Optical Review最新文献

Aquatic display, which forms a floating image in water without a screen, used in behavioral experiments of aquatic organisms as optical stimuli, and accurately determining the imaging position in the water is important for aquatic display. We derive a formula for the imaging distance of an aquatic image by an aquatic display, including both the thickness and refractive index of the water tank by using paraxial approximation. To examine the accuracy of the derived theoretical formula, the imaging distances are estimated at various imaging distances. Our theoretical formula is measured to have 4% error by comparing with experimental results.

In this paper, we propose and experimentally demonstrate an artificial intelligence (AI)-enabled efficient modulation classification technique for underwater optical wireless communication (UOWC) systems. Specifically, time-domain waveform histograms are adopted as classification features, where three modulation formats including direct current biased optical orthogonal frequency division multiplexing (DCO-OFDM), asymmetrically clipped optical OFDM (ACO-OFDM) and pulse amplitude modulation (PAM) are considered. Moreover, AI algorithms such as decision trees (DT), k-nearest neighbors (k-NN), support vector machines (SVM) and convolutional neural networks (CNN) are utilized to realize efficient modulation classification based on the obtained waveform histogram features. Experimental results demonstrate that all the four algorithms can achieve accuracy surpassing 95% when the received signal-to-noise ratio (SNR) exceeds 6.3 dB. Furthermore, increasing the number of symbols in histograms enhances classification accuracy, whereas altering the number of histogram bins has minimal impact on classification accuracy.

Cylindrical lens is irreplaceable in the field of beam manipulation, which can generate new types of light field by diffraction effect, providing possible tools in micrography, optical micromanipulation and biomedicine field in future. The diffraction light field distributions of the Bessel beam and bottle beam passed though a cylindrical lens are studied in this paper using both experiment and simulation methods. In terms of simulation, Collins formula, combined Huygens Fresnel diffraction integral formula and optical matrix, is used to calculate the diffraction patterns. Specially, the thickness and refractive factors of the lenses in the optical system are introduced into the matrices in this paper, so that the lens is no longer approximated as a thin film, and the bottle beam diffracted by a cylindrical lens is first studied. The simulation and experimental images are broadly consistent for both those two diffraction phenomena.

We report an orthogonal polarization dual-wavelength Nd:GdVO₄ crystal laser with 880 nm LD directly pumping. By adjusting the tilting angle of an uncoated BK7 glass plate inserted in the cavity to change the transmittance of two polarization emission to balance the gain and cavity losses of these emission, an orthogonal polarization dual-wavelength laser at 1340.9 nm (π-polarization) and 1344.4 nm (σ-polarization) is obtained. To the best of our knowledge, this is the first demonstration of orthogonal polarization dual-wavelength lasers in Nd:GdVO₄ crystal at 1.3 μm. With an incident pump power of 13.9 W, the total output power of the dual-wavelength laser is about 1.18 W, with individual power of 0.45 W and 0.68 W at 1340.9 and 1344.4 nm respectively. Such dual-wavelength laser is potential to apply for terahertz emission with nonlinear difference frequency technology.

We present a new partially coherent pulsed source with spatiotemporal coupling. The stochastic optical pulse, which we call a spatiotemporal coupled cosine–Gaussian-correlated Schell-model pulsed (STC–CGCSMP) source, has its spatial and temporal (or spectral) dimensions coupled by a stochastic factor. Within the frame of the extended Collins formula, we derive the expression for the two-point, two-frequency cross-spectral density (CSD) function as this such source propagates through an ABCD optical system. We then simulate the spectral density, the two-point, two-frequency CSD, and the spectral degree of coherence to discuss how the spatiotemporal coupling factor affects the beam structure during transmission. Our theoretical models enrich the classical theory of propagating stochastic optical pulses and may provide a feasible method for further exploration of novel kinds of optical field modulation.

In this paper, a parallel polarization-beam-splitter-based fiber optic filter with adjustable channel spacing is proposed and demonstrated. The transmission characteristics of the proposed filter are simulated and analyzed using the transmission matrix theory. Simulation results show that the filter can generate three different channel spacings by adjusting different polarization controllers (PCs) in front of the polarization beam splitter (PBS). The experiment confirms the feasibility of a multi-wavelength fiber laser (MWFL) constructed based on this filter in achieving channel spacing switching. Its wavelength spacing can be switched between 0.46 nm, 0.66 nm, and 0.88 nm, matching the simulated results of the filter. The power fluctuations between the outputs of the three-channel spacing outputs are less than 1.17 dB, 0.89 dB, and 0.98 dB, and the wavelength fluctuations are less than 0.18 nm, 0.14 nm, and 0.13 nm, respectively.

The shift–rotation method is an absolute testing method that has attracted much attention in recent years, and detection accuracy at the subnanometer level has been achieved. However, for flat absolute calibration, the power aberration cannot be calibrated via the traditional shift–rotation absolute testing method. To solve this problem, we propose a shift–rotation absolute testing method based on autocollimation, which detects the tilt error of the tested mirror caused by the external environment and guides the adjustment of the stage to remove it. Simulations and experiments are conducted to prove this theory. A comparison with liquid experiments shows that the autocollimated shift–rotation method can achieve accurate absolute power aberration and can compensate for the shortcomings of the traditional shift–rotation method.

To enable the operation of a mid-wave infrared (MWIR) camera under vacuum and low-temperature conditions for space-based Earth imaging optical systems, research was conducted on the optical system, mechanical structure, and vacuum and low-temperature testing methods employed in the MWIR optical system. A low-temperature MWIR camera was designed to operate under normal atmospheric pressure, vacuum, and low-temperature conditions. The camera comprises independent optical lenses, an MWIR dewar, an image processing unit, a vacuum refrigeration unit, and preset water cooling pipes. The MWIR lens consists of a front lens unit, a focusing lens unit with a two-stage reduction mechanism, and a rear lens. The assembly temperature of the MWIR camera is 293 K with an operational temperature of 100 K, and the temperature variation does not exceed 193 K. A structural thermal-optical performance analysis of the MWIR lens was conducted to evaluate the optical performance degradation caused by temperature changes. The measurement of the MWIR lens was described using an MWIR interferometer and a spherical standard MWIR mirror, providing on-axis and off-axis wave aberrations. One method was proposed to test the modulation transfer function of the MWIR camera under two different conditions. Experimental results confirmed that the overall design of the MWIR camera ensures normal operation in a vacuum low-temperature environment.

Optical fiber X-ray sensors have the potential to realize real-time dose monitoring of precision radiotherapy. However, an over-response phenomenon can occur when using an optical fiber sensor (OFXS) filled with inorganic scintillator (Gd₂O₂S:Tb) to measure the off-axis ratio (OAR) curve. The aim of this paper is to study the mechanism responsible for the over-response. Due to the complex particle distribution present in water phantoms, the Monte Carlo-based code GEANT4 was used to model the response of the scintillator. The energy response of the scintillator to photons and electrons was initially simulated, which subsequently allowed the OAR curve to be simulated and the results were compared with experiment. To analyze the energy distribution of particles in different positions, electron spectroscopy was simulated together with the photon spectrum at the position from the central axis to a distance of 14.5 cm away from the center. Finally, three metal (Al, Cu, Sn) caps were made for the OFXS to prevent the low-energy photons penetrating the OFXS, and the OARs measurements were repeated. The results show that the scintillator exhibits higher sensitivity to photons with energy below 0.5 MeV, while for electrons, the scintillator has a higher sensitivity to high-energy electrons. Simulations for electron spectroscopy and the photon spectrum show that there are many low-energy photons with relatively few low-energy electrons. The OARs measured using the OFXS with metal caps show that the over-response can be mitigated using a high-Z metal cap. The measurements demonstrate that the OAR cure measured using an OFXS fitted with a Sn cap exhibits the closest response to that measured using an IC.

The folded optics for HMD (head-mounted display), commonly referred to as pancake optics, is widely used to realize a compact HMD headset. The optics has the advantage of compactness, but also has a big drawback of lowering light efficiency. To overcome the issue, we proposed novel HMD pancake optics named “DP (double path) pancake optics” to achieve both compactness and high light efficiency simultaneously. In this paper, we introduce the principle of our “DP pancake optics” and review our prototype. We describe optical simulation results to find a highly balanced design among thickness, lens power, and magnification ratio. We also describe fabrication study of, such as polarization state and alignment accuracy. We successfully have fabricated two prototypes with 90° FOV (field of view), one of which is 20.6 mm optics thickness and the other is 25.5 mm optics thickness. The latter prototype especially shows high MTF with a 1200 ppi (pixel per inch) resolution LCD (liquid crystal display). Both prototypes have 1.8 times higher light efficiency than that of conventional one. In addition, to further expand the DP pancake optics, we also describe the improved design with wider FOV for future prototype fabrication. Therefore, we also show the optical simulation result of the improved design.