Suspended ring resonators formed by both single-mode waveguide (SMW) and multi-mode waveguide (MMW) are designed, fabricated and characterized near 3.4 μm by thermal tuning and near 4.5 μm and 5.2 μm by tunable quantum cascade lasers. The dispersion property is analyzed by simulation in regards to frequency comb generation. The taper width is optimized for maximum coupling. Measurement setup is built up and described. For the SMW ring resonator, the intrinsic quality factor is fitted to be 6,800 and 16,000 near 5.2 μm and 4.5 μm, respectively. For the MMW ring resonator, it rises to 35,000 near 4.5 μm. Transmission spectrum distortion is observed at high input power, and is modeled as heat effect. Thermal tuning rate is experimentally confirmed at 0.21 nm/°C. Based on the measured distortion and heat simulation, absorption loss is estimated. All-optical modulation is conducted to estimate the response time of this process. It can be shown that main loss is from surface thus is reducible by improving surface quality. On-chip electrical heater is designed and preliminary experiment indicate the feasibility to pattern it with our Electron Beam Lithography system.