Optical device and spectroscopic device

An optical device comprising:

• an incident optical system;
• an analysis optical system;
• and
• a length measurement optical system, wherein
• the incident optical system includes
• a laser light source that emits laser light, and
• an incident light dividing element that divides the laser light into first divided light and second divided light,
• the analysis optical system includes
• a first light dividing element that divides the first divided light into one and the other and then mixes the one first divided light and the other first divided light,
• a first mirror that adds a first modulation signal to the one first divided light by moving in an incident direction of the one first divided light and reflecting the one first divided light,
• a second mirror that reflects the other first divided light, and
• a first light receiving element that receives the first divided light including the first modulation signal and a sample-derived signal generated by a sample, and outputs a first light receiving signal, and
• the length measurement optical system includes
• a second light dividing element that divides the second divided light into one and the other and then mixes the one second divided light and the other second divided light,
• an optical feedback unit that feeds back the one second divided light emitted from the second light dividing element to the second light dividing element, and
• a second light receiving element that receives the second divided light including a displacement signal generated by reflection of the other second divided light by the first mirror and outputs a second light receiving signal.