JP2012182311A - Light source device, and imaging device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light source device capable of sweeping a wavelength to a short wavelength suitable for an OCT device for an eyeground at a high speed.SOLUTION: A light source device capable of changing an oscillation wavelength comprises an optical amplification medium for amplifying lights, and an optical resonator. The optical resonator has a first reflection member positioned on one side of the optical amplification medium, and second and third reflection members positioned on the other side of the optical amplification medium. The second and third reflection members reflect a flux of lights amplified by the optical amplification medium in a direction of the optical amplification medium while it is spatially separated in a radial direction of the flux of lights. The light source device changes the oscillation wavelength by changing an optical path length difference between a first optical path defined to include the first reflection member, the optical amplification medium, and the second reflection member, and a second optical path defined to include the first reflection member, the optical amplification medium, and the third reflection member, with an optical path length difference adjusting member capable of changing the optical path length difference.

Description

  The present invention relates to a light source device capable of changing an oscillation wavelength and an imaging device using the same.

As light sources, particularly laser light sources, various types having variable oscillation wavelengths have been used in the fields of communication networks and inspection devices.
In the field of communication networks, high-speed wavelength switching is required, and in the field of inspection equipment, high-speed and wide-range wavelength sweeping is desired.
Applications of the wavelength tunable (sweep) light source in the inspection apparatus include a laser spectrometer, a dispersion measuring instrument, a film thickness measuring instrument, and a wavelength sweep type optical interference tomography (Swept Source Optical Coherence Tomography) apparatus.

  Optical interference tomography (hereinafter also referred to as OCT) captures a tomographic image of a specimen using low coherence optical interference. This is an imaging technique that has been actively researched in the medical field in recent years because of the micron-order spatial resolution and non-invasiveness.

  Currently, OCT is capable of obtaining a tomographic image with a resolution in the depth direction of several microns and a depth of several mm, and is used for ophthalmic photography, dental photography, and the like.

The wavelength sweep type (SS-OCT) apparatus sweeps the oscillation wavelength (frequency) of a light source in terms of time. This falls into the category of Fourier domain (FD) OCT. Similarly, the spectral region (spectral domain: SD) OCT that falls into the category of FDOCT requires a spectroscope that separates interference light, but since a spectroscope is not used, the loss of light amount is small and high SN ratio image acquisition is also possible. Expected.
When a medical imaging apparatus is configured using a wavelength-swept light source, the faster the sweep speed, the shorter the image acquisition time, and the living body observation in which the living tissue is observed as it is in the living body without being collected from the living body (so-called in (situ-in vivo imaging) is also suitable.
Patent Document 1 discloses a wavelength tunable light source including an optical amplifying medium and a reflector using a diffraction grating outside the optical amplifying medium. FIG. 12 shows a light source device described in Patent Document 1.

  In FIG. 12, the light emitted from the optical amplifying medium 1201 enters the diffraction grating 1206 via the optical branching element 1234, and the light having the Bragg wavelength returns to the optical amplifying medium 1201 as reflected light, and is optically amplified to be fiber. 1244. Reference numeral 1240 denotes a total reflection mirror, and 1242 denotes an isolator. Here, since the diffraction grating 1206 is rotatable, the wavelength of the reflected light is variable.

Patent Document 2 discloses a wavelength selection element constituting an optical amplifying medium and a wavelength tunable light source including a reflector outside the optical amplifying medium. FIG. 13 shows a Fabry-Perot type wavelength selective element disclosed in Patent Document 2.
In FIG. 13, the movable membrane reflector 1314 and the concave reflector 1316 constitute an optical resonator, and the resonator length 1318 is changed by applying a voltage between the drive electrode 1312 and the membrane reflector 1314. To select the wavelength.
The element of FIG. 13 uses two reflectors, a membrane reflector 1314 and a concave reflector 1316, and a frequency difference between resonance peaks determined by the interval between the two reflectors, that is, a free spectral range (Free Spectral Range). According to FSR), the wavelength is selectively transmitted or reflected.

US Pat. No. 5,862,162 US Pat. No. 6,373,632

The light source device disclosed in Patent Document 1 is not suitable for high-speed wavelength sweeping of 30 KHz or higher because wavelength selection is performed by changing the incident angle of light by mechanically driving a diffraction grating.
In the wavelength selection element disclosed in Patent Document 2, when the FSR is set to 45 to 80 nm, the interval between the two reflectors is 15 μm to 25 μm.
However, when an attempt is made to construct a wavelength selection element with an insertion center wavelength suitable for application to the light source of an OCT apparatus for the fundus of 840 nm and FSR of 80 nm, the distance between the two reflectors is as narrow as 4.4 μm. It is necessary to take a value. The fact is that it is difficult to realize high-speed driving of the movable reflector at 100 KHz or more at such narrow intervals even if details such as electrode arrangement are devised.
An object of the present invention is to provide a light source device capable of high-speed wavelength insertion / extraction at a wavelength suitable for an OCT apparatus.

  A light source device provided by the present invention is a light source device that includes an optical amplification medium that amplifies light and an optical resonator, and is capable of changing an oscillation wavelength, and the optical resonator includes the optical amplification medium. A first reflecting member located on one side; and second and third reflecting members located on the other side of the optical amplifying medium, wherein the second and third reflecting members are The light beam amplified by the light amplification medium is reflected in the direction of the light amplification medium in a state of being spatially separated in the radial direction of the light beam, and the first reflection member, the light amplification medium, and the second The optical path length difference between the first optical path defined including the reflecting member and the second optical path defined including the first reflecting member, the optical amplification medium, and the third reflecting member is variable. The oscillation wavelength is changed by changing the optical path length difference by an optical path length difference adjusting member. That.

  In the light source device of the present invention, the luminous flux is spatially separated into two, the separated luminous fluxes are reflected by the second and third reflecting members and returned to the optical amplification medium, and the optical path length difference between the two optical paths The optical path length difference is changed by the optical path length difference adjusting means for making the variable variable. By individually reflecting the light beams in a separated state, the degree of freedom of arranging the reflecting member is increased, and the reflecting member can be arranged at a position where high-speed driving is possible. Thereby, wavelength sweep drive of 100 KHz or more can be realized.

The schematic diagram which shows an example of the light source device of this invention The figure explaining the principle of the apparatus of this invention Explanatory drawing of the optical path length difference adjustment member applicable to the light source device of this invention The schematic diagram which shows an example of the light source device of this invention The schematic diagram which shows an example of the light source device of this invention The schematic diagram which shows an example of the light source device of this invention Schematic diagram of the light source device of the present invention using a surface emitting optical amplification medium Schematic diagram showing an example of using a piezo as the optical path length difference adjusting member The schematic diagram which shows an example which used EO for the optical path length difference adjustment member The schematic diagram which shows another example using EO for the optical path length difference adjustment member The schematic diagram which shows an example of the OCT apparatus using the light source device of this invention Schematic diagram showing the prior art (Patent Document 1) Schematic diagram showing the prior art (Patent Document 2)

  The light source device of the present invention includes an optical resonator having a first reflecting member located on one side of an optical amplification medium and second and third reflecting members located on the other side. That is, the second and third reflecting members function as the other resonator that performs the wavelength insertion and wavelength selection functions.

The second and third reflecting members reflect the light beam amplified by the light amplification medium in the direction of the light amplification medium while being separated in the radial direction of the light beam. As an example, the light beam can be separated by dividing the light beam in the radial direction within a cross section perpendicular to the traveling direction of the light beam using a light beam separating element provided in the optical path.
The luminous flux divided and guided in two directions enters the second and third reflecting members. Therefore, the light is reflected individually, returns to the opposite optical path, reaches the optical amplifying medium, and is multiplexed in the optical amplifying medium.

  Here, after the light beam is separated by the light beam separation element, the optical path difference adjustment that makes the optical path length difference between the first optical path leading to the second reflecting member and the second optical path leading to the third reflecting member variable. The member is driven to change the oscillation wavelength. That is, the oscillation wavelength can be changed by changing the optical path length difference.

Here, when the light beam separation element is used, the light beam separation element can also be regarded as a split member that splits the light beam amplified by the light amplifying member into wavefronts (splits the wavefront spatially).
According to this aspect, the light source device of the present invention includes an optical amplifying medium that amplifies light, a splitting member that splits a light beam of light amplified by the optical amplifying member, and one side of the optical amplifying medium. And the second and third reflecting members located on the other side of the optical amplifying medium, and the second reflecting member is one of the light beams divided by the dividing member. Is reflected back to the optical amplifying medium through the split member, and the third reflective member reflects the other of the light beams split by the split member and passes through the split member. It includes a form that is supposed to be returned to the medium.

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

  FIG. 1 is a diagram showing an example of a light source device of the present invention.

In FIG. 1, reference numeral 101 denotes an optical amplifying medium that amplifies light and generates a coherent light beam. A reflective film 105 that functions as an optical resonator is applied to one of both end faces, and a non-reflective film 108 is provided to the other. It has been subjected. Reference numeral 102 denotes a condensing lens for condensing light (divergent light beam) emitted from the optical amplification medium, and reference numeral 103 denotes a light beam emitted from the optical amplification medium. Reference numeral 104 denotes a light beam separation element that spatially divides the light beam 103.
The reflective film 105 functions as a first reflective member located on one side of the optical amplification medium 101. Reference numerals 106 and 107 denote second and third reflecting members, respectively, which are paired with the first reflecting member 105 to constitute an optical resonator. The second reflecting member 107 includes an optical path length difference adjusting member 109 that changes the position of the reflecting member 107 in the direction in which the light beam travels.

When electrical energy is applied to the optical amplifying medium 101 from a power source (not shown), radiated light is generated inside, and the radiated light is amplified and propagates from the optical amplifying medium 101 toward both end faces. The light beam that has traveled to the side on which the non-reflective film 108 is applied propagates through the air while diverging in accordance with the light propagation law, and is incident on the condenser lens 102 with the diameter of the light beam. Since this light beam has astigmatism due to the characteristics of the optical amplifying medium, the wavefront is asymmetrical on the optical axis. However, if the optical system (not shown) provided as necessary is installed in front of the condenser lens 102, the optical axis Converted to the target spherical wave. This light beam propagates as the focused light 103 after passing through the condenser lens 102.
The light beam 103 is divided into two in the radial direction of the light beam 103 (spatially) by the light beam separation element 104, and the divided light beams 103a and 103b are installed so as to reflect these vertically, respectively. Concentrate toward.

Next, the condensed light flux returns to the optical path through which it has passed in the past, passes through the light flux separation element 104 and the condenser lens 102, and is combined and amplified in the optical amplification medium 101.
In the light source device of this example, the light resonates between the reflecting member 105 and the reflecting members 106 and 107 with the optical amplification medium 101 interposed therebetween, and the wavelength is selected. Here, the reflection member 106 has a function of a light source in addition to a function as a resonator, and has a characteristic of having both reflection and transmission.

  Next, the principle of inserting and subtracting wavelengths by changing the position of the reflecting member 107 will be described.

FIG. 2 is an explanatory diagram thereof. In FIG. 2, an A-B optical path is an optical output optical path for extracting light from the B side, and A-D is an optical path modulation optical path as an optical path for changing the optical path length. The insertion principle of this wavelength is that the resonance wavelength in the optical output optical path of AB and the resonance wavelength in the optical path modulation optical path of A-D share the optical amplifier 101 in each optical path, and therefore oscillate at the same wavelength. Take advantage of what you do. The length of the optical output optical path is Lo, and the optical path modulation optical path (A-D optical path) is longer than Lo by an amount L1 determined from the wavelength insertion width described later, and further, only the distance x is used for wavelength interpolation. It is assumed that the optical path modulation distance is long.
For the sake of easy understanding, it is assumed that x = 0, and resonance occurs at a common wavelength λo in the modulation AB optical path and the AD optical path of the optical path modulation.

  Next, it is assumed that the wavelength changes by δλ when the reflecting member 107 is moved to x = δx. A relational expression between δx and δλ at this time will be described.

  First, equations that hold for the A-D modulated optical path will be described. When the number of waves in the AD modulation optical path is changed by x = δx and the wavelength δλ is changed, the following equation (1) is established.

  The left side is the reciprocal optical path of the optical path (Lo + L1), and the resonance condition is that the wave number becomes an integer. Therefore, the number of waves is the number obtained by dividing the round-trip optical path by the wavelength.

  On the other hand, since the right side changes by δx to the optical path (Lo + L1) by moving the reflecting member 107, the wavelength also changes by δλ accordingly. What is important here is that the number of waves does not change on either the left or right side.

  Next, an equation that holds for the AB output optical path will be described. Since the optical path L1 is fixed to the AB output optical path, the following expression (2) is established.

The left side is an integer representing the number of waves when the wavelength changes from λo to δλ. On the other hand, on the right side, it is important to change the number of waves by one from the first λo. This is because, as described above, the wavelength changes without changing the optical path Lo, so the number of resonating waves changes by one.
When the equations δx and δλ are derived from the equations (1) and (2), the following equation (3) is obtained.

  Assuming that L1 >> λo, Equation (3) can be simply described as Equation (4) below.

  Next, L1 is a relational expression of λo and Δλ (Free Spectral Range: FSR determined from the gain width of the optical amplifying medium).

First, when the FSR of the _AD modulation optical path is Δν _AD , Expression (5) is obtained.

Next, when the FSR of the A-B output optical path is Δν _AB , Expression (6) is obtained.

  Here, c is the speed of light in vacuum.

From Equation (5) and Equation (6), Equation (7) is obtained when the frequency width Δν _Lo until the difference between these FSRs becomes the Δν _AB interval.

  On the other hand, Expression (8) is obtained from a general relationship between one frequency and a wavelength.

  Therefore, Formula (9) is obtained.

  Here, when Lo >> L1, Equation (9) is simplified, and L1 is represented by the following Equation (10).

Thus, L1 can be expressed by λo and Δλ. This formula matches the spacing between Fabry-Perot elements and the FSR formula.
Therefore, instead of disposing two Fabry-Perot reflectors in the traveling direction of the light flux as in the wavelength selection element described in Patent Document 2, one reflector of the pair of reflectors Spatally separated in the direction perpendicular to the traveling direction.
In the present system in which the light beams divided into two are returned by the separated reflectors, an effect equivalent to that of a Fabry-Perot element can be realized.

  Next, the following equation (11) is obtained from the equations (4) and (10) regarding the relationship between δλ and δx.

  As a specific example, when λo = 0.84 microns and Δλ = 0.08 microns, the following equation (12) is obtained from the equation (11).

  From these equations (10) and (12), it can be estimated that L1 = 4.41 microns and the maximum value of δx is 421 nanometers.

Here, in the OCT apparatus using the light source device of the present invention, the insertion wavelength width and the resolution in the thickness direction of the subject, the sampling pitch width of the insertion wavelength and the detectable width in the thickness direction of the subject (depth direction) )
The sampling wavelength interval δΛ of the inserted wavelength and the maximum width L in the thickness direction (optical axis direction) of the object to be detected that can be detected by the OCT apparatus have a relationship of the following expression (13).

  Further, the width Δ of the insertion wavelength is Δλ, and the resolution ΔL in the thickness direction (optical axis direction) of the object that can be detected by the OCT apparatus is expressed by the following equation (14).

In the present invention, as an optical amplification medium for amplifying light, in addition to a semiconductor optical amplifier (SOA), a rare earth-doped (ion-doped) optical fiber containing erbium, yttrium or the like, a dye is added to the optical fiber Thus, those that amplify with a dye can be employed.
The rare earth-doped optical fiber is suitable for obtaining good noise characteristics with high gain. In the dye-doped optical fiber, the choice of the variable wavelength is increased by appropriately selecting the fluorescent dye material or its host material.

  The semiconductor optical amplifier is preferable because it is small and can be controlled at high speed. As the semiconductor optical amplifier, both a reflection type optical amplifier and a traveling waveform optical amplifier can be used. As a material constituting the semiconductor optical amplifier, a compound semiconductor constituting a general semiconductor laser or the like can be used. Specifically, compounds such as InGaAs, InAsP, GaAlSb, GaAsP, AlGaAs, and GaN are used. A semiconductor can be mentioned. The semiconductor optical amplifier can be appropriately selected and employed from among those having a gain center wavelength of, for example, 840 nm, 1060 nm, 1300 nm, and 1550 nm according to the use of the light source.

  The first reflecting member constituting the optical resonator of the present invention can be composed of a reflecting member that is equivalent to or similar to a mirror that constitutes a Fabry-Perot optical resonator, or a partially transmissive mirror. More specifically, it can be constituted of a mirror constituted by a wall interface of a semiconductor crystal, a mirror constituted by polishing glass or the like, and a mirror coated with a thin film such as a metal film.

The second and third reflecting members constituting the optical resonator are arranged so as to reflect the light beam amplified by the light amplification medium in the direction of the light amplification medium in a state separated in the radial direction of the light beam. However, the material constituting the reflecting member itself can be the same as the above-described reflecting member. However, since the optical resonator is configured together with the first reflecting member, it is necessary to have a reflectance different from the reflectance of the first reflecting member.
The second and third reflecting members reflect the light beam amplified by the optical amplifying medium in a state of being separated in the radial direction of the light beam, but a reflective prism can be used for separating the light beam, The separation of the light beam can also be performed by arranging the second and third reflecting members side by side in a region irradiated with the light beam (parallel light beam). When a reflective prism is used, the light beam may be separated with the ridge line of the prism as a boundary. It is preferable that the angle forming the ridge line of the reflecting prism is an angle at which principal rays separated from the light beam are parallel to each other. Details will be described later in Examples.

  Further, the first optical path defined including the first reflecting member, the optical amplifying medium, and the second reflecting member, and the first optical path defined including the first reflecting member, the optical amplifying medium, and the third reflecting member. The optical path length difference adjusting member that makes the optical path length difference between the second optical path and the second optical path variable can be configured using an electrostrictive element, a micro mechanical displacement element, an electro-optical element, or the like.

  Hereinafter, the present invention will be described in detail with specific examples. The following description will be made with reference to the drawings. In the drawings, the same parts are denoted by the same reference symbols in principle, and redundant description will be omitted as much as possible.

Example 1
FIG. 1 is a schematic diagram showing an example of a light source device of the present invention.
In FIG. 1, reference numeral 101 denotes an optical amplifying medium that generates a coherent light beam, and a semiconductor optical amplifier having an emission spectrum with a central wavelength of 0.84 μm is used. One of both end faces of the optical amplifying medium 101 constitutes a reflector or reflecting film 105 as a first reflecting member of the optical resonator. The other is provided with a non-reflective film 108. Reference numeral 102 denotes a condensing lens for converging a divergent light beam emitted from the optical amplification medium, and reference numeral 103 denotes a light beam emitted from the optical amplification medium 101. A reflective prism 104 functions as a light beam separating element that divides the light beam 103. Reference numerals 106 and 107 denote second and third reflecting members, respectively, which form a plurality of optical resonators in pairs with the first reflecting member 105. The second reflecting member 106 also has a function as an output part of the light source in addition to a function as an optical resonator, and has both a light reflecting function and a transmitting function. The third reflecting member 107 includes an electrostrictive element 109 as an optical path length difference adjusting member that changes the position of the reflecting member 107 in the direction in which the light beam travels.

  When electrical energy is applied to the optical amplifying medium 101 from a power source (not shown), radiated light is generated inside, and the radiated light is amplified and propagates from the optical amplifying medium 101 toward both end faces. The light beam that has traveled to the side on which the non-reflective film 108 is applied propagates through the air while diverging in accordance with the light propagation law, and is incident on the condenser lens 102 with the diameter of the light beam. Since this light beam has astigmatism due to the characteristics of the optical amplifying medium, the wavefront is asymmetrical on the optical axis. However, if the optical system (not shown) provided as necessary is installed in front of the condenser lens 102, the optical axis Converted to the target spherical wave. This light beam propagates as the focused light 103 after passing through the condenser lens 102. At this time, the luminous flux separating element 104 divides the region in the aperture direction of the luminous flux 103 into two parts, and is divided into 103a and 103b, and the second reflecting member 106 and the third reflecting member 107 installed so as to reflect vertically. Concentrate toward. The light beam reflected by the reflecting members 106 and 107 enters the optical amplifying medium 101 through a path opposite to the forward path, is amplified, is reflected by the first reflecting member 105 on the opposite side, and enters the amplifying medium 101 again. The light is amplified. In this manner, light reflection and amplification are repeated between the first reflecting member 105 and the second reflecting member 106 and between the first reflecting member 105 and the third reflecting member 107, and output. As the light 106, light transmitted through the second reflecting member 106 is obtained.

  Next, the principle of subtracting the wavelength in this embodiment will be described.

  FIG. 3 is an enlarged view of the optical path length difference adjusting member. In FIG. 3, reference numeral 116 denotes an electrostrictive element for giving a modulated optical path length δx, and here, a piezo element is used. Reference numeral 117 denotes an optical path modulation base that mechanically integrates the piezo element 116, the second reflecting member 106, the third reflecting member 107, and the light beam separating element. In the light source device of the present embodiment, the optical path length of the optical resonator including the first reflecting member 105, the optical amplifying medium 101, and the second reflecting member 106, the first reflecting member 105, and the optical amplifying medium. A constant optical path length difference L1 is given to the optical path length of the optical resonator including the 101 and the third reflecting member 107. These light beams 103 are divided into 103a and 103b and reflected by a light beam separating element 104 formed of a reflective prism. Here, it is assumed that the light beam 103 is composed of a principal ray 103aa and a principal ray 103bb. At this time, the angle of the reflection surface of the light beam separating element 104 is set so that the principal ray 103aa and the reflected light beam 103a and the principal ray 103bb and the reflected light beam 103b are perpendicular to each other. By doing so, the optical path length of the optical resonator including the reflecting member 105 and the reflecting member 106 even if there is a mechanical disturbance in the direction of 103 in the paper with respect to the optical amplifying medium 101 and the reflecting member 105 and the vertical direction thereof. The difference between the optical path length of the optical resonator including the reflecting member 105 and the reflecting member 107 does not change.

As a specific numerical example, assuming that the oscillation center wavelength λo = 0.84 μm and the sweep wavelength (range) Δλ = 0.08 μm, the optical path length difference L1 = 4. 41 μm and the moving distance δx = 421 nm of the reflecting member 107 are obtained.
L14.41 μm is set when the effective NA of the condenser lens 102 is designed to be about 0.1, the reflecting members 106 and 107 can be set within the depth of focus, and the relative positions of the optical path modulation base 107 and the light beam separation element 104 can be set. L1 = 4.41 μm was realized by the initial correction.

  Next, the moving distance δx of the reflecting member 107 will be examined.

Although the maximum value of δx is 421 nm, since a single element of a piezo element has a displacement of about 1 nm per 1 volt, 421 volts is applied to a single-layer piezo element from a voltage application device (not shown) (a multilayer of 40 layers). In the case of a piezo element, a displacement of 421 nm was realized by applying approximately 10 volts per layer.
Here, when the applied voltage of the single layer piezo is changed to -200, -100, 0, +100, +200 volts,
δx = −200 nm, −100 nm, 0.100 nm, and 200 nm.
At this time, from equation (12),
δλ = −38 nm, −19 nm, 0.19 nm, and 38 nm are obtained.
Since the output wavelength is λo + δλ, the change in wavelength can be obtained as follows.
That is, λ = 802 nm, 821 nm, 859 nm, and 878 nm. By controlling the driving voltage of the piezo element in this way, wavelength insertion / subtraction becomes possible.
By driving the voltage applied to the piezo element at 100 KHz or higher, a light source having a wavelength pulling speed of 100 KHz or higher was realized.

  Next, the resolution of the tomographic image obtained by applying this light source to the OCT apparatus and the detectable depth will be shown.

The sampling interval Δλ of the inserted wavelength and the maximum width L of the subject in the thickness direction (optical axis direction) that can be detected by OCT are as shown in the above equation (13).
The maximum width L in the thickness direction (optical axis direction) of the object to be detected is a sampling wavelength interval δΛ of 0.08 nm. Assuming that the center insertion wavelength λo is 0.84 μm, from the equation (13),
L = 4.41 mm.
Further, the detectable resolution ΔL in the thickness direction (optical axis direction) of the subject is Δλ = 0.08 μm from the equation (14).
ΔL = 4.4 μm.

  As described above, by applying the wavelength insertion light source of this embodiment to the light source of the OCT apparatus, a maximum test depth of 4.41 mm and a resolution of 4.4 μm can be realized.

(Example 2)
The light source device of Example 2 will be described with reference to FIG.
The light source device shown in FIG. 4 is similar to the device shown in FIG. 1 except that a reflecting member 106b is disposed in place of the third reflecting member 107 in FIG. 1 and a second reflecting member 106a is used. This is the difference from the apparatus of FIG.
Here, the second reflecting member 106a also serves as an output (transmission) function of the light source in addition to the reflection function of the resonator as in the first embodiment. In the second embodiment, the third reflecting member 106b is different from the reflecting member 106 in the first embodiment in that the reflecting member has a low reflectance.

In this embodiment, the reflectance of the third reflecting member 106b is made lower than that of the reflecting member 107 in FIG. 1, and the oscillation between the second reflecting member 106a and the third reflecting member 106b is suppressed. It is.
Regarding the insertion speed, wavelength insertion of 100 KHz or more can be realized by the piezo element as in the first embodiment.
In this way, a wavelength insertion light source with a stable sweep wavelength can be realized.

  By using this for the light source of the OCT apparatus, a clear tomographic image can be obtained without reducing the resolution and the detectable depth.

(Example 3)
An example of the light source device shown in FIG. 5 will be described.
The apparatus of this example is an example in which the size in the direction perpendicular to the optical axis direction is reduced compared to the apparatuses shown in the first and second embodiments.
In the first embodiment, the light beam is reflected and separated in two directions by the light beam separation prism 104. However, in this embodiment, as shown in FIG. 103a which comprises 103 employ | adopts the structure which lets a space pass. With this configuration, compared to the apparatus described in the first and second embodiments,
The size was reduced with respect to the plane direction perpendicular to the optical axis direction of the 103 luminous flux, thereby realizing size saving. Further, since 104b reflects only one side of the light beam 103 and the influence of the surface accuracy of the reflecting surface of the light beam separating element 104b is only half, it is possible to control the insertion wavelength with accuracy and to reduce the size of the light source. .

Example 4
FIG. 6 is a schematic diagram illustrating a light source device according to a fourth embodiment. The apparatus of this example has a configuration that enables downsizing and further high-speed insertion as compared with the apparatus of the first embodiment.
In the apparatus of FIG. 6, the light beam from the optical amplification medium 101 is converted into a parallel light beam by the lens 102. This parallel light beam is divided into two parts 103a and 103b, which are similarly reflected by the reflecting members 106 and 107, respectively. Thereby, since there is no light beam separation element, further downsizing of the apparatus can be realized.
In addition, the distance between the reflecting member 105 constituting one optical resonator and the reflecting members 106 and 107 constituting the other optical resonator can be shortened.

As a specific example, when this distance is 50 mm, the time required for light to reciprocate through this resonator is 0.3 nSec.
If the time for generating light of a certain wavelength is 1 nSec, it is understood that light can reciprocate three times in this optical resonator. If the wavelength to be generated is 1000 points, wavelength insertion of 1 MHz or more can be realized. In this way, by shortening the resonator length and setting the driving frequency of the light beam path variable modulation to 1 MHz or more, a wavelength insertion light source capable of high-speed wavelength sweep of 1 MHz can be realized with a small apparatus.

(Example 5)
An example of the light source device shown in FIG. 7 will be described. This is an example of further downsizing the apparatus of the fourth embodiment.
In this embodiment, a surface emitting type (surface light emitting element type) optical amplifier is employed as the optical amplifying medium 101 instead of the conventional edge emitting type semiconductor optical amplifier.
This eliminates the need for the condensing lens 102 employed in the apparatus of FIG. 6, and allows the light beams 103a and 103b emitted from the optical amplification medium to be reflected by the reflecting members 106 and 107, respectively. By adopting this configuration, it is possible to realize a small-sized light source with a wavelength of several millimeters to several centimeters capable of wavelength insertion and extraction at high speed.

(Example 6)
The present embodiment is an example in which the optical path length difference adjusting member described in the apparatus of FIG. 3 is configured by a mechanical minute displacement mechanism.
FIG. 8 shows a feature of this example. Reference numeral 119 in FIG. 8 denotes a mechanical micro displacement mechanism constituted by a MEMS (Micro Electro Mechanical Systems) element.
The MEMS element 119 includes a bent portion (hinge) and an electrode part 120, and the reflective member 107 can be displaced by about 400 nm by applying a potential difference to the electrode part 120.
Furthermore, in the apparatus of this example, instability due to air fluctuation is improved. In order to stabilize the optical path from when the light beam 103 is divided by the light beam separation element 104 to when it returns to the light beam separation element again, most of the optical path is covered with a glass material 115 to reduce air fluctuation. With this configuration, it is possible to realize a light source device with a stable wavelength insertion / extraction.

(Example 7)
In this embodiment, the optical path length difference adjusting member described with reference to the apparatus of FIGS. 3 and 8 is configured using an EO (Electro-Optic) element. FIG. 9 shows a feature of this example. In FIG. 9, reference numeral 118 denotes a thin film of lithium niobate that produces an electro-optic effect, and 114 denotes a transparent electrode. Lithium niobate has a high nonlinear constant γ that produces an electro-optic effect, which is about 30 pm / V. Relationship between the voltage and the refractive index, when the thickness of the crystal to apply a voltage d, the refractive index and n _e, the following formula is valid (15).

Considering the moving distance δx = 421 nm of the reflecting member 107 obtained in Example 1, a voltage satisfying Δnd = 480 nm as a value larger than 421 nm is calculated to be 3000 V from Equation (15).
From this, when the lithium niobate layer is made 30 layers, if driving at about 100 V per layer, the wavelength can be inserted with a width of about 80 nm with 0.84 μm as the center wavelength as in the first embodiment.

(Example 8)
FIG. 10 shows a modification of the example shown in FIG. In FIG. 10, a bulk lithium niobate 118 is adopted for the thin film lithium niobate of FIG. 9, and an electrode 114 having a function of reflecting a light beam is adopted for the transparent electrode 114 of FIG. Yes.
As shown in FIG. 10, when the angle θ formed by the electrode 114 satisfies the following equation (16), the incident light beam and the outgoing light beam are parallel.

  At this time, in the electrode direction, the luminous flux is

Pass through times.

  For example, if θ = 45 ° as shown in FIG. 10, n = 4 and the light beam passes three times in the electrode direction. With such a configuration, since the optical path in the lithium niobate 118 becomes longer, a desired wavelength insertion / subtraction can be realized with more constant voltage driving.

Example 9
This example is an example of an optical coherence tomography apparatus (OCT) provided with the wavelength insertion light source device of the present invention.
The OCT apparatus interferes with the reflected light from the specimen having a plurality of interfaces in the optical axis direction obtained in one arm (measurement unit) and the reflected light from the reference surface obtained in the other arm (reference unit). The tomographic information is obtained by Fourier transforming the modulated interference signal obtained by inserting and subtracting the wavelength of the light source.

FIG. 11 is a schematic diagram showing an example of the OCT apparatus of the present invention.
In FIG. 11, 1182 indicates a light source unit using the wavelength-interpolation light source device of the present invention, and 1186 indicates a retina of the fundus constituting the eye which is a specimen. Reference numeral 1190 denotes a mirror for scanning the fundus oculi, and constitutes a specimen measurement unit together with an optical fiber 1185 that transmits reflected light from the specimen 1186.
Reference numeral 1188 denotes a reference mirror, which constitutes a reference unit together with an optical fiber 1187 that transmits reflected light from the reference mirror.
Reference numeral 1184 denotes a fiber coupler that composes an interference unit by combining reflected light (light beam) from the specimen measurement unit and reflected light (light beam) from the reference unit. Reference numeral 1495 denotes a photoelectric conversion element as a light detection unit that detects interference light (modulation interference signal) from the interference unit.
Reference numeral 1196 denotes a computer as an image processing unit that digitizes electrically detected signals, performs data processing such as Fourier transform, and constructs a tomographic image of the specimen. That is, a tomographic image is obtained based on the light detected by the light detection unit. Reference numeral 1197 denotes a display for visualizing the tomographic image.
The light beam emitted from the light source unit 1182 passes through the fiber 1183 and branches in two directions by the coupler 1184.

One branched light beam passes through the fiber 1185 and irradiates the retina of the eye, which is the specimen. The reflected light again passes through the fiber 1185 and returns to the fiber coupler 1184.
The other branched light beam passes through the fiber 1187 and irradiates the reference mirror 1188. This reflected light passes again through the fiber 1187 and returns to the fiber coupler 1184.
After the reflected light from the test surface interferes with the reflected light from the reference surface by the coupler 1184, the light enters the photoelectric conversion element 1195 through the fiber 1194.

At this time, when the wavelength of the light emitted from the light source unit 1182 is swept and changed, a modulated interference signal corresponding to the tomographic structure is obtained as described above.
A tomographic signal is obtained by digitizing this signal and Fourier transforming it with a computer 1196. Since this is a tomographic signal as a point, an optical tomographic image can be obtained by scanning the mirror 1190 to measure a tomographic signal in a one-dimensional direction and visualizing it on the display 1197.
The OCT apparatus of the present example uses the light source apparatus of the present invention for the light source unit 1182. The light source apparatus according to the present invention can detect an optical tomographic image at a high speed because an insertion speed of 100 KHz or more can be obtained. An OCT apparatus having a high depth and high detection resolution in the depth direction can be provided.

DESCRIPTION OF SYMBOLS 101 Optical amplification medium 103 Light beam 105 1st reflection member 106 2nd reflection member 107 3rd reflection member 109 Optical path length difference adjustment member

Claims (10)

  A light source device capable of changing an oscillation wavelength, comprising: an optical amplification medium that amplifies light; and an optical resonator, wherein the optical resonator is a first reflection located on one side of the optical amplification medium And a second and a third reflecting member positioned on the other side of the optical amplifying medium, wherein the second and third reflecting members are light beams amplified by the optical amplifying medium. Is reflected in the direction of the optical amplifying medium in a state of being spatially separated in the radial direction of the light beam, and is defined including the first reflecting member, the optical amplifying medium, and the second reflecting member. The optical path is adjusted by an optical path length difference adjusting member that makes the optical path length difference variable between one optical path and a second optical path defined by including the first reflecting member, the optical amplification medium, and the third reflecting member. A light source device characterized by changing the oscillation wavelength by changing a length difference.   The light source device according to claim 1, wherein the light beam is separated by a reflective prism.   3. The light source device according to claim 2, wherein the second and third reflecting members are arranged at a position where a light beam passing through the reflective prism is condensed.   The light source device according to claim 2, wherein the light beam is separated at a ridge line of the reflective prism.   The light source device according to claim 4, wherein an angle forming the ridge line of the reflecting prism is an angle at which principal rays separated from the light flux are parallel to each other.   The light source device according to claim 1, wherein the separation of the light beam is performed by the second and third reflecting members located in a region irradiated with a parallel light beam that has passed through a lens.   The light source device according to claim 1, wherein the separation of the light beam is performed by the second and third reflecting members located in a region irradiated with the light beam emitted from the surface light emitting element.   The light source device according to claim 1, wherein the optical path length difference adjusting member uses any one of an electrostrictive element, a micro mechanical displacement element, and an electro-optical element.   An optical amplifying medium for amplifying light, a splitting member for splitting the light flux amplified by the optical amplifying member, a first reflecting member located on one side of the optical amplifying medium, and the optical amplifying The second and third reflecting members are located on the other side of the medium, the second reflecting member reflects one of the light beams divided by the dividing member, and the light amplification is performed via the dividing member. The third reflecting member reflects the other of the light beams divided by the dividing member and returns to the optical amplification medium through the dividing member. A first optical path defined including the optical amplifying medium and the second reflecting member; a second optical path defined including the first reflecting member, the optical amplifying medium and the third reflecting member; The optical path length difference is changed by an optical path length difference adjusting member that makes the optical path length difference variable. Light source and wherein the changing the oscillation wavelength. A light source unit using the light source device according to any one of claims 1 to 9,
A sample measurement unit that irradiates the sample with light from the light source unit and transmits reflected light from the sample;
A reference unit for irradiating a reference mirror with light from the light source unit and transmitting reflected light from the reference mirror;
An interference unit that causes reflected light from the specimen measurement unit and reflected light from the reference unit to interfere with each other;
A light detection unit for detecting interference light from the interference unit;
An image processing unit that obtains a tomographic image of the specimen based on the light detected by the light detection unit;
An optical coherence tomographic imaging apparatus comprising: