CN211602925U - Terahertz microstructure double-core optical fiber ultra-sensitive microfluidic sensor - Google Patents
Terahertz microstructure double-core optical fiber ultra-sensitive microfluidic sensor Download PDFInfo
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- CN211602925U CN211602925U CN201921626226.7U CN201921626226U CN211602925U CN 211602925 U CN211602925 U CN 211602925U CN 201921626226 U CN201921626226 U CN 201921626226U CN 211602925 U CN211602925 U CN 211602925U
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Abstract
The utility model provides a terahertz microstructure twin-core optic fibre ultrasensitive microfluid sensor, its basic structure comprises coat, covering and two fibre cores of the left and right sides, and characterized by left core is input port, and right core is output port, and optic fibre cross section structure is for designing a plurality of air holes in the substrate material, and wherein the covering comprises the circular air hole of size unanimity, and the design satisfies the sub-wavelength micro air hole array of arithmetic layering condition in left core, fills the microfluid that awaits measuring in the right core. The utility model discloses utilize terahertz wave's broadband characteristic and the mode coupling effect of two core optic fibre, constructed a broadband, ultrasensitive microfluid refractive index sensor. The method has wide application prospect in the fields of biology, chemistry, medicine and the like with high precision requirements on sensing and measurement.
Description
Technical Field
The utility model relates to an optical fiber sensing and measurement field, concretely relates to broadband, super sensitive refractive index sensor based on terahertz micro-structure fibre core photonic crystal optic fibre now.
Background
Photonic Crystal Fibers (PCFs) are also known as Holey Fibers (HF), or Micro Structured Fibers (MSFs). Russell et al first proposed the concept of photonic crystal fiber in 1991, and since then opened a new page in the history of fiber development. Knight et al succeeded in 1996 for the first time in the fabrication of photonic crystal fiber, the first index-guided photonic crystal fiber in the world. In 1998, the first photonic crystal fiber based on the photonic band gap principle was successfully drawn. Since then, research on PCF has been on the move, with a rising heat. Currently, research on photonic crystal fiber waveguides and devices has penetrated into various fields and has been commercialized in large numbers. According to the practical application requirements, people continuously design various photonic crystal fibers with novel structures, including high birefringence PCF, single-mode single-polarization PCF, multi-cladding structures, multi-core coupling structures, microstructure fiber core PCF, filling type PCF and the like. The current research focus is mainly embodied in the research of new materials, new structures and new functions.
With the continuous development of terahertz technology, people quickly apply the concept of photonic crystal fiber to terahertz wave bands. In 2002, Han et al used tubes and rods of high density polyethylene material to push photonic crystal fibers, which were experimentally measured, and found that the fibers had lower loss and dispersion in the 0.1-3THz frequency range. Subsequently, Masahiro et al reported that a terahertz polarization maintaining optical fiber made of a polytetrafluoroethylene material has a low loss coefficient and is easy to prepare. Gong et al have studied terahertz hollow-core photonic crystal fibers and found that they have a wide photonic band gap. In 2009, Nielsen et al reported a low loss terahertz photonic crystal fiber made from the polymer material Topas (cyclic olefin copolymer). Topas is a soft polymer material, and has the advantages of low loss in the terahertz waveband, easiness in bending and the like. The fiber is capable of single mode operation over a wide frequency range with very low loss and material dispersion.
In the terahertz field, a functional device based on photonic crystal fiber is applied, online operation can be realized, and connection loss is reduced, so that a terahertz system is developed towards flexibility, miniaturization and portability. Devices such as terahertz modulators, filters, optical switches, directional couplers, optical fiber sensors and the like based on photonic crystal fibers have wide application potential in the terahertz field.
Disclosure of Invention
The utility model discloses to the limitation of microfluid optical fiber sensor in the aspect of bandwidth, sensitivity etc. in the past, based on the matching coupling effect of two-core photonic crystal optic fibre, provided a terahertz broadband ultrasensitive microfluid sensor.
The ultra-sensitive micro-fluid sensor based on the terahertz microstructure double-core optical fiber comprises a cladding, a left fiber core, a right fiber core and a coating layer. Wherein the left core is an input port and the right core is an output port. The cross section structure of the optical fiber is that a plurality of air holes are arranged in a polymer material, wherein a cladding layer is composed of round air holes which are arranged in a triangular lattice mode and have the same size. The left core is composed of elliptical air holes with different sizes. The duty cycle (air hole area/material area) of the core microstructure is less than the cladding, therefore the fiber is a refractive index guided photonic crystal fiber.
In the ultra-sensitive micro-fluid sensor based on the terahertz microstructure double-core optical fiber, in order to improve the refractive index sensitivity of the device, a sub-wavelength elliptical micro-air hole meeting the equal-difference layering condition is introduced into the left core of the optical fiber. The right core is filled with the microfluid to be measured. The left core asymmetric microstructure is used to form high mode birefringence to better match the linear polarization characteristics of the input THz wave.
The equal-difference layered design is that on the cross section of the optical fiber, the fiber core microstructure is divided into a plurality of layers, the microstructure basic unit is an ellipse, the short half shaft of the central ellipse is r, and the size of the short half shaft of the ellipse is increased by a fixed length r every outward layer.
According to the ultra-sensitive micro-fluid sensor based on the terahertz microstructure double-core optical fiber, the purpose of designing the left core microstructure is to introduce high-mode birefringence, so that the fiber core microstructure can also be designed into other asymmetric structures, such as rectangular holes, round hole tetragonal lattice arrays, round hole pair arrays, similar bow tie structures and the like.
According to the ultra-sensitive microfluid sensor based on the terahertz microstructure double-core optical fiber, when microfluid with a certain specific refractive index is filled in the right core, the dispersion curves of the two cores in the fundamental mode Y polarization mode only have one intersection point due to different slopes of the dispersion curves of the two cores. At the intersection point, the two core Y polarizations will be strongly coupled. Only terahertz waves of a certain frequency in the left core will be coupled to the right core. That is, in the operating frequency range, the right core of a microfluid with a certain refractive index can only match with the left core of a terahertz wave with a certain frequency. The refractive index of the microfluid can be accurately obtained by measuring the frequency of the terahertz wave at the output port of the right core. Simultaneously, because incident terahertz wave has the broadband characteristic, consequently the microfluid sensor also has the broadband characteristic.
According to the ultra-sensitive microfluidic sensor based on the terahertz microstructure dual-core optical fiber, optional substrate materials include but are not limited to the following polymer materials: PP (polypropylene), HDPE (high density polyethylene), ABS (acrylonitrile-butadiene-styrene copolymer), PMMA (polymethyl methacrylate), TOPAS (cyclic olefin polymer).
Preferably, the fiber cladding is designed with circular air holes in a triangular lattice arrangement.
Preferably, the left core microstructure basic unit is designed as an ellipse.
Preferably, the left core microstructure is a triangular lattice arrangement.
Preferably, the optical fiber substrate material is selected from Topas.
The utility model discloses possess following advantage: 1. mode coupling occurs only at the intersection of the two-core dispersion curves, so that the sensor can accurately detect small changes in the refractive index of the microfluid; 2. because incident terahertz wave has the broadband characteristic, consequently the utility model discloses a microfluid sensor has the broadband characteristic too; 3. because the left core adopts the design of an equal-difference layered microstructure, the mode birefringence is effectively increased, and the linear polarization characteristic of the THz wave at the input end is better matched; 4. with the widespread application of 3D printing technology, various optical fiber devices based on complex microstructured cores will be more easily manufactured. Therefore, the ultra-sensitive microfluidic sensor based on the terahertz microstructure dual-core optical fiber has a very wide application prospect in the fields of biology, chemistry, medicine and the like with high precision requirements on sensing and measurement.
Drawings
Fig. 1 is an example schematic diagram of an ultrasensitive microfluidic sensor 100 based on a terahertz microstructure dual-core fiber: the device consists of a coating layer 12, a cladding 11, a left core 13 and a right core 14. The left core 13 is an input port, and the right core 14 is an output port.
FIG. 2 is a schematic cross-sectional view of a terahertz ultrasensitive microfluidic sensor.
FIG. 3 is a schematic cross-sectional view of a left core microstructure of a terahertz ultrasensitive microfluidic sensor.
FIG. 4 is a dispersion curve corresponding to the Y-polarization mode of the two-core fundamental mode when the right-core microfluid has different refractive index variations.
FIG. 5 is a partial enlargement of the dispersion curve, with the dispersion curve having a cross-point of two cores at 1THz, corresponding to a liquid refractive index of 1.37108.
Fig. 6 is a mode field distribution of two-core fundamental mode Y polarization mode when the microfluidic refractive index n =1.37108 and the incident terahertz wave frequencies are 0.99THz, 1THz and 1.01 THz.
FIG. 7 is the relationship between the terahertz frequency at the right core output port and the refractive index of the microfluid to be measured.
Detailed Description
The present invention will be described in detail with reference to the accompanying drawings and examples.
Example (c): the basic structure of the broadband and ultrasensitive refractive index sensor 100 based on the terahertz microstructure fiber core photonic crystal fiber is composed of a coating layer 12, a cladding 11, a left core 13 and a right core 14, wherein the left core 13 is an input port, and the right core 14 is an output port.
The cladding consists of circular air holes 21 arranged in a triangular lattice, the diameter of the air holes D =420
Lattice constant L =450
。
The left core microstructure adopts an equal-difference layered design and consists of elliptical air holes 13 arranged in a triangular lattice manner, and the lattice constant l =40
The major and minor semiaxes of the ellipse are a and b, a: b =3: 1. Let b = r, then a =3 r. The central microstructure ellipse 30 has a minor axis length of 3
The first layer microstructure 31 has an elliptical minor axis length of 4
The length of the minor axis of the ellipse of the second layer microstructure 32 is 5
The length of the elliptical short axis of the third layer of microstructure 33 is 6
The fourth layer microstructure 34 has a minor axis length of 7
The fifth layer microstructure 35 has an elliptical minor axis length of 8
。
And microfluid with specific refractive index is introduced into the right core, and the dispersion curve of the fundamental mode Y polarization mode of the two cores has only one intersection point due to the difference of the slopes of the dispersion curves of the two cores. At the intersection point, only terahertz waves of a certain frequency in the left core will couple to the right core. That is, in the operating frequency range, the right core of a microfluid with a certain refractive index can only match with the left core of a terahertz wave with a certain frequency. The refractive index of the microfluid can be accurately obtained by measuring the frequency of the terahertz wave at the output port of the right core. Simultaneously, because incident terahertz wave has the broadband characteristic, consequently the microfluid sensor also has the broadband characteristic. The device has an operating bandwidth of 0.5-1.5THz and a measured refractive index in the range of 1.36149-1.380665. In the vicinity of 1THz, the sensitivity of the device was 51.22 THz/RIU.
In this example, the fiber substrate material 22 is selected from a cyclic olefin polymer TOPAS, which has a relatively constant refractive index of 1.53 in the terahertz band.
Optical fiber fabrication can be done in two ways. The size of the microstructure of the terahertz optical fiber device is large, so that the optical fiber can be manufactured by adopting a 3D printing mode with a polymer as a base material. Conventional fiber drawing methods may also be employed: the optical fiber preform is manufactured by using polymer waveguides with the same shape but different hollow sizes in a layered close packing mode, and a similar microstructure can be obtained after drawing.
Claims (4)
1. A terahertz microstructure double-core optical fiber ultra-sensitive microfluidic sensor is characterized in that a left core is an input port, a right core is an output port, the cross section structure of an optical fiber is that a plurality of air holes are designed in a substrate material, the cladding is composed of round air holes with the same size, a sub-wavelength micro air hole array meeting an equal-difference layering condition is designed in the left core, and microfluid to be detected is filled in the right core.
2. The terahertz microstructure dual-core fiber ultrasensitive microfluidic sensor according to claim 1, wherein the fiber cladding is in a triangular lattice arrangement, and the lattice constant can be set to 450 μm.
3. The terahertz microstructure dual-core optical fiber ultrasensitive microfluidic sensor according to claim 1, wherein the left core microstructure is an elliptical air hole which is arranged in a triangular lattice manner and meets an equal-difference layering condition, and a lattice constant can be set to be 40 μm.
4. The terahertz microstructure dual-core optical fiber ultrasensitive microfluidic sensor according to claim 1, wherein the left core microstructure is designed by equal-difference layering, namely, on the cross section of the optical fiber, the fiber core microstructure is divided into a plurality of layers, the microstructure basic unit is an ellipse, and the ratio of the major semi-axis a to the minor semi-axis b of the ellipse is 3:1, the minor semi-axis of the central ellipse is r, and the dimension of the minor semi-axis of the ellipse is increased by a fixed length delta r every layer outwards.
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