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We report a fiber sensor capable of simultaneously measuring temperature and strain. A fiber Bragg grating (FBG) was incorporated in a Lyot fiber filter (LFF) by fusion splicing an FBG and a section of high birefringence fiber (PM fiber), which is an elliptical core side-hole fiber, and then placing them between two polarizers. Measured in the transmission mode, the fringe resulting from the LFF and the resonance wavelength dip of the FBG have different responses when a variation of temperature or strain is applied. The proposed device can therefore measure both strain and temperature simultaneously.

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(-3) pm (corresponding to approximately 0.1 MHz), which is less than the bandwidth of the conventional SFBG filters by a factor of 10(2)-10(4). The proposed grating and filter can find potential applications with slow light and dual-wavelength single-longitudinal-mode fiber lasers.

We report a simple fiber sensor for measurement of high temperature with high sensitivity. The sensing head is a multimode-single mode-multimode (MM-SM-MM) fiber configuration formed by splicing a section of uncoated single mode fiber (SMF) with two short sections of multimode fibers (MMF) whose core is composed of pure silica. Because of the mode-field mismatch at the splicing points of the SMF with 2 sections of MMFs, as well as index matching between the core of the MMF and the cladding of the SMF, optical power from the lead-in fiber can be partly coupled to the cladding modes of the SMF through the MMF. The cladding modes of the SMF then re-coupled to the lead-out fiber, in the same fashion. Due to the effective index difference between the core and cladding modes, an interference pattern in the transmission spectrum of the proposed device was obtained. The interference pattern was found to shift to the longer wavelength region with respect to temperature variation. The temperature sensor can measure temperature stably up to more than 900 degrees C with sensitivity of 0.088 nm/ degrees C.

Silver nanocrystal-incorporated germano-silicate optical fiber was fabricated by modified chemical vapor deposition and solution doping techniques. By measuring the wavelength shift of the fringes obtained from the long-period fiber grating pair, upon pumping with an argon-ion laser at 499 nm, the resonant nonlinear refractive index around 1550 nm was estimated to be 5.4 x 10(-16) m(2)/W. The observed high resonant optical nonlinearity of the silver nanocrystal-incorporated fiber is attributed to the contribution from the surface plasmon resonance of silver nanocrystals embedded in the fiber core. (C) 2008 American Institute of Physics.

We investigate the effects of co-doping of boron on the index difference between the core and cladding of the optical fiber, the temperature and bending sensitivities of a long-period fiber grating (LPFG), and the resonance wavelength separation between the core mode and the first cladding mode of a fiber Bragg grating (FBG). We observe that the index difference between the core and cladding decreases with the slope of 1.69×10−4/SCCM and that the temperature sensitivity of the resonance wavelength shift of LPFG decreased with the slope of 0.01145 nm/°C/SCCM. The measurement results indicate that, as the amount of the co-doped boron is increased, the bending sensitivity of LPFGs increases, while the resonance wavelength separation between the core mode and the first cladding mode of FBGs decreases. These results may be used for design of Ge-B co-doped optical fibers with the desired characteristics suitable for optical fiber communication and sensing applications.

We propose a simple semiconductor optical amplifier–based fiber laser configuration for achieving multiwavelength oscillation at room temperature, in which a few-mode fiber Bragg grating was used as the wavelength-selective component. An amplitude variation of 0.8 dB over a 180-sec period was obtained for triple-wavelength oscillation at room temperature, which is more stable than that of erbium doped fiber (EDF)–based fiber laser with similar configuration. This multiwavelength laser can be switched between dual- and triple-wavelength operations by properly adjusting the polarization controller in the cavity. The lasing wavelength could be effectively tuned using the thermal heating method, and the output power variation was very small compared with that of the EDF-based fiber laser. This multiwavelength laser has the advantage of simple configuration, good stability, and wavelength tuning with small output power variation.

We firstly report on the fabrication of Cu(2+)-doped germano-silicate glass fiber for nonlinear optical devices application by using modified chemical vapor deposition and solution doping processes. Broadband absorption near 700nm due to the 3d-shell electron transitions of Cu(2+) ions from the ground state to the excited states was observed. The resonant nonlinearity of the Cu(2+)-doped fiber was estimated to be 5.5x10(-17)m(2)/W by measuring the phase shift of the fringes obtained from the long-period fiber grating pair upon pumping with a laser diode at 980nm and non-resonant nonlinearities were also measured to be 4.114x10(-21)m(2)/W by the continuous wave self-phase modulation method.

The temperature sensitivity of modal birefringence (dB/dT) of different types of polarization-maintaining fibers with side holes was measured using a Sagnac loop interferometer. The thermal expansion coefficient can be varied by controlling the amount of germanium doped in the core region. Using this method, dB/dT could be made higher (~10(-7)/ degrees C) than that of standard PMFs (~10(-8)/ degrees C) or comparable to that of standard PMFs (~10(-9)/ degrees C).

We propose and experimentally demonstrate a tunable multi-wavelength SOA fiber laser based on a Sagnac loop mirror using elliptical core side-hole fiber. We fabricated different types of elliptical core side-hole fiber with elliptical or circular cladding shape. The measured modal birefringence of the fabricated fiber was 1.7x10(-4) (elliptical shape) and 1.16x10(-4) (circular shape), respectively. By carefully adjusting the polarization controller inside the cavity, we could obtain 18 discrete channels with SNR over 30 dB and channel spacing of 0.8 nm and 10 discrete channels with SNR over 30 dB and channel spacing of ~1.4 nm. The proposed fiber laser was rather stable and the temporal power fluctuation was less than 0.8 dB. In addition, by thermally heating the elliptical core side-hole fiber in the Sagnac loop, we could obtain a tunable multi-wavelength fiber laser.

We propose and experimentally demonstrate a simple multiwavelength Raman fiber laser based on few-mode fiber Bragg gratings without additional multichannel filters. The multiwavelength Raman laser output has a high extinction ratio of more than 45 dB. The multiwavelength output is so stable that the peak power fluctuation is less than 0.5 dB. The number of lasing wavelengths can be adjusted, corresponding to the properties of few-mode Bragg gratings with multiple resonant wavelengths. By the thermal tuning method, the lasing wavelength of each channel can be effectively controlled, and the laser's tunability is measured to be 10.5 pm/ degrees C.

We present an upstream transmission method in- dependent of temperature characteristics of the remote node (RN) in a WDM-PON. This method employs a self-injection locked Fabry-Perot laser diode (F-P LD) for upstream trans- mission in the optical network unit (ONU). Using this method, the sidemodes of the F-P LD are suppressed, and the F-P LD is matched to the center wavelength of the wave- length distributor/combiner placed at the RN. The experi- mental results confirm that bidirectional error-free transmis

A practically tunable multiwavelength Raman fiber laser based on few-mode fiber Bragg gratings without additional multichannel filters is investigated. We achieved high quality of the Raman laser output with a high extinction ratio of more than 45 dB. The number of lasing wavelengths can be adjusted by the properties of few-mode Bragg gratings with multiple resonant wavelengths. The lasing wavelength of Raman fiber laser can be readily controlled by the tension and compression strain, which correspond to the directional bending curvature change. The dynamic range of lasing wavelength change was more than 15 nm.

We present a method of helical long-period fiber grating (H-LPFG) fabrication by use of a CO2 laser for use as an optical torque sensor. A conventional optical fiber grating has periodic vertical index changes along its fiber axis, but a H-LPFG has a screw-type index modulation. The helical index modulation is obtained with the asymmetric index change caused by a single-side laser beam exposure. The H-LPFG shows peak shifts with codirectional or contradirectional torsion to the helix. Also, the polarization-dependent loss is measured to be relatively small compared with that of a conventional long-period fiber grating.

The systematic analysis of the relationship between temperature sensitivity of long-period fiber gratings and the doping concentrations of GeO 2 and B 2 O 3 in the core and cladding regions, depending on their structure ofthe refractive index profile, is investigated. Based on this analysis, the temperature sensitivities of fiber gratings are suppressed and enhanced to 0.002 and -0.44 nm/°C, respectively. We also discuss the versatile applications of long-period fiber gratings to gain-flattening filters of optical amplifiers and strain/temperature sensors, corresponding to their temperature sensitivity. The theoretical and experimental results are very useful for the design of optical communication devices and mechanical sensors based on long-period fiber gratings.

Unambiguous simultaneous measurement of strain and temperature based on dual long-period fiber gratings by controlling their thermal and strain sensitivities is proposed and experimentally demonstrated. The difference in the wavelength peak shift and the separation with the variation of strain and temperature allows discrimination between the strain and temperature effects, respectively.

The effect of stress-induced birefringence on polarization-dependent transmission characteristics was thoroughly investigated for a long-period fiber grating (LPFG) that was fabricated by use of a stress relaxation method with a CO2 laser. A series of two-dimensional axial stress profiles for one complete period of a LPFG was measured with an optical tomographic measurement technique. We found that the asymmetry in the stress distribution of the cladding was much larger than in the core of the LPFG. The splitting of polarization-dependent loss peaks in the optical transmission spectrum was calculated based on the measured asymmetric stress profiles and was compared with an experimental result.

We developed a Finite Element package to analyze cladding mode field extensions into the air-holes of photonics crystal fiber for refractive index sensing. Our analysis could determine the most sensitive cladding mode for liquid sensing.