[0054]

number

[0055] The optical output P output from the resonator and the photon density S have the relationship shown in equation (9).

[0056]

number

[0057] Here, the results of the simulation for the second reference example will be described. For the second reference example, the lateral optical confinement factor Γ r The simulation was carried out by inputting the current monitor waveform shown in Figure 7. The carrier density N and threshold carrier density N th The simulation results for the optical output are shown in FIG. 12.

[0058] As shown in FIGS. 11 and 12, immediately after about 5 ns when the pulse current is injected, the carrier density N reaches the threshold carrier density N th The relaxation oscillation is exceeded and an optical pulse is output. After that, an equilibrium state is reached and a constant tail light is output. In this way, the simulation results are close to the actual measurement results shown in Figure 7.

[0059] Next, the results of the simulation for the first reference example will be described. For the first reference example, the lateral optical confinement factor Γ r is less than 1, and the lateral optical confinement factor Γ r The simulation was performed by inputting the current monitor waveform shown in Figure 8, with the lateral optical confinement factor Γ as a function that decreases as the carrier density N increases.r The reason why is used as the above function is to take into account the influence of the refractive index change due to the carrier plasma effect. Figure 13 shows an example of the function. Figure 14 shows the simulation results of the optical output.

[0060] As shown in Fig. 14, an optical pulse output is obtained at the timing when the injection of the pulse current is stopped. In this way, the simulation results are close to the actual measurement results shown in Fig. 8.

[0061] To analyze this result in detail, we calculated the carrier density N and threshold carrier density N under the condition of a pulse width of 2.5 ns. th , photon density S and lateral optical confinement factor Γ r The simulation results are shown in Fig. 15. In Fig. 15(a), the carrier density N and the threshold carrier density N th and photon density S, and Fig. 15(b) shows the lateral optical confinement factor Γ r The simulation results are shown below.

[0062] Lateral optical confinement factor Γ r is a function of the carrier density N, so that in the range of 3 ns to 5.5 ns during which the pulse current is injected, the lateral optical confinement factor Γ r In this range, the lateral optical confinement factor Γ r As the threshold carrier density N th rises, and N <N th Therefore, stimulated emission is unlikely to occur, and the photon density S does not increase. When the pulse current injection starts to decrease at 5.5 ns, the lateral optical confinement factor Γ r rises again, and in the process, the photon density S is generated in a pulsed manner. Fig. 16 shows a graph in which the time axis in Fig. 15 is expanded in the range of 5 ns to 6 ns.

[0063] When the pulse current injection starts to decrease at about 5.5 ns, the carrier density N starts to decrease. At the same time, the lateral optical confinement factor Γ r The threshold carrier density N thThe threshold carrier density N th decreases faster, so in the process of decreasing carrier density N, N>N th During this time, the photon density S first rises due to spontaneous emission, and once the photon density S has increased to a certain level, stimulated emission becomes dominant and the photon density S rises sharply. At the same time, the carrier density N drops sharply, and then N falls again. <N th This causes a sudden drop in photon density.

[0064] In this way, the simulation was able to reproduce the phenomenon in which an optical pulse is output when the injection of the pulse current is stopped.

[0065] The rise time of the optical pulse is determined by the threshold carrier density N th decreases faster than the carrier lifetime. In other words, from equation (6), the lateral optical confinement factor Γ r The faster the increase in , the shorter the rise time. The decay time of the optical pulse depends on the photon lifetime. Figure 17 shows examples of actual measurement results and simulation results of optical pulses. Figure 17(a) shows the actual measurement results, and Figure 17(b) shows the simulation results.

[0066] Pulse width is 1 / e of the peak value 2 If we define the time width as the width at which the above occurs, the measured result is 86 ps, and the simulated result is 81 ps. Here, e is the natural logarithm. According to this model, the optical pulse width is shorter than the injected pulse current, and can be shortened without being limited by the time width of the injected pulse current.

[0067] (First embodiment) Next, a first embodiment will be described. The first embodiment relates to a surface-emitting surface-emitting laser. The first embodiment differs from the first reference example mainly in the configuration of the cavity and mesa, and has a multi-junction structure. Fig. 18 is a cross-sectional view showing the surface-emitting laser according to the first embodiment.

[0068] The surface-emitting laser 300 according to the first embodiment is, for example, a VCSEL employing an oxide confinement structure. The surface-emitting laser 300 includes an n-type GaAs substrate 110, an n-type DBR 120, a resonator 30, a p-type DBR 140, an oxide confinement layer 150, an upper electrode 160, and a lower electrode 170.

[0069] In the first embodiment, light is emitted in a direction perpendicular to the surface of the n-type GaAs substrate 110. Hereinafter, the direction perpendicular to the surface of the n-type GaAs substrate 110 may be referred to as the vertical direction, and the direction parallel to the surface of the n-type GaAs substrate 110 may be referred to as the horizontal direction or in-plane direction.

[0070] The resonator 30 is on top of the n-type DBR 120. The p-type DBR 140 is on top of the resonator 30. The resonator 30 has a spacer layer 31, an active layer 32, a tunnel junction 33, an active layer 34, a tunnel junction 35, an active layer 36, and a spacer layer 37. The spacer layer 31 is on top of the n-type DBR 120. The active layer 32 is on top of the spacer layer 31. The tunnel junction 33 is on top of the active layer 32. The active layer 34 is on top of the tunnel junction 33. The tunnel junction 35 is on top of the active layer 34. The active layer 36 is on top of the tunnel junction 35. The spacer layer 37 is on top of the active layer 36. The p-type DBR 140 is on top of the spacer layer 37.

[0071] The spacer layers 31 and 37 are made of, for example, Al 0.2 Ga 0.8 The active layers 32, 34, and 36 are, for example, InGaAs layers. The active layers 32, 34, and 36 have, for example, a multiple quantum well structure including multiple quantum well layers and barrier layers. For example, the quantum well layers are InGaAs layers, and the barrier layers are AlGaAs layers. For example, the emission wavelength of the active layers 32, 34, and 36 is 940 nm. That is, the surface-emitting laser 300 is a surface-emitting laser in the 940 nm band.

[0072] The tunnel junction 33 has an n-type layer 33n and a p-type layer 33p, and the tunnel junction 35 has an n-type layer 35n and a p-type layer 35p. The n-type layer 33n is on the active layer 32, and the p-type layer 33p is on the n-type layer 33n. The n-type layer 35n is on the active layer 34, and the p-type layer 35p is on the n-type layer 35n. For example, the n-type layers 33n and 35n are n-type layers having a thickness of 5 nm to 20 nm. ++ The p-type layers 33p and 35p are AlGaAs layers, and the p-type layers 33p and 35p are p ++ For example, the n-type impurity concentration of the n-type layers 33n and 35n is 5×10 18 cm -3 The p-type impurity concentration of the p-type layers 33p and 35p is 5×10 19 cm -3 is.

[0073] In the resonator 30, the active layers 32, 34, and 36 are provided at positions corresponding to antinodes of the standing wave of the oscillating light so as not to reduce the light emission efficiency. In addition, in the resonator 30, the tunnel junctions 33 and 35 are provided at positions corresponding to nodes of the standing wave so as to avoid light absorption. The positions of the active layers 32, 34, and 36 are not limited to positions corresponding to antinodes of the standing wave, but it is preferable that the active layers 32, 34, and 36 be provided at positions closer to the antinode than the midpoint between the antinode and node of the standing wave of the oscillating light.

[0074] In this embodiment, the p-type DBR 140 and the resonator 30 form a mesa 380. However, in this embodiment, in which a current confinement region is formed by oxidation confinement, it is sufficient that at least the oxidized confinement layer 150 and the semiconductor layers located above the oxidized confinement layer 150 are formed in a mesa shape. Furthermore, by forming at least the active layer to be included in the mesa, it is possible to prevent light generated in the active layer from leaking laterally.

[0075] The other configurations are the same as those of the first reference example.

[0076] In the first embodiment, a continuous optical pulse train is unlikely to occur after an optical pulse output is generated, because the injection of pulse current is reduced when an optical pulse is generated, making relaxation oscillation unlikely to occur.

[0077] Furthermore, tail light is less likely to occur after an optical pulse output is generated, because the injection of pulse current is reduced after the optical pulse is generated, making it difficult for the carrier density to increase.

[0078] Furthermore, since the optical pulse is output immediately after the injection of the pulse current is stopped, the timing at which the optical pulse is output can be controlled arbitrarily.

[0079] Furthermore, the width of the optical pulse generated by the first embodiment is shorter than the width of the injected pulse current. Since there is no need to shorten the pulse current width even when a large current is used, the device is less susceptible to the effects of parasitic inductance.

[0080] According to the first embodiment, variations in the oscillation characteristics of multiple quantum well layers are suppressed, thereby achieving both high pulse output and short pulse width. For example, when gain-switched oscillation is simply applied to a surface-emitting laser with a conventional multi-junction structure, relaxation oscillation at the rising edge of a pulse current input is utilized. As a result, the number of carriers in each well is likely to vary due to variations in the injection current into each well. Variations in the injection current are caused, for example, by differences in current density due to differences in the distance from the oxide confinement layer or variations in the electrical characteristics (CR characteristics) of the tunnel junction. Therefore, the value and time change of the number of carriers at the rising edge after the current pulse input differ for each well. This results in variations in the oscillation characteristics, a decrease in peak output, and a widening of the pulse width. In contrast, in the first embodiment, short-pulse oscillation does not occur at the rising edge, but after sufficient carriers are supplied to each well and a stable state is reached. This reduces the influence of transient variations in the number of carriers, thereby suppressing variations in the oscillation characteristics of multiple quantum well layers.

[0081] A surface-emitting laser array is formed by arranging a plurality of surface-emitting lasers 300 according to the first embodiment in parallel, and optical pulses are simultaneously output, thereby making it possible to obtain a larger optical peak output. Although the current injected into the surface-emitting laser array is larger than the current injected into a single surface-emitting laser 300, the width of the optical pulses output by the surface-emitting lasers 300 is narrower than the width of the injected pulse current, so that it is possible to output optical pulses with a small width.

[0082] The pulse width of the light output from the surface-emitting laser 300 according to the first embodiment is not limited, but is, for example, 1 ns or less, preferably 500 ps or less, and more preferably 100 ps or less.

[0083] In the first embodiment, the thickness of the oxidized region 151 at a position 3 μm outward from the inner edge of the inner region 154, i.e., at a position 3 μm from the tip of the boundary between the non-oxidized region 152 and the oxidized region 151, is preferably no more than twice the thickness of the non-oxidized region 152. For example, when the thickness of the non-oxidized region 152 is 31 nm, the thickness at a position 3 μm outward from the inner edge of the inner region 154 is preferably no more than 62 nm, and may be 54 nm. When the distance from the side surface of the mesa 280 to the inner edge of the oxidized region 151 (oxidation distance) is in the range of 8 μm to 11 μm, the distance of 3 μm corresponds to 28% to 38% of the oxidation distance. When the thicknesses of the oxidized region 251 and the non-oxidized region 252 were measured at a position 3 μm outward from the inner edge of the oxidized region 251 in the second reference example, the former was 79 nm and the latter was 31 nm, which was 2.55 times the latter. The inventors compared and evaluated elements with various oxide confinement structures, and found that when the ratio was 2 or less, the lateral optical confinement factor Γ r It was found that this reduced the size of the laser beam, making it easier to obtain high-power, short-pulse light without tailing.

[0084] The area of ​​the non-oxidized region 152 in plan view (current confinement area) is 120 μm 2 As a result of comparative evaluation of elements having various non-oxidized regions 152, the inventors of the present invention found that the non-oxidized region 152 is 120 μm or less. 2It was found that when the area of ​​the non-oxidized region 152 is larger than 50 μm, the phenomenon of an optical pulse being output immediately after the injection of the pulse current is stopped is less likely to occur. It was also found that the smaller the non-oxidized region 152 is, the more likely it is that an optical pulse with a high peak output is obtained. 2 ~120μm 2 10 shows the results of measuring peak light output for samples in the range of 1000 to 10000.

[0085] (Second embodiment) Next, a second embodiment will be described. The second embodiment relates to a surface emission type surface emitting laser. Fig. 20 is a cross-sectional view showing the surface emitting laser according to the second embodiment.

[0086] The surface-emitting laser 400 according to the second embodiment is a VCSEL having a current confinement structure using, for example, a buried tunnel junction (BTJ). The surface-emitting laser 400 includes an n-type GaAs substrate 110, an n-type DBR 120, a resonator 30, a p-type DBR 441, a BTJ region 450, a p-type DBR 442, an upper electrode 160, and a lower electrode 170.

[0087] The p-type DBR 441 is located above the resonator 30. The p-type DBR 441 is a semiconductor multilayer reflector formed, for example, by stacking multiple p-type semiconductor films. The BTJ region 450 is located above a portion of the p-type DBR 441. The BTJ region 450 includes a p-type layer 451 and an n-type layer 452. The p-type DBR 442 is located above the p-type DBR 441 and covers the BTJ region 450. The p-type DBR 442 is a semiconductor multilayer reflector formed, for example, by stacking multiple p-type semiconductor films. The p-type DBR 442, the p-type DBR 441, and the resonator 30 form a mesa 480. The BTJ region 450 is located at the center of the mesa 480 within the plane.

[0088] The p-type layer 451 is located on the p-type DBR 441, and the n-type layer 452 is located on the p-type layer 451. The p-type layer 451 contains p-type impurities at a higher concentration than the p-type semiconductor film that constitutes the p-type DBR 441. The n-type layer 452 contains n-type impurities at a higher concentration than the n-type semiconductor film that constitutes the p-type DBR 442. For example, the thickness of the p-type layer 451 is 5 nm to 20 nm, and the thickness of the n-type layer 452 is 5 nm to 20 nm. In plan view, the portion inside the outline of the BTJ region 450 of the mesa 480 is an example of a high refractive index region, and the portion outside the outline of the BTJ region 450 of the mesa 480 is an example of a low refractive index region.

[0089] The upper electrode 160 contacts the upper surface of the p-type DBR 442. The lower electrode 170 contacts the lower surface of the n-type GaAs substrate 110. The pair of the upper electrode 160 and the lower electrode 170 is an example of an electrode pair.

[0090] In the second embodiment, no current flows between the p-type DBR 441 and the p-type DBR 442 due to a reverse bias. A current flows between the p-type layer 451 and the n-type layer 452 due to a buried tunnel junction. Therefore, the current path between the upper electrode 160 and the lower electrode 170 is narrowed to the center of the mesa 480 where the BTJ region 450 is located. Furthermore, because the BTJ region 450 forms a step and is covered by the p-type DBR 442, the refractive index within the surface of the mesa 480 is high at the center and low around it. Therefore, the surface-emitting laser 400 exhibits lateral optical confinement.

[0091] Therefore, in the second embodiment, an optical pulse can be output by injecting a pulse current similar to that in the first embodiment.

[0092] (Third embodiment) Next, a third embodiment will be described.

[0093] As mentioned above, in order to improve the short pulse output, it is preferable to increase the number of carriers accumulated in the active layer. th It is important to create a situation where

[0094] In other words, when the current injection is stopped, the carrier density in the central area near the active layer from the current confinement structure decreases due to carrier diffusion, spontaneous emission, and non-radiative recombination, and the transverse mode distribution that had been spreading due to the plasma effect becomes distributed in the center of the device. As a result, N>N th This creates a state where short pulse oscillation occurs, but reducing the number of carriers lost due to recombination during this period is important for improving pulse output.

[0095] In the above example, the current injection to obtain output is a means of suppressing oscillation by causing a change in refractive index due to the plasma effect, so a certain amount of accumulated carriers must be eliminated before short-pulse oscillation occurs. If the refractive index could be changed by a means other than the plasma effect, regardless of the amount of injected current or the amount of accumulated carriers, it would be possible to effectively convert the accumulated carriers into short-pulse output and extract it, enabling more efficient, high-output short-pulse operation.

[0096] The electric field effect of a multiple quantum well structure is an effective means of externally modulating this refractive index. In a multiple quantum well structure, applying an electric field perpendicular to the well plane changes the refractive index, i.e., decreases the refractive index.

[0097] The change in refractive index due to an electric field in a quantum well structure has been reported in, for example, Non-Patent Document 1, Non-Patent Document 2, Non-Patent Document 3, Non-Patent Document 4, etc. Non-Patent Document 1 reports that in a quantum well structure made of InGaAsP and InP with a thickness of 30 nm, (Δn / n) / E=3×10 -8 It has been theoretically reported that a value of Δn / n = 3 × 10 [cm / V] can be obtained. For example, when an electric field of 100 kV / cm is applied (a bias of 0.3 V for a quantum well of 30 nm), -3 , that is, Δn≒-9×10 -3 The value is about that.

[0098] In Non-Patent Documents 2 and 3, measurements were actually carried out in a multiple quantum well structure consisting of GaAs with a thickness of 10 nm and AlAs with a thickness of 30 nm, and it was found that (Δn / n) / E=4×10 at room temperature. -7 This means that when an electric field of 100 kV / cm is applied, Δn≒-4×10 -2 and a value larger than the theoretical value in Non-Patent Document 1 is observed. Non-Patent Document 3 shows the red shift of the interband transition energy and the change in refractive index due to the quantum confined Stark effect caused by the application of an electric field. Furthermore, Non-Patent Document 4 shows that Δn≒-3×10 -2 The value is reported as the experimental result.

[0099] As described above, by utilizing the electric field effect of the multiple quantum well structure, Δn ≒ -1 × 10 -2 It is possible to obtain a refractive index change equal to or greater than the plasma effect of the order of magnitude. By utilizing this, it is possible to further improve the controllability and output of short pulse operation.

[0100] Therefore, by placing this multiple quantum well structure near the resonator and applying an electric field, the refractive index of the quantum wells in the multiple quantum well structure decreases, which acts to cancel out the effective refractive index difference Δn0 obtained by the oxide confinement, as shown in Figure 10. In this way, it becomes possible to provide a new means for changing the effective refractive index difference Δn other than the plasma effect. Furthermore, by controlling the effective refractive index difference Δn by the electric field applied to the multiple quantum well structure, it becomes possible to control the timing of short pulse oscillation, which is laser oscillation.

[0101] The third embodiment utilizes the field effect of a multiple quantum well structure. The third embodiment relates to a surface-emitting surface-emitting laser. Fig. 21 is a cross-sectional view showing the surface-emitting laser according to the third embodiment.

[0102] The surface-emitting laser 500 according to the third embodiment is, for example, a VCSEL employing oxide confinement, similar to the first embodiment. The surface-emitting laser 500 includes an n-type GaAs substrate 110, an n-type DBR 120, a resonator 30, a first p-type DBR 541, a second p-type DBR 542, an oxide confinement layer 150, a multiple quantum well structure 590, a first upper electrode 561, a second upper electrode 562, and a lower electrode 170. The surface-emitting laser 500 further includes a first contact layer 591, a second contact layer 592, and a third contact layer 593.

[0103] The first p-type DBR 541 is located on the resonator 30. The first p-type DBR 541 includes an oxide constriction layer 150. A first contact layer 591 is located on the first p-type DBR 541. A multiple quantum well structure 590 is located on the first contact layer 591. The second p-type DBR 542 is located on the multiple quantum well structure 590. A second contact layer 592 is located on the second p-type DBR 542. A third contact layer 593 is located between the n-type GaAs substrate 110 and the bottom electrode 170. The n-type DBR 120, the resonator 30, the first p-type DBR 541, and the first contact layer 591 form a cylindrical mesa post 580. The first p-type DBR 541 is an example of a first upper reflector, and the second p-type DBR 542 is an example of a second upper reflector.

[0104] For example, the n-type DBR120 has 40 pairs of n-type Al 0.1 Ga 0.9 As film and Al 0.9 Ga 0.1 For example, the first p-type DBR541 contains four pairs of p-type Al 0.1 Ga 0.9 As film and Al 0.9 Ga 0.1 For example, the second p-type DBR542 contains 16 pairs of p-type Al 0.1 Ga 0.9 As film and Al 0.9 Ga 0.1The multi-quantum well structure 590 is made up of multiple semiconductor layers, including, for example, 20 pairs of InGaAs and AlGaAs films. The first contact layer 591 and the second contact layer 592 are, for example, p-type GaAs layers. The third contact layer 593 is, for example, an n-type GaAs layer.

[0105] The first and second embodiments may have a second contact layer 592 and a third contact layer 593 .

[0106] The band-to-band energy of the multi-quantum well structure 590 for refractive index modulation is set to be approximately equal to the photon energy of the lasing wavelength when an electric field is applied. The application of an electric field reduces the effective bandgap energy due to the quantum confinement Stark effect. This red-shifts the wavelength of the absorption edge, allowing light of longer wavelengths to be absorbed. When the effective bandgap energy under an electric field is greater than the photon energy, absorption loss can be reduced. When the effective bandgap energy is smaller, absorption loss can be further suppressed. The oxidized constriction layer 150 provided in the first p-type DBR 541 is formed by forming a 20-nm-thick p-type AlAs selective oxidation layer in the first p-type DBR 541, forming a cylindrical mesa post 580, and then oxidizing the p-type AlAs selective oxidation layer in heated water vapor. The multi-quantum well structure 590, the second p-type DBR 542, and the second contact layer 592 are, for example, cylindrical in shape. The planar shape of the mesa post 580 is not limited to a circle, but may be any shape such as a square, a rectangle, or a hexagon.

[0107] The first upper electrode 561 has a ring-shaped planar shape, and is located on the surface of the first contact layer 591. The second upper electrode 562 has a ring-shaped planar shape, and is located on the surface of the second contact layer 592. The lower electrode 170 is located on the back surface of the third contact layer 593.

[0108] A first power supply 581 is connected to a first electrode pair having a first upper electrode 561 and a lower electrode 170. The first power supply 581 injects a current into the active layers 32, 34, and 36 in the resonator 30. A second power supply 582 is connected to a second electrode pair having a second upper electrode 562 and a lower electrode 170. The second power supply 582 applies an electric field to a multiple quantum well structure 590 for refractive index modulation. Although the second upper reflecting mirror may be undoped, using a second p-type DBR 542 as the second upper reflecting mirror reduces the electrical resistance of the second upper reflecting mirror and enables a reduction in the voltage applied from the second power supply 582 to the multiple quantum well structure 590.

[0109] Next, the operation of the surface-emitting laser 500 will be described in detail. First, the second power supply unit 582 applies an electric field to the multiple quantum well structure 590. When an electric field is applied, the effective refractive index at the center of the device, i.e., the center of the surface-emitting laser 500, decreases compared to the effective refractive index difference Δn0 obtained by the oxidized constriction layer 150 when no electric field is applied. In other words, when an electric field is applied to the multiple quantum well structure 590, the effective refractive index difference Δn becomes smaller than the effective refractive index difference Δn0.

[0110] Next, the first power supply 581 starts injecting current into the active layers 32, 34, and 36 in the resonator 30. At this time, the plasma effect further reduces the effective refractive index difference Δn. Due to the above two effects, the transverse mode distribution in the central part of the element becomes smaller, oscillation is suppressed, and carriers are accumulated in the active layers 32, 34, and 36.

[0111] When the electric field effect of the multiple quantum well structure 590 is used in combination, the effective refractive index difference Δn0 due to the oxide constriction layer 150 is set to be slightly larger. Then, by combining the electric field effect of the multiple quantum well structure 590 and the refractive index change due to the carrier plasma effect, the threshold carrier density N th and the carrier density N. In other words, a state is set in which oscillation suppression is performed by both the plasma effect and the electric field effect.

[0112] Next, the second power supply 582 stops applying an electric field to the multiple quantum well structure 590 for refractive index modulation. As a result, the interband transition energy of the multiple quantum well structure 590 increases. That is, the red shift due to the quantum confined Stark effect disappears, the structure becomes transparent to the oscillation wavelength, and the effective refractive index difference Δn increases. The increased effective refractive index difference Δn widens the transverse mode distribution in the central portion of the device. As a result, the oscillation threshold decreases, and short pulse oscillation occurs immediately. At this time, if the first power supply 581 also stops current injection into the active layers 32, 34, and 36 in the resonator 30, a larger refractive index change can be obtained.

[0113] If oscillation is suppressed solely by the plasma effect, the effective refractive index difference Δn, which has been reduced by the plasma effect, recovers to a state where oscillation is possible after the current injection into the active layers 32, 34, and 36 is stopped, as follows: The carriers accumulated in the active layers 32, 34, and 36 are reduced by diffusion from the current injection path or by recombination processes in the active region. However, the carriers that do not contribute to oscillation during this time are lost.

[0114] In contrast, in the third embodiment, the refractive index change occurs immediately by controlling the electric field applied to the multiple quantum well structure 590 from the second power supply unit 582, so it is possible to significantly reduce carriers that do not contribute to oscillation. Therefore, it is possible to significantly improve the peak output, especially at the start of oscillation. The effective refractive index difference Δn0 due to the oxidized constricting layer 150 can be changed by changing the thickness of the oxidized constricting layer 150, and can be increased by making the oxidized constricting layer 150 thicker.

[0115] Furthermore, the effective refractive index difference Δn0 due to the oxide constriction layer 150 is set so that oscillation starts when the application of an electric field to the multiple quantum well structure 590 is stopped. Therefore, according to the third embodiment, the plasma effect and the electric field effect can be combined. Therefore, oscillation can be more strongly suppressed than when the plasma effect is used alone. As a result, the number of carriers accumulated in the active layer can be increased, and the peak output during short pulse oscillation can be improved.

[0116] Thus, the greater the change in refractive index due to the electric field effect, the greater the oscillation suppression effect, and the greater the number of accumulated carriers. Furthermore, while maintaining this oscillation suppression effect, the effective refractive index difference Δn0 due to the oxidized constriction layer 150 can be set to a large value, thereby increasing the amount of change in the oscillation threshold when the electric field application is stopped. Therefore, the number of ineffective carriers that disappear before the short pulse oscillation begins can be reduced, and both of these effects are effective for achieving higher output.

[0117] The multiple quantum well structure 590 can be placed anywhere along the laser light path as long as it can produce a refractive index change due to the electric field effect. In addition, the amount of refractive index change due to the electric field effect in the multiple quantum well structure 590 can be increased by placing the multiple quantum well structure 590 closer to the active layers 32, 34, and 36 or by increasing the number of quantum wells.

[0118] In the third embodiment, an optical pulse is output immediately when the application of an electric field to the multiple quantum well structure 590 is stopped, so the timing at which the optical pulse is output can be set arbitrarily.

[0119] Furthermore, the number of accumulated carriers can be increased, and ineffective carriers that do not contribute to oscillation can be reduced, so that a high output can be obtained.

[0120] In the third embodiment, a continuous optical pulse train is unlikely to occur after an optical pulse output occurs. This is because, when the electric field application is stopped and the current application is stopped, the injection of the pulse current is reduced by the time an optical pulse is generated, making relaxation oscillation unlikely to occur.

[0121] Furthermore, tail light is less likely to occur after an optical pulse output is generated. This is because when the electric field application is stopped and the current application is also stopped, the injection of the pulse current is reduced after the optical pulse is generated, making it difficult for the carrier density to increase.

[0122] Furthermore, the width of the optical pulse generated by the third embodiment is shorter than the width of the injected pulse current, so there is no need to shorten the pulse current width even when a large current is used, making it less susceptible to the effects of parasitic inductance.

[0123] As in the first embodiment, a surface-emitting laser array is formed by arranging a plurality of surface-emitting lasers 500 according to the third embodiment in parallel, and optical pulses are simultaneously output, thereby making it possible to obtain a larger optical peak output. Although the current injected into the surface-emitting laser array is larger than the current injected into a single surface-emitting laser 500, the width of the optical pulse output by the surface-emitting laser 500 is narrower than the width of the injected pulse current, so that an optical pulse with a small width can be output.

[0124] As in the first embodiment, the pulse width of the light output from the surface-emitting laser 500 according to the third embodiment is not limited, but is, for example, 1 ns or less, preferably 500 ps or less, and more preferably 100 ps or less.

[0125] As in the first embodiment, in the third embodiment, it is preferable that the thickness of the oxidized region 151 at a position 3 μm outward from the inner edge of the inner region 154, i.e., at a position 3 μm from the tip of the boundary between the non-oxidized region 152 and the oxidized region 151, is less than twice the thickness of the non-oxidized region 152.

[0126] In addition, similarly to the first embodiment, in the third embodiment, the area of ​​the non-oxidized region 152 in plan view (current confinement area) is 120 μm 2 It is desirable that the following:

[0127] (Fourth embodiment) Next, a fourth embodiment will be described. The fourth embodiment relates to a surface-emitting surface-emitting laser. The fourth embodiment differs from the third embodiment mainly in the configuration of the second upper electrode. FIG. 22A is a top view showing the surface-emitting laser according to the fourth embodiment. FIG. 22B is a cross-sectional view showing the surface-emitting laser according to the fourth embodiment. FIG. 22B corresponds to a cross-sectional view taken along line XXIIB-XXIIB in FIG. 22A.

[0128] The surface-emitting laser 600 according to the fourth embodiment has a second upper electrode 662 instead of the second upper electrode 562. The second upper electrode 662 is a transparent electrode. The second upper electrode 662 has a substantially circular planar shape, and as shown in FIG. 22A, is located at the center of the first p-type DBR 541, which is cylindrical in plan view. As shown in FIG. 22B, the second upper electrode 662 is drawn out from the center, and a second power supply unit 582 is connected to the second upper electrode 662 at an outer portion that does not interfere with the transmission of laser light.

[0129] The other configurations are the same as those of the third embodiment.

[0130] Since the second upper electrode 662 is a transparent electrode, the second upper electrode 662 does not prevent transmission of laser light. Furthermore, in the fourth embodiment, an electric field can be applied in a concentrated manner to the center of the multiple quantum well structure 590 in plan view. Therefore, the surface-emitting laser 600 can selectively reduce the effective refractive index in the center of the device.

[0131] Therefore, it becomes possible to reduce the intensity of the transverse mode distribution in the central part of the element and to spread the distribution to the peripheral part of the element, thereby effectively reducing the effective refractive index difference Δn.

[0132] In this way, the fourth embodiment can also achieve the same effects as the third embodiment. Furthermore, according to the fourth embodiment, the second upper electrode 662 is provided in the central portion of the element in a plan view, so that the amount of change in refractive index can be increased. Therefore, a laser beam with a higher output can be obtained.

[0133] Alternatively, an undoped second upper reflector may be used instead of the second p-type DBR 542, and the second contact layer 592 may be omitted. In this case, the lateral spread of the electric field can be further suppressed, further improving selectivity. For example, the second upper reflector may be made of a dielectric material such as SiN or SiO2.

[0134] (Fifth embodiment) Next, a fifth embodiment will be described. The fifth embodiment relates to a back-emission surface-emitting laser. The fifth embodiment differs from the third embodiment mainly in the configurations of the lower electrode and the second upper electrode. Fig. 23 is a cross-sectional view showing the surface-emitting laser according to the fifth embodiment.

[0135] In the surface-emitting laser 700 according to the fifth embodiment, the total number of pairs of upper multilayer reflectors consisting of the first p-type DBR 541 and the second p-type DBR 542 is 40 pairs, and the total number of pairs of lower multilayer reflectors consisting of the n-type DBR 120 is 20 pairs.

[0136] The surface-emitting laser 700 has a lower electrode 770 instead of the lower electrode 170. An opening 771 is formed in the lower electrode 770. The opening 771 is formed so as to overlap the non-oxidized region 152 in plan view.

[0137] The surface-emitting laser 700 has a second upper electrode 762 instead of the second upper electrode 562. The second upper electrode 762 is located in the center of the first p-type DBR 541, which has a cylindrical shape in plan view.

[0138] The other configurations are the same as those of the third embodiment.

[0139] In the fifth embodiment, the optical output is emitted toward the n-type GaAs substrate 110, that is, the rear surface side. Since the opening 771 is formed in the lower electrode 770, the optical output can be extracted without being obstructed by the lower electrode 770.

[0140] Furthermore, since the second upper electrode 762 is located at the center of the first p-type DBR 541, which is cylindrical in plan view, the electric field can be concentrated in the center of the multiple quantum well structure 590 in plan view. Therefore, similar to the fourth embodiment, the effective refractive index at the center of the element can be selectively reduced.

[0141] Therefore, it becomes possible to reduce the intensity of the transverse mode distribution in the central part of the element and to spread the distribution to the peripheral part of the element, thereby effectively reducing the effective refractive index difference Δn.

[0142] In this way, the fifth embodiment can also achieve the same effects as the third embodiment.

[0143] Alternatively, an undoped second upper reflector may be used instead of the second p-type DBR 542, and the second contact layer 592 may be omitted. In this case, the lateral spread of the electric field can be further suppressed, further improving selectivity. For example, the second upper reflector may be made of a dielectric material such as SiN or SiO2.

[0144] (Sixth embodiment) Next, a sixth embodiment will be described. The sixth embodiment relates to a back-emission surface-emitting laser. The sixth embodiment differs from the fifth embodiment mainly in the configuration of the current confinement structure. Fig. 24 is a cross-sectional view showing the surface-emitting laser according to the sixth embodiment.

[0145] The surface-emitting laser 800 according to the sixth embodiment is a VCSEL having a current confinement structure using, for example, a BTJ. The surface-emitting laser 800 has a BTJ region 850 instead of the oxide confinement layer 150.

[0146] The BTJ region 850 is formed as follows: During the formation of the first p-type DBR 841, a p-type impurity is doped at a higher concentration than the first p-type DBR 841. ++ The GaAs layer and the n-type DBR 120 are doped with n-type impurities at a higher concentration than the n-type DBR 120. ++ First, a GaAs layer is grown. Then, growth is stopped and the two layers are removed except for the central portion of the device by wet selective etching. After the BTJ region 850 is formed, the remainder of the first p-type DBR 841 is regrowth on top of it.

[0147] The other configurations are the same as those in the fifth embodiment.

[0148] When a forward bias is applied to the first electrode pair consisting of the lower electrode 770 and the first upper electrode 561, p ++ GaAs layer and n ++ A reverse bias is applied to the GaAs layer. ++ GaAs layer to n ++ By band-to-band tunneling of electrons into the GaAs layer, p ++ Holes are generated in the GaAs layer and injected into the active layers 32 , 34 and 36 in the resonator 30 .

[0149] In the BTJ region 850, a small difference in refractive index occurs in the lateral direction due to the difference in Al composition of the AlGaAs material, and this difference in refractive index forms a weak lateral optical confinement. The magnitude of this difference is small enough to change the effective refractive index difference Δn due to the change in refractive index caused by the carrier plasma effect and the electric field effect of the multiple quantum wells, and short pulse oscillation can be achieved.

[0150] In this way, the sixth embodiment can also achieve the same effects as the fifth embodiment.

[0151] (Seventh embodiment) Next, a seventh embodiment will be described. The seventh embodiment relates to a surface-emitting surface-emitting laser. The seventh embodiment differs from the third embodiment mainly in the configuration of the second upper reflecting mirror. Fig. 25 is a cross-sectional view showing the surface-emitting laser according to the seventh embodiment.

[0152] The surface-emitting laser 900 according to the seventh embodiment has a second p-type DBR 942 instead of the second p-type DBR 542. A second contact layer 592 is located on the multiple quantum well structure 590, and the second p-type DBR 942 is located on the second contact layer 592. The second p-type DBR 942 is located inside the second upper electrode 562 in plan view.

[0153] The other structures are the same as those of the third embodiment.

[0154] In the seventh embodiment, an electric field can be applied to the multiple quantum well structure 590 without passing through the second p-type DBR 942. Therefore, according to the seventh embodiment, the electric field in the multiple quantum well structure 590 can be made stronger than in the third embodiment. Therefore, in the seventh embodiment, the amount of change in refractive index due to the electric field effect can be made larger.

[0155] Therefore, according to the seventh embodiment, a laser beam with a higher output can be obtained.

[0156] Alternatively, an undoped second upper reflector may be used instead of the second p-type DBR 942, and the second contact layer 592 may be omitted. In this case, the lateral spread of the electric field can be further suppressed, further improving selectivity. For example, the second upper reflector may be made of a dielectric material such as SiN or SiO2.

[0157] (Eighth embodiment) Next, an eighth embodiment will be described. The eighth embodiment relates to a surface-emitting surface-emitting laser. The eighth embodiment differs from the third embodiment mainly in the configurations of the first upper reflector and the spacer layer. Fig. 26 is a cross-sectional view showing the surface-emitting laser according to the eighth embodiment.

[0158] The surface-emitting laser 1000 according to the eighth embodiment has a spacer layer 1037 instead of the spacer layer 37 and the first p-type DBR 541. The spacer layer 1037 is thicker than the spacer layer 37, and includes an oxide constriction layer 150.

[0159] The other configurations are the same as those of the third embodiment.

[0160] The eighth embodiment can also achieve the same effects as the third embodiment.

[0161] In the third to eighth embodiments, the multiple quantum well structure 590 for obtaining the field effect is provided between the active layers 32, 34, and 36 and the second p-type DBR 542 or 942, but the present disclosure is not limited to this. The multiple quantum well structure 590 can be disposed anywhere along the path of the laser light to obtain the effect, as long as it is located in a place where a refractive index change due to the field effect can be obtained.

[0162] (Ninth embodiment) Next, a ninth embodiment will be described. The ninth embodiment relates to a laser device. Fig. 27 is a diagram showing a laser device according to the ninth embodiment.

[0163] The laser device 1300 according to the ninth embodiment includes the surface-emitting laser 500 according to the third embodiment and a power supply device 1301. The power supply device 1301 includes a first power supply device 581 and a second power supply device 582. The first power supply device 581 is connected to the first upper electrode 561 and the lower electrode 170. The second power supply device 582 is connected to the first upper electrode 561 and the second upper electrode 562. The first power supply device 581 injects a current into the surface-emitting laser 500, and the second power supply device 582 supplies an electric field to the surface-emitting laser 500.

[0164] The duty ratio of the current injected from the first power supply device 581 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 pulse current repetition frequency is f [Hz], the duty ratio corresponds to f × t (%). Figure 28 shows the relationship between the duty ratio and the peak output of the optical pulse when the pulse current width is 2.5 ns.

[0165] As shown in Figure 28, when the duty ratio exceeds 0.5%, the optical peak output tends to decrease. The following model is considered to explain this. First, as the duty ratio increases, the amount of heat generated in the current confinement region (non-oxidized region 152) due to the injected pulse current increases. This increases the temperature in the center of the current confinement region, where the current is concentrated, relative to the periphery, resulting in a temperature difference. As a result, the refractive index in the center of the current confinement region increases due to the thermal lens effect, increasing the lateral optical confinement factor. 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 due to increases and decreases in the pulse current decreases. When the influence of refractive index changes decreases, the phenomenon of optical pulse output immediately after the injection of the pulse current is stopped becomes less likely. On the other hand, when the duty ratio is 0.5% or less, the influence of refractive index changes due to the thermal lens effect becomes sufficiently small, and the refractive index changes caused by the confinement structure become dominant, resulting in an almost constant peak output.

[0166] Note that instead of the surface-emitting laser 500 according to the third embodiment, a surface-emitting laser according to any one of the fourth to eighth embodiments may be used.

[0167] (Tenth embodiment) Next, a tenth embodiment will be described. The tenth embodiment relates to a distance measurement device. Fig. 29 is a diagram showing the distance measurement device according to the tenth embodiment. The distance measurement device is an example of a detection device.

[0168] A distance measurement device 1400 according to the tenth embodiment is a distance measurement device using a TOF (Time of Flight) method. The distance measurement device 1400 includes a light emitting element 1410, a light receiving element 1420, and a drive circuit 1430. The light emitting element 1410 emits an emitted light beam (irradiated light 1411) toward a distance measurement object 1450. The light receiving element 1420 receives reflected light 1421 from the distance measurement object 1450. The drive circuit 1430 drives the light emitting element 1410 and calculates the round-trip distance to the distance measurement object 1450 by detecting the time difference between the emission timing of the emitted light beam and the reception timing of the reflected light 1421 by the light receiving element 1420.

[0169] The light emitting element 1410 may include a plurality of surface emitting lasers according to any one of Embodiments 1 to 8. The pulse repetition frequency is, for example, in the range of several kHz to several tens of MHz.

[0170] The light receiving element 1420 is, for example, a photodiode (PD), an avalanche photodiode (APD), or a single-photon avalanche diode (SPAD). The light receiving element 1420 may include a plurality of light receiving elements arranged in an array. The light receiving element 1420 is an example of a detection unit.

[0171] 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.

[0172] The surface-emitting lasers according to the first to eighth embodiments 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 distance measurement device 1400 according to the tenth embodiment, the shorter the pulse width of the optical pulse, the higher the peak output allowed by safety standards, so it is possible to achieve both high accuracy and long distances while satisfying eye safety.

[0173] (Eleventh embodiment) Next, an eleventh embodiment will be described. The eleventh embodiment relates to a moving body. FIG. 30 is a diagram showing an automobile as an example of a moving body according to the eleventh embodiment. The distance measurement device 1400 described in the tenth embodiment is provided above the front surface (for example, above the windshield) of an automobile 1100 as an example of a moving body according to the eleventh embodiment. The distance measurement device 1400 measures the distance to an object 1102 around the automobile 1100. The measurement result of the distance measurement device 1400 is input to a control unit of the automobile 1100, 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 in the automobile 1100 to a driver 1101 of the automobile 1100 based on the measurement result of the distance measurement device 1400.

[0174] As described above, in the eleventh embodiment, by providing the distance measurement device 1400 in the automobile 1100, it is possible to recognize the position of the object 1102 around the automobile 1100 with high accuracy. The mounting position of the distance measurement device 1400 is not limited to the upper front of the automobile 1100, but it may be mounted on the side or rear. Also, in this example, the distance measurement device 1400 is provided in the automobile 1100, but the distance measurement device 1400 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.

[0175] 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. [Explanation of symbols]

[0176] 30 resonator 31, 37 Spacer layer 32, 34, 36 active layer 33, 35 Tunnel junctions 120 n-type DBR 140, 441, 442 p-type DBR 150 Oxidized constriction layer 151 Oxidation Region 152 Non-oxidized region 160 Upper electrode 170 Lower electrode 180, 280, 380, 480 Mesa 300, 400, 500, 600, 700, 800, 900, 1000 surface-emitting lasers 450, 850 BTJ area 451 p-type layer 452 n-type layer 541 1st p type DBR 542 2nd p type DBR 580 Mesa Post 581 First Power Supply 582 Second Power Supply 590 Multiple quantum well structure 1100 Automobiles (mobile vehicles) 1300 Laser Device 1400 Distance Measuring Device [Prior art documents] [Patent documents]

[0177] [Patent Document 1] U.S. Patent No. 8,934,514 [Non-patent literature]

[0178] [Non-Patent Document 1] H. Yamamoto, M. Asada and Y. Suematsu, "Electric-field-induced refractive index variation in quantum-well structure", Electron. Lett., 21 pp 579-580 (1985) [Non-patent document 2] H. Nagai, M. Yamanishi, Y. Kan and I. Suemune, "Field-induced modulation of refractive index and absorption coefficient in a GaAs / AlGaAs quantum well structure", Elect. Lett., 22 pp 888-889 (1986) [Non-patent document 3] H. Nagai, M. Yamanishi, Y. Kan, I. Suemune, Y. Ide and R. Lang, "Exciton-induced dispersion of electroreflectance in a GaAs / AlAs quantum well structure at room temperature", Extended abstract of the 18th conference on Solid State Devices and Materials, pp 591-594 (1986) [Non-patent document 4] JS Weiner, DAB Miller and DS Chemla, "Quadratic electro-optics effect due to the quantum confined Stark effect in quantum wells", Appl. Phys. Lett., 50, 13, pp 842-844 (1987) [Non-patent document 5] K.J. Ebeling;M. Grabherr;R. Jager;R. Michalzik, "Diode cascade quantum well VCSEL", 1997 Digest of the IEEE / LEOS Summer Topical Meeting: Vertical-Cavity Lasers, WB1, p.p.61, 1997

Claims

1. a resonator including a plurality of active layers and tunnel junctions between the plurality of active layers; a plurality of reflecting mirrors facing each other across the resonator; a first pair of electrodes connected to a first power supply and capable of injecting a current into the active layer; and a period during which a pulse current is injected by the first power supply device is defined as a current injection period, and a period after the current injection period during which the injection of the pulse current is stopped and the value of the current injected into the resonator is reduced below 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. 2. The surface-emitting laser according to claim 1, comprising, in a plane perpendicular to the light emission direction, a high-refractive-index region having a relatively high refractive index and a low-refractive-index region having a refractive index lower than that of the high-refractive-index region and surrounding the high-refractive-index region.

3. the low refractive index region is formed by oxidation constriction, 3. The surface-emitting laser according to claim 2, wherein the thickness of said low refractive index region at a position 3 μm from an end of a boundary between said low refractive index region and said high refractive index region is 62 nm or less.

4. The area of ​​the region surrounded by the tip of the boundary between the low refractive index region and the high refractive index region in a plane perpendicular to the light emission direction is 120 μm ２ 4. The surface-emitting laser according to claim 2, wherein:

5. 3. The surface-emitting laser according to claim 2, wherein the high refractive index region and the low refractive index region are formed by a buried tunnel junction.

6. a multiple quantum well structure made of a plurality of semiconductor layers and provided in a path of laser light emitted by the active layer and the plurality of reflecting mirrors; a second pair of electrodes connected to a second power supply and capable of applying an electric field in a direction perpendicular to a well surface of the multiple quantum well structure; and a period during which an electric field is applied by the second power supply device is defined as an electric field application period, and a period after the electric field application period during which the electric field is reduced in magnitude to a value lower than that during the electric field application period is defined as an electric field reduction period, at least a part of the electric field application period includes at least a part of the current injection period, Laser oscillation does not occur during the electric field application period, and laser oscillation occurs during the electric field reduction period.

6. The surface-emitting laser according to claim 1.

7. the plurality of reflectors include a lower reflector provided below the active layer and a first upper reflector formed above the active layer; 7. The surface-emitting laser according to claim 6, wherein the multiple quantum well structure is disposed above the active layer.

8. the first upper reflecting mirror is formed in a columnar shape, 8. The surface-emitting laser according to claim 7, wherein at least a portion of one of the second electrode pair is disposed in a central portion of the first upper reflecting mirror.

9. A surface-emitting laser according to any one of claims 1 to 5; a first power supply connected to the first electrode pair and configured to inject a current into the surface-emitting laser; A laser device comprising:

10. A surface-emitting laser according to any one of claims 6 to 8; a first power supply connected to the first electrode pair; a second power supply connected to the second electrode pair; A laser device comprising:

11. The laser device according to claim 10 , wherein the electric field application period starts before the current injection period starts.

12. 12. The laser device according to claim 10, wherein the current reduction period starts simultaneously with or after the start of the electric field reduction period.

13. 13. The laser device according to claim 9, wherein an optical pulse having a time width shorter than the current injection period is output.

14. the current injection period and the current reduction period are repeated multiple times, 14. The laser device according to claim 9, wherein a ratio of the current injection period to the current reduction period is 0.5% or less.

15. A laser device according to any one of claims 9 to 14; a detection unit that detects light emitted from the surface-emitting laser and reflected by an object; A detection device comprising:

16. The detection device according to claim 15 , wherein the distance to the object is calculated based on a signal from the detection unit.

17. A moving object comprising the detection device according to claim 15 or 16.

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