JP2016149532A - Wavelength variable laser device and optical coherence tomography - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wavelength variable laser device capable of improving a wavelength variation width, and an optical coherence tomography employing the wavelength variable laser device.SOLUTION: The wavelength variable laser device comprises: a first reflector; a second reflector; an active layer that is formed between the first reflector and the second reflector; a quantum well structure layer to which a reverse bias voltage is applied to generate quantum confined Stark effects; and an electrode for applying the reverse bias voltage to the quantum well structure layer. A gap is formed between the active layer and the second reflector, and a resonance wavelength is swept by changing a length of the gap. When sweeping the resonance wavelength, the electrode changes the application of the reverse bias voltage to be applied to the quantum well structure layer in accordance with the length of the gap.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a wavelength tunable laser device and an optical coherence tomometer using the wavelength tunable laser device.

  Recently, a tunable laser apparatus that can change the wavelength of the emitted laser light has attracted attention. As one of the wavelength tunable laser devices, a vertical cavity surface emitting laser (VCSEL) device has been proposed. In the vertical cavity surface emitting laser device, the distance between the two reflecting mirrors is changed by displacing one of the two reflecting mirrors, thereby changing the oscillation wavelength of the laser beam, that is, the resonance wavelength. . As a movable part (movable mechanism) for displacing the reflecting mirror, one applying a micro electro mechanical system (MEMS) technology has been proposed. A vertical cavity surface emitting laser device to which MEMS technology is applied is referred to as a MEMS-VCSEL.

  The MEMS-VCSEL can change the wavelength continuously. In addition, since the movable part of the MEMS-VCSEL is fine, the movable part can be displaced at high speed, and therefore the wavelength can be changed at high speed. Further, the MEMS-VCSEL has low power consumption. Due to such characteristics, MEMS-VCSEL has attracted much attention.

Connie J. Chang-Hasnain, Fellow, IEEE, “Tunable VCSEL”, IEEE Journal on Selected Topics in Quantum Electronics, Vol. 6, No. 6, pp.978-987, 2000

  However, the conventional vertical cavity surface emitting laser device cannot always provide a sufficiently wide wavelength variable width.

  An object of the present invention is to provide a wavelength tunable laser device capable of improving the wavelength tunable width.

  According to one aspect of the present invention, a first reflecting mirror, a second reflecting mirror, an active layer formed between the first reflecting mirror and the second reflecting mirror, and a reverse bias voltage are provided. A quantum well structure layer in which a quantum confined Stark effect is generated by applying a voltage, and an electrode for applying a reverse bias voltage to the quantum well structure layer, the active layer and the second reflector A gap is formed between them, and the resonance wavelength is swept by changing the length of the gap, and at the time of sweeping the resonance wavelength, the electrode is placed in the quantum well structure layer according to the length of the gap. A wavelength tunable laser device is provided that changes the reverse bias voltage to be applied.

  According to the present invention, it is possible to provide a wavelength tunable laser device having a wide variable wavelength width.

It is sectional drawing and a top view which show the wavelength tunable laser apparatus by 1st Embodiment of this invention. It is sectional drawing of the upper reflective mirror of the wavelength tunable laser apparatus by this embodiment. It is a graph which shows the relationship between the length of a gap | gap, an oscillation wavelength, and a mode. 4 is a graph showing a relationship between an initial gap length and a wavelength tunable width in the wavelength tunable laser device according to the first embodiment of the present invention. It is the schematic which shows the measuring apparatus by 1st Embodiment of this invention. It is sectional drawing and a top view which show the wavelength tunable laser apparatus by 2nd Embodiment of this invention. It is a figure which shows the drive method of the wavelength tunable laser apparatus by 3rd Embodiment of this invention. It is sectional drawing which shows the wavelength tunable laser apparatus by 4th Embodiment of this invention. It is a graph which shows the simulation result in the vertical cavity surface emitting laser apparatus by a reference example. It is a graph which shows the relationship between the length of a gap | interval, an oscillation wavelength, and a mode in the wavelength tunable laser apparatus by a comparative example.

  In the conventional vertical cavity surface emitting laser device, a sufficiently wide wavelength tunable width cannot always be obtained. The reason why a sufficiently wide wavelength tunable width is not necessarily obtained in the conventional vertical cavity surface emitting laser device is as follows.

  That is, in the vertical cavity surface emitting laser device, the beam-like support portion is displaced by applying a voltage to the beam-like support portion that supports the upper reflecting mirror, for example. When a voltage is applied to the beam-shaped support, electrostatic attraction occurs, and the beam-shaped support is displaced in a direction that reduces the length of the gap existing between the upper and lower reflectors. To do. The beam-shaped support portion is held in a state where the repulsive force of the spring and the electrostatic attractive force are balanced on the beam-shaped support portion. If the voltage applied to the beam-shaped support exceeds a certain voltage, the balance between the spring repulsive force and the electrostatic attraction in the beam-shaped support cannot be obtained, and the beam existing on the member below the beam-shaped support The shaped support part comes into contact. Generally, when a displacement of about one third of the length of the initial gap occurs in the beam-shaped support portion, the balance between the repulsive force of the spring and the electrostatic attractive force in the beam-shaped support portion cannot be obtained, A beam-shaped support part will contact the member which exists under the beam-shaped support part. In this way, the displacement of the beam-like support portion is limited to about one third of the initial gap length. Such a restriction is referred to as a third restriction. Since the amount of displacement of the beam-like support portion is limited to about one third of the initial gap length, it is preferable that the initial gap length is larger from the viewpoint of one third limitation.

  On the other hand, when the interval between the lower reflecting mirror and the upper reflecting mirror is simply changed, a transition from one mode to another mode, that is, mode hopping occurs. Mode hopping occurs because there are a plurality of longitudinal modes in a wavelength range where laser oscillation is possible. If the longitudinal mode interval is wider than the wavelength range in which laser oscillation is possible, mode hopping will not occur. That is, if there is no other longitudinal mode within the wavelength range where laser oscillation is possible, there is no hopping destination mode, and mode hopping does not occur. If there is no other longitudinal mode in the wavelength range where laser oscillation is possible, the oscillation wavelength, that is, the resonance wavelength can be changed over the entire wavelength range where laser oscillation is possible. As a method for widening the longitudinal mode interval, it is possible to narrow the interval between the lower reflecting mirror and the upper reflecting mirror. If the distance between the lower reflecting mirror and the upper reflecting mirror is reduced, the length of the gap is also reduced. Therefore, it is preferable to reduce the length of the gap from the viewpoint of suppressing mode hopping.

  As described above, in the vertical cavity surface emitting laser device, it is better to increase the initial gap length from the viewpoint of one third restriction, and from the viewpoint of suppressing mode hopping, It is better to reduce the length of the gap. That is, in the vertical cavity surface emitting laser device, there is a trade-off relationship with respect to the initial gap length.

  FIG. 9 is a graph showing a simulation result in the vertical cavity surface emitting laser device according to the reference example. The dot-dash line plot shows the amount of change in oscillation wavelength that occurs when a displacement of one-third of the initial gap length is caused in the beam-like support. That is, the dot-dash line plot shows the difference between the oscillation wavelength before displacement and the oscillation wavelength after displacement, that is, the wavelength difference between the oscillation wavelengths before and after the displacement. The dashed plot shows the longitudinal mode spacing corresponding to the initial gap length, ie, the wavelength difference between the modes corresponding to the initial gap length.

  As can be seen from FIG. 9, the wavelength difference when a displacement of one third of the initial gap length is generated increases as the initial gap length increases. On the other hand, the longitudinal mode interval corresponding to the initial gap length decreases as the initial gap length increases.

  As can be seen from FIG. 9, the largest wavelength difference is obtained when the initial gap length is about 1.7 μm. If the initial gap length is set to about 1.7 μm, a wavelength difference of about 70 nm, that is, a wavelength variable width of about 70 nm can be obtained.

  For the above reasons, the conventional wavelength tunable laser device cannot always obtain a sufficiently wide wavelength tunable width.

  As a result of intensive studies, the present inventor has come up with the idea of improving the wavelength tunable width as follows.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.

[First Embodiment]
A wavelength tunable laser device according to a first embodiment of the present invention and a measurement apparatus using the wavelength tunable laser device will be described with reference to FIGS.

(Wavelength tunable laser device)
First, the wavelength tunable laser device 10 according to the present embodiment will be described.

  The wavelength tunable laser device 10 according to the present embodiment is a wavelength tunable laser device to which the MEMS technology is applied, more specifically, a vertical cavity surface emitting laser device (MEMS-VCSEL) to which the MEMS technology is applied.

  FIG. 1A is a cross-sectional view showing the wavelength tunable laser device according to the present embodiment.

  As shown in FIG. 1A, a reflecting mirror (first reflecting mirror, lower reflecting mirror) 102 is formed on a substrate 101. For example, an n-type GaAs substrate is used as the substrate 101. For example, a DBR (Distributed Bragg Reflector) is formed as the lower reflecting mirror 102. The lower reflecting mirror 102 is constituted by, for example, an alternate stack including 30 pairs of GaAs layers and AlAs layers each having an optical film thickness of ¼ of λc1. λc1 is the center wavelength of the high reflection band of the lower reflecting mirror 102, and is, for example, about 1057 nm in this embodiment. In the specification of the present application, the high reflection band of the reflecting mirror is a wavelength band in which the reflectance sufficient for enabling laser oscillation is obtained in the reflecting mirror, specifically, 98% or more. It means the wavelength band where the reflectance is obtained in the reflecting mirror. Note that an electrode (n-side electrode, back electrode) 110 is formed on the back surface (lower surface) of the substrate 101.

An active layer 103 is formed on the lower reflecting mirror 102, that is, on the first reflecting mirror. The active layer 103 includes a quantum well (not shown) in which an In _0.35 GaAs layer (not shown) having a thickness of about 8 nm is sandwiched between GaAsP layers (not shown). The active layer 103 further includes a quantum well (not shown) in which an In _0.32 GaAs layer (not shown) having a thickness of about 8 nm is sandwiched between GaAsP layers (not shown). P (phosphorus) has the effect of reducing the lattice constant relative to GaAs. On the other hand, In (indium) has the effect of increasing the lattice constant relative to GaAs. For this reason, in the active layer 103 including the InGaAs layer and the GaAsP layer, the cumulative strain is suppressed. The conductivity type of the active layer 103 is, for example, i-type (undoped). The active layer 103 is configured so that the wavelength when the threshold current becomes the minimum value is located on the short wavelength side with respect to the center wavelengths λc1 and λc2 of the high reflection bands of the reflecting mirrors 102 and 106. The gain of the active layer 103 at wavelengths shorter than λc1 and λc2 is larger than the gain of the active layer 103 at wavelengths longer than λc1 and λc2. Here, the threshold current is a minimum current capable of laser oscillation.

  On the active layer 103, two support portions 107 are arranged apart from each other. Above the active layer 103, a quantum well structure layer (multiple quantum well structure layer, QCSE layer) 105 in which a quantum confined Stark effect (QCSE) is generated is formed. The quantum confined Stark effect is a phenomenon in which the absorption edge wavelength shifts to the longer wavelength side when an electric field is applied to the quantum well structure. A beam-shaped support portion 122 is formed by the quantum well structure layer 105. That is, the quantum well structure layer 105 also serves as the beam-shaped support portion 122. The beam-shaped support part 122 is formed using the MEMS technology. Both ends of the beam-shaped support part 122 are fixed by the support part 107. The beam-shaped support part 122 supports the upper reflecting mirror 106 so as to be displaceable. A mechanism (movable mechanism, support mechanism) that changes the distance between the lower reflecting mirror 102 and the upper reflecting mirror 106 is configured by such a beam-shaped support portion 122. In other words, a mechanism for changing the gap between the lower reflecting mirror 102 and the upper reflecting mirror 106 is configured by the beam-shaped support portion 122. It can be considered that the quantum well structure layer 105 and the upper reflecting mirror 106 together constitute a movable mechanism (movable part) 122. The thickness of the support part 107 is set to about 3.8 μm, for example. For this reason, the length of the gap (air gap) 104 in a state where no voltage is applied to the beam-shaped support portion 122, that is, in the initial state is, for example, about 3.8 μm. That is, in the present embodiment, the length of the gap 104 in a state where no voltage is applied to the beam-shaped support portion 122, that is, in a state where the distance between the lower reflecting mirror 102 and the upper reflecting mirror 106 is not changed, It is larger than 1.7 μm. That is, the length of the gap 104 when no voltage is applied to the beam-like support portion 122 is greater than 1.7 μm.

The quantum well structure layer 105 includes, for example, a quantum well (not shown) in which an In _0.32 GaAs layer (not shown) having a thickness of about 6 nm is sandwiched between GaAs layers (not shown). The quantum well structure layer 105 is preferably a multiple quantum well structure in which quantum well structures are multiplexed. On the lower surface side of the quantum well structure layer 105, for example, an n-type semiconductor layer (not shown) is formed. For example, an n-type doped Al _0.2 GaAs layer is formed as the n-type semiconductor layer. On the other hand, on the upper surface side of the quantum well structure layer 105, for example, a p-type semiconductor layer (not shown) is formed. As the p-type semiconductor layer, for example, a p-type doped Al _0.2 GaAs layer is formed. Thus, the quantum well structure layer 105 has a pin structure in which a p-type semiconductor layer and an n-type semiconductor layer are formed above and below an i-type (non-doped) quantum well structure. Applying a voltage to the quantum well structure layer 105 means applying a voltage to the pin structure of the quantum well structure layer 105, more specifically, the p-type semiconductor layer of the quantum well structure layer 105 and It means applying a reverse bias (reverse voltage) between the n-type semiconductor layer. By applying a negative voltage to the p-type semiconductor layer side and a positive voltage to the n-type semiconductor layer side, a reverse bias is applied to the quantum well structure layer 105.

  In a state where no voltage is applied to the quantum well structure layer 105, the band gap of the quantum well structure layer 105 is set so that the absorption edge wavelength of the quantum well structure layer 105 is not located in the high reflection band of the reflectors 102 and 106. Is set. In a state where no reverse bias voltage is applied to the quantum well structure layer 105, the absorption edge of the quantum well structure layer 105 is on the short wavelength side of the shortest wavelength in the sweep range of the resonance wavelength. In a state where no voltage is applied to the quantum well structure layer 105, that is, in a state where no reverse bias is applied, the quantum well structure layer 105 is resistant to oscillation in the high reflection band of the reflecting mirrors 102 and 106. There is no particular effect.

  On the other hand, when a voltage is applied to the quantum well structure layer 105, the band gap of the quantum well structure layer 105 is set so that the absorption edge wavelength of the quantum well structure layer 105 is located in the high reflection band of the reflectors 102 and 106. Is set. Specifically, when a voltage is applied to the quantum well structure layer 105, the quantum well structure layer 105 is configured such that absorption occurs at a wavelength shorter than the center wavelengths λc1 and λc2 of the high reflection bands of the reflectors 102 and 106. Is configured. Therefore, in a state where a voltage is applied to the quantum well structure layer 105, oscillation is inhibited on the short wavelength side with respect to the center wavelengths λc1 and λc2 of the high reflection bands of the reflecting mirrors 102 and 106. That is, a reverse bias voltage is applied to the quantum well structure layer 105 when oscillating at a wavelength longer than a predetermined wavelength.

A reflecting mirror (second reflecting mirror, upper reflecting mirror) 106 is formed on the quantum well structure layer 105, that is, on the beam-shaped support portion 122. The upper reflecting mirror 106 is supported by a beam-like support part 122 so as to be displaceable. For example, a DBR is formed as the upper reflecting mirror 106. FIG. 2 is a cross-sectional view of the upper reflecting mirror of the wavelength tunable laser device according to the present embodiment. As shown in FIG. 2, the upper reflecting mirror 106 includes, for example, an alternating laminated film including 15 pairs of SiO ₂ layers 301 and TiO ₂ layers 302 each having an optical film thickness of ¼ of λc2. have. λc2 is the center wavelength of the high reflection band of the upper reflecting mirror 106, and is, for example, about 1057 nm in this embodiment.

An intermediate refractive index layer 303 having an intermediate refractive index between SiO ₂ and TiO ₂ is formed on the upper side of the uppermost TiO ₂ layer 302 of the alternate laminated film composed of the SiO ₂ layer 301 and the TiO ₂ layer 302. Has been. For example, a SiN layer is used as the intermediate refractive index layer 303. The optical film thickness of the intermediate refractive index layer 303 is set to be larger than a quarter of the center wavelength λc2 of the high reflection band of the upper reflecting mirror 106. More specifically, the optical film thickness of the intermediate refractive index layer 303 is set to, for example, 1.05 times a quarter of the center wavelength λc2 of the high reflection band of the upper reflecting mirror 106.

  Since the intermediate refractive index layer 303 is formed on the upper reflecting mirror 106, the reflectance of the upper reflecting mirror 106 is minimized at a wavelength corresponding to the thickness of the intermediate refractive index layer 303, that is, a dip. Is observed. In the present embodiment, since the optical film thickness of the intermediate refractive index layer 303 is larger than a quarter of the center wavelength λc2 of the high reflection band of the upper reflecting mirror 106, the center wavelength λc2 of the high reflection band of the upper reflecting mirror 106 is larger. A dip is observed on the long wavelength side. Since a dip is observed on the long wavelength side with respect to the center wavelength λc2 of the high reflection band of the upper reflecting mirror 106, the threshold gain is larger on the long wavelength side than the center wavelength λc2 of the high reflection band of the upper reflecting mirror 106. It is relatively high. For this reason, the threshold gain is relatively low on the short wavelength side with respect to the center wavelength λc2 of the high reflection band of the upper reflecting mirror 106. The threshold gain is a gain when the laser oscillation is obtained with the gain exceeding the loss. Thus, in the present embodiment, the upper reflecting mirror 106 is configured so that the threshold gain on the short wavelength side is relatively low and the threshold gain on the high wavelength side is relatively high. Therefore, in a state where no voltage is applied to the quantum well structure layer 105, oscillation tends to occur on the short wavelength side with respect to the center wavelength λc2 of the high reflection band of the upper reflecting mirror 106.

  FIG. 1B is a plan view of the wavelength tunable laser device according to the present embodiment. FIG. 1B shows the wavelength tunable laser device 10 according to the present embodiment as viewed from the upper surface side.

  As shown in FIG. 1B, on the substrate 101, two support portions 107 are arranged apart from each other. Both ends of the beam-shaped support part 122 formed by using the MEMS technology are fixed by the support part 107. A region 123 indicated by a broken line in FIG. 1B conceptually indicates a region where light emission occurs. A region 123 where light emission occurs is a part of the laser unit 124.

  The electrode 111 is for injecting current into the active layer 103 and is in contact with the upper surface of the active layer 103. The electrode 113 is for applying a voltage to the quantum well structure layer 105, and is connected to a p-type semiconductor layer located on the upper surface of the quantum well structure layer 105. The electrode 112 is for applying a voltage to the quantum well structure layer 105, and is connected to an n-type semiconductor layer located on the lower surface of the quantum well structure layer 105. When a reverse bias is applied to the quantum well structure layer 105, the potential of the electrode 112 connected to the n-type semiconductor layer located on the lower surface of the quantum well structure layer 105 is located on the upper surface of the quantum well structure layer 105. It is set higher than the potential of the electrode 113 connected to the p-type semiconductor layer. In the present embodiment, the quantum well structure layer 105 can be controlled by changing the voltage applied between the pair of electrodes 112, 113, that is, the one electrode 112 and the other electrode 113.

  Further, in this embodiment, by changing the voltage applied between the electrode 110 and the electrode 112, the beam-shaped support part 122 can be displaced, and the oscillation wavelength, that is, the resonance wavelength can be swept.

  The resonator 12 of the wavelength tunable laser device 10 according to the present embodiment includes a lower reflecting mirror 102, an active layer 103, a quantum well structure layer 105, an upper reflecting mirror 106, a lower reflecting mirror 102, and an upper reflecting mirror 106. And a mechanism (movable mechanism) 122 for changing the interval. A gap 104 whose length changes in accordance with a change in the distance between the lower reflecting mirror 102 and the upper reflecting mirror 106 exists between the lower reflecting mirror 102 and the upper reflecting mirror 106.

  Thus, the wavelength tunable laser device 10 according to the present embodiment is configured.

  FIG. 3 is a graph showing the relationship between the gap length, the oscillation wavelength, and the mode. The horizontal axis indicates the length of the gap 104. The vertical axis represents the oscillation wavelength of the laser light.

  As can be seen from FIG. 3, the length of the gap 104 is, for example, about 3.8 μm when no voltage is applied to the beam-like support portion 122. When the length of the gap 104 is about 3.8 μm, for example, there is a mode that resonates at a wavelength of about 1098 nm. This resonance mode (longitudinal mode) is referred to herein as mode B. As can be seen from FIG. 3, when the length of the gap 104 is about 3.8 μm, there is a mode that resonates at a wavelength shorter than 1098 nm. This resonance mode is referred to herein as mode A.

  When the gap between the reflecting mirror 102 and the reflecting mirror 106 is reduced until the length of the gap 104 is, for example, about 3.0 μm, the oscillation wavelength of mode B is, for example, about 1007 nm. As can be seen from FIG. 3, when the length of the gap 104 is about 3.0 μm, there is a mode that resonates at a wavelength longer than 1007 nm. This resonance mode is referred to herein as mode C.

  In the present embodiment, there are a plurality of modes, that is, two or more modes, within the high reflection bands of the reflecting mirrors 102 and 106, that is, within a range in which the oscillation wavelength of the laser light can be changed. More specifically, in the present embodiment, there are three modes within a range in which the oscillation wavelength of the laser light can be changed. For this reason, when the interval between the lower reflecting mirror 102 and the upper reflecting mirror 106 is simply changed, a transition from mode B to the other modes A and C, that is, mode hopping may occur.

  Therefore, in the present embodiment, mode hopping is prevented by appropriately controlling the voltage applied to the quantum well structure layer 105 according to the length of the gap between the lower reflecting mirror 102 and the upper reflecting mirror 106, thereby preventing wide hopping. Oscillation in mode B is maintained in the wavelength band.

  When resonating at a wavelength longer than 1057 nm, which is the center wavelength λc1, λc2 of the high reflection band of the reflecting mirrors 102, 106, current is injected into the active layer 103 and a voltage (reverse bias) is applied to the quantum well structure layer 105. Apply. Specifically, the potential of the electrode 112 and the potential of the electrode 113 are set so that the potential of the electrode 112 is, for example, about 10 V higher than the potential of the electrode 113. When a reverse bias is applied to the quantum well structure layer 105, the absorption edge wavelength in the quantum well structure layer 105 shifts to the long wavelength side, so that the short wavelength side of the central wavelengths λc1 and λc2 of the high reflection band of the reflector 106 Oscillation is inhibited. Therefore, when a reverse bias is applied to the quantum well structure layer 105, reliable oscillation at a relatively long wavelength is realized.

  On the other hand, when resonating at a wavelength shorter than 1057 nm, which is the central wavelength λc1, λc2 of the high reflection band of the reflecting mirrors 102, 106, current is injected into the active layer 103, but voltage is applied to the quantum well structure layer 105. Is not applied. Specifically, the potential difference between the electrode 112 and the electrode 113 is set to 0V. If no voltage is applied to the quantum well structure layer 105, the absorption edge wavelength of the quantum well structure layer 105 is shorter than the high reflection bands of the reflecting mirrors 102 and 106. As described above, in the present embodiment, the upper reflecting mirror 106 is configured such that the threshold gain on the short wavelength side is relatively low and the threshold gain on the high wavelength side is relatively high. Therefore, in a state where no voltage is applied to the quantum well structure layer 105, oscillation tends to occur on the short wavelength side with respect to the center wavelength λc2 of the high reflection band of the upper reflecting mirror 106. For this reason, in the state where no voltage is applied to the quantum well structure layer 105, reliable oscillation in a relatively short wavelength region is realized.

  The length of the gap 104 corresponding to 1057 nm which is the center wavelength λc1 and λc2 of the high reflection bands of the reflecting mirrors 102 and 106 is, for example, about 3.4 μm. Accordingly, when the length of the gap 104 is, for example, 3.4 μm or more, a voltage is applied to the quantum well structure layer 105 in order to realize reliable oscillation at a relatively long wavelength. On the other hand, when the length of the gap 104 is, for example, less than 3.4 μm, no voltage is applied to the quantum well structure layer 105 in order to realize reliable oscillation at a relatively short wavelength.

  The length of the gap 104 can be changed by changing the voltage applied to the beam-like support portion 122. That is, the length of the gap 104 can be changed by changing the voltage applied between the electrode 110 and the electrode 112. Note that when the voltage applied to the beam-shaped support portion 122 is changed, the length of the gap 104 changes because when the voltage applied to the beam-shaped support portion 122 is changed, the beam-shaped support portion 122 is changed. This is because the electrostatic attraction that works changes. That is, the gap length is changed by applying an alternating voltage to the beam-shaped support portion 122 and vibrating the upper reflecting mirror 106. Further, the application of the reverse bias voltage applied to the quantum well structure layer 105 is changed in accordance with the amplitude change of the alternating voltage applied to the support part 122.

  The voltage applied to the electrode 112 when the length of the gap 104 is, for example, 3.4 μm can be obtained in advance. Therefore, when the voltage applied to the electrode 112 is such that the length of the gap 104 is 3.4 μm or more, a voltage is applied to the quantum well structure layer 105. That is, when the voltage applied to the electrode 112 is equal to or lower than a predetermined voltage, the voltage between the electrode 112 and the electrode 113 is set to about 10 V, for example. On the other hand, when a voltage such that the length of the gap 104 is less than 3.4 μm is applied to the electrode 112, no voltage is applied to the quantum well structure layer 105. That is, when the voltage applied to the electrode 112 is higher than the predetermined voltage, the voltage between the electrode 112 and the electrode 113 is set to 0V.

  In the present embodiment, for example, the oscillation wavelength of the laser light is swept around the center wavelengths λc1 and λc2 of the high reflection bands of the reflecting mirrors 102 and 106.

  In order to control the application of voltage to the quantum well structure layer 105 in this way, the voltage applied to the quantum well structure layer 105 when the gap length is greater than or equal to a predetermined value is less than the predetermined value. In some cases, the voltage is larger than the voltage applied to the quantum well structure layer 105.

  As described above, in this embodiment, when oscillation is performed at a relatively long wavelength, a reliable oscillation at a relatively long wavelength is realized by applying a voltage to the quantum well structure layer 105. On the other hand, when oscillating at a relatively short wavelength, by applying no voltage to the quantum well structure layer 105, reliable oscillation at a relatively short wavelength is realized. For this reason, according to this embodiment, mode hopping can be reliably prevented, and a wavelength tunable laser device having a wide wavelength tunable width can be obtained.

(Evaluation results)
Next, the evaluation result of the wavelength tunable laser device according to the present embodiment will be described.

  FIG. 10 is a graph showing the relationship between the gap length, the oscillation wavelength, and the mode in the wavelength tunable laser device according to the comparative example. In the comparative example, the oscillation wavelength is changed by simply changing the distance between the lower reflecting mirror and the upper reflecting mirror. That is, in the comparative example, the quantum well structure layer 105 as in the present embodiment is not provided.

  In the comparative example, the initial gap length was about 1.5 μm. When the initial gap length is 1.5 μm, if a displacement of one third of the initial gap length is generated, the gap length becomes 1.0 μm.

  As can be seen from FIG. 10, when the gap length is changed from 1.5 μm to 1.0 μm, the oscillation wavelength changes by about 68 nm. If the length of the gap is smaller than 1.0 μm, the one-third restriction will not be satisfied, and there is a possibility that the balance between the repulsive force of the spring and the electrostatic attractive force in the beam-like support portion may not be achieved. It is not preferable to make the value smaller than 1.0 μm. For this reason, in the wavelength tunable laser device according to the comparative example, the wavelength tunable width is about 68 nm.

  On the other hand, in the present embodiment, when sweeping the resonance wavelength, the voltage application to the quantum well structure layer 105 is controlled according to the length of the gap between the lower reflecting mirror 102 and the upper reflecting mirror 106. Hopping can be reliably prevented. Therefore, in the present embodiment, there is no restriction due to the longitudinal mode interval as plotted with a broken line in FIG. Therefore, according to the present embodiment, the length of the gap 104 when no voltage is applied to the beam-like support portion 122 can be significantly increased. According to the present embodiment, since the length of the initial gap 104 can be remarkably increased, the length of about one third of the length of the initial gap 104 is sufficiently thick. For this reason, according to this embodiment, it becomes possible to change an oscillation wavelength in a very wide wavelength range.

  When the length of the gap 104 is changed from, for example, 3.8 μm to 3.0 μm, as can be seen from FIG. 3, for example, in the wavelength region of about 1007 nm to 1098 nm, the mode B changes to the other modes A and C. The oscillation wavelength can be changed without causing mode hopping. The wavelength difference between the wavelength 1098 nm and the wavelength 1007 nm is 91 nm. That is, in this embodiment, a wavelength variable width of, for example, about 91 nm is obtained.

  FIG. 4 is a graph showing the relationship between the initial gap length and the variable wavelength width in the variable wavelength laser device according to the present embodiment. The horizontal axis indicates the initial gap length, and the vertical axis indicates the wavelength variable width.

  As can be seen from FIG. 4, when the length of the initial gap 104 is set to 3.8 μm, the wavelength variable width can be about 91 nm.

  When the oscillation wavelength is changed from 1098 nm to 1007 nm, the length of the gap 104 changes from 3.8 μm to 3.0 μm. The difference between the length of 3.8 μm and the length of 3.0 μm, that is, the amount of change in the length of the gap 104 is about 0.8 μm. The amount of change in the length of the gap 104 of 0.8 μm is sufficiently small with respect to one third of the length of the initial gap 104. Therefore, even if the oscillation wavelength is changed from 1098 nm to 1007 nm, there is a sufficient margin for the one third restriction.

  Thus, according to the present embodiment, a wavelength tunable laser device having an extremely wide wavelength tunable width can be obtained.

(measuring device)
Next, the measurement apparatus using the wavelength tunable laser apparatus according to the present embodiment will be described with reference to FIG. FIG. 5 is a schematic view showing the measuring apparatus according to the present embodiment.

  Here, the case where the wavelength tunable laser device 10 according to the present embodiment is used for the light source unit 801 of an optical coherence tomography (OCT apparatus: Optical Coherence Tomography apparatus) will be described as an example, but the present invention is not limited to this. . The wavelength tunable laser device 10 according to the present embodiment is not limited to the light source unit 801 of the optical coherence tomography, and can be used for various applications. Since an optical coherence tomometer using a wavelength tunable laser device as the light source unit 801 does not require the use of a spectroscope, the loss of light amount is small and a tomographic image with a high S / N ratio can be acquired.

  As illustrated in FIG. 5, the measurement apparatus (OCT apparatus) 8 according to the present embodiment includes a light source unit 801, an interference optical system 802, a light detection unit 803, and an information acquisition unit 804.

  The light source unit 801 uses the wavelength tunable laser device 10 according to the present embodiment.

  The information acquisition unit 804 has a Fourier transformer (not shown). Here, the information acquisition unit 804 having a Fourier transformer means that the information acquisition unit 804 has a function of performing Fourier transform on the input data. The embodiment is not particularly limited. One example is a case where the information acquisition unit 804 has a calculation unit (not shown), and the calculation unit has a function of performing Fourier transform. More specifically, the calculation unit is a computer having a CPU (Central Processing Unit), and the computer executes an application having a Fourier transform function. Another example is a case where the information acquisition unit 804 has a Fourier transform circuit having a Fourier transform function.

  The light output from the light source unit 801 passes through the interference optical system 802 and becomes interference light including information on the object 812 that is a measurement target (measurement target), and the interference light is received by the light detection unit 803.

  The light detection unit 803 may be a differential detection type photodetector or a simple intensity monitor type photodetector.

  Information on the time waveform of the intensity of the interference light received by the light detection unit 803 is output from the light detection unit 803 to the information acquisition unit 804.

  The information acquisition unit 804 acquires information on the object 812 (for example, information on a tomographic image) by acquiring the peak value of the time waveform of the intensity of the received interference light and performing Fourier transform.

  Hereinafter, a detailed description will be given of the process from when light is emitted from the light source unit 801 until information on a tomographic image of the object 812 as a measurement target is obtained.

  The light emitted from the light source unit 801 passes through the fiber 805, enters the coupler 806, and is branched into irradiation light that passes through the irradiation light fiber 807 and reference light that passes through the reference light fiber 808. . As the coupler 806, a 3 dB coupler which is a coupler having a branching ratio of 1: 1 is used. The coupler 806 can operate in a single mode in the wavelength band of light emitted from the light source unit 801.

  Irradiation light propagating through the fiber 807 passes through the collimator 809 to become parallel light and is reflected by the mirror 810. The light reflected by the mirror 810 is irradiated to the object 812 through the lens 811 and reflected by each layer in the depth direction of the object 812.

  On the other hand, the reference light propagating in the fiber 808 is reflected by the mirror 814 through the collimator 813.

  In the coupler 806, interference light is generated by the reflected light from the object 812 and the reflected light from the mirror 814. The light thus interfered passes through the fiber 815, is collected through the collimator 816, and is received by the light detection unit 803.

  Information on the intensity of the interference light received by the light detection unit 803 is converted into electrical information such as a voltage and sent to the information acquisition unit 804.

  The information acquisition unit 804 processes interference light intensity data, specifically, performs Fourier transform to obtain tomographic image information. The interference light intensity data that is subjected to Fourier transform is usually data sampled at equal wave intervals, but is not limited to this, and may be data sampled at equal wavelength intervals. .

  The information of the tomographic image acquired in this way is sent from the information acquisition unit 804 to the image display unit 817 and can be displayed as an image.

  Note that a three-dimensional tomographic image of the object 812 to be measured can be obtained by scanning the mirror 810 in a direction perpendicular to the direction in which the irradiation light is incident.

  Although not shown, the intensity of light emitted from the light source unit 801 may be monitored successively, and the data may be used for amplitude correction of the signal of the intensity of interference light.

  The information acquisition unit 804 can control the light source unit 801 via the electric circuit 818. As described above, in this embodiment, when the tunable laser device is oscillated with a relatively long wavelength, a voltage is applied to the quantum well structure layer 105. On the other hand, when the tunable laser device is oscillated with a relatively short wavelength, no voltage is applied to the quantum well structure layer 105. Control of voltage application to the quantum well structure layer 105 can be performed by, for example, the information acquisition unit 804. That is, the information acquisition unit 804 can function as a control unit that controls application of a voltage to the quantum well structure layer 105. The information acquisition unit (control unit) 804 controls voltage application to the quantum well structure layer 105 by appropriately setting a voltage between the electrode 112 and the electrode 113 via the electric circuit 818. In addition, the information acquisition unit (control unit) 804 displaces the movable mechanism 122 by appropriately setting the voltage between the electrode 110 and the electrode 112 via the electric circuit 818, thereby causing the wavelength tunable laser device 10 to The oscillation wavelength of the emitted laser light is changed. In addition, the information acquisition unit (control unit) 804 injects current into the active layer 103 connected to the electrode 111 via the electric circuit 818.

  Here, the case where the information acquisition unit 804 controls the application of voltage to the quantum well structure layer 105 has been described as an example, but the present invention is not limited to this. You may make it control the application of the voltage with respect to the quantum well structure layer 105 using the control part (not shown) separate from the information acquisition part 804. FIG. Further, the voltage applied to the electrode 112 connected to the movable mechanism 122 may be controlled by a control unit separate from the information acquisition unit 804 to change the oscillation wavelength of the laser light emitted from the wavelength tunable laser device 10. . Further, a current may be injected into the active layer 103 by a control unit separate from the information acquisition unit 804. In this case, a control unit separate from the information acquisition unit 804 may be provided in the light source unit 801, or may be provided separately from the light source unit 801.

  The measurement apparatus 8 according to the present embodiment is useful when acquiring information related to a tomographic image of a living body such as an animal or a person in fields such as ophthalmology, dentistry, and dermatology. The information related to the tomographic image of the living body includes not only the tomographic image of the living body itself but also numerical data necessary for obtaining the tomographic image of the living body. In particular, the measurement apparatus 8 according to the present embodiment is suitable when the measurement target is the fundus of the human body and information regarding a tomographic image of the fundus is acquired.

  The wavelength tunable laser device 10 according to the present embodiment has a very wide wavelength tunable width as described above. For this reason, if the wavelength tunable laser device 10 according to the present embodiment is used, the measuring device 8 capable of acquiring a high resolution tomographic image can be realized.

  Here, the case where the wavelength tunable laser device 10 according to the present embodiment is used as the light source of the measuring device 8 has been described as an example, but the present invention is not limited to this. For example, the wavelength tunable laser device 10 according to the present embodiment may be used as a light source for optical communication or may be used as a light source for optical measurement.

[Second Embodiment]
A wavelength tunable laser device according to a second embodiment of the present invention will be described with reference to FIG. FIG. 6A is a cross-sectional view showing the wavelength tunable laser device according to the present embodiment. FIG. 6B is a plan view showing the wavelength tunable laser device according to the present embodiment. The same components as those in the wavelength tunable laser device according to the first embodiment shown in FIGS. 1 to 5 are denoted by the same reference numerals, and description thereof is omitted or simplified.

  In the wavelength tunable laser device according to the present embodiment, an upper reflecting mirror 206 is configured by a high-index contrast subwavelength grating (HCG) 204.

  As shown in FIG. 6, a quantum well structure layer 202 is formed above the active layer 103. The quantum well structure layer 202 constitutes a beam-shaped support portion (movable mechanism) 222. It can be considered that the movable mechanism 222 is configured by the quantum well structure layer 202 and the upper reflector layer 201 described later.

  On the quantum well structure layer 202, an upper reflector layer 201 for forming an upper reflector 206 having a high refractive index difference subwavelength diffraction grating 204 is formed. A plurality of grating grooves (grating grooves) 203 of the high refractive index difference sub-wavelength diffraction grating 204 constituting the upper reflecting mirror 206 are formed not only in the upper reflecting mirror layer 201 but also in the quantum well structure layer 202. The lattice groove 203 is formed so as to reach the lower surface of the quantum well structure layer 202 from the upper surface of the upper reflecting mirror layer 201.

  Although the grating groove 203 of the high refractive index difference sub-wavelength diffraction grating 204 is formed not only in the upper reflector layer 201 but also in the quantum well structure layer 202, the bias applied to the quantum well structure layer 202 is a reverse bias. Therefore, no adverse effect is caused by the current or the like.

  The movable mechanism 222 using the high refractive index difference sub-wavelength diffraction grating 204 is light and thin. For this reason, according to this embodiment, it is possible to displace the movable mechanism 222 at high speed. For this reason, according to the present embodiment, it is possible to provide a wavelength tunable laser device capable of changing the wavelength at high speed.

  As described above, the upper reflecting mirror 206 may be configured by the high refractive index difference sub-wavelength diffraction grating 204. Also according to this embodiment, it is possible to obtain a wavelength tunable laser device having a very wide wavelength tunable width.

[Third Embodiment]
A wavelength tunable laser device according to a third embodiment of the present invention will be described with reference to FIG. FIG. 7 is a diagram illustrating a driving method of the wavelength tunable laser device according to the present embodiment. The same components as those of the wavelength tunable laser device according to the first or second embodiment shown in FIGS. 1A to 6B are denoted by the same reference numerals, and description thereof is omitted or simplified.

  The configuration of the tunable laser apparatus according to the present embodiment is the same as that of the tunable laser apparatus 10 according to the first embodiment, for example.

  In the present embodiment, the voltage applied to the electrode 112 for displacing the beam-shaped support portion 122 is gradually increased from 0 V, and the quantum well structure layer 105 is not subjected to the voltage applied to the electrode 112 until reaching a predetermined voltage. Apply voltage. The predetermined voltage is, for example, a voltage when the oscillation wavelength is slightly longer than the center wavelength of the wavelength variable range. More specifically, the predetermined voltage is a voltage when the oscillation wavelength is, for example, 1063 nm. When a voltage is applied to the quantum well structure layer 105, oscillation at a relatively short wavelength is hindered, so that oscillation is reliably performed at a relatively long wavelength. For this reason, for example, when oscillating at a wavelength longer than 1063 nm, oscillation occurs in mode B. Thus, the length of the gap 104 is reduced in a state where a voltage is applied to the quantum well structure layer 105, that is, in a state where a reverse bias is applied to the quantum well structure layer 105.

  Then, when the voltage applied to the electrode 112 for displacing the beam-shaped support portion 122 reaches a predetermined voltage, the application of the voltage to the quantum well structure layer 105 is stopped. Then, the mode A on the shorter wavelength side than the mode B is likely to oscillate, and the transition from the mode B to the mode A, that is, mode hopping occurs. When mode hopping from mode B to mode A occurs, the oscillation wavelength is, for example, about 1005 nm. As described above, the upper reflecting mirror 106 is configured such that the threshold gain on the short wavelength side is relatively low and the threshold gain on the high wavelength side is relatively high. Therefore, in a state where no voltage is applied to the quantum well structure layer 105, oscillation tends to occur on the short wavelength side with respect to the center wavelength λc2 of the high reflection band of the upper reflecting mirror 106. Therefore, in a state where no voltage is applied to the quantum well structure layer 105, oscillation is reliably performed at a relatively short wavelength.

  After mode hopping occurs, the voltage applied to the electrode 112 for displacing the beam-like support portion 122 is gradually reduced. When the voltage applied to the electrode 112 is gradually reduced, oscillation in mode A is maintained, and when the voltage applied to the electrode 112 becomes 0 V, the oscillation wavelength is about 1048 nm. Thus, the length of the gap 104 is increased in the state where no voltage is applied to the quantum well structure layer 105.

  Thereafter, when voltage application to the quantum well structure layer 105 is resumed, the oscillation wavelength becomes, for example, about 1098 nm. That is, when a voltage is applied to the quantum well structure layer 105, the oscillation wavelength returns to the initial state. When a voltage is applied to the quantum well structure layer 105, oscillation at a relatively low wavelength is inhibited, so that mode hopping from mode A to mode B can be reliably caused.

  In order to perform such control, in the present embodiment, the voltage applied to the quantum well structure layer 105 when the length of the gap 104 is decreased is the quantum well structure when the length of the gap 104 is increased. The voltage applied to layer 105 is greater than the voltage applied.

  Thus, in this embodiment, mode hopping is intentionally generated. In this embodiment, the wavelength tunable width obtained by reciprocating the beam-like support portion 122 is substantially the same as the wavelength tunable width obtained in the first embodiment. Therefore, the tunable laser device may be operated as in this embodiment. In the present embodiment, after the mode hopping is generated, the voltage applied to the electrode 112 for displacing the beam-shaped support portion 122 is gradually reduced, so the displacement amount of the beam-shaped support portion 122 is the first amount. It is about half that of the embodiment. According to this embodiment, since the voltage applied to the beam-shaped support part 122 may be small, power consumption can be reduced.

  In the above-described sweep, the voltage applied to the quantum well structure layer 105 when reducing the length of the gap 104 is larger than the voltage applied to the quantum well structure layer 105 when increasing the length of the gap 104. It was set. However, the relationship between the increase / decrease in the length of the gap 104 and the voltage applied to the quantum well structure layer 105 is not limited to the combination described above, and the same wavelength range can be swept by the reverse combination. is there. Specifically, the voltage applied to the quantum well structure layer 105 when reducing the length of the gap 104 is made smaller than the voltage applied to the quantum well structure layer 105 when increasing the length of the gap 104. It is also possible to perform wavelength sweeping. In this case, driving in the direction opposite to the arrow shown in FIG. 7 is performed. First, the length of the gap 104 is reduced in a state where the voltage applied to the quantum well structure layer 105 is relatively low, that is, in an oscillation state in mode A shown in FIG. Thereby, the oscillation wavelength is swept from about 1048 nm to about 1005 nm. Thereafter, the voltage applied to the quantum well structure layer 105 is increased to cause mode hopping, and the oscillation mode is changed to mode B. As a result, the oscillation wavelength becomes around 1063 nm. Thereafter, the oscillation wavelength is increased by increasing the length of the gap 104 while maintaining the voltage applied to the quantum well structure layer 105, that is, in the state of oscillation in mode B, and the oscillation wavelength is swept to around 1098 nm. can do.

[Fourth Embodiment]
A wavelength tunable laser device according to a fourth embodiment of the present invention will be described with reference to FIG. FIG. 8A is a cross-sectional view showing the wavelength tunable laser device according to the present embodiment. FIG. 8B is a plan view showing the wavelength tunable laser device according to the present embodiment. The same components as those of the wavelength tunable laser apparatus according to the first to third embodiments shown in FIGS. 1 to 7 are denoted by the same reference numerals, and description thereof is omitted or simplified.

  In the tunable laser device according to the present embodiment, a quantum well structure layer 105 is formed on an active layer 103.

  As shown in FIG. 8, a quantum well structure layer 105 is formed on the active layer 103. The quantum well structure layer 105 is formed directly on the active layer 103.

  Support portions 107 are formed on the quantum well structure layer 105 so as to be spaced apart from each other.

  An upper reflecting mirror 106 is located above the quantum well structure layer 105. Both ends of the upper reflecting mirror 106 are fixed by a support portion 107. In the present embodiment, the movable mechanism 122 is configured by the upper reflecting mirror 106.

  The electrode 113 is electrically connected to the upper surface of the movable mechanism 122. The electrode 112 is electrically connected to the upper surface of the quantum well structure layer 105. The electrode 111 is electrically connected to the upper surface of the active layer 103, that is, the lower surface of the quantum well structure layer 105. The movable mechanism 122 is displaced by changing the voltage applied between the electrode 113 and the electrode 112. By applying a voltage between the electrode 112 and the electrode 111, the quantum confined Stark effect in the quantum well structure layer 105 is controlled. Current injection into the active layer 103 is performed by applying a voltage between the electrode 111 and the electrode 110.

  The driving method of the wavelength tunable laser device according to the present embodiment is the same as the operation method of the wavelength tunable laser device according to the first embodiment or the third embodiment, and thus description thereof is omitted.

  As described above, the quantum well structure layer 105 may be positioned below the gap 104. Also according to this embodiment, it is possible to obtain a wavelength tunable laser device having a very wide wavelength tunable width.

[Modified Embodiment]
The present invention is not limited to the above embodiment, and various modifications are possible.

  For example, in the third embodiment, the case where mode hopping is intentionally generated in the wavelength tunable laser apparatus of the first embodiment has been described as an example, but mode hopping is also intentionally performed in the wavelength tunable laser apparatus according to the second or fourth embodiment. May be generated. Also in the wavelength tunable laser device according to the second or fourth embodiment, the quantum well structure layer 105 that generates the quantum confined Stark effect is provided. Therefore, the wavelength tunable laser device according to the second or fourth embodiment can be operated as in the third embodiment.

  Moreover, although the case where the structure of the active layer 103 was a quantum well structure was demonstrated to the example in the said embodiment, the structure of the active layer 103 is not limited to a quantum well structure. For example, the active layer may have another structure such as a bulk or a quantum dot.

  In the first, third, and fourth embodiments, the case where the DBR is used as the reflecting mirrors 102 and 106 has been described as an example. However, the present invention is not limited to this. For example, a high refractive index difference subwavelength grating or the like may be used as the reflecting mirrors 102 and 106.

  Further, in the second embodiment, the case where a high refractive index difference sub-wavelength diffraction grating is used for the upper reflecting mirror 106 has been described as an example. Good.

  In the above embodiment, the case where the oscillation wavelength is swept around the center wavelengths λc1 and λc2 of the high reflection bands of the reflecting mirrors 102, 106, and 206 has been described as an example. However, the present invention is not limited to this. For example, the center wavelengths λc1 and λc2 of the high reflection band of the reflecting mirrors 102, 106, and 206 may be shifted from the center wavelength of the band that changes the oscillation wavelength.

  In the above embodiment, the case where the center wavelength λc1 of the high reflection region of the first reflecting mirror 102 is the same as the center wavelength λc2 of the high reflection region of the second reflecting mirrors 106 and 206 has been described as an example. However, the present invention is not limited to this. For example, the center wavelength λc1 of the high reflection region of the first reflecting mirror 102 may be shifted from the center wavelength λc2 of the high reflection region of the second reflecting mirrors 106 and 206.

  In the above embodiment, the case where the quantum well structure layer 105 is located above the active layer 103 has been described as an example. However, the present invention is not limited to this. The quantum well structure layer 105 may be positioned below the active layer 103.

  In the above embodiment, the case where the electrode 112 serves as both an electrode for applying a voltage to the movable mechanism 122 and an electrode for applying a voltage to the quantum well structure layer 105 has been described as an example. It is not limited to this. An electrode for applying a voltage to the movable mechanism 122 and an electrode for applying a voltage to the quantum well structure layer 105 may be provided separately.

  In the first embodiment, the case where the quantum well structure layer 105 constitutes the movable mechanism 122 has been described as an example. However, a beam-shaped support portion (movable mechanism) 122 is provided separately from the quantum well structure layer 105. You may do it.

  In the second embodiment, the case where the quantum well structure layer 202 forms the movable mechanism 122 has been described as an example. However, a beam-shaped support portion (movable mechanism) 122 is provided separately from the quantum well structure layer 202. You may do it.

  In the fourth embodiment, the case where the upper reflecting mirror 106 constitutes the movable mechanism 122 has been described as an example. However, a beam-like support portion (movable mechanism) 122 is provided separately from the upper reflecting mirror 106. May be.

  In the above embodiment, the case where both ends of the beam-shaped support portion (movable mechanism) 122 are fixed, that is, the case where the movable mechanism 122 is a both-end fixed beam has been described as an example. It is not a thing. For example, the movable mechanism 122 may be a cantilever in which only one side is fixed.

  In the above-described embodiment, the case where the distance between the lower reflecting mirror 102 and the upper reflecting mirrors 106 and 206 is changed by the movable mechanism 122 including the beam-shaped support portion has been described as an example. However, the present invention is not limited to this. Absent. Various mechanisms (movable mechanism, support mechanism) capable of changing the distance between the lower reflecting mirror 102 and the upper reflecting mirrors 106 and 206 can be used as appropriate.

  In the above embodiment, the wavelength tunable laser device having a central wavelength in the wavelength tunable region of 1057 nm, that is, the wavelength tunable laser device in the 1060 nm band is described as an example, but the present invention is not limited to this. For example, the present invention can be applied to a wavelength variable laser device in the 850 nm band. Various wavelength band tunable laser devices can be obtained by appropriately setting the composition and film thickness of each component.

  In the above embodiment, the intermediate refractive index layer 303 is formed to relatively reduce the threshold gain on the short wavelength side. However, a method for relatively reducing the threshold gain on the short wavelength side is described below. It is not limited to. For example, by setting the optical film thickness of one or more layers in the reflecting mirror 106 to about one half of the central wavelength λc of the reflecting mirror, the threshold gain on the short wavelength side is relatively lowered. Is possible.

  In the above-described embodiment, the case where the upper reflective mirror 206 is provided with the high refractive index difference sub-wavelength diffraction grating 204 has been described as an example. However, the lower reflective mirror 102 may be provided with the high refractive index difference sub-wavelength diffraction grating. Good.

  In the above embodiment, the intermediate refractive index layer is formed on the upper reflecting mirror 106. However, the present invention is not limited to this. For example, the intermediate refractive index layer may be formed on the lower reflecting mirror 102. In this case, for example, if an intermediate refractive index layer having an intermediate refractive index between GaAs and AlAs is formed below the lowermost AlAs layer of the alternately laminated film composed of GaAs layers and AlAs layers, Good.

(Other examples)
The present invention supplies a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and one or more processors in a computer of the system or apparatus read and execute the program This process can be realized. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

DESCRIPTION OF SYMBOLS 8 ... Measuring apparatus 10 ... Variable wavelength laser apparatus 12 ... Resonator 101 ... Substrate 102 ... Lower reflecting mirror 103 ... Active layer 105 ... Quantum well structure layer 106 ... Upper reflecting mirror 107 ... Support part 110, 111, 112, 113 ... Electrode 122 ... Beam-shaped support, movable mechanism

Claims (13)

A first reflector;
A second reflector;
An active layer formed between the first reflecting mirror and the second reflecting mirror;
A quantum well structure layer in which a quantum confined Stark effect is generated by applying a reverse bias voltage;
An electrode for applying a reverse bias voltage to the quantum well structure layer,
A gap is formed between the active layer and the second reflecting mirror;
The resonant wavelength is swept by changing the length of the gap,
The wavelength tunable laser device according to claim 1, wherein the reverse bias voltage applied to the quantum well structure layer is changed according to a length of the gap when the resonance wavelength is swept. The voltage applied to the quantum well structure layer when the gap length is greater than or equal to a predetermined value is greater than the voltage applied to the quantum well structure layer when the gap length is less than the predetermined value. The wavelength tunable laser device according to claim 1, wherein: The voltage applied to the quantum well structure layer when decreasing the gap length is greater than the voltage applied to the quantum well structure layer when increasing the gap length. Item 3. The wavelength tunable laser device according to Item 1 or 2. At least one of the first reflecting mirror and the second reflecting mirror is a distributed Bragg reflection in which a first layer and a second layer having a refractive index higher than that of the first layer are alternately stacked. The wavelength tunable laser device according to any one of claims 1 to 3, further comprising a mirror. 5. The wavelength tunable according to claim 1, wherein at least one of the first reflecting mirror and the second reflecting mirror includes a high refractive index difference subwavelength diffraction grating. 6. Laser device. 6. The length of the gap in a state where the distance between the first reflecting mirror and the second reflecting mirror is not changed is greater than 1.7 μm. 6. The wavelength tunable laser device described in 1. The wavelength tunable laser device according to claim 1, wherein the quantum well structure layer has a multiple quantum well structure. A pair of electrodes for applying a voltage to the quantum well structure layer;
The quantum well structure layer has a p-type semiconductor layer and an n-type semiconductor layer,
One of the pair of electrodes is electrically connected to the p-type semiconductor layer, and the other of the pair of electrodes is electrically connected to the n-type semiconductor layer. The wavelength tunable laser device according to claim 1. Applying an alternating voltage to a support portion supporting the second reflecting mirror to vibrate the second reflecting mirror;
The wavelength tunable laser according to any one of claims 1 to 8, wherein the electrode changes the reverse bias voltage applied to the quantum well structure layer in response to a change in amplitude of the alternating voltage. apparatus. 10. The wavelength tunable according to claim 1, wherein a gain of the active layer at a wavelength shorter than a predetermined wavelength is larger than a gain of the active layer at a wavelength longer than the predetermined wavelength. Laser device. When the electrode does not apply the reverse bias voltage to the quantum well structure layer, the absorption edge of the quantum well structure layer is on the shorter wavelength side than the shortest wavelength in the sweep range of the resonance wavelength. The wavelength tunable laser device according to claim 1. 12. The wavelength tunable according to claim 1, wherein, when oscillating at a wavelength longer than a predetermined wavelength, the electrode applies the reverse bias voltage to the quantum well structure layer. Laser device. The wavelength tunable laser device according to any one of claims 1 to 12,
The light from the wavelength tunable laser device is branched into irradiation light and reference light irradiated on the measurement object, and interference light caused by reflected light and reference light irradiated on the measurement object is reflected. An interference optical system to be generated;
A light detector that receives the interference light;
An optical coherence tomography device comprising: an information acquisition unit that acquires information of the measurement object based on a signal from the light detection unit.

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