AU2020100986A4

AU2020100986A4 - A BSWs nano-microscopic imaging device based on coaxial dual-waveguide fiber

Info

Publication number: AU2020100986A4
Application number: AU2020100986A
Authority: AU
Inventors: Jingkai JI; Libo Yuan
Original assignee: Guilin University of Electronic Technology
Current assignee: Guilin University of Electronic Technology
Priority date: 2020-06-11
Filing date: 2020-06-11
Publication date: 2020-07-16
Anticipated expiration: 2028-06-11

Abstract

The invention provides a Bloch Surface Waves (BSWs) nano-microscopic imaging device based on coaxial dual-waveguide fiber (CDF). Its characteristics are: it consists of a CDF 1, a CDF Coupler 2, a camera 3, a computer 4, a light source 5 and a fiber 6. A sufficiently large wave vector can excite the surface of the multi-layer dielectric film base to produce BSWs, which is very sensitive to environmental changes. Using the annular core 1-2 of the CDF to have the laser excite the BSWs to interact with the sample, eliminating the trailing of the BSWs on the sample. Simultaneously, using the middle core of the CDF to collect scattered light, and process via the camera to obtain a high signal-to-noise ratio and high resolution imaging. The invention uses special fibers that effectively reduce costs and optimize structure, achieving portable high signal to-noise ratio and high-resolution micro-nano-microscopic imaging. 1/4 DRAWINGS 4F computer camera light source 5 FIG. 1 1-2 FIG. 2

Description

1/4 DRAWINGS

4F

computer

camera

light source 5

FIG. 1

1-2

FIG. 2

DESCRIPTION TITLE OF INVENTION

A BSWs nano-microscopic imaging device based on coaxial dual-waveguide fiber

TECHNICAL FIELD

[0001] The invention relates to a Bloch Surface Waves (BSWs) nano-microscopic imaging

device based on coaxial dual-waveguide fiber (CDF), which belongs to the field of optical fiber

microscopic imaging.

BACKGROUND ART

[0002] Optical microscopes are the most common and effective tool for scientific research in

optical detection. When using a conventional microscope, the minimum distance between two

objects that can be clearly distinguished depends on the limits of the microscope. In order to

better observe the microscopic world, researchers are dedicated to develop various methods to

improve resolution. Ultra-resolution imaging technology also continues to make breakthroughs,

typically represented by Confocal Microscopy, Excited Emission Depletion Microscopy (STED),

Photo Activation Localization Microscopy (PALM) and etc. It is worth noting that the optical

paths used in all of the ultra-resolution imaging techniques here are far-field leak radiation

imaging systems.

[0003] Fluorescence detection is an important tool in the biological sciences. Surface binding

techniques capturing antibodies DNA oligomers or target molecules and etc. are often used in

clinical diagnostics and DNA analysis. For example, "In situ single-molecule imaging with

attoliter detection using objective total internal refection confocal microscopy" and "Eyen

illumination in total internal refection fluorescence microscopy using laser light" propose a total

internal reflection (TIR) generated evanescent waves that can be used for light field surface

imaging. Using TIR method to measure, the incident light needs to be greater than the critical

angle to incident, exciting the evanescent field, the longitudinal penetration depth of the

evanescent field is about 100nm, which is a kind of local electromagnetic field. This local

electromagnetic field allows selective observation of biomolecules on the sample surface, and

this technique is critical in optical fields such as cellular and molecular biology. Using TIR

illumination can selectively image the sample surface, minimizing the phase background signal

and improving the signal-to-noise ratio (SNR).

[0004] Many methods based on surface signal detection fail to collect fluorescent signals that are

weakly bound to the surface. However, for many types of biological imaging experiments, the

detection of the sample's phase radiation signal can also provide a useful signal, thus requiring

both measurement of fluorescence signals in tightly bound molecules and measurement of phase

target molecular signals. In these cases, selectively exciting surface or phase target molecules is

very useful. Surface binding fluorescence signal measurements allow the phase signals to be

minimally collected, thus saving the step of washing away unbound fluorophores. However, TIR

has difficulty in obtaining the long evanescent depth of the electromagnetic field, so it is difficult

to detect the phase signal. Fluorescence microscope is a typical means of wide-field illumination

or phase imaging away from glass substrate surface. Surface or phase imaging can be achieved

using total internal refection fluorescence (TIRFM) and fluorescence microscope, respectively;

however, it is difficult to achieve simultaneous bursts of both types of imaging. Simultaneously

achieving the switching between the two imaging technologies requires precise mechanical

alignment, which is difficult to perform in practice.

[0005] The emergence of surface wave microscopy solves the above difficulty, surface wave microscopy is the use of surface waves, mainly the BSWs of metal and air cross-section, as an illumination light source, using its strong localization of propagation on the surface and high sensitivity to the perturbation at the interface, to achieve high-sensitivity imaging of surface samples near the metal film layer. Chinese patent CN103837499A proposes a micro-zone spectroscopic measurement device based on broadband surface plasma wave, mainly using high numerical aperture microscope and broadband radially polarized light or radially polarized white light to construct the spectroscopic measurement device. High spatial resolution can be obtained based on this device. Chinese patent CN105628655A proposes an optical microscope based on BSWs with a high resolution and without fluorescence labeling, which excites plasma surface resonance on a plasma resonance sensing chip, thereby obtaining a high spatial resolution. The main microscopic techniques mentioned above have significant limitations in their practical applications, the problems being:

[0006] 1. Poor SNR. During the traditional surface wave microscopic imaging, the surface wave of the excitement field and the scattered surface wave of the sample will interfere with each other, and a strong trailing will be formed along one side of the excitement direction of the sample, the trailing length is equal to the decay length of the surface wave along the surface, and the signal of the trailing and the sample scattered signal will be leaked down and collected by the imaging system, significantly reducing the imaging SNR.

[0007] 2. Poor spatial resolution. Also due to the trailing, when imaging actual samples with boundaries by the traditional surface wave imaging system, streaky trailing is produced at the boundaries, which significantly reduces the resolution.

[0008] 3. Poor temporal resolution. The surface wave imaging system developed in recent years, in order to improve the resolution, often requires multi-length multi-angle acquisition of images, and then use the algorithm to eliminate the imaging trailing to improve the resolution. The problem posed is that each microscopic image takes a lot of time to obtain, and the temporal resolution is poor, making it impossible to make real-time observations.

[0009] 4. A single, costly working environment. Traditional surface wave imaging systems use

only one type of base, the metal film, as an imaging base, has special requirements for the

working environment. It cannot work in water, is also prone to oxidation, cannot be reused and is

costly.

[0010] Chinese patent CN109239020A proposes a surface wave imaging system based on rotary

illumination, which eliminates the trailing of the surface wave after it acts on the sample through

a galvanom scanning system, and improves the SNR and resolution of surface wave microscopy

imaging. However, devices used are of various types and large volume, which makes it heavy

and inconvenient.

[0011] Single-fiber imaging uses one multi-mode fiber for imaging, which is both an imaging

device and a transmitting device, allowing a scene within the field of view of one part of the

fiber to be transmitted to the other end at once without the need for additional scanning devices

and imaging lenses, and belongs to a wide-field fiber imaging technology. After nearly 10 years

of development, single fiber imaging technology has made great progress in imaging

mechanism, imaging quality and applied research, but there are still many deficiencies in the

imaging speed and resolution.

[0012] The invention discloses a BSWs nano-microscopic imaging device based on CDF.

Overcoming the deficiencies of traditional surface wave imaging microscopy with low SNR,

poor temporal and spatial resolution and high cost. It uses a CDF, which uses BSWs waves to

acquire high resolution and high SNR scattering signals, and in the meantime uses fiber imaging

to acquire images. The simulation of BSWs and acquisition of image signal uses the same fiber.

High-quality images can be obtained and portable microscopic detection imaging can be

achieved.

SUMMARY OF INVENTION

[0013] The purpose of the invention is to provide a surface-enhanced nano-microscopic assistant

device with a simple structure, good stability, low cost and easy assembly, which enables real

time observation of non-fixed surface samples, obtaining high SNR and high resolution imaging

of surface samples based on a CDF BSWs nano-microscopic imaging device.

[0014] The purpose of the invention is achieved as follows:

[0015] A BSWs nano-microscopic imaging device based on CDF, it consists of a CDF 1, a CDF

Coupler 2, a camera 3, a computer 4, a light source 5 and a fiber 6. Its characteristics are: the

light emitted by the light source 5 passes through the CDF-Coupler 2 via a beam of the fiber 6,

enters the annular core 1-2 of the CDF 1, after the micromachining of the fiber end so that the

linearly polarized light and the multi-layer dielectric film base of the fiber taper circular table

end can be at a specific angle, the angle can be calculated based on known parameters. The laser

passes through the annular core 1-2 of the CDF 1 to form a beam of light illumination sample

with a specific incidence angle, which has a large enough wave vector to effectively excite the

existing BSWs in the surface multi-layer dielectric film base. When the BSWs propagate through

the sample, it emits scattered signal light and surface trailing. The laser is incident by the annular

core 1-2 of the CDF 1 and excites the BSWs in 360 degrees, which can effectively eliminate

surface trailing. The scattered light is collected by the middle core 1-1 of the CDF 1 connected to

the camera 3, and an interferogram is formed on the camera 3 with another beam of light from

the light source. The computer 4 using an off-axis digital holographic algorithm to restore the

image on computer by using the value and the phase of the image extracted from the fiber, so that high resolution and contrast surface wave microscopic imaging can be achieved.

[0016] The annular core 1-2 of the CDF 1 is an optical fiber with a symmetrical circular waveguide along the axis and has a large core diameter fiber core in the middle. As shown in FIG. 2, 1-2 is the annular core of the CDF, 1-1 is the middle core of the CDF. This middle core has a larger diameter and scatters signal light that will contain the image information in the light field. Information including intensity distribution, phase distribution and beam wavefront and etc. is input into the computer 4 by the camera 3 and the image is transformed by processing.

[0017] The imaging method of the BSWs nano-microscopic imaging device based on CDF uses the principle of single multi-mode fiber imaging. The principle of single multi-mode optical fiber imaging is described in details in the literature "Scanner-Free and Wide-Field Endoscopic Imaging by Using a Single Multimode Optical Fiber". As shown in FIG. 7, the laser emits a laser to split the light in two, then uses a reflector to reflect the transmitted light and coupled to the optical fiber via the reflector BS2, then the other end of the fiber is the plane to be measured OP, illuminates the target object. Then the light collected by the fiber returns to the IP and enters the camera, and is combined with the light reflected into the camera via BS3 by the B Ibeam to form an interference image in the camera. The off-axis digital holographic algorithm is used to extract the value and phase of the image from the fiber to restore the image on the computer.

[0018] The imaging method of the BSWs nano-microscopic imaging device based on CDF is optimized and improved based on the single multi-mode fiber imaging described above. Using the CDF, which can replace the complex optical path in FIG. 7. The light source 5 divides the light into two beams via the fiber 6, one beam of light enters the annular core 1-2 of the CDF 1 via the CDF-Coupler 2, and the BSWs illumination sample is excited by converging at the other end of the CDF, and the scattered light passes through the middle core 1-1 of the CDF 1 via the CDF-Coupler, then passes through fiber 6 and form an interference image on the camera 6 with another beam of light from the light source 5, using an off-axis digital holography algorithm to extract the value and phase of the image from the fiber to restore the image on the computer.

[0019] The multi-layer dielectric film base is to plate the CDF end face with a multi-layer non

metallic dielectric, which is resistant to oxidative denaturation and can be repeatedly cleaned for

use.

[0020] The multi-layer dielectric film base can support the BSWs mode by processing a

nanoscale thickness film; by varying the refractive index and thickness of the individual layers it

can be designed to support multi-layer dielectric nano-films with different wavelengths and types

of BSWs modes (TE/TM) as imaging base. As shown in FIG. 4, through theoretical calculations

to obtain properties of the reflectance with the incident angel 0 of S wave and P wave BSWs, and

obtain the best incident angle with the best resonance effects. From FIG. 4, it can be seen that

both S wave and P wave can produce resonant effects that excite BSWs. The resonance peak

obtained for the incidence angle 0 chosen gives the best effect.

[0021] The CDF 1 used in the system, use the parameters of the multi-layer dielectric film base

and the known ambient refractive index, to obtain the relationship diagram of the BSWs

reflectance with the resonance angle, and the best incident angle is obtained. The CDF 1 with the

desired angle 0 at the end of the cone fiber is obtained by the micromachining process as shown

in FIG. 3.

[0022] The BSWs nano-microscopic imaging device based on CDF is an annular core 1-2

transmission light source of CDF 1 with an angle of 0. As shown in FIG. 5, the laser can excite

BSWs in 360 degrees surrounding the center, thereby eliminating the imaging surface trailing

caused by single direction of the BSWs enhanced effects, and eventually obtain high SNR and

high-resolution images.

[0023] The BSWs nano-microscopic imaging device based on CDF, wherein the scattering light enters the camera 3 by the middle core 1-1 of the CDF and is processed by the computer 4 to obtain high resolution and high SNR images.

[0024] The BSWs nano-microscopic imaging device based on CDF enables portable microscopic imaging.

BRIEF DESCRIPTION OF DRAWINGS

[0025] FIG. 1 is a schematic diagram of the BSWs nano-microscopic imaging device based on CDF, including a CDF 1, a CDF-Coupler 2, a camera 3, a computer 4 and a light source 5.

[0026] FIG. 2 is a cross-sectional view of a CDF, with 1-2 being the annular core of the CDF and 1-1 being the middle core of the CDF.

[0027] FIG. 3 is a diagram of the grinding process of the annular core 1-2 of the CDF 1, start grinding with FIG. (a), with the fiber and the grinding disc rotating simultaneously to ensure symmetry of the processed fiber; (b) is a diagram of the grinding process; (c) is a diagram of the effect of the finished grinding; and (d) is the definition of the fiber grinding angle.

[0028] FIG. 4 is a diagram of the BSWs energy reflectance in relation to the angle of the incident wave.

[0029] FIG. 5 is a schematic diagram of a 360-degree excited BSWs.

[0030] FIG. 6 is a schematic diagram of a CDF taper, 8 is a multi-layer dielectric film, and 7 is a small ball to be measured.

[0031] FIG. 7 is a schematic diagram of the principle of a single multi-mode fiber imaging.

DESCRIPTION OF EMBODIMENTS

[0032] The invention is further described below in conjunction with the drawings and specific embodiments.

[0033] FIG. 1 is a schematic diagram of the structure of a BSWs nano-microscopic imaging device based on CDF of the invention, the structure comprises a CDF 1, a CDF-Coupler 2, a camera 3, a computer 4, and a light source 5, wherein the end surface structure of the CDF 1 is shown in FIG. 2.

[0034] Embodiment 1:

[0035] Firstly, the multi-layer dielectric film base 1 is fabricated, and the glass plate is coated with 10 layers of alternating refractive index nano dielectric films with materials being Si02 and

Si3 N 4 . The thickness of each layer is 240nm, 88nm, 105nm, 88nm, 105nm, 88nm, 105nm, 88nm, 105nm, 88nm, 105nm, 88nm, 105nm and 88nm. From this film parameters, calculate the relationship between the BSWs and the angle of incident light as shown in FIG. 4, respectively showing the relationship diagram of S wave and P wave. The first resonant peak chosen has a corresponding angle of 42 degrees.

[0036] Using 42 degrees as the 0 angle, grind the CDF 1 as the method shown in FIG. 3 to obtain

a taper end with an angle of 0.

[0037] In the composition: the light emitted by the light source 5 passes through the CDF

Coupler 2 via a beam of the fiber 6, enters the annular core 1-2 of the CDF 1, after the

micromachining of the fiber end so that the linearly polarized light and the multi-layer dielectric

film base of the fiber taper circular table end can be at a specific angle, the angle can be

calculated based on known parameters. The laser passes through the annular core 1-2 of the CDF

1 to form a beam of light illumination sample with a specific incidence angle, which has a large

enough wave vector to effectively excite the existing BSWs in the multi-layer dielectric film

base. When the BSWs propagate through the sample, it emits scattered signal light and surface

trailing. The laser is incident by the annular core 1-2 of the CDF 1 and excites the BSWs in 360

degrees, which can effectively eliminate surface trailing. The scattered light is collected by the

middle core 1-1 of the CDF 1 connected to the camera 3, and an interferogram is formed on the

camera 3 with another beam of light from the light source. The computer 4 using an off-axis

digital holographic algorithm to restore the image on computer by using the value and the phase

of the image extracted from the fiber, so that high resolution and contrast surface wave

microscopic imaging can be achieved.

Claims

1. A Bloch Surface Waves (BSWs) nano-microscopic imaging device based on coaxial dual

waveguide fiber (CDF), it is characterized by: it consists of a CDF 1, a CDF-Coupler 2, a camera

3, a computer 4, a light source 5 and a fiber 6. In the composition: the light emitted by the light

source 5 passes through the CDF-Coupler 2 via a beam of the fiber 6, enters the annular core 1-2

of the CDF 1, after the micromachining of the fiber end so that the linearly polarized light and

the multi-layer dielectric film base of the fiber taper circular table end can be at a specific angle,

the angle can be calculated based on known parameters. The laser passes through the annular

core 1-2 of the CDF 1 to form a beam of light illumination sample with a specific incidence

angle, which has a large enough wave vector to effectively excite the existing the BSWs exist in

the multi-layer dielectric film base. When the BSWs propagate through the sample, it emits

scattered signal light and surface trailing. The laser is incident by the annular core 1-2 of the

CDF 1 and excites the BSWs in 360 degrees, which can effectively eliminate surface trailing.

The scattered light is collected by the middle core 1-1 of the CDF 1 connected to the camera 3,

and an interferogram is formed on the camera 3 with another beam of light from the light source.

The computer 4 using an off-axis digital holographic algorithm to restore the image on computer

by using the value and the phase of the image extracted from the fiber, so that high resolution

and contrast surface wave microscopic imaging can be achieved.

2. As claimed in claim 1, a BSWs nano-microscopic imaging device based on CDF, the CDF

1 used is an optical fiber with a symmetrical circular waveguide along the axis and has a large

core diameter fiber core in the middle.

3. As claimed in claim 1, a BSWs nano-microscopic imaging device based on CDF, its

characteristics are: by the use of the annular core 1-2 of the CDF 1 to transmit incident light,

which can simultaneously excite BSWs in 360 degrees, thereby eliminating the imaging surface

trailing caused by single direction excitement of the BSWs. Using the annular core 1-2 of the

CDF 1 to collect backscattered light, adopting the fiber imaging technology to obtain high

signal-to-noise ratio and high-resolution images.