Polymer Microring Resonators Research Articles

Ultrafast ultrasound imaging by optical polymer microring resonator array and a dual optical frequency comb: a theoretical concept

Ultrafast ultrasound imaging by optical polymer microring resonator array and a dual optical frequency comb: a theoretical concept

High Q-factor Polymer Microring Resonators Realized by Versatile Damascene Soft Nanoimprinting Lithography.

High-quality-factor microring resonators are highly desirable in many applications. Fabricating a microring resonator typically requires delicate instruments to ensure a smooth side wall of waveguides and 100-nm critical feature size in the coupling region. In this work, we demonstrate a new method "damascene soft nanoimprinting lithography" that can create high-fidelity waveguide by simply backfill an imprinted cladding template with a high refractive index polymer core. This method can easily realize high Q-factor polymer microring resonators (e.g., ~5 x 105 around 770 nm wavelength) without the use of any expensive instruments and can be conducted in a normal lab environment. The high Q-factors can be attributed to the residual layer-free feature and controllable meniscus cross-section profile of the filled polymer core. Furthermore, the new method is compatible with different polymers, yields low fabrication defects, enables new functionalities, and allows flexible substrate. These benefits can broaden the applicability of the fabricated microring resonator.

Waveguide Coupled Polymer Micro-Ring Resonator in a D-Shaped Fiber

Waveguide Coupled Polymer Micro-Ring Resonator in a D-Shaped Fiber

Efficient four-wave mixing wavelength conversion in a hybrid silicon slot and polymer microring resonator.

We present a silicon slot microring resonator for efficient frequency conversion via four-wave mixing (FWM). The slot consists of a narrow silicon waveguide pair with a gap of 80 nm, which is filled with a nonlinear optical polymer. The group velocity dispersion for the microring is controlled by engineering the geometry of the slot structure. Because of the large buildup factor of the slot microring, an FWM conversion efficiency of -27.4 dB is achieved with an optical pump power of less than 1.0 mW. From the measured power dependence of FWM generation, a nonlinear refractive index coefficient of 1.31 × 10-17 m2 W-1 is obtained at a wavelength of 1562 nm. This work presents a hybrid silicon slot and polymer microring as a potential nonlinear device for applications in integrated photonic devices.

Photonic molecules stacked on multicore optical fiber for vapor sensing

We designed and fabricated photonic molecules on the tiny end facet of a multicore optical fiber. The photonic molecules are three pairs of coupled polymer micro-ring resonators, which are stacked on the fiber in three layers. The normal mode splitting of the photonic molecules is simulated and observed experimentally. It is shown that if the absorption of vapors causes both the radii and refractive index changes of the rings, the two branches of the split resonant modes show different wavelength shifts. The photonic molecules were fabricated by the two-photon lithography technology and show good sensitivity to various organic vapors.

"Optical tentacle" of suspended polymer micro-rings on a multicore fiber facet for vapor sensing.

We designed a new type of gas sensor, an optical tentacle, made of highly integrated polymer micro-ring resonators in three-dimensional space on the tiny end-facet of a multicore optical fiber. Two pairs of three polymer micro-ring resonators were hung symmetrically on both sides of three suspended micro-waveguides as the sensing units. The micro-waveguides interlace to form a three-layer nested configuration, which makes the multicore optical fiber a "tentacle" for vapors of volatile organic compounds. Both experiments and theoretical simulation confirmed that the symmetrical coupling of multiple pairs of rings with the micro-waveguide had better resonance than the single ring setup. This is because the symmetrical light modes in the waveguides couple with the rings separately. All the optical micro-components were fabricated by the two-photon lithography technology on the end facet of multicore optical fiber. The optical tentacle shows good sensitivity and reversibility. This approach can also be adopted for sensor array design on a chip. Furthermore, optical sensors that can sense vapors with multiple constituents may be achieved in the future by adding selective sensitive materials to or on the surface of the rings.

Narrow bandwidth optimization using a polymer microring resonator in a thulium–holmium fiber laser cavity

A thulium–holmium fiber (THDF) laser cavity has been demonstrated with a SU-8 polymer microring resonator (PMRR) in the cavity. The PMRR has a 500μm radius and fabricated using the lithography method, with the SU-8 polymer acting as a host material. The butt coupling method was used for the horizontal coupling of light from a ultra-high numerical aperture (UHNA) fiber to the polymer waveguide. Lasing in the cavity without the PMRR is obtained at a center wavelength of 1.910μm, 1.869μm when the PMMR is inserted into the cavity. A maximum power of -5 dBm was extracted from the laser oscillator, and the laser linewidth was measured to be ∼26.6 kHz by radio-frequency spectrum analyzer analysis. The PMRR was able to generate an output with a free spectral range of 0.79μm at a frequency of 59.25 GHz.

Tuning the performance of polymeric microring resonator with femtosecond laser

Microring resonator realized by femtosecond laser-induced two-photon photopolymerization in photoresist SU-8 and the factors influencing the performance of the microring resonator are demonstrated in this study with unique advantages of flexibility, high precision, and possible three-dimensional fabrication. By varying the laser parameters, it is possible to tune the performance of the polymeric microring resonator through the adjustment of different specifications, including the magnitudes of the radius and cross section. It is revealed that the free spectral range of the microring resonator is closely related with the parameters such as ring radius, resonance wavelength, cross section of the microring, and the polarization of the light. The ring resonator with a radius of 60μm shows a free spectral range of 3.9 nm, which linearly increases as the curvature of the ring increases. Though the value of the free spectral range does not vary for a multiple microring, the full-width half-maximum of the resonance is larger for the microring resonator consisting of multiple rings. The polarization modes of the microring resonator exhibit different resonance wavelengths due to different effective refractive indices, which opens new venues for the applications of microring resonators.

Ultrahigh Q Polymer Microring Resonators for Biosensing Applications

The capability of an ultrahigh Q polymer microring resonator as a biosensing system is systematically investigated. By optimizing the device design and fabrication process, the device operates in the slightly under-coupled regime with a record intrinsic Q factor of 8.0 × 105, which offers a high sensitivity and low detection limit. In surface mass detection, a surface mass density of 12.7 pg/mm2 of bovine serum albumin is detected due to the physical adsorption. The noise-equivalent detection limit is approximately 5.3 pg/mm2 in a wavelength-shift scheme and 55.9 fg/mm2 in an intensity-variation scheme. These results show that the best sensing performance with the on-chip polymer ring resonator system is achieved.

A large free spectral range of 74.92 GHz in comb peaks generated by SU-8 polymer micro-ring resonators: simulation and experiment

The feasibility of integrated SU-8 polymeric optical waveguides on a silicon platform was demonstrated experimentally and supported by simulation. Micro-ring resonator (MRR) configurations were designed and fabricated using SU-8 polymer. Simulation is carried out using the finite-difference time-domain method to improve the design. Both the simulation and experimental results confirm that SU-8 can be successfully used in the optical MRR. Passive MMI-coupled SU-8 single coupler and double coupler with a free spectral range of 74.92 GHz is achieved practically and corresponds with the simulation result. Moreover, other important parameters such as the full width at half maximum, Q factor and finesse are calculated from the simulation and practical results to support the feasibility of the SU-8 polymer MRR.

Femtosecond laser fabricated polymer microring resonator for sensing applications

A microring resonator realised by femtosecond laser two-photon photopolymerisation in an epoxy-based negative photoresist (SU-8) is proposed and demonstrated, which is further proved to be capable of temperature and refractive index sensing by monitoring the shift of the resonance wavelength of the interferometric pattern. The experimental results indicate refractive index sensitivity of 12.50 nm/refractive index unit (redshift) and temperature sensitivity of −9.51 × 10−2 nm/oC (blueshift), respectively.

Polymer micro-ring resonator integrated with a fiber ring laser for ultrasound detection.

Polymer micro-ring resonators fabricated by a direct laser writing technique are presented as sensors for ultrasound detection. The optical micro-ring resonator consists of a micro-ring waveguide that acts as a wavelength selective feedback mirror to an erbium-doped fiber-ring laser (FRL). The micro-ring resonator reflection spectrum determines the lasing frequencies of the FRL. Acoustic waves, which cause strain or deformation of the micro-ring resonator, lead to shifts of the resonance wavelength and thereby shifts in the FRL lasing spectrum. The spectral shifts are demodulated using an unbalanced Michelson interferometer. The experiments demonstrate that polymer micro-ring resonators integrated with a FRL can be used as adaptive high-frequency ultrasound detectors.

Novel ultrasound detector based on small slot micro-ring resonator with ultrahigh Q factor

An ultrasound detector based on a novel slot micro-ring resonator (SMRR) with ultrahigh Q factor and small size is proposed in this study. The theoretical Q factor of SMRR can be approximately 8.34×108 with bending radius of merely 12µm. The ultrahigh Q factor leads to an enhanced sensitivity that is approximately two orders of that of state-of-the-art ultrasound detector based on polymer micro-ring resonator. Moreover, the 3dB bandwidth of the ultrasound detector is approximately 540MHz, thereby leading to an ultrahigh axial resolution of 1.2µm. The proposed detector is also CMOS compatible and can be easily and extensively integrated to be maximized in photoacoustic microscopy.

Fabrication and Characterization of High-Optical-Quality-Factor Hybrid Polymer Microring Resonators Operating at Very Near Infrared Wavelengths

In this paper, we present a new fabrication method for large-area hybrid polymer microring resonators using a rib waveguide configuration with a minimum residual layer down to 40 nm by ultraviolet (UV) nanoimprint lithography. In a first step, a negative photoresist (SU8-2) patterned by photolithography on an SiO 2/silicon wafer was used as a master mold. Flexible soft molds using perfluoropolyether (PFPE)-based elastomers for high-resolution replica molding are explored in the imprinting process flow. High-quality devices with $Q$ -factors up to 39 000 and finesses up to $F \sim 14$ were demonstrated for very-near infrared wavelengths (around 900 nm). Finally, we report that the resonances can be thermooptically tuned by 0.05 nm/°C at 896 nm, thus demonstrating that, at shorter wavelengths, the fabricated microring resonators are less sensitive to temperature change, compared with longer wavelengths. The results of this paper demonstrate the capability of our method to fabricate optical devices with high performance for operation in a single mode at wavelengths where cheap light sources are available and water absorption is much lower than at far-infrared wavelengths. Because of this, it is expected that the fabricated structures have high potential for biosensing applications.

Integrated polymer micro-ring resonators for optical sensing applications

Micro-resonators (MR) have become a key element for integrated optical sensors due to their integration capability and their easy fabrication with low cost polymer materials. Nowadays, there is a growing need on MRs as highly sensitive and selective functions especially in the areas of food and health. The context of this work is to implement and study integrated micro-ring resonators devoted to sensing applications. They are fabricated by processing SU8 polymer as core layer and PMATRIFE polymer as lower cladding layer. The refractive index of the polymers and of the waveguide structure as a function of the wavelength is presented. Using these results, a theoretical study of the coupling between ring and straight waveguides has been undertaken in order to define the MR design. Sub-micronic gaps of 0.5 μm to 1 μm between the ring and the straight waveguides have been successfully achieved with UV (i-lines) photolithography. Different superstrates such as air, water, and aqueous solutions with glucose at different concentrations have been studied. First results show a good normalized transmission contrast of 0.98, a resonator quality factor around 1.5 × 104 corresponding to a coupling ratio of 14.7%, and ring propagation losses around 5 dB/cm. Preliminary sensing experiments have been performed for different concentrations of glucose; a sensitivity of 115 ± 8 nm/RIU at 1550 nm has been obtained with this couple of polymers.

Flow through ring resonator sensing platform

Polymeric microring resonator platform employing a flow-through approach is realized. A reduction of more than one order of magnitude of the sensor response time respect to standard flow-over approach is obtained.

Efficient design of polymer micro-ring resonator filters based on coupled mode theory and finite difference mode solver

Polymer photonics have been identified as a strong candidate technology for producing low-cost optical devices. In this paper, we provide a time efficient framework for designing polymer micro-ring devices based on Coupled Mode Theory (CMT) and a Finite Difference Mode Solver. We benchmark two alternative methods for modeling the coupling regions of the micro-ring filter in 3D. We deduce that compared to full blown finite difference time domain simulations, CMT can provide accurate results in just a small fraction of time. The proposed model allows the study of bending losses on the spectral properties of the device, that can be otherwise modelled using time demanding FDTD or less accurate simplified analytical expressions.

Photoelastic ultrasound detection using ultra-high-Q silica optical resonators.

As a result of its non-invasive and non-destructive nature, ultrasound imaging has found a variety of applications in a wide range of fields, including healthcare and electronics. One accurate and sensitive approach for detecting ultrasound waves is based on optical microcavities. Previous research using polymer microring resonators demonstrated detection based on the deformation of the cavity induced by the ultrasound wave. An alternative detection approach is based on the photoelastic effect in which the ultrasound wave induces a strain in the material that is converted to a refractive index change. In the present work, photoelastic-based ultrasound detection is experimentally demonstrated using ultra high quality factor silica optical microcavities. As a result of the increase in Q and in coupled power, the noise equivalent pressure is reduced, and the device response is increased. A finite element method model that includes both the acoustics and optics components of this system is developed, and the predictive accuracy of the model is determined.

Photoacoustic probe using a microring resonator ultrasonic sensor for endoscopic applications.

We designed an all-optical photoacoustic (PA) probe for endoscopic applications by employing an optically transparent, coverslip-type, polymeric microring resonator ultrasonic sensor. We experimentally quantified the axial, tangential, and radial resolutions and angular sensitive stability of this probe. Using this probe, we achieved volumetric imaging of several phantoms. Our all-optical probe design offers clear benefit in integrating PA endoscope with other optical endoscopic imaging modalities to facilitate the transformation from bench to bedside.

Simple ku‐band radio over fiber system with high‐dispersion tolerance using a polymer‐based microring resonator filter

AbstractThis article presents an optical single sideband (SSB) signal generation in radio over fiber system using a polymeric microring resonator as an optical notch filter, alleviating the fiber chromatic dispersion‐induced carrier fading problem. With this technique, optical SSB radio frequency (RF) signal with a RF frequency of 14.35 GHz carrying 40‐Mbps quadrature phase shift keying vector signal is generated. This signal is transmitted over 25‐km standard single‐mode fiber successfully, and the received signal error vector magnitude is 5.8% rms. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:1129–1133, 2014