Thermo-optical switch

Details Thermo-optical switch Thermo-optical switch

1999-10-25

2001-08-28

Sikder, Mohammad (Department: 2872)

Optical waveguides

With optical coupler

Switch

C385S015000, C385S014000

Reexamination Certificate

active

06282335

ABSTRACT:

BACKGROUND OF THE INVENTION
In currently employed optical communications networks, messages are transmitted via optical fibres whereas the switching of the messages at the network nodes takes place electrically as previously. The messages incoming in the form of optical signals are for this purpose converted by suitable converters into electric signals, switched electrically, and then re-converted into optical signals.
In future optical communications networks, the switching is also to take place optically. In this context one often refers to “transparent” optical communications networks, as the message is transmitted from transmitter to receiver continuously as a light signal. Optical switches are of particular significance in such communications networks. Their function is to switch-over incoming optical signals to one of a plurality of outputs. Optical switches are required to facilitate high switching speeds, to attenuate passing-through light to the least extent possible, and also to be cost-efficient and reliable.
A number of different concepts have been developed for optical switches. Thus for example EP-B1-0 494 768 has disclosed an optical switch wherein a plurality of optical waveguides intersect at right angles in one plane. The intersection points are provided with a groove extending diagonally to the optical waveguides. An oil can be robotically introduced into this groove and sucked out again. Depending upon whether oil is present in the groove or not, a light beam passes through the intersection point or is laterally deflected into the intersecting waveguide. In the case of this known switch, it is possible to form switching matrices with a very large surface area; however the disadvantage exists that the switching speeds are very low due to the required robotic movements.
Another concept for an optical switch is known from an article by N. Keil et al. entitled “Polymer Waveguide Optical Switch With ←40 dB Polarisation Independent Crosstalk”, Electronic Letters, Mar. 28, 1996, Vol. 32, No. 7, p. 655-657. The switch described therein is based on the principle of an optical directional coupler. In directional couplers two optical waveguides arranged in one plane extend at a short distance one beside another over a coupling length L. An essential feature of the proposed concept is that the optical waveguides consist of a polymer which exhibits a considerably more marked thermo-optical effect than glass for example. This means that even small temperature changes strongly affect the refractive index of the polymer. With the aid of heating electrodes arranged in the region of the coupling length, the temperature of the two optical waveguides, and thus their refractive index, can be separately controlled. In this way the effective coupling length can be set such that light guided in a waveguide either remains in this waveguide (straight position) or is coupled into the adjacent waveguide (intersecting position). Switches of a higher order (e.g. 4×4 switches) are obtained by cascading a plurality of such 2×2 switches. It is disadvantageous however that in the case of this switch light is guided only in polymer waveguides which, despite having favourable thermo-optical properties, relatively strongly attenuate light of the wavelengths normally used.
JP-1-200 233 A Abstract has disclosed an optical switch in which two different waveguide channels can be operated using one electrode. Here the channels are connected with an intersection.
SUMMARY OF THE INVENTION
Therefore the object of the invention is to provide an optical switch which permits high switching speeds, attenuates passing-through light to the least possible extent, and is simple to produce.
In transparent optical communications systems, optical switches are required to switch-over incoming optical signals to one of a plurality of outputs. The object of the invention is to provide an optical switch which permits high switching speeds, attenuates passing-through light to the least possible extent, and moreover is cost-efficient and reliable.
In accordance with the invention, a plurality of glass waveguides (GWL
1
. . . GWL
4
) are arranged in a first plane. In an overlying plane there is arranged at least one polymer waveguide (PWLA) which forms an acute angle with the glass waveguides. Where the polymer waveguide intersects the underlying glass waveguides, vertical coupling regions are formed. The coupling properties can be selectively influenced with the aid of heating electrodes (EA
1
. . . EA
4
; EB
1
. . . EEB
4
). In order to switch light from one glass waveguide into another, the temperature of the vertical coupling regions is set such that light is coupled up from the one glass waveguide into the polymer waveguide, guided therein, and coupled down into the desired glass waveguide in another coupling region.
A number of glass waveguides are arranged in a first plane. In an overlying plane there is arranged at least one polymer waveguide which forms an acute angle with the glass waveguide. Vertical coupling regions are formed where the polymer waveguide intersects the underlying glass waveguides. The coupling properties in these regions can be influenced by reducing the temperature of the polymer waveguide core therein. For this purpose heating electrodes are arranged on the upper side of the switch.
If light is to be switched from one glass waveguide into another, the temperature of the vertical coupling regions is set such that light is coupled up from the one glass waveguide into the polymer waveguide, guided therein, and coupled down into the desired glass waveguide in another coupling region.
The switch according to the invention combines the following advantages:
a) As the thermo-optical effect in polymers is very marked, only small switching powers are required. The quantity of heat to be discharged is correspondingly small.
b) Due to the combination of glass- and polymer waveguides according to the invention, the attenuation of the switch is very low. This is due in particular to two causes:
i) Light is mainly guided in glass waveguides which have a very low attenuation in the wavelength ranges used for optical communications. In the polymer waveguides in which the attenuation is higher, the light is guided only across a short distance.
ii) In known switches based on the principle of directional couplers, the coupling region is located in one plane. The coupling region is the region in which the two optical waveguides are arranged at such a close distance relative to one another that cross-coupling is possible. This close arrangement inevitably requires the optical waveguides to possess curved portions. However, curves disadvantageously affect the properties of the waveguide as either light losses occur or the waveguide cross-section must be reduced by setting a higher refractive index difference between waveguide core and waveguide cladding. A reduced waveguide cross-section leads however to mis-matching of the modal fields upon the coupling of the waveguide to an optical fibre, whereby the attenuation properties of the switch are impaired. On the other hand, the switch according to the invention can also be constructed without curved portions as here polymer waveguide and glass waveguides intersect in two different planes.
c) Costly materials, such as for example lithium niobate, gallium arsenide or indium phosphide on which many known switches are based, are not required.
Here the terms “glass waveguide” and “polymer waveguide” relate only to the corresponding waveguide cores. A glass waveguide is thus an optical waveguide whose waveguide core consists of glass. Similar applies to the at least one polymer waveguide. For the functioning of the switch according to the invention, the material from which the waveguide cladding layers are in each case composed is basically immaterial. It should merely be ensured that here again the difference in refractive index between waveguide core and waveguide cladding required for the optical wave guidance is adhered to.
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