An on-chip waveguide multi-pass optical amplifier based on mode multiplexing and an amplification method thereof

Abstract

The application discloses an on-chip waveguide multi-pass optical amplifier based on mode multiplexing and an amplification method thereof. The amplifier comprises an edge coupler assembly, a mode conversion assembly, an active multi-mode amplification waveguide and a loop waveguide. The mode conversion assembly is used for converting the signal light between the fundamental mode and the high-order mode. The active multi-mode amplification waveguide supports the transmission of the fundamental mode and the high-order mode and amplifies the signal light under the action of pump light. The pump light is input from one end or both ends of the active multi-mode amplification waveguide. After the signal light enters the active multi-mode amplification waveguide to obtain the first-pass amplification in the fundamental mode, the signal light is converted into the high-order mode and enters again to obtain the second-pass amplification. The signal light continues to be converted into higher-order modes for multi-pass amplification, and finally is converted into the fundamental mode and output. The application enables the same signal light to complete multi-pass propagation in different modes and obtain gain respectively through mode multiplexing, thereby improving the effective action times and action length of the signal light and the gain medium in a limited area.

Description

Technical Field

[0001] This invention relates to the field of integrated optoelectronic devices and on-chip optical amplification technology, specifically an on-chip waveguide multi-pass optical amplifier based on mode multiplexing and its amplification method. Background Technology

[0002] With the development of optical communication, data centers, microwave photonics, on-chip optical interconnects, and integrated optical sensing technologies, on-chip optical amplifiers play a crucial role in improving system link budget, compensating for on-chip insertion loss, and enhancing on-chip optical signal transmission capabilities. By introducing active gain materials into on-chip waveguides, signal light can be amplified under the action of pump light, thereby realizing compact and integrable on-chip optical amplification functions.

[0003] Traditional on-chip waveguide optical amplifiers typically employ a single mode propagating within an active waveguide. The signal light enters the active gain waveguide in its fundamental mode and interacts with the gain medium during propagation, thereby achieving optical gain. This type of structure offers advantages such as simplicity, stable transmission, and ease of system integration. However, its amplification performance is limited by factors including the active gain material, pump absorption efficiency, population inversion degree, mode field confinement factor, effective mode area, and waveguide transmission loss.

[0004] In single-mode, single-pass propagation on-chip optical amplifier structures, further improving the overall gain typically requires increasing the active waveguide length, pump power, or gain dielectric concentration. However, increasing the active waveguide length increases chip area and propagation loss, and may introduce bending losses and process inhomogeneities; increasing pump power increases system power consumption and thermal effects; and increasing gain dielectric concentration may lead to ion clustering, concentration quenching, or additional absorption losses. Therefore, the gain improvement of traditional single-mode, single-pass waveguide optical amplifier structures within a limited chip area is limited.

[0005] Multimode waveguides can support multiple intrinsic modes, including the fundamental mode and higher-order modes. Different modes have different transverse field distributions, effective mode areas, and overlap relationships with the gain region. If mode multiplexing and mode conversion techniques can be used to allow the same signal light to propagate sequentially in the fundamental mode and at least one higher-order mode within the active amplification region and be amplified separately, the effective number and duration of interactions between the signal light and the gain medium can be increased without simply increasing the linear length of the device, thereby improving the on-chip optical amplification effect.

[0006] However, the propagation of higher-order modes in multimode active waveguides is susceptible to bending loss, mode crosstalk, and unwanted mode coupling. Especially when using helical, serpentine, or folded waveguide structures within a limited chip area, higher-order modes are more prone to radiation loss or mode conversion in curved regions. Therefore, a comprehensive design is needed for the width, effective mode area, mode field confinement factor, bending structure, and mode multiplexing structure of the multimode amplifying waveguide to ensure low-loss propagation and effective optical gain for both the fundamental mode and at least one higher-order mode.

[0007] Furthermore, in on-chip waveguide optical amplifiers, the method of combining pump and signal beams also affects device complexity and insertion loss. Adding a wavelength division multiplexer on-chip increases the number of passive components and design complexity, and may introduce additional insertion loss. By combining the pump and signal beams off-chip and inputting them to the on-chip waveguide via an edge coupler, the on-chip optical path structure can be simplified, and the loss of on-chip passive components can be reduced.

[0008] Therefore, there is an urgent need for an on-chip waveguide multipath optical amplifier based on mode multiplexing. Through the coordinated design of edge couplers, mode conversion components, active multimode amplification waveguides and loop waveguides, the same signal light can propagate in the active multimode amplification waveguide in the fundamental mode and at least one higher-order mode in sequence and obtain optical gain respectively, thereby improving the on-chip amplification efficiency and total gain within a limited chip area. Summary of the Invention

[0009] To overcome the shortcomings of the prior art, this invention provides an on-chip waveguide multi-pass optical amplifier based on mode multiplexing and its amplification method. This on-chip waveguide multi-pass optical amplifier uses a mode conversion component to convert the input signal light between the fundamental mode and at least one higher-order mode, and allows the signal light of different modes to propagate sequentially in an active multimode amplification waveguide and obtain optical gain, ultimately converting it into the fundamental mode output.

[0010] The technical solution of the present invention is as follows: The on-chip waveguide multi-pass optical amplifier based on mode multiplexing proposed in this invention includes an edge coupler component, a mode conversion component, an active multimode amplification waveguide, and a loop waveguide.

[0011] The edge coupler assembly is used to couple the pump light and signal light after off-chip beam combining to the on-chip waveguide, or to couple the pump light input from outside the chip to the on-chip waveguide, and to output the amplified signal light from the on-chip waveguide. The edge coupler can be an end-face coupler, an inverted tapered coupler, a mode converter, or other structures capable of coupling external optical fibers to the on-chip waveguide.

[0012] The mode conversion component includes at least one mode multiplexer and at least one mode demultiplexer. The mode multiplexer is used to convert the signal light from a first mode to a second mode, and the mode demultiplexer is used to convert the amplified second mode back to the first mode or the target output mode. The mode multiplexer and the mode demultiplexer can be asymmetric directional couplers, multimode interference couplers, adiabatic mode converters, phase-matched mode converters, or combinations thereof. The fundamental mode and the at least one higher-order mode can include two or more of the following modes: TE0 mode, TE1 mode, TE2 mode, TM0 mode, TM1 mode, and TM2 mode. The first mode can be a fundamental mode or a low-order mode, and the second mode can be a higher-order mode.

[0013] In a preferred embodiment, the fundamental mode and at least one higher-order mode are TE0 mode, TE1 mode, and TE2 mode. The input signal light propagates in the active multimode amplification waveguide in TE0 mode, TE1 mode, and TE2 mode respectively, and obtains optical gain. Then, it is converted to TE0 mode output by a mode demultiplexer.

[0014] Active multimode amplifying waveguides are used to support the transmission of the fundamental mode and at least one higher-order mode, and to act as pump light. The signal light in different modes is optically amplified. The active multimode amplification waveguide is composed of an active gain material capable of providing optical gain under the action of pump light. The active gain material can be one or more of rare earth ion doped gain materials, III-V group semiconductor gain materials, quantum dot gain materials, organic gain materials, and two-dimensional material gain materials. The rare earth ion doped gain material can be selected from one or more of rare earth ion doped lithium niobate, rare earth ion doped lithium tantalate, rare earth ion doped silicon nitride, rare earth ion doped alumina, rare earth ion doped glass, and rare earth ion doped oxide crystal. The rare earth ions include one or more of erbium ions, ytterbium ions, thulium ions, neodymium ions, holmium ions, and praseodymium ions.

[0015] A loop waveguide is positioned between the mode demultiplexer and the mode multiplexer to guide the signal light amplified in the previous stage to the mode conversion and amplification path in the next stage. Through the loop waveguide, the same signal light can pass through the active multimode amplification waveguide multiple times in different modes, thereby achieving on-chip multi-path optical amplification.

[0016] The pump light and the signal light are combined off-chip via a combiner and then input to the on-chip waveguide through the same edge coupler. The combiner can be a fiber wavelength division multiplexer. The pump light can be input from one end of the active multimode amplifier waveguide to form a unidirectional pump structure, or from both ends of the active multimode amplifier waveguide to form a bidirectional pump structure. The bidirectional pump structure helps improve the uniformity of the pump light distribution along the propagation direction in the active multimode amplifier waveguide, reducing pump depletion and gain non-uniformity problems caused by unidirectional pumping.

[0017] In one embodiment, the pump light and signal light are combined off-chip using a combiner, and the combined pump light and signal light are then input to the on-chip waveguide through the same edge coupler. The combiner can be a fiber wavelength division multiplexer. Because the pump light and signal light are combined off-chip, there is no need for an on-chip wavelength division multiplexer, which reduces the number of on-chip passive components, lowers on-chip insertion loss, and reduces design complexity.

[0018] The waveguide width of the active multimode amplification waveguide is determined based on the transmission loss, effective mode area, and mode field confinement factor of the fundamental mode and at least one higher-order mode. The effective mode area characterizes the distribution range of the optical field in the waveguide cross-section, while the mode field confinement factor characterizes the degree of overlap between different modes and the active gain region. By designing the waveguide width, both the fundamental mode and at least one higher-order mode can be transmitted in the active multimode amplification waveguide with low transmission loss and good gain. The active multimode amplification waveguide can be a helical waveguide structure, a serpentine waveguide structure, a folded waveguide structure, or a wraparound waveguide structure to increase the effective amplification length within a limited chip area. In a preferred embodiment, the active multimode amplification waveguide is an Archimedean spiral waveguide structure. The Archimedean spiral waveguide structure can provide a longer propagation path within a limited chip area and allows the bending radius to change continuously along the propagation direction, which is beneficial for reducing radiation loss and mode crosstalk of higher-order modes during bending propagation.

[0019] In a further embodiment, the helical center transition region of the active multimode amplification waveguide employs one or more of a 180-degree Euler bend waveguide, a gradually curvature bend waveguide, or a circular arc bend waveguide to reduce bending loss in the helical center transition region and suppress undesirable coupling between different modes.

[0020] In summary, the signal light enters the active multimode amplification waveguide from the edge coupler assembly, is amplified in the active multimode amplification waveguide, passes through the mode demultiplexer and mode multiplexer in the mode conversion assembly, and the loop waveguide, and completes multi-pass amplification in the active multimode amplification waveguide before being output through the edge coupler assembly.

[0021] This invention also provides an on-chip waveguide multi-pass optical amplification method based on mode multiplexing, comprising the following steps: combining pump light and signal light off-chip and coupling them to the on-chip waveguide via an edge coupler; or, combining the signal light and the first pump light off-chip and inputting them from one end of an active multimode amplification waveguide via an edge coupler, and inputting the second pump light from the other end of the active multimode amplification waveguide via another edge coupler; causing the signal light to enter the active multimode amplification waveguide in its fundamental mode and obtain first-pass optical amplification under the action of the pump light; converting the first-pass amplified signal light into at least one higher-order mode via a mode conversion component; causing the at least one higher-order mode to re-enter the active multimode amplification waveguide and obtain second-pass optical amplification under the action of the pump light; further converting the signal light into a higher-order mode as needed and continuing multi-pass optical amplification in the active multimode amplification waveguide; and converting the finally amplified signal light into its fundamental mode output via a mode demultiplexer.

[0022] In a preferred embodiment, the signal light is amplified in the active multimode amplification waveguide in TE0 mode for the first pass, then converted to TE1 mode by a TE1 mode multiplexer for the second pass; the TE1 mode is converted to TE0 mode by a TE1 mode demultiplexer, then converted to TE2 mode by a TE2 mode multiplexer for the third pass; the TE2 mode is converted to TE0 mode by a TE2 mode demultiplexer for output.

[0023] The beneficial effects of the technical solution provided by this invention are: 1. This invention utilizes waveguide mode multiplexing technology to enable the same signal light to propagate sequentially in an active multimode amplification waveguide in the fundamental mode and at least one higher-order mode, thereby obtaining optical gain respectively. This increases the effective number of interactions and the interaction length between the signal light and the gain medium within a limited chip area.

[0024] 2. This invention achieves the beam combining of pump light and signal light through off-chip beam combining devices, and inputs the combined pump light and signal light into the on-chip waveguide through an edge coupler. There is no need to set up a wavelength division multiplexer on the chip, which helps to reduce the number of passive devices on the chip, insertion loss and design complexity.

[0025] 3. This invention can employ either a unidirectional or bidirectional pumping structure to adapt to design requirements for different gain materials, different pump powers, and different amplification lengths.

[0026] 4. This invention converts the amplified higher-order modes into the fundamental mode output through a mode demultiplexer, which is beneficial for compatibility with subsequent single-mode on-chip optical paths.

[0027] 5. The active multimode amplification waveguide of the present invention is designed according to the effective mode area, mode field confinement factor and transmission loss of different modes, and adopts one or more of the Archimedes spiral waveguide structure, the gradually curvature bending structure or the Euler bending structure to increase the amplification path length within a limited chip area, while reducing the radiation loss and mode crosstalk of higher-order modes in the bending region, thereby improving the amplification effect of different modes in the active waveguide.

[0028] 6. The active multimode amplification waveguide of the present invention can be based on various on-chip gain platforms such as rare earth ion doped gain materials, III-V group semiconductor gain materials, quantum dot gain materials, and organic gain materials, and has good scalability. Attached Figure Description

[0029] Figure 1 This is a schematic diagram illustrating the working process of the on-chip waveguide multi-pass optical amplifier based on mode multiplexing according to the present invention. Figure 2 This is a three-dimensional structural schematic diagram of the on-chip waveguide multi-pass optical amplifier based on mode multiplexing according to the present invention; Figure 3 This is a schematic diagram of the planar structure of the on-chip waveguide multi-pass optical amplifier based on mode multiplexing according to the present invention.

[0030] Explanation of reference numerals in the attached figures: 1: Edge coupler; 2: TE1 mode multiplexer; 3: TE2 mode multiplexer; 4: Multimode gain amplification spiral; 5: TE2 mode demultiplexer; 6: TE1 mode demultiplexer.

[0031] In the figure, the connecting waveguides that connect the mode demultiplexer and the mode multiplexer form a loop waveguide, which is used to guide the signal light that has been amplified in the previous stage to the mode conversion and amplification path in the next stage.

[0032] Figures 1 to 3 This is only used to illustrate the overall structural relationship, mode conversion relationship and optical path connection method of the present invention, and is not intended to limit the actual size, specific shape, number of turns, spacing and relative proportion of each waveguide, mode multiplexer, mode demultiplexer and multimode gain amplification spiral. Detailed Implementation

[0033] The following description, in conjunction with the accompanying drawings and specific embodiments, further illustrates the invention. These embodiments are merely for the purpose of providing a more detailed and specific account of the invention and are not intended to limit the invention in any way. After reading this invention, any modifications of the invention in various equivalent forms by those skilled in the art fall within the scope defined by the appended claims.

[0034] Example 1: Overall Structure of On-Chip Waveguide Multipass Optical Amplifier This embodiment provides an on-chip waveguide multi-pass optical amplifier based on mode multiplexing, such as... Figures 1 to 3 As shown, the system includes an edge coupler 1, a TE1 mode multiplexer 2, a TE2 mode multiplexer 3, a multimode gain amplification spiral 4, a TE2 mode demultiplexer 5, and a TE1 mode demultiplexer 6. The connecting waveguides linking the TE1 mode demultiplexer 6 and the TE2 mode multiplexer 3, and the connecting waveguides linking the mode conversion device and the multimode gain amplification spiral 4, constitute a loop waveguide. Figure 1 The diagram illustrates the complete optical path of the pump light and signal light, from input via an edge coupler, through mode multiplexer conversion, multi-pass amplification in a multimode gain amplification spiral, and output via mode demultiplexer. Figure 2 The diagram illustrates the three-dimensional structure of the aforementioned on-chip waveguide multi-path optical amplifier, showing the overall layout and connection relationships of the edge coupler 1, TE1 mode multiplexer 2, TE2 mode multiplexer 3, multimode gain amplification spiral 4, TE2 mode demultiplexer 5, and TE1 mode demultiplexer 6. Figure 3 The diagram illustrates the planar structure of the on-chip waveguide multipath optical amplifier, further showing the relative positions and waveguide connection paths between the mode multiplexers, mode demultiplexers, and multimode gain amplification spirals.

[0035] Edge coupler 1 is used to couple the pump light and signal light after off-chip beam combining to the on-chip waveguide, or to couple the pump light input from off-chip to the on-chip waveguide, and can also be used to output the amplified signal light from the on-chip waveguide. Edge coupler 1 can be set at the input and output ends of the on-chip waveguide to realize the input and output of pump light, signal light and amplified signal light.

[0036] TE1 mode multiplexer 2 is used to convert the signal light from TE0 mode to TE1 mode, so that the signal light can enter the multimode gain amplification spiral 4 in TE1 mode and obtain optical amplification. TE2 mode multiplexer 3 is used to convert the signal light from TE0 mode to TE2 mode, so that the signal light can enter the multimode gain amplification spiral 4 in TE2 mode and obtain optical amplification.

[0037] Multimode gain amplification spiral 4 is an active multimode amplification waveguide used to support the transmission of TE0, TE1, and TE2 modes, and to optically amplify the signal light in different modes under the action of pump light. By having the input signal light pass through the multimode gain amplification spiral 4 in different modes sequentially, the effective number of interactions and the effective interaction length between the signal light and the active gain material can be increased.

[0038] TE2 mode demultiplexer 5 is used to convert the TE2 mode after the third amplification to TE0 mode or target output mode. TE1 mode demultiplexer 6 is used to convert the TE1 mode after the second amplification back to TE0 mode and guide it to the next mode conversion path.

[0039] The loop waveguide is used to transmit the signal light amplified in the previous stage to the mode multiplexer in the next stage, so that the signal light can pass through the multimode gain amplification spiral 4 multiple times in different modes.

[0040] Example 2: Multi-pass amplification process based on TE mode multiplexing In this embodiment, the input signal light first enters the on-chip waveguide through the edge coupler 1, and then enters the multimode gain amplification spiral 4 in TE0 mode. When the TE0 mode propagates in the multimode gain amplification spiral 4, it obtains the first stage of optical amplification under the action of the pump light.

[0041] After the first stage of amplification, the TE0 mode is transmitted to the TE1 mode multiplexer 2 via the loop waveguide. The TE1 mode multiplexer 2 converts the TE0 mode into the TE1 mode, so that the TE1 mode re-enters the multimode gain amplification spiral 4 and obtains a second stage of optical amplification during propagation.

[0042] After the second amplification, the TE1 mode is converted to the TE0 mode by the TE1 mode demultiplexer 6. The converted TE0 mode is then transmitted to the TE2 mode multiplexer 3 via a loop waveguide. The TE2 mode multiplexer 3 converts the TE0 mode to the TE2 mode, causing the TE2 mode to re-enter the multimode gain amplification spiral 4 and obtain a third optical amplification under the action of the pump light.

[0043] After the third amplification, the TE2 mode is converted into the TE0 mode or the target output mode by the TE2 mode demultiplexer 5, and then output through the edge coupler 1 or the on-chip output waveguide.

[0044] Through the above process, the input signal light can pass through the multimode gain amplification spiral 4 in TE0 mode, TE1 mode and TE2 mode in the same on-chip waveguide multi-pass optical amplifier. Between two adjacent amplification passes, it is first converted back to TE0 mode and then converted to the next higher-order mode, thereby increasing the effective amplification times and effective amplification length within a limited chip area.

[0045] Specifically, the signal light is amplified in the active multimode amplification waveguide in TE0 mode, then converted to TE1 mode by a TE1 mode multiplexer and amplified in the second stage; the TE1 mode is converted to TE0 mode by a TE1 mode demultiplexer, then converted to TE2 mode by a TE2 mode multiplexer and amplified in the third stage; the TE2 mode is converted to TE0 mode by a TE2 mode demultiplexer and output.

[0046] Example 3: Multimode Gain Amplification Spiral Design In this embodiment, the multimode gain amplification spiral 4 is made of an active gain material, used to provide optical gain for signal light in different modes under the action of pump light. The active gain material can be rare-earth ion-doped lithium niobate, rare-earth ion-doped lithium tantalate, rare-earth ion-doped silicon nitride, rare-earth ion-doped alumina, rare-earth ion-doped glass, rare-earth ion-doped oxide crystal, III-V semiconductor gain material, quantum dot gain material, organic gain material, two-dimensional material gain material, or other materials that can provide on-chip optical gain under the action of pump light.

[0047] The waveguide width of the multimode gain amplification spiral 4 is designed based on the transmission loss, effective mode area, and mode field confinement factor of the TE0, TE1, and TE2 modes. For the multimode gain amplification spiral 4, the waveguide width needs to be sufficient to support the transmission of the target higher-order modes while avoiding excessive participation of non-target modes in propagation. By selecting an appropriate waveguide width, the TE0, TE1, and TE2 modes can all have low transmission loss, good mode field confinement factor, and suitable effective mode area.

[0048] In the specific design, the effective refractive index, effective mode area, mode field confinement factor, and bending loss of the TE0, TE1, and TE2 modes under different waveguide widths can be calculated separately, and the structural dimensions of the multimode gain amplification helix 4 can be determined based on the calculation results. The structural dimensions may include parameters such as waveguide width, waveguide height, helix spacing, effective propagation length, and minimum bending radius.

[0049] In one specific implementation, the waveguide width of the multimode gain amplification spiral 4 is 2.5μm to 9μm, the waveguide height is 0.2μm to 1μm, and the spiral spacing is 2.5μm to 6.5μm.

[0050] Example 4: Spiral Active Multimode Amplifying Waveguide To increase the effective amplification length within a limited chip area, the multimode gain amplification spiral 4 can adopt a spiral waveguide structure, a serpentine waveguide structure, a folded waveguide structure, or a wraparound waveguide structure.

[0051] In a preferred embodiment, the multimode gain amplification helix 4 employs an Archimedean spiral waveguide structure. The Archimedean spiral structure can provide a longer propagation path within a limited area and reduce radiation loss and mode crosstalk of higher-order modes in the curved region through a continuously varying bending radius.

[0052] In the central transition region of the multimode gain amplification spiral 4, one or more of the following can be employed: a 180-degree Euler bent waveguide, a gradually curvature bent waveguide, or a circular arc bent waveguide. This bent structure is used to reduce bending loss in the central transition region and suppress undesirable coupling between the TE0, TE1, and TE2 modes.

[0053] Figures 1 to 3 The multimode gain amplification spiral 4 in the diagram is only used to illustrate the overall path form of the active multimode amplification waveguide and is not used to limit the actual number of spiral turns, spiral spacing, bending radius, waveguide length and their relative proportions.

[0054] Example 5: Mode Multiplexer and Mode Demultiplexer TE1 mode multiplexer 2, TE2 mode multiplexer 3, TE2 mode demultiplexer 5 and TE1 mode demultiplexer 6 can be asymmetric directional couplers, multimode interference couplers, adiabatic mode converters, phase-matched mode converters or combinations thereof.

[0055] In one specific embodiment, the TE1 mode multiplexer 2 adopts an asymmetric directional coupler structure. By designing the width, spacing, and coupling length of adjacent waveguides, the TE0 mode in one waveguide and the TE1 mode in the multimode waveguide on the other side satisfy the phase matching condition, thereby realizing the conversion from TE0 mode to TE1 mode.

[0056] Similarly, the TE2 mode multiplexer 3 can achieve the conversion from TE0 mode to TE2 mode through a phase-matching structure. The TE1 mode demultiplexer 6 can adopt a structure that is the opposite or equivalent to that of the TE1 mode multiplexer 2, and is used to convert the TE1 mode after the second stage of amplification back to TE0 mode. The TE2 mode demultiplexer 5 can adopt a structure that is the opposite or equivalent to that of the TE2 mode multiplexer 3, and is used to convert the TE2 mode after the third stage of amplification back to TE0 mode or the target output mode.

[0057] In this embodiment, TE1 mode multiplexer 2 and TE1 mode demultiplexer 6 correspond to the mode conversion before and after the second stage of amplification, and TE2 mode multiplexer 3 and TE2 mode demultiplexer 5 correspond to the mode conversion before and after the third stage of amplification. Through the above multiplexing and demultiplexing structure, the signal light can be restored to TE0 mode before entering the next stage of higher-order mode amplification, thereby improving the controllability of the mode conversion process and the compatibility with the connection of the loop waveguide.

[0058] Example 6: Off-chip beam combining input and pumping method In this embodiment, the pump light and signal light are combined off-chip using an off-chip combiner. The off-chip combiner can be a fiber wavelength division multiplexer or other device capable of combining the pump light and signal light. The combined pump light and signal light are then input into the on-chip waveguide via edge coupler 1 and jointly enter the multimode gain amplification spiral 4. This method eliminates the need for an on-chip wavelength division multiplexer, reducing the number of on-chip passive components, lowering on-chip insertion loss, and reducing design complexity.

[0059] In one embodiment, the pump light is input from one end of the multimode gain amplification spiral 4, forming a unidirectional pump structure. The unidirectional pump structure features a simple optical path, a small number of input ports, and ease of testing.

[0060] In another embodiment, the pump light is input from both ends of the multimode gain amplification spiral 4, forming a bidirectional pumping structure. The bidirectional pumping structure can improve the uniformity of the pump light distribution along the propagation direction within the multimode gain amplification spiral 4, reducing pump depletion and gain non-uniformity problems caused by unidirectional pumping.

[0061] In the bidirectional pumping embodiment, the signal light and the first pump light can be combined off-chip and then input into the on-chip waveguide by one side edge coupler 1, and the second pump light can be input into the on-chip waveguide by the other side edge coupler 1, so that the pump light is injected from both ends of the multimode gain amplification spiral 4.

[0062] Example 7: On-chip waveguide multi-pass optical amplification method This embodiment also provides an on-chip waveguide multi-pass optical amplification method based on mode multiplexing.

[0063] First, the pump light and signal light are combined off-chip and coupled to the on-chip waveguide via edge coupler 1. Alternatively, the signal light and the first pump light are combined off-chip and input from one end of the multimode gain amplification screw 4, while the second pump light is input from the other end of the multimode gain amplification screw 4 via another edge coupler 1.

[0064] Secondly, the signal light is made to enter the multimode gain amplification spiral 4 in TE0 mode, and the first stage of optical amplification is obtained under the action of pump light.

[0065] Then, the TE0 mode after the first pass of amplification is converted into TE1 mode by the TE1 mode multiplexer 2, so that the TE1 mode re-enters the multimode gain amplification spiral 4 and obtains the second pass of optical amplification.

[0066] Furthermore, the TE1 mode after the second amplification is converted back to the TE0 mode by the TE1 mode demultiplexer 6, and the converted TE0 mode is transmitted to the TE2 mode multiplexer 3 through the loop waveguide.

[0067] Subsequently, the TE0 mode is converted to the TE2 mode by the TE2 mode multiplexer 3, so that the TE2 mode re-enters the multimode gain amplification spiral 4 and obtains the third optical amplification.

[0068] Finally, the TE2 mode after the third stage amplification is converted into TE0 mode or target output mode by the TE2 mode demultiplexer 5, and output through the edge coupler 1 or on-chip output waveguide.

[0069] The above process is only used to illustrate a preferred implementation of the present invention. In other embodiments, the signal light may also be amplified twice between the fundamental mode and a higher-order mode, or amplified multiple times between the fundamental mode and multiple higher-order modes; the mode used may also be a TM mode or other intrinsic modes that can be supported by on-chip waveguides.

Claims

1. An on-chip waveguide multi-pass optical amplifier based on mode multiplexing, characterized in that, include: An edge coupler assembly is used to couple the pump light and signal light after off-chip beam combining to the on-chip waveguide, or to couple the pump light input from off-chip to the on-chip waveguide, and to output the amplified signal light from the on-chip waveguide; At least one active multimode amplification waveguide is provided to support the transmission of the fundamental mode and at least one higher-order mode, and to optically amplify the signal light in the fundamental mode and the at least one higher-order mode under the action of pump light. A mode conversion component, comprising at least one mode multiplexer and at least one mode demultiplexer, wherein the mode multiplexer is used to convert signal light from a first mode to a second mode, and the mode demultiplexer is used to convert the amplified second mode back to the first mode or a target output mode. A loop waveguide, disposed between the mode demultiplexer and the mode multiplexer, is used to guide the signal light amplified in the previous stage to the mode conversion and amplification path in the next stage. The pump light is input from one or both ends of the active multimode amplification waveguide, and the signal light propagates in the active multimode amplification waveguide in at least two passes in the fundamental mode and at least one higher-order mode, and obtains optical gain respectively, so as to realize on-chip multi-pass optical amplification based on mode multiplexing. The signal light enters the active multimode amplification waveguide from the edge coupler assembly, is amplified in the active multimode amplification waveguide, passes through the mode demultiplexer and mode multiplexer in the mode conversion assembly, and the loop waveguide, completes multi-pass amplification in the active multimode amplification waveguide, and is output through the edge coupler assembly.

2. The on-chip waveguide multi-pass optical amplifier based on mode multiplexing according to claim 1, characterized in that: The fundamental mode and the at least one higher-order mode include two or more of the following modes: TE0 mode, TE1 mode, TE2 mode, TM0 mode, TM1 mode, and TM2 mode.

3. The on-chip waveguide multi-pass optical amplifier based on mode multiplexing according to claim 1, characterized in that: The first mode is a fundamental mode or a low-order mode, and the second mode is a high-order mode.

4. The on-chip waveguide multi-pass optical amplifier based on mode multiplexing according to claim 1, characterized in that: The active multimode amplification waveguide is made of an active gain material that can provide optical gain under the action of pump light.

5. The on-chip waveguide multi-pass optical amplifier based on mode multiplexing according to claim 4, characterized in that: The rare earth ions include one or more of erbium ions, ytterbium ions, thulium ions, neodymium ions, holmium ions, and praseodymium ions.

6. The on-chip waveguide multi-pass optical amplifier based on mode multiplexing according to claim 1, characterized in that: The waveguide width of the active multimode amplification waveguide is determined based on the transmission loss, effective mode area, and mode field confinement factor of the fundamental mode and the at least one higher-order mode, so that the fundamental mode and the at least one higher-order mode can both be transmitted in the active multimode amplification waveguide and obtain optical gain.

7. The on-chip waveguide multi-pass optical amplifier based on mode multiplexing according to claim 1, characterized in that: The active multimode amplification waveguide is a spiral waveguide structure, a serpentine waveguide structure, a folded waveguide structure, or a wraparound waveguide structure, in order to increase the effective amplification length within a limited chip area.

8. The on-chip waveguide multi-pass optical amplifier based on mode multiplexing according to claim 7, characterized in that: The active multimode amplification waveguide is a helical waveguide structure. Its helical center transition region adopts one or more of the following: a 180-degree Euler bend waveguide, a gradually curvature bend waveguide, or a circular arc bend waveguide, in order to reduce bending loss and suppress undesirable coupling between different modes.

9. The on-chip waveguide multi-pass optical amplifier based on mode multiplexing according to claim 1, characterized in that: The mode multiplexer and the mode demultiplexer are asymmetric directional couplers, multimode interference couplers, adiabatic mode converters, phase-matched mode converters, or combinations thereof.

10. The on-chip waveguide multi-pass optical amplifier based on mode multiplexing according to claim 1, characterized in that: The pump light and the signal light are combined off-chip by a beam combiner and then input to the on-chip waveguide through the same edge coupler.

11. The on-chip waveguide multi-pass optical amplifier based on mode multiplexing according to claim 1, characterized in that: The pump light is input from one end of the active multimode amplification waveguide to form a unidirectional pump structure.

12. The on-chip waveguide multi-pass optical amplifier based on mode multiplexing according to claim 1, characterized in that: The pump light is input from both ends of the active multimode amplified waveguide to form a bidirectional pump structure.

13. The on-chip waveguide multi-pass optical amplifier based on mode multiplexing according to claim 1, characterized in that: The signal light is amplified in the active multimode amplification waveguide in TE0 mode for the first pass, then converted to TE1 mode by a TE1 mode multiplexer for the second pass; the TE1 mode is converted to TE0 mode by a TE1 mode demultiplexer, then converted to TE2 mode by a TE2 mode multiplexer for the third pass; the TE2 mode is converted to TE0 mode by a TE2 mode demultiplexer for output.

14. A method for on-chip waveguide multi-pass optical amplification based on mode multiplexing, characterized in that, Includes the following steps: The pump light and signal light are combined off-chip and coupled to the on-chip waveguide via an edge coupler; alternatively, the signal light and the first pump light are combined off-chip and input from one end of the active multimode amplification waveguide via an edge coupler, while the second pump light is input from the other end of the active multimode amplification waveguide via another edge coupler; the signal light enters the active multimode amplification waveguide in its fundamental mode and undergoes first-pass optical amplification under the action of the pump light; the signal light after the first-pass amplification is converted into at least one higher-order mode by a mode conversion component; the at least one higher-order mode re-enters the active multimode amplification waveguide and undergoes second-pass optical amplification under the action of the pump light; as needed, the signal light is further converted into a higher-order mode and continues to undergo multi-pass optical amplification in the active multimode amplification waveguide; the finally amplified signal light is converted back into its fundamental mode output by a mode demultiplexer.

15. The on-chip waveguide multi-pass optical amplification method based on mode multiplexing according to claim 14, characterized in that: The signal light is amplified in the active multimode amplification waveguide in TE0 mode for the first pass, then converted to TE1 mode by a TE1 mode multiplexer for the second pass; the TE1 mode is converted to TE0 mode by a TE1 mode demultiplexer, then converted to TE2 mode by a TE2 mode multiplexer for the third pass; the TE2 mode is converted to TE0 mode by a TE2 mode demultiplexer for output.

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