Tunable add/drop optical filter

• US 5,606,439 A
• Filed: 04/10/1996
• Issued: 02/25/1997
• Est. Priority Date: 04/10/1996
• Status: Expired due to Term

• Current Assignee: EC-Optics Technology Inc.
• Original Assignee: Macro-Vision Technology Incorporated
• Inventors: Wu, Kuang-Yi
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): NGUYEN, TIEP HUU
• Application Number:
  US08/629,523
• Time in Patent Office: 321 Days
• Field of Search: 359/73, 359/63, 385/11, 385/14, 385/31, 385/39, 385/15, 385/20
• US Class Current: 349/117
• CPC Class Codes: G02B 6/272 comprising polarisation means for beam splitting and combining
• CPC Class Codes: G02B 6/2746 comprising non-reciprocal devices, e.g. isolators, FRM, circulators, quasi-isolators magneto-optic non-reciprocal devices G02F1/093
• CPC Class Codes: G02B 6/2766 Manipulating the plane of polarisation from one input polarisation to another output polarisation, e.g. polarisation rotators, linear to circular polarisation converters
• CPC Class Codes: G02B 6/2773 Polarisation splitting or combining
• CPC Class Codes: G02B 6/29302 based on birefringence or polarisation, e.g. wavelength dependent birefringence, polarisation interferometers
• CPC Class Codes: G02B 6/29358 Multiple beam interferometer external to a light guide, e.g. Fabry-Pérot, etalon, VIPA plate, OTDL plate, continuous interferometer, parallel plate resonator G02B6/29347, G02B6/29349, G02B6/2935, G02B6/29361 take precedence; resonator evanescently coupled to light guide G02B6/29335
• CPC Class Codes: G02B 6/29361 Interference filters, e.g. multilayer coatings, thin film filters, dichroic splitters or mirrors based on multilayers, WDM filters
• CPC Class Codes: G02B 6/29383 Adding and dropping
• CPC Class Codes: G02B 6/29395 configurable, e.g. tunable or reconfigurable switching G02B6/35
• CPC Class Codes: G02F 1/09 based on magneto-optical elements, e.g. exhibiting Faraday effect
• CPC Class Codes: G02F 1/31 Digital deflection, i.e. optical switchingG02F1/33 takes precedence
• CPC Class Codes: H04J 14/021 Reconfigurable arrangements, e.g. reconfigurable optical add/drop multiplexers [ROADM] or tunable optical add/drop multiplexers [TOADM]
• CPC Class Codes: H04J 14/0212 using optical switches or wavelength selective switches [WSS]
• CPC Class Codes: H04Q 11/0003 Details

Abstract

In all-optical networks, optical switching and routing become the most important issues for interconnecting the transport network layers. This invention describes a novel tunable optical add/drop filter for the all-optical wavelength-division-multiplexing (WDM) network applications. This filter can add or drop part of the high transmission capacity signals of a WDM link. It can be used to decentralized access point in the access network or as small core network node to realizing branching points in the network topology. It works in both wavelength and space domains. It has the advantages of: 1) High throughput and low voltage operation; 2) Wide tuning range and therefore, high channel capacity; 3) High isolation and high directivity between input and output ports; 4) Compact device packaging is possible as compares to the conventional grating and mechanical switching type of add/drop filter; 5) Multiple ports add/drop tunable filters can be realized with this invention to interconnect multiple WDM networks. This novel add/drop filter can be used in various WDM topologies. It enhances the performance of the conventional tunable filter by re-routing the rejected wavelengths back to network, which not only save the precious optical energy, but also cut down the return loss of the device.

Claims

1. A tunable add/drop filter which comprises:

a non-reciprocal setup for optical channels return to WDM network, a tunable filter for predetermined optical channel selection, and a reciprocal optical add/drop setup for add/drop operations, where, the non-reciprocal optical setup is a combination of an optical birefringent element which has a thickness of d, a Faraday rotator that rotates eigen polarization of input light beams by 45°

, a polarization beam combiner and a right angle prism placed at an entrance side of the birefringent element to recombine returned optical signals;

the tunable filter for selectively dropping or adding the optical channels; and

the reciprocal optical add/drop setup comprises of two optical birefringent elements with thickness of (1/2)d, and with their polarization eigen planes oriented at 45° and

-45°

relatively to a polarization eigen plane of the first birefringent element in the non-reciprocal setup, respectively.

2. The tunable add/drop filter of claim 1, wherein said tunable filter is a liquid crystal based, birefringent filter, a pair of halfwave plates are added to the front and back facets of the filter;

said two halfwave plates are placed to intersect two orthogonally polarized incident light paths, respectively;

a first one of the halfwave plates is placed on a first light path that rotates an ordinary light wave into extra-ordinary light wave that aligns a polarization of the light wave to an optical axis of the liquid crystal film;

a second one of the halfwave plates is placed on a second light path that rotates the extra-ordinary light wave into ordinary light wave.

3. The tunable add/drop filter of claim 2, wherein said tunable birefringent filter is a patterned liquid crystal based filter with a plurality of sections;

each filter section can selectively filter through optical channel and said tunable add/drop filter forms a tunable multiple-port add/drop filter.