CN113848609A

CN113848609A - Photonic integrated coupling structure and photonic integrated device

Info

Publication number: CN113848609A
Application number: CN202111140358.0A
Authority: CN
Inventors: 李思敏; 姚笑笑; 潘时龙
Original assignee: Nanjing University of Aeronautics and Astronautics
Current assignee: Nanjing University of Aeronautics and Astronautics
Priority date: 2021-09-28
Filing date: 2021-09-28
Publication date: 2021-12-28

Abstract

The invention discloses a photon integrated coupling structure, which is formed by bonding an upper active plane optical waveguide and a lower passive plane optical waveguide along a direction perpendicular to the transmission direction of optical signals; the active optical waveguide has different widths at both ends. The active layer, the active layer includes a first tapered structure whose width gradually increases from one end with a narrow width to the other end; the passive planar optical waveguide is a substrate layer, a buried oxide layer from bottom to top in order , a waveguide layer, the end portion of the waveguide layer is a second tapered structure whose width gradually decreases toward the end portion and has the same shape and size as the first tapered structure; the first tapered structure is the same as the first tapered structure. The directions of the biconical structures are opposite and their projections on the direction perpendicular to the transmission direction of the optical signal overlap. The invention also discloses a photonic integrated device. Compared with the prior art, the present invention can realize higher-efficiency coupling between the side-emitting semiconductor laser and the planar optical waveguide, and has a simpler structure.

Description

Photonic integrated coupling structure and photonic integrated device

Technical Field

The invention relates to the technical field of photonic integration, in particular to a photonic integrated coupling structure for coupling a side-emitting semiconductor laser with a planar optical waveguide.

Background

Fiber optic communication has been a revolutionary technology that has emerged in the last 30 years. Nowadays, optical communication is also used for the internet, and there is a necessary trend to develop highly integrated chips. Silicon optical interconnection chips made of silicon-on-insulator (SOI) materials have received much attention in the interconnection field due to their advantages of low loss, mature process, low cost, etc. However, for some devices, such as lasers and modulators, silicon has an indirect bandgap and low luminance, making silicon photonics a lack of light sources. Thus, the actual lasers used in silicon photonics today are still hybrid integrated III-V semiconductors. For this reason, various iii-v/Si hybrid integration techniques have emerged, including material growth, direct bonding, adhesive bonding, metal bonding, and flip chip bonding. In all integration technologies, achieving high efficiency coupling of iii-v/Si chips is key to improving the performance of the hybrid integrated device. Different light emitting powers can be obtained by designing different coupling structures.

Emerging applications place higher demands on some photonic integrated devices, such as modulators requiring modulation bandwidths in excess of 100 GHz, while silicon-based modulator theoretical bandwidth limitations are estimated to be around 60 GHz. In addition, silicon-based modulators do not meet the requirements of integrated microwave photonics pure phase modulation and good linearity. Under these circumstances, people aim at Lithium Niobate (LN), which is an excellent electro-optic material with small loss, large electro-optic coefficient, pure linearity of modulation response, and large modulation bandwidth. However, the optical confinement of conventional bulk LN waveguides is very weak and the device footprint is large, which is impractical in large-scale photonic integrated circuits. In order to improve the effective refractive index contrast and thus increase optical confinement, lithium niobate-on-insulator (LNOI) has become an attractive platform for integrated devices, which is a development trend of future high-performance photonic integrated devices.

Facing the same problem of lacking light source, realizing the high-efficiency coupling of the III-V/LNOI chip is the key to realizing the lithium niobate optical interconnection chip. A common coupling method is to use an additional waveguide between the laser and the modulator, such as a conventional lensed fiber or a polymer waveguide. A surface grating coupler or an edge coupler is used to couple the fiber to the chip. The surface grating coupler has the advantages of strong wafer-level detection capability, small volume, high error tolerance and the like. However, this method has the disadvantages of low coupling efficiency, narrow bandwidth, high polarization sensitivity, and the like. The edge coupler has the advantages of high coupling efficiency, large bandwidth and the like, but also has the defects of large volume, complex process and the like.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provide a photonic integrated coupling structure which can realize more efficient coupling between a semiconductor laser emitting from the side surface and a planar optical waveguide and has a simpler structure.

The invention specifically adopts the following technical scheme to solve the technical problems:

a photon integrated coupling structure is formed by bonding an upper active planar optical waveguide and a lower passive planar optical waveguide along the direction vertical to the transmission direction of optical signals; the active optical waveguide is provided with an active layer with two ends having different widths, and the active layer comprises a first conical structure with the width gradually increasing from one end with the narrower width to the other end; the passive planar optical waveguide comprises a substrate layer, a buried oxide layer and a waveguide layer from bottom to top in sequence, and the end part of the waveguide layer is a second conical structure, the width of the second conical structure is gradually reduced towards the end part, and the shape and the size of the second conical structure are the same as those of the first conical structure; the first conical structure and the second conical structure are opposite in direction, and projections of the first conical structure and the second conical structure in the direction perpendicular to the transmission direction of the optical signal are overlapped.

Further, the active layer of the active planar optical waveguide further comprises a third tapered structure having a width gradually increasing from the wide end of the first tapered structure toward the other end of the active layer, and the rate of increase in the width of the third tapered structure is greater than the rate of increase in the width of the first tapered structure.

Preferably, the active planar optical waveguide is a group iii-v active waveguide.

Preferably, the waveguide layer of the passive planar optical waveguide is a thin-film lithium niobate waveguide.

Further, the active planar optical waveguide further comprises a buffer layer and a cladding layer sandwiching the active layer.

On the basis, the following technical scheme can be obtained:

a photonic integrated device comprising a photonic integrated coupling structure according to any of the above claims.

Compared with the prior art, the technical scheme of the invention has the following beneficial effects:

the invention designs the taper structures with the same size and shape for the active planar optical waveguide and the passive planar optical waveguide respectively, and adopts a vertical integrated coupling mode, thereby realizing high coupling efficiency, and simultaneously, the structure of the device is simpler and the integration level is higher.

Drawings

FIG. 1 is a schematic three-dimensional structure of an embodiment;

FIG. 2 is a schematic longitudinal sectional view of the embodiment;

FIG. 3 is a cross-sectional view of energy delivery of an embodiment;

FIG. 4 is a graph of the relationship between the length of the overlap interval and the coupling efficiency of the embodiment;

the following reference numerals are included in the figures:

1. substrate layer, 2, buried oxide layer, 3, waveguide layer, 30, width-graded section, 31, width-invariant section, 4, buffer layer, 5, quantum well active layer, 50, width-graded section, 51, width-graded section, 52, width-invariant section, 6, cladding layer, 60, width-graded section, 61, width-graded section, 62, width-invariant section.

Detailed Description

Aiming at the coupling problem of a semiconductor laser and a planar optical waveguide which are emitted from the side surface, the invention designs conical structures with the same size and shape for an active planar optical waveguide and a passive planar optical waveguide respectively, and adopts a vertical integrated coupling mode, thereby realizing high coupling efficiency, and simultaneously, the structure of the device is simpler and the integration level is higher.

Specifically, the photonic integrated coupling structure provided by the invention is formed by bonding an active planar optical waveguide on an upper layer and a passive planar optical waveguide on a lower layer along a direction vertical to the transmission direction of optical signals; the active optical waveguide is provided with an active layer with two ends having different widths, and the active layer comprises a first conical structure with the width gradually increasing from one end with the narrower width to the other end; the passive planar optical waveguide comprises a substrate layer, a buried oxide layer and a waveguide layer from bottom to top in sequence, and the end part of the waveguide layer is a second conical structure, the width of the second conical structure is gradually reduced towards the end part, and the shape and the size of the second conical structure are the same as those of the first conical structure; the first conical structure and the second conical structure are opposite in direction, and projections of the first conical structure and the second conical structure in the direction perpendicular to the transmission direction of the optical signal are overlapped.

In the above technical solution, the coupling efficiency can be further optimized by adjusting the projection overlapping area of the first tapered structure and the second tapered structure.

The photonic integrated coupling structure can be independently used as a photonic integrated device, and can also be further integrated with a semiconductor laser with side emission and/or a high-q micro-ring resonator, a high-speed modulator and other devices.

For the public understanding, the technical scheme of the invention is explained in detail by a specific embodiment and the accompanying drawings:

the photonic integrated coupling structure of this embodiment is, as shown in fig. 1 and fig. 2, formed by bonding an upper active planar optical waveguide and a lower passive planar optical waveguide along a direction perpendicular to an optical signal transmission direction; wherein the passive planar optical waveguide comprises from bottom to top: substrate layer 1, buried oxide layer 2, waveguide layer 3, and active planar optical waveguide includes from bottom to top: a buffer layer 4, a quantum well active layer 5 and a cladding layer 6; in this embodiment, the substrate layer 1 is made of silicon, the buried oxide layer 2 is made of silicon dioxide, and the waveguide layer 3 is made of lithium niobate (LiNbO)₃) The thin film, the buffer layer 4 and the cladding layer 6 are both made of InP, and the quantum well active layer 5 is made of InGaAsP; according to the materials of the active planar optical waveguide and the passive planar optical waveguide, the DVS-BCB (divinylsiloxane bis-benzocyclobutene) is adopted as the bonding material in the embodiment. As shown in fig. 1, the waveguide layer 3 is entirely divided into a gradual width section 30 and a constant width section 31, and the width of the gradual width section 30 is gradually reduced to form a tapered structure; the quantum well active layer 5 and the cladding layer 6 are entirely divided into a width-graded region 50, a width-graded region 51, a width-invariant region 52, a width-graded region 60, a width-graded region 61,A constant width section 62; obviously, the width gradually-changing section 50, the width gradually-changing section 51, the width gradually-changing section 60 and the width gradually-changing section 61 respectively form a tapered structure with gradually-changing width, the width change rate of the width gradually-changing section 51 is greater than that of the width gradually-changing section 50, and the width change rate of the width gradually-changing section 61 is greater than that of the width gradually-changing section 60; the direction of the width tapering section 50 is opposite to the direction of the width tapering section 30 (i.e. the pointed directions of the two tapered structures) and there is an overlap in the projections of the two in a direction perpendicular to the direction of transmission of the optical signal. With this coupling structure, the optical field can be efficiently coupled from the III-V group active waveguide into the LNOI waveguide.

The structural parameters of the embodiment are specifically as follows, the thickness of the oxygen buried layer 2 is 2 mu m, the thickness of the lithium niobate thin film is 380 nm, the thickness of the buffer layer 4 is 335nm, the thickness of the quantum well active layer 5 is 210nm, and the thickness of the cladding layer 6 is 2 mu m. The width of the width gradient section 30 of the standard single-mode thin film lithium niobate waveguide is 1 μm at the wide end and 400nm at the narrow end. The width of the wide end of the quantum well 5 width gradual change section 50 is 1 mu m, and the width of the narrow end is 400 nm; the width of the wide end of the width gradually-changing section 51 is 1.7 μm, and the width of the narrow end is 1 μm. The width of the wide end of the cladding 6 width gradual change section 60 is 1 mu m, and the width of the narrow end is 400 nm; the width of the wide end of the width gradual change section 61 is 1.7 μm, and the width of the narrow end is 1 μm. Wherein the lengths of 30, 50 and 60 are 150 [ mu ] m, and the lengths of 51 and 61 are 30 [ mu ] m.

Fig. 3 is a simulated energy transmission cross-section of the photonic integrated coupling structure of the embodiment.

The coupling efficiency of the photonic integrated coupling structure is related to the projected overlap area between the width-graded section 50 and the width-graded section 30, so the coupling efficiency can be further optimized by adjusting the projected overlap area between the two tapered structures (i.e., the width-graded section 50 and the width-graded section 30). FIG. 4 shows the variation of the coupling efficiency when the length of the projection overlap interval of the two cone-shaped structures is in the range of 130 μm-148 μm, and it can be seen that the coupling efficiency of the photonic integrated coupling structure is above 93%, and reaches the maximum value of 93.98% when the length of the overlap interval is 144 μm.

In summary, the invention provides a vertical coupling structure based on evanescent field effect, which adopts a tapered structure to utilize waveguide evanescent effect to realize high-efficiency coupling between a side-emitting laser and a planar waveguide, and provides a potential vision for the preparation of large-bandwidth devices.

Claims

1. A photon integrated coupling structure is characterized in that, the active planar optical waveguide of the upper layer and the passive planar optical waveguide of the lower layer are bonded along a direction perpendicular to the transmission direction of the optical signal; the active optical waveguide has two ends. Active layers with different widths, the active layer includes a first tapered structure whose width gradually increases from the narrower end to the other end; the passive planar optical waveguide is the substrate layer, the buried an oxygen layer and a waveguide layer, the end portion of the waveguide layer is a second tapered structure whose width gradually decreases toward the end portion and has the same shape and size as the first tapered structure; the first tapered structure The direction is opposite to that of the second cone structure and the projections of the two in the direction perpendicular to the transmission direction of the optical signal overlap.

2 . The photon integrated coupling structure according to claim 1 , wherein the active layer of the active planar optical waveguide further comprises a width gradually increasing from the wide end of the first tapered structure toward the other end of the active layer. 3 . A large third tapered structure, and the rate of increase in width of the third tapered structure is greater than the rate of increase in width of the first tapered structure.

3 . The photonic integrated coupling structure according to claim 1 or 2 , wherein the active planar optical waveguide is a group III-V active waveguide. 4 .

4. The photonic integrated coupling structure according to claim 1 or 2, wherein the waveguide layer of the passive planar optical waveguide is a thin-film lithium niobate waveguide.

5. The photonic integrated coupling structure according to claim 1 or 2, wherein the active planar optical waveguide further comprises a buffer layer and a cladding layer sandwiching the active layer.

6. A photonic integrated device, characterized by comprising the photonic integrated coupling structure as claimed in claim 1.