1. Field of the Invention
The present invention relates to a free-space optical switch for switching an optical signal path in fields of optical communication, information processing, etc.
It is to be noted that in this specification, the term xe2x80x9cmicromirrorxe2x80x9d represents a micro-electro-mechanical system (MEMS) mirror.
2. Description of the Prior Art
FIG. 11 shows an arrangement of a free-space optical switch described at page 168 in a tutorial xe2x80x9cOptical-Layer Networking: Opportunities for and Progress in Lightwave Micromachinesxe2x80x9d by L. Y. Lin et al. in proceedings of the 25th Optical Fiber Communication Conference (OFC 2000). In FIG. 11, a signal light ray incident from an input port array 11 is reflected at a desired angle by an input micromirror array 21 and is propagated to an output port array 12 through angular control of an output micromirror array. Namely, a signal light array 31 incident from a port 111 in the input port array 11 is initially reflected at a desired angle by a micromirror 211 in the input micromirror array 21 and is propagated to a desired port 121 in the output port array 12 through angular control of a micromirror 221 in the output micromirror array 22.
Then, as a switching function of the optical switch, the output port 121 is switched to an output port 122. To this end, the micromirror 211 of the input micromirror array 21 undergoes angular change so as to propagate to a micromirror 222 of the output micromirror array 22 the signal light ray 31 from the input port 111 and the micromirror 222 performs corresponding angular control of the signal light ray 31 so as to propagate the signal light ray 31 to the output port 122 such that the optical path is switched. In angular control of the micromirrors in switching of the optical path, when the optical path proceeds from the micromirror 211 at one diagonal end of one micromirror array 21 in the opposing micromirror arrays 21 and 22 to the micromirror 222 at the other diagonal end of the other micromirror array 22, the micromirror 211 undergoes a maximum angular change.
Meanwhile, FIG. 12 shows an arrangement of a free-space optical switch described at page 167 of the above mentioned tutorial. In FIG. 12, a fixed mirror 4 is arranged and the input port array 11 and the output port array 12 of FIG. 11 are integrally formed into a port array 13, while the input micromirror array 21 and the output micromirror array 22 of FIG. 11 are integrally formed into a micromirror array 23 such that a function similar to that of FIG. 11 is fulfilled. Also in the arrangement of FIG. 12, when the optical path proceeds from the micromirror 211 to a micromirror 223 which are, respectively, disposed at one diagonal end and the other diagonal end in the integral micromirror array 23, the micromirror 211 undergoes a maximum angular change.
In the conventional optical switches of FIGS. 11 and 12, the micromirrors 211, 221, 222 and 223 should be subjected to angular control. However, the micromirror produced by micromachine technology has such a drawback that it is structurally difficult to cause a large angular change owing to difficulty in materializing a large scale in a vertical direction of the micromirror in comparison with that in a horizontal direction of the micromirror in thin film deposition technology, etching technology or the like.
Meanwhile, the micromirror is disadvantageous in that since it is difficult to produce a large driving force such as electrostatic force, magnetic field of the like in the vertical direction of the micromirror in terms of its driving principle, it is difficult to effect a large angular change.
Accordingly, an essential object of the present invention is to provide, with a view to eliminating the above mentioned drawbacks of prior art free-space optical switches, a free-space optical switch which is highly reliable by minimizing amount of angular change of an input micromirror or is more compact by minimizing an overall optical path length in case the amount of angular change of the input micromirror is identical on the contrary.
In order to accomplish this object of the present invention, a free-space optical switch according to the present invention comprises: a micro-electro-mechanical system (MEMS) mirror array for switching an optical transmission path, in which an input MEMS mirror array and an output MEMS mirror array confronting an input fiber port array and an output fiber port array, respectively are provided, wherein the input MEMS mirror array and the output MEMS mirror array are formed integrally with each other; wherein instead of equally dividing the MEMS mirror array into the input MEMS mirror array and the output MEMS mirror array simply by a single boundary line, one or both of the input MEMS mirror array and the output MEMS mirror array are further divided so as to be arranged.