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).

Background

Communication technology under the background of the multimedia and big data era develops rapidly, and the traditional electric-electric interconnection is difficult to meet the development requirement of high-speed and large-capacity communication. In recent years, optical communication systems developed by photonic integration technology have been the focus of research due to their advantages of low energy consumption, large bandwidth, low delay, etc. The key problems of research are that on-chip optical-optical interconnection, electro-optical modulation, optical/electrical or electrical/optical conversion and the like with high integration level are realized by using the electro-optical characteristics of different types of materials and the high refractive index difference of a waveguide core layer and a cladding layer. Efficient coupling between optical fibers and waveguide chips is one of the key technologies for optical integration, and is a common problem faced by all optical integration modules. The silicon nitride material has lower absorption loss in the near infrared and visible light wavelength ranges and is widely applied to optical waveguide devices, while the mode spot of the silicon nitride waveguide device is generally in a micro-nano size, the mode spot of an optical fiber is generally in a micro-nano size, and the direct alignment coupling of the waveguide and the optical fiber can generate larger mode field mismatch loss. The 850nm (nanometer) band is one of the commonly used bands for optical communication, and how to realize the efficient coupling of the optical fiber and the waveguide chip is also a problem to be solved. Grating coupling (vertical coupling) and end-face coupling (horizontal coupling) are two common approaches used in photonic integrated chip spot converters, and grating couplers typically have limited bandwidth and high polarization dependence. Compared with a grating coupler, the end-face coupler has larger bandwidth and lower polarization dependence.

Disclosure of Invention

The invention aims to provide an optical fiber and waveguide coupling spot size converter with 850nm waveband, which solves the problem of low coupling efficiency of optical fiber and waveguide in 850nm waveband in the prior art.

The technical scheme adopted by the invention is that,

an optical fiber and waveguide coupling spot size converter with 850nm waveband comprises a lower cladding, wherein the upper end surface of the lower cladding is sequentially covered with a three-port Y-branch lower cladding and an SU-8 tapered structure;

wherein, along the length direction of the lower 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 in sequence through the waveguide component and the waveguide group, and the optical fiber and the waveguide coupling spot size converter are integrally formed;

under the condition that an 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.

The present invention is also characterized in that,

the waveguide assembly comprises a first bent waveguide, a straight waveguide and a second bent waveguide, the first bent waveguide and the second bent waveguide are arranged in a Y shape corresponding to the straight waveguide, the open end of the Y shape is connected with the SU-8 tapered structure, and the gathering end of the Y shape is connected with the waveguide group.

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

The waveguide group comprises a first waveguide and a second waveguide which are connected with the gathering end of the Y-shaped and are sequentially arranged, the first waveguide is arranged to be of a trapezoid structure, the lower bottom of the trapezoid structure is connected with the gathering end of the Y-shaped, the upper bottom of the trapezoid structure is connected with the second waveguide, and the second waveguide is arranged to be of a rectangular structure.

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

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

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

The invention has the beneficial effects that: the invention provides an optical fiber and waveguide coupling mode spot converter with 850nm wave band, wherein an input waveguide is of SU-8 adiabatic taper structure, the thickness and width are gradually reduced in the optical signal transmission direction so as to realize mode field matching with a three-port Y-branch structure with silicon nitride as a waveguide core layer, and finally, an optical signal is output through a three-port Y-branch single mode to complete the conversion of mode spots. The optical fiber matching with different mode spot sizes can be realized by simply and physically cutting the SU-8 conical structure, so that the coupling efficiency of the optical fiber and the waveguide is effectively improved, and the flexibility is strong.

Drawings

FIG. 1 is a schematic diagram of a 850nm band optical fiber and waveguide coupled spot size converter according to the present invention;

FIG. 2 is a detailed view of an 850nm band fiber-waveguide coupled spot-size converter according to the present invention;

FIG. 3 is a schematic top view of a 850nm band fiber-to-waveguide coupled spot-size converter in accordance with the present invention;

FIG. 4 is a graph of the tolerance of lateral alignment of an optical fiber and a spot-size converter in a 850nm band fiber-waveguide coupled spot-size converter of the present invention;

FIG. 5 is a graph of the tolerance of the longitudinal alignment of an optical fiber and a spot-size converter in an 850nm band fiber-waveguide coupled spot-size converter of the present invention.

In the figure, 1, a lower cladding, 2, a three-port Y-branch lower cladding, 3, SU-8 tapered structure, 4, a first curved waveguide, 5, a straight waveguide, 6, a second curved waveguide, 7, a first waveguide, 8, a second waveguide, and 9, a three-port Y-branch upper cladding.

Detailed Description

The following describes a 850nm band optical fiber and waveguide coupled spot-size converter in detail with reference to the accompanying drawings and embodiments.

As shown in fig. 1, fig. 2 and fig. 3, an optical fiber and waveguide coupled spot-size converter of 850nm band comprises a lower cladding 1, an SU-8 tapered structure 3, a three-port Y-branch lower cladding 2, a three-port Y-branch waveguide, and a three-port Y-branch upper cladding 9; the three-port Y-branch waveguide is composed of a first curved waveguide 4, a straight waveguide 5, a second curved waveguide 6, a ladder-shaped first waveguide 7 and a rectangular second waveguide 8. The upper cladding of the SU-8 conical structure 3 is air and is configured as a frustum pyramid, the frustum pyramid is subjected to adiabatic compression with the size in the vertical and horizontal directions in the transmission direction, matching with the end surface light field of the three-port Y-branch waveguide is achieved, transmission and compression of the light field are performed through a first curved waveguide 4, a straight waveguide 5, a second curved waveguide 6 and a trapezoidal first waveguide 7 in the three-port Y-branch waveguide, and finally single-mode output is performed through a rectangular second waveguide 8.

The structure and the working principle of the 850nm waveband optical fiber and waveguide coupling spot size converter are as follows: the method comprises the steps that a conical structure is processed on a silicon dioxide lower cladding layer by adopting SU-8 materials, the SU-8 conical structure 3 is a first-stage mode spot conversion module, an optical field transmitted by an optical fiber is efficiently coupled into the SU-8 conical structure 3, and the size of a mode spot is converted from large to small by gradually reducing the sizes of the SU-8 conical structure 3 in the vertical direction and the horizontal direction in the optical field transmission direction;

the method comprises the steps that a lower cladding 2 which is a thin silica layer of a three-port Y branch is covered on a silica lower cladding 1, a first bending waveguide 4, a straight waveguide 5 and a second bending waveguide 6 of a second-stage mode spot conversion module are made of silicon nitride materials, and a three-port Y branch upper cladding 9 which is arranged on the three-port Y branch upper cladding correspondingly is adopted, firstly, optical field energy output by an SU-8 conical structure 3 is matched, and then the first bending waveguide 4, the straight waveguide 5 and the second bending waveguide 6 are gradually combined in the optical field transmission direction, so that transition of the optical field energy and compression of the light spot size are completed;

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

The 850nm band optical fiber and waveguide coupled spot-size converter of the present invention is further described in detail by the following specific examples.

Examples

Gaussian lens beams with the diameter of 2.5 microns (micrometer) at the wavelength of 850nm are adopted to replace light fields emitted by the tapered lens fibers, the lower cladding 1, the three-port Y-branch lower cladding 2 and the three-port Y-branch upper cladding 9 are made of silicon dioxide, and the refractive index is 1.453; the input waveguide is an SU-8 conical structure 3, the refractive index is 1.577, the three-port Y-branch waveguide material is silicon nitride, and the refractive index is 1.993;

the thickness of the lower cladding 1 was 3 μm, the thickness of the three-port Y-branch lower cladding 2 was 0.15 μm, and the thickness of the three-port Y-branch upper cladding 9 was 2 μm. The SU-8 tapered structure 3 has a length of 160 μm, a thickness and a width of an end surface connected to the optical fiber of 3.4 μm, and a thickness and a width of an end surface connected to the three-port Y-branch waveguide of 0.8 μm and 2.1 μm, respectively. The first curved waveguide 4, the straight waveguide 5, and the second curved waveguide 6 each had a thickness of 0.3 μm and a width of 0.18 μm, and the branched waveguides at the input end face of the three-port Y-branch were each 0.57 μm in interval and 27 μm in length. The first waveguide 7 has a width of 0.54 μm at the end surface connected to the first curved waveguide 4, the straight waveguide 5, and the second curved waveguide 6, a width of 0.45 μm at the end surface connected to the second waveguide 8, and a width of 0.45 μm at the second waveguide 8. Graphs of the transverse and longitudinal alignment tolerances of the TE and TM polarization states of the fiber and waveguide at 850nm wavelength are shown in FIGS. 4 and 5; it can be seen that the 1dB lateral alignment tolerance ranges for the TE and TM polarization states are about + -300 nm in the horizontal direction, about-400 nm to +300nm in the 1dB longitudinal alignment tolerance range for the TE polarization state and about-400 to +200nm in the vertical direction, and about-400 to +200nm for the 1dB longitudinal alignment tolerance range for the TM polarization state.

The invention relates to an optical fiber and waveguide coupling spot size converter with 850nm waveband, which is designed aiming at the problem of low optical fiber and waveguide coupling efficiency existing in the current 850nm waveband, improves the coupling efficiency of an optical fiber and a waveguide chip, has higher flexibility and adaptability, and is suitable for popularization and use.