Optical communication network system and subscriber-side optical transmission device

Abstract

The present invention provides an optical communication network system, a central office optical transmission device, and a subscriber optical transmission device that transmit control signals to each subscriber optical transmission device without hindrance when the central office optical transmission device is connected to multiple subscriber optical transmission devices using an optical branch transmission path. [Solution] An optical communication network system 1 in which a central office optical transmission device 10 and a plurality of subscriber-side optical transmission devices (ONUs) are connected by an optical distribution network 116, wherein the central office optical transmission device includes a plurality of optical transmission termination units (OLTs), an optical multiplexer that generates a downlink frequency multiplexed signal by wavelength division multiplexing a downlink optical signal, and an intensity modulator that holds a time division multiplexed control signal obtained by time division multiplexing a downlink control signal, generates a downlink frequency multiplexed signal by intensity modulating the downlink frequency multiplexed signal accordingly, and sends it to the optical branch transmission path side. The subscriber-side optical transmission device demodulates the time division multiplexed control signal from the downlink frequency multiplexed signal and extracts the downlink control signal from the demodulated time division multiplexed control signal.

Description

Technical Field

[0001] The present invention relates to an optical communication network system, a central office side optical transmission device, and a subscriber side optical transmission device, and can be applied to an optical communication network system such as a PON (Passive Optical Network), for example.

Background Art

[0002] Currently, due to the evolution of mobile terminals, the expansion of the use of SNS centered on video sharing, the spread of unmanned online services due to the progress of artificial intelligence (AI) technology, etc., the communication demand is rapidly increasing, and there is also a demand for increased capacity in the transmission devices of subscriber-side optical networks.

[0003] In a conventional subscriber-side optical network, an optical transmission system called PON (Passive Optical Network) is applied. In PON, a plurality of optical transceiver devices provided on the subscriber side are connected to one optical transceiver device provided on the central office side via a partially shared optical fiber transmission path, and one-to-many communication between the central office and a plurality of subscribers is performed using optical multiplexing / multiple access transmission technology.

[0004] In NG-PON2 standardized by ITU-T (International Telecommunication Union Telecommunication Standardization Sector), time division multiplexing / multiple access (TDM (Time Division-Multiplexing) / TDMA (time division-Multiple access)) and wavelength division multiplexing (WDM (Wavelength Division Multiplexing)) technologies are combined to define a total transmission capacity of up to 40 Gb / s (see Non-Patent Document 1).

[0005] Here, we will explain the configuration of a conventional NG-PON2 (optical communication network system compatible with NG-PON2). In a conventional NG-PON2, the OLT (Optical Line Terminal), which is the optical transmission device on the central office side, and the ONU (Optical Network Unit), which is the optical transmission device on the subscriber side, are connected by optical branch transmission paths that are branched by multiplexers. Furthermore, each OLT that makes up a conventional NG-PON2 transmits / receives optical signals having individual wavelengths that constitute wavelength division multiplexing signals. In addition, the multiplexers that make up a conventional NG-PON2 combine the signal light of different wavelengths sent from each OLT in downlink communication, and separate each wavelength of the wavelength division multiplexing signal in uplink communication. Furthermore, the optical distribution network that makes up a conventional NG-PON2 is composed of passive optical elements such as optical fibers, optical couplers, and optical branchers. In downlink communication, it transmits and branches the wavelength division multiplexing signals bundled by the multiplexers and distributes them to each ONU, and in uplink communication, it combines and transmits the optical signals sent from each ONU to the central office side. Furthermore, the ONU that constitutes the conventional NG-PON2 is the subscriber-side termination device and possesses a wavelength selection function, transmitting / receiving signals of the wavelengths assigned to it.

[0006] Thus, one of the features of conventional NG-PON2 is the adoption of WDM technology. Furthermore, conventional NG-PON2 defines a control channel called AMCC (Auxiliary-Management And Control Channel), through which the wavelengths used in the system are arranged and distributed, and a wavelength channel is assigned to each ONU. The AMCC signal is superimposed so as not to interfere with the low-frequency side of the user signal in the frequency domain, and can coexist with user optical signals of any format in the time / wavelength domain as long as no interference occurs.

[0007] Details of conventional AMCC signals are described in Non-Patent Literature 2. Specifically, Non-Patent Literature 2 describes the conventional AMCC signal transmission and reception procedure as follows: In conventional AMCC signal processing, the transmitting side uses an external modulator to intensity modulate the main signal light. In addition, in conventional AMCC signal processing, by making the modulation speed smaller than the lowest frequency of the user signal spectrum, the AMCC signal and the user signal can be separated in the frequency domain. Furthermore, in conventional AMCC signal processing, by making the modulation index of intensity modulation sufficiently small, waveform distortion of the user signal can be sufficiently reduced. Moreover, in conventional AMCC signal processing, the receiving side can detect the AMCC signal by branching a portion of the transmitted superimposed signal, directly detecting it and filtering out only the low-frequency components, or by using a narrowband photodetector and electrical circuit. Furthermore, in conventional AMCC signal processing, after detecting the remainder of the branched received light, the user signal can be extracted by removing the AMCC signal in the frequency domain.

[0008] On the other hand, 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 by utilizing advances in digital signal processing (DSP) technology, to subscriber optical networks with transmission distances of at most 20 kilometers. In conventional coherent optical transmission, continuous light (LO light) output from a locally oscillating (LO) light source is coupled to the received light at the receiving end, and after photoelectric conversion, their beat components are detected as electrical signals (coherent detection). Since conventional coherent detection detects the phase information of the received light, multi-level modulation formats that use phase information for signal identification, such as QPSK (Quadrature Phase Shift Keying) and QAM (Quadrature Amplitude Modulation), can be adopted for optical signals, enabling high-speed transmission bitrates while suppressing increases in modulation speed. Furthermore, in conventional coherent optical transmission processing, by using a sufficiently large LO optical power, electrical signals with a high signal-to-noise ratio can be detected, improving reception sensitivity compared to the intensity-modulated optical signal reception formats conventionally used in PON systems. This is a favorable characteristic for PON systems, where branching losses in the optical distribution network are large.

[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, due to the bandwidth limitation of the electrical circuit including the photodetector, the desired signal is not detected if the frequency difference between the received light and the LO light is greater than the frequency bandwidth of that electrical circuit. Conventionally, colorless detection, which 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 Non-Patent Document 3, etc. This characteristic leads to the omission of some optical components, which is particularly advantageous for PON systems where miniaturization and cost reduction are required on the subscriber's 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 a 100G Coherent PON System for 5G Optical Conversion," 2016 IEICE Communications 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 [Overview of the project] [Problems that the invention aims to solve]

[0011] As described above, conventionally, constructing PON systems employing coherent transmission technology and WDM technology is a promising means of meeting the demand for increased transmission capacity. Furthermore, in conventional PON systems using coherent transmission, colorless detection can be said to be a means of miniaturizing and reducing the cost of the ONU. However, in conventional PON systems using coherent transmission, in downlink communication, the ONU does not have an optical filter, and in AMCC signal reception, the received light is directly detected, so the AMCC signal reception section detects the AMCC signals of all channels included in the WDM signal. In other words, in conventional PON systems using coherent transmission, there was a risk of interference between the AMCC signals of all users in the AMCC signal reception section of each ONU.

[0012] In light of the above-mentioned problems, there is a need for an optical communication network system that can transmit control signals (e.g., AMCC signals, etc.) from the central office optical transmission device to each subscriber optical transmission device without any problems when the central office optical transmission device and multiple subscriber optical transmission devices are connected using an optical branch transmission path. [Means for solving the problem]

[0013] The first aspect of the present invention relates to an optical communication network system in which a central office optical transmission device and a plurality of subscriber-side optical transmission devices are connected by an optical branch transmission path, wherein the central office optical transmission device comprises a plurality of optical transmission termination units that transmit and receive signals with any of the subscriber-side optical transmission devices, an optical multiplexer that generates a downlink frequency multiplexed signal by wavelength division multiplexing the downlink optical signals transmitted from each of the optical transmission termination units, and a central office intensity modulation means that holds a time division multiplexed control signal obtained by time division multiplexing the downlink control signal for each of the subscriber-side optical transmission devices, and modulates the downlink frequency multiplexed signal with intensity according to the time division multiplexed control signal to generate an intensity modulated downlink frequency multiplexed signal and transmits it to the optical branch transmission path side, and each of the subscriber-side optical transmission devices comprises a demodulation means for demodulating the time division multiplexed control signal from the intensity modulated downlink frequency multiplexed signal, and an extraction means for extracting the downlink control signal addressed to itself from the demodulated time division multiplexed control signal.

[0014] The second aspect of the present invention relates to a central office optical transmission device that constitutes an optical communication network system in which a central office optical transmission device and a plurality of subscriber-side optical transmission devices are connected by an optical branch transmission path, characterized in that the central office optical transmission device comprises a plurality of optical transmission termination units that transmit and receive signals with any of the subscriber-side optical transmission devices, an optical multiplexer that generates a downlink frequency multiplexed signal by wavelength division multiplexing the downlink optical signal sent from each of the optical transmission termination units, a central office intensity modulation means that holds a time division multiplexed control signal obtained by time division multiplexing the downlink control signal to each of the subscriber-side optical transmission devices, modulates the downlink frequency multiplexed signal in accordance with the time division multiplexed control signal to generate an intensity modulated downlink frequency multiplexed signal and sends it to the optical branch transmission path side, and an optical demultiplexer that, when an uplink multiplexed signal sent from each of the subscriber-side optical transmission devices and wavelength division multiplexed on the optical branch transmission path is supplied, demultiplexes the uplink multiplexed signal to extract an uplink signal of a single carrier wavelength and supplies it to each of the optical transmission termination units.

[0015] The third aspect of the present invention relates to a subscriber-side optical transmission device that constitutes an optical communication network system in which a central office-side optical transmission device and a plurality of subscriber-side optical transmission devices are connected by an optical branch transmission path. The subscriber-side optical transmission device is characterized in that, when a plurality of downlink optical signals are frequency multiplexed and a plurality of downlink control signals are further frequency multiplexed and intensity modulated by a time-division multiplexed control signal is supplied from the optical branch transmission path, the subscriber-side optical transmission device has a demodulation means for demodulating the time-division multiplexed control signal from the intensity-modulated downlink frequency multiplexed signal, and an extraction means for extracting a downlink control signal destined for the device itself from the demodulated time-division multiplexed control signal. [Effects of the Invention]

[0016] According to the present invention, when a central office-side optical transmission device and a plurality of subscriber-side optical transmission devices are connected using an optical branch transmission path, control signals can be transmitted from the central office-side optical transmission device to each subscriber optical transmission device without any problems. [Brief explanation of the drawing]

[0017] [Figure 1]It is a block diagram showing the functional configuration of an optical communication network system (including a station-side optical transmission device and a subscriber-side optical transmission device) according to the first embodiment. [Figure 2] It is a block diagram showing the functional configuration of an optical communication network system (including a station-side optical transmission device and a subscriber-side optical transmission device) according to the second embodiment.

Embodiments for Carrying Out the Invention

[0018] (A) First Embodiment Hereinafter, a first embodiment of an optical communication network system, a station-side optical transmission device, and a subscriber-side optical transmission device according to the present invention 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 a station-side optical transmission device 10 as a station-side optical transmission device and N (N is an integer of 2 or more) ONUs 121 (121-1 to 121-N) as subscriber-side optical transmission devices. The station-side optical transmission device 10 and the ONUs 121 (121-1 to 121-N) are connected by an optical distribution network 116 as a plurality of branched (N-branched) optical branch transmission paths, and the station-side optical transmission device 10 and the ONUs 121-1 to 121-N are transmitting and receiving optical signals bidirectionally. That is, in the optical communication network system 1, the station-side 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 local optical transmission device 10 to the ONU 121 is referred to as "downlink", and the direction from the ONU 121 to the local optical transmission device 10 is referred to as "uplink". Also, in the following, an integer k (any one of 1 to N) is introduced as a symbol for generally representing an arbitrary ONU 121, and "-k" is appended to the elements unique to an arbitrary ONU 121-k. Furthermore, in the following, when explaining the k-th ONU 121-k, the phrases such as "the k-th" and "inside the k-th ONU" may be omitted.

[0022] The optical distribution network 116 is a one-to-many bidirectional transmission path (a branched optical distribution transmission path) composed of passive optical elements such as optical fibers and optical couplers / splitters, having one port on the local side and N or more ports on the subscriber side.

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

[0024] Also, in this embodiment, it is assumed that subscriber-side devices SE (SE-1 to SE-N) are respectively connected to the lower sides (subscriber sides) of the ONUs 121 (121-1 to 121-N). The subscriber-side devices SE (SE-1 to SE-N) correspond to subscriber-side communication devices such as routers, PCs, and switching hubs. Also, in this embodiment, it is assumed that an upper-side device UE is connected to the upper side of the local optical transmission device 10. The upper-side device UE corresponds to network devices such as routers and switching hubs.

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

[0026] The local optical transmission device 10 has M optical transmission 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 processing unit 118.

[0027] The number of OLT101s provided by the station-side optical transmission device 10 may be M or more. Furthermore, in the following, the symbol j will be introduced to represent any OLT101 in general terms, and elements specific to any OLT101-j will be denoted with "-j". In addition, in the following, when describing the j-th OLT101-j, phrases such as "the j-th" or "within the j-th OLT" may be omitted. Furthermore, in Figure 1, the code for the downlink information signal (hereinafter referred to as the "downlink transmission information signal") received by the j-th OLT101-j from the upstream device UE is 108-j. Also in Figure 1, the code for the uplink information signal (hereinafter referred to as the "uplink transmission information signal") transmitted by the j-th OLT101-j to the upstream device UE is 110-j.

[0028] The control signal processing unit 118 receives downlink AMCC signals (hereinafter referred to as "downlink transmission AMCC signals") 119-1 to 119-M from each OLT 101-1 to OLT-M and generates a signal (hereinafter referred to as "multiplexed downlink transmission AMCC signal" or "time-division multiplexed control signal") 111 by time-division multiplexing the downlink transmission AMCC signals 119-1 to 119-M. The control signal processing unit 118 supplies the multiplexed downlink transmission AMCC signal 111 to the intensity modulator 114.

[0029] The optical multiplexer 112 is a means for combining multiple optical signals having different carrier wavelengths, and has more than M input ports (more than the number of OLT 101s) and one output port.

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

[0031] The intensity modulator 114 is a means for intensity-modulating the light output from the optical multiplexer 112 according to the multiplexed downlink 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 of 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 direction of input and output is specified, the optical directional coupler 115 can be configured using, for example, a directional optical coupler, optical splitter, or optical circulator.

[0033] Next, we will describe the internal configuration of each OLT101.

[0034] In this embodiment, OLT101-1 to 101-M are assumed to have similar configurations. Below, the internal configuration of the jth OLT101-j will be described, with OLT101-1 to 101-M being the representative.

[0035] As shown in Figure 1, the j-th OLT 101-j includes a continuous light source 102-j, an optical modulator 103-j, a photodetector 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 communication by the OLT 101-j. The communication control unit 117-j supplies the downlink transmission AMCC signal 119-k addressed to the ONU 121-k to the control signal processing unit 118.

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

[0038] The optical modulator 103-j is a means of modulating the output light from the continuous light source 102-j according to the downlink transmission information signal 108-j and outputting the modulated light. The output of the optical modulator 103-j becomes the output of the jth OLT 101-j.

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

[0040] The light receiver 104-j converts one of the output light signals from the optical splitter 107-j into an electrical signal and outputs it to the communication control unit 117-j as the AMCC signal 109-k received from the ONU 121-k (hereinafter referred to as the "uplink received AMCC signal").

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

[0042] Next, we will explain the internal configuration of each ONU121.

[0043] In this embodiment, ONU121-1 to 121-N are assumed to have a similar configuration. Below, the internal configuration of the kth ONU121-k will be described as a representative example of ONU121-1 to 121-N.

[0044] In Figure 1, the code for the upstream information signal (hereinafter referred to as the "upstream transmission information signal") received by ONU121-k from the subscriber-side device SE-k is set to 132-k. Also in Figure 1, the code for the downstream information signal (hereinafter referred to as the "downstream transmission information signal") transmitted by ONU121-k to the subscriber-side device SE-k is set to 130-k.

[0045] ONU121-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] In Figure 1, the code for the downlink AMCC signal received by the communication control unit 134-k (hereinafter referred to as the "downlink received AMCC signal") is 131-k. Also in Figure 1, the code for the uplink AMCC signal transmitted by the communication control unit 134-k to the optical distribution network 116 side (PON side) (hereinafter referred to as the "uplink transmitted AMCC signal") is 133-k.

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

[0049] The optical modulator 128-k modulates the output light from the continuous light source 127-k according to the uplink transmission information signal 132-k supplied from the subscriber-side device SE-k, and outputs 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 of splitting the input optical signal from the ONU 121-k into two outputs.

[0051] The light receiver 126-k is a means of converting one of the output light signals from the optical splitter 125-k into an electrical signal and outputting it to the communication control unit 134-1 as the downlink received AMCC signal 131-k received from the OLT 101-k.

[0052] The optical modulator 128-k modulates according to the uplink transmission information signal 132-k.

[0053] The coherent receiver 124 has two input ports and one output port, and is a means of outputting an electrical signal which is the beat component of the remaining output light of the optical splitter 125-k and the output continuous light of the local oscillator 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 according to the uplink 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 splitter 125-k. Since the direction of input and output of the optical directional coupler 122-k is specified, it can be realized using, for example, a directional optical coupler, optical splitter, or optical circulator.

[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, I will explain the operation of the entire optical communication network system 1.

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

[0059] In this embodiment, OLT101-1 to 101-M communicate with ONU121-1 to 121-N, respectively. Furthermore, OLT101-1 to 101-M are described as transmitting downstream information signals to ONU121-1 to ONU121-N using optical signals with wavelengths λ1 to λM, respectively. In addition, in this embodiment, ONU121-1 to ONU121-N are described as transmitting upstream information signals to OLT101-1 to 101-M using optical signals with wavelengths ν1 to νM, respectively. That is, OLT101-j transmits a downstream signal to ONU121-k at a wavelength of λj, and ONU121-k transmits an upstream signal to OLT101-j at a wavelength of νj.

[0060] In the following section, we will describe the communication between OLT101-j and ONU121-k, representing one of the simultaneously connected lines in the optical communication network system 1.

[0061] First, let's explain the downlink communication between OLT101-j and ONU121-k.

[0062] Here, we assume that the downlink transmission information signal 108-j is supplied to the OLT101-j from the upper-level device UE. In the OLT101-j, the downlink transmission information signal 108-j is supplied to the optical modulator 103-j.

[0063] In OLT101-j, continuous light of wavelength λj generated from continuous light source 102-j is modulated using optical modulator 103-j according to downlink transmission information signal 108-j to generate an optical information signal. M OLTs 101-1 to 101-M similarly transmit optical information signals. 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 combined by optical multiplexer 112 to generate a WDM signal (hereinafter referred to as the "downlink WDM signal" or "downlink frequency multiplexed signal").

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

[0065] In this case, it is desirable that the components of the multiplexed downlink transmission AMCC signal 111, which are frequency multiplexed onto the intensity-modulated downlink WDM signal, be superimposed in such a way that they do not interfere with the low-frequency side of the downlink WDM signal (information signal). For example, in the intensity-modulated downlink WDM signal, it is desirable that the components of the multiplexed downlink transmission AMCC signal 111 have frequencies lower than all the frequencies included in the downlink WDM signal in the frequency domain.

[0066] In ONU121-k, the optical signal received from the optical distribution network 116 (hereinafter referred to as the "received optical signal") is supplied to the receiving section (optical splitter 125-k side) using the optical directional coupler 122-k. In this receiving section, a portion of the received optical signal, which has been split by the optical splitter 125-k, is converted into an electrical signal using the photodetector 126-k. If the frequency band of the photodetector 126-k and the subsequent electrical circuit are designed to have a low-pass characteristic that allows only the AMCC signal component to pass through, the photodetector 126-k can directly convert the intensity of the received optical signal into an electrical signal, thereby obtaining the downlink received AMCC signal 131-k.

[0067] The downlink received AMCC signal 131-k contains time-division multiplexed AMCC information for N ONU 121. For example, the photodetector 126-k can reconstruct the AMCC information for ONU 121-k by extracting the AMCC information for the time slot pre-set for ONU 121-k in the control layer of the optical communication network system 1 (PON). Alternatively, for example, when the station-side optical transmission device 10 (control signal processing unit 118) time-division multiplexes the AMCC information, it may be possible to perform processing to include the address information (identifier) ​​of the destination ONU 121 in each AMCC piece of information, and the photodetector 126-k may detect the desired address information (address information of its own device) from the downlink received AMCC signal 131-k and extract only the AMCC information containing that address information.

[0068] Meanwhile, the remaining portion of the received optical signal branched by the optical splitter 125-k is supplied to the coherent receiver 124-k. The coherent receiver 124-k extracts the downlink received information signal 130-k by performing coherent detection on the received optical signal using the continuous light supplied from the local oscillator light source 123-k. Here, by setting the wavelength of the continuous light output from the local oscillator light source 123-k to the same λj as the OLT 101-j side (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 circuit are designed to have a high-pass characteristic 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 downlink received information signal 130-k to the subscriber-side device SE-1.

[0069] Next, we will explain the uplink communication between OLT101-j and ONU121-k.

[0070] Here, it is assumed that the uplink 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 uplink transmission information signal 132-k is supplied to the optical modulator 128-k. In the ONU 121-k, the optical modulator 128-k modulates the continuous light of wavelength νj generated from the continuous light source 127-k according to the uplink transmission information signal 132-k to generate an optical information signal. This optical information signal is then subjected to small-amplitude intensity modulation by the intensity modulator 129-k according to the uplink transmission AMCC signal 133-k. This operation yields a signal in which the uplink transmission information signal 132-k and the uplink transmission AMCC signal 133-k are superimposed and multiplexed. This superimposed and multiplexed signal is then sent to the optical distribution network 116 side (OLT 101-k side) through the optical directional coupler 122-k.

[0071] In the optical distribution network 116, superimposed signals of different wavelengths transmitted from N ONUs 121 are combined in the uplink direction to form a WDM signal (hereinafter referred to as the "uplink WDM signal") which arrives at the central office optical transmission device 10. This uplink WDM signal is supplied to the optical demultiplexer 113 through the optical directional coupler 115 at the central office optical transmission device 10. The uplink WDM signal is then demultiplexed by the optical demultiplexer 113 to OLTs 101 corresponding to the wavelength channel, and each OLT 101 receives its respective demultiplexed light. In OLT 101-j, the uplink received information signal 110-j and the uplink received AMCC signal 109-j are reconstructed. Here, in OLT 101-j, in order to reconstruct the uplink received information signal 110-j, the wavelength of the continuous light output from the local oscillator light source 106-j becomes νj. Furthermore, since the optical signal received by OLT101-j is the optical signal of the desired channel among the wavelength channels included in the uplink WDM signal, the reconstructed uplink received AMCC signal 109-j will only contain the AMCC signal of the desired channel (the AMCC signal addressed to itself).

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

[0073] Next, we will explain the wavelength of the optical signals used in optical communication network system 1.

[0074] The wavelength νj of the continuous light generated from the continuous light source 127-k may coincide with one of the carrier wavelengths of the wavelength channels included in the downlink WDM signal. However, if they coincide, backscattering in the optical distribution network 116 results in a mixture of light from one direction and scattered light from the other direction, which is then demodulated by the coherent receiver (124-k, 105-j). Therefore, it is desirable that the wavelength νj is different from all of the carrier wavelengths of the wavelength channels included in the downlink WDM signal. In other words, it is desirable that wavelengths λ1 to λM and ν1 to νM are all different wavelengths. Similarly, the wavelength λj of the continuous light generated from the continuous light source 102-j in the OLT 101-j may coincide with one of the carrier wavelengths of the wavelength channels included in the uplink WDM signal. However, if they coincide, backscattering in the optical distribution network 116 causes a mixture of light from one direction and scattered light from the other direction, which is then demodulated by the coherent receiver (124-k, 105-j). Therefore, it is desirable that the wavelength λj differs from all of the carrier wavelengths of the wavelength channels included in the uplink WDM signal. Furthermore, similarly, there is a concern that AMCC signals may be received mixed up in the uplink and downlink due to backscattering in the optical distribution network 116. For this reason, it is desirable that, for example, in the optical communication network system 1, the AMCC signals are frequency multiplexed in the uplink and downlink, and that a means of frequency separation is applied in the electrical circuits after the photodetectors (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-to-End Optical Paths Using AMCC Signals in an All-Photonics Network," 2022 IEICE General Conference, 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, information signals are transmitted between the central office optical transmission device 10 and the ONU 121 by optical coherent transmission, enabling high-speed and high-capacity upgrades when upgrading subscriber optical networks. In particular, the optical communication network system 1 of the first embodiment has the advantage of enabling wavelength control using AMCC, which is adopted in standard NG-PON2.

[0078] Furthermore, in the first embodiment, the station-side optical transmission device 10 generates a multiplexed downlink transmission AMCC signal 111 by multiplexing downlink transmission AMCC signals 119-1 to 119-N, and then obtains an intensity-modulated downlink WDM signal by intensity-modulating the downlink WDM signal according to the multiplexed downlink transmission AMCC signal 111, and sends it to the optical distribution network 116. Then, in the first embodiment, the ONU 121 demodulates the multiplexed downlink transmission AMCC signal 111 from the intensity-modulated downlink WDM signal, and obtains an AMCC signal addressed to itself from the demodulated multiplexed downlink transmission AMCC signal 111. As a result, even if colorless reception is performed by the coherent optical transmission method in each ONU 121, each ONU 121 can independently communicate its respective AMCC signal with the station-side optical transmission device 10 (OLT 101). In other words, the ONU121 of the first embodiment can communicate AMCC signals with the central office optical transmission device 10 (OLT101) without having to install the variable optical filter that was present in the 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 the increase in size and power consumption of the devices.

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

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

[0081] In Figure 2, the same reference numerals or corresponding numerals are used for the same or corresponding parts as in Figure 1 described above.

[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 central office-side optical transmission device 10, ONU 121, and optical distribution network 116 are replaced by the central office-side optical transmission device 10A, ONU 121A, and optical distribution network 116A, respectively.

[0084] In the first embodiment, the optical distribution network 116 was shared by both the uplink and downlink signals. However, in the optical distribution network 116A of the second embodiment, the uplink unidirectional transmission path 401 for transmitting downlink signals and the uplink unidirectional transmission path 402 for transmitting uplink signals are separated.

[0085] In the first embodiment, since one optical distribution network 116 was shared for both uplink and downlink signals, it was necessary to apply different wavelengths to the uplink and downlink signals. However, in the second embodiment, the downlink unidirectional transmission line 401 and the uplink unidirectional transmission line 402 are separated, 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, we will explain the differences in the configuration of the station-side optical transmission device 10A compared to the first embodiment.

[0087] In the station-side optical transmission device 10A, the optical directional coupler 115 is omitted compared to the first embodiment. Furthermore, in the station-side optical transmission device 10A, the downlink unidirectional transmission path 401 is directly connected to the intensity modulator 114. Also, in the station-side optical transmission device 10A, the uplink unidirectional transmission path 402 is directly connected to the optical demultiplexer 113.

[0088] Next, we will explain the differences in the configuration of OLT101A-j compared to the first embodiment.

[0089] The OLT101A-j differs from the first embodiment in that the continuous light source 102-j and the local oscillator light source 106-j are replaced by a continuous light source 202-j and an 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 is a means for splitting the output light of the continuous light source 202-j into two, outputting one to the optical modulator 103-j and the other to the coherent receiver 105-j. In other words, in the first embodiment, the OLT101-j had two light sources (continuous light source 102 and local oscillator light source 106) for transmission and reception, but in the second embodiment, the OLT101A-j, the light from one light source (continuous light source 202-j) is split and shared for both transmission and reception.

[0090] Next, we will explain the differences in the configuration of the ONU121A-k compared to the first embodiment.

[0091] In the ONU121A-k, the optical directional coupler 122-k is omitted compared to the first embodiment. Furthermore, in the ONU121A-k, the downlink unidirectional transmission line 401 is directly connected to the coherent receiver 124-k. Also, in the ONU121A-k, the uplink unidirectional transmission line 402 is directly connected to the intensity modulator 129-k.

[0092] Furthermore, ONU121A-k differs from the first embodiment in that the continuous light source 127-k and local oscillator light source 123-k are replaced by a continuous light source 223-k and an 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 is a means for splitting the output light of the continuous light source 223-k into two, outputting one to the optical modulator 128-k and the other to the coherent receiver 124-k. In other words, in the first embodiment, ONU121-k had two light sources (continuous light source 127 and local oscillator light source 123) for transmission and reception, but in the second embodiment, ONU121A-k, the light from one light source (continuous light source 223-k) is split and shared 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 compared to the first embodiment will be described.

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

[0096] As described above, the OLT101A-j and ONU121A-k share a common continuous light source for both the transmitting and receiving sides, with each having a single continuous light source, 202-j and 223-k, respectively. Therefore, the OLT101A-j and ONU121A-k transmit and receive optical signals using the same wavelength for both downlink and uplink communication.

[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), since the transmission paths are separate for downstream and upstream communication, backscattering on the transmission path prevents the coherent receivers 124-k and 105-j from demodulating light that is a mixture of optical signals from one direction and scattered light from the other direction. Therefore, in the optical communication network system 1A of the second embodiment, even if the downstream signal light and the upstream signal light are of the same wavelength, no degradation of transmission quality due to the influence of the backscattered light occurs.

[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 OLT101A-j and ONU121A-k can achieve effects such as a reduction in the number of active elements (light sources), a reduction in power consumption, and miniaturization of the device.

[0101] In the optical communication network system 1A of the second embodiment, since the transmission paths are separated for downlink and uplink communication, the number of wavelengths required for transmitting and receiving information signals can be reduced by half, and the available wavelength bandwidth can be increased accordingly. As a result, in the optical communication network system 1A of the second embodiment, it is possible to add another wavelength channel or introduce another optical system in the freed-up bandwidth. Such effects contribute to increasing the capacity, increasing the number of users, and increasing the number of services of the system using the optical communication network system 1A. [Explanation of Symbols]

[0102] 1,1A…Optical communication network system, 10,10A…Central-side optical transmission equipment, 101,101A…OLT, 102…Continuous light source, 106…Local oscillator light source, 108…Transmitted information signal, 111…Transmitted 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…Transmitted AMCC signal, 121,121A…ONU, 123…Local oscillator light source, 124 ...Coherent receiver, 125...Optical splitter, 126...Photodetector, 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 line, 402...Upstream unidirectional transmission line, SE...Subscriber-side equipment, UE...Higher-level equipment

Claims

1. In an optical communication network system in which a central office-side optical transmission device and multiple subscriber-side optical transmission devices are connected by an optical branch transmission path, The aforementioned station-side optical transmission device is, A plurality of optical transmission termination units that transmit and receive signals with any of the subscriber-side optical transmission devices, An optical multiplexer generates a downstream frequency multiplexed signal by wavelength division multiplexing the downstream optical signals transmitted from each of the aforementioned optical transmission terminations, The system includes a central office-side intensity modulation means that holds a time-division multiplexed control signal obtained by time-division multiplexing the downlink control signals for each of the subscriber-side optical transmission devices, and generates an intensity-modulated downlink frequency multiplexed signal by intensity-modulating the downlink frequency multiplexed signal according to the time-division multiplexed control signal, and sends it to the optical branch transmission path side. Each of the subscriber-side optical transmission devices is Demodulation means for demodulating the time-division multiplexed control signal from the intensity-modulated down-frequency multiplexed signal, It includes an extraction means for extracting the downlink control signal destined for the device from the demodulated time-division multiplexed control signal. An optical communication network system characterized by the following features.

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

3. The optical communication network system according to claim 2, characterized in that the downlink control signal is an AMCC signal.

4. The optical communication network system according to claim 1, characterized in that the optical branching transmission path is composed of a downlink unidirectional transmission path used only for downlink communication and an uplink unidirectional transmission path used only for uplink communication.

5. In the central office-side optical transmission device that constitutes an optical communication network system in which the central office-side optical transmission device and a plurality of subscriber-side optical transmission devices are connected by an optical branch transmission path, A plurality of optical transmission termination units that transmit and receive signals with any of the subscriber-side optical transmission devices, An optical multiplexer generates a downstream frequency multiplexed signal by wavelength division multiplexing the downstream optical signals transmitted from each of the aforementioned optical transmission terminations, A central office-side intensity modulation means holds a time-division multiplexed control signal obtained by time-division multiplexing the downlink control signals for each of the subscriber-side optical transmission devices, and generates an intensity-modulated downlink frequency multiplexed signal by intensity-modulating the downlink frequency multiplexed signal according to the time-division multiplexed control signal, which is then sent to the optical branch transmission path side. When an uplink multiplexed signal, transmitted from each subscriber-side optical transmission device and wavelength-division multiplexed on the optical branch transmission path, is supplied, the uplink multiplexed signal is decoupled to extract an uplink signal of a single carrier wavelength, and supplied to each optical transmission termination. A station-side optical transmission device characterized by having the following features.

6. In a subscriber-side optical transmission device that constitutes an optical communication network system in which a central office-side optical transmission device and a plurality of subscriber-side optical transmission devices are connected by an optical branch transmission path, When multiple downlink optical signals are frequency multiplexed, and multiple downlink control signals are time-division multiplexed, and an intensity-modulated downlink frequency multiplexed signal is supplied from the optical branch transmission line, a demodulation means demodulates the time-division multiplexed control signals from the intensity-modulated downlink frequency multiplexed signal, Extraction means for extracting a downlink control signal destined for the device from the demodulated time-division multiplexed control signal, A subscriber-side optical transmission device characterized by having the following features.

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