JP2009200133A - Wavelength scanning light source, and wavelength scanning optical coherence tomographic apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wavelength scanning light source of a simple configuration using a distributed reflector type semiconductor laser, capable of scanning wavelength at high speed, and to provide a wavelength scanning optical coherence tomographic apparatus using the light source. <P>SOLUTION: The wavelength scanning light source contains the distributed reflector type semiconductor laser having an active region and a distributed reflector region including a passive waveguide layer and current blocks on a semiconductor substrate. The current blocks are made of a material showing a refraction factor approximately equal to that of the surrounding portion when a current is not applied and harder to flow current than the surrounding portion. The current blocks are arranged so that their intervals vary gradually in the waveguide direction of the passive waveguide layer. When current is applied, the current blocks spatially vary the density of the current crossing the passive waveguide layer regularly by their current regulating action to produce regions whose refraction factor varies spatially and regularly in the passive waveguide layer. As the result, light coming from the active region laser-oscillates at a wavelength in accordance with the spatial regularity. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a wavelength scanning light source that scans a wavelength at high speed, and to a wavelength scanning optical coherence tomography apparatus using the same.

  In recent years, as one of non-destructive tomographic techniques used in the medical field, etc., optical tomographic imaging method “Optical Coherence Tomography” (OCT; Optical Coherence Tomography) using temporally low coherence light as a probe (probe) ) Optical coherence tomography includes types such as wavelength scanning optical coherence tomography, Fourier domain optical coherence tomography, polarization sensitive optical coherence tomography, etc. FIG. 8 shows a wavelength scanning optical coherence tomography device. (For example, refer to Patent Document 1 and FIG. 1).

  In the wavelength scanning optical coherence tomography apparatus 80 shown in FIG. 8, the output light emitted from the wavelength scanning light source 200 is sent to the fiber coupler 82 through the first fiber 81. In the fiber coupler 82, the output light is divided into object light that is irradiated onto the measurement object 84 through the second fiber 83 and reference light that is irradiated onto the fixed reference mirror 86 through the third fiber 85.

  The object light is irradiated and reflected on the object to be measured 84 through the second fiber 83, the lens 87, the scanning mirror 88 and the lens 89 having variable angles, and returns to the fiber coupler 82 through the same route. The reference light is irradiated and reflected on the fixed reference mirror 86 through the third fiber 85, the lens 90, and the lens 91, and returns to the fiber coupler 82 through the same route.

  Then, the object light and the reference light are overlapped by the fiber coupler 82, sent to the light detector 93 (photodiode or the like) through the fourth fiber 92, detected as a spectrum interference signal, and taken into the processing means 94 such as a computer. It is. Based on the detection output of the light detector 93, cross-sectional images in the depth direction (A direction) of the measurement object 84 and the scanning direction (B direction) of the scanning mirror 88 are formed. Reference numeral 95 denotes display means such as a display connected to the processing means 94.

  The wavelength scanning light source 200 is a light source that scans while changing the wavelength with time, that is, a light source whose wavelength has time dependency. This makes it possible to obtain the reflectance distribution in the depth direction of the object to be measured 84 and to obtain the structure in the depth direction without scanning (moving, A-scanning) the fixed reference mirror 86, and scanning in the primary direction ( A two-dimensional tomographic image can be formed only by performing (B scan).

  Next, FIG. 9 shows an example of the configuration of the wavelength scanning light source used in such a wavelength scanning optical coherence tomography apparatus 80 (see, for example, Patent Document 2 and FIG. 1).

  This wavelength scanning light source 200 includes an optical fiber 201 to form a loop. A gain medium 202, an optical circulator 203, an optical coupler 204, and a polarization controller 205 are provided in a part of this loop. The gain medium 202 includes an erbium-doped fiber 206, a fiber-pumped semiconductor laser 207 that makes pump light incident on the erbium-doped fiber 206, and a WDM coupler 208. This pumping semiconductor laser 207 amplifies the light transmitted through the erbium doped fiber 206. The optical circulator 203 regulates the direction of light passing through the optical fiber 201 in the direction of the arrow as shown. The optical coupler 204 extracts a part of the light in the optical fiber loop, and the polarization controller 205 defines the polarization direction of the light transmitted through the optical fiber loop in a certain direction.

  A terminal 203 c of the optical circulator 203 is connected to the collimating lens 212 via the optical fiber 211. The collimating lens 212 converts the light from the optical fiber 211 into parallel light, and a polarizer 213 and a polygon mirror 214 are disposed on the optical axis. The polygon mirror 214 reflects the parallel light by changing the angle within the range shown in the drawing by rotating along the axis perpendicular to the paper surface. A cylindrical lens 215, a band pass filter 216, and a mirror 217 are provided on the optical axis of the reflected light. The cylindrical lens 215 refracts the reflected light so that it is always in a constant direction regardless of the rotation angle of the polygon mirror 214. The mirror 217 has a reflecting surface perpendicular to the optical axis emitted from the cylindrical lens 215. The band-pass filter 216 is an optical interference type dielectric multilayer filter in which a large number of dielectric multilayer films are stacked. The optical film thickness of the multilayer film is changed with respect to the scanning direction of the illustrated light, and the selected wavelength is continuously changed. It is configured to let you. The drive unit 218 rotates the polygon mirror 214 at a constant speed. The polarizer 213 defines the polarization direction of light transmitted between the collimating lens 212 and the polygon mirror 214 in a predetermined direction.

The wavelength scanning light source 200 configured in this manner operates as follows. The pumping semiconductor laser 207 is driven to pump the optical fiber loop through the WDM coupler 208. Light added from the terminal 203 a by the action of the optical circulator 203 enters the optical fiber 211 from the terminal 203 c and becomes parallel light by the collimating lens 212. Then, the light is reflected at a position indicated by a solid line in FIG. 9 according to the rotational position of the polygon mirror 214, and converted to an optical axis perpendicular to the reflection surface of the mirror 217 by the cylindrical lens 215. Light having a wavelength that passes through the bandpass filter 216 enters the mirror 217, is reflected by the mirror 217, and is added to the collimator lens 212 via the bandpass filter 216, the cylindrical lens 215, and the polygon mirror 214 again. Further, the light beam is added to the optical fiber loop from the optical circulator 203 through the collimator lens 212. The polarization controller 205 adjusts the polarization of light transmitted through the optical fiber loop in a certain direction. A part of the laser light oscillated in the optical fiber loop in this way is taken out via the optical coupler 204.
JP 2007-101365 A JP 2006-24876 A

  Since the wavelength scanning light source configured in this way is configured to perform wavelength scanning with a polygon mirror, a lens, etc., when an impact or vibration is applied to the device (wavelength scanning light source), a lens, a polarizer, etc. There is a risk that the optical system parts may be damaged or the wavelength to be scanned may be changed. In addition, since the apparatus is composed of a large number of components such as an excitation light source, an optical fiber, a polygon mirror, and a lens, there is a problem that the apparatus itself is increased in size.

  Furthermore, since a polygon mirror is used as a configuration for scanning the wavelength, the maximum scanning speed is limited to about 20 kHz (see, for example, paragraph 0030 of Patent Document 2).

In order to achieve the above object, a wavelength scanning light source according to claim 1 of the present invention comprises:
An active region (51) including an active layer (25) above the semiconductor substrate (23), a passive waveguide layer (24) formed continuously with the active layer, and the vicinity of the passive waveguide layer A distributed reflection region (50) including a plurality of current blocks (31) regularly arranged in the waveguide direction of the passive waveguide layer is formed in the waveguide direction of the passive waveguide layer; A distributed reflection type semiconductor laser (60) in which an electrode (40) is formed below the semiconductor substrate, an excitation electrode (71) is formed above the active region, and a plurality of reflection electrodes (41) are formed above the distributed reflection region. 70) including a wavelength scanning light source,
The current block is formed of a material having a refractive index substantially equal to that of the surrounding portion in a state where no current is injected between the electrode and the reflecting electrode, and the current is less likely to flow from the surrounding portion, and It is formed so that the interval gradually changes along the waveguide direction of the passive waveguide layer,
In a state where current is injected between the electrode and the reflective electrode, the current block spatially and regularly changes the density of the current across the passive waveguide layer by the current regulating action of the current block. Causing the passive waveguide layer to have a region in which the refractive index changes spatially and regularly, and the light incident from the active region oscillates at a wavelength according to the spatial regularity,
A bias current in which a modulation signal is superimposed on each of the plurality of reflection electrodes is injected with a phase difference, so that the portion where the bias current is injected moves spatially and continuously, and the oscillation wavelength Are scanned.

In order to achieve the above object, the wavelength scanning light source according to claim 2 of the present invention comprises:
An active region (51) including an active layer (25) above the semiconductor substrate (23), a passive waveguide layer (24) formed continuously with the active layer, and the vicinity of the passive waveguide layer A distributed reflection region (50) including a plurality of current blocks (31) regularly arranged in the waveguide direction of the passive waveguide layer is formed in the waveguide direction of the passive waveguide layer; A distributed reflection type semiconductor laser in which an electrode (40) is formed below the semiconductor substrate, an excitation electrode (71) is formed above the active region, and a plurality of reflection electrodes (41) is formed above the distributed reflection region. And
The current block is formed of a material having a refractive index substantially equal to that of the surrounding portion in a state where no current is injected between the electrode and the reflecting electrode, and the current is less likely to flow from the surrounding portion, and The distributed reflection type semiconductor laser (60, 70) formed so that its interval gradually changes along the waveguide direction of the passive waveguide layer;
A plurality of current drivers (10) provided for each of the plurality of reflection electrodes, for injecting a bias current into the plurality of reflection electrodes;
A modulation signal applying unit (11) for generating a modulation signal for modulating the bias current and superimposing the modulation signal on the bias current;
A control unit (12) for controlling the plurality of current driving units and the modulation signal applying unit so as to modulate a current injected into the plurality of reflection electrodes and generate a predetermined phase difference therebetween;
In a state where current is injected between the electrode and the reflective electrode, the current block spatially and regularly changes the density of the current across the passive waveguide layer by the current regulating action of the current block. Causing the passive waveguide layer to have a region in which the refractive index changes spatially and regularly, and the light incident from the active region oscillates at a wavelength according to the spatial regularity,
The bias current applied with the modulation signal to the plurality of reflection electrodes is injected with a phase difference, so that the portion where the bias current is injected moves spatially and continuously, and the oscillation wavelength Are scanned.

In order to achieve the object, a wavelength scanning light source according to a third aspect of the present invention is the wavelength scanning light source according to any one of the first and second aspects,
The current block is formed in at least one of an n-type cladding layer (23) and a p-type cladding layer (22) provided above and below the passive waveguide layer.

In order to achieve the above object, a wavelength scanning light source according to claim 4 of the present invention is the wavelength scanning light source according to claim 3,
The current block has a conductivity type opposite to that of the surrounding cladding layer.

In order to achieve the object, the wavelength scanning light source according to claim 5 of the present invention is the wavelength scanning light source according to any one of claims 1 to 3,
The current block is made of a high resistance material.

In order to achieve the object, a wavelength scanning light source according to a sixth aspect of the present invention is the wavelength scanning light source according to any one of the first to fifth aspects,
The width of the passive waveguide layer is formed so as to change along the waveguide direction of the passive waveguide layer.

In order to achieve the above object, a wavelength scanning optical coherence tomography apparatus according to claim 7 of the present invention includes:
A wavelength scanning light source, a fixed reference mirror and a scanning mirror that respectively receive output light from the wavelength scanning light source via a fiber coupler, and return light from the fixed reference mirror and the scanning mirror, respectively. In a wavelength scanning optical coherence tomography apparatus including a photodetector that receives the signal from the optical detector and a processing unit that receives and processes a signal from the photodetector,
The wavelength scanning light source is the wavelength scanning light source according to any one of claims 1 to 6.

  As described above, the wavelength scanning light source of the present invention includes the distributed reflection type semiconductor laser, the current driving unit, the modulation signal applying unit, and the control unit, and the basic configuration is only the semiconductor light emitting element. Even when an impact or vibration is applied to the wavelength scanning light source), the optical system component is not damaged or the scanning wavelength is not changed, and the apparatus itself can be downsized. Further, since the wavelength scanning is performed by the controlled distributed reflection type semiconductor laser alone, the wavelength scanning speed can be remarkably improved. Specifically, a scanning speed of 10 MHz or more can be realized. Furthermore, since the number of parts is small, the part cost and the manufacturing cost can be suppressed, and it is possible to manufacture at a low cost.

  Furthermore, since the wavelength scanning optical coherence tomography apparatus of the present invention employs the wavelength scanning light source having a scanning speed of 10 MHz or more as described above, it is possible to significantly reduce the measurement time of the object to be measured. is there.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[First Embodiment]
1 to 3 show the structure of the wavelength scanning light source 1 of the embodiment. The wavelength scanning light source 1 generates a distributed reflection semiconductor laser 60, a current driver 10 that injects a bias current I into each electrode 41 of the distributed reflection semiconductor laser 60, and a modulation signal that modulates the bias current. The modulation signal applying unit 11 superimposes the modulation signal on the bias current, and the control unit 12 that controls the current driving unit 10 and the modulation signal applying unit 11. 2 is a plan view of the distributed reflection type semiconductor laser 60, and FIG. 3 is a front view of the distributed reflection type semiconductor laser 60. As shown in FIG.

  The distributed reflection type semiconductor laser 60 is composed of a distributed reflection region 50 and an active region 51. The distributed reflection region 50 includes an n-type substrate 23 made of n-type indium phosphorus (n-InP), and a passive waveguide layer 24 having a constant width above the n-type substrate 23 and p-type indium phosphorus (p-InP). The p-type cladding layers 22 are sequentially formed. The upper layer portion of the n-type substrate 23 functions as an n-type clad layer for preventing leakage of light to the outside together with the p-type clad layer 22. Note that an n-type cladding layer made of n-type indium phosphorus (n-InP) may be separately provided between the n-type substrate 23 and the passive waveguide layer 24.

  The passive waveguide layer 24 is formed, for example, by indium gallium arsenide phosphorus (InGaAsP) so as to be continuous with a predetermined width, and has a smaller band gap (higher refractive index) than the cladding layer so as to form a waveguide that propagates light. Is set.

  Inside the p-type cladding layer 22, a current block 31 having a predetermined length is regularly arranged along the passive waveguide layer 24 in a direction intersecting the passive waveguide layer 24 in the vicinity of the passive waveguide layer 24. . Specifically, a pitch Λx of the current blocks 31 arranged along the passive waveguide layer 24 having a constant width gradually increases toward the active region 51, that is, a chirped grating structure.

  The active region 51 extends the p-type cladding layer 22 and the n-type substrate 23 (including the n-type cladding layer) of the distributed reflection region 50 to one end side, and the extended p-type cladding layer 22 and the n-type substrate 23 An active layer 25 having a band gap for emitting light is formed therebetween.

  The current block 31 exhibits a refractive index substantially equal to that of the surrounding portion (in this case, the p-type cladding layer 22) in the current non-injection state, and current flows from the surrounding portion (in this case, the p-type cladding layer 22) in the current injection state. It is difficult to form. For example, a pn junction is formed between the p-type cladding layer and an n-InP material that makes it difficult for current to flow, or an Fe-doped i-InP material that has a higher electrical resistance than the p-type cladding layer 22. Has been.

  On the lower surface side (n-type substrate 23 side) of the distributed reflection region 50 and the active region 51, a common electrode 40 (hereinafter sometimes simply referred to as an electrode) is formed over almost the entire surface. Needless to say, the distributed reflection region 50 and the active region 51 may be composed of separate electrodes.

Above the distributed reflection region 50, a plurality of N reflection electrodes 41 _{1 to} 41 _N are arranged at regular intervals so that the current block 31 is sandwiched between the common electrodes 40 and currents can be injected independently into regions having different intervals. Is arranged in. An excitation electrode 71 is disposed above the active region 51.

In the distributed reflection type semiconductor laser 60 having the above configuration, when no current is injected between any of the common electrode 40 and the reflection electrodes 41 _{1 to} 41 _N , the passive waveguide layer 24 is connected to the active region from one end side 60a. Thus, the waveguide has a substantially constant refractive index.

The current driving portions ₁₀ 1 to 10 _N are configured in the reflective electrode ₄₁ every 1 to 41 _N of the plurality N, it injects a bias current _I 1 ~I _N to each of the electrodes ₄₁ 1 to 41 _N.

Modulation signal applying unit 11 generates a modulation signal for modulating a bias current _I 1 ~I _N from the current driver 10 superimposes the modulated signal to the bias current _I 1 ~I _N. The modulation frequency signal is, for example, a sine wave signal. The modulation frequency signal is not limited to a sine wave signal, and may be a periodic signal such as a triangular wave signal.

The control unit 12 modulates the current flowing through the reflecting electrodes 41 _{1 to} 41 _N and gives a suitable phase difference between them, so that a continuous wavelength scanning operation is performed and the current driving unit 10 and the modulation signal. The application unit 11 is controlled.

Here, the operation principle of the distributed reflection type semiconductor laser 60 having the above configuration will be described with reference to FIGS. Figure 4, which shows a part of the distributed reflection region 50 schematically here are equally spaced pitch of the current block 31 at lambda _1. When a predetermined current I _X is injected between the electrodes 41 _X and 40 as shown in FIG. 4, the current from the p-type cladding layer 22 toward the passive waveguide layer 24 is concentrated in the gap of the current block 31. Will flow.

Therefore, in the portion where the current block 31 of the passive waveguide layer 24 is provided, as shown in FIG. 5, the portions having a coarse current density and the dense portions are alternately arranged at intervals corresponding to the interval Λ ₁ of the current block 31. Due to the plasma effect, the refractive index of the dense region is smaller than the refractive index of the coarse region.

In other words, the region where the refractive index in the passive waveguide layer 24 are different becomes periodically occur that at intervals lambda ₁ of the current block 31, the refractive index of the Bragg reflection of light between reflected from the boundary portion that changes mutually stressed conditions,
λ _B 1 = 2n ₁ Λ ₁ (n ₁ is the equivalent refractive index of the waveguide)
Reflection occurs at a wavelength λ _B 1 that satisfies

In the distributed reflection type semiconductor laser 60 of the first embodiment, since the current block 31 has a chirped grating structure, a predetermined distance is provided between the common electrode 40 and the reflection electrodes 41 _{1 to} 41 _{N in} the distributed reflection region 50. When the currents I _{1 to} I _N are injected, the passive waveguide layer 24 enters a state where laser oscillation occurs at the Bragg wavelength of the portion where the current is injected.

Next, the operation of the wavelength scanning light source 1 configured as described above will be described. When a predetermined current _Id is injected between the excitation electrode 71 and the common electrode 40, light is emitted from the active layer 25, and a part of the light enters the passive waveguide layer 24 from the end 24a of the passive waveguide layer.

Here, it is assumed that the reflection wavelength of the current block 31 in the distributed reflection region 50 is within the band of the emitted light. In the distributed reflection region 50, bias currents I ₁ ′ to I _N ′ in which modulation signals are superimposed on the electrodes 41 _{1 to} 41 _N are injected with a phase difference. The light incident on the passive waveguide layer 24 is reflected and amplified between the element end face 60a and the current block 31, and a part of the light is emitted as light having a continuous wavelength from the element end face 60b, for example.

That is, in a state where current is injected between the common electrode 40 and the reflection electrode 41, the current block 31 spatially changes the density of current crossing the passive waveguide layer 24 due to the current regulating action of the current block 31. A region where the refractive index is spatially regularly changed is generated in the passive waveguide layer 24 by changing regularly. The light incident from the active region 51 oscillates at a Bragg wavelength according to the spatial regularity. Bias currents I ₁ ′ to I _N ′ in which modulation signals are applied to the plurality of reflection electrodes 41 _{1 to} 41 _N are injected with a phase difference between the bias currents I ₁ ′ to I _N ′. The injected part moves continuously in space, and the Bragg wavelength is scanned. The scanning speed is 10 MHz or higher.

  In the above description, the n-type or high-resistance material current block 31 is arranged inside the p-type clad layer 22, but the n-type clad layer (the portion of the n-type substrate 23 near the passive waveguide layer 24). P-type or high-resistance material current blocks 31 may be arranged to form the current block group 30, or the current blocks 31 may be arranged on both cladding layers at the same pitch.

  It is also possible to form a layer having a refractive index intermediate to that of the cladding layer in the vicinity of the passive waveguide layer 24 and to form the current block 31 therein.

  Next, a manufacturing method of the basic structure of the distributed reflection type semiconductor laser 60 will be described with reference to FIG.

  First, as shown in FIG. 6A, on an n-type InP substrate 100, a lower optical confinement layer 101 made of InGaAsP (hereinafter referred to as a lower SCH layer 101), an active layer 102 made of InGaAsP, and made of InGaAsP. Upper optical confinement layer 103 (hereinafter referred to as upper SCH layer 103) is grown by metal organic vapor phase epitaxy (hereinafter referred to simply as “grow”).

  Note that the SCH layers 101 and 103 and the active layer 102 generally have a multilayer internal structure. That is, widely known structures such as a graded index SCH structure and a multiple quantum well active layer structure are possible. The quantum well layer may use not only InGaAsP but also InGaAs or a layer containing Al. The composition of each layer can be appropriately designed in accordance with the target oscillation wavelength band. Further, the SCH layer is not essential.

Next, after a SiO ₂ film 104 is formed on the surface, a photoresist (hereinafter simply referred to as a resist) is applied to the entire surface, and a photolithography process is performed so that the resist remains only in a portion that becomes an active region. Then, the exposed SiO ₂ is removed by using a dry etching method such as reactive ion etching or a wet etching method such as hydrofluoric acid, and then using the remaining SiO ₂ film 104 as an etching mask, wet etching using sulfuric acid or the like. The upper SCH layer 101, the active layer 102, and the lower CH layer 103 are partially removed using a method. FIG. 6B shows a state where even the residual resist has been removed.

Thereafter, using the SiO ₂ film 104 as a growth inhibition mask, a passive waveguide layer 105 made of InGaAsP is grown on the exposed InP substrate 100, and the SiO ₂ film 104 is removed by hydrofluoric acid, as shown in FIG. It is a state.

  The composition of InGaAsP in the passive waveguide layer 105 makes the band gap energy larger than that of the active layer 102. For example, in the case of a laser having a wavelength of 1.55 μm, the range is set to 1.2 to 1.45 μm.

  Subsequently, as shown in FIG. 6D, a p-type InP spacer layer 106 and an n-type InP current blocking layer 107 are grown on the entire surface. The spacer layer 106 is integrated with the clad layer and becomes a part thereof when the clad layer is grown later.

  Next, after applying a resist to the entire surface, a diffraction grating resist 108 is formed in a portion that becomes a distributed reflection region (current block group) by an electron beam drawing method or an interference exposure method. FIG. 6E shows a state in which the resist in the active region is completely removed, but the resist may remain on the entire active region.

  Then, wet etching is performed with an etchant using saturated bromine water or the like, and the current block 31 is etched into a diffraction grating shape. Since the difference between the etching rates of n-type InP and p-type InP is slight, time adjustment is performed so that the etching is stopped when the etching progresses partway through the spacer layer 106 as shown in FIG. FIG. 6F shows a state in which the resist is removed after etching. Needless to say, when the entire active region is covered with resist, the p-type InP and spacer layer 106 in the active region are not etched at all.

  Next, a p-type InP clad layer 106 'is grown so as to cover these entire surfaces. Since the spacer layer 106 and the clad layer 106 ′ have the same composition, they are also depicted integrally in FIG.

  Finally, although the detailed steps are omitted, the whole is formed into a striped mesa by photolithography and etching, both sides of the mesa are embedded with BH layers 110 and 111 of p-type InP and n-type InP, and p is formed on the entire upper surface. The type InP upper cladding layer 112 and the p-type InGaAs contact layer 113 are grown to complete the crystal growth process.

  Subsequently, the p-side electrode 114 is formed on the p-type InGaAs contact layer 113 by vapor deposition, but the electrodes are formed separately so that different currents can flow in the active region and the distributed reflection region.

  In order to further increase the isolation resistance, it is desirable to remove the contact layer 113 at the isolation portion by etching. The n-type InP substrate 100 is polished to a thickness of about 100 μm by polishing, and then an n-type electrode 115 is formed. A cross-sectional view and a front view of the resulting structure are shown in FIGS. 6 (h) and 6 (i). The end face is formed by cleaving, and is coated with a dielectric multilayer film as necessary. Note that a plurality of p-side electrodes formed above the distributed reflection region are actually configured, but in FIG. 6H, only one is omitted from the illustration.

  In the above description, the current block 31 is n-type, but may be an insulating InP (high resistance material) such as Fe-doped.

[Second Embodiment]
Next, another wavelength scanning light source of the present invention will be described with reference to FIG. FIG. 7 shows only the distributed reflection type semiconductor laser 70 of the wavelength scanning light source of the second embodiment. The configurations of the control unit 12, the current driving unit 10, and the modulation signal applying unit 11 are the same as those in the first embodiment, and are not shown.

  The distributed reflection type semiconductor laser 70 in the wavelength scanning light source of the second embodiment has a chirped grating structure in which the interval Λx of the current blocks 31 is gradually increased toward the one end 70a. Further, the width of the passive waveguide layer 24 gradually increases toward the one end 70a, and a curved waveguide structure is formed in which the passive waveguide layer 24 is bent and in contact with the one end 70a. An effective chirped grating is realized by the structure of gradually increasing the passive waveguide layer width and the bent waveguide structure. Therefore, a larger wavelength scanning width can be realized by combining with the chirped grating structure of the current block 31 described above. In addition, since the element end face 60a is inclined with respect to the passive waveguide layer 24, the end face reflectivity with respect to unnecessary light can be suppressed to be low, and better spectrum characteristics can be obtained.

  In the case where the intervals Λx of the current blocks 31 are equal, the passive waveguide layer 24 can be effectively used as a straight waveguide structure whose width gradually increases or a curved waveguide structure whose width is constant. A chirped grating can be created. Although the wavelength width that can be scanned is smaller than that of the above-described embodiment, it can be applied to the wavelength-tunable light source of the present invention.

[Third Embodiment]
Next, the wavelength scanning optical coherence tomography apparatus of the present invention will be described. The basic configuration of the wavelength scanning optical coherence tomography apparatus of the present invention is the same as that of the conventional wavelength scanning optical coherence tomography apparatus shown in FIG. The wavelength scanning light source 200 of the present invention described in the first and second embodiments is applied to the wavelength scanning light source 200 in FIG.

  Since the wavelength scanning light source of the first and second embodiments achieves a scanning speed of 10 MHz or higher, the wavelength scanning optical coherence tomography apparatus of the present invention to which this is applied has a measurement time of an object to be measured. Can be significantly shortened compared to the prior art.

Wavelength scanning light source of first embodiment of the present invention The top view of the distributed reflection type semiconductor laser of the wavelength scanning light source of 1st Embodiment of this invention The front view of the distributed reflection type semiconductor laser of the wavelength scanning light source of 1st Embodiment of this invention Operation explanatory diagram of distributed reflection area of embodiment Operation explanatory diagram of distributed reflection area of embodiment The figure for demonstrating the manufacturing method of the distributed reflection type semiconductor laser of the wavelength scanning light source of embodiment Structure diagram of distributed reflection type semiconductor laser of wavelength scanning light source of second embodiment of the present invention The figure which shows the structure of a wavelength scanning optical coherence tomography apparatus The figure which shows the structure of the conventional wavelength scanning type light source

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Wavelength scanning light source 10 ... Current drive part 11 ... Modulation signal application part 12 ... Control part 22 ... p-type clad layer 23 ... n-type substrate 24 ... Passive waveguide layer 25 ... Active layer 31... Current block 40... Common electrode 41 _{1 to} 41 _N ... Reflective electrode 50... Distributed reflection region 51... Active region 60 and 70. Scanning optical coherence tomography apparatus 81, 83, 85, 92 ... optical fiber 82 ... fiber coupler,
84 …… Measurement object 86 …… Fixed reference mirror 87 …… Lens 88 …… Scanning mirrors 89, 90, 91 …… Lens 93 …… Photo detector 94 …… Processing means 95 …… Display means 200 …… Wavelength scanning Mold light source

Claims (7)

An active region (51) including an active layer (25) above the semiconductor substrate (23), a passive waveguide layer (24) formed continuously with the active layer, and the vicinity of the passive waveguide layer A distributed reflection region (50) including a plurality of current blocks (31) regularly arranged in the waveguide direction of the passive waveguide layer is formed in the waveguide direction of the passive waveguide layer; A distributed reflection type semiconductor laser (60) in which an electrode (40) is formed below the semiconductor substrate, an excitation electrode (71) is formed above the active region, and a plurality of reflection electrodes (41) are formed above the distributed reflection region. 70) including a wavelength scanning light source,
The current block is formed of a material having a refractive index substantially equal to that of the surrounding portion in a state where no current is injected between the electrode and the reflecting electrode, and the current is less likely to flow from the surrounding portion, and It is formed so that the interval gradually changes along the waveguide direction of the passive waveguide layer,
In a state where current is injected between the electrode and the reflective electrode, the current block spatially and regularly changes the density of the current across the passive waveguide layer by the current regulating action of the current block. Causing the passive waveguide layer to have a region in which the refractive index changes spatially and regularly, and the light incident from the active region oscillates at a wavelength according to the spatial regularity,
A bias current in which a modulation signal is superimposed on each of the plurality of reflection electrodes is injected with a phase difference, so that the portion where the bias current is injected moves spatially and continuously, and the oscillation wavelength A wavelength scanning type light source characterized by being scanned. An active region (51) including an active layer (25) above the semiconductor substrate (23), a passive waveguide layer (24) formed continuously with the active layer, and the vicinity of the passive waveguide layer A distributed reflection region (50) including a plurality of current blocks (31) regularly arranged in the waveguide direction of the passive waveguide layer is formed in the waveguide direction of the passive waveguide layer; A distributed reflection type semiconductor laser in which an electrode (40) is formed below the semiconductor substrate, an excitation electrode (71) is formed above the active region, and a plurality of reflection electrodes (41) is formed above the distributed reflection region. And
The current block is formed of a material having a refractive index substantially equal to that of the surrounding portion in a state where no current is injected between the electrode and the reflecting electrode, and the current is less likely to flow from the surrounding portion, and The distributed reflection type semiconductor laser (60, 70) formed so that its interval gradually changes along the waveguide direction of the passive waveguide layer;
A plurality of current drivers (10) provided for each of the plurality of reflection electrodes, for injecting a bias current into the plurality of reflection electrodes;
A modulation signal applying unit (11) for generating a modulation signal for modulating the bias current and superimposing the modulation signal on the bias current;
A control unit (12) for controlling the plurality of current driving units and the modulation signal applying unit so as to modulate a current injected into the plurality of reflection electrodes and generate a predetermined phase difference therebetween;
In a state where current is injected between the electrode and the reflective electrode, the current block spatially and regularly changes the density of the current across the passive waveguide layer by the current regulating action of the current block. Causing the passive waveguide layer to have a region in which the refractive index changes spatially and regularly, and the light incident from the active region oscillates at a wavelength according to the spatial regularity,
The bias current applied with the modulation signal to the plurality of reflection electrodes is injected with a phase difference, so that the portion where the bias current is injected moves spatially and continuously, and the oscillation wavelength A wavelength scanning type light source characterized by being scanned.   The current block is formed in at least one of an n-type cladding layer (23) and a p-type cladding layer (22) provided above and below the passive waveguide layer. The wavelength scanning light source of any one of 1-2.   4. The wavelength scanning light source according to claim 3, wherein the current block has a conductivity type opposite to that of a surrounding clad layer.   The wavelength scanning light source according to claim 1, wherein the current block is made of a high resistance material.   6. The wavelength scanning light source according to claim 1, wherein a width of the passive waveguide layer is formed so as to change along a waveguide direction of the passive waveguide layer. . A wavelength scanning light source, a fixed reference mirror and a scanning mirror that respectively receive output light from the wavelength scanning light source via a fiber coupler, and return light from the fixed reference mirror and the scanning mirror, respectively. In a wavelength scanning optical coherence tomography apparatus including a photodetector that receives the signal from the optical detector and a processing unit that receives and processes a signal from the photodetector,
The wavelength scanning optical coherence tomography apparatus, wherein the wavelength scanning light source is the wavelength scanning light source according to any one of claims 1 to 6.

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