Systems and methods for providing a three-port reconfigurable optical add-drop multiplexer with an improved edge profile and add/drop flexibility
The technology described herein provides a low-cost three-port reconfigurable optical add-drop multiplexer (ROADM) with an improved edge profile and add/drop flexibility. The technology described herein further provides a tunable spectral filter utilizing two sets of gratings and lenses and a two-axis micro-electro-mechanical system (MEMS) mirror with a selectively shaped cut-out disposed within the middle of the collimated optical path.
1. A tunable filter for use in an optical communications network, comprising:
a pair of gratings;
a pair of transform lenses;
wherein the pair of gratings and the pair of transform lenses are utilized for spatially separating and recombining a multiple wavelength input signal;
a mirror with a cut-out, the cut-out being of a predetermined shape and disposed in between the transform lenses and disposed within in the middle of a collimated optical path, allowing a wavelength, of the multiple wavelength input signal, to pass through, and allowing another wavelength, of the multiple wavelength input signal, to be reflected;
wherein a wavelength, of the multiple wavelength input signal, which passes through the cut-out is a drop signal, and a wavelength, of the multiple wavelength input signal, which is reflected by the mirror is an express signal; and
a two-axis mirror at an input side of the tunable filter, the two-axis mirror used to control the bandwidth and the wavelength of a drop signal by adjusting the angle and position of the multiple wavelength input signal relative to a first grating of the pair of gratings.
2. The tunable filter of claim 1 , wherein the mirror is a micro-electromechanical system mirror with two axes of rotation, one axis representing bandwidth and one axis representing wavelength.
3. The tunable filter of claim 1 , wherein the optical bandwidth becomes wider or narrower as determined by the shape of the cut-out.
4. The tunable filter of claim 1 , wherein the tunable filter is operative for hitless tuning, and hitless tuning is achieved by using a cut-out area based on design rules, moving a dispersed light line of the spatially separated multiple wavelength input signal away from the cut-out area, changing the wavelength and then moving back to an appropriate position to achieve a desired bandwidth.
5. The tunable filter of claim 1 , further comprising:
a cylindric transform lens, the lens being disposed between the two-axis mirror at an input side of the tunable filter and the first grating of the pair of gratings.
6. The tunable filter of claim 1 , wherein the cut-out of a predetermined shape is in the shape of a staircase profile, improving an edge profile of the filter response without changing the optics design and relaxing the tolerances for control of the two-axis mirror.
7. The tunable filter of claim 1 , wherein the cut-out of a predetermined shape is in a varied shape, allowing multiple combinations of add/drop channels, including non-adjacent channels, to be encoded.
8. The tunable filter of claim 7 , further comprising:
a second tunable filter with a cut-out that is in a varied shape that is complementary to the shape of the cut-out in the tunable filter, further improving the flexibility of a ROADM node by allowing a large number of channel combinations to be added or dropped.
9. The tunable filter of claim 1 , wherein the tunable filter is a three-port hitless reconfigurable add-drop multiplexer.
10. The tunable filter of claim 9 , wherein the tunable filter is concatenated with a second three-port hitless reconfigurable add-drop multiplexer, wherein the cut-out of the second three-port hitless reconfigurable add-drop multiplexer is complementary to the cut-out of the three-port hitless reconfigurable add-drop multiplexer, thereby providing a larger number of channel combinations to be added or dropped.
11. A method for filtering an optical signal utilizing a tunable filter, comprising:
providing a multiple wavelength input signal;
utilizing a tunable filer comprising a pair of gratings and a pair of transform lenses, wherein the pair of gratings and the pair of transform lenses are spatially separating and recombining the multiple wavelength input signal;
utilizing a mirror with a cut-out, the cut-out being of a predetermined shape and disposed in between the transform lenses and disposed within in the middle of a collimated optical path, allowing a wavelength, of the multiple wavelength input signal, to pass through, and allowing another wavelength, of the multiple wavelength input signal, to be reflected;
wherein a wavelength, of the multiple wavelength input signal, which passes through the cut-out is a drop signal, and a wavelength, of the multiple wavelength input signal, which is reflected by the mirror is an express signal; and
utilizing a two-axis mirror at an input side of the tunable filter, controlling control the bandwidth and the wavelength of a drop signal by adjusting the angle and position of the multiple wavelength input signal relative to a first grating of the pair of gratings.
12. The method for filtering an optical signal utilizing a tunable filter of claim 11 , wherein the mirror is a micro-electromechanical system mirror with two axes of rotation, one axis representing bandwidth and one axis representing wavelength.
13. The method for filtering an optical signal utilizing a tunable filter of claim 11 , wherein the optical bandwidth becomes wider or narrower as determined by the shape of the cut-out.
14. The method for filtering an optical signal utilizing a tunable filter of claim 11 , wherein the tunable filter is operative for hitless tuning, and hitless tuning is achieved by using a cut-out area based on design rules, moving a dispersed light line of the spatially separated multiple wavelength input signal away from the cut-out area, changing the wavelength and then moving back to an appropriate position to achieve a desired bandwidth.
15. The method for filtering an optical signal utilizing a tunable filter of claim 11 , further comprising:
utilizing a cylindric transform lens, the lens being disposed between the two-axis mirror at an input side of the tunable filter and the first grating of the pair of gratings.
16. The method for filtering an optical signal utilizing a tunable filter of claim 11 , wherein the cut-out of a predetermined shape is in the shape of a staircase profile, improving an edge profile of the filter response without changing the optics design and relaxing the tolerances for control of the two-axis mirror.
17. The method for filtering an optical signal utilizing a tunable filter of claim 11 , wherein the cut-out of a predetermined shape is in a varied shape, allowing multiple combinations of add/drop channels, including non-adjacent channels, to be encoded.
18. The method for filtering an optical signal utilizing a tunable filter of claim 17 , further comprising:
utilizing a second tunable filter with a cut-out that is in a varied shape that is complementary to the shape of the cut-out in the tunable filter, further improving the flexibility of a ROADM node by allowing a large number of channel combinations to be added or dropped.
19. The method for filtering an optical signal utilizing a tunable filter of claim 11 , wherein the tunable filter is a three-port hitless reconfigurable add-drop multiplexer.
20. The method for filtering an optical signal utilizing a tunable filter of claim 19 , further comprising:
concatenating the tunable filter with a second three-port hitless reconfigurable add-drop multiplexer, wherein the cut-out of the second three-port hitless reconfigurable add-drop multiplexer is complementary to the cut-out of the three-port hitless reconfigurable add-drop multiplexer, thereby providing a larger number of channel combinations to be added or dropped.