A method for preparing ultrashort Bragg gratings in microfluidic channels using fiber probes based on femtosecond lasers

Abstract

The present invention belongs to the technical field of optical fiber device fabrication and discloses a method for fabricating a microchannel ultra-short fiber Bragg grating (FBG) using a femtosecond laser. The microprobe-based ultra-short FBG is fabricated using single-mode optical fiber tapering, discharge fusion splicing, and femtosecond laser microchannel etching. The microprobe's size can be controlled by adjusting the discharge intensity, discharge time, and number of discharges in the splicer, as well as the movement time and distance of the electrodes on both sides. The period and number of periods of the ultra-short FBG etched in the microprobe can be controlled by adjusting the movement path of the femtosecond laser focus. This method produces a compact, mass-producible, and stable ultra-short fiber Bragg grating based on the microprobe, playing a crucial role in the production and application of fiber Bragg grating-based optical fiber sensors. This method avoids the use of specialized optical fibers, reducing the cost of optical fiber device fabrication. Microprobes of varying diameters and lengths, as well as ultra-short FBGs with varying periods and numbers of periods, can be fabricated according to different application areas. In addition, ultrashort FBG based on micro-probes can be used to detect parameters such as refractive index, high temperature, and humidity.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical fiber device manufacturing, and relates to a method for preparing an optical fiber probe type microchannel ultra-short Bragg grating (ultra-short FBG) based on femtosecond laser. Background Art

[0002] Fiber optic sensors, with their lightweight, compact structure, corrosion resistance, and electromagnetic interference immunity, offer significant advantages over traditional electronic sensors in several areas, such as human disease detection, complex and unpredictable ocean parameters, and electric field measurement. Currently, the most widely studied all-fiber sensors are interferometric and fiber Bragg grating (FBG) sensors. Interferometric fiber optic sensors can be categorized as Fabry-Perot interferometers, Mach-Zehnder interferometers, Sagnac interferometers, and Michelson interferometers, while fiber Bragg grating (FBG) sensors can be categorized as long-period fiber Bragg gratings (LPFGs) and fiber Bragg gratings (FBGs). In 2003, S.J. Mihailov et al. successfully inscribed FBGs in non-sensitized, conventional communication optical fibers using a phase mask method combined with an 800nm ​​IR femtosecond laser. In 2004, A. Martinez et al. inscribed first-, second-, and third-order FBGs in non-sensitized, single-mode communication optical fibers using a point-by-point inscription method combined with an IR femtosecond laser. Fiber Bragg Gratings (FBGs) are a very important fiber optic device. Compared with other types of fiber optic sensors, they are easier to demodulate and have better stability. They have important applications in fiber optic sensing, fiber optic communications, and other fields. Traditionally, FBGs are prepared by irradiating the optical fiber with ultraviolet light through a mask. This preparation method is relatively inflexible. With the development of femtosecond lasers, the direct writing of FBGs using femtosecond lasers has gradually matured. However, the FBGs prepared by these two methods are generally longer than 2000 microns. When measuring the refractive index, FBGs are difficult to achieve point-by-point measurement and have low sensitivity. In practical applications, such as human cell detection, sensors must be compact, highly sensitive, and stable. Therefore, how to simply and efficiently prepare compact, highly sensitive fiber Bragg gratings has become a key research direction in the field of fiber FBG device fabrication technology. Summary of the Invention

[0003] The present invention addresses the difficulties in fabricating optical fiber Bragg gratings (FBGs), their large size, and low sensitivity. It proposes a compact, highly sensitive, mass-producible, and stable microprobe-based ultrashort fiber Bragg grating (FBG), which plays a crucial role in the production and application of grating-based optical fiber sensors. The microprobe-based ultrashort FBG is fabricated using single-mode optical fiber tapering, discharge fusion, and femtosecond laser microchannel etching. The size of the microprobe can be controlled by adjusting the discharge intensity, discharge time, and number of discharges in the fusion splicer, as well as the movement time and distance of the electrodes on both sides. The period and number of ultrashort FBGs inscribed in the microprobe can be controlled by adjusting the writing path of the femtosecond laser. This method offers the advantages of high fabrication repeatability, simple operation, and flexible design.

[0004] The specific technical solutions of the present invention are:

[0005] A method for preparing an ultrashort Bragg grating in a microfluidic channel using a fiber probe based on a femtosecond laser comprises the following steps:

[0006] (1) Discharge, taper, and fuse the single-mode optical fiber at the axial center to obtain two single-sided tapered optical fibers;

[0007] (2) Replace the left tapered fiber with a single-mode fiber, adjust the position of the single-side tapered fiber and the single-mode fiber, perform discharge welding, and a micro probe appears on the end face of the single-mode fiber;

[0008] (3) The single-mode optical fiber with a microprobe is placed on the three-dimensional moving platform of the femtosecond laser. The power, frequency, wavelength and laser focus moving path of the femtosecond laser are set. The tip of the microprobe is beveled at a 45° angle. The parameters of the femtosecond laser are adjusted. The microchannel constituting the ultrashort FBG is etched in the microprobe to obtain the target parameters of the ultrashort fiber Bragg grating based on the microprobe.

[0009] The discharge operation described in steps (1) and (2) and the position adjustment described in step (2) are performed by a welding machine. The microprobe tip is beveled to a 45° angle and the microchannel constituting the ultrashort FBG is etched in the microprobe described in step (3) by a femtosecond laser.

[0010] The present invention has the following beneficial effects:

[0011] (1) In the present invention, a welding machine is used to draw and fuse the cone, and the discharge intensity, discharge time, discharge times, and moving distance of the electrodes on both sides can be flexibly controlled by a program.

[0012] (2) In the present invention, the tip of the microprobe is beveled at a 45° angle using a femtosecond laser, which effectively prevents the introduction of unnecessary interference.

[0013] (3) In the present invention, a femtosecond laser is used to etch the microchannels constituting the ultrashort FBG into the microprobe. The period and number of periods of the fiber grating are controllable, and the laser focus movement path is controlled by a program, resulting in extremely high preparation repeatability. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a schematic diagram of the structure of an ultrashort fiber Bragg grating based on a micro-probe.

[0015] Figure 2 This is a flow chart of the preparation of microprobes.

[0016] Figure 3 (a) and (b) are microscope images and resulting spectra of ultrashort FBGs with period numbers of 11 and 28, respectively.

[0017] Figure 4 (a) and (b) are the response of the spectrum of the ultrashort fiber Bragg grating to the change of refractive index and the fitting curve, respectively. DETAILED DESCRIPTION

[0018] In order to make the above objects and advantages more understandable, the present invention is further described below with reference to the accompanying drawings and specific embodiments.

[0019] The specific implementation process of the present invention is as follows:

[0020] The production of this sensor generally requires three steps, namely the production of microprobes, beveling of the microprobe tip, and etching of ultrashort fiber Bragg gratings. In the process of producing the microprobes, the single-mode optical fiber is tapered and fused multiple times, and finally a microprobe with a length of about 200μm and a diameter of about 30μm is successfully produced. The parameters of the fusion splicer are set as follows: discharge time 5000ms, discharge intensity 3unit, Z-axis pulling distance 1000μm, and the first taper effect is as follows: Figure 2 Then, open the right fiber clamp and move the left clamp 150μm to the left. The fiber position after moving is as follows: Figure 2 (b) As shown. Then, the second discharge taper is carried out, and the cone waist is melted to obtain a single-sided cone with a smaller diameter and a single-sided cone with a larger diameter. The single-sided cone with a smaller diameter is replaced with a single-mode fiber so that the end face of the single-mode fiber is 150μm away from the discharge center, as shown in Figure 2 Finally, the third discharge taper is performed and the micro-probe is fused to the end face of the single-mode optical fiber, as shown in (c). Figure 2 (d) To prevent diffraction at the microprobe tip, a femtosecond laser was used to create a 45° bevel. The femtosecond laser used in the experiment had a central wavelength of 520 nm, a frequency of 10 kHz, and a power of 10 μW. A bottom-up, row-by-row cutting method was used, with a scanning speed of 48 μm / s at the laser focus.

[0021] During the etching process of the ultrashort fiber Bragg grating, the frequency and power of the femtosecond laser were adjusted to 5 kHz and 2 μw, respectively. 29 lines were scanned in sequence along the Y direction on a plane. The scanning length of each line was 6 μm, the line-to-line interval was 5.35 μm, and the scanning speed of the laser focus was set to 20 μm / s. After one plane was scanned, the laser focus moved downward by 0.5 μm along the Z axis and continued to scan the next plane until all 60 planes were scanned, and the ultrashort FBG was prepared. By adjusting the number of plane scanning lines, ultrashort FBGs with different period numbers can be produced. The spectra and microscope images of ultrashort FBGs with periods of 11 and 28 are shown in Figure 2. Figure 3 As shown in (a) and (b).

[0022] The response of the ultrashort FBG to the refractive index change is as follows: Figure 4 (a) is shown. The experimental data is fitted and the fitting curve is shown as Figure 4 (b) shows that within the refractive index range of 1.3323 to 1.378, the sensor sensitivity can reach 600.5622 nm / RIU. To our knowledge, this is the highest sensitivity achieved by a fiber Bragg grating structure in measuring refractive index. While ensuring high sensitivity, the structure exhibits high linearity (R 2 = 0.9986). Four identical measurements were performed on the same sensor, with each measurement taking place one hour apart. The error information can be represented by the error bars in Figure 4(b).

Claims

1. A method for preparing an ultrashort Bragg grating in a microfluidic channel using a fiber probe based on a femtosecond laser, characterized in that: The steps include: (1) Discharge, taper, and fuse the single-mode optical fiber at its axial center to obtain two single-sided tapered optical fibers; (2) Replace the left tapered fiber with a single-mode fiber, adjust the positions of the tapered fiber and the single-mode fiber, perform discharge welding, and a micro-probe appears on the end face of the single-mode fiber; the probe has a length of 200 μm and a diameter of 30 μm; (3) A single-mode optical fiber with a microprobe is placed on a three-dimensional moving platform of a femtosecond laser. The power, frequency, wavelength, and focus moving path of the femtosecond laser are set. The tip of the microprobe is beveled at a 45° angle. The femtosecond laser parameters are adjusted. The microchannel constituting the ultrashort FBG is etched in the microprobe to obtain an ultrashort fiber Bragg grating with target parameters based on the microprobe. The discharge operation in steps (1) and (2) and the position adjustment in step (2) are completed by a welding machine; the parameters of the welding machine are set as follows: discharge time 5000ms, discharge intensity 3unit, Z-axis pulling distance 1000μm; The microchannel of the ultrashort FBG described in step (3) is etched in the microprobe by a femtosecond laser; during the etching process, the frequency and power of the femtosecond laser are adjusted to 5 kHz and 2 μw, respectively; 29 lines are scanned in sequence along the Y direction on a plane, the scanning length of each line is 6 μm, the line-to-line interval is 5.35 μm, and the scanning speed of the laser focus is set to 20 μm / s; after one plane is scanned, the laser focus moves downward by 0.5 μm along the Z axis and continues to scan the next plane until all 60 planes are scanned, and the ultrashort FBG is completed.

Images