CN118432724A - A method for integrating terahertz-free space optical transceiver - Google Patents

Abstract

The invention discloses a terahertz-free space optical transceiver integration method, which comprises (1) generating terahertz optical signals by a transmitting end and then generating terahertz electric signals by UTC-PD; (2) Dividing the modulated optical signal into two paths, wherein one path of signal is subjected to photoelectric conversion through UTC-PD, the other path of signal is pulled out, and parallel light is generated through a self-focusing rod to serve as light to be incident; (3) A material plate is arranged behind the UTC-PD, terahertz electric signals generated by the UTC-PD directly penetrate through the material plate, parallel light passing through a self-focusing rod is incident on the material plate, and the angle of the material plate is adjusted, so that the reflected light and the transmitted electric terahertz signals are on the same path.

Description

A terahertz-free space optical transceiver integration method

Technical Field

The present invention relates to the technical fields of Hertz communication, free space optical communication, terahertz optical reception and coherent detection, and in particular to a method for integrating a terahertz-free space optical transceiver.

Background technique

Free space optical communication (FSO) plays an important role in scenarios that require high-speed, high-bandwidth, reliable and secure communication, such as satellite-to-ground communication, satellite-to-satellite communication, wireless access network and other communication scenarios, due to its rich spectrum resources, no need for spectrum authorization, high spectrum efficiency, narrow beam angle, and low loss under good weather conditions. Especially in point-to-point communication, the narrow beam angle of FSO makes it almost unaffected by multipath effects, greatly reducing the complexity of the DSP carrier recovery algorithm at the receiving end. However, weather conditions such as rain, fog, and clouds in the atmosphere will affect the transmission performance of FSO, resulting in signal attenuation and transmission interruption. The transmission distance of FSO is limited by the ability of light wave propagation and atmospheric absorption. At the same time, it needs to align the visible path between the transmitter and the receiver, requiring high directional accuracy and alignment process. In addition, light waves transmitted in the air are easily interfered by factors such as atmospheric turbulence, dust, and vibration in the environment, which will affect the transmission quality and stability of FSO signals. In comparison, terahertz waves (THz) have strong penetration capabilities, rich spectrum resources, and ultra-wideband advantages, and can achieve reliable transmission in harsh environments. However, in order to overcome signal attenuation and environmental interference, terahertz communication usually requires higher transmission power and is easily affected by multipath effects and signal fading, resulting in large changes in the transmission channel. Therefore, if terahertz electrical signals and free-space optical signals are fused and transmitted, the respective advantages of FSO and THz transmission can be combined to achieve high-speed broadband communication in all environments. The FSO/THz transceiver integrated system will provide greater broadband wireless transmission capacity, meet the growing demand for high-speed data, and provide key solutions for the next generation of wireless networks beyond 5G.

At present, relevant researchers have made progress in the combined transmission of terahertz and FSO. In the study [Wang K, Yu J, Wei Y, et al. Delivery of 1.196-Tb/s signal over 800M789 based on RF/FSO convergence [C] // 45th European Conference on Optical Communication (ECOC 2019). IET, 2019: 1-4.], a RF/FSO hybrid fusion system was reported. The system consists of two FSO links and two RF links, supporting a transmission rate of 1.196-Tb/s. The literature [Singya PK, Makki B, D’Errico A, et al. Hybrid FSO/THz-based backhaul network for mmWave terrestrial communication [J]. IEEE Transactions on Wireless Communications, 2022.] adopts a hybrid backhaul dual-hop network based on FSO/THz to provide high data transmission rates to the ground through millimeter wave access links. In the literature [Sharma S, Madhukumar A S. On the Performance of Hybrid THz/FSO system[J]. IEEE Communications Letters, 2023.], a hybrid terahertz/free space optical system is proposed, in which data is transmitted simultaneously on two links and combined at the destination using maximum ratio combining (MRC). The results show that the performance of the hybrid system is significantly improved under severe weather conditions. In the literature [Sharma S, Madhukumar A S. On the Performanceof Hybrid THz/FSO system[J]. IEEE Communications Letters, 2023.], a hybrid FSO/RF terahertz (THz) relay system is designed, which selects forward decoding relay, considers FSO/RF hybrid communication based on adaptive combining scheme before the relay node, and uses THz link to access users after the relay node.

Although the above research combines terahertz and free-space optical communications, the existing methods either connect terahertz and FSO links in series for data transmission, or require two independent FSO and THz devices to achieve parallel transmission functions. The transmitters of the mentioned parallel transmission systems are separate and independent. If the hardware of terahertz and FSO can be integrated and shared, the complexity and weight of the transmitter will be greatly reduced. Therefore, this scheme proposes a fusion transmission method that allows THz and FSO to share a transmitter to achieve high-speed broadband communication in all environments. It can effectively expand the next-generation wireless network architecture and obtain greater broadband wireless transmission capacity under various environmental conditions.

Summary of the invention

Based on the technical problems existing in the background technology, the present invention proposes a terahertz-free space optical transceiver integration method.

In order to achieve the above object, the present invention adopts the following technical solution:

A method for integrating a terahertz-free space optical transceiver comprises the following steps: (1) after a terahertz optical signal is generated at a transmitting end, a UTC-PD is used to generate a terahertz electrical signal; (2) the modulated optical signal is divided into two paths, one of which is photoelectrically converted by the UTC-PD, and the other is pulled out and parallel light is generated by a self-focusing rod as the incident light; (3) a material plate is arranged behind the UTC-PD, the terahertz electrical signal generated by the UTC-PD directly passes through the material plate, and the parallel light passing through the self-focusing rod is incident on the material plate, and the material plate is adjusted to The angle of the reflected light and the transmitted electrical terahertz signal is in the same path. The material, size, thickness and other factors of the material plate need to be considered; (4): After the THz/FSO fusion signal is generated, it passes through a lens and is then transmitted by a wireless channel. At the receiving end, the terahertz electrical signal and the optical signal are received simultaneously by independent receivers; (5): The signal is sampled using an oscilloscope (OSC); (6): The sampled signal is sent to the DSP module for offline digital signal processing. For different signals, the corresponding carrier recovery algorithm is used for signal recovery; (7): The SNR and BER are calculated to evaluate the performance of the solution.

Preferably, step (1) adopts a terahertz and free space optical fusion transmission mode, and THz and FSO share a transmitter.

Preferably, the material plate used in step (3) includes but is not limited to PMMA, PP or other materials that are transparent to electrical and optical terahertz and can reflect light, and need to reflect 10% of the energy.

Preferably, in step (1), photon-assisted terahertz signal generation, electronic devices directly generating terahertz signals or terahertz quantum cascade lasers are used.

Preferably, it is applicable to a variety of communication systems, including but not limited to photon-assisted millimeter-wave terahertz systems, polarization-multiplexed coherent transmission systems, direct modulation and direct detection systems, and is applicable to various signal formats, including but not limited to QPSK, 16QAM, high-order QAM signals, PAM signals, OFDM and DMT signals.

Preferably, the idea of fusion transmission is applicable to various polarization forms, including but not limited to single polarization transmission and dual polarization transmission.

Preferably, the terahertz electrical signal and the optical signal at the transmitting end are fused and generated, and the terahertz electrical signal and the optical signal at the receiving end are received simultaneously by an independent receiver, the optical terahertz receiver is aligned with the transmitter, and the electrical terahertz receiver is arranged within 1 meter of the optical receiver.

Preferably, the optical terahertz signal is amplified by an erbium-doped fiber amplifier (EDFA) and sent to an integrated coherent receiver (ICR), where a local oscillator LO signal is used for homodyne detection, and finally the signal is captured by an oscilloscope (OSC) and then processed offline by DSP.

Preferably, the electrical terahertz signal is first focused by a lens and then received by a terahertz antenna; the signal is first enhanced using a low noise amplifier (LNA), and then a local oscillator (LO) drives a mixer to achieve down-conversion, after amplification by an electrical amplifier (EA), the signal is captured by an oscilloscope (OSC), and then offline DSP processing is performed.

Preferably, the carrier recovery algorithm in DSP includes but is not limited to clock recovery algorithm, dispersion compensation algorithm, CMA/CMMA equalization algorithm, frequency offset compensation algorithm (FOE), phase offset compensation algorithm (CPE), DDLMS blind equalization algorithm, MIMO-VLNE algorithm, and the algorithm parameters can be specifically selected according to different systems, different channel characteristics, different transmission indicators and other specific circumstances.

Compared with the prior art, the present invention has the following beneficial effects:

Compared with traditional terahertz or FSO transmission systems, the present invention adopts a THz and FSO shared transmitter mode to realize the fusion transmission of THz and FSO, reduce the complexity and weight of the transmitter, increase the transmission distance and bandwidth, greatly broaden the physical architecture of future optical and terahertz communications, and bring more possibilities for high-speed broadband long-distance communications in all environments. In summary, the FSO/THz transceiver integrated system designed in this solution will provide greater broadband wireless transmission capacity, meet the growing demand for high-speed data, and provide key technical support for the next generation of wireless networks beyond 5G.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows the system architecture of the integrated terahertz and FSO fusion transmission transceiver solution

Detailed ways

In order to make the purpose, technical solution and beneficial effects of the present invention more clearly understood, the technical solution of the present invention is further described below in conjunction with embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

Example

In this embodiment, a terahertz-free space optical transceiver integration method is proposed, including the following steps: (1): after the transmitting end generates a terahertz optical signal, a UTC-PD is used to generate a terahertz electrical signal; (2): the modulated optical signal is divided into two paths, one of which is photoelectrically converted by the UTC-PD, and the other is pulled out and parallel light is generated through a self-focusing rod as the incident light; (3): a material plate is set after the UTC-PD, and the terahertz electrical signal generated by the UTC-PD directly passes through the material plate, and the parallel light passing through the self-focusing rod is incident on the material plate, and the terahertz electrical signal generated by the UTC-PD is directly transmitted through the material plate, and the parallel light passing through the self-focusing rod is incident on the material plate, and the terahertz electrical signal generated by the UTC-PD is directly transmitted through the material plate, and the parallel light passing through the self-focusing rod is incident on the material plate, and the terahertz electrical signal generated by the UTC-PD is directly transmitted through the material plate, and the parallel light passing through the self-focusing rod is incident on the material plate, and the terahertz electrical signal generated by the UTC-PD is directly transmitted through the UTC-PD ... The angle of the material plate is adjusted so that the reflected light and the transmitted electrical terahertz signal are on the same path. Factors such as the material, size, and thickness of the material plate need to be considered; (4): After the THz/FSO fusion signal is generated, it passes through a lens and is then transmitted through a wireless channel. At the receiving end, the terahertz electrical signal and the optical signal are received simultaneously by independent receivers; (5): The signal is sampled using an oscilloscope (OSC); (6): The sampled signal is sent to the DSP module for offline digital signal processing. For different signals, the corresponding carrier recovery algorithm is used for signal recovery; (7): SNR and BER are calculated to evaluate the performance of the solution;

The modulated signal is divided into two paths, and a material plate is designed behind the UTC-PD. One path of light passes through the UTC-PD to generate a terahertz electrical signal and passes through the material plate; the other path of light is connected to a self-focusing rod to generate parallel light, which is reflected by the material plate so that it is transmitted on the same path as the electrical terahertz signal, thereby realizing the integrated transmission of terahertz electrical and optical signals.

Photodetectors are important devices for generating terahertz signals. For terahertz transmission systems above 300 GHz, high output power can be obtained in the terahertz range only if they have high response, high saturation output power and wide bandwidth response. Single-line carrier photodiodes (UTC-PDs) can meet these key requirements. The electron transmission time in their depletion layer is short and the space charge effect is low, which can provide high bandwidth response for UTC devices. Therefore, this design uses UTC-PDs to generate terahertz electrical signals. The integration of UTC-PDs and resonant antennas can further improve the radiation output power and bandwidth, so this design also includes this integrated structure.

After the terahertz optical signal is generated, it is considered to be divided into two paths, one of which is converted into photoelectricity by UTC-PD, and the other is pulled out and generates parallel light through a self-focusing rod as the incident light; the key to this design is to set a material plate behind the UTC-PD, and the terahertz electrical signal generated by the UTC-PD directly passes through the material plate, and the parallel light passing through the self-focusing rod is incident on the material plate at the same time. By adjusting the angle of the material plate, the reflected light and the terahertz electrical signal are on the same path, completing the fusion transmission of the THz/FSO shared transmitter. Therefore, the material plate needs to meet the following conditions: first, it is required to be transparent to the electrical terahertz signal; second, it is required to be able to reflect the optical signal. The ideal state is total reflection, but in reality, as long as 10% of the light is reflected, a good amplification effect can be achieved; polypropylene (Polypropylene, PP) or polymethyl methacrylate (Polymethyl methacrylate) is considered. methacrylate, PMMA) is used as the material of the material board; PP is a non-polar plastic with the advantages of light weight, high strength, good heat resistance, etc., and is easy to process and manufacture; PMMA is a high molecular polymer, that is, organic glass, which has the characteristics of good light transmittance and strong weather resistance; these two plastics have good transmission performance in the terahertz frequency band, are wear-resistant and have low processing costs, so they can be used in this system; experimental tests show that the loss of 428.4GHz terahertz signal penetrating 5mm thick PP board is less than 1dB, which is almost transparent to terahertz signals and can reflect light; 428.4GHz terahertz signal penetrates 5mm thick PP board The loss through a 5mm thick PMMA board is about 13dB. Light reflection can also occur, and because the surface of PMMA has good mirror reflection characteristics, the reflection performance of PMMA is better than that of PP, and the reflected light intensity is greater; the specific reflection ratio depends on factors such as the incident angle, surface conditions, material thickness and refractive index; which material to use should depend on the specific situation; after the optical terahertz signal is generated at the transmitting end, the signal is divided into two paths. One signal uses a tunable optical attenuator (ATT) to adjust the signal power entering the UTC-PD. The terahertz electrical signal will be generated in the UTC-PD at a beat frequency and transmitted through the integrated butterfly antenna. The terahertz signal is transmitted along a line, and the other signal generates parallel light through the self-focusing rod and is incident on the material plate. By adjusting the angle of the material plate, the reflected light and the other transmitted light are on the same path, and then a lens is used to converge the terahertz signal and the FSO beam; at the receiving end, the terahertz electrical signal and the optical signal are received simultaneously by independent receivers; the optical terahertz receiver is aligned with the transmitter, and the electrical terahertz receiver is set within 1 meter of the optical receiver. The received optical terahertz signal is amplified by an erbium-doped fiber amplifier (EDFA) and sent to an integrated coherent receiver (ICR). A local oscillator LO signal is used for homodyne detection, and finally an oscilloscope is used to detect the terahertz signal. (OSC) captures the signal and then performs offline DSP processing; the electrical terahertz signal is first focused by a lens and then received by a terahertz antenna; the signal is first enhanced by a low noise amplifier (LNA), and then the mixer is driven by a local oscillator (LO) to achieve down-conversion. After amplification by an electrical amplifier (EA), the signal is captured by an oscilloscope (OSC) and then processed by offline DSP; it mainly includes digital down-conversion, clock recovery algorithm, dispersion compensation algorithm, CMA/CMMA equalization algorithm, frequency offset compensation algorithm (FOE), phase offset compensation algorithm (CPE), DDLMS blind equalization algorithm, MIMO-VLNE algorithm, etc.

Step (1) adopts the fusion transmission mode of terahertz and free space optical. THz and FSO share the transmitter, which can reduce the system complexity, improve the wireless communication capacity, and is suitable for transmission in all environments.

The material plate used in step (3) includes but is not limited to PMMA, PP or other materials that are transparent to electrical and optical terahertz and can reflect light, and need to reflect 10% of the energy.

In step (1), photons are used to assist in generating terahertz signals, electronic devices are used to directly generate terahertz signals, or terahertz quantum cascade lasers are used.

It is applicable to a variety of communication systems, including but not limited to photon-assisted millimeter-wave terahertz systems, polarization-multiplexed coherent transmission systems, direct modulation and direct detection systems, and is applicable to various signal formats, including but not limited to QPSK, 16QAM, high-order QAM signals, PAM signals, OFDM and DMT signals.

The idea of fusion transmission is applicable to various polarization forms, including but not limited to single polarization transmission and dual polarization transmission.

The terahertz electrical signal and optical signal are fused and generated at the transmitting end, and the terahertz electrical signal and optical signal are received simultaneously by an independent receiver at the receiving end. The optical terahertz receiver is aimed at the transmitter, and the electrical terahertz receiver is set within 1 meter to the left and right of the optical receiver.

The optical terahertz signal is amplified by an erbium-doped fiber amplifier (EDFA) and sent to an integrated coherent receiver (ICR). A local oscillator (LO) signal is used for homodyne detection. Finally, an oscilloscope (OSC) is used to capture the signal and then perform offline DSP processing.

The electrical terahertz signal is first focused by a lens and then received by a terahertz antenna; the signal is first enhanced using a low-noise amplifier (LNA), and then down-converted using a local oscillator (LO) to drive a mixer. After being amplified by an electrical amplifier (EA), the signal is captured by an oscilloscope (OSC) and then processed offline by DSP.

The carrier recovery algorithm in DSP includes but is not limited to clock recovery algorithm, dispersion compensation algorithm, CMA/CMMA equalization algorithm, frequency offset compensation algorithm (FOE), phase offset compensation algorithm (CPE), DDLMS blind equalization algorithm, MIMO-VLNE algorithm. The algorithm parameters can be selected according to different systems, different channel characteristics, different transmission indicators and other specific conditions.

Before down-conversion, a low noise amplifier (LNA) can be used to enhance the signal, and then a local oscillator (LO) can be used to drive the mixer to achieve down-conversion. The signal can then be amplified as needed, and finally an oscilloscope (OSC) can be used to capture the signal, and then offline DSP processing can be performed. UTC-PD: Single Line Carrier Photodiode;

OC: Optical Coupler;

ATT: Tunable Optical Attenuator;

Lens: lens;

HA: Horn antenna;

LNA: low noise amplifier;

LO: Local Oscillator;

Mixer: mixer;

EA: electrical amplifier;

ICR: Integrated Coherent Receiver;

OSC: oscilloscope;

DSP: Digital Signal Processing.

The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims (10)

1. A method for integrating a terahertz-free space optical transceiver, characterized in that it comprises the following steps: (1): After the transmitter generates a terahertz optical signal, the UTC-PD is used to generate a terahertz electrical signal; (2): The modulated optical signal is divided into two paths, one of which is converted into photoelectric signals by UTC-PD, and the other is pulled out and generates parallel light through a self-focusing rod as the incident light; (3): A material plate is set behind the UTC-PD. The terahertz electrical signal generated by the UTC-PD directly passes through the material plate. At the same time, the parallel light passing through the self-focusing rod is incident on the material plate. By adjusting the angle of the material plate, the reflected light and the transmitted electrical terahertz signal are on the same path; (4): After the THz/FSO fusion signal is generated, it passes through a lens and is then transmitted through a wireless channel. At the receiving end, the terahertz electrical signal and the optical signal are received simultaneously by independent receivers; (5): Use an oscilloscope (OSC) to sample the signal; (6): The sampled signal is sent to the DSP module for offline digital signal processing. For different signals, the corresponding carrier recovery algorithm is used to recover the signal; (7): Calculate SNR and BER to evaluate the performance of the solution. 2. A terahertz-free space optical transceiver integration method according to claim 1, characterized in that step (1) adopts a terahertz and free space optical fusion transmission mode, and THz and FSO share a transmitter. 3. A terahertz-free space optical transceiver integration method according to claim 1, characterized in that the material plate used in step (3) includes PMMA, PP or a material that is transparent to electrical and optical terahertz and can reflect light, and needs to reflect 10% of the energy. 4. The method for integrating a terahertz-free space optical transceiver according to claim 1, characterized in that in step (1), a photon-assisted terahertz signal is generated, an electronic device directly generates a terahertz signal, or a terahertz quantum cascade laser is used. 5. According to claim 1, a terahertz-free space optical transceiver integration method is characterized in that it is applicable to a variety of communication systems including photon-assisted millimeter wave terahertz systems, polarization multiplexed coherent transmission systems, direct modulation and direct detection systems, and is applicable to signal formats including QPSK, 16QAM, high-order QAM signals, PAM signals, OFDM and DMT signals. 6. A terahertz-free space optical transceiver integration method according to claim 1, characterized in that the idea of fusion transmission is applicable to polarization forms, including single polarization transmission and dual polarization direction transmission. 7. A terahertz-free space optical transceiver integration method according to claim 1, characterized in that the terahertz electrical signal and the optical signal at the transmitting end are fused and generated, the terahertz electrical signal and the optical signal at the receiving end are received simultaneously by an independent receiver, the optical terahertz receiver is aligned with the transmitter, and the electrical terahertz receiver is set within a range of about 1 meter of the optical receiver. 8. The method of integrating terahertz and free-space optical transceiver according to claim 1 is characterized in that the optical terahertz signal is amplified by an erbium-doped fiber amplifier (EDFA) and then sent to an integrated coherent receiver (ICR), a local oscillator LO signal is used for homodyne detection, and finally an oscilloscope (OSC) is used to capture the signal, and then offline DSP processing is performed. 9. A terahertz-free space optical transceiver integration method according to claim 1, characterized in that the electrical terahertz signal is first focused by a lens and then received by a terahertz antenna; a low noise amplifier (LNA) is first used to enhance the signal, and then a local oscillator (LO) is used to drive the mixer to achieve down-conversion, after amplification by an electrical amplifier (EA), the signal is captured by an oscilloscope (OSC), and then offline DSP processing is performed. 10. A terahertz-free space optical transceiver integration method according to claim 1, characterized in that the carrier recovery algorithm in the DSP includes a clock recovery algorithm, a dispersion compensation algorithm, a CMA/CMMA equalization algorithm, a frequency offset compensation algorithm (FOE), a phase offset compensation algorithm (CPE), a DDLMS blind equalization algorithm, and a MIMO-VLNE algorithm, and the algorithm parameters are selected according to different systems, different channel characteristics, and different transmission indicators.