Fiber laser hydrophone based on double diaphragms: Theory and experiment

A fiber laser hydrophone with enhanced sensitivity is demonstrated. Two diaphragms with a hard core fixed at each center are used as the sensing element. Theoretical analysis shows that the Young's modulus of the diaphragm and the radius of the hard core have significant effect on the acoustic sensitivity. Experiments are carried out to test this effect and the performance of the hydrophone. The experimental result agrees well with the theoretical result, and a sensitivity of 7 nm/MPa has been achieved.

Numerical analysis of gain saturation, noise figure, and carrier distribution for quantum-dot semiconductor-optical amplifiers

The gain saturation behaviors and noise figure are numerically analyzed for quantum-dot semiconductor optical amplifiers (QD-SOAs). The carrier and photon distributions in the longitudinal direction as well as the photon energy dependent facet reflectivity are accounted in the rate equations, which are solved with output amplified spontaneous emission spectrum as iterative variables. The longitudinal distributions of the occupation probabilities and spectral-hole burning are presented for electrons in the excited and ground states of quantum dots. The saturation output power 19.7 dBm and device gain 20.6 dB are obtained for a QD-SOA with the cavity length of 6 rum at the bias current of 500 mA. The influences of them electron intradot relaxation time and the QD capture time on the gain spectrum are simulated with the relaxation time of 1, 30, and 60 ps and capture time of 1, 5, and 10 ps. The noise figure as low as 3.5 dB is expected due to the strong polarization sensitive spontaneous emission. The characteristics of gain saturation and noise figure versus input signal power for QD-SOAs are similar to that of semiconductor. linear optical amplifiers with gain clamping by vertical laser fields.

Fiber Bragg grating pressure sensor with enhanced sensitivity

A novel fiber Bragg grating (FBG) pressure sensor with the enhanced sensitivity has been demonstrated. A piston-like diaphragm with a hard core in the center is used to enhance the sensitivity. Both the theoretical analysis and the experimental result show that the radius of the hard core has significant effect on the pressure sensitivity. When the radius of the hard core is 1.5 mm, a pressure sensitivity of 7.23 nm/MPa has been achieved.

DISCRETELY TUNABLE FIBER RING LASER USING FBG TUNABLE FILTER AND MACH-ZEHNDER INTERFEROMETER

A discretely tunable Er-doped fiber-ring laser using a fiber Mach-Zehnder interferometer (MZI) and a tunable fiber Bragg grating (FBG) is proposed. In this scheme, the combination of MZI and FBG acts as a discrete wavelength selector. Analysis of its transmission function shows that discrete wavelength tuning can be realized, and experiments demonstrate 64 single-mode outputs with a mode spacing of 181.7 pm, and the output power is quite stable in the whole tuning range. (C) 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51 2595-2598, 2009; Published online in Wiley InterScience (www. interscience.wiley.com). DOI 10.1002/mop.24690

FREQUENCY RESPONSE OF FIBER RING RESONATOR AND ITS APPLICATION IN DFB LASER WAVELENGTH VARIATION MEASUREMENT

Frequency response of a fiber ring resonator (FRR) composed of an ordinary optical coupler and a segment of optical fiber is theoretically and experimentally investigated. The frequency response equation based oil small-signal modulation is derived and studied in detail. It is shown that the shape of the frequency response curve is very sensitive to the wavelength; as a result, the FRR can be applied to measure the wavelength of a lightwave source with high resolution. With this method, we demonstrate the measurement of tiny changes of wavelength of a DFB laser. (C) 2009 Wiley Periodicals. Inc. Microwave Opt Technol Lett 51 2444-2448, 2009 Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24608

Elimination of environmental noise in interferometric wavelength shift demodulation for dynamic fiber Bragg grating sensor array

We present a novel reference compensation method for eliminating environmental noise in interferometric wavelength shift demodulation for dynamic fiber Bragg grating (FBG) sensors. By employing a shielded wavelength-division-multiplexed reference FBG in the system the environmental noise is mea, sured from the reference channel, and then subtracted from the demodulation result of each sensor channel. An approximate 40 dB reduction of the environmental noise has been experimentally achieved over a frequency range from 20 Hz to 2 kHz. This method is also suitable for the elimination of broadband environmental noise. The corresponding FBG sensor array system proposed in this paper has shown a wave-length resolution of 7 x 10(-4) pm/root Hz. (c) 2009 Elsevier B.V. All rights reserved.

MEMBRANE-BASED FIBER BRAGG GRATING PRESSURE SENSOR WITH HIGH SENSITIVITY

A fiber Bragg grating (FBG) pressure sensor packaged by using a hard core in the membrane is presented. By utilizing the unique membrane-based FBG packagine method, its pressure sensitivity has been effectively enhanced. The pressure sensitivity of the FBG reaches 5.75 X 10(-3)/MPa within the pressure range of 0.0.16 Mpa. (C) 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51 1279-1281, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24335

Fiber Bragg grating pressure sensor with ultrahigh sensitivity and reduced temperature sensitivity

A fiber Bragg grating (FBG) pressure sensing scheme based on a flat diaphragm and an L-shaped lever is presented. An L-shaped lever transfers the pressure-induced defection of the flat diaphragm to the axial elongation of the FBG. The curve where the L-shaped lever contacts the diaphragm is a segment of an Archimedes spiral, which is used to enhance the responsivity. Because the thermal expansion coefficient of the quartz-glass L-shaped lever and the steel sensor shell is different, the temperature effect is compensated for by optimizing the dimension parameters. Theoretical analysis is presented, and the experimental results show that an ultrahigh pressure responsivity of 244 pm/kPa and a low temperature responsivity of 2.8 pm/degrees C are achieved. (c) 2009 Society of Photo-Optical Instrumentation Engineers. [DOI 10.1117/1.3081058]

White light emission from fiber pigtailed laser module

We fabricated a phosphor-conversion white light using an InGaN laser diode that emits 445 nm and phosphor that emit in the yellow. The InGaN laser diode was coupled to an optical fiber firstly and the phosphor was excited by the laser light output from the fiber. At 350 mA injection current the luminous flux and the luminous efficacy was 73 lm and 42.7 lm/W, respectively. The luminance was estimated to be 50 cd/mm(2). The relationship of the luminous flux and the luminous efficacy of the white light with injection current were measured and discussed.

An optimized design of a fiber optic hydrophone based on a flat diaphragm and multilayer fiber coils: A theoretical approach

In this paper, we present a theoretical approach to optimize the design of a fiber optic hydrophone based on a flat diaphragm and multilayer fiber coils. In this theoretical analysis, both the radial and tangential strain induced fiber length changes are taken into account. The result shows that the position of the fiber coils and the number of the fiber layers have significant effects on the sensitivity, of the hydrophone. By optimizing these parameters, a higher sensitivity can be achieved. Sample hydrophones are fabricated and tested. The experimental result is in good agreement with the theoretical result, which shows this theoretical approach is effective in optimizing the design of the fiber optic hydrophone. (C) 2008 Elsevier Ltd. All rights reserved.

Pump-Suppressed Nondegenerate Four-Wave Mixing in a Highly Nonlinear Photonic Crystal Fiber Sagnac Loop

We propose a configuration for suppressing pumps in a broad- and flat-hand tunable nondegenerate four-wave mixing (FWM) wavelength converter. The signal and pumps are coupled into a highly nonlinear photonic crystal fiber symmetrical Sagnac loop. After the FWM wavelength conversion in the loop, the idler is separated from the pumps without a filter. In our experiment, a flat wavelength conversion bandwidth of 36 rim, conversion efficiency of-11 dB., pump-to-signal suppression ratio of 48 dB, and idler-to-pump suppression ratio of 15 dB are achieved.

All-optical continuously tunable delay with a high linear-chirp-rate fiber Bragg grating based on four-wave mixing in a highly-nonlinear photonic crystal fiber

A scheme for hi-fi all-optical continuously tunable delay is proposed. The signal wavelength is converted to a desired idler wavelength and converted back after being delayed by a high linear-chirp-rate (HLCR) fiber Bragg grating (FBG) based on four-wave mixing (FWM) in a highly-nonlinear photonic crystal fiber (HN-PCF). In our experiment, 400 ps (more than 8 full width of half maximum, FWHM) tunable delay is achieved for a 10 GHz clock pulse with relative pulse width broaden ratio (RPWBR) of 2.08%. The power penalty is only 0.3 dB at 10(-9) BER for a 10 Gb/s 2(31)-1 pseudo random bit sequence (PRBS) data. (c) 2009 Elsevier B.V. All rights reserved.

Passive Q-switched mode locking of double-clading Yb : fiber laser with ion-implanted GaAs

We report the technique of the ion-implanted semi-insulating GaAs wafer used for passive Q-switched mode locking in double-cladding Yb:fiber laser. The wafer was implanted with 400-keV energy, 10(16)/cm(2) dose As+ ions, and was annealed at 600degreesC for 20 min. At the pump power of 5W, we achieved output power of 200mW. The repetition rate of envelope of Q-switched mode locking is 50-kHz with a FWHM envelope of 4mus. The repetition rate of mode locked pulse train was found to be 15-MHz. This is the first report of such a kind of laser to the best of our knowledge.

Photon iterative numerical technique for steady-state simulation of gain-clamped semiconductor optical amplifiers

The photon iterative numerical technique, which chooses the outputs of the amplified spontaneous emission spectrum and lasing mode as iteration variables to solve the rate equations, is proposed and applied to analyse the steady behaviour of conventional semiconductor optical amplifiers (SOAs) and gain-clamped semiconductor optical amplifiers (GCSOAs). Numerical results show that the photon iterative method is a much faster and more efficient algorithm than the conventional approach, which chooses the carrier density distribution of the SOAs as the iterative variable. It is also found that the photon iterative method has almost the same computing efficiency for conventional SOAs and GCSOAs.

Temperature-independent fiber Bragg grating strain sensor using bimetal cantilever

A new packaged fiber Bragg grating using bimetal cantilever beam as the strain agent is presented. The grating is two-point attached on one specific surface of the bimetal beam which consists of two metallic material with different thermal-expansion coefficient. Thereby the grating can be compressed or stretched along with the cantilever beam while temperature varies and temperature compensation can be realized. At the same time, grating chirping can be avoided for the particular attaching method. Experiment results demonstrated that the device is able to automatically compensate temperature induced wavelength shift. The temperature dependence of Bragg wavelength reduced to -0.4 pm/degrees C over the temperature range from -20 to 60 degrees C. This fiber grating package technique is cost effective and can be used in strain sensing. (c) 2005 Elsevier Inc. All rights reserved.