Apparatus for measuring the performance of an optical detector, and related measurement methods.

Abstract

The apparatus (10) for measuring the performance of an optical detector (20) comprises: - Cryostat (17) - a holder (19) capable of receiving a detector (20), fixed inside the cryostat (17); - means for measuring the performance of the detector (20); a shield (12a-12b) arranged around the holder (19) capable of limiting radiation that may reach the holder in the wavelength range of the detector (20); - a single-mode optical fiber (16) in the wavelength range of the detector (20), inserted into the opening (15) of the cryostat (17); at least one light flux generating module (50) incorporating a fiber light source (23) capable of generating a light flux in an optical fiber (16); Equipped with.

Description

Technical Field

[0001] The present invention relates to an apparatus for measuring the performance of an optical detector and related measurement methods. More particularly, the present invention relates to detectors that implement quantum phenomena operating at low temperatures and that must be cooled to cryogenic temperatures, typically in the range of 50 to 200 K.

[0002] The present invention is intended to be applied to measuring the performance of detectors in the visible range, in the near infrared, i.e., infrared (also referred to as "Short-Wavelength InfraRed" or SWIR) having wavelengths in the range of 1 to 2.5 micrometers, in the mid infrared (also referred to as "Mid-Wavelength InfraRed" or MWIR) having wavelengths in the range of 3 to 8 micrometers, and in the far infrared (also referred to as "Long-Wavelength InfraRed" or LWIR) having wavelengths in the range of 8 to 14 micrometers.

[0003] Thus, the present invention may be applied to a number of detectors and to a number of distinct regions. More particularly, the present invention is intended to provide high-precision measurements for characterizing the performance of detectors intended for highly demanding applications, such as for example applications in the space field.

Background Art

[0004] To characterize the performance of quantum detectors, especially before they are mounted on satellites, - radiometric measurements, - residual magnetic measurements, - dark current measurements, and - spectral response measurements among other things, may be carried out.

[0005] Radiation measurements are intended to measure the output level response of the detector 20 in response to a beam of photons incident on the detector 20. For this purpose, as illustrated in Figure 1a, the radiation testbench 100 is equipped with a light source 101 that conventionally allows the acquisition of a pseudo-blackbody emission law with an emission peak of approximately 1 micrometer.

[0006] Typically, this light source 101 may have a color temperature of approximately 2,700 Kelvin and a light intensity of several tens of watts. In the sense of the present invention, "color temperature" characterizes the light source by comparison with an ideal material that emits light only through thermal action. Such a light source 101 conventionally comprises a winding that forms a resistor. However, the light L11 generated by this type of light source 101 is extremely non-uniform, and at long-field views, it is possible to observe light variations due to the shape of the resistor winding of the light source 101.

[0007] To correct this drawback, an integrating sphere 102 is used at the output of the light source 101 to obtain a more uniform luminous flux L12. More precisely, this integrating sphere 102 is driven by the light source 101 through an adjustable aperture 103. In fact, the adjustable aperture 103 allows adjustment of the amount of photons while maintaining a constant current for the light source 101, in order to ensure the stability of the light source 101. Furthermore, the adjustable aperture 103 does not change the distribution of light rays at the output of the integrating sphere 102.

[0008] To control the amount of photons entering the integrating sphere 102, a reference detector 104 is provided on the integrating sphere 102 to measure the amount of photons present in the integrating sphere 102. The controller 110 controls the power of the light source 101 and the aperture ratio of the aperture 103 according to the amount of photons searched and measured by the reference detector 104.

[0009] The luminous flux L12 at the output of the integrating sphere 102 penetrates a thermal enclosure 105, whose inner walls are intended to absorb radiation in the wavelength range of interest. This thermal enclosure 105 incorporates a shield 106, which allows for limiting the viewing angle of the detector 20. More precisely, stray light is captured by the shield 106 and absorbed by the walls of the thermal enclosure 105, so that only the luminous flux directly transmitted by the integrating sphere 102 reaches the detector 20.

[0010] The thermalization of the thermalized enclosure 105 makes it possible to limit the luminescence capacitance of the walls. For example, the enclosure can be maintained at a temperature of 12°C while the room temperature is substantially 22°C.

[0011] Therefore, the luminous flux L13 at the output of the thermal enclosure 105 reaches the detector 20 directly. The detector 20 is embedded in a cryostat 107, which is intended to replicate the operating conditions of the detector 20. For example, for space applications, the detector 20 may operate at extremely low temperatures and under vacuum.

[0012] More precisely, the vacuum level in cryostat 107 is 10 -5 mbar is sufficient, while the temperature of the cryostat 107 can be around 180K for the short-wavelength infrared detector, between 150K and 110K for the mid-wavelength infrared detector, and between 60K and 100K for the long-wavelength infrared detector.

[0013] To limit the propagation of the luminous flux L13 within the cryostat 107, a shielding body 112 may also be provided around the detector 20. With respect to this radiation test bench 100, the shielding body 112 is open to receive the luminous flux L13.

[0014] If there is a pressure difference and a temperature difference between the cryostat 107 and the thermal enclosure 105, the cryostat 107 is insulated from the thermal enclosure 105. The light beam L13 enters the cryostat 107 through the optical window 111. Between the optical window 111 and the shielding body 112, the cryostat is equipped with a filter that is conventionally set to be sized to allow only the wavelength range used by the detector 20 to pass through.

[0015] Furthermore, the detector 20 conventionally comprises an assembly of sensing elements or pixels. Conventionally, it is desired to measure the output levels of these sensing elements in response to a beam of incident photons. For this purpose, the detector 20 is assembled to a movable holder 108 using a displacement member 109 in order to adjust the center point P10 for receiving the light beam L13 so that this center point P10 is located at the center of the detector 20 before measuring the output level of the detector 20.

[0016] To perform the radiometric measurement, in the first step 120 illustrated in Figure 1b, the operator first assembles the detector 20 into the mobile holder 108 of the cryostat 107. The operator then controls the cryostat 107 to be under vacuum during the second step 121.

[0017] If the desired vacuum level is high, the cryostat 107 must be kept under vacuum for a particularly long time, conventionally 4 to 8 hours, during which time frequent control of pressure and temperature is required. Once the desired vacuum level is reached, in the third step 122, the cryostat 107 is cooled to the desired temperature. This third step 122 of cooling the cryostat 107 generally lasts for 1 to 3 hours.

[0018] Once these preparation steps for the cryostat 107 are complete, in step 123, the operator performs various radiation measurements on various sensitive elements.

[0019] For this purpose, the operator controls the displacement of the movable holder 108 to adjust the center point P10 for receiving the light beam L13 so that this center point P10 is located at the center of the detector 20. The output level of the sensitive element P10 is then measured for multiple photon quantities by changing the aperture of the diaphragm 103.

[0020] Therefore, measurements are performed one after another to measure the output levels of all the sensitive elements in the detector 20. Typically, these measurements together require nearly a full day of operation for the operator.

[0021] At the end of the measurement, in step 124, the temperature of the cryostat 107 must be gradually and slowly raised so that it returns to room temperature. To protect the physical integrity of the detector, this step 124 requires nearly a full day of operation, requiring frequent control of pressure and temperature. The final step 125 involves raising the vacuum level, after which the cryostat 107 can be removed from the radiation test bench 100. Overall, steps 120 through 125 together require nearly a week of operation for the operator.

[0022] Before or after obtaining performance data for the detector 20 in the radiation test bench 100, the detector 20 can be analyzed on another test bench, such as the residual magnetic test bench 200 shown in Figure 2a. For this purpose, the cryostat 107 is removed from the radiation test bench 100 and installed in the residual magnetic test bench 200.

[0023] Prior to installing the cryostat 107 with the detector 20 into the residual magnetism test bench 200, the filter attached to the shield 112 of the cryostat 107 may be changed.

[0024] The residual magnetic measurement is intended to observe the effect of the temporal variation of the scene on the detector's image. For this purpose, it is investigated whether the image previously captured by the detector affects the image being read out (residual magnetic effect), and for detectors that perform integration during readout, whether the image being integrated by the detector affects the image being read out (pre-residual magnetic effect).

[0025] To perform this measurement, it is necessary to use a light source 201 having a light intensity with controlled temporal variation. For this reason, the light source 201 is associated with a mechanical shutter 202 capable of closing the output of the light source 201 with a response time on the order of 1 millisecond.

[0026] The light source 201 may be the same as the light source 101 of the radiation test bench 100.

[0027] To perform the residual magnetic measurement, in the first step 220 illustrated in FIG. 2b, the operator first assembles the cryostat 107 on the residual magnetic test bench 200. The operator then controls, in the second step 221, placing the cryostat 107 under vacuum and, in the third step 222, cooling the cryostat 107.

[0028] When these steps of preparing the cryostat 107 are completed, in step 223, the operator performs different residual magnetic measurements. For this purpose, the operator controls the acquisition of a plurality of consecutive images that are changed during the closing time of the shutter 202, and the operator detects the pre-residual magnetic or residual magnetic effect on the acquired image by comparing the acquired image with a reference image. The residual magnetic effect appears when the acquired image exhibits artifacts related to the influence of previous images, while the pre-residual magnetic effect appears when the image being read out exhibits artifacts related to the influence of the image being integrated (acquired in the IWR, "Integrated While Read", mode) for a detector that performs integration during readout.

[0029] Similar to the radiation test bench 100, once the residual magnetism measurement is complete, the operator controls the temperature increase of the cryostat 107 in step 224 and the pressure increase in step 225. Overall, steps 220 through 225 together require several days of operation for the operator.

[0030] Before or after obtaining performance data for the detector 20 on the residual magnetism test bench 200, the detector 20 may be analyzed on a dark current test bench 300, such as the one illustrated in Figure 3a. For this purpose, the cryostat 107 is removed from the residual magnetism test bench 200 and installed on the dark current bench 300.

[0031] Darkness measurement, or dark current measurement, is intended to measure the dark current of the detector 20, i.e., the leakage current of components integrated into the detector 20 where magnetic flux is absent. The dark current level affects the detector performance. In fact, the higher the dark current, the higher the number of defective pixels, and the greater the dark current noise affects the general noise of the detector 20.

[0032] Therefore, dark current measurement partially sets the operating temperature of the detector 20. To measure dark current, the current inherent in the magnetic flux emanating from the test bench must be negligible with respect to the dark current to be measured.

[0033] Therefore, it is also important to vary the temperature during this measurement to ensure that the measured dark current is not formed from the background magnetic flux.

[0034] For this purpose, prior to the installation of the cryostat 107 incorporating the detector 20 into the dark current bench 300, the filter is removed from the shield 112 of the cryostat 107 and replaced with the shutter 313 to isolate the detector 20. Furthermore, the optical window 111 may also be covered with an opaque cover 311 to further isolate the detector 20.

[0035] These two levels of optical isolation allow for the measurement of the leakage current of the sensing element of the detector 20 by changing the temperature of the cryostat 107.

[0036] For this purpose, as illustrated in Figure 3b, the operator must also control the assembly of the detector 20 into the cryostat 107 in the first step 320, then the placement of the cryostat 107 under vacuum in the second step 321, and the cooling of the cryostat 107 in the third step 322. After measuring the leakage current of each sensing element in step 323, the operator controls the increase in the temperature of the cryostat 107 in step 324, and the increase in pressure in step 325. Overall, steps 320 to 325 together still require approximately one week of operation for the operator.

[0037] The final test bench is intended to obtain the spectral response of detector 20. Measuring the spectral response allows us to obtain the wavelength response of the pixels of detector 20. In reality, whatever technique is used, the response of detector 20 is not uniform with respect to wavelength. It can depend on many technical parameters.

[0038] Knowing the spectral response is often necessary, especially when it is desired that an optical filter be used before the detector 20. Therefore, it is possible to predict whether or not certain wavelengths should be filtered depending on the desired application.

[0039] To perform spectral response measurements, the wavelength of the monochromatic light beam L42 must be changed, and the ratio of the response of detector 20 to the response of a reference detector 404 having a known spectral response must be measured.

[0040] For this purpose, as illustrated in Figure 4a, the spectral response testbench 400 conventionally includes a light source 401 whose luminous flux is wavelength-modulated by a controller 410. The light source 401 may be the same as the light source 101 of the radiation testbench 100.

[0041] The luminous flux L41 generated by the light source 401 is transmitted to a diffraction grating 414, which enables the acquisition of a monochromatic luminous flux L42. The monochromatic luminous flux L42 is then processed by a filter 415 to eliminate higher-order effects of the diffraction grating 414 before being inserted into the integrating sphere 402. This integrating sphere 402 enables the generation of a luminous flux L44 for the detector 20 in addition to the luminous flux for the reference detector 404. For this purpose, the cryostat 107 of the detector is equipped with an open shielding body 112 and an equally open optical window 111. A filter may be incorporated into the shielding body 112 if possible.

[0042] To use the spectral response test bench 400, the operator must further control the following: in the first step 420, as illustrated in Figure 4b, assemble the detector 20 onto the cryostat 107; then in the second step 421, place the cryostat 107 under vacuum; and in the third step 422, cool the cryostat 107. After performing the spectral response measurement in step 423, the operator controls the increase in temperature of the cryostat 107 in step 424, and the increase in pressure in step 425. Overall, steps 420 through 425 together still require approximately one week of operation for the operator.

[0043] Therefore, in order to fully characterize the detector 20, the cryostat 107 must be transported between benches 100, 200, 300, and 400, and one or more operators must perform all steps 120-125, 220-225, 320-325, and 420-425. Thus, the full characterization of the detector 20 now requires approximately one month of work for the operator.

[0044] Furthermore, these different test benches, 100, 200, 300, and 400, also have significant bulk. [Overview of the project] [Problems that the invention aims to solve]

[0045] Therefore, the technical problem of the present invention is to characterize a detector more easily and quickly by performing multiple separate measurements, such as radiometric measurements, residual magnetic measurements, dark current measurements, and spectral response measurements. [Means for solving the problem]

[0046] To address this technical problem, the present invention provides a single test bench that allows different measurements to be performed without moving the detector. For this purpose, the detector is housed within a cryostat, which has a single-mode optical fiber that penetrates through its interior, intended to transmit a light beam in front of the detector.

[0047] A single-mode optical fiber has two ends: a first end located inside the cryostat, and a second end located outside the cryostat to which multiple beam generation modules containing fiber light sources can be connected for performing multiple separate measurements, such as radiation measurements, residual magnetism measurements, dark current measurements, and spectral response measurements.

[0048] For this purpose, according to a first aspect, the present invention is an apparatus for measuring the performance of an optical detector, - A cryostat capable of placing a detector under expected operating conditions, and equipped with means for placing it under vacuum and cooling it, - Means for measuring detector performance, - A holder that is fixed inside the cryostat and capable of receiving a detector, - Shielding elements placed around the retainer to limit radiation that can reach the retainer in the wavelength range of the detector, This relates to a device that includes the following features.

[0049] The present invention relates to a measuring device - A single-mode optical fiber in the operating wavelength range of the detector, inserted into the aperture of the cryostat, and A first end fixed to the opening of the shielding body and projecting a light beam onto all or part of the detector, The second end of the cryostat, which is intended to receive the light beam, An optical fiber equipped with, - At least two light beam generation modules, each incorporating a fiber light source capable of generating a light beam at the second end of an optical fiber, Equipped with, The means for measuring detector performance is capable of measuring the performance according to the light beam received at the second end, and multiple separate measurements can be performed by changing the module connected to the second end.

[0050] In the sense of the present invention, a "fiber light source" is a light source in which the generated light beam is coupled with the modes of an optical fiber associated with the light source. This fiber light source may be, for example, a light-emitting diode, a supercontinuum light source, or a laser. A supercontinuum light source can be obtained by directing a laser beam onto a material having nonlinear optical transmission characteristics, as the path of the laser beam through the material changes the spectrum of the laser beam.

[0051] A fiber optic light source refers to a light source coupled with an optical fiber, where the light beam emitted from the primary light source is guided through the inside of the optical fiber to the fiber output. The coupling between the light source and the fiber may be achieved by an array of two components and / or by using intermediate components (lenses, prisms, etc.).

[0052] The present invention therefore enables multiple measurements to be performed without moving the detector within the cryostat and without requiring it to be repeatedly placed under vacuum, by changing the light beam injected into the optical fiber using a module for generating the light beam. As a result, since the cryostat can remain on the same test bench and in the same state during the light beam changes, it is no longer necessary to perform numerous pressure increase / decrease and temperature increase / decrease stages.

[0053] The present invention therefore includes replacing the bulky elements of a radiometric and spectral response testbench, namely the light source and integrating sphere, with a module that incorporates a fiber optic light source and a single-mode optical fiber.

[0054] In fact, the luminous flux generated by fiber optic light sources, such as light-emitting diodes, has lower power than conventional light sources and exhibits a non-uniform spatial distribution due to its structure. It is thought that homogenization can be achieved using an integrating sphere. However, the use of an integrating sphere results in significant power loss, making it difficult to obtain the desired power level.

[0055] To solve this problem, the present invention provides the use of a single-mode optical fiber that spatially filters the light beam emitted from the fiber light source, enabling uniform divergence in its output, for example, in the form of a Gaussian beam, without loss of luminosity.

[0056] Therefore, the single-mode characteristics of the optical fiber allow for compensation of non-uniformity, and as a result, the optical flux transmitted to the detector at the output of the single-mode optical fiber is equivalent to the optical flux used in current technology.

[0057] As is well known, the single-mode characteristics of an optical fiber are obtained by selecting the step index (NA) and core diameter (a) of the optical fiber such that the normalized frequency (V) is on the order of 1 to 2.405, according to the following relationship:

[0058]

number

[0059] In the equation, λ corresponds to the wavelength of interest of the detector.

[0060] In the sense of the present invention, a "single-mode" optical fiber is an optical fiber having a normalized frequency (V) in the range of 1.2 to 3.8 in the wavelength range of interest. In fact, within this normalized frequency range, most of the wavelength range exhibits single-mode behavior, and the optical fiber is hardly affected by coupling with external light beams. Therefore, the optical fiber provides efficient isolation from disturbances.

[0061] The use of optical fiber also has other advantages.

[0062] In fact, optical fibers may be selected to have an optical sheath capable of filtering external radiation very efficiently and supporting the transmission of the light beam in the wavelength range of interest to the detector. Therefore, for applications in the mid-wavelength or long-wavelength infrared, optical fibers with silica cores are not optimal due to silica absorption.

[0063] Preferably, the optical fiber is formed from fluorinated glass, with a core made from a polycrystalline material such as Zblan, chalcogenide, or silver chloride or silver bromide. Zblan derives its name from the elements contained in fluorinated glass, particularly zirconium, barium, lanthanum, aluminum, and sodium, and it has high performance for mid-wavelength infrared applications with wavelengths in the range of 3 to 8 micrometers. Chalcogenide glass optical fibers have a broad transparency region in the infrared and significant nonlinear optical properties. Therefore, chalcogenide glass optical fibers are suitable for mid-wavelength infrared and long-wavelength infrared applications. Optical fibers with cores made from polycrystalline materials have been widely developed, and they therefore have a relatively low cost and allow for ensuring uniformity of the light beam transmitted to the detector in the entire infrared region.

[0064] Furthermore, the optical fiber may be incorporated into the cryostat with a very small aperture to limit the risk of temperature or pressure loss.

[0065] Furthermore, the use of optical fibers makes it possible to utilize integrated optical functions emanating from telecommunications.

[0066] Therefore, in order to perform radiation measurements, one of the beam generation modules, intended to be connected to the second end of the optical fiber, - A fiber light source intended to generate a light beam inside the first feeder optical fiber, - An optical attenuator capable of limiting the light beam, connected between the first feeder optical fiber and the second feeder optical fiber, - An optical splitter connected to a second feeder optical fiber, capable of splitting the optical beam of the second feeder optical fiber into third and fourth feeder optical fibers, wherein the third feeder optical fiber is connected to the second end of an optical fiber inserted into a cryostat, - A reference detector connected to a fourth feeder optical fiber, capable of measuring the luminous flux at the output of an optical splitter in order to control the power of the fiber light source and optical attenuator to obtain the expected measured luminous intensity, It is equipped with.

[0067] As a result, by implementing low-bulk optical elements in a limited manner, it is possible to perform radiation measurements as efficiently as those performed on current radiation test benches.

[0068] One of the beam generation modules, intended to be connected to the second end of the optical fiber for residual magnetism measurements, - A fiber light source intended to generate a light beam inside the first feeder optical fiber, - An optical shutter capable of blocking the light beam, connected between a first feeder optical fiber and a second feeder optical fiber, - An optical splitter connected to a second feeder optical fiber, capable of splitting the optical beam of the second feeder optical fiber into third and fourth feeder optical fibers, wherein the third feeder optical fiber is connected to the second end of an optical fiber inserted into a cryostat, - A reference detector connected to a fourth feeder optical fiber, capable of controlling the light beam at the output of the optical splitter. It is equipped with.

[0069] Unlike conventional residual magnetism test benches, this embodiment allows the use of an optical or acousto-optical shutter instead of a mechanical shutter. Here, the optical or acousto-optical shutter exhibits a response time on the order of 1 microsecond, while the mechanical shutter has a response time on the order of, for example, 1 millisecond. Therefore, residual magnetism measurements can be more accurate.

[0070] Furthermore, the subsequently implemented luminous flux generation module may be used to measure dark current by shutting off the power supply to the fiber optic light source. In fact, by using an optical fiber with a normalized frequency (V) in the range of 1.5 to 3 in the wavelength range of interest, the wavelength of the ambient light flux cannot be coupled with the optical fiber. Therefore, the use of a cover is not necessary.

[0071] To perform spectral response measurements, one of the beam generation modules, intended to be connected to the second end of the optical fiber, - A fiber light source intended to generate a light beam inside the first feeder optical fiber, - A diffraction grating connected to the first feeder optical fiber, - A filter connected to the output of the diffraction grating, - The second feeder optical fiber connected to the output of the second filter and It is equipped with.

[0072] Therefore, radiometric measurements, residual magnetic measurements, dark current measurements, and spectral response measurements can be performed using a fiber optic light source connected to an optical fiber inserted into the cryostat, and as a result, it is not necessary to move the detector between two measurements.

[0073] Therefore, to move from one measurement to another, it is not necessary to change the vacuum level or temperature of the cryostat; it is sufficient to change the operating mode and / or the luminous flux generation module. Thus, this device makes it possible to perform all necessary measurements in a simplified manner.

[0074] Therefore, according to a second aspect, the present invention relates to a method for measuring the performance of an optical detector using a measuring device of the type described above. This method is - The step of assembling a detector whose performance is to be measured into a cryostat holder, - The step of placing the cryostat under vacuum until the desired operating vacuum level for the detector is reached, - A step of cooling the cryostat until the desired operating temperature of the detector is reached, - The step of connecting the first optical beam generation module to the second end of the optical fiber, - A step to measure the detector performance, - A step of separating the first module from the second end of the optical fiber, - The step of connecting a second optical beam generation module to the second end of the optical fiber, - A step to measure the detector performance, - The step of heating the cryostat until it reaches room temperature, - The steps of returning the cryostat to ambient pressure and removing the detector and Includes.

[0075] Preferably, four separate measurements are performed, and therefore this method, - The step of connecting a first beam generation module for performing radiation measurements to the second end of the optical fiber, - Detector radiation measurement step, - A step of separating the first optical beam generation module from the second end of the optical fiber, - A step of connecting a second optical beam generation module for performing residual magnetism measurements to the second end of the optical fiber, - A step of measuring the residual magnetism of the detector, - A step of measuring the dark current of the detector, - A step of separating the second optical beam generation module from the second end of the optical fiber, - A third beam generation module for performing spectral response measurements is connected to the second end of the optical fiber. - Steps to measure the spectral response of the detector and Includes.

[0076] The present invention will be best understood by reading the following description, the details of which are given merely as examples and are developed in relation to the accompanying drawings, where the same reference numerals relate to the same elements. [Brief explanation of the drawing]

[0077] [Figure 1a] This is a simplified representation of the current technology's radiation testbench. [Figure 1b] Figure 1a shows an example of the steps involved in implementing a bench-based radiometric measurement. [Figure 2a] This is a simplified representation of the current technology's residual magnetism test bench. [Figure 2b] Figure 2a shows an example of the steps involved in implementing residual magnetism measurement based on the bench. [Figure 3a] This is a simplified representation of the current technology's dark current test bench. [Figure 3b] Figure 3a shows an example of the steps involved in implementing dark current measurement based on the bench. [Figure 4a] This is a simplified representation of the current technology's spectral testbench. [Figure 4b] Figure 4a shows an example of the steps involved in implementing a bench-based spectral measurement. [Figure 5] This is a simplified representation of an apparatus for measuring the performance of an optical detector according to one embodiment of the present invention. [Figure 6] Figure 5 shows a schematic example of the configuration of the measuring device used to obtain radiometric measurements. [Figure 7] Figure 5 shows an example of the configuration of the measuring apparatus used to obtain residual magnetism measurements. [Figure 8] Figure 5 shows an example of the configuration of the measuring apparatus used to obtain spectral measurements. [Figure 9] This is an example of the variation in luminous flux at the output of a fiber optic light source in the configuration shown in Figure 6. [Figure 10] Figure 6 illustrates an example of the variation in optical flux at the output of an optical fiber inserted into a cryostat. [Figure 11] This is an example of the variation in the light beam on the detector in the configuration shown in Figure 6. [Figure 12] Figure 1a shows an example of the variation in luminous flux at the output of an integrating sphere in a radiation test bench using the current technology. [Figure 13] Figure 1a shows an example of the variation in luminous flux at the input of the optical window in the current technology radiation test bench. [Figure 14] Figure 1a shows an example of the variation in light beam on the detector in a current technology radiation test bench. [Figure 15] This is an example of the steps for implementing radiation measurement, residual magnetism measurement, dark current measurement, and spectral measurement according to one embodiment of the method of the present invention. [Modes for carrying out the invention]

[0078] As illustrated in Figure 5, the present invention aims to provide a test apparatus 10 that enables the characterization of the performance of an optical detector 20. For this purpose, the optical detector 20 is mounted on a cryostat 17 using a retainer 19. The retainer 19 may be formed from a plate intended to receive the electronic circuit into which the detector 20 is mounted. Thus, the retainer 19 may receive power connectors for the electronic circuit of the detector 20 assembly.

[0079] The retainer 19 is coupled to the inner wall of the cryostat 17 using legs 18. Typically, four legs 18 are positioned at the four corners of the retainer plate 19. To power the detector 20 and transmit information feedback signals, the cryostat 17 is conventionally crossed by a set of connectors, not shown in Figure 5. Thus, once the detector 20 is assembled to the retainer 19, the latter can be powered and controlled as well as its operation under conditions expected during use of the detector 20.

[0080] For example, detector 20 may be intended for space applications where detector 20 operates at extremely low temperatures and ultra-high vacuum levels. Therefore, the cryostat includes means for placing detector 20 under vacuum and cooling it, which would allow it to be placed under its expected operating conditions.

[0081] The apparatus for measuring the power supply and detector performance is conventionally located outside the cryostat 17, along with means for cooling the cryostat 17 and placing it under vacuum.

[0082] Around the detector 20, the cryostat 17 is provided with a shield intended to limit the radiation that can reach the retainer 19 in the wavelength range of the detector 20. In the example of Figure 5, the shield is formed of two parts. A parallelepiped or cylindrical portion 12a is attached to the inner wall of the cryostat 17 or to the retainer 19. More specifically, the parallelepiped or cylindrical portion 12a of the shield extends beyond the height of the retainer 19 with respect to the inner wall of the cryostat to which the legs 18 are attached. Above this first parallelepiped or cylindrical portion 12a, a second pyramidal or conical portion 12b is provided beyond the detector 20. At the apex of this pyramidal or conical portion 12b, the shield has an opening to receive the first end 14 of an optical fiber 16. This optical fiber 16 also passes through an opening 15 of the cryostat, which is positioned in front of the opening of the pyramidal or conical portion 12b of the shield.

[0083] Of course, the shape of the shield can be changed without altering the present invention. For example, the shield may have a tapered portion or a first cylindrical portion with any other shape at its apex that allows for the formation of a small opening in front of the detector 20. In fact, the present invention gives the shield of the cryostat 17 two distinct roles: - The first role is to block undesirable light beams present in cryostat 17, and - A second role: to position the first end 14 of the optical fiber 16 in front of the detector 20.

[0084] In fact, the first end 14 of the optical fiber 16 must be positioned such that the light beam emanating from this first end 14 primarily covers the focal plane of the detector 20. For this purpose, the dimensions of the cryostat must be adapted to the need to guide this first end 14 of the optical fiber 16. For example, the volume of the cryostat 17 is 250 cm³. 3 From 1,000cm 3 It may be within this range. Thereafter, the volume of the cryostat 17 may be three times larger than the volume of a cryostat of current technology, and this volume depends on the type of optical fiber 16 used and its numerical aperture at the level of the first end 14. The numerical aperture characterizes the receiving cone at the input of the fiber and the propagation cone at the output of the fiber. For example, the numerical aperture of the optical fiber 16 may be selected between 0.1 and 0.4 in single mode.

[0085] Preferably, the materials of the inner wall of the cryostat 17, the shields 12a and 12b, the retainer 19, and the legs 18 are selected to limit the desorption and attachment of molecules when the detector 20 is placed under vacuum. Similarly, the aperture 15 of the cryostat 17 is preferably sized to match the diameter of the optical fiber 16 to limit the intake of stray light flux into the cryostat 17.

[0086] More specifically, the optical fiber 16 is a single-mode optical fiber primarily in the wavelength range of the detector 20. This single-mode characteristic of the optical fiber 16 indicates that the optical fiber preferably has a normalized frequency in the range of 1.2 to 3.8 in the wavelength range of interest. For example, the optical fiber may have a core made from Zblan, chalcogenide glass, or a polycrystalline material. Furthermore, the optical fiber 16 may be covered with a sheath, such as an acrylate sheath, selected to particularly limit the risk of stray light transmission to the detector 20. The sheath may be formed from the same material as the optical fiber 16, which is therefore associated with dopants that allow for the definition of a transmission window, and thus the spectral bands in which the optical fiber 16 can be used.

[0087] By using an optical fiber whose normalization frequency is in the range of 1.2 to 3.8 in the wavelength range of interest of the detector 20, the optical fiber 16 is less susceptible to the incorporation of external stray flux from one end, in particular, because these stray fluxes have wavelengths that are clearly distinct from those that can be coupled with the optical fiber 16. Furthermore, the sheath limits the risk of integration of stray flux outside the end of the optical fiber 16.

[0088] In order to transmit a beam of light inside the optical fiber 16, the second end 22 of the optical fiber 16 is intended to receive the beam of light from the fiber light sources 23, 33, and 43.

[0089] This fiber optic light source is preferably incorporated into a beam generation module used according to the desired measurement. Thus, the detector 20 may be incorporated into the cryostat 17, and the second end 22 of the optical fiber may receive a beam generation module according to the desired measurement.

[0090] This fiber light source, intended to transmit a beam of light to the second end 22 of the optical fiber 16, is formed from, for example, a light-emitting diode, a supercontinuum light source, or a laser light source.

[0091] When radiation measurements are desired, the beam generation module 50 includes, for example, a fiber optic light source 23 connected to a first feeder optical fiber 28, as illustrated in Figure 6. This feeder optical fiber is connected to an optical attenuator 24, which allows for limiting the beam transmitted across the first feeder optical fiber 28. At the output of the attenuator 24, a second feeder optical fiber 29 is implemented to transmit the beam at the output of the optical attenuator 24 to an optical splitter 25. This optical splitter 25 includes two outputs: a first output connected to a third feeder optical fiber 30, which itself is connected to the second end 22 of the optical fiber 16, and a fourth feeder optical fiber 31 connected to a reference detector 26.

[0092] The controller 11 controls the power of the fiber light source 23 and the attenuation rate of the optical attenuator 24 according to the desired amount of photons measured by the reference detector 26.

[0093] Figure 9 illustrates the spectral distribution of the light beam generated in the optical fiber 23 at the output of the fiber light source 23. In Figures 9 to 14, the spectral distribution of the light beam at the fiber output is given by W / cm² with respect to the wavelength in nanometers. 2 This is illustrated in the diagram. This spectral distribution may be measured using a spectroradiometer. Furthermore, this spectral distribution of the light flux at the fiber output is also known as the "spectral density of the energy flux."

[0094] In the example shown in Figure 9, the use of the fiber light source 23 and the optical fiber 28 already makes it possible to obtain a luminous flux that occupies the center of the wavelength range of interest and has a very acceptable luminous intensity.

[0095] Figure 10 illustrates the luminous flux L1 at the output of the optical fiber 16 in the cryostat 17 after passing through the optical attenuator. It can be observed that this luminous flux L1 retains its spectral width but has a reduced light intensity. Figure 11 illustrates the luminous flux measured at the detector 20 after the propagation of this luminous flux L1 within the cryostat. Here again, the luminous flux measured at the detector 20 retains a very accurate spectral width but has lost some of its luminosity.

[0096] Therefore, the use of the fiber light source 23 and the optical fibers 28, 29, 30, and 16 adapted to the transmission mode of the fiber light source 23 enables the efficient transmission of a beam of light with a very small bulk element. For comparison, Figure 12 illustrates the beam of light L12 at the output of the integrating sphere 102 in Figure 1a, and it can be observed that this beam of light has a considerably less precise spectral width than the beam of light transmitted by the fiber light source 23 and the optical fibers 28, 29, 30, and 16 in association.

[0097] Similarly, in the example of Figure 1a, the luminous flux L13 at the input of the cryostat is illustrated in Figure 13 and also has a significant spectral width. Only after passing through the filter of the shielding body 112 does the spectral width of the luminous flux in the current technology decrease. Therefore, as illustrated in Figure 14, the luminous flux transmitted to the detector 20 in the current technology radiation test bench also has a spectral width similar to that of the present invention, but with a lower light intensity level.

[0098] As a result, the present invention enables the generation of a more powerful luminous beam that is as accurate as that transmitted by existing radiant test benches, such as those illustrated in Figure 1a, due to its lower cost, less bulk, and lower power consumption.

[0099] Furthermore, the possibility of changing the light beam generation module without having to move the cryostat 17 allows for a significant improvement in measurement speed compared to the use of multiple consecutive benches with current technology.

[0100] In addition to module 50, as illustrated in Figure 6, for radiation measurements, module 51 can also be connected for residual magnetism measurements.

[0101] This module 51 includes a fiber optic light source 33, for example, the same light source as the light source 23 of module 50, or a light source having different characteristics. This fiber optic light source 33 is connected to a first feeder optical fiber and is itself connected to an optical shutter 35. The optical shutter 35 is connected to a second feeder optical fiber 29 and is itself connected to an optical splitter 25. This optical splitter 25 has two outputs: - The first output, which is connected to the third feeder optical fiber 30 and is itself connected to the second end 22 of the optical fiber 16, - A second output connected to a fourth feeder optical fiber 31 connected to a reference detector 34.

[0102] The controller 11 allows control of the light beam emitted by the fiber optic light source and the optical shutter 35 in order to measure the remanent magnetism and pre-residual magnetism effect by comparing the images acquired by the detector 20 and the reference detector 34.

[0103] To obtain dark current measurements, it is not necessary to use a dedicated luminous flux generation module; it is sufficient to turn off the fiber optic light source 23 or 33 of the luminous flux generation module 50 or 51.

[0104] In fact, without the luminous flux generated by the fiber light source 23 or 33, the wavelength of the ambient light flux cannot be coupled with the optical fiber, and as a result, it is possible to efficiently measure the dark current.

[0105] With respect to the spectral response, as illustrated in Figure 8, the beam generation module 52 may be connected to the second end 22 of the optical fiber 16. For example, this module 52 includes a fiber light source 43 connected to a first feeder optical fiber 44. This first feeder optical fiber 44 is also connected to a diffraction grating 46. The output of the diffraction grating 46 is projected onto a filter 47 that allows limiting the diffraction order of the beam at the output of the diffraction grating 46. This filtered beam is integrated in a second feeder optical fiber 30. This second feeder optical fiber 30 is connected to the second end 22 of the optical fiber 16.

[0106] Therefore, the controller 11 can control the parameters of the diffraction grating 46 in order to perform spectral response measurements.

[0107] To perform spectral response measurements, the wavelength of the light beam at the output of fiber 16 must be changed, and the ratio of the response of detector 20 to the response of a reference detector with a known spectral response must be measured.

[0108] For this purpose, in order to directly obtain the ratio of the response of detector 20 to the response of the reference detector, the reference detector may be positioned next to detector 20 in the cryostat.

[0109] As a variation, the reference detector may be positioned on a second cryostat having similar characteristics to that of the cryostat 17 of detector 20, and this second cryostat also incorporates an optical fiber 16 capable of receiving a light beam. After or before measurements are taken on detector 20, the optical fiber 30 can be connected to the optical fiber of the second cryostat to perform the same measurements on the reference detector. The ratio of the response of detector 20 to the response of the reference detector is therefore calculated at the end of the two measurement stages on detector 20 and the reference detector.

[0110] As illustrated in Figure 15, a method for measuring the performance of the optical detector 20 may include a first step 60 of assembling the detector 20 into the cryostat holder 19. A second step 61 consists of placing the cryostat under vacuum until the detector 20 reaches a desired operating vacuum level. Means for cooling the cryostat 17 are then implemented in step 62, and simultaneously, in step 63, a first light beam generation module may be connected to the second end 22 of the optical fiber 16. Once the light beam generation modules 50-52 are connected to the second end 22 of the optical fiber 16, the performance of the detector 20 can be measured in step 64.

[0111] Next, once all measurements of the detector 20's performance have been performed using the connected modules 50-52, modules 50-52 can be separated in step 65. During this separation of modules 50-52, it is not necessary to change the temperature or vacuum level of the cryostat 17, and as a result, in step 66, the second modules 50-52 can then be connected to the optical fiber 16. Then, based on the new modules 50-52 connected to the optical fiber 16, the performance of the detector 20 can be measured in step 67.

[0112] Therefore, multiple modules 50-52 can be connected in sequence to the optical fiber 16 without needing to change the temperature or vacuum level of the cryostat 17.

[0113] For example, you may perform the following sequence of steps: Step 63: Connecting the generating module 50 to enable radiometric measurements. Step 64: Radiation measurement of the performance of detector 20. Step 65: Separation of Module 50, Step 66: Connecting module 51 to measure residual magnetism. Step 67: Measurement of the residual magnetism of the detector. Step 68: Measurement of the dark current of the detector by turning off the fiber optic light source 33 of module 51.

[0114] Once residual magnetism and dark current measurements are performed by module 51, the following steps are then performed in sequence: Step 69: Separation of module 51, Step 70: Connecting module 52, which enables measurement of spectral response. Step 71: Measurement of the spectral response of detector 20.

[0115] Regardless of the number of modules 50-52 connected to the optical fiber 16 to characterize the detector 20, the method ends with step 72 of heating the cryostat 17 and step 73 of returning the cryostat 17 to ambient pressure and removing the detector 20.

[0116] Therefore, the present invention makes it possible to obtain an apparatus 10 for measuring the performance of an optical detector 20 which has low bulk and limited cost with respect to the use of multiple test benches. In fact, the present invention makes it possible to swap out the light beam generation modules and couple them to optical fibers partially incorporated into the cryostat 17. This possibility of coupling different modules 50-52 to the optical fiber 16 makes it possible to improve the speed and time required to perform all measurements.

[0117] For example, when it is desired to characterize the detector 20 by performing radiation measurements, residual magnetism measurements, dark current measurements, and spectral response measurements, the present invention makes it possible to obtain a division of the measurement time by a coefficient in the range of 5 to 10.

[0118] Furthermore, it was observed that the accuracy of the obtained measurements was higher than that obtained with current technology. In fact, the repeatability of measurements is estimated to be 0.1% for current technology devices, while the present invention makes it possible to obtain a repeatability of 0.01%. This repeatability is calculated by repeating the same measurement many times and by calculating the divergence between these measurements. [Explanation of symbols]

[0119] 10 Test equipment 11 Controllers 12a Parallelepiped or cylindrical part 12b Pyramid or cone 14 The first edge 15 Opening 16 Optical Fibers 17. Cryostat 18 legs 19 Cage 20 Optical Pixels 22 The second end 23, 33, 43 Fiber optic light source 24 Optical attenuator 25 Optical Splitter 26 Reference detector 28. First feeder optical fiber 29, 30 Second feeder optical fiber 30. Third feeder optical fiber 31. The fourth feeder optical fiber 34 Reference detector 35 light shutter 44 First feeder optical fiber 46 Diffraction Gratings 47 Filters 50, 51, 52 Light Beam Generation Modules L1 luminous flux

Claims

1. An apparatus (10) for measuring the performance of an optical detector (20), - A cryostat (17) capable of placing the optical detector (20) under its expected operating conditions, comprising means for placing it under vacuum and cooling it, - A holder (19) that is fixed inside the cryostat (17) and capable of receiving the optical detector (20), - Means for measuring the performance of the optical detector (20), - Shielding bodies (12a to 12b) arranged around the retainer (19) that are capable of limiting radiation that may reach the retainer in the wavelength range of the optical detector (20) and In a measuring device (10) equipped with, - A single-mode optical fiber (16) in the wavelength range of the optical detector (20), wherein the optical fiber (16) is inserted into the aperture (15) of the cryostat (17), and A first end (14) is fixed to the opening of the shielding body (12a to 12b) and projects a light beam onto the entire or a part of the optical detector (20), The second end (22) on the outside of the cryostat (17), which is intended to receive the light beam, An optical fiber (16) and - At least two modules (50-52) for generating the light beam, each incorporating a fiber light source (23, 33, 43) capable of generating a light beam at the second end (22) of the optical fiber (16), Equipped with, An apparatus for measuring the performance of an optical detector (20), characterized in that the means for measuring the performance of the optical detector (20) is capable of measuring the performance according to the light beam received at the second end (22), and a plurality of separate measurements can be performed by replacing the modules (50-52) connected to the second end (22).

2. An apparatus for measuring the performance of an optical detector (20) according to claim 1, wherein the fiber light sources (23, 33, 43) are formed from light-emitting diodes, supercontinuum light sources, or lasers.

3. An apparatus for measuring the performance of an optical detector (20) according to claim 1, wherein a core made of fluorinated glass, chalcogenide glass, or polycrystalline material is formed on the optical fiber (16).

4. A first luminous flux generating module (50), which is one of the modules, is intended to be connected to the second end (22) of the optical fiber (16) in order to perform radiation measurements. - A fiber light source (23) intended to generate a light beam inside the first feeder optical fiber (28), - An optical attenuator (24) capable of limiting the light beam, the attenuator (24) being connected between the first feeder optical fiber (28) and the second feeder optical fiber (29), - An optical splitter (25) connected to the second feeder optical fiber (29) capable of splitting the optical beam of the second feeder optical fiber (29) into a third feeder optical fiber (30) and a fourth feeder optical fiber (31), wherein the third feeder optical fiber (30) is connected to the second end (22) of the optical fiber (16) inserted into the cryostat (17), - A reference detector (26) connected to the fourth feeder optical fiber (31), and capable of measuring the luminous flux at the output of the optical splitter (25) in order to obtain a predicted luminous intensity by controlling the power of the fiber light source (23) and the optical attenuator (24), An apparatus for measuring the performance of the optical detector (20) according to claim 1, comprising the above.

5. A second light beam generation module (51), which is one of the modules, is intended to be connected to the second end (22) of the optical fiber (16) in order to perform residual magnetism measurements. - A fiber light source (33) intended to generate a light beam inside the first feeder optical fiber (28), - An optical shutter (35) capable of blocking the light beam is connected between the first feeder optical fiber (28) and the second feeder optical fiber (29), - An optical splitter (25) connected to the second feeder optical fiber (29) capable of splitting the optical beam of the second feeder optical fiber (29) into a third feeder optical fiber (30) and a fourth feeder optical fiber (31), wherein the third feeder optical fiber (30) is connected to the second end (22) of the optical fiber (16) inserted into the cryostat (17), - A reference detector (34) connected to the fourth feeder optical fiber (31) is capable of controlling the light beam at the output of the optical splitter (25), An apparatus for measuring the performance of the optical detector (20) according to claim 1, comprising the above.

6. An apparatus for measuring the performance of an optical detector (20) according to claim 5, wherein the second light beam generation module (51), which is intended to be connected to the second end (22) of the optical fiber (16) for performing residual magnetism measurements, is also implemented for performing dark current measurements by cutting off the power supply to the fiber light source (33).

7. An apparatus for measuring the performance of an optical detector (20) according to claim 1, wherein the optical fiber (16) has a normalized frequency (V) in the range of 1.2 to 3.8 in the wavelength range of interest.

8. A third beam generation module (52), which is one of the modules, is intended to be connected to the second end (22) of the optical fiber (16) in order to perform spectral response measurements. - A fiber light source (43) intended to generate a light beam inside the first feeder optical fiber (44), - A diffraction grating (46) connected to the first feeder optical fiber (44), - A filter (47) connected to the output of the diffraction grating (46), - A second feeder optical fiber (48) connected to the output of the filter (47), An apparatus for measuring the performance of the optical detector (20) according to claim 1, comprising the above.

9. A method for measuring the performance of an optical detector (20) using an apparatus for measuring the performance of an optical detector (20) according to any one of claims 1 to 8, - Step (60) of assembling the optical detector (20) to the holder (19) of the cryostat (17), - Step (61) of placing the cryostat (17) under vacuum until the optical detector (20) reaches a desired operating vacuum level, - Step (62) of cooling the cryostat (17) until the optical detector (20) reaches a desired operating temperature, - Step (63) of connecting the first optical beam generation module (50-52) to the second end (22) of the optical fiber (16), - A step (64) to measure the performance of the optical detector (20), - A step (65) of separating the first light beam generation module (50-52) from the second end (22) of the optical fiber (16), - Step (66) of connecting the second optical fiber (16) to the second end (22) of the optical fiber (16), - A step (67) to measure the performance of the optical detector (20), - A step (72) of heating the cryostat (17) until it reaches room temperature, - Step (73) of returning the cryostat (17) to ambient pressure and removing the optical detector (20), Methods that include...

10. - A step (63) of connecting a first light beam generation module (50) for performing radiation measurement to the second end (22) of the optical fiber (16), - The radiation measurement step (64) of the optical detector (20), - A step (65) of separating the first light beam generation module (50) from the second end (22) of the optical fiber (16), - A step (66) of connecting a second optical beam generation module (51) for performing residual magnetism measurement to the second end (22) of the optical fiber (16), - A step (67) of measuring the residual magnetism of the optical detector (20), - A step (68) of measuring the dark current of the optical detector (20), - A step (69) of separating the second optical fiber (16) from the second end (22) of the optical fiber (16), - Step (70) of connecting a third optical beam generation module (52) for performing spectral response measurement to the second end (22) of the optical fiber (16), - A step (71) of measuring the spectral response of the optical detector (20), The method according to claim 9, including the method described in claim 9.

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