US-20260126591-A1 - WAVELENGTH SELECTIVE SWITCH WITH MULTIPLE DEFLECTOR ARRAYS

US20260126591A1US 20260126591 A1US20260126591 A1US 20260126591A1US-20260126591-A1

Abstract

A wavelength selective switch includes a waveguide array for providing an input light beam, a polarizing collimator for splitting the input light beam into polarized collimated first and second sub-beams propagating along non-overlapping optical paths, and a dispersive element for angularly dispersing the first and second sub-beams into wavelength components. First and second angle-to-offset elements are provided for focusing the wavelength components of the first and second sub-beams. A first deflector array and a second, different deflector array are disposed at focal planes of the first and second angle-to-offset elements respectively for redirecting the wavelength components to propagate back through the optical train for in-coupling into a waveguide of the waveguide array. Such a configuration of the wavelength selective switch allows the use of inexpensive standard deflector arrays.

Inventors

Chenjun Fan
Wenlu Wang
Zuowen Jiang

Assignees

O-NET TECHNOLOGIES (CANADA) INC.
O-NET TECHNOLOGIES (SHENZHEN) GROUP CO., LTD

Dates

Publication Date: 20260507
Application Date: 20230901

Claims (20)

1 . A wavelength selective switch (WSS) comprising: a waveguide array for providing an input light beam; a polarizing collimator coupled to the waveguide array for splitting the input light beam into polarized collimated first and second sub-beams propagating along non-overlapping optical paths; a dispersive element coupled to the polarizing collimator for angularly dispersing the first and second sub-beams into wavelength components; first and second angle-to-offset elements for focusing the wavelength components of the first and second sub-beams, respectively; and a first deflector array and a second, different deflector array, disposed at focal planes of the first and second angle-to-offset elements respectively, for redirecting the wavelength components to propagate back through the first and second angle-to-offset elements respectively, the dispersive element, and the polarizing collimator for in-coupling into a waveguide of the waveguide array.
2 . The WSS of claim 1 , wherein: the dispersive element is configured to disperse the first and second sub-beams into the wavelength components in a first plane; the first and second angle-to-offset elements are configured to focus the wavelength components of the first and second sub-beams, respectively, in the first plane; and the first and second deflector arrays are configured to redirect the wavelength components in spaced apart planes perpendicular to the first plane.
3 . The WSS of claim 2 , wherein the first and second angle-to-offset elements each comprise an acylindrical lens having a non-zero optical power in the first plane, and a substantially zero optical power in a plane perpendicular to the first plane.
4 . The WSS of claim 2 , wherein waveguides of the waveguide array are disposed in a plane perpendicular to the first plane, wherein the polarizing collimator comprises a birefringent element optically coupled to each waveguide of the waveguide array, for angularly separating the first and second sub-beams in the first plane.
5 . The WSS of claim 4 , wherein the polarizing collimator further comprises a rotationally symmetric lens having a first focal length and disposed substantially one first focal length downstream of the birefringent element, for collimating the first and second sub-beams to propagate parallel to one another.
6 . The WSS of claim 1 , further comprising a polarization rotator in an optical path of at least one of the first or second sub-beams upstream of the dispersive element, for converting a polarization state of at least one of the first or second sub-beams such that the first and second sub-beams have a substantially same polarization state.
7 . The WSS of claim 2 , further comprising a prismatic beam expander for expanding the first and second sub-beams in the first plane, wherein the prismatic beam expander is disposed in an optical path of the first and second sub-beams between the polarizing collimator and the dispersive element.
8 . The WSS of claim 1 , wherein the dispersive element comprises first and second diffraction gratings for dispersing the first and second sub-beams, respectively, into the wavelength components, wherein the first and second diffraction gratings are disposed in different planes separated by a non-zero distance therebetween.
9 . The WSS of claim 8 , wherein the dispersive element further comprises first and second in-coupling prisms coupled to the first and second diffraction gratings respectively, for receiving the first and second sub-beams respectively, and for coupling the first and second sub-beams to the first and second diffraction gratings respectively.
10 . The WSS of claim 9 , wherein the first and second in-coupling prisms are disposed parallel one another and optically joined by an interface layer therebetween extending along parallel paths of propagation of the first and second sub-beams in the first and second in-coupling prisms respectively, such that during alignment of the WSS, a relative position of the first and second in-coupling prisms along the paths of propagation is adjustable by sliding at least one of the first or second in-coupling prism along the interface layer.
11 . The WSS of claim 10 , wherein an optical path of the wavelength components of the second sub-beam dispersed by the second diffraction grating comprises in sequence the second in-coupling prism, the interface layer, and the first in-coupling prism.
12 . A dual grism comprising: first and second in-coupling prisms for receiving and propagating therein first and second spaced apart sub-beams, respectively, of a light beam; and first and second diffraction gratings coupled to the first and second in-coupling prisms respectively, for dispersing the first and second sub-beams respectively into first and second wavelength components respectively, wherein the first and second diffraction gratings are disposed in different planes separated by a non-zero distance therebetween; wherein the first and second in-coupling prisms are disposed parallel one another and optically joined by an interface layer therebetween extending along parallel paths of propagation of the first and second sub-beams in the first and second in-coupling prisms respectively.
13 . The dual grism of claim 12 wherein, during alignment of the dual grism, a relative position of the first and second in-coupling prisms along the parallel paths of propagation is adjustable by sliding at least one of the first or second in-coupling prism along the interface layer.
14 . The dual grism of claim 12 , wherein an optical path of the second wavelength components comprises in sequence the second in-coupling prism, the interface layer, and the first in-coupling prism; and wherein, during alignment of the second in-coupling prism by sliding the second in-coupling prism along the interface layer, the optical path of the first wavelength components substantially does not change.
15 . The dual grism of claim 14 , further comprising a first out-coupling prism optically joined to the first in-coupling prism via a first layer therebetween, for out-coupling the first wavelength components from the first in-coupling prism, such that during alignment of the dual grism, a position of the first out-coupling prism is adjustable by sliding the first out-coupling prism along the first layer, for adjusting an optical path length of the first wavelength components without adjusting an optical path length of the second wavelength components.
16 . The dual grism of claim 14 , further comprising a second out-coupling prism optically joined to the first in-coupling prism via a second layer therebetween, for out-coupling the second wavelength components from the first in-coupling prism, such that during alignment of the dual grism, a position of the second out-coupling prism is adjustable by sliding the second out-coupling prism along the second layer, for adjusting an optical path length of the second wavelength components without adjusting an optical path length of the first wavelength components.
17 . The dual grism of claim 12 , wherein the first and second in-coupling prisms each comprise first to fourth conterminous faces, wherein: the second face of the first in-coupling prism is coupled to the fourth face of the second in-coupling prism via the interface layer; the first and second sub-beams are received at the first faces of the first and second in-coupling prisms respectively; and the first and second diffraction gratings are coupled to the third faces of the first and second in-coupling prisms respectively.
18 . A method for aligning a wavelength selective switch comprising a polarizing collimator for splitting an input light beam into polarized collimated first and second sub-beams, the method comprising: aligning the polarizing collimator to provide the first and second sub-beams propagating along non-overlapping optical paths; aligning a first portion of a dispersive element for dispersing the first sub-beam into first wavelength components impinging onto a first angle-to-offset element independently of alignment of the second sub-beam, for the first angle-to-offset element to focus the first wavelength components onto a first deflector array; and aligning a second, different portion of the dispersive element for dispersing the second sub-beam into second wavelength components impinging onto a second angle-to-offset element independently of alignment of the first sub-beam, for the second angle-to-offset element to focus the second wavelength components onto a second, separate deflector array.
19 . The method of claim 18 , wherein: the first and second portions of the dispersive element comprise first and second in-coupling prisms respectively for in-coupling the first and second sub-beams respectively, wherein the first and second in-coupling prisms are optically coupled to one another by an interface therebetween; the aligning of the first portion of the dispersive element comprises aligning the first portion relative to the first angle-to-offset element; and the aligning of the second portion of the dispersive element comprises sliding the second in-coupling prism relative to the first in-coupling prism along the interface; wherein in operation, the second wavelength components propagate in sequence through the second in-coupling prism, the interface, and the first in-coupling prism.
20 . The method of claim 19 , wherein: the first and second portions of the dispersive element comprise first and second out-coupling prisms respectively for out-coupling the first and second wavelength components, respectively, from the dispersive element, wherein the first and second out-coupling prisms are optically coupled to the first in-coupling prism via first and second layers therebetween, respectively; and the aligning of the second portion of the dispersive element further comprises aligning the second out-coupling prism by sliding the second out-coupling prism along the second layer, for adjusting an optical path length of the second wavelength components independently of an optical path length of the first wavelength components.

Description

REFERENCE TO RELATED APPLICATION This application claims priority from U.S. Provisional Patent Application No. 63/380,827, filed on Oct. 25, 2022, entitled “Wavelength Selective Switch with Multiple Deflector Arrays”, and incorporated herein by reference in its entirety. TECHNICAL FIELD The present disclosure relates to optical switching devices, and in particular to wavelength selective optical switches. BACKGROUND Wavelength selective switches are types of optical switches that can redirect light between input and output port(s) in a wavelength-selective manner. A light signal propagating in an optical network is independently modulated at a plurality of wavelengths, forming so-called wavelength channels. The wavelength channels are spaced apart from one another by fixed or flexible optical frequency spacings known as ITU (International Telecommunications Union) grid, typically evenly spaced at 37.5 GHz, 50 GHz, 75 GHz, 100 GHz, 200 GHz etc. in an infrared wavelength range of between approximately 1.3 micrometers and 1.6 micrometers. Some wavelength selective switches are capable of independently switching individual wavelength channels or entire wavelength bands between different optical fibers in an optical network. The optical network may include multiple optical fibers linking different nodes in a same city or town (metro optical networks), in different cities of a same country, and even nodes disposed in different countries or on different continents (long-haul optical networks). While being highly functional and versatile, wavelength selective switches often include a multitude of customized free-space and/or waveguiding optical and electro-optical components. Some of the components may need to be aligned to one another with sub-micrometer precision, which drives up manufacturing costs of these devices. Furthermore, wavelength selective switches need to be compact and environmentally stable, which further complicates their design and assembly. It would be advantageous to provide an inexpensive wavelength selective switch suitable for low-cost mass production. BRIEF DESCRIPTION OF THE DRAWINGS Exemplary embodiments will now be described in conjunction with the drawings, in which: FIG. 1A is a schematic top view of a wavelength selective switch of this disclosure using two separate deflector arrays to redirect sub-beams carrying two polarization components of an input light beam; FIG. 1B is a schematic side view of the wavelength selective switch of FIG. 1A; FIG. 2A is an unfolded top-view optical ray diagram of an embodiment of the wavelength selective switch of FIGS. 1A and 1B, the wavelength selective switch having a reflective diffraction grating for dispersing light into wavelength components; FIG. 2B is a side-view optical ray diagram of the wavelength selective switch of FIG. 2A, with the diffraction grating turned by 90 degrees about the optical axis, for ease of illustration; FIG. 3 is a top-view optical ray diagram of an embodiment of the wavelength selective switch embodiment of FIGS. 2A and 2B using a complex grism with two diffraction gratings offset from one another; FIG. 4 is a top-view optical ray diagram of an embodiment of the wavelength selective switch embodiment of FIG. 3 using a dual grism including an optically coupled pair of rhomboid-like grisms; FIG. 5 is a magnified top view of a back end of the wavelength selective switch of FIG. 4 showing directions of alignment of in-and out-coupling prisms of the dual grism; FIG. 6 is a magnified top view of the dual grism illustrating the back end alignment of the wavelength selective switch; and FIG. 7 is a flow chart of a method for alignment of a wavelength selective switch of this disclosure. DETAILED DESCRIPTION While the present teachings are described in conjunction with various embodiments and examples, it is not intended that the present teachings be limited to such embodiments. On the contrary, the present teachings encompass various alternatives and equivalents, as will be appreciated by those of skill in the art. All statements herein reciting principles, aspects, and embodiments of this disclosure, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents as well as equivalents developed in the future, i.e. any elements developed that perform the same function, regardless of structure. As used herein, the terms “first”, “second”, and so forth are not intended to imply sequential ordering, but rather are intended to distinguish one element from another, unless explicitly stated. Similarly, sequential ordering of method steps does not imply a sequential order of their execution, unless explicitly stated. In FIGS. 1A, B to FIG. 6, similar reference numerals denote similar elements. The scale of manufacturing of a product is one of largest cost factors for the product. Mass-produc