In the last couple of decades huge effort has been put into development of photonics platforms based on various materials such as Si, Si3N4, InP, LiNbO3, GaAs and others. Only few of them (Si, Si3N4, InP) have turned into eco-systems resembling semiconductors industry of design house, foundries, fabless companies and multi project wafer (MPW) services of photonics integrated circuits (PICs). While various photonic platforms have matured to industrial level, they still have numerous challenges including limits set by material properties, expensive fabrication and complicated hybrid integration.
Polymer materials provide numerous advantages over semiconductor and oxide/nitride platforms: combination of passive and active elements, simple fabrication techniques, Integration of other elements for hybrid platform, wide wavelength range and multilayer structure.
We will present the results of developed polymer photonic platform with active and passive elements based on SU-8 and polymethylmethacrylate photoresist.
In recent years whispering gallery mode (WGM) resonators have attracted interest due to their various potential passive (filters, resonators, sensors) and active (lasers, four-wave mixing) applications. By choosing an appropriate material with very low absorption, and fabricating a very smooth surface, WGM resonators can reach ultra-high quality (Q) factors. Additionally, the surface of the WGM resonator can be functionalized with nanoparticles or nanomaterial layers, which can enhance optical properties. Recently, we have been interested in the functionalization of the WGM resonator surface for active applications. WGM resonators are suitable for nonlinear optical interactions due to their ultra-high Q factors, significantly lowering necessary pumping power. WGM resonators can be used to generate optical frequency combs (OFCs), which have many applications in optical clocks, spectroscopy, and communications. After coating WGM resonator with quantum dots, besides the OFC generation, we have observed the third harmonic generation. Functionalization with erbium ions leads to the observation of lasing.
We demonstrate an integrated on-chip whispering gallery mode (WGM) ring resonator tested for humidity sensing. When developed, SU-8 is chemically and mechanically stable, as well as optically transparent above 400 nm wavelength and it has a high refractive index. Therefore, it is a suitable material for optical WGM resonators. When light is coupled in the resonator, it circulates along the surface for prolonged periods of time interacting with the surrounding environment. Resonance wavelength depends on the refractive index and/or the radius of the resonator. Polymers, including SU-8, are sensitive to gas and temperature changes in the environment. We tested the ring resonators in changing relative humidity (RH). Due to changes in RH, the refractive index of SU-8 changes, and we observed a shift in the resonance wavelength. While the sensitivity was average compared to similar studies using other materials or geometries, the ring geometry showed excellent response and recovery times. This property is important in many areas, such as industrial production and environmental monitoring.
We have created a highly sensitive humidity sensor that is based on glycerol droplet. Glycerol is hygroscopic and has a specific glycerol-water ratio for every relative humidity (RH) %. It is cheap and environmentally friendly. We use the droplet as a whispering gallery mode (WGM) microresonator. WGMs are known for their high Q factors, which lead to high sensitivity and precision. As RH changes, the resonant wavelength shifts due to a change in the droplet’s radius and refractive index. We have successfully created an experimental set-up and original data analysis method that allow us to follow the resonant wavelength shift in real-time. Results show that the sensor has an average sensitivity of 2.85 nm/% RH in the 50–70 % RH range, it is stable and has a long lifetime. To further investigate the properties of the glycerol droplet sensor, we tested its selectivity and tried two coupling methods (free-space and tapered fiber). We decided to test the sensor’s response to two different gases – ethanol and acetone. Results show that glycerol is highly selective and does not absorb ethanol/acetone molecules, meaning that it can be used for trustworthy humidity measurements.
The whispering gallery modes (WGM) micro resonators are based on elliptical objects, which can be made from optically transparent materials, The geometry of the object enables optical wave circulating inside the ellipse using total internal reflection. If there is a monochromatic light source with constant intensity to the ellipse, constructive interference may be observed. Poly methyl methacrylate acrylic (PMMA) WGM micro resonators are commercially available with typical optical quality factor of 103-104. These could limit problems with WGM micro resonator expensive manufacturing. Thanks to advances in high resolution image processing, read-outs using spectroscopy (single photo detector) could be replaced with image processing. Image processing (4.5μm/px) allows to split elliptical WGM micro resonator in regions and analyze separate sectors of the ellipse, which can used as a representation of surface irregularity interaction with higher order special mode groups. In the present work new type of image processing for micro-resonators were developed, to analyze intensity distribution in separate regions for the PMMA WGM micro-resonators (40-70 μm). Resonators were coupled using a tapered fiber and fixed wavelength VCSEL laser (760nm). Temperature was change from 20-80 0C which affected the PMMA refractive index (α), for 760nm dn/dT = -1.32 10-4 (0C-1) and thermal expansion (β) dR/dT = 2.60 10-4(0C-1). Combining the following physical changes, total changes (α+ β), WGM PMMA micro-resonator mode mapping was obtained. The following work offers new type of intensity processing methods for measuring applications using PMMA WGM micro resonators.
Whispering gallery mode resonators (WGMRs) are small axial symmetrical structures from transparent material, that can exceptionally well confine light within, thus making them ideal for studying light-matter interactions and using them as sensors. Various WGMR designs can be simulated using COMSOL Multiphysics. Sometimes an extra layer is coated on the surface of the resonator for achieving desirable effects. The extra layer changes quality factor of the resonator and ads extra modes for some frequencies. Different methods and studies are used for the exploration of this topic such as changing the thickness of the coating and using random functions to describe the roughness of the surface, which in micro and nanoscale makes a difference.
Optical frequency combs (OFC) using different kinds of whispering-gallery-mode (WGM) microresonators have already shown different applications and especially their applications in fiber optical communication systems as replacements of laser-arrays. For this application the free spectral range (FSR) of 200 GHz or less is desirable. Besides the fabrication material for microspheres, the resonator radius can be modified to change the FSR. In this paper use of silica microspheres for OFC represents an inexpensive alternative over the other microcombs: microring, microdisk, and microtoroid. We experimentally present a microsphere fabrication process from a different kind of silica (SiO2) fibers by use of the hydrogen-oxygen melting technique. We experimentally review the OFC generation process the main microresonator parameters as FSR, Q-factor and evaluate the resulting WGM resonator generated OFC comb light source for further applications. An OFC was excited inside a 166 μm silica microsphere WGM resonators using a 1548 nm laser light. The obtained broadband OFC spanned from 1400-1700 nm with FSR of (397 ± 10) GHz.
Whispering gallery mode resonators (WGMRs) are very interesting for sensing because a resonance shift could be caused by any perturbation of the surrounding environment. Additionally such a resonator is coated with nanomaterials to tailor and enhance the sensitivity for a specific purpose. WGMR were fabricated using standard telecommunication fiber and a hydrogen flame, characterized using the scan method to obtain the quality factors and then coated with gold nanoparticles (Au NPs) using dip coating method and characterized again for comparison. Au NPs were chosen because their positive impact on microresonator sensitivity has been mentioned before and the surface can later be functionalized. The deposited layer was investigated and new properties no over-coupling due to Van der Waals forces and suppression of higher order modes were observed after coating the resonator. To observe the localized surface plasmon resonance a glucose sensor test was performed using the WGMRs coated with Au NPs and glucose oxidase. Comparing the results with control measurements, the resonance shifted more for samples with Au NPs.
Whispering Gallery Mode (WGM) resonators are very sensitive to nanoparticles attaching to the surface. We simulate this process using COMSOL Wave Optics module. Our spherical WGM resonators are produced by melting a tip of an optical fiber and we measure optical Q factors in the 105 range. Molecular oxygen lines of the air in the 760 nm region are used as reference markers when looking for the shifts of the WGM resonance lines. We demonstrate WGM microresonator surface coating with a layer of ZnO nanorods as well as with polystyrene microspheres. Coatings produce increased contact surface. Additional layer of antigens/antibodies will be coated to make high-specificity biosensors.
In this paper we report first results from the developed cavity ring-down spectrometer for application in human breath analysis for the diagnostics of diabetes and later for early detection of lung cancer. Our cavity ring-down spectrometer works in UV region with pulsed Nd:YAG laser at 266 nm wavelength. First experiments allow us to determine acetone and benzene at the level bellow ppm. In our experiment, first results from breath samples from volunteers after doing different activities were collected and examined. Influence of the smoking on the breath signals also was examined.
In this paper we report the current stage of the development of a cavity ring-down spectrometer (CRDS) system using exhaled human breath analysis for the diagnostics of different diseases like diabetes and later lung cancer. The portable CRDS system is made in ultraviolet spectral region using Nd:Yag laser 266 nm pulsed light. Calibration of the CRDS system was performed using generated samples by KinTek automated permeation tube system and self-prepared mixtures with known concentration of benzene and acetone in air. First experiments showed that the limits of detection for benzene and acetone are several tens of ppb.
In this paper we show our first results of research for creation a detector for benzene vapor and possibly other volatile organic compounds detection in air based on Zeeman atomic absorption technique. First the detailed study of benzene absorption spectra with high resolution spectrometer Jobin-Yvon 1000M was done. The absorption spectra of benzene were registered in the spectral range from 200-900 nm. More detailed analysis was done for the 240 – 260 nm spectral range to test a possibility to detect benzene by means of emission line of 254 nm of mercury.
Christian Parthey, Arthur Matveev, Janis Alnis, Axel Beyer, Randolf Pohl, Katharina Predehl, Thomas Udem, Nikolai Kolachevsky, Michel Abgrall, Daniele Rovera, Christophe Salomon, Philippe Laurent, Theodor Hänsch
We present a measurement of the 1S-2S transition frequency in atomic hydrogen by two-photon spectroscopy
yielding f1S-2S = 2 466 061 413 187 035 (10) Hz corresponding to a fractional frequency uncertainty of 4.2×10-15.
The result presents a more than three times improvement on the previous best measurement.
We purpose a new method for 1s-2s spectroscopy of atomic hydrogen. Our method is based on a new detection
scheme, utilizing a three-photon ionization to obtain a signal correspondent to the excitation of atoms into 2s
state. We report about assembling and test of a proton detection system for this measurement. To measure a
second order Doppler shift we purpose a delayed detection scheme. Using this method we plan to reduce the
uncertainty of the absolute frequency measurement to the 10-15 domain.
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