Design and Analysis of 4×4 Arrayed Waveguide Grating Multiplexer

The operation principle of an arrayed waveguide grating(AWG) multiplexer is introduced and the 4×4 AWG with following design parameters is discussed in detail, such as the choice of wavelength, the neighboring arrayed waveguide distance ΔL, the channel frequency interval Δf, and the free spectral range. The structure of 4×4 AWG is designed and the result of stimulated test is also given. Analysis shows that the 4×4 AWG is characterized by a wide dynamic range, low crosstalk, better spectrum properties, and a compact structure.

Analyzing the Location of the Transmission Windows in Phase-shifted Fiber Grating

Using the matrix approach,we analyzed the relation between the location of the transmission in stop band and the phase shift,and discussed the problem of varying the bandwidth of the transmission window.These theoretical results in this paper have important significance for actual application of the phase-shifted fiber grating.

Analysis of Optical Signal Transmission Characteristics in AWG Multi/Demultiplexer with Electromagnetic Field Theory

Based on the electromagnetic field theory, the optical signal transmission characteristics in input/output waveguides, slab waveguides and arrayed waveguides of the arrayed waveguide grating (AWG) multi/demultiplexer are analyzed. The relationship between the physical parameters such as geometry sizes and relative refractive index in AWG multi/demultiplexer and the optical signal transmission characteristics are discussed. This theoretical study can be used for optimizing the design and improving the performance of the AWG multi/demultiplexer.

Analysis of Sampled Fiber Bragg Grating Based on the Photonic Crystal Theory

One of the most basic characteristics of photonic crystal is frequency band gap. When defects are introduced into the periodic photonic crystal, a number of defect modes appear in the stop band. In this paper, we exploit transfer matrix method based on photonic crystal theory, and assume the sampled fiber Bragg grating as one-dimensional dual photonic crystal with a large size defect. Characteristics of the sampled fiber Bragg grating are analyzed. Experimental results show that the sampled fiber Bragg grating has many reflective peaks. Its reflectivity, center wavelength, reflective peak intervals and band width all change with the grating parameters, including grating length, duty ratio of the material with high dielectric constant, and index modulation depth and period. Results agree with the conventional couple mode theory which can be used when analyzing other characteristics of the sampled fiber Bragg grating or applying it into practice.

10-Gb/s Transmission in WDM PON Employing Reflective Semiconductor Optical Amplifier and Fibre Bragg Grating Equaliser

We propose a 10-Gb/s Wavelength- Division-Multiplexed Passive Optical Network （WDM-PON） scheme with upstream transmi- ssion employing Reflective Semiconductor Op- tical Amplifier （RSOA） and Fibre Bragg Gra- ting （FBG） optical equaliser. Transmissions of 10-Gb/s non return-to-zero signals using a 1.2- GHz RSOA and FBG optical equaliser with different setups are demonstrated. Significant performance improvement and 40-kin standard single mode fibre transmission are achieved using FBG optical equaliser and Remotely Pum- ped Erbium-Doped Fibre Amplifier （RP-EDFA）, where they are used to equalise the output of the band-limited RSOA and amplify the seed light and upstream signal, respectively.

基于空间滤波测速系统的分析和验证

光电测量技术由于具有抗干扰和非接触的特点,在工业生产中被广泛应用。介绍了一种基于空间滤波原理的非接触速度测量方法。该方法将传输光栅作为空间滤波器,对运动信号进行滤波,由光电检测器检测信号,处理后得到速度信息。通过仿真和实验证明该方法具有很高的测速精度,能够在实际应用中得到推广。

Study on transmission characteristics of photonic crystal fiber gratings with periodic air hole deformation

The paper studies a kind of improved photonic crystal fiber gratings fabricated by CO2 laser heating method. The effective refractive index of cladding induced by periodic air hole deformation is computed using multipole method, and the rela-tionship between the effective refractive index and the collapse of air-holes is discussed, thereby the modulation expression of effective refractive index is obtained. The grating transmission characteristics are simulated. The results indicate that with the diameter of air-holes increasing from 3.3 ~m to 3.7 μm, the resonance wavelength shows blue-shift, the resonance peak intensifies, and the bandwidth becomes narrow. As the collapse degree of cladding enhances, the resonance wave- length shows red-shift, the transmission increases, and the bandwidth tends to narrow.

Characteristic analysis of a novel F-P interferometer based on a pair of FBGs with built-in LPFGs

The transmission characteristics of a Fabry-Perot （F-P） interferometer based on a fiber Bragg grating （FBG） pair with a built-in long-period fiber grating （LPFG） are theoretically analyzed, and the shift of transmission interference fringe as a function of environmental refractive index is acquired. The influence of the lengths of F-P cavity, LPFG and FBG on the transmission characteristics of the proposed interferometer has been numerieaUy investigated, and the simulation results indicate that the sensitivity of refractive index reaches 2.27 × 10-6 for an optical spectrum analyzer （OSA） with a resolution of 1 pm.

Advances and New Applications Using the Acousto-Optic Effect in Optical Fibers

This work presents a short review of the current research on the acousto-optic mechanism applied to optical fibers. The role of the piezoelectric element and the acousto-optic modulator in the excitation of flexural and longitudinal acoustic modes in the frequency range up to 1.2 MHz is highlighted. A combination of the finite elements and the transfer matrix methods is used to simulate the interaction of the waves with Bragg and long period gratings. Results show a very good agreement with experimental data. Recent applications such as the writing of gratings under the acoustic excitation and a novel viscometer sensor based on the acousto-optic mechanism are discussed.

Extraction efficiency enhancement of LEDs using 2-D photonic crystal

Using photonic crystals (PCs), the extraction efficiency of the light-emitting diodes (LEDs) can be greatly enhanced by the effects of photonic band gap (PBG) and grating diffraction. The two theoretical methods are also discussed. Meanwhile, we demonstrate that LEDs can achieve high extraction efficiency by employing photonic crystal as diffraction grating. PCs with square lattice of cylindrical unit cells are fabricated in GaN layer of GaN-based blue LED. We present a theoretical discussion on the extraction efficiency of PC-LED, which relies on the effective medium theory and transmission matrix method to investigate the effect of lattice constant. The results show that the extraction efficiency of the high performance LEDs can achieve 61.8% when the lattice constant is 270 nm.

An AWG-based 10 Gbit/s colorless WDM-PON system using a chirp-managed directly modulated laser

We propose an arrayed waveguide grating(AWG)-based 10 Gbit/s per channel full duplex wavelength division multiplexing passive optical network(WDM-PON).A chirp managed directly modulated laser with return-to-zero(RZ) differential phase shift keying(DPSK) modulation technique is utilized for downlink(DL) direction,and then the downlink signal is re-modulated for the uplink(UL) direction using intensity modulation technique with the data rate of 10 Gbit/s per channel.A successful WDM-PON transmission operation with the data rate of 10 Gbit/s per channel over a distance of 25 km without any optical amplification or dispersion compensation is demonstrated with low power penalty.

Fabrication of triangular fiber Bragg grating based on the one-step method

A new method is presented to fabricate the triangular fiber Bragg grating(TFBG).The fabrication device is simple,only requires a single exposure and does not need to write complicated program.The transfer matrix method is used to design the fiber Bragg grating,and the grating resonant wavelength and the grating reflectivity can be controlled in order to achieve the triangular spectrum.With different fiber tilt angles,the available bandwidth of TFBG,the linearity and the oblique gradient are also different.In the experiment,the angles 1°,1.5° and 2° are chosen.The results show that the best angle value is 1.5°,and the TFBG has a good linearity,greater gradient and wider available bandwidth.

Optical pulse shaping based on a double-phase-shifted fiber Bragg grating

Based on the transfer matrix method,a detailed theoretical and numerical study on double-phase-shifted fiber Bragg grating(FBG)is investigated.Temporal responses of the double-phase-shifted FBG to optical pulse are analyzed and the influence of the two phase-shifts’position on the reflected output pulse is evaluated.Results demonstrate that very different temporal pulse waveforms can be achieved by adjusting the length ratio(α=L2/L1).Specifically,a transform-limited Gaussian input optical pulse can be shaped into flat-top square pulse(α=1.81)or two identical optical pulse sequences(α=1.93).

Analysis of Transmission Characteristics of Tilted Long Period Fiber Gratings With Full Vector Complex Coupled Mode Theory

Based on the full vector complex coupled mode theory, a detailed analysis is made on the transmission spectrum characteristics of tilted long period fiber gratings. New transmission peaks are observed, which are located beside the long wavelength side of each transmission peak in the transmission spectrum of normal long period fiber gratings. The emerging transmission peaks are quite sensitive to both the grating tilted angle and the surrounding refractive index, and the corresponding relationship is discussed. Furthermore, a novel sensing characteristic is investigated about the tilted long period fiber gratings, which is related to the transmission resonant wavelength and peak amplitude.