Tunable optical add/drop multiplexer

1. A tunable optical add/drop module (TOADM) comprising:

an input/output port for inputting an input optical beam with a plurality of optical wavelength channels, and for outputting an output optical beam with at least one of the plurality of optical wavelength channels;

an add/drop port for outputting a drop beam with at least one of the optical wavelength channels;

a tiltable mirror rotatable about a rotation axis to one of a plurality of tilt angles for directing the optical beam along one of a plurality of different paths;

a fixed thin film filter (TFF) positioned to receive the input optical beam along any one of the plurality of different paths for splitting the optical beam into a transmittance beam, which includes the at least one drop channel, and a reflection beam, which includes at least one of the plurality of optical channels in the output beam, wherein each one of the plurality of different paths corresponds to a different wavelength channel to be dropped;

a first general retro-reflector means for reflecting said transmitted beam back with a lateral shift in position to the add/drop port via the thin film filter and the tiltable mirror; and

a second general retro-reflector means for reflecting said reflected beam back to the input/output port via the thin film filter and the tiltable mirror.

2. The TOADM according to claim 1 , wherein the add/drop port is also for inputting an add beam comprising at least one optical channel, which is redirected by the tiltable mirror to the thin film filter, which redirects the add beam to the first general retro-reflector for redirecting the add beam to the input/output port via the thin film filter and the tiltable mirror for combination into the output beam.

3. The TOADM according to claim 1 , wherein said tiltable mirror comprises a tilting MEMs actuator.

4. The TOADM according to claim 1 , wherein said first general retro-reflector means comprises: an in-plane retro-reflector for reflecting the transmitted beam back in a same plane as the input/output port, and an out-of-plane retro-reflector for reflecting said transmitted beam back with a lateral shift in position into a different plane, which includes the add/drop port; whereby said first general retro-reflector means and said tiltable mirror direct the transmitted beam from said TFF back through the TFF for a second time, and out the add/drop port.

5. The TOADM according to claim 1 , said second general retro-reflector means comprises: a first and second fixed mirrors for reflecting the reflected beam back in a same plane as the input/output port; whereby said first fixed mirror reflects the reflected beam off of the tiltable mirror to the second fixed mirror, which reflects the reflected beam back along the same path to said tiltable mirror, said first fixed mirror, the TFF for a second time, and out the input/output port.

6. The TOADM according to claim 1 , wherein said first general retro-reflector comprises: a first lens, and a first mirrored surface located at the focal plane of said first lens; wherein the rotating axis of said tiltable mirror is on another focal plane of said first lens; wherein the optical axis of the first lens intersects the rotating axis of tiltable mirror; and wherein the center of the input optical beam is incident on the rotation axis of said tiltable mirror.

7. The TOADM according to claim 6 , wherein said first lens is a symmetrical lens for reflecting the transmit beam from the TFF back through the TFF a second time in a same plane as the add/drop port.

8. The TOADM according to claim 1 , wherein said second general retro-reflector comprises: a second lens, and a second mirrored surface located at the focal plane of said second lens; wherein the rotation axis of said tiltable mirror is on another focal plane of said second lens; and wherein a center of the input optical beam is incident on the rotation axis of said tiltable mirror.

9. The TOADM according to claim 8 , wherein said second lens is a cylindrical lens defined by an optical axis for directing the transmit beam from the TFF back along a path parallel to the optical axis of the second lens and normal to the second mirrored surface, whereby the second mirrored surface directs the reflected beam straight back through the second lens and off of the TFF a second time in a same plane as the input/output port.

10. The TOADM according to claim 1 , further comprising an angular sensor for measuring the tilt angle of the tiltable mirror; and an optical channel monitor for monitoring the drop beam to ensure the tilt angle of the tiltable mirror is set correctly.

11. The TOADM according to claim 1 , wherein said thin film filter is a hitless thin film filter comprise a filter area and a reflection area; further comprising an optical path switch means to switch the beam from said filter area to reflection area and vice versa, while the tiltable mirror is being rotated.

12. The TOADM according to claim 1 , wherein said thin film filter is a hitless thin film filter comprise a filter area and a reflection area, whose phase and group delay are matched; further comprising an optical path switch means to switch the beam from said filter area to reflection area and vice versa, while the tiltable mirror is being rotated.

13. The TOADM according to claim 11 , wherein the optical path switch means comprises a first rotating block on one side of said TFF for refracting the input optical beam from the filter area to the reflection area, while the rotating mirror is being rotated.

14. The TOADM according to claim 1 , further comprising a first circulator optically coupled to the input/output port having an input port for inputting the input optical beam and an output port for outputting the reflected beam.

15. The TOADM according to claim 2 , further comprising a second circulator optically coupled to the add/drop port having an input port for inputting the add beam and an output port for outputting the transmitted beam.