CN116125598A - A Photonic Lantern Mode Multiplexer/Demultiplexer Based on Auxiliary Waveguide - Google Patents

Abstract

The invention discloses a photon lantern type multiplexing/de-multiplexing device based on an auxiliary waveguide, and belongs to the field of integrated photonics and optical interconnection. The photon lantern structure is adopted, and the additional auxiliary single-mode waveguide is introduced into the conventional photon lantern structure, so that the optimized photon lantern mode multiplexing/de-multiplexing device has more symmetrical multimode waveguide geometric structure and mode field distribution, the coupling loss and mode correlation loss between the photon lantern mode multiplexing/de-multiplexing device and the corresponding multimode optical fibers are effectively reduced, the device mode purity is improved, and the crosstalk of a multiplexing-de-multiplexing system is reduced. The invention has wide application prospect in the fields of integrated photonics and optical interconnection, and fills the blank of the related technical field.

Description

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

Technical Field

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

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.

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.

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.

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 multiple LP _mn modes, where m is the angular mode number and n is the radial mode number. 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.

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

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.

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.

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.

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.

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.

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.

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.

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

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.

As a preference,

和

模式；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 respectively

and

model;

和LP₀₂模式；2) When the number of the single-mode waveguides is 6, correspondingly, 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 mode;

和LP₀₂模式。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 mode.

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.

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

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.

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 achieve flexible and efficient 3D manufacturing with sub-micron feature sizes, which can further promote the development trend of functionalization, miniaturization and integration.

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.

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

1 is a schematic diagram of a photon lantern-type mode multiplexer/demultiplexer based on an auxiliary waveguide in a 3LP mode provided by an embodiment of the present invention;

FIG2 is a schematic diagram of an arrangement and combination of output waveguide end faces provided in an embodiment of the present invention;

FIG. 3 is a diagram showing a pattern of light spots output by a device according to an embodiment of the present invention.

DETAILED DESCRIPTION

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.

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.

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.

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.

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.

Specifically, 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 mode supported by the multimode waveguide matches the mode supported by the multimode optical fiber.

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

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.

Specifically,

和

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

and

model;

和LP₀₂模式；2) When the number of the single-mode waveguides is 6, correspondingly, 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 mode;

和LP₀₂模式。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 mode.

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.

The present invention will be described in detail below by taking a 3LP mode auxiliary waveguide-based photon lantern mode multiplexer/demultiplexer as an example in conjunction with FIGS. 1 to 3 .

Example

The present invention provides a photon lantern-type mode multiplexer/demultiplexer based on auxiliary waveguides, which is prepared in a quartz glass substrate by femtosecond laser direct writing technology. FIG1 is a schematic diagram of a photon lantern-type mode multiplexer/demultiplexer based on auxiliary waveguides in a 3LP mode. As shown in FIG1 , the device structure includes a single-mode waveguide array, a gradient coupling region containing an auxiliary waveguide, and a multimode waveguide. The single-mode waveguide array is composed of three independent non-coupled single-mode waveguides, each of which has a size of about 9 μm and a refractive index difference of about 3×10 ^-3 . The size of the single-mode waveguide is similar to that of a 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 127 μm, which is consistent with the optical fiber spacing of a conventional single-mode optical fiber array to facilitate mutual coupling.

和

模式，并且与相应的多模光纤支持的模式一致。根据上述结构可知，在一维排布的单模波导转变至二维同心圆环排布过程中，每根单模波导与其它所有波导形成独特的耦合结构，该结构各异性引入了模式选择性，使得每根单模波导模式对应于多模波导一个特定多模模式，其中中间单模波导对应激发LP₀₁模式，左右单模波导分别对应激发

和

模式。通过合理设计耦合结构之间的耦合间距和耦合长度，可以实现该器件对这3个LP模式的激发，尤其是在辅助波导的协助下，多模波导的中心对称性和轴对称性使得这种模式激发更加完美，大大提高了模式选择性。如图3所示为实际加工出的3LP模式基于辅助波导的光子灯笼型模式复用器输出光斑模式图。从图3可以看出，该器件能激发出高度轴对称且中心对称的LP₀₁，

和

模式。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 FIG2. The auxiliary waveguide neither increases the input waveguide mode nor the output waveguide mode, but is simply used to optimize the combination arrangement of the single-mode waveguide array, so that the mode supported by the multi-mode waveguide is more matched with the mode supported by the multi-mode optical fiber. The size of the multi-mode waveguide prepared at the same time is about 15μm, which is close to the core size of the corresponding multi-mode optical fiber of 14.8μm, and the two have similar mode field sizes. The number of modes supported by the multi-mode waveguide is 3, namely LP ₀₁ ,

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 into 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 excitation of the LP ₀₁ mode, and the left and right single-mode waveguides correspond to the excitation of the LP 02 mode, respectively.

and

Mode. By reasonably 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. As shown in Figure 3, the output spot pattern of the photon lantern-type mode multiplexer based on the auxiliary waveguide for the 3LP mode actually processed is shown. As can be seen from Figure 3, the device can excite highly axisymmetric and centrally symmetric LP ₀₁ ,

and

model.

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 (8)

1. The photon lantern type multiplexing/demultiplexing device based on the auxiliary waveguide is characterized by comprising a single-mode waveguide array, a gradual change coupling area containing the auxiliary waveguide and a multimode waveguide, wherein the single-mode waveguide array comprises M independent non-coupling single-mode waveguides, the gradual change coupling area containing the auxiliary waveguide comprises N auxiliary single-mode waveguides, the M single-mode waveguides and the N single-mode waveguides are gradually close to each other until coupling is achieved, and fusion is finally achieved; the multimode waveguides are formed by fusing M+N single-mode waveguides, the M+N single-mode waveguides forming the multimode waveguides are axisymmetric and centrally symmetric, and the number of modes supported by the multimode waveguides corresponds to the number M of the single-mode waveguides; m is more than or equal to 3, N is more than or equal to 1, and M and N are positive integers.

2. The auxiliary waveguide-based photonic lantern-type multiplexer/demultiplexer according to claim 1, wherein M single-mode waveguides and N auxiliary single-mode waveguides in the graded coupling region containing auxiliary waveguides are linearly arranged in one dimension to form a two-dimensional concentric ring arrangement in the process of gradually approaching to each other for coupling.

3. An auxiliary waveguide based photonic lantern mode multiplexer/demultiplexer according to claim 1, wherein the number M of single mode waveguides in the array of single mode waveguides comprises 3,6 and 10; the number N of corresponding auxiliary single-mode waveguides is 1,1 and 2, respectively.

4. The auxiliary waveguide-based photonic lantern mode multiplexer/demultiplexer of claim 1, wherein the array of single mode waveguides is connected to an array of single mode fibers, and the M single mode waveguides have a geometry, a mode field size, and an arrangement distribution matching those of the array of single mode fibers.

5. The auxiliary waveguide-based photonic lantern mode multiplexer/demultiplexer of claim 1, wherein the multimode waveguide is connected to a multimode optical fiber, the multimode waveguide geometry and mode field dimensions are matched to the multimode optical fiber, and the multimode waveguide support mode is matched to the multimode optical fiber support mode.

6. An auxiliary waveguide based photonic lantern mode multiplexer/demultiplexer as claimed in claim 1 and wherein the auxiliary waveguide based photonic lantern mode multiplexer/demultiplexer is fabricated by a femtosecond laser direct write technique.

7. An auxiliary waveguide based photonic lantern type multiplexer/demultiplexer according to claim 1 or 6, wherein the auxiliary waveguide based photonic lantern type multiplexer/demultiplexer is fabricated in a transparent material.

8. An auxiliary waveguide based photonic lantern mode multiplexer/demultiplexer as claimed in claim 3, wherein,

when m=3, the 4 single-mode waveguides forming the multimode waveguide are distributed symmetrically at equal intervals in a single ring, and the modes generated by the multimode waveguide port are linear polarization LP modes, which are LP respectively ₀₁ ，

And->

A mode;

when m=6, 7 single-mode waveguides forming the multimode waveguide are distributed in a double-ring equidistant symmetrical manner, the inner ring is composed of 1 waveguide, the outer ring is composed of 6 waveguides, the modes generated by the multimode waveguide port are linear polarization LP modes, and the modes are LP modes respectively ₀₁ ，

And LP ₀₂ A mode;

when m=10, 12 single-mode waveguides forming the multimode waveguide are distributed in a double-ring equidistant symmetrical manner, the inner ring is composed of 4 waveguides, the outer ring is composed of 8 waveguides, the modes generated by the ports of the multimode waveguide are linear polarization LP modes, and the modes are LP modes respectively ₀₁ ，

And LP ₀₂ A mode. />

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