CN109470661B - Gus Hansen displacement type SPR sensor based on M-Z interference structure - Google Patents

Gus Hansen displacement type SPR sensor based on M-Z interference structure Download PDF

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CN109470661B
CN109470661B CN201811481736.XA CN201811481736A CN109470661B CN 109470661 B CN109470661 B CN 109470661B CN 201811481736 A CN201811481736 A CN 201811481736A CN 109470661 B CN109470661 B CN 109470661B
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刘振超
王怡沁
何赛灵
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Zhejiang University ZJU
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Abstract

The invention discloses a Gus Hansen displacement type SPR sensor based on an M-Z interference structure. The invention comprises a laser, a polarization beam splitter prism, an SPR sensing module, a beam splitter, a plane mirror, a wedge-shaped substrate, a polaroid and a light intensity detector. The laser is decomposed into TE and TM light with the same direction after passing through the polarization beam splitter prism and the plane mirror group, and after passing through the SPR sensing module, the TM light has a small Gus Hansen displacement compared with the TE light. When the Gus Hansen displacement carrying the refractive index information of the sensing sample changes, the interference light intensity of the TM light passing through the M-Z interference structure changes. The invention accurately converts the tiny Guoshansen displacement into the optical path difference, and utilizes the light intensity detector to detect the interference light intensity to reflect the optical path difference, thereby improving the detection precision and detection limit of the tiny Guoshansen displacement, and taking TE light as reference, improving the stability and signal-to-noise ratio of the system.

Description

Gus Hansen displacement type SPR sensor based on M-Z interference structure
Technical Field
The invention belongs to the field of optical sensing, and relates to a Gus Hansen displacement type SPR sensor based on an M-Z interference structure.
Background
Surface Plasmon Resonance (SPR) is a metal physical optical phenomenon. Under the condition of total reflection, incident light generates evanescent waves at a total reflection interface and simultaneously generates Gus Hansen displacement. The SPR phenomenon is a resonance absorption phenomenon generated when an evanescent wave and a surface plasmon wave of a sensor chip satisfy a wave vector matching. When the SPR phenomenon occurs, most of the energy of incident light is coupled into a surface plasmon wave accompanied by amplification of the goos hansen shift. Can be with incident light decomposition for vibration direction mutually perpendicular's TM component and TE component, generally speaking, the SPR phenomenon can't be aroused to the TE component, and the SPR phenomenon can be aroused to the TM component to enlarge the Gus hansen displacement, the Gus hansen displacement that should enlarge simultaneously is influenced by the refractive index change on sensing chip surface greatly, thereby can realize the real-time detection to the refractive index of sensing chip surface sample through the change volume that detects TM component Gus hansen displacement.
An M-Z interferometer is a structure that uses amplitude-splitting to generate two beams, thereby achieving interference. The Mach-Zehnder interferometer is composed of a laser source, two beam splitters, two reflectors and a light intensity detector, wherein laser is divided into two beams by the first beam splitter, the two beams are respectively reflected by the reflectors and then combined into one beam at the second beam splitter, interference occurs, and the interference light intensity is detected by the light intensity detector. The paths of the two beams are strictly separated, so that the interference light intensity depends on the optical path difference of the two beams in propagation, and medium change information in the paths, such as the change of gas density caused by temperature change, the influence of gas flow and the like, influences the optical path difference of the two beams in propagation paths, and finally causes the change of the interference light intensity. The mach-zehnder interferometer may be used to implement sensing of information about changes in the medium in the optical propagation path.
The Gus Hansen displacement is small, and the Gus Hansen displacement variation caused by the change of the refractive index of the detection liquid is also small. In order to detect the goos hansen shift and the variation of the goos hansen shift after the refractive index is changed, a high-precision position detector is required. The smaller the refractive index change is, the smaller the Gus Hansen displacement variation is, and the higher the precision requirement on the position detector is. This limits the application of the goos hansen shift-type SPR sensor. Therefore, the invention provides the Gus Hansen displacement type SPR sensor based on the M-Z interference structure, which converts the Gus Hansen displacement variation into the interference light intensity variation and improves the detection precision of the Gus Hansen displacement, thereby improving the detection limit of the Gus Hansen displacement type SPR sensor.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides the Gus Hansen displacement type SPR sensor based on the M-Z interference structure, solves the requirement on the precision of a displacement detector in the prior art, and enhances the detection limit of a Gus Hansen displacement type SPR system.
The invention comprises a laser, a polarization beam splitter prism, an SPR sensing module, a beam splitter, a plane reflector, a wedge-shaped substrate, a polaroid and a light intensity detector, wherein light emitted by a laser source is divided into two independent beams of TM light and TE light by the combination of the polarization beam splitter prism and the reflector, Gus Hansen displacement is converted into optical path difference by an M-Z interference structure after passing through the SPR sensing module, interference occurs, and the interference light passes through the polaroid and is detected by the light intensity detector to obtain interference light intensity.
In a further specific implementation, the M-Z interference structure is composed of two beam splitters, two plane mirrors and a wedge-shaped substrate, wherein a light beam is split into two light beams by the first beam splitter, one light beam is reflected by one plane mirror after passing through the wedge-shaped substrate, and the other light beam is combined into one light beam at the second beam splitter after being reflected by the other plane mirror, and interference occurs.
In a further embodiment, the beam splitter and the plane mirror in the M-Z interference structure are parallel to each other and both form an angle of 45 ° with the beam.
In a further specific implementation, the two reflecting mirrors are perpendicular to each other and form an included angle of 45 degrees with a connecting line of the two polarization splitting prisms.
In a further specific implementation, in two optical paths of the M-Z interference structure, a wedge-shaped substrate is placed in one optical path to convert the goos-hansen shift into an optical path difference, the wedge-shaped substrate can also be replaced by a refractive prism, a non-parallel plane mirror group and the like, and the other optical path is not provided with the wedge-shaped substrate or is provided with the wedge-shaped substrate or the parallel flat plate with different wedge angles.
In a further specific implementation, the interference light intensity of the TM light and the TE light is measured by adjusting the angle of the polarizer so that the light transmitted through the polarizer is only TM light or TE light.
The invention has the beneficial effects that: the invention can improve the detection precision of the micro Gus Hansen displacement by accurately converting the micro Gus Hansen displacement into the optical path amount in the double-beam interference and reflecting the optical path change by detecting the interference light intensity by the light intensity detector, thereby improving the detection limit of the system compared with the traditional Gus Hansen displacement SPR system, and eliminating a plurality of common mode errors and improving the stability and the signal-to-noise ratio of the system by respectively reading the interference light intensity of TM light and TE light and taking the interference light intensity variation of the TE light as reference.
Drawings
FIG. 1 is a system diagram of a Guoshansen displacement SPR sensor based on an M-Z interference structure of the present invention.
FIG. 2 is a schematic diagram of the principle of increasing the detection limit of a Gus Hansen shift-type SPR sensor based on an M-Z interference structure.
Description of reference numerals:
the device comprises a 1-laser, a 2-polarization beam splitter prism, a 3-polarization beam splitter prism, a 4-plane reflector, a 5-plane reflector, a 6-SPR sensing module, a 7-beam splitter, an 8-wedge-shaped substrate, a 9-plane reflector, a 10-plane reflector, an 11-beam splitter, a 12-polarizing plate, a 13-light intensity detector and a 14-computer.
Detailed Description
The invention is described in further detail below with reference to the accompanying drawings:
the invention comprises a laser 1, polarization beam splitting prisms 2, 3, an SPR sensing module 6, beam splitters 7, 11, plane reflectors 4, 5, 9, 10, a wedge-shaped substrate 8, a polaroid 12 and a light intensity detector 13, wherein light emitted by the laser 1 is divided into two independent beams of TM light and TE light by the combination of the polarization beam splitting prisms 2, 3 and the plane reflectors 4, 5, after passing through the SPR sensing detection part SPR sensing module 6, the TM light generates Gus Hansen displacement, the Gus Hansen displacement is converted into optical path difference by the combination of the beam splitters 7, 11, the plane reflectors 9, 10 and the wedge-shaped substrate 8, and the TM light and the TE light are respectively interfered. The interference light intensity of the TM light and the TE light is respectively read by controlling the polarization angle of the polaroid 13, and the Guoshansen displacement generated by the TM light is represented by taking the change of the interference light intensity of the TE light as a reference difference.
The principle of increasing the detection limit of the M-Z interference structure-based Guoshansen shift type SPR sensor is described below with reference to FIG. 2.
TE light and TM 'light before and after the SPR sensing module sample refractive index changes are selected for analysis, when the sample refractive index at the SPR sensing prism changes, Gus Hansen displacement generated by the TM light passing through the SPR sensing prism changes, so that light can slightly translate, and the TM' light has smaller offset than the TM light as shown in figure 2. After passing through the beam splitter A, TM 'light is divided into an upper light path and a lower light path, the path of the TM' light on the lower light path is not changed, and in the upper light path with the wedge-shaped flat plate, the length of the TM 'light passing through the wedge-shaped substrate is changed, so that the optical path difference of the upper TM' light and the lower TM 'light is changed, and therefore the interference light intensity of the TM' light is changed compared with the interference light intensity of the TM light at the beam splitter B. Since the TE light does not generate the SPR phenomenon, the TE light does not substantially generate a shift when the refractive index of the sample of the SPR sensing block is changed, and thus the TE light can be used as a reference to eliminate a common mode error due to a slight disturbance of an optical system or the like.
The reason why the detection limit of SPR sensing systems based on the illustrated structure is improved over conventional goos hansen SPR sensing systems is theorized below.
Suppose that: the optical path difference of TE light, TM light and TM' light after passing through two paths of propagation paths of the M-Z interference structure is li(i ═ 1, 2, 3); the light intensity of the TE light, the TM light and the TM' light before passing through the beam splitter A is I respectivelyi(i ═ 1, 2, 3); the TM light intensity before passing through the SPR sensing module is I0The beam splitting ratio of the beam splitter A, B is 1: 1, the wedge angle of the wedge-shaped substrate is α, the sample refractive index change of TM light and TM 'light is delta n, the light ray shift is delta x', the reflectivity change delta r at the SPR sensing module is obtained, and the refractive index of the wedge-shaped substrate is nwRefractive index of air na(ii) a The light source wavelength is lambda.
As can be seen from the graph, the difference between the optical path length of TM' light and that of TM light is l2-l3＝(nw-na) Δ x 'tan α ═ a Δ x', where a ═ nw-na) tan α is a constant coefficient, and the resolution precision of the light intensity detector is Id(ii) a The resolution precision of the traditional Gus Hansen displacement type SPR system for detecting displacement is xd。
Therefore, the interference light intensity of the TE light, the TM light and the TM' light after passing through the M-Z interference structure is as follows:
Figure BDA0001893554120000041
difference value Delta I between interference light intensity of TM' and interference light intensity of TM lightdComprises the following steps:
Figure BDA0001893554120000042
substitution of the above formula into2-l3＝(nw-na) Δ x' tan α, then:
Figure BDA0001893554120000043
and I3-I2＝I0Δ r, therefore:
Figure BDA0001893554120000044
the cosine function is expanded:
Figure BDA0001893554120000045
when the optical path difference of TM light is
Figure BDA0001893554120000047
(where k is a natural number), the intensity of the interference of TM light and TE light is most sensitive to changes in Gus Hansen shift. The optical path difference of TM light is adjusted by adjusting the position of the wedge-shaped flat plate. Under the condition of the catalyst from
Figure BDA0001893554120000046
Therefore, the formula (1) can be simplified as follows:
Figure BDA0001893554120000051
the difference value Delta I between the interference light intensity of TM' and TM lightdComprises the following steps:
Figure BDA0001893554120000052
the sensitivity k' of the system is therefore:
Figure BDA0001893554120000053
when in use
Figure BDA0001893554120000054
In smaller terms, the above equation can be approximated as:
Figure BDA0001893554120000055
and traditional goos hansen displacement type SPR system direct measurement goos hansen displacement, its sensitivity k is:
Figure BDA0001893554120000056
this system compares with the detection limit of traditional goos hansen type system, has:
Figure BDA0001893554120000057
substituting k' to obtain:
Figure BDA0001893554120000058
wherein
Figure BDA0001893554120000059
The sensitivity of traditional Gus Hansen SPR and the sensitivity of traditional light intensity SPR are respectively substituted into the expression, and the following are provided:
Figure BDA00018935541200000510
k and kIGenerally, the number of detection limit enhancement times is determined by the nature of the SPR sensing module, and therefore, the number of detection limit enhancement times can be increased by adjusting the power of the light source, the wavelength of the light source, the selection of the wedge-shaped substrate and the method for selecting the light intensity detection with higher precision.
In connection with the example, the wedge angle α is chosen to be 0.5 °, nw＝1.58，na1, so a equals 0.005, light source wavelength λ 632.8nm, light intensity power I before passing through SPR sensing module0When SPR phenomenon generally occurs, I is 5mW2＝0.1I0Then, I2＝0.5mW，xdAssumed to be 10 μm, IdAssumed to be 1 μ W, in general kIApproximately 30RIU-1K is approximately 100mm RIU-1Thus, it can be calculated that:
β＝0.075+124.115≈124
therefore, compared with the traditional Gus Hansen displacement type system, the detection limit of the system is improved by about two orders of magnitude in combination with the actual situation. And in practical cases, the first term in the expression of β is generally relatively small and the second term is decisive, so β can be generally reduced to:
Figure BDA0001893554120000061
the invention can improve the detection precision of the micro Gus Hansen displacement by accurately converting the micro Gus Hansen displacement into the optical path amount in the double-beam interference and reflecting the optical path change by detecting the interference light intensity by the light intensity detector, thereby improving the detection limit of the system compared with the traditional Gus Hansen displacement SPR system, and eliminating a plurality of common mode errors and improving the stability and the signal-to-noise ratio of the system by respectively reading the interference light intensity of TM light and TE light and taking the interference light intensity variation of the TE light as reference.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.

Claims (5)

1. Gus Hansen displacement type SPR sensor based on M-Z interference structure, including laser instrument, polarization beam splitting prism, SPR sensing module, beam splitter, plane mirror, wedge base plate, polaroid, light intensity detector, its characterized in that: light emitted by a laser light source is divided into two independent beams of TM light and TE light by the combination of a polarization beam splitter prism and a reflector, after passing through an SPR sensing module, Gus Hansen displacement is converted into optical path length difference through an M-Z interference structure, interference occurs, and after passing through a polaroid, the interference light is detected by a light intensity detector to obtain interference light intensity;
the M-Z interference structure is composed of two beam splitters, two plane reflectors and a wedge-shaped substrate, wherein a light beam is split into two beams after passing through the first beam splitter, one beam is reflected by one plane reflector after passing through the wedge-shaped substrate, and the other beam are combined into one beam at the second beam splitter after being reflected by the other plane reflector, and interference is generated.
2. The SPR sensor of claim 1 based on the goos hansen shift model of M-Z interference structure, wherein: in the M-Z interference structure, the beam splitter and the plane reflector are parallel to each other and form an included angle of 45 degrees with the light beam.
3. The SPR sensor of claim 1 based on the goos hansen shift model of M-Z interference structure, wherein: the two reflectors are mutually vertical and have an included angle of 45 degrees with the connecting line of the two polarization splitting prisms.
4. The SPR sensor of claim 1 based on the goos hansen shift model of M-Z interference structure, wherein: in two paths of light paths of the M-Z interference structure, a wedge-shaped substrate is placed in one path of light path to convert the Gus Hansen displacement into an optical path difference, the wedge-shaped substrate is replaced by a refraction prism or a non-parallel plane reflector group, and the other path of light path is not provided with the wedge-shaped substrate or is provided with the wedge-shaped substrate or the parallel flat plate with different wedge angles.
5. The SPR sensor of claim 1 based on the goos hansen shift model of M-Z interference structure, wherein: the interference light intensity of the TM light and the TE light is measured by adjusting the angle of the polaroid to ensure that the light transmitted through the polaroid is only the TM light or the TE light.
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