Method and apparatus for wavelength selective switch

Patent metadata

Field	Value
Publication number	US-9008470-B2
Application number	US-201313753202-A
Country	US
Kind code	B2
Filing date	Jan 29, 2013
Priority date	Jan 30, 2012
Publication date	Apr 14, 2015
Grant date	Apr 14, 2015

Abstract

Apparatus and method embodiments are provided for implementing a wavelength selective switch (WSS). The embodiments use combinations of switchable polarization grating (SPG) and LC cells and combinations of polymer polarization grating (PPG) and LC cells to achieve 1×N WSS systems. An embodiment optical switch includes a liquid crystal cell and a SPG cell adjacent to the liquid crystal cell. The SPG includes liquid crystal material between two photo-alignment layers, an electrode layer overlying each photo-alignment layer, and a glass substrate overlying each electrode layer. An embodiment method includes polarizing an incident light beam at a circular polarization before diffracting, at a polarization grating, the polarized incident light beam in a determined angle that corresponds to a diffraction order in accordance to the circular polarization of the incident light beam and a hologram pattern direction formed inside the polarization grating.

First claim

What is claimed is:

1. An optical switch comprising:
a liquid crystal cell; and
a switchable polarization grating (SPG) cell adjacent to the liquid crystal cell, the SPG comprising:
a first glass substrate;
a first electrode layer overlying the first glass substrate;
a photo-alignment layer overlying the first electrode layer;
liquid crystal material overlying the photo-alignment layer;
a second photo-alignment layer overlying the liquid crystal material, the first photo-alignment layer and the second photo-alignment layer comprising photosensitive polymer that have been physically altered by exposure using two interfering light beams with opposite handedness of circular polarization;
a second electrode layer overlying the second photo-alignment layer; and
a second glass substrate overlying the second electrode layer.

2. The optical switch of claim 1 , further comprising:
a variable optical attenuator (VOA) comprising a second liquid crystal cell and a polarizer;
a quarter wave plate positioned between the VOA and the liquid crystal cell;
a prism or minor positioned next to the SPG cell on an opposite side from the liquid crystal cell; and
one or more pairs of an additional liquid crystal cell and an additional corresponding SPG cell positioned between the SPG cell and the prism or minor,
wherein the optical switch is a 1×3 N optical switch configured to optically connect one common port to 3 N separate ports, where N is a number of pairs of liquid crystal cells and corresponding SPG cells in the optical switch.

3. The optical switch of claim 1 , further comprising:
a variable optical attenuator (VOA), comprising a second liquid crystal cell and a polarizer;
a prism or minor positioned next to the SPG cell on an opposite side from the liquid crystal cell; and
one or more additional SPG cells positioned between the SPG cell and the prism or minor,
wherein the optical switch is a 1×(2 N+1 −1) optical switch configured to optically connect one common port to 2 N+1 −1 separate ports, where N is a number of SPG cells in the optical switch.

4. The optical switch of claim 3 , wherein the liquid crystal cell is configured as a switchable quarter wave plate to convert an incident light polarization from linear polarization into right-handed or left-handed circular polarization.

5. The optical switch of claim 1 , further comprising:
a variable optical attenuator (VOA), comprising the liquid crystal cell and a polarizer;
a quarter wave plate positioned between the VOA and the SPG cell;
a prism or minor positioned next to the SPG cell on an opposite side from the VOA; and
one or more additional SPG cells positioned between the SPG cell and the prism or minor,
wherein the optical switch is a 1×2 N optical switch configured to optically connect one common port to 2 N separate ports, where N is a number of SPG cells in the optical switch.

6. The optical switch of claim 1 , wherein both the liquid crystal cell and the SPG cell comprise a plurality of pixels corresponding to wavelength channels and aligned perpendicular to a direction of a plurality of parallel light beam paths through the optical switch corresponding to optical switch ports, and wherein the optical switch is designed to have equal distance between parallel output light beams from the optical switch.

7. The optical switch of claim 1 , further comprising:
a fiber array that transmits and receives one or more incident light beams to and from the liquid crystal cell and the SPG cell;
a micro lens array positioned on the optical path next to the fiber array;
a beam displacer positioned on the optical path next to the micro lens array;
a half wave plate array positioned on the optical path next to the beam displacer;
a cylindrical lens positioned on the optical path between the half wave plate array and the liquid crystal cell with the SPG cell;
a cylindrical reflection minor facing the liquid crystal cell and the SPG cell behind the cylindrical lens on the optical path and positioned to reflect a light beam that is passed through the cylindrical lens back through the cylindrical lens; and
a grating facing the cylindrical reflection minor behind the cylindrical lens on the optical path and positioned to diffract a light beam that is passed through the cylindrical lens back onto the cylindrical lens.

8. The optical switch of claim 1 , wherein the SPG cell is configured to, with no applied voltage or a first applied voltage between the first electrode layer and the second first electrode layer, diffract an incident light beam that has a circular polarization in a determined direction and reverse the circular polarization's handedness of the diffracted incident light beam.

9. The optical switch of claim 8 , wherein the SPG cell is configured to, with a second applied voltage between the first electrode layer and the second first electrode layer, pass an incident light beam through the SPG cell without diffraction and without change in polarization.

10. The optical switch of claim 1 , wherein the liquid crystal cell is configured to, with no applied voltage or a first applied voltage across the liquid crystal cell, pass an incident light beam that has a circular polarization to the SPG cell after reversing the circular polarization's handedness and alternatively, with a second applied voltage across the liquid crystal cell, pass the incident light beam without changing the circular polarization's handedness.

Assignees

• Huawei Tech Co Ltd

Inventors

• Mao Chongchang
• Li Minchun
• Chen Bo
• Fang Yang

Classifications

• G02B5/12

  Reflex reflectors · CPC title

• G02F2203/05

  wavelength dependent · CPC title

• G02B26/0808

  by means of one or more diffracting elements · CPC title

• H04Q2011/0015

  using splitting combining · CPC title

• G02F2001/13355

  Physics · mapped topic