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1.
Appl Opt ; 57(15): 4067-4074, 2018 May 20.
Artigo em Inglês | MEDLINE | ID: mdl-29791380

RESUMO

Specular reflection from the surface of targets or prepared specimens represents a significant problem in optical microscopy and related optical imaging techniques as usually the surface reflection does not contribute to the desired signal. Solutions exist for many of these imaging techniques; however, remedial techniques for imaging based on laser feedback interferometry (LFI) are absent. We propose a reflection cancellation technique based on crossed-polarization filtering that is tailored for a typical LFI configuration. The technique is validated with three experimental designs, and a significant improvement of about 40 dB in the ratio of the diffuse and specular LFI signal is observed. Applications of this principle extend from specular reflection removal to characterization of target materials in industrial to biomedical domains.

2.
Biomed Opt Express ; 8(9): 4037-4048, 2017 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-28966845

RESUMO

Tomographic imaging of soft tissue such as skin has a potential role in cancer detection. The penetration of infrared wavelengths makes a confocal approach based on laser feedback interferometry feasible. We present a compact system using a semiconductor laser as both transmitter and receiver. Numerical and physical models based on the known optical properties of keratinocyte cancers were developed. We validated the technique on three phantoms containing macro-structural changes in optical properties. Experimental results were in agreement with numerical simulations and structural changes were evident which would permit discrimination of healthy tissue and tumour. Furthermore, cancer type discrimination was also able to be visualized using this imaging technique.

3.
Sensors (Basel) ; 16(9)2016 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-27598157

RESUMO

Optical interrogation of suspicious skin lesions is standard care in the management of skin cancer worldwide. Morphological and functional markers of malignancy are often combined to improve expert human diagnostic power. We propose the evaluation of the combination of two independent optical biomarkers of skin tumours concurrently. The morphological modality of reflectance confocal microscopy (RCM) is combined with the functional modality of laser Doppler flowmetry, which is capable of quantifying tissue perfusion. To realize the idea, we propose laser feedback interferometry as an implementation of RCM, which is able to detect the Doppler signal in addition to the confocal reflectance signal. Based on the proposed technique, we study numerical models of skin tissue incorporating two optical biomarkers of malignancy: (i) abnormal red blood cell velocities and concentrations and (ii) anomalous optical properties manifested through tissue confocal reflectance, using Monte Carlo simulation. We also conduct a laboratory experiment on a microfluidic channel containing a dynamic turbid medium, to validate the efficacy of the technique. We quantify the performance of the technique by examining a signal to background ratio (SBR) in both the numerical and experimental models, and it is shown that both simulated and experimental SBRs improve consistently using this technique. This work indicates the feasibility of an optical instrument, which may have a role in enhanced imaging of skin malignancies.


Assuntos
Diagnóstico por Imagem , Fluxometria por Laser-Doppler/métodos , Microscopia Confocal/métodos , Método de Monte Carlo , Neoplasias Cutâneas/diagnóstico , Humanos , Interferometria , Análise Numérica Assistida por Computador , Reprodutibilidade dos Testes , Processamento de Sinais Assistido por Computador
4.
Appl Opt ; 54(1): 18-26, 2015 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-25967002

RESUMO

We present a comprehensive analysis of factors influencing the morphology of the Doppler spectrum obtained from a laser-feedback interferometer. We explore the effect of optical system parameters on three spectral characteristics: central Doppler frequency, broadening, and signal-to-noise ratio. We perform four sets of experiments and replicate the results using a Monte Carlo simulation calibrated to the backscattering profile of the target. We classify the optical system parameters as having a strong or weak influence on the Doppler spectrum. The calibrated Monte Carlo approach accurately reproduces experimental results, and allows one to investigate the detailed contribution of system parameters to the Doppler spectrum, which are difficult to isolate in experiment.

5.
Opt Lett ; 39(2): 394-7, 2014 Jan 15.
Artigo em Inglês | MEDLINE | ID: mdl-24562155

RESUMO

We compare the performance of a self-mixing (SM) sensing system based on an uncooled monolithic array of 24×1 vertical-cavity surface-emitting lasers (VCSELs) in two modes of operation: single active channel and the concurrent multichannel operation. We find that the signal-to-noise ratio of individual SM sensors in a VCSEL array is markedly improved by multichannel operation, as a consequence of the increased operational temperature of the sensors. The performance improvement can be further increased by manufacturing VCSEL arrays with smaller pitch. This has the potential to produce an imaging system with high spatial and temporal resolutions that can be operated without temperature stabilization.

6.
Appl Opt ; 48(5): 979-84, 2009 Feb 10.
Artigo em Inglês | MEDLINE | ID: mdl-19209214

RESUMO

We propose and optimize a hybrid erbium-doped fiber amplifier/fiber Raman amplifier (EDFA/FRA). A large number of parameters of a wide-band hybrid amplifier consisting of an erbium-doped fiber amplifier (EDFA) and a fiber Raman amplifier (FRA) have been optimized using an effective and fast global optimization method called particle swarm optimization. Two types of hybrid EDFA/FRA with six- and 10-pumped FRAs have been optimized. A large number of variables affect the hybrid EDFA/FRA performance, thus we need a global optimization method to be able to deal with these variables. Particle swarm optimization helps us to find optimum parameters of a hybrid EDFA/FRA and reduce the gain spectrum variations to 2.91 and 2.03 dB for the six and 10 pumped FRAs, respectively. The optimum design supports the amplification of 60 signal channels in the wavelength range of 1529.2-1627.1 nm for a wavelength-division multiplexing system.

7.
J Opt Soc Am A Opt Image Sci Vis ; 25(12): 3059-66, 2008 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-19037397

RESUMO

The pumping scheme of multipumped distributed fiber Raman amplifiers is optimized by a powerful method called particle swarm optimization. By use of particle swarm optimization, we optimize both pump powers and frequencies of multipumped Raman amplifiers with a high number of pumps. Particle swarm optimization is a fast and effective method, and it surpasses other optimization methods, such as the genetic algorithm, for optimizing fiber amplifiers. It is shown that the computational efficiency of particle swarm optimization is significantly better than that of the genetic algorithm, reducing the time of computation to one third, and its implementation is more straightforward. A gain bandwidth of 92.1 nm and a gain variation of 0.49 dB in the range of 1524.5-1616.6 nm are obtained by this method, using ten backward pumps in a 60-km-long amplifier. The gain variation reduction is due to the inclusion of pump frequencies in the optimization process.

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