Aperture Transmission Research Articles

Coherent ghost imaging via phase compensation

The 4-f optical illumination structure is widely used in coherent ghost imaging (CGI) system but its imaging field of view (FOV) is usually restricted by the transmission aperture of the lens. Therefore, this optical illumination structure cannot be applied to remote imaging. Based on conventional imaging illumination structure, a large-FOV CGI via phase compensation (CGI-PC) is proposed and its imaging property is investigated. The experimental results demonstrate that both the FOV and the quality of CGI can be dramatically improved when a lens is introduced into the receiving system to compensate the system’s spatial phase difference. Factors influencing the quality of CGI-PC are also discussed.

Orthogonality of non-coaxial Laguerre-Gaussian beams.

The conventional orthogonality of Laguerre-Gaussian (LG) beams is widely recognized and serves as the fundamental basis for mode division multiplexing utilizing LG beams as channels. However, this conventional orthogonality holds true only when two LG beams share the same axis. Whether non-coaxial LG beams, with parallel axes separated by a distance, are orthogonal to each other remains an open question. To address this issue and reveal the orthogonality of non-coaxial LG beams, we analytically derive the projection of one LG beam onto another. This projection exhibits a helical phase and a rotationally symmetric amplitude with dark rings present. These dark rings indicate that two non-coaxial LG beams are indeed orthogonal to each other when their axes are appropriately separated. Furthermore, any pair of non-coaxial LG beams within a set also exhibit orthogonality when their axes are fixed at a certain separation distance. This novel form of orthogonality predicts an innovative compound multiplexing technique that simultaneously combines mode and space, enabling more efficient packing of multiple LG beams within a single transmission aperture while maintaining parallel and closely spaced beam axes.

Self-induced back-action for aperture trapping: Bethe-Rayleigh theory.

A dielectric (nano)particle can influence the local electromagnetic field and thereby alter its interaction with that field through the process of self-induced back-action. While this phenomenon is usually considered theoretically as a change in a cavity resonance frequency, such theoretical approaches are not as appropriate when considering systems away from resonance, such as with a subwavelength aperture in a metal film. Here we consider the interaction between an aperture, modelled with Bethe theory as a magnetic dipole, and a Rayleigh particle, modelled as an electric dipole. Using this magnetic dipole - electric dipole interaction, we quantify the self-induced back-action of the particle on the aperture transmission and the optical trapping potential. The model shows quantitative agreement with finite-difference time-domain simulations. This shows that the physics of self-induced back-action for an aperture and a nanoparticle can be understood in terms of dipole-dipole coupling.

New analytical diffraction expressions for the Fresnel–Fraunhofer transition regime

We propose a method to obtain improved expressions for the diffraction of circular apertures in the boundary between near and far field. The method is based on an analysis of the center value of the diffraction pattern derived from the Fresnel expression. The method is shown to be applied to both amplitude, phase, and complex apertures, and is compared to Fresnel propagation in simulations. We show how these new expressions allow for the use of the Fraunhofer approximation at Fresnel numbers at least twice as large as the conventional expressions. This facilitates analytical Fraunhofer propagation to be used for much larger apertures, at shorter propagation distances, and with more complex aperture transmission functions.

Wavefront measurement of a large aperture high image quality off-axis Fresnel lens.

Large aperture off-axis Fresnel lens will play an important role in the future 10 m scale aperture transmission space telescope system. Improving diffraction efficiency and wavefront image quality is always the goal of engineering applications. A 4-level off-axis fresnel lens with Ф350 mm effective aperture was fabricated through overlay etching technique by laser direct writing system. The wavefront aberration characteristics of the off-axis Fresnel lens at 632.8 nm wavelength are analyzed and discussed in detail, and the large aperture off-axis Fresnel lenses wavefront aberration measurement scheme, including a high-precision plane reflector, measured LAOFL, CGH, interferometer and laser tracker to compensate for certain low-order aberrations caused by LAOFL imperfect imaging, is proposed. Wavefront aberration of 0.020 λ(1/50 λ) RMS was achieved. This work presented the best results to our knowledge among the same field with similar aperture in open publications and provided a strong foundation for the future 10 m scale aperture transmission space telescope system.

Development of compact entangled photon-pair sources for satellites

Satellites are expected to play a significant role in the future of global quantum networks. Small satellites such as those following CubeSat standards may enable space-based quantum networks. CubeSat type satellites require less resources to develop and deploy and can be used to rapidly qualify technologies in orbit. The constraints of small satellites drive the development of compact quantum light sources, which will be useful even if the final satellite volume is large due to transmitter aperture requirements. In this article, we discuss the state-of-the-art in compact entangled photon-pair sources and suggest challenges that must be met by new source designs.

Ultrasonic nonlinear fields generated from transmitters with varied aperture angles

The transmitter aperture dependence of the ultrasonic nonlinear field was investigated by using Westervelt equation, Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation and spheroidal beam equation (SBE) models. 1.0-MHz focusing spherical transducers with varied half aperture angles from 10° to 40° was employed as the transmitter, the curvatures of which were fixed as 8 cm. The results show that: (1) KZK equation could simulate the acoustic distribution well for half aperture angle less than 20°; (2) the divergence between KZK equation and Westervelt equation is in proportion to the half aperture angle and surface pressure amplitude; (3) although the focus pressure was different for KZK and Westervelt equation, the shape of focal region of KZK equation was almost the same of Westervelt equation; and (4) the SBE model could simulate the acoustic distribution for a large aperture angle range.

Transmission conditions for clear depiction of thoracic spine based on difference between reflection and scattering characteristics of medical ultrasound

In epidural anesthesia, it is difficult to specify the puncture position of the anesthesia needle. We have proposed an ultrasonic method to depict the thoracic spine using the different characteristics of reflection from bone and scattering from muscle tissue. In the present paper, we investigated the transmission aperture’s width of the ultrasound probe to emphasize the differences in the reflection and scattering characteristics. First, we determined the optimum transmission aperture’s width using a simulation experiment. Next, we measured reflection and scattering signals by changing the transmission aperture’s width in a water tank experiment and confirmed that the results corresponded to the simulations. However, as the transmission aperture’s width increased, the lateral resolution at the focal point improved. Therefore, better imaging of the human thoracic vertebrae can be achieved by selecting the transmission aperture’s width, which considers the effect on lateral resolution.

Iceland spar and birefringent filter (BF) development

Birefringent crystals for BF are required to provide the necessary linear aperture, wavefront quality, and filter transmission in a given spectral region. Based on the review of foreign and domestic BF developments, the difficulties in using crystals from known deposits are examined. The Institute of Solar-Terrestrial Physics has developed BFs with extreme characteristics, using an innovative method for enriching crystals from East Siberian deposits and new methods for optical treatment and control of BF elements. We present the characteristics of the filters. Further progress in the creation of BFs in our country depends on the availability of necessary synthetic crystals and natural crystal of Iceland spar, which turned out to be a difficult fate in Russia.

Исландский шпат и разработка интерференционно-поляризационных фильтров (ИПФ)

Birefringent crystals for BF are required to provide the necessary linear aperture, wavefront quality, and filter transmission in a given spectral region. Based on the review of foreign and domestic BF developments, the difficulties in using crystals from known deposits are examined. The Institute of Solar-Terrestrial Physics has developed BFs with extreme characteristics, using an innovative method for enriching crystals from East Siberian deposits and new methods for optical treatment and control of BF elements. We present the characteristics of the filters. Further progress in the creation of BFs in our country depends on the availability of necessary synthetic crystals and natural crystal of Iceland spar, which turned out to be a difficult fate in Russia.

Optimization of incoherent beam combining in turbulent atmosphere

Incoherent beam combining possesses many advantages not only in the design and control of system structure, but also in the propagation under some condition. In present paper we investigate analytically the propagation of coherent and incoherent combined beam. Results show that when the maximum on-axis intensity is selected as the criterion, the optimization of the number of the channels for incoherent beam combining is obtained according to the transmitter aperture size and the coherence length of turbulence. The number of the channels for incoherent beam combining has an optimal value when the transmitter and turbulence coherence length is unchanged. The propagation of incoherent beam combining is better, at least not worse than that of coherent beam combining under some conditions. The investigation will help to select and optimize the parameters of the incoherent beam combining in some applications.

Performance optimization of an intersatellite optical wireless system using linearly polarized modes

Modern optical communication has advanced from the use of merely lengthy optical fibers to using features of the powerful wireless system and optics resulting in the use of lasers to transmit data at a much greater rate. This gave way to the optical wireless communication system growing roots into space communications. In this work, an intersatellite optical wireless communication link has been analyzed for studying the performance of the system considering linearly polarized modes. The link performance has been investigated in terms of the quality factor (Q factor) as a function of the transmission wavelength, detector type, data rate, distance, transmitter aperture diameter, and pointing error angle. The optimized results of the system reveal that the LP01 mode performs better with the non-return-to-zero modulation scheme at the 850 nm wavelength using a PIN photodiode.

Analysis on space transmission model of the Microwave Wireless Power Transfer system

Abstract This paper systematically analyzes the main link that imposes restrictions on the overall efficiency of the Microwave Wireless Power Transfer (MWPT) system–space transmission. Three typical transmission models of aperture transmission in the near-field area, radiation-focused transmission in the middle-field area, and Friis transmission in the far-field area of radiation were analyzed and calculated. Then, the applicable conditions and efficiency of three-models were compared. And the influence of antenna electrical parameters on the efficiency of the MWPT system was discussed. In the end, three typical space transmission models of aerial vehicles, satellites, and islands were studied. The influence of the medium on the transmission efficiency was emphatically analyzed. This paper aims to summarize the general laws of space transmission of microwave energy. Provide a theoretical reference for related scientific research and engineering practice.

High attitude platform free space optics system using various filtering operations for fifth generation system

This paper presents high attitude platform Free space optics (HAP-FSO) channels using various filtering operations for fifth generation (5G) system. Performance analysis is done utilizing different types of optical filters such as Bessel, Trapezoidal, Gaussian and Rectangular. A comparison is carried out between our proposed scheme and reported counterpart. HAP-FSO performances have been investigated to be taken into account the effects of different factors such as transmission distance, transmitting aperture diameter, beam divergence, transmitter aperture diameter, and receiver diameter. Simulation analysis is performed in highly recognized software tool called Optisystem™ to validate the implementation and performance of the proposed system. It is found that the most extreme quality calculation can be accomplished via utilizing Gaussian optical channel in comparison with distinctive optical channels. In particular, with increasing data rate up to 5G coverage range application, minimum BER value is increased for all type of filters. But the trapezoidal filter achieved better results compared with other types of filters.

Numerical comparison between DPSK 33, DPSK 66 and duo binary in WOC system

OWC systems have turned into a state-of-the-art technology because of their superior performance uniqueness and its innumerable characteristic as compared to its RF. One of the OWC application is inter-satellite wireless optical communication (Is-WOC), this framework can be improved by using different ways such as advanced modulation formats and aperture diameter. We demonstrate an analysis based on the aperture diameter effect in transmission of single channel with 40 Gb/s Is-WOC system using three different modulation methods, differential phase-shift keying (DPSK) with a duty ratio to 66% and 33% and duobinary. Choosing these three modulations from various modulation format is done depending on the advantage they provide where the DPSK gives to fiber nonlinearity a powerful robustness and less susceptible to SPM and XPM and for system requirements of dispersion compensation in duobinary, it provides higher chromatic dispersion tolerance mitigate. The result shows the effect of different transmitter aperture diameter (from 2 to 20 cm) for a constant distance 200 km accomplished by quality factor and minimum BER. We conclude there is a great loss in the small aperture diameter, even in the presence of best modulation format, therefore as the aperture diameter increase the Q-factor increase, but some increased rise is linear and the other is changing from linear to non-linear in a fixed Q-factor point equal to 5.63.

X-ray fan beam coded aperture transmission and diffraction imaging for fast material analysis

X-ray transmission imaging has been used in a variety of applications for high-resolution measurements based on shape and density. Similarly, X-ray diffraction (XRD) imaging has been used widely for molecular structure-based identification of materials. Combining these X-ray methods has the potential to provide high-resolution material identification, exceeding the capabilities of either modality alone. However, XRD imaging methods have been limited in application by their long measurement times and poor spatial resolution, which has generally precluded combined, rapid measurements of X-ray transmission and diffraction. In this work, we present a novel X-ray fan beam coded aperture transmission and diffraction imaging system, developed using commercially available components, for rapid and accurate non-destructive imaging of industrial and biomedical specimens. The imaging system uses a 160 kV Bremsstrahlung X-ray source while achieving a spatial resolution of ≈ 1 × 1 mm2 and a spectral accuracy of > 95% with only 15 s exposures per 150 mm fan beam slice. Applications of this technology are reported in geological imaging, pharmaceutical inspection, and medical diagnosis. The performance of the imaging system indicates improved material differentiation relative to transmission imaging alone at scan times suitable for a variety of industrial and biomedical applications.

Frequency-Tunable Terahertz Plasmonic Structure Based on the Solid Immersed Method for Sensing.

Terahertz waves are located in the frequency band between radio waves and light, and they are being considered for various applications as a light source. Generally, the use of light requires focusing; however, when a terahertz wave is irradiated onto a small detector or a small measurement sample, its wavelength, which is much longer than that of visible light, causes problems. The diffraction limit may make it impossible to focus the terahertz light down to the desired range by using common lenses. The Bull’s Eye structure, which is a plasmonic structure, is a promising tool for focusing the terahertz light beyond the diffraction limit and into the sub-wavelength region. By utilizing the surface plasmon propagation, the electric field intensity and transmission coefficient can be enhanced. In this study, we improved the electric field intensity and light focusing in a small region by adapting the solid immersion method (SIM) from our previous study, which had a frequency-tunable nonconcentric Bull’s Eye structure. Through electromagnetic field analysis, the electric field intensity was confirmed to be approximately 20 times higher than that of the case without the SIM, and the transmission measurements confirmed that the transmission through an aperture had a gap of 1/20 that of the wavelength. This fabricated device can be used in imaging and sensing applications because of the close contact between the transmission aperture and the measurement sample.

Large aperture transmission optical element detection method based on dOTF

Large aperture transmission optical element detection method based on dOTF

Methods for Improving the Distance of Microwave Wireless Power Transmission With a Given Beam Collection Efficiency

Transmission distance of microwave wireless power transmission (MWPT) is a more important index than transmission efficiency and beam collection efficiency (BCE) in some specific applications, which should be analyzed and extended. To maximize the distance of MWPT, the model of MWPT between two planar antennas is built and formulated mathematically in this letter. Methods for improving the distance of MWPT between planar circular antennas with a given BCE are introduced. Optimal phase distribution for maximum transmission distance is derived based on functional analysis theory. Optimal amplitude distribution is obtained through numerical optimization. Numerical cases are calculated and compared to validate the methods. Finally, relationship between maximum transmission distance and aperture size is shown for approximate estimation.

Anomalous blueshift of aperture resonance enabled by the loss of a thin film

The substrate effects on aperture resonance have been widely studied because the resonance peak position is key for sensing, communications, and field enhancement applications. So far, the theoretical works have focused on the lossless infinite substrate case, which only explains the resonance peak redshift by the substrate index. The loss effect has not been investigated yet because lossy infinite substrate significantly reduces the aperture transmission. Therefore, this work studied the loss effect on aperture resonance via an analytic model of the transmission though slot antennas on a finite substrate. When the substrate thickness was very thin compared to the wavelength, the transmittance remained high even for a large imaginary part of the refractive index; furthermore, the developed model predicted a strong blueshift when this imaginary part exceeds the real part. Besides, the zero of the imaginary part of the coupling strength was crucial in determining the resonance frequency for both infinite and finite substrates. Thus, this study can contribute to the material characterization, label-free detection, and efficient design of active metamaterials.