阅读说明：本技术 片上泵浦-信号光共振的铒硅酸盐激光器及其制备方法 (Erbium silicate laser of on-chip pump-signal light resonance and preparation method thereof ) 是由 王兴军 周佩奇 何燕冬 于 2019-11-01 设计创作，主要内容包括：本发明实施例提供的片上泵浦-信号光共振的铒硅酸盐激光器及其制备方法,包括激光有源区和混合谐振腔,混合谐振腔加载在激光有源区的上表面；激光有源区由下至上依次设置有硅衬底层和增益介质层；增益介质层为氮化硅层与铒硅酸盐层交替结构,增益介质层的上下表面均为氮化硅层；混合谐振腔为条形波导结构,用于控制光场在激光有源区中沿波导方向传输,保证泵浦光与信号光在腔中同时进行谐振增强,以提高泵浦的吸收效率和信号光的谐振强度。通过采用铒硅酸盐化合物作为光增益材料,有效的提升了材料单位距离的光学增益；降低了波导的传输损耗；设置条形加载的谐振腔波导结构,解决了铒硅酸盐激光谐振腔的刻蚀困难的同时提高了激光的输出特性。(The erbium silicate laser for on-chip pumping-signal light resonance and the preparation method thereof provided by the embodiment of the invention comprise a laser active area and a mixed resonant cavity, wherein the mixed resonant cavity is loaded on the upper surface of the laser active area; the laser active region is sequentially provided with a silicon substrate layer and a gain medium layer from bottom to top; the gain medium layer is of a structure in which silicon nitride layers and erbium silicate layers are alternated, and the upper surface and the lower surface of the gain medium layer are both silicon nitride layers; the mixed resonant cavity is of a strip waveguide structure and is used for controlling the transmission of a light field in a laser active region along the waveguide direction, so that the simultaneous resonance enhancement of the pump light and the signal light in the cavity is ensured, and the absorption efficiency of the pump and the resonance intensity of the signal light are improved. By adopting the erbium silicate compound as the optical gain material, the optical gain of the material per unit distance is effectively improved; the transmission loss of the waveguide is reduced; the strip-type loaded resonant cavity waveguide structure is arranged, so that the problem of difficulty in etching the erbium silicate laser resonant cavity is solved, and the output characteristic of laser is improved.)

1. An erbium silicate laser for on-chip pump-signal light resonance, comprising: the laser device comprises a laser active area and a hybrid resonant cavity, wherein the hybrid resonant cavity is coupled and loaded on the upper surface of the laser active area;

the laser active region is sequentially provided with a silicon substrate layer and a gain medium layer from bottom to top;

the gain medium layer is of a structure in which silicon nitride layers and erbium silicate layers are alternated, and the upper surface and the lower surface of the gain medium layer are both the silicon nitride layers;

the hybrid resonant cavity is of a strip waveguide structure and is used for controlling the transmission of a light field in the laser active region along the waveguide direction.

2. An on-chip pump-signal optically resonant erbium silicate laser according to claim 1, characterized in that the hybrid cavity is constituted by a pump resonant external cavity and a signal resonant external cavity.

3. An on-chip pump-signal optically resonant erbium silicate laser according to claim 2, characterized in that the pump resonant external cavity comprises a first DBR resonator and a second DBR resonator, and the signal resonant external cavity comprises a first DFB resonator and a second DFB resonator, wherein:

the first DBR resonator, the first DFB resonator, the second DBR resonator and the second DFB resonator are all of grating structures and are sequentially coupled and connected from front to back according to the direction of an optical path;

the first DBR resonator is used for receiving pump light and forming a pump front reflection area;

the first DFB resonator is a main resonant cavity and is used for carrying out resonance enhancement on signal light;

the second DBR resonator forms a pump back reflection region for back reflection of the pump light and isolating the pump light from entering the second DFB resonator region;

the second DFB resonator is a secondary resonant cavity.

4. An on-chip pump-signal optical resonant erbium silicate laser according to claim 3, characterized in that the first and second DFB resonators are the same size.

5. An on-chip pump-signal optical resonant erbium silicate laser according to claim 3, characterized in that 1/4 phase shifting regions are provided in the first DFB resonator.

6. An on-chip pump-signal optical resonant erbium silicate laser according to claim 1, characterized in that a first SiO is provided intermediate the silicon substrate layer and the gain medium layer₂An isolation layer with a second SiO layer arranged between the mixed resonant cavity and the laser active region₂An isolation layer.

7. A preparation method of an erbium silicate laser with on-chip pump-signal light resonance is characterized by comprising the following steps:

step S1, growing a silicon nitride layer with a first preset thickness on the silicon substrate layer based on a low-pressure chemical vapor deposition method;

step S2, growing an erbium silicate gain layer with a second preset thickness on the silicon nitride layer;

step S3, growing the silicon nitride layer again on the erbium silicate gain layer;

step S4, repeating the steps S2-S3 until an erbium silicate-silicon nitride alternating structure with a preset number of layers is obtained, wherein the upper surface and the lower surface of the erbium silicate-silicon nitride alternating structure are both silicon nitride layers;

step S5, depositing SiO with preset thickness on the upper surface of the erbium silicate-silicon nitride alternating structure₂A layer;

step S6, based on photolithography, etching the SiO layer₂Loading a template of the mixed resonant cavity layer by layer;

and step S7, etching the mixed resonant cavity on the template of the mixed resonant cavity based on the ion etching technology.

8. The method for manufacturing an on-chip pump-signal optical resonance erbium silicate laser according to claim 7, further comprising, before said step S1:

on the basis of a thermal oxidation process,disposing a first SiO on the silicon substrate layer₂An isolation layer.

9. A method of fabricating an on-chip pump-signal optical resonant erbium silicate laser as claimed in claim 7 wherein said etching of said hybrid cavity on a template of said hybrid cavity comprises: designing the structure and the size of the hybrid resonant cavity, and etching the hybrid resonant cavity according to the structure and the size;

wherein the designing the structure of the hybrid resonant cavity comprises:

the first DBR resonator, the first DFB resonator, the second DBR resonator and the second DFB resonator are sequentially coupled from front to back in the direction of an optical path to form a mixed resonant cavity, and the mixed resonant cavity is of a grating structure; the first DBR resonator and the second DBR resonator form a pumping resonance external cavity; the first DFB resonator and the second DFB resonator form a signal resonant external cavity;

the designing the size of the hybrid resonant cavity comprises:

acquiring grating periods of the first DBR resonator and the first DFB resonator based on a Bragg condition formula;

acquiring grating duty ratios and grating tooth depths of the first DBR resonator and the first DFB resonator based on a signal light reflectivity calculation formula;

determining grating parameters of the second DBR resonator based on the Q value matching relationship between the pump resonance external cavity and the erbium silicate-silicon nitride alternating structure;

and determining the grating parameters of the first DFB resonator as the grating parameters of the second DFB resonator.

10. A method of fabricating an on-chip pump-signal optical resonant erbium silicate laser as claimed in claim 9,

the bragg condition formula is:

the signal light reflectivity calculation formula is as follows: r ═ tanh (kl);

wherein lambda is the grating period, lambda is the central wavelength of the resonator, n_effIs the effective refractive index corresponding to the waveguide cross section of the hybrid resonant cavity, R is the reflectivity, D is the grating duty cycle, L is the length of the resonant cavity, k is the grating coupling coefficient, and h is the tooth depth.

Technical Field

The invention relates to the technical field of photoelectron, in particular to an erbium silicate laser for on-chip pump-signal light resonance and a preparation method thereof.

Background

In recent years, silicon-based optoelectronic technology has played an increasingly important role in important fields such as optical communication and data centers, and has been rapidly developed. Among them, the silicon-based laser, as a key device of the silicon-based optoelectronic device, especially a narrow linewidth laser, has a huge application potential due to its advantages of high coherence, high frequency stability, wide wavelength tuning, etc. Therefore, the integration of the high-performance narrow linewidth laser on the silicon-based optoelectronic platform is of great significance to the application in the fields of ultra-high-speed optical communication, long-distance laser communication, ultra-high resolution laser radar, optical sensing and the like. However, the investigation of silicon-based light sources is quite challenging due to the indirect band nature of silicon.

In conventional research, this difficulty has been addressed by hybrid integrated III-V silicon-based lasers, which have been designed to control the gain and loss at different wavelengths by integrating frequency selective structures in the resonator or by coupling mode selective devices to each other outside the resonator, thereby compressing the laser linewidth. Phase-shifted Distributed Feedback (DFB) or Distributed Bragg Reflector (DBR) resonators have been shown to produce optical laser linewidths on the order of MHz.

However, the above method requires complicated manufacturing steps and has high temperature sensitivity, which has great limitations. Compared with the monolithic erbium (Er) -doped silicon-based laser, the monolithic Er-doped silicon-based laser has the advantages of temperature insensitivity, long light-emitting life, low noise and compatibility with Complementary Metal Oxide Semiconductor (CMOS) technology, is more favorable for large-scale integration of the silicon-based laser, can realize kHz line width by combining with a phase-shift DFB resonant cavity, and has better development prospect.

However, the existing silicon-based erbium-doped laser cannot realize high-quality narrow linewidth laser output and cannot meet the on-chip requirements of a silicon-based optoelectronic chip. The reason is that on one hand, the output power required by the on-chip silicon-based laser at least exceeds 30mW, and in order to meet the requirement of low power consumption, the pumping efficiency must be further improved to reduce the pumping power; on the other hand, future ultra-narrow linewidth laser applications require narrower laser linewidths, such as on the order of sub-kHz or Hz. Existing narrow linewidth lasers cannot meet these requirements. As indicated by Schawlow-Townes linewidths, higher laser output power, higher laser efficiency, or higher quality factor (Q) resonators are required to further increase linewidths.

Disclosure of Invention

In order to effectively overcome the defect that requirements on output power, laser efficiency and quality factors of pump laser are too strict when ultra-narrow linewidth laser is obtained in the prior art, the embodiment of the invention provides an on-chip pump-signal light resonance erbium silicate laser and a preparation method thereof.

In one aspect, an embodiment of the present invention provides an on-chip pump-signal light resonant erbium silicate laser, including: the laser device comprises a laser active area and a hybrid resonant cavity, wherein the hybrid resonant cavity is coupled and loaded on the upper surface of the laser active area; the laser active region is sequentially provided with a silicon substrate layer and a gain medium layer from bottom to top; the gain medium layer is of a structure in which silicon nitride layers and erbium silicate layers are alternated, and the upper surface and the lower surface of the gain medium layer are both silicon nitride layers; the hybrid resonant cavity is of a strip waveguide structure and is used for controlling the transmission of an optical field in the laser active region along the waveguide direction.

Further, the mixing resonant cavity is composed of a pumping resonant external cavity and a signal resonant external cavity.

Further, the pump resonant external cavity includes a first DBR resonator and a second DBR resonator, and the signal resonant external cavity includes a first DFB resonator and a second DFB resonator, wherein:

the first DBR resonator, the first DFB resonator, the second DBR resonator and the second DFB resonator are all of grating structures and are sequentially coupled and connected from front to back according to the direction of an optical path; the first DBR resonator is used for receiving the pump light and forming a pump front reflection area; the first DFB resonator is a main resonant cavity and is used for carrying out resonance enhancement on signal light; the second DBR resonator forms a pumping back reflection area which is used for performing back reflection on the pumping light and isolating the pumping light from entering the second DFB resonator area; the second DFB resonator is a secondary resonant cavity.

Further, the first DFB resonator and the second DFB resonator have the same size.

Further, an 1/4 phase shift region is provided in the first DFB resonator described above.

Further, a first SiO layer is arranged between the silicon substrate layer and the gain medium layer₂An isolation layer with a second SiO layer arranged between the mixed resonant cavity and the laser active region₂An isolation layer.

On the other hand, the embodiment of the invention also provides a preparation method of the erbium silicate laser with on-chip pump-signal light resonance, which comprises the following steps:

step S1, growing a silicon nitride layer with a first preset thickness on the silicon substrate layer based on a low-pressure chemical vapor deposition method; step S2, growing an erbium silicate gain layer with a second preset thickness on the silicon nitride layer; step S3, growing a silicon nitride layer on the erbium silicate gain layer again; step S4, repeating the steps S2-S3 until a preset number of layers of erbium silicate-silicon nitride alternating structures are obtained, wherein the upper and lower surfaces of the erbium silicate-silicon nitride alternating structures are silicon nitride layers; step S5, depositing SiO with preset thickness on the upper surface of the erbium silicate-silicon nitride alternating structure₂A layer; step S6, based on photolithography, on SiO₂Loading a template of the mixed resonant cavity layer by layer; and step S7, etching a mixed resonant cavity on the template of the mixed resonant cavity based on the ion etching technology.

Further, before step S1, the method further includes: arranging a first SiO on a silicon substrate layer based on a thermal oxidation process₂An isolation layer.

Further, the etching the hybrid resonant cavity on the template of the hybrid resonant cavity includes: designing the structure and the size of the hybrid resonant cavity, and etching the hybrid resonant cavity according to the structure and the size;

wherein, the structure of the mixed resonant cavity of design includes: the first DBR resonator, the first DFB resonator, the second DBR resonator and the second DFB resonator are sequentially coupled from front to back in the direction of an optical path to form a mixed resonant cavity, and the mixed resonant cavity is of a grating structure; the first DBR resonator and the second DBR resonator form a pumping resonance external cavity; the first DFB resonator and the second DFB resonator form a signal resonance external cavity;

designing the dimensions of the hybrid resonator comprises:

acquiring grating periods of a first DBR resonator and a first DFB resonator based on a Bragg condition formula; acquiring the grating duty ratio and the grating tooth depth of the first DBR resonator and the first DFB resonator based on a signal light reflectivity calculation formula;

determining grating parameters of the second DBR resonator based on the Q value matching relation of the pump resonance external cavity and the erbium silicate-silicon nitride alternative structure;

and determining the grating parameters of the first DFB resonator as the grating parameters of the second DFB resonator.

Further, the bragg condition formula is:

the signal light reflectivity calculation formula is as follows: r ═ tanh (kl);

wherein lambda is the grating period, lambda is the central wavelength of the resonator, n_effIs the effective refractive index corresponding to the waveguide cross section of the hybrid resonant cavity, R is the reflectivity, D is the grating duty cycle, L is the length of the resonant cavity, k is the grating coupling coefficient, and h is the tooth depth.

According to the on-chip pump-signal light resonance erbium silicate laser and the preparation method thereof, firstly, the gain medium layer formed by the silicon nitride layer and the erbium silicate layer is arranged, so that the erbium concentration in the gain layer is improved, the transmission loss in waveguide transmission is effectively reduced, and the optical gain of an amplifier in unit distance is greatly improved; secondly, through setting up the mixed resonant cavity, can guarantee that pump light and signal light carry out the resonance reinforcing simultaneously in the chamber to improve the absorption efficiency of pumping and the resonance intensity of signal light, the effectual linewidth and the threshold value that reduces the laser instrument, in order to form stable narrow linewidth laser output.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and those skilled in the art can also obtain other drawings according to the drawings without creative efforts.

Fig. 1 is a schematic structural diagram of an on-chip pump-signal light resonant erbium silicate laser provided in an embodiment of the present invention;

fig. 2 is a schematic structural cross-sectional view of an on-chip pump-signal light resonant erbium silicate laser provided in an embodiment of the present invention;

fig. 3 is a schematic cross-sectional view of a hybrid resonator of an on-chip pump-signal light resonant erbium silicate laser according to an embodiment of the present invention;

fig. 4 is a schematic flow chart of a method for manufacturing an on-chip pump-signal light resonant erbium silicate laser according to an embodiment of the present invention;

FIG. 5 is a schematic diagram of a design of parameters of a hybrid resonator according to an embodiment of the present invention;

FIG. 6 is a schematic diagram of another design parameter of a hybrid resonator according to an embodiment of the present invention

FIG. 7 is a schematic diagram of the energy level structure of erbium silicate provided by an embodiment of the present invention;

fig. 8 is a schematic diagram of a simulation result of laser output characteristics according to an embodiment of the present invention;

fig. 9 is a schematic diagram of a simulation result of a laser line width characteristic according to an embodiment of the present invention;

fig. 10 is a schematic flow chart of a method for manufacturing another on-chip pump-signal light resonant erbium silicate laser according to an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

On one hand, although the monolithic erbium (Er) -doped silicon-based laser at present has the advantages of temperature insensitivity, long luminescence life, low noise and compatibility with Complementary Metal Oxide Semiconductor (CMOS) technology, the maximum erbium concentration in an Er-doped medium can only reach-10 due to the limitation of solid solubility²⁰cm^-3The highest gain can only reach 2-5 dB/cm, so that the further improvement of the output performance of the laser is limited. To further improve the gain characteristics of the material, it is necessary to increase the erbium concentration in the erbium-doped medium.

On the other hand, the current silicon-based erbium-doped laser has high requirements on pumping efficiency and pumping power, so that the linewidth of the DFB resonant cavity is strictly limited by the length and the loss factor of the resonator, and the cavity feedback is still at a lower level, high-quality narrow linewidth laser output cannot be realized, and the requirements on a chip of a silicon-based optoelectronic chip cannot be met.

In view of the above disadvantages, as shown in fig. 1, the embodiment of the present invention provides an on-chip pump-signal light resonant erbium silicate laser, including but not limited to: the laser device comprises a laser active area and a hybrid resonant cavity, wherein the hybrid resonant cavity is coupled and loaded on the upper surface of the laser active area; the laser active region is sequentially provided with a silicon substrate layer and a gain medium layer from bottom to top; the gain medium layer is of a structure in which silicon nitride layers and erbium silicate layers are alternated, and the upper surface and the lower surface of the gain medium layer are both silicon nitride layers; the hybrid resonant cavity is of a strip waveguide structure and is used for controlling the transmission of an optical field in a laser active region along the waveguide direction.

Firstly, the material for manufacturing the erbium silicate layer in the embodiment of the invention can be selected from erbium-ytterbium co-doped silicate compounds, so that the concentration of erbium which actually plays a role in gain in the erbium silicate layer is not limited by solid solubility, and the concentration of erbium can be increased by one to two orders of magnitude, and the maximum concentration can reach-10²²cm^-3And the doping of ytterbium ion can improve the absorption cross section of the material to the pump light by one order of magnitude, and the characteristics greatly improve the optical gain of the amplifier per unit distance to 10²dB/cm, so that it is possible to furtherThe performance such as laser output power, conversion efficiency is improved, the size of the device is reduced, and the requirement of high-density integration is met.

Moreover, due to the low loss characteristic of silicon nitride (silicon nitride has a higher refractive index than Er silicate), the erbium silicate and the silicon nitride form an alternate mixed thin film structure, so that the transmission loss during waveguide transmission can be effectively reduced, and the net gain of the material is improved. In addition, the silicon nitride layer can also be used as a thermal expansion buffer layer, and the thermal expansion coefficient of the silicon nitride layer is between that of the substrate and the erbium silicate, so that the erbium silicate-silicon nitride alternate mixed film can effectively inhibit the stress generated by the film after high-temperature annealing and reduce the surface loss.

The thickness and number of layers of the erbium silicate film and the silicon nitride sub-layer can be respectively optimized in the embodiment of the invention, so that the pump and signal modes in the gain layer have higher limiting factors to provide enough gain and lower waveguide loss.

Finally, in the embodiment of the present invention, the strip waveguide structure is loaded on the upper surface of the laser active region, so that the erbium silicate waveguide laser provided by the embodiment of the present invention realizes on-chip pumping. The mixed resonant cavity is used as a DFB main resonant cavity, so that the limiting factor of a gain layer is improved, the overlapping strength of pump light and signal light is improved, stable narrow linewidth laser output is formed, etching of a gain material is not needed, and difficulty in equipment preparation is effectively reduced.

Specifically, after the pump light generated by the pump laser is incident through the left side of the gain medium layer shown in fig. 1, the pump light is controlled to be transmitted in the waveguide direction in the laser active region under the waveguide effect of the hybrid resonant cavity, that is, the pump light is transmitted in the direction corresponding to the hybrid resonant cavity, and the conversion is completed, so that the laser output with the preset line width is obtained.

According to the on-chip pump-signal light resonance erbium silicate laser provided by the embodiment of the invention, firstly, the erbium concentration in the gain layer is improved by arranging the gain medium layer formed by the silicon nitride layer and the erbium silicate layer, so that the transmission loss in waveguide transmission is effectively reduced, and the optical gain of an amplifier in unit distance is greatly improved; secondly, through setting up the mixed resonant cavity, can guarantee that pump light and signal light carry out the resonance reinforcing simultaneously in the chamber to improve the absorption efficiency of pumping and the resonance intensity of signal light, the effectual linewidth and the threshold value that reduces the laser instrument, in order to form stable narrow linewidth laser output.

An on-chip pump-signal optical resonant erbium silicate laser is based on the above-described embodiment, as an alternative embodiment, wherein the hybrid cavity is formed by a pump resonant external cavity and a signal resonant external cavity.

Specifically, the central wavelength of the pump resonant external cavity is equal to the wavelength of the pump light, and is mainly used for improving the resonance intensity of the entering pump light (980nm) and improving the absorption efficiency of the pump light. The signal resonance external cavity is used as a main resonant cavity generated by the signal light, so that the resonance intensity of the signal light is improved, and the laser output efficiency is improved.

Based on the content of the foregoing embodiment, as an alternative embodiment, the pump resonant external cavity mainly includes a first DBR resonator and a second DBR resonator; the signal resonance external cavity mainly comprises a first DFB resonator and a second DFB resonator, wherein:

the first DBR resonator, the first DFB resonator, the second DBR resonator and the second DFB resonator are all of grating structures and are sequentially coupled and connected from front to back according to the direction of an optical path; the first DBR resonator is used for receiving the pump light and forming a pump front reflection area; the first DFB resonator is a main resonant cavity and is used for carrying out resonance enhancement on signal light; the second DBR resonator forms a pumped reflective region. The second DFB resonator is used for carrying out back reflection on the pump light and isolating the pump light from entering the second DFB resonator region; the second DFB resonator is a secondary resonant cavity.

In all embodiments of the present invention, the signal light with the wavelength of 1535nm is obtained by the pump light with the wavelength of 980nm as an example, and the description is not to be construed as limiting the protection scope of the embodiments of the present invention.

In the embodiment of the invention, the material of the mixed resonant cavity is made of silicon-based material, such as SiO₂That is, the hybrid resonant cavity is a silicon-based strip-loading waveguide structure, and can be divided into four regions, each region being composed of different regionsThe grating composition is as follows:

region 1 (pump front reflector) is formed by a first DBR resonator, whose center wavelength is 980nm, located at the left end of the hybrid resonator shown in fig. 1, and serves to receive the pump light and to reflect it externally during pumping.

Region 2, which is the main cavity for signal light to generate laser output, provides the main optical feedback for the laser output, and is formed by a first DFB resonator having a center wavelength of 1535 nm. Single longitudinal mode output control of erbium silicate waveguide lasers is generally applicable to cavities with large values of κ L (k being the grating coupling coefficient and L being the length of the cavity), but the laser output power is low due to weak optical feedback and low gain with short cavity lengths; while a longer cavity length may limit the effective transmission distance of the pump light, in the erbium silicate waveguide laser provided in the embodiment of the present invention, reasonable grating parameters (such as period, duty cycle, tooth depth, etc.) are designed by following basic DFB parameters, in consideration of two aspects.

And a region 3 (pump back reflection region) formed by a second DBR resonator having a center wavelength of 980nm, which forms a 980nm pump resonant external cavity together with the first DBR resonator to form a 980nm pump resonance in the main cavity, thereby greatly improving the absorption efficiency of the pump light.

The region 4 formed by the second DFB resonator, which is the second DFB resonator forming the secondary resonator, has a center wavelength of the signal light (1535nm) and acts as a DFB mirror at 1535nm at the end of the hybrid resonator, providing additional optical feedback for signal light acquisition. This second DFB resonator can provide pure signal light reflection when the pump light is completely isolated by region 3. The design of adding the second DFB resonator is adopted, the feedback of the signal light is further enhanced, the external signal light resonance can be generated outside the main resonant cavity, and the phase change is not generated, so that the output power and the conversion efficiency of the laser are further improved, and the pumping threshold is reduced.

Based on the above description of the embodiments, as an alternative embodiment, the first DFB resonator and the second DFB resonator have the same size.

The grating size of the second DFB resonator is designed to be the same as that of the first DFB resonator, so that the generation of phase difference of 1535nm signal light can be prevented. Meanwhile, the optical feedback efficiency of the optical signal can be further improved by designing the cavity length of the second DFB resonator and optimizing the end face reflectivity.

Based on the contents of the above embodiments, as an alternative embodiment, an 1/4 phase shift region is provided in the first DFB resonator.

In the embodiment of the present invention, an 1/4 phase shift region may be introduced into the first DFB resonator (i.e., region 2) to suppress the phase shift during the transmission of the signal light, and ensure the single-mode stable output of the laser light.

Further, in the embodiment of the present invention, a first SiO layer may be disposed between the silicon substrate layer and the gain medium layer₂The isolation layer can also be provided with a second SiO between the mixed resonant cavity and the laser active region₂An isolation layer.

Wherein the second SiO is arranged between the mixed resonant cavity and the laser active region₂The isolation layer is used for reducing the light guide effect of the light field in the high-refractive-index material and ensuring the single-mode transmission of the optical signal; and the loading area (the second SiO) can be adjusted according to the requirement₂Isolation layer) to the optical field of the gain layer, the resonance condition of the resonator can be controlled more effectively.

Wherein a first SiO is arranged between the silicon substrate layer and the gain medium layer₂The isolation layer can effectively reduce the leakage light flowing to the substrate and improve the preparation efficiency.

Fig. 2 and fig. 3 respectively show a schematic structural cross-sectional view of an erbium silicate waveguide laser and a schematic cross-sectional view of a hybrid cavity provided by an embodiment of the present invention, and from the contents in the two figures, grating parameters involved in the structural distribution of the entire laser can be known. Wherein W_stip-loaderIs the width of the hybrid resonator, t_strip-loadedTotal height of the hybrid resonator, t_spacerIs first SiO₂The thickness of the isolation layer is such that,t_nitrideis the thickness of the silicon nitride layer, t_ErThickness of erbium silicate layer, t_{oxide substrate}The thickness of the second isolation layer is the same for each silicon nitride layer and the erbium silicate layer. In fig. 3, the grating periods of the first DBR resonator and the second DBR resonator are the same as Λ_DBR，L_DBR1Length of the first DBR resonator, L_DBR2Denotes the length, L, of the second DBR resonator_ASDenotes the length, L, of the first DFB resonator_RSDenotes the length, W, of the second DFB resonator_DBR1Inner height of teeth, L, of the first DBR resonator_DBR2Denotes the intra-tooth height, L, of the second DBR resonator_ASDenotes the intra-tooth height, L, of the first DFB resonator_RSDenotes the height of the second DFB resonator within the tooth, and the height of the whole mixed resonant cavity is W_wgMay be through W_wgSubtracting the intra-tooth height of each different region obtains the tooth height of each resonator.

As shown in fig. 4, in an embodiment of the present invention, a method for manufacturing an on-chip pump-signal light resonant erbium silicate laser is provided, which includes, but is not limited to, the following steps:

step S1, growing a silicon nitride layer with a first preset thickness on the silicon substrate layer based on a low-pressure chemical vapor deposition method; step S2, growing an erbium silicate gain layer with a second preset thickness on the silicon nitride layer; step S3, growing the silicon nitride layer again on the erbium silicate gain layer; step S4, repeating the steps S2-S3 until a preset number of layers of erbium silicate-silicon nitride alternating structures are obtained, wherein the upper and lower surfaces of the erbium silicate-silicon nitride alternating structures are silicon nitride layers; step S5, depositing SiO with preset thickness on the upper surface of the erbium silicate-silicon nitride alternating structure₂A layer; step S6, based on photolithography, on SiO₂Loading a template of the mixed resonant cavity layer by layer; and step S7, etching a mixed resonant cavity on the template of the mixed resonant cavity based on the ion etching technology.

Further, the first SiO layer may be disposed on the silicon substrate layer based on a thermal oxidation process before performing the above-described step S1₂An isolation layer.

Further, etching the hybrid resonant cavity on a template of the hybrid resonant cavity includes: designing the structure and the size of the hybrid resonant cavity, and etching the hybrid resonant cavity according to the structure and the size;

wherein designing the structure of the hybrid resonant cavity comprises: the first DBR resonator, the first DFB resonator, the second DBR resonator and the second DFB resonator are sequentially coupled from front to back in the direction of an optical path to form a mixed resonant cavity, and the mixed resonant cavity is of a grating structure; the first DBR resonator and the second DBR resonator form a pumping resonance external cavity; the first and second DFB resonators form a signal resonant external cavity.

Wherein designing the dimensions of the hybrid resonant cavity comprises: acquiring grating periods of a first DBR resonator and a first DFB resonator based on a Bragg condition formula; acquiring the grating duty ratio and the grating tooth depth of the first DBR resonator and the first DFB resonator based on a signal light reflectivity calculation formula; determining grating parameters of the second DBR resonator based on the Q value matching relation of the pump resonance external cavity and the erbium silicate-silicon nitride alternative structure; and determining the grating parameters of the first DFB resonator as the grating parameters of the second DFB resonator.

Wherein, the Bragg condition formula is as follows:

the signal light reflectivity calculation formula is as follows: r ═ tanh (kl);

wherein lambda is the grating period, lambda is the central wavelength of the resonator, n_effIs the effective refractive index corresponding to the waveguide cross section of the hybrid resonant cavity, R is the reflectivity, D is the grating duty cycle, L is the length of the resonant cavity, k is the grating coupling coefficient, and h is the tooth depth.

In the method for manufacturing an on-chip pump-signal light resonant erbium silicate laser provided by the embodiment of the present invention, firstly, the design work of the above parameters needs to be completed according to the use condition of the on-chip pump-signal light resonant erbium silicate laser.

On one hand, in order to improve the absorption efficiency and signal light feedback of the laser, a laser resonant cavity with a higher quality factor (Q value) needs to be designed, which not only can greatly reduce the linewidth and threshold of the laser, but also can improve the output power and efficiency of the laser.

On the other hand, in the alternative mixing of the erbium silicate film with high gain and the silicon nitride film with low loss, how to design the coupling relationship between the erbium silicate film and the silicon nitride film ensures high gain and effectively reduces the transmission loss of the waveguide, which is a very key ring for realizing the laser. Particularly, erbium ions have rich energy level structures, and relate to a plurality of energy level transition processes, a stimulated radiation amplification process in the corresponding energy level of the high-gain erbium silicate material needs to be obtained, a loss mechanism is fully combined with a silicon nitride material, a relevant theoretical model is established, the gain characteristic of the material is accurately predicted, and finally, the process of efficiently preparing the erbium silicate-silicon nitride mixed film can be completed.

On the other hand, the design of the hybrid resonant cavity is a decisive factor for realizing high-performance and narrow-linewidth laser output of the waveguide laser. Therefore, in the embodiment of the invention, the optical field interaction mechanism of each part in the resonant cavity is obtained by optimizing the parameters of each component part of the hybrid resonant cavity, so that the design of the whole laser is completed.

In the preparation method provided by the embodiment of the invention, the key parameters, such as the thickness of the erbium silicate film and the thickness of the silicon nitride layer, the size of the mixed resonant cavity or SiO, are designed by optimization₂The thickness of the spacer layer is set to improve the confinement factor in the gain layer and the overlapping strength of the pump light and the signal light. Wherein the length of the first DFB cavity should be set within a reasonable range, since the single longitudinal mode output control of erbium silicate waveguide lasers is generally applicable to cavities with large values of κ L. A shorter cavity length has weak optical feedback and lower gain, resulting in lower laser output power. But too long a cavity length also limits the effective transmission distance of the pump.

Further, the design of the second DFB cavity is done in combination with the length of the second DBR resonator to ensure that the pump is completely isolated by region 3 and does not enter region 4. This design would allow a 1535nm DFB grating in region 4 to provide pure signal light feedback without the need for unnecessary gain.

Wherein, in order to ensure that the resonant loss of the 980nm pump light in the external cavity is less than that in the main cavity, the Q value of the first DBR resonant cavity needs to be controlled. The method specifically comprises the following steps: determining the grating parameters of the second DBR resonator, and designing the grating parameters of the first DBR resonator to satisfy the critical coupling matching relationship between the Q value of the outer cavity of the DBR and the Q value of the inner cavity of the DFB. A matching diagram of external Q and internal Q values based on different cavity lengths is shown in FIG. 5, wherein the abscissa is the Tooth Depth (Tooth Depth) of the cavity, the left ordinate is the quality Factor Q (quality Factor Q) of the cavity, and the right ordinate represents the Reflectivity (Reflectivity), l₁-l₅Respectively, to the lines of different cavity length values indicated in the figures. Then, each matching point in fig. 5 is obtained, wherein the matching point is the intersection of the line of different cavity length values and the black curve in the graph.

The grating size of the second DFB resonator is the same as that of the first DFB resonator, so that phase difference of optical signal light can be effectively prevented. The cavity length of the DFB resonator can be designed and the end face reflectivity optimized to ensure sufficient optical feedback. The specific design schematic diagram is shown in fig. 6, and for different input pump powers, different optimal cavity lengths should be selected as reasonable parameter values of the second DFB resonant cavity. In the figure P_pThe abscissa represents the Reflectivity of the resonant cavity (Reflectivity) and the ordinate represents the output optical signal power (OutputPower).

Further, in the signal resonant external cavity of the on-chip pump-signal light resonant erbium silicate laser provided by the embodiment of the invention, laser transmission can be divided into active area transmission and reflection area transmission, and characteristics of the laser can be described mathematically through a coupling mode theory. The signal optical power is divided into forward and reverse propagation modes at the first and second DFB resonances (including region 2 and region 4). In the case of a uniform bragg grating, the signal coupling between the two directionally propagating modes with gain effects is described by the following system of coupled mode equations (setting the left end of the hybrid cavity to z-0):

where A (z) and B (z) are the amplitudes of the forward and backward propagating modes, respectively, j is an imaginary unit, θ is the phase shift during the DFB grating transmission, and can be set to 0 and π before and after the 1/4 phase shift region, respectively, Δ β is an indication of the Bragg condition deviation, L_DBR1Length of the first DBR resonator, L_DBR2Denotes the length, L, of the second DBR resonator_ASDenotes the length, L, of the first DFB resonator_RSDenotes the length of the second DFB resonator, and denotes g_s(z) is the net gain coefficient per unit length of erbium silicate to signal light, which can be expressed as:

g_s(z)＝Γ_s[σ₂₁N₂(z)-σ₁₂N₁(z)]-α(v_s)，

wherein N is₁And N₂Respectively represent the ground state energy level of erbium ions (⁴I_15/2) And excited state energy level (⁴I_13/2) Average number of particles of (a); by using the multi-energy-level model of the erbium-ytterbium silicate system as shown in fig. 7, the average population of erbium ions on each energy level can be calculated by solving the steady-state rate equation; sigma₁₂And σ₂₁Absorption and emission cross sections of erbium ion to signal light, α (v)_s) Is the propagation loss of signal light per unit length in the waveguide and depends on the thickness ratio of the erbium silicate layer to the silicon nitride sub-layer.

Further, in the pumped resonant external cavity of the on-chip pumped-signal light resonant erbium silicate laser provided by the embodiment of the present invention, laser transmission can be divided into forward and backward propagation modes, and the gratings of the first DBR cavity and the second DBR cavity can be equivalent to end mirrors. The pumping bidirectional transmission equation is as follows:

wherein

And

respectively represent ytterbium ions in the ground state level: (⁴F_7/2) And excited state energy level (⁴F_5/2) The average particle number of (a) can be calculated by using a multi-level model of the erbium-ytterbium silicate system shown in fig. 7. Sigma₁₃Is the absorption cross section of erbium ion to pump light.

And

α (v) absorption and emission cross-sections of ytterbium ion for pump light, respectively_p) Is the propagation loss of the pump light per unit length in the waveguide and also depends on the thickness ratio of the erbium silicate layer to the silicon nitride sub-layer. The final laser output power is proportional to the sum of the square of the amplitude of the signal light, which can be described as:

by combining the rate equation and the transmission equation, the laser characteristics of the device can be predicted, and the simulation results of the laser output characteristics and the laser linewidth characteristics are respectively shown in fig. 8 and fig. 9.

Based on the content of the above embodiment, the grating parameters of the hybrid resonant cavity are obtained, and the template of the hybrid resonant cavity is manufactured.

Further, as shown in fig. 10, in an embodiment of the present invention, a method for manufacturing an on-chip pump-signal light resonant erbium silicate laser is provided, including the following steps:

firstly, preparing a silicon substrate (Si substrate) with a flat and smooth upper surface; uniformly growing first SiO on the upper surface of the silicon substrate layer based on a thermal oxidation process₂An isolation layer; based on Low Pressure Chemical Vapor Deposition (LPCVD), on the first SiO₂Uniformly growing an erbium silicate gain layer (Er silicate) with a preset thickness on the isolation layer; depositing a silicon nitride layer (Si) over the obtained erbium silicate gain layer₃N₄) Alternately repeating the steps according to the method until an erbium silicate-silicon nitride alternating structure consisting of an erbium silicate gain layer and a silicon nitride layer is obtained; depositing SiO with preset thickness on the surface of the erbium silicate-silicon nitride alternating structure₂Layer (SiO)₂spacer) (the SiO)₂The thickness of the layer is larger than the total height of the preset mixing resonant cavity); on the basis of photolithography techniques, in the SiO₂The layer loads a template of the hybrid resonant cavity, and the hybrid resonant cavity is etched on the template of the hybrid resonant cavity based on the template (strip-loaded waveguide) of the hybrid resonant cavity.

The above-described embodiments of the apparatus are merely illustrative, and the units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of the present embodiment. One of ordinary skill in the art can understand and implement it without inventive effort.

Finally, it should be noted that: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.