The invention relates to a method and substrate car- rier for coupling a photon or light source to an optical fiber .

WO2006/135789 discloses such a method that provides a new avenue for creating smaller and potentially more powerful computers. In such devices light particles, or photons, are used to convey information. A photon may represent a single quantum bit of information. The instant invention is however not restricted to this application but generally applies to the fast developing field of quantum technologies, especially involving quantum communication and quantum cryptography.

The doctors thesis "Nanowire-based Quantum Photonics" by Gabriele Bulgarini, 2014, ISBN 978-90-8593-185-0 discloses such a method comprising the steps of:

• identifying the photon or light source from plural photon or light sources, said photon or light sources be- ing embedded in an embedding material;

• isolating the identified photon or light source with at least part of the embedding material surrounding it;

• centering the identified photon or light source ex ^¬ actly in the center of the embedding material, wherein the embedding material is given an external diameter that matches an internal diameter of an alignment sleeve wherein the optical fiber is received; and

• placing the identified photon or light source sur ^¬ rounded by the embedding material in said alignment sleeve.

More specifically according to this doctor's thesis nanowire waveguides are first grown in ordered arrays on a substrate. Subsequently a layer of positive resist for photo ^¬ lithography is spun on the sample substrate. The resist covers the entire length of the nanowires. In a micro- photoluminescence setup, the nanowires are then investigated at low temperature in order to select the best candidate for connecting to a fiber to provide a plug and play single-photon generator. Criteria applied for the selection are the bright- ness of the source, purity of single-photon statistics and the linewidth of the emission spectrum. Once the best candidate is selected, a UV laser will be utilized for photolithography at cryogenic temperatures. The resist is exposed around the se- lected nanowire with a resolution up to 50 nm diameter wherein the nanowire is exactly located in the center of the exposed resist. After lift-off of the remaining unexposed resist, the exposed positive resist will protect the nanowire in the sub ^¬ sequent dry etching step. Then a disk is etched in the sub- strate, surrounding the nanowire, with dimensions defined dur ^¬ ing the photolithography step. The disk diameter is precisely set to 1.25 mm, that is the diameter of commercial alignment sleeves hosting single-mode fibers inside fiber cables. Hence, the processed nanowire chip thus fits exactly the dimensions of fiber sleeves and self-aligns to the optical fiber for max ^¬ imizing the collection of single photon's.

It is an object of the invention to provide an alter ^¬ native, stable, robust and reliable manner and device for cou ^¬ pling a photon or light source to an optical fiber.

It is a further object of the invention to make it possible that more flexibility is provided in selecting the type of photon source that may be used for coupling to an op ^¬ tical fiber.

These and other objects of the invention which may become apparent from the following disclosure are provided in a method having the features of one or more of the appended claims .

The method of the invention comprises the following steps (the steps need not be executed in the given order) :

· providing a first semiconductor substrate comprising one or more, preferably microscopic, sources of photons or light;

• shaping the first semiconductor substrate to prede ^¬ fined dimensions;

· providing a second substrate with a cutout with di ^¬ mensions capable to receive therein said first semicon ^¬ ductor substrate shaped into said predefined dimensions;

• placing the first semiconductor substrate in the cut ^¬ out of the second substrate; • selecting a photon or light source comprised in the first semiconductor substrate;

• centering said selected photon or light source in the middle of the second substrate, by removing such second substrate material that extends beyond an external diame ^¬ ter of a disk of such material having the selected photon or light source in the middle, which external diameter matches an internal diameter of the alignment sleeve wherein the optical fiber is received.

In the step of selecting a photon or light source it is in one embodiment of the method according to the invention preferable to provide markers on the second substrate with the first semiconductor substrate with the microscopic sources of photons or light received in said second substrate, followed by

selecting a photon or light source and identifying its location with reference to said markers. This makes the subsequent step of centering the selected photon or light source in the middle of the second substrate relatively easy.

As will be clear from the foregoing the said disk of the second substrate is made to measure to the internal diameter of the alignment sleeve, and contains the photon or light source precisely in the middle. This position

corresponds to the core of the optical fiber, which is the part where photons are guided and propagated to guarantee the best photon or light transmission across optical networks.

The invention is also embodied in a first semiconduc ^¬ tor substrate provided with one or more microscopic sources of photons or light, which substrate is provided with predefined dimensions and placed in a cutout of a second substrate, wherein the cutout has dimensions capable to receive the first semi-conductor substrate which is shaped to said predefined dimensions; and wherein the second substrate material is shaped to arrange that a selected photon or light source com- prised in the first semiconductor substrate is centered in the middle of the second substrate. This disk shaped second sub ^¬ strate is provided with a diameter matching an internal diame ^¬ ter of an alignment sleeve for aligning a photon or light source of said semiconductor substrate with an optical fiber received in said alignment sleeve.

Preferably further the disk is provided with a tail for handling the carrier.

It is important to note that the method of the invention is universal and therefore applies for photon or light sources of any material (quantum sources, diodes, micro- lasers) . The required alignment of the photon or light source with the optical fiber comes automatic with implementation of the method of the invention and does not require any further manual intervention.

The method of the invention preferably makes use of the universally applicable anisotropic etching method as known from US 7,479,461 (said document herein incorporated by reference) which is applied to silicon and silicon oxide layers simultaneously, and which is capable to define very precise structures.

Preferably shaping the first semiconductor substrate is done to dimensions of approximately l x l mm, and the sec- ond substrate is preferably provided with a cutout having di ^¬ mensions wherein the first semiconductor substrate can be snugly fitted.

Suitably shaping the first semiconductor substrate is executed with a dicer, and providing a cutout in the second substrate is executed with lithography and etching of the sub ^¬ strate. Operating a dicer and litography and etching are as such known to the skilled person and require no further eluci ^¬ dation .

Further it is preferred to fix the first semiconduc- tor substrate to the second substrate by bonding or gluing the shaped first semiconductor substrate in the cutout of the sec ^¬ ond substrate.

It is further preferred to provide metallic markers on the second substrate with the first semiconductor substrate received therein, by lithography and subsequent metallic mark ^¬ er deposition. These process steps are as such also known to the skilled person and require no further elucidation.

Selecting a suitable photon or light source prefera ^¬ bly employs luminescence spectroscopy. Finally making use of the above mentioned anisotropic etching is preferably carried out in the process of centering the selected photon or light source exactly in the middle of the second substrate. This is done by lithography followed by etching for removal of such material that extends beyond an external diameter of a disk of such material having the se ^¬ lected photon or light source in the middle, which external diameter then is made to match an internal diameter of the alignment sleeve wherein the optical fiber is received so as to align the selected photon or light source with the fiber.

The invention will hereinafter be further elucidated with reference to the drawing of a nonlimiting exemplary embodiment of manufacturing and placing a substrate carrier according to the invention in an alignment sleeve.

In the drawing:

-figure 1 depicts a sequence of process steps to man ^¬ ufacture a substrate carrier according to the invention; and

-figure 2 depicts the placement of the substrate car ^¬ rier according to the invention in a mating sleeve that is used for connection and alignment of two optical fibers.

Whenever in the figures the same reference numerals are applied, these numerals refer to the same parts.

Making reference first to figure 1 the steps of manu ^¬ facturing a substrate carrier according to the invention are shown; notably in figure 1A it is shown to provide a first semiconductor substrate 1 comprising one or more microscopic sources 2 of photons or light.

In figure IB the selection of a photon or light source 3 taken from the collection of microscopic sources 2 of photons or light that is comprised in the first semiconductor substrate 1 is shown. Selecting a photon or light source 3 is preferably executed by luminescence spectroscopy. It is ex ^¬ plicitly pointed out that selecting this photon or light source 3 can within the terms of the invention also be delayed until after the first semiconductor substrate 1 has been pro ^¬ vided with the appropriate dimensions to fit it and having it placed into a cutout of a second substrate as explained here ^¬ inafter . Figure 1C shows the result of the first semiconductor substrate 1 being tailored to predefined dimensions. The first semiconductor substrate having these predefined dimensions is now depicted with reference 1'. The first semiconductor sub- strate 1' can for instance have dimensions of approximately 1 x 1 mm. Shaping the first semiconductor substrate 1 is preferably executed with a dicer.

Figure ID shows that a second substrate 4 is provided with a cutout 5 with dimensions capable to receive therein the earlier mentioned first semiconductor substrate 1' which is shaped to its predefined dimensions as shown in figure 1C. Preferably the second substrate 4 is provided with a cutout 5 having dimensions wherein the first semiconductor substrate 1' can be snugly fitted. Providing the cutout 5 in the second substrate 4 is preferably executed with lithography and etch ^¬ ing of the wafer of the second substrate 4.

In figure IE it is shown that the first semiconductor substrate 1' is placed in the cut-out 5 of the second sub ^¬ strate 4. It is preferred that the shaped first semiconductor substrate 1' is bonded or glued in the cutout 5 of the second substrate 4.

After that centering of the selected photon or light source 3 in the middle of the second substrate 4 can be exe ^¬ cuted. In this process effective use can be made of markers 6 on the second substrate 4 with the first semi-conductor sub ^¬ strate 1' received therein, wherein the location of the se ^¬ lected photon or light source 3 is identified with reference to said markers 6. Once again it is pointed out that the se ^¬ lection of the photon or light source 3 that will be centered in the middle of the second substrate 4 can be carried out im ^¬ mediately prior to this centering step, after the first semi ^¬ conductor substrate 1' is received in the cutout 5 of the sec ^¬ ond substrate 4.

Preferably the markers 6 are embodied on the second substrate 4 as metallic markers when the first semiconductor substrate 1' is already received therein. This can be suitably executed by lithography and subsequent metallic marker deposi ^¬ tion . Further figure IE symbolizes by the orthogonal arrows a and b that around the first semiconductor substrate 1' and in the second substrate 4 a dashed circular cutting line will be appropriately positioned in order to center the selected photon or light source 3 in the middle of the second substrate material 4. The cutting can then be performed after establishing a definite circular cutting line. The cutting can be performed by lithography followed by etching for removal of such material that extends beyond an external diameter of a cylin- der of such material having the selected photon or light source 3 in the middle, which external diameter matches an in ^¬ ternal diameter of an alignment sleeve wherein the optical fi ^¬ ber is received or to be received. The result of this process step is provided in figure IF, which shows the selected photon or light source 3 in the center of the resulting second sub ^¬ strate material 4' with the appropriate dimensions for fitting into the said alignment sleeve. Figure IF thus shows the substrate carrier of the invention comprising a first semiconductor substrate 1' with one or more microscopic sources of photons or light, which substrate 1' is provided with prede ^¬ fined dimensions and placed in a cutout 5 of a second sub ^¬ strate 4', and wherein the cut-out 5 is dimensioned to snugly receive therein the first semiconductor substrate 1' which is shaped to said predefined dimensions; and wherein the second substrate material 4' is shaped to arrange that a selected photon or light source 3 comprised in the first semiconductor substrate 1' is centered in the middle of the second substrate 4'. Accordingly the substrate carrier is generally shaped as a disk with a diameter matching an internal diameter of an alignment sleeve for aligning the photon or light source 3 that is centered in the middle of the second substrate 4' with an optical fiber received or to be received in an alignment sleeve in which the second substrate 4' is to be placed.

In figure 2 the substrate carrier of the invention is shown after mounting in an alignment sleeve 7. Reference 1' denotes the semiconductor substrate containing one of more photon sources, preferably being microscopic. As already men ^¬ tioned typical dimensions of the semiconductor substrate 1' can be 1 mm x 1 mm. Reference 4' denotes the substrate carrier of the in ^¬ vention wherein semiconductor substrate 1' is placed. The sub ^¬ strate carrier 4' is designed to have an external diameter slightly less than the internal diameter of the mating sleeve depicted with reference 7. Said mating sleeve 7 can be used for tight connection and mutual alignment of two optical fi ^¬ bers .

Figure 2 shows further that substrate carrier 4' is preferably provided with an extended part 8 (which can be called the tail' ) that serves for the handling of the sub ^¬ strate carrier 4' and its positioning inside the mating sleeve 7. The alignment method of the invention as disclosed herein enables to align the center of the optical fiber, which is used as a waveguide for photons, to the photon source (s) 3 lo- cated in the semiconductor substrate 1'.

Although the invention has been discussed in the foregoing with reference to an exemplary embodiment of the method and substrate carrier of the invention, the invention is not restricted to this particular embodiment which can be varied in many ways without departing from the invention. The discussed exemplary embodiment shall therefore not be used to construe the appended claims strictly in accordance therewith. On the contrary the embodiment is merely intended to explain the wording of the appended claims without intent to limit the claims to this exemplary embodiment. The scope of protection of the invention shall therefore be construed in accordance with the appended claims only, wherein a possible ambiguity in the wording of the claims shall be resolved using this exem ^¬ plary embodiment.