CN115755279A - On-chip optical amplifying coupler and forming method thereof - Google Patents

Abstract

The disclosed embodiments provide an on-chip optical amplification coupler and a method of forming the same, the method including: etching the initial substrate to form the multimode coupler; depositing a medium material with a preset thickness and doped with rare earth ions on the multimode coupler to form a gain cladding of the multimode coupler; depositing a bonding medium layer on the gain cladding layer; and inversely bonding a pump laser on the bonding medium layer to form the on-chip optical amplification coupler.

Description

On-chip optical amplifying coupler and forming method thereof

Technical Field

The present disclosure relates to the field of semiconductor technology, and more particularly, but not exclusively, to an on-chip optical amplifying coupler and method of forming the same.

Background

Various configurations have been used to implement optical couplers including directional couplers, Y-branch waveguides and Multi-Mode Interference (MMI) couplers. The optical coupler based on the MMI structure has the advantages of small structure size, small influence of structure parameters on optical field distribution, large process tolerance, polarization insensitivity and the like, and plays an important role in the development of integrated optoelectronics.

However, since the self-imaging length of the MMI is related to the effective refractive index of each order mode, the output performance of the MMI device needs to be controlled by adjusting the refractive index of the device, and when the MMI is implemented in a high-index high-refractive-index contrast platform (such as a Silicon On Insulator (SOI)), the adjustment of the effective refractive index becomes difficult, so that the performance thereof is significantly degraded. Meanwhile, the traditional MMI optical beam splitter is difficult to realize arbitrary light splitting. On the other hand, as the scale of the optical device in the integrated optoelectronic circuit is increased, a large amount of attenuation is generated during the transmission of light, and the transmission performance of the whole system is seriously affected by the loss on the whole chip, so that it is necessary to compensate the signal optical attenuation during the optical transmission process to meet the requirements of high information transmission rate and large information transmission capacity in optical communication and optical networks.

Disclosure of Invention

In view of the above, the embodiments of the present disclosure provide an on-chip optical amplifying coupler and a method for forming the same.

The technical scheme of the disclosure is realized as follows:

in a first aspect, an embodiment of the present disclosure provides an on-chip optical amplifying coupler, which sequentially includes: substrate layer, coupler layer, gain cladding and integrated pumping layer, wherein: the coupler layer comprises a multimode coupler; the gain cladding layer is a dielectric layer doped with rare earth ions, and forms a hybrid waveguide structure with the multimode coupler in the coupler layer; light is partially coupled into the dielectric layer in the form of evanescent waves in the transmission and coupling processes, so that optical gain is provided for light transmission; the integrated pumping layer includes a pumping laser to provide pumping light to the gain cladding.

In a second aspect, embodiments of the present disclosure provide a method of forming an on-chip optical amplifying coupler, the method including: etching the initial substrate to form a multi-mode coupler; depositing a medium material with a preset thickness and doped with rare earth ions on the multimode coupler to form a gain cladding of the multimode coupler; depositing a bonding medium layer on the gain cladding layer; and inversely bonding a pump laser on the bonding medium layer to form the on-chip optical amplification coupler.

In an embodiment of the present disclosure, an on-chip optical amplifying coupler sequentially includes from bottom to top: the device comprises a substrate layer, a coupler layer, a gain cladding layer and an integrated pumping layer; firstly, etching an initial substrate to form a multi-mode coupler; secondly, depositing a medium material with a preset thickness and doped with rare earth ions on the multimode coupler to form a gain cladding of the multimode coupler; then, depositing a bonding medium layer on the gain cladding layer; and finally, inversely bonding a pump laser on the bonding medium layer to form the on-chip optical amplification coupler. From the above, the on-chip optical amplification coupler based on the gain cladding and the multimode coupler composite structure can realize on-chip power coupling and optical amplification by using the rare earth ion doped dielectric material as the gain cladding of the multimode coupler, and can expand the functions of the traditional device.

In other embodiments, by using the bragg grating structure on the side wall of the asymmetric grating type multimode coupling region, on one hand, the effective refractive index of the device can be effectively regulated and controlled, asymmetric multimode interference is generated, and the power distribution performance is improved; on the other hand, the feedback effect can be provided for optical transmission, and the optical amplification efficiency of the device is improved.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the technical aspects of the disclosure.

Drawings

In the drawings, which are not necessarily drawn to scale, like reference numerals may describe similar components in different views. Like reference numerals having different letter suffixes may represent different examples of similar components. The drawings illustrate generally, by way of example, but not by way of limitation, various embodiments discussed herein.

Fig. 1 is a schematic structural diagram of an on-chip optical amplifying coupler according to an embodiment of the present disclosure;

fig. 2 is a schematic structural diagram of a multimode coupler applied to an on-chip optical amplifying coupler according to an embodiment of the present disclosure;

fig. 3 is a schematic three-dimensional structure diagram of an on-chip optical amplifying coupler according to an embodiment of the present disclosure;

fig. 4 is a simulation diagram of the gain effect of an on-chip amplification coupler according to an embodiment of the disclosure;

fig. 5 is a schematic flow chart illustrating an implementation of a method for forming an on-chip optical amplifying coupler according to an embodiment of the present disclosure;

fig. 6 is a schematic structural diagram of a process for forming an on-chip optical amplifying coupler according to an embodiment of the present disclosure.

Detailed Description

Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure 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 disclosure. It will be apparent, however, to one skilled in the art, that the present disclosure may be practiced without one or more of these specific details. In other instances, well-known features of the art have not been described in order to avoid obscuring the present disclosure; that is, not all features of an actual embodiment are described herein, and well-known functions and constructions 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 … …," "adjacent … …," "connected to," or "coupled to" another element or layer, it can be directly on, adjacent, connected or coupled to the other element or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being "directly on … …," "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 disclosure. And the discussion of a second element, component, region, layer or section does not necessarily imply that the first element, component, region, layer or section is necessarily present in the disclosure.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. 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.

In recent years, silicon On Insulator (SOI) has been increasingly used as an important platform for integrated optoelectronic chip fabrication. SOI is compatible with Complementary Metal Oxide Semiconductor (CMOS) fabrication processes, has high optical field confinement capability due to its high refractive index contrast, very low leakage loss, and great potential in the miniaturization of photonic circuits. The on-chip waveguide device prepared based on the platform has the characteristics of high speed and strong radiation resistance, and has wide application prospect.

The on-chip optical coupler is an important component in an integrated optoelectronic circuit, is a passive optical device for realizing optical power transmission distribution among a plurality of optical paths or between an active optical device and the optical paths, and has important application in the transmission process of on-chip optical signals. In the field of communication, optical couplers are widely applied to on-chip experiments and performance detection; in terms of signal transmission, optical signals are distributed and transmitted through an optical coupler; in wavelength division multiplexing transmission systems and optical amplifiers, optical couplers must also be used for combining and combining light of each wavelength.

The basic principle of the multimode interference type optical power coupler is to use the principle of self-imaging of light. In a multimode waveguide, all excited guided modes interfere with each other and periodically exhibit 1 or more replicated images of the input field along the propagation direction of the waveguide. By selecting the appropriate length of the multimode coupling region, the optical power can be distributed into two or more output waveguides, resulting in an optical power distribution.

Some concepts related to the present disclosure will be presented below:

SOI refers to a substrate technology that replaces the traditional bulk substrate silicon with an "engineered" substrate, which consists of three layers:

1) A very thick bulk substrate silicon substrate layer, which mainly serves to provide mechanical support for the two layers above;

2) A relatively thin insulating silicon dioxide interlayer;

3) A thin top layer of single crystal silicon on which etched (optical) waveguides are formed.

Evanescent waves are also known as: the evanescent wave and the evanescent wave are near-field light waves which are transmitted along the direction of a medium interface and have amplitudes attenuated in an exponential form along the depth direction vertical to the interface when the evanescent wave and the evanescent wave are incident from an optically dense medium to an optically sparse medium and are totally reflected.

The (optical) waveguide is composed of media with different refractive indexes, and can generate a guide (channel) structure for transversely binding the optical wave to enable the optical wave to be transmitted along the longitudinal direction. The most basic structure is a planar/thin film waveguide, and a ridge waveguide, a strip waveguide, a hybrid waveguide and the like are classified according to the structure.

Planar waveguide (planar waveguide) is also called: a thin film waveguide (waveguide) in which the refractive index distribution of the waveguide is a plane parallel to the propagation direction (longitudinal direction) of light waves. The most common planar waveguide is composed of three materials, i.e., a cladding layer, a core layer and a substrate, wherein the refractive index of the core layer is higher than that of the cladding layer (or called cladding layer) and the substrate, and light waves are constrained in one dimension, so that the energy of the light waves is constrained at the core layer and the vicinity thereof and is transmitted along the longitudinal direction of the waveguide.

A Y-branch waveguide (Y-branch waveguide), a planar optical waveguide for splitting an optical path into two optical paths or combining two optical paths into one optical path, is known as a Y-shaped waveguide and is generally made of lithium niobate.

Optical couplers (optical couplers or photo-couplers) are optical devices (including optical fibers or optical waveguides) that use the optical coupling principle to realize the mutual exchange of light in different optical paths. It is used in active and passive optical devices such as laser, optical amplifier, optical beam splitter, optical modulator and optical switch.

Optical coupling is used to split or combine optical power at the same wavelength to guide the optical signal from one medium to another.

Effective refractive index (effective refractive index), which is used to describe the amount of phase propagation velocity of an optical wave mode in a medium of a particular structure. The value is the ratio of the propagation constant of the waveguide mode to the vacuum wave number of the light.

Bragg gratings (Bragg gratings) are a type of grating used to selectively reflect or diffract light waves having a wavelength satisfying the Bragg condition.

End-face coupling (end-face coupling) is also called: butt-coupling (butt-coupling) is commonly used in the fields of filtering, beam deflection, beam shaping, etc. When the electromagnetic field of the transmitted light wave is emitted from the end face of the optical fiber or the waveguide and is coupled to the incident end of the next-stage optical fiber or the waveguide, the energy of the electromagnetic field is transferred from the emitting face to the incident face. The coupling characteristic is influenced by various end effects of the optical fiber or the waveguide, a group of equations of amplitude change rules in the longitudinal transmission process of the outgoing and incoming two light wave electromagnetic fields along the waveguide or the optical fiber can be solved by Maxwell equations and waveguide or optical fiber distortion to obtain the end face coupling condition, the solving result can quantitatively describe the mode light wave electromagnetic field coupling process, various factors influencing coupling can be analyzed, and the problems of the light wave electromagnetic field amplitude of a coupling mode, the power exchange degree between modes and the like under different conditions can be solved.

Embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings.

Referring to fig. 1, the on-chip optical amplifying coupler provided in the embodiment of the present disclosure sequentially includes, from bottom to top: substrate layer 11, coupler layer 12, gain cladding layer 13, and integrated pump layer 14, wherein:

the coupler layer 12 includes a multimode coupler;

the gain cladding layer 13 is a dielectric layer doped with rare earth ions, and forms a mixed waveguide structure with the multimode coupler in the coupler layer 12; the light is partially coupled into the dielectric layer in the form of evanescent waves in the transmission and coupling processes, so that optical gain is provided for light transmission;

the integrated pump layer 14 includes a pump laser to provide pump light to the gain cladding layer 13.

In the embodiments of the present disclosure, the substrate layer is generally selected based on a standard SOI platform, which is an important platform for integrated photonic device fabrication. SOI is compatible with CMOS fabrication processes, has high optical field confinement capability due to its high refractive index contrast, very low leakage loss, and great potential in the miniaturization of photonic circuits. The on-chip waveguide device prepared based on the platform has the characteristics of high speed and strong radiation resistance, and has wide application prospect.

Here, a grating-type multimode coupler structure is etched on the top monocrystalline silicon layer using an etching technique to form a coupler layer; wherein, the thickness of the top silicon material is based on 220nm, and the top silicon material can be directly used as the waveguide thickness of the coupler layer.

The selection of the gain cladding material adopts a rare earth ion doped medium material as the gain cladding, the rare earth element has rich energy level structure, and the ions of the rare earth element can be used as efficient luminescent centers and are an effective luminescent candidate scheme on a chip; meanwhile, in order to realize larger net gain optical amplification on a small-size waveguide structure, a gain cladding gain medium layer is required to have higher ion doping concentration and smaller transmission loss; the erbium-doped aluminum oxide material system deposited by the atomic layer is used as a gain cladding gain medium layer, so that the optical active erbium concentration can be higher, the film quality is better, and stronger gain can be generated in the standard communication wavelength range.

Based on the above embodiments, a multimode coupler applied to an on-chip optical amplifying coupler according to another embodiment of the present disclosure is further provided, and referring to fig. 2, the multimode coupler includes: an input port 21, a grating type multimode coupling region 22 and an output port 23; the single-mode or multi-mode light beam injected from the input port 21 passes through the grating multi-mode coupling region 22 to be excited into multiple guided modes, and coherent superposition is generated in the propagation direction of the light, so that a light field consistent with the input port 21 is output at the output port 23.

The single-mode or multi-mode light beam injected from the input port passes through the grating multi-mode coupling region to be excited into multi-order guided modes, different propagation constants are provided among the multi-order guided modes, coherent superposition is generated in the propagation direction of the light, and therefore the light field consistent with the input port is output at the output port, namely self-imaging is generated, and effective distribution of on-chip optical power is finally completed.

In some embodiments, referring to fig. 2, the input port 21 and the output port 23 are both tapered waveguide structures.

The input port and the output port are on-chip waveguides which are of standard SOI waveguide structures and used for realizing efficient on-chip signal transmission, the size parameters of the input port and the output port are determined by referring to the size of a standard process device, and meanwhile, the input port and the output port are designed into tapered structures, so that efficient end face coupling is realized.

In some embodiments, referring to fig. 2, the two sidewalls of the grating-type multimode coupling region 22 employ bragg grating structures 221 and 222; the bragg grating structure provides feedback for optical transmission to cause the grating-type multimode coupling region 22 to resonate partially.

Here, in the grating type multimode coupling region, bragg gratings are distributed on two side walls of the grating type multimode coupling region, and the phase change and the coupling coefficient are relatively small; meanwhile, the Bragg gratings on the two side walls adopt different grating parameters, and an asymmetric Bragg grating structure is formed by regulating and controlling the grating tooth depths of different gratings on the two sides, so that the limitation of the traditional MMI self-mirror image principle on the output light power splitting ratio is broken through, the light power beam splitter in any proportion is realized, and all the advantages of the MMI light power beam splitter, such as large process tolerance, wide working bandwidth, low insertion loss and the like, are maintained.

In some embodiments, different grating parameters are used for the two sidewalls of the bragg grating structure, wherein the grating parameters include grating period, grating tooth depth and duty cycle. For example, referring to fig. 2, the two sidewalls 221 and 222 of the bragg grating use different grating tooth depths. The grating period is adjusted according to the central wavelength of the resonant cavity oscillation so as to keep consistent with the strongest spectral peak of the gain cladding material; the grating tooth depth and the duty ratio of the Bragg grating structure are adjusted according to the refractive index distribution of the optical field mode in the grating so as to control the coupling coefficient of the Bragg grating structure.

Here, the specific parameter design of the bragg grating includes: grating period, grating tooth depth and duty cycle. The grating period controls the central wavelength of the resonant oscillation in the whole region, needs to be kept consistent with the strongest spectral peak of the gain cladding material, usually 1535nm, and is established according to the Bragg condition. The grating duty cycle controls the refractive index distribution of the optical field mode in the grating, and further influences the coupling coefficient of the grating, and the duty cycle is 1:1. The grating tooth depth mainly changes the highest effective refractive index and the low effective refractive index in the grating, and the coupling strength of the grating is determined together with the design of the grating duty ratio, the tooth depth and the length, so that the coupling efficiency of a light field is influenced.

Here, bragg gratings based on erbium-doped media typically have a grating strength of 4 to 7 to guarantee single longitudinal mode operation; meanwhile, the output light power beam splitting ratio can be controlled by adjusting the grating tooth depths on the two sides.

It should be noted that the total length of the grating type multimode coupling region is determined according to the self-imaging length of the MMI and the optimal cavity length of the gain, and is usually set to be an integral multiple of the self-imaging length to generate good interference coupling; meanwhile, according to the optimal cavity length under the action of the rare earth ion doped gain cladding, under different pumping powers, the total length of the grating type multimode coupling region is set within a reasonable range: with weak optical feedback and low gain at shorter lengths. As the length of the device increases, the rare earth ion population inversion effect in the gain cladding layer will be reduced and the gain effect will be reduced.

In some embodiments, referring to fig. 1, the gain cladding 13 is an erbium doped material prepared using atomic layer deposition or magnetron sputtering or laser deposition methods; the coupler layer 12 is made of a waveguide material of silicon or silicon nitride.

Here, the gain cladding and the lower coupler form a hybrid waveguide structure, and light is partially coupled into the gain cladding material in the form of evanescent waves in the transmission and coupling processes, so as to provide optical gain for light transmission. Compared with the silica cladding adopted in the traditional scheme, the dielectric material doped with rare earth ions has higher refractive index as the gain cladding, and can more effectively realize the control of the regulation and control of the effective refractive index and the optical field distribution. The effective refractive index of the hybrid waveguide and the longitudinal distribution of the optical field mode field are changed by adjusting the thickness of the gain cladding, thereby optimizing the evanescent wave coupling efficiency between the hybrid waveguide and the gain cladding in the optical transmission process and adjusting the gain effect in the optical transmission process.

In some embodiments, referring to fig. 1, an integrated pump layer 14 is disposed over the gain cladding layer 13 by bonding, and pump light emitted from the pump laser enters the gain material by vertical coupling to activate rare earth ions, thereby generating optical gain.

In some embodiments, the VCSEL employs a strained semiconductor multiple quantum well or semiconductor quantum dot structure as a pumping active region.

Referring to fig. 5, a method for forming an on-chip optical amplifying coupler according to an embodiment of the present disclosure may include steps S501 to S504, where:

step S501, etching an initial substrate to form a multimode coupler;

in practice, the initial substrate may be etched using a dry or wet etch process to form the multimode coupler.

The etching gas used in the dry etching process may include: trifluoromethane (CHF 3), carbon tetrafluoride (CF 4), hydrogen bromide (HBr), and chlorine (Cl 2). In other embodiments, the etching gas may also include other fluorocarbon-based gases, such as one or more of difluoromethane (CH 2F 2), octafluoropropane (C3F 8), perfluorobutadiene (C4F 6), octafluorocyclobutane (C4F 8), and octafluorocyclopentene (C5F 8). The etching solution used in the wet etching process may include a diluted hydrofluoric acid solution.

Step S502, depositing a medium material with a preset thickness and doped with rare earth ions on the multimode coupler to form a gain cladding of the multimode coupler;

step S503, depositing a bonding medium layer on the gain cladding layer;

here, a thin film of silicon dioxide and silicon nitride is deposited as a bonding dielectric layer on the deposited gain cladding layer by Plasma Enhanced Chemical Vapor Deposition (PECVD).

Step S504, a pump laser is inversely bonded on the bonding medium layer to form the on-chip optical amplification coupler.

In some embodiments, to improve the bonding quality, the hydrogen and water content of the bonding medium is reduced by a thermal annealing process; and then activating the surface by adopting a reactive ion etching and bonding method to complete the flip integration of the gain cladding and the heterogeneous of the pumping source.

In some embodiments, after depositing the bonding medium layer on the gain cladding layer, the method further comprises: and (3) after the surface of the bonding medium layer is activated by reactive ion etching, polishing the bonding medium layer, and inversely bonding a pump laser on the polished bonding medium layer.

In order to effectively solve the technical problems of refractive index regulation and light attenuation compensation in transmission in the conventional on-chip coupler structure, the disclosure provides an on-chip optical amplification coupler with a composite structure based on a gain cladding, a multimode interference coupler and a Bragg grating, and on-chip optical power coupling and optical amplification are realized simultaneously.

Referring to fig. 3, the three-dimensional structure 30 of the on-chip optical amplifying coupler provided by the embodiment of the present disclosure includes: an input waveguiding region 31, a grating-type multimode coupling region 22 and an output waveguiding region 32, wherein the input waveguiding region 31 comprises one input port 21 and the output waveguiding region 32 comprises two output ports 23. The single-mode or multi-mode light beam injected from the input port 21 of the input waveguide area 31 by the optical signal transmitted by the system-on-chip will be excited into multi-order guided modes through the grating multi-mode coupling area 22, the guided modes of each order have different propagation constants, and coherent superposition is generated in the propagation direction of the light, so that the light field consistent with the input field is output at a specific position, that is, self-imaging is generated, and then the light is output from the output port 23 of the output waveguide area 32, and finally, the effective distribution of the optical power on-chip is completed. Synchronously, optical signals partially enter the gain cladding layer in an evanescent wave coupling mode in the transmission process and interact with the gain material to finish on-chip optical amplification.

Referring to fig. 1, the on-chip optical amplification coupler is sequentially provided with a substrate layer, a coupler layer, a gain cladding layer and an integrated pumping layer from bottom to top.

The gain cladding layer is a dielectric layer doped with rare earth ions, and forms a hybrid waveguide structure with the lower coupler, and light can be partially coupled into the gain cladding layer material in the form of evanescent waves in the transmission and coupling processes, so that optical gain is provided for light transmission. The rare earth gain cladding with higher refractive index replaces the traditional oxide layer to be used as the cladding of the waveguide coupler, so that the regulation and control of the effective refractive index can be more effectively realized while the gain is provided, and the thickness of the gain cladding can be adjusted according to the effective refractive index, mode field distribution and gain effect of the waveguide; and the dielectric material doped with rare earth ions has the advantages of insensitive polarization, low noise, excellent temperature performance and large high-speed bandwidth, is better compatible with a CMOS (complementary metal oxide semiconductor) process, has low cost and is more suitable for on-chip integration.

Here, the coupler layer is based on an MMI structure and is composed of an input port, a grating type multimode coupling region and an output port. The single-mode or multi-mode light beam injected from the input port passes through the grating multi-mode coupling region to be excited into multi-order guided modes, different propagation constants are provided among the guided modes of each order, and coherent superposition is generated in the propagation direction of the light, so that a light field consistent with an input field is output at a specific position, namely self-imaging is generated. The input port and the output port are of tapered waveguide structures and are used for efficient end face coupling of signals.

Referring to fig. 2, bragg grating structures are designed on two side walls of the grating type multimode coupling region, so that on one hand, the effective refractive index of the MMI coupler can be effectively regulated and controlled, and depends on the geometric structure of the bragg grating, the refractive index of the constituent materials and the polarization state of light, and on the other hand, the bragg grating structures provide a feedback effect for light transmission, so that the multimode coupling region (also called as an interference region) of the optical field grating generates partial resonance, and the amplification efficiency of the gain cladding is improved. The grating period is adjusted according to the central wavelength of the resonant cavity oscillation, and needs to be kept consistent with the strongest spectral peak of the gain cladding material; the depth of the grating teeth and the duty ratio are adjusted according to the refractive index distribution of the optical field mode in the grating to control the coupling coefficient of the grating, and the effective refractive index of the coupler can be designed to be any value between the refractive indexes of two materials formed by the coupler in principle; meanwhile, a grating structure introduced into the grating type multimode coupling region can be designed into an up-down asymmetric mode, namely two side walls adopt different grating parameters, and the asymmetric structure can cause asymmetric multimode interference, so that the limitation of the traditional MMI self-mirror image principle on the output light power splitting ratio is broken through, and the light power distribution of any proportion is realized. The total length of the grating type multimode coupling region is adjusted according to the self-imaging length of the MMI and the optimal cavity length of the gain, and the grating type multimode coupling region provides a good gain effect while ensuring power distribution.

Here, the gain cladding is an erbium-doped material prepared by utilizing an atomic layer deposition or magnetron sputtering or laser deposition method; the coupler layer is made of standard waveguide material of silicon or silicon nitride;

the integrated pumping layer is a vertical cavity surface emitting pump laser and provides pumping light with high electro-optic conversion efficiency for the lower gain cladding. A pump laser is pasted above the gain cladding layer in a bonding mode, and emitted pump light enters the gain cladding layer material in a vertical coupling mode to activate rare earth ions to generate optical gain. The thickness design of the integrated pumping layer is adjusted according to the optical field coupling in the vertical direction, and the interaction between the pumping source and the gain packet layer is optimized.

Here, the vertical cavity surface emitting pump laser may employ a strain-type semiconductor Multiple Quantum Well (MQW) or a semiconductor Quantum dot structure as a pumping active region.

The gain effect simulation of the on-chip optical amplification coupler provided by the embodiment of the disclosure, referring to fig. 4, under the condition that the total lengths of the couplers are the same, the gain effect of the on-chip optical amplification coupler is increased along with the increase of the pumping power and gradually saturates; when the pumping power is 25mW, the gain of the on-chip optical amplification coupler is increased along with the increase of the total length of the coupler, and the gain starts to be rapidly reduced after the optimal length is reached; when the pumping power is 50mW, the gain of the on-chip optical amplification coupler is increased along with the increase of the total length of the coupler and gradually saturated; the gain of the on-chip optical amplification coupler increases with the total coupler length when the pump power is 75mW or 100 mW.

As can be seen from the above, since a longer resonant cavity length causes an insufficient pumping distance, which results in a difficulty in forming population inversion, the material of the gain cladding layer directly absorbs the signal light rather than generating a gain effect, and thus the gain effect is greatly reduced. In order to ensure that the device provides better gain effect while ensuring power distribution, the total length range of the coupler can be controlled in the order of hundreds of microns.

Referring to fig. 6, an embodiment of the present disclosure further provides a schematic structural diagram of a forming process of an on-chip optical amplifying coupler, and a manufacturing method of the on-chip optical amplifying coupler may be implemented through steps S601 to S601, where:

step S601, etching on the top silicon by utilizing an etching technology based on an SOI platform to form a grating type multimode interference coupler structure;

step S602, selectively depositing a rare earth ion doped gain cladding layer with a preset thickness in a groove by utilizing processes such as atomic layer deposition, magnetron sputtering or laser deposition;

step S603, performing planarization processing on the surface of the gain cladding layer;

here, silicon dioxide and silicon nitride films are deposited as bonding dielectric layers on the deposited gain cladding layer by PECVD, and surface activation is performed by reactive ion etching, followed by chemical mechanical polishing to smooth the surface roughness of the bonding dielectric to meet the bonding requirements.

Step S604, depositing a pump source material on a pump material growth substrate to prepare a pump laser;

step S605, activating the gain cladding and the surface of the pump laser by adopting a reactive ion etching and bonding method to realize the flip integration of the gain cladding and the pump laser, and removing a pump material growth substrate by mechanical dilution and chemical etching; to form an on-chip optical amplifying coupler.

Here, in order to improve the bonding quality, the contents of hydrogen and water in the bonding medium are reduced by a thermal annealing process.

Step S606, performing a conventional photolithography process of glue spreading, developing, and etching on the on-chip optical amplification coupler, and depositing an electrode.

Here, the electrode material may include a metal, a metal nitride, or a metal silicide, for example, titanium nitride (TiN). In some embodiments, the electrode may be formed by any suitable Deposition process, for example, a Chemical Vapor Deposition (CVD) process, a Physical Vapor Deposition (PVD) process, an Atomic Layer Deposition (ALD) process, a Plasma Enhanced Chemical Vapor Deposition (PECVD) process, a spin coating process, a thin film process, or the like, and the method for forming the electrode is not limited in the embodiments of the present disclosure.

The preparation method can integrate the pump on the chip well, indirectly realize the amplification of the electric pump and improve the integration level of the chip. The etching width and depth of the grating structure are defined by the line width of the etching mask pattern and the maximum etching depth.

The grating type multimode coupling region disclosed by the invention has two advantages: on one hand, the effective refractive index of the MMI coupler can be effectively regulated and controlled, and the effective refractive index depends on the geometric structure of the Bragg grating, the refractive index of the composition material and the polarization state of light; on the other hand, the Bragg grating structure provides a feedback effect for light transmission, so that the light field grating type multimode coupling region generates partial resonance, and the gain effect of the gain cladding is improved.

The embodiment of the disclosure provides an on-chip optical amplification coupler with a composite structure based on a gain cladding material, a multimode interference coupler and a Bragg grating, which utilizes a rare earth material as a cladding of the multimode interference coupler structure, simultaneously realizes on-chip power coupling and optical amplification, and expands the functions of a traditional device. The effective refractive index of the device is effectively regulated and controlled through the asymmetric side wall Bragg grating structure, asymmetric multimode interference is generated, and the power distribution performance is improved; meanwhile, a feedback effect is provided for optical transmission, and the optical amplification efficiency of the device is improved. The scheme can meet the requirements of small-size, low-cost and high-gain integrated optical amplification devices, and opens up a new idea for on-chip amplification and coupling research.

Logic "high" levels and logic "low" levels may be used to describe the logic levels of an electrical signal. A signal having a logic "high" level may be distinguished from a signal having a logic "low" level. For example, when a signal having a first voltage corresponds to a signal having a logic "high" level, a signal having a second voltage corresponds to a signal having a logic "low" level. In one embodiment, the logic "high" level may be set to a voltage level higher than the voltage level of the logic "low" level. Further, the logic levels of the signals may be set to be different or opposite, depending on the embodiment. For example, a certain signal having a logic "high" level in one embodiment may be set to have a logic "low" level in another embodiment.

In the several embodiments provided in the present disclosure, it should be understood that the disclosed apparatus and method may be implemented in a non-target manner. The above-described device embodiments are merely illustrative, for example, the division of the unit is only a logical functional division, and there may be other division ways in actual implementation, such as: multiple units or components may be combined, or may be integrated into another system, or some features may be omitted, or not implemented. Additionally, the various components shown or discussed are coupled or directly coupled to each other.

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 multiple network units; some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.

The features disclosed in the several method or apparatus embodiments provided in this disclosure may be combined in any combination to arrive at a new method or apparatus embodiment without conflict.

The above description is only a few embodiments of the present disclosure, but the scope of the embodiments of the present disclosure is not limited thereto, and any person skilled in the art can easily conceive of changes or substitutions within the technical scope of the embodiments of the present disclosure, and all the changes or substitutions should be covered by the scope of the embodiments of the present disclosure. Therefore, the protection scope of the embodiments of the present disclosure shall be subject to the protection scope of the claims.

Claims (10)

1. An on-chip optical amplifying coupler, comprising in order: substrate layer, coupler layer, gain cladding and integrated pumping layer, wherein:

the coupler layer comprises a multimode coupler;

the gain cladding layer is a dielectric layer doped with rare earth ions, and forms a hybrid waveguide structure with the multimode coupler in the coupler layer; light is partially coupled into the dielectric layer in the form of evanescent waves in the transmission and coupling processes, so that optical gain is provided for light transmission;

the integrated pumping layer includes a pump laser to provide pump light to the gain cladding.

2. The on-chip optical amplifying coupler according to claim 1, wherein the multi-mode coupler comprises: the system comprises an input port, a grating type multimode coupling area and an output port;

the single-mode or multi-mode light beam injected from the input port passes through the grating multi-mode coupling region to be excited into a multi-order guided mode, and coherent superposition is generated in the propagation direction of light, so that an optical field consistent with the input port is output at the output port.

3. The on-chip optical amplifying coupler of claim 2, wherein the input port and the output port are both tapered waveguide structures.

4. The on-chip optical amplifying coupler of claim 2, wherein the two sidewalls of the grating type multimode coupling region adopt a bragg grating structure;

the Bragg grating structure provides a feedback effect for optical transmission, so that the grating type multimode coupling region generates partial resonance.

5. The on-chip optical amplifying coupler of claim 2, wherein the two side walls of the bragg grating structure adopt different grating parameters, wherein the grating parameters comprise grating period, grating tooth depth and duty ratio;

the grating period is adjusted according to the central wavelength of the resonant cavity oscillation so as to keep consistent with the strongest spectral peak of the gain cladding material;

the grating tooth depth and the duty ratio of the Bragg grating structure are adjusted according to the refractive index distribution of the optical field mode in the grating so as to control the coupling coefficient of the Bragg grating structure.

6. The on-chip optical amplification coupler of any of claims 1 to 5, wherein the gain cladding layer is an erbium doped material prepared by atomic layer deposition or magnetron sputtering or laser deposition;

the coupler layer is made of waveguide material of silicon or silicon nitride.

7. The on-chip optical amplifying coupler according to any one of claims 1 to 5, wherein the integrated pumping layer is disposed above the gain cladding layer by bonding, and pumping light emitted from the pumping laser enters the gain material by vertical coupling to activate rare earth ions, thereby generating optical gain.

8. The on-chip optical amplifying coupler of any one of claims 1 to 5, wherein the VCSEL employs a strained semiconductor multiple quantum well or semiconductor quantum dot structure as a pumping active region.

9. A method of forming an on-chip amplified coupler, the method comprising:

etching the initial substrate to form the multimode coupler;

depositing a medium material with a preset thickness and doped with rare earth ions on the multimode coupler to form a gain cladding of the multimode coupler;

depositing a bonding medium layer on the gain cladding layer;

and inversely bonding a pump laser on the bonding medium layer to form the on-chip optical amplification coupler.

10. The method of claim 9, wherein after depositing a bonding medium layer on the gain cladding layer, the method further comprises:

and polishing the bonding medium layer after surface activation is carried out on the bonding medium layer by utilizing reactive ion etching, and inversely bonding a pump laser on the polished bonding medium layer.

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