Electrical transmission or interconnection systems – Wave form or wave shape determinative or pulse-producing...
Reexamination Certificate
1999-11-03
2001-10-30
Jackson, Stephen W. (Department: 2836)
Electrical transmission or interconnection systems
Wave form or wave shape determinative or pulse-producing...
C327S570000, C372S025000
Reexamination Certificate
active
06310409
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an optically programmable electric generator of arbitrary time profiles.
PRIOR ART
The documents “The National Ignition Facility Front End Laser System” by S. C. Burkhart, et al.,
Proceeding of the First Annual International Conference on Solid State Lasers for Application to Inertial Confinement Fusion Conference,
pp. 48-58, SPIE Vol. 2623, April 1995; “Temporal Pulse Shaping of Fiber Optic Laser Beams” by S. C. Burkhart, et al.,
Inertial Confinement Fusion,
pp 75-81, ICF Quarterly Report, Vol. 6, No. 2, February 1996; and “Driver/Source/Time Shaping” by Y. Hourmand,
Technical note DRIF/DCRE
443/96 dated Jul. 2, 1996, describe a pulse-forming device controlled by a computer using GaAs field-effect transistors, but these devices are limited frequency-wise and voltage-wise.
DESCRIPTION OF THE INVENTION
The present invention relates to an optically programmable electric generator of arbitrary time profiles, characterised in that it comprises a first ultrahigh frequency triggering line and a second ultrahigh frequency discharge line resistively coupled, by points, in that the first line is triggered by a voltage transition of duration less than one nanosecond, for example a pulse or a step, in that at least one point is taken off from the first line by at least one photoconductor in static resistance mode, directly coupled to the second line, illuminated by a programmable light source, a resistive load being connected at the output of this generator.
Advantageously a capacitor can optionally be disposed between each photoconductor and the second line making it possible to provide D.C. isolation of the first line from the second. The photoconductors are made of semiconductor materials taken from among the following materials: silicon, gallium arsenide. Each programmable light source can be an ultraviolet/visible/infrared gas tube, or a laser or light emitting semiconductor diode.
Advantageously each light source can be supplied by an independent current source controlled voltage-wise, the input signal of this current source being delivered by a programmable multi-way voltage generator driven by a computer.
Advantageously each programmable light source produces a variable illumination, programmed with reference to a set point, which defines the value of the resistance of the photoconductor, to which it is coupled, at the instant the generator is triggered.
Advantageously the two lines are straight strip lines made from metallic deposits on two substrates respectively associated with two dielectrics of different dielectric constants. The two ultrahigh frequency lines each have a characteristic resistance of between 10 &OHgr; and 100 &OHgr;, the substrate having a loss tangent tg &dgr;≈10
−3
at 10 GHz. The triggering of the first line can be an electrical or photoelectrical triggering, of indexed or pulsed type. A filter can be disposed between the output and the load, which makes it possible to smooth the time profile obtained.
Advantageously the programming step is between thirty picoseconds and one nanosecond. It is defined by the spacing between two photoresistances.
Such an electric generator of time profiles, preprogrammed by photoconductors, which is triggered by another generator, allows the time shaping (TS) of short pulses. Depending on the size of the time slot in which the profile must be programmed, and the triggering generator available, the step &Dgr;t can vary between a few tens and a few hundreds of picoseconds.
In an advantageous use, this generator can be coupled to an electro-optical crystal using the Pockels effect to implement a laser pulse amplitude modulator.
Compared with the devices of the prior art, the generator of the invention has many original characteristics, and notably the following:
The coupling by photoconductors in optically preprogrammed resistance mode, and therefore the time shaping generator function, is programmable electronically.
The time shaping principle is based on an electrical circuit for programming by components preprogrammed in “quasi-static” mode, as opposed, for example, to the devices described in (1) “National Ignition Facility Front End Laser System” by S. C. Burkhart, R. J. Beach, J. H. Crane, J. M. Davin, M. D. Perny, and R. B. Wilcox,
Solid State Lasers for Application to Inertial Confinement Fusion Conference,
proceedings, page 48, Monterey, Calif., May 31-Jun. 2, 1995; (2) “Temporal Pulse Shaping of Fiber Optic Laser Beams” by S. C. Burkhart and F. A. Penko,
Inertial Confinement Fusion,
ICF Quarterly Report, Jan. -Mar. 1996, Vol. 6, No. 2; and (3) “Driver/Source/Time Shaping” by Y. Hourmand,
Technical note DRIF/DCRE
443/96 dated Jul. 2, 1996, using components switched under dynamic conditions.
There are no high-speed active components, apart from triggering, of the GaAs field-effect transistor switch type, as in (1) “National Ignition Facility Front End Laser System” by S. C. Burkhart, R. J. Beach, J. H. Crane, J. M. Davin, M. D. Perny, and R. B. Wilcox,
Solid State Lasers for Application to Inertial Confinement Fusion Conference,
proceedings, page 48, Monterey, Calif., May 31-Jun. 2, 1995; (2) “Temporal Pulse Shaping of Fiber Optic Laser Beams” by S. C. Burkhart and F. A. Penko,
Inertial Confinement Fusion,
ICF Quarterly Report, Jan. -Mar. 1996, Vol. 6, No. 2; and (3) “Driver/Source/Time Shaping” by Y. Hourmand,
Technical note DRIF/DCRE
443/96 dated Jul. 2, 1996, for example. In such a case, the high-frequency behaviour is limited by the speed of the field-effect transistors.
In the generator of the invention, the high-frequency limitation is due solely to the triggering generator and the losses in the lines.
It is possible to obtain a very large dynamic range in the programming of the photoconductors Rj in resistance mode, the photoconductors being illuminated in quasi-continuous mode. The limit on the dynamic range is due to the “signal
oise” ratio on the preprogrammed value Rj, and therefore the dark current of the photoconductor and the noise of the illumination source. This ratio, which can exceed 30 dB, is a function of the photoconductor implementation conditions.
There is no jitter of the time steps with respect to the triggering transition, by comparison with devices not using a single triggering source.
The invention is simple and versatile from an electronic and optoelectronic point of view. It is of low cost, if the laser diode optical programming sources (at present still expensive) are replaced by gas tubes. It has a small volume with regard to integrability, compared with solutions using discrete electrical components, for ultrahigh frequencies, of the variable attenuator type.
The use of photoconductors under quasi-static conditions, for making the time shaping generator programmable, makes it possible to combine all the advantages for a better “high voltage/large dynamic range/high frequency” compromise. With triggering using a photoconductor, the shaping of electrical or optical pulses (via an electro-optical modulator) can be performed with the following characteristics:
time step between 30 and 100 picoseconds;
voltage levels exceeding 5 kVolts;
programming dynamic range between 10 and 30 dB minimum.
One of the immediate applications of the generator of the invention is that of allowing the time shaping of an optical pulse provided by a laser, by chopping by means of an electro-optical modulator according to a predefined profile at the instant of the arrival of the triggering pulse.
A large number of other applications can be envisaged, as soon as it is necessary to provide, at a resistive load, a voltage profile falling within a previously defined time template, and within a range of levels which can extend from a few volts to a number of kilovolts.
REFERENCES:
patent: 4482816 (1984-11-01), Richardson et al.
patent: 4670662 (1987-06-01), Goldstein et al.
patent: 5789994 (1998-08-01), Case et al.
patent: 5987045 (1999-11-01), Albares et al.
Burkhart, S.C., et al., “National Ignition Facility Front End Laser System”,Solid S
Burns Doane , Swecker, Mathis LLP
Commissariat A l'Energie Atomique
DeBeradinis Robert L.
Jackson Stephen W.
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