Optical fiber long-period grating with solgel coating for gas sensor

The novel long-period fiber grating (LPFG) film sensor is composed of the long-period grating coated with solgel-derived sensitive films. The characteristics of the transmissivity of the LPFG film sensor are studied. By analyzing the relation among the sensitivity S-n, the thin film optical parameters, and the fiber grating parameters, the optimal design parameters of the LPFG film sensor are obtained. Data simulation shows that the resolution of the refractive index of this LPFG film sensor is predicted to be 10(-8). Experimentally, a LPFG film sensor for detection Of C2H5OH was fabricated, and a preliminary gas-sensing test was performed. (c) 2006 Optical Society of America.

beam-shaping microstructure optical fiber

Microstructure optical fiber with uniform intensity distribution of the fundamental mode is proposed. The design guide line and characteristics of this kind fiber are demonstrated. The relationship between refractive index profile and structure parameters is investigated. The mechanism of forming uniform fundamental mode in these fibers is analyzed.

Electronic structure and optical gain saturation of InAs1-xNx/GaAs quantum dots

The electronic band structures and optical gains of InAs1-xNx/GaAs pyramid quantum dots (QDs) are calculated using the ten-band k . p model and the valence force field method. The optical gains are calculated using the zero-dimensional optical gain formula with taking into consideration of both homogeneous and inhomogeneous broadenings due to the size fluctuation of quantum dots which follows a normal distribution. With the variation of QD sizes and nitrogen composition, it can be shown that the nitrogen composition and the strains can significantly affect the energy levels especially the conduction band which has repulsion interaction with nitrogen resonant state due to the band anticrossing interaction. It facilitates to achieve emission of longer wavelength (1.33 or 1.55 mu m) lasers for optical fiber communication system. For QD with higher nitrogen composition, it has longer emission wavelength and less detrimental effect of higher excited state transition, but nitrogen composition can affect the maximum gain depending on the factors of transition matrix element and the Fermi-Dirac distributions for electrons in the conduction bands and holes in the valence bands respectively. For larger QD, its maximum optical gain is greater at lower carrier density, but it is slowly surpassed by smaller QD as carrier concentration increases. Larger QD can reach its saturation gain faster, but this saturation gain is smaller than that of smaller QD. So the trade-off between longer wavelength, maximum optical, saturation gain, and differential gain must be considered to select the appropriate QD size according to the specific application requirement. (C) 2009 American Institute of Physics. [DOI 10.1063/1.3143025]

Simulation and fabrication of thermo-optic variable optical attenuators based on multimode interference coupler

A type of thermo-optic variable optical attenuator based on multimode interference coupler is proposed. The optical field propagation properties of the devices are simulated using finite difference beam propagation method. The propagation loss of the fabricated device is 2-4.2 dB at the wavelength range 1510-1610 nm. The total power consumption is 370 mW and the maximum attenuation is more than 25 dB, which almost can meet the requirements of optical fiber communication systems.

Electronic structure and optical gain saturation of InAs1-xNx/GaAs quantum dots

The electronic band structures and optical gains of InAs1-xNx/GaAs pyramid quantum dots (QDs) are calculated using the ten-band k . p model and the valence force field method. The optical gains are calculated using the zero-dimensional optical gain formula with taking into consideration of both homogeneous and inhomogeneous broadenings due to the size fluctuation of quantum dots which follows a normal distribution. With the variation of QD sizes and nitrogen composition, it can be shown that the nitrogen composition and the strains can significantly affect the energy levels especially the conduction band which has repulsion interaction with nitrogen resonant state due to the band anticrossing interaction. It facilitates to achieve emission of longer wavelength (1.33 or 1.55 mu m) lasers for optical fiber communication system. For QD with higher nitrogen composition, it has longer emission wavelength and less detrimental effect of higher excited state transition, but nitrogen composition can affect the maximum gain depending on the factors of transition matrix element and the Fermi-Dirac distributions for electrons in the conduction bands and holes in the valence bands respectively. For larger QD, its maximum optical gain is greater at lower carrier density, but it is slowly surpassed by smaller QD as carrier concentration increases. Larger QD can reach its saturation gain faster, but this saturation gain is smaller than that of smaller QD. So the trade-off between longer wavelength, maximum optical, saturation gain, and differential gain must be considered to select the appropriate QD size according to the specific application requirement. (C) 2009 American Institute of Physics. [DOI: 10.1063/1.3143025]

A New Technique for Side Pumping of Double-Clad Fiber Lasers

We report a new technique, called SAP, for side pumping of double-clad, rare-earth-doped fiber lasers using fiber-coupled pump sources. The highest coupling efficiency can even exceed 92% in theory with this structure.

Diffractive Grating Based Out-of-Plane Coupling between Silicon Nanowire and Optical Fiber

Submitted by 阎军 (yanj@red.semi.ac.cn) on 2010-06-04T07:55:26Z No. of bitstreams: 1 Diffractive Grating Based Out-of-Plane Coupling between Silicon Nanowire and Optical Fiber.pdf: 232805 bytes, checksum: 0bd17756b8a703bf8337dd25bbddaca3 (MD5)

Transient and nonlinear analysis of slow-light pulse propagation in an optical fiber via stimulated Brillouin scattering

We investigate slow-light pulse propagation in an optical fiber via transient stimulated Brillouin scattering. Space-time evolution of a generating slow-light pulse is numerically calculated by solving three-wave coupled-mode equations between a pump beam, an acoustic wave, and a counterpropagating signal pulse. Our mathematical treatments are applicable to both narrowband and broadband pump cases. We show that the time delay of 85% pulse width can be obtained for a signal pulse of the order of subnanosecond pulse width by using a broadband pump, while the signal pulse is broadened only by 40% of the input signal pulse. The physical origin of the pulse broadening and distortion is explained in terms of the temporal decay of the induced acoustic field. (C) 2009 Optical Society of America

Reducing group-velocity-dispersion-dependent broadening of stimulated Brillouin scattering slow light in an optical fiber by use of a single pump laser

We propose a method of effectively extending the stimulated Brillouin scattering (SBS) gain bandwidth in a single-mode optical fiber to reduce group-velocity-dispersion (GVD)-dependent pulse spread of SBS slow light. This can be done by overlapping doublet SBS gain spectra synthesized from a single pump laser. Numerical calculations are performed to verify our proposed method. We find that there exists the optimum spectral separation between two center frequencies of the doublet SBS gain spectrum with respect to the inherent spectral width of the pump laser, which makes it possible to effectively reduce the signal pulse broadening due to GVD. We show that the maximum time delay of the amplified signal pulse can be approximately two times longer than that by a previously reported method using a single broadband pump laser. (c) 2008 Optical Society of America.

Zero-broadening SBS slow light propagation in an optical fiber using two broadband pump beams

A new method of tailoring stimulated Brillouin scattering (SBS) gain spectrum for slow light propagation is proposed by use of two Gaussian-shaped broadband pump beams with different powers and spectral widths. The central frequency interval between the two pump beams are carefully set to be two inherent Brillouin frequency shift, ensuring that the gain spectrum of one pump has the same central frequency with the loss spectrum of the other one. Different gain profiles are obtained and analyzed. Among them a special gain profile is found that ensures a zero-broadening of the signal pulse independent of the Brillouin gain. This is owing to the compensation between the positive gain-dependent broadening and the negative GVD (group velocity dispersion) dependent broadening. The relationship of two pump beams is also found for constructing such a gain profile. It provides us a new idea of managing the broadening of SBS-based slow pulse by artificially constructing and optimizing the profile of gain spectrum. (c) 2008 Optical Society of America.

Guiding mode in elliptical core microstructured polymer optical fiber

A kind of microstructured polymer optical fiber with elliptical core has been fabricated by adopting in-situ chemical polymerization technology and the secondary sleeving draw-stretching technique. Microscope photography demonstrates the clear hole-structure retained in the fiber. Though the holes distortion is visible, initial laser experiment indicates that light can be strongly confined in the elliptical core region, and the mode field is split obviously and presents the multi-mode characteristic. Numerical modeling is carried out for the real fiber with the measured parameters, including the external diameter of 150 pin, the average holes diameter of 3.3 mu m, and the average hole spacing of 6.3 mu m. by using full-vector plane wave method. The guided mode fields of the numerical simulation are consistent with the experiment result. This fiber shows the strong multi-mode and weak birefringence in the visible and near-infrared band, and has possibility for achieving the fiber mode convertors, mode selective couplers and so on.

Distortion management of SBS slow light in a single-mode optical fiber by optimization of broadband SBS gain spectrum

SPIE

Fabrication of microstructured polymer optical fiber preform

SPIE