Reducing the temperature sensitivity of SOI waveguide-based biosensors

Abstract

Label-free photonic biosensors fabricated on silicon-on-insulator (SOI) can provide compact size, high evanescent field strength at the silicon waveguide surface, and volume fabrication potential. However, due to the large thermo optic coefficient of water-based biosamples, the sensors are temperature-sensitive. Consequently, active temperature control is usually used. However, for low cost applications, active temperature control is often not feasible.Here, we use the opposite polarity of the thermo-optic coefficients of silicon and water to demonstrate a photonic slot waveguide with a distribution of power between sample and silicon that aims to give athermal operation in water.Based on simulations, we made three waveguide designs close to the athermal point, and asymmetric integrated MachZehnder interferometers for their characterization. The devices were fabricated on SOI with a 220 nm device layer and 2 µm buried oxide, by electron beam lithography of hydrogen silsesquioxane (HSQ) resist, and etching in a Cl 2 /HBr/O 2 /He plasma. With Cargile 50350 fused silica matching oil as top cladding, the group index of the three guides varies from 1.9 to 2.8 at 1550 nm. The temperature sensitivity of the devices varied from -70 to -160 pm/K under the same conditions. A temperature sensitivity of -2 pm/K is projected with water as top cladding.

Two-channel highly sensitive sensors based on 4 × 4 multimode interference couplers

“…In order to overcome the effect of the temperature and phase fluctuations, we can use some approaches including both active and passive methods. For example, the local heating of silicon itself to dynamically compensate for any temperature fluctuations [29], material cladding with negative thermo-optic coefficient [30][31][32][33], MZI cascading intensity interrogation [34], control of the thermal drift by tailoring the degree of optical confinement in silicon waveguides with different waveguide widths [35], and ultra-thin silicon waveguides [36] can be used for reducing the thermal drift.…”

Silicon-Nanowire-Based 100-GHz-Spaced 16λ DWDM, 800-GHz-Spaced 8λ LR-8, and 20-nm-Spaced 4λ CWDM Optical Demultiplexers for High-Density Interconnects in Datacenters

“…In the measurement of the single-mode fiber-based optical transmittance of the fabricated devices, the temperature of the device was controlled to 25 degrees Celsius. It has been well known that, compared with the case for silicon dioxide, the refractive index change for single-crystalline silicon is much more sensitive to external temperature variation by a factor of 10 [65][66][67][68]. Since silicon has a relatively large thermo-optic coefficient of 1.8 × 10 −4 [1/K] [65], the filter spectral peak for various kinds of optical DeMUXs tends to shift to the longer wavelength side by up to 0.07 [nm/K] as the temperature increases.…”

Athermal optical waveguide microring biosensor with intensity interrogation

“…The first one is to utilize the opposite thermo optic coefficients (TOCs, dn/dT) of the water solution (dn/dT: $ À10 À 4 /K [11]) and the waveguide core (Si 3 N 4 , SiO 2 : $10 À 5 /K [12]; Si: $ 10 À 4 /K [13]), which is derived from the athermalization of optical waveguide filter devices with the negative TOC of polymer or TiO 2 as the upper cladding [14][15][16]. In [17] the slot waveguide of silicon-on-isolator (SOI) was proposed to distribute properly the optical power between sample and silicon aiming to give athermal operation. However, the optimal structure for athermal operation does not work for high sensitivity.…”