WO2021243886A1 - Photo-generated terahertz-over-fiber passive optical network system and transmission method - Google Patents

Abstract

Embodiments of the present invention relate to the technical field of optical communications. Disclosed are a photo-generated terahertz-over-fiber passive optical network system and a transmission method. The present invention comprises: an optical line terminal, feed-in optical fibers, a remote node, distributed optical fibers, and optical network units. At the optical line terminal, a comb-shaped spectrum generator driven by a radio frequency signal generator generates a group of optical phase-coherent multi-wavelength optical carriers, which are divided into three parts by an optical splitter, wherein one of the three parts is used as a data optical carrier, and the other two are used as optical heterodyne beating optical carriers. The three optical carriers are transmitted to the remote node by means of their respective feed-in optical fibers, and the remote node is connected to the individual optical network units by means of the distributed optical fibers. The present invention achieves the transmission purposes of flexible point-to-multipoint configuration with carrier frequencies of above several hundred GHz and bi-directional receiving and transmission.

Description

Photo-generated light-carrying terahertz passive optical network system and transmission method Technical field

The present invention relates to the field of optical communication technology, and in particular to a passive optical network system and transmission method of a light-generated light-carrying terahertz passive optical network.

Background technique

As the demand for mobile data traffic has exploded, low-frequency spectrum resources have become increasingly scarce, and the bandwidth limitations of millimeter-wave wireless communications have become more and more obvious. The carrier frequency of wireless communications has begun to develop towards the THz frequency band, which generally refers to the THz frequency band. Electromagnetic waves with a frequency range of 0.1 to 10 THz are 1 to 4 orders of magnitude higher than the microwave frequency band, and the amount of information transmitted has a significant increase in the order of magnitude, and can even provide a transmission rate comparable to optical fiber. Combined with high-level coding modulation technology and multi-dimensional multiplexing mechanism, it can further increase the transmission capacity of wireless communication and meet the communication requirements of large-capacity transmission scenarios. It is of great significance to the goal of'communications full spectrum' in the post 5G and 6G era.

At present, the terahertz wireless communication system is mainly based on microwave frequency multiplication. The baseband signal is modulated in the low-frequency microwave band, and the THz wave is generated through a frequency multiplier or combined with harmonic mixing, and then radiated through an antenna through a power amplifier. . Although this method has a simple transmitter structure and easy integration of devices, it is limited by the development of silicon-based integration technology of indium phosphide and gallium arsenide materials, and the realization of high-speed communication systems above 100Gbit/s in higher frequency bands still faces Technical challenges. At present, the highest THz carrier generated by the frequency doubling method is 625 GHz. This method is difficult to implement, and the cost is high. It requires up and down conversion and multiple modulation mixing techniques; the conversion loss of electronic devices makes the transmission and reception power lower, so The transmission rate is not high, and the transmission system is complicated and costly.

Using optical carrier radio frequency technology, the laser generates two or more optical carrier beams, and modulates the baseband signal to a beam of optical carrier through an optical modulator. The photoelectric conversion function of the single-line carrier photodetector (UTC-PD) is used to convert Two beams of optical carriers generate THz signals at heterodyne beat frequencies. This method combines the advantages of optical fiber communication and wireless communication. Compared with traditional microwave-based frequency doubling technology, it has the following advantages: THz signal generation technology based on optical heterodyne beat frequency mechanism , With the help of UTC-PD, by increasing the wavelength interval of the two optical carriers, it is easier to realize a high carrier frequency THz communication system; using various high-order modulation formats and various multiplexing mechanisms can effectively improve the spectrum utilization rate and achieve The high transmission rate makes it easier to implement a large-capacity THz communication system; it is easier to achieve seamless integration with the optical access network represented by the passive optical network PON. A seamless bridge is achieved between them, providing end users with ultra-fast access rates and a smooth and stable wireless access experience.

The most researched before is the microwave passive optical network (RoF-PON) system, which uses the "photo-generated microwave" technology. Since the microwave carrier frequency is basically below 100GHz, it participates in the data optical carrier and oscillating light wave of the optical heterodyne beat frequency. They are basically all in the same wavelength channel, so the design of the RoF-PON system is relatively simple and straightforward, and it is not suitable for ToF-PON systems with carrier frequencies above 275GHz. ToF-PON) system, the bandwidth of the terahertz wave is higher, the data optical carrier and the beat frequency optical carrier cannot be transmitted in the same wavelength channel, so the present invention puts the beat frequency optical carrier and the data optical carrier in the two wavelength channels separately Transmission, and then generate a terahertz wave at the beat frequency of the remote antenna unit (single-line carrier photodetector UTC-PD) of the optical network unit. Optical-borne terahertz passive optical network systems and transmission methods have become a promising research direction in the future, but so far, there is still a lack of feasible solutions and limited to microwave and millimeter waves.

Summary of the invention

The present invention provides a light-borne optical terahertz passive optical network system and transmission method, which realizes the point-to-multipoint flexible configuration of terahertz waves with carrier frequencies above several hundred GHz and the transmission purpose of two-way transceiving; and Two mechanisms for generating terahertz waves are introduced. Among them, the terahertz wave generated based on the double heterodyne beat frequency mechanism has greater amplitude intensity. When the data optical carrier is beaten with the two beat frequency optical carriers, the two terahertz waves are generated. When the phase of the wave is the same, the wireless transmission distance of the terahertz signal can be increased.

To achieve the foregoing objective, the embodiments of the present invention adopt the following technical solutions:

In the first aspect, a photo-generated optically carried terahertz passive optical network system is provided, which includes: an optical line terminal (1), three feed-in optical fibers (15), a remote node (16), and N distributed optical fibers (18) ) And N optical network units (19), where N is a positive integer; the optical line terminal (1) is connected to the remote node (16) through three feed-in optical fibers (15); the optical network unit (19) is distributed The optical fiber (18) is connected to the remote node (16), and one distributed optical fiber (18) corresponds to an optical network unit (19).

Specifically, the optical line terminal (1) includes: a first radio frequency signal generator (2), a comb spectrum generator (3), a first erbium-doped fiber amplifier (4), and a first optical splitter (5) , Multi-channel downstream optical transceiver module, first band pass filter (13) and second band pass filter (14); among them, the first radio frequency signal generator (2) and comb spectrum generator (3) input ports Connect, the output port of the comb spectrum generator (3) is connected with the first erbium-doped fiber amplifier (4), and the first erbium-doped fiber amplifier (4) is connected with the first optical splitter (5); the first optical splitter The output port of the device (5) is divided into three, one of which inputs multiple downstream optical transceiver modules, and the other two are respectively connected to the first band pass filter (13) and the second band pass filter (14). The multi-channel downstream optical transceiver module includes: a first 1×N arrayed waveguide grating (6), an N-channel downstream optical transceiver sub-module, and a second N×1 arrayed waveguide grating (12); wherein, the first optical branch The output port of the device (5) is divided into three channels, one is connected to the left port of the first 1×N arrayed waveguide grating (6), and the right N ports of the first 1×N arrayed waveguide grating (6) are connected to the The input port of the downstream optical transceiver submodule on the N road is connected, and the output port of the downstream optical transceiver submodule on the N road is connected with the left input port of the second N×1 arrayed waveguide grating (12).

Further, the uplink and downlink optical transceiver sub-modules include: a downlink data generator (7), a Mach-Zehnder modulator (8), a receiver (9), an optical power detector (10) and a first optical circulator (11); Among them, the output port of the first 1×N arrayed waveguide grating (6) is connected to the input port of the Mach-Zehnder modulator (8), and the output port of the downstream data generator (7) is connected to the Mach-Zehnder modulator (8) is connected to the radio frequency input port, the output port of the Mach-Zehnder modulator (8) is connected to the first port of the first optical circulator (11); the second port of the first optical circulator (11) is connected to the second N ×1 The corresponding input port of the arrayed waveguide grating (12) is connected, the third port of the first optical circulator (11) is connected to the input port of the upstream optical power detector (10), and the output of the upstream optical power detector (10) The port is connected with the input port of the uplink receiver (9).

Specifically, the remote node (16) is the third N×N cyclic arrayed waveguide grating (17); the optical line terminal (1) passes through three feed-in fibers (15) and the third N×N cyclic arrayed waveguide grating (17) ) The left port is connected, and the right port of the third N×N cyclic arrayed waveguide grating (17) is respectively connected with N distributed optical fibers (18) to N optical network units (19).

Specifically, the components of each optical network unit (19) include: a second optical circulator (20), a second erbium-doped fiber amplifier (21), a third optical circulator (22), and a first Bragg grating filter (23), third optical combiner (24), second optical splitter (25), single-line carrier photodetector (26), horn antenna (27), mixer (28), second RF signal generator (29), amplifier (30), phase modulator (31), fourth optical circulator (32) and second Bragg grating filter (33); among them, the corresponding distribution of the optical network unit (19) The optical fiber (18) is connected to the second port of the second optical circulator (20) in the optical network unit (19), and the third port of the second optical circulator (20) is connected to the second erbium-doped fiber amplifier (21). ) Is connected to the input port, the output port of the second erbium-doped fiber amplifier (21) is connected to the first port of the third optical circulator (22), and the second port of the third optical circulator (22) is connected to the first Bragg grating The input port of the filter (23) is connected, the third port of the third optical circulator (22) is connected to the input port of the third optical combiner (24), and the output port of the first Bragg grating filter (23) is connected to the The input port of the two optical splitter (25) is connected; the output port of the second optical splitter (25) outputs two channels, one of which is connected to the input port of the third optical combiner (24), and the other is connected to the phase modulator The input port of (31) is connected; the output port of the third optical combiner (24) is connected to a single-line carrier photodetector (26).

Further, the output port of the horn antenna (27) is connected to the port of the mixer (28), the second radio frequency signal generator (29) is connected to the input port of the mixer (28), and the frequency of the mixer (28) is The output port is connected to the input port of the amplifier (30), the output port of the amplifier (30) is connected to the modulation control port of the phase modulator (31), and the output port of the phase modulator (31) is connected to the fourth optical circulator (32). The first port is connected, the second port of the fourth optical circulator (32) is connected to the port of the second Bragg grating filter (33), and the third port of the fourth optical circulator (32) is connected to the second optical circulator ( 20) The first port connection.

In a second aspect, a transmission method for an optically generated optically carried terahertz passive optical network system is provided. According to the generated optical phase-coherent multi-wavelength optical carrier, a three-way optical carrier group is obtained, and the three-way optical carrier group is fed through The incoming optical fiber (15) is transmitted to the remote node (16); the remote node (16) is connected to the optical network unit (19) through the distributed optical fiber (18), and the optical heterodyne beat mechanism is used in the optical network unit (19) The terahertz wave is generated and transmitted downstream to the user terminal; the optical network unit (19) receives the terahertz wave generated by the user terminal and transmits it to the optical line terminal (1) through the remote node (16).

Specifically, the mechanism for generating terahertz waves by the optical heterodyne beat mechanism includes: a single heterodyne beat mechanism and a double heterodyne beat mechanism.

The optically generated optically carried terahertz passive optical network system and transmission method provided by the embodiments of the present invention realize the purpose of flexible point-to-multipoint configuration and two-way transmission and reception of terahertz waves with carrier frequencies above several hundred GHz; and The mechanism of generating terahertz waves, in which the terahertz wave generated based on the double heterodyne beat frequency mechanism has a greater amplitude intensity. When the data optical carrier is beaten with the two beat frequency optical carriers, the two terahertz waves generated are relative to each other. When the bits are the same, the wireless transmission distance of the terahertz signal can be increased.

Description of the drawings

In order to more clearly describe the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings needed in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative work, other drawings can be obtained from these drawings.

FIG. 1 is a schematic diagram of the structure of a photo-generated light-carrying passive optical network system provided by an embodiment of the present invention;

2 is a system structure and transmission mode based on single heterodyne beat frequency technology provided by an embodiment of the present invention;

Fig. 3 is a system structure and transmission mode based on double heterodyne beat frequency technology provided by an embodiment of the present invention;

The symbols in the drawings respectively indicate: line terminal OLT (1), first radio frequency signal generator (2), comb spectrum generator (3), first erbium-doped fiber amplifier EDFA (4), first optical splitter Router OS (5), first 1×N arrayed waveguide grating (6), downstream data generator (7), Mach-Zehnder modulator MZM (8), receiver RX (9), optical power detector US- PD (10), first optical circulator (11), second N×1 arrayed waveguide grating (12), first band pass filter BPF (13), second band pass filter BPF (14), feed Optical fiber (15), remote node RN (16), third N×N cyclic arrayed waveguide grating (17), distributed optical fiber (18), optical network unit ONU (19), second optical circulator (20) , The second erbium-doped fiber amplifier (21), the third optical circulator (22), the first Bragg grating filter (23), the third optical combiner (24), the second optical splitter (25), single line Carrier photodetector (26), horn antenna (27), mixer (28), second RF signal generator (29), amplifier (30), phase modulator (31), fourth optical circulator (32), the second Bragg grating filter (33), the fifth optical circulator (34), and the third Bragg grating filter (35).

detailed description

In order to enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Hereinafter, embodiments of the present invention will be described in detail, and examples of the embodiments are shown in the accompanying drawings, in which the same or similar reference numerals indicate the same or similar elements or elements with the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary, and are only used to explain the present invention, and cannot be construed as limiting the present invention. Those skilled in the art can understand that, unless specifically stated otherwise, the singular forms "a", "an", "said" and "the" used herein may also include plural forms. It should be further understood that the term "comprising" used in the specification of the present invention refers to the presence of the described features, integers, steps, operations, elements and/or components, but does not exclude the presence or addition of one or more other features, Integers, steps, operations, elements, components, and/or groups of them. It should be understood that when we refer to an element as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element, or intervening elements may also be present. In addition, "connected" or "coupled" as used herein may include wireless connection or coupling. The term "and/or" as used herein includes any unit and all combinations of one or more of the associated listed items. Those skilled in the art can understand that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meanings as those commonly understood by those of ordinary skill in the art to which the present invention belongs. It should also be understood that terms such as those defined in general dictionaries should be understood to have a meaning consistent with the meaning in the context of the prior art, and unless defined as here, they will not be used in idealized or overly formal meanings. explain.

The photo-generated optically carried terahertz passive optical network system provided by the embodiment of the present invention, as shown in FIG. 1, specifically includes:

An optical line terminal (1), three feed-in optical fibers (15), a remote node (16), N distributed optical fibers (18) and N optical network units (19), where N is a positive integer.

The optical line terminal (1) is connected with the remote node (16) through three feed-in optical fibers (15).

The optical network unit (19) is connected to the remote node (16) through a distributed optical fiber (18), wherein one distributed optical fiber (18) corresponds to an optical network unit (19).

In this embodiment, the optical line terminal (1) includes: a first radio frequency signal generator (2), a comb spectrum generator (3), a first erbium-doped fiber amplifier (4), and a first optical splitter ( 5) Multi-channel downstream optical transceiver module, first band pass filter (13) and second band pass filter (14).

Among them, the first radio frequency signal generator (2) is connected to the input port of the comb spectrum generator (3), and the output port of the comb spectrum generator (3) is connected to the first erbium-doped fiber amplifier (4). The optical fiber amplifier (4) is connected with the first optical splitter (5).

The output port of the first optical splitter (5) is divided into three, one of which inputs multiple downstream optical transceiver modules, and the other two are respectively connected to the first band pass filter (13) and the second band pass filter (14) .

In this embodiment, the multi-channel downstream optical transceiver module includes:

The first 1×N arrayed waveguide grating (6), the N-way downstream optical transceiver sub-module, and the second N×1 arrayed waveguide grating (12).

Among them, the output port of the first optical splitter (5) is divided into three paths, one is connected to the left port of the first 1×N arrayed waveguide grating (6), and the first 1×N arrayed waveguide grating (6) is on the right. The N ports on the side are respectively connected with the input ports of the downstream optical transceiver submodules on the N roads, and the output ports of the downstream optical transceiver submodules on the N roads are connected with the left input port of the second N×1 arrayed waveguide grating (12). It should be noted that 1×N in the 1×N first arrayed waveguide grating refers to 1 input port on the left and N output ports on the right. The 1×N first arrayed waveguide grating has the function of demultiplexing; Therefore, N×1 in the N×1 second arrayed waveguide grating refers to N input ports on the left side and 1 output port on the right side. The N×1 second arrayed waveguide grating has the function of multiplexing. This belongs to the general expression in the field, especially the arrayed waveguide grating (AWG), and those skilled in the art can understand this expression.

Specifically, the uplink and downlink optical transceiver sub-modules include: a downlink data generator (7), a Mach-Zehnder modulator (8), a receiver (9), an optical power detector (10) and a first optical circulator (11).

Among them, the output port of the first 1×N arrayed waveguide grating (6) is connected to the input port of the Mach-Zehnder modulator (8), and the output port of the downstream data generator (7) is connected to the Mach-Zehnder modulator (8). The radio frequency input port is connected, and the output port of the Mach-Zehnder modulator (8) is connected to the first port of the first optical circulator (11).

The second port of the first optical circulator (11) is connected to the input port corresponding to the second N×1 arrayed waveguide grating (12), and the third port of the first optical circulator (11) is connected to the upstream optical power detector (10). ) Is connected to the input port, and the output port of the upstream optical power detector (10) is connected to the input port of the upstream receiver (9).

In this embodiment, the remote node (16) is the third N×N cyclic arrayed waveguide grating (17). It should be noted that the third N×N cyclic arrayed waveguide grating refers to N input ports on the left and N output ports on the right. The N×N cyclic arrayed waveguide grating has wavelength routing cyclicality.

The optical line terminal (1) is connected to the left port of the third N×N cyclic arrayed waveguide grating (17) through three feed-in fibers (15), and the right port of the third N×N cyclic arrayed waveguide grating (17) is respectively connected to N distributed optical fibers (18) are connected to N optical network units (19).

In this embodiment, the components of each optical network unit (19) include: a second optical circulator (20), a second erbium-doped fiber amplifier (21), a third optical circulator (22), and a first Bragg Grating filter (23), third optical combiner (24), second optical splitter (25), single-row carrier photodetector (26), horn antenna (27), mixer (28), The second radio frequency signal generator (29), the amplifier (30), the phase modulator (31), the fourth optical circulator (32) and the second Bragg grating filter (33).

Among them, the distributed optical fiber (18) corresponding to the optical network unit (19) is connected to the second port of the second optical circulator (20) in the optical network unit (19), and the second port of the second optical circulator (20) is The three ports are connected to the input port of the second erbium-doped fiber amplifier (21), the output port of the second erbium-doped fiber amplifier (21) is connected to the first port of the third optical circulator (22), and the third optical circulator ( The second port of 22) is connected to the input port of the first Bragg grating filter (23), the third port of the third optical circulator (22) is connected to the input port of the third optical combiner (24), and the first Bragg The output port of the grating filter (23) is connected to the input port of the second optical splitter (25).

The output port of the second optical splitter (25) outputs two channels, one of which is connected to the input port of the third optical combiner (24), and the other is connected to the input port of the phase modulator (31).

The output port of the third optical combiner (24) is connected to a single-row carrier photodetector (26).

Specifically, the output port of the horn antenna (27) is connected to the port of the mixer (28), the second radio frequency signal generator (29) is connected to the input port of the mixer (28), and the frequency of the mixer (28) is The output port is connected to the input port of the amplifier (30), the output port of the amplifier (30) is connected to the modulation control port of the phase modulator (31), and the output port of the phase modulator (31) is connected to the fourth optical circulator (32). The first port is connected, the second port of the fourth optical circulator (32) is connected to the port of the second Bragg grating filter (33), and the third port of the fourth optical circulator (32) is connected to the second optical circulator ( 20) The first port connection.

In this embodiment, there is also provided a transmission method for a light-generated optically carried terahertz passive optical network system, including:

According to the generated optical phase coherent multi-wavelength optical carrier, a three-way optical carrier group is obtained, and the three-way optical carrier group is transmitted to the remote node (16) through the feed-in optical fiber (15).

The remote node (16) is connected to the optical network unit (19) via a distributed optical fiber (18), and the optical network unit (19) generates a terahertz wave through an optical heterodyne beat frequency mechanism, and transmits the terahertz wave downstream to the user terminal;

The optical network unit (19) receives the terahertz wave generated by the user terminal and transmits it to the optical line terminal (1) through the remote node (16).

Specifically, according to the generated optical phase-coherent multi-wavelength optical carrier, a three-way optical carrier group is obtained, and the three-way optical carrier group is transmitted to the remote node (16) via the feed-in optical fiber (15), including :

The first radio frequency signal generator (2) in the optical line terminal (1) drives the comb spectrum generator (3) to generate a group of optical phase-coherent multi-wavelength optical carriers (λ ₁ ～λ _N ), where λ represents the wavelength , N is a positive integer greater than 1;

The multi-wavelength optical carrier is amplified by the first erbium-doped fiber amplifier (4) and then input to the first optical splitter (5), and is divided into three by the first optical splitter (5);

After being divided into three by the first optical splitter (5), one of them is used as a data optical carrier group to input multiple downstream optical transceiver modules, and the other two are respectively input to the first band pass filter (13) and the second band Filtering by the pass filter (14), wherein the first band pass filter (13) and the second band pass filter (14) output the corresponding optical carrier group, which is used as the beat frequency optical carrier of the optical heterodyne beat frequency;

In the multi-channel downstream optical transceiver module, the data optical carrier group is input to the left port of the first 1×N arrayed waveguide grating (6), and the N ports on the right side of the first 1×N arrayed waveguide grating (6) are connected to the N ports respectively. The input port of the downstream optical transceiver sub-module on the road is connected to complete the downstream data modulation and transmission and the upstream data demodulation and reception.

The above-mentioned three optical carrier groups are respectively transmitted to the remote node (16) through respective feed-in optical fibers (15).

Specifically, the remote node (16) is connected to the optical network unit (19) via a distributed optical fiber (18), and the optical network unit (19) generates a terahertz wave through an optical heterodyne beat frequency mechanism, and transmits it downstream to the user terminal; The network unit (19) receives the terahertz wave generated by the user terminal and transmits it to the optical line terminal (1) through the remote node (16). include:

At the remote node (16), the feed-in optical fiber (15) carrying the data optical carrier group and the beat frequency optical carrier group is connected to the left port of the third N×N cyclic arrayed waveguide grating (17), according to the generated terahertz The required frequency of the carrier, corresponding to the Δ wavelength interval, select the corresponding port connection on the left side of the third N×N cyclic arrayed waveguide grating (17), and N ports on the right side of the third N×N cyclic arrayed waveguide grating (17) The data optical carrier and the beat frequency optical carrier output by the port are separated by Δ wavelength, and the right N ports of the third N×N cyclic arrayed waveguide grating (17) are respectively connected with N distributed optical fibers (18).

In N optical network units (19), N distributed optical fibers (18) are connected to N optical network units (19), and data optical carriers and beat frequency optical carriers with a wavelength interval of Δ are input to each optical network unit (19) The single-line carrier photodetector (26) at the location, the single-line carrier photodetector (26) generates a terahertz signal through the optical heterodyne beat frequency mechanism to complete the downlink data transmission;

The horn antenna (27) receives the uplink transmission terahertz signal and the low-frequency radio frequency signal generated by the second radio frequency signal generator (29) is input into the mixer (28) for down conversion, and the output port of the mixer (28) is output The intermediate frequency signal is input to the amplifier (30), amplified by the amplifier (30), and then input to the phase modulator (31), modulated by the phase modulator (31), and then passed through the fourth optical circulator (32) and the second Bragg grating filter ( 33) After filtering, uplink transmission to the remote node (16), and then uplink transmission to the optical line terminal (1) through the remote node (16) to complete the coherent reception of uplink data.

In this embodiment, the mechanism for generating terahertz waves by the optical heterodyne beat mechanism includes: a single heterodyne beat mechanism and a double heterodyne beat mechanism. The choice of the input port and output port of the third N×N cyclic arrayed waveguide grating under the two optical heterodyne beat frequency mechanisms is different, the transmission mode and the number of service users will be different.

1) As shown in Figure 2, the transmission method for generating terahertz waves based on the single heterodyne beat frequency mechanism includes:

According to the wavelength "circularity" of the third N×N cyclic arrayed waveguide grating (17), each data optical carrier in the single heterodyne beat frequency mechanism corresponds to a beat frequency optical carrier, and the wavelength separation between the beat frequency optical carrier and the data optical carrier Is the Δ wavelength. The relationship between the wavelength λ _{d of the data optical carrier and the wavelength λ R0 of the} beat-frequency optical carrier is expressed as: λ _R0 =λ _(d+Δ) , when1≤d≤N-Δ, that is, λ _R0 corresponds to λ _{(d+Δ) )} The wavelength of this data optical carrier, and 1+Δ≤d≤N-Δ; or, λ _R0 =λ _(d-Δ) , whenN-Δ+1≤d≤N, that is, λ _R0 corresponds to λ _{(d- Δ)} The wavelength of this data optical carrier, and 1+Δ≤d≤N-Δ.

The specific transmission method is: the optical line terminal (1) is connected to the remote node (16) through three feed-in optical fibers (15), and the remote node (16) passes through an N×N third cyclic arrayed waveguide grating (17) and N A distributed optical fiber (18) connects N optical network units (19). At the optical line terminal (1), the first radio frequency signal generator (2) drives the comb spectrum generator (3) to generate a set of optical phase-coherent multi-wavelength optical carriers (λ ₁ ～λ _N ), which passes through the first erbium-doped The optical fiber amplifier EDFA (4) is amplified and then input to the first optical splitter (5), which is divided into three by the optical splitter, one of which enters the multi-channel downstream optical transceiver module, and the other two respectively input two band-pass filters (13, 14) Filter, output the corresponding optical carrier group from the two band-pass filters (13, 14) as the beat frequency optical carrier of the subsequent optical heterodyne beat frequency. The optical carrier group output after filtering by the first band-pass filter (13) is (λ _1+Δ ～λ _N ), and the optical carrier group output after filtering by the second band-pass filter (14) is (λ _{N+ 1-2Δ} ~ λ _N-Δ ). The optical carrier entering the multi-channel downstream optical transceiver module is input into the first 1×N arrayed waveguide grating (6) demultiplexed and demultiplexed into N channels of different wavelengths, and then input into the N channels of downstream optical transceiver sub-modules to complete the downstream data modulation and the upstream The data is received, and then multiplexed by a second N×1 arrayed waveguide grating (12) and then coupled into one feed-in optical fiber (15), and finally to the other two feed-in optical fibers (15) for transmitting beat frequency optical carriers Input the remote node (16) together. The remote node (16) is mainly composed of a third N×N cyclic arrayed waveguide grating (17). A feed-in optical fiber (15) carrying the data optical carrier is connected to the third N ×N cyclic arrayed waveguide grating (17) is the first port on the left side, so that N data optical carriers (λ ₁ ～λ _N ) are sequentially on the N ports on the right side of the third N×N cyclic arrayed waveguide grating (17) Are decomposed; in addition, two feed-in fibers (15) carrying beat frequency optical carriers are respectively connected to the (Δ+1) and (N)ths on the left side of the third N×N cyclic arrayed waveguide grating (17) -Δ+1) port, the optical carrier group (λ _1+Δ ～λ _N ) is connected to the third N×N cyclic arrayed waveguide grating (17) on the left side of the (Δ+1) via the feed-in optical fiber (15) ) Port, the optical carrier group (λ _N+1-2Δ ～λ _N-Δ ) is connected to the third N×N cyclic arrayed waveguide grating (17) on the left side of the (N-Δ+ 1) No. port, so that the beat frequency optical carrier wavelength and the corresponding data optical carrier wavelength are separated by Δ wavelength, which corresponds to the required terahertz carrier frequency. For example, the two wavelengths routed to the first port on the right side of the third N×N cyclic arrayed waveguide grating (17) are the data wave wavelength λ ₁ and the beat frequency optical carrier wavelength λ _1+Δ , which are routed to the third N×N The two wavelengths on the second port on the right side of the cyclic arrayed waveguide grating (17) are the data wavelength λ ₂ and the beat frequency optical carrier wavelength λ _2+Δ . The data optical carrier and beat frequency optical carrier output on the (N-Δ) ports are λ _N-Δ and λ _{N respectively} . Since the beat frequency optical carrier output from the (N-Δ+1) port on the right side of the third N×N cyclic arrayed waveguide grating (17) to the Nth port exceeds that from the third N×N cyclic arrayed waveguide grating (17) The wavelength range of the beat frequency optical carrier input on the port (Δ+1) on the left side needs to be the (N-Δ+1)th on the left side of the third N×N cyclic arrayed waveguide grating (17) The beat frequency optical carrier group input on the port is (λ _N+1-2Δ ～λ _N-Δ ), that is, the third N×N cyclic arrayed waveguide grating (17) on the left side of the third feed-in fiber input ( The beat frequency optical carrier group input on port N-Δ+1), the data optical carrier and beat frequency output on the (N-Δ+1) port on the right side of the N×N third circular arrayed waveguide grating (17) The frequency optical carriers are λ _N-Δ+1 and λ _{N-2Δ+1 respectively} . The data optical carrier and the beat frequency optical carrier output on the Nth port on the right side of the N×N third circular arrayed waveguide grating (17) are respectively Λ _N and λ _N-Δ , the data optical carrier and beat frequency optical carrier output from each port on the right side of the third N×N cyclic arrayed waveguide grating (17) are transmitted through the same distributed optical fiber (18) respectively The terahertz wave is generated by beating the remote antenna unit to the corresponding ONU (19) of each optical network unit. This transmission method can serve N users.

In the optical network unit ONU-1, the data optical carrier λ ₁ and the beat frequency optical carrier λ _{1+Δ are} input to the second port of the second optical circulator (20), and from the third port of the second optical circulator (20) After the output, input the second erbium-doped fiber amplifier (21) to amplify together, and input the third optical circulator (22) and the first Bragg grating filter (23) to convert the data optical carrier λ ₁ and the beat frequency optical carrier λ _1+Δ Separate. The beat frequency optical carrier λ _{1+Δ is} then divided into two by a second optical splitter OS (25), and a part of λ _{1+Δ is} input to the third optical combiner (24) together with the data wavelength λ _{1 again.} Together, then perform optical heterodyne beat frequency in the single-line carrier photodetector UTC-PD (26) to obtain the downlink terahertz signal, the carrier frequency of which is f _THz = c|1/λ ₁ -1/λ _1+Δ |(c is the speed of light in vacuum). The other part of the beat-frequency optical carrier λ _1+Δ is reused as the optical carrier of the uplink terahertz signal. The horn antenna (27) of the optical network unit ONU (19) receives the terahertz signal transmitted by the user terminal. The terahertz signal and the second The low frequency radio frequency signal generated by the radio frequency signal generator (29) is input to the mixer (28) for down conversion, and the intermediate frequency signal output from the output port of the mixer (28) is input to the amplifier (30), and then amplified by the amplifier (30) Input the phase modulator PM (31), the phase modulator PM (31) loads the upstream terahertz signal on the continuous wave λ _1+Δ to form a double-sideband optical signal, and then passes through the fourth optical circulator (32) and the second The Bragg grating filter FBG (33) filters out one of the sidebands to obtain the optical baseband signal λ ₁ that carries the uplink terahertz data, and transmits it to the OLT (1) upstream to complete the upstream coherent reception.

2) As shown in Figure 3, in terms of system architecture, compared to the system structure of the single heterodyne beat mechanism shown in Figure 2, the system structure of the double heterodyne beat mechanism is added to the optical network unit module. The fifth optical circulator (34) and the third Bragg grating filter (35), two beat frequency optical carriers λ ₁ , λ _{1+2Δ are} input to the first port of the fifth optical circulator (34), the fifth optical circulator (34) The second output port is connected to the third Bragg grating filter (35), and the beat frequency optical carrier λ _{1+2Δ is} output from the third port of the fifth optical circulator (34) as the data optical carrier of the uplink terahertz signal , And input the phase modulator PM (31). The transmission method for generating terahertz waves based on the double heterodyne beat frequency mechanism includes:

According to the wavelength "circularity" of the third N×N cyclic arrayed waveguide grating (17), each data optical carrier in the double heterodyne beat frequency mechanism corresponds to two beat frequency optical carriers. The difference between the beat frequency optical carrier and the data optical carrier is The interval between the upper and lower wavelengths is Δ wavelength. The relationship between the wavelength λ _{d of the data optical carrier and the wavelength λ R0 of the} beat frequency optical carrier is expressed as: λ _R0 = λ _{(d+Δ) and} λ _(d-Δ) , when1+Δ≤d≤N-Δ, namely λ _R0 corresponds to the wavelength of the two data optical carriers _{λ (d+Δ)} and λ _{(d-Δ), and 1+Δ≤d≤N-Δ.}

The specific transmission method is: the optical line terminal (1) is connected to the remote node (16) through three feed-in optical fibers (15), and the remote node (16) is connected through (N-2Δ) distributed optical fibers (18) (N -2Δ) optical network unit groups (19). At the optical line terminal (1), the first radio frequency signal generator (2) drives the comb spectrum generator (3) to generate a set of optical phase-coherent multi-wavelength optical carriers (λ ₁ ～λ _N ), which passes through the first erbium-doped The optical fiber amplifier EDFA (4) is amplified and then input to the first optical splitter (5), which is divided into three by the optical splitter, one of which enters the multi-channel downstream optical transceiver module to complete the downstream data modulation and upstream data reception; the other two Two band-pass filters (13, 14) are respectively input to the path, and the corresponding optical carrier group is output after filtering from the two band-pass filters (13, 14) as the beat frequency optical carrier group of the subsequent optical heterodyne beat frequency. The optical carrier group filtered by the first band-pass filter (13) is (λ _1+2Δ ～λ _N ), and the optical carrier group filtered by the second band-pass filter (14) is ( λ ₁ ～λ _N-2Δ ). The optical carrier entering the multi-channel downstream optical transceiver module is input to the first 1×N arrayed waveguide grating (6) demultiplexed and demultiplexed to (N-2Δ) different wavelengths, and then input (N-2Δ) downstream optical transceivers respectively The module completes downlink data modulation and uplink data reception, and is multiplexed by a second N×1 arrayed waveguide grating (12) and then coupled into a feed-in optical fiber (15), and finally transmits the beat frequency optical carrier with the other two channels The feed-in optical fiber (15) is input to the remote node (16) together. The remote node (16) is mainly composed of a third N×N cyclic arrayed waveguide grating (17), which carries the data optical carrier group. The optical fiber (15) is connected to the first port on the left side of the third N×N cyclic arrayed waveguide grating (17), so that the (N-2Δ) road data optical carrier (λ _Δ+1 ～λ _N-Δ ) is in the order of the first port The (Δ+1)～(N-Δ) ports on the right side of the three N×N cyclic arrayed waveguide gratings (17) are decomposed; in addition, two feed-in optical fibers (15) carrying beat frequency optical carriers, respectively Connected to the (Δ+1) and (N-Δ+1) ports on the left side of the third N×N cyclic arrayed waveguide grating (17), the optical carrier group (λ _1+2Δ ～λ _N ) The feed-in optical fiber (15) is connected to the No. (Δ+1) port on the left side of the third N×N cyclic arrayed waveguide grating (17), and the optical carrier group (λ ₁ ～λ _N-2Δ ) passes through the feed-in optical fiber ( 15) Connect the (N-Δ+1) port on the left side of the third N×N cyclic arrayed waveguide grating (17), so as to route to a different port on the right side of the third N×N cyclic arrayed waveguide grating (17) The two beat frequency optical carrier wavelengths and the corresponding data optical carrier wavelength are spaced by Δ wavelength up and down, corresponding to the required terahertz carrier frequency. For example, the wavelength on the (Δ+1) port on the right side of the N×N third cyclic arrayed waveguide grating (17) is the data wavelength λ _1+Δ and two beat frequency optical carriers λ ₁ and λ _1+2Δ , the routing _{To the data optical carrier λ N-Δ} and two remote oscillation carriers and λ _N and λ _N-2Δ output on the (N-Δ)th port on the right side of the third N×N cyclic arrayed waveguide grating (17). The data optical carrier and the beat frequency optical carrier output from each port on the right side of the third N×N cyclic arrayed waveguide grating (17) are respectively transmitted to the corresponding optical network unit ONU through the same distributed optical fiber (18). 19), and then perform a double heterodyne beat frequency on the remote antenna unit (single-line carrier photodetector) to generate terahertz waves. This transmission method can serve (N-2Δ) users.

In the optical network unit ONU-1, the data optical carrier λ _1+Δ and the two beat frequency optical carriers λ ₁ and λ _1+2Δ are input to the second port of the second optical circulator (20) together, and the second optical circulator is transmitted from the second optical circulator. After the output of the third port of the device (20), the second erbium-doped fiber amplifier (21) is inputted to amplify together, and the third optical circulator (22) and the first Bragg grating filter (23) are inputted to transfer the data optical carrier λ _{1 +Δ is} separated from the two beat frequency optical carriers λ ₁ and λ _1+2Δ. The beat frequency optical carrier λ ₁ , λ _{1+2Δ is} then divided into two by a second optical splitter OS (25), one of which enters the third optical combiner (24) and is again coupled with the data optical carrier λ _1+Δ Together, the terahertz signal is obtained by double-heterodyne beat frequency in the single-line carrier photodetector UTC-PD (26), which is transmitted downstream to the user terminal. Another beat frequency optical carrier λ _1+2Δ , λ _{1 is} input to the fifth optical circulator (34) and the third Bragg grating filter (35), and the output beat frequency optical carrier λ _1+2Δ is reused as the uplink terahertz signal The data optical carrier is input to the phase modulator PM (31). The horn antenna (27) of the optical network unit ONU (19) receives the terahertz signal transmitted by the user terminal, and the terahertz signal is input to the mixer (28) together with the low-frequency RF signal generated by the second RF signal generator (29) Frequency conversion, the intermediate frequency signal output from the output port of the mixer (28) is input to the amplifier (30), amplified by the amplifier (30), and then input to the phase modulator PM (31), and the phase modulator PM (31) will the amplified terahertz The signal is loaded on the continuous wave λ _1+2Δ to form a double-sideband optical signal, and then one of the sidebands is filtered out through the fourth optical circulator (32) and the second Bragg grating filter FBG (33) to obtain the carrying uplink terahertz The optical signal λ _{1+Δ of the} data is transmitted upstream to the OLT (1) to complete the upstream coherent reception.

When the terahertz wave is generated based on the double heterodyne beat frequency mechanism, the phase stabilization technology is used to adjust the carrier phase so that the data optical carrier and the two terahertz waves generated after the two beat frequency optical carriers have the same phase, the mechanism produces The amplitude intensity of the terahertz wave is greater than the amplitude intensity of the terahertz wave obtained by the single-optical heterodyne beat frequency, and the increase of the optical power is beneficial to increase the wireless transmission distance of the terahertz signal.

This embodiment uses an optical method to generate terahertz waves, which has the advantages of low cost, easy adjustment, low phase noise, and freedom from bandwidth limitations. At the same time, it can be integrated with the optical fiber transmission system to realize a large-capacity, low-cost converged access system. Specifically, on the basis of ROF-PON, a new light-generated optically-carrying terahertz passive optical network system (OG-TOF-PON) and its transmission method are proposed. The system generates terahertz waves based on a single heterodyne beat frequency mechanism or a double heterodyne beat frequency mechanism, and uses the "circularity" of the wavelength routing of the N×N cyclic arrayed waveguide grating (AWG) to realize the data optical carrier and the beat frequency light. The purpose of carrier point-to-multipoint flexible configuration and two-way transmission and reception. In addition, for the OG-TOF-PON system, the bandwidth of the terahertz wave is above 300 GHz, and the data optical carrier and the beat frequency optical carrier cannot be transmitted in the same fiber channel. Therefore, the present invention puts the beat frequency optical carrier and the data optical carrier in the same optical fiber channel. The two channels are transmitted separately, and then the terahertz wave is generated at the beat frequency of the remote antenna unit of the optical network unit (19). In the OG-ToF-PON system, terahertz wave (THz) generation technology involving two optical heterodyne beat frequency mechanisms: single heterodyne beat frequency mechanism and double heterodyne beat frequency mechanism, two optical heterodyne beat frequencies The choice of the input port and output port of the N×N cyclic arrayed waveguide grating under the mechanism is different, the signal transmission mode of the system and the number of service users will be different.

This embodiment has at least the following advantages:

1) For the first time, an optically-generated optical terahertz passive optical network system (OG-TOF-PON) is proposed.

2) The system uses the "circularity" of the wavelength routing of the N×N cyclic arrayed waveguide grating to realize the data optical carrier wavelength and beat frequency optical carrier wavelength routing, thereby meeting the requirements of terahertz wave generation.

3) The OG-TOF-PON system based on the double heterodyne beat frequency mechanism. When the data optical carrier and the two beat frequency optical carriers have the same phases as the two terahertz waves generated after the beat frequency, the mechanism generates the terahertz wave The amplitude intensity is larger than the amplitude intensity of the terahertz wave obtained by the single-optical heterodyne beat frequency, and the optical power increases, which is beneficial to increase the wireless transmission distance of the terahertz wave.

In addition, the terahertz generation technology based on the double heterodyne beat frequency mechanism provided in this embodiment uses the wavelength "circularity" of the N×N cyclic arrayed waveguide grating passive optical router to realize the point-to-multipoint two-way transmission and reception of information The transmission method is similar to that of a system based on a single heterodyne beat frequency mechanism. In the double heterodyne beat frequency mechanism, each data optical carrier corresponds to two beat frequency optical carrier carriers. The upper and lower intervals between the beat frequency optical carrier and the data optical carrier are Δ wavelengths. When the data optical carrier is separated from the two beat frequency optical carriers, When the phases of the two terahertz waves generated after the carrier beat frequency are the same, the amplitude intensity of the terahertz wave generated by this mechanism is greater than the amplitude intensity of the terahertz wave obtained by the single-optical heterodyne beat frequency. The wireless transmission distance of the Hertz signal. This transmission method can serve (N-2Δ) users.

The steps of the method or algorithm described in combination with the disclosure of the present application can be implemented in a hardware manner, or can be implemented in a manner in which a processor executes software instructions. Software instructions can be composed of corresponding software modules, which can be stored in random access memory (RandomAccessMemory, RAM), flash memory, read-only memory (ReadOnlyMemory, ROM), and erasable programmable read-only memory (ErasableProgrammableROM, EPROM) , Electrically Erasable Programmable Read-Only Memory (Electrically EPROM, EEPROM), register, hard disk, mobile hard disk, CD-ROM or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor, so that the processor can read information from the storage medium and can write information to the storage medium. Of course, the storage medium may also be an integral part of the processor.

Those skilled in the art should be aware that, in one or more of the foregoing examples, the functions described in this application can be implemented by hardware, software, firmware, or any combination thereof. When implemented by software, these functions can be stored in a computer-readable medium or transmitted as one or more instructions or codes on the computer-readable medium. The computer-readable medium includes a computer storage medium and a communication medium, where the communication medium includes any medium that facilitates the transfer of a computer program from one place to another. The storage medium may be any available medium that can be accessed by a general-purpose or special-purpose computer.

The specific implementations described above further describe the purpose, technical solutions, and beneficial effects of the application. It should be understood that the foregoing are only specific implementations of the application and are not intended to limit the scope of the application. The scope of protection, any modification, equivalent replacement, improvement, etc. made on the basis of the technical solution of this application shall be included in the scope of protection of this application.

Claims (10)

1. A kind of light-generated light-carrying terahertz passive optical network system, including: optical line terminal (1), three feed-in optical fibers (15), remote node (16), N distributed optical fibers (18) and N optical fibers Network unit (19), where N is a positive integer;

   The optical line terminal (1) is connected to the remote node (16) through three feed-in optical fibers (15);

   The optical network unit (19) is connected to the remote node (16) through a distributed optical fiber (18), wherein one distributed optical fiber (18) corresponds to an optical network unit (19).
2. The system according to claim 1, characterized in that the optical line terminal (1) comprises: a first radio frequency signal generator (2), a comb spectrum generator (3), and a first erbium-doped fiber amplifier (4) , The first optical splitter (5), the multi-channel downstream optical transceiver module, the first band pass filter (13) and the second band pass filter (14);

   Among them, the first radio frequency signal generator (2) is connected to the input port of the comb spectrum generator (3), the output port of the comb spectrum generator (3) is connected to the first erbium-doped fiber amplifier (4), and the first doped The erbium fiber amplifier (4) is connected with the first optical splitter (5);

   The output port of the first optical splitter (5) is divided into three, one of which inputs multiple downstream optical transceiver modules, and the other two are respectively connected to the first band pass filter (13) and the second band pass filter (14) .
3. The system according to claim 2, wherein the multi-channel downstream optical transceiver module comprises:

   The first 1×N arrayed waveguide grating (6), the N-way downstream optical transceiver sub-module, and the second N×1 arrayed waveguide grating (12);

   Among them, the output port of the first optical splitter (5) is divided into three paths, one is connected to the left port of the first 1×N arrayed waveguide grating (6), and the first 1×N arrayed waveguide grating (6) is on the right. The N ports on the side are respectively connected with the input ports of the downstream optical transceiver submodules on the N roads, and the output ports of the downstream optical transceiver submodules on the N roads are connected with the left input port of the second N×1 arrayed waveguide grating (12).
4. The system according to claim 3, wherein the uplink and downlink optical transceiver sub-modules include: a downlink data generator (7), a Mach-Zehnder modulator (8), a receiver (9), and optical power detection器(10) and the first optical circulator (11);

   Among them, the output port of the first 1×N arrayed waveguide grating (6) is connected to the input port of the Mach-Zehnder modulator (8), and the output port of the downstream data generator (7) is connected to the Mach-Zehnder modulator (8). The radio frequency input port is connected, and the output port of the Mach-Zehnder modulator (8) is connected to the first port of the first optical circulator (11);

   The second port of the first optical circulator (11) is connected to the input port corresponding to the second N×1 arrayed waveguide grating (12), and the third port of the first optical circulator (11) is connected to the upstream optical power detector (10). ) Is connected to the input port, and the output port of the upstream optical power detector (10) is connected to the input port of the upstream receiver (9).
5. The system according to claim 1, wherein the remote node (16) is a third N×N cyclic arrayed waveguide grating (17);

   The optical line terminal (1) is connected to the left port of the third N×N cyclic arrayed waveguide grating (17) through three feed-in fibers (15), and the right port of the third N×N cyclic arrayed waveguide grating (17) is respectively connected to N distributed optical fibers (18) are connected to N optical network units (19).
6. The system according to claim 1, wherein the components of each optical network unit (19) include: a second optical circulator (20), a second erbium-doped fiber amplifier (21), and a third optical ring Detector (22), first Bragg grating filter (23), third optical combiner (24), second optical splitter (25), single-row carrier photodetector (26), horn antenna (27) , Mixer (28), second radio frequency signal generator (29), amplifier (30), phase modulator (31), fourth optical circulator (32) and second Bragg grating filter (33);

   Among them, the distributed optical fiber (18) corresponding to the optical network unit (19) is connected to the second port of the second optical circulator (20) in the optical network unit (19), and the second port of the second optical circulator (20) is The three ports are connected to the input port of the second erbium-doped fiber amplifier (21), the output port of the second erbium-doped fiber amplifier (21) is connected to the first port of the third optical circulator (22), and the third optical circulator ( The second port of 22) is connected to the input port of the first Bragg grating filter (23), the third port of the third optical circulator (22) is connected to the input port of the third optical combiner (24), and the first Bragg The output port of the grating filter (23) is connected to the input port of the second optical splitter (25);

   The output port of the second optical splitter (25) outputs two channels, one of which is connected to the input port of the third optical combiner (24), and the other is connected to the input port of the phase modulator (31);

   The output port of the third optical combiner (24) is connected to a single-row carrier photodetector (26).
7. The system according to claim 6, characterized in that the output port of the horn antenna (27) is connected to the port of the mixer (28), and the second radio frequency signal generator (29) is input to the mixer (28), and the mixer (28) is mixed The output port of the frequency converter (28) is connected to the input port of the amplifier (30), the output port of the amplifier (30) is connected to the modulation control port of the phase modulator (31), and the output port of the phase modulator (31) is connected to the fourth optical ring The first port of the shaper (32) is connected, the second port of the fourth optical circulator (32) is connected to the port of the second Bragg grating filter (33), and the third port of the fourth optical circulator (32) is connected to The first port of the second optical circulator (20) is connected.
8. A transmission method of a light-generated optically carried terahertz passive optical network system is characterized in that, according to the generated optical phase-coherent multi-wavelength optical carrier, a three-channel optical carrier group is obtained, and the three-channel optical carrier group is fed through Type optical fiber (15) is transmitted to the remote node (16);

   The remote node (16) is connected to the optical network unit (19) via a distributed optical fiber (18), and the optical network unit (19) generates a terahertz wave through an optical heterodyne beat frequency mechanism, and transmits the terahertz wave downstream to the user terminal;

   The optical network unit (19) receives the terahertz wave generated by the user terminal and transmits it to the optical line terminal (1) through the remote node (16).
9. The method according to claim 8, wherein the mechanism for generating terahertz waves by the optical heterodyne beat mechanism includes: a single heterodyne beat mechanism and a double heterodyne beat mechanism.
10. The method according to claim 9, characterized in that, in the process of generating the terahertz wave through the double heterodyne beat frequency mechanism:

    The beat frequency optical carrier is divided into two by the second optical splitter OS (25). One of the beat frequency optical carriers is input to the fifth optical circulator (34) and the third Bragg grating filter (35), and the output beat The frequency optical carrier is re-used as the data optical carrier of the uplink terahertz signal and is input to the phase modulator PM(31);

    Among them, in the double heterodyne beat frequency mechanism, each data optical carrier corresponds to two beat frequency optical carriers. The upper and lower wavelength intervals of the beat frequency optical carrier and the data optical carrier are Δ wavelengths, and the data optical carrier is connected to the two beat frequency optical carriers respectively. The phases of the two terahertz waves generated after the beating of the optical carrier are the same.

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