Radiation-induced attenuation self-compensating effect in super-fluorescent fiber source

The compact super-fluorescent fiber source （SFS） output spectra variations at different pump currents and under different dose of gamma-ray radiation were measured and compared respectively. The radiation-induced attenuation （RIA） self-compensating effect in SFS based on photo-bleaching was found and the general mathematic model of SFS output spectra variations was made. The radiation-induced background attenuation （RIBA） at the pump wavelength was identified to be the main cause of the total output power and spectra variations and the variations can then be compensated by active control of the pump power to enhance the self-compensating effect. With closed-loop feedback control of pump current, double-pass backward （DPB） configuration and spectrum re-shaping technology, an SFS prototype was made and tested. The mean-wavelength stability of about 87.4 ppm and output power instability of less than 5% were achieved under up to 200 krad （Si） gamma-ray irradiation.

Experimental Research on Erbium-doped Superfluorescent Fiber Source

The effects of the variations in fiber length,fiber mirror reflectance on efficiency and output power are experimentally investigated for erbium-doped double pass backward superfluorescent fiber sources (SFSs).The influence of fiber length on mean wavelength stability (MWS) has also been demonstrated.By incorporating a short section of un-pumped erbium-doped fiber (EDF) at the output port,the pump power dependent on MWS becomes independent of pumped EDF length.This is a novel phenomenon that hasn’t been reported up to now,and should be helpful to SFS fabrication and theory analysis.By using a fiber Michelson interferometer as spectrum slicing component,a multi-wavelength fiber source (MWFS) with ～20 channels (from 1 542 nm to 1 559 nm) is got.The MWFS has a channel spacing of ～0.8 nm which satisfies ITU-standard.The intensity fluctuation among channels is less than 0.5 dB,and the extinction ratio of all channels is above 14 dB.This kind of MWFS should be useful to wavelength division multiplexing systems.

Quantification of glycated hemoglobin indicator HbA1c through near-infrared spectroscopy

A new strategy for quantitative analysis of a major clinical biochemical indicator called glycatedhemoglobin(Hb·A1c)was proposed.The technique was based on the simultaneous near-infrared(NIR)spectral determination of hemoglobin(Hb)and absolute HbAlc content(Hb·HbA1c)inhuman hemolysate samples.Wavelength selections were accomplished using the improvedmoving window partial least square(MWPLS)method for stability.Each model was establishedusing an approach based on randomness,similarity,and stability to obtain objective,stable,andpractical models.The optimal wavebands obtained using MWPLS were 958 to 1036 nm for Hband 1492 to 1858 nm for Hb·HbA1c,which were within the NIR overtone region.The validationroot mean square error and validation correlation coeficients of prediction(V-SEP,V-Rp)were 3.4g L^(-1) and 0.967 for Hb,respectively,whereas the corresponding values for Hb.HbAic were 0.63 g L^(-1) and 0.913.The corresponding V-SEP and V-Rp were 0.40% and 0.829 for the relativepercentage of HbA1c.The experimental results confirm the feasibility for the quantification of HbAlc based on simultaneous NIR spectroscopic analyses of Hb and Hb·HbA1c.

Multi-Component and Multi-Point Trace Gas Sensing in Wavelength Modulation Spectroscopy Based on Wavelength Stabilization

Multi-component and multi-point trace gas sensing in the wavelength modulation spectroscopy is demonstrated based on the frequency-division multiplexing and time-division multiplexing technology.A reference photodetector is connected in series with a reference gas cell with the constant concentration to measure the second-harmonics peak of the components for wavelength stabilization in real time.The central wavelengths of the distributed feedback lasers are locked to the target gas absorption centers by the reference second-harmonics signal using a digital proportional-integral-derivative controller.The distributed feedback lasers with different wavelengths and modulation frequencies are injected into the gas cell to achieve multi-components gas measurement by the frequency-division multiplexing technology.In addition,multi-point trace gas sensing is achieved by the time-division multiplexing technology using a photoswitch and a relay unit.We use this scheme to detect methane(CH4)at 1650.9 nm and water vapor(H2O)at 1368.597 nm as a proof of principle with the gas cell path length of 10 cm.The minimum detection limits achieved for H2O and CH4 are 1.13 ppm and 11.85 ppm respectively,with three-point gas cell measurement;thus 10.5-fold and 10.1-fold improvements are achieved in comparison with the traditional wavelength modulation spectroscopy.Meanwhile,their excellent R-square values reach 0.9983 and 0.99564 for the concentration ranges of 500 ppm to 2000 ppm and 800 ppm to 2700 ppm,respectively.

Improved spectral characteristics of 980 nm broad area slotted Fabry-Perot diode lasers

A novel broad area slotted Fabry-Perot diode laser is designed and fabricated. Using a new semi- analytical method, we introduce effective refractive index perturbations in the form of etched slot features into a conventional 980 nm broad area Fabry-Perot cavity, and the spectral characteristics of the device are expected to be noticeably improved. A low density of slot features is formed by using standard optical lithography and inductively coupled plasma dry etching. The experimental results show that the full spectral width at half-maximum is less than 0.4 rim, meanwhile, the thermal shift of the emission spectrum is decreased from 0.26 to 0.07 nm/℃ over a temperature range of 10 to 60℃. The improved spectral characteristics of the device are proved to be attributed to such slotted Fabry-Perot laser structures.

Experimental optimization of an erbium-doped super-fluorescent fiber source for fiber optic gyroscopes

Double-pass forward and double-pass backward erbium-doped super-fluorescent fiber sources（EDSFSs） were combined in one configuration.A 980 nm laser diode pumped the same erbium-doped fiber from both directions using a coupler as a power splitter.The double-pass configuration was achieved by coating the fiber end face.Firstly,an optimal fiber length was found to obtain a high stability of output light wavelength with pump power, and then 1530/1550 nm wavelength division multiplexing was used for spectrum planarization,which expanded the bandwidth to more than 22 nm.The final step was a test of temperature stability.The results show that the rate of the central wavelength change kept to below 3.5 ppm/℃in the range of -40 to 60℃and 1-2 ppm/℃in the range of 20-30℃.Considering all the three factors of the fiber optic gyro applications,we selected 80 mA as the pump current,in which case the central wavelength temperature instability was calculated as 2.70 ppm/℃, 3 dB bandwidth 22.85 nm,spectral flatness 0.2 dB,output power 5.17 mW and power efficiency up to 9.92%.This experimental result has a significant reference value to the selection of devices and proper design of ED-SFSs for the application of high-precision fiber optic gyroscopes.