A method and system for coupling optical fibers

Abstract

This disclosure teaches a method of alignment of a plurality of optical fibers being arranged in a fiber array, to a plurality of detectors being arranged in a detector array. At least one detector has an alignment structure with a reflectivity different from the reflectivity of the detector array surface. The disclosed method comprises the steps of directing light to the detector surface and measuring reflectivity of the detector surface with an optical sensor during the alignment of ones of the multiple optical fibers to ones of the plurality of detectors. Relative positions of the plurality of optical fibers and the plurality of detectors are determined on the basis of variation of the reflectivity. The fiber array and the detector array are moved and affixed to enable the alignment of the plurality of optical fibers with corresponding ones of the plurality of detectors.

Description

DescriptonTitle: A METHOD AND SYSTEM FOR COUPLING OPTICAL FIBERS CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority of German patent application DE 10 2024 139 715.2, filed on 23 December 2024. The entire disclosure of the German patent application DE 102024 139715.2 is hereby incorporated herein by reference.FIELD OF INVENTION

[0002] This invention relates to a method and apparatus of alignment of a plurality of optical fibers with e.g., multiple single photon detectors.B ACKROUND INFORMATION

[0003] Rapid development in integrated optoelectronic devices and quantum photonic architectures creates a need for optical fiber to chip coupling with low losses. Deep reactive ion etching (DRIE) is a process which is used to etch deep, vertical structures into materials, such as silicon. The DRIE process-based coupling of the optical fiber to the chip offers a high precision but is expensive and time consuming.

[0004] In the paper “Automated, deep reactive ion etching free fiber coupling to nanophotonic devices” by Fabian Flassig, Rasmus Flaschmann, Thomas Kainz, Sven Ernst, Stefan Strohauer, Christian Schmid, Lucio Zugliani, Kai Muller and Jonathan J. Finley, available at https: / / arxiv.org / abs / 2201.06328, downloaded on 17 October 2024, a method is disclosed for coupling the single fiber with a single photon detector. This method is termed “star-shape alignment fiber coupling mechanism” (SAM). The paper teaches a star-shaped structure that is fabricated around the single photon detector. The surface of this star-shaped structure has a different reflectivity from the other surface of a detector array of the single photon detectors. During the coupling process, a small spot of light is projected onto the detector array from the opticalfiber. The light reflected from the detector array is measured while moving the optical fiber. The shape of the star-shaped structure is known, and an algorithm can calculate the position of the spot of light from the optical fiber on the surface of the detector array. The relative position of the optical fiber to the single-photon detector is thus known. An automated movement is then initiated to align the optical fiber with the single-photon detector and both the optical fiber and the single-photon detector are fixed to each other in a way that the optical fiber and the single-photon detector keep their alignment during a cooling down process to cryogenic temperature and a reheating process to room temperature.

[0005] The system and method disclosed in Flassig et al. are for the coupling of a single single-photon detector with a single optical fiber and has been found to work well. There is, however, a need for connecting arrays with multiple ones of the optical fibers with corresponding ones of the single-photon detectors.

[0006] The coupling process for multiple fibers and connecting arrays must be extended and refined. For example, the rotation of one or both components (i.e., the optical fiber or the single-photon detector) in relation to each other is not decisive when there is a single one of the optical fibers and one of the single-photon detectors. However, with more than one component, then this rotation needs to be considered, since it is impossible to couple all the optical fibers with all the single-photon detectors if the components are twisted relative to each other. There is therefore a need to be able to couple an array of multiple optical fibers to multiple ones of the singlephoton detectors.SUMMARY OF THE INVENTION

[0007] This disclosure teaches a method of alignment of a plurality of optical fibers, the plurality of optical fibers being arranged in a fiber array, to a plurality of detectors being arranged in a detector array. At least one of the plurality of detectors has a detector surface with a first reflectivity and alignment structures having an alignment structure surface with a second reflectivity. The first reflectivity is different from thesecond reflectivity. The disclosed method comprises the steps of directing light to the detector surface and measuring reflectivity of the detector surface with an optical sensor during the alignment of ones of the multiple optical fibers to ones of the plurality of detectors. In the next step, relative positions of the plurality of optical fibers and the plurality of detectors are determined on the basis of variation of the reflectivity. The fiber array and the detector array are moved to enable the alignment of the plurality of optical fibers with corresponding ones of the plurality of detectors. The fiber array is affixed to the detector array on completion of the alignment.

[0008] The measurement of the reflectivity enables an accurate determination of the relative position of the plurality of optical fibers and the plurality of detectors and thus an alignment to enable the fiber array to be affixed to the detector array.

[0009] In another aspect, the method further comprises moving the plurality of detectors and the plurality of optical fibers to align at a normal distance to one another. This movement enables greater efficiency in the detection of photons if the normal distance is a focal distance from at least one lens section. The lens section is placed in between the plurality of optical fibers and the plurality of detectors. Alternatively, the lens section is attached to one of the plurality of optical fibers or to one of the plurality of detectors.

[0010] In another aspect, the method further comprises tilting the fiber array while measuring the reflectivity of the detector surface until a detector connection surface and a fiber array connection surface are determined to be plane parallel to another. The determination of the plane-parallelism enables the connection of several pairs of single-photon detectors and optical fibers at the same time.

[0011] In another aspect, the method further comprises measuring reflectivity of the detector surface with an optical sensor while moving the fiber array and the detector array plane parallel to each other.

[0012] In another aspect, the method further comprises calculating the relative position and rotation of the fiber array and the detector array with an algorithm.

[0013] In another aspect, the method further comprises evaluating the precision of the calculated position and rotation of the fiber array and the detector array, repeating the evaluation, and continuing the evaluation if the degree of precision is not sufficient, otherwise continuing the method of alignment if precision is sufficient. This ensures a high success rate of precise couplings and therefore less scrap.

[0014] The invention features further a combination of a plurality of optical fibers arranged in a fiber array with a plurality of detectors arranged in a detector array. At least two of the plurality of detectors are provided with an alignment structure arranged on a detector surface of the detector array and an alignment structure surface of the alignment structure has a first reflectivity. As noted above, the detector surface has a second reflectivity, and the first reflectivity is different from the second reflectivity.

[0015] The previously described combination of fiber array and detector array can further comprise a plurality of spacers. The spacers are arranged to keep the detector surface and the lens section of the optical fibers at a normal distance. The normal distance can be a focal distance from the lens section to the detector surface.BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Fig. 1 A shows a frontal view of a detector with alignment structures and spacers.

[0017] Fig. IB shows a side view of a fiber array.

[0018] Fig. 2 shows a side view during alignment method.

[0019] Fig. 3 shows a flow diagram of the alignment method.

[0020] Fig. 4 shows three examples of misaligned fiber arrays.DETAILED DESCRIPTION OF THE INVENTION

[0021] The invention will now be described on the basis of the drawings. It will be understood that the embodiments and aspects of the invention described herein are only examples and do not limit the protective scope of the claims in any way. The invention is defined by the claims and their equivalents. It will be understood that features of one aspect or embodiment of the invention can be combined with a feature of a different aspect or aspects and / or embodiments of the invention.

[0022] Fig. 1A shows a frontal view of a detector array 100. The detector array 100 comprises a plurality of 110 detectors located on a detector connection surface 120. The detector connection surface 120 comprises further a plurality of alignment structures 150 and a plurality of spacers 150 located thereon. The detector connection surface 120 is adapted to be connected to fiber end 215 of optical fibers 210 in a fiber array 200, as shown in Fig. 2. In the non-limiting example of Fig. 1A, the detector array 100 comprises five detectors 110. Three of these five detectors 110a, 110b and 110c are surrounded by alignment structures 150. The alignment structures 150 are used during the alignment process, as will be described later in connection with Fig.3. Fig. 1 A shows two of the spacers 170a and 170b depicted at the comers 130 of the detector array 100.

[0023] Fig. IB shows a frontal view of the fiber array 200. The fiber array 200 comprises a plurality of optical fibers 210 with the optical fiber ends 215 being arranged on a fiber array connection surface 240. The optical fiber ends 215 are arranged to be connected to ones of the plurality of detectors 110 located on the detector connection surface 120. In the non-limiting example of Fig. IB, the fiber array 200 comprises five optical fibers 210 which correspond to the five detectors 110 shown in Fig. 1A. The optical fibers 210 are used during the alignment process, as will be described later in connection with Fig. 3.

[0024] In one aspect of the invention, it is possible to include micro-lenses on the optical fiber ends 215 and / or on ones of the plurality of detectors 110. In a furtheraspect of the invention, the micro-lenses are located between the optical fiber ends 215 and the detectors 110. The micro-lenses focus the light from the optical fiber ends 215 onto the detectors 110.

[0025] Fig. 2 shows a side view of the detector array 100 and a side view of the fiber array 200 in a position at the beginning (step S400) of the alignment process. The detector array 100 on the left-hand side of Fig. 2 corresponds to the detector array 100 of Fig. 1A and the fiber array 200 on the right-hand side of Fig. 2 corresponds to the fiber array 200 of Fig. IB. The detector connection surface 120 positioned on the right-hand side of the detector array 100 in Fig. 2 is facing towards the fiber array connection surface 240. The fiber array connection surface 240 is on the left-hand side of the fiber array 200 facing the detector connection surface 120. The detector connection surface 120 and the fiber array connection surface 240 are separated by a normal distance 230.

[0026] The optical fibers 210 can be split into Y-cables by splitting one of the ends of the optical fibers 210 and the resulting cables to have three terminations. The unsplit end of the optical fiber ends 215 is arranged on the fiber array connection surface 240. One of the split ends is a detector termination 217 that is connected with an optical sensor 300. The other one of the split ends is a light source termination 218 that is connected with a light source 320.

[0027] If the optical fibers 210 are not split into Y-cables, the end opposite to the end 215 that is arranged on the fiber array connection surface 240 is named detectorsource end 216.

[0028] Either the detector-source end 216 or the light source end 218 is connected to the light source 320 to transmit the light 310 through the optical fiber end 215. In the non-limiting example of Fig. 2, the light 310 emerges from two of these five optical fiber ends 215. The light 310 shines onto the detector connection surface 120. In one aspect of the invention, an optical sensor 300 is positioned next to the detector connection surface 120 and the fiber array connection surface 240. In a different aspectof the invention, the optical sensor 300 is connected with the detector end 217 of the optical fibers 210. In a third aspect of the invention, the optical sensor 300 is connected with the detector-source-end 216.

[0029] Fig. 3 shows a flow diagram of the alignment method. The method comprises a first step S400 of directing the light 310 to the detector connection surface 120.

[0030] The reflectivity of the detector connection surface 120 is measured with the optical sensor 300 in step S405 and the fiber array 200 is tilted until the measurement indicates plane parallelism.

[0031] In step S410 the reflectivity of the detector connection surface 120 is measured with the optical sensor 300 while the detector array 100 and the fiber array 200 are moved plane parallelly.

[0032] In step S415 an algorithm 350 calculates the relative position and rotation of the fiber array connection surface 240 and the detector connection surface 120.

[0033] In step S420 the algorithm calculates the uncertainty measurement of the result of step S415. If the measurements uncertainty is outside tolerance values, step S410 and the following steps are repeated. If the uncertainty measurement is within the tolerance value, the alignment process proceeds with step S430.

[0034] The fiber array 200 and the detector array 100 are then moved to enable the alignment of the plurality of optical fibers 210 with the corresponding ones of the plurality of detectors 110 in step S430.

[0035] In optional step S435, a reflectivity measurement is performed when the fiber array 200 is in alignment with the detector array 100, as determined in step S430. The reflectivity measurement is conducted by passing the light 310 with the light beams 315 through the optical fibers 210 onto the surface of the detector array 100. The measurement of the reflectivity of the individual light beams 315 on the surfaceof the detector array 100 enables a determination of the type of surface 120; 140; 160; 165; 240 from which the individual light beams 315 are reflected. Therefore, it is possible to determine if the optical fibers 210 or the fiber array 200 is aligned correctly to the detector array 100. If the reflectivity measurement confirms the correct alignment of the fiber array 200 relative to the detector array 100, the alignment process proceeds with step S440. If the reflectivity measurement indicates a misalignment, the process starts again with one of the preceding steps S400; S405; S410.

[0036] In step S440, the fiber array 200 is affixed to the detector array 100 on completion of the alignment. The normal distance 230 at a final alignment position 370 is determined by the spacers 170, should the spacers 170 be present.

[0037] Fig. 4 shows examples of slightly misaligned fiber arrays 200 during the reflectivity measurements, as performed in the optional step S435. All three figures, Fig. 4A, Fig. 4B and Fig 4C, illustrate different alignments of the fiber array 200 opposite to the detector array 100. The detector arrays 100 are shown with the detector surface 140, the detectors 110 and the secondary alignment structures 155. The secondary alignment structures 155 are implemented as rings surrounding the detectors 110 in this example. The secondary alignment structures 155 could also have different shapes, be located at different positions or cover the detectors 110. The fiber arrays 200 are shown with optical fiber ends 215. One light beam 315 per optical fiber end 215 is emerging from the optical fiber ends 215. The light beams 315 are radiating towards the detector array 100.

[0038] Fig. 4A shows an example of a xy -misalignment 380. The fiber array 200 is slightly moved to one direction perpendicular to the light beams 315. The light beams 315 therefore miss the detectors 110.

[0039] Fig. 4B is an example of a tilting -misalignment 390. The fiber array 200 is slightly tilted relative to the detector array 100. The light beams 315 therefore miss the detectors 110.

[0040] In Fig. 4C is an example of a combination of xy-misalignment 380 and tilting- misalignment 390. The fiber array 200 is slightly moved to one direction perpendicular to the light beams 315 and the fiber array 200 is slightly tilted relative to the detector array 100. In this combination of the misalignments, it is possible that some of the light beams 315 hit their corresponding detector 110, while other ones of the light beams 315 miss the detectors 110. In the example of Fig. 4C, the light beam 315a hits the corresponding detector 110. The light beam 315b misses the corresponding detector 110 but hits the secondary alignment structure 155 surrounding the corresponding detector 110. The light beam 315c misses the detector 110 and hits the detector surface 140. The reflectivity measurement performed for the example of Fig. 4C would give three different values for the light beams 315a, 315b and 315c. The algorithm compares these values to the expected values and can determine a degree of the misalignment.

[0041] In one aspect of the invention, the secondary alignment structure 155 can be placed on the detectors 110 and be removed before affixing the detector array 100 with the fiber array 200 in step S440. The differences in reflectivity can be utilized in the same way as described in the description of Fig. 4.REFERENCE NUMERALS100 Detector array110 Detector120 Detector connection surface140 Detector surface150 Alignment structures155 Secondary alignment structures160 Alignment structure surface165 Secondary alignment structure surface170 Spacer200 Fiber array210 Optical fibers215 Optical fiber end216 Detector-source end217 Detector end218 Light source end220 Lens section230 Normal distance240 Fiber array connection surface300 Optical sensor310 Light315 Light beams320 Light source350 Algorithm370 Final alignment position380 xy-misalignment390 tilting-misalignment1000 Method of alignment

Claims

Claims1. A method of alignment (1000) of a plurality of optical fibers (210), the plurality of optical fibers being arranged in a fiber array (200), to a plurality of detectors (110) being arranged in a detector array (100), wherein at least one of the plurality of detectors (110) has a detector surface (140) with a first reflectivity and alignment structures (150) having an alignment structure surface (160) with a second reflectivity, the first reflectivity being different from the second reflectivity, the method comprising the steps ofdirecting (S400) light (310) to the detector surface (140);measuring (S410) reflectivity of the detector surface (140) with an optical sensor (300) during the alignment of ones of the multiple optical fibers (210) to ones of the plurality of detectors (110);determining (S420) relative positions of the plurality of optical fibers (210) and the plurality of detectors (110) on the basis of variation of the reflectivity and thereby moving (S430) the fiber array (200) and the detector array (100) to enable the alignment of the plurality of optical fibers (210) with corresponding ones of the plurality of detectors (110); affixing (S440) the fiber array (200) to the detector array (100) on completion of the alignment.

2. The method of claim 1, further comprising moving (S430) the plurality of detectors (110) and the plurality of optical fibers (210) to align at a normal distance to one another.

3. The method of any of the above claims, wherein the normal distance is a focal distance from at least one lens section (220), wherein the at least one lens section (220) is placed in between the plurality of optical fibers (210) and the plurality of detectors (110), or the at least one lens section (220) is) or attached to one of the plurality of optical fibers (210) or to one of the plurality of detectors (110).

4. The method of any of the above claims, further comprising tilting (S405) the fiber array (200) while measuring the reflectivity of the detector surface (140) until a detector connection surface (120) and a fiber array connection surface (240) are determined to be plane parallel to another.

5. The method of any of the above claims, further comprising measuring (S410) reflectivity of the detector surface (140) with an optical sensor (300) while moving the fiber array (200) and the detector array (100) plan parallelly to each other.

6. The method of any of the above claims, further comprising calculating (S415) the relative position and rotation of the fiber array (200) and the detector array (100) with an algorithm (350).

7. The method of any of the above claims, further comprising evaluating (S420) the precision of the calculated position and rotation of the fiber array (200) and the detector array (100), repeating and continuing if precision is not sufficient, continuing the method of alignment (1000) if precision is sufficient.

8. The method of any of the above claims, further comprising performing a reflectivity measuring (S435) to determine whether the optical fibers (210) are aligned with the detectors (110), and, if the alignment is correct, continuing with step S440, or, if the alignment is not correct, starting over with steps S400; S405 or S410.

9. A combination of:- a plurality of optical fibers (210) arranged in a fiber array (200); and- a plurality of detectors (110) arranged in a detector array (100), wherein at least two of the plurality of detectors (110) are provided with an alignment structure (150) arranged on a detector surface (140) of the detector array (100) and wherein an alignment structure surface (160) of the alignment structure (150) has a first reflectivity and the detector surface (140) has a second reflectivity, the first reflectivity being different from the second reflectivity.

10. The combination of claim 9, further comprising a plurality of spacers (170), the plurality of spacers (170) being arranged to keep the detector surface (140) and the lens section (220) of the optical fibers (210) at a normal distance (230).

11. The combination of claim 9 or 10, wherein the normal distance (230) is a focaldistance from the at least one lens section (220) to the detector surface (140).

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