Gun-Duk Kim

Silicon photonic temperature sensor employing a ring resonator manufactured using a standard CMOS process

An ultra-small integrated photonic temperature sensor has been proposed and demonstrated which incorporates a silicon ring resonator linked to a vertical grating coupler. It was manufactured using a 0.18 μm standard CMOS process, rendering a homogeneous integration into other electrical/optical devices. The temperature variation was measured by monitoring the shift in the resonant wavelength of the silicon resonator, which was induced by the thermo-optic effect and the thermal expansion effect. The dependence of its sensing capability upon the waveguide width of the resonator was intensively probed both theoretically and experimentally. The best achieved sensitivity was about 83 pm/°C for a waveguide width of 500 nm, while the sensitivity was boosted by ~10 pm/°C by adjusting the waveguide width from 300 nm to 500 nm. Finally, the response speed of the sensor was as fast as ~6 μs.

Hybrid Si-LiNbO 3 microring electro-optically tunable resonators for active photonic devices

Hybrid Si-LiNbO₃ electro-optic tunable ring resonators have been proposed and demonstrated as a path to achieving ultracompact and high-speed electro-optic devices. Free standing single crystal LiNbO₃ microplatelets (~mm long and ~1 μm thick) were obtained from a z-cut LiNbO₃ substrate by ion implantation and thermal treatment. The platelets were transferred and thermally bonded on top of Si resonators that were fabricated in a Si-on-insulator platform by a 0.18 μm standard complementary metal-oxide-semiconductor process. For the hybrid microring resonator, a free spectral range of 16.5 nm, a finesse F of ~1.67 × 10², a Q-factor of ~1.68 × 10⁴, and an effective r coefficient of ~1.7 pm/V were achieved for the TE mode. These values are in good agreement with the calculated results.

Photonic Microwave Channel Selective Filter Incorporating a Thermooptic Switch Based on Tunable Ring Resonators

A photonic microwave (MW) channel selective filter was demonstrated incorporating a 1times2 switch based on two tunable polymeric resonators with different free-spectral ranges (FSRs). Each resonator plays a role as an ON-OFF switch through the thermooptic effect, consisting of two cascaded rings with an electrode formed on one of them. The optical signal carrying the MW signal is routed to either port of the switch and detected to exhibit the filtered output at the frequency determined by the FSR of the corresponding resonator. When the channel centered at 10 GHz was chosen, the extinction ratio was ~30 dB, the bandwidth 1 GHz, and the electrical power consumption 4.1 mW. And for the other channel located at 20 GHz, we have achieved the extinction ratio of ~30 dB, the bandwidth of 2 GHz, and the required power of 8.0 mW. Finally, the crosstalk between the selected and blocked channels was higher than 24 dB.

Refractometric sensor utilizing a vertically coupled polymeric microdisk resonator incorporating a high refractive index overlay.

A refractometric sensor resorting to a vertically coupled polymeric microdisk resonator was demonstrated, estimating the refractive index (RI) of an analyte by monitoring the resonant wavelength shift in its transfer characteristics. The disk resonator was especially overlaid with a high RI TiO2 film, thereby reinforcing the interaction of the evanescent field of its guided mode with the analyte. The sensitivity of the sensor was theoretically and experimentally confirmed to be enhanced by adjusting the overlay thickness. The fabricated sensor provided the maximum sensitivity of approximately 294 nm/RIU (refractive index unit) with the 40-nm-thick overlay, which is equivalent to an improvement of 150% compared with the case without the overlay.

Temperature Compensated Refractometric Biosensor Exploiting Ring Resonators

A temperature compensated refractometric biosensor in polymeric waveguides was demonstrated by integrating a vertically coupled ring resonator with a laterally coupled ring resonator playing the role of monitoring the temperature. The proposed main sensing part was evaluated by observing the concentration of an aqueous glucose solution, and it was found to work decently around room temperature, yielding the sensitivity of ~120 pm/(g/dL), and the temperature monitoring part offered a temperature sensitivity of -172 pm/degC. With the help of the temperature compensation, the measurement error of the main sensor resulting from the temperature variation was substantially reduced from 1.33 (g/dL)/degC down to 0.03 (g/dL)/degC.

Tunable-Resonator-Based Temperature Sensor Interrogated through Optical Power Detection

An interrogation scheme based on optical power monitoring was proposed and implemented to demonstrate a compact photonic temperature sensor, which incorporates a tunable silicon resonator with a heating electrode, a single-wavelength light source, and a photodetector. The temperature is basically determined by tracking the notch of the resonator, which is displaced by the thermal effects. By utilizing the proposed interrogation scheme, which did not require any complex spectral scanning, the ambient temperature was successfully estimated with a resolution of better than 0.1 °C over the range of 20 to 50 °C, and the electrical power consumption was ~600 mW.

Ultra Small Silicon Resonator Based Temperature Sensor

An ultra small temperature sensor was proposed and implemented utilizing a silicon ring resonator with a 4-?m ring radius. The observed sensitivity was ~85 pm/ o C over the 38 o C range around the room temperature.

Highly Sensitive Integrated Photonic Temperature Sensor Exploiting a Polymeric Microring Resonator

A highly sensitive integrated photonic temperature sensor was proposed and developed incorporating a polymeric microring resonator. The change in the ambient temperature was estimated by observing the shift in the resonant wavelength of the resonator induced via the thermooptic effect. For the purpose of enhancing its sensitivity, the sensor was built by implementing a polymeric resonator exhibiting a high thermooptic coefficient on a silicon substrate with a small coefficient of thermal expansion. For the range of from to near the room temperature, the fabricated sensor yielded a sensitivity of as high as 165 and a resolution of better than . And its performance was found to be hardly affected by the variation in the refractive index of the target analyte, which was applied to the surface of the sensor. It is hence expected that the sensor could be integrated with other refractormetric optical sensors, thereby compensating for the fatal error caused by the change in the ambient temperature.

Hybrid Si-LiNbO 3 micro-ring resonators for active microphotonic devices

A hybrid structure of Si-LiNbO3 micro-ring resonator was fabricated. Free standing single crystal LiNbO3 microplatelets (mm long and 1 um thick) were obtained from a bulk LiNbO3 wafer by ion implantation and thermal shock. They were then transferred, positioned and bonded to Si micro-ring structure. In this hybrid structure, a large portion of the TM field is located above and below the Si waveguide. Then, the effective index of the Si waveguide can be changed by varying the refractive index of the LiNbO3 cladding layer. Theoretical calculation with finite difference method proved that the ratio between effective index change of the Si waveguide and index change of LiNbO3 cladding layer was 0.31 (ΔnSi/ΔnLNO=0.31) for TM mode. Then, calculated ΔnSi was about 1×10-4 with 3 V. The effective r coefficient of Si and tuning sensitivity were about 7.2 pm/V and 2.55 GHz/V, respectively. These values are comparable to current active Si photonics with plasma dispersion methods. In addition, high speed modulation (over 40 GHz) is possible in this hybrid structure. This demonstration of a single crystalline LiNbO3 acting as the upper cladding shows the possibility of integrating a very good EO and NLO material into the silicon-on-insulator photonics technology.

Photonic temperature sensor based on an active silicon resonator manufactured using a CMOS process

A photonic temperature sensor based on an active silicon CMOS resonator was proposed and built. It features a simple measurement scheme, a high sensitivity and a wide operation range.