Free-space multi-port wavelength router with broad...

Details Free-space multi-port wavelength router with broad... Free-space multi-port wavelength router with broad...

1999-10-08

2003-10-21

Chan, Jason (Department: 2633)

Optical communications

Multiplex

Wavelength division or frequency division

C398S082000, C398S084000, C398S079000, C385S024000, C385S015000, C385S031000, C385S033000

Reexamination Certificate

active

06634810

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to wavelength routers for use in fiber optic communications systems and, more particularly, to a wavelength router for directing discrete channels in a wavelength division multiplexed (WDM) optical signal to select output optic ports.
2. Description of the Related Art
Wavelength routers have many applications in WDM networks and can be used, for example, as a single input port device to demultiplex wavelength channels. Such routers can also be used as a multi-input device
10
as shown in
FIG. 1
for providing wrap-around routing to output ports, as is known in the art, and for interconnecting nodes of a network. For example, device
10
in
FIG. 1
has an equal number of input ports
12
(shown as A, B, C, and D) and output ports
14
. When a WDM signal &lgr; having wavelengths &lgr;
1
, &lgr;
2
, &lgr;
3
, &lgr;
4
is input to the router through input fiber A, the wavelengths are routed, as shown, such that &lgr;
1
is output on output fiber
14
A, &lgr;
2
on output fiber
14
B, etc. For wrap-around routing the input signal &lgr; is provided on a different input port (e.g. port
12
B), in which case output port
14
B receives channel &lgr;
1
, output port
14
C receives &lgr;
2
, output port
14
D receives &lgr;
3
and output port
14
A receives &lgr;
4
.
Presently, N×N routers having an equal number of input ports, output ports and wavelengths are constructed using a planar waveguide structure such as an arrayed waveguide grating or Dragone router. Such routers, however, do not operate with multimode fibers or multimode waveguide systems, thereby limiting their utility in local area network applications. Moreover, such routers do not accommodate broad wavelength channels, thus requiring the use of costly narrow and precise lasers for proper operation.
SUMMARY OF THE INVENTION
The present invention is directed to a multi-port wavelength router for directing a WDM optical signal having a plurality of adjacent-in-wavelength channels to select output ports. The WDM signal is provided by or to an input port, which is preferably a linear array of optic fibers, and is directed to a lens. The lens collimates the received WDM signal onto a planar grating which demultiplexes the channels in a first direction by providing angular separation along a first direction to the channels as a function of the channel wavelengths. The demultiplexed signal is directed back through the lens for focusing and then provided to an array of optical elements. The optical element array is positioned so that each element receives a channel, imparts to that channel a spatial displacement along a second direction, and directs the displaced channel back through the lens for re-collimation on the grating. The first direction angular displacement is cancelled out by the grating through the second pass and the spatially displaced channels are then reflected back to the lens which focuses the channels to the output ports. In this embodiment, a linear array of input fibers oriented along the first direction can be used to rout the discrete channels to a two-dimensional array of output fibers.
In another embodiment, an N×N router having an equal number of output ports and input ports is realized by providing an additional second displacement to the channels in a direction angularly offset from the second direction. This is accomplished through use of a reflective element which causes a second pass to occur through the router before the displaced channels are provided to the output ports.
As an alternative to a second pass through a single router, a second router stage positioned at an angle relative to the optical axis of the first router stage may be employed. This further embodiment allows the use of a planar surface device, such as a modulator or add/drop element, disposed between the two router stages to thereby allow for selective manipulation of the individual channels.


REFERENCES:
patent: 5999672 (1999-12-01), Hunter et al.
patent: 6097519 (2000-08-01), Ford et al.
patent: 6108471 (2000-08-01), Zhang et al.
patent: 6204946 (2001-03-01), Aksyuk et al.
patent: 6275630 (2001-08-01), Yang et al.
patent: 6307657 (2001-10-01), Ford
patent: 6337935 (2002-01-01), Ford et al.

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