Publishing type：Research paper (scientific journal)  

We have proposed an arrayed waveguide grating router (AWGR) network with a loopback function by optical switches (OSWs) that are located on optical nodes that allow the arbitrarily reconfigured wavelength path architecture. In order to easily manage the architecture, we have also proposed the method expressed network topology so that it could also calculate network information based on topologies and be helpful for a network controller that needed topology information. However, since the proposed method outputs the wavelength path from the OSW state, it is impossible to calculate the required OSW states from the information between the nodes where the wavelength path is multiplexed. If we employ the inverse matrix calculation to know the required OSW states, we must know all matrices except OSW state in advance, which is unrealistic. Thus, in this study, our proposed method simulates the case that the target network has only the required path and, calculates wavelength path routes and required OSW states. In addition, from the network management perspective, we need an interface easy for network administrators to manage, but previous proposals have only considered basic calculation methods. In this study, we develop an application with a graphical user interface for network administrators, which can show the required wavelength path and OSW states when the information between the nodes where the wavelength paths are multiplexed is inputted into the application.

DOI： 10.24507/ijicic.18.02.591

Authorship：Corresponding author   Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

Fringe projection profilometry is a high-precision method used to measure the 3D shape of an object by projecting sinusoidal fringes onto an object.However, fringes projected onto a metallic or shiny object are distorted nonlinearly, which causes significant measurement errors.Ahigh-precision measurement method for shiny objects that employs computer graphics (CG) and deep learning is proposed.We trained a deep neural network by projecting fringes on a shiny object in CG space.Our results show that the method can reduce the nonlinear fringe distortion caused by gloss in real space.

DOI： 10.1364/AO.450723

PubMed

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

Software-defined networking (SDN) is one of the network virtualization tech-nologies that has gained attention recently, and it has now been implemented in networks. SDN can reduce the network management workload by flexibly changing many network device parameters and centralizing control methods specific to the network devices. How-ever, SDN-enabled network devices are currently expensive, posing a barrier to SDN adoption in enterprise and data center networks. In this study, an event-driven remote configuration function based on monitoring input packets in a router/switch control system using inexpensive Internet of Things devices is proposed to reduce the cost of SDN deployment and network management workload. We developed the proposed function and evaluated its performance on an experimental network. The experimental results are dis-cussed, and the effectiveness of the proposed function is verified.

DOI： 10.24507/icicelb.13.02.145

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

Recently, software-defined networking (SDN) is one of the network virtualization technologies that has attracted significant attention. SDN allows network devices to be controlled centrally and flexibly, allowing for changes to configuration parameters, packet-exchange settings, and quality of service in routing, among other things. Furthermore, SDN reduces network administrators’ network management workloads. SDN-enabled network devices, on the other hand, are generally more expensive than legacy network devices, and the total cost is a significant barrier when SDN is deployed in a datacenter, enterprise, and small-scale networks. In this paper, from the viewpoint of the cost and network management workload, we propose a network management and control system based on SDN for Internet protocol (IP) over the world wide web (WWW) using low-cost single-board computers. To validate the work of the proposal system, we designed and constructed a small-scale experimental system that mimicked a part of the proposal system and conducted experiments by using two functions. The experiment result showed that the proposed system worked properly. As a result, using the proposed system can significantly reduce total construction costs when compared to replacing all legacy network devices with SDN-enabled ones. To be more specifically, the total cost of SDN-enabled network devices multiplied by the number of devices can be reduced to the cost of a single Raspberry Pi multiplied by the number of nodes. Furthermore, our proposal system also contributes to reducing the management workload for network administrators and guaranteeing a certain level of security for network devices.

DOI： 10.24507/ijicic.18.03.755

Publishing type：Research paper (scientific journal)  

We have proposed a broadband hybrid light source that combines a super luminescent diode (SLD) and thulium-doped fiber amplifier (TDFA) and operates in the 1.8 µm band. This light source can improve the characteristics of the output spectrum by amplifying the output light of the SLD with TDFA. In this study, we investigate the dependence of the output spectral characteristics of the hybrid broadband light source on the thulium-doped fiber (TDF) length used in the TDFA as well as the output spectra of three newly developed SLDs of 1660, 1690, and 1730 nm bands. In the evaluation of the output bandwidth, there are various definitions of output bandwidth, but we adopted the bandwidth with power density of over −40 dBm/0.1 nm. This is because it is possible to evaluate in this band with a dynamic range of “30 dB/0.1 nm” by using a general optical spectrum analyzer. The hybrid light source achieves the bandwidth of 332 nm, from 1579 to 1911 nm, and a high total output power of over 15 dBm. The maximum ripple was less than ∼0.1 dB, which is similar to the maximum value of that of the SLD, without any deterioration in the ripple characteristics owing to the hybrid configuration of the SLD and TDFA.

DOI： 10.1364/AO.439019

PubMed

Authorship：Corresponding author   Publishing type：Research paper (scientific journal)  

Fringe projection profilometry (FPP) is a technique used for obtaining the three-dimensional shape of an object in fields such as reverse engineering, cultural heritage, and computer vision. The FPP measurement accuracy significantly depends on the arrangement of the measurement system, measurement space conditions, equipment setting, and object characteristics. However, experimental verification of the measurement conditions is time-consuming and expensive. This study presents a simulator that can set a broader range of measurement conditions. This simulator was developed using Unity, which is an integrated development environment for video games. The proposed simulator can be configured with a graphical user interface for device placement and operation, and it can freely adjust the aperture, exposure time, and depth-of-field of the camera. The measurement simulation results for a CAD model obtained using the proposed simulator are presented. The results indicate that camera defocus or unfit exposure time causes phase measurement errors.

DOI： 10.1007/s10043-021-00704-1

Publishing type：Research paper (scientific journal)  

Software-defined networking (SDN), which enables networks to be controlled centrally and can change parameters flexibly such as their topology, settings for packet-exchanging, and quality of service is one of the network virtualization technologies that have attracted significant attention recently. Besides, it has been widely used because it reduces network administrator’s workloads of network management. However, SDN-enabled network devices are generally expensive, and the network construction cost is a significant factor when SDN is deployed in a network of enterprises and data centers. In this paper, from the viewpoint of the cost and network management workload, we propose a router/switch control system for Internet protocol over an optical network with database function over World Wide Web using cost-effective Internet of Things devices. We designed and constructed the proposed system. Besides, we conducted experiments using the remote control function in the proposed system, which can change the port status of network devices. The experiment results proved that the proposed system works correctly. Therefore, by using the proposed system, SDN-enabled network construction cost can be significantly reduced compared to replacing legacy network devices with SDN-enabled network devices. To be more precise, the cost of a single SDN-enabled network device can be reduced to the cost of a single Raspberry Pi as IoT device, and the total cost can be reduced in proportion to the scale of the network. Furthermore, we discuss future studies to be considered for further cost reduction.

DOI： 10.24507/ijicic.17.05.1617

Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

This letter reports a proof-of-concept experiment conducted on a novel application of the multi-core fibre (MCF), where image reconstruction is based on a single-pixel imaging (SPI) technique and the diffraction pattern emitted from an MCF. The technique is intended to reduce the size of the SPI system, the applications of which can now be extended with the help of this study.

DOI： 10.1049/ell2.12200

Publishing type：Research paper (international conference proceedings)   International / domestic magazine：International journal  

We propose a cost-effective method for temperature measurement range changing of the Ethernet-based optical fiber sensing system, and also show experimental results about the temperature measurement range changeability with a variable optical attenuator.

Publishing type：Research paper (international conference proceedings)   International / domestic magazine：International journal  

We propose a cost-effective method for temperature measurement range changing of the Ethernet-based optical fiber sensing system, and also show experimental results about the temperature measurement range changeability with a variable optical attenuator.

Publishing type：Research paper (scientific journal)  

In our previous study, we proposed an arrayed waveguide grating – STAR network with a loopback function to avoid traffic congestion and inefficient utilization of wavelength path capacity. The proposed network can relocate wavelength paths in response to traffic demand by controlling simple optical switches. However, the network management of the proposed method seems complicated because of the change in the wavelength path topology and fluctuation of its accumulated optical loss due to wavelength path re-location. Therefore, we previously proposed a calculation method that is suitable for the AWG-STAR network with a loopback function to solve the issue that it is difficult to manage a reconfigurable network. The proposed method enables network operators to easily calculate and manage the dynamic relocatable wavelength path topology. However, it cannot calculate the transit nodes and the accumulated optical loss along each wavelength path. In this paper, we propose a method for calculating the wavelength path and signal power. The proposed method expressed network topology so that this method could also calculate network information based on topologies such as distance and latency and be helpful for a network controller that needs topology information. The proposed method minimizes the operating expenses for complex networks by clarifying path relations among nodes.

DOI： 10.24507/ijicic.16.06.1959

Publishing type：Research paper (international conference proceedings)  

We simulated the gain change caused by inter-core cross-gain modulation on cladding-pumped multicore erbium-doped fibers with 7-37 cores by using the average-erbium-population inversion model. It is clear that the pump power and gain modulation had a trade-off relationship with the cladding diameter, and a gain change of less than approximately 0.5 dB was realized by setting the minimum cladding thickness to 23 m.

DOI： 10.1109/OECC48412.2020.9273637

Publishing type：Research paper (international conference proceedings)  

To clarify an inexpensive method for constructing a software-defined network (SDN) environment, we propose a router control function for non-SDN-supported routers using IoT devices possessing a common user interface based on OpenFlow. An experimental demonstration using the proposed function is shown.

DOI： 10.1109/OECC48412.2020.9273564

Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

A secure free-space optical (FSO) communication system that physically introduces a two-dimensional pattern as a key is proposed for further improving the possibility of FSO communication. This paper presents the results of basic experiments conducted with the proposed encryption system for FSO communication that confirm the encryption and restoration of binary data streams in the proposed system configuration. Further, we define a pattern selection measure to improve the quality of the decoded signal in the encryption method by using a spatial pattern, and also evaluate the decoded signal obtained from the experimental results.

DOI： 10.35848/1347-4065/ab9486

Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)  

© The Institution of Engineering and Technology 2020. A new implementation of the weight vector in a classifier based on an optical system using a volume holographic filter with a vector decomposition algorithm is proposed for high-speed data classification. Using a volume holographic filter, the correlation between the input and the decomposed weight vector is calculated for the classification score, which is the output from the decision function in the optical classifier. The authors experimentally demonstrate the core concept and confirm the effectiveness of the proposed method by executing a two-class classification problem using a volume hologram medium.

DOI： 10.1049/el.2019.3371

Authorship：Lead author,　Corresponding author   Publishing type：Research paper (international conference proceedings)  

A single-pixel imaging (SPI) system using a multi-core fiber (MCF), which is referred to as MCF-SPI, is proposed. It combines the MCF technology and SPI algorithm. A preliminary experiment of the spatial pattern generation was demonstrated using an MCF.

Authorship：Lead author,　Corresponding author   Publishing type：Research paper (international conference proceedings)  

A single-pixel imaging (SPI) system using a multi-core fiber (MCF), which is referred to as MCF-SPI, is proposed. It combines the MCF technology and SPI algorithm. A preliminary experiment of the spatial pattern generation was demonstrated using an MCF.

Publishing type：Research paper (international conference proceedings)  

We previously proposed a three-dimensional microscopic imaging system for objects hidden behind scattering media using in-line phase-shift digital holography, which simultaneously captures amplitude and phase information. However, as the thickness of the scattering medium increases, the influence of scattering is enhanced, and the reconstructed image of the object behind the scattering medium deteriorates. In this paper, we report the evaluation of this image using a near-infrared light source with a wavelength of 780 nm that is capable of deep tissue penetration. A favorable microscopic image of the object behind the rat-skin sample of 912 μm-thickness was successfully reconstructed.

DOI： 10.1117/12.2573228

Publishing type：Research paper (international conference proceedings)  

© 2019 Optical Society of America. Microscopic three-dimensional imaging and phase quantification for objects hidden behind a scattering medium by using in-line phase-shift digital holography are proposed. A spatial resolution of 1.81 µm and highly accurate quantitative phase imaging are demonstrated for objects behind a scatter plate. Three-dimensional imaging was confirmed using objects with a depth difference of 1.32 mm. Further, imaging was performed using rat skin as a demonstration for imaging through a complex multilayer scattering medium, where a spatial resolution close to the theoretically predicted value was achieved by experiment.

DOI： 10.1364/AO.58.00G345

PubMed

Publishing type：Research paper (international conference proceedings)  

The quality of a decrypted signal depends on the two intensity patterns of the input signal, which correspond to the 1-bit states '1' and '0,' in a two-dimensional encryption system. In this study, we discuss via simulations the selection of spatial patterns to improve the decrypted signals.

DOI： 10.23919/MOC46630.2019.8982752

Publishing type：Research paper (scientific journal)  

© The Institution of Engineering and Technology 2019. We simulated the differential modal gain (DMG) property of WDM amplification characteristics for a ring-core erbium-doped fibre (RC-EDF) to clarify the possibility of an RC-EDF being used as a three- to five-signal LP-mode amplification medium. The authors defined two parameters, DMGYY-XX and WDGXX. The former and the latter are the difference between the gains of the LPXX mode and the LPYY mode at the shortest wavelength, and the gains of the LPXX mode at the shortest and longest wavelengths of WDM signal channel, respectively. XX and YY indicate the signal LP mode number. The authors present contour diagrams of the maximum DMGYY-XX and maximum WDGXX on the allowable three- to five-signal LP-mode areas of the RC-EDF. They confirm that it is possible to realise the amplification with a maximum DMGYY-XX of ≤2 dB, ≤1 dB, and about 2 dB for the 3, 4, and 5-LP modes and a maximum WDGXX of ≤ 1 dB for the three- to five-LP mode. The authors found that it is possible to realise an amplifier for 3-5 LP modes that operate with a relatively low DMG by using RC-EDF.

DOI： 10.1049/el.2019.2273

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work  

With increased use of smartphones and social networking services, the amount of unstructured image data has been increasing significantly. A high-speed search method is required to use such data for big data analysis. Holographic optical correlation is a promising technique for this purpose. This study introduces a recording method that realizes speedup in an optical correlator. High-density recording is effective for achieving not only speedup, but also high capacity. However, the high-density recording by shortening the shift amount in shift-multiplexed recording results in a large error in the calculated correlation rate owing to crosstalk from adjacent holograms. To suppress this crosstalk, we propose a low-correlation data interleaving method that rearranges the recording order of image data based on the correlation rate with the last recorded image data. We analytically and experimentally confirmed that the proposed method improves the recording density and the correlation speed to 1.33 times.

DOI： 10.7567/1347-4065/ab333b

Publishing type：Research paper (scientific journal)  

A digital holographic microscope (DHM) can noninvasively acquire amplitude and quantitative phase information such as the thickness and refractive index of microscopic objects. However, conventional DHMs with a two-beam interference optical system require strict alignment, a large complex optical system, and other optomechanical parts. In this paper, we present a planar lightwave circuit DHM (PLC-DHM) with no moving parts and no lenses, developed by optimizing the design of the PLC and optical systems. The developed PLC-DHM accurately acquires microscopic intensity and phase distribution. Furthermore, to make this PLC-DHM system accessible to users without professional knowledge of a DHM, we developed a near-real-time PLC-DHM system with a graphical user interface. A spatial resolution of 1.6 μm was achieved and highly accurate quantitative phase imaging has been realized.

DOI： 10.7567/1347-4065/ab333a

Publishing type：Research paper (scientific journal)   Kind of work：Joint Work   International / domestic magazine：International journal  

Computational ghost imaging (CGI) has received increasing attention as a single pixel imaging technique. However, the application of the CGI technique to moving objects requires further investigation because it requires a large number of patterns at high speeds. In this study, we propose and experimentally demonstrate optical correlator-based CGI as a step towards high-speed CGI. Our optical correlator plays the role of a spatial light modulator and correlates a target object to known patterns of general computational imaging. We experimentally verified that the RMS error of the reconstructed images is similar to that of the numerical calculations. If one reconstructed image is acquired using 1000 random binary patterns, the imaging frame rate of 133.7 fps will be achieved. This provides high-speed CGI applicable to moving objects and other phenomena.

DOI： 10.7567/1347-4065/ab2f6b

Publishing type：Research paper (international conference proceedings)  

We propose single-pixel imaging using a multi-core fiber. We confirmed the possibility of the system by setting the distance between the light-emitting end of the multi-core fiber and the object at an appropriate position.

DOI： 10.23919/PS.2019.8818098

Publishing type：Research paper (international conference proceedings)  

OpenFlow-based remote control system for the optical switch in AWG-STAR with a loopback function using IoT device is proposed as a low-cost solution to extend the scope of a software-defined network to physical layer.

DOI： 10.23919/PS.2019.8817804

Authorship：Lead author,　Corresponding author   Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

The importance of encryption in free-space optical communication systems has been increasing due to their widespread use. Herein, for the first time, the authors propose a novel two-dimensional encryption system for free-space optical communication using two spatial patterns as encryption keys. A data stream is physically encrypted with optical signals to reduce the risk of unauthorised third-party intrusion into communication. The encryption and restoration of a binary data stream using the proposed encryption system are confirmed by simulation results. The authors believe that, in the future, the proposed system could be used as an encryption method at the physical layer level to achieve the desired level of safety determined by the user.

DOI： 10.1049/el.2019.0899

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

Optical correlation systems have been developed as hardware that is useful for high-speed and large-scale data analysis. Among them, our system using the disk-type hologram is promising because it can effectively utilize the control techniques of conventional optical disks. In previous work, however, we used a very simple disk structure consisting of a mirror substrate, photopolymer, and cover glass, and tracking control was not performed. Consequently, it was difficult to stably record a large amount of data in the long range of the circumference since the hologram recording position deviates from the disk circumference due to surface deflection and eccentricity attributed to rotation without tracking controls. In this study, we aim to stabilize the optical correlation system by introducing a new disk structure and conventional servo control. We confirmed that both sufficient correlation signal and servo control signals can be detected with the simple disk structure due to the signal detection principle of the optical correlation.

DOI： 10.1007/s10043-019-00501-x

Publishing type：Research paper (scientific journal)   International / domestic magazine：International journal  

Optical fiber sensors have numerous advantages over electrical sensors. However, in some cases, sensing systems based on optical fiber sensors are inferior to electrical sensors in terms of cost because expensive instruments are required. Therefore, cost-effective options must be developed. Here, inexpensive optical transceivers (OTRs) for Ethernet were used instead of a broadband light source and optical spectrum analyzer, and a CO 2 laser-induced long-period fiber grating (LPFG) was used as a temperature sensor. The sensing system was implemented introducing OTRs and LPFG in an experimental internet protocol (IP) over Ethernet. The results showed that a low-cost sensing system can estimate the ambient temperature of the LPFG based on the no-reply rate for the internet control message protocol echo request. Regarding the sensing performance, the measurable range was ∼100°C with 4.5°C errors.

DOI： 10.1364/AO.58.002366

PubMed

Publishing type：Research paper (international conference proceedings)  

We describe our developed planar lightwave circuit digital holographic microscope (PLC-DHM) with no moving parts and lenses. The PLC-DHM can accurately measure the microscopic intensity and phase distribution, has a spatial resolution of 1.6 um, and provides highly accurate quantitative phase imaging. We also demonstrate three-dimensional and quantitative phase imaging of several biosamples using our PLC-DHM.

Kind of work：Joint Work  

Kind of work：Joint Work  

Kind of work：Joint Work  

Kind of work：Joint Work  

Kind of work：Joint Work  

Presentation type：Oral presentation (invited, special)  

Presentation type：Oral presentation (invited, special)  

Presentation type：Oral presentation (invited, special)  

Presentation type：Poster presentation  

Presentation type：Poster presentation  

Presentation type：Poster presentation  

Presentation type：Poster presentation  

Presentation type：Oral presentation (general)  

Presentation type：Oral presentation (general)  

Presentation type：Poster presentation  

Presentation type：Poster presentation  

Presentation type：Oral presentation (general)  

Presentation type：Poster presentation  

Presentation type：Poster presentation  

Presentation type：Poster presentation  

Presentation type：Poster presentation  

Presentation type：Poster presentation  

Presentation type：Poster presentation  

Presentation type：Poster presentation  

Presentation type：Oral presentation (general)