Mode spot converter and method of making the same

Abstract

The present disclosure provides a mode spot converter and a preparation method thereof, which are used for directly coupling an optical fiber and a photoelectric detector chip. The mode spot converter comprises a substrate, a ridge waveguide formed on the substrate, and the ridge waveguide comprises a ridge single-mode waveguide, a tapered ridge waveguide and a widened ridge waveguide connected in sequence along a direction parallel to the surface of the substrate. The widened ridge waveguide is used for connecting an optical fiber and matching the mode field of the optical fiber. The tapered ridge waveguide is used for amplifying and concentrating the mode spot of the light wave output by the optical fiber. The ridge single-mode waveguide is used for coupling the light wave after mode spot conversion to the photoelectric detector chip. The mode spot converter improves the coupling efficiency, accuracy and tolerance, and transmission efficiency, greatly reduces the loss of directly coupling a single-mode optical fiber and a ridge single-mode waveguide, and has high compact integration and low packaging cost.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to the field of integrated optics, and in particular to a mode spot converter and a method for manufacturing the same. BACKGROUND

[0002] With the maturity and gradual practicalization of high-speed and large-capacity optical communication technology, the demand for research and development of optical integrated devices has increased dramatically. One of the key technologies for the practicalization of various optical integrated devices is to achieve effective coupling of optical waveguides and optical fibers. Ridges optical waveguides are widely used in optical integrated devices due to their superiorities in transmission characteristics and manufacturing processes. Due to the great difference in shape and size of the cross section of the ridge optical waveguide and the single-mode optical fiber, and the great difference in refractive index, there is a serious mode field mismatch when the single-mode optical fiber and the ridge optical waveguide are connected and coupled. Especially in semiconductor optical quantum well devices, in order to ensure single-mode transmission, the cross section of the ridge optical waveguide is generally only about 1 μm. Therefore, if the single-mode optical fiber and the ridge optical waveguide are directly coupled, the loss will be high. The existing coupling scheme may have problems such as back reflection and mode mismatch loss. SUMMARY

[0003] In view of the above technical problems, the present disclosure provides a mode spot converter and a method for manufacturing the same, which at least partially solves the technical problems of high loss of direct coupling of existing single-mode optical fiber and ridge optical waveguide, and back reflection and mode mismatch loss of existing coupling mode.

[0004] The first aspect of the present disclosure provides a mode spot converter for coupling an optical fiber with a photodetector chip, comprising: a substrate; a ridge waveguide formed on the substrate, the ridge waveguide comprising a ridge single-mode waveguide, a tapered ridge waveguide and a widened ridge waveguide connected in sequence along a direction parallel to the surface of the substrate; wherein the widened ridge waveguide is used to connect the optical fiber and match the mode field of the optical fiber; the tapered ridge waveguide is used to amplify and concentrate the mode spot of the optical wave output by the optical fiber; and the ridge single-mode waveguide is used to couple the light wave after mode spot conversion to the photodetector chip.

[0005] According to an embodiment of the present disclosure, the tapered ridge waveguide extends into the widened ridge waveguide.

[0006] According to an embodiment of the present disclosure, the tapered ridge waveguide extends into the widened ridge waveguide to a position of one-third to one-half of the length of the widened ridge waveguide.

[0007] According to an embodiment of the present disclosure, in the direction of the ridge single-mode waveguide pointing to the widened ridge waveguide, the height and width of the tapered ridge waveguide linearly decrease, forming a transverse tapered ridge waveguide.

[0008] According to an embodiment of the present disclosure, the material of the substrate is InP, and the tapered ridge waveguide adopts InP of different components. x Ga1-x As y P 1-y Layers, different components of In x Ga 1-x As y P 1-y The layers form a transversely tapered, tapered ridge waveguide. The materials for the ridge-shaped single-mode waveguide and the widened ridge waveguide are InGaAsP.

[0009] According to embodiments of this disclosure, the thickness of the substrate is 300 μm to 400 μm, and the thickness of the tapered ridge waveguide is less than or equal to 1 μm.

[0010] According to embodiments of this disclosure, the width of the tapered ridge waveguide is different from the width of the ridged single-mode waveguide.

[0011] According to embodiments of this disclosure, the ridge height and ridge width of the ridge waveguide are determined by the reflection coefficient of the ridge waveguide.

[0012] According to embodiments of this disclosure, the pattern converter is a thermally adiabatic structure.

[0013] The second aspect of this disclosure provides a method for fabricating a mode spot converter, used to fabricate a mode spot converter as claimed in any one of claims 1-9. The fabrication method includes: determining a substrate; fabricating a ridge waveguide on the substrate, wherein the ridge waveguide includes a ridge single-mode waveguide, a tapered ridge waveguide, and a widened ridge waveguide connected sequentially along a direction parallel to the surface of the substrate.

[0014] Widened ridge waveguides are used to connect optical fibers and match the mode field of the optical fibers; tapered ridge waveguides are used to amplify the mode of the light waves output from the optical fiber and concentrate the transmission of the light waves; ridged single-mode waveguides are used to couple the light waves after mode conversion to the photodetector chip.

[0015] The speckle converter and its preparation method provided according to the embodiments of this disclosure have at least the following beneficial effects;

[0016] The ridge waveguide is configured as a ridge single-mode waveguide, a tapered ridge waveguide, and a widened ridge waveguide connected in sequence. The widened ridge waveguide matches the mode field of the optical fiber, and the tapered ridge waveguide is used to amplify and concentrate the mode spot of the light wave output from the optical fiber. When docked with the optical fiber, it has a good size match in the vertical direction, which improves coupling efficiency, accuracy and tolerance, and transmission efficiency, and can greatly reduce the loss of direct coupling between single-mode optical fiber and ridge single-mode waveguide.

[0017] Furthermore, the ridged single-mode waveguide and the broadened ridge waveguide are made of InGaAsP, while the tapered graded ridge waveguide uses In with different compositions. x Ga 1-x As y P 1-yThe layer can form a horizontal (lateral) conical structure, which makes the overall mode conversion efficiency high and the required size smaller. Furthermore, the substrate material is InP, which utilizes the monolithic integration advantages of the InP material system to realize compact, highly integrated waveguide devices and reduce packaging costs.

[0018] Furthermore, the tapered ridge waveguide extends into the widened ridge waveguide to better confine the light waves so that they do not disperse into the air, while avoiding damage to the tip of the high-refractive-index tapered ridge waveguide due to the polishing process in actual manufacturing.

[0019] Furthermore, the width of the tapered ridge waveguide differs from that of the ridged single-mode waveguide, which can further reduce coupling loss.

[0020] In addition, the ridge waveguide is a vertical cone shape, which can control the local optical dose through linewidth and has a high mode conversion efficiency of up to 98% or more. Attached Figure Description

[0021] The above and other objects, features and advantages of this disclosure will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0022] Figure 1 A schematic diagram of a pattern converter according to an embodiment of the present disclosure is shown.

[0023] Figure 2A A top view of a pattern converter according to an embodiment of the present disclosure is shown schematically.

[0024] Figure 2B A schematic left view of a speckle converter according to an embodiment of the present disclosure is shown.

[0025] Figure 2C A schematic right view of a pattern converter according to an embodiment of the present disclosure is shown.

[0026] Figure 3 The diagram illustrates the relationship between the conversion efficiency of the mode converter and the length of the tapered ridge waveguide according to an embodiment of the present disclosure. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this disclosure clearer, the following detailed description is provided in conjunction with specific embodiments and accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without inventive effort are within the scope of protection of this disclosure.

[0028] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0029] In this disclosure, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this disclosure according to the specific circumstances.

[0030] In the description of this disclosure, it should be understood that the terms "longitudinal", "length", "circumferential", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this disclosure and simplifying the description, and do not indicate or imply that the subsystem or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this disclosure.

[0031] Throughout the accompanying drawings, identical elements are represented by the same or similar reference numerals. Conventional structures or configurations have been omitted where they may cause confusion in understanding this disclosure. Furthermore, the shapes, dimensions, and positional relationships of the components in the drawings do not reflect their actual size, scale, or actual positional relationships. Additionally, any reference symbols enclosed in parentheses should not be construed as limiting this disclosure.

[0032] Similarly, to simplify this disclosure and aid in understanding one or more of the various aspects of the disclosure, in the above description of exemplary embodiments of the present disclosure, various features of the present disclosure are sometimes grouped together in a single embodiment, figure, or description thereof. The use of terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refers to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the present disclosure. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0033] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this disclosure, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0034] Figure 1 A schematic diagram of a pattern converter according to an embodiment of the present disclosure is shown.

[0035] like Figure 1 As shown, this mode converter is used to couple an optical fiber to a photodetector chip. For example, it may include a substrate 1 and a ridge waveguide 2 formed on the substrate 1. The ridge waveguide 2 includes a broadened ridge waveguide 21, a tapered ridge waveguide 22, and a ridge single-mode waveguide 23 connected sequentially along a direction parallel to the surface of the substrate 1. Wherein:

[0036] The widened ridge waveguide 21 is used to connect optical fibers and match the mode field of the optical fibers. The tapered ridge waveguide 22 is used to amplify the mode pattern of the light wave output from the optical fiber and concentrate the transmission of the light wave. The ridged single-mode waveguide 23 is used to couple the mode-converted light wave to the photodetector chip.

[0037] Specifically, the widened ridge waveguide 21 and the tapered ridge waveguide 22 are the core areas of the entire mode-spot converter structure, used to achieve efficient coupling between the single-mode fiber and the photodetector chip with low loss. The light wave is highly concentrated and undergoes mode conversion in the tapered ridge waveguide 22. This facilitates high coupling matching between the mode field and the single-mode fiber mode field, and the increased mode spot size couples with the ridged single-mode waveguide 23 to transmit the light beam to the high-speed detector chip. The light transmission direction is from input to output; after entering the tapered ridge waveguide 22 from the widened ridge waveguide 21, the mode spot radius gradually increases.

[0038] In this embodiment of the disclosure, the material of the substrate 1 can be InP, for example, an n-doped InP (n-InP) substrate can be used.

[0039] In this embodiment, the materials for the widened ridge waveguide 21 and the ridge-shaped single-mode waveguide 22 can be InGaAsP. The height and width of the tapered ridge waveguide 23 change linearly. Specifically, the trend of the linear change in the height and width of the tapered ridge waveguide 23 can be as follows: along the direction of the ridge-shaped single-mode waveguide pointing to the widened ridge waveguide, the height and width of the tapered ridge waveguide decrease linearly, forming a transverse tapered ridge waveguide.

[0040] Tapered tapered ridge waveguide 23 uses In with different compositions x Ga 1-x As y P1-y The layer, with its refractive index varying with its gradually increasing width, forms a transverse tapered waveguide to adjust the horizontal mode field distribution, highly concentrating the transmission of light waves. Here, x and y represent the content of each component element. Specifically, InP and In... x Ga 1-x As y P 1-y The interface between the two compositions is formed by the epitaxial growth of different compositions; therefore, an interface must be inserted between the substrate and the growth layer. This disclosure considers parameters such as band gap, band gap energy, wavelength, layer thickness, and lattice mismatch; the height and position of the absorption peak; and the refractive index obtained using parameters measured by elliptic polarization spectroscopy, showing a linear relationship between the refractive index near the band gap and the band gap energy. Different In compositions... x Ga 1-x As y P 1-y In at the bottom layer x Ga l-x As y P 1-y The InP layer has better lattice fit with the InP layer. Preferably, the photoluminescence spectrum peak Q is 1.05, the thickness is 250 nm, and the refractive index is n1 = 3.342. The refractive index of the multilayer increases linearly and gradually. A suitable longer wavelength with photon energy lower than the half-bandgap energy of the material is selected, and the InP layer is reasonably adjusted. x Ga 1-x As y P 1-y The composition of the layers can also achieve smooth energy transmission in the waveguide structure, with the optical path propagating along the horizontal direction. The width of the large-size mode field waveguide in the waveguide increases with the transmission distance, and its mode field also gradually increases, extending into the widened waveguide, thereby improving the transmission efficiency of light.

[0041] Furthermore, the substrate thickness is 300 μm to 400 μm, and the thickness of the tapered ridge waveguide is less than or equal to 1 μm. Coupling loss is reduced through dimensional design.

[0042] In this embodiment, the tapered ridge waveguide 22 can extend into the widened ridge waveguide 21. Preferably, the tapered ridge waveguide 22 extends into one-third to one-half of the widened ridge waveguide 21. Through the design of the extension structure and extension dimensions, light waves are better confined to prevent them from scattering in the air, guiding the light waves from the optical fiber into the high-refractive-index tapered ridge waveguide 22. Furthermore, damage to the tip of the high-refractive-index tapered ridge waveguide 22 due to the polishing process in actual manufacturing is avoided.

[0043] In this embodiment of the disclosure, the width of the tapered ridge waveguide is different from the width of the ridge single-mode waveguide, which can further reduce coupling loss.

[0044] In this embodiment of the disclosure, the mode converter is an adiabatic structure to avoid back reflection and increase losses.

[0045] In the embodiments disclosed herein, the ridge height, ridge width, ridge length, etc. of the ridge waveguide are determined by the reflection coefficient of the ridge waveguide.

[0046] Figure 2A A schematic top view of a speckle converter according to an embodiment of the present disclosure is shown. Figure 2B A schematic left view of a speckle converter according to an embodiment of the present disclosure is shown. Figure 2C A schematic right view of a pattern converter according to an embodiment of the present disclosure is shown.

[0047] like Figures 2A-2C As shown, by combining the design theory of minimum coupling loss, the overall size of the mode converter (ridge height H1, ridge height H2, ridge width W1, ridge width W2, ridge length L) can be made small and the coupling efficiency high.

[0048] For example, Figures 2B-2C The end-face model of the ridge waveguide is given. As the ridge height gradually changes from 150 nm to 600 nm, the change in end-face coupling loss α1 will not exceed 0.1 dB. The end-face coupling loss α1 of the TM polarization state changes abruptly at ridge heights of 200 nm and 250 nm, thus the ridge height range can be determined.

[0049] The ridge height H1 has a relatively small impact on the end-face coupling loss α1. A ridge height H1 that is too low will weaken the waveguide's ability to confine light waves, while a ridge height that is too high will introduce significant sidewall losses. This applies to the InGaAsP used in the embodiments of this disclosure and In with different compositions. x Ga 1-x As y P 1-y For the layer, 300nm can be selected as a suitable ridge height H1.

[0050] After determining the ridge height H1, the other parameter affecting the end-face coupling loss α1 is the width W2 of the widened ridge waveguide 21. The end-face coupling loss α1 between the cross-section of the widened ridge waveguide 21 and the fiber cross-section can be calculated using Fresnel's formula:

[0051] α TE = -10*1g(1-R) TE )

[0052] α TM = -10*1g(1-R) TM )

[0053] Calculate the end-face coupling loss α between the broadened ridge waveguide 21 section and the fiber section corresponding to the TE polarization state. TEThe end-face coupling loss α between the broadened ridge waveguide 21 cross section and the fiber cross section corresponding to the TM polarization state TM R TE To broaden the reflection coefficient of ridge waveguide 21 for the TE polarization state, R TM To broaden the reflection coefficient of the ridge waveguide 21 for the TM polarization state.

[0054] For example, if an input light wavelength of 1550nm is selected, the diameter of a standard single-mode fiber is generally 6 to 10 micrometers. As the width W2 of the widened ridge waveguide 21 increases, the end-face coupling loss α1 gradually decreases. When the width W2 is 4μm, the loss value reaches its minimum. At this time, the mode field size of the fiber and the widened ridge waveguide 21 are closest. If the width W2 of the widened ridge waveguide 21 is further increased, the end-face coupling loss α1 will gradually increase due to the mode field mismatch.

[0055] The main parameter affecting transmission loss is the length L of the tapered ridge waveguide 22. Due to structural complexity and boundary condition limitations, a fast and accurate numerical simulation method is used to study the coupling problem between optical fiber and ridged single-mode waveguide, based on Maxwell's equations:

[0056]

[0057] Given an input field E(x, y, z) = 0, the distribution of the spatial field z > 0 can be obtained, and the length L of the tapered ridge waveguide 22 can then be obtained.

[0058] The gradient range of the tapered graded ridge waveguide 22 can be determined as follows: extract scattering parameters, with input signals a1 and a2, and output signals b1 and b2, according to...

[0059]

[0060] Determine the waveguide length of the tapered ridge waveguide 22.

[0061] Figure 3 The diagram illustrates the relationship between the conversion efficiency of the mode converter and the length of the tapered ridge waveguide according to an embodiment of the present disclosure.

[0062] like Figure 3 As shown, the conversion efficiency η of the mode spot converter is greater than 98%. Especially when the waveguide length of the tapered ridge waveguide 22 is about 20 micrometers, the conversion efficiency η of the mode spot converter reaches its maximum, the scattering parameter approaches 1, and the transmission loss is small.

[0063] Based on the above-described mode converter, the alignment tolerance of the mode converter for TE polarized light is ±1.2μm in the x-direction and ±1.5μm in the y-direction; and the alignment tolerance for TM polarized light is ±1.1μm in the x-direction and ±1.5μm in the y-direction.

[0064] Based on the same inventive concept, this disclosure also provides a method for fabricating a mode-spot converter, used in the aforementioned mode-spot converter. The fabrication method includes: determining a substrate; fabricating a ridge waveguide on the substrate, wherein the ridge waveguide includes a ridge single-mode waveguide, a tapered ridge waveguide, and a broadened ridge waveguide sequentially connected along a direction parallel to the substrate surface. The broadened ridge waveguide is used to connect an optical fiber and match the mode field of the optical fiber; the tapered ridge waveguide is used to amplify and concentrate the mode spot of the light wave output from the optical fiber for transmission. The ridge single-mode waveguide is used to couple the mode-spot converted light wave to a photodetector chip.

[0065] It should be noted that the specific implementation details and technical effects of the preparation method embodiments provided in this disclosure are the same as those of the pattern converter embodiments, and will not be repeated here.

[0066] In summary, the mode converter provided in this embodiment utilizes a tapered ridge waveguide that can simultaneously constrain the transmitted light waves in both horizontal and vertical directions. The input end of the widened ridge waveguide is directly coupled to the single-mode fiber, resulting in high mode field matching between the widened ridge waveguide end and the single-mode fiber, leading to low loss. The tapered ridge waveguide extends into the widened ridge waveguide, allowing light energy to be transmitted into it. The high-refractive-index tapered structure enables high integration of light transmission, improving transmission efficiency. The highly integrated light waves are then transmitted to the high-speed photodetector chip within the ridged single-mode waveguide with very low transmission loss, effectively solving the problems of high loss and transmission loss in the coupling between the single-mode fiber and the waveguide.

[0067] The specific embodiments described above further illustrate the purpose, technical solutions, and beneficial effects of this disclosure. It should be understood that the above descriptions are merely specific embodiments of this disclosure and are not intended to limit this disclosure. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this disclosure should be included within the protection scope of this disclosure.

Claims

1. A mode spot converter, characterized by, A device for directly coupling an optical fiber to a photodetector chip, comprising: a substrate; a ridge waveguide formed on the substrate, the ridge waveguide comprising a single-mode ridge waveguide, a tapered ridge waveguide, and a widened ridge waveguide connected in sequence along a direction parallel to a surface of the substrate; wherein the widened ridge waveguide is configured to connect the optical fiber and match a mode field of the optical fiber, the tapered ridge waveguide is configured to amplify and concentrate a light wave output by the optical fiber, and the single-mode ridge waveguide is configured to couple the light wave after mode field conversion to the photodetector chip; the tapered ridge waveguide extends into the widened ridge waveguide; in a direction from the single-mode ridge waveguide to the widened ridge waveguide, a height and a width of the tapered ridge waveguide linearly decrease to form the tapered ridge waveguide.

2. The mode spot converter of claim 1, wherein, the tapered ridge waveguide extends into the widened ridge waveguide to a position of one-third to one-half of a length of the widened ridge waveguide.

3. The mode spot converter of claim 1, wherein, The material of the substrate is InP, the taper ridge waveguide is composed of In x Ga 1-x As y P 1-y layers of different components, the taper ridge waveguide is composed of In x Ga 1-x As y P 1-y layers of different components, the taper ridge waveguide is composed of InGaAsP.

4. The mode spot converter of claim 1, wherein, the substrate has a thickness of 300 μm to 400 μm, and the tapered ridge waveguide has a thickness of 1 μm or less.

5. The mode spot converter of claim 1, wherein, the width of the tapered ridge waveguide is different from a width of the single-mode ridge waveguide.

6. The mode spot converter of claim 1, wherein, a ridge height and a ridge width of the ridge waveguide are determined by a reflection coefficient of the ridge waveguide.

7. The mode spot converter of claim 1, wherein, the mode field converter is an adiabatic structure.

8. A method for producing a mode spot converter for producing a mode spot converter according to any one of claims 1 to 7, characterized in that a method for manufacturing the device, comprising: determining a substrate; forming a ridge waveguide on the substrate, wherein the ridge waveguide comprises a single-mode ridge waveguide, a tapered ridge waveguide, and a widened ridge waveguide connected in sequence along a direction parallel to a surface of the substrate; the widened ridge waveguide is configured to connect the optical fiber and match a mode field of the optical fiber; the tapered ridge waveguide is configured to amplify and concentrate a light wave output by the optical fiber; and the single-mode ridge waveguide is configured to couple the light wave after mode field conversion to the photodetector chip; the tapered ridge waveguide extends into the widened ridge waveguide; in a direction from the single-mode ridge waveguide to the widened ridge waveguide, a height and a width of the tapered ridge waveguide linearly decrease to form the tapered ridge waveguide.

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