A miniature spectrometer comprises an input unit, a stray light filtering structure, and a miniature diffraction grating. The input unit receives a first optical signal and a second optical signal. The stray light filtering structure has first and second filter sections to filter out the second optical signal. The first and second filter sections have first and second dentate structures disposed on opposite sides. The first and second dentate structures define an optical channel for the transmission of the first optical signal. The second optical signal enters into the first or the second dentate structure and is filtered out by the first or the second dentate structure. The miniature diffraction grating receives the first optical signal from the stray light filtering structure and separates the first optical signal into a plurality of spectral components.