CN104777531A - Dynamic adjusting method for focal length based on graded-refractive-index fluid micro lens - Google Patents

Abstract

A method for dynamically adjusting the focal length based on a graded-index fluid microlens, comprising the following steps: (1) injecting a core fluid and a cladding fluid into the microcavity through a core fluid channel and a cladding fluid channel, the core fluid and the cladding fluid There is only diffusion and convective movement between the cladding fluids without chemical reaction. The cladding fluid surrounds the core fluid in a balanced manner. There is no relative slip between the core fluid and the cladding fluid. The core fluid and the cladding fluid Fluids are two kinds of fluids with different refractive indices; (2) The beam propagation direction of the microlens is consistent with the fluid flow direction; (3) By adjusting the fluid velocity, temperature, concentration or the type of microfluid, the fluid diffusion process is controlled to realize micro Adjustment of the spatial distribution of the refractive index in the cavity; (4) under the condition of low fluid flow rate, the dynamic adjustment of the focal length can be realized through the change of the fluid mass fraction or the change of the flow rate. The present invention can effectively and dynamically adjust the focal length and has good flexibility.

Description

A Dynamic Adjustment Method of Focus Length Based on Gradient Index Fluid Microlens

technical field

The invention belongs to the field of optical microlenses, in particular to a method for dynamically adjusting focal length based on fluid microlenses with gradient refractive index.

Background technique

Existing fluid microlenses usually use liquid-liquid lenses, which are generally off-chip focusing fluid microlenses, which cannot realize the integration of on-chip systems. Recently, Professor Whitesides' group developed a microlens that can dynamically adjust the curvature of the liquid-liquid lens surface, realizing the adjustable focal length in the chip (Tang, Sindy K.Y.; Stan, Claudiu A.; Whitesides, George M, Dynamically reconfigurable liquid-core liquid-cladding lens in amicrofluidic channel, Lab.Chip.,8(2008):395-401, Dynamically adjustable liquid core layer-liquid cladding lens based on microfluidic channel, Lab on a Chip, 8(2008) :395-401). However, the microlens realized by the liquid-liquid lens interface needs a high laminar flow velocity to keep the surface stable, which means that in order to ensure the stable and continuous operation of the microlens, a large flow of liquid must be continuously injected.

Contents of the invention

In order to overcome the shortcomings of existing fluid microlenses that cannot dynamically adjust the distance and have poor flexibility, the present invention provides a dynamic focal length adjustment method based on gradient index fluid microlenses that can effectively and dynamically adjust the focal length and has good flexibility.

The technical solution adopted by the present invention to solve its technical problems is:

A method for dynamically adjusting focal length based on a graded-index fluid microlens. The dynamic adjustment method for focal length adopts a fluid microlens with on-chip focal length and focal spot dynamically adjustable. The fluid microlens includes a microcavity, a core layer flow channel, a package Layer flow channels and outlet flow channels, the clad flow channels communicate with the surrounding circle of the inlet of the microcavity, the core layer flow channels communicate with the core layer inlet, and the inner diameter of the core layer inlet is less than the The inner diameter of the microcavity is small, and the inlet of the core layer is on the same axis as the microcavity, and the outlet of the inlet of the core layer communicates with the flow channel of the cladding layer and faces the inlet of the microcavity. The outlet of the microcavity communicates with the outlet channel;

The method for dynamically adjusting the focal length includes the following steps:

(1) Inject the core layer fluid and the cladding fluid into the microcavity through the core layer flow channel and the cladding layer flow channel, and the core layer fluid and the cladding layer fluid only have diffusion and convective movement between each other. No chemical reaction occurs, the cladding fluid surrounds the core fluid in a balanced manner, there is no relative slip between the core fluid and the cladding fluid, and the core fluid and the cladding fluid are two kinds of fluids with different refractive indices fluid;

(2) The light beam propagation direction of the microlens is consistent with the fluid flow direction;

(3) Control the fluid diffusion process by adjusting the fluid flow rate, temperature, concentration or type of microfluid, so as to realize the regulation and control of the spatial distribution of the refractive index in the microcavity;

(4) In the case of a low fluid flow rate (less than 5×10 ³ pL/s), the low flow rate means that the flow rate is less than 5×10 ³ pL/s, and the dynamic adjustment of the focal length is realized by changing the fluid mass fraction or changing the flow rate .

Further, in the step (3), the diffusion and convection process is determined by the fluid average velocity U and the diffusion coefficient D, wherein the diffusion coefficient D is affected by the concentration C and temperature T, so the fluid average velocity U, concentration C and temperature T are changed It can regulate the performance of the gradient index fluid microlens.

Furthermore, in the step (3), assuming that the temperature of the liquid is constant, the diffusion coefficient D, concentration C and average velocity U of the liquid will be the influencing factors of the diffusion and convection process, directly determining the focusing performance of the gradient index fluid microlens .

In the step (4), keep the temperature of the liquid, the flow rate, and the type of the microfluid constant, and obtain the influence of the change of the fluid mass fraction on the distribution of the refractive index of the fluid in the microcavity, thereby realizing the continuation of the focal length of the gradient index fluid microlens Dynamic adjustment.

In the step (4), keep the temperature of the liquid, the mass fraction, and the type of the microfluid constant, and obtain the influence of the change of flow velocity on the distribution of the refractive index of the fluid in the microcavity, thereby realizing the continuous dynamics of the focal length of the gradient index fluid microlens adjust.

The core flow channel and the cladding flow channel are arranged in parallel, and the cladding flow channel and the axis of the microcavity are arranged perpendicular to each other.

The technical idea of the present invention is: compared with the above-mentioned liquid-liquid lens, the gradient index fluid microlens (L-GRIN) works based on the diffusion and convection principle of laminar flow with different refractive indices, rather than relying on a fixed liquid-liquid curved surface , so high-level flow velocities are not required, and the consumption of liquid has been proven to be more than 100 times less than that of liquid-liquid lenses. And the L-GRIN microlens realizes the refractive index gradient by dynamically adjusting the fluid conditions instead of changing the curvature of the microlens surface, so its optical properties can be tuned in real time. From a principle point of view, it is possible to realize the dynamic adjustment of the on-chip focal length of the gradient index fluid microlens (L-GRIN).

The beneficial effects of the present invention are mainly manifested in that the focal length can be effectively and dynamically adjusted, and the adjustment flexibility is good.

Description of drawings

Figure 1 is a structural diagram of a fluidic microlens with on-chip focal length and focal spot dynamically adjustable, where x, y, and z represent coordinate axes, the x-axis direction represents the direction of fluid flow and the direction of incident beam propagation, and yoz represents vertical light The section of the axis, xoy represents the section containing the optical axis.

Fig. 2 is a cross-sectional view of a fluid microlens with on-chip focal length and focal spot dynamically adjustable.

Fig. 3 is a distribution diagram of cross-sectional refractive index at five different locations.

Fig. 4 is a resultant deformation trend diagram of the focal length adjusted by adjusting the mass fraction.

Fig. 5 is a graph showing different refractive index distributions along the direction of liquid flow in the cross section.

Figure 6 is a diagram of the influence of flow velocity on focal length.

Detailed ways

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

Referring to Figures 1 to 6, a focal length dynamic adjustment method based on a graded index fluid microlens, the focal length dynamic adjustment method uses a fluid microlens with on-chip focal length and focal spot dynamically adjustable, and the fluid microlens includes a microcavity 1. The core flow channel 2, the clad flow channel 3 and the outlet flow channel 4, the clad flow channel 3 is connected with the surrounding circle of the entrance of the microcavity 1, the core layer flow channel 2 is connected with the core The layer inlet 5 communicates, the inner diameter of the core layer inlet 5 is smaller than the inner diameter of the microcavity 1, and the core layer inlet 5 is on the same axis as the microcavity 1, and the outlet of the core layer inlet 5 is in communication with the cladding flow channel 3 and facing the inlet of the microcavity 1, and the outlet of the microcavity 1 is in communication with the outlet flow channel 4;

The method for dynamically adjusting the focal length includes the following steps:

(1) Inject the core layer fluid and the cladding fluid into the microcavity through the core layer flow channel and the cladding layer flow channel, and the core layer fluid and the cladding layer fluid only have diffusion and convective movement between each other. No chemical reaction occurs, the cladding fluid surrounds the core fluid in a balanced manner, there is no relative slip between the core fluid and the cladding fluid, and the core fluid and the cladding fluid are two kinds of fluids with different refractive indices fluid;

(2) The light beam propagation direction of the microlens is consistent with the fluid flow direction;

(3) Control the fluid diffusion process by adjusting the fluid flow rate, temperature, concentration or type of microfluid, so as to realize the regulation and control of the spatial distribution of the refractive index in the microcavity;

(4) In the case of a low fluid flow rate (less than 5×10 ³ pL/s), the low flow rate means that the flow rate is less than 5×10 ³ pL/s, and the dynamic adjustment of the focal length is realized by changing the fluid mass fraction or changing the flow rate .

Further, in the step (3), the diffusion and convection process is determined by the fluid average velocity U and the diffusion coefficient D, wherein the diffusion coefficient D is affected by the concentration C and temperature T, so the fluid average velocity U, concentration C and temperature T are changed It can regulate the performance of the gradient index fluid microlens.

Furthermore, in the step (3), assuming that the temperature of the liquid is constant, the diffusion coefficient D, concentration C and average velocity U of the liquid will be the influencing factors of the diffusion and convection process, directly determining the focusing performance of the gradient index fluid microlens .

In the step (4), keep the temperature of the liquid, the flow rate, and the type of the microfluid constant, and obtain the influence of the change of the fluid mass fraction on the distribution of the refractive index of the fluid in the microcavity, thereby realizing the continuation of the focal length of the gradient index fluid microlens Dynamic adjustment.

In the step (4), keep the temperature of the liquid, the mass fraction, and the type of the microfluid constant, and obtain the influence of the change of flow velocity on the distribution of the refractive index of the fluid in the microcavity, thereby realizing the continuous dynamics of the focal length of the gradient index fluid microlens adjust.

The core channel 2 and the cladding channel 3 are arranged in parallel, and the axes of the cladding channel 3 and the microcavity 1 are arranged perpendicular to each other.

In this embodiment, the core layer liquid and the cladding layer liquid are respectively injected through the core layer inlet 5 and the cladding layer inlet, and flow out through the outlet respectively. The main part of the fluid microlens is a miniature cylindrical cavity, and the diffusion and convection process of the fluid in the cylindrical cavity will have a gradient refractive index distribution. The cross-section design of the fluid microlens is shown in Figure 2, the inlet diameter is designed to be 50 μm, and the diameter of the cladding inlet is designed to be 150 μm. Ethylene glycol solution (core liquid) and deionized water (DI, cladding liquid) are injected into the cavity at the same time, and the axisymmetric gradient refractive index distribution on the xoy section: the near-axis refractive index is the largest, along the direction of the central axis of the cavity and vertical The refractive index distribution in the axial direction gradually decreases.

The parameters are simulated and optimized using the finite element method (FEM) and ray tracing. The refractive index distribution of the device can be obtained by simulating and calculating the concentration of the two-phase fluid in the microcavity after the diffusion and convection process stabilizes. In the microcavity, the diffusion and convection of the fluid affect the refractive index distribution of the fluid microlens. In the process of convection and diffusion, U=(Q _core +Q _clad )/R ² π represents the fluid velocity of the cavity, and the distribution of Q _core and Q _clad Represents the flow velocity of the core and cladding, and R is the diameter of the cladding fluid.

Because the decisive factors of the diffusion and convection process include the fluid average velocity U and the diffusion coefficient D, and the diffusion coefficient is affected by the concentration C and temperature T, so changing the fluid average velocity U, concentration and temperature will have a great impact on the performance of the fluid microlens important regulatory role. For example, when the mass fraction in ethylene glycol solution changes from 0.025 to 0.95, the diffusion coefficient between deionized water and ethylene glycol changes from 3.75×10 ^-10 m ² /s to 1.17×10 ^-9 m ² /s . In addition, when the mass fraction of ethylene glycol is 0.8, the diffusion coefficient of the liquid changes from 3.15×10 ^-10 m ² /s to 6.45×10 ^-10 m ² /s when the temperature changes from 30°C to 50°C. Therefore, on the premise that the temperature of the liquid is assumed to be constant, the diffusion coefficient D, concentration C and average velocity U of the liquid will be the main factors affecting the diffusion and convection process, which directly determine the focusing performance of the microlens. It is assumed that deionized water and ethylene glycol solution are selected as the cladding and core liquids, respectively, and the calculation is performed assuming that the cladding and core liquid flow rates are the same and there is no relative slippage. Effective focus adjustment can be achieved at low flow rates, and focal spot size adjustment can be achieved at high flow rates. Therefore, the focal length can be achieved by adjusting the velocity of the fluid.

In order to form the diffusion convection effect, high refractive index ethylene glycol (n _core = 1.432) and low refractive index deionized water (n _clad = 1.332) will be injected into the microcavity of the designed microlens along the same direction . From the injection of the core layer and cladding liquid into the microcavity, the process of diffusion and convection begins to take place, where U and D will be definite values. And this initial velocity can be calculated by the formula U=(Q _core +Q _clad )/R ² π. Considering that the cross-sectional area of the cladding is 8 times that of the core, in order to keep the core and cladding fluids from slipping relative to each other, Q _clad /Q _core =8 is also adopted in the simulation process. In order to illustrate the importance of the influence of the diffusion coefficient D on the distribution of the conversion rate, here is the distribution of the refractive index of the xoy section under different diffusion coefficients, D=1×10 ^-9 m ² /s and D=4×10 ^-10 m ² /s.

The simulation results with a large diffusion coefficient have obvious diffusion effects along the horizontal and vertical directions, while the gradient effect of the refractive index distribution with a small diffusion coefficient is not obvious. This shows that the diffusion coefficient is a very effective means to control the distribution of the graded refractive index, which also directly affects the performance of the microlens. Due to the change of ambient temperature, the diffusion coefficient of the liquid will be greatly affected, so the adjustment of the diffusion coefficient can be realized by changing the temperature of the liquid.

The core layer and cladding liquid with lower flow rate will have a stronger diffusion effect, and the factors affecting the diffusion process of the liquid include diffusion coefficient D, flow rate U and concentration C. Therefore, the adjustment of the focal length of the microlens can be realized by changing the concentration and flow rate of the liquid and the mass fraction of the ethylene glycol solution.

The influence of the solution mass fraction: Since the concentration of the solution will directly affect the diffusion coefficient, the change of the diffusion coefficient will directly affect the change of the microlens. During the diffusion convection process in the microcavity, the effect of diffusion along the flow direction becomes more and more obvious. However, this diffusion leads to different liquid concentrations at different locations, and this concentration change will directly reflect on the diffusion coefficient at each location, so the diffusion coefficient is not constant throughout the process. This phenomenon is especially prominent in concentrated solutions. So far, there is no exact expression to describe the variation law of this phenomenon. Therefore, in order to simplify the calculation complexity, a solution with a low concentration, an ethylene glycol solution with a mass fraction of 0.05 to 0.4, and a constant diffusion coefficient D are used for simulation in the process of diffusion and convection. Liquids with different concentrations use different diffusion coefficients to describe the law of diffusion coefficients. Also in order to keep the core and cladding liquids without relative slip, and keep a constant value (Q _core =1×10 ³ pL/s, Q _clad =8×10 ³ pL/s). The simulated quality scores were simulated multiple times from 0.05 to 0.4 with a step size of 0.05. Figure 3 selects the cross-sectional refractive index distribution at five different positions for comparison. The positions from the entrance are 50 μm, 100 μm, 150 μm, 200 μm and 250 μm. The calculation results show that the sharpness of the central part of the refractive index increases with the The quality score increases with the increase. The resulting deformation trends for the focal length adjusted by the adjusted mass fraction are shown in Fig. 4.

The change in focal length decreases from 942 μm to 11 μm when the mass fraction increases from 0.05 to 0.4. The calculation result is enough to explain the change of mass fraction, which is an important factor to control the focal length.

Change of flow velocity: In order to compare the influence of flow velocity on the distribution of refractive index, ethylene glycol is used as the core liquid, deionized water is used as the cladding liquid, and the two-phase fluid is injected into the microfluidic chamber along the same direction on the premise that there is no relative sliding. . The flow rate is changed from 0.5×10 ³ pL/s to 5×10 ³ pL/s, assuming that the diffusion coefficient D=8×10 ^-10 m ² /s, the viscosity coefficient μ=1×10 ^-3 Pa·s, and the mass The score is a fixed value of 0.3 to simulate the refractive index distribution of the microcavity and the focusing effect on the incident light at different flow rates.

The change of the flow rate is from 0.5×10 ³ pL/s to 5×10 ³ pL/s with a step interval of 0.5×10 ³ pL/s. The simulation results show that the refractive index distribution can be adjusted by adjusting the flow rate when the diffusion coefficient remains unchanged. This control is reflected in the control of the focal length through the calculation of the ray tracing method. Figure 5 shows the different refractive index distributions in the cross-section along the direction of liquid flow, and the positions are 50 μm, 100 μm, 150 μm, 200 μm and 250 μm, respectively. The influence of flow velocity on focal length is shown in Fig. 6 respectively.

In the fluid microlens of this embodiment, regulating the mass fraction of ethylene glycol (core layer liquid) and the flow velocity of the two liquids is an effective method to change the focal length of the output beam: when the mass fraction is raised from 0.05 to 0.4, the focal length is from 0.05 to 0.4. 942 μm decreased to 11 μm; while keeping the flow rate constant, the microlens focal length change decreased from 127.1 μm to 8 μm by increasing the core layer flow rate from 0.5×10 ³ pL/s to 5×10 ³ pL/s.

Claims (6)

1. A focal length dynamic adjustment method based on a graded-index fluid microlens, characterized in that: the focal length dynamic adjustment method adopts a dynamically adjustable fluid microlens with an in-chip focal length and a focal spot, and the fluid microlens includes a microcavity, A core layer flow channel, a clad layer flow channel and an outlet flow channel, the clad layer flow channel communicates with the surrounding circle of the inlet of the microcavity, the core layer flow channel communicates with the core layer inlet, and the core layer The inner diameter of the inlet is smaller than the inner diameter of the microcavity, and the inlet of the core layer is on the same axis as the microcavity, and the outlet of the inlet of the core layer communicates with the cladding flow channel and faces the The inlet of the microcavity, the outlet of the microchamber communicates with the outlet channel; The method for dynamically adjusting the focal length includes the following steps: (1) Inject the core layer fluid and the cladding fluid into the microcavity through the core layer flow channel and the cladding layer flow channel, and the core layer fluid and the cladding layer fluid only have diffusion and convective movement between each other. No chemical reaction occurs, the cladding fluid surrounds the core fluid in a balanced manner, there is no relative slip between the core fluid and the cladding fluid, and the core fluid and the cladding fluid are two kinds of fluids with different refractive indices fluid; (2) The light beam propagation direction of the microlens is consistent with the fluid flow direction; (3) Control the fluid diffusion process by adjusting the fluid flow rate, temperature, concentration or type of microfluid, so as to realize the regulation and control of the spatial distribution of the refractive index in the microcavity; (4) It is carried out at a low fluid flow rate, the low flow rate being less than 5×10 ³ pL/s, and the dynamic adjustment of the focal length is realized by changing the fluid mass fraction or changing the flow rate. 2. a kind of focal length dynamic adjustment method based on graded index fluid microlens as claimed in claim 1, is characterized in that: in described step (3), described diffusion convection process is formed by fluid average velocity U and diffusion coefficient D It is determined that the diffusion coefficient D is affected by the concentration C and temperature T, so changing the fluid average velocity U, concentration C and temperature T can regulate the performance of the graded index fluid microlens. 3. a kind of focal length dynamic adjustment method based on graded index fluid microlens as claimed in claim 1 or 2, it is characterized in that: in described step (3), when assuming that liquid temperature is constant, the diffusion coefficient D of liquid , concentration C and average velocity U will be the influencing factors of the diffusion and convection process, which directly determine the focusing performance of the graded index fluid microlens. 4. a kind of focal length dynamic adjustment method based on gradient index fluid microlens as claimed in claim 1 or 2, is characterized in that: in described step (4), keep liquid temperature, flow rate, microfluidic kind constant, The influence of fluid mass fraction change on the distribution of fluid refractive index in the microcavity is obtained, so as to realize the continuous dynamic adjustment of the focal length of the gradient index fluid microlens. 5. a kind of focal length dynamic adjustment method based on graded index fluid microlens as claimed in claim 1 or 2, is characterized in that: in described step (4), keep liquid temperature, mass fraction, microfluidic kind constant , the influence of flow rate change on the distribution of fluid refractive index in the microcavity is obtained, so as to realize the continuous dynamic adjustment of the focal length of the gradient index fluid microlens. 6. A kind of focal length dynamic adjustment method based on graded index fluid microlens as claimed in claim 1 or 2, it is characterized in that: described core flow passage, cladding flow passage are arranged in parallel, and described cladding flow The channels and the axis of the microcavity are arranged perpendicular to each other.