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WO2016125474A1 - Dispositif laser accordable en longueur d'onde et appareil de tomographie par cohérence optique - Google Patents

Dispositif laser accordable en longueur d'onde et appareil de tomographie par cohérence optique Download PDF

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Publication number
WO2016125474A1
WO2016125474A1 PCT/JP2016/000455 JP2016000455W WO2016125474A1 WO 2016125474 A1 WO2016125474 A1 WO 2016125474A1 JP 2016000455 W JP2016000455 W JP 2016000455W WO 2016125474 A1 WO2016125474 A1 WO 2016125474A1
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WIPO (PCT)
Prior art keywords
active layer
wavelength
reflector
laser device
gap
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PCT/JP2016/000455
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English (en)
Inventor
Takeshi Uchida
Takako Suga
Takeshi Yoshioka
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Canon Kabushiki Kaisha
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Publication of WO2016125474A1 publication Critical patent/WO2016125474A1/fr

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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/18—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities
    • H01S5/183—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
    • H01S5/18361—Structure of the reflectors, e.g. hybrid mirrors
    • H01S5/18363—Structure of the reflectors, e.g. hybrid mirrors comprising air layers
    • H01S5/18366—Membrane DBR, i.e. a movable DBR on top of the VCSEL
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02001—Interferometers characterised by controlling or generating intrinsic radiation properties
    • G01B9/02002—Interferometers characterised by controlling or generating intrinsic radiation properties using two or more frequencies
    • G01B9/02004—Interferometers characterised by controlling or generating intrinsic radiation properties using two or more frequencies using frequency scans
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/0209—Low-coherence interferometers
    • G01B9/02091—Tomographic interferometers, e.g. based on optical coherence
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/18—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities
    • H01S5/183—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
    • H01S5/18397—Plurality of active layers vertically stacked in a cavity for multi-wavelength emission

Definitions

  • the present invention relates to a wavelength tunable laser device and an optical coherence tomography apparatus using the wavelength tunable laser device.
  • a wavelength tunable laser device that can change a wavelength of laser light emitted therefrom is attracting attention.
  • a vertical cavity surface emitting laser (VCSEL) device is proposed (NPL 1).
  • NPL 1 a vertical cavity surface emitting laser
  • MEMS micro electro mechanical systems
  • a vertical cavity surface emitting laser device to which the MEMS technology is applied is referred to as a MEMS-VCSEL.
  • the MEMS-VCSEL can continuously change the wavelength. Further, in the MEMS-VCSEL, the movable portion is minute. Therefore, the movable portion can be displaced at high speed, and thus, the wavelength can be changed at high speed. Further, the MEMS-VCSEL has low power consumption. Such characteristics of the MEMS-VCSEL attract great attention thereto.
  • NPL 1 Connie J. Chang-Hasnain, Fellow, IEEE, "Tunable VCSEL", IEEE Journal on Selected Topics in Quantum Electronics, Vol. 6, No. 6, pp. 978-987, 2000.
  • a wavelength tunable laser device including: a first reflector; a second reflector; and an active layer formed between the first reflector and the second reflector, wherein the wavelength tunable laser device has a gap formed between the active layer and the second reflector, and a length of the gap is changed to change a resonance wavelength
  • the active layer includes: a first active layer; and a second active layer formed above the first active layer and having a peak wavelength of a gain spectrum that is different from a peak wavelength of a gain spectrum of the first active layer, and wherein each of excitation of the first active layer and excitation of the second active layer is controlled depending on the length of the gap.
  • An optical coherence tomography apparatus including: a wavelength tunable laser device including: a first reflector; a second reflector; and an active layer formed between the first reflector and the second reflector, wherein the wavelength tunable laser device has a gap formed between the active layer and the second reflector, and a length of the gap is changed to change a resonance wavelength, wherein the active layer includes: a first active layer; and a second active layer formed above the first active layer and having a peak wavelength of a gain spectrum that is different from a peak wavelength of a gain spectrum of the first active layer, and wherein each of excitation of the first active layer and excitation of the second active layer is controlled depending on the length of the gap, the optical coherence tomography apparatus further including: a coherence optical system configured to branch light from the wavelength tunable laser device into radiation light to be radiated to a measurement object and reference light, and to generate coherent light with reflection light of the radiation light radiated to the measurement object and the
  • each of the excitation of the first active layer and the excitation of the second active layer is controlled depending on the length of the gap between the first reflector and the second reflector.
  • the wavelength tunable laser device having a wide wavelength tunable width and an optical coherence tomography apparatus using the wavelength tunable laser can be provided.
  • FIG. 1A is a plan view for illustrating a wavelength tunable laser device according to a first embodiment of the present invention.
  • FIG. 1B is a sectional view for illustrating a wavelength tunable laser device according to a first embodiment of the present invention.
  • FIG. 2 is a graph for showing a relationship among a gap length, an oscillation wavelength, and modes.
  • FIG. 3 is a graph for 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.
  • FIG. 4 is a schematic view for illustrating a measuring device according to the first embodiment of the present invention.
  • FIG. 5 is a sectional view for illustrating a wavelength tunable laser device according to a second embodiment of the present invention.
  • FIG. 1A is a plan view for illustrating a wavelength tunable laser device according to a first embodiment of the present invention.
  • FIG. 1B is a sectional view for illustrating a wavelength tunable laser device
  • FIG. 6 is a sectional view for illustrating a wavelength tunable laser device according to a third embodiment of the present invention.
  • FIG. 7 is a sectional view for illustrating a wavelength tunable laser device according to a fourth embodiment of the present invention.
  • FIG. 8 is a graph for showing a method of driving a wavelength tunable laser device according to a fifth embodiment of the present invention.
  • FIG. 9 is a graph for showing a result of a simulation in a vertical cavity surface emitting laser device according to a reference example.
  • FIG. 10 is a graph for showing a relationship among a gap length, an oscillation wavelength, and modes in a wavelength tunable laser device according to a comparative example.
  • a sufficiently wide wavelength tunable width cannot necessarily be acquired.
  • a sufficiently wide wavelength tunable width cannot necessarily be acquired for the following reasons.
  • the beam-like supporting portion In the vertical cavity surface emitting laser device, by applying a voltage to, for example, a beam-like supporting portion configured to support an upper reflector, the beam-like supporting portion is displaced.
  • a voltage When the voltage is applied to the beam-like supporting portion, an electrostatic attractive force is generated to displace the beam-like supporting portion in a direction of reducing a length of a gap existing between the upper reflector and a lower reflector.
  • the beam-like supporting portion is held under a state in which resilience of a spring on the beam-like supporting portion and the electrostatic attractive force are balanced with each other.
  • the mode hopping occurs due to existence of a plurality of longitudinal modes in a wavelength range in which laser oscillations are allowed. If a longitudinal mode spacing is wider than the wavelength range in which laser oscillations are allowed, the mode hopping does not occur. Specifically, if another longitudinal mode does not exist in the wavelength range in which laser oscillations are allowed, there is no mode to be hopped to, and thus, the mode hopping does not occur.
  • an oscillation wavelength that is, a resonance wavelength
  • a resonance wavelength can be changed over the entire wavelength range in which laser oscillations are allowed.
  • the initial gap length be large, and, from the viewpoint of inhibiting the mode hopping, it is preferred that the initial gap length be small.
  • the vertical cavity surface emitting laser device has a trade-off relationship with respect to the initial gap length.
  • FIG. 9 is a graph for showing a result of a simulation in a vertical cavity surface emitting laser device according to a reference example.
  • Plots on the dot-and-dash line represent an amount of change in oscillation wavelength when a beam-like supporting portion is displaced by 1/3 of an initial gap length.
  • the plots on the dot-and-dash line represent a difference between an oscillation wavelength before the displacement and an oscillation wavelength after the displacement, that is, a wavelength difference in oscillation wavelength between before and after the displacement.
  • Plots on the broken line represent a longitudinal mode spacing corresponding to the initial gap length, that is, a wavelength difference between modes corresponding to the initial gap length.
  • the wavelength difference when the beam-like supporting portion is displaced by 1/3 of the initial gap length becomes larger.
  • the longitudinal mode spacing corresponding to the initial gap length becomes smaller.
  • the largest wavelength difference is acquired when the initial gap length is about 1.7 ⁇ m.
  • the initial gap length is set to be about 1.7 ⁇ m, a wavelength difference of about 70 nm, that is, a wavelength tunable width of about 70 nm can be acquired.
  • the result of the simulation shown in FIG. 9 is in a case in which a center wavelength of a wavelength tunable range is about 1,060 nm.
  • an optimum value of the initial gap length is not necessarily about 1.7 ⁇ m.
  • a vertical cavity surface emitting laser device in an 850 nm range has an oscillation wavelength that is smaller by about 20% than an oscillation wavelength of a vertical cavity surface emitting laser device in a 1,060 nm range.
  • a dimension of a resonator of the vertical cavity surface emitting laser device in the 850 nm range is smaller by about 20% than a dimension of a resonator of the vertical cavity surface emitting laser device in the 1,060 nm range. It follows that an optimum value of an initial gap length of the vertical cavity surface emitting laser device in the 850 nm range is smaller by about 20% than the optimum value of the initial gap length of the vertical cavity surface emitting laser device in the 1,060 nm range.
  • a wavelength tunable laser device according to a first embodiment of the present invention and a measuring device using the wavelength tunable laser device are described with reference to FIG. 1A to FIG. 5.
  • wavelength tunable laser device 10 First, a wavelength tunable laser device 10 according to this embodiment is described.
  • the wavelength tunable laser device 10 is a wavelength tunable laser device to which a MEMS technology is applied, and more specifically, a vertical cavity surface emitting laser device to which the MEMS technology is applied (MEMS-VCSEL).
  • MEMS-VCSEL vertical cavity surface emitting laser device to which the MEMS technology is applied
  • FIG. 1A is a plan view for illustrating the wavelength tunable laser device according to this embodiment.
  • FIG. 1A is an illustration of the wavelength tunable laser device 10 according to this embodiment when seen from an upper surface side thereof.
  • two supporting portions 121 are arranged on a substrate 101 so as to be apart from each other. Both ends of a beam-like movable portion 122 formed using the MEMS technology are fixed by the supporting portions 121, respectively.
  • the beam-like movable portion 122 is provided for displaceably supporting a reflector 106 to be described below.
  • the beam-like movable portion 122 forms a mechanism configured to change a spacing between a lower reflector 102 and the upper reflector 106 (movable mechanism, supporting mechanism).
  • the beam-like movable portion 122 forms a mechanism configured to change a length of a gap between the lower reflector 102 and the upper reflector 106.
  • a region 123 surrounded by the broken lines in FIG. 1A conceptually represents a region in which light emission occurs.
  • An electrode 150 configured to inject a current into an active layer 140 is formed on a first semiconductor layer 141.
  • the electrode 150 is electrically connected to the first semiconductor layer 141.
  • an electrode 151 configured to inject a current into an active layer 142 is formed on a second semiconductor layer 143.
  • the electrode 151 is electrically connected to the second semiconductor layer 143.
  • an electrode 113 configured to apply a voltage to the beam-like movable portion 122 is formed on the supporting portion 121.
  • the electrode 113 is electrically connected to the beam-like movable portion 122.
  • FIG. 1A is a sectional view of the wavelength tunable laser device according to this embodiment.
  • FIG. 1B corresponds to a section taken along the line I-I' of FIG. 1A.
  • the reflector (first reflector, lower reflector) 102 is formed on the substrate 101.
  • the substrate 101 for example, an n-type GaAs substrate is used.
  • the lower reflector 102 for example, a distributed bragg reflector (DBR) is formed.
  • the lower reflector 102 is formed of, for example, alternately laminated films including thirty pairs of a GaAs layer and an AlAs layer each having an optical thickness of 1/4 ⁇ c1.
  • ⁇ c1 is a center wavelength of a high reflectivity band of the lower reflector 102, and is, for example, about 1,060 nm in this embodiment.
  • high reflectivity band of reflector means a wavelength band in which the reflector can acquire a sufficient reflectivity for allowing laser oscillations, and specifically means a wavelength band in which the reflector can acquire a reflectivity of 98% or larger.
  • an electrode (rear surface electrode) 110 is formed on a rear surface (lower surface) of the substrate 101.
  • the active layer (first active layer) 140 is formed on the lower reflector 102, that is, on the first reflector.
  • the first active layer 140 is an active layer having a quantum well structure in which, for example, an InGaAs layer (not shown) is sandwiched between GaAsP layers (not shown).
  • the InGaAs layer has a thickness of, for example, about 8 nm.
  • the InGaAs layer is set to have an In composition ratio of, for example, 24%.
  • a light emission wavelength corresponding to an energy difference between an excitation level and a ground level in the first active layer 140 is, for example, about 1,050 nm.
  • a peak wavelength of an excitation spectrum of the first active layer 140 is, for example, about 1,050 nm.
  • the light emission wavelength corresponding to the energy difference between the excitation level and the ground level in the first active layer 140 is smaller than the center wavelength of the high reflectivity bands of the reflectors 102 and 106 of 1,060 nm.
  • Phosphorus (P) has the action of reducing a lattice constant of GaAs.
  • Indium (In) has the action of increasing the lattice constant of GaAs. Therefore, an accumulative strain is inhibited in the active layer 140 including the InGaAs layer and the GaAsP layers.
  • the first active layer 140 has a conductivity type of, for example, an i type (undoped).
  • the semiconductor layer (first semiconductor layer) 141 is formed on the active layer 140, that is, on the first active layer.
  • the first semiconductor layer 141 has a conductivity type of, for example, a p type.
  • the active layer (second active layer) 142 is formed on the first semiconductor layer 141.
  • the second active layer 142 is an active layer having a quantum well structure in which, for example, an InGaAs layer (not shown) is sandwiched between GaAsP layers (not shown).
  • the InGaAs layer has a thickness of, for example, about 8 nm.
  • a basic material of the first active layer 140 and a basic material of the second active layer 142 are the same, but the composition is different. Specifically, the In composition ratio of the InGaAs layer in the first active layer 140 and an In composition ratio of the InGaAs layer in the second active layer 142 are different from each other.
  • the In composition ratio of the InGaAs layer is set to be, for example, 27%.
  • a light emission wavelength corresponding to an energy difference between an excitation level and a ground level in the second active layer 142 is, for example, about 1,070 nm.
  • a peak wavelength of an excitation spectrum of the second active layer 142 is, for example, about 1,070 nm.
  • the peak wavelength of the excitation spectrum of the second active layer 142 is different from the peak wavelength of the excitation spectrum of the first active layer 140.
  • the light emission wavelength corresponding to the energy difference between the excitation level and the ground level in the second active layer 142 is larger than the center wavelength of the high reflectivity bands of the reflectors 102 and 106 of 1,060 nm.
  • P has the action of reducing the lattice constant of GaAs.
  • In has the action of increasing the lattice constant of GaAs. Therefore, the accumulative strain is inhibited also in the second active layer 142 including the InGaAs layer and the GaAsP layers.
  • the second active layer 142 has a conductivity type of, for example, the i type (undoped).
  • the semiconductor layer (second semiconductor layer) 143 is formed on the second active layer 142.
  • the second semiconductor layer 143 has a conductivity type that is opposite to the conductivity type of the first semiconductor layer 141.
  • the second semiconductor layer 143 has a conductivity type of, for example, an n type.
  • a laminate 103 including the first active layer 140, the first semiconductor layer 141, the second active layer 142, and the second semiconductor layer 143 is formed on the lower reflector 102.
  • the beam-like supporting portion (beam) 122 formed using the MEMS technology is located above the laminate 103. As described above, the beam-like movable portion 122 is provided for displaceably supporting the upper reflector 106.
  • a gap 104 that is, an air gap 104, exists between the laminate 103 and the movable portion 122. In other words, the gap 104 exists between the lower reflector 102 and the upper reflector 106. Therefore, the movable portion 122 is freely displaceable in a direction of a normal to a main surface of the substrate 101.
  • the gap 104 has a length (height) of, for example, about 3.8 ⁇ m under a state in which no voltage is applied to the beam-like movable portion 122.
  • the gap 104 has a length that is larger than 1.7 ⁇ m under the state in which no voltage is applied to the beam-like movable portion 122, that is, under a state in which the spacing between the lower reflector 102 and the upper reflector 106 is not changed.
  • the length of the gap 104 under the state in which no voltage is applied to the beam-like movable portion 122 is larger than 1.7 ⁇ m.
  • the length of the gap 104 under the state in which no voltage is applied to the beam-like movable portion 122 is larger than 1.6 times the center wavelength of the high reflectivity bands of the reflectors 102 and 106.
  • the length of the gap 104 is also referred to as an air gap length.
  • both the ends of the beam-like movable portion 122 are respectively fixed by the two supporting portions (fixing portions, holding portions) 121 formed on the substrate 101.
  • the beam-like movable portion 122 is a both-ends fixed beam (double supported beam) having the ends being fixed by the supporting portions 121, respectively.
  • the length of the gap 104 under the state in which no voltage is applied is about 3.8 ⁇ m is described as an example, but the length of the gap 104 under the state in which no voltage is applied is not limited to about 3.8 ⁇ m, and may be set as appropriate.
  • the electrode 150 configured to inject a current into the first active layer 140 is formed on the first semiconductor layer 141. Further, as described above, the electrode 151 configured to inject a current into the second active layer 142 is formed on the second semiconductor layer 143.
  • the reflector (second reflector, upper reflector) 106 is formed on the beam-like movable portion 122.
  • the upper reflector 106 is displaceably supported by the beam-like movable portion 122.
  • a DBR is formed as the upper reflector 106.
  • the upper reflector 106 is formed of, for example, alternately laminated films including ten pairs of an SiO 2 layer and a TiO 2 layer each having an optical thickness of 1/4 ⁇ c2.
  • ⁇ c2 is a center wavelength of the high reflectivity band of the upper reflector 106, and is, for example, about 1,060 nm in this embodiment.
  • a resonator 12 of the wavelength tunable laser device 10 includes the lower reflector 102, the first active layer 140, the second active layer 142, the upper reflector 106, and the mechanism 122 configured to change the spacing between the lower reflector and the upper reflector.
  • the gap 104 having a length that changes along with a change in spacing between the lower reflector 102 and the upper reflector 106 exists between the lower reflector 102 and the upper reflector 106. In this way, the wavelength tunable laser device 10 according to this embodiment is formed.
  • FIG. 2 is a graph for showing a relationship among the gap length, the oscillation wavelength, and modes.
  • the horizontal axis denotes the length of the gap 104.
  • the vertical axis denotes the oscillation wavelength of laser light.
  • the length of the gap 104 is, for example, about 3.8 ⁇ m.
  • the length of the gap 104 is about 3.8 ⁇ m, there exists a mode in which resonance occurs at a wavelength of, for example, about 1,098 nm.
  • This resonance mode (longitudinal mode) is herein referred to as Mode B.
  • Mode A As can be seen from FIG. 2, when the length of the gap 104 is about 3.8 ⁇ m, there exists another mode in which resonance occurs at a wavelength shorter than 1,098 nm. This resonance mode is herein referred to as Mode A.
  • the oscillation wavelength in Mode B is, for example, about 1,007 nm.
  • the length of the gap 104 is about 3.0 ⁇ m, there exists still another mode in which resonance occurs at a wavelength longer than 1,007 nm. This resonance mode is herein referred to as Mode C.
  • a plurality of modes that is, two or more modes, exist in a range in which the oscillation wavelength of laser light can be changed. More specifically, in this embodiment, the three modes exist in the range in which the oscillation wavelength of laser light can be changed. Therefore, when the spacing between the lower reflector 102 and the upper reflector 106 is simply changed, transition from Mode B to other modes: Mode A and Mode C, that is, mode hopping, may occur.
  • Both the center wavelength ⁇ c1 of the high reflectivity band of the lower reflector 102 and the center wavelength ⁇ c2 of the high reflectivity band of the upper reflector 106 are 1,060 nm.
  • the second active layer 142 that realizes a large gain in a wavelength range longer than the center wavelengths ⁇ c1 and ⁇ c2 is excited.
  • the first active layer 140 that realizes a large gain in a wavelength range shorter than the center wavelengths ⁇ c1 and ⁇ c2 is excited.
  • the length of the gap 104 corresponding to 1,060 nm that is the center wavelengths ⁇ c1 and ⁇ c2 of the high reflectivity bands of the reflectors 102 and 106 is, for example, about 3.4 ⁇ m. Therefore, when the length of the gap 104 is, for example, 3.4 ⁇ m or larger, the second active layer 142 that realizes a large gain in a wavelength range longer than the center wavelengths ⁇ c1 and ⁇ c2 is excited. On the other hand, when the length of the gap 104 is, for example, smaller than 3.4 ⁇ m, the first active layer 140 that realizes a large gain in a wavelength range shorter than the center wavelengths ⁇ c1 and ⁇ c2 is excited.
  • the strength of the excitation of the second active layer 142 when the length of the gap 104 is equal to or larger than a predetermined value is higher than the strength of the excitation of the second active layer 142 when the length of the gap 104 is smaller than the predetermined value. Further, the strength of the excitation of the first active layer 140 when the length of the gap 104 is equal to or larger than the predetermined value is lower than the strength of the excitation of the first active layer 140 when the length of the gap 104 is smaller than the predetermined value.
  • the length of the gap 104 can be changed by changing a voltage applied to the beam-like movable portion 122.
  • the length of the gap 104 can be changed by changing a voltage applied to the electrode 113.
  • the length of the gap 104 is changed by changing the voltage applied to the beam-like movable portion 122 because, by changing the voltage applied to the beam-like movable portion 122, an electrostatic attractive force that acts on the beam-like movable portion 122 is changed.
  • the voltage applied to the electrode 113 which sets the length of the gap 104 to be, for example, 3.4 ⁇ m, can be determined in advance. Therefore, when the voltage applied to the electrode 113 is a voltage with which the length of the gap 104 is 3.4 ⁇ m or larger, the second active layer 142 that realizes a large gain in a wavelength range longer than the center wavelengths ⁇ c1 and ⁇ c2 is excited. In other words, when the voltage applied to the electrode 113 is equal to or smaller than the predetermined voltage, the second active layer 142 that realizes a large gain in a wavelength range longer than the center wavelengths ⁇ c1 and ⁇ c2 is excited.
  • the first active layer 140 that realizes a large gain in a wavelength range shorter than the center wavelengths ⁇ c1 and ⁇ c2 is excited.
  • the voltage applied to the electrode 113 is larger than the predetermined voltage, the first active layer 140 that realizes a large gain in a wavelength range shorter than the center wavelengths ⁇ c1 and ⁇ c2 is excited.
  • the light emission wavelength corresponding to the energy difference between the excitation level and the ground level in the second active layer 142 is, for example, about 1,070 nm.
  • the peak wavelength of the excitation spectrum of the second active layer 142 is, for example, about 1,070 nm.
  • the light emission wavelength corresponding to the energy difference between the excitation level and the ground level in the first active layer 140 is smaller than the light emission wavelength corresponding to the energy difference between the excitation level and the ground level in the second active layer 142.
  • the light emission wavelength corresponding to the energy difference between the excitation level and the ground level is about 1,050 nm.
  • the peak wavelength of the excitation spectrum of the first active layer 140 is, for example, about 1,050 nm. Therefore, oscillation in a wavelength range around 1,050 nm is inhibited by the first active layer 140.
  • the light emission wavelength corresponding to the energy difference between the excitation level and the ground level in the first active layer 140 is about 1,050 nm.
  • the peak wavelength of the gain spectrum of the first active layer 140 is about 1,050 nm.
  • a gain on a shorter wavelength side can be sufficiently large. This is realized by the quantum well having a rectangular density of states and a large difference in band gap between an In 0.24 GaAs quantum well layer and a GaAsP barrier layer.
  • the first active layer 140 is excited through injection of a current into the first active layer 140, a relatively large gain can be acquired in a wavelength range of, for example, about 1,007 nm to about 1,060 nm.
  • the oscillation wavelength of laser light is swept with, for example, the center wavelengths ⁇ c1 and ⁇ c2 of the high reflectivity bands of the reflectors 102 and 106 being a center of the sweep.
  • a wavelength difference between Mode A and Mode B that is, a longitudinal mode spacing between Mode A and Mode B
  • a wavelength difference between Mode B and Mode C that is, a longitudinal mode spacing between Mode B and Mode C
  • an ordinary active layer such as a bulk or a quantum well
  • the above-mentioned numerical value of 30 nm is a numerical value in the case of a wavelength tunable laser device of a 1,060 nm range.
  • the numerical value of 30 nm comes from an energy distribution of carriers in the quantum well, and, at room temperature, the numerical value is about 30 nm when the wavelength is 1,060 nm. Therefore, with regard to a wavelength tunable laser device of a wavelength band other than 1,060 nm, it is appropriated that not the wavelength difference but an energy difference is used in the description.
  • An energy difference corresponding to a wavelength difference of 30 nm in the 1,060 nm range is 33 meV. Therefore, it is preferred that the longitudinal mode spacing be larger than a wavelength difference corresponding to the energy difference of 33 meV in the oscillation wavelength.
  • FIG. 10 is a graph for showing a relationship among the gap length, the oscillation wavelength, and the modes in a wavelength tunable laser device according to a comparative example.
  • the comparative example changes the oscillation wavelength by simply changing the spacing between the lower reflector and the upper reflector. Specifically, according to the comparative example, current injection into the active layer is not adjusted depending on the length of the gap between the lower reflector and the upper reflector.
  • the initial gap length is about 1.5 ⁇ m.
  • the gap length becomes 1.0 ⁇ m.
  • the wavelength tunable width is about 68 nm.
  • excitation of the first active layer and excitation of the second active layer are controlled depending on the length of the gap between the lower reflector and the upper reflector, and thus, mode hopping can be prevented with reliability. Therefore, according to this embodiment, there is no restriction that is due to the longitudinal mode spacing as represented by the plots on the broken line in FIG. 9. Therefore, according to this embodiment, under the state in which no voltage is applied to the beam-like supporting portion 122, the length of the gap 104 can be considerably larger than 1.6 times the center wavelengths ⁇ c1 and ⁇ c2 of the high reflectivity bands of the reflectors 102 and 106.
  • the initial length of the gap 104 can be considerably large, and thus, a length that is about 1/3 of the initial length of the gap 104 is sufficiently large. Therefore, according to this embodiment, the oscillation wavelength, that is, the resonance wavelength, can be changed in an extremely wide wavelength range.
  • the oscillation wavelength can be changed without occurrence of mode hopping from Mode B to other modes: Mode A and Mode C.
  • the wavelength difference between the wavelength of 1,098 nm and the wavelength of 1,007 nm is 91 nm.
  • a wavelength tunable width of, for example, about 91 nm can be acquired.
  • FIG. 3 is a graph for showing a relationship between the initial gap length and the wavelength tunable width in the wavelength tunable laser device according to this embodiment.
  • the horizontal axis denotes the initial gap length and the vertical axis denotes the wavelength tunable width.
  • the wavelength tunable width can be about 91 nm.
  • the length of the gap 104 is changed from 3.8 ⁇ m to 3.0 ⁇ m.
  • the amount of change in length of the gap 104 of 0.8 ⁇ m is sufficiently small with respect to 1/3 of the initial length of the gap 104. Therefore, even when the oscillation wavelength is changed from 1,098 nm to 1,007 nm, a sufficient margin to the 1/3 rule is secured.
  • a wavelength tunable laser device having an extremely wide wavelength tunable width can be acquired.
  • FIG. 4 is a schematic view for illustrating the measuring device according to this embodiment.
  • the wavelength tunable laser device 10 according to this embodiment is used for a light source portion 801 of an optical coherence tomography (OCT) apparatus, but the present invention is not limited thereto.
  • the wavelength tunable laser device 10 according to this embodiment is not limited to the light source portion 801 of the optical coherence tomography apparatus, and can be used for various purposes.
  • the optical coherence tomography apparatus in which the wavelength tunable laser device is used for the light source portion 801 eliminates the need for a spectroscope, and can thus acquire a tomographic image with low loss in light amount and a high S/N ratio.
  • a measuring device (OCT device) 8 includes the light source portion 801, a coherence optical system 802, an optical detection portion 803, and an information acquisition portion 804.
  • the wavelength tunable laser device 10 according to this embodiment is used for the light source portion 801.
  • the information acquisition portion 804 includes a Fourier transformer (not shown).
  • the phrase "the information acquisition portion 804 includes a Fourier transformer” herein means that the information acquisition portion 804 has the function of performing a Fourier transform on data input thereto, and the mode of the Fourier transformer is not particularly limited.
  • the information acquisition portion 804 includes an arithmetic portion (not shown) and the arithmetic portion has the function of performing a Fourier transform. More specifically, the arithmetic portion is a computer including a central processing unit (CPU), and the computer runs an application having the function of performing a Fourier transform.
  • the information acquisition portion 804 includes a Fourier transform circuit having the function of performing a Fourier transform.
  • Light that is output from the light source portion 801 passes through the coherence optical system 802 to be coherent light including information on an object 812 to be measured (measurement object), and the coherent light is received by the optical detection portion 803.
  • the optical detection portion 803 may be a photodetector of a differential detection type or may be a photodetector of a simple intensity monitor type.
  • Information on a time waveform of intensity of the coherent light received by the optical detection portion 803 is output from the optical detection portion 803 to the information acquisition portion 804.
  • the information acquisition portion 804 acquires information on the object 812 (for example, information on a tomographic image thereof) by acquiring a peak value of the time waveform of the intensity of the received coherent light and performing a Fourier transform.
  • Light emitted from the light source portion 801 passes through a fiber 805, enters a coupler 806, and then, is branched into radiation light that passes through a fiber 807 for radiation light and reference light that passes through a fiber 808 for reference light.
  • a 3dB coupler that is a coupler having a branching ratio of 1:1 is used.
  • the coupler 806 can operate in a single mode in a wavelength band of light emitted from the light source portion 801.
  • the radiation light propagating through the fiber 807 passes through a collimator 809 to be collimated light and is reflected by a mirror 810.
  • Light reflected by the mirror 810 passes through a lens 811 to be radiated to the object 812, and is reflected by respective layers in a depth direction of the object 812.
  • the reference light propagating through the fiber 808 passes through a collimator 813 and is reflected by a mirror 814.
  • coherent light is generated with the reflection light from the object 812 and the reflection light from the mirror 814.
  • the coherent light generated in this way passes through a fiber 815, passes through a collimator 816 to be condensed, and is received by the optical detection portion 803.
  • the information on the intensity of the coherent light received by the optical detection portion 803 is converted into electrical information such as a voltage, and is sent to the information acquisition portion 804.
  • the information acquisition portion 804 processes the data on the intensity of the coherent light, specifically, performs a Fourier transform, to acquire information on the tomographic image.
  • the data on the intensity of the coherent light on which a Fourier transform is performed is data sampled at equal wavenumber intervals in general, but the present invention is not limited thereto, and the data may be data sampled at equal wavelength intervals.
  • the information on the tomographic image acquired in this way is sent from the information acquisition portion 804 to an image display portion 817 and can be displayed as an image.
  • a three-dimensional tomographic image of the object 812 to be measured can also be acquired.
  • intensity of light emitted from the light source portion 801 may be successively monitored and data thereof may be used for correcting an amplitude of a signal for indicating the intensity of the coherent light.
  • the information acquisition portion 804 can control the light source portion 801 via an electric circuit 818.
  • the second active layer 142 that acquires a gain in a relatively long wavelength range is excited.
  • the first active layer 140 that acquires a gain in a relatively short wavelength range is excited.
  • the excitation of the first active layer 140 and the excitation of the second active layer 142 can be controlled by, for example, the information acquisition portion 804.
  • the information acquisition portion 804 can function as a control portion configured to control the excitation of the first active layer 140 and the excitation of the second active layer 142.
  • the information acquisition portion (control portion) 804 controls the excitation of the first active layer 140 and the excitation of the second active layer 142 through appropriate application of a voltage to the electrodes 150 and 151 via the electric circuit 818. Further, the information acquisition portion (control portion) 804 displaces the beam-like movable portion 122 through appropriate application of a voltage to the electrode 113 via the electric circuit 818, thereby changing the oscillation wavelength of laser light emitted from the wavelength tunable laser device.
  • the information acquisition portion 804 controls the excitation of the first active layer 140 and the excitation of the second active layer 142, but the present invention is not limited thereto.
  • the excitation of the first active layer 140 and the excitation of the second active layer 142 may be controlled using a control portion (not shown) other than the information acquisition portion 804.
  • a control portion other than the information acquisition portion 804 may control a voltage to be applied to the electrode 113 connected to the beam-like movable portion 122, thereby changing the oscillation wavelength of laser light emitted from the wavelength tunable laser device.
  • the control portion other than the information acquisition portion 804 may be formed in the light source portion 801 or may be formed separately from the light source portion 801.
  • the measuring apparatus 8 is useful for, for example, acquiring information on a tomographic image of a living body such as an animal or a human being in the field of ophthalmology, dentistry, dermatology, and the like.
  • information on a tomographic image of a living body includes not only the tomographic image itself of the living body but also a numerical data necessary for acquiring the tomographic image of the living body.
  • an object to be measured by the measuring apparatus 8 according to this embodiment is a fundus of a human body, and the measuring apparatus 8 according to this embodiment is suitable for acquiring information on a tomographic image of the fundus.
  • the wavelength tunable laser device 10 according to this embodiment has an extremely wide wavelength tunable width. Therefore, by using the wavelength tunable laser device 10 according to this embodiment, the measuring apparatus 8 that can acquire a high-resolution tomographic image can be realized.
  • the wavelength tunable laser device 10 according to this embodiment is used as a light source of the measuring apparatus 8, but the present invention is not limited thereto.
  • the wavelength tunable laser device 10 according to this embodiment may be used as a light source for optical communication, or may be used as a light source for optical measurement.
  • FIG. 5 is a sectional view for illustrating the wavelength tunable laser device according to this embodiment.
  • the same components as in the wavelength tunable laser device and the like according to the first embodiment illustrated in FIG. 1A to FIG. 4 are represented by the same reference numerals, and description thereof is omitted or simplified.
  • the wavelength tunable laser device excites a second active layer 242 by radiating pumping light thereto.
  • the second active layer 242 is formed between the first semiconductor layer 141 and the second semiconductor layer 143.
  • the second active layer 242 is excited when light of a predetermined wavelength is radiated thereto.
  • light emitted from a pumping light source 820 (pumping light) is radiated to the second active layer 242.
  • the pumping light source 820 for example, an edge-emitting semiconductor laser device can be used.
  • the wavelength of pumping light emitted from the pumping light source 820 is, for example, about 670 nm.
  • a barrier layer of the second active layer 242 functions as an absorbing layer configured to absorb pumping light to generate carriers.
  • the composition of the barrier layer of the second active layer 242 is, for example, Al 0.25 GaAs.
  • the second active layer 242 can be excited by light emitted from the pumping light source 820, and thus, the electrode 151 (see FIG. 1B) configured to inject a current into the second active layer 242 is not formed.
  • the electrode 151 (see FIG. 1B) configured to inject a current into the second active layer 242, and thus, the number of electrodes to be formed on the substrate 101 can be reduced.
  • the number of electrodes required to be formed on the substrate 101 is small, and thus, the degree of difficulty in manufacturing is low and the number of processing steps is small. Therefore, according to this embodiment, manufacturing yield can be improved and manufacturing costs can be reduced.
  • mode hopping can be prevented with reliability and the oscillation wavelength can be changed in an extremely wide wavelength range.
  • the pumping light source 820 may be controlled by the information acquisition portion (control portion) 804, or may be controlled by a control portion formed separately from the information acquisition portion 804.
  • the second active layer 242 may be excited by radiating light thereto.
  • the oscillation wavelength can be changed in an extremely wide wavelength range.
  • FIG. 6 is a sectional view for illustrating the wavelength tunable laser device according to this embodiment.
  • the same components as in the wavelength tunable laser device and the like according to the first and second embodiments illustrated in FIG. 1A to FIG. 5 are represented by the same reference numerals, and description thereof is omitted or simplified.
  • the wavelength tunable laser device uses radiation of light not only for exciting a second active layer 342 but also for exciting a first active layer 340.
  • the first active layer 340 is formed between the lower reflector 102 and the first semiconductor layer 141.
  • the first active layer 340 is set to have an In composition ratio of, for example, about 24%.
  • a light emission wavelength corresponding to an energy difference between an excitation level and a ground level in the first active layer 340 is, for example, about 1,050 nm.
  • a barrier layer of the active layer 340 is formed of, for example, Al 0.05 GaAs.
  • the second active layer 342 is formed between the first semiconductor layer 141 and the second semiconductor layer 143.
  • the second active layer 342 is set to have an In composition ratio of, for example, 27%.
  • a light emission wavelength corresponding to an energy difference between an excitation level and a ground level in the second active layer 342 is, for example, about 1,070 nm.
  • a barrier layer of the second active layer 342 is formed of, for example, Al 0.25 GaAs.
  • light emitted from a pumping light source 821 is radiated to the second active layer 342 and the first active layer 340.
  • first active layer 340 When the first active layer 340 is excited, for example, pumping light of a relatively long wavelength is radiated thereto. In this case, pumping light that is used for exciting the first active layer 340 has a wavelength of, for example, about 808 nm.
  • second active layer 342 when the second active layer 342 is excited, for example, pumping light of a relatively short wavelength is radiated thereto. In this case, pumping light that is used for exciting the second active layer 342 has a wavelength of, for example, about 670 nm.
  • These two kinds of pumping light are incident from a side on which the beam-like movable portion 122 is formed, that is, from above the substrate 101, so as to be coaxial with each other.
  • two kinds of pumping light having different wavelengths are radiated as appropriate.
  • a light source of the two kinds of pumping light having different wavelengths similarly to the case of the second embodiment, for example, an edge-emitting semiconductor laser device or the like can be used.
  • Pumping light emitted from the pumping light source 821 first reaches the second active layer 342 existing above the first active layer 340. Most part of the second active layer 342 is occupied by the barrier layer thereof, and the barrier layer of the second active layer 342 has a band gap of, for example, about 1.73 eV. Energy of photons of pumping light having a wavelength of 670 nm is higher than energy of the band gap of the barrier layer of the second active layer 342. Therefore, when pumping light having a wavelength of 670 nm is radiated, the pumping light having a wavelength of 670 nm is mainly absorbed by the second active layer 342.
  • the second active layer 342 is mainly excited. Pumping light having a wavelength of 670 nm is sufficiently absorbed by the second active layer 342, and thus, the first active layer 340 existing below the second active layer 342 is hardly excited.
  • Energy of photons of pumping light having a wavelength of 808 nm is lower than energy of the band gap of the barrier layer of the second active layer 342. Therefore, pumping light having a wavelength of 808 nm is not absorbed by the second active layer 342 and passes through the second active layer 342. Energy of photons of pumping light having a wavelength of 808 nm is higher than energy of a band gap of the barrier layer of Al 0.05 GaAs of the first active layer 340. Therefore, when pumping light having a wavelength of 808 nm is radiated, the pumping light having a wavelength of 808 nm is absorbed by the barrier layer of the first active layer 340. Therefore, when pumping light having a wavelength of 808 nm is radiated, the first active layer 340 is excited.
  • the active layers 340 and 342 can be selectively excited.
  • the oscillation wavelength can be changed in an extremely wide wavelength range.
  • FIG. 7 is a sectional view for illustrating the wavelength tunable laser device according to this embodiment.
  • the same components as in the wavelength tunable laser device and the like according to the first to third embodiments illustrated in FIG. 1A to FIG. 6 are represented by the same reference numerals, and description thereof is omitted or simplified.
  • the semiconductor layer 141 does not exist between the first active layer 140 and the second active layer 142.
  • the second active layer 142 is directly formed on the first active layer 140.
  • a semiconductor layer 443 is formed on the second active layer 142.
  • the semiconductor layer 443 has a conductivity type of, for example, the p type.
  • An electrode 450 is formed on the semiconductor layer 443.
  • the substrate 101 has a conductivity type of, for example, the n type
  • the active layers 140 and 142 have a conductivity type of the i type (undoped)
  • the semiconductor layer 443 has a conductivity type of, for example, the p type.
  • the conductivity type is an n-i-p type.
  • two different quantum wells (active layers) 140 and 142 exist in the i-type region between the n-type region 101 and the p-type region 443.
  • the first active layer 140 and the second active layer 142 are respectively located so as to correspond to locations of antinodes of a standing wave of laser light.
  • the first active layer 140 and the second active layer 142 are respectively located so as to correspond to locations of antinodes of the standing wave generated when oscillation is induced at 1,060 nm that is the center wavelength of the wavelength tunable range (high reflectivity band).
  • the first active layer 140 and the second active layer 142 are located so as to correspond to locations of adjacent antinodes of the standing wave, respectively.
  • the first active layer 140 and the second active layer 142 are located so as to correspond to locations of antinodes of the standing wave, respectively, for the purpose of acquiring a sufficient overlap of light.
  • a center location of a quantum well group forming the active layers 140 and 142 be equal to a maximum value of antinodes of the standing wave.
  • a deviation occurs due to a manufacturing error or the like.
  • a node-to-node range (range between one node and a node next to the one node) of one standing wave can be represented as a range of 1/2 (location of the one node) to 3/2 (location of the node next to the one node), where a spacing between one antinode and an antinode next to the one antinode is represented by 1. Therefore, a condition for the first active layer 140 to be located in one node-to-node range of the standing wave and for the second active layer 142 to be located in a node-to-node range next to the one node-to-node range is as follows.
  • condition for the first active layer 140 and the second active layer 142 to be located as described above can be represented as a range of 1/2 to 3/2 of the spacing between antinodes of the standing wave with reference to the location of the antinode corresponding to the first active layer 140.
  • first active layer 140 and the second active layer 142 may be located so as to respectively correspond to locations of antinodes of the standing wave, which are apart from each other.
  • location of the second active layer 142 can be represented as a location apart from a location, at which the node-to-node range of the standing wave in which the first active layer 140 exists has the maximum value, by a distance of 1/2 or more of the spacing between antinodes of the standing wave.
  • the wavelength tunable laser device 10 changes the oscillation wavelength by changing magnitude of an injected current, and thus, output of laser light is changed depending on a change in amount of the injected current.
  • a semiconductor optical amplifier (SOA) (not shown) may be arranged in a stage subsequent to the wavelength tunable laser device 10 according to this embodiment.
  • a semiconductor optical amplifier is arranged in a stage subsequent to the wavelength tunable laser device 10 and an amplification factor of the semiconductor optical amplifier is controlled as appropriate, thereby being capable of finally emitting laser light as stable output from the semiconductor optical amplifier.
  • the excitation of the first active layer 140 and the excitation of the second active layer 142 are controlled. Also according to this embodiment, the excitation of the first active layer 140 and the excitation of the second active layer 142 can be controlled, and thus, mode hopping can be prevented with reliability and the oscillation wavelength can be changed in an extremely wide wavelength range.
  • the number of electrodes required to be formed on the substrate 101 is small, and thus, the degree of difficulty in manufacturing is low and the number of processing steps is small. Therefore, according to this embodiment, manufacturing yield can be improved and manufacturing costs can be reduced.
  • FIG. 8 is a graph for showing a method of driving the wavelength tunable laser device according to this embodiment.
  • the same components as in the wavelength tunable laser device and the like according to the first to fourth embodiments illustrated in FIG. 1A to FIG. 7 are represented by the same reference numerals, and description thereof is omitted or simplified.
  • the wavelength tunable laser device has a structure similar to, for example, that of the wavelength tunable laser device 10 according to the first embodiment. However, according to this embodiment, a balance between the excitation of the first active layer 140 and the excitation of the second active layer 142 is adjusted to intentionally cause mode hopping from Mode A to Mode B.
  • a voltage applied to the electrode 113 configured to displace the beam-like movable portion 122 is gradually raised from 0 V, and a current is injected into the second active layer 142 until the voltage applied to the electrode 113 reaches a predetermined voltage.
  • the predetermined voltage is, for example, a voltage at which the oscillation wavelength is 1,060 nm that is the center wavelength of the wavelength tunable range.
  • the current injection into the second active layer 142 is stopped, and a current is injected into the first active layer 140.
  • the current injection is switched from into the second active layer 142 to into the first active layer 140.
  • oscillation in Mode A on a shorter wavelength side is more liable to be induced than Mode B, and transition from Mode B to Mode A, that is, mode hopping, occurs.
  • the oscillation wavelength is, for example, about 1,007 nm.
  • the peak wavelength of the gain spectrum of the first active layer 140 is set to be sufficiently low with respect to 1,060 nm that is the center wavelength of the wavelength tunable range, and thus, the mode hopping from Mode B to Mode A can occur with reliability.
  • the voltage applied to the electrode 113 configured to displace the beam-like movable portion 122 is gradually lowered.
  • the oscillation in Mode A is maintained.
  • the voltage applied to the electrode 113 becomes 0 V the oscillation wavelength is about 1,050 nm.
  • the oscillation wavelength is about 1,098 nm.
  • the oscillation wavelength returns to the initial state.
  • the peak wavelength of the gain spectrum of the second active layer 142 is set to be sufficiently high with respect to 1,060 nm that is the center wavelength of the wavelength tunable range, and thus, the mode hopping from Mode A to Mode B can occur with reliability.
  • the mode hopping is intentionally caused.
  • the wavelength tunable width acquired by reciprocation of the beam-like movable portion 122 according to this embodiment is similar to the wavelength tunable width acquired in the first embodiment. Therefore, the wavelength tunable laser device may be operated as in this embodiment.
  • the voltage applied to the electrode 113 configured to displace the beam-like movable portion 122 is gradually lowered, and thus, an amount of displacement of the beam-like movable portion 122 is about a half of that in the case of the first embodiment.
  • the voltage applied to the beam-like movable portion 122 may be low, and thus, power consumption and the like can be achieved.
  • the mode hopping is intentionally caused in the wavelength tunable laser device according to the first embodiment
  • the mode hopping may be intentionally caused also in the wavelength tunable laser devices according to the second to fourth embodiments.
  • the two active layers 140 and 142 different from each other are formed also in the wavelength tunable laser devices according to the second to fourth embodiments. Therefore, also in the wavelength tunable laser devices according to the second to fourth embodiments, by appropriately controlling the balance between the excitation of the active layer 140 and the excitation of the active layer 142, the gain spectrum can be controlled as appropriate as in the fifth embodiment. Therefore, the wavelength tunable laser devices according to the second to fourth embodiments can also be operated as in the fifth embodiment.
  • the method of intentionally causing the mode hopping is not limited to appropriately adjusting the balance between the excitation of the active layer 140 and the excitation of the active layer 142.
  • the peak wavelength of the gain spectrum of the first active layer 140 according to the fifth embodiment may be set to be lower than that in the case of the first embodiment.
  • the mode hopping from Mode B to Mode A can occur with reliability.
  • the current injection may be switched from into the second active layer 242 to into the first active layer 140 at a wavelength slightly higher than the center wavelength of the high reflectivity bands of the reflectors 102 and 106. This also enables occurrence of the mode hopping from Mode B to Mode A with reliability.
  • the wavelength tunable laser devices in which the center wavelength of the wavelength tunable range is 1,060 nm, that is, the wavelength tunable laser devices of the 1,060 nm range are described as examples, but the present invention is not limited thereto.
  • the present invention may be applied to a wavelength tunable laser device in which the center wavelength of the wavelength tunable range is 850 nm, that is, a wavelength tunable laser device of the 850 nm range.
  • the center wavelength of the wavelength tunable range is set to be a wavelength different from 1,060 nm in the second embodiment or the third embodiment, the wavelength of pumping light may be set as appropriate depending on band gaps of the respective components.
  • the active layers 140 and 142 have the quantum well structures is described as an example, but the structures of the active layers 140 and 142 are not limited to the quantum well structures.
  • the active layers 140 and 142 may be active layers having other structures such as a bulk or a quantum dot.
  • HCGs high-index contrast subwavelength gratings
  • the excitation of the second active layer 242 is controlled by pumping light radiation and the excitation of the first active layer 140 is controlled by current injection is described as an example, but the present invention is not limited thereto.
  • the excitation of the second active layer 242 may be controlled by current injection and the excitation of the first active layer 140 may be controlled by pumping light radiation.
  • the excitation of the one of the first active layer 140 and the second active layer 242 may be controlled.
  • the excitation of another one of the first active layer 140 and the second active layer 242 may be controlled.
  • the oscillation wavelength is swept with the center wavelengths ⁇ c1 and ⁇ c2 of the high reflectivity bands of the reflectors 102 and 106 being the center of the sweep is described as an example, but the present invention is not limited thereto.
  • the center wavelengths ⁇ c1 and ⁇ c2 of the high reflectivity bands of the reflectors 102 and 106 and the center wavelength of the band in which the oscillation wavelength is changed may be different from each other.
  • the center wavelength ⁇ c1 of the high reflectivity band of the first reflector 102 and the center wavelength ⁇ c2 of the high reflectivity band of the second reflector 106 are the same is described as an example, but the present invention is not limited thereto.
  • the center wavelength ⁇ c1 of the high reflectivity band of the first reflector 102 and the center wavelength ⁇ c2 of the high reflectivity band of the second reflector 106 may be different from each other.
  • the present invention is not limited thereto.
  • the current injected into the second active layer 142 may be set to be larger than the current injected into the first active layer 140.
  • the current injected into the first active layer 140 may be set to be larger than the current injected into the second active layer 142.
  • the magnitude relationship between the current injected into the first active layer 140 and the current injected into the second active layer 142 may be adjusted as appropriate, which may be similarly applied to the second to fifth embodiments.
  • the gain in the second active layer 142, 242, or 342 may be set to be relatively large with respect to the gain in the first active layer 140 or 340.
  • the gain in the first active layer 140 or 340 may be set to be relatively large with respect to the gain in the second active layer 142, 242, or 342.
  • an active layer that realizes a large gain in a relatively short wavelength range is used as the first active layer 140 or 340 and an active layer that realizes a large gain in a relatively long wavelength range is used as the second active layer 142, 242, or 342, but the present invention is not limited thereto.
  • An active layer that realizes a large gain in a relatively long wavelength range may be used as the first active layer 140 or 340 and an active layer that realizes a large gain in a relatively short wavelength range may be used as the second active layer 142, 242, or 342.
  • the upper reflector 106 is arranged on the beam-like movable portion 122 as an example, but the present invention is not limited thereto.
  • the upper reflector 106 may be fixed to a lower surface side of the beam-like movable portion 122.
  • the beam-like movable portion 122 and the upper reflector 106 are separate from each other is described as an example, but the present invention is not limited thereto.
  • the upper reflector 106 may also serve as the beam-like supporting portion.
  • the beam-like movable portion 122 may be a cantilever having one end being fixed.
  • measuring device 10 wavelength tunable laser device 12 resonator 101 substrate 102 lower reflector 103 laminate 104 gap, air gap 106 upper reflector 110, 113 electrode 122 beam-like movable portion, movable mechanism 140 first active layer 141 first semiconductor layer 142 second active layer 143 second semiconductor layer 150, 151 electrode

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Abstract

L'invention concerne un dispositif laser accordable en longueur d'onde, comprenant: un premier réflecteur (102); un deuxième réflecteur (106); et une couche active (140) formée entre le premier réflecteur et le deuxième réflecteur, le dispositif laser accordable en longueur d'onde présentant un interstice (104) formé entre la couche active et le deuxième réflecteur, et une longueur de l'interstice étant modifiée pour modifier une longueur d'onde de résonance, la couche active comprenant: une première couche active (140); et une deuxième couche active (142) formée au-dessus de la première couche active et présentant une longueur d'onde de pic d'un spectre de gain qui est différente d'une longueur d'onde de pic d'un spectre de gain de la première couche active, et l'excitation de la première couche active et l'excitation de la deuxième couche active étant toutes deux commandées en fonction de la longueur de l'interstice.
PCT/JP2016/000455 2015-02-05 2016-01-29 Dispositif laser accordable en longueur d'onde et appareil de tomographie par cohérence optique WO2016125474A1 (fr)

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