WO2022165927A1

WO2022165927A1 - Scattering tapered-tip fiber optic probe used for exciting and collecting near-field optical signal and working method therefor

Info

Publication number: WO2022165927A1
Application number: PCT/CN2021/081043
Authority: WO
Inventors: 杨树明; 王飞; 李少博; 吉培瑞; 程碧瑶; 张国锋
Original assignee: 西安交通大学
Priority date: 2021-02-04
Filing date: 2021-03-16
Publication date: 2022-08-11
Also published as: CN112964908B; CN112964908A

Abstract

A scattering tapered-tip fiber optic probe used for exciting and collecting a near-field optical signal and a working method therefor. The probe comprises an optical fiber and a cone. The cone is provided on an end surface of an optical fiber core (1). A metal film (5) covers the surface of the cone. The diameter of the bottom surface of the cone is less than the diameter of the end surface of the optical fiber core (1). The area between the edge of the bottom surface of the cone and the edge of the end surface of the optical fiber core (1) is a light-transmitting area (9). The light-transmitting area (9) is present between the edge of the bottom surface of the cone and the edge of the end surface of the optical fiber core (1); therefore, a tip-scattered signal can be collected directly in a near field of a sample surface by using the light-transmitting area (9), thus increasing signal strength, reducing a large amount of far-field ambient noise, and increasing the signal-to-noise ratio. The probe also provides the functions of an atomic force microscopic probe, implements nanoscale ultra-high resolution measurements of the surface morphology and an optical image of a sample, overcomes the limits of optical diffraction, and is directly applicable in commercial near-field optical microscope testing.

Description

A scattering tapered tip optical fiber probe for exciting and collecting near-field optical signals and its working method

technical field

The invention belongs to the fields of near-field optical imaging, topography measurement and optical fiber waveguides on the surface of micro-nano structures, and relates to a scattering-type tapered tip optical fiber probe for exciting and collecting near-field optical signals and a working method thereof.

Background technique

The invention of the microscope opened the door to the microscopic world, and with the development of science, we realized that the optical diffraction limit can limit the highest resolution of optical microscopes. Therefore, breaking the optical diffraction limit has become the main direction of the development of a new generation of microscopes. In the next 100 years, the successive invention of a series of nanometer-scale high-resolution measurement equipment such as scanning probe microscopes and scanning electron microscopes allowed us to finally enter the field of nanometers. However, these non-optical measurement methods all have the disadvantage of damaging the sample, and of course they cannot obtain optical super-resolution images, so the near-field optical microscope came into being.

Near-field optical microscopy can detect in the optical near field of the sample, which is not limited by the optical diffraction limit, thus achieving nanometer-level measurement resolution. Commonly used near-field optical probes are mainly divided into porous probes and non-porous probes. For the hole probe, when the hole is too small, the light transmission of the small hole is too low, and the effective information is insufficient; and when the hole is too large, the measurement resolution will be reduced, so the current resolution of the hole probe For tens of nanometers, it is necessary to design new probes that effectively solve the above problems to improve the measurement resolution. For non-porous probes, the size of the probe tip determines the highest resolution of measurement, so currently non-porous probes can achieve high-resolution measurements of ten nanometers, but this method will have a lot of background noise, so it is necessary to Combining complex noise reduction methods to achieve better measurement results makes the measurement process cumbersome. The above problems about near-field optical microscopy are also the main problems in this field in recent decades, and no matter which problem is solved, it will bring great scientific development.

SUMMARY OF THE INVENTION

In order to solve the problems existing in the prior art, the purpose of the present invention is to provide a scattering tapered tip optical fiber probe for exciting and collecting near-field optical signals and a working method thereof. The present invention can excite near-field optical signals. The collection can also be realized, which greatly improves the signal-to-noise ratio.

The technical scheme adopted in the present invention is as follows:

A scattering-type tapered tip optical fiber probe for exciting and collecting near-field optical signals, comprising an optical fiber and a cone, the cone is arranged on the end face of the fiber core, and the surface of the cone is covered with a metal film, so the The diameter of the bottom surface of the cone is smaller than the diameter of the end surface of the optical fiber core, and the area between the bottom surface edge of the cone and the edge of the end surface of the optical fiber core is a light-transmitting area.

Preferably, the width of the light-transmitting region is not less than half the wavelength of the light incident on the cone, and not more than twice the wavelength of the light incident on the cone.

Preferably, the cone angle of the cone is 20°˜50°, and the diameter of the cone tip is 1-100 nm.

Preferably, the cone includes an optical fiber portion, and the optical fiber portion is a conical or truncated optical fiber. When the optical fiber portion is a circular truncated optical fiber, the top of the optical fiber portion is further provided with a conical metal portion. The optical fiber and the conical metal part together form the cone; the metal film covered on the surface of the cone is a light-transmitting metal film.

Preferably, the metal film is provided on the surface of the light-transmitting area.

Preferably, the thickness of the metal film is 10-200 nm.

Preferably, the shape of the light-transmitting area is a circular ring.

Preferably, the end of the optical fiber where the cone is arranged is in the shape of a truncated cone, and the exposed surface of the optical fiber core is covered with a light-proof metal film.

Preferably, the material of the metal film is gold, silver, aluminum, chromium or titanium; the material of the anti-light transmission metal film is gold, silver, aluminum, chromium or titanium.

The working method of the scattering tapered tip optical fiber probe for exciting and collecting near-field optical signals as described above in the present invention includes the following processes:

installing the scattering tapered tip optical fiber probe for exciting and collecting near-field optical signals on a near-field optical microscope;

When testing the sample, the laser beam is incident on the cone through the fiber core, and a localized light spot is formed on the top of the cone;

When the cone interacts with the surface of the sample, the near-field light of the sample surface is scattered around, and the light-transmitting area directly collects the scattered light in the near-field of the sample and transmits it to the far end through the fiber core.

The present invention has the following beneficial effects:

Compared with the traditional near-field optical probe, the scattering tapered tip optical fiber probe for exciting and collecting near-field optical signals involved in the present invention has very prominent features and advantages, and the details are as follows: A cone is provided, which serves as the tip of the entire probe. By controlling the size of the tip of the cone, the measurement resolution of the entire probe can be controlled, so that the probe of the present invention can reach the highest value of the current near-field optical microscope. By controlling the size of the top of the cone at the nanoscale, the probe of the present invention can obtain the surface topography of the nanoscale sample while measuring the optical image, thereby realizing the simultaneous measurement of multiple physical quantities. The diameter of the bottom of the cone is smaller than the diameter of the end face of the fiber core, and the area between the edge of the bottom surface of the cone and the edge of the end face of the fiber core is the light-transmitting area. Collecting the scattered signal from the tip increases the signal strength and reduces a large amount of far-field background noise, thereby improving the signal-to-noise ratio.

Further, the width of the light-transmitting area is not less than half the wavelength of the light incident on the cone, and not more than twice the wavelength of the light incident on the cone, and the width of the light-transmitting area ensures that there is enough light flux for collecting near-field light. , while reducing the interference of space stray light.

Further, the cone angle of the cone is 20° to 50°. At this cone angle, the intensity of the collected near-field light is strong, which can meet the detection requirements. The intensity of the field light will decrease sharply, making the signal very weak. The diameter of the needle tip will affect the near-field local spot excited at the needle tip. The smaller the diameter, the higher the measurement resolution. Therefore, the diameter of the cone tip of the present invention is 1-100 nm.

Further, the cone includes an optical fiber part, the optical fiber part is a cone-shaped or truncated optical fiber, and the metal film covered on the surface of the cone is a light-transmitting metal film, so the probe of the present invention can also pass through the cone part on the surface of the sample. The near-field directly collects the tip scattered signal, which further improves the signal strength, reduces a large amount of far-field background noise, and improves the signal-to-noise ratio.

Further, the metal film is provided on the surface of the light-transmitting area. Due to the small size of the cone and the light-transmitting area, when the metal film is prepared on the surface of the cone, the light-transmitting area is difficult to block. The metal films are all prepared, which can reduce the difficulty in preparing the metal films on the surface of the cone.

Further, the thickness of the metal film is 10-200 nm, and the thickness of the metal film can ensure that light can be coupled into the optical fiber, and at the same time, due to the existence of the metal film, surface plasmons will be excited to achieve the effect of optical field enhancement. When the film thickness is too thick, light cannot pass through.

Further, since the diameter of the existing optical fibers is relatively large, in order to obtain the probe of the present invention, so that the size of each part meets the requirements, then it is necessary to set the end of the optical fiber where the cone is arranged into a truncated cone to reduce the size of the end so that It can be matched with the cone shown; because the end of the cone on the optical fiber is set as a truncated cone, so that part of the fiber core will be exposed, in order to prevent stray light from entering the fiber core from the circular mesa The signal-to-noise ratio is affected, so the end of the optical fiber core needs to be treated with anti-light transmission. Therefore, in the present invention, the exposed surface of the optical fiber core at the end is covered with an anti-light transmission metal film.

Description of drawings

1 is a schematic diagram of the structure and working principle of a scattering tapered tip optical fiber probe for exciting and collecting near-field optical signals according to an embodiment of the present invention;

2 is a schematic structural diagram of the working principle probe of a scattering tapered tip optical fiber probe for exciting and collecting near-field optical signals according to an embodiment of the present invention;

FIG. 3 is a schematic diagram of a near-field optical image result of measuring a standard rhombus grating sample in an embodiment of the present invention.

In the picture: 1 fiber core, 2 fiber cladding, 3 light-proof metal film, 4 fiber cone, 5 metal film, 6 sample, 7 fiber cone, 8-metal cone, 9-light transmission area.

Detailed ways

The present invention will be clearly and specifically described below with reference to the accompanying drawings and specific implementation methods.

Referring to FIG. 1 and FIG. 2 , the scattering tapered tip optical fiber probe for exciting and collecting near-field optical signals of the present invention includes an optical fiber and a cone, the cone is arranged on the end face of the fiber core 1, and the cone is The surface of the body is covered with a metal film 5. First, the metal film 5 can effectively excite the surface plasmon resonance under the incident laser, thereby enhancing the intensity of the scattered light signal on the surface of the sample. Secondly, the tip of the cone will form when the external laser is incident. The localized light spot scatters the near-field optical signal excited by the sample surface to the surrounding area. The fiber core at the back end of the probe is connected to the bottom of the cone, which can collect the optical signal scattered by the cone tip in the near field of the sample surface and transmit it to the far end. The diameter of the bottom surface of the cone is smaller than the diameter of the end surface of the optical fiber core 1 , and the area between the bottom surface edge of the cone and the edge of the end surface of the optical fiber core 1 is the light-transmitting area 9 . In the present invention, the smaller the size of the cone tip of the cone, the higher the resolution can be achieved, and the height of the cone is different according to the change of the incident laser wavelength.

As a preferred embodiment of the present invention, the width of the light-transmitting region 9 (that is, the distance between the edge of the bottom surface of the cone and the edge of the end face of the optical fiber core 1 ) is not less than half of the wavelength of the light incident on the cone, not greater than the incident wavelength twice the wavelength of the light wave to the cone.

As a preferred embodiment of the present invention, the cone angle of the cone is 20°˜50°, and the top of the cone (in the orientation shown in FIG. 1 and FIG. 2 , the top of the cone is the lower vertex of the cone, Also known as cone tip) is an arc transition, a tiny spherical surface with a diameter of 1-100nm.

As a preferred embodiment of the present invention, the cone includes an optical fiber portion, and the optical fiber portion is a conical or truncated optical fiber, that is, the optical fiber cone 4 (as shown in FIG. 1 ) or the optical fiber truncated 7 (as shown in FIG. 2 ) When the optical fiber portion is a circular truncated optical fiber 7, the top of the circular truncated optical fiber 7 is also provided with a conical metal portion (that is, a metal cone 8), and the optical fiber circular truncated 7 and the metal cone 8 together form the cone; at this time , the metal film 5 covered on the surface of the cone is set as a light-transmitting metal film, which can directly collect the tip scattered signal in the near field of the sample surface through the cone part, which further improves the signal strength, reduces a large amount of far-field background noise, and improves the the signal-to-noise ratio. In this embodiment, the light-transmitting area 9 and the cone portion together form a collection port for optical signals.

As a preferred embodiment of the present invention, the metal film 5 is provided on the surface of the light-transmitting area.

As a preferred embodiment of the present invention, the thickness of the metal film 5 is 10-200 nm.

As a preferred embodiment of the present invention, the shape of the light-transmitting region is a circular ring.

As a preferred embodiment of the present invention, the end of the optical fiber where the cone is arranged is set as a truncated cone, and the exposed surface of the optical fiber core 1 is covered with an anti-light transmission metal film 3. The anti-light transmission metal film 3 can both It can prevent stray light from entering the optical fiber core and affect the signal-to-noise ratio, and can also prevent the optical signal entering the optical fiber core from leaking out from the side of the circular susceptor to ensure the strength of the signal. The diameter of the end face of this end of the fiber core 1 needs to be larger than the wavelength of the incident laser light, so as to collect more optical signals. In addition, since the outside of the optical fiber core is also covered with the optical fiber cladding 2, when preparing the anti-light transmission metal film 3 for the above-mentioned circular truncated end of the optical fiber core, it is necessary to jointly prepare the anti-transmission metal film 3 on the optical fiber cladding 2 and the optical fiber core. The light-transmitting metal film 3 can prevent the optical signal from leaking from the part between the optical fiber cladding 2 and the optical fiber core.

As a preferred embodiment of the present invention, the material of the metal film 5 is gold, silver, aluminum, chromium or titanium; the material of the anti-light transmission metal film 3 is gold, silver, aluminum, chromium or titanium. The higher the light transmittance of the metal film 5, the better, the lower the light transmittance of the anti-light-transmitting metal film 3, the better.

When the sample 6 is tested, the laser beam is incident on the cone through the fiber core 1, and a localized light spot is formed on the top of the cone;

When the cone interacts with the surface of the sample 6, the near-field light on the surface of the sample 6 scatters around, and the light-transmitting area directly collects the scattered light in the near-field of the sample 6 and transmits it to the far end through the fiber core 1.

Example

As shown in FIG. 1 and FIG. 2 , in this embodiment, the end of the optical fiber where the cone is arranged is set to be a truncated cone, and the optical fiber cladding 2 and the optical fiber core are jointly prepared with a light-proof metal film 3 . The part is an optical fiber cone 4, there is a circular light-transmitting area 9 between the optical fiber cone 4 and the end face of the optical fiber core, and a layer of light-transmitting metal film 5 is arranged on the surface of the optical fiber cone 4 and the light-transmitting area 9; The material of the film 3 is gold, and the material of the metal film 5 is gold; the dimensions of each part of the probe in this embodiment are shown in Table 1:

Table 1

Anti-transmission metal film

Fiber Taper Tip

Fiber cone

Metal film width

Metal film thickness

厚度thickness	直径diameter	锥角cone angle
600nm600nm	100nm100nm	30°30°	1000nm1000nm	30nm30nm

The measurement method using the scattering tapered tip optical fiber probe for exciting and collecting near-field optical signals in this embodiment includes the following steps:

1) The fiber probe is directly applied to the near-field optical microscope, and the sample test can be started after the probe is installed.

2) When a laser beam is incident on the tip of the probe cone through the optical fiber, due to the existence of the metal film on the surface of the cone tip, the localized plasmon resonance at the tip can be enhanced, so a localized light spot will be formed at the tip of the cone.

3) When the probe interacts with the sample surface, the near-field light on the sample surface will be scattered around. At this time, the light-transmitting area 9 of the probe core and the surface collection port of the fiber cone 4 can directly collect the scattered light in the near-field of the sample. and delivered to the far end through the fiber. Therefore, the collection of near-field optical signals on the sample surface is realized, breaking the optical diffraction limit.

As shown in Figure 3, from the near-field optical imaging results, there is a clear contrast between light and dark at the edge of the diamond-shaped structure, and the signal-to-noise ratio is very high. Feasibility of probes for measurement.

To sum up, the scattering tapered tip optical fiber probe for excitation and collection of near-field optical signals proposed by the present invention, the tapered structure of the tip of the probe has the characteristics of high resolution of the near-field non-porous probe, while the probe That is, the near-field optical signal can be excited and the collection can be realized, which greatly improves the signal-to-noise ratio. Due to the nano-scale tapered tip, the probe can simultaneously obtain nano-scale sample surface topography in one measurement. The probe of the invention also has the function of an atomic force microscope probe, can realize the measurement of the surface morphology of the sample and the ultra-high resolution of the optical image at the nanometer level, breaks through the optical diffraction limit, and can be directly used in the commercial near-field optical microscope test.

Claims

A scattering-type tapered tip optical fiber probe for exciting and collecting near-field optical signals, characterized in that it comprises an optical fiber and a cone, the cone is arranged on the end face of the fiber core (1), and the cone is The surface is covered with a metal film (5), the diameter of the bottom surface of the cone is smaller than the diameter of the end face of the optical fiber core (1), and the area between the edge of the bottom surface of the cone and the edge of the end face of the optical fiber core (1) is transparent. light area.
The scattering tapered tip fiber probe for exciting and collecting near-field optical signals according to claim 1, wherein the width of the light-transmitting region is not less than half of the wavelength of the light incident on the cone, No more than twice the wavelength of the light wave incident on the cone.
The scattering tapered tip optical fiber probe for exciting and collecting near-field optical signals according to claim 1, wherein the cone angle of the cone is 20°-50°, and the tip of the cone is 20° to 50°. The diameter is 1-100nm.
The scattering tapered tip optical fiber probe for exciting and collecting near-field optical signals according to claim 1, wherein the cone comprises an optical fiber part, and the optical fiber part is in the shape of a cone or a truncated cone The optical fiber, when the optical fiber part is a truncated optical fiber, the top of the optical fiber part is also provided with a conical metal part, and the truncated optical fiber and the conical metal part together form the cone;

The metal film (5) covered on the surface of the cone is a light-transmitting metal film.
The scattering-type tapered-tip optical fiber probe for exciting and collecting near-field optical signals according to claim 4, characterized in that the metal film (5) is provided on the surface of the light-transmitting area.
The scattering tapered tip optical fiber probe for exciting and collecting near-field optical signals according to claim 4 or 5, characterized in that the thickness of the metal film (5) is 10-200 nm.
The scattering tapered tip optical fiber probe for excitation and collection of near-field optical signals according to claim 1, wherein the shape of the light-transmitting region is a circular ring.
The scattering tapered tip optical fiber probe for excitation and collection of near-field optical signals according to claim 1, wherein the end of the optical fiber where the cone is provided is truncated, and the fiber core ( 1) The exposed surface of the end is covered with an anti-light transmission metal film (3).
A scattering tapered tip optical fiber probe for exciting and collecting near-field optical signals according to claim 8, characterized in that the metal film (5) is made of gold, silver, aluminum, chromium or Titanium; the material of the anti-light transmission metal film (3) is gold, silver, aluminum, chromium or titanium.
The working method of the scattering tapered tip optical fiber probe for exciting and collecting near-field optical signals according to any one of claims 1-9, characterized in that, the method comprises the following steps:

installing the scattering tapered tip optical fiber probe for exciting and collecting near-field optical signals on a near-field optical microscope;

When the sample (6) is tested, the laser beam is incident on the cone through the fiber core (1), and a localized light spot is formed on the top of the cone;

When the cone interacts with the surface of the sample (6), the near-field light on the surface of the sample (6) is scattered around, and the light-transmitting area directly collects the scattered light in the near-field of the sample (6), and passes through the fiber core (1). ) to the remote end.