Optical communication network system and subscriber-side optical transmission device

Abstract

Provided are an optical communication network system, a station-side optical transmission device, and a subscriber-side optical transmission device, which transmit control signals to each subscriber-side optical transmission device without any problems when a station-side optical transmission device is connected to a plurality of subscriber-side optical transmission devices using an optical branch transmission path. [Solution] In an optical communication network system 1, a central office optical transmission device 10 and multiple subscriber-side optical transmission devices (ONUs) are connected via an optical distribution network 116. The central office optical transmission device includes multiple optical transmission terminals (OLTs), an optical multiplexer that wavelength-division multiplexes downstream optical signals to generate downstream frequency-multiplexed signals, and an intensity modulator that holds a time-division multiplexed control signal obtained by time-division multiplexing downstream control signals, intensity-modulates the downstream frequency-multiplexed signals accordingly to generate downstream frequency-multiplexed signals, and transmits the downstream frequency-multiplexed signals to the optical branch transmission line side. The subscriber-side optical transmission device demodulates the time-division multiplexed control signal from the downstream frequency-multiplexed signal, and extracts the downstream control signal from the demodulated time-division multiplexed control signal.

Description

[Technical Field]

[0001] This invention relates to an optical communication network system. Mu and The present invention relates to a subscriber-side optical transmission device and can be applied to an optical communication network system such as a PON (Passive Optical Network). [Background technology]

[0002] Currently, demand for communications is rapidly increasing due to the evolution of mobile devices, the growing use of social networking sites, particularly video sharing, and the spread of unmanned online services due to advances in artificial intelligence (AI) technology, and there is a demand for increased capacity in transmission equipment for subscriber optical networks.

[0003] Conventional subscriber optical networks use an optical transmission system called PON (Passive Optical Network). In a PON, one optical transceiver device at the central office is connected to multiple optical transceivers at subscribers via a partially shared optical fiber transmission line, and point-to-multipoint communication is performed between the central office and multiple subscribers using optical multiplexing / multiple access transmission technology.

[0004] NG-PON2, standardized by the International Telecommunication Union Telecommunication Standardization Sector (ITU-T), combines time division multiplexing / multiple access (TDM / TDMA) and wavelength division multiplexing (WDM) technologies to specify a maximum total transmission capacity of 40 Gb / s (see Non-Patent Document 1).

[0005] Here, we will explain the configuration of a conventional NG-PON2 (an optical communication network system compatible with NG-PON2). In conventional NG-PON2, an optical line terminal (OLT) serving as an optical transmission device at the central office side and an optical network unit (ONU) serving as an optical transmission device at the subscriber side are connected via an optical branch transmission path branched by a multiplexer / demultiplexer. Each OLT in a conventional NG-PON2 system transmits and receives optical signals with individual wavelengths constituting a wavelength division multiplexed signal. Furthermore, a multiplexer / demultiplexer in a conventional NG-PON2 system multiplexes the signal light of different wavelengths transmitted from each OLT in downstream communications, and demultiplexes each wavelength of the wavelength division multiplexed signal in upstream communications. Furthermore, the optical distribution network in a conventional NG-PON2 system is composed of passive optical elements such as optical fibers, optical couplers, and optical splitters. In downstream communications, the multiplexer transmits and splits the wavelength division multiplexed signal bundled by the multiplexer and distributes it to each ONU. In upstream communications, the optical signals transmitted from each ONU are combined and transmitted to the central office. Furthermore, the ONUs that make up conventional NG-PON2 are terminal devices on the subscriber side, have wavelength selection functions, and transmit / receive signals of the assigned wavelengths.

[0006] As such, one of the features of conventional NG-PON2 is its use of WDM technology. Conventional NG-PON2 also specifies a control channel called AMCC (Auxiliary-Management And Control Channel), which allocates and allocates wavelengths used in the system and assigns wavelength channels to each ONU. The AMCC signal is superimposed on the low-frequency side of the user signal in the frequency domain so as not to interfere with it, and can coexist in the time / wavelength domain with user optical signals of any format as long as no interference occurs.

[0007] Details of conventional AMCC signals are described in Non-Patent Document 2. Specifically, Non-Patent Document 2 describes the conventional AMCC signal transmission and reception procedures as follows: In conventional AMCC signal processing, the transmitting side intensity-modulates the main signal light using an external modulator. Furthermore, in conventional AMCC signal processing, the AMCC signal and the user signal can be separated in the frequency domain by setting the modulation rate lower than the lowest frequency of the user signal spectrum. Furthermore, in conventional AMCC signal processing, waveform distortion of the user signal can be sufficiently reduced by sufficiently reducing the modulation index of the intensity modulation. Furthermore, in conventional AMCC signal processing, the receiving side can detect the AMCC signal by branching off a portion of the transmitted superimposed signal, directly detecting it, and extracting only the low-frequency components using a filter, or by using a narrow-band optical receiver and electrical circuit. Furthermore, in conventional AMCC signal processing, the remaining branched received light is detected, and the AMCC signal can be extracted in the frequency domain by removing the AMCC signal.

[0008] Meanwhile, research is underway to apply coherent optical transmission technology, which has traditionally been applied to backbone optical networks with transmission distances of several hundred to several thousand kilometers, to subscriber optical networks with transmission distances of only 20 km, by leveraging advances in digital signal processing (DSP). In conventional coherent optical transmission, continuous light (LO light) output from a locally oscillating (LO) light source is coupled with the received light at the receiving end, and the resulting beat component is detected as an electrical signal after photoelectric conversion (coherent detection). Since conventional coherent detection detects the phase information of the received light, multilevel modulation formats such as QPSK (Quadrature Phase Shift Keying) and QAM (Quadrature Amplitude Modulation), which use phase information for signal identification, can be adopted for the optical signal, enabling higher transmission bit rates while suppressing increases in modulation speed. Furthermore, in conventional coherent optical transmission processing, by setting the LO optical power sufficiently high, it is possible to detect electrical signals with a high signal-to-noise ratio, and the receiving sensitivity can be improved compared to the intensity modulation format optical signal receiving conventionally used in PON systems. This is an advantageous characteristic for PON systems, which have large branching losses in the optical distribution network.

[0009] Furthermore, in conventional coherent detection, the desired signal is detected as an electrical signal whose magnitude is the product of the electric field amplitudes of the received light and the LO light, and whose frequency is the difference between them. However, in conventional coherent detection, the desired signal cannot be detected if the frequency difference between the received light and the LO light is greater than the frequency band of the electrical circuit due to the bandwidth limitation of the electrical circuit including the optical receiver. Previously, colorless detection that utilizes such characteristics of coherent detection to detect only the signal light of the desired wavelength from a WDM signal without using an optical filter has been reported in, for example, Non-Patent Document 3. This characteristic leads to the elimination of some optical components and is particularly advantageous for PON systems, where miniaturization and cost reduction are required on the subscriber side. [Prior art documents] [Non-patent literature]

[0010] [Non-Patent Document 1] ITU-T Recommendation G.989 series,“40-Gigabit-capable passive optical networks (NG-PON2)” [Non-patent document 2] Satoshi Yoshima et al., "A Study on AMCC Signal Multiplexing in 100G Coherent PON Systems for 5G Optical Accommodation," 2016 IEICE Communication Society Conference, B-8-51 [Non-patent document 3] Ryosuke-Natsumoto, et al., “Scalable and Fast Optical Circuit Switch Based on Colorless Coherent Detection: Design Principle and Experimental Demonstration,”-Kournal of Lightwave Technology, vol. 39, no. 8, pp. 2263-2274, Apr. 15, 2021 Summary of the Invention [Problem to be solved by the invention]

[0011] As described above, building a PON system using coherent transmission and WDM technologies has traditionally been a promising way to meet the demand for increased transmission capacity. Furthermore, in a PON using conventional coherent transmission, colorless detection can be considered a means to reduce the size and cost of ONUs. However, in a PON using conventional coherent transmission, the ONU does not have an optical filter for downstream communications, and the received AMCC signal is directly detected. Therefore, the AMCC signal receiving section detects all AMCC signals contained in the WDM signal. In other words, in a PON using conventional coherent transmission, there is a risk of interference between the AMCC signals of all users at the AMCC signal receiving section of each ONU.

[0012] In view of the above problems, there is a demand for an optical communication network system that can transmit control signals (e.g., AMCC signals) from a station-side optical transmission device to each of the subscriber-side optical transmission devices without any problems when the station-side optical transmission device and the multiple subscriber-side optical transmission devices are connected using an optical branching transmission line. [Means for solving the problem]

[0013] The first invention of the present invention is an optical communication network system in which a station-side optical transmission device and a plurality of subscriber-side optical transmission devices are connected by optical branching transmission lines, wherein the station-side optical transmission device comprises a plurality of optical transmission terminals for transmitting and receiving signals to any of the subscriber-side optical transmission devices, an optical multiplexer for wavelength-division multiplexing downstream optical signals sent from each of the optical transmission terminals to generate downstream frequency-multiplexed signals, and station-side intensity modulation means for holding time-division multiplexed control signals obtained by time-division multiplexing downstream control signals for each of the subscriber-side optical transmission devices, intensity-modulating the downstream frequency-multiplexed signals in accordance with the time-division multiplexing control signals, generating intensity-modulated downstream frequency-multiplexed signals, and sending them to the optical branching transmission line side, and each of the subscriber-side optical transmission devices comprises By directly detecting the intensity of , the time division multiplexing control signal extraction do extraction and extraction means for extracting the downstream control signal addressed to the apparatus itself from the demodulated time division multiplexed control signal.

[0015] No. 2 The present invention provides a subscriber-side optical transmission device that constitutes an optical communication network system in which a station-side optical transmission device and a plurality of subscriber-side optical transmission devices are connected by an optical branch transmission line, wherein when a plurality of downstream optical signals are frequency-multiplexed and an intensity-modulated downstream frequency-multiplexed signal obtained by intensity-modulating a plurality of downstream control signals with a time-division multiplexed control signal is supplied from the optical branch transmission line, the intensity-modulated downstream frequency-multiplexed signal is By directly detecting the intensity of , the time division multiplexing control signal extraction do extractionand extraction means for extracting a downstream control signal addressed to the apparatus itself from the demodulated time division multiplexed control signal. [Effects of the Invention]

[0016] According to the present invention, when an optical transmission device on the station side and multiple optical transmission devices on the subscriber side are connected using an optical branching transmission line, control signals can be transmitted from the optical transmission device on the station side to each optical transmission device on the subscriber side without any problems. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a block diagram showing a functional configuration of an optical communication network system (including a station-side optical transmission device and a subscriber-side optical transmission device) according to a first embodiment. [Figure 2] FIG. 10 is a block diagram showing a functional configuration of an optical communication network system (including a station-side optical transmission device and a subscriber-side optical transmission device) according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0018] (A) First embodiment Hereinafter, the optical communication network system according to the present invention will be described. Mu and A first embodiment of the subscriber-side optical transmission device will be described in detail with reference to the drawings.

[0019] (A-1) Configuration of the First Embodiment FIG. 1 is a block diagram showing the overall configuration of an optical communication network system 1 according to the first embodiment.

[0020] The optical communication network system 1 includes an optical transmission device 10 serving as an optical transmission device on the station side and N (N is an integer equal to or greater than 2) ONUs 121 (121-1 to 121-N) serving as optical transmission devices on the subscriber side. The optical transmission device 10 and the ONUs 121 (121-1 to 121-N) are connected by an optical distribution network 116 serving as an optical branching transmission path with multiple branches (N branches), and the optical transmission device 10 and the ONUs 121-1 to 121-N transmit and receive optical signals in both directions. That is, in the optical communication network system 1, the optical transmission device 10 and the ONUs 121-1 to 121-N are connected by a PON using the optical distribution network 116.

[0021] In the following, the direction from the optical transmission device 10 to the ONU 121 will be referred to as "downstream," and the direction from the ONU 121 to the optical transmission device 10 will be referred to as "upstream." Furthermore, in the following, k (an integer from 1 to N) will be introduced as a symbol to generally represent any ONU 121, and elements specific to any ONU 121-k will be appended with "-k." Furthermore, in the following, when describing the kth ONU 121-k, terms such as "the kth" or "within the kth ONU" may be omitted.

[0022] The optical distribution network 116 is a one-to-many bidirectional transmission line (multiple branched optical branch transmission lines) configured with optical fibers and passive optical elements such as optical couplers and branchers, and has one port on the central office side and N or more ports on the subscriber side.

[0023] The ONUs 121-1 to 121-N are optical transmission terminals on the subscriber side, each having one bidirectional port, and are connected to one of the subscriber-side ports of the optical distribution network 116.

[0024] In this embodiment, it is assumed that a subscriber-side device SE (SE-1 to SE-N) is connected to the downstream side (subscriber side) of each ONU 121 (121-1 to 121-N). The subscriber-side device SE (SE-1 to SE-N) corresponds to a subscriber-side communication device such as a router, PC, or switching hub. In this embodiment, it is assumed that an upstream device UE is connected to the upstream side of the station-side optical transmission device 10. The upstream device UE corresponds to a network device such as a router or switching hub.

[0025] Next, the internal configuration of the optical transmission device 10 on the station side will be described.

[0026] The optical transmission device 10 at the central office side includes M optical line terminals (OLTs) 101 (101-1 to 101-N), an optical multiplexer 112, an optical demultiplexer 113, an intensity modulator 114, an optical directional coupler 115, and a control signal processor 118.

[0027] The number of OLTs 101 included in the optical transmission device 10 at the central office may be M or more. In the following, j will be used as a symbol to generally represent any OLT 101, and elements specific to any OLT 101-j will be prefixed with "-j". In the following, when describing the j-th OLT 101-j, terms such as "the j-th" or "within the j-th OLT" may be omitted. In addition, in FIG. 1, a downstream information signal received by the j-th OLT 101-j from the upstream device UE side (hereinafter referred to as a "downstream transmission information signal") is denoted by 108-j. In addition, in FIG. 1, an upstream information signal transmitted by the j-th OLT 101-j to the upstream device UE side (hereinafter referred to as an "upstream transmission information signal") is denoted by 110-j.

[0028] The control signal processing unit 118 is a means for receiving downstream AMCC signals (hereinafter referred to as "downstream transmission AMCC signals") 119-1 to 119-M from the respective OLTs 101-1 to OLT-M, and generating a signal 111 obtained by time-division multiplexing the downstream transmission AMCC signals 119-1 to 119-M (hereinafter referred to as "multiplexed downstream transmission AMCC signal" or "time-division multiplexed control signal") The control signal processing unit 118 supplies the multiplexed downstream transmission AMCC signal 111 to the intensity modulator 114.

[0029] The optical multiplexer 112 is a means for multiplexing a plurality of optical systems having different carrier wavelengths, and has M or more input ports (greater than the number of OLTs 101) and one output port.

[0030] The optical demultiplexer 113 is a means for demultiplexing a WDM signal (a signal including multiple carrier waves) into light having a single carrier wavelength, and has one input port and M or more output ports (greater than the number of OLTs 101).

[0031] The intensity modulator 114 is a means for intensity-modulating the light output from the optical multiplexer 112 in accordance with the multiplexed downstream transmission AMCC signal 111 supplied from the control signal processing unit 118 .

[0032] The optical directional coupler 115 has one input port and two input ports, and is a means for outputting the output light of the intensity modulator 114 to the optical distribution network 116, and outputting the output light of the optical distribution network 116 to the optical demultiplexer 113. Since the input and output directions of the optical directional coupler 115 are specified, it can be configured using, for example, a directional optical coupler, optical branching device, or optical circulator.

[0033] Next, the internal configuration of each OLT 101 will be described.

[0034] In this embodiment, the OLTs 101-1 to 101-M have the same configuration. Below, the internal configuration of the j-th OLT 101-j will be described as a representative of the OLTs 101-1 to 101-M.

[0035] As shown in FIG. 1, the jth OLT 101-j includes a continuous light source 102-j, an optical modulator 103-j, an optical receiver 104-j, a coherent receiver 105-j, a local oscillator light source 106-j, an optical splitter 107-j, and a communication control unit 117-j.

[0036] The communication control unit 117-j is a means for controlling the communication by the OLT 101-j, and supplies the control signal processing unit 118 with a downstream transmission AMCC signal 119-k addressed to the ONU 121-k.

[0037] The continuous light source 102-j and the local oscillation light source 106-j are light sources that generate continuous light.

[0038] The optical modulator 103-j modulates the output light of the continuous light source 102-j in accordance with the downstream transmission information signal 108-j and outputs the modulated light. The output of the optical modulator 103-j becomes the output of the j-th OLT 101-j.

[0039] The optical splitter 107-j has one input port and two output ports, and is a means for splitting the input light of the j-th OLT 101-j into two and outputting the split light.

[0040] The optical receiver 104-j is a means for converting one of the output lights of the optical branching device 107-j into an electrical signal and outputting it to the communication control unit 117-j as an AMCC signal received from the ONU 121-k (hereinafter referred to as the "upstream received AMCC signal") 109-k.

[0041] The coherent receiver 105-j has two input ports and one output port, and is a means for outputting an electrical signal that is a beat component between the remaining output light of the optical splitter 107-j and the continuous light output from the local oscillation light source 106-j as the jth upstream received information signal 110-j.

[0042] Next, the internal configuration of each ONU 121 will be described.

[0043] In this embodiment, it is assumed that the ONUs 121-1 to 121-N have the same configuration. The internal configuration of the k-th ONU 121-k will be described below as a representative of the ONUs 121-1 to 121-N.

[0044] In Fig. 1, the upstream information signal (hereinafter referred to as "upstream transmission information signal") that ONU 121-k receives from the subscriber device SE-k side is designated by the code 132-k. Also, in Fig. 1, the downstream information signal (hereinafter referred to as "downstream transmission information signal") that ONU 121-k transmits to the subscriber device SE-k side is designated by the code 130-k.

[0045] The ONU 121-k includes an optical directional coupler 122-k, a local oscillator light source 123-k, a coherent receiver 124-k, an optical splitter 125-k, a photodetector 126-k, a continuous light source 127-k, an optical modulator 128-k, an intensity modulator 129-k, and a communication control unit 134-k.

[0046] The communication control unit 134-k is a means for performing communication control processing for the entire ONU 121-k.

[0047] 1, the downstream AMCC signal received by the communication control unit 134-k (hereinafter referred to as the "downstream received AMCC signal") is designated by the symbol 131-k. Also, in FIG. 1, the upstream AMCC signal transmitted by the communication control unit 134-k to the optical distribution network 116 side (PON side) (hereinafter referred to as the "upstream transmitted AMCC signal") is designated by the symbol 133-k.

[0048] The continuous light source 127-k and the local oscillation light source 123-k are light sources that generate continuous light.

[0049] The optical modulator 128-k is a means for modulating the output light of the continuous light source 127-k in accordance with an upstream transmission information signal 132-k supplied from the subscriber side device SE-k, and outputting the modulated light to the intensity modulator 129-k.

[0050] The optical splitter 125-k has one input port and two output ports, and is a means for splitting the input light of the ONU 121-k into two and outputting them.

[0051] The optical receiver 126-k is means for converting one of the output lights of the optical branching device 125-k into an electrical signal and outputting it to the communication control unit 134-1 as a downstream reception AMCC signal 131-k received from the OLT 101-k.

[0052] The optical modulator 128-k performs modulation in accordance with the upstream transmission information signal 132-k.

[0053] The coherent receiver 124 has two input ports and one output port, and is a means for outputting an electrical signal that is a beat component between the remaining output light of the optical splitter 125-k and the continuous light output from the local oscillation light source 123-k as a downstream received information signal 130-k.

[0054] The intensity modulator 129-k is a means for intensity-modulating the light output from the optical modulator 128-k in accordance with the upstream transmission AMCC signal 133-k.

[0055] The optical directional coupler 122-k has one input port and two input ports, and is a means for outputting the output light of the intensity modulator 129-k to the optical distribution network 116 and outputting the output light of the optical distribution network 116 to the optical branching device 125-k. Since the input and output directions of the optical directional coupler 122-k are specified, it can be realized using, for example, a directional optical coupler, optical branching device, optical circulator, or the like.

[0056] (A-2) Operation of the First Embodiment Next, the operation of the optical communication network system 1 according to the first embodiment will be described.

[0057] First, the overall operation of the optical communication network system 1 will be described.

[0058] Generally, a PON system is a point-to-multipoint communication system in which one OLT accommodates multiple ONUs. Furthermore, in a PON system, multiple access is generally achieved by time division or wavelength division between ONUs. In the optical communication network system 1 of this embodiment, a configuration in which multiple access is achieved by wavelength division multiplexing (WDM) using one optical distribution network 116 will be described, but the present invention is not limited to this.

[0059] In this embodiment, OLTs 101-1 to 101-M communicate with ONUs 121-1 to 121-N, respectively. Here, OLTs 101-1 to 101-M are described as transmitting downstream information signals to ONUs 121-1 to 121-N using optical signals with wavelengths λ1 to λM, respectively. Furthermore, in this embodiment, ONUs 121-1 to 121-N are described as transmitting upstream information signals to OLTs 101-1 to 101-M using optical signals with wavelengths v1 to vM, respectively. That is, OLT 101-j transmits downstream signals to ONU 121-k with a wavelength of λj, and ONU 121-k transmits upstream signals to OLT 101-j with a wavelength of vj.

[0060] In the following, communication between the OLT 101-j and the ONU 121-k will be described as one of the simultaneously connected lines in the optical communication network system 1.

[0061] First, downstream communication between the OLT 101-j and the ONU 121-k will be described.

[0062] Here, it is assumed that a downstream transmission information signal 108-j is supplied from the upper level device UE side to the OLT 101-j, and in the OLT 101-j, the downstream transmission information signal 108-j is supplied to an optical modulator 103-j.

[0063] In OLT 101-j, continuous light having a wavelength λj generated from continuous light source 102-j is modulated by optical modulator 103-j in accordance with downstream transmission information signal 108-j to generate an optical information signal. Optical information signals are transmitted in the same manner from M OLTs 101-1 to 101-M. If the wavelengths of the continuous light generated by different OLTs 101 are set to be different, the carrier wavelengths of the optical information signals transmitted from those OLTs 101 will be different. These optical information signals with different carrier wavelengths are multiplexed in optical multiplexer 112 to generate a WDM signal (hereinafter referred to as the "downstream WDM signal" or "downstream frequency multiplexed signal").

[0064] The downstream WDM signal is intensity-modulated to a small amplitude by the intensity modulator 114 in accordance with the multiplexed downstream transmission AMCC signal 111. This operation results in a signal (hereinafter also referred to as the "intensity-modulated downstream WDM signal") in which the multiplexed downstream transmission AMCC signal 111 and the downstream transmission information signal 108 are superimposed and multiplexed. The intensity-modulated downstream WDM signal is then sent to the optical distribution network 116 side (ONU 121-k side) through the optical directional coupler 115.

[0065] At this time, it is desirable that the components of the multiplexed downstream transmission AMCC signal 111 that are frequency-multiplexed onto the intensity-modulated downstream WDM signal are superimposed so as not to interfere with the low-frequency side of the downstream WDM signal (information signal). For example, in the intensity-modulated downstream WDM signal, it is desirable that the components of the multiplexed downstream transmission AMCC signal 111 have frequencies lower in the frequency domain than all frequencies included in the downstream WDM signal.

[0066] In ONU 121-k, an optical signal (hereinafter referred to as the "received optical signal") received from the optical distribution network 116 using optical directional coupler 122-k is supplied to the receiving section (optical splitter 125-k side). Then, in the receiving section, a portion of the received optical signal split by optical splitter 125-k is converted into an electrical signal using optical receiver 126-k. Here, if the frequency band of optical receiver 126-k and the subsequent electrical circuitry are designed to have low-pass characteristics that allow only the AMCC signal component to pass, optical receiver 126-k can directly convert the intensity of the received optical signal into an electrical signal, thereby obtaining downstream received AMCC signal 131-k.

[0067] The downstream reception AMCC signal 131-k is time-division multiplexed with AMCC information addressed to N ONUs 121. For example, the optical receiver 126-k can restore the AMCC information addressed to the ONU 121-k by extracting the AMCC information of a time slot that has been set in advance for the ONU 121-k in the control layer of the optical communication network system 1 (PON). Furthermore, for example, when the station-side optical transmission device 10 (control signal processing unit 118) time-division multiplexes the AMCC information, the optical receiver 126-k may execute a process to include address information (identifier) ​​of the destination ONU 121 in each AMCC information, and detect desired address information (address information of its own device) from the downstream reception AMCC signal 131-k and extract only the AMCC information that includes the address information.

[0068] Meanwhile, the remaining received optical signal branched by the optical branching unit 125-k is supplied to the coherent receiver 124-k. The coherent receiver 124-k performs coherent detection on the received optical signal using continuous light supplied from the local oscillator light source 123-k to extract the downstream received information signal 130-k. Here, by setting the wavelength of the continuous light output from the local oscillator light source 123-k to the same λj as that of the OLT 101-j (continuous light source 102-j), the coherent receiver 124-k demodulates only the optical signal of the wavelength channel containing the received information addressed to the ONU 121-k. Here, if the frequency band of the coherent receiver 124 and the subsequent electrical circuitry are designed to have high-pass characteristics that can block only the AMCC signal component, the coherent receiver 124 can restore only the received information addressed to the ONU 121-k. The coherent receiver 124 supplies the acquired downstream reception information signal 130-k to the subscriber side equipment SE-1.

[0069] Next, upstream communication between the OLT 101-j and the ONU 121-k will be described.

[0070] Here, it is assumed that an upstream transmission information signal 132-k is supplied from the subscriber-side device SE-k to the ONU 121-k. In the ONU 121-k, the upstream transmission information signal 132-k is supplied to the optical modulator 128-k. In the ONU 121-k, the continuous light having a wavelength νj generated by the continuous light source 127-k is modulated by the optical modulator 128-k in accordance with the upstream transmission information signal 132-k to generate an optical information signal. The optical information signal is intensity-modulated by the intensity modulator 129-k with a small amplitude in accordance with the upstream transmission AMCC signal 133-k. This operation results in a signal in which the upstream transmission information signal 132-k and the upstream transmission AMCC signal 133-k are superimposed and multiplexed. The superimposed and multiplexed signal is then transmitted to the optical distribution network 116 (OLT 101-k) through the optical directional coupler 122-k.

[0071] In the optical distribution network 116, superimposed signals of different wavelengths transmitted from N ONUs 121 in the upstream direction are combined to form a WDM signal (hereinafter referred to as the "upstream WDM signal"), which arrives at the optical transmission device 10 at the central office. In the optical transmission device 10 at the central office, the upstream WDM signal is supplied to the optical demultiplexer 113 via the optical directional coupler 115. The upstream WDM signal is then demultiplexed by the optical demultiplexer 113 to the OLTs 101 according to the wavelength channels, and each OLT 101 receives the demultiplexed light. In the OLT 101-j, the upstream received information signal 110-j and the upstream received AMCC signal 109-j are restored. Here, in the OLT 101-j, in order to restore the upstream received information signal 110-j, the wavelength of the continuous light output from the local oscillation light source 106-j becomes vj. Furthermore, since the optical signal received by OLT 101-j is an optical signal of the desired channel among the wavelength channels contained in the upstream WDM signal, the restored upstream received AMCC signal 109-j will only contain the AMCC signal of the desired channel (AMCC signal addressed to itself).

[0072] As described above, in the optical communication network system 1, information signals and AMCC signals are processed.

[0073] Next, the wavelengths of optical signals used in the optical communication network system 1 will be described.

[0074] The wavelength vj of the continuous light generated from the continuous light source 127-k may match one of the carrier wavelengths of the wavelength channels included in the downstream communication WDM signal, but in the case where it matches, the coherent receivers (124-k, 105-j) demodulate light that is a mixture of an optical signal in one direction and scattered light in the other direction due to backscattering in the optical distribution network 116. Therefore, it is desirable that the wavelength vj be different from all of the carrier wavelengths of the wavelength channels included in the downstream communication WDM signal. In other words, it is desirable that the wavelengths λ1 to λM and v1 to vM are all different wavelengths. Similarly, the wavelength λj of the continuous light generated by the continuous light source 102-j in the OLT 101-j may match one of the carrier wavelengths of the wavelength channels included in the upstream WDM signal. However, if the wavelength λj matches, the coherent receiver (124-k, 105-j) will demodulate a mixture of one-way optical signals and other-way scattered light due to backscattering in the optical distribution network 116. Therefore, it is desirable that the wavelength λj be different from all of the carrier wavelengths of the wavelength channels included in the upstream WDM signal. Furthermore, there is a concern that the AMCC signals may be received mixedly in the upstream and downstream due to backscattering in the optical distribution network 116. Therefore, for example, in the optical communication network system 1, it is desirable to frequency-multiplex the AMCC signals in the upstream and downstream directions and apply a means for frequency separation in the electrical circuit after the optical receivers (104-j, 126-k). The above configuration may be realized, for example, by using the technology described in Reference 1 below.

[0075] [Reference 1] Takuya Kanai et al., "Study on management and control of operational end-end optical paths using AMCC signals in All-Photonics Networks," 2022 IEICE General Conference on Communications, B-8-3.

[0076] (A-3) Effects of the First Embodiment According to the first embodiment, the following effects can be achieved.

[0077] In the optical communication network system 1 of the first embodiment, transmission of information signals between the optical transmission device 10 at the central office and the ONU 121 is realized by optical coherent transmission, which enables high-speed and large-capacity upgrades of the subscriber optical network. In particular, the optical communication network system 1 of the first embodiment has the advantage of being able to realize wavelength control using AMCC, which is adopted in standard NG-PON2.

[0078] Furthermore, the optical transmission device 10 at the optical station side in the first embodiment generates a multiplexed downstream transmission AMCC signal 111 by multiplexing downstream transmission AMCC signals 119-1 to 119-N, and further intensity-modulates the downstream WDM signal in accordance with the multiplexed downstream transmission AMCC signal 111 to obtain an intensity-modulated downstream WDM signal, which is then sent to the optical distribution network 116. Then, the ONU 121 at the optical station side demodulates the multiplexed downstream transmission AMCC signal 111 from the intensity-modulated downstream WDM signal, and obtains an AMCC signal addressed to the ONU 121 from the demodulated multiplexed downstream transmission AMCC signal 111. This allows each ONU 121 to independently communicate its own AMCC signal with the optical transmission device 10 at the optical station side (OLT 101), even when colorless reception is performed using a coherent optical transmission method. In other words, the ONU 121 of the first embodiment can communicate an AMCC signal with the optical transmission device 10 (OLT 101) at the central office side without being equipped with a tunable optical filter that is provided in a conventional WDM-PON (NG-PON2). As a result, in the first embodiment, even if each device is made coherent to increase capacity, it is possible to suppress an increase in the size and power consumption of the device.

[0079] (B) Second embodiment Hereinafter, the optical communication network system according to the present invention will be described. Mu and A second embodiment of the subscriber-side optical transmission device will be described in detail with reference to the drawings.

[0080] (B-1) Configuration of the second embodiment FIG. 2 is a block diagram showing the overall configuration of an optical communication network system 1A according to the second embodiment.

[0081] In FIG. 2, the same or corresponding parts as those in FIG. 1 are denoted by the same or corresponding reference numerals.

[0082] The following describes the differences between the optical communication network system 1A of the second embodiment and the first embodiment.

[0083] The optical communication network system 1A of the second embodiment differs from the first embodiment in that the optical transmission device 10, the ONU 121, and the optical distribution network 116 are replaced with an optical transmission device 10A, an ONU 121A, and an optical distribution network 116A, respectively.

[0084] In the first embodiment, one optical distribution network 116 is shared by upstream signals and downstream signals, but in the optical distribution network 116A of the second embodiment, the network is divided into a downstream unidirectional transmission path 401 for transmitting downstream signals and an upstream unidirectional transmission path 402 for transmitting upstream signals.

[0085] In the first embodiment, the upstream signal and the downstream signal shared one optical distribution network 116, so it was necessary to apply different wavelengths to the upstream signal and the downstream signal, but in the second embodiment, they are separated into a downstream unidirectional transmission line 401 and an upstream unidirectional transmission line 402, so there is no problem in applying a light source with a common wavelength for transmission and reception in each OLT 101A and each ONU 121A. As a result, in each device of the second embodiment, the number of some elements can be reduced compared to the first embodiment.

[0086] Next, differences in the configuration of the optical transmission device 10A from the first embodiment will be described.

[0087] In the optical transmission device 10A on the station side, the optical directional coupler 115 is omitted compared to the first embodiment. In the optical transmission device 10A on the station side, the downstream unidirectional transmission line 401 is directly connected to the intensity modulator 114. In addition, in the optical transmission device 10A on the station side, the upstream unidirectional transmission line 402 is directly connected to the optical demultiplexer 113.

[0088] Next, differences in the configuration of the OLT 101A-j from the first embodiment will be described.

[0089] The OLT 101A-j differs from the first embodiment in that the continuous light source 102-j and local oscillator light source 106-j are replaced with a continuous light source 202-j and optical splitter 206-j. The continuous light source 202-j is a means for generating continuous light. The optical splitter 206-j has one input port and two output ports, and splits the output light of the continuous light source 202-j into two, one for the optical modulator 103-j and the other for the coherent receiver 105-j. That is, in the first embodiment, the OLT 101-j was equipped with two light sources (the continuous light source 102 and the local oscillator light source 106), one for transmission and one for reception, but the OLT 101A-j of the second embodiment is configured to split the light from a single light source (the continuous light source 202-j) and share it for both transmission and reception.

[0090] Next, differences in the configuration of ONU 121A-k from the first embodiment will be described.

[0091] In the ONU 121A-k, the optical directional coupler 122-k is omitted compared to the first embodiment. In the ONU 121A-k, the downstream unidirectional transmission path 401 is directly connected to the coherent receiver 124-k. In the ONU 121A-k, the upstream unidirectional transmission path 402 is directly connected to the intensity modulator 129-k.

[0092] Furthermore, the ONU 121A-k differs from the first embodiment in that the continuous light source 127-k and local oscillator light source 123-k are replaced with a continuous light source 223-k and optical splitter 227-k. The continuous light source 223-k is a means for generating continuous light. The optical splitter 227-k has one input port and two output ports, and splits the output light of the continuous light source 223-k into two, one for the optical modulator 128-k and the other for the coherent receiver 124-k. That is, in the first embodiment, the ONU 121-k has two light sources (the continuous light source 127 and the local oscillator light source 123) for transmission and reception, but the ONU 121A-k of the second embodiment is configured to split the light from a single light source (the continuous light source 223-k) and share it for both transmission and reception.

[0093] (B-2) Operation of the Second Embodiment Next, the operation of the optical communication network system 1A according to the second embodiment will be described.

[0094] In the following, only the differences in the operation of the optical communication network system 1A from the first embodiment will be described.

[0095] The optical distribution network 116A (downstream unidirectional transmission line 401 and upstream unidirectional transmission line 402) is a one-to-multiple unidirectional transmission line for both downstream and upstream communications. Figure 2 shows a device configuration suitable for optical transmission on such a transmission line.

[0096] As described above, in the OLT 101A-j and the ONU 121A-k, the transmitting and receiving sides share a single continuous light source, i.e., the continuous light source 202-j, 223-k, respectively. Therefore, optical signals are transmitted and received using the same wavelength for downstream and upstream communications between the OLT 101A-j and the ONU 121A-k.

[0097] Unlike the first embodiment, the optical distribution network 116A (downstream unidirectional transmission path 401 and upstream unidirectional transmission path 402) is not a bidirectional transmission path, so bidirectional communication is possible even if the optical directional coupler 115 and the optical directional coupler 122 of each ONU 121A are omitted.

[0098] In the optical distribution network 116A (downstream unidirectional transmission path 401 and upstream unidirectional transmission path 402), the transmission paths are separate for downstream communication and upstream communication, so that light in which an optical signal in one direction and scattered light in the other direction are mixed due to backscattering on the transmission path is not demodulated by the coherent receivers 124-k and 105-j. Therefore, in the optical communication network system 1A of the second embodiment, even if the downstream signal light and the upstream signal light have the same wavelength, no degradation in transmission quality occurs due to the influence of the backscattered light.

[0099] (B-3) Effects of the Second Embodiment According to the second embodiment, in addition to the effects of the first embodiment, the following effects can be achieved.

[0100] In the optical communication network system 1A of the second embodiment, the OLT 101A-j and the ONU 121A-k can achieve the effects of reducing the number of light sources that are active elements, reducing power consumption, and downsizing the device.

[0101] In the optical communication network system 1A of the second embodiment, because the transmission paths are separated for downstream communication and upstream communication, the number of wavelengths required for transmitting and receiving information signals can be reduced by half, thereby increasing the available wavelength band. As a result, in the optical communication network system 1A of the second embodiment, it becomes possible to add another wavelength channel to the available band or to introduce another optical system. Such an effect contributes to increasing the capacity, number of users, and number of services of a system using the optical communication network system 1A. [Explanation of symbols]

[0102] 1, 1A... optical communication network system, 10, 10A... station side optical transmission device, 101, 101A... OLT, 102... continuous light source, 106... local oscillation light source, 108... transmission information signal, 111... transmission AMCC signal, 112... optical multiplexer, 113... optical demultiplexer, 114... intensity modulator, 115... optical directional coupler, 116, 116A... optical distribution network, 118... control signal processing unit, 119... transmission AMCC signal, 121, 121A... ONU, 123... local oscillation light source, 124 ...coherent receiver, 125...optical splitter, 126...optical receiver, 127...continuous light source, 128...optical modulator, 129...intensity modulator, 130...received information signal, 131...received AMCC signal, 132...transmitted information signal, 133...transmitted AMCC signal, 134...communication control unit, 202...continuous light source, 206...optical splitter, 223...continuous light source, 227...optical splitter, 401...downstream unidirectional transmission path, 402...upstream unidirectional transmission path, SE...subscriber side device, UE...upstream side device

Claims

1. In an optical communication network system in which a station-side optical transmission device and a plurality of subscriber-side optical transmission devices are connected by optical branching transmission lines, the optical transmission device at the station side, a plurality of optical transmission terminals for transmitting and receiving signals to and from any one of the subscriber-side optical transmission devices; an optical multiplexer that wavelength-division multiplexes downstream optical signals sent from each of the optical transmission terminals to generate downstream frequency-multiplexed signals; a station-side intensity modulation means for holding a time-division multiplexed control signal obtained by time-division multiplexing downstream control signals for each of the subscriber-side optical transmission devices, intensity-modulating the downstream frequency-multiplexed signal in accordance with the time-division multiplexed control signal, generating an intensity-modulated downstream frequency-multiplexed signal, and transmitting the intensity-modulated downstream frequency-multiplexed signal to the optical branch transmission line side; Each of the subscriber-side optical transmission devices is an extracting means for directly detecting the intensity of the intensity-modulated downstream frequency multiplexed signal to extract the time division multiplexing control signal; and extracting means for extracting the downstream control signal addressed to the device itself from the demodulated time division multiplexed control signal. An optical communication network system comprising:

2. 2. The optical communication network system according to claim 1, wherein each of the subscriber-side optical transmission devices further comprises a coherent receiver that demodulates the intensity-modulated downstream frequency-multiplexed signal transmitted from the optical transmission terminal unit by coherent detection.

3. 3. The optical communication network system according to claim 2, wherein the downstream control signal is an AMCC signal.

4. 2. The optical communication network system according to claim 1, wherein the optical branch transmission line is composed of a downstream unidirectional transmission line used only for downstream communication and an upstream unidirectional transmission line used only for upstream communication.

5. In the subscriber-side optical transmission device constituting an optical communication network system in which a station-side optical transmission device and a plurality of subscriber-side optical transmission devices are connected by optical branching transmission lines, an extraction means for, when an intensity-modulated downstream frequency-multiplexed signal is supplied from the optical branch transmission line, the intensity-modulated downstream frequency-multiplexed signal being obtained by frequency-multiplexing a plurality of downstream optical signals and further intensity-modulating the downstream control signals with a time-division multiplexed control signal, directly detecting the intensity of the intensity-modulated downstream frequency-multiplexed signal and extracting the time-division multiplexed control signal; extraction means for extracting a downstream control signal addressed to the device itself from the demodulated time division multiplexed control signal; A subscriber-side optical transmission device comprising:

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