Optical switch

Details Optical switch Optical switch

2000-04-26

2002-09-03

Kim, Ellen E. (Department: 2874)

Optical waveguides

With optical coupler

Switch

C385S016000

Reexamination Certificate

active

06445845

ABSTRACT:

This application is based on Japanese Patent Application Nos. 11-119386 (1999) filed Apr. 27, 1999 and 11-139529 (1999) filed May 20, 1999 in Japan, the contents of which are incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical switch for an optical add drop multiplexer (OADM), an optical cross-connection (OXC) or an auxiliary system switching. The optical switch is used for light path routing/switching in a subscriber optical network such as a fiber to the desk (FTTD) or an optical local area network (LAN), and in an infrastructure optical network system such as optical interconnections in a communication processing apparatus.
Further, the present invention relates to an optical switch that is polarization insensitive within an optical communication wavelength bandwidth between 1.3 and 1.65 &mgr;m and an optical part comprising this optical switch.
2. Description of the Related Art
In these days of the advent of multimedia communication, much attention is being paid to a wavelength division multiplexing (WDM) type network in which all relevant operations such as switching and routing are performed using light, in order to accommodate a future increase in demands for transmission capacity. A key device for the WDM type network is an optical switch for the OADM or an optical switch for the OXC. The optical switch is an essential device providing flexibility and reliability for a subscriber optical network such as a FTTD or a LAN, and an infrastructure optical network system such as optical interconnections in a communication processing apparatus.
In a view of both good connectivity with optical fibers and mass production, thermo-optics (TO) switches using silica-based planar lightwave circuits (PLC) technology are generally used as optical switch for OADM or OXC. These TO switches are capable of switching in several microseconds. However, they have various problems; that is, they must be continuously supplied with an electric voltage in order to maintain the ON switching state (they have no self-latching function). Both their extinction ratio (>35 dB) and their crosstalk (<−35 dB) are not enough for the optical network systems, and their size are also large.
In contrast, mechanical switches are superior to the TO switch in the point of that they have the self-latching function and can easily achieve a high extinction ratio (>50 dB) and a low crosstalk (<−50 dB).
By way of examples, a mechanical switch has been proposed, which can switch a light path because mercury sealed in its slit is moved by powering up micro thin-film electrodes provided near a slit formed at a crossing point of optical waveguides crossing each other in an optical waveguide layer (Makoto Sato, “Electro capillarity Optical Switch,” IEICE TRANS. COMMUN., VOL. E77-B, No. 2, PP. 197-203, FEBRUARY 1994). In addition, similar to the mechanical switch, an optical switch has been proposed, which can switch the light path because a magnetic fluid, an optical reflective fluid, an optical transmissible fluid sealed in its slit are moved by using a magnetic field generator provided near the slit, similar to the above mechanical switch (Yasuhide Nishide et al., “Waveguide Type Optical Switch,” Japanese Patent Application No. 5-8854 (1993) [Official Gazette of Japanese Patent Application Laid-open No. 6-222294 (1994)]). Furthermore another optical switch similar to a mechanical switch has been proposed, which can switch the light path because refractive index matching liquid sealed in its slit is moved by heating micro thin-film heaters provided near the slit, similar to the above one (Hiroyoshi Togo et al. “Optical Switch and Method of Fabricating the Switch,” Japanese Patent Application Laid-open No. 10-333062 (1998]). An optical switch using a number of such kinds of optical switches has also been proposed.
The conventional mechanical switches, however, switch the light path by utilizing the reflection wall on only one side of the slit fabricated at the crossing point of the crossing optical waveguides.
FIGS. 5A and 5B
show an example of an optical selector switch for a light path switching comprised of a conventional mechanical switch. In
FIG. 5A
, reference numeral
1
designates crossing optical waveguides, reference numeral
2
designates a slit which crosses in a diagonal direction at each crossing point of the optical waveguides
1
, and reference numeral
3
designates refractive index matching liquid sealed in the slit
2
that has a refractive index equal to that of cores of the optical waveguides
1
.
Specifically, in the normal (transmitting) state shown in
FIG. 5A
, when the reflective index matching liquid
3
is present at the crossing point of the optical waveguides
1
, optical incident signals from an input end a of the crossing optical waveguide (in a horizontal direction of the drawing) pass straight through the slit
2
and are emitted to an output end A, as shown by the broken line. However, in the switching (reflecting) state in
FIG. 5B
, when the refractive index matching liquid
3
moves away from the crossing point of the optical waveguides
1
, optical incident signals from the input end a are reflected by the total internal reflection on one side wall of the slit
2
near the input end a, and then emitted to an output end B as shown as a dot-line of the drawing.
In addition, as shown in
FIG. 5A
, when the refractive index matching liquid
3
is present at the crossing point of the optical waveguides
1
, optical incident signals from an input end b of the crossing optical waveguide pass straight through the slit
2
and are emitted to the output end B. However, as shown in
FIG. 5B
, when the refractive index matching liquid
3
moves away from the crossing point of the optical waveguides
1
, optical incident signals from the input end b cannot be totally reflected and propagated to the output end A because the side wall of the slit
2
near the input end b side is offset from an ideal reflection plane (a vertical plane located on a bisector of an interior angle at the crossing point of the optical waveguides
1
) toward the input end b by a distance corresponding to the width of the slit
2
. Thus, in this case, due to a decrease in an amount of the light propagated from the input end b to the output end A, the difference between the intensity of the optical signal outputted from the output end A and the intensity of the optical signal outputted from the output end B increases.
To eliminate the difference in optical signal intensity between the output ends A and B, an additional system for amplifying or attenuating the optical signal reflected by or passed through the slit is required, so that the entire structure of the optical switch becomes substantially complicated. This is disadvantageous in that fabrication cost of the optical switch increases and in that the price of the optical switch itself rises.
Thus, a single conventional mechanical switch provides only two inputs and two outputs (two bar functions) in the transmitting state, provides one input and one output (one cross function) in the reflecting state, and cannot work as 2×2 switch having two bar functions and two cross functions.
Accordingly, to construct a 2×2 optical switch using conventional mechanical switch elements, three or more mechanical switch elements, must be combined together in a form as shown in
FIGS. 6A and 6B
.
FIG. 6A
shows the normal (transmitting) state, while
FIG. 6B
shows the switching (reflecting) state. Moreover, to construct an optical array or a matrix switch using N combined 2×2 optical switches, 3N or more of the above 2×2 optical switches must be combined together. Consequently, to construct a large-scale optical matrix switch, a large number of switches are conventionally required, preventing size reduction.
As described above, the conventional optical switches are disadvantageous in that a 2×2 optical switch cannot be constructed using

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