JP2013041860A - Light source device, and optical tomographic image capturing device having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light source device having a low-cost and easy-to-fabricate structure and capable of narrowing an oscillation line width, as a light source device having a variable oscillation wavelength.SOLUTION: The light source device has: a collimator lens 102 collimating outgoing light of semiconductor optical amplification medium; a diffraction grating 103 giving the collimated light flux an angle dispersion different for a wavelength; a condenser lens 104 collecting the light flux to which the angle dispersion is given to a position different for the wavelength; and wavelength selection means having reflection parts or transmission parts that scan in a focal plane by the condenser lens and reflect or transmit light having a part of wavelengths. In the wavelength selection means, the reflection parts or the transmission parts formed to have such a uniform width having an optical power are arranged on a rotatable circular plate-shaped substrate. In accordance with rotation of the circular plate-shaped substrate, a wavelength of the outgoing light reflected or transmitted by the reflection parts or the transmission parts is changed to a light collection spot by the condenser lens that is provided on a surface of the circular plate-shaped substrate, and thereby, the light source device is made operate as a wavelength sweeping light source.

Description

  The present invention relates to a light source device capable of changing an oscillation wavelength and an optical tomographic imaging apparatus having the light source device.

In a technique for making the oscillation wavelength of a light source, particularly a laser light source variable, both high speed of wavelength sweeping and narrow line width are desired.
In wavelength swept optical coherence tomography (SS-OCT), spectral interference is used to obtain depth information. Since such a tomographic imaging apparatus based on optical interference does not use a spectroscope, it is expected to acquire an image with a high SN ratio with little loss of light.
When the optical tomographic imaging apparatus to which the SS-OCT technology is applied constitutes a medical imaging apparatus, the higher the sweep speed, the shorter the image acquisition time, and the more suitable for observing living tissue alive. It is.
Also, these parameters are important because the spatial resolution of a tomographic image can be increased as the wavelength sweep width is wider. Specifically, when the wavelength sweep width Δλ and the oscillation wavelength λ0, the depth resolution is expressed by the following equation.

Therefore, in order to increase the depth resolution, the wavelength sweep width needs to be increased, and a broadband wavelength sweep light source is required.
The OCT technique is a technique that can obtain a tomographic image up to a depth of several millimeters with a resolution in the depth direction of several microns, and is used for fundus photography.
Patent Document 1 and Patent Document 2 disclose light source technologies in which the emission wavelength is variable.

In Patent Document 1, light from a gain medium is dispersed by a diffraction grating, and the dispersed light is collected at different positions for each wavelength.
By preparing a narrow slit mirror for reflecting only the light having a part of the dispersed wavelength in the vicinity of the condensing position, only the light having a specific wavelength is returned to the gain medium by the reflecting mirror. It has a resonator configuration.
Further, the slit mirror is formed on the surface of a rotating disk introduced perpendicular to the optical axis, and the position of the slit mirror moves with the rotation of the disk.
Depending on the position of the slit mirror, the position of the slit mirror with respect to the separated light changes, and the wavelength reflected by the slit mirror and returning to the optical amplifier changes, thereby operating as a wavelength variable light source.
Patent Document 2 uses the same optical system as Patent Document 1, but the slit mirror in Patent Document 1 is replaced with a transmissive slit, and a reflection mirror is provided on the rear side to return light to the optical amplifier. doing.

Special table 2007-526620 gazette JP 2008-98395 A

In SS-OCT, interference of reflectance spectrum from an object is acquired while sweeping the wavelength of the light source.
For this reason, the spectral line width of the light source needs to be narrower than the wavelength interval between the points of the spectrum acquisition.
For example, when the sweep band is set to 840 nm ± 40 nm, assuming that the spectrum is acquired at 1000 points in this band, the line width needs to be 0.08 nm or less in order to acquire each spectrum point separately. It is.
Also, in order to increase the coherence distance in interference measurement (in terms of coherence length), a light source with a narrow bandwidth is desirable.

As described above, as a light source using SS-OCT, it is required to realize a high-speed and wide-band wavelength sweep and a light source having a narrow band width during the sweep.
In the light sources in Patent Document 1 and Patent Document 2 described above, the oscillation line width depends on the width of the slit mirror or the width of the transmission slit, so that a narrow slit is produced in order to narrow the oscillation line width. is necessary.
However, when the slit width is on the order of several microns, high process accuracy is required to produce a narrow slit. Therefore, it is a problem in constructing a light source with a narrow oscillation line width that is inexpensive and easy to manufacture.

  In view of the above problems, the present invention provides a light source device having a structure that is inexpensive and easy to manufacture as a light source device having a variable oscillation wavelength, and capable of narrowing the oscillation line width, and a light having the light source device An object is to provide a tomographic imaging apparatus.

The light source device of the present invention comprises:
A semiconductor optical amplification medium;
A collimating lens for collimating the light emitted from the semiconductor optical amplification medium;
A diffraction grating that gives the collimated beam a different angular dispersion depending on the wavelength;
A condensing lens that condenses the light flux given angular dispersion by the diffraction grating at different positions depending on the wavelength;
A wavelength selection means comprising a reflection part for reflecting the light of a part of the wavelength by scanning the focal plane by the condenser lens or a transmission part for transmission;
In the light source device having
The wavelength selection means, the reflection part or the transmission part formed in a uniform width having optical power, on a rotatable disk-shaped substrate,
Along with the rotation of the disk-shaped substrate, the light-condensing spot on the surface of the disk-shaped substrate by the condensing lens is reflected or transmitted by the reflection part or the transmission part arranged on the substrate. Change the wavelength of the light emitted from the semiconductor optical amplification medium,
It operates as a wavelength swept light source.
In addition, the optical tomographic imaging apparatus of the present invention has a light source device, irradiates the inspection object with light from the light source device, and transmits the reflected light from the inspection object,
A reference unit that irradiates a reference mirror with light from the light source device and transmits reflected light from the reference mirror;
An interference unit that causes interference between reflected light from the measurement unit of the inspection object and reflected light from the reference unit;
A light detection unit for detecting interference light from the interference unit;
An optical tomographic imaging apparatus that captures a tomographic image of the inspection object using light detected by the light detection unit,
The light source device is constituted by the light source device described above.

  According to the present invention, as a light source device having a variable oscillation wavelength, a light source device that has a structure that is inexpensive and easy to manufacture and that can narrow an oscillation line width, and an optical tomographic image pickup having the light source device are provided. An apparatus can be realized.

The figure explaining the structural example of the light source device in embodiment of this invention. The figure explaining the structural example which used the rotation slit disc in embodiment of this invention as the transmission type. The figure explaining the structural example which used the rotation slit disc in embodiment of this invention as the transmission type. The figure explaining the structural example which does not form a light-shielding member in the rotation slit disc in embodiment of this invention. The figure explaining the structural example which made the light transmissive member in embodiment of this invention a different form. The figure explaining the structural example which used the rotation slit disc in embodiment of this invention as a reflection type. The figure explaining the structural example which used the rotation slit disc in embodiment of this invention as a reflection type. The figure explaining the structural example of the light source device in Example 1 of this invention. The figure explaining the structure of the reflection part of the light source device in Example 1 of this invention. The figure explaining the structural example of the light source device in Example 2 of this invention. The figure explaining the structure of the permeation | transmission part of the light source device in Example 2 of this invention. The figure explaining the structural example of the optical tomographic imaging apparatus in Example 3 of this invention. The figure explaining the structural example for carrying out the differential detection of the interference signal in Example 3 of this invention. The figure explaining operation | movement of the rotation slit disc in embodiment of this invention.

Below, the structural example of the light source device in embodiment of this invention is demonstrated.
The light source device of the present embodiment includes a semiconductor optical amplifying medium (semiconductor optical amplifier), and a light beam collimated by a collimating lens with light emitted from the semiconductor optical amplifying medium is given angular dispersion different from the wavelength by a diffraction grating. .
The light flux given this angular dispersion is condensed at different positions by the wavelength by the condenser lens.
And it scans the inside of the focal plane by the said condensing lens, and it is comprised so that the light of a one part wavelength may be reflected or permeate | transmitted by the wavelength selection means provided with the reflection part or the transmission part.
A specific configuration example of this light source device is shown in FIG.
However, the present invention is not limited by the configuration of the present embodiment.
FIG. 1A is a schematic diagram of a light source device in the present embodiment.
As shown in FIG. 1A, an optical resonator 100 is constituted by a semiconductor optical amplifier 101, a collimator 102, a diffraction grating 103, a condenser lens 104, and a rotating slit disk (wavelength selection means) 105.
In the rotating slit disk 105, a reflection part or a transmission part formed in equal width having optical power is arranged on a rotatable disk-shaped substrate.
In FIG. 1A, the periodic structure of the diffraction grating is formed in the direction perpendicular to the paper surface. In the case where the rotary slit disk 105 is a reflection type wavelength selection element, the above configuration is used. However, in the case where the rotation slit disk 105 is a transmission type wavelength selection element, the light reflection mirrors 111 are arranged to face each other. The Further, a drive control unit 107 is connected to the optical amplifier 101. Then, the transmitted light from the diffraction grating 103 is reflected by the mirror 108 and coupled to the optical fiber 110 through the condenser lens 109, so that the output of the light source device of the present embodiment is taken out of the resonator. .
The drive control unit 107 is a device for inputting energy to the optical amplifier and controlling the gain thereof, and includes a power supply device and a PC for controlling them.
The resonator length of the optical resonator 100 is preferably suppressed to about 5 cm or less, for example, in order to perform a wavelength sweep operation with a narrow line width at high speed.

In the light source device of the present embodiment, it is the rotating slit disk 105 that selects the oscillation wavelength (FIG. 1B).
The rotating slit disk 105 selects a wavelength of light existing in the resonator by selectively transmitting or reflecting a part of the light collected by the diffraction grating 103 at different focal positions for each wavelength.
As the rotating slit disk rotates, the oscillation wavelength changes (FIG. 14).
Although there are a plurality of openings 113, when the rotation angle of the rotating slit disk 105 when a slit of the opening begins to cross the spectral condensing spot 114 is θs1, and θe1 when the slit ends, the oscillation wavelength is shown in FIG. As shown, the rotation angle changes from λs to λe.
Then, the oscillation stops when the opening is removed from the spectral focused spot. Then, when the rotation angle when the next opening starts to cross the spectral focused spot is θs2, and the rotation angle when the next opening ends is θe2, the oscillation wavelength is similarly converted from λs to λe.
By repeating this operation, the light source of the present invention operates as a wavelength swept light source.

The rotating slit disk 105 is provided with a light shielding part 112 and an opening 113. Then, the light dispersed by the diffraction grating is condensed on the rotating slit disk as a spectral condensing spot 114.
The spectral focused spot 114 is wavelength-resolved in the circumferential direction of the rotating slit disk. Then, a part of the dispersed wavelength is cut out by the opening. It is also preferable to monitor the rotation of the slit with respect to the rotation origin detection slit 115 using light from a light source or light from another light source.

Next, the element configuration when the rotating slit disk is of a transmission type will be described with reference to FIGS.
FIG. 2A is a schematic view focusing on an opening into which light separated by a diffraction grating is incident.
In the configuration of FIG. 2, wavelength selection is performed using a transmission-type rotating slit disk having optical power and a subsequent reflecting mirror.
The light shielding unit 201 has an opening 202. A light transmitting member 203 is disposed below the light shielding portion 201, and the light transmitting member 203 has an optical power portion 204 in the opening 202. Then, the reflection mirror 205 is disposed in the subsequent stage.
Here, the case where the optical power unit 204 functions as a convex lens will be described. It is assumed that light having a wavelength of λ1 to light having a wavelength of λ5 is incident on the opening 202 out of the light split by the diffraction grating 103 and collected by the condenser lens 104.

As shown in FIG. 2B, the width of the opening 202 is a, the distance from the opening to the reflecting mirror (opposite distance to the light reflecting mirror) is L, and the focal length of the optical power unit is f.
At this time, since the optical power part exists in the opening, a part of the light incident on the opening 202 is refracted by the optical power, and the focal position is a position other than the surface of the light reflecting mirror behind the transmission part. It becomes.
Further, after being reflected by the light reflecting mirror, it is shielded by the light shielding part.
That is, when the wavelength range of light reaching the transmission part from the optical amplifier is Δλ, and a predetermined wavelength selection range Δλ ′, the wavelength width of the light incident on the opening 202, that is, λ5−λ1 = Δλ is The wavelength selection condition becomes more severe due to the optical power, and Δλ ′.
This corresponds to the fact that the wavelength selectivity is effectively improved by the optical power. In order to suppress it to a predetermined wavelength width Δλ ′ or less, the focal length f of the optical power in the aperture and the facing distance L to the light reflecting mirror satisfy the following formula (1) from geometric considerations. is necessary.

Further, the above description is a discussion in the case where the optical power in the aperture corresponds to a convex lens. Similarly, even when the optical power in the aperture corresponds to a concave lens, a condition can be defined for the focal length f.
As shown in FIG. 3, a light shielding part 301, an opening 302, a light transmission member 303, an optical power part 304, and a reflection mirror 305 are arranged.
In the case where the focal position of the concave lens is defined as shown in FIG. 3, the optical power in the aperture is determined in order to suppress the optical power to a predetermined wavelength width Δλ ′ or less from the geometrical consideration as in the case of the convex lens. The focal length f and the facing distance L to the light reflecting mirror must satisfy the following formula (2).

As shown in FIGS. 4A and 4B, the rotating slit disk does not necessarily require a light shielding member.
It is also preferable to adopt a structure in which the light transmitting member 401 has a structure in which the convex lens portion 402 and the concave lens portion 403 are periodically provided, and effective narrow width openings are periodically arranged.
Further, when a suitable lens shape is a spherical lens and only a paraxial ray is considered, if it is a thin lens, for example, the following equation (3) can be used.

At this time, the radius of curvature of the front surface of the lens is r1, the radius of curvature of the rear surface is r2, and a value that defines the focal length of the focal point formed on the rear surface side of the lens from the lens center is written as f1.
For a lens with one flat surface, the curvature radius r of the flat surface may be infinite.
Furthermore, the optical power in the opening is not limited to the form provided by the convex lens or concave lens shape as described above.
For example, as shown in FIG. 5, even a flat light transmitting member 501 has a refractive index distribution such as a high refractive index portion 502 or a low refractive index portion 503 inside, so that it corresponds to a convex lens or a concave lens. It may be one that expresses power.
The optical power of the transmissive member is also preferably a cylindrical lens-like power. In this case, the optical power is preferably provided only in the direction in which the dispersed light is dispersed depending on the wavelength.

Further, for example, the configuration in the case where the rotating slit disk is of a reflection type is shown in FIGS.
FIG. 6 shows the vicinity of the opening of a reflective rotary slit disk having optical power.
The light shielding unit 601 has an opening 602. A reflective portion 603 is disposed below the light shielding portion 601, and the reflective portion 603 has an optical power portion 604 in the opening 602. In this case, the reflecting portion 603 can be constituted by a concave mirror or a convex mirror.
Of the light split by the diffraction grating 103 and collected by the condenser lens 104, light having a wavelength λ1 to light having a wavelength λ5 enters the opening 602.
Assume that the half width of the opening 602 is a, the distance from the opening to the exit pupil is L, the radius of the exit pupil is A, the optical power portion is a spherical surface, and the radius of curvature is r. At this time, since the optical power portion exists in the opening, a part of the light incident on the opening is reflected at an angle different from the incident light by the optical power portion. Some are blocked by the exit pupil and cannot return to the semiconductor optical amplifier.
That is, the wavelength selection condition for the wavelength width of the light incident on the opening 602, that is, λ5−λ1 = Δλ, becomes stricter due to the optical power of the opening.
It is assumed that only light within the width b within the aperture is wavelength-selected, and a predetermined wavelength selection width is set as Δλ ′.
In order to suppress the wavelength width Δλ to be equal to or smaller than the predetermined wavelength selection width Δλ ′, the following equation (4) is used for the curvature radius r of the optical power portion in the opening and the width (half width of the reflecting portion) a of the opening. It is necessary to satisfy.
However, it is assumed that the width a of the opening satisfies a << R with respect to the radius R of the exit pupil.

In order for the wavelength width after wavelength selection to be less than or equal to the predetermined wavelength width, it is necessary to set r so that Δλ ′ is less than or equal to the predetermined line width.
Further, the above description is an argument when the reflecting surface in the opening has a convex shape. However, the same consideration as above can be derived for the radius of curvature r even when the reflecting surface is concave.

As shown in FIG. 7, the rotary slit portion does not necessarily require a light shielding member.
As a configuration of the light reflecting member 703, for example, a configuration in which the concave reflecting portions 701 are periodically arranged as shown in FIG.
It is also preferable to adopt a configuration in which the convex reflection portions 702 are periodically arranged as shown in FIG. 7B and the openings are effectively periodically arranged.
Further, the optical power of the reflecting member may be a cylindrical mirror power.
In this case, the optical power is configured to have only the direction in which the dispersed light is dispersed depending on the wavelength.

As a method for creating such an element shape, for example, in the case of a transmission type, if the light transmission member is SiO ₂ , the concave structure is isotropic dry etching using fluorine compound plasma, or hydrofluoric acid (HF ) Wet etching is performed. Thereafter, the light shielding layer can be formed and patterned.
Examples of the material of the light shielding layer include chromium oxide, but are not limited thereto. A material having a large absorption at the oscillation wavelength of the light source is preferred.
Further, both the concave and convex structures can be produced by forming a light-shielding layer and patterning it after forming a curved surface structure in advance on the light transmitting member by an imprint technique or the like. Further, the target of imprinting may be, for example, the transparent substrate itself, or a material obtained by applying a transparent resin or the like with high processability on the transparent substrate.
The material of the light transmitting member is not limited to SiO ₂ , and any material having a high transmittance in the oscillation wavelength band of the light source is suitable.

In the case of the reflective type, for example, when the light reflecting member is a SiO ₂ substrate on which a metal reflecting film is formed, the concave structure becomes a reflecting layer after the substrate is wet-etched with HF in advance. It can also be produced by depositing and patterning a light shielding layer after depositing a metal.
Both the concave and convex structures may be imprinted on the metal reflective layer, or a reflective metal layer is formed on the SiO ₂ substrate by forming a curved structure in advance by imprint technology, etc. Can be fabricated by patterning and patterning.

Conversely, as a simple process, when a slit-like mirror is patterned on a disk-like substrate surface having a smooth surface, the substrate surface shape is processed in advance before forming the mirror portion. ,
Alternatively, it is difficult to form a significant curved surface shape having optical power unless special measures are taken such as forming the metal surface into a curved surface shape after the reflective surface is formed.
When manufacturing by a process of depositing metal on a flat substrate, for example, when sputtering or vapor deposition is performed, the metal film surface is an uneven structure of metal grains, that is, an aggregate of metal fine particles having a diameter of several nanometers. Only fine irregularities that are not regarded as curved surfaces are formed.
In order to improve the wavelength resolution, it is possible to construct a wavelength tunable light source that does not use a structure that is difficult to manufacture, such as a slit having a narrower width, and that has an easy-to-create structure and a narrow oscillation line width.

Examples of the present invention will be described below.
[Example 1]
As a first embodiment, a configuration example of a light source device to which the present invention is applied will be described with reference to FIG. However, the present invention is not limited in any way by the configuration of the embodiments described below.
FIG. 8A is a side view of the light source of the present invention.
In FIG. 8A, an optical resonator 800 is constituted by a semiconductor optical amplifier 801, a collimator 802, a diffraction grating 803, a condenser lens 804, and a rotating slit disk 805.
The gain band of the semiconductor optical amplifier is from 800 nm to 880 nm. The rotating slit disk 805 is a reflective wavelength selection element. However, the rotating slit disk is not limited to the reflection type, and may be a transmission type wavelength selection element.
In that case, the reflecting mirror is arranged at the rear stage of the rotating slit disk. Further, an LD driver 807 is connected to the optical amplifier 801. Then, the transmitted light from the diffraction grating 803 is reflected by the mirror 808 and coupled to the optical fiber 810 through the condenser lens 809 so that the output of the light source of the present invention is taken out of the resonator.

The LD driver 807 is a device for supplying energy to the optical amplifier and controlling its gain.
The LD driver 807 is connected to the control device 814. The control device 814 controls the LD driver and the rotary slit control device 811.
The rotary slit controller 811 controls the rotational speed of the rotary slit disk, supplies power, and the like.
The rotating slit disk has a reflecting portion 813 and a light shielding portion 812 (FIG. 8B). The light shielding portion is made of chromium oxide having a thickness of 100 nm.
The reflecting portion is formed by forming aluminum with a thickness of 100 nm on a quartz substrate.
The focused spot 815 is focused by wavelength dispersion in the circumferential direction of the rotating slit disk. It is also preferable to detect the origin of the rotation slit by the rotation origin detection slit 816.

In this embodiment, the length of the optical path from the semiconductor optical amplifier 801 to the surface of the rotary slit disk 805 is the resonator length, which is 50 mm.
The light from the semiconductor optical amplifier is split by the diffraction grating, and light with a wavelength of 800 nm to 880 nm is split into a width of 5 mm on the surface of the rotating slit disk 805 and condensed at different positions for each wavelength.
This condensing position is on the surface of the rotating slit disk (on the surface of the disk-shaped substrate), and the reflection wavelength on the rotating slit disk moves with respect to the condensing spot, so that the reflected wavelength is Change and operate as a wavelength swept light source.

The condenser lens 804 has a focal length of 100 mm and a diameter of 5 mm. The exit pupil viewed from the reflection unit 813 is configured so as to substantially match the condenser lens.
Here, as shown in FIG. 9, the reflecting portion 813 has a convex shape inside.
An opening 902 is formed in part of the light shielding layer 901, and a recess 904 formed in the reflective layer 903 is disposed in the opening 902.
The width of the opening 902 is 10 μm. Therefore, the wavelength width reaching the width of the opening is 0.32 nm.
In order to set the wavelength selection width to 0.08 nm, a spherical surface having a radius of curvature of about 50 μm is formed as the recess 904. Specifically, this shape corresponds to a shape in which the center portion of the concave shape is recessed by about 1 μm from the end of the opening. This is a configuration derived from the mathematical formulas described in the embodiments.
That is, when the concave surface is considered as a simple spherical surface, a predetermined wavelength resolution can be achieved by providing a depression of 1 μm or more.
Thus, even if the width of the opening is wide, it is possible to significantly narrow the actual wavelength selection width by providing optical power in the opening.

In the present embodiment, the rotating slit disk has a concave shape in the opening, but the content of the present invention is not limited to this. The shape in the opening may be a convex shape.
In order to realize the predetermined wavelength selectivity, the curvature radius of the concave shape and the convex shape may be set using the relational expressions described in the embodiments.
Alternatively, the distance from the mirror to the exit pupil may be adjusted.
Moreover, the cylindrical mirror shape which has the optical power in an opening part only in the direction of the period of a diffraction grating may be sufficient.

[Example 2]
As a second embodiment, a configuration example of a light source device having a different form from the first embodiment will be described with reference to FIG.
FIG. 10A is a side view of the light source device of this embodiment.
In FIG. 10A, an optical resonator 1000 is constituted by a semiconductor optical amplifier 1001, a collimator 1002, a diffraction grating 1003, a condenser lens 1004, and a rotating slit disk 1005.
The gain band of the semiconductor optical amplifier is 1000 nm to 1100 nm. The rotating slit disk 1005 is a transmission type wavelength selection element. However, the rotating slit disk is not limited to the transmission type.
A reflection mirror 1015 is arranged at the rear stage of the rotating slit disk. The reflection mirror is installed at a distance of 1 mm from the diffraction grating side surface of the rotary slit. Further, an LD driver 1007 is connected to the optical amplifier 1001. The transmitted light from the diffraction grating 1003 is reflected by a mirror 1008 and coupled to an optical fiber 1010 through a condenser lens 1009, whereby the output of the light source of the present invention is extracted out of the resonator.

The LD driver 1007 is a device for supplying energy to the optical amplifier and controlling its gain.
The LD driver 1007 is connected to the control device 1014. The control device 1014 controls the LD driver and the rotary slit control device 1011.
The rotary slit controller 1011 controls the rotational speed of the rotary slit disk, supplies power, and the like.
The rotating slit disk has a transmission part 1013 and a light shielding part 1012 (FIG. 10B).
The light shielding portion is made of chromium oxide having a thickness of 100 nm. The transmission part is formed by forming a recess on a quartz substrate by HF solution treatment.
The focused spot 1016 is focused by wavelength dispersion in the circumferential direction of the opening slit disk.
It is also preferable to detect the origin of the rotation slit by the rotation origin detection slit 1017.

In the present embodiment, the length of the optical path from the semiconductor optical amplifier 1001 to the surface of the rotating slit disk 1005 is the resonator length, which is 50 mm.
The light from the semiconductor optical amplifier is split by the diffraction grating, and light with a wavelength of 1000 nm to 1100 nm is split into a width of 6.25 mm on the surface of the rotating slit disk 1005 and condensed at different positions for each wavelength.
This condensing position is on the surface of the rotating slit disk, and the transmitted wavelength on the rotating slit disk moves with respect to the condensing spot, so that the transmitted wavelength changes and operates as a wavelength swept light source. .

Here, as shown in FIG. 11, the transmissive portion 1013 has an opening 1102 formed in a part of a 1101 light shielding layer having a concave shape inside, and a reflection layer 1103 is formed in the opening 1102. A recessed portion 1104 is disposed.
The width of the opening 1102 here is 40 μm. The refractive index of the transmission part is 1.46.

The wavelength width reaching the width of the opening is 0.8 nm.
In order to set the wavelength selection width to 0.08 nm, a spherical surface having a radius of curvature of about 61 μm is formed as the recess 1104.
Specifically, this shape corresponds to a shape in which the center portion of the concave shape is recessed by about 3.3 μm from the end of the opening.
Therefore, when the concave portion is considered as a spherical surface, a predetermined wavelength resolution can be achieved if the concave portion is recessed by 3.3 μm or more.
Thus, even if the width of the opening is wide, it is possible to significantly narrow the actual wavelength selection width by providing optical power in the opening.

In the present embodiment, the rotating slit disk has a concave shape in the opening, but the content of the present invention is not limited to this. The shape in the opening may be a convex shape.
In order to realize the predetermined wavelength selectivity, the focal length may be set using the relational expression described in the embodiment.
Or you may adjust the distance from an opening part to a reflective mirror.
Moreover, the cylindrical lens shape which has the optical power in an opening part only in the direction of the period of a diffraction grating may be sufficient.

[Example 3]
In Example 3, a configuration example of an optical tomographic imaging apparatus using the light source device of the present invention will be described with reference to FIG.
As shown in FIG. 12, the optical tomographic imaging apparatus according to the present embodiment includes a variable wavelength light source 1201 constituting a light source unit, a reference light path optical fiber 1202 constituting a reference unit, a fiber coupler 1203 constituting an interference unit, and a reflection unit. A mirror 1204 is arranged.
Further, an inspection light path optical fiber 1205, an irradiation condensing optical system 1206, and an irradiation position scanning mirror 1207 constituting a measurement unit of the inspection object that transmits reflected light from the inspection object are connected.
In addition to this, a light receiving fiber 1208 constituting a light detection unit, a photodetector 1209, an irradiation fiber 1210, a signal processing device 1211 constituting an image processing unit, and an image output monitor 1213 are connected. And the light source control apparatus 1212 which comprises a light source part is connected, and an optical tomographic imaging device is comprised. Reference numeral 1214 denotes an object to be inspected.
In this embodiment, the fiber constituting the interference optical system is constituted by a single mode fiber in the wavelength band of the light source, and the various fiber couplers are constituted by 3 dB couplers. However, the configuration of the present invention is limited to such a configuration. It is not a thing.

The wavelength tunable light source in the present embodiment controls its oscillation wavelength and intensity and its temporal change by a light source control device.
The light emitted from the wavelength tunable light source is divided and introduced into a reference light optical path fiber and an inspection light optical path fiber by a fiber coupler.
Further, a reflection mirror is disposed at the tip of the reference light path optical fiber, and the light is reflected by the reflection mirror and introduced into the light receiving fiber to reach the photodetector.
At the same time, the light introduced into the inspection light path fiber by the fiber coupler is irradiated onto the inspection object, and backscattered light is generated from the inside and the surface of the inspection object.
The backscattered light is condensed from the fiber coupler to the photodetector through the irradiation condensing optical system.
The light received by the photodetector is converted into a spectrum signal by a signal processing device, and further subjected to Fourier transform to obtain depth information of the inspection object. The acquired depth information is displayed on the image output monitor.
At the same time, the signal processing device oscillates a driving signal for the irradiation position scanning mirror and also sends a wavelength variable light source control signal.
Since the light source device of the present embodiment has a long coherence length because the line width is narrow, it is possible to acquire an interference image from a position equidistant to a position far from the reference mirror of the OCT image.
This corresponds to the fact that an interference signal can be obtained even if the optical path length difference between two optical paths constituting the interference optical system is long due to a long coherence length, that is, a long coherence distance.
For this reason, it is preferable that the line width of the light source is narrow because a deep structure of the inspection object can be detected.

Although the simplest configuration is shown in FIG. 12, an optical system for differentially detecting interference signals as shown in FIG. 13, for example, may be used.
In FIG. 13, a variable wavelength light source 1301 constituting a light source unit, an isolator 1302, a reference optical path fiber 1306 constituting a reference unit, a polarization controller 1318, a fiber coupler 1305 constituting an interference unit, and a reflection mirror 1307 are arranged. To do.
Further, an inspection light path optical fiber 1314, a polarization controller 1319, an irradiation condensing optical system 1315, and an irradiation position scanning mirror 1308, which constitute a measurement unit of the inspection object, are connected.
In addition, a fiber coupler 1303, a fiber coupler 1304, a light receiving fiber 1316, a light receiving fiber 1317, a balance photodetector 1310, a signal processing device 1311 forming an image processing unit, and an image output monitor 1313 are connected. .
And the light source control apparatus 1312 which comprises a light source part is connected, and an optical tomographic imaging device is comprised. Reference numeral 1309 denotes an inspection object.
Although not shown, a configuration in which the intensity of light emitted from the light source is successively monitored and the data is used for amplitude correction of the interference signal is also suitable.

DESCRIPTION OF SYMBOLS 100: Optical resonator 101: Semiconductor optical amplifier 102: Collimator 103: Diffraction grating 104: Condensing lens 105: Rotating slit disk 107: Drive control part 108: Mirror 109: Condensing lens 110: Optical fiber 111: Reflection mirror 112 : Light shielding part 113: Opening part 114: Spectral focused spot 115: Rotation origin detection slit

Claims (9)

A semiconductor optical amplification medium;
A collimating lens for collimating the light emitted from the semiconductor optical amplification medium;
A diffraction grating that gives the collimated beam a different angular dispersion depending on the wavelength;
A condensing lens that condenses the light flux given angular dispersion by the diffraction grating at different positions depending on the wavelength;
A wavelength selection means comprising a reflection part for reflecting the light of a part of the wavelength by scanning the focal plane by the condenser lens or a transmission part for transmission;
In the light source device having
The wavelength selection means is arranged on the disk-shaped substrate that can be rotated, the reflection part or the transmission part formed in equal width having optical power,
Along with the rotation of the disk-shaped substrate, the condensing spot on the surface of the disk-shaped substrate by the condensing lens is reflected or transmitted by the reflecting portion or the transmitting portion arranged on the substrate. Changing the wavelength of the light emitted from the semiconductor optical amplification medium;
A light source device that operates as a wavelength swept light source.   The light source device according to claim 1, wherein the transmission unit has a negative optical power and is provided to face a light reflection mirror. When the facing distance to the light reflecting mirror is L, the wavelength range of light reaching the transmission part from the semiconductor optical amplification medium is Δλ, and the focal length of the transmission part is f,
3. The light source device according to claim 2, wherein the focal length f of the transmission portion and the facing distance L to the light reflection mirror satisfy the following expression for a predetermined wavelength selection range Δλ ′.

  The transmissive part has a positive optical power, is provided to face the light reflecting mirror, and a focal position by the transmissive part is a position other than the surface of the light reflecting mirror behind the transmissive part. The light source device according to claim 1. When the facing distance to the light reflecting mirror is L, the wavelength range of light reaching the transmitting part from the optical amplifier is Δλ, and the focal length of the transmitting part is f,
5. The light source device according to claim 4, wherein the focal length f of the transmission portion and the facing distance L to the light reflection mirror satisfy the following expression for a predetermined wavelength selection range Δλ ′.

  The light source device according to claim 1, wherein the reflection unit is configured by a concave mirror or a convex mirror. The half width of the reflecting portion is a, the radius of curvature of the concave mirror or convex mirror is r, the half width of the exit pupil of the optical system viewed from the reflecting portion is A, the distance from the reflecting portion to the exit pupil is L, and the light enters the reflecting portion. The wavelength range of light is Δλ, the predetermined wavelength selection range is Δλ ′,
The light source device according to claim 6, wherein when a is a << R with respect to a radius R of the exit pupil, the light source device according to claim 6 satisfies the following expression.

  The light source device according to claim 1, wherein the reflection unit has the optical power in a direction of a period of the diffraction grating. A light source device, irradiating the inspection object with light from the light source device, and transmitting reflected light from the inspection object;
A reference unit that irradiates a reference mirror with light from the light source device and transmits reflected light from the reference mirror;
An interference unit that causes interference between reflected light from the measurement unit of the inspection object and reflected light from the reference unit;
A light detection unit for detecting interference light from the interference unit;
An optical tomographic imaging apparatus that captures a tomographic image of the inspection object using light detected by the light detection unit,
An optical tomographic imaging apparatus, wherein the light source device is configured by the light source device according to any one of claims 1 to 8.

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