CN104568839A - Biosensor based on cascade connection of optical resonant cavity and reflective polarization converter - Google Patents

Abstract

The invention discloses a biosensor based on the cascade connection of an optical resonant cavity and a reflective polarization converter, comprising a broadband light source, a circulator, a detector, an optical resonant cavity and a reflective polarization converter; the first port of the circulator and the broadband The light source is connected, the second port is connected to the input end of the optical resonant cavity, and the third port is connected to the detector; the output end of the optical resonant cavity is connected to the reflective polarization converter; the biological surface film with specific adsorption function in the optical resonant cavity ; The biological surface film is in contact with the liquid to be measured. The present invention utilizes that after the components to be detected in the liquid to be tested are absorbed by the biological surface film, the effective refractive index changes of the two polarization states in the optical resonant cavity are different, resulting in different shifts of the resonance peaks of the two polarization states, thereby A vernier effect is generated, which amplifies the movement of the sensor transmission spectrum envelope and converts it into a change of output power, reduces the manufacturing cost of the sensor, and greatly eliminates the temperature sensitivity.

Description

Biosensor Based on Cascaded Optical Resonator and Reflective Polarization Converter

technical field

The invention relates to an optical biosensor, in particular to a biosensor based on the cascade connection of an optical resonant cavity and a reflective polarization converter.

Background technique

Optical sensors are very promising detection tools in areas such as biomedical diagnostics, environmental monitoring, and food safety. Optical sensors have many advantages: strong immunity to electromagnetic interference, label-free detection, and easy fabrication of optoelectronic integrated chips. Based on silicon-on-insulator (SOI) evanescent wave sensor, due to its high sensitivity, high integration and compatibility with CMOS technology, it has attracted the attention of researchers at home and abroad. The light waves satisfying the resonance conditions will be coupled into the optical resonant cavity, and the light waves will decay exponentially in the measured liquid in the form of evanescent waves. When the measured liquid changes, the resonance condition of the optical resonant cavity also changes, and the change of the measured substance can be obtained by measuring the shift of the resonance wavelength or the change of the light energy with a fixed wavelength near the resonance wavelength. How to improve the sensitivity of the sensor is a problem that researchers have been concerned about. Although high-Q optical resonators can improve the sensitivity of optical biosensors, they require high-resolution spectrometers or narrow linewidth tunable lasers, which increase the cost of optical biosensors.

The optical sensor using double resonator cascaded to generate the vernier effect does not require a high-resolution spectrometer or a narrow linewidth laser, which can greatly reduce the cost of the sensor while improving the sensitivity of the sensor. The magnification of the sensitivity of this sensor is inversely proportional to the difference in the free spectral range (FSR) of the two optical resonators (sensing cavity and reference cavity), so two optical resonators with equal structures can obtain the maximum sensitivity. However, because the upper cladding of the sensing cavity is the measured liquid, and the upper cladding of the reference cavity is a fixed low-refractive index material, plus the errors of the manufacturing process such as photolithography and etching, it is difficult to prepare the same FSR in practical applications. Two optical resonant cavities, the final sensitivity is greatly affected; moreover, because the upper cladding material of the sensing ring and the reference ring are different, the thermal expansion coefficient is different, so it is difficult to eliminate the influence of temperature on the sensor characteristics.

Contents of the invention

The purpose of the present invention is to provide a biosensor based on the cascade connection of optical resonant cavity and reflective polarization converter, which uses the combination of optical resonant cavity and reflective polarization converter to utilize the effective refractive index change of optical resonant cavity under two polarization states The difference between the two forms a vernier effect, which converts the spectral detection information into the change of the total output power of the transmission, thereby greatly reducing the production cost of the optical sensor; at the same time, the reference optical resonant cavity and the sensing optical resonant cavity are the same resonant cavity, which solves the problem of two It is difficult to make an optical resonant cavity with the same FSR, and it can also greatly eliminate the influence of temperature on the sensor.

The purpose of the present invention is achieved through the following technical solutions: a biosensor based on optical resonant cavity and reflective polarization converter cascaded, including broadband light source, circulator, detector, optical resonant cavity and reflective polarization converter The first port of the circulator is connected to the broadband light source; the second port of the circulator is connected to the input end of the optical resonant cavity; the third port of the circulator is connected to the detector; the optical resonant cavity The output end is connected with the reflective polarization converter; the surface of the waveguide core layer in the optical resonant cavity has a biological surface film with specific adsorption function; the biological surface film of the optical resonant cavity is in contact with the liquid to be measured; the reflective type The polarization converter includes a polarization converter and mirrors.

Further, by adjusting the thickness of the biological surface film, the effective refractive index of the optical resonant cavity for both TE and TM modes of polarized light is the same, so that all the resonance frequencies of the optical resonant cavity for the TE mode are the same as those for the TM mode All resonant frequencies coincide.

Further, the specific adsorption of the biological surface film in the optical resonant cavity to the substance to be tested in the measured liquid causes the effective refractive index of the TM mode of the optical resonant cavity to change drastically, but the effective refractive index of the TE mode changes slowly, so that When a resonant frequency of the optical resonant cavity for the TE mode coincides with a resonant frequency for the TM mode, other adjacent resonant peaks do not completely coincide, thereby producing a vernier effect.

Further, the optical resonant cavity has periodic filtering characteristics, such as a Fabry Perot cavity or a ring resonant cavity.

Further, the optical resonant cavity can be formed by using a planar integrated optical waveguide, or discrete optical elements, or optical fibers.

The beneficial effects of the present invention are: the present invention uses the input light source as a broadband light source, reducing the cost of the sensor; the optical resonant cavity can use an integrated optical waveguide device, making the sensor smaller in size, more portable, and easy to realize high-throughput and multi-parameter measurement; Using biomimetic molecular modification technology, the biological surface film with specific adsorption function is modified in the optical resonant cavity to make the sensor have specific detection function; the effective refractive index of the two polarization states of light changes with the change of the measured substance, only using A single optical resonant cavity can form a vernier effect, which improves the integration of the sensor and reduces the cost of use; there is no temperature-sensitive characteristic caused by the different thermal expansion coefficients of the cladding materials on the reference resonant cavity and the sensing resonant cavity; by adjusting the biological Molecular modification of the film thickness is very convenient to achieve the same effective refractive index of the two resonant cavities in TE and TM modes, thereby significantly improving the sensitivity of the sensor.

Description of drawings

1 is a schematic diagram of a biosensor based on cascaded optical resonant cavity and reflective polarization converter;

2 is a schematic diagram of an end face of an optical resonant cavity in an optical biosensor;

Fig. 3 is a schematic diagram of the output spectrum curve of the broadband light source;

Fig. 4 is a schematic diagram of the change curve of the effective refractive index of the waveguide with the thickness of the biological surface film in the TE and TM modes;

Figure 5 is a schematic diagram of the total output spectrum of the sensor before and after the measured substance is adsorbed;

Fig. 6 is a schematic diagram of the relationship between the optical power received by the detector and the thickness of the biological surface film;

In the figure, broadband light source 1, circulator 2, detector 3, optical resonant cavity 4, reflective polarization converter 5, first port 21 of circulator 2, second port 22 of circulator 2, optical resonant cavity 4 Input end 41, third port 23 of circulator 2, output end 42 of optical resonant cavity 4, polarization converter 51, mirror 52, waveguide core layer 81 in optical resonant cavity 4, biological surface film 6, measured liquid 7 , The lower cladding layer 82 of the waveguide core layer.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Example

As shown in Figure 1, the present invention is based on an optical biosensor cascaded with an optical resonant cavity and a reflective polarization converter, including a broadband light source 1, a circulator 2, a detector 3, an optical resonant cavity 4 and a reflective polarization converter 5; the first port 21 of the circulator 2 is connected to the broadband light source 1; the second port 22 of the circulator 2 is connected to the input end 41 of the optical resonant cavity 4; the third port 23 of the circulator 2 is connected to the detector 3; the output end 42 of the optical resonant cavity 4 is connected to the reflective polarization converter 5; the reflective polarization converter 5 includes a polarization converter 51 and a mirror 52.

As shown in Figure 2, the surface of the waveguide core layer 81 in the optical resonant cavity 4 has a biological surface film 6 with specific adsorption function; the biological surface film 6 of the optical resonant cavity is in contact with the measured liquid 7; The lower cladding layer 82 is a low refractive index material.

The light emitted by the broadband light source 1 passes through the first port 21 of the circulator 2, and enters the optical resonant cavity 4 from the second port 22 of the circulator 2. After the light of a polarization mode interacts with the biological surface film 6, it is reflected After being reflected by the polarization converter 5 , it enters the optical resonant cavity 4 again, and the light of another polarization mode interacts with the biological surface film 6 again, and is finally output to the detector 3 from the third port 23 of the circulator 2 .

As shown in FIG. 3 , the output spectrum of the broadband light source 1 has a center wavelength around 1555 nm. In this example, the ring resonant cavity in the planar integrated optical waveguide is selected as the optical resonant cavity of the sensor. The design selects SOI (silicon-on-insulator) material. The waveguide core layer 81 has a height of 250nm and a width of 240m. The ratio is 1.33, and the radius of the ring resonator is 13 μm. The polarization converter 51 is made of magneto-optic crystal material. The TE and TM modes respectively indicate that the vibration direction of the electric field is parallel to and perpendicular to the interface between the biological surface membrane 6 and the waveguide core layer 81 .

As shown in Figure 4, the bionic molecular modification technology is used to adjust the thickness of the biological surface film 6. When the thickness is 27nm (initial state), TE and TM have the same effective refractive index. The transmission spectra of the optical resonator under the two polarization modes overlap, because the optical power received by the detector 3 is the integral of the entire outgoing spectral curve, so the maximum optical power value is reached at this time, and the outgoing spectral curve is shown by the solid line in Figure 5 Show; After the substance to be measured in the measured liquid 7 is adsorbed by the biological surface film 6, the thickness of the biological surface film 6 increases, the effective refractive index for the TE mode changes slowly, and the effective refractive index for the TM mode changes very large, resulting in The effective refractive indices of TE and TM are different, and the output spectrum curves of the optical resonator under the two polarization modes do not overlap. At this time, the optical power received by the detector 3 decreases, and the output spectrum curve is shown as the dotted line in Fig. 5 . Therefore, the change of the film thickness of the biological surface can be detected by measuring the change of the total optical power in the entire spectrum, so as to know the content of the substance to be tested in the liquid 7 to be tested, as shown in FIG. 6 . In this example, the highest sensitivity is 0.5dB/nm. If the smallest measurable power change is 0.01dB, the minimum change thickness of biological surface film detection is 2.0×10 ^-2 nm.

The above-mentioned embodiments are used to illustrate the present invention, but not to limit the present invention. Within the spirit of the present invention and the protection scope of the claims, any modification and change made to the present invention will fall into the protection scope of the present invention.

Claims (5)

1. A biosensor based on cascaded optical resonant cavity and reflective polarization converter, characterized in that it includes a broadband light source (1), a circulator (2), a detector (3), an optical resonant cavity (4) and A reflective polarization converter (5); the first port (21) of the circulator (2) is connected to the broadband light source (1); the second port (22) of the circulator (2) is connected to the optical resonant cavity ( 4) is connected to the input end (41); the third port (23) of the circulator (2) is connected to the detector (3); the output end (42) of the optical resonant cavity (4) is connected to the reflective polarization The converter (5) is connected; the surface of the waveguide core layer (81) in the optical resonant cavity (4) has a biological surface film (6) with a specific adsorption function; the biological surface film (6) of the optical resonant cavity (6) and The measured liquid (7) is in contact; the reflective polarization converter (5) includes a polarization converter (51) and a reflective mirror (52). 2. A biosensor based on cascaded optical resonant cavity and reflective polarization converter according to claim 1, characterized in that the optical resonant cavity (4) is realized by adjusting the thickness of the biological surface film (6). The effective refractive index for both polarized light in TE and TM modes is the same, so that all resonance frequencies of the optical resonant cavity (4) for TE modes coincide with all resonance frequencies for TM modes. 3. A biosensor based on cascaded optical resonant cavity and reflective polarization converter according to claim 1, characterized in that, the biological surface film (6) has a great influence on the measured substance in the measured liquid (7). Specific adsorption causes the effective refractive index of the TM mode of the optical resonant cavity (4) to change drastically, but the effective refractive index of the TE mode changes slowly, so that a resonant frequency of the optical resonant cavity (4) for the TE mode is the same as that for the TM When one resonant frequency of the mode coincides, the other adjacent resonant peaks do not completely coincide, resulting in a vernier effect. 4. A biosensor based on cascaded optical resonant cavity and reflective polarization converter according to claim 1, characterized in that, the optical resonant cavity (4) has a structure with periodic filtering characteristics, such as Fabry Poi Luo cavity, or ring resonant cavity. 5. A biosensor based on cascaded optical resonant cavity and reflective polarization converter according to claim 1, characterized in that the optical resonant cavity (4) can use planar integrated optical waveguides or discrete optical components, or fiber optics.