We propose a design for silicon-on-chip integrated eight-channel wavelength division multiplexing (WDM) demultiplexer, which consists of parallel-arrayed one-dimensional (1-D) photonic crystal nanobeam cavities (PCNCs) with high-Q over 105 and large free spectral range of ∼200 nm. To the best of our knowledge, this is for the first time that a 1-D PCNC-based demultiplexer is presented. The performance of the device is investigated theoretically by using three-dimensional finite-difference time-domain method. To enable eight-channel parallel arrayed 1-D PCNCs to be coupled to on-chip optical networks for higher integration and multiplex application, an 1 × 8 taper-type equal optical power splitter is used to connect all channels simultaneously. The total device footprint is as small as 12 μm × 15 μm (width × length), which is decreased by five times compared to that per channel in the recent two-dimensional (2-D) PC-based demultiplexer. Moreover, the average channel spacing smaller than 115 GHz is achieved, which is more than two times smaller than that of 2-D PC nanocavity devices, demonstrating that the arrayed nanocavities have the potential for developing ultracompact 100-GHz spaced filters in a dense WDM system. Thus, we believe that the results demonstrated in this work is promising for the future on-chip photonics integrated circuits and optical communication systems.
Recently, due to its superior characteristics and simple manufacture, such as small size, low loss, high sensitivity and convenience to couple, the optical fiber sensor has become one of the most promising sensors. In order to achieve the most effective realization of light propagation by changing the structure of sensors, FOM(S •Q/λres) ,which is determined by two significant variables Q-factor and sensitivity, as a trade-off parameter should be optimized to a high value. In typical sensors, a high Q can be achieved by confining the optical field in the high refractive index dielectric region to make an interaction between analytes and evanescent field of the resonant mode. However, the ignored sensitivity is relatively low with a high Q achieved, which means that the resonant wavelength shift changes non-obviously when the refractive index increases. Meanwhile, the sensitivity also leads to a less desirable FOM. Therefore, a gradient structure, which can enhance the performance of sensors by achieving high Q and high sensitivity, has been developed by Kim et al. later. Here, by introducing parabolic-tapered structure, the light field localized overlaps strongly and sufficiently with analytes. And based on a one-dimensional photonic-crystal nanofiber air-mode cavity, a creative optical fiber sensor is proposed by combining good stability and transmission characteristics of fiber and strengths of tapered structure, realizing excellent FOM ~4.7 x 105 with high Q-factors (Q~106) and high sensitivities (<700 nm/RIU).
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