Hiroyuki Kowa

Accurate Measurement of Light Modulation Properties of Piezoelectric Polymer

In order to study the light modulation properties due to the electrooptical effect, we prepared piezoelectric poly(L-lactic acid) (PLLA) films by drawing and annealing, and ferroelectric polyurea-5 (PU5) by vapor deposition. In all PLLA films fabricated in this study, we found that light amplitude modulation (LM) caused by applying an electric field occurs, using our experimental system based on the heterodyne interferometry principle. However, the LM was very weak. LM in the recrystallized PLLA film is stronger than those in the other PLLA films. The occurrence of LM in PU5 was confirmed using our experimental system. Such results have not been reported until now. Here, we emphasize that the occurrence of LM in PLLA fabricated by the drawing and annealing method and in PU5 film fabricated by the vapor-deposition method is clarified in this study for the first time.

Two-dimensional measurement of birefringence dispersion using spectroscopic polarized light

This paper describes a method and system for the measuring the two-dimensional distribution of birefringence dispersion. An optical arrangement consists of a white light source, parallel polarizers, a CCD camera, and an acousto-optic tunable filter for selecting wavelength of the incident light. The intensity of spectroscopic polarized light changes sinusoidally as a function of wave number, and its period changes slightly because of birefringence dispersion. The fast Fourier transform method is used to analyze the birefringence dispersion from the spectroscopic polarized light. One hundred twenty-eight captured images are used for the analysis. Some experimental results on 2-D birefringence dispersion distributions are shown for the demonstration of this method.

Development of a visual encryption device using higher-order birefringence

We propose and demonstrate a novel visual encryption device composed of higher-order birefringent elements. When an optical material with higher-order birefringence is placed between a pair of polarizers and illuminated by white light, it appears only white. In contrast, when it is illuminated by monochromatic light, the transmitted intensity varies depending cosinusoidally on the wavelength. An array of such materials can express information (e.g., letters and/or images) by controlling the birefringence of each pixel. If birefringence phase retardation can be adjusted for a specific wavelength, the information will be clearly displayed when it is illuminated at this wavelength. We denote this wavelength a key wavelength. The encryption device was fabricated by controlling the amount of higher-order birefringence to achieve high contrast only by using polarized illumination at the key wavelength. Thus, the information stored in the encryption device can be decoded only by illuminating it at the key wavelength. To demonstrate the validity of this encryption principle, we constructed a 3 × 3 pixel device in which commercial retarder films were laminated. The device was illuminated by a monochromatic light. When a readout experiment was performed using the monochromatic light at the key wavelength, the stored letter was clearly visible. On the other hand, when pixel brightness was randomly distributed with illumination at the wavelength other than the key wavelength, the letter could not be recognized. Furthermore, the stored information can be easily distributed to multiple physical keys that display arbitrary images. In this case, the birefringence phase retardation is obtained by summing the values of retardation of each pixel of the physical keys. In the experimental device, the observed image was decoded by superimposing the two images using different physical keys.

Simultaneous measurement of linear and circular birefringence with heterodyne interferometry

We present a novel technique to measure both linear and circular birefringence, simultaneously. This technique is based on an optical heterodyne interferometry which is performed by an orthogonally polarized two frequency laser. Two orthogonal components of the optical beat signal are detected by two-phase lock-in amplifier. The two components change sinusoidally with the rotation of azimuth angle of polarization devices. The retardation and the orientation of linear birefringence and the rotation angle of circular birefringence can be calculated by applying a Fourier analysis to the two sinusoidal variations. The measurement sensitivity for this method is verified by using the combination of a Babinet Soleil compensator and a half-wave plate as a sample. It is demonstrated that the birefringence of commercially available twisted nematic liquid crystal cell where a driving voltage is applied can be measured by using the proposed technique.

Birefringence Polarimeter Using Dual LiNbO3 Electrooptic Crystal Modulators

A birefringence polarimeter that uses dual LiNbO3 electrooptic crystal modulators operating at a frequency ratio of 4:1 is described. The significance of this polarimeter is that the birefringent parameters of a sample are obtained only from the modulated polarization status. The measurement, therefore, avoids depolarization effects resulting from the sample itself and the rest of the optical system. The high speed and accuracy of this polarimeter are shown by measurements using a quarter-wave plate, a Babinet–Soleil compensator, and a phase modulator.

Measurement of Pockels Effect in Piezoelectric Chiral Polymer Film

The possibility has been indicated that a piezoelectric polymer with helical chirality (chiral polymer) such as poly-L-lactic acid (PLLA) shows a large linear electrooptical constant (Pockels effect). However, the linear electrooptical constant of a PLLA film may be very small because such a film fabricated by the conventional method has a complex high-order structure with intermingled crystalline and amorphous regions. In order to measure the small linear electrooptical constant of a PLLA film, we developed a new measurement system, which is based on the heterodyne interferometry principle. In this system, the accuracy of retardation is 0.08 nm and the measurement time is 0.1 s. In our attempt to realize a PLLA film with a large linear electrooptical constant, we fabricated a PLLA film, which was heated to 120°C under 320 MPa. Finally, using our new measurement system, we obtained a linear electrooptical constant of 0.070 pm/V in the PLLA film, which is very small compared with those of other famous Pockels materials. However, the linear electrooptical constant of the PLLA film is clarified in this study for the first time.

Image detection system for 157-nm using fluorescent glass

An image detection system for vacuum ultra-violet region used a F2 laser (157nm) as a light source is proposed. A fluorescent glass (LUMILASS-G9) is employed to convert UV light into visible light. Characteristics of fluorescent glass are studied. Some beam profiles of F2 laser are analyzed as a demonstration of the imaging detection. A VUV interferometer is proposed.

Birefringence dispersion measurement by geometric phase

A measurement method of birefringence dispersion by geometric phase is described. The measurement system consists of a polarizer, a quarter wave plate, a rotating analyzer and a spectrometer. The detected intensity by a spectrometer changes sinusoidaly along wave number. A phase shifting method is applied to analyze birefringence dispersion. The total amounts of phase change in all of wavelengths are same, because geometric phase produces by cyclic changes of a state of polarization on the Poincaré sphere. The birefringence dispersion of Babinet-Soleil compensator, polymer films and a liquid crystal phase modulator is measured. Compared measured these results with literature values of birefringence dispersion, measured data agrees well. The measurement results shown the birefringence dispersion measurement by geometric phase is available to practical applications.

Extraction of polarization properties of the individual components of a layered system by using spectroscopic Mueller matrix analysis

In semiconductor and optics fields, some devices are constructed with layered systems including two or three individual layers. Measurement of polarization properties of the individual components of these layered systems is often desired. In this paper, we present methods allowing the simultaneous extraction of the polarization parameters of the individual components by analyzing spectroscopic Mueller matrices (measured at two wavelengths). We have studied both retarder-retarder and retarder-polarizer-retarder systems. The validities of the methods were successfully tested using both simulations and real polarization systems.

Mueller matrix polarimeter in 157nm

A vacuum Mueller matrix polarimeter is developed for measurement of the Mueller matrix of samples, partially, calcium fluoride materials in 157nm wavelength. From the measured Mueller matrix with no sample present, we found the influence of absorption error in the detector and orientation error in quarter-wave plates on measurement results. The birefringence of samples is determined from the Mueller matrix. Experimental results show this Mueller matrix polarimeter is available to be used for characterizing the intrinsic birefringence of materials for processed lens at the 157nm lithography.