CN113406751B - A fiber-waveguide coupling mode-spot converter in 850nm band - Google Patents

Abstract

The invention relates to an optical fiber and waveguide coupling spot size converter with 850nm waveband, which comprises a lower cladding, a three-port Y-branch lower cladding, an SU-8 conical structure, a waveguide component, a waveguide group and a three-port Y-branch upper cladding; the lower cladding and the SU-8 conical structure form a first-stage spot size conversion module, the lower cladding, the three-port Y-branch lower cladding and the three-port Y-branch upper cladding respectively form a second-stage spot size conversion module and a third-stage spot size conversion module with the waveguide component and the waveguide group, and the whole structure is integrally formed; when the optical field transmitted by the optical fiber enters the converter, the first-stage spot size conversion module, the second-stage spot size conversion module and the third-stage spot size conversion module perform transition compression on the optical field, and the optical field is converted into a single mode and then output. The invention has reasonable design, effectively improves the coupling efficiency of the optical fiber and the waveguide and has stronger flexibility.

Description

A fiber-waveguide coupling mode-spot converter in 850nm band

technical field

The invention belongs to the technical field of optical communication, and in particular relates to an optical fiber and waveguide coupling mode spot converter with a wavelength of 850 nm.

Background technique

With the rapid development of communication technology in the context of multimedia and big data era, traditional electrical-electrical interconnection has been difficult to meet the development needs of high-speed and large-capacity communications. In recent years, optical communication systems developed using photonic integration technology have become a research hotspot due to their advantages of low energy consumption, large bandwidth, and low delay. Utilizing the electro-optical properties of different types of materials and the high refractive index difference between the waveguide core and cladding, the realization of highly integrated on-chip optical-optical interconnection, electro-optical modulation, and optical/electrical or electrical/optical conversion has become a key research issue. Efficient coupling between optical fibers and waveguide chips is one of the key technologies of optical integration and a common problem faced by all optical integrated modules. Silicon nitride material has low absorption loss in the near-infrared and visible wavelength range, and is widely used in optical waveguide devices, while the mode spot of silicon nitride waveguide device is generally in micro-nano size, and the mode spot of optical fiber is generally in micron size , the direct alignment coupling between the waveguide and the fiber will cause a large mode field mismatch loss. The 850nm (nanometer) band is one of the commonly used bands for optical communication. How to realize the efficient coupling between optical fibers and waveguide chips is also a problem that we need to solve. Grating coupling (vertical coupling) and end-face coupling (horizontal coupling) are two commonly used modes of mode-spot converters for photonic integrated chips. Grating couplers usually have limited bandwidth and high polarization dependence. Compared to grating couplers, end-face couplers have larger bandwidths and lower polarization dependence.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide an optical fiber and waveguide coupling mode spot converter in the 850 nm band, which solves the problem of low coupling efficiency between the optical fiber and the waveguide in the 850 nm band in the prior art.

The technical scheme adopted in the present invention is,

An 850nm waveband optical fiber and waveguide coupling mode spot converter, comprising a lower cladding, the upper end face of the lower cladding is sequentially covered with a three-port Y-branch lower cladding and a SU-8 tapered structure, and a three-port Y-branch lower cladding The upper end face is covered with a waveguide assembly, one side of the waveguide assembly is connected to the SU-8 tapered structure, and the other side is connected to the waveguide group, and the upper end face of the waveguide assembly is covered with a three-port Y-branch upper cladding corresponding to the three-port Y-branch lower cladding;

Among them, along the length direction of the lower cladding layer: the lower cladding layer and the SU-8 tapered structure form the first-stage mode spot conversion module, the lower cladding layer, the three-port Y branch lower cladding layer and the three-port Y branch upper cladding layer, pass through A second-stage mode spot conversion module and a third-stage mode spot conversion module are formed in sequence with the waveguide assembly and the waveguide group respectively, and the overall structure of the optical fiber and the waveguide coupling mode spot converter is integrally formed;

When the optical field transmitted by the optical fiber enters the optical fiber and waveguide coupling mode spot converter, the first-stage mode-spot conversion module, the second-stage mode-spot conversion module and the third-stage mode-spot conversion module compress the light field transitionally and convert the It is output after single mode.

The present invention is also characterized in that,

The waveguide assembly includes a first curved waveguide, a straight waveguide, and a second curved waveguide. The first curved waveguide and the second curved waveguide are arranged in a Y-shape corresponding to the straight waveguide. The open end of the Y-shape is connected to the SU-8 tapered structure. The Y-shape The convergent end connects the waveguide group.

The materials of the first curved waveguide, the straight waveguide, the second curved waveguide and the waveguide group are all made of silicon nitride.

The waveguide group includes a first waveguide and a second waveguide which are connected to the gathering end of the Y-shaped structure in sequence, the first waveguide is set in a trapezoidal structure, the lower base of the trapezoidal structure is connected to the gathering end of the Y-shaped structure, and the upper base of the trapezoidal structure is connected to the second waveguide. The second waveguide is arranged in a rectangular structure.

The SU-8 conical structure is a prismatic structure, and the upper bottom of the prismatic structure is connected with the open end of the Y-shape.

The lower cladding layer, the three-port Y-branch lower cladding layer, and the three-port Y-branch upper cladding layer are all made of silicon dioxide.

The thickness dimension of the upper cladding layer of the three-port Y-branch is greater than the thickness dimension of the lower cladding layer of the three-port Y-branch.

The beneficial effects of the present invention are as follows: the present invention provides an optical fiber and waveguide coupling mode spot converter with a wavelength of 850 nm. The mode field matching of the three-port Y-branch structure with silicon nitride as the waveguide core layer is realized, and finally the optical signal is outputted through the three-port Y-branch single-mode to complete the mode spot conversion. By simply physically cutting the SU-8 tapered structure, it can be matched with optical fibers of different mode spot sizes, which effectively improves the coupling efficiency between the optical fiber and the waveguide, and has strong flexibility.

Description of drawings

Fig. 1 is the structure schematic diagram of a kind of 850nm waveband optical fiber and waveguide coupling mode spot converter of the present invention;

FIG. 2 is a detailed schematic diagram of an optical fiber and waveguide coupling mode spot converter in an 850 nm waveband of the present invention;

3 is a schematic plan view of an optical fiber and waveguide coupling mode spot converter in an 850nm waveband of the present invention;

Fig. 4 is a kind of 850nm wave band optical fiber and waveguide coupling mode spot converter in the optical fiber and the mode spot converter lateral alignment tolerance curve diagram;

FIG. 5 is a graph showing the longitudinal alignment tolerance of the optical fiber and the mode spot converter in an optical fiber and waveguide coupling mode spot converter in an 850 nm wavelength band according to the present invention.

In the figure, 1. Lower cladding, 2. Three-port Y-branch lower cladding, 3. SU-8 tapered structure, 4. First curved waveguide, 5. Straight waveguide, 6. Second curved waveguide, 7. No. One waveguide, 8. Second waveguide, 9. Three-port Y-branch upper cladding.

Detailed ways

A fiber-waveguide coupling mode spot converter in the 850 nm wavelength band of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

As shown in Fig. 1, Fig. 2 and Fig. 3, an optical fiber and waveguide coupling mode spot converter in 850nm wavelength band, including lower cladding 1, SU-8 tapered structure 3, three-port Y branch lower cladding 2, three ports Y branch waveguide and three-port Y branch upper cladding 9; wherein, the three-port Y branch waveguide consists of a first curved waveguide 4, a straight waveguide 5, a second curved waveguide 6, a trapezoidal first waveguide 7 and a rectangular Two waveguides are composed of 8. The upper cladding layer of the SU-8 conical structure 3 is air, which is set as a prism. By performing adiabatic compression of the vertical and horizontal dimensions of the prism in the transmission direction, the matching with the end face light field of the three-port Y-branch waveguide is realized. , transmit and compress the optical field through the first curved waveguide 4, straight waveguide 5, second curved waveguide 6 and trapezoidal first waveguide 7 in the three-port Y-branched waveguide, and finally output the single-mode output through the rectangular second waveguide 8 .

The structure and working principle of an optical fiber and waveguide coupling mode spot converter in the 850nm wavelength band of the present invention are as follows: the SU-8 material is used on the silicon dioxide lower cladding to process the tapered structure, and the SU-8 tapered structure 3 is the first The first-level mode spot conversion module efficiently couples the optical field transmitted by the optical fiber into the SU-8 tapered structure 3. By gradually reducing the vertical and horizontal dimensions of the SU-8 tapered structure 3 in the optical field transmission direction, Complete the conversion of the size of the mold spot from large to small;

The lower cladding layer 1 using silicon dioxide is covered with a layer of the lower cladding layer 2 which is a thin silicon dioxide layer for the three-port Y branch, the first curved waveguide 4, the straight waveguide 5, the first curved waveguide 4, the straight The two-curved waveguide 6 is made of silicon nitride material, and the three-port Y-branch upper cladding layer corresponds to the three-port Y-branch upper cladding layer 9 disposed thereon. First, the optical field energy output by the SU-8 tapered structure 3 is matched. , and then by gradually merging the first curved waveguide 4, the straight waveguide 5, and the second curved waveguide 6 in the transmission direction of the light field, the transition of the light field energy and the compression of the spot size are completed;

The first waveguide 7 and the second waveguide 8 are made of silicon nitride material, and the size of the waveguide in the horizontal direction along the transmission direction of the optical field is adiabatically reduced to a single-mode size, and the optical field output from the second-stage mode spot conversion module is converted from The multi-mode to single-mode conversion is finally passed through the silicon nitride rectangular second waveguide 8 single-mode output.

The optical fiber and waveguide coupling mode spot converter in the 850 nm wavelength band of the present invention will be further described in detail below through specific embodiments.

Example

A Gaussian lens beam with a diameter of 2.5μm (microns) at a wavelength of 850nm is used to replace the light field emitted by the tapered lens fiber. Silicon oxide, the refractive index is 1.453; the input waveguide is SU-8 tapered structure 3, the refractive index is 1.577, and the three-port Y-branch waveguide material is silicon nitride, and the refractive index is 1.993;

The thickness of the lower cladding layer 1 is 3 μm, the thickness of the three-port Y-branch lower cladding layer 2 is 0.15 μm, and the thickness of the three-port Y-branch upper cladding layer 9 is 2 μm. The length of the SU-8 tapered structure 3 is 160 μm, the thickness and width of the end face connected to the optical fiber are 3.4 μm, and the thickness and width of the end face connected to the three-port Y-branch waveguide are 0.8 μm and 2.1 μm, respectively. The thickness of the first curved waveguide 4 , the straight waveguide 5 , and the second curved waveguide 6 are all 0.3 μm and 0.18 μm in width. The spacing between the branch waveguides at the input end face of the three-port Y branch is 0.57 μm, and the length is all 27 μm. The width of the end face of the first waveguide 7 connected to the first curved waveguide 4, the straight waveguide 5, and the second curved waveguide 6 is 0.54 μm, the width of the end face connected to the second waveguide 8 is 0.45 μm, and the width of the second waveguide 8 is 0.45 μm. The lateral and longitudinal alignment tolerance curves of the TE polarization state and the TM polarization state of the fiber and the waveguide at 850nm wavelength are shown in Figure 4 and Figure 5; it can be seen that the TE polarization state and the TM polarization state are aligned in the horizontal direction by 1dB. The tolerance range is about ±300nm, the 1dB longitudinal alignment tolerance range for the TE polarization state in the vertical direction is about -400nm to +300nm, and the 1dB longitudinal alignment tolerance range for the TM polarization state is about -400nm to +200nm.

The present invention is an optical fiber and waveguide coupling mode spot converter in the 850 nm band, aiming at the problem of low coupling efficiency between the optical fiber and the waveguide in the 850 nm band, a mode spot converter in the 850 nm band is designed, which improves the optical fiber and the waveguide chip. The coupling efficiency of the converter is relatively high, and the flexibility and adaptability of the converter are relatively strong, which is suitable for popularization and use.

Claims (7)

1. The 850 nm-waveband optical fiber and waveguide coupling spot size converter is characterized by comprising a lower cladding (1), wherein the upper end face of the lower cladding (1) is sequentially covered with a three-port Y-branch lower cladding (2) and an SU-8 tapered structure (3), the upper end face of the three-port Y-branch lower cladding (2) is covered with a waveguide assembly, one side of the waveguide assembly is connected with the SU-8 tapered structure (3), the other side of the waveguide assembly is connected with a waveguide group, and the upper end face of the waveguide assembly corresponds to the three-port Y-branch lower cladding (2) and is covered with a three-port Y-branch upper cladding (9);

wherein, along the length direction of the lower cladding (1): the lower cladding (1) and the SU-8 tapered structure (3) form a first-stage spot size conversion module, the lower cladding (1), the three-port Y-branch lower cladding (2) and the three-port Y-branch upper cladding (9) respectively form a second-stage spot size conversion module and a third-stage spot size conversion module in sequence through a waveguide component and a waveguide group, and the optical fiber and the integral structure of the waveguide coupling spot size converter are integrally formed;

under the condition that the optical field transmitted by the optical fiber enters the optical fiber and waveguide coupling spot size converter, the first-stage spot size conversion module, the second-stage spot size conversion module and the third-stage spot size conversion module perform transition compression on the optical field, and the optical field is converted into a single mode and then output.

2. The 850 nm-waveband fiber-waveguide coupled spot size converter according to claim 1, wherein the waveguide assembly comprises a first curved waveguide (4), a straight waveguide (5) and a second curved waveguide (6), the first curved waveguide (4) and the second curved waveguide (6) are arranged in a Y shape corresponding to the straight waveguide (5), the open end of the Y shape is connected with the SU-8 tapered structure (3), and the converging end of the Y shape is connected with the waveguide group.

3. An 850nm band optical fiber-waveguide coupled spot converter as claimed in claim 2, wherein the first curved waveguide (4), the straight waveguide (5), the second curved waveguide (6) and the waveguide group are made of silicon nitride.

4. The 850 nm-waveband optical fiber and waveguide coupling spot size converter according to claim 2, wherein the waveguide group comprises a first waveguide (7) and a second waveguide (8) which are sequentially arranged at a convergence end connected with a Y-type, the first waveguide (7) is arranged into a trapezoid structure, the lower bottom of the trapezoid structure is connected with the convergence end of the Y-type, the upper bottom of the trapezoid structure is connected with the second waveguide (8), and the second waveguide (8) is arranged into a rectangular structure.

5. An 850nm band optical fiber and waveguide coupled spot converter according to claim 2, wherein the SU-8 cone-shaped structure (3) is a frustum of prism, and the upper bottom of the frustum of prism is connected with the open end of the Y-shape.

6. An 850nm band optical fiber and waveguide coupled spot converter as claimed in claim 1, wherein said lower cladding (1), said three port Y-branch lower cladding (2) and said three port Y-branch upper cladding (9) are made of silica.

7. An 850nm band optical fiber-waveguide coupled spot converter according to claim 1, wherein the thickness dimension of the three-port Y-branch upper cladding (9) is larger than the thickness dimension of the three-port Y-branch lower cladding (2).

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