Coherent light generators – Particular beam control device – Modulation
Reexamination Certificate
2001-08-31
2003-05-13
Scott, Jr., Leon (Department: 2828)
Coherent light generators
Particular beam control device
Modulation
C372S013000, C372S026000, C372S009000, C359S205100, C359S310000
Reexamination Certificate
active
06563845
ABSTRACT:
The invention relates to an optical modulation device for coupling an entering radiation field to at least one of two exiting radiation fields, comprising an acousto-optical modulator, a first sound (e.g., acoustic) wave field travelling through the acousto-optically active medium of this modulator in a sound propagation direction and by means of a first acousto-optical modulation dividing a radiation field incident in an entry direction and coupled to the entering radiation field essentially into a transmitted branch propagating in the direction of a beam axis of the incident radiation field and a diffracted branch extending with its beam axis at an angle of diffraction of the first order in relation to the beam axis of the transmitted branch, wherein an angle bisector between the beam axis of the incident radiation field and the beam axis of the diffracted branch extends approximately parallel to the sound propagation direction of the sound wave field.
Optical modulation devices of this type are known, for example, from the book “Fundamentals of Photonics” of Bahaa E. A. Saleh and Malvin Carl Teich, John Reiley and Sons, New York, 1991, page 799 to page 831.
In the case of these modulation devices there is, however, the problem that when these modulation devices are intended to be used for the switching of radiation fields, diffraction efficiencies of up to 100% must be achieved and these can be achieved, if at all, only with considerable resources.
The object underlying the invention is therefore to improve an optical modulation device of the generic type in such a manner that as efficient a switching of the incident radiation field as possible between the exiting radiation fields is possible.
This object is accomplished in accordance with the invention, in an optical modulation device of the type described at the outset, in that a radiation guide system is provided which deflects the diffracted branch resulting during the first acousto-optical modulation and the transmitted branch such that with their beam axes extending approximately at the angle of diffraction of the first order relative to one another they interact with a travelling second sound wave field having approximately the same frequency as the first sound wave field in order to generate a second acousto-optical modulation, whereby essentially a diffracted and a transmitted branch respectively result from the deflected, diffracted branch and the deflected, transmitted branch, that the direction of propagation of the second sound wave field is aligned relative to the deflected, diffracted branch and the deflected, transmitted branch such that the transmitted branch resulting from the deflected, diffracted branch and the diffracted branch resulting from the deflected, transmitted branch propagate in approximately the same direction, are superimposed at least partially and thereby have essentially the same frequency so that these at least partially superimposed branches form a first radiation field as a result of essentially constructive interference, and in addition the transmitted branch resulting from the deflected, transmitted branch and the diffracted branch resulting from the deflected, diffracted branch propagate in the same direction, are at least partially superimposed and thereby have essentially the same frequency so that these at least partially superimposed branches form a second radiation field as a result of essentially destructive interference, and that the first radiation field is coupled to the first exiting radiation field and the second radiation field to the second exiting radiation field.
The advantage of the inventive solution is to be seen in the fact that as a result of the inventive execution of the second acousto-optical modulation in such a manner that two respective branches result which are superimposed and have the same frequency, constructive and destructive interference can respectively be used to form the first radiation field and the second radiation field from the respective branches.
As a result, large variations in intensity between the first and second radiation fields are possible at a low diffraction efficiency. For example, it is sufficient to be able to operate the first acousto-optical modulation and the second acousto-optical modulation with a diffraction efficiency of at the most 50% in order to couple the entering radiation field completely into the first radiation field or the second radiation field.
This allows, in particular, use of simple optical modulators and a lower high-frequency power for generating the sound wave fields and so, as a result, the acousto-optical modulators can, altogether, be constructed and operated more simply.
Particularly high intensities of the first radiation field may be obtained when the branches forming the first radiation field are superimposed in essential parts.
A partial superposition is also sufficient with respect to the branches forming the second radiation field, wherein for achieving intensities which are as high as possible the branches forming the second radiation field are likewise superimposed in essential parts where possible.
With respect to generating the first and second sound wave fields it would, in principle, be conceivable to use different sound generators with different sound frequency generators.
However, in order to ensure that the frequencies of the first and second sound wave fields are as close to one another as possible or even identical it is preferably provided for the first and second sound wave fields to be generated with a single sound frequency generator.
Furthermore, in order to achieve as uniform a diffraction efficiency as possible during the first acousto-optical modulation and the second acousto-optical modulation it is preferably provided for the first and the second sound wave fields to have amplitudes of essentially the same size.
In the case of an inventive modulation device a concept which is as simple as possible provides for the first acousto-optical modulation and the second acousto-optical modulation to take place in separate acousto-optical modulators so that it is also possible, due to this separation of the acousto-optical modulators, to vary the individual, acousto-optical modulations with respect to the diffraction efficiency.
This solution is particularly favorable when the diffraction efficiency of the first acousto-optical modulation or the second acousto-optical modulation is intended to be different in relation to the diffraction efficiency of the respectively other acousto-optical modulation.
With this solution, it is possible, in particular, to select optional intensities of the first radiation field and the second radiation field.
However, in order to be able to ensure in as simple a manner as possible that the first and the second acousto-optical modulations take place with the same frequency and under the same overall conditions, it is preferably provided for the first acousto-optical modulation and the second acousto-optical modulation to take place in the same acousto-optical modulator, in which a single sound wave then propagates and a single grating of wave fronts is generated, at which the two acousto-optical modulations take place.
Even when carrying out the two acousto-optical modulations in one and the same modulator it is possible to have the first acousto-optical modulation and the second acousto-optical modulation carried out in the same acousto-optical modulator essentially spatially separable so that a simple separation of the first radiation field and the second radiation field from the incident radiation field is also possible.
The construction of the radiation guide device and the radiation guidance itself may, in particular, be simplified even more when the first acousto-optical modulation and the second acousto-optical modulation take place essentially in the same volume area of the acousto-optical modulator so that, as a result, it is also ensured that the same conditions exist for the two acousto-optical modulations.
No further details have so far been
Haas-Laser GmbH + Co. KG
Jr. Leon Scott
Lipsitz Barry R.
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