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Mass concrete is widely used in large-scale projects, including metro upper cover structures, water conservancy dams, and heavy equipment foundations, among others, necessitating the process of health monitoring in mass concrete construction. The development of reliable and simple strength-monitoring methods for mass concrete is challenging because the inner temperature of mass concrete is high and changes a lot. This study proposes a strength-monitoring approach for mass concrete using barium titanate–bismuth ferrite/polyvinylidene fluoride (BT–BFO/PVDF) nanocomposite piezoelectric sensors, wherein the new sensors are embedded as actuators and sensors in mass concrete. The stress wave generated by the BT–BFO/PVDF piezoelectric sensors is used to monitor the specimen's strength for 28 days. The piezoelectric voltage received by the sensors in mass concrete is analyzed. The experimental results indicate that the signal received by the BT–BFO/PVDF sensors is not easily affected by the internal temperature of mass concrete compared with that of the traditional PVDF piezoelectric sensors. The signal parameters sensitive to concrete strength variation and the change trend of concrete strength are closely related to the piezoelectric voltage. Therefore, the proposed approach using BT–BFO/PVDF nanocomposite piezoelectric sensors is efficient (error < 10%) in mass concrete monitoring. Moreover, the monitoring results do not need temperature compensation. The physical meaning of the obtained strength prediction formula is proposed. An experimental system based on PVDF dynamic strain-sensing characteristics is established. [ABSTRACT FROM AUTHOR]

High birefringence induced by rhombic air-hole photonic crystal fibers (PCFs) is numerically analyzed by using the finite-element method. The birefringence of a few kinds of PCFs was investigated with different parameters related to rhombic holes, including the rhombic-hole shape, size, and spacing. It was found that the birefringence of the proposed rhombic-hole PC F in this study is relatively larger than that of an elliptical-hole PCF with the same air-filling fraction (f = 0.0375) when the ratio of the rhombic-hole diagonal length is equal to the elliptical-hole ellipticity. OCIS codes: 060.0060, 060.5295.

We observed intense green upconversion emission from [Tb.sup.3+] centered at 546 nm due to transition [sup.5][D.sub.4] [right arrow] [sup.7][F.sub.5] in [Tb.sup.3+]/[Yb.sup.3+] codoped alumino-germano-silicate optical fibers by direct excitation of [Yb.sup.3+] ions with a laser diode at 976 nm. A two-photon cooperative energy transfer upconversion among a pair of [Yb.sup.3+] donor ions and a [Tb.sup.3+] acceptor ion are responsible for the observed green emission. Appropriately increasing the concentration of [Tb.sup.3+] relative to [Yb.sup.3+] was found to facilitate the energy transfer upconversion process from [Yb.sup.3+] to [Tb.sup.3+], while an excess of [Tb.sup.3+] ions inversely introduced more of the concentration quenching effect and phonon-assistant backward energy transfer from [Tb.sup.3+] to [Yb.sup.3+] and, therefore, damaged the observed green emission. The intensity of the observed green emission was found optimum for a concentration ratio of [Tb.sup.3+] to [Yb.sup.3+] of 2 : 1 in alumino-germano-silicate optical glass fibers. [c] 2010 Optical Society of America OCIS codes: 140.3613, 140.7300, 060.2290.

A tellurium-doped germanosilicate optical fiber was developed by modified chemical vapor deposition and solution doping techniques. Using the continuous-wave self-phase modulation method, the nonresonant nonlinear refractive index, [n.sub.2], was measured to be 5.52 x [10.sup.-20] [m.sup.2]/W, which is 2 to 3 times that of the undoped germanosilicate glass fiber. Polyhedron structures Te[O.sub.3] and Te[O.sub.4] with Ge[O.sub.4] and Si[O.sub.4] are believed responsible for lower phonon energy, more nonbridging oxygens, and a larger hyperpolarization, leading to the observed higher nonresonant optical nonlinearity. OCIS codes: 060.2280, 190.4370.

We have theoretically proposed and experimentally demonstrated a new kind of ultranarrow identical-dual-bandpass sampled fiber Bragg gratings (SFBGs) with a [pi] phase shift technique. The spacing of two bandpasses of the proposed grating can be flexibly adjusted by changing the sampled period, and any desired spacing can be achieved in principle. An experimental example shows that the transmission peaks of two narrow transmission-band are near 1549.1 and 1550.1 nm. Based on the proposed SFBG, an ultranarrow identical-dual-channel filter is designed. Two channels of the proposed filter have an equal bandwidth, an even strength, and the same group delay. The bandwidth of each channel of our filter is as small as 1 pm and up to [10.sup.-3] pm (corresponding to ~0.1 MHz), which is less than the bandwidth of the conventional SFBG filters by a factor of [10.sup.2]-[10.sup.4]. The proposed grating and filter can find potential applications with slow light and dual-wavelength single-longitudinal-mode fiber lasers. OCIS codes: 060.3735, 050.2770, 060.2340.

We demonstrated the controllable acquisition of optical gated spectra from a chirped supercontinuum (SC) pulse based on ultrafast transient lens (TrL) effect. Comparing with CS2, the gated spectra had much narrower spectral bandwidths using tellurite glass (Te glass) as the nonlinear medium due to its ultrafast nonlinear response. Experimental results showed that the chirp structure of the SC pulse measured by TrL method was quite accordant with that measured by femtosecond optical Kerr gate method. [ABSTRACT FROM AUTHOR]