Optical communication network system, communication method, station-side optical transmission device, and subscriber-side optical transmission device

Abstract

An optical communication network system is provided that reduces the scale of a circuit for compensating for dispersion and the like of a transmitted optical signal. [Solution] The present invention relates to an optical communication network system in which a station-side optical transmission device and multiple subscriber-side optical transmission devices are connected by optical branching transmission paths. The station-side optical transmission device of the present invention has fixed compensation means for compensating for a fixed amount of dispersion in a received signal, and adaptive compensation means for compensating for distortion in an output signal of the fixed compensation means. The subscriber-side optical transmission device of the present invention also has fixed compensation means for compensating for a fixed amount of dispersion in a received signal, and adaptive compensation means for compensating for distortion in an output signal of the fixed compensation means. Furthermore, each fixed compensation means compensates for dispersion that occurs when the optical branching transmission path is set to a distance in the range from longer than 0 to shorter than the maximum distance.

Description

[Technical field]

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

[0002] In recent years, the demand for communications has been rapidly increasing due to the development of mobile applications such as smartphones, the emergence of IoT (Internet of Things) technology, the increase in web conferences due to the spread of remote work, and the development of virtualization technologies such as metaverse and digital twin, and so on, and there is a demand for larger capacity in transmission equipment for subscriber optical networks. Therefore, research is being conducted to apply optical transmission technology that has traditionally been applied to backbone optical networks with transmission distances of hundreds to thousands of kilometers to subscriber optical networks with transmission distances of up to 20 km by utilizing the development of digital signal processing (DSP) technology.

[0003] Meanwhile, in the world of digital signal processing technology, optical transceiver devices and DSP devices that realize optical transmission of over 100 Gb / s per line have already been commercialized. For example, a conventional DSP integrated circuit is shown in Non-Patent Document 1. By using the DSP integrated circuit of Non-Patent Document 1, PtP (Point-To-Point) optical transmission in which two transmission devices are connected in a facing manner is possible. In addition, an optical transmission system called PON is applied to existing subscriber optical networks. In PON, one optical transceiver device provided on the station side is connected to multiple optical transceiver devices provided on the subscriber side via a partially shared optical fiber transmission line, and the station and multiple subscribers perform one-to-multiple communication using PtMP (Point-to-MultiPoint; optical multiplexing / multiple access transmission technology). Optical fiber, which is the transmission line of PON, has a characteristic called dispersion, and light of different wavelengths propagates in the optical fiber at different phase velocities (see Non-Patent Document 2). Conventionally, a quantity called dispersion parameter D is generally used as a parameter that represents the dispersion characteristic of optical fiber. The dispersion parameter D is expressed in units of ps / nm / km, where "ps" represents the propagation time difference between light with different wavelengths, "nm" represents the wavelength difference between the lights, and "km" represents the propagation distance. In other words, the dispersion parameter D represents the "propagation time difference between light with a unit wavelength difference propagating a unit distance."

[0004] In conventional PONs, when transmitting signals optically, the binary information time series transmitted and received in the electrical domain is converted into a time series signal called a symbol sequence, which is a format suitable for transmission. An optical signal modulated with a symbol sequence signal is composed of a pulse time series having a pulse waveform corresponding to each symbol. When an optical signal propagates through a transmission line with dispersion characteristics, the light of various wavelengths forming the pulses causes different propagation delays, and as a result, each pulse waveform spreads, resulting in a phenomenon in which pulses of adjacent time slots overlap at the receiving side. Such pulse overlap causes reception errors in PONs. Therefore, in the DSP device of Non-Patent Document 1, an equalization circuit is provided in the receiving circuit to compensate for waveform distortion such as such pulse spread in order to reduce reception errors. Specifically, in the DSP device of Non-Patent Document 1, a dispersion value occurring in the optical transmission line is estimated from the material of the optical fiber and the transmission distance before the transmission system is put into operation, and the equalization circuit portion is provided with a fixed equalization means for compensating for the estimated dispersion value, and an adaptive equalization means for compensating for residual dispersion, which becomes an error between the estimated dispersion value and the actual transmission line dispersion value.

[0005] Conventionally, Non-Patent Document 3 (Fig. 5) shows an example of implementing an FIR filter for dispersion compensation using a DSP equalization circuit. In the FIR filter of Non-Patent Document 3, a time series signal input in sampling time units is weighted and added, and a number of consecutive sample values ​​called the number of taps are sequentially output (convolution processing). The dispersion value that can be compensated for by the FIR filter (DSP equalization circuit) shown in Non-Patent Document 3 depends on the number of taps, etc. And, as shown in Non-Patent Document 4, dispersion compensation is possible if the maximum delay time that can be provided by the FIR filter is greater than the propagation time difference between the wavelength components at both ends of the optical signal spectrum. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] O. Ishida, et al., “Power Efficient DSP Implementation for 100G-and-Beyond Multi-Haul Coherent Fiber-Optic Communications,” OFC2016, W3G.3. [Non-Patent Document 2] Edited by Yoshihiro Konishi and written by Akiya Yamamoto, "Optical Fiber Communication Technology" (Section 3.2 Dispersion), Nikkan Kogyo Shimbun, pp.48-59 [Non-Patent Document 3] Kazuo Kikuchi, "Adaptive Equalization Technique for Digital Coherent Optical Receivers," IEICE Transactions on Information and Communications Engineering, Vol. J96-B, No. 3, pp. 212-219, 2013. [Non-Patent Document 4] Tianhua Xu, et al., “Chromatic dispersion compensation in coherent transmission system using digital filters,” Optics Express, vol. 18, no. 15, pp. 16243-16257, Jul. 19, 2010. Summary of the Invention [Problem to be solved by the invention]

[0007] However, conventionally, when using an FIR filter to compensate for dispersion and the like in optical transmission in a DSP equalization circuit, in order to compensate for the effects of larger dispersion, it is necessary to use an FIR filter with a larger number of taps as the equalization circuit, as described above, which results in problems such as increased circuit size and power consumption of the DSP circuit.

[0008] In view of the above problems, there is a demand for an optical communication network system that can reduce the scale of circuits for compensating for dispersion and the like of transmitted optical signals. [Means for solving the problem]

[0009] The first 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 an optical branching transmission path, the station-side optical transmission device has a station-side fixed compensating means for compensating for a fixed amount of dispersion in a signal received from the optical branching transmission path, and a station-side adaptive compensation means for compensating for distortion of an output signal of the station-side fixed compensating means, each of the subscriber-side optical transmission devices has a subscriber-side fixed compensating means for compensating for a fixed amount of dispersion in a signal received from the optical branching transmission path, and a subscriber-side adaptive compensation means for compensating for distortion of an output signal of the subscriber-side fixed compensating means, and the station-side fixed compensating means and the subscriber-side fixed compensating means compensate for dispersion that occurs when the optical branching transmission path is set to any distance in a range longer than 0 and shorter than a maximum distance.

[0010] The second present invention is a communication method performed by 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 paths, the station-side optical transmission device has a station-side fixed compensating means and a station-side adaptive compensation means, each of the subscriber-side optical transmission devices has a subscriber-side fixed compensating means and a subscriber-side adaptive compensation means, the station-side fixed compensating means compensates for a fixed amount of dispersion in a signal received from the optical branching transmission path, the station-side adaptive compensation means compensates for distortion of an output signal from the station-side fixed compensating means, the subscriber-side fixed compensating means compensates for a fixed amount of dispersion in a signal received from the optical branching transmission path, the subscriber-side adaptive compensation means compensates for distortion of an output signal from the subscriber-side fixed compensating means, and the station-side fixed compensating means and the subscriber-side fixed compensating means compensate for dispersion occurring when the optical branching transmission path is set to any distance in a range longer than 0 and shorter than a maximum distance.

[0011] The third invention of the present invention is characterized in that in a station-side optical transmission device connected to a plurality of subscriber-side optical transmission devices by optical branching transmission lines, the station-side fixed compensating means performs a fixed amount of compensation for dispersion in a signal received from the optical branching transmission line, and station-side adaptive compensating means performs compensation for distortion of an output signal of the station-side fixed compensating means, the station-side fixed compensating means compensating for dispersion occurring when the optical branching transmission line is set to any distance within a range from 0 to shorter than a maximum distance.

[0012] The fourth invention of the present invention is characterized in that, in a subscriber-side optical transmission device connected to a station-side optical transmission device by an optical branching transmission line, the subscriber-side fixed compensation means compensates for a fixed amount of dispersion in a signal received from the optical branching transmission line, and a subscriber-side adaptive compensation means compensates for distortion in an output signal of the subscriber-side fixed compensation means, and the subscriber-side fixed compensation means compensates for dispersion that occurs when the optical branching transmission line is set to any distance in a range between longer than 0 and shorter than a maximum distance.

[0013] A fifth aspect 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, the station-side optical transmission device having a pre-distortion imparting means for imparting a waveform distortion having an inverse characteristic to a fixed amount of dispersion to a signal to be sent to the optical branching transmission line, a station-side fixed compensation means for compensating for the fixed amount of dispersion in a signal received from the optical branching transmission line, and a station-side adaptive compensation means for compensating for distortion of an output signal of the station-side fixed compensation means, each of the subscriber-side optical transmission devices having a subscriber-side adaptive compensation means for compensating for distortion of the signal received from the optical branching transmission line, the pre-distortion imparting means imparts a waveform distortion having an inverse characteristic to dispersion that occurs when the optical branching transmission line is set to a distance in a range from longer than 0 to shorter than a maximum distance, and the station-side fixed compensation means compensates for dispersion that occurs when the optical branching transmission line is set to a distance in a range from longer than 0 to shorter than a maximum distance.

[0014] A sixth aspect of the present invention is a communication method performed by 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 station-side optical transmission device having a pre-distortion adding means, a station-side fixed compensation means, and a station-side adaptive compensation means, each of the subscriber-side optical transmission devices having a subscriber-side adaptive compensation means, the pre-distortion adding means adding waveform distortion having an inverse characteristic to a fixed amount of dispersion to a signal to be sent to the optical branching transmission line, the station-side fixed compensation means compensating for the fixed amount of dispersion for a signal received from the optical branching transmission line, the station-side adaptive compensation means compensating for distortion of an output signal of the station-side fixed compensation means, the subscriber-side adaptive compensation means compensating for distortion of a signal received from the optical branching transmission line, the pre-distortion adding means adding waveform distortion having an inverse characteristic to dispersion occurring when the optical branching transmission line is set to a distance in a range from longer than 0 to shorter than a maximum distance, and the station-side fixed compensation means compensating for dispersion occurring when the optical branching transmission line is set to a distance in a range from longer than 0 to shorter than a maximum distance.

[0015] A seventh aspect of the present invention is a station-side optical transmission device connected to a plurality of subscriber-side optical transmission devices via optical branching transmission lines, the station-side optical transmission device comprising: pre-distortion imparting means for imparting waveform distortion having an inverse characteristic to a fixed amount of dispersion to a signal to be sent to the optical branching transmission line; station-side fixed compensation means for compensating for the fixed amount of dispersion in a signal received from the optical branching transmission line; and station-side adaptive compensation means for compensating for distortion of an output signal of the station-side fixed compensation means, wherein the pre-distortion imparting means imparts waveform distortion having an inverse characteristic to dispersion occurring when the optical branching transmission line is set to a distance within a range from longer than 0 to shorter than a maximum distance, and the station-side fixed compensation means compensates for dispersion occurring when the optical branching transmission line is set to a distance within a range from longer than 0 to shorter than a maximum distance.

[0016] The eighth aspect of the present invention is characterized in that, in a subscriber-side optical transmission device connected to a station-side optical transmission device by an optical branching transmission line, when a signal to which waveform distortion having an inverse characteristic to a fixed amount of dispersion has been imparted in advance in the station-side optical transmission device is received from the optical branching transmission line, the subscriber-side adaptive compensation means compensates for the distortion of the received signal, and the fixed amount is the dispersion that occurs when the optical branching transmission line is set to any distance within a range from longer than 0 to shorter than a maximum distance. Effect of the Invention

[0017] According to the present invention, it is possible to provide an optical communication network system that reduces the scale of a circuit for compensating for dispersion and the like of a transmitted optical signal. [Brief description of the drawings]

[0018] [Figure 1] 1 is a block diagram showing an overall configuration of an optical communication network system according to a first embodiment. [Diagram 2] FIG. 11 is a block diagram showing an overall configuration of an optical communication network system according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] (A) First embodiment Hereinafter, a first embodiment of an optical communication network system, a communication method, 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.

[0020] (A-1) Configuration of the First Embodiment FIG. 1 is a block diagram showing an overall configuration of an optical communication network system 1 according to the first embodiment.

[0021] The optical communication network system 1 includes an optical transmission device 402 on the station side and optical transmission devices 401 (401-1 to 401-m) on the subscriber side, the number of which is m (m is an integer of 2 or more). The optical transmission device 402 on the station side and the optical transmission devices 401 (401-1 to 401-m) on the subscriber side are connected by an optical transmission path 600 (PtMP optical transmission path; optical fiber) as an optical branch transmission path with multiple branches (m branches), and the optical transmission device 402 on the station side and the optical transmission devices 401 (401-1 to 401-m) transmit and receive optical signals in both directions. That is, in the optical communication network system 1, the optical transmission device 402 on the station side and the optical transmission devices 401 (401-1 to 401-m) on the subscriber side are connected by a PON using the optical transmission path 600. In the following, the direction from the optical transmission device 402 on the station side to the optical transmission device 401 on the subscriber side is called "downstream," and the direction from the optical transmission device 401 on the subscriber side to the optical transmission device 402 on the station side is called "upstream." In Fig. 1, the flow of downstream communication is shown by a solid line, and the flow of upstream communication is shown by a dashed line (this also applies to Fig. 2 of the second embodiment described later).

[0022] In the following, k (any integer from 1 to m) is a symbol that generalizes any subscriber k, and elements specific to the subscriber k are marked with "k." For example, the subscriber-side optical transmission device 401 of the subscriber k is represented as "subscriber-side optical transmission device 401-k."

[0023] In this embodiment, it is assumed that a subscriber-side host 700 (700-1 to 700-m) is connected to the lower side (subscriber side) of each subscriber-side optical transmission device 401 (401-1 to 401-m). The subscriber-side host 700 corresponds to a subscriber-side communication device such as a router, a PC, a switching hub, etc. In addition, in this embodiment, it is assumed that a termination device 800 of a core-side network 900 is connected to the upper side of the station-side optical transmission device 402. The termination device 800 corresponds to a network device such as a router or a switching hub, etc. That is, in this embodiment, the optical communication network system 1 relays and transmits communication between each subscriber-side host 700 and the core-side network 900.

[0024] In this embodiment, the optical transmission line 600 is divided into a downstream optical transmission line 610 for transmitting downstream optical signals and an upstream transmission line 620 for transmitting upstream optical signals, but the optical transmission line may be shared in the upstream and downstream directions by wavelength division duplexing. Also, the optical transmission line 600 in this embodiment is a star topology as shown in Fig. 1, but may be a bus topology.

[0025] The downstream optical transmission line 610 is split into m paths by a splitter 613. The upstream optical transmission line 620 is also split into m paths by a splitter 623.

[0026] 1, in the downstream optical transmission path 610, a portion connected to the optical transmission device on the station side 402 is designated as a downstream common optical transmission path 611, and a portion connected to the optical transmission device on the subscriber side 401 (401-1 to 401-m) is designated as a downstream branch optical transmission path 612 (612-1 to 612-m). Also, in FIG. 1, in the upstream optical transmission path 620, a portion connected to the optical transmission device on the station side 402 is designated as an upstream common optical transmission path 621, and a portion connected to the optical transmission device on the subscriber side 401 (401-1 to 401-m) is designated as an upstream branch optical transmission path 622 (622-1 to 622-m). For example, an upstream branch optical transmission path 622-k and a downstream branch optical transmission path 612-k are connected to the optical transmission device on the subscriber side 401-k (k is any one of 1 to m).

[0027] In addition, in FIG. 1, for the sake of convenience, elements that are not related to the essential parts of the present invention, such as binary information processing means (e.g., optical components such as a light source and a photodetector, a framer, and an error correction processing means) that constitute the optical communication network system 1, are omitted from the illustration.

[0028] Next, the internal configuration of the subscriber-side optical transmission device 401 will be described.

[0029] In this embodiment, the description will be given on the assumption that all of the subscriber-side optical transmission devices 401-1 to 401-m have the same configuration. Here, an example of the internal configuration of the subscriber-side optical transmission device 401-k will be described.

[0030] 1, the subscriber-side optical transmission device 401-k has a subscriber-side symbol mapper 211-k, a subscriber-side digital / analog conversion means 212-k, a subscriber-side analog / digital conversion means 221-k, a subscriber-side fixed equalization means 422-k, a subscriber-side adaptive equalization means 223-k, and a subscriber-side symbol demapper 224-k. In each subscriber-side optical transmission device 401, the subscriber-side symbol mapper 211-k and the subscriber-side digital / analog conversion means 212-k are components related to upstream communication, and the subscriber-side analog / digital conversion means 221-k, the subscriber-side fixed equalization means 422-k, the subscriber-side adaptive equalization means 223-k, and the subscriber-side symbol demapper 224-k are components related to downstream communication.

[0031] Next, a configuration for upstream communication of the subscriber-side optical transmission device 401-k will be described.

[0032] The subscriber-side symbol mapper 211-k converts a binary information sequence (upstream signal) sent from the subscriber-side host 700 into a digital symbol sequence and outputs it.

[0033] The subscriber-side analog / digital conversion means 221-k converts the symbol sequence of the upstream data (upstream signal) output from the subscriber-side symbol mapper 211-k into an analog signal (an optical signal that can be sent onto a PON) and sends it onto the connected upstream tributary optical transmission path 622-k.

[0034] Next, a configuration for downstream communication of the subscriber-side optical transmission device 401-k will be described.

[0035] The subscriber-side analog / digital conversion means 221-k converts the analog signal transmitted from the downstream branch optical transmission line 612-k into a digital signal and outputs it.

[0036] The subscriber-side fixed equalization means 422-k performs a fixed amount (constant amount) of dispersion compensation on the digital signal output by the subscriber-side analog / digital conversion means 221-k using a DSP equalization circuit (hereinafter, this dispersion compensation by the DSP equalization circuit is referred to as "fixed equalization" or "fixed compensation"). Note that the amount of dispersion performed by the subscriber-side fixed equalization means 422-k is assumed to be the same in each subscriber-side optical transmission device 401-k. Details of the amount of dispersion compensated by the subscriber-side fixed equalization means 422-k will be described later.

[0037] The subscriber-side adaptive equalization means 223-k compensates for residual dispersion in the output signal (digital signal) of the subscriber-side fixed equalization means 422-k by using a DSP equalization circuit (hereinafter, dispersion compensation by this DSP equalization circuit is referred to as "adaptive equalization" or "adaptive compensation"). The subscriber-side adaptive equalization means 223-k performs processing to compensate for the error between the dispersion value compensated for by the fixed equalization in the subscriber-side fixed equalization means 422-k and the dispersion value that actually occurs in the downstream optical transmission line 610.

[0038] The subscriber-side symbol demapper 224-k converts the symbol sequence output by the subscriber-side adaptive equalization means 223-k into a binary information sequence and outputs it to the subscriber-side host 700.

[0039] Next, the configuration of the station-side optical transmission device 402 will be described.

[0040] 1, the station-side optical transmission device 402 includes station-side symbol mappers 231 (231-1 to 231-m), station-side symbol demappers 244 (244-1 to 244-m), station-side digital / analog conversion means 332, station-side analog / digital conversion means 341, time division multiplexing means 350, station-side fixed equalization means 442, and station-side adaptive equalization means 443. The station-side symbol mappers 231-k and station-side symbol demappers 244-k are components that perform processing for communication with the subscriber-side optical transmission device 401-k.

[0041] In the station-side optical transmission device 402, the station-side analog / digital conversion means 341, the station-side fixed equalization means 442, the station-side adaptive equalization means 443, and the station-side symbol demapper 244 (244-1 to 244-m) are components related to upstream communication, and the station-side symbol mappers 231 (231-1 to 231-m), the station-side digital / analog conversion means 332, and the time division multiplexing means 350 are components related to downstream communication.

[0042] Next, a configuration for downstream communication of the station-side optical transmission device 402 will be described.

[0043] In the optical transmission device 402, the binary information sequence transmitted from the termination device 800 of the core network 900 is distributed for each subscriber (each subscriber-side optical transmission device 401) and supplied to the corresponding optical transmission device 231. For example, the binary information sequence, which is transmission information addressed to the optical transmission device 401-k (subscriber k), is distributed to the optical transmission device 231-k.

[0044] Each station symbol mapper 231 converts the supplied binary information sequence into a digital symbol sequence and supplies it to the time division multiplexing means 350. In other words, all symbol sequences addressed to all subscribers (symbol sequences for downstream communication) are supplied to the time division multiplexing means 350.

[0045] The time division multiplexing means 350 time division multiplexes the symbol sequences addressed to all the subscribers and supplies the same to the station side digital / analog conversion means 332 .

[0046] The station side digital / analog conversion means 332 converts the supplied symbol sequence into an analog signal and outputs it to the downstream common optical transmission line 611 .

[0047] As described above, in the station-side optical transmission device 402, the transmission signals (downstream signal symbol series) addressed to all subscribers are time-division multiplexed by the time-division multiplexing means 350, and optically modulated using one system of digital / analog conversion means 332.

[0048] Next, a configuration for upstream communication of the optical transmission device 402 on the station side will be described.

[0049] An analog signal transmitted from the upstream common optical transmission line 621 is supplied to the station side analog / digital conversion means 341 .

[0050] The station side analog / digital conversion means 341 converts an analog signal sent from the upstream common optical transmission line 621 into a digital signal and outputs it.

[0051] The station-side fixed equalization means 442 performs fixed equalization (compensates for a fixed amount of dispersion by a DSP equalization circuit) on the digital signal output from the station-side analog / digital conversion means 341 and outputs the result. Details of the dispersion value compensated for by the station-side fixed equalization means 442 will be described later.

[0052] The station side adaptive equalization means 443 performs adaptive equalization (compensating for residual dispersion, etc., by a DSP equalization circuit) on the output signal of the station side fixed equalization means 442 and outputs the result as a symbol sequence. The station side adaptive equalization means 443 performs processing to compensate for the error between the dispersion value compensated for by fixed equalization in the station side fixed equalization means 442 and the dispersion value actually occurring in the upstream optical transmission path 620. The station side adaptive equalization means 443 distributes the output symbol sequence to each subscriber and supplies it to the station side symbol demapper 244 of the corresponding subscriber. For example, the station side adaptive equalization means 443 supplies a symbol sequence based on a signal supplied from subscriber k (subscriber side optical transmission device 401-k) to the station side symbol demapper 244-k.

[0053] Each of the station-side symbol demappers 244 converts the supplied symbol sequence into a binary information sequence and outputs it. At this time, the station-side symbol demapper 244-k outputs the output binary information sequence as the binary information sequence transmitted from the subscriber k (the subscriber-side optical transmission device 401-k). The station-side optical transmission device 402 multiplexes the binary information sequences (i.e., the binary information sequences from all the subscribers) obtained from the station-side symbol demappers 244-1 to 244-m, and transmits the multiplexed sequence to the termination device 800 of the core-side network 900.

[0054] In this embodiment, the station side fixed equalization means 442 and the subscriber side fixed equalization means 422 are collectively referred to simply as "fixed equalization means" or "fixed compensation means." Also, in this embodiment, the station side adaptive equalization means 443 and the subscriber side adaptive equalization means 223 are collectively referred to simply as "adaptive equalization means" or "adaptive compensation means."

[0055] (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.

[0056] First, the process of upstream communication for the subscriber-side optical transmission device 401-k (subscriber k) in the optical communication network system 1 will be described.

[0057] The subscriber-side symbol mapper 211-k of the subscriber-side optical transmission device 401-k converts the binary information sequence sent from the subscriber-side host 700-k into a digital symbol sequence and supplies it to the subscriber-side digital / analog conversion means 212-k. The subscriber-side analog / digital conversion means 221-k converts the supplied symbol sequence into an analog signal and sends it to the upstream branch optical transmission line 622-k. The analog signal sent to the branch optical transmission line 622-k is supplied to the station-side analog / digital conversion means 341 of the station-side optical transmission device 402 via the upstream common optical transmission line 621. The station-side analog / digital conversion means 341 converts the analog signal sent from the upstream common optical transmission line 621 into a digital signal and supplies it to the station-side fixed equalization means 442. The station-side fixed equalization means 442 performs fixed equalization on the supplied digital signal and supplies it to the station-side adaptive equalization means 443. The station side adaptive equalization means 443 adaptively equalizes the supplied signal to generate a symbol sequence and supplies it to the station side symbol demapper 244-k. The station side symbol demapper 244-k converts the supplied symbol sequence into a binary information sequence and sends it to the termination device 800 of the core side network 900.

[0058] Next, downstream communication processing for the subscriber-side optical transmission device 401-k (subscriber k) in the optical communication network system 1 will be described.

[0059] In the station-side optical transmission device 402, a binary information sequence addressed to a subscriber k (subscriber-side optical transmission device 401-k) sent from a termination device 800 of a core-side network 900 is supplied to a station-side symbol demapper 244-k. Then, the station-side symbol demapper 244-k converts the supplied binary information sequence into a digital symbol sequence and supplies it to a time division multiplexing means 350. The time division multiplexing means 350 time-division multiplexes the supplied symbol sequence and supplies it to a station-side digital / analog conversion means 332. The station-side digital / analog conversion means 332 converts the supplied symbol sequence into an analog signal and sends it to a downstream common optical transmission path 611. The analog signal sent to the downstream common optical transmission path 611 is supplied to a subscriber-side analog / digital conversion means 221-k of the subscriber-side optical transmission device 401-k via a downstream branch optical transmission path 612-k. The subscriber-side analog / digital conversion means 221-k converts the analog signal sent from the downstream branch optical transmission line 612-k into a digital signal and supplies it to the subscriber-side fixed equalization means 422-k. The subscriber-side fixed equalization means 422-k performs fixed equalization on the supplied digital signal and supplies it to the subscriber-side adaptive equalization means 223-k. The subscriber-side adaptive equalization means 223-k adaptively equalizes the supplied digital signal to generate a symbol sequence and supplies it to the subscriber-side symbol demapper 224-k. The subscriber-side symbol demapper 224-k converts the supplied symbol sequence into a binary information sequence and supplies it to the subscriber-side host 700-k.

[0060] Next, the processes relating to adaptive equalization and fixed equalization in the optical communication network system 1 will be described.

[0061] Conventionally, the optical transmission distance (maximum distance that can be transmitted) in a PON is stipulated by standardization organizations such as the International Telecommunication Union Telecommunication Standardization Sector (ITU-T) and the Institute of Electrical and Electronics Engineers (IEEE), and is at most 20 km. Here, this optical transmission distance (maximum distance that can be transmitted) is represented as "Lmax". Also, here, the optical transmission path distance between the station side optical transmission device 402 and the subscriber k (the subscriber side optical transmission device 401-k) is represented as "Lk". Then, the optical signal received by the subscriber side optical transmission device 401-k in downstream communication is distorted due to the influence of the accumulated dispersion D×Lk occurring in the transmission path. Similarly, the optical signal sent by the kth subscriber side optical transmission device 401-k in upstream communication and received by the station side optical transmission device 402 is distorted due to the influence of the accumulated dispersion D×Lk occurring in the transmission path.

[0062] Here, the cumulative dispersion amount that can be compensated by the subscriber-side fixed equalization means 422-k of each subscriber-side optical transmission device 401 (hereinafter, also simply referred to as "dispersion amount" or "dispersion value") is set as "Sfix" (assuming that Sfix in all subscriber-side optical transmission devices 401 is the same value), and the influence of dispersion generated in the output signal of the subscriber-side fixed equalization means 422-k of the subscriber-side optical transmission device 401-k in the downstream communication (hereinafter, referred to as "residual dispersion amount" or "residual dispersion value") is set as "Sres_k". And here, when Sfix = D×Lmax / 2 is set, Sres_k = D(Lk - Lmax / 2). In the subscriber-side optical transmission device 401-k, for the output signal of the subscriber-side fixed equalization means 422-k, subsequent subscriber-side adaptive equalization means 223-k performs adaptive equalization to compensate for the residual dispersion Sres_k. Similarly, in the station-side optical transmission device 402, when the cumulative dispersion amount that can be compensated by the station-side fixed equalization means 442 is set as Sfix, in the upstream communication, for the signal from subscriber k (subscriber-side optical transmission device 401-k), the influence of dispersion generated in the output signal of the station-side fixed equalization means 442 is Sres_k when expressed as the cumulative dispersion value. In the station-side optical transmission device 402, the output signal of the station-side fixed equalization means 442 is adaptively equalized by the station-side adaptive equalization means 443 to compensate for the residual dispersion Sres_k.

[0063] Here, when Lk > Lmax / 2, in the optical communication network system 1, the influence of dispersion generated by optical transmission is partially compensated by the fixed equalization means (station-side fixed equalization means 442 and subscriber-side fixed equalization means 422-k), and the remaining influence can be compensated by the adaptive equalization means (station-side adaptive equalization means 443 and subscriber-side adaptive equalization means 223-k). On the other hand, when Lk < Lmax / 2, in the optical communication network system 1, the influence of dispersion generated by optical transmission is overcompensated by the fixed equalization means (station-side fixed equalization means 442 and subscriber-side fixed equalization means 422-k), and the overcompensated influence can be compensated by the adaptive equalization means (station-side adaptive equalization means 443 and subscriber-side adaptive equalization means 223-k). Therefore, the sign of the residual dispersion Sres_k is reversed between the two cases (when Lk > Lmax / 2 and when Lk < Lmax / 2).

[0064] Here, since 0<=Lk<=Lmax, the range of the absolute value |Sres_k| of the residual dispersion Sres_k is 0<=|Sres_k|<=|Sfix|. Therefore, the number of taps of the FIR filter required for residual dispersion compensation in the subscriber side adaptive equalization means 223-k and the station side adaptive equalization means 443 is equal to or less than the number of taps of the subscriber side fixed equalization means 422-k and the station side fixed equalization means 442.

[0065] The adaptive equalization process by the subscriber side adaptive equalization means 223-k and the station side adaptive equalization means 443 may be designed to compensate for waveform distortion caused by influences other than dispersion that are not dependent on the optical transmission distance. For example, the adaptive equalization process by the subscriber side adaptive equalization means 223-k and the station side adaptive equalization means 443 is suitable for compensating for waveform distortion that varies over time (for example, waveform distortion caused by fluctuations in the sampling clock, waveform distortion caused by fluctuations in the polarization state of the optical signal, etc.). The subscriber side adaptive equalization means 223-k and the station side adaptive equalization means 443 require a certain number of taps even if they are not dependent on the optical transmission distance in order to compensate for the above-mentioned waveform distortion that varies over time. In the subscriber side adaptive equalization means 223-k and the station side adaptive equalization means 443, if the number of taps of the FIR filter required for dispersion compensation is equal to or less than the number of taps of the FIR filter required to compensate for the above-mentioned waveform distortion, it is possible to simultaneously compensate for dispersion and waveform distortion caused by influences other than dispersion, regardless of the transmission distance.

[0066] Next, the number of taps N of the FIR filter required for dispersion compensation in each adaptive equalization means (the subscriber side adaptive equalization means 223-k and the station side adaptive equalization means 443) will be considered.

[0067] First, if the wavelength width of the signal spectrum is Δλ and the transmission distance is L, the pulse spreading time due to the effect of dispersion is τ D can be calculated using the following formula (1). τ D = DLΔλ … (1)

[0068] Furthermore, if the speed of light in a vacuum is c, the frequency is f, and the wavelength is λ, then λ can be calculated using the following equation (2). λ=c / f …(2)

[0069] Furthermore, the relationship between the frequency width Δf and Δλ of the signal spectrum is expressed by the following equation (3). Here, it is assumed that the signal carrier wavelength λ0 is sufficiently larger than the spectrum width Δλ. Therefore, τ D can be expressed as the following equation (4).

number

[0070] Here, the frequency width of the signal spectrum is the symbol rate R sym On the other hand, if we assume that the number of taps in the FIR filter is N and that it operates at a clock speed equal to the symbol rate, the maximum time difference τ FIR can be expressed by the following equation (6).

number

[0071] Here, in each adaptive equalization means (the subscriber side adaptive equalization means 223-k and the station side adaptive equalization means 443), τ FIR ≧|τ D When |, dispersion compensation is possible, so the required number of taps N can be expressed by the following equation (7).

number

[0072] Next, a specific example of the required number of taps N will be described.

[0073] Here, the speed of light c = 3 × 10 8Let L be "m / s" and the signal light wavelength λ0 be 1550 [nm]. Generally, in a PON, a standard optical fiber (SMF: Single Mode Fiber) with a dispersion parameter D = +17 "ps / nm / km" at a wavelength of 1550 [nm] is laid, so here, it is assumed that the optical fiber constituting the optical transmission line 600 also has a dispersion parameter D = +17 "ps / nm / km" at a wavelength of 1550 [nm]. Here, L = Lmax / 2 = 10 [km]. Furthermore, in order to achieve signal transmission of over 100 Gb / s, a multi-level modulation method and polarization multiplexing are used, and the symbol rate R sym = 50 [Gbaud]. Substituting the above parameters into equation (7), N≧7.807, so the required number of taps N is 8 or more. Furthermore, in each adaptive equalization means (subscriber side adaptive equalization means 223-k and station side adaptive equalization means 443), if the DSP is operated with a 2x oversampling clock, the required number of taps N is 16 or more.

[0074] From the above, it can be seen that the number of taps required by the fixed equalization means (station side fixed equalization means 442 and subscriber side fixed equalization means 422-k) and the adaptive equalization means (subscriber side adaptive equalization means 223-k and station side adaptive equalization means 443) can be approximately the same (for example, about 8 to 16). Specifically, for example, if the number of taps of the FIR filter used by the fixed equalization means (station side fixed equalization means 442 and subscriber side fixed equalization means 422-k) is 16 and the number of taps of the FIR filter used by the adaptive equalization means (subscriber side adaptive equalization means 223-k and station side adaptive equalization means 443) is 16, dispersion compensation is possible by the fixed equalization means, and other waveform distortions can also be compensated for by the adaptive equalization means.

[0075] (A-3) Effects of the First Embodiment According to the first embodiment, the following effects can be obtained.

[0076] In the optical communication network system 1 of the first embodiment, each fixed equalization means (the station side fixed equalization means 442 and the subscriber side fixed equalization means 422-k) is configured to compensate for half the dispersion that occurs when Lk is set to the maximum value (Lmax). As a result, in the optical communication network system 1 of the first embodiment, by making the number of taps required for the fixed equalization means and the adaptive equalization means (the subscriber side adaptive equalization means 223-k and the station side adaptive equalization means 443) approximately the same, dispersion compensation is possible with the fixed equalization means, and other waveform distortions can also be compensated for with the adaptive equalization means.

[0077] Furthermore, in conventional PON, the central office (OLT) needs to have fixed equalization means and adaptive equalization means for the number of subscribers (ONUs), but in the optical communication network system 1 of the first embodiment, the processing contents of the fixed equalization means and adaptive equalization means for each subscriber can be uniform (conventionally, fixed equalization according to the transmission distance for each subscriber was required, but in the first embodiment, it is not necessary to separate for each subscriber), so that they can be consolidated into one and the circuit scale (DSP circuit scale) can be reduced. This leads to effects such as reduced equipment costs for the central office fixed equalization means 442 and reduced power consumption.

[0078] Furthermore, in a conventional PON, it was necessary to provide each subscriber (ONU) with fixed equalization means and adaptive equalization means that perform processing according to the transmission distance between the OLT and the subscriber, but in the optical communication network system 1 of the first embodiment, the processing contents of the fixed equalization means and adaptive equalization means in each subscriber-side optical transmission device 401 can be made uniform, just like in the optical communication network system 1 at the central office, so that the configuration of the subscriber-side optical transmission device 401 can be unified into one type, facilitating mass production of the subscriber-side optical transmission device 401. This leads to effects such as reduced equipment costs for the subscriber-side optical transmission device 401 in the entire optical communication network system 1.

[0079] (B) Second embodiment Hereinafter, a second embodiment of an optical transmission device and an optical communication network system according to the present invention 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 a second embodiment of the present invention. In Fig. 2, the same or corresponding parts as those in Fig. 1 are denoted by the same or corresponding reference numerals.

[0081] The following describes an optical communication network system 1A according to the second embodiment, focusing on the differences from the first embodiment.

[0082] The optical communication network system 1A of the second embodiment differs in that the station-side optical transmission device 402 and the subscriber-side optical transmission device 401 (401-1 to 401-m) are replaced with a station-side optical transmission device 402A and a subscriber-side optical transmission device 401A (401A-1 to 401A-m).

[0083] The subscriber-side optical transmission device 401A-k differs from the first embodiment in that the subscriber-side fixed equalization means 422-k is omitted and the output signal of the subscriber-side analog / digital conversion means 221-k is directly supplied to the subscriber-side adaptive equalization means 223-k.

[0084] The optical transmission device 402A on the station side differs from the first embodiment in that it additionally includes a pre-equalization means 522 on the station side. In the optical transmission device 402A on the station side, an output signal of the time division multiplexing means 350 is supplied to the pre-equalization means 522 on the station side. In the optical transmission device 402A on the station side, an output signal of the pre-equalization means 522 on the station side is supplied to the digital-to-analog conversion means 332 on the station side.

[0085] As described above, the optical communication network system 1A of the second embodiment has the same configuration as the first embodiment with respect to upstream communication, but with respect to downstream communication, the station-side optical transmission device 402A is equipped with a function corresponding to the subscriber-side fixed equalization means 422 provided in the subscriber-side optical transmission device 401 in the first embodiment as the station-side pre-equalization means 522.

[0086] (B-2) Operation of the Second Embodiment Next, the operation of the optical communication network system 1A according to the first embodiment will be described, focusing on the differences from the first embodiment.

[0087] As described above, in the second embodiment, the processing of the station side pre-equalization means 522 in downstream communication is different, so the operation of this station side pre-equalization means 522 will be mainly described.

[0088] In downstream communication, the station side optical transmission device 402A imparts an accumulated dispersion of Sfix=-D×Lmax / 2 to the optical signal with the station side pre-equalization means 522 for optical transmission to the subscriber side optical transmission device 401A-k. That is, the station side optical transmission device 402A transmits an optical signal with a waveform distorted in advance (an optical signal with distortion corresponding to the distortion generated in the downstream optical transmission line 610). In other words, the station side pre-equalization means 522 performs a process of imparting a waveform distortion with an inverse characteristic to the dispersion compensated for by the fixed equalization of the subscriber side fixed equalization means 422-k in the first embodiment to the optical signal to be transmitted, using a DSP equalization circuit (hereinafter, the process of imparting distortion by the DSP equalization circuit is referred to as "pre-equalization" or "distortion imparting"). Hereinafter, the station side pre-equalization means 522 is also referred to simply as "pre-equalization means" or "pre-distortion imparting means".

[0089] The total distance of the downstream common optical transmission line 611 and the downstream tributary optical transmission line 612-k is Lk, and an accumulated dispersion of D×Lk is imparted to the optical signal, and at the input to the k-th subscriber-side optical transmission device 401A-k, the optical signal is affected by the accumulated dispersion Sres_k=D(Lk-Lmax / 2), causing waveform distortion. The subscriber-side adaptive equalization means 223-k can compensate for the accumulated dispersion Sres_k.

[0090] Here, since 0<=Lk<=Lmax, the range of the absolute value |Sres_k| of the residual dispersion Sres_k is 0<=|Sres_k|<=|Sfix|. Therefore, the number of taps of the FIR filter required for residual dispersion compensation in the subscriber-side adaptive equalization means 223-k is equal to or less than the number of taps of the station-side fixed equalization means 442. Therefore, as in the first embodiment, in downstream communication of the optical communication network system 1A, if the number of taps of the FIR filter required for dispersion compensation is equal to or less than the number of taps of the FIR filter required for compensating for such waveform distortion, waveform distortion due to dispersion, etc. can be compensated for regardless of the transmission distance.

[0091] (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.

[0092] In the optical communication network system 1A of the second embodiment, the fixed equalization means is integrated into the optical transmission device 402A at the station side, thereby making it possible to reduce the overall DSP circuit scale. This leads to effects such as reduction in the cost of the devices constituting the entire optical communication network system 1A and reduction in power consumption.

[0093] In the optical communication network system 1A of the second embodiment, the configuration (DSP circuit scale, etc.) of the subscriber-side optical transmission device 401A is simplified, thereby making it possible to achieve effects such as reducing the size of the hardware and reducing power consumption. This improvement is useful for a one-to-many communication network in which the environment for installing the subscriber-side device is harsh, such as "small installation volume" or "poor power supply conditions."

[0094] (C) Other embodiments The present invention is not limited to the above-described embodiments, and may include modified embodiments such as those exemplified below.

[0095] (C-1) In the optical communication network system 1, 1A of each of the above embodiments, an FIR filter that performs convolution processing in the time domain (time-domain equalization, TDE) has been shown as a means for realizing equalization means (each adaptive equalization means and fixed equalization means) in a DSP circuit. As a means equivalent to convolution processing, there is a means called frequency-domain equalization (FDE), which performs discrete Fourier transformation (DFT) on an input signal, multiplies it by a frequency transfer function, performs inverse discrete Fourier transformation (IDFT) on it, and returns it to the time domain signal format and outputs it. DFT / IDFT processes the input signal sequence while reading it in block units. In such block processing, a method (overlap method) is generally used in which a certain block is read and processed, and then a part of the sequence at the rear end of the block is read again (overlap) and the next new sequence is read to form the next block and process it, so that a mismatch with the signal obtained by equivalent TDE does not occur at the boundary of consecutive blocks. The overlap sequence length is related to the number of taps of the equivalent TDE, and the greater the number of taps of the equalization TDE, the longer the overlap sequence length. A memory element is required to hold the overlap sequence, and the circuit scale increases accordingly. Also, as the overlap sequence length increases, the block size increases, and the number of DFT / IDFT points increases. Therefore, when FDE means are used in a DSP circuit, the circuit scale increases as the amount of dispersion to be compensated increases.

[0096] From the above, it can be seen that the same effect can be obtained even if the above-mentioned FDE means is applied to the equalization means (each adaptive equalization means and fixed equalization means) in the optical communication network systems 1 and 1A of the above-mentioned embodiments. In other words, in the optical communication network systems 1 and 1A of the above-mentioned embodiments, the equalization means (each adaptive equalization means and fixed equalization means) is not limited to TDE or the like, and FDE may be applied.

[0097] In the first embodiment, regarding the dispersion amount Sfix (hereinafter also referred to as the "fixed compensation amount") compensated by each fixed equalization means (the station-side fixed equalization means 442 and the subscriber-side fixed equalization means 422-k), it was set as half of the dispersion amount that occurs when Lk is the maximum value (Lmax) (that is, the dispersion amount that occurs when Lk is Lmax / 2). However, the fixed compensation amount is not limited to this, and it may be set as the dispersion amount that occurs when Lk is a transmission distance longer than 0 and shorter than the maximum (Lmax) (0 < Lk < Lmax). That is, the fixed compensation amount Sfix may be set as the dispersion amount that occurs within the range of 0 < Lk < Lmax.

[0098] Here, when the transmission distance corresponding to Sfix [ps / nm] is x [Km] (0 < x < Lmax), the dispersion amount (hereinafter also referred to as the "adaptive compensation amount") Saeq [ps / nm] to be compensated by each adaptive equalization means (the station-side adaptive equalization means 443 and the subscriber-side adaptive equalization means 223-k) is considered. In the following, when the dispersion amount is expressed as D A with a subscript A, it will be explained that the subscript A represents the transmission distance on the optical transmission path 600. That is, D A indicates the dispersion amount that occurs when the transmission distance is A.

[0099] Here, the dispersion amount affected by the signal immediately after reception in the receiving device of the optical signal is D x Therefore, the dispersion amount affected by the signal after fixed equalization is D x + Sfix. Thus, Saeq = -(D x + Sfix). For example, here, if Sfix = -D Lmax / 2 is set, then Saeq = D (Lmax / 2-x) . Also, if Sfix = 0 (that is, the dispersion amount that occurs when the transmission distance is 0 km) is set, then Saeq = -D x . Furthermore, if Sfix = -D Lmax is set, then Saeq = D (Lmax-x)That is, as described above, since 0 <= x <= Lmax, the possible values of the dispersion amount Saeq given by adaptive equalization are -DLmax <= Saeq <= DLmax. Note that since x and Lmax are distances, they are non-negative values, and D is a positive value in the wavelength band (around 1.55 μm) typically used in optical fiber communication. Therefore, in fixed equalization for the purpose of dispersion compensation, Sfix is a negative value. In other words, Sfix is a value with the opposite sign (i.e., a negative value) to the dispersion corresponding to the transmission distance in the range of 0 < Lk < Lmax.

[0100] Here, when the transmission distances corresponding to the fixed compensation amount Sfix are changed to 0, Lmax / 2, and Lmax (that is, when the fixed compensation amount Sfix is changed to 0, -D Lmax / 2 , -D Lmax ), the number of taps of the DSP equalization circuit used in each fixed equalization means and each adaptive equalization means is examined by the same calculation formula as in the above embodiment.

[0101] When the transmission distance is Lmax / 2 (Sfix = -D Lmax / 2 ), the number of taps required for each fixed equalization means is 8, and the number of taps required for each adaptive equalization means is also 8.

[0102] When the transmission distance is 0 (Sfix = 0), the number of taps required for each fixed equalization means is 1, and the number of taps required for each adaptive equalization means is 15. Note that for the fixed equalization means, the number of taps being 1 means that the signal passes through directly, that is, the input signal is output as it is.

[0103] When the transmission distance is Lmax (Sfix = -D Lmax ), the number of taps required for each fixed equalization means is 15, and the number of taps required for each adaptive equalization means is also 15. In this case, since the adaptive equalization means needs to correspond to all transmission distances (all distances up to Lmax), it is necessary to use the maximum value among the number of taps of adaptive equalization obtained for each transmission distance as the required number of taps for adaptive equalization.

[0104] As described above, in this example, it can be seen that depending on the fixed compensation amount Sfix that adapts to the fixed equalization means, the number of taps required for the fixed equalization means and the adaptive equalization means varies between 1 and 15 respectively. Also, from the above, when the transmission distance corresponding to the fixed equalization is Lmax / 2, it can be seen that the number of taps of the fixed equalization means and the adaptive equalization means are arranged in a well-balanced and efficient configuration. On the other hand, when the transmission distance corresponding to the fixed equalization is extremely short, such as 0, the number of taps of the fixed equalization means becomes the minimum (number of taps 1), but there is a bias in that the dispersion compensation has to be done only by the adaptive equalization means, so the total number of taps required for the entire optical communication network system 1 becomes larger compared to the case where the transmission distance is Lmax / 2. Also, when the transmission distance corresponding to the fixed equalization greatly exceeds Lmax / 2, such as in the case of Lmax, since it is necessary to set the maximum value among the number of taps of the adaptive equalization obtained for each transmission distance as the number of taps required for the adaptive equalization (because it is necessary to cope with overcompensation by the fixed equalization), the total number of taps required for the entire optical communication network system 1 becomes larger compared to the case where the transmission distance is Lmax / 2.

[0105] From the above, in the first embodiment, the transmission distance corresponding to the fixed compensation amount Sfix for each fixed equalization means varies between a distance longer than 0 and shorter than Lmax (that is, 0 < Sfix < -D Lmax even when it varies), it can be seen that by arranging a DSP equalization circuit with the number of taps (the number of taps that can compensate for the residual dispersion and waveform distortion due to overcompensation at the output of the fixed equalization means) that can correspond to it in each adaptive equalization means, appropriate adaptive equalization can be achieved.

[0106] Also, similarly in the second embodiment, for the local-side pre-equalization means 522, a process of pre-applying waveform distortion with inverse characteristics to the dispersion that occurs when the transmission distance Lk is set to be longer than 0 and shorter than the maximum (Lmax) (0 < Lk < Lmax) in the same manner as the above fixed equalization means may be performed, and a DSP equalization circuit with the number of taps that can correspond to it may be arranged in the subscriber-side adaptive equalization means 223-k.

Explanation of Reference Numerals

[0107] 1, 1A...optical communication network system, 211, 211-1 to 211-m, 211-k...subscriber side symbol mapper, 212-1 to 212-m, 212-k...subscriber side digital / analog conversion means, 221, 221-1 to 221-m, 221-k...subscriber side analog / digital conversion means, 223, 223-1 to 223-m, 223-k...subscriber side adaptive equalization means , 224, 224-1 to 224-m, 224-k... subscriber side symbol demapper, 231, 231-1 to 231-m, 231... station side symbol mapper, 244, 244-1 to 244-m, 244-k... station side symbol demapper, 332... station side digital / analog conversion means, 341... station side analog / digital conversion means, 350... time division multiplexing means, 401, 401-1 to 401- m, 401-k, 401A, 401A-1 to 401A-m, 401A-k... subscriber-side optical transmission device, 402, 402A... station-side optical transmission device, 422, 422-1 to 422-m, 422-k... subscriber-side fixed equalization means, 442... station-side fixed equalization means, 443... station-side adaptive equalization means, 522... station-side pre-equalization means, 600... optical transmission path, 610... downstream optical transmission path, 611... downstream common optical Transmission path, 612, 612-1 to 612-m, 612-k... downstream branch optical transmission path, 613, splitter, 620... upstream optical transmission path, 621... upstream common optical transmission path, 622, 622-1 to 622-m, 622-k... upstream branch optical transmission path, 623... splitter, 700, 700-1 to 700-m, 700-k... subscriber side host, 800... termination device, 900... core side network

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 station side optical transmission device includes: a station-side fixed compensation means for compensating for a fixed amount of dispersion in a signal received from the optical branch transmission line; a station side adaptive compensation means for compensating for distortion of an output signal of the station side fixed compensation means, Each of the subscriber-side optical transmission devices a subscriber-side fixed compensation means for compensating for a fixed amount of dispersion in a signal received from the optical branch transmission line; a subscriber side adaptive compensation means for compensating for distortion of an output signal of the subscriber side fixed compensation means, The station-side fixed compensation means and the subscriber-side fixed compensation means compensate for dispersion that occurs when the optical branch transmission line is set to any distance in a range longer than 0 and shorter than the maximum distance. An optical communication network system comprising:

2. 2. The optical communication network system according to claim 1, wherein said station-side fixed compensating means and said subscriber-side fixed compensating means compensate for dispersion occurring when said optical branch transmission line is set to half its maximum distance.

3. 3. The optical communication network system according to claim 2, wherein the station side fixed compensation means, the station side adaptive compensation means, the subscriber side fixed compensation means and the subscriber side adaptive compensation means all perform processing to compensate for dispersion using an FIR filter.

4. 4. The optical communication network system according to claim 3, wherein the station side fixed compensation means, the station side adaptive compensation means, the subscriber side fixed compensation means and the subscriber side adaptive compensation means all perform dispersion compensation processing using FIR filters having the same number of taps.

5. 5. The optical communication network system according to claim 4, wherein the FIR filters provided in the station side fixed compensation means, the station side adaptive compensation means, the subscriber side fixed compensation means and the subscriber side adaptive compensation means are all configured using a DSP equalization circuit.

6. A communication method performed 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, comprising: the optical transmission device at the station side includes a fixed compensation unit and an adaptive compensation unit at the station side; Each of the subscriber-side optical transmission devices has a subscriber-side fixed compensation means and a subscriber-side adaptive compensation means, the station-side fixed compensation means compensates for dispersion in a signal received from the optical branch transmission line by a fixed amount; the station side adaptive compensation means compensates for distortion in the output signal of the station side fixed compensation means; the subscriber-side fixed compensation means compensates for a fixed amount of dispersion in the signal received from the optical branch transmission line; said subscriber side adaptive compensation means compensates for distortion in the output signal of said subscriber side fixed compensation means; The station-side fixed compensation means and the subscriber-side fixed compensation means compensate for dispersion that occurs when the optical branch transmission line is set to any distance in a range longer than 0 and shorter than the maximum distance. A communication method comprising:

7. In a station-side optical transmission device connected to a plurality of subscriber-side optical transmission devices by optical branching transmission lines, a station-side fixed compensation means for compensating for a fixed amount of dispersion in a signal received from the optical branch transmission line; a station side adaptive compensation means for compensating for distortion of an output signal of the station side fixed compensation means, The station-side fixed compensation means compensates for dispersion that occurs when the optical branch transmission line is set to a distance in a range longer than 0 and shorter than a maximum distance.

2. A station-side optical transmission device comprising:

8. In a subscriber-side optical transmission device connected to a station-side optical transmission device by an optical branch transmission line, a subscriber-side fixed compensation means for compensating for a fixed amount of dispersion in a signal received from the optical branch transmission line; a subscriber side adaptive compensation means for compensating for distortion of an output signal of the subscriber side fixed compensation means, The subscriber-side fixed compensation means compensates for dispersion that occurs when the optical branch transmission line is set to any distance in a range longer than 0 and shorter than the maximum distance. A subscriber-side optical transmission device.

9. 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 station side optical transmission device includes: a pre-distortion imparting means for imparting a waveform distortion having a fixed amount of dispersion and an inverse characteristic to the signal to be sent to the optical branch transmission line; a station-side fixed compensation means for compensating for a fixed amount of dispersion in a signal received from the optical branch transmission line; a station side adaptive compensation means for compensating for distortion of an output signal of the station side fixed compensation means, Each of the subscriber-side optical transmission devices is a subscriber side adaptive compensation means for compensating for distortion of a signal received from the optical branch transmission line; the pre-distortion imparting means imparts a waveform distortion having an inverse characteristic of dispersion that occurs when the optical branch transmission line is set to a distance in a range longer than 0 and shorter than a maximum distance, The station-side fixed compensation means compensates for dispersion that occurs when the optical branch transmission line is set to a distance in a range longer than 0 and shorter than a maximum distance. An optical communication network system comprising:

10. A communication method performed 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, comprising: the optical transmission device at the station side includes a pre-distortion applying means, a fixed compensation means at the station side, and an adaptive compensation means at the station side; Each of the subscriber-side optical transmission devices has a subscriber-side adaptive compensation means, the pre-distortion imparting means imparts a waveform distortion having an inverse characteristic to a fixed amount of dispersion to a signal to be transmitted to the optical branch transmission line; the station-side fixed compensation means compensates for a fixed amount of dispersion in the signal received from the optical branch transmission line; the station side adaptive compensation means compensates for distortion in the output signal of the station side fixed compensation means; The subscriber side adaptive compensation means compensates for distortion of the signal received from the optical branch transmission line, the pre-distortion imparting means imparts a waveform distortion having an inverse characteristic of dispersion that occurs when the optical branch transmission line is set to a distance in a range longer than 0 and shorter than a maximum distance, The station-side fixed compensation means compensates for dispersion that occurs when the optical branch transmission line is set to a distance in a range longer than 0 and shorter than a maximum distance. A communication method comprising:

11. In a station-side optical transmission device connected to a plurality of subscriber-side optical transmission devices by optical branching transmission lines, a pre-distortion imparting means for imparting a waveform distortion having a fixed amount of dispersion and an inverse characteristic to the signal to be sent to the optical branch transmission line; a station-side fixed compensation means for compensating for a fixed amount of dispersion in a signal received from the optical branch transmission line; a station side adaptive compensation means for compensating for distortion of an output signal of the station side fixed compensation means, the pre-distortion imparting means imparts a waveform distortion having an inverse characteristic of dispersion that occurs when the optical branch transmission line is set to a distance in a range longer than 0 and shorter than a maximum distance, The station-side fixed compensation means compensates for dispersion that occurs when the optical branch transmission line is set to a distance in a range longer than 0 and shorter than a maximum distance.

2. A station-side optical transmission device comprising:

12. In a subscriber-side optical transmission device connected to a station-side optical transmission device by an optical branch transmission line, a subscriber-side adaptive compensation means for compensating for the distortion of a signal received when a signal having a waveform distortion that is an inverse characteristic to a fixed amount of dispersion previously imparted to the station-side optical transmission device is received from the optical branch transmission line; The fixed amount is the dispersion that occurs when the optical branch transmission line is set to any distance in the range longer than 0 and shorter than the maximum distance. A subscriber-side optical transmission device.

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