Katsuichi Kitagawa - Academia.edu (original) (raw)
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Papers by Katsuichi Kitagawa
Applied Optics, 2008
A fiber optic sensor for simultaneous measurement of refractive index and temperature is presente... more A fiber optic sensor for simultaneous measurement of refractive index and temperature is presented. The sensing probe is realized by introducing a multimode interference device inside a high birefringence fiber loop mirror resulting in a configuration capable of refractive index and temperature discrimination. The multimode interference peak is sensitive to the surrounding refractive index (90 nm/RIU) and slightly responsive to the temperature (0.01 nm/ • C). On the other hand, the birefringent fiber loop mirror is highly sensitive to temperature (2.36 nm/ • C) and it has almost no response to refractive index. Using a power ratiometric peak detection scheme, a temperature independent refractive index measurement can be achieved with a resolution of ±2.25 × 10 −5 RIU.
Seimitsu Kōgakkaishi, 2012
To overcome the phase ambiguity problem in phase-shifting interferometry, multi-wavelength interf... more To overcome the phase ambiguity problem in phase-shifting interferometry, multi-wavelength interferometry has been long investigated. However, its industrial application has been limited because of its complex optical configurations. This paper introduces a surface profiler which uses a low-cost and simple three-wavelength imaging system consisting of a whitelight illuminator, a multi-bandpass filter and a color CCD camera. The algorithms used and experimental results are presented.
We have developed a novel film thickness measurement algorithm (GMFT), which estimates the film t... more We have developed a novel film thickness measurement algorithm (GMFT), which estimates the film thickness distribution from a color image captured by a color camera and three-wavelength light source. In this paper, we present some results of sensitivity analysis, propose an algorithm to reduce the measurement error, and discuss the measurement possibility of ultra-thin films.
2.2 Carrier fringe introduction method Carrier fringes are introduced by tilting the reference pl... more 2.2 Carrier fringe introduction method Carrier fringes are introduced by tilting the reference plane and the phase is detected. The surface profile is obtained by the Fourier transform method [2] or the spatial phase synchronization method [35]. However, since these fringe analysis methods are derived under the assumption that the uneven frequency of the measurement target surface is sufficiently lower than the frequency of carrier fringes, there is a problem that high-frequency components are lost and horizontal resolution decreases [6].
Crosstalk compensation is an essential technique in three-wavelength single-shot interferometry w... more Crosstalk compensation is an essential technique in three-wavelength single-shot interferometry which uses a commercially available RGB LED illuminator and a color camera in the imaging system. To estimate the crosstalk coefficient more easily than the conventional method, we have developed a new method which does not require three images. Instead, it estimates the coefficients from a single image by fitting the observed RGB data to a model function which is derived from a crosstalk model and an interference model. The test results agreed well with those by the conventional method.
We propose a method for determining the refractive-index profile of axially symmetric optical fib... more We propose a method for determining the refractive-index profile of axially symmetric optical fibers from transverse interferograms obtained by a Mach-Zehnder interferometer. The profile is obtained from the interferogram data by a model-fitting algorithm which uses the Abel transform of an approximate polynomial expression of the profile. This algorithm is simple to use, easily applicable to multi-layer fibers, and does not require the Fourier transform. The proposed method is validated through computer simulations and actual experiments.
A crosstalk compensation technique is proposed for three-wavelength single-shot interferometry. T... more A crosstalk compensation technique is proposed for three-wavelength single-shot interferometry. This technique is essential when a commercially available RGB LED illuminator and a color camera are used for the imaging system. Based on a linear model, the crosstalk compensation algorithm is derived. The crosstalk coefficients are obtained from the linear regression analysis of the R,G,B signals in three images captured with a different LED illumination. The effectiveness of the proposed technique has been confirmed by several methods. Finally, it has been applied to the single-shot interferometric measurement of 1 m step height. The algorithms used and experimental results are presented.
Conventional transparent film thickness measurement methods such as spectroscopy are basically ca... more Conventional transparent film thickness measurement methods such as spectroscopy are basically capable of measuring a single point at a time, and the spatial resolution is limited. We propose a novel areal film thickness measurement method by extending the Global Model Fitting algorithm developed for three-wavelength interferometric surface profiling. It estimates the film thickness distribution from a color image captured by a color camera with three-wavelength illumination. The validity of the proposed method is demonstrated by computer simulations and actual experiments.
Wavelength scanning interferometry is a known technique to precisely measure the surface topograp... more Wavelength scanning interferometry is a known technique to precisely measure the surface topography and plate thickness for transparent materials, such as glass. However, conventional methods have some problems in the practical applications that they require precise sample surface position adjustments relative to the reference surface, and highly accurate linear wavelength scanning. We propose a leastsquares model-fitting algorithm which estimates the surface topography and plate thickness from the interferograms obtained by arbitrary wavelength shift. The LD wavelength tuned by temperature control is measured by a wavelength meter, and the measured values are used in the data analysis. The validity of the proposed method is proved by computer simulations and actual experiments. The atual test results showed good agreement with those by a conventional method, and a onesigma repeatability of 2 nm was obtained.
1.Introduction For measuring the thickness of plastic film or its coating film, various methods h... more 1.Introduction For measuring the thickness of plastic film or its coating film, various methods have been used, such as (1) infrared method, (2) radiation method (β-ray, γ-ray, X-ray, fluorescent X-ray, etc.), (3) spectroscopic method, (4) optical interference method, (5) electrostatic capacity method, (6) microwave method, etc. However, most of them are point measurement and mechanical scanning of the sample or the instrument is necessary to obtain the thickness distribution. On the other hand, the surface profiler that uses optical interference is widely used in the industry because it can measure surface profiles in the field of view of a camera collectively at high accuracy and at high speed [1]. Consider the application of this device to the thickness measurement of plastic films. The author has already proposed and put into practical use a method for simultaneously measuring the front and back surface profiles and film thickness distribution of a transparent film by interferog...
Two-Dimensional Frequency Estimation for Fringe Analysis by Phase Gradient Detection Katsuichi KI... more Two-Dimensional Frequency Estimation for Fringe Analysis by Phase Gradient Detection Katsuichi KITAGAWA A new frequency estimation technique is proposed, which enables us to estimate two-dimensional frequencies of interferometric fringes with high accuracy and low computational cost. It is accomplished by phase gradient detection, where phases are calculated by a local model fitting algorithm for carrier pattern analysis. The algorithms used and experimental results are presented.
SICE Trans. on Industrial Application, 2009
A new frequency estimation technique is proposed, which enables us to estimate two-dimensional fr... more A new frequency estimation technique is proposed, which enables us to estimate two-dimensional frequencies of interferometric fringes with high accuracy and low computational cost. It is accomplished by phase gradient detection, where phases are calculated by a local model fitting algorithm for carrier pattern analysis. The algorithms used and experimental results are presented.
In the Vertical Scanning White-Light Interferometry, two peaks appear in the interference wavefor... more In the Vertical Scanning White-Light Interferometry, two peaks appear in the interference waveform if a transparent film exists on the surface to be measured. An algorithm has been developed that can detect the position of those peaks quickly and accurately, and a “Film Profiler” has been put into practical use, which is able to measure both the profiles of front and back surfaces and the thickness distribution of a transparent film simultaneously. This technique is applicable to transparent films with the optical thickness of approximately 1m or greater, and it is used effectively in semiconductor and LCD manufacturing processes.
Applied Optics, 2008
A fiber optic sensor for simultaneous measurement of refractive index and temperature is presente... more A fiber optic sensor for simultaneous measurement of refractive index and temperature is presented. The sensing probe is realized by introducing a multimode interference device inside a high birefringence fiber loop mirror resulting in a configuration capable of refractive index and temperature discrimination. The multimode interference peak is sensitive to the surrounding refractive index (90 nm/RIU) and slightly responsive to the temperature (0.01 nm/ • C). On the other hand, the birefringent fiber loop mirror is highly sensitive to temperature (2.36 nm/ • C) and it has almost no response to refractive index. Using a power ratiometric peak detection scheme, a temperature independent refractive index measurement can be achieved with a resolution of ±2.25 × 10 −5 RIU.
Seimitsu Kōgakkaishi, 2012
To overcome the phase ambiguity problem in phase-shifting interferometry, multi-wavelength interf... more To overcome the phase ambiguity problem in phase-shifting interferometry, multi-wavelength interferometry has been long investigated. However, its industrial application has been limited because of its complex optical configurations. This paper introduces a surface profiler which uses a low-cost and simple three-wavelength imaging system consisting of a whitelight illuminator, a multi-bandpass filter and a color CCD camera. The algorithms used and experimental results are presented.
We have developed a novel film thickness measurement algorithm (GMFT), which estimates the film t... more We have developed a novel film thickness measurement algorithm (GMFT), which estimates the film thickness distribution from a color image captured by a color camera and three-wavelength light source. In this paper, we present some results of sensitivity analysis, propose an algorithm to reduce the measurement error, and discuss the measurement possibility of ultra-thin films.
2.2 Carrier fringe introduction method Carrier fringes are introduced by tilting the reference pl... more 2.2 Carrier fringe introduction method Carrier fringes are introduced by tilting the reference plane and the phase is detected. The surface profile is obtained by the Fourier transform method [2] or the spatial phase synchronization method [35]. However, since these fringe analysis methods are derived under the assumption that the uneven frequency of the measurement target surface is sufficiently lower than the frequency of carrier fringes, there is a problem that high-frequency components are lost and horizontal resolution decreases [6].
Crosstalk compensation is an essential technique in three-wavelength single-shot interferometry w... more Crosstalk compensation is an essential technique in three-wavelength single-shot interferometry which uses a commercially available RGB LED illuminator and a color camera in the imaging system. To estimate the crosstalk coefficient more easily than the conventional method, we have developed a new method which does not require three images. Instead, it estimates the coefficients from a single image by fitting the observed RGB data to a model function which is derived from a crosstalk model and an interference model. The test results agreed well with those by the conventional method.
We propose a method for determining the refractive-index profile of axially symmetric optical fib... more We propose a method for determining the refractive-index profile of axially symmetric optical fibers from transverse interferograms obtained by a Mach-Zehnder interferometer. The profile is obtained from the interferogram data by a model-fitting algorithm which uses the Abel transform of an approximate polynomial expression of the profile. This algorithm is simple to use, easily applicable to multi-layer fibers, and does not require the Fourier transform. The proposed method is validated through computer simulations and actual experiments.
A crosstalk compensation technique is proposed for three-wavelength single-shot interferometry. T... more A crosstalk compensation technique is proposed for three-wavelength single-shot interferometry. This technique is essential when a commercially available RGB LED illuminator and a color camera are used for the imaging system. Based on a linear model, the crosstalk compensation algorithm is derived. The crosstalk coefficients are obtained from the linear regression analysis of the R,G,B signals in three images captured with a different LED illumination. The effectiveness of the proposed technique has been confirmed by several methods. Finally, it has been applied to the single-shot interferometric measurement of 1 m step height. The algorithms used and experimental results are presented.
Conventional transparent film thickness measurement methods such as spectroscopy are basically ca... more Conventional transparent film thickness measurement methods such as spectroscopy are basically capable of measuring a single point at a time, and the spatial resolution is limited. We propose a novel areal film thickness measurement method by extending the Global Model Fitting algorithm developed for three-wavelength interferometric surface profiling. It estimates the film thickness distribution from a color image captured by a color camera with three-wavelength illumination. The validity of the proposed method is demonstrated by computer simulations and actual experiments.
Wavelength scanning interferometry is a known technique to precisely measure the surface topograp... more Wavelength scanning interferometry is a known technique to precisely measure the surface topography and plate thickness for transparent materials, such as glass. However, conventional methods have some problems in the practical applications that they require precise sample surface position adjustments relative to the reference surface, and highly accurate linear wavelength scanning. We propose a leastsquares model-fitting algorithm which estimates the surface topography and plate thickness from the interferograms obtained by arbitrary wavelength shift. The LD wavelength tuned by temperature control is measured by a wavelength meter, and the measured values are used in the data analysis. The validity of the proposed method is proved by computer simulations and actual experiments. The atual test results showed good agreement with those by a conventional method, and a onesigma repeatability of 2 nm was obtained.
1.Introduction For measuring the thickness of plastic film or its coating film, various methods h... more 1.Introduction For measuring the thickness of plastic film or its coating film, various methods have been used, such as (1) infrared method, (2) radiation method (β-ray, γ-ray, X-ray, fluorescent X-ray, etc.), (3) spectroscopic method, (4) optical interference method, (5) electrostatic capacity method, (6) microwave method, etc. However, most of them are point measurement and mechanical scanning of the sample or the instrument is necessary to obtain the thickness distribution. On the other hand, the surface profiler that uses optical interference is widely used in the industry because it can measure surface profiles in the field of view of a camera collectively at high accuracy and at high speed [1]. Consider the application of this device to the thickness measurement of plastic films. The author has already proposed and put into practical use a method for simultaneously measuring the front and back surface profiles and film thickness distribution of a transparent film by interferog...
Two-Dimensional Frequency Estimation for Fringe Analysis by Phase Gradient Detection Katsuichi KI... more Two-Dimensional Frequency Estimation for Fringe Analysis by Phase Gradient Detection Katsuichi KITAGAWA A new frequency estimation technique is proposed, which enables us to estimate two-dimensional frequencies of interferometric fringes with high accuracy and low computational cost. It is accomplished by phase gradient detection, where phases are calculated by a local model fitting algorithm for carrier pattern analysis. The algorithms used and experimental results are presented.
SICE Trans. on Industrial Application, 2009
A new frequency estimation technique is proposed, which enables us to estimate two-dimensional fr... more A new frequency estimation technique is proposed, which enables us to estimate two-dimensional frequencies of interferometric fringes with high accuracy and low computational cost. It is accomplished by phase gradient detection, where phases are calculated by a local model fitting algorithm for carrier pattern analysis. The algorithms used and experimental results are presented.
In the Vertical Scanning White-Light Interferometry, two peaks appear in the interference wavefor... more In the Vertical Scanning White-Light Interferometry, two peaks appear in the interference waveform if a transparent film exists on the surface to be measured. An algorithm has been developed that can detect the position of those peaks quickly and accurately, and a “Film Profiler” has been put into practical use, which is able to measure both the profiles of front and back surfaces and the thickness distribution of a transparent film simultaneously. This technique is applicable to transparent films with the optical thickness of approximately 1m or greater, and it is used effectively in semiconductor and LCD manufacturing processes.
Doctoral Dissertation, University of Tokyo, 2011
An automatic film thickness measurement system for ink-jet color filters has been developed using... more An automatic film thickness measurement system for ink-jet color filters has been developed using the three-wavelength single-shot method. First, the effect of the direction of the introduced fringes was considered, and it was demonstrated that horizontal fringes were better than vertical fringes in the case of this measurement target.
Next, we developed the auto-focus and alignment techniques necessary for automation. Both of them were realized by fringe image processing without any new hardware.
From the test results with actual samples, it was confirmed that the measurement repeatability on the nanometer order was achieved without any special vibration isolation mechanism.
In order to further improve the vibration resistance and speed of the system, we have developed a high-brightness three-wavelength illumination method using a multi-bandpass filter (MBPF). We have also reduced the computation time by more than one digit by adopting the GPU and developing a Look-Up-Table height calculation algorithm. As a result, an automatic film thickness measurement system with a high measurement speed of 1.5 s per image (1.5 micro second per pixel) has been developed.
Doctoral Dissertation, University of Tokyo, 2011
We have proposed a method of determining the thickness profile of a stand-alone transparent film ... more We have proposed a method of determining the thickness profile of a stand-alone transparent film by inserting it into the optical path of an interference system and determining the film thickness from the change in the measurement results of the reference surface. First, the basic principle was confirmed by the wide-field-of-view interferometer. In addition, in the microscope-type interferometer, the effect of the sample height was investigated, and the practicality of the two-step measurement method was confirmed. This method can easily and stably measure the thickness profile of a transparent film using a commercially available reflective-type surface profiler, without being affected by the position or waviness of the sample. This method can also be applied to ultra-thin and multi-layered films.
Next, we proposed a method for simultaneous measurement of the film thickness and refractive index of transparent films and plates using white-light interferometry. The effectiveness of the method was confirmed by measuring thin glass plates and plastic films using a commercially available surface profiler. It is characterized by the ability to obtain four types of three-dimensional data, including the surface profile, back surface profile, film thickness profile, and refractive index profile of the transparent film, in a non-destructive, non-contact manner.
Doctoral Dissertation, University of Tokyo, 2011
In this chapter, a three-wavelength single-shot method is proposed as a new interference measurem... more In this chapter, a three-wavelength single-shot method is proposed as a new interference measurement method. An inexpensive and compact three-wavelength simultaneous imaging interference optical system is composed of a commercial LED lighting system and a color camera. From the color interference fringe image obtained by this system, the 3D shape is obtained by extracting the phase information for each wavelength. We have established the following techniques required:
(1) Crosstalk compensation method
(2) Frequency estimation method
(3) Wavelength calibration method
(4) Phase calculation method
(5) Three-wavelength unwrapping method
As a result of the above development, we were able to measure the surface topography of an actual sample with a steep step of more than 1000 nm.
Doctoral Dissertation, University of Tokyo, 2011
In this chapter, a two-wavelength single-shot method is proposed as a new interference measuremen... more In this chapter, a two-wavelength single-shot method is proposed as a new interference measurement method. This method combines an inexpensive and compact dual-wavelength simultaneous imaging system consisting of a commercial LED light and a color camera with a fringe image analysis algorithm named Local Model Fitting (LMF) method. It was confirmed that an actual surface profile with a steep step of 350 nm can be measured correctly.
Doctoral Dissertation, University of Tokyo, 2011
We have developed a signal processing algorithm (KF method) that achieves simultaneous measuremen... more We have developed a signal processing algorithm (KF method) that achieves simultaneous measurement of surface height, back-surface height, and film thickness distribution of the surface covered with transparent film by positively utilizing the reflection signal from the film back-surface, which was conventionally treated as "disturbance". It can be applied to thick films with a film thickness of about 1 um or more, and was put into practical use in 2002 as the world's first film profiler. We also proposed a refractive index estimation method that can be used when the back-surface is flat. Furthermore, we developed the NF algorithm applicable to thin film with a film thickness of about 1 um or less, and put it into practical use in 2006 as the world's first practical thin film profiling algorithm.
Doctoral Dissertation, University of Tokyo, 2011
In this chapter, we proposed a local model fitting method (LMF method) as a new fringe image anal... more In this chapter, we proposed a local model fitting method (LMF method) as a new fringe image analysis algorithm. This method is characterized by less high-frequency component blunting and lower computational cost than the conventional Fourier transform method. Through computer experiments and actual sample experiments, it was confirmed that the surface profile with a sharp step difference of 50 nm can be measured correctly.
Doctoral Dissertation, University of Tokyo, 2011
In order to improve the measurement accuracy of the white light interferometry, we proposed an al... more In order to improve the measurement accuracy of the white light interferometry, we proposed an algorithm that uses the phase information (named WSI method). The equivalent wavelength is obtained from the spectrum of the interferogram, and the scanning speed is determined based on this wavelength. The approximate height is calculated from the image number where the modulation peaks, and the height is corrected using the phase calculated from the intensity data in the vicinity. From an experiment using a surface profiler incorporating this algorithm, we obtained a measurement reproducibility (sigma) of 0.91 nm for a 1 um step. This is about 7 times more accurate than the VSI method, and the accuracy can be improved without increasing the calculation time. However, when the target is a rough surface, wavelength jump noise was observed, and it was clarified that it comes from the modulation and phase offset phenomenon.
Doctoral Dissertation, University of Tokyo, 2011
In order to further expand the measurement range of the three-wavelength single-shot method, we e... more In order to further expand the measurement range of the three-wavelength single-shot method, we established a search method for the optimum combination of wavelengths. In this process, the relationship between the equivalent wavelength method and the coincidence method was clarified. Assuming the use of a commercially available color camera, we selected 470nm(B)-560nm(G)-600nm(R) as the optimum combination of wavelengths. An illumination system of this wavelength was constructed with three halogen illuminators and a three-branch optical fiber light guide. As a result, we succeeded in measuring a standard step sample of 4 um.
Doctoral Dissertation, University of Tokyo, 2011
In order to measure the surface profile using white light interference at high speed, we devised ... more In order to measure the surface profile using white light interference at high speed, we devised a new algorithm to find the peak position from the interference waveform. Applying the bandpass sampling theorem, the envelope function of the interference waveform is directly reconstructed from the sub-Nyquist sampling data. As a result, the sampling interval can be increased to about 10 times that of the conventional method, achieving the world's fastest scanning speed of 60 um/s. We have developed and commercialized a profiler incorporating this algorithm and confirmed its practicality.