Lossy Mode Research Articles

Interdigital concept in photonic sensors based on an array of lossy mode resonances

Multi-parameter detection is key in the domain of sensors. Here it is demonstrated that an indium tin oxide (ITO) nanocoating can be used to generate multiple lossy mode resonances (LMRs) in the optical spectrum. To achieve this, a nanocoating with a gradient in thickness is generated on the surface of a planar waveguide, permitting broadening of the LMR because the position of an LMR in the optical spectrum is directly related to the nanocoating thickness. The nanocoating with a gradient in thickness contributes multiple LMRs, each one centred at a different wavelength. With a further etching or deposition using a mask, a pattern of deposited and non-deposited regions can be created, resulting in isolation of the LMRs by preventing LMR overlap. This enables tracking of each central wavelength separately, which can be tuned through control of the gradient or nanocoating pattern. The array of LMR-based sensors is a photonics analogue to the interdigital concept in electronics, enabling multiple resonances to be used for multiparameter sensing.

Material platform for realization of a "fiber-like" lossy mode resonance response in a simple Kretschmann-Raether geometry.

The lossy mode resonance (LMR) phenomenon is almost exclusively limited to fiber optics, since the thin film configuration yields a relatively shallow resonance dip compared to its fiber counterpart. In this Letter, we bridge this frustrating intensity gap between these basic configurations by choosing vacuum-deposited metallic indium-rich indium tin oxide as the coating material. LMR attenuation as high as -14.3dB for transverse electric and -6.4dB for transverse magnetic polarization is achieved experimentally via a commonly used Kretschmann-Raether geometry and that too for a film thickness of ≈70nm. Such a high degree of LMR response is attributed to the metallic indium generated interbands, leading to a high extinction coefficient in the visible range. A modified transfer matrix method, which takes into account the surface roughness of the films through application of the anisotropic Bruggeman effective medium approximation, is developed to realize the experimental LMR spectra numerically.

Beyond near-infrared lossy mode resonances with fluoride glass optical fiber.

The objective of this Letter consists of the exploration of the lossy mode resonance (LMR) phenomenon beyond the near-infrared region and specifically in the short wave infrared region (SWIR) and medium wave infrared region (MWIR). The experimental and theoretical results show for the first time, to the best of our knowledge, not only LMRs in these regions, but also the utilization of fluoride glass optical fiber associated with this phenomenon. The fabricated devices consist of a nanometric thin-film of titanium dioxide used as LMR generating material, which probed extraordinary sensitivities to external refractive index (RI) variations. RI sensitivity was studied in the SWIR and MWIR under different conditions, such as the LMR wavelength range or the order of resonance, showing a tremendous potential for the detection of minute concentrations of gaseous or biological compounds in different media.

Development of a Temperature-Controlled Optical Planar Waveguide Sensor with Lossy Mode Resonance for Refractive Index Measurement

The generation of lossy mode resonances (LMR) with a metallic oxide film deposited on an optical fiber has attracted the attention of many applications. However, an LMR-based optical fiber sensor is frangible, and therefore it does not allow control of the temperature and is not suited to mass production. This paper aims to develop a temperature-controlled lossy mode resonance (TC-LMR) sensor on an optical planar waveguide with an active temperature control function in which an ITO film is not only used as the LMR resonance but also to provide the heating function to achieve the benefits of compact size and active temperature control. A simple flat model about the heat transfer mechanism is proposed to determine the heating time constant for the applied voltages. The TC-LMR sensor is evaluated experimentally for refractive index measurement using a glycerol solution. The heating temperature functions relative to the controlled voltages for water and glycerol are obtained to verify the performance of the TC-LMR sensor. The TC-LMR sensor is a valuable sensing device that can be used in clinical testing and point of care for programming heating with precise temperature control.

Lossy Mode Resonances Generated in Planar Configuration for Two-Parameter Sensing

This work shows a new sensor structure for simultaneous measurement of two parameters, temperature and refractive index. The optical configuration consists of incidence of light on the edge of a soda-lime coverslip fully coated with a CuO thin film and partially coated with a PDMS thick layer. This planar configuration permitted to generate two separated lossy mode resonances (LMRs): one centered at 600 nm and the other at 1000 nm. The second resonance is induced by the PDMS layer and it can be used to measure the temperature due to its high thermo-optic coefficient (the sensitivity is −1.75 nm/°C in the temperature range from 20 to 40 °C), whereas the first resonance is used for sensing refractive index with sensitivity of 1460 nm/RIU in the refractive index range from 1.3328 and 1.37. Finally, a calibration test was carried out using a calibrated oil series with refractive index ranging from 1.33 to 1.36. This work demonstrates the possibility of generating multiples resonances in a single structure as simple as a coverslip, which can be used as a multi-parameter interchangeable sensor, especially suitable for biological applications or the detection of heavy metals in water.

Wavelength and intensity based lossy mode resonance breathing sensor

Copper oxide (CuO) allows the generation of lossy mode resonance (LMR) in a wide wavelength range of the optical spectrum, both in the visible and the near-infrared (NIR). For this, it is necessary to use a configuration based on the lateral incidence of light on the edge of a planar waveguide structure. On the other hand, the use of additional coatings of tin oxide (SnO2) and agarose allows an increase in the sensitivity of the sensor, in response to the breathing monitoring. The sensors were characterized, both in intensity and wavelength. In both cases their behavior depends on the position of the LMR in the optical spectrum. Therefore, it is convenient to extract the design rules that allow an optimal behavior of the sensor. In this sense, sensors located in the NIR presented a better behavior in terms of sensitivity and quality of the signal. In addition, the devices were tested in different conditions: repetitive tests at different distances, oral and nasal breathing, and breathing after doing physical exercise.

Subtle Application of Electrical Field-Induced Lossy Mode Resonance to Enhance Performance of Optical Planar Waveguide Biosensor.

Many studies concern the generation of lossy mode resonances (LMRs) using metallic oxide thin films that are deposited on optical fiber. However, the LMR-based optical fiber sensors are frangible, do not allow easy surface modification, and are not suited to mass production. This study proposes an electrical field-induced LMR-based biosensor with an optical planar waveguide to replace surface modification and allow the mass production of protein biosensors and accelerate the speed of the analyte to decrease the detection time. Experimentally, the biosensor is evaluated using charged serum albumin molecules and characterized in terms of the LMR wavelength shift using an externally applied voltage for different durations. The externally applied voltage generates a significant electric field, which drives the non-neutralized biomolecules and increases the LMR wavelength shift. Our experimental results demonstrate that there are two different mechanisms of adsorption of serum albumin molecules for short-term and long-term observations. These are used to calculate the sensitivity of the biosensor. This electrical field-induced method is highly significant for the development and fabrication of LMR-based biosensors.

Fiber optic Lossy Mode Resonance based sensor for aggressive liquids

A fiber-optic sensor for chemically aggressive environments, such as concentrated solutions of acids and alkalis, has been manufactured. The sensor is based on a single-mode optical fiber with a chemically etched cladding, coated with a thin film of tin dioxide (SnO2) by metalorganic chemical vapor deposition (MOCVD). In the transmission spectra of a SnO2 coated taper lossy mode resonances (LMRs) were observed, the maximum of which shifted to the long-wavelength part of the spectrum, with an increase in the thickness of the deposited film. At a deposition temperature of 345 °C, it was possible to detect the separation of the transverse electric (TE) and transverse magnetic (TM) LMRs for resonances up to the third order. From the change in the position of the 1-st TE LMR, the refractive index and the molar concentration of acids and alkalis in such aggressive liquids as aqueous solutions of HCl, HNO3, H2SO4, NaOH were determined, which, according to our information, is demonstrated for the first time. The high chemical durability of the coating was confirmed by its insusceptibility to aqua regia (AR). The sensitivity of the sensor to changes in the surrounding medium refractive index (SMRI) and the molar concentration of acids was more than 5260 nm/RIU and 32 nm/M, respectively.

Fiber Optic Gas Sensors Based on Lossy Mode Resonances and Sensing Materials Used Therefor: A Comprehensive Review.

Pollution in cities induces harmful effects on human health, which continuously increases the global demand of gas sensors for air quality control and monitoring. In the same manner, the industrial sector requests new gas sensors for their productive processes. Moreover, the association between exhaled gases and a wide range of diseases or health conditions opens the door for new diagnostic applications. The large number of applications for gas sensors has permitted the development of multiple sensing technologies. Among them, optical fiber gas sensors enable their utilization in remote locations, confined spaces or hostile environments as well as corrosive or explosive atmospheres. Particularly, Lossy Mode Resonance (LMR)-based optical fiber sensors employ the traditional metal oxides used for gas sensing purposes for the generation of the resonances. Some research has been conducted on the development of LMR-based optical fiber gas sensors; however, they have not been fully exploited yet and offer optimal possibilities for improvement. This review gives the reader a complete overview of the works focused on the utilization of LMR-based optical fiber sensors for gas sensing applications, summarizing the materials used for the development of these sensors as well as the fabrication procedures and the performance of these devices.

High-sensitivity fiber optic magnetic field sensor based on lossy mode resonance and hollow core-offset structure

An optical fiber magnetic field sensor based on lossy mode resonance (LMR) was designed. Furthermore, a hollow core-offset structure was designed to enhance the performance. Due to the destruction of the circular symmetry structure, the sensor has strong birefringence, resulting in x-polarization and y-polarization with two independent resonance valleys. The refractive index changes from 1.358 to 1.390 and a high sensitivity of 11,483.12 nm/RIU was obtained. In addition, the influence of structural parameters on the sensor was investigated. Magnetic field sensitivities of 893 pm/Gs and 754 pm/Gs were obtained theoretically. The feasibility of LMR is demonstrated for magnetic field measurements and a reference is provided for an optical fiber magnetic field.

Fiber Optic Sensing With Lossy Mode Resonances: Applications and Perspectives

This review focuses on the recent advances in lossy more resonance (LMR) fiber optic sensors. LMR sensors present many interesting features also in comparison with surface plasmon resonance (SPR), the most widespread resonance-based sensing platform. Two key parameters determine the performance of LMR sensors: geometrical configuration and material supporting the LMR. After reviewing those aspects and some fundamentals of the theory, the review focuses on the sensing mechanisms, mainly based on refractometry, and their possible applications. Many examples from the literature are reported ranging from electric field to pressure sensors and from gas detection to biosensors. Such vibrant activity on LMR sensors confirms the potentiality of this technology making it a very promising platform for sensor development.

A near lossless three-dimensional medical image compression technique using 3D-discrete wavelet transform

In the field of medical image processing, there are several imaging modalities that emerged and produced high quality of images that imposes to greater amount of storage space as well as bandwidth for transmission. Therefore, there is always a great need to develop compression techniques on such images. Moreover, they produce three-dimensional images by sequence of 2D slices and process each as like 2D image. Therefore, it is essential that every medical image processing operation needs to converge on 3D space (three-dimensional image). In this paper, we provide the wavelet-based image compression technique that can be directly applied on the 3D images itself. We apply 3D DWT on a 3D volume and the resultant coefficients are taken to further compression process (like thresholding, entropy encoding). The inverse processes are performed for decompression to reconstruct the images. The effects of the results based on different wavelets are assessed and the results of lossy mode are compared in terms to lossless mode.

Refractive index and salinity sensors by gallium-doped zinc oxide thin film coated on side-polished fibers

This work presents a high-sensitivity refractive index and salinity sensor by using fiber-optic side-polishing and electron-beam evaporation techniques. Thin film coated on the flat surface of side-polished fibers can generate a lossy mode resonance (LMR) effect. A gallium-doped zinc oxide (GZO) thin film was prepared by an electron-beam evaporation with the ion assisted deposition method. The residual thickness of the side-polished fiber was 76.5 μm, and GZO film thickness of 69 nm was deposited on the flat surface of the side-polished fiber to fabricate LMR-based fiber sensors. The variation in the optical spectrum of LMR-based fiber sensors was measured by different refractive index saline solutions. The LMR wavelength shift is caused by the refractive index change, which is nearly proportional to the salinity. The corresponding sensitivity of the proposed fiber-optic sensor was 3059 nm/RIU (refractive index unit) for the refractive index range of 1.333 to 1.398. To evaluate the sensitivity of LMR salinity sensors, the saline solution salinities of 3.6%, 7.3%, 10.9%, 14.6%, 18.2% and 21.9% were measured in this work. The experimental result shows that the sensitivity of the proposed salinity sensor is 9.94 nm/%.

A near lossless three-dimensional medical image compression technique using 3D-discrete wavelet transform

In the field of medical image processing, there are several imaging modalities that emerged and produced high quality of images that imposes to greater amount of storage space as well as bandwidth for transmission. Therefore, there is always a great need to develop compression techniques on such images. Moreover, they produce three-dimensional images by sequence of 2D slices and process each as like 2D image. Therefore, it is essential that every medical image processing operation needs to converge on 3D space (three-dimensional image). In this paper, we provide the wavelet-based image compression technique that can be directly applied on the 3D images itself. We apply 3D DWT on a 3D volume and the resultant coefficients are taken to further compression process (like thresholding, entropy encoding). The inverse processes are performed for decompression to reconstruct the images. The effects of the results based on different wavelets are assessed and the results of lossy mode are compared in terms to lossless mode.

Lossy mode resonance sensor assisted by dual long-period fiber gratings with core-mode blocker

A novel sensor configuration consisting of TiO2 film and dual long-period fiber gratings (LPFG) with an in-between core-mode blocker (CMB) is proposed and numerically investigated. TiO2 film is on the cladding surface of separation fiber between two identical LPFGs and lossy mode resonance (LMR) is induced by a single cladding mode which is coupled from core mode by the first grating. Afterwards, the cladding mode influenced by LMR is recoupled into core mode by the second grating. As a result, the output spectrum is characterized as a dip in the top of a bandpass spectrum curve. The central wavelength of this dip is sensitive to surrounding refractive index and the numerical analysis reveals that the sensitivity reaches 5075 nm/RIU with excellent linearity. In this configuration, the bandwidth of attenuation dip is reduced in a great manner since LMR is induced by a single cladding mode. Moreover, this sensor configuration synthesizes the advantages of both LMR and LPFG, which offers additional degrees of freedom in the sensor design.

Effect of high index buffer layer in PbSe clad waveguide to design a visible range polarizer

Polarization properties of PbSe clad optical waveguide are exploited theoretically, in the visible range at λ = 0.6328 μm. Due to semiconducting nature, lead selenide (PbSe) supports lossy modes and showed oscillatory behavior in generated attenuation curves. It is observed that at different PbSe thicknesses, TM or TE guided modes may be selectively attenuated. High attenuation in waveguide modes mainly occurred due to the phase matching between lossy modes supported by PbSe cladding and lossless waveguide modes. It is proposed that by placing a high index buffer layer between PbSe cladding and waveguide, phase matching can be improved further. This property can be utilized to design highly efficient polarizers. Significant results are presented to show the effect of different buffer indices (1.55, 1.88 and 2.67). At the buffer index value 1.88, TE and TM pass polarizers can be designed with extinction ratios 501 dB and 316 dB respectively. Also, an extensively high attenuation loss of 243299 dBcm-1 can be achieved with buffer index 2.67 for TM mode polarization. Obtained results are well supported by generated field plots for the proposed polarizing structures.

Lossy Mode Resonance Sensors Based on Double ITO/TiO2 and Triple TiO2/ITO/TiO2 Thin Film Coated Single Mode Fiber Taper

Based on the previously developed computer program for rigorous calculation of modes in optical fibers containing layers of various materials of arbitrary, including nanometer, thickness, the calculation and optimization of single-mode double adiabatic tapers covered with one, two and three-layer films: ITO, ITO/TiO2, TiO2/ITO/TiO2 of equal thickness is performed, with the aim of their application as the environment refractive index sensors. It is shown that in the range of wavelengths 1.00–1.6 µm, two, and in particular, three-layer coatings not only can increase the sensitivity, but also significantly reduce the width of the lossy mode resonance (LMR), which, in turn, leads to a significant increase in the figure of merit (FOM) of the sensor, defined as the sensitivity/width of the LMR.

Lossy mode resonance-based highly sensitive fiber optic refractive index sensor using the bilayer of FTO/HfO2 for operation in the visible region

A lossy mode resonance (LMR) based fiber optic refractive index (RI) sensor utilizing a layer of fluorine-doped tin oxide (FTO) over the unclad core of the fiber is theoretically analyzed. To enhance its sensitivity, the thickness of the FTO layer is optimized. For further sensitivity enhancement, an over-layer of two different materials, T i O 2 and H f O 2 , is used. The sensitivity of F T O / T i O 2 and F T O / H f O 2 bilayer based LMR sensors increases with the increase in the thickness of the over-layer for a fixed thickness of the bilayer. Further, the sensitivity of the sensor utilizing the F T O / H f O 2 bilayer is found to be more than the sensitivity of the F T O / T i O 2 bilayer sensor. To keep the operating spectral range of the sensor in the visible region, the total thickness of the bilayer is adjusted. It is found that a total bilayer thickness of 30 nm with 90% thickness of H f O 2 gives the maximum sensitivity of 4400 nm/RIU for 1.33 RI of the sensing medium, which is more than three times the sensitivity of the FTO coated LMR sensor. The sensitivity of the proposed LMR sensor utilizing the F T O / H f O 2 bilayer is compared with the other LMR sensors reported in the literature, and it is found that the proposed sensor possesses the highest sensitivity. The other advantage of the proposed sensor is that it works in the visible region, which reduces the cost of the sensor.

High Figure of Merit in Lossy Mode Resonance Sensors with PtSe2 Thin Film

Lossy mode resonance (LMR) sensors not only support transverse magnetic mode (TM) but also respond to transverse electric (TE) polarization, which has the advantage over traditional surface plasmon resonance sensing supporting only a single TM polarization. We theoretically propose an LMR sensor that can detect the refractive index (RI) changes based on the Kretschmann configuration with PtSe2 material. The refractive index parameter of PtSe2 film is fitted through experimental measurements, and the performance of LMR sensor with PtSe2 is theoretically calculated. The figure of merit (FOM) of the sensor performance has been significantly improved, and the maximum FOM with 626 RIU−1 has been acquired.

Collective Dissipative Molecule Formation in a Cavity.

We propose a mechanism to realize high-yield molecular formation from ultracold atoms. Atom pairs are continuously excited by a laser, and a collective decay into the molecular ground state is induced by a coupling to a lossy cavity mode. Using a combination of analytical and numerical techniques, we demonstrate that the molecular yield can be improved by simply increasing the number of atoms, and can overcome efficiencies of state-of-the-art association schemes. We discuss realistic experimental setups for diatomic polar and nonpolar molecules, opening up collective light matter interactions as a tool for quantum state engineering, enhanced molecule formation, collective dynamics, and cavity mediated chemistry.