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WO2003065098A1 - Dispositif photonique integre et procede de fabrication du dispositif photonique - Google Patents

Dispositif photonique integre et procede de fabrication du dispositif photonique Download PDF

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Publication number
WO2003065098A1
WO2003065098A1 PCT/CA2003/000125 CA0300125W WO03065098A1 WO 2003065098 A1 WO2003065098 A1 WO 2003065098A1 CA 0300125 W CA0300125 W CA 0300125W WO 03065098 A1 WO03065098 A1 WO 03065098A1
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WO
WIPO (PCT)
Prior art keywords
waveguides
thickness
cladding layer
sidewalls
photonic device
Prior art date
Application number
PCT/CA2003/000125
Other languages
English (en)
Inventor
Muthukumaran Packirisamy
Andre Delage
Original Assignee
Lnl Technologies Canada, 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 Technologies Canada, Inc. filed Critical Lnl Technologies Canada, Inc.
Publication of WO2003065098A1 publication Critical patent/WO2003065098A1/fr

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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
    • G02B6/12007—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 forming wavelength selective elements, e.g. multiplexer, demultiplexer
    • G02B6/12009—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 forming wavelength selective elements, e.g. multiplexer, demultiplexer comprising arrayed waveguide grating [AWG] devices, i.e. with a phased array of waveguides
    • G02B6/12016—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 forming wavelength selective elements, e.g. multiplexer, demultiplexer comprising arrayed waveguide grating [AWG] devices, i.e. with a phased array of waveguides characterised by the input or output waveguides, e.g. tapered waveguide ends, coupled together pairs of output waveguides
    • 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
    • G02B6/12007—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 forming wavelength selective elements, e.g. multiplexer, demultiplexer
    • 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

Definitions

  • This invention relates to the field of photonics, and more particularly to a photonic device, such as a wavelength routing device for use in a wavelength division multiplexed communications system.
  • demultiplexer/multiplexers are used to manipulate wavelengths corresponding to different channels.
  • adjacent channel isolation is worsened by the wider spectral response and cross coupling between the waveguides. This problem will become more severe for future optical devices as the frequency spacing between the different carrying wavelength signal decreases while the physical spacing between the waveguides carrying the signal is reduced to minimize the foot print of the device.
  • Corrado Dragone for example, uses a slot in the core of the input waveguides in order to increase the bandwidths at 1dB and 3dB levels. But these two approaches have a drawback of increased crosstalk or reduced channel isolation due to wider bandwidths at 20dB and 30dB levels. There are no techniques presently available to further improve the adjacent channel isolation without increasing this spacing. The prior art fabrication technique limits the miniaturisation of the devices. Also, the introduction of a flatter pass band for the upper part of the response curve (at 1 or 3dB level) tends to increase the crosstalk. The only known solution to alleviate this effect is to increase the size of the die. Furthermore, the presence of two straight waveguides in close proximity to each other affects the propagation of the light in the other waveguide through coupling, adding a possible contribution to crosstalk if the waveguides stay together for a long distance.
  • the novel technique in accordance with the invention employs a finite thickness of cladding on the side of the core which will confine the waveguide modes laterally in such a way that it leads to reduced coupling with adjacent waveguides and narrower spectral response.
  • the benefits of this technique are smaller devices, better crosstalk (adjacent channels), lower background due to crosstalk from non-adjacent channels and easier design of the output waveguide positions.
  • a photonic device comprising an integrated photonic device having a plurality of input/output waveguides, said input/output waveguides each including a core having a top and sidewalls, and a cladding layer over the top and sidewalls of said core, said cladding layer having a reduced thickness over said sidewalls for at least a portion of the length of said core so as to improve the adjacent channel isolation.
  • the invention offers a simple method to reduce the bandwidths at 20dB and 30dB levels that can be used individually or in combination with the prior art methods in order to increase the adjacent channel isolation.
  • the present invention lends itself to microfabrication.
  • the portion of reduced thickness can be formed through microfabrication techniques or by additional etching of cladding layer.
  • the invention also provides a method of making an integrated photonic device having a plurality of input/output waveguides with reduced coupling between adjacent waveguides, comprising depositing a core layer having sidewalls and a top; and depositing a cladding layer over said core layer, said cladding layer having a reduced thickness over said sidewalls so as to improve adjacent channel isolation.
  • Figure 1 shows a scheme for adjacent channel response
  • Figure 2 is a diagram of an Arrayed Waveguide Grating Device
  • Figure 3 is a diagram of an Echelle Grating device
  • Figure 4 is a diagram of a wavelength routing/Multiplexing/Demultiplexing device
  • Figure 5 is a 2D scheme showing an output buried waveguide with both lateral and vertical mode profiles
  • Figure 6 is a 1 D scheme showing a buried waveguide with lateral mode profile
  • Figure 7 is a 2D scheme showing an output buried waveguide with reduced side clad thickness
  • Figure 8 shows the predicted spectral response with different side clad thickness (widths) along with Test results
  • Figure 9 shows the predicted bandwidth at 20dB level with different side clad thickness
  • Figure 10 shows the predicted bandwidth at 30dB level with different side clad thickness
  • Figurel 1a is a sectional view of three waveguides forming part of an array with the waveguides having reduced side cladding thickness near the imaging plane;
  • Figure 11 b is a sectional view taken along the line A-A in Figure 11a;
  • Figures 12a and 12b show schemes for waveguides with different side cladding thickness, CASE A and CASE B respectively;
  • Figure 13 shows the spectral response of a demultiplexer with an output waveguide as shown in Figure 12a;
  • Figure 14 shows the spectral response of a demultiplexer with an output waveguide as shown in Figure 12b;
  • Figure 15 shows the coupling results for CASE A waveguides using for 3D Beam Propagation;
  • Figure 16 shows the coupled state at the end of 1mm propagation for CASE A waveguides using 3D BPM
  • Figure 17 shows the coupling with fundamental mode of the adjacent waveguide along the propagation distance
  • Figure 18 shows the coupling results for CASE B waveguides used for 3D Beam Propagation
  • Figure 19 shows the coupled state at the end of 1mm propagation for CASE B waveguides using 3D BPM; and Figure 20 shows the coupling with fundamental mode of the adjacent waveguide along the propagation distance for CASE B.
  • the shape of the spectral response defines the useful bandwidths and crosstalk.
  • the spectral response for adjacent channels is schematically given in Figure 1 , in which the broken lines show the original response in accordance with the prior art and the broken lines show the narrower response achievable in accordance with the principles of the invention .
  • the bandwidths at 1dB and 3dB level have to be wider and the bandwidths at 20dB and 30dB levels have to be narrower.
  • the photonic device can be an arrayed waveguide grating based device as shown in Figure 2, an Echelle grating based device as shown in Figure 3, or any other optical wavelength filter/router as schematically shown in Figure 4 that has waveguides forming the input or outputs.
  • the optical device can have single or multitude of input and output waveguides, and slab waveguide areas optically connecting the input/output waveguides and wavelength dispersive grating element as shown in Figure 4.
  • the arrayed waveguide device has input waveguides 1 for wavelengths ⁇ i ... ⁇ n , output waveguides 2 for wavelengths ⁇ i ... ⁇ n , input and output slab couplers 3a, 3b and focussing arc 4.
  • the Echelle grating has an input waveguide 1 and multiple output waveguides 2 on a Rowland circle 5.
  • the grating is designated 6.
  • the imaging plane is designated 7 and a generic dispersive grating element is designated 8.
  • Buried waveguides are used, in general, as both input and output waveguides.
  • the distance between the output waveguides is linearly related to the spacing between the channel wavelengths or the channel spacing.
  • the distance between the output waveguides is fixed by the channel spacing of the device. Hence, it becomes very important to narrow the spectral response of the channel without changing the distance between the waveguides.
  • the two dimensional cross section of a typical output buried waveguide is shown in Figure 5.
  • the waveguide has a silicon substrate 10, a buffer layer 12, and a cladding layer 14 surrounding the core 16.
  • An air layer 18 lies over the cladding layer 14.
  • the vertical and lateral field profiles are also schematically shown in this figure.
  • the thickness of the cladding layer 14 both on the top and the sides of the core determines the mode profile. In general, the thickness of the cladding layer 14 is chosen to be large enough to reduce the propagation loss.
  • Figure 5 shows the vertical and lateral mode profiles 11, 13. In the case of optical demultiplexers, the spectral response of the channel is determined by the lateral mode profile apart from the vertical profile.
  • a one dimensional scheme of the waveguide as shown in Figure 6 is used.
  • the width of the cladding 14 in Figure 6 can represent the horizontal thickness of the cladding layer 14a covering the core from the sides.
  • Width of the waveguide core 5 ⁇ m
  • the reduction of the cladding thickness need not be carried on the entire length of the output waveguides. It ' can, for example, be restricted to some length at the start of the output waveguides in region 15 near the imaging plane 17, as shown in Figures 11a and 11 b, after which the waveguides can be sufficiently fanned out with larger spacing between the adjacent waveguides.
  • the waveguides 20 can represent either input or output waveguides. In general, the distance between the waveguides, d, at the imaging plane can be higher than 2.5 times of the core width in order to reduce the coupling between the waveguides as the light propagates from the imaging plane.
  • the coupling between the waveguides and the channel isolation determine the minimum distance the distance between the waveguides.
  • the present invention helps in reducing the coupling between the waveguide and increasing the adjacent channel isolation. The above effect is illustrated with the examples shown in Figure 12a (CASE A) and Figure 12b (CASE B).
  • the distance between the waveguides was in the order of 2.5 times of the core width.
  • the distance between the waveguides is only 9 ⁇ m while the core width is 4 ⁇ m.
  • the parameters for case A and case B are shown in the following table.
  • the spectral response has been predicted for an Echelle grating based demultiplexer with the output waveguides as shown in Figure 12.-
  • the predicted spectral responses for two channels are shown in Figures 13 and 14 for cases A and B, respectively.
  • Figure 14 shows a narrower response with finite side clad thickness when compared to the response shown in Figure 13 for the structure of Figure 12a.
  • the following table compares the spectral response parameters for both the comparative example shown in Figure 12a and the embodiment shown in Figure 12b.
  • the table presents the reduced bandwidths at 20dB and 30dB levels with waveguides as shown in Figure 12b. It can also be seen that it is possible to improve the adjacent channel isolation from 22.9dB to 28.2dB by using the finite clad thickness.
  • the light in a waveguide should propagate without being coupled to the adjacent waveguides. Coupling increases the crosstalk with adjacent channels.
  • BPM Beam Propagation Method
  • Figure 15 shows the scheme of CASE A output waveguides used for the three dimensional BPM analysis.
  • the coupling results are given in Figures 16 and 17.
  • 1mm long waveguides are used for propagation.
  • the fundamental mode When the fundamental mode is injected in the top waveguide, it can couple into the bottom waveguide depending upon the propagation distance and the clad thickness between the cores of the waveguides.
  • the Power Overlap Integral (POI) between the fundamental mode of the adjacent waveguide and the propagating mode, shown in Figure 17, is a measure of power coupled into the adjacent waveguide.
  • Figure 17 shows a possible coupling of 40% power at the end of 1 mm propagation for CASE A output waveguide.
  • FIG 18 shows the scheme of CASE B output waveguides used for the 3D BPM analysis and the coupling results are given in Figures 19 and 20. 1mm long waveguides are used for propagation. The coupled state at the end of light propagation obtained using 3D BPM analysis is shown in Figure 19. This figure shows no coupling from the top waveguide to bottom waveguide.
  • the Power Overlap Integral (POI) between fundamental mode of the adjacent waveguide and the propagating mode is shown in Figure 20.
  • This figure shows a possible coupling of 0.16% power at the end of 1mm propagation for CASE B output waveguide. This coupling is over 200 times less than the previous case.
  • Table 2 presents the cross coupling at the propagation distance of 500um, as an example. It can be seen from these results that the present invention improved the coupling from -9.50dB to -34.37dB.
  • Table 2 Cross Coupling using 3DBPM at 500 ⁇ m propagation distance
  • the reduced side clad thickness narrows the spectral response overall and reduces bandwidths at 20dB and 30dB levels for both closely and normally spaced waveguides.
  • the reduction of side clad thickness isolates the channels from adjacent channels, leading to higher channel isolation. It was possible to obtain around 6dB improvement in adjacent channel isolation even for closely spaced waveguides.
  • novel structures in accordance with the present invention open up the possibility of fabricating new devices with closely spaced waveguides and with very low coupling between them. It is possible to improve the coupling between straight waveguides from -9.5dB to -34.37dB for closely spaced waveguides.
  • This invention also helps in reducing the distance between the waveguides and hence the size of the device for a given channel spacing. This invention can thus assist in reducing the foot print of the device.
  • the described technique can be used in conjunction with other passband widening methods for steeper response at 20dB and 30dB levels and better channel isolation.
  • the novel technique can easily be implemented by manipulating the step coverage or other directionality preferences of thin film deposition methods, or by introducing deep etching of cladding layer.
  • This invention is also very useful for increasing the adjacent channel isolation for those devices where the distance between the waveguides is not large enough and is constrained by the channel spacing.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Optical Integrated Circuits (AREA)

Abstract

Un dispositif photonique intégré comprend plusieurs guides d'ondes d'entrée / de sortie. Chaque guide d'ondes d'entrée / de sortie comprend une âme (16) possédant des parois supérieure et latérales ainsi qu'une couche de revêtement (14 a/b) disposée par-dessus des parois supérieure et latérales de l'âme. La couche de revêtement présente une épaisseur réduite sur les parois latérales, ce qui permet d'améliorer l'isolation du canal adjacent.
PCT/CA2003/000125 2002-01-31 2003-01-31 Dispositif photonique integre et procede de fabrication du dispositif photonique WO2003065098A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US35255902P 2002-01-31 2002-01-31
US60/352,559 2002-01-31

Publications (1)

Publication Number Publication Date
WO2003065098A1 true WO2003065098A1 (fr) 2003-08-07

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Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5629992A (en) * 1995-09-14 1997-05-13 Bell Communications Research, Inc. Passband flattening of integrated optical filters
US5930419A (en) * 1995-12-22 1999-07-27 Corning, Inc. Wavelength demultiplexer constructed using integrated optics
US6049644A (en) * 1997-05-13 2000-04-11 Lucent Technologies Inc. Optical routing device having a substantially flat passband
JP2000171648A (ja) * 1998-12-02 2000-06-23 Nec Corp アレイ導波路格子
JP2001051135A (ja) * 1999-08-06 2001-02-23 Hitachi Cable Ltd 光波長合分波器

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5629992A (en) * 1995-09-14 1997-05-13 Bell Communications Research, Inc. Passband flattening of integrated optical filters
US5930419A (en) * 1995-12-22 1999-07-27 Corning, Inc. Wavelength demultiplexer constructed using integrated optics
US6049644A (en) * 1997-05-13 2000-04-11 Lucent Technologies Inc. Optical routing device having a substantially flat passband
JP2000171648A (ja) * 1998-12-02 2000-06-23 Nec Corp アレイ導波路格子
JP2001051135A (ja) * 1999-08-06 2001-02-23 Hitachi Cable Ltd 光波長合分波器

Non-Patent Citations (2)

* Cited by examiner, † Cited by third party
Title
PATENT ABSTRACTS OF JAPAN vol. 2000, no. 09 13 October 2000 (2000-10-13) *
PATENT ABSTRACTS OF JAPAN vol. 2000, no. 19 5 June 2001 (2001-06-05) *

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