Heterodyne grating interferometry system based on secondary diffraction

A heterodyne grating interferometry system based on secondary diffraction comprising a single-frequency laser, an input optical fiber, an acousto-optic modulator, a reading head, a measurement grating, an output optical fiber, a photoelectric converter and an electronic signal processing unit,

• wherein the single-frequency laser emits a single-frequency laser beam, which enters the acousto-optic modulator through the input optical fiber, and is divided into a reference light and measurement light to be input to the reading head, wherein the reading head and the measurement grating convert the reference light and measurement light into a reference interference optical signal and a measurement interference optical signal and send them to the photoelectric converter through the output optical fiber,
• wherein the photoelectric converter converts the measurement interference optical signal and the reference interference optical signal into a measurement interference electrical signal and a reference interference electrical signal and sends them to the electronic signal processing unit, and calculates 2-degree-of-freedom linear displacement of the measurement grating,
• wherein the reading head comprises an interferometer lens group, the single-frequency laser emits multiple single-frequency laser beams, the multiple single-frequency laser beams are divided into multiple beams of reference light and multiple beams of measurement light by the acousto-optic modulator,
• wherein the multiple beams of reference light and the multiple beams of measurement light are transmitted in a space-separated manner, and enter the interferometer lens group at respective different positions, and generate multiple channels of measurement interference signals and multiple channels of reference interference signals,
• wherein the interferometer lens group comprises a plurality of reflectors, a plurality of quarter-wave plates, a plurality of polarization beam splitters, a plurality of retroreflectors, a plurality of lateral beam splitter prisms and a plurality of refractors,
• wherein the single-frequency laser emits the multiple single-frequency laser beams, and the multiple single-frequency laser beams are divided into multiple beams of reference light and multiple beams of measurement light by the acousto-optic modulator,
• wherein each of the multiple beams of reference light enters respective polarization beam splitters and each of the multiple beams of measurement light enter respective polarization beam splitters so as to be reflected and transmitted, to form multiple beams of reflected measurement light, multiple beams of transmitted measurement light, multiple beams of reflected reference light and multiple beams of transmitted reference light,
• wherein the multiple beams of reflected measurement light pass through the respective quarter-wave plates, the respective refractors, the measurement grating, the respective refractors, the respective quarter-wave plates, the respective polarization beam splitters and the respective retroreflectors to be reflected multiple times, to form multiple beams of first measurement light,
• wherein the multiple beams of transmitted measurement light pass through respective lateral beam splitter prisms to form multiple beams of second measurement light,
• wherein the multiple beams of reflected reference light pass through the respective quarter-wave plates, the respective reflectors, the respective polarization beam splitters, the respective retroreflectors and the respective lateral beam splitter prisms to be reflected multiple times, to form multiple beams of first reference light,
• wherein the multiple beams of transmitted reference light pass through respective lateral beam splitter prisms to form multiple beams of second reference light, and
• wherein the multiple beams of first measurement light and the multiple beams of second measurement light interfere with the reference light to form the multiple channels of measurement interference signals, and the multiple beams of first reference light and second reference light interfere with the measurement light to form the multiple channels of reference interference signals.