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 manufacturing an optical probe (1), and a method for optical testing of at least one micro-optical component (50). The invention relates to an optical probe (1) comprising:-a probe head (10) wherein the optical properties of the probe head (10) are calibrated and wherein the probe head (10) comprises a test circuit (2) wherein the test circuit (2) is fixed on a mechanical support; -at least one micro-optical element (20), where the micro-optical element (20) is a separate component with respect to the test circuit (2) and is in mechanical contact with the test circuit (2), where the micro-optical element (20) is configured to optically couple light between the test circuit (2) and the micro-optical component (50), thereby being configured to determine an optical performance of the micro-optical component (50).

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 method for manufacturing an optical probe, and a method for optical testing of at least one micro-optical component.

[0002] Specifically, the optical probe can be used for the manufacturing, calibration, testing, and preselection of micro-optical components, which are particularly configured for optical communication, sensor applications, medical sensors, automotive applications, quantum applications, or environmental sensing; however, the optical probe can also be used in other applications. Background Art

[0003] Optical probes configured for optical coupling to photonic integrated circuits featuring 3D-printed optics on a fiber array are known. 3D-printed optics for optical packaging are further known. 3D-printed free-form probes for beam shaping of light exiting a photonic integrated circuit are still further known.

[0004] WO 2018 / 083191 A1 discloses the manufacturing of micro-optics for beam expansion on a photonic integrated circuit for optical packaging.

[0005] Trappen M. et al., "3D-printed optical probes for wafer-level testing of photonic integrated circuits", (Optics Express 28, 37996-38007, 2020) discloses probing 3D-printed optics on a fiber array of a wafer by inserting 3D-printed micro-optics consisting of mirrors and lenses into etched trenches of the wafer.

[0006] Singer S. et al., "3D-printed facet-attached optical elements for beam shaping in optical phased arrays", (Opt. Express 30, 46564-46574, 2022) discloses 3D-printed micro-optical elements on the facets of an optical phased array.

[0007] WO 2023 / 132785 A1 discloses an apparatus for wafer-level testing of semiconductor devices, where the semiconductor device includes an optoelectronic unit, an optical interface, and an optical fiber array optically coupled between the optoelectronic unit and the optical interface. The optoelectronic unit transmits one or more optical test signals to the semiconductor device and receives one or more optical response signals from the semiconductor device for testing at least one function of the semiconductor device. The optical interface optically couples the optical fiber array and the semiconductor device. In addition, the optical interface includes a steering element for steering the optical test signals to the semiconductor device and steering the response signals to the optical fiber array.

[0008] US 2018 / 0143245 A1 discloses an integrated optical probe card and a system for performing wafer testing of an optical microelectromechanical system (MEMS) structure having an in-plane optical axis. One or more micro-optical bench assemblies can be utilized to perform on-wafer optical screening of the optical MEMS structure to change the direction of light between an out-of-plane direction perpendicular to the in-plane optical axis and an in-plane direction parallel to the in-plane optical axis so as to enable testing of the optical MEMS structure by vertically injecting light.

[0009] EP 4 001 980 A1 discloses systems and methods for testing a photonic integrated circuit (PIC) using an optical probe having an out-of-plane edge coupler for transmitting test signals between the out-of-plane probe and an edge-coupled photonic waveguide in the plane of the PIC. To accommodate the size of the optical probe, test trenches can be fabricated in the PIC near the edge coupler of the waveguide. The optical probe can be displaced relative to the detector along one or more axes to position the free end of the detector within the test trench and align the out-of-plane edge coupler of the probe with the edge coupler of the PIC waveguide. Thus, the PIC can be probed at the wafer level without first dicing the wafer into PIC chips or bars. The optical probe can be physically coupled to the detector through a contact sensor to detect and / or avoid physical contact between the probe and the PIC.

[0010] In addition, WO 2022 / 266760 A1 and Stefan Singer et al., "3D-printed facet-attached optical elements for beam shaping in optical phased arrays", (arxiv.org, Cornell University Library, Cornell University Library, Ithaca, NY 14853, March 24, 2022) disclose optical coupling mechanisms forming the background of the present invention.

[0011] Problem to be solved:

[0012] Accordingly, an object of the present invention is to provide an optical probe configured for optical testing of at least one micro-optical component, a method for manufacturing an optical probe, and a method for optical testing of at least one micro-optical component, which at least partially overcome the above problems of the prior art.

[0013] A specific object of the present invention is to provide an optical probe and a method configured for optical testing of components at the die, batch, and wafer levels. Preferably, the optical probe should have a small probe head that can be inserted into and probed into the grooves of a wafer, where the grooves can preferably be 250 µm or less, more preferably 100 µm or less, and particularly 80 µm or less. In addition, the optical probe should be configured for a small pitch, preferably 127 µm or less, more preferably 80 µm or less, and particularly 50 µm or less. Here, a high pitch accuracy with σ = 1000 nm or greater and a low mode field size variation with σ = 10% or less will be particularly preferred.

[0014] In addition, the optical probe should be configured for a high port count, preferably at least 24, more preferably at least 64, and particularly at least 128. Preferably, a small mode field should be available at the coupling position of the test circuit, which is preferably 10 μm or less, more preferably 5 μm or less, and particularly twice the operating wavelength or less. In addition, calibration of probe variations is also possible. The optical probe should be configured for robust detection even at high working distances. Additionally, it will be preferred to achieve a high test throughput. Preferably, the optical probe can implement at least one additional function, such as distance measurement, local detection of polarization, multiplexing, modulation, spectral analysis, intensity and phase measurement, heterodyne detection, and transmission of signals.

[0015] It is particularly desirable that the optical probe be configured to operate in the near-ultraviolet, visible, near-infrared, and mid-infrared ranges, covering a wavelength range of 100 nm to 10 µm, preferably 200 nm to 4 µm, more preferably 530 nm to 2 µm, and particularly at least 1250 nm to 1650 nm. A high reproducibility of the optical coupling between the probe head and at least one micro-optical component with a variation of 0.5 dB or less, more preferably 0.25 dB or less, will be preferred. Summary of the Invention

[0016] This problem is solved by an optical probe configured for optical testing of at least one micro-optical component, a method for manufacturing 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 that can be implemented in isolation or in any combination are listed in the dependent claims and the following entire description.

[0017] In a first aspect, the present invention relates to an optical probe configured for the optical testing of at least one micro-optical component. According to the present invention, the optical probe comprises:

[0018] - a probe head, wherein the probe head is calibrated and wherein the probe head comprises a test circuit, wherein the test circuit is fixed to a mechanical support;

[0019] - at least one micro-optical element, wherein the micro-optical element is a separate element with respect to the test circuit and is in mechanical contact with the test circuit,

[0020] wherein the micro-optical element is configured to optically couple light between the test circuit and the micro-optical component, and thereby is configured to determine the optical performance of the micro-optical component.

[0021] As generally used, the term "optical probe" refers to an optical device configured for the optical testing of at least one micro-optical component. Additionally, the optical probe may exhibit at least one of a mechanical function, an electrical function, or an optical function, as described in more detail below. For the purpose of optical testing, the optical probe used herein comprises a probe head having a test circuit, wherein the probe head can be aligned in a manner such that light can be optically coupled between the test circuit and the micro-optical component. As further generally used, the term "probe head" refers to the terminal piece of the optical probe, wherein the terminal piece comprises a micro-optical element configured to optically couple light between the test circuit 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 movable dynamically in an easy manner, the probe head may preferably exhibit a low weight.

[0022] As already indicated above, the optical probe is configured for the 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 comprise a wafer having a plurality of photonic integrated circuits or single-photon integrated circuits. Generally, the micro-optical component may comprise a plurality of optical structures inherently presenting small dimensions (preferably 10 µm or less, more preferably 5 µm or less, especially 1 µm or less), which are configured to perform an intended function (especially a groove serving as a waveguide or a grating) or have a total size of 10 mm or less. In a preferred embodiment, the micro-optical component may be fabricated on a photonic platform selected particularly from SOI (silicon-on-insulator), InP (indium phosphide), SiN (silicon nitride), or LNOI (lithium niobate on insulator). In an alternative embodiment, the micro-optical component may be a non-planar component, especially an optical element selected from a microlens, a grating, an optical isolator, or a mirror.

[0023] As further indicated above, the optical probe includes a probe head having a test circuit. As generally used, the term "test circuit" refers to at least one photonic integrated circuit that is configured to characterize the performance of a micro-optical component. The test circuit may preferably include the same material, manufacturing batch, wafer, or technology as the micro-optical element. However, different types of test circuits may also be used. For the purpose of optical testing of at least one micro-optical component, the test circuit may have an active optical structure (especially at least one selected from light sources such as lasers or superluminescent light-emitting diodes (SLEDs) or detectors such as Ge photodiodes), or it may be coupled to an optical fiber or an optical fiber array to be observable particularly by a macroscopic optical instrument. As generally used, the term "optical fiber" refers to an elongated circular optical element configured to guide light by using a facet, where the term "facet" refers to the end face of an optical waveguide structure (especially a waveguide) through which light is transmitted or received. As further generally used, the term "optical fiber array" refers to at least one optical fiber associated with at least one mechanical element (preferably selected from a glass block or an array of V-grooves). In a preferred embodiment, the test circuit may have at least one of an electrical function, a distance sensor, a mechanical sensor, an acceleration sensor, a force sensor, or a structure with a microelectromechanical system (MEMS). In addition, other embodiments of the test circuit are also feasible.

[0024] As generally used, the term "photonic integrated circuit" refers to a planar device that includes at least one of a waveguide or a photonic device, the waveguide or photonic device having at least one surface-emitting device 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" indicates that the corresponding device is obtained by using 2D lithography on a planar substrate. Based on this definition, an optical fiber is not included by a photonic integrated circuit, while devices produced using the ioNext platform, SiN, SOI, or silicon-rich oxide are components of a photonic integrated device. A photonic integrated circuit may include active and passive waveguide devices, preferably selected from a photodetector, a light source, an optical modulator, a spectral analyzer, a power splitter or polarization splitter, a filter or stripper, or a multiplexer. A photonic integrated circuit may also exhibit at least one advanced electrical function, especially a transistor, a CMOS component, a wire, or an electrical waveguide. In a particularly preferred embodiment, the test circuit and the micro-optical component may be a photonic integrated circuit. In an alternative embodiment, the micro-optical component can be an optical integrated circuit or a micro-optical device.

[0025] As further indicated above, the optical probe further comprises at least one micro-optical element. As generally used, the term "micro-optical element" refers to an optical structure configured to modify the propagation of light (in particular by at least one of focusing, diverging, steering, deflecting, wave-guiding or rotating the polarization of light). To this end, the micro-optical element may preferably comprise at least one element selected from the following: 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 an optical element with a whispering gallery guiding mechanism. The micro-optical element may preferably be a three-dimensional element, where the term "three-dimensional element" refers to an object having an extension of at least 1 μm in all spatial directions. Preferably, the micro-optical element may have at least one free-form surface, where 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 a total extension of 1000 µm or less, more preferably 500 µm or less, particularly 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, particularly 20 nm or less, as measured by at least one of an atomic force microscope (AFM) or a white light interferometer. Preferably, the micro-optical element may be transparent from 250 nm to 4500 nm, more preferably at least from 530 nm to 1650 nm; however, different transparent wavelength ranges are also possible.

[0026] Preferably, the micro-optical element can be manufactured by using a polymeric material (especially an acrylic material), particularly by photo-curing the polymeric material. In this context, an additive process can preferably be used; however, it is also feasible to use at least one of different types of polymeric materials or processes. Preferably, the micro-optical element can be manufactured in such a way that an alignment accuracy of at least 1000 nm, more preferably at least 500 nm, particularly at least 100 nm, relative to the coupling position at the test circuit can be obtained. Accordingly, the mode field pitch variation of the micro-optical element can preferably be 1000 nm or less, more preferably 500 nm or less, particularly 100 nm or less. Preferably, the micro-optical element can be manufactured on the test circuit, particularly by using a direct-write method, in such a way that an alignment accuracy of at least one optically effective part of the micro-optical element and / or a part of the micro-optical element that interacts with light of at least 1 μm, more preferably at least 500 nm, particularly at least 100 nm can be obtained. Preferably, the micro-optical element can be manufactured in such a way that a shape accuracy of at least 1 μm, more preferably at least 500 nm, particularly at least 100 nm of the micro-optical element can be obtained.

[0027] The optical structure of the micro-optical element configured to modify the propagation of light can preferably be configured to produce a mode field diameter that modifies the wavelength of light by 50 μm. In this context, producing the mode field diameter refers to an optical arrangement configured to produce a mode field with a corresponding mode field diameter. For example, at a wavelength of 1.55 µm of the incident light, the mode field diameter can preferably be from 1.55 µm to 50 µm. As generally used, the term "mode field diameter" refers to the diameter at the 1 / e² intensity of the waist of the light beam; however, it is also feasible to use different definitions. Generally, the mode field diameter can be measured at the waist of the light beam, which can typically be aligned with the coupling position to achieve optimal coupling between the probe head and at least one micro-optical component. The 1-σ variation of the mode field between different structures can preferably be 20% or less, more preferably 10% or less, while the resulting coupling variation can preferably be 5% or less when coupled into the same component.

[0028] In a preferred embodiment, the test circuit can reduce the mode field diameter at the coupling position of the test circuit to produce a divergent light beam emitted from the coupling position of the test circuit. This embodiment allows for the design of particularly small micro-optical elements with a relatively large working distance. A mode field of the test circuit that is smaller than the mode field of the optical fiber core can result in a micro-optical element with a reduced size and thus enable probing into narrower trenches. Additionally, the manufacturing time of the micro-optical element can be reduced.

[0029] In a preferred embodiment, the test circuit may be configured to modify the pitch or the mode field diameter of the fiber array. As generally used, the term "pitch" refers to the distance between two objects (especially optical elements), two coupling positions, two mode fields, or two parallel waveguides. The pitch may be irregular or constant. Preferred pitches may be selected from values of 80 μm, 127 μm, or 250 μm; however, it is also feasible to use different values. A micro-optical component having a specific pitch is used herein as a micro-optical component including at least a pair of coupling positions, mode fields, or parallel waveguides having a specific distance. A pitch variation refers to a deviation from the specification. Further, the expression "modification of the pitch" refers to changing the value of the pitch (e.g., from a pitch of 127 µm at the fiber array to a different pitch of 25 µm at the micro-optical component) or equalizing the pitch (by, e.g., compensating for small variations in the pitch of the fiber array). In this document, the term "equalization" refers to the process of reducing the pitch inaccuracy of the fiber array (usually up to 1 µm) to a pitch variation of at least 500 nm, preferably at least 100 nm, particularly at least 50 nm. Preferably, the equalization may be combined with a calibration measurement taking into account transmission variations. The term "fiber array" may refer to the above definition. In a preferred embodiment, the test circuit may match different pitches to specifically overcome known drawbacks: currently, a pitch below 80 μm cannot be achieved by using a fiber array as an optical fiber, and the optical fiber has a typical minimum diameter of 80 μm. Procedures for reducing the optical fiber diameter to 80 μm or less usually result in large pitch variations and are thus not desirable.

[0030] In a particular embodiment, the probe head may be configured to be used as an optical phase array. As generally used, the term "optical phase array" refers to an optical element having at least one mode field. Generally, a plurality of individual mode fields may be used. At least one of the phase, intensity, or polarization of at least one mode field may be modified to manipulate the field distribution emitted by the mode field. In a preferred embodiment, a waveguide array at the test circuit facet can be used, preferably in combination with a cone for expanding the mode field. The phase and intensity of the light emitted by the waveguides at the facet can be modified by using devices (especially Mach-Zehnder interferometers) configured to control the phase and / or intensity within the photonic integrated circuit.

[0031] As further indicated above, the micro-optical element is a separate element with respect to the test circuit. As generally used, the expression that two unit elements are "separate from" each other means that the two unit elements include different materials and / or are manufactured by applying at least one processing step independently of the other element to at least one of the elements. For example, a prism can be 3D printed on an already existing optical fiber without changing the optical fiber, and thus the prism is considered separate from the optical fiber. In contrast, if the prism can be introduced into an already existing optical fiber (e.g., by milling, etching, or polishing the prism into the optical fiber), the prism is not considered separate from the optical fiber.

[0032] As further indicated above, the micro-optical element is in mechanical contact with the test circuit. As further generally used, the term "mechanical contact" refers to the spatial configuration of two unit elements, where the two unit elements maintain their spatial positions relative to each other. In this document, the mechanical contact can be direct mechanical contact or indirect mechanical contact. The term "direct mechanical contact" indicates a spatial arrangement where the two unit elements are in contact with each other at an adjacent point or surface, while the term "indirect mechanical contact" indicates another spatial arrangement where the two unit elements maintain their spatial positions by using at least one additional element. For example, the at least one additional element can be a common carrier to which the two unit elements are mounted or a separate element between the two unit elements. In a preferred embodiment, the micro-optical element can be in mechanical contact with the test circuit by attaching the micro-optical element to a facet included in the test circuit, or a 3D printed spacer can be placed between the micro-optical element and the test circuit, or the micro-optical element can be attached to a mechanical support (especially a fixture), and the mechanical support can be in direct or indirect mechanical contact with the test circuit. To this end, the micro-optical element is fixed to a mechanical support that is in mechanical contact with the test circuit. As generally used, the term "fixing" refers to a specific process applied to one or two elements or the resulting arrangement with respect to one or two elements, whereby a temporary or permanent mechanical contact between the two elements includes maintaining their positions relative to each other in all six degrees of freedom during the fixing time. Preferably, a mechanical carrier (preferably a bonding element, such as a mechanical clamp) can be used to fix the two elements; however, it is also conceivable to use different types of mechanical carriers. Alternatively or additionally, the process can include applying at least one adhesive (preferably a UV curable adhesive) and curing the adhesive or using a mechanical clamp. In a preferred embodiment, an adhesion promoter can be used to increase the robustness of the mechanical contact.

[0033] According to the present invention, a micro-optical element is configured to optically couple light between a test circuit and a micro-optical assembly. As generally used, the term "light" refers to electromagnetic radiation in the near-ultraviolet range, visible range, near-infrared range, and mid-infrared range, covering a wavelength range of 100 nm to 10 µm, preferably 200 nm to 4 µm, more preferably 400 nm to 2.5 µm, and particularly at least 1250 nm to 1650 nm. More generally, the term "optically couple" refers to the process of transmitting light between two optical elements, preferably two waveguide-based elements. For example, the coupling process may include transmitting light from a laser into an optical waveguide or transmitting light between two single optical waveguides. Preferably, the coupling process can be performed in a manner that maximizes the optical coupling between the two optical elements, particularly by translating or tilting at least one of the optical elements relative to each other. Specifically, the term "coupling efficiency" is generally used to indicate the resulting effect of the optical coupling achieved by the coupling process between two optical elements. Preferably, the coupling efficiency between two optical waveguides can be 0.5 dB to 3 dB. However, as known to those skilled in the art, in some embodiments, only significantly lower coupling efficiencies can be acceptable.

[0034] According to the present invention, a micro-optical element configured to optically couple light between a test circuit and a micro-optical assembly is configured to determine the optical performance of the micro-optical assembly. As used herein, the term "optical performance" refers to at least one parameter indicating at least one property of at least one optical element. Herein, the optical performance may preferably be for an optical micro-optical element. However, it may also refer to the optical performance of at least one additional optical element, particularly selected from a photonic integrated circuit, a probe head, a micro-optical assembly, and an optical fiber array. The optical performance may particularly refer to at least one of the following: the coupling efficiency of a known mode field to the micro-optical assembly, polarization properties, back-reflection properties, pitch accuracy, waveguide propagation loss, the 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, the amplification factor of a semiconductor optical amplifier (SOA), the responsivity of a photodiode, the bandwidth of the optical element in the time domain and / or frequency domain, back-reflection, the bit error rate of optical data transmission, pitch, transmission; however, it is also feasible to use at least one additional parameter.

[0035] To this end, the test circuit may have an optical function, where the optical function may be independent of the optical function of operating the micro-optical element. Additionally, the test circuit may have at least one of a mechanical function or an electrical function. As generally used, the term "optical function" indicates that the test circuit includes at least one photonic integrated circuit, which is configured to characterize at least one optical property of the micro-optical component described above. Similarly, the term "mechanical function" indicates that the test circuit includes at least one function, which is configured to characterize at least one mechanical property of the micro-optical component, particularly selected from at least one parameter of a MEMS actuator, particularly the response time or the mechanical behavior of a surface acoustic wave sensor. Furthermore, the term "electrical function" indicates that the test circuit includes at least one function, which is configured to characterize at least one electrical property of the micro-optical component, particularly selected from characteristic parameters of a semiconductor junction (such as capacitance), the performance of a modulator, the operating parameters of a laser, or at least one of the photocurrent configured to measure resistance.

[0036] Generally speaking, characterizing an optical property refers to the measurement of the property. The purpose of characterizing an optical property is to determine the optical property by generating a temporary optical coupling. In this context, the measurement of an optical property may particularly include measuring at least one of pitch, mode field, the angular distribution of light emitted from a self-probe, the coupling efficiency to a known component, and the transmission from an optical fiber connected to a probe to free space. Additionally, the measurement of an optical property may include measuring at least one mechanical or electrical property that results in at least one optical signal, such as the characterization of a micromachined switch for switching light between waveguides. In contrast, an optical package is not used in this context to characterize the optical properties of a micro-optical component because the optical package provides a permanent optical connection to affect the operation of the micro-optical component rather than measuring its optical properties.

[0037] In a preferred embodiment, the optical properties of the probe head can be calibrated. As generally used, the term "calibration" refers to the measurement of a property to be considered in subsequent steps. Preferably, calibration may include numerical compensation for measuring coupling loss, rework, scrapping of components, or changing measurement parameters based on characterizing optical properties in subsequent steps.

[0038] In another aspect, the present invention relates to a method for manufacturing an optical probe (particularly the optical probe described elsewhere herein). The method includes at least the following steps i) and ii):

[0039] (i) Providing a probe head, where the probe head includes a test circuit; and

[0040] (ii) Manufacturing at least one micro-optical element on the test circuit by using a direct-write process, where the micro-optical element is manufactured as a separate element with respect to the test circuit and is in mechanical contact with the test circuit.

[0041] The micro-optical element is configured to optically couple light between the test circuit and the micro-optical component, thereby being configured to determine the optical performance of the micro-optical component.

[0042] In this document, the indicated steps may preferably be performed in the given order, starting with step (i) and ending with step (ii). However, any or all of the indicated steps may also be repeated several times and / or partially performed simultaneously.

[0043] According to step (i), a probe head is provided, wherein the probe head includes a test circuit. The terms "probe head" and "test circuit" may refer to the definitions above.

[0044] According to step (ii), at least one micro-optical element is fabricated on the test circuit by using a direct writing process, wherein the micro-optical element is fabricated as a separate element with respect to the test circuit and mechanically contacts the test circuit in such a way that the micro-optical element is configured to optically couple light between the test circuit and the micro-optical component, thereby being configured to determine the optical performance of the micro-optical component. In particular, fabricating at least one micro-optical element on the test circuit can contribute to the accurate alignment of the optical probe with the micro-optical component. The terms "micro-optical element", "separate element" and "mechanical contact" may refer to the definitions above.

[0045] As generally used, the term "direct writing process" refers to a process in which a programmable beam (specifically selected from a photon beam or an electron beam) changes the solubility of a material (especially a photoresist) in such a way 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 an acrylic material that crosslinks after irradiation, preferably by using a femtosecond laser and a negative resist. For example, by laser irradiation, the acrylic material polymerizes in such a way that it is not easily cured after the development step. Preferably, the light distribution can be spatially modified when irradiating the photoresist. More preferably, the spatial light distribution can be spatially modified by scanning the laser beam using a galvo scanner or by dynamically changing the light mask (especially by a spatial light modulator). In this document, 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 herein to cure the photoresist; however, it is also feasible to use different types of irradiation.

[0046] In a preferred embodiment, the micro-optical element can be fabricated on a test circuit, which can preferably be connected to a single-mode fiber array. In another preferred embodiment, the test circuit can be fabricated in the same wafer run as the micro-optical component or in the same manufacturing steps of an interposer configured to couple another micro-optical component to an optical fiber. In this way, any complex pitch sequence matching different pitches of the test circuit can be achieved. Additionally, the time and effort required to fabricate the optical probe can be reduced in this way, especially since the test circuit is available at the same time point as the micro-optical component.

[0047] Fabricating the micro-optical element on the test circuit rather than on the fiber array presents various advantages in terms of reliability. Due to the limited manufacturing accuracy of the V-groove array and due to core-cladding non-concentricity and fixation inaccuracies, the fiber array has a typical pitch accuracy of 0.5 µm, with a σ usually of about 0.2 µm. For small mode field diameters at the micro-optical element, which are typically 3 µm and smaller, large coupling efficiency variations can occur if the optical lens can be aligned with the fiber core of the fiber array. In contrast, the photonic integrated circuit includes a relatively perfect pitch with a pitch accuracy of 50 nm or less, especially since it is defined by lithographic precision. If the micro-optical element can be aligned with the coupling positions of the test circuit, it becomes possible to fabricate an optical probe with a nearly perfect pitch. Although the fiber array will still have pitch inaccuracies and coupling variations can occur at the coupling positions between the fiber array and the test circuit, the mode field size can be matched to the fiber array connection facet to about 10 µm, thus making the pitch inaccuracies of the fiber array less relevant, especially since the pitch inaccuracies are smaller relative to the mode field diameter of the optical fiber. Additionally, the coupling efficiency variations between the fiber array and the test circuit can be calibrated. Furthermore, the test circuit can have integrated sensor elements, thereby avoiding the coupling to the fiber array.

[0048] In a preferred embodiment, the method can further include the following steps:

[0049] (iii) detecting at least one marker within the test circuit before step (ii);

[0050] (iv) fabricating at least one marker configured for alignment during step (ii).

[0051] As generally used, the term "marker" refers to a structure configured for alignment in at least one degree of freedom. In this document, a marker can be a structure specifically or implicitly dedicated to this purpose, or it can be a functional element of a test circuit, particularly selected from waveguides or ridges. A particular marker can have been included by the test circuit during step (i), or it can be fabricated during the direct writing process in step (ii). In particular, a marker can facilitate alignment between the probe head and the micro-optical component for optically coupling light. In this way, automatic alignment between the probe head and the micro-optical component relative to each other can be achieved.

[0052] In another preferred embodiment, alternatively or additionally, the method further includes at least one of the following steps:

[0053] (v) Detecting light emitted from the test circuit before step (ii); or

[0054] (vi) Optically coupling light into the test circuit for detecting the coupling position before step (ii).

[0055] In yet another preferred embodiment, alternatively or additionally, the method can further include at least one of the following steps:

[0056] (vii) Fixing the test circuit to a mechanical support before step (ii);

[0057] (viii) Applying an adhesion promoter to the test circuit before step (ii); or

[0058] (ix) Aligning the micro-optical element relative to the optical fiber core included by the test circuit to a variation of at least 1 μm, preferably at least 500 nm, preferably at least 100 nm.

[0059] As generally used, the term "adhesion promoter" refers to a substance that can be included by a photoresist or applied separately, or to a procedural step configured to treat a surface for increasing the adhesiveness of the surface (especially compared to not using an adhesion promoter). Preferably, the adhesion promoter can be selected from: functionalization of the surface, especially plasma treatment or silanization; removal of the surface layer; an etching step; or a coating step, for example by using a material inherently having good adhesiveness, such as chromium. In a preferred embodiment, the adhesion promoter can be integrated into the photoresist by including an additive known to enhance adhesiveness. However, it is also feasible to use different types of adhesion promoters.

[0060] In another preferred embodiment, alternatively or additionally, the method can further include the following step:

[0061] (x) Calibrating the optical performance of the optical probe (1) before step (ii).

[0062] For more details on the method for manufacturing the optical probe, reference may be made to the disclosure of the optical probe provided elsewhere in this document.

[0063] In another aspect, the present invention relates to a method for optical testing of at least one micro-optical component, in particular by using the optical probe described elsewhere in this document. The method comprises the following steps a) to c):

[0064] a) Providing an optical probe, wherein the optical probe comprises a probe head (wherein the optical properties of the probe head are calibrated) and at least one micro-optical element, wherein the probe head comprises a test circuit, wherein the test circuit is fixed on a mechanical support, and wherein the micro-optical element is a separate element with respect to the test circuit and is in mechanical contact with the test circuit; and

[0065] b) Positioning the probe head in such a way that light is optically coupled between the test circuit and the micro-optical component by means of the micro-optical element; and

[0066] c) Determining the optical properties of the micro-optical component by measuring an optical signal indicative of the optical properties of the micro-optical component.

[0067] In this document, the indicated steps may preferably be performed in the given order, starting with step a) and ending with step c). However, any or all of the indicated steps may also be repeated several times and / or partially performed simultaneously.

[0068] According to step a), an optical probe is provided, preferably the optical probe described elsewhere in this document.

[0069] According to step b), the probe head is positioned in such a way that light is optically coupled between the test circuit and the micro-optical component by means of the micro-optical element.

[0070] 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.

[0071] 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:

[0072] d) Calibrating the optical properties of the probe head before performing step (b);

[0073] e) Modifying the optical signal by using an optical phase array;

[0074] f) Inserting at least a part of the micro-optical element into a groove comprised by the micro-optical component in such a way that light is optically coupled between the test circuit and the micro-optical component; or

[0075] g) Matching the pitch of at least two micro-optical elements to a coupling position located at the surface of the micro-optical component by using the test circuit.

[0076] For more details on the method for optical testing (especially by using an optical probe) of at least one micro-optical component, reference may be made to the disclosure of the optical probe provided elsewhere in this document.

[0077] Regarding the prior art, optical probes and related methods exhibit the following advantages. The optical probe can be configured for optical testing of components at the die, batch, and wafer levels. The optical probe can have a small probe head that can be inserted into and probed into the trenches of a wafer, where the trenches can preferably be 250 µm or less, more preferably 100 µm or less, especially 80 µm or less. In addition, the optical probe can be configured for small pitch, preferably 127 µm or less, more preferably 80 µm or less, especially 50 µm or less. In this document, it is possible to have a high pitch accuracy of σ = 300 nm or better and a low modal field size variation of σ = 10% or less.

[0078] In addition, the optical probe can be configured for high port count, preferably at least 24, more preferably at least 64, especially at least 128. Preferably, a small modal field can be obtained at the coupling position of the test circuit, preferably 10 μm or less, more preferably 5 μm or less, especially twice the operating wavelength or less. In addition, a calibration of the probe variation can be feasible. The optical probe can be configured for robust detection even at high working distances. Preferably, the optical probe can implement one or more functions, such as distance measurement, local detection of polarization, multiplexing, modulation, spectral analysis, intensity and phase measurement, heterodyne detection, and signal transmittance. Additionally, it is feasible to achieve high test throughput through parallelization, measurement of more than 1 channel, or switching that does not involve mechanical movement.

[0079] In addition, the optical probe can be configured to operate in the near-ultraviolet range, visible range, near-infrared range, and mid-infrared range, covering a wavelength range of 100 nm to 10 µm, preferably 200 nm to 4 µm, more preferably 400 nm to 2 µm, especially at least 1250 nm to 1650 nm. High reproducibility of the optical coupling between the probe head and at least one micro-optical component with a variation of 0.5 dB or less, more preferably 0.25 dB or less, can be obtained.

[0080] Compared with the present invention, WO 2023 / 132785A1 discloses non-contact optical detection, but does not mention 3D printed structures with sub-micron accuracy, alignment markers, or calibration functions.

[0081] In further comparison with the present invention, US 2018 / 0143245 A1 discloses an optical probe card, but lacks details about a 3D printed structure with sub-micron accuracy, alignment markers, and calibration functions.

[0082] In further comparison with the present invention, EP 4 001 980 A1 discloses 3D printing, but does not have a specific accuracy for achieving specific light propagation characteristics or use alignment markers and calibration functions.

[0083] As used herein, the terms "having", "including", or "comprising" or any grammatical variations thereof are used in a non-exclusive manner. Thus, these terms can refer to a situation where there are no additional features in the entity described herein other than the features introduced by these terms, and also to a situation where one or more additional features are present. As an example, the expressions "A has B", "A includes B", and "A comprises B" can refer to a situation where there are no other elements in A other than B (i.e., a situation where A consists solely and exclusively of B), and also to a situation where one or more additional elements (such as element C, elements C and D, or even additional elements) are present in entity A other than B.

[0084] As further used herein, the terms "preferably", "more preferably", "particularly", "more particularly", or similar terms are used in conjunction with optional features and do not limit alternative possibilities. Thus, the features introduced by these terms are optional features and are not intended to limit the scope of the claims in any way. Those skilled in the art will recognize that the present invention can be carried out by using alternative features. Similarly, the features introduced by "in an embodiment of the present invention" or similar expressions are intended to be optional features and there is no limitation on alternative embodiments of the present invention, no limitation on the scope of the present invention, and no limitation on the possibility of combining the features introduced in this way with other features of the present invention. Brief Description of the Drawings

[0085] In the following description of the preferred embodiments, the further optional features and embodiments of the present invention are preferably disclosed in more detail in conjunction with the dependent claims. Among them, as those skilled in the art will realize, each optional feature can be implemented in an isolated manner and in any feasible combination. It should be emphasized here that the scope of the present invention is not limited by the preferred embodiments. In the figures:

[0086] Figures 1 to 7 Exemplary embodiments of optical probes configured for optical testing of micro-optical components are shown respectively;

[0087] Figure 8 Exemplary embodiments of markers are shown;

[0088] Figures 9 and 10 show exemplary embodiments of test circuits;

[0089] Figure 11 and Figure 12 further exemplary embodiments of an optical probe configured for optical testing of a micro - optical component are shown;

[0090] FIG. 13 shows a top - plan view of a facet for a test circuit;

[0091] FIG. 14 shows Figure 2 a projection of an exemplary embodiment of an optical probe;

[0092] Figure 15 another exemplary embodiment of an optical probe configured for optical testing of a micro - optical component is shown;

[0093] Figure 16 a method for manufacturing a probe head is shown;

[0094] Figure 17 another exemplary embodiment of an optical probe configured for optical testing of a micro - optical component is shown;

[0095] Figure 18 experimental results obtained in the modal - field diameter statistics of 250 micro - optical elements are shown; and

[0096] Figure 19 and Figure 20 further exemplary embodiments of a probe head are shown respectively. DETAILED DESCRIPTION

[0097] 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 includes a micro - optical element 20 configured to optically couple light 3 between the micro - optical component 50 and a test circuit 2 at a coupling position 51, 14, where the light 3 passes through facets 103, 102 respectively. In Figure 1 the exemplary embodiment, the micro - optical element 20 is configured to change the direction of the light 3 by an angle 26 of 90°. As an alternative (not depicted here), the angle 26 can be different angles, typically from 0° to 100°. A preferred value of the angle 26 can be from 80° to 90° to ensure that total internal reflection (TIR) of the reflective surface 23 does not fail. If the angle 26 is different from 90° (e.g., 80°), then the probe head 10 can be tilted clockwise by 10°, as Figure 8As shown. Light 3 can travel from the test circuit 2 to the micro - optical component 50, from the micro - optical component 50 to the test circuit 2, or travel in both directions simultaneously. The micro - optical component 50 is fixed to a mechanical support (such as a chuck 7) permanently or by using a vacuum tool. In some embodiments, the optical function of a functional element 56 (which is part of the micro - optical component 50, such as a waveguide, laser, or photodiode, which can be coupled to the waveguide 58) can be characterized, such as the optical transmission properties of the waveguide 58 or the spot - size converter at the coupling position of the micro - optical component 50.

[0098] In Figure 1 an exemplary embodiment, a lens 24 and a plane mirror as a reflective surface 23 are used to cause total internal reflection. As an alternative (not depicted here), a flat surface and a curved mirror or a combination thereof can be used. To ensure total internal reflection, the refractive index n of the micro - optical element 20 should be at least 1.53. The reflective surface 23 can be a metal - coated mirror to especially avoid total internal reflection failure. The test circuit 2 includes at least one waveguide 25, where the waveguide 25 is configured to direct light to a functional element 59, such as a photodetector or a polarization - sensitive separator having two photodetectors configured for analyzing polarization. As an alternative (not depicted here), the functional element 59 can also be a light source. In other embodiments, the test circuit 2 can optically couple light to an optical fiber array ( Figure 4 ) and preferably modify the mode - field diameter (compared to the optical fiber 12) or the pitch of the waveguides (compared to the optical fiber array 11). This embodiment can preferably not include any functional element 59.

[0099] In Figure 1 an exemplary embodiment, the test circuit 2 is mounted here on the fixture 4 or directly on the translation stage 5. The part of the optical probe 1 that can be moved relative to the micro - optical component 50 is regarded as the probe head 10. All components are preferably designed to be quite dynamic during movement and thus lightweight. The translation stage 5 can preferably be configured to control six degrees of freedom and can preferably be quite dynamic to allow rapid testing of various micro - optical components 50. The test circuit 2 can generate, receive, or generate and receive signals that are configured to probe the optical performance of the micro - optical component 50 or a part thereof (especially the functional element 56, the waveguide 58, or the coupling position 51). The optical performance can also include information about the quality of the facet 103, the coupling position 51, and especially about the spot - size converter within the waveguide 58. Light 3 can be used to align the probe head 10 relative to the micro - optical component 50. The test circuit 2 can also be configured to generate signals indicating the proximity, distance, and collision of at least one object (especially the micro - optical component 50 or the mechanical support 7). The signals can be generated especially by using a LiDAR device, a mechanical detection mechanism, an interferometric device, or a capacitive signal; however, it is also possible to use different devices or mechanisms.

[0100] AsFigure 1 As further shown in, the translation stage 5 is mounted to the mechanical support 6. The chuck 7 is a mounting device on which the micro-optical component 50 can be temporarily or permanently fixed. Preferably, a wafer chuck with vacuum holes can be used, where the micro-optical component 50 can be part of the wafer 60. Herein, the chuck 7 can be translated relative to the optical probe 1.

[0101] Figure 2 Another exemplary embodiment of the optical probe 1 configured for optical testing of the micro-optical components 50, 50b, 50c is shown. As Figure 2 schematically depicted in, the micro-optical component 50 is herein included by the wafer 60. Generally, the wafer 60 can have a size of 6 inches, preferably 8 inches, particularly 12 inches or larger and can include at least 1000 micro-optical components, where the micro-optical components 50, 50b, 50c are Figure 2 exemplarily shown in. Optical signals that can indicate the optical performance of the micro-optical components 50, 50b can be performed in the trenches 55, which can include saw streets for wafer singulation or can have been etched for the purpose of wafer-level testing. Alternatively or additionally, V-grooves etched into the wafer 60 for fiber alignment can be used for optical testing. The movable chuck 7 and / or the translation stage 5 can be moved to sequentially scan at least a portion of the micro-optical components 50, 50b within the wafer 60.

[0102] Figure 3 Another exemplary embodiment of the optical probe 1 configured for optical testing of the micro-optical component 50 is shown. As Figure 3 schematically depicted in, a second probe 1b is herein additionally used for optical testing of the second coupling position 52 of the micro-optical component 50. This exemplary embodiment is configured for optical testing of a micro-optical component 50 having two or more coupling positions 51, 52. The probe heads 10, 16 can be aligned with the micro-optical component 50 respectively. This exemplary embodiment can be used in particular for a micro-optical component 50 having two or more coupling positions 51, 52 (which can preferably be tested simultaneously). For example, the micro-optical component 50 can be selected from a distributed feedback (DFB) laser (where no facets are reflecting, but two facets (and also the rear facet) are transmitting) or an amplifier (such as a semiconductor optical amplifier (SOA)) or a gain material (such as erbium) doped integrated photonics chip). In a similar configuration, at least one additional micro-optical component 50, such as at least one of a micro-lens, an isolator or a beam splitter cube, can be tested.

[0103] Figure 4 Another exemplary embodiment of the optical probe 1 configured for optical testing of the micro-optical component 50 is shown. As Figure 4As schematically depicted, the test circuit 2 is optically coupled to the fiber array 11 at a second coupling location 14b of the test circuit 2. This exemplary embodiment can be configured for pitch conversion from a pitch of the fiber array 11, which is typically 80 μm or 127 μm or 250 μm, to a pitch below 80 μm, such as 25 μm. In addition to pitch conversion, the test circuit 2 can be further configured for mode reshaping. Herein, the test circuit 2 can be based on a platform, preferably selected from ioNext, SiN, Triplex, Si-rich glass, a photonics platform fabricated in a lamination process, an ion diffusion platform, a platform structured in a polymer or etched in glass. This embodiment can be particularly advantageous for testing narrow pitches less than 80 μm.

[0104] Figure 5 Another exemplary embodiment of an optical probe 1 configured for optical testing of a micro-optical component 50 is shown. As Figure 5 schematically depicted, the test circuit 2 is in mechanical contact with the circuit 30. In particular, the test circuit 2 can be part of the circuit 30, or the circuit can be part of the test circuit 2, for example, because the test circuit 2 can include at least one electrical function. This exemplary embodiment has a distance sensor 31 included by the circuit 30, which is configured to measure the distance 32 to the wafer 60. Alternatively or additionally, the distance sensor 31 can be configured to measure the depth or presence of the trench 55. The distance sensor 31 can preferably be selected from a capacitive sensor, an inductive sensor, or an optical sensor. In another embodiment (not depicted herein), the distance sensor 31 can be included by the test circuit 2 without the circuit 30, for example, by generating a distance sensor signal to measure the distance 32 via an additional waveguide 25.

[0105] Figure 6 Another exemplary embodiment of an optical probe 1 configured for optical testing of a micro-optical component 50 is shown. As Figure 6 schematically depicted, the optical probe 1 is configured for optical testing of a grating coupler 105 that emits at an angle 26, which can typically be 95° to 115°, typically 100°. Herein, the refractive surface 24 can be implemented in such a way that it can deflect light at an angle of 10° with respect to the surface normal to match the light emission 3 with the grating coupler 105 to particularly achieve high optical coupling to the micro-optical component 50. Additionally, the angle 26 can be fine-tuned by a translation stage 5. In another embodiment, the refractive surface 24 can be an optical lens that emits in the direction of the waveguide 25, while the entire probe head 10 can be tilted at an angle of 26 minus 90°, typically 0° to 20°, preferably 10°, see Figure 8 . Such tilting can preferably be implemented by using a part 4b of a fixture and a micro-optical element 20, and fine-tuned by using a translation stage 5.

[0106] Figure 7 Shows another exemplary embodiment of an optical probe 1 configured for optical testing of a micro-optical component 50. As Figure 7 schematically depicted, the test circuit 2 is or includes a light source or an array of light sources, particularly selected from lasers, laser rods, optical amplifiers (SOAs), or superluminescent light-emitting diodes (SLEDs). When the test circuit 2 is operable, the coupling performance can be measured by using a functional element 56, which can be an optical device, particularly a photodiode. As an alternative (not depicted here), the optical coupling can be measured by using another optical element, preferably an optical fiber coupled to the micro-optical component 50, a second probe head 6, a grating coupler coupled to the waveguide 58, and a camera. The facet 103 can be further equipped with an optical lens. The test circuit 2 can be fixed to the mechanical support 4 by a vacuum chuck or (for example) permanently fixed by using an adhesive or an adhesion promoter.

[0107] Figure 8 Shows an exemplary embodiment of a 3D printed marker 21. The marker 21 can preferably be produced in the same printing process as the micro-optical element 20 and can be well aligned with both the micro-optical element 20 and the coupling location 14, particularly at least to 10 μm, preferably to 5 μm, especially to 1 μm. The marker 21 can be visible in the field of view of a top-down camera 33, which can be configured to provide simplified alignment of the probe head 10 with the micro-optical component 50 (particularly the wafer 60) and the trench 55. To avoid blocking the line of sight of the top-down camera 33 on the marker 21, the mechanical fixture 4 has a portion 4b configured to fix the test circuit 2 at a specific angle. The angle can preferably be 5° to 15° with respect to the surface normal. To avoid mechanical contact between the test circuit 2 and the surface of the wafer 60, Figure 8 the exemplary test circuit 2 shown includes a chamfer 18. The area of the chamfer 18 is indicated here by a dashed line. Without the chamfer 18, mechanical contact could occur at the location presented by the chamfer 18, which would damage at least a portion of the micro-optical component 50 (particularly the wafer 60). In addition, the micro-optical element 20 is configured here in such a way that light 3 is emitted horizontally onto the surface of the micro-optical component 50 (particularly the wafer 60). This configuration can be achieved by tilting the reflective surface 23.

[0108] FIG. 9 shows an exemplary embodiment of a test circuit 2 connected to an optical fiber array 11. As Figure 9a and Figure 9bAs schematically depicted, the test circuit 2 is configured to translate the pitch 28 at the facets of the test circuit 2, which is typically 80 μm or 127 μm or 250 μm, to a pitch 27 at the coupling position of the test circuit 2 that is typically less than 80 μm. To this end, a plurality of optical fibers 12 are connected to a single micro-optical element 20. However, in some embodiments, the pitch 27 may be 80 μm or greater. The following may be particularly advantageous:

[0109] - An extremely constant pitch is required because the accuracy of the pitch 27 is better than that of the pitch 28, where in this case, the coupling loss at the second coupling position 14b of the test circuit 2 can be calibrated;

[0110] - An irregular pitch is desired, for example, an alternating first pitch of 127 µm and a second pitch of 350 µm; or

[0111] - At least one additional function within the test circuit 2 may be desired, such as polarization splitting.

[0112] In this embodiment, the pitch may also be 80 μm or less.

[0113] Herein, the waveguide 25 and the optical fiber core 13 can maintain polarization. Additionally, the width 29a can be from 2 μm to 10 mm, preferably 2 mm or less. In Figure 9a the exemplary embodiment, each single waveguide 25 is coupled to a separate channel in the micro-optical element 20, while in Figure 9b the exemplary embodiment, more than one waveguide 25e is simultaneously coupled into a single channel and to a single element 20e in the micro-optical element 20. Additionally, multiplexing can be implemented by connecting several micro-optical elements 20 to a single optical fiber 12b.

[0114] FIG. 10 shows a further exemplary embodiment of the test circuit 2. In Figure 10aIn an exemplary embodiment, the polarization splitter 40 is configured to split light with orthogonal E vectors into two polarization channels 41, 42, which are coupled to two optical fibers 12. The waveguide 25b is configured herein in such a way that it does not change the polarization between the facet 102 of the test circuit 2 and the polarization splitter 40. In particular, this advantage can be achieved by a straight, birefringent or short waveguide. Furthermore, the micro-optical element 20 is configured herein in such a way that it does not change the polarization between the facet 103 of the micro-optical assembly 50 and the facet 102 of the test circuit 2. In particular, this advantage can be achieved by providing the micro-optical element 20 as an optical lens without a reflective surface or by ensuring that light can illuminate the reflective surface 23 in such a way that no phase or intensity changes occur between different polarization components (which can be the case for light with the E field in the plane of reflection or perpendicular to the plane of reflection). The plane of reflection is the plane defined by the incident and reflected light at a flat surface. Alternatively, the change in polarization of the reflective surface can be considered numerically, in particular by using Fresnel equations, calibration or training measurements. In another embodiment, the complete Mueller matrix can be determined by measuring both the phase and intensity of the two polarization channels 41, 42. Furthermore, the polarization of at least a part of the light in the two polarization channels 41, 42 can be rotated by 90° and the light can interfere with each other at the detector.

[0115] In Figure 10b an exemplary embodiment, the light of the two polarization channels 41, 42 is coupled to a functional element 59, which can in particular be a waveguide-integrated photodiode. Optionally, the polarization of the light can be rotated by 90° or a different angle before being coupled to an optical fiber or the functional element 59, in particular a photodetector.

[0116] In Figure 10c an exemplary embodiment, the light is coupled to a functional element 59. Herein, the functional element 59 is configured to test the properties of the micro-optical assembly 50 by transmitting or receiving or by simultaneously receiving and transmitting light. In particular, the functional element 59 can be selected from at least one of the following: a photodiode, in particular a PIN, PN or APD; a waveguide-integrated photodiode; an IQ receiver; a beam combiner; an optical modulator; a light source, in particular a laser or an SLED; an amplifier, in particular an SOA; an IQ modulator; an intensity modulator; a polarization splitter; a polarization stripper; a polarization filter, in particular a nominal coupler; or a polarization rotator. Herein, the waveguide 25 can be single-mode or multi-mode. Furthermore, the waveguide 25 can be configured at an angle ≠ 0° with respect to the facet 102 of the test circuit 2 to particularly reduce reflections. Furthermore, the micro-optical element 20 can only have angled surfaces with respect to the light propagation to particularly avoid back reflections, see Figure 11 . The functional element 59, in particular an IQ receiver or a beam combiner, can be used to measure the phase of two light beams relative to each other and can be used as a feedback signal to trim the waveguide 58.

[0117] Figure 11 Another exemplary embodiment of an optical probe 1 configured for optical testing of a micro-optical component 50 is shown. Herein, waveguides 25c, 58b are configured to be non-normal to the surfaces of facets 102, 103, respectively. The refractive surface 24 of the micro-optical element 20 deflects light 3 in such a way that it can be well coupled between waveguides 25c, 58b. To this end, the refractive surface 24 of the micro-optical element 20 may not have an optically effective surface perpendicular to the beam propagation direction of light 3. This embodiment can be advantageous, especially because it can suppress back reflections due to angled surfaces. In another embodiment (not depicted herein), it can also be advantageous that the reflective surface 23 does not have a surface perpendicular to the propagation direction of light 3. In yet another embodiment (not depicted herein), an optical isolator and / or an additional anti-reflection coating can be used on at least one of facets 102, 103 or on the refractive surface 24 of the micro-optical element 20.

[0118] Figure 12 Another exemplary embodiment of an optical probe 1 configured for optical testing of micro-optical components 50, 50b, 50c is shown. As Figure 12 schematically depicted, the test circuit 2 has a large number of coupling locations 14. Herein, several or all of the coupling locations 14 are equipped with one or more micro-optical elements 20. Each coupling location 14 can be selected from a grating coupler, a photodetector, an adiabatic taper, an etched facet, an etched facet at an angle of 30° to 120° with respect to the surface normal of facet 102, or a VCSEL array. If the coupling location 14 that emits or receives light is only slightly significantly perpendicular to facet 102, the micro-optical element 20 can be or include a refractive surface 24, which can Figure 6The light 3 perpendicular to the facet 102 is shaped in the schematically shown manner such that it can be largely received. Alternatively, the probe head 10 can be designed to have a minimum or maximum change in sensitivity with respect to the amount of light 3 coupled into the coupling position 14 by using a high-NA lens or a low-NA lens as the refractive surface 24, where NA represents "numerical aperture". This embodiment can be used to measure the spatial and / or angular distribution of the light 3. The light 3 can come from the micro-optical component 50, then the coupling position 14 can receive the light 3, or the light 3 can be transmitted into the micro-optical component 50, and then the coupling position 14 can emit the light 3. The probe head 10 can act as a Shack-Hartmann sensor, especially by measuring at least one of the propagation direction or intensity of the light 3. During the measurement, the probe head 10 can be moved according to a programmed pattern for subsampling, especially by measuring the light 3 at more positions than where the micro-optical elements 20 are present. In a preferred embodiment, at least one region 19 can be removed, especially by thinning, etching, or milling, to fit the probe head 10 into a smaller groove 55. Alternatively, the thin test circuit 2 has a thickness 19b that is preferably 730 µm or less, more preferably 100 µm or less, over the entire component or at least in the region 19. In a further preferred embodiment, a thin substrate prepared especially by using a direct bandgap semiconductor can be used.

[0119] FIG. 13 shows a plan view of the facet 102 of the test circuit 2. As Figure 13a schematically depicted, each micro-optical element 20 has a preferred diameter 110a. As Figure 13b schematically depicted, each micro-optical element 20 has a diameter 110b, where adjacent micro-optical elements 20 intersect. As Figure 13c schematically depicted, each micro-optical element 20 has a diameter 110b, where adjacent micro-optical elements 20 are separated by leaving a gap 111. The gap 111 can be beneficial for mechanically decoupling adjacent micro-optical elements 20, which is preferably used for higher reliability of the probe head 10.

[0120] Figure 14a shows a further exemplary embodiment of the optical probe 1 in the projection direction along +z according to Figure 2 . The dashed lines indicate parts of the elements of the drawing that are not visible due to being covered by another element. As Figure 14a schematically depicted, the micro-optical component 50 includes waveguides 58 each having a pitch 28b. In a preferred embodiment, the pitch 28b can be 30 µm or less. However, providing a probe with a pitch 27 that can match the pitch 28b will result in rather small micro-optical elements 20, thus resulting in a short working distance 34 or poor coupling between the coupling positions 14 and 51 due to the micro-optical elements 20 being too small. In Figure 14aIn an embodiment, instead of coupling to the opposed coupling positions 14, 51, a plurality of coupling positions 14 are preferably coupled to at least one waveguide 58c at the coupling position 51b. This arrangement can be achieved by interfering light from the plurality of coupling positions 14, where the light has a phase adjusted in such a way that the light constructively interferes at the coupling position 51b, such that the mode field generated at the coupling position 51b preferably corresponds to the mode field that is optimally coupled into the coupling position 51b. The mode field that is optimally coupled into the coupling position 51b is the mode field that corresponds as much as possible to the coupling position 51b in terms of intensity distribution and phase distribution. To generate this mode field, the phase and amplitude of the light emitted by the coupling positions 14 are adjusted in such a way that concentric wavefronts are generated at the center of the coupling position 51b. Additionally, coupling sites 14 that are further away from the coupling position 51b can reduce the intensity to generate an appropriate mode field size. In Figure 14a the embodiment used, the principle can be referred to as an "optical phase array". The appropriate phase can be adjusted by cascaded phase shifters within the test circuit 2. The phase shifters can be operated by changing the refractive index to control the phase and / or intensity of the light, in particular by using at least one of heat, current injected into a semiconductor junction, a piezoelectric element, a voltage applied to a material that changes its refractive index under an electric field, or a silicon-organic composite modulator. The optical phase array is configured to address a plurality of coupling positions 51b without mechanical movement. The mode field distribution at the coupling position 51b can also be determined by alternately distributing the mode field in such a way that the coupling can be maximized or by adjusting the light 3 to an appropriate test light distribution (especially a very small or large mode field or a mode field that can be scanned along the facet 103 when monitoring the coupling of the light 3), such that the mode field at the coupling position 51b can be determined especially by deconvolution. The micro-optical element 20 can be further configured to enable the light to preferably propagate from each coupling position 14 to each coupling position 51. This can be achieved in particular by Figure 14a designing each micro-optical element 20 with a high NA in the Figure 14a plane of the figure of. In summary, by using the exemplary embodiment of the optical probe 1 according to Figure 14a under the adjustment of the incident angle in the plane of the figure of, a large number of coupling positions 14 (especially more than 100) with a small pitch (especially 30 μm or less) can be detected in a short time (preferably within 100 ms or less per connection) by using a large working distance (especially 30 μm or more). Alternatively or additionally, a plurality of mode fields can be generated, especially for allowing the detection of components with a highly irregular pitch 28b or for using a single probe head 10 to detect various different micro-optical components 50.

[0121] Figure 14bShows a further exemplary embodiment of the optical probe 1 in the observation projection direction along +x according to FIG. 14. Here, each refractive surface 24 of the coupling position 14 extends along the waveguide 25 in such a way that light can be well focused in the out-of-plane direction. Preferably, each coupling position 14 is at the same height as the simultaneous emission elements in FIG. 14, or such that each refractive surface 24 captures at least 50%, preferably 90%, of the emission of the light distribution emitted by the coupling position 51 in the out-of-plane direction according to Figure 14b and. Figure 14b The out-of-plane direction emits at least 50%, preferably 90%, of the emitted light distribution.

[0122] Figure 15 Shows another exemplary embodiment of the optical probe 1 configured for optical testing of the micro-optical components 50, 50b, 50c. As Figure 15 Schematically depicted in, the test circuit 2 has a position-sensitive device 14c. In combination with the refractive surface 24, the position-sensitive device 14c can detect the inclination angle of the facet 103b (dashed line) and can distinguish the inclination angle of the facet 103b from the straight facet 103. This procedure can identify non-perpendicular facets, which are common manufacturing deviations. The optical probe 1 is configured to detect the inclined facet 103b by detecting the light propagating along the central ray 3d. For this purpose, the position-sensitive device 14c can preferably be located in or near the Fourier plane of the central ray 3d, which causes the center of the light distribution to be displaced on the position-sensitive device 14c depending on the orientation of the inclined facet 103b. In an alternative embodiment (not depicted here), the position-sensitive device 14c can be located in the imaging plane for imaging the coupling position 51.

[0123] Figure 16 Shows a method for manufacturing the probe head 10. The objective lens 201 generates a laser beam 202 configured to cure the photoresist 200. Alternatively, the solubility of the photoresist 200 can be changed by irradiating the laser beam 202. The structure 20b constituting the micro-optical element is manufactured by three-dimensionally scanning the laser beam 202. To align another structure 20c constituting another micro-optical element with the coupling position 14, light 15 can be coupled into the test circuit 2. The light 15 is selected in such a way that it can be transmitted by the waveguide 25. The lithography system 210 has a detector configured to detect the position of the light 15 that excites the test circuit 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 through the coupling position 14 into the probe head 10 and detected at the optical fiber core 13 or by a detector within the test circuit 2 coupled to the probe head 10. As another alternative, features within the test circuit 2 (especially the waveguide 25 or markers 21 (not depicted here)) can be used for alignment. For this purpose, the light of the laser beam 202 reflected at features (such as the facet 104) coupled into the waveguide 25 and within the waveguide 25 or at the optical fiber core 13 can be detected.

[0124] Figure 17 Shows another exemplary embodiment of an optical probe 1 configured for optical testing of a micro-optical component 50. As Figure 17 schematically depicted, the micro-optical element 20 has a mechanical support 8 configured to provide a specific distance (in particular 5 μm to 250 μm) between the refractive surface 24 and the facet 102. The micro-optical element 20 may also be attached to the fixture 4 of the test circuit 2 (instead of using the mechanical support 8 in the form of a strut), in which case the fixture 4 may preferably be configured in such a way that it is not flush with the facet 102 but protrudes from the facet 102. The refractive surface 24b, which is implemented as an optical lens here, can reduce the divergence of the light 3 to avoid total internal reflection failure at the region 9. Additionally, the angle 26 can exceed 90° to mitigate total internal reflection failure. Alternatively or in addition to the refractive surface 24b, the test circuit 2 may have at least one optically 3D printed element (preferably a chip-on mode field converter) configured to reduce the divergence of the light 3, which is manufactured close to the facet 102. If the divergent light 3e emitted or collected at the pitch at the facet 103b can be more divergent than the light emitted by a standard single-mode fiber (such as the single-mode fiber 28), then the embodiment according to Figure 17 may be advantageous.

[0125] Figure 18 Shows the experimental results obtained in the mode field diameter statistics of 250 micro-optical elements 20 implemented as optical lenses. Here, the mode field diameter W is normalized to the design mode field w0. A relative mode field diameter of, for example, 1.04 would imply a mode field 4% larger than the design, for example, w = 10.4 µm instead of w0 = 10 µm. A standard deviation of 2% can thus be achieved.

[0126] Figure 19Another exemplary embodiment is shown, in which the probe head 10 includes a probe card made of a printed circuit board (PCB), a wafer, or a planar optical waveguide circuit (PLC) (including both an electrical cantilever 411 and an electrical transmission line 412, as well as a microelectromechanical system (MEMS) actuator 420 having an optical waveguide). Preferably, the hole or via 401 may allow the probe head 10 to be aligned with the micro-optical component 50 by observing the fiducial 402. By using a probe card including optical, electrical, and mechanical functions, the electrical cantilever 411 can be aligned with the electrical contact pad 410 of the wafer 60 during the initial contact step. After the contact step, the micro-optical element 20 can be aligned to couple the light 3 by using the MEMS actuator 420. In particular, the MEMS actuator 420 can move the micro-optical element 20 by at least 1 μm, preferably at least 10 μm, especially at least 25 μm or more. In other embodiments, there may be multiple cantilevers 411 and multiple micro-optical elements 20, at least 1000 in some embodiments. The PLC may further include an optical switch, an optical splitter, or an optical detector. The PLC may be electrically connected or connected to the optical probe 1 by using an optical fiber array 11. Additionally, the optical probe 1 may include a distance sensor 31 configured to measure the distance 32 between the distance sensor 31 and the surface of the wafer 60. The distance sensor 31 may preferably be selected from at least one of an optical sensor or a capacitive sensor.

[0127] Figure 20 Another exemplary embodiment is shown, in which the probe head 10 is configured to test the function of the beam shaping element 430, particularly the emission direction. For this purpose, the MEMS actuator 420 may be configured to provide at least one of rotation or translation of the micro-optical element 20. In this embodiment, the micro-optical element 20 is configured to turn the light 3 to an angle that allows it to be coupled into the grating coupler 105. The reflective surface 23 is also configured to turn the light from the waveguide 25 towards the surface of the wafer 60.

[0128] Description of Reference Numerals

[0129] 1, 1b: Optical probe

[0130] 2: Test circuit

[0131] 3: Light coupled between the test circuit and the micro-optical component

[0132] 3b: Light coupled between the grating coupler and the micro-optical component

[0133] 3c: Phase front of the light coupled between the test circuit and the micro-optical component

[0134] 3d: Beam path in the case of a facet

[0135] 3e: Divergent light emitted or collected by the pitch at the facet

[0136] 4: Fixture for the test circuit

[0137] 4b: Portion of the test circuit configured to mount the test circuit at an angle compared to mounting directly on the surface

[0138] 4c: Surface, portion of the fixture of the test circuit substantially perpendicular to the surface of the wafer

[0139] 5: Translation stage, typically with six degrees of freedom

[0140] 6: Mechanical support, carrier

[0141] 7: Mechanical support for the micro-optical component and the wafer, chuck

[0142] 8: Mechanical support, part of the micro-optical element

[0143] 9: Region where total internal reflection fails without reducing the divergence of the light coupled between the test circuit and the micro-optical component at the refracting surface

[0144] 10: Probe head

[0145] 11: Fiber optic array

[0146] 12: Optical fiber

[0147] 12b: Optical fiber

[0148] 13: Optical fiber core

[0149] 14: Coupling position of the test circuit

[0150] 14b: Second coupling position of the test circuit

[0151] 14c: Position sensitive device, such as PSD, CCD, COMS or image sensor

[0152] 15: Light coupled into the probe head

[0153] 16: Second probe head

[0154] 18: Chamfer in the test circuit

[0155] 19: Thinned, etched, milled or thin region in the test circuit

[0156] 19b: Resulting thickness of the test circuit after removing the thinned region in the test circuit

[0157] 20: Micro-optical element

[0158] 20b: As-manufactured micro-optical element

[0159] 20c: Micro-optical element being manufactured

[0160] 20d: Micro-optical element behind the test circuit when viewed from the observation direction

[0161] 20e: Individual element of the micro-optical element

[0162] 21: (3D printed) marker

[0163] 23: Reflective surface, such as a total internal reflection mirror

[0164] 24: Refractive surface (optical lens)

[0165] 24b: Refractive surface that reduces the divergence of light coupled between the test circuit and the micro-optical component

[0166] 25: Waveguide, which is part of the test circuit

[0167] 25b: Optical waveguide configured to maintain polarization, for example by being short, straight, or birefringent or a combination thereof

[0168] 25c: Angled waveguide that is not normal to the facet of the test circuit configured for attaching the micro-optical element

[0169] 25e: Optical waveguide, which is part of the test circuit

[0170] 26, 26b: Angles

[0171] 27: Pitch of the coupling position of the test circuit at the facet of the test circuit

[0172] 28: Pitch at the facet of the test circuit that is configured for attaching the micro-optical component

[0173] 28b: Pitch at the facet of the micro-optical component

[0174] 29a: Width of the test circuit, which can extend over the test circuit or only over the area intended to be inserted into the trenches etched into the wafer or cavity

[0175] 29b: Thickness of the light coupled between the test circuit and the micro-optical component, which can extend over the test circuit or only over the area intended to be inserted into the trenches etched into the wafer or cavity

[0176] 30: Circuit

[0177] 31: Distance sensor

[0178] 32: Distance between the distance sensor and the surface of the wafer

[0179] 33: Overhead camera

[0180] 34: Free working distance

[0181] 35: Vacuum tool or permanent fixture

[0182] 40: Polarization splitter

[0183] 41: Polarization channel "TM"

[0184] 42: Polarization channel "TE"

[0185] 50: Micro-optical component

[0186] 50b, 50c: Another micro-optical component, thousands of which can exist per wafer

[0187] 51, 52: Coupling positions of the micro-optical component

[0188] 51b: Coupling position of the currently addressed micro-optical component

[0189] 55: Groove etched into the wafer

[0190] 56: Functional element, which is part of the micro-optical component, such as a waveguide, a laser, or a photodiode

[0191] 57: Bottom of the deep etch

[0192] 58: Waveguide, which is part of the micro-optical component

[0193] 58b: Angled waveguide with an inclined facet that is not normal to the micro-optical component

[0194] 58c: Waveguide currently addressed by light (i.e., light currently coupled from the waveguide to the probe head and vice versa) that is coupled between the test circuit and the micro-optical component

[0195] 59: Functional element part of the test circuit, such as a photodetector or a light source

[0196] 60: Wafer

[0197] 102: Facet of the test circuit configured to attach a micro-optical element

[0198] 103: Facet of the micro-optical component

[0199] 103b: Inclined facet of the micro-optical component

[0200] 104: Facet of the test circuit configured to attach the micro-optical component

[0201] 105: Grating coupler

[0202] 110a: The diameter of the micro-optical element, which is less than or equal to the pitch of the coupling position of the test circuit at the facet of the test circuit

[0203] 110b: The diameter of the micro-optical element, which is greater than the pitch of the coupling position of the test circuit at the facet of the test circuit

[0204] 111: The gap between micro-optical elements having a diameter of 110b

[0205] 200: (Liquid) photoresist

[0206] 201: Objective lens for manufacturing micro-optical elements

[0207] 202: Laser beam of the objective lens

[0208] 210: Lithography system

[0209] 401: Hole or through-hole, which is configured to allow observation of the reference point in the arrow direction

[0210] 402: Reference point, which is part of the micro-optical component

[0211] 410: Electrical contact pad, which is part of the micro-optical component

[0212] 411: Electrical cantilever, which is part of the probe head

[0213] 412: Electrical transmission line, which is part of the probe head

[0214] 420: MEMS actuator including a waveguide, which is part of the probe head

[0215] 421: Moving direction of the MEMS actuator

[0216] 423: Rotation direction provided by the MEMS actuator

[0217] 430: Beam shaping element.

Claims

1. An optical probe (1) configured for optical testing of at least one micro-optical component (50), the optical probe comprising: A probe head (10), wherein the optical performance of the probe head (10) is calibrated and wherein the probe head (10) comprises a test circuit (2), wherein the test circuit (2) is fixed to a mechanical support; at least one micro-optical element (20), wherein the micro-optical element (20) is a separate element with respect to the test circuit (2) and is in mechanical contact with the test circuit (2), The micro-optical element (20) is configured to optically couple light between the test circuit (2) and the micro-optical component (50), thereby being configured to determine an optical property of the micro-optical component (50).

2. The optical probe according to the preceding claim, wherein the micro-optical element (20) comprises a photoresist produced on the test circuit (2).

3. The optical probe according to any of the preceding claims, wherein the test circuit (2) is coupled to an optical fiber array (11).

4. The optical probe according to the preceding claim, wherein the test circuit (2) is configured to modify the pitch or mode field diameter of the optical fiber array (11).

5. The optical probe according to any one of the preceding claims, wherein the test circuit (2) has at least one of the following: Mechanical functions; Electrical functions; An optical function, wherein the optical function is independent of the optical function of the micro-optical element (20).

6. The optical probe according to any one of the preceding claims, wherein the test circuit (2) comprises at least one of the following: Photodetector; light source; Optical modulators; Spectrum analyzer; Power splitter; Polarization splitters, filters or strippers; Multiplexer.

7. The optical probe according to any of the preceding claims, wherein the pitch of the test circuit (2) is 80 μm or less.

8. The optical probe according to any of the preceding claims, wherein the mode field pitch of the micro-optical element (20) varies by 1000 nm or less.

9. The optical probe according to any one of the preceding claims, wherein the standard deviation of the variation in mode field diameter is 20% or less of the mean mode field.

10. The optical probe according to any of the preceding claims, wherein the probe head (10) is configured to function as an optical phase array.

11. A method for manufacturing an optical probe (1) configured for optical testing of at least one micro-optical component (50), in particular an optical probe (1) according to any one of the preceding claims, the method comprising the following steps: (i) providing a probe head (10), wherein the optical performance of the probe head (10) is calibrated and wherein the probe head (10) comprises a test circuit (2), wherein the test circuit (2) is fixed to a mechanical support (6); and (ii) manufacturing at least one micro-optical element (20) on the test circuit (2) by using a direct writing process, wherein the micro-optical element (20) is manufactured as a separate element with respect to the test circuit (2) and in mechanical contact with the test circuit (2), The micro-optical element (20) is configured to optically couple light between the test circuit (2) and the micro-optical component (50), thereby being configured to determine an optical property of the micro-optical component (50).

12. The method according to the preceding claim, further comprising at least one of the following steps: (iii) detecting at least one marker (21) within the test circuit (2) before step (ii); (iv) manufacturing at least one marker (21) configured for alignment during step (ii); (v) detecting light emitted from the test circuit (2) before step (ii); (vi) optically coupling the light into the test circuit (2) before step (ii) for detecting a coupling position (51); (vii) prior to step (ii), fixing the test circuit (2) on a mechanical support (6); (viii) applying an adhesion promoter to the test circuit (2) prior to step (ii); (ix) aligning the micro-optical element (20) relative to an optical fiber core (13) comprised by the test circuit (2) to a variation of at least 1 μm; (x) calibrating the optical performance of the optical probe (1) before step (ii).

13. A method for optical testing of at least one micro-optical component (50), the method 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 optical performance of the probe head (10) is calibrated and wherein the probe head (10) comprises a test circuit (2), wherein the test circuit (2) is fixed on a mechanical support (6), and wherein the micro-optical element (20) is a separate element with respect to the test circuit (2) and is in mechanical contact with the test circuit (2); and b) positioning the probe head (10) in such a way that the micro-optical element (20) optically couples light between the test circuit (2) and the micro-optical assembly (50); 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).

14. The method according to the preceding claim, wherein the micro-optical element (20) comprises a photoresist produced on the test circuit (2).

15. The method according to any one of the preceding two claims, further comprising at least one of the following steps: d) calibrating the optical performance of the probe head (10) before performing step (b); e) modifying the optical signal by using an optical phase array; f) inserting at least a portion of the micro-optical element (20) into a groove (55) comprised by the micro-optical component (50) in such a way that the light is optically coupled between the test circuit (2) and the micro-optical component (50); g) matching the pitch of at least two micro-optical elements (20) to a coupling location (51) located at a surface of the micro-optical component (50) by using the test circuit (2).

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