OPTICAL COMPONENTS AND METHOD FOR THEIR MANUFACTURE

Description

[0001] The invention relates to a spectrometer or a demultiplexer with at least one first waveguide, which is an optical fiber with a first core and a cladding surrounding the first core, wherein second cores are inserted into the cladding to form second waveguides, wherein the first core and every second core are guided side by side and spaced apart in a longitudinal section and a Bragg grating is arranged in each of these longitudinal sections.

[0002] Furthermore, the invention relates to a method for producing such a spectrometer or demultiplexer by point-to-point exposure of a substrate with a short pulse laser.

[0003] US2013208358 relates to a spectrometer written in a substrate and having a first nucleus and a number of second nuclei.

[0004] An optical component is known from US 5,978,530. This known component contains two waveguides, each with a core and a cladding surrounding the core. The core of each waveguide contains a fiber Bragg grating, which consists of a plurality of spatial regions with varying refractive indices, each spaced at a predetermined distance from the others. This predetermined distance defines the grating constant of the fiber Bragg grating. The two waveguides are each embedded in a glass block. The glass blocks are polished on one long side, at least partially removing the cladding of the waveguide. In a subsequent manufacturing step, the two glass blocks are joined together so that light can pass from the core of the first waveguide to the core of the second waveguide via evanescent coupling.The fiber Bragg grating acts as a filter element, so that at the outputs of the optical component, on the one hand, an optical signal is provided which has a wavelength defined by the grating constant, and on the other hand, at another output, an optical signal is provided which no longer contains this wavelength.

[0005] This well-known optical component can be used as an add-drop filter in an optical WDM (wavelength division multiplex) system, i.e., a data transmission system in which different data streams are transported on assigned optical carrier signals of different wavelengths. The grating constant of the fiber Bragg grating defines the wavelength of a carrier signal that is removed from the input signal.

[0006] A disadvantage of this well-known optical component is the considerable effort involved in its manufacture. Production requires precise mechanical machining and exact positioning of the two waveguides relative to each other to achieve the desired component properties. The necessary polishing and positioning process increases the risk of producing defective parts, which is why these well-known optical components have not yet achieved widespread adoption.

[0007] Based on the prior art, the invention is thus based on the objective of simplifying the manufacture of spectrometers or demultiplexers and expanding their application possibilities. Furthermore, the objective to be achieved with the present invention can be seen as providing a spectrometer or demultiplexer that requires less installation space.

[0008] The problem is solved according to the invention by a device according to claim 1 and a method according to claim 10.

[0009] Advantageous further developments of the invention can be found in the dependent claims.

[0010] The invention will now be explained, without limiting the general concept, with reference to exemplary embodiments shown in the accompanying figures. These show: Figure 1 an embodiment of an add-drop filter that is not the subject of the present invention. Figure 2 shows a spectrometer according to the present invention. Figure 3 explains different arrangements of waveguides and Bragg gratings. Figure 4 Figure 1 shows a waveguide-integrated spectrometer according to the present invention. Figure 5 shows the transmission behavior of the add-drop filter according to Figure 1 .

[0011] Figure 1shows an add-drop filter that is not the subject of the present invention.

[0012] An optical signal containing multiple digital data streams, each encoded on a separate carrier signal of a different wavelength, can be fed into the add-drop filter. Such an optical input signal can also be referred to as a WDM (wavelength division multiplex) signal.

[0013] The add-drop filter has the function of removing a single data stream with a predefinable carrier frequency or wavelength from the WDM signal and / or adding a carrier signal with a predefinable wavelength. For this purpose, the optical component 5 according to the present invention includes a substrate 4, which can consist, for example, of a polymer, glass, quartz, or a semiconductor material such as silicon, germanium, or a compound semiconductor. In some embodiments of the invention, the substrate 4 can contain a plurality of substrates that integrate several optical and / or electronic components. For example, the substrate 4 can contain quartz to accommodate optical components, and a silicon substrate can be applied to the quartz substrate 4 by flip-chip bonding, adhesive bonding, or welding, which accommodates electronic components.

[0014] Substrate 4 has a predefinable refractive index.

[0015] By modifying predefined surface or spatial regions of the substrate 4, the refractive index can be changed within predefined ranges. For this purpose, the substrate 4 can, for example, be provided with dopants and / or exposed to electromagnetic radiation. In some embodiments of the invention, the electromagnetic radiation can be provided by a short-pulse laser with a pulse duration of less than 1 ps, less than 100 fs, or less than 20 fs. By adjusting the laser power, feed rate, pulse duration, pulse shape, and number of overwrite cycles, the refractive index contrast, i.e., the change in the refractive index, can be varied and adapted to predefined target values.

[0016] In the illustrated embodiment, a first core 11 is formed in the substrate 4 through appropriate material processing, which is surrounded by a first cladding 12. The cladding 12 is formed from the material of the substrate 4. The differences in refractive index between the core 11 and the cladding 12 are selected such that an optical signal can be guided through the core 11 by total internal reflection at the interface.

[0017] Furthermore, the optical component 5 has a second nucleus 21, which is also formed by a spatial region with a different refractive index, so that optical signals can also be guided through total internal reflection in the second nucleus 21.

[0018] Both the first waveguide 1 with the first core 11 and the second waveguide 2 with the second core 21 terminate on opposite sides of the approximately rectangular substrate 4, so that the optical component 5 has four connections, which are designated Port 1, Port 2, Port 3 and Port 4.

[0019] The first core 11 and the second core 21 have a longitudinal section 25 in which they run approximately parallel to each other. In some embodiments of the invention, a mismatch can exist between the first core 11 and the second core 21, which prevents or reduces the coupling of optical signals between the cores. The mismatch can be caused by different refractive index contrasts between the core and the cladding and / or different diameters and / or different cross-sections of the cores 11 and 21. Due to the mismatch, an optical signal guided in one core cannot couple evanescently to the other core.

[0020] Furthermore, a Bragg grating 3 is arranged in the second core. In some embodiments of the invention, the Bragg grating 3 can be a chirped Bragg grating, an apodized Bragg grating, or a phase-shifting or Pi-shaped Bragg grating. The Bragg grating allows light of a predefinable wavelength or wavelength range to pass between the first core 11 and the second core 21, regardless of the mismatch. The wavelength or wavelength range is defined by the grating constant of the Bragg grating.

[0021] If a WDM signal is coupled into port 1, it propagates to port 2 in the first core 11. In longitudinal section 25, an evanescent coupling of a subspectrum of the WDM signal into the second core 21 takes place. Light of a predefinable wavelength or wavelength range, defined by the grating constant of the Bragg grating 3, is reflected so that it is available at port 4.

[0022] Alternatively or additionally, an optical signal with the wavelength defined by the Bragg grating 3 can be coupled into port 4. An optical signal without this wavelength can be supplied to port 2. Both input signals are then combined and available at port 1. Thus, the Figure 1The optical component 5 shown according to the first embodiment of the invention is suitable for removing a specific carrier signal from a WDM signal and providing it at port 4 or optionally adding another data signal, with the same carrier frequency, to the WDM signal provided at port 2.

[0023] Unlike known optical components with similar function, the component according to the invention can be easily provided with reproducible quality by laser material processing, hot stamping, printing or similar methods.

[0024] In the case of laser material processing, component 5 can be quickly adapted to different requirements. For example, by changing the lattice constant of the Bragg grating 3, a different sub-signal can be selected from the WDM signal. This only requires modifying the manufacturing data supplied to the laser processing system, which is easily accomplished using appropriate computer software. Such laser material processing also enables reliable reproducibility of the structures written into the substrate 4, eliminating the need for further mechanical processing steps such as polishing, grinding, or joining. This makes the manufacturing process less susceptible to errors, potentially increasing production yield and quality.

[0025] Figure 2 Shown is a spectrometer according to the present invention. The spectrometer according to the second embodiment also contains a substrate.4, which has a predefinable refractive index and whose refractive index is changed in predefinable spatial regions. In the case of the second embodiment, this can also be achieved by exposing the substrate 4, for example by point-to-point exposure with a laser or by masking and subsequent area exposure.

[0026] The optical component 5 according to the second embodiment comprises a first core 11, which extends along a longitudinal edge of the substrate 4. The first core 11 is surrounded by the cladding 12, which in this case is also formed from the material of the substrate 4. The first core 11 can be produced, for example, by exposing the material 4 to light and thereby inducing a change in the refractive index. According to the present invention, the first core 11 and the surrounding cladding 12 are glass fibers or polymer fibers embedded in the material of the substrate 4.

[0027] In or next to the first core 11, there is a plurality of Bragg gratings 3. In the illustrated embodiment, eight Bragg gratings 3a, 3b, 3c, 3d, 3e, 3f, 3g and 3h are shown. However, the number of Bragg gratings can also be larger or smaller and, in some embodiments of the invention, may be between approximately 4 and approximately 20.

[0028] Each Bragg grating is associated with a second nucleus 21a, 21b, 21c, 21d, 21e, 21f, 21g, and 21h. Every second nucleus has a longitudinal section 25 in which the second nucleus 21 runs alongside the first nucleus 11, thus enabling evanescent coupling of optical signals. The Bragg gratings 3 associated with the second nuclei act as filters, so that only light of a predefined wavelength, determined by the grating constant, can pass into the respective second nucleus 21.

[0029] The light guided in the second core 21 is coupled out at its end, which can be located, for example, at an edge of the substrate 4. In this way, a number of output waveguides corresponding to the number of second cores 21 and the number of Bragg gratings 3 is available, each providing light of a predefinable wavelength or wavelength range. An optical component 5 according to the second embodiment of the invention can be used as a demultiplexer for a WDM signal in optical communications or as a spectrometer, for example, for reading out a fiber optic sensor. In some embodiments of the invention, a photodiode array can also be located directly at the edge of the substrate 4 instead of the output waveguides.

[0030] Based on the Figure 3The arrangement of at least one Bragg grating 3 in various embodiments of the invention is explained, as shown in the cross-sections of the first core 11 and the second core 21 in the region of the longitudinal section 25. Figures 3a, 3b, 3c, 3d, 3e und 3fEach of the illustrated embodiments comprises a first core 11 and a second core 21. In the illustrated embodiments, the cores each have a circular cross-section. The second core 21 has a smaller diameter and a smaller area than the first core 11. For example, the first core 11 can be configured as a multi-mode waveguide and the second core 21 as a single-mode waveguide. In other embodiments of the invention, both cores can have an identical cross-section, or the first core 11 can have a smaller cross-section than the second core 21. In some embodiments of the invention, the two cores can have different refractive index contrasts with the surrounding material. In some embodiments of the invention, the refractive index contrast of the first core 11 can be greater than the refractive index contrast of the second core 21.

[0031] As from Figure 3As can be seen, cores 11 and 21 are spaced apart from each other, meaning that the areas assigned to the respective cores do not overlap in a direction perpendicular to the propagation direction. The distance is chosen to allow evanescent coupling. In some embodiments of the invention, the distance can be between approximately 0.1 and approximately 5 wavelengths or between approximately 0.3 and approximately 3 wavelengths of the signals propagating in the waveguides. In some embodiments of the invention, the distance can be between approximately 100 nm and approximately 5 µm, or between approximately 200 nm and approximately 4 µm, or between approximately 300 nm and approximately 4 µm, or between approximately 400 nm and approximately 3 µm, or between approximately 500 nm and approximately 3 µm.

[0032] The following shows different arrangements of the nuclei and their respective associated Bragg lattices: Figure 3aFigure 1 shows a second core 21 with a single Bragg grating 3. In this embodiment, the first core 11 does not contain a Bragg grating. The cross-section of the Figure 3a This corresponds to an embodiment which is already evident from the Figure 1 was explained in more detail. Figure 3b Figure 1 shows an embodiment with two Bragg gratings 3a and 3b, which are arranged in the first core 11 and in the second core 21 respectively.

[0033] According to the embodiment which is in Figure 3c As shown, only the first core 11 contains a Bragg lattice 3, whereas the second core 21 was manufactured without a Bragg lattice.

[0034] Figure 3d This describes an embodiment of the invention in which three Bragg gratings 3 are used. These are arranged in the substrate 4, specifically in the space 26 between the first core 11 and the second core 21.

[0035] Figure 3eFigure 3 also shows three Bragg gratings 3, which are arranged at the interface of the first nucleus 21 to the surrounding material of the substrate 4. In this case as well, the Bragg gratings 3 face the slit 26 and thus the first nucleus 11.

[0036] Figure 3f Figure 1 shows an embodiment with a plurality of Bragg gratings 3, all of which are arranged in the first core 21. In the illustrated embodiment, six Bragg gratings 3 are present. In other embodiments of the invention, the number of Bragg gratings can be greater or lesser.

[0037] Figure 3This explains that the positioning and / or shape of the inscribed Bragg grating 3 within the longitudinal section 25 can vary. Depending on the intended application of the optical component 5, the at least one Bragg grating 3 can be arranged within one waveguide, within both waveguides, or between both waveguides. In some embodiments of the invention, the shape of the at least one Bragg grating can be adapted to the shape of a waveguide core.

[0038] Figure 4 Shows a spectrometer or a demultiplexer according to the present invention, which is arranged directly in an optical fiber and thus requires only a small additional installation space.

[0039] The substrate 4 according to the third embodiment comprises a first waveguide 1, which has a first core 11 and a cladding 12 surrounding it. The waveguide 1 can be a commonly used, known optical fiber or a polymer fiber. Such fibers are known from optical communications technology. The cladding 12 of such an optical fiber can, for example, have a cylindrical shape, with the core 11, which has a round cross-section, being embedded coaxially in the cladding 12. Single-mode or multi-mode fibers can be used. In some embodiments of the invention, the first core can transport several modes, which are coupled out to a plurality of second cores, each of which can transport only one mode.

[0040] The first waveguide 1 is modified by laser processing so that at least one second core 21 is formed in the cladding 12 of the first waveguide 1. In the illustrated embodiment, four second cores 21a, 21b, 21c, and 21d are shown. In other embodiments of the invention, however, the number of second cores can be greater or lesser. Each second core 21 has an associated longitudinal section 25a, 25b, 25c, and 25d, which runs alongside the first core 11, thus enabling evanescent coupling of the optical signal from the first core 11 to the second core 21.

[0041] In longitudinal section 25, there is an associated Bragg grating 3, as described above. If the four Bragg gratings 3a, 3b, 3c and 3d have different grating constants, a predefinable wavelength or wavelength range is maintained in every second core 21.

[0042] The second cores 21 terminate at the outer surface of the waveguide 1. A photodiode array 6 can be arranged there.

[0043] The photodiode array 6 can have a shape complementary to the lateral surface of the waveguide 1 and, for example, partially cover it in the form of a ring or a hemisphere. In the illustrated embodiment, the photodiode array 6 has four photodiodes 61, 62, 63 and 64, each of which receives the light from a second core 21a, 21b, 21c and 21d and converts it into electrical signals.

[0044] If a WDM signal from a telecommunications system is carried on the first waveguide 1, each photodiode of the photodiode array 6 can receive a data stream of a predefined carrier signal defined by the grating constant of the Bragg grating 3a. If the waveguide 1 is part of a fiber optic sensor system, the Figure 4The third embodiment of the invention shown can be used as an integrated spectrometer to evaluate the measured values ​​of optical sensors without having to accept additional installation space and additional susceptibility to error through external spectrometers.

[0045] Figure 5 shows the transmission behavior of the add-drop filter according to Figure 1 The wavelength is shown on the abscissa and the intensity of the light on the ordinate. Figure 5 The optical signal at port 4 of the first embodiment of the invention is shown according to Figure 1 . How Figure 5 As shown, the integrated Bragg grating allows for the definition of a narrow reflection area. This enables the processing of WDM signals with a small channel spacing.

[0046] Naturally, the invention is not limited to the embodiments shown. The foregoing description is therefore not to be considered limiting, but rather explanatory. The following claims are to be understood as meaning that a named feature is present in at least one embodiment of the invention. This does not preclude the presence of further features. Where the claims and the foregoing description define "first" and "second" embodiments, this designation serves to distinguish between two similar embodiments without establishing any hierarchy.

Claims

1. Spectrometer or demultiplexer (5) comprising at least one first waveguide (1) which is an optical fiber having a first core (11) and a casing (12) surrounding the first core, wherein second cores (21a, 21b, 21c, 21d) are introduced into the casing (12), to form second waveguides (2), wherein the first core (11) and each second core (21a, 21b, 21c, 21d) are guided side by side and at a distance from one another in a longitudinal section (25), and one Bragg grating (3a, 3b, 3c, 3d) each is arranged in this longitudinal section.

2. Spectrometer or demultiplexer according to claim 1, characterized in that the distance between the first core (11) and the second core (21a, 21b, 21c, 21d) in the longitudinal section (25a, 25b, 25c, 25d) is approximately 0.1 and approximately 5 wavelengths or approximately 0.3 and approximately 3 wavelengths of the signals propagating in the first core (11), or characterized in that the distance between the first core (11) and the second core (21a, 21b, 21c, 21d) in the longitudinal section (25a, 25b, 25c, 25d) is between approximately 100 nm and approximately 5 µm or between approximately 200 nm and approximately 4 µm or between approximately 300 nm and approximately 4 µm or between approximately 400 nm and approximately 3 µm or between approximately 500 nm and approximately 3 µm.

3. Spectrometer or demultiplexer according to claims 1 to 2, characterized in that a photodiode array is arranged on a casing surface of the first waveguide (1), which array is designed to receive optical signals from the second cores (21a, 21b, 21c, 21d).

4. Spectrometer or demultiplexer according to any one of claims 1 to 3, characterized in that at least one waveguide (1, 2) is a single-mode waveguide and at least one waveguide (2, 1) is a multi-mode waveguide.

5. Spectrometer or demultiplexer according to any one of claims 1 to 4, characterized in that the Bragg grating (3a, 3b, 3c, 3d) is arranged in the first core (11) and / or in that the Bragg grating (3a, 3b, 3c, 3d) is arranged in the second core (21a, 21b, 21c, 21d) and / or in that the Bragg grating (3a, 3b, 3c, 3d) is arranged in the casing (12) between the first core (11) and the second core (21a, 21b, 21c, 21d).

6. Spectrometer or demultiplexer according to claim 5, characterized in that each of the Bragg gratings (3a, 3b, 3c, 3d) has a different grating constant.

7. Spectrometer or demultiplexer according to any one of claims 1 to 6, characterized in that there is a mismatch between the first core (11) and the second core (21a, 21b, 21c, 21d), said mismatch preventing or reducing a coupling of optical signals between the cores (11, 21a, 21b, 21c, 21d).

8. Spectrometer or demultiplexer according to claim 7, characterized in that the mismatch is created by different refractive index contrasts between core (11, 21a, 21b, 21c, 21d) and casing (12) and / or different diameters and / or different cross-sections of the cores (11, 21a, 21b, 21c, 21d).

9. Spectrometer or demultiplexer according to any one of claims 1 to 8, characterized in that at least one Bragg grating (3a, 3b, 3c, 3d) is designed as a chirped Bragg grating and / or in that at least one Bragg grating (3a, 3b, 3c, 3d) is designed as an apodized Bragg grating and / or in that at least one Bragg grating (3a, 3b, 3c, 3d) is designed as a pi-shaped Bragg grating.

10. Method for producing a demultiplexer or a spectrometer, comprising the following steps: providing an optical fiber having a first core (11) and a casing (12) which surrounds the first core as first waveguide (1) and point-to-point exposure of the casing (12) with a short-pulse laser, such that the refractive index changes in the exposed areas, wherein at least one second core (21a, 21b, 21c, 21d) is inscribed in the casing (12) in such a way that a second waveguide (2) is formed and the first core (11) and the second core (21a, 21b, 21c, 21d) run side by side and adjacent to one another in a longitudinal section (25a, 25b, 25c, 25d) and point-to-point exposure of the casing (12) with a short-pulse laser, such that at least one Bragg grating (3a, 3b, 3c, 3d) is inscribed in the casing (12) between the first core (11) and the second core (21a, 21b, 21c, 21d), and / or point-to-point exposure of the first core (11), such that in the first core (11) at least one Bragg grating (3a, 3b, 3c, 3d) is inscribed and / or point-to-point exposure of the second core, such that in the second core (21a, 21b, 21c, 21d) at least one Bragg grating (3a, 3b, 3c, 3d) is inscribed, such that in the longitudinal section (25a, 25b, 25c, 25d) there is at least one Bragg grating (3a, 3b, 3c, 3d).

11. Method according to claim 10, characterized in that the distance between the first core (11) and the second core (21a, 21b, 21c, 21d) in the longitudinal section (25a, 25b, 25c, 25d) is between approximately 100 nm and approximately 5 µm or between approximately 200 nm and approximately 4 µm or between approximately 300 nm and approximately 4 µm or between approximately 400 nm and approximately 3 µm or between approximately 500 nm and approximately 3 µm.

12. Method according to any one of claims 10 or 11, characterized in that the number of single pulses which influence a point or spot, the pulse shape, the pulse energy, the feed rate and / or the number of overwrite processes is varied.

13. Method according to any one of claims 10 to 12, characterized in that a mismatch between the first core (11) and the second core (21a, 21b, 21c, 21d) is created, which prevents or reduces a coupling of optical signals between the cores (11, 21a, 21b, 21c, 21d).

14. Method according to any one of claims 10 to 13, characterized in that the Bragg gratings (3a, 3b, 3c, 3d) each have a different grating constant.

15. Method according to any one of claims 10 to 14, characterized in that a photodiode array is arranged on a casing surface of the first waveguide (1), which array is designed to receive optical signals from the second cores (21a, 21b, 21c, 21d).