In this paper, a ratiometric wavelength monitor at around 1550 nm based on the passive Silicon-on-Insulator (SOI) integrated device is proposed, theoretically investigated and fabricated. This monitor is made of a single Mach-Zehnder Interferometer (MZI) with direction coupler acting as edge filter. The ouput spectral response is designed to be ‘X-type’. The device shows a resolution of better than 0.4 nm over the wavelength range from 1505 nm to 1585 nm with a discrimination range of 30.5 dB from 15.5 dB to -15dB, which is suitable for wavelength measurement. Based on the single mode principle, the waveguide has a 220 nm×500 nm cross section for TM-polarized mode, and the total chip size is only 18 um×20 um. In conclusion, this proposed ratiometric wavelength monitor based on a single Mach-Zehnder Interferometer on SOI platform can realize the excellent resolution over large wavelength range.
A method for measuring blood oxygenation and blood flow rate using a single widely tunable semiconductor laser is proposed and investigated. It is shown that a 700-nm-band tunable laser gives the highest sensitivity for blood oxygen measurement. The corresponding tunable laser is designed using the V-coupled cavity structure. The wavelength tuning range can reach 8 nm, which is sufficient for the blood oxygenation measurement in the 700-nm-band by using the Beer- Lambert law. In contrast to conventional blood oxygenation measurement method based on two LEDs, the laser can be used at the same time to measure the blood flow rate based on the Doppler principle.
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