Optical waveguides – With optical coupler – Switch
Reexamination Certificate
2000-06-21
2002-02-05
Healy, Brian (Department: 2874)
Optical waveguides
With optical coupler
Switch
C385S002000, C385S004000, C385S008000, C385S043000, C385S045000, C385S049000
Reexamination Certificate
active
06345131
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an optical switch, and more particularly to a thermo-optic switch using a small drive power while exhibiting a reduction in the coupling loss caused by the coupling to optical fibers and a switch speed of several hundred microseconds or less. The present invention also relates to a method for manufacturing the thermo-optic switch and a method for changing an optical line switching using the thermo-optic switch.
2. Description of the Related Art
Examples of optical switches, thermo-optic switches, or electro-optic switches, incorporated by reference herein, are found in U.S. Pat. No. 5,121,450 to Elliot Eichen et al. entitled
Fiber Optical Y-Junction
, U.S. Pat. No. 5,418,868 to Leonard G. Cohen et al. entitled
Thermally Activated Optical Switch
; U.S. Pat. No. 5,623,566 to Hyung J. Lee et al. entitled
Network With Thermally Induced Waveguide
, U.S. Pat. No. 5,970,186 to John T. Kenney et al. entitled
Hybrid Digital Electro-Optic Switch
, and U.S. Pat. No. 6,067,387 to Min Cheol Oh et al. entitled
Electro-Optic Polymer Waveguide Device For Decreasing Driving Voltage And An Optical Loss And Method Of Making The Same.
Generally, a thermo-optic switch is a device for changing an optical line using a variation in the refractive index of the material of the device depending on a variation in temperature applied to it, the material of the device. Thermo-optic switches are mainly classified into a Mach-Zehnder interference type, a directional coupler type, and a digital type.
FIG. 1
illustrates an example of a digital thermo-optic switch. As shown in
FIG. 1
, the digital thermo-optic switch includes a substrate
10
, a lower clad layer
120
, a core layer
130
, an upper clad layer
140
, and a heater
150
.
FIG. 2
is a schematic view illustrating the operation principle of a digital thermo-optic switch using a mode evolution principle. The digital thermo-optic switch has a branched waveguide structure having branched waveguides
210
. Electrodes
220
, which are made of a metal, such as gold, exhibiting a superior thermal conductivity, are formed on each branched waveguide
210
. When heat is applied to one of the electrodes
220
, it is transferred from the electrode
220
to the branched waveguide
210
arranged beneath the electrode
220
, so that the branched waveguide
210
exhibits a reduced effective refractive index. As a result, a difference of effective refractive index occurs between the branched waveguides
210
. Accordingly, an input light is switched to the branched waveguide
210
in accordance with a mode evolution thereof. In Mach-Zehnder interference or directional coupler type thermo-optic switches using an inter-mode interference phenomenon, a light switching operation is achieved by virtue of a line length difference between two branched waveguides resulting from a difference between the effective refractive indices of those branched waveguides.
Thermo-optic switches may be implemented using waveguides having an embedded structure or a rib structure. A thermo-optic switch, which has the embedded structure, is manufactured using materials exhibiting a refractive index difference ranged from 0.3% to 0.6% in order to reduce the coupling loss caused by the coupling to optical fibers. Typically, the thermo-optic switch has a core thickness of 6 to 8 &mgr;m and a total waveguide thickness of 25 to 40 &mgr;m. In this case, an optical fiber coupling loss of 0.5 dB/facet or less is exhibited.
FIG. 3
illustrates a cross section of the thermo-optic switch having the embedded structure. As shown in
FIG. 3
, the thermo-optic switch includes a heat sink
310
, a clad
320
, branched waveguide cores
330
, and electrodes
340
. In such a thermo-optic switch having the above mentioned embedded structure, heat applied to one of the electrodes
340
is transferred to an associated one of branched waveguide cores
330
in a thickness direction in an isotropic fashion. For this reason, where the thermo-optic switch has a large total waveguide thickness, heat is not only transferred to a desired one of the waveguides, but also transferred to the remaining waveguide in a considerable amount. As a result, it is difficult to obtain an efficient thermo-optic effect. Furthermore, the transfer of heat to the heat sink
310
arranged beneath the waveguides is carried out at a lowered rate. For this reason, the time taken for the applied heat to be completely discharged out of the waveguides is also unacceptably lengthened. In other words, the switching speed of this type of thermo-optic switch is too slow.
FIG. 4
is a cross-sectional view illustrating a thermo-optic switch having the rib structure. As shown in
FIG. 4
, the thermo-optic switch includes a heat sink
410
, a lower clad
420
, a core
430
, an upper clad
440
, and electrodes
450
. In the case of thermo-optic switches, which have the rib structure, materials exhibiting a refractive index difference ranged from 1% to 10% are typically it used. Where materials exhibiting a high refractive index difference are used to manufacture a thermo-optic switch having the rib structure, it is possible to obtain a total waveguide thickness of 15 &mgr;m or less because the clad of the thermo-optic switch affected by an evanescent field formed in the thickness direction of the waveguides can be formed to be very thin. In this case, accordingly, heat applied to one of the electrodes
450
is transferred only to a desired one of the waveguides of core
430
. As a result, it is possible to greatly reduce the transfer of heat to the remaining waveguide. Since the total waveguide thickness corresponds to ½ the total waveguide thickness in the general embedded structure, the distance between each electrode and the heat sink is correspondingly short. As a result, an easy heat discharge is obtained. In addition, the drive power used for the thermo-optic switch can be considerably reduced. There is a disadvantage, however, in that a large coupling loss occurs in the thermo-optic switch having the rib structure due to a mode size difference from optical fibers to which the thermo-optic switch is coupled. For this reason, it is difficult to manufacture a thermo-optic switch having a small coupling loss.
As is apparent from the above description, thermo-optic switches, which have an embedded structure or a rib structure, have the following problems. That is, in the case of a thermo-optic switch having the embedded structure, which has an advantage in that the coupling loss caused by the coupling to optical fibers can be reduced to 0.5 dB/facet or less, it is difficult to achieve an efficient switching operation because the distance between each electrode and each associated waveguide is considerably large because of a large total waveguide thickness of 25 to 40 &mgr;m. As a result, the thermo-optic switch exhibits a relatively low switching speed. In the case of a thermo-optic switch having the rib structure, it can have a small total thickness of 10 &mgr;m or less by virtue of a high refractive index difference exhibited in the rib structure. Accordingly, the drive power used in the thermo-optic switch can be reduced, as compared to that used in the thermo-optic switch having the embedded structure. Also, there is an improvement in switching speed. However, the thermo-optic switch having the rib structure has a disadvantage in that a large coupling loss occurs due to a mode size difference from optical fibers to which the thermo-optic switch is coupled. For this reason, it is difficult to manufacture a proficient thermo-optic switch having a small coupling loss.
SUMMARY OF THE INVENTION
Therefore, an object of the invention is to provide an improved thermo-optic switch.
Another object of the invention is to provide a thermo-optic switch which has a rib structure exhibiting a coupling loss, caused by the coupling to optical fibers, reduced to 0.5 dB/facet or less and having a reduced distance between each electrode thereof and a heat sink thereof,
Jang Woo-Hyuk
Kim Hyun-Ki
Kim Jung-Hee
Lee Yong-Woo
Rhee Tae-Hyung
Bushnell , Esq. Robert E.
Healy Brian
Samsung Electronics Co,. Ltd.
Wood Kevin S
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