Device and method for detecting optical impulses

Abstract

Optical Pulse Detection Device and Method The present invention relates to an optical pulse detection device (10), the detection device (10) comprising: a single detector (12) comprising N independent detection surfaces (20) of the same dimensions, N being an integer greater than or equal to two, the N detection surfaces (20) being suitable for receiving an optical pulse of identical power surface density on all the detection surfaces (20), M signal processing chain(s) (14) for the output signals of the N detection surfaces (20), M being an integer between 1 and N, each processing chain (14) comprising an amplification unit (22) having an amplification gain and a filtering unit (24),each processing chain (14) being connected to one or more detection surfaces (20) distinct from any other possible processing chains (14) such that each detection surface (20) is connected to one or more of the M processing chains (14). Figure for the abbreviation: 2,

Description

Title of the invention: Device and method for detecting optical pulses

[0001] The present invention relates to an optical pulse detection device. The present invention also relates to an associated method for detecting optical pulses.

[0002] Optical pulse detection is useful for many applications, particularly in the field of laser warning detectors.

[0003] For this purpose, it is known to use several detectors to detect an optical pulse. However, this solution is bulky and expensive. It also often requires the use of separate optics.

[0004] Other solutions use only a single-element detector. However, such a detector combined with a preamplifier is subject to clipping, preventing the full dynamic range from being captured. Thus, this solution only provides a portion of the dynamic range before clipping. Potentially important information, such as signal modulation, is then lost and cannot be processed by signal processing methods to extract the pulse to be detected.

[0005] The aim of the invention is then to propose a more compact means of detecting optical pulses and allowing the measurement of an optical pulse with a better signal-to-noise ratio or a greater dynamic range than in the prior art.

[0006] To this end, the invention relates to an optical pulse detection device, the detection device comprising: - a single detector comprising N independent detection surfaces of the same dimensions, N being an integer greater than or equal to two, the N detection surfaces being suitable for receiving an optical pulse of identical power density across all detection surfaces, - M signal processing chain(s) at the output of the N detection surfaces, M being an integer between 1 and N, each processing chain comprising an amplification unit having an amplification gain and a filtering unit, each processing chain being connected to one or more detection surfaces distinct from any other processing chains such that each detection surface is connected to one or more of the M processing chains,

[0007] the detection device being in one of the following configurations: • a first configuration in which M is equal to 1 so that all the detection surfaces are connected to a single processing chain), the output of the single processing chain forming a single output (S) for the detection device, or • a second configuration in which M is equal to N so that each detection surface is connected to a separate processing chain, the amplification gains being the same for the amplification units of the N processing chains, the outputs of the N processing chains being summed to form a single output (S) for the detection device, or • a third configuration in which M is between 2 and N and the outputs of the M processing chains form M outputs for the detection device, the amplification gain of the amplification unit of each processing chain and the number of distinct detection surfaces connected to each processing chain being such that each processing chain covers a different dynamic range from the other processing chains.

[0008] According to other advantageous aspects of the invention, the detection device comprises one or more of the following features, taken individually or in all technically possible combinations:

[0009] - in the third configuration, the amplification gain of the amplification unit of each processing chain and the number of distinct detection surfaces connected to each processing chain are such that the dynamics of the M processing chains overlap;

[0010] - in the third configuration, the M processing chains cover a total dynamic range greater than or equal to 90 dB, preferably greater than or equal to 100 dB;

[0011] - in the third configuration, the amplification units of the processing chains connected to the same number of detection surfaces have different amplification gains;

[0012] - the detection device further comprises a measuring unit suitable for performing a barycentric weighing of the luminous flux received on the N detection surfaces and a calculation unit for the direction of origin of the received luminous flux as a function of the barycentric weighing performed;

[0013] - N is equal to 4 so that the single detector is a four-quadrant detector;

[0014] - the filtering unit of each processing chain includes a bandpass filter.

[0015] The invention also relates to a method for detecting optical pulses, the method being implemented by a detection device as described above, the detection method comprising: - the reception of an optical pulse by the N detection surfaces of the single detector, the optical pulse having an identical power density on all detection surfaces, - the processing of the output signals from the N detection surfaces by the M processing chains, and - the detection of the optical pulse as a function of the processed signals.

[0016] According to other advantageous aspects of the invention, the method also includes measuring the amplitude and / or shape and / or direction of the detected optical pulse.

[0017] The invention will become clearer upon reading the following description, given solely by way of non-limiting example, and made with reference to the drawings in which:

[0018] [Fig-1] [Fig.1] is a schematic representation of an example of a device Optical pulse detection comprising a single detector having N detection surfaces, and M signal processing chains output from the N detection surfaces,

[0019] [Fig.2] [Fig.2] is a schematic representation of an example of a device detection according to a third configuration with M=N and distinct amplification gains for each processing chain,

[0020] [Fig.3] [Fig.3] is an example of a graph representing the evolution of the output voltage of each processing chain as a function of the peak light power of the optical pulse for the different processing chains of [Fig.2],

[0021] [Fig.4] [Fig.4] is a schematic representation of an example of a device detection according to a second configuration with M=N, identical amplification gains for each processing chain, and a common output resulting from the sum of the outputs of the N processing chains,

[0022] [Fig. 5] [Fig. 5] is a schematic representation of an example of a device detection according to a third configuration with 1 < M < N,

[0023] [Fig.6] [Fig.6] is a schematic representation of another example of a detection device according to a third configuration with 1 < M < N,

[0024] [Fig.7] [Fig.7] is a schematic representation of yet another example of a detection device according to a third configuration with 1 < M < N, and

[0025] [Fig.8] [Fig.8] is a schematic representation of a detection device according to a first configuration with M=1 so that all detection surfaces are connected to a single processing chain.

[0026] A device for detecting optical pulses 10 is illustrated by [Fig.1].

[0027] Optical pulses are, for example, coming from a laser device.

[0028] The detection device 10 comprises a single detector 12 and M processing chain(s) 14.

[0029] The single detector 12 comprises N detection surfaces 20. N is an integer greater than or equal to two. A detection surface 20 is a portion of the overall detection surface of the detector that collects photons only on that portion and delivers a signal proportional to this collection on a separate output.

[0030] The N detection surfaces 20 have the same dimensions.

[0031] The N detection surfaces 20 are independent, that is to say that the optical flux An impact received on one surface has no impact on the other surfaces.

[0032] The N detection surfaces 20 are suitable for receiving an optical pulse of identical power surface density on all the detection surfaces 20.

[0033] In an example of implementation, as illustrated by Figures 2 and 4 to 8, N is equal to 4 so that the single detector 12 is a four-quadrant detector. Each detection surface 20 is then formed by one of the quadrants.

[0034] The M processing chain(s) 14 are suitable for processing, in particular for amplifying and filtering, the output signals from the N detection surfaces 20. M is an integer between 1 and N.

[0035] Each processing chain 14 is connected to one or more detection surfaces 20 distinct from any other processing chains 14 so that each detection surface 20 is connected to the one or one of the M processing chains 14.

[0036] Each processing chain 14 includes an amplification unit 22 having an amplification gain and a filtering unit 24.

[0037] The amplification unit 22 is suitable for amplifying one or more signals from the detection surfaces 20.

[0038] In one embodiment, as illustrated by Figures 2 and 4 to 8, the amplification unit 22 comprises an operational amplifier 30 with a resistive element 32 connected to the terminals of the operational amplifier 30. The gain of the amplification unit 22 is a function of the resistance of the resistive element 32.

[0039] For simplicity of presentation, the resistive elements 32 appear on the diagrams of figures 2 and 4 to 8 represented by resistances Rfl, Rf2, Rf3, Rf4, Rfl2, Rf34, Rfl23, Rfl234. However, these resistances can be replaced by impedances generally formed by their parallel connection with a capacitor.

[0040] Thus:

[0041] Rfl can be replaced by Zfl = parallel connection of Rfl and Cfl,

[0042] Rf2 can be replaced by Zf2 = parallel connection of Rf2 and Cf2,

[0043] Rf3 can be replaced by Zf3 = parallel connection of Rf3 and Cf3,

[0044] Rf4 can be replaced by Zf4 = parallel connection of Rf4 and Cf4,

[0045] Rfl2 can be replaced by Zfl2 = parallel connection of Rfl2 and Cfl2,

[0046] Rf34 can be replaced by Zf34 = parallel connection of Rf34 and Cf34,

[0047] Rfl23 can be replaced by Zfl23 = parallel connection of Rfl23 and Cfl23, and

[0048] Rfl234 can be replaced by Zfl234 = parallel connection of Rfl234 and Cfl234

[0049] In the diagrams and in the remainder of this document, only the resistances Rf are represented and referred to, although they can be replaced by equivalent impedances as described above.

[0050] The filtering unit 24 of each processing chain 14 is suitable for filtering the output signal of the processing chain 14 over the dynamic range covered by the processing chain 14. Preferably, the filtering unit 24 is optimized on the dynamic range of the processing chain 14 and on the Signal to Noise ratio (SNR).

[0051] The filtering unit 24 includes, for example, a bandpass filter.

[0052] In one example implementation, to optimize the SNR, the cutoff frequency of the filtering unit 24 is chosen according to: - characteristics of the optical signal at the input of the single detector 12 (static power surface density, pulse time profile), and - electrical characteristics of the single detector 12 and the amplification unit 22 (detector capacitance, input capacitance of the amplification unit 22, current noise spectral density of the detector and the amplification unit 22 and voltage noise spectral density of the amplification unit 22, transimpedance resistance value)

[0053] This optimization can be achieved using analog simulation.

[0054] The detection device 10 is in one of the following configurations among: a first configuration (example illustrated in [Fig.8]), a second configuration (example illustrated in [Fig.4]), and a third configuration (example illustrated in figures 2 and 5 to 7).

[0055] According to the first configuration, illustrated as an example in [Fig. 8], M is equal to 1 so that all the detection surfaces 20 are connected to a single processing chain 14. The output of the single processing chain 14 forms a single output S for the detection device 10. The advantage of this configuration is the use of a detector with multiple detection surfaces instead of a single-element detector of equivalent total area. The static optical power illuminating each detection surface 20 is thus lower than that which would illuminate a single-element detector of equivalent area. As a result, the Schottky noise generated by each detection surface 20 is lower, leading to a higher capacitive noise emergence frequency, allowing a higher cutoff frequency of the filtering unit 24, which improves the SNR.Furthermore, in the case of a four-quadrant detector, such a detector is less expensive than a single-element detector because the . Four-quadrant detectors are manufactured in larger series for laser-guided munitions.

[0056] According to the second configuration, illustrated as an example in [Fig. 4], M is equal to N so that each detection surface 20 is connected to a separate processing chain 14. The amplification gains are the same for the amplification units of the N processing chains 14. The outputs of the N processing chains 14 are summed to form a single output S for the detection device 10. This second configuration makes it possible to detect an optical pulse with a better signal-to-noise ratio than detection on a single-element detector (a single detection surface 20). In particular, the total capacitance presented at the input of each of the processing chains 14 is lower; the amplification unit 22 is therefore easier to implement and can more readily have a higher bandwidth. The resistances Rf1 to Rf4 can be higher if the dynamic range allows.In fact, the noise contribution of resistors Rf1 to Rf4 decreases, and the capacitive noise emergence frequency increases, allowing for a higher cutoff frequency of the filter unit 24. Furthermore, since the area of ​​each detection surface 20 is smaller than the total area of ​​an equivalent single-element detector, the static optical power illuminating each detection surface 20 is lower than that which would illuminate a single element of the same equivalent area. Consequently, the Schottky noise generated by this detection surface 20 is lower, resulting in a higher capacitive noise emergence frequency, which in turn allows for a higher cutoff frequency of the filter unit 24. All of this contributes to an improvement in the signal-to-noise ratio (SNR).

[0057] According to the third configuration, illustrated by example in Figures 2 and 5 to 7, M is between 2 and N. The outputs of the M processing chains 14 form M outputs for the detection device 10. The amplification gain of the amplification unit 22 of each processing chain 14 and the number of distinct detection surfaces 20 connected to each processing chain 14 are such that each processing chain 14 has a different dynamic range from the other processing chains 14. The dynamic range corresponds to the range of the signal output from the detection surfaces 20 that can be processed by the processing chain 14 without clipping.

[0058] Preferably, in the third configuration, the amplification gain of the amplification unit 22 of each processing chain 14 and the number of distinct detection surfaces 20 connected to each processing chain 14 are such that the dynamics of the M processing chains 14 overlap.

[0059] Preferably, in the third configuration, the M processing chains 14 cover a total dynamic range greater than or equal to 90 dB, preferably greater than or equal to 100 dB.

[0060] Preferably, in the third configuration, the amplification units of the processing chains 14 connected to the same number of detection surfaces 20 have different amplification gains.

[0061] For example, [Fig. 2] illustrates a detection device 10 according to a third configuration with M=N. In this case, the amplification gains of the amplification units of the processing chains 14 are different, making it possible to obtain a different dynamic range for each processing chain 14. In particular, [Fig. 3] illustrates the dynamic ranges covered by each processing chain 14. The amplification gains have in this case been chosen so that the dynamic ranges of the different processing chains 14 overlap.

[0062] In the example of [Fig.5], N=4, M=2 and 3 detection surfaces 20 are connected to 1 same processing chain 14 and 1 detection surface 20 is connected to the other processing chain 14. The amplification gains of the two processing chains 14 can in this case be different or identical.

[0063] In the example of [Fig.6], N=4, M=2, 2 detection surfaces 20 are connected to the same processing chain 14 and 2 detection surfaces 20 are connected to the other processing chain 14. The amplification gains of the two processing chains 14 are different in this case.

[0064] In the example of [Fig. 7], N=4, M=3, two detection surfaces 20 are connected to the same processing chain 14, and two detection surfaces 20 are each connected to two other separate processing chains 14. The amplification gains of the two processing chains 14 connected to a single detection surface 20 are different in this case.

[0065] Preferably, the detection device 10 further comprises a measuring unit for performing a barycentric weighing of the luminous flux received on the N detection surfaces 20, and a calculation unit for determining the direction from which the received luminous flux originates based on the barycentric weighing performed. The measuring unit allows for the evaluation of the quantity of optical signal received relative to the other detection surfaces 20.

[0066] An example of a detection method implemented by the detection device 10 will now be described.

[0067] The detection method includes receiving an optical pulse by the N detection surfaces 20 of the single detector 12, the optical pulse having an identical power surface density on all the detection surfaces 20.

[0068] The detection process then includes the processing of the output signals from the N detection surfaces 20 by the M processing chains 14.

[0069] Finally, the detection method includes the detection of the optical pulse as a function of the processed signals.

[0070] Optionally, the method also includes measuring the amplitude and / or shape and / or direction of the detected optical pulse.

[0071] Thus, the present detection device 10 makes it possible to provide a measurement of the level of an optical pulse in a large dynamic range (typically greater than 100dB), or in a lower dynamic range but with a better signal-to-noise ratio, in a compact environment using a single optical channel.

[0072] In particular, in the first and second configurations, due to the summation of either the signals from all the detection surfaces 20 or the output signals from all the processing chains 14, the signal-to-noise ratio is optimized compared to a final signal originating from only one of the detection surfaces 20, or from a single-element detector of equivalent surface area. The third configuration, on the other hand, allows the signal to be measured over a wider dynamic range, potentially with measurements having an optimized signal-to-noise ratio for some of the channels resulting from the summation of the signals from several detection surfaces 20.

[0073] More specifically, for all configurations, compared to a uniform detector with the same surface area as the total surface area of ​​the detector, capacitive noise only appears at a higher frequency, allowing for each detection surface 20 to have better optimization of the Signal / Noise Ratio because the optimal frequency is higher.

[0074] In addition, the bandwidth achievable with an amplifier coupled to a single detection surface 20 of the detector is higher than that which would be obtained with a single-element detector of the same surface.

[0075] Finally, particularly for the second and third configurations, the processing of each channel independently and the choice of summing the signals digitally or not depending on the dynamics allows, in the case of a four-quadrant detector, a gain in dynamics of a factor of 4 in output voltage, i.e. 6 dB in optical power or 12dB in output voltage.

[0076] Other notable advantages are: - the simplicity of the electronics, - the compactness of the solution, as it only requires one detector unit, - In the case of using 4-quadrant detectors, there is a financial gain because these detectors are produced in large quantities, and are therefore cheaper than a single-element detector of the same surface area. - the fact that each channel is noise-optimized, allowing for better sensitivity for each dynamic range, and - depending on the configurations, coverage of a significant dynamic range without saturation, on the order of 100 dB or more.

[0077] A person skilled in the art will understand that the embodiments and variants described above can be combined with each other provided that they are technically compatible.

Claims

1. Demands Optical pulse detection device (10), the detection device (10) comprising: - a single detector (12) comprising N independent detection surfaces (20) of the same dimensions, N being an integer greater than or equal to two, the N detection surfaces (20) being suitable for receiving an optical pulse of identical power density on all detection surfaces (20), - M signal processing chain(s) (14) for the output signals of the N detection surfaces (20), M being an integer between 1 and N, each processing chain (14) comprising an amplification unit (22) having an amplification gain and a filtering unit (24), each processing chain (14) being connected to one or more detection surfaces (20) distinct from any other processing chains (14) such that each detection surface (20) is connected to one or more of the M processing chains (14), the detection device (10) being in one of the following configurations:

2.

3.

4. • a first configuration in which M is equal to 1 so that all the detection surfaces (20) are connected to a single processing chain (14), the output of the single processing chain (14) forming a single output (S) for the detection device (10), or • a second configuration in which M is equal to N such that each detection surface (20) is connected to a separate processing chain (14), the amplification gains being the same for the amplification units of the N processing chains (14), the outputs of the N processing chains (14) being summed to form a single output (S) for the detection device (10), or • a third configuration in which M is between 2 and N and the outputs of the M processing chains (14) form M outputs for the detection device (10), the amplification gain of the amplification unit (22) of each processing chain (14) and the number of distinct detection surfaces (20) connected to each processing chain (14) being such that each processing chain (14) covers a different dynamic range from the other processing chains (14). Detection device (10) according to claim 1, wherein in the third configuration, the amplification gain of the amplification unit (22) of each processing chain (14) and the number of distinct detection surfaces (20) connected to each processing chain (14) are such that the dynamics of the M processing chains (14) overlap. Detection device (10) according to claim 2, wherein in the third configuration, the M processing chains (14) cover a total dynamic range greater than or equal to 90 dB, preferably greater than or equal to 100 dB. Detection device (10) according to any one of claims 1 to 3, wherein in the third configuration, the amplification units of the processing chains (14) connected to the same number of detection surfaces (20) have different amplification gains.

5. Detection device (10) according to any one of claims 1 to 4, wherein the detection device (10) further comprises a measuring unit suitable for performing a barycentric weighing of the luminous flux received on the N detection surfaces (20) and a calculation unit for the direction of origin of the luminous flux received as a function of the barycentric weighing performed.

6. Detection device (10) according to any one of claims 1 to 5, wherein N is equal to 4 so that the single detector (12) is a four-quadrant detector.

7. Detection device (10) according to any one of claims 1 to 6, wherein the filtering unit (24) of each processing chain (14) comprises a bandpass filter.

8. A method for detecting optical pulses, the method being implemented by a detection device (10) according to any one of claims 1 to 7, the detection method comprising: - the reception of an optical pulse by the N detection surfaces (20) of the single detector (12), the optical pulse having an identical power surface density on all the detection surfaces (20), - the processing of the signals at the output of the N detection surfaces (20) by the M processing chains (14), and - the detection of the optical pulse as a function of the processed signals.

9. A method according to claim 8, wherein the method also comprises measuring the amplitude and / or shape and / or direction of the detected optical pulse.

Images