EP1151331A1 - Composants optiques - Google Patents

Composants optiques

Info

Publication number
EP1151331A1
EP1151331A1 EP00902761A EP00902761A EP1151331A1 EP 1151331 A1 EP1151331 A1 EP 1151331A1 EP 00902761 A EP00902761 A EP 00902761A EP 00902761 A EP00902761 A EP 00902761A EP 1151331 A1 EP1151331 A1 EP 1151331A1
Authority
EP
European Patent Office
Prior art keywords
grating structure
grating
reflective
series
discontinuity
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.)
Withdrawn
Application number
EP00902761A
Other languages
German (de)
English (en)
Inventor
Ian Hugh White
Richard Vincent Penty
Michael Cowin
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.)
University of Bristol
Original Assignee
University of Bristol
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 University of Bristol filed Critical University of Bristol
Publication of EP1151331A1 publication Critical patent/EP1151331A1/fr
Withdrawn legal-status Critical Current

Links

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

Definitions

  • the present invention relates to optical components and in particular to optical grating components.
  • Optical gratings are used in a number of different applications to divide optical signals into a number of components of different respective wavelengths. Applications include sensing, spectroscopy, and other forms of optical signal processing.
  • WDM wavelength division multiplexing
  • One conventional device is a wavelength dependent coupler, such as that described in "Strong Bragg gratings for WDM devices in nonsensitised low loss Ge doped waveguides", Electronics Letters, vol.32, no.23, p.2151, 1996.
  • Another conventional device is a Bragg reflecting filter, such as that described in "Fabrication of wavelength tunable
  • optical crosstalk is a key performance consideration for practical implementation.
  • compactness of such components which has an important impact upon the component count per wafer, ultimate yield on manufacture and so the ultimate cost per unit component .
  • FIGS 1 and 2 illustrate a 2DIO single element device which is formed in an optical substrate layer 1.
  • the device is typically fabricated on a silicon base material (not shown for clarity) and has upper and lower cladding layers 3 (shown only partially for clarity) which contain any optical signals so that they propagate in the plane of the core layer (ie. in two dimensions) .
  • Optical signals 2 are input to the substrate 1 of the device via a single mode input optical waveguide 4.
  • the input optical signal containing a number of spectral channels, propagates through the input waveguide 4 and emerges into a slab region of the substrate 1 in which confinement by the upper and lower cladding regions 3 occurs only in a direction perpendicular to the plane of the device.
  • the transversely diverging output beam from the guide is collimated by an input etched mirror structure 6 and is guided to illuminate a transmission grating structure 10.
  • the known grating structure 10 consists of a series of triangular reflecting elements 10 x ..10 x . ,10 n arranged so as to form a distributed series of elements, with each element spaced from the next in the series. The elements are spaced so that the optical signals input to and output from the elements are not blocked by the neighbouring elements.
  • An incident wavefront is split into multiple sections and a constant phase delay added to each section upon reflection by each transmission grating element.
  • Each section of the wavefront emerges from the grating and interferes with the other section to produce an interference pattern in the far field.
  • the pattern consists of a series of peaks and troughs corresponding to where constructive and destructive interference occur respectively. As such this component can be used to spatially separate a wavelength division multiplexed signal.
  • the diffracted output from the grating structure 10 is then focussed onto a set of output waveguides by an output etched mirror structure 8.
  • the signals carried by input signal have respective wavelengths and so have respective different angles of diffraction. Each signal is thereby focussed to a particular output waveguide 12 for output from the device.
  • Optical crosstalk in such components imposes a major limit to the practical implementation of multi- wavelength optical cross-connects networks.
  • Experimental studies on an established multi-wavelength transport network (MWTN) demonstrator have highlighted optical crosstalk to be one of the key performance considerations in the network design and performance specifications .
  • Crosstalk in the 2DIO demultiplexer can be caused by component imperfections such as internal reflections, multiplexer/demultiplexer leakage and stray and scattered light.
  • an equally important consideration is the crosstalk due to spectral overlapping between adjacent channels. This is a result of overlapping foci due to the limited wavelength resolution of the 2DIO grating.
  • the grating elements 10 n each act very small mirrors. As is the case for all mirrors a reversal of the image from each of these micro-mirror grating elements occurs. This reversal effect does not affect the reflection of a plane wave from the grating as such a wave has a uniform amplitude and phase across the grating. However, in the case of gaussian beam illumination it has been found that due to the rapidly varying amplitude distribution on the grating this reversal effect can result in substantial variations in the amplitude distribution of the reflected beam as illustrated in Figure 4.
  • Modelling shows that a doubling of the higher order interference mode profile is observed due to the perturbation of the amplitude profile of the reflected gaussian distribution caused by image reversal on reflection from the grating elements. This ultimately leads to a reduction in the power contained within the designed diffraction mode of the component and a subsequent increase in the crosstalk floor of the resultant component.
  • One of the major sources of stray or scattered light within previous 2DIO demultiplexers is due to imperfect grating element fabrication as illustrated in Figure 3.
  • the quality of the vertices of the triangular grating elements 10 n is highly dependent upon the fabrication process employed to manufacture the device . Due to the limited resolution of the mask and photolithographic process usually used to produce such a device, the vertices 16 of the elements suffer from rounding. This results in a periodic modulation in the amplitude and phase of the reflected beam.
  • Such rounding of the vertices also results in the effective shortening of the reflective surface (L nom to L eff ) and causes gaps in the phase distribution as shown in Figure 4.
  • the result is the superposition of amplitude and phase gratings with identical periods.
  • the power content of the main mode falls with a reduction of the reflector width and the power content of the first and second higher order modes increases almost linearly drawing power away from the main mode with reflector width reduction.
  • rounding of the grating element vertices results in a degradation of grating efficiency and significantly increases power coupling into higher order diffraction modes . This leads to a reduction in power within the designed diffraction mode of the component and a subsequent increase in the crosstalk floor of the resultant component .
  • an optical grating structure formed on a substrate material, the grating structure comprising a plurality of grating elements arranged to form a distributed series, each grating element except the first in the series being spaced from the previous in the series, wherein each grating element defines first and second reflective discontinuities, the first discontinuity being arranged for receiving an optical signal, and for guiding that signal to the second discontinuity.
  • Figure 1 is a schematic view of a previously considered demultiplexer device
  • Figure 2 is a plan view of a grating structure of the device of Figure 1;
  • Figure 3 is a detailed view of part of the grating structure of Figure 2;
  • Figure 4 illustrates input and output fields of the device of Figures 1 , 2 and 3 ;
  • Figure 5 is a plan view of part of an optical grating structure embodying the present invention.
  • Figures 6a to 6d are scanning electron microscope images of an optical grating structure embodying the present invention
  • Figure 7 is a schematic view of an etching process for use in producing the optical grating structure of
  • Figure 8 illustrates a mask used in the process of
  • Figure 7; and Figure 9 is a graph showing the wavelength response of the optical grating structure of Figures 5 to 8. DESCRIPTION OF THE PREFERRED EMBODIMENT
  • Figure 5 shows an optical grating structure embodying the present invention. Similar to the known structure described above, a distributed series of grating elements is provided on a substrate material . For a two dimensional device, the substrate can carry cladding layers which confine propagation of optical signals to be within the plane of the substrate layer.
  • Each grating element except the first in the series, is spaced from the previous element structure in the series .
  • the grating structure is arranged to receive an input optical signal and to output a diffracted output optical signal.
  • a demultiplexer device incorporating a grating structure embodying the present invention includes input and output ports through which respective input and output signals are transferred.
  • a demultiplexer device incorporating such a grating structure and as in the previously described demultiplexer device, use is made of slab waveguide propagation to guide an input multiplexed optical signal from an input waveguide via a collimating reflector onto the grating structure.
  • a reflector focuses the signals from the elements onto an array of output guides of the device.
  • Each output waveguide receives an output signal of a predetermined wavelength.
  • a grating structure embodying the present invention includes grating elements which each provide two reflective regions, an input region 50 and an output region 52.
  • the regions are provided by respective reflective discontinuities in the substrate.
  • the discontinuities can be provided by any suitable means.
  • the refractive index of the substrate can be adjusted, for example by doping, to give a step change.
  • a cavity can be formed, for example by etching, in the substrate. The boundary surface of the cavity can then define a reflective surface.
  • the cavities could be filled with material different to that of the substrate.
  • the skilled person will be able to provide the required reflective regions in a number of ways which are covered by the scope of this invention.
  • the surfaces 50 and 52 are provided by edges of substantially triangular structures etched into the core layer.
  • the ends of the two triangular structures preferably meet to provide a single continuous etched structure, as shown in the drawings .
  • the grating element may be provided by a single continuous element which defines the two reflective regions, or may be provided by two or more elements which may be separated from one another.
  • the term "grating element" in the context of the present invention is intended to cover both of these possibilities, such that the present invention is not simply limited to the specific embodiment shown in the drawings which uses a single composite etched structure, but can be provided by respective distinct configurations .
  • the provision of two reflecting regions corrects the inversion of the optical signal that occurs with a single surface, thereby overcoming one of the major disadvantages of the prior art device.
  • the angle of incidence upon the individual grating elements is preferably the same as in the previous design. However, the angle of incidence of the input optical signals upon the complete grating (with respect to the grating normal) is decreased because of the double reflective region (mirror) configuration. With the double mirror configuration, when the input beam is gaussian, then the focussed spot at the output will also be gaussian.
  • the grating elements are arranged such that the input light beam 54 to one of the elements 10 n is effectively limited by an outer edge of the next element 10 n+1 . In this configuration, only a portion of the reflective regions reflect the optical signal.
  • each reflective region extends past the extent of the incoming optical signal (i.e. the reflective regions incorporate extensions past the minimum length required for reflection) .
  • This construction removes any rounding effect of one end of the reflecting region, by effectively removing that end.
  • the corner will appear to all incoming light to be perfectly formed. This naturally gives enhanced performance, since the rounding losses can be effectively reduced.
  • the other end of the grating element is still be defined by the end point of the reflecting region, since the element concerned must not block or interfere with the input signal of the next element in the series .
  • the cavity that provides the reflecting region may be of another shape such that some of the incident wavefield is blocked and perhaps reflected by the cavity .
  • Rounding effects of the outer vertices of the elements can be further reduced or even eliminated by the use of a double masking technique which is the subject of a co-pending UK patent application. Briefly, such a technique uses two mask layers and a intermediate sacrificial layer to define accurately the end vertices .
  • Grating element height h neff cos(# ⁇ ) 1
  • a 4 channel polymeric wavelength division multiplexer based upon a slab waveguide and the double reflective transmission grating was designed and fabricated.
  • the channel spacing was 200 GHz (l. ⁇ nm) and was designed and realised for operation within the erbium doped fibre amplifier (EDFA) window.
  • EDFA erbium doped fibre amplifier
  • the double reflective grating (DRG) demultiplexer was designed to operate around 1538nm with a diffraction order of 48 and an effective refractive index of 1.51.
  • the DRG has input and output waveguides, parabolic mirrors with a focal length of 2318mm and a transmission grating which consists of 71 double reflective elements with a pitch of 28.4mm.
  • the input and output waveguides are separated by 250mm at each facet for fibre coupling.
  • the device was fabricated on a silicon substrate utilising the standard commercial polymers of PMMA and PMGI as cladding and optical core layers respectively. Multiple polymer layers were applied using spin coating techniques yielding a refractive index step of 0.02. The formation of input/output waveguides, parabolic mirrors and DRG elements was achieved in a single deep reactive ion etch step with silicone based photoresist as a mask layer patterned by standard photolithography. The component was diced out of the wafer yielding a die that is only 6x3.5mm. Transfer loss associated with butt coupling optical fibres to the waveguides is of the order of 4dB per endface, and the planar waveguide loss was measured using the cutback method and was found to be 3dB/cm at 1540nm
  • the demultiplexing performance of the device was tested using a wavelength tunable laser source.
  • the transmission of all four outputs in figure 6 are shown against wavelength as measured with unpolarised light injected into the device.
  • the insertion loss of the device in the passbands varies between 20-22dB of which 8dB can be attributed to waveguide propagation loss, 8dB to fibre coupling loss and 4dB to loss from the reflective elements .
  • the background crosstalk level is ⁇ 15dB and the usable passband width is 1.4nm.
  • the double reflector grating (DRG) demultiplexer embodying the invention is compact and results in a compression of the overall width of the component due to the decrease in the angle of incidence allowed (wrt grating normal) , whilst maintaining an actual angle of incidence upon the grating facet that is within the critical angle for total internal reflection.
  • embodiments of the present invention can provide improved grating structures that are suitable for use in a number of different applications .
  • the WDM signal demultiplexer described above is purely used as an example of one such application.
  • a device utilising a grating embodying the invention can provide improved performance and reliability over previously considered devices .
  • the device since the device is relatively easily fabricated from polymer materials, the cost of manufacturing the device can be lowered.

Landscapes

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

Abstract

L'invention concerne une structure de réseau optique sur un substrat, qui comprend plusieurs éléments de réseau (10) disposés en série distribuée (10). Chaque élément, à l'exception du premier, est espacé par rapport à l'élément précédent de la série, définissant des première et seconde discontinuités de réflexion (50, 52). La première discontinuité (50) est conçue pour recevoir un signal optique et guider ce signal vers la seconde discontinuité (52).
EP00902761A 1999-02-11 2000-02-10 Composants optiques Withdrawn EP1151331A1 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
GBGB9903112.2A GB9903112D0 (en) 1999-02-11 1999-02-11 Optical components
GB9903112 1999-02-11
PCT/GB2000/000422 WO2000048025A1 (fr) 1999-02-11 2000-02-10 Composants optiques

Publications (1)

Publication Number Publication Date
EP1151331A1 true EP1151331A1 (fr) 2001-11-07

Family

ID=10847568

Family Applications (1)

Application Number Title Priority Date Filing Date
EP00902761A Withdrawn EP1151331A1 (fr) 1999-02-11 2000-02-10 Composants optiques

Country Status (5)

Country Link
EP (1) EP1151331A1 (fr)
AU (1) AU765250B2 (fr)
CA (1) CA2364270A1 (fr)
GB (1) GB9903112D0 (fr)
WO (1) WO2000048025A1 (fr)

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP1506440A4 (fr) * 2002-05-17 2005-08-10 Nanoventions Inc Guides d'ondes optiques plans
US7068885B2 (en) 2004-03-24 2006-06-27 Enablence, Inc. Double diffraction grating planar lightwave circuit
KR20070011327A (ko) * 2004-03-24 2007-01-24 인에이블런스 아이엔씨. 이중 회절 격자 평면 광도파관 회로

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2222891B (en) * 1988-09-17 1992-01-08 Stc Plc Diffraction grating
GB2316759A (en) * 1996-07-30 1998-03-04 Northern Telecom Ltd Optical multiplexer/demultiplexer having diffraction gratings in tandem

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO0048025A1 *

Also Published As

Publication number Publication date
AU765250B2 (en) 2003-09-11
GB9903112D0 (en) 1999-04-07
WO2000048025A1 (fr) 2000-08-17
AU2450200A (en) 2000-08-29
CA2364270A1 (fr) 2000-08-17

Similar Documents

Publication Publication Date Title
US7376308B2 (en) Optical off-chip interconnects in multichannel planar waveguide devices
US7447403B2 (en) Integrated etched multilayer grating based wavelength demultiplexer
US7634165B2 (en) Monolithic tunable lasers and reflectors
Horst et al. Silicon-on-insulator echelle grating WDM demultiplexers with two stigmatic points
US5581639A (en) Raman-nath diffraction grating
JP2001141946A (ja) 合分波素子
JP2006106769A (ja) 光機能デバイス
US20030206681A1 (en) Integrating element for optical fiber communication systems based on photonic multi-bandgap quasi-crystals having optimized transfer functions
US6404946B1 (en) Arrayed waveguide grating type optical multiplexer/demultiplexer
US7587112B2 (en) Optical device and light control method
US20030206694A1 (en) Photonic multi-bandgap lightwave device and methods for manufacturing thereof
US20230161101A1 (en) Devices and methods exploiting waveguide supercells
US6591038B1 (en) Optical interleaver and demultiplexing apparatus for wavelength division multiplexed optical communications
WO2001086848A1 (fr) Multiplexeur et demultiplexeur en longueur d'onde optique
US7200302B2 (en) Planar lightwave Fabry-Perot filter
KR100594040B1 (ko) 듀얼 밴드 파장분할 다중화기
US6904203B2 (en) Passband flattened demultiplexer employing segmented reflectors and other devices derived therefrom
AU765250B2 (en) Optical components
EP1209453A2 (fr) Monochromateur et multiplexeur en longueur d'onde l'utilisant
WO2002079863A2 (fr) Filtres optoelectroniques
US7295732B2 (en) Wavelength selective device
JP3396012B2 (ja) 光学素子および光集積素子
US6650796B2 (en) Waveguide optical frequency router
Cowin et al. Polymeric wavelength division multiplexer
JP3643058B2 (ja) 導波路形回折格子

Legal Events

Date Code Title Description
PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

Free format text: ORIGINAL CODE: 0009012

17P Request for examination filed

Effective date: 20010903

AK Designated contracting states

Kind code of ref document: A1

Designated state(s): AT BE CH CY DE DK ES FI FR GB GR IE IT LI LU MC NL PT SE

17Q First examination report despatched

Effective date: 20011211

GRAP Despatch of communication of intention to grant a patent

Free format text: ORIGINAL CODE: EPIDOSNIGR1

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: THE APPLICATION IS DEEMED TO BE WITHDRAWN

18D Application deemed to be withdrawn

Effective date: 20040803