Arai M.,Nippon Telegraph and Telephone |
Arai M.,Japan Society of Applied Physics |
Kobayashi W.,Nippon Telegraph and Telephone |
Kobayashi W.,Institute of Electronics and Information and Communication Engineers IEICE |
Kohtoku M.,Nippon Telegraph and Telephone
NTT Technical Review | Year: 2012
In this article, we review our efforts to reduce the power consumption of optical transmitter modules for Ethernet and telecommunications use. To reduce the power consumption, we aim to eliminate the light source's temperature controller and improve the stability of the output power and modulation characteristics under ambient temperature conditions. We describe a 1.3-μm-range metamorphic laser on a GaAs substrate that exhibits improved temperature characteristics. It has a characteristic temperature of 220 K and is capable of lasing up to 200°C. In addition, the bias current for 10-Gbit/s modulation at high temperature has been reduced. This laser is promising for uncooled light sources operating with low power consumption.
Hashimoto D.,Nippon Telegraph and Telephone |
Hashimoto D.,Japan Society of Applied Physics |
Shimizu K.,Nippon Telegraph and Telephone
NTT Technical Review | Year: 2014
We have been investigating hyperfine sublevels of 167Er3+ ions doped in a silicate glass fiber with the objective of demonstrating quantum memory in the 1.5-μm telecommunication band. Memory time is determined by the stability of hyperfine sublevels (the lifetime) of 167Er3+ ions, so it is therefore necessary to clarify the lifetime properties. This article describes (i) the anomalous temperature dependence of the lifetime that was unexpectedly discovered in the lifetime measurements and (ii) the physical properties of glass that resulted in the anomalous phenomenon. Copyright 2014 NTT Technical Review All Rights Reserved.
News Article | August 22, 2016
A proposed technique provides a simple and computationally inexpensive method for enhancing the spatial resolution and reducing the speckle noise of reconstructed images. The process of computer holography involves the digital generation of holographic interference patterns. This technique is used in a wide range of applications, such as in 3D displays,1 projectors,2, 3 diffractive optical elements,4 and encryption.5 The calculation of holograms from 2D and 3D objects generally requires the addition of a random phase to widely diffuse the object light (which mainly comprises low-frequency components of narrow-angle object light). This approach is illustrated in Figure 1, where an original image—see Figure 1(a)—and image reconstructions from holograms generated with and without the random phase are shown. When the random phase is not used—see Figure 1(b)—it is nearly impossible for the original image to be retrieved in the reconstruction. This is because the narrow-spreading object light means that it cannot be recorded on the hologram. In contrast, when the random phase is used—see Figure 1(c)—the reconstructed hologram retrieves the original image well. Although the random phase technique has been used in computer holography since the 1960s,6 it unfortunately leads to a considerable amount of speckle noise in the reconstructed image. Figure 1. Illustration of the random phase technique for computer holography. An original image is shown in (a), along with reconstructions that are generated—(b) without and (c) with the random phase—from holograms of the original images. In the currently available computationally efficient methods, the object light that is processed via the random phase method is uncontrollable, and it leads to the speckle noise and to the degradation of the spatial resolution of the reconstructed image. It is possible to use iterative optimization methods, e.g., the Gerchberg–Saxton algorithm,7 to reduce the speckle noise and improve the spatial resolution of the holograms, but these methods are time-consuming. The development of new methods for obtaining high-quality images via computer holography is therefore greatly desired. We have recently reported a simple and computationally inexpensive method known as ‘random phase-free computer holography’ with which we can drastically reduce the speckle noise and enhance the image quality.8–13 We achieve this by multiplying the object light with the virtual convergence light. The effectiveness of our method means that our reconstruction—see Figure 2(a)—of the image in Figure 1(a) has lower speckle noise than in the reconstructions of Figure 1(b) or (c). We also demonstrate—see Figure 2(b) and (c)—that the spatial resolution achieved with our proposed method is better than that of the random phase method. Figure 2. Illustrating the effectiveness of the proposed random phase-free computer holography technique. (a) A reconstructed image—from the original, in Figure Illustrating the effectiveness of the proposed random phase-free computer holography technique. (a) A reconstructed image—from the original, in Figure 1 (a)—generated using this approach has low speckle noise. Images of the USAF1951 test target obtained using (b) the random phase method and (c) the proposed random phase-free method. Our simple proposed method involves the multiplication of the object with the virtual convergence light, followed by the calculation of numerical diffraction from the object (see Figure 3). The complex amplitude of the object light, u (x , y ), on the image plane is multiplied using the convergence light, w(x , y ), which is given by: where λ is the wavelength, and f is the focal length (which is equal to z +z ). The distance between the focus point of the convergence light and the hologram, z , is set to the distance at which the hologram just fits in the cone of the convergence light, and z is the distance between the object and the hologram. We derive the value of f from a simple geometric relation, S /2: S /2=z : f , where the areas of the image and the hologram are given by S ×S and S ×S , respectively. Figure 3. The setup of the calculation involved in the proposed phase-free method. f : Focal length. z and z : Distance between the focus point of the convergence light and the hologram, and between the object, u (x , y ), and the hologram, respectively. Dimensions of the image and the hologram are denoted by S and S , respectively. The effectiveness of our technique14 arises because the convergence light can be used to change the directions of the 0th-, +1st-, and –1st-order wave vectors of an object to the hologram. The original and changed wave vectors are represented by the solid black and red arrows in Figure 4(a), respectively. In other words, the object light is equally distributed on the hologram. For comparison, we illustrate the equivalent situation for a Fourier hologram in Figure 4(b). In this case, if f of the convergence light is equal to z , the 0th-order light of the object is strongly concentrated on a small area of the hologram (as indicated by the blue dashed arrows). This is a well-known problem with Fourier holograms. In addition, a high dynamic range of the hologram arises from this concentration. The effective utilization of the dynamic range is particularly important for the amplitude hologram because the amplitude of spatial light modulators (SLMs) only has an 8bit dynamic range. In contrast, with our proposed method, the concentration is dispersed over the entire hologram and our average dynamic range is lower by a factor of 5–10 for the situation illustrated in Figure 4(b). This is therefore a favorable feature for use in low-dynamic range SLMs. Figure 4. Intuitive illustration of the effectiveness of convergence light for (a) the proposed phase-free method and (b) a Fourier hologram. Unlike with other projection methods, holographic projection does not intrinsically require any lenses (e.g., a zoom lens). Indeed, the lensless zoomable holographic system—see Figure 5(a)—is extremely simple because it requires only an SLM and light source, and it is therefore a promising technique for use in ultrasmall projectors. Furthermore, our proposed methodology is applicable to lensless zoomable holographic projection.3, 15,16 To demonstrate this application of our approach, we used an amplitude-modulated liquid crystal display (L3C07U from EPSON) that had a resolution of 1920×1080 pixels and a pixel pitch of 8.5μm. We also used a 120mW semiconductor laser, at a wavelength of 532nm, as the light source. To generate the amplitude holograms, we took the real part of the complex amplitude on the hologram. The optical reconstructions from the holograms we thus obtained, through the random phase and proposed random phase-free methods, are shown in Figure 5(b). Our use of the scaled diffraction17 means that both reconstructions can be zoomed without using the zoom lens. The optical reconstruction obtained through our proposed method has a higher quality (lower speckle noise and a sharper image) than that obtained via the random phase method. Our proposed method is also effective for color image reconstructions.13 Lensless zoomable color reconstructions that we produced using the random phase method and the random phase-free method are shown in Figure 6, where the latter is clearly superior. Figure 5. (a) Schematic diagram of lensless zoomable holographic projection. SLM: Spatial light modulator. (b) Lensless zoomable optical reconstructions from holograms obtained via the random phase and proposed phase-free methods. Magnification (M) values for each set of images are given. Figure 6. Lensless zoomable color reconstructions obtained using the random phase and proposed phase-free methods. In summary, we have introduced a simple and computationally inexpensive method that can be used to increase the spatial resolution and reduce the speckle noise of computer-generated holograms. In our random phase-free approach, we multiply the object light with the virtual convergence light. We have also demonstrated the suitability and effectiveness of the technique for a number of applications. In our future work we will investigate the feasibility of our proposed method for holographic 3D display, encryption, and multiple-spot generation. This work is partially supported by Japan Society for the Promotion of Science KAKENHI grants (16K00151 and 25330125). All of the results presented here were obtained using our numerical library for wave optics.18 Chiba University Tomoyoshi Shimobaba received his PhD from Chiba University in 2002 and is now an associate professor. His research interests are computer holography and its applications. He is a member of SPIE, the Optical Society (OSA), the Optical Society of Japan (OSJ), the Institute of Image Information and Television Engineers (ITE), and the Institute of Electronics, Information, and Communication Engineers (IEICE). Takashi Kakue is an assistant professor. He received his PhD from Kyoto Institute of Technology, Japan, in 2012. His research interests are holography, digital holography, computer holography, holographic interferometry, 3D imaging, high-speed imaging, and ultrafast optics. He is a member of OSA, IEEE, SPIE, OSJ, the Japan Society of Applied Physics, the Information Processing Society of Japan (IPSJ), the Laser Society of Japan, and ITE. Tomoyoshi Ito is a professor. He received his PhD from the University of Tokyo, Japan, in 1994. His research interests are high-performance computing and its applications, such as electronic holography for 3D TV. He is a member of the Association for Computing Machinery, OSA, ITE, IEICE, IPSJ, and the Astronomical Society of Japan. 7. R. W. Gerchberg, W. O. Saxton, A practical algorithm for the determination of phase from image and diffraction plane pictures, Optik 35, p. 237-246, 1972. 10. T. Shimobaba, T. Kakue, Y. Endo, R. Hirayama, D. Hiyama, S. Hasegawa, Y. Nagahama, et al., Improvement of the image quality of random phase-free holography using an iterative method, Opt. Commun. 355, p. 596-601, 2015. 13. T. Shimobaba, M. Makowski, Y. Nagahama, Y. Endo, R. Hirayama, D. Hiyama, S. Hasegawa, et al., Color computer-generated hologram generation using the random phase-free method and color space conversion, Appl. Opt. 55, p. 4159-4165, 2016. 16. I. Ducin, T. Shimobaba, M. Makowski, K. Kakarenko, A. Kowalczyk, J. Suszek, M. Bieda, A. Kolodziejczyk, M. Sypek, Holographic projection of images with step-less zoom and noise suppression by pixel separation, Opt. Commun. 340, p. 131-135, 2015.
Kakitsuka T.,Nano structure Photonic Device Research Group |
Kakitsuka T.,Japan Society of Applied Physics |
Matsuo S.,Nano structure Photonic Device Research Group |
Matsuo S.,Japan Society of Applied Physics
NTT Technical Review | Year: 2012
This article introduces current-injection photonic-crystal lasers featuring ultralow power consumption, which were achieved by using photonic-crystal nanocavities and small buried active regions fabricated through a crystal regrowth process. They should provide light sources suitable for future lowerpower- consumption information and communications technology (ICT) devices.
Sun L.,Tokyo University of Information Sciences |
Shibata T.,Japan Society of Applied Physics
IEEE Transactions on Circuits and Systems for Video Technology | Year: 2014
This paper presents an unsupervised object extraction system that extracts a single object from natural scenes without relying on color information. The contour information and texture information are analyzed through separate oriented-edge-based processing channels and then combined to complement each other. Contour candidates are extracted from multiresolution edge maps, whereas the local texture information is compactly represented by an oriented-edge-based feature vector and then analyzed by K-means clustering. The object region is determined by merging the results of two separate analysis channels based on the simple assumption that the object is located centrally in the scene. As a result, the object region has been successfully extracted from the scene with a well-defined single boundary line. Both subjective and objective evaluations were carried out and it is shown that the proposed algorithm handles the challenges of complex background well, using only gray-scale images. © 2013 IEEE.
Zhu H.,University of Tokyo |
Shibata T.,Japan Society of Applied Physics |
Shibata T.,Japan Aerospace Exploration Agency
IEEE Transactions on Circuits and Systems for Video Technology | Year: 2014
A very-large-scale integration capable of extracting motion features from moving images in real time has been developed employing row-parallel and pixel-parallel architectures based on the digital pixel sensor technology. Directional edge filtering of input images is carried out in row-parallel processing to minimize the chip real estate. To achieve a real-time response of the system, a fully pixel-parallel architecture has been explored in adaptive binarization of filtered images for essential feature extraction as well as in their temporal integration and derivative operations. As a result, self-speed-adaptive motion feature extraction has been established. The chip was designed and fabricated in a 65-nm CMOS technology and used to build an object detection system. Motion-sensitive target image localization was demonstrated as an illustrative example. © 1991-2012 IEEE.
Japan Society of Applied Physics | Date: 2011-07-26
Downloadable electronic publications, namely, magazines and newsletters in the field of applied physics and science; exposed cinematographic films; exposed slide films; slide film mounts; recorded video discs and video tapes featuring educational lessons in applied physics and science. Printed matter, namely, magazines, periodicals, newspapers, newsletters and brochures in the field of applied physics and science; photographs; photograph stands.
Japan Society of Applied Physics | Date: 2011-08-30
Downloadable electronic publications, namely, magazines and newsletters in the field of applied physics and science; exposed cinematographic films; exposed slide films; slide film mounts; recorded video discs and video tapes featuring educational lessons in applied physics and science. Printed matter, namely, magazines, periodicals, newspapers, newsletters and brochures in the field of applied physics and science.
Japan Society of Applied Physics | Date: 2011-01-18
Downloadable electronic publications, namely, magazines and newsletters in the field of applied physics and science; exposed cinematographic films; exposed slide films; slide film mounts; pre-recorded video discs and video tapes featuring educational lessons in applied physics and science; video discs and video tapes recorded with educational lessons in the field of applied physics and science. Printed matter, namely, magazines, periodicals, newspapers, newsletters and brochures in the field of applied physics and science; photographs; photograph stands. Arranging of seminars; Conducting seminars in the field of applied physics and science; providing non-downloadable electronic publications in the nature of magazines, periodicals and newsletters in the field of applied physics and science; production of video tape film in the fields of education, culture, entertainment and sports; publication of books; education services, namely, providing classes, seminars, workshops, tutoring, and mentoring in the field of applied physics and science.
Nakatsugawa M.,Japan Society of Applied Physics
NTT Technical Review | Year: 2012
This report summarizes the activities and outcomes of the Radiocommunication Assembly 2012 (RA- 12) and World Radiocommunication Conference 2012 (WRC-12), which were held from January to February 2012 in Geneva, Switzerland. RA and WRC are the major conferences of ITU-R (International Telecommunication Union, Radiocommunication Sector).