On-chip silicon-based photoconductive terahertz emitter and communication system between silicon-based optoelectronic chips

Abstract

An on-chip photoconductive terahertz wave emitter structurally comprises a silicon-based waveguide, a silicon-based waveguide mode converter and a photoconductive antenna. Based on an existing silicon-based waveguide platform, a photoconductive antenna is integrated on a silicon-based chip, and on-chip terahertz wave emission is achieved with extremely low power consumption. Wherein the on-chip waveguide platform and the mode converter provide strong light limiting capability, realize gathering of light field energy in a small range and are used for exciting the photoconductive antenna, and the photoconductive antenna adopts an extremely small slit working mode, so that emission of terahertz waves is ensured to be realized by low-power pulse laser and low-voltage control.

Description

Technical Field

[0001] The present invention relates to on-chip integration of terahertz emission devices, in particular to an on-chip silicon-based photoconductive terahertz emitter and a communication system between silicon-based optoelectronic chips. Background Art

[0002] As an indirect bandgap semiconductor, silicon has good transmittance and high refractive index in the near-infrared band. The near-infrared band is the main working wavelength of optical fiber communication. Therefore, silicon is suitable for use as a material for optical components such as optical waveguides and optical modulators. Thanks to the existing semiconductor industry, silicon-based optoelectronic devices have developed rapidly, and on-chip optical wave devices in the communication band are relatively mature. On-chip low-loss transmission and excellent light field control capabilities in the 1550nm communication band can already be achieved. Silicon-based optoelectronics is a technology with great potential. It combines the mature process of silicon materials with the powerful capabilities of optoelectronics, and is promoting the development of next-generation high-speed communications, data processing and sensing technologies. However, short-distance communication between silicon-based chips is often achieved through optical fiber and waveguide connections, which causes complex and high-cost systems. At the same time, this method cannot achieve free-space communication between chips.

[0003] The terahertz band (0.1-10THz) is located between microwaves and infrared light, and has unique characteristics such as strong penetration, low energy, high resolution, and wide bandwidth. It can penetrate non-conductive materials and is widely used in medicine, non-destructive testing, security inspection, spectral analysis and other fields, such as for detecting explosives, imaging cancer cells, and material defect detection. Terahertz waves have potential in high-speed communications and can achieve ultra-high-speed data transmission. However, they face technical challenges such as low efficiency of the emission source and detector, atmospheric absorption, and it is difficult to achieve small-scale integration of terahertz devices.

[0004] Common methods for generating terahertz waves include photoconductive antennas, quantum cascade lasers, and optical rectification. Photoconductive antennas are one of the commonly used pulsed terahertz radiation emission and detection devices in imaging applications. They consist of a metal antenna pattern made on a semiconductor substrate. Compared with other methods, photoconductive antennas have many significant advantages. They can generate terahertz radiation over a wide bandwidth and do not require a complex low-temperature environment, making them suitable for room temperature operation. At the same time, photoconductive antennas can generate terahertz pulses with high temporal resolution through ultrafast laser pulse excitation, which is suitable for precision applications such as time-domain spectroscopy and imaging. Compared with quantum cascade lasers and nonlinear optical rectification, photoconductive antennas have a relatively simple structure, strong stability, convenient operation, and easy integration.

[0005] From electron tubes to transistors to integrated circuits, and now to the integrated optical circuits, all of these demonstrate that people want to miniaturize various information processing devices. Combining silicon-based platforms with photoconductors can achieve on-chip integration of terahertz emitters, stimulate terahertz wave emission with low power, and further contribute to free-space communication between multiple silicon-based chips. Summary of the invention

[0006] In order to overcome the above-mentioned shortcomings of the prior art, the present invention provides an on-chip silicon-based photoconductive terahertz transmitter and a communication system between silicon-based optoelectronic chips, which realizes on-chip integration of terahertz transmitter devices by combining silicon-based light field control devices with photoconductive antennas. Terahertz wave emission is achieved by low-power pulsed laser injection.

[0007] The technical solution of the present invention is as follows:

[0008] The on-chip photoconductive terahertz transmitter proposed in the present invention comprises a silicon-based waveguide, a silicon-based waveguide mode converter and a photoconductive antenna, which together constitute a terahertz wave transmitter system by being integrated on a substrate.

[0009] Among them, the silicon-based waveguide can achieve low-loss transmission in the 1550nm band. It is a rectangular waveguide made using semiconductor technology, with a height of 220nm and a width of 500nm.

[0010] The silicon-based waveguide mode converter is connected to the silicon-based waveguide to convert the optical signal from the ordinary waveguide mode to the slit waveguide mode, thereby limiting the light field to a size of tens of nanometers to enhance the optical power per unit area. The mode converter adopts a structure combining a sub-wavelength grating structure and a tapered waveguide. By reasonably designing the period and duty cycle of the grating structure and optimizing the size of the tapered structure, efficient conversion from the ordinary waveguide mode to the slit waveguide mode can be achieved.

[0011] The photoconductive antenna is connected to the silicon-based waveguide mode converter and is composed of a semiconductor material and a metal antenna. The semiconductor material has good absorption characteristics for a wavelength of 1550nm and is used to generate carriers and generate photocurrent under light excitation. The metal antenna adopts a small gap structure, and the gap width expands as the light propagates to match the light field divergence and improve efficiency. The small gap photoconductive antenna can realize terahertz wave emission under low bias voltage control.

[0012] The specific implementation process is that 1550nm femtosecond pulse light is input from the silicon-based waveguide, and the optical power per unit area is increased through the mode converter. Then, the semiconductor material in the photoconductive antenna is stimulated by the photoconductive effect to generate carriers and generate photocurrent. After the laser pulse ends, due to the high degree of defects inside the material, the carriers will quickly recombine, causing the current density to decay exponentially. This photocurrent will stimulate the generation of electromagnetic radiation pulses. When the laser pulse duration is at the femtosecond level, the emission of terahertz waves can be achieved.

[0013] The present invention also provides a communication system between silicon-based optoelectronic chips, which is characterized in that it includes at least two silicon-based optoelectronic chips and the above-mentioned on-chip silicon-based photoconductive terahertz transmitter, wherein the transmitter is integrated on one of the silicon-based optoelectronic chips and is used to convert the output light into terahertz wave radiation as a communication signal between different silicon-based optoelectronic chips.

[0014] The beneficial effects of the technical solution provided by the present invention are:

[0015] 1. The structure of the present invention combining silicon-based devices and photoconductive antennas opens up a new way for the miniaturization of terahertz emission devices, and the device has high flexibility and scalability, which further promotes the large-scale application of terahertz photoconductive antennas.

[0016] 2. The silicon-based waveguide mode converter of the present invention adopts a structure that combines a subwavelength grating and a tapered waveguide to achieve efficient conversion of waveguide modes and focus the light field energy on a scale of tens of nm. At the same time, the subwavelength grating structure can effectively reduce the impact of backscattering in the conversion process on the silicon-based system.

[0017] 3. The present invention adopts an ultra-small gap photoconductive antenna structure, which can realize terahertz wave emission under a relatively small bias voltage with ultra-low power incident light excitation and has a relatively high conversion efficiency.

[0018] 4. The present invention can be combined with the existing silicon-based communication system to realize the terahertz wave emission of silicon-based chips, thereby further solving the free-space communication problem between silicon-based optoelectronic chips. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the combination of a silicon-based system and an on-chip silicon-based photoconductive terahertz emitter;

[0020] Figure 2 Schematic diagram of the planar structure of the on-chip silicon-based photoconductive terahertz emitter;

[0021] Figure 3 Schematic diagram of the three-dimensional structure of the on-chip silicon-based photoconductive terahertz emitter;

[0022] Figure 4is a transmittance curve of the waveguide mode converter;

[0023] Figure 5 Schematic diagram of the excitation process of on-chip silicon-based photoconductive terahertz emitter. DETAILED DESCRIPTION

[0024] The following is further described in conjunction with the accompanying drawings and specific embodiments, which are only used to introduce the present invention in more detail and specifically, and are not intended to limit the present invention in any form. After reading the present invention, the modification of various equivalent forms of the present invention by those skilled in the art all belongs to the scope limited by the appended claims of the present application.

[0025] 1. Design of on-chip silicon-based photoconductive terahertz emitter

[0026] An on-chip integrated photoconductive antenna terahertz transmitter is designed based on a silicon-based platform. The specific structure is as follows Figure 2 and Figure 3 As shown, a silicon-based waveguide, a silicon-based waveguide mode converter, and a photoconductive antenna are integrated on a substrate to form a terahertz wave transmitter system.

[0027] Silicon-based waveguide 1: As a transmission channel for optical signals, this embodiment adopts a rectangular waveguide structure with a width of 500nm and a height of 220nm, which can achieve low-loss transmission in the 1550nm band.

[0028] Silicon-based waveguide mode converter 2: used to convert optical signals from ordinary waveguide mode to slit waveguide mode to achieve local enhancement of the light field. The sub-wavelength grating and tapered waveguide are combined to achieve the transition of waveguide mode. Through the appropriate period, duty cycle and size of the tapered structure, efficient mode conversion at a distance of 4um is achieved, and the influence of backscattering on the silicon-based system during the mode conversion process can be suppressed.

[0029] Photoconductive antenna 3: It is composed of semiconductor materials and metal antennas. Semiconductor materials have high defects, which can shorten the carrier lifetime, increase the response speed and enhance the electric field, which helps to generate shorter terahertz pulses and wider frequency bands, and improve the emission efficiency of terahertz waves. At the same time, semiconductor materials should have good absorption characteristics for 1550nm wavelength to ensure the optical excitation of communication waveguides. The metal antenna adopts a small gap structure to improve the conversion efficiency, and can achieve high-efficiency emission of terahertz waves under low bias voltage and low excitation power. In order to match the divergence of the light field in the semiconductor material, the gap width expands as the light propagates.

[0030] 2. Generation of on-chip silicon-based photoconductive terahertz emitters

[0031] The 1550nm femtosecond pulse light is input from the silicon-based waveguide 1, and after passing through the silicon-based waveguide mode converter 2, the light field gradually transitions from the ordinary waveguide mode to the slit waveguide mode. The conical structure can effectively realize the transformation of the light field, while the subwavelength grating structure suppresses the diffraction of light in the cladding and reduces the transmission loss. Compared with the original conversion structure, it has a considerable conversion efficiency in a smaller occupied area and can effectively reduce the impact of backscattering on the original system during the mode conversion process. When the light field slowly transitions to the slit waveguide, due to the high refractive index contrast of the dielectric material and the continuity of the field, the electric field is concentrated in the slit, thereby effectively controlling the light on a smaller scale, realizing the field localization effect, and significantly enhancing the electric field strength.

[0032] Subsequently, the localized light field excites the semiconductor material in the photoconductive antenna to generate carriers through the photoconductive effect, thereby generating a photocurrent. After the laser pulse ends, due to the high degree of defects inside the material, the carriers quickly recombine, causing the current density to decay exponentially. This photocurrent will stimulate the generation of electromagnetic radiation pulses, and the emission of electromagnetic pulses is positively correlated with the intensity and change of the current.

[0033]

[0034] When the laser pulse duration is in the femtosecond range, terahertz wave emission can be achieved.

[0035] 3. Combination of on-chip silicon-based photoconductive terahertz emitters and silicon-based chips

[0036] Silicon-based optoelectronic chips have developed rapidly in recent years and have become one of the key technologies to promote optical communications, data centers, high-performance computing, and sensing. The core concept of silicon photonic chips is to integrate optical devices (such as light sources, modulators, detectors, etc.) on silicon-based chips, and process and transmit data through optical signals rather than electrical signals to achieve higher speeds and lower power consumption. However, short-distance silicon-based chip communications are often connected through optical fibers and waveguides, which is not only complex and costly, but also difficult to achieve long-distance inter-chip communication.

[0037] The on-chip silicon-based photoconductive terahertz emitter proposed in the present invention provides an effective solution to this problem. Figure 1 The silicon-based optoelectronic chip structure shown in the figure integrates the emitter on the silicon-based chip, and the output light generates terahertz wave radiation after passing through the on-chip silicon-based photoconductive terahertz emitter. This radiated terahertz wave can be used as a communication signal between different silicon-based chips to achieve high-speed, low-power chip-to-chip communication. This innovative design not only simplifies the connection between silicon-based chips, but also improves the communication speed and efficiency, providing a new solution for signal transmission between silicon-based optoelectronic chips.

Claims

1. An on-chip photoconductive terahertz emitter, characterized in that: include: Silicon-based waveguide, using a rectangular waveguide structure, is used to achieve low-loss transmission in the 1550nm band; A silicon-based waveguide mode converter, connected to the silicon-based waveguide, for converting an optical signal from a normal waveguide mode to a slit waveguide mode to achieve local enhancement of the optical field, wherein the mode converter adopts a structure combining a sub-wavelength grating and a tapered waveguide; The photoconductive antenna is connected to the silicon-based waveguide mode converter and includes a semiconductor material and a metal antenna. The semiconductor material has good absorption characteristics for a wavelength of 1550nm and is used to generate carriers and generate photocurrent under light excitation. The metal antenna adopts a small gap structure, and the gap width expands as the light propagates to match the light field divergence and improve efficiency.

2. The on-chip photoconductive terahertz emitter according to claim 1, characterized in that: The silicon-based waveguide mode converter realizes efficient conversion of the light field from a common waveguide mode to a slit waveguide mode by finding a suitable period and duty cycle as well as the size of the tapered structure.

3. The on-chip photoconductive terahertz emitter according to claim 1, characterized in that: The metal antenna realizes the emission of terahertz waves under the conditions of low bias voltage and low excitation power.

4. A communication system between silicon-based optoelectronic chips, characterized in that: The invention comprises at least two silicon-based optoelectronic chips and an on-chip silicon-based photoconductive terahertz emitter according to any one of claims 1 to 3, wherein the emitter is integrated on one of the silicon-based optoelectronic chips and is used for converting output light into terahertz wave radiation as a communication signal between different silicon-based optoelectronic chips.

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