Experimental comparison of Yb/Al/Ce and Yb/Al/P co-doped fibers on the suppression of transverse mode instability

We presented an experimental comparison of the core-composition difference on the suppression of the photodarkening and transverse mode instability effects. Two core-composition fibers, entailing Yb/Al/Ce and Yb/Al/P co-doped fibers, were fabricated by MCVD process combined with solution doping technique. The parameters of two fibers were almost the same. The PD-induced loss at equilibrium was 3.94 dB/m at 702 nm in Yb/Al/Ce fiber, while it was 0.99 dB/m in Yb/Al/P fiber. To obtain a deeper understanding of the impact of PD on laser performance, a bidirectional pumping fiber amplifier was constructed. Compared with Yb/Al/Ce co-doped fiber, the TMI thresholds of Yb/Al/P co-doped fiber were enhanced in co-pumped and counter-pumped schemes. Meanwhile, the slope efficiency in bidirectional scheme was promoted by 4%. Moreover, the transmittance at 638 nm confirmed the superior PD resistance of Yb/Al/P co-doped fiber. These experimental results pave the way for the further development of high-power fiber lasers

Numerical investigation of GHz repetition rate fundamentally mode-locked all-fiber lasers

GHz repetition rate fundamentally mode-locked lasers have attracted great interest for a variety of scientific and practical applications. A passively mode-locked laser in all-fiber format has the advantages of high stability, maintenance-free operation, super compactness, and reliability. In this paper, we present numerical investigation on passive mode-locking of all-fiber lasers operating at repetition rates of 1-20 GHz. Our calculations show that the reflectivity of the output coupler, the small signal gain of the doped fiber, the total net cavity dispersion, and the modulation depth of the saturable absorber are the key parameters for producing stable fundamentally mode-locked pulses at GHz repetition rates in very short all-fiber linear cavities. The instabilities of GHz repetition rate fundamentally mode-locked all-fiber lasers with different parameters were calculated and analyzed. Compared to a regular MHz repetition rate mode-locked all-fiber laser, the pump power range for the mode-locking of a GHz repetition rate all-fiber laser is much larger due to the several orders of magnitude lower accumulated nonlinearity in the fiber cavity The presented numerical study provides valuable guidance for the design and development of highly stable mode-locked all-fiber lasers operating at GHz repetition rates.National Science Foundation Engineering Research Center for Integrated Access Networks [EEC-0812072]; Technology Research Initiative Fund (TRIF) Photonics Initiative of the University of Arizona; National Natural Science Foundation of China (NSFC) [61575075]Open access journalThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]

Preliminary study on the optical diagnosis of orbital rhabdomyosarcoma by Raman spectroscopy

Abstract To investigate the Raman spectral features of orbital rhabdomyosarcoma (ORMS) tissue and normal orbital tissue in vitro, and to explore the feasibility of Raman spectroscopy for the optical diagnosis of ORMS. 23 specimens of ORMS and 27 specimens of normal orbital tissue were obtained from resection surgery and measured in vitro using Raman spectroscopy coupled to a fiber optic probe. The important spectral differences between the tissue categories were exploited for tissue classification with the multivariate statistical techniques of principal component analysis (PCA) and linear discriminant analysis (LDA). Compared to normal tissue, the Raman peak intensities located at 1450 and 1655 cm−1 were significantly lower for ORMS (p < 0.05), while the peak intensities located at 721, 758, 1002, 1088, 1156, 1206, 1340, 1526 cm−1 were significantly higher (p < 0.05). Raman spectra differences between normal tissue and ORMS could be attributed to the changes in the relative amounts of biochemical components, such as nucleic acids, tryptophan, phenylalanine, carotenoid and lipids. The Raman spectroscopy technique together with PCA-LDA modeling provides a diagnostic accuracy of 90.0%, sensitivity of 91.3%, and specificity of 88.9% for ORMS identification. Significant differences in Raman peak intensities exist between normal orbital tissue and ORMS. This work demonstrated for the first time that the Raman spectroscopy associated with PCA-LDA diagnostic algorithms has promising potential for accurate, rapid and noninvasive optical diagnosis of ORMS at the molecular level

Fiber tip Michelson interferometer for temperature sensing based on polymer-filled suspended core fiber

A low-cost fiber tip temperature sensor is proposed and experimentally demonstrated. It is based on the Michelson interferometer (MI) structure which is partially filled with polymer-UV glue in the suspended core fiber (SCF). Due to the greater thermal properties of UV glue compared with the silica optical fiber, the length of the inner cavity in the MI structure is susceptible to temperature modulation, resulting in the interference wavelength drift. Experimental results show that the sensor achieves a sensitivity of −164 pm/°C in the temperature range of 25–60 °C, and the sensor offers good wavelength and power stability at room temperature. In addition, the sensor has advantages such as robust, small size, and low cost, especially the reflective tip structure is more suitable for remote sensing in practical applications.Agency for Science, Technology and Research (A*STAR)This work is supported by grant from A*Star science and engineering research council (SERC), grant no. 1992200001

Signal-to-Noise Ratio Enhancement of Silicon Nanowires Biosensor with Rolling Circle Amplification

Herein, we describe a novel approach for rapid, label-free and specific DNA detection by applying rolling circle amplification (RCA) based on silicon nanowire field-effect transistor (SiNW-FET) for the first time. Highly responsive SiNWs were fabricated with a complementary metal oxide semiconductor (CMOS) compatible anisotropic self-stop etching technique which eliminated the need for hybrid method. The probe DNA was immobilized on the surface of SiNW, followed by sandwich hybridization with the perfectly matched target DNA and RCA primer that acted as a primer to hybridize the RCA template. The RCA reaction created a long single-stranded DNA (ssDNA) product and thus enhanced the electronic responses of SiNW significantly. The signal-to-noise ratio (SNR) as a figure-of-merit was analyzed to estimate the signal enhancement and possible detection limit. The nanosensor showed highly sensitive concentration-dependent conductance change in response to specific target DNA sequences. Because of the binding of an abundance of repeated sequences of RCA products, the SNR of >20 for 1 fM DNA detection was achieved, implying a detection floor of 50 aM. This RCA-based SiNW biosensor also discriminated perfectly matched target DNA from one-base mismatched DNA with high selectivity due to the substantially reduced nonspecific binding onto the SiNW surface through RCA. The combination of SiNW FET sensor with RCA will increase diagnostic capacity and the ability of laboratories to detect unexpected viruses, making it a potential tool for early diagnosis of gene-related diseases