A narrow-band add-drop filter based on an anti-symmetric cladding-modulated multimode Bragg grating (CMMBG) is demonstrated on the silicon-on-insulator (SOI) platform. The CMMBG is implemented by using periodic placements of silicon cubes along a multimode waveguide. The coupling strength is varied by changing the distance between the cubes and the multimode waveguide. An unlimited free-spectral range (FSR) and weak coupling strengths for TE0-TE1 modes conversion are achieved. Sidewall-misalignment-modulation (SMM) apodization is applied to achieve a high sidelobe suppression ratio (SLSR). The experimental results show that the designed filtering device has a 3-dB bandwidth of 0.8 nm, an insertion loss of -0.65 dB and a SLSR of 20.3 dB. The devices with different grating duty cycles and multimode waveguide widths were also fabricated and analyzed. Our devices are promising for on-chip applications that require narrow bandwidths such as WDM channel filters.

The aim of this study is to investigate the autofluorescence spectral characteristics of normal and cancerous nasopharyngeal tissues and to extract the potential spectral features for diagnosis of nasopharyngeal carcinoma (NPC). The autofluorescence excitation-emission matrix (EEM) of 37 normal and 34 cancerous nasopharyngeal tissues were recorded by a FLS920 spectrofluorimeter system in vitro. Based on the alteration in proportions of collagen and NAD(P)H, the integrated fluorescence intensity of I _{455 ± 10 nm} and I _{380 ± 10 nm} were used to calculated the ratio values by a two-peak ratio algorithm to diagnose NPC tissues at 340 nm excited. Furthermore by applying the receiver operating characteristic curve (ROC), the 340 nm excitation yielded an average sensitivity and specificity of 88.2 and 91.9%, respectively. These results may have practical implications for diagnosis of NPC.

Recently, we reported induced anoxia as a limiting factor for photodynamic tumor therapy (PDT). This effect occurs in vivo if the amount of generated singlet oxygen that undergoes chemical reactions with cellular components exceeds the local oxygen supply. The amount of generated singlet oxygen depends mainly on photosensitizer (PS) accumulation, efficiency, and illumination intensity. With illumination intensities above a certain threshold, singlet oxygen is limited to the blood vessel and the nearest vicinity; lower intensities allow singlet oxygen generation also in tissue which is a few cell layers away from the vessels. While all experiments so far were limited to light intensities above this threshold, we report experimental results for intensities at both sides of the threshold for the first time, giving proof for the described model. Using time-resolved optical detection in NIR, we demonstrate characteristic, illumination intensity-dependent changes in signal kinetics of singlet oxygen and photosensitizer phosphorescence in vivo. The described analysis allows for better optimization and coordination of PDT drugs and treatment, as well as new diagnostic methods based on gated PS phosphorescence, for which we report a first in vivo feasibility test.