Elements Of Optical System Research Articles

Vertical Cavity Surface Emitting Laser technology: A comprehensive review

Vertical Cavity Surface Emitting Laser (VCSEL) technology has become an indispensable element in optical communication systems and optoelectronics due to its many advantages, and the unique characteristics of VCSELs, including vertical emission, high-speed operation, and low power consumption, have attracted much interest from researchers and industry professionals. This paper provides a comprehensive overview of VCSELs, explaining their basic principles and two commonly used structures. It also delves into the field of optical communications, highlighting the challenges faced in the current development, from which it introduces the significant progress made by VCSELs over the past decade in various applications such as high-speed data transmission, multi-mode communications, and long-distance networks. In addition, this study provides valuable insights into the future trajectory and potential evolution of VCSEL technology to facilitate further research and innovation in the field of communications. By providing a holistic analysis, this study is a valuable resource for scientists and researchers to help them realize the full potential of VCSELs in advancing optical communication technologies to meet the ever-changing needs of modern communication networks.

Surrogate-model-based dwell time optimization for atmospheric pressure plasma jet finishing

With the rapidly increasing requirements for high-precision optical elements in modern optical systems, atmospheric pressure plasma jet (APPJ) finishing has attracted wide attention due to its high material removal efficiency and superior surface quality. However, the temperature fluctuation in the localized processing footprint, induced by the heated plasma and varying dwell time, emerges as a critical factor that oscillates the etching rate and thus degrades the deterministic removal control. Existing dwell time solution algorithms only apply under the assumption that the material removal rate exhibits temporal and spatial constancy, which is not the case in APPJ finishing. To address this challenge, a surrogate-model-based dwell time optimization approach for the temperature-dependent tool influence function (TIF) is proposed in this study. Firstly, a temperature-dependent TIF is proposed to quantitatively describe the thermal effect, and the corresponding calibration method is established. Subsequently, a thermodynamic simulation model is established to simulate the temperature of the localized processing footprint. By integrating the temperature-dependent TIF with the temperature prediction model, a novel dwell time optimization algorithm is proposed to alleviate the error caused by the temperature fluctuation. Given the prohibitive long computation time of the thermodynamic simulation model, a data-driven surrogate model based on Long Short Term Memory (LSTM), capable of rapid temperature prediction, is trained through the customized simulation dataset. The effectiveness of the proposed surrogate-model-based dwell time optimization algorithm is verified through simulations and experiments. Compared to traditional dwell time solution algorithms, the proposed approach yields a 47.12 % improvement in machining precision.

Synchronization of two chaotic microresonator frequency combs.

We explore the synchronization of chaotic microresonator frequency combs, emphasizing the modulation instability state, which is known for its inherent chaotic behaviors. Our study confirms that the synchronization of two such combs is feasible by injecting the output from the lead microresonator into the next microresonator's input. We also identify the optimal parameters for this synchronization. Remarkably, even partial injection from the leader is sufficient for synchronization, paving the way for versatile future system configurations. Such systems could simultaneously utilize distinct spectral components for synchronization and transmission. This work advances our understanding of chaotic microresonator combs, showing them to be pivotal elements in next-generation optical communication systems.

Comparative analysis of optical data center switches

Abstract In the recent past, there has been an explosive growth in data traffic within data center systems. This rapid increase in data volume has put significant constraints on the speed of current data communication networks, which are predominantly based on electronic controllers and memory. The speed limitations of electronic devices hinder their ability to process data at higher rates efficiently. To address this issue and enable faster data processing, the use of optical communication emerges as the most promising solution. Optical communication leverages the capabilities of light signals and optical components, which can handle data at much higher rates compared to their electronic counterparts. One key element in optical communication systems is the utilization of fiber delay lines (FDLs) as optical storage for packets. FDLs offer the ability to temporarily store and delay optical signals, providing buffering capabilities within optical networks. These FDLs can be configured in various setups, including feed forward, feed backward, and recirculating configurations, each with its own set of advantages and disadvantages. In this context, this article explores several state-of-the-art arrayed waveguide grating (AWG)-based optical packet switch (OPSW) architectures. These switches are designed to efficiently route and manage optical packets within data center networks. Each architecture is summarized, highlighting its unique features and capabilities. To compare the different AWG-based OPSW architectures, various key parameters are considered, such as the cost, physical losses, bit error rate (BER), and the number of tunable components required. These parameters are critical in determining the performance, efficiency, and cost-effectiveness of the switches.

Polarisation Control in Arrays of Microlenses and Gratings: Performance in Visible-IR Spectral Ranges.

Microlens arrays (MLAs) which are increasingly popular micro-optical elements in compact integrated optical systems were fabricated using a femtosecond direct laser write (fs-DLW) technique in the low-shrinkage SZ2080TM photoresist. High-fidelity definition of 3D surfaces on IR transparent CaF2 substrates allowed to achieve ∼50% transmittance in the chemical fingerprinting spectral region 2-5 μm wavelengths since MLAs were only ∼10 μm high corresponding to the numerical aperture of 0.3 (the lens height is comparable with the IR wavelength). To combine diffractive and refractive capabilities in miniaturised optical setup, a graphene oxide (GO) grating acting as a linear polariser was also fabricated by fs-DLW by ablation of a 1 μm-thick GO thin film. Such an ultra-thin GO polariser can be integrated with the fabricated MLA to add dispersion control at the focal plane. Pairs of MLAs and GO polarisers were characterised throughout the visible-IR spectral window and numerical modelling was used to simulate their performance. A good match between the experimental results of MLA focusing and simulations was achieved.

Design, Fabrication and Analysis of a Hybrid-Order Monolithic Imaging Diffractive Lens on a Germanium Substrate

Diffractive optical elements are gradually replacing some conventional optical elements and becoming a key component of optical systems due to their unique phase modulation function. However, the imaging performance will be reduced due to the fact that this single-sided microstructured lens still produces chromatic aberration. Therefore, the key issue for the application of diffractive optical elements in optical systems is the reduction of chromatic aberration, and diffractive lenses with double-sided microstructures are proposed as a solution. This research describes the design and analysis of a 70-mm-diameter, 296-mm-focal-length double-sided microstructured hybrid-order monolithic imaging diffractive lens operating in the mid-wave infrared region (3.7-4.7 μm). The design minimizes chromatic aberration by up to 30 times compared to a standard harmonic diffractive lens and improves the image performance of a single-lens optical system operating in the infrared range. Experiments indicate that this design is capable of achieving single-lens imaging with high sensitivity for optical systems with a measured NETD ≤ 50 mK. The analysis of the experiments yielded suggestions for future research.

Slanted TiO2 Metagratings for Large‐Angle, High‐Efficiency Anomalous Refraction in the Visible

AbstractDiffractive gratings are crucial elements for optical systems but suffer from rapid power drop at large angles. Recently, metagratings have shown their capability of deflecting light in an arbitrary direction. However, the experimental efficiency at large‐angle is still low and the zeroth‐order crosstalk is difficult to suppress. Here a new approach for large‐angle and high‐efficiency anomalous refraction in the visible spectrum is demonstrated. By introducing out‐of‐plane asymmetry, it is shown that meta‐atoms with simple configurations have similar degrees of freedom as their topologically optimized counterparts. Consequently, the slanted titanium dioxide (TiO2) metagratings can steer light to 80° with high relative efficiency (98.5%) and absolute efficiency (89.5%), which represents the ratio of the energy in target diffraction order to the total transmittance energy and to the total incident energy, respectively. Most importantly, the simple configurations make the TiO2 metagratings easy to fabricate, and the experimental efficiency for large (80°) angle of refraction is preserved at a considerably high value of 94.0% (relative) and 83.6% (absolute). This approach represents an effective route in meta‐devices and shall trigger new classes of high‐performance nanophotonic systems.

Spatial geometrical calibration of optoelectronic devices

Space equipment experiences high thermal and mechanical loads that cause deformation of its structures, as well as elements of optical systems and radiation receivers, which can lead to changes in the mutual position of the optoelectronic device elements, disturbing its alignment, degrading image quality and increasing pointing errors. This paper presents a method of spatial geometric calibration that does not require additional equipment and investigates the dependence of the identification results on the viewing angle. The proposed methodology of optoelectronic instrument calibration is intended to improve efficiency, reliability and survivability of automated spacecrafts during their operation.

Hardware implementation of a neuron for neuromorphic optical system

Specific features of neuromorphic systems construction and aspects of basic elements functions realisation are discussed. Hardware implementations of basic elements of pulsed neuromorphic optical system - synapses and neurones - based on the phase state change of thin-film structures made of chalcogenide materials under the influence of laser pulses are described. Calculations of optical characteristics of GeSbTe thin films in multilayer structures have been carried out. The hardware implementation of the main functions of optical neurons was analysed on the model with multilayer coatings based on phase-changeable materials.

Пассивные стекла в системах наблюдения

The analysis of the possibilities of determining the spectrum of electromagnetic radiation from celestial objects using the optical-electronic system of the telescope using CCD receivers is carried out. It is shown that with the introduction of new CCD-type receivers into photometry, the efficiency of observing celestial objects has significantly increased, but despite the positive result, it is necessary to eliminate problems when registering objects with weak radiation during measurements. The purpose of the article is based on the results of experimental studies of thermomechanical and optical properties of multicomponent glasses to provide a justification for the introduction of new materials with a wider transmission range of radiation in various spectra as elements of optical systems of telescopes. In the course of research of new optical materials using the spectroscopy method, optimal compositions of multicomponent glasses were found, allowing to perceive electromagnetic radiation from celestial bodies in various ranges of the infrared spectrum. In conclusion, the results of the study are presented, showing that the introduction of indium and lead fluorides into the composition of multicomponent glass significantly increases the transmission range, which will increase the efficiency of the optical system when using these materials for its elements.

Derivation of closed-form ellipsoidal X-ray mirror shapes from Fermat's principle.

Ellipsoidal and plane-elliptical surfaces are widely used as reflective, point-to-point focusing elements in many optical systems, including X-ray optics. Here the classical optical path function approach of Fermat is applied to derive a closed-form expression for these surfaces that are uniquely described by the object and image distances and the angle of incidence at a point on a mirror surface. A compact description facilitates design, modeling, fabrication, and testing to arbitrary accuracy. Congruent surfaces in two useful coordinate systems - a system centered on the ellipsoid's axes of symmetry and a mirror-centered or `vertex' system with the surface tangent to the xy plane at the mirror's center - are presented. Expressions for the local slope and radii of curvature are derived from the result, and the first several terms of the Maclauren series expansion are provided about the mirror center.

Compact silicon-based polarization-independent 1.55/2 μm wavelength diplexer based on a multimode interference coupler with multiple shallow grooves

Faced with the rapid growth of internet traffic demand, which has posed a huge challenge to the current fiber-based communications systems, expanding the telecommunications bands from traditional near-infrared (NIR) region to mid-infrared (MIR) region is emerging as an attractive solution. And on-chip wavelength division multiplexing (WDM) application for NIR/MIR wavelengths is an essential element in future optical telecommunication systems. Here, we propose a compact silicon-based polarization-independent wavelength diplexer for the NIR/MIR wavelengths of 1.55/2 μm, where multiple rectangular grooves are shallowly etched on the silicon MMI waveguide for introducing the refractive-index perturbations on the MMI waveguide eigenmodes. And this refractive-index perturbation scheme provides a simple and scalable method to manipulate the four beat lengths of the two wavelengths at TE- or TM-polarization in a single waveguide via self-imaging effect, leading to a compact footprint. By optimizing the structural parameters, both NIR/MIR wavelength demultiplexing and polarization independence, for the first time, are obtained simultaneously in the present single device. From the results, the proposed diplexer is only 21.6 μm in length, and shows a wide bandwidth of ∼ 100/120 nm around the wavelength of 1.55/2 μm for insertion loss (IL) < 1 dB and extinction ratio (ER) > 15 dB. Moreover, we also realize a compact and polarization-independent wavelength diplexer for 1.31/2 μm by flexibly changing the dimensions, showing the flexibility and extensibility of our refractive-index perturbation scheme. Besides, fabrication tolerances are analyzed and mode propagation profiles are also demonstrated.

Condensing optical system design using a light guide-cylindrical hybrid lens.

We present a novel lens model, to the best of our knowledge, that redistributes the light flux from an LED and generates the required shape of illumination. A cylindrical lens is widely applied as a condensing optical element in non-imaging optical systems. In this work, a light guide is introduced into the design of a cylindrical lens. Different from the universal cylindrical lens, this one is divided into a light guide surface and a cylindrical surface. The light guide surface leads rays from an LED to a cylindrical surface, making it possible to decrease substantially the width of the lens in comparison with a universal cylindrical lens. That is, the lens model acts as a light guide to lead light rays in the transversal direction and acts as a cylindrical lens in the longitudinal direction. This lens is much easier and more economical to design and manufacture in comparison with conventional cylindrical surface lenses or freeform surface lenses used to produce elongated irradiance distribution. The simulation run by the optical software LightTools shows that the lens designed in the new method, to the best of our knowledge, has a much smaller size than the conventional cylindrical lens, and the uniformity of illumination and efficiency of energy are also quite good. Results show that the efficiency of an elongated lighting area reaches 83.3%.

Controllable Polarization and Diffraction Modulated Multi‐Functionality Based on Metasurface

AbstractDiffraction gratings are crucial optical elements in various optical systems, which can realize tailored diffraction energy distributions as well as phase modulations based on Fourier series. Meanwhile, the polarization gratings can produce arbitrarily specified polarization states on a set of desired diffraction orders for realizing polarimeter. However, simultaneously and independently tailoring the encoded phase profiles and polarization states in different diffraction orders has not been investigated previously. Here, a dielectric metasurface with the capability of generating different holographic images (generalized phase profiles) in different diffraction orders with controllable polarization states is proposed. Such functionality is achieved by applying the double‐phase method into the metasurface design process for manipulating the complex amplitude distributions of two orthogonal polarization bases. Furthermore, in order to prove that the proposed design strategy is suitable to achieve complicated wavefront modulation in a straightforward and convenient manner, a vectorial holographic image with spatially continuous polarization distribution is also obtained without any iteration process. The proposed method may pave the way to achieve a variety of applications such as beam shaping, polarization imaging as well as multifunctional optical systems.

Design of ring resonator based comparator using 2-D photonic crystal

Optical comparators are a key element in optical systems that are vital for the construction of all optical digital frameworks used in optical data processing. The framework for constructing a one-bit optical comparator using photonic crystal ring resonators is presented for maximum throughput. The photonic crystal resonator rings can be linear or nonlinear, depending on the application. Silicon rods in air are employed to create the resonant cavity in the structure for comparator design. The cylindrical rods are made from silicon, which are used in the design of the comparator. Ring resonator structure has been utilized in designing the 2D photonic crystal-based comparator. The input wavelength of 1.5 µm has been applied to both the input ports of comparator for simulating the structure and the quality factor of 648 has been achieved for presented design. The proposed design compares two signals applied at both the input ports of the comparator and generates the signal at the output port.

Polarization-Insensitive Beam Splitter with Variable Split Angles and Ratios Based on Phase Gradient Metasurfaces.

The beam splitter is a common and critical element in optical systems. Traditional beam splitters composed of prisms or wave plates are difficult to be applied to miniaturized optical systems because they are bulky and heavy. The realization of the nanoscale beam splitter with a flexible function has attracted much attention from researchers. Here, we proposed a polarization-insensitive beam splitter with a variable split angle and ratio based on the phase gradient metasurface, which is composed of two types of nanorod arrays with opposite phase gradients. Different split angles are achieved by changing the magnitude of the phase gradient based on the principle of Snell’s law of refraction, and different split ratios are achieved by adding a phase buffer with different areas. In the designed four types of beam splitters for different functions, the split angle is variable in the range of 12–29°, and the split ratio is variable in the range of 0.1–1. The beam splitter has a high beam splitting efficiency above 0.3 at the wavelength of 480–600 nm and a weak polarization dependence. The proposed beam splitter has the advantages of a small size and easy integration, and it can be applied to various optical systems such as multiplexers and interferometers for integrated optical circuits.

Optical refracting properties, birefringence and order parameter in mixtures of liquid crystals: Direct smectic A – Isotropic and reverse isotropic – Smectic A phase transitions

Due to the physical anisotropic and self-assembling nature, liquid crystalline materials holdvery important place in theoretical, experimental and applied physics. Besides, liquid crystals are important materials as working and active elements in various technical devices, optical and optoelectronic systems and technological processes.In this work investigations of the thermo-optical properties of the monomorphic smectogens are presented. Homogeneous binary mixtures of 4-n-alkyl-4′-cyanobiphenyl mesogens were objects in these investigations. The optical refracting and birefringent properties, and behavior of the order parameter at the direct smectic A – isotropic and reverse isotropic – smectic A phase transitions are considered. Temperature dependences of the mean refracting index n, refracting indices for the ordinary no and extraordinary ne rays, and birefringence Δn have been determined. Temperature dependences of the order parameter for the heating – cooling circular cycle at phase transitions are presented.

Polarization-insensitive interferometer based on a hybrid integrated planar light-wave circuit

Interferometers are essential elements in classical and quantum optical systems. The strictly required stability when extracting the phase of photons is vulnerable to polarization variation and phase shift induced by environment disturbance. Here, we implement polarization-insensitive interferometers by combining silica planar light-wave circuit chips and Faraday rotator mirrors. Two asymmetric interferometers with temperature controllers are connected in series to evaluate the single-photon interference. Average interference visibility over 12 h is above 99%, and the variations are less than 0.5%, even with active random polarization disturbance. The experiment results verify that the hybrid chip is available for high-demand applications like quantum key distribution and entanglement measurement.

Demonstration of high-speed thin-film lithium-niobate-on-insulator optical modulators at the 2-µm wavelength.

Optical communication wavelength is being extended from the near-infrared band of 1.31/1.55 µm to the mid-infrared band of 2 µm or beyond for satisfying the increasing demands for high-capacity long-distance data transmissions. An efficient electro-optic (EO) modulator working at 2 µm is highly desired as one of the indispensable elements for optical systems. Lithium niobate (LiNbO3) with a large second-order nonlinear coefficient is widely used in various EO modulators. Here, we experimentally demonstrate the first Mach-Zehnder EO modulator working at 2 µm based on the emerging thin-film LiNbO3 platform. The demonstrated device exhibits a voltage-length product of 3.67 V·cm and a 3-dB-bandwidth of >22 GHz which is limited by the 18 GHz response bandwidth of the photodetector available in the lab. Open eye-diagrams of the 25 Gb/s on-off keying (OOK) signals modulated by the fabricated Mach-Zehnder EO modulator is also measured experimentally with a SNR of about 14 dB.

Microlenses arrays: Fabrication, materials, and applications.

Microlenses have become an indispensable optical element in many optical systems. The advancement of technology has led to a wider variety of microlenses fabrication methods, but these methods suffer from, more or less, some limitations. In this article, we review the manufacturing technology of microlenses from the direct and indirect perspectives. First, we present several fabrication methods and their advantages and disadvantages are discussed. Then, we discuss the commonly used materials for fabricating microlenses and the applications of microlenses in various fields. Finally, we point out the prospects for the future development of microlenses and their fabrication methods.