Photonic crystal based structures have been considered for optical communication applications. A class of novel symmetric structures consisting of cavities and waveguides have been proposed to serve as optical add-drop multiplexers. Light transfer processes in these structures are analyzed briefly. The problem of deviating from the perfect accidental degeneracy is addressed for practical designs, and the backscattering intensities are shown low for the slight deviations. Anomalous light refraction at a surface of a photonic crystal has also been studied. The limitations of prior theoretical methods for the transmission problem are discussed. An outline of a new analytic theory that overcomes these limitations is presented. Photonic crystals are fabricated on polymer multi-layer films and integrated with conventional channel waveguides.
Data bit rate, 1dB pass band and device dimensions are the key properties of dense wavelength division multiplexer (DWDM) devices. For blazed grating based DWDM structure, analysis shows that the bit rate is limited by the pulse broadening introduced by the grating. To reduce the pulse broadening, the output fiber array channel-to-channel pitch must be reduced. By decreasing the output channel pitch, 1dB pass band can be increased and the device dimensions can be shrunk. In this paper, we propose an ion-exchanged glass waveguide chip to be inserted into the WDM device in order to reduce the output channel spacing. To fabricate the low loss fiber compatible waveguides, two-step K+-Na+ and Ag+-Na+ ion-exchange process using BK7 glass as the substrate has been investigated. The optimal process conditions have been found. The waveguides fabricated by this two-step process have a propagation loss of 0.3dB/cm, a coupling loss to single mode fiber of 0.4dB and a polarization dependent loss of 0.1dB for 5cm long waveguides. The design of a 48 channel DWDM with this glass waveguide chip is given.
Wavelength division multiplexing (WDM) and demultiplexing (WDDM) devices are considered to be one of the key elements in optical networks. WDM device by using conventional, such as thin film filter and AWG based devices, can only be used as one device either multiplexing or demultiplexing. Here we propose a novel structure for WDM device, which is based on free-space diffraction-grating multiplexer/demultiplexer technology. By using multi-deck fiber arrays one device can function as both multiplexers and demultiplexers simutaneouly. In this paper we will give the structure and working principle for such device. We will also discuss the optical design issues. Finally we will present our experimental results. The devices can be used for bi-directional transmissions and optical transceivers in optical networks.
Communication between computing systems is recognized as the main limitation to increasing the speed of all-electronic systems beyond levels currently achieved in existing supercomputers. Optical interconnects hold great promise in eliminating current communication bottlenecks because of properties that stem from optics inherent parallelism. Wavelength-division multiplexing (WDM) technology, by which multiple optical channels can be simultaneously transmitted at different wavelengths through a single optical transmission medium is a useful means of making full use of optics parallelism over a wide wavelength region. In this talk, we review the working principles of wavelength division (de) multiplexers (WD(D)M) for optoelectronic interconnection in high-throughput optical links and address the optical design issues of Wd9D)Ms. Several grating-based WD9D)M structures are analyzed. We report experimental data for several versions of WD(D)Ms which exhibit low insertion loss, high reliability, and low cost.
We design a hybrid free-space wavelength-division multiplexers (MUX) that favor integration of matured high performance grating-based MUX and planar waveguide devices. By optimizing the component interfaces, we pursuit a divide-and-conquer method in the proposed hybrid integration. Meanwhile, a novel 6-channel coarse MUX based on layered diffractive optics is successfully designed. These two methods combined are promising in integrating multiple optical functions with cost-effective mass production.
We construct a passive grating-based wavelength-division (de)multiplexer (MUX/DMUX) for single-mode-fiber networks. The MUX/DMUX has almost identical bi-directional filtering characteristics on optical signals at wavelengths around 1550 nm. With total insertion loss less than 3 dB and an enlarged passing band of each channel, the encapsulated device exhibits very stable performance under temperature variation and is immune from mechanical vibration. The insertion loss of this device changes about 1 dB at temperatures from 25 degree(s)C to 60 degree(s)C, while the enter wavelength of each channel drifts about 8.3 X 10-4 nm/(nm(DOT) degree(s)C). Better results are expected with further optimization on the design. The device successfully demultiplexes 231 -1 PRBS signals up to 3.5 Gb/s per channel in an emulated amplifier-free local- area networks (LAN's) and metropolitan-area networks transmission. It is plausible the cost-effective MUX/DEMUX is an excellent candidate to meet 10 Gb/s all-optical multi- wavelength short-link applications.
In this paper, we first review the working principle of grating-base wavelength division (de)multiplexers (WD(D)M) for optical networks. Then key device parameters for WDM multiplexers, including insertion loss, isolation, channel passband, wavelength accuracy, polarization-dependent loss and temperature sensitivity are provided to evaluate the performance for the devices. After that, issues regarding optical design of grating-based WD(D)Ms for commercial uses are addressed. Next, several grating-based WD(D)M structures are analyzed with the procedures to optimize design of grating-based wavelength division (de)multiplexers. Based on these designs and analyses, we give the procedures of optimal design of devices with experimental data.
We describe the design and performance of a multimode 8- channel, 200 GHz-spaced dense wavelength division demultiplexer using a high order blazed grating. The mean insertion loss of this DEMUX is 1.95 dB. Adjacent crosstalk is measured to be better than -45 dB. The temperature test cycling from 20 to 60 degree(s)C indicates that the wavelength thermal drift is less than 0.00033 nm/ degree(s)C. The device has multi-mode fibers for both input and output, which is good for the optical networks in both metropolitan and local areas. The device is not sensitive to the disturbance of temperature and environment, so no temperature controller is needed.
The design, packaging, and performance of a novel 32 channel, 100GHz dense wavelength division
demultiplexer (DWDM) using the 22w' diffraction order of an Echelle grating is described. A fully
packaged prototype operating in the 1 .54 to 1 .57-rim spectral range is built and tested. The insertion losses
of all 32 channels are within -3.0±0.2 dB. The crosstalk between adjacent channels for all the 32 channels
is in the neighborhood of -30dB, and average 1dB optical pass band is O.256nm.
Key words: Wavelength division demultiplexing, Echelle grating, dispersion ability, DWDM packaging
The novel structure of DWM(D)M in the applications of optoelectronics interconnects is proposed, which combines of planar optics and chirp grating. The chirp grating in the devices functions as both dispersive element and lens, which makes the device cost-effective. In this paper, grating- based WDM is intruded first. Then the novel structure of DWDM based on the combination of planar optics and chirp grating is given. The issues for designing such device are discussed next. Finally, the preliminary experimental work is given. The results show the WDM device based on this structure is promising in data communications and optoelectronic interconnects from board to board or from machine to machine.
A 32-channel wavelength-division demultiplexer has been designed and tested. Intended for commercial use, the instrument is designed to be rugged, stable, and insensitive to temperature variations. Operating in the 1.54-1.57-micrometers spectral range, the unit uses single-mode fiber input and multi-mode fiber output. The optics consists of a Littrow plane-grating spectrograph that uses the same lens for collimation and for focusing. In order to reduce the size of the device, the gratin is used at a large diffraction angle. A coarse ruling is used in a high diffraction order, which results in a device that has a low polarization-dependent loss. The mean insertion loss for all channels was 3.1 dB, and the standard deviation of the insertion loss was 0.23 dB. The mean channel bandwidth was 0.26 dB.
Close-form expressions are used to analyze the spatial and angular linearity of the out-coupling volume holograms in wavelength division multiplexing/demultiplexing (WDM/WDDM). Optimal spatial linear out-coupling regimes are located. Some design criteria for volume holographic WDDM applicable to 800nm, 1300nm, and 1550nm optical wavelength window are addressed. As a design example, we deploy these criteria to design a passive surface normal input/output wavelength division demultiplexer working in the wavelength range of 768-864 nm. Coupling of the demultiplexed optical signal from the substrate modes to a linear multi-mode fiber array is verified with experiment. The importance of the spatial linearity of the out-coupling in volume holographic WDDM structure is highlighted and possible coupling of the signal to linear single-mode fiber array is mentioned.
In FTIR film thickness measurement system, traditional process for determining film thickness is optical interference method or absorption method. In practice, both interference effect and absorption effect make a partial contribution to spectrum respectively. When both of the tow effects have influence on measurement, neither interference method nor absorption method can be individually used to determine the film thickness accurately. A new mathematical correction method is described for FTIR film thickness measurement in this case. Employing this new mathematical correction method, the effects of interference and absorption can be apart form each other effectively. The film thickness measurement accuracy of (lambda) /100 has been achieved.
A high-speed automatic agricultural produce grading and sorting system using color CCD and new color identification algorithm has been developed. In a typical application, the system can sort almonds into tow output grades according to their color. Almonds ar rich in 18 kinds of amino acids and 13 kinds of micro minerals and vitamins and can be made into almond drink. In order to ensure the drink quality, almonds must be sorted carefully before being made into a drink. Using this system, almonds can be sorted into two grades: up to grade and below grade almonds or foreign materials. A color CCD inspects the almonds passing on a conveyor of rotating rollers, a color identification algorithm grades almonds and distinguishes foreign materials from almonds. Employing an elaborately designed mechanism, the below grade almonds and foreign materials can be removed effectively from the raw almonds. This system can be easily adapted for inspecting and sorting other kinds of agricultural produce such as peanuts, beans tomatoes and so on.
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