An optical signal transmitter based on a thin-film lithium niobate photonic integrated circuit vertical coupling platform

Abstract

The present invention discloses an optical signal transmitter based on a thin-film lithium niobate photonic integrated circuit vertical coupling platform, the transmitter comprising a first substrate, a second substrate, a continuous wave laser, a focusing lens, a collimating lens, a micro-prism, a redirecting device, a modulator optical waveguide and an electrode. The continuous wave laser, the focusing lens and the collimating lens are fixed on the first substrate, and the redirecting device, the modulator optical waveguide and the electrode are fixed on the second substrate. The optical signal emitted by the continuous wave laser is focused by the focusing lens and then adjusted in direction by the collimating lens, enters the micro-prism from a right-angle surface, is reflected by an inclined surface and then emitted from another right-angle surface, and enters the modulator optical waveguide after being redirected by the redirecting device. The thin-film lithium niobate waveguide modulates the optical signal according to the electrical signal of the electrode and transmits it outward. The design adjusts the incident angle by rotating the collimating lens, improves the coupling efficiency, and realizes efficient optical signal transmission and system performance optimization.

Description

Technical Field

[0001] The invention relates to the field of electro-optic modulators, and in particular to an optical signal transmitter based on a thin-film lithium niobate photonic integrated circuit vertical coupling platform. Background Art

[0002] With the rapid development of optical communication technology, optoelectronic integrated circuits (OEICs) are increasingly used in high-speed, large-capacity data transmission. Among many optoelectronic materials, lithium niobate (LiNbO3, referred to as LN) has become a very important material due to its excellent electro-optical effect and wide bandwidth performance. In particular, thin-film lithium niobate has great application potential in photonic integrated circuits (PICs) due to its high integration and superior performance.

[0003] Traditional optical signal coupling methods mainly rely on planar coupling, but this coupling method has problems such as low coupling efficiency, difficult alignment, and poor system stability. In recent years, vertical coupling technology has gradually become a new solution, which can effectively improve coupling efficiency and simplify the optical signal path. However, there are still some technical difficulties in the vertical coupling technology of photonic integrated circuits based on thin-film lithium niobate, mainly including efficient coupling of optical signals between different devices, improvement of overall system performance, and cost control.

[0004] In order to overcome these problems, the present invention proposes an optical signal transmitter based on a thin-film lithium niobate photonic integrated circuit vertical coupling platform, aiming to improve the coupling efficiency of the optical signal and the overall system performance by optimizing the structural design and coupling method. Summary of the invention

[0005] The present invention mainly provides an optical signal transmitter based on a thin-film lithium niobate photonic integrated circuit vertical coupling platform, aiming to improve the optical signal coupling efficiency and overall performance.

[0006] The present invention solves the above technical problems mainly through the following technical solutions: an optical signal transmitter based on a thin-film lithium niobate photonic integrated circuit vertical coupling platform, comprising:

[0007] A first substrate, a second substrate, a continuous wave laser, a focusing lens, a collimating lens, a micro prism, a redirecting device, a modulator optical waveguide and an electrode. The continuous wave laser, the focusing lens and the collimating lens are fixed on the first substrate. The laser emission direction of the continuous wave laser is directly opposite to the focusing lens and the collimating lens in sequence. The micro prism is a right-angle prism. The micro prism is fixed on the collimating lens and one right-angle surface of the micro prism is used as a light incident surface and is perpendicular to the light signal emission direction of the collimating lens. The other right-angle surface of the collimating lens is used as a light exit surface and faces the incident surface of the redirecting device. The input end of the modulator optical waveguide faces the exit surface of the redirecting device. The modulator optical waveguide includes a thin-film lithium niobate waveguide. The electrode is arranged in parallel with the thin-film lithium niobate waveguide. The redirecting device, the modulator optical waveguide and the electrode are all fixed on the second substrate.

[0008] The continuous wave laser is fixed on the substrate by eutectic bonding. The light signal emitted by it is focused by the focusing lens and then adjusted by the collimating lens. It enters the micro prism from the right angle surface and then is reflected by the inclined surface and emitted from another right angle surface. After being redirected by the redirection device, it enters the modulator optical waveguide. The thin film lithium niobate waveguide modulates the optical signal according to the electrical signal of the electrode and finally transmits it outward through the optical fiber. The right-angle prism is relatively easy to process and align, and no special surface treatment is required because this design is achieved by total internal reflection (TIR), usually by injection molding in one step. The first substrate and the second substrate can be made of materials such as silicon (Si), silicon dioxide (SiO2), aluminum nitride (AlN) or aluminum oxide (Al2O3). The thermal expansion coefficient of the second substrate matches the lithium niobate waveguide. The first substrate can be made of the same material as the second substrate. In this case, the first substrate and the second substrate can be integrally formed. The modulator optical waveguide is covered with a cladding layer to provide protection and enhance performance.

[0009] Preferably, a groove is formed on the first substrate, and the collimating lens is rotatably mounted in the groove. The collimating lens adjusts the light signal emission angle by rotating to achieve coupling with the modulator below.

[0010] The focusing lens and the collimating lens are both installed in the groove, and the collimating lens can rotate around its own central axis, thereby driving the micro-prism to rotate. By rotating the collimating lens with the micro-prism, the incident angle of the redirecting device can be conveniently adjusted, making the alignment process of the light beam more flexible and accurate, and active fine-tuning can be achieved, thereby improving the coupling efficiency.

[0011] Preferably, the modulator optical waveguide includes an inverse tapered mode converter, which includes a first wide portion for receiving an optical signal from a redirecting device, the first wide portion extending in the optical signal transmission direction to have a first narrow portion for redirecting the optical signal, and a coupling surface of the first narrow portion being parallel to the optical signal transmission direction; the optical input end of the thin film lithium niobate waveguide is a tapered waveguide matching the inverse tapered mode converter, the tapered waveguide includes a second narrow portion for receiving and redirecting the optical signal, the coupling surface of the second narrow portion is parallel to the coupling surface of the first narrow portion, and the second narrow portion extending in the optical signal transmission direction to have a second wide portion; the optical signal is coupled from the first narrow portion to the second narrow portion through an evanescent wave.

[0012] An inverse tapered mode converter is an optical device used to adjust and optimize the size of the light mode in an optical fiber or waveguide. It gradually changes the width of the waveguide so that the mode field distribution of the light gradually transitions from a large size to a small size, or vice versa. The inverse tapered mode converter is made of silicon nitride (SiN), silicon (Si) or a high refractive index polymer material, and can also be generated by 3D printing.

[0013] The narrower section of the inverse tapered mode converter is located below the narrower section of the tapered waveguide. An optical signal is provided to the wider section of the inverse tapered mode converter. The optical signal propagates in the direction of the narrower section within the inverse tapered mode converter. In the narrower section of the inverse tapered mode converter, the optical signal is redirected downward into the narrower section of the tapered waveguide through evanescent wave (decaying wave) coupling to achieve optical redirection coupling. The narrower section of the tapered waveguide redirects the input optical signal into a substantially horizontal direction to propagate toward its wider section. The tapered waveguide can be configured as a mode converter to change (e.g., reduce) the mode field diameter (e.g., spot size) of the input optical signal for efficient coupling into the lithium niobate waveguide.

[0014] Preferably, the light-emitting surface of the micro prism includes a focusing lens structure.

[0015] The optical signal in the micro prism is focused by a focusing lens when it is emitted, thereby achieving mode spot matching with the subsequent optical path, ensuring minimal loss of the optical signal during transmission and improving the transmission efficiency and performance of the overall system.

[0016] Preferably, the optical signal transmitter based on the thin-film lithium niobate photonic integrated circuit vertical coupling platform further includes an optical isolator, which is arranged between the focusing lens and the collimating lens.

[0017] Optical isolators can reduce reflections and interference, improve the transmission quality of optical signals, and enhance the stability and performance of the system.

[0018] Preferably, the redirecting device is a parabolic lens or a 45-degree reflector or a polymer lens.

[0019] If the optical signal emitted by the micro-prism is already matched with the modulated optical waveguide, a 45-degree reflector can be used to simply redirect the optical signal; if there is still a certain mode difference between the optical signal emitted by the micro-prism and the modulated optical waveguide, a parabolic reflector or a polymer lens can be used to perform mode field conversion (reduce the mode spot) while reflecting (refracting) to achieve better coupling. The incident surface and the output surface of the redirection device are both the reflection surfaces of the parabolic lens, the 45-degree reflector or the polymer lens.

[0020] Preferably, the redirection device is a grating coupler, and the periodic structure of the grating coupler refracts and couples the optical signal. When the incident optical signal enters the grating coupler, the optical signal interacts with the grating structure to produce a diffraction effect. The diffracted light beam in a specific direction is effectively coupled into the waveguide, thereby realizing the import or export of the optical signal.

[0021] Preferably, the thermal expansion coefficient of the second substrate matches the thermal expansion coefficient of lithium niobate.

[0022] Vertical coupling performs better in thermal stability, and matching thermal expansion coefficients can reduce stress and coupling loss caused by thermal expansion coefficient mismatch due to material expansion or contraction caused by temperature changes. This is of great significance to stability and reliability in practical applications.

[0023] The substantial effects brought about by the present invention are: 1. Efficient integration and optical isolator configuration: It realizes the efficient integration of thin-film lithium niobate and laser, so that the optical signal can be transmitted stably and efficiently; the laser can be configured with an optical isolator, which further improves the transmission quality of the optical signal, reduces reflection and interference, and improves the stability and performance of the system. 2. Convenient adjustment of the incident angle: By rotating the collimating lens with a prism, the incident angle can be conveniently adjusted. This design makes the alignment process of the light beam more flexible and precise, can achieve active fine-tuning, and improves the coupling efficiency. 3. Passive alignment and large-scale production: Several key components of the laser realize passive alignment, which greatly simplifies the assembly process and improves production efficiency; this design is suitable for large-scale production, reduces the difficulty and cost of manufacturing, and improves the consistency and reliability of the product. 4. Reduce costs: The existing laser packaging process and components are used to effectively reduce production costs; mature technologies and processes are used to reduce uncertainties and risks in the development and manufacturing process. 5. Mode spot matching: A focusing reflective lens is integrated on the optical waveguide of the lithium niobate modulator chip to achieve mode spot size matching; this design ensures that the optical signal has minimal loss during transmission and improves the transmission efficiency and performance of the overall system. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1It is a schematic diagram of the structure of an optical signal transmitter based on a thin-film lithium niobate photonic integrated circuit vertical coupling platform of the present invention;

[0025] Figure 2 yes Figure 1 A side view of the optical signal transmitter shown;

[0026] Figure 3 It is a schematic diagram of an inverse tapered mode converter and a tapered waveguide structure of the present invention;

[0027] Figure 4 is a partial side view of another optical signal transmitter of the present invention;

[0028] Figure 5 It is a partial side view of another optical signal transmitter of the present invention. DETAILED DESCRIPTION

[0029] The technical solution of the present invention is further specifically described below through embodiments and in conjunction with the accompanying drawings.

[0030] Embodiment 1: Figure 1 The structure of the optical signal transmitter based on the thin-film lithium niobate photonic integrated circuit vertical coupling platform of this embodiment is shown. The platform includes a continuous wave (CW) laser 110, which is fixed on the first substrate 111 by eutectic bonding. The first substrate 111 can be silicon (Si) or other dielectric materials, such as silicon dioxide (SiO2), aluminum nitride (AlN), aluminum oxide (Al2O3), etc. The light emitted by the continuous wave laser 110 passes through a focusing lens 112, an optional optical isolator 113 and a collimating lens 114. The focusing lens 112, the optical isolator 113 and the collimating lens 114 are all placed in a precisely cut or etched flat bottom V-groove on the first substrate 111 and passively aligned to the continuous wave laser 110.

[0031] The micro prism 115 is pre-fixed on the collimating lens 114, and the micro prism can be made of silicon (Si), optical glass or a high refractive index polymer material. A focusing lens structure 116 can be prepared on the light-emitting surface of the micro prism 115 by integral molding or etching to match the mode profile of the optical waveguide. The direction of the light beam can be adjusted by rotating the collimating lens 114. The light from the micro prism 115 is vertically coupled to the optical waveguide on the second substrate 117, and the second substrate 117 can be a material such as silicon (Si), silicon dioxide (SiO2), lithium niobate (LiNbO3) whose thermal expansion coefficient matches that of lithium niobate. The structure on the entire second substrate is called a modulator.

[0032] The optical waveguide at the input end of the modulator is composed of a micro-reflector 118 and an inverse-tapered mode converter 119. The micro-reflector 118 can be a parabolic reflector ablated by laser or a polymer micro-mirror. Depending on the specific application, the inverse-tapered mode converter 119 can be directly manufactured on the second substrate 117, such as silicon nitride (SiN), silicon (Si) or a high refractive index polymer, or generated by 3D printing polymer. The incident light passing through the micro-reflector 118 is further focused and coupled to the optical waveguide of the thin film lithium niobate (TFLN) modulator through the mode converter 119. The modulator optical waveguide 120 can be made of etched lithium niobate (LiNbO3), silicon nitride (SiN), silicon (Si), polymer or other suitable materials. The electrical signal is input through the electrode 122, and the modulated light is output through the optical fiber 123.

[0033] Figure 2 yes Figure 1 A side view of the structure shown, with detailed descriptions of the various components as follows:

[0034] A continuous wave laser 110 is used as a light source to generate a light beam. The light beam is initially focused by a focusing lens 112 and then passes through an optional optical isolator 113 to eliminate unnecessary reflections and feedback. The light beam after passing through the optical isolator enters a collimating lens 114 to further collimate the light beam.

[0035] The collimated light beam is converted in direction by a micro prism 115 fixed on the collimating lens 114. The micro prism 115 can be made of silicon (Si), optical glass or a high refractive index polymer material. In order to better match the mode profile of the optical waveguide, a focusing lens structure 116 can be optionally formed or etched on the light emitting surface of the micro prism 115.

[0036] The light beam output from the micro-triangular prism 115 is vertically coupled into the modulator optical waveguide 120. The modulator optical waveguide 120 is located on the second substrate (modulator substrate) 117, and the substrate material can be a material with matching thermal expansion coefficients such as silicon (Si), silicon dioxide (SiO2), lithium niobate (LiNbO3), etc. The input end of the optical waveguide includes a micro-reflector 118, which can be a laser-ablated parabolic reflector, a 45-degree reflector, or a polymer micro-mirror.

[0037] After passing through the micro-reflector 118, the light is mode-converted by the inverse-tapered mode converter 119. Depending on the specific application, the inverse-tapered mode converter 119 can be made of silicon nitride (SiN), silicon (Si) or a high-refractive-index polymer material, or generated by 3D printing. The mode-converted optical signal is coupled into the optical waveguide 120 of the thin-film lithium niobate (TFLN) modulator to finally achieve signal modulation. The modulator optical waveguide is covered with a cladding layer 121 to protect the optical waveguide and improve its performance.

[0038] like Figure 3 As shown, the inverse tapered mode converter includes a first wide portion 310 for receiving an optical signal from a redirecting device, the first wide portion 310 extends a first narrow portion 311 for redirecting the optical signal in the direction of optical signal transmission, and the coupling surface of the first narrow portion 311 is parallel to the direction of optical signal transmission; the optical input end of the thin-film lithium niobate waveguide is a tapered waveguide matched with the inverse tapered mode converter, the tapered waveguide includes a second narrow portion 312 for receiving and redirecting the optical signal, the coupling surface of the second narrow portion 312 is parallel to the coupling surface of the first narrow portion, and the second narrow portion extends a second wide portion 313 in the direction of optical signal transmission; the optical signal is coupled from the first narrow portion 311 to the second narrow portion 312 through an evanescent wave. Figure 2 Due to size limitations, the side view structure of the inverse tapered mode converter and tapered waveguide cannot be shown. Figure 3 shall prevail.

[0039] An inverse tapered mode converter is an optical device used to adjust and optimize the size of the light mode in an optical fiber or waveguide. It gradually changes the width of the waveguide so that the mode field distribution of the light gradually transitions from a large size to a small size, or vice versa. The inverse tapered mode converter is made of silicon nitride (SiN), silicon (Si) or a high refractive index polymer material, and can also be generated by 3D printing.

[0040] The narrower section of the inverse tapered mode converter is located below the narrower section of the tapered waveguide. An optical signal is provided to the wider section of the inverse tapered mode converter. The optical signal propagates in the direction of the narrower section within the inverse tapered mode converter. In the narrower section of the inverse tapered mode converter, the optical signal is redirected downward into the narrower section of the tapered waveguide through evanescent wave (decaying wave) coupling to achieve optical redirection coupling. The narrower section of the tapered waveguide redirects the input optical signal into a substantially horizontal direction to propagate toward its wider section. The tapered waveguide can be configured as a mode converter to change (e.g., reduce) the mode field diameter (e.g., spot size) of the input optical signal for efficient coupling into the lithium niobate waveguide.

[0041] Embodiment 2: Figure 4 Another partial schematic diagram of an optical signal transmitter modulator based on a thin film lithium niobate photonic integrated circuit vertical coupling platform is shown. In addition to the laser ablated parabolic reflector used in Example 1, vertical coupling in an optical waveguide can also be achieved by other methods.

[0042] Figure 4In the embodiment, vertical coupling is achieved by a 45-degree reflector 412. The 45-degree reflector 412 formed on the second substrate 117 can be manufactured by laser ablation or mirror cutting technology. Depending on the specific application, the inverse tapered mode converter 119 can be made of silicon nitride (SiN), silicon (Si) or a high refractive index polymer material, or generated by 3D printing. Light is transmitted through the inverse tapered mode converter 119, and the mode-converted light is coupled into the modulator optical waveguide 120 through an evanescent wave, thereby achieving mode conversion. The cladding layer 121 covers the optical waveguide to protect its structure and improve its performance.

[0043] Embodiment 3: Figure 5 Another partial schematic diagram of an optical signal transmitter modulator based on a thin-film lithium niobate photonic integrated circuit vertical coupling platform is shown. In this embodiment, vertical coupling is achieved through a grating coupler 512. The grating coupler 512 is located on a substrate 117. Depending on the specific application, the inverse tapered mode converter 119 can be made of silicon nitride (SiN), silicon (Si) or a high refractive index polymer material, or generated by 3D printing. Light is transmitted through the inverse tapered mode converter 119, and the mode-converted light is coupled into the modulator optical waveguide 120 through an evanescent wave, thereby achieving mode conversion. The cladding layer 121 is also covered on the optical waveguide to provide protection and enhance performance. The substrate material can be a material with matching thermal expansion coefficients such as silicon (Si), silicon dioxide (SiO2), and lithium niobate (LiNbO3).

[0044] The specific embodiments described herein are merely examples of the spirit of the present invention. Those skilled in the art may make various modifications or additions to the specific embodiments described or replace them in similar ways, but they will not deviate from the spirit of the present invention or exceed the scope defined by the appended claims.

[0045] Although the term focusing lens, micro prism, optical waveguide, etc. is frequently used in this article, the possibility of using other terms is not excluded. These terms are used only to more conveniently describe and explain the essence of the present invention; interpreting them as any additional limitation is contrary to the spirit of the present invention.

Claims

1. An optical signal transmitter based on a thin-film lithium niobate photonic integrated circuit vertical coupling platform, characterized in that: include: A first substrate, a second substrate, a continuous wave laser, a focusing lens, a collimating lens, a micro prism, a redirecting device, a modulator optical waveguide and an electrode, wherein the continuous wave laser, the focusing lens and the collimating lens are fixed on the first substrate, the laser emission direction of the continuous wave laser is directly opposite to the focusing lens and the collimating lens in sequence, the micro prism is a right-angle prism, the micro prism is fixed on the collimating lens and one right-angle surface of the micro prism is used as a light incident surface and is perpendicular to the light signal emission direction of the collimating lens, the other right-angle surface of the collimating lens is used as a light exit surface and faces the incident surface of the redirecting device, the input end of the modulator optical waveguide faces the exit surface of the redirecting device, the modulator optical waveguide includes a thin-film lithium niobate waveguide, the electrode is arranged in parallel with the thin-film lithium niobate waveguide, and the redirecting device, the modulator optical waveguide and the electrode are all fixed on the second substrate; The first substrate is provided with a groove, in which the collimating lens is rotatably mounted. The collimating lens drives the micro-prism to rotate to adjust the vertical emission angle of the optical signal, so as to achieve coupling with the modulator below.

2. The optical signal transmitter based on the thin film lithium niobate photonic integrated circuit vertical coupling platform according to claim 1, characterized in that: The modulator optical waveguide includes an inverse tapered mode converter, which includes a first wide portion for receiving an optical signal from a redirecting device, the first wide portion extending with a first narrow portion for redirecting the optical signal in the direction of optical signal transmission, and a coupling surface of the first narrow portion being parallel to the direction of optical signal transmission; the optical input end of the thin-film lithium niobate waveguide is a tapered waveguide matching the inverse tapered mode converter, the tapered waveguide includes a second narrow portion for receiving and redirecting the optical signal, the coupling surface of the second narrow portion is parallel to the coupling surface of the first narrow portion, and the second narrow portion extending with a second wide portion in the direction of optical signal transmission; the optical signal is coupled from the first narrow portion to the second narrow portion through an evanescent wave.

3. An optical signal transmitter based on a thin-film lithium niobate photonic integrated circuit vertical coupling platform according to claim 1 or 2, characterized in that: The light-emitting surface of the micro-prism comprises a focusing lens structure.

4. The optical signal transmitter based on the thin film lithium niobate photonic integrated circuit vertical coupling platform according to claim 1, characterized in that: An optical isolator is also included, and the optical isolator is disposed between the focusing lens and the collimating lens.

5. The optical signal transmitter based on the thin film lithium niobate photonic integrated circuit vertical coupling platform according to claim 3, characterized in that: The redirecting device is a parabolic lens or a 45-degree reflector or a polymer lens.

6. The optical signal transmitter based on the thin film lithium niobate photonic integrated circuit vertical coupling platform according to claim 3, characterized in that: The redirection device is a grating coupler, and the periodic structure of the grating coupler refracts the optical signal and couples it into the optical signal.

7. The optical signal transmitter based on the thin film lithium niobate photonic integrated circuit vertical coupling platform according to claim 1, characterized in that: The thermal expansion coefficient of the second substrate matches the thermal expansion coefficient of lithium niobate.

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