Light-emitting device and range-measuring device

Abstract

To reduce the temperature dependence of a light output characteristics in a surface-emitting light emitting device with a saturable absorption layer.SOLUTION: A light emitting device has a resonator comprising a first reflector and a second reflector arranged on a semiconductor substrate, and a resonator spacer section positioned between the first and second reflectors and comprising an active layer and a saturable absorption layer. The first reflector, resonator spacer section, and second reflector are stacked in this order on the semiconductor substrate, the active layer comprises an asymmetric quantum well structure containing a plurality of types of quantum wells with different wavelengths corresponding to the bandgap, and the gain peak wavelength of the active layer is shorter than the laser oscillation wavelength of the resonator.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to a light-emitting device and a distance-measuring device. [Background technology]

[0002] Vertical cavity surface-emitting lasers (VCSELs) are being developed as light sources for LiDAR (Light Detection and Ranging) systems and 3D (Dimension) sensors. Patent document 1 describes a VCSEL configured to generate optical pulses with a short pulse width and high peak value by providing a saturable absorption layer in the laser resonator. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-176886 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] The VCSEL described in Patent Document 1 has the feature of being able to output extremely short pulses of light with a high peak value of several hundred ps at the start of oscillation, and when applied to a light source device in a LiDAR system, for example, improvements in distance measurement distance and distance measurement accuracy can be expected. However, VCSELs with a saturable absorption layer have a greater wavelength dependence with respect to temperature compared to VCSELs without a saturable absorption layer, which could potentially negate the advantages of applying them to a LiDAR system. [Means for solving the problem]

[0005] The purpose of this disclosure is to provide a technique for reducing the temperature dependence of the optical output characteristics in a surface-emitting light-emitting device having a saturable absorption layer.

[0006] According to one disclosure of this specification, a light-emitting device is provided, comprising a resonator disposed on a semiconductor substrate and including a first reflector and a second reflector, and a resonator spacer portion disposed between the first reflector and the second reflector and including an active layer and a saturable absorption layer, wherein the first reflector, the resonator spacer portion and the second reflector are stacked in this order on the semiconductor substrate, the active layer has an asymmetric quantum well structure including a plurality of quantum wells of different wavelengths corresponding to the band gap, and the gain peak wavelength of the active layer is shorter than the laser oscillation wavelength of the resonator.

[0007] Furthermore, according to another disclosure of this specification, a light-emitting device is provided having a resonator disposed on a semiconductor substrate and including a first reflector and a second reflector, and a resonator spacer portion disposed between the first reflector and the second reflector and including an active layer and a saturable absorption layer, wherein the first reflector, the resonator spacer portion and the second reflector are stacked in this order on the semiconductor substrate, the active layer has an asymmetric quantum well structure including a plurality of quantum wells of different wavelengths corresponding to the band gap, and the gain peak wavelength of the active layer is set such that the gain of the active layer at the laser oscillation wavelength of the resonator is a first value at a first temperature and a second value greater than the first value at a second temperature higher than the first temperature.

[0008] Furthermore, according to yet another disclosure of this specification, a light-emitting device is provided that includes a quantum well comprising a resonator disposed on a semiconductor substrate and including a first reflector and a second reflector, and a resonator spacer portion disposed between the first reflector and the second reflector and including an active layer and a saturable absorption layer, wherein the first reflector, the resonator spacer portion and the second reflector are stacked in this order on the semiconductor substrate, the gain peak wavelength of the active layer is shorter than the laser oscillation wavelength of the resonator, and the saturable absorption layer has a wavelength corresponding to its band gap that is longer than the laser oscillation wavelength.

[0009] Furthermore, according to yet another disclosure of this specification, a light-emitting device is provided which includes a resonator disposed on a semiconductor substrate and comprising a first reflector and a second reflector, and a resonator spacer portion disposed between the first reflector and the second reflector and comprising an active layer and a saturable absorption layer, wherein the first reflector, the resonator spacer portion and the second reflector are stacked in this order on the semiconductor substrate, and the gain peak wavelength of the active layer is set such that the gain of the active layer at the laser oscillation wavelength of the resonator is a first value at a first temperature and a second value greater than the first value at a second temperature higher than the first temperature, and the saturable absorption layer comprises a quantum well whose band gap wavelength is longer than the laser oscillation wavelength. [Effects of the Invention]

[0010] According to this disclosure, in a surface-emitting light-emitting device having a saturable absorption layer, the temperature dependence of the optical output characteristics can be reduced. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic cross-sectional view showing an example of the configuration of a light-emitting device according to the first embodiment. [Figure 2A] This graph shows the optical output characteristics of a VCSEL element with a saturable absorption layer at room temperature. [Figure 2B] This graph shows the optical output characteristics of a VCSEL element with a saturable absorption layer at high temperatures. [Figure 3A] This graph shows the relationship between the gain spectrum of the active layer at room temperature, the optical absorption spectrum of the saturable absorption layer, and the laser oscillation wavelength in a typical light-emitting device. [Figure 3B] This graph shows the relationship between the gain spectrum of the active layer at high temperatures, the optical absorption spectrum of the saturable absorption layer, and the laser oscillation wavelength in a typical light-emitting device. [Figure 4A] This graph shows the relationship between the gain spectrum of the active layer at room temperature, the optical absorption spectrum of the saturable absorption layer, and the laser oscillation wavelength in the light-emitting device according to the first embodiment. [Figure 4B] It is a graph showing the relationship between the gain spectrum at high temperature of the active layer, the optical absorption spectrum of the saturable absorption layer, and the laser oscillation wavelength in the light-emitting device according to the first embodiment. [Figure 5] It is a graph showing the result obtained by calculating the gain spectrum of the active layer in the light-emitting device according to the first embodiment. [Figure 6] It is a graph showing the result obtained by calculating the optical absorption spectrum of the saturable absorption layer in the light-emitting device according to the first embodiment. [Figure 7] It is a graph showing the result obtained by calculating the gain spectrum of the active layer in the light-emitting device according to the comparative example. [Figure 8] It is a diagram showing the temperature change of the optical output characteristics in the light-emitting device according to the first embodiment. [Figure 9] It is a graph showing the result obtained by calculating the optical absorption spectrum of the saturable absorption layer in the light-emitting device according to the second embodiment. [Figure 10] It is a graph showing the result obtained by calculating the optical absorption spectrum and its differential spectrum of the saturable absorption layer in the light-emitting device according to the second embodiment. [Figure 11] It is a graph showing the result obtained by calculating the gain spectrum of the active layer in the light-emitting device according to the third embodiment. [Figure 12] It is a diagram showing the temperature change of the optical output characteristics in the light-emitting device according to the third embodiment. [Figure 13] It is a perspective view showing the light-emitting device according to the fourth embodiment. [Figure 14] It is a top view of the light-emitting device according to the fourth embodiment. [Figure 15] It is a schematic cross-sectional view showing the schematic configuration of the light-emitting device according to the fifth embodiment. [Figure 16] It is a block diagram showing the schematic configuration of the distance measuring device according to the sixth embodiment. [Figure 17] It is a block diagram showing the schematic configuration of the distance measuring device according to the seventh embodiment. [Figure 18]This is a schematic cross-sectional view showing an example of the configuration of a surface-emitting laser array in a distance measuring device according to the seventh embodiment. [Figure 19A] This is a block diagram showing an example of the configuration of the equipment according to the eighth embodiment. [Figure 19B] This is a block diagram showing an example of the configuration of a mobile body according to the eighth embodiment. [Modes for carrying out the invention]

[0012] [First Embodiment] The light-emitting device according to the first embodiment will be described with reference to Figure 1. Figure 1 is a schematic cross-sectional view showing an example of the configuration of the light-emitting device according to this embodiment.

[0013] The light-emitting device 100 according to this embodiment is a vertical-cavity surface-emitting laser (VCSEL) having a distributed Bragg reflector (DBR). The light-emitting device 100 may consist of a semiconductor substrate 10, a lower DBR layer 12, a non-doped spacer portion 14, a resonator portion 18, an upper DBR layer 28, electrodes 40, 42, and a protective film 44, as shown in Figure 1, for example. The lower DBR layer 12 is provided on the semiconductor substrate 10. The non-doped spacer portion 14 is provided on the lower DBR layer 12. The resonator portion 18 is provided on the non-doped spacer portion 14. The upper DBR layer 28 is provided on the resonator portion 18. The layer located between the lower DBR layer 12 and the upper DBR layer 28 (the non-doped spacer portion 14 and the resonator portion 18) is the resonator spacer portion.

[0014] A saturable absorption layer 16 is provided within the undoped spacer portion 14. The resonator portion 18 is composed of an n-type layer 20 provided on the undoped spacer portion 14, an undoped spacer portion 22 provided on the n-type layer 20, and a p-type layer 26 provided on the undoped spacer portion 22. An active layer 24 is provided within the undoped spacer portion 22. A current constriction layer 38 is provided within the upper DBR layer 28.

[0015] The undoped spacer portion 22, the p-type layer 26, and the upper DBR layer 28 are processed into a mesa shape. An electrode 40 electrically connected to the n-type layer 20 is provided on the n-type layer 20 that is exposed by processing the undoped spacer portion 22, the p-type layer 26, and the upper DBR layer 28 into a mesa shape. An electrode 42 electrically connected to the upper DBR layer 28 is provided on the upper DBR layer 28. A protective film 44 is provided on the upper surface of the n-type layer 20 and the sides and top surface of the mesa, excluding at least a portion of the surfaces of the electrodes 40 and 42.

[0016] The semiconductor substrate 10 may be made of, for example, a GaAs substrate. The lower DBR layer 12 may be made of, for example, Al with an optical film thickness of 1 / 4λc. 0.1 GaAs layer and Al 0.9 The structure can be constructed by stacking 35 pairs of laminates, with each pair consisting of a GaAs layer and a laminate. Here, λc is the central wavelength of the high-reflection band of the lower DBR layer 12, and is not particularly limited, but in this embodiment it is set to 940 nm.

[0017] The saturable absorption layer 16 may be composed of multiple quantum wells, for example, consisting of three quantum wells, each containing an 8 nm thick InGaAs well layer sandwiched between 10 nm thick AlGaAs barrier layers. The remaining portion of the undoped spacer 14 may be composed of an undoped GaAs layer.

[0018] The resonator section 18 is composed of a pin junction consisting of an n-type layer 20, an undoped spacer section 22, and a p-type layer 26. The active layer 24 placed in the undoped spacer section 22 may be composed of a multiple quantum well including, for example, three quantum wells, each consisting of an 8 nm thick InGaAs well layer sandwiched between 10 nm thick AlGaAs barrier layers. The n-type layer 20 may be composed of an n-type AlGaAs layer, the p-type layer 26 of a p-type AlGaAs layer, and the remaining portion of the undoped spacer section 22 of an undoped GaAs layer.

[0019] In this embodiment, the light-emitting device 100 is designed such that the gain peak wavelength at room temperature is located at a shorter wavelength than the laser oscillation wavelength at room temperature. The reason for designing the active layer 24 in this way will be explained below.

[0020] VCSEL elements with a saturable absorption layer have the advantage of being able to output extremely short pulses of light with high peak values ​​of several hundred ps at the start of oscillation. For example, when applied to the light source device of a LiDAR system, improvements in distance measurement distance and accuracy can be expected. However, after diligent research by the inventors on VCSEL elements with a saturable absorption layer, it was found that the emission characteristics, such as the timing of light pulse generation and peak light intensity, are greatly affected by temperature.

[0021] Figures 2A and 2B are graphs showing the optical output characteristics of a VCSEL element having a saturable absorption layer. Figure 2A shows the optical output characteristics at room temperature (20°C), and Figure 2B shows the optical output characteristics at high temperature (80°C). As shown in Figures 2A and 2B, the timing of the optical pulse generation is delayed by approximately 0.9 nsec as the temperature rises from 20°C to 80°C. In addition, the peak optical intensity decreases by approximately 30% as the temperature rises from 20°C to 80°C. The inventors speculate on the cause of this characteristic degradation observed in the optical output characteristics as follows.

[0022] The gain spectrum of the active layer, the optical absorption spectrum of the saturable absorption layer, and the laser oscillation wavelength all exhibit a characteristic shift towards longer wavelengths as the temperature increases. The amount of shift towards longer wavelengths varies depending on the constituent materials of the light-emitting device, but in a light-emitting device constructed with the aforementioned material system, both the gain spectrum of the active layer and the optical absorption spectrum of the saturable absorption layer shift towards longer wavelengths at a rate of approximately 0.4 nm / K. The laser oscillation wavelength also shifts towards longer wavelengths with increasing temperature, but the rate is approximately 0.07 nm / K, which is small compared to the temperature dependence of the gain spectrum of the active layer and the optical absorption spectrum of the saturable absorption layer. As a result, changes in temperature cause a change in the correlation between the gain spectrum of the active layer, the optical absorption spectrum of the saturable absorption layer, and the laser oscillation wavelength. It should be noted that the temperature dependence of the gain spectrum of the active layer and the optical absorption spectrum of the saturable absorption layer described above is determined by the physical properties of the semiconductor materials constituting the light-emitting device, and it is difficult to directly control these.

[0023] Figures 3A and 3B are graphs showing the relationship between the gain spectrum of the active layer, the optical absorption spectrum of the saturable absorption layer, and the laser oscillation wavelength in a typical light-emitting device. Figure 3A shows the characteristics at room temperature, and Figure 3B shows the characteristics at high temperature. In each figure, the dashed line represents the gain spectrum of the active layer, the double dashed line represents the optical absorption spectrum of the saturable absorption layer, and the dotted line represents the laser oscillation wavelength.

[0024] In a typical VCSEL element, the emission wavelength of the active layer is designed so that the gain peak wavelength is located near the laser oscillation wavelength, as shown in Figure 3A, for example. When the temperature rises in this VCSEL element, the gain spectrum of the active layer and the optical absorption spectrum of the saturable absorption layer shift to longer wavelengths relative to the laser oscillation wavelength, as shown in Figure 3B.

[0025] When the gain spectrum of the active layer shifts to longer wavelengths relative to the laser oscillation wavelength, and the laser oscillation wavelength is located at a shorter wavelength than the gain peak wavelength, the gain at the laser oscillation wavelength decreases compared to room temperature, as shown in Figure 3B. Furthermore, when the optical absorption spectrum of the saturable absorption layer shifts to longer wavelengths relative to the laser oscillation wavelength, optical absorption at the laser oscillation wavelength increases. Both of these phenomena lead to changes that make laser oscillation more difficult, and it is thought that these phenomena, in combination, cause a delay in the timing of optical pulse generation and a decrease in emission characteristics such as peak light intensity.

[0026] From this perspective, in the light-emitting device of this embodiment, the gain peak wavelength of the active layer 24 is designed such that the direction of change in the gain of the active layer 24 with respect to temperature changes and the direction of change in the light absorption of the saturable absorption layer 16 are in opposite directions. From one perspective, this method may involve designing the gain peak wavelength of the active layer 24 such that the gain peak wavelength at room temperature is shorter than the laser oscillation wavelength at room temperature. From another perspective, the gain peak wavelength of the active layer 24 may be designed such that the gain at the laser oscillation wavelength at a first temperature is a first value, and the gain at the laser oscillation wavelength at a second temperature higher than the first temperature is a second value greater than the first value. Here, the first temperature may be, for example, room temperature, and the second temperature may be, for example, the maximum ambient temperature expected during operation.

[0027] Figures 4A and 4B are graphs showing the relationship between the gain spectrum of the active layer, the optical absorption spectrum of the saturable absorption layer, and the laser oscillation wavelength in the light-emitting device of this embodiment. Figure 4A shows the characteristics at room temperature, and Figure 4B shows the characteristics at high temperature.

[0028] As shown in Figures 3A and 3B, the gain of the active layer 24 decreases as the wavelength moves from the gain peak wavelength toward shorter wavelengths, and also as the wavelength moves toward longer wavelengths. Therefore, in the light-emitting device of this embodiment, for example, as shown in Figure 4A, the active layer 24 is designed so that the gain peak wavelength at room temperature is on the shorter wavelength side than the laser oscillation wavelength at room temperature. With this configuration, even if the gain spectrum of the active layer 24 shifts toward longer wavelengths relative to the laser oscillation wavelength at high temperatures, as shown in Figure 4B, the gain at the laser oscillation wavelength does not decrease, and can even be increased.

[0029] As shown in Figures 3A and 3B, the light absorption in the saturable absorption layer 16 increases with shorter wavelengths. Therefore, when the light absorption spectrum shifts to longer wavelengths relative to the laser oscillation wavelength at high temperatures, the light absorption in the saturable absorption layer 16 increases. However, by designing the active layer 24 so that the gain peak wavelength at room temperature is shorter than the laser oscillation wavelength at room temperature, at least a portion of the increase in light absorption by the saturable absorption layer 16 can be offset by an increase in gain. This reduces the discrepancy in the correlation between the gain spectrum and light absorption spectrum and the laser oscillation wavelength due to temperature changes, and consequently suppresses changes in the light emission characteristics of the light-emitting device due to temperature changes.

[0030] The gain peak wavelength of the active layer 24 at high temperatures does not necessarily have to be shorter than the laser oscillation wavelength at high temperatures. If the gain at high temperatures exceeds the gain at room temperature, at least a portion of the increase in light absorption by the saturable absorption layer 16 can be offset by the increase in gain, and the effects of this embodiment can be achieved. In other words, as described above, the gain peak wavelength of the active layer 24 should be adjusted so that the gain at the laser oscillation wavelength at the first temperature is a first value, and the gain at the laser oscillation wavelength at the second temperature, which is higher than the first temperature, is a second value that is greater than the first value.

[0031] In conventional VCSEL devices, when prioritizing high-temperature performance optimization, it is conceivable to shift the gain peak wavelength of the active layer to a shorter wavelength than the laser oscillation wavelength. Such a design can achieve a reduction in threshold current and improvement in optical output at high temperatures. However, in the case of VCSEL devices with a saturable absorption layer, as the temperature rises, not only the gain spectrum of the active layer but also the optical absorption spectrum of the saturable absorption layer shifts to longer wavelengths, as mentioned above. Therefore, shifting the gain peak wavelength of the active layer to a shorter wavelength than the laser oscillation wavelength does not necessarily improve the optical output characteristics.

[0032] This disclosure is not intended to improve optical output characteristics, but rather to reduce the temperature dependence of the timing of the short optical pulse generated at the start of oscillation. This disclosure is a design concept that shifts the gain peak wavelength of the active layer to a shorter wavelength than the laser oscillation wavelength to counteract the increase in the absorption coefficient of the saturable absorption layer due to temperature increase, and is not a general design concept for VCSEL elements with a saturable absorption layer. In LiDAR systems, stabilizing the timing of the optical pulse reflected from the target object is important because it directly affects the distance measurement accuracy. On the other hand, while the optical intensity of the optical pulse needs to be above the minimum required for timing detection, it is sufficient to know when the light was detected, so the need to stabilize the optical intensity within a certain range is significantly lower compared to VCSELs used in optical communication systems and electrophotographic systems. Based on the requirements of such LiDAR systems, this disclosure is designed to reduce the temperature dependence of the optical pulse generation timing by shortening the gain peak of the active layer to a wavelength shorter than the oscillation wavelength, rather than stabilizing the temperature dependence of the optical intensity.

[0033] Figure 5 is a graph showing the calculated gain spectrum of the active layer 24 in the light-emitting device according to this embodiment. Figure 5 is a calculation example where the gain peak wavelength of the active layer 24 at room temperature is set to 920 nm, which is 20 nm shorter than the laser oscillation wavelength of 940 nm. The vertical axis represents a carrier concentration of 3.2 × 10⁻¹⁶. 18 cm -3 This shows the average gain coefficient of the three-layer quantum well at that time. The horizontal axis represents wavelength.

[0034] Figure 6 is a graph showing the results of calculating the optical absorption spectrum of the saturable absorption layer 16 in the light-emitting device according to this embodiment. Figure 6 is a calculation example when the wavelength corresponding to the band gap of the quantum well constituting the saturable absorption layer 16 is set to 940 nm, the same as the laser oscillation wavelength. Here, the band gap of the quantum well refers to the energy difference between the ground levels in the conductor and valence band that occur within the quantum well, and is also referred to as the band gap of the quantum well below this value. The band gap Eg of the quantum well constituting the saturable absorption layer 16 at this time is 1.319 eV. The vertical axis shows the average absorption coefficient of the three quantum wells. The horizontal axis shows the wavelength. In Figure 6, the absorption coefficient is shown as a negative value to make the relationship with the gain coefficient of the active layer 24 easier to understand visually. A larger absolute value of the absorption coefficient indicates greater optical absorption.

[0035] Figure 7 also shows a comparative example of a calculation when the gain peak wavelength of the active layer 24 at room temperature is set to 940 nm, the same as the laser oscillation wavelength. In the calculation, the active layer 24 was assumed to be a multiple quantum well structure containing three quantum wells, similar to this embodiment. The vertical axis represents a carrier concentration of 3.2 × 10⁻¹⁶. 18 cm -3 This shows the average gain coefficient of the three-layer quantum well at that time. The horizontal axis represents wavelength.

[0036] Here, based on the calculation results in Figures 5 to 7, we assume that the temperature rises from 25°C to 85°C. Due to this temperature difference, a difference of approximately 20 nm ((0.4 nm / K - 0.07 nm / K) × 60°C = 19.8 nm) occurs between the wavelength shift of the gain spectrum and optical absorption spectrum and the wavelength shift of the laser oscillation wavelength. Figure 8 summarizes the changes in the gain coefficient of the active layer 24 and the absorption coefficient of the saturable absorption layer 16 associated with this 20 nm wavelength shift in the gain spectrum and optical absorption spectrum.

[0037] As shown in Figure 8, in the comparative example, as the temperature rises, the gain of the active layer 24 decreases and the light absorption of the saturable absorption layer 16 increases, resulting in a large change in the overall light output characteristics with respect to temperature. In contrast, in the light-emitting device of this embodiment (example), the gain of the active layer 24 can be increased as the temperature rises, and the overall change in the light output characteristics with respect to temperature can be reduced compared to the comparative example.

[0038] Thus, according to this embodiment, in a VCSEL element having a saturable absorption layer, the gain peak wavelength of the active layer is set to a shorter wavelength than the laser oscillation wavelength of the resonator, thereby reducing the temperature dependence of the optical output characteristics.

[0039] Furthermore, as mentioned above, the gain peak wavelength of the active layer 24 at high temperatures does not necessarily have to be shorter than the laser oscillation wavelength at high temperatures. That is, if the gain at high temperatures exceeds the gain at room temperature, at least a portion of the increase in light absorption by the saturable absorption layer 16 can be offset by the increase in gain, and the effects of this embodiment can be achieved. In other words, the lower limit of the gain peak wavelength of the active layer 24 may be the wavelength at which the gain at that time is the same as the gain when the temperature rises from 25°C to 85°C, i.e., when the wavelength shift is about 20 nm ((0.4 nm / K - 0.07 nm / K) × 60°C = 19.8 nm). The gain peak wavelength when the wavelength shift is 20 nm becomes the limit on the longer wavelength side of the gain peak wavelength of the active layer 24. In Figure 5, the gain is the same at both the 10 nm shorter wavelength side and the 10 nm longer wavelength side of the gain peak wavelength. Therefore, in this case, the laser oscillation wavelength should be set to a wavelength 10 nm longer than the gain peak wavelength. The lower limit of the desirable shift of the gain peak wavelength toward shorter wavelengths depends on the operating temperature range, but one indicator is 10 nm.

[0040] [Second Embodiment] The light-emitting device according to the second embodiment will be described with reference to Figures 9 and 10. Components similar to those in the light-emitting device according to the first embodiment are denoted by the same reference numerals, and their descriptions are omitted or simplified.

[0041] The light-emitting device according to this embodiment is the same as the light-emitting device according to the first embodiment, except that the wavelength corresponding to the band gap of the quantum well constituting the saturable absorption layer 16 is different. That is, in the light-emitting device of the first embodiment, the wavelength corresponding to the band gap of the quantum well constituting the saturable absorption layer 16 was set to the same wavelength as the laser oscillation wavelength. In contrast, in the light-emitting device of this embodiment, the wavelength corresponding to the band gap of the quantum well constituting the saturable absorption layer 16 is set to a wavelength that is longer than the laser oscillation wavelength.

[0042] Figure 9 is a graph showing the results of calculating the optical absorption spectrum of the saturable absorption layer 16. In the calculation, a multiple quantum well structure including three quantum well layers was assumed as the saturable absorption layer 16, similar to the first embodiment. In Figure 9, the dashed line represents a calculation example (Example 1) where the wavelength corresponding to the band gap of the quantum wells constituting the saturable absorption layer 16 is 940 nm, the same as the laser oscillation wavelength, and corresponds to the configuration of the first embodiment. The solid line represents a calculation example (Example 2) where the wavelength corresponding to the band gap of the quantum wells constituting the saturable absorption layer 16 is 955 nm, which is a longer wavelength than the laser oscillation wavelength, and corresponds to the configuration of this embodiment. The band gap Eg of the quantum wells constituting the saturable absorption layer 16 in this case is 1.298 eV. The vertical axis shows the average absorption coefficient of the three quantum wells. The horizontal axis shows the wavelength.

[0043] As shown in Figure 9, by shifting the wavelength corresponding to the band gap of the quantum well constituting the saturable absorption layer 16 to the longer wavelength side, the optical absorption spectrum of the saturable absorption layer 16 is also shifted to the longer wavelength side. As a result, the change in the absorption coefficient of the saturable absorption layer 16 in the wavelength range of 920 nm to 940 nm (i.e., the range from 920 nm to 940 nm) is smaller in Example 2 than in Example 1. Specifically, the change in the absorption coefficient of the saturable absorption layer 16 in the wavelength range of 920 nm to 940 nm is 2468 [cm²] in Example 1. -1 In contrast to Example 2, the result was 1527 [cm²]. -1This means that by shifting the wavelength corresponding to the band gap of the quantum well structure constituting the saturable absorption layer 16 to the longer wavelength side, the temperature dependence of the optical absorption of the saturable absorption layer 16 at the laser oscillation wavelength can be reduced. Therefore, according to the configuration of this embodiment, the change in optical output characteristics due to temperature changes can be reduced even further than in the case of the first embodiment.

[0044] Figure 10 shows the optical absorption spectrum and its differential spectrum (slope) of the saturable absorption layer in Figure 9. In the differential spectrum, there is a maximum point of slope near the wavelength corresponding to the band gap, and the slope decreases toward shorter wavelengths near the laser oscillation wavelength of 940 nm in Example 2.

[0045] Around 922 nm, where the slope is minimal, the change in the absorption coefficient of the saturable absorption layer 16 with respect to temperature, which is the issue addressed in this disclosure, becomes small. However, actual devices are not used only around a specific temperature point, so it is required that the characteristics be stable over a certain temperature range. Therefore, one of the preferred ranges for the laser oscillation wavelength is a range where the slope of the absorption coefficient is small, which is below the midpoint between the peak near the wavelength corresponding to the band gap and the minimum value around 922 nm. Since the temperature range of laser applications includes room temperature in the vast majority of cases, it is preferable that the laser oscillation wavelength at room temperature falls within a range where the slope of the absorption coefficient is small.

[0046] Therefore, as shown in FIG. 10, the preferred range of the laser oscillation wavelength at room temperature is from 907 nm to 941 nm, and more preferably, considering temperature shift at high temperature etc., it is from 922 nm to 941 nm with a margin on the shorter wavelength side. In Example 2, since the wavelength corresponding to the bandgap of the saturable absorption layer 16 is 955 nm, the wavelength range where the laser oscillation wavelength at room temperature is 14 nm to 48 nm shorter than the wavelength corresponding to the bandgap of the saturable absorption layer 16 is preferred. More preferably, the wavelength range where the laser oscillation wavelength at room temperature is 14 nm to 33 nm shorter than the wavelength corresponding to the bandgap of the saturable absorption layer 16 is preferred. Also, the preferred wavelength range can be rephrased in terms of the difference in the energy of photons corresponding to each wavelength.

[0047] Also, when comparing the absorption coefficients of the saturable absorption layer 16 at the same wavelength, the absorption coefficient in Example 1 is smaller than the absorption coefficient in Example 2. This means that in the configuration of this embodiment, even if the absorption coefficient of the saturable absorption layer 16 is reduced to the same level as in Example 1, light output characteristics equivalent to those of Example 1 can be obtained. That is, according to the configuration of this embodiment, while achieving the same effect as the first embodiment, it is also possible to reduce the number of quantum well layers constituting the saturable absorption layer 16. Thereby, the manufacturing process of the light emitting device can be simplified.

[0048] The specific number of quantum wells in this case will be described below. In the saturable absorption layer of Example 1 having the same configuration as the saturable absorption layer of the comparative example, the absorption coefficient at the laser oscillation wavelength of 940 nm at room temperature is -2141 cm as shown in FIG. 6. -1 That is, it is possible to generate a short and high-peak-value light pulse with this absorption coefficient. On the other hand, the absorption coefficient in the above-described preferred wavelength range in Example 2, specifically, in the wavelength range where the wavelength is 14 nm to 48 nm shorter than the wavelength corresponding to the bandgap of the saturable absorption layer is -4012 cm -1 to -6684 cm -1In both Example 1 and Example 2, the saturable absorption layer 16 has 3 quantum wells. However, in Example 2, because the absorption coefficient is larger, it is possible to reduce the number of quantum wells to lower the absorption coefficient when light passes through the saturable absorption layer 16 to about the same level as in Example 1. Specifically, based on the ratio of the absorption coefficient of Example 1 to the absorption coefficient of Example 2, it is possible to reduce the number of quantum wells in the saturable absorption layer 16 by a range of 0.32 to 0.53 times. In Example 2, since the number of quantum wells is 3, it is possible to reduce the number of quantum wells to 1 by a factor of 0.32.

[0049] Incidentally, in Example 2 as well, the number of quantum wells in the active layer 24 is 3. In other words, a preferred ratio of the number of quantum wells between the saturable absorption layer 16 and the active layer 24 from the viewpoint of absorption coefficient in Example 2 also includes 1:3.

[0050] Furthermore, from the perspective of the temperature dependence of the absorption coefficient, the change in the absorption coefficient of the saturable absorption layer due to temperature was 1527 [cm²] in Example 2. -1 ] There is, and the increase in the gain of the active layer is the same as in Example 1, 562 [cm²]. -1 Therefore, from the viewpoint of reducing the change in the absorption coefficient to a level comparable to the increase in gain, a ratio of 1:3 between the number of quantum wells in the saturable absorption layer 16 and the active layer 24 is within a more preferable range.

[0051] Based on the above, a more preferable range for the ratio of the number of quantum wells in the saturable absorption layer 16 to the active layer 24 is 1:1 to 1:3. However, even outside this range, as described in this embodiment, the effects of this embodiment can be achieved by setting the wavelength corresponding to the band gap of the quantum wells constituting the saturable absorption layer 16 to a wavelength longer than the laser oscillation wavelength.

[0052] In this embodiment, the active layer 24 has only one pin junction. However, a multi-junction configuration in which pin-junction active layers 24 are stacked with tunnel junctions in between can also be adopted for the active layer. In that case, the number of quantum wells in the active layer 24 is the sum of the number of quantum wells present in the pin junctions of all active layers. This is because the number of quantum well layers between the upper and lower reflectors is the number of quantum wells that give gain to light. Therefore, it is more preferable that the relationship between this sum and the number of quantum wells in the saturable absorption layer is within the range described above.

[0053] Thus, according to this embodiment, in a VCSEL element having a saturable absorption layer, the gain peak wavelength of the active layer is set to a shorter wavelength than the laser oscillation wavelength of the resonator, thereby reducing the temperature dependence of the optical output characteristics. Furthermore, by setting the wavelength corresponding to the band gap of the quantum well constituting the saturable absorption layer to a longer wavelength than the laser oscillation wavelength, the temperature dependence of the optical output characteristics can be further reduced.

[0054] In this embodiment, the absorption coefficient of the saturable absorption layer 16 is increased, which increases the proportion of light absorbed within the resonator. Therefore, this design is undesirable from the viewpoint of light extraction efficiency at both room temperature and high temperatures, and may lead to a decrease in optical output. On the other hand, in LiDAR applications, as mentioned above, the stability of the timing of short pulse generation is directly related to the distance measurement accuracy and is therefore more important. In this embodiment, in a VCSEL element having a saturable absorption layer 16, the gain peak wavelength of the active layer 24 is set to a shorter wavelength than the laser oscillation wavelength of the resonator. Then, the wavelength corresponding to the band gap of the quantum well constituting the saturable absorption layer 16 is set to a longer wavelength than the laser oscillation wavelength, thereby canceling out the respective gains and absorptions. This configuration can be said to solve the problems of Patent Document 1 and achieve the effect of stabilizing the timing of short pulse generation.

[0055] [Third Embodiment] A light-emitting device according to the third embodiment will be described with reference to Figure 11. Components similar to those in the light-emitting device according to the first or second embodiment will be denoted by the same reference numerals, and their descriptions will be omitted or simplified.

[0056] The light-emitting device according to this embodiment differs from the light-emitting device of the first embodiment in that the quantum wells constituting the active layer 24 are composed of so-called asymmetric quantum wells, which include multiple types of quantum wells with different wavelengths corresponding to the band gaps of the quantum wells. By applying an asymmetric quantum well structure to the active layer 24, the number of control parameters increases, making it possible to design a more desirable gain shape. Furthermore, asymmetric quantum wells have the advantage of being able to emit light at high energy levels even at low carrier densities.

[0057] Generally, asymmetric quantum well structures are used to obtain broadband emission and gain. Therefore, they are used in light sources that emit light over a wide wavelength range, such as superluminescent diodes and tunable lasers with mechanisms that actively adjust the resonant wavelength of the VCSEL using MEMS, etc., resulting in wavelength differences of up to 50 nm. On the other hand, asymmetric quantum wells are rarely used in conventional VCSELs, where the lower and upper mirrors are made of semiconductor crystals and the resonator is fixed as a solid. This is because even if gain is generated in wavelength bands outside the oscillation wavelength range, the gain and the energy used to generate it are not effectively utilized, negatively impacting optical output and threshold values. In other words, it could lead to a decrease in optical output.

[0058] On the other hand, in this disclosure, an asymmetric quantum well structure is introduced to achieve both the cancellation of the temperature dependence of the absorption coefficient of the saturable absorption layer, which is not normally present in VCSELs, and improved characteristics at room temperature, thereby realizing a more favorable gain spectrum. Therefore, the gain spectrum generated by the asymmetric quantum well structure of this embodiment is not a gain spectrum favorable for the broadband light source described above, specifically a flat gain spectrum over a wide wavelength band, but rather a bell-shaped gain spectrum with a peak at a certain wavelength.

[0059] Figure 11 is a graph showing the calculated gain spectrum of the active layer in the light-emitting device according to this embodiment. In the calculation, the active layer 24 was assumed to be a multiple quantum well structure containing a total of four quantum well layers: three quantum wells with a band gap wavelength of 920 nm and one quantum well with a band gap wavelength of 940 nm. The laser oscillation wavelength was set to 940 nm. The vertical axis represents a carrier concentration of 3.2 × 10⁻⁶. 18 cm -3 This shows the average gain coefficient of the quantum well at [a specific time]. The horizontal axis represents the wavelength.

[0060] In the light-emitting device of this embodiment, the gain coefficient at room temperature, that is, the average gain coefficient of the quantum well at 940 nm, which is the laser oscillation wavelength at room temperature, is 510 cm², as shown in Figure 11. -1 This is the approximate value. This value is 369 cm² in the case of the light-emitting device of the first embodiment. -1 This value is larger than [value]. This means that the light-emitting device of this embodiment is more likely to oscillate at room temperature and can reduce the threshold current compared to the light-emitting device of the first embodiment.

[0061] Here, based on the calculation results in Figures 5, 6, and 11, let's consider the case where the temperature rises from 25°C to 85°C. Due to this temperature difference, a difference of approximately 20 nm occurs between the wavelength shift amount of the gain spectrum and optical absorption spectrum and the wavelength shift amount of the laser oscillation wavelength, as mentioned above. Figure 12 summarizes the changes in the gain coefficient of the active layer 24 and the absorption coefficient of the saturable absorption layer 16 that accompany this 20 nm wavelength shift in the gain spectrum and optical absorption spectrum.

[0062] As shown in Figure 12, the change in light output characteristics with respect to temperature in the light-emitting device of this embodiment (Example 3) is slightly increased compared to the first embodiment, but it can be reduced compared to the comparative example described above.

[0063] Thus, according to this embodiment, in a VCSEL element having a saturable absorption layer, the gain peak wavelength of the active layer is set to a shorter wavelength than the laser oscillation wavelength of the resonator, thereby reducing the temperature dependence of the optical output characteristics. Furthermore, by applying an asymmetric quantum well structure to the active layer, the design flexibility of the optical output characteristics can be improved.

[0064] As described above, this disclosure is based on the idea of ​​offsetting the increase in the absorption coefficient of the saturable absorption layer 16 due to the temperature rise by designing the active layer 24 so that its gain increases with increasing temperature. In other words, a configuration is needed in which the gain increases as the wavelength range in which the laser oscillates decreases, typically from the laser oscillation wavelength at room temperature to shorter wavelengths. Such a gain spectrum can be achieved by making the number of long-wavelength quantum wells and short-wavelength quantum wells that make up the asymmetric quantum well the same, or by having more short-wavelength quantum wells than long-wavelength quantum wells. Example 3 also has such a configuration.

[0065] Furthermore, the upper limit of the preferred wavelength difference corresponding to the band gap between a long-wavelength quantum well and a short-wavelength quantum well is 40 nm. That is, as is clear from Figure 5, the half-width at half maximum (the wavelength range from the peak value to half of the peak value) of the gain spectrum produced by a single quantum well is 20 nm. Therefore, in order to stack two or more quantum wells to create a configuration in which the gain increases as the wavelength decreases from the laser oscillation wavelength at room temperature to a shorter wavelength, as described above, it is necessary to stack the gains with a half-width shorter than half maximum.

[0066] Incidentally, when actually manufacturing a quantum well structure, the wavelength corresponding to the band gap often varies by about 3 nm to 5 nm. In other words, wavelength differences smaller than that essentially result in the configurations of Example 1 and Example 2. Therefore, in order to stably provide a wavelength difference corresponding to the band gaps of the long-wavelength quantum well and the short-wavelength quantum well and to realize the effects of this embodiment, it is practical to set the wavelength difference to 5 nm or more. For this reason, the preferred range for the wavelength difference corresponding to the band gaps of the long-wavelength quantum well and the short-wavelength quantum well constituting the asymmetric quantum well of this embodiment is 5 nm to 40 nm.

[0067] Furthermore, the asymmetric quantum well structure of this embodiment and the configuration of Example 2, in which the wavelength corresponding to the band gap of the quantum well constituting the saturable absorption layer 16 is set to a longer wavelength than the laser oscillation wavelength, can be combined, and the preferred ranges of each can be used.

[0068] The band gap of a quantum well is related to the photoluminescence (PL) emission wavelength, which is a common inspection item during manufacturing, and can be determined from the PL emission wavelength. A theoretical relationship has also been established between the quantum well gain peak and the PL emission wavelength, and the quantum well gain peak wavelength under specific conditions can be determined from the PL emission wavelength.

[0069] In the light-emitting devices of the first to third embodiments described above, there are two electrodes in each case, and these electrodes have the function of injecting current into the active layer, but no electrodes are provided for electrically controlling the saturable absorption layer. For example, in the first embodiment, current is injected into the active layer 24 by electrodes 40 and 42. In a configuration in which the optical absorption characteristics of the saturable absorption layer 16 are not controlled by electrical means such as current injection or the application of a reverse bias voltage, as described above, the oscillation timing changes when the gain of the active layer 24 and the absorption coefficient of the saturable absorption layer 16 change with temperature. Therefore, in order to suppress temperature changes in the oscillation timing, it is important to have a configuration that cancels out the gain change and absorption change due to temperature change.

[0070] On the other hand, unlike the configuration of the present disclosure, there are also known VCSELs using a saturable absorption layer, in which both the active layer and the saturable absorption layer are sandwiched between p-type and n-type semiconductor layers in a pin configuration. This VCSEL has electrodes that electrically contact each of the p-type and n-type layers sandwiching the active layer, as well as electrodes that electrically contact each of the p-type and n-type layers sandwiching the saturable absorption layer. In this configuration, any two of the four electrodes can be combined into one electrode. Therefore, the number of electrodes is generally three or four.

[0071] In this configuration, carriers for light emission are injected into the active layer by applying a voltage in the forward direction of the pin. Furthermore, a voltage is applied to the saturable absorption layer in either the forward or reverse direction of the pin, and the oscillation timing is controlled by the voltage applied to the saturable absorption layer and its variation over time. In this configuration, the oscillation timing is controlled by changing the characteristics of the saturable absorption layer, such as its absorption coefficient, by applying a voltage or current to the saturable absorption layer. It is preferable to design the absorption coefficient of the saturable absorption layer to be sufficiently large to prevent oscillation when the laser is not oscillating, while conversely, it is preferable to design the absorption coefficient of the saturable absorption layer to be sufficiently small when the laser is oscillating. As in this disclosure, it is undesirable to set the gain and absorption coefficient of the saturable absorption layer to be just below the oscillation condition, such that the state transitions from non-oscillating to oscillating after a certain period of time. Instead, a sufficiently large absorption coefficient for a sufficiently non-oscillating state and a sufficiently small absorption coefficient for a sufficiently oscillating state are achieved through electrical control. Therefore, it is possible to make changes beyond the change in the absorption coefficient of the saturable absorption layer due to temperature changes through electrical control, and the need to cancel out the gain of the active layer and the absorption coefficient of the saturable absorption layer as in this disclosure is low.

[0072] While the VCSEL described in Patent Document 1 has advantages such as simplified manufacturing processes and reduced power supply requirements due to its two-electrode configuration, it lacks electrical control of the saturable absorption layer. Therefore, the timing of short pulse generation is predominantly determined by the relationship between the gain of the active layer and the absorption coefficient of the saturable absorption layer. This leads to the problem that the timing of short pulse generation, which is crucial in LiDAR systems, changes with temperature. Accordingly, the configuration in this disclosure that cancels out the gain of the active layer and the absorption coefficient of the saturable absorption layer is particularly effective in VCSEL configurations that do not electrically change the optical absorption characteristics of the saturable absorption layer and have only two electrodes for injecting current into the active layer.

[0073] [Fourth Embodiment] A light-emitting device according to the fourth embodiment will be described with reference to Figures 13 and 14. Figure 13 is a perspective view showing the light-emitting device according to this embodiment. Figure 14 is a top view of the light-emitting device according to this embodiment.

[0074] The light-emitting device 100 according to this embodiment is a so-called VCSEL array, which is constructed by arranging a plurality of light-emitting devices 100 according to the first to third embodiments in a two-dimensional array. The cross-section along line AA' in Figure 14 roughly corresponds to the cross-sectional view in Figure 1. Each of the light-emitting parts 50 in Figure 13 corresponds to the mesa part in Figure 1. The semiconductor substrate 10 in Figure 13 corresponds to the n-type layer 20 from the semiconductor substrate 10 in Figure 1.

[0075] Figures 13 and 14 show only 12 light-emitting units 50 arranged in a 4x3 array for simplification of the drawings. However, in a typical VCSEL array, for example, 3600 VCSELs arranged in a 60x60 array are provided on the same semiconductor substrate 10. The diameter of the light-emitting unit 50 is, for example, 10 μm. The light-emitting units 50 are arranged such that the vertical and horizontal spacing between the centers of the light-emitting units 50 in a plan view is, for example, 50 μm. The chip size of the light-emitting device 100 is, for example, 3.3 mm x 3.3 mm.

[0076] Each electrode 40 corresponding to a light-emitting unit 50 is electrically connected to a common anode electrode 40C via wiring (not shown). Each electrode 42 corresponding to a light-emitting unit 50 is electrically connected to a common cathode electrode 42C. The common anode electrode 40C and the common cathode electrode 42C are common electrodes for multiple light-emitting units 50 constituting the VCSEL array. Au wires (not shown) are electrically and physically connected to the common anode electrode 40C and the common cathode electrode 42C. The current driving the light-emitting device 100 is injected from an external circuit via the common anode electrode 40C and the common cathode electrode 42C. The common anode electrode 40C and the common cathode electrode 42C have a strip-like shape with a width of, for example, 100 μm and a length of, for example, 1.5 mm.

[0077] Thus, according to this embodiment, a VCSEL array using the light-emitting device 100 of the first to third embodiments can be realized.

[0078] [Fifth Embodiment] The fifth embodiment of the light-emitting device will be described with reference to Figure 15. Components similar to those in the first to fourth embodiments of the light-emitting device will be denoted by the same reference numerals, and their descriptions will be omitted or simplified. Figure 15 is a schematic cross-sectional view showing the general configuration of the light-emitting device according to this embodiment.

[0079] In this embodiment, we will describe an example in which the light-emitting device according to the fourth embodiment is applied to a light-emitting device that emits light in the SWIR (Short Wavelength Infrared Region) band.

[0080] The light-emitting device 100 according to this embodiment further includes a VCSEL chip 160 in addition to the light-emitting device 100 according to the fourth embodiment. The VCSEL chip 160 is bonded to the light-emitting surfaces of a plurality of light-emitting units 50 that constitute the VCSEL array. The VCSEL chip 160 is a light-emitting element that oscillates using light emitted from the light-emitting units 50 as excitation light and emits light in the SWIR band.

[0081] The VCSEL chip 160 may consist of an InP substrate 162, an upper reflector 164, a resonator spacer portion 166, a lower reflector 172, and an AR (Anti-Reflection) coating 174. The upper reflector 164, the resonator spacer portion 166, and the lower reflector 172 are laminated in this order on one side of the InP substrate 162. The AR coating 174 is provided on the other side of the InP substrate 162. The VCSEL chip 160 is bonded to the light-emitting portion 50 such that the side of the lower reflector 172 faces the light-emitting portion 50.

[0082] The upper reflector 164 can be constructed, for example, by stacking seven pairs of laminates of an SiO2 layer and a TiO2 layer, each having an optical thickness of 1 / 4λc. Here, λc is the central wavelength of the high-reflection band of the upper reflector 164, and in this embodiment, it is 1550 nm. The resonator spacer portion 166 can be constructed by a pin junction consisting of an n-type layer, an undoped spacer portion, and a p-type layer. The undoped spacer portion is provided with, for example, five quantum well layers, each consisting of an InGaAs well layer 168 with a thickness of 8 nm sandwiched between InGaAsP light-absorbing layers 170 (only one layer is shown in the figure). The lower reflector 172 can be constructed, for example, by stacking multiple pairs of laminates of an InP layer and an InGaAsP layer, each having an optical thickness of 1 / 4λc. By configuring the upper reflector 164 to have a lower reflectivity than the lower reflector 172, the light oscillating between the upper reflector 164 and the lower reflector 172 is extracted to the InP substrate 162 side and emitted to the outside via the AR coating 174. The AR coating 174 serves to prevent reflection at the interface with the InP substrate 162.

[0083] The light-emitting unit 50 emits light with a wavelength of, for example, 940 nm. The light emitted from the light-emitting unit 50 passes through the lower reflector 172 and enters the resonator spacer 166, where it is absorbed by the InGaAsP light absorption layer 170. The light absorbed by the InGaAsP light absorption layer 170 generates electrons and holes, which enter the InGaAs well layer 168, and gain is generated when their density exceeds the transparent carrier density. In this way, laser oscillation occurs in the VCSEL chip 160, allowing the light-emitting device 100 to emit laser light in the 1550 nm wavelength band.

[0084] In this embodiment, the VCSEL chip 160 excited by light with a wavelength of 940 nm was a VCSEL in the 1550 nm wavelength band, but it is not limited to this. For example, the VCSEL chip 160 may be a VCSEL that emits light in a wavelength band other than the 1550 nm band, for example, in the 1900 nm wavelength band. Also, the VCSEL chip 160 may constitute a VCSEL array in which multiple VCSEL elements are arranged, or an LED chip may be provided instead of the VCSEL chip 160.

[0085] [Sixth Embodiment] A distance measuring device according to the sixth embodiment will be described with reference to Figure 16. Figure 16 is a block diagram showing the schematic configuration of the distance measuring device according to this embodiment.

[0086] The distance measuring device 200 according to this embodiment is a distance measuring device (LiDAR device) in which the light-emitting device 100 of the fourth or fifth embodiment is applied as the light source.

[0087] The distance measuring device 200 according to this embodiment may consist of a control unit 210, a surface-emitting laser array driver 212, a surface-emitting laser array 214, a light-emitting optical system 218, a light-receiving optical system 220, an image sensor 222, and a distance data processing unit 224.

[0088] The surface-emitting laser array 214 is a package-mounted light-emitting device 100 according to the fourth or fifth embodiment. The surface-emitting laser array driver 212 is a drive unit that receives a drive signal from the control unit 210, generates a drive current for oscillating the surface-emitting laser array 214, and outputs it to the surface-emitting laser array 214. As described above, the surface-emitting laser array driver 212 injects current into the active layer and does not perform electrical control to change the characteristics of the saturable absorption layer. Therefore, the surface-emitting laser array driver 212 is electrically connected to the p-type layer and n-type layer located above and below the active layer. Note that the surface-emitting laser array 214 and the surface-emitting laser array driver 212 may be a single light-emitting device.

[0089] The light-emitting optical system 218 is an optical system that emits laser light generated by the surface-emitting laser array 214 toward the range to be measured. The light-receiving optical system 220 is an optical system that guides the laser light reflected by the object to be measured 1000 to the image sensor 222. In Figure 16, the light-emitting optical system 218 and the light-receiving optical system 220 are represented by a single convex lens-shaped component, but these are not composed of only a single convex lens-shaped component, but are composed of a lens group made up of multiple lenses.

[0090] The image sensor 222 is a photoelectric conversion device in which multiple pixels, including a photoelectric conversion unit, are arranged in a two-dimensional array, and is a light receiving device that outputs an electrical signal corresponding to the incident light. The image sensor 222 may be an imaging device such as a CMOS image sensor. The distance data processing unit 224 functions as a distance information acquisition unit that generates and outputs information regarding the distance to the object to be measured 1000 located within the distance measurement target range, based on the signal from the image sensor 222. The distance data processing unit 224 only needs to be electrically connected to the image sensor 222, and may be located in the same package as the image sensor 222, or in a separate package from the image sensor 222.

[0091] The control unit 210 is composed of an information processing device including a microcomputer and logic circuits, and functions as a central processing unit that controls the operation of the distance measuring device 200, including the operation control of each part and various calculation processing.

[0092] As mentioned above, a suitable light-emitting device for a LiDAR system is one that can generate light pulses with a short pulse width and high peak value. Specifically, the ideal light pulse width for a light source suitable for a LiDAR system is, for example, in the range of 50 ps to 1 ns. On the other hand, from the electrical standpoint of the VCSEL and the VCSEL driver, it is not easy to emit light with such a short pulse width. Since the VCSEL emits light in response to the amount of current injected, in order to make the light pulse about 50 ps to 1 ns, the current pulse driving the VCSEL must be of a similar magnitude. In other words, the circuit from the driver to the VCSEL needs to have excellent electrical characteristics in the high-frequency band, such as 1 GHz or 10 GHz, and to handle currents exceeding 1 A. This presents the challenge of higher costs compared to configuring the electrical transmission section to the driver and VCSEL using only electrical circuits that handle lower frequency bands.

[0093] Therefore, in this embodiment, by using the light-emitting device 100 described in the fourth or fifth embodiment as the surface-emitting laser array 214, the VCSEL itself is configured to generate short pulses. This avoids increasing the cost of the driver unit and electrical transmission unit while achieving optical pulses of approximately 50 ps to 1 ns, which are desirable for LiDAR systems.

[0094] Next, the operation of the distance measuring device according to this embodiment will be explained with reference to Figure 16. First, the control unit 210 outputs a drive signal to the surface-emitting laser array driver 212. The surface-emitting laser array driver 212 receives the drive signal from the control unit 210 and injects a current of a predetermined value into the surface-emitting laser array 214. As a result, the surface-emitting laser array 214 oscillates and laser light is output from the surface-emitting laser array 214. At this time, the pulse width of the light emitted from the surface-emitting laser array 214 is narrower than the pulse width of the injected current, as described above.

[0095] The laser light generated by the surface-emitting laser array 214 is emitted by the light-emitting optical system 218 toward the distance measurement target area. Of the laser light irradiated onto the object to be measured 1000 within the distance measurement target area, the laser light reflected by the object to be measured 1000 and incident on the light-receiving optical system 220 is guided by the light-receiving optical system 220 to the image sensor 222.

[0096] Each pixel of the image sensor 222 generates an electrical signal pulse corresponding to the timing of the incident laser light. The electrical signal pulses generated by the image sensor 222 are input to the distance data processing unit 224.

[0097] The distance data processing unit 224 generates distance information to the object 1000 along the direction of light propagation based on the reception timing of the electrical signal pulses output from the image sensor 222. By calculating distance information based on the electrical signal pulses output from each pixel of the image sensor 222, three-dimensional information of the object 1000 can be obtained.

[0098] Thus, according to this embodiment, a high-performance distance measuring device equipped with a light-emitting device capable of generating light pulses with a short light pulse width and high peak value can be realized.

[0099] The distance measuring device 200 of this embodiment can be applied, for example, to control devices in the automotive field to prevent collisions with other vehicles, or to control devices for automatic driving that follows other vehicles. Furthermore, the distance measuring device 200 of this embodiment can be applied not only to automobiles, but also to other moving objects (mobile devices) such as ships, aircraft, or industrial robots, as well as to moving object detection systems. The distance measuring device 200 of this embodiment can be widely applied to devices that utilize information about objects recognized three-dimensionally, including distance information. These moving objects may be configured to include the distance measuring device of this embodiment and control means for controlling the moving object based on distance information acquired by the distance measuring device.

[0100] Furthermore, the three-dimensional information, including depth, obtainable by the distance measuring device 200 of this embodiment can also be used in image capture devices, image processing devices, display devices, etc. For example, it is possible to use the three-dimensional information obtained by the distance measuring device 200 of this embodiment to display a virtual object on top of a real-world image without any sense of incongruity. In addition, by saving the three-dimensional information together with the image information, it is possible to correct the blur of the captured image after shooting.

[0101] [Seventh Embodiment] The distance measuring device according to the seventh embodiment will be described with reference to Figures 17 and 18. Figure 17 is a block diagram showing the schematic configuration of the distance measuring device according to this embodiment. Figure 18 is a schematic cross-sectional view showing an example of the configuration of the surface-emitting laser array in the distance measuring device according to this embodiment. Components similar to those in the distance measuring device according to the sixth embodiment are denoted by the same reference numerals, and their descriptions are omitted or simplified.

[0102] The distance measuring device 200 according to this embodiment differs from the distance measuring device according to the sixth embodiment in that the surface-emitting laser array 214 further includes a light emission timing monitor unit 216, as shown in Figure 17. Other aspects of the distance measuring device 200 according to this embodiment are the same as those of the distance measuring device according to the sixth embodiment.

[0103] The surface-emitting laser array 214 includes, for example, a light-emitting device 100, a light-emitting timing monitor unit 216, a base 110, and a window material 120, as shown in Figure 18. The base 110 is part of a package on which the light-emitting device 100 and the light-emitting timing monitor unit 216 are mounted, and has recesses for housing the light-emitting device 100 and the light-emitting timing monitor unit 216. The base 110 may be made of, for example, ceramic. The window material 120 is fixed to the base 110 so as to close the recesses of the base 110 on which the light-emitting device 100 and the light-emitting timing monitor unit 216 are mounted. The light-emitting device 100 is a light-emitting device 100 according to the fourth embodiment. The light-emitting timing monitor unit 216 is made of, for example, a semiconductor substrate having a square shape of 0.3 mm square, and has, for example, a photodiode with a light-receiving area diameter of 100 μm as a light-receiving element.

[0104] The common anode electrode 40C and common cathode electrode 42C of the light-emitting device 100, and the anode and cathode of the photodiodes constituting the light emission timing monitor unit 216 are electrically connected to electrodes (not shown) provided on the outer circumference of the base 110. The pulse current supplied from the surface-emitting laser array driver 212 is supplied to the light-emitting device 100 via the electrodes provided on the base 110. In addition, the electrical signal generated by the light emission timing monitor unit 216 is supplied to the distance data processing unit 224 via the electrodes provided on the base 110.

[0105] Next, the operation of the distance measuring device according to this embodiment will be explained using Figures 17 and 18. First, the control unit 210 outputs a drive signal to the surface-emitting laser array driver 212. The surface-emitting laser array driver 212 receives the drive signal from the control unit 210 and injects a current of a predetermined value into the light-emitting device 100 of the surface-emitting laser array 214. As a result, the light-emitting device 100 oscillates and laser light is output from the light-emitting device 100. At this time, the pulse width of the light emitted from the light-emitting device 100 is narrower than the pulse width of the injected current, as described above.

[0106] The laser light generated by the light-emitting device 100 is emitted from the surface-emitting laser array 214 through the window material 120 and directed towards the range measurement target area by the light-emitting optical system 218. At this time, although the window material 120 is coated with AR, some of the light is reflected by the window material 120 and incident on the light emission timing monitor unit 216.

[0107] The light emission timing monitor unit 216 converts the incident light into an electrical signal and outputs it to the distance data processing unit 224. The distance data processing unit 224 generates information regarding the distance to the object to be measured 1000 along the direction of light propagation, based on the time difference between the timing of receiving the electrical signal pulse from the image sensor 222 and the timing of receiving the electrical signal from the light emission timing monitor unit 216. Then, by calculating distance information based on the electrical signal pulse output from each pixel of the image sensor 222, it acquires three-dimensional information of the object to be measured 1000.

[0108] In a LiDAR system, the distance to the object is calculated based on the time difference between the emission of laser light and its reflection back from the object. Therefore, to improve the distance measurement accuracy, it is necessary to know with higher precision the timing at which the emission pulse is generated in the light-emitting device 100. For example, if the time detection accuracy of the light-receiving side is about 50 ps, ​​it is preferable that the accuracy of the information on the timing of pulse generation on the light-emitting side is less than 50 ps.

[0109] In this regard, the distance measuring device 200 of this embodiment detects the emission timing of the surface-emitting laser array 214 using the emission timing monitor unit 216. The distance information is then calculated using the emission timing detected by the emission timing monitor unit 216. Therefore, even if the emission timing of the surface-emitting laser array 214 is shifted due to factors such as ambient temperature, the distance measuring accuracy of the distance measuring device 200 is not affected, and high distance measuring accuracy can be maintained.

[0110] Thus, according to this embodiment, in a distance measuring device that uses light pulses with high peak values ​​and short pulses, the influence of changes in ambient temperature on distance measuring accuracy can be further reduced.

[0111] [Eighth Embodiment] The equipment and mobile body according to the eighth embodiment will be described with reference to Figures 19A and 19B. Figure 19A is a block diagram showing an example configuration of the equipment according to this embodiment. Figure 19B is a block diagram showing an example configuration of the mobile body according to this embodiment.

[0112] Figure 19A shows an example of the configuration of equipment mounted on a vehicle as an in-vehicle camera. Equipment 300 includes a distance measuring unit 303 that measures the distance to an object to be measured, and a collision determination unit 304 that determines whether or not there is a possibility of collision based on the distance measured by the distance measuring unit 303. The distance measuring unit 303 may be configured, for example, by the distance measuring device 200 described in the sixth or seventh embodiment. Here, the distance measuring unit 303 is an example of distance information acquisition means that acquires distance information to an object to be measured. That is, distance information is information related to the distance to an object to be measured, etc.

[0113] Device 300 is connected to a vehicle information acquisition device 310 and can acquire vehicle information such as vehicle speed, yaw rate, and steering angle. Device 300 is also connected to a control ECU 320, which is a control device that outputs a control signal to generate braking force on the vehicle based on the collision determination result from the collision determination unit 304. Furthermore, device 300 is also connected to a warning device 330 that issues a warning to the driver based on the collision determination result from the collision determination unit 304. For example, if the collision determination result from the collision determination unit 304 indicates a high probability of collision, the control ECU 320 performs vehicle control to avoid a collision or mitigate damage by applying the brakes, releasing the accelerator, or suppressing engine output. The warning device 330 warns the user by sounding an alarm, displaying warning information on a screen such as a car navigation system, or vibrating the seatbelt or steering wheel. These devices of device 300 function as a mobile control unit that controls the vehicle's operations as described above.

[0114] In this embodiment, the device 300 measures the distance around the vehicle, for example, in front of or behind it. Figure 19B shows the device when measuring the distance in front of the vehicle (distance measurement range 350). The vehicle information acquisition device 310, acting as a distance measurement control means, sends an instruction to the device 300 or the distance measurement unit 303 to perform the distance measurement operation. This configuration allows for further improvement of the accuracy of distance measurement.

[0115] In this embodiment, an example of control to prevent collision with other vehicles has been described, but it can also be applied to control that follows other vehicles automatically, or control that prevents the vehicle from straying from its lane, etc. Furthermore, the device is not limited to vehicles such as automobiles, but can be applied to mobile objects (mobile devices) such as ships, aircraft, satellites, industrial robots, and consumer robots. In addition, it is not limited to mobile objects, but can be applied to a wide range of devices that utilize object recognition or biometric recognition, such as intelligent transportation systems (ITS) and surveillance systems.

[0116] [Modified Embodiment] This disclosure is not limited to the embodiments described above and can be modified in various ways. For example, an example in which some configurations of one embodiment are added to another embodiment, or in which some configurations of another embodiment are replaced, is also an embodiment of the present disclosure.

[0117] Furthermore, in the first to third embodiments described above, GaAs, AlGaAs, and InGaAs were given as examples of semiconductor materials capable of crystal growth when a GaAs substrate is used as the semiconductor substrate 10, but the semiconductor substrate 10 is not limited to a GaAs substrate. For example, an InP substrate can also be used as the semiconductor substrate 10. Examples of semiconductor materials capable of crystal growth when an InP substrate is used as the semiconductor substrate 10 include InP, InGaAs, InGaP, InGaAsP, and so on.

[0118] Furthermore, the DBR layer in the light-emitting device according to the first to third embodiments described above does not necessarily have to be made of a semiconductor material; it may be made of a material other than a semiconductor material. In this case as well, by configuring it to perform the same functions as in the first to third embodiments, the same effects as in these embodiments can be achieved.

[0119] Furthermore, the embodiments described above are merely examples of concrete implementations in carrying out this disclosure, and the technical scope of this disclosure should not be interpreted as being limited by them. In other words, this disclosure can be implemented in various ways without departing from its technical concept or its main features.

[0120] The above-disclosed embodiment includes the following configuration. (Composition 1) A resonator is placed on a semiconductor substrate and includes a first reflector and a second reflector, The device has a resonator spacer portion disposed between the first reflector and the second reflector, which includes an active layer and a saturable absorption layer, The first reflector, the resonator spacer, and the second reflector are stacked on the semiconductor substrate in this order. The active layer has an asymmetric quantum well structure that includes multiple types of quantum wells with different wavelengths corresponding to the band gap. The gain peak wavelength of the active layer is shorter than the laser oscillation wavelength of the resonator. A light-emitting device characterized by the following features. (Configuration 2) A resonator is placed on a semiconductor substrate and includes a first reflector and a second reflector, The device has a resonator spacer portion disposed between the first reflector and the second reflector, which includes an active layer and a saturable absorption layer, The first reflector, the resonator spacer, and the second reflector are stacked on the semiconductor substrate in this order. The active layer has an asymmetric quantum well structure that includes multiple types of quantum wells with different wavelengths corresponding to the band gap. The gain peak wavelength of the active layer is set such that the gain of the active layer at the laser oscillation wavelength of the resonator is a first value at a first temperature and a second value greater than the first value at a second temperature higher than the first temperature. A light-emitting device characterized by the following features. (Composition 3) The first temperature is room temperature, and the second temperature is the ambient temperature during operation. The light-emitting device according to configuration 2, characterized in that it is a light-emitting device. (Composition 4) The gain peak wavelength is shorter than the laser oscillation wavelength. A light-emitting device according to configuration 2 or 3, characterized by the above. (Composition 5) The active layer includes a quantum well whose band gap wavelength is shorter than the laser oscillation wavelength. A light-emitting device according to any one of configurations 1 to 4, characterized by the above. (Composition 6) The saturable absorption layer includes a quantum well whose band gap wavelength is the same as the laser oscillation wavelength. A light-emitting device according to any one of configurations 1 to 5, characterized by the above. (Composition 7) The saturable absorption layer includes a quantum well whose band gap wavelength is longer than the laser oscillation wavelength. A light-emitting device according to any one of configurations 1 to 5, characterized by the above. (Composition 8) The ratio of the number of quantum wells in the saturable absorption layer to the number of quantum wells in the active layer is in the range of 1:1 to 1:3. The light-emitting device according to claim 6 or 7, characterized in that it is as described above. (Composition 9) The asymmetric quantum well structure includes a first quantum well whose wavelength corresponding to the band gap is a first wavelength, and a second quantum well whose wavelength corresponding to the band gap is a second wavelength, wherein the difference between the first wavelength and the second wavelength is 5 nm or more. A light-emitting device according to any one of configurations 1 to 8, characterized by the above. (Composition 10) A resonator is placed on a semiconductor substrate and includes a first reflector and a second reflector, The device has a resonator spacer portion disposed between the first reflector and the second reflector, which includes an active layer and a saturable absorption layer, The first reflector, the resonator spacer, and the second reflector are stacked on the semiconductor substrate in this order. The gain peak wavelength of the active layer is shorter than the laser oscillation wavelength of the resonator. The saturable absorption layer includes a quantum well whose band gap wavelength is longer than the laser oscillation wavelength. A light-emitting device characterized by the following features. (Composition 11) A resonator is placed on a semiconductor substrate and includes a first reflector and a second reflector, The device has a resonator spacer portion disposed between the first reflector and the second reflector, which includes an active layer and a saturable absorption layer, The first reflector, the resonator spacer, and the second reflector are stacked on the semiconductor substrate in this order. The gain peak wavelength of the active layer is set such that the gain of the active layer at the laser oscillation wavelength of the resonator is a first value at a first temperature and a second value greater than the first value at a second temperature higher than the first temperature. The saturable absorption layer includes a quantum well whose band gap wavelength is longer than the laser oscillation wavelength. A light-emitting device characterized by the following features. (Composition 12) The first temperature is room temperature, and the second temperature is the ambient temperature during operation. The light-emitting device according to configuration 11, characterized by the features described above. (Composition 13) The gain peak wavelength is shorter than the laser oscillation wavelength. A light-emitting device according to configuration 11 or 12, characterized by the above. (Composition 14) The active layer includes a quantum well whose band gap wavelength is shorter than the laser oscillation wavelength. A light-emitting device according to any one of configurations 10 to 13, characterized by the above. (Composition 15) The active layer has an asymmetric quantum well structure that includes multiple types of quantum wells with different wavelengths corresponding to the band gap. A light-emitting device according to any one of configurations 10 to 14, characterized by the above. (Composition 16) The asymmetric quantum well structure includes a first quantum well whose wavelength corresponding to the band gap is a first wavelength, and a second quantum well whose wavelength corresponding to the band gap is a second wavelength, wherein the difference between the first wavelength and the second wavelength is 5 nm or more. The light-emitting device according to configuration 15, characterized by the above. (Composition 17) The ratio of the number of quantum wells in the saturable absorption layer to the number of quantum wells in the active layer is in the range of 1:1 to 1:3. A light-emitting device according to any one of configurations 10 to 16, characterized in that (Composition 18) The system has a plurality of light-emitting parts, each including the resonator, the resonator spacer, and the saturable absorption layer. A light-emitting device according to any one of configurations 1 to 17, characterized by the above. (Composition 19) The second resonator includes a third reflector and a fourth reflector, and the second resonator spacer portion includes a second active layer disposed between the third reflector and the fourth reflector. The second resonator emits light of a different wavelength from the laser oscillation wavelength excited in the second active layer by the laser oscillation wavelength. A light-emitting device according to any one of configurations 1 to 18, characterized by the above. (Composition 20) The first and second reflectors are distributed Bragg reflectors. A light-emitting device according to any one of configurations 1 to 19, characterized by the above. (Composition 21) A light-emitting device according to any one of configurations 1 to 20, A light receiving device that receives light emitted from the light-emitting device and reflected by the object to be measured, A distance information acquisition unit acquires information regarding the distance to the object to be measured based on the time difference between the timing at which light is emitted from the light-emitting device and the timing at which the light-receiving device receives the light. A distance measuring device characterized by having the following features. (Composition 22) It is mounted in the same package as the aforementioned light-emitting device and further comprises a light-receiving element that receives light emitted from the aforementioned light-emitting device, The light-receiving element detects the timing at which light is emitted from the light-emitting device. The distance measuring device according to configuration 21, characterized in that... (Composition 23) It is a mobile object, A distance measuring device as described in configuration 21 or 22, Control means for controlling the moving body based on the distance information acquired by the distance measuring device. A mobile body characterized by having the following features. [Explanation of symbols]

[0121] 10… Semiconductor substrates 12...Lower DBR layer 16…Saturable absorption layer 24…Active layer 28...Top DBR layer

Claims

1. A resonator is placed on a semiconductor substrate and includes a first reflector and a second reflector, The first reflector and the second reflector are disposed between the two, and the resonator spacer portion includes an active layer and a saturable absorption layer, The first reflector, the resonator spacer, and the second reflector are stacked on the semiconductor substrate in this order. The active layer has an asymmetric quantum well structure that includes multiple types of quantum wells with different wavelengths corresponding to the band gap. The gain peak wavelength of the active layer is shorter than the laser oscillation wavelength of the resonator. A light-emitting device characterized by the following features.

2. A resonator is placed on a semiconductor substrate and includes a first reflector and a second reflector, The first reflector and the second reflector are disposed between the two, and the resonator spacer portion includes an active layer and a saturable absorption layer, The first reflector, the resonator spacer, and the second reflector are stacked on the semiconductor substrate in this order. The active layer has an asymmetric quantum well structure that includes multiple types of quantum wells with different wavelengths corresponding to the band gap. The gain peak wavelength of the active layer is set such that the gain of the active layer at the laser oscillation wavelength of the resonator is a first value at a first temperature, and a second value greater than the first value at a second temperature higher than the first temperature. A light-emitting device characterized by the following features.

3. The first temperature is room temperature, and the second temperature is the ambient temperature during operation. The light-emitting device according to feature 2.

4. The gain peak wavelength is shorter than the laser oscillation wavelength. The light-emitting device according to feature 2.

5. The active layer includes a quantum well whose band gap wavelength is shorter than the laser oscillation wavelength. The light-emitting device according to any one of claims 1 to 4.

6. The saturable absorption layer includes a quantum well whose band gap wavelength is the same as the laser oscillation wavelength. The light-emitting device according to any one of claims 1 to 4.

7. The saturable absorption layer includes a quantum well whose band gap wavelength is longer than the laser oscillation wavelength. The light-emitting device according to any one of claims 1 to 4.

8. The ratio of the number of quantum wells in the saturable absorption layer to the number of quantum wells in the active layer is in the range of 1:1 to 1:

3. The light-emitting device according to claim 6, characterized by the features described above.

9. The asymmetric quantum well structure includes a first quantum well whose wavelength corresponding to the band gap is a first wavelength, and a second quantum well whose wavelength corresponding to the band gap is a second wavelength, wherein the difference between the first wavelength and the second wavelength is 5 nm or more. The light-emitting device according to any one of claims 1 to 4.

10. The asymmetric quantum well structure includes a quantum well with a short wavelength corresponding to the band gap and a quantum well with a long wavelength corresponding to the band gap, The number of short-wavelength quantum wells corresponding to the band gap is equal to or greater than the number of long-wavelength quantum wells corresponding to the band gap. The light-emitting device according to any one of claims 1 to 4.

11. A resonator is placed on a semiconductor substrate and includes a first reflector and a second reflector, The first reflector and the second reflector are disposed between the two, and the resonator spacer portion includes an active layer and a saturable absorption layer, The first reflector, the resonator spacer, and the second reflector are stacked on the semiconductor substrate in this order. The gain peak wavelength of the active layer is shorter than the laser oscillation wavelength of the resonator. The saturable absorption layer includes a quantum well whose band gap wavelength is longer than the laser oscillation wavelength. A light-emitting device characterized by the following features.

12. A resonator is placed on a semiconductor substrate and includes a first reflector and a second reflector, The first reflector and the second reflector are disposed between the two, and the resonator spacer portion includes an active layer and a saturable absorption layer, The first reflector, the resonator spacer, and the second reflector are stacked on the semiconductor substrate in this order. The gain peak wavelength of the active layer is set such that the gain of the active layer at the laser oscillation wavelength of the resonator is a first value at a first temperature and a second value greater than the first value at a second temperature higher than the first temperature. The saturable absorption layer includes a quantum well whose band gap wavelength is longer than the laser oscillation wavelength. A light-emitting device characterized by the following features.

13. The first temperature is room temperature, and the second temperature is the ambient temperature during operation. The light-emitting device according to feature 12.

14. The gain peak wavelength is shorter than the laser oscillation wavelength. The light-emitting device according to feature 12.

15. The active layer includes a quantum well whose band gap wavelength is shorter than the laser oscillation wavelength. The light-emitting device according to any one of claims 11 to 14.

16. The active layer has an asymmetric quantum well structure that includes multiple types of quantum wells with different wavelengths corresponding to the band gap. The light-emitting device according to any one of claims 11 to 14.

17. The asymmetric quantum well structure includes a first quantum well whose wavelength corresponding to the band gap is a first wavelength, and a second quantum well whose wavelength corresponding to the band gap is a second wavelength, wherein the difference between the first wavelength and the second wavelength is 5 nm or more. The light-emitting device according to claim 16, characterized in that it is a light-emitting device.

18. The ratio of the number of quantum wells in the saturable absorption layer to the number of quantum wells in the active layer is in the range of 1:1 to 1:

3. The light-emitting device according to any one of claims 11 to 14.

19. The saturable absorption layer has a wavelength corresponding to the band gap that is 14 nm to 48 nm shorter than the laser oscillation wavelength. The ratio of the number of quantum wells in the saturable absorption layer to the number of quantum wells in the active layer is in the range of 1:1 to 1:

3. The light-emitting device according to any one of claims 11 to 14.

20. The system has a plurality of light-emitting parts, each including the resonator, the resonator spacer, and the saturable absorption layer. The light-emitting device according to any one of claims 1 to 4 and 11 to 14.

21. The device further comprises a second resonator including a third reflector and a fourth reflector, and a second resonator spacer portion including a second active layer disposed between the third reflector and the fourth reflector. The second resonator emits light of a different wavelength from the laser oscillation wavelength excited in the second active layer by the laser oscillation wavelength. The light-emitting device according to any one of claims 1 to 4 and 11 to 14.

22. The first and second reflectors are distributed Bragg reflectors. The light-emitting device according to any one of claims 1 to 4 and 11 to 14.

23. A light-emitting device according to any one of claims 1 to 4 and 11 to 14, A light receiving device that receives light emitted from the light-emitting device and reflected by the object to be measured, A distance information acquisition unit acquires information regarding the distance to the object to be measured based on the time difference between the timing at which light is emitted from the light-emitting device and the timing at which the light-receiving device receives the light. A distance measuring device characterized by having the following features.

24. It is mounted in the same package as the aforementioned light-emitting device and further comprises a light-receiving element that receives light emitted from the aforementioned light-emitting device, The light-receiving element detects the timing at which light is emitted from the light-emitting device. The distance measuring device according to feature 23.

25. It is a mobile object, The distance measuring device according to claim 23, Control means for controlling the moving body based on the distance information acquired by the distance measuring device. A mobile body characterized by having the following features.

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