Launch optics with optical path compensation for a wavelength selective switch

• US 9,341,870 B1
• Filed: 11/26/2014
• Issued: 05/17/2016
• Est. Priority Date: 11/26/2014
• Status: Active Grant

• Current Assignee: Molex LLC (KOCH Industries Incorporated)
• Original Assignee: Nistica, Inc. (KOCH Industries Incorporated)
• Inventors: Wagener, Jefferson L., Haller, Mitchell E.
• Primary Examiner(s): Lester, Evelyn A
• Application Number:
  US14/554,633
• Publication Number:
  US 20160147092A1
• Time in Patent Office: 538 Days
• Field of Search: 359/223.1, 359/279, 359/290, 359/291, 359/298, 385/16, 385/39
• US Class Current: 1/1
• CPC Class Codes: G02B 1/005 made of photonic crystals or photonic band gap materials photonic band-gap structures or photonic lattices in integrated optics G02B6/1225; photonic band-gap structures or photonic lattices in optical fibres G02B6/02295
• CPC Class Codes: G02B 26/00 Optical devices or arrangements for the control of light using movable or deformable optical elements control of light by modification of the optical properties of the media of the elements involved therein G02F1/00
• CPC Class Codes: G02B 26/001 based on interference in an adjustable optical cavity interference filters G02B5/28; devices or arrangements using multiple reflections in spectrometry or monochromators G01J3/26
• CPC Class Codes: G02B 26/005 based on electrowetting
• CPC Class Codes: G02B 26/007 the movable or deformable optical element controlling the colour, i.e. a spectral characteristic, of the light
• CPC Class Codes: G02B 26/06 for controlling the phase of light G02B26/08 takes precedence , measuring optical phase difference G01J9/00
• CPC Class Codes: G02B 26/0816 by means of one or more reflecting elements
• CPC Class Codes: G02B 26/0833 the reflecting element being a micromechanical device, e.g. a MEMS mirror, DMD G02B26/0825 takes precedence; micromechanical devices in general B81B
• CPC Class Codes: G02B 27/0068 having means for controlling the degree of correction, e.g. using phase modulators, movable elements controlling the phase of light using moving or deformable elements G02B26/06
• CPC Class Codes: G02B 27/0172 characterised by optical features
• CPC Class Codes: G02B 27/1026 for use with reflective spatial light modulators
• CPC Class Codes: G02B 27/283 used for beam splitting or combining
• CPC Class Codes: G02B 27/286 for controlling or changing the state of polarisation, e.g. transforming one polarisation state into another G02B5/3083 takes precedence; light guide coupling means utilising polarising elements G02B6/34
• CPC Class Codes: G02B 5/1814 structurally combined with one or more further optical elements, e.g. lenses, mirrors, prisms or other diffraction gratings G02B5/189 takes precedence
• CPC Class Codes: G02B 5/30 Polarising elements light-modulating devices with active elements G02F1/00
• CPC Class Codes: G02B 5/3083 Birefringent or phase retarding elements G02B5/3008, G02B5/3016 take precedence; systems for polarisation control G02B27/286; manufacturing phase modulating patterns by lithographic processes G03F7/001
• CPC Class Codes: G02B 6/2773 Polarisation splitting or combining
• CPC Class Codes: G02B 6/2861 using fibre optic delay lines and optical elements associated with them, e.g. for use in signal processing, e.g. filtering delay lines in general H03H, H01P9/00; optical computing devices G06E
• CPC Class Codes: G02B 6/354 Switching arrangements, i.e. number of input/output ports and interconnection types
• CPC Class Codes: G02F 1/133606 including a specially adapted diffusing, scattering or light controlling members
• CPC Class Codes: G02F 2202/32 : Photonic crystals
• CPC Class Codes: G02F 2203/12 : spatial light modulator
• CPC Class Codes: G02F 2203/50 : Phase-only modulation
• CPC Class Codes: H04Q 11/0005 : Switch and router aspects
• CPC Class Codes: H04Q 2011/0026 : using free space propagation (e.g. lenses, mirrors)
• CPC Class Codes: H04Q 2011/0035 : using miscellaneous components, e.g. circulator, polarisation, acousto/thermo optical

Abstract

An optical device includes an optical port array, a first walk-off crystal, a first half-wave plate, a second walk-off crystal and a segmented half-wave plate. The optical port array has a first and second plurality of ports for receiving optical beams. The first walk-off crystal spatially separates the beams into first and second portions that are in first and second orthogonal polarization states, respectively. The first portions are walked-off by the first walk-off crystal and the second portions pass therethrough without being walked-off. The first half-wave plate rotates the polarization state of the first and second portions of the optical beams. The second walk-off crystal is oriented in an opposite direction from the first walk-off crystal such that the second portions are walked-off by the second walk-off crystal and the first portions pass therethrough without being walked-off. The segmented half-wave plate receives the first or second portions of the beams.

Claims

1. A method for compensating for a difference in optical path length traversed by first and second optical portions of an optical beam which are in orthogonal polarization states, comprising:

receiving the optical beam at the input port;

directing the optical beam to a first walk-off crystal for spatially separating the optical beam into first and second optical portions that are in first and second polarization states, respectively, the first and second polarization states being orthogonal to one another, the first optical portion being walked-off by the walk-off crystal and the second optical portion passing therethrough without being walked-off;

rotating the polarization state of the first and second optical portions;

after rotating the polarization state of the first and second optical portions, directing the first and second optical portions to a second walk-off crystal being oriented in an opposite direction from the first walk-off crystal so that the second optical component is walked-off by the walk-off crystal and the first optical component passes therethrough without being walked-off, a thickness of the first and second walk-off crystals being selected to adjust the optical path lengths traversed by each of the first and second optical portions.

2. The method of claim 1 wherein the thickness of the first and second walk-off crystals is further selected to compensate for an optical path difference that arises from one or more upstream or downstream optical elements that is traversed by one of the first and second optical portions and not the other of the first and second optical portions.

3. The method of claim 1 wherein the optical element is a half-wave plate located downstream from the first and second walk-off crystals.

4. The method of claim 1 wherein the first input port is angularly offset with respect to the second input about an axis parallel to the wavelength dispersion axis.

5. A method for directing wavelength components of an optical beam from an input port of a port array to at least one output port of the port array, comprising:

receiving a first optical beam at a first input port of the port array associated with a first wavelength selective switch;

receiving a second optical beam at a second input port of the port array associated with a second wavelength selective switch;

directing the first optical beam to a first walk-off crystal for spatially separating the first optical beam into first and second optical portions that are in first and second polarization states, respectively, the first and second polarization states being orthogonal to one another, the first optical portion being walked-off by the walk-off crystal and the second optical portion passing therethrough without being walked-off;

directing the second optical beam to the first walk-off crystal for spatially separating the second optical beam into third and fourth optical portions that are in the first and second polarization states, respectively, the third optical portion being walked-off by the first walk-off crystal and the fourth optical portion passing therethrough without being walked-off;

rotating the polarization state of the first, second, third and fourth optical portions;

after rotating the polarization state of the first, second, third and fourth optical portions, directing the first, second, third and fourth optical portions to a second walk-off crystal being oriented in an opposite direction from the first walk-off crystal so that the second and fourth optical portions are walked-off by the second walk-off crystal and the first and third optical components pass therethrough without being walked-off, a thickness of the walk-off crystals being selected to adjust the optical path lengths traversed by each of the first, second, third and fourth optical portions;

spatially separating the wavelength components of the first, second, third and fourth optical portions;

focusing the spatially separated wavelength components onto a programmable optical phase modulator so that the wavelength components of the first and second optical beams are spatially separated along a wavelength dispersion axis of the modulator; and

adjusting a phase shift profile of the modulator along the second direction to selectively direct individual ones of the wavelength components to an output port.

6. The method of claim 5 wherein the thickness of the first and second walk-off crystals is further selected to compensate for an optical path difference that arises from one or more upstream or downstream optical elements that is traversed by one of the first and second optical portions and not the other of the first and second optical portions and that is traversed by one of the third and fourth optical portions and not the other of the third and fourth optical portions.

7. The method of claim 5 wherein the optical element is a half-wave plate located downstream from the first and second walk-off crystals.

8. The method of claim 5 wherein the first input port is angularly offset with respect to the second input about an axis parallel to the wavelength dispersion axis.

9. An optical device, comprising:

an optical port array having a first plurality of ports for receiving optical beams and a second plurality of ports for receiving optical beams;

a first walk-off crystal for spatially separating each of the optical beams into first and second optical portions that are in first and second polarization states, respectively, the first and second polarization states being orthogonal to one another, the first optical portions being walked-off by the first walk-off crystal and the second optical portions passing therethrough without being walked-off;

a first half-wave plate for rotating the polarization state of the first and second optical portions of the optical beams;

a second walk-off crystal being oriented in an opposite direction from the first walk-off crystal such that the second optical portions are walked-off by the second walk-off crystal and the first portions pass therethrough without being walked-off; and

a segmented half-wave plate for receiving the second optical portions of the optical beams or the first optical portions of the optical beams.

10. The optical device of claim 9 wherein a thickness of the first and second walk-off crystals being selected to adjust the optical path lengths traversed by each of the first and second optical portions to compensate for an optical path difference that arises from the first optical portions or the second optical portions traversing the segmented half-wave plate and the other of the first and second optical portions not traversing the segmented half-wave plate.

11. The optical device of claim 9 further comprising:

a dispersion element receiving the first and second optical portions of the optical beams and spatially separating the first and second optical portions into a plurality of wavelength components along a wavelength dispersion axis, a port axis being orthogonal to the wavelength dispersion axis, the first plurality of ports extending in a first plane that includes the port axis and the second plurality of ports extending in a second plane that includes the port axis, the first and second planes being parallel to one another and offset from one another along the wavelength dispersion axis, the first plurality of ports being angularly offset with respect to the second plurality of ports about an axis parallel to the wavelength dispersion axis;

a focusing element for focusing the plurality of wavelength components; and

a programmable optical phase modulator for receiving the focused plurality of wavelength components, the modulator being configured to steer the wavelength components received from any one of the first plurality of ports to a selected one of the first plurality of ports and being further configured to steer the wavelength components received from any one of the second plurality of ports to a selected one of the second plurality of ports.

12. The optical device of claim 9 wherein the first plurality of ports are interleaved with the second plurality of ports along the port axis.

13. The optical device of claim 9 wherein the programmable optical phase modulator includes a liquid crystal-based phase modulator.

14. The optical device of claim 13 wherein the liquid crystal-based phase modulator is a LCoS device.

15. The optical device of claim 11 wherein the dispersive element is selected from the group consisting of a diffraction grating and a prism.

16. The optical device of claim 11 further comprising an optical system for magnifying the optical beam received from the optical port array and directing the magnified optical beam to the dispersion element.

17. The optical device of claim 16 wherein the optical system has a first magnification factor in a first direction and a second magnification factor in a second direction orthogonal to the first direction, the first magnification factor being different from the second magnification factor.

18. The optical device of claim 17 wherein the first direction is parallel to a wavelength dispersion axis along which the optical beams are spatially separated, the first magnification factor being less than the second magnification factor.