Thermooptical modulator

Details Thermooptical modulator Thermooptical modulator

2000-04-24

2001-09-25

Epps, Georgia (Department: 2873)

Optical: systems and elements

Optical modulator

Light wave temporal modulation

C359S245000, C359S237000, C385S001000, C385S002000, C385S008000

Reexamination Certificate

active

06295158

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a thermooptical modulator with a wave guide having a switching section, a refracting section bordering the switching section and extending transversely to the signal propagation direction in the wave guide and a first heating element extending in the refracting section along its boundary with the wave guide. A thermooptical modulator of this type was disclosed at the conference entitled “Photonics West-Optoelectronics 99” on Jan. 25, 1999 in San Jose, Calif., U.S.A. by W. Bernhard, R. Müller-Fiedler, T. Pertsch and C. Wächter. This lecture was reported after that in the Proceedings SPIE Volume 3620.
This known modulator is based on the following principle of operation. A wave guide mode is guided in a signal propagation direction to the boundary of a wave guide through total reflection. There, where the wave guide borders the refracting section, a total reflection occurs, at least on one side of the wave guide; the mode propagates in the refracting section; and no noteworthy light intensity emerges into the section of the wave guide, where it separates again from the refracting section. In its resting state this type of structure is practically impenetrable for the mode.
In order to be able to modulate the intensity of the light passing through the structure, a heating element is provided along the boundary between the wave guide and the refracting section. If this refracting section is heated in the vicinity of the boundary, the refractive index of this section is decreased, so that the mode propagates in the wave guide, also in the refracting section, and passes through the modulator without a reduction in intensity or with little intensity reduction. The transmission of the structure may thus be controlled in a simple way by turning the heating element on and off.
Polymeric material having a noteworthy or marked thermooptic effect can be used as the material for the wave guide and the bending section. A thermooptic effect means that its index of refraction changes significantly with changing temperature.
However these polymeric materials do not completely relax into their initial state after their temperature is returned to its initial value after a temperature change so that a small residual index of refraction change remains even after the temperature is returned to its initial value. Because of this residual index of refraction change a portion of the light passes through the modulator, even when the heating element is turned off. For engineering applications, especially with integrated optical circuits for optical telecommunications networks, however a rapid and complete suppression of the signal to be modulated and a rapid and complete shut off of the modulator are required.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a thermooptical modulator of the above-described type that does not suffer from the above-described disadvantage.
It is another object of the present invention to provide a thermooptical modulator of the above-described type that has a reproducible and rapid switching time between a state in which it is completely conducting and another state in which it is completely non-conducting.
These objects, and others, which will be made more apparent hereinafter, are attained in a thermooptical modulator with a wave guide having a switching section, a refracting section bordering the switching section and extending transversely to the signal propagation direction in the wave guide and a first heating element extending on the refracting section along its boundary with the wave guide.
According to the invention a second heating element is provided in addition to the first heating element and this second heating element extends on the wave guide along the boundary.
A thermooptical modulator is provided by the invention, which can be switched from a practically completely permeable state so that it is practically completely impenetrable in the shortest possible time. For this purpose a second heating element is provided, which extends along the boundary of the refracting section on the wave guide. When the modulator is switched from a penetrable to an impenetrable state, the first heating element is turned off in the usual manner, so that the boundary of the refracting section cools and its refractive index decreases approximately to that of the wave guide bordering it. The original value of the refractive index is however not exactly reached again by the cooling. In order to perform a complete adjustment or matching in the shortest possible time, the second heating element can be turned on, which heats the wave guide at least in its switching section bordering the refracting section. This leads to a reduction of the index of refraction of the wave guide in the switching section. As soon as the index of refraction reaches that of the adjacent portion of the refracting section or exceeds it, light can again pass substantially unhindered into the refracting section and the modulator is again impenetrable.
According to a preferred embodiment the first heating element extends transversely to the signal propagation direction only over a part of the width of the refracting section. When the first heating element is put into operation in this modulator and the second heating element compensates for the index of refraction difference at the boundary between the wave guide and the index of refraction section, a transition zone arises on the side of the first heating element facing the wave guide, in which the index of refraction changes so that light scattered from the wave guide into the index of refraction section is then directed back toward it. In order to avoid this a third heating element is provided appropriately on the side of the first heating element facing away from the second heating element, which can be operated in order to compensate for the refraction index difference in this transitional region and to avoid reflection at this boundary zone.
The modulator appropriately includes an additional driver circuit which receives signals for turning on and turning off the modulator and provides the heating element with energy in a suitable manner.


REFERENCES:
patent: 4270847 (1981-06-01), Meyer
patent: 5009483 (1991-04-01), Rockwell, III
patent: 5657148 (1997-08-01), Feuer
“Cross Reduction in Switching Network by Asymmetrical On-off Switches” by W. Bernhard et al, in Photo West-Optoelectronics 99, Jan. 25, 1999, San Jose CA, USA.

Affiliated with

Also associated with

Rating

Thermooptical modulator does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Thermooptical modulator, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Thermooptical modulator will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2525781