Wavelength multiplexing processor

Abstract

A wavelength multiplexing system is presented comprising at least one basic functional unit extending between input and output light ports. The basic functional unit comprises at least one multi-core fiber. The multi-core fiber comprises N cores configured for supporting transmission of N wavelength channels λ.sub.1, . . . , λ.sub.n, wherein each of said at least one multi-core fibers is configured to apply a predetermined encoding pattern to the wavelength channels enabling linear mixing between them while propagating through multiple cores of said multi-core fiber. The encoding pattern may be configured to affect light propagation paths in the cores by inducing a predetermined dispersion pattern causing linear interaction and mixing between the channels; or may be configured to affect spectral encoding of the channels being transmitted through the cores by applying different weights to the channels.

Claims

1. A wavelength multiplexing system comprising at least one basic functional unit extending between input and output light ports, the basic functional unit comprising at least one multi-core fiber, the multi-core fiber comprising N cores configured for supporting transmission of N wavelength channels λ.sub.1, . . . , λ.sub.n, wherein each of said at least one multi-core fibers is configured to apply a predetermined encoding pattern to the wavelength channels enabling linear mixing between them while propagating through multiple cores of said multi-core fiber.

2. The wavelength multiplexing system according to claim 1, wherein said predetermined encoding pattern is defined by N non-linear processings applied to the N channels, respectively.

3. The wavelength multiplexing system according to claim 2, wherein said predetermined encoding pattern is a dispersion pattern.

4. The wavelength multiplexing system according to claim 3, wherein said N cores of the multi-core fiber are configured as supercontinuum generators defining N zero-dispersion points for N wavelengths λ.sub.1, . . . , λ.sub.n, respectively, thereby performing spectral broadening of the N channels around said N wavelengths.

5. The wavelength multiplexing system according to claim 4, wherein said N cores of the multi-core fiber are configured as photonic crystal fibers (PCFs).

6. The wavelength multiplexing system according to claim 1, wherein said predetermined encoding pattern is defined by tunable spectral filtering of the wavelength channels λ.sub.1, . . . , λ.sub.n to perform weighted mixing of the channels.

7. The wavelength multiplexing system according to claim 6, comprising a tunable spectral filter device comprising N tunable spectral filters associated with the N wavelength channels, each of said N tunable spectral filters being configured and operable as a birefringent filter applying a different weight function to the respective light channel.

8. An optical fiber unit configured and operable for use in a wavelength multiplexing system between input and output ports of the system, the optical fiber unit comprising at least one multi-core fiber, the multi-core fiber comprising N cores configured for supporting transmission of N wavelength channels λ.sub.1, . . . , λ.sub.n, wherein each of said at least one multi-core fibers is configured to apply a predetermined encoding pattern to the wavelength channels enabling linear mixing between them while propagating through multiple cores of said multi-core fiber, said predetermined encoding pattern being characterized by one of the following: affecting light propagation paths in the cores by inducing a predetermined dispersion pattern causing linear interaction and mixing between the channels; and affecting spectral encoding of the channels being transmitted through the cores by applying different weights to the channels.

9. The optical fiber unit according to claim 8, wherein said predetermined encoding pattern affects light propagation paths in the cores by inducing the predetermined dispersion pattern causing linear interaction and mixing between the channels, said predetermined encoding pattern being defined by N non-linear processings applied to the N channels, respectively.

10. The optical fiber unit according to claim 9, wherein said predetermined encoding pattern is a dispersion pattern.

11. The optical fiber unit according to claim 10, wherein said N cores of the multi-core fiber are configured as supercontinuum generators defining N zero-dispersion points for N wavelengths λ.sub.1, . . . , λ.sub.n, respectively, thereby performing spectral broadening of the N channels around said N wavelengths.

12. The optical fiber unit according to claim 11, wherein said N cores of the multi-core fiber are configured as photonic crystal fibers (PCFs).

13. The optical fiber unit according to claim 8, wherein said predetermined encoding pattern affects spectral encoding of the channels being transmitted through the cores by applying different weights to the channels, said predetermined encoding pattern being defined by tunable spectral filtering of the wavelength channels λ.sub.1, . . . , λ.sub.n to perform weighted mixing of the channels.

14. The optical fiber unit according to claim 13, comprising a tunable spectral filter device comprising N tunable spectral filters associated with the N wavelength channels, each of said N tunable spectral filters being configured and operable as a birefringent filter applying a different weight function to the respective light channel.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting examples only, with reference to the accompanying drawings, in which:

[0017] FIG. 1 schematically exemplifies a multi-dimensional WDM system utilizing multicore fiber unit(s) each configured as a multiplexer, according to some embodiments of the invention;

[0018] FIG. 2 exemplifies the general principles of configuring the individual fiber core to have a zero dispersion point for a certain central wavelength to thereby achieve spectral broadening around said central wavelength, according to some embodiments of the invention;

[0019] FIG. 3 schematically exemplifies a multi-dimensional WDM system utilizing a multicore fiber unit configured as a multiplexer, according to some other embodiments of the invention; and

[0020] FIG. 4 exemplifies a tunable spectral filter suitable to be used in the system of FIG. 3 in association with a wavelength channel (fiber core).

DETAILED DESCRIPTION OF EMBODIMENTS

[0021] Referring to FIG. 1, there is schematically illustrated a device 10 which is configured to be used as a basic functional unit of a WDM system according to some embodiments of the invention. The device 10 includes at least one multi-core fiber unit 12. The fiber unit includes a number M (M≥1) of multi-core fibers. The multi-core fiber unit(s) 12 extend(s) between input and output ports 14 and 16 of the WDM system.

[0022] In the present non-limiting example of FIG. 1, the multi-core fiber unit 12 is exemplified as including a single multi-core fiber (M=1), extending between the input and output ports 14 and 16. However, it should be understood that the principles of the invention are not limited to the number of fiber units, as well as to the number of multi-core fibers in each fiber units and the number of multiple cores of the fiber.

[0023] Also, it should be noted that the multi-core fibers units forming the WDM system may or may not be identical in the number of fibers or number of cores.

[0024] The multi-core fiber 12 has a plurality/array of N cores C.sub.1, . . . C.sub.n, supporting N different wavelengths λ.sub.1, . . . , λ.sub.n, and is configured and operable as a multi-dimensional wavelength multiplexing processor for processing respective N input data channels (light signals) of wavelengths λ.sub.1, . . . , λ.sub.n, by encoding the light signals via a non-linear effect, to enable linear interaction and mixing between the channels.

[0025] The above can be achieved by configuring each i-th fiber core C.sub.i, as a supercontinuum generator broadening the light signal around its respective central wavelength λ.sub.1. For example, this can be implemented by configuring the fiber core as a photonic crystal fiber (PCF) having substantially zero dispersion for the certain wavelength (i.e., wavelength of the respective channel).

[0026] The general principles of such fiber core configuration are known and do not for part of the invention. In a single-mode optical fiber, the zero-dispersion wavelength is the wavelength or wavelengths at which material dispersion and waveguide dispersion cancel one another. In multi-mode optical fiber, this refers to the minimal-dispersion wavelength, i.e. the wavelength at which the material dispersion is minimum, i.e. essentially zero.

[0027] Some examples of the construction and operation of such zero dispersion PCF are described in the following articles: Kokou Firmin Fiaboe et al., “Photonic crystal fibers with flattened zero dispersion for supercontinuum generation”, Advanced Electromagnetics, Vol. 8, NO. 4, September 2019; Pranaw Kumar et al., “Design of nonlinear photonic crystal fibers with ultra flattened zero dispersion for super continuum generation”, ETRI Journal Wiley, August 2019; Partha Sona Maji, Partha Roy, “Supercontinuum generation in ultra flat near zero dispersion PCF with selective liquid infiltration”, Optik 125 (2014) 5986-5992.

[0028] As shown schematically in FIG. 2, exemplifying a fiber core structure, the core material (semiconductor) is patterned to form a predetermined arrangement of spaced-apart air holes which may be filled by another suitable material. This may for example be optically active gas or highly nonlinear liquid. Suitable materials include those exhibiting high Kerr or photorefractive effect, e.g. liquid crystals or quantum dot solutions.

[0029] Such photonic crystal fibers have chromatic dispersion characteristics allowing a strong nonlinear interaction over a significant length of the fiber. This enables to provide the fiber with tailored chromatic dispersion properties while maintaining nonlinearity. This is because high chromatic dispersion promotes supercontinuum generation if the pump wavelength falls at an unstable dispersion equilibrium.

[0030] Hence, for the purpose of the present invention, the features of the pattern (holes and spaces dimensions) and refractive indices of the materials are selected to define the zero dispersion point for a certain wavelength. These parameters include, for example, the hole periodicity, diameter and fill factor.

[0031] According to the invention, the entire arrangement of N so-patterned PCFs (cores C.sub.1, . . . C.sub.n) define N different zero-dispersion points for central wavelengths λ.sub.1, . . . , λ.sub.n according to the N WDM channels of an ITU grid that is to be mixed. By this, the wavelengths of the broadened spectra of different channels can linearly interact with one another via non-linear effect.

[0032] Demultiplexing of the channels can be implemented by using an arrayed waveguide grating (AWG) at the output of the super continuum multi-core fiber unit 12.

[0033] Reference is now made to FIG. 3 which schematically exemplifies a functional device of a WDM system 100 utilizing at least one multicore fiber unit 112 configured as a multi-dimensional multiplexing processor, according to some other embodiments of the invention. Similarly, to the above-described system 10, the multicore fiber unit 112 (which in this non-limiting example is also shown as a single multi-core fiber) extends between input and output ports 14 and 16. Here, the multi-core fiber 12, including N cores C.sub.1, . . . C.sub.n, supporting N different wavelengths λ.sub.1, . . . , λ.sub.n, is associated with (equipped with) a tunable spectral unit formed by respective N tunable spectral filters TSF.sub.1, . . . TSF.sub.n, associated with the N cores. Each i-th tunable spectral filter TSF.sub.1 is configured to encode the respective wavelength channel by applying thereto a different weight.

[0034] The tunable spectral filter may be configured based on a Solc filter, for example as described in the article G. Shabtay, E. Eidinger, Z. Zalevsky, D. Mendlovic and E. Marom, “Tunable birefringent filters—optimal iterative design” Opt. Express 10 1534-1541 (2002). The spectral filtering is based on birefringent effects utilizing phase shifts between orthogonal polarizations of light to obtain a narrow band filter. An example of such filter TSF.sub.1 is shown in FIG. 4. The filter includes a sequence of M tilted retardation plates RP.sub.1, . . . RP.sub.m, enclosed between polarizers P.sub.1 and P.sub.2.

[0035] Such N tunable spectral filters TSF.sub.1, . . . TSF.sub.n apply N different weight functions WF.sub.1, . . . WF.sub.n, for side lobes attenuation of the N channels λ.sub.1, . . . , λ.sub.n. As a result, all the spectral information of the N channels is added together resulting in weighted mixing of the channels.