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WO2000048029A1 - Isolateur optique compact a ports multiples - Google Patents

Isolateur optique compact a ports multiples Download PDF

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Publication number
WO2000048029A1
WO2000048029A1 PCT/US2000/001254 US0001254W WO0048029A1 WO 2000048029 A1 WO2000048029 A1 WO 2000048029A1 US 0001254 W US0001254 W US 0001254W WO 0048029 A1 WO0048029 A1 WO 0048029A1
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Prior art keywords
optical isolator
optical
array
polarizer
core
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Ceased
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PCT/US2000/001254
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English (en)
Inventor
Ping Xie
Yonglin Huang
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Oclaro Photonics Inc
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Oclaro Photonics Inc
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Application filed by Oclaro Photonics Inc filed Critical Oclaro Photonics Inc
Priority to AU24159/00A priority Critical patent/AU2415900A/en
Publication of WO2000048029A1 publication Critical patent/WO2000048029A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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    • 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
    • G02B6/27—Optical coupling means with polarisation selective and adjusting means
    • G02B6/2746—Optical coupling means with polarisation selective and adjusting means comprising non-reciprocal devices, e.g. isolators, FRM, circulators, quasi-isolators

Definitions

  • An optical isolator transmits optical signals in one direction but blocks optical signals propagating in the opposite direction.
  • Optical isolators find use, among other areas, in fiber optic networks at the output of laser diodes coupled to optical fibers in a fiber optic network.
  • Laser diodes can be quite sensitive to optical signal reflections from other optical elements downstream of the laser diodes.
  • Optical signal reflections may cause a shift in output wavelength of a laser diode, or output power loss.
  • Optical isolators are used to block such reflections, effectively isolating laser diodes from perturbations due to downstream optical elements.
  • an optical isolator device for an optical fiber communication network, that the isolator be polarization insensitive.
  • a light beam propagated through an ordinary optical fiber has an arbitrary polarization.
  • the polarization state changes due to the factors including varying ambient temperature and deformation of the fiber.
  • polarization insensitive optical isolator devices reference may be made to, for example, United States Patent Nos. 4,548,478, issued October 22, 1985 and 4,239,329, issued December 16, 1980.
  • a single optical isolator device disclosed in the above U.S. Patent No. 4,548,478 is disclosed as having a first birefringent crystal wedge for splitting an incident light beam into an ordinary ray and an extraordinary ray, a Faraday rotator for rotating the polarization direction of the two rays from the first crystal wedge by 45 degrees, and a second birefringent crystal wedge for combining the two polarization components that have passed the Faraday rotator.
  • a reflection of the output beam of the isolator device is propagated through the device in the opposite direction, the relation between the polarizations is reversed in the first crystal wedge.
  • the forward and reverse beams do not follow the same optical path, thus isolation is achieved.
  • This kind of isolator device is free from changes in loss caused by the changes in the polarization of the input beam since light in the isolator device moves in a constant manner without regard to the polarization orientation of the input beam.
  • a series of birefringent wedges interposed with non-reciprocal Faraday rotators can be placed in series.
  • a first birefringent crystal plate, a Faraday rotator, a second birefringent crystal plate, a Faraday rotator and a third birefringent crystal plate may be sequentially arranged in this order, as disclosed in Summaries of 1991 Spring Conference of The Institute of Electronics, Information and Communication Engineers, pp. 4-125.
  • the isolator device of U.S. Patent No. 4,239,329 is, in principle, the same as the above-stated isolator device except that the birefringent crystal wedges are replaced by birefrigent walk-off crystals and an additional reciprocal polarization rotator is also added.
  • the light from one optical fiber is separated into ordinary and extraordinary ray by a first birefrigent crystal member. Both rays are subjected to a total of 90° polarization rotation by transmitting in a forward direction through a Faraday rotator having an angle of polarization rotation of 45° and through a reciprocal polarization rotator having an angle of polarization rotation of 45°.
  • the ordinary and extra-ordinary rays may then be recombined at the second birefringent crystal member.
  • the relation between the polarization components is reversed in the first crystal member.
  • the forward and reverse beams do not follow the same optical path, thus isolation is achieved.
  • Optical isolators have become ubiquitous in modern fiber optic networks, particularly in telecommunications networks, because of their role in reducing laser diode output wavelength drift and signal power loss. As the complexity of these networks has increased, the number of laser diodes in a given network has also increased. Accordingly, the need for large numbers of optical isolators in a given network or optical circuit has also increased
  • Second sleeves each holding an end section of a second optical fiber and a second collimating element may be fixed in the parallel grooves on the other side of the perpendicular groove.
  • An optical isolator core subassembly having first and second strips of birefringent polarizer material, and a strip of Faraday rotator material between the first and second strips of birefringent polarizer materials is fixed in the perpendicular groove.
  • Each optical isolator is disclosed as being formed by a first sleeve, first collimating lens, the optical isolator core subassembly, the second collimating lens and the second sleeve in a parallel groove between a first optical fiber and a second optical fiber having end sections held respectively in the first and second sleeves.
  • the invention relates to an optical isolator array for optically isolating at least one optical signal comprising a first beam bender; a first optical isolator core optically coupled to the beam bender; a second beam bender, optically coupled to the first optical isolator core; and the second beam bender located on a side of the optical isolator core opposite from the first beam bender, wherein the first beam bender, first optical isolator core, and second beam bender all are located along a propagation path of an optical signal propagating through the optical isolator array.
  • the invention in another aspect, relates to a method of isolating an optical signal comprising providing an optical isolator array comprising one or more isolator stages, wherein each isolator stage comprises an optical isolator core optically coupled to a set of optical signals; inserting an optical signal into the optical isolator array; and optically isolating the optical signal.
  • the invention relates to a method of optically isolating multiple spatially separate optical signals comprising generating a set of optical signals propagating along propagation paths; converging the propagation paths thereby converging the set of optical signals; and propagating the set of optical signals through at least one optical isolator core.
  • FIG. 1 shows a side view of an optical isolator array according to the invention.
  • FIG. 2 shows a side view of a single stage optical isolator array according to the invention.
  • FIG. 3 shows a side view of a two stage optical isolator array according to the invention.
  • FIG. 4 shows a side view of a two stage optical isolator array according to the invention, having a different configuration.
  • FIG. 5 shows a side view of an optical isolator array, according to the invention, that incorporates birefringent walk-off crystals.
  • FIG. 6 shows a side view of a two stage optical isolator array, according to the invention, that incorporates birefringent walk-off crystals.
  • FIGS. 7A-B show a top and side view of another embodiment of an optical isolator array according to the invention.
  • FIGS. 7C-D show a cross-sectional view of an optical isolator array according to the invention, with the relative spatial positions of the polarization components indicated.
  • FIGS. 8A-B shows a top and side view of a multiple stage optical isolator array according to the invention.
  • An optical isolator is typically comprised of a subassembly of an isolator core, an input fiber assembly, and an output fiber assembly.
  • a free space isolator comprises only an isolator core subassembly.
  • An optical isolator array is disclosed in the present invention.
  • Optical isolator arrays comprise a set of converging optical signals, and a single optical isolator core through which all the optical signals pass.
  • the set of optical signals comprise optical signals that are spatially separate
  • the optical signals are caused to converge by beam benders that turn the optical signals propagating through them through a determinable angle. The angle is determined by factors including, but not limited to, the angle of incidence, and the direction of propagation.
  • beam benders of which the inventive optical array is comprised, are used to bend optical signals to converge to at least one focal point, permitting shared use of a single optical device by at least one, preferably two or more, optical signals.
  • FIG. 1 shows a set of converging optical signals 102 with convergence point 104.
  • This is a set of interest, i.e. a set of converging optical signals that are desired to be isolated; and may be a sub-set of a larger set of optical signals being processed as part of a larger optical circuit.
  • Also shown are is a representation of an optical isolator cores that may be placed at positions 106, 108 and 110. At each of positions 106, 108 and 110, the optical isolator core is placed so that each individual signal of the set of converging optical signals passes through a single optical isolator core.
  • an optical isolator core on the set of converging optical signals as shown creates the inventive optical isolator array.
  • Particular advantages of the invention may be seen by inspecting the relative size of the optical isolator core at positions 106, 108 and 110 that is needed to include all of the converging optical signals.
  • the optical isolator core at position 106 needs to be spatially the largest optical isolator core, followed by the optical isolator cores at positions 108 and 110, respectively.
  • the optical isolator core is located at or near a convergence point of propagation paths of optical signals propagating through the optical isolator array.
  • Another preferable method for reducing costs of hardware or optical elements, according to the invention is by changing the focusing, collimation, or convergence/divergence of sets of optical signals.
  • the relatively expensive optical isolator cores may be spatially located in such a fashion as to minimize their cost, such as at a convergence point, or at a point where the set of optical signals has been collimated.
  • changing the focusing, collimation, or convergence/divergence of sets of optical signals may be accomplished by using one or more beam benders.
  • Preferable beam benders according to the invention may be based on either polarization insensitive beam turning, for example through a lens or polarization sensitive turning, for example through a birefringent prism system.
  • alignment of multiple sets of optical signals propagating through the inventive optical isolator array may be achievable simultaneously. For example, by aligning only one or two signals across the optical isolator array, the remaining signals may be isolated and aligned.
  • This particular advantage of the invention may be achieved by mounting input fiber arrays and output fiber arrays in precisely fabricated grooves or bores in mounting pieces such that the relative position of the input fiber arrays, carrying the input optical signals, matches that of the output fiber arrays, carrying the output optical signals. This reduces alignment time, and increases output yields.
  • Polarization sensitive angle turning may be preferably achieved by having an optical signal be incident upon a birefringent crystal at an angle with respect to the crystal's c axis. Beams with different polarization vectors may experience different angles of refraction because of the difference in index of refraction in beam bender birefringent crystals.
  • the polarization sensitive beam bender comprises a Wollaston, Rochon, or modified Wollaston or Rochon prism, a Senarmont prism or other polarization dependent angle turning optical elements. These prisms produce separate beam pathways by refractive separation of a beams transmitted through the prism at polarization vector dependent angles.
  • optical isolator cores along the optical isolator array may be optically coupled in series to increase the degree of isolation by forming a single or multiple stage isolator.
  • a two-stage isolator array may comprise two isolator cores with total isolation twice that of each individual isolator core. It is a particular advantage of the invention that significant increases in optical isolation may be achieved for a number of optical signals at a lesser increase in component cost as compared to conventional isolators.
  • optical isolator cores may be usable in the practice of the invention. Functionally, optical isolator cores may be arranged such that a pair of polarizers sandwich a non-reciprocal (i.e. Faraday) rotator.
  • Suitable polarizers comprise birefringent wedges, birefringent walk-off crystals, Wollaston prisms, Rochon prisms and the like.
  • Suitable non-reciprocal rotators comprise latching Faraday garnet (doesn't require a magnet) and non-latching garnet (usually requires a magnet).
  • One arrangement according to the invention comprises a pair of birefringent wedges sandwiching a non-reciprocal rotator. Another arrangement is shown in FIG. 5, discussed below, which uses a pair of birefringent walk-off crystals that sandwich a non-reciprocal rotator and a reciprocal rotator.
  • Polarization insensitive turning may be achieved, in part, by propagating an optical signal through, for example, a polarization insensitive beam bender such as a lens, at a distance from the lens' principal axis.
  • a polarization insensitive beam bender such as a lens
  • a wide variety of lenses may be useful in the practice of the invention, including, but not limited to, GRIN lenses, asperic lenses, plano-convex lenses, ball lenses, and the like.
  • This embodiment is illustrated in FIG. 2, wherein two lenses are used to converge and then collimate a set of input optical signals.
  • Optical isolator array 200 includes first beam bender 202, second beam bender 204, and optical isolator core 206.
  • Optical isolator core 206 includes first birefringent wedge 208, second birefringent wedge 212, and non-reciprocal rotator 210.
  • First beam bender 202 and second beam bender 204 are located on either side of optical isolator core 206, along a propagation path of input optical signals 214 and output optical signals 218.
  • first birefringent wedge 208 and second birefringent wedge 212 are located on either side of non-reciprocal rotator 210, along a propagation path of input optical signals 214 and output optical signals 218.
  • input optical signals 214 propagate through first beam bender 202, in this case a focusing lens, and are bent to form a set of converging optical signals 216.
  • the set of converging optical signals 216 then propagates through optical isolator core 206.
  • Non-reciprocal rotator 210 rotates the polarization direction of both polarization components by 45 degrees.
  • second birefringent wedge 212 Upon propagating through second birefringent wedge 212, both polarization components will be bent to propagate along the same optical path. Further discussion of optical isolator core 206's operation may be found in U.S. Patent No.
  • first beam bender 202 may serve two functions. First, it collimates the optical signal from each individual fiber. Second, it causes convergence of the set of converging optical signals 216. Similarly, second beam bender 204 serves two functions. First, it causes a set of diverging optical signals to become collimated. Second, it focuses each collimated optical signal into its respective receiving fiber to enhance the coupling efficiency.
  • first beam bender 202 may have modified the beam profile of the optical signals
  • second beam bender 204 may serve to correct the beam profile of output optical signals 218 back to be substantially the same as that of input optical signals 214.
  • the impact of the beam benders, in producing a converging point (or area, or zone, etc.) through which all the optical signals pass, is to enable multiple signals to pass through a single device. This enables a reduction in optical footprint, cost, etc.
  • optical isolator core used in optical isolator array 200 is usually not polarization mode dispersion free (PMD-free), as in the case of a single isolator built with that core, because of the use of the brirefringent wedges.
  • a compensation plate may be used.
  • Such a compensation plate may include a birefringent plate that possesses an optical path difference or differential group velocity delay between its two polarization eigenstates. If the plate is designed to have the same amount of PMD but in opposite sign with respect to the isolator core, PMD of the combined isolator core and compensation plate will be eliminated or substantially reduced.
  • additional compensation plate adds alignment complexity and cost to the optical isolator array.
  • PMD-free, or substantially PMD-free, optical isolator array 300 which is configured such that a compensation plate is not needed, is shown in FIG. 3.
  • Optical isolator array 300 possesses an additional advantage over optical isolator array 200 in that it is a multiple stage optical isolator array.
  • PMD- free, or substantially PMD-free, operation may be achieved by adding a second optical isolator core based on birefringent wedges having an opposite sign PMD as compared to the first optical isolator core that is also based on birefringent wedges.
  • An example of a PMD compensated isolator device is disclosed in U.S. Patent No. 5,557,692.
  • Optical isolator array 300 includes first beam bender 202, second beam bender 204, optical isolator core 206 and second optical isolator core 302.
  • Optical isolator core 206 includes first birefringent wedge 208, second birefringent wedge 212, and non-reciprocal rotator 210.
  • Second optical isolator core 302 includes third birefringent wedge 304, fourth birefringent wedge 308, and second non-reciprocal rotator 306.
  • First beam bender 202 and second beam bender 204 are located on either side of optical isolator core 206, along a propagation path of input optical signals 214 and output optical signals 218.
  • first birefringent wedge 208 and second birefringent wedge 212 are located on either side of non-reciprocal rotator 210, along a propagation path of input optical signals 214 and output optical signals 218.
  • Second optical isolator core 302 is located between optical isolator core 206 and second beam bender 204, along a propagation path of input optical signals 214 and output optical signals 218.
  • third birefringent wedge 304 and fourth birefringent wedge 308 are located on either side of second non-reciprocal rotator 306, along a propagation path of input optical signals 214 and output optical signals 218.
  • input optical signals 214 propagate through first beam bender 202, in this case a focusing lens, and are bent to form a set of converging optical signals 216.
  • the set of converging optical signals 216 then propagates through optical isolator core 206.
  • the operation of optical isolator core 206 has been generally described above.
  • the optical signals emerging from optical isolator core 206 propagate through second optical isolator core 302, for a second stage of optical isolation.
  • the optical signals are then collimated by second beam bender 204 and are outputted from the optical isolator array as output optical signals 218.
  • optical isolator core 206's operation or second optical isolator core 302's operation may be found in U.S. Patent No. 4,548,478 to Shirasaki, The impact of the beam benders, in producing a converging point (or area, or zone, etc.) through which all the optical signals pass, is to enable multiple signals to pass through a single device. This enables a reduction in optical footprint, cost, etc.
  • FIG. 4 shows an alternative arrangement to multiple stage optical isolator array 300.
  • the beam benders are located between the optical isolator cores, instead of the other way around.
  • Optical isolator array 400 includes first beam bender 202, second beam bender 204, optical isolator core 206 and second optical isolator core 302.
  • Optical isolator core 206 includes first birefringent wedge 208, second birefringent wedge 212, and non-reciprocal rotator 210.
  • Second optical isolator core 302 includes third birefringent wedge 304, fourth birefringent wedge 308, and second non-reciprocal rotator 306.
  • First beam bender 202 and second beam bender 204 are located between optical isolator core 206 and second optical isolator core 302, along a propagation path of input optical signals 214 and output optical signals 218.
  • first birefringent wedge 208 and second birefringent wedge 212 are located on either side of non-reciprocal rotator 210, along a propagation path of input optical signals 214 and output optical signals 218.
  • second optical isolator core 302 third birefringent wedge 304 and fourth birefringent wedge 308 are located on either side of second non-reciprocal rotator 306, along a propagation path of input optical signals 214 and output optical signals 218.
  • optical isolator core 206 In operation, input optical signals 214 propagate through optical isolator core 206.
  • the operation of optical isolator core 206 has been generally described above.
  • the optical signals then pass through first beam bender 202, in this case a focusing lens, and are bent to form a set of converging optical signals 416.
  • the set of converging optical signals 216 then propagates through convergence point 418, after which they diverge and are collimated by second beam bender 204.
  • the optical signals propagate through second optical isolator core 302, for a second stage of optical isolation and are outputted from the optical isolator array as output optical signals 218.
  • optical isolator array 400 Any optical signals reflected backwards along the output optical signal's propagation path are bent along a different path so as to prevent the optical signals from returning to the point at which the input optical signals are introduced into optical isolator array 400. This effect produces optical isolation.
  • the advantages of optical isolator array 400 are similar to those of optical isolator array 300, in that optical isolator array 400 operates with a greater degree of isolation, and with low cost compared to conventional isolators. Further, use of two isolator cores having opposite PMD relative to one another may result in substantially PMD-free operation.
  • FIG. 5 shows an embodiment of optical isolator array 500, according to the invention.
  • Optical isolator array 500 includes a new configuration of optical isolator cores, based on a pair of birefringent walk-off crystals, rather than birefringent wedges. Further, optical isolator array 500 achieves substantially PMD-free operation in a different manner to the manner previously discussed in the description of the birefringent wedge embodiments.
  • Optical isolator array 500 includes first beam bender 202, second beam bender 204, and optical isolator core 506.
  • Optical isolator core 506 includes first birefringent walk-off crystal 502, second birefringent walk-off crystal 504, reciprocal rotator 508, and non-reciprocal rotator 210.
  • First beam bender 202 and second beam bender 204 are located on either side of optical isolator core 506, along a propagation path of input optical signals 214 and output optical signals 218.
  • first birefringent walk-off crystal 502 and second birefringent walk-off crystal 504 are located on either side of non-reciprocal rotator 210 and reciprocal rotator 508, along a propagation path of input optical signals 214 and output optical signals 218.
  • Non-reciprocal rotators include Faraday rotators; reciprocal rotators include half-wave plates.
  • input optical signals 214 propagate through first beam bender 202, in this case a focusing lens, and are bent to form a set of converging optical signals 216.
  • the set of converging optical signals 216 then propagates through optical isolator core 506.
  • first birefringent walk-off crystal 502 spatially separates the components of input optical signals 214 that are polarized perpendicularly to each other.
  • second birefringent walk-off crystal 504 spatially recombines the components, meaning that the inventive optical isolator arrays are inherently polarization insensitive and are useful in, among other uses, telecommunications applications.
  • first birefringent walk-off crystal 502 and second birefringent walk-off crystal 504 are positioned such that the ordinary component is not laterally displaced during propagation through the inventive optical isolator arrays.
  • the extraordinary component is displaced in one direction by the first birefringent walk-off crystal 502 (for example, up), and in the other direction direction by the second birefringent walk-off crystal 504 (for example, down).
  • Such an arrangement of the birefringent walk-off crystals promotes PMD-free, or substantially PMD-free, operation may be achieved without introducing an additional compensation plate.
  • a further advantage is that single stage PMD-free, or substantially PMD-free, operation may be achieved as compared to birefringent wedge-based optical isolator cores.
  • birefringent crystals are usually significantly greater than that of birefringent wedges, thus potentially adding to the component cost of this embodiment of the inventive optical isolator array as compared to the birefringent wedge embodiments.
  • use of birefringent crystals necessitates the use of reciprocal rotators or a third birefringent crystal for recombining two perpendicular polarization beams. Such a configuration adds costs versus a birefringent wedge embodiment that does not necessarily require use of a reciprocal rotator to achieve substantially PMD-free performance.
  • optical signals emerging from optical isolator core 506 are collimated by second beam bender 204 and are outputted from the optical isolator array as output optical signals 218. Any optical signals reflected backwards along the output optical signal's propagation path are bent along a different path so as to prevent the optical signals from returning to the point at which the input optical signals are introduced into optical isolator array 500. This effect produces optical isolation. Further discussion of optical isolator core 506's operation may be found in U.S. Patent No.
  • Optical isolator array 600 is another example of a multiple stage optical isolator array.
  • Optical isolator array 600 is constructed with optical isolator cores that use birefringent walk-off crystals, similarly to optical isolator array 500, described above.
  • Optical isolator array 600 includes includes first beam bender 202, second beam bender 204, optical isolator core 506 and second optical isolator core 602.
  • Optical isolator core 506 includes first birefringent walk-off crystal 502, second birefringent walk-off crystal 504, reciprocal rotator 508, and non-reciprocal rotator 210.
  • Second optical isolator core 602 includes third birefringent walk-off crystal 604, fourth birefringent walk-off crystal 608, second reciprocal rotator 610, and second non-reciprocal rotator 606.
  • First beam bender 202 and second beam bender 204 are located on either side of optical isolator core 506, along a propagation path of input optical signals 214 and output optical signals 218.
  • first birefringent walk-off crystal 502 and second birefringent walk-off crystal 504 are located on either side of non-reciprocal rotator 210 and reciprocal rotator 508, along a propagation path of input optical signals 214 and output optical signals 218.
  • Second optical isolator core 602 is located between optical isolator core 506 and second beam bender 204, along a propagation path of input optical signals 214 and output optical signals 218.
  • third birefringent walk-off crystal 604 and fourth birefringent walk-off crystal 608 are located on either side of second non-reciprocal rotator 606 and reciprocal rotator 610, along a propagation path of input optical signals 214 and output optical signals 218.
  • input optical signals 214 propagate through first beam bender 202, in this case a focusing lens, and are bent to form a set of converging optical signals.
  • the set of converging optical signals then propagates through optical isolator core 506.
  • the optical signals emerging from optical isolator core 506 propagate through second optical isolator core 602, for a second stage of optical isolation.
  • the optical signals are then collimated by second beam bender 204 and are outputted from the optical isolator array as output optical signals 218. Any optical signals reflected backwards along the output optical signal's propagation path are bent along a different path so as to prevent the optical signals from returning to the point at which the input optical signals are introduced into optical isolator array 600. This effect produces optical isolation.
  • optical isolator core 600 The impact of the beam benders, in producing a converging point (or area, or zone, etc.) through which all the optical signals pass, is to enable multiple signals to pass through a single device. This enables a reduction in optical footprint, cost, etc.
  • additional stages of optical isolation may be added to optical isolator core 600 to increase the amount of optical isolation delivered by optical isolator core 600.
  • FIGS. 7A-B show top and side views of an embodiment of an inventive optical isolator array.
  • the optical isolator core shown in FIGS. 7A- B show beam benders comprising modified Wollaston prisms.
  • Conventional Wollaston prisms are formed by two birefringent wedges. In such prisms, the optical axes of each birefringent wedge are substantially perpendicular to one another and one of the optical axes is perpendicular to the direction of wedge interface.
  • Conventional Wollaston and Rochon prisms are discussed further in Hecht, Optics 292 & 329 (1987) (2d. ed. Addison- Wesley).
  • the optical axis of each of its wedges are oriented perpendicularly to each other and 45 degrees in a plane that is normal to the normal incidence direction with respect to the optical axis in a conventional Wollaston prism.
  • the optical axis of one of the wedges is oriented normal to the first interface, which is the same as in a conventional Rochon prism. The first interface is normal to the normal incidence of the optical signal.
  • the optical axis in the other wedge is oriented 45 degrees in the second interface (the second interface being parallel to the first interface and at the opposite end of the modified Rochon prism) with respect to the optical axis orientation the wedge would possess in a conventional Rochon prism.
  • FIGS. 7A-B show a view of optical isolator array 700, according to the invention.
  • Optical isolator core need not have each of its component elements physically coupled, so long as they are optically coupled.
  • an optical isolation core of optical isolator array 700 comprises two polarizers (first beam displacer/combiner 722 and second beam displacer/combiner 750, discussed below), and two non-reciprocal rotators (first nonreciprocal rotator 726 and second nonreciprocal rotator 746).
  • Optical isolator array 700 includes first optical port 702, third optical port 704, second optical port 706, fourth optical port 708, first imaging element 770, second imaging element 772, first beam displacer/combiner 722, first nonreciprocal rotator 726, first beam benders 730A-D, second beam benders 740A-D, second nonreciprocal rotator 746, and second beam displacer/combiner 750.
  • Optical isolator array 700 possesses a longitudinal axis, along which the various optical components are distributed, and a proximal and distal end.
  • First optical port 702, and third optical port 704 are located at a proximal end, and second optical port 706 and fourth optical port 708 are located at a distal end of the optical isolator array.
  • the first, second, third and fourth optical ports may comprise integrated optical circuits or optical fibers.
  • First imaging element 770 may be preferably located on the optical path between the first and third optical ports and the first beam displacer/combiner.
  • Second imaging element 772 may be preferably located on the optical path between the second and fourth optical ports and the second beam displacer/combiner.
  • the first or second imaging element may be a collimating lens.
  • the imaging element may be a Grin lens.
  • First beam displacer/combiner 722 is optically coupled distally to the first and third optical ports.
  • the first beam displacer/combiner is a birefringent crystal.
  • the first beam displacer/combiner comprises Yttrium Orthovanadate, calcite, rutile or alpha-BBO.
  • First nonreciprocal rotator 726 comprises a nonreciprocal Faraday polarization rotator and is optically coupled distally from the first beam displacer/combiner.
  • first nonreciprocal rotator 726 comprises yttrium-iron-garnet (YIG), or Bi-added thick film crystals.
  • the Bi-added thick film crystals preferably comprise a combination of (YbTbBi) 3 Fe 5 O 12 and (GdBi) 3 (FeAIGa) 5 O 12) or of Y.I. G. and Y 3x Bi x Fe 5 O 12 .
  • First beam benders 730A-D comprise two pairs (i.e. four) of birefringent wedges that are optically coupled distally to the first nonreciprocal rotators and to each other.
  • the first beam benders comprise one or more prisms.
  • the first beam benders comprises a set of Wollaston, Rochon or modified Wollaston or Rochon prisms.
  • the beam benders may comprise modified Wollaston prisms.
  • the beam benders which are indicated in optical isolator array 400 by the pairs of beam benders 730A-B, 730C-D, 740A-B, and 740C-D, are stacked in the embodiment as shown.
  • the arrangement of beam benders 730A-B and 730C-D is identical, except that they are rotated by 180 degrees with respect to the optical isolator array's longitudinal axis.
  • beam benders 740A-B and 740C-D are identical, except for their 180 degrees rotation with respect to the optical isolator array's longitudinal axis.
  • beam benders 730C-D are stacked on top of beam benders 730C-D, to form a stacked set of beam benders.
  • beam benders 740C-D are stacked on top of beam benders 740A- B to form a stacked set of beam benders.
  • the effect of these stacked sets of beam benders is to permit angle turning of both the top and bottom components that are orthogonal to each other in the same direction without having to change their orientation.
  • first and second beam benders 740A-D that is located distally from first beam benders 730A-D.
  • the first and second beam benders are therefore spaced apart from one another.
  • Second nonreciprocal rotator 746 comprises a nonreciprocal Faraday polarization rotator and is optically coupled distally from the second beam benders.
  • the second nonreciprocal rotators comprise yttrium-iron-garnet (YIG), or Bi-added thick film crystals.
  • the Bi- added thick film crystals comprise a combination of (YbTbBi) 3 Fe 5 O 12 and (GdBi) 3 (FeAIGa) 5 O 12 , or of YIG and Y 3x Bi x Fe 5 O 12 .
  • Second beam displacer/combiner 750 is optically coupled distally from the second nonreciprocal rotators and proximally from the second optical port.
  • first beam displacer/combiner 722 acts as a polarization sensitive beam displacement plate.
  • the arbitrarily polarized light is decomposed into two orthogonal polarization components.
  • the first component is an ordinary light ray (O-ray) and the other component is an extraordinary light ray (E-ray).
  • O-ray ordinary light ray
  • E-ray extraordinary light ray
  • the E-ray walks off vertically from the O-ray through the first beam displacer/combiner, with the result that there is a top and bottom component.
  • the components then enter first nonreciprocal rotator 726.
  • first nonreciprocal rotator 726 rotates by 45 degrees clockwise both the top and bottom components of light passing through it from first optical port 702 to second optical port 706.
  • the relative directions of rotation imparted by first nonreciprocal rotator 726 and second nonreciprocal rotator 746 may be respectively reversed.
  • first beam benders 730A-D Upon exiting the first nonreciprocal rotators, the components enter first beam benders 730A-D.
  • the first beam benders turn both polarization components towards the longitudinal axis of the optical isolator array without changing their polarization orientation.
  • the components then exit the first beam bender and transit complete gap 736.
  • the components next pass through second beam benders 740A-D, which bend the components such that their propagation directions are changed.
  • the first and second beam benders and the complete gap are adjusted so as to achieve alignment of the components with the longitudinal axis of the second imaging element and/or second optical port 706, as discussed above.
  • the components then enter second nonreciprocal rotator 746.
  • second nonreciprocal rotator 746 rotates by 45 degrees clockwise both top and bottom components of light passing through it from first optical port 702 to second optical port 706.
  • the components then pass through second beam displacer/combiner 750, where the beams are recombined.
  • the recombined light beam then passes through second optical port 706 via second imaging element 772.
  • Arbitrarily polarized light reflected back through optical port 706 will travel along a different path as it will be refracted at the interface between beam benders 740D and 740C, and at the interface between beam benders 740A and 740B. This refraction effectively isolates the signal passing from first optical port 702 to second optical port 706.
  • optical isolator array 700 is capable of simultaneously isolating optical signals propagating through the optical isolator array.
  • This simultaneous optical isolation feature is highly desirable, as it permits design of optical circuits possessing smaller optical footprints and lower costs as compared with conventional optical isolator core designs.
  • two or more signals may be isolated by passing the signals through a single isolator array according to the invention.
  • the operation of optical isolator array 700 is illustrated in the cross sectional schematic representations shown in FIGS. 7C-D. FIG.
  • FIG. 7C shows how the two orthogonal components of unpolarized light entering at first optical port 702 are manipulated so as to arrive at second optical port 706.
  • the two unpolarized orthogonal components are shown at cross section A- A, as they exit first imaging element 770 and enter the first beam displacer/combiner.
  • cross-section B-B upon exiting first beam displacer/combiner 722, the top component is shown as being walked off vertically from the bottom component, and both the top and bottom components are shown as being shifted equidistantly in the same direction - - to the left of the cross-section of the optical isolator array - due to action of first imaging element 770.
  • FIG. 7D shows how the two orthogonal components of unpolarized light entering at fourth optical port 708 are manipulated so as to arrive at third optical port 704.
  • the two unpolarized orthogonal components are shown at cross section F-F, as they exit second imaging element 772 and enter second beam displacer/combiner 750.
  • first nonreciprocal rotator 726 upon exiting first nonreciprocal rotator 726, the polarization of both the top and bottom components is shown as being rotated 45 degrees clockwise.
  • first beam displacer/combiner 722 upon exiting first beam displacer/combiner 722, the two components are recombined to exit at third optical port 704.
  • Arbitrarily polarized light reflected back through third optical port 704 e.g. part of an optical signal reflected from a component downstream of the optical isolator array
  • Second beam displacer/combiner 750 also promotes isolation of the optical signal.
  • FIGS. 8A-B show top and side elevations of another optical isolator array according to the invention, in a multiple stage optical isolator array configuration, with a different configuration of optical isolator cores and beam benders.
  • the addition of end portions with beam displacer/combiners and non-reciprocal rotators provides for polarization of normal light beams that varies depending on the propagation direction of the incoming light beam. This allows optical isolator arrays to be built that isolate input signals with arbitrary polarization orientation and arbitrary degrees of polarization.
  • Multiple stage optical isolator array 800 includes: first optical port 802, third optical port 804, second optical port 806, fourth optical port 822, fifth optical port 820, and sixth optical port 824, first end portion 870, center portion 880, and second end portion 890.
  • First end portion 870 includes first beam displacer/combiner 810, first nonreciprocal rotator 826A, and first reciprocal rotator 827.
  • Center portion 880 includes first imaging element 830, beam bender 808, 812, and second imaging element 832.
  • Second end portion 890 includes second nonreciprocal rotator 836A, second reciprocal rotator 837, and second beam displacer/combiner 840.
  • First end portion 870 is optically coupled distally to the first and third optical ports, and is located in an opposing relationship to second end portion 890.
  • First beam displacer/combiner 810 is optically coupled distally to the first, third, and fifth optical ports 802, 804, and 820.
  • first beam displacer/combiner 810 is a birefringent crystal.
  • first beam displacer/combiner 810 comprises Yttrium Orthovanadate, calcite, rutile or alpha-BBO (barium borate).
  • First nonreciprocal rotator 826A comprises nonreciprocal Faraday polarization rotators and are optically coupled distally from first beam displacer/combiner 810.
  • first nonreciprocal rotators 826A-B comprise yttrium-iron-garnet (YIG), or Bi-added thick film crystals.
  • the Bi-added thick film crystals preferably comprise a combination of (BiTb) 3 (FeGa) 5 O 12 , (YbTbBi) 3 Fe 5 O 12 and (GdBi) 3 (FeAIGa) 5 O 12 , or of YIG and Y 3x Bi x Fe 5 O 12 .
  • reciprocal rotator 827 Optically coupled on a side of first non-reciprocal rotator 826A opposite from first beam displacer/combiner 810 is reciprocal rotator 827, which is preferably a half-wave plate.
  • center portion 880 Optically coupled distally to first end portion 870 is center portion 880. Included in center portion 880 are walk-off crystals 828 and 834, imaging elements 830 and 808, together with complete gap 812. Walk-off crystal 828 is optically coupled distally to first reciprocal rotator 827. Imaging element 830 is optically coupled to walk-off crystal 828. Imaging element 832 is optically coupled, across complete gap 812, to imaging element 830, thus defining complete gap 812. In a preferable embodiment, either or both of the imaging elements comprise aspheric lenses. Each of the imaging elements 830, 832 has a common focal point 852. Walk-off crystal 834 is optically coupled to imaging element 832.
  • Second end portion 890 Optically coupled distally to center portion 880 is second end portion 890.
  • Second end portion 890 comprises second reciprocal rotator 837, which is optically coupled to second nonreciprocal rotator 836A, which is in turn optically coupled to walk-off crystal 834.
  • Second nonreciprocal rotator 836A may comprise a nonreciprocal Faraday polarization rotator.
  • second nonreciprocal rotator 836A comprises yttrium-iron-garnet (YIG), or Bi-added thick film crystals.
  • the Bi-added thick film crystals preferably comprise a combination of (YbTbBi) 3 Fe 5 O 12 and (GdBi) 3 (FeAIGa) 5 O 12 , or of YIG and Y 3x Bi x Fe 5 O 12 .
  • Reciprocal rotator 837 preferably comprises a half-wave plate.
  • Second beam displacer/combiner 840 is optically coupled distally from second nonreciprocal rotator 836A and proximally from second optical port 806, fourth optical port 822, and sixth optical port 824. In operation, arbitrarily polarized polarized light from first optical port 802 enters first beam displacer/combiner 810, which acts as a polarization sensitive beam displacement plate.
  • first beam displacer/combiner 810 The arbitrarily polarized light is decomposed into two rays with orthogonal polarization vectors.
  • the first ray is an ordinary light ray (O-ray) and the other ray is an extraordinary light ray (E-ray).
  • the E-ray walks off vertically from the O-ray through first beam displacer/combiner 810, with the result that there is a top and bottom ray, relative to the longitudinal axis.
  • the rays then enter first nonreciprocal rotator 826A.
  • first nonreciprocal rotator 826A rotates by 45 degrees clockwise a ray of light passing through it from first optical port 802 to second optical port 806.
  • first nonreciprocal rotator 826A rotates by 45 degrees counter clockwise a ray of light passing through it from first optical port 802 to second optical port 806. The rays then enter first reciprocal rotator 827.
  • first reciprocal rotator 827 rotates by 45 degrees clockwise a ray of light passing through it from first optical port 802 to second optical port 806.
  • first reciprocal rotator 827 rotates by 45 degrees counter clockwise a ray of light passing through it from first optical port 802 to second optical port 806.
  • first reciprocal rotator 827 Upon exiting first reciprocal rotator 827, the polarization orientation of both rays have been rotated 90 degrees and are still orthogonal to each other before entering walk-off crystal 828. As they propagate through walk- off crystal 828, the rays are recombined. The recombined rays next enter imaging element 830. Imaging element 830 bends distally propagating light from optical port 802 and collimates the beam in the process. At this point, the rays have passed through the first stage of the multiple stage optical isolator array 800. Any reflected light propagating in a proximal direction along the path of the rays will be refracted away from the path, as shown in FIG. 8B.
  • optical isolation may be found in U.S. Patent No. 4,239,329, to Matsumoto, hereby incorporated by reference in its entirety.
  • the arrangement, as described so far, provides sufficient isolation to function as an independent optical isolator array.
  • the first stage of multiple stage optical isolator array 800 provides about 30 dB of optical isolation.
  • optical isolator cores may be added.
  • the isolator stages are coupled across complete gap 812.
  • Light propagating across complete gap 812 enters imaging element 832.
  • Imaging element 832 performs a symmetrical function to imaging element 830 in bending distally propagating light to a path parallel to the longitudinal axis.
  • the imaging elements 830, 832 may alternately comprise one or more collimating lenses and prisms in series to collimate and bend the light.
  • the lenses may have uniform index of refraction or may be fabricated with a graded index of refraction.
  • the lens are fabricated with graded indices of refraction, e.g. GRIN lenses.
  • second reciprocal rotator 837 rotates by 45 degrees counterclockwise a polarized ray of light passing through it from first optical port 802 to second optical port 806. In another preferable embodiment, second reciprocal rotator 837 rotates by 45 degrees clockwise a polarized ray of light passing through it from first optical port 802 to second optical port 806.
  • second nonreciprocal rotator 836A rotates by 45 degrees counterclockwise a polarized ray of light passing through it from first optical port 802 to second optical port 806.
  • second nonreciprocal rotator 836A rotates by 45 degrees clockwise a polarized ray of light passing through it from first optical port 802 to second optical port 806.
  • the rays then pass through second beam displacer/combiner 840, where the rays are recombined.
  • the recombined light beam then passes through second optical port 806.
  • the rays have passed through a second stage of the multiple stage optical isolator array 800. Any reflected light propagating in a proximal direction along the path of the rays will be refracted away from the path, as shown in FIG. 8B.
  • the arrangement, as described so far, provides sufficient isolation to function as an independent optical isolator array.
  • the second stage of multiple stage optical isolator array 800 provides about 30 dB of optical isolation.
  • the two stages of optical isolation shown in optical isolator array 800 provide about 60 dB of optical isolation.
  • multiple signals may be isolated simultaneously using the same primary structure. The number of signals that may be simultaneously optically isolated using multiple stage optical isolator array 800 is limited primarily by the required spacing between the various optical ports. In certain embodiments, the spacing between the optical port locations may be adjusted by increasing or shortening the length of complete gap 812.
  • thermally expanded core (TEC) fibers may be used to reduce alignment sensitivity.
  • inventive optical isolator array may be used in telecommunications systems such as wavelength division multiplexers and EDFA's.

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  • General Physics & Mathematics (AREA)
  • Optics & Photonics (AREA)

Abstract

L"invention concerne un isolateur de Faraday à fibres optiques, à ports mutiples, permettant d"isoler de multiples signaux optiques spatialement séparés. Un premier et un second déflecteur de faisceaux sont utilisés afin de réduire à un minimum la taille du dispositif. Dans un mode de réalisation, on utilise des lentilles (202, 204) pour les déflecteurs de faisceaux et ces derniers sont placés de chaque côté du coeur (210) de l"isolateur, le point de convergence des signaux spatialement séparés étant situé au coeur de l"isolateur. Dans un autre mode de réalisation, les premier et second déflecteurs de faisceaux comprennent tous deux deux paires de prismes biréfringents (730a-d, 740a-d), et sont situés entre les coeurs de l"isolateur (726, 746).
PCT/US2000/001254 1999-02-11 2000-01-19 Isolateur optique compact a ports multiples Ceased WO2000048029A1 (fr)

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AU24159/00A AU2415900A (en) 1999-02-11 2000-01-19 Compact multiple port optical isolator

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US12000699P 1999-02-11 1999-02-11
US60/120,006 1999-02-11
US34663999A 1999-07-01 1999-07-01
US09/346,639 1999-07-01

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US6362919B1 (en) 2000-08-22 2002-03-26 Axsun Technologies, Inc. Laser system with multi-stripe diode chip and integrated beam combiner
EP2916400A3 (fr) * 2014-03-03 2015-10-07 V-Gen Ltd. Isolateur hybride et extension de mode pour amplificateurs laser à fibre
WO2024066048A1 (fr) * 2022-09-28 2024-04-04 四川华岭光子科技有限公司 Ensemble de couplage de trajet optique et module optique ayant un ensemble de couplage de trajet optique

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DE19630737A1 (de) * 1995-08-04 1997-02-06 Samsung Electronics Co Ltd Lichtverstärker mit einem mehrstufigen optischen Isolator
EP0814361A1 (fr) * 1996-06-20 1997-12-29 Fujitsu Limited Dispositif optique
WO1998023983A1 (fr) * 1996-11-30 1998-06-04 Samsung Electronics Co., Ltd. Photocoupleur
US5850493A (en) * 1997-07-18 1998-12-15 Cheng; Yihao Device for focusing light through an optical component
US5956441A (en) * 1996-06-14 1999-09-21 Lucent Technologies, Inc. Multiple port optical component such as an isolater or the like
EP0965867A1 (fr) * 1998-06-18 1999-12-22 Hewlett-Packard Company Circulateur optique à voies multiples utilisant une lentille d'imagerie et un élément optique correctif

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GB2264181A (en) * 1992-02-17 1993-08-18 Chichibu Cement Kk Optical isolator
US5557692A (en) * 1993-01-21 1996-09-17 E-Tek Dynamics, Inc. Optical isolator with low polarization mode dispersion
US5566259A (en) * 1994-12-13 1996-10-15 E-Tek Dynamics, Inc. Dual stage optical device with low polarization mode dispersion
WO1996019743A1 (fr) * 1994-12-21 1996-06-27 E-Tek Dynamics, Inc. Coupleur optique integrable et dispositifs et systemes obtenus
DE19630737A1 (de) * 1995-08-04 1997-02-06 Samsung Electronics Co Ltd Lichtverstärker mit einem mehrstufigen optischen Isolator
US5956441A (en) * 1996-06-14 1999-09-21 Lucent Technologies, Inc. Multiple port optical component such as an isolater or the like
EP0814361A1 (fr) * 1996-06-20 1997-12-29 Fujitsu Limited Dispositif optique
WO1998023983A1 (fr) * 1996-11-30 1998-06-04 Samsung Electronics Co., Ltd. Photocoupleur
US5850493A (en) * 1997-07-18 1998-12-15 Cheng; Yihao Device for focusing light through an optical component
EP0965867A1 (fr) * 1998-06-18 1999-12-22 Hewlett-Packard Company Circulateur optique à voies multiples utilisant une lentille d'imagerie et un élément optique correctif

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Publication number Priority date Publication date Assignee Title
US6362919B1 (en) 2000-08-22 2002-03-26 Axsun Technologies, Inc. Laser system with multi-stripe diode chip and integrated beam combiner
EP2916400A3 (fr) * 2014-03-03 2015-10-07 V-Gen Ltd. Isolateur hybride et extension de mode pour amplificateurs laser à fibre
US9407053B2 (en) 2014-03-03 2016-08-02 V-Gen Ltd. Hybrid isolator and mode expander for fiber laser amplifiers
WO2024066048A1 (fr) * 2022-09-28 2024-04-04 四川华岭光子科技有限公司 Ensemble de couplage de trajet optique et module optique ayant un ensemble de couplage de trajet optique

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