Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2000-05-10
2002-05-28
Mack, Ricky (Department: 2873)
Optical waveguides
With optical coupler
Switch
Reexamination Certificate
active
06396974
ABSTRACT:
This application is based on Patent Application No. 11-129406(1999) filed May 11, 1999 in Japan, the content of which is incorporated hereinto by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical switch for use in an optical communication system or the like for routing or switching an optical path, and is particularly effective in application to a large-scale matrix optical switch.
2. Description of the Related Art
A variety of optical switches have been proposed, in which a refractive index-matching liquid with a refractive index substantially equal to that of the optical waveguides is sealed in slits formed at crossing points of crossing optical waveguides and moved to switch optical paths at the crossing points of the optical waveguides.
For example, the optical switch disclosed in Japanese Patent Application Laid-open No. 9-133932 (1997) has m optical waveguides not crossing one another in a substrate and n optical waveguides not crossing one another therein, wherein the m optical waveguides cross the n optical waveguides. This optical switch further includes slits each having wall surfaces inclined at a predetermined angle relative to optical axes of these optical waveguides and means (micro heaters) each provided at a corresponding one of the crossing points for generating heat near the corresponding slit. An optically transparent liquid having a refractive index approximate to the refractive index of the optical waveguides is sealed in a part of each of the slits. This optical switch switches optical paths by allowing the micro heaters to generate heat to move the liquid within the slits.
FIG. 1
is an electric wiring diagram of a conventional optical switch according to the above publication.
One element
31
in the illustrated matrix comprises two micro heaters
32
a
,
32
b
connected in series to different diodes
33
a
,
33
b
, and the two series circuits are connected in parallel so that one of the diodes has a polarity opposite to the other diode. One of two common connected nodes of each series circuit is connected to an upper layer wiring, while the other common connected node is connected to a lower layer wiring.
In addition, Japanese Patent Application Laid-open No. 10-73775 (1998) discloses a method for assembling the optical switch proposed by the above publication. Specifically, as shown in
FIG. 2
, a silica-based optical waveguide layer
22
is formed on a substrate
21
made of silicon, and a thin metal film such as titanium or chromium with relatively high resistance and another thin metal film such as gold with low resistance are deposited on the optical waveguide layer
22
, utilizing the sputtering method or the vacuum evaporation method. Then, a combined method of a photolithography process and a dry etching process is used for treating both the thin films to produce micro heaters
26
, electric wirings
25
, and a slit, and a silicon layer is then deposited on the optical waveguide layer
22
. Subsequently, a substrate
27
made of Pyrex Glass (trade mark) is bonded to the silicon layer with anodic bonding so as to cover the slit, thereby forming a slit
24
at a crossing point between optical waveguides
23
. On the other hand, an injection path
29
is formed in a bonding surface of the optical waveguide layer
22
or the substrate
27
. Thus, the optical switch according to the above publication is obtained by precisely injecting an appropriate amount of refractive index-matching liquid
31
into the slit
24
, through an injection port
30
of the injection path
29
by a method such as pressure control and then blocking the injection port
30
with epoxy resin or the like.
In applying such a conventional optical switch to a large-scale optical matrix switch, the following problems occur.
The above matrix requires at least two micro heaters
26
in one element of the matrix switch. That is, the at least two micro heaters
26
are required to move the refractive index-matching liquid
31
within one slit
24
. Since three electric wirings
25
are required to independently supply power to the micro heaters
26
of one element, (2n+1) electric wirings
25
are required for an optical switch comprising n elements arranged in a single row even if a common wiring is used as grounds for the micro heaters
26
. Furthermore, (2n+1)×m electric wirings
25
are required for an (n×m) optical switch with n elements arranged in m rows.
In addition, to form the optical matrix switch on an electric circuit board, together with a drive circuit for the micro heaters
26
or another circuit mounted thereon, electric wirings
25
of the optical switch must be arranged on an end surface of the optical waveguide layer
22
so that the electric wirings
25
of the optical switch and electric wirings of the electric circuit board can be connected together utilizing the wire bonding method or the like. Thus, the electric wirings
25
must be arranged in such a manner that sufficiently large intervals are provided between the elements, significantly increasing in size of the optical switch. Consequently, it is difficult to manufacture the electric wirings
25
or the like utilizing a combined method of photolithography and dry etching.
In addition, in the above optical switch, to arrange n×m elements on the optical waveguide layer
22
and to form an injection port
30
corresponding to each slit
24
in each of the side wall surfaces of the substrate
27
, large intervals are required between the elements and each slit must be covered by anodically bonding a plurality of substrates
27
together, thereby requiring a large amount of time and labor for manufacturing. On the other hand, to form an injection port
30
corresponding to each slit
24
in a top surface of the substrate
27
, injection ports
30
penetrating the optical waveguide layer
22
in a fashion corresponding to optical waveguides
23
formed at a pitch of 250 &mgr;m must be densely formed in a substrate
27
of thickness 0.3 mm, for which anodic bonding can be easily carried out. Consequently, formation of the injection ports
30
is very difficult even with dry etching or the micro blasting method. Then, if the thickness of the substrate
27
is reduced to facilitate manufacturing, the substrate
27
may be broken during anodic bonding.
On the other hand, in supplying power to the micro heaters
32
a
,
32
b
in
FIG. 1
, power consumption may increase rapidly according to increasement in wiring length due to the augmented scale of the switch.
As another problem, current may leak at wirings other than those leading to the desired micro heaters or at other micro heaters, thereby preventing power from being supplied only to the desired micro heaters for the purpose of driving the liquid. This problem grows serious as the switch scale enlarges.
In addition, if the above optical switch has an n≠m matrix configuration, the leakage current differs between a row direction and a column direction, whereby other micro heaters may be heated to cause the switch elements to malfunction. Even without the malfunction of the switch elements, the leakage current may disadvantageously vary the optical characteristics of the optical switch.
The present invention provides an optical switch that can solve these problems, and it is a first object of the present invention to provide an optical switch that facilitates size reduction while improving productivity even if it is of a matrix type.
It is a second object of the present invention to provide an optical switch that can efficiently supply power to desired micro heaters while reducing power consumption.
It is a third object of the present invention to provide an optical switch that can prevent malfunctions and variations in optical characteristics caused by leakage current even if it has an n≠m matrix configuration.
It is a fourth object of the present invention to provide an optical switch that can eliminate the adverse effects of leakage current.
SUMMARY OF THE INVENTION
T
Makihara Mitsuhiro
Sato Makoto
Shimokawa Fusao
Frank Robert J.
Harrington Alicia M
Nippon Telegraph & Telephone Corporation
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