| 1. |
- Andres, Bustamante, et al.
(författare)
-
Digital Image Processing and Development of Machine Learning Models for the Discrimination of Corneal Pathology : An Experimental Model
- 2021
-
Ingår i: Photonics. - : MDPI. - 2304-6732. ; 8:4
-
Tidskriftsartikel (refereegranskat)abstract
- Machine learning (ML) has an impressive capacity to learn and analyze a large volume of data. This study aimed to train different algorithms to discriminate between healthy and pathologic corneal images by evaluating digitally processed spectral-domain optical coherence tomography (SD-OCT) corneal images. A set of 22 SD-OCT images belonging to a random set of corneal pathologies was compared to 71 healthy corneas (control group). A binary classification method was applied where three approaches of ML were explored. Once all images were analyzed, representative areas from every digital image were also extracted, processed and analyzed for a statistical feature comparison between healthy and pathologic corneas. The best performance was obtained from transfer learning-support vector machine (TL-SVM) (AUC = 0.94, SPE 88%, SEN 100%) and transfer learning-random forest (TL- RF) method (AUC = 0.92, SPE 84%, SEN 100%), followed by convolutional neural network (CNN) (AUC = 0.84, SPE 77%, SEN 91%) and random forest (AUC = 0.77, SPE 60%, SEN 95%). The highest diagnostic accuracy in classifying corneal images was achieved with the TL-SVM and the TL-RF models. In image classification, CNN was a strong predictor. This pilot experimental study developed a systematic mechanized system to discern pathologic from healthy corneas using a small sample.
|
|
| 2. |
- Castillo Tapia, Pilar, et al.
(författare)
-
Dispersion Analysis of Twist-Symmetric Dielectric Waveguides
- 2021
-
Ingår i: Photonics. - : MDPI AG. - 2304-6732. ; 8:6, s. 206-206
-
Tidskriftsartikel (refereegranskat)abstract
- We propose a circular twist-symmetric dielectric waveguide that is polarization-selective.In the practical implementation of optical fibers, a selective circular polarization is more convenientthan its linearly polarized counterpart where previous knowledge of the emitted polarization fromthe transmitter is unknown. The analysis of the waveguide was conducted with three methods: aneigenmode approach, simulation of a truncated structure, and the so-called multimodal transfermatrix method (MMTMM). The presented simulations demonstrate that the operational band canbe manipulated by tuning the parameters of the structure. Furthermore, the MMTMM allows for adirect and accurate calculation of the attenuation constant of the rejected circular polarization.
|
|
| 3. |
- Christoforo, M. Greyson, et al.
(författare)
-
Transient response of organo-metal-halide solar cells analyzed by time-resolved current-voltage measurements
- 2015
-
Ingår i: Photonics. - : MDPI AG. - 2304-6732. ; 2:4, s. 1101-1115
-
Tidskriftsartikel (refereegranskat)abstract
- The determination of the power conversion efficiency of solar cells based on organo-metal-halides is subject to an ongoing debate. As solar cell devices may exhibit very slow transient response, current-voltage scans in different directions may not be congruent, which is an effect often referred to as hysteresis. We here discuss time-resolved current-voltage measurements as a means to evaluate appropriate delay times (voltage settling times) to be used in current-voltage measurements of solar cells. Furthermore, this method allows the analysis of transient current response to extract time constants that can be used to compare characteristic differences between devices of varying architecture types, selective contacts and changes in devices due to storage or degradation conditions.
|
|
| 4. |
- Di Mitri, Simone, et al.
(författare)
-
Scaling of Beam Collective Effects with Bunch Charge in the CompactLight Free-Electron Laser
- 2020
-
Ingår i: Photonics. - : MDPI. - 2304-6732. ; 7:4
-
Tidskriftsartikel (refereegranskat)abstract
- The CompactLight European consortium is designing a state-of-the-art X-ray free-electron laser driven by radiofrequency X-band technology. Rooted in experimental data on photo-injector performance in the recent literature, this study estimates analytically and numerically the performance of the CompactLight delivery system for bunch charges in the range 75-300 pC. Space-charge forces in the injector, linac transverse wakefield, and coherent synchrotron radiation in bunch compressors are all taken into account. The study confirms efficient lasing in the soft X-rays regime with pulse energies up to hundreds of microjoules at repetition rates as high as 1 kHz.
|
|
| 5. |
- Engholm, Magnus, et al.
(författare)
-
A bio-compatible fiber optic pH sensor based on a thin core interferometric technique
- 2019
-
Ingår i: Photonics. - : MDPI AG. - 2304-6732. ; 6:1
-
Tidskriftsartikel (refereegranskat)abstract
- There is an increasing demand for compact, reliable and versatile sensor concepts for pH-level monitoring within several industrial, chemical as well as bio-medical applications. Many pH sensors concepts have been proposed, however, there is still a need for improved sensor solutions with respect to reliability, durability and miniaturization but also for multiparameter sensing. Here we present a conceptual verification, which includes theoretical simulations as well as experimental evaluation of a fiber optic pH-sensor based on a bio-compatible pH sensitive material not previously used in this context. The fiber optic sensor is based on a Mach-Zehnder interferometric technique, where the pH sensitive material is coated on a short, typically 20-25 mm thin core fiber spliced between two standard single mode fibers. The working principle of the sensor is simulated by using COMSOL Multiphysics. The simulations are used as a guideline for the construction of the sensors that have been experimentally evaluated in different liquids with pH ranging from 1.95 to 11.89. The results are promising, showing the potential for the development of bio-compatible fiber optic pH sensor with short response time, high sensitivity and broad measurement range. The developed sensor concept can find future use in many medical- or bio-chemical applications as well as in environmental monitoring of large areas. Challenges encountered during the sensor development due to variation in the design parameters are discussed. © 2019 by the authors.
|
|
| 6. |
- Feng, Xingxing, et al.
(författare)
-
Numerical Study of Parallel Optoelectronic Reservoir Computing to Enhance Nonlinear Channel Equalization
- 2021
-
Ingår i: Photonics. - : MDPI AG. - 2304-6732. ; 8:10
-
Tidskriftsartikel (refereegranskat)abstract
- Nonlinear impairment is one of the critical limits to enhancing the performance of high-speed communication systems. Traditional digital signal processing (DSP)-based nonlinear channel equalization schemes are influenced by limited bandwidth, high power consumption, and high processing latency. Optoelectronic reservoir computing (RC) is considered a promising optical signal processing (OSP) technique with merits such as large bandwidth, high power efficiency, and low training complexity. In this paper, optoelectronic RC was employed to solve the nonlinear channel equalization problem. A parallel optoelectronic RC scheme with a dual-polarization Mach-Zehnder modulator (DPol-MZM) is proposed and demonstrated numerically. The nonlinear channel equalization performance was greatly enhanced compared with the traditional optoelectronic RC and the Volterra-based nonlinear DSP schemes. In addition, the system efficiency was improved with a single DPol-MZM.
|
|
| 7. |
- Kakkar, Aditya, et al.
(författare)
-
Equalization Enhanced Phase Noise in Coherent Optical Systems with Digital Pre- and Post-Processing
- 2016
-
Ingår i: Photonics. - : MDPI AG. - 2304-6732. ; 3:2
-
Tidskriftsartikel (refereegranskat)abstract
- We present an extensive study of equalization enhanced phase noise (EEPN) in coherent optical system for all practical electronic dispersion compensation configurations. It is shown that there are only eight practicable all-electronic impairment mitigation configurations. The non-linear and time variant analysis reveals that the existence and the cause of EEPN depend on the digital signal processing (DSP) schemes. There are three schemes that in principle do not cause EEPN. Analysis further reveals the statistical equivalence of the remaining five system configurations resulting in EEPN. In three of them, EEPN is due to phase noise of the transmitting laser, while in the remaining two, EEPN is caused by the local oscillator. We provide a simple look-up table for the system designer to make an informative decision regarding practicable configuration choice and design.
|
|
| 8. |
- Kjellberg, Mikko Erik, et al.
(författare)
-
Enhanced Absorption in InP Nanodisk Arrays on Ultra-Thin-Film Silicon for Solar Cell Applications
- 2022
-
Ingår i: Photonics. - : MDPI AG. - 2304-6732. ; 9:3
-
Tidskriftsartikel (refereegranskat)abstract
- The photovoltaic (PV) market today is dominated by silicon (Si)-based solar cells, which, however, can be improved in performance and cost by developing technologies that use less material. We propose an indium phosphide (InP) nanoresonator array on silicon ultra-thin film with a combined thickness of 0.5 mu m to 2 mu m as a solution to minimize cost and maximize power efficiency. This paper focuses on simultaneously achieving broadband antireflection and enhanced absorption in thin-film Si with integrated InP nanodisk arrays. Electromagnetic simulations are used to design and optimize the reflectance and absorption of the proposed design. By varying the height and radius of the InP nanodisks on the Si substrate, together with the array pitch, a weighted reflectance minimum, with respect to the AM1.5 solar spectrum, of 2.9% is obtained in the wavelength range of 400 nm to 1100 nm. The antireflective properties are found to be a combination of a Mie-resonance-induced strong forward-scattering into the structure and an effective index-matching to the Si substrate. In terms of absorption, even up to 2 mu m from the Si surface the InP nanodisk/Si structure consistently shows superior performance compared to plain Si as well as a Si nanodisk/Si structure. At a depth of 500 nm from the surface of the substrate, the absorption values were found to be 47.5% for the InP nanodisk/Si structure compared to only 18.2% for a plain Si substrate. This shows that direct bandgap InP nanoresonator arrays on thin-film Si solar cells can be a novel design to enhance the absorption efficiency of the cell.
|
|
| 9. |
- Navarro, Jaime Rodrigo, et al.
(författare)
-
Blind phase search with angular quantization noise mitigation for efficient carrier phase recovery
- 2017
-
Ingår i: Photonics. - : MDPI AG. - 2304-6732. ; 4:2
-
Tidskriftsartikel (refereegranskat)abstract
- The inherent discrete phase search nature of the conventional blind phase search (C-BPS) algorithm is found to introduce angular quantization noise in its phase noise estimator. The angular quantization noise found in the C-BPS is shown to limit its achievable performance and its potential low complexity implementation. A novel filtered BPS algorithm (F-BPS) is proposed and demonstrated to mitigate this quantization noise by performing a low pass filter operation on the C-BPS phase noise estimator. The improved performance of the proposed F-BPS algorithm makes it possible to significantly reduce the number of necessary test phases to achieve the C-BPS performance, thereby allowing for a drastic reduction of its practical implementation complexity. The proposed F-BPS scheme performance is evaluated on a 28-Gbaud 16QAM and 64QAM both in simulations and experimentally. Results confirm a substantial improvement of the performance along with a significant reduction of its potential implementation complexity compared to that of the C-BPS.
|
|
| 10. |
- Navarro, Jaime Rodrigo, et al.
(författare)
-
Two-Stage n-PSK Partitioning Carrier Phase Recovery Scheme for Circular mQAM Coherent Optical Systems
- 2016
-
Ingår i: Photonics. - : MDPI AG. - 2304-6732. ; 3:2
-
Tidskriftsartikel (refereegranskat)abstract
- A novel two-stage n-PSK partitioning carrier phase recovery (CPR) scheme for circular multilevel quadrature amplitude modulation (C-mQAM) constellations is presented. The first stage of the algorithm provides an initial rough estimation of the received constellation, which is utilized in the second stage for CPR. The performance of the proposed algorithm is studied through extensive simulations at the forward error correction bit error rate targets of 3.8 x 10(-3) and 1 x 10(-2) and is compared with different CPR algorithms. A significant improvement in the combined linewidth symbol duration product (Delta vT(s)) tolerance is achieved compared to the single-stage n-PSK partitioning scheme. Superior performance in the Delta vT(s) tolerance compared to the blind phase search algorithm is also reported. The relative improvements with respect to other CPR schemes are also validated experimentally for a 28-Gbaud C-16QAM back-to-back transmission system. The computational complexity of the proposed CPR scheme is studied, and reduction factors of 24.5 broken vertical bar 30.1 and 59.1 broken vertical bar 63.3 are achieved for C-16QAM and C-64QAM, respectively, compared to single-stage BPS in the form of multipliers broken vertical bar adders.
|
|
