Large-bandwidth integrated optical beam splitter based on sub-wavelength grating and preparation method thereof

Abstract

The invention relates to a large-bandwidth integrated optical beam splitter based on a sub-wavelength grating and a preparation method of the large-bandwidth integrated optical beam splitter, and belongs to the technical field of integrated photonic devices and semiconductors. The large-bandwidth integrated optical beam splitter comprises a substrate, a first cladding, a waveguide layer, a glass layer and a second cladding, the substrate, the first cladding, the waveguide layer, the glass layer and the second cladding are sequentially arranged from bottom to top, the waveguide layer is arranged in the glass layer, and the waveguide layer is connected with the upper surface of the first cladding; the optical beam splitter provided by the invention can achieve the effects of low insertion loss, uniform light splitting and low phase error in a large bandwidth range; the gaps in the grating structure of the waveguide layer can be stably filled by the glass layer formed by spin-coating the glass reagent, air gaps are prevented from occurring when the gaps in the grating structure are filled, the manufacturing reliability of the beam splitter is improved, and the optical beam splitter can be suitable for large-scale optical calculation and optical interconnection scenes.

Description

Technical Field

[0001] The present invention relates to the technical field of integrated photonic devices and semiconductor manufacturing, and in particular to a high-bandwidth integrated optical beam splitter based on a sub-wavelength grating and a preparation method thereof. Background Art

[0002] With the development of optical communication and optical computing technologies, the demand for high-performance integrated photonic chips is growing. As a linear optical element, integrated optical beam splitters play a vital role in optical communication and optical computing systems. Currently, common integrated optical beam splitters include directional couplers and multimode interference couplers, which can distribute light beams to different channels or combine light beams from different channels. Combining 2×2 integrated optical beam splitters as basic units into linear optical systems can realize optical switching and optical routing functions in optical communication networks, and matrix-vector operations in optical computing applications. Of these two types of integrated optical beam splitters, multimode interference couplers have lower wavelength sensitivity. However, as the scale of linear integrated optical circuits expands, the differences in transmittance at different wavelengths will accumulate step by step, highlighting the problem of bandwidth limitation.

[0003] Subwavelength grating structures have unique optical properties. When used to construct integrated optical waveguides, their ability to adjust mode dispersion provides the possibility of realizing large-bandwidth integrated optical components. In order to obtain a large-bandwidth integrated optical beam splitter, in addition to the need to carefully design parameters such as period and duty cycle to obtain excellent theoretical performance, it is also necessary to consider compatibility with existing semiconductor manufacturing processes and the stability of the manufacturing method. The challenges that exist in the actual manufacturing process are mainly manifested in: subwavelength gratings are small in size, and have higher requirements for high-precision lithography and etching technology; on the other hand, conventional chemical vapor deposition methods for making claddings easily form pores in the grating.

[0004] Therefore, considering the comprehensive performance and reliability, developing a large-bandwidth integrated optical beam splitter based on subwavelength grating design is of great significance to promoting the development of optical communication and optical computing technology. Summary of the invention

[0005] The object of the present invention is to overcome the deficiencies of the prior art and provide a high-bandwidth integrated optical beam splitter based on a sub-wavelength grating and a preparation method thereof.

[0006] To achieve the above object, the technical solution adopted by the present invention is:

[0007] In a first aspect, the present invention provides a high-bandwidth integrated optical beam splitter based on a subwavelength grating, comprising a substrate, a first cladding, a waveguide layer, a glass layer and a second cladding, wherein the substrate, the first cladding, the waveguide layer, the glass layer and the second cladding are arranged in sequence from bottom to top, the waveguide layer is connected to the upper surface of the first cladding, the glass layer wraps the side surface and the upper surface of the waveguide layer, the waveguide layer comprises two input waveguides, two input-end mode conversion regions, a multimode interference region, two output-end mode conversion regions and two output waveguides, the two input waveguides are connected to the two input-end mode conversion regions in a one-to-one correspondence, the two output waveguides are connected to the two output-end mode conversion regions in a one-to-one correspondence, and the multimode interference region is located between the input-end mode conversion region and the output-end mode conversion region.

[0008] Preferably, the input-end mode conversion region comprises a first tapered waveguide and first sub-wavelength gratings arranged on both sides of the first tapered waveguide, the tip of the first tapered waveguide faces the multi-mode interference region, and the width of the first sub-wavelength grating increases linearly along the light transmission direction;

[0009] And / or, the output end mode conversion region comprises a second tapered waveguide and second sub-wavelength gratings arranged on both sides of the second tapered waveguide, the tip of the second tapered waveguide faces the multi-mode interference region, and the width of the second sub-wavelength grating increases linearly along the light transmission direction;

[0010] And / or, the multimode interference region is provided with a third sub-wavelength grating.

[0011] Preferably, the period Λ1 of the first sub-wavelength grating is 300-400 nm, and the duty cycle η1 is 0.4-0.6;

[0012] And / or, the period Λ2 of the second sub-wavelength grating is 300-400 nm, and the duty cycle η2 is 0.4-0.6;

[0013] And / or, the period Λ3 of the third sub-wavelength grating is 300-400 nm, and the duty cycle η3 is 0.4-0.6.

[0014] Preferably, the length L1 of the input-end mode conversion region is equal to the length L2 of the output-end mode conversion region.

[0015] Preferably, the waveguide layer is made of silicon nitride, the thickness of the waveguide layer is 300-600 nm, and the refractive index of the waveguide layer is 1.95-2.15.

[0016] Preferably, the material of the first cladding layer is silicon dioxide, the thickness of the first cladding layer is 3000-4000 nm, and the refractive index of the first cladding layer is 1.44-1.46.

[0017] Preferably, the material of the second cladding layer is silicon dioxide, the thickness of the second cladding layer is 1500-3000 nm, and the refractive index of the second cladding layer is 1.44-1.46.

[0018] Preferably, the substrate is made of silicon.

[0019] Preferably, the thickness of the glass layer is 600-800 nm, and the refractive index of the glass layer is 1.37-1.39.

[0020] In a second aspect, the present invention provides a method for preparing a high-bandwidth integrated optical beam splitter based on a sub-wavelength grating as described in the first aspect, comprising the following steps:

[0021] S1. providing a thermally oxidized silicon wafer, wherein the thermally oxidized silicon wafer comprises a substrate and a first cladding layer arranged sequentially from bottom to top;

[0022] S2, depositing a silicon nitride film on the upper surface of the first cladding layer by chemical vapor deposition;

[0023] S3, spin-coating a photoresist on the upper surface of the silicon nitride film, curing it to form a photoresist layer, using electron beam lithography to expose the required structural pattern, using reactive ion etching to etch the silicon nitride film to form a waveguide layer, and removing the photoresist using oxygen plasma;

[0024] S4, spin-coating a spin-coated glass reagent on the upper surface of the first cladding layer, and making the spin-coated glass reagent submerge the waveguide layer, and forming a glass layer after curing;

[0025] S5. Depositing silicon oxide on the upper surface of the glass layer by chemical vapor deposition to form a second cladding layer.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention can achieve low insertion loss, uniform light splitting and low phase error effects within a wide bandwidth by setting an input end mode conversion zone between the input waveguide and the multimode interference zone and setting an output end mode conversion zone between the output waveguide and the multimode interference zone.

[0028] Compared with conventional sub-wavelength grating waveguide devices, the present invention sets a waveguide layer in the glass layer, so that the optical beam splitter of the present invention can be suitable for large-scale optical computing and optical interconnection scenarios. The glass layer formed by spin-coating a glass reagent can stably fill the gaps in the grating structure of the waveguide layer, avoiding the occurrence of air gaps when filling the gaps in the grating structure, thereby improving the reliability of beam splitter manufacturing. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1A partial cross-sectional view of a high-bandwidth integrated optical beam splitter based on a sub-wavelength grating provided by the present invention;

[0030] Figure 2 A schematic plan view of a waveguide layer provided by the present invention.

[0031] In the figure, 1-substrate, 2-first cladding, 3-waveguide layer, 4-glass layer, 5-second cladding, 31-input waveguide, 32-first tapered waveguide, 33-first sub-wavelength grating, 34-second tapered waveguide, 35-second sub-wavelength grating, 36-third sub-wavelength grating, 37-output waveguide. DETAILED DESCRIPTION

[0032] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0033] In a first aspect, the present invention provides a high-bandwidth integrated optical beam splitter based on a subwavelength grating, comprising a substrate 1, a first cladding 2, a glass layer 4 and a second cladding 5 arranged in sequence, a waveguide layer 3 is arranged in the glass layer 4, the waveguide layer 3 is connected to the upper surface of the first cladding 2, the glass layer 4 wraps the side and upper surface of the waveguide layer 3, the waveguide layer 3 comprises two input waveguides 31, two input-end mode conversion regions, a multimode interference region, two output-end mode conversion regions and two output waveguides 37, the two input waveguides 31 are connected to the two input-end mode conversion regions in a one-to-one correspondence, the two output waveguides 37 are connected to the two output-end mode conversion regions in a one-to-one correspondence, and the multimode interference region is located between the input-end mode conversion region and the output-end mode conversion region.

[0034] The present invention can achieve low insertion loss, uniform light splitting and low phase error effects within a wide bandwidth by setting an input end mode conversion zone between the input waveguide 31 and the multimode interference zone and setting an output end mode conversion zone between the output waveguide 37 and the multimode interference zone.

[0035] Compared with the silica cladding, the present invention covers the waveguide layer 3 with a glass layer 4. The glass layer 4 can more stably fill the gaps in the grating structure of the waveguide layer 3, avoiding the appearance of air gaps when filling the gaps in the grating structure, thereby improving the reliability of beam splitter manufacturing, and making the optical beam splitter of the present invention suitable for large-scale optical computing and optical interconnection scenarios.

[0036] In one embodiment, the input end mode conversion region is composed of a first tapered waveguide 32 and a first sub-wavelength grating 33 arranged on both sides of the first tapered waveguide 32. The tip of the first tapered waveguide 32 faces the multi-mode interference region. The width of the other end of the first tapered waveguide 32 is the same as the width W1 of the input waveguide 31. The width of the first sub-wavelength grating 33 increases linearly from W1 to W2 along the light transmission direction, W1 is 800~1200nm, and W2 is 1500~2500nm; the period Λ1 of the first sub-wavelength grating 33 structure is 300~400nm, and the duty cycle η1 is 0.4~0.6nm.

[0037] The output end mode conversion region is composed of a second tapered waveguide 34 and a second sub-wavelength grating 35 arranged on both sides of the second tapered waveguide 34. The tip of the second tapered waveguide 34 faces the multi-mode interference region. The width of the other end of the second tapered waveguide 34 is the same as the width W4 of the input waveguide 31. The width of the second sub-wavelength grating 35 decreases linearly from W4 to W3 along the light transmission direction. W3 is 800-1200nm, and W4 is 1500-2500nm. The period Λ2 of the second sub-wavelength grating 35 is 300-400nm, and the duty cycle η2 is 0.4-0.6nm.

[0038] The multi-mode interference region is provided with a third sub-wavelength grating 36 , the period Λ3 of the third sub-wavelength grating 36 is 300-400 nm, and the duty cycle η3 is 0.4-0.6.

[0039] Specifically, Λ1=Λ2=Λ3, η1=η2=η3. When the beam splitter meets this condition, the refractive index of the waveguide layer 3 is continuous, which avoids the sudden change of the refractive index of the waveguide layer 3 and affects the performance of the beam splitter.

[0040] In one embodiment, the length L1 of the input-end mode conversion region is equal to the length L2 of the output-end mode conversion region.

[0041] The inventors have found that according to the equivalent medium theory, the equivalent refractive index in the two directions parallel and perpendicular to the periodic interface is written as and Where n1 and n2 represent the refractive index of the two materials constituting the subwavelength grating (n1>n2), and η is the duty ratio of the material with a larger refractive index of the two materials. Specifically in the embodiment of the present invention, material 1 is silicon nitride, which is the material of the waveguide layer 3, and material 2 is a glass layer 4 formed by spin coating. λ is the wavelength, Λ is the grating period, and η ranges from 0.4 to 0.6. Under the subwavelength condition, Λ is much smaller than λ, and n || is the equivalent refractive index in the direction of the electric field parallel to the periodic interface, n ⊥ is the equivalent refractive index in the direction of the electric field perpendicular to the periodic interface.

[0042] The high bandwidth integrated optical beam splitter supports TE0 mode operation in the input strip waveguide and outputs in TE0 mode in the output strip waveguide.

[0043] The length L3 of the multimode interference zone is preferably 3L π / 2, where L π is the beat length between the two lowest-order TE modes, L π =π / (β1-β2). TE mode refers to the transverse electric mode (TE), which refers to the electromagnetic wave in which the electric field polarization direction is perpendicular to the propagation direction, among which TE0 and TE1 are the two lowest order modes.

[0044] The present invention can obtain a sub-wavelength grating waveguide design whose beat length is insensitive to wavelength changes by adjusting parameters such as the period and duty cycle of each sub-wavelength grating, and change the effective refractive index and beat length of different modes in the multi-mode interference region, thereby adjusting parameter indicators such as device size, additional loss, spectral uniformity and phase error. The operating wavelength of the wide-bandwidth integrated optical beam splitter described in the present invention can cover the O, E, S, C and L bands commonly used in optical communications. Within the operating wavelength range of 1250 to 1625 nm, the insertion loss in the wide-bandwidth integrated optical beam splitter is less than 0.25 dB, the spectral imbalance is less than 0.15 dB, and the phase error is less than 0.16 rad. In one embodiment, the material of substrate 1 is silicon.

[0045] In one embodiment, the material of the first cladding layer 2 is silicon dioxide, the thickness h1 of the first cladding layer 2 is 3000-4000 nm, and the refractive index of the first cladding layer 2 is 1.44-1.46.

[0046] In one embodiment, the material of the waveguide layer 3 is silicon nitride, the thickness h2 of the waveguide layer 3 is 300-600 nm, and the refractive index of the waveguide layer 3 is 1.95-2.15.

[0047] In one embodiment, the thickness h3 of the glass layer 4 is 600 to 800 nm, and the refractive index of the glass layer 4 is 1.37 to 1.39.

[0048] Specifically, h3>h2.

[0049] In one embodiment, the material of the second cladding layer 5 is silicon dioxide, the thickness h4 of the second cladding layer 5 is 1500 to 3000 nm, and the refractive index of the second cladding layer 5 is 1.44 to 1.46.

[0050] In a second aspect, the present invention provides a method for preparing a high-bandwidth integrated optical beam splitter based on a sub-wavelength grating as in the first aspect, comprising the following steps:

[0051] S1, providing a thermally oxidized silicon wafer, wherein the thermally oxidized silicon wafer comprises a substrate 1 and a first cladding layer 2 arranged sequentially from bottom to top;

[0052] S2, depositing a silicon nitride film on the upper surface of the first cladding layer 2 by chemical vapor deposition;

[0053] S3, spin-coating a photoresist on the upper surface of the silicon nitride film, pre-baking to form a photoresist layer, using electron beam lithography to expose the required structural pattern, using reactive ion etching to etch the silicon nitride film to form a waveguide layer 3, and then removing the photoresist using oxygen plasma;

[0054] S4, spin-coating a glass coating agent on the upper surface of the first cladding layer 2, and making the glass coating agent submerge the waveguide layer 3, and forming a glass layer 4 after curing;

[0055] S5 . Deposit silicon oxide on the upper surface of the glass layer 4 by chemical vapor deposition to form a second cladding layer 5 .

[0056] The present invention can better fill the gaps in the grating structure by first covering the waveguide layer 3 with spin-coated glass and then chemically vapor depositing a second cladding structure of silicon dioxide and a corresponding manufacturing method, thereby solving the problem of forming air gaps when directly depositing silicon dioxide to fill the grating gaps in the prior art. The advantage of the preparation method of the present invention in stability is conducive to the industrialization and promotion of the present invention.

[0057] In the description of the present invention, it should be noted that the terms "first", "second" and "third" are only used for descriptive purposes and cannot be understood as indicating the number of the indicated technical features. Therefore, the features defined as "first", "second" and "third" may explicitly or implicitly include at least one of the features. All directional indicators (such as up and down) in the present invention are only used to explain the relative position relationship, movement status, etc. between the various parts under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0058] In the description of the present invention, it should also be noted that the terms "include", "have" and any variations thereof are intended to cover non-exclusive inclusions.

[0059] For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A high-bandwidth integrated optical beam splitter based on a sub-wavelength grating, characterized in that: The invention comprises a substrate, a first cladding, a waveguide layer, a glass layer and a second cladding, wherein the substrate, the first cladding, the waveguide layer, the glass layer and the second cladding are arranged in sequence from bottom to top, the waveguide layer is connected to the upper surface of the first cladding, the glass layer wraps the side surface and the upper surface of the waveguide layer, the waveguide layer comprises two input waveguides, two input end mode conversion regions, a multimode interference region, two output end mode conversion regions and two output waveguides, the two input waveguides are connected to the two input end mode conversion regions in a one-to-one correspondence, the two output waveguides are connected to the two output end mode conversion regions in a one-to-one correspondence, and the multimode interference region is located between the input end mode conversion region and the output end mode conversion region.

2. The high-bandwidth integrated optical beam splitter based on sub-wavelength grating according to claim 1, characterized in that: The input end mode conversion region comprises a first tapered waveguide and a first sub-wavelength grating disposed on both sides of the first tapered waveguide, the tip of the first tapered waveguide faces the multi-mode interference region, and the width of the first sub-wavelength grating increases linearly along the light transmission direction; And / or, the output end mode conversion region comprises a second tapered waveguide and second sub-wavelength gratings arranged on both sides of the second tapered waveguide, the tip of the second tapered waveguide faces the multi-mode interference region, and the width of the second sub-wavelength grating increases linearly along the light transmission direction; And / or, the multimode interference region is provided with a third sub-wavelength grating.

3. The high-bandwidth integrated optical beam splitter based on sub-wavelength grating as claimed in claim 2, characterized in that: The period Λ1 of the first sub-wavelength grating is 300-400 nm, and the duty cycle η1 is 0.4-0.6; And / or, the period Λ2 of the second sub-wavelength grating is 300-400 nm, and the duty cycle η2 is 0.4-0.6; And / or, the period Λ3 of the third sub-wavelength grating is 300-400 nm, and the duty cycle η3 is 0.4-0.

6.

4. The high-bandwidth integrated optical beam splitter based on sub-wavelength grating according to claim 1, characterized in that: The length L1 of the input-end mode conversion region is equal to the length L2 of the output-end mode conversion region.

5. The high-bandwidth integrated optical beam splitter based on sub-wavelength grating according to claim 1, characterized in that: The material of the waveguide layer is silicon nitride, the thickness of the waveguide layer is 300-600 nm, and the refractive index of the waveguide layer is 1.95-2.

15.

6. The high-bandwidth integrated optical beam splitter based on sub-wavelength grating according to claim 1, characterized in that: The material of the first cladding layer is silicon dioxide, the thickness of the first cladding layer is 3000-4000 nm, and the refractive index of the first cladding layer is 1.44-1.

46.

7. The high-bandwidth integrated optical beam splitter based on sub-wavelength grating according to claim 1, characterized in that: The material of the second cladding layer is silicon dioxide, the thickness of the second cladding layer is 1500-3000 nm, and the refractive index of the second cladding layer is 1.44-1.

46.

8. The high-bandwidth integrated optical beam splitter based on sub-wavelength grating according to claim 1, characterized in that: The substrate is made of silicon.

9. The high-bandwidth integrated optical beam splitter based on sub-wavelength grating according to claim 1, characterized in that: The thickness of the glass layer is 600-800 nm, and the refractive index of the glass layer is 1.37-1.

39.

10. A method for preparing a high-bandwidth integrated optical beam splitter based on a sub-wavelength grating as claimed in any one of claims 1 to 9, characterized in that: The steps include: S1. providing a thermally oxidized silicon wafer, wherein the thermally oxidized silicon wafer comprises a substrate and a first cladding layer arranged sequentially from bottom to top; S2, depositing a silicon nitride film on the upper surface of the first cladding layer by chemical vapor deposition; S3, spin-coating a photoresist on the upper surface of the silicon nitride film to form a photoresist layer, using electron beam lithography to expose the required structural pattern, using reactive ion etching to etch the silicon nitride film to form a waveguide layer, and then removing the photoresist using oxygen plasma; S4, spin-coating a spin-coated glass reagent on the upper surface of the first cladding layer, and making the spin-coated glass reagent submerge the waveguide layer, and forming a glass layer after curing; S5. Depositing silicon oxide on the upper surface of the glass layer by chemical vapor deposition to form a second cladding layer.

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