Fluid analyzer

A fluid analyzer comprising:

• a substrate;
• a quantum cascade laser formed on a surface of the substrate and including a first light-emitting surface and a second light-emitting surface located at opposite ends of the quantum cascade laser in a predetermined direction, the predetermined direction being parallel to the surface of the substrate;
• a quantum cascade detector formed on the surface of the substrate and including a same layer structure as the quantum cascade laser and a light incident surface facing the second light-emitting surface in the predetermined direction;
• and
• an optical element disposed on an optical path of light emitted from the first light-emitting surface across an inspection region in which a fluid to be analyzed is to be disposed, wherein the optical element is configured to reflect the light to feed a return light to the first light-emitting surface,
• wherein the second light-emitting surface of the quantum cascade laser is configured to transmit an output light to the light incident surface of the quantum cascade detector, and
• wherein an intensity of the output light varies in response to the return light received at the first light-emitting surface of the quantum cascade laser.