CN221078974U - Module spot converter and optical module - Google Patents

Abstract

The application discloses a spot-size converter and an optical module, the spot-size converter includes: a lithium niobate substrate having opposed first and second surfaces; an optical waveguide located within the first surface; the optical waveguide comprises a proton exchange region disposed within the surface of the lithium niobate substrate; wherein in a direction parallel to the first surface, the optical waveguide includes: an input part, a gradual change part and an output part which are sequentially arranged; the input portion has a first mode field diameter and the output portion has a second mode field diameter, the first mode field diameter being greater than the second mode field diameter; the mode field diameter of the graded portion is graded from a first mode field diameter to a second mode field diameter. According to the application, the proton exchange area is formed in the surface of the lithium niobate substrate, so that the optical waveguide is formed in the surface of the lithium niobate substrate, the spot-size converter has a polarizing function, and when the spot-size converter is connected with the integrated optical chip, a front polarizer is not needed, so that the volume of an optical system and the optical insertion loss are reduced, and the popularization and the application of the integrated optical technology are facilitated.

Description

Module spot converter and optical module

Technical Field

The application relates to the technical field of optical devices, in particular to a spot-size converter and an optical module.

Background

In recent years, integrated optical technologies including silicon phototechnology, lithium niobate thin film technology, and the like have been rapidly developed. For example, silicon optical technology is widely used in the fields of data centers, optical communication, radar, sensing, and the like. The nano lithium niobate thin film technology has a series of applications in a plurality of directions such as modulator, frequency comb, optical frequency conversion, filter and the like. The typical characteristic of the application is that the size of the optical waveguide is smaller than 1um, and the integration level of the optical device and the system is greatly improved in the nanoscale range (nanometer optical waveguide), and the volume and the power consumption of the device are obviously reduced. The reduced size of the optical waveguide presents another problem in that the coupling loss with the single mode optical fiber is large.

The core diameter of the single-mode fiber is greatly different from the waveguide size of the integrated optical chip, and the direct coupling loss of the single-mode fiber and the nano optical waveguide exceeds 20dB. The problem of coupling of a single-mode fiber and a nano optical waveguide is solved in two ways: the grating coupling is coupled to the end face. The grating coupling can reach about 2dB of coupling loss, but the working bandwidth is limited, and the grating coupling is sensitive to the polarization direction of input light, and is currently used in the test process of chips. End-face coupling requires reduced coupling losses through a mode-spot-size converter. Mode spot converters typically use wedge waveguides to increase or decrease the mode field diameter, typically requiring the fabrication of two or more dielectric layers to achieve mode field size conversion in two directions to match the mode field of a single mode fiber to a nanowaveguide. The scheme has complex process and abrupt discontinuity of mode field, which results in high optical insertion loss.

Besides wedge waveguide, the mode spot converter can be manufactured on the glass substrate, the insertion loss of the mode spot converter is less than 1dB, the mode field of the single-mode fiber with the diameter of 10 μm can be reduced to 4 x 3um at the output end, and the mode spot converter is the only mode spot converter product currently used commercially. The conventional glass substrate spot-size converter, while having a low manufacturing cost, does not facilitate the integration of optical devices.

Disclosure of utility model

In view of the above, the present application provides a spot-size converter and an optical module, which have the following schemes:

a spot-size converter comprising:

A lithium niobate substrate having opposed first and second surfaces;

An optical waveguide located within the first surface; the optical waveguide comprises a proton exchange region disposed within the surface of the lithium niobate substrate;

Wherein in a direction parallel to the first surface, the optical waveguide includes: an input part, a gradual change part and an output part which are sequentially arranged; the input portion has a first mode field diameter and the output portion has a second mode field diameter, the first mode field diameter being greater than the second mode field diameter; the mode field diameter of the graded portion is graded from a first mode field diameter to a second mode field diameter.

Preferably, in the above-mentioned spot-size converter, one end of the input portion, which is far away from the output portion, is used for connecting a pigtail, and the pigtail is a single-mode fiber;

The first mode field diameter is adapted to the diameter of a single mode fiber.

Preferably, in the above-described spot-size converter, the first mode field diameter is in a range of 9 μm to 12 μm.

Preferably, in the above-described spot-size converter, the optical waveguide has a single-output-end structure, and the input section, the gradation section, and the output section are sequentially arranged in a straight line in the first surface in a direction parallel to the first surface.

Preferably, in the above-described spot-size converter, an end of the output portion remote from the input portion is used for connecting to the integrated optical chip, and the second mode field diameter is adapted to a mode field diameter of an optical waveguide in the integrated optical chip.

Preferably, in the above-described spot-size converter, the second mode field diameter is in a range of 0.2 μm to 5 μm.

Preferably, in the above-mentioned spot-size converter, the optical waveguide has a multiple-output structure, and has 2 ^N output ends, and N is a positive integer;

The output part has N branch structures; the N branch structures are sequentially from the 1 st branch structure to the N branch structure; the i-th branch structure has 2 ⁱ parallel branch structures, i is a positive integer not more than N; wherein, every two branch structures in the branch structure of the back stage are correspondingly connected with one branch structure in the branch structure of the front stage; the two branch structures of the first-stage branch structure are connected with one end of the gradual change part far away from the output part; the ends of the 2 ^N branch structures in the N-th branch structure, which are far away from the input part, are all output ends of the optical waveguide.

Preferably, in the above-mentioned spot-size converter, further comprising:

a modulating electrode on the first surface.

Preferably, in the above-mentioned mode spot-size converter, the optical waveguide is also a titanium diffusion region so that the optical waveguide can maintain the polarization state of the input light.

The present application also provides an optical module comprising:

An integrated optical chip;

The input end and the output end of the integrated optical chip are respectively connected with the spot-size converter of any one of the above-mentioned, the output part of the spot-size converter is connected with the optical waveguide in the integrated optical chip;

the input parts of the spot-size converter are respectively connected with tail fibers.

As can be seen from the above description, in the spot-size converter and the optical module provided by the technical solution of the present application, the spot-size converter includes: a lithium niobate substrate having opposed first and second surfaces; an optical waveguide located within the first surface; the optical waveguide comprises a proton exchange region disposed within the surface of the lithium niobate substrate; wherein in a direction parallel to the first surface, the optical waveguide includes: an input part, a gradual change part and an output part which are sequentially arranged; the input portion has a first mode field diameter and the output portion has a second mode field diameter, the first mode field diameter being greater than the second mode field diameter; the mode field diameter of the graded portion is graded from a first mode field diameter to a second mode field diameter. According to the application, the proton exchange area is formed in the surface of the lithium niobate substrate, so that the optical waveguide is formed in the surface of the lithium niobate substrate, the spot-size converter has a polarizing function, and when the spot-size converter is connected with the integrated optical chip, a front polarizer is not needed, so that the volume of an optical system and the optical insertion loss are reduced, and the popularization and the application of the integrated optical technology are facilitated.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the related art, the drawings required for the description of the embodiments or the prior art will be briefly described below, and it is apparent that the drawings in the following description are only embodiments of the present application, and other drawings may be obtained according to the provided drawings without inventive effort to those skilled in the art.

The structures, proportions, sizes, etc. shown in the drawings are shown only in connection with the present disclosure, and therefore should not be construed as limiting the application, but rather as limiting the scope of the application, so that any structural modifications, proportional changes, or dimensional adjustments should fall within the scope of the application without affecting the efficacy or achievement thereof.

Fig. 1 is a schematic structural diagram of a spot-size converter according to an embodiment of the present application;

FIG. 2 is a cross-sectional view of the spot-size converter of FIG. 1 taken along the length thereof;

FIG. 3 is a cross-sectional view of the spot-size converter of FIG. 1 taken perpendicular to the length of the input section;

FIG. 4 is a cross-sectional view of the spot-size converter of FIG. 1 taken perpendicular to the length of the transition portion;

FIG. 5 is a cross-sectional view of the spot-size converter of FIG. 1 taken perpendicular to the length of the output section;

fig. 6 to 11 are device structure diagrams of a manufacturing method of a spot-size converter according to an embodiment of the present application in different process steps;

fig. 12 is a schematic structural diagram of a multi-output-end spot-size converter according to an embodiment of the present application;

FIG. 13 is a schematic diagram of another embodiment of a multi-output spot-size converter according to the present application;

FIG. 14 is a top view of a spot-size converter according to an embodiment of the application;

fig. 15 is a schematic structural diagram of an optical module according to an embodiment of the present application.

Detailed Description

Embodiments of the present application will now be described more fully hereinafter with reference to the accompanying drawings, in which it is shown, however, in which some, but not all embodiments of the application are shown. All other embodiments, which can be made by those skilled in the art based on the embodiments of the application without making any inventive effort, are intended to be within the scope of the application.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present application without departing from the spirit or scope of the application. Accordingly, it is intended that the present application covers the modifications and variations of this application provided they come within the scope of the appended claims (the claims) and their equivalents. The embodiments provided by the embodiments of the present application may be combined with each other without contradiction.

In the design and processing of the integrated optical chip, the width and the height of the optical waveguide are not equal in most cases, such as a typical silicon optical waveguide size of 0.5×0.2um and a typical lithium niobate thin film optical waveguide size of 0.45×0.34um, which makes the integrated optical waveguide sensitive to the polarization state of the input light, and an additional device is required to control the polarization degree of freedom, and a polarizer function is required to be added at the front end of the integrated optical chip.

Since glass is an amorphous material, an optical waveguide formed on a glass substrate by using an ion exchange technology has no birefringence effect and does not have the function of a polarizer. Therefore, the spot-size converter using the glass substrate needs to be provided with a polarizer in front of the integrated optical chip, which increases the volume and optical insertion loss of the optical system, and is inconvenient for popularization and application of the integrated optical technology.

In view of this, the embodiment of the application provides a spot-size converter and an optical module, the spot-size converter is made of a lithium niobate substrate, and the optical waveguide is a proton exchange area disposed in the surface of the lithium niobate substrate. The proton exchange technology only forms the waveguide of the extraordinary ray, and does not form the optical waveguide for the ordinary ray, so the proton exchange area is formed on the surface of the lithium niobate substrate by the proton exchange technology to serve as the optical waveguide, the mode spot converter has a polarizing function, the polarization extinction ratio can reach more than 45dB, and the polarization extinction ratio of the optical waveguide chip subjected to dispersion irradiation treatment can even reach 80dB.

In order that the above-recited objects, features and advantages of the present application will become more readily apparent, a more particular description of the application will be rendered by reference to the appended drawings and appended detailed description.

Referring to fig. 1 to 5, fig. 1 is a schematic structural diagram of a spot size converter according to an embodiment of the present application, fig. 2 is a cross-sectional view of the spot size converter shown in fig. 1 along a length direction, fig. 3 is a cross-sectional view of the spot size converter shown in fig. 1 perpendicular to a length direction of an input portion, fig. 4 is a cross-sectional view of the spot size converter shown in fig. 1 perpendicular to a length direction of a gradual change portion, fig. 5 is a cross-sectional view of the spot size converter shown in fig. 1 perpendicular to a length direction of an output portion, and the spot size converter includes:

A lithium niobate substrate 11, the lithium niobate substrate 11 having opposite first and second surfaces;

an optical waveguide 12 located within the first surface; the optical waveguide 12 includes a proton exchange region disposed within the surface of the lithium niobate substrate 11;

Wherein in a direction parallel to the first surface, the optical waveguide 12 comprises: an input section 121, a gradation section 122, and an output section 123 arranged in this order; the input portion 121 has a first mode field diameter and the output portion 123 has a second mode field diameter, the first mode field diameter being greater than the second mode field diameter; the mode field diameter of the graded portion 122 is graded from a first mode field diameter to a second mode field diameter.

In the embodiment of the present application, the optical waveguide 12 is formed in the surface of the lithium niobate substrate 11 by forming a proton exchange region in the surface of the lithium niobate substrate 11. The lithium niobate crystal is a birefringent crystal, and light propagating along the crystallographic Y-axis has its polarization direction split into two directions, extraordinary (e) and ordinary (o) light. Therefore, after the lithium niobate is subjected to a proton exchange process, the refractive index of the extraordinary ray is increased, and the refractive index of the ordinary ray is slightly reduced, so that a proton exchange area is formed on the surface of the lithium niobate substrate by a proton exchange technology and is used as an optical waveguide, and the polarization function is realized.

Wherein the proton exchange area is an integral structure. The first mode field diameter is larger than the second mode field diameter, and the mode field diameter of the gradation portion 122 is gradually changed from the first mode field diameter to the second mode field diameter in a direction from an end of the gradation portion 122 toward the input portion 121 to an end toward the output portion 123, so that the optical waveguide 12 achieves continuous smooth transition of the mode field diameter in both the width and depth directions.

The core diameter of the single-mode fiber is generally between 9um and 12um, and a larger gap exists between the single-mode fiber and the waveguide size (typical value of 0.4 um) of the integrated optical chip, and the mode spot converter provided by the embodiment of the application can be adopted to realize the coupling of the single-mode fiber and the integrated optical chip, so that the loss of direct coupling of the single-mode fiber and the nano optical waveguide in the integrated optical chip is reduced.

In the spot-size converter provided by the embodiment of the application, one end of the input part 121, which is far away from the output part 123, is used for connecting with a tail fiber, and the tail fiber is a single-mode fiber; the diameter of the first mode field is matched with the diameter of the single-mode fiber, namely, the diameter of the first mode field is the same as or approximately the same as the diameter of the single-mode fiber, so that the loss of direct coupling between the single-mode fiber and the nano-optical waveguide in the integrated optical chip is reduced.

The core diameter of the single-mode fiber is generally between 9um and 12um, and the corresponding range of the first mode field diameter is 9um to 12um, so that the first mode field diameter is matched with the diameter of the single-mode fiber. Preferably, the first mode field diameter may be set to 10 μm.

In the spot-size converter according to the present embodiment, the output portion 123 is connected to the integrated optical chip at an end remote from the input portion 121, and the second mode field diameter is adapted to the mode field diameter of the optical waveguide in the integrated optical chip. And the second mode field diameter is matched with the mode field diameter of the optical waveguide in the integrated optical chip, so that the mode spot-size converter is convenient to couple with the integrated optical chip.

The optical waveguide in the integrated optical chip is a nano optical waveguide, and the range of the second mode field diameter is correspondingly set to be 0.2-5 μm, so that the second mode field diameter is matched with the mode field diameter of the optical waveguide in the integrated optical chip, and preferably, the second mode field diameter can be set to be 0.4 μm.

In the manner shown in fig. 1 to 5, the optical waveguide 12 has a single-output-end structure, and the input portion 121, the gradation portion 122, and the output portion 123 are sequentially arranged in a straight line within the first surface in a direction parallel to the first surface.

The mode spot-size converter is fabricated by proton exchange optical waveguide, and it is necessary to realize continuous smooth conversion of the mode field diameter in both the width and depth directions of the optical waveguide 12, i.e., to make the first mode field diameter larger than the second mode field diameter, and the mode field diameter of the graded portion 122 is graded from the first mode field diameter to the second mode field diameter in the direction from the end of the graded portion 122 facing the input portion 121 to the end facing the output portion 123. However, the continuous transition from a large mode field to a small mode field can be realized through the mask plate design in the width direction of the mode spot converter formed by the conventional single proton exchange technology, but the optical waveguide with the same depth can be formed in the depth direction, and the requirements of the mode spot converter on continuous conversion in the width direction and the depth direction are not met.

In view of this, the embodiment of the present application further provides a method for manufacturing the foregoing spot size converter by using a multiple proton exchange process, where the method is shown in fig. 6-11, and the continuous smooth transition of the mode field diameter is achieved by multiple photolithography, exchange, and annealing steps to obtain the continuous smooth transition of the mode field diameter in both the width and depth directions, so as to manufacture the spot size converter with low insertion loss provided in the embodiment of the present application.

Referring to fig. 6 to 11, fig. 6 to 11 are device structure diagrams of a manufacturing method of a spot-size converter according to an embodiment of the present application in different process steps, where the manufacturing method includes:

Step S11: as shown in fig. 6 and 7, the first proton exchange is performed on the lithium niobate substrate 11 based on the first mask 21, and a first proton exchange region 111 adapted to the hollowed-out region 211 on the first mask 21 is formed in the lithium niobate substrate 11.

In this step, the hollowed-out area 211 on the first mask 21 is matched with the pattern of the optical waveguide 12 on the first surface to be prepared, i.e. the pattern of the hollowed-out area 211 is the same as or slightly smaller than the pattern of the entire optical waveguide 12 on the first surface.

Step S12: as shown in fig. 8 and 9, the second proton exchange is performed on the lithium niobate substrate 11 based on the second mask 22, and a second proton exchange area 112 adapted to the hollowed-out area 221 on the second mask 22 is formed in the lithium niobate substrate 11.

In this step, the pattern of the hollowed-out area 221 on the second mask 22 and the pattern of the input portion 121 on the first surface are adapted, that is, the pattern of the hollowed-out area 221 and the pattern of the input portion 121 on the first surface are the same or slightly smaller than the pattern of the input portion 121 on the first surface, so that after the second proton exchange, the area exchange depth of the first proton exchange area 111 corresponding to the input portion 121 can be deepened on the basis of the first proton exchange area 111, thereby forming the second proton exchange area 112.

Step S13: as shown in fig. 10 and 11, the third proton exchange is performed on the lithium niobate substrate 11 based on the third mask 23, and a third proton exchange region 113 adapted to the hollowed-out area 231 on the third mask 23 is formed in the lithium niobate substrate 11.

In this step, the pattern of the hollowed-out area 231 on the third mask 23 and the pattern of the gradual change portion 122 on the first surface are adapted, that is, the pattern of the hollowed-out area 231 and the pattern of the gradual change portion 122 on the first surface are the same as or slightly smaller than the pattern of the gradual change portion 122 on the first surface, so that after the third proton exchange, the area exchange depth of the second proton exchange area 112 corresponding to the gradual change portion 122 can be deepened on the basis of the second proton exchange area 112, thereby forming the third proton exchange area 113.

After completion of the third proton exchange, as shown in fig. 11, the exchange depths are sequentially reduced in three regions of the lithium niobate substrate 11 corresponding to the input portion 121, the gradation portion 122, and the output portion 123, and the exchange depths in the same region are the same. In other ways, the region corresponding to the graded portion 122 may be configured to form a plurality of gradients of exchange audits by a plurality of proton exchanges.

Step S14: based on the third proton exchange zone 113 formed after the third proton exchange, an annealing treatment is performed to form the spot-size converter as shown in fig. 1-5.

Insertion loss is an important indicator of the mode-spot-size converter and is related to the degree of smoothness of the change in the mode field diameter of the optical waveguide 12. The smaller the mode field diameter discontinuity of the optical waveguide from the input portion 121 to the output portion 123, the smaller the insertion loss. In order to realize continuous smooth transition of the mode field diameter of the optical waveguide 12, the manufacturing method of the multi-proton exchange mode spot-size converter forms the smooth transition optical waveguide 12 through three times of proton exchange processes and annealing. In other methods, four or more exchanges may be used to make the change in the optical waveguide mode field diameter of graded portion 122 more continuously smooth in order to minimize the concentration differences after the transition zone proton exchange.

In the fabrication method shown in fig. 6 to 11, a single-output spot-size converter is illustrated as an example, and it is apparent that the fabrication method is equally applicable to a multi-output spot-size converter in the following embodiments. And (3) correspondingly arranging a plurality of masks of the required pattern structure based on the pattern structure of the required preparation optical waveguide 12, and carrying out photoetching, exchange and annealing for a plurality of times to prepare the multi-output-end spot-size converter.

Referring to fig. 12 and 13, fig. 12 is a schematic structural diagram of a multi-output spot-size converter according to an embodiment of the present application, fig. 13 is a schematic structural diagram of another multi-output spot-size converter according to an embodiment of the present application, and fig. 12 and 13 are top views of a lithium niobate substrate 11 on a first surface. For a spot-size converter with multiple outputs 13, the optical waveguide 12 is a multiple output structure with 2 ^N outputs and N is a positive integer.

The output section 123 has N branch structures; the N branch structures are sequentially from the 1 st branch structure to the N branch structure; the i-th branch structure has 2 ⁱ parallel branch structures, i is a positive integer not more than N; wherein, every two branch structures in the branch structure of the back stage are correspondingly connected with one branch structure in the branch structure of the front stage; the two branch structures of the first-stage branch structure are connected with one end of the gradual change part far away from the output part; the ends of the 2 ^N branch structures of the nth stage branch structure, which are far away from the input portion 121, are all output ends of the optical waveguide 12. The mode is based on a multi-stage Y-shaped structure, and the mode spot-size converter with multiple output ends is realized.

For the multi-output mode spot-size converter, the mode field diameters of the 1 st-stage branch structure to the N-stage branch structure can be set to be sequentially reduced.

As shown in fig. 12, there is a spot-size converter with 2 output terminals 13, where n=1. The output section 123 has 1 branching structure including 2 parallel branch structures each corresponding to one output terminal 13, and has 2 output terminals 13 in total.

As shown in fig. 13, a spot-size converter with 4 output terminals 13 is shown, where n=2. The output portion 123 has 2 branch structures, the 1 st branch structure has 2 parallel branch structures, the 2 nd branch structure has 4 parallel branch structures, and each branch structure in the 1 st branch structure is correspondingly connected with two branch structures in the 2 nd branch structure. The 4 parallel branch structures in the 2 nd-stage branch structure respectively correspond to one output end 13, and have 4 output ends 13 in total.

As can be seen from the above description, the spot-size converter comprises at least one output 13 and the output section 123 comprises at least one branch structure. The single-output spot-size converter corresponds to the output section 123 comprising a branch structure.

Referring to fig. 14, fig. 14 is a top view of a spot-size converter according to an embodiment of the present application, where, based on the above embodiment, the spot-size converter shown in fig. 14 further includes: a modulating electrode 14 on the first surface. In a direction parallel to the first surface, modulation electrodes 14 are respectively disposed on two sides of the branch structure where the output end is located.

Fig. 14 illustrates an example of a dual-output spot-size converter, and it is apparent that the spot-size converter of fig. 1 or other multi-output spot-size converters may be provided with a modulating electrode 14 on the first surface, so that two sides of the branch structure where the output terminal 13 is located are respectively provided with a modulating electrode 14.

In embodiments of the present application, the optical waveguide may also be a titanium diffusion region, such that the optical waveguide 12 is capable of maintaining the polarization state of the input light.

As can be seen from the above description, the spot-size converter provided by the embodiment of the application has a polarizing function, and can be coupled with the integrated optical chip with low loss, so that the integrated optical chip does not need a pre-polarizer, the size of the chip can be reduced, and the optical link loss can be reduced.

Based on the above embodiments, another embodiment of the present application also provides an optical module, and the structure of the optical module may be as shown in fig. 15.

Referring to fig. 15, fig. 15 is a schematic structural diagram of an optical module according to an embodiment of the present application, where the optical module includes:

An integrated optical chip 31;

The input end and the output end of the integrated optical chip 31 are respectively connected with the spot-size converter 32 provided by the embodiment, and the output part of the spot-size converter 32 is connected with the optical waveguide in the integrated optical chip 31;

wherein the input portions of the spot-size converter 32 are respectively connected with pigtails 33. The pigtail 33 is a single mode fiber.

In the embodiment of the present application, the spot-size converter 32 and the single-mode fiber are adhered and fixed by the optical adhesive to form a coupling module, and then the output parts of the spot-size converters in the two coupling modules are respectively connected to the input end and the output end of the integrated optical chip 31.

The mode spot converter provided by the embodiment of the application is used for realizing the coupling between the single-mode fiber and the integrated optical chip 31, and the coupling module structure can realize the alignment and fixation of the coupling module and the integrated optical chip 31 only by one-time coupling process when in application, thereby improving the working efficiency of the coupling process of the integrated optical chip 31, simplifying the coupling packaging structure of the integrated optical chip 31 and being beneficial to popularization and application of the integrated optical chip.

The integrated optical chip 31 may be a silicon photonic chip, a lithium niobate thin film chip, an indium phosphide (InP) chip, a silicon nitride (SiN) chip, or the like.

In the present specification, each embodiment is described in a progressive manner, or a parallel manner, or a combination of progressive and parallel manners, and each embodiment is mainly described as a difference from other embodiments, and identical and similar parts between the embodiments are all enough to refer to each other. For the optical module disclosed in the embodiment, since the optical module corresponds to the spot-size converter disclosed in the embodiment, the description is relatively simple, and the relevant parts refer to the description of the corresponding parts of the spot-size converter.

It is to be noted, however, that the description of the drawings and embodiments are illustrative and not restrictive. Like reference numerals refer to like structures throughout the embodiments of the specification. In addition, the drawings may exaggerate the thicknesses of some layers, films, panels, regions, etc. for understanding and ease of description. It will also be understood that when an element such as a layer, film, region or substrate is referred to as being "on" another element, it can be directly on the other element or intervening elements may be present. In addition, "on …" refers to positioning an element on or under another element, but not essentially on the upper side of the other element according to the direction of gravity.

The terms "upper," "lower," "top," "bottom," "inner," "outer," and the like are used for convenience in describing and simplifying the description based on the orientation or positional relationship shown in the drawings, and do not denote or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore should not be construed as limiting the application. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present.

It is further noted that relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that an article or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such article or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in an article or device comprising the element.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the application. Thus, the present application is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (10)

1. A spot-size converter, comprising:

A lithium niobate substrate having opposed first and second surfaces;

An optical waveguide located within the first surface; the optical waveguide comprises a proton exchange region disposed within the surface of the lithium niobate substrate;

Wherein in a direction parallel to the first surface, the optical waveguide includes: an input part, a gradual change part and an output part which are sequentially arranged; the input portion having a first mode field diameter and the output portion having a second mode field diameter, the first mode field diameter being greater than the second mode field diameter; the mode field diameter of the graded portion is graded from the first mode field diameter to the second mode field diameter.

2. The spot-size converter according to claim 1, wherein an end of the input portion remote from the output portion is configured to be connected to a pigtail, the pigtail being a single-mode optical fiber;

the first mode field diameter is adapted to a diameter of the single mode fiber.

3. The spot-size converter according to claim 1 or 2, wherein the first mode field diameter is in the range of 9 μm to 12 μm.

4. The spot-size converter according to claim 1, wherein the optical waveguide has a single output end structure, and the input portion, the gradation portion, and the output portion are sequentially arranged in a straight line in the first surface in a direction parallel to the first surface.

5. The spot-size converter according to claim 1, wherein an end of the output section remote from the input section is adapted to be connected to an integrated optical chip, and wherein the second mode field diameter is adapted to a mode field diameter of an optical waveguide in the integrated optical chip.

6. The spot-size converter according to claim 1, wherein the second mode field diameter is in the range of 0.2 μm to 5 μm.

7. The spot-size converter according to claim 1 wherein the optical waveguide has a multiple output structure with 2 ^N outputs and N is a positive integer;

The output part has N branch structures; the N branch structures are sequentially from the 1 st branch structure to the N branch structure; the i-th branch structure has 2 ⁱ parallel branch structures, i is a positive integer not more than N; wherein each two branch structures in the next-stage branch structure are correspondingly connected with one branch structure in the previous-stage branch structure; the two branch structures of the level 1 branch structure are connected with one end of the gradual change part far away from the output part; and one end, far away from the input part, of each of the 2 ^N branch structures in the N-th branch structure is an output end of the optical waveguide.

8. The spot-size converter according to claim 1, further comprising:

A modulating electrode on the first surface.

9. The spot-size converter according to claim 1, wherein the optical waveguide is a titanium diffusion region such that the optical waveguide is capable of maintaining a polarization state of input light.

10. An optical module, comprising:

An integrated optical chip;

The input end and the output end of the integrated optical chip are respectively connected with a spot-size converter according to any one of claims 1-9, and the output part of the spot-size converter is connected with the optical waveguide in the integrated optical chip;

The input parts of the spot-size converter are respectively connected with tail fibers.