Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R29/00—Arrangements for measuring or indicating electric quantities not covered by groups G01R19/00 - G01R27/00
  • G01R29/02—Measuring characteristics of individual pulses, e.g. deviation from pulse flatness, rise time or duration
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R13/00—Arrangements for displaying electric variables or waveforms
  • G01R13/20—Cathode-ray oscilloscopes
  • G01R13/22—Circuits therefor
  • G01R13/34—Circuits for representing a single waveform by sampling, e.g. for very high frequencies
  • G01R13/347—Circuits for representing a single waveform by sampling, e.g. for very high frequencies using electro-optic elements
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
  • G01R19/0046—Arrangements for measuring currents or voltages or for indicating presence or sign thereof characterised by a specific application or detail not covered by any other subgroup of G01R19/00
  • G01R19/0053—Noise discrimination; Analog sampling; Measuring transients
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T29/00—Metal working
  • Y10T29/49—Method of mechanical manufacture
  • Y10T29/49002—Electrical device making
  • Y10T29/49117—Conductor or circuit manufacturing
  • Y10T29/49204—Contact or terminal manufacturing
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T29/00—Metal working
  • Y10T29/49—Method of mechanical manufacture
  • Y10T29/49002—Electrical device making
  • Y10T29/49117—Conductor or circuit manufacturing
  • Y10T29/49204—Contact or terminal manufacturing
  • Y10T29/49208—Contact or terminal manufacturing by assembling plural parts

Definitions

• the invention relates to the field of electrical samplers, in particular for pulses having short or very short durations.
• Pulse metrology makes it possible to describe the temporal evolution of a signal, or of an electrical pulse, in particular of its voltage or of its energy, when this signal, or this pulse, is unique (non-repetitive), and very brief (that is to say has a duration of the order of a few tens of picoseconds).
• Such pulses to be measured generally come from very fast radiation detectors, which convert into electrical pulses the energy of a radiation pulse which they receive, for example an X or gamma, or visible, or infrared radiation pulse.
• Such radiation can be emitted by ultrafast radiation sources, such as lasers or synchrotron radiation sources, or can be the result of a laser-matter interaction caused by an ultrafast laser (i.e. the duration of the pulse is in the picosecond or femtosecond domain).
• the invention can be applied to any measurement of a very brief, non-repetitive electrical signal, in particular in the physics of events, or in the measurement of events, generated by picosecond phenomena.
• FIG. 1 It comprises a propagation line 2 into which is introduced, and along which propagates, a pulse signal 4 to be measured.
• sampling doors 6 made of a photoconductive material (CdTe).
• CdTe photoconductive material
• These sampling gates are associated with sampling lines 8, each being itself followed by a means for reading the charges. All of the means for reading the charges are assembled in a device 10 for reading the charges.
• Each sampling gate 6 is closed by means of a light pulse 14 of "" triggering: it takes as much of light trigger pulses that there are sampling gates. This device therefore requires a picosecond optical flash of a few tens of nanojoules to trigger the sampling.
• the samplers of this device (photoconductors) therefore take part of the signal present at their level on the line. They are placed in parallel on this propagation line.
• FIG. 2 An optoelectronic sampling system, incorporating a device of the type described above, was disclosed in the thesis of Vincent GERBE (Joseph Fourier University, Grenoble, September 24, 1993). This system is shown diagrammatically in FIG. 2. It includes a sampler 1, at 16 photoswitches, operating on the principle described above in conjunction with FIG. 1. A picosecond laser, not shown in the figure, delivers pulses 16, at a rate of 0.2 Hertz, and at a wavelength of 0 , 53 ⁇ m. A set of 18-24 mirrors constitutes an optical delay. The beam is then focused by means of a cylindrical lens 26 on all of the photoconductors. The irradiated surface is thus of the order of 4 cm ⁇ 100 ⁇ m.
• a pulse to be analyzed (of width at mid-height equal to approximately 150 picoseconds) is generated by a detector 28 of the pre-irradiated GaAs type n, illuminated by a part of the beam.
• the pulse can be viewed, after sampling, on a viewing device 30.
• the sampling device 1 has 16 sampling channels, the sampling step being 18 picoseconds.
• Such a device is fixed with regard to the total length of the pulse that the device is capable of analyzing. Similarly, it is fixed with regard to the sampling step and therefore the precision with which one wants to analyze the pulse: indeed, p the sampling interval ⁇ T is equal to -, where p
• the ultra-fast laser pulse (time width between 1.2 and 1.6 picoseconds, and energy per pulse between 200 and
• each stud photoconductor has a dimension of the order of 120x20 ⁇ m 2 , ie an area of about 2.10 "3 mm 2 per photoconductor.
• the efficiency defined by the ratio between the injected power and the useful power, is therefore very low .
• the laser here a frequency-doubled YAG laser
• the photoconductive pads therefore do not receive the same energy with each laser shot. It would therefore be desirable to have an optical interface making it possible to attenuate the influence of spatial instabilities, while having a simple implementation.
• the invention firstly relates to a single electrical pulse analysis device comprising an electrical circuit consisting of a propagation line comprising, on a regular basis, optoelectronic switches constituted by photoconductive pads, each being connected to a corresponding analysis line, and an optical device making it possible to illuminate the switches with a laser beam or portions of a laser beam, two adjacent switches being illuminated successively, not simultaneously.
• a successive sampling of the photoconductors is therefore carried out, which makes it possible, with the same propagation structure, to sample with a smaller or larger pitch than that corresponding to the spacing of the lines on the structure.
• the optical device makes it possible to use the analysis device in variable ranges with regard to the total length of the pulse that it is capable of analyzing, and the sampling step (therefore the precision) with which one wants to analyze the impulse.
• the invention also relates to a single electrical pulse analysis device comprising an electrical circuit consisting of a propagation line comprising, on a regular basis, optoelectronic switches constituted by photoconductive pads, each of them being connected to a corresponding analysis line, and an optical device making it possible to illuminate the switches with portions of a laser beam, each portion of the beam corresponding to a switch, this optical device introducing an optical delay between two neighboring portions of laser beam corresponding to two photoconductors neighboring the propagation line.
• the optical device comprises a bundle of optical fibers of variable length from one fiber to another.
• This system is easily interchangeable. If, from one fiber to another, the total length is increased by A £, the sampling interval will be varied by approximately ⁇ ⁇ ⁇ / V f , where V f is the speed of propagation of light in the fiber. In addition, the energy efficiency of this system is better than in the case where a single cylindrical lens is used. This system also has a very simple implementation.
• the fibers can be positioned in grooves of an etched substrate.
• Focusing means can also be arranged at the outlet of the optical fibers, for example in a groove or cavities etched in a substrate.
• the fibers are held on one side in a holding tube and, on the other side, in a holding device.
• the optical device comprises an energy distributor made up of optical guides produced in a substrate.
• the optical device comprises a reflector provided with reflecting zones arranged so as to introduce an optical delay.
• the optical device comprises a stepped device introducing a delay from one portion of the beam to another.
• the invention also relates to a single electrical pulse analysis device comprising an electrical circuit consisting of a propagation line comprising, on a regular basis, optoelectronic switches constituted by photoconductive pads, each being connected to a line d 'corresponding analysis, and an optical device for illuminating the switches with a laser beam, this optical device comprising a plane mirror located parallel to the propagation line and the analysis lines.
• the photoconductors can be arranged along the propagation line at a pitch p greater than the pitch p m defined by:
• V where L is the width of an analysis line, V c the propagation speed of an electrical signal in the propagation line and t the average recombination time of the photoconductors. This prevents the return of an electric pulse, due to an impedance mismatch at each pad, from disturbing the sampled signal.
• the n photoconductive pads are preferably arranged at a pitch p along the propagation line, a distance b separating the first pad from the line end line, the following relationship being satisfied for any pad N (2 ⁇ N ⁇ n) and for all k, l ⁇ k ⁇ Nl:
• V c denotes the speed of propagation of an electrical signal in the line
• ⁇ t is the duration of the time interval separating the illumination, by the beam laser, from two neighboring studs.
• the pads are preferably arranged along the line at a pitch p, the duration ⁇ t of the time interval separating the illumination, by the laser beam, of two neighboring pads, being such that: ⁇ ⁇ t
• V c is the propagation speed of an electrical signal in the propagation line.
• the second disturbance created by each light pulse, on each pad, then does not disturb the sampling of the other pads.
• FIGS. 3 to 8 relate to a first embodiment of the invention, using optical fibers
• FIG. 9 represents a second embodiment of the invention, with guided optics
• - Figures 10 and 11 relate to a third embodiment of the invention, with reflecting surfaces
• - Figure 12 relates to a fourth embodiment in which the parallel beam, of wavelength of illumination of the photoconductors being fixed , passes through a prism
• FIGS. 13 and 14 relate to a fifth embodiment of the invention, with an optical staircase
• FIGS. 15 to 17 illustrate the propagation of disturbances along the propagation line
• FIG. 18 shows a propagation line with a straight part and a bend part, or "S".
• the sampling interval ⁇ T of the electrical signal is therefore:
• ⁇ T ⁇ t + p / V c , where p is the pitch between two neighboring photoconductors and V c is the speed of movement of the signal in the propagation line.
• ⁇ T can be negative or positive.
• the successive sampling of the photoconductors makes it possible, with the same propagation structure, to sample with a smaller or larger pitch than that corresponding to the spacing of the lines on the structure.
• references 32-1, ..., 32-5 designate photodetector pads of an analysis device of the type described above in connection with FIG. 1.
• the free end of each of the fibers 34-1, ..., 34-5 faces a photodetector pad.
• the dimensions of each of the studs are gxl, where g denotes the "gap", or spacing, and where 1 denotes the width of the stud.
• g 50 ⁇ m
• l 120 ⁇ m.
• g must be large enough to avoid distortion of the signal propagating on the line by capacitive influence of the sampling lines. However, too large a g decreases the sensitivity of the system.
• the fibers are of increasing length, preferably regularly increasing: the length of the fiber 34-1 is greater than that of the fiber 34-2, which is itself greater than that of the fiber 34-3, etc.
• the distance between the fiber outputs and the photodetector pads of the analysis device is constant.
• the fibers are multimode fibers with an index gradient, which makes it possible to obtain a fairly low dispersion.
• These are for example fibers with a core diameter of 100 ⁇ m, a mantle diameter of 140 ⁇ m and a numerical aperture of 0.29 (“PSI" fibers), or fibers with a core diameter of 50.5 ⁇ m, a mantle diameter of 125 ⁇ m and 0.21 digital aperture (“NSG” type fibers).
• FIG. 4 represents, in perspective, the positioning of two fibers 34-1, 34-2 facing a strip 32 of photodetector.
• a lens 36-1, 36-2 can be arranged in the path of the beam, between the output face of each of the fibers and the corresponding photodetector pad.
• the exit faces of the fibers are more than 0.5 mm from the photodetectors 35-i or from the array 32 of photodetectors. At such a distance, there is no problem of disturbance of the electrical signal circulating in the line and, on the other hand, it is thus possible to overcome the problems that could arise from flatness defects in different elements.
• g for example 50 ⁇ m
• the fibers can be integrated into a block of fibers holding them.
• a bar can integrate the n lenses 36-1, 36-2 " spaced apart at the pitch p of the studs, which simplifies the positioning of the assembly.
• FIG. 5 represents an assembly comprising a strip 32 of photodetector, a strip 36 of lens, and a device 34 for holding the fibers.
• the distance D between the lens strip 36 and the strip 32 of photodetectors is, as said above, preferably greater than or equal to 0.5 mm.
• the distance d between the lens strip and the fiber holding device can be variable: it can for example be 0 (the two devices 34 and 36 are then glued to each other).
• FIG. 6 Another device 38 for linear positioning and holding the fibers is illustrated in Figure 6.
• This device comprises a machined substrate 40, for example ceramic.
• the machining makes it possible to produce a channel 42 for each fiber.
• Focusing means for example balls, can also be maintained by this substrate.
• FIG. 6 shows the support 38 into which a fiber 46 and a focusing ball 48 are introduced.
• the support 38 allows the positioning and bonding of the balls in the groove 44. In place of the groove, microcavities can be provided.
• the fibers are bonded in the channels 42 provided for this purpose.
• FIG. 8 represents the mounting of the fibers, on the one hand in a holding tube 50 (on the injection side of the laser beam in the fibers) and on the other hand in a device 52 for holding and linear positioning of the fibers.
• the fibers are, for example, approximately
• a beam which is placed in front of the laser which delivers the pulses for example a doubled YAG laser (frequency equal to 530 nm).
• a laser device can provide a subpicosecond pulse. If one wishes to deposit a few nanojoules on each photoconductive pad (which is necessary to achieve a significant drop in resistivity of the photoconductor) the power at the output of each fiber is therefore of the order of a few kilowatts.
• the multimode fibers used, with index gradient (which makes it possible to obtain a low dispersion and to inject a lot of power) have a tolerance between them of ⁇ lOO ⁇ m in length (which corresponds to
• the fibers are stripped in the collective holding tube 50 and sheathed in the substrate 52 for linear positioning.
• FIG. 9 shows a 1 to 8 distributor.
• Optical guides 53-1, 53-2, 53-3, ... are formed for example of silver diffused zones, buried in a glass substrate, as described by F. ST ANDRE, P. BENECH, A. KEVORKIAN "Modeling of a semileaky waveguide, SPIE, vol. 1583 (1981)
• multimode guides are used.
• monomode potassium guides can also be used. The length of the different guides makes it possible to obtain, at the outlet of the distributor 51, the desired time offsets.
• FIG. 10 Another way of obtaining a device for forming time-shifted laser pulses is to produce a staircase reflecting structure, as illustrated in FIG. 10.
• the reference 32 also designates a photoconductive strip 32-1, 32-2, 32-3.
• a pulsed laser beam 54 passes through a cylindrical lens 56.
• Reflective zones 58-1, 58-2, 58-3 make it possible to direct portions of the laser beam on each of the photoconductive elements.
• the reflective areas are arranged so that the optical path, from one beam to another, is increasing: thus the photoconductors are not illuminated at the same time, but at different times.
• the sampling interval between two successive illuminations is fixed. This embodiment is further illustrated in FIG. 11.
• the reflective zones 58-1, 58-2, 58-3 are produced on the surface of a support 60 on sides H and D.
• the lower edge of the support is arranged at a distance E from the strip 32 of photoconductors.
• the distance E does not intervene for a variation of ⁇ T.
• This system makes it possible to obtain a better energy yield than with a cylindrical lens alone.
• the parallel beam, of wavelength of illumination of the photoconductors being fixed, passes through a corner prism at the apex ⁇ .
• FIG. 13 Another embodiment is illustrated in FIG. 13 where the reference 56 also designates a cylindrical lens.
• the laser beam 54 encounters on its path a glass staircase 66, the steps of which have a height m, each step corresponding to a photoconductive pad of a strip 32 of photoconductors.
• the staircase is located at a distance E from the bar 32.
• a staircase 68 having the shape illustrated in FIG. 14.
• the planes 68-1, 68-2.68-3 of the different steps, which the different portions of the beam cross laser, are connected by planar surfaces which are not perpendicular to them, but inclined at an angle ⁇ with respect to the normal.
• stairs with a different step height m give sampling intervals ⁇ T which vary.
• m constant, a variation of the pitch p makes it possible to vary ⁇ T.
• FIG. 15 represents two photoconductors 32-1, 32-2, with the corresponding sampling lines 33-1, 33-2, of width L.
• the pitch of the photoconductor strip is p.
• the electrical pulse propagating in line 2 will undergo, at each pad, a variation in impedance, and therefore a reflection.
• perturbation 76 propagating in the other direction
• perturbation 76 propagating in the other direction
• the attenuation of the signal over such a length is very important, and all the more so as the frequency is high (attenuation of approximately -ldB on a line of 1 cm at 30 GHz). We therefore seek to reduce the useful length, and to delay the laser pulses to make a sampling interval of 9ps.
• the minimum boring distance b is 172.5 ⁇ m and the maximum boring distance b is 2.22cm.
• the optical interface is a system of 64 fibers, the length difference between two neighboring fibers is 1.5 mm. They can be positioned opposite the studs with a linear positioning system.
• the advantage of such a device is to be able to analyze even longer pulses, either by keeping 64 points and by increasing the illumination delay from one pad to another (solution II), or by increasing the number of points and keeping the illumination delay from one fiber to the next
• Solutions II and III for analyzing long electrical signals make it possible to measure pulses of the order of 2 ns.
• Solution III has an advantage compared to solution II, it is its very high resolution (220 points instead of 64 points), but such a resolution is not necessarily always necessary.
• the total length is greater than or equal to nxp + length of I pad
• a 64-point sampler with a 180 ⁇ m pitch matched with different fiber bundles therefore seems a good solution. It allows a slightly deformed pulse measurement and above all a good flexibility as for the sampling interval. Indeed, we can vary the sampling interval from less than 9 ps to more than 30 ps and therefore the width of the pulse that we can measure will vary from less than 567 ps to more than 1.89 ns .

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• 1997
  • 1997-07-23 FR FR9709363A patent/FR2766576B1/fr not_active Expired - Fee Related
• 1998
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  • 1998-07-21 WO PCT/FR1998/001604 patent/WO1999005534A1/fr not_active Application Discontinuation
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