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Real-time monitoring of heartbeat signals using multimode fiber optic microvibration sensing technology is crucial for diagnosing cardiovascular diseases, but the heartbeat signals are very weak and susceptible to noise interference, leading to inaccurate diagnostic results. In this paper, a combined enhanced discrete wavelet transform (DWT) and non-local mean estimation (NLM) denoising method is proposed to remove noise from heartbeat signals, which adaptively determines the filtering parameters of the DWT-NLM composite method using objective noise reduction quality assessment metrics by denoising different ECG signals from multiple databases with the addition of additive Gaussian white noise (AGW) with different signal-to-noise ratios (SNRs). The noise reduction results are compared with those of NLM, enhanced DWT, and conventional DWT combined with NLM method. The results show that the output SNR of the proposed method is significantly higher than the other methods compared in the range of −5 to 25 dB input SNR. Further, the proposed method is employed for noise reduction of heartbeat signals measured by fiber optic microvibration sensing. It is worth mentioning that the proposed method does not need to obtain the exact noise level, but only the adaptive filtering parameters based on the autocorrelation nature of the denoised signal. This work greatly improves the signal quality of the multimode fiber microvibration sensing system and helps to improve the diagnostic accuracy. [ABSTRACT FROM AUTHOR]

We present a stable and switchable dual-wavelength erbium-doped fiber laser. In the ring cavity, an inverse-Gaussian apodized fiber Bragg grating serves as an ultranarrow dual-wavelength passband filter, a semiconductor optical amplifier biased in the low-gain regime reduces the gain competition of the two wavelengths, and a feedback fiber loop acts as a mode filter to guarantee a stable single-longitudinalmode operation. Two lasing lines with a wavelength separation of approximately 0.1 nm are obtained experimentally. A microwave signal at 12.51 GHz is demonstrated by beating the dual wavelengths at a photodetector. [c] 2010 Optical Society of America OCIS codes: 060.2330, 060.3510, 060.3735.

An all-fiber sensor scheme for simultaneous strain and temperature measurement is presented. The sensing head is formed by serially connecting a polarization maintaining photonic-crystal-fiber-based intermodal interferometer (IMI) with a fiber Bragg grating (FBG). The IMI, exhibiting an opposite strain response as compared to that of the FBG, is highly sensitive to strain, while it is insensitive to temperature. This has potential for improving the strain and temperature measurement resolutions. A sensor resolution of [+ or -] 8.3 [micro][epsilon] in strain and [+ or -] 2[degrees]C in temperature are experimentally achieved within a strain range of 0-957.6 [micro][epsilon] and a temperature range of 24[degrees]C-64[degrees]C, respectively. OCIS codes: 060.2310, 060.2370.

We demonstrate a novel all-fiber nanotube Q-switched low-threshold linear cavity tunable erbium-doped fiber laser (EDFL). With a compact and low insertion loss carbon nanotube based saturable absorber connected in a linear EDFL cavity, a low pump threshold of 18.57 mW is obtained. The pulse repetition rate can be adjusted from 8.12 to 72.2 kHz by varying the pump power from 18.57 to 118.8 mW. In addition, the emission wavelength can be adjusted from 1545.04 to 1549.99 nm by tuning the central wavelength of the fiber Bragg grating, which serves as an end mirror of the laser cavity. OCIS codes: 060.2310, 140.3500, 060.3510, 140.3540.

A low-splicing-loss polarization-maintaining photonic-crystal-fiber (PMPCF)-based optical fiber Sagnac interferometer (OFSI) and its cladding-mode effect are demonstrated experimentally and analytically. An OFSI with minimum splicing loss of about 2.6 dB is achieved. The weak cladding modes induced by residual mode field diameter mismatch at the fusion splice cause a filtering effect on the transmission spectra of the OFSIs. This is especially noticeable for short length PMPCF-based OFSIs. Experimental results show that the relatively maximum ripple fluctuation induced by the cladding mode can reach 5.7%. The cladding-mode effect can be eliminated by slightly bending the PMPCF, but this introduces additional insertion loss. OCIS codes: 060.2310, 060.2340.