Resonant Micro Research Articles

Low temperature PECVD processes for the fabrication of integrated symmetrical resonant UV210 organic/semiconductor structures

The resonant structures used as sensors for investigating specific dark and opaque substances may pose difficulties due to their potential aggressiveness towards photonic chips and the risk of destruction upon contact. To avoid it, this study presents a detailed description of a novel symmetrical waveguide structure with UV210 enclosed between Si/SiO2 bi-layers implemented for integrated photonics. The fabrication process is thoroughly explained, accompanied by various analyses conducted for characterizations purposes. The structure is composed of an organic UV210 material developed using deep UV lithography at 248 nm and fabricated onto an oxidized silicon layer, resulting in a Si/SiO2 bi-layer configuration. This process enables the fabrication of µm-scale access waveguides and racetrack Micro-Resonators (MRs) with a 400-nanometers gap. Several multilayer families have been produced using various low-temperature PECVD processes to obtain symmetrical Si/SiO2/UV210/Si/SiO2 structures and then properly characterized using non-destructive analyses and imaging techniques. The advantage of structural symmetry is primarily related to the electromagnetism and guidance equations, which eliminate the requirement for a cut-off thickness (or frequency), enabling significant miniaturization. Additionally, the upper cladding composed of a Si/SiO2 bi-layer offers protection against potentially aggressive substances directly in contact with the organic waveguide core and MRs. Different bi-layer upper cladding families, produced under various PECVD conditions, were characterized using XPS to understand the bonding mechanism between the silicon and UV210 organic. In addition, ellipsometric analyses were conducted to determine the real and imaginary components of the refractive index of the global structure and the upper cladding bi-layer. Structure imaging were obtained by Raman analyses and optical statistical measurements were conducted on four different types of heterostructures, with silica temperatures ranging from 120°C to 150°C during the second PECVD process. The resonance analysis, performed through Free Spectral Range (FSR) measurements, allowed us to draw conclusions regarding the stability and reproducibility of the fabrication process, as well as the impact of PECVD processes conditions on the optical measurements. Such optoelectronic resonant elements and hybrid heterostructures enable the investigation of aggressive substances in direct contact.

Stress isolations for resonant pressure micro sensors

This paper presents stress isolations for resonant pressure micro sensors that are supported by fixed isolation layers during assembly. While the resonant frequencies of the two resonators experience shifts due to measured pressures, they are susceptible to environmental perturbations. The proposed stress-isolated assembly in this study effectively mitigates the adverse effects of environmental noise and stabilizes the intrinsic frequencies of the resonators. Specifically, when subjected to temperature variations within the range of -55∼85 °C, the accuracy of the stress-isolated resonant pressure microsensor was determined to be ±0.01% FS. Similarly, during 3-axis random vibration tests, the accuracy of these stress-isolated resonant pressure microsensors was quantified as ±0.01% FS in response to environmental vibrations.

Nonlinear vibrational analysis and linearization error investigation in size-dependent resonant pressure microsensors

Dynamic and vibrational behavior of nonlinear resonant pressure micro sensors is studied in this paper using a proposed dynamic model. The basic part of the device is a microplate deflects due to external pressure in presence of electrostatic actuation. The frequency changes because of the microplate deformation is used to estimate the external pressure. For modeling of the micro sensor, the nonlinear governing equation of size dependent microplate in polar coordinate system and based on the modified couple stress theory is presented. Assuming specified number of Taylor expansion terms for electrostatic force, the linear and nonlinear ODE is obtained and nonlinear equation is solved both with multiple time scales method (MTS) and finite difference numerical method. Results indicate that considering finite terms of Taylor expansion (1 term for linear and three terms for MTS method) is the source of error in estimation of pressure or system stability. Using sufficient terms of Taylor Expansion, the error in linear and MTS solutions is vanished. Therefore, the limited values of microplate vibrational amplitude is extracted to increase the accuracy of the sensor in linear action. The effect of size dependency, applied voltage on nonlinear behavior and linearization error is also studied.

2.5D+ plasma etching for a continuously adjustable sidewall angle in SiO2

We present a systematic investigation of an SiO2 etching process using a standard fluorocarbon chemistry ICP-RIE etch tool with a cryogenically cooled electrode. Our goal is to enable the control of the SiO2 feature morphology, i.e., the sidewall angle, in order to add a degree of freedom for the design of resonant micro-/nanooptical elements. For such elements as e.g., whispering gallery mode resonators with specific mode profiles, it is essential to maintain low surface roughness. To this end, we investigate a variety of gas compositions. For statistical evaluation, we use a surface response methodology for several parameters and investigate the influence of the substrate temperature on the sidewall angle. Different hypotheses from the literature for the cause of non-anisotropic etch behavior are discussed for our specific case. Various investigations based on the prior hypothesis are presented, which provide more information about the pseudo-isotropic etch profile. Finally, we present two use cases: firstly, a classical anisotropic etch with a high aspect ratio and very low roughness (<1 nm), and secondly, an etch process for the fabrication of whispering gallery mode resonators that confine the light at the bottom of the resonator.

Variables Impacting Silicone Oil Migration and Biologics in Prefilled Syringes

Prefilled syringes (PFS) as a primary container for parenteral drug products offer significant advantages, such as fast delivery time, ease of self-administration and fewer dosing errors. Despite the benefits that PFS can provide to patients, the silicone oil pre-coated on the glass barrels has shown migration into the drug product, which can impact particle formation and syringe functionality. Health authorities have urged product developers to better understand the susceptibility of drug products to particle formation in PFS due to silicone oil. In the market, there are multiple syringe sources provided by various PFS suppliers. Due to current supply chain shortages and procurement preferences for commercial products, the PFS source may change in the middle of development. Additionally, health authorities require establishing source duality. Therefore, it is crucial to understand how different syringe sources and formulation compositions impact the drug product quality. Here, several design of experiments (DOE) are executed that focus on the risk of silicone oil migration induced by syringe sources, surfactants, protein types, stress, etc. We utilized Resonant Mass Measurement (RMM) and Micro Flow Imaging (MFI) to characterize silicone oil and proteinaceous particle distribution in both micron and submicron size ranges, as well as ICP-MS to quantify silicon content. The protein aggregation and PFS functionality were also monitored in the stability study. The results show that silicone oil migration is impacted more by syringe source, siliconization process and surfactant (type & concentration). The break loose force and extrusion force across all syringe sources increase significantly as protein concentration and storage temperature increase. Protein stability is found to be impacted by its molecular properties and is less impacted by the presence of silicone oil, which is the same inference drawn in other literatures. A detailed evaluation described in this paper enables a thorough and optimal selection of primary container closure and de-risks the impact of silicone oil on drug product stability.

Three closed loop noise suppression method for resonant micro optical gyroscope

For resonant micro-optical gyroscope (R-MOG), backscattering noise and optical Kerr noise are the main noises that affect the output accuracy of the gyroscope, and it is difficult to suppress them completely. This paper introduces a method to suppress the optical Kerr noise generated by the front end by compensating the optical power difference while suppressing the backscattered noise. Based on a single light source, the system changes the frequency difference between clockwise and counterclockwise optical paths through double-phase modulation, so as to improve the carrier rejection ratio and suppress the backscattered noise. At the same time, a high-speed feedback loop based on intensity modulator is designed, which is added to the optical loop to enhance the optical power, so as to reduce the impact of optical Kerr noise. The experimental results show that this method effectively suppresses the backscattered noise and optical Kerr noise, improves the output accuracy of the gyro by two orders of magnitude, and finally observes the long-term bias stability of 0.982°/h.

Interferometric cavity ringdown technique for ultrahigh Q-factor microresonators

Microresonators (MRs) are key components in integrated optics. As a result, the estimation of their energy storage capacity as measured by the quality factor (Q) is crucial. However, in MRs with high/ultrahigh Q, the wall-surface roughness dominates the intrinsic Q and generates a coupling between counter-propagating modes. This splits the usual sharp single resonance and makes the use of classical methods to assess Q difficult. Here, we theoretically show that an interferometric excitation can be exploited in a cavity ringdown (CRD) method to measure the ultimate Q of a MR. In fact, under suitable conditions, the resonant doublet merges into a single Lorentzian, and the time dynamics of the MR assumes the usual behavior of a single-mode resonator unaffected by backscattering. This allows us to obtain a typical exponential decay in the charging and discharging time of the MR, and thus, to estimate its ultimate Q by measuring the photon lifetime.

Improving the thermal reliability of photonic chiplets on multicore processors

Silicon photonics is a promising technology for high-performance inter/intra-chip networks. Although chiplet technologies help to integrate photonic network with processors and memories, thermal reliability remains a major challenge for photonic networks. Thermal variations are common in chiplet-based systems. Due to thermo-optic effects, photonic switches, such as microresonators (MRs), suffer from temperature-dependent wavelength shifts. To improve the thermal reliability of photonic chiplets, we propose an effective bridging and tuning method, called BAT. Our method enhances the temperature channel transition among MRs and minimize bit errors during temperature changes. BAT is integrated with thermal tuning, electrical tuning, laser tuning, and receiver tuning. We optimize MR design, control logic, tuning circuit, thermal floorplan, and network protection mechanism for BAT. Compared to state-of-the-art methods, BAT achieves a 10−12 bit-error-rate for photonic chiplets, saves up to 70.0% of the thermal tuning power, and improves up to a 1.17X system energy efficiency.

Investigation on the complex and tunable laser chaos generated by the microresonator optical combs injection

A novel method to generate high complexity and wavelength-tunable laser chaos is proposed by injecting nonlinear frequency combs from a microresonator (MR) into a semiconductor laser. The nonlinear dynamics and chaotic characteristics are simulated. The results show that chaos with permutation entropy of 0.997, spectral entropy of 0.953, spectrum bandwidth of 32.4 GHz, the flatness of 0.38 dB/GHz can be generated. Compared with the conventional optical feedback injection system and the phase conjugate feedback injection system, the MR injection system can generate better chaos with bandwidth enhancement and complexity improvement at lower bias currents. The time delay signature introduced by the MR can be completely concealed, which provides support for chaotic secure communication. Furthermore, the microresonator injection (MRI) system is flexible and expandable. Laser chaos with tunable wavelength can be generated by changing the working wavelength of the slave laser. And if multiple lasers with free spectral range interval are connected to MR parallelly, up to 93 high-performance chaotic carriers with a cross-correlation as low as about 0.1 can be realized in short, conventional, and long wavelength bands simultaneously. This scheme provides a foundation for multiple parallel chaotic carriers and large-capacity chaotic secure communication.

Three Closed Loop Noise Suppression Method for Resonant Micro Optical Gyroscope

Three Closed Loop Noise Suppression Method for Resonant Micro Optical Gyroscope

Ultrafine Aerosol Particle Sizer Based on Piezoresistive Microcantilever Resonators with Integrated Air-Flow Channel.

To monitor airborne nano-sized particles (NPs), a single-chip differential mobility particle sizer (DMPS) based on resonant micro cantilevers in defined micro-fluidic channels (µFCs) is introduced. A size bin of the positive-charged fraction of particles herein is separated from the air stream by aligning their trajectories onto the cantilever under the action of a perpendicular electrostatic field of variable strength. We use previously described µFCs and piezoresistive micro cantilevers (PMCs) of 16 ng mass fabricated using micro electro mechanical system (MEMS) technology, which offer a limit of detection of captured particle mass of 0.26 pg and a minimum detectable particulate mass concentration in air of 0.75 µg/m3. Mobility sizing in 4 bins of a nebulized carbon aerosol NPs is demonstrated based on finite element modelling (FEM) combined with a-priori knowledge of particle charge state. Good agreement of better than 14% of mass concentration is observed in a chamber test for the novel MEMS-DMPS vs. a simultaneously operated standard fast mobility particle sizer (FMPS) as reference instrument. Refreshing of polluted cantilevers is feasible without de-mounting the sensor chip from its package by multiply purging them alternately in acetone steam and clean air.

L-band Raman lasing in chalcogenide glass microresonator started by thermal mode pulling with auxiliary red diode laser

Chalcogenide glass microresonators (MRs) with whispering gallery modes (WGMs) having a huge third-order nonlinearity are an attractive platform for producing miniature photonic devices, such as Raman lasers in the near- and mid-IR range. However, the excitation of a proper WGM, leading to the start of a new wavelength generation, requires smart passive or active control. Here we propose and demonstrate a simple and cheap way to start a single-mode Raman laser in a chalcogenide glass MR pumped by a standard telecom CW laser at a constant wavelength using a red laser diode for the thermal control of WGMs leading to mode pulling. We attain single-mode Raman lasing at 1620 nm in As2S3 glass MR using a C-band pump laser at 1530 nm and a red laser diode at 650 nm.

Resonant micro optic gyroscope equipped with multi-turn waveguide ring resonator

Waveguide ring resonator (WRR) is beneficial to the miniaturization and integration of the resonant micro optic gyroscope (RMOG). The shot-noise-limited sensitivity of the RMOG equipped with the multi-turn WRR is derived. The simulation results show that when the crossing loss or the waveguide propagation loss is higher than 0.07 dB/crossing or 1.2 dB/m, the WRR of multi-turn structure does no good to the sensitivity of the RMOG. Two configurations of the WRR are introduced and tested. According to the measured waveguide propagation loss and crossing loss, the optimal angular random walk (ARW) is obtained when the RMOG equipped with a WRR of 2 or 3 turns. The ARW of the RMOG equipped with a 3-turn WRR is measured at different laser output power which agrees well with the theoretical value.

The noise suppression in resonant micro optic gyroscopes based on dual light sources method

In Resonant Micro-Optical Gyroscopes (R-MOG), optical backscatter noise is generally considered to be one of the largest noises which also greatly limits the improvement of accuracy. A suppression method based on dual light sources is designed in this paper, in which two tunable semiconductor lasers are used to provide light for clockwise (CW) and counterclockwise (CCW), respectively. Two independent lasers have been frequency divided and phase locked by Optical Phase-Locked Loop (OPLL). In this way, high-frequency noise caused by interference between the backscatter light and the signal light can be filtered out, completely. The frequency noise for dual-lasers has also been effectively suppressed by adjusting the OPLL bandwidth. Then, intensity modulators with second harmonic feedback have been used to achieve the stabilization of the optical power in the cavity. The results show that, the influence of the interfering light intensity is reduced by about an order of magnitude compared with the single-phase modulation technology in single laser system and the bias stability has stood at 0.00448∘/s.

Recent development of resonant micro cavity in resonant micro-optical gyro

Resonant micro-optical gyros (RMOG) based on Sagnac effect has great potential in integration, miniaturization and sensitivity, which has broad application prospects in the fields of micro nano satellite attitude control, robot control, medical diagnosis and detection instruments, and has become a research hotspot in recent years. Resonant micro cavity as the core sensing element of resonator micro optical gyroscope, the optical characteristics of which are closely related to the performance of gyroscope system. The research progress of resonator has seriously restricted the development of RMOG. At present, integrated optical technology, micro nano optical processing technology and the application of new materials can reduce the weight and size of the resonator, reduce the cost and power consumption, and increase the reliability and performance index of the system. Combined with the information disclosed by periodical conference and related research institutions, the development status, basic principle and characteristic parameters of resonant micro optical gyroscope were briefly introduced. Various new structure designs of resonant micro cavity at home and abroad were listed, and the characteristics and potential of different structures were analyzed. In addition, the new materials for fabrication of resonant micro cavity at home and abroad were reviewed, and the optical properties of different materials were summarized. The future development direction and technical development path of resonator micro cavity for resonator micro optical gyroscope were preliminarily discussed.

Polarization converter of single photons on a two-dimensional quantum dot in an optical microresonator

A polarization conversion of a single photon using a semiconductor quantum dot (QD) coupling to a two-mode optical microresonator (MR) is studied. The rotation angle of the polarization vector depends on the orientation of QD axes with respect to MR ones, parameters of the system, and a conversion regime. A nanostructure based on a two-dimensional photonic crystal coupling to a single-electron QD is considered as the possible converter design. It is shown that this structure can also act as a beam splitter and perform the quantum operation NOT on a spatial photon qubit.

Porosity calibration in a 4-layer porous silicon structure to fabricate a micro-resonator with well-defined refractive indices and dedicated to biosensing applications

Abstract Calibration of the porosity as well as the electrochemical anodization rate in a 4-layer porous silicon (PSi) waveguide structure, including a guiding, a confinement and two technological barrier layers, is studied and validated. The objective is to process using standard photolithography a 4-layer PSi micro-resonator (MR) that will be butt-coupled with polymer waveguide and used for biosensing applications. The knowledge of the porosity and thus the refractive index of each PSi layer is then crucial to fabricate the hybrid optical component. The presence of the two PSi barrier layers is necessary to prevent the infiltration of polymers or resin during the process but influences the porosity and the anodization rate of both the guiding and the confinement PSi layers. Their porosity is lower than if these layers had been manufactured separately (one layer only) and the anodization rate is on the contrary higher. Taking into consideration the calibration results to obtain the target thicknesses and refractive indices of the guiding and the confinement PSi layers respectively, a MR based on the 4-layer PSi structure is fabricated. The PSi MR experimental transmission spectrum well corresponds to the simulated one which has been calculated from porosity calibration results and from experimental dimensions of the component measured by scanning electron microscope observations. Finally, a promising theoretical surface sensitivity of 0.06 nm/(pg/mm2) for Bovin Serum Albumin detection with a limit of detection of 0.1 pg/mm2 has been calculated for the PSi MR.

Validating the Critical Point of Spontaneous Parametric Downconversion for Over 600 Scanning MEMS Micromirrors on Wafer Level

Sensors and actuators based on resonant micro-electro-mechanical systems (MEMS), such as scanning micro mirrors, are well-established in automotive and consumer products. As the areas of application broaden, the requirements for the MEMS are increasing. Devices outside of the performance specifications have to be rejected which is costly due to the high processing times of MEMS technologies. In particular, nonlinear system behavior is often found to cause unexpected device failure or performance issues. Thus, accurate simulation or rather system models which account for nonlinear sensor dynamics can not only increase process yield, but more importantly, lead to a comprehensive understanding of the underlying physics and to improved MEMS design. We have studied [1] the possibility of a rather drastic device failure induced by nonlinearities on the example of a resonant scanning MEMS micro mirror. On the level of a few selected chips, we have carefully measured the complex nonlinear system behavior and modeled it by a nonlinear mode-coupling phenomenon known as spontaneous parametric down-conversion (SPDC). The most intriguing feature of SPDC is the sudden change from a rather linear to a nonlinear system behavior at the critical oscillation amplitude. However, the threshold only lies within the range of the mirror's operational amplitude, if certain frequency resonance conditions regarding the mechanical modes are met. Thus, the critical amplitude strongly depends on the frequency spectrum of the MEMS design which in turn is largely influenced by fabrication imperfections. We validate the dependence of the critical amplitude on the resonance condition by measuring it for over 600 micro mirrors on wafer-level. Our work does not only validate the theory of SPDC with measurements on such a large scale, but also demonstrates modeling strategies which are essential for MEMS product design.

Electromechanical behavior of graphene foams

Graphene foam (GF)—a three-dimensional porous structure that comprises several graphene layers—has excellent physical properties and, consequently, exciting possible applications. In this work, we report the mechanical behavior of GFs that were grown using high-temperature chemical vapor deposition (CVD) and subjected to electrostatic tensile loads. We show that such loads reduce the mechanical stiffness of the GF (Young's modulus in the kilo-Pascal range) and release prestresses generated during growth. In addition, GF demonstrates electrostatic resonance. By characterizing the fundamental electromechanical behavior of GF, this Letter paves the way toward the development of novel GF-based devices, such as GF electrostatic resonant sensors, flexible capacitors, and micro- and nanoelectromechanical devices.

Electro-thermal excitation of parametric resonances in double-clamped micro beams

We report on a simple yet efficient approach allowing direct electrothermal excitation of parametric resonance (PR) in double-clamped flexible nano- and microscale beams. The application of a time-harmonic voltage between the beam's ends leads to the electric current and Joule's heating of the entire beam, which induces a time-periodic axial stress and results in excitation of the structure lateral vibrations through the PR mechanism. The proposed approach has an advantage, simplifying fabrication and integration and reducing the influence of residual stress, and thermal mismatch, unlike conventional piezoelectric, photothermal, or electrostatic actuation approaches, which require additional piezoelectric layers, light sources, or electrodes in the proximity of a vibrating beam. Single crystal silicon, nominally 500 μm long, 30 μm wide, and 5 μm thick beams were fabricated by deep reactive ion etching and operated at a pressure of ≈1.9 mTorr. The experimental results, consistent with the reduced order and numerical model predictions, demonstrate the feasibility of the suggested excitation scenario, which could be implemented in resonant sensors, timing devices, signal processing, and micro and nanomechanical logical elements.