Cylindrically polarized light, more particularly radially and azimuthally polarized light, are desirable for a number of important applications. These applications include, but are not limited to, lithography, electron acceleration, material processing, and metrology. There are currently no simple methods or devices for converting a linearly polarized Gaussian beam of light into a radially or azimuthally polarized beam of light.
For example, it is possible to use multi-mode fibers in conjunction with a number of micro optic components such as asymmetric phase plates, half wave plates, and polarization controllers to convert an input Gaussian beam to a cylindrically polarized beam. In these approaches, one typically needs to first convert the input Gaussian beam to an asymmetric beam using a phase plate and then use a number of polarization components to enable conversion to a cylindrical polarization mode. This approach can be efficient but the required number of relatively expensive components typically necessitates an expensive and cumbersome device.
A method for the generation of cylindrical vector beams based on the design of a multicore optical fiber is presented. The principle of operation is based on the property of birefringence in polarization maintaining elliptical cores. This design consists of N elliptical cores symmetrically arranged in a circular array about the fiber axis, where the orientation of each core's major axes has an azimuthally varying distribution, i.e., the angular orientation of each core's major axis varies as a function of the angular position of the core in the circular array. The guided mode of each core rotates an incident polarization according to the core's orientation in the array, and the array's overall birefringence can be described using a Jones matrix analysis. Coherent superposition of the azimuthally distributed polarization outputs from each individual core in the far field produces a cylindrically symmetric amplitude and polarization state. In this way, a Gaussian beam coupled at the fiber input can be transformed into a cylindrical vector beam. This method does not rely on the direct excitation of the higher order TM, TE, and HE fiber modes. Stokes polarimetry measurements of the fiber output in the near and far field can be used for experimental investigation of the fabrication of multicore fiber designs according to the present disclosure with, for example, N=6 cores of varying core size and spacing. These measurements can be used to investigate the efficiency of the design and to generate numerical simulations of the far field output for scaling to more than N=6 cores and for varying core spacing.
Hence, the present disclosure introduces a multicore optical component capable of converting linearly or circularly polarized input radiation to cylindrically polarized radiation, including both radial and azimuthal polarization. Multicore optical components according to the present disclosure can be fabricated as unitary redrawn optical components.
We propose the use of an array of polarizing single mode elliptical cores for the purpose of converting an arbitrary incoming polarization, i.e. linear or circularly polarized light, to cylindrical vector beams that have azimuthally varying polarization. The cores are properly aligned and the component is cut to an appropriate length that allows the polarization in each core to rotate to the desired orientation.
Generally,
Each elliptical core 20 rotates the polarization as would a half waveplate. The orientation of each elliptical core is chosen so that the polarization of the input light, being linearly polarized as in
φ=(180/N)*n+θ
where n is the core number and θ is an offset angle including 0°.
The multicore optical component may be an optical fiber bundle drawn, for example, from a fiber perform comprising a plurality of core canes. For example, in one contemplated embodiment, the multicore optical component comprises a six-core device fabricated using six core canes contained within a fiber perform tube. Core canes of this nature may, for example, be characterized by a 2 to 1 ratio of cladding diameter to core diameter. The core of the core cane may, for example, be characterized by a major axis that is between approximately two and approximately three times larger than the minor axis. It is contemplated that smaller diameter filler canes without a core can be incorporated into the tube to fill the tube with glass.
The multicore optical component of the present disclosure may be designed such that the modal volume can be increased to an arbitrarily large number. Indeed, it is contemplated that the number of cores is not limited to six, eight or even one annular row. In any case, the orientation of the major polarization axis of each core is such that a complete revolution of all the axes occurs around the circumference of the component. In addition, although the optical component of the present disclosure is referred to herein as a multicore optical fiber, it is contemplated that the component may be presented in a variety of forms, e.g., as a composite of multiple guided wave cores.
In the embodiment illustrated in
φ=(180/N)*n,
where φ is the orientation of the major axis of the elliptical core and n is the core number, i.e. 1, 2, 3, 4, . . .
It is contemplated that the respective major axes of the elliptical cores can be offset from those illustrated in
φ=(180/N)*n+θ.
where n is the core number, i.e. 1, 2, 3, 4 . . . , and θ is an offset angle including 0°.
It is further contemplated that variations in the direction of polarization of the input light will generate variations in the nature of the cylindrically polarized output light. For example, the respective directions of polarization of the input radiation in
Having described the subject matter of the present disclosure in detail and by reference to specific embodiments thereof, it is noted that the various details disclosed herein should not be taken to imply that these details relate to elements that are essential components of the various embodiments described herein, even in cases where a particular element is illustrated in each of the drawings that accompany the present description. Rather, the claims appended hereto should be taken as the sole representation of the breadth of the present disclosure and the corresponding scope of the various inventions described herein. Further, it will be apparent that modifications and variations are possible without departing from the scope of the invention defined in the appended claims. More specifically, although some aspects of the present disclosure are identified herein as preferred or particularly advantageous, it is contemplated that the present disclosure is not necessarily limited to these aspects.
This application claims the benefit of priority under 35 U.S.C. §119 of U.S. Provisional Application Ser. No. 61/363,459, filed Jul. 12, 2010, the content of which is relied upon and incorporated herein by reference.
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/US2011/043625 | 7/12/2011 | WO | 00 | 3/27/2013 |
Number | Date | Country | |
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61363459 | Jul 2010 | US |