CZ309415B6 - Composite optical fibre for holographic endoscopy - Google Patents

Abstract

A composite optical fibre for holographic endoscopy comprising a GRIN fibre (1) with a proximal end for connecting to an endoscopic instrument, and in addition an SI fibre (2) fixed by its proximal end to the distal end of the GRIN fibre (1) 0.1 to 10 mm, long better 150 µm to 2 mm, preferably 200 µm to 1 mm.

Description

Composite optical fiber for holographic endoscopy

Field of technology

The invention relates to a composite optical fiber for use in holographic multimodal endoscopy, an endoscopic probe containing this composite optical fiber and an endoscopic device containing this endoscopic probe.

Current state of the art

Holographic multimodal endoscopy enables the acquisition of high-resolution optical images of structures deep within sensitive tissue (eg, the brain) of living animal models and humans via a minimally invasive optical fiber, with fibers typically 100 µm in diameter.

An important type of imaging in microscopy is coherent Raman scattering (CARS) imaging. This contrast mechanism enables imaging with chemical contrast of biologically important components - lipids, proteins, etc. In addition to the importance of lipid imaging, a particularly promising application appears to be the rapid in situ diagnosis of tumors, where CARS is one of the imaging methods used, often together, e.g. with two-photon fluorescence (TPEF) and with second harmonic generation (SHG) imaging.

A disadvantage is that when using optical fibers, including multimode (multimode) fibers, in endoscopes for CARS imaging, a signal is generated in the fiber itself due to four-wave mixing (FWM) and other nonlinear processes, especially when femtosecond excitation sources are used. This background results in a significant reduction in contrast in images. The background signal is strong in single-mode fibers, where all the light is concentrated in a region of a few micrometers in diameter, and in gradient multimode fibers (GRIN-type fibers), where the self-imaging property of the fiber leads to the formation of narrow foci inside the fiber (in both cases, the intensity is high , and FWM is so effective).

The background spectrally overlaps with the CARS signal generated in the sample, so it cannot be filtered out when the same fiber (either single-mode or multi-mode) is used for both excitation and detection. The background cannot even be measured and then subtracted for two reasons:

a) The background and CARS signal of the sample are both coherent and the detected signal is the interference between them

b) For tissue imaging, the generated signal is backscattered within the tissue, and the background signal level detected would thus be significantly affected by the scattering properties of the tissue and thus vary with position in the sample.

The essence of the invention

Disadvantages of the prior art are eliminated by a composite optical fiber for holographic endoscopy, which contains a GRIN fiber, which has a proximal end for connection with an endoscopic device, contains an SI fiber, which is fixed with its proximal end to the distal end of the GRIN fiber, and which has a length of 0.1 up to 10 mm, preferably 150 pm to 2 mm, preferably 200 pm to 1 mm.

Advantageously, the GRIN fiber has a length of at least 10 mm, preferably at least 20 mm.

The SI fiber is attached to the GRIN fiber preferably coaxially.

- 1 CZ 309415 B6

It is also preferred that the GRIN fiber has an outer diameter of 0.05 mm to 2 mm and a core diameter of 0.02 mm to 1.9 mm, and/or that the SI fiber has an outer diameter of 0.05 mm to 2 mm and a core diameter of 0 .02mm to 1.9mm.

Disadvantages of the prior art are also eliminated by an endoscopic probe for holographic endoscopy, which includes a connector for connecting to an endoscopic device, and the above-described composite optical fiber, the proximal end of which is connected to a connector for connecting to an endoscopic device.

The disadvantages of the prior art are also eliminated by an endoscopic device for holographic endoscopy, which contains:

- a femtosecond source of laser radiation adapted to transmit a Stokes beam and a pumping beam,

- a spatial light modulator, arranged in the path of the Stokes beam and the pump beam emitted from the femtosecond laser radiation source,

- a module for correcting the polarization of light, arranged in the path of the beam supplied from the spatial light modulator,

- a first focusing lens arranged in the path of the beam emerging from the light polarization correction module, and

- the above-mentioned composite optical fiber, which has its proximal end facing the first focusing lens for the input of the beam focused by the first focusing lens into the composite optical fiber.

Advantageously, the endoscopic device includes a second dichroic mirror arranged in the path of the beam emerging from the light polarization correction module between the light polarization module and the first focusing lens and a third dichroic mirror, the second dichroic mirror being arranged to reflect back-reflected radiation from the tissue through the composite optical fiber to the third dichroic mirror.

Advantageously, this endoscopic device additionally includes:

- a photomultiplier for the detection of two-photon epi-fluorescence excitation, which is arranged in the path of the beam reflected from the third dichroic mirror, and

- a photomultiplier for the detection of coherent Raman scattering, which is arranged in the path of the beam passing through the third dichroic mirror.

Advantageously, a prism arranged in the path of the beam fed from the light polarization correction module is also included between the light polarization correction module and the second dichroic mirror.

It is also advantageous if the endoscopic device includes a calibration module for calibrating the endoscopic device by focusing the beams fed into the composite optical fiber to the region in front of the distal end of the composite optical fiber.

-2CZ 309415 B6

Clarification of drawings

The invention is further described on the basis of exemplary embodiments and drawings, where Fig. 1 schematically shows a conventional gradient multimode fiber and the generated background when used as an endoscopic probe, Fig. 2 schematically shows a composite optical fiber according to the invention and the generated background, Fig. 3 is a comparison of the images obtained with the GRIN fiber alone and with the composite optical fiber according to the invention, both of the background alone without samples and with samples, in this case a 2 μm polystyrene ball, and Fig. 4 shows a simplified diagram of the endoscopic device with the composite optical fiber according to the invention.

Examples of implementation of the invention

Gradient multimode optical fibers are fibers in which the refractive index decreases with distance from the fiber axis.

Fig. 1 schematically shows a conventional gradient multimode fiber, i.e. GRIN fiber 1, for use in endoscopy and the background obtained from it, where high intensity foci are clearly visible inside the fiber, produced as images of the excitation point behind the distal end of GRIN fiber 1 generated due to self-imaging properties of a gradient fiber. When imaging the sample with GRIN fiber 1, a focused spot is created in the sample in front of the distal end of GRIN fiber 1. Due to the self-imaging property of GRIN fiber 1, not only this intense focused point but also its images formed inside the fiber will appear in the resulting image.

Fig. 2 schematically shows a composite optical fiber according to the invention, which includes a GRIN fiber 1, which has a proximal end intended for connection to an endoscopic device and a distal end, to which an SI fiber 2, i.e. a fiber with a step index, is fixed coaxially with its proximal face quarry.

At the same time, the distal end of the composite optical fiber is designed to be inserted into the examined sample.

In an exemplary embodiment, GRIN fiber 1 has a length of 30 mm, an outer diameter of 125 μm, a core diameter of 62.5 μm, a numerical aperture of NA = 0.3, and both faces are planar. The core of the GRIN fiber 1 can be, for example, germanium-doped quartz glass and the shell of pure, or fluorine-doped, quartz glass.

In general, GRIN fibers 1 having a length of at least 10 mm, preferably at least 15 mm, preferably at least 20 mm, can be used for this invention. Preferably, the length of the GRIN fiber 1 is shorter than 100 mm, its outer diameter is preferably in the range of 50 μm to 2 mm and the core diameter in the range of 20 μm to 1.9 mm, preferably 40 to 200 μm.

In the given exemplary embodiment, SI fiber 2 has a length of 250 μm, an outer diameter of 110 μm, a core diameter of 100 μm, a numerical aperture NA = 0.37, and both faces are planar. The core can be, for example, germanium-doped quartz glass and the cladding fluorine-doped quartz glass (for example, CeramOptec Optran Ultra WFGE fiber).

Generally, SI fibers 2 having a length of 0.1 to 10 mm, more preferably 150 μm to 2 mm, most preferably 200 μm to 1 mm, an outer diameter in the range of 50 μm to 2 mm, and a core diameter in the range of 20 μm can be used for this invention. up to 1.9 mm, better 40 to 200 μm. Suitable materials for SI fiber 2 also include soft glasses or plastics.

Fibers 1, 2 are preferably welded to each other.

Due to the construction of the composite optical fiber according to the invention, self-imaging fields are prevented from forming narrow foci within the composite optical fiber. In principle, if the fields at the output end of GRIN fiber 1 were to form a random speckle pattern, the foci that are created anyway via the self-imaging effect would be broken up into speckles of orders of magnitude lower intensity.

To achieve this effect, the composite optical fiber according to the invention consists of a relatively long GRIN fiber 1, so that the probe bandwidth is sufficient to focus the femtosecond pulses, and a relatively short SI fiber 2 welded at the distal end.

The background is thus reduced by one order of magnitude when using an endoscopic probe containing such a composite optical fiber without increasing the diameter of the endoscopic probe and without fundamentally reducing the focusing ability of the endoscopic probe.

The composite optical fiber endoscopic probe of the invention retains all other properties of the probe containing the GRIN fiber itself: lateral and axial size of the focused spot, the ratio of focused spot intensity to background intensity, and the range in which the wavelength can be set after initial calibration. Furthermore, since the attached SI fiber 2 has only a small effect on the dispersion of the composite optical fiber, the spectral resolution or chemical contrast of the so-called "spectrally focused" CARS (required when using femtosecond pulses) is not affected. Since the dispersion is the same for all points within the field of view, conventional pulse shaping means can be used to keep the pulse short, resulting in efficient excitation of TPEF, SHG and other signals. Therefore, all imaging methods using femtosecond lasers used for optical biopsy are supported.

For use in endoscopy, this composite optical fiber is preferably glued by the proximal end of the GRIN fiber 1 to a ferrule (not shown), which is adapted to be fixed in the respective holder of the endoscopy device.

An exemplary embodiment of the entire endoscopic device shown schematically in Fig. 5, especially from the point of view of its function, contains a femtosecond source 3 of laser radiation, representing an excitation source that is adapted to generate two synchronized sequences of pulses with different wavelengths, specifically a beam with a wavelength of 1040 nm as a Stokes beam, and a tunable beam in the 800 nm region as a pumping beam.

In the path of the Stokes beam, the first block 31 of SF57 type glass is arranged in this exemplary embodiment with a thickness of 220 mm and behind it the first corner reflector 33 for adjusting the delay of the Stokes beam. A first auxiliary mirror 34 is arranged in the path of the beam reflected from the first corner reflector 33.

In the path of the pumping beam, a second block 32 of SF57 type glass is arranged in this exemplary embodiment with a thickness of 220 mm, and behind it is arranged a first dichroic mirror 35 for reflecting the pumping beam onto the second auxiliary mirror 36. At the same time, the first dichroic mirror 35 is arranged in the path of the Stokes beam, which after its reflection from the first auxiliary mirror 34 passes through this first dichroic mirror 35.

In the path of the overlapping beams in this way, a second auxiliary mirror 36 is arranged behind the first dichroic mirror 35, and in their path, after reflection from the second auxiliary mirror 36, the first connecting lens 37 and behind it the first collimating lens 38 and behind it the phase spatial modulator 39 of the light on based on liquid crystals.

In the path of the light reflected from the spatial modulator 39, a second connecting lens 80 is then arranged and behind it a deflecting mirror 41 to collect part of the radiation, which is further guided as a reference beam through the slit in the first diaphragm 43 for use in the calibration module 50, as described below .

-4CZ 309415 B6

In the path of the light that passed through the second converging lens 80, a directional mirror 21 of the first set of directional mirrors 21 is arranged, which brings the first working part of the light beam that passed through the second converging lens 80 through the third collimating lens 84 to the module 20 for correcting the polarization of light from its one side, where it passes through the first half-wave plate 82 into the polarization divider 83.

In the path of the light that passed through the second converging lens 80, a directional mirror 22 of the second set of directional mirrors 22 is additionally arranged, which brings the second working part of the light beam that passed through the second converging lens 80 through the fourth collimating lens 81 to the module 20 for correcting the polarization of light from the other side where it passes through the second half-wave plate 84 to the polarization splitter 83 where the first working part of the beam and the second working part of the beam merge and together exit the light polarization module 20.

In the path of the beam coming out of the module 20 for polarizing light, i.e. the beam composed of the beam reflected from the polarizing divider 83 and the beam passed through the polarizing divider 83, a seventh auxiliary mirror 86 is arranged, followed by a prism 87, the plane of which is associated with the plane of the spatial light modulator 39 .

In the path of the beam emerging from the prism 87, there is already a second dichroic mirror 62, behind it the first focusing lens 64 and behind it the composite optical fiber according to the invention, i.e. the GRIN fiber 1 turned with its proximal end and the SI fiber 2 welded to its distal end for insertion into examined tissues 10.

A third dichroic mirror 63 is arranged in the path of the beam of light returning through the composite optical fiber, through the first focusing lens 64 and subsequently reflected from the second dichroic mirror 62.

In the path of the partial beam reflected from the third dichroic mirror 63, a second connecting lens 65 is arranged, behind it a first filter 66 and behind it a photomultiplier 68 for the detection of two-photon epi-fluorescence excitation (epi-TPEF).

A third auxiliary mirror 69 is arranged in the path of the partial beam that passed through the third dichroic mirror 63, and in the path of the beam reflected from it, a third connecting lens 70 is arranged, followed by a second filter 71 and behind it a photomultiplier 72 for the detection of coherent Raman scattering (epi-CARS ).

The drawing also shows the calibration module 50, which contains the second corner reflector 51, which is arranged in the path of the reference beam fed through the slit 43, further reflected from the fourth auxiliary mirror 42, through the second collimating lens 44 and successively reflected from the fifth auxiliary mirror 45, of the sixth auxiliary mirror 46 and the reflective rectangular prism 47.

In the calibration module 50, a non-polarizing splitter 52 is arranged in the path of the reference beam reflected from the second corner reflector 51, while a camera 53 is arranged in the path of the beam from the non-polarizing divider 52.

The calibration module 50 also includes a lens 54, which can be set to a position where the distal end of the SI fiber 2 of the composite optical fiber is facing it. On the other side, the fifth dichroic mirror 55 is turned towards it, while in the path of the beam that passed through this fifth dichroic mirror 55, a second focusing lens 56, a third filter 57 and a photomultiplier 58 are arranged for the detection of coherent Raman scattering in transmitted light (trans-CARS) .

An achromatic doublet 59 is arranged in the path of the beam reflected from the fifth dichroic mirror 55, followed by a non-polarizing splitter 52 and a camera 53. The camera 53 can be, for example, CMOS-based.

The calibration module 50 is removable from the endoscopic device.

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The shown endoscopic device further includes a stabilization module 90, which contains a second diaphragm 91, a polarizer 92, a fourth dichroic mirror 93 and a pair of photodiodes 94, 95, and these components are arranged in such a way that the beam reflected from the second dichroic mirror 62 passes through the slit of the second diaphragm 91, the polarizer 92 and the fourth dichroic mirror 93 divide it into two parts, each of which falls on one of the photodiodes 94. 95.

During the operation of the endoscopic device, a Stokes beam and a pumping beam are generated using the femtosecond laser 3, which are overlapped with each other with an adjustable delay and brought to the spatial light modulator 20. 4 beams emerge from the spatial light modulator:

- the so-called zero diffraction order in the direction of direct reflection, which is not used and is not even shown in the drawing,

- reference volume used in calibration,

- two work volumes.

All four beams pass through the second converging lens 80. which allows them to be separated in its focal plane.

The zero-order beam and the reference beam are reflected from the deflecting mirror 41. The reference beam passes through a slit in the first aperture 43. The unwanted zero-order beam is filtered out by this slit.

A pair of working beams is fed to the module 20 for correcting the polarization of light, where the polarization of the working beams is rotated by means of half-wave plates 82, 85 and they are combined by means of a polarization splitter 83 of the beam.

To measure and stabilize the relative phase between a pair of optical paths during imaging, part of the beam is taken and fed to the stabilization module 90, where it passes through a polarizer 92 with axes oriented at an angle of 45° and is subsequently divided by the fourth dichroic mirror 93 into a part corresponding to the Stokes beam and a part corresponding to pumping bundle and these parts are sensed by photodiodes 94, 95.

Since the holograms produced on the light polarization module 20 are in the form of sums of diffraction gratings, the phase modulation is wavelength dependent. To tune the wavelength of the source 3 of laser radiation while maintaining the quality of focus, a prism located in the plane coupled with the plane of the module 20 for polarizing light is used.

During imaging, the CARS signals and TPEF signals obtained from the composite optical fiber by back reflection from the examined tissue 10 are reflected from the second dichroic mirror 62 to the third dichroic mirror 63, where they are divided into a signal fed to a photomultiplier 68 for detection of two-photon epi-fluorescence excitation and a signal fed to photomultiplier 72 to detect coherent Raman scattering.

For calibration, the light supplied from the composite optical fiber, after passing through the objective 54, is reflected from the fifth dichroic mirror 55 and passes through the achromatic doublet 59 and the non-polarizing splitter 52 to the camera 53, and the purpose of calibration is to focus the working parts of the beam in the area in front of the distal end of the composite optical fiber.

After calibration, the light supplied from the composite optical fiber, after passing through the objective 54 and the fifth dichroic mirror 55, is guided through the second focusing lens 56 and the third filter 57 to the photomultiplier 58.

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The composite optical fiber described above is particularly useful as an endoscopic probe for optical biopsy in sensitive tissue, such as brain tissue. Using such a composite optical fiber, for example, multimodal imaging can be performed, in which myelin in the white matter is imaged using coherent Raman scattering and cerebellar fibers with green fluorescent protein expression using two-photon fluorescence.

Although a particularly advantageous exemplary embodiment and a number of its possible modifications and changes have been described, it is clear that a person skilled in the art will easily find other possible alternatives to these embodiments. In particular, the auxiliary mirrors do not have to be present at all and serve only to route the beams to the 10 functional components. Therefore, the scope of protection is not limited to these exemplary embodiments, but rather is given by the definition of the appended patent claims.

Claims (10)

PATENT CLAIMS 1. A composite optical fiber for holographic endoscopy comprising a GRIN fiber (1) having a proximal end for connection to an endoscopic device, characterized in that it comprises an SI fiber (2) which is fixed by its proximal end to the distal end of the GRIN fiber (1) and which has a length of 0.1 to 10 mm, preferably 150 pm to 2 mm, most preferably 200 pm to 1 mm. 2. Composite optical fiber according to claim 1, characterized in that the GRIN fiber (1) has a length of at least 10 mm, preferably at least 20 mm. 3. Composite optical fiber according to claim 1 or 2, characterized in that the SI fiber (2) is fixed to the GRIN fiber (1) coaxially. 4. Composite optical fiber according to any one of claims 1 to 3, characterized in that the GRIN fiber (1) has an outer diameter of 0.05 mm to 2 mm and a core diameter of 0.02 mm to 1.9 mm, and/or SI the fiber (2) has an outer diameter of 0.05 mm to 2 mm and a core diameter of 0.02 mm to 1.9 mm. 5. An endoscopic probe for holographic endoscopy, which includes a connector for connecting to an endoscopic device, characterized in that it contains a composite optical fiber according to any one of claims 1 to 4, the proximal end of which is connected to a connector for connecting to an endoscopic device. 6. Endoscopic device for holographic endoscopy, characterized in that it contains - a femtosecond source (3) of laser radiation adapted to transmit a Stokes beam and a pumping beam, - a spatial modulator (39) of light, arranged in the path of the Stokes beam and the pumping beam emitted from the femtosecond source (3) of laser radiation, - module (20) for correcting the polarization of light, arranged in the path of the beam supplied from the spatial light modulator (39), - a first focusing lens (64) arranged in the path of the beam emerging from the module (20) for correcting the polarization of light, and - a composite optical fiber according to any one of claims 1 to 4, which has its proximal end facing the first focusing lens (64) for the input of the beam focused by the first focusing lens (64) into the composite optical fiber. 7. Endoscopic device according to claim 6, characterized in that it contains a second dichroic mirror (62) arranged in the path of the beam emerging from the module (20) for correcting the polarization of light between the module (20) for polarizing light and the first focusing lens (64) and a third dichroic mirror (63), wherein the second dichroic mirror (62) is arranged to reflect back-reflected radiation from the tissue (10) through the composite optical fiber onto the third dichroic mirror (63). 8. Endoscopic device according to claim 7, characterized in that it contains - a photomultiplier (68) for detecting two-photon epi-fluorescence excitation, which is arranged in the path of the beam reflected from the third dichroic mirror (63), and - a photomultiplier (72) for detecting coherent Raman scattering, which is arranged in the path of the beam passing through the third dichroic mirror (63). 9. Endoscopic device according to claim 7 or 8, characterized in that it contains a prism (87) arranged in the path of the beam supplied from the module (20) for correcting the polarization of light between the module (20) for correcting the polarization of light and the second dichroic mirror (62) . -8 CZ 309415 B6 10. An endoscopic device according to claim 7 or 8 or 9, characterized in that it contains a calibration module (50) for calibrating the endoscopic device by focusing the beams fed into the composite optical fiber to the region in front of the distal end of the composite optical fiber. 3 drawings