ABSTRACT
The most important optical component in an optical fiber endoscope is its objective lens. To achieve a high imaging performance level, the development of an ultra-compact objective lens is thus the key to an ultra-thin optical fiber endoscope. In this work, we use femtosecond laser 3D printing to develop a series of micro objective lenses with different optical designs. The imaging resolution and field-of-view performances of these printed micro objective lenses are investigated via both simulations and experiments. For the first time, multiple micro objective lenses with different fields of view are printed on the end face of a single imaging optical fiber, thus realizing the perfect integration of an optical fiber and objective lenses. This work demonstrates the considerable potential of femtosecond laser 3D printing in the fabrication of micro-optical systems and provides a reliable solution for the development of an ultrathin fiber endoscope.
ABSTRACT
We propose a humidity sensor using an excessively tilted fiber grating (Ex-TFG) coated with agarose fabricated using femtosecond laser processing. The processed grating showcases remarkable differentiation between TE and TM modes, achieving an exceptionally narrow bandwidth of approximately 1.5 nm and an impressive modulation depth of up to 15 dB for both modes. We exposed the agarose-coated TFG sensor to various relative humidity levels and monitored the resonance wavelength to test its humidity sensing capability. Our findings demonstrated that the sensor exhibited a rapid response time (2-4 s) and showed a high response sensitivity (18.5 pm/%RH) between the humidity changes and the resonant wavelength shifts. The high sensitivity, linearity, repeatability, low hysteresis, and excellent long-term stability of the TFG humidity sensor, as demonstrated in our experimental results, make it an attractive option for environmental monitoring or biomedical diagnosis.
ABSTRACT
We investigate the propagation dynamics of the soliton-sinc, a kind of novel hybrid pulse, in the presence of higher-order effects with emphasis on the third-order dispersion (TOD) and Raman effects. At variance with the fundamental sech soliton, the traits of the band-limited soliton-sinc pulse can effectively manipulate the radiation process of dispersive waves (DWs) induced by the TOD. The energy enhancement and the radiated frequency tunability strongly depend on the band-limited parameter. A modified phase-matching condition is proposed for predicting the resonant frequency of the DWs emitted by soliton-sinc pulses, which is verified by the numerically calculated results. In addition, Raman-induced frequency shift (RIFS) of the soliton sinc pulse increases exponentially with a decrease of the band-limited parameter. Finally, we further discuss the simultaneous contribution of the Raman and TOD effects to the generation of the DWs emitted from the soliton-sinc pulses. The Raman effect can then either reduce or amplify the radiated DWs depending on the sign of the TOD. These results show that soliton-sinc optical pulses should be relevant for practical applications such as broadband supercontinuum spectra generation as well as nonlinear frequency conversion.
ABSTRACT
The authors made a theoretical analysis and experiment research on the relation of time-resolved coherent anti-Stokes Raman scattering (T-CARS) intensity and the sample concentrations in this paper. It was proved experimentally that the T-CARS intensity is quadratic at the concentration higher than 35%, but is linear with the sample concentration at the concentration lower than 20%, which fits with theoretical analysis. And the research results correct inaccurate previous perceptions, which is conducive to better interpretation and application of the CARS process. The linear relation between the intensity of the CARS with the sample concentration at low concentrations indicates that the CARS is allowed for direct and precise concentration measurements, therefore it will be of great importance in biology and biochemistry.
