On-chip wavelength adaptive multimode distribution weak feedback structure and line width compression device thereof

Abstract

The invention provides an on-chip wavelength adaptive multimode distribution weak feedback structure and a linewidth compression device thereof, the on-chip wavelength adaptive multimode distribution weak feedback structure comprises a spot-size converter and a multimode waveguide which are connected, and the spot-size converter converts first single-mode laser into multimode laser and transmits the multimode laser to the multimode waveguide; the multi-mode waveguide excites a high-order mode when transmitting the multi-mode laser to a non-uniform position of the multi-mode waveguide, and the multi-mode laser and the high-order mode laser generate scattered light signals reversely transmitted back to the spot-size converter in the process of transmitting along the multi-mode waveguide; the spot-size converter is used for converting the scattered light signal into second single-mode laser and outputting the second single-mode laser, so that the distribution weak feedback of the first single-mode laser is realized; the first single-mode laser is laser with any wavelength; and the cross section and the non-uniform characteristics of the multi-mode waveguide are designed to improve the strength and phase uniformity of scattered light signals, so that the weak distribution feedback effect is improved. According to the invention, a distribution weak feedback signal collection mode is expanded from a one-dimensional space to a two-dimensional space, and on-chip wavelength adaptive distribution weak feedback tuning can be realized.

Description

Technical Field

[0001] The invention belongs to the field of laser line width compression, and in particular relates to an on-chip wavelength adaptive multi-mode distributed weak feedback structure and a line width compression device thereof. Background Art

[0002] Wavelength adaptive distributed weak feedback is an advanced laser architecture that can deeply compress laser linewidth and suppress laser noise. The distributed weak feedback signal can continuously perturb and modify the phase information of the laser main cavity oscillation mode. It has the characteristics of non-wavelength selection and phase self-matching. It has great potential applications in narrow linewidth laser fields such as wavelength tuning, wavelength scanning, and multi-wavelength laser arrays. However, the wavelength adaptive distributed weak feedback laser architecture faces technical challenges in miniaturization and integration, mainly from two aspects: 1. At present, due to process problems, the silicon-based single-mode waveguide has high waveguide roughness, large scattering loss, and scattering is difficult to use, which makes it difficult to integrate the weak feedback structure on the chip. 2. The resonant cavity backscattering structure requires the laser wavelength to match the resonant wavelength of the resonant cavity. At present, external components can be used to tune the resonant wavelength of the resonant cavity to achieve wavelength adaptive distributed weak feedback tuning, but these external components cannot be integrated on the chip, so it is impossible to achieve on-chip wavelength adaptive distributed weak feedback tuning. Summary of the invention

[0003] The present invention provides an on-chip wavelength adaptive multi-mode distributed weak feedback structure and a linewidth compression device thereof, so as to solve the problem that the current distributed weak feedback structure cannot be integrated on-chip due to its large scattering loss, and the existing resonant wavelength tuning component of the distributed weak feedback structure cannot be integrated on-chip, thereby failing to realize on-chip wavelength adaptive distributed weak feedback tuning.

[0004] According to a first aspect of an embodiment of the present invention, there is provided an on-chip wavelength adaptive multimode distributed weak feedback structure, comprising a connected spot converter and a multimode waveguide, wherein the spot converter converts a first single-mode laser into a multimode laser and transmits it to the multimode waveguide; the multimode waveguide excites a high-order mode when transmitting the multimode laser to an uneven location thereof, and the multimode laser and the high-order mode laser generate a scattered light signal which is transmitted back to the spot converter in the process of being transmitted along the multimode waveguide; the spot converter converts the scattered light signal into a second single-mode laser output, thereby realizing distributed weak feedback of the first single-mode laser; the first single-mode laser is a laser of any wavelength;

[0005] The cross section and uneven features of the multimode waveguide are designed to improve the intensity and phase uniformity of the scattered light signal, thereby improving the distributed weak feedback effect.

[0006] In an optional implementation, the larger the cross-sectional area of ​​the multimode waveguide is, the greater the number of the high-order modes is, and the higher the phase uniformity of the scattered light signal is.

[0007] In another optional implementation, the larger the cross-sectional area of ​​the multimode waveguide is, the less contact the optical signal has with the edge of the multimode waveguide, the smaller the scattering loss is, and the greater the intensity of the back-scattered effective light signal is; however, if the cross-sectional area of ​​the multimode waveguide is too large, the order of the high-order mode will increase. When the scattering angle of the high-order mode laser is too large, the scattering loss will increase, the difficulty of collecting the scattered light signal will increase, and the intensity of the back-scattered effective light signal will decrease.

[0008] In another optional implementation, the space occupied by the multimode waveguide is reduced by bending the multimode waveguide; and for the bends of the multimode waveguide, the optical signal loss is reduced by at least one of reducing the radius of curvature and reducing the number of bends.

[0009] In another optional implementation, for the bends of the multimode waveguide, the larger the radius of curvature of the multimode waveguide, the smaller the bending loss and the smaller the optical signal loss; the fewer the number of bends of the multimode waveguide, the less contact the optical signal has with the edge of the multimode waveguide, the smaller the bending loss and the smaller the optical signal loss.

[0010] In another optional implementation, the multimode waveguide includes two spirally curved waveguides and an S-type waveguide. The two spirally curved waveguides are coiled around each other to form a "mosquito coil" shape, and the two spirally curved waveguides are spaced apart. The S-type waveguide is arranged inside the two spirally curved waveguides and its two ends are respectively connected to the inner ends of the two spirally curved waveguides, and the outer free end of one of the spirally curved waveguides is connected to the mode spot converter.

[0011] In another optional implementation, the outer free end of the other spirally curved waveguide is an inclined structure to avoid end face reflection; the multimode waveguide is a scattering enhanced multimode waveguide; and the cross-sectional area of ​​the mode spot converter gradually increases from the first end at which the first single-mode laser is input to the second end at which the multimode laser is output.

[0012] In another optional implementation, the two spirally curved waveguides are circular or square spiral structures.

[0013] According to a second aspect of the present invention, there is further provided a linewidth compression device, comprising a beam splitter, a gain chip and the above-mentioned on-chip wavelength adaptive multimode distributed weak feedback structure, wherein the gain chip is connected to a first end of the beam splitter, a second end of the beam splitter is connected to a mode spot converter in the on-chip wavelength adaptive multimode distributed weak feedback structure, and a third end serves as a linewidth compression output end;

[0014] The gain chip transmits the first single-mode laser to the spot converter through the beam splitter, the spot converter converts the first single-mode laser into a multi-mode laser, and the multi-mode waveguide in the on-chip wavelength adaptive multi-mode distributed weak feedback structure performs distributed weak feedback processing on the multi-mode laser to obtain a scattered light signal after line width compression that is transmitted back to the spot converter;

[0015] The mode spot converter converts the scattered light signal into a second single-mode laser and transmits it to the beam splitter. Thereafter, the beam splitter sends a portion of the second single-mode laser to the gain chip for gain amplification, and the other portion is output from the third end of the beam splitter, and this cycle is repeated until the line width compression balance is achieved.

[0016] In an optional implementation, a lens and an isolator are further included, and the third end of the beam splitter is connected to the isolator through the lens.

[0017] The beneficial effects of the present invention are:

[0018] 1. The present invention provides a mode spot converter, which converts the single-mode laser into a multi-mode laser before inputting the single-mode laser into the multi-mode waveguide, thereby reducing the loss of the input single-mode laser; compared with the single-mode laser distributed weak feedback, the present invention adopts the multi-mode laser distributed weak feedback to improve the phase uniformity of the generated scattered light signal; the multi-mode laser generates a high-order mode laser during the transmission process of the multi-mode waveguide, and the high-order mode laser is transmitted along the multi-mode waveguide together with the multi-mode laser, and a scattered light signal is generated during the transmission process, thereby further improving the intensity and phase uniformity of the scattered light signal, and by designing the cross-section and unevenness characteristics of the multi-mode waveguide, the intensity and phase uniformity of the scattered light signal can be further improved. The present invention has a high uniformity of position, and thus the distributed weak feedback signal collection method is extended from one-dimensional space to two-dimensional space, which greatly shortens the physical length of the required waveguide (i.e., greatly improves the distributed weak feedback effect of the multimode waveguide per unit length), and at the same time ensures the randomness and uniformity of the feedback signal phase, making it possible to integrate the distributed weak feedback structure on-chip; the first single-mode laser input by the present invention can be a laser of any wavelength, and the present invention can convert a single-mode laser of any wavelength into a multi-mode laser, and then perform distributed weak feedback processing on the multi-mode laser, thereby realizing distributed weak feedback of a single-mode laser of any wavelength, and the present invention does not need to rely on an external wavelength tuning component that cannot be integrated on-chip, so on-chip wavelength adaptive distributed weak feedback tuning can be realized;

[0019] The present invention can reduce the contact between the optical signal and the edge of the multimode waveguide by designing the cross-sectional area of ​​the multimode waveguide, thereby reducing the scattering loss caused by the roughness of the waveguide edge; when the present invention realizes distributed weak feedback, the multimode laser is propagated in the multimode waveguide, and the laser power is dispersed into different modes during the propagation process, thereby reducing the energy density and avoiding excessive single-point feedback power, which destroys the dynamic balance of distributed feedback; in addition, different modes have different equivalent optical paths, and multi-phase feedback can be realized at the same feedback point, reducing the requirements and process difficulty of scattering processing;

[0020] 2. The present invention designs the arrangement of the multimode waveguide according to the bending design rules of the multimode waveguide, so that the multimode waveguide includes two spirally curved waveguides and an S-shaped waveguide, the two spirally curved waveguides are coiled together to form a "mosquito-repellent coil" shape, and the S-shaped waveguide is arranged inside the two spirally curved waveguides and its two ends are respectively connected to the inner ends of the two spirally curved waveguides. In this way, while improving the weak feedback effect of the multimode waveguide distribution per unit length, the space occupied by the multimode waveguide of the same length can be reduced, and the optical loss caused by the arrangement of the multimode waveguide can be minimized;

[0021] 3. The present invention sets the outer free end of another spiral curved waveguide in the multimode waveguide as an inclined structure, which can avoid end face reflection; the present invention adopts a scattering-enhanced multimode waveguide, which can further improve the distributed weak feedback effect per unit length; the present invention makes the geometric structure of the mode spot converter satisfy a gradual function in the laser transmission direction, so that the cross-sectional area of ​​the mode spot converter gradually increases along the direction from single mode to multimode, which can improve the collection efficiency of backscattering;

[0022] 4. The present invention designs the arrangement of the multimode waveguide into a square spiral arrangement. Compared with the circular spiral arrangement, the square spiral arrangement has a higher degree of spatial integration, and a longer multimode waveguide can be integrated in the same area. In addition, compared with the circular spiral arrangement, the optical signal in the square spiral arrangement has less contact with the edge of the multimode waveguide, and the scattering loss is lower;

[0023] 5. The present invention applies the on-chip wavelength adaptive multi-mode distributed weak feedback structure to the linewidth compression scenario, which can improve the linewidth compression effect and realize on-chip linewidth compression. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic structural diagram of an embodiment of the on-chip wavelength adaptive multi-mode distributed weak feedback structure of the present invention;

[0025] Figure 2 It is a schematic structural diagram of another embodiment of the on-chip wavelength adaptive multi-mode distributed weak feedback structure of the present invention;

[0026] Figure 3 yes Figure 2Schematic diagram of light field distribution of the on-chip wavelength adaptive multi-mode distributed weak feedback structure;

[0027] Figure 4 is a schematic structural diagram of the outer free end of another spirally curved waveguide in the multimode waveguide of the present invention;

[0028] Figure 5 It is a schematic diagram of the structure of the scattering enhanced multimode waveguide of the present invention;

[0029] Figure 6 It is a structural schematic diagram of the pattern spot converter of the present invention;

[0030] Figure 7 yes Figure 2 A schematic diagram of the chip structure of the on-chip wavelength adaptive multi-mode distributed weak feedback structure is shown;

[0031] Figure 8 It is a structural schematic diagram of another embodiment of the on-chip wavelength adaptive multi-mode distributed weak feedback structure of the present invention;

[0032] Fig. 9 It is a schematic structural diagram of the line width compression device of the present invention. DETAILED DESCRIPTION

[0033] In order to enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention and to make the above-mentioned purposes, features and advantages of the embodiments of the present invention more obvious and understandable, the technical solutions in the embodiments of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0034] In the description of the present invention, unless otherwise specified and limited, it should be noted that the term "connection" should be understood in a broad sense. For example, it can be a mechanical connection or an electrical connection, or it can be the internal connection between two elements. It can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0035] See also Figure 1, is a schematic diagram of an embodiment of the on-chip wavelength adaptive multi-mode distributed weak feedback structure of the present invention. The on-chip wavelength adaptive multi-mode distributed weak feedback structure may include a connected spot converter 1 and a multi-mode waveguide 2, wherein the spot converter 1 converts a first single-mode laser into a multi-mode laser and transmits it to the multi-mode waveguide 2; the multi-mode waveguide 2 excites a high-order mode when transmitting the multi-mode laser to its uneven location, and the multi-mode laser and the high-order mode laser generate a scattered light signal that is transmitted back to the spot converter 1 during the transmission along the multi-mode waveguide 2; the spot converter 1 converts the scattered light signal into a second single-mode laser output, thereby realizing the distributed weak feedback of the first single-mode laser; the first single-mode laser can be a laser of any wavelength; the cross section and uneven location features of the multi-mode waveguide are designed to improve the intensity and phase uniformity of the scattered light signal, thereby improving the distributed weak feedback effect.

[0036] In this embodiment, the cross section of the multimode waveguide can be rectangular (i.e., strip waveguide) or "convex" (i.e., ridge waveguide), and the cross section of the multimode waveguide can be the same at all locations along the line. The mode spot converter and the multimode waveguide can both be arranged on a chip.

[0037] The mode spot converter can be arranged between the single-mode waveguide and the multi-mode waveguide, and it has two functions: one is to match the mode field of the single-mode waveguide and the multi-mode waveguide, and convert the first single-mode laser received by it into a multi-mode laser; the other is to facilitate the collection of the scattered light signal transmitted back in the reverse direction, and convert the received scattered light signal into the second single-mode laser output. When the distributed weak feedback structure is integrated on the chip, due to the limitation of the process, the roughness of the single-mode waveguide is high and the scattering loss is large. In order to achieve the corresponding distributed weak feedback effect, a longer single-mode waveguide needs to be set, which cannot be integrated on the chip. For this reason, the present invention proposes to use a multi-mode waveguide to perform distributed weak feedback processing on the single-mode laser. At this time, if the single-mode laser is directly input into the multi-mode waveguide, the mode field mutation will cause the divergence angle of the single-mode laser to be too large, thereby causing a large loss of the single-mode laser. Therefore, the present invention sets a mode spot converter before the multi-mode waveguide, and the mode spot converter converts the first single-mode laser into a multi-mode laser to reduce the loss of the input single-mode laser.

[0038] The present invention can design the cross section of the multimode waveguide so that the multimode waveguide itself has the conditions for multimode transmission, so that the multimode laser can be transmitted along the multimode waveguide. The present invention also provides a waveguide unevenness on the multimode waveguide. When the multimode laser is transmitted to the unevenness, the high-order mode excited by the high-order mode laser is transmitted in the multimode waveguide together with the multimode laser input into the multimode waveguide. During the transmission process, a backscattered light signal (such as a Rayleigh scattered light signal) is generated. The scattered light signal is transmitted to the mode spot converter and converted into a second single-mode laser output by the mode spot converter. By converting the input single-mode laser into a multimode laser and using a multimode waveguide to perform distributed weak feedback processing on the multimode laser, the intensity and phase uniformity of the scattered light signal can be improved, thereby improving the distributed weak feedback effect. In order to improve the intensity and phase uniformity of the scattered light signal, the cross section and unevenness characteristics of the multimode waveguide can be designed.

[0039] Among them, the larger the cross-sectional area of ​​the multimode waveguide, the more the number of the high-order modes, and the higher the phase randomness and uniformity of the scattered light signal. The larger the cross-sectional area of ​​the multimode waveguide, the less the optical signal (including the multimode laser, the high-order mode laser and the scattered light signal) contacts the edge of the multimode waveguide, the smaller the scattering loss (the scattering loss can be caused by the optical signal being transmitted to the rough edge of the waveguide), and the greater the intensity of the back-scattered effective light signal; but when the cross-sectional area of ​​the multimode waveguide is too large, the order of the high-order mode increases, and when the scattering angle of the high-order mode laser is too large, the scattering loss increases, the difficulty of collecting the scattered light signal increases, and the intensity of the back-scattered effective light signal decreases. It can be seen that the larger the cross-sectional area of ​​the multimode waveguide is, the better. When designing the cross-sectional area of ​​the multimode waveguide, it is necessary to consider the effect of the cross-sectional area on the phase uniformity and intensity of the scattered light signal.

[0040] In addition, the present invention can arrange the multimode waveguide by bending the multimode waveguide, thereby reducing the space occupied by the multimode waveguide; for the bends of the multimode waveguide, the optical loss can be reduced by adopting at least one of reducing the radius of curvature and reducing the number of bends. Specifically, for the bends of the multimode waveguide, the larger the radius of curvature of the multimode waveguide, the smaller the bending loss and the smaller the optical loss; the fewer the number of bends of the multimode waveguide, the less contact the optical signal has with the edge of the multimode waveguide, the smaller the bending loss and the smaller the optical loss. At this point, the arrangement of the multimode waveguide can be designed according to the above-mentioned multimode waveguide bending design principles to ensure that a longer multimode waveguide is integrated in a smaller on-chip space, while minimizing the optical loss caused by the arrangement of the multimode waveguide.

[0041] It can be seen from the above embodiments that the present invention sets a mode spot converter, and the mode spot converter converts the single-mode laser into a multi-mode laser before inputting the single-mode laser into the multi-mode waveguide, so that the loss of the input single-mode laser can be reduced; compared with the single-mode laser distributed weak feedback, the present invention adopts multi-mode laser distributed weak feedback to improve the phase uniformity of the generated scattered light signal; the multi-mode laser will generate a high-order mode laser during the transmission process of the multi-mode waveguide, and the high-order mode laser will be transmitted along the multi-mode waveguide together with the multi-mode laser, and a scattered light signal will be generated during the transmission process, so that the intensity and phase uniformity of the scattered light signal can be further improved, and by designing the cross-section and uneven characteristics of the multi-mode waveguide, the intensity of the scattered light signal can be further improved. The invention improves the uniformity of the distributed weak feedback signal and the phase uniformity, thereby expanding the distributed weak feedback signal collection method from one-dimensional space to two-dimensional space, greatly shortening the physical length of the required waveguide (i.e., greatly improving the distributed weak feedback effect of the multi-mode waveguide per unit length), while ensuring the randomness and uniformity of the feedback signal phase, making it possible to integrate the distributed weak feedback structure on-chip; the first single-mode laser input by the invention can be a laser of any wavelength, and the invention can convert a single-mode laser of any wavelength into a multi-mode laser, and then perform distributed weak feedback processing on the multi-mode laser, thereby realizing distributed weak feedback of a single-mode laser of any wavelength, and the invention does not need to rely on an external wavelength tuning component that cannot be integrated on-chip, and thus can realize on-chip wavelength adaptive distributed weak feedback tuning.

[0042] The present invention can reduce the contact between the optical signal and the edge of the multimode waveguide and reduce the scattering loss caused by the roughness of the waveguide edge by designing the cross-sectional area of ​​the multimode waveguide; when the present invention realizes distributed weak feedback, the multimode laser is propagated in the multimode waveguide, and the laser power is dispersed into different modes during the propagation process, thereby reducing the energy density and avoiding excessive single-point feedback power, which destroys the dynamic balance of distributed feedback; in addition, different modes have different equivalent optical paths, and multi-phase feedback can be realized at the same feedback point, reducing the requirements and process difficulty of scattering processing.

[0043] See also Figure 2 , is a flow chart of another embodiment of the on-chip wavelength adaptive multi-mode distributed weak feedback structure of the present invention. Figure 2 and Figure 1The difference between the on-chip wavelength adaptive multimode distributed weak feedback structure shown is that the multimode waveguide 2 may include two spirally curved waveguides 21 and an S-type waveguide 22. The two spirally curved waveguides 21 are coiled around each other in a "mosquito coil" shape. The two spirally curved waveguides 21 are arranged at intervals. The S-type waveguide 22 is arranged inside the two spirally curved waveguides 21 and its two ends are respectively connected to the inner ends of the two spirally curved waveguides 21. The outer free end 23 of one of the spirally curved waveguides 21 is connected to the mode spot converter 1. It should be noted that if the interval between the two spirally curved waveguides 21 is too large, it will affect the integration of the multimode waveguide, while if it is too small, optical signal coupling will occur, resulting in large losses. Therefore, the interval between the two spirally curved waveguides must be large enough to avoid crosstalk during optical signal transmission. The light field distribution diagram of this embodiment is shown in the figure below. Figure 3 shown.

[0044] Figure 2 and Figure 1 The difference of the on-chip wavelength adaptive multimode distributed weak feedback structure is that, combined with Figures 4 to 6 As shown, the outer free end 24 of another spirally curved waveguide in the multimode waveguide 2 is an inclined structure (for example, an inclined surface formed by shearing) to avoid end face reflection; the multimode waveguide can be a scattering enhanced multimode waveguide (for example, a femtosecond laser or ion implantation technology can be used to perform scattering enhancement processing on an ordinary multimode waveguide to form Figure 5 The cross-sectional area of ​​the spot converter gradually increases from the first end where the first single-mode laser is input to the second end where the multi-mode laser is output. The present invention makes the geometric structure of the spot converter satisfy a gradient function in the direction of laser transmission, so that the cross-sectional area of ​​the spot converter gradually increases along the direction from single mode to multi-mode, which can improve the collection efficiency of backscattering. In this embodiment, the two spirally curved waveguides can be circular spiral structures, and combined with Figure 7 As shown, the mode spot converter 1 and the multimode waveguide 2 can be fixed on the insulating layer 3 of the chip, and then the oxide layer 4 is used to package the mode spot converter 1 and the multimode waveguide 2, thereby improving the structural integration and stability.

[0045] It can be seen from the above embodiments that the present invention sets a mode spot converter, and the mode spot converter converts the single-mode laser into a multi-mode laser before inputting the single-mode laser into the multi-mode waveguide, so that the loss of the input single-mode laser can be reduced; compared with the single-mode laser distributed weak feedback, the present invention adopts multi-mode laser distributed weak feedback to improve the phase uniformity of the generated scattered light signal; the multi-mode laser will generate a high-order mode laser during the transmission process of the multi-mode waveguide, and the high-order mode laser will be transmitted along the multi-mode waveguide together with the multi-mode laser, and a scattered light signal will be generated during the transmission process, so that the intensity and phase uniformity of the scattered light signal can be further improved, and by designing the cross-section and uneven characteristics of the multi-mode waveguide, the intensity of the scattered light signal can be further improved. The invention improves the uniformity of the distributed weak feedback signal and the phase uniformity, thereby expanding the distributed weak feedback signal collection method from one-dimensional space to two-dimensional space, greatly shortening the physical length of the required waveguide (i.e., greatly improving the distributed weak feedback effect of the multi-mode waveguide per unit length), while ensuring the randomness and uniformity of the feedback signal phase, making it possible to integrate the distributed weak feedback structure on-chip; the first single-mode laser input by the invention can be a laser of any wavelength, and the invention can convert a single-mode laser of any wavelength into a multi-mode laser, and then perform distributed weak feedback processing on the multi-mode laser, thereby realizing distributed weak feedback of a single-mode laser of any wavelength, and the invention does not need to rely on an external wavelength tuning component that cannot be integrated on-chip, and thus can realize on-chip wavelength adaptive distributed weak feedback tuning.

[0046] The present invention can reduce the contact between the optical signal and the edge of the multimode waveguide and reduce the scattering loss caused by the roughness of the waveguide edge by designing the cross-sectional area of ​​the multimode waveguide; when the present invention realizes distributed weak feedback, the multimode laser is propagated in the multimode waveguide, and the laser power is dispersed into different modes during the propagation process, thereby reducing the energy density and avoiding excessive single-point feedback power, which destroys the dynamic balance of distributed feedback; in addition, different modes have different equivalent optical paths, and multi-phase feedback can be realized at the same feedback point, reducing the requirements and process difficulty of scattering processing.

[0047] In addition, the present invention designs the arrangement of the multimode waveguide according to the multimode waveguide bending design rules, so that the multimode waveguide includes two spirally curved waveguides and an S-type waveguide, the two spirally curved waveguides are coiled around each other in a "mosquito coil" shape, and the S-type waveguide is arranged inside the two spirally curved waveguides and its two ends are respectively connected to the inner ends of the two spirally curved waveguides. In this way, while improving the weak feedback effect of the multimode waveguide distribution per unit length, the space occupied by the multimode waveguide of the same length can be reduced, and at the same time, the optical loss caused by the arrangement of the multimode waveguide is minimized.

[0048] See also Figure 8 , which is a flow chart of another embodiment of the on-chip wavelength adaptive multi-mode distributed weak feedback structure of the present invention. Figure 8 and Figure 2 The difference between the on-chip wavelength adaptive multimode distributed weak feedback structure shown is that the two spiral curved waveguides are square spiral structures. The present invention designs the arrangement of the multimode waveguide into a square spiral arrangement. Compared with the circular spiral arrangement, the spatial integration of the square spiral arrangement is higher, and the same area can integrate longer multimode waveguides. Compared with the circular spiral arrangement, the square spiral arrangement has less contact between the optical signal and the edge of the multimode waveguide, and the scattering loss is lower. In addition, the waveguide radius changes more smoothly under the circular spiral arrangement, which can reduce the excitation of high-order modes and is more suitable for certain applications requiring large mode field single-mode.

[0049] In addition, the present invention also provides a line width compression device, such as Fig. 9 As shown, it may include a beam splitter 5, a gain chip 6 and the above-mentioned on-chip wavelength adaptive multi-mode distributed weak feedback structure 7, wherein the gain chip 6 is connected to the first end of the beam splitter 5, the second end of the beam splitter 5 is connected to the mode spot converter 1 in the on-chip wavelength adaptive multi-mode distributed weak feedback structure 7, and the third end serves as the line width compression output end; the gain chip 6 transmits the first single-mode laser to the mode spot converter 1 through the beam splitter 5, the mode spot converter 1 converts the first single-mode laser into a multi-mode laser, and the multi-mode waveguide 2 in the on-chip wavelength adaptive multi-mode distributed weak feedback structure 7 performs distributed weak feedback processing on the multi-mode laser to obtain a scattered light signal after line width compression that is transmitted back to the mode spot converter 1; the mode spot converter 1 converts the scattered light signal into a second single-mode laser and transmits it to the beam splitter 5, after which the beam splitter 5 sends a part of the second single-mode laser to the gain chip 6 for gain amplification, and the other part is output from the third end of the beam splitter 5, and this cycle is repeated until the line width compression balance is reached. The line width compression device may further include a lens 8 and an isolator 9 , and the third end of the beam splitter 5 is connected to the isolator 9 via the lens 8 .

[0050] It can be seen from the above embodiments that the present invention applies the on-chip wavelength adaptive multi-mode distributed weak feedback structure to the linewidth compression scenario, which can improve the linewidth compression effect and realize on-chip linewidth compression.

[0051] Those skilled in the art will readily appreciate other embodiments of the present invention after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses or adaptations of the present invention that follow the general principles of the present invention and include common knowledge or customary techniques in the art that are not disclosed by the present invention. The specification and examples are to be considered exemplary only, and the true scope and spirit of the present invention are indicated by the following claims.

[0052] It will be appreciated that the invention is not limited to the precise construction that has been described above and shown in the drawings and that various modifications and changes may be made without departing from its scope. The scope of the invention is governed solely by the appended claims.

Claims

1. An on-chip wavelength adaptive multi-mode distributed weak feedback structure, characterized in that: It comprises a mode spot converter and a multimode waveguide connected to each other, wherein the mode spot converter converts a first single-mode laser into a multimode laser and transmits it to the multimode waveguide; the multimode waveguide excites a high-order mode when transmitting the multimode laser to its uneven location, and the multimode laser and the high-order mode laser generate a scattered light signal which is transmitted back to the mode spot converter in the process of being transmitted along the multimode waveguide; the mode spot converter converts the scattered light signal into a second single-mode laser output, thereby realizing distributed weak feedback of the first single-mode laser; the first single-mode laser is a laser of any wavelength; The cross section and uneven features of the multimode waveguide are designed to improve the intensity and phase uniformity of the scattered light signal, thereby improving the distributed weak feedback effect.

2. The on-chip wavelength adaptive multimode distributed weak feedback structure according to claim 1, characterized in that: The larger the cross-sectional area of ​​the multimode waveguide is, the greater the number of the high-order modes is, and the higher the phase uniformity of the scattered light signal is.

3. The on-chip wavelength adaptive multimode distributed weak feedback structure according to claim 2, characterized in that: The larger the cross-sectional area of ​​the multimode waveguide, the less contact the optical signal has with the edge of the multimode waveguide, the smaller the scattering loss, and the greater the intensity of the back-scattered effective optical signal; however, if the cross-sectional area of ​​the multimode waveguide is too large, the order of the high-order mode will increase. When the scattering angle of the high-order mode laser is too large, the scattering loss will increase, the difficulty of collecting the scattered optical signal will increase, and the intensity of the back-scattered effective optical signal will decrease.

4. The on-chip wavelength adaptive multimode distributed weak feedback structure according to claim 3, characterized in that: The space occupied by the multimode waveguide is reduced by bending the multimode waveguide; and the optical loss is reduced by at least one of reducing the radius of curvature and reducing the number of bends at the bends of the multimode waveguide.

5. The on-chip wavelength adaptive multi-mode distributed weak feedback structure according to claim 4, characterized in that: For the bending part of the multimode waveguide, the larger the curvature radius of the multimode waveguide, the smaller the bending loss and the smaller the optical loss; the fewer the number of bends of the multimode waveguide, the less contact the optical signal has with the edge of the multimode waveguide, the smaller the bending loss and the smaller the optical loss.

6. The on-chip wavelength adaptive multi-mode distributed weak feedback structure according to any one of claims 1 to 5, characterized in that: The multimode waveguide includes two spirally curved waveguides and an S-shaped waveguide. The two spirally curved waveguides are coiled around each other to form a "mosquito coil" shape. The two spirally curved waveguides are arranged at an interval. The S-shaped waveguide is arranged inside the two spirally curved waveguides and its two ends are respectively connected to the inner ends of the two spirally curved waveguides. The outer free end of one of the spirally curved waveguides is connected to the mode spot converter.

7. The on-chip wavelength adaptive multimode distributed weak feedback structure according to claim 6, characterized in that: The outer free end of the other spirally curved waveguide is an inclined structure to avoid end face reflection; the multimode waveguide is a scattering enhanced multimode waveguide; the cross-sectional area of ​​the mode spot converter gradually increases from the first end where the first single-mode laser is input to the second end where the multimode laser is output.

8. The on-chip wavelength adaptive multi-mode distributed weak feedback structure according to claim 6, characterized in that: The two spirally curved waveguides are circular or square spiral structures.

9. A line width compression device, characterized in that: It comprises a beam splitter, a gain chip and the on-chip wavelength adaptive multi-mode distributed weak feedback structure according to any one of claims 1 to 8, wherein the gain chip is connected to a first end of the beam splitter, a second end of the beam splitter is connected to a mode spot converter in the on-chip wavelength adaptive multi-mode distributed weak feedback structure, and a third end is used as a line width compression output end; The gain chip transmits the first single-mode laser to the spot converter through the beam splitter, the spot converter converts the first single-mode laser into a multi-mode laser, and the multi-mode waveguide in the on-chip wavelength adaptive multi-mode distributed weak feedback structure performs distributed weak feedback processing on the multi-mode laser to obtain a scattered light signal after line width compression that is transmitted back to the spot converter; The mode spot converter converts the scattered light signal into a second single-mode laser and transmits it to the beam splitter. Thereafter, the beam splitter sends a portion of the second single-mode laser to the gain chip for gain amplification, and the other portion is output from the third end of the beam splitter, and this cycle is repeated until the line width compression balance is achieved.

10. The line width compression device according to claim 9, characterized in that: It also includes a lens and an isolator, and the third end of the beam splitter is connected to the isolator through the lens.

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