Microfluidic switch based on photothermal vortices and tilted fiber Bragg grating

Microfluidic switches are important operating units in microfluidics that enable controlled fluid flow on the chip, providing more functionality of platform. Most fiber based photofluidic devices mainly modulate temperature gradient and microflow by varying optical power. However, only power regulation limits the diversity of the optical field, which makes it difficult to achieve microfluidic control at different localized regions. Here, optical field of a tilted fiber Bragg grating (TFBG) can be theoretically modulated by the incident light wavelength and direction based on the finite element method. A photothermal vortices based microfluidic switch is built by TFBG with multiple linear heat sources. In the simulation, when the incident light is coupled in the forward or reverse direction of TFBG, the reflected position of the optical field is positively moved along the grating region as the wavelength increases. In the experiment, the opening of the microfluidic at different positions and directions can be clearly observed when the wavelength-matched laser is incident at the TFBG in the forward or reverse direction. It is believed that the microfluidic switch provides ideas for more flexible operation and functional integration for photothermal microfluidic devices in the future.