Laser device, detection device, moving body, and driving method of laser device

Abstract

To provide a surface emitting laser capable of obtaining short pulse light with reduced trailing, a laser device, a detection device, a moving body, and a method for driving a surface emitting laser.SOLUTION: A surface emitting laser includes: an active layer 530; a plurality of reflection mirrors opposed to each other across the active layer; a multiple quantum well structure 590 provided in a path of a laser beam composed of a plurality of semiconductor layers emitted by the active layer and the plurality of reflection mirrors; a first electrode pair connected to a first power supply device 581 and capable of injecting a current into the active layer; and a second electrode pair connected to a second power supply device 582 and capable of applying an electric field in a direction perpendicular to a well surface of the multiple quantum well structure. A period of time during which an electric field is applied by the second power supply device is set as an electric field application period. A period of time after the electric field application period and in which magnitude of an electric field is lowered than the electric field application period is set as an electric field reduction period. At least part of a current injection period is included in at least part of the electric field application period. Laser oscillation is not performed during the electric field application period and laser oscillation is performed during the electric field reduction period.SELECTED DRAWING: Figure 17

Description

Technical Field

[0001] The present invention , ray relates to a user device, a detection device, a moving body, and Laser device a driving method thereof.

Background Art

[0002] Safety standards for lasers with respect to the human eye are classified according to the eye-safe class and are defined by IEC 60825-1 Ed.3 (equivalent domestic standard JIS C 6802). In order to use a distance measurement device in various environments, it is desirable to meet the Class 1 standard that does not require safety measures or warnings. As one of the Class 1 standards, an upper limit of the average power is defined. In the case of pulsed light, the peak output, pulse width, and duty ratio are converted to the average power and compared with the standard value. Since the shorter the pulse width of the optical pulse, the higher the allowable peak output, a laser light source with a high peak output and a short pulse width is useful for achieving both high precision and long distance in a TOF (Time Of Flight) sensor while satisfying eye safety.

[0003] As means for realizing short pulse widths of 1 ns or less, there are gain switching, Q switching, mode locking, and the like. Gain switching is a means for realizing a pulse width of 100 ps or less by utilizing the relaxation oscillation phenomenon. Since it can be realized only by controlling the pulse current, the configuration is simpler than that of Q switching or mode locking.

[0004] However, in gain switching, in order to utilize the relaxation oscillation phenomenon, multiple pulse trains are likely to be output after the first pulse. Alternatively, after the relaxation oscillation subsides, a tail light (trailing) with a wide pulse width is likely to be output. These phenomena are not desirable for applications. For example, when detecting in Geiger mode using a Single Photon Avalanche Diode (SPAD), only the highest peak output becomes the sensing target. If there are multiple pulses other than the target pulse, they become noise, and the tail light is unnecessary energy, which is disadvantageous from the perspective of eye safety.

Summary of the Invention

Problems to be Solved by the Invention

[0005] There is room for study in surface emitting lasers that can generate short pulse light with reduced trailing.

[0006] The present invention , skirt can obtain short pulse light with reduced trailing ray - a laser device, a detection device, a moving body, and Laser device aims to provide a driving method therefor.

Means for Solving the Problems

[0007] According to one aspect of the disclosed technology, Laser device is a surface-emitting laser, a first power supply device, and a second power supply device, wherein the surface-emitting laser composed of an active layer, a plurality of reflectors facing each other with the active layer interposed therebetween, a multiple quantum well structure provided in the path of the laser light emitted by the active layer and the plurality of reflectors, the a first pair of electrodes connected to a first power supply device and capable of injecting current into the active layer, the It is connected to a second power supply device and has a second pair of electrodes capable of applying an electric field in a direction perpendicular to the well surface of the multiple quantum well structure. The period during which current is injected by the first power supply device is defined as the current injection period, the period after the current injection period and during which the current value injected into the active layer is lower than the current value during the current injection period is defined as the current decrease period, the period during which an electric field is applied by the second power supply device is defined as the electric field application period, and the period after the electric field application period and during which the magnitude of the electric field is lower than the magnitude of the electric field during the electric field application period is defined as the electric field decrease period. At least a part of the current injection period is included in at least a part of the electric field application period, laser oscillation does not occur during the electric field application period, and laser oscillation occurs during the electric field decrease period. such that the current decrease period starts simultaneously with or after the start of the electric field decrease period 。

Advantages of the Invention

[0008] According to the disclosed technology, short-pulse light with reduced trailing can be obtained.

Brief Description of the Drawings

[0009]

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Mode for Carrying Out the Invention

[0010] Before describing embodiments of the present disclosure, first, its principle will be described using reference examples. In this specification and the drawings, for components having substantially the same functional configuration, the same reference numerals may be given to omit redundant descriptions.

[0011] (First Reference Example) First, the first reference example will be described. The first reference example relates to a surface-emitting laser. FIG. 1 is a cross-sectional view showing the surface-emitting laser according to the first reference example.

[0012] The surface-emitting laser 100 according to the first reference example is, for example, a vertical cavity surface emitting laser (VCSEL) that employs oxidation constriction. 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 oxidation constriction layer 150, an upper electrode 160, and a lower electrode 170.

[0013] 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 longitudinal direction, and the direction parallel to the surface of the n-type GaAs substrate 110 may be referred to as the lateral direction or the in-plane direction.

[0014] The n-type DBR 120 is on the n-type GaAs substrate 110. The n-type DBR 120 is, for example, a semiconductor multilayer film reflector formed by laminating a plurality of n-type semiconductor films. The active layer 130 is on the n-type DBR 120. The active layer 130 includes, for example, a plurality of quantum well layers and barrier layers. The active layer 130 is included in the resonator. The p-type DBR 140 is on the active layer 130. The p-type DBR 140 is, for example, a semiconductor multilayer film reflector formed by laminating a plurality of p-type semiconductor films.

[0015] The upper electrode 160 is formed in an annular shape in 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 the upper electrode 160 and the lower electrode 170 is an example of an electrode pair. However, the positions of the electrodes are not limited to this, and any position where current can be injected into the active layer is acceptable. For example, an intracavity structure in which the electrodes are arranged directly on the spacer layer of the resonator instead of via the DBR may be used.

[0016] The p-type DBR 140 includes, for example, an oxidation constriction layer 150. The oxidation constriction layer 150 contains Al. The oxidation 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 includes a p-type AlAs layer 155 and two p-type Al 0.85 Ga 0.15 As layers 156 sandwiching the p-type AlAs layer 155 in the longitudinal direction. The oxidized region 151 is composed 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 Al 0.85 Ga 0.15 As layer 156 is 3.04. In plan view, the inner part inside the inner edge of the oxidized region 151 of the mesa 180 is an example of a high refractive index region, and the outer part outside the inner edge of the oxidized region 151 of the mesa 180 is an example of a low refractive index region. Note that instead of the p-type Al 0.85 Ga 0.15 As layer 156, a p-type Al x Ga 1-x 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 constitute the mesa 180. However, in this embodiment where a current constriction region is formed by oxidation constriction, at least the oxidation constriction layer 150 and the semiconductor layer located above the oxidation constriction layer 150 may be formed in a mesa shape. Also, by forming at least the active layer to be included in the mesa, it is possible to prevent the light generated in the active layer from leaking laterally.

[0017] Here, the oxidized narrowing layer 150 will be described in detail. FIG. 2 is a cross-sectional view showing the oxidized narrowing layer and its vicinity in the first reference example.

[0018] As shown in FIG. 2, the oxidized region 151 has, in plan view, an annular outer region 153 and an annular inner region 154. The outer region 153 is exposed on the side surface of the mesa 180. The outer region 153 is a region where the thickness changes such that the contact surface of the surface is located outside the oxidized region 151 in cross-sectional view, and the inner region 154 is a region where the thickness changes such that the contact surface of the surface is located inside the oxidized region 151 in cross-sectional view. The inner region 154 is inside the outer region 153. The thickness of the inner region 154 coincides with the thickness of the outer region 153 at the boundary with the outer region 153, and becomes thinner as it approaches the center of the mesa 180. The inner region 154 has a tapered shape that gradually thickens from the inner edge to the boundary with the outer region 153 in cross-sectional view. The non-oxidized region 152 is inside the outer region 153. A part of the non-oxidized region 152 sandwiches the inner region 154 in the longitudinal direction. Another part of the non-oxidized region 152 is 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 is the thickness of the portion on the center side of the mesa 180 from 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 about 8 μm to 11 μm.

[0019] The oxidized region 151 is formed, for example, by the oxidized narrowing of a p-type AlAs layer and a p-type Al 0.85 Ga 0.15 As layer. For example, the oxidized region 151 can be formed by the oxidation treatment of a p-type AlAs layer and a p-type Al 0.85 Ga 0.15 As layer in a high-temperature steam environment. Even if the same p-type AlAs layer and p-type Al 0.85 Ga 0.15 As layer is oxidized, depending on the oxidation conditions, the p-type AlAs layer and p-type Al 0.85 Ga 0.15The structure of the oxidized constriction layer obtained from the As layer can be different. Therefore, a layer that becomes the oxidized constriction layer 150 by oxidation, for example, a p-type AlAs layer and a p-type Al 0.85 Ga 0.15 Even if the structures of the p-type AlAs layer and the p-type Al

[0020] Here, while comparing with the second reference example, the operation and effect of the first reference example will be described. FIG. 3 is a cross-sectional view showing the oxidized constriction layer and its vicinity in the second reference example.

[0021] In the second reference example, the oxidized constriction layer 150 has an oxidized region 951 and a non-oxidized region 952 instead of the oxidized region 151 and the non-oxidized region 152. The oxidized region 951 has an annular planar shape and surrounds the non-oxidized region 952. The non-oxidized region 952 is composed of a p-type AlAs layer 955 and two p-type Al 0.85 Ga 0.15 As layers 956 that sandwich the p-type AlAs layer 955 in the longitudinal direction. The oxidized region 951 has an annular outer region 953 and an annular inner region 954 in plan view. The outer region 953 is exposed on the side surface of the mesa 180. The thickness of the outer region 953 is constant in the in-plane direction. The inner region 954 is inside the outer region 953. The thickness of the inner region 954 coincides with the thickness of the outer region 953 at the boundary with the outer region 953 and becomes thinner as it approaches the center of the mesa 180. The inner region 954 has a tapered shape that gradually thickens from the inner edge to the boundary with the outer region 953 in cross-sectional view. The non-oxidized region 952 is inside the outer region 953. A part of the non-oxidized region 952 sandwiches the inner region 954 in the longitudinal direction. The other part of the non-oxidized region 952 is inside the inner edge of the inner region 954 in plan view. For example, the distance from the side surface of the mesa 180 to the inner edge of the oxidized region 951 is in the range of about 8 μm to 11 μm. The thicknesses of the oxidized region 951 and the non-oxidized region 952 are equal to the thickness of the oxidized constriction layer 150.

[0022] First, the measurement results for the first reference example and the second reference example will be described. FIG. 4 is an equivalent circuit diagram showing the circuit used for the measurement.

[0023] In this circuit, a current monitoring resistor 12 is connected in series to the surface emitting laser 11 corresponding to the first reference example or the second reference example. Also, a voltmeter 13 is connected in parallel to the resistor 12. Further, the light output from the surface emitting laser 11 is received by a broadband high-speed photodiode and converted into a voltage signal, and the voltage signal is observed with an oscilloscope.

[0024] FIG. 5 is a diagram showing the measured results for the second reference example. FIG. 5(a) shows the measured results when the pulse width is about 2 ns, FIG. 5(b) shows the measured results when the pulse width is about 9 ns, and FIG. 5(c) shows the measured results when the pulse width is about 17 ns. In the measurements of FIGS. 5(a) to 5(c), the magnitude of the bias current and the amplitude of the pulse current are common. FIG. 5 shows the current flowing through the resistor 12 and the optical output measured by the high-speed photodiode. The current flowing through the resistor 12 can be calculated using the voltmeter 13.

[0025] As shown in FIG. 5, in the second reference example, regardless of the magnitude of the pulse width, an optical pulse is output immediately after the pulse current is injected, and thereafter, until the injection of the pulse current stops, it reaches an equilibrium state and a constant tail light is output. The leading optical pulse is due to relaxation oscillation and is a typical gain switching drive. Even if the pulse width is changed, the timing at which the optical pulse is generated does not change. 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. In order to suppress the output of the tail light, it is conceivable to stop the current injection immediately after the optical pulse is output. However, since the time width of the optical pulse due to relaxation oscillation is 100 ps or less, when the magnitude of the current is as large as 10 A or more, it is difficult to stop the current injection within a time of 100 ps or less immediately after the optical pulse is output.

[0026] FIG. 6 is a diagram showing the measurement results for the first reference example. FIG. 6(a) shows the measurement results when the pulse width is about 0.8 ns, FIG. 6(b) shows the measurement results when the pulse width is 1.3 ns, and FIG. 6(c) shows the measurement results when the pulse width is 2.5 ns. In the measurements of FIGS. 6(a) to 6(c), the magnitude of the bias current and the amplitude of the pulse current are common. FIG. 6 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.

[0027] As shown in FIG. 6, in the first reference example, no optical output occurs while the pulse current is being injected, and an optical pulse is output immediately after the injection of the pulse current decreases. Also, almost no tail light is seen after the optical pulse is output. If the optical output is due to gain switching, even if the width of the pulse current is changed, the timing at which the optical pulse occurs does not change. In contrast, in the first reference example, an optical pulse is output triggered by the decrease in the injection of the pulse current. Therefore, it can be said that the optical output in the first reference example is not normal gain switching using the relaxation oscillation phenomenon.

[0028] Thus, the mechanisms and modes of the optical output are clearly different between the first reference example and the second reference example. This difference is explained as follows.

[0029] In a surface-emitting laser, the laser light propagates in the resonator in a direction perpendicular to the oxidation constriction layer. Therefore, the thicker the oxidation constriction layer, the longer the equivalent waveguide length depending on the refractive index difference, and the greater the lateral light confinement effect. When the DBR including the oxidation constriction layer is regarded as an equivalent waveguide structure, when the equivalent refractive index difference is large as shown in Fig. 7(a), the electric field intensity distribution of the laser light is concentrated near the center. On the other hand, when the equivalent refractive index difference is small as shown in Fig. 7(b), the electric field intensity distribution of the laser light spreads to the peripheral oxidation region. Comparing the first reference example and the second reference example, in the first reference example, since the oxidation constriction layer 150 includes the inner region 154, the equivalent refractive index difference becomes small in the first reference example. Therefore, in the second reference example, as shown in Fig. 7(a), the electric field intensity distribution of the laser light is concentrated near the center, while in the first reference example, as shown in Fig. 7(b), the electric field intensity distribution of the laser light spreads to the oxidation region 151.

[0030] Here, the lateral light confinement coefficient is defined by Equation (1) as the ratio of "the integrated intensity of the electric field in the same radius region as the current passing region" to "the integrated intensity of the electric field in the lateral cross section passing through the center of the surface-emitting laser element". Here, a corresponds to the radius of the current passing region, and Φ represents the rotation direction with the direction perpendicular to the substrate as the rotation axis.

[0031]

Equation

[0032] Next, a model of the phenomenon that occurs when the injection of the pulsed current is stopped will be described. In the state where the pulsed current is being injected, due to the oxidized constriction layer, the current path is concentrated near the center of the mesa, and the carrier density is in a high state. At this time, in the non-oxidized region with a high carrier density, an effect occurs where the refractive index decreases due to the carrier plasma effect. 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 literature "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 the refractive index is shown by Equation (2). Here, N is the carrier density.

[0033]

Number

[0034] Fig. 8 schematically shows the equivalent refractive index and the electric field strength distribution during the period when the pulsed current is injected (Fig. 8(a)) and during the period when the injection of the pulsed current is stopped and it decreases (Fig. 8(b)). During the period when the pulsed current is injected, the carrier plasma effect acts in the direction to cancel the equivalent refractive index difference (n1 - n0) caused by the oxidized narrow layer, and the equivalent refractive index difference becomes (n2 - n0). When the injection of the pulsed current decreases in this state, the action of the carrier plasma effect disappears, and the equivalent refractive index difference returns to (n1 - n0). As a result, the photons that have spread to the peripheral part of the mesa are collected at the central part of the mesa, and the photon density in the non-oxidized region increases. That is, it changes to a state where the lateral optical confinement is strong. When the injection of the pulsed current stops, 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 starts, and the accumulated carriers are consumed all at once and an optical pulse is output. The period when the pulsed current is injected is an example of the current injection period, and the period when the injection of the pulsed current is stopped and it decreases is an example of the current decrease period.

[0035] The results of verifying the above model by simulation are shown below. The rate equations for the carrier density and the photon density are shown in Eqs. (3) and (4).

[0036]

Number

[0037]

Number

[0038] Here, the contents indicated by each character in Eqs. (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 [cm​​3 τ n (N): Carrier lifetime [s] v g : Group velocity [cm / s] g(N,S): Gain [1 / cm] Γ a : Optical confinement factor τ p : Photon lifetime [s] β: Spontaneous emission coupling coefficient g 0 : 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: Light frequency [1 / s]

[0039] The gain g(N,S) is expressed by Equation (5).

[0040]

Equation

[0041] The optical confinement factor Γ a is defined as the product of the lateral optical confinement factor Γ r and the longitudinal optical confinement factor Γ z as shown in Equation (6).

[0042]

Equation

[0043] The threshold carrier density N th is expressed by Equation (7).

[0044]

Equation

[0045] Threshold current I th and the threshold carrier density N th There is a relationship of Equation (8) between them.

[0046]

Number

[0047] There is a relationship of Equation (9) between the optical output P output from the resonator and the photon density S.

[0048]

Number

[0049] Here, the simulation results for the second reference example will be described. For the second reference example, the lateral optical confinement factor Γ r was set to 1, and the simulation was performed by inputting the current monitor waveform shown in FIG. 5. The simulation results for the carrier density N and the threshold carrier density N th are shown in FIG. 9, and the simulation results for the optical output are shown in FIG. 10.

[0050] As shown in FIGS. 9 and 10, at about 5 ns when the pulsed current is injected, immediately thereafter, the carrier density N exceeds the threshold carrier density N th , and an optical pulse due to relaxation oscillation is output. After that, it reaches an equilibrium state and a certain tail light is output. Thus, in the simulation, results close to the measured results shown in FIG. 5 are obtained.

[0051] Next, the simulation results 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 ras a function that decreases as the carrier density N increases, and the simulation was carried out by inputting the current monitor waveform shown in FIG. 6. The lateral optical confinement factor Γ r was set as the above function in order to incorporate the influence of the refractive index change due to the carrier plasma effect. FIG. 11 is a diagram showing an example of the function. The simulation results of the optical output are shown in FIG. 12.

[0052] As shown in FIG. 12, an optical pulse output is obtained at the timing when the injection of the pulsed current is stopped. Thus, in the simulation, results close to the measured results shown in FIG. 6 are obtained.

[0053] To analyze this result in detail, the carrier density N, the threshold carrier density N th , the photon density S, and the lateral optical confinement factor Γ r in the condition where the pulse width is 2.5 ns are shown in FIG. 13 as the simulation results. FIG. 13(a) shows the simulation results of the carrier density N, the threshold carrier density N th and the photon density S, and FIG. 13(b) shows the simulation results of the lateral optical confinement factor Γ r .

[0054] Since the lateral optical confinement factor Γ r is a function of the carrier density N, the lateral optical confinement factor Γ r decreases in the range of 3 ns to 5.5 ns during which the pulsed current is injected. In this range, as the lateral optical confinement factor Γ r decreases, the threshold carrier density N th increases, and since N < N th , stimulated emission hardly occurs and the photon density S does not increase. When the injection of the pulsed current starts to decrease at the time of 5.5 ns, the lateral optical confinement factor Γ r rises again, and in this process, the photon density S occurs in pulses. FIG. 14 shows a graph in which the time axis is enlarged in the range of 5 ns to 6 ns in FIG. 13.

[0055] When the injection of the pulsed current starts to decrease at around 5.5 ns, the carrier density N begins to decrease. At the same time, the lateral optical confinement factor Γ r also increases, and the threshold carrier density N th decreases. Since the threshold carrier density N th decreases faster than the carrier density N decreases, there is a time when N > N th during the process of the carrier density N decreasing. At this time, first, the photon density S increases due to spontaneous emission. When the photon density S increases to a certain extent, stimulated emission becomes dominant and the photon density S rapidly increases. At the same time, the carrier density N rapidly decreases, and when N < N th again, the photon density rapidly decreases.

[0056] In this way, the phenomenon of optical pulse output triggered by the stop of the pulsed current injection was reproduced by simulation.

[0057] The rise time of the optical pulse becomes shorter when the threshold carrier density N th decreases faster than the carrier lifetime. That is, from Equation (6), the faster the increase in the lateral optical confinement factor Γ r , the shorter the rise time. The decay time of the optical pulse depends on the photon lifetime. An example of the measured result and simulation result of the optical pulse is shown in FIG. 15. FIG. 15(a) shows the measured result, and FIG. 15(b) shows the simulation result.

[0058] Defining the pulse width as the time width where it is 1 / e 2 or more of the peak value, it is 86 ps in the measured result and 81 ps in the simulation result. Here, e is the natural logarithm. According to this model, the width of the optical pulse is shorter than the pulsed current injected, and it can be shortened without being limited by the time width of the pulsed current injected.

[0059] In the first reference example, a continuous optical pulse train is unlikely to occur after the optical pulse output occurs. This is because when the optical pulse occurs, the injection of the pulsed current is decreasing, and relaxation oscillation is unlikely to occur.

[0060] Also, after the optical pulse output occurs, tail light is less likely to occur. This is because after the optical pulse occurs, the injection of the pulse current decreases, and it is difficult for the carrier density to increase.

[0061] Also, since an 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 arbitrarily controlled.

[0062] Also, the width of the optical pulse generated by the first reference example is shorter than the width of the injected pulse current. Since it is not necessary to shorten the pulse current width even when the current is increased, it is less affected by parasitic inductance.

[0063] By arranging a plurality of surface-emitting lasers 100 according to the first reference example in parallel to form a surface-emitting laser array and outputting optical pulses simultaneously, a larger optical peak output can be obtained. The current injected into the surface-emitting laser array is larger than the current injected into a single surface-emitting laser 100. However, since the width of the optical pulse output by the surface-emitting laser 100 is narrower than the width of the injected pulse current, a small optical pulse width can be output.

[0064] The pulse width of the light output from the surface-emitting laser 100 according to the first reference example is not limited, but is, for example, 1 ns or less, preferably 500 ps or less, and more preferably 100 ps or less.

[0065] In the first reference example, the thickness of the oxidized region 151 at a position 3 μm away from the inner edge of the inner region 154, that is, at a position 3 μm from the tip of the boundary between the non-oxidized region 152 and the oxidized region 151, is preferably not 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 away from the inner edge of the inner region 154 is preferably 62 nm or less, and may be 54 nm. When the distance (oxidation distance) from the side surface of the mesa 180 to the inner edge of the oxidized region 151 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 thickness of the oxidized region 951 and the thickness of the non-oxidized region 152 were measured at a position 3 μm away from the inner edge of the oxidized region 951 during the actual measurement of the above reference example, the former was 79 nm and the latter was 31 nm, and the former was 2.55 times the latter. As a result of the inventors' comparative evaluation of various elements with an oxidation constriction structure, when the ratio is 2 or less, the lateral optical confinement factor Γ r becomes small, and it has been found that it is easy to obtain short-pulse light with high output and no trailing edge.

[0066] The area of the non-oxidized region 152 (current constriction area) in plan view is preferably 120 μm 2 or less. As a result of the inventors' comparative evaluation of various elements of the non-oxidized region 152, when the non-oxidized region 152 exceeds 120 μm 2 , it has been found that the phenomenon of outputting an optical pulse immediately after stopping the injection of the pulse current may not easily occur. It has also been found that a smaller non-oxidized region 152 makes it easier to obtain an optical pulse with a higher peak output. FIG. 16 is a diagram showing the measurement results of the peak optical output for samples in the range of 50 μm 2 to 120 μm 2 for the area of the non-oxidized region.

[0067] As can be understood from the principle shown in the above first reference example, in order to improve the obtained short-pulse output, it is preferable to increase the number of carriers accumulated in the active layer. Also, after the current injection is stopped, it is important to create a state where N > N th in as short a time as possible.

[0068] That is, when current injection is stopped, due to carrier diffusion, natural emission, and non-radiative recombination, the carrier density in the central part near the active layer decreases from the current constriction structure, and the lateral mode distribution that has spread due to the plasma effect becomes distributed in the central part of the device. As a result, a state where N > N th is created and short-pulse oscillation occurs. However, reducing the carriers lost by recombination during this period is important for improving the pulse output.

[0069] In the above example, since the current injection for obtaining output serves as a means to suppress oscillation by causing a refractive index change due to the plasma effect, a certain amount of accumulated carriers needs to disappear before short-pulse oscillation occurs. If the refractive index can be changed by means other than the plasma effect regardless of the injected current amount and the amount of accumulated carriers, it is possible to effectively convert the accumulated carriers into short-pulse output and extract them, enabling more efficient and higher-output short-pulse operation.

[0070] As a means of externally modulating this refractive index, the electro-optic effect of a multiple quantum well structure is effective. In a multiple quantum well structure, by applying an electric field in a direction perpendicular to the well surface, a change in refractive index, that is, a decrease in refractive index, can be obtained.

[0071] Regarding the refractive index change due to the electric field of a quantum well structure, there are reports in, for example, Non-Patent Document 1, Non-Patent Document 2, Non-Patent Document 3, Non-Patent Document 4, etc. In Non-Patent Document 1, in a quantum well structure composed of InGaAsP and InP with a thickness of 30 nm, it is theoretically reported that a value of (Δn / n) / E = 3×10 -8 [cm / V] can be obtained. This means that when an electric field of, for example, 100 [kV / cm] is applied (a bias of 0.3 V for a 30-nm quantum well), Δn / n = 3×10 -3 , that is, Δn ≒ -9×10 -3 or so.

[0072] In Non-Patent Documents 2 and 3, measurements were actually carried out in a multiple quantum well structure composed of GaAs with a thickness of 10 nm and AlAs with a thickness of 30 nm, and a value of (Δn / n) / E = 4×10 -7 [cm / V] was observed at room temperature. 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 a red shift in the interband transition energy and a change in the refractive index due to the quantum confinement Stark effect associated with the application of an electric field. Also, in Non-Patent Document 4, a value of Δn ≒ -3×10 -2 is reported as an experimental result.

[0073] As described above, by utilizing the electric field effect of the multiple quantum well structure, it is possible to obtain a refractive index change equal to or greater than that of the plasma effect on the order of Δn ≒ -1×10 -2 with a practical applied electric field of 100 [kV / cm]. By utilizing this, it becomes possible to further improve the controllability and output of short-pulse operation.

[0074] Therefore, by arranging this multiple quantum well structure near the resonator and applying an electric field, the refractive index of the multiple quantum well part decreases and acts in a direction to cancel the effective refractive index difference Δn0 obtained by the oxidation structure, as shown in FIG. 8. In this way, it becomes possible to newly provide a means for changing the effective refractive index difference Δn in addition to the plasma effect. Furthermore, by controlling the effective refractive index difference Δn by the electric field applied to the multiple quantum well, it becomes possible to control the timing of short-pulse oscillation, which is laser oscillation.

[0075] (First Embodiment) Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. The first embodiment relates to a surface-emitting laser. FIG. 17 is a cross-sectional view of a top-emitting surface-emitting laser 500 with a wavelength in the 940 nm band created based on the above principle according to the first embodiment.

[0076] This surface-emitting laser 500 is a VCSEL that employs, for example, oxide constriction, similar to the first reference example. The surface-emitting laser 500 includes an n-type GaAs substrate 510, an n-type DBR 520, an active layer 530, a first p-type DBR 541, an oxide constriction layer 550, a contact layer 563, a contact layer 565, a first upper electrode 561, and a lower electrode 570. Further, the surface-emitting laser 500 includes resonator spacer layers 511 and 512, a multiple quantum well structure 590, a second p-type DBR 542, and a second upper electrode 562. The cylindrical mesa post 580 includes the n-type DBR 520, the resonator spacer layer 512, the active layer 530, the resonator spacer layer 511, the oxide constriction layer 550, the first p-type DBR 541, and the contact layer 563. Note that the first power supply device 581 and the second power supply device 582 each represent a power supply device that supplies current and an electric field to the surface-emitting laser 500.

[0077] The n-type DBR 520 is on the n-type GaAs substrate 510 as a lower mirror. The n-type DBR 520 consists of 40 pairs of n-type Al 0.1 Ga 0.9 As and Al 0.9 Ga 0.1 As. The resonator spacer layer 511 is on the n-type DBR 520. The resonator spacer layer 511 consists of Al 0.2 Ga 0.8 As. The active layer 530 is on the resonator spacer layer 511. The active layer 530 is a multiple quantum well active layer having InGaAs as a well layer and AlGaAs as a barrier layer. The resonator spacer layer 512 is on the active layer 530. The resonator spacer layer 512 consists of Al 0.2 Ga 0.8 As. The first p-type DBR 541 is on the resonator spacer layer 512 as a first upper mirror. The first p-type DBR 541 consists of 4 pairs of p-type Al 0.1 Ga 0.9 As and Al 0.9 Ga 0.1 As. The contact layer 563 is on the first p-type DBR 541. The contact layer 563 consists of p-type GaAs.

[0078] The surface-emitting laser 500 further includes a multiple quantum well structure 590 for undoped refractive index modulation, a second p-type DBR 542, and a contact layer 564. The multiple quantum well structure 590 is on the contact layer 563. The multiple quantum well structure 590 is composed of a plurality of semiconductor layers, and for example, consists of 20 pairs of In 0 GaAs and AlGaAs. The second p-type DBR 542 is on the multiple quantum well structure 590 as the second upper mirror. The second p-type DBR 542 consists of 16 pairs of p-type Al 0.1 Ga 0.9 As and Al 0.9 Ga 0.1 As. The contact layer 564 is on the second p-type DBR 542. The contact layer 564 consists of p-type GaAs. The contact layer 565 is on the back surface of the n-type GaAs substrate 510. The contact layer 565 consists of n-type GaAs.

[0079] For the multiple quantum well structure 590 for refractive index modulation, the energy between bands is set to be approximately the same as the photon energy of the oscillation wavelength when an electric field is applied. When an electric field is applied, the effective bandgap energy becomes smaller due to the quantum confinement Stark effect. Therefore, the wavelength of the absorption edge undergoes a red shift, enabling absorption of longer-wavelength light. When the effective bandgap energy during this electric field application is greater than the photon energy, absorption loss can be reduced, and when it is smaller, oscillation can be more effectively suppressed by the absorption loss. Also, the oxidation constriction layer 550 provided in the first p-type DBR 541 is formed by forming a p-type AlAs selective oxidation layer with a thickness of 20 nm in the first p-type DBR 541 to form a cylindrical mesa post 580, and then oxidizing the p-type AlAs selective oxidation layer in hot water vapor. The cylindrical mesa post 580 consists of the n-type DBR 520, the resonator spacer layers 511, 512, the active layer 530, the first p-type DBR 541, and the contact layer 563. Note that the multiple quantum well structure 590, the second p-type DBR 542, and the contact layer 564 are cylindrical. Note that the shape of the mesa post is not limited to circular, and can be any shape such as square, rectangular, hexagonal, etc.

[0080] Further, the lower electrode 570 is on the back surface of the contact layer 565 on the n-type GaAs substrate 510. The first upper electrode 561 is annular and on the surface of the contact layer 563 on the first p-type DBR 541. The second upper electrode 562 is annular and on the surface of the contact layer 564 on the second p-type EDBR 542. The first power supply device 581 injects current into the active layer through the first electrode pair composed of the first upper electrode 561 and the lower electrode 570. The second power supply device 582 applies an electric field to the multiple quantum well structure 590 for refractive index modulation through the second electrode pair composed of the lower electrode 570 and the second upper electrode 562. Here, the second p-type DBR 542 may be undoped, but when doped, the applied voltage from the second power supply device 582 to the multiple quantum well structure 590 can be reduced.

[0081] Next, the operating principle of the surface emitting laser 500 will be specifically described. First, the second power supply device 582 applies an electric field to the multiple quantum well structure 590 in advance. The effective refractive index at the center of the element decreases with respect to the effective refractive index difference Δn0 obtained by the oxidation constriction layer 550 when no electric field is applied, by applying the electric field. That is, the effective refractive index difference Δn is made smaller than the effective refractive index difference Δn0.

[0082] Next, the first power supply device 581 starts injecting current into the active layer 530. At this time, due to the plasma effect, the effective refractive index difference Δn becomes even smaller. By the above two actions, the lateral mode distribution at the center of the element becomes smaller, oscillation is suppressed, and carriers are accumulated in the active layer 530.

[0083] When using the combination of the electric field effect of the multiple quantum well structure, the effective refractive index difference Δn0 due to the oxidation constriction layer 550 is set slightly larger. Then, by combining the refractive index changes due to the electric field effect of the multiple quantum well structure 590 and the plasma effect of the carriers, it becomes the relationship between the threshold carrier density N th and the carrier density N as shown in Fig. 13(a). That is, it is set to a state where oscillation is suppressed by both the plasma effect and the electric field effect.

[0084] Next, when the second power supply device 582 stops applying an electric field to the multiple quantum well structure 590 for refractive index modulation, the interband transition energy of this multiple quantum well structure 590 increases. That is, the red shift due to the quantum confinement Stark effect disappears, it becomes transparent to the oscillation wavelength, and the effective refractive index difference Δn increases. Due to the increase in the effective refractive index difference Δn, the lateral mode distribution at the center of the element becomes larger, reducing the oscillation threshold, and short-pulse oscillation immediately occurs. At this time, if the first power supply device 581 also stops current injection into the active layer 530 simultaneously, a larger refractive index change can be obtained.

[0085] When oscillation was suppressed only by the plasma effect, after the current injection into the active layer 530 stopped, the effective refractive index difference Δn that had decreased due to the plasma effect recovered to an oscillatable state as follows. That is, the carriers accumulated in the active layer 530 diffuse from the current injection path or decrease due to the recombination process in the active region, thereby recovering. However, carriers that do not contribute to the oscillation during that time are lost.

[0086] In contrast, in the first embodiment, since the refractive index change occurs immediately by controlling the applied electric field from the second power supply device 582 to the multiple quantum well structure 590, it is possible to significantly reduce carriers that do not contribute to oscillation. Therefore, in particular, the peak output at the start of oscillation can be significantly improved. Incidentally, the effective refractive index difference Δn0 due to the oxidation constriction layer 550 can be changed by changing the thickness of the oxidation constriction layer 550 and the like, and can be increased by making the oxidation constriction layer 550 thicker.

[0087] Also, the effective refractive index difference Δn0 due to the oxidation constriction layer 550 is set so that oscillation starts when the electric field application to the multiple quantum well structure 590 stops. Therefore, according to the first embodiment, the plasma effect and the electric field effect can be combined. Therefore, oscillation can be suppressed more strongly than in the case of the plasma effect alone. Therefore, the number of carriers accumulated in the active layer can be increased, and the peak output during short-pulse oscillation can be improved.

[0088] Thus, the greater the amount of change in refractive index due to the electric field effect, the greater the oscillation suppression effect obtained and the greater the number of carriers that can be accumulated. Also, while maintaining this oscillation suppression effect, by setting a large effective refractive index difference Δn0 by the oxidation constriction layer 550, it becomes possible to increase the amount of change in the oscillation threshold when the application of the electric field is stopped. Therefore, the number of ineffective carriers that disappear before the start of oscillation of the short pulse can be reduced, and in any case, an effect can be obtained for increasing the output power.

[0089] Note that the multiple quantum well structure 590 can obtain an effect regardless of being disposed at any position in the laser light path as long as a change in refractive index due to the electric field effect can be obtained. In addition, by bringing the multiple quantum well structure 590 closer to the active layer 530 or increasing the number of quantum wells, the amount of change in refractive index due to the electric field effect on the multiple quantum well structure can be increased.

[0090] In the first embodiment, since an optical pulse is output immediately when the application of the electric field to the multiple quantum well structure is stopped, the timing at which the optical pulse is output can be arbitrarily set.

[0091] Also, since the number of carriers that can be accumulated can be increased and ineffective carriers that do not contribute to oscillation can be reduced, high output can be obtained.

[0092] In the first embodiment, it is difficult for a continuous optical pulse train to occur after the optical pulse output occurs. The reason is that when the application of the electric field is stopped and the application of the current is stopped, the injection of the pulse current decreases when the optical pulse occurs, and relaxation oscillation hardly occurs.

[0093] Also, it is difficult for tail light to occur after the optical pulse output occurs. The reason is that when the application of the electric field is stopped and the application of the current is stopped, the injection of the pulse current decreases after the optical pulse occurs, and the carrier density hardly increases.

[0094] In addition, the width of the optical pulse generated according to the first embodiment is shorter than the width of the injected pulse current. Since it is not necessary to shorten the pulse current width even when the current is increased, it is less affected by parasitic inductance.

[0095] Similar to the first reference example, by arranging a plurality of surface-emitting lasers 500 according to the first embodiment in parallel to form a surface-emitting laser array and outputting optical pulses simultaneously, a larger optical peak output can be obtained. The current injected into the surface-emitting laser array is larger than the current injected into a single surface-emitting laser 500. However, since the width of the optical pulse output by the surface-emitting laser 500 is narrower than the width of the injected pulse current, a small optical pulse width can be output.

[0096] Similar to the first reference example, the pulse width of the light output from the surface-emitting laser 500 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.

[0097] In the first embodiment, when the oxidation constriction layer 550 has the same configuration as in the first reference example, the thickness of the oxidation region 551 at a position 3 μm away from the inner edge of the inner region 554 toward the outside, that is, at a position 3 μm from the tip of the boundary between the non-oxidation region 552 and the oxidation region 551, is preferably not more than twice the thickness of the non-oxidation region 552.

[0098] Also, similar to the first reference example, in the first embodiment as well, as described with reference to FIG. 16 of the first reference example, the area of the non-oxidation region 552 (current constriction area) in plan view is 120 μm 2 or less, which is desirable.

[0099] (Second Embodiment) Next, the second embodiment will be described. The second embodiment relates to a surface-emitting laser. FIG. 18 is a cross-sectional view showing the surface-emitting laser according to the second embodiment.

[0100] The surface-emitting laser 600 according to the second embodiment is the same as that of the first embodiment except for the second upper electrode 662 formed on the second p-type DBR 542. Therefore, descriptions of parts other than the second upper electrode 662 are omitted.

[0101] Since the surface-emitting laser 600 is of the top-emission type, the second upper electrode 662 formed on the second p-type DBR 542 is a transparent electrode so as not to prevent the transmission of the laser. Fig. 18(b) is a top view of the surface-emitting laser 600, and the cross section along the line segment A-A' is shown in Fig. 18(a). The second upper electrode 662 is circular and is located at the center of the columnar first p-type DBR 541 in plan view as shown in Fig. 18(b). As shown in Fig. 18(a), the second upper electrode 662 is drawn out from the central portion and connected to the second power supply device 582 at the outer portion that does not prevent the transmission of the laser. With the electrode configuration as shown in Fig. 18, an electric field can be selectively applied concentratedly to the refractive index modulation multiple quantum well structure in the central portion of the surface-emitting laser 600 in plan view. Therefore, the surface-emitting laser 600 can selectively reduce the effective refractive index of the central portion of the element.

[0102] Therefore, it is possible to reduce the intensity of the lateral mode distribution in the central portion of the element and spread the distribution to the peripheral portion of the element, and effectively reduce the effective refractive index difference Δn. Also, the second p-type DBR 542 is made undoped, and by adopting a configuration excluding the contact layer on the second p-type DBR 542, the spread of the electric field in the lateral direction can be suppressed, so that the selectivity can be further improved. Further, the second p-type DBR 542 may be configured using a material such as a dielectric such as SiN or SiO 2 etc.

[0103] As described above, also in the second embodiment, the same effects as those of the first embodiment can be obtained, and further, by providing the second upper electrode at the central portion of the element, the amount of change in the refractive index can be increased, so that a high-output laser beam can be obtained.

[0104] (Third Embodiment) Next, the third embodiment will be described. The third embodiment relates to a surface-emitting laser. FIG. 19 is a cross-sectional view showing the surface-emitting laser according to the third embodiment.

[0105] The surface-emitting laser 700 according to the third embodiment is a back-side emission type 940 nm band surface-emitting laser element. In the surface-emitting laser 700 of FIG. 19, the total number of pairs of the upper multilayer film mirrors composed of the first p-type DBR 541 and the second p-type DBR 542 is 40 pairs, and the number of pairs of the lower multilayer film mirrors composed of the n-type DBR 520 is 20 pairs, and the light output is emitted to the substrate side, that is, the back side.

[0106] An opening is provided in the lower electrode 770 corresponding to the element emission portion on the substrate side so that the light output can be extracted. Further, a second upper electrode 762 is provided in the central portion of the element of the second p-type DBR 542 so that an electric field can be selectively applied to the multiple quantum well structure for refractive index modulation in the central portion of the element. When an electrode is formed in the central portion of the element in this way, the effective refractive index of the central portion of the element can be reduced in the same manner as in the second embodiment described above.

[0107] Therefore, it is possible to reduce the intensity of the lateral mode distribution in the central portion of the element and spread the distribution to the peripheral portion of the element, and effectively reduce the effective refractive index difference Δn. Further, when the second p-type DBR 542 is undoped and the contact layer on the second p-type DBR 542 is removed, the spread of the electric field in the lateral direction can be further suppressed. By further suppressing the spread of the electric field in the lateral direction, the selectivity can be further improved. Further, the second p-type DBR 542 may be formed of a material such as a dielectric such as SiN or SiO 2 etc.

[0108] As described above, also in the third embodiment, the same effects as those in the second embodiment can be obtained.

[0109] (Fourth Embodiment) Next, the fourth embodiment will be described. The fourth embodiment relates to a surface-emitting laser. FIG. 20 is a cross-sectional view showing the surface-emitting laser according to the fourth embodiment.

[0110] The surface-emitting laser 800 according to the fourth embodiment is a VCSEL having a current confinement structure by, for example, BTJ (Buried tunnel junction). The surface-emitting laser 800 is obtained by changing the current confinement structure from a selective oxidation structure to an embedded tunnel junction 850 in the surface-emitting laser 700 of the third embodiment, which is a back-surface emission type.

[0111] The embedded tunnel junction 850 is configured as follows. During the formation of the first p-type DBR 841, p-doped GaAs layer with a higher concentration of p than the first p-type DBR 841 and n-doped GaAs with a higher concentration of p than the n-type DBR 520 are grown. Then, the growth is stopped once, and the above two layers other than the central part of the element are removed by wet selective etching. After forming the embedded tunnel junction 850, the rest of the first p-type DBR 841 is regrown thereon. ++ GaAs layer and n-doped GaAs with a higher concentration of p than the n-type DBR 520 are grown. ++ After that, once the growth is stopped, the above two layers other than the central part of the element are removed by wet selective etching to form the embedded tunnel junction 850. After forming the embedded tunnel junction 850, the rest of the first p-type DBR 841 is regrown thereon.

[0112] When a forward bias is applied to the lower electrode 770 and the first upper electrode 561, which are electrodes for injecting current into the active layer 530, a reverse bias is applied to the p-doped GaAs layer and the n-doped GaAs layer. As a result, electrons tunnel between the p-doped GaAs layer and the n-doped GaAs layer across the bandgap, generating holes in the p-doped GaAs layer and injecting them into the active layer 530. ++ GaAs layer and n-doped GaAs layer ++ GaAs layer, a reverse bias is applied. As a result, electrons tunnel between the p-doped GaAs layer and the n-doped GaAs layer, generating holes in the p-doped GaAs layer and injecting them into the active layer 530. ++ GaAs layer to the n-doped GaAs layer ++ GaAs layer, electrons tunnel between the p-doped GaAs layer and the n-doped GaAs layer across the bandgap, generating holes in the p-doped GaAs layer and injecting them into the active layer 530. ++ GaAs layer, holes are generated and injected into the active layer 530.

[0113] In this embedded tunnel junction portion, a small refractive index difference due to the difference in the Al composition of the AlGaAs material occurs in the lateral direction, and based on this refractive index difference, weak lateral optical confinement is formed. Its magnitude is such that it can change the effective refractive index difference Δn due to the plasma effect of carriers and the electric field effect of multiple quantum wells, etc., and short-pulse oscillation can be performed.

[0114] As described above, even in the fourth embodiment, the same effects as those of the second embodiment can be obtained.

[0115] (Fifth Embodiment) Next, the fifth embodiment will be described. The fifth embodiment relates to a surface-emitting laser. FIG. 21 is a cross-sectional view showing the surface-emitting laser according to the fifth embodiment.

[0116] The surface-emitting laser 900 according to the fifth embodiment is obtained by deforming the second p-type DBR and the second upper electrode in the surface-emitting laser 500 of the first embodiment, which is of the surface-emitting type. In the surface-emitting laser 900, the second upper electrode 962 is provided on the upper surface of the multiple quantum well structure 590 instead of the upper surface of the second p-type DBR 942. With such a structure, an electric field can be applied to the multiple quantum well structure 590 without passing through the second p-type DBR 942, and in the fifth embodiment, the electric field of the multiple quantum well structure 590 can be strengthened more than that in the first embodiment. Therefore, in the fifth embodiment, the amount of change in refractive index due to the electro-optic effect can be increased.

[0117] Therefore, even in the fifth embodiment, the same effects as those of the first embodiment can be obtained, and furthermore, since the amount of change in refractive index can be increased, a high-output laser beam can be obtained.

[0118] (Sixth Embodiment) Next, the sixth embodiment will be described. The sixth embodiment relates to a surface-emitting laser. FIG. 22 is a cross-sectional view showing the surface-emitting laser according to the sixth embodiment.

[0119] The surface-emitting laser 1000 according to the sixth embodiment is obtained by thickening the resonator spacer layer 1012 instead of the first p-type DBR 541 in the surface-emitting laser 500 of the first embodiment, which is of the surface-emitting type. Further, in the surface-emitting laser 1000, an oxidation constriction layer 1050 is formed inside the resonator spacer layer 1012. Even with such a structure, the same effects as those of the first embodiment can be obtained.

[0120] In the first to sixth embodiments, the structure in which a multiple quantum well structure for obtaining an electro-optic effect is provided between the active layer and the second p-type DBR has been described. However, the present invention is not limited to this, and the multiple quantum well structure can obtain an effect regardless of where it is arranged in the path of the laser beam as long as a refractive index change due to the electro-optic effect can be obtained.

[0121] (Embodiment 7) Next, Embodiment 7 will be described. Embodiment 7 relates to a laser device. FIG. 23 is a diagram showing a laser device according to Embodiment 7.

[0122] The laser device 300 according to Embodiment 7 includes a surface-emitting laser 500 according to Embodiment 1 and a power supply device 301. The power supply device 301 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 570. 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 current into the surface-emitting laser 500, and the second power supply device 582 supplies an electric field to the surface-emitting laser 500.

[0123] The duty ratio of the current injection from the first power supply device 581 is preferably 0.5% or less. That is, the current injection period and the current decrease period are repeated a plurality of times, and the ratio of the current injection period to the current decrease period is preferably 0.5% or less. The duty ratio is the ratio of the time during which a current pulse is injected in a unit time. When the pulse current width is t [s] and the repetition frequency of the pulse current is f [Hz], the duty ratio corresponds to f × t (%). FIG. 24 is a diagram showing the relationship between the duty ratio and the peak output of the optical pulse when the pulse current width is 2.5 ns.

[0124] As shown in FIG. 24, when the duty ratio exceeds 0.5%, the optical peak output tends to decrease. The following model can be considered as the reason. First, as the duty ratio increases, the amount of heat generated in the current constriction region (non-oxidized region 152) due to the injected pulsed current increases. As a result, the temperature of the central part where the current is concentrated rises with respect to the peripheral part of the current constriction region, resulting in a temperature difference. Consequently, due to the thermal lens effect, the refractive index of the central part of the current constriction region increases, and the lateral optical confinement factor becomes larger. When the lateral optical confinement factor becomes larger due to the thermal lens effect, the influence of the refractive index change caused by the carrier plasma effect generated by the increase and decrease of the pulsed current becomes smaller. When the influence of the refractive index change becomes smaller, the phenomenon of outputting an optical pulse immediately after stopping the injection of the pulsed current becomes less likely to occur. On the other hand, if the duty ratio is 0.5% or less, the influence of the refractive index change due to the thermal lens effect becomes sufficiently small, and the refractive index change derived from the constriction structure becomes dominant. Therefore, it is considered that the peak output is almost constant and does not change.

[0125] Instead of the surface-emitting laser 500 according to the first embodiment, any one of the surface-emitting lasers 600 to 1000 according to the second to sixth embodiments may be used.

[0126] (Eighth Embodiment) Next, the eighth embodiment will be described. The eighth embodiment relates to a distance measuring device. FIG. 25 is a diagram showing the distance measuring device according to the eighth embodiment. The distance measuring device is an example of a detection device.

[0127] The distance measurement device 400 according to the eighth embodiment is a distance measurement device using the TOF (Time of Flight) method. The distance measurement device 400 includes a light emitting element 410, a light receiving element 420, and a drive circuit 430. The light emitting element 410 irradiates a light emitting beam (irradiation light 411) toward a distance measurement target object 450 for distance measurement. The light receiving element 420 receives the reflected light 421 from the distance measurement target object 450. The drive circuit 430 drives the light emitting element 410 and calculates the round-trip distance to the distance measurement target object 450 by detecting the time difference between the light emission timing of the light emitting beam and the light reception timing of the reflected light 421 by the light receiving element 420.

[0128] The light emitting element 410 may include a plurality of surface emitting lasers 500 to 1000 according to the first to sixth embodiments. The repetition frequency of the pulse is, for example, in the range of several kHz to several tens of MHz.

[0129] The light receiving element 420 is, for example, a photodiode (PD), an avalanche photodiode (APD), or a single photon avalanche diode (SPAD). The light receiving element 420 may include a plurality of light receiving elements arranged in an array. The light receiving element 420 is an example of a detection unit.

[0130] In distance measurement using the TOF method, it is important to separate the signal from the distance measurement target object and the noise. When measuring a distance measurement target object that is farther away and when measuring a distance measurement target object with a lower reflectivity, it is preferable to use a more sensitive light receiving element to obtain the signal from the target object. However, when using a more sensitive light receiving element, the possibility of erroneously detecting background light noise or shot noise increases. To separate the signal and the noise, it is also conceivable to increase the threshold value of the received light signal, but if the peak output of the light emitting beam is not increased accordingly, it becomes difficult to receive the signal light from the distance measurement target object. However, the output of the light emitting beam is restricted by the laser safety standard.

[0131] According to the surface-emitting lasers 500 to 1000 according to the first to sixth embodiments, an optical pulse with a pulse width of about 100 ps can be output. This is about 1 / 10 compared to the optical pulse width of several ns output by conventional surface-emitting lasers. According to the distance measurement device according to the eighth embodiment, since the shorter the pulse width of the optical pulse, the higher the peak output allowed by the safety standard, it is possible to achieve both high precision and long distance while satisfying eye safety.

[0132] (Ninth Embodiment) Next, the ninth embodiment will be described. The ninth embodiment relates to a moving body. FIG. 26 is a diagram showing an automobile as an example of a moving body according to the ninth embodiment. Above the front of an automobile 1100 as an example of a moving body according to the ninth embodiment (for example, the upper part of the windshield), the distance measurement device 400 described in the eighth embodiment is provided. The distance measurement device 400 measures the distance to an object 1102 around the automobile 1100. The measurement result of the distance measurement device 400 is input to a control unit included in the automobile 1100, and the control unit controls the operation of the moving body based on this measurement result. Alternatively, the control unit may perform a warning display on a display unit provided in the automobile 1100 for the driver 1101 of the automobile 1100 based on the measurement result of the distance measurement device 400.

[0133] As described above, in the ninth embodiment, by providing the distance measurement device 400 in the automobile 1100, the position of the object 1102 around the automobile 1100 can be recognized with high precision. Note that the mounting position of the distance measurement device 400 is not limited to the upper front of the automobile 1100, and it may be mounted on the side or the rear. Also, in this example, the distance measurement device 400 is provided in the automobile 1100, but the distance measurement device 400 may be provided in an aircraft or a ship. Further, it may be provided in a moving body that performs autonomous movement without a driver, such as a drone and a robot.

[0134] Although the preferred embodiments and the like have been described in detail above, the present invention is not limited to the above-described embodiments and the like, and various modifications and substitutions can be made to the above-described embodiments and the like without departing from the scope described in the claims.

Description of Symbols

[0135] 300 Laser device 400 Distance measurement device 500, 600, 700, 800, 900, 1000 Surface-emitting laser 511, 512, 1012 Resonator spacer layer 520 n-type DBR 530 Active layer 541 First p-type DBR 542 Second p-type DBR 550, 1050 Oxidation narrowing layer 551 Oxidation region 552 Non-oxidation region 561 First upper electrode 562, 662, 762, 962 Second upper electrode 563, 564, 565 Contact layer 570, 770 Lower electrode 580 Mesa post 590 Multiple quantum well structure 850 Tunnel junction 1100 Automobile (mobile body)

Prior Art Documents

Patent Documents

[0136]

Patent Document 1

Non-Patent Documents

[0137]

Non-Patent Document 1

Non-Patent Document 2

Claims

1. A surface emitting laser, a first power supply device, a second power supply device, and having wherein the surface emitting laser has an active layer, a plurality of reflecting mirrors facing each other with the active layer therebetween, is composed of a plurality of semiconductor layers, and has a multiple quantum well structure provided in a path of laser light emitted by the active layer and the plurality of reflecting mirrors, a first electrode pair connected to the first power supply device and capable of injecting current into the active layer, a second electrode pair connected to the second power supply device and capable of applying an electric field in a direction perpendicular to the well surface of the multiple quantum well structure, and having wherein a period during which current is injected by the first power supply device is defined as a current injection period, a period after the current injection period and during which a current value injected into the active layer is lower than the current value during the current injection period is defined as a current decrease period, 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 and during which a magnitude of the electric field is lower than the magnitude of the electric field during the electric field application period is defined as an electric field decrease period, at least a part of the current injection period is included in at least a part of the electric field application period, laser oscillation does not occur during the electric field application period, and laser oscillation occurs during the electric field decrease period, a laser device in which the current decrease period starts simultaneously with or after the start of the electric field decrease period.

2. A surface emitting laser, a first power supply device, a second power supply device, and having wherein the surface emitting laser has an active layer, a plurality of reflecting mirrors facing each other with the active layer therebetween, is composed of a plurality of semiconductor layers, and has a multiple quantum well structure provided in a path of laser light emitted by the active layer and the plurality of reflecting mirrors, a first electrode pair connected to the first power supply device and capable of injecting current into the active layer, a second electrode pair connected to the second power supply device and capable of applying an electric field in a direction perpendicular to the well surface of the multiple quantum well structure, and having wherein a period during which current is injected by the first power supply device is defined as a current injection period, a period after the current injection period and during which a current value injected into the active layer is lower than the current value during the current injection period is defined as a current decrease period, 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 and during which a magnitude of the electric field is lower than the magnitude of the electric field during the electric field application period is defined as an electric field decrease period, at least a part of the current injection period is included in at least a part of the electric field application period, No laser oscillation occurs during the electric field application period, and laser oscillation occurs during the electric field decreasing period. The current injection period and the current decreasing period are repeated a plurality of times. A laser device, wherein a ratio of the current injection period to the current decreasing period is 0.5% or less.

3. The plurality of reflectors include a lower reflector provided below the active layer and a first upper reflector formed above the active layer, and the multiple quantum well structure is disposed above the active layer. The laser device according to claim 1 or 2.

4. The first upper reflector is formed in a columnar shape, and one of the second electrode pairs is disposed at least partially in a central portion of the first upper reflector. The laser device according to claim 3.

5. The laser device according to any one of claims 1 to 4, which outputs an optical pulse shorter than the current injection period on a time axis.

6. The laser device according to any one of claims 1 to 5, wherein the electric field application period starts before the start of the current injection period.

7. A laser device according to any one of claims 1 to 6, a detection unit that detects light emitted from the surface-emitting laser and reflected by an object, and a detection device comprising the same.

8. The detection device according to claim 7, which calculates a distance to the object based on a signal from the detection device.

9. A moving body comprising the detection device according to claim 8.

10. A driving method of a laser device having a surface-emitting laser, a first power supply device, and a second power supply device, The surface-emitting laser includes an active layer, a plurality of reflectors facing each other with the active layer therebetween, a multiple quantum well structure provided in a path of laser light and composed of a plurality of semiconductor layers, a first electrode pair connected to the first power supply device and capable of injecting current into the active layer, a second electrode pair connected to the second power supply device and capable of applying an electric field in a direction perpendicular to a well surface of the multiple quantum well structure, and has a period during which current is injected by the first power supply device is defined as a current injection period, a period after the current injection period and during which a current value injected into the active layer decreases from a current value during the current injection period is defined as a current decreasing period, 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 and during which a magnitude of the electric field during the electric field application period decreases is defined as an electric field decreasing period. At least a part of the current injection period is included in at least a part of the electric field application period. Laser oscillation does not occur during the electric field application period, and laser oscillation occurs during the electric field decreasing period. A driving method for a laser device, wherein the current decreasing period starts simultaneously with or after the start of the electric field decreasing period. **Claim 11**: A driving method for a laser device having a surface emitting laser, a first power supply device, and a second power supply device, The surface emitting laser includes: An active layer, A plurality of reflecting mirrors facing each other with the active layer interposed therebetween, A multiple quantum well structure provided in the path of the laser beam and composed of a plurality of semiconductor layers, A first pair of electrodes connected to the first power supply device and capable of injecting current into the active layer, A second pair of electrodes connected to the second power supply device and capable of applying an electric field in a direction perpendicular to the well surface of the multiple quantum well structure, And has: The period during which current is injected by the first power supply device is defined as the current injection period, the period after the current injection period and during which the current value injected into the active layer is lower than the current value during the current injection period is defined as the current decreasing period, the period during which an electric field is applied by the second power supply device is defined as the electric field application period, and the period after the electric field application period and during which the magnitude of the electric field is lower than the magnitude of the electric field during the electric field application period is defined as the electric field decreasing period. At least a part of the current injection period is included in at least a part of the electric field application period. Laser oscillation does not occur during the electric field application period, and laser oscillation occurs during the electric field decreasing period. The current injection period and the current decreasing period are repeated a plurality of times. A driving method for a laser device, wherein the ratio of the current injection period to the current decreasing period is 0.5% or less.

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