Optical probes and related methods

Abstract

The present invention relates to optical coupling between optical components, and more particularly, to an optical probe (1) configured for optical testing of at least one micro-optical component (50), a method for producing an optical probe (1), and a method for optical testing of at least one micro-optical component (50). The optical probe (1) comprises:-a probe head (10), wherein the probe head (10) comprises a test assembly (2); -at least one micro-optical element (20), where the micro-optical element (20) is a separate element with respect to the test component (2) and is in mechanical contact with the test component (2), where the micro-optical element (20) is configured to optically couple light (3) between the test component (2) and the micro-optical component (50), thereby being configured to determine an optical property of the micro-optical component (50), and wherein the micro-optical element (20) is configured to operate in an index matching liquid (17).

Description

Technical Field

[0001] The present invention relates to optical coupling between optical components, and more particularly to an optical probe configured for optical testing of at least one micro-optical component, a use thereof, a method for producing the optical probe, and a method for optical testing of at least one micro-optical component.

[0002] In particular, optical probes can be used for the manufacture, calibration, testing and preselection of micro-optical components, which are particularly configured for optical communications, sensor applications, medical sensors, automotive applications, quantum applications or environmental sensing; however, the use of optical probes in other applications is also possible. Background Art

[0003] Optical probes configured for optical coupling to photonic integrated circuits featuring 3D-printed optics on an optical fiber array are known. 3D-printed optics for optical packaging are further known. 3D-printed freeform probes for beam shaping light exiting a photonic integrated circuit are further known. Optical probes using a refractive index matching liquid between the optical probe and the integrated photonic circuit are further known.

[0004] WO 2018 / 083191 A1 discloses the fabrication of micro-optical devices for beam expansion on photonic integrated circuits for optical packaging.

[0005] US 6925238 B2 discloses the use of index matching materials to reduce reflections during detection.

[0006] “3D-printed optical probes for wafer-level testing of photonic integrated circuits” (Optics Express 28, 37996-38007, 2020) by Trappen M. et al. discloses 3D-printed optical devices on optical fiber arrays on a wafer by inserting 3D-printed micro-optical devices consisting of mirrors and lenses into etched grooves in the wafer.

[0007] “Experiments on Metamaterials with Negative Effective StaticCompressibility” by Qu et al. (Phys. Rev. X 7, 041060, 2017) discloses a process for producing air-enclosed hollow structures.

[0008] “CMOS Compatible Monolithic Fiber Attach Solution with Reliable Performance and Self-alignment” by Peng et al. (OFC, Th 31.4, 2022) describes a photonic coupling interface designed to operate in a refractive index matching liquid.

[0009] Issues to be resolved

[0010] Therefore, the object of the present invention is to provide an optical probe configured for optical testing of at least one micro-optical component and its use, a method for producing an optical probe, and a method for optical testing of at least one micro-optical component, which at least partially overcome the above-mentioned problems of the current state-of-the-art technology.

[0011] A specific object of the present invention is to provide an optical probe and a method configured for optical testing of components at die, batch and wafer level. Preferably, the optical probe should have a compact probe head that can be inserted into and probe in a groove of a wafer, wherein the groove may be preferably 250 μm or less, more preferably 100 μm or less, in particular 80 μm or less. Furthermore, the optical probe should be configured for a small pitch, preferably 127 μm or less, more preferably 80 μm or less, in particular 50 μm or less, in particular down to a pitch of 20 μm. In this context, a low pitch accuracy with three sigma = 1000 nm or less and a low modal field size variation with one sigma = 10% or less would be particularly preferred.

[0012] Furthermore, the optical probe should be configured for a high port count, preferably at least 24, more preferably at least 64, and in particular at least 128. Preferably, a small modal field (preferably 10 μm or less, more preferably 5 μm or less, in particular twice the operating wavelength or less) should be available at the coupling location of the test assembly. Furthermore, calibration of probe variations should be possible, for example by using a test chip comprising a waveguide with known properties, wherein the test chip is positioned on the wafer chuck. The optical probe should be configured for robust probing even at high working distances (preferably at least 10 μm, more preferably at least 20 μm, and in particular at least 40 μm). Furthermore, achieving high test throughput would be preferred, for example by probing at least two, preferably multiple, channels simultaneously.

[0013] It is particularly desirable that the optical probe be configured to operate in the near-ultraviolet range, the visible range, the near-infrared range, and the mid-infrared range (meaning a wavelength range of 100 nm to 10 μm, preferably 200 nm to 4 μm, more preferably 530 nm to 2.7 μm, and in particular at least 1250 nm to 1650 nm). High reproducibility of the optical coupling between the probe head and the at least one micro-optical component with a variation of 0.5 dB or less, more preferably 0.25 dB or less, would be preferred both for coupling a single channel and for simultaneously coupling light from multiple channels without realigning the probe for each channel. Summary of the Invention

[0014] This problem is solved by an optical probe configured for optical testing of at least one micro-optical component, a method for producing an optical probe, and a method for optical testing of at least one micro-optical component, having the features of the independent claims. Preferred embodiments, which can be implemented in isolation or in any arbitrary combination, are listed in the dependent claims and throughout the following description.

[0015] In a first aspect, the present invention relates to an optical probe configured for optical testing of at least one micro-optical component. According to the invention, the optical probe comprises:

[0016] - a probe head, wherein the probe head comprises a test assembly;

[0017] at least one micro-optical element, wherein the micro-optical element is a separate element relative to the test assembly and is in mechanical contact with the test assembly,

[0018] wherein the micro-optical element is configured to optically couple light between the test assembly and the micro-optical assembly, thereby being configured to determine an optical property of the micro-optical assembly, and wherein the micro-optical element is configured to operate in an index matching liquid.

[0019] As commonly used, the term "optical probe" refers to an optical device that is configured for optical testing of at least one micro-optical component. In addition, the optical probe may exhibit at least one of mechanical functionality, electrical functionality or optical functionality, as described in more detail below. For the purpose of optical testing, the optical probe as used herein comprises a probe head having a test component, wherein the probe head can be aligned so that light can be coupled between the test component and the micro-optical component. As further commonly used, the term "probe head" refers to a terminal piece of the optical probe, wherein the terminal piece comprises a micro-optical element configured to optically couple light between the test component and the micro-optical component. In a particularly preferred embodiment, the probe head is movable relative to the micro-optical component to be tested. For the purpose of being able to be moved dynamically in an easy manner, the probe head may preferably exhibit a low weight.

[0020] As already indicated above, the optical probe is configured for optical testing of at least one micro-optical component. As generally used, the term "micro-optical component" refers to a device under test, wherein the device may preferably be or include a wafer having a plurality of photonic integrated circuits or individual photonic integrated circuits. Generally, the micro-optical component may include a plurality of optical structures that are inherently small in size, preferably 10 μm or less, more preferably 5 μm or less, in particular 1 μm or less, configured to perform the intended function, in particular as a waveguide, or have an overall size of 10 mm or less. In a preferred embodiment, the micro-optical component may be produced on a photonic platform, in particular selected from SOI (silicon on insulator), InP (indium phosphide), SiN (silicon nitride) or LNOI (lithium niobate thin film). In an alternative embodiment, the micro-optical component may be a non-planar component, in particular an optical element selected from microlenses, gratings, optical isolators or mirrors.

[0021] In a particularly preferred embodiment, the optical probe (particularly at least one of the probe head or the micro-optical assembly) may have at least one liquid protection element. It may further include a microfluidic chip. As commonly used, the term "microfluidic chip" refers to an electronic component configured to operate a refractive index matching liquid. To this end, the microfluidic chip may have at least one of the following:

[0022] -Liquid dispensing element;

[0023] -Hollow core optical fiber;

[0024] - a liquid protection element; or

[0025] -Liquid removal element.

[0026] As commonly used, the term "liquid dispensing element" refers to a mechanical element or an electromechanical element that is configured to dispense at least a portion of a refractive index matching liquid. Preferably, the at least one liquid dispensing element can be selected from a storage tank and a dispensing nozzle; however, the use of other liquid dispensing elements may also be feasible. As further commonly used, the term "hollow core fiber" refers to an elongated element with a hollow core that is configured to receive, transport and manipulate at least a portion of a refractive index matching liquid and may be configured simultaneously or continuously to guide light. As further used herein, the term "liquid protection element" refers to a mechanical element at the surface of a probe head or micro-optical component that is configured to control (in particular, limit) the diffusion of at least a portion of the refractive index matching liquid. In particular, the wetting behavior of the surface of the probe head or micro-optical component can be adjusted by coating the respective surface of the probe head or micro-optical component, in particular by exhibiting a lotus effect or sharp edges, thereby preventing liquid diffusion. For this purpose, metals, oxides, oxide removal, fluorinated coatings, organic coatings or structured surfaces can be used; however, the use of other coatings may also be feasible. In this context, the structured surface can be selected in particular from capillaries, sharp edges, or pores configured to control (in particular, restrict) the spread of a liquid; however, the use of different structured surfaces is also possible. The liquid protection element can be produced in particular by 3D printing a selected coating onto the surface of the probe head, preferably in a single process step together with the production of the micro-optical element. As further generally used, the term "liquid removal element" refers to a mechanical element or electromechanical element configured to remove at least a portion of the refractive index matching liquid. Preferably, the at least one liquid removal element can be selected from a drain outlet and a drain sump; however, the use of other liquid removal elements is also possible.

[0027] As further indicated above, the optical probe comprises a probe head having a test component. As commonly used, the term "test component" refers to an optical component configured to transmit or collect light from a device under test, in particular a micro-optical component as described elsewhere herein. The test component may preferably be selected from an optical fiber, an optical fiber array, a waveguide, a photonic integrated circuit, a planar transparent substrate, a curved transparent substrate or an optical element, in particular an optical lens or an objective lens. The test component may be a test circuit. The test circuit may preferably comprise the same material, manufacturing batch, wafer or technology as the micro-optical element. However, it is also feasible to use a different type of test circuit. For the purpose of optical testing of at least one micro-optical component, the test circuit may have an active optical structure, in particular selected from at least one of a light source (such as a laser source or a super-brightness light-emitting diode (SLED)) or a detector (such as a Ge photodiode), or it may be coupled to an optical fiber or an optical fiber array, in particular observable by a macroscopic optical instrument. As commonly used, the term "optical fiber" refers to an elongated, circular optical element configured to guide light through the use of facets, wherein the term "facet" refers to the terminal surface of a light-guiding structure (particularly a waveguide) through which light is transmitted or received. As further commonly used, the term "fiber array" refers to at least one optical fiber connected to at least one mechanical element, preferably selected from a glass block or a V-groove array. In a preferred embodiment, the test circuit can have at least one of the following: an electrical functionality, a distance sensor, a mechanical sensor, an acceleration sensor, a force sensor, or a structure comprising a microelectromechanical system (MEMS). Other embodiments of the test circuit are also possible.

[0028] As commonly used, the term "photonic integrated circuit" refers to a planar device comprising at least one of a waveguide or a photonic device, the photonic device having at least one surface-emitting or photosensitive device, preferably selected from a photodiode, an image sensor, or a vertical-cavity surface-emitting laser (VCSEL). As used herein, the term "planar" refers to a corresponding device obtained by using 2D lithography on a planar substrate. Based on this definition, photonic integrated circuits do not include optical fibers, while devices produced using the ioNext platform, SiN, SOI, or silicon-rich oxides are components of photonic integrated devices. Photonic integrated circuits may include active and passive waveguide devices, preferably selected from photodetectors, light sources, optical modulators, spectrum analyzers, power dividers or polarization splitters, filters or strippers, or multiplexers. Photonic integrated circuits may also exhibit at least one advanced electrical functionality, particularly a transistor, a CMOS component, an electrical wire, or an electric waveguide. In particularly preferred embodiments, the test circuit and the micro-optical component may be a photonic integrated circuit. In alternative embodiments, the micro-optical component may be an optical integrated circuit or a micro-optical device.

[0029] As already further indicated above, the optical probe further comprises at least one micro-optical element. As commonly used, the term "micro-optical element" refers to an optical structure configured for modifying the propagation of light, in particular by at least one of focusing the light, diverging the light, redirecting the light, deflecting the light, waveguiding the light or rotating the polarization of the light. For this purpose, the micro-optical element may preferably comprise at least one element selected from the group consisting of: a mirror, in particular a total internal reflection mirror or a metal mirror; an optical lens; a grating; an optical waveguide, in particular a non-planar waveguide; a photonic wire bond; a light cone; an optical metamaterial; or a whispering gallery waveguide. As commonly used, the term "photonic wire bond" or "PWB" refers to a 3D printed free-form waveguide, wherein the waveguide may preferably be a single-mode waveguide, which may optionally be polarization-maintaining and which may preferably be operated in a high refractive index contrast configuration. In this document, the term "high refractive index contrast configuration" may be expressed by the following conditions:

[0030] n1-n2>0.1,

[0031] Where n1 is the refractive index of the waveguide, and where n2 is the refractive index of the surrounding medium. As further commonly used, the term "whispering gallery waveguide" refers to an optical element having a whispering gallery guiding mechanism, wherein the optical element is a continuous disk or cylinder or a portion thereof, and light travels tangentially to the surface of the disk or cylinder through the optical component. As further commonly used, the term "total internal reflection" refers to a process in which light propagates in a medium having a higher refractive index compared to the higher refractive index of the surrounding medium, wherein the light interacts with the interface between the two media so that the light is contained in the material with the higher refractive index. Therefore, light can be guided in particular in a waveguide, in particular in a single-mode waveguide, or reflected at a surface. An optical element designed to maintain internal reflection is configured to implement a process in which light propagating from a material with a higher refractive index is reflected at an optical interface of the optical element (if the reflection angle is below the critical angle). In the case of a waveguide, the optical element is designed so that the radius of curvature is selected so that at least 90% of the incident light is not emitted with a 90° bend.

[0032] The micro-optical element may preferably be a three-dimensional element, where the term "three-dimensional element" refers to an object having an extent of at least 1 μm in all spatial directions and obtained in a direct 3D printing process. Preferably, the micro-optical element may have at least one free-form surface, wherein at least one free-form surface may be a computer-programmable surface. More preferably, the micro-optical element may have a 3D free-form structure. Preferably, the micro-optical element may have an overall extent of 1000 μm or less, more preferably 500 μm or less, in particular 250 μm or less. Preferably, the micro-optical element may have at least one optical surface with a root mean square surface roughness of 250 nm or less, more preferably 100 nm or less, in particular 20 nm or less, as measured by at least one of atomic force microscopy (AFM) or white light interferometry. Preferably, the micro-optical element may be transparent from 250 nm to 4500 nm, more preferably from at least 530 nm to 2700 nm; however, different transparency wavelength ranges are also possible.

[0033] Preferably, the micro-optical element can be produced using a polymer material, particularly an acrylic material, particularly by photocuring the polymer material. In this context, additive manufacturing processes are preferably used; however, the use of at least one of different polymer materials or manufacturing processes is also feasible. Preferably, the micro-optical element can be produced such that an alignment accuracy of at least 1000 nm, more preferably at least 500 nm, and particularly at least 100 nm can be achieved relative to the coupling position at the test component. Consequently, the modal field pitch of the micro-optical element can preferably vary by 1000 nm or less, more preferably 500 nm or less, and particularly 100 nm or less. Preferably, the micro-optical element can be produced, particularly using a direct write method, such that an alignment accuracy of at least 1 μm, more preferably at least 500 nm, and particularly at least 100 nm can be achieved for at least one optically active portion of the micro-optical element and / or the portion of the micro-optical element that interacts with light. Preferably, the micro-optical element can be produced such that a shape accuracy of at least 1 μm, more preferably at least 500 nm, and particularly at least 100 nm can be achieved. As used herein, the term "shape accuracy" refers to the maximum deviation expected for a single device when measurements are performed using appropriate metrology and the measured shape is compared to the designed shape.

[0034] The optical structure of the micro-optical element configured to modify the propagation of light may preferably be configured to generate a modal field diameter for a wavelength of light up to 50 μm. Preferably, the modal field diameter generated may be close to the modal field at the coupling position of the micro-optical component. In this document, generating a modal field diameter refers to an optical configuration configured to generate a modal field with a corresponding modal field diameter. As an example, at a wavelength of 1.55 μm of incident light, the modal field diameter may preferably be 1.55 μm to 50 μm. As commonly used, the term modal field diameter refers to the modal field diameter at 1 / e of the beam waist of the light beam. 2 Diameter at intensity; however, different definitions are possible. Generally, the modal field diameter is measured at the beam waist, which is typically aligned with the coupling location for optimal coupling between the probe head and at least one micro-optical component. The one-sigma variation of the modal field between different structures is preferably 20% or less, more preferably 10% or less, while the resulting coupling variation when coupled into the same component is preferably 5% or less.

[0035] In a preferred embodiment, the test assembly can reduce the modal field diameter at the test assembly's coupling location to produce a diverging beam emitted from the test assembly's coupling location. This embodiment allows for the design of particularly compact micro-optical elements with relatively large working distances. Compared to the modal field of the fiber core, the smaller modal field of the test assembly can result in a micro-optical element with reduced size, thus enabling probing in narrower trenches. Furthermore, the generation time of the micro-optical element can be reduced.

[0036] As indicated above, the micro-optical element is configured to operate in an index-matching liquid. As commonly used, the term "index-matching liquid" refers to a liquid medium having a refractive index that is different from the refractive index of air or vacuum. In particular, the refractive index of the index-matching liquid may be at least 1.01. In a preferred embodiment, the index-matching liquid may be selected from at least one of the following:

[0037] - a liquid which is gaseous at room temperature, in particular oxygen, nitrogen, hydrogen or carbon dioxide, or a cryogenic liquid such as helium, wherein the liquid may comprise at least one halogenated molecule, in particular at least one fluorinated molecule, wherein the molecule may preferably be a hydrocarbon;

[0038] -water;

[0039] - a solvent, in particular chosen from acetone, 1-methoxy-2-propyl acetate (PGMEA), 1-methoxy-2-propanol (PGME) or 2-propanol (IPA);

[0040] - polysiloxanes;

[0041] -monomer;

[0042] - an uncured adhesive, in particular a UV-curable adhesive or an adhesive designed for optical encapsulation, in particular chosen from epoxy adhesives or acrylic adhesives; or

[0043] A liquid designed to exhibit a wetting behavior of the micro-optical component, wherein the specific liquid can preferably be configured for wetting at least one optically functional part of the micro-optical component, but avoiding further spreading of the liquid.

[0044] However, the use of other index matching liquids is also feasible.

[0045] As generally used, the phrase "configured to operate in an index-matching liquid" refers to a design procedure, particularly a computational or simulation step, in which the refractive index of the index-matching liquid must be taken into account for proper operation of the micro-optical element, particularly to avoid a degradation of transmission through the index-matching liquid by at least 1 dB. In particular, the design procedure uses lens surfaces having a stronger curvature than a corresponding lens design for air to achieve the same numerical aperture (NA).

[0046] In a preferred embodiment, at least one optical interface can be tilted relative to the direction of light propagation, in particular to suppress unwanted back reflections. Preferably, an angled fiber array with an angle of 5° to 20° can be used. In addition, a suitable design can be used to compensate for the effects of the tilt.

[0047] In another preferred embodiment, at least one surface can be designed to generate an elliptical modal field at the beam waist (in particular at the focus) to match the modal field at at least one coupling location of the micro-optical component. Preferably, an elliptical modal field without astigmatism can be used, which has at least two optical interfaces in the case of a circular modal field at the coupling location of the test component, in particular when the working distance can be considered as a free parameter.

[0048] In a preferred embodiment, the test assembly can be configured to provide a modal field having a selected pitch and a selected modal field diameter. As generally used, the term "pitch" refers to the distance between two objects (particularly optical elements), two coupling locations, two modal fields, or two parallel waveguides. The pitch can be irregular or constant. Preferred pitches can be selected from values ​​of 80 μm and below, 127 μm, or 250 μm; however, different values ​​are also possible. A micro-optical component having a specific pitch is herein defined as a micro-optical component comprising at least one pair of coupling locations, at least one pair of modal fields, or at least one pair of parallel waveguides having a specific distance. Pitch variation refers to a deviation from a specification. Furthermore, the expression "pitch modification" refers to changing the value of the pitch, for example, from a pitch of 127 μm at the optical fiber array connected to the test assembly to a different pitch at the micro-optical component, for example, 20 μm, or to equalizing the pitch by, for example, compensating for small variations in the pitch of the optical fiber array. In this context, the term "equalization" refers to the process of reducing the pitch inaccuracy of a fiber array, typically up to 1 μm, to a pitch variation of at least 500 nm, preferably at least 100 nm, and in particular at least 50 nm. Equalization can preferably be combined with a calibration measurement that takes transmission variations into account. For the term "fiber array", reference is made to the definition above. In a preferred embodiment, the test assembly can be adapted to different pitches, in particular to overcome the known disadvantage that pitches below 80 μm cannot currently be achieved by using fiber arrays with a typical minimum diameter of 80 μm as optical fibers. Processes that can reduce the fiber diameter to 80 μm or less can generally result in larger pitch variations and are therefore undesirable.

[0049] In a particular embodiment, the probe head can be configured to function as an optical phase array. As commonly used, the term "optical phase array" refers to an optical element having at least one modal field. Generally, a plurality of separate modal fields can be used. At least one of the phase, intensity, or polarization of at least one modal field can be modified to manipulate the field distribution emitted by the modal field. In a preferred embodiment, an array of waveguides at the facets of the test assembly can be used, preferably in combination with a taper that expands the modal field. The position and intensity of the light emitted by the waveguides at the facets can be modified by using a device configured to control the phase and / or intensity within the photonic integrated circuit, in particular a Mach-Zehnder interferometer.

[0050] As already indicated further above, the micro-optical element is an element that is separate from the test assembly. As generally used, the expression that two separate elements are "separate" from each other refers to a spatial configuration in which the two separate elements comprise different materials and / or are produced by applying at least one processing step to at least one of the elements independently of the other of the elements. As an example, a prism can be 3D-printed on an existing optical fiber, thereby not modifying the optical fiber, so that the prism is considered to be separate from the optical fiber. In contrast, if a prism can be introduced into an existing optical fiber, for example by milling, etching or polishing the prism into the optical fiber, the prism is not considered to be separate from the optical fiber. The feature that the micro-optical element is an element that is separate from the test assembly presents the following advantages: the design freedom and precision of the micro-optical element can be higher than that of a micro-optical element that is not an element that is separate from the test assembly.

[0051] As further indicated above, the micro-optical element is in mechanical contact with the test assembly. As further commonly used, the term "mechanical contact" refers to a spatial configuration of two separate elements in which the two separate elements maintain their spatial positions relative to each other. In this document, mechanical contact can be direct mechanical contact or indirect mechanical contact. The term "direct mechanical contact" indicates a spatial configuration in which the two separate elements contact each other at adjacent points or surfaces, while the term "indirect mechanical contact" indicates another spatial configuration in which the two separate elements maintain their spatial positions through the use of at least one other element. As an example, the at least one other element can be a common carrier to which the two separate elements are mounted, or a separator element between the two separate elements. In a preferred embodiment, the micro-optical element can be brought into mechanical contact with the test assembly by attaching the micro-optical element to a small face included in the test assembly, or a 3D-printed spacer can be placed between the micro-optical element and the test assembly, or the micro-optical element can be attached to a mechanical support (particularly a fixture) that can directly or indirectly mechanically contact the test assembly. For this purpose, the micro-optical element can be fixed to a mechanical support that is in mechanical contact with the test assembly. As commonly used, the term "fixing" refers to a specific process applied to one or two elements, wherein the specific process results in permanent mechanical contact between the two elements. Preferably, a bonding element (such as a mechanical clamp) can be used to fix the two elements. In this context, the process may particularly include applying at least one adhesive, preferably a UV-curable adhesive, and curing the adhesive or the mechanical clamp. In a preferred embodiment, an adhesion promoter can be used to increase the robustness of the mechanical contact.

[0052] According to the present invention, a micro-optical element is configured to optically couple light between a test assembly and a micro-optical assembly. As generally used, the term "light" refers to electromagnetic radiation in the near-ultraviolet, visible, near-infrared, and mid-infrared ranges (referring to a wavelength range of 100 nm to 10 μm, preferably 200 nm to 4 μm, more preferably 400 nm to 2.7 μm, and in particular at least 1250 nm to 1650 nm). More generally, the term "optical coupling" refers to the process of transferring light between two optical elements, preferably two waveguide-based elements. As examples, the coupling process can include transferring light from a laser into an optical waveguide or transferring light between two separate optical waveguides. Preferably, the coupling process is performed so as to maximize the optical coupling between the two optical elements, particularly by translating or tilting at least one of the optical elements relative to one another. In another preferred embodiment, tolerance can be maximized, for example by using a large modal field, where the term "tolerance" refers to the modification of the optical coupling relative to at least one of translational or rotational movement.

[0053] In particular, the term "coupling efficiency" is generally used to indicate the effect of the optical coupling achieved by the coupling process between two optical elements. Preferably, the coupling efficiency between the two optical waveguides may be 0.5 dB to 3 dB. However, in certain embodiments known to those skilled in the art, only significantly lower coupling efficiencies are acceptable. Furthermore, the term "coupling tolerance" corresponds to a 1 dB reduction relative to the translational movement. The coupling tolerance may preferably be at least 0.5 μm, preferably at least 1 μm, more preferably at least 2 μm in the lateral direction relative to the light beam, and at least 2 μm, preferably at least 5 μm, more preferably at least 10 μm in the direction of the light beam. Similarly, the rotational tolerance may preferably be at least 0.1°, preferably at least 0.5°, more preferably at least 1°.

[0054] According to the present invention, a micro-optical element configured to optically couple light between a test assembly and a micro-optical assembly is configured to determine an optical performance of the micro-optical assembly. As used herein, the term "optical performance" refers to at least one parameter indicative of at least one property of at least one optical element. In this context, optical performance may preferably refer to an optical micro-optical assembly, but may also refer to an optical performance of at least one other optical element (particularly selected from a probe head, a micro-optical element, a test assembly, and particularly a photonic integrated circuit or an optical fiber array). The optical performance may particularly refer to at least one of the following: coupling efficiency of a known modal field to a micro-optical component, polarization properties, backreflection properties, pitch accuracy, waveguide propagation losses, spatial and / or angular distribution of light emitted into free space, modulator performance (such as modulation speed), extinction ratio, laser performance (such as relative intensity noise), photocurrent-voltage (LIV) characteristics, linewidth, amplification of a semiconductor optical amplifier (SOA), responsivity of a photodiode, bandwidth of an optical element in the time and / or frequency domain, backreflection, bit error rate of optical data transmission, pitch, transmission; however, it is also feasible to use at least one other parameter.

[0055] For this purpose, the test assembly may have optical functionality, wherein this optical functionality may be independent of the optical functionality for operating the micro-optical element. Furthermore, the test assembly may have at least one of mechanical functionality and electrical functionality. As commonly used, the term "optical functionality" indicates that the test assembly includes at least one photonic integrated circuit configured to characterize at least one optical property of the micro-optical component, as described above. Similarly, the term "mechanical functionality" indicates that the test assembly includes at least one functionality configured to characterize at least one mechanical property of the micro-optical component (in particular, selected from at least one parameter of a MEMS actuator, in particular the response time, or the mechanical behavior of a surface acoustic wave sensor). Furthermore, the term "electrical functionality" indicates that the test assembly includes at least one functionality configured to characterize at least one electrical property of the micro-optical component (in particular, selected from at least one of a characteristic parameter of a semiconductor junction (such as capacitance), the performance of a modulator, an operating parameter of a laser, or a photocurrent configured to measure resistance).

[0056] Generally, characterizing optical performance refers to measuring performance. The purpose of characterizing optical performance is to generate a temporary optical coupling to determine the optical performance. In this context, the measurement of optical performance may specifically include measuring at least one of the following: pitch, modal field, angular distribution of light emitted from the probe, coupling efficiency to a known component, and transmission from an optical fiber connected to the probe into free space. In addition, the measurement of optical performance may include measuring at least one mechanical or electrical property that results in at least one optical signal, such as the characterization of a micromechanical switch used to switch light between waveguides. In contrast, optical packaging is not used in this context to characterize the optical performance of a micro-optical assembly, as the optical packaging provides a permanent optical connection to enable operation of the micro-optical assembly rather than to measure its optical performance.

[0057] In a preferred embodiment, the optical performance of the probe head can be calibrated. As generally used, the term "calibration" refers to the measurement of performance that is considered in subsequent steps. Preferably, calibration can include numerical compensation of measured coupling losses, reworking, scrapping components, or changing measurement parameters based on characterizing optical performance in subsequent steps.

[0058] In another aspect, the present invention relates to the use of an optical probe as disclosed elsewhere herein, wherein the optical probe is configured for optical testing of a micro-optical component, wherein the micro-optical component comprises at least one of:

[0059] - Liquid protection elements;

[0060] - a structure configured to operate in a refractive index matching liquid, wherein the structure is in particular selected from an optical structure, a mechanical structure or an optomechanical structure;

[0061] a metamaterial taper configured to operate in the index-matching liquid, wherein the taper is particularly selected from a metamaterial taper, a suspended taper or an adiabatic taper;

[0062] And / or wherein the micro-optical assembly is configured to operate in a liquid cryogenic environment.

[0063] As commonly used, the term "operating in a liquid cryogenic environment" refers to a process in which an optical probe and micro-optical components are at least partially immersed in a cryogenic liquid during optical testing of at least one micro-optical component. To this end, at least one material can be selected for the optical probe and micro-optical component that is known to neither damage nor delaminate at low temperatures, particularly due to good adhesion, soft consistency, small diameter, matched coefficient of thermal expansion (CTE), or material interlocking. Preferably, changes in at least one optical property (particularly selected from refractive index, optical path length, or light absorption) or at least one mechanical property (particularly selected from length change, bending, deformation, or twisting) are avoided by appropriate design or pre-compensation to operate at the required low temperatures.

[0064] In another aspect, the present invention relates to a method for producing an optical probe, in particular an optical probe as described elsewhere herein. The method comprises at least the following steps i) and ii):

[0065] (i) providing a probe head, wherein the probe head includes a test assembly; and

[0066] (ii) producing at least one micro-optical element by using a direct writing process, wherein the micro-optical element is produced as a separate element relative to the test assembly and in mechanical contact with the test assembly,

[0067] wherein the micro-optical element is configured to optically couple light between the test assembly and a micro-optical assembly, thereby being configured to determine an optical property of the micro-optical assembly, and wherein the micro-optical element is configured to operate in an index matching liquid.

[0068] Herein, the indicated steps can preferably be performed in a given order, starting with step (i) and ending with step (ii). However, any or all of the indicated steps can also be repeated several times and / or performed partially simultaneously.

[0069] According to step (i), a probe head is provided, wherein the probe head comprises a test component. For the terms "probe head" and "test component", reference is made to the above definitions.

[0070] According to step (ii), at least one micro-optical element is produced using a direct writing process, wherein the micro-optical element is produced as a separate element relative to the test assembly and is in mechanical contact with the test assembly, such that the micro-optical element is configured to optically couple light between the test assembly and the micro-optical assembly, thereby being configured to determine the optical properties of the micro-optical assembly. For the terms "micro-optical element," "separate element," and "mechanical contact," reference may be made to the definitions above. As generally used, the term "direct writing process" refers to a process in which a programmable light beam (particularly selected from a photon beam or an electron beam) modifies the solubility of a material (particularly a photoresist) such that the desired structure is obtained after a development step. In a particularly preferred embodiment, a multi-photon absorption process of a material is used, preferably a multi-photon absorption process of an acrylic material that crosslinks under irradiation, preferably using an fs laser and a negative resist. As an example, by laser irradiation, the acrylic material is polymerized so that it is less susceptible to curing after the development step. Preferably, the light distribution can be spatially modified when the photoresist is irradiated. More preferably, the spatial light distribution can be spatially modified by scanning the laser beam using a galvanometer scanner, or by dynamically changing the mask, in particular by a spatial light modulator. In this context, the irradiation can change the solubility of the photoresist. In particular, the photoresist can be liquid before irradiation and can be cured after irradiation. Particularly preferably, two-photon polymerization or multi-photon polymerization can be used in this context for curing the photoresist; however, the use of different types of irradiation is also feasible. After irradiation, the structure can be developed using at least one solvent, which is configured to remove uncured resist portions, in particular selected from 1-methoxy-2-propyl acetate (PGMEA), 1-methoxy-2-propanol (PGME) or 2-propanol (IPA).

[0071] In a preferred embodiment, the micro-optical element can be produced on a test assembly, a single-mode fiber array, or a transparent substrate that can be connected to a single-mode fiber array. In another preferred embodiment, the test assembly can be produced in the same wafer batch as the micro-optical component or in the same production step of an interposer configured to couple other micro-optical components to optical fibers. In this way, arbitrarily complex pitch sequences can be achieved to match the different pitches of the test assembly. In addition, the time and effort required to produce the optical probe can be reduced in this way, particularly because the test assembly and the micro-optical component can be obtained at the same time.

[0072] Fabricating micro-optics on a test assembly rather than on a fiber array offers various advantages in terms of reliability. Due to the limited production accuracy of V-groove arrays and due to core-cladding non-concentricity and fixturing inaccuracies, fiber arrays have a typical pitch accuracy of 0.5 μm, with a typical standard deviation of approximately 0.2 μm. For small modal field diameters at micro-optics, typically 3 μm or less, large coupling efficiency variations can occur if optical lenses can be aligned to the fiber cores of the fiber array. In contrast, photonic integrated circuits include relatively perfect pitches with pitch accuracy of 50 nm or less, particularly because they are defined with lithographic precision. If micro-optics can be aligned to the coupling locations of the test assembly, it becomes possible to produce optical probes with near-perfect pitches. If the test assembly includes a photonic integrated circuit connected to a fiber array, the fiber array may still have pitch inaccuracies, and coupling variations can occur at the coupling locations between the fiber array and the test assembly. However, the modal field size can be matched to approximately 10 μm toward the fiber array connection facet, thereby making the pitch inaccuracy of the fiber array less relevant, particularly because the pitch inaccuracy is small relative to the modal field diameter of the fiber. Furthermore, variations in the coupling efficiency between the fiber array and the test assembly can be calibrated. Furthermore, the test assembly can have an integrated sensor element or transmitter element, thereby avoiding coupling to the fiber array. Furthermore, the test assembly can have at least one distance sensor, particularly selected from an optical distance sensor or an electrical distance sensor, which can be configured to simplify navigation when a droplet of index-matching liquid is dispensed at the probe tip.

[0073] In a preferred embodiment, the method may further comprise the following steps:

[0074] (iii) applying an adhesion promoter to the test component prior to step (ii);

[0075] (iv) before step (ii), mounting at least one micro-optical element on a support.

[0076] As commonly used, the term "adhesion promoter" refers to a substance that can be included in a photoresist or can be applied separately, or refers to a process step configured to treat a surface to increase the adhesion of the surface (particularly compared to not using an adhesion promoter). Preferably, the adhesion promoter can be selected from surface functionalization, particularly plasma treatment or silanization, surface layer removal, etching steps, or coating steps, for example by using a material that inherently has good adhesion, such as chromium. In a preferred embodiment, the adhesion promoter can be integrated into the photoresist by including an additive known to enhance adhesion. However, the use of different types of adhesion promoters is also feasible.

[0077] In another preferred embodiment, the method may further comprise the following steps:

[0078] (v) detecting at least one marker within the test component prior to step (ii);

[0079] (vi) generating at least one mark configured for alignment during step (ii);

[0080] As commonly used, the term "marker" refers to a structure configured for alignment in at least one degree of freedom. In this context, a mark can be a structure explicitly or implicitly dedicated to this purpose, or it can be a functional element of the test assembly, which is particularly selected from a waveguide or a ridge. The specific mark can already be included by the test assembly during step (i), or it can be generated during step (ii) in a direct write process. In particular, the mark can facilitate alignment between the probe head and the micro-optical component for optically coupling light. In this way, automatic alignment of the probe head and the micro-optical component relative to each other can be achieved. The mark can preferably be designed or positioned so that observation of the mark is not disturbed by the refractive index matching liquid.

[0081] In another preferred embodiment, alternatively or additionally, the method further comprises at least one of the following steps:

[0082] (vii) detecting light emitted from the test assembly prior to step (ii);

[0083] (viii) optically coupling light into the test assembly prior to step (ii) to detect the coupling position;

[0084] (ix) applying a refractive index matching liquid at the coupling location such that the light is at least partially transmitted through the refractive index matching liquid;

[0085] (x) aligning the micro-optical element relative to the core of an optical fiber comprised by the test assembly to achieve a variation of at least 1 μm, preferably at least 500 nm, preferably at least 100 nm;

[0086] (xi) calibrating the optical properties of the optical probe after step (ii); wherein the optical properties of the optical probe may preferably be calibrated in a material having the same refractive index as the index matching liquid.

[0087] For further details on methods for producing optical probes, reference may be made to the disclosure of optical probes as provided elsewhere herein.

[0088] In another aspect, the present invention relates to a method for optically testing at least one micro-optical component, in particular by using an optical probe as described elsewhere herein. The method comprises the following steps a) to c):

[0089] a) providing an optical probe, wherein the optical probe comprises a probe head and at least one micro-optical element, wherein the probe head comprises a test assembly, wherein the micro-optical element is a separate element relative to the test assembly and is in mechanical contact with the test assembly; and

[0090] b) positioning the probe head such that the micro-optical element optically couples light between the test assembly and the micro-optical component, wherein the light at least partially propagates through an index matching liquid, wherein the index matching liquid is at least partially in contact with the at least one micro-optical component; and

[0091] c) determining the optical performance of the micro-optical component by measuring an optical signal indicative of the optical performance of the micro-optical component.

[0092] In this context, the indicated steps can preferably be performed in the given order, starting with step a) and ending with step c). However, any or all of the indicated steps can also be repeated several times and / or performed partially simultaneously.

[0093] According to step a), an optical probe is provided, preferably an optical probe as described elsewhere herein.

[0094] According to step b), the probe head is positioned such that the micro-optical element optically couples light between the test component and the micro-optical component.

[0095] According to step c), the optical properties of the micro-optical component are determined by measuring an optical signal indicative of the optical properties of the micro-optical component.

[0096] In a particularly preferred embodiment, the method for optical testing of at least one micro-optical component may further comprise at least one of the following steps:

[0097] d) prior to performing step (b), calibrating the optical properties of the probe tip, preferably in a refractive index matching liquid;

[0098] e) inserting at least a portion of the micro-optical element into a groove comprised by the micro-optical assembly such that light is optically coupled between the test assembly and the micro-optical assembly;

[0099] f) dispensing a refractive index matching liquid before or during step b);

[0100] g) removing the index matching liquid during or after step b) or step c);

[0101] h) determining the optical properties of the micro-optical component before, under or after applying the refractive index matching liquid during step c);

[0102] i) changing the temperature of the micro-optical component or its surface at least during step c);

[0103] j) treating the optical probe in a critical point dryer at least during step c); or

[0104] k) operating the optical probe at least during step c) by using a broadband light source having a linewidth of at least 5 nm.

[0105] For further details regarding the method for optically testing at least one micro-optical component, in particular by using an optical probe, reference may be made to the disclosure of the optical probe as provided elsewhere herein.

[0106] As used herein, the terms "having," "including," or "comprising," or any grammatical variations thereof, are used in a non-exclusive manner. Thus, these terms may refer to both situations in which, besides the features introduced by these terms, no other features are present in the entity described in this context, as well as situations in which one or more other features are present. As an example, the expressions "A has B," "A includes B," and "A comprises B" may refer to situations in which, besides B, no other elements are present in A (i.e., situations in which A consists solely and exclusively of B), as well as situations in which, besides B, one or more other elements (such as element C, elements C and D, or even other elements) are present in entity A.

[0107] As further used herein, the terms "preferably", "more preferably", "particularly", "more particularly" or similar terms are used in conjunction with optional features, without limiting the alternative possibilities. Therefore, the features introduced by these terms are optional features and are not intended to limit the scope of the invention patent application in any way. Those skilled in the art will recognize that the present invention can be carried out by using alternative features. Similarly, features introduced by "in an embodiment of the present invention" or similar expressions are intended to be optional features, without any limitation on alternative embodiments of the present invention, without any limitation on the scope of the present invention, and without any limitation on the possibility of combining features introduced in this manner with other features of the present invention.

[0108] Advantages of the present invention

[0109] The optical probe and the related methods exhibit the following advantages over the prior art. The optical probe can be configured for optical testing of components at the die, batch and wafer level. The optical probe can have a compact probe head that can be inserted into and probe in a groove of a wafer, wherein the groove can preferably be 250 μm or less, more preferably 100 μm or less, in particular 80 μm or less. In addition, the optical probe can be configured for a small pitch, preferably 127 μm or less, more preferably 80 μm or less, in particular 50 μm or less. In this context, a high pitch accuracy with a standard deviation of 300 nm or more preferably a standard deviation and a low modal field size variation with a standard deviation of 10% or less is possible.

[0110] Furthermore, the optical probe can be configured for a high port count, preferably at least 24, more preferably at least 64, and in particular at least 128. Preferably, a small modal field (preferably 10 μm or less, more preferably 5 μm or less, in particular twice the operating wavelength or less) is available at the coupling location of the test component. Furthermore, calibration of probe variations can be possible. The optical probe can be configured for robust detection even at high working distances. Preferably, the optical probe can implement one or more functionalities such as distance measurement, local detection of polarization, multiplexing, modulation, spectral analysis, intensity and phase measurement, heterodyne detection, and signal transmittance. Furthermore, it is possible to achieve high test throughput by measuring more than one channel in parallel or by switching without mechanical movement.

[0111] Furthermore, the optical probe can be configured to operate in the near-ultraviolet range, the visible range, the near-infrared range, and the mid-infrared range (meaning a wavelength range of 100 nm to 10 μm, preferably 200 nm to 4 μm, more preferably 400 nm to 2.7 μm, and in particular at least 1250 nm to 1650 nm). High reproducibility of the optical coupling between the probe head and the at least one micro-optical component can be achieved, with a variation of 0.5 dB or less, more preferably 0.25 dB or less.

[0112] Furthermore, the optical probe according to the present invention is configured for reliably characterizing the performance of a micro-optical component, wherein at least one optically functional part of the micro-optical component (such as a coupling location) can be easily immersed in a refractive index matching liquid without adverse effects. In this way, the performance of the micro-optical component can be characterized, which is optically close to or identical to the expected operation of the micro-optical component. Thus, the present invention allows a high degree of design freedom, in particular for performing test measurements, preferably at a refractive index similar to the final operation of the device. If operated in air, the micro-optical component to be tested may not function well or be commensurate with its final application. If the test measurements can be performed in air, they cannot be considered to be representative of the final operation of the tested device. The optical probe and the associated method are advantageously suitable for cryogenic environments and immersion in cryogenic liquids (such as liquid nitrogen or liquid helium).

[0113] Furthermore, an optical probe according to the present invention may include an optical element operable or configured to operate both in a liquid environment, such as a liquid having a refractive index of at least 1.2, and in air. In a preferred embodiment, this optical element may be selected from a flat mirror, a curved mirror, or a free-form mirror coated with a metallic reflective layer, a dielectric, a microstructured surface, a moth-eye surface produced by 3D printing, a surface exhibiting a lotus effect, an air-retaining structure, a grating, or a cavity. The surface of the optical element may also be configured such that all light rays traverse the surface perpendicularly, making the refractive index of the probe's environment irrelevant. This preferred embodiment allows the use of the same probe for both tests in air and liquid, or in liquids with different refractive indices, thereby allowing for comparative measurements and reducing product variation. In particular, reflections can alter the performance of optical components, such as lasers, or can alter the performance of optical mode field converter structures. Therefore, test measurements are preferably performed in a liquid medium having a refractive index different from that of air (i.e., at least n = 1.01). Advantageously, the index-matching liquid does not hinder alignment of the optical probe with the micro-optical component. It is suitable for edge couplers and grating couplers and does not change polarization. In addition, the present invention generally does not involve other steps that require vacuum; therefore, its use is easy, straightforward and cost-effective.

[0114] Furthermore, the index-matching liquid can be dispensed coarsely, optionally in contact with the complete micro-optical element, at least a partial or complete probe head, and optionally in contact with the complete wafer. This particular embodiment allows the use of a technically robust and cost-effective dispensing system, since the index-matching liquid does not have to be confined to certain areas, such as only the space between the lens and the micro-optical component, specifically corresponding to the coupling location. Confining the cladding to such a small portion of the component would require a complex and unreliable dispensing technique, which is avoided by using the present invention.

[0115] The index-matching liquid inherently includes a substance configured to go beyond the simple suppression of back reflections at the facets. In particular, the index-matching liquid avoids parasitic reflections at the top oxide-air and bottom oxide-silicon interfaces, thereby allowing the spot size converter to function properly. Advantageously, the index-matching liquid can be or include a curable adhesive, preferably a curable epoxy. In this context, the epoxy can additionally exhibit mechanical functionality, particularly for permanently securing the optical components to be connected. In particular, optical single-mode optical fibers can be secured in V-grooves of SOI chips. Operation of optical probes and micro-optical components can be performed in an index-matching liquid having a refractive index of 1.01 to 2.0, preferably 1.35 to 1.5. The index-matching liquid can be affected by light, heat, or moisture. As a further advantage, it is possible to calibrate the optical probe in the desired environment, as well as in the desired environment where the refractive index and other optically significant effects are of concern. BRIEF DESCRIPTION OF THE DRAWINGS

[0116] Further optional features and embodiments of the present invention are disclosed in more detail in the subsequent description of the preferred embodiments, preferably in conjunction with the dependent claims. It will be appreciated by those skilled in the art that each optional feature can be implemented in isolation or in any feasible combination. It should be emphasized that the scope of the present invention is not limited to the preferred embodiments. In the drawings:

[0117] Figure 1 and Figure 2 each illustrating an illustrative embodiment of an optical probe configured for optical testing of micro-optical components;

[0118] Figure 3 and Figure 4 each showing an exemplary embodiment of a probe head and a micro-optical element;

[0119] Figure 5 Another exemplary embodiment of an optical probe is shown;

[0120] FIG6 illustrates an exemplary embodiment of a test assembly and a micro-optical assembly;

[0121] FIG7 shows a facet view pointing toward the facet of the test assembly;

[0122] Figure 8 and Figure 9 each illustrating another exemplary embodiment of an optical probe and a micro-optical assembly;

[0123] FIG10 shows another exemplary embodiment of a test assembly and a micro-optical element;

[0124] Figure 11 Another exemplary embodiment of an optical probe is shown; and

[0125] FIG. 12 illustrates an illustrative embodiment of a method for producing a probe head. DETAILED DESCRIPTION

[0126] Figure 1 An exemplary embodiment of an optical probe 1 configured for optical testing of a micro-optical component 50 is shown. The optical probe 1 comprises a micro-optical element 20 configured for optically coupling light 3 between the micro-optical component 50 and a test component 2 at coupling locations 51, 14, wherein the light 3 is transmitted through facets 103, 102, respectively. Figure 1 In an exemplary embodiment, micro-optical element 20 is configured to redirect light 3 at an angle 26 of 90°. Light 3 can travel from test assembly 2 to micro-optical assembly 50, from micro-optical assembly 50 to test assembly 2, or in both directions simultaneously. Micro-optical assembly 50 is affixed to a mechanical support, such as chuck 7, either permanently or by using a vacuum tool or at least one adhesive. In some embodiments, the optical functionality of a functional component element 56 (e.g., a waveguide, a laser, or a photodiode, which can be coupled to a waveguide 58) that is part of micro-optical assembly 50 can be characterized, for example, by using the optical transmission properties of waveguide 58 or a spot size converter at the coupling location of micro-optical assembly 50. Several probe heads 10 can be aligned simultaneously or sequentially to the coupling location of micro-optical assembly 50, for example, to test multi-port devices such as semiconductor optical amplifiers (SOAs). Probe heads 10 can have several channels for coupling, particularly by having multiple coupling locations 51.

[0127] like Figure 1 , the probe head 10 is at least partially embedded in an index-matching liquid 17. The refractive surface 24 is designed to operate in the index-matching liquid 17; as an example, the refractive index of the index-matching liquid 17 is taken into account during the design of the shape of the refractive surface 24. The reflective surface 23 is also designed to operate in the index-matching liquid 17. Here, the reflective surface 23 can be designed so that total internal reflection is not defeated due to the reduced refractive index of the material of the micro-optical element 20 relative to the index-matching liquid 17 compared to the micro-optical element 20 relative to air or a vacuum.

[0128] For this purpose, containment structure 45 is used. Containment structure 45 can have gaps to ensure that the liquid photoresist can escape cavity 46 during the development step, or cavity 46 can be filled with a medium that preferably has a low refractive index (particularly lower than the refractive index of index-matching liquid 17 and micro-optical element 20). This medium can be dispensed during the manufacturing process of micro-optical element 20, prior to chemical development of the liquid photoresist, in place of the liquid photoresist. Index-matching liquid 17 can preferably be selected so that it does not penetrate cavity 46. Examples include high-viscosity liquids or liquids with surface tension that do not allow 17 to penetrate 46. Furthermore, containment structure 45 or another portion of micro-optical element 20 can be designed to allow the use of index-matching liquid 17 that does not penetrate cavity 46, particularly by creating a nanostructured surface exhibiting a lotus effect, by implementing 3D-printed valves or capillaries, or by sealing cavity 46. Alternatively or additionally, air-retaining structures, such as tips or points, can be used. Preferably, the method disclosed by Qu et al. (see above) can be used to create cavity 46. In another embodiment, reflective surface 23 can focus light 3 to coupling location 51, while refractive surface 24 can be designed to operate identically or similarly in the absence and presence of index-matching liquid 17, particularly by configuring refractive surface 24 so that light passes through refractive surface 24 perpendicular to its surface, or by providing refractive surface 24 with a flat surface. As used herein, the term "similarly operating" refers to a configuration in which the coupling efficiency of light 3 into micro-optical component 50 exhibits a difference of no more than 6 dB, preferably no more than 3 dB, and more preferably no more than 1 dB in the presence of index-matching liquid 17 compared to the absence of index-matching liquid 17.

[0129] Figure 2 Another exemplary embodiment of the optical probe 1 is shown, in which the refractive index matching liquid 17 covers a larger area of ​​the optical probe 1 or the probe head 10 and the micro-optical assembly 50. The complete configuration can be encapsulated in, for example, a cryostat, a vacuum chamber, or a critical point dryer. The critical point dryer can allow the refractive index matching liquid 17 to be removed or replaced with at least one other liquid. The cryostat can allow testing at low temperatures, wherein the refractive index matching liquid 17 can be selected from substances commonly used in cryostats, such as liquid helium or nitrogen. The refractive index matching liquid 17 can also only partially cover the optical probe 1, wherein the refractive index matching liquid 17 can in particular not be in contact with the translation stage 5 included by the optical probe 1.

[0130] FIG. 3 shows various exemplary embodiments of a probe head 10 including a test assembly 2 and a micro-optical element 20 .

[0131] like Figure 3a, the micro-optical element 20 features a 3D printed waveguide 71, in particular a photonic wire bond (PWB). The photonic wire bond may be designed such that at least 50%, preferably at least 90%, more preferably at least 95% of the light 3 transmitted by the optical fiber 12 is redirected in a designed manner, in particular by selecting an appropriate refractive index contrast, radius of curvature and waveguide diameter. The waveguide diameter and refractive index contrast are selected such that the photonic wire bond is a single-mode photonic wire bond, preferably exhibiting a refractive index of 1.4 to 1.63, in particular 1.53. Preferred resists for making the photonic wire bond may include commercial resists from the VanCore range or similar products. The cavity 46 may preferably be filled with a refractive index matching liquid 17, a specially designed material for photonic wire bonds (e.g. from the VanClad range), similar products or air. In the case where the optical fiber 12 may be polarization maintaining, the photonic wire bond may further preferably be polarization maintaining, or may be used according to Figure 11 Configuration. Waveguide 71 can be a multimode waveguide, preferably having a gradient-index fiber configured to reduce modal dispersion. Mechanical support 8 can be the containment structure 45, or separate from the containment structure 45. Furthermore, micro-optical element 20 can be the containment structure 45 itself. Taper 70 can adapt the modal field from optical fiber 12 to the modal field of the photonic wire junction, wherein a typical reduction from a first value of 5 μm to 12 μm to a second value of 1 μm to 3 μm can be used for single-mode operation in the near-infrared region with a wavelength of 1 μm to 2 μm. For other wavelengths, the modal field diameter can be scaled according to the wavelength. The photonic wire junction can preferably have a minimum bend radius of at least 30 μm, more preferably at least 60 μm, and in particular at least 100 μm. The photonic wire junction can be designed as a polarization-preserving waveguide 71b, for example by exhibiting birefringence designed to have an elliptical cross-section.

[0132] Figure 3b Another exemplary embodiment of the test assembly 2 and the micro-optical element 20 is shown, in which a whispering gallery waveguide 72 is used.

[0133] Figure 3c Another exemplary embodiment of a test assembly 2 and a micro-optical element 20 is shown, wherein the refractive index between the material of the micro-optical element 20 and the index-matching liquid 17 is so high that total internal reflection is not lost at angle 26. For the indicated angle 26 of 90°, the angle of the chief ray 3f of the light 3 relative to the surface normal 26c is 45°. In this embodiment, to achieve the desired total internal reflection of the chief ray 3f, the angle of the chief ray 3f relative to the surface normal is preferably as follows: If the micro-optical element 20 has a refractive index n1=1.53, then the index-matching liquid 17 must have a refractive index n1 of not greater than 1.08. cIf the micro-optical element 20 has a refractive index n1 = 1.62, the refractive index matching liquid 17 must have a refractive index n1 less than 1.14. c . Alternatively or additionally, the reflective surface 23 may be coated with a thin film 23b. The thin film may be or include a metal, in particular selected from at least one of Al, Au, Cr, Ni, Ag or Pt, or a dielectric material. In the present context, the term "thin film" means that the thickness of the film is below the desired wavelength. As an alternative, a thick film of a low refractive index polymer (preferably fluorinated) may be used. In the present context, the term "thick film" means that the thickness of the film is greater than the evanescent field of the total internal reflection. The coating may also be used for the purpose of modifying the wetting behavior. Preferably, a coating may be used that does not change the polarization of the light by using a polarization that is not in the reflection plane of the reflective surface 23. This means that the phase shift of s-polarized light and p-polarized light is essentially the same upon reflection. This can be achieved by tailoring different reflective layers depending on the polarization direction or by using metamaterials that reflect without changing the phase.

[0134] In order to support at least the light 3 is reflected, because of the high refractive index contrast n between the refractive index matching liquid 17 and the reflective surface 23 c In this case, shallower rays may be reflected while steeper rays may not be reflected, so the refractive index matching liquid 17 and the reflective surface 23 may have alternative shapes, such as Figure 3d The shape of the reflective surface 23a depicted in FIG. The advantages thereof can be in particular: up to a lower refractive index contrast n c , other rays except the main ray 3f are reflected, and the focusing property is independent of the refractive index of the refractive index matching liquid 17.

[0135] Alternatively or additionally, such as Figure 3e As shown in FIG, the test assembly 2 can be tilted vertically relative to the surface 50a of the micro-optical assembly 50 at an angle of preferably 0° to 85°. Figure 1 、 Figure 6b 、 Figure 8 or Figure 9 . At shallower angles of 30° or less, V-grooves array 12c may mechanically interfere with 50. To achieve shallower angles of 30° or less, instead of using V-grooves 12c, V-grooves 12d, as depicted by dashed lines, may be used. In this embodiment, deflection angle 26 can be larger, in particular further away from the critical angle for total internal reflection, while still achieving emission of light 3 substantially within surface 50a of micro-optical component 50.

[0136] Figure 3f Another exemplary embodiment of the test assembly 2 and the micro-optical element 20 is shown, wherein several reflections at several reflective surfaces 23 ensure that total internal reflection does not fail.

[0137] Figure 3gAnother exemplary embodiment of the test assembly 2 and micro-optical element 20 is shown, in which the refractive surface 24 can be designed as a refractive surface 24a, thereby changing the direction of the principal ray 3f and other rays of light 3 while also changing the divergence. In a specific embodiment or example, the beam of light 3 can be focused. In an alternative embodiment, the divergence may not be changed and the light 3 may simply be deflected. This suppresses backreflections in the optical fiber core 13 or the micro-optical component 50 at the refractive surface 24. In a preferred embodiment, the light 3 can be transmitted substantially at the Brewster angle. In this case, the refractive surface 24 is tilted so that the light 3 strikes the refractive surface 24 approximately at the Brewster angle. If this is not possible for all portions of the light 3, simulations can be performed, which can be configured to optimize the shape of the refractive surface 24 for low backreflection. Furthermore, the propagation direction of the light 3 may not be in the plane of the surface 50a of the micro-optical component 50 but may be at an angle relative to the surface 50a of the micro-optical component 50. Furthermore, the surface of the coupling location 14 may be tilted relative to the propagation direction of the light 3 , thereby changing the propagation direction of the light 3 and suppressing back reflection.

[0138] Figure 3h Another exemplary embodiment of a test assembly 2 and a micro-optical element 20 is shown, having cavities 46. Cavities 46 may preferably be filled with air, another gas, a vacuum, or a low-refractive-index polymer, preferably having a lower refractive index than the material of the micro-optical element 20, preferably no greater than 1.4, more preferably no greater than 1.31, and particularly close to 1. One of the cavities 46 serves as the refractive surface 24, while the other serves as the reflective surface 23. In this embodiment, the index-matching liquid 17 may have a refractive index comparable to or higher than that of the micro-optical element 20. In embodiments where the index-matching liquid 17 can substantially match the refractive index of the micro-optical element 20, the refractive surface 24b has no optical functionality. Alternatively, in instances where the index-matching liquid 17 and the micro-optical element 20 may not have the same refractive index, the refractive surface 24b may function in the same manner as the refractive surface 24 and may focus or defocus the light 3. If the refractive indices of the index-matching liquid 17 and the micro-optical element 20 do not match, the refractive surface 24b can be designed so that it is substantially perpendicular to the ray of light 3, tangential to the phase wavefront of light 3, or at a Brewster angle to avoid undesired reflections. If the light 3 is to be emitted substantially colinearly with the optical fiber core 13, the reflective surface 23 and the cavity 46 can be omitted, and the probe head 10 can operate substantially like a lensed fiber without deflecting light.

[0139] Figure 4Another exemplary embodiment of a probe head 10 and a micro-optical element 20 is shown, more particularly for calibration, qualification, analysis or testing of the functionality of the probe head. For this purpose, a high NA objective immersion lens can be operated in a refractive index matching liquid 17, wherein the numerical aperture (NA) can preferably exceed 1.0, more preferably exceed 1.2. Preferably, an objective lens 81 configured to be adjustable with respect to the refractive index can be used. The focal plane of the objective lens 81 can preferably be aligned to a focus 80. By optionally numerically correcting the finite point spread function, the modal field at the focus 80 can be measured. In addition, the objective lens 81 can be translated in the propagation direction of the light 3, wherein the radiation is captured at a defined distance. By numerical calculation, the modal field can be determined with high accuracy, for example by fitting a Gaussian beam to the captured light distribution or by using an iterative algorithm (such as the Gerchberg-Saxton algorithm). In particular, the modal field diameter, the propagation direction, M can be measured and calibrated. 2 The measurement can be performed using a far-field analysis device, such as a scanning slit profilometer or goniometer with a photodetector. In this embodiment, the far-field analyzer is preferably separated from the index-matching liquid 17 by a transparent planar window. This embodiment can also be used to test the functionality of the objective lens 81.

[0140] Figure 5 FIG. 5 shows another exemplary embodiment of an optical probe 1 configured for optical testing of a micro-optical component 50. As schematically depicted here, a cladding 17 completely surrounds the micro-optical element 20. Figure 5 As further shown in FIG, the optical probe 1 is configured for optical testing of a grating coupler 105 that emits at an angle 26, which may typically be between 95° and 115°, typically 100°. In this context, the refractive surface 24 may be specifically implemented such that it deflects the light 3 at an angle of 10° from the surface normal, so that the emission of the light 3 matches the grating coupler 10, in particular to achieve high optical coupling to the micro-optical component 50. In addition, the angle 26 may be fine-tuned by using a translation stage 5. In another embodiment, the refractive surface 24 may be an optical lens that emits in a direction along the optical fiber core 13, and the complete probe head 10 may be tilted at an angle 26 minus 90°, typically between 0° and 20°, preferably 10°, see FIG. Figure 8 Such tilting can preferably be implemented by using a portion 4 b of the fixture 4 and the micro-optical element 20 , which is fine-tuned using the translation stage 5 .

[0141] Figure 6a An exemplary embodiment of a test assembly 2 and a micro-optical assembly 50 (particularly a wafer 60) is shown, further comprising a 3D-printed marker element 21. The marker element 21 can preferably be produced in the same printing process as the micro-optical assembly 20 and can be well aligned to both the micro-optical assembly 20 and the coupling location 14, particularly to at least 10 μm, preferably 5 μm, and particularly 1 μm. The marker element 21 can be visible in the field of view of a top-down camera 33, which can be configured to simplify alignment of the probe head 10 to the micro-optical assembly 50 (particularly the wafer 60) and the trench 55. The position of the marker element 21 can be calibrated relative to one of the micro-optical assembly 50 (particularly the wafer 60), the focal point 80, the top-down camera 33, or the mechanical support 7. To prevent the top-down camera 33 from obstructing its view of the marker element 21, the mechanical fixture 4 has a portion 4b that can be configured to secure the test assembly 2 at an angle. This angle can preferably be 5° to 15° compared to the surface normal of the wafer. To prevent mechanical contact between the test assembly 2 and the surface of the wafer 60, the exemplary test assembly 2 depicted here includes chamfers 18. Without chamfers 18, mechanical contact could occur at the location presented by chamfers 18, which would damage at least a portion of the micro-optical assembly 50 (particularly, the wafer 60). Furthermore, the micro-optical element 20 is configured here so that light 3 is emitted horizontally onto the surface of the micro-optical assembly 50 (particularly, the wafer 60). This configuration can be achieved by tilting the reflective surface 23. The marker element 21 can be positioned sufficiently far from the index-matching liquid 17 so that the view of the top-view camera 33 onto the surface of the micro-optical assembly 50 (particularly, the wafer 60) is not disturbed. To this end, the marker can be moved out of or into the drawing plane to be sufficiently far from the index-matching liquid 17. This allows the probe head 10 to be precisely aligned with the micro-optical assembly 50 (particularly, the wafer 60) using the marker element 21. Alternatively, the top-view camera 33 may be an immersion objective, and the index matching liquid 17 may be in contact with the top-view camera 33 and the marking elements 21. Typically, at least two marking elements 21 may be used.

[0142] Figure 6bAnother exemplary embodiment of a test assembly 2 and a micro-optical component 50 (particularly a wafer 60) is shown, further employing a distance sensor 31. Here, the distance sensor 31 can be configured to measure a distance 32 from a portion of the micro-optical component 50 (particularly the wafer 60), particularly the distance 32 to the surface 50a or the deeply etched bottom 57, the distance 32 to a mechanical support for the micro-optical component 50 (particularly the wafer 60), or the distance 32 to at least one calibration structure within the optical probe 1. The distance sensor 31 can be a micro-optical element attached to another optical fiber core and can be designed to operate in an index-matching liquid 17. The distance sensor 31 can generate a modal field of the desired size at the surface to be measured. A small size may be preferred for high spatial resolution measurements. The optical fiber to which the distance sensor 31 can be connected can lead to an interferometer, such as an optical coherence tomography or a white-light interferometer. The distance sensor 31 can also be configured to measure the distance 32 based on colorimetric principles. The distance sensor 31 can interact with specially designed marker structures within the micro-optical assembly 50 (particularly the wafer 60). These marker structures can guide the probe head 10 to the desired location, similar to landing lights guiding an airplane to an airport runway. These marker structures can be configured to produce a highly discriminative back-reflected feature or signal that guides the probe head to the correct location, such as a retroreflector or grating. The distance sensor 31 can also be selected from optical sensors, mechanical sensors, or electrical sensors, such as capacitive sensors, including atomic force microscopes.

[0143] 7 shows a facet view directed towards a facet 102 of a test assembly 2 having a plurality of micro-optical elements 20, wherein the coupling locations 14 in adjacent micro-optical elements 20 are separated by a pitch 27. Figure 7a As schematically depicted in FIG, each micro-optical element 20 has a preferred diameter 110a. Figure 7b As schematically depicted in FIG, each micro-optical element 20 has a diameter 110b where adjacent micro-optical elements 20 intersect. Figure 7c , each micro-optical element 20 has a diameter 110b, wherein adjacent micro-optical elements 20 are separated by leaving gaps 111. The gaps 111 may be advantageous for mechanically decoupling adjacent micro-optical elements 20, which is preferred for higher reliability of the probe head 10.

[0144] Figure 8 Another exemplary embodiment of the optical probe 1 and the micro-optical assembly 50 is shown, which has liquid protection elements 36, 37 configured to limit the spread of the refractive index matching liquid 17. Exemplary implementations of the liquid protection elements 36, 37 may be selected from at least one of the following:

[0145] - Tips, spikes, gratings, corrugated surfaces or nanostructured surfaces;

[0146] - Surfaces with low surface wettability, such as fluorinated surfaces;

[0147] - gaps, grooves, trenches, in particular with suspended films; or

[0148] -Barriers, capillaries that control liquids.

[0149] Figure 9 Another exemplary embodiment of the optical probe 1 and micro-optical assembly 50 is shown, having a dispensing nozzle 38 and a removal nozzle 39 configured to dispense or remove, respectively, a refractive index matching liquid 17. Additional nozzles or the same nozzle can further be used to dispense a cleaning liquid to remove the refractive index matching liquid 17, such as by blowing with gaseous nitrogen, or using an inkjet print head to locally dispense the refractive index matching liquid 17. Alternatively or additionally, a device configured to heat and evaporate the refractive index matching liquid 17 can be used. As another alternative or additionally, a critical point dryer or other device configured to spin a wafer 60 or a disk on which the micro-optical assembly 50 can be mounted can be used to remove the refractive index matching liquid 17. The nozzle can be fixed to a translation stage, such as the translation stage 5, or can remain stationary, or can be attached to a mechanical support 7 that can be moved relative to the probe head 10.

[0150] Figure 10a Another exemplary embodiment of the test assembly 2 and micro-optical element 20 is shown, in which the dispensing nozzle 38 and the removal nozzle 39 are embodied as channels of hollow-core optical fibers. Here, the optical fibers 12 are embodied as hollow-core optical fibers or fiber bundles having two hollow-core optical fibers configured for dispensing and removing the index-matching liquid 17, respectively, and also having an optical fiber core 13 configured for transmitting light. At least one of the dispensing nozzle 38 or the removal nozzle 39 may include at least one 3D-printed extension, which may preferably be manufactured in the same manufacturing step as the micro-optical element 20. The dispensing nozzle 38 and / or the removal nozzle 39, including at least one extension, may be configured to ensure that the index-matching liquid 17 is preferably largely removed, or to clean the reflective surface 23.

[0151] Figure 10b Another exemplary embodiment of the test assembly 2 and the micro-optical element 20 is shown, wherein the dispensing nozzle 38 and the removal nozzle 39 are embodied as part of a microfluidic chip 40 that can be fixed to the probe head 10 or can be moved relative to the probe head 10 .

[0152] Figure 11Another exemplary embodiment of an optical probe 1 is shown, in which the testing assembly 2 includes a transparent substrate 2a. Here, the transparent substrate 2a has a substantially planar window through which light 3a can pass from the micro-optical element 20 to the free-space imaging and testing device 82, and vice versa, from the free-space imaging and testing device 82 to the micro-optical element 20, or in both directions. The imaging device can be or include a microscope waveguide assembly, such as an optical fiber, in an intermediate imaging plane. The imaging device can couple light into or receive light from the coupling location 51 of the micro-optical assembly 50.

[0153] Figure 12a An exemplary embodiment of a method for producing a probe head 10 is shown. An objective lens 201 generates a laser beam 202 configured to cure a photoresist 200. Alternatively, the solubility of the photoresist 200 can be changed by irradiation with the laser beam 202. By scanning in three dimensions with the laser beam 202, a structure 20b in the micro-optical element 20 to be manufactured is generated. In order to align the structure 20c in the micro-optical element 20 to be manufactured to the coupling position 14, light 15 can be coupled into the test component 2. The light 15 is selected so that it can be transmitted through the optical waveguide 25. A lithography system 210 has a detector configured to detect the position of the light 15 that excites the test component 2 through the coupling position 14. The detector can be a CCD camera or a confocal detector. Alternatively, the laser beam 202 can be coupled to the probe head 10 through the coupling position 14 and can be detected at the optical fiber core 13 or by a detector within the test component 2 coupled to the probe head 10. As another alternative, features within the test assembly 2, in particular the optical waveguide 25 or the marker element 21 (not depicted here), can be used for alignment. For this purpose, light from a laser beam 202 coupled into the optical fiber core 13 and reflected at features within the optical waveguide 25, such as the facet 104, or at the optical fiber core 13 can be detected. After irradiation, the liquid photoresist 200 is preferably removed using a solvent.

[0154] Figure 12b Another exemplary embodiment of a method for producing a probe head 10 is shown. Here, the probe head 10 is positioned so that the lithography system 210 views the optical fiber core from the side. This allows the liquid protection element 36 and the marker element 21 to be manufactured relatively far from the coupling location 14 of the test component, preferably at a distance of at least 200 μm, more preferably at least 500 μm, and especially at least 1000 μm; however, greater distances may also be feasible.

[0155] Reference Signs List

[0156] 1.1b: Optical probe

[0157] 2: Test components

[0158] 2a: Transparent substrate of the test component

[0159] 3.3a: Light coupled between the test component and the micro-optical component

[0160] 3f: Chief Ray

[0161] 4: Fixtures for testing components

[0162] 4b: Portion of a fixture for a test assembly configured to mount the test assembly at an angle compared to mounting directly on a surface

[0163] 4c: Surface, which is the part of the fixture used to test the component that is essentially perpendicular to the surface of the wafer 5: Translation stage, typically 6 degrees of freedom

[0164] 6: Mechanical support parts and carriers

[0165] 7: Mechanical supports and chucks for micro-optical components and wafers

[0166] 8: Mechanical support, which is part of the micro-optical element

[0167] 10: Probe head

[0168] 11: Fiber Array

[0169] 12: Fiber optic

[0170] 12a: Hollow-core fiber

[0171] 12c, 12d: Glass block with at least one V-shaped groove / V-shaped groove array / V-shaped groove

[0172] 13: Fiber core

[0173] 14: Test component coupling position

[0174] 15: Light coupled into the probe head

[0175] 16: Second probe head

[0176] 17: Index matching liquid / cladding

[0177] 18: Chamfers in test components

[0178] 20: Micro-optical components

[0179] 20b, 20c: Structures in the micro-optical element to be manufactured

[0180] 21: (3D printing) marking components

[0181] 23: Reflective surfaces, such as total internal reflection mirrors

[0182] 23a: Reflective surface with alternative shapes

[0183] 23b: Thin film coating the reflective surface

[0184] 24: Refracting surfaces, such as optical lenses or prisms

[0185] 24a: Refractive surfaces that change the direction of light, particularly the main ray

[0186] 24b: Refractive surface that reduces the divergence of light coupled between the test component and the micro-optical component

[0187] 25: Optical waveguide, which is part of the test assembly

[0188] 26: Angle

[0189] 26c: Surface Normal

[0190] 27: Pitch of the coupling position of the test component at the small face of the test component

[0191] 31: Distance sensor

[0192] 32: The distance between the distance sensor and the surface of the wafer

[0193] 33: Looking down at the camera

[0194] 34: Free working distance

[0195] 35: Vacuum tool or permanent fixture

[0196] 36: Liquid protection element, which is part of the probe head

[0197] 37: Liquid protection element, which is part of the micro-optical component

[0198] 38: Liquid dispensing elements, such as dispensing nozzles

[0199] 39: Liquid removal elements, such as removal nozzles

[0200] 40: Microfluidic Chip

[0201] 45: Accommodating structure

[0202] 46: Cavity

[0203] 50, 50c: Micro-optical components

[0204] 50a, 50b: Surfaces of micro-optical components

[0205] 51: Coupling position of micro-optical components

[0206] 55: Grooves etched into the wafer

[0207] 56: Functional element, which is part of a micro-optical component, such as a waveguide, laser or photodiode

[0208] 57: Deep etched bottom

[0209] 58: Waveguide, which is part of the micro-optical component

[0210] 60: Wafer

[0211] 70: tapered portion

[0212] 71: Waveguide

[0213] 71b: Waveguide configured to maintain polarization of light

[0214] 72: Whispering Gallery Waveguide

[0215] 80: Focus

[0216] 81: Objective lens

[0217] 82: Free Space Imaging and Testing Setup

[0218] 102: A facet of a test assembly configured for attaching a micro-optical element

[0219] 103: Facets of micro-optical components

[0220] 105: Grating Coupler

[0221] 110a: diameter of the micro-optical element, which is less than or equal to the pitch of the coupling locations of the test component at the facet of the test component

[0222] 110b: Diameter of the micro-optical element, which is larger than the pitch of the coupling locations of the test component at the facet of the test component

[0223] 111: gap between micro-optical elements with diameter 110b

[0224] 200: (Liquid) Photoresist

[0225] 201: Objective lenses for the manufacture of micro-optical elements

[0226] 202: Laser beam of objective lens

[0227] 210: Lithography System

Claims

1. An optical probe (1) configured for optical testing of at least one micro-optical component (50), comprising: A probe head (10), wherein the probe head (10) includes a test assembly (2); at least one micro-optical element (20), wherein the micro-optical element (20) is a separate element relative to the test assembly (2) and is in mechanical contact with the test assembly (2), The micro-optical element (20) is configured to optically couple light (3) between the test assembly (2) and the micro-optical component (50), thereby being configured to determine an optical property of the micro-optical component (50), and wherein the micro-optical element (20) is configured to operate in a refractive index matching liquid (17).

2. The optical probe (1) according to the preceding claim, further configured to operate the refractive index matching liquid (17) by having at least one of the following: a liquid dispensing element (38), wherein the liquid dispensing element (38) is configured to dispense at least a portion of the refractive index matching liquid (17); a hollow core optical fiber (12a), wherein the hollow core optical fiber (12a) is configured to receive the at least one portion of the index matching liquid (17); a liquid protection element (36), wherein the liquid protection element (36) is configured to control the spreading of the at least one portion of the refractive index matching liquid (17); a liquid removal element (39), wherein the liquid removal element (39) is configured to remove the at least one portion of the index matching liquid (17); Microfluidic chip (40).

3. The optical probe (1) according to any one of the preceding claims, wherein the micro-optical element (20) has at least one of the following: cavity (46); waveguide (71); a reflective surface (23), wherein the reflective surface (23) is configured to deflect the light (3) by at least 10°, or wherein at least two reflective surfaces (23) are configured to reflect the light (3); a refractive surface (24); wherein the refractive surface (24) is configured to deflect the light (3) by at least 2°; a functional surface configured to modify at least one of a refractive property or a wetting property; At least one high refractive index material, wherein the high refractive index material has a refractive index of at least 1.

6.

4. The optical probe (1) according to any of the preceding claims, wherein the micro-optical element (20) comprises at least one optical fiber (12), wherein the optical fiber (12) is inclined at an angle of at least 5° relative to the surface normal of the micro-optical component (50).

5. The optical probe (1) according to any one of the preceding claims, wherein the optical probe (1) is configured for coupling at at least two coupling locations (51) of the micro-optical component (50).

6. The optical probe (1) according to any one of the preceding claims, wherein the micro-optical element (20) satisfies at least one accuracy selected from at least one of the following: The shape accuracy of the micro-optical element (20) is at least 250 nm; The alignment accuracy of the micro-optical element (20) relative to the coupling position (14) of the test assembly (2) is at least 1000 nm; The pitch accuracy between two micro-optical elements (20) is at least 1000 nm; At least 10% modal field accuracy.

7. The optical probe (1) according to the preceding claim, wherein the optical properties of the probe head (10) are calibrated.

8. The optical probe (1) according to any one of the preceding claims, wherein at least one of the probe head (10) or the micro-optical assembly (50) comprises at least one marking element (21), wherein the marking element (21) is configured for alignment of the probe head (10) relative to the micro-optical assembly (50).

9. The optical probe (1) according to any one of the preceding claims, wherein the test assembly (2) comprises at least one of the following: Optical fiber array (11); A transparent substrate (2a).

10. Use of an optical probe (1) according to any one of the preceding claims, wherein the optical probe (1) is configured for optical testing of a micro-optical component (50), wherein the micro-optical component (50) comprises at least one of the following: Liquid protection element (37); a structure configured to operate in said index matching liquid (17), wherein said structure is particularly selected from an optical structure, a mechanical structure or an optomechanical structure; a metamaterial taper configured to operate in the index matching liquid (17), wherein the taper is particularly selected from a metamaterial taper, a suspended taper or an adiabatic taper; and / or The micro-optical assembly (50) is configured to operate in a liquid cryogenic environment.

11. A method for producing an optical probe (1) configured for optical testing of at least one micro-optical component (50), the optical probe (1), in particular the optical probe (1) according to any of the preceding claims referring to the optical probe (1), comprising the following steps: (i) providing a probe head (10), wherein the probe head (10) comprises a test assembly (2); and (ii) producing at least one micro-optical element (20) by using a direct writing process, wherein the micro-optical element (20) is produced as a separate element relative to the test component (2) and in mechanical contact with the test component (2), The micro-optical element (20) is configured to optically couple light (3) between the test assembly (2) and a micro-optical component (50), thereby being configured to determine an optical property of the micro-optical component (50), and the micro-optical element (20) is configured to operate in a refractive index matching liquid (17).

12. The method according to the preceding claim, further comprising at least one of the following steps: (iii) applying an adhesion promoter to the test component (2) prior to step (ii); (iv) Mounting the at least one micro-optical element (20) on a support (4) before step (ii).

13. The method according to any one of claims 11 and 12, wherein the micro-optical element (20) is produced during step (ii) by using an additive manufacturing method.

14. A method for optical testing of at least one micro-optical component (50), comprising the following steps: a) providing an optical probe (1), wherein the optical probe (1) comprises a probe head (10) and at least one micro-optical element (20), wherein the probe head (10) comprises a test component (2), wherein the micro-optical element (20) is a separate element relative to the test component (2) and is in mechanical contact with the test component (2); and b) positioning the probe head (10) such that the micro-optical element (20) optically couples light (3) between the test assembly (2) and the micro-optical component (50), wherein the light (3) at least partially propagates through a refractive index matching liquid (17), wherein the refractive index matching liquid (17) is at least partially in contact with the at least one micro-optical component (20); and c) determining the optical performance of the micro-optical component (50) by measuring an optical signal indicative of the optical performance of the micro-optical component (50).

15. The method according to the preceding claim, further comprising at least one of the following steps: d) calibrating the optical performance of the probe head (10) before step b); e) inserting at least a portion of the micro-optical element (20) into a groove (55) during step b), wherein the groove (55) is comprised by the micro-optical component (50), so that the light (3) is optically coupled between the test component (2) and the micro-optical component (50); f) dispensing the refractive index matching liquid (17) before or during step b); g) removing the index matching liquid (17) during or after step b) or step c); h) determining the optical properties of the micro-optical component (50) before, under or after applying the refractive index matching liquid (17) during step c); i) modifying the temperature of the micro-optical component (50) or its surface (50a) at least during step c); j) treating the optical probe (1) in a critical point dryer at least during step c); k) operating the optical probe (1) at least during step c) by using a broadband light source having a linewidth of at least 5 nm.

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