Fiber-based cryogenic near-field optical microscope

Abstract

The present invention discloses a fiber-based cryogenic near-field optical microscope for measuring samples, which includes an optical part and a scanning mechanical part. The optical part includes a light source, a fiber coupler, an interference arm, a detector and a near-field coupling structure. The light source is fixedly connected to the first incident port of the fiber coupler, and the detector is fixedly connected to the second incident port of the fiber coupler. The fiber-based cryogenic near-field optical microscope disclosed by the present invention not only eliminates the debugging and calibration process of the light beam guiding mechanism, but also avoids the position drift influence caused by the aging of the system mechanical components. It has the advantages of better anti-environmental interference ability, little influence of the installation position by the actual installation environment, and can more economically reach ultra-low temperature environments of 1.2K and 4K, etc.

Description

Technical Field

[0001] The present invention belongs to the technical field of scanning near-field optical microscopes, and particularly relates to a fiber-based cryogenic near-field optical microscope. Background Art

[0002] Scanning near-field optical microscope (SNOM) is an optical imaging solution that breaks through the diffraction limit of conventional optical microscopes, and can achieve synchronous and precise measurement of key properties such as the morphology, composition, and mechanics of sample materials at the nanoscale. At the same time, due to its non-contact detection principle, it can perform non-destructive measurement on samples, thus having greater advantages in the field of biological materials.

[0003] Existing SNOM systems mainly consist of two parts: an optical part that constrains and detects and analyzes light beams, and a scanning mechanical part that controls the sample and the probe. Among them, the scanning mechanical part is an atomic force microscope (AFM), and a mature AFM can be directly used, or a system with the same function specifically designed according to the AFM principle for special applications. The optical part often adopts a light beam guiding mechanism designed based on the principle of Michelson interferometer, and is accompanied by control motors, light beam detectors, and signal amplification and demodulation devices required for interference measurement. However, the light beams controlled by the light beam guiding mechanism built based on the principle of Michelson interferometer are located in free space. Due to the scale of the scanning probe, the accuracy requirement is very high, and each light beam deflection element often needs to have an adjustment function, otherwise the light beam cannot be successfully guided to the specified area. The existence of a large number of optical element adjustment frames brings two problems: one is that the optical element adjustment frames occupy a large space, and the whole mechanism is more restricted by the external dimensions of the adjustment frames. At the same time, any mechanical adjustment frame more or less has the phenomenon that the moving mechanism ages over time, which will cause the calibrated light beam to shift after a period of time and lose its original function; the other is that in a cryogenic system, the introduction of free space light must open a window, which will cause the temperature to rise due to external radiation.

[0004] In view of the problems existing in the current SNOM system, the present invention proposes a fiber-based cryogenic near-field optical microscope with a fully fiberized SNOM light beam guiding mechanism. Summary of the Invention

[0005] The main object of the present invention is to provide a fiber-based cryogenic near-field optical microscope, which not only omits the debugging and calibration process of the light beam guiding mechanism, but also avoids the position drift influence caused by the aging of the mechanical components of the system. It has the advantages of better anti-environmental interference ability, less influence of the installation position on the actual installation environment, and being able to more economically reach ultra-low temperature environments of 1.2K and 4K.

[0006] Another object of the present invention is to provide a fiber-based cryogenic near-field optical microscope for measuring a sample, which includes an optical part and a scanning mechanical part. The optical part includes a light source, a fiber coupler, an interference arm, a detector, and a near-field coupling structure, wherein:

[0007] The light source is fixedly connected to the first incident port of the fiber coupler, and the detector is fixedly connected to the second incident port of the fiber coupler;

[0008] The first output port of the fiber coupler is fixedly connected to the near-field coupling structure, and the near-field coupling structure is used to converge the light beam emitted by the light source onto the effective near-field scattering region of the tip of the scanning probe of the scanning mechanical part (the structure of the scanning probe of the scattering near-field microscope of the present invention is a cantilever beam and a probe, and there is a metal coating on the probe and the cantilever beam), and collect the near-field information of the sample. The second output port of the fiber coupler is fixedly connected to the interference arm.

[0009] The near-field scattered light beam (the near-field information of the collected sample) collected by the near-field coupling structure will return to the fiber coupler along the original path. Among them, a high proportion of the energy will enter the detector, and a low proportion of the energy will enter the fiber isolator and be blocked. The main optical axis of the near-field coupling structure forms an angle of 30° with the surface of the sample, and the entire structure is fixed on a three-dimensional displacement stage driven by a piezoelectric stepping motor to achieve precise coupling with the tip of the scanning probe.

[0010] When the first output port is for the first incident port, it outputs a low-power signal, and when the first output port is for the second incident port, it outputs a high-power signal;

[0011] When the second output port is for the second incident port, it outputs a low-power signal, and when the second output port is for the first incident port, it outputs a high-power signal.

[0012] The fiber coupler is a 2x2 fiber splitter. The fiber splitter selected in the present invention is bidirectional transmission and the energy distribution ratio is 9:1. It can split the light beam incident from any port according to the energy ratio of 9:1 and output it from two output ports.

[0013] As a further preferred technical solution of the above technical solution, the light source includes a laser and a fiber isolator. The fiber isolator is fixedly connected to the first incident port of the fiber coupler, and the end of the fiber isolator away from the fiber coupler is fixedly connected to the laser (the laser is used as the system light source, and its parameters such as wavelength and power are determined by the sample to be studied).

[0014] As a further preferred technical solution of the above technical solution, the laser includes a laser source, an optical lens group, a first optical fiber, a first fixing structure, and a drive control circuit. The laser source, the optical lens group, and the first optical fiber are all installed on the first fixing structure. The optical lens group is installed between the laser source and the first optical fiber. The first optical fiber is connected to one end of the optical fiber isolator close to the laser.

[0015] As a further preferred technical solution of the above technical solution, the interference arm includes an optical fiber stretcher driven by a piezoelectric ceramic and a second optical fiber with a reverse coupler installed at the end. The second optical fiber is wound and fixed on the optical fiber stretcher. One end of the second optical fiber away from the reverse coupler is fixedly connected to the second output port of the optical fiber coupler. The reverse coupler can reversely transmit the light beam in the second optical fiber with extremely low loss to the optical fiber coupler. Among them, a high proportion of the energy will enter the optical fiber isolator and be blocked, and a low proportion of the energy will enter the detector. The optical fiber stretcher can drive the optical fiber to achieve a stretching change of several hundred nanometers at a frequency of hundreds of hertz through the piezoelectric ceramic, causing a change in the optical path of the light beam in the second optical fiber, so as to realize interference measurement and improve the signal-to-noise ratio.

[0016] As a further preferred technical solution of the above technical solution, the near-field coupling structure includes a transmission optical fiber, a collimating lens, a coupling lens, and a second fixing structure. The transmission optical fiber, the collimating lens, and the coupling lens are all installed on the second fixing structure. The collimating lens is installed between the transmission optical fiber and the coupling lens. The transmission optical fiber is connected to the first output port.

[0017] Among them, the part of the transmitted light close to the collimating lens is a vitrified optical fiber head or a ceramized optical fiber head for easy structural fixation and alignment packaging. The collimating lens is a medium-long focal length aspherical lens with a focal length range of 18 - 40 mm, and the coupling lens is a short focal length aspherical lens with a focal length range of 7 - 15 mm. Description of the Drawings

[0018] Figure 1 is a schematic structural diagram of the fiber-based cryogenic near-field optical microscope of the present invention.

[0019] Figure 2 is a schematic structural diagram of the laser of the fiber-based cryogenic near-field optical microscope of the present invention.

[0020] Figure 3 is a schematic structural diagram of the near-field coupling structure of the fiber-based cryogenic near-field optical microscope of the present invention.

[0021] The reference numerals include: 10, a light source; 11, a laser; 111, a laser source; 112, an optical lens group; 113, a first fixing structure; 114, a first optical fiber; 12, an optical fiber isolator; 20, an optical fiber coupler; 30, an interference arm; 31, an optical fiber stretcher; 32, a second optical fiber; 33, a reverse coupler; 40, a detector; 50, a near-field coupling structure; 51, a transmission optical fiber; 52, a collimating lens; 53, a coupling lens; 54, a second fixing structure; 60, a scanning probe. Detailed implementation manners

[0022] The following description is used to disclose the present invention so that those skilled in the art can implement the present invention. The preferred embodiments in the following description are only examples, and those skilled in the art can think of other obvious variations. The basic principles defined in the following description of the present invention can be applied to other implementation manners, variant schemes, improvement schemes, equivalent schemes, and other technical schemes that do not depart from the spirit and scope of the present invention.

[0023] Referring to the Figure 1 , Figure 1 is a schematic structural diagram of the fiber-based cryogenic near-field optical microscope of the present invention, Figure 2 is a schematic structural diagram of the laser of the fiber-based cryogenic near-field optical microscope of the present invention, Figure 3 is a schematic structural diagram of the near-field coupling structure of the fiber-based cryogenic near-field optical microscope of the present invention.

[0024] In the preferred embodiment of the present invention, those skilled in the art should note that the scanning mechanical part and the sample involved in the present invention can be regarded as the prior art.

[0025] Preferred embodiment.

[0026] The present invention discloses a fiber-based cryogenic near-field optical microscope for measuring a sample, including an optical part and a scanning mechanical part, and is characterized in that the optical part includes a light source 10, an optical fiber coupler 20, an interference arm 30, a detector 40, and a near-field coupling structure 50, wherein:

[0027] The light source 10 is fixedly connected to the first incident port of the optical fiber coupler 20, and the detector 40 is fixedly connected to the second incident port of the optical fiber coupler 20;

[0028] The first output port of the fiber optic coupler 20 is fixedly connected to the near-field coupling structure 50, which is used to converge the light beam emitted by the light source 10 onto the effective near-field scattering region at the tip of the scanning probe 60 of the scanning mechanical part (the structure of the scanning probe 60 of the scattering near-field microscope of the present invention is a cantilever beam and a probe, and there is a metal coating on the probe and the cantilever beam), and collect the near-field information of the sample. The second output port of the fiber optic coupler 20 is fixedly connected to the interference arm 30.

[0029] The near-field scattered light beam (the near-field information of the collected sample) collected by the near-field coupling structure 50 will return to the fiber optic coupler 20 along the original path. Among them, a high proportion of the energy will enter the detector 40, and a low proportion of the energy will enter the fiber optic isolator 12 and be blocked. The main optical axis of the near-field coupling structure 50 forms an angle of 30° with the surface of the sample. The entire structure is fixed on a three-dimensional displacement stage driven by a piezoelectric stepping motor to achieve precise coupling with the tip of the scanning probe 60.

[0030] When the first output port is for the first input port, it outputs a low-power signal; when the first output port is for the second input port, it outputs a high-power signal.

[0031] When the second output port is for the second input port, it outputs a low-power signal; when the second output port is for the first input port, it outputs a high-power signal.

[0032] The fiber optic coupler 20 is a 2x2 fiber optic splitter. The fiber optic splitter selected in the present invention is for bidirectional transmission and the energy distribution ratio is 9:1. It can split the light beam incident from any port according to the energy ratio of 9:1 and output it from two output ports.

[0033] Specifically, the light source 10 includes a laser 11 (preferably a single-mode fiber-coupled laser) and a fiber optic isolator 12. The fiber optic isolator 12 is fixedly connected to the first input port of the fiber optic coupler 20, and one end of the fiber optic isolator 12 away from the fiber optic coupler 20 is fixedly connected to the laser 11 (the laser 11 is used as the system light source, and its parameters such as wavelength and power are determined by the sample to be studied).

[0034] More specifically, the laser 11 includes a laser source 111, an optical lens group 112, a first optical fiber 114, a first fixing structure 113, and a drive control circuit. The laser source 111, the optical lens group 112, and the first optical fiber 114 are all installed on the first fixing structure 113. The optical lens group 112 is installed between the laser source 111 and the first optical fiber 114. The first optical fiber 114 is connected to one end of the fiber optic isolator 12 close to the laser 11.

[0035] The laser source 111 outputs in free space. The output light beam of the laser source is coupled into a single-mode optical fiber by using an optical lens group 112 to form a laser 11 and then connected to this system.

[0036] Furthermore, the interference arm 30 includes an optical fiber stretcher 31 driven by a piezoelectric ceramic and a second optical fiber 32 with a reverse coupler 33 mounted at the end. The second optical fiber 32 is wound and fixed on the optical fiber stretcher 31. One end of the second optical fiber 32 far from the reverse coupler 33 is fixedly connected to the second output port of the optical fiber coupler 20. The reverse coupler 33 can reversely transmit the light beam in the second optical fiber 32 with extremely low loss to the optical fiber coupler 20. Among them, a high proportion of the energy will enter the optical fiber isolator 12 and be blocked, and a low proportion of the energy will enter the detector 40. The optical fiber stretcher 31 can, through the drive of the piezoelectric ceramic, make the optical fiber achieve a telescopic change of several hundred nanometers at a frequency of the order of hundreds of Hertz, causing a change in the optical path of the light beam in the second optical fiber 32 to realize interference measurement and improve the signal-to-noise ratio.

[0037] Even further, the near-field coupling structure 50 includes a transmission optical fiber 51, a collimating lens 52, a coupling lens 53, and a second fixing structure 54. The transmission optical fiber 51, the collimating lens 52, and the coupling lens 53 are all mounted on the second fixing structure 54. The collimating lens 52 is mounted between the transmission optical fiber 51 and the coupling lens 53. The transmission optical fiber 51 is connected to the first output port.

[0038] Preferably, the part of the transmission optical fiber 51 close to the collimating lens is a vitrified optical fiber head or a ceramized optical fiber head for easy structural fixation and alignment packaging. The collimating lens is a medium-long focal length aspherical lens with a focal length range of 18 - 40 mm, preferably 18.4 mm. The coupling lens is a short focal length aspherical lens with a focal length range of 7 - 15 mm, preferably 8 mm.

[0039] Preferably, the interfaces of the optical fibers involved in the present invention are all of FC / APC specifications and are connected through FC / APC fiber flanges.

[0040] Preferably, the optical part (i.e., the light beam guiding mechanism) of the present invention can also adopt a mechanism built based on the principle of a Michelson interferometer with the light beam in free space. The light beam originally directly introduced into the sample scanning probe is first coupled into an optical fiber, and then conducted through the optical fiber to the sample scanning probe for optical coupling. It can be expressed as coupling the light beam converging on the scanning probe in the original free space optical path into a first optical fiber through a lens group (a product similar to the optical lens group 112), and the first optical fiber is connected to one end of the near-field coupling structure 50 far from the collimating / converging lens.

[0041] This solution of changing the near-field coupling part of the system to optical fiber transmission can also effectively alleviate the complexity of the ultra-low temperature system.

[0042] It is worth mentioning that the technical features such as the scanning mechanism part and the sample involved in this invention patent application should be regarded as the prior art. For the specific structures, working principles, possible control methods, and spatial arrangement methods of these technical features, conventional selections in the art can be adopted, and they should not be regarded as the invention points of this invention patent. This invention patent will not be further specifically elaborated.

[0043] For those skilled in the art, it is still possible to modify the technical solutions described in the foregoing embodiments or make equivalent replacements for some of the technical features. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection scope of the present invention.

Claims

1. An optical fiber-based cryogenic near-field optical microscope for measuring a sample, comprising an optical part and a scanning mechanical part, characterized in that, The optical part includes a light source, an optical fiber coupler, an interference arm, a detector, and a near-field coupling structure, where: The light source is fixedly connected to the first incident port of the optical fiber coupler, and the detector is fixedly connected to the second incident port of the optical fiber coupler; The first output port of the optical fiber coupler is fixedly connected to the near-field coupling structure, and the near-field coupling structure is used to converge the light beam emitted by the light source onto the effective near-field scattering region of the tip of the scanning probe of the scanning mechanical part and collect the near-field information of the sample. The second output port of the optical fiber coupler is fixedly connected to the interference arm; The near-field scattered light beam collected by the near-field coupling structure will return to the optical fiber coupler along the original path. Among them, a high proportion of the energy will enter the detector, and a low proportion of the energy will enter the optical fiber isolator and be blocked. The main optical axis of the near-field coupling structure forms an angle of 30° with the surface of the sample. The entire structure is fixed on a three-dimensional displacement stage driven by a piezoelectric stepping motor to achieve precise coupling with the tip of the scanning probe; For the optical fiber coupler: When the first output port is for the first incident port, it outputs a low-power signal. When the first output port is for the second incident port, it outputs a high-power signal; When the second output port is for the second incident port, it outputs a low-power signal. When the second output port is for the first incident port, it outputs a high-power signal; The optical fiber coupler is for bidirectional transmission and the energy distribution ratio is 9:

1. The light beam incident from any port is split by an energy ratio of 9:1 and output from two output ports; The interference arm includes an optical fiber stretcher driven by a piezoelectric ceramic and a second optical fiber with a reverse coupler installed at the end. The second optical fiber is wound and fixed on the optical fiber stretcher. One end of the second optical fiber far from the reverse coupler is fixedly connected to the second output port of the optical fiber coupler. The reverse coupler transmits the light beam in the second optical fiber back to the optical fiber coupler with extremely low loss. Among them, a high proportion of the energy will enter the optical fiber isolator and be blocked, and a low proportion of the energy will enter the detector. The optical fiber stretcher drives the optical fiber to achieve a telescopic change of several hundred nanometers at a frequency of hundreds of Hertz through the piezoelectric ceramic, causing a change in the optical path of the light beam in the second optical fiber to realize interference measurement and improve the signal-to-noise ratio.

2. The cryogenic near-field optical microscope based on optical fiber according to claim 1, wherein The light source includes a laser and an optical fiber isolator. The optical fiber isolator is fixedly connected to the first incident port of the optical fiber coupler, and one end of the optical fiber isolator far from the optical fiber coupler is fixedly connected to the laser; 3. The cryogenic near-field optical microscope based on optical fiber according to claim 2, wherein The laser includes a laser source, an optical lens group, a first optical fiber, a first fixing structure, and a drive control circuit. The laser source, the optical lens group, and the first optical fiber are all installed on the first fixing structure. The optical lens group is installed between the laser source and the first optical fiber. The first optical fiber is connected to one end of the optical fiber isolator close to the laser; 4. The cryogenic near-field optical microscope based on optical fiber according to claim 3, characterized in that, The near-field coupling structure includes a transmission optical fiber, a collimating lens, a coupling lens, and a second fixing structure. The transmission optical fiber, the collimating lens, and the coupling lens are all installed on the second fixing structure. The collimating lens is installed between the transmission optical fiber and the coupling lens. The transmission optical fiber is connected to the first output port.

Images