Thermo-optic Effect Of Silicon Research Articles

Thermal near-field tuning of silicon Mie nanoparticles

Abstract Tunable high-refractive-index nanostructures are highly desired for realizing photonic devices with a compact footprint. By harnessing the large thermo-optic effect in silicon, we show reversible and wide thermal tuning of both the far- and near-fields of Mie resonances in isolated silicon nanospheres in the visible range. We perform in situ heating in a transmission electron microscope and electron energy-loss spectroscopy to show that the Mie resonances exhibit large spectral shifts upon heating. We leverage the spectral shifts to demonstrate near-field tuning between different Mie resonances. By combining electron energy-loss spectroscopy with energy-dispersive X-ray analysis, we show a reversible and stable operation of single silicon nanospheres up to a temperature of 1073 K. Our results demonstrate that thermal actuation offers dynamic near-field tuning of Mie resonances, which may open up applications in tunable nonlinear optics, Raman scattering, and light emission.

Design and fabrication of wavelength tunable AWGs based on the thermo-optic effect

In this Letter, a 16 channel 200 GHz wavelength tunable arrayed waveguide grating (AWG) is designed and fabricated based on the silicon on insulator platform. Considering that the performance of the AWG, such as central wavelength and crosstalk, is sensitive to the dimension variation of waveguides, the error analysis of the AWG with width fluctuations is worked out using the transfer function method. A heater is designed to realize the wavelength tunability of the AWG based on the thermo-optic effect of silicon. The measured results show that the insertion loss of the AWG is about 6 dB, and the crosstalk is 7.5 dB. The wavelength tunability of 1.1 nm is achieved at 276 mW power consumption, and more wavelength shifts will gain at larger power consumption.

On-Chip Mid-Infrared Photothermal Spectroscopy Using Suspended Silicon-on-Insulator Microring Resonators

Mid-infrared spectroscopic techniques rely on the specific ”fingerprint” absorption lines of molecules in the mid-infrared band to detect the presence and concentration of these molecules. Despite being very sensitive and selective, bulky and expensive equipment such as cooled mid-infrared detectors is required for conventional systems. In this paper, we demonstrate a miniature CMOS-compatible Silicon-on-Insulator (SOI) photothermal transducer for mid-infrared spectroscopy which can potentially be made in high volumes and at a low cost. The optical absorption of an analyte in the mid-infrared wavelength range (3.25–3.6 μm) is thermally transduced to an optical transmission change of a microring resonator through the thermo-optic effect in silicon. The photothermal signal is further enhanced by locally removing the silicon substrate beneath the transducer, hereby increasing the effective thermal isolation by a factor of 40. As a proof-of-concept, the absorption spectrum of a polymer that has been locally p...

Tunable Grating Couplers for Broadband Operation Using Thermo-Optic Effect in Silicon

We demonstrate a tunable grating coupler for broadband operation using an impurity-doped thermo-optic heater fabricated by complementary metal–oxide–semiconductor-compatible processes. As a thermo-optic heater, a p-n diode is employed to have a p-type region inside of an in-coupling grating connected with outside p+/n+ contacts and is heated directly by a current flow through the grating. Applying a forward-bias voltage of 7 V, we shift the central wavelength of the grating coupler from 1525 to 1574 nm with a coupling efficiency of close to −4 dB. Considering a 1-dB bandwidth at each central wavelength, we extend the operational bandwidth to nearly 90 nm. A thermal tuning efficiency of 0.23 nm/mW and transient responses of 32/ $22~\mu \text{s}$ for heating/cooling times are obtained.

Design of thermo-optic tunable optical filter based on Si/Air DBR and polymer Fabry–Perot microcavity in SOI

An integrated tunable optical filter (TOF) based on thermo-optic effect in silicon on insulator (SOI) rib waveguide is designed and simulated. The device is comprised of two high refractivity contrast Si/Air stacks, functioning as high reflectivity of DBRs (distributed Bragg reflectors) and separating by a variable refractive index polymer Fabry–Perot (F–P) cavity. The designed device exhibits Q=24077, FWHM=0.065nm and finesse=566. Wavelength tuning is achieved through thermal modulation of refractive variation of the cavity. As the cavity polymer is heated, the refractive index of the cavity decreases. When the temperature of cavity polymer changes within 105, the central wavelength gets a continuous 35nm shift from 1530nm to 1565nm, which can operate the whole C-band in the WDM (wavelength division multiplexing) networks. Moreover, by calculating, the tuning sensitivity is about 0.33nm/°C. Owing to the compact size and excellent characteristics of integration, the proposed component has a promising utilization in spectroscopy and optical communication.

Fano resonances in integrated silicon Bragg reflectors for sensing applications

We investigate theoretically and experimentally Fano resonances in integrated silicon Bragg reflectors. These asymmetric resonances are obtained by interference between light reflected from the Bragg waveguide and from the end facet. The Bragg reflectors were designed and modeled using the 1D transfer matrix method, and they were fabricated in standard silicon wafers using a CMOS-compatible process. The results show that the shape and asymmetry of the Fano resonances depend on the relative phase of the reflected light from the Bragg reflectors and end facet. This phase relationship can be controlled to optimize the lineshapes for sensing applications. Temperature sensing in these integrated Bragg reflectors are experimentally demonstrated with a temperature sensitivity of 77 pm/°C based on the thermo-optic effect of silicon.

Thermo-Optic Tunable Optical Filter Based on Fabry-Perot Microcavities in SOI

An integrated TOF (Tunable Optical Filter) based on thermo-optic effect in Silicon on insulator (SOI) rib waveguide is designed and simulated. The device is comprised of two high refractivity contrast Si/Air stacks, functioning as high reflectivity of DBRs and separated by a variable refractive index Si F-P cavity. The output characteristics are calculated and simulated based on Transfer Matrix Method (TMM). Wavelength tuning is achieved through thermal modulation of refractive variation of the cavity.As the cavity Si is heated,the refractive index of the cavity increases.When the temperature of cavity Si changes within100°C，the central wavelength gets a continuous 8nm shift from 1550nm to 1558nm, which is right located in the WDM (Wavelength division multiplexing) networks operating at C-band. Moreover, by calculating, the tuning sensitivity is about 0.08nm/°C. Owing to the compact size and excellent characteristics of integration, the proposed component has a promising utilization in spectroscopy and optical communication.

Miniature 10 kHz thermo-optic delay line in silicon

The scanning delay line is a key component of time-domain optical coherence tomography systems. It has evolved since its inception toward higher scan rates and simpler implementation. However, existing approaches still suffer from drawbacks in terms of size, cost, and complexity, and they are not suitable for implementation using integrated optics. In this Letter, we report a rapid scanning delay line based on the thermo-optic effect of silicon at λ = 1.3 μm manufactured around a generic planar lightwave circuit technology. The reported device attained line scan rates of 10 kHz and demonstrated a scan range of 0.95 mm without suffering any observable loss of resolution (15 µm FWHM) owing to depth-dependent chromatic dispersion.

Optimization of metallic microheaters for high-speed reconfigurable silicon photonics

The strong thermooptic effect in silicon enables low-power and low-loss reconfiguration of large-scale silicon photonics. Thermal reconfiguration through the integration of metallic microheaters has been one of the more widely used reconfiguration techniques in silicon photonics. In this paper, structural and material optimizations are carried out through heat transport modeling to improve the reconfiguration speed of such devices, and the results are experimentally verified. Around 4 micros reconfiguration time are shown for the optimized structures. Moreover, sub-microsecond reconfiguration time is experimentally demonstrated through the pulsed excitation of the microheaters. The limitation of this pulsed excitation scheme is also discussed through an accurate system-level model developed for the microheater response.

Low power and compact reconfigurable multiplexing devices based on silicon microring resonators

We present thermally reconfigurable multiplexing devices based on silicon microring resonators with low tuning power and low thermal crosstalk. Micro-heaters on top of the rings are employed to tune the resonant wavelengths through the thermo-optic effect of silicon. We achieve a low tuning power of 21 mW per free spectral range for a single ring by exploiting thermal isolation trenches close to the ring waveguides. Negligible thermal crosstalk is demonstrated for rings spaced by 15 microm, enabling compact multiplexing devices. The tuning time constant is demonstrated to be less than 10 micros.

1$\,\times\,$4 Wavelength Reconfigurable Photonic Switch Using Thermally Tuned Microring Resonators Fabricated on Silicon Substrate

Micro-ring resonators have been traditionally fabricated using expensive III-V materials such as InP or GaAs. Device tuning is typically to utilize the electro-optic effect of the III-V materials that usually leads to complex device layer structures. As another tuning approach, thermo-optic tuning of micro-ring resonators is commonly achieved by heating up the whole chip. In general, it is more challenging to achieve highly localized heating on a common chip for independent tuning of multiple micro-ring resonators residing on the same substrate. To address these issues, we describe the development of wavelength reconfigurable photonic switching using thermally tuned micro-ring resonators fabricated on a low-cost silicon-on-insulator substrate. Independent tuning of multiple micro-ring resonators, spaced at 250 µm, is realized with highly localized micro heaters (50×50 µm 2 per heater area) fabricated on the same silicon substrate. Owing to the large thermo-optic effect of silicon (∆n/∆T=1.8×10 -4 K -1 ), 8 mA heating current is sufficient to tune a micro-ring resonator with a 3-dB spectral line width of 0.1 nm by 2.5 nm while creating a minor peak shift of less than 0.04 nm for an adjacent resonator. The switching response time is about 1 ms. A 1×4 wavelength reconfigurable photonic switch device has been demonstrated. With a resonator diameter of approximately 10 µm (greater than 18 nm in free spectral range of each micro-ring resonator), larger port-count switch matrix with wavelength reconfiguration on a small device foot print is feasible for the development of large-scale integrated photonics.

Temperature dependence analysis of the thermo-optic effect in silicon by single and double oscillator models

The thermo-optic coefficient (dn/dT) of crystalline silicon has been critically analyzed in the temperature range 300–600 K, at the fiber optic communication wavelength of 1.5 μm. The temperature dependence has been attributed to the variation of the interband transition energies at some critical points of the silicon band structure. The experimental data have been fitted using single and double oscillator models. In particular, the double oscillator model, which is physically correlated to the silicon band structure, has been exploited to extrapolate the temperature dependence of the interband transition energies at some points (critical points) of the combined density of states. The extracted parameters are in good agreement with the data reported in the literature. Finally, in connection with both of the oscillator approximations, an analysis based on thermodynamic considerations is carried out, and electron–hole formation entropy and specific heat are calculated. The consistency of the obtained results validate the reliability of the proposed analysis.

Thermo-optic effect exploitation in silicon microstructures

The strong thermo-optic effect in silicon has been exploited for the fabrication of new sensing and communication devices. A temperature sensor, an electromagnetic energy sensor and an optical modulator are in particular presented. These devices, all working on interferometric principles, have been realized by means of the silicon standard microelectronic technologies, and are therefore suitable for full integration with on-chip circuitry. New thermo-optical materials are finally proposed with superior characteriztics, which still maintain the compatibility with VLSI technology.

Thermo-optical modulation at 1.5μm in silicon etalon

Experimental results on thermo-optical induced modulation in a silicon etalon at 1.5/m are reported. The measurements have also allowed an accurate determination of the thermooptic effect in silicon at this wavelength.