Wavelength Measurement System Research Articles

Wireless wavelength measurement system with temperature compensation using filter-free wavelength sensors

Abstract Portable wavelength detection systems have been developed for various environmental and biochemical applications. Conventional systems have some limitations as they are unable to adapt to changes in wavelength and rely on optical filters or slits to distinguish between different wavelengths. To address these limitations, a filter-free wavelength sensor system was proposed, utilizing the absorption coefficient of silicon to identify wavelengths. The proposed system comprises an analog circuit for measuring photocurrent from a filter-free wavelength sensor, integrated with a temperature sensor and microcontroller for signal processing. The proposed system can measure currents with a resolution of 1.2 pA within a 30 nA range, achieving a coefficient of determination of 0.999 for measured currents in relation to light intensity. The microcontroller features a temperature compensation algorithm, enabling wireless control and data transmission. Applying temperature compensation reduced the rate of errors in the data by 61%. By eliminating the need for optical components, a wireless measurement system was developed that can accurately identify wavelengths.

Neural network-based optimization of sub-diffuse reflectance spectroscopy for improved parameter prediction and efficient data collection.

In this study, a general and systematical investigation of sub-diffuse reflectance spectroscopy is implemented. A Gegenbauer-kernel phase function-based Monte Carlo is adopted to describe photon transport more efficiently. To improve the computational efficiency and accuracy, two neural network algorithms, namely, back propagation neural network and radial basis function neural network are utilized to predict the absorption coefficient , reduced scattering coefficient and sub-diffusive quantifier , simultaneously, at multiple source-detector separations (SDS). The predicted results show that the three parameters can be predicated accurately by selecting five SDSs or above. Based on the simulation results, a four wavelength (520, 650, 785 and 830 nm) measurement system using five SDSs is designed by adopting phase-lock-in technique. Furtherly, the trained neural-network models are utilized to extract optical properties from the phantom and in vivo experimental data. The results verify the feasibility and effectiveness of our proposed system and methods in mucosal disease diagnosis.

Hybrid gratings for cladding mode based power self-reference temperature measurement

A hybrid long period grating (LPG)/fiber Bragg grating (FBG) cladding mode coupling and recoupling based ratiometrical temperature sensor is proposed and investigated experimentally. Strong counter-propagation cladding mode is achieved through properly designing the hybrid gratings structure. Experimental results demonstrate that the intensity of backward cladding mode and FBG resonance in hybrid grating show ratiometrical temperature sensitivity and light source induced inaccuracy can be effectively compensated through power self-reference which provides a simple and cost-effective intensity related temperature measurement solution with self-power reference while complex wavelength measurement systems can be avoided.

The Use of a Fiber Comb Filter Fabricated by a CO$_{2}$ Laser Irradiation to Improve the Resolution of a Ratiometric Wavelength Measurement System

An edge filter-based ratiometric wavelength measurement system is modeled and analyzed in this paper. The results confirm that the noise of input signal and photodetectors limits the resolution of the wavelength measurement system. The achievable resolution is calculated for a given noise level of the input signal and photodetectors' resolution. An improved ratiometric wavelength measurement system consisting of two fiber comb filters is presented both theoretically and experimentally, which performs coarse and fine wavelength measurements simultaneously. The resolution of the system is significantly improved to better than 5 pm while maintaining the potential for high measurement speed and wide measurable wavelength range.

Study of the effect of source signal bandwidth on ratiometric wavelength measurement

We derive an analytic equation for a ratiometric wavelength measurement system and analyze the influence of the optical source signal bandwidth. Our investigation shows that in a particular optical sensing system, the higher the bandwidth of the optical signal, the better resolution the system will achieve. Experiments based on two types of optical signals (output signal of a tunable laser and a fiber Bragg grating) were carried out, and experimental results verified both the simulation results and the theoretical analysis.

A study of the effect of the position of an edge filter within a ratiometric wavelength measurement system

The effect of the position of an edge filter within a ratiometric wavelength measurement system was investigated based on three cases: (1) the reflected fibre Bragg grating (FBG) signal passes through both the reference arm and the edge filter arm, (2) the reflected FBG signal is connected directly to the edge filter arm and does not pass through the reference arm, (3) the edge filter sits in line with the FBG and thus the source power is filtered prior to reaching the FBG. Both numerical simulations and experimental results show that cases 1 and 2 have similar system performance whilst case 3 is the best arrangement which offers the highest wavelength resolution.

Optimum design for maximum wavelength resolution for an edge filter-based ratiometric system

This paper provides a straightforward design method for achieving a maximum wavelength resolution for an edge filter-based ratiometric system. An analysis of the influence of a range of factors on the resolution of the ratiometric wavelength measurement system was carried out. The investigation shows that, for a given input optical signal and when the working wavelength range is known, it is relatively straightforward to select an optimum slope for the edge filter that will yield a maximum resolution for the system. An experimental verification is carried out using a tunable laser and three macrobending fibre edge filters, with a good match between experimental and simulation results.

基于磁流体的新型光纤电流传感器研究

A novel fiber optic Fabry-Perot (F-P) current sensor is developed based on magnetic fluid as the medium in F-P interference cavity. A signal demodulation method based on slanted fiber Bragg grating (FBG) wavelength measurement system is proposed. Theory and principle of electromagnetic-controlled refractive index of the magnetic fluid is described, as well as the structure of the sensor system. Preliminary experiments are carried out, and the results indicate that there is a fairly good linearity of the measurement characteristic. The thickness of magnetic fluid film and initial concentration will affect the measurement results.

Laser wavelength measurement system based on optical wedge interference

Laser wavelength measurement system based on optical wedge interference

Analysis of temperature dependence for a ratiometric wavelength measurement system using SMS fiber structure based edge filters

Temperature dependence of an edge filter based on singlemode–multimode–singlemode (SMS) fiber structure is investigated numerically and experimentally. The experimental results and numerical results are in good agreement within an operational temperature range from 10 °C to 40 °C. It is found that the thermo-optic coefficient (TOC) has a more significant effect on the temperature dependence of an SMS edge filter compared to the thermal expansion coefficient (TEC). In the ratiometric wavelength measurement using two SMS edge filters, a small temperature variation can induce the ratio variation and in turn the wavelength measurement error. It is found the SMS edge filter’s response to both wavelength and temperature is linear. It is proposed that self-monitoring of temperature can be carried out using an updated ratiometric scheme. Self-monitoring of the temperature reduces temperature induced wavelength error to ±0.7 pm at 1545 nm, regardless of the ambient temperature variation.

Generalized design process for fiber-bend-loss-based edge filters for a wavelength measurement system

We investigate and present a generalized methodology for the design of a fiber-bend-loss-based edge filter, starting with the task of evaluating and selecting suitable fibers and then considering the design of a fiber-bending-loss edge filter. As an example to illustrate the methodology, a Corning SMF28e fiber with a 900 microm diameter is selected and two sample edge filters are designed for experimental verification. The designed edge filters are compact, easy to fabricate, meet target spectral specifications, and show low polarization-dependent loss, confirming the effectiveness of the proposed methodology for fiber-bend-loss-based edge filter design.

Temperature-Induced Instabilities in Macro-Bend Fiber Based Wavelength Measurement Systems

An investigation of temperature-induced instabilities in a wavelength measurement system based on macro-bend fiber filter used in the ratiometric scheme are presented. Two wavelength measurement systems based on macro-bend fiber, a standard low bend loss single-mode fiber filter based system and a high bend loss fiber filter based system are considered. In the case of a low bend loss fiber filter based system, the oscillatory variation in the ratio response with temperature and the difference in the temperature-induced ratio variation at different wavelengths makes the temperature corrected calibration of the system unfeasible, which is essential for precise wavelength measurements. The high bend loss fiber filter based system is more sensitive to temperature than the low bend loss fiber filter based system, but critically for the high bend loss fiber filter based system the ratio has a linear variation with temperature, which can be corrected by a suitable temperature calibration process. Comprehensive studies on the temperature dependence of both the macro-bend fiber filter system and its effect on wavelength measurements are presented in this paper.

Modeling and Analysis of the Effect of Noise on an Edge Filter Based Ratiometric Wavelength Measurement System

Theoretical modeling, analysis, and experimental investigation of effect of noise on an edge filter based ratiometric wavelength measurement system have been carried out. A basic noise model for a ratiometric wavelength measurement system which considers both optical and electrical noise is presented. The ratio response of the system has been theoretically modeled considering the limited signal-to-noise ratio (SNR) of source and noise of the receiver circuit and experimentally verified using a macrobend fiber edge filter based ratiometric system. It is shown both theoretically and experimentally that increasing the slope of the edge filter is not necessarily an efficient solution to increasing the resolution of the system and the effect of noise must be accounted for. The resolution of the system changes with wavelength, and an optimization of slope of the ratio of the system is necessary to determine the best possible resolution for a wider wavelength range. In the demonstrated example, we have shown that for systems with slopes of 0.16, 0.22, and 0.31 dB/nm, one can achieve 10-pm resolution for a range of 36, 22, and 16 nm, respectively, starting from 1500 nm in the presence of receiver noise at -10-dBm input power and with an optical signal SNR of 50 dB.

Ratiometric wavelength monitor based on singlemode‐multimode‐singlemode fiber structure

AbstractAn all‐fiber ratiometric wavelength monitor for optical wavelength measurement is proposed and investigated theoretically as well as experimentally. Two edge filters with opposite slope spectral responses based on the singlemode‐multimode‐singlemode (SMS) fiber structures are developed. A ratiometric wavelength measurement system employing the developed SMS edge filters demonstrates a high discrimination range of 20.41 dB and a potential wavelength measurement resolution of 10 pm over a wavelength range from 1530 to 1560 nm. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 3036–3039, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23894

A Low Polarization Sensitivity All-Fiber Wavelength Measurement System

A low polarization-sensitive all-fiber wavelength measurement system using a twisted macro-bend fiber edge filter together with polarization-insensitive (PI) 3-dB coupler is presented. Eliminating the polarization-dependent loss (PDL) is essential when macro-bending single-mode fiber is utilized as an edge filter. A new bending configuration to eliminate the PDL of a fiber edge filter is proposed in this letter by twisting the fiber by 90deg between two bending sections with equal length. The PDL of this configuration retains a low value even while the bending length is increased to achieve a steeper response for the edge filter. This configuration together with a PI 3-dB coupler makes the system to have very low polarization sensitivity and as a result high wavelength accuracy can be achieved.

Effect of polarisation-dependent loss on the performance accuracy of a ratiometric wavelength measurement system

The polarisation-dependent loss (PDL) of a ratiometric wavelength measurement system and its influence on system's accuracy are investigated theoretically and experimentally. The PDL of a ratiometric system and the corresponding power ratio fluctuation is modelled, from which the accuracy of the measured wavelength can be estimated. An all-fibre wavelength measurement system is built to allow comparison of modelled and actual results. The measured ratio variation lies within the estimated limits. The measured wavelength error reaches about 1.41±0.09 nm at 1550 nm in the demonstrated example (with an edge filter of average slope 0.22 dB/nm), which indicates the significant influence of PDL on the accuracy of a ratiometric wavelength measurement system.

Resolution investigation of a ratiometric wavelength measurement system

Theoretical analysis and experimental investigations are presented on the resolution of a ratiometric wavelength measurement system. Theoretical modeling indicates that the resolution of a ratiometric wavelength measurement system is determined by the signal-to-noise ratio of the input signal and the noise of the photodetectors associated with optical-to-electronic conversion. For experimental verification, a ratiometric system employing a macrobending standard single-mode fiber is developed and corresponding results are in good agreement with the theoretical prediction.

Effect of SNR of input signal on the accuracy of a ratiometric wavelength measurement system

AbstractThe impact of a change in signal‐to‐noise ratio (SNR) of the input signal on the accuracy of a ratiometric wavelength measurement system is studied. The variation of the output ratio of the system due to the change in SNR of the input signal is modeled and the experimental investigation has been carried out, and both indicate that the accuracy is influenced significantly by variations in the SNR of the input signal. The demonstration example shows a wavelength shift of 0.055 nm when the SNR of the input signal varies from 47 dB to 42 dB (the measurable range is from 1500 nm to 1600 nm and the edge filter used has a slope of 0.15 dB/nm). © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1022–1024, 2007; Published online in Wiley InterScience (www.interscience.wiley.com).DOI 10.1002/mop.22328

Low-cost wavelength measurement based on a macrobending single-mode fiber

A low-cost all-fiber wavelength measurement technique is proposed and demonstrated. A macrobending standard single-mode fiber is developed as an edge filter with an optimal design and simple surface processing. A ratiometric wavelength measurement system employing the developed macrobending fiber filter demonstrates a resolution of approximately 10 pm in a wavelength range from 1,500 to 1,560 nm with ease of assembly and calibration.

Study of transmission response of edge filters employed in wavelength measurements

The ratiometric wavelength-measurement system is modeled and an optimal design of transmission response of the employed edge filter is demonstrated in the context of a limited signal-to-noise ratio of the signal source. The corresponding experimental investigation is presented. The impact of the limited signal-to-noise ratio of the signal source on determining the optimal transmission response of edge filters for a wavelength-measurement application is shown theoretically and experimentally.