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Anti-resonant hollow core fibers (AR-HCFs) provide a promising solution for photothermal spectroscopy and photoacoustic imaging applications. Here, the AR-HCF serves as a micro platform to induce the photothermal/photoacoustic effect. Since the Bragg structure can induce multiple AR effects compared with the general AR-HCF, we proposed a novel device, the AR-BHCF (AR-HCF with Bragg cladding), to enhance the excitation efficiency. The simulation and experimental results validate that the AR-BHCF dominates in having a stronger ability to confine the optical field in the air core indeed. Then, the acoustic signal stimulated by the photoacoustic effect will propagate along with the fiber axial, and part of it will penetrate out of the AR-BHCF. The results revealed that the transmission bandwidth of the acoustic wave in the AR-BHCF ranges from 1 Hz to 1 MHz, covering infrasound to ultrasound. In particular, a constant coefficient of 0.5 exists in the acoustic wave fading process, related to the propagation frequency and time. The acoustic signal can be monitored in real time, assisted by the ultra-highly sensitive sensor head. Therefore, BHCF-based devices combined with photoacoustic techniques may accelerate their sensing applications. Meanwhile, this scheme shines a light on the theoretical foundation of novel short-haul distributed acoustic sensing. [ABSTRACT FROM AUTHOR]

We report on the multi-state soliton generation in a chirped fiber Bragg grating (CFBG) based bidirectional mode-locked fiber laser. In particular, a $\theta $ -shape associate cavity is designed to introduce reverse dispersion distributions in counter-propagation directions through incorporating the bidirectional reflection of the CFBG into the lasing oscillator. With a relatively compact cavity configuration, the clockwise (CW) and counterclockwise (CCW) directions are managed into large anomalous and normal dispersion regimes, respectively. Consequently, conventional solitons (CSs) and dissipative solitons (DSs) can be emitted from the counter-propagation directions. To the best of our knowledge, it is the first report of CS/DS generation in a CFBG based bidirectional fiber laser. This investigation can contribute to research community of multiplexed ultrafast fiber lasers. [ABSTRACT FROM AUTHOR]

A simple magnetic field sensor by using an optical fiber Bragg grating (FBG) cascaded by a cleaved optical fiber end, which is surrounded with magnetic fluid (MF), is experimentally demonstrated. Magnetic field changes Fresnel reflectivity of the fiber end face through refractive index change of the MF, leading to a modulation to the reflection background in the reflection spectrum of the FBG. By comparing intensity difference between the FBG reflection peak, which is not sensitive to the external magnetic field, and the reflection background, magnetic field measurement is achieved successfully. High accuracy and stability can be realized because influence of power level fluctuation of the optical source on measurement results can be eliminated. Furthermore, temperature can be measured simultaneously from reflection wavelength shift of the FBG that is helpful to further compensate the effect of temperature on magnetic field measurement. [ABSTRACT FROM PUBLISHER]

We present a temperature and strain fiber sensor utilizing fiber Bragg grating (FBG) inscribed in silica-germanate few-mode fiber. The temperature and strain sensitivities of resonant wavelength formed by mode LP01 self-coupling and mode LP01-LP11 cross-coupling are investigated theoretically and characterized experimentally. Two resonant wavelengths demonstrate different temperature sensitivities of 11.5 pm/°C 10.6 pm/°C, respectively, due to different mode profile, while the strain sensitivities are quite similar with a value of 0.9 pm/με. By using FBG character matrix, the proposed fiber sensor can measure those two parameters simultaneously within a compact and cost-effective setup. [ABSTRACT FROM PUBLISHER]

A continuously tunable microwave photonic notch filter is proposed and experimentally demonstrated. This filter is based on the differential group delay generated by a high-birefringence linearly chirped fiber Bragg grating. The tunability is realized by applying gradient tension to the grating. Free spectral range tuning by 9.27 GHz with more than 35 dB notch rejection is achieved. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:121-123, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25679 [ABSTRACT FROM AUTHOR]

Polarization-maintaining fibers (PMFs) have always received great attention in fiber optic communication systems and components which are sensitive to polarization. Moreover, they are widely applied for high-accuracy detection and sensing devices, such as fiber gyroscope, electric/magnetic sensors, multi-parameter sensors, and so on. Here, we demonstrated the combination of a fiber Bragg grating (FBG) and Sagnac interference in the same section of a new type of PANDA-structure PMF for the simultaneous measurement of axial strain and temperature. This specialty PMF features two stress-applied parts made of lanthanum-aluminum co-doped silicate (SiO2-Al2O3-La2O3, SAL) glass, which has a higher thermal expansion coefficient than borosilicate glass used commonly in commercial PMFs. Furthermore, the FBG inscribed in this SAL PMF not only aids the device in discriminating strain and temperature, but also calibrates the phase birefringence of the SAL PMF more precisely thanks to the much narrower bandwidth of grating peaks. By analyzing the variation of wavelength interval between two FBG peaks, the underlying mechanism of the phase birefringence responding to temperature and strain is revealed. It explains exactly the sensing behavior of the SAL PMF based Sagnac interference dip. A numerical simulation on the SAL PMF's internal stress and consequent modal effective refractive indices was performed to double confirm the calibration of fiber's phase birefringence. [ABSTRACT FROM AUTHOR]

Abstract: This paper proposes a novel bi-directional hybrid fiber amplifier using a single-wavelength pump laser diode (LD) at 1495nm. The hybrid amplifier is theoretically applied in a 50km bi-directional local area network (LAN) with 26ch×10Gb/s for bi-directional transmission. Thirteen C-band channels serve as downlink signals while the other 13 L-band channels are employed as uplink signals. Without loss of generality, four channels (two from each band) are experimentally analyzed. Erbium doped fiber (EDF) provides amplification for the C-band channels and Raman amplification amplifies the L-band channels. The pump efficiency is improved by employing a double-pass scheme for both the Erbium doped fiber amplifier (EDFA) and Raman fiber amplifier (RFA). The chromatic dispersion incurred by all the channels is precisely compensated for by inserting a fiber Bragg grating (FBG) array in appropriate locations along the dispersion compensating fiber (DCF) segments. Moreover, gain equalization of all the channels is achieved by adjusting the FBG reflectivity. Both the simulation results and experimental measurements confirm the proposed device feasibility and potential application in a bi-directional LAN. [ABSTRACT FROM AUTHOR]

Abstract: We show analytically as well as demonstrate experimentally an approach to generate microwave waveforms with wide chirp tuning range. The approach is based on the interference of two temporally-stretched pulses which are time-delayed with respect to each other and having different frequency chirp. This approach is realized by an unbalanced Mach Zehnder Interferometer (MZI) incorporating a linearly-chirped fiber-Bragg-grating (LCFBG) whose group-delay-dispersion (GDD) can be tuned across a wide range. In general, tuning the GDD of the LCFBG changes the chirp rate of the generated microwave waveform and tuning the relative time-delay between the interferometer arms changes the center frequency of the generated microwave waveform. Balanced photodetection is also implemented to obtain DC-free microwave waveforms. Based on this approach, we demonstrate the generation of microwave waveforms with different center frequencies and with the chirp rates ranging from∼−126.7GHz/ns to ∼+120.8GHz/ns, including the zero-chirp case. [Copyright &y& Elsevier]