Performance Of Optical System Research Articles

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.

All Fiber Vector Magnetometer Based on Nitrogen-Vacancy Center.

Magnetometers based on nitrogen-vacancy (NV) centers in diamonds have promising applications in fields of living systems biology, condensed matter physics, and industry. This paper proposes a portable and flexible all-fiber NV center vector magnetometer by using fibers to substitute all conventional spatial optical elements, realizing laser excitation and fluorescence collection of micro-diamond with multi-mode fibers simultaneously and efficiently. An optical model is established to investigate multi-mode fiber interrogation of micro-diamond to estimate the optical performance of NV center system. A new analysis method is proposed to extract the magnitude and direction of the magnetic field, combining the morphology of the micro-diamond, thus realizing μm-scale vector magnetic field detection at the tip of the fiber probe. Experimental testing shows our fabricated magnetometer has a sensitivity of 0.73 nT/Hz1/2, demonstrating its feasibility and performance in comparison with conventional confocal NV center magnetometers. This research presents a robust and compact magnetic endoscopy and remote-magnetic measurement approach, which will substantially promote the practical application of magnetometers based on NV centers.

Investigation on the machinability of copper-coated monocrystalline silicon by applying elliptical vibration diamond cutting

Although monocrystalline silicon exhibits promising microstructural properties for enhancing the performance of optical systems, precise and efficient silicon fabrication is still challenging due to its brittleness. In the present work, we demonstrate the ductile machinability of copper-coated silicon by applying elliptical vibration diamond cutting. Firstly, the influence of the copper coating on the ductile machinability of silicon was experimentally investigated by applying ordinary diamond cutting, showing that the critical depth of cut (DOC) for the ductile-to-brittle transition increased from 118 to 418 nm due to the advantages of the copper coating. This provided hydrostatic pressure in the microcutting regime and the compressive force on the subsurface defects to prevent crack propagation. Subsequently, grooving tests on coated and uncoated silicon were performed by applying elliptical vibration cutting (EVC). Due to the small instantaneous uncut chip thickness in each vibration cycle, the critical DOC by EVC for uncoated silicon increased to 459 nm. Applying the favorable copper coating process, the critical DOC by EVC for coated silicon increased to about 988 nm. The ductile machinability of silicon was efficiently improved by combining EVC and the coating process. Furthermore, the influence of vibration amplitude and cutting speed on the ductile machinability of silicon was explored in detail, leading to the optimized machining conditions for the ductile machining of silicon. Finally, based on these fundamental results, ultra-precision microlenses on silicon were efficiently fabricated, which is appropriate for further industrial applications.

Implementation of 23 Gbps optical wireless link for 750 km inter-aircraft communications

Optical device research and development is crucial for the implementation of miniaturized wireless optical transmission systems that are capable of transmitting large amounts of data at fast speeds. This work presents the design and evaluation of an optical link for the inter-aircraft interconnects. At the transmitter, the vertically cavity surface emission laser (VCSEL) is used to generate a directly modulated non-return to zero (NRZ) signal. In the receiver, direct detection and Gaussian low-pass filtering are used. The system’s performance is evaluated and compared with and without the use of filtration at the detector. BER, sensitivities, and data transmission capability are used to evaluate the performance of optical wireless systems using optisystem software. The range and data rate are enhanced 9-fold and 4-fold, respectively, in comparison to earlier schemes. The results presented show a transmission range of 750 km at a 23 Gbps data rate with a BER of 10−29.

Importance Sampling Over Monte Carlo Technique to Estimate Wireless Infrared On-Chip Communication

Optical code division multiple access (OCDMA) represents the development of optical communication. The advantages of OCDMA such as, asynchronous multiuser communication transmission, flexibility, ample bandwidth and scalability; have made this technique a better candidate to be proposed for next generation network on chip. In this paper, performance of on-chip OCDMA communication system is analyzed. Analytical techniques for estimating the performance of optical communication systems are difficult, complicated and no complete analytical treatment of the problem has been obtained before. Simulation techniques such as Monte Carlo (MC) are used to obtain reasonable estimates of these systems performance. For optical communications, Monte Carlo require excessively large sample sizes which makes it cumbersome in terms of physical resources, and are not practical for estimating very low values of error probabilities. Modified Monte-Carlo (Importance sampling/IS) method was used to reduce the number of simulation tests for estimating error probabilities for optical communications systems by modifying the probability density function of the on-chip noise process. Simulation results are presented and assessed in term of bit error rate (BER), showing the contribution of IS relatively to MC.

Aperture-averaged scintillation for a weak underwater turbulence-affected Gaussian beam using the OTOPS model.

The calculation of optical system performance for laser beam propagation in optical turbulence, such as bit error rate (BER), signal-to-noise ratio, and probability of fade, requires the knowledge of scintillation. In this paper, we show the analytical expressions of the aperture-averaged scintillation using a new recently introduced power spectrum of the refractive index fluctuations for underwater turbulence, the oceanic turbulence optical power spectrum (OTOPS). In addition, we use this main result to investigate the impact of weak oceanic turbulence on free-space optical system performance for a propagating Gaussian beam wave. Similar to the atmospheric turbulence case, results show that aperture averaging can reduce the mean BER and the probability of fade several orders of magnitude if the receiver aperture is chosen with a diameter larger than the Fresnel zone, L/k. Being valid for weak turbulence regime in any natural waters, results present the variations of irradiance fluctuations and the performance of underwater optical wireless communication systems depending on the practical values of average temperature and average salinity concentration that can be encountered in any world's waters.

Performance Evaluation of MIMO-OFDM-FSO with Modified Receiver

The performance of free space optical communication system using multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) with a modified receiver structure is evaluated in this paper referred to as MIMO-OFDM-FSO with the modified receiver (MIMO-OFDM-FSO-MR). Utilizing equal gain combining the analysis is done by taking closed-form expression of average bit error rate and throughput. The simulation is performed to estimate various performance parameters such as throughput and bit error rate (BER) for the proposed MIMO-OFDM-FSO-MR model under different turbulence and weather conditions. Simulation reveals that the proposed model exhibits significant BER performance and provides better throughput and spectral efficiency as compared with conventional FSO systems, OFDM-FSO systems, MIMO-FSO systems and Low-density Parity Check (LDPC) coded MIMO-OFDM-FSO systems.

Fiberless optical communication: issues and challenges

Abstract To fulfill the requirement of high data rate with variable quality of service, optical wireless communication is a better option in comparison to existing RF system and is a favorable technological candidate for future optical communication. In wireless optical communication, information is transmitted by propagation of optical wave through the atmosphere. The detrimental effects of channel parameters can acutely limit the utility of an optical wireless communication system. The paper first reviews different channel models in the context to outdoor wireless communication. Different impairments that affect the performance of outdoor optical communication systems and different techniques to mitigate these impairments are then investigated. The upper layer protocols for free space optical communication are also discussed.

Wideband Multichannel Nyquist-Spaced Long-Haul Optical Transmission Influenced by Enhanced Equalization Phase Noise.

Enhanced equalization phase noise (EEPN), generated from the uncompensated dispersion experienced by laser phase noises, can cause serious damage to the transmission quality of optical fiber systems. In this work, the performance of a wideband Nyquist-spaced long-haul nonlinear optical fiber communication systems suffering from EEPN is investigated and discussed through split-step numerical simulations and analytical models based on the perturbation analysis, in the cases of digital nonlinearity compensation (NLC) and electronic dispersion compensation (EDC). The efficiency and the accuracy of the analytical models were validated via simulations, considering the different symbol rates and modulation formats. The performance of the C-band transmission was comprehensively studied based on the model. Our results reveal that the growth of symbol rates and transmission distances aggravates the distortions in the C-band system.

Performance and polarization response of slit homogenizers for the GeoCarb mission

Abstract. The observing strategy of the Geostationary Carbon Observatory (GeoCarb), which is a “step and stare” approach, can lead to distortions in the instrument spectral response function (ISRF) when there are gradients in brightness across instrument field of view. These distortions induce errors in the retrieved trace gases. In order to minimize these errors, the GeoCarb instrument design was modified to include a “slit homogenizer” whose purpose is to scramble the pattern of the incoming light and effectively remove the ISRF distortions caused by the variations in illumination across the slit. As a risk reduction, GeoCarb procured six different homogenizers and had them tested for performance in a benchtop optical system. The major finding is that the homogenizer performance depends strongly on the polarization of the incoming light, with the sensitivity growing as a function of wavelength. The width of the ISRF is substantially smaller when the light is vertically polarized (orthogonal to the slit length) compared to horizontally polarized (parallel to the slit length), and the throughput is accordingly reduced. These effects are due to the effects of the gold coating and high incidence angles present in the GeoCarb homogenizer design, which was verified using a polarization-dependent model generalized from previous homogenizer modeling work. The results strongly recommend controlling the polarization of the light entering a similar implementation using a polarizer, depolarizer, or polarization scrambler for other instruments attempting to mitigate scene illumination non-uniformity effects, as well as a robust characterization of the polarization sensitivity of all key subsystems.

Combined antifogging and antireflective double nanostructured coatings for LiDAR applications.

To increase the performance of optical systems, a good antireflective coating is required to ensure low reflectance and high transmittance of optical surfaces. Further problems, such as fogging that causes light scattering, negatively affect the image quality. This implies that other functional properties are also required. Presented here is a highly promising combination of an antireflective double nanostructure on top of an antifog coating with long-term stable properties, generated in a commercial plasma-ion-assisted coating chamber. It is demonstrated that the nanostructures do not affect the antifog properties and can be successfully used for many applications.

Dual-carrier multiplexed laser-based hybrid transmitter for high data-rate indoor optical wireless communication

In this paper we experimentally demonstrate dual-carrier modulation scheme to achieve spectrally efficient OFDM transmission in an optical wireless communication link using a hybrid laser-LED transmitter. The hybrid transmitter used in this work consists of two near infrared laser diodes at 785 nm and 808 nm used to separately modulate the real and imaginary components of the complex OFDM waveforms, collinearly combined and subsequently mixed with white LED array at a diffuser surface for indoor illumination. At the receiver end, two separate high-speed photodetectors with spectral filters are used to detect the real and imaginary components and subsequently combined to generate the complex OFDM waveforms. The optical system performance is characterized to quantify the beam spread, spot-size and spectral content of the laser beams and white LED array. The communication performance is also characterized using 16, 32, and 64-QAM/OFDM with 1, 1.25 and 1.5 Giga-samples/second sampling rates. The best communication performance with a net data-rate of 4.2 Gbps for 64-QAM/OFDM at an optimum sampling rate of 1.5 G-Samples/second is demonstrated. The dual-carrier modulation scheme studied in this work helps achieve improved spectral efficiency for OFDM transmission in an OWC link using dual transmitter-receiver pair, while at the same time requiring simplified electronic front-ends and encoding/decoding algorithms.

Design and analyses of BER performance in a tri-directional optical transmission system

The aim of the paper is to verify the stability of the tri-directional fiber transmission system. The design of transmission methods is different wavelengths modulated in the electrical signal of 10 Gbit/s and 2.5 Gbit/s based on the corresponding architectures. The goals are to measure the influence of the signal with the same and adjacent channel interference. The experimental architecture is designed in parallel. We chose the wavelength of 1552.5 nm as the receiving signal to keep the scheme working in the same conditions for comparison. In addition, we insert an additional 25 km and 50 km single-mode fiber (SMF). The result shows that power penalty can be improved within a range of 2–3 dB if a bandpass filter (BPF) is inserted before the measurement equipment. The standard in the experiment requires a wavelength spacing of 0.8 nm between each channel. The result shows that in transmission methods with different wavelengths and distances, the power penalties are 0.304 dB, 0.595 dB, and 1.173 dB, respectively. As the transmission speed decreases with different distances of 0 km, 25 km, and 50 km, the power penalties are 0.101 dB, 0.385 dB, and 0.538 dB, respectively. With the hybrid speed under different distances, the power penalties are 0.278 dB, 0.404 dB, and 0.551 dB. The tri-directional transmission can be divided into with or without an optical switch connection, while the function of the optical switch is to divide the system into the cross and parallel switching modes. According to experimental results, the power loss is in a range of 2–4 dB, and the power reimbursement is slightly increased by 0.1–0.2 dB. To compare the results with the worst condition, the power penalties for no optical switch (OSW), OSW in bar state, and OSW in cross state are 0.756 dB, 0.317 dB, and 0.329 dB, respectively.

Hybrid Dispersion Engineering based on Chiral Metamirror

AbstractDispersion is one of the key performances of optical systems. As a man‐made device, metasurface is a notable alternative for dispersion manipulation and has been developed vigorously in recent years. However, the currently reported dispersion manipulation principle of meta‐atoms only relies on controlling the propagation phase in the operation frequency band or several working wavelengths. In this paper, the chirality‐assisted phase is introduced as an additional degree of freedom to engineer the dispersion characteristics of the meta‐atom, and the strategy is theoretically demonstrated. The dispersion characteristic of the chiral meta‐atom working in a reflective manner is discussed in detail within the working bandwidth. Then, two hybrid dispersion‐engineered metamirrors (HDEMs) are proposed and constructed to demonstrate versatile dispersion manipulation in the working frequency band, including achromatic focusing for the lower half band and hyper dispersive focusing for the upper half band, and hyper dispersive focusing and abnormal dispersive focusing in the lower and upper half band, respectively. Both full‐wave simulation and measured performances verify the validity and flexibility of the proposed strategy. This work exploits a new degree of freedom for dispersion manipulation, providing a new approach for dispersion‐engineered metasurfaces design.

Transient optical simulation by coupling elastic multibody systems, finite elements, and ray tracing

Transient dynamical–thermoelastic–optical system simulation is an important expansion of classical ray tracing through rigid, resting lenses because the operating performance of high-precision optical systems can be influenced by dynamical excitations or thermal gradients. In this paper an approach for an integrated optical system simulation using the coupling of elastic multibody system simulations, thermoelastic finite element analysis and gradient-index ray tracing is presented. Transient mechanical rigid body motions and elastic deformations, thermally induced refraction index changes, and thermal elastic deformations can be considered simultaneously in the ray tracing using the presented method. The calculation of the dynamical and thermal disturbances, the data transfer and coupling, and the gradient index ray tracing method are introduced. Finally, the approach is applied on a transient triplet lens optical system and some investigation results are shown.

The Applications of Digital Signal Processing Techniques for Enhancing the Performance of High Speed Optical Communication Systems

This paper presents Improving performance of 112 Gbits optical coherent communications systems using digital signal processing techniques to compensate linear impairments that are exposed to the signal during its propagation in optical fiber. In this paper, different multi-level modulation formats (DP-QPSK, DP 8PSK, DP- 16PSK and DP-16-QAM) were compared for the same data rate at different distances from the transmitter without amplification. the comparison was done by measuring bit error rate value. We used digital signal processing techniques for linear effects compensation. Where chromatic dispersion was compensated using a simple digital filter, and Polarization mod dispersion was realized by applying the constant-modulus algorithm (CMA). The phase and frequency mismatch between the transmitter and the local oscillator in the receiver was compensated using the modified Viterbi-Viterbi algorithm. We used the Optical simulator Opti-system , which was linked with MATLAB R2011 in order to implementation DSP algorithms and analyze obtained results.

Improving infra-red polarized imaging efficiency in a bilayer wire-grid polarizer.

The optical, plasmonic, and imaging performance of an infra-red polarized system exceeds that of a conventional infra-red detector due to its high resolution and precision. The wire-grid polarizer has large potential for use in an infra-red polarized imaging device owing to its large polarization efficiency. In this study, we theoretically and experimentally investigate a method to improve the polarization efficiency of a wire-grid polarizer. Here, we demonstrated a high-performance wire grid polarizer with a maximum extinction ratio (ER) of 355 using a bilayer structure and dielectric material in the mid-wavelength infra-red (MWIR) region (3000 nm-5000 nm), which is a 4 times higher ER value than that of the monolayer structure. More interestingly, we were able to improve the performance of the bilayer wire-grid polarizer by devising a method to improve the surface roughness using Ar ion milling. The ER for the after-milled sample was 1255, which was markedly larger than that of the before-milled sample. The results of transmittance measurement confirmed that the improvement in the ER was due to the Fabry-Perot (F-P) phenomenon caused by constructive or destructive interference in the bilayer wire-grid structure and the enhancement of the surface smoothness. These results will help design a polarizer structure that will maximize the polarization efficiency and realize a high-performance infrared polarized imaging system.

Main Factor Analysis for Imaging Performance of Hand-Held Full-Field Optical Coherence Tomography System with Dual Interferometers

Main Factor Analysis for Imaging Performance of Hand-Held Full-Field Optical Coherence Tomography System with Dual Interferometers

Feasibility study of using various optical filters in conjunction with indoor visible light communication system

In modern telecommunication engineering, visible light communication (VLC) is developing a competitive advantage over the traditional RF data communication model since it uses light to transmit data. Optical filters play an important role in optical communication systems to enhance the transmission rate of bit-error rate (BER), especially as a result of noisy environments. We investigate the VLC signal performance induced by four types of filters, including Bessel, Gaussian, rectangular, and trapezoidal filters. The BER is considered an important aspect of improving optical system performance, as it indicates less crosstalk and fewer interferences within the system and is analyzed using eye diagram opening penalties. In our simulation results, the Gaussian filter performs best among these four types of filters. In this paper, a VLC indoor model is developed and simulated using an eye diagram, a bit error rate, and a transmission distance for the proposed model. The results from this study show significant improvements of Gaussian filter over other optical filters for next-generation optical networking systems, the overall BER of a Gaussian filter-based indoor VLC system is less than 9.6 × 10–15, when the bandwidth of the optical filter is 5 nm at the quality factor of 14 dB.

Cophasing detection of the segmented diffractive optical elements with the phase diversity method

The diffractive optical elements (DOEs) have the advantages of lightweight, low-cost, loose surface-figure tolerances and convenient folding, which provides a direction for next-generation large (>20 m) space telescopes. However, the cophasing of the DOEs limits its application in telescopes and decreases the optical system performance. The phase diversity method is studied and introduced to solve the cophasing detection of the two segmented DOEs. An improved experimental system is set up using the phase diversity method, and the experiment results show that the piston error and tilt error of the two mirrors are 0.03λ and 0.05 μrad, respectively, which meet the actual needs of the cophasing errors.