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Made available in DSpace on 2022-05-01T13:41:39Z (GMT). No. of bitstreams: 0 Previous issue date: 2022-01-01 The failure of polymer composites is complex due to the independent and interacting damage mechanisms. The availability of several failure criteria demands a reasonable discernment of each criterion in order to obtain a consistent response to make an assertive selection. The importance of this decision is present in simulation works using finite element method and it is of particular interest of the industry and designers, once an optimized project is the goal. This study regards a carbon/epoxy laminate based on plain weave fabric subjected to tensile load and numerical simulations using finite element method was applied to compare the widely used Maximum Stress, Tsai-Wu, Hoffman, Tsai-Hill, Hashin and Puck failure criteria. Experimental tensile tests were carried out and fractographic analysis was performed in order to validate the finite element model and the applicability of the failure criteria. The model presented a good agreement with the experimental results and the correlation between the fractographic analysis and the failure criteria results allowed to select the Puck criterion as the proper and adequate for the studied composite laminate subjected to tensile load. Department of Mechanical Engineering UNESP–Universidade Estadual Paulista, São Paulo Federal Institute of Education Science and Technology of São Paulo IFSP, São Paulo Institute of Science and Technology Federal University of São Paulo–UNIFESP, São Paulo Aeronautics Institute of Technology ITA, São Paulo Department of Mechanical Engineering UNESP–Universidade Estadual Paulista, São Paulo

We propose a method to perform the quantum state tomography (QST) of an $\mathit{n}$-partite qudit state embedded in single photons using the Hong-Ou-Mandel (HOM) interference between the target state and probe state. This method requires only passive beam splitters for the HOM interference and removes all active optical devices in the target modes to control the measurement bases needed in conventional QST. Hence, it is applicable to various degree of freedom of the target state without altering the measurement setup. Moreover, a faithful estimation is realized even with classical probe light such as laser and thermal light. As a proof-of-principle, we performed the experimental demonstration using a polarization qubit. Regardless of the photon statistics of the probe light, the estimated results of state reconstruction are as accurate as those verified by conventional QST., 8 pages, 4 figures

Free-space optical (FSO) systems are compulsory to realize high capacity and interference-free communication links from low-Earth orbit (LEO) satellite constellations as well as spacecraft and space stations to the Earth. To be integrated with high-capacity ground networks, the collected portion of the incident beam should be coupled into an optical fiber. To accurately evaluate the signal-to-noise ratio (SNR) and bit-error rate (BER) performance metrics, the probability density function (PDF) of fiber coupling efficiency (CE) must be determined. Previous studies have experimentally verified the CE PDF for a single-mode fiber, however, there is no such investigation for the CE PDF of a multi-mode fiber (MMF) in a LEO-to-ground FSO downlink. In this paper, for the first time, the CE PDF for a 200-μm MMF is experimentally investigated using data from an FSO downlink from the Small Optical Link for International Space Station (SOLISS) terminal to a 40-cm sub-aperture optical ground station (OGS) supported by a fine-tracking system. An average CE of 5.45 dB was also achieved given that the alignment between SOLISS and OGS was not optimal. In addition, using the angle-of-arrival (AoA) and received power data, the statistical characteristics such as channel coherence time, power spectral density, spectrogram, and PDFs of AoA, beam misalignments, and atmospheric turbulence-induced fluctuations are revealed and compared with the state-of-the-art theoretical background.

Submitted by Bruno Mikio Fujiwara Marques (bmikio@yahoo.com.br) on 2022-04-07T13:26:24Z No. of bitstreams: 1 Tese - Bruno Mikio - Defesa-revA-Final.pdf: 7883734 bytes, checksum: 4d1526fb91f815d48bfbd84a7d1043e6 (MD5) Approved for entry into archive by Pamella Benevides Gonçalves null (pamella@feg.unesp.br) on 2022-04-11T11:16:11Z (GMT) No. of bitstreams: 1 marques_bmf_dr_guara.pdf: 7883734 bytes, checksum: 4d1526fb91f815d48bfbd84a7d1043e6 (MD5) Made available in DSpace on 2022-04-11T11:16:11Z (GMT). No. of bitstreams: 1 marques_bmf_dr_guara.pdf: 7883734 bytes, checksum: 4d1526fb91f815d48bfbd84a7d1043e6 (MD5) Previous issue date: 2022-03-04 Para juntas aparafusadas de alta responsabilidade, a aplicação de uma força inicial de tração no parafuso, denominada pré-carregamento, é essencial devido à compressão aplicada às partes unidas, aumentando o atrito entre elas e melhorando a resistência mecânica da junta tanto submetida à carga externa de tração quanto à de cisalhamento. Além disso, sabe-se que o torque necessário para produzir um determinado pré-carregamento é função da geometria da rosca e dos coeficientes de atrito dos materiais envolvidos. Essas variáveis combinadas na equação de obtenção do torque denominam-se coeficiente de torque e o seu valor influencia diretamente o pré-carregamento. No entanto, para juntas de materiais compósitos, os valores do coeficiente de torque são considerados em poucos estudos e de maneira aproximada e superficial, sendo comum utilizar os resultados obtidos para juntas de materiais metálicos como referência, acarretando em componentes de materiais compósitos com baixa eficiência e dimensionados incorretamente. Dessa forma, este trabalho apresenta um estudo sobre juntas aparafusadas de materiais compósitos de matriz epóxi reforçada com fibra de carbono, a fim de analisar e definir os coeficientes de torque aplicáveis a esses materiais, como também avaliar os efeitos de diferentes valores de torque sobre o laminado, demonstrando a relação entre a carga de prova do parafuso e o pré-carregamento. As análises contemplaram a utilização do método analítico geral e de Motosh, do método dos elementos finitos com modelos tridimensionais e equacionamentos não-lineares, contemplando contatos e aplicação do critério de falha de Hashin. Também foram realizados ensaios experimentais de aplicação de torque, de resistência da junta em tração e análise fractográfica. Os resultados dos ensaios de aplicação de torque demonstraram que o coeficiente de torque aplicável para a junta de material compósito é aproximadamente 50% maior do que o aplicado para juntas metálicas, independentemente do valor de torque utilizado. Assim, os pré-carregamentos obtidos experimentalmente apresentaram valores até 39,4% menores do que os calculados utilizando o coeficiente de torque recomendado para juntas metálicas. Outra contribuição deste trabalho foi a recomendação na utilização de pré-carregamentos entre 68% e 100% da carga de prova do parafuso. No entanto, os resultados dos ensaios de resistência da junta em tração indicaram que não houve aumento da carga de falha por tração utilizando um pré-carregamento de 100% da carga de prova do parafuso, quando comparado com corpos de prova submetidos a pré-carregamento com relação de 80,2%, não apresentando vantagem deste último para condições de carregamentos estáticos. Além disso, a análise fractográfica revelou que os diferentes pré-carregamentos aplicados não influenciaram nos modos de falha observados na superfície de fratura dos corpos de prova. Considering high responsibility bolted joints, the application of initial tension force entitled preload is essential due the compression effect over the joint components, increasing the friction forces between them and improving the joint mechanical strength even when it is submitted to an external tensile load than a shear load. Moreover, the torque to generate the preload is dependent on the thread geometry and the coefficient of friction between the involved materials. These variables in the equation to obtain the torque is entitled coefficient of torque and its value directly influences the preload. However, for composite material joints, the coefficients of torque are considered approximately and superficially in few studies, using the values for metallic material joints as a reference, resulting in low efficient components of composite material and incorrectly dimensioned. Thus, this work presents a study of bolted joints in carbon fiber reinforced epoxy to analyze and determine the applicable coefficients of torque for this type of material, and the effect of different torque values over the laminate indicating the relation between the bolt proof load and the preload. The analysis regarded the application of the general and Motosh analytical methods, finite element method with tridimensional models and non-linear equations, contact between the components and the use of Hashin failure criterion. It was also performed torque application tests, tension tests and fractography analysis. The torque application tests results showed the coefficient of torque for composite material joints is approximately 50% higher than the applied coefficient in metallic joints, independently of the torque value. Thus, the experimental preloads values were 39,4% lower than the ones obtained analytically using the coefficient used for metallic joints. Another contribution of this study was the recommendation to apply preloads between 68% to 100% of the bolt proof load. However, the tensile tests results demonstrated that the tensile failure load did not increase due a preload corresponding a 100% of bolt proof load in comparison with specimens submitted to 80,2% of proof load, not presenting an advantage for static load conditions. Furthermore, the fractographic analysis showed that the different preloads do not present an influence in the observed failure modes on the fracture surfaces of the specimens.

We demonstrate the first continuous variable quantum key distribution (CV-QKD) system with fully digital phase and polarization tracking, enabling the first wavelength division multiplexing experiment for CV-QKD. We transmit 194 × 0.5 GHz channels with 25 GHz channel spacing, demonstrating an aggregate estimated asymptotic secret key rate of 172.6 Mbit/s over 25 km.

The quantum key distribution network with Vernam's One Time Pad encryption and secret sharing are powerful security tools to realize an information theoretically secure distributed storage system. In our previous work, a single-password-authenticated secret sharing scheme based on the QKD network and Shamir's secret sharing was experimentally demonstrated; it confirmed ITS data transmission, storage, authentication, and integrity. To achieve data integrity, an ITS message authentication code tag is employed and a data owner of the secret sharing performs both the MAC tag generation and verification. However, for a scenario in which the data owner and end users are different entities, the above approach may not work since the data owner can cheat the end users. In this paper, we resolve this problem by proposing an ITS integrity protection scheme employing a third-party verification with time-stamp., 12 pages, 5 figures; Accepted in IEEE trans. Quantum Technology

Satellite laser communication is a promising solution to satisfy the increasing demand for high-capacity wireless communications. Satellite laser communication has several advantages over its radio frequency counterparts, such as a higher capacity with a broader bandwidth and transmission security provided by highly directional laser beams. However, the received optical power fluctuations induced by atmospheric scintillation cause burst errors, requiring the employment of high-performance error correction codes, such as turbo or low-density parity check (LDPC) codes. Recently, polar code has been attracting significant attention, primarily because of its lower encoding and decoding computational complexity and its high performance, reaching the Shannon limit. We have reported a long-distance experiment using 7.8-km terrestrial free-space optical (FSO) communication links and compared the performance of polar and LDPC codes. Our experimental results revealed the advantage of polar codes over LDPC codes when channel state information (CSI) was not available. In FSO communications suffering from atmospheric fading, it is known that we can enhance the error-correction performance of these codes by utilizing a channel equalization technique based on the estimated CSI. In this study, we present the results of long-distance transmission experiments using polar codes with channel equalization. As a result, equalization improves the error-correction performance. Moreover, even with channel equalization, the block error rate of polar codes is better than that of LDPC codes, as in our previous report.

We investigate the excess noise induced by crosstalk in a trench-assisted homogeneous 19-core fiber for a continuous variable quantum key distribution (CV-QKD) receiver. Crosstalk is studied for both 30 wavelength division multiplexing channels of 24.5-Gbaud PM-16QAM with 100-GHz channel spacing and for an amplified spontaneous emission signal with 37.5-GHz bandwidth. We show that in-band crosstalk from neighboring cores prohibits secret key generation. However, it is possible to place CV-QKD channels at wavelengths not used by the classical channels even though wideband amplified spontaneous emission noise is present. The excess noise induced by crosstalk from a neighboring core is shown to be time-dependent.

Quantum key distribution (QKD) can offer communication with unconditional security and is a promising technology to protect next generation communication systems. For QKD to see commercial success, several key challenges have to be solved, such as integrating QKD signals into existing fiber optical networks. In this paper, we present experimental verification of QKD co-propagating with a large number of wavelength division multiplexing (WDM) coherent data channels. We show successful secret key generation over 24 h for a continuous-variable QKD channel jointly transmitted with 100 WDM channels of erbium doped fiber amplified polarization multiplexed 16-ary quadrature amplitude modulation signals amounting to a datarate of 18.3 Tbit/s. Compared to previous co-propagation results in the C-band, we demonstrate more than a factor of 10 increase in the number of WDM channels and more than 90 times higher classical bitrate, showing the co-propagation with Tbit/s data-carrying channels. The security of communications networks is a fundamental challenge of the current era, particularly with the move towards quantum communications. The authors perform joint transmission of quantum key distribution and up to 100 classical communication channels in the same fiber and report an average secret key rate of 27.2 kbit/s over a 24 h operation period where the classical data rate amounted to 18.3 Tbit/s.

One of the peculiar features in quantum mechanics is that a superposition of macroscopically distinct states can exist. In optical system, this is highlighted by a superposition of coherent states (SCS), i.e. a superposition of classical states. Recently this highly nontrivial quantum state and its variant have been demonstrated experimentally. Here we demonstrate the superposition of coherent states in quantum measurement which is also a key concept in quantum mechanics. More precisely, we propose and implement a projection measurement onto an arbitrary superposition of two weak coherent states in optical system. The measurement operators are reconstructed experimentally by a novel quantum detector tomography protocol. Our device is realized by combining the displacement operation and photon counting, well established technologies, and thus has implications in various optical quantum information processing applications.

Heralded single photons (HSPs) generated by spontaneous parametric down-conversion (SPDC) are useful resource to achieve various photonic quantum information processing. Given a large-scale experiment which needs multiple HSPs, increasing the generation rate with suppressing higher-order pair creation is desirable. One of the promising ways is to use a pump laser with a GHz-order repetition rate. In such a high repetition rate regime, however, single-photon detectors can only partially identify the pulses. Hence, we develop a simple model to consider that effect on the spectral purity, and experimentally demonstrate a high-visibility Hong-Ou-Mandel interference between two independent HSPs generated by SPDC with 3.2 GHz-repetition-rate mode-locked pump pulses. The observed visibility of 0.88(3) is in good agreement with our theoretical model., 11 pages, 6 figures

Free-space optical (FSO) communications are becoming promising schemes for high-capacity wireless links due to their plentiful characteristics originated from higher carrier frequency. These characteristics also yield a greater security advantage over radio frequency counterparts: the physical ability of a wiretapper is reasonably restricted due to the high directionality of communication beam and the line-of-sight configuration of the link. Secret key agreement over FSO links (FSO-SKA) employs this security advantage as well as the post-processing over an authenticated public channel to establish an information-theoretic secure key which cannot be broken even with unbounded computer resources. In the previous works, the authors demonstrated the full-field implementations of FSO-SKA with a 7.8-km FSO link testbed including a probing station to estimate the possible wiretapping risks from the sidelobe of the communication beam. In the demonstration, however, there is still room to improve the secret key rate by exploiting the optical fading which contains additional information about random states of the FSO links. We here propose a novel protocol for FSO-SKA employing such channel state information. In the protocol, the legitimate receiver decides whether to discard the received symbols or not according to the received optical power at the time. Based on the experimental data from the FSO link testbed, we demonstrate that the proposed protocol improves the secret key rate compared with our previous result. To our best knowledge, this is the first demonstration that exploits the effect of atmospheric turbulences to improve the security performance of communication systems. We anticipate that this idea will be applicable on the broader areas of FSO communications and opens a way toward practical wireless network spanned by FSO links.

In recent years, the demand for high-speed communication has been increasing. Satellite laser communication is one of the infrastructures that can realize this demand. However, in free-space optics (FSO) that use satellite laser communications, a scintillation occurs when the light passes through the atmosphere, resulting in a burst error. To prevent this, a strong error correction code is required. The polar code, one of such channel coding schemes, has been recently proposed. We have considered applying polar codes into FSO channels and have evaluated its performances through computer simulations. However, the experiments of polar code transmission in an outdoor FSO channel has not been studied. Therefore, in this paper, we conduct an experiment in polar code transmission in a terrestrial FSO channel instead of a satellite FSO as the first step of study, and then analyze the performance from the transmission results.

Beam splitters and phase shifters compose linear photonic circuits and are the most fundamental elements in photon-based quantum information processing. While integration of these linear components on a chip for spatial modes has been dramatically developed in recent years [1], there is another approach for integrated quantum circuits : wavelength division multiplexing (WDM). The degrees of freedom of light allow photons exhibiting different wavelengths to exist independently in the same space, therefore using such characteristics can allow further integrating of photons and modes in a small space.

To realize the practical implementation of device-independent quantum key distribution (DIQKD), the main difficulty is that its security is solely based on the detection loophole-free violation of the Clauser-Horne-Shimony-Holt (CHSH) inequality i.e. the CHSH value S > 2 [1]. To circumvent the inevitable losses in the transmission channels which create the detection loophole, several probabilistic methods to recover the nonlicality have been proposed. Here, we theoretically and experimentally investigate the optimal strategy for the method utilizing linear optical entanglement swapping relay (ESR) with photon pairs from spontaneous parametric-down conversion (SPDC) sources [2,3]. In the previous methods, it is common to employ the ESR node in Bob's system as shown in Fig. 1(a) (Hereafter, we call this configuration the local-heralding (LH).). We employ another configuration: The middle-heralding (MH) shown in Fig. 1(b), where the ESR node is placed in the middle of Alice and Bob similar to the measurement device independent QKD. We numerically compare S of the above two schemes by using the numerical simulation based on the characteristic-function approach [3]. The results are shown in Fig. 1(c). We see that the larger values of S are expected in the MH scheme when the dark count probabilities (ν) of the detectors are considered. In experiment, we perform the Bell-test experiment using the ESR with SPDC sources. We employ the MH scheme, and measure S changing the transmission losses. The experimental parameters (the average photon numbers and measurement angles) are chosen such that S is maximized under the condition of the experimental imperfections (mode-mismatch, dark count and so on) and the assumption of the unit local detection efficiencies (η = 1). While the overall detection efficiencies of our system (η ∼ 15 %) are not the range of directly observing the violation of the CHSH inequality, S obtained by the experiment well agree with the numerical simulation with experimental parameters. When the overall transmission loss is set to be 10 dB, which corresponds to the transmittance of a 50 km-optical fiber, we observe S exp = 1.478, while S th = 1.487 is expected by the numerical simulation. This result means that our numerical simulation can rigorously model the experiment. This allows us to estimate the nonlocality of the quantum state just before the local detection losses by the numerical simulation. The CHSH value is estimated to be S exp η=1= 2.104 > 2, which indicates that the quantum state with experimental imperfections possesses the potential to violate the CHSH inequality.

Research and development of a novel method for a secure free-space optical communication system has been done in NICT since 2018, and demonstration experiments between an aircraft and a transportable optical ground station are planned in near future. In order to establish a stable and highly accurate optical communication link, the system must have a fine pointing mechanism in both the aircraft and the ground station. A compact and light-weight tracking system is required to be mounted on the aircraft, and there will be needed to have an adjustment function of the beam divergence control to allow stable communication under various altitude and atmospheric conditions. The transportable optical ground station should maintain vibration resistance when moving, and it must be easily deployed on each site where is the appropriate optical ground station site with respect to atmospheric turbulence condition.