A photonic lantern-type mode multiplexer / demultiplexer based on auxiliary waveguide

Abstract

The present invention discloses a photon lantern type mode multiplexer / demultiplexer based on auxiliary waveguide, belonging to the field of integrated photonics and optical interconnection. The present invention adopts a photon lantern structure, and introduces an additional auxiliary single-mode waveguide into a conventional photon lantern structure, so that the optimized photon lantern type mode multiplexer / demultiplexer has a more symmetrical multimode waveguide geometry and mode field distribution, effectively reducing the coupling loss and mode-related loss with the corresponding multimode optical fiber, improving the device mode purity and reducing the crosstalk of the multiplexing-demultiplexing system. The present invention has broad application prospects in the field of integrated photonics and optical interconnection, and fills the gap in the relevant technical field.

Description

Technical Field

[0001] The present invention belongs to the field of integrated photonics and optical interconnection, and more particularly, relates to a photon lantern-type mode multiplexer / demultiplexer based on auxiliary waveguide. Background Art

[0002] As the scale of the Internet grows, in order to cope with the growing demand for communication capacity, the communication capacity of a single optical fiber has always maintained a high-speed development trend. However, the current transmission capacity of a single single-mode optical fiber is infinitely close to the nonlinear Shannon limit. When the large-scale physical dimension resources such as frequency / wavelength, amplitude / phase, and time are unable to support the continuous growth of the current capacity, a new "communication capacity crisis" will occur. To this end, new physical dimension resources need to be developed. Fortunately, the spatial dimension of light waves currently has huge potential for communication capacity growth. Therefore, in recent years, people have conducted a lot of research on space division multiplexing technology to expand the transmission capacity of optical communication networks.

[0003] One of the challenges in achieving space-division multiplexing is the selective excitation and detection of high-order modes and multiple parallel signals. So far, space-division multiplexing can be achieved by using large optical devices such as phase plates, spatial light modulators and mode couplers. However, in order to make space-division multiplexing more practical, people urgently need simpler, more compact, wider bandwidth and lower loss fiber / waveguide based multiplexing solutions. Photonic lanterns are ideal devices that meet these conditions. They have the advantages of being almost lossless, scalable to support multiple modes, broadband, simple to manufacture, and their mode selectivity can be customized. Photonic lanterns are low-loss devices that connect a single multimode waveguide to multiple single-mode waveguides. One end of the device is a multimode optical fiber that meets specific mode conditions, and the other end is several single-mode optical fibers. Because the structure of the optical fiber photonic lantern device is similar to that of a lantern, it is called a photonic lantern. Photonic lanterns can transmit light beams from a single-mode waveguide to a multimode waveguide with low loss to form a mode multiplexer; or vice versa, from a multimode waveguide to a single-mode waveguide with low loss to form a mode demultiplexer. Photonic lanterns can be made in three different ways. The first two are fiber taper methods, namely single-mode fiber bundle taper method and multi-core fiber taper method; the third is to make them in transparent materials (usually glass materials) through femtosecond laser direct writing technology. High-intensity lasers can change the refractive index of glass materials, so that various waveguide structures can be engraved in the glass. A series of single-mode waveguide arrays are engraved in the glass. By designing their writing trajectories, they can be gradually combined to form a multimode waveguide structure, and finally form a photonic lantern structure.

[0004] Usually, the single-mode end of the photon lantern is an independent non-coupled single-mode waveguide array, which is equivalent to a multi-mode system whose spatial mode is the array supermode. Therefore, the number of degenerate or non-degenerate supermodes is equal to the number of single-mode waveguides at the input end. When the number of modes supported in the single-mode waveguide array and the multi-mode waveguide is different, according to the second law of thermodynamics, any remaining mode dimensions will cause loss. Therefore, when a photon lantern structure can be used as a multiplexer and demultiplexer at the same time, the single-mode waveguide array and the multi-mode waveguide of the photon lantern must meet the mode number matching to achieve theoretical lossless transmission.

[0005] In order to achieve low-loss transmission, the output mode field of the multimode waveguide must match the mode field of the connected multimode fiber as much as possible. Taking step-index multimode fiber as an example, it can transmit a variety of LP mn mode, where m is the angular mode and n is the radial mode. The single-mode waveguides of the multimode waveguides that make up the photon lantern should be arranged on m concentric rings. At the same time, in order to meet the matching of the number of modes at the input and output ends of the photon lantern, the number of single-mode waveguides on each concentric ring is 2n. max +1, which is an odd number.

[0006] This waveguide arrangement is usually regarded as the optimal photon lantern arrangement. However, in essence, the odd number of single-mode waveguides on each concentric ring makes the multimode waveguide structure naturally non-centrosymmetric, so that there is always a certain geometric structure and mode field structure mismatch between it and the centrosymmetric multimode optical fiber structure. In addition, in order to introduce mode selectivity, single-mode waveguides with different core sizes are generally selected, which will also cause the geometric structure of the multimode waveguide to be asymmetric, making it theoretically impossible for the photon lantern arrangement to achieve lossless transmission, and at the same time affecting the device mode selectivity and the crosstalk of the multiplexing-demultiplexing system. Summary of the invention

[0007] In view of the defects of the prior art, the present invention provides a photon lantern-type mode multiplexer / demultiplexer based on an auxiliary waveguide, aiming to provide a photon lantern-type mode multiplexer / demultiplexer based on an auxiliary waveguide, which can support femtosecond laser direct writing technology, breaking through the limitation that the matching degree between the multimode waveguide supported mode of the traditional mode multiplexer / demultiplexer and the corresponding multimode optical fiber supported mode is not high, and has broad application prospects in the fields of integrated photonics and optical interconnection, filling the gap in the relevant technical field.

[0008] To achieve the above-mentioned purpose, the present invention provides a photon lantern type mode multiplexer / demultiplexer based on auxiliary waveguides. An auxiliary waveguide is introduced into the photon lantern structure. The auxiliary waveguide neither increases the input waveguide mode nor the output waveguide mode, but is used to optimize the combination arrangement of the single-mode waveguide array, so that the multimode waveguide structure has both axial symmetry and central symmetry, so that the mode supported by the device is more matched with the mode supported by the multimode optical fiber. By adding an auxiliary waveguide, the mode selectivity and mode purity of the photon lantern device can be effectively improved, the coupling loss between the photon lantern device and the multimode optical fiber can be reduced, and the crosstalk of the mode multiplexing-demultiplexing system can be reduced.

[0009] The present invention provides a photon lantern-type mode multiplexer / demultiplexer based on auxiliary waveguides, comprising a single-mode waveguide array, a gradient coupling region containing auxiliary waveguides and a multimode waveguide, wherein the single-mode waveguide array comprises M (M≥3, a positive integer) mutually independent non-coupled single-mode waveguides, and the gradient coupling region containing auxiliary waveguides additionally introduces N (N≥1, a positive integer) auxiliary single-mode waveguides, wherein the M single-mode waveguides and the additional N single-mode waveguides gradually approach each other until they are coupled and finally merged; the multimode waveguide is composed of the fusion of M+N single-mode waveguides, and the M+N single-mode waveguides constituting the multimode waveguide are axially symmetrical and centrally symmetrically distributed, and the number of modes supported by the multimode waveguide corresponds to the number M of single-mode waveguides.

[0010] Furthermore, the M single-mode waveguides and the additional N auxiliary single-mode waveguides in the gradient coupling region containing the auxiliary waveguides are arranged from a one-dimensional linear arrangement to a two-dimensional concentric ring arrangement during the process of mutual coupling and approaching.

[0011] Preferably, in the auxiliary waveguide-based photonic lantern mode multiplexer-demultiplexer, the number M of single-mode waveguides includes 3, 6 and 10; the corresponding number N of auxiliary single-mode waveguides is 1, 1 and 2 respectively.

[0012] Furthermore, the single-mode waveguide array is connected to the single-mode optical fiber array, and the geometric dimensions, mode field dimensions and arrangement distribution of the M single-mode waveguides match those of the single-mode optical fiber array.

[0013] Furthermore, the multimode waveguide is connected to the multimode optical fiber, the geometrical dimensions and mode field dimensions of the multimode waveguide match those of the multimode optical fiber, and the modes supported by the multimode waveguide match those supported by the multimode optical fiber.

[0014] Furthermore, the single-mode waveguide, the tapered coupling region and the composite multi-mode waveguide are all prepared by femtosecond laser direct writing technology.

[0015] Furthermore, the photon lantern type mode multiplexing and demultiplexing device can be prepared in transparent materials such as glass, crystal and optical ceramics. Preferably, the present invention uses a quartz glass substrate.

[0016] As a preference,

[0017] 1) When the number of the single-mode waveguides is 3, correspondingly, the four single-mode waveguides constituting the multimode waveguide are symmetrically distributed in a single ring with equal spacing, and the mode generated by the multimode waveguide port is a linearly polarized LP mode, which are respectively and model;

[0018] 2) When the number of the single-mode waveguides is 6, the 7 single-mode waveguides constituting the multimode waveguide are symmetrically distributed in double rings with equal spacing, the inner ring is composed of 1 waveguide, and the outer ring is composed of 6 waveguides. The mode generated by the multimode waveguide port is a linearly polarized LP mode, which are LP 01 , and LP 02 model;

[0019] 3) When the number of the single-mode waveguides is 10, correspondingly, the 12 single-mode waveguides constituting the multimode waveguide are symmetrically distributed in double rings with equal spacing, the inner ring is composed of 4 waveguides, and the outer ring is composed of 8 waveguides. The mode generated by the multimode waveguide port is a linearly polarized LP mode, which are LP 01 , and LP 02 model.

[0020] Preferably, multiple groups of photon lantern-type mode multiplexers / demultiplexers based on guided waveguides can be prepared in the same substrate material. By rationally arranging the spatial layout of multiple groups of devices, the preparation of multi-core multi-mode mode multiplexer / demultiplexer devices can be achieved.

[0021] Through the above technical solution conceived by the present invention, compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. The present invention breaks through the limitation that the multimode waveguide support mode and the corresponding multimode optical fiber support mode in the traditional mode multiplexer / demultiplexer have low matching degree. By introducing the auxiliary waveguide, the multimode waveguide support mode and the corresponding multimode optical fiber support mode can be perfectly matched in theory, thereby effectively improving the mode selectivity and mode purity of the photon lantern device, reducing the coupling loss between the photon lantern device and the multimode optical fiber, and reducing the crosstalk of the mode multiplexing-demultiplexing system.

[0023] 2. The present invention adopts femtosecond laser direct writing technology, which has the advantages of 3D processing, high precision, flexibility, maskless processing and the ability to process a variety of materials. It can realize flexible and efficient 3D manufacturing with sub-micron feature sizes, which can further promote the development trend of functionalization, miniaturization and integration.

[0024] 3. The present invention can arbitrarily customize the trajectory of the optical waveguide through femtosecond laser direct writing technology. It only needs to reasonably plan the waveguide trajectory to achieve mode selectivity through completely identical single-mode optical waveguide parameters, and customize the waveguide size that constitutes the multi-mode waveguide, which greatly reduces the process complexity and greatly improves the compatibility with the existing optical fiber communication system.

[0025] 4. The auxiliary waveguide-based photonic lantern-type mode multiplexer / demultiplexer designed in the present invention has the advantages of compact structure, low loss, low crosstalk, etc., and can be widely used in multi-dimensional and multi-channel optical interconnect chip integration. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of a photon lantern-type mode multiplexer / demultiplexer based on auxiliary waveguide in a 3LP mode provided by an embodiment of the present invention;

[0027] Figure 2 is a schematic diagram of the arrangement and combination of output waveguide end faces provided by an embodiment of the present invention;

[0028] Figure 3 This is a diagram of the device output light spot pattern provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0029] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0030] The present invention provides a photon lantern-type mode multiplexer / demultiplexer based on auxiliary waveguides, comprising a single-mode waveguide array, a gradient coupling region containing auxiliary waveguides and a multimode waveguide, wherein the single-mode waveguide array comprises M (M≥3, a positive integer) mutually independent non-coupled single-mode waveguides, and the gradient coupling region containing auxiliary waveguides additionally introduces N (N≥1, a positive integer) auxiliary single-mode waveguides, wherein the M single-mode waveguides and the additional N single-mode waveguides gradually approach each other until they are coupled and finally merged; the multimode waveguide is composed of the fusion of M+N single-mode waveguides, and the M+N single-mode waveguides constituting the multimode waveguide are axially symmetrical and centrally symmetrically distributed, and the number of modes supported by the multimode waveguide corresponds to the number M of single-mode waveguides.

[0031] Specifically, the M single-mode waveguides and the additional N auxiliary single-mode waveguides in the gradient coupling region containing the auxiliary waveguides are arranged from a one-dimensional linear arrangement to a two-dimensional concentric ring arrangement during the process of mutual coupling and approaching.

[0032] Specifically, the number M of single-mode waveguides of the auxiliary waveguide-based photonic lantern mode multiplexer-demultiplexer includes 3, 6 and 10; the corresponding number N of auxiliary single-mode waveguides is 1, 1 and 2 respectively.

[0033] Specifically, the single-mode waveguide array is connected to the single-mode optical fiber array, and the geometric dimensions, mode field dimensions and arrangement distribution of the M single-mode waveguides match those of the single-mode optical fiber array.

[0034] Specifically, the multimode waveguide is connected to the multimode optical fiber, the geometrical dimensions and mode field dimensions of the multimode waveguide match those of the multimode optical fiber, and the modes supported by the multimode waveguide match those supported by the multimode optical fiber.

[0035] Specifically, the single-mode waveguide, the tapered coupling region and the composite multi-mode waveguide are all prepared by femtosecond laser direct writing technology.

[0036] Specifically, the photon lantern type mode multiplexing and demultiplexing device can be prepared in transparent materials such as glass, crystal and optical ceramics. Preferably, the present invention uses a quartz glass substrate.

[0037] Specifically,

[0038] 1) When the number of the single-mode waveguides is 3, the four single-mode waveguides constituting the multimode waveguide are symmetrically distributed in a single ring with equal spacing, and the mode generated by the multimode waveguide port is a linearly polarized LP mode, which are LP 01 , and model;

[0039] 2) When the number of the single-mode waveguides is 6, the 7 single-mode waveguides constituting the multimode waveguide are symmetrically distributed in double rings with equal spacing, the inner ring is composed of 1 waveguide, and the outer ring is composed of 6 waveguides. The mode generated by the multimode waveguide port is a linearly polarized LP mode, which are LP 01 , and LP 02 model;

[0040] 3) When the number of the single-mode waveguides is 10, correspondingly, the 12 single-mode waveguides constituting the multimode waveguide are symmetrically distributed in double rings with equal spacing, the inner ring is composed of 4 waveguides, and the outer ring is composed of 8 waveguides. The mode generated by the multimode waveguide port is a linearly polarized LP mode, which are LP 01 , and LP 02 model.

[0041] Specifically, multiple groups of photon lantern-type mode multiplexers / demultiplexers based on guided waveguides can be prepared in the same substrate material. By rationally arranging the spatial arrangement of multiple groups of devices, the preparation of multi-core multi-mode mode multiplexer / demultiplexer devices can be achieved.

[0042] The following is an example of a 3LP mode based photonic lantern mode multiplexer / demultiplexer based on auxiliary waveguide. Figure 1-Figure 3 The present invention is described in detail.

[0043] Example

[0044] The present invention provides a photon lantern-type mode multiplexer / demultiplexer based on auxiliary waveguide, which is prepared in a quartz glass substrate by femtosecond laser direct writing technology. Figure 1 Figure 1 is a schematic diagram of a photonic lantern-type mode multiplexer / demultiplexer based on auxiliary waveguide for 3LP mode. Figure 1 The device structure shown in the figure includes a single-mode waveguide array, a gradient coupling region containing auxiliary waveguides, and a multimode waveguide. The single-mode waveguide array is composed of three independent non-coupled single-mode waveguides. The size of each processed waveguide is about 9 μm, and the refractive index difference is about 3×10 -3 The size of the single-mode waveguide is similar to that of the conventional single-mode optical fiber core, and the refractive index difference is also similar, so the two also have similar mode field sizes. The three single-mode waveguides in the single-mode waveguide array are arranged horizontally with an interval of 127μm, which is consistent with the fiber spacing of the conventional single-mode optical fiber array to facilitate mutual coupling.

[0045] An additional auxiliary single-mode waveguide is introduced into the gradient coupling zone containing the auxiliary waveguide, wherein the three single-mode waveguides and the additional auxiliary single-mode waveguide gradually approach each other for coupling and finally form a two-dimensional concentric ring arrangement, and finally the four single-mode waveguides merge to form a multi-mode waveguide. Due to the introduction of the auxiliary waveguide, the four single-mode waveguides constituting the multi-mode waveguide are axially symmetrical and centrally symmetrically distributed, as shown in FIG. Figure 2 As shown. The auxiliary waveguide neither increases the input waveguide mode nor the output waveguide mode, but is simply used to optimize the combination and arrangement of the single-mode waveguide array, so that the mode supported by the multimode waveguide is more closely matched with the mode supported by the multimode optical fiber. The size of the multimode waveguide prepared at the same time is about 15μm, which is close to the core size of the corresponding multimode optical fiber 14.8μm, and the two have similar mode field sizes. The number of modes supported by the multimode waveguide is 3, namely LP01 , and mode, and is consistent with the mode supported by the corresponding multimode optical fiber. According to the above structure, in the process of transforming the single-mode waveguide arranged in one dimension to the two-dimensional concentric ring arrangement, each single-mode waveguide forms a unique coupling structure with all other waveguides. The heterogeneity of this structure introduces mode selectivity, so that each single-mode waveguide mode corresponds to a specific multimode mode of the multimode waveguide, where the middle single-mode waveguide corresponds to the excited LP 01 mode, the left and right single-mode waveguides are excited and By rationally designing the coupling spacing and coupling length between the coupling structures, the device can excite the three LP modes. Especially with the assistance of the auxiliary waveguide, the central symmetry and axial symmetry of the multimode waveguide make this mode excitation more perfect, greatly improving the mode selectivity. Figure 3 The figure shows the output light spot pattern of the photon lantern-type mode multiplexer based on auxiliary waveguide in the actual 3LP mode. Figure 3 It can be seen that the device can excite highly axisymmetric and centrosymmetric LP 01 , and model.

[0046] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A photonic lantern-type mode multiplexer / demultiplexer based on auxiliary waveguide, characterized in that: The invention comprises a single-mode waveguide array, a gradient coupling region containing auxiliary waveguides, and a multimode waveguide, wherein the single-mode waveguide array comprises M independent non-coupled single-mode waveguides, the gradient coupling region containing auxiliary waveguides comprises N auxiliary single-mode waveguides, and the M single-mode waveguides and the N auxiliary single-mode waveguides in the gradient coupling region containing auxiliary waveguides are arranged in a one-dimensional linear manner and gradually approach each other to form a two-dimensional concentric ring arrangement in the process of coupling, wherein the M single-mode waveguides and the N auxiliary single-mode waveguides gradually approach each other until coupling and finally fusion; the multimode waveguide is composed of the fusion of M+N single-mode waveguides, the M+N single-mode waveguides constituting the multimode waveguide are axially symmetrical and centrally symmetrically distributed, and the number of modes supported by the multimode waveguide corresponds to the number M of single-mode waveguides; M , N , M and N are both positive integers.

2. The photonic lantern mode multiplexer / demultiplexer based on auxiliary waveguide according to claim 1, characterized in that: The number M of single-mode waveguides in the single-mode waveguide array includes 3, 6 and 10; the corresponding number N of auxiliary single-mode waveguides is 1, 1 and 2 respectively.

3. The photonic lantern-type mode multiplexer / demultiplexer based on auxiliary waveguide according to claim 1, characterized in that: The single-mode waveguide array is connected to the single-mode optical fiber array, and the geometric dimensions, mode field dimensions and arrangement distribution of the M single-mode waveguides match those of the single-mode optical fiber array.

4. The photonic lantern-type mode multiplexer / demultiplexer based on auxiliary waveguide according to claim 1, characterized in that: The multimode waveguide is connected to the multimode optical fiber, the geometric size and mode field size of the multimode waveguide match those of the multimode optical fiber, and the multimode waveguide support mode matches that of the multimode optical fiber.

5. The photonic lantern-type mode multiplexer / demultiplexer based on auxiliary waveguide according to claim 1, characterized in that: The auxiliary waveguide-based photon lantern-type mode multiplexer / demultiplexer is prepared by femtosecond laser direct writing technology.

6. A photonic lantern-type mode multiplexer / demultiplexer based on auxiliary waveguide according to claim 1 or 5, characterized in that: The auxiliary waveguide-based photonic lantern-type mode multiplexer / demultiplexer is fabricated in a transparent material.

7. The photonic lantern-type mode multiplexer / demultiplexer based on auxiliary waveguide according to claim 2, characterized in that: When M=3, the four single-mode waveguides constituting the multimode waveguide are symmetrically distributed in a single ring with equal spacing, and the mode generated by the multimode waveguide port is a linearly polarized LP mode, which are respectively , and model; When M=6, the seven single-mode waveguides constituting the multimode waveguide are symmetrically distributed in double rings with equal spacing, the inner ring is composed of one waveguide, and the outer ring is composed of six waveguides. The mode generated by the multimode waveguide port is a linearly polarized LP mode, which are respectively , , , , and model; When M=10, the 12 single-mode waveguides constituting the multimode waveguide are symmetrically distributed in double rings with equal spacing, the inner ring is composed of 4 waveguides, and the outer ring is composed of 8 waveguides. The mode generated by the multimode waveguide port is a linearly polarized LP mode, which are respectively , , , , , , , , and model.

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