A compact temperature sensor based on a fiber loop mirror (FLM) combined with an alcohol-filled high-birefringence photonic crystal fiber (PCF) is proposed and experimentally demonstrated. The output of the FLM is an interference spectrum with many resonant dips, of which the wavelengths are quite sensitive to the change of the refractive index of the filled alcohol for the interference of the FLM. Simulation analysis predicts a high temperature sensitivity, and experimental results show it reaches up to 6.6 nm/°C for the 6.1-cm-long PCF used in the FLM.
Recently,
more and more attention has been given to a semiconductor
oxide-based surface-enhanced Raman spectroscopy substrate for its
great stability and biocompatibility. However, its poor SERS sensitivity
limits the applications of semiconductor oxide SERS substrates. In
this paper, we provide a facile reduction method to modulate oxygen
vacancy concentrations in oxide SERS substrates. Using MoO2 as an example, the resonance coupling as well as charge transfer
between the semiconductor oxide SERS substrate and the target molecules
were promoted for the reason of artificial oxygen vacancy embodied
in the Raman signals being improved. By using the TEM, SEM, and XPS
measurements, we confirmed that we successfully prepared defective
MoO2–x
with a polycrystalline surface.
MoO2–x
modulated oxygen vacancy
treated with 6 wt % Li shows a very high detection sensitivity of
10–8 M (4.79 ug/L) for R6G, and the intensity of
the Raman signal was highly enhanced. Because of the existence of
defective energy levels, resonance coupling, as well as charge transfer
between semiconductor and molecules, was obviously promoted. More
importantly, the method of modulating oxygen vacancy can be widely
used in semiconductor oxide materials for its chemical enhancement
capacity can be promoted by artificial oxygen vacancy.
A novel mode-locking method based on the nonlinear multimode interference in the stretched graded-index multimode optical fiber (GIMF) is proposed in this Letter. The simple device geometry, where the light is coupled in and out of the stretched GIMF via single-mode fibers, is demonstrated to exhibit the temporal intensity discrimination required for mode locking. The nonlinear saturable absorber (SA) characteristics of the device are controllable by simply adjusting the strength of the stretching applied. The modulation depth of the device, which consists of ∼23.5 cm GIMF, is tuned from 10.37% to 22.27%. Such a simple SA enables the wavelength-switchable mode-locking operation in a ring Er-doped fiber laser, and ultrafast pulses with a pulse width of 506 fs at 1572.5 nm and 416 fs at 1591.4 nm were generated. The versatility and simplicity of the SA device, together with the possibility of scaling the pulse energy, make it highly attractive in ultrafast photonics.
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