WO1998036302A1 - Dispositifs et procede optiques - Google Patents

Dispositifs et procede optiques Download PDF

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Publication number
WO1998036302A1
WO1998036302A1 PCT/AU1998/000089 AU9800089W WO9836302A1 WO 1998036302 A1 WO1998036302 A1 WO 1998036302A1 AU 9800089 W AU9800089 W AU 9800089W WO 9836302 A1 WO9836302 A1 WO 9836302A1
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WO
WIPO (PCT)
Prior art keywords
port
wavelength
light
band
selective
Prior art date
Application number
PCT/AU1998/000089
Other languages
English (en)
Inventor
Martin Charles Elias
Stephen John Madden
Original Assignee
Aofr Pty. Ltd.
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 Aofr Pty. Ltd. filed Critical Aofr Pty. Ltd.
Priority to AU59738/98A priority Critical patent/AU731587B2/en
Priority to EP98902853A priority patent/EP0960349A4/fr
Priority to CA002280964A priority patent/CA2280964A1/fr
Priority to JP53516998A priority patent/JP2001511905A/ja
Publication of WO1998036302A1 publication Critical patent/WO1998036302A1/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
    • G02B6/24—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
    • G02B6/29316—Light guides comprising a diffractive element, e.g. grating in or on the light guide such that diffracted light is confined in the light guide
    • G02B6/29317—Light guides of the optical fibre type
    • 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
    • G02B6/29346—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 wave or beam interference
    • G02B6/2935—Mach-Zehnder configuration, i.e. comprising separate splitting and combining means
    • G02B6/29352—Mach-Zehnder configuration, i.e. comprising separate splitting and combining means in a light guide
    • G02B6/29353—Mach-Zehnder configuration, i.e. comprising separate splitting and combining means in a light guide with a wavelength selective element in at least one light guide interferometer arm, e.g. grating, interference filter, resonator
    • 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
    • G02B6/29346—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 wave or beam interference
    • G02B6/2935—Mach-Zehnder configuration, i.e. comprising separate splitting and combining means
    • G02B6/29352—Mach-Zehnder configuration, i.e. comprising separate splitting and combining means in a light guide
    • G02B6/29355—Cascade arrangement of interferometers
    • 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
    • G02B6/29379—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 characterised by the function or use of the complete device
    • G02B6/2938—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 characterised by the function or use of the complete device for multiplexing or demultiplexing, i.e. combining or separating wavelengths, e.g. 1xN, NxM
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J14/00—Optical multiplex systems
    • H04J14/02—Wavelength-division multiplex systems
    • 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
    • G02B6/02—Optical fibres with cladding with or without a coating
    • G02B6/02057—Optical fibres with cladding with or without a coating comprising gratings
    • G02B6/02076—Refractive index modulation gratings, e.g. Bragg gratings

Definitions

  • This invention relates to optical devices for dividing light having a mix of wavelengths and a number of discrete wavelength bands. It also relates to optical devices for combining light in a number of discrete wavelength bands into light having a mix of wavelengths.
  • Devices of this type have application in optical fibre communication systems using wavelength division multiplexing (WDM) and demultiplexing (WDD).
  • WDM wavelength division multiplexing
  • WDD demultiplexing
  • the filters or other wavelength selective devices are used to extract discrete wavelength bands from a signal comprising a mix of wavelengths. Sequential use of such devices is required to obtain the required number of discrete wavelength channels.
  • Known devices can be divided into those which utilise optical components to which the light travels in free space and those in which the light is divided whilst propagating in an optical waveguide such as an optical fibre or planar optical device. In practice, optical waveguides are required for the transmission of light signals over any significant distance and normally optical fibres are used for this purpose. If a WDM/WDD device uses discrete optical components and free space propagation then the light must be extracted from the optical fibre, focused into the optical system and usually relaunched into another optical fibre. This procedure creates various problems including difficulties in alignment, a device of inconveniently large size, and a lack of ruggedness.
  • United States Patent 4,900, 119 describes a narrow band wavelength selective optical device in which the separation of a narrow band of wavelengths can be achieved wholly within an optical fibre.
  • a series of such devices can be used to sequentially tap narrow bands of wavelength from a light signal to provide for WDM and WDD.
  • a difficulty with these prior art devices is that the insertion losses for each of the narrow band wavelength selective devices are cumulative and thus provide increasing attenuation of the outputs in the order in which they are tapped from the input signal. It is not uncommon for a 16 channel device of this type to attenuate the signal by as much as 8dB.
  • United States Patent 5,583,683 describes an optical multiplexing/demultiplexing device which utilises a multiport optical block with variable thickness multi-cavity interference filters extending over the multiple ports. Input light is separated into individual bands by the transmission selectivity of the filter at each port. The wavelengths not transmitted are reflected to other ports with different filters. By using multiple reflections several bandwidth channels can be removed from a multiplexed signal. In common with one of the class of devices described above this device performs the division of the input light after it has been extracted from the transmitting wave guide and requires the separated channels to be relaunched for subsequent transmission. Additionally the device requires the use of a multilayer filter of complex construction to provide the desired filtering at each port.
  • Another object of this invention is to provide a wavelength selective optical device for use in wavelength dividing of optical signals.
  • an optical wavelength selective device can be constructed to separate from light having a mix of wavelengths an intermediate wavelength band narrower than the input wavelength band but broader than the desired discrete output wavelength bands.
  • this invention provides an optical device for dividing input light having a mix of wavelengths into at least two output wavelength bands, said device including two optical wavelength selective devices of the kind having a first port, a second port and a third port optically interconnected at least partly by one or more waveguides, in which wavelength selective means in the waveguide(s) route input light of selected wavelength band at said first port to said third port and route input light of other wavelengths at said first port to said second port, a first of said selective devices having the third port optically connected by waveguide to the first port of a second of said devices or the second port optically connected by waveguide to the first port of said second device, wherein said wavelength selective means of said first device route to the corresponding second or third port light in a first wavelength band significantly broader than a second wavelength band of light routed to the corresponding second or third port by the wavelength selective means of the second selective device.
  • the first wavelength band is at least 10% to 20% broader than the second wavelength band.
  • the other wavelengths include a third wavelength band having a width substantially equal to the selected wavelength band.
  • this invention provides an optical device for dividing input light having a mix of wavelengths into a plurality of discrete output wavelength bands said device including at least three optical wavelength selective devices of the kind having a first port, a second port and a third port optically interconnected at least partly by one or more waveguides, in which wavelength selective means in the waveguide(s) route input light of selected wavelength band at said first port to said third port and route input light of other wavelengths at said first port to said second port, a first of said selective devices having the second port optically connected by waveguide to the first port of a second of said devices and the third port optically connected by waveguide to the first port of a third of said devices, wherein said wavelength selective means of said first device route to the corresponding third port light in a first intermediate wavelength band broader than any of said discrete bands and route to the corresponding second port light having a wavelength outside said first intermediate band including a second intermediate band broader than any of said discrete bands, said wavelength selective means of said second selective device route to at least one of the
  • the first, second and third ports of the wavelength selective devices are optically interconnected by one or more waveguides.
  • the wavelength selective devices are preferably formed by coupled optical waveguides with wavelength selective optical gratings within or adjacent to the coupled region.
  • the wavelength selective devices can, for example, include a grating frustrated coupler or a Mach-Zehnder interferometer.
  • the waveguides are formed by optical fibres.
  • the wavelength selective devices preferably include a fourth port and input light of the other wavelengths at the third port and input light in the selected band at the second port are routed to the fourth port.
  • the fourth port is optically terminated.
  • the optical device can include further wavelength selective means to either reflect light of the other wavelengths routed for output to the third port as input to the third port or reflect light in the selected wavelength band routed for output to the second port as input to the second port.
  • the further wavelength selective means both reflect light of the other wavelengths routed for output to the third port as input to the third port and reflect light in the selected wavelength band routed for output to the second port as input to the second port.
  • the further wavelength selective means preferably includes one or more wavelength selective gratings in the waveguides.
  • the wavelength selective device can also include a circulator with three optically connected waveguides forming the first second and third ports.
  • the wavelength selective means is preferably formed by a wavelength selective grating in the waveguide forming the second port.
  • the wavelength selective devices are preferably arranged such that input light of the other wavelengths at the third port is not routed for output at the first or second ports and including further wavelength selective means in the waveguides to reflect light of the other wavelengths routed for output to the third port as input to the third port.
  • the wavelength selective means of said second selective device route to both the corresponding second and third ports light respectively in first and second output wavelength bands each narrower than the second intermediate band and the wavelength selective means of the third selective device route to both the corresponding second and third ports light respectively in third and fourth output wavelength bands each narrower than the first intermediate band.
  • Each of the first, second third and fourth output bands are preferably broader than said discrete bands.
  • the first and second intermediate wavelength bands are of substantially equal width. More preferably, the first and second output bands are of substantially equal width and the third and fourth output bands are of substantially equal width.
  • the selected wavelength band of each of the selective devices is shorter in wavelength than wavelength band included in the other wavelengths routed by the same selective device.
  • the output of a last stage of the selective devices provides the discrete wavelength bands
  • the selected wavelength band of each of the selective devices not in the last stage is shorter in wavelength than a wavelength band included in the other wavelengths routed by the same selective device and wherein the selected wavelength band of each of the selective devices in the last stage is longer than the wavelength band included in the other wavelengths routed by the same selective device.
  • Filters can preferably be associated with the second port of one or more of the selective devices to inhibit output of light of selected out of band wavelengths.
  • the optical device comprises further wavelength selective devices respectively optically connected to the second and third ports of the second and third wavelength selective devices to further subdivide the wavelength bands.
  • the wavelength selective means of the subsequent wavelength selective devices transmit light of a narrower wavelength band than the wavelength selective means of the preceding wavelength selective device.
  • this invention provides an optical device for combining light of a first wavelength band with light of a second wavelength band into an output light having a mix of wavelengths of said first wavelength band and said second wavelength band
  • said device including two optical wavelength selective devices of the kind having a first port, a second port and a third port optically interconnected at least partly by one or more waveguides in which wavelength selective means in the waveguide(s) route input light of a selected wavelength band at said third port to said first port and route input light of other wavelengths at said second port to said first port, a first of said selective devices having the second port optically connected by waveguide to the first port of a second of said devices or the third port optically connected by waveguide to the first port of said second device, wherein said wavelength selective means of said first device route input light to third port for output at the corresponding first port in a first wavelength band significantly broader than a second wavelength band of light routed for output to the corresponding first port from the corresponding third port by the wavelength selective means of said second selective device.
  • the first wavelength band is at least 10% to 20% broader than the second wavelength band.
  • the other wavelengths preferably include a third wavelength band having a width substantially equal to the selected wavelength band.
  • this invention provides an optical device for combining a plurality of discrete wavelength bands of input light into an output light having a mix of wavelengths of said first wavelength band and said second wavelength band
  • said device including at least three optical waveguide wavelength selective devices of the kind having a first port, a second port and a third port optically interconnected at least partly by one or more waveguides, in which said wavelength selective means route input light of a selected wavelength band at said third port to said first port and route input light of other wavelengths at said second port to said first port, a first of said selective devices having the second port optically connected by waveguide to the first port of a second of said devices and the third port optically connected by waveguide to the first port of a third of said devices, wherein said wavelength selective means of said first device routed from the corresponding third port to the first port light in a first intermediate wavelength band broader than any of said discrete bands and routed from the corresponding second port to the first port light having a wavelength outside said first intermediate band including a second intermediate band broader than any of
  • the wavelength selective means of the second selective device route from both the corresponding second and third ports to the first port light respectively in first and second input wavelength bands each narrower than the second intermediate band and the wavelength selective means of the third selective device route from both the corresponding second and third ports to the first port light respectively in third and fourth input wavelength bands each narrower than the first intermediate band.
  • Each of said first, second third and fourth input bands are preferably broader than the discrete bands.
  • the first and second intermediate wavelength bands are of substantially equal width. It is also preferred that the first and second input bands are of substantially equal width and the third and fourth input bands are of substantially equal width.
  • the device preferably includes further wavelength selective devices respectively optically connected by waveguide to the second and third ports of both the second and third wavelength selective devices. In this way n of said discrete wavelength bands can be combined using n-1 wavelength selective devices.
  • each wavelength selective device inputs at the second and third ports light in a wavelength band substantially equal in width and the discrete wavelength bands are of substantially equal width.
  • the first, second and third ports of the wavelength selective devices are optically interconnected by one or more waveguides.
  • the wavelength selective devices are formed by coupled optical waveguides with wavelength selective optical gratings within or adjacent to the coupled region.
  • the wavelength selective devices can include a grating frustrated coupler or a Mach-Zehnder interferometer.
  • the waveguides are formed by optical fibres. In other forms of the invention the waveguides can be formed in planar optical devices, for example.
  • the wavelength selective devices can in one form of the invention include a circulator with three optically connected waveguides forming the first second and third ports.
  • the wavelength selective means is formed by a wavelength selective grating in the waveguide forming the second port.
  • the wavelength selective device is preferably an interferometer arrangement formed by at least two optical waveguides optically coupled together at spaced apart locations to form the arms of the interferometer.
  • the wavelength selective means preferably comprises a Bragg grating formed in each of the arms of the interferometer.
  • optical couplers between the waveguides and the path lengths of the arms of the interferometer are arranged to provide the desired output, or absence of output, at the various ports formed by the waveguides extending from the optical couplers away from the interferometer formed between the couplers.
  • the optical couplers have 3dB coupling ratios so that light is divided equally between the two arms of the interferometer.
  • a Bragg grating is formed in each of the arms and provides for reflection of light of a selected wavelength band.
  • the waveguides are formed by optical fibres and the coupling between the fibres is achieved using a fused biconic taper.
  • 3x3 or 4x4 optical fibre couplers of known type can be used to provide multiple outputs of the reflected band widths for input to corresponding multiple wavelength selective devices.
  • this invention provides a wavelength selective optical device of the kind having a first port, a second port and a third port optically interconnected at least partly by one or more waveguides and in which wavelength selective means in said waveguide(s) route input light of selected wavelength band at said first port for output at said third port and route input light of other wavelengths for output at said second port, said device being arranged such that input light of said other wavelengths at said third port is not routed for output at said first or second ports and including further wavelength selective means in said waveguide(s) to reflect light of said other wavelengths routed for output to said third port as input to said third port.
  • this invention provides a wavelength selective optical waveguide device of the kind having a first port, a second port and a third port optically interconnected by one or more waveguides and in which wavelength selective means in said waveguide(s) route input light of selected wavelength band at said first port for output at said third port and route input light of other wavelengths for output at said second port, said device being arranged such that input light of said other wavelengths at said third port is not routed for output at said first or second ports and input light in said selected wavelength band at second port is not routed for output at said first or third ports and including further wavelength selective means in said waveguide(s) to either reflect light of said other wavelengths routed for output to said third port as input to said third port or reflect light in said selected wavelength band routed for output to said second port as input to said second port.
  • the further wavelength selective means in the waveguide(s) both reflect light of the other wavelengths routed for output to the third port as input to the third port and reflect light in the selected wavelength band routed for output to the second port as input to the second port.
  • this invention also provides a method for dividing input light having a mix of wavelengths into a plurality of discrete output wavelength bands said method including the steps of dividing said input light into light in a first intermediate wavelength band broader than any of said discrete bands and light having a wavelength range outside said first intermediate band including a second intermediate band broader than any of said discrete bands, and subsequently dividing light in said first intermediate band into light in a first output wavelength band narrower than said first intermediate wavelength band and light of a wavelength outside said first output wavelength band, and dividing light in said second intermediate band into at least light in a second output wavelength band narrower than said second intermediate wavelength band and light outside said second output wavelength band.
  • this invention also provides a method for combining a plurality of discrete wavelength bands of input light into an output light band having a mix of wavelengths including the steps of combining a first light input including light in a first wavelength band with a second light input including light in a second wavelength band to produce light in a first intermediate wavelength band broader than said discrete wavelength bands and narrower than said output light band, and combining a third light input including light in a third wavelength band with a fourth light input including light in a fourth wavelength band to produce light in a second intermediate wavelength band broader than said discrete wavelength bands and narrower than said output light band and combining light in said first and second intermediate wavelength bands to produce light in an output band broader than either than said first and second intermediate wavelength bands.
  • the first, second, third and fourth wavelength bands are each broader than the discrete bands.
  • the first and second intermediate wavelength bands are of substantially equal width.
  • the first and second output wavelength bands are of substantially equal width and third and fourth output wavelength bands are of substantially equal width or that all are of equal width.
  • the optical device of this invention provides for the division of light of mixed wavelengths into a number of channels or combination of a number of bandwidth channels with a lesser number of insertion losses than in the prior art devices.
  • the invention is readily scalable to provide for any required number of channels.
  • the discrete channels can be provided in any spacing or width by appropriate selection of the characteristics of each frequency selective device. This has particular application in long links where non linear mixing can be avoided by using unequal channel spacings.
  • the present invention also provides for greater attenuation of out of band wavelength light because each of the discrete channels undergoes several stages of division or combination rather than a single stage by selective filtering of the prior art.
  • the present invention also allows the division to be achieved wholly within the optical waveguide and thus avoids the losses and alignment difficulties associated with prior art devices that achieve division using discrete optical elements and free space propagation.
  • An additional advantage of the signals staying within an optical waveguide, and in particular an optical fibre, is that different parts of the dividing tree do not have to be in the same physical location. This can be useful in the layout of typical broadband communications networks such as hybrid fibre coax systems, for example.
  • the optical waveguide device of this invention also has the advantage of allowing upgrading without replacing existing components.
  • a change to narrower channel bandwidths can be easily accommodated by the addition of a further stage or stages of wavelength selective devices.
  • extra channels can be accommodated by providing an additional stage or stages of wavelength selective devices at the head of the tree. This feature is of considerable practical importance in allowing accommodation in changes of telecommunication standards and allowing users to initially install a system readily capable of upgrade to meet increased load.
  • Figure 1 is a schematic diagram of a 16 channel wavelength dividing device according to this invention.
  • Figure 2 is a schematic diagram of a wavelength selective device forming part of the invention shown in Figure 1.
  • Figure 3 is a schematic diagram of an alternative wavelength selective device forming part of the invention shown in Figure 1 ;
  • Figure 4 is a schematic diagram showing a modification to reduce cross talk
  • Figure 5 is a graph of transmission against wavelength illustration showing cross talk between adjacent wavelength channels.
  • Figure 1 shows a 16 channel wavelength dividing device 1 according to this invention.
  • the device 1 comprises 15 wavelength selective devices 2 to 16 interconnected by optical fibres 17.
  • Figure 2 shows one wavelength selective device 2.
  • the device 2 comprises two lengths of standard telecommunications grade optical fibre optically coupled at spaced apart locations 20 and 21 by means of a fused tapered coupler of known type produced by the applicant. The coupling ratio of the couplers is 3dB.
  • Identical Bragg gratings 22 are formed in each of the optical fibres 18,19 between the couplers 20,21.
  • the Bragg gratings are formed using known techniques such as by the selective irradiation of the fibre material using ultraviolet light to change the refractive index of the fibre.
  • the Bragg gratings can be written into the fibre to provide for reflection of light of selected wavelength. Gratings as fine as 0.02 nm and as coarse as 150 nm have been formed in optical fibres. These gratings readily provide for reflection of light having a wavelength as short as 400 nm to the upper wavelength transmission limit for optical fibres. By using a grating of composite spacing a band of selected wavelengths can be reflected by the Bragg grating. In practice very sharply defined reflection characteristics can be achieved and a discrimination of 27dB over 0.2 nm has been found to be possible.
  • the device 2 has a first port 23, a second port 25, a third port 26 and a fourth port 24 optically interconnected by the optical fibres 18,19.
  • the couplers 20,21 and Bragg gratings 22 form wavelength selective means which route input light of selected wavelength band at the first port 23 to the third port 26 and route light of other wavelengths at the first port 23 to the second port 25.
  • device 2 operates in the known manner of a Mach-Zehnder interferometer. If an input light signal of wavelength mix ⁇ t to ⁇ 16 is launched into fibre 18 at input port 23 it is divided at coupler 20 between fibres 18 and 19 in equal amounts. A phase shift of ⁇ /2 exists between the optical signals in fibres 18 and 19.
  • the signal in each of fibres 18 and 19 encounters Bragg gratings 22.
  • the reflection characteristics of the grating are set such that light having wavelengths ⁇ 1 to ⁇ 8 are reflected.
  • Light having wavelengths ⁇ 9 to ⁇ 16 are transmitted and reach coupler 21.
  • coupler 21 half of the light from each of fibres 18 and 19 is respectively coupled to the other of the fibres.
  • the coupled light again has a ⁇ /2 phase shift.
  • the two components of light in fibre 18 are out of phase by ⁇ and thus complete cancellation occurs. That is, there is no output at output port 24 of fibre 18.
  • the light components in fibre 19 are however in phase and constructive interference results in output of light having wavelengths ⁇ 9 to ⁇ 16 at output port 25 of fibre 19.
  • the components of light reflected by Bragg gratings 22 return to coupler 20 and are again coupled to the other fibre 18,19 with a ⁇ /2 phase shift. As a consequence the light components in fibre 18 are out of phase by ⁇ and thus total cancellation occurs to provide no output at port 23.
  • the components in fibre 19 are in phase and provide an output at third port
  • an input of light having selected wavelength bands ⁇ x to ⁇ 8 at third port 26 will result in an output of light having the same wavelength bands ⁇ t to ⁇ g at first port 23 and nil output at second port 25 or fourth port 24.
  • an input of light having other wavelength bands ⁇ 9 to ⁇ 16 at second port 25 will result in an output of light having the same wavelength bands ⁇ 9 to ⁇ 16 at first port 23 and nil output at third port 26 and fourth port 24.
  • input light at the third port 26 outside the selected wavelength bands ⁇ j to ⁇ 8 is routed to fourth port 24 with nil output to first port 23 and second port 25.
  • Input in the wavelength bands ⁇ t to ⁇ 8 at the second port 25 is routed to the fourth port 24 with nil output to first port 23 and third port 26.
  • path lengths for the light between the gratings and the couplers are equal so that the appropriate phase relationships are maintained. It will also be apparent to those skilled in the art that these path lengths can be adjusted as required for example by modifying the refractive index of the fibre using ultraviolet light to appropriately tune the phase matching.
  • the device 2 allows a light input to the first port 23 having wavelengths ⁇ , to ⁇ 16 to be divided into an intermediate component having wavelengths ⁇ , to ⁇ 8 and another intermediate component having wavelengths ⁇ 9 to ⁇ 16 . It will be apparent that the component having wavelengths ⁇ 9 to ⁇ 16 also includes any out of band wavelengths since they will not be reflected by the Bragg grating.
  • the output at port 26 of selective device 2 becomes the input to selective device 10.
  • the output at port 25 of selective device 2 becomes the input to port 23 of selective device 3.
  • Selective device 3 again divides the light into components having wavelengths ⁇ 9 to ⁇ 12 and ⁇ 13 to ⁇ 16 (plus any of out of band signal).
  • wavelength selective device 10 divides wavelengths ⁇ t to ⁇ 8 into components of ⁇ t to ⁇ 4 and ⁇ 5 to ⁇ 8 . This process is repeated in each of the remaining wavelength selective devices to divide the input signal into discrete wavelength bands ⁇ , to ⁇ 16 as shown.
  • any out of band light can be dealt with by introducing another wavelength selective device (not shown) prior to wavelength selective device 2.
  • This device is configured to provide a reflected output of wavelengths ⁇ x to ⁇ 16 which is provided as the input to wavelength selective device 2.
  • the non reflected (or passed) component from the wavelength selective device contains only out of band wavelengths and would not be used.
  • Alternatively in the arrangement shown in Figure 1 only the output ⁇ 16 of selective device 5 contains out of band light.
  • another filtering device (not shown) can be added to separate light of wavelength ⁇ 16 from out of band light.
  • crosstalk filters can be added to all the remaining even numbered wavelength outputs.
  • FIG. 3 shows an alternative wavelength selective device 30 for use in this invention.
  • the wavelength selective device 30 comprises a circulator 31 of known type optically connected to optical fibres 32, 33, 34.
  • Optical fibres 32, 33, 34 respectively form first, second and third ports of the device 30.
  • Optical fibre 33 has a Bragg grating 35 written into the fibre in the manner described above. The Bragg grating is written to reflect light in a wavelength band ⁇ a . In this way the selective device operates to route input light containing wavelengths in the band ⁇ a+b to the other two ports 33 and 34.
  • the circulator 31 outputs to the optical fibre 33 the input to optical fibre 32.
  • the grating 35 reflects the selected wavelength band ⁇ a as input to the second port 33 and hence into the circulator 31.
  • wavelengths ⁇ b are transmitted by the grating to form the output of other wavelengths at second port 33.
  • the circulator 31 outputs light in the wavelength band ⁇ a at the third port 24. It will be apparent that in this way the selective device 30 can be used to perform the same division as the selective device 2 described above.
  • a further filter can also be used in the output of the selective devices to reflect the unwanted wavelength component and reduce crosstalk.
  • the further filter is usually an additional Bragg grating written into the optical fibre to reflect the unwanted component.
  • the selective devices are Mach-Zehnder interferometers the wavelengths reflected by the extra grating are directed to the fourth port which can be optically terminated. This avoids the resonance condition caused by having more than one grating of the same wavelength in the same optical path and which results in increased noise.
  • a circulator of the kind described in relation to Figure 3 is used as the selective device a further filter can only be used on the third port since an additional filter on the second port would lead to an optical resonance condition.
  • the reflected unwanted wavelengths 5 are input at the third port and consequently are not output at the first and second ports. In practice the input to the third port is lost as radiation from the circulator.
  • the extra filters usually in the form of gratings provide exceptionally high cross talk attenuation for the adjacent bands.
  • Figure 4 shows an arrangement used to remove crosstalk incorporating the above technique.
  • Two wavelength selective devices 41,42 of the optical fibre interferometer type described above are arranged at the last stage of the tree structure shown in Figure 1. That is, selective device 41 corresponds to each of devices 5, 6, 8, 9, 12, 13, 15, and 16.
  • device 41 is connected to either output of a preceding device and receives as input a signal containing two adjacent discrete wavelength bands ⁇ a , ⁇ b .
  • Device 41 has gratings selected to reflect the shorter wavelength band ⁇ a which is output at third port 26 as previously described.
  • a further filter in the form of a Bragg grating 43 is provided in the output.
  • the grating 43 is selected to reflect wavelengths in the band ⁇ b . Any signal in the ⁇ b band
  • the second and fourth ports 25,24 of the device 42 are optically terminated.
  • Figure 5 graphically illustrates what happens at the last separation formed by any one of devices 5, 6, 8, 9 12, 13, 15 or 16 of Figure 1.
  • the device described in relation to Figure 1 is described in relation to Figure
  • the trace marked “blue” is the transfer function versus wavelength from the input port 23 of selective device 2 to the output port 26 of any one of the selective devices 5,6,8,9,12,13,15,16 in the last stage of the device 1 shown in Figure 1. This corresponds to the odd numbered discrete wavelengths ⁇ t> ⁇ 3 ... .
  • the trace marked “red” is the transfer function versus wavelength from the input port 23 of selective device 2 to the output port 25 of any one of the selective devices 5,6,8,9,12,13,15,16 in die last stage of the device 1 shown in Figure 1 including the extra filter 42 but without the grating 43 shown in Figure 4. This corresponds to the even numbered discrete wavelengths ⁇ 2 ⁇ 4 ... but not including ⁇ 16 which includes any out of band component.
  • the only significant cross talk is represented by the part of the blue trace between 1548 and 1549 nm and gives a relative amount of power in this wavelength range that exits port 26 of device 41.
  • the grating 43 removes this crosstalk.
  • the relative amount of power in the 1547 to 1548 nm range that exits port 25 is much lower because it combines the effects of the selectivity of the red filter with the fact that most of the input power in the blue or shorter wavelength range has been removed by the preceding blue or shorter wavelength range filter.
  • the filtering can be reversed at the last stage. That is, the longer wavelength component becomes the selected component that is reflected and the shorter wavelength component is transmitted. This leaves the residual cross talk term being a side lobe on the short wavelength side of the red filter. These tend to be lower than the side lobe levels on the long wavelength side. It is possible to change the order of the wavelength filtering at the last stage because the cladding mode effects that increase the insertion loss of gratings on the short wavelength side are far enough away in wavelength.

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

Abstract

Dispositif optique (1) servant à diviser une lumière d'entrée présentant un mélange de longueurs d'ondes (μ1 à μ16) en bandes de longueurs d'ondes discrètes de sortie (μ1 à μ16) et à combiner ces bandes de longueurs d'ondes discrètes (μ1 à μ16) en une sortie de longueurs d'ondes mélangées (μ1 à μ16) . Ce dispositif (1) comprend au moins trois composants optiques (2, 3, 10) sélectifs de longueur d'onde et possédant au moins un premier accès (23), un deuxième accès (25) et un troisième accès (26) reliés optiquement les uns aux autres au moins partiellement par un ou plusieurs guides d'ondes (18, 19). Le deuxième accès (25) d'un premier des composants sélectifs (2) est relié optiquement par un guide d'onde au premier accès (23) d'un deuxième (3) de ces composants et le troisième accès (26) est relié optiquement par une guide d'onde au premier accès (23) d'un troisième (10) de ces composants.
PCT/AU1998/000089 1997-02-14 1998-02-13 Dispositifs et procede optiques WO1998036302A1 (fr)

Priority Applications (4)

Application Number Priority Date Filing Date Title
AU59738/98A AU731587B2 (en) 1997-02-14 1998-02-13 Optical devices and methods
EP98902853A EP0960349A4 (fr) 1997-02-14 1998-02-13 Dispositifs et procede optiques
CA002280964A CA2280964A1 (fr) 1997-02-14 1998-02-13 Dispositifs et procede optiques
JP53516998A JP2001511905A (ja) 1997-02-14 1998-02-13 光装置及び方法

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
AUPO5116 1997-02-14
AUPO5116A AUPO511697A0 (en) 1997-02-14 1997-02-14 An optical waveguide guide

Publications (1)

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WO1998036302A1 true WO1998036302A1 (fr) 1998-08-20

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WO (1) WO1998036302A1 (fr)

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Publication number Priority date Publication date Assignee Title
WO1999059281A1 (fr) * 1998-05-12 1999-11-18 Siemens Aktiengesellschaft Multiplexeur et demultiplexeur optiques
GB2345399A (en) * 1998-07-14 2000-07-05 Nortel Networks Corp Wideband optical service channel for wavelength division multiplexed networks

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GB2295247A (en) * 1994-11-16 1996-05-22 Northern Telecom Ltd Optical waveguide grating filter having two or three gratings
EP0724314A1 (fr) * 1995-01-27 1996-07-31 PIRELLI CAVI S.p.A. Système de télécommunication optique bidirectionnel comprenant un amplificateur optique bidirectionnel

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IT1265018B1 (it) * 1993-08-10 1996-10-17 Cselt Centro Studi Lab Telecom Dispositivo per l'estrazione e il reinserimento di una portante ottica in reti di comunicazione ottica.
US5457760A (en) * 1994-05-06 1995-10-10 At&T Ipm Corp. Wavelength division optical multiplexing elements
GB9423105D0 (en) * 1994-11-16 1995-01-04 Northern Telecom Ltd Optical wave grating filter
US5557439A (en) * 1995-07-25 1996-09-17 Ciena Corporation Expandable wavelength division multiplexed optical communications systems

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Publication number Priority date Publication date Assignee Title
GB2295247A (en) * 1994-11-16 1996-05-22 Northern Telecom Ltd Optical waveguide grating filter having two or three gratings
EP0724314A1 (fr) * 1995-01-27 1996-07-31 PIRELLI CAVI S.p.A. Système de télécommunication optique bidirectionnel comprenant un amplificateur optique bidirectionnel

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Title
PATENT ABSTRACTS OF JAPAN, Vol. 18, No. 629; & JP,A,06 244 797 (FUJI ELECTROCHEM CO LTD) 2 September 1994. *
PATENT ABSTRACTS OF JAPAN, Vol. 95, No. 3; & JP,A,06 347 836 (NIPPON TELEGR & TELEPH) 22 December 1994. *
PATENT ABSTRACTS OF JAPAN, Vol. 96, No. 4; & JP,A,07 336 324 (NIPPON TELEGR & TELEPH CORP) 23 December 1995. *
See also references of EP0960349A4 *

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1999059281A1 (fr) * 1998-05-12 1999-11-18 Siemens Aktiengesellschaft Multiplexeur et demultiplexeur optiques
GB2345399A (en) * 1998-07-14 2000-07-05 Nortel Networks Corp Wideband optical service channel for wavelength division multiplexed networks
GB2345399B (en) * 1998-07-14 2001-07-11 Nortel Networks Corp Wideband optical service channel for wave division networks
US6263130B1 (en) 1998-07-14 2001-07-17 Nortel Networks Limited Wideband optical service channel for wave division networks

Also Published As

Publication number Publication date
EP0960349A1 (fr) 1999-12-01
AUPO511697A0 (en) 1997-04-11
JP2001511905A (ja) 2001-08-14
EP0960349A4 (fr) 2000-11-02
CA2280964A1 (fr) 1998-08-20

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