Yang Bu | University of the Chinese academy of sciences (original) (raw)

Papers by Yang Bu

In confocal scanning imaging system, using apodization masks can improve the system resolution. A... more In confocal scanning imaging system, using apodization masks can improve the system resolution. A mask based on circle grating function with different spacing is presented and made, which is simple and easy to practically make and apply. The experiments of using a mask are performed in a reflection-mode fiber confocal scanning microscope. The intensity response curves in transverse and axial direction of this system are given. A sharp straight edge of a flat object is measured. And the 2D image of a biological organism is also given. The results demonstrate that adding this apodization mask does not reduce the axial resolution while improve the transverse resolution.

Two optical sectioning imaging technologies with visible laser and near infrared laser illuminati... more Two optical sectioning imaging technologies with visible laser and near infrared laser illumination to apply industrial and biologic detection are presented respectively in this paper. One of them is based on fiber optical confocal scanning microscopy, the other is imaging-relay arrangement with small visible field. The systems have resolution of submicron at lateral direction and nanometer resolution in axial direction and wider work range about submillimeter magnitude.

Since the self-pumped phase-conjugate (SPPC) mirrors generated by total internal reflections (Cat... more Since the self-pumped phase-conjugate (SPPC) mirrors generated by total internal reflections (Cat conjugator) in photorefractive crystals were discovered, they have shown great application potentials in many fields. However, the response time of phase-conjugate generation in photorefractive crystals is slower under continuous-wave illumination than required for many applications. Consequently, much attention has been attracted in the area of photorefractive researches using short laser pulses with high peak intensity, and the photorefractive characteristics under pulse conditions have been intensively investigated. The light source usually utilized are Nd:YAG lasers. Recently, SPPC mirrors with a light source of laser diode (LD) has been used in many applications because of the excellent features of low price, compact structure, and frequency tunability of LDs. As a light source for pulse operation, LD can be utilized in such fields as optical communication, optical measurements, and so on. We report the performance of self-pumped phase conjugation in Ce:BaTiO/sub 3/ with repetitively pulsed nanosecond pulses from a LD.

A position sensor based on slit imaging is proposed and its measurement principle is described. A... more A position sensor based on slit imaging is proposed and its measurement principle is described. An imaging slit is illuminated by a collimated laser beam with square-wave modulation and imaged on a detection double slit through a 4f system. A magnified image of the detection double slit is formed on a bi-cell detector. The position of the imaging slit is obtained by detecting light intensity on two parts of the bi-cell detector. In experiments, the feasibility of the sensor was verified. The repeatability was less than 40 nm.

This paper proposes an analytical model to describe the mask diffraction in EUV lithography. The ... more This paper proposes an analytical model to describe the mask diffraction in EUV lithography. The model is used to improve the understanding of the EUV mask performance and to analyze relevant mask topography effects. The multilayer and absorber constituting the EUV mask are simulated separately in this model. The light incident on the mask is first diffracted by the absorber, and then reflected by the multilayer and propagated upwards through the absorber again. The multilayer reflection is calculated by a mirror approximation, and the absorber transmission is calculated by a modified Kirchhoff model, where the absorber is considered to be thin and located in a certain plane. Moreover, an analytical expression of the diffraction spectrum of masks with arbitrary pattern orientation is derived. Comparisons with rigorous simulation are used to validate the accuracy of the developed model. It predicts mask diffraction of 16nm wide line and space features. For 0.35 NA EUV systems with an incidence angle of 6° the simulated CD errors are below 0.5 nm, with a pattern pitch ranging from 32nm to 250nm.

Optik, 2001

The performance of laser-diode (LD) self-pumped phase-conjugation (SPPC) using cerium-doped bariu... more The performance of laser-diode (LD) self-pumped phase-conjugation (SPPC) using cerium-doped barium titanate (Ce:BaTiO 3 ) crystal was investigated. The reflectivity of the phase conjugator against the incident angle and the incident position was measured in two configurations, and the reflectivity could reach as high as 74%. According to the optical path patterns appearing in the crystal, it is believed that the LD-SPPC in Ce:BaTiO 3 is established by a stimulated photorefractive backscattering and four-wave mixing mechanism.

Science China-physics Mechanics & Astronomy, 2008

Optical frequency domain phase conjugation (FDPC) is based on phase conjugation of spectrum of an... more Optical frequency domain phase conjugation (FDPC) is based on phase conjugation of spectrum of an input signal. It is equivalent to the phase conjugation and the time reversal of the temporal envelope of an input signal. The use of FDPC to control polarization signal distortion in birefringent optical fiber systems is proposed. Evolution of polarization signals in the system using midway FDPC is analyzed theoretically and simulated numerically. It is shown that the distortion of polarization signals can be controlled effectively by FDPC. The impairments due to dispersion and nonlinear effects can be suppressed simultaneously.

Optik, 2001

Self-pumped phase conjugation was performed in a photorefractive cerium-doped barium titanate cry... more Self-pumped phase conjugation was performed in a photorefractive cerium-doped barium titanate crystal by nanosecond pulses from a laser diode. The reflectivity of the phase conjugator against the incident angle and the incident position was measured in two configurations. The steadystarte reflectivity of the pulsed phase-conjugate wave increases and the response time decreases as pulse width of incident pulses increases. Fig. 1. Setup for self-pumped phase-conjugate experiments using nanosecond pulses from a laser diode: PBS, polarizing beam splitter.

Optics and Laser Technology, 2001

In this paper, the displacement of an object is measured with a photothermal phase-modulating las... more In this paper, the displacement of an object is measured with a photothermal phase-modulating laser diode interferometer. A feedback control system is designed to reduce the measurement errors caused by the uctuations in the optical wavelength of the laser diode and the vibrations of the optical components in the interferometer. A new method is proposed to enlarge the measuring range of displacement. Using this method, the measuring range is enlarged from half wavelength to nearly 125 m and the measurement accuracy is about 1 nm. The simulation and experimental results have shown the usefulness of the method and the feedback control system.

A polarization modulator based on splitting with a Savart plate and rotation of an analyzer for a... more A polarization modulator based on splitting with a Savart plate and rotation of an analyzer for a moire system with grating imaging is presented, and its modulation principle is analyzed. The polarization modulator is simple and achromatic. It is composed of a polarizer, a Savart plate, and an analyzer. The polarizer and the Savart plate are placed in front of the index grating to split the image of the scale grating in the moire system. The analyzer is placed behind the grating and rotated to realize the modulation of the moire signal. The analyzer can be rotated either continually with high speed or step by step with low speed to form different modulation modes. The polarization modulator makes the moire system insensitive to the change of initial intensity. In experiments, we verified the usefulness of the polarization modulator.

Journal of The Optical Society of America B-optical Physics, 2008

We propose a theoretical model for analyzing the dynamics of a periodically driven semiconductor ... more We propose a theoretical model for analyzing the dynamics of a periodically driven semiconductor laser subject to optical feedback from a microcantilever. We numerically investigate the temporal evolution of the light intensity of the semiconductor laser, and we show the interspikes of the light intensity. These interspikes of light intensity are also demonstrated in our experiment. The validity of the theoretical model is verified. The observed phenomenon has a potential application for resonant sensing.

Optics and Laser Technology, 2001

An adaptive ÿlter for preprocessing wrapped phase image with high noise content has been develope... more An adaptive ÿlter for preprocessing wrapped phase image with high noise content has been developed. The window size of this median ÿlter is adjustable according to its location in the noisy phase image. This size-adjustable median ÿlter has not only high noise-rejection ability, but also both good phase-jump identiÿcation and image-detail preservation properties. Phase unwrapping can then be done to recover the real phase image without the hampering in uence of noise, especially the noise near the phase jumps. Both numerical simulation and experimental results used to examine the e ectiveness of this adaptive ÿlter are presented.

Since the self-pumped phase-conjugate (SPPC) mirrors generated by total internal reflections (Cat... more Since the self-pumped phase-conjugate (SPPC) mirrors generated by total internal reflections (Cat conjugator) in photorefractive crystals were discovered, they have shown great application potentials in many fields. However, the response time of phase-conjugate generation in photorefractive crystals is slower under continuous-wave illumination than required for many applications. Consequently, much attention has been attracted in the area of photorefractive researches using short laser pulses with high peak intensity, and the photorefractive characteristics under pulse conditions have been intensively investigated. The light source usually utilized are Nd:YAG lasers. Recently, SPPC mirrors with a light source of laser diode (LD) has been used in many applications because of the excellent features of low price, compact structure, and frequency tunability of LDs. As a light source for pulse operation, LD can be utilized in such fields as optical communication, optical measurements, and so on. We report the performance of self-pumped phase conjugation in Ce:BaTiO/sub 3/ with repetitively pulsed nanosecond pulses from a LD.

A position sensor based on slit imaging is proposed and its measurement principle is described. A... more A position sensor based on slit imaging is proposed and its measurement principle is described. An imaging slit is illuminated by a collimated laser beam with square-wave modulation and imaged on a detection double slit through a 4f system. A magnified image of the detection double slit is formed on a bi-cell detector. The position of the imaging slit is obtained by detecting light intensity on two parts of the bi-cell detector. In experiments, the feasibility of the sensor was verified. The repeatability was less than 40 nm.

This paper proposes an analytical model to describe the mask diffraction in EUV lithography. The ... more This paper proposes an analytical model to describe the mask diffraction in EUV lithography. The model is used to improve the understanding of the EUV mask performance and to analyze relevant mask topography effects. The multilayer and absorber constituting the EUV mask are simulated separately in this model. The light incident on the mask is first diffracted by the absorber, and then reflected by the multilayer and propagated upwards through the absorber again. The multilayer reflection is calculated by a mirror approximation, and the absorber transmission is calculated by a modified Kirchhoff model, where the absorber is considered to be thin and located in a certain plane. Moreover, an analytical expression of the diffraction spectrum of masks with arbitrary pattern orientation is derived. Comparisons with rigorous simulation are used to validate the accuracy of the developed model. It predicts mask diffraction of 16nm wide line and space features. For 0.35 NA EUV systems with an incidence angle of 6° the simulated CD errors are below 0.5 nm, with a pattern pitch ranging from 32nm to 250nm.

Optik, 2001

The performance of laser-diode (LD) self-pumped phase-conjugation (SPPC) using cerium-doped bariu... more The performance of laser-diode (LD) self-pumped phase-conjugation (SPPC) using cerium-doped barium titanate (Ce:BaTiO 3 ) crystal was investigated. The reflectivity of the phase conjugator against the incident angle and the incident position was measured in two configurations, and the reflectivity could reach as high as 74%. According to the optical path patterns appearing in the crystal, it is believed that the LD-SPPC in Ce:BaTiO 3 is established by a stimulated photorefractive backscattering and four-wave mixing mechanism.

Science China-physics Mechanics & Astronomy, 2008

Optical frequency domain phase conjugation (FDPC) is based on phase conjugation of spectrum of an... more Optical frequency domain phase conjugation (FDPC) is based on phase conjugation of spectrum of an input signal. It is equivalent to the phase conjugation and the time reversal of the temporal envelope of an input signal. The use of FDPC to control polarization signal distortion in birefringent optical fiber systems is proposed. Evolution of polarization signals in the system using midway FDPC is analyzed theoretically and simulated numerically. It is shown that the distortion of polarization signals can be controlled effectively by FDPC. The impairments due to dispersion and nonlinear effects can be suppressed simultaneously.

Optik, 2001

Self-pumped phase conjugation was performed in a photorefractive cerium-doped barium titanate cry... more Self-pumped phase conjugation was performed in a photorefractive cerium-doped barium titanate crystal by nanosecond pulses from a laser diode. The reflectivity of the phase conjugator against the incident angle and the incident position was measured in two configurations. The steadystarte reflectivity of the pulsed phase-conjugate wave increases and the response time decreases as pulse width of incident pulses increases. Fig. 1. Setup for self-pumped phase-conjugate experiments using nanosecond pulses from a laser diode: PBS, polarizing beam splitter.

Optics and Laser Technology, 2001

In this paper, the displacement of an object is measured with a photothermal phase-modulating las... more In this paper, the displacement of an object is measured with a photothermal phase-modulating laser diode interferometer. A feedback control system is designed to reduce the measurement errors caused by the uctuations in the optical wavelength of the laser diode and the vibrations of the optical components in the interferometer. A new method is proposed to enlarge the measuring range of displacement. Using this method, the measuring range is enlarged from half wavelength to nearly 125 m and the measurement accuracy is about 1 nm. The simulation and experimental results have shown the usefulness of the method and the feedback control system.

A polarization modulator based on splitting with a Savart plate and rotation of an analyzer for a... more A polarization modulator based on splitting with a Savart plate and rotation of an analyzer for a moire system with grating imaging is presented, and its modulation principle is analyzed. The polarization modulator is simple and achromatic. It is composed of a polarizer, a Savart plate, and an analyzer. The polarizer and the Savart plate are placed in front of the index grating to split the image of the scale grating in the moire system. The analyzer is placed behind the grating and rotated to realize the modulation of the moire signal. The analyzer can be rotated either continually with high speed or step by step with low speed to form different modulation modes. The polarization modulator makes the moire system insensitive to the change of initial intensity. In experiments, we verified the usefulness of the polarization modulator.

In confocal scanning imaging system, using apodization masks can improve the system resolution. A... more In confocal scanning imaging system, using apodization masks can improve the system resolution. A mask based on circle grating function with different spacing is presented and made, which is simple and easy to practically make and apply. The experiments of using a mask are performed in a reflection-mode fiber confocal scanning microscope. The intensity response curves in transverse and axial direction of this system are given. A sharp straight edge of a flat object is measured. And the 2D image of a biological organism is also given. The results demonstrate that adding this apodization mask does not reduce the axial resolution while improve the transverse resolution.

Two optical sectioning imaging technologies with visible laser and near infrared laser illuminati... more Two optical sectioning imaging technologies with visible laser and near infrared laser illumination to apply industrial and biologic detection are presented respectively in this paper. One of them is based on fiber optical confocal scanning microscopy, the other is imaging-relay arrangement with small visible field. The systems have resolution of submicron at lateral direction and nanometer resolution in axial direction and wider work range about submillimeter magnitude.

Since the self-pumped phase-conjugate (SPPC) mirrors generated by total internal reflections (Cat... more Since the self-pumped phase-conjugate (SPPC) mirrors generated by total internal reflections (Cat conjugator) in photorefractive crystals were discovered, they have shown great application potentials in many fields. However, the response time of phase-conjugate generation in photorefractive crystals is slower under continuous-wave illumination than required for many applications. Consequently, much attention has been attracted in the area of photorefractive researches using short laser pulses with high peak intensity, and the photorefractive characteristics under pulse conditions have been intensively investigated. The light source usually utilized are Nd:YAG lasers. Recently, SPPC mirrors with a light source of laser diode (LD) has been used in many applications because of the excellent features of low price, compact structure, and frequency tunability of LDs. As a light source for pulse operation, LD can be utilized in such fields as optical communication, optical measurements, and so on. We report the performance of self-pumped phase conjugation in Ce:BaTiO/sub 3/ with repetitively pulsed nanosecond pulses from a LD.

A position sensor based on slit imaging is proposed and its measurement principle is described. A... more A position sensor based on slit imaging is proposed and its measurement principle is described. An imaging slit is illuminated by a collimated laser beam with square-wave modulation and imaged on a detection double slit through a 4f system. A magnified image of the detection double slit is formed on a bi-cell detector. The position of the imaging slit is obtained by detecting light intensity on two parts of the bi-cell detector. In experiments, the feasibility of the sensor was verified. The repeatability was less than 40 nm.

This paper proposes an analytical model to describe the mask diffraction in EUV lithography. The ... more This paper proposes an analytical model to describe the mask diffraction in EUV lithography. The model is used to improve the understanding of the EUV mask performance and to analyze relevant mask topography effects. The multilayer and absorber constituting the EUV mask are simulated separately in this model. The light incident on the mask is first diffracted by the absorber, and then reflected by the multilayer and propagated upwards through the absorber again. The multilayer reflection is calculated by a mirror approximation, and the absorber transmission is calculated by a modified Kirchhoff model, where the absorber is considered to be thin and located in a certain plane. Moreover, an analytical expression of the diffraction spectrum of masks with arbitrary pattern orientation is derived. Comparisons with rigorous simulation are used to validate the accuracy of the developed model. It predicts mask diffraction of 16nm wide line and space features. For 0.35 NA EUV systems with an incidence angle of 6° the simulated CD errors are below 0.5 nm, with a pattern pitch ranging from 32nm to 250nm.

Optik, 2001

The performance of laser-diode (LD) self-pumped phase-conjugation (SPPC) using cerium-doped bariu... more The performance of laser-diode (LD) self-pumped phase-conjugation (SPPC) using cerium-doped barium titanate (Ce:BaTiO 3 ) crystal was investigated. The reflectivity of the phase conjugator against the incident angle and the incident position was measured in two configurations, and the reflectivity could reach as high as 74%. According to the optical path patterns appearing in the crystal, it is believed that the LD-SPPC in Ce:BaTiO 3 is established by a stimulated photorefractive backscattering and four-wave mixing mechanism.

Science China-physics Mechanics & Astronomy, 2008

Optical frequency domain phase conjugation (FDPC) is based on phase conjugation of spectrum of an... more Optical frequency domain phase conjugation (FDPC) is based on phase conjugation of spectrum of an input signal. It is equivalent to the phase conjugation and the time reversal of the temporal envelope of an input signal. The use of FDPC to control polarization signal distortion in birefringent optical fiber systems is proposed. Evolution of polarization signals in the system using midway FDPC is analyzed theoretically and simulated numerically. It is shown that the distortion of polarization signals can be controlled effectively by FDPC. The impairments due to dispersion and nonlinear effects can be suppressed simultaneously.

Optik, 2001

Self-pumped phase conjugation was performed in a photorefractive cerium-doped barium titanate cry... more Self-pumped phase conjugation was performed in a photorefractive cerium-doped barium titanate crystal by nanosecond pulses from a laser diode. The reflectivity of the phase conjugator against the incident angle and the incident position was measured in two configurations. The steadystarte reflectivity of the pulsed phase-conjugate wave increases and the response time decreases as pulse width of incident pulses increases. Fig. 1. Setup for self-pumped phase-conjugate experiments using nanosecond pulses from a laser diode: PBS, polarizing beam splitter.

Optics and Laser Technology, 2001

In this paper, the displacement of an object is measured with a photothermal phase-modulating las... more In this paper, the displacement of an object is measured with a photothermal phase-modulating laser diode interferometer. A feedback control system is designed to reduce the measurement errors caused by the uctuations in the optical wavelength of the laser diode and the vibrations of the optical components in the interferometer. A new method is proposed to enlarge the measuring range of displacement. Using this method, the measuring range is enlarged from half wavelength to nearly 125 m and the measurement accuracy is about 1 nm. The simulation and experimental results have shown the usefulness of the method and the feedback control system.

A polarization modulator based on splitting with a Savart plate and rotation of an analyzer for a... more A polarization modulator based on splitting with a Savart plate and rotation of an analyzer for a moire system with grating imaging is presented, and its modulation principle is analyzed. The polarization modulator is simple and achromatic. It is composed of a polarizer, a Savart plate, and an analyzer. The polarizer and the Savart plate are placed in front of the index grating to split the image of the scale grating in the moire system. The analyzer is placed behind the grating and rotated to realize the modulation of the moire signal. The analyzer can be rotated either continually with high speed or step by step with low speed to form different modulation modes. The polarization modulator makes the moire system insensitive to the change of initial intensity. In experiments, we verified the usefulness of the polarization modulator.

Journal of The Optical Society of America B-optical Physics, 2008

We propose a theoretical model for analyzing the dynamics of a periodically driven semiconductor ... more We propose a theoretical model for analyzing the dynamics of a periodically driven semiconductor laser subject to optical feedback from a microcantilever. We numerically investigate the temporal evolution of the light intensity of the semiconductor laser, and we show the interspikes of the light intensity. These interspikes of light intensity are also demonstrated in our experiment. The validity of the theoretical model is verified. The observed phenomenon has a potential application for resonant sensing.

Optics and Laser Technology, 2001

An adaptive ÿlter for preprocessing wrapped phase image with high noise content has been develope... more An adaptive ÿlter for preprocessing wrapped phase image with high noise content has been developed. The window size of this median ÿlter is adjustable according to its location in the noisy phase image. This size-adjustable median ÿlter has not only high noise-rejection ability, but also both good phase-jump identiÿcation and image-detail preservation properties. Phase unwrapping can then be done to recover the real phase image without the hampering in uence of noise, especially the noise near the phase jumps. Both numerical simulation and experimental results used to examine the e ectiveness of this adaptive ÿlter are presented.

Since the self-pumped phase-conjugate (SPPC) mirrors generated by total internal reflections (Cat... more Since the self-pumped phase-conjugate (SPPC) mirrors generated by total internal reflections (Cat conjugator) in photorefractive crystals were discovered, they have shown great application potentials in many fields. However, the response time of phase-conjugate generation in photorefractive crystals is slower under continuous-wave illumination than required for many applications. Consequently, much attention has been attracted in the area of photorefractive researches using short laser pulses with high peak intensity, and the photorefractive characteristics under pulse conditions have been intensively investigated. The light source usually utilized are Nd:YAG lasers. Recently, SPPC mirrors with a light source of laser diode (LD) has been used in many applications because of the excellent features of low price, compact structure, and frequency tunability of LDs. As a light source for pulse operation, LD can be utilized in such fields as optical communication, optical measurements, and so on. We report the performance of self-pumped phase conjugation in Ce:BaTiO/sub 3/ with repetitively pulsed nanosecond pulses from a LD.

A position sensor based on slit imaging is proposed and its measurement principle is described. A... more A position sensor based on slit imaging is proposed and its measurement principle is described. An imaging slit is illuminated by a collimated laser beam with square-wave modulation and imaged on a detection double slit through a 4f system. A magnified image of the detection double slit is formed on a bi-cell detector. The position of the imaging slit is obtained by detecting light intensity on two parts of the bi-cell detector. In experiments, the feasibility of the sensor was verified. The repeatability was less than 40 nm.

This paper proposes an analytical model to describe the mask diffraction in EUV lithography. The ... more This paper proposes an analytical model to describe the mask diffraction in EUV lithography. The model is used to improve the understanding of the EUV mask performance and to analyze relevant mask topography effects. The multilayer and absorber constituting the EUV mask are simulated separately in this model. The light incident on the mask is first diffracted by the absorber, and then reflected by the multilayer and propagated upwards through the absorber again. The multilayer reflection is calculated by a mirror approximation, and the absorber transmission is calculated by a modified Kirchhoff model, where the absorber is considered to be thin and located in a certain plane. Moreover, an analytical expression of the diffraction spectrum of masks with arbitrary pattern orientation is derived. Comparisons with rigorous simulation are used to validate the accuracy of the developed model. It predicts mask diffraction of 16nm wide line and space features. For 0.35 NA EUV systems with an incidence angle of 6° the simulated CD errors are below 0.5 nm, with a pattern pitch ranging from 32nm to 250nm.

Optik, 2001

The performance of laser-diode (LD) self-pumped phase-conjugation (SPPC) using cerium-doped bariu... more The performance of laser-diode (LD) self-pumped phase-conjugation (SPPC) using cerium-doped barium titanate (Ce:BaTiO 3 ) crystal was investigated. The reflectivity of the phase conjugator against the incident angle and the incident position was measured in two configurations, and the reflectivity could reach as high as 74%. According to the optical path patterns appearing in the crystal, it is believed that the LD-SPPC in Ce:BaTiO 3 is established by a stimulated photorefractive backscattering and four-wave mixing mechanism.

Science China-physics Mechanics & Astronomy, 2008

Optical frequency domain phase conjugation (FDPC) is based on phase conjugation of spectrum of an... more Optical frequency domain phase conjugation (FDPC) is based on phase conjugation of spectrum of an input signal. It is equivalent to the phase conjugation and the time reversal of the temporal envelope of an input signal. The use of FDPC to control polarization signal distortion in birefringent optical fiber systems is proposed. Evolution of polarization signals in the system using midway FDPC is analyzed theoretically and simulated numerically. It is shown that the distortion of polarization signals can be controlled effectively by FDPC. The impairments due to dispersion and nonlinear effects can be suppressed simultaneously.

Optik, 2001

Self-pumped phase conjugation was performed in a photorefractive cerium-doped barium titanate cry... more Self-pumped phase conjugation was performed in a photorefractive cerium-doped barium titanate crystal by nanosecond pulses from a laser diode. The reflectivity of the phase conjugator against the incident angle and the incident position was measured in two configurations. The steadystarte reflectivity of the pulsed phase-conjugate wave increases and the response time decreases as pulse width of incident pulses increases. Fig. 1. Setup for self-pumped phase-conjugate experiments using nanosecond pulses from a laser diode: PBS, polarizing beam splitter.

Optics and Laser Technology, 2001

In this paper, the displacement of an object is measured with a photothermal phase-modulating las... more In this paper, the displacement of an object is measured with a photothermal phase-modulating laser diode interferometer. A feedback control system is designed to reduce the measurement errors caused by the uctuations in the optical wavelength of the laser diode and the vibrations of the optical components in the interferometer. A new method is proposed to enlarge the measuring range of displacement. Using this method, the measuring range is enlarged from half wavelength to nearly 125 m and the measurement accuracy is about 1 nm. The simulation and experimental results have shown the usefulness of the method and the feedback control system.

A polarization modulator based on splitting with a Savart plate and rotation of an analyzer for a... more A polarization modulator based on splitting with a Savart plate and rotation of an analyzer for a moire system with grating imaging is presented, and its modulation principle is analyzed. The polarization modulator is simple and achromatic. It is composed of a polarizer, a Savart plate, and an analyzer. The polarizer and the Savart plate are placed in front of the index grating to split the image of the scale grating in the moire system. The analyzer is placed behind the grating and rotated to realize the modulation of the moire signal. The analyzer can be rotated either continually with high speed or step by step with low speed to form different modulation modes. The polarization modulator makes the moire system insensitive to the change of initial intensity. In experiments, we verified the usefulness of the polarization modulator.