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
  • G02B6/12011—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 arrayed waveguides, e.g. comprising a filled groove in the array section
• • 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
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04J—MULTIPLEX COMMUNICATION
  • H04J14/00—Optical multiplex systems
  • H04J14/02—Wavelength-division multiplex systems
  • H04J14/03—WDM arrangements
  • H04J14/0307—Multiplexers; Demultiplexers
• • 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
  • G02B2006/12166—Manufacturing methods
  • G02B2006/12195—Tapering

Definitions

• the present invention relates to a wavelength demultiplexer that is constructed using integrated optics and, more particularly, such a demultiplexer that comprises a) at least one inlet wave-guide that is fed by a plurality of optical signals in several different wavelength channels; b) a plurality of outlet wave-guides, whereby each one is traversed by one of the aforementioned wavelength channels; c) an assembly of adjacent integrated wave-guides connected from one side to the inlet wave-guides and, from the other side, to the outlet wave-guides through an inlet connector and an outlet connector, respectively, whereby the lengths of the guides of the assembly increase incrementally from guide to guide in a manner such that the assembly constitutes a phase network; d) a mode-expanding wave-guide arranged at the inlet of the inlet connector; and e) a plurality of mode-reducing wave-guides arranged at the outlet of the outlet connector and connected in each case to one of the outlet wave-guides.
• Such demultiplexers are known, in particular, from US- A-5 002 350.
• This connection is unfavorable to the [type of] demultiplexation, that was investigated, m the way that this is established in US-A-5 136 671.
• an important problem in such a demultiplexer is that of optimizing the width of the band passing into each of the separated channels for an acceptable predetermined cross ⁇ talk limit level.
• the present invention aims precisely to construct an optical wavelength demultiplexer with small losses of luminous energy without recourse to the strong coupling mentioned above in which the width of the band passing through each of the separated channels is optimized in accordance with a low predetermined level of cross-talk.
• the mode-expanding guide is arranged at the inlet of the inlet connector and is connected to the inlet guide and the mode-reducing guides are arranged at the outlet of the outlet connector and are each connected to the outlet wave-guides and are identical m terms of geometry with a width that varies linearly m accordance with their length and the width of the aforementioned expanding and reducing guides at their connection to the associated connector is fixed m order to optimize the width of the band passing through a channel while limiting the cross-talk between the outlet channels to a predetermined level.
• the arrangement also comprises a ode- reducing wave-guide between the inlet connector and one end of each of the guides of the assembly of wave-guides that form a phase network and a mode-expanding wave-guide between the other end of each of the guides of this assembly and the outlet connector, whereby these expanding and reducing guides are identical in terms of geometry, with a width varying linearly m accordance with their length and whereby they are provided with dimensions for reducing proximity coupling between the guides of the aforementioned assembly at a predetermined low level.
• Figure 1 is an arrangement showing the principal elements of the demultiplexer in accordance with the invention.
• Figures 2 and 3 are arrangements of the inlet connector and the outlet connector, respectively, that form part of the demultiplexer of Figure 1;
• Figure 5 is a graph that permits one to explain the process of optimizing the width of the band passing through a channel as a function of the accepted cross-talk limit level, whereby this is implemented using the design of the demultiplexer in accordance with the invention.
• all the wave-guides of the demultiplexer in accordance with the invention are mono-modal.
• These guides as well as the connectors are integrated into a flat substrate made from glass by means, for example, of any of the well known techniques using integrated optics, such as ion diffusion or chemical deposition in the vapor phase (known by the acronym CVD) .
• the function of this demultiplexer is to separate the rays, that have been mixed in this way m the guide 1, in such a way that the rays with wavelengths ⁇ : to ⁇ , are found again m the outlet guides 5 : to 5., respectively, at the outlet of the demultiplexer D.
• the assembly 3 of wave-guides must function as a phase network.
• it can comprise a plurality of adjacent wave-guides (25 for example) in a known manner, whereby the lengths of the wave- guides increase from guide to guide by an increment ⁇ L.
• This increment ⁇ L defines a proportional de-phasing ⁇ between the rays that are propagating m any two adjacent wave-guides of the assembly 3 that therefore functions as a phase network.
• the core layer 7 comprises a "free" propagation region 9, i.e. without lateral confinement, whereby this region 9 is interposed between the regions 10 and 11 where such confinement is present.
• the inlet of the expander 12 is connected to the outlet of the inlet guide 1, whereas the outlet of the expander 12 is connected to the core region 9 m which the propagation of the rays is not confined laterally.
• These inlets of the mode-reducer 13 are distributed regularly, with a spacing p, transversely to the outlet of the region 9 on a circular arc of radius R of which the center of curvature coincides with the outlet of the mode-expander 12.
• the inlet connector 1 could be connected to more than one inlet wave-guide and thus comprise as many mode- expanders that would be distributed on an arc of a circle of the same radius R and thus the center of curvature would be situated at the center of the arc of the circle defined by the inlets of the mode-reducers 13, in accordance with a confocal arrangement.
• the outlet connector 4 depicted by Figure 4 is designed and constructed by following the principles expounded above m conjunction with the description of the inlet connector 2.
• the connector 4 like the connector 2, comprises a core region 14 in which the propagation of light is effected without lateral confinement and whereby this core region is connected to the outlets of the guides of the assembly 3 (the phase network) through a set of mode-expanding guides 15 j that are distributed regularly, in accordance with the spacing p, on an arc of a circle of radius R like the reducers 13, of the connector 2.
• the rays of wavelength ⁇ x that are introduced into the inlet guide 1 of the demultiplexer D are each collected by one of the outlet guides 5 through the mode-reducers 16 x that are arranged regularly, in accordance with a spacing p', on an arc of a circle of radius R in accordance with the confocal arrangement described for the connector 2.
• This is an appropriate choice of the curvi-linear abscissa x of each reducer 16 ⁇ on the arc of a circle of radius R and of spacing p 1 separating these reducers that permits one to achieve the desired demultiplexation of rays of wavelength ⁇ x (i 1 to 8 in the form of embodiment depicted) .
• This abscissa x can be expressed by the relationship:
• x x is the abscissa corresponding to the wavelength A ⁇ * n care and n s are the effective indices of a mode that is propagated in a wave-guide and in a plane guide (9 or 14) respectively; is the diffraction order.
• the central wavelength ⁇ 0 of the group of demultiplexed wavelengths that is diffracted at the center of curvature of the arc formed by the mode-expanders 15 : at the outlet of the phase network 3 and the separation ⁇ of these wavelengths are expressed by the relationships:
• dx m.R.n t ri d ⁇ n t .p.n w A ⁇ dx/dX is the dispersion of the wavelengths of the device.
• n g n u (1 - dn w /d ⁇ ) is the group index.
• Attenuation (Att dB ) expressed in decibels that is achieved by an optical device receiving a signal of power P and transmitting a signal of power P 2 is represented in decibels (dB) by the relationship:
• the mode- expander 12 and the mode-reducers 16 are of identical geometry and have a tapering form, whereby their width varies linearly with their length.
• the expansion or the reduction of the modes that they determine can be selected in such a way as to optimize the width of the band passing through a demultiplexed channel (to 3 dB for example) by maintaining a cross-talk limit level that is then measured by the attenuation of the residual optical signal at wavelengths of channels other than the demultiplexed channel.
• the geometry of the mode-expanders and mode-reducers used at the inlet and at the outlet of the demultiplexer D are identical in such a way as to minimize losses of luminous energy because, in this way, one avoids all maladjustments of mode between the inlet guides and the outlet guides.
• the mode-reducers 13. and the mode- expanders 15 2 installed at the two ends of the wave-guides of the phase network 3 are also of identical geometry with a width that varies linearly in accordance with their length and whereby they are provided with dimensions that reduce, to a negligible value, the proximity coupling between the guides of the network.
• Proximity coupling is responsible for the transfer of light between a given guide of the network toward its neighboring guides and can also be characterized by the attenuation of the optical signal remaining in the guide after traversing the phase network. This attenuation can be calculated by means of the general relationship above if one supposes that a single guide of the network is excited by the signal P ; and transmits the signal P 2 .
• proximity coupling between the guides of the network can be neglected if the attenuation of the signal in each guide of the network is greater than 20 dB. This characteristic, that is favorable for good functioning of the demultiplexer in accordance with the invention, is not present in the demultiplexer that is described in US-A-5 002 350 that was cited earlier.
• the mode-expander 12 and the mode-reducers 16 1 are provided with those dimensions that are in accordance with the compromise to be attained between the cross-talk that is aimed for in the adjacent channels and the width, in terms of wavelengths, of the channels.
• the reducers 16 placed at the outlet of the outlet connector 4 are arranged in such a way as to achieve selection in terras of the desired wavelength. In the case where one chooses to arrange the mode-reducers 16.
• the demultiplexer with the dispersion dx/d ⁇ (expressed in ⁇ m/nm) produces channels that are regularly separated by ⁇ (expressed in nm) in terms of wavelengths in accordance with the relationship:
• the mode diffracted by the phase network 3 at the outlet of the outlet connector 4 is identical to the mode formed at the outlet of the mode-expander 12 at the inlet of the inlet connector 2 and its position x x depends on the wavelength ⁇ , of the channel being considered.
• the light that is fed into the mode-reducer 16. at the outlet of the outlet connector 4 is the collection integral between the diffracted mode and that accepted at the inlet of the mode-reducers.
• the coupling coefficient that is characterized by attenuation of the optical signal with adjacent wavelengths of the channel, that is being considered can simply be depicted by the function:
• Att dB is the attenuation of the optical signal expressed in decibels
• ⁇ is a wavelength adjacent to the wavelength ⁇ x of the channel being considered
• w is the radius of the mode measured at 1/e 2 of the maximum of the intensity profile formed at the outlet of the expander 12 of the inlet connector and at the inlets of the mode-reducers 16 x of the outlet connector.
• the function (1) is depicted in the graph in Figure 5 for two different values of the radius of the mode w.
• the curve 17 that has the larger curvature at the center of the channel ⁇ x corresponds to a radius of mode w of 4 ⁇ m and the curve 18 corresponds to a radius of mode w of 6 ⁇ m.
• each demultiplexed channel can be used in a functioning band ⁇ d ⁇ around its central wavelength
• the cross-talk Xtalk of a demultiplexed channel in its adjacent channels can be calculated by substituting the separation in terms of wavelength ( ⁇ -d ⁇ ) of the center of the channel at the term ⁇ - ⁇ 1 by the following relationship:
• the cross-talk Xtalk for the curve 17 is above 49 dB and is far superior to the usual specification for cross- talk of 22 dB.
• the width, in terms of wavelength, of the channels increases from 0.66 nm to 0.88 nm, i.e. a band width, at 3 dB attenuation, that is greater than the utilization band ⁇
• the cross-talk in excess of 22 decibels can be converted into a larger width (in terms of wavelength) of the channels by regulating the radius of the communal mode w formed at the outlet of the mode-expander (s) 12 and at the inlets of the mode-reducers 16:.
• the selection of this radius w permits one to provide the required dimensions for the end of large width of the expander or the reducer whose width must evidently be of the order of 2 w.
• diffraction order (m) that provides 8 channels with a separation of 1.6 nm in the free spectral interval (ISL) of the network 3.
• ISL free spectral interval
• the inlet ends and outlet ends of the guides of the assembly 3 must be as close as possible, whereby proximity coupling between the channels must, however, be maintained with an attenuation greater than 20 dB as one has seen above.
• the parameters thus calculated permit the construction both of the inlet connector 2 and the outlet connector 4, whereby these should be identical (to within the number of inlets for connector 2 and the outlets for connector 4) in order to avoid all maladjustments of mode between the inlet guides and the outlet guides.
• the inlet connector can be connected to several inlet guides through equally many mode-expanders, whereby these inlets can be used alternatively.
• the demultiplexer in accordance with the invention could also be used in the form of an optical wavelength multiplexer in accordance with the principle of the reversal of light.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Microelectronics & Electronic Packaging (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Optical Integrated Circuits (AREA)

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• 1995
  • 1995-12-22 FR FR9515372A patent/FR2742882B1/fr not_active Expired - Fee Related
• 1996
  • 1996-12-09 EP EP96945603A patent/EP0811281A4/de not_active Withdrawn
  • 1996-12-09 JP JP9523717A patent/JPH11501135A/ja active Pending
  • 1996-12-09 AU AU16852/97A patent/AU721743B2/en not_active Ceased
  • 1996-12-09 CN CN96192003.3A patent/CN1176031A/zh active Pending
  • 1996-12-09 CA CA002213134A patent/CA2213134A1/en not_active Abandoned
  • 1996-12-09 WO PCT/US1996/019865 patent/WO1997023969A1/en not_active Ceased
  • 1996-12-19 TW TW085115952A patent/TW316952B/zh active
• 1997
  • 1997-08-22 KR KR19970705844A patent/KR19980702444A/ko not_active Ceased

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