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Room-temperature multiwavelength erbium-doped fiber ring laser employing sinusoidal phase-modulation feedback

An effective method for achieving a room-temperature multiwavelength erbium-doped fiber ring laser is presented. Simultaneous multiwavelength lasing with 0.5-nm intervals is achieved both experimentally and theoretically by addition of sinusoidal phase modulation in the ring cavity to prevent single-wavelength oscillation.

A New Approach for the Design of Wideband Digital Integrator and Differentiator

This brief presents a general theory of the Newton-Cotes digital integrators which is derived by applying the z-transform technique to the closed-form Newton-Cotes integration formula. Based on this developed theory, a new wideband third-order trapezoidal digital integrator is found to be a class of trapezoidal digital integrators. The novel wideband third-order trapezoidal integrator accurately approximates the ideal integrator over the whole Nyquist frequency range and compares favourably with existing integrators. Based on the designed wideband third-order trapezoidal integrator, a new wideband digital differentiator is designed, which approximates the ideal differentiator reasonably well over the whole Nyquist frequency range and compares favourably with existing differentiators. The low orders and high accuracies of the novel wideband trapezoidal integrator and the new wideband differentiator make them attractive for real-time applications

Design of an optical temporal integrator based on a phase-shifted fiber Bragg grating in transmission

We present a theoretical study of a new application of a simple pi-phase-shifted fiber Bragg grating (PSFBG) in transmission mode as a high-speed optical temporal integrator. The PSFBG consists of two concatenated identical uniform FBGs with a pi phase shift between them. When the reflectivities of the FBGs are extremely close to 100%, the transmissive PSFBG can perform the time integral of the complex envelope of an arbitrary input optical signal with high accuracy. As an example, the integrator is numerically shown to be able to convert an input Gaussian pulse into an optical step signal.

Multiwavelength Raman fiber laser with a continuously-tunable spacing

A spacing-tunable multiwavelength Raman fiber laser with an independently-adjustable channel number is proposed and demonstrated. It uses a novel free-spectral-range (FSR)-tunable comb filter based on a superimposed chirped-fiber Bragg grating (CFBG) and a linear cavity formed by a bandwidth-tunable CFBG reflector, a pumped highly-nonlinear fiber for Raman gain, and an optical circulator based loop mirror. Multiwavelength laser operations with spacing tuning from 0.3 to 0.6 nm and channel number adjustment from 2 to 10 have been achieved.

A novel temperature-insensitive fiber Bragg grating sensor for displacement measurement

This paper presents the design and development of an optical fiber Bragg grating based displacement sensor. A fiber Bragg grating is glued at a slant orientation onto the lateral side of a specially designed cantilever beam. It is found that the bandwidth of the FBG based sensor changes linearly with the variation of the displacement at the free end of the beam due to the displacement-induced strain gradient. Displacement sensing is realized by measuring the reflected optical power of the signal from the grating with a photodetector. A linear response of 37.9 mV mm−1 was obtained within a displacement range of 9.0 mm. This sensor is also cost-effective due to the use of a simple demodulation method and is inherently temperature insensitive, eliminating the need for temperature compensation.

Simple reflow technique for fabrication of a microlens array in solgel glass.

A simple reflow method for fabrication of refractive microlens arrays in inorganic-organic SiO2-ZrO2 solgel glass is presented. To our knowledge, this is the first report that presents a simple reflow technique for transforming a negatively induced hybrid solgel material into desirable spherical microlenses. It is shown that the microlenses have excellent smooth surfaces and uniform dimensions. The reflow technique is considerably cheaper than use of a high-energy beam-sensitive gray-scale mask and is suitable for mass production.

A largely tunable CFBG-based dispersion compensator with fixed center wavelength.

A largely tunable chirped fiber Bragg grating (CFBG)-based dispersion compensator with fixed center wavelength is demonstrated. Tunable dispersion ranging from 178 to 2126 ps/nm, corresponding to a large range of 3-db bandwidth from 0.42 to 5.04 nm, is realized by using a 10 cm-long CFBG with an original bandwidth of 1.61 nm. The variation in center wavelength is less than 0.2 nm.

Thermally tunable narrow-bandpass filter based on a linearly chirped fiber Bragg grating.

We propose a new method for the development of a tunable optical bandpass filter (TOBF) based on a linearly chirped fiber Bragg grating (LCFBG). A NiCr wire heater is used to heat the LCFBG at a small point to introduce a narrow passband within the stop band of the LCFBG. The central wavelength of the passband is tuned by scanning the wire heater along the LCFBG. As an example demonstrating the effectiveness of the proposed method, we demonstrate a TOBF with a very small 3-dB bandwidth of approximately 7 pm, a tuning range of 16.4 nm, and a rejection ratio of more than 25 dB. Compared with previously reported tunable-fiber-based bandpass filters, this method provides the advantages of a large tuning range, continuous tunability, a switchable passband, a simple tuning mechanism, low cost, and narrow bandwidth.

Electrically tunable dispersion compensator with fixed center wavelength using fiber Bragg grating

We present the design and development of a novel tunable dispersion compensator with fixed center wavelength that is based on the electrical adjustment of the chirp of a fiber Bragg grating (FBG). Both temperature gradient and strain gradient are employed to adjust the chirp of the FBG jointly. The electrical current flowing through the taper on-fiber thin-film heater will introduce a temperature gradient on the FBG. The shrinkage of a negative thermal expansion coefficient (NTEC) ceramic due to the temperature rise will compress the tapered FBG mounted inside it, and this will introduce a strain gradient on the FBG. The center wavelength of the FBG will be kept fixed because the effect of temperature rise on the FBG and the effect of compression of the FBG will offset each other. Applying an electrical power of less than 0.68 W, we demonstrate a linearly chirped FBG whose dispersion can be continuously adjusted from -178 ps/nm to -302 ps/nm with a central wavelength shift of as small as 0.16 nm.

A Dual-Wavelength Fiber Laser Sensor System for Measurement of Temperature and Strain

A strain and temperature-sensing scheme based on a dual-wavelength fiber laser is demonstrated experimentally. By measuring the change in the wavelength separation of the two lasing wavelengths and the shift of any of two lasing wavelengths, the measured strain and temperature are very linear and have a strain sensitivity of 0.15 pm/muepsiv over a range of 0-2400 muepsiv and a temperature sensitivity of 14.3 pm/degC over a range of 22degC-230degC, respectively.