CN115912044A - On-chip laser and forming method thereof - Google Patents

Abstract

The embodiment of the application provides an on-chip laser and a forming method thereof, wherein the method comprises the following steps: providing a base, wherein the base comprises a substrate and an active layer positioned on the substrate, and the material of the active layer comprises lithium niobate doped with rare earth ions; forming a loading waveguide on the substrate, wherein the loading waveguide comprises a Mach-Zehnder waveguide with two arms adopting a Bragg grating structure, or the loading waveguide comprises a resonant cavity waveguide with a side wall connected with an input end adopting a Bragg grating structure and a Mach-Zehnder waveguide connected with an output end; and modulation electrodes are deposited and formed on two sides of two arms of the Mach-Zehnder waveguide.

Description

On-chip laser and forming method thereof

Technical Field

The present application relates to the field of on-chip laser technology, and relates to, but is not limited to, an on-chip laser and a method of forming the same.

Background

The on-chip laser is an important component of a photoelectric integrated system, is a key for realizing high-speed, broadband, low-cost and low-power-consumption optical interconnection, and is also a basis for developing a high-speed broadband information transmission system. The performance of an on-chip laser as an on-chip light source directly affects the overall performance of the optoelectronic integrated circuit. The rare earth ion doped dielectric waveguide laser is a great core competitiveness of an on-chip light source device, and attracts a great deal of attention at present.

The rare earth elements have rich energy level structures, ions can be used as efficient luminescent centers, photons with different wavelengths can be emitted according to different application requirements, and the rare earth elements are one of the best luminescent materials. The energy level structure of rare earth erbium (Er) ions can generate wide-spectrum luminescence near 1.5 micrometers (mum), corresponds to a common optical communication waveband, is relatively stable in photon wavelength, and is not easily influenced by pumping power and a matrix environment. Therefore, erbium-doped light sources are promising candidates as standard wavelength light sources in optoelectronic technologies.

Erbium doped fiber amplifiers have achieved great success today. It is a cornerstone that constitutes the current global optical fiber communication network because it provides high gain and low noise optical signal amplification. The long fluorescent lifetime of erbium ions also gives on-chip amplifiers low noise performance compared to integrated semiconductor optical amplifiers, which has led to extensive research on erbium-doped loaded waveguide amplifiers, with the selection of various host materials, including for example Lithium Niobate (LNOI), phosphates, silicates, alumina and tellurium oxide, etc., all reported to perform well. However, it remains challenging for these erbium platforms to achieve both high internal net gain and high unit length gain, but this is very important for compact and useful integrated light sources.

Recently, rare earth ion doped lithium niobate (Re: LNOI) on an insulator has attracted great interest due to the ability to achieve high rare earth ion doping concentrations, good mode confinement, and low loss waveguides simultaneously. Lithium niobate has the advantage that on-chip modulation can be performed, making it useful as a local signal processing source for optical communication systems; furthermore, lithium niobate allows for selective area doping by diffusion of rare earth ions; furthermore, LNOI have proven to be a powerful platform for a variety of photonic applications, including electro-optical modulation, micro-modulation, supercontinuum generation, second harmonic generation, optical parametric oscillation, acousto-optic devices, and the like. LNOI platform based integrated light sources may therefore support high speed optical modulation, high total internal net gain and better laser output.

Nevertheless, currently no on-chip tunable lasers for high-gain rare earth ion doped lithium niobate have been established. How to realize a light source device with integrated functions of a light source, modulation, amplification and the like on an LNOI platform by utilizing the gain characteristic and the modulation characteristic of the rare earth ion doped lithium niobate material is a new direction for the development of integrated photons.

Disclosure of Invention

In view of the above, embodiments of the present application provide an on-chip laser and a method for forming the same.

In a first aspect, an embodiment of the present application provides a method for forming an on-chip laser, where the method includes: providing a base, wherein the base comprises a substrate and an active layer positioned on the substrate, and the material of the active layer comprises lithium niobate doped with rare earth ions; forming a loading waveguide on the substrate, wherein the loading waveguide comprises a Mach-Zehnder waveguide with two arms adopting a Bragg grating structure, or the loading waveguide comprises a resonant cavity waveguide with a side wall adopting the Bragg grating structure connected with an input end and a Mach-Zehnder waveguide connected with an output end; and modulation electrodes are deposited on two sides of two arms of the Mach-Zehnder waveguide.

In some embodiments, forming a loaded waveguide on the substrate comprises: depositing a loading layer on the substrate; and etching the loading layer to form the loading waveguide.

In some embodiments, before forming the loaded waveguide on the substrate, further comprising: and depositing an isolation layer on the substrate to protect the active layer in the process of forming the loading waveguide and adjust the guiding capacity of the loading waveguide to the optical field of the formed laser.

In some embodiments, further comprising: forming couplers at both ends of the loaded waveguide while forming the loaded waveguide; the first end of the first coupler is used for receiving pump light, the second end of the first coupler is connected with the input end of the loading waveguide, the first end of the second coupler is connected with the output end of the loading waveguide, and the second end of the second coupler is used for outputting output light generated by wave combination of the loading waveguide.

In some embodiments, forming modulating electrodes on both sides of the arms of the mach-zehnder waveguide includes: forming a photoresist layer on the substrate and the loading waveguide; patterning the photoresist layer to form a photoresist layer having the modulation electrode pattern; depositing an electrode material on the photoresist layer having the modulating electrode pattern; and removing the electrode material on the photoresist layer and the photoresist layer to form the modulation electrode.

In a second aspect, an embodiment of the present application further provides an on-chip laser, including: a substrate; an active layer on the substrate, wherein the material of the active layer comprises lithium niobate doped with rare earth ions; the loading waveguide is positioned on the active layer and comprises a Mach-Zehnder waveguide with two arms adopting a Bragg grating structure, or comprises a resonant cavity waveguide with side walls adopting the Bragg grating structure and connected with an input end and a Mach-Zehnder waveguide connected with an output end; and the modulation electrodes are positioned on two sides of two arms of the Mach-Zehnder waveguide.

In some embodiments, further comprising: the isolation layer is positioned on the active layer and used for protecting the active layer in the process of forming the loading waveguide and adjusting the guiding capacity of the loading waveguide to the laser field; and the couplers are positioned at two ends of the loading waveguide, wherein a first end of the first coupler is used for receiving pump light, a second end of the first coupler is connected with an input end of the loading waveguide, a first end of the second coupler is connected with an output end of the loading waveguide, and a second end of the second coupler is used for outputting output light generated by wave combination of the loading waveguides.

In some embodiments, the Mach-Zehnder waveguide further includes two Y-branch waveguides, where a first end of a first Y-branch waveguide is an input end of the Mach-Zehnder waveguide, and a second end of the first Y-branch waveguide is connected to first ends of two arms of the Mach-Zehnder waveguide; the second ends of the two arms of the Mach-Zehnder waveguide are connected with the first end of a second Y-branch waveguide, and the second end of the second Y-branch waveguide is used as the output end of the Mach-Zehnder waveguide and is used for outputting output light generated by the combined wave of the Mach-Zehnder waveguide; the structures of the two Y-branch waveguides comprise a sine-cosine structure or a double-arc structure.

In some embodiments, the material of the loading layer comprises tantalum oxide, silicon nitride, titanium dioxide; the active layer has a thickness comprising 360 nanometers (nm) or 600nm; the thickness of the isolation layer ranges from 50nm to 200nm.

In some embodiments, the modulating electrode comprises a traveling wave electrode or a segmented modulating electrode; the Bragg grating structure comprises long teeth and short teeth, and two continuous long teeth are arranged in the center of the Bragg grating structure.

The embodiment of the application provides an on-chip modulation type laser based on a rare earth doped lithium niobate material, which utilizes the rare earth doped lithium niobate material as an active layer, combines a Bragg grating structure and a Mach-Zehnder structure to form a loaded waveguide, realizes laser output and laser modulation on a chip, and expands the functions of the traditional device. The two loading waveguide structures provided correspond to the internal and external modulation modes of the laser, the scheme can meet the requirement of a high-speed lumped on-chip light source device, and a new thought is developed for the research of the generation and modulation of on-chip laser.

Drawings

Fig. 1A is a schematic flowchart of a method for forming an on-chip laser according to an embodiment of the present disclosure;

fig. 1B to fig. 3D are schematic structural diagrams of a forming process of an on-chip laser according to an embodiment of the present application.

Detailed Description

Exemplary embodiments disclosed in the present application will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present application are shown in the drawings, it should be understood that the present application may be embodied in various forms and should not be limited to the specific embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the present application. It will be apparent, however, to one skilled in the art, that the present application may be practiced without one or more of these specific details. In other instances, well-known features have not been described in order to avoid obscuring the present application; that is, not all features of an actual embodiment are described herein, and well-known functions and structures are not described in detail.

In the drawings, the size of layers, regions, elements, and relative sizes may be exaggerated for clarity. Like reference numerals refer to like elements throughout.

It will be understood that when an element or layer is referred to as being "on" \8230; \8230 ";," - \8230;, "\8230"; "adjacent to," "connected to," or "coupled to" other elements or layers, it can be directly on, adjacent to, connected to, or coupled to the other elements or layers, or intervening elements or layers may be present. In contrast, when an element is referred to as being "directly on," 8230; \8230 ";," "directly adjacent," "directly connected to," or "directly coupled to" another element or layer, there are no intervening elements or layers present. It will be understood that, although the terms first, second, third, etc. may be used to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer or section from another element, component, region, layer or section. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the present application. And the discussion of a second element, component, region, layer or section does not imply that a first element, component, region, layer or section is necessarily present in the application.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. As used herein, the term "and/or" includes any and all combinations of the associated listed items.

The embodiment of the present application provides a method for forming an on-chip laser, as shown in fig. 1A, the method includes steps S101 to S103, where:

step S101: providing a base, wherein the base comprises a substrate and an active layer positioned on the substrate, and the material of the active layer comprises lithium niobate doped with rare earth ions;

here, the substrate may include a single-layer substrate such as a silicon (Si) substrate, a germanium (Ge) substrate, a silicon germanium (SiGe) substrate, a quartz substrate, or a glass substrate; a multi-layer substrate may also be included, such as a Silicon On Insulator (SOI) substrate, a Lithium Niobate On Insulator (LNOI) substrate, or a Germanium On Insulator (GOI) substrate, among others.

In some embodiments, an oxide layer may also be formed on the single-layer or multi-layer substrate. The material of the oxide layer may include, for example, silicon dioxide. The thickness of the oxide layer may be larger than 5 μm to prevent leakage of the optical fields of the pump light and the formed light towards the substrate.

The active layer is made of the rare earth ion doped lithium niobate material, so that the light modulation output can be realized by utilizing the inherent good electro-optic effect characteristic of the lithium niobate, selective area doping is carried out through diffusion of the rare earth ions, the rich energy level structure of the rare earth ions is used as an efficient light emitting center, photons with different wavelengths are emitted according to different application requirements, and the active layer has the advantages of high speed adjustability, low noise, excellent temperature performance and large bandwidth. The thickness of the active layer can be adjusted according to the effective refractive index of the waveguide, the mode field distribution (i.e., the size and position of the optical spot), and the gain effect. In some embodiments, the thickness of the active layer may include: 360nm or 600nm, so that the active layer has better light transmission mode and gain effect.

The rare earth ion may be any rare earth ion, such as erbium ion, lanthanum (La) ion, cerium (Ce) ion, praseodymium (Pr) ion, neodymium (Nd) ion, promethium (Pm) ion, samarium (Sm) ion, europium (Eu) ion, gadolinium (Gd) ion, terbium (Tb) ion, dysprosium (Dy), holmium (Ho) ion, erbium ion, or the like. The energy level structure of the rare earth erbium ions can generate wide-spectrum luminescence near 1.5 mu m, corresponds to a common optical communication waveband, has relatively stable photon wavelength, and is not easily influenced by pumping power and a matrix environment. Therefore, erbium-doped light sources are promising candidates as standard wavelength light sources in optoelectronic technologies. Therefore, the lithium niobate doped with rare earth ions herein may be lithium niobate doped with erbium ions.

In some embodiments, the laser generation region of the active region may be doped with rare earth ions to generate laser light under the action of the pump light and the resonant cavity. In some embodiments, the forming process of the rare earth ion-doped lithium niobate thin film may include: preparing the lithium niobate crystal into a lithium niobate film based on an intelligent stripping 'Smart-cut' technology; and then injecting rare earth ions into the lithium niobate thin film through an ion injection process.

In some embodiments, the active layer may be formed directly on the substrate (e.g., by directly using the LNOI substrate), or the substrate may be integrated with the active layer by thin film transfer or bonding after the substrate is formed, so as to form the substrate.

Fig. 1B is a schematic structural diagram of a provided base, wherein the base 10 includes a substrate 101 and an active layer 102 on the substrate 101.

Step S102: forming a loading waveguide on the substrate, wherein the loading waveguide comprises a Mach-Zehnder waveguide with two arms adopting a Bragg grating structure, or the loading waveguide comprises a resonant cavity waveguide with a side wall connected with an input end adopting a Bragg grating structure and a Mach-Zehnder waveguide connected with an output end;

here, the loading waveguide refers to a guiding (channel) structure composed of media with different refractive indexes and capable of transversely constraining an optical wave to be transmitted along a longitudinal direction. The types of loading waveguides may include circular loading waveguides (optical fibers), planar (or thin film) loading waveguides, channel loading waveguides, and the like. The etching process may be a dry etching process, such as a plasma etching process, a reactive ion etching process, or an ion milling process.

The loading waveguide formed may include two structures:

the first structure is as follows: the Mach-Zehnder waveguide with two arms adopting a Bragg grating structure is included;

the second structure is as follows: the optical fiber resonator comprises a resonant cavity waveguide with a Bragg grating structure on the side wall connected with an input end and a Mach-Zehnder waveguide connected with an output end.

In general, the mach-zehnder waveguide includes two Y-branch waveguides and upper and lower arm waveguides, wherein the first end of the first Y-branch waveguide is the input end of the mach-zehnder waveguide, and the second end of the first Y-branch waveguide is connected to the first ends of the upper and lower arm waveguides; the second end of the two-arm waveguide is connected with the first end of the second Y-branch waveguide, and the second end of the second Y-branch waveguide is used as the output end of the Mach-Zehnder waveguide and is used for outputting output light generated by the combined wave of the Mach-Zehnder waveguides.

The resonant cavity is a cavity in which light waves are reflected back and forth to provide optical energy feedback, and is an essential component of a laser for generating laser light. The bragg grating structure is a reflective structure that includes a periodic refractive index modulation. In general, the bragg grating structure includes long teeth and short teeth arranged periodically, wherein one long tooth and one short tooth form one period.

As shown in fig. 1C, a loading waveguide 105 is formed on the substrate 10.

Fig. 1D and 1F show top views of two configurations of loaded waveguides for a clearer understanding of the loaded waveguide configuration. FIG. 1D is a top view of a first configuration of loaded waveguides. It can be seen that the loading waveguide of the first structure provided in the embodiments of the present application is a loading waveguide formed based on a mach-zehnder waveguide. The mach-zehnder waveguide 20 includes a first Y-branch waveguide 202a, a second Y-branch waveguide 202b, and a two-arm waveguide 201, and the two-arm waveguide 201 adopts a bragg grating structure 23, thereby forming a loaded waveguide of a first structure.

Fig. 1E is an enlarged view of the region B in fig. 1D, and it can be seen that the bragg grating structure includes long teeth 301 and short teeth 302 arranged periodically, wherein one long tooth 301 and one short tooth 302 form one period.

FIG. 1F is a top view of a second configuration of loaded waveguides. It can be seen that the loading waveguide of the second structure provided in the embodiment of the present application includes a resonant cavity waveguide 22 and a mach-zehnder waveguide 20, where a bragg grating structure 23 is adopted on a sidewall of the resonant cavity waveguide 22, the resonant cavity waveguide 22 is connected to an input end of the loading waveguide, and the mach-zehnder waveguide 20 is connected to an output end of the loading waveguide, so as to form the loading waveguide of the second structure.

In some embodiments, the material for loading the waveguide may be a material having a refractive index close to that of lithium niobate. For example, the materials of the loading waveguide may include: tantalum oxide, silicon nitride, titanium dioxide, and the like. Therefore, the loaded waveguide has a small refractive index difference between the horizontal direction and the active layer to guide light to be transmitted in the active layer, so that the mode radius is large in the process of transmitting laser light, single-mode transmission is easily achieved, and the mismatch of the mode connected with the single-mode optical fiber is small.

In some embodiments, the thickness and width of the loading waveguide can be adjusted according to the material of the loading waveguide, the distribution of the light mode in the loading waveguide, the limiting factor (the constraint capability of light in the waveguide) and the mode size, and the key is to improve the limiting capability of the loading waveguide to the optical field to ensure the optimal transmission and gain effects; meanwhile, the overlapping strength between the pump light and the exciting light field is improved (the interaction between the pump light and the exciting light is improved), and the optimization of the loaded waveguide limiting factor is realized.

For the design of the width and the thickness of the loading waveguide, when the size of the strip loading waveguide is small, the limitation effect of the loading waveguide on an optical field is weak, the loading waveguide is multi-mode transmission, and a guided mode effect cannot be formed. Therefore, the optical field mode spot in the active layer cross section can be substantially completely concentrated in the active layer below the loaded waveguide by designing the appropriate width and thickness, thereby maximizing the confinement factor. The embodiment of the application provides the principle of the width and thickness design of the loaded waveguide, but the range of the width and thickness of the loaded waveguide is not limited.

The parameter design of the Bragg grating structure comprises the following steps: grating period, grating tooth depth and duty cycle. Wherein the grating period determines the center wavelength of the resonator oscillation. Depending on the bragg condition, the center wavelength of the resonant cavity oscillation may be close to or coincide with the strongest spectral peak of the rare earth ion luminescence. The design of the duty ratio, the tooth depth and the length of the grating jointly determines the coupling strength of the grating, and further influences the coupling efficiency of the optical field. The grating duty cycle, tooth depth and length can be adjusted according to the following equations (1) and (2) to obtain a greater coupling strength.

A＝kL (2)；

Wherein k is the coupling coefficient of the grating, D is the duty cycle, n _h Is the highest effective refractive index, n _l The size of the tooth depth affects the highest and lowest effective index, a being the coupling strength and L being the length.

In some embodiments, the length of the loaded waveguide in which the grating is located can be controlled to be in the millimeter (mm) range, and design considerations can be taken into account in conjunction with optimal pump length and modulation efficiency. In some embodiments, to achieve single mode resonance at the bragg wavelength, an additional round-trip phase may be added to the bragg grating structure to satisfy the resonance condition. For example, a 1/4 phase shift region may be introduced in the central portion of the bragg grating structure to stabilize the output of the single mode laser, thereby suppressing the phase shift during signal transmission. In some embodiments, the introduction of a 1/4 phase shift region may be achieved by introducing two long teeth in succession in the central region of the bragg grating. The embodiment of the present application does not limit the manner of introducing the 1/4 phase shift region. In the process of forming the Bragg grating structure, the etching width and the etching depth are defined by the line width and the maximum etching depth of the etching mask pattern.

In some embodiments, the Y-branch waveguide may employ a symmetric two-branch optical waveguide structure. The material and the width of the two-branch waveguide structure can be the same, so that the optical transmission characteristics of the two-branch waveguide are the same. To prevent large radiation losses, the angle of the arms of the two-branch waveguide can be smaller. In some embodiments, the Y-branch waveguide may be designed as a sine-cosine type or a double-arc type, so that the transmission loss of the loading waveguide splitting/combining can be effectively reduced, and higher integration level can be realized.

In some embodiments, the step S102 may be performed by depositing or patterning (etching) a loading waveguide on the substrate, which is not limited in this application.

In some embodiments, before the step S102 "forming a loading waveguide on the substrate", the following steps may be further included: and depositing an isolation layer on the substrate to protect the active layer in the process of forming the loading waveguide and adjusting the guiding capacity of the loading waveguide to the optical field of the formed laser.

Here, the material of the isolation layer may include silicon dioxide. Wherein the thickness of the isolation layer can be adjusted according to the confinement factor of the optical mode in the loaded waveguide region. In practice, the thickness of the isolation layer is designed to ensure that the loaded waveguide forms an effective mode. Generally, single-mode transmission is gradually formed in the loaded waveguide along with the increase of the thickness of the isolation layer, but the loading waveguide has weaker and weaker binding effect on an optical field, and the optical field laterally diffuses into the whole active layer, so that the intensity of laser is reduced. Therefore, the thickness of the isolation layer needs to be moderate, and can be designed in the order of hundreds of nm, for example, the thickness of the isolation layer can be in the range of 50nm to 200nm.

The setting of isolation layer has following effect: on one hand, the active layer can be protected in the preparation process of the loading layer; on the other hand, the guided mode state of the loading waveguide can be more effectively controlled, and the guiding capability of the loading waveguide to the light field of the formed laser can be adjusted.

Fig. 1G is a schematic structural diagram of a spacer layer formed on a substrate. Wherein the isolation layer 103 is located on the substrate 10. Fig. 1H is a schematic view of a structure obtained after forming a loaded waveguide in the case where an isolation layer is formed on a substrate. Wherein the loaded waveguide 105 is located on the isolation layer 103, thereby realizing protection of the active layer during formation of the loaded waveguide by the isolation layer.

In some embodiments, after forming the isolation layer, chemical mechanical polishing of the isolation layer may be further included to reduce surface roughness of the isolation layer, thereby reducing light reflection by the isolation layer.

Step S103: and modulation electrodes are deposited on two sides of two arms of the Mach-Zehnder waveguide.

Here, the modulation electrode is used to change the refractive index of the loaded waveguide. In some embodiments, the modulating electrode may employ a traveling wave electrode structure, parallel to the optical waveguide. Therefore, the transmission directions of the microwave and the light wave are consistent, and the electric signal and the optical signal can be transmitted forwards at the same phase speed, so that the electric field is positively acted on the light wave to play a modulation effect; and the structure can overcome the influence of transition time and interelectrode capacitance, thereby improving the electro-optic modulation rate. Parameters of the modulating electrode structure, such as width and thickness, may be adjusted according to phase matching conditions of the electrical and optical signals.

In some embodiments, the modulating electrode may employ a segmented modulating electrode structure. In practice, each segment of the modulating electrode is electrically connected to a separate electrode. Therefore, the loss caused by the transmission of the radio-frequency signal on the traveling wave electrode can be obviously reduced, and the bandwidth of the modulator is obviously improved. In some embodiments, the modulation electrode may be a thick gold electrode, and the electro-optic bandwidth of the electro-optic modulator is increased by optimizing the size of the electrode to realize the speed matching between the microwave and the optical wave.

Fig. 1I is a schematic diagram of a structure obtained after forming a modulation electrode, in which modulation electrodes 21 are located on both sides of the loading waveguide 105.

In order to more clearly understand the position relationship between the modulation electrode and the loading waveguide. Fig. 1D is a schematic top view of the modulation electrode formed in the first loaded waveguide structure. The modulation electrodes 21 are located on two sides of two arms 201 (namely, the two-arm waveguides) of the mach-zehnder waveguide in the loaded waveguide, and the modulation electrodes 21 include three electrodes in total, which are respectively located on the upper arm, between the two arms and below the lower arm of the mach-zehnder waveguide.

Under this configuration, direct modulation is achieved while the laser is generated. The two arms of Bragg grating type waveguides realize the generation and modulation of laser by utilizing the luminescence of rare earth ions and the electro-optic effect of lithium niobate, the two Y-branch waveguides finish the function of light combination, and the modulation electrodes provide driving voltage required by realizing the electro-optic effect. The process of generating and modulating the laser light is as follows:

the first step is as follows: the input pump light enters the loading waveguide from the input end and is respectively transmitted through an upper branch and a lower branch in the Y direction, in the process, the rare earth doped lithium niobate material absorbs the pump light to generate stimulated radiation, and the transmission loading waveguide is designed into a Bragg grating structure, so that photons generated by the stimulated radiation of rare earth ions in the doped lithium niobate are reflected and limited in the cavity, the photon concentration in the cavity is increased, the stimulated radiation intensity is improved, and the loss and gain in the cavity are balanced;

the second step is that: under the action of the Bragg grating structure, the refractive index in the light transmission direction generates periodic change, the light wave is partially and periodically reflected in the process of propagation, and the laser mode in the cavity is coupled in the forward direction (the transmission direction of the laser) and the backward direction (the reflection direction of the laser). The period of the Bragg grating is designed to be consistent with or very close to the light-emitting wavelength frequency of the rare earth ions, so that the light field in the active layer can be driven to form laser oscillation, and two paths of laser output are generated.

The third step: the loading waveguide and the modulation electrodes arranged on two sides of the loading waveguide form a phase modulator, and the effective refractive index of the loading waveguide can be changed after voltage is applied to the modulation electrodes, so that phase difference can be generated after two beams of light pass through the first Y-branch waveguide, and the amplitude of output light is changed due to wave combination interference at the second Y-branch waveguide, thereby realizing intensity modulation. Under the condition that the upper branch and the lower branch are completely symmetrical (the Bragg grating structures of the upper arm and the lower arm are ensured to be consistent), if no modulation voltage is added, the upper branch and the lower branch are converged to generate direct laser output; if the modulation voltage is applied to the modulation electrode, the phase difference of the two branch signals occurs due to electro-optic induction; coherent constructive or coherent destructive of the two paths of laser output is realized according to the phase difference of 0 or pi, so that the modulation of the laser output is completed, and finally the laser output is output from the output end.

In some embodiments, the loaded waveguide and the modulation electrodes disposed on two sides of the loaded waveguide form a push-pull structure, and at this time, the polarities of the electric fields of the two arms are opposite, so that the phase shifts are also opposite, and the total phase variation of the device is twice that of a single-arm phase modulator, thereby increasing the modulation speed of the laser.

Fig. 1F is a schematic diagram of a structure obtained after forming the modulation electrode in the case of forming the loaded waveguide of the second structure. Similarly, the modulation electrodes 21 are located on two sides of two arms 201 of the Mach-Zehnder waveguide in the loading waveguide, and the modulation electrodes 21 include three electrodes in total, which are respectively located on the upper arm, between the two arms and under the lower arm of the Mach-Zehnder waveguide. The difference points are that: two arms 201 of a Mach-Zehnder waveguide in the loading waveguide with the first structure are Bragg grating structures; the loaded waveguide of the second structure has a structure in which the two arms 201 of the mach-zehnder waveguide are not bragg gratings.

In this structure, the laser output is generated first, and then modulation is performed, and the generation and modulation processes of the laser are separated. The resonant cavity waveguide is positioned in the laser generation area and used for generating laser; the Mach-Zehnder waveguide is located in the laser modulation region and is used for modulating the intensity of the laser light. The process of generating and modulating the laser light is as follows:

the first step is as follows: the input pump light enters the loading waveguide from the input end, the rare earth doped lithium niobate material absorbs the pump light to generate stimulated radiation, and one path of laser output is generated through the resonant cavity waveguide;

the second step: the loading waveguide and the modulation electrodes arranged on two sides of the loading waveguide form a phase modulator, and applied voltage causes the change of the refractive index of the loading waveguide, so that the phase of transmitted light is changed, and phase modulation is realized.

It should be noted that the loaded waveguide of the second structure is similar to the loaded waveguide of the first structure in the principle of laser generation and modulation, and can be understood by referring to the loaded waveguide of the first structure.

The embodiment of the application provides an on-chip modulation type laser based on a rare earth doped lithium niobate material, which utilizes the rare earth doped lithium niobate material as an active layer, combines a Bragg grating structure and a Mach-Zehnder structure to form a loaded waveguide, realizes laser output and laser modulation on a chip, and expands the functions of the traditional device. The two loading waveguide structures correspond to the internal and external modulation modes of the laser, the scheme can meet the requirement of a high-speed lumped on-chip light source device, and a new thought is developed for the research of the generation and modulation of on-chip laser.

In some embodiments, the implementation of step S102 "forming a loaded waveguide on the substrate" may include steps S1021 and S1022, wherein:

step S1021: depositing a loading layer on the substrate;

here, the implementation of step S1021 may be formed using any one of deposition processes.

The loading layer is used to form a loading waveguide. The material of the loading layer can be a material with low etching difficulty and refractive index close to that of lithium niobate. For example, the materials of the loading layer may include: tantalum oxide, silicon nitride, titanium dioxide, and the like. In the embodiment of the application, the loading layer is formed above the active layer, so that the problem of high etching difficulty of the active layer can be avoided when a loading waveguide is formed, and a good guided mode effect can be formed.

Fig. 2 is a schematic view of a structure obtained by forming a loading layer. Wherein the loading layer 104 is located above the substrate 10.

Step S1022: and etching the loading layer to form the loading waveguide.

Here, the step S1022 may be performed by using a dry etching process, such as a plasma etching process, a reactive ion etching process, or an ion milling process, to form the loading waveguide. The embodiment of the application provides a realization step for forming the loading waveguide in a graphical mode.

In some embodiments, the method further comprises the following step S201:

step S201: forming couplers at both ends of the loaded waveguide while forming the loaded waveguide; the first end of the first coupler is used for receiving pump light, the second end of the first coupler is connected with the input end of the loading waveguide, the first end of the second coupler is connected with the output end of the loading waveguide, and the second end of the second coupler is used for outputting output light generated by the wave combination of the loading waveguide.

Here, the coupler refers to a device for coupling a silicon chip and an optical fiber to each other, and is used to reduce loss during optical transmission to increase the intensity of output light.

The coupler will be described below by taking a waveguide of a first structure as an example. Referring to fig. 1D, a first end of the first coupler 24 is configured to receive the pump light, a second end of the first coupler 24 is connected to an input end of the loading waveguide, a first end of the second coupler 25 is connected to an output end of the loading waveguide, and a second end of the second coupler 25 is configured to output light generated by combining the waves of the loading waveguide.

In the embodiment of the application, the loaded waveguide is formed, and meanwhile, the couplers positioned at two ends of the loaded waveguide are formed, so that the loss in the optical transmission process is reduced by using the couplers.

In some embodiments, the implementation of step S103 "depositing and forming modulation electrodes on both sides of the two arms of the mach-zehnder waveguide" may include steps S1031 to S1034, where:

step S1031: forming a photoresist layer on the substrate and the loading waveguide;

here, the photoresist layer is a layer formed by coating photoresist, which is classified into positive photoresist and negative photoresist according to polarity, with the difference that: the exposed areas of the negative photoresist become hard and remain after exposure and development, and the unexposed parts are dissolved by a developer; after the positive photoresist is exposed, the connected polymers in the exposed area can be broken and softened due to the photo-dissolution effect and are finally dissolved by a developer, and the unexposed part is remained.

In some embodiments, in the case where the loading waveguide is formed after the isolation layer is formed on the substrate, the performing of the step S1031 may form a photoresist layer on the loading waveguide and the isolation layer.

As shown in fig. 3A, a photoresist layer 301 is formed on the loaded waveguide 105 and the isolation layer 103.

Step S1032: patterning the photoresist layer to form a photoresist layer having the modulation electrode pattern;

here, the photoresist layer is exposed and developed, and a portion of the photoresist layer is dissolved away to form the photoresist layer having the modulation electrode pattern.

As shown in FIG. 3B, the photoresist layer 301 is patterned to form the photoresist layer 301 with the modulating electrode pattern 302.

Step S1033: depositing an electrode material on the photoresist layer having the modulating electrode pattern;

here, step S1033 may be performed by using any deposition process to form the electrode material.

As shown in FIG. 3C, electrode material 303 is deposited on the photoresist layer 301 with the modulating electrode pattern 302.

Step S1034: and removing the electrode material on the photoresist layer and the photoresist layer to form the modulation electrode.

Here, step S1034 may be performed by removing the electrode material and the photoresist layer on the photoresist layer using a dry etching process or a metal stripping process, so as to form the modulation electrode.

As shown in FIG. 3C, the electrode material 303 and photoresist layer 301 on photoresist layer 301 are removed to form the modulation electrode 21 as shown in FIG. 3D.

In the embodiment of the application, the modulation electrodes positioned at two sides of two arms of the Mach-Zehnder waveguide are formed by coating photoresist layers on the substrate and the loading waveguide, then exposing, developing, depositing the metal electrode and finally removing redundant photoresist and electrode materials.

An embodiment of the present application further provides an on-chip laser, as shown in fig. 1I, the on-chip laser includes:

a substrate 101;

an active layer 102 located on the substrate 101, wherein the material of the active layer 102 includes lithium niobate doped with rare earth ions;

a loading waveguide 105 located on the active layer 102, where the loading waveguide 105 includes a mach-zehnder waveguide having two arms adopting a bragg grating structure, or the loading waveguide includes a resonant cavity waveguide whose side wall connected to the input end adopts a bragg grating structure and a mach-zehnder waveguide connected to the output end;

the modulation electrodes 21 are located on both sides of the arms of the Mach-Zehnder waveguide.

In some embodiments, as shown in fig. 3D, the on-chip laser further comprises:

an isolation layer 103, located on the active layer 102, for protecting the active layer during the process of forming a loaded waveguide and adjusting the guiding ability of the loaded waveguide to the optical field of the formed laser;

in some embodiments, as shown in fig. 1D, the on-chip laser further comprises:

and the couplers are positioned at two ends of the loading waveguide, wherein a first end of the first coupler 24 is used for receiving the pump light, a second end of the first coupler 24 is connected with an input end of the loading waveguide, a first end of the second coupler 25 is connected with an output end of the loading waveguide, and a second end of the second coupler 25 is used for outputting output light generated by the wave combination of the loading waveguide.

In some embodiments, as shown in fig. 1D, the mach-zehnder waveguide 20 also includes two Y-branch waveguides, wherein,

the first end of the first Y-branch waveguide 202a is the input end of the mach-zehnder waveguide 20, and the second end of the first Y-branch waveguide 202a is connected to the first ends of the two arms 201 of the mach-zehnder waveguide; the second ends of the two arms 201 of the mach-zehnder waveguide are connected with the first end of a second Y-branch waveguide 202b, and the second end of the second Y-branch waveguide 202b is used as the output end of the mach-zehnder waveguide 20 and is used for outputting the output light generated by the combined wave of the mach-zehnder waveguide 20;

the structures of the two Y-branch waveguides comprise a sine-cosine structure or a double-arc structure.

In some embodiments, the material of the loading layer includes tantalum oxide, silicon nitride, titanium dioxide; the thickness of the active layer comprises 360nm or 600nm; the thickness of the spacer layer ranges from 50nm to 200nm.

In some embodiments, the modulating electrode comprises a traveling wave electrode or a segmented modulating electrode; the Bragg grating structure comprises long teeth and short teeth, and two continuous long teeth are arranged in the center of the Bragg grating structure.

The features disclosed in the several method or structure embodiments provided in the present application may be combined in any combination to arrive at new method or structure embodiments without conflict.

The above description of the embodiments of the semiconductor structure, similar to the above description of the embodiments of the method, has similar advantageous effects as the embodiments of the method. For technical details not disclosed in the embodiments of the semiconductor structure of the present application, reference is made to the description of the embodiments of the method of the present application for understanding.

The above description is only exemplary of the present application and should not be taken as limiting the scope of the present application, and any modifications, equivalents, improvements, etc. made within the spirit and principle of the present application should be included in the scope of the present application.

Claims (10)

1. A method of forming an on-chip laser, comprising:

providing a base, wherein the base comprises a substrate and an active layer positioned on the substrate, and the material of the active layer comprises lithium niobate doped with rare earth ions;

forming a loading waveguide on the substrate, wherein the loading waveguide comprises a Mach-Zehnder waveguide with two arms adopting a Bragg grating structure, or the loading waveguide comprises a resonant cavity waveguide with a side wall adopting the Bragg grating structure connected with an input end and a Mach-Zehnder waveguide connected with an output end;

and modulation electrodes are deposited and formed on two sides of two arms of the Mach-Zehnder waveguide.

2. The method of claim 1, wherein forming a loaded waveguide on the substrate comprises:

depositing a loading layer on the substrate;

and etching the loading layer to form the loading waveguide.

3. The method of claim 1, further comprising, prior to forming a loaded waveguide on the substrate:

and depositing an isolation layer on the substrate to protect the active layer in the process of forming the loading waveguide and adjust the guiding capacity of the loading waveguide to the optical field of the formed laser.

4. The method of any of claims 1 to 3, further comprising:

forming couplers at both ends of the loaded waveguide at the same time as the loaded waveguide;

the first end of the first coupler is used for receiving pump light, the second end of the first coupler is connected with the input end of the loading waveguide, the first end of the second coupler is connected with the output end of the loading waveguide, and the second end of the second coupler is used for outputting output light generated by wave combination of the loading waveguide.

5. A method according to any one of claims 1 to 3, wherein forming the modulating electrodes on both sides of the two arms of the mach-zehnder waveguide comprises:

forming a photoresist layer on the substrate and the loading waveguide;

patterning the photoresist layer to form a photoresist layer having the modulation electrode pattern;

depositing an electrode material on the photoresist layer having the modulating electrode pattern;

and removing the electrode material on the photoresist layer and the photoresist layer to form the modulation electrode.

6. An on-chip laser, comprising:

a substrate;

an active layer on the substrate, wherein the material of the active layer comprises lithium niobate doped with rare earth ions;

the loading waveguide is positioned on the active layer and comprises a Mach-Zehnder waveguide with two arms adopting a Bragg grating structure, or the loading waveguide comprises a resonant cavity waveguide with the side wall connected with the input end adopting the Bragg grating structure and a Mach-Zehnder waveguide connected with the output end;

and the modulation electrodes are positioned on two sides of two arms of the Mach-Zehnder waveguide.

7. The on-chip laser of claim 6, further comprising:

the isolation layer is positioned on the active layer and used for protecting the active layer in the process of forming the loading waveguide and adjusting the guiding capacity of the loading waveguide to the optical field of the formed laser;

and the couplers are positioned at two ends of the loading waveguide, wherein a first end of the first coupler is used for receiving pump light, a second end of the first coupler is connected with an input end of the loading waveguide, a first end of the second coupler is connected with an output end of the loading waveguide, and a second end of the second coupler is used for outputting output light generated by wave combination of the loading waveguides.

8. The on-chip laser of claim 6, wherein the Mach-Zehnder waveguide further includes two Y-branch waveguides, wherein,

the first end of the first Y-branch waveguide is the input end of the Mach-Zehnder waveguide, and the second end of the first Y-branch waveguide is connected with the first ends of the two arms of the Mach-Zehnder waveguide; the second ends of the two arms of the Mach-Zehnder waveguide are connected with the first end of a second Y-branch waveguide, and the second end of the second Y-branch waveguide is used as the output end of the Mach-Zehnder waveguide and is used for outputting output light generated by the combined wave of the Mach-Zehnder waveguide;

the structures of the two Y-branch waveguides comprise a sine-cosine structure or a double-arc structure.

9. The on-chip laser according to claim 7,

the material of the loading layer comprises tantalum oxide, silicon nitride and titanium dioxide;

the thickness of the active layer comprises 360nm or 600nm;

the thickness of the isolation layer ranges from 50nm to 200nm.

10. The on-chip laser according to any of claims 6 to 9,

the modulation electrode comprises a traveling wave electrode or a segmented modulation electrode;

the Bragg grating structure comprises long teeth and short teeth, and two continuous long teeth are arranged in the center of the Bragg grating structure.

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