Nonlinear All-Optical Diffractive Deep Neural Network with 10.6 μm Wavelength for Image ClassificationRead the full article
International Journal of Optics publishes both fundamental and highly applied studies on the nature of light, its properties and behaviours, and its interaction with matter.
Chief Editor, Professor Cerullo, leads the Ultrafast Spectroscopy group at the Department of Physics at the Polytechnic University of Milan. His research activity has mainly focused on the physics and applications of ultrashort pulse lasers.
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Analysis of the Noise Reduction Characteristics of a Diffuser with Fizeau Interferometry
To solve the coherent noise problem of an interference image, the method of a rotating diffuser was adopted to change the coherence of a beam to reduce the noise of the interference system. The relationship between the speed of the diffuser and the signal-to-noise ratio (SNR) of the fringe contrast system was simulated to obtain the diffuser control parameters needed for the best interference fringe state. The fringe contrast of each image and the SNR of the system were analyzed. The results showed that the increased speed of the diffuser reduced the contrast of the interference image to a certain extent, but the increased speed also effectively improved the SNR and facilitated the subsequent interference image processing. Due to the coherent noise in the interferometric system, the method of the rotated diffuser reduced the coherence of the light beam to suppress the noise of the interference image. By analyzing the coherent noise reduction characteristics of the rotated diffuser with different surface roughnesses, the relationship between the surface roughness and the noise contrast for different rotation speeds was simulated, and the effective roughness range with the noise reduction effect was selected. A noise reduction system was built based on Fizeau interference, and the noise contrast of the interference image was collected and calculated. The effective range of σh/λ was 0.2–0.5 when the rotation speed was 10 r/s, while the effective range of σh/λ was 0.4–0.6 when the rotation speed was 100 r/s. The experimental results showed that the surface roughness and wavelength ratio σh/λ of the rotated diffuser increased when the noise contrast tended toward 1, but the effective range of the surface roughness decreased with the increase of the rotational speed of the diffuser.
Design and Numerical Analysis of a Novel Rectangular PCF (R-PCF)-Based Biochemical Sensor (BCS) in the THz Regime
A novel PCF-based sensor has been presented in this paper to sense different chemicals and biocomponents. The proposed biochemical sensor (BCS) comprises a simple arrangement of rectangular holes. The competence of this BCS in detecting analytes is evaluated employing the full-vector finite element method (FEM). Performance metrics prove the competence of this BCS in sensing various analytes that have a refractive index in the range of 1.33–1.48. The proposed BCS shows ultralower values for both the bulk absorption and confinement loss. This BCS attains a maximum of about 95.82% relative sensitivity at 2.5 THz. Also, the dispersion for this sensor is only 0.12 ± 0.011 ps/THz/cm at the same point of interest. These results prove that the proposed BCS will play a key role in sensing toxic chemicals, illegal drugs, biocomponents, etc. Besides, the simple rectangle-based PCF structure ensures the feasibility of fabrication by practicing the existing fabrication strategies.
Design and Management of Stray Light for Compact Final Optics Assembly on the High Energy Laser System
In this study, a model is proposed to design and manage the stray light of a compact final optics assembly (FOA) for a high energy laser system. Based on the method we proposed, the high-order stray light can be managed to optimizing the position and angle of the optical elements. A light trap is designed to manage the first-order stray light with high fluence. Applying the method, we provide an experimental demonstration to designing a compact FOA. By comparing the cleaning results with no management testing result, it proves that using the above design and management, it can achieve the great improvement of cleanliness from ISO Class 5 to Class 3, which is significant to improve the output capability of the high energy laser system. In addition, we also verify the stray light by an optical field paper. It demonstrates that the field characteristics and position calculation of stray light are reliable.
Intensity Distribution of Partially Coherent Array Finite Airy Beams Propagating in Atmospheric Turbulence
Based on the extended Huygens–Fresnel integral and the Rytov phase structure function, the closed-form expression of a partially coherent array finite Airy beams (PCAFABs) cutting through the Kolmogorov atmospheric turbulence is derived in the space domain under the paraxial approximation. The characteristics of the PCAFABs evoluting in the atmospheric environment are investigated in detail on the basis of the derived wave propagation formulae. We mainly illustrate the intensity profile of this beam changed with the truncation parameter, coherence length, and turbulence factor at several cross sections of the atmospheric space by means of numerical figures. It is convinced that the present concept and derived conclusions will provide useful exploration for learning the optical properties of the PCAFABs transmitting in the atmospheric turbulence, especially for free-space optical communication area.
Spectral Efficient Asymmetrically Clipped Hybrid FBMC for Visible Light Communication
Filter bank multicarrier (FBMC) modulation has shown sufficient potential for wireless communication. A hybrid optical FBMC technique is proposed to improve the spectral efficiency of a visible light communication (VLC) system. In this technique, a hybrid asymmetrically clipped optical offset quadrature amplitude modulation FBMC (HACO-OQAM-FBMC) modulation technique is used. Asymmetrically clipped optical FBMC (ACO-FBMC) is used for odd subcarriers, and pulse amplitude modulation-discrete multitone (PAM-DMT) is used for the even subcarriers. The proposed hybrid scheme uses an intensity modulation/direct detection (IM/DD) channel. It is shown that there is no interference on odd subcarriers using the proposed method and receiver demodulation is similar to that of ACO-FBMC receiver. However, clipping noise of ACO-FBMC falls on PAM-DMT subcarriers, which can be cancelled at receiver processing after estimation. The analytical performance of the proposed technique is compared using parameters, namely, bit error rate (BER), spectral efficiency, computational complexity, and peak to average power ratio (PAPR). It is found that HACO-OQAM-FBMC is more spectral efficient than ACO-FBMC and other OFDM-based techniques.
An All-Solid Dispersion-Compensating Photonic Crystal Fiber Based on Mode Coupling Mechanism in Dual-Concentric Core
An all-solid dispersion-compensating photonic crystal fiber based on mode coupling mechanism in dual-concentric core has been proposed. The mode coupling characteristics, dispersion, confinement loss of the fiber, and the influence on dispersion of some structure parameters are simulated by full-vector finite element method. By using the relationship between phase matching wavelengths and coupling strength with the change of fiber microstructure parameters, an all-solid dual-concentric-core dispersion-compensating photonic crystal fiber is presented. The structure parameters on dispersion characteristic are investigated. The results demonstrate that the proposed fiber has a large negative dispersion value 8465 ps/(nm·km) at 1550 nm. The effective mode area and the splicing loss to the standard single mode fiber are 12.8 μm2 and 1.89 dB at 1550 nm, respectively. At 1550 nm, the confinement loss is less than 1 × 10−3 dB/km and the bending loss with 2 cm bending diameter is less than 1 × 10−2 dB/km.