CN113608300B - Double-color grating coupler with crosstalk suppression function and preparation method thereof - Google Patents

Abstract

The present invention proposes a two-color grating coupler with a crosstalk suppression function, which includes a substrate and a grating coupling structure located on the upper surface of the substrate. The two sides of the grating coupling structure are respectively provided with a first transmission waveguide and a second transmission waveguide. The first transmission waveguide and the second transmission waveguide are respectively provided with a first Bragg grating reflector and a second Bragg grating reflector; wherein, the grating coupling structure is a periodic grating structure, which is used to detect any central wavelength of the incident dual-band light Two-color coupling is performed with the center wavelength two; the first transmission waveguide is used for transmission of the center wavelength one, and the second transmission waveguide is used for transmission of the center wavelength two. Among them, the first Bragg grating reflector and the second Bragg grating reflector form an asymmetric DBR structure to realize crosstalk wavelength suppression and coupling efficiency improvement, and the first transmission waveguide and the second transmission waveguide form an asymmetric transmission waveguide to further improve the two-color coupling efficiency. Purpose.

Description

A two-color grating coupler with crosstalk suppression function and its preparation method

technical field

The invention relates to the technical field of optoelectronic devices, in particular to a two-color grating coupler with a crosstalk suppression function and a preparation method thereof.

Background technique

The infrared spectrum can be divided into three bands: near-infrared (NIR: 0.78-2 μm), mid-infrared (MIR: 2-14 μm) and far-infrared (FIR: 14-1000 μm). Since the mid-infrared band covers the chemical molecular fingerprint area and two atmospheric windows (3-5μm and 8-12μm), which are very important in science and technology, the development of mid-infrared light transmission and detection technology is very important for military and civilian fields, such as Chemical analysis, gas detection, environmental monitoring, laser radar, free space optical communication and remote sensing technology are all of great significance.

At present, for the mid-infrared band, the development of on-chip integration of photonic devices is relatively lagging behind. Most of the existing grating couplers only optimize the coupling efficiency for a single wavelength, and many application scenarios in the future need to combine mid-infrared light belonging to two atmospheric window bands. Coupled to different waveguides on the chip for transmission to achieve parallel processing of information and noise suppression. In 2007, Günther Roelkens and others realized an integrated grating coupler based on a diffraction grating structure, which can be used for optical multiplexing or demultiplexing of light with wavelengths of 1310nm and 1490nm, using a one-dimensional grating structure to achieve spatial separation of the two wavelengths. In 2009, He Sailing of Zhejiang University and others used a one-dimensional diffraction grating coupling structure to realize the function of a polarization beam splitter. The waves propagate in opposite directions. However, the existing research has the following problems or deficiencies: 1. The current two-color grating coupling is limited to the research on near-infrared communication bands such as 1550nm and 1310nm, and the mid-infrared two-color grating coupler is still to be developed; 2. At present The way to improve the grating coupling efficiency is mainly by building a vertical reflection structure, reducing the transmission loss at the bottom of the waveguide, or reducing the reverse coupling loss, etc. The efficiency improvement methods are limited, so more efficiency improvement methods need to be developed; 3. In When realizing two-color coupling, the existing wavelength crosstalk problem (the coupling energy of the wavelength in the direction of the reverse port) still needs to be solved.

Contents of the invention

The present invention provides a two-color grating coupler with a crosstalk suppression function and a preparation method thereof in order to overcome the serious wavelength crosstalk problem of the grating coupling device described in the prior art when realizing two-color coupling.

In order to solve the problems of the technologies described above, the technical solution of the present invention is as follows:

A two-color grating coupler with a crosstalk suppression function, including a substrate, and a grating coupling structure located on the upper surface of the substrate, a first transmission waveguide and a second transmission waveguide are respectively arranged on both sides of the grating coupling structure, The first transmission waveguide and the second transmission waveguide are respectively provided with a first Bragg grating reflector and a second Bragg grating reflector; wherein, the grating coupling structure is a periodic grating structure, which is used to detect the incident dual-band light Any central wavelength 1 and central wavelength 2 perform dual-color coupling; the first transmission waveguide is used to transmit the central wavelength 1, and the second transmission waveguide is used to transmit the central wavelength 2.

During use, the dual-band optical signal is incident on the surface of the grating coupling structure at a certain incident angle through the guidance of the input fiber, and the grating coupling structure realizes the coupling of light from space to the waveguide, and realizes the space separation transmission; The first Bragg grating reflector and the second Bragg grating reflector on both sides form an asymmetric DBR (distributed Bragg reflection, distributed Bragg reflector) crosstalk suppression structure, wherein the first Bragg grating reflector allows the center wavelength of the dual-band light One pass, reflective filtering is performed on the central wavelength two, the second Bragg grating reflector allows the central wavelength two in the dual-band light to pass through, and reflective filtering is performed on the central wavelength one, thereby realizing crosstalk wavelength suppression; the first transmission waveguide and the second transmission waveguide The waveguide efficiently transmits the wavelength light output by the first Bragg grating reflector and the second Bragg grating reflector respectively.

As a preferred solution, the parameters of the grating coupling structure are set according to the Bragg diffraction conditions of the center wavelength 1 and the center wavelength 2, so as to realize the coupling transmission of the two wavelengths.

As a preferred solution, the reflection wavelengths of the first Bragg grating reflector and the second Bragg grating reflector are respectively the wavelengths corresponding to the central wavelength and causing crosstalk in the light propagation direction.

As a preferred solution, the etching depth of the first Bragg grating reflector is equal to the thickness of the first transmission waveguide; the etching depth of the second Bragg grating reflector is equal to the thickness of the second transmission waveguide.

Wherein, the thickness of the first transmission waveguide is optimized according to the center wavelength 1, and the thickness of the second transmission waveguide is optimized according to the center wavelength 2. The two form an asymmetric transmission waveguide structure, which can further improve the two-color coupling efficiency.

As a preferred solution, the first transmission waveguide, the first Bragg grating reflector, the grating coupling structure, the second Bragg grating reflector and the second transmission waveguide all use waveguide materials for dual-band optical transmission.

As a preferred solution, the substrate includes a silicon-on-insulator (SOI) substrate, silicon, germanium, glass, sapphire, gallium arsenide, indium phosphide, quartz, calcium fluoride, magnesium fluoride, barium fluoride, selenide One or more of zinc, zinc sulfide, potassium chloride, and potassium bromide.

The present invention also proposes a preparation method for preparing the two-color grating coupler proposed by any of the above technical solutions, which includes the following steps:

S1: preparing a waveguide layer on the surface of the substrate;

S2: Perform photolithography on the waveguide layer to obtain the photoresist patterns of the first transmission waveguide, the first Bragg grating reflector, the grating coupling structure, the second Bragg grating reflector, and the second transmission waveguide respectively on the waveguide layer;

S3: Etching is performed on the waveguide layer according to the etching depths respectively set for the first transmission waveguide, the first Bragg grating reflector, the grating coupling structure, the second Bragg grating reflector, and the second transmission waveguide to obtain a two-color grating coupler .

As a preferred solution, the technology used to prepare the waveguide layer on the surface of the substrate includes one or more combinations of magnetron sputtering preparation method, epitaxy preparation method, and electron beam evaporation preparation method.

As a preferred solution, the techniques used for photolithography on the waveguide layer include superdiffraction nanolithography based on femtosecond laser direct writing, maskless superdiffraction nanolithography based on femtosecond laser projection, and electron beam lithography. technology, traditional mask-based nanolithography, or a combination of more.

As a preferred solution, the technique used for etching on the waveguide layer includes inductively coupled plasma etching or reactive ion etching.

Compared with the prior art, the beneficial effect of the technical solution of the present invention is: the present invention uses the first Bragg grating reflector and the second Bragg grating reflector to form an asymmetric DBR crosstalk suppression structure to realize crosstalk wavelength suppression and coupling efficiency improvement; through the grating The coupling structure realizes two-color light coupling in the mid-infrared band and separate transmission; the first transmission waveguide and the second transmission waveguide are used to form an asymmetric transmission waveguide to further improve the two-color coupling efficiency.

Description of drawings

FIG. 1 is a schematic structural diagram of a two-color grating coupler with a crosstalk suppression function in Embodiment 1. FIG.

FIG. 2 is a side view of the waveguide layer of the two-color grating coupler with crosstalk suppression function in Embodiment 1. FIG.

Fig. 3 is a coupling efficiency spectrum diagram in the case of using a symmetrical transmission waveguide and no crosstalk suppression structure.

Fig. 4 is a coupling efficiency spectrum diagram in the case of adopting a symmetrical transmission waveguide and an asymmetrical DBR crosstalk suppression structure.

FIG. 5 is a spectral diagram of coupling efficiency in the case of using the two-color grating coupler with crosstalk suppression function of Embodiment 1. FIG.

FIG. 6 is a flow chart of the preparation method of the two-color grating coupler with crosstalk suppression function according to the second embodiment.

Wherein, 1-substrate, 2-first transmission waveguide, 3-first Bragg grating reflector, 4-grating coupling structure, 5-second Bragg grating reflector, 6-second transmission waveguide.

Detailed ways

The accompanying drawings are for illustrative purposes only and cannot be construed as limiting the patent;

In order to better illustrate this embodiment, some parts in the drawings will be omitted, enlarged or reduced, and do not represent the size of the actual product;

For those skilled in the art, it is understandable that some well-known structures and descriptions thereof may be omitted in the drawings.

The technical solutions of the present invention will be further described below in conjunction with the accompanying drawings and embodiments.

Example 1

This embodiment proposes a two-color grating coupler with a crosstalk suppression function, as shown in FIGS. 1-2 , which are structural schematic diagrams of the two-color grating coupler with a crosstalk suppression function in this embodiment.

The two-color grating coupler with crosstalk suppression function proposed in this embodiment includes:

substrate1;

The grating coupling structure 4 located on the upper surface of the substrate, the first transmission waveguide 2 and the second transmission waveguide 6 are respectively arranged on both sides of the grating coupling structure 4, the first transmission waveguide 2 and the second transmission waveguide 6 A first Bragg grating reflector 3 and a second Bragg grating reflector 5 are respectively arranged in it;

Wherein, the grating coupling structure 4 is a periodic grating structure, which is used for dual-color coupling of any central wavelength 1 and central wavelength 2 in the incident dual-band light;

The thickness of the first Bragg grating reflector 3 is equal to that of the first transmission waveguide 2 (for transmitting the center wavelength one in the dual-band light); the second Bragg grating reflector 5 and the second transmission waveguide 6 ( The central wavelength 2) used to transmit dual-band light has the same thickness; the reflection wavelengths of the first Bragg grating reflector 3 and the second Bragg grating reflector 5 are wavelengths that cause crosstalk in the light propagation direction corresponding to the central wavelength.

The grating coupling structure 4 in this embodiment is used to realize the coupling of light from space to the waveguide; the first Bragg grating reflector 3 and the second Bragg grating reflector 5 form an asymmetric DBR crosstalk suppression structure, which is used to realize crosstalk wavelength suppression , which is used to improve the coupling efficiency; the first transmission waveguide 2 and the second transmission waveguide 6 form an asymmetric waveguide transmission structure, and the thicknesses are respectively set according to the optimized transmission conditions of the target transmission wavelength to improve the coupling efficiency.

In the specific implementation process, the two-color grating coupler with crosstalk suppression function is applied to the two-color optical coupling of 3-5 μm and 8-12 μm in the mid-infrared band. The transmission wavelength λ ₁ in the 8-12 μm band corresponds to a central wavelength of 8.5 μm, and the transmission wavelength λ ₂ in the 3-5 μm band corresponds to a central wavelength of 5 μm.

In this embodiment, the first transmission waveguide 2, the first Bragg grating reflector 3, the grating coupling structure 4, the second Bragg grating reflector 5, and the second transmission waveguide 6 all use waveguide materials for dual-band optical transmission. Bottom 1 adopts SOI substrate, silicon, germanium, glass, sapphire, gallium arsenide, indium phosphide, quartz, calcium fluoride, magnesium fluoride, barium fluoride, zinc selenide, zinc sulfide, potassium chloride, bromide One or more of potassium. The above-mentioned substrate materials are respectively suitable for two-color grating couplers with different wavelength bands and different incidence modes (ie, upper incidence and back incidence).

Specifically, the substrate 1 in this embodiment adopts an SOI substrate, and a Ge waveguide layer is arranged on the substrate 1. The first transmission waveguide 2, the first Bragg grating reflector 3, the grating coupling structure 4, and the second Bragg grating reflector Both the device 5 and the second transmission waveguide 6 are located in the Ge waveguide layer.

The grating coupling structure 4 in this embodiment is a periodic grating structure, and its parameter setting meets the Bragg diffraction conditions of _λ1 and _λ2 , specifically, the coupling grating period Λ is set to 2.71 μm, and the duty ratio DC=w/Λ is set is 0.51, the number of cycles is set to 9, and the etching depth is set to 1.2 μm.

Further, the first Bragg grating reflector 3 realizes reflection filtering for the crosstalk in the 5 μm band, and at the same time ensures that light with a central wavelength of 8.5 μm can be transmitted normally, and the coupling efficiency is not affected. The first Bragg grating reflector in this embodiment The grid spacing _d1 of 3 is set to 0.2 μm, the grid width _d2 is set to 0.56 μm, and the thickness _h1 is set to 1.74 μm.

Similarly, the second Bragg grating reflector 5 realizes reflection filtering for the 8.5 μm band crosstalk, and at the same time ensures that the 5 μm center wavelength light can be transmitted normally, and the coupling efficiency is not affected. The second Bragg grating reflector in this embodiment The grid spacing _d3 of 5 is set to 0.28 μm, the grid width _d4 is set to 1 μm, and the thickness _h2 is set to 1.2 μm.

The first transmission waveguide 2 in this embodiment is for more efficient transmission of light with a central wavelength of 8.5 μm, and its thickness _h1 is set to 1.74 μm; the second transmission waveguide 6 is for more efficient transmission of light with a central wavelength of 5 μm, and its thickness h ₂ is set to 1.2 μm.

The mid-infrared fiber is used as the input fiber, and its input wavelength covers two bands of 3-5μm and 8-12μm, and the input fiber uses the incident angle of -5° (5° counterclockwise with the direction of the vertical grating surface) to transmit the dual-band light Incident to the surface of the grating coupling structure 4, the incident light passes through the grating coupling structure 4 to realize the coupling of light from space to the waveguide, and then the 8-12 μm band transmission wavelength λ ₁ is along the first transmission waveguide 2, through the first Bragg grating reflector 3 Transmitting to the left, the transmission wavelength _λ2 in the 3-5 μm band travels along the second transmission waveguide 6 and transmits to the right through the second Bragg grating reflector 4.

In the case of using a symmetrical transmission waveguide and no crosstalk suppression structure, its two-color coupling efficiency is shown in Figure 3. The coupling efficiency of the left port corresponding to the central wavelength of 8.5 μm is 38.1%, and the coupling efficiency of the right port for the central wavelength of 5 μm is 51.4%. The crosstalk is over 20%. Using a symmetrical transmission waveguide and an asymmetrical DBR crosstalk suppression structure, its bilateral coupling efficiency is shown in Figure 4. The coupling efficiency of the 8.5 μm left port is 40.86%, and the 5 μm coupling efficiency of the right port is 54.89%. The bilateral crosstalk is suppressed to about 10%. And the bilateral expected coupling efficiency has been improved to a certain extent.

However, the coupling efficiency of the two-color grating coupler composed of the asymmetric transmission waveguide and the asymmetric DBR crosstalk suppression structure of this embodiment is shown in Figure 5. While maintaining the crosstalk suppression effect, the two-color coupling efficiency is further improved. The 8.5μm coupling efficiency of the left port is 44.38%, and the 5μm coupling efficiency of the right port is 60.08%.

It can be seen that the two-color grating coupler with crosstalk suppression function in this embodiment adopts an asymmetric transmission waveguide and an asymmetric DBR crosstalk suppression structure, realizes two-color light coupling in the mid-infrared band through the grating coupling structure 4, and realizes separate transmission, and then passes Constructing an asymmetric DBR crosstalk suppression structure for different central wavelengths can effectively suppress crosstalk and achieve a certain increase in the expected two-color coupling efficiency; further optimize the thickness of the transmission waveguide for different wavelengths to construct an asymmetric transmission waveguide structure , while maintaining the crosstalk suppression function, the two-color coupling efficiency can be greatly improved.

Example 2

This embodiment proposes a preparation method for preparing the two-color grating coupler proposed in Embodiment 1. As shown in FIG. 6 , it is a flow chart of the manufacturing method of the two-color grating coupler of this embodiment.

In the preparation method of the two-color grating coupler proposed in this embodiment, it includes the following steps:

S1: preparing a waveguide layer on the surface of the substrate 1;

S2: Perform photolithography on the waveguide layer to obtain the light of the first transmission waveguide 2, the first Bragg grating reflector 3, the grating coupling structure 4, the second Bragg grating reflector 5, and the second transmission waveguide 6 respectively on the waveguide layer Engraving graphics;

S3: Etching on the waveguide layer according to the etching depths set respectively by the first transmission waveguide 2, the first Bragg grating reflector 3, the grating coupling structure 4, the second Bragg grating reflector 5, and the second transmission waveguide 6, Get a two-color grating coupler.

In this embodiment, the techniques used to prepare the waveguide layer on the surface of the substrate 1 include:

1. Magnetron sputtering preparation method: the glow discharge is excited by controlling the voltage loaded on the target, and the generated ions are used to bombard the target to obtain sputtered atoms, which are then deposited on the surface of the substrate 1 to form a waveguide layer material;

2. Epitaxial preparation method: the technology of growing a single crystal thin film on a single crystal substrate 1, the new single crystal thin layer grown according to the crystal phase of the substrate is the epitaxial layer, including chemical vapor deposition (CVD), molecular beam epitaxy (MBE )wait;

3. Electron beam evaporation preparation method: under vacuum conditions, high-energy electron beams are used to directly heat the evaporation material, so that the evaporation material is vaporized and transported to the substrate 1, and condensed on the substrate 1 to form a waveguide layer material.

Techniques used for photolithography on waveguide layers include:

1. Maskless superdiffraction nanolithography technology based on the main principle of degenerate/nondegenerate two-photon absorption polymerization effect, mainly including: superdiffraction nanolithography technology based on femtosecond laser direct writing; femtosecond laser projection based Maskless super-diffraction nanolithography technology;

2. Electron beam lithography technology;

3. Nano-lithography technology based on traditional masks, etc.

Techniques for etching on the waveguide layer include: Inductively Coupled Plasma Etching (ICP) and/or Reactive Ion Etching (RIE) techniques.

The same or similar reference numerals correspond to the same or similar components;

The terms describing the positional relationship in the drawings are only for illustrative purposes and cannot be interpreted as limitations on this patent;

Apparently, the above-mentioned embodiments of the present invention are only examples for clearly illustrating the present invention, rather than limiting the implementation of the present invention. For those of ordinary skill in the art, other changes or changes in different forms can be made on the basis of the above description. It is not necessary and impossible to exhaustively list all the implementation manners here. All modifications, equivalent replacements and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the claims of the present invention.

Claims (10)

1. A two-color grating coupler with crosstalk suppression function, characterized in that it comprises a substrate (1), and a grating coupling structure (4) positioned on the upper surface of the substrate, the grating coupling structure (4) A first transmission waveguide (2) and a second transmission waveguide (6) are respectively arranged on both sides, and a first Bragg grating reflector (3) is respectively arranged in the first transmission waveguide (2) and the second transmission waveguide (6). ) and the second Bragg grating reflector (5); wherein, the grating coupling structure (4) is a periodic grating structure, which is used to carry out two-color coupling to any center wavelength one and center wavelength two in the incident dual-band light; The first transmission waveguide (2) is used to transmit the central wavelength one, and the second transmission waveguide (6) is used to transmit the central wavelength two; the first Bragg grating reflector (3) allows the central wavelength in the dual-band light When one passes through, reflective filtering is performed on the central wavelength two, and the second Bragg grating reflector (5) allows the central wavelength two in the dual-band light to pass through, and reflective filtering is performed on the central wavelength one. 2. The two-color grating coupler according to claim 1, characterized in that, the parameters of the grating coupling structure (4) are set according to the Bragg diffraction conditions of center wavelength one and center wavelength two. 3. The two-color grating coupler according to claim 1, characterized in that, the reflection wavelengths of the first Bragg grating reflector (3) and the second Bragg grating reflector (5) are respectively corresponding to the central wavelength light propagation direction wavelengths that cause crosstalk. 4. The two-color grating coupler according to claim 1, characterized in that, the etching depth of the first Bragg grating reflector (3) is equal to the thickness of the first transmission waveguide (2); The etching depth of the two Bragg grating reflectors (5) is equal to the thickness of the second transmission waveguide (6). 5. The two-color grating coupler according to claim 1, characterized in that, the first transmission waveguide (2), the first Bragg grating reflector (3), the grating coupling structure (4), the second Bragg grating reflector Both the device (5) and the second transmission waveguide (6) use waveguide materials for dual-band optical transmission. 6. The two-color grating coupler according to any one of claims 1 to 5, characterized in that the substrate (1) comprises a silicon-on-insulator (SOI) substrate, silicon, germanium, glass, sapphire, arsenide One or more of gallium, indium phosphide, quartz, calcium fluoride, magnesium fluoride, barium fluoride, zinc selenide, zinc sulfide, potassium chloride, and potassium bromide. 7. A preparation method for preparing the two-color grating coupler with crosstalk suppression function as claimed in any one of claims 1 to 6, characterized in that it comprises the following steps: S1: preparing a waveguide layer on the surface of the substrate (1); S2: Perform photolithography on the waveguide layer to obtain the first transmission waveguide (2), the first Bragg grating reflector (3), the grating coupling structure (4), the second Bragg grating reflector (5), and the second transmission waveguide (6) Photoresist patterns respectively on the waveguide layer; S3: Etching according to the first transmission waveguide (2), the first Bragg grating reflector (3), the grating coupling structure (4), the second Bragg grating reflector (5), and the second transmission waveguide (6) Depth, etching is performed on the waveguide layer to obtain a two-color grating coupler. 8. The preparation method according to claim 7, characterized in that, the technology used to prepare the waveguide layer on the surface of the substrate (1) includes magnetron sputtering preparation method, epitaxial preparation method, electron beam evaporation preparation method one or more. 9. The preparation method according to claim 7, characterized in that, the technology adopted for photolithography on the waveguide layer includes super-diffraction nano-lithography technology based on femtosecond laser direct writing, maskless technology based on femtosecond laser projection One or more of mode superdiffraction nano-lithography, electron beam lithography, and traditional mask-based nano-lithography. 10 . The preparation method according to claim 7 , wherein the technique used for etching on the waveguide layer includes inductively coupled plasma etching or reactive ion etching. 11 .

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