We propose and demonstrate a high-resolution and high-sensitivity tunable liquid refractive index (RI) sensor interrogated using a microwave photonic filter (MPF) with two taps implemented based on optical polarization orthogonality. In the structure, a fiber laser with its wavelength determined by a microfiber Bragg grating (mFBG) is employed as a light source. A chirped fiber Bragg grating (CFBG) is incorporated in one tap, and an optical tunable delay line (TDL) is included in the other tap. The sensing information is encoded in the laser wavelength caused by the RI change, which will cause a change in the time delay difference between the two taps due to the wavelength-dependent group delay of the CFBG, which would result in a change in the MPF frequency response. By monitoring the spectral response, the sensing information is detected. The spectral response of the MPF is tuned by controlling the length of the TDL, which would lead to a change in the sensor sensitivity. An experiment is performed. The results show, for three TDL time delays of 300 ps, 400 ps and 500 ps, the liquid RI sensitivities are 50.621 GHz/ RIU, 37.293 GHz/RIU and 26.015 GHz/RIU, respectively, and the corresponding resolutions are 8.0253×10-5 RIU, 1.0893×10-4 RIU and 1.5616×10-4 RIU.
A real-time gas vacuum sensor interrogated based on a microwave photonic method at high speed and high resolution is proposed and demonstrated. The sensor is a microfiber Mach-Zehnder interferometer (mMZI) with its wavelength sensitive to the gas concentration. Instead of detecting the wavelength shift of the mMZI spectrum in the optical domain, we convert the mMZI spectrum to the time domain by spectral shaping and wavelength-to-time (SS-WTT) mapping and apply a digital signal processor (DSP) to realize the cross-correlation to estimate the wavelength shift of the mMZI. The sensitivity and resolution of the proposed gas vacuum sensor are -0.586 ps/ppm and 34.13 ppm with a concentration range from 0 to 1.4×104 ppm, respectively.
As a typical tumor suppressor and transcription factor in cancer biology, p53 protein is involved in DNA repair, the cell cycle regulation and programmed cell death. The p53 protein in human blood can be linked with tissue alterations for more than 50% human cancer, and its concentration can be used for early-stage cancer diagnostics and related risk assessments. In this work, we demonstrated a high resolution biomedical sensor. It is based on a micro Bragg fiber grating (mFBG) as a sensing probe to form lasing in a fiber laser ring resonant cavity. It is able to detect the p53 protein by measuring the fiber laser wavelength via the optical wavelength meter (OWM). Compared with the traditional sensing system based on the full-spectrum measurement, a higher signal-to-noise ratio and more stable output can be obtained, which improves the wavelength resolution and measurement speed. The optical fiber biomedical sensor successfully maintains its specificity for p53 protein, and has a promising application in clinical oncology diagnosis.
A high speed TFBG-SPR sensing demodulation system based on microwave photonics interrogation is proposed theoretically. The wavelength shifting of the SPR envelope in optical domain is converted to the microwave pulse shifting in time domain. The RI resolution is improved by one order of magnitude compared with wavelength demodulation, and the sensing speed is as high as 40 KHz.
We propose and demonstrate a simple multiwavelength erbium-doped fiber laser (EDFL) scheme based on a WaveShaper. The WaveShaper can not only act as a multichannel filter but can also introduce wavelength-dependent loss (WDL) in the laser cavity. The WDL can effectively suppress the mode competition caused by the homogeneous gain broadening of the EDF. As a result, up to an 11-wavelength lasing operation with a wavelength spacing of 0.8 nm has been achieved. The power distribution among wavelengths is uniform and the measured power fluctuation of each wavelength is less than 1 dB.
An incoherent microwave photonic filter (MPF), based on multiwavelength phase modulation (PM) and a WaveShaper, is proposed and investigated. The multiwavelength erbium-doped fiber laser provides multiple taps, while the WaveShaper and a dispersive device perform PM to amplitude modulation (AM) conversion. The WaveShaper can also induce both spectral shaping effect for the taps and a different phase for radio-frequency signal during the PM-to-AM conversion. Principle analysis of MPF based on PM-to-AM conversion is discussed. Simulation is carried out to investigate the influence of WaveShaper parameters on the frequency response of the MPF. Through adjustment of the WaveShaper, MPFs with positive, negative, or complex coefficients are also obtained in the experiment. Experimental observations agree well with the simulation results and discussions are given.
We propose a side-hole polarization-maintaining photonic crystal fiber (PM-PCF) with ultrahigh polarimetric sensitivity
to hydrostatic pressure. Modal birefringence B as large as 2.34×10-3 and polarimetric pressure sensitivity dB/dp as high
as -2.28×10-5 MPa-1 were achieved at 1.55 μm for the proposed fiber. Combining the advantages of both side-hole fibers
and PM-PCFs, the proposed fiber is an ideal candidate for future applications of pressure sensing.
A room-temperature multiwavelength erbium-doped fiber laser (EDFL) based on a nonlinear high-birefringence fiber loop mirror (HiBi-FLM) is proposed and demonstrated. The nonlinear HiBi-FLM can induce not only wavelength-dependent loss (WDL) but also intensity-dependent loss (IDL). WDL and IDL can effectively suppress the mode competition caused by homogeneous gain broadening of the erbium-doped fiber (EDF), and ensure stable and uniform power distribution over wavelengths. As a result, up to 50-wavelength lasing operations with wavelength spacing of 0.8 nm, and more than 100-wavelength operations with wavelength spacing of 0.14 nm are achieved. The power distribution over the wavelengths is uniform, and the power fluctuation in each wavelength is smaller than 0.2 dB.
A wavelength switchable multiwavelength actively mode-locked fiber-ring laser based on highly nonlinear photonic crystal fiber (PCF) and polarization-dependent mode coupling to multimode-fiber Bragg grating (MMFBG) is proposed. Twenty meters of highly nonlinear dispersion-shifted PCF (DS-PCF) is inserted into the fiber ring cavity to suppress gain competition through the four-wave-mixing (FWM) effect. A mode scrambler is attached to the multimode fiber (MMF) to introduce a polarization-dependent mode coupling to the MMFBG. Through changing polarization in the cavity, stable and switchable one-wavelength, two-wavelength (wavelength spacing of 0.8 and 2.4 nm), and three-wavelength simultaneously actively mode-locked optical pulse trains at a repetition rate of 5 GHz are obtained. We show that high nonlinearity introduced by the nonlinear PCF in the cavity can improve significantly supermode suppression ratio (SMSR) of the multiwavelength pulses generated and a sidemode suppression ratio (SMSR) of 58 dB is realized.
A multi-wavelength erbium-doped fiber laser using a Moire Bragg grating in polarization-maintaining fiber is proposed. Two Moire Bragg gratings in Polarization-maintaining fiber are respectively fabricated successfully through stretching and double, triplicate exposure method. The two gratings fabricated respectively have four and six reflection peaks and are respectively incorporated in the linear erbium-doped fiber laser cavities to perform mode-selection and output coupler functions. The proposed laser can be made to operate in simultaneous four-wavelength or six-wavelength operations when the EDF is cooled in liquid nitrogen (77K).
A simple technique for the generation of bright and dark pulses train from continuous-wave (cw) light is presented. The principle is based on direct external nonlinear modulation and a simple theoretical explanation was given. Conversion between bright and dark pulses can be obtained by simple adjustment of the bias level and modulation depth of the modulator. The repetition rate of the pulses is twice the driven signal frequency.
A synchronously pumped mode-locked Yetterbium-doped Fiber Laser which has the advantages of simple design and broad applications is obtained when the pump semiconductor laser current is modulated sinusoidally at the appropriate frequency. Steady pulses were obtained on harmonic mode-locked status. At the repetition rate of 623kHz,the pulse width is about 50ns,the average output power is 2.34 mW.
An all fiber Q-switched laser with Mach-Zehnder Interferometer configuration has been reported. A fiber Bragg grating is used to achieve frequency-choice and tuning. The laser can generate stable optical pulse at center wavelength 1561nm, peak power 2.6w, pulse width 4.2?s at repetition rate 760Hz, pumped by a laser diode 980nm. Self-mode locking in the Q- switched all fiber laser has been demonstrated. If changing period of fiber grating through adjusting stress or temperature, we can obtain continuous wavelength tunable output optical pulse and the tunable range is about 5nm.
We present the ultrashort electromagnetic pulses radiation system. The radiation antenna device are both illuminated by picosecond optical pulses, and the other same device for reception. Fabricated on a GaAs substrate, the antenna device consists of double-shottky-band and quasi-exponential antenna. We have obtained broad-band electromagnetic pulse radiation.
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