In this paper, we present a numerically study of the nanoscale refractive index sensor based on periodically modulated graphene ribbon arrays with finite-difference time-domain method (FDTD). The results show that the resonance wavelengths of the graphene metamaterials structure have an approximate linear correlation with the refractive index of the dielectric substrate, which can be used as the refractive index sensor exhibits a higher sensitive of 3069.1 nm/RIU. Furthermore, the resonant wavelength of the structure tends to exhibit a clearly blue shift with the Fermi-level (Ef) of graphene ribbons increasing. And the shift of the resonant peak ups to 4906.3 nm per unit Fermi level. Besides, the influence of ribbon-width and Fermi level of the graphene on the performance of sensor are investigated in details. We believe that the work is useful for the design and application of the plasmonic refractive index sensors based on a grapheme ribbon array.
The influence of bias current and ASE injection power on the side-mode suppression ratio (SMSR), relative intensity noise (RIN) and gain of the ASE-injection wavelength-locked Fabry-Perot laser diode (F-P LD) have been studied experimentally. Results show that the SMSR and RIN depend on the bias current for a given ASE, and there is different optimum bias current in terms of the SMSR and RIN. With the influence of detailed spontaneous recombination mechanism and its temperature dependence and the temperature- and wavelength-dependent material gain, we propose a static model of the wavelength-locked F-P LD based on nonlinear etalon theory. The temperature dependence of gain and saturation power of wavelength-locked F-P LD is analyzed theoretically with the model. The results show that the saturation power increases as we increase the operation temperature, while it decreases as we increase the reflectivity of front facet.
We constructed a reflection L-band erbium-doped fiber amplifier based on fiber loop mirror, which reflects the backward ASE to the EDF as a secondary pumping source. A gain of 30 dB increased 6 dB compared to the forward end-pumped EDFA has been achieved in the wavelength region from 1570 to 1603 nm. In order to improve the gain and NF further, we constructed a novel configuration for reflection L-band erbium-doped fiber amplifier via inserting a 980 nm LD in the input part. Adjusting the ratio of power of the two LDs, the gain and NF are greatly improved in different degree in the region from 1565 to 1615 nm. Compared to the configuration pumped by only 1480 nm LD with given power, the gain enhanced 1.5-9.9 dB and the NF decreases 1.3-9.4 dB.
A new approach for displacement sensing based on chirp effect of fiber Bragg grating under strain-gradient is proposed and demonstrated in this paper. Strain gradient chirp of fiber Bragg grating is realized by attaching the grating slantways on a side face of a simple cantilever beam. The strain gradient, which is formed along the grating when the free of the beam is curved, produces a linear variation in the grating pitch .The theoretical formulae are derived and the experimental results are given. Because bandwidth of the grating is temperature-insensitive, the cross talk between displacement and temperature is avoided. This device has many characteristics, such as simple configuration, good noise immunity, and good linearity (about 0.9992). It is promising to be used into in-process displacement measurement.
A cascaded M-Z fiber interferometer has been analyzed,which is made of several 3dB couplers in series. Theoretical analysis and numerical simulation indicate that a good comb-like curve will be obtained when the length difference ? L of interference arms is given a certain value in order. Side-mode suppression ratio (SSR) will increase as adding of the number of interference arms.
A group of equations deduced from thulium-doped fiber amplifier (TDFA) rate equations and light propagation equations, introducing the overlapping factors between the (pump and signal) light intensities and the thulium dopant distributions inside the fiber core, is presented in this paper. Using the group of equations, the small signal gain and optimum fiber length and threshold pump power characteristics ofthe amplifier are simulated.
In this letter, the gain characteristics of the erbium-doped fiber ring amplifier at below laser threshold using a I :99 coupler, which feed back 1% ofthe output power into the ring cavity, has been studied. In the same condition, the gain of the erbium-doped fiber line amplifier has been measured, which is lower 3.2dB than that of the erbium-doped fiber ring amplifier. In the region of 1520-1570nm, the gain ofthe erbium-doped fiber ring amplifier is bigger 1.5-2.5dB than that oferbium-doped fiber line amplifier.
We introduce a novel electric current sensor, which is based on a fiber Bragg grating covered by a uniform coat of aluminum thin film which was deposited on the FBG by a simple evaporation method. The Bragg wavelength of the fiber grating shifts when the current flowing through the film varies due to the Joule heat generated by the current. The relationship between the square of the current intensity and the wavelength shift is basically linear. In the experiment, the maximum current can be measured was 43.1 mA with the wavelength sift of about 4 nm and the current sensitivity was about 2.31 X 10-3 nm/(mA)2.
Without any stabilizing equipment, a multi-wavelength fiber linear cavity laser in L-band was obtained at the room temperature. The cavity was formed by two linear fiber loops. Utilizing the birefringence of the single mode fiber, we can make the reflectivity of these fiber-loops vary periodically with the wavelength. Two polarization controllers (PCs) were inserted into fiber loops. By changing the states of PCs, the number of the lasing wavelengths and wavelength spaces can be controlled.
A new displacement measuring scheme based on simply supported beam is reported and demonstrated. The theoretical formula is derived and the experimental results are given. This device has many characteristics, such as simple structure, high sensitivity and good linearity. It is promising to be used into in-process displacement measurement.
A curvature sensor based on fiber Bragg grating (FBG) is demonstrated in this paper. Two FBGs are surface-bonded on opposite sides of a flexible beam to track the local curvature variation. The bending-induced strain causes opposite changes in their Bragg wavelengths. As a result, temperature-independent curvature measurement with sensitivity of 3.21nm/mMIN1 is achieved by monitoring spacing between the two Bragg wavelengths. The experimental results agree well with the theoretical analysis.
A novel technique for fiber Bragg grating sensor is introduced. The sensor is successfully used to measure wavelength-shift induced to strain and temperature. The experiment results agree with the theory and indicate that the sensor has good linear response capacity and high intensity signal and signal to noise ratio.
We introduce a novel simple current sensor, which is based on a fiber Bragg grating covered by a uniform coat of aluminum thin film. The Bragg wavelength of the fiber grating will shift when the current flowing through the film varies due to the Joule heat generated by the current. The relationship between the square of the current intensity and the wavelength shift is basically linear. In the experiment, we got a current sensitivity of about 2.31x10MIN3nm(mA)2.