Optical Waveguide-Type Laser Interference Velocimeter for Measurement of Ultra-Low Speeds

An integrated optical waveguide-type laser velocimeter has been proposed and demonstrated at the central wavelength of 1550 nm. The micro-fabricated and photo-lithographically defined the integrated sensor head has dimensions in the range of 0.25 mm $\times3.50$ mm. The velocities in the range of $5.0\times 10 ^{-2} \mu \text{m}\cdot \text{s}$ ⁻¹ to $2.2\times 10\,\,^{6} \mu \text{m}\cdot \text{s}$ ⁻¹ , and a resolution of $5.0\times 10\,\,^{-2} \mu \text{m}\cdot \text{s}$ ⁻¹ have been achieved in the experiment. Through three experimental measurements and data calculation in the measured velocity range, the average relative error is less than 0.52%. This small size semiconductor sensor velocimeter uses semiconductor materials (silicon dioxide, SiO ₂ ) to make key sensor elements. The refractive indexes of waveguide core, upper cladding and lower cladding material are 1.448, 1.442 and 1.444. The optical interference fringes were used for velocity measurement, and the collected scattered light signal was used for velocity analysis. The apparent advantages of small size, high precision with large dynamic range, low cost, and high batch-fabrication uniformity make the velocimeter suitable for non-invasive measurement of ultra-low speeds of gases, liquids or solids at the near-surface.