We propose to introduce a phase shift in each ring of the multi-stage interleavers based on add-drop resonator Mach–Zehnder interferometer to quantitatively measure the wavelength offset of each interleaver, thus a demultiplexer with uniformly segmented multi-channel output can be obtained. It is found that the additional phase of a certain interleaver is equal to the offset value of this stage plus the accumulated offset value of all previous stages. Following this rule, the quantitative cascade rule can be summarized, and theoretically an infinite-channel demultiplexer will be obtained. Combining fine-tuning and thermal tuning machining method, this cascade rule can guide the fabrication of stable and tunable demultiplexers in the integrated silicon photonics technology. Our method will provide a potential application for the fabrication of dense wavelength-division multiplexing systems with ultra-large capacity.
A vector curvature sensor based on a single fiber Bragg grating (FBG) is proposed and experimentally demonstrated. The sensor is easily fabricated by encapsulating an FBG on a thin steel plate with ultraviolet glue. When the FBG deviates from the neutral plane, its effective refractive index and grating constant are changed by bending, therefore, the sensor can realize curvature measurement. Due to the opposite stress direction on the two sides of the neutral plane during bending, the sensor can realize vector measurement of curvature. The curvature sensitivity of the sensor in convex and concave bending is 558.42 pm/m-1 and -818.09 pm/m-1, respectively. This sensor has the advantage of simple structure, low cost, and easy industrial production. It has potential applications in engineering health monitoring and deformation measurement.