On-chip laser

Abstract

The invention provides an on-chip laser which can be applied to the technical field of micro-nano optoelectronic integration. The laser includes: a substrate; a laser body disposed on the substrate and extending in a first direction; and a cladding surrounding the laser body in a second direction intersecting the first direction; wherein the laser main body comprises a gain region, a micro-ring resonant cavity region, a first Bragg resonant cavity region and a second Bragg resonant cavity region, and the first Bragg resonant cavity region and the second Bragg resonant cavity region are respectively arranged at two sides of the micro-ring resonant cavity region; under the condition that an optical signal is generated in the gain area, the optical signal repeatedly goes back and forth in the first Bragg resonant cavity area, the micro-ring resonant cavity area and the second Bragg resonant cavity area, so that a laser signal is obtained.

Description

Technical Field

[0001] The present disclosure relates to the field of micro-nano optoelectronic integration technology, and in particular, to an on-chip laser. Background Art

[0002] With the development of microelectronics, big data and the Internet of Things (IoT), chips are facing higher requirements. On this basis, integrated circuits are transitioning towards integrated photonic chips, with the goal of achieving photon generation and ultra-high-speed data transmission and processing.

[0003] On-chip integrated light sources such as lasers can provide coherent light sources for optoelectronic integrated chips and generate optical information. Their performance determines the application scope and implementation functions of the chip. However, due to the lack of mature solutions for on-chip integrated light sources, the development of silicon photonics technology has been restricted. Therefore, as the core of optoelectronic integrated chips, on-chip light sources with high luminous efficiency, good laser performance, high integration, emission matching the wavelength of optical communication and compatible with CMOS (Complementary Metal Oxide Semiconductor) processes have become a research boom. On this basis, related technologies have problems such as incompatibility between on-chip integrated light sources and CMOS processes, mismatch between luminous wavelengths and optical communication wavelengths, poor laser performance, low integration, and low coupling efficiency with on-chip devices. Summary of the invention

[0004] In view of this, the present disclosure provides an on-chip laser.

[0005] One aspect of the present disclosure provides an on-chip laser, comprising: a substrate; a laser body arranged on the substrate and extending along a first direction; and a cladding surrounding the laser body in a second direction intersecting the first direction; wherein the laser body comprises a gain region, a microring resonant cavity region, a first Bragg resonant cavity region, and a second Bragg resonant cavity region, and the first Bragg resonant cavity region and the second Bragg resonant cavity region are respectively arranged on both sides of the microring resonant cavity region; when an optical signal is generated in the gain region, the optical signal repeatedly travels back and forth in the first Bragg resonant cavity region, the microring resonant cavity region, and the second Bragg resonant cavity region, thereby obtaining a laser signal.

[0006] According to an embodiment of the present disclosure, the gain region is connected to one end of the first Bragg resonant cavity region or the second Bragg resonant cavity region close to the microring resonant cavity region, and is coupled to the microring resonant cavity region.

[0007] According to an embodiment of the present disclosure, the gain region extends along a first direction, and an end of the gain region in the first direction is tapered so as to converge a multi-mode optical signal into a single-mode optical signal.

[0008] According to an embodiment of the present disclosure, the first Bragg reflector in the first Bragg resonant cavity region is substantially configured as a total reflective mirror, the reflectivity of the second Bragg reflector in the second Bragg resonant cavity region is lower than that of the first Bragg reflector, and one end of the second Bragg resonant cavity region away from the microring resonant cavity region is connected to the grating coupler.

[0009] According to an embodiment of the present disclosure, the reflectivity of the first Bragg reflector is greater than or equal to 99% and less than or equal to 100%; the reflectivity of the second Bragg reflector is greater than or equal to 90% and less than or equal to 99%.

[0010] According to an embodiment of the present disclosure, the first Bragg resonant cavity region includes a first Bragg reflector formed based on a first strip waveguide and a first extension portion of the first strip waveguide protruding from the first Bragg reflector; the second Bragg resonant cavity region includes a second Bragg reflector formed based on a second strip waveguide and a second extension portion of the second strip waveguide protruding from the second Bragg reflector; the first Bragg resonant cavity region is coupled to the microring resonant cavity region through the first extension portion, and the second Bragg resonant cavity region is coupled to the microring resonant cavity region through the second extension portion.

[0011] According to an embodiment of the present disclosure, the first strip waveguide and the second strip waveguide extend along the first direction, the gratings of the first Bragg reflector are arranged on both sides of the first strip waveguide in the second direction, and the gratings of the second Bragg reflector are arranged on both sides of the second strip waveguide in the second direction.

[0012] According to an embodiment of the present disclosure, the grating period of the first Bragg reflector is greater than the grating period of the second Bragg reflector; the grating period number range of the first Bragg reflector is 120~200; the grating period number range of the second Bragg reflector is 60~200; the grating duty cycle range of the first Bragg reflector and the second Bragg reflector is both 40%~60%; the width range of the first strip waveguide and the second strip waveguide is both 800 nm~1100 nm; the grating tooth length value of the first Bragg reflector is 200 nm~1200 nm larger than the width value of the first strip waveguide; the grating tooth length value of the second Bragg reflector is 200 nm~1200 nm larger than the width value of the second strip waveguide.

[0013] According to an embodiment of the present disclosure, the first Bragg resonant cavity region and the second Bragg resonant cavity region are parallel to each other in the second direction, and the microcavity resonant region is arranged between the first Bragg resonant cavity region and the second Bragg resonant cavity region in the second direction.

[0014] According to an embodiment of the present disclosure, the coupling spacing between the first Bragg resonant cavity region and the microring resonant region is 150 nm~500 nm; the coupling spacing between the second Bragg resonant cavity region and the microring resonant region is 150 nm~500 nm; the microring radius of the microring resonant region is 10 μm~30 μm; the material includes silicon nitride; the material of the substrate includes silicon; and the material of the cladding includes silicon dioxide.

[0015] According to the embodiments of the present disclosure, after the laser of the present disclosure forms a laser mode through the resonance principle of the first Bragg resonant cavity region and the second Bragg resonant cavity region, the required laser mode is selected by using the filtering function of the micro-ring resonant cavity region to obtain the required laser signal. Based on this, the laser of the present disclosure can obtain a narrow line width and maintain a stable single-mode behavior, and improve the SMSR (Side-Mode Suppression Ratio) of the resonant cavity in the laser, and reduce the FSR (Free Spectral Range) and FWHM (Full Width at Half Maxima). In addition, since the first Bragg resonant cavity region, the second Bragg resonant cavity region and the micro-ring resonant cavity region can be directly manufactured on the same substrate, a high coupling efficiency with other on-chip devices can be obtained.

[0016] Based on this, the present disclosure solves the problems in the related art such as incompatibility between on-chip integrated light source and CMOS process, mismatch between light emission wavelength and optical communication wavelength, poor laser performance, low integration, and low coupling efficiency with on-chip devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above and other objects, features and advantages of the present disclosure will become more apparent through the following description of the embodiments of the present disclosure with reference to the accompanying drawings, in which:

[0018] Figure 1 Schematic diagram of a laser according to a first embodiment of the present disclosure Figure 1 .

[0019] Figure 2 Schematic diagram of a laser according to a first embodiment of the present disclosure Figure 2 .

[0020] Figure 3 A schematic diagram of a laser according to a second embodiment of the present disclosure is schematically shown.

[0021] Figure 4 A schematic diagram schematically shows the relationship between the mode effective refractive index and the waveguide width when the waveguide thickness is the same according to an embodiment of the present disclosure.

[0022] Figure 5The electric field distribution diagram of the laser when the waveguide size is 400 nm*800 nm according to an embodiment of the present disclosure is schematically shown.

[0023] Figure 6 The structural diagram of a DBR (Distributed Bragg Reflector) reflector according to an embodiment of the present disclosure is schematically shown.

[0024] Figure 7 A schematic diagram of a curve showing how the maximum reflectivity of a DBR grating varies with the number of grating periods according to an embodiment of the present disclosure is schematically shown.

[0025] Figure 8 A schematic diagram of a curve showing the variation of the maximum reflectivity of a DBR grating with the grating tooth length according to an embodiment of the present disclosure is schematically shown.

[0026] Fig. 9 A schematic diagram of a curve showing the variation of the maximum reflectivity of a DBR grating with the grating tooth length according to an embodiment of the present disclosure is schematically shown.

[0027] Fig.10 A schematic diagram schematically shows the reflection spectra of the DBR gratings on both sides of the laser body according to an embodiment of the present disclosure.

[0028] Fig.11 A schematic top view of a microring resonant cavity region according to an embodiment of the present disclosure is shown schematically.

[0029] Fig.12 The filtering effect diagram of a single microring resonant cavity region according to an embodiment of the present disclosure is schematically shown.

[0030] Fig.13 A schematic diagram schematically shows the normalized resonance intensity of laser light of a laser according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0031] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the present disclosure. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present disclosure. However, it is apparent that one or more embodiments may also be implemented without these specific details. In addition, in the following description, descriptions of known structures and technologies are omitted to avoid unnecessary confusion of the concepts of the present disclosure.

[0032] The terms used herein are only for describing specific embodiments and are not intended to limit the present disclosure. The terms "comprise", "include", etc. used herein indicate the existence of the features, steps, operations and / or components, but do not exclude the existence or addition of one or more other features, steps, operations or components.

[0033] All terms (including technical and scientific terms) used herein have the meanings commonly understood by those skilled in the art unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0034] When using expressions such as "at least one of A, B, and C, etc.", they should generally be interpreted according to the meaning of the expression commonly understood by those skilled in the art (for example, "a system having at least one of A, B, and C" should include but is not limited to a system having A alone, B alone, C alone, A and B, A and C, B and C, and / or A, B, C, etc.).

[0035] According to the embodiments of the present disclosure, photonic integration based on silicon on insulator (SOI) is developing rapidly, and the key advantages of silicon photonic integration technology are large substrate area, mature CMOS compatible process and monolithic integration. These features, coupled with the high refractive index difference in the silicon photonic platform, can mass-produce highly integrated integrated photonic devices at a relatively low cost. On this basis, with the continuous accumulation of technology and the gradual increase in industrial demand, photonic integration technology has entered a relatively rapid development period. In its development history, a variety of integrated optical material systems have been developed. In addition to the common SOI platform, there are mainly III / V compound semiconductors (InP, GaAs), silicon nitride (Silicon Nitride) and other platforms. The main advantages and disadvantages of these materials as photonic integration platforms are shown in Table 1.

[0036] Table 1 Advantages and disadvantages of SOI and Silicon Nitride integrated photonic platforms

[0037]

[0038] It can be seen that compared with SOI, silicon nitride is a CMOS-compatible material with a moderate refractive index difference. Its advantages are that there is almost no free carrier absorption in silicon nitride optical waveguides within the communication wavelength range; and its lowest-order nonlinear polarizability is about 20 times smaller than that of silicon, which means that silicon nitride optical waveguides can withstand higher optical power than SOI optical waveguides; in addition, since the thermo-optical coefficient of silicon nitride is about 5 times smaller than that of silicon, silicon nitride photonic components are much less sensitive to temperature than silicon photonic components, making them more suitable for harsh environments and more popular. When the cladding is silicon dioxide (SiO2, refractive index n=1.45), silicon nitride optical waveguides (refractive index n=2) have a relatively small core-cladding refractive index difference compared to SOI (refractive index n=3.48), reducing scattering losses caused by rough side walls. And because silicon nitride optical waveguides have a lower refractive index, at the same wavelength, the device size is larger, which is conducive to subsequent electron beam exposure and etching on the device.

[0039] The requirements for on-chip laser research are narrow linewidth and high power, and the key to unlocking high power and narrow linewidth is to reduce waveguide losses. The typical waveguide loss of SOI-based photonic integration platforms is 1 to 2 dB / cm, which is mainly due to scattering losses caused by sidewall roughness. The waveguide loss of silicon nitride waveguides can be an order of magnitude lower in principle. Based on this, silicon nitride optical waveguides have excellent optical properties, making the use of silicon nitride materials to make optical integrated devices is becoming an active research field.

[0040] According to the embodiments of the present disclosure, the structures suitable for on-chip resonant cavities mainly include micro-ring (or micro-disk) resonant cavities and DBR resonant cavities. For on-chip lasers, it is hoped that stable single-mode behavior can be maintained while reducing the line width. When designing a laser with a micro-ring as a resonant cavity, a trade-off needs to be made between insertion loss and bandwidth. Since the coupling coefficient is positively correlated with the reflectivity of the resonant cavity, a coupling coefficient that is too low means that while obtaining a narrow line width, the reflectivity of the resonant cavity is too low, causing the light to lose too much power when circulating in the ring, while a coupling coefficient that is too high means that while obtaining a higher reflectivity, the ability of the resonant cavity to select a single cavity mode is affected, making it difficult to take into account both high reflectivity and narrow line width.

[0041] The reflectors at both ends of the DBR resonant cavity are composed of Bragg gratings. Since the reflectivity of the Bragg grating is positively correlated with the product of the coupling coefficient and the cavity length, the length of the grating can be increased while reducing the grating coupling coefficient. This method can reduce the width of the reflection spectrum while keeping the reflectivity unchanged, thereby maintaining stable single-mode behavior while achieving narrow line width. However, this method lengthens the cavity length of the DBR resonant cavity, resulting in a shortened cavity mode interval, which seriously affects the performance of the resonant cavity. Therefore, in the present disclosure, the defect of shortened cavity mode interval is effectively solved by introducing a microring in the middle of the double-sided Bragg grating. The principle of this method is: although the introduction of a microring will lengthen the cavity length and shorten the cavity mode interval, it can make more full use of the space, and can only emit cavity modes that meet both the microring resonance conditions and the DBR resonant cavity resonance conditions, thereby improving the defect of shortened cavity mode to a certain extent. At the same time, the introduction of a microring structure can further improve the SMSR of the resonant cavity and reduce the FWHM. Therefore, the DBR+microring resonant cavity can be used as an on-chip resonant cavity to realize on-chip laser.

[0042] In view of this, in order to solve the technical problems of large loss of on-chip integrated light source, poor laser performance, mismatch between emitted light and communication wavelength and incompatibility with CMOS process in related technologies, the present invention utilizes the low loss characteristics of silicon nitride platform, the resonance characteristics of DBR resonant cavity, the filtering characteristics of microring and the compatibility with silicon-based CMOS integration process to design a silicon-based compatible on-chip laser of microring + DBR in the communication band, which has the advantages of low loss, high luminous efficiency, high integration, matching of luminous wavelength with communication wavelength, good laser performance, compatibility with CMOS process and high miniaturization and integration. Compared with the previous external lasers, the laser disclosed in the present invention can be directly manufactured on chip and can achieve 100% coupling efficiency with on-chip devices, which is conducive to the integrated integration of silicon-based optical devices and is of great significance to the development of photonic integrated circuits.

[0043] Figure 1 Schematic diagram of a laser according to a first embodiment of the present disclosure Figure 1 .

[0044] Figure 2 Schematic diagram of a laser according to a first embodiment of the present disclosure Figure 2 .

[0045] like Figure 1 and Figure 2 As shown, the laser of this embodiment includes: a substrate 100 , a laser body 200 disposed on the substrate 100 and extending along a first direction X, and a cladding 300 surrounding the laser body 200 in a second direction Y intersecting the first direction X.

[0046] In the embodiment of the present disclosure, the substrate 100 is used to support the laser body 200. The material of the substrate 100 includes silicon, etc. Silicon is compatible with CMOS technology and can be better integrated with other on-chip devices.

[0047] The cladding 300 may include a first cladding 310 and a second cladding 320 stacked in the vertical direction Z. The first cladding 310 is disposed on the upper surface of the substrate 100. The laser body 200 is disposed on the upper surface of the first cladding 310. The second cladding 320 is disposed to cover the laser body 200 and the first cladding 310, thereby constituting the cladding 300 surrounding the laser body 200 in the second direction Y together with the first cladding 310. The cladding 300 covers the surface of the device body and plays a role of protection and light field confinement. The material of the cladding 320 includes silicon dioxide, the thickness of which is 4.4 μm, and the refractive index of which is 1.444 at a wavelength of 1550 nm.

[0048] The material of the laser body 200 includes silicon nitride and the like. For example, the material of the waveguide in the laser body 200 is silicon nitride. Compared with silicon waveguides, silicon nitride waveguides can withstand higher optical power, have good stability, lower loss, and are smaller in size and more conducive to integration. For another example, the laser body 200 is made of low-loss silicon nitride material, with a thickness of 0.3 µm to 0.45 µm, preferably 0.4 µm, and a refractive index of 1.996 at a wavelength of 1550 nm.

[0049] like Figure 3 As shown, the laser body 200 includes a gain region 230 , a microring resonant cavity region 240 , a first Bragg resonant cavity region 210 and a second Bragg resonant cavity region 220 .

[0050] The gain region 230 is bonded with a gain material. For example, the gain region 230 is connected to one end of the first Bragg resonant cavity region 210 or the second Bragg resonant cavity region 220 close to the microring resonant cavity region 240, and is coupled to the microring resonant cavity region 240. By bonding the gain material to the gain region 230, using a laser to pump the luminescent material, a light excitation process is generated, and the light can be successfully introduced from the luminescent material into the waveguide in the laser body 200 through the waveguide optical coupling theory (i.e., evanescent wave coupling). Based on this, the laser can complete functions such as light resonance, high-performance laser mode selection (i.e., filtering), and gain material integration. For example, in the case where the gain region 230 generates an optical signal, the optical signal repeatedly travels back and forth in the first Bragg resonant cavity region 210, the microring resonant cavity region 240, and the second Bragg resonant cavity region 220, thereby obtaining a laser signal.

[0051] It can be understood that by making the middle of the gain region 230 wider than the end in the first direction X, the multi-mode optical signal entering the gain region 230 can be converged, so that a single-mode optical signal can be obtained. Based on this, in the embodiment of the present disclosure, the gain region 230 extends along the first direction X, and the end of the gain region 230 in the first direction X is tapered, so as to converge the multi-mode optical signal into a single-mode optical signal.

[0052] The first Bragg resonant cavity region 210 and the second Bragg resonant cavity region 220 correspond to the above-mentioned DBR resonant cavity. The first Bragg resonant cavity region 210 and the second Bragg resonant cavity region 220 are respectively arranged on both sides of the microring resonant cavity region 240. Specifically, the first Bragg resonant cavity region 210 and the second Bragg resonant cavity region 220 are parallel to each other in the second direction Y, and the microcavity resonant region is arranged between the first Bragg resonant cavity region 210 and the second Bragg resonant cavity region 220 in the second direction Y.

[0053] For example, the first Bragg resonant cavity region 210 includes a first Bragg reflector 211 formed based on a first strip waveguide 211_1 and a first extension portion of the first strip waveguide 211_1 protruding from the first Bragg reflector 211. The second Bragg resonant cavity region 220 includes a second Bragg reflector 221 formed based on a second strip waveguide 221_1 and a second extension portion of the second strip waveguide 221_1 protruding from the second Bragg reflector 221. The first Bragg resonant cavity region 210 is coupled to the microring resonant cavity region 240 through the first extension portion, and the second Bragg resonant cavity region 220 is coupled to the microring resonant cavity region 240 through the second extension portion.

[0054] On this basis, the present disclosure does not specifically limit the position of the gain region 230, as long as the optical signal generated by the gain region 230 can be transmitted back and forth in the laser. Figure 3 It can be seen that in one embodiment of the present disclosure, the gain region 230 is located between the second extension portion and the second Bragg reflector 221. However, the embodiments of the present disclosure are not limited thereto, and the gain region 230 is located between the first extension portion and the first Bragg reflector 211; or, the gain region 230 may also be located between the microring resonant cavity region 240 and the first extension portion; or, the gain region 230 may also be located between the microring resonant cavity region 240 and the second extension portion.

[0055] Taking into account the difficulty of processing, cavity performance and device size, the parameters of each part of the cavity should be optimized within a certain range. The parameters that affect the cavity performance mainly include waveguide width, microring radius and microring coupling spacing. Figure 4 The relationship between the mode effective refractive index and the waveguide width when the wavelength is 1550nm and the waveguide thickness is 400nm is used to obtain the maximum waveguide size for single-mode transmission. Figure 4TE0, TM0, TE1 and TM1 represent different modes that can be transmitted in the waveguide, and cutoff represents the cutoff refractive index that can be transmitted in the waveguide (since the waveguide is set in the silica cladding, cutoff=1.444 here)

[0056] It can be seen that when the waveguide width is less than 1.1 microns, single TE (Transverse Electric) mode transmission can be maintained. In this embodiment, the waveguide width is selected to be 0.8 microns and the thickness is 0.4 microns. The electric field distribution is as follows: Figure 5 It should be noted that Figure 5 In the figure, z corresponds to the thickness and y corresponds to the waveguide width. Considering the stable transmission of single mode in the waveguide, the waveguide size needs to be set in the range of 800 nm to 1100 nm. Therefore, the width range of the first strip waveguide 211_1 and the second strip waveguide 221_1 is 800 nm to 1100 nm. Considering the coupling efficiency and processing difficulty, the coupling spacing is kept in the range of 150 nm to 500 nm as much as possible. Therefore, the coupling spacing between the first Bragg resonant cavity area 210 and the microring resonant area is 150 nm to 500 nm, preferably 400 nm. The coupling spacing between the second Bragg resonant cavity area 220 and the microring resonant area is 150 nm to 500 nm, preferably 400 nm.

[0057] refer to Figure 6 In the embodiment of the present disclosure, the first strip waveguide 211_1 and the second strip waveguide 221_1 extend along the first direction X, the gratings of the first Bragg reflector 211 are arranged on both sides of the first strip waveguide 211_1 in the second direction Y, and the gratings of the second Bragg reflector 221 are arranged on both sides of the second strip waveguide 221_1 in the second direction Y.

[0058] The first Bragg reflector 211 in the first Bragg resonant cavity region is substantially configured as a total reflective mirror, the reflectivity of the second Bragg reflector 221 in the second Bragg resonant cavity region 220 is lower than that of the first Bragg reflector 211, and one end of the second Bragg resonant cavity region 220 away from the microring resonant cavity region 240 is connected to the grating coupler. For example, the reflectivity of the first Bragg reflector 211 is greater than or equal to 99% and less than or equal to 100%, preferably 100%. The reflectivity of the second Bragg reflector 221 is greater than or equal to 90% and less than or equal to 99%, preferably 99%.

[0059] The reflectors are distributed at both ends of the laser body 200. Ideally, one end is a full reflector and the other end is a reflector with a reflectivity of more than 99%, so that the laser in the cavity can be emitted through this end. The light reflected back to the gain medium can continue to induce new stimulated radiation. The stimulated radiation photons travel back and forth in the cavity many times to form coherent continuous oscillations, and thus a laser is obtained. Therefore, by reasonably adjusting the number of periods of the DBR gratings on both sides, the reflectivity of the DBR grating on one side is made to reach 100% as much as possible as a high reflection end, and the reflectivity of the DBR grating on the other side is slightly lower than that of the other side as a low reflection end, so that the light waves that meet the Bragg conditions can travel back and forth many times in the laser body 200 to form coherent continuous oscillations and form lasers. By connecting a grating coupler at the low reflection end, the required laser mode can be received from the coupler.

[0060] The parameters that affect the performance of the resonant cavity mainly include the number of grating periods, the grating tooth length, and the grating duty cycle. Taking into account the difficulty of processing, the performance of the resonant cavity, and the size of the device, the parameter optimization of each part in the resonant cavity must be within a certain range. Taking into account the difficulty of processing, the grating duty cycle needs to be controlled between 40% and 60%. Therefore, the grating duty cycle range of the first Bragg reflector 211 and the second Bragg reflector 221 is 40% to 60%. Taking into account the difficulty of processing, the grating tooth length needs to be greater than the waveguide width of 200nm to 1200nm. Therefore, the grating tooth length value of the first Bragg reflector 211 is 200 nm to 1200 nm larger than the width value of the first strip waveguide 211_1. The grating tooth length value of the second Bragg reflector 221 is 200 nm to 1200 nm larger than the width value of the second strip waveguide 221_1. Considering the device size, the number of double-sided grating periods is controlled within N=200 as much as possible, wherein the reflectivity of the total reflection end is kept at 99% as much as possible, and the reflection efficiency of the partial reflection end is controlled at about 90%. Therefore, the grating period of the first Bragg reflector 211 is greater than the grating period of the second Bragg reflector 221. The grating period number of the first Bragg reflector 211 ranges from 120 to 200. The grating period number of the second Bragg reflector 221 ranges from 60 to 200.

[0061] According to the embodiment of the present disclosure, when light is transmitted in the DBR resonant cavity after being emitted from the gain region 230, the Bragg grating in the DBR resonant cavity has a strong selectivity for the wavelength, and only the Bragg wavelength that meets the Bragg condition is Only then can it participate in feedback and be reflected by the grating. Therefore, only light that meets the conditions can resonate in the DBR resonant cavity. By reasonably designing the tooth length, period and duty cycle of the DBR grating, light in the communication band (around 1550nm) can resonate in the resonant cavity to form a laser mode. However, for on-chip lasers, it is necessary to maintain stable single-mode behavior while reducing the line width. Since the reflectors at both ends of the DBR resonant cavity are composed of Bragg gratings, the reflectivity of the Bragg grating is positively correlated with the product of the coupling coefficient and the cavity length:

[0062] (1)

[0063] Where R is the grating reflectivity, k is the coupling coefficient, and L is the grating length.

[0064] In this way, the grating length can be increased while reducing the grating coupling coefficient. This method can reduce the width of the reflection spectrum while maintaining the reflectivity unchanged, and maintain stable single-mode behavior while achieving narrow line width. However, this method will increase the cavity length of the DBR resonant cavity, resulting in a shorter cavity mode interval. On this basis, in order to effectively solve the problem of shortened cavity mode interval, the present invention introduces a microring in the middle of the double-sided Bragg grating.

[0065] Figure 6 The schematic diagram of the DBR structure is shown schematically. When light is emitted by the device and then transmitted in the DBR, the Bragg grating in the DBR resonant cavity has a strong selection effect on the wavelength. Only the Bragg wavelength that meets the Bragg condition can participate in the feedback and be reflected by the grating, so that the light resonates in the DBR resonant cavity, that is, it satisfies the following equation:

[0066] (2)

[0067] in, represents the grating period. n eff represents the effective refractive index in the DBR waveguide. is the wavelength of light. m is a positive integer, indicating the grating order.

[0068] Based on formula (5), the grating period can be designed by combining the emission wavelength and the effective refractive index of the waveguide. From the above formula, it can be seen that the grating period is proportional to the grating order, that is, the larger the m, the The larger the grating period, the larger the device is. Under the same conditions such as grating duty cycle, etching depth, and grating length, the reflectivity of low-order gratings is higher than that of high-order gratings, and the light loss is lower, which can obtain better device performance. However, low-order gratings have higher requirements on the manufacturing process, and require more precise and costly electron beam exposure or photolithography exposure processes. High-order gratings have lower requirements on process equipment due to their larger grating period, which greatly reduces the manufacturing cost of the device. Therefore, the grating order can be designed according to the process. Since the loss of second-order and above gratings is large, and the current processing equipment can meet the accuracy of first-order gratings, a first-order grating is selected, that is, m=1, and the grating period is obtained. It is 470nm.

[0069] However, the grating duty cycle , grating tooth length L and grating period number N will affect the reflection characteristics of the DBR grating. Figure 7 and Figure 8 That is, the grating period number N, the grating tooth length L, and the grating duty cycle The influence on the grating reflection characteristics, such as Figure 7 As shown, when the grating duty cycle and grating tooth length are constant, the maximum reflectivity of the DBR grating is proportional to the number of periods. In order to obtain a smaller size and a larger FSR, the number of periods at the high reflection end of the DBR is preferably 120, and the number of grating periods at the low reflection end is preferably 60; Figure 8 The figure shows the relationship between the maximum reflectivity of the DBR grating and the grating tooth length when the grating period number and the grating duty cycle are constant. It can be seen that when the tooth length L is 1.4 microns, the maximum reflectivity has not increased significantly, and as the tooth length increases, the processing difficulty will be higher, and the half-height width of the reflection spectrum will gradually increase. Therefore, the tooth length L of the embodiment of the present disclosure is preferably 1.4 microns; Fig. 9 The figure shows the relationship between the maximum reflectivity of the DBR grating and the grating duty cycle when the grating period number and grating tooth length are constant. It can be seen that the overall trend is to increase first and then decrease. In order to reduce the processing error, the grating duty cycle is selected to be 50%. Fig.10 That is, it shows the reflection spectrum of the DBR grating under the above conditions, which can meet our needs well.

[0070] The microring resonant cavity area 240 is used to filter the light transmitted in the laser body 200. Only light with a wavelength that meets the microring resonance condition can continue to resonate in the resonant cavity. Therefore, the microring radius is reasonably designed to align the resonant cavity mode wavelength and the microring filter wavelength around the communication wavelength, so that the filtering effect can be achieved, and finally a high-performance laser signal can be emitted at the low-reflection end of the DBR.

[0071] In order for the microring to have a filtering effect, the FSR (Free Spectral Range) of the microring resonant cavity itself needs to be larger than the FSR of the DBR resonant cavity. The upper limit of the microring radius can be obtained as 30 μm using the following formula (3):

[0072] (3)

[0073] in, is the emission wavelength. R is the radius of the micro-ring. is the group refractive index, expressed as:

[0074] (4)

[0075] At the same time, in order to reduce the difficulty of process and device testing, the lower limit of the microring radius is set at 10μm. Therefore, the microring radius of the microring resonance zone is 10 µm~30 µm, preferably 22.41µm.

[0076] Fig.11 The schematic diagram of the structure of a single dual-channel microring is shown. When light is emitted from the input end and then transmitted in the microring, the light coupling condition needs to be met in order for the light to resonate in the microring, that is, the following equation is satisfied:

[0077] (5)

[0078] in, is the emission wavelength, n eff is the effective refractive index of the waveguide, R is the radius of the microring, and n is the resonance order.

[0079] Since the resonance order is not fixed and can be designed by oneself, it is possible to allow light of different wavelengths to be transmitted through resonance together. Therefore, the difference between the two resonance wavelengths is set as the free spectrum range, satisfying the above formula (3).

[0080] The embodiments of the present disclosure are mainly aimed at light waves with a wavelength of 1500 nm to 1600 nm, specifically, light waves with a wavelength of 1550 nm. In order to reduce bending loss and make the FSR as large as possible, the selection of the bending radius is particularly important. Through optimization, the microring radius of 22.41 µm can well meet the requirements. When the input light in the straight waveguide (i.e., strip waveguide) passes through the intermediate coupling region, part of the light is coupled to the ring waveguide (i.e., the microring resonant cavity region 240), and part of the light remains in the straight waveguide. After the light coupled into the ring waveguide propagates through a circumference, it comes to the coupling region again, and part of the light will be coupled into the straight waveguide, and part of the light will remain in the ring waveguide. And so on and so forth. Therefore, the coupling spacing between the strip waveguide and the microring is particularly important. Through continuous calculation and optimization, when the coupling spacing d is 400 nm, it is critical coupling. Fig.12 The filtering effect of the micro-ring is schematically shown.

[0081] Therefore, the present disclosure selects light that meets the Bragg wavelength through the first Bragg resonant cavity area 210 and the second Bragg resonant cavity area 220 to resonate in the laser body 200, and selects the cavity mode that meets the microring resonance condition through the filtering performance of the microring resonant cavity area 240, so that the FSR, FWHM and SMSR of the resonant cavity can be effectively optimized. In order to achieve narrow line width while maintaining stable single-mode behavior, a microring is introduced into the DBR resonant cavity. The introduction of the microring will increase the length of the cavity and shorten the cavity mode interval, but only the cavity mode that meets the microring resonance condition can be emitted, that is, the filtering effect can be achieved. At the same time, simulation verification finds that the introduction of the microring structure can further improve the SMSR of the resonant cavity and reduce the FWHM.

[0082] Fig.13 The schematic diagram shows the comparison of the normalized resonance intensity of the laser emitted from the low reflection end of the DBR resonant cavity in the embodiment of the present disclosure (microring + DBR) and the related art. Fig.13It can be seen that although the addition of the microring makes the cavity length of the entire laser body 200 longer, since only the cavity mode that meets the microring resonance condition can be emitted, the FSR of the laser mode is significantly increased. The mode wavelength obtained by the microring + DBR resonant cavity is 1550.62 nm, which meets the requirements of the communication wavelength. The obtained FWHM is about 0.104 nm, FSR is about 10 nm, and SMSR is about 2.88; while the laser mode FWHM obtained by the DBR resonant cavity alone is about 0.41 nm, FSR is about 6 nm, and SMSR is about 1.2. Therefore, the addition of the microring can significantly improve the resonant cavity performance. The design of the waveguide material and the resonant cavity structure in the laser will affect the ultimate effect of the entire on-chip transmission. Based on this, the present invention regulates the quality factor of the resonant cavity by designing the size and coupling of the DBR and the microring, and uses silicon nitride material and silicon dioxide material to make the device and the cladding 300 to reduce the loss. Compared with the laser resonant cavity in the related art, it has the advantages of higher light extraction efficiency, better laser performance (SMSR, FSR, FWHM), matching of the light emitting wavelength with the optical communication wavelength, compatibility with CMOS process and high integration, and 100% coupling with on-chip devices. It is more conducive to the integrated integration of silicon-based optical devices, greatly expanding its application range, and is of great significance to the development of photonic integrated circuits.

[0083] According to the embodiments of the present disclosure, after the laser of the present disclosure forms a laser mode through the resonance principle of the first Bragg resonant cavity area 210 and the second Bragg resonant cavity area 220, the required laser mode is selected by using the filtering function of the micro-ring resonant cavity area 240 to obtain the required laser signal. Based on this, the laser of the present disclosure can obtain a narrow line width and maintain a stable single-mode behavior, and improve the SMSR of the resonant cavity in the laser, and reduce the FSR and FWHM. In addition, since the first Bragg resonant cavity area 210, the second Bragg resonant cavity area 220 and the micro-ring resonant cavity area 240 can be directly manufactured on the substrate 100, a high coupling efficiency with other on-chip devices can be obtained.

[0084] Based on this, the present disclosure solves the problems in the related art such as the incompatibility of on-chip integrated light sources with CMOS processes, the mismatch between the light emission wavelength and the optical communication wavelength, poor laser performance (SMSR, FSR, FWHM), low integration, and low coupling efficiency with on-chip devices.

[0085] It will be appreciated by those skilled in the art that the features described in the various embodiments of the present disclosure may be combined and / or combined in a variety of ways, even if such combinations or combinations are not explicitly described in the present disclosure. In particular, without departing from the spirit and teachings of the present disclosure, the features described in the various embodiments of the present disclosure may be combined and / or combined in a variety of ways. All of these combinations and / or combinations fall within the scope of the present disclosure.

[0086] The embodiments of the present disclosure are described above. However, these embodiments are only for illustrative purposes and are not intended to limit the scope of the present disclosure. Although the embodiments are described above, this does not mean that the measures in the various embodiments cannot be used in combination to advantage. Without departing from the scope of the present disclosure, those skilled in the art may make a variety of substitutions and modifications, which should all fall within the scope of the present disclosure.

Claims

1. An on-chip laser comprising: substrate; A laser body disposed on the substrate and extending along a first direction; as well as a cladding surrounding the laser body in a second direction intersecting the first direction; Wherein, the laser body comprises a gain region, a micro-ring resonant cavity region, a first Bragg resonant cavity region and a second Bragg resonant cavity region, and the first Bragg resonant cavity region and the second Bragg resonant cavity region are respectively arranged on both sides of the micro-ring resonant cavity region; When the gain region generates an optical signal, the optical signal repeatedly travels back and forth in the first Bragg resonant cavity region, the microring resonant cavity region, and the second Bragg resonant cavity region, thereby obtaining a laser signal.

2. The laser according to claim 1, wherein: The gain region is connected to one end of the first Bragg resonant cavity region or the second Bragg resonant cavity region close to the microring resonant cavity region, and is coupled to the microring resonant cavity region.

3. The laser according to claim 2, wherein: The gain region extends along the first direction, and an end of the gain region in the first direction is tapered so as to converge a multi-mode optical signal into a single-mode optical signal.

4. The laser according to claim 1, wherein: The first Bragg reflector in the first Bragg resonant cavity region is substantially configured as a total reflective mirror, the reflectivity of the second Bragg reflector in the second Bragg resonant cavity region is lower than that of the first Bragg reflector, and one end of the second Bragg resonant cavity region away from the microring resonant cavity region is connected to a grating coupler.

5. The laser according to claim 4, wherein: The reflectivity of the first Bragg reflector is greater than or equal to 99% and less than or equal to 100%; the reflectivity of the second Bragg reflector is greater than or equal to 90% and less than or equal to 99%.

6. The laser according to claim 1, wherein The first Bragg resonant cavity region includes a first Bragg reflector formed based on a first strip waveguide and a first extension portion of the first strip waveguide protruding from the first Bragg reflector; The second Bragg resonant cavity region includes a second Bragg reflector formed based on a second strip waveguide and a second extension portion of the second strip waveguide protruding from the second Bragg reflector; The first Bragg resonant cavity region is coupled to the microring resonant cavity region through the first extension portion, and the second Bragg resonant cavity region is coupled to the microring resonant cavity region through the second extension portion.

7. The laser according to claim 6, wherein: The first strip waveguide and the second strip waveguide extend along the first direction, the gratings of the first Bragg reflector are arranged on both sides of the first strip waveguide in the second direction, and the gratings of the second Bragg reflector are arranged on both sides of the second strip waveguide in the second direction.

8. The laser according to any one of claims 4 to 7, wherein: The grating period of the first Bragg reflector is greater than the grating period of the second Bragg reflector; The grating period number of the first Bragg reflector ranges from 120 to 200; The grating period number of the second Bragg reflector ranges from 60 to 200; The grating duty ratio range of the first Bragg reflector and the second Bragg reflector is 40% to 60%; The width of the first strip waveguide and the second strip waveguide are both in the range of 800 nm to 1100 nm; The grating tooth length of the first Bragg reflector is 200 nm to 1200 nm greater than the width of the first strip waveguide; The grating tooth length of the second Bragg reflector is 200 nm to 1200 nm greater than the width of the second strip waveguide.

9. The laser according to any one of claims 1 to 7, wherein: The first Bragg resonant cavity region and the second Bragg resonant cavity region are parallel to each other in the second direction, and the microcavity resonant cavity region is arranged between the first Bragg resonant cavity region and the second Bragg resonant cavity region in the second direction.

10. The laser according to any one of claims 1 to 7, wherein: The coupling spacing between the first Bragg resonant cavity region and the microring resonant region is 150 nm to 500 nm; The coupling spacing between the second Bragg resonant cavity region and the microring resonant region is 150 nm to 500 nm; The microring radius of the microring resonance region is 10 μm to 30 μm; The material of the waveguide includes silicon nitride; The material of the substrate includes silicon; The material of the cladding layer includes silicon dioxide.

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