| With the development of optofluidics,more and more optical devices have been introduced into the optofluidic networks.Combined with the characteristics of easy manipulation and reconfiguration of liquid,the tunability of optical devices is realized.Tunable optofluidic devices provide a new direction for biochemical analysis and information transmission.As a binary optical device,Dammann grating is widely used in optical interconnection and parallel information reading,but it has not been introduced into optofluidic network.As an important part of on-chip optical system,in-plane optofluidic lens has obvious advantages of adjustable focal length and reconfigurable geometric structure compared with its solid counterpart.Based on the optofluidic technology,we proposed a tunable optofluidic Damman grating and an viscous force-driven in-plane tunable optofluidic lens,and their properties are tested.We have carried on the following research,1.Taking the optofluidic lens as the example,all the driving modes of tunable optofluidic devices are summarized.The modulation of optofluidic devices is mainly realized by adjusting the properties of the liquid(refractive index or refractive index gradient)or by controlling the shape of the interface.At present,liquid refractive index is mainly modulated by using liquid crystal as the liquid media or adjusting the mixing ratio of two mixable solution.Thermal diffusion or molecule diffusion could be used to establish refractive index gradient.The methods used to modulate the interface shape include temperature controlling charge injection,electrowetting effect,dielectrophoretic force,pneumatic control,hydrodynamic control and so on.2.Based on the design theory of Dammann grating,the structural parameters of1:7 × 7 Dammann grating are calculated by MATLAB.The grating adopts a liquid-solid hybrid structure,and the diffraction function structure is processed by photolithography.A microfluidic mixer mixes two solutions with different flow rate ratios to control the refractive index of the mixed liquid entering the grating chip.The refractive index of the mixed liquid ranges from 1.351-1.473.Experiments show that when the parameter N is an integer,the grating has a good beam splitting effect,the 7× 7 spots are arranged in order with good uniformity.For λ = 632.8 nm,the spot size uniformity is 78.38%,and the power uniformity is 71.01%.For λ = 532 nm,the spot size and power uniformity are 77.17% and 64.32%,respectively.Experiments have also proved that this grating has applicability to near-infrared light.Tunable optofluidic Dammann grating can not only realize the functions of traditional Dammann grating,but also could be used to generate lattice light sources in optofluidic network.Each sub light source could be coupled into each layer of microchip to realize various optical operations and enrich the functions of optofluidic chip.3.Based on the theory of viscosity,we proposed a new tunable in-plane optofluidic lens driven by viscous force.68# white mineral oil was selected as the optical medium.As liquid filling amount increases,the viscous force is enhanced,and the gas-liquid interface gradually becomes flat from convex shape,which verifies the tunability of the lens.The interface vertex curvature has a linear relationship with the interface-entrance wall distance,and the linearity rate is 99.6%.Experiments demonstrate the continuous tuning of focal length(f)from 17.7 mm to 45.1 mm.When f < 35.5 mm,the positive longitudinal spherical aberration is effectively suppressed below 0.078.Through ZEMAX simulation,we confirmed that the gas-liquid interface with even polynomial profile has the function of aberration compensation.The transverse spherical aberration of the spherical reflector is well suppressed and limited to the range of ±47 μm,and the light spot improvement rate is over 90%,up to 99%. |
