JP7683464B2 - Optical device, distance measuring device and moving object - Google Patents

Description

This application relates to an optical device, a distance measuring device, and a moving object.

Tunable wavelength lasers have been known for use as light sources in devices such as FMCW-LiDAR (Frequency-Modulated Continuous Wave Light Detection and Ranging).

Also disclosed is a configuration that includes an optical resonator including first and second mirrors, a gain region interposed between the first and second mirrors, and an electrostatically driven MEMS (Micro Electro Mechanical Systems) driving mechanism, and that adjusts the gap between the first and second mirrors using the MEMS driving mechanism (see, for example, Patent Document 1).

However, the configuration of Patent Document 1 leaves room for improvement in changing the wavelength of the laser light quickly and over a wide wavelength range.

The objective of the present invention is to change the wavelength of laser light quickly and over a wide wavelength range.

An optical device according to one aspect of the present invention is an optical device that emits laser light, and includes a light emitting unit, a first reflecting unit and a second reflecting unit that face each other across the light emitting unit, a base that holds the second reflecting unit with a gap between the light emitting unit and the second reflecting unit, and a piezoelectric member that deforms in response to an applied drive voltage, the base including a first region and a second region that is less rigid than the first region, the second reflecting unit and the piezoelectric member being provided in the second region, the piezoelectric member deforming the second region in response to application of the drive voltage to drive the second reflecting unit, and emitting laser light whose wavelength changes in response to the distance between the first reflecting unit and the second reflecting unit.

The present invention makes it possible to change the wavelength of laser light quickly and over a wide wavelength range.

1A and 1B are diagrams showing an example of the configuration of a light source device according to a first embodiment, in which (a) is a plan view and (b) is a cross-sectional view taken along the line AA' in (a). FIG. 4 is an enlarged cross-sectional view showing an example of the configuration around the base portion. FIG. 1 is a cross-sectional view showing a configuration example of a VCSEL element. 5A and 5B are diagrams showing an example of the operation of the second region, in which FIG. 5A shows the generation of stress, and FIG. 5B shows the deformation of the second region. 10A and 10B are diagrams showing another example of the operation of the second region, in which FIG. 10A shows the generation of stress, and FIG. 10B shows the deformation of the second region. FIG. 11 is a diagram illustrating an example of vibration of a second region. 11 is a diagram illustrating an example of the relationship between the drive voltage and the displacement amount of a second reflecting portion. FIG. 11 is a diagram showing an example of the relationship between the distance between reflecting portions and the wavelength. 5 is a diagram showing the relationship between the drive voltage of a piezoelectric element and the wavelength of laser light emitted from a light source device. 5A and 5B are enlarged cross-sectional views showing modified examples of the configuration around the second region, in which FIG. 5A is a view of a first example, and FIG. 5B is a view of a second example. FIG. 13 is a plan view showing a first modified example of the base portion. 12 is a cross-sectional view taken along line AA' of FIG. FIG. 13 is a plan view showing a second modified example of the base portion. 14 is a cross-sectional view taken along the line BB' of FIG. 13. FIG. 13 is a plan view showing a third modified example of the base portion. 16 is a cross-sectional view taken along the line CC' of FIG. 15. FIG. 13 is a plan view showing an example of the configuration of a light source device according to a second embodiment. FIG. 13 is a plan view showing an example of the configuration of a light source device according to a third embodiment. FIG. 13 is a block diagram showing an example of the configuration of a laser radar device according to a fourth embodiment. 11 is a diagram showing an example of the relationship between the driving voltage and the displacement amount of a reflecting portion of a light source device according to a comparative example. FIG. 13 is a diagram showing an automobile as an example of a moving body according to a fifth embodiment.

Below, a description will be given of an embodiment of the invention with reference to the drawings. In each drawing, the same components are given the same reference numerals, and duplicate descriptions will be omitted as appropriate.

The embodiments shown below are illustrative of optical devices for embodying the technical ideas of the present invention, and are not intended to limit the present invention to the embodiments shown below. Unless otherwise specified, the shapes of the components described below, their relative positions, parameter values, etc. are intended to be illustrative and not to limit the scope of the present invention. Furthermore, the sizes and positional relationships of the components shown in the drawings may be exaggerated to make the explanation clearer.

The optical device according to the embodiment has a light-emitting section, a first reflecting section and a second reflecting section that face each other across the light-emitting section, a base that holds the second reflecting section with a gap between the light-emitting section and the second reflecting section, and a piezoelectric member that deforms in response to an applied drive voltage, and the base includes a first region and a second region that is less rigid than the first region, and the second reflecting section and the piezoelectric member are provided in the second region.

The distance between the first and second reflecting sections, which sandwich the light emitting section, corresponds to the resonator length. When a drive voltage is applied, the piezoelectric member deforms the second region to drive the second reflecting section, and the optical device emits laser light whose wavelength changes depending on the distance between the first and second reflecting sections.

For example, in a method in which the resonator length is changed by electrostatically driving a movable part, the driving of the movable part at high speed and with a large amount of displacement is limited due to limitations on the resonant frequency or spring constant of the movable part. Therefore, there is room for improvement in changing the wavelength of the laser light at high speed and over a wide wavelength range.

In the embodiment, the thin second region is deformed by a piezoelectric member, thereby driving the second reflector with a large amount of displacement at high speed, thereby changing the resonator length. This makes it possible to change the wavelength of the laser light at high speed and over a wide wavelength range.

In the following, an embodiment will be described in which a light source device that emits laser light of multiple wavelengths in parallel is taken as an example of an optical device. In the figures shown below, a specific direction in a plane parallel to the reflecting surface of the first reflecting unit is taken as the X-axis direction, a direction perpendicular to the X-axis in a plane parallel to the reflecting surface of the first reflecting unit is taken as the Y-axis direction, and a direction perpendicular to both the X-axis and the Y-axis is taken as the Z-axis direction. The light source device emits laser light along the Z-axis direction.

However, these axes are for convenience of explanation, and there are no particular restrictions on the orientation of the optical device, so the optical device can be used in any orientation.

[First embodiment]
The light source device according to the first embodiment will be described.

<Configuration example of light source device 1>
(Overall configuration example)
First, the overall configuration of a light source device 1 will be described with reference to FIG.

Figure 1 is a diagram illustrating an example of the overall configuration of a light source device 1. Figure 1(a) is a plan view, and Figure 1(b) is a cross-sectional view taken along the A-A' cutting line in Figure 1(a). As shown in Figure 1, the light source device 1 has a base 10, a joint 13, and a VCSEL (Vertical Cavity Surface Emitting LASER) element 20.

The base 10 is a plate-like member having a first region 11 and a second region 12, and formed in a quadrangular shape in a planar view. The second region 12 is a region that is approximately circular in a planar view and is provided near the center of the base 10, and functions as a movable part. The second region 12 is formed to be thinner (length in the Z-axis direction) than the first region 11. The first region 11 corresponds to the region of the base 10 other than the second region, and functions as a support part.

The second region 12 includes a second reflecting section 121 and a piezoelectric element 122 on the surface on the negative Z-axis side. The surface on the Z-axis side of the second region 12 faces the light-emitting section 211 described below, and therefore corresponds to the surface of the second region that faces the light-emitting section 211.

The second reflecting portion 121 is formed near the center of the second region 12 and is a component that is approximately circular in plan view. The piezoelectric element 122 is an example of a piezoelectric member provided around the second reflecting portion 121. The piezoelectric element 122 is provided in a circular ring shape around the second reflecting portion 121. Note that the piezoelectric element 122 does not necessarily have to be in a circular ring shape as long as it is provided around the second reflecting portion 121.

The piezoelectric element 122 deforms (e.g. expands and contracts) in response to a drive voltage applied via the electrodes. The second region 12 elastically deforms in response to the deformation of the piezoelectric element 122, allowing the second reflecting portion 121 to be displaced in the Z-axis direction.

The light source device 1 has the VCSEL element 20 disposed on the negative Z-axis side of the base 10 with a joint 13 interposed therebetween. The joint 13 bonds and fixes the base 10 and the VCSEL element 20 together by atomic diffusion bonding or the like.

The VCSEL element 20 includes a mesa 21 and a first reflector 22. The mesa 21 is an island-shaped structure that includes a light-emitting portion 211. The VCSEL element 20 has the first reflector 22 disposed on the opposite side of the light-emitting portion 211 from the second reflector 121 (the negative Z-axis direction side).

The light-emitting unit 211 emits light by a current injected through the electrode. The first reflecting unit 22 and the second reflecting unit 121 form a resonator via the light-emitting unit 211, and the light emitted by each light-emitting unit 211 is reflected by the first reflecting unit 22 and the second reflecting unit 121, and is amplified as it travels back and forth between the first reflecting unit 22 and the second reflecting unit 121.

More specifically, the light emitted by the light-emitting unit 211 is reflected by both the reflecting surface 22A of the first reflecting unit 22 and the reflecting surface 121A of the second reflecting unit 121, and is amplified as it travels back and forth between the reflecting surface 22A and the reflecting surface 121A.

The amplified light oscillates as laser light when the gain and loss are balanced, and the light emitting unit 211 can emit laser light. The light source device 1 emits laser light from either the second reflecting unit 121 or the first reflecting unit 22, whichever has the lower reflectance. When the reflectance of the second reflecting unit 121 is low, the light source device 1 emits laser light from the emission direction 31 side in FIG. 1(b), and when the reflectance of the first reflecting unit 22 is low, the light source device 1 emits laser light from the emission direction 32 side in FIG. 1(b).

When a drive voltage is applied to the piezoelectric element 122, the second reflecting portion 121 is displaced in the Z-axis direction in response to the elastic deformation of the second region 12. This changes the distance between the first reflecting portion 22 and the second reflecting portion 121, and the resonator length changes. The light emitting portion 211 can emit laser light whose wavelength changes in response to the change in the resonator length.

(Configuration example of base 10)
Next, the configuration around the base 10 will be described with reference to Fig. 2. Fig. 2 is an enlarged cross-sectional view illustrating an example of the configuration around the base 10.

The base 10 is manufactured by processing a single SOI (Silicon On Insulator) substrate through etching or other processes, and then forming the second reflecting portion 121 and the piezoelectric element 122 on the processed substrate.

As shown in FIG. 2, the first region 11 is composed of a support layer 111, an oxide insulating layer 112, a silicon active layer 113, etc. The member constituting the second region 12 may be composed of only the silicon active layer 113 by etching away the support layer 111 and the oxide insulating layer 112 from the SOI substrate, or may be composed of the silicon active layer, the oxide insulating layer, and the support layer.

The second region 12 has a smaller thickness in the Z-axis direction compared to its length in the X-axis or Y-axis direction, and therefore has low rigidity and elasticity in the Z-axis direction. The second region 12 is movable due to deformation of the piezoelectric element 122. The first region 11 has a higher rigidity than the second region 12, so even if the piezoelectric element 122 deforms, the deformation of the first region 11 is small, and the second region 12 can be supported.

The second reflecting portion 121 is provided on the surface of the first region 11 on the negative side of the Z axis. The second reflecting portion 121 includes a configuration having the reflectance required for laser oscillation, such as a multilayer mirror or a metal thin film formed on the member constituting the second region 12, in which two or more types of thin films having a refractive index difference are alternately stacked, or an HCG (High Contrast Grating) in which a periodic structure with a thickness equivalent to the wavelength is formed on the member constituting the second region 12.

The piezoelectric element 122 is formed by stacking a lower electrode 122A, a piezoelectric portion 122B, and an upper electrode 122C on the second region 12. A protective film 122D is provided on the upper electrode 122C to protect the piezoelectric element 122.

The upper electrode 122C and the lower electrode 122A are made of gold (Au), platinum (Pt), or the like. The piezoelectric portion 122B is made of, for example, a piezoelectric material such as lead zirconate titanate (PZT) or aluminum nitride (AlN). In order to prevent short circuits between the piezoelectric elements 122, an insulating layer may be formed between the piezoelectric elements. When a positive or negative voltage is applied in the polarization direction, the piezoelectric portion 122B undergoes deformation (e.g., expansion and contraction) proportional to the potential of the applied voltage, thereby exerting the so-called inverse piezoelectric effect.

The joint 13 is formed by laminating an adhesive layer, a diffusion prevention layer, and a bonding layer along the positive to negative direction of the Z axis. Titanium (Ti) can be used for the bonding layer, platinum (Pt) for the diffusion prevention layer, and gold (Au) or aluminum oxide (Al ₂ O) can be used for the adhesive layer.

The planar shape of the second region 12 is not limited to a circular shape, and may be a square, triangular, elliptical, asymmetrical, or the like. The second reflecting portion 121 and the piezoelectric element 122 do not have to be entirely formed within the second region 12, and may be partially included within the first region 11.

In addition, in this embodiment, a configuration in which two joints 13 are provided on either side of the piezoelectric element 122 is exemplified, but at least one joint 13 may be provided. When there is one joint 13, the symmetry of the shape is increased by surrounding the piezoelectric element 122, and the inclination between the base 10 and the VCSEL element 20 when joined to the VCSEL element 20 can be suppressed. In this case, it is preferable to open a part of the joint 13 in order to draw the wiring for driving the piezoelectric element 122 outside the joint 13.

When two or more joints 13 are provided, it is preferable to arrange them symmetrically with respect to the center of the second reflector 121 in the plane of the second reflector 121, since this can suppress the tilt between the base 10 and the VCSEL element 20. For example, when three joints 13 are provided, it is preferable to arrange them at positions 120 degrees with respect to the center of the second reflector 121. When four joints 13 are provided, it is preferable to arrange them on all four sides of the second reflector 121.

In addition, by electrically connecting the piezoelectric element 122 and the joint 13, the joint 13 can function as an electrode.

If the second reflecting portion 121 is provided near the center of the annular piezoelectric element 122, the two do not overlap in the Z-axis direction, preventing a decrease in the reflectance of the second reflecting portion 121.

(Configuration Example of VCSEL Element 20)
The configuration of the VCSEL element 20 will now be described with reference to Fig. 3. Fig. 3 is a cross-sectional view illustrating an example of the configuration of the VCSEL element 20.

The light source device 1 configures a resonator with the first reflector 22 of the VCSEL element 20 and the second reflector 121 provided separately from the VCSEL element 20. Therefore, the VCSEL element 20 can be called a half-VCSEL because it is a surface-emitting semiconductor laser that has only one reflector of the resonator.

As shown in FIG. 3, the VCSEL element 20 has a mesa 21, a first reflector 22, a semiconductor substrate 23, an anti-reflection film 24, and a groove 25. The first reflector 22, a spacer layer 221, and the mesa 21 are laminated on the positive Z-axis side of the semiconductor substrate 23, and the anti-reflection film 24 is formed on the negative Z-axis side of the semiconductor substrate 23. The groove 25 is provided by etching away the spacer layer 221 and the first reflector 22 around the mesa 21.

The first reflecting portion 22 is a semiconductor multilayer reflecting mirror formed on a semiconductor substrate 23 such as an n-GaAs substrate. The first reflecting portion 22 has, for example, a low refractive index layer made of n-Al0.9Ga0.1As and a high refractive index layer made of n-Al0.2Ga0.8As.

Between each refractive index layer of the first reflecting section 22, a composition gradient layer, for example 20 nm thick, is provided, in which the composition is gradually changed from one composition to the other, in order to reduce electrical resistance. The film thickness of each refractive index layer is set to have an optical thickness of λ/4, including 1/2 of the adjacent composition gradient layer, where λ is the wavelength. When the optical thickness is λ/4, the actual thickness D of the layer is D = λ/4n (where n is the refractive index of the medium of the layer).

The spacer layer 221 is, for example, a non-doped AlGaInP layer and is formed on the first reflector 22.

The mesa 21 includes a light emitting portion 211, a spacer layer 212, a selective oxidation layer 213, a pair of semiconductor multilayer film reflectors 214, a contact layer 215, an insulating layer 216, and an electrode 217.

The spacer layer 212 is formed on the light emitting section 211. The spacer layer 212 is, for example, a non-doped AlGaInP layer.

The portion including the spacer layer 212 and the light emitting portion 211 is also called the resonator structure (resonator region), and includes 1/2 of the adjacent composition gradient layer, and its thickness is set to be the optical thickness of one wavelength (λ).

The mesa 21 has a light emitting section 211 between the spacer layer 221 and the spacer layer 212. The light emitting section 211 emits light when a current is injected, and amplifies the light traveling back and forth between the first reflecting section 22 and the second reflecting section 121 that constitute the resonator. The light emitting section 211 can also be called an active layer. The light emitting section 211 is an active layer with a triple quantum well structure having three quantum well layers and four barrier layers. Each quantum well layer is an InGaAs layer or the like, and each barrier layer is an AlGaAs layer or the like. The light emitting section 211 is provided in the center of the resonator structure, which is a position corresponding to an antinode in the standing wave distribution of the electric field, so that a high stimulated emission probability can be obtained.

The selective oxidation layer 213 includes an oxidized region 213a and a non-oxidized region 213b. The selective oxidation layer 213 includes p-AlAs, etc., and is inserted between a pair of semiconductor multilayer film reflectors 214 with a thickness of 30 nm. The insertion position can be within the second pair of high refractive index layer and low refractive index layer counting from the spacer layer 212. The selective oxidation layer 213 may include layers such as compositionally graded layers and intermediate layers above and below, and here the layers that are actually oxidized are collectively referred to as the selective oxidation layer.

The contact layer 215 is formed on the semiconductor multilayer reflector 214. The contact layer 215 is a p-GaAs layer or the like.

The mesa 21 and the groove portion 25 can be formed by removing a portion of the contact layer 215, the semiconductor multilayer reflector 214, the spacer layer 212, and the light emitting portion 211 by etching.

The mesa 21 includes an insulating layer 216 on its surface. Examples of materials that can be used for the insulating layer 216 include SiN, SiON, and SiO2. The insulating layer 216 includes an opening 218 that exposes a portion of the contact layer 215 of the mesa 21. The insulating layer 216 includes the opening 218 at a position that overlaps with the non-oxidized region 213b in a plan view.

The insulating layer 216 on the mesa 21 has an electrode 217 electrically connected to the contact layer 215 through an opening 218. The electrode 217 can be, for example, a laminated film in which Ti/Pt/Au are laminated in this order from the insulating layer 216 side.

The groove portion 25 has an insulating layer 216 on its surface, and the insulating layer 216 includes an opening 252 that exposes a portion of the semiconductor substrate 23.

The insulating layer 216 on the groove 25 includes an electrode 251 electrically connected to the contact layer 215 through an opening 252. The electrode 251 may be, for example, a laminated film in which germanium alloy (AuGe)/nickel (Ni)/gold (Au) are laminated in this order from the semiconductor substrate 23 side.

The wiring 219 is electrically connected to each of the electrodes 217 and 251. For example, the wiring 219 may be a laminated film in which Ti/Pt/Au are laminated from the semiconductor substrate side.

<Operation example of light source device 1>
(Operation example of second area 12)
4A and 4B are diagrams illustrating an example of the operation of the second region 12. Fig. 4A is a diagram illustrating the generation of stress, and Fig. 4B is a diagram illustrating the deformation of the second region.

When a drive voltage is applied to the piezoelectric element 122 provided in the second region 12 so that the piezoelectric element 122 contracts, the piezoelectric element 122 contracts. Because the end of the second region 12 is connected to the first region 11, the end of the second region 12 does not displace in the Z direction even if the piezoelectric element 122 deforms.

Since the piezoelectric element 122 is bonded to the second region 12, the contraction stress S is transmitted to the second region 12. A neutral axis N exists at a predetermined position in the Z-axis direction within the second region 12. A compressive stress Ta is generated on the piezoelectric element 122 side of the neutral axis N in the second region 12, and a tensile stress Tb is generated on the opposite side of the neutral axis N to the piezoelectric element 122. The second region 12 elastically deforms in response to the compressive stress Ta and the tensile stress Tb, and as shown in FIG. 4(b), the second region 12 bends and the surface of the second region 12 is displaced in the negative direction of the Z-axis.

Conversely, when a driving voltage is applied so that the piezoelectric element 122 expands, tensile stress is generated on the piezoelectric element 122 side of the neutral axis N in the second region 12, and compressive stress is generated on the opposite side of the neutral axis N from the piezoelectric element 122. In response to this stress, the second region 12 elastically deforms, bending the second region 12 and displacing the surface of the second region 12 in the positive direction of the Z axis.

Next, FIG. 5 is a diagram for explaining another example of the operation of the second region 12. FIG. 5(a) is a diagram for explaining the generation of stress, and FIG. 5(b) is a diagram for explaining the deformation of the second region 12. As shown in FIG. 5, two piezoelectric elements 122E and 122F are provided on the surface of the second region 12 on the positive side of the Z axis.

When a drive voltage is applied so that the piezoelectric elements 122E and 122F each contract, the second region 12 deforms in the same manner as in FIG. 4(a). In the region where the piezoelectric elements 122E and 122F are not formed, a stress is generated in the opposite direction to the stress directly below the piezoelectric elements 122E and 122F. As a result, as shown in FIG. 5(b), a part of the second region 12 bends so as to protrude in the positive direction of the Z axis. The amount of displacement of this region differs depending on the dimension in the in-plane direction. In other words, in the region where the piezoelectric elements 122E and 122F are not formed, the amount of displacement differs depending on the area of the region.

Figure 6 is a diagram illustrating an example of vibration of the second region 12. When a drive voltage is applied to the piezoelectric element 122 and the second region 12 is vibrated at a resonant frequency determined by the dimensions, shape, etc. of the second region 12, the second region 12 vibrates in a state that satisfies the equation of motion of the second region 12.

If the second region 12 is a circular region with a radius a and the entire outer periphery of the second region 12 is fixed, the displacement u(r, φ, t) in the Z-axis direction at the position r from the center of the second region 12, the angle φ, and the time t is expressed by the following equations (1) to (3).

（１）式のＡ、Ｂ、Ｃ及びＤは定数を表し、Ｊｍｎはベッセル関数を表し、ｍ（＝０、１、２、・・・)はベッセル関数の次数を表す。ｎ（ｎ＝１、２、３、・・・)はベッセル関数の値が０になるｎ番目のrを意味する。（２）式のＴは内部応力を表し、ρは密度を表し、ｈは第２領域１２の厚みを表す。

In formula (1), A, B, C, and D represent constants, Jmn represents a Bessel function, and m (= 0, 1, 2, ...) represents the order of the Bessel function. n (n = 1, 2, 3, ...) means the nth r at which the value of the Bessel function becomes 0. In formula (2), T represents internal stress, ρ represents density, and h represents the thickness of the second region 12.

Since the outer periphery of the second region 12 is fixed, the displacement in the Z-axis direction is zero at all times t. For example, in the first resonance, there is no point on the second region 12 where the displacement is always zero except for the outer periphery. Therefore, in the first resonance, the radius a corresponds to the first zero point in the Bessel function.

The values of the zero points of the Bessel function are also predetermined. The first one is 2.405, and the second one is 5.520. In other words, the value of the Bessel function at any position r (r≦a) is the following value at the time of first resonance.

By substituting the time t, which is determined by the dimensions of the second reflecting portion 121, stress information, the resonant frequency, etc., into the above equation u(r, φ, t), the amount of displacement of the second reflecting portion 121 per unit time during resonance can be estimated.

In FIG. 6, the second region 12 is resonantly vibrating. As a result, the position of the second reflector 121 provided in the second region 12 in the Z-axis direction changes, and the resonator length changes. The wavelength of the laser light emitted by the light emitting unit 211 changes in response to the change in the resonator length.

In order to linearly change the wavelength of the laser light in response to the driving voltage applied to the piezoelectric element 122, it is preferable to determine the driving voltage based on the amount of displacement per time, which is determined by the dimensions and frequency of the second region 12.

The wavelength of the laser light can also be changed by vibrating the second region 12 at a frequency sufficiently far from the resonant frequency. In this case, it is not possible to obtain a large amount of displacement equivalent to that obtained by resonant driving, but since the amount of displacement does not vary greatly with frequency fluctuations, this is advantageous in that the wavelength of the laser light can be changed at various frequencies.

When there is a linear relationship between the drive voltage and the amount of displacement, if the drive voltage changes linearly with time, the amount of displacement also changes linearly with time. By utilizing this, it is easier to control the wavelength compared to resonant driving.

Here, FIG. 7 is a diagram showing an example of the relationship between the drive voltage of the piezoelectric element 122 and the displacement amount of the second reflecting portion 121. As shown in FIG. 7, the drive voltage of the piezoelectric element 122 and the displacement amount of the second reflecting portion 121 have a linear relationship.

(Example of the relationship between the distance between reflectors and wavelength)
Next, Fig. 8 is a diagram showing an example of the relationship between the distance between the first reflecting portion 22 and the second reflecting portion 121 and the wavelength of the laser light emitted by the light emitting portion 211. As shown in Fig. 8, when the distance between the reflecting portions is long, that is, when the resonator length is long, the wavelength of the laser light emitted by the light emitting portion 211 also becomes long. Conversely, when the distance between the reflecting portions is short, the wavelength of the laser light also becomes short.

The linearity of the wavelength of the laser light with respect to time is determined by the linearity of the displacement in the Z-axis direction with respect to the drive voltage applied to the piezoelectric element 122, and the linearity of the wavelength of the laser light with respect to the resonator length. For example, if the displacement in the Z-axis direction has a linear relationship with the drive voltage, the resonator length will also change linearly with respect to the drive voltage.

In addition, in FIG. 8, if the distance between the reflecting sections is changed in a region where the wavelength of the laser light changes relatively linearly with respect to the length of the distance between the reflecting sections, the wavelength of the laser light can be changed linearly with respect to the drive voltage.

In addition, when the second region 12 is driven at a frequency far from the resonant frequency, the relationship between the drive voltage and the amount of displacement becomes very close to linear. Therefore, by selecting a region in which the distance between the reflecting parts and the wavelength of the laser light change linearly, the wavelength of the laser light can be changed linearly with respect to time without distorting the drive voltage nonlinearly.

<Functions and Effects of Light Source Device 1>
Next, the effects of the light source device 1 will be described.

Tunable lasers used as light sources for FMCW-LiDAR devices and the like have been known for some time. Also disclosed is a configuration that includes an optical resonator including first and second mirrors, a gain region interposed between the first and second mirrors, and an electrostatically driven MEMS drive mechanism, and that adjusts the gap between the first and second mirrors using the MEMS drive mechanism.

However, in the electrostatic drive method, the amount of displacement and drive speed (resonant frequency) are determined by the balance between the electrostatic attractive force acting between parallel plates arranged with a gap between them and the restoring force of the movable part connected to the parallel plates.

For example, if one of the parallel plates is fixed to a fixed part and the other is connected to a support part via a movable part, the electrostatic attractive force depends on the area W of the parallel plates, the vacuum dielectric constant ε, the driving voltage V and the displacement x, and the spring restoring force depends on the spring constant k and the displacement x. When a driving voltage is applied, a displacement x is obtained in which the electrostatic attractive force and the spring restoring force are balanced.

The resonant frequency f of a parallel plate can be expressed using the spring constant k, the constant c, and the mass m of the parallel plate. Based on these relationships, the larger the spring constant, the smaller the displacement x and the larger the resonant frequency f. Furthermore, the mass m is expressed as the product of the area W, the thickness h, and the density ρ.

From the above relationship, it can be seen that in order to shift the curve showing the relationship between the resonant frequency and the amount of displacement limited by the spring constant to the side of larger displacement at higher speeds (high frequencies), it is necessary to reduce the density, make the thickness thinner, and increase the driving voltage.

For example, to increase the resonant frequency by 10 times, with other variables fixed, it is necessary to increase the density by 1/100, the thickness by 1/100, and the voltage by 10 times. To reduce the density by 1/100, new materials must be developed, and new materials must also be developed to reduce the thickness of the moving parts. Developing such materials is not easy. Furthermore, increasing the driving voltage may be limited by the specifications of the size, operational reliability, power consumption, etc. of optical devices such as light source devices.

For these reasons, with the electrostatic drive method, it is difficult to drive the parallel plates at high speed with a large amount of displacement to change the resonator length, and there is room for improvement in changing the wavelength of the laser light at high speed and over a wide wavelength range.

In this embodiment, the light source device 1 has a light emitting section 211, a first reflecting section 22 and a second reflecting section 121 that face each other across the light emitting section 211, a base 10 that holds the second reflecting section 121 with a gap between the light emitting section 211 and the second reflecting section 121, and a piezoelectric element 122 (piezoelectric member) that deforms in response to an applied drive voltage. The base 10 includes a first region 11 and a second region 12 that has a lower rigidity than the first region 11. The second reflecting section 121 and the piezoelectric element 122 are provided in the second region 12. When a drive voltage is applied, the piezoelectric element 122 deforms the second region 12 to drive the second reflecting section 121, and emits laser light whose wavelength changes in response to the distance between the first reflecting section 22 and the second reflecting section 121.

The rigidity varies depending on the dimensions of the object (length, thickness, etc.) and the elastic modulus of the material constituting the object. In this embodiment, the second region is formed thinner than the first region 11, thereby realizing a relatively high rigidity first region 11 and a low rigidity second region 12. The resonance frequency of the movable part is determined by its dimensions and the mechanical properties of the material constituting it. If the material constituting it is constant, the larger the dimensions of the movable part, the lower the spring constant, and the resonance frequency, which is proportional to the spring constant, decreases. However, if a support part with higher rigidity than the movable part is provided around the movable part, the substantial fixed end of the movable part can be approximated to the vicinity of the boundary between the low rigidity region and the high rigidity region. In other words, the vicinity of the boundary between the first region 11 and the second region 12 can be made the substantial fixed end of the second region 12. On the other hand, by using a material with higher rigidity than the second region as the material constituting the first region 11, it is also possible to realize a relatively high rigidity first region 11 and a low rigidity second region 12 without thickening the first region 11.

In addition to forming low-rigidity and high-rigidity regions in the base 10 as described above, the base 10 may not have a high-rigidity region such as the support layer 111, and the fixed end of the movable part may be defined by making the part where the low-rigidity layer (e.g., the silicon active layer 113) and the joint 13 are connected a high-rigidity region. In this case, it is preferable to make the base 10 itself sufficiently small so as not to reduce the spring constant and to maintain the mechanical strength of the low-rigidity movable part.

The piezoelectric element 122 drives the second reflector 121 to change the resonator length, which corresponds to the distance between the first reflector 22 and the second reflector 121, and the light emitting unit 211 emits laser light whose wavelength changes according to the resonator length.

The thin second region 12 is deformed by the piezoelectric element 122 to drive the second reflecting portion 121, so that the second reflecting portion 121 can be driven at high speed and with a large amount of displacement to change the resonator length. For example, the second reflecting portion 121 can be driven at a driving speed of 1 MHz or more and with a displacement of 200 nm or more. This allows the wavelength of the laser light to be changed quickly and over a wide wavelength range.

Here, FIG. 9 is a diagram showing the relationship between the drive voltage of the piezoelectric element 122 and the wavelength of the laser light emitted from the light source device 1. As an example, the wavelength range of the tunable laser light is in the range of 920 [nm] to 950 [nm], and the drive voltage width is 5 [V] or less. Since the volumetric deformation amount of the piezoelectric element with respect to the drive voltage is close to linear, the displacement amount in the Z direction of the second region 12 and the second reflecting portion 121 displaced by the deformation of the piezoelectric element is also close to linear. Furthermore, by displacing the second reflecting portion 121 near the region in FIG. 8 where the change in the oscillation wavelength with respect to the distance between the reflecting portions (resonator length) is close to linear (in the example of FIG. 8, the oscillation wavelength is around 940 nm), the wavelength of the laser light emitted from the light source device 1 with respect to the drive voltage becomes close to linear.

Reducing the volume of the voltage signal source is essential to miniaturizing the light source device 1 and the device in which the light source device 1 is mounted. In general, as the voltage and its modulation speed increase, the volume of the voltage driving source tends to increase. Furthermore, if a function to correct the nonlinearity of the wavelength becomes necessary, the volume of the voltage driving source becomes even larger. Since the light source device 1 has high wavelength linearity with respect to the driving voltage and has a sufficient wavelength change width even at a low driving voltage, it is possible to realize a miniaturized tunable laser light source device in which the wavelength changes at a speed of the order of MHz.

In addition, in this embodiment, the piezoelectric element 122 is provided in a circular ring shape around the second reflecting portion 121 in the second region 12. This allows a driving force to be applied evenly to the second reflecting portion 121 from the direction around the second reflecting portion 121, making it easy to control the displacement of the second reflecting portion 121.

<Modifications of the Configuration of the Piezoelectric Element 122>
In the above-described embodiment, the piezoelectric element 122 is provided on the surface of the second region 12 facing the light emitting portion 211, but the present invention is not limited to this. Fig. 10 is an enlarged cross-sectional view showing modified examples of the configuration around the second region 12. Fig. 10(a) is a diagram showing a first example, and Fig. 10(b) is a diagram showing a second example.

As shown in FIG. 10(a), the light source device 1a is arranged such that the piezoelectric element 122 is provided on the opposite side of the second reflecting portion 121 across the second region 12, and the second reflecting portion 121 and the piezoelectric element 122 have an overlapping region. In this configuration, the area of the piezoelectric element 122 is not limited by the second reflecting portion 121, so the area of the piezoelectric element 122 can be increased. Increasing the area of the piezoelectric element 122 increases the stress generated by the piezoelectric element 122, allowing the second reflecting portion 121 to be displaced more greatly.

As shown in FIG. 10(b), the light source device 1b has a piezoelectric element 122 on the negative Z-axis side of the second region 12, and the second reflecting portion 121 is laminated on the negative Z-axis side of the piezoelectric element 122. With this configuration, the area of the piezoelectric element 122 can be increased without being limited by the second reflecting portion 121, and the piezoelectric element 122 and the second reflecting portion 121 can be formed on one side of the second region 12, reducing the effort required for film formation on both sides of the second region 12.

Note that, although FIG. 10(b) illustrates a configuration in which the piezoelectric element 122 and the second reflecting portion 121 are provided on the negative Z-axis side of the second region 12, the piezoelectric element 122 and the second reflecting portion 121 can also be provided on the positive Z-axis side of the second region 12.

<Modifications of the base 10>
11 and 12 are diagrams showing a first modified example of the base portion 10. Fig. 11 is a plan view, and Fig. 12 is a cross-sectional view taken along the line AA' of Fig. 11.

As shown in Figures 11 and 12, the second region 12 of the base 10 includes a plurality of movable beams 314 that connect the second reflecting portion 121 and the first region 11. The shape of the movable beams 314 does not need to be linear, and may be curved or have bent portions. The number of movable beams 314 may be two or more. It is preferable that the two or more movable beams 314 are arranged so as to be rotationally symmetric, which makes it easy to drive the second reflecting portion 121 in the Z direction while maintaining the parallelism between the second reflecting portion 121 and the first reflecting portion 22.

The movable beam 314 can be formed by removing the support layer 111, the oxide insulating layer 112, and the silicon active layer 113 in the region 316 by a semiconductor process such as dry etching. The region on the periphery of the region 316 becomes the first region 11. The piezoelectric element 322 is also formed by a semiconductor process on the movable beam 314 in the second region 12 and on the region of the first region 11 that corresponds to the periphery of the region 316. By adjusting the dimensions of the movable beam 314, the spring constant of the movable beam 314 can be changed, and the relationship between the resonant frequency of the second reflecting portion 121 and the amount of displacement in the Z direction when the second reflecting portion 121 resonates can be set.

In the base 10 of this modified example, the piezoelectric element 322 is formed on both the movable beam 314 and the outer periphery of the region 316, and by applying a voltage at the same time, the amount of displacement of the second reflecting portion 121 in the Z direction during resonance can be increased. When the volume of the piezoelectric element 322 on the movable beam 314 changes due to the application of a voltage, the movable beam 314 on which the piezoelectric element 322 is formed is deformed, and the position of the second reflecting portion 121 changes. For example, when a sinusoidal voltage is applied to the piezoelectric element 322 on the movable beam 314, the position of the second reflecting portion 121 changes sinusoidally over time along the Z direction. On the other hand, when a voltage signal of a frequency equal to or close to the resonant frequency of the movable beam 314 is applied to the piezoelectric element, the movable beam 314 is excited, a resonant phenomenon occurs, and a larger amount of displacement can be obtained than in a non-resonant state.

When a similar sine wave voltage signal is applied to the piezoelectric element 322 on the outer periphery of the region 316, the silicon active layer 113 near the outer periphery of the region 316 deforms with a small amount of displacement relative to the movable beam 314. When this vibration is transmitted to the mechanically connected movable beam 314, the movable beam 314 is excited and a resonance phenomenon occurs. Therefore, by deforming both the movable beam 314, which is desired to achieve a large amount of displacement at high speed, and the region located on the outer periphery of the movable beam 314 and to which the movable beam 314 is mechanically connected, by contracting and expanding the piezoelectric element 322, it is possible to move the second reflecting portion 121 on the movable beam 314 at high speed and with a large amount of displacement.

Figures 13 and 14 are diagrams showing a second modified example of the base 10. Figure 13 is a plan view, and Figure 14 is a cross-sectional view taken along the line B-B' in Figure 13.

As shown in Figures 13 and 14, in the second modification, a reflector part 311 having HCG (High Contrast Grating) that ensures the reflectance by periodically opening holes in a part of the silicon active layer 113 is used as the second reflector part 121. In general, the resonance frequency of the movable beam 314 is inversely proportional to its mass. A reflector part made of a multilayer mirror in which multiple thin films are stacked or a metal thin film has a large mass. On the other hand, since HCG can achieve the same reflectance with a single layer of silicon, the resonance frequency can be increased by using the reflector part 311 as the second reflector part 121. The material of the reflector part 311 is not limited to silicon, and any material having a refractive index different from the refractive index of the space through which light propagates may be used. In addition, in the second modification, the second reflector 121 in the first modification is configured as a reflector 311 having an HCG, but the second reflector 121 in the first embodiment (FIG. 1) may be configured as a reflector 311 having an HCG.

Figures 15 and 16 are diagrams showing a third modified example of the base 10. Figure 15 is a plan view, and Figure 16 is a cross-sectional view taken along the line CC' in Figure 15.

As shown in Figures 15 and 16, in the third modification, unlike the first modification, the material constituting the movable beam 314 is the multilayer film reflector 315 rather than the silicon active layer 113. In the second modification, the HCG is formed on the movable beam 314 made of the silicon active layer 113 to form the reflector section 311, but in this modification, the material of the movable beam 314 itself is the multilayer film reflector 315 to form the second reflector section 121. In the reflector section made of a multilayer film mirror or a metal thin film, a process of forming a reflector on the silicon active layer 313 is required, and in the HCG reflector section, a process of forming a periodic structure of HCG on the silicon active layer 313 is required. In this modification, the function of moving the multilayer film reflector 315 and the function of reflecting light can be realized in a single configuration, so the processing process of this element can be omitted.

Furthermore, by adjusting the number of layers of the multilayer film and controlling the reflectance, the emission direction of the tunable laser light emitted from the light source device 1 can be selected. For example, in the configuration of the base 10 according to the first and second modified examples, it is not appropriate to emit laser light having a wavelength in the absorption band of the silicon active layer 113 through the silicon active layer 113. On the other hand, in the configuration of the base 10 according to this modified example, since the silicon active layer 113 is not used, even if the laser light has a wavelength in the absorption band of the silicon active layer 113, the laser light can be emitted from the second reflector 121 side (the emission direction 31 side in FIG. 1(b)). In the third modified example, the silicon active layer 113 constituting the movable beam 314 according to the first modified example is configured as a multilayer film reflector 315, but the silicon active layer 113 of the first embodiment may be configured as a multilayer film reflector.

In the first to third modified examples, at least two movable beams 314 are included as part of the second region 12. As an example, the movable beam 314 is 1 μm to 100 μm in the short direction, 10 μm to 1000 μm in the long direction, and 50 nm to 100 μm in the thickness direction. By setting the movable beam 314 to these dimensions, it is possible to miniaturize the device while simultaneously achieving a high resonant frequency (e.g., 1 MHz or more) and an expanded wavelength sweep width.

[Second embodiment]
Next, a light source device 1c according to a second embodiment will be described. The same components as those described in the first embodiment will be denoted by the same reference numerals, and duplicated descriptions will be omitted as appropriate. This also applies to the following embodiments.

Figure 17 is a plan view illustrating an example of the configuration of light source device 1c. As shown in Figure 17, light source device 1c differs from the first embodiment in that it includes a second base 110 that holds the base 10. The second base 110 includes a second support 100 and second movable parts 13a and 13b. The second support 100 is an example of the third region, and the second movable parts 13a and 13b are an example of the fourth region.

The second movable part 13a has a meandering structure (meander structure) in which the movable beams 131a and 132a are connected at the end 162a, and the movable beams 133a and 134a are connected at the end 161a, and one end of the second movable part 13a is connected to the second support part 100 via the first connection part 151a, and the other end of the second movable part 13a is connected to the base part 10 via the second connection part 152a. The movable beams 131a, 132a, 133a, and 134a are each an example of a beam member.

The movable beams 131a, 132a, 133a, and 134a each include a piezoelectric element 141a, 142a, 143a, and 144a on the surface on the negative side of the Z axis. The piezoelectric elements 141a, 142a, 143a, and 144a are each an example of a base drive unit.

The piezoelectric elements 141a, 142a, 143a, and 144a deform (e.g., expand and contract) in response to a drive voltage applied via an electrode provided on the second support portion 100. The movable beams 131a and 132a elastically deform in response to the deformation of the piezoelectric elements 141a and 142a, and the movable beams 133a and 134a elastically deform in response to the deformation of the piezoelectric elements 143a and 144a, thereby allowing the base 10 to be displaced in the Z-axis direction.

The second movable part 13b has a meandering structure in which the movable beams 131b and 132b are connected at the end 161b, and the movable beams 133b and 134b are connected at the end 162b, and one end of the second movable part 13b is connected to the second support part 100 via the first connection part 151b, and the other end of the second movable part 13b is connected to the base part 10 via the second connection part 152b. The movable beams 131b, 132b, 133b, and 134b are each an example of a beam member.

The movable beams 131b, 132b, 133b, and 134b each include a piezoelectric element 141b, 142b, 143b, and 144b on the surface on the negative side of the Z axis. The piezoelectric elements 141b, 142b, 143b, and 144b are each an example of a base drive unit.

The piezoelectric elements 141b, 142b, 143b, and 144b deform (e.g., expand and contract) in response to a drive voltage applied via an electrode provided on the second support portion 100. The movable beams 131b and 132b elastically deform in response to the deformation of the piezoelectric elements 141b and 142b, and the movable beams 133b and 134b elastically deform in response to the deformation of the piezoelectric elements 143b and 144b, thereby allowing the base 10 to be displaced in the Z-axis direction.

The movable beams 131a, 132a, 133a, 134a, 131b, 132b, 133b, and 134b are formed thinner than the first region of the base 10 and the second support portion 100, and have lower rigidity than the first region of the base 10 and the second support portion 100. This allows the vicinity of the first connection portion 151a and the vicinity of the second connection portion 152a to be the substantial fixed end of the second movable portion 13a, and the vicinity of the first connection portion 151b and the vicinity of the second connection portion 152b to be the substantial fixed end of the second movable portion 13b.

When the amount of displacement caused by the second movable part 13a is equal to the amount of displacement caused by the second movable part 13b, the base part 10 can be translated in the Z-axis direction by that amount of displacement. When the amount of displacement caused by the second movable part 13a is different from the amount of displacement caused by the second movable part 13b, the base part 10 can be tilted along the Y-axis direction.

For example, when the amount of displacement caused by the second movable part 13a is smaller than the amount of displacement caused by the second movable part 13b, the negative Y-axis side of the base 10 is displaced relatively less in the negative Z-axis direction, and the positive Y-axis side of the base 10 is displaced relatively more in the negative Z-axis direction. This allows the base 10 to be tilted along the Y-axis direction.

Note that FIG. 17 shows the side of the base 10 on which the second reflector 121 is provided. The VCSEL element 20 is disposed on the negative Z-axis side of the second support 100, and the second support 100 and the VCSEL element 20 are joined via the joint 13.

Here, in the manufacture of the light source device 1 shown in the first embodiment, the distance along the Z-axis direction between the VCSEL element 20 and the base 10 may vary for each of the multiple light source devices 1 manufactured. If this distance deviates from the desired distance between the reflectors, it may not be possible to emit laser light of the desired wavelength.

The task of adjusting the distance between the VCSEL element 20 and the base 10 during bonding to correct the distance between the reflecting parts takes time and effort. Furthermore, when applying an offset driving voltage to the piezoelectric element 122 and translating the second reflecting part 121 in the Z-axis direction to correct the distance between the reflecting parts, there is a limit to the amount of translation of the second reflecting part 121 in the Z-axis direction. Therefore, if there is a large deviation from the desired distance between the reflecting parts, the distance between the reflecting parts may not be fully corrected.

In this embodiment, a bias voltage is applied to the piezoelectric elements (141a, 142a, 143a, 144a, 141b, 142b, 143b, and 144b) of the second movable parts 13a and 13b, and the base part 10 is driven in the Z-axis direction by the second movable parts 13a and 13b, thereby changing and correcting the distance between the VCSEL element 20 and the base part 10. This reduces the work required to correct the distance between the VCSEL element 20 and the base part 10, and makes it easy to correct the distance between the reflecting parts.

In addition, because the second movable parts 13a and 13b each have a serpentine structure, the base 10 can be displaced more significantly compared to driving by the piezoelectric element 122. Therefore, even if there is a large deviation from the desired distance between the reflecting parts, the distance between the reflecting parts can be corrected.

Furthermore, if the VCSEL element 20 and the base 10 are tilted, the second movable parts 13a and 13b can be used to tilt the base 10, thereby changing the tilt angle of the base 10 relative to the VCSEL element 20 for correction. Note that correction may also be performed by changing both the distance between the reflectors and the tilt angle of the base 10 relative to the VCSEL element 20.

Furthermore, the light source device 1c can separate the drive of the second reflector 121 and the drive of the base 10 and drive them separately. In other words, the wavelength of the laser light can be continuously and quickly modulated by applying a drive voltage that changes continuously and periodically with time, such as a sine wave, a triangular wave, or a sawtooth wave, to the piezoelectric element 122 on the second region of the base while maintaining the bias voltage applied to the piezoelectric elements of the second movable parts 13a and 13b. In addition, by changing the value of the bias voltage applied to the piezoelectric elements of the second movable parts 13a and 13b, the center wavelength can be adjusted while maintaining the width of the continuous wavelength change. This function is due to the synergistic effect of the second movable parts 13a and 13b, which can greatly change the distance between the reflectors, and the second region, which can sweep the wavelength at high speed. In addition, with conventional electrostatic tunable lasers, it is difficult to simultaneously achieve continuous high-speed modulation of the wavelength of the laser light and adjustment of the center wavelength of the laser light. This is because electrostatic actuators use electrostatic attraction that acts uniformly between two opposing surfaces with an air gap between them to drive the reflector, meaning that the driving points and driving characteristics cannot be divided within the surface.

In order to drive the second reflector 121 and the base 10 separately, it is preferable that the resonant frequency of the base 10 connected to the second movable parts 13a and 13b via the first connection part 151a and the second connection part 152a, respectively, is different from the resonant frequency of the second reflector 121 in the second region 12 by 50 Hz or more. When the second reflector 121 is vibrated at the resonant frequency of the second region 12, if the resonant frequency of the base 10 is equal to or the absolute difference between the resonant frequencies of the two is less than 50 Hz, the vibration of the second reflector 121 excites the base 10 itself including the second reflector 121, and the position of the base 10, whose displacement is fixed by the bias voltage, may fluctuate. By creating a difference between the resonant frequency of the base 10 and the second movable parts 13a and 13b and the resonant frequency of the second reflecting part 121 and the second region 12, particularly by making the difference 50 Hz or more, it is possible to stably sweep the wavelength of the laser light at high speed while changing the distance between the reflecting parts to change the central wavelength of the laser light.

When the driving frequency of the second reflecting portion 121 is made higher than the driving frequency of the base portion 10, it is preferable that the second region 12 has higher rigidity than the movable beams (131a, 132a, 133a, 134a, 131b, 132b, 133b, and 134b) of the second movable portions 13a and 13b. Furthermore, it is preferable that the mass of the second region 12 is smaller than the mass of the second movable portions 13a and 13b.

In this embodiment, a configuration having two second movable parts 13a and 13b is exemplified, but the light source device 1c can also have three or more movable parts. In addition, a meandering structure having two movable beams 131a and 131b is exemplified as the structure of the second movable parts 13a and 13b, but the second movable parts 13a and 13b can also have a meandering structure having three or more movable beams.

[Third embodiment]
Next, a light source device 1d according to a third embodiment will be described.

Figure 18 is a plan view illustrating an example of the configuration of light source device 1d. As shown in Figure 18, light source device 1d is obtained by replacing the base 10 of light source device 1c of the second embodiment with base 10d. Light source device 1d has base 10d. Base 10d has four second regions 12a, 12b, 12c, and 12d. The four second regions 12a, 12b, 12c, and 12d are two-dimensionally arranged within the plane of base 10d.

The second region 12a has a second reflecting portion 121a and a piezoelectric element 122a arranged in a ring shape around the second reflecting portion 121a, and the second region 12b has a second reflecting portion 121b and a piezoelectric element 122b arranged in a ring shape around the second reflecting portion 121b. The second region 12c has a second reflecting portion 121c and a piezoelectric element 122c arranged in a ring shape around the second reflecting portion 121c, and the second region 12d has a second reflecting portion 121d and a piezoelectric element 122d arranged in a ring shape around the second reflecting portion 121d.

The piezoelectric element 122a can drive the second reflecting portion 121a, the piezoelectric element 122b can drive the second reflecting portion 121b, the piezoelectric element 122c can drive the second reflecting portion 121c, and the piezoelectric element 122d can drive the second reflecting portion 121d independently.

The function and configuration of the second regions 12a, 12b, 12c, and 12d are the same as those of the second region 12, and the function and configuration of the second reflecting portions 121a, 121b, 121c, and 121d are the same as those of the second reflecting portion 121. The function and configuration of the piezoelectric elements 122a, 122b, 122c, and 122d are the same as those of the piezoelectric element 122.

Note that FIG. 18 shows the side of the base 10d on which the second reflectors 121a, 121b, 121c, and 121d are provided. The VCSEL element 20 is disposed on the negative Z-axis side of the second support 100, and the second support 100 and the VCSEL element 20 are joined via the joint 13.

The VCSEL element 20 also has a number of light-emitting sections 211 arranged in one-to-one correspondence with the second reflectors 121a, 121b, 121c, and 121d. The second reflectors 121a, 121b, 121c, and 121d each form a resonator with the first reflector 22 via the number of light-emitting sections 211, and the number of light-emitting sections 211 can emit laser light with a wavelength corresponding to the resonator length.

In this way, by having the multiple light-emitting units 211 emit laser light, the light source device 1d can increase the amount of laser light. Furthermore, by driving the multiple light-emitting units 211 to emit laser light at different times, the light-emitting time of each light-emitting unit 211 can be shortened, the heat generated by emitting laser light can be suppressed, and the time that the light source device 1d emits laser light as a whole can be extended.

[Fourth embodiment]
Next, a laser radar device 200 according to a fourth embodiment will be described. Fig. 19 is a block diagram illustrating an example of the configuration of the laser radar device 200, which is an example of a distance measurement device. The laser radar device 200 is, for example, an FMCW-LiDAR device that measures the distance to an object.

As shown in FIG. 19, the laser radar device 200 includes a light source device 1, an optical coupler 202, an optical mixer 203, a photodetector 204, an AD converter 205, and a frequency analysis processor 206.

The light source device 1 emits tunable laser light whose wavelength changes according to the drive voltage. The optical coupler 202 splits the tunable laser light from the light source device 1 into two at a predetermined energy ratio. The optical coupler 202 irradiates one of the split tunable laser lights as an illumination wave 230 onto the object 300, and inputs the other to the optical mixer 203 as a reference wave 231.

The return wave 232, which is the irradiated tunable laser light reflected or scattered by the object 300, enters the optical mixer 203. The optical mixer 203 superimposes the return wave 232 and the reference wave 231 to generate an interference wave.

At this time, the return wave 232 has a time delay due to the distance from the object 300. If the object 300 is moving relative to the laser radar device 200, a frequency shift also occurs due to the Doppler effect.

The optical detector 204 receives the interference wave generated by the optical mixer 203 and outputs a voltage signal corresponding to the optical intensity of the interference wave. The voltage signal (beat signal) obtained from the interference wave generated by the optical mixer 203 contains the frequency difference between the reference wave 231 and the return wave 232 and the frequency shift due to the Doppler effect.

The AD converter 205 performs A/D (Analog/Digital) conversion on the analog voltage signal input from the photodetector 204, and outputs the digital signal to the frequency analysis processor 206. The frequency analysis processor 206 analyzes the input digital signal using a Fourier transform or the like, and calculates the frequency difference between the reference wave 231 and the return wave 232 from the frequency peak information detected by the analysis. The laser radar device 200 acquires and outputs at least one of information on the distance to the object 300 and the relative speed of the object 300 based on this frequency difference.

Here, in conventional FMCW-LiDAR devices that use tunable laser light, if the linearity of the wavelength change over time of the tunable laser light is poor, the measurement accuracy can be significantly reduced.

By using the light source device 1, the laser radar device 200 can use tunable laser light for measurements, which changes at high speed and over a wide wavelength range and has good linearity of wavelength change over time. This can improve measurement accuracy.

When scanning a distance measurement space two-dimensionally with continuous light of a tunable laser beam to obtain a three-dimensional point cloud, it is preferable to perform a wavelength sweep once for each point cloud. Note that wavelength sweeping refers to changing the wavelength over time. Furthermore, the distance measurement space refers to the space to which the distance is to be measured.

If the number of ranging points per frame of the laser radar device 200 is N and the frame rate is F, then a wavelength sweep speed of at least F x N times per second, or F x N [Hz], is required.

For example, assuming that the number of distance measuring points is the product of the number of horizontal points and the number of vertical points, and the number of distance measuring points in each direction is ¹⁰² , the total number of points is ^104. Furthermore, if the frame rate is ¹⁰² , the minimum required wavelength sweep speed is ¹⁰⁴ × ¹⁰² = ¹⁰⁶ [Hz], or 1 [MHz].

Therefore, in order to achieve high frame rates and high resolution for the laser radar device 200, it is necessary to increase the wavelength sweep speed to approximately MHz.

The measurement accuracy of the laser radar device 200 depends not only on the linearity of the wavelength sweep but also on the width of the variable wavelength range. Specifically, the wider the wavelength range, the higher the measurement accuracy, and distance measurements on the order of sub-millimeters become possible. In order to expand the wavelength range, it is preferable to increase the displacement of the second reflecting section 121 and lengthen the distance between the reflecting sections.

In a light source device according to a comparative example, which drives a movable part using an electrostatic drive method, the amount of displacement of the reflective part caused by driving the movable part is not proportional to the first power of the voltage. Here, FIG. 20 shows an example of the relationship between the drive voltage and the amount of displacement of the reflective part in a light source device according to a comparative example. As shown in FIG. 20, the slope of the amount of displacement relative to the drive voltage is not constant.

This phenomenon occurs because the position of the reflecting part is determined by the condition where the electrostatic attractive force acting between the reflecting part and the flat plate placed opposite it is balanced with the spring restoring force of the moving part, and because the electrostatic attractive force is proportional to the square of the voltage.

Therefore, in order to apply a light source device that drives a moving part using an electrostatic drive method to a laser radar device, it is necessary to distort the drive voltage in advance to ensure linearity of the wavelength sweep, which makes the control complicated.

The resonant frequency of the moving part is proportional to the square root of the inverse of the density of the moving part, the square root of the inverse of the thickness, and the driving voltage. Therefore, to increase the resonant frequency by 10 times, assuming that other parameters are fixed, it is necessary to reduce the density or thickness by 1/100, or increase the driving voltage by 10 times.

It is not easy to reduce density and thickness while maintaining the mechanical strength required to prevent damage to moving parts. In addition, increasing the driving voltage may be limited by specifications such as the size, operational reliability, and power consumption of optical devices such as light sources.

The resonant frequency of the moving part of the electrostatic drive system is inversely proportional to the amount of displacement. Therefore, even if driving at around MHz is achieved, it is not possible to obtain a sufficient amount of displacement to simultaneously expand the wavelength range. In this way, if a light source device that drives the moving part using an electrostatic drive system is applied to an FMCW-LiDAR type laser radar device, high measurement accuracy may not be obtained.

By using the light source device 1 according to the embodiment, it is possible to use tunable laser light whose wavelength changes at high speed and over a wide wavelength range. This allows the laser radar device 200 to have a high frame rate, improve the spatial resolution of the object 300 within a plane (within the XY plane), and improve the measurement accuracy of at least one of the distance to the object 300 or the relative speed of the object 300 with respect to the laser radar device 200.

[Fifth embodiment]
Next, the fifth embodiment will be described. The fifth embodiment relates to a moving body. FIG. 21 is a diagram showing an automobile as an example of a moving body according to the fifth embodiment. The laser radar device 200 of the fourth embodiment is provided on the upper front surface (for example, the upper part of the windshield) of an automobile 500 as an example of a moving body according to the fifth embodiment. The laser radar device 200 is an example of a distance measuring device that measures at least one of the distance to an object or the speed of the object. In this embodiment, the laser radar device 200 measures the distance to an object 502 (object) around the automobile 500. The measurement result of the laser radar device 200 is input to a control unit of the automobile 500, and the control unit controls the operation of the moving body based on the measurement result. Alternatively, the control unit may display a warning on a display unit provided in the automobile 500 to a driver 501 of the automobile 500 based on the measurement result of the laser radar device 200.

In this way, in the fifth embodiment, by installing the laser radar device 200 on the automobile 500, the position of the object 502 around the automobile 500 can be recognized with high accuracy. The mounting position of the laser radar device 200 is not limited to the upper front of the automobile 500, but it may be mounted on the side or rear. Also, in this example, the laser radar device 200 is installed on the automobile 500, but the laser radar device 200 may be installed on an aircraft or a ship. Also, it may be installed on a moving object that moves autonomously without a driver, such as a drone or a robot.

Although the embodiments have been described above, the present invention is not limited to the specifically disclosed embodiments above, and various modifications and variations are possible without departing from the scope of the claims.

In addition, all the numbers such as ordinal numbers and quantities used above are merely examples to specifically explain the technology of the present invention, and the present invention is not limited to the exemplified numbers. In addition, the connections between the components are merely examples to specifically explain the technology of the present invention, and the connections that realize the functions of the present invention are not limited to these.

1. Light source device (an example of an optical device)
10: base portion 11: first region 12: second region 121: second reflecting portion 122: piezoelectric element (an example of a piezoelectric member)
314 Movable beam 13 Joint portion 110 Second base portion 13a, 13b Second movable portion 131a, 132a, 133a, 134a Movable beams 131b, 132b, 133b, 134b Movable beams 141a, 142a, 143a, 144a Piezoelectric element (an example of a base driving portion)
141b, 142b, 143b, 144b: Piezoelectric element (an example of a base drive unit)
20 VCSEL element 21 Mesa 22 First reflecting portion 211 Light emitting portion 200 Laser radar device (an example of a distance measuring device)
500 Automobile (an example of a moving object)
501 Driver

Patent No. 6328112

Claims (17)

An optical device that emits laser light, comprising:
A light emitting portion;
a first reflecting section and a second reflecting section opposed to each other with the light emitting section therebetween;
a base that holds the second reflecting portion with a gap between the light emitting portion and the second reflecting portion;
a piezoelectric member that deforms in response to an applied drive voltage;
The base portion includes a first region and a second region having a lower rigidity than the first region,
the second reflecting portion and the piezoelectric member are provided in the second region, and application of the drive voltage causes the piezoelectric member to deform the second region to drive the second reflecting portion, thereby emitting laser light whose wavelength changes depending on the distance between the first reflecting portion and the second reflecting portion. The optical device according to claim 1, wherein the second region is formed thinner than the first region. The optical device according to claim 1 or 2, wherein at least a portion of the piezoelectric member is provided around the second reflecting portion in the second region. The optical device according to any one of claims 1 to 3, wherein the second reflecting portion and the piezoelectric member have an overlapping area. The optical device according to any one of claims 1 to 4, wherein the piezoelectric member is provided on a surface of the second region facing the light-emitting portion. The optical device according to any one of claims 1 to 4, wherein the piezoelectric member is provided on a surface of the second region opposite to a surface facing the light-emitting portion. A second base portion that holds the base portion;
A base drive unit that drives the base unit,
the second base portion has a third region and a fourth region having a lower rigidity than the third region and connecting the base portion and the third region;
The optical device according to any one of claims 1 to 6, wherein the base driving unit changes at least one of the distance between the first reflecting unit and the second reflecting unit or the inclination angle of the second reflecting unit relative to the first reflecting unit by deforming the fourth region to drive the base. The optical device according to claim 7, wherein the resonant frequency of the second reflector and the second region is different from the resonant frequency of the base and the third region. The optical device according to claim 7 or 8, wherein the fourth region has a meandering structure in which adjacent beam members are connected at their ends. Two or more of the fourth regions;
The optical device according to claim 7 , further comprising: two or more base drive units provided for each of two or more of the fourth regions, the two or more base drive units configured to drive the base. the base portion includes a plurality of the second regions,
The optical device according to claim 1 , wherein each of the second regions includes the second reflecting portion and the piezoelectric member. The optical device according to claim 11, wherein the piezoelectric member independently drives the second reflecting portion. The optical device according to any one of claims 1 to 12, wherein the second reflecting portion is a reflecting mirror formed on a member that constitutes the second region. The optical device according to any one of claims 1 to 12, wherein the second reflecting portion includes a periodic structure formed in a member that constitutes the second region. The optical device according to any one of claims 1 to 12, wherein the member constituting the second region includes a multilayer reflector. A distance measuring device for measuring at least one of a distance to an object or a speed of the object,
16. An optical device according to claim 1 ,
A distance measuring device that measures at least one of the distance and the speed based on return light from the object of the laser light irradiated from the optical device to the object. A moving object comprising the distance measuring device according to claim 16.

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