Curved diffraction grating, spectrometer and manufacturing method of curved diffraction grating

A spectrometer, comprising:

• an incident unit having an incident slit for receiving an optical signal;
• a curved diffraction grating comprising a substrate and a metal layer, wherein the substrate is a two-dimensional curved plate structure and has a first surface, a second surface and a plurality of microstructures, the first surface is disposed opposite to the second surface, the microstructures are disposed on the second surface, each of the microstructures is a saw-tooth structure and has a first groove surface and a second groove surface, an included angle between a normal line of the second surface and a normal line of the second groove surface of at least a part of the microstructures is substantially equal to a blazed angle of the curved diffraction grating, the metal layer is disposed on the microstructures and has a plurality of diffraction structures corresponding to the microstructures, the second surface focuses the optical signal, and the diffraction structures diffracts the optical signal into a plurality of spectral components;
• and
• a sensing unit for receiving the spectral components.

A manufacturing method of a curved diffraction grating, comprising following steps of:

• placing a substrate and a first mold in a pressure chamber, wherein the substrate has a first surface and a second surface, and the second surface is disposed corresponding to the first mold;
• heating the first mold and injecting a gas into the pressure chamber to form a plurality of microstructures on the second surface, each of the microstructures is a saw-tooth structure and has a first groove surface and a second groove surface, and an included angle between a normal line of the second surface and a normal line of the second groove surface of at least a part of the microstructures is substantially equal to a blazed angle of the curved diffraction grating;
• placing the substrate and a second mold in the pressure chamber, wherein the second mold has a concave surface, the concave surface is a two-dimensional curved plate structure, and the first surface is disposed opposite to the concave surface;
• heating the second mold and injecting a gas into the pressure chamber to shape the substrate into a two-dimensional curved plate structure, wherein the second surface configured with the microstructures is a concave surface;
• and
• depositing a metal layer on the second surface of the substrate, wherein the metal layer has a plurality of diffraction structures corresponding to the microstructures.