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Publications

Partial etch phase (PEP) optical elements for high-volume applications

T. W. Mossberg ; J. M. Hannigan and D. Iazikov

Proc. SPIE 10115, Advanced Fabrication Technologies for Micro/Nano Optics and Photonics X, 1011504 (February 20, 2017); doi:10.1117/12.2250038;

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Using binary etch and sub-wavelength DUV photolithography, we have designed and fabricated a variety of flat optical devices (lenses, vortex phase plates, vortex plus lens, and diffusers) useful in telecommunications and other areas. The devices provide the precision and low cost associated with modern semi-conductor manufacturing and offer unique functional performance. Since the design method involves selective binary removal of substrate material we designate derivative devices partial etch phase (PEP) devices. Design principles and fabricated device performance are described.


Diffraction-limited performance of flat-substrate reflective imaging gratings patterned by DUV photolithography
Christoph M. Greiner, D. Iazikov and T. W. Mossberg , Optics Express, Vol. 14, No. 25, pp. 11952 � 11957 (2006)
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We report on the first demonstration of flat substrate imaging gratings fabricated by deep ultraviolet (DUV) photoreduction lithography, which uniquely offers sub-100-nm resolution and spatial coherence over centimeter scales. Reflective focusing gratings, designed according to holographic principle, were fabricated on 300-mm silicon wafers by immersion DUV lithography. Spatial coherence of the fabrication process is evident in measured diffraction-limited imaging function. Flat-substrate gratings, with lines of arbitrary spacing and curvature, offer both dispersion and general spatial wavefront transformation combining the function of multiple optical elements. Fabrication at the sub-100-nm resolution level allows high-line-count, low-order efficient gratings even into the deep ultraviolet region. Nanoreplication of gratings at the wafer level provides a pathway to devices of ultimate low cost.


Million-Q Reflection-Based Integrated Resonators Patterned With Deep Ultraviolet Photolithography
Christoph M. Greiner, D. Iazikov and T. W. Mossberg , Photonics Technology Letters, Vol. 18, No. 24, pp. 2677 � 2679 (2006)
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We describe million- one- and two-dimensional integrated reflective resonators based on ultralow-loss etched Bragg reflectors patterned on silica-on-silicon slab and channel waveguides using deep ultraviolet photoreduction lithography. Measured device performance, obtained in the limit of high reflectivity, provides insights in loss mechanisms operative in the subject systems. Implementation of integrated reflection-based resonators with high- and finesse values promises new directions in photonic integration with applications in sensing, filtering, and signal transport.


Interleaved sampled Bragg gratings with concatenated spectrum
J.M. Castro, J.E. Castillo, R. Kostuk, C.M. Greiner, D. Iazikov, T.W. Mossberg and D.F. Geraghty, Photonics Technology Letters, Vol. 18, No. 15, pp. 1615 � 1617 (2006)
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We design and demonstrate interleaved sampled Bragg gratings with concatenated spectrum which produce high channel counts with simple design and fabrication. These gratings can be applied in multichannel filtering, dispersion compensation, and many other functions. The devices were implemented as reduction-photolithographically written anti-symmetric Bragg gratings.


Integrated holographic filters for flat passband optical multiplexers
D. Iazikov, C. M. Greiner, and T. W. Mossberg, Optics Express, Vol. 14, No. 8, pp. 3497 � 3502 (2006)
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Lithographically rendered, slab-waveguide-based, volume holographic filters are shown, via fabrication and test, capable of providing fully integrated, single-mode compatible, flat-topped and low loss filtering for wide bandwidth multiplexers as, for example, used in coarse wavelength division multiplexing (CWDM). Single-mode compatibility is preserved since the filters operate via multi-path interference like thin-film filters rather than the angular dispersion typically utilized by grating type devices. Flexible apodization, entirely consistent with simple binary etch, is employed to provide steep passband falloff. High reflectivity and wide bandwidth is enabled through a tailored dual core waveguide geometry providing for mode concentration on the diffractive elements.


Compact OCDMA Encoders Based on the Antisymmetric Waveguide Bragg Grating
Jose M. Castro, Ivan Djordjevic, Lyubo Minkov, Christoph M. Greiner, Dmitri Iazikov, Thomas W. Mossberg, and David F. Geraghty, Photonics Technology Letters, Vol. 18, No. 7, pp. 892 – 894 (2006)
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Optical code-division multiple-access (OCDMA) networks require simple encoders/decoders enabling the integration of optical devices for further development. In this letter, we use silica-on-silicon antisymmetric waveguide Bragg grating devices to demonstrate compact and versatile OCDMA encoder/decoders. These devices use mode conversion to perform all-optical functions on chip.


Optical add�drop multiplexers based on the antisymmetric waveguide Bragg grating
Jose M. Castro, David F. Geraghty, Seppo Honkanen, Christoph M. Greiner, Dmitri Iazikov, and Thomas W. Mossberg, Applied Optics, Vol. 45, No. 6, pp 1236-1243 (2006)
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A novel optical add�drop multiplexer (OADM) based on a null coupler with an antisymmetric grating was designed and experimentally demonstrated. The antisymmetric grating exclusively produces a reflection with mode conversion in a two-mode waveguide. This improves the performance compared with previous demonstrations that used tilted Bragg gratings. Our design minimizes noise and cross talk produced by reflection without mode conversion. In addition, operational bandwidth and, versatility are improved while the compactness and simplicity of the null coupler OADM are maintained.


Demonstration of mode conversion using anti-symmetric waveguide Bragg gratings
Jose M. Castro, David F. Geraghty, Seppo Honkanen, Christoph M. Greiner, Dmitri Iazikov and Thomas W. Mossberg, Optics Express, Vol. 13, No. 11, pp. 4180 � 4184 (2005)
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We experimentally demonstrate a novel grating which only produces reflection with mode conversion in a two-mode waveguide. That characteristic can improve the performance of optical devices that currently use tilted Bragg gratings to provide the mode conversion. Tilted Bragg gratings produce also reflections without mode conversion which increases noise and crosstalk of the optical device.


Integrated Holographic Encoder for Wavelength-Hopping/Time-Spreading Optical CDMA
Yue-Kai Haung, Varghese Baby, Paul R. Prucnal, Christoph M. Greiner, Dmitri Iazikov and Thomas W. Mossberg, Photonics Technology Letters, Vol. 17, No. 4, pp. 825 – 827 (2005)
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We report on the application of an integrated holographic device to the generation of two-dimensional (time-frequency) optical codes for use in optical code-division multiplexing based on wavelength encoding/time spreading. The dual code device is based on two holographic Bragg reflectors and allows one to encode data with either one of two complementary diagonal 16-chip temporal-spectral codes.


Interferometric Amplitude Apodization of Integrated Gratings
T. W. Mossberg, C. Greiner, and D. Iazikov, Optics Express, Vol. 13, No. 7, pp. 2419 – 2426 (2005)
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Modern photolithography with its sub-hundred-nanometer-scale resolution and cm-scale spatial coherence provides for the creation of powerful waveguide diffractive structures useful as integrated spectral filters, multiplexers, spatial signal routers, interconnects, etc. Application of such structures is facilitated by a lithographically friendly means of amplitude apodization, which allows for programming of general spectral and spatial transfer functions. We describe here an approach to implementing flexible binary-etch-compatible diffractive amplitude control based on the decomposition of diffractive structures into subregions each of whose diffractive contours are spatially positioned so as to interferometrically control the net diffractive amplitude and phase of the subregion. The present approach is uniquely powerful because it allows for substantial decoupling of amplitude and phase apodization.


Low-loss silica-on-silicon two-dimensional Fabry�Perot cavity based on holographic Bragg reflectors
Christoph M. Greiner, Dmitri Iazikov, and Thomas W. Mossberg, Optics Letters, Vol. 30, No. 1, pp. 38 � 40 (2005)
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We report on the demonstration of an integrated slab-waveguide-based concentric Fabry-Perot resonator that employs holographic Bragg reflectors as cavity mirrors. The cavity, produced in a low-loss silica-on-silicon slab waveguide by high-fidelity deep-ultraviolet photolithographic fabrication, exhibits a reflectivity-limited Q factor of approximately 105. Increasing the mirror’s reflectivity will provide Q values similar to those of silica-based ring resonators, whereas the folded Fabry-Perot resonator design allows access to a substantially larger free spectral range by cavity shortening.


Wavelength Division Multiplexing Based on Apodized Planar Holographic Bragg Reflectors
C. M. Greiner, D. Iazikov and T. W. Mossberg, Applied Optics, Vol. 43, No. 23, pp. 4575 – 4583, (2004)
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We report wavelength division multiplexing based on lithographically fabricated slab-waveguide contained planar holographic Bragg reflectors (HBRs). Partial HBR diffractive contour writing and contour displacement are successfully demonstrated to enable precise bandpass engineering of multiplexer transfer functions and make possible compact-footprint devices based on hologram overlay. Fourand eight-channel multiplexers with channel spacings of ~50 and ~100 GHz, improved sidelobe suppression, and flattop passbands are demonstrated. When a second-order apodization effect, comprising effective waveguide refractive-index variation with written contour fraction, and the effect of hologram overlap on the hologram reflective amplitude are included in the simulation, excellent agreement between predicted and observed spectral passband profiles is obtained. With demonstrated simulation capability, the ability to fabricate general desired passband profiles becomes tractable.


Planar-waveguide integrated spectral comparator
T. W. Mossberg, D. Iazikov and C. Greiner, Journal of the Optical Society of America A, Vol. 21, No. 6, pp. 1088 – 1092, (2004)
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A cost-effective yet robust and versatile dual-channel spectral comparator is presented. The silica-on-silicon planar-waveguide integrated device includes two holographic Bragg-grating reflectors (HBRs) with complementary spectral transfer functions. Output comprises projections of input signal spectra onto the complementary spectral channels. Spectral comparators may be useful in optical code-division multiplexing, optical packet decoding, spectral target recognition, and the identification of molecular spectra. HBRs may be considered to be mode-specific photonic crystals.


Apodizable Integrated Filters for Coarse WDM and FTTH-Type Applications
D. Iazikov, C. Greiner and T. W. Mossberg, Journal of Lightwave Technology, Vol. 22, No. 5, pp. 1402 – 1407, (2004)
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A dual-channel integrated multiplexer, based on holographic Bragg reflector (HBR) devices and exhibiting flat-top, 4-nm-wide channels is demonstrated. Theory calibrated by the achieved performance indicates that HBR waveguide grating devices can be implemented to provide fully integrated and high-performance multiplexer solutions for CWDM and FTTH applications.


Bandpass engineering of lithographically-scribed channel-waveguide Bragg gratings
C. Greiner, T. W. Mossberg, and D. Iazikov, Optics Letters, Vol. 29, No. 8, pp 806-808 (2004)
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We propose and demonstrate a powerful approach to spectral bandpass engineering (apodization) of one-dimensional channel-waveguide Bragg ref lectors. Bandpass engineering is accomplished by precise photolithographic control of the length and the longitudinal placement of individual grating lines, which provides unique line-by-line diffractive amplitude and phase control. Channel-waveguide gratings that exhibit complex filtering functions have been fabricated and modeled. When a second-order apodization effect that comprises effective waveguide refractive-index variation with grating-line length is included in the simulation, extraordinary agreement between predicted and observed spectral passband profiles is obtained.


Fourier-Transform-Limited Performance of a Lithographically-Scribed Planar Holographic Bragg Reflector
C. Greiner, D. Iazikov and T. W. Mossberg, Photonic Technology Letters, Vol. 16, No. 3, pp 840-842 (2004)
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Planar holographic Bragg reflectors (HBRs) are computer-generated two-dimensional (2-D) slab-waveguide-based refractive-index gratings. HBRs provide the spectral filtering function of fiber Bragg gratings but-enabled by the 2-D slab waveguide geometry-add the capability to spatially route signals. Here, we report on a silica-on-silicon-based focusing HBR providing 17 GHz, essentially Fourier-transform-limited, spectral resolution. This result comprises the first time deep ultraviolet projection lithography is successfully applied to the fabrication of a 2-D Bragg reflector on the centimeter scale. The 2-D Bragg filter occupies a compact 0.3 cm2 footprint and provides diffraction-limited spatial input-output beam mapping.


Effective grayscale in lithographically scribed planar holographic Bragg reflectors
D. Iazikov, C. Greiner, and T. W. Mossberg, Applied Optics, Vol. 43, No. 5, pp 1149-1155 (2004)
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We demonstrate that holographic Bragg reflector grating structures, which are photolithographically scribed in planar waveguides, support a unique approach to apodization and overlay that uses fixed-depth etching and partial contour writing to achieve continuous reflective amplitude control.


Lithographically-fabricated planar holographic Bragg reflectors
C. Greiner, D. Iazikov, and T. W. Mossberg, Journal of Lightwave Technology, Vol. 22, No. 1, pp 136-145 (2004)
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Planar holographic Bragg reflectors (HBRs) are computer-generated slab-waveguide holograms. They operate in two dimensions to provide powerful free-space-like spectral and spatial processing of optical signals in an integrated optics environment. An HBR typically images an input port to an output port while applying a specific spectral filtering function. HBRs are fully consistent with robust photolithographic or imprint-based fabrication and can be flexibly designed to offer a wide range of spatial wavefront control and single and multichannel spectral transfer functions. We report on lithographically fabricated, focusing HBRs implemented in the silica-on-silicon format whose spectral and spatial performances reach fundamental device limits set, respectively, by Fourier transform and diffractive constraints. We also demonstrate that HBRs support a unique process-friendly approach to apodization and overlay that uses fixed-depth etching and partial contour writing to achieve continuous reflective amplitude control of constitutive diffractive elements.


Planar holographic optical processing devices
T. W. Mossberg, Optics Letters, Vol. 26, No. 7, pp 414-416 (2001)
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Time-domain optical processing implemented through linear spectral filtering offers unique potential for future high-bandwidth communications systems. One key to realization of this potential is the development of robust, cost-effective, fully integrated filtering devices. A new spectral filtering device concept, derived from the unique properties of index holograms stamped or otherwise written in thin planar waveguide slabs, is described. The holograms that are described provide for high-resolution spectral filtering while at the same time mapping general input spatial waveforms to desired output waveforms.


Submicron planar waveguide diffractive photonics
T. W. Mossberg, C. Greiner, and D. Iazikov, Proceedings from SPIE Conference on Integrated Optics: Devices, Materials and Technologies IX, Photonics West, paper 5728-23, pp. 203-211 (2005)
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Recent advances in semiconductor fabrication tools, which now support 100-nm pixilation and centimeter-scale spatial coherence, create intriguing new opportunities in integrated photonics. Application of the latest generation of fabrication tools allows for the implementation of broad new photonic device function based on 2D distributed diffractive structures such as holographic Bragg reflectors (HBRs) – devices that provide generalized spatial routing of signals within a planar waveguide circuit (e. g. silica-on-silicon) while at the same time providing powerful spectral filtering function. HBRs and other 2D distributed diffractive devices promise to open disruptive pathways to integrated photonic solutions characterized by high performance, small footprint, and extremely low cost especially when fabricated via stamping/nanoimprinting.


Multi-channel integrated optical filters for spectral signature recognition
Dmitri Iazikov, Christoph M. Greiner, and Thomas Mossberg, Proceedings from SPIE Conference on Instruments, Science, and Methods for Geospace and Planetary Remote Sensing, paper 5660-29, pp 287-293 (2004)
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Recent advances in the development of two-dimensional holographic Bragg reflectors in planar lightwave circuits have demonstrated the feasibility of highly customizable multi-wavelength filters based on photonics nanostructures programmable to recognize spectra with up to 2000 spectral lines. Such filters rival or exceed performance of free space gratings, thin film filters and Bragg gratings and may be monolithically integrated with detectors in III-V active materials or as passive devices in silica. This new technological platform holds a great promise of being nextgeneration optical engine for spectral signature recognition in the field of remote sensing, biological, chemical and defense applications.


Integrated Photonics based on Planar Holographic Bragg Reflectors
C. Greiner*, D. Iazikov and T. W. Mossberg, Photonics for Space Environments IX, edited by Edward W. Taylor, Proceedings of SPIE Vol. 5554-18, pp. 169-173 (2004)
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Integrated holographics is a novel photonics technology made possible by recent advances in semiconductor manufacturing technology and planar waveguide fabrication. The technology’s corner stone, the holographic Bragg reflector (HBR), is a slab-waveguide based, nanoscale, refractive-index structure that merges, for the first time, powerful features of holography, such as single-element spectral and spatial signal processing and overlay of multiple structures, with a highly integrated environment. As a building block for photonic circuits, the HBR’s holographic signal mapping comprises a unique and novel way of on-chip signal routing and transport that is free-space-like but fully integrated. Signals propagate and overlap freely as they are imaged from active element to active element – an architecture that eliminates the need for constraining electronics-style channel-waveguides and associated space requirements and opens the door to unique integrated photonic circuits of very compact footprint. Photolithographic HBR fabrication was recently demonstrated to provide complete amplitude and phase control over individual HBR diffractive elements thus offering the powerful ability to implement almost arbitrary phase-coherent spectral filtering functions. This is enabling to a broad range of optics-on-a-chip devices including compact multiplexers, tailored passband optical filters, optical switch fabrics, spectral comparators, and correlator based optical look-up tables.


Fully Integrated Holographic-Bragg-Reflector Based Mux/Demux Devices
D. Iazikov, C. Greiner, and T. W. Mossberg, Proceedings from SPIE Conference on Integrated Optics: Devices, Materials and Technologies VIII, Photonics West, paper 5355-13, pp. 96 – 102 (2004)
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A dual-channel, integrated, multiplexer, based on holographic Bragg reflector (HBR) devices and exhibiting flat-top, 4-nm-wide channels is demonstrated. Theory calibrated by the achieved performance indicates that HBR waveguide grating devices can be implemented to provide fully integrated and high performance multiplexer solutions for CWDM and FTTH applications. The enabling HBR devices can be regarded as mode-specific photonic crystals, i. e. photonic crystals whose spatial structure is tailored to interact with a specific signal mode or a very narrow range of such modes. Unlike standard bandgap-based photonic crystals, mode-specific photonic crystals may be effectively implemented with low-refractive-index-contrast and hence low-loss materials.


Spectral Engineering of Lithographically-Scribed Channel Waveguide Gratings
C. Greiner, D. Iazikov and T. W. Mossberg, Proceedings from SPIE Conference on Optical Components and Materials, Photonics West, paper 5350-10, pp. 66 – 71 (2004)
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We propose and demonstrate a powerful new approach to spectral bandpass engineering (apodization) of one-dimensional channel-waveguide Bragg reflectors. Bandpass engineering is accomplished via precise photolithographic control over the transverse width and longitudinal placement of individual grating lines which, respectively, provide unique line-by-line diffractive amplitude and phase control. Several channel waveguide gratings exhibiting complex filtering functions based on the present apodization method have been fabricated and modeled. They include an essentially polarization -insensitive 4-nm wide flat-top filter with steep roll-off and a multi-passband spectral decoder, useful, e.g., for optical spectral code-division multiplexing or spectral signature recognition. When a second-order apodization effect, comprising effective waveguide refractive index variation with grating-line transverse width, is included in the simulation, extraordinary agreement between predicted and observed spectral passband profiles is obtained.


Ultra-Small Footprint Silica-on-Silicon WDM Based on Holographic Bragg Reflectors
D. Iazikov, C. Greiner and T. W. Mossberg, Proceedings from SPIE Conference on Physics and Simulation of Optoelectronic Devices XII, Photonics West, paper 5349-32, pp. 236 – 246 (2004)
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We report on wavelength-division-multiplexing (WDM) based on lithographically-fabricated slabwaveguide-contained planar holographic Bragg reflectors (HBRs). Partial HBR diffractive contour writing and contour displacement are successfully demonstrated to enable precise bandpass engineering of multiplexer transfer functions and make possible compact-footprint devices based on hologram overlay. Four and eight channel multiplexers with channel spacings of ~ 50 and ~100 GHz, improved sidelobe suppression and flat-top passbands are demonstrated. When a second-order apodization effect, comprising effective waveguide refractive index variation with written contour fraction, and the impact of hologram overlap on the hologram reflective amplitude are included in the simulation, excellent agreement between predicted and observed spectral passband profiles is obtained. With demonstrated simulation capability, the ability to fabricate general desired passband profiles becomes tractable.


Effective grayscale in lithographically scribed planar holographic Bragg reflectors
D. Iazikov, C. Greiner and T. W. Mossberg, Proceedings from Conference on Nano- and Micro-Optics for Information Systems, SPIE’s 48th Annual Meeting, paper 5225-26, pp. 155-162 (2003)
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We demonstrate that holographic Bragg reflector grating structures, photolithographically scribed in planar waveguides, support a unique approach to apodization and overlay that uses fixed-depth etching and partial contour writing to achieve continuous reflective amplitude control.


Compact footprint focusing lithographically scribed planar holographic Bragg reflector
C. Greiner, D. Iazikov, and T. W. Mossberg, Proceedings from Conference on Nano- and Micro-Optics for Information Systems, SPIE’s 48th Annual Meeting, paper 5225-25, pp.133-139 (2003)
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Planar holographic Bragg reflectors (HBR’s) are slab-waveguide-based computer-generated two-dimensional in-plane refractive-index holograms. The slab waveguide allows signals to propagate freely in two dimensions, a geometry that enables HBR’s to offer powerful holographic function in the form of simultaneous spectral and spatial signal processing in a single element. Owing to their planar structure HBR’s are fully consistent with photolithographic fabrication which provides complete amplitude and phase control over individual diffractive elements thus providing a flexible means to precisely engineer device spectral transfer functions. Here, we report on a photolithographically-fabricated silica-on-silicon slab-waveguide based HBR that provides 17 GHz, essentially Fourier-transform limited, spectral resolution in a device footprint of only 0.3 cm2. The device maps the input beam to a spatially distinct output with diffraction-limited performance. Our results conclusively establish that the silica-on-silicon format and submicron photolithography can provide fully coherent planar holographic structures of centimeter scale.


Integrated-Holographic Coarse-Wavelength-Division Multiplexers Patterned by DUV Photolithography
Christoph M. Greiner, Dmitri Iazikov, and Thomas W. Mossberg, Journal of Lightwave Technology, Vol. 25, No. 1, pp. 146-150 (2007).
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We demonstrate monolithically integrated four and eight-channel coarse-wavelength-division multiplexers with low insertion loss (IL) and wide flat-top passbands based on integrated-holographic filters. Like thin-film filters (TFFs), integrated-holographic filters function via a multipath interference and thus offer flexible passband control without the IL penalty that passband shaping typically incurs in single-mode angularly dispersive devices. Unlike TFF-based multiplexers, the multiplexers described here are based on the silica-on-silicon planar lightwave circuit platform rather than discrete optics and thus uniquely provide powerful TFF-like filtering function in fully integrated format. The multiplexer performance demonstrated is superior to the integrated solutions demonstrated to date, and competitive with discrete TFF-based devices.


Novel Multicode-Processing Platform for Wavelength-Hopping Time-Spreading Optical CDMA: A Path to Device Miniaturization and Enhanced Network Functionality
Yue-Kai Huang, Varghese Baby, Ivan Glesk, Camille-Sophie Bres, Christoph M. Greiner, Dmitri Iazikov, Thomas W. Mossberg, and Paul R. Prucnal, IEEE Journal of Selected Toptics in Quantum Electronics, VOL. 13, NO. 5, SEPTEMBER/OCTOBER 2007.
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Abstract�Cost-effective, robust, code-processing photonic devices are essential for the adoption of optical code-division multiple access in future commercial and military network applications. Progress in several technology platforms for code processing is summarized. In particular, we focus on developments in a technology platform based on holographic Bragg reflectors that allow the processing of multiple codes simultaneously, with lowfootprint. Results of simultaneous en/decoding of two wavelength-hopping timespreading codes using a single device are presented. Several applications are presented where multicode-processing capability can result in significant simplification of node and system architectures and, thus, provide feasible implementation of schemes to obtain enhanced network performance such as security and scalability.


Single integrated device for optical CDMA code processing in dual-code environment
Yue-Kai Huang, Ivan Glesk, Christoph M. Greiner, Dmitri Iazkov, Thomas W. Mossberg, Ting Wang, and Paul R. Prucnal, Optics Express, Vol. 15, No. 12, pp. 7327-7334 (2007).
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We report on the design, fabrication and performance of a matching integrated optical CDMA encoder-decoder pair based on holographic Bragg reflector technology. Simultaneous encoding/decoding operation of two multiple wavelength-hopping time-spreading codes was successfully demonstrated and shown to support two error-free OCDMA links at OC-24. A double-pass scheme was employed in the devices to enable the use of longer code length.