Sinusoidal phase modulation type laser self-mixing interferometer and measuring method thereof

Abstract

The invention discloses a sinusoidal phase modulation type laser self-mixing interferometer and a measuring method thereof. The interferometer comprises a helium-neon laser, a variable neutral density filter, an electro-optical crystal modulator, a target to be measured, a photoelectric detector and a signal generator. The signal generator is used for generating sinusoidal signals with frequency of omega<m>, wherein one loop of signals is used for driving the electro-optical crystal modulator, one loop of signals is used as base-frequency signal output and the other loop of signals passes through a frequency doubler and a phase shifter and then outputs doubled-frequency signals with frequency of 2 omega<m>. The output of the photoelectric detector is amplified by an operational amplifier and then is respectively mixed with the base-frequency signals and the doubled-frequency signals to obtain two loops of signals. The signals are subject to low-pass filtering and then a computer unit controls an analog-to-digital conversion unit to acquire and demodulate a phase, so as to obtain and display the real-time displacement of the target to be measured. After the interferometer is calibrated, relative measurement accuracy of 10<-6>*L can be obtained, the measurement uncertainties within the measurement ranges of 100mum and 300mum are respectively 10nm and 0.15mum, and the measurable speed range is 0-60mm/s.

Description

technical field [0001] The invention relates to the technical field of precise displacement measurement, in particular to a laser self-mixing interferometer and its measurement method involving high resolution and large measurement range. Background technique [0002] Displacement measuring instruments are the most basic part of many measuring instruments. Many other physical, chemical or biomass measurements are based on displacement measurement. Therefore, displacement measuring instruments are widely used in information science, life science, industrial production, space technology and national defense technology. has been widely used. With the rapid development of research fields such as information technology, advanced manufacturing industry, and biomedicine, displacement measuring instruments with high sensitivity, high measurement accuracy and large measurement range are required in many applications. For example, lithographic control of large-scale integrated circui...

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Problems solved by technology

Among them, capacitive displacement sensors, eddy current displacement sensors, etc. have smaller volume and lower price, but the disadvantage of such small displacement sensors is that there is nonlinearity in principle, and the linear measurement range is small and needs to be calibrated.

The laser interferometer is based on the method of optical interference, using the wavelength of light as the measuring ruler, which can realize the resolution of displacement measurement at the nanometer level. It is an important tool for large-scale precision displacement measurement in the fields of science, engineering and industry. The instrument system is complex, the cost is high, and it is a large and expensive instrument. In addition, the measured object in the specific use process is the cooperation target

For example, the 5529A dual-frequency interferometer of the American Agilent Company has a reference optical path and a measurement optical path in the optical part, so it needs to be used with a polarization beam splitter, a reference mirror, and a measured mirror. Its measurement resolution can reach 10nm, and the measured target mirror is usually Corner cube prism, larger in size and heavier in quality

However, in many applications, the analyte itself is a non-complex, and its surface cannot fix the cooperative target.

For example, in the displacement measurement of micro-electromechanical systems, the device is small in size and light in weight, and a slight measurement force will cause deformation or even damage to the measured structure

Existing laser interferometers are not suitable for precise displacement measurement of such non-cooperating targets

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