KR101369926B1 - Wide Band Splitter and Multi Wavelength Band Optical Coherence Tomography - Google Patents

Abstract

The present invention relates to a wideband optical splitter. The broadband optical splitter includes an optical splitter including a core providing first and second waveguides and a cladding surrounding the core, wherein the refractive index of the core is n ₁ , the refractive index of the clad is n ₂ , and 1 / the core width. When 2 is called ρ,
kρ (n ₁ ² -n ₂ ² ) ^1/2 <π / 2 (where k = 2π / λ (λ is the wavelength of light))
Satisfied relationships,
When the first waveguide and the second waveguide are coupled in a first section and a second section, the length of the first section is L1, the length of the second section is L2, and the second section from the first section. When the optical path difference to ΔL is
420 µm ≤ L1 ≤ 480 µm,
750 µm ≤ L2 ≤ 850 µm,
0.6 μm ≦ ΔL ≦ 0.9 μm,
It is characterized by satisfying the relationship.

Description

Wideband optical splitter and optical tomography apparatus capable of securing images of multi-wavelength band using the same {Wide Band Splitter and Multi Wavelength Band Optical Coherence Tomography}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wideband optical splitter and an optical tomographic imaging apparatus capable of securing images of a multi-wavelength band using the same. The present invention relates to an optical tomography imaging apparatus capable of acquiring an image of a sample in a multi-wavelength band using the same.

Optical coherence tomography (OCT) has been widely studied because it can realize non-invasive images. Optical tomography imaging devices can provide sophisticated tomographic images of biosamples based on low coherence interferometers. In general, as the light source becomes wider, an optical tomography imaging apparatus having high resolution may be realized. Recently, a superluminescent diode, a white light sourse, a short pulse laser, and a supercontinuum light source are widely used as broadband light sources.

However, in spite of these broadband light sources, optical tomographic imaging apparatus based on optical fibers has a limitation in bandwidth. Since OCT systems are interferometers, a key component in fiber-based OCTs is the optical splitter, which typically has a low bandwidth with blocking wavelengths around single-mode and multi-mode around 1200 nm. Has

In order to overcome this problem, PCF optical splitters have been used by utilizing the single-mode characteristics of the entire photonic crystal fiber (PCF). PCF optical splitters can accommodate a wide range of light sources in OCT systems based on fiber optics, making many applications in high resolution systems. The PCF optical splitter is manufactured by a melt-fusion method, which has a high excess loss of 3 to 6 dB due to destruction and contamination of the air hole structure. In addition, the asymmetrical arrangement of air holes causes many polarization states and causes large changes in optical power.

To solve this problem, we made a block array using PCF and packaged a commercial splitter chip and block array to reduce high excess loss and high polarization dependency loss. However, such a commercial splitter chip specifies that it has a single mode of 1200 nm or more and cannot be used for a wavelength of Spectral Domain OCT (SD-OCT) operating below 1000 nm. In case of SD-OCT over 1000nm, InGaAs line CCD should be used, which is much more expensive than Si line CCD below 1000nm.

Therefore, in order to implement a lower cost and multi-wavelength SD-OCT system, a broadband optical splitter that operates in a wide band of 1000 nm or less, has a low excess loss, and is capable of mass production is required.

On the other hand, the existing optical fiber-based SD-OCT system was able to implement an image in a single wavelength band according to the purpose. In order to acquire an image of a multi-wavelength band, a system having a wavelength band has to be provided, thereby increasing the cost. Therefore, there is a need for an optical tomography imaging apparatus that accommodates a light source in a wide wavelength region so as to acquire an image in multiple wavelength bands or to simultaneously acquire an image for multiple wavelengths.

The present invention has been made to solve the above problems, a broadband optical splitter which operates in a single mode in a broadband wavelength region and has a constant distribution ratio, and by using the same, to obtain an image of a sample in a multi-wavelength band. It is an object of the present invention to provide an optical tomography imaging device.

The broadband optical splitter according to an aspect of the present invention for solving the above problems, in the optical splitter comprising a core for providing the first and second waveguides and a cladding surrounding the core, the refractive index of the core n ₁ , When the refractive index of the clad is n ₂ , 1/2 of the core width ρ,

kρ (n ₁ ² -n ₂ ² ) ^1/2 <π / 2 (where k = 2π / λ (λ is the wavelength of light))

Satisfied relationships,

When the first waveguide and the second waveguide are coupled in a first section and a second section, the length of the first section is L1, the length of the second section is L2, and the second section from the first section. When the optical path difference to ΔL is

420 µm ≤ L1 ≤ 480 µm,

750 µm ≤ L2 ≤ 850 µm,

0.6 μm ≦ ΔL ≦ 0.9 μm,

Is satisfied.

In addition, the first and second waveguides preferably operate in a single mode in the wavelength range of the visible light band to the near infrared band.

The optical fiber array block may include: a first optical fiber array block in which first and second optical fibers are respectively connected to an input terminal of the first waveguide and an input terminal of the second waveguide; And a second optical fiber array block in which third and fourth optical fibers are connected to the output terminal of the first waveguide and the output terminal of the second waveguide, respectively.

On the other hand, an optical tomographic imaging apparatus capable of securing an image of a multi-wavelength band using a wideband optical splitter according to another aspect of the present invention, a wideband optical splitter; A light source for providing light to the broadband optical splitter; The light source is divided into a first light source and a second light source via the broadband light splitter, and a reference stage for reflecting the first light source by a reflection mirror; A sample stage at which the second light source is reflected by a sample; The first light source and the second light source reflected from the reference stage and the sample stage are combined again through the broadband optical splitter, and acquire an interference fringe signal formed by a path difference between the first and second light sources. Spectrometer; A frame grabber for transmitting the interference fringe signal; And a computer for receiving the interference fringe signal and converting the interference fringe signal into an image.

In addition, the light source preferably provides light in the visible light band to the near infrared band.

In addition, the light source sequentially provides light having two or more different wavelengths selected from the visible light band to the near infrared band, and the spectrometer has a plurality of gratings for dividing the two or more different wavelengths by wavelength. It is preferable.

A broadband optical splitter and an optical tomographic imaging apparatus capable of securing an image of a multi-wavelength band using the same are operated in a single mode in a wide-band wavelength region, have a constant distribution ratio, and can acquire an image of a sample in the multi-wavelength band. The present invention provides an effect of simultaneously acquiring an image of a sample for a plurality of different wavelengths.

1 is a schematic configuration diagram of a Spectral Domain OCT (SD-OCT),
2 is a perspective view of a broadband optical splitter according to an aspect of the present invention;
3 is a cross-sectional view taken along line III-III of FIG. 2;
4 is a cross-sectional view taken along the line IV-IV of FIG. 2;
5 is a left side view of FIG. 2;
6 to 8 are graphs showing the distribution ratio of light by the broadband optical splitter according to the embodiment of the present invention;
9 and 10 are graphs showing a distribution ratio of light by a conventional optical splitter;
11 is a block diagram of an optical tomography imaging apparatus according to another aspect of the present invention;
12 is an image of samples obtained using an optical tomography imaging apparatus according to the present invention.

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the accompanying drawings.

1 is a schematic configuration diagram of a Spectral Domain OCT (SD-OCT), and FIG. 2 is a perspective view of a broadband optical splitter according to an aspect of the present invention. 3 is a cross-sectional view taken along the line III-III of FIG. 2, FIG. 4 is a cross-sectional view taken along the line IV-IV of FIG. 2, and FIG. 5 is a left side view of FIG.

First, referring to FIG. 1, a configuration of Spectral Domain Optical Coherence Tomography (SD-OCT) using an interferometer is as follows. The applied light source 210 is separated into the reference stage 220 and the sample stage 230 in the optical splitter.

The light reflected from the reference stage 220 and the sample stage 230 passes through the optical splitter again, and an interference fringe is formed by the optical path difference. The interference fringe is obtained at spectrometer 240 and is configured to obtain an image using the interference fringe signal.

An optical splitter according to one aspect of the present invention operates in a single mode in a wide wavelength range and provides a constant coupling ratio.

3 and 4, the broadband optical splitter 100 according to the present invention has two waveguides coupled to each other to have a so-called Mahzander structure. The broadband optical splitter 100 includes a core 1 providing first and second waveguides 10 and 20, and a clad 2 surrounding the core 1. Referring to FIG. 4, a broadband optical splitter 100 includes a core 1 on which a clad 2 is placed on a Si substrate 4 and provided as first and second waveguides 10 and 20 inside the clad 2. ) Is placed.

First, in order for the first and second waveguides 10 and 20 to operate in a single mode, the refractive index of the core 1 is n ₁ , the refractive index of the clad 2 is n ₂ , and the core width W is 1 / When 2 is called ρ,

kρ (n ₁ ² -n ₂ ² ) ^1/2 <π / 2 (where k = 2π / λ (λ is the wavelength of light))

Satisfy the relationship.

That is, the _first and second waveguides 10 and 20 operate in a single mode by appropriately adjusting the refractive index n ₁ of the core 1, the refractive index n ₂ of the clad ₂ , and the half width of the core width W. Implement to

When kρ (n ₁ ² -n ₂ ² ) ^1/2 is greater than π / 2, the first and second waveguides 10 and 20 operate in a multi-mode. When the light operates in the multi-mode, the light returned from the sample stage 230 or the reference stage 220 causes a large number of interference fringes, and the unnecessary interference fringes act as noise when acquiring an image. The broadband optical splitter 100 is implemented such that the first and second waveguides 10 and 20 operate in a single mode.

Referring to FIG. 3, in the broadband optical splitter 100 according to the present invention, two strands of the first and second waveguides 10 and 20 are coupled in a first section and a second section.

When the length of the first section is L1, the length of the second section is L2, and the optical path difference from the first section to the second section is ΔL, 420 μm ≦ L1 ≦ 480 μm and 750 μm ≦ L2 ≤ 850 µm, and 0.6 µm ≤ ΔL ≤ 0.9 µm.

The broadband optical splitter 100 according to the present invention is to provide an optical splitter having a constant distribution ratio in a wide wavelength range, particularly in the visible and near infrared wavelength range, and as described above, the values of L1, L2, and ΔL are in the above range. Broadband optical splitter 100 is implemented having a constant distribution ratio of 40% to 60% when at.

Referring to FIG. 2, the above-described Mahzender structure is disposed inside the splitter chip 30, and a block array is coupled to the splitter chip 30. The block array includes a first optical fiber array block 40 and a second optical fiber array block 50 which are respectively coupled to both ends of the splitter chip 30.

The first optical fiber array block 40 includes a first optical fiber 41 and a second optical fiber 42 connected to an input terminal 11 of the first waveguide and an input terminal 21 of the second waveguide, respectively. It is composed. Specifically, referring to FIG. 5, the first optical fiber array block 40 is manufactured by placing the first optical fiber 41 and the second optical fiber 42 in a V groove and curing the resin using a UV curing resin.

The second optical fiber array block 50 includes a third optical fiber 51 and a fourth optical fiber 52 connected to an output terminal 12 of the first waveguide and an output terminal 22 of the second waveguide, respectively. It is composed. In detail, the second optical fiber array block 50 also holds the third optical fiber 51 and the fourth optical fiber 52 in the V-groove similarly to the first optical fiber array block 40 and is cured using a UV curing resin. By doing so, the second optical fiber array block 50 is produced.

In the broadband optical splitter 100 and the optical tomography imaging apparatus using the same, the light source 210 is provided to the input terminal 11 of the first waveguide. Of course, the light source 210 may be provided to the input terminal 21 of the second waveguide. In the present embodiment, the input terminal 21 of the second waveguide serves as a deductor terminal to which the spectrometer 240 is connected (see FIG. 11).

FIG. 2 illustrates a state in which the splitter chip 30 having the waveguide coupled to the Mahzender structure and the first and second optical fiber array blocks 40 and 50 are packaged.

Broadband optical splitter 100 according to the embodiment of the present invention according to the above configuration provides a constant light distribution ratio (coupling ratio) in the wavelength range of the broadband. The optical distribution ratio is distributed to the output end 12 of the first waveguide and the output end 22 of the second waveguide while the light source 210 entering the input terminal 11 of the first waveguide passes through the Mahzender structure of the optical splitter. It refers to the ratio, and means that the divided light proceeds by being divided into the reference stage 220 and the sample stage 230.

Accordingly, the broadband optical splitter 100 according to the embodiment of the present invention provides a constant light distribution ratio in a wide wavelength range, even though the wavelength range of the light applied to the first waveguide 10 is wide. It means that it provides a light splitter that can be uniformly distributed light to the sample stage 230. Therefore, it provides an effect that can use the wavelength of various bands at the same time.

Specifically, referring to Figures 6 to 10 as follows. 6 to 8 are graphs showing the distribution ratio of light by the broadband optical splitter 100 according to the embodiment of the present invention, and FIGS. 9 and 10 are graphs showing the distribution ratio of light by the conventional optical splitter.

6 to 8, it can be seen that the broadband optical splitter 100 according to the embodiment of the present invention provides a constant light distribution ratio from 640 nm to 1100 nm. On the other hand, referring to Figures 9 and 10, the conventional optical splitter has 633nm as the center wavelength, has a constant distribution ratio (about 40 ~ 60%) in the range of about 20nm. For example, it can be seen that coupling (distribution) does not occur in the 840 nm band.

The fact that the coupling does not occur is that the light entering the first waveguide 10 is not distributed through the optical splitter, but proceeds only to the reference end 220 or the sample end 230 so that an interference fringe cannot be obtained. The image may not be acquired by the spectrometer 240.

On the other hand, according to another aspect of the present invention, there is provided an optical tomography imaging apparatus capable of securing an image of a multi-wavelength band using a wideband optical splitter.

In the optical tomography imaging apparatus capable of securing an image of a multi-wavelength band using a wideband optical splitter according to the present embodiment, the above-described wideband optical splitter 100, a light source 210, a reference stage 220, a sample stage 230, Spectrometer 240, frame grabber 250, and computer 260.

The configuration of the broadband optical splitter 100 is described in detail above, and thus a detailed description thereof will be omitted.

The light source 210 provides light to the broadband optical splitter 100. The light source 210 is provided to the first waveguide 10 side of the broadband optical splitter 100. In the present embodiment, the light source 210 may provide light in the visible light band or the near infrared band.

In addition, the light source 210 may sequentially provide light having two or more different wavelengths selected from the visible light band and the near infrared band.

That is, the optical tomography imaging apparatus according to the embodiment of the present invention can acquire an image using a single optical splitter in a wide wavelength band, and further, by sequentially providing a plurality of wavelengths having different wavelengths for each wavelength. It will provide an effect to acquire an image.

Referring to FIG. 11, the optical tomography imaging apparatus according to the present exemplary embodiment provides the light source 210 with the light sources 210 having wavelengths of 630 nm, 840 nm, and 930 nm to the wideband optical splitter 100 in order. The figure is shown.

The light source 210 is distributed (coupled) through the mahenter structure of the broadband optical splitter 100 and distributed to the first light source 211 and the second light source 212.

The reference stage 220 includes a reflective mirror 221 and the first light source 211 is reflected by the reflective mirror 221. The sample stage 230 is where the sample 231 is placed, and the second light source 212 is reflected by the sample 231. The configuration of the reference stage 220 and the sample stage 230 employs a configuration of a general optical tomography imaging apparatus, and thus, detailed description thereof will be omitted.

The first light source 211 and the second light source 212 reflected from the reference stage 220 and the sample stage 230 pass through the broadband light splitter 100 again, wherein the first and second light sources 211 and 212 ) Are combined with each other.

That is, when the light source 210 is provided to the first waveguide 10 side, the light source 210 is distributed to the first and second light sources 211 and 212 while passing through the Mahzander structure, and proceeds to the reference end 220 and the sample end 230. The first and second light sources 211 and 212 reflected by the reference terminal 220 and the sample terminal 230 are coupled to each other while passing through the mahzen structure of the broadband optical splitter 100 and move toward the second waveguide 20. (A arrow direction).

The spectrometer 240 has an interference fringe signal when the first light source 211 and the second light source 212 reflected by the reference stage 220 and the sample stage 230 form an interference fringe by a path difference. Acquire it. When two or more different wavelengths are provided to the light source 210, the spectrometer 240 may include a plurality of gratings 241 for dividing the two or more different wavelengths by wavelength.

In the present embodiment, the spectrometer 240 is composed of a collimator, a lens, wavelength grating 241, a line CCD camera. In the present embodiment, the grating 241 is sequentially disposed wavelength-specific grating 241 having a wavelength of 680nm, 840nm, 930nm corresponding to the light source 210 described above. Since the configuration of the spectrometer 240 is based on a known configuration, a detailed description thereof will be omitted.

The interference fringe signal obtained by the spectrometer 240 is transmitted to the computer 260 by the frame grabber 250. The computer 260 receives the interference fringe signal, obtains depth information of the sample 231 through an inverse fast Fourier transform, and obtains a 2D image using the sample. The sample 231 may be obtained using the 2D scanner. Scanning the area of) produces a 3D image.

12 is an image of samples 231 obtained using an optical tomography imaging apparatus according to the present invention. Specifically, the upper three images are 3D images of a human finger fingerprint, and the lower three images are 3D images of the little finger.

It can be seen that the resolution of each wavelength of 680 nm, 840 nm, and 930 nm provided sequentially differs in depth, and that the acquired image of each wavelength remains different. For example, in the case of 930 nm, the image of the vein 3 of the little finger can be obtained. By obtaining different image information for each depth in the downward direction of the surface of the sample 231 such as a human fingerprint or a little finger, sample 231 information regarding various wavelengths may be usefully acquired at the same time.

As such, the broadband optical splitter 100 according to the present invention operates in a single mode in the wavelength range of the visible light band to the near infrared band, can provide a relatively constant distribution ratio of light, and mass production is possible based on the optical fiber. It is expected to be widely applied to optical tomography systems. Such broadband optical splitter 100 has not been studied worldwide yet.

In addition, the optical tomography imaging apparatus using the broadband optical splitter according to the present invention takes full advantage of the broadband optical splitter 100 to easily acquire a sample 231 image in a wide wavelength region using a single optical splitter. In addition, by providing different wavelengths sequentially, it provides an effect that can implement the image for each wavelength at the same time.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, and many modifications may be made without departing from the scope of the present invention.

1 ... core 2 ... clad
3 ... Vein 4 ... Si Substrate
10 ... first waveguide 11 ... first waveguide input terminal
12 ... first waveguide output stage 20 ... second waveguide
21 ... second waveguide input stage 22 ... second waveguide output stage
30 ... splitter chip 40 ... first optical fiber array block
41 ... the first optical fiber 42 ... the second optical fiber
50 ... second optical fiber array block 51 ... third optical fiber
52 ... fourth optical fiber 100 ... broadband optical splitter
210 ... light source 211 ... first light source
212 ... first light source 220 ... reference stage
221 ... mirror mirror 230 ... sample stage
231 Sample 240 Spectrometer
241 ... Grating 250 ... Frame Grabber
260 ... Computer

Claims (6)

An optical splitter comprising a core providing first and second waveguides and a cladding surrounding the core,
When the refractive index of the core is n ₁ , the refractive index of the clad is n ₂ , and half of the core width is ρ,
kρ (n ₁ ² -n ₂ ² ) ^1/2 <π / 2 (where k = 2π / λ (λ is the wavelength of light))
Satisfied relationships,
When the first waveguide and the second waveguide are coupled in a first section and a second section, the length of the first section is L1, the length of the second section is L2, and the second section from the first section. When the optical path difference to ΔL is
420 µm ≤ L1 ≤ 480 µm,
750 µm ≤ L2 ≤ 850 µm,
0.6 μm ≦ ΔL ≦ 0.9 μm,
Satisfying the relationship
A first optical fiber array block in which first and second optical fibers are respectively connected to an input terminal of the first waveguide and an input terminal of the second waveguide; And
And a second optical fiber array block in which third and fourth optical fibers are connected to the output terminal of the first waveguide and the output terminal of the second waveguide, respectively. The method of claim 1,
And said first and second waveguides operate in a single mode in the wavelength range of visible light band to near infrared band. delete The broadband optical splitter according to claim 1 or 2;
A light source for providing light to the broadband optical splitter;
The light source is divided into a first light source and a second light source via the broadband light splitter, and a reference stage for reflecting the first light source by a reflection mirror;
A sample stage at which the second light source is reflected by a sample;
The first light source and the second light source reflected from the reference stage and the sample stage are combined again through the broadband optical splitter, and acquire an interference fringe signal formed by a path difference between the first and second light sources. Spectrometer;
A frame grabber for transmitting the interference fringe signal;
And a computer for receiving the interference fringe signal and converting the image into an image. 2. An optical tomography apparatus capable of securing an image of a multi-wavelength band using a wideband optical splitter. 5. The method of claim 4,
The light source is an optical tomography imaging device capable of securing an image of a multi-wavelength band using a broadband optical splitter, characterized in that to provide light in the visible light band to the near infrared band. 5. The method of claim 4,
The light source sequentially provides light having two or more different wavelengths selected from the visible light band to the near infrared band,
The spectrometer has a plurality of gratings for dividing the two or more different wavelengths for each wavelength, the optical tomography imaging device capable of securing an image of a multi-wavelength band using a wideband optical splitter.

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