Planar Polymer Waveguides Research Articles

Polymer Waveguide Sensor Based on Evanescent Bragg Grating for Lab-on-a-Chip Applications.

In this work, an evanescent Bragg grating sensor inscribed in a few-mode planar polymer waveguide was integrated into microchannel structures and characterized by various chemical applications. The planar waveguide and the microchannels consisted of epoxide-based polymers. The Bragg grating structure was postprocessed by using point-by-point direct inscription technology. By monitoring the central wavelength shift of the reflected Bragg signal, the sensor showed a temperature sensitivity of -47.75 pm/K. Moreover, the functionality of the evanescent field-based measurements is demonstrated with two application examples: the refractive index sensing of different aqueous solutions and gas-phase hydrogen concentration detection. For the latter application, the sensor was additionally coated with a functional layer based on palladium nanoparticles. During the refractive index sensing measurement, the sensor achieved a sensitivity of 6.5 nm/RIU from air to 99.9% pure isopropyl alcohol. For the gas-phase hydrogen detection, the coated sensor achieved a reproducible concentration detection up to 4 vol% hydrogen. According to the reported experimental results, the integrated Bragg-grating-based waveguide sensor demonstrates high potential for applications based on the lab-on-a-chip concept.

Label-free long-range detection of prostate cancer biomarkers based on surface-enhanced Raman scattering

In the field of prostate cancer based on surface-enhanced Raman scattering (SERS), the repeatability of detection is crucial for its practical application in clinical medicine. We propose to use a new SERS substrate based on a polymer planar waveguide in combination with microfluidic technology and utilized in the label-free detection of prostate-specific antigen (PSA) in serum. The experimental results show that the detection limit of the substrate for PSA sample solution is as low as 10 pg ml−1. Additionally, the optimal transmission length for PSA is determined to be 9 mm. Further examinations encompass repetitive testing of serum samples spiked with PSA at a concentration of 4 ng ml−1, revealing a relative standard deviation (RSD) of 5.01%. This outcome is compared with single-point detection, manifesting a notable enhancement of 9.81% in terms of RSD, signifying a marked improvement in repeatability. Notably, our method not only capitalizes on the long-range averaging effect to enhance the repeatability of Raman signals, but also circumvents sample damage resulting from direct laser irradiation.

Mach–Zehnder interferometric analysis of planar polymer waveguide having an adlayer of WS2 for biosensing applications

Abstract To enhance the sensing performance of a four-layer planar polymer optical waveguide, an adlayer of tungsten disulfide material is introduced. Also, the proposed waveguide is used to demonstrate theoretically the detection of uric acid concentration in blood or urine. The heterostructure of two-dimensional WS2 offers excellent dry lubricity with respect to any other 2D substance, such as graphite or molybdenum disulfide. The proposed waveguide is analyzed using the common path Mach–Zehnder interferometric method. The dispersion characteristic i.e., the effective refractive indices and thickness of proposed waveguide is plotted for a particular wavelength range to optimize the thickness of film layer. The difference in propagation constant and output interference signal for changing the cover medium is calculated. Using the output interference signal, the phase sensitivity 213 degree/RIU is obtained in the proposed waveguide. The maximum obtained sensitivity, limit of detection and limit of quantification for uric acid concentration in the proposed waveguide structure is 6.86 × 10−2 degree mM−1, 0.061 mM and 0.203 mM, respectively.

Experimental detection of chlorpyrifos by MoS2 coated planar polymer waveguide sensor utilizing common path interferometric principle

A common path Mach-Zehnder interferometer is fabricated using a planer polymer waveguide having MoS2 as an adlayer for chlorpyrifos detection. The dispersion characteristic and cutoff condition of proposed waveguide are obtained theoretically and hence the cutoff film thickness is optimized to get TE0 and TM0 propagating modes. Variations between the phase shift of propagating modes with the concentration of pure chlorpyrifos and its commercial sample are obtained. A good linear variation between phase shift and concentration of chlorpyrifos is obtained in our fabricated waveguide for all considered temperatures. The obtained maximum sensitivity, minimum limit of detection, and limit of quantification of chlorpyrifos are 5.66 degree/μM, 1.57 μM, and 5.24 μM respectively, at 45° C. The capability of the fabricated sensor to generate distinct response for a pure and commercial sample of chlorpyrifos at different concentration and temperature were confirmed by principal component analysis. Since the response of sensor is better for commercial samples at a lower temperature, therefore it is recommended that the concentration of chlorpyrifos in commercial samples should be measured at low temperatures.

Combined thermomechanical and optical simulations of planar-optical polymer waveguides

In this work, we describe a theoretical approach for combined thermal, mechanical and optical simulation and analysis of planar polymer waveguides. We consider a finite element approach for thermal and stress/deformation simulation. Also, a Crank-Nicholson finite difference beam propagation method (CN-BPM) is implemented to perform the optical simulation. The results of the finite element (thermo-mechanical) analysis are coupled with the CN-BPM results to carry out the optical simulation of poly(methyl methacrylate) (PMMA) waveguides as function of temperature. For thermal simulation, a model was designed where a polysilicon microheater was added to the upper cladding of the PMMA waveguides to vary the temperature between 20 °C and 200 °C. Thus, the impact of the induced temperature gradients on the refractive index modulation of the PMMA waveguides and the corresponding change in numerical aperture are obtained. In addition, the temperature gradients influence the beam intensity profiles and the movement of the primary eyes within the optical waveguides, thus, impacting the optical properties. Furthermore, the thermally induced mechanical stress and deformation were calculated for transverse and axial directions. In the next step, validation of the model by systematic experimental studies will be performed. In general, our approach provides a toolbox for more comprehensive multi-physics theoretical analysis of polymer-optical waveguides which, in future, can be extended to more complex and functional structures as required for flexible sensor networks, as example.

Multi-Channel Single-Mode Polymer Waveguide Fabricated Using the Mosquito Method

We experimentally demonstrate that the Mosquito method is capable of fabricating polymer optical waveguides with single-mode cores. The Mosquito method we developed is a technique to form planar polymer waveguides using a commercially available microdispenser. In this article, the flow of the core monomer dispensed from the tip of the needle is simulated using fluid analysis software. The results show that the shape of the needle periphery significantly affects the fabrication of perfectly circular cross-sectional cores. In addition, we demonstrate that the Mosquito method is capable of reducing the MFD variation to 0.4 μm. We find such a small MFD fluctuation is comparable to that of typical single-mode optical fibers.

Refractive Index Sensor Based on Metal-Clad Planar Polymer Waveguide Operating at 850 nm

A metal-clad planar polymer waveguide refractive index sensor based on epoxy (EPO) polymer materials by using light intensity interrogation at 850 nm is designed. The polymethyl methacrylate (PMMA) material is deployed as the low refractive index (RI) buffer layer in order to better couple the optical guided mode and the surface plasmon polaritons (SPP) mode for working in water environment. The effects of the gold film thickness, PMMA buffer layer thickness, waveguide layer thickness, waveguide width, and gold length on the sensor sensing characteristics have been comprehensively studied. Simulation results demonstrate that the normalized transmission increases quasi-linearly with the increment of RI of the analyte from 1.33 to 1.46. The sensitivity is 491.5 dB/RIU, corresponding to a high RI resolution of 2.6×10−9 RIU. The designed SPP-based optical waveguide sensor is low-cost, wide-range, and high-precision, and has a broad application prospect in biochemical sensing with merits of miniaturization, flexibility, and multiplexing.

Epoxy polymer optical waveguide for micro-opto-electro-mechanical systems

The paper reports on the fabrication and characterisation of E3135 epoxy polymer planar waveguides fabricated onto allyl diglycol carbonate substrate. We measured transmission spectra from the visible to near-infrared region and studied waveguiding properties by the m-line spectroscopy using six lasers (532.0, 654.2, 846.4, 1308.2, 1549.1 and 1652.1 nm). Optical scattering losses of the planar waveguides were measured by the fibre scanning method. The lowest values of the optical losses were 0.33 dB/cm at 632.8 nm and 0.35 dB/cm at 850 nm. Our research showed that the epoxy polymer E3135 is a promising material for the implementation into the MOEMS structures with higher integration density, thus it allows for realisation low-cost and feasibly elaborated MOEMS components.

Estimation of cover sensitivity of a planar polymer waveguide through double path broadband difference interferometeric analysis

Broadband difference interferometeric analysis of a double path planar polymer optical waveguide is presented for bio-sensing applications. Mathematical formulation of intensity of output signal is obtained using interferometeric analysis. Further, the dispersion equation is obtained by matching the field at core cladding interface that gives the cutoff film thickness for TE0 and TM0 modes in considered spectral range. The waveguide is analyzed by propagating either same polarized (TETE or TMTM) modes or unlike polarized (TETM) modes in the reference arm and sensing arm. It is observed that difference of propagation constant for same polarized mode increases with increase of wavelength while for unlike polarized modes it first increases up to a maximum value and then decreases in the considered wavelength range. The maxima of output interference signal shifted prominently with the cover refractive index for the wavelength range near the maximum value of propagation constant difference. The obtained sensitivity 9.226 for unlike polarized modes in arms is much larger than the sensitivity 0.071 of same polarized modes in arms.

Synthesis and Characterization of a Novel Erbium Doped Poly(vinyl alcohol) Films for Multifunctional Optical Materials

Polymer films based on poly vinyl alcohol (PVA) doped with different contents (0, 4, 8, 16, 20 and 28) wt% of Erbium(III) ions were synthesized by the simple solution casting technique. The structural characteristics of the films were studied by X-ray diffraction pattern (XRD), Fourier transform infrared (FT-IR) spectroscopy and atomic force microscopy measurements (AFM) measurement whereas the optical behavior of these films have been investigated using UV–Vis-NIR spectroscopy and photoluminescence measurements. The structural parameters of the interplanar (d) spacing, crystallite length (L) and the average interchain separation determined from the XRD and the absorption bands of the active IR groups recorded in FT-IR spectra indicate bonding of positively charged Er3+ ions with negatively charged OH groups of the PVA chains. The average cluster size (D) of the samples estimated from AFM data shows larger values than that obtained from XRD measurements. The optical gaps obtained from absorption spectra fitting and Tauch relations are approximately equal and slightly decreased by Er3+ ions incorporation in the PVA matrix whereas the high frequency refractive indices estimated according to Moss and Dimitrov formulae showing small increase. Three intense peaks of 607 nm, 733 nm and 783 nm wavelengths due to energy levels transitions of erbium were recorded in the photoluminescence spectra PVA–Er3+. The collected data support consideration of PVA–Er3+ films as a promising optical polymer material in microptics, planar polymer waveguides, polymer optical fiber and polymer light emitting diodes applications.

Structural and optical characterization of [(PVA:PVP)-Cu2+] composite films for promising semiconducting polymer devices

High quality semiconducting polymers of copper ions doped poly(vinyl alcohol) (PVA):poly(vinyl pyrrolidone) (50:50 wt%) [(PVA:PVP)-x wt % Cu2+] [x = 0,3,5,15 and 20 wt%] composite films were successfully prepared by the conventional solution casting method. The characterizations of the films were investigated by XRD scan, FT-IR and UV–Vis–NIR spectroscopic analysis. The obtained values of the d-spacing and crystallite length D parameters from Gaussian fitting of the broad XRD peaks of the virgin PVA, [(PVA:PVP)-x wt % Cu2+] polymer composite blend films indicate the miscibility and compatibility of the blend constituents and bonding of positively charged Cu2+ ions with negatively charged OH groups of the polymer chains. The optical energy gaps and the high frequency refractive indices are strongly affected by incorporation of Cu2+ ions in the (PVA:PVP) blend chains where the optical gap decreased from 4.68 eV for pure (PVA:PVP) polymer blend to 2.95 eV for [(PVA:PVP)-20 wt % Cu2+] and the high frequency refractive index increased from 2.42 to 2.78. Based on the collected results, the copper ions doped (PVA:PVP) polymer blend composite films can be considered as a promising, new and facile material for UV filters, semiconducting polymer devices, planar polymer waveguides and polymer solar cells designing.

High-temperature stable and sterilizable waveguide Bragg grating in planar cyclo-olefin copolymer

In this Letter, we demonstrate a high-temperature stable polymer planar waveguide Bragg grating based on cyclo-olefin copolymers. The high glass transition temperature of the polymer material amounting to 178°C, in conjunction with a high-temperature stable UV-curable adhesive used to connect the polymer sensor to a standard single-mode fiber, enables temperature readings of up to 160°C while exhibiting a temperature sensitivity of -7.3 pm/°C. The reflected power of the Bragg wavelength remains constant up to a temperature of 130°C before declining at higher temperatures with an overall reduction of 2.5dB at 160°C. However, decreasing temperature results in a complete recovery of the peak power, facilitating steam pressure sterilization (129°C, 0.17MPa) of the polymer planar waveguide Bragg grating.

Planar polymer waveguides with a graded-index profile resulting from intermixing of methacrylates in closed microchannels

Graded-index waveguides are known to exhibit lower losses and considerably larger bandwidths compared to step-index waveguides. The present work reports on a new concept for realizing such waveguides on a planar substrate by capillary filling microchannels (cladding) with monomer solution (core). A graded-index profile is obtained by intermixing between the core and cladding material at the microchannel interface. To this end, various ratios of methyl methacrylate (MMA) and octafluoropentyl methacrylate (OFPMA) were evaluated as starting monomers and the results showed that the polymers P50:50 (50:50 MMA:OFPMA) and P0:100 (100% OFPMA) were suitable to be applied as waveguide core and cladding material respectively. Light guiding in the resulting P50:50/P0:100 waveguides was demonstrated and the refractive-index profile was quantified and compared with that of conventional step-index waveguides. The results for both cases were clearly different and a gradual refractive index transition between the core and cladding was found for the newly developed waveguides. Although the concept has been demonstrated in a research environment, it also has potential for upscaling by employing drop-on-demand dispensing of polymer waveguide material in pre-patterned microchannels, for example in a roll-to-roll environment.

TiO2 surface functionalization of COC based planar waveguide Bragg gratings for refractive index sensing

We demonstrate the applicability of a planar waveguide Bragg grating in cyclo-olefin copolymer (COC) for refractive index sensing. The polymer planar waveguide Bragg grating fabricated using a single writing step technique is coated with a high-index layer of titanium dioxide (TiO2) leading to a distinct birefringence. This in turn results in the splitting of the Bragg reflection into two distinct Bragg wavelengths, which strongly differ regarding their refractive index sensitivities. Where one wavelength is only slightly affected by the ambient refractive index, the second Bragg peak shows a strong sensitivity. Furthermore, we investigate the temperature behaviour of the functionalized sensor and discuss it with respect to applications in refractive index sensing.

Competitive Evaluation of Planar Embedded Glass and Polymer Waveguides in Data Center Environments

Optical printed circuit board (OPCB) waveguide materials and fabrication methods have advanced considerably over the past 15 years, giving rise to two classes of embedded planar graded index waveguide based on polymer and glass. We consider the performance of these two emerging waveguide classes in view of the anticipated deployment in data center environments of optical transceivers based on directly modulated multimode short wavelength VCSELs against those based on longer wavelength single-mode photonic integrated circuits. We describe the fabrication of graded index polymer waveguides, using the Mosquito and photo-addressing methods, and graded index glass waveguides, using ion diffusion on thin glass foils. A comparative characterization was carried out on the waveguide classes to show a clear reciprocal dependence of the performance of different waveguide classes on wavelength. Furthermore, the different waveguide types were connected into an optically disaggregated data switch and storage system to evaluate and validate their suitability for deployment in future data center environments.

Fabrication of a metal clad planar polymer waveguide based sensor for detection of low-refractive-index-contrast of liquid

A four layer polymer film based planar waveguide having a metallic clad is fabricated and analysed. The fabricated waveguide is validated for detection of small variation in the refractive index of aqueous media solution. It is observed that with increase of refractive index of aqueous media solution, the mode coupling angle of incident light increases. As the thickness of polymer film is increased from 810nm to 1650nm, this mode coupling angle is shifted toward higher angle of incidence. The angular interrogation of our fabricated waveguide shows that the maximum obtained sensitivity is 30deg/RIU for 810nm polymer film waveguide. Also, our analysis shows that the obtained experimental results are in good agreement with theoretical results.

Efficient Optical Amplification in a Sandwich-Type Active-Passive Polymer Waveguide Containing Perylenediimides

Polymer waveguides doped with luminescent materials serve as a suitable flexible platform for active elements (lasers and amplifiers) in on-chip optical circuits. However, at present, the best parameters (lowest thresholds) achieved with these devices are obtained with the use of the stripe excitation technique in the framework of which external illumination of an active material along the whole length of the waveguide is realized that is not convenient for the waveguide on-chip integration and requires high peak energies due to the large excitation area. In the present work, an elegant method is proposed to overcome this obstacle and provide efficient active material pumping along the whole waveguide length with use of on-chip integration compatible edge-type excitation light injection. This novel type of planar active-passive polymer waveguides includes a thin (50–100 nm) active layer of poly(methyl methacrylate) (PMMA), which is heavily doped with highly luminescent perylenediimide (PDI) molecules, san...

Properties of the Optical Planar Polymer Waveguides Deposited on Printed Circuit Boards

Properties of the Optical Planar Polymer Waveguides Deposited on Printed Circuit Boards

Fabrication and characterization of planar Bragg gratings in TOPAS polymer substrates

We report on the fabrication of polymer planar waveguides with inscribed Bragg gratings in TOPAS employing an efficient UV based single writing step technique using excimer laser. Phase shifting Mach–Zehnder interferometry indicates an UV induced increase of the refractive index in TOPAS of 6×10−4 and a modification depth of about 30μm, respectively. The planar Bragg grating structures in the cyclo-olefin copolymer are characterized by a high reflectivity of about 93% and are studied with respect to their potential in optical waveguide sensing, namely temperature and strain sensing. While the Bragg reflection shows almost no cross sensitivity against humidity, it exhibits a spectral blue shift with increasing temperature of −6.5pm/°C after multiple thermal annealing cycles. Compressive and tensile strain measurements reveal a sensitivity of 0.70pm/μɛ.

Response characterization of a fiber optic sensor array with dye-coated planar waveguide for detection of volatile organic compounds.

We have developed a multi-array side-polished optical-fiber gas sensor for the detection of volatile organic compound (VOC) gases. The side-polished optical-fiber coupled with a polymer planar waveguide (PWG) provides high sensitivity to alterations in refractive index. The PWG was fabricated by coating a solvatochromic dye with poly(vinylpyrrolidone). To confirm the effectiveness of the sensor, five different sensing membranes were fabricated by coating the side-polished optical-fiber using the solvatochromic dyes Reinhardt's dye, Nile red, 4-aminophthalimide, 4-amino-N-methylphthalimide, and 4-(dimethylamino)cinnamaldehyde, which have different polarities that cause changes in the effective refractive index of the sensing membrane owing to evanescent field coupling. The fabricated gas detection system was tested with five types of VOC gases, namely acetic acid, benzene, dimethylamine, ethanol, and toluene at concentrations of 1, 2,…,10 ppb. Second-regression and principal component analyses showed that the response properties of the proposed VOC gas sensor were linearly shifted bathochromically, and each gas showed different response characteristics.