Thermal Tuning Research Articles

Contention-Aware Routing for Thermal-Reliable Optical Networks-on-Chip

Optical network-on-chip (ONoC) architecture offers ultrahigh bandwidth, low latency, and low power dissipation for new-generation manycore systems. However, the benefits in communication performance and energy efficiency will be diminished by communication contention. The intrinsic thermal susceptibility is another challenge for ONoC designs. Under on-chip temperature variations, core functional devices suffer from significant thermal-induced optical power loss, which seriously threatens ONoCs’ reliability. In this article, we develop novel routing techniques to resolve both issues for ONoCs. By analyzing the thermal effect in ONoCs, we first present a routing criterion at the network level. Combined with device-level thermal tuning, it can implement thermal-reliable ONoCs. Two routing approaches, including a mixed-integer linear programming (MILP) model and a heuristic algorithm (called CAR), are further proposed to minimize communication conflicts based on guaranteed thermal reliability, and meanwhile, maximize the communication energy efficiency in the presence of on-chip thermal variations. By applying the criterion, our approaches achieve excellent performance with largely reduced complexity of design space exploration. The evaluation results based on both synthetic traffic patterns and realistic benchmarks validate the effectiveness of our approaches with an average of 126.95% improvement in communication performance and 16.12% reduction in energy overhead compared to state-of-the-art techniques. CAR only introduces 7.20% performance difference compared to the MILP model and is more scalable to large-size ONoCs.

Improved thermal stability of luminescence by anion modification in Na2Y(MoO4)(PO4):Tb3+,Eu3+ red-emitting phosphors

Abstract Polyhedral anions have been used as supporting host structure to improve the luminescent properties of phosphors. However, the underlying mechanism for improving the thermal stability of luminescence by anion modification is rarely studied. In this paper, it was reported for the first time that thermal quenching and luminescent properties of red-emitting phosphors, Na2-nY(MoO4)1+n(PO4)1-n:Tb3+,Eu3+, can be adjusted by the ratio of acid radicals. Rietveld refinements and Debye temperature calculations show that the subtle replacement of [MoO4]2– by [PO4]3– results in the shrinkage of the crystal lattice and an improvement in lattice rigidity of the host, but does not change the crystal type. A detailed explanation of the mechanism for adjustable thermal stability of luminescence is provided via temperature-dependent X-ray diffraction, Raman, formation energy, and work function. The strategy of anion modification reveals an effective method for improving the thermal stability and tuning the luminescent spectra of phosphors, it also sheds light on the development of new phosphors. Furthermore, Na1.4Tb0.5(MoO4)1.6(PO4)0.4:0.5Eu3+ red-emitting phosphor with an internal quantum efficiency of 66.67% can be efficiently excited with blue light (465 nm) and the integrated intensity at 425 K is 86.4% of that at 300 K. The controllable local structure-dependent luminescence makes this novel red-emitting phosphor attractive for both blue and near-UV chips based WLEDs.

Thermal tuning of light-emitting diode wavelength as an implication of the Varshni equation

In this article, we show that the variation of the wavelength of a non-pumped light-emitting diode (LED) is practically linear with temperature, a novel consequence of Varshni's widely accepted empirical expression. This formula models the bandgap variation for most semiconductors from 0K to their high-temperature limits, subject to fitting parameters. Therefore, we suggest an external thermal mechanism that can be used to tune the wavelength of a constant-current biased LED and also to stabilize its wavelength. Furthermore, we demonstrate the approach on published AlN data and show that the fitting parameters follow trivially. In addition, we suggest a novel method to characterize semiconductors. Finally, we present the results of experimental measurements on several commercial LEDs.

Design of Hybrid Plasmonic Multi-Quantum-Well Electro-Reflective Modulators Towards <100 fJ/bit Photonic Links

Realization of on-board and inter-chip optical interconnects requires a photonic data link with power consumption well below their electrical counterparts (i.e., 50 Gb/s requires 2–4 pJ/bit/channel. External reverse-biased modulators could drastically reduce this power consumption. Here we design ultralow power GaAs/AlGaAs multi quantum well electro-reflective modulators operating at 1 V for facile integration with polymer “optical bridges”, utilizing coupled quantum confined Stark effect between adjacent quantum wells and optical coupling to hybrid surface plasmon-slab modes for significantly enhanced extinction ratio and spectral bandwidth. Distinctive from conventional electro-optical or electro-absorption modulators, this new design synergistically leverages ultra-large changes in both refractive index (|Δn|∼0.05) and absorption coefficient (Δα∼104 cm−1), achieving 35-50 dB extinction ratio at 1 V reverse bias with a low insertion loss of 1–3 dB, an incident angle tolerance of ∼5°, and a spectral bandwidth of 7–10 nm. The modulator power consumption is ∼1.9 fJ/bit without the need of thermal tuning, and the RC-limited bandwidth well exceeds 100 GHz. This new modulator enables high bandwidth and ultralow power optical interconnect networks at >100 Gb/s/channel and <100 fJ/bit/channel compatible with ever-scaling CMOS technologies.

Thermal Tuning of Plasmofluidic Disk Resonators Filled With a Liquid Crystal: Its Narrow-Trench Filling and Arrangement

Plasmonic waveguides are hybrid plasmonic waveguides based on strong light confinement in a fluid filling narrow trenches bounded by silicon and metal surfaces. They might be expected to work as a tunable device with a large phase change if (1) a liquid crystal (LC) fills such trenches, (2) the LC molecules are ideally aligned in the direction normal to the cross-sections of the trenches, and (3) they are electrically oriented in the direction normal to the surfaces. However, to our knowledge, even the first two assumptions have never been confirmed to be correct. Here, we investigate LC-filled plasmofluidic disk resonators to check the correctness of the assumptions. We show that their resonance wavelengths decrease as the LC temperature increases and that the resonance wavelengths decrease rapidly near the clearing point of the LC. This indicates that the 30-nm-wide trenches are really filled with the LC but that the LC molecules are oriented toward the direction normal to the surfaces. The real arrangement of the LC molecules in the trenches may make the phase change obtainable from the plasmofluidic waveguide about two times smaller than expected from the ideal arrangement. This work may lead to development of phase-tunable LC-filled plasmofluidic waveguide devices.

Narrow-linewidth thermally tuned multi-channel interference widely tunable semiconductor laser with thermal tuning power below 50 mW

A thermally tuned multi-channel interference widely tunable semiconductor laser is designed and demonstrated, for the first time to our knowledge, that realizes a tuning range of more than 45 nm, side-mode suppression ratios up to 56 dB, and Lorentzian linewidth below 160 kHz. AlGaInAs multiple quantum wells (MQWs) were used to reduce linewidth, which have a lower linewidth enhancement factor compared with InGaAsP MQWs. To decrease the power consumption of micro-heaters, air gaps were fabricated below the arm phase sections. For a 75 μm long suspended thermal tuning waveguide, about 6.3 mW micro-heater tuning power is needed for a 2 π round-trip phase change. Total micro-heater tuning power required is less than 50 mW across the whole tuning range, which is lower than that of the reported thermally tuned tunable semiconductor lasers.

Thermal design management of highly mechanically stable wavelength shifter using photonic crystal waveguide

Abstract A thermally tunable device based on photonic crystal waveguide integrated with the micro-hotplate on its surface is proposed. A design strategy for modelling of temperature and stress in the MHP is investigated for providing robustness and high mechanical stability in the reconfigurable device. The required temperature is obtained under stress elongation fatigue limit for thermal tuning applications in optical devices. The performance parameters like confinement factor, wavelength transfer coefficient and extinction ratio are obtained as 78.2%, 0.086 nm/K and 30.04 dB respectively with an excess loss of only 0.20 dB. The response-time in the optimized device is 12 μs for achieving the switching spectral shift of 26 nm in the transmission spectrum of PCW. The reconfigurable device platform offers a great potential for wide range of tuning in switches and filters applications

Actuation Dependency of Frequency Tuning in MEMS Resonators

This letter shows that active tuning of MEMS resonators through temperature is highly dependent on the actuation mechanism used, and demonstrates the adverse effects of using substrate conductive heating characterization results to predict device’s performance in their final application, where Joule heating is most likely to be used. A buckled VO2-based SiO2 tunable MEMS resonator is used in the study, where the thermal frequency stability or active tuning of the resonant frequency is thermally induced. The VO2 phase transition is triggered by substrate heating and Joule heating. When using Joule heating, the increasing strain energy during the phase transition results in a monotonic increase in resonant frequency, with a maximum resonant frequency shift of 11.9%. For substrate heating, the resonant frequency shift is non-monotonic and shows a 10.6% increase followed by a 7.8% decrease. The different frequency shift patterns that are observed for two heating mechanisms can be attributed to different stress-strain responses. [2019-0256]

Mid-infrared chalcogenide microfiber knot resonators

A novel type of mid-IR microresonator, the chalcogenide glass (ChG) microfiber knot resonator (MKR), is demonstrated, showing easy fabrication, fiber-compatible features, resonance tunability, and high robustness. ChG microfibers with typical diameters around 3 μm are taper-drawn from As 2 S 3 glass fibers and assembled into MKRs in liquid without surface damage. The measured Q factor of a typical 824 μm diameter ChG MKR is about 2.84 × 10 4 at the wavelength of 4469.14 nm. The free spectral range (FSR) of the MKR can be tuned from 2.0 nm (28.4 GHz) to 9.6 nm (135.9 GHz) by tightening the knot structure in liquid. Benefitting from the high thermal expansion coefficient of As 2 S 3 glass, the MKR exhibits a thermal tuning rate of 110 pm · ° C − 1 at the resonance peak. When embedded in polymethyl methacrylate (PMMA) film, a 551 μm diameter MKR retains a Q factor of 1.1 × 10 4 . The ChG MKRs demonstrated here are highly promising for resonator-based optical technologies and applications in the mid-IR spectral range.

SiOC-Coated Silicon Nitride Platform for Efficient Phase Actuators

In this paper, integration of silicon oxycarbide (SiOC) and silicon nitride (Si3N4) platforms was demonstrated to realize ultra-efficient thermal tuning of photonic integrated circuits. Si3N4 being a fascinating photonic material with moderate refractive index (n ≈ 2) and ultra-low loss, lacks thermo-optic coefficient that makes thermal phase actuators long and dissipate high powers. Integration of SiOC coating with a comparable refractive index (n = 2.2) boosts the effective thermo-optic efficiency of Si3N4 photonic circuits by almost an order of magnitude with no additional loss. An SiOC layer was deposited by the reactive RF magnetron sputtering technique from the SiC target at room temperature. The structural, chemical and optical characterizations of the sputter deposited SiOC layer were performed with SEM, AFM, EDS and spectroscopic ellipsometry. The results of SiOC-coated Si3N4 and pristine Si3N4 photonic devices were discussed and compared. SiOC was demonstrated as an enabling platform for low-loss and power-efficient thermal phase actuators in conventional photonic technologies with application in reconfigurable photonic systems.

Liquid‐Crystal‐Mediated Active Waveguides toward Programmable Integrated Optics

AbstractOptics, playing an ever‐important role in life, is developing toward miniaturization and integration. Particularly, the field programming of integrated optics will benefit its functionality and durability, thus is highly pursued. Here, through precisely controlling the space‐variant orientations of anisotropic liquid crystals (LCs), various graded‐index waveguides are demonstrated in a homogeneous medium. Straight/bending waveguides and ring resonators are fabricated via LC photopatterning. They exhibit pronounced polychromatic light‐guiding performance. Thanks to their intrinsic external‐stimuli responsivity, the thermal switchability and polarization tunability are verified. By selectively polymerizing, robust functional components and active connecting waveguides can be realized on the same chip. It provides a practical and universal solution to programmable integrated optics, and extends the applications of microstructured soft matter even in wearable photonics.

Enhanced Thermally Tunable Optical Filter and its Applications in Erbium-Doped Fiber Lasers

In this letter, an enhanced thermally tunable filter design based on a stack of three layers and a long external sleeve at the tip of a single mode fiber is presented. Here, two of these layers and the sleeve are thermo-sensitive. Moreover, it is shown that by using the sleeve with a large length compared with the thicknesses of the layers, the thermal tuning mechanism can be considerably enhanced. Furthermore, the mathematical model of the enhanced filter is presented and it is experimentally supported. Finally, a tunable single-wavelength erbium doped fiber laser based on this filter was implemented. This laser can be tuned ~19 nm by applying a temperature change of just 2.7°C achieving a resolution of 6.89 nm/°C.

Tunable, Single-Wavelength Fiber Ring Lasers Based on Rare Earth-Doped, Double-Peanut Fiber Interferometers

Single-wavelength fiber ring lasers are demonstrated using rare earth-doped, double-peanut fiber interferometers (RD-DPFIs) as the tunable narrow-band filters. With the relatively stronger opto-thermal effect, thermal tunability of the Ytterbium-doped DPFI (YD-DPFI) is effectively enhanced, as compared to the Erbium-doped DPFI (ED-DPFI). The ED-DPFI achieves single-wavelength lasing with a side-mode suppression ratio (SMSR) of a50 dB, a 3 dB bandwidth of <0.02 nm, and a wavelength tuning range from 1531.92–1544.28 nm. The YD-DPFI achieves a single-wavelength lasing with a SMSR of a40 dB, a 3 dB bandwidth of <0.04 nm, and a wavelength tuning range from 1036.50–1027.25 nm. In addition, laser output stabilities are also investigated. The proposed lasers have high stability and cost-effectiveness which may be useful for optical communication and sensing systems.

Design of a broadband Ge1-xSix electro-absorption modulator based on the Franz-Keldysh effect with thermal tuning.

We present the design of an adiabatic taper coupled Ge1-xSix electro-absorption modulator, which is based on Franz-Keldysh effect. The device has an active region of 0.8×50 µm2, an extinction ratio of more than 6 dB and an insertion loss less than 3 dB at the wavelength of 1550 nm. The operating bandwidth can be broadened to more than 90 nm by an AlN block assisted heater with only 6.2 mW energy consumption. Moreover, the operating wavelength shift caused by material composition deviation can be compensated to the expected wavelength by thermal tuning. This design may play an important role in next-generation, high-density optical integrations for datacom and high-performance computing.

Wideband Electrically Controlled Vernier Frequency Tunable Terahertz Quantum Cascade Laser

Frequency tuning in terahertz frequency quantum cascade lasers is challenging because of low thermal and current tuning coefficients. Moreover, photonic designs like Vernier selection based sampled...

All-optical tuning of a diamond micro-disk resonator on silicon

High-quality integrated diamond photonic devices have previously been demonstrated in applications from non-linear photonics to on-chip quantum optics. However, the small sample sizes of single crystal material available, and the difficulty in tuning its optical properties, are barriers to the scaling of these technologies. Both of these issues can be addressed by integrating micrometer-scale diamond devices onto host photonic integrated circuits using a highly accurate micro-assembly method. In this work a diamond micro-disk resonator is integrated with a standard single-mode silicon-on-insulator waveguide, exhibiting an average loaded Q -factor of 3.1 × 10 4 across a range of spatial modes, with a maximum loaded Q -factor of 1.05 × 10 5 . The micrometer-scale device size and high thermal impedance of the silica interface layer allow for significant thermal loading and continuous resonant wavelength tuning across a 450 pm range using a milliwatt-level optical pump. This diamond-on-demand integration technique paves the way for tunable devices coupled across large-scale photonic circuits.

Tunable anomalous Hall conductivity through volume-wise magnetic competition in a topological kagome magnet

Magnetic topological phases of quantum matter are an emerging frontier in physics and material science. Along these lines, several kagome magnets have appeared as the most promising platforms. Here, we explore magnetic correlations in the kagome magnet Co3Sn2S2. Using muon spin-rotation, we present evidence for competing magnetic orders in the kagome lattice of this compound. Our results show that while the sample exhibits an out-of-plane ferromagnetic ground state, an in-plane antiferromagnetic state appears at temperatures above 90 K, eventually attaining a volume fraction of 80% around 170 K, before reaching a non-magnetic state. Strikingly, the reduction of the anomalous Hall conductivity (AHC) above 90 K linearly follows the disappearance of the volume fraction of the ferromagnetic state. We further show that the competition of these magnetic phases is tunable through applying either an external magnetic field or hydrostatic pressure. Our results taken together suggest the thermal and quantum tuning of Berry curvature induced AHC via external tuning of magnetic order.

Broadly tunable and low power penalty radio frequency phase shifter using a coupled silicon microcavity.

We present a continuously tunable silicon photonics assisted radio frequency (RF) phase shifter using a coupled microring resonator. Using the coupled cavity, we demonstrate a sub-1 dB power penalty for a RF bandwidth of 34.5 GHz (9-43.5 GHz) and a phase shift of π over the reported frequency range. Rigorous optimization of the cavity design using the coupled-mode theory is carried out to realize ultranarrow resonance peaks with a low-extinction ratio and large phase shift. Thermal tuning of the cavity is used to tune the phase while all-optical tuning is exploited to achieve broadband operation. We present a detailed simulation and experimental study of the proposed configuration. The proposed device configuration exhibits a configurable resonance linewidth and extinction ratio that allows for a broad bandwidth and an extremely low power penalty microwave phase shifter. We believe the demonstration would allow better integration of the on-chip functional elements of integrated microwave photonics.

Silicon-based flexible-grid mode- and wavelength-selective switch utilizing microring resonators and Y-junctions

In this article, a design of integrated flexible-grid mode- and wavelength-selective switch consisting of silicon-based symmetric Y-junctions and double-series coupled microring resonators with interferometric couplers is introduced in detail. Using thermal tuning, the described device is capable of routing each mode and wavelength signal from the input port to any output port flexibly and independently, forming different bandwidths as needed. For fixed field coupling coefficients, the device can support multiple different wavelength-channel spacings. A silicon-based flexible-grid 1 × 6 mode- and wavelength-selective switch is carefully designed and analyzed as an example. The designed device works for two mode channels and three wavelength channels. The wavelength-channel spacing can vary from 0.10 to 0.80 nm and the 3-dB bandwidth changes from 0.08 to 2.00 nm. When the wavelength-channel spacing is set to be 0.80 nm, the extinction ratio is greater than 50.90 dB and the crosstalk is less than −15.36 dB.

Fully Reconfigurable Waveguide Bragg Gratings for Programmable Photonic Signal Processing

Fiber Bragg gratings have been invented for over three decades now and have been intensively employed in optical communication and sensor systems. The key limitation of a fiber Bragg grating is that once fabricated, it is hard to be tuned or with very limited tunability via thermal or mechanical tuning. Recently, great efforts have been directed into the study of realizing Bragg gratings on silicon-on-insulator (SOI) platform. The key advantage of Bragg gratings based on SOI is that the gratings can be fast and electrically reconfigured with the use of free-carrier plasma dispersion effect in silicon, which can be employed for fast programmable photonic signal processing. In this article, Bragg gratings based on SOI that are electrically programmable will be reviewed and their use for advanced programmable optical and microwave signal processing will be discussed.