Experimental Demonstration of Holographic Demultiplexer using Volume Diffraction Grating Based on Photopolymer
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Abstract:
A 42 channel demultiplexer for dense wavelength division multiplexing(WDM) using photopoly-mer volumetric diffraction grating that has excellent optical properties and low cost capability, has been designed and optically demonstrated. From the experimental results, we have obtained the 3 dB bandwidth of 0.18 nm, crosstalk suppression of 20 dB and channel uniformity of 1.6 dB for 50 GHB channel spacing.Keywords:
Demultiplexer
Channel spacing
Diffraction efficiency
Crosstalk
Diffraction efficiency
Photoresist
Groove (engineering)
Monochromatic color
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Abstract : The method of blazed holographic diffraction gratings fabrication by transformation of an original symmetric grating grooves into asymmetric ones using inclined vacuum deposition of silver and additional chemical etching have been developed. As photoresist material for gratings recording light-sensitive chalcogenide glassy As2Se3 layers were used. The shape of grating grooves was determined with an atomic force microscope. Angular and spectral dependencies of the diffraction efficiency of the gratings were found, and a relation between optical features and the grating surface pattern was analyzed.
Diffraction efficiency
Photoresist
Electromagnetically induced grating
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Optical coupling between preferential-order volume diffraction grating couplers fabricated on independent substrates is demonstrated. The coupling efficiency between gratings is quantified as a function of both grating and waveguide fabrication technology and relative angular position of the two substrates. A maximum grating-to-grating coupling efficiency of 31% is reported for coupling between two nonoptimized, nonfocusing, unpatterned volume grating couplers.
Diffraction efficiency
Electromagnetically induced grating
Waveguide
Ultrasonic grating
Guided-mode resonance
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The authors report a 480 channel 10 GHz spaced multi/demultiplexer achieved by using a three-stage parallel connection approach consisting of a WDM splitter, two 100 GHz spaced AWGS and 64 10 GHz spaced AWGs. The channel crosstalk to neighbouring and all other channels is < –20 dB. The multi/demultiplexer is capable of covering the entire wavelength range (1525–1564 nm) of silica-based optical fibre amplifiers. The channel spacing between every adjacent channel is measured and the results described.
Demultiplexer
Splitter
Channel spacing
Crosstalk
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Diffraction gratings are used in many optical systems as beam splitters. In these applications the diffraction grating must (1) have high diffraction efficiency and (2) produce uniform intensities in the central block of diffracted beams. High diffraction efficiency is attained by making the grating a phase grating. In this paper we discuss in some detail the use of pulse width modulation (PWM) and pulse position modulation (PPM) to create grating structures that produce uniform central diffracted beams. By using these modulation techniques and proper phase relief for the grating, the diffraction grating can have a diffraction efficiency of 70% or more. Some examples of multiple beam diffraction gratings produced by using PWM and PPM are shown.
Diffraction efficiency
Ultrasonic grating
Electromagnetically induced grating
Beam splitter
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The method of blazed holographic diffraction gratings fabricated by transformation of an original symmetric grating grooves into asymmetric ones using additional inclined irradiation by a monochromatic, or white light and repeated chemical etching have been developed. As photoresist material for gratings recording light-sensitive As2Se3 layers were used. Numerical modeling of the asymmetric groove formations was also carried out. The numerical results are in a good agreement with experimental groove profiles obtained by D3000 NanoScope. The asymmetry of produced gratings are clearly displayed in angular and spectral dependencies of the diffraction efficiency. The investigations shown that by changing the original grating formation parameters and the additional treatment conditions it is possible to produce blazed holographic gratings with designated groove form and blazed angle.
Diffraction efficiency
Photoresist
Groove (engineering)
Monochromatic color
Electromagnetically induced grating
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A 60-channel WDM demultiplexer based on a concave grating with 0.144 nm channel spacing in the 1.5 µm wavelength region was fabricated. The demultiplexer comprises SiO2/SiON/SiO2 waveguides on Si and an individual channel has a full width at half maximum spectral width of 0.09 nm.
Demultiplexer
Channel spacing
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The next-generation diffraction grating not only requires a nonmechanical control and a remote control to generate a diffraction pattern but also requires a tunable period. Here, we propose a stimuli-responsive liquid crystal (LC) phase grating with a tunable period and a diffraction order. The stimuli-responsive LC diffraction grating is composed of periodically arranged electrodes on a double-sided glass substrate. By adjusting the driving scheme, the pitch and diffraction order of the LC grating can be switched between three different modes. The experimental results show that the LC grating has a lower driving voltage (∼5 V). In addition, the tunable LC grating can achieve more diffraction orders, which can be applied to a holographic display to achieve a wide-viewing angle and an enlarged size.
Diffraction efficiency
Ultrasonic grating
Electromagnetically induced grating
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One of the factors determining the diffraction efficiency of the grating of a surface-relief hologram is the refractive index of the material. The refractive index of the photopolymer constituting a reproduced grating is smaller than that of the photoresist constituting the master grating. To reproduce the grating with a high diffraction efficiency, we studied how to optimize the grating shape. We found that a grating 0.5 μm wide required a master grating 0.9 μm wide to get the highest diffraction efficiency and that the reproduced grating had to be at least 1 μm deep. We fabricated a master and stamp and replicated gratings with a diffraction efficiency of 78 ±5%.
Diffraction efficiency
Electromagnetically induced grating
Ultrasonic grating
Photoresist
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We present a new design for N-channel wavelength division demultiplexer using multistage multimode interference (MMI) structure. First, the general formulation for an N-channel demultiplexer in multimode area has been discussed. In this paper, we proposed a single parameter for designing a demultiplexer with desired wavelengths, number of output channels and channel spacing. Then we simulated an 8-channel wavelength demultiplexer with high quality factor in the telecommunication range. The simulated structure shows 5 nm channel spacing and 2451 average quality factor. The excellent properties of this formulation are the high quality factor and its capability for choosing the desired number of output channels and channel spacing. The beam propagation method is used for simulation of the proposed device.
Demultiplexer
Channel spacing
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