We propose an all-fiber band-rejection filter with a tunable bandwidth, which is realized by putting a normal long-period fiber grating in series with a rotary long-period fiber grating written in a twisted single-mode fiber by CO(2) laser pulses. Bandwidth tuning is achieved by applying torsion to the composite grating. Our experimental filter shows a bandwidth tuning of approximately 16.3 nm at a rejection level of approximately 15 dB and a polarization-dependent loss lower than approximately 0.9 dB.

On top of a crystalline silicon wafer, heterojunction solar cells have a thin layer of amorphous silicon (a-Si) placed on them. The efficiency of heterojunction solar cells can be increased by decreasing the electron complex loss by adding an intrinsic passivation layer to a monocrystalline silicon (c-Si) substrate. In this study, we examine the development of the intrinsic passivation layer deposition technique on c-Si substrates over the previous ten years by several research teams. First, a description of the structure, benefits, and passivation of heterojunction solar cells is given. Following that, the impact of modifying process variables on the functionality of the passivation layer and cell efficiency is explored in terms of the passivation material, hydrogen dilution ratio, substrate temperature, and post-deposition annealing. Last but not least, the ideal process parameters are summed up and potential future research areas are predicted. One of the best ways to increase the conversion efficiency of heterojunction solar cells is through surface passivation technology, and future domestic and international research will focus heavily on the process technology of its intrinsic passivation layer.

No abstract

An ultra-long-period fiber grating with periodic grooves structure (G-ULPFG) fabricated by using an edge-writing method with high frequency CO 2 laser pulses is reported, for the first time to our knowledge. The experimental results show that the different resonant peaks of the G-ULPFG have different temperature and refractive index sensitivities, and in particular, the refractive index sensitivity is much larger than that of conventional ULPFG due to the edge-groove structure. Such a G-ULPFG could be used as a highly sensitive optical refractometer with temperature self-compensation.

No abstract