Refractive-index sensor

A refractive-index sensor, comprising:

• a photonic crystal microcavity structure comprising a photonic crystal layer having a plurality of first holes and at least one second hole defined therein, the first holes being arranged in a regular pattern of first staggered parallel rows, a middle row, and a regular pattern of second staggered parallel rows in the photonic crystal layer, the middle row being between the first and second staggered parallel rows, the at least one second hole being located at a middle of the middle row of first holes, a diameter of the at least one second hole being larger than a diameter of the first holes, the number of first holes at one side of the at least one second hole in the middle row being less than half the number of first holes in any of the other rows thereby defining an input waveguide, and the number of first holes at the other side of the at least one second hole in the middle row being less than half the number of first holes in any of the other rows thereby defining an output waveguide;
• a light source disposed adjacent to the input waveguide;
• and
• a detector disposed adjacent to the output waveguide.