JP6742690B2 - Fiber ring laser, optical pulse, and optical tomography - Google Patents

Description

The present invention relates to a fiber ring laser, an optical pulse generated by the fiber ring laser, and a Fourier domain optical tomographic imaging apparatus using a light pulse generated by the fiber ring laser as a light source.

2. Description of the Related Art An optical tomographic imaging apparatus (OCT) that generates a tomographic image of a living tissue by applying the principle of an interferometer is known. The optical tomographic imaging apparatus separates low coherence light into measurement light and reference light, and irradiates the living tissue with the measurement light. The measurement light applied to the living tissue is scattered or reflected by the living tissue. The backscattered reflected light returns to the optical tomographic imaging device. The optical tomographic imaging apparatus causes reflected light to interfere with reference light to generate interference light, and uses the interference light to image the intensity of scattered light at a plurality of depths of biological tissue. Among such optical tomographic imaging apparatuses, those that image the intensity of scattered light at a plurality of depths of living tissue by Fourier transforming wavelength distribution data of interference light are Fourier domain optical tomographic imaging apparatuses ( It is called FD-OCT), and has an advantage that the number of moving parts is small and the entire apparatus can be made lighter and more stable than an optical tomographic imaging apparatus of another type.

Optical tomographic imaging devices are also used in ophthalmic retinal diagnosis. For example, in order to obtain a tomographic image of the macula at the center of the retina, irradiation light having a wavelength of 0.8 μm is used. In this wavelength band, light absorption of water is small, and an optical tomographic imaging apparatus using irradiation light in this wavelength band generates a tomographic image capable of identifying living tissue of the retina such as the pigmented capsule photoreceptor layer. ..

On the other hand, in order to image the capillary network under the pigmented capsule or the living tissue in the deep part of the lamina cribrosa, the vitreous body is different from the light of wavelength 0.8 μm band scattered or reflected by the living tissue of the retina. It is necessary to use, as the measurement light, light in a different wavelength band, which is different from the light in the wavelength band of 1.5 μm that is absorbed by. The wavelength band from 980 nm to 1150 nm is called the "second water window", and the light in this wavelength band has a low absorption rate in the vitreous body. Further, the light in the wavelength band of 980 nm to 1150 nm, when irradiated from the cornea side, enters the fundus without being captured by the retina that absorbs visible light and converts it into an electric signal. Light in the wavelength band of 980 nm to 1150 nm is required to image the capillary network under the pigmented capsule and the living tissue in the deep part of the lamina cribrosa using an optical tomographic imaging apparatus.

A fiber ring laser including a Yb-doped fiber has been conventionally known as one of light sources that generate a light source in a wavelength band of 980 nm to 1150 nm. For example, it is known that a fiber ring laser provided with a Yb-doped fiber produces a noise-like light pulse (Non-Patent Document 1). A spike peculiar to a noise-like optical pulse is observed at a time difference of zero picoseconds in the graph of the intensity autocorrelation waveform of an optical pulse generated by a fiber ring laser equipped with a Yb-doped fiber (see FIG. 3(b)).

However, its spectral distribution width is a narrow band of about 10 nm (see FIG. 3(a)). On the other hand, since the optical tomographic imaging apparatus uses the principle of the interferometer, like the interferometer, unless the measurement light of the optical tomographic imaging apparatus has a wide band, the resolution in the depth direction is not improved. That is, there is a problem that sufficient resolution in the depth direction cannot be obtained even when the narrow band optical pulse generated by the fiber ring laser is used as the measurement light of the optical tomographic imaging apparatus.

Therefore, when used as the measurement light of the optical tomographic imaging apparatus, an image of the living tissue of the fundus part having sufficient resolution in the depth direction can be obtained, and a wide band light of 100 nm to 110 nm having a central wavelength of about 1050 nm is obtained. At present, it is required to generate pulses.

Kobtsev, Sergey, et al. "Generation of double-scale femto/pico-second optical lumps in mode-locked fiber lasers." Optics Express 17.23 (2009): 20707-20713.

The present invention has been made in view of the present circumstances, and an object of the present invention is to solve the above-mentioned problems in the related art and achieve the following objects. That is, the present invention provides a wideband optical pulse having a center wavelength of about 1050 nm, which is capable of obtaining an image of a living tissue of a fundus portion having sufficient resolution in the depth direction when used for measurement light of FD-OCT. An object of the present invention is to provide a fiber ring laser to be generated, a light pulse generated by the fiber ring laser, and an FD-OCT using a light pulse generated by the fiber ring laser as a light source.

The means for solving the above problems are as follows. That is,
<1> An excitation light source that generates excitation light,
A first optical coupler on which the excitation light is incident;
A Yb-doped fiber that is excited by the excitation light that is incident from the first optical coupler;
A first single-mode fiber that propagates emission light emitted by the Yb-doped fiber that is excited by the excitation light when the excitation light source generates the excitation light;
An isolator for preventing light propagation in a direction opposite to the direction in which the excitation light enters the Yb-doped fiber,
A fiber ring laser for forming a light pulse from the emitted light,
The fiber ring laser is characterized in that the length of the first single mode fiber is 55 cm or more and 68 cm or less.
In the fiber ring laser, when the excitation light generated by the excitation light source enters the Yb-doped fiber, the emission light is emitted. The light pulse is formed when the emitted light propagates through the first single mode fiber, passes through the isolator, and orbits the ring-shaped optical path of the fiber ring laser. At this time, since the length of the first single mode fiber is 55 cm or more and 68 cm or less, a wide band light of 100 nm to 110 nm having a center wavelength of about 1050 nm, which is suitable for imaging living tissue of the fundus part. A pulse is formed.
<2> An optical pulse produced by the fiber ring laser according to <1>.
<3> The fiber ring laser according to <1> above,
A branching section for branching the light pulse incident from the fiber ring laser into a measurement light and a reference light,
Irradiating the measurement light to the measured object, an irradiation light receiving unit for receiving the reflected light from the measured object,
When the measurement light is applied to the measured object, an interference light measurement unit that measures the interference light between the reflected light and the reference light to generate measurement data,
From the measurement data, an image generator that calculates the intensity of the reflected light at a plurality of depth positions of the measured object to generate a one-dimensional tomographic image in the depth direction of the measured object,
An optical tomographic imaging apparatus comprising:
In the optical tomographic imaging apparatus, when the fiber ring laser according to <1> causes the optical pulse to enter the branching unit, the optical pulse is branched into the measurement light and the reference light. When the branching part makes the measuring light incident on the irradiation/light receiving part and the irradiation/light receiving part irradiates the measuring light to the measured object, the reflected light is reflected from the measured object. When the irradiation light receiving unit receives the reflected light and makes the reflected light incident on the interference light measuring unit, the interference light of the measurement light and the reference light is measured, and the measurement data is generated. When the image generator inputs the measurement data, a one-dimensional tomographic image in the depth direction of the measured object is generated.

ADVANTAGE OF THE INVENTION According to this invention, the said various problems in the past can be solved, the said objective can be achieved, and when used for the measurement light of FD-OCT, the biological tissue of the fundus part which has sufficient resolution in a depth direction. Is used as a light source, a fiber ring laser that generates a broad-band optical pulse of 100 nm to 110 nm having a center wavelength of approximately 1050 nm, a light pulse generated by the fiber ring laser, and a light pulse generated by the fiber ring laser. FD-OCT can be provided.

FIG. 1 is a schematic diagram of a fiber ring laser 1000 which is an example of the fiber ring laser according to the present invention. FIG. 2 is a graph showing a waveform of an optical pulse generated by the fiber ring laser 1000 according to the present invention and a waveform of a normal mode-locked optical pulse. FIG. 3 is a graph showing a spectral distribution of a noise-like optical pulse generated by the fiber ring laser 1000 according to the present invention and a conventional mode-locked optical pulse. FIG. 4 is a graph showing an intensity autocorrelation waveform of a noise-like light pulse generated by the fiber ring laser 1000 according to the present invention. FIG. 5 is a graph showing an interference autocorrelation waveform of a noise-like optical pulse generated by the fiber ring laser 1000 according to the present invention. FIG. 6 is a graph showing the spectrum distribution of the noise-like optical pulse when the optical axis of the second λ/4 wave plate 1120 is rotated in the fiber ring laser 1000 according to the present invention. FIG. 7 is a graph showing the spectrum distribution of the noise-like optical pulse when the length of the first single mode fiber 1040 is changed in the fiber ring laser 1000 according to the present invention. FIG. 8 is a graph showing a spectral distribution of a noise-like optical pulse when the length of the Yb-doped fiber 1030 is changed in the fiber ring laser 1000 according to the present invention. FIG. 9 is a block diagram of an optical tomographic imaging apparatus 2000 which is an example of an optical tomographic imaging apparatus including the fiber ring laser 1000 according to the present invention.

The fiber ring laser of the present invention includes an excitation light source that generates excitation light, a first optical coupler on which the excitation light is incident, and a Yb-doped fiber that is excited by the excitation light incident from the first optical coupler. When the excitation light source generates excitation light, a first single mode fiber that propagates the emission light emitted by the Yb-doped fiber that is excited by the excitation light, and a direction opposite to the direction in which the excitation light enters the Yb-doped fiber And an isolator for preventing light propagation, the emitted light forms an optical pulse, and the length of the first single-mode fiber is 55 cm or more and 68 cm or less. By making the length of the first single mode fiber longer than the length of 10 cm which has been conventionally used, noise-like oscillation is stably generated. When the length of the first single mode fiber is longer than 70 cm, noise-like oscillation does not occur and CW oscillation occurs. When the length of the first single-mode fiber is changed within the range of 20 cm to 70 cm, the best noise-like oscillation occurs when the length is 55 cm or more and 68 cm or less.
The noise-like optical pulse generated by the fiber ring laser according to the present invention can be suitably used for an optical tomographic imaging apparatus for diagnosis of the fundus of the eye, and can be expected to approach the mechanism of glaucoma generation, for example.

It is preferable that the absorption loss of the Yb-doped fiber at the center wavelength of the excitation light is 2700 dB/m or more and 2800 dB/m or less, and the length of the Yb-doped fiber is 20 cm or more and 29 cm or less. By setting the absorption loss at the center wavelength of the Yb-doped fiber to 2750 dB/m, which is higher than that of 1200 dB/m used conventionally, and making it longer than the length of 15 cm used conventionally, noise-like oscillation becomes stable. appear.

The absorption loss of the Yb-doped fiber at the center wavelength of the excitation light is 2700 dB/m or more and 2800 dB/m or less, and the length of the first single-mode fiber is 1 when the length of the Yb-doped fiber is 1. It is preferably 0.964 or more and 2.428 or less. By setting the length of the first single-mode fiber according to the length of the Yb-doped fiber, noise-like oscillation is stably generated.

The fiber ring laser includes a first collimator on which the excitation light and the emission light emitted from the first single-mode fiber are incident, and a first collimator on which the excitation light and the emission light emitted from the first collimator are incident. One λ/4 wave plate and a first λ/2 wave plate, and an optical pulse from the excitation light and the emission light emitted from the first λ/4 wave plate and the first λ/2 wave plate. It is preferable to further include a polarizing element for separating the parts. In this way, the noise-like light pulse can be separated from the excitation light and extracted, and the remaining light further circulates in the ring-shaped optical path of the fiber ring laser. The polarizing element is preferably a polarizing beam splitter.

The fiber ring laser includes a dispersion compensating optical element for compensating the group velocity dispersion of the light pulse emitted from the polarizing element, and a pumping light and an emitting light emitted from the dispersion compensating optical element, which are incident on the isolator. It is preferable to further include one mirror. By doing so, the optical pulse is shaped by compensating the influence of the group velocity dispersion of the optical pulse.

The dispersion compensating optical element includes a first diffraction grating and a second diffraction grating arranged in parallel, and a second mirror, and the excitation light is diffracted by the first diffraction grating and the second diffraction grating. , And then reflected by the second mirror and then diffracted by the second diffraction grating and the first diffraction grating, the effect of the group velocity dispersion of the light pulse is preferably compensated. In this way, by compensating for the influence of group velocity dispersion by using the passive optical element, the configuration of the fiber ring laser becomes simpler as compared with the case of using the active optical element.

The fiber ring laser has a second λ/4 wavelength plate on which the emitted light emitted from the isolator is incident, and a second collimator on which the emitted light emitted from the second λ/4 wavelength plate is incident. , And a second single mode fiber coupling the second collimator and the first optical coupler. By adjusting the optical axis of the second λ/4 wave plate, the spectral distribution of the generated light pulse can be adjusted.

A fiber ring laser includes: the first λ/4 wave plate, the first λ/2 wave plate, the second λ/4 wave plate, the polarization beam splitter, the first diffraction grating, and the first diffraction grating. More preferably, it comprises two diffraction gratings and all of said second mirrors. The first λ/4 wavelength plate and the first ½ wavelength plate may be used to control the deflection direction to extract only the horizontally polarized portion whose polarization is controlled by the polarization beam splitter from the fiber ring laser resonator. it can. By using the first diffraction grating, the second diffraction grating, and the second mirror diffraction grating, it is possible to control the dispersion in the fiber ring laser resonator.

It is preferable that the excitation light source is a laser diode that generates light with a wavelength of about 915 nm or excitation light with a wavelength of about 975 nm. The Yb-doped fiber absorbs the excitation light from the excitation light source and emits the emitted light of 1000 nm to 1070 nm.

The light pulse of the present invention is produced by the fiber ring laser of the present invention. In the noise-like light pulse generated by the fiber ring laser according to the present invention, each pulse has a different shape, but as a whole, a large number of light pulses are gathered to obtain a broad spectrum distribution. When many light pulses are combined, the spectral distribution has a peak at about 1050 nm and a broad band of 100 nm to 110 nm. When the noise-like optical pulse thus obtained is used as the measuring optical pulse of the optical tomographic imaging apparatus, when the object to be measured is living tissue of the fundus part, it is possible to obtain a high resolution of the deep part of the lamina cribrosa of the optic disc. Allows for observation. The noise-like optical pulse according to the present invention can be preferably used in an optical tomographic imaging apparatus for fundus diagnosis, and can be expected to approach the mechanism of glaucoma generation, for example.

The optical tomographic imaging apparatus of the present invention irradiates the fiber ring laser of the present invention, a branch portion for branching an optical pulse incident from the fiber ring laser into a measurement light and a reference light, and a measurement light to an object to be measured, An irradiation light receiving unit that receives the reflected light from the measured object, and an interference light measurement unit that measures the interference light between the reflected light and the reference light when the measuring light is irradiated to the measured object to generate measurement data. And an image generation unit that calculates the intensity of the reflected light at a plurality of depth positions of the measured object from the measurement data and generates a one-dimensional tomographic image in the depth direction of the measured object. By using the optical pulse incident from the fiber ring laser of the present invention, the optical tomographic imaging apparatus of the present invention can obtain an image of the living tissue of the fundus portion having sufficient resolution in the depth direction.

The interference light measurement unit includes a spectroscopic element and an optical sensor, the spectroscopic element decomposes the incident interference light into wavelength components, and the optical sensor measures the intensity of each wavelength component of the interference light decomposed into wavelength components. It is preferable to generate the measurement data by measuring, and it is preferable that the image generating unit calculates the intensity of the reflected light at a plurality of depth positions of the measured object from the measurement data by using Fourier transform. In this way, unlike the time-domain optical tomographic imaging apparatus, the reflected light at multiple depth positions of the measured object can be measured by one measurement without performing multiple measurements at multiple depth positions. The intensity of can be calculated.

The irradiation detection unit includes a scanning unit that scans the object to be measured in a plane perpendicular to the depth direction of the object to be measured, and the image generation unit is a primary unit generated at each position in the surface scanned by the scanning unit. It is preferable to generate a three-dimensional tomographic image of the measurement object from the original tomographic image. The three-dimensional tomographic image thus obtained enables high-resolution observation of the deep part of the lamina cribrosa of the optic disc when the object to be measured is living tissue of the fundus. The optical tomographic imaging apparatus according to the present invention can be suitably used for diagnosis of the fundus of the eye, and can be expected to approach the mechanism of glaucoma generation, for example.

FIG. 1 is a schematic diagram of a fiber ring laser 1000 which is an example of the fiber ring laser according to the present invention. The fiber ring laser 1000 includes an excitation light source 1010, a first optical coupler 1020, a Yb-doped fiber 1030, a first single mode fiber 1040, a first collimator 1050, a first λ/4 wave plate 1060, and a first λ/4 wavelength plate 1060. λ/2 wave plate 1070, polarizing element 1080, dispersion compensation optical element 1090, first mirror 1100, isolator 1110, second λ/4 wave plate 1120, second collimator 1130, and second single mode fiber. 1140.

The excitation light source 1010 generates excitation light for exciting the Yb-doped fiber 1030 included in the fiber ring laser 1000. In one example, the excitation light source 1010 may be a light source that generates light with a wavelength of about 915 nm or low coherent light with a wavelength of about 975 nm, and may be a laser diode.

The pumping light from the pumping light source 1010 is then passed through the first optical coupler 1020, the Yb-doped fiber 1030, the first single-mode fiber 1040, the first collimator 1050, the first λ/4 wavelength plate 1060, The first λ/2 wave plate 1070, the polarizing element 1080, the dispersion compensation optical element 1090, the first mirror 1100, the isolator 1110, the second λ/4 wave plate 1120, the second collimator 1130, and the second collimator 1130. The light is incident on the ring-shaped optical path of the fiber ring laser 1000 including the single mode fiber 1140. The excitation light source 1010 and the first optical coupler 1020 may be coupled by a single mode fiber. The first optical coupler 1020 may be a wavelength division multiplexing communication coupler (WDM).

The excitation light that has entered the ring-shaped optical path of the fiber ring laser 1000 via the first optical coupler 1020 then enters the Yb-doped fiber 1030. The Yb-doped fiber 1030 absorbs light with a wavelength of about 915 nm or excitation light with a wavelength of about 975 nm from the excitation light source, and emits emission light of 1030 nm to 1070 nm. In one example, the absorption loss at the central wavelength of the excitation light of the Yb-doped fiber 1030 is 2750 dB/m or less, and the length is 28 cm. Of the emitted light having a wavelength of 1030 nm to 1070 nm, it is combined with the in-phase component of the emitted light that circulates in the ring-shaped optical path of the fiber ring laser 1000, and an optical pulse is generated. The generated optical pulse goes around the ring-shaped optical path together with the excitation light. Since the Yb-doped fiber 1030 has a positive dispersion value, the optical pulse propagating through the Yb-doped fiber 1030 is upchirped due to the influence of group velocity dispersion, and its pulse width is expanded.

The fibers used in the fiber ring laser 1000 are preferably polarization independent. Then, due to the non-linear polarization rotation generated in the fiber, the polarization of the excitation light propagates in the fiber while rotating as elliptically polarized light.
When the fiber ring laser 1000 is installed, the length and the arrangement of the Yb-doped fiber 1030 and the first single-mode fiber 1040 are determined, and the pumping light accordingly generates the Yb-doped fiber 1030 and the first single-mode fiber 1040. The polarization state when propagating is determined.

The light that has passed through the first single mode fiber 1040 and the first collimator 1050 is incident on the first λ/4 wave plate 1060. In the first λ/4 wave plate 1060, it is preferable to adjust the optical axis of the first λ/4 wave plate 1060 so as to return the polarization of the excitation light from the elliptically polarized light to the linearly polarized light. The light emitted from the first λ/4 wave plate 1060 is incident on the first λ/2 wave plate 1070. In the first λ/2 wave plate 1070, the polarization direction of the linearly polarized light is rotated.

The light pulse emitted from the first λ/2 wave plate 1070 is then incident on the polarization element 1080 together with the excitation light. The polarizing element 1080 splits the incident light into polarized light components. In one example, the polarizing element 1080 is preferably a polarizing beam splitter. It is preferable to adjust the optical axis of the first λ/2 wavelength plate 1070 so that the polarization direction of the linearly polarized light is rotated to the P polarization direction of the polarizing element 1080. The polarizing element 1080 transmits the P-polarized excitation light that has passed through the first λ/2 wave plate 1070 and becomes P-polarized light, while transmitting the P-polarized component of the optical pulse that has entered the polarizing element 1080 together with the excitation light and It reflects the S-polarized component of the light pulse, which has the same horizontal polarization as element 1080. The reflected light pulse can be extracted as an output light pulse of the fiber ring laser 1000 in a state separated from the excitation light.

The light pulse transmitted through the polarizing element 1080 is then incident on the dispersion compensating optical element 1090 together with the excitation light. The dispersion compensating optical element 1090 shapes the optical pulse by compensating the influence of the group velocity dispersion of the optical pulse.

In one example, the dispersion compensating optical element 1090 may include a pair of parallel arranged diffraction gratings 1092 and 1094 and a second mirror 1096. The dispersion compensating optical element 1090 utilizes the property that the diffraction grating diffracts different frequency components in different directions, and uses a pair of diffraction gratings 1092 and 1094 and a second mirror 1096 arranged in parallel to change the optical path length to frequency. By varying depending on the component, the influence of the group velocity dispersion of the incident light pulse is compensated. As the dispersion compensating optical element 1090, a fiber having negative dispersion in the wavelength band of 1000 nm may be used instead of the diffraction gratings 1092 and 1094.

The light pulse transmitted through the dispersion compensating optical element 1090 is then reflected by the first mirror 1100 and enters the isolator 1110. The isolator 1110 transmits light in one direction and blocks light in the opposite direction.

The optical pulse transmitted through the isolator 1110 is incident on the second collimator 1130 via the second λ/4 wave plate 1120. The light pulse emitted from the second collimator 1130 propagates through the second single-mode fiber 1140 and is incident on the first optical coupler 1020, and is rotated counterclockwise in the ring-shaped optical path of the fiber ring laser 1000. Orbit around.

FIG. 2 is a graph showing a waveform of an optical pulse generated by the fiber ring laser 1000 according to the present invention and a waveform of a conventional mode-locked optical pulse. A conventional mode-locked optical pulse is shown in the upper part, and an optical pulse generated by the fiber ring laser 1000 is shown in the lower part. Each of the conventional mode-locked optical pulses has the same shape, whereas the optical pulse generated by the fiber ring laser 1000 has a different shape and is a noise-like optical pulse. I understand.

FIG. 3 is a graph showing a spectral distribution of a noise-like optical pulse generated by the fiber ring laser 1000 according to the present invention and a conventional mode-locked optical pulse. The spectrum distribution of the conventional mode-locked light pulse indicated by the label ML in the graph has peaks at wavelengths of about 1020 nm and 1090 nm, and has a shape in which the peaks are depressed. On the other hand, the spectral distribution of the fiber ring laser 1000 indicated by the label NL in the graph has a bell-shaped shape having peaks at wavelengths of approximately 1050 nm and 1100 nm. An optical pulse having such a substantially bell-shaped spectral distribution is an optical slice according to the present invention to which the principle of an interferometer is applied without applying a spectral distribution correction filter for correcting the spectral distribution of the optical pulse. It is suitable because it can be used as a pulsed light source for an imaging device.

As described above, in the noise-like light pulse generated by the fiber ring laser 1000 according to the present invention, each light pulse has a different shape, but as a whole, a large number of light pulses are gathered to obtain a broad spectrum distribution. To be When many light pulses are combined, the spectral distribution has a peak at a wavelength of about 1050 nm and a wavelength of about 1100 nm, has a wide band of 100 nm to 110 nm, and is stable.

4 and 5 are graphs showing an intensity autocorrelation waveform and an interference autocorrelation waveform of a noise-like optical pulse generated by the fiber ring laser 1000 according to the present invention, respectively. At a time difference of zero picoseconds, a spike having a width of about 100 femtoseconds is observed. Such spikes are not observed in the conventional graph showing the autocorrelation waveform of the mode-locked optical pulse, and characterize the noise-like optical pulse. In the fiber ring laser 1000, it is considered that such a noise-like optical pulse may have been generated due to the non-linear effect of the first single mode fiber 1040 and the Yb-doped fiber 1030.

In the fiber ring laser 1000 according to the present invention, one of the features of the present invention is that the length of the first single mode fiber 1040 is 55 cm or more and 68 cm or less. It was thought that the length of the first single mode fiber 1040 must be shortened in order to prevent the distortion of the spatial beam shape and the collapse of the pulse shape due to the nonlinear phase shift. Conventionally, the first single mode fiber 1040 has a length of 10 cm. However, it can be seen from the results shown in FIGS. 2 to 5 that the fiber ring laser 1000 in which the length of the first single mode fiber 1040 is 58 cm causes noise-like oscillation. Even when the length of the first single mode fiber 1040 was set to 55 cm or more and 68 cm or less, it was observed that the fiber ring laser 1000 oscillated like noise.

In the fiber ring laser 1000 according to the present invention, when the length of the first single-mode fiber 1040 is changed in the range of 20 cm to 70 cm, the best noise-like oscillation occurs when the length is 55 cm or more and 68 cm or less, and 70 cm When it exceeded, CW oscillation occurred. As described above, in the fiber ring laser 1000, the length of the first single mode fiber 1040 is critical.

In the fiber ring laser 1000 according to the present invention, the absorption loss at the central wavelength of the excitation light of the Yb-doped fiber 1030 is 2750 dB/m and the length is 28 cm, which is also one of the features of the present invention. It is conventionally considered that when the length of the Yb-doped fiber 1030 is increased, re-absorption occurs and the oscillation intensity is weakened. Whether the Yb-doped fiber having an absorption loss of 1200 dB/m at the central wavelength is used for a length of 30 cm. , Or Yb-doped fiber with an absorption loss of 2750 dB/m at the center wavelength was used for a length of 15 cm.

FIG. 6 is a graph showing the spectrum distribution of the noise-like optical pulse when the optical axis of the second λ/4 wave plate 1120 is rotated in the fiber ring laser 1000 according to the present invention. Thus, it can be seen that the spectral distribution of the noise-like light pulse generated by the fiber ring laser 1000 also depends on the orientation of the optical axis of the second λ/4 wave plate 1120. Adjusting the optical axis to control the energy stored in the fiber ring laser cavity and to control the intensity of the nonlinear effect produces the desired spectral distribution as shown in FIG.

FIG. 7 is a graph showing the spectrum distribution of the noise-like optical pulse when the length of the first single mode fiber 1040 is changed in the fiber ring laser 1000 according to the present invention. In FIG. 7, each of the Yb-doped fibers 1030 has a length of 28 cm. When the length of the first single-mode fiber 1040 is 58 cm and 66 cm, a good noise-like optical pulse having a substantially bell-shaped spectral distribution is generated, whereas the length of the first single-mode fiber 1040 is long. When the distance is 23 cm, there are peaks at wavelengths of approximately 1000 nm, wavelengths of approximately 1030 nm, and wavelengths of approximately 1070 nm, and the peaks are sunk in between.

FIG. 8 is a graph showing a spectral distribution of a noise-like optical pulse when the length of the Yb-doped fiber 1030 is changed in the fiber ring laser 1000 according to the present invention. In FIG. 8, the length of each of the first single mode fibers 1040 is 58 cm. In any case, a noise-like optical pulse having a substantially bell-shaped spectral distribution is generated. The full width at half maximum of the spectrum distribution when the length of the Yb-doped fiber 1030 is 17 cm, 20 cm, and 28 cm is about 50 nm, about 100 nm, and about 120 nm, respectively, and the longer the Yb-doped fiber 1030, the wider the spectrum distribution width. ..

In the fiber ring laser 1000 according to the present invention, the length of the first single mode fiber 1040 may be adjusted according to the length of the Yb-doped fiber 1030. In one example, when the length of the Yb-doped fiber 1030 is set to 1, the length of the first single-mode fiber 1040 is adjusted to 1.964 or more and 2.428 or less according to the length of the Yb-doped fiber 1030. The length of the first single mode fiber 1040 may be adjusted.

FIG. 9 is a block diagram of an optical tomographic imaging apparatus 2000 which is an example of an optical tomographic imaging apparatus including the fiber ring laser 1000 according to the present invention. The optical tomographic imaging apparatus 2000 includes a pulse light source generation unit 2010, a branching/synthesizing unit 2020, an irradiation detection unit 2030, a reference light reflection unit 2050, an interference light measurement unit 2060, and an image generation unit 2070. The optical tomographic imaging apparatus 2000 outputs a tomographic image of the measured object 2040 from the image generation unit 2070. The optical tomographic imaging apparatus 2000 has a configuration using a Michelson-type interferometer, but instead of this, a Mach-Zehnder-type interferometer may be used.

The light pulse incident from the pulse light source generation unit 2010 is branched into the measurement light pulse and the reference light pulse in the branching and combining unit 2020. The pulse light source generation unit 2010 may be the fiber ring laser 1000. The branching/combining unit 2020 may be a polarization beam splitter.

The measurement light pulse branched into the measurement light in the branching/combining unit 2020 is incident on the irradiation detection unit 2030. The irradiation detection unit 2030 includes a scanning unit in one example. The irradiation detection unit 2030 irradiates the measured object 2040 with a measurement light pulse while the scanning unit scans the measured object 2040 in a plane perpendicular to the depth direction of the measured object 2040. The scanning unit may be a galvano scanner.

The measurement light pulse reflected by the measured object 2040 is incident on the branching combining unit 2020 via the irradiation detecting unit 2030, and combined with the reference light pulse reflected by the reference light reflecting unit 2050 to form an interference light pulse, It is incident on the interference light measuring unit 2060. In the present embodiment, both the branching and combining of the measurement light pulse and the reference light pulse are performed in the branching and combining unit 2020, but the branching and combining may be performed by different optical elements.

The interference light measurement unit 2060 decomposes the incident interference light pulse into wavelength components using, for example, a spectroscopic element such as a diffraction grating or a prism. Next, the interference light measurement unit 2060 measures the intensity of each wavelength component of the interference light pulse decomposed into wavelength components using the optical sensor to generate measurement data, and the generated measurement data is sent to the image generation unit 2070. input. The optical sensor may be a line sensor.

The image generation unit 2070 inputs the measurement data, calculates the intensities of the reflected light at a plurality of depth positions of the measured object 2040 from the measured data using Fourier transform, and determines the primary in the depth direction of the measured object. Generate an original tomographic image. The Fourier transform may be performed by numerical calculation using a fast Fourier transform algorithm or the like. In one example, the image generation unit 20 collects the one-dimensional tomographic images generated by the image generation unit 2070 at each position scanned by the scanning unit included in the irradiation detection unit 2030, so that the image generation unit 20 can generate a three-dimensional tomographic image of the measured object 2040. To generate. When the measured object 2040 is a living tissue of the fundus, the three-dimensional tomographic image thus obtained enables observation of the deep part of the lamina cribrosa of the optic disc with high resolution. The optical tomographic imaging apparatus according to the present invention can be suitably used for diagnosis of the fundus of the eye, and can be expected to approach the mechanism of glaucoma generation, for example.

As described above, the fiber ring laser of the present invention, the optical pulse generated by the fiber ring laser of the present invention, and the optical tomographic imaging apparatus using the optical pulse generated by the fiber ring laser of the present invention as a pulse light source have been described in detail, The present invention is not limited to the above embodiment, and various modifications may be made without departing from the scope of the present invention.

Examples of aspects of the present invention include the following.
<1> An excitation light source that generates excitation light,
A first optical coupler on which the excitation light is incident;
A Yb-doped fiber that is excited by the excitation light that is incident from the first optical coupler;
A first single-mode fiber that propagates emission light emitted by the Yb-doped fiber that is excited by the excitation light when the excitation light source generates the excitation light;
An isolator for preventing light propagation in a direction opposite to the direction in which the excitation light enters the Yb-doped fiber,
A fiber ring laser for forming a light pulse from the emitted light,
The fiber ring laser is characterized in that the length of the first single mode fiber is 55 cm or more and 68 cm or less.
<2> The absorption loss at the central wavelength of the excitation light of the Yb-doped fiber is 2700 dB/m or more and 2800 dB/m or less, and the length of the Yb-doped fiber is 20 cm or more and 29 cm or less. Fiber ring laser.
<3> The absorption loss at the central wavelength of the excitation light of the Yb-doped fiber is 2700 dB/m or more and 2800 dB/m or less, and when the length of the Yb-doped fiber is 1, the first single-mode fiber The fiber ring laser according to <1>, having a length of 1.964 or more and 2.428 or less.
<4> The fiber ring laser according to any one of <1> to <3>, wherein the first single-mode fiber has a length of 58 cm.
<5> A first collimator on which the excitation light and the emission light emitted from the first single mode fiber are incident,
A first λ/4 wave plate and a first λ/2 wave plate on which the excitation light and the emitted light emitted from the first collimator are incident;
A polarizing element for separating a part of the optical pulse from the excitation light and the emission light emitted from the first λ/4 wave plate and the first λ/2 wave plate,
The fiber ring laser according to any one of <1> to <4>, further comprising:
<6> The polarization element is the fiber ring laser according to <5>, which is a polarization beam splitter.
<7> A dispersion compensating optical element for compensating for group velocity dispersion of the light pulse emitted from the polarizing element,
A first mirror that reflects the excitation light and the emitted light emitted from the dispersion compensating optical element to enter the isolator;
The fiber ring laser according to any one of <1> to <6>, further comprising:
<8> The dispersion compensation optical element,
A first diffraction grating and a second diffraction grating arranged in parallel,
A second mirror,
Equipped with
When the excitation light is diffracted by the first diffraction grating and the second diffraction grating, reflected by the second mirror, and then diffracted by the second diffraction grating and the first diffraction grating, The fiber ring laser according to <7>, in which the influence of the group velocity dispersion of the optical pulse is compensated.
<9> A second λ/4 wavelength plate on which the emitted light emitted from the isolator is incident,
A second collimator on which the excitation light and the emitted light emitted from the second λ/4 wave plate are incident;
A second single mode fiber coupling the second collimator and the first optical coupler;
The fiber ring laser according to any one of <1> to <8>.
<10> The excitation light source is the fiber ring laser according to any one of <1> to <9>, which is a laser diode that generates light having a wavelength of about 915 nm or excitation light of a wavelength of about 975 nm.
<11> An optical pulse generated by the fiber ring laser according to any one of <1> to <10>.
<12>
The fiber ring laser according to any one of <1> to <10>,
A branching section for branching an optical pulse incident from the fiber ring laser into a measurement light and a reference light,
Irradiating the measurement light to the measured object, an irradiation light receiving unit for receiving the reflected light from the measured object,
When the measurement light is applied to the measured object, an interference light measurement unit that measures the interference light between the reflected light and the reference light to generate measurement data,
From the measurement data, an image generator that calculates the intensity of the reflected light at a plurality of depth positions of the measured object to generate a one-dimensional tomographic image in the depth direction of the measured object,
It is an optical tomographic imaging apparatus provided with.
<13> The interference light measuring unit includes a spectroscopic element and an optical sensor,
The spectroscopic element decomposes the incident interference light into wavelength components,
The optical tomographic imaging apparatus according to <12>, wherein the optical sensor generates measurement data by measuring the intensity of each wavelength component of the interference light decomposed into wavelength components.
<14> In any one of <12> to <13>, the image generation unit calculates the intensity of the reflected light at a plurality of depth positions of the measured object from the measurement data by using Fourier transform. The described optical tomographic imaging apparatus.
<15> The irradiation detection unit includes a scanning unit that scans the measured object in a plane perpendicular to the depth direction of the measured object, and the image generation unit includes the in-plane scanned by the scanning unit. The optical tomographic imaging apparatus according to any one of <12> to <14>, which generates a three-dimensional tomographic image of the measurement object from the one-dimensional tomographic image generated at each position.

Claims (10)

An excitation light source that generates excitation light,
A first optical coupler on which the excitation light is incident;
A Yb-doped fiber that is excited by the excitation light that is incident from the first optical coupler;
A first single-mode fiber that propagates emission light emitted by the Yb-doped fiber that is excited by the excitation light when the excitation light source generates the excitation light;
An isolator for preventing light propagation in a direction opposite to the direction in which the excitation light enters the Yb-doped fiber,
A fiber ring laser for forming a light pulse from the emitted light,
The length of the first single mode fiber is 55 cm or more and 68 cm or less,
An absorption loss of the Yb-doped fiber at a central wavelength of the excitation light is 2700 dB/m or more and 2800 dB/m or less, and a length of the Yb-doped fiber is 20 cm or more and 29 cm or less. An excitation light source that generates excitation light,
A first optical coupler on which the excitation light is incident;
A Yb-doped fiber that is excited by the excitation light that is incident from the first optical coupler;
A first single-mode fiber that propagates emission light emitted by the Yb-doped fiber that is excited by the excitation light when the excitation light source generates the excitation light;
An isolator for preventing light propagation in a direction opposite to the direction in which the excitation light enters the Yb-doped fiber,
A fiber ring laser for forming a light pulse from the emitted light,
The length of the first single mode fiber is 55 cm or more and 68 cm or less,
The absorption loss at the center wavelength of the excitation light of the Yb-doped fiber is 2700 dB/m or more and 2800 dB/m or less, and the length of the first single-mode fiber is 1 when the length of the Yb-doped fiber is 1. The fiber ring laser is characterized in that it is 1.964 or more and 2.428 or less. A first collimator on which the excitation light and the emitted light emitted from the first single mode fiber are incident;
A first λ/4 wave plate and a first λ/2 wave plate on which the excitation light and the emitted light emitted from the first collimator are incident;
A polarizing element for separating a part of the optical pulse from the excitation light and the emission light emitted from the first λ/4 wave plate and the first λ/2 wave plate,
The fiber ring laser according to claim 1, further comprising: A dispersion compensating optical element for compensating the group velocity dispersion of the optical pulse emitted from the polarizing element,
A first mirror that reflects the excitation light and the emitted light emitted from the dispersion compensating optical element to enter the isolator;
The fiber ring laser according to claim 3 , further comprising: The dispersion compensation optical element,
A first diffraction grating and a second diffraction grating arranged in parallel,
A second mirror,
Equipped with
When the excitation light is diffracted by the first diffraction grating and the second diffraction grating, reflected by the second mirror, and then diffracted by the second diffraction grating and the first diffraction grating, The fiber ring laser according to claim 4, wherein the influence of the group velocity dispersion of the light pulse is compensated. A second λ/4 wave plate on which the emitted light emitted from the isolator is incident;
A second collimator on which the excitation light and the emitted light emitted from the second λ/4 wave plate are incident;
A second single mode fiber coupling the second collimator and the first optical coupler;
The fiber ring laser according to claim 1, further comprising: An optical pulse produced by the fiber ring laser according to claim 1. A fiber ring laser according to any one of claims 1 to 6,
A branching section for branching an optical pulse incident from the fiber ring laser into a measurement light and a reference light,
Irradiating the measurement light to the measured object, an irradiation light receiving unit for receiving the reflected light from the measured object,
When the measurement light is applied to the measured object, an interference light measurement unit that measures the interference light between the reflected light and the reference light to generate measurement data,
From the measurement data, an image generator that calculates the intensity of the reflected light at a plurality of depth positions of the measured object to generate a one-dimensional tomographic image in the depth direction of the measured object,
An optical tomographic imaging apparatus comprising: The interference light measuring unit includes a spectroscopic element and an optical sensor,
The spectroscopic element decomposes the incident interference light into wavelength components,
The optical tomographic imaging apparatus according to claim 8, wherein the optical sensor generates measurement data by measuring an intensity of each wavelength component of the interference light decomposed into wavelength components. An irradiation detector is further provided,
The irradiation detection unit includes a scanning unit that scans the measured object in a plane perpendicular to the depth direction of the measured object, the image generation unit, each of the in-plane scanned by the scanning unit. wherein the one-dimensional tomographic image generated in a position, wherein to generate a three-dimensional tomographic image of the object body, the optical tomographic imaging apparatus according to any one of claims 8 9.