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Etched diffraction grating demultiplexers with large free-spectral range and large grating facets
KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP. KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP. KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
State Key Laboratory of Modern Optical Instrumentation, Zhejiang University.
KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP. KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.ORCID iD: 0000-0002-3401-1125
2006 (English)In: IEEE Photonics Technology Letters, ISSN 1041-1135, E-ISSN 1941-0174, Vol. 18, no 24, 2695-2697 p.Article in journal (Refereed) Published
Abstract [en]

A design for etched diffraction grating demultiplexers is presented to obtain both large grating facets and a larger free-spectral range (FSR) using the optimal chirped diffraction orders for different facets. The large grating facets by using a large diffraction order contribute to lowering the manufacturing difficulty, and can provide lower polarization-dependent loss. However, usually the large diffraction order must lower the FSR of the device by all means. Based on the present design, the FSR can overlay the whole diffraction envelop for a special order, but avoid the influence of the adjacent diffraction envelops. Calculations indicate that the extinction ratio between the operated order and adjacent orders can attain a 35 dB or so, which makes the crosstalk from channels in adjacent envelops to those in the operated diffraction envelop acceptable.

Place, publisher, year, edition, pages
2006. Vol. 18, no 24, 2695-2697 p.
Keyword [en]
Demultiplexing, diffraction order, free-spectral range (FSR), gratings, optical planar waveguide components, wavelength-division multiplexing (WDM)
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:kth:diva-24176DOI: 10.1109/LPT.2006.888046ISI: 000243173300166Scopus ID: 2-s2.0-33845863719OAI: oai:DiVA.org:kth-24176DiVA: diva2:344609
Note
QC 20100819Available from: 2010-08-19 Created: 2010-08-19 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Design, Fabrication and Characterization of Planar Lightwave Circuits Based on Silicon Nanowire Platform
Open this publication in new window or tab >>Design, Fabrication and Characterization of Planar Lightwave Circuits Based on Silicon Nanowire Platform
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Optical devices based on Planar Lightwave Circuit (PLC) technology have well been studied due to their inherited advantages from Integrated Circuits (IC), such as: small size, high reliability, mass production and potential integration with microelectronics. Among all the materials, silicon nanowire platform gains more and more interest. The large refractive index difference between core and cladding allows tremendous reduction of the component size. This thesis studies theoretically and experimentally some integrated optical devices based on silicon nanophotonic platform, including echelle grating demultiplexers and photonic crystals.

Some of the numerical methods are introduced first. Scalar integral diffraction method is efficient for calculating the diffraction efficiency of gratings. Beam propagation method and finite-difference time-domain method are also introduced, for simulating the light propagation along the devices.

The fabrication technology and characterization methods are described. The fabrication steps involve: plasma assisted film deposition, E-beam lithography, RIE-etching. All these steps are proceeded under cleanroom environment. The characterization is mainly based on two methods: end-fire coupling and vertical grating coupling. The grating coupler is more efficient compared with the butt-coupling between fiber and nanowires, but is worse solution for final packaging.

Two types of components have been realized and characterized with the above technology. The echelle grating demultiplexer is one of the key components in WDM networks. A method for increasing the diffraction efficiency based on total internal reflection is applied, and a significant improvement of the diffraction efficiency of more than 3dB is achieved. A novel cross-order echelle grating-based triplexer, a bidirectional transceiver for application in the Passive Optical Networks (PON), has been designed and fabricated, which can multi/demultiplex three channels located at 1310nm, 1490nm and 1550nm. Polarization dependence issue of echelle grating demultiplexers has been studied. Two polarization compensation schemes have been proposed, which are for the first time polarization insensitive designs of echelle grating demultiplexers based on silicon nanowire platform.

Photonic crystal devices are also addressed in the thesis. There has been little research on the photonic crystal cavity based on pillar type. A silicon pillar type photonic crystal cavity has been fabricated with the measured Q value as high as about 104, and with an extremely high sensitivity for the changing of the background material or the effective diameter of the pillars. This kind of structure has the advantage on sensing applications compared to the air-hole type structure.

Place, publisher, year, edition, pages
Stockholm: KTH, 2009. 62 p.
Series
Trita-ICT/MAP, 2009:5
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:kth:diva-10620 (URN)
Public defence
2009-06-12, C1,Electrum 1, Isafjordsgatan 26, Kista, 10:00 (English)
Opponent
Supervisors
Note
QC 20100820Available from: 2009-06-04 Created: 2009-06-04 Last updated: 2011-11-28Bibliographically approved
2. Electromagnetic simulation and design of etched diffraction grating demultiplexers
Open this publication in new window or tab >>Electromagnetic simulation and design of etched diffraction grating demultiplexers
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Among various planar lightwave circuits for multiplexing/demultiplexing in an optical communication system, etched diffraction gratings (EDGs) have shown great potential due to their compactness and high spectral finesse. Conventional numerical methods for grating simulation cannot be used to simulate an EDG demultiplexer of large size (in terms of the wavelength). In the present thesis, the polarization-dependent characteristics of an EDG demultiplexer are analyzed with a boundary element method (BEM) for both an echelle grating coated with a metal and a dielectric grating with total internal reflection (TIR) facets. For EDGs with metal-coated facets, we use a more effective method, namely, method of moments (MoM). Futhermore, a fast simulation method for EDGs with TIR facets is presented based on the Kirchhoff–Huygens principle and the Goos-Hänchen shift. This simple method has a good agreement with a BEM over a wide range of practical parameters of the device.

Several novel designs are presented in order to improve the performances of EDGs. (1) By making some appropriate roughness on the surface of the shaded facets, the PDL of the demultiplexer can be effectively reduced over a large bandwith. (2) For EDGs based on Si nanowire structures, we compensate the polarization-dependent wavelength dispersion (PDλ) in the whole operational spectrum by introducing a polarization compensation area in its free propagation region. (3) An EDG demultiplexer with suppressed sidelobe is designed. The designed EDG demultiplexer can give a crosstalk as small as 50 dB in theory. (4) By chirping the diffraction order for each facet, we minimize the envelope intensity for the other adjacent diffraction orders to achieve a negligible return loss in a large spectral width. (5) A design for EDG demultiplexers is presented to obtain both large grating facets and a larger free spectral range (FSR) using the optimal chirped diffraction orders for different facets.

The influences of the fabrication errors (e.g., rounded effect, surface roughness and point defect in the waveguide) on the performance (such as the insertion loss, the polarization dependent loss and the chromatic dispersion) of an EDG demultiplexer are also analyzed in detail.

Silicon nanowire waveguides and related EDGs are studied. An EDG demultiplexer with 10 nm spacing is finally fabricated and characterized.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. X, 113 p.
Series
Trita-EE, ISSN 1653-5146 ; 2008:078
Keyword
etched diffraction grating, wavelength division multiplexing, passive devices, diffraction grating, planar waveguide devices, DWDM, optical communication.
National Category
Telecommunications
Identifiers
urn:nbn:se:kth:diva-4791 (URN)
Public defence
2008-06-11, Entreplan D3, Lindstedtsv 5, main campus of KTH, 10:00
Opponent
Supervisors
Note
QC 20100910Available from: 2008-06-02 Created: 2008-06-02 Last updated: 2010-09-10Bibliographically approved

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