Lens-free infrared multispectral imaging device and method of manufacture

Abstract

The present invention provides a lens-free infrared imaging device (1) intended for imaging a sample (2), comprising at least one light source (3, 3a, 3b) configured to emit light according to several wavelengths in the infrared range, and at least one sensor (4) configured to interact with the sample and detect a portion of the emitted light, characterized in that the sensor comprises a plurality of pixels (41), and the sensor (4) is configured to detect a reflected portion of the emitted light. The present invention also provides a method for manufacturing this device.

Description

[Technical Field]

[0001] The present invention relates to the field of lens-free infrared imaging. The present invention will have particularly advantageous, but not exclusive, application in the imaging of biological tissue. [Background technology]

[0002] Many fields of application, such as agribusiness, medicine, and healthcare, require the detection and identification of chemical or biochemical compounds for contamination detection and diagnostic purposes. Infrared (IR) spectroscopy is a widely used analytical technique for detecting and identifying such chemical or biochemical compounds.

[0003] A known solution for generating an image of the sample to be analyzed is to map the sample via a microscope and a Fourier transform IR (FTIR) spectrometer coupled with a polychromatic IR light source. Such a system makes it possible to scan the sample and obtain multispectral images with a spatial resolution of about 10 μm. The drawback of this type of solution is that it requires a resolution of several mm. 2 or a few centimeters 2 The disadvantages of such systems are that the analysis of a large sample surface area is time consuming, the field of view of the sample that is imaged is limited, and such systems are complex, expensive, and large.

[0004] With the advent of quantum cascade lasers (QCLs), it is now possible to generate multiple monochromatic IR light sources covering the spectral range of polychromatic IR sources. It is then no longer necessary to use an FTIR spectrometer to spectrally analyze the light interacting with the sample. An infrared-sensitive detector is sufficient to quantify the intensity of the light transmitted or scattered by the sample for each wavelength of the QCL.

[0005] Furthermore, by using an IR imager containing multiple detectors, typically bolometers, forming a pixel matrix, it is possible to achieve multispectral imaging without the use of an FTIR spectrometer. Such a solution allows for the generation of a wide field of view and spatially resolved images without scanning the object. This subsequently makes multispectral imaging in the mid-infrared faster. Furthermore, such instruments, including QCLs and IR imagers, can be relatively compact. This allows for the design of portable IR multispectral imaging devices.

[0006] Non-Patent Document 1 discloses an IR imaging device for observing samples, particularly biological samples. Chapter 5 of this document, "5. Microspectroscopy of Thin Tissue Sections," specifically mentions the coupling of a QCL and a bolometer in an IR multispectral imaging system. This allows for the observation of a sample in the form of a thin strip by placing the sample between a QCL-based light source and a bolometer-based image sensor. Therefore, a wide-field image can be acquired without scanning the object. This reduces the image acquisition time. Therefore, the amount of analysis achieved by IR multispectral imaging is significantly increased.

[0007] Such devices therefore allow for the acquisition of spatially resolved spectral information without scanning the sample. Over a wide field of view, multiple images of the sample can be acquired, each a function of the sample's spectral response to light emitted by a different QCL. This makes it possible to perform diagnostics on biological tissue, for example, to determine cancerous and healthy zones.

[0008] The drawback of this device is that the sample must be prepared in the form of a thin strip, thus necessitating sampling of the object to be imaged. This sampling is invasive, and does not allow for in vivo medical measurements or in situ quality control, i.e., directly on the object.

[0009] Therefore, there is a need to provide a non-invasive, compact IR multispectral device that is capable of producing wide-field images with short acquisition times. [Prior art documents] [Non-patent literature]

[0010] [Non-Patent Document 1] K. Isensee et al., Biomedical applications of mid-infrared quantum cascade lasers - a review, The Analyst, vol.143, no.24, pp.5888‐5911, 2018 Summary of the Invention [Problem to be solved by the invention]

[0011] The present invention aims to propose a device that at least partially overcomes the drawbacks of the current solutions mentioned above.

[0012] Another object of the present invention relates to a method for manufacturing a non-invasive IR multispectral imaging device.

[0013] Other objects, features, and advantages of the present invention will become apparent upon consideration of the following description and the accompanying drawings. It will be understood that other advantages are also incorporated. In particular, the particular characteristics and particular advantages of the apparatus may be applied to the method, mutatis mutandis, and vice versa. [Means for solving the problem]

[0014] To achieve these aims, the invention proposes a lens-free infrared imaging device intended for imaging a sample or object, said device comprising at least one light source configured to emit light according to several wavelengths in the infrared range, and at least one sensor configured to detect a portion of the emitted light upon interaction with the sample or object, said sensor comprising a plurality of pixels.

[0015] Advantageously, the sensor is configured to detect reflected portions of the emitted light, in particular along a detection direction having a direction opposite to the emission direction of the light emitted by the light source.

[0016] In this method, there is no need to shape the sample to be imaged. The device advantageously allows imaging at least a portion of a sample or object non-invasively and without sampling. For example, it is sufficient to place the device in the immediate vicinity of the sample to be imaged in order to acquire multiple images with several wavelengths in the IR range.

[0017] This device also allows these images to be generated with reduced acquisition times: each image is actually acquired directly in a single acquisition, in contrast to systems based on the mapping principle, which require an acquisition at each point of the image to be generated.

[0018] The device further advantageously does not have an optical lens for forming an image on the sensor, which greatly simplifies the instrumentation, reduces the cost of the device, further reduces the bulkiness of the device, and improves the compactness of the device.

[0019] Furthermore, there is no need to provide space between the IR light source and the IR imager to introduce the sample, and the bulk of such a device is also reduced.

[0020] The present invention also relates to a method for using such a reflective IR spectrum imaging device, where the device is in contact with or close to the area of ​​a sample to be imaged, with the distance between the area to be imaged and the sensor being less than 200 μm. This maximizes the flow of reflected light collected by the sensor. Such use is particularly advantageous for diagnosing biological tissue, for example, in the field of histopathology to distinguish between healthy and tumorous tissue.

[0021] The invention also relates to a method for manufacturing a device in which the light source is a secondary light source formed by a photonic chip comprising a plurality of emitters in the form of passive extraction structures, said passive extraction structures being combined with a primary light source configured to emit light according to several wavelengths in the IR range, said method comprising the steps of: providing a primary light source; forming a photonic chip intended to re-emit at its emission surface light emitted from a primary light source; providing a sensor on a detection surface, the sensor comprising a plurality of pixels capable of detecting a portion of the light emitted by the primary light source; Assembling the photonic chip and the sensor so that the emitting surface and the receiving surface face one and the same side; coupling a primary light source to a passive extraction structure of a photonic chip; At least includes.

[0022] The objects, goals, features and advantages of the present invention will become apparent from the following detailed description of embodiments of the invention illustrated by the accompanying drawings. [Brief explanation of the drawings]

[0023] [Figure 1A] 1 shows a schematic perspective view of an IR multispectral imaging device according to an embodiment of the present invention; [Figure 1B] FIG. 1B is an enlarged view of a portion of the device shown in FIG. 1A. [Figure 2]1 illustrates a schematic cross-sectional view of an IR multispectral imaging device according to an embodiment of the present invention; [Figure 3] 1 shows a calculation of the flow of light reflected by the sample and received by a pixel of the IR imager as a function of the distance between the pixel and the sample. [Figure 4] 1 shows a schematic perspective view of a photonic chip according to an embodiment of the present invention; [Figure 5] 2 shows a schematic top view of the relative arrangement of pixels of a detection matrix and emitters of an emission matrix according to an embodiment of the present invention; [Figure 6A] 1A and 1B show schematic cross-sectional views of passive outcoupling structures formed on a photonic chip facing a waveguide according to an embodiment of the present invention; [Figure 6B] 10A and 10B show schematic cross-sectional views of passive outcoupling structures formed on a photonic chip facing a waveguide according to another embodiment of the present invention; [Figure 7] 1 illustrates a cross-sectional view of a matrix IR sensor and a photonic chip stacked together according to an embodiment of the present invention; [Figure 8A] 1 shows a schematic top view of a detection matrix according to an embodiment of the present invention; [Figure 8B] 1 shows a schematic top view of a light-emitting matrix according to an embodiment of the present invention; [Figure 8C] 1 shows a schematic top view of the superposition of an emission matrix and a detection matrix according to an embodiment of the present invention; [Figure 9A] 1A and 1B show schematic cross-sectional views of the assembly of a first substrate including passive outcoupling structures with a second substrate including waveguides to form a photonic chip according to an embodiment of the present invention; [Figure 9B] As shown in Figure 9A, the resulting photonic chip after assembly is shown schematically in a cross-sectional view. [Figure 10] 10A to 10H schematically illustrate steps for fabricating a passive extraction structure according to an embodiment of the present invention. [Figure 11]11A to 11D show schematic steps for fabricating a waveguide according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] The drawings are given as examples and are not limiting of the invention. They constitute a schematic representation of principles intended to facilitate understanding of the invention and are not necessarily adapted to the scale of a real application. In particular, the dimensions of the various structures (extraction, waveguides, pixels) are not shown to scale.

[0025] Before commencing a detailed review of the embodiments of the present invention, it should be noted that, optionally, the present invention includes at least one of the following optional features, which may be used in conjunction with or as an alternative:

[0026] According to one example, the light source has an emission surface intended to emit light in the direction of the sample to be imaged, and the sensor has a detection surface intended to receive the portion of the light emitted by the light source that is reflected by the sample, said emission surface and detection surface facing the same side of the device.

[0027] According to one example, the at least one light source comprises a primary light source configured to emit light at several wavelengths in the infrared range combined with a secondary light source configured to re-emit said light in several radiation directions, the radiation surface being arranged at the secondary light source and the primary light source being moved outside the radiation area of ​​the radiation surface.

[0028] According to one example, the light source and the sensor are stacked on top of each other.

[0029] According to one example, the light source and sensor are positioned relative to each other such that during operation the light source is closer to the sample than the sensor.

[0030] According to one example, the light source and sensor are positioned relative to each other such that during operation the sensor is closer to the sample than the light source.

[0031] According to one example, the light source and the sensor are positioned relative to each other such that, during operation, the sensor and the light source are positioned at substantially the same distance from the sample.

[0032] According to one example, the pixels of the sensor are formed by bolometers.

[0033] According to one example, the light source is formed at least in part by a photonic chip that includes a plurality of emitting elements.

[0034] According to one example, the emitters are arranged in the form of an emissive matrix. According to one example, the pixels of the sensor are arranged in the form of a detection matrix.

[0035] According to one example, the photonic chip is overlaid on the sensor. According to one example, the emitters alternate with the pixels of the sensor in projection in the stack direction of the photonic chip and the sensor.

[0036] According to one example, the emitter surrounds the pixels of the sensor in projection in the stack direction of the photonic chip and the sensor. According to one example, the photonic chip at least partially forms the secondary light source.

[0037] According to one example, the emitter is a passive extraction structure coupled to the primary light source. Passive extraction structures advantageously allow for the avoidance of electronics (active structures), thereby enabling the miniaturization of the device. This makes it possible to limit or even eliminate local heating of the emitter, which is a major challenge for wavelengths in the infrared range.

[0038] According to one example, the photonic chip includes a waveguide configured to couple the passive outcoupling structure with the primary light source.

[0039] According to one example, the photonic chip includes a waveguide configured to direct light emitted by the primary light source to a passive outcoupling structure.

[0040] According to one example, the thickness of the photonic chip is between 100 microns and 2 mm. Such a thickness is advantageously 2 mm or less, allowing at least one light source, typically a secondary light source, to be placed close enough to the sensor. This limits or avoids light losses between the secondary light source and the sensor. This also improves the spatial resolution of this lens-free device.

[0041] According to one example, each passive extraction structure has at least one facet tilted at an angle between 30° and 60° relative to the emitting surface.

[0042] According to one example, a facet of the passive extraction structure faces the waveguide and is configured to reflect light exiting the waveguide according to a plurality of radiation directions to form an extraction mirror. According to one example, the primary light source includes a plurality of quantum cascade lasers QCLs.

[0043] According to one example, the formation of a photonic chip includes: forming passive extraction structures protruding from a first surface of the first silicon based substrate by etching the substrate; forming a waveguide facing an extraction structure, the waveguide configured to guide light emitted by the primary light source to the extraction structure; Includes.

[0044] According to one example, the waveguide is formed directly on a first surface of a first silicon-based substrate in at least one layer made of a material different from silicon, and the passive outcoupling structure is formed in said at least one layer.

[0045] According to one example, the waveguide is formed on the second surface of the second substrate, and the second substrate is assembled with the first substrate such that the waveguide faces the extraction structure of the first substrate.

[0046] According to one example, the method further includes thinning the second substrate from a side opposite the second side.

[0047] According to one example, the passive extraction structures are etched to have at least one facet each tilted at an angle between 30° and 60° relative to the first surface.

[0048] According to one example, metal deposition is performed on each of said at least one facet to form an extraction mirror.

[0049] The present invention has as its preferred field of application a platform for diagnosing biological tissue by non-invasive optical analysis in the mid-infrared (MIR) spectral range.

[0050] In one embodiment, a device according to the invention, combining an array of QCLs and intermediate lens-free IR detectors arranged to enable reflected IR multispectral imaging, in particular enables such diagnostics to be performed non-invasively.

[0051] The device according to the invention can be advantageously manufactured using conventional microfabrication techniques, in particular silicon techniques developed in the field of microelectronics.

[0052] Hereinafter, the term "absorption" or its equivalents refers to the phenomenon whereby energy from an electromagnetic wave is converted into another form of energy, for example, in the form of heat.

[0053] Hereinafter, the term "diffusion" or its equivalents refers to the phenomenon whereby a propagation medium produces a distribution of energy from an electromagnetic wave, for example light energy, in many directions.

[0054] Hereinafter, the term "reflection" or its equivalents refers to the phenomenon of re-emission from a surface of incident optical radiation in one or more directions opposite to the incident direction. In the present invention, a surface is considered reflective as long as it re-emits at least a portion of the incident optical radiation. A reflective surface can be characterized by a reflectivity coefficient between 0 and 1. Reflection can be specular (one reflection direction) or diffuse (multiple reflection directions).

[0055] An object or material that is "transparent to a given wavelength" or simply "transparent" means that it passes at least 90% of the light intensity of light having that wavelength. For example, a silicon wafer that is 1 mm thick or less transmits light with wavelengths between 6 μm and 10 μm. Light loss due to absorption in silicon is less than 5 dB / cm in this wavelength range.

[0056] The incident light radiation is emitted by one or more corresponding primary light sources. The light emitted by these sources is in the infrared range, preferably the mid-infrared range, i.e., the wavelength range from 5 μm to 11 μm. These primary light sources typically include several monochromatic or quasi-monochromatic lasers, each with a dominant wavelength. The dominant wavelength is the only wavelength emitted by a monochromatic laser, or the wavelength that is predominantly emitted by a quasi-monochromatic laser.

[0057] The device according to the invention further comprises a "sensor". This sensor is usually provided in the form of an IR photodetector matrix forming pixels. The terms "sensor" and "imaging device" are therefore used synonymously in the specification.

[0058] A structural element or layer "based on" material A means a structural element or layer that contains only this material A or that contains this material A and other materials, such as doping or alloying elements. Thus, when a transparent substrate is referred to as being "silicon-based," it means that it can be made of silicon only or silicon and possibly other materials, such as impurities or germanium.

[0059] In this application, diameter, width and length are measured transverse to the axis of the stack, and thickness or depth is measured along the axis of the stack.

[0060] In this specification, the expression "lens-free" means that the device does not include any optical elements in the form of lenses on the light beam path between the emission surface of the light source and the sensor.

[0061] The present invention can be used for imaging samples, particularly biological samples, in particular in vivo samples. Thus, the IR multispectral imaging device can be applied directly to the skin of a patient requiring diagnosis. The light source's radiation plane is preferably positioned substantially parallel to the sample's surface. Therefore, the light source's main radiation direction is substantially perpendicular to the sample's surface.

[0062] Preferably, the light source is configured to emit light through each emitter into a portion of space around the main emission direction. In particular, the portion of space may be a cone-shaped portion, the axis of which is the main emission direction. The main emission direction may be perpendicular to the emission surface of the light source. In general, the direction of the emitted light beam has a majority component along the main emission direction and a minority component along a direction perpendicular to the main emission direction.

[0063] Advantageously, the emitters of the light source have parallel main emission directions.

[0064] Preferably, each pixel of the sensor is configured to receive light from a portion of the space around a primary detection direction, which may be perpendicular to the detection surface of the sensor. In general, the direction of the detected light rays coming from the reflection has a majority component along the primary detection direction and a minority component along a direction perpendicular to the primary detection direction.

[0065] Advantageously, the pixels of the sensor have parallel main detection directions.

[0066] Preferably, the main detection direction and the main emission direction are parallel. Advantageously, the main detection direction and / or the main emission direction are perpendicular to the surface of the sample.

[0067] According to one aspect of the present invention, the detection direction and the emission direction are opposite directions. This does not mean that the directions are parallel, since both emitted and reflected light generally cover a certain portion of space. However, their major components have opposite directions.

[0068] According to the invention, the device is configured so that light exits the device in the direction of the sample and a portion of this light that is reflected re-enters the device after interacting with the sample.

[0069] According to the embodiment, the sensor and the light source are superimposed. This extends to the relative arrangement of these two elements, at least with respect to the emission and detection surfaces. However, the superposition does not necessarily mean that the emitter and the pixel are superimposed in the projection along the stack axis. In particular, according to this projection, the emitter can surround the pixel, or vice versa.

[0070] It is specified that within the scope of the present invention, the terms "on," "overlying," "covering," or "underlying," or their equivalents, do not mean "in contact." Thus, for example, a photonic chip covering an imaging device does not necessarily mean that they are in direct contact with each other, but rather that the photonic chip is in direct contact with the imaging device or at least partially covers the imaging device while being separated by at least one other layer or at least one other element.

[0071] Unless otherwise stated, technical features described in detail for a given embodiment can be combined in an indefinite manner with technical features described in the context of other embodiments described by way of example. In particular, the number of emitters or extraction structures, different patterns of light-emitting or light-receiving matrices, and / or different forms of elements of the devices shown in the figures can be combined to form further embodiments not necessarily shown or described. Such embodiments are expressly not excluded from the present invention.

[0072] The terms "substantially", "approximately", and "about" mean "almost 10%", or when this relates to an angular direction, "almost 10°", preferably "almost 5°". Thus, a direction substantially perpendicular to a plane means a direction having an angle of 90±10° to the plane.

[0073] 1A, 1B and 2, a first example of a device according to the invention will now be described. As shown in Figure 1A, a reflective IR imaging device 1 is intended to be in close proximity to or in contact with a sample 2 to be imaged, such as biological tissue or an agro-industrial product.

[0074] The device 1 typically comprises a body 5 that houses the light source 3 and the imaging device 4. The body 5 may be presented as a cylinder as shown in FIG. 1A, or more generally as any shape that has good ergonomics, for example to facilitate handling of the device 1.

[0075] The body 5 may include peripheral components such as a power supply or power connection 6, or at least one optical fiber 7. Such an optical fiber 7 may in particular provide a view of the area of ​​the sample 2 to be imaged. It may be connected to a camera, which may improve the accuracy of direct positioning of the device relative to the sample, e.g., a possible carcinoma of a patient.

[0076] The body 5 includes a light source 3 and an imager 4 at its distal end. FIG. 1B shows an enlarged view of the distal end of the device 1. The light source 3 and the imager 4 can typically be stacked. For example, the light source 3 and the imager 4 form a stack along the z-direction, with the light source 3 positioned near the distal end of the device 1 and the imager 4 positioned slightly recessed from the distal end relative to the light source 3. The light source 3 has an emission surface 300 intended to emit light. The imager 4 has a detection surface 400 intended to receive light reflected by the sample 2. To enable such reflection imaging, the emission and detection surfaces 300, 400 face the same side toward the sample 2 to be analyzed.

[0077] The imaging device 4 is configured to detect light in the IR or MIR region. It typically comprises IR bolometers distributed to form a pixel matrix. The imaging device 4 may be associated with control electronics 42 and / or a regulator 43 intended to thermalize the IR bolometers.

[0078] The light source 3 can be a primary light source 3a or a secondary light source 3b. As shown in Figure 2, the device can typically comprise a primary light source 3a combined with an emitter 31 forming a secondary light source 3b. In this case, the emitter 31 is a passive extraction structure. According to a possibility not shown, the emitter 31 is a light emitting diode (LED) and directly forms the primary light source 3a.

[0079] As shown in Figure 2, the device preferably comprises a primary light source 3a coupled to a secondary light source 3b, which allows the primary light source 3a to be moved, which allows the size of the light source 3 at the distal end of the device to be reduced.

[0080] The primary light source 3a may typically include a quantum cascade laser (QCL) 32 emitting light at a wavelength between 5 μm and 10 μm. In particular, the primary light source 3a may include multiple QCLs, each configured to simultaneously emit different wavelengths. Each of the QCLs 32 may be associated with multiple emitters 31 of the secondary light source 3b. The emission surface 300 is thus increased, which allows for a wider and / or more uniform illumination of the area of ​​the sample 2 to be imaged.

[0081] In this case, the emitter 31 is preferably a passive out-coupling structure coupled to the QCL 32 via a mirror 321, an optical fiber, or a waveguide 312. The emitter 31 and the waveguide 312 are typically grouped together in a photonic chip 30. In this embodiment, the photonic chip 30 is placed on an imaging device 4 formed by a bolometer matrix. The distance separating the photonic chip 30 from the sensitive part of the bolometer, or the distance separating the emission surface 300 from the detection surface 400, is approximately several tens of microns, for example, between 10 μm and 200 μm. Light coming from the QCL 32 is guided by the waveguide 312 to the passive out-coupling structure forming the emitter 31 and then directed by the emitter 31 towards the sample 2. The emitter 31 typically forms a light-emitting matrix configured to uniformly illuminate the area of ​​the sample 2 to be imaged. The sample 2 typically absorbs, reflects, or scatters the light emitted or re-emitted by the emitter 31. The bolometer matrix, arranged behind the photonic chip 30, is configured to receive the reflected portion of the light. Advantageously, the photonic chip 30 is silicon-based. Silicon is transparent to IR and MIR wavelengths. This allows the photonic chip 30 to be placed in front of the imaging device 4 without obscuring the bolometers. The photonic chip 30 may also be made of another material that is transparent to IR and MIR wavelengths, for example, germanium-based.

[0082] Figure 3 shows a Lambertian reflecting object with a reflectance equal to 1, with a reflectance of 10 mW / cm 23 shows the result of the reflected light flow collected by a 25 μm pixel (bolometer) when illuminated with . When the distance between the pixel and the object is 250 μm, the pixel receives a reflected light flow with an optical power of approximately 3 nW. Such power is perfectly detectable by the pixel of an IR imager, especially an IR bolometer type. As shown in FIG. 3, the smaller the distance between the area of ​​the sample 2 to be imaged and the imager 4, the greater the reflected light flow collected by the imager 4. Furthermore, the spatial resolution of the lens-free device 1 decreases with increasing distance between the area of ​​the sample 2 to be imaged and the imager 4. Therefore, advantageously, the photonic chip 30 has a thickness along the z-direction of 300 μm or less, preferably 250 μm or less, and preferably 200 μm or less.

[0083] The device 1 is preferably used in direct contact with or in close proximity to the area of ​​the sample 2 to be imaged. In particular, the emitting surface 300 can be positioned relative to the area to be imaged. In this way, the distance between the area to be imaged and the sensor can be 250 μm or less, preferably less than 200 μm. This allows maximizing the flow of reflected light collected by the sensor.

[0084] 4 shows an example of a photonic chip 30. In this example, the passive outcoupling structure 311 is arranged around an opening 34 of the photonic chip 30. This opening 34 can be configured to at least partially accommodate the imaging device 4. The emitting matrix thus surrounds the detecting matrix in projection along the z direction. The opening 34 allows beams reflected by the sample to pass towards the imaging device 4 (not shown). These reflected beams typically have a main detection direction along the axis z in the +z direction.

[0085] The passive outcoupling structures 311 are configured to re-emit the incident beams towards a sample (not shown), these incident beams typically having a main direction of emission in the -z direction along axis z.

[0086] The passive out-coupling structures 311 are preferably coupled to the waveguides 312, 312a, and 312b, and preferably each passive out-coupling structure 311 is individually coupled to a single waveguide 312b. According to one example, the photonic chip 30 comprises an optical input 33 intended to receive the light emitted by the primary light source 3a. This optical input 33 feeds a main waveguide 312a, which transports the light to all passive out-coupling structures 311. Each secondary waveguide 312b may be associated with a specific passive out-coupling structure 311. The secondary waveguide 312b may be coupled to the main waveguide 312a, for example, by evanescent coupling, as shown in FIG. 4. The use of multiple waveguides allows for more optical power to pass through. This also allows for simultaneous illumination of a sample according to different wavelengths of the QCL.

[0087] The passive outcoupling structures 311 presented in this example can be replaced by emitters 31, e.g., LEDs. In this case, it is not necessary to use waveguides 312. A combination of different types of emitters 31, e.g., LEDs, and passive outcoupling structures 311 can be considered. Some emitters 31 can be, e.g., LEDs, and some other emitters 31 can be, e.g., passive outcoupling structures 311. In this case, waveguides 312 can be associated with the passive outcoupling structures 311 to transport the light emitted by the LEDs and each point of the light-emitting matrix.

[0088] FIG. 5 shows another example of the distribution of the emitters 31. In this example, the emission and detection matrices 310, 410 at least partially overlap in the projection along the z axis. Each emitter 31 is therefore surrounded by a pixel 41 of the imaging device 4. This makes it possible to obtain a relatively homogeneous and uniform emission surface in the plane of the sheet. The distribution of the pixels 41 and the emitters 31 is preferably performed so as to obtain a good compromise between the emission and detection surface. The pixels 41 can be masked by the emitters 31. This allows for a simplified design of the bolometer matrix while maintaining an acceptable detection surface.

[0089] 6A and 6B show two particular embodiments of a passive outcoupling structure 311 and a waveguide 312. The waveguide 312 is configured to guide light with wavelengths between 5 μm and 11 μm. In the example of FIG. 6A, the waveguide 312 and the outcoupling structure 311 are formed in a germanium or silicon germanium SiGe-based layer 11 on a silicon Si-based substrate 10. The structuring of the waveguide 312 and the outcoupling structure 311 can therefore be carried out according to a so-called monolithic approach. This makes it possible to form the waveguide 312 and the outcoupling structure 311 directly on one and the same substrate 10.

[0090] The waveguide 312 typically includes a cladding formed by the layer 11 and a core 13 formed within the layer 11. The cladding is made of, for example, SiGe with a germanium content of about 20%. The core 13 is made of, for example, SiGe or Ge with a germanium content of about 40%. The waveguide 312 has an output facet F that is tilted relative to the bottom surface of the substrate 10. G Such tilted facets can typically be obtained by tetramethylammonium hydroxide (TMAH) or potassium hydroxide (KOH) based wet etching. Other waveguide materials can be used, such as, but not limited to, CaF2, BaF2, ZnS, ZnSe, CdSe, SiN, AlN, Ta2O5, TiO2, ZrO2, amorphous carbon, chalcogenides, etc.

[0091] The extraction structure 311 is formed directly in the layer 11, which here is made, for example, of SiGe with a germanium content of about 20%. The extraction structure 311 is typically formed on a facet F inclined with respect to the bottom surface of the substrate 10. E The inclination angle can be between 30° and 60° relative to the base, for example, about 45° or 55°. E is the output facet F of the waveguide 312 G It is placed facing the Facet F Eis configured to reflect light exiting the waveguide 312 in an emission or re-emission direction having a major component substantially perpendicular to the base surface. E is preferably metallized with a metal layer 12. The facet F of the extraction structure 311 E typically forms the extraction mirror.

[0092] 6B, the outcoupling structure 311 is formed in a silicon Si-based substrate 10, and the waveguide 312 is formed in a germanium or silicon germanium SiGe-based layer 11. The structuring of the waveguide 312 can therefore be carried out on a second substrate independent of the substrate 10 containing the outcoupling structure 311, according to the so-called heterogenic approach. In this example, the waveguide 312 also comprises a cladding formed by layer 11 and a core 13 formed in layer 11, as described above. The waveguide 312 has an output facet F perpendicular to the bottom surface of the substrate 10. G Such a vertical facet can typically be obtained by dry etching, for example with a plasma. The extraction structure 311 is here formed directly in the substrate 10. It also has an output facet F of the waveguide 312. G Facet F facing E This facet F E is graded as described above and is preferably metallized.

[0093] 7 shows a device comprising a photonic chip 30 having a face 308 intended to be in proximity to or in contact with a sample 2, typically a biological sample. The device further comprises an imaging device 4 comprising a plurality of pixels 41, for example in the form of a microbolometer matrix. The photonic chip 30 has a face 302 opposite face 310. This face 302 is here intended to be in proximity to or in contact with the pixels 41 of the imaging device 4.

[0094] The photonic chip 30 is preferably configured to illuminate the sample 2 with mid-infrared radiation uniformly in the emission direction E. The photonic chip 30 is typically transparent in the mid-infrared radiation so as to pass a portion of the light backscattered or reflected by the sample 2 through to the pixels 41 in the detection direction D.

[0095] The photonic chip 30 comprises an outcoupling structure 311 and a waveguide 312 arranged, for example, as described with reference to FIG. 6B.

[0096] 8A to 8C show a distribution of pixels 41 and emitters 31 that allows for avoiding or limiting shadowing of pixels 41 by emitters 31. FIG. 8A shows a detector matrix 410 in which pixels 41 are separated from one another by inter-pixel regions 411. FIG. 8B shows an emitter matrix 310 in which the extraction structures 311 forming the emitter matrix 31, e.g., micromirrors, are positioned so that they coincide with the inter-pixel regions 411 of the detector matrix 410 once they are superimposed. FIG. 8C shows the superimposition of the emitter and detector matrices 310, 410. The micromirrors are preferably positioned at the intersections of the inter-pixel regions 411. This allows for the placement of waveguides between the micromirrors and between the intersections of the superimposed inter-pixel regions 411 (not shown). Thus, the pixels 41 of the imaging device are not shadowed by the micromirrors and / or the waveguides of the photonic chip.

[0097] 9A and 9B illustrate the principle of forming a photonic chip according to the heterogeneous approach. According to this approach, an outcoupling structure 311 is formed on the first surface 101 of a first silicon-based substrate 10a, and a waveguide 312 is formed on the second surface 102 of a second silicon-based substrate 10b. Hereinafter, the first substrate 10a, which supports the outcoupling structure 311 in the form of a micromirror, is referred to as the "mirror wafer." The second substrate 10b, which supports the waveguide 312, is referred to as the "waveguide wafer." The photonic chip 30 is then formed by assembling the waveguide and mirror wafers on their surfaces 102 and 101.

[0098] Microelectronics technology makes it possible to manufacture these wafers and assemble them compactly with sufficient integration precision to form the photonic chip 30.

[0099] Figures 10A to 10H show the steps for manufacturing a mirror wafer. Figure 10A illustrates the provision of a silicon (100) substrate 10a. The crystal orientation of the substrate is selected in particular according to the anisotropic etching chemistry used to etch the mirror facets. A hard mask 14, typically silicon nitride-based, is deposited on the substrate 10a, for example by low-pressure chemical vapor deposition (LPCVD) (Figure 10B). A photosensitive resin pattern 15 is then defined by photolithography (Figure 10C). The hard mask 14 is etched (Figure 10D) and the resin is removed (Figure 10E).

[0100] The substrate 10a is then etched by anisotropic etching of Si in, for example, tetramethylammonium hydroxide (TMAH), or potassium hydroxide (KOH), or pyrocatechol and water (EDP)-based alkaline solutions (FIG. 10F). The facet F obtained after etching EThe slope of the facets can vary depending on the crystallographic orientation of the substrate, the nature of the hard mask, and the etching solution used. Typically, slope angles of 54.7° or 45° can be achieved. This technique allows for very smooth facets to be obtained. Other techniques allow for the creation of sloped facets. The lithography technique, commonly called "graytone," consists of varying the energy dose during lithography of the resin used for the etching mask. The resin pattern has a gradient that, after development, is transferred to the substrate by dry etching, e.g., RIE (reactive ion etching).

[0101] The height of the extraction structure thus formed can be selected according to the height of the waveguides produced on the waveguide wafer and / or the width of the inter-pixel region, which is typically between 9 and 11 μm.

[0102] Next, the hard mask 14 is removed (FIG. 10G) and facet F E Facet F is metallized (Fig. 10H). E Metallization can be achieved by depositing a titanium-gold (Ti / Au) bilayer. The Ti / Au deposit typically has a thickness between 50 and 500 nm. Metallization can be achieved by stenciling or, more commonly, by photolithography and etching. Alternatively, metallization can be achieved by creeping. The creeping deposition technique consists of depositing a material, such as a metal, on the structure to be covered, e.g., the facet. Annealing then allows the material to undergo a glass transition, allowing the structure's shape to be shaped. The metal ensures the reflective function of the micromirror. It also advantageously allows for easy mechanical assembly of the mirror wafer and the waveguide wafer during thermocompression bonding.

[0103] Figures 11A to 11D illustrate the steps for fabricating a waveguide wafer. Figure 11A shows the provision of a silicon substrate 10b. Epitaxial growth makes it possible to form layers 11 and 13, which respectively form the cladding and core of the waveguide (Figure 11B). Layer 11 is formed, for example, by epitaxial growth of SiGe with 40% Ge, and layer 13 is formed, for example, by epitaxial growth of Ge. The deposited thickness is typically about 3 µm for Ge and 3-5 µm for SiGe. The waveguide obtained in Figure 11B is a flat waveguide, called a 2D guide, which extends over the entire surface of the substrate 10b.

[0104] A seal line 105 made of gold Au is then defined and created around the periphery of the waveguide wafer by deposition / lithography / etching steps, which seal line 105 allows the assembly of the mirror and the waveguide wafer.

[0105] Next, the outcoupling areas 313 intended to house the outcoupling structures 311 during assembly are defined by lithography / etching (FIG. 11D).

[0106] The mirror wafer and the waveguide wafer are then assembled. Assembly by Au-Au thermocompression bonding is preferably used. Metal-metal thermocompression bonding has the advantage that it can be performed at low temperatures (<400°C), typically around 250°C, in addition to being relatively simple and inexpensive to implement. Other assembly techniques are possible (eutectic bonding, direct bonding, polymer bonding, etc.). The alignment tolerance for this type of assembly by thermocompression bonding is on the order of a few microns, typically + / - 5µm.

[0107] After assembly, thinning of the waveguide wafer is preferably performed from face 103 as shown in Figure 9A. After thinning, the substrate 10b preferably has a thickness of 300 μm or less, which ultimately allows for a reduced distance between the surface of the sample to be analyzed and the sensor. The wafer obtained from the assembly can be cut into several photonic chips.

[0108] The invention is not limited to the described embodiments, but extends to any embodiment falling within the scope of claim 1. [Explanation of symbols]

[0109] 1. Lens-free infrared imaging device 2 Sample 3 light source 3a Primary light source 3b Secondary light source 4 sensors 10a First substrate 10b Second substrate 12 Metal Deposition 30 Photonic Chip 31 Emitter 41 pixels 101 First Side 102 Second Side 300 radiating surface 311 Passive extraction structure 312 Waveguide 400 detection surface 410 Detection Matrix

Claims

1. A lens-free infrared imaging device (1) intended for imaging a sample (2), comprising at least one light source (3, 3a, 3b) configured to emit light according to several wavelengths in the infrared range, the at least one light source (3, 3a, 3b) has an emission surface (300) intended to emit light in the direction of the sample (2) to be imaged, the device (1) further comprises at least one sensor (4) configured to interact with the sample and detect a reflected portion of the emitted light, the sensor comprising a plurality of pixels (41) and having a detection surface (400) intended to receive the reflected portion of the emitted light, the emission surface (300) and the detection surface (400) facing one and the same side of the device (1), the at least one light source (3, 3a, 3b) comprising a primary light source (3a) configured to emit light according to several wavelengths in the infrared range combined with secondary light sources (3b) configured to re-emit light in several emission directions (E), the emission surface (300) being located at the secondary light source (3b) and the primary light source (3a) being moved outside the emission area of ​​the emission surface (300), 10. An apparatus, characterized in that the secondary light source (3b) is at least partially formed by a photonic chip (30) comprising a plurality of passive outcoupling structures (311) coupled to the primary light source (3a).

2. 2. The device according to claim 1, wherein the light sources (3, 3a, 3b) and the sensors (4) are stacked on top of each other.

3. 3. The device of claim 1, wherein the emitters are arranged in the form of a light-emitting matrix, all of the emitters being the plurality of passive extraction structures, or some of the emitters are the plurality of passive extraction structures and some of the emitters are LEDs; the pixels of the sensor are arranged in the form of a detection matrix, and the photonic chip is superimposed on the sensor such that, in projection of the photonic chip and the sensor in the stacking direction z, the emitters alternate with the pixels of the sensor.

4. 4. The device according to claim 1, wherein the photonic chip (30) is superimposed on the sensor (4), and in projection in the stacking direction (z) of the photonic chip (30) and the sensor (4), the emitter (31) surrounds the pixel (41) of the sensor (4).

5. 5. The device of claim 1, wherein the photonic chip (30) comprises a waveguide (312) configured to guide light emitted by the primary light source (3a) to the passive outcoupling structure (311).

6. Each of the passive extraction structures (311) has at least one facet (F) inclined at an angle between 30° and 60° with respect to the emitting surface (300). Ｅ 6. The apparatus of claim 5, further comprising a facet (312) facing the waveguide (312) and configured to reflect light exiting the waveguide (312) in a plurality of radial directions (E) to form an extraction mirror.

7. 7. The device according to any one of claims 1 to 6, wherein the photonic chip (30) has a thickness of 300 μm or less.

8. Providing a primary light source (3a); forming a photonic chip (30) intended to re-emit at its emission surface (300) the light emitted by said primary light source (3a); providing a sensor (4) comprising a plurality of pixels (41) capable of detecting a portion of the light emitted by said primary light source (3 a) on a detection surface (400); Assembling the photonic chip (30) and the sensor (4) so ​​that the emission surface (300) and the detection surface (400) face the same side of the device (1); coupling the primary light source (3a) to the passive outcoupling structure (311) of the photonic chip (30); A method for manufacturing a lens-free thermal imaging device (1) according to any one of claims 1 to 7, comprising:

9. The step of forming the photonic chip (30) comprises: Etching the first silicon-based substrate (10a) to form passive extraction structures (311) protruding from a first surface (101) of the first silicon-based substrate (10a); forming a waveguide (312) facing the extraction structure (311), said waveguide (312) being configured to guide light emitted by the primary light source (3 a) towards the extraction structure (311); The method of claim 8, comprising:

10. 10. The method of claim 9, wherein the waveguide (312) is formed directly on the first surface (101) of the first silicon-based substrate (10a) in at least one layer (11, 13) of a material different from silicon, and the passive outcoupling structure (311) is formed in the at least one layer (11).

11. 10. The method of claim 9, wherein the waveguide (312) is formed on a second surface (102) of the second substrate (10b), the second substrate (10b) is assembled with the first substrate (10a) such that the waveguide (312) faces the extraction structure (311) of the first substrate (10a), and the method further comprises the step of thinning the second substrate (10b) from a surface (103) opposite the second surface (102).

12. The passive extraction structure (311) has at least one facet (F) inclined at an angle between 30° and 60° with respect to the first surface (101). Ｅ ) each of said at least one facet (F ) is etched to form an extraction mirror. Ｅ 12. The method of claim 8, wherein a metal deposition (12) is performed on each of the first and second electrodes.

13. 8. A method of using the device (1) according to any one of claims 1 to 7, wherein the device (1) is in contact with or in close proximity to the area to be imaged of the sample (2) such that the distance between the area to be imaged and the sensor (4) is less than 200 μm.

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