Thermal Tuning Research Articles

Reconfigurable Sorting of Nanoparticles on a Thermal Tuning Silicon Based Optofluidic Chip

We numerically demonstrate a scheme of optofluidic sorting of nanoparticles on a silicon-based lab-on-a-chip system, with reconfigurable and multilevel sorting size thresholds. Size-dependent sorting of nanoparticles originates from the size-dependent distribution of trapping potential wells, which determines whether a nanoparticle can jump back and forth between parallel waveguides in weakly coupling condition. In numerical modeling, we find that it is easier for larger ones to transfer and the size threshold is power ratio dependent. By setting a thermal tuning ring-assisted Mach-Zehnder interferometer ahead, we can adjust effectively the input power ratio of the parallel waveguides as well as the potential well distribution across them, working as a thermal tuning reconfigurable sorting unit. Consequently, a tree cascaded unit with different thresholds is also presented to be a reconfigurable multilevel sorting unit. The proposed design offers a simple and ultracompact scheme for the reconfigurable and multilevel optofluidic sorting of nanoparticles on thermo-optofluidics chip for the first time.

Controllable Thermal-Frequency Tuning of a Terahertz Gyrotron

Gyrotron performance is sensitive to cavity structure parameters, and the cavity shape is temperature dependent due to thermal deformation induced by temperature rise from ohmic loss power on finite-conductivity cavity wall. Accordingly, this paper studies a frequency-tuning scheme for terahertz gyrotron by properly controlling the cavity thermal deformation. By combining gyrotron nonlinear theory and finite-element method software, controllable thermal-frequency-tuning capability of a continuous-wave 263-GHz gyrotron is systematically investigated, toward maintaining gyrotron operating under gyromonotron condition in frequency-tuning band, and achieving high efficiency in broadband frequency-tuning range. After studying cavity thermal distribution, structure deformation, and electron beam–wave interaction, an optimized cavity structure with transition sections on both ends is proposed. Simulation predicts that with the two-transition-section cavity, via additional thermal tuning, the continuous-frequency-tuning band is capable of reaching 1.75 GHz, which is 5 times of the initial bandwidth. Furthermore, using the thermal-frequency-tuning technology, impressive high efficiency above 17% is obtainable in the whole frequency-tuning range.

Thermal tuning on band gaps of 2D phononic crystals considering adhesive layers

Phononic crystals are very attractive in many applications, such as noise reduction, filters and vibration isolation, due to their special forbidden band gap structures. In the present paper, the investigation of tunable band gaps of 2D phononic crystals with adhesive layers based on thermal changing is conducted. Based on the lumped-mass method, an analytical model of 2D phononic crystals with relatively thin adhesive layers is established, in which the in-plane and out-of-plane modes are both in consideration. The adhesive material is sensitive to temperature so that the band structure can be tuned and controlled by temperature variation. As temperature increases from 20 °C–80 °C, the first band gap shifts to the frequency zone around 10 kHz, which is included by the audible frequency range. The results propose an important guideline for applications, such as noise suppression using the 2D phononic crystals.

Design of a High Extinction Ratio Tunable Graphene on White Graphene Polarizer

A thermally/electrically tunable graphene on white graphene polarizer is proposed, in which the resonant coupling between the plasmonic surface modes of the structure and the transverse electric (TE) [or transverse magnetic (TM)] polarized incident wave is used to absorb this polarization, while the TM (or TE) polarized incident wave is totally reflected. It is then shown that the thermal and electrical tunability of surface conductivity of graphene can be used to control the optical properties of the proposed polarizer, including the selection of the desired polarization, and adjusting the amplitude of the reflected (desired) polarization. The application of the hexagonal boron-nitride (white graphene) as the substrate of graphene increases the propagation of the surface waves of the structure, which in turn results in the very high polarization extinction ratio of 75 dB. Moreover, the ultra-small insertion loss of 0.022 dB and relatively large bandwidth of ~ 60 nm are calculated for the proposed polarizer.

Photonic Integrated Circuit Based on Hybrid III–V/Silicon Integration

This paper summarizes the recent advances of integrated hybrid InP/SOI lasers and transmitters based on edge coupling. First, we review the different integration methods between III–V material and silicon. Then, we focus on using an external III–V chip coupled via edge coupling to our silicon photonic integrated circuit. The paper reports on the results of wavelength tunable lasers containing one or two ring resonators as well as an integrated reflectivity tunable mirror. We demonstrate that a wide thermal tuning range, exceeding the C band, with a high side mode suppression ratio above 35 dB can be achieved. Design of external silicon cavities enables the realization of a broad range of on-chip functionalities as well as advanced hybrid transmitters. Parallel wavelength tunable cavities and compact variable optical attenuator-controlled arrayed waveguide gratings on silicon are integrated with a reflective semiconductor optical amplifiers, creating fast wavelength switching lasers. Furthermore, integrated transmitters that combine silicon modulators with tunable hybrid III–V/Si lasers are reported. The integrated transmitter for on–off keying signal generation exhibits more than 30 nm wavelength tunability and excellent bit-error-rate performance up to 40 Gb/s. A multichannel integrated transmitter is then reported with combined silicon-based arrayed waveguide gratings laser cavity and multiple ring modulators. Finally, an advanced wavelength-tunable hybrid III–V/Si transmitter with two microring modulators nested in a Mach–Zehnder interferometer is demonstrated for quadrature phase-shift keying generation where a BPSK signal is generated by each ring.

Photovoltaic effect and photopolarization in Pb[(Mg1/3Nb2/3)0.68Ti0.32]O3 crystal

Ferroelectric photovoltaic materials are an alternative to semiconductor-based photovoltaics and offer the advantage of above bandgap photovoltage generation. However, there are few known compounds, and photovoltaic efficiencies remain low. Here, we report the discovery of a photovoltaic effect in undoped lead magnesium niobate-lead titanate crystal and a significant improvement in the photovoltaic response under suitable electric fields and temperatures. The photovoltaic effect is maximum near the electric-field-driven ferroelectric dipole reorientation, and increases threefold near the Curie temperature. Moreover, at ferroelectric saturation, the photovoltaic response exhibits clear remanent and transient effects. The transient-remanent combinations together with electric and thermal tuning possibilities indicate photoferroelectric crystals as emerging elements for photovoltaics and optoelectronics, relevant to all-optical information storage and beyond.

Thermal Stability and Tuning of Thermoelectric Properties of Ag1−xSb1+xTe2+x (0 ≤ x ≤ 0.4) Alloys

Introduction of nonstoichiometry to AgSbTe2-based materials is considered to be an effective way to tune thermoelectric properties similarly to extrinsic doping. To prove this postulate, a systematic physicochemical study of the Ag1−xSb1+xTe2+x alloys (0 ≤ x ≤ 0.4) was performed. In order to investigate the influence of the cooling rate after synthesis on phase composition and thermoelectric performance, slowly cooled and quenched Ag1−xSb1+xTe2+x alloys (x = 0; 0.1; 0.17; 0.19; 0.3; 0.4) were prepared. Single-phase material composed of the β phase (NaCl structure type) was obtained for the quenched x = 0.19 sample only. The other alloys must be regarded as multi-phase materials. The cooling rate affects the formation of the phases in the Ag-Sb-Te system and influences mainly electronic properties, carrier mobility and carrier concentration. The extremely low lattice thermal conductivity is an effect of the mosaic nanostructure. The maximal value of the figure of merit ZTmax = 1.2 is observed at 610 K for the slowly cooled multi-phase sample Ag0.9Sb1.1Te2.1. Thermoelectric properties are repeatedly reproducible up to 490 K.

Thermal tuning of graphene-embedded waveguide filters based on the polymer–silica hybrid structure

Graphene-embedded waveguide filters have been widely used in the areas of polarization and mode filtering because of their characteristics of easy fabrication, high integration, and high extinction ratio. In this article, we propose thermal tuning filters based on a graphene-embedded polymer–silica hybrid waveguide. Compared to previously reported filters, this device can realize the efficient adjustment of the relative position between the optical field and graphene layer by thermal tuning. Consequently, the polarization and mode filtering properties of the filter can be adjusted by thermal tuning. This high-efficiency tuning characteristic is due to the opposite thermo-optic coefficient of the polymer and silica material. Furthermore, a layer with a low refractive index is embedded in the polymer–silica hybrid core to increase the tuning efficiency. The optical absorption, mode properties, and thermal field distributions were simulated. It was found that such single-mode filters could realize Ex11-pass or Ex11-stop selection, and the attenuation variation (Δα) was optimized to 32.20 dB cm−1 (Ex11 mode) using the top electrode and air trench structure with ΔT = 10 K and P = 48.39 mW in the single-mode waveguide. For the multimode waveguide filters, the attenuation variation (Δα) of the Exmn modes (Ex11, Ex12, and Ex21) was also calculated. Such thermal tuning filters were found to be compatible with chemical potential regulation graphene modulators and filters, and they can be applied to broadband photonic integrated circuits and mode division multiplexing systems.

Enhancing the thermoelectric performance of ZnO epitaxial films by Ga doping and thermal tuning

Ga doping combined with optimization of the deposition temperature could be a promising strategy for enhancing the thermoelectric properties of ZnO-based epitaxial films.

Thermal and electrical wavelength tuning of Bragg reflection with ultraviolet light absorbers in polymer-stabilized cholesteric liquid crystals

A dual thermal and electrical polymer-stabilized cholesteric liquid crystal has been fabricated by using ultraviolet light absorbers. The Bragg reflection can be autonomously controlled by temperature and manually by an electric field.

Bidirectional reconfiguration and thermal tuning of microcantilever metamaterial device operating from 77 K to 400 K

We experimentally report the bidirectional reconfiguration of an out-of-plane deformable microcantilever based metamaterial for advanced and dynamic manipulation of terahertz waves. The microcantilever is made of a bimaterial stack with a large difference in the coefficient of thermal expansion of the constituent materials. This allows for the continuous deformation of microcantilevers in upward or downward direction in response to positive or negative temperature gradient, respectively. The fundamental resonance frequency of the fabricated microcantilever metamaterial is measured at 0.4 THz at room temperature of 293 K. With decreasing temperature, the resonance frequency continuously blue shifts by 30 GHz at 77 K. On the other hand, with increasing temperature, the resonance frequency gradually red shifts by 80 GHz and saturates at 0.32 THz for 400 K. Furthermore, as the temperature is increased above room temperature, which results in the downward actuation of the microcantilever, a significant resonance line-narrowing with an enhanced quality factor is observed due to tight field confinement in the metamaterial structure. The thermal control of the microcantilever possesses numerous inherent advantages such as enhanced tunable range (∼37.5% in this work compared to previously reported microcantilever metamaterials), continuous tunability, and repeatable operations. The microcantilever metamaterial also shows high robustness to operate at cryogenic conditions and hence opens up the possibility of using meta-devices in harsh environments such as space, polar, and deep sea applications.

Thermal tuning of electrical and dielectric characteristics of Mn-doped Zn0.95Fe0.05O dilute magnetic semiconductors

Structural and hence the electrical properties of transition metal doped ZnO-based dilute magnetic semiconductors can effectively be tuned thermally for their potential utilization in high temperature modern day spintronic devices. In this work, we investigate the effect of Mn doping on structural and its consequent effects on the electrical characteristics of Zn0.95−xMnxFe0.05O (x = 0.00, 0.01, 0.02, 0.03, 0.04 and 0.05) synthesized using sol–gel auto-combustion. X-ray diffraction analysis indicated that the synthesized samples had the pure wurtzite-type hexagonal crystal structure. Average crystallite size as determined using Scherrer’s formula was decreased with the increase of Mn doping while the porosity was increased. Temperature dependent dielectric measurements revealed that dielectric constant and dielectric loss was increased by increasing the temperature for Mn-doped samples. The conductivity was also enhanced with increasing temperature due to the enhanced evolution of charge carriers between the grains. Temperature dependent impedance spectroscopy confirmed that resistance and reactance were inverse function of the temperature revealing negative temperature coefficient of resistance. Nyquist plot shows semi-circular behavior attributed to the grain boundary effect.

Design of a Flexible-Grid 1 × 2 Wavelength-Selective Switch Using Silicon Microring Resonators

In this paper, a compact integrated flexible-grid 1 × 2 wavelength-selective switch is proposed. The device is designed by utilizing a structure with nine reconfigurable add-drop silicon microring resonators. Using thermal tuning, the transmission spectra of silicon microring resonators are coherently combined to provide adjustable bandwidths as desired. The operation principle and detailed analysis of the designed device are presented. Calculation results show the bandwidth tuning for the spectrum with the large bandwidth varies from 0.56 to 4.09 nm and the bandwidth tuning for the spectrum with the moderate bandwidth ranges from 0.38 to 2.64 nm. The integrated flexible-grid 1 × 2 wavelength-selective switch with the maximum bandwidth tunability has a maximum crosstalk of −11.5 dB.

Spectral and Modal Properties of a Mid-IR Spherical Microlaser

Whispering gallery mode (WGM) lasers are well-known for their small sizes, low thresholds and narrow linewidths, and have been the subject of research and development for more than two decades. However most of the initial reports and studies have focused on near-IR and visible WGM microlasers. Recent advances in the synthesis, doping and processing of high quality mid-IR transparent glasses have provided the means to extend the wavelengths of these microlasers to the mid-IR range. In this paper, we present a detailed characterization of a compact and low-cost mid-IR spherical WGM microlaser based on heavily doped Er:ZBLAN glass operating near 2.7 um with an estimated linewidth less than 1.1 MHz. We describe experimental results on observed single-mode and multimode spectra, thermal tuning, and polarization characteristics of such microlasers. Using a simple analysis of spherical microresonator modes and including considerations of pump and laser mode overlap we provide guidelines for optimized microlaser design.

Directional mechanical and thermal properties of single-layer black phosphorus by classical molecular dynamics

Black phosphorus (BP) has received attention due to its own higher carrier mobility and layer dependent electronic properties, such as direct band gap. Interestingly, the single layer black phosphorus (SLBP) has had large popularity in applications related to thermoelectric, optoelectronic, and electronic devices. Here, we investigate the phonon spectrum, thermal conductivities, and stress strain effects. Robust anisotropy was mainly observed in the thermal conductivities together with the alongside zigzag (ZZ) direction value, compared to the armchair (AC) directions. We also investigated the attitude of stress that was anisotropic in both directions, and the stress effects were two times greater across the ZZ path than those in the AC direction at a low temperature. We obtained a Young’s modulus of 63.77 and 20.74 GPa in the AC and ZZ directions, respectively, for a strain range of 0.01. These results had good agreement with first principle calculations. Our study here is useful and significant for the thermal tuning of phosphorus-based nanoelectronics and thermalelectric applications of phosphorus.

Dynamically controlled electromagnetically induced transparency in terahertz graphene metamaterial for modulation and slow light applications

By patterning two graphene resonators on a SiO2/Si substrate, a dynamically controlled electromagnetically induced transparency (EIT) in the terahertz graphene metamaterial was numerically studied through tuning the structural parameter and Fermi energy of graphene. The calculated surface current distributions demonstrate that the distinct EIT window in the graphene metamaterial results from the near-field coupling of two graphene resonators. Moreover, the EIT window can be actively controlled by tuning Fermi energy combined states of two resonators. When the Fermi energy combined state of two resonators changes from (0.21 and 0.16 eV) to (0.4 and 0.11 eV), the amplitude modulation depth of the EIT peak is 97.8% at 0.45 THz, and the corresponding enhanced factor of group delay with 6 times is obtained. This study offers an alternative tuning method to existing optical, thermal, and relative distance tuning, delivering a promising potential for designing active and miniaturized THz devices.

A 40-Gb/s PAM-4 Transmitter Based on a Ring-Resonator Optical DAC in 45-nm SOI CMOS

The next generations of large-scale data-centers and supercomputers demand optical interconnects to migrate to 400G and beyond. Microring modulators in silicon-photonics VLSI chips are promising devices to meet this demand due to their energy efficiency and compatibility with dense wavelength division multiplexed chip-to-chip optical I/O. Higher order pulse amplitude modulation (PAM) schemes can be exploited to mitigate their fundamental energy–bandwidth tradeoff at the system level for high data rates. In this paper, we propose an optical digital-to-analog converter based on a segmented microring resonator, capable of operating at 20 GS/s with improved linearity over conventional optical multi-level generators that can be used in a variety of applications such as optical arbitrary waveform generators and PAM transmitters. Using this technique, we demonstrate a PAM-4 transmitter that directly converts the digital data into optical levels in a commercially available 45-nm SOI CMOS process. We achieved 40-Gb/s PAM-4 transmission at 42-fJ/b modulator and driver energies, and 685-fJ/b total transmitter energy efficiency with an area bandwidth density of 0.67 Tb/s/mm2. The transmitter incorporates a thermal tuning feedback loop to address the thermal and process variations of microrings’ resonance wavelength. This scheme is suitable for system-on-chip applications with a large number of I/O links, such as switches and general-purpose and specialized processors in large-scale computing and storage systems.

Optical Power Monitoring with Ultrahigh Sensitivity in Silicon Waveguides and Ring Resonators

We demonstrate optical power monitoring using a silicon resistor enabled by the surface and defect states-induced photoconductance effect. Ultrahigh optical power detection sensitivity of −40 dBm under a low AC drive voltage of 5 mV is obtained with the facilitation of a lock-in amplifier circuitry. The detection scheme is applied to monitor the resonances in single and coupled-ring resonators. Intracavity resonance spectrum is successfully measured at both the static and the thermal tuning conditions. The demonstration opens a compelling new way for nonintrusive on-chip optical power detection by exploiting doped silicon resistor-based thermooptic heaters.

Geometric tuning: spectroscopy using whispering-gallery resonator frequency-synthesizers

Continuous fine-tuning of nonlinear processes in whispering-gallery resonators is still in its infancy. We demonstrate an innovative, fast, and compact tuning-method by enlarging a ring-like whispering-gallery resonator made out of lithium niobate with the help of a piezo actuator disk embedded inside the resonator. The radial expansion of the actuator forces the resonator to change its size and shape. This process is much faster than thermal tuning and has the additional benefit of a smaller dispersion. Using just this method to tune the resonator, a second-harmonic process pumped at around 1 μm wavelength can be tuned mode-hop-free over a range of 28 GHz, and an optical parametric oscillator pumped at the same wavelength achieved 4.5 GHz continuous tuning. In addition to presenting and demonstrating this novel concept, the influence of the elasto-optic effect and the refractive-index dispersion are discussed, and an analytic model to predict the wavelength dependent tuning efficiency is presented.

Integrated reconfigurable photonic filters based on interferometric fractional Hilbert transforms.

In this paper, we present integrated reconfigurable photonic filters using fractional Hilbert transformers (FrHTs) and optical phase tuning structure within the silica-on-silicon platform. The proposed structure, including grating-based FrHTs, an X-coupler, and a pair of thermal tuning filaments, is fabricated through the direct UV grating writing technique. The thermal tuning effect is realized by the controllable microheaters located on the two arms of the X-coupler. We investigate the 200GHz maximum bandwidth photonic FrHTs based on apodized planar Bragg gratings, and analyze the reflection spectrum responses. Through device integration and thermal modulation, the device could operate as photonic notch filters with 5GHz linewidth and controllable single sideband suppression filters with measured 12dB suppression ratio. A 50GHz instantaneous frequency measuring system using this device is also schematically proposed and analyzed with potential 3dB measurement improvement. The device could be configured with these multiple functions according to need. The reconfigurable structure has great potential in ultrafast all-optical signal processing fields.