SPOT-SIZE CONVERTER AND PHOTONIC DEVICE

A spot-size converter is provided. The spot-size converter includes a first end face and a second end face, and further includes a substrate, and an isolation layer, a first waveguide and a covering layer which are located on a side of the substrate. The first waveguide includes a flat-plate layer and a ridge layer. The flat-plate layer includes a first wide end extending to the first end face and a first narrow end extending to the second end face or having a distance from the second end face, and the flat-plate layer has a width decreasing in a gradient from the first wide end to the first narrow end and includes a first equal-width portion adjacent to the first narrow end. The ridge layer includes a second wide end extending to the first end face and a second narrow end having a distance from the first narrow end.

TECHNICAL FIELD

The present disclosure relates to the technical field of photons, and in particular, to a spot-size converter and a photonic device.

BACKGROUND

An optical waveguide is a dielectric apparatus that guides the propagation of light waves therein, and is also referred to as a dielectric optical waveguide. There are mainly two types of optical waveguides: one type is integrated optical waveguides, comprising a planar dielectric optical waveguide and a slab dielectric optical waveguide, which generally serve as a part of an optoelectronic integrated device, so they are referred to as integrated optical waveguides; and the other type is cylindrical optical waveguides, which are usually referred to as optical fibers.

A technology of coupling the integrated optical waveguide to the optical fiber has very wide and important applications in the fields of optical communications, microwave photonics, laser beam deflection, wavefront modulation, etc. Edge coupling is a common way used to couple the integrated optical waveguide to the optical fiber.

However, how to improve the coupling efficiency between the integrated optical waveguide and the optical fiber has always been an important topic under research for those skilled in the art because of the great difference in spot size between the integrated optical waveguide and the optical fiber.

SUMMARY

According to one aspect of the present disclosure, a spot-size converter is provided, comprising a first end face configured to be coupled to an integrated optical waveguide, and a second end face parallel to the first end face and configured to be coupled to an optical fiber. The spot-size converter comprises:a substrate;an isolation layer located on a side of the substrate, and having an orthographic projection on the substrate that substantially coincides with the substrate;a first waveguide located on a side of the isolation layer away from the substrate, and comprising:a flat-plate layer comprising a first wide end extending to the first end face and a first narrow end extending to the second end face or having a distance from the second end face, the flat-plate layer having a width which decreases in a gradient from the first wide end to the first narrow end and comprising a first equal-width portion adjacent to the first narrow end, wherein a width direction is parallel to the substrate and parallel to the first end face; anda ridge layer stacked on a side of the flat-plate layer away from the substrate, the ridge layer comprising a second wide end extending to the first end face and a second narrow end having a distance from the first narrow end, the ridge layer having a width which decreases in a gradient from the second wide end to the second narrow end and comprising a second equal-width portion adjacent to the second narrow end; anda covering layer located on a side of the first waveguide away from the substrate, extending to the second end face, and extending to cover at least an end of the second equal-width portion away from the second end face, wherein a part of the covering layer close to the second end face and a part of the isolation layer close to the second end face form a second waveguide.

According to another aspect of the present disclosure, a photonic device is provided, comprising a spot-size converter according to any one of the foregoing technical solutions.

These and other aspects of the present disclosure will be clear from the embodiments described below, and will be clarified with reference to the embodiments described below.

DETAILED DESCRIPTION

Only some example embodiments are briefly described below. As can be appreciated by those skilled in the art, the described embodiments can be modified in various ways without departing from the spirit or scope of the present disclosure. Accordingly, the accompanying drawings and the description are considered as illustrative in nature, and not as restrictive.

Although spot-size converters in some related technologies can functionally realize the coupling between an integrated optical waveguide and an optical fiber, the coupling efficiency between the integrated optical waveguide and the optical fiber is not high because of the large difference in spot size therebetween, resulting in a high loss of light energy. For example, the spot size of the integrated optical waveguide is generally of the order of hundreds of nanometers, while the spot size of the optical fiber, such as a flat-ended optical fiber, is of the order of tens of microns. Lost light energy may lead to severe heating of a coupling end face, thereby affecting the reliability and service life of a device. It can be understood that the coupling efficiency is a ratio of optical power emitted by the integrated optical waveguide to optical power received by the optical fiber, or a ratio of optical power emitted by the optical fiber to optical power received by the integrated optical waveguide.

Embodiments of the present disclosure provide a spot-size converter and a photonic device, which can not only perform spot size conversion, but also have a low optical loss during the spot size conversion, so that the coupling efficiency between an integrated optical waveguide and an optical fiber can be improved.

As shown inFIGS.1A,1B,1C,2A and2B, a spot-size converter100according to some embodiments of the present disclosure comprises a first end face100aconfigured to be coupled to an integrated optical waveguide (not shown) and a second end face100bparallel to the first end face100aand configured to be coupled to an optical fiber (not shown). The spot-size converter100structurally comprises a substrate101, and an isolation layer102, a first waveguide103and a covering layer104which are located on a side of the substrate101and are sequentially arranged in a direction away from the substrate101.

An orthographic projection of the isolation layer102on the substrate101substantially coincides with the substrate101. The first waveguide103comprises a flat-plate layer31and a ridge layer32stacked on a side of the flat-plate layer31away from the substrate101. The flat-plate layer31comprises a first wide end31aextending to the first end face100aand a first narrow end31bextending to the second end face100b. The flat-plate layer31has a width decreasing in a gradient from the first wide end31ato the first narrow end31band comprises a first equal-width portion311adjacent to the first narrow end31b. The ridge layer32comprises a second wide end32aextending to the first end face100a, and a second narrow end32bhaving a distance from the first narrow end31b. The ridge layer32has a width decreasing in a gradient from the second wide end32ato the second narrow end32band comprises a second equal-width portion321adjacent to the second narrow end32b. The covering layer104extends to the second end face100b, and extends to cover at least an end of the second equal-width portion321away from the second end face100b. A part of the covering layer104close to the second end face100band a part of the isolation layer102close to the second end face100bjointly form a second waveguide42.

As shown inFIG.1A, in addition to comprising the first end face100aand the second end face100b, the spot-size converter100further comprises a first side surface100cand a second side surface100dwhich are arranged in parallel to each other and orthogonal to the first end face100aand the second end face100b. The first end face100ais configured to be coupled to the integrated optical waveguide, and the second end face100bis configured to be coupled to the optical fiber. It is possible that the first end face100ais be used as an optical input end face of the spot-size converter100, and the second end face100bis used as an optical output end face of the spot-size converter100. Specifically, light is input from the first wide end31aand the second wide end32aof the first waveguide103, and is output from the second waveguide42. It is also possible that the first end face100ais used as an optical output end face of the spot-size converter100, and the second end face100bis used as an optical input end face of the spot-size converter100. Specifically, light is input from the second waveguide42, and is output from the first wide end31aand the second wide end32aof the first waveguide103.

In the embodiments of the present disclosure, it is defined that a width direction is parallel to the substrate101and the first end face100a, a length direction is parallel to the substrate101and perpendicular to the first end face100a, and a height direction and a thickness direction are perpendicular to the substrate101. For a three-dimensional structure with a certain thickness or height, taking the first equal-width portion311as an example, it can be understood that its width is the width of its orthographic projection on the substrate101, and that its length is the length of its orthographic projection on the substrate101. By the orthographic projection of the isolation layer102on the substrate101substantially coinciding with the substrate101, it can be understood that when viewed from the direction perpendicular to the substrate101(for example, in the top view direction), with process errors ignored, it is considered that the contour shapes of the orthographic projection and the substrate are consistent and coincident.

In the embodiments of the present disclosure, a refractive index n1 of the first waveguide103, a refractive index n2 of the covering layer104, a refractive index n3 of the isolation layer102and a refractive index n4 of the substrate101satisfy: n1>n2>n3.

As shown inFIG.1A, the first waveguide103is a ridge waveguide having a series of excellent characteristics such as a low dominant mode cutoff frequency, a wide band, and low impedance. The refractive index of the isolation layer102and the refractive index of the covering layer104are less than that of the first waveguide103, so that light can be mainly confined to transmitting in the ridge waveguide to achieve the above advantages of the ridge waveguide. A part of the covering layer104close to the second end face100band a part of the isolation layer102close to the second end face100bjointly form a second waveguide42. The size of the second waveguide42is greater than that of the first narrow end31b, and can match the spot size of the optical fiber, thereby improving the coupling to the optical fiber at the second end face100b.

When the light is transmitted from the first end face100ato the second end face100bof the spot-size converter100, a part of the light escapes from the first equal-width portion311into the second waveguide42, and continues to be transmitted in the second waveguide42until the light reaches the second end face100b, so as to form, at the second end face100b, a spot size matching that of the optical fiber. On the contrary, when the light is transmitted from the second end face100bto the first end face100aof the spot-size converter100, the light enters the first equal-width portion311from the second waveguide42, that is, the light enters the first waveguide103through the second waveguide42. The refractive index of the substrate101is generally greater than that of the isolation layer102. The substrate101is, for example, a silicon substrate.

The specific structural form of the first waveguide103is not limited. As shown inFIGS.2A and2B, in some embodiments, the first waveguide103is of an axisymmetric structure, and a symmetry axis of the first waveguide103is perpendicular to the second end face100b. The flat-plate layer31comprises a first equal-width portion311, a first gradually-widening portion312, a third equal-width portion313, a second gradually-widening portion314and a fourth equal-width portion315which are sequentially arranged in a direction away from the first narrow end31b. The ridge layer32comprises a second equal-width portion321, a third gradually-widening portion322and a fifth equal-width portion323which are sequentially arranged in a direction away from the second narrow end32b. Any one of the first gradually-widening portion312, the second gradually-widening portion314and the third gradually-widening portion322has a width gradually increasing in a direction away from the second end face100b.

It should be noted that the embodiments of the present disclosure are not limited to designing the first waveguide as an axisymmetric structure, and the first waveguide may also be of an asymmetric structure. For example, the flat-plate layer and/or the ridge layer of the first waveguide may also have a gradient change only on a single side.

The flat-plate layer31and the ridge layer32of the first waveguide103each may be formed by one patterning process. For example, the flat-plate layer31is first formed by one patterning process, and the ridge layer32is formed by another patterning process. Each patterning process may comprise film formation, photoresist coating, exposure, development, etching, photoresist stripping and other procedures. In the exposure procedure, it is necessary to use a mask to block a non-etched area.

The flat-plate layer31and the ridge layer32of the first waveguide103may also be formed by one patterning process comprising two exposures. For example, after film formation and photoresist coating, a film pattern in an area where the first waveguide103is located is first formed by one exposure and subsequent procedures, and then a final structure of the flat-plate layer31and the ridge layer32is formed by another exposure and subsequent procedures.

In the embodiments of the present disclosure, in a direction away from the first end face100a, the flat-plate layer31of the first waveguide103has a width decreasing in a gradient, and the ridge layer32also has a width decreasing in a gradient. Due to the gradient structure characteristics of the flat-plate layer31and the ridge layer32, relatively moderate spot-size modulation can be performed on the light transmitted in the first waveguide103, so as to minimize the light transmission loss and improve the coupling efficiency of the spot-size converter100.

In addition, a certain distance is provided between the second narrow end32bof the ridge layer32and the first narrow end31bof the flat-plate layer31of the first waveguide103. With this design, the first equal-width portion311can perform steady-state spot-size modulation on the light output from the first waveguide103(or the light entering the first waveguide103), facilitating the improvement of the stability of optical transmission; and due to the aforementioned distance, when the flat-plate layer31and the ridge layer32are manufactured by two patterning processes or one patterning process comprising two exposures, requirements for the alignment accuracy of a mask can be reduced, facilitating the reduction of the difficulty and cost of process control.

In some embodiments of the present disclosure, the first equal-width portion311is prismatic and a cross section thereof parallel to the first end face100ais triangular or trapezoidal, for example, in the shape of an isosceles triangle or an isosceles trapezoid. When light is transmitted from the first end face100ato the second end face100bof the spot-size converter100, this design allows more light to escape from the first equal-width portion311into the second waveguide42. When the light is transmitted from the second end face100bto the first end face100aof the spot-size converter100, the design allows the light to enter the first equal-width portion311more easily from the second waveguide42, that is, more light is allowed to enter the first waveguide103through the second waveguide42. Therefore, the above cross-sectional shape design of the first equal-width portion311can further improve the coupling efficiency between the integrated optical waveguide and the optical fiber. In addition, the second equal-width portion321may also be prismatic and a cross section thereof parallel to the first end face100amay also be triangular or trapezoidal, for example, in the shape of an isosceles triangle or an isosceles trapezoid, to allow the light to enter the flat-plate layer31more easily from the second equal-width portion321.

In the embodiments of the present disclosure, in the direction away from the second end face100b, a width variation trend of the first gradually-widening portion312may be linear or nonlinear, a width variation trend of the second gradually-widening portion314may be linear or nonlinear, and a width variation trend of the third gradually-widening portion322may be linear or nonlinear. As shown inFIG.2B, in this embodiment, in the direction away from the second end face100b, the widths of the first gradually-widening portion312and the third gradually-widening portion322increase linearly and gradually, and the width of the second gradually-widening portion314increases nonlinearly and gradually.

The linear width variation trend can realize the smooth modulation of the spot size in a shorter distance. The nonlinear width variation trend can realize more moderate and stable modulation of the spot size, and the shape curve of a gradually-changing portion can be flexibly adjusted according to specific requirements to obtain a better adjustment effect.

As shown inFIGS.1A and1C, in some embodiments of the present disclosure, the first narrow end31bof the flat-plate layer31extends to the second end face100b. In this way, the first narrow end31balso serves as a part of a port for outputting to the optical fiber or receiving input from the optical fiber. As shown inFIG.3, in some other embodiments of the present disclosure, there may also be a distance g between the first narrow end31bof the flat-plate layer31and the second end face100b, so that an end of the isolation layer102and an end of the covering layer104that extend to the second end face100bserve as ports for outputting to the optical fiber or receiving inputs from the optical fiber.

As shown inFIGS.1A and2A, the fourth equal-width portion315of the flat-plate layer31may also extend to the first side surface100cand the second side surface100d, that is, the width of the fourth equal-width portion315is maximized. In this way, the spot-size converter100can be adapted to an integrated optical waveguide with a larger spot size, thereby improving the applicability of the spot-size converter100.

In some embodiments of the present disclosure, a top edge of the first narrow end31bhas a width w6not greater than 400 nanometers; and/or the width w4of the covering layer104at the second end face is not less than 1 micron and not greater than 20 microns. The specific structural size of the spot-size converter100may be specifically designed according to performance requirements of the device in combination with experience, which is not specifically limited in the present disclosure.

A part of the covering layer104and a part of the isolation layer102that are close to the second end face100bjointly form a second waveguide42with a lower refractive index. One end of the covering layer104needs to extend to the second end face100b, and the other end thereof needs to extend to cover at least the second equal-width portion321, that is, to extend to at least the end of the second equal-width portion321away from the second end face100b. The specific shape design of the covering layer104is not limited. Adjusting the shape and size of the covering layer104is to adjust the structural size of the second waveguide42, and then to adjust the size of the spot size of the second end face100b. Therefore, the shape and size of the covering layer104can be flexibly modulated as required, so as to achieve the best matching with the spot size of the optical fiber.

In some embodiments of the present disclosure, the covering layer104is of an axisymmetric structure with respect to a symmetry axis, and the covering layer104extends to cover at least an end of the third gradually-widening portion322away from the second end face100b, so as to fully achieve its function in the second waveguide42and reduce the escape loss of light. The embodiments of the present disclosure are not limited to designing the covering layer as an axisymmetric structure, and the covering layer may also be of an asymmetric structure.

As shown inFIG.3, in some embodiments, the covering layer104is of an axisymmetric structure with respect to the symmetry axis, and the covering layer104extends to cover at least the end of the third gradually-widening portion322away from the second end face100b, an orthographic projection of the covering layer104on the substrate101is rectangular, and the width of the covering layer104(equal to the width w4of the covering layer104at the second end face) is greater than the width w3of the third equal-width portion313. Similarly, in these embodiments, the covering layer may also be of an asymmetric structure. By the orthographic projection of the covering layer104on the substrate101being rectangular, it is meant that a contour of the orthographic projection on the substrate101is rectangular, and a side wall of the covering layer104may be perpendicular to or form other included angles with the substrate101.

As shown inFIG.4, in some other embodiments, the covering layer104is of an axisymmetric structure with respect to the symmetry axis, and the covering layer104extends to cover at least the end of the third gradually-widening portion322away from the second end face100b, the covering layer104comprises an eighth equal-width portion411, a tapered portion412and a ninth equal-width portion413which are sequentially arranged in the direction away from the second end face100b. The tapered portion412has a width gradually decreasing in the direction away from the second end face100b, and the ninth equal-width portion413has a width w5greater than the width w3of the third equal-width portion313. Obviously, the width of the eighth equal-width portion411(equal to the width w4of the covering layer104at the second end face) is also greater than the width w3of the third equal-width portion313. Similarly, in these embodiments, the covering layer may also be of an asymmetric structure, for example, have a gradient change only on a single side.

In addition, the covering layer may also be designed to cover the entire first waveguide. For example, the covering layer further comprises a tenth portion located on a side of the ninth equal-width portion away from the second end face, and the tenth portion has a width greater than that of the ninth equal-width portion. In a specific embodiment, on the side of the ninth equal-width portion away from the second end face, the width of the covering layer increases in a gradient, so as to cover the entire first waveguide.

In this design, the width of the covering layer104increases in a gradient in the direction away from the first end face100a, which is opposite to the width variation trend of the flat-plate layer31and the ridge layer32of the first waveguide103. This design is equivalent to the increased size of the second waveguide42. When light is transmitted from the first end face100ato the second end face100bof the spot-size converter100, more light escaping from the first waveguide103can enter the second waveguide42and be moderately modulated in spot size by a gradient structure of the second waveguide42, so as to reduce the light loss. When the light is transmitted from the second end face100bto the first end face100aof the spot-size converter100, more light can enter the second waveguide42and be moderately modulated in spot size by the gradient structure of the second waveguide42, and then enter the first waveguide103. Therefore, the shape design of the covering layer104can further improve the coupling efficiency between the integrated optical waveguide and the optical fiber.

As shown inFIG.5, in still some other embodiments, the covering layer104covers the entire first waveguide103and is of an axisymmetric structure with respect to the symmetry axis, and the covering layer104has a width increasing in a gradient in the direction away from the second end face100b. The covering layer104comprises a sixth equal-width portion421, a fourth gradually-widening portion422and a seventh equal-width portion423which are sequentially arranged in the direction away from the second end face100b. The sixth equal-width portion421has a width (equal to the width w4of the covering layer104at the second end face) greater than the width w3of the third equal-width portion313, and the fourth gradually-widening portion422has a width gradually increasing in the direction away from the second end face100b. Similarly, in these embodiments, the covering layer may also be of an asymmetric structure, for example, have a gradient change only on a single side.

As shown inFIG.6, in yet some other embodiments, the covering layer104covers the entire first waveguide103and is of an axisymmetric structure with respect to the symmetry axis, and the covering layer104has a width increasing in a gradient in the direction away from the second end face100b. The covering layer104comprises a sixth equal-width portion431and a seventh equal-width portion433which are sequentially arranged in the direction away from the second end face100b. The sixth equal-width portion431has a width (equal to the width w4of the covering layer104at the second end face) greater than the width w3of the third equal-width portion313. Similarly, in these embodiments, the covering layer may also be of an asymmetric structure, for example, have a gradient change only on a single side.

As shown inFIG.7, an embodiment of the present disclosure further provides a photonic device1, comprising a spot-size converter100according to any one of the aforementioned embodiments. The specific product type of the photonic device1is not limited, for example, it may be an electro-optical modulator, a splitter, a star coupler, a variable optical attenuator (VOA), an optical switch, an interleaver, an array waveguide grating (AWG), and the like.

The spot-size converter100is integrated in the photonic device1. Since the spot-size converter100has a higher coupling efficiency, the optical loss of the photonic device1is smaller and the performance is improved.

It should be understood that, in this description, the orientations or positional relationships or dimensions denoted by the terms, such as “center”, “longitudinal”, “transverse”, “length”, “width”, “thickness”, “upper”, “lower”, “front”, “rear”, “left”, “right”, “vertical”, “horizontal”, “top”, “bottom”, “inner”, “outer”, “clockwise”, “counterclockwise”, “axial”, “radial” and “circumferential”, are the orientations or positional relationships or dimensions shown on the basis of the accompanying drawings, and these terms are used merely for ease of description, rather than indicating or implying that the apparatus or element referred to must have particular orientations and be constructed and operated in the particular orientations, and therefore should not be construed as limiting the scope of protection of the present disclosure.

In addition, the terms “first”, “second” and “third” are merely for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, the features defined with “first”, “second” and “third” may explicitly or implicitly comprise one or more features. In the description of the present disclosure, the term “a plurality of” means two or more, unless otherwise explicitly and specifically defined.

In the present disclosure, unless expressly stated or defined otherwise, the terms such as “mounting”, “connection”, “connected” and “fixing” should be interpreted broadly, for example, they may be a fixed connection, a detachable connection, or an integrated connection; may be mechanical connection, or electrical connection, or communication; and may be a direct connection or an indirect connection by means of an intermediate medium, or may be internal communication between two elements or interaction between the two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present disclosure can be understood according to specific circumstances.

In the present disclosure, unless expressly stated or limited otherwise, the expression of the first feature being “above” or “below” the second feature may comprise the case that the first feature is in direct contact with the second feature, and may also comprise the case that the first feature and the second feature are not in direct contact but are contacted via another feature therebetween. Furthermore, the first feature being “over”, “above” or “on” the second feature comprises the case that the first feature is directly or obliquely above the second feature, or merely indicates that the first feature is at a higher level than the second feature. The first feature being “below”, “under” or “beneath” the second feature comprises the case that the first feature is directly or obliquely below the second feature, or merely indicates that the first feature is at a lower level than the second feature.

This description provides many different implementations or examples that can be used to implement the present disclosure. It should be understood that these different implementations or examples are purely illustrative and are not intended to limit the scope of protection of the present disclosure in any way. On the basis of the disclosure of the description of the present disclosure, those skilled in the art will be able to conceive of various changes or substitutions. All these changes or substitutions shall fall within the scope of protection of the present disclosure. Therefore, the scope of protection of the present disclosure shall be subject to the scope of protection of the claims.