All‐optical multi‐wavelength header recognition using superimposed Bragg gratings based correlators

We have demonstrated that an optical correlator, based on superimposed Bragg gratings, can be used as all‐optical multi‐wavelength header recognition in optical packet switching networks. The proposed correlator is composed of two superimposed gratings in conjunction with variable delay lines. These superimposed Bragg gratings are used to demultiplex and multiplex the wavelength components of multi‐wavelength header bit patterns. The variable delay lines create a wavelength profile that can be matched with any arbitrary bit patterns. Simulation results for all optical recognition of four‐bit patterns at 10 Gbps are reported. The results show that when the header bit pattern matches the wavelength profile of the correlator, the generated auto‐correlation function will include a high amplitude peak; otherwise, a cross‐correlation function with low amplitude peaks will be generated in the output of the correlator. Considering this idea, multi‐wavelength header is recognized by using all‐optical processing method. Copyright © 2012 John Wiley & Sons, Ltd.     

High-efficiency semiconductor resonant-cavity light-emittingdiodes: a review

An overview of highly efficient resonant-cavity light-emitting diodes is presented. First, the basics of dipole emission in planar cavities are reviewed. From these, a number of design rules are derived. We point out some guidelines for comparison of high-efficiency light-emitting diodes, and use these to review the state-of-the-art devices in different material systems and at different wavelengths. We also discuss some advanced techniques based on gratings or photonic crystals to improve the efficiency of these devices     

N/spl times/N arrayed waveguide gratings with improved frequency accuracy

The limitations imposed by the frequency standards on the performance of N/spl times/N arrayed waveguide gratings (AWGs) are reviewed for different device layouts. An improved design that allows for an enhanced frequency accuracy of the transmission response of the device is presented and experimentally verified. The maximum deviation from the frequency standards is reduced by almost a factor of two in a 32 /spl times/ 32 AWG with 100 GHz channel spacing.     

A novel electrically tunable dispersion compensation system

We propose a system for tuning with an electrical signal dispersion compensation over a broad range of transmission distances for different transmission bit rates. It is composed of chirped gratings and a phase modulator with an electrical modulation signal varying to achieve the tuning in the link length for which the dispersion is compensated. It is demonstrated that with fiber gratings and a phase modulator in the proposed configuration, a broader tuning range than with the prechirp technique is achieved. The influence of the fiber grating ripples in the system behavior is also considered     

Frequency range extension of actively mode-locked lasers integratedwith electroabsorption modulators using chirped gratings

We have fabricated actively mode-locked lasers integrated with electroabsorption modulators and chirped gratings. A chirped grating with a large chirp rate of 1.45 Å/μm can be realized by using multiphase-shifted patterns. Short pulses of 4-6 ps were generated over a wide frequency range from 18.9-19.8 GHz. We observed jumps in the wavelength during detuning. These jumps arise from multiple lobes in the reflectivity spectrum. It is found that the wavelength jumps cause increases in the intensity noise. We showed that by reducing the grating length from 150 to 100 μm the sidelobes were suppressed and the detuning frequency range of over 1% could be realized. A smaller pulsewidth was obtained for the negatively-chirped gratings when compared to the positively chirped gratings     

基于光纤光栅传感器的智能电器温度场监测

介绍了布拉格光纤光栅传感器工作原理,针对光纤光栅传感器检测智能电器温度场的关键技术,提出一种基于分布式光纤温度传感原理的智能电器在线监测系统的技术架构,并做了相应的分析.该技术可提高智能电器设备的可靠性.     

Design and realization of long-period grating devices inconventional and high birefringence fibers and their novel applicationsas fiber-optic load sensors

We report the design and fabrication of long-period fiber gratings with single and cascaded structures in conventional and high birefringence (hi-bi) fibers using amplitude mask and point-by-point writing techniques. We also report a novel application of long-period gratings produced in nonhigh-birefringence fiber as fiber-optic load sensors exhibiting very high transverse strain sensitivity. Sensitivity some 800 times greater than previously reported fiber Bragg grating (FBG) sensors has been achieved     

Calculation of dispersion in arrayed waveguide grating demultiplexers by a shifting-image method

It is shown that, as a first approximation, chromatic dispersion in demultiplexers based on arrayed waveguide gratings (AWGs) is proportional to the local spatial curvature of the wavefronts of the field at the output of the input guide, whose image shifts across the output guide as frequency changes. More accurate results can be obtained by convolving the input field with the AWG impulse response and the output guide mode. This approach to the calculation of dispersion provides physical insights from the field of imaging, not available with the commonly used method which relies on a Fourier series approach. Spherical wavefronts lead to constant dispersion. The use of a parabolic taper at the end of the input guide can lead to large amounts of dispersion, varying across the filter passband; this case is treated in detail. The method can also be adapted for use with demultiplexers based on reflective echelle gratings.     

Tunable optical nanocavity based on modulation of near-field coupling between subwavelength periodic nanostructures

We present the design and analysis of a tunable resonant optical filter based on modulation of the near-field coupling between two subwavelength periodic nanostructures embedded in a Fabry-Pe/spl acute/rot cavity. Due to the transverse localization of the optical field in the subwavelength gratings, their relative positioning strongly influences the near-field coupling between them and, thus, affects the resonance of the cavity. Rigorous electromagnetic analysis tools are applied to determine the optical characteristics of the filter with respect to the nanostructure lateral alignment, small variations in the shape of the nanostructures, and the physical separation of the nanostructures.     

Incoherent Beam Combining of Continuous-Wave and Pulsed Yb-Doped Fiber Amplifiers

We review the technique of incoherent beam combining and show experimentally the combination of four continuous wave fiber amplifiers to an average power of 2 kW and four pulsed 2 ns fiber amplifiers to an average power of 187 W (pulse energy 3.7 mJ) using binary dielectric gratings. The scaling potential and limitations are discussed in detail.     

InGaAs angled-grating distributed Bragg reflector lasers integrated with grating outcoupler for collimation

An angled-grating distributed Bragg reflector (DBR) laser integrated with a grating outcoupler (GO) is proposed and demonstrated. It consists of an angled broad-area gain stripe surrounded by angled DBR (/spl alpha/-DBR) gratings parallel to the gain stripe and two DBR gratings for feedback at the stripe ends, and a GO for emitting a collimated output beam. Due to distributed Bragg reflection in the /spl alpha/-DBR gratings, filamentation can be suppressed. Single-mode lasing up to 69 mW peak power was obtained under pulse condition. A collimated output beam with divergence angles, close to the diffraction limit, was obtained. These results confirm the effectiveness of the /spl alpha/-DBR gratings.     

A Rigorous,Coupled-Wave Transfer Matrix Method for Two-Dimensional Threshold Analysis of Distributed Feedback Semiconductor Lasers

A rigorous, truly two-dimensional method for threshold analysis of distributed feedback (DFB) lasers based on a coupled wave transfer matrix formalism is presented. The method makes it possible to systematically study the effect of the various structural and material properties parameters of the laser on the threshold gain and lasing frequency. Since the optical fields inside and outside the laser are very accurately represented in our analysis, the small differences in gain of pairs of longitudinal laser modes symmetrically located on both sides of the gap can be more accurately calculated than in any previous work. The analysis is applicable to gratings of any shape for both the TE and TM modes, but numerical results are given only for first-order gratings with rectangular and triangular tooth-shape. Reflectivities of the laser end facets have been calculated from first principles in some typical cases rather than treated as given parameters.     

AWG technologies for dense WDM applications

This paper reviews the recent technologies supporting arrayed waveguide gratings (AWGs) based on planar lightwave circuits. From the practical point of view, I describe new technologies such as an athermalization and the high-contrast waveguide that includes the mode field transfer needed for low connection loss with conventional optical fiber. As AWG applications, I present new types of AWG modules such as a dynamic gain equalizer and a variable optical attenuator (VOA) MUX/DEMUX. Both of these will play an important role for next-generation wavelength-division multiplexing networks.     

啁啾光纤光栅制作方法

啁啾光纤光栅是一种可用于光纤通信、光纤传感和光纤光源等光纤技术的重要器件。如何有效地制作所需要的啁啾光纤光栅是一个广为关注的问题。本文对观有的啁啾光纤光栅制作方法作了简单介绍和比较，讨论了各种方法的缺点。     

Coupled resonator optical waveguides

Properties of the recently introduced family of coupled resonator optical waveguides (CROWs) are reviewed, particularly with reference to CROWs designed as planar waveguides in two-dimensional photonic crystal slabs to enhance nonlinear interactions and develop novel all-optical information processing devices. Topics covered include: pulse propagation both in the nondispersive approximation and to all orders of dispersion, and the coupled mode theory of nonlinear optics with pulses in CROWs and its applications to second-harmonic generation and wave coupling via field-induced refractive-index gratings. We also review recent experimental progress in the fabrication and characterization of CROWs, and applications of the CROW concept to fiber gratings and microwave waveguides     

Monolithically integrated eight-channel WDM modulator with narrow channel spacing and high throughput

We demonstrate an eight-channel wavelength division multiplexing (WDM) modulator module that monolithically integrates arrayed waveguide gratings and semiconductor optical amplifiers and electroabsorption optical modulators arrays. The compact module can generate individual optical signals for each WDM channel with low optical and electrical crosstalk. We show two configurations for the narrow channel spacing of 25 GHz and high throughput of beyond 80 Gb/s. Combining this WDM modulator with a multi-wavelength light source is a promising approach to creating a compact WDM optical transmitter.     

Simulation and design of integrated femtosecond passively mode-locked semiconductor ring lasers including integrated passive pulse shaping components

In this paper, a model is presented for the simulation of integrated passively mode-locked InP-InGaAsP ring laser systems that include active components such as an amplifier and saturable absorber, and passive components that can be frequency dispersive. These dispersive components can have a complex frequency dependence, such as arrayed waveguide gratings (AWGs). The model is a lumped-element model that is used as a design tool for developing integrated femtosecond pulse sources with internal dispersion control. Simulations based on an InP/InGaAsP amplifier and absorber show the possibility of laser designs that are able to generate pulses with pulse durations down to 300 fs in the 1550-nm wavelength range. The designs are based on femtosecond laser systems in bulk and fiber optics that are published in the literature. The femtosecond laser sources presented here can be realized using existing InP-InGaAsP active-passive integration technology.     

WDM operation of a hybrid emitter integrating a wide-bandwidthon-chip mirror

A wide-bandwidth on-chip mirror based on a deeply etched Bragg grating localized over 10 μm is presented; it exhibits reflectivity over more than 25 nm. Integration within a laser-Mach-Zehnder modulator is shown and the wavelength-division multiplexing capability of the device demonstrated in a hybrid Bragg reflector configuration, by showing operation of the same InP chip with fiber gratings from 1534 to 1558 nm     

Chirped fiber Bragg gratings for electrically tunable time delay lines

In this paper, a continuously variable delay line for phased array antennas is presented. The proposed delay line operates at a single wavelength and is based on properly designed linearly chirped fiber Bragg gratings. Continuous true time delay can be achieved by changing the temperature or strain along the grating region. Numerical results show that the delay line can be used for wide-band beamforming at radio frequencies up to 30 GHz with 1 ps as minimum time delay.