External cavity chip, tunable external cavity laser and laser radar

Abstract

The invention is suitable for the technical field of laser radars, and provides an external cavity chip, a tunable external cavity laser and a laser radar. The outer cavity chip comprises an input coupler, a plurality of optical switches and a plurality of outer cavity loops which are sequentially communicated through an optical path; wherein the input coupler is used for coupling an optical signal provided by an external light source into the external cavity chip; the plurality of optical switches are provided with a plurality of signal output ends; each outer cavity loop comprises a resonance module, the resonance module comprises a plurality of tunable micro-ring resonant cavities, the plurality of tunable micro-ring resonant cavities are sequentially cascaded through a connecting module to form a cascade structure, and a vernier effect can be formed between every two adjacent tunable micro-ring resonant cavities; and the plurality of optical switches are used for switching to any external cavity loop, so that optical signals are emitted through the external cavity loop. According to the external cavity chip, the tunable external cavity laser and the laser radar provided by the invention, the modulation rate and the wavelength switching rate can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lidar, and particularly relates to an external cavity chip, a tunable external cavity laser, and a lidar. Background Art

[0002] In current photon applications, the silicon-based tunable external cavity semiconductor laser, known for its ultra-small size, easy integration, excellent performance, and convenient modulation, is an important choice for the light source of integrated systems that cannot be ignored. The structure of a conventional silicon-based external cavity semiconductor laser consists of a gain chip or a reflective semiconductor optical amplifier (SOA) and a silicon-based integrated external cavity, enabling it to meet the three elements of a laser: a pump source, a resonator cavity, and a gain medium. Among them, the gain chip provides pumping for the entire laser and operates as a gain medium; the silicon-based integrated external cavity serves as the wavelength selection part, providing selective feedback for the broadband laser provided by the gain chip, and only the light that meets a specific wavelength can return to the gain medium. Wavelength selection is usually achieved by using a structure based on a reflective grating or by using the Vernier Effect of two micro-ring resonators (MRRs). By adjusting the refractive index of the optical devices in the structure based on the thermo-optic effect or the electro-optic effect, wavelength tuning can be realized. At the same time, the ultra-high reflection at the non-light-emitting end of the gain chip and the reflection of the silicon-based external cavity form the overall optical resonator. When the optical gain provided by the gain medium is greater than the optical loss of the overall resonator, the external cavity laser can achieve wavelength-selective laser emission. The performance of a silicon-based tunable external cavity semiconductor laser, such as its modulation rate, wavelength switching speed, linewidth, and wavelength tuning range, is highly related to the optical characteristics of the silicon-based external cavity.

[0003] Generally, silicon-based external cavity semiconductor lasers are tuned based on the thermo-optic effect of silicon or silicon nitride. Modulators based on the thermo-optic effect of silicon waveguides have a relatively higher modulation rate and a relatively faster wavelength switching speed. However, silicon waveguides usually have large losses and suffer from effects such as two-photon absorption, which greatly limit parameters such as the output laser linewidth and side mode suppression ratio of external cavity lasers based on silicon waveguides. Although the loss of external cavity lasers based on silicon nitride waveguides is smaller than that of silicon waveguides, the modulator based on the thermo-optic effect of silicon nitride waveguides has a slow modulation rate and it is difficult to meet the requirement of the wavelength switching speed needed for FMCW (Frequency Modulated Continuous Wave) ranging. Of course, there are still various implementation schemes nowadays. For example, modulators based on the electro-optic effect of silicon have an extremely fast modulation rate but also introduce large losses; ultra-high-speed modulators based on lithium niobate thin films are limited by the development of technology and are difficult to be used on a large scale; in addition, there are also high-speed modulators based on piezoelectric ceramics, and the technology is not yet mature. Therefore, under the existing technological level, how to improve the wavelength switching speed of silicon-based tunable external cavity semiconductor lasers is an urgent problem to be solved. Summary of the Invention

[0004] The purpose of the present invention is to provide an external cavity chip, a tunable external cavity laser, and a lidar, aiming to improve the wavelength switching speed of silicon-based tunable external cavity semiconductor lasers.

[0005] The present invention is implemented as follows. In the first aspect, an external cavity chip is provided, which includes an input coupler, a plurality of optical switches, and a plurality of external cavity loops that are optically connected in sequence.

[0006] Among them, the input coupler is used to couple the optical signal provided by an external light source into the external cavity chip.

[0007] The plurality of optical switches have a plurality of signal output terminals.

[0008] The plurality of external cavity loops are connected to the plurality of signal output terminals in a one-to-one correspondence; each external cavity loop includes a resonance module, and the resonance module includes a plurality of tunable microring resonators. The plurality of tunable microring resonators are cascaded in sequence through a connection module to form a cascaded structure, and a Vernier effect can be formed between adjacent two tunable microring resonators.

[0009] The plurality of optical switches are used to switch to any one of the external cavity loops, so that the optical signal exits through the external cavity loop.

[0010] In some embodiments, the optical switch includes a Mach-Zehnder interferometer. Each Mach-Zehnder interferometer has two signal output terminals, and at least one arm of the Mach-Zehnder interferometer is provided with a first phase shifter.

[0011] In some embodiments, the first phase shifter is a thin-film lithium niobate electro-optic modulator based on heterogeneous integration, a compressive stress modulator based on piezoelectric ceramics, a thermo-optic phase shifter based on a silicon waveguide, or an electro-optic phase shifter based on a silicon waveguide.

[0012] In some embodiments, the external cavity loop further includes a second phase shifter connecting the signal output end and the resonant module.

[0013] In some embodiments, the second phase shifter is a thin-film lithium niobate electro-optic modulator based on heterogeneous integration, a compressive stress modulator based on piezoelectric ceramics, a thermo-optic phase shifter based on a silicon waveguide, or an electro-optic phase shifter based on a silicon waveguide.

[0014] In some embodiments, the connection module includes: a waveguide; or, a combined structure of a waveguide and one of the tunable microring resonators.

[0015] In some embodiments, the external cavity loop further includes a second directional coupler and an output coupler;

[0016] The second directional coupler receives the optical signal and provides it to the resonant module, selects the optical signal through the resonant module, and couples out the selected optical signal successively through the second directional coupler and the output coupler.

[0017] In some embodiments, the second directional coupler is a 2×2 directional coupler;

[0018] Among them, the optical signal received through the first end of the second directional coupler is split into two input light beams in the second directional coupler; one of the input light beams is successively coupled into the resonant module through the second end of the second directional coupler and the first end of the resonant module, and after passing through the cascaded structure of the resonant module, it is coupled into the second directional coupler through the second end of the resonant module and the third end of the second directional coupler, and is provided to the output coupler by the fourth end of the second directional coupler; the other input light beam is successively coupled into the resonant module through the third end of the second directional coupler and the second end of the resonant module, and after passing through the cascaded structure of the resonant module, it is coupled into the second directional coupler through the first end of the resonant module and the second end of the second directional coupler, and is provided to the output coupler by the fourth end of the second directional coupler.

[0019] In some embodiments, the external cavity loop further includes a Sagnac loop;

[0020] The first end of the resonant module is coupled to the signal output end through a waveguide, and the second end of the resonant module is coupled to the Sagnac loop.

[0021] In some embodiments, the cascaded structure is a two-stage cascaded structure, which is composed of two tunable microring resonators. There is a difference in the cavity lengths of the two tunable microring resonators, and the cavity lengths of the two tunable microring resonators are both integer multiples of the difference.

[0022] In some embodiments, the cascaded structure is a cascaded structure formed by cascading 3 or more of the above-mentioned tunable microring resonators in sequence, and the differences in the cavity lengths of every two adjacent tunable microring resonators are all different.

[0023] In a second aspect, a tunable external cavity laser is provided, which includes a light source and the external cavity chip provided in any of the above embodiments, wherein the light source is used to provide an optical signal for the external cavity chip.

[0024] In some embodiments, the light source is a semiconductor optical amplifier; one end of the light source facing away from the external cavity chip has a high reflectivity, with a reflectivity ≥ 90%, and the output end has a low reflectivity, with a reflectivity ≤ 0.01%; the gain wavelength of the light source is in the communication band.

[0025] In a third aspect, a lidar is provided, which includes a laser module, a transmitting module, a detecting module, a detecting module, and a data processing module, wherein the laser module includes the tunable external cavity laser provided in any of the above embodiments.

[0026] The technical effect of the first aspect of the present invention relative to the prior art is that an optical switch with a modulation rate much higher than that of the resonant module can improve the wavelength switching speed to a certain extent. Applying the external cavity chip provided in the embodiments of the present invention can enable a silicon-based tunable semiconductor laser to meet the usage requirements in fields such as FMCW ranging and phased array lidar.

[0027] It can be understood that the beneficial effects of the above second aspect to the third aspect can refer to the relevant descriptions in the above first aspect, and will not be elaborated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for describing the embodiments of the present invention or the prior art. Obviously, the following described drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0029] Figure 1 is a schematic structural diagram of the tunable external cavity laser provided by the embodiment of the present invention;

[0030] Figure 2It is a schematic structural diagram of an optical switch in a tunable external cavity laser provided by an embodiment of the present invention;

[0031] Figure 3 It is a schematic diagram of the transmittance change of an optical switch in a tunable external cavity laser provided by an embodiment of the present invention;

[0032] Figure 4 It is a schematic diagram of the working principle of a tunable external cavity laser provided by an embodiment of the present invention;

[0033] Figure 5 It is a schematic structural diagram of an external cavity loop in a tunable external cavity laser provided by an embodiment of the present invention;

[0034] Figure 6 It is a schematic structural diagram of an external cavity loop in a tunable external cavity laser provided by another embodiment of the present invention;

[0035] Figure 7 It is a schematic structural diagram of an external cavity loop in a tunable external cavity laser provided by another embodiment of the present invention;

[0036] Figure 8 It is a schematic structural diagram of an external cavity loop in a tunable external cavity laser provided by another embodiment of the present invention.

[0037] Description of reference numerals:

[0038] 100, external cavity chip; 110, input coupler; 120, optical switch array; 121, Mach-Zehnder interferometer; 122, signal output terminal; 123, first phase shifter; 124, first directional coupler; 130, external cavity loop array; 130a, external cavity loop; 131, tunable microring resonator; 132, connection module; 133, second directional coupler; 134, output coupler; 135, Sagnac loop; 140, second phase shifter; 200, light source. Detailed description of the specific implementation

[0039] The embodiments of the present invention will be described in detail below. Examples of the embodiments are shown in the drawings, where the same or similar reference numerals denote the same or similar elements or elements with the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are intended to explain the present invention and should not be construed as limiting the present invention.

[0040] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "length", "width", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be construed as a limitation to the present invention.

[0041] In addition, the terms "first" and "second" are only used for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present invention, "a plurality of" means two or more unless otherwise specifically defined.

[0042] In the present invention, unless otherwise clearly specified and limited, the terms "mounted", "connected", "connected to", "fixed", etc. should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0043] In order to make the purpose, technical solution and advantages of the present invention more clear and understandable, the present invention will be further described in detail below with reference to the drawings and embodiments.

[0044] A lidar generally includes a transmitting module and a detecting module. The transmitting module includes a laser light source and a transmitting optical system. Depending on its type, different lasers can be used for the laser light source, such as gas lasers, solid-state lasers, semiconductor lasers, dye lasers, etc. Among them, semiconductor lasers are playing an increasingly important role due to their advantages in terms of size, power consumption, etc. Optical communication systems and optical chips for next-generation interconnected transmission, due to their complexity and extremely high requirements for performance, also put forward higher requirements for the performance indicators of the required semiconductor lasers, such as line width, tunable range, output power, size, modulation rate, wavelength switching speed, etc. Among them, semiconductor lasers with ultra-fast modulation rates and wavelength switching speeds are of core significance in current photon applications, such as coherent optical communication systems, optical detection and ranging, optical sensing, precision metrology and timing, etc. In particular, today's application-oriented frequency-modulated continuous wave (FMCW) ranging systems have very high requirements for the modulation rate and wavelength switching degree of the light source.

[0045] However, ordinary semiconductor lasers have defects such as poor spectral stability and wide spectral linewidth, which limit their applications in relatively complex optical communication systems. External cavity semiconductor lasers, on the other hand, have advantages such as narrower laser linewidth, wider wavelength tuning range, smaller chirp, and excellent spectral characteristics, and can be well applied in complex optical communication systems, such as dense wavelength division multiplexing fiber optic communication systems and coherent optical communication systems.

[0046] Specifically, an external cavity semiconductor laser is formed by adding some optical feedback elements outside the laser tube, so as to form an external cavity between the rear reflecting surface of the laser tube and the optical feedback elements. As mentioned above, external cavity semiconductor lasers have two typical structures. Among them, the silicon-based photon chip external cavity narrow linewidth semiconductor laser combines the wide tuning and narrow linewidth characteristics of the external cavity structure, as well as the low power consumption and high reliability characteristics of the monolithic integrated structure, and has better performance.

[0047] Conventional tunable external cavity lasers mainly consist of two parts, including a light source and an external cavity chip. The light source is generally integrated with the external cavity chip through a coupler for efficient coupling. The external cavity chip serves as the wavelength selection part and provides selective feedback on the broadband laser provided by the light source. In related technologies, devices in the external cavity chip, such as phase modulators and MRRs, usually achieve the tunable performance of MRRs based on the thermo-optic effect of silicon or silicon nitride. The modulator based on the thermo-optic effect of silicon waveguides has a relatively higher modulation rate, but silicon waveguides usually have large losses and there are effects such as two-photon absorption, which greatly limit parameters such as the output laser linewidth and side mode suppression ratio of external cavity lasers based on silicon waveguides; while the external cavity based on silicon nitride waveguides has smaller losses compared to silicon waveguides, but the phase modulator based on the thermo-optic effect of silicon nitride waveguides has a slow modulation rate and it is difficult to meet the requirements of high modulation rates required for FMCW ranging.

[0048] In view of the above problems, the embodiments of the present invention provide an external cavity chip. By utilizing the channel selection characteristics of the on-chip optical switch, the external cavity chip can improve the wavelength switching speed to a certain extent, enabling the silicon-based tunable semiconductor laser applying this external cavity chip to meet the requirements in fields such as FMCW ranging and phased array lidar. When the external cavity chip adopts a high-speed phase shifter, the modulation rate can also be improved to a certain extent.

[0049] Please refer to Figures 1 to 5 As shown, the external cavity chip 100 includes an input coupler 110, a plurality of optical switches, and a plurality of external cavity loops 130a that are optically connected in sequence.

[0050] Among them, the input coupler 110 is used to couple the optical signal provided by the external light source 200 into the external cavity chip 100.

[0051] The plurality of optical switches have a plurality of signal output terminals 122.

[0052] A plurality of external cavity loops 130a are connected to a plurality of signal output terminals 122 in one-to-one correspondence; each external cavity loop includes a resonance module, the resonance module includes a plurality of tunable microring resonators 131, and the plurality of tunable microring resonators 131 are cascaded in sequence through a connection module 132 to form a cascaded structure, and a Vernier effect can be formed between two adjacent tunable microring resonators 131.

[0053] A plurality of optical switches are used to switch to any one of the external cavity loops 130a, so that an optical signal is emitted through the external cavity loop 130a.

[0054] The optical switch can adopt a Mach-Zehnder interferometer (MZI), or a microring resonator structure, or other structures, and can be specifically selected according to the usage requirements. A plurality of optical switches can be arranged in an array to form an optical switch array 120, as Figure 1 shown by the dashed box Ⅰ in the figure. The transmittance change of the optical switch is as Figure 3 shown.

[0055] The plurality of external cavity loops 130a can also be arranged in an array to form an external cavity loop array 130, as Figure 1 shown by the dashed box Ⅱ in the figure.

[0056] The fact that the plurality of tunable microring resonators 131 are cascaded in sequence through the connection module 132 means that the plurality of tunable microring resonators 131 are arranged in sequence, and any two adjacent tunable microring resonators 131 are connected by an optical path through a connection module 132.

[0057] For the convenience of understanding, now taking two tunable microring resonators 131 and a plurality of optical switches composed of cascaded Mach-Zehnder interferometers (MZIs) 121 as an example, as Figure 1 shown in the figure, the principle of the resonance module provided by the embodiment of the present invention is described.

[0058] The free spectral ranges of the two tunable microring resonators 131 are both:

[0059]

[0060] where λ is the resonance wavelength of the tunable microring resonator 131, Δλ is the wavelength interval between adjacent resonance modes of the tunable microring resonator 131, ng is the group refractive index of the waveguide of the tunable microring resonator 131, and L is the cavity length of the tunable microring resonator 131.

[0061] Among them, the cavity lengths of the two tunable microring resonators 131 are different, and the cavity lengths of the two tunable microring resonators 131 are both integer multiples of this difference. Therefore, the Vernier effect of the microring resonator can be utilized to expand the free spectral range of the entire external cavity, and the free spectral range and resonance mode of the tunable microring resonator 131 can be shifted by means of thermal tuning, so as to achieve the purpose of selecting the laser wavelength output. The FSR of the external cavity after the Vernier effect is:

[0062]

[0063] Among them, FSR₁ and FSR₂ are the free spectral ranges of the two tunable microring resonators 131 respectively.

[0064] Therefore, the above-mentioned resonance module can achieve the effect of expanding the tunable range. In addition, since FSR is not only related to the cavity length of the resonator, but also related to the refractive index, wavelength, etc., the FSR of the tunable microring resonator 131 can also be expanded by other means.

[0065] The transmittance functions of the two signal output ends 122 of the MZI in multiple optical switches are as follows:

[0066]

[0067]

[0068] Among them, t and k are the amplitude transmission coefficient and amplitude coupling coefficient of the directional coupling in the MZI respectively, φ₁ and φ₂ are the phases of the upper and lower arms in the MZI respectively. When φ₁ - φ₂ = mπ (m = 0, 1, 2,...), channel selection can be realized, so that the input light is completely output from the upper channel or the lower channel. By designing the phase difference arrangement of the two arms of the MZI in different multi-channel optical switches, the single input can be selectively output in different channels.

[0069] Among them, the modulation rate of the first phase shifter in the optical switch array 120 is vs, and the wavelength switching speed of a single external cavity loop is vc. When the multi-channel optical switch outputs in one channel, a single wavelength output can be realized by tuning the external cavity loop. At the same time, all the other external cavity loops are tuned simultaneously, so that the wavelength is selected at a different wavelength compared with the laser output at this time. By adjusting the phase difference arrangement of the two arms of the phase shifter of the multi-channel optical switch, the input is selected in another external cavity loop channel, then an ultra-fast wavelength switching speed can be realized. At this time, the wavelength switching speed becomes N*vc compared with the original wavelength switching speed of a single external cavity loop, where N is the number of output channels of the optical switch array 120, that is, the number of signal output ends 122. For example Figure 1For the optical switch array 120 with 8 outputs, the wavelength switching speed is increased to 8 times the original, greatly improving the wavelength switching speed of the tunable external cavity laser system. On this basis, if a high-speed phase shifter is used for the phase shifter in the external cavity loop, the tunable external cavity laser can also achieve a very high modulation rate.

[0070] The working principle of the tunable external cavity laser using the external cavity chip 100 provided by the embodiment of the present invention is as Figure 4 shown:

[0071] When the laser is powered on, each external cavity loop 130a in the multiple external cavity loops 130a has its own initial bias value, which is respectively fixed to its own wavelength and is in a state of ready to output. The multi-channel optical switch also has an initial bias and selects one path to conduct. Then the selected path is conducted into one external cavity loop 130a, and a laser wavelength is selected for output. Then the multi-channel optical switch is powered on, the conduction branch of the optical switch is changed, another external cavity loop 130a is selected, and the selected external cavity loop 130a outputs a wavelength, completing a wavelength switching. At the same time, the previous external cavity loop 130a that has already output is powered on to switch the wavelength and is in a state of ready to output. By repeating the above operations, the final wavelength switching speed depends on the wavelength switching speed of a single external cavity loop 130a multiplied by the number of external cavity loops 130a and the magnitude of the optical switch switching speed. By selecting a high-speed optical switch, a wavelength switching speed multiple times that of the original single external cavity loop 130a can be achieved, realizing high-speed wavelength switching.

[0072] In summary, the external cavity chip 100 provided by the embodiment of the present invention includes an input coupler 110, multiple optical switches, and multiple external cavity loops that are optically connected in sequence. The multiple external cavity loops are respectively connected to multiple signal output ends 122 of the multiple optical switches in one-to-one correspondence; each external cavity loop includes a resonance module, and the resonance module includes multiple tunable micro-ring resonators 131. The multiple tunable micro-ring resonators 131 are cascaded in sequence through a connection module 132 to form a cascaded structure. A Vernier effect can be formed between two adjacent tunable micro-ring resonators 131. Using an optical switch with a modulation rate much higher than that of the resonance module can improve the wavelength switching speed to a certain extent. Applying the external cavity chip 100 provided by the embodiment of the present invention can enable the silicon-based tunable semiconductor laser to meet the usage requirements in fields such as FMCW ranging and phased array lidar.

[0073] As Figure 2 shown, in some embodiments, the optical switch includes a Mach-Zehnder interferometer 121. Each Mach-Zehnder interferometer 121 has two signal output ends 122, and at least one arm of the Mach-Zehnder interferometer 121 is provided with a first phase shifter 123.

[0074] Multiple optical switches can be arranged in an array to form an optical switch array 120, as shown in the dashed box I in Figure 1 as shown in Figure 2 and is composed of cascaded Mach-Zehnder interferometers (MZIs) 121. As shown, a single MZI typically consists of a first directional coupler 124 connecting two waveguides as the upper and lower arms, with one or both arms modulated by a first phase shifter 123 and then connected to a first directional coupler 124.

[0075] The optical switch adopting the structure provided by this embodiment is easier to control compared with the structure adopting a microring resonator.

[0076] As shown in Figure 2 in some embodiments, the first phase shifter 123 is a thin-film lithium niobate electro-optic modulator based on heterogeneous integration, a compressive stress modulator based on piezoelectric ceramics, a thermo-optic phase shifter based on a silicon waveguide, or an electro-optic phase shifter based on a silicon waveguide.

[0077] The first phase shifter 123 adopting the solution provided by this embodiment, except when the first phase shifter 123 is a thermo-optic phase shifter based on a silicon waveguide, has a faster adjustment speed in other solutions, which helps to improve the modulation rate and wavelength switching speed of the external cavity chip 100. When the first phase shifter 123 is a thermo-optic phase shifter based on a silicon waveguide, its adjustment speed is generally also faster than the adjustment rate of the external cavity loop, which helps to improve the modulation rate and wavelength switching speed of the external cavity chip 100.

[0078] The power splitting ratio of the first directional coupler 124 can be flexibly selected according to the usage requirements. To make the optical signal powers at the two output ends of the first directional coupler 124 equivalent, in some embodiments, the power splitting ratio of the first directional coupler 124 in the Mach-Zehnder interferometer 121 is 5:5.

[0079] As shown in Figure 1 in some embodiments, the external cavity loop further includes a second phase shifter 140 connecting the signal output end 122 and the resonant module.

[0080] Relying only on each tunable microring resonator 131 for frequency modulation and wavelength adjustment often cannot make the output light reach the optimal state. However, adopting the solution provided by this embodiment, the second phase shifter 140 can be used for frequency modulation and fine wavelength adjustment to optimize the performance of the output light. When both the first phase shifter 123 and the second phase shifter 140 are high-speed phase shifters, the tunable external cavity laser can not only improve the wavelength switching speed but also achieve a very high modulation rate.

[0081] The above-mentioned second phase shifter 140 employs a thermo-optic phase shifter, an electro-optic phase shifter, or a piezoresistive stress modulator. Among them, when the second phase shifter 140 uses a thermo-optic phase shifter, it has advantages such as low power consumption and low loss. Moreover, the thermo-optic phase shifter is realized based on the thermo-optic effect of silicon material. Due to the high thermo-optic coefficient of silicon material, the thermo-optic modulation that adjusts the optical properties of the silicon waveguide by changing the temperature of the silicon material plays an important role in silicon-based optical devices, especially in the fields of low cost and low-frequency modulation, and has high attractiveness. When the second phase shifter 140 uses an electro-optic phase shifter or a piezoresistive stress modulator, it has characteristics such as high performance and low power consumption.

[0082] In some embodiments, the second phase shifter 140 is a thin-film lithium niobate electro-optic modulator based on heterogeneous integration, a piezoresistive stress modulator based on piezoelectric ceramics, a thermo-optic phase shifter based on a silicon waveguide, or an electro-optic phase shifter based on a silicon waveguide.

[0083] Adopting the solution provided in this embodiment enables the modulation rate of the tunable microring resonator 131 to be relatively high. In some embodiments, the tunable microring resonator 131 is made of lithium niobate material.

[0084] Adopting the solution provided in this embodiment can enable the tunable microring resonator 131 to achieve the wavelength tuning function by using lithium niobate electro-optic modulation, and the tuning speed is fast.

[0085] The connection module 132 can have various setting methods, and can be specifically and flexibly selected according to the usage requirements.

[0086] In some embodiments, the connection module 132 includes a waveguide. The waveguide can be a straight waveguide or a bent waveguide. When the connection module 132 adopts a straight waveguide (as Figure 5 shown) or a bent waveguide (as Figure 6 shown), the structure is simple and convenient for preparation.

[0087] Please refer to Figure 7 shown. In some other embodiments, the connection module 132 includes a combined structure of a waveguide and a tunable microring resonator 131. The tunable microring resonator 131 is connected to the corresponding tunable microring resonator 131 through a waveguide. The corresponding tunable microring resonator 131 refers to the tunable microring resonator 131 adjacent to the tunable microring resonator 131. The waveguide can adopt a straight waveguide or a bent waveguide according to the usage requirements.

[0088] The cavity length of the tunable microring resonator 131 can be different from the cavity length of the adjacent tunable microring resonator 131, so as to form a Vernier effect between the tunable microring resonator 131 and the adjacent tunable microring resonator 131, so as to further improve the side mode suppression ratio.

[0089] Please refer to Figure 5As shown, in some embodiments, the external cavity loop further includes a second directional coupler 133 and an output coupler 134.

[0090] The second directional coupler 133 receives an optical signal and provides it to the resonant module. The resonant module selects the optical signal, and the selected optical signal is coupled out successively through the second directional coupler 133 and the output coupler 134.

[0091] The second directional coupler 133 in this embodiment can be a 2*2 coupler, a 3*2 coupler, an M*N star coupler, etc., as long as it can achieve the corresponding functions.

[0092] The external cavity chip 100 provided by the embodiments of the present invention adopts the resonant module provided by any of the above embodiments, expands the Vernier effect of the tunable external cavity laser using the external cavity chip 100 provided by the embodiments of the present invention, greatly expands the tunable range of the laser, and can maintain the narrow linewidth and tunable characteristics of the silicon-based external cavity.

[0093] In some embodiments, the second directional coupler 133 has a first end, a second end, a third end, and a fourth end. The first end, the second end, the third end, and the fourth end of the second directional coupler 133 are respectively connected to the output end of the input coupler 110, the first end of the resonant module, the second end of the resonant module, and the input end of the output coupler 134 through optical paths. Specifically, the second directional coupler 133 can be a 2×2 directional coupler 133.

[0094] Among them, the optical signal received through the first end of the second directional coupler 133 is split into two input light beams in the second directional coupler 133. One of the input light beams is coupled into the resonant module successively through the second end of the second directional coupler 133 and the first end of the resonant module, and after passing through the cascaded structure of the resonant module, it is coupled into the second directional coupler 133 through the second end of the resonant module and the third end of the second directional coupler 133, and is provided to the output coupler 134 by the fourth end of the second directional coupler 133; the other input light beam is coupled into the resonant module successively through the third end of the second directional coupler 133 and the second end of the resonant module, and after passing through the cascaded structure of the resonant module, it is coupled into the second directional coupler 133 through the first end of the resonant module and the second end of the second directional coupler 133, and is provided to the output coupler 134 by the fourth end of the second directional coupler 133.

[0095] For ease of description, taking the example that the resonant module includes two tunable microring resonators 131 as shown in the figure, the working principle of the tunable external cavity laser using the external cavity chip 100 provided by the embodiments of the present invention is described as follows:

[0096] The light source 200 emits an optical signal, which is coupled into the external cavity chip 100 through the input coupler 110. Then, the optical signal enters the second directional coupler 133 through the first end, and is divided into two beams by the second directional coupler 133. One beam is coupled into the resonant module through the second end, and the other beam is coupled into the resonant module through the third end.

[0097] The optical signal entering the resonant module through the second end first propagates in the first tunable microring resonator 131. When passing through the connection region between the tunable microring resonator 131 and the connection module 132, it is transmitted into the connection module 132, and then transmitted through the connection module 132 into the second tunable microring resonator 131. Then, it is output through the download end of the second tunable microring resonator 131 and enters the second directional coupler 133 through the third end.

[0098] Then, the optical signal entering the second directional coupler 133 is again divided into two beams by the second directional coupler 133. One beam is output through the first end and the input coupler 110 and fed back to the external light source 200 to form a loop, and the other beam is coupled out of the external cavity chip 100 through the fourth end and the output coupler 134.

[0099] The external cavity chip 100 provided in this embodiment has a simple structure and is convenient for assembly.

[0100] Please refer to Figure 8 As shown, in some other embodiments, the external cavity loop further includes a Sagnac loop 135.

[0101] The first end of the resonant module is coupled to the signal output end 122 through a waveguide, and the second end of the resonant module is coupled to the Sagnac loop 135.

[0102] For ease of description, now taking Figure 8 As shown, taking the resonant module including two tunable microring resonators 131 as an example, the working principle of the tunable external cavity laser using the external cavity chip 100 provided in the embodiment of the present invention is described:

[0103] The light source 200 emits an optical signal, which is coupled into the external cavity chip 100 through the input coupler 110. Then, the optical signal enters the cascaded structure. The optical signal first propagates in the first tunable microring resonator 131. Then, when the optical signal passes through the connection region between the first tunable microring resonator 131 and the connection module 132, it is transmitted into the connection module 132, and then transmitted through the connection module 132 into the second tunable microring resonator 131. Then, it is output through the second tunable microring resonator 131.

[0104] Subsequently, the optical signal enters the Sagnac loop 135. First, it passes through the first coupler, and the input optical field is divided into two coherent optical beams that propagate clockwise and counterclockwise. One of the optical beams passes through the phase shifter and undergoes a phase change. The two optical beams pass through the second coupler and the ring circuit and finally return to the first coupler to undergo coherent interference, and are output from two output ports. The intensities of the optical beams output from the two output ports depend on the relative phase of the two optical beams. By adjusting the phase shifter, the relative phase of the two optical beams can be changed, thereby changing the intensities of the optical beams output from the two output ports. The optical beam output from the output port in the Sagnac loop 135 that is not connected to the tunable microring resonator 131 can be directly output from the external cavity chip 100. The optical beam output from the output port in the Sagnac loop 135 that is connected to the tunable microring resonator 131 is reflected and sequentially passes through the second tunable microring resonator 131, the connection module 132, the first tunable microring resonator 131, and the input coupler 110 to be coupled out of the external cavity chip 100 in the reverse direction.

[0105] The above-mentioned phase shifter is a slow phase shifter based on the thermo-optic effect.

[0106] The external cavity chip 100 provided by the embodiment of the present invention adopts the resonance module provided by any one of the above embodiments, which expands the tunable range of the tunable external cavity laser using the external cavity chip 100 provided by the embodiment of the present invention, and can maintain the narrow linewidth and tunable characteristics of the silicon-based external cavity.

[0107] Please refer to Figure 5 As shown, in some embodiments, the cascade structure is a two-stage cascade structure, which is composed of two tunable microring resonators. The cavity lengths of the two tunable microring resonators 131 are different, and the cavity lengths of the two tunable microring resonators 131 are both integer multiples of the difference.

[0108] Adopting the structure provided by this embodiment for the resonance module can achieve the effect of expanding the tunable range, and the structure of the resonance module is simple and convenient for assembly.

[0109] In other embodiments, the cascade structure is a cascade structure formed by cascading 3 or more tunable microring resonators 131 in sequence, and the differences in the cavity lengths of every two adjacent tunable microring resonators 131 are all different. By adopting the solution provided by this embodiment, the Vernier effect of more than three microring resonators can be utilized to expand the free spectral range of the entire external cavity, and at the same time improve the side mode suppression ratio. Moreover, the free spectral range and resonance mode of the tunable microring resonator 131 can be moved by means of thermal tuning, so as to achieve the purpose of selecting the output of the laser wavelength.

[0110] Adopting the structure provided by this embodiment for the resonance module, the structure is simple. Compared with the two-stage cascade structure, it is beneficial to improve the side mode suppression ratio, so that the silicon-based external cavity maintains the characteristics of narrow linewidth, high side mode suppression ratio and wide tunability.

[0111] When the cascade structure is an N - stage (N is an integer greater than 1) cascade structure, the resonant module receives two input light beams input from the outside. One of the input light beams enters the resonant module through the input end of the first - stage tunable microring resonator 131, and after passing through N tunable microring resonators 131 in sequence, it is coupled out of the resonant module through the download end of the N - th stage tunable microring resonator 131; the other input light beam is input into the resonant module through the download end of the N - th stage tunable microring resonator 131, and after passing through N tunable microring resonators 131 in sequence, it is coupled out of the resonant module through the input end of the first - stage tunable microring resonator 131.

[0112] The cascade structure in this embodiment can achieve bidirectional transmission of light beams. In this way, when designing the optical path, only the optical path input / output structures are set at both ends of the cascade structure, and the closure of the entire optical path can be achieved without setting a loop structure outside the cascade structure, making the structure of the entire resonant module simple and facilitating design and assembly.

[0113] The specific type of the above - mentioned input coupler 110 can be determined according to the specific type of the light source 200. For example, when the light source 200 uses a semiconductor optical amplifier (SOA, Semiconductor Optical Amplifier), the corresponding input coupler 110 uses a mode - field converter; when the light source 200 uses a laser diode (LD) chip, the input coupler 110 can be etched on the external cavity chip 100; when the light source 200 uses a vertical cavity surface - emitting laser, the corresponding input coupler 110 uses a grating coupler; the light source 200 and the input coupler 110 are bonded in the form of a flip chip.

[0114] In some embodiments, both the input coupler 110 and the output coupler 134 use mode - field converters. At this time, the external light source 200 can use a semiconductor optical amplifier to make full use of the existing semiconductor laser technology and facilitate integration with other optical devices. The use of mode - field converters for the input coupler 110 and the output coupler 134 can make the mode - field size of the devices in the external cavity chip 100 for connecting to external devices consistent with the mode - field size of the external devices, so as to reduce the coupling loss.

[0115] To make the coupling efficiency of the input coupler 110 and the output coupler 134 relatively high, in some embodiments, the input coupler 110 and the output coupler 134 are respectively an inverted - taper coupler, a positive - taper coupler, a cantilever - beam coupler or a trident - type coupler.

[0116] In the above embodiments, the power splitting ratio of the second directional coupler 133 can be flexibly selected according to the usage requirements. To make the linewidth of the optical signal output from the fourth terminal relatively narrow and the output power relatively high, in some embodiments, the power splitting ratio of the second directional coupler 133 is 5:5.

[0117] Please refer to Figure 1 As shown, in another embodiment of the present invention, a tunable external cavity laser is provided, which includes a light source 200 and the external cavity chip 100 provided in the above embodiments, where the light source 200 is used to provide an optical signal for the external cavity chip 100. The input end of the input coupler 110 is coupled to the output end of the light source 200.

[0118] In this embodiment, the specific type of the input coupler 110 depends on the specific type of the light source 200. When the light source 200 uses a semiconductor optical amplifier (SOA), the corresponding input coupler 110 uses a mode spot converter; when the light source 200 uses a laser diode (LD) chip, the input coupler 110 can be etched on the external cavity chip 100; when the light source 200 uses a vertical cavity surface emitting laser, the corresponding input coupler 110 uses a grating coupler; the light source 200 and the input coupler 110 are bonded in a flip chip form.

[0119] In addition to the above devices, the tunable external cavity laser in this embodiment may further include a housing, an optical fiber, etc., which can be specifically determined according to the design requirements.

[0120] The tunable external cavity laser provided by the embodiments of the present invention adopts the external cavity chip 100 provided by the above embodiments, and utilizes the double micro-ring resonator coupling effect combined with the vernier effect to greatly expand the tunable range of the laser.

[0121] In some embodiments, the light source 200 is a semiconductor optical amplifier, and the end of the light source 200 away from the external cavity chip 100 has a preset reflectivity. The preset reflectivity can be set according to the use requirements. If a high reflectivity is required, the preset reflectivity is ≥90%. At this time, the output end of the light source 200 (that is, the end of the light source 200 close to the external cavity chip 100) can be coated with an anti-reflection film to have a low reflectivity, and the reflectivity is ≤0.01%; if light can be emitted from this end, the preset reflectivity can use other values. The gain wavelength of the light source 200 is in the communication band and can be achieved by quantum wells or quantum dot materials of groups III and V. The light source 200 adopts the setting method of this embodiment, which has a simple structure and a small size. It can make full use of the existing semiconductor laser technology, has a mature manufacturing process, low cost, long life, low power consumption, and is easy to integrate with other optical devices.

[0122] In some embodiments, the light source 200 is a Fabry-Perot laser.

[0123] The light source 200 adopts Fabry-Perot laser, which has mature technology and is easy to obtain.

[0124] In another embodiment of the present invention, a laser radar is provided, comprising a laser module, a transmitting module, a detecting module, a detecting module and a data processing module, wherein the laser module comprises the tunable external cavity laser provided in any of the above embodiments.

[0125] The transmitting module in this embodiment can adopt the existing transmitting module on the market. The detecting module in this embodiment can adopt the existing detecting module on the market. The data processing module in this embodiment can adopt the existing data processing module on the market. The laser radar in this embodiment, in addition to the above-mentioned laser module, transmitting module, detecting module and data processing module, can also include at least one of a housing and a scanning device, which can be determined according to the use requirements.

[0126] The laser radar provided by the embodiment of the present invention includes the tunable external cavity laser provided by the above embodiment. On the one hand, it greatly expands the tunable range of the laser; on the other hand, it can maintain the narrow linewidth and tunable characteristics of the silicon-based external cavity, which can effectively improve the scanning angle of the laser radar.

[0127] The above description is only a preferred embodiment of the present invention, and only specifically describes the technical principle of the present invention. These descriptions are only for explaining the principle of the present invention and cannot be interpreted as limiting the scope of protection of the present invention in any way. Based on the explanation here, any modification, equivalent substitution and improvement made within the spirit and principle of the present invention, and other specific embodiments of the present invention that can be associated with by technicians in this field without creative labor, should be included in the scope of protection of the present invention.

Claims

1. An external cavity chip, characterized in that, It includes an input coupler, a plurality of optical switches, and a plurality of external cavity loops that are optically connected in sequence. Among them, the input coupler is used to couple the optical signal provided by an external light source into the external cavity chip. The plurality of optical switches have a plurality of signal output terminals. The plurality of external cavity loops are connected to the plurality of signal output terminals in a one-to-one correspondence; each of the external cavity loops includes a resonance module, the resonance module includes a plurality of tunable microring resonators, and the plurality of tunable microring resonators are cascaded in sequence through a connection module to form a cascaded structure, and a Vernier effect can be formed between two adjacent tunable microring resonators. The plurality of optical switches are used to switch to any one of the external cavity loops so that the optical signal exits through the external cavity loop.

2. The external cavity chip according to claim 1, wherein The optical switch includes a Mach-Zehnder interferometer, each Mach-Zehnder interferometer has two signal output terminals, and at least one arm of the Mach-Zehnder interferometer is provided with a first phase shifter.

3. The external cavity chip according to claim 2, wherein The first phase shifter is a thin-film lithium niobate electro-optic modulator based on heterogeneous integration, a compressive stress modulator based on piezoelectric ceramics, a thermo-optic phase shifter based on a silicon waveguide, or an electro-optic phase shifter based on a silicon waveguide.

4. The external cavity chip according to claim 1, characterized in that The external cavity loop further includes a second phase shifter connecting the signal output terminal and the resonance module.

5. The external cavity chip according to claim 4, characterized in that, The second phase shifter is a thin-film lithium niobate electro-optic modulator based on heterogeneous integration, a compressive stress modulator based on piezoelectric ceramics, a thermo-optic phase shifter based on a silicon waveguide, or an electro-optic phase shifter based on a silicon waveguide.

6. The external cavity chip according to claim 1, characterized in that, The connection module includes: a waveguide; or, a combined structure of a waveguide and one of the tunable microring resonators.

7. The external cavity chip according to claim 1, characterized in that, The external cavity loop further includes a second directional coupler and an output coupler. The second directional coupler receives the optical signal and provides it to the resonance module, selects the optical signal through the resonance module, and couples out the selected optical signal through the second directional coupler and the output coupler in sequence.

8. The external cavity chip according to claim 7, wherein, The second directional coupler is a 2×2 directional coupler. Among them, the optical signal received through the first end of the second directional coupler is split into two input light beams in the second directional coupler; one of the input light beams is coupled into the resonance module through the second end of the second directional coupler and the first end of the resonance module in sequence, and after passing through the cascaded structure of the resonance module, it is coupled into the second directional coupler through the second end of the resonance module and the third end of the second directional coupler, and is provided to the output coupler by the fourth end of the second directional coupler; the other input light beam is coupled into the resonance module through the third end of the second directional coupler and the second end of the resonance module in sequence, and after passing through the cascaded structure of the resonance module, it is coupled into the second directional coupler through the first end of the resonance module and the second end of the second directional coupler, and is provided to the output coupler by the fourth end of the second directional coupler.

9. The external cavity chip according to claim 1, characterized in that The external cavity loop further includes a Sagnac loop. The first end of the resonance module is coupled to the signal output terminal through a waveguide, and the second end of the resonance module is coupled to the Sagnac loop.

10. The external cavity chip according to any one of claims 1-9, characterized in that, The cascade structure is a two-stage cascade structure, which is composed of two tunable microring resonators. There is a difference in the cavity lengths of the two tunable microring resonators, and the cavity lengths of the two tunable microring resonators are both integer multiples of the difference.

11. The external cavity chip according to any one of claims 1-9, characterized in that, The cascade structure is a cascade structure formed by cascading 3 or more of the above-mentioned tunable microring resonators in sequence, and the differences in the cavity lengths of every two adjacent tunable microring resonators are all different.

12. A tunable external cavity laser, characterized in that, It includes a light source and the external cavity chip according to any one of claims 1-11, wherein the light source is used to provide an optical signal for the external cavity chip.

13. The tunable external cavity laser according to claim 12, characterized in that, The light source is a semiconductor optical amplifier; one end of the light source facing away from the external cavity chip has a high reflectivity, the reflectivity ≥ 90%, and the output end has a low reflectivity, the reflectivity ≤ 0.01%; the gain wavelength of the light source is in the communication band.

14. A lidar, characterized in that, It includes a laser module, a transmitting module, a detecting module, a detecting module, and a data processing module, wherein the laser module includes the tunable external cavity laser according to claim 12 or 13.

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