Optical quality ZnSe films and low loss waveguides on Si substrates for mid-infrared applications

Zinc Selenide (ZnSe) is a promising mid-infrared waveguide material with high refractive index and wide transparency. Optical quality ZnSe thin films were deposited on silicon substrates by RF sputtering and thermal evaporation, and characterized and compared for material and optical properties. Evaporated films were found to be denser and smoother than sputtered films. Rib waveguides were fabricated from these films and evaporated films exhibited losses as low as 0.6 dB/cm at wavelengths between 2.5 µm and 3.7 µm. The films were also used as isolation/lower cladding layers on Si with GeTe4 as the waveguide core and propagation losses were determined in this wavelength range

Quantification of lung surfactant lipid (dipalmitoylphosphatidylcholine/sphingomyelin) ratio in binary liposomes using Raman spectroscopy

Early diagnosis of neonatal respiratory distress syndrome (nRDS) is important in reducing the mortality of preterm babies. Knowledge of the ratio of two components of lung surfactant, dipalmitoylphosphatidylcholine (DPPC), and sphingomyelin (SM) can be used as biomarkers of lung maturity and inform treatment. Raman spectroscopy is a powerful tool to analyze vibrational spectra of organic molecules which requires only limited sample preparation steps and, unlike IR spectroscopy, is not masked by water absorption. In this paper, we explore the potential of using Raman spectroscopy as a tool to estimate the ratio of DPPC and SM from aqueous vesicles of binary mixture of DPPC and SM. We demonstrate that the ratio of DPPC and SM can be estimated by estimating the ratio of intensity of CO stretch of DPPC and CC stretch of SM as well as CO stretch of DPPC and amide I of SM. Further, we employ a partial least squares regression (PLSR) model to automate the estimation and demonstrate that PLSR method can predict the DPPC and SM ratio with an R2 value of 0.968

Fabrication and characterization of high-contrast mid-infrared GeTe₄ channel waveguides

We report the fabrication and characterization of high index contrast (Δn ~ 0.9) GeTe4 channel waveguides on ZnSe substrate for evanescent-field based biosensing applications in the mid-infrared spectral region. GeTe4 films were deposited by RF sputtering and characterized for their structure, composition, transparency and dispersion. The lift-off technique was used to pattern the waveguide channels. Waveguiding between 2.5-3.7 µm and 6.4-7.5 µm was demonstrated and mode intensity profile and estimated propagation losses are given for the 3.5 µm wavelength

Er-doped KY_(1-x-y)Gd_xLu_y(WO₄)₂ surface channel waveguides

Channel waveguides on KY1-x-yGdxLuy(WO4)2 epitaxial films doped with Er3+ were obtained by ion beam milling and guided modes at wavelengths near 1.5µm confirmed single mode behaviour. Absorption and emission spectra of these waveguides agree with those of bulk crystals of the same family, showing potential for a planar waveguide laser

Broadband 2 × 2 multimode interference coupler for mid-infrared wavelengths

Versión aceptada del artículo publicado en Optics Letters (https://doi.org/10.1364/OL.439985).Beam splitters are core components of photonic integrated circuits and are often implemented with multimode interference couplers. While these devices offer high performance, their operational bandwidth is still restrictive for sensing applications in the mid-infrared wavelength range. Here we experimentally demonstrate a subwavelength-structured 2×2 multimode interference coupler with high performance in the 3.1−3.7µm range, doubling the bandwidth of a conventional device

Optical nonlinearities of tellurite glasses with ultrawide Raman bands

Many multicomponent tellurite based glass systems containing heavy metal oxides, alkaline earth oxides and P2O5 with ultrawide Raman bands promising for Raman amplifiers have been designed and fabricated. The third order nonlinear optical susceptibility (χ(3)) is one of the key parameters deciding the Raman gain coefficient and is also useful for many optical processes including optical switching. Therefore, it is very important to have an estimate of the value of χ(3) for this new category of glass compositions. χ(3) of the above mentioned tellurite based glass systems have been measured using the third harmonic generation (THG) and are discussed in this paper. The relation between linear refractive index and χ(3) is also discussed briefly. The tellurite glasses fabricated in the present study have χ(3) values as high as 225 x 10-14 esu, whereas χ(3) of silica glass is 2.8 x 10-14 esu

Wideband integrated photonics for chemical detection at surfaces

Photonic technologies are revolutionising our access to chemical and biochemical information, driven by the demand for fast, low-cost, automated chemical analysis in a multiplicity of applications from food safety, water quality, security, personal and preventative medicine and rapid point-of-care diagnostics. The scale of integration, low cost and robustness of the microfabrication approaches which have enabled the pervasiveness of consumer electronics are expected to enable widespread deployment of chemical and bioanalytical microsystems. Optical techniques have traditionally played a major role in quantitative chemical analysis and remain the mainstay of detection in “lab-on-chip” systems, but the degree of optical functionality integrated within these systems remains limited, and they have yet to benefit fully from the massive growth in optical telecommunications technologies in recent decades. Biosensor and lab-on-chip research and commercialisation have both also been hampered by the lack of integrated photonic platforms which can operate over both the near-infrared (NIR) spectral region at wavelengths from about 0.7µm to 2µm and the mid-infrared (MIR) region from about 2µm to 20µm, which would enable new opportunities for sensitive, selective, label-free biochemical analysis. Progress on optofluidic integration for a “lab-on-chip” platform and on new materials and approaches for high-sensitivity waveguide evanescent spectroscopies in the NIR and MIR will be described

Wideband amorphous materials for integrated photonic devices

Glass integrated photonics is a well-established technology which has found many applications in passive devices for telecommunications, rare-earth-doped optical amplifiers and chemical sensing, for example. Silicate glasses, limited to visible and near infrared wavelengths, have dominated this field and there is now an increasing need for integrated photonic devices operating at longer wavelengths, particularly for sensing applications. Photonic technologies are revolutionising our access to chemical and biochemical information, driven by the demand for fast, low-cost, automated chemical analysis in a multiplicity of applications from food safety, water quality, security, personal and preventative medicine and rapid point-of-care diagnostics. The scale of integration, low cost and robustness of the microfabrication approaches which have enabled the pervasiveness of consumer electronics are expected to enable widespread deployment of chemical and bioanalytical microsystems. Optical techniques have traditionally played a major role in quantitative chemical analysis and remain the mainstay of detection in “lab-on-chip” systems, but the degree of optical functionality integrated within these systems remains limited, and they have yet to benefit fully from the massive growth in photonics telecommunications technologies in recent decades. Biosensor and lab-on-chip research and commercialisation have both also been hampered by the lack of integrated photonic platforms which can operate over both the near-infrared (NIR) spectral region at wavelengths from about 0.7μm to 2μm and the mid-infrared (MIR) region from about 2μm to 18μm, which would enable new opportunities for sensitive, selective, label-free biochemical analysis. Progress on new materials and approaches for high-sensitivity waveguide evanescent spectroscopies in the NIR and MIR will be described.<br/

High contrast mid-infrared chalcogenide waveguides for biosensing applications

Mid-infrared spectral band from 2 µm - 20 µm is ideal for label-free biosensing as the fundamental vibrations of many significant biomolecules take place in this region. Mid-infrared absorption spectroscopy using FTIR has been exploited for the last few decades to provide sensing capabilities for biomedical diagnostics. However, the sensitivity and the detection limit of the sample under test can be tremendously improved by using the evanescent field based integrated planar waveguide devices. In this paper, we present the fabrication and characterization results of chalcogenide waveguides transparent in the mid-infrared region for such applications. GeTe4 waveguides on ZnSe substrates were fabricated using lift-off technique. Lift-off resist was used to create the patterns on ZnSe substrate using photolithography and GeTe4 was deposited on these patterned samples using RF sputtering. The lift-off resist was stripped off to obtain the desired channels. The waveguides were characterized in both mid wave (2.5 µm - 3.7 µm) and long wave (6.4 µm - 7.5 µm) spectral bands using optical parametric oscillator-based laser source and quantum cascade laser, respectively [1]. Fig. 1 (a) and (b) show the cross-section and top view of the infrared camera images of the output facet of a GeTe4 channel waveguide showing light guidance at lambda = 3.5 µm and lambda = 6.5 µm, respectively

Photonic Nanojet Generation Using Integrated Silicon Photonic Chip with Hemispherical Structures

Photonic nanojet (PNJ) is a tightly focused diffractionless travelling beam generated by dielectric microparticles. The location of the PNJ depends on the refractive index of the material and it usually recedes to the interior of the microparticle when the refractive index is higher than 2, making high index materials unsuitable to produce useful PNJs while high index favours narrower PNJs. Here we demonstrate a design of CMOS compatible high index on-chip photonic nanojet based on silicon. The proposed design consists of a silicon hemisphere on a silicon substrate. The PNJs generated can be tuned by changing the radius and sphericity of the hemisphere. Oblate spheroids generate PNJs further away from the refracting surface and the PNJ length exceeds 17λ when the sphericity of the spheroid is 2.25 The proposed device can have potential applications in focal plane arrays, enhanced Raman spectroscopy, and optofluidic chips