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WO2003046624A1 - Reseau en escalier metallise a dependance reduite de la polarisation utilisant des couches dielectriques d'espacement - Google Patents

Reseau en escalier metallise a dependance reduite de la polarisation utilisant des couches dielectriques d'espacement Download PDF

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Publication number
WO2003046624A1
WO2003046624A1 PCT/CA2002/001798 CA0201798W WO03046624A1 WO 2003046624 A1 WO2003046624 A1 WO 2003046624A1 CA 0201798 W CA0201798 W CA 0201798W WO 03046624 A1 WO03046624 A1 WO 03046624A1
Authority
WO
WIPO (PCT)
Prior art keywords
layer
dielectric layer
core layer
reflecting
echelle grating
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/CA2002/001798
Other languages
English (en)
Inventor
Dan-Xia Xu
Andre Delage
Kokou Dossou
Siegfried Janz
Pavel Cheben
Lynden Erickson
Boris Lamontagne
Sylvain Charbonneau
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
LNL OPTENIA Inc
Original Assignee
LNL OPTENIA Inc
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by LNL OPTENIA Inc filed Critical LNL OPTENIA Inc
Priority to AU2002349214A priority Critical patent/AU2002349214A1/en
Publication of WO2003046624A1 publication Critical patent/WO2003046624A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B6/122—Basic optical elements, e.g. light-guiding paths
    • G02B6/124—Geodesic lenses or integrated gratings
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/18—Diffraction gratings
    • G02B5/1861—Reflection gratings characterised by their structure, e.g. step profile, contours of substrate or grooves, pitch variations, materials
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B6/122—Basic optical elements, e.g. light-guiding paths
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B2006/12083—Constructional arrangements
    • G02B2006/12104—Mirror; Reflectors or the like
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
    • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
    • G02B2006/12083—Constructional arrangements
    • G02B2006/12107—Grating
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
    • G02B6/24—Coupling light guides
    • G02B6/26—Optical coupling means
    • G02B6/28—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals
    • G02B6/293—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means
    • G02B6/29304—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating
    • G02B6/29305—Optical coupling means having data bus means, i.e. plural waveguides interconnected and providing an inherently bidirectional system by mixing and splitting signals with wavelength selective means operating by diffraction, e.g. grating as bulk element, i.e. free space arrangement external to a light guide
    • G02B6/29311—Diffractive element operating in transmission

Definitions

  • This invention relates to the field of photonics, and more particularly to a method of improving the polarization dependent loss of a metallic reflecting grating.
  • the Metallization of reflection gratings such as Echelle gratings, made of glass is essential to enhance the grating reflectivity in the infrared range.
  • the metal typically aluminum, will inevitably cover the reflecting facets, the non-reflecting facets, as well as partially covering the top of the core layer.
  • the presence of the metal on the non-reflecting facet and on top of the core layer of an echelle grating introduces a large polarisation dependent loss (PDL).
  • PDL polarisation dependent loss
  • Polarisation dependent loss (PDL) in Echelle gratings results from the combination of several effects. It can be loosely divided into two types: PDL that originates from the wavelength dependent behaviours of the TE and TM modes ( ⁇ -dependent PDL), and PDL that manifests as an insertion loss for one particular polarization (PDL DC offset).
  • the TM mode has a tendency to form a plasmon mode and energy is concentrated along the metallic-dielectric interface, whereas the TE mode is repelled very slightly.
  • the absorption by metal over a short distance e.g.; ⁇ 20 ⁇ m
  • the perturbation to the modes for the length under the metal causes a decreased coupling back to the slab region of the grating, primarily for the TM mode.
  • This effect mainly introduces a PDL DC offset.
  • the Metallization of the glass grating is practically the only technique used to improve reflectivity of a glass grating.
  • the Echelle grating becomes a very reliable compact device able to compete favourably with AWG (Arrayed Waveguide Grating) technology.
  • a dielectric layer introduced between a core glass layer and the metal in reflection grating to reduce the PDL without significantly interfering with the reflectivity characteristic of the metal.
  • the present invention provides an echelle grating comprising a core layer; a plurality of reflecting and non-reflecting facets; a metal reflecting layer on at least some of said non-reflecting facets; and a first dielectric layer between said core layer and said metal reflecting layer to reduce polarization dependent loss.
  • the first dielectric layer reduces the TE field at the interface and thus shifts the TE diffracted field and beams so that they become closer to the TM polarization.
  • the invention also provides a method of making an echelle grating comprising the steps of providing a core layer; forming a plurality of reflecting and non-reflecting facets at least in said core layer; depositing a first dielectric layer over said core layer on said facets; and depositing a metal reflecting layer to reduce polarization dependent loss a metal on at least some of said non-reflecting facets over said first dielectric layer.
  • the echelle grating can be made using conventional deposition and etching techniques known in the art. Brief Description of the Drawings
  • Figure 1 a is a top view of a prior art echelle grating
  • Figure 1 b is a cross sectional view showing a reflecting facet
  • Figure 2a is a top view of an echelle grating constructed in accordance with the principles of the invention
  • Figure 2b is a cross sectional view of a reflecting facet of the grating shown in Figure 2a;
  • Figure 3 is a plot showing the reflectivity of a multilayer structure consisting of glass, a MgF 2 spacer of 0.8 ⁇ m and a thick aluminium coating as a function of angle of incidence;
  • Figure 4 is a plot showing the insertion loss of a metallized Echelle grating DEMUX with and without the spacer.
  • the prior art Echelle grating has a metal layer on the non- reflecting facets 1 a as well as the reflecting facets 1 b.
  • An Echelle grating consists of a series of alternate reflecting facets and non-reflecting facets formed in a slab waveguide.
  • the reflecting facets are disposed to reflect incident light shown by arrow 2 back to form the diffraction pattern.
  • the "non-reflecting" facets 1a are disposed substantially parallel to the incident light and extend between adjacent reflecting facets 1 b so that they do not participate in reflecting the light back for diffraction. It will be understood that the "non- reflecting" facets may still per se be reflective.
  • the intensity of the incoming light 2 is reflected by the facets 1 b to form the different orders of diffraction 3, 4 depending on both the polarisation and on the wavelength.
  • a detailed study by the inventors indicates that the boundary conditions of the TM field at the metallic surface perpendicular to the field propagation (non-reflecting facet) is responsible for the PDL discussed above. The boundary conditions at this interface reduce the TM field to 0 while the TE is not affected.
  • Figure 1 b shows a cross section of the Echelle grating, which in a manner known per se comprises a buffer layer 7, a core layer 6.
  • the facets are formed by etching the into the buffer layer 7 through the core layer 6.
  • a reflective aluminium metal layer 5 is deposited on the facets 1 over the exposed core layer 6 and buffer layer 7. It will be seen that the reflective coating 5 also partially covers the top of the core layer 6.
  • Figure 2b shows an arrangement similar to that shown in Figure 1b except that a dielectric layer 8 is disposed under the metal layer 5.
  • the introduction of this dielectric layer 8 reduces the TE field at the interface with the glass core layer 6.
  • the TE diffracted field and diffracted beams (3, 4) become closer to the TM polarization.
  • the grating thus shows less polarisation dependence.
  • this spacer layer 8 is related to its index of refraction.
  • the index of refraction of the spacer can be either smaller or larger than the index of the glass core 6, but different physical effects occur for each situation.
  • a lower index material such as MgF 2 of index 1.38, introduces total internal reflection for thickness of the order of the wavelength or larger. This increases the interaction of the TE polarisation with the non-reflecting surface.
  • materials with a larger index of refraction such as SiN x , with an index of refraction n ⁇ 1.955, or TiO x with an index of refraction n ⁇ 2.2, an appropriate (resonant) thickness can always be found that reduces the local field to almost zero for both polarisations.
  • the dielectric layer 8 can be seen located between the metal layer 5 and the core of the slab waveguide 10.
  • the reflectivity of the TE and TM modes of propagation should behave the same way for normal and grazing incidence.
  • Figure 3 shows that this is true for a metal layer of aluminum and a dielectric layer of MgF 2 . 0° is the direction normal to the surface of the reflecting facet.
  • SiN x films can be grown with the same reflectivity characteristics.
  • Figure 4 illustrates the improvement obtained by introducing a dielectric spacer of 0.8 ⁇ m of MgF 2 under the aluminum reflective layer.
  • the dielectric layer has an index of refraction of 1.38.
  • the metal is essentially perfectly conducting.
  • the plots c shows the insertion loss without a dielectric spacer and the plots d show the insertion loss with a dielectric spacer. Subtraction of the curves c, c shows that there is a net polarization dependent loss without the dielectric spacer that varies from 0 dB at 1525nm to 2.5 dB at 1570 nm. The actual PDL is even higher due to losses in a non- perfect metal.
  • Figure 4 shows that the TM mode is practically not affected compared to the TE mode.
  • the envelope of the TE mode is more lossy and shifted to about the same position of the TM mode, resulting in a smaller polarisation dependent loss, which is almost independent of the wavelength.
  • Experimental evidence confirms these theoretical predictions for dielectrics having higher and lower refractive index.
  • a second layer of dielectric 9, with lower index than the core layer 6 in this case, can also be introduced between the core layer 6 and the metal layer 5.
  • This layer reduces the perturbation of the metal 5 on the TM mode, and therefore reduces the associated PDL.
  • an index step of 0.012 which is similar to the buffer layer 7 shown in Fig. 2b, simulations have shown that 0.5 ⁇ m of dielectric spacer can effectively reduce the related PDL.
  • the invention is applicable to echelle gratings having a staircase design generally and includes echelon gratings.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Diffracting Gratings Or Hologram Optical Elements (AREA)

Abstract

L'invention porte sur un réseau en escalier situé sur le bord d'un guide d'ondes intégré. Le guide d'ondes comporte une couche tampon (7) et une couche centrale (6). Le réseau est gravé dans la couche tampon en traversant la couche centrale. Le réseau est recouvert d'une couche diélectrique (8). La couche diélectrique est recouverte d'une couche métallique (5). La couche diélectrique placée entre la couche centrale et la couche métallique réfléchissante réduit la dépendance de la polarisation du réseau.
PCT/CA2002/001798 2001-11-26 2002-11-26 Reseau en escalier metallise a dependance reduite de la polarisation utilisant des couches dielectriques d'espacement Ceased WO2003046624A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU2002349214A AU2002349214A1 (en) 2001-11-26 2002-11-26 Metallised echelle grating with reduced polarisation dependence using dielectric spacer layers

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US33254201P 2001-11-26 2001-11-26
US60/332,542 2001-11-26

Publications (1)

Publication Number Publication Date
WO2003046624A1 true WO2003046624A1 (fr) 2003-06-05

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Family Applications (1)

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PCT/CA2002/001798 Ceased WO2003046624A1 (fr) 2001-11-26 2002-11-26 Reseau en escalier metallise a dependance reduite de la polarisation utilisant des couches dielectriques d'espacement

Country Status (2)

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AU (1) AU2002349214A1 (fr)
WO (1) WO2003046624A1 (fr)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2244114A1 (fr) * 2009-04-20 2010-10-27 BAE Systems PLC Réseau à surface en relief dans un guide d`onde optique comportant une sufrace refléchissante et couche diélectrique conforme à celle-ci
WO2010122330A1 (fr) * 2009-04-20 2010-10-28 Bae Systems Plc Réseau à relief de surface dans un guide d'ondes optique pourvu d'une surface réfléchissante et d'une couche diélectrique épousant la forme de la surface
WO2022041312A1 (fr) * 2020-08-24 2022-03-03 苏州大学 Réseau d'immersion à réflexion métallique à faible polarisation et à efficacité de diffraction élevée, et système optique

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3237508A (en) * 1962-04-12 1966-03-01 Bausch & Lomb Reflecting diffraction grating for minimizing anomalies
WO1998000751A1 (fr) * 1996-07-02 1998-01-08 Corning Incorporated Reseau de diffraction presentant une sensibilite reduite a la polarisation
WO2001077738A2 (fr) * 2000-04-07 2001-10-18 Zolo Technologies, Inc. Procede et dispositif d'attenuation de la sensibilite a la polarisation des reseaux de diffraction des equipements de communication a fibres optiques
EP1191360A2 (fr) * 2000-09-21 2002-03-27 Nippon Sheet Glass Co., Ltd. Réseau diffractif à réflexion
EP1209453A2 (fr) * 2000-11-09 2002-05-29 Mitsubishi Gas Chemical Company, Inc. Monochromateur et multiplexeur en longueur d'onde l'utilisant

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3237508A (en) * 1962-04-12 1966-03-01 Bausch & Lomb Reflecting diffraction grating for minimizing anomalies
WO1998000751A1 (fr) * 1996-07-02 1998-01-08 Corning Incorporated Reseau de diffraction presentant une sensibilite reduite a la polarisation
WO2001077738A2 (fr) * 2000-04-07 2001-10-18 Zolo Technologies, Inc. Procede et dispositif d'attenuation de la sensibilite a la polarisation des reseaux de diffraction des equipements de communication a fibres optiques
EP1191360A2 (fr) * 2000-09-21 2002-03-27 Nippon Sheet Glass Co., Ltd. Réseau diffractif à réflexion
EP1209453A2 (fr) * 2000-11-09 2002-05-29 Mitsubishi Gas Chemical Company, Inc. Monochromateur et multiplexeur en longueur d'onde l'utilisant

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2244114A1 (fr) * 2009-04-20 2010-10-27 BAE Systems PLC Réseau à surface en relief dans un guide d`onde optique comportant une sufrace refléchissante et couche diélectrique conforme à celle-ci
WO2010122330A1 (fr) * 2009-04-20 2010-10-28 Bae Systems Plc Réseau à relief de surface dans un guide d'ondes optique pourvu d'une surface réfléchissante et d'une couche diélectrique épousant la forme de la surface
US10642039B2 (en) 2009-04-20 2020-05-05 Bae Systems Plc Surface relief grating in an optical waveguide having a reflecting surface and dielectric layer conforming to the surface
WO2022041312A1 (fr) * 2020-08-24 2022-03-03 苏州大学 Réseau d'immersion à réflexion métallique à faible polarisation et à efficacité de diffraction élevée, et système optique

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Publication number Publication date
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