Dielectric waveguide multi-mode interferometer and interferometer

Abstract

A dielectric waveguide multi-mode interferometer and an interferometer. A multi-mode waveguide (1) and a light absorber (4) are provided. One end of the multi-mode waveguide (1) is connected to M input channels (2), and another end is connected to N output channels (3), M and N being positive integers. The light absorber (4) comprises a waveguide cladding layer (41), and an optical waveguide core (42) and absorption material layer (43) which are enclosed within the waveguide cladding layer (41), a gap existing between the optical waveguide core (42) and the absorption material layer (43). The optical waveguide core (42) comprises a first end portion and a second end portion. The radial size of the optical waveguide core (42) gradually decreases from the first end portion to the second end portion, and the first end portion of the optical waveguide core (42) of the light absorber (4) is connected to an end portion of the multi-mode waveguide (1) in which the light absorber (4) is located. The materials of the multi-mode waveguide (1) and the optical waveguide core (42) of the light absorber (4) are both dielectric. The light absorber (4) arranged at an end portion of the multi-mode waveguide (1) may reduce bottom return loss and eliminate reflected light, so that the reflected light is absorbed by the absorption material layer (43), thereby reducing reflection.

Description

A dielectric waveguide multimode interference coupler and interferometer Technical Field

[0001] The present invention relates to the field of optical components, and in particular to a dielectric waveguide multimode interference coupler and an interferometer. Technical Background

[0002] A multimode interferometer (MMI) is a multimode interference structure based on an optical waveguide platform. It has numerous applications in optical chips, including light splitting, combining, and mixing. The number of input and output ports of an MMI coupler can be M and N, with M >= 1 and N >= 1. As shown in Figure 1, because the MMI region of an MMI coupler is a rectangle, there are multiple waveguide width changes between the MMI region and the input and output waveguides, and the four right corners typically have right angles. This always results in a certain amount of reflection, known as return loss. MMI couplers can be used to form various optical waveguide structures, devices, and optical chips, such as Mach-Zehnder interferometer modulators, Sagnac interferometers, interferometric optical gyroscopes, optical switches, or semiconductor ring lasers. In many applications, optical chips and systems are sensitive to light reflections, so it is necessary to find ways to reduce reflections in MMI couplers.

[0003] Dielectric optical waveguides (such as silicon dioxide, polymer, silicon nitride, aluminum nitride and other waveguides) cannot absorb reflected light and stray light by forming absorbers through ion doping like waveguides made of semiconductor materials such as silicon. Therefore, for multimode interference couplers based on dielectric waveguides, a simple method is to use a transition structure to transmit light from the dielectric optical waveguide to a semiconductor material such as silicon, and then use an ion-doped semiconductor waveguide as an absorber. However, this will introduce an additional transition structure, making the component structure complicated. Another method is to use an absorbing material such as germanium (Ge). Germanium on silicon is widely used in integrated optical components and can be used as a photodetector, but the epitaxial growth of germanium will affect the yield of integrated optical components, thereby affecting the cost; in addition, the surfaces of the dielectric optical waveguide and the germanium absorber can introduce some unwanted additional reflections.

[0004] Therefore, a new dielectric waveguide multimode interference coupler and interferometer are urgently needed to improve the above problems.

[0005] Summary of the Invention

[0006] The object of the present invention is to provide a dielectric waveguide multimode interference coupler and interferometer, which are used to solve the reflection problem existing in existing multimode interference couplers and interferometers, reduce bottom return loss, and eliminate reflected light.

[0007] In a first aspect, the present invention provides a dielectric waveguide multimode interference coupler, comprising:

[0008] A multimode waveguide, wherein one end of the multimode waveguide is connected to M input channels and the other end is connected to N output channels, where M and N are positive integers;

[0009] A light absorber, the light absorber comprising a waveguide cladding, an optical waveguide core and an absorption material layer enclosed within the waveguide cladding; wherein a gap exists between the optical waveguide core and the absorption material layer, the optical waveguide core comprising a first end and a second end, and a radial dimension of the optical waveguide core gradually decreases from the first end to the second end;

[0010] The light absorber is provided on at least one end of the multimode waveguide, and the first end of the optical waveguide core of the light absorber is connected to the end of the multimode waveguide where the light absorber is located;

[0011] The materials of the multimode waveguide and the optical waveguide core of the optical absorber are both dielectric.

[0012] The multimode interference coupler of the present invention has the following beneficial effects: by providing a multimode waveguide and an optical absorber, one end of the multimode waveguide is connected to M input channels and the other end is connected to N output channels, where M and N are positive integers; the optical absorber includes a waveguide cladding, an optical waveguide core and an absorption material layer enclosed in the waveguide cladding; wherein a gap exists between the optical waveguide core and the absorption material layer, the optical waveguide core includes a first end and a second end, and the radial dimension of the optical waveguide core gradually decreases from the first end to the second end; the optical absorber is provided on at least one end of the multimode waveguide, and the first end of the optical waveguide core of the optical absorber is connected to the end of the multimode waveguide where the optical absorber is located; the materials of the optical waveguide core of the multimode waveguide and the optical waveguide core of the optical absorber are both dielectric; the optical absorber provided at the end of the multimode waveguide can reduce bottom return loss and eliminate reflected light, so that the reflected light is absorbed by the absorption material layer, thereby reducing reflection of the multimode interference coupler and / or interferometer.

[0013] Optionally, the arrangement direction of the light absorber is adjustable. This has the beneficial effect that, by making the arrangement direction of the light absorber adjustable, the absorber can be placed in a desired direction, thereby improving the absorption efficiency of reflected light and reducing bottom return loss.

[0014] Optionally, the light absorbers at different right angles of the multimode waveguide are arranged in the same or different directions. This advantageously allows the light absorbers at different right angles of the multimode waveguide to be arranged in the same or different directions, thereby effectively reducing reflections from the multimode interference coupler.

[0015] Optionally, a light absorber is provided at least one of two adjacent right angles at the end portion where the input channel or output channel of the multimode waveguide is located, and each light absorber is disposed in a direction parallel to or at a certain angle with the length of the multimode waveguide. This advantageously improves the light absorber's efficiency in absorbing reflected light from the input channel when at least one of two adjacent right angles at the end portion where the input channel or output channel of the multimode waveguide is located is disposed, and each light absorber is disposed in a direction parallel to or at a certain angle with the length of the multimode waveguide.

[0016] Optionally, a light absorber is provided at each of the four right angles at the end of the multimode waveguide, and each light absorber is arranged parallel to or at a certain angle to the length of the multimode waveguide. This advantageously allows light reflected from the four right angles of the multimode waveguide to be absorbed, thereby reducing reflection from the multimode interference coupler.

[0017] Optionally, a light absorber is provided at each of the four right angles at the end of the multimode waveguide, and the first end of the optical waveguide core of each light absorber is connected to the right angle of the multimode waveguide where the light absorber is located. This advantageously improves the absorption efficiency of reflected light by providing the first ends of the light absorbers at the four right angles at the end of the multimode waveguide with direct connection to the right angle of the multimode waveguide where the light absorber is located.

[0018] Optionally, also include:

[0019] A polarization rotator is provided, wherein the first end of the optical waveguide core of the optical absorber is connected at a right angle to the multimode waveguide in which the optical absorber resides. The polarization rotator advantageously rotates input transverse electric field (TE) mode polarized light by 90 degrees, converting it into transverse magnetic field (TM) mode polarized light, which is then output to the optical absorber. Because the optical absorber has a higher absorption efficiency for TM polarized light, this structure can more effectively absorb light waves.

[0020] Optionally, the optical waveguide core is tapered or wedge-shaped, and is arranged linearly, or in a spiral or folded ring configuration in two-dimensional or three-dimensional space. This advantageously allows the optical waveguide core to be tapered or wedge-shaped, so that the tapered or wedge-shaped dielectric waveguide gradually increases the optical mode size. As the optical mode profile expands, the tail of the optical mode (a non-physical structure; the tail refers to the edge of the optical film field formed by the light spot expanding outward) begins to contact the upper absorbing material layer. Absorption introduced by the absorbing material layer attenuates the optical power propagating along the waveguide, while the adiabatic mode transition is sufficiently smooth to avoid sudden changes. This significantly reduces back reflections. Arranging the optical waveguide core linearly, or in a spiral or folded ring configuration in two-dimensional or three-dimensional space (e.g., spiraling / folding upward or downward) helps save space on optical integrated circuit components, leading to a higher degree of integration of the optical integrated circuit components.

[0021] Optionally, the absorption material layer is located above the optical waveguide core, or to the side of the optical waveguide core, or obliquely to the side of the optical waveguide core, or below the optical waveguide core. This advantageously allows the shape of the light absorber to be adjusted as needed, making it suitable for different usage scenarios.

[0022] In a second aspect, the present invention further provides an interferometer, comprising a multimode interference coupler of any possible design according to the first aspect and a waveguide trace or coil connected to an input channel or an output channel of the multimode interference coupler.

[0023] Optionally, the interferometer is a Mach-Zehnder interferometer modulator, a Sagnac interferometer, an interferometric optical gyroscope, an optical switch or a semiconductor ring laser.

[0024] For the beneficial effects of the second aspect, reference may be made to the description of the first aspect above.

[0025] Optionally, when the interferometer is a Sagnac interferometer, at least one of two adjacent right angles on the end portion of the multimode waveguide of the multimode interference coupler where the input channel is located is provided with a light absorber, and the arrangement direction of each light absorber is parallel to or at a certain angle to the length direction of the multimode waveguide;

[0026] One output channel of the multimode waveguide is connected to one end of the coil, and the other output channel is connected to the other end of the coil. The Sagnac interferometer advantageously provides a light absorber at at least two adjacent right angles at the end where the input channel of the multimode waveguide resides, with each light absorber positioned parallel to or at a certain angle to the length of the multimode waveguide. This allows the Sagnac interferometer to fully reflect light, thereby minimizing losses during the reflection process.

[0027] Optionally, when the interferometer is an interferometric optical gyroscope, at least one of the four right angles at the end of the multimode waveguide of the multimode interference coupler is provided with a light absorber, and the arrangement direction of each light absorber is parallel to or at a certain angle to the length direction of the multimode waveguide; wherein the coil is a spiral coil;

[0028] One output channel of the multimode waveguide is connected to one end of the spiral coil, and the other output channel is connected to the other end of the spiral coil; wherein the windings of the spiral coil are located on the same plane or on different planes in three-dimensional space; when the spiral coils are located on the same plane, there is a waveguide crossing. Its beneficial effect is that by providing a light absorber at at least one of the four right angles at the end of the multimode waveguide of the interferometric optical gyroscope, and the arrangement direction of each light absorber is parallel to or at a certain angle to the length direction of the multimode waveguide, the reflection of the interferometric optical gyroscope can be improved; by setting the coil as a spiral coil, and the windings of the spiral coil are located on the same plane or on different planes in three-dimensional space, and when the spiral coils are located on the same plane, there is a waveguide crossing, the shape of the spiral coil can be adjusted according to actual needs, thereby improving the integration level of integrated circuit components.

[0029] Optionally, the spiral coils are integrated into the same chip, into different chips, or are externally coupled fiber spiral coils. This advantageously allows the interferometric optical gyroscope to be adapted to different usage scenarios by integrating the spiral coils into the same chip, into different chips, or as externally coupled fiber spiral coils.

[0030] Optionally, when the interferometer is a Mach-Zehnder interferometer, the Mach-Zehnder interferometer includes a first multimode interference coupler, a second multimode interference coupler, a first waveguide trace, and a second waveguide trace;

[0031] A light absorber is provided at two adjacent right angles or at a certain angle on the end portion of the first multimode waveguide of the first multimode interference coupler where the input channel is located, and the arrangement direction of each light absorber is parallel to or at a certain angle to the length direction of the first multimode waveguide;

[0032] At least one of the two adjacent right angles on the end portion of the second multimode waveguide of the second multimode interference coupler where the output channel is located is provided with a light absorber, and the arrangement direction of each light absorber is parallel to or at a certain angle to the length direction of the second multimode waveguide;

[0033] An output channel of the first multimode waveguide is connected to an input channel of the second multimode waveguide through the first waveguide trace;

[0034] The other output channel of the first multimode waveguide is connected to the input channel at the other end of the second multimode waveguide via the second waveguide trace; wherein the first waveguide trace and the second waveguide trace have the same or different lengths. The advantageous effect is that by configuring a Mach-Zehnder interferometer including a first multimode interference coupler, a second multimode interference coupler, a first waveguide trace, and a second waveguide trace, and disposing four optical absorbers at two right angles at the end where the input channel of the first multimode interference coupler is located and at two right angles at the end where the output channel of the second multimode interference coupler is located, bottom return loss can be reduced, reflected light can be eliminated, and reflected light can be absorbed by the absorption material layer, thereby reducing reflection in the Mach-Zehnder interferometer. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG1 is a schematic structural diagram of a 1×2 multimode interference coupler in the prior art;

[0036] FIG2 is a schematic structural diagram of a 1×2 multimode interference coupler provided by an embodiment of the present invention;

[0037] FIG3 is a side view of a 1×2 multimode interference coupler provided by an embodiment of the present invention;

[0038] FIG4 is a schematic diagram of an overall structure of a light absorber provided in an embodiment of the present invention;

[0039] FIG5 is another schematic diagram of the overall structure of a light absorber provided in an embodiment of the present invention;

[0040] FIG6 is a schematic structural diagram of an M×N multimode interference coupler provided in an embodiment of the present invention;

[0041] FIG7 is a schematic structural diagram of a 1×2 multimode interference coupler provided in an embodiment of the present invention;

[0042] FIG8 is a schematic structural diagram of a 1×1 multimode interference coupler provided in an embodiment of the present invention;

[0043] FIG9 is a schematic structural diagram of a 1×2 multimode interference coupler including a polarization rotator provided in an embodiment of the present invention;

[0044] FIG10 is a schematic structural diagram of a 2×1 multimode interference coupler provided in an embodiment of the present invention;

[0045] FIG11 shows the transmission and reflection spectra of a conventional 2×1 multimode interference coupler without an optical absorber;

[0046] FIG12 shows the transmission and reflection spectra of a conventional 2×1 multimode interference coupler containing an optical absorber;

[0047] FIG13 is a diagram showing the light intensity distribution of a conventional 2×1 multimode interference coupler without a light absorber;

[0048] FIG14 is a diagram showing the light intensity distribution of a conventional 2×1 multimode interference coupler containing a light absorber;

[0049] FIG15 is a schematic structural diagram of a Sagnac interferometer provided in an embodiment of the present invention;

[0050] FIG16 is a reflection spectrum of a Sagnac interferometer based on a dielectric waveguide multimode interference coupler without an absorber;

[0051] FIG17 is a reflection spectrum of a Sagnac interferometer based on a dielectric waveguide multimode interference coupler with an absorber;

[0052] FIG18 is a diagram showing the light intensity distribution of a Sagnac interferometer based on a dielectric waveguide multimode interference coupler without an absorber;

[0053] FIG19 is a diagram showing the light intensity distribution of a Sagnac interferometer based on a dielectric waveguide multimode interference coupler with an absorber;

[0054] FIG20 is a schematic diagram of a partial structure of an interferometric optical gyroscope provided in an embodiment of the present invention;

[0055] FIG21 is a schematic structural diagram of a Mach-Zehnder interferometer provided in an embodiment of the present invention.

[0056] Numbers in the figure:

[0057] 1. Multimode waveguide; 2. Input channel; 3. Output channel; 4. Light absorber; 5. Polarization rotator; 6. Coil; 7. First multimode interference coupler; 8. Second multimode interference coupler; 9. First waveguide trace; 10. Second waveguide trace;

[0058] 41. Waveguide cladding; 42. Optical waveguide core; 43. Absorption material layer.

[0059] Summary of the Invention

[0060] In order to make the purpose, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention. Unless otherwise defined, the technical terms or scientific terms used herein should be the common meanings understood by people with ordinary skills in the field to which the present invention belongs. The words "including" and similar words used in this article mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects.

[0061] Taking a spiral shape as an example, as shown in Figures 2 and 3, the present invention provides a dielectric waveguide multimode interference coupler. A light absorber 4 is added to the multimode waveguide 1 of the dielectric waveguide multimode interference coupler to eliminate unwanted reflected light. Figure 2 shows a top view, while Figure 3 shows a side view. By placing light absorbers 4 at corners of the multimode waveguide 1 of the multimode interference coupler where they are prone to co-reflection, the light that would otherwise be reflected is absorbed, preventing it from being reflected. This reduces bottom return loss and eliminates reflected light. The optical absorber 4 comprises a waveguide cladding 41 (not shown), an optical waveguide core 42 enclosed within the waveguide cladding 41, and an absorbing material layer 43. A gap exists between the optical waveguide core 42 and the absorbing material layer 43. The optical waveguide core 42 comprises a first end and a second end, with the radial dimension of the optical waveguide core 42 gradually decreasing from the first end to the second end. The optical absorber 4 is disposed on at least one end of the multimode waveguide 1, and the first end of the optical waveguide core 42 of the optical absorber 4 is connected to the end of the multimode waveguide 1 where the optical absorber 4 is located. The multimode waveguide 1 and the optical waveguide core 42 of the optical absorber are both made of dielectric materials. The optical absorber 4 is connected to the corner via a connecting waveguide, which can be routed in a desired direction and has no restrictions on its size or distance from the port. It is worth noting that the optical waveguide core 42 shown in FIG. 2 as being arranged in a spiral shape can also be arranged in a straight line or in a folded ring shape, or even in a spiral shape or in a folded ring shape in two-dimensional space or three-dimensional space.

[0062] In some specific embodiments, as shown in Figures 4 and 5, the optical waveguide core 42 is tapered or wedge-shaped, i.e., its radial dimension gradually decreases from the first end to the second end of the optical waveguide core 42. The optical waveguide core 42 is arranged in a straight line, a spiral, or a folded ring in two or three dimensions. Specifically, as light propagates along the wedge-shaped optical waveguide core with gradually decreasing radial dimension, the waveguide's ability to confine the light field gradually weakens, causing the light distribution in the optical waveguide core 42 to decrease and the light distribution in the waveguide cladding 41 to increase, i.e., the optical mode field size gradually increases. As the optical mode profile expands, the evanescent wave field at the periphery of the optical mode (the edge of the optical mode field formed by the outward diffusion of the larger light spot) begins to contact the upper absorbing material layer 43. Due to absorption introduced by the absorbing material layer 43, the optical power propagating along the waveguide is attenuated. The gradual transition of the tapered or wedge shape is sufficiently smooth to avoid abrupt changes, thereby significantly reducing back reflections. The optical waveguide core 42 is arranged in a linear configuration, or in a spiral configuration or a folded ring configuration in two or three dimensions to save space on the optical integrated circuit components, thereby achieving a higher level of integration of the optical integrated circuit components. The absorption material layer 43 is located above the optical waveguide core 42, or to the side (one or both sides) of the optical waveguide core 42, or below the optical waveguide core 42, or to the oblique side of the dielectric optical waveguide (e.g., the lower right side as shown in FIG4 , or the upper left side as shown in FIG5 ). The absorption material layer 43 is made of metal, silicon, or other materials. Optionally, the silicon absorption layer can be doped through ion implantation to form a PN junction or a PIN junction; the PN junction or the PIN junction is used to remove free carriers converted from light absorption by applying a reverse bias voltage. The optical absorber 4 does not require the use of an ion implantation doping process, nor does it require the introduction of other materials such as germanium, making its structure easy to manufacture. This is different from the two existing solutions (i.e., using a transition structure or using the absorption material germanium (Ge). It is worth noting that, taking Figures 4 and 5 as an example, in three-dimensional space, in addition to the two planes where the two ends (the first end and the second end) of the optical waveguide core 42 are located, the absorption material layer 43 can be disposed at any position around the optical waveguide core 42.

[0063] The multimode waveguide 1 of the multimode interference coupler shown in Figures 2 and 3 includes one input channel 2 and two output channels 3. It should be understood that, as shown in Figure 6 , the multimode waveguide 1 of the multimode interference coupler can be expanded to include M input channels 2 and N output channels 3, where M and N are positive integers. As shown in Figure 6 , the optical absorbers 4 are positioned at all four corners of the multimode interference coupler, or as shown in Figure 2 , at two corners (or partial corners) at the ends of the input channels 2 of the multiplexer.

[0064] For example, FIG7 shows a 1×2 multimode interference coupler (one input channel 2, two output channels 3), and FIG8 shows a 1×1 multimode interference coupler (one input channel 2, one output channel 3).

[0065] In some embodiments, as shown in FIG6 , the arrangement direction of the light absorber 4 is adjustable.

[0066] In some specific embodiments, as shown in FIG6 , the light absorbers 4 at different right angles of the multimode waveguide 1 are arranged in the same or different directions.

[0067] It is worth noting that the multimode waveguide 1 has a certain thickness in three-dimensional space, and the thickness of the optical waveguide core 42 of the optical absorber 4 is the same as the thickness of the multimode waveguide 1 (see FIG3 ). For example, the top views shown in FIG1 and FIG2 are regarded as the top surface of the multimode waveguide 1 (the surface opposite to the top surface is the bottom surface), and the side view shown in FIG3 is regarded as the left side surface of the multimode waveguide 1 (the surface opposite to the left side is the right side surface). The end surface of the end where the input channel 2 of the multimode waveguide 1 is located is the front surface, and the end surface where the output channel 3 is located is the back surface (opposite to the front surface). Therefore, in three-dimensional space, In the embodiment, the front / back side of the multimode waveguide 1 is divided into three adjacent regions along the thickness direction (the region where the input channel / output channel is located in the middle and the regions on both sides of the input channel). The right angles of the present invention actually refer to the regions of the multimode waveguide 1 on both sides of the input channel, or the regions on both sides of the output channel. When the light absorber 4 is provided, the optical waveguide core 42 is close to the edge where the front side and the left side (or right side) of the multimode waveguide 1 are connected, or the optical waveguide core 42 is close to the edge where the back side and the left side (or right side) of the multimode waveguide 1 are connected.

[0068] In some specific embodiments, as shown in FIG6 , a light absorber 4 is provided at two adjacent right angles at the end where the input channel 2 of the multimode waveguide 1 is located, and each light absorber 4 is arranged parallel to or at a certain angle to the length of the multimode waveguide 1. A light absorber 4 is also provided at two adjacent right angles at the end where the output channel 3 of the multimode waveguide 1 is located, and both light absorbers 4 are arranged parallel to the length of the multimode waveguide 1. The arrangement direction of the light absorbers 4 does not intersect with the length of the multimode waveguide 1 to achieve absorption of reflected light. Therefore, whether the light absorber 4 is provided at the end where the input channel 2 is located or the end where the output channel 3 is located, it is sufficient to ensure that the optical waveguide core 42 of the light absorber 4 does not intersect with the multimode waveguide 1. It should be understood that although the light absorbers 4 at the two adjacent right angles at the end where the output channel 3 is located are arranged in the same direction in FIG6 , they may be arranged differently in actual use. For example, the upper light absorber 4 may be arranged parallel to the length of the multimode waveguide 1, while the lower light absorber 4 may be arranged at a downward angle.

[0069] In some specific embodiments, as shown in FIG8 , a light absorber 4 is provided at each of the four right angles at the end of the multimode waveguide 1 , and the arrangement direction of each light absorber 4 is parallel to the length direction of the multimode waveguide 1 .

[0070] In some specific embodiments, as shown in FIG6 , a light absorber 4 is provided at each of the four right angles at the end of the multimode waveguide 1 , and the first end of the optical waveguide core 42 of each light absorber 4 is connected to the right angle of the multimode waveguide 1 where the light absorber 4 is located.

[0071] In some embodiments, as shown in FIG9 , the multimode interference coupler further includes a polarization rotator 5 . The first end of the optical waveguide core 42 of the optical absorber 4 is connected at a right angle to the multimode waveguide 1 where the optical absorber 4 resides via the polarization rotator 5 . The polarization rotator 5 is configured to rotate input transverse electric field (TE) mode polarized light by 90 degrees, converting it into transverse magnetic field (TM) mode polarized light, and outputting the TM polarized light. The optical absorber 4 is configured to absorb the TM polarized light. Because the optical absorber 4 has a higher absorption efficiency for TM polarized light, this structure can more effectively absorb light waves.

[0072] For example, as shown in FIG10 , a 2×1 multimode interference coupler is shown, in which the optical waveguide core 42 is made of silicon nitride and the absorption material is aluminum metal. FIG11-14 illustrate the role of the optical absorber 4 in this 2×1 multimode interference coupler. Specifically, FIG11 shows the transmission spectrum and reflection spectrum of a conventional 2×1 multimode interference coupler without the optical absorber 4, wherein the reflected light intensity at the two entrances is between -30dB and -35dB. FIG12 shows the transmission spectrum and reflection spectrum of a conventional 2×1 multimode interference coupler with the optical absorber 4, wherein the reflected light intensity at the two entrances is reduced to between -35dB and -40dB. FIG13 and FIG14 are light intensity distribution diagrams of the above two multimode interference couplers. It can be seen that the present invention can effectively reduce the bottom return loss and eliminate the reflected light by arranging the optical absorber 4 at the corner of the multimode waveguide 1 of the multimode interference coupler, so that the reflected light is absorbed by the absorption material layer 43, thereby reducing the reflection of the multimode interference coupler.

[0073] As shown in Figures 15, 20, and 21, an interferometer includes a multimode interference coupler, a light absorber 4 disposed at a corner of a multimode waveguide 1 of the multimode interference coupler, and a waveguide trace or coil 6 connected to the multimode waveguide 1 of the multimode interference coupler. The interferometer is a Mach-Zehnder interferometer modulator, a Sagnac interferometer, an interferometric optical gyroscope, an optical switch, or a semiconductor ring laser.

[0074] Exemplarily, as shown in Figure 15, when the interferometer is a Sagnac interferometer, a light absorber 4 is provided at two adjacent right angles on the end of the input channel 2 of the multimode waveguide 1 of the multimode interference coupler, and the setting direction of each light absorber 4 is parallel to the length direction of the multimode waveguide 1; one output channel 3 of the multimode waveguide 1 is connected to one end of the coil 6, and the other output channel 3 is connected to the other end of the coil 6.

[0075] In this Sagnac interferometer, the material of the optical waveguide core 42 of the optical absorber 4 is silicon nitride, and the absorption material is aluminum metal. This Sagnac interferometer is used to reflect all light and minimize the loss during the reflection process. Figures 16-19 illustrate the role of the optical absorber 4 in this Sagnac interferometer. Figure 16 shows the reflection spectrum of a Sagnac interferometer based on a dielectric waveguide multimode interference coupler without the optical absorber 4, and its loss is approximately between 0.3dB and 0.5dB. Figure 17 shows the reflection spectrum of a Sagnac interferometer based on a dielectric waveguide multimode interference coupler with the optical absorber 4, and its loss is approximately between 0.1dB and 0.15dB. Figures 18 and 19 are light intensity distribution diagrams of the above two multimode interference couplers. It can be seen that the Sagnac interferometer using the multimode interference coupler of the present invention including the optical absorber 4 can effectively reduce the bottom return loss, eliminate reflected light, and allow the reflected light to be absorbed by the absorption material layer 43, thereby reducing the reflection of the interferometer.

[0076] For example, as shown in FIG20 , when the interferometer is an interferometric optical gyroscope, a light absorber 4 is provided at each of the four right angles at the end of the multimode waveguide 1 of the multimode interference coupler, and each light absorber 4 is arranged parallel to the length of the multimode waveguide 1. The coil 6 is a spiral coil. One output channel 3 of the multimode waveguide 1 is connected to one end of the spiral coil, and another output channel 3 is connected to the other end of the spiral coil. The spiral coil can be wound in various ways and is not limited to being on the same plane, but can also be on different planes in three-dimensional space. When the spiral coils are located on the same plane, there is a waveguide intersection. Furthermore, the spiral coils can be integrated into the same chip, on another chip, or can be externally coupled optical fiber spiral coils.

[0077] For example, as shown in FIG21 , when the interferometer is a Mach-Zehnder interferometer, the Mach-Zehnder interferometer includes a first multimode interference coupler 7, a second multimode interference coupler 8, a first waveguide trace 9, and a second waveguide trace 10; a light absorber 4 is provided at two adjacent right angles on the end portion where the input channel 2 of the first multimode waveguide 1 of the first multimode interference coupler 7 is located, and the setting direction of each light absorber 4 is parallel to the length direction of the first multimode waveguide 1; the output channel 2 of the second multimode waveguide 1 of the second multimode interference coupler 8 is parallel to the length direction of the first multimode waveguide 1; 3 is provided at two adjacent right angles on the end thereof, and the arrangement direction of each light absorber 4 is parallel to the length direction of the second multimode waveguide 1; an output channel 3 of the first multimode waveguide 1 is connected to an input channel 2 of the second multimode waveguide 1 through the first waveguide trace 9; the other output channel 3 of the first multimode waveguide 1 is connected to the input channel 2 at the other end of the second multimode waveguide 1 through the second waveguide trace 10; wherein the lengths of the first waveguide trace and the second waveguide trace are the same or different.

[0078] The integrated material platform on which the above-mentioned structure is based includes, but is not limited to, silicon nitride, silicon dioxide, aluminum oxide, indium phosphide, lithium niobate, barium titanate, and polymers. The waveguide types include, but are not limited to, channel waveguides, ridge waveguides, slot waveguides, diffused waveguides, and photonic crystal waveguides. The operating wavelength range of the structure includes, but is not limited to, the visible light band, O band, E band, S band, C band, L band, U band, and mid-infrared band. The application areas of the structure include optical communications, optical interconnects, optical switches, lidar, semiconductor ring lasers, interferometric optical gyroscopes, beam steering, optical sensing, free-space optical communications, optical storage, optical computing, etc.

[0079] While the embodiments of the present invention have been described in detail above, it will be apparent to those skilled in the art that various modifications and variations of these embodiments are possible. However, it should be understood that such modifications and variations are within the scope and spirit of the present invention as set forth in the claims. Furthermore, the invention described herein is susceptible to other embodiments and may be practiced or implemented in a variety of ways.

Claims

1. A dielectric waveguide multimode interference coupler, characterized in that: include: A multimode waveguide, wherein one end of the multimode waveguide is connected to M input channels, and the other end of the multimode waveguide is connected to N output channels, wherein M and N are positive integers; A light absorber, the light absorber comprising a waveguide cladding, and an optical waveguide core and an absorption material layer enclosed in the waveguide cladding; wherein there is a gap between the optical waveguide core and the absorption material layer, the optical waveguide core comprises a first end and a second end, and a radial dimension of the optical waveguide core gradually decreases from the first end to the second end; The optical absorber is disposed on at least one end of the multimode waveguide, and a first end of the optical waveguide core of the optical absorber is connected to an end of the multimode waveguide where the optical absorber is located; The materials of the multimode waveguide and the optical waveguide core of the optical absorber are both dielectric.

2. The multimode interference coupler according to claim 1, characterized in that: The arrangement direction of the light absorber is adjustable.

3. The multimode interference coupler according to claim 2, characterized in that: The light absorbers at different right angles of the multimode waveguide may be arranged in the same or different directions.

4. The multimode interference coupler according to claim 3, characterized in that: At least one of the two adjacent right angles on the end where the input channel or output channel of the multimode waveguide is located is provided with a light absorber, and the setting direction of each light absorber is parallel to or at a certain angle to the length direction of the multimode waveguide.

5. The multimode interference coupler according to claim 3, characterized in that: A light absorber is disposed at each of the four right angles at the end of the multimode waveguide, and the arrangement direction of each light absorber is parallel to or at a certain angle to the length direction of the multimode waveguide.

6. The multimode interference coupler according to claim 1, characterized in that: A light absorber is arranged at each of the four right angles at the end of the multimode waveguide, and the first end of the optical waveguide core of each light absorber is connected to the right angle of the multimode waveguide where the light absorber is located.

7. The multimode interference coupler according to claim 1, characterized in that: Also includes: A polarization rotator is provided, wherein the first end of the optical waveguide core of the optical absorber is connected at a right angle to the multimode waveguide where the optical absorber is located through the polarization rotator.

8. The multimode interference coupler according to any one of claims 1 to 7, characterized in that: The shape of the optical waveguide core is conical or wedge-shaped, and the optical waveguide core is arranged in a straight line, or in a spiral shape or in a folded ring shape in a two-dimensional space or a three-dimensional space.

9. The multimode interference coupler according to any one of claims 1 to 7, characterized in that: The absorption material layer is located on the upper layer of the optical waveguide core, or on the side of the optical waveguide core, or on the oblique side of the optical waveguide core, or on the lower layer of the optical waveguide core.

10. An interferometer, characterized in that: The interferometer comprises the multimode interference coupler as described in any one of claims 1 to 9 and a waveguide trace or a coil connected to an input channel or an output channel of the multimode interference coupler.

11. The interferometer according to claim 10, characterized in that The interferometer is a Mach-Zehnder interferometer modulator, a Sagnac interferometer, an interferometric optical gyroscope, an optical switch or a semiconductor ring laser.

12. The interferometer according to claim 11, characterized in that When the interferometer is a Sagnac interferometer, at least one of the two adjacent right angles on the end of the multimode waveguide where the input channel of the multimode interference coupler is located is provided with a light absorber, and the arrangement direction of each light absorber is parallel to or at a certain angle to the length direction of the multimode waveguide; One output channel of the multimode waveguide is connected to one end of the coil, and the other output channel is connected to the other end of the coil.

13. The interferometer according to claim 11, characterized in that When the interferometer is an interference type optical gyroscope, at least one of the four right angles at the end of the multimode waveguide of the multimode interference coupler is provided with a light absorber, and the setting direction of each light absorber is parallel to or at a certain angle to the length direction of the multimode waveguide; wherein the coil is a spiral coil; One output channel of the multimode waveguide is connected to one end of the spiral coil, and the other output channel is connected to the other end of the spiral coil; wherein the windings of the spiral coil are located on the same plane or on different planes in a three-dimensional space; when the spiral coils are located on the same plane, waveguide crossing is contained.

14. The interferometer according to claim 13, characterized in that The spiral coil is integrated in the same chip, in different chips, or is an externally coupled optical fiber spiral coil.

15. The interferometer according to claim 11, characterized in that When the interferometer is a Mach-Zehnder interferometer, the Mach-Zehnder interferometer comprises a first multimode interference coupler, a second multimode interference coupler, a first waveguide trace and a second waveguide trace; At least one of the two adjacent right angles on the end of the input channel of the first multimode waveguide of the first multimode interference coupler is provided with a light absorber, and the arrangement direction of each light absorber is parallel to or at a certain angle to the length direction of the first multimode waveguide; At least one of the two adjacent right angles on the end where the output channel of the second multimode waveguide of the second multimode interference coupler is located is provided with a light absorber, and the arrangement direction of each light absorber is parallel to or at a certain angle to the length direction of the second multimode waveguide; An output channel of the first multimode waveguide is connected to an input channel of the second multimode waveguide through the first waveguide routing; Another output channel of the first multimode waveguide is connected to another input channel of the second multimode waveguide through the second waveguide line; wherein the lengths of the first waveguide line and the second waveguide line are the same or different.

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