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WO1998016804A1 - Dispositif optique non reciproque a points d'acces multiples - Google Patents

Dispositif optique non reciproque a points d'acces multiples Download PDF

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Publication number
WO1998016804A1
WO1998016804A1 PCT/US1997/018516 US9718516W WO9816804A1 WO 1998016804 A1 WO1998016804 A1 WO 1998016804A1 US 9718516 W US9718516 W US 9718516W WO 9816804 A1 WO9816804 A1 WO 9816804A1
Authority
WO
WIPO (PCT)
Prior art keywords
polarization
pair
reciprocal
light beam
ports
Prior art date
Application number
PCT/US1997/018516
Other languages
English (en)
Inventor
Wei-Zhong Li
Vincent Au-Yeung
Guojiang Hu
Original Assignee
U.S.A. Kaifa Technology, 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 U.S.A. Kaifa Technology, Inc. filed Critical U.S.A. Kaifa Technology, Inc.
Priority to AU48196/97A priority Critical patent/AU4819697A/en
Publication of WO1998016804A1 publication Critical patent/WO1998016804A1/fr

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Classifications

    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
    • G02B27/28—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for polarising
    • G02B27/283—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for polarising used for beam splitting or combining
    • G—PHYSICS
    • G02—OPTICS
    • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
    • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
    • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
    • G02F1/09—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on magneto-optical elements, e.g. exhibiting Faraday effect
    • G02F1/093—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on magneto-optical elements, e.g. exhibiting Faraday effect used as non-reciprocal devices, e.g. optical isolators, circulators

Definitions

  • This invention relates generally to non-reciprocal optical devices, and in particular to optical circulators, isolators and other optical devices using birefringent walk-off elements as polarization splitters and combiners (PSCs) .
  • PSCs polarization splitters and combiners
  • Single mode optical fiber has gained rapid acceptance in a variety of actual and proposed optical communications systems (e.g., CATV, fiber to the home (FTTH), wavelength division multiplexed (WDM) transmission systems, and coherent communications) .
  • optical communications systems e.g., CATV, fiber to the home (FTTH), wavelength division multiplexed (WDM) transmission systems, and coherent communications.
  • optical isolators and circulators are only partially successful in satisfying the above requirements. To be practical these components must not only be easy and inexpensive to manufacture. In addition, they have to exhibit low insertion loss at the transmission wavelengths and high isolation of unwanted signals (e.g., reflection). Isolation is particularly critical in many systems sensitive to spurious reflection. For example, distributed feedback (DFB) lasers tend to be unstable when their output couples back into the lasing cavity. While expense is important in nearly all applications, it is particularly critical in high volume, low- cost projects such as FTTH. Isolation and expense are also common issues in systems using optical amplifiers. That is because reflections can induce an amplifier to oscillate.
  • DFB distributed feedback
  • the circulator structure is intricate and the fabrication of the cross-stack polarization beam splitters is very difficult.
  • Yohj i discloses a circulator exhibiting the same desirable isolation characteristics. This circulator is made by replacing the cross-stack polarization beam splitter with a conventional PSC containing birefringent crystal blocks. Insertion loss and isolation of a four-port circulator made in this manner were measured at ⁇ 1.9 dB and > 42.3 dB , respectively.
  • U.S. Patent 5,319,483 to Krasinski et al addresses a polarization independent low cross-talk optical circulator.
  • This device uses reciprocal Faraday rotation elements for controlling the polarization of the light beams. The extinction rate for this circulator is fairly low.
  • the overall structure of the device is complex and its many parts necessitate exact alignment procedures . As a result, the manufacture of this device is costly and difficult.
  • Koga discloses an optical circulator which takes advantage of a pair of Faraday rotators with opposite directions of rotation. Although this device has fewer elements, its construction still requires precise alignment of the optical axis for the rotation elements .
  • the walk-off or beam separation technique used by Koga relies on large birefringent crystals. This results in the whole device being unnecessarily sizable. Furthermore, its isolation is also rather low.
  • the invention aims at achieving a high extinction ratio in the PSC.
  • Another object of the invention is to reduce the size of the device by optimizing the polarization separation performance of the birefringent walk-off elements.
  • Still another object of the invention is to ensure that the device makes use of the fewest parts possible and is easy to fabricate .
  • a multi-port non- reciprocal optical device with at least two ports for receiving and emitting a light beam.
  • the light beam consists of radiation of a first polarization and of a second polarization orthogonal to the first polarization.
  • a first birefringent walk-off element preferably a birefringent crystal made of a material selected from among rutile, calcite and Yittrium Orthovanadate, is positioned between the ports.
  • the walk-off element splits the advancing light beam along a first diagonal into an ordinary beam of the first polarization and an extraordinary beam of the second polarization. Conversely, the walk-off element combines the ordinary beam and the extraordinary beam on the reverse or return path along the diagonal to reconstruct the light beam.
  • a first pair of non-reciprocal rotation elements preferably non-reciprocal Faraday rotators such as latching Faraday rotators or ordinary Faraday rotators are placed in the paths of the ordinary and extraordinary beams . These rotators render the first and second polarizations parallel. This is done, for example, by rotating the first polarization by 45° and the second polarization by 45° as well.
  • a polarization dependent deflecting element receives the ordinary beam and the extraordinary beam.
  • the deflecting element is characterized by a reflecting polarization and a transmitting polarization which is orthogonal to the reflecting polarization.
  • the deflecting element can be a polarizing beam splitter.
  • the beam splitter is made of a pair of right angle prisms cemented hypotenuse-face to hypotenuse-face .
  • a multilayer dielectric film is preferably placed between the pair of prisms.
  • a second pair of non-reciprocal rotation elements is placed in the paths of the ordinary and extraordinary beams for rendering the first and second polarization orthogonal. This is best accomplished by rotating the first polarization by 45° and also rotating the second polarization by 45°. Again, the rotating elements are preferably Faraday rotators .
  • a second birefringent walk-off element is positioned between the ports for splitting the light beam or combining the ordinary and extraordinary beams .
  • This element is analogous to the first one.
  • both walk-off elements have their optical axes oriented at 45° to the axes (x and y) defining input facets of the birefringent crystal .
  • the input ports are GRIN lenses. These are well-suited for receiving and emitting the light beam. Further, the light beam can be received and emitted by single mode or multi-mode optical fibers. The number of ports may vary.
  • Fig. 1 is an isometric view of a multi-port non-reciprocal optical device according to the invention.
  • Fig. 2 is an isometric view of a walk-off element from the device of Fig. 1.
  • Fig. 3 is an isometric view of a pair for Faraday rotators from the device of Fig. 1.
  • Fig. 5 is a plan top view of a different non-reciprocal optical device according to the invention.
  • Fig. 7 is a plan top view of yet another non-reciprocal optical device according to the invention.
  • Fig. 9 is a plan top view of a three-port circulators according to the invention.
  • FIG. 1 An embodiment of a four port non-reciprocal optical device 10 according to the invention is shown in Fig. 1.
  • Device 10 has four ports 12, 14, 16 and 18 fed by corresponding optical fibers 22, 24, 26 and 28. All ports 12, 14, 16 and 18 are designed for receiving and emitting light. Fibers 22, 24, 26 and 28 are multi-mode or single mode fibers.
  • Lenses 32, 34, 36 and 38 assigned to corresponding ports 12, 14, 16 and 18 serve to couple light into and out of device 10. It is preferable that faces 2, 4, 6, 8 of lenses 32, 34, 36, 38 be slanted and coated to improve in-coupling and limit unwanted scattering. Techniques to achieve this result are well-known in the art. In the present embodiment lenses 32, 34, 36, 38 are of the GRIN-type and their faces 2, 4, 6, 8 are slightly inclined.
  • a light beam 20 enters device 10 through port 12. Once admitted it is incident on an input facet 42 of a birefringent walk-off element 52.
  • element 52 is one of four analogous walk-off elements 52, 54, 56 and 58 having corresponding input facets 42, 44, 46 and 48.
  • Suitable materials for elements 52, 54, 56 58 include rutile, calcite, Yittrium Orthovanadate and the like.
  • walk-off elements 52, 54, 56, 58 are birefringent crystals.
  • optical axes 90 of all elements 52, 54, 56, 58 are in the plane oriented at 45° to the axes defining input facets 42, 44, 46 and 48. This is shown in detail by Fig. 2 using element 52 as an example.
  • a vector 91 defines the 45° angle to the sides of facet 42.
  • Optical axis 90 is oriented at an angle ⁇ to vector 91.
  • vector 91 and optical axis 90 define the above-mentioned plane which is inclined at 45° to the axes sides of input facet 42.
  • the magnitude of angle ⁇ is obtained from the well-known relation:
  • a walk-off distance in element 52 is defined as follows:
  • Dw o a tan( ⁇ ) where a is the length of element 52 traversed by beams 130 and 132 as indicated.
  • a is the length of element 52 traversed by beams 130 and 132 as indicated.
  • the reason for the separation of the two beams is due to the difference in the refractive indices .
  • extraordinary beam 132 will travel forward or advance along a short diagonal 134 diverging quickly away from the straight path taken by ordinary beam 130.
  • ordinary beam 130 and extraordinary beam 132 are on their return path, they will be efficiently combined along diagonal 134.
  • ordinary beam 130 will retain a first polarization 140 and extraordinary beam 132 will have a second polarization 142.
  • Polarizations 140 and 142 are orthogonal to each other.
  • output facets 62, 64, 66 and 68 face corresponding pairs of non-reciprocal rotation elements 72, 74, 76, 78 each consisting of two individual rotators 82; 92, 84; 94, 86; 96 and 88; 98.
  • the rotation sense of each rotator 82; 92, 84; 94, 86; 96 and 88; 98 is discussed below.
  • rotators 82,-92, 84; 94, 86; 96 and 88; 98 are either regular Faraday rotators or latching Faraday rotators . The latter operate without a bias magnet and are consequently preferred.
  • Fig. 3 illustrates the operation of pair of elements 72 consisting of rotators 82 and 92.
  • Corresponding magnetic fields Bi and B 2 are generated by suitable sources (e.g., solenoids; not shown) or permanent magnets in the event of latching-type rotators 82, 92.
  • the direction of fields Bi and B 2 determines how the polarization of light passing through rotators 82 and 92 is altered.
  • fields Bi and B 2 are anti-aligned to produce 45° contrary polarization rotations. This causes first polarization 140 of ordinary beam 130 to rotate by 45° to the position shown.
  • second polarization 142 of extraordinary beam 132 is also turned by 45°. The two 45° polarization rotations are opposite in sense.
  • first and second polarizations 140 and 142 end up being parallel.
  • elements 102 and 104 are polarizing beam splitters and combiners (PSCs) .
  • PSCs polarizing beam splitters and combiners
  • the property of splitters 102 and 104 dictates that light having a transmitting polarization will pass through splitters 102 and 104. Meanwhile, light having a reflecting polarization will be reflected. This function is ensured by reflecting films 106 and 108.
  • the latter may be made of a multilayer dielectric films.
  • beam splitters 102 and 104 are made of a pair of right angle prisms 112; 122 and 114; 124.
  • Multilayer films 106 and 108 are sandwiched by prisms 112; 122 and 114; 124, which are cemented together hypotenuse- face to hypotenuse- face.
  • FIG. 1 The operation of device 10 is best visualized by referring back to Fig. 1 and following the diagrams of Figs. 4A-4C.
  • FIG. 1 illustrate light beam 20 traveling from port 12 to port 14, from port 14 to port 16 and from port 16 to port 18.
  • the polarization rotations are shown explicitly.
  • first and second polarizations 140 and 142 of beams 130 and 132 are "walked-off" in element 52 by distance D wo .
  • rotators 82 and 92 rotate polarizations 140 and 142 by 45° clockwise and counter-clockwise, respectively.
  • polarizations 140 and 142 are parallel to each other .
  • polarizations 140, 142 are aligned with the intrinsic transmitting polarization and are thus passed on to rotators 84 and 94.
  • polarizations 140, 142 are rotated by another 45° each and are again orthogonal to each other. Then, inside element 54, following upon the return path, ordinary and extraordinary beams 130 and 132 are combined again, as indicated by merged polarizations 140, 142, and delivered to port 14.
  • device 10 is a circulator, since no light can return to original port 12 by following the path of light beam 20 from port 14 back to port 12. Instead, as show in Fig. 4B, light beam 20 passes from port 14 to port 16 along the direction indicated by arrow B.
  • the "walk-off" between beams 130 and 132 carrying polarizations 140 and 142 occurs in crystal 54. Clockwise and counter-clockwise 45° rotations in rotators 84 and 94 render polarizations 140 and 142 parallel. In this state, polarizations 140 and 142 are aligned with the reflecting polarization of beam splitter 102.
  • Beams 130 and 132 are consequently reflected by splitter 102 or, more precisely, by film 106 along a direction perpendicular to arrow B (x-direction) and travel to splitter 104, where they are aligned with splitter's 104 reflecting polarization. Again reflected, this time along the direction of arrow B, beams 130 and 132 pass through rotators 86 and 96. These rotate polarizations 140 and 142 by 45° to render them orthogonal. Crystal 56 reunites beams 130 and 132 into light beam 20, and the latter exits device 10 through port 16.
  • Fig. 4C shows how light beam 20 passes from port 16 to port 18 along the direction indicated by arrow A.
  • the "walk-off" takes place in crystal 56.
  • Rotators 86 and 96 induce 45° rotations of polarizations 140 and 142, such that they are parallel and aligned with the transmitting direction of splitter 104.
  • Beams 130 and 132 thus pass through splitter 104 to rotators 88 and 98 to be rotated such that their polarizations 140 and 142 are again orthogonal.
  • Crystal 58 rejoins beams 130 and 132 into light beam 20 which then issues forth through port 18.
  • Device 10 is a multi-port non-reciprocal optical device, in particular a circulator, with a low insertion loss and a high extinction ratio in polarization separation. This is chiefly due to the use of polarizing beam splitters 102 and 104.
  • polarization beam splitter 104 can be replaced by a highly reflective element such as a reflecting prism or a glass plate with a highly reflective coating while retaining the same advantages .
  • polarization axis 90 in the plane set at 45° to the sides of input facets of crystals 52, 54, 56 and 58 ensures that the polarization separation performance is optimized.
  • the "walk-off" along diagonal 134 allows one to do away with half-wave plates and use non-reciprocal rotators 82; 92, 84 ; 94 , 86; 96 and 88; 98 immediately past crystals 52, 54, 56 and 58. This eliminates the need for precise alignment procedures (commonly required to properly orient the optical axes of half-wave plates), reduces the number of parts, and greatly simplifies the design of circulator 10 in comparison to prior art units.
  • circulator 200 is shown exploded and in top plan view in Fig. 5.
  • circulator 200 has four ports 202, 204, 206 and 208 equipped with lenses 212, 214, 216, 218 and fed by optical fibers 222, 224, 226 and 228.
  • the faces of lenses 212, 214, 216, 218 are inclined to improve the in- coupling efficiency of light.
  • Birefringent walk-off elements 232, 234, 236 and 238 are set up as in the above-discussed embodiment for separating the input light into its ordinary and extraordinary component beams (not shown).
  • Non-reciprocal Faraday rotators 242; 252, 244; 254, 246; 256, 248; 258 are set on polarization dependent deflecting elements 260, 262 and 264.
  • Elements 260 and 264 are prisms with reflective films 266 and 268.
  • element 262 is a full beam splitter with reflecting film 280.
  • Device 200 is an efficient, simple and low-cost circulator endowed with the aforementioned advantages. Its geometry, in particular the arrangement of ports 202, 204, 206 and 208 makes it suitable for many different applications.
  • FIG. 7 Yet another embodiment of a device 300 according to the invention is illustrated in Fig. 7. Except for the different geometrical arrangement of ports 302, 304, 306, 308 and a different set of polarization dependent deflecting elements 342, 344, 346, 348, 350, 352.
  • This device is similar to the previous embodiments. It has fibers 312, 314, 316, 318 coupled into device 300 through lenses 322, 324, 326, 328 leading to walk-off elements 332, 334, 336 and 338.
  • device 300 also has non-reciprocal Faraday rotators 362,372, 364,374, 366,376 and 368,378.
  • Figs. 8A-C show how light beam 20 propagates from port to port. This process is analogous to those described above.
  • Fig. 8A shows the progress of beam 20 from port 302 to port 304 along directions indicated by arrows A, B and C.
  • Fig. 8B shows beam 20 on its path from port 304 to 306 through four deflecting elements 344, 346, 350 and 348.
  • the passage of beam 20 from port 306 to 308 can be seen in Fig. 8C.
  • circulator 300 The additional advantage of circulator 300 is that all ports 302, 304, 306 and 308 are arranged on the same side. This is advantageous for applications under geometrical constraints from all but one side.
  • Fig. 9 illustrates yet another non-reciprocal optical device 400 with three ports 402, 404 and 406.
  • Device 400 functions as a circulator and uses fibers 412, 414, 416 in conjunction with lenses 422, 424 and 426 for efficient transmission of light. It also has three walk-off elements 432, 434 and 436 arranged facing three sides of a beam splitter 450. The latter has non-reciprocal Faraday rotators 462; 472, 464; 474, 466; 476 on the sides facing elements 432, 434 and 436.
  • Device 400 operates according to the same principles as the previous embodiments.
  • the advantage of its design resides in the efficient use of a single beam splitter 450. Further, losses due to multiple reflections and scattering are minimized in this structure. Ports 402, 404 and 406 are far apart for easy access and connection.

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  • Physics & Mathematics (AREA)
  • Nonlinear Science (AREA)
  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)

Abstract

Dispositif optique non réciproque à points d'accès multiples possédant des points d'accès qui servent à recevoir et à émettre un rayon de lumière ayant une première et une deuxième polarisation orthogonales. Le dispositif utilise des éléments biréfringents de déviation (52,54,56 et 58) qui sont, de préférence, des cristaux biréfringents ayant des axes optiques orientés à 45° par rapport aux axes qui définissent les faces d'entrée du cristal. Les cristaux sont placés entre les points d'accès de manière à diviser le rayon de lumière qui se propage le long d'une première diagonale en un rayon ordinaire et un rayon extraordinaire possédant une première et une seconde polarisation. A l'inverse, les éléments de déviation combinent le rayon ordinaire et le rayon extraordinaire sur le chemin de retour le long de la diagonale pour recréer le rayon de lumière. Des paires d'éléments de rotation non réciproques (82, 92; 84, 94; 86, 96 et 88, 98) sont placées sur les chemins des rayons ordinaire et extraordinaire pour faire pivoter les polarisations de 45° et les rendre parallèles ou orthogonales, de manière à ce que un élément de déflexion (102 ou 104) dépendant de la polarisation transmette ou réfléchisse les deux rayons. Le dispositif peut fonctionner comme un circulateur, un atténuateur ou un commutateur optique ou comme un photocoupleur.
PCT/US1997/018516 1996-10-15 1997-10-15 Dispositif optique non reciproque a points d'acces multiples WO1998016804A1 (fr)

Priority Applications (1)

Application Number Priority Date Filing Date Title
AU48196/97A AU4819697A (en) 1996-10-15 1997-10-15 Multiport non-reciprocal optical device

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US73075696A 1996-10-15 1996-10-15
US08/730,756 1996-10-15

Publications (1)

Publication Number Publication Date
WO1998016804A1 true WO1998016804A1 (fr) 1998-04-23

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PCT/US1997/018516 WO1998016804A1 (fr) 1996-10-15 1997-10-15 Dispositif optique non reciproque a points d'acces multiples

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Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5535329A (en) * 1978-09-04 1980-03-12 Nippon Telegr & Teleph Corp <Ntt> Light circulator
US5682446A (en) * 1995-10-13 1997-10-28 E-Tek Dynamics, Inc. Polarization mode dispersion-free circulator
US5689593A (en) * 1995-10-13 1997-11-18 E-Tek Dynamics, Inc. Compact fiberoptic circulator with low polarization mode dispersion

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5535329A (en) * 1978-09-04 1980-03-12 Nippon Telegr & Teleph Corp <Ntt> Light circulator
US5682446A (en) * 1995-10-13 1997-10-28 E-Tek Dynamics, Inc. Polarization mode dispersion-free circulator
US5689593A (en) * 1995-10-13 1997-11-18 E-Tek Dynamics, Inc. Compact fiberoptic circulator with low polarization mode dispersion

Also Published As

Publication number Publication date
AU4819697A (en) 1998-05-11

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