Patent ID: 8377389

Claim:
A microfluidic circuit comprising: a light, absorptive substrate, a light transmissive substrate stacked on said light absorptive substrate, wherein said light transmissive substrate has a thickness d and a refraction index n, and a microchannel at a bottom face of said light transmissive substrate, wherein the microchannel has a width w, and wherein a value of (d/w)tan [90−θ−sin −1 {(sin(90−θ))/n}] is at least 0.1, where θ is an incident angle of directed light transmitted to said microchannel, wherein the light transmissive substrate is welded with the light absorptive substrate for bonding by directing light through the light transmissive substrate, wherein said light transmissive substrate includes a light attenuation region that includes a cavity having a face that is not perpendicular to the directed light and the attenuates an amount of transmitted light to said microchannel by random reflection when light is directed through said light transmissive substrate, wherein the light attenuation region at the light transmissive substrate contains a light blocking material composed of carbon black, and wherein the microchannel does not have heat deformation.