KR100549783B1 - Wavelength-division-multiplexed passive optical network - Google Patents

Abstract

Disclosed is a wavelength division multiplex passive optical subscriber network. The system of the present invention employs a transmitter comprising an error correcting code encoder and a receiver comprising an error correcting code decoder, multiplexers and demultiplexing having periodic propagation characteristics, or both, using a single strand of Characterized in that the bidirectional communication using the optical fiber. According to the present invention, the structure of the network is simple, economical, reduces optical power loss, can suppress the effects of bit noise, can improve the reception sensitivity, and expands to accommodate more than 80 subscribers, Digital broadcasting service can be provided by simple modification of transceiver.

Wavelength division multiplexing passive optical subscriber network, non-interfering light source, direct modulation, error correction code, periodic transmission

Description

Wavelength-division-multiplexed passive optical network             

1 is a system configuration diagram of a conventional general wavelength division multiplexing passive optical subscriber network;

2 and 3 are system configuration diagrams for explaining a wavelength division multiplexing passive optical subscriber network using the spectral division scheme according to the first and second embodiments of the present invention;

4 to 6 are system configuration diagrams for explaining a bidirectional wavelength division multiplexing passive optical subscriber network using the technical spirit of the first and second embodiments described above;

7 is a graph showing the output light spectrum of SLD and LED used as transmitter in Example 5;

8 is an eye diagram before and after transmission when the length of the SMF in Example 5 is 10 km;

9 is a graph showing the BER measured by transmitting a signal as shown in FIG. 8 above;

10 is a graph showing a BER measured by transmitting a signal as shown in FIG. 8 above;

FIG. 11 is measured using an experimental schematic diagram and an experimental schematic diagram for quantifying chromatic dispersion affecting a spectral splitting type wavelength division multiplexing passive optical subscriber network using multiple light outputs as in the embodiments of the present invention. Graph showing frequency response characteristics;

FIG. 12 shows the power penalty measured with varying transmission distances when the bidirectional wavelength division multiplexing passive optical subscriber network according to Example 5 has a poor frequency response characteristic due to color dispersion as shown in FIG. One graph;

FIG. 13 shows the BER performance of the up-down signal when the optical fiber length is 20 km in the bidirectional wavelength division multiplex passive optical subscriber network according to the fifth embodiment, the DPCC is added to the 622 Mbps downlink signal, and the BTC (128,120) is applied to the 155 Mbps uplink signal. Graph measuring BER performance when ² was added;

14 shows a bidirectional wavelength division multiplexing passive optical subscriber network according to the fifth embodiment, wherein the channel spacing of the AWG is 100 GHz, the transmission speed of the downlink signal is 622 Mbps, the output optical power of the SLD is 2 dBm, and the reception sensitivity of the receiver is shown in FIG. Is a graph showing the optical power margin of the downlink signal when -37 dBm;

Fig. 15 shows a bidirectional wavelength division multiplexing passive optical subscriber network according to the fifth embodiment, wherein the channel spacing of the AWG is 50 GHz, the transmission speed of the downlink signal is 622 Mbps, the output optical power of the SLD is 2 dBm, and the receiver sensitivity before transmission is shown. Is a graph showing the optical power margin of the downlink signal when -37 dBm; And

FIG. 16 is a graph illustrating a spectrum of a subcarrier multiplexed optical signal when a digital broadcasting service is provided using a wavelength division multiplexing bidirectional wavelength division multiplexing passive optical subscriber network using a spectrum division scheme according to the fifth embodiment.

The present invention relates to a wavelength-division-multiplexed passive optical network (hereinafter referred to as WDM-PON), and in particular to a single stranded optical fiber using a spectral division type non-interfering light source. The present invention relates to a wavelength division multiplex passive optical subscriber network capable of implementing bidirectional communication.

Recently, various data services and multimedia services including the Internet are rapidly increasing, and the transmission capacity is required in not only a long distance optical communication network but also a subscriber network. Subscriber network should be easy to install and maintain / manage the network by implementing outdoor network with passive device and at the same time economically. In order to solve this demand, WDM-PON, which provides multiple subscribers with multiple optical signals using one optical fiber while providing optical signals with different wavelengths to other subscribers, has been in the spotlight. WDM-PON is able to transfer large amounts of data, and it is easy to manage and maintain the network, and has excellent scalability and security. Furthermore, each wavelength has an advantage of providing different kinds of services.

In implementing such WDM-PON, the first consideration is economics. For this purpose, the light source, the modulation method of the optical signal, the structure of the subscriber network, and the utilization method of conventional single mode fiber (hereinafter referred to as SMF) that are widely installed are important. In addition, high-speed, long-distance transmission should be possible even with low-cost light sources, and should have excellent scalability.

1 is a system configuration diagram of a conventional WDM-PON.

Referring to FIG. 1, in a central office, N transmitters output light output of different wavelengths, and these signals are multiplexed by a multiplexer. The multiplexed signals are demultiplexed by a demultiplexer at a local node through a downlink fiber, and the optical signals of each wavelength are transmitted to and received from different subscribers. Conversely, the uplink signal is transmitted from the subscriber to the central base station using an additional multiplexer / demultiplexer, uplink fiber after driving transmitters with different wavelengths.

In general, the conventional technology provides a distributed feedback laser (DFB-laser) having a different wavelength for each subscriber, whether in the up or down direction, and drives each signal, and then uses an optical signal using a plurality of multiplexers / demultiplexers. The two-way optical fiber was required by unidirectional transmission to one fiber. On the other hand, in order to bidirectional communication using a single fiber, it is necessary to distinguish both the wavelengths used for the uplink and downlink optical signals, so it is called an interleave or an optical bandpass filter (hereinafter referred to as OBPF). The same optical filter was additionally needed.

That is, the system as shown in FIG. 1 has to provide a light source having a different wavelength for each subscriber, so it is difficult to mass-produce optical devices used, and it is economical because two optical fibers are needed or additional optical devices such as OBPF are required. Difficulties in implementing WDM-PON.

On the other hand, in order to economically implement WDM-PON, a wide wavelength such as a general low power LED, a high output light emitting diode (hereinafter referred to as SLD), and amplified spontaneous emission (hereinafter referred to as ASE). A method of transmitting spectrum-slicing and transmitting an incoherent light source having a band has been proposed. The great advantage of the spectrum division type WDM-PON is that the light source of the same specification can be provided to each subscriber, so the mass production of the optical device is easy. In addition, since the light source has non-interfering characteristics, it is resistant to crosstalk, and even if the light spectrum of the LED is changed by temperature or the characteristics of the AWG, which is a wavelength dividing element, are reduced, the signal degradation in the WDM-PON is small.

However, the conventional WDM-PON spectrum splitting method using LED has the disadvantage that the transmission speed is limited to 10Mbps or less because of the small light output and low modulation rate, and corresponding to one wavelength per subscriber to suppress the dispersion effect. The use of optical power led to a lack of optical power margin (P _OPM ) [Ref: MH Reeve, AR Hunwicks, SG Methley, L. Bickers, and S. Hornung, “LED spectral slicing for single-mode local loop application, " Electron. Lett. , vol. 24, pp. 389-390, Mar. 1988.].

In addition, the transmission method of spectral segmentation of SLD has a higher light output than LED, which enables high-speed transmission of 155 Mbps. However, the optical power margin is not enough and additional OBPF and optical amplifier exist due to signal degradation due to bit noise. It is difficult to further increase the speed, and the transmission method that spectrum-divides ASE requires expensive external modulator, optical amplifier, and multiple OBPFs for high-speed communication at 500 Mbps, thereby implementing inexpensive WDM-PON. [Ref .: DK Jung, SK Shin, CH Lee, and YC Chung, "Wavelength-division-multiplexed passive optical network based on spectrum slicing techniques," IEEE Photon. Technol. Lett ., Vol. 10, pp. 1334-1336, June 1998.]. In addition, the transmission distance is less than 10km and the maximum number of subscribers can be secured even in one-way transmission due to the optical bit noise generated by the spectral split light source, the color dispersion in the optical fiber, and the reduction of optical power margin due to the loss of optical devices. Was limited to.

On the other hand, there are two methods of converting an electrical signal into an optical signal, a direct modulation method and an external modulation method. Among them, a method of directly modulating a light source simplifies a transmitting end and provides an optical subscriber network structure. Eliminating the additional devices used in the network reduces the complexity of the network and makes it easier to maintain and manage the network. However, even in this case, there is a need to facilitate the practical installation of the optical subscriber network while increasing the efficiency of using the optical fiber by using bidirectional transmission of the existing single-mode optical fiber as it is.

The technical problem of the present invention for solving the above-described problems of the prior art, while directly modulating the non-interfering light source, while performing the high-speed communication by suppressing the influence of bit noise and dispersion in the optical fiber, by ensuring a sufficient optical power margin It is possible to provide long-distance transmission with mode optical fiber, secure subscribers over 80 channels, and provide superior performance and economical wavelength division multiplex passive optical subscriber network by bidirectional communication using single fiber.

The wavelength division multiplexing passive optical subscriber network using the spectral splitting method according to the first example of the present invention for achieving the above technical problem comprises: at least one of which includes an error correcting code encoder and modulates each non-interfering light source directly A transmitter comprising a transmitter for outputting an optical signal and a passive wavelength division multiplexer for multiplexing the optical signals output from the transmitters; A passive wavelength division demultiplexer for demultiplexing the multiplexed signal, and at least one receiver includes an error correcting code decoder corresponding to the error correcting code encoder and receives the demultiplexed optical signal and converts the demultiplexed optical signal into an electrical signal Receiving end consisting of; An optical fiber connecting the wavelength division multiplexer and the wavelength division multiplexer is provided.

A wavelength division multiplexing passive optical subscriber network using a spectral splitting method according to a second example of the present invention for achieving the above technical problem comprises: transmitters for directly modulating a non-interfering light source and outputting an optical signal, and periodic transmission A transmitter having a characteristic and comprising a passive wavelength division multiplexer for multiplexing optical signals output from the transmitters; A receiver comprising a passive wavelength division demultiplexer having a periodic transmission characteristic and demultiplexing the multiplexed signal, and receivers receiving the demultiplexed optical signal and converting the demultiplexed optical signal into an electrical signal; An optical fiber connecting the wavelength division multiplexer and the wavelength division multiplexer is provided.

In this case, the transmitter includes an error correcting code encoder, and the receiver includes an error correcting code decoder corresponding to the error correcting code encoder.

In order to achieve the above technical problem, a bidirectional wavelength division multiplexing passive optical subscriber network using a spectrum division method according to a third example of the present invention is:

The central base station includes: a plurality of first transmitters for directly modulating a non-interfering light source and outputting an optical signal; A passive wavelength division multiplexer having a periodic transmission characteristic and multiplexing optical signals output from the first transmitters; A passive wavelength division multiplexer having periodic transmission characteristics and demultiplexing the multiplexed signal; First receivers for receiving the demultiplexed optical signal and converting the optical signal into an electrical signal; A first optical cycler optically connected to the wavelength division multiplexer and the wavelength division multiplexer,

The local base station is provided with a multiplexer / demultiplexer optically connected to the first optical circulator via an optical fiber,

Each of the pressurized clusters; A second optical cycler optically coupled to the multiplexer / demultiplexer; A second transmitter optically coupled to the second optical circulator and outputting an optical signal by directly modulating a non-interfering light source; And a second receiver optically connected to the second optical circulator and configured to receive the demultiplexed optical signal and convert the optical signal into an electrical signal.

In order to achieve the above technical problem, a bidirectional wavelength division multiplexing passive optical subscriber network using a spectral division scheme according to a fourth example of the present invention is:

The central base station includes: a plurality of first transmitters for directly modulating a non-interfering light source and outputting an optical signal; A passive first wavelength division multiplexer having a periodic transmission characteristic and multiplexing optical signals output from the first transmitters; A passive first wavelength division multiplexer having a periodic transmission characteristic and demultiplexing the multiplexed signal; First receivers for receiving the demultiplexed optical signal and converting the optical signal into an electrical signal; A first optical cycler optically connected to the wavelength division multiplexer and the first wavelength division multiplexer;

The local base station includes: a passive second wavelength division multiplexer having periodic transmission characteristics and receiving and multiplexing optical signals; A passive second wavelength division multiplexer having periodic transmission characteristics and demultiplexing the multiplexed signal; A second optical cycler optically connected to the second wavelength division multiplexer and the second wavelength division multiplexer and optically connected to the first optical cycler,

Each of the pressurized clusters; A second transmitter optically coupled to the second multiplexer and directly modulating a non-interfering light source to output an optical signal; And a second receiver optically connected to the second demultiplexer and receiving a demultiplexed optical signal and converting the optical signal into an electrical signal.

Wherein at least one of the first transmitters selected from the first transmitters and at least one second transmitters selected from the second transmitters includes an error correcting code encoder; At least one first receiver selected from the first receivers and at least one second receiver selected from the second receivers include an error correcting decoder corresponding to the error correcting encoder. It is done.

Furthermore, at least one first transmitter selected from the first transmitters may include a distributed predistortion circuit.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.

Example 1

2 is a system configuration diagram for explaining a WDM-PON using a spectrum division scheme according to a first embodiment of the present invention.

Referring to FIG. 2, a WDM-PON using a spectrum division scheme according to a first embodiment of the present invention includes a transmitter including receivers and a passive wavelength division multiplexer, receivers, and passive wavelength division. A receiving end including a demultiplexer and an optical fiber connecting the wavelength division multiplexer and the wavelength division demultiplexer are provided.

Transmitters transmit light output by directly modulating a non-interfering light source having a beam width greater than 40 nm generated by an LED, SLD or semiconductor optical amplifier (SOA).

The multiplexer multiplexes and outputs optical signals output from transmitters.

The optical fiber transmits the multiplexed optical signal output from the transmitter to the demultiplexer.

The demultiplexer demultiplexes the multiplexed signal received through the optical fiber for each wavelength and outputs the demultiplexed signal.

The receivers include a photo diode (hereinafter referred to as PD) or an avalanche photo diode (hereinafter referred to as APD) and receive the demultiplexed optical signals, respectively, to receive an electrical signal. Convert to

Single mode optical fiber is used as the optical fiber when the center wavelength band of 1290 to 1310 nm of the non-interfering light source of the transmitting end is used, and dispersion transition optical fiber or non-zero fiber is used as the optical fiber when the central wavelength band of the non-interfering light source of the transmitting end is 1510 to 1610 nm. Point dispersion transition optical fibers are used.

In the case of using the transmitters and receivers as conventional transceivers, the loss of the optical power caused by the spectral division when the multiple optical output is used as well as the insertion loss of the elements in the WDM-PON is referred to as the division loss. ), The optical power incident on the receiver is too small, making it difficult to speed up the signal. Accordingly, at least one of the transmitters used in the WDM-PON according to the first embodiment of the present invention, such as transmitter K and transmitter N in FIG. 2, may be referred to as an FEC encoder. At least one receiver, such as receiver K and receiver N in FIG. 2, includes an error correcting code decoder (hereinafter referred to as an FEC decoder). FEC refers to a technology that can correct an error caused by noise or distortion after transmission by adding a certain amount of overhead (OH) to a signal to be sent. To introduce FEC, add an encoder to the transmitter and a decoder to the receiver. Therefore, due to the error correction effect of the signal by the FEC can be transmitted without error even with a smaller optical power than conventional, it is possible to perform a high-speed transmission of 155Mbps or more using a general LED even when the split loss is large. In addition, by applying the FEC to the transmitters and the receivers, a simple modification of the transmitter and the receiver can provide a digital video service with little modification of the structure of the WDM-PON. In other words, the transmitter N shown in FIG. 1 performs subcarrier multiplexing on a high speed data signal and a digital video signal coded through an FEC encoder using an RF combiner. Then, the signal is received by the receiver N through a multiplexer and a demultiplexer, and the received signal is separated into a data signal and a digital video signal in an optical layer, and the data signal is divided into a digital video signal by a PD or an APD. Are converted into electrical signals through the digital video signal PD.

Example 2

3 is a system configuration diagram illustrating a WDM-PON using a spectrum division scheme according to a second embodiment of the present invention.

Compared to Embodiment 1 described above with reference to FIG. 3, the passive wavelength division multiplexer and the passive wavelength division multiplexer have periodic transmission characteristics, thereby improving signal degradation due to optical power margin and bit noise. It is characterized in that. Therefore, repeated description is omitted. Applying the above-described FEC to receivers and transmitters in this embodiment is optional.

The conventional technology using the spectral division method transmits only a single light output corresponding to one wavelength to each subscriber, so there is a problem of lack of optical power when using a small light output LED. Accordingly, optical amplifiers are required. However, the bit noise generated during spectral division makes it difficult to speed up.

Therefore, in the present invention, as shown in FIG. 3, the multiplexer and the demultiplexer were used as a waveguide type diffraction grating (Cyclic AWG) hereinafter having periodic transmission characteristics. Due to this, since the divided optical signal to each subscriber shows multiple light outputs, a separate optical filter is not required to filter it again, thereby simplifying the structure of the WDM-PON and significantly reducing the splitting loss. Can be directly modulated for high speed transmission. At this time, the distortion of the signal can be suppressed by using an optical fiber having a zero dispersion wavelength in the wavelength band of the light source or a small dispersion value as a transmission medium to suppress deterioration of the signal due to color dispersion.

Equation 1 below shows the relationship between the split loss (L _{slincing-loss} ) and the number of multiple light outputs (N _eff ).

Referring to Equation 1, the number of multiple light outputs (N _eff ) is the free-spectral range (FSR) of the AWG used as the multiplexer and demultiplexer and the full-width half maximum (FWHMF) of the non-interfering light source. Since it is defined as the ratio of, it can be seen that as the FSR value decreases, the splitting loss decreases significantly. Here, the free spectral range (FSR) refers to the frequency interval of optical outputs generated by the periodic output characteristics on the optical spectrum of the AWG. If the channel interval is constant, as the FSR increases, the proposed WDM-PON can accommodate more subscribers. Will be.

Equation 2 below shows the relationship between the power penalty ΔP _beat-noise and the number of multiple light outputs N _eff due to spontaneous-spontaneous beat noise.

In Equation 2, r is an extinction ratio, q is a Q-factor generally used to obtain a required bit-error rate (hereinafter, referred to as BER), and B _e is an electrical bandwidth of a receiver, B _o Is the bandwidth of the AWG used, m is the number of polarizations. Therefore, as the number of multiple light outputs increases, the performance against bit noise improves.

On the other hand, according to the second embodiment of the present invention, since the average propagation speed of each output is different when multiple optical outputs having different wavelengths in the optical fiber proceed through the optical fiber, performance degradation of the optical signal may occur due to color dispersion in the optical fiber. It may be. In this case, the output arriving late at the receiver interferes with the adjacent signal arriving at the early stage, causing the signal to be distorted, resulting in a power penalty.

Equation 3 below is a theoretical expression representing the power penalty ΔP _dispersion by color dispersion.

이다. In Equation 3, x denotes an index for displaying extra noise when an APD receiver is used, B denotes a transmission rate, L denotes a transmission distance, and S _T2 denotes a group delay varian of a signal.

to be.

Referring to Equation 3, as the transmission speed and the transmission distance increase, the overall color dispersion increases, so that the power penalty increases rapidly. In addition, when the color dispersion value in the optical fiber is large, the group speed dispersion value is so large that transmission may be impossible. In this case, it can be overcome by limiting the wavelength band of the non-interfering light source used to the region where the zero dispersion wavelength of the transmission medium exists. On the other hand, when the difference between the center wavelength of the non-interfering light source and the zero-dispersion wavelength of the transmission medium is large and the transmission distance is long, the dispersion precompensation circuit (DPCC) is referred to at least one selected from the transmitters. By adding, we can improve the performance of WDM-PON.

As described above, in the wavelength division multiplexing WDM-PON using the spectral division scheme according to the second embodiment of the present invention, the power penalty due to the division loss, the bit noise and the color dispersion is characterized by the characteristics of the used light source and the AWG. Depends largely on In order to utilize this from the viewpoint of the subscriber network, if the optical power margin (P _OPM ), which is an index that can indicate the margin of the WDM-PON, is defined as Equation 4 below.

Where P _LED is SLD or LED output power of SLD or LED, P _{sensitivity, BTB} is receiver sensitivity in back-to-back condition, L _{Insertion -loss} is the total insertion loss of optical components of the AWG, SMF and optical circulators used inside the WDM-PON, L _slicing-loss is the splitting loss, and ΔP is the bit noise, color dispersion, and crosstalk respectively. Represents the amount of power penalty.

Referring to Equation 4, the optical power margin in the WDM-PON according to the second embodiment of the present invention is that the larger the output optical power of the SLD or LED, the better the reception sensitivity of the receiver, The smaller the insertion loss, the better. The reception sensitivity can be further improved by applying FEC to the transmitter and the receiver as in the first embodiment, and the power penalty caused by each factor can be suppressed as described above.

On the other hand, in the case of using a wavelength division multiplexer and a demultiplexer having a periodic transmission characteristic with a transmitter and a receiver including an FEC, the transmitter and the wavelength division multiplexer are located at the central base station, and the receiver is placed at the subscriber end and the wavelength division demultiplexing is performed. It can be used for high-speed signal transmission in the downward direction by placing the transmitter at the local base station, the transmitter and the demultiplexer in the central base station, and the wavelength division multiplexer at the local base station. .

Hereinafter, the bidirectional wavelength division multiplexing WDM-PON using the technical spirits of the first and second embodiments will be described. Embodiments according to the present invention to be described later, unlike the conventional spectral split type optical subscriber network transmits the downlink signal and the uplink signal using one strand of the optical fiber, characterized in that the bidirectional signal is separated through the optical circulator do.

4 to 6 are system configuration diagrams for describing a bidirectional WDM-PON using the technical spirits of the first and second embodiments.

Example 3

Referring to FIG. 4, a central base station includes a multiplexer having a plurality of first transmitters connected to each other and having periodic transmission characteristics, a demultiplexer connected to a plurality of first receivers and having periodic transmission characteristics, and a multiplexer and a demultiplexer. An optically connected first optical circulator is installed. In addition, the local base station is provided with a multiplexer / demultiplexer connected to the first optical circulator through an optical fiber. Subscribers are connected to the multiplexer / demultiplexer, respectively. The subscriber end comprises a second optical cycle optically coupled to the multiplexer / demultiplexer, and a second transmitter and a second receiver optically coupled to the second optical cycle, respectively. The first and second optical circulators pass the signals in the forward direction and suppress the signals in the reverse direction, thereby separating the directions of the downlink signal and the uplink signal.

Downstream signals output from the plurality of first transmitters at the central base station are multiplexed by a multiplexer, demultiplexed at the local base station via the first optical circulator and the optical fiber, and then provide multiple optical outputs to each subscriber. The second receiver receiving the light output is converted into an electrical signal. Meanwhile, upstream signals transmitted by each subscriber are output from the second transmitter and multiplexed in the multiplexer / demultiplexer via the second optical cycler. The multiplexed signal passes through a low dispersion optical fiber, which is a transmission medium, is demultiplexed by a demultiplexer through a first optical circulator at a central base station, and is input to a first receiver.

As described above, the bidirectional WDM-PON of the present invention is characterized in that transmission is possible even if the wavelength bands of the uplink signal and the downlink signal are the same. In general, SLD and LED, which are non-interfering light sources, have a wide line width of more than 45nm in the light spectrum, whereas the wavelength of the zero-dispersion band of the general SMF is narrow within 30nm, so it is downward for bidirectional communication using one optical fiber. There is a problem that it is difficult to make the center wavelength of the signal and the uplink signal different. Therefore, in the bidirectional WDM-PON, the center wavelength of the downlink signal and the uplink signal is almost similar in the proposed bidirectional WDM-PON, but the optical circulator is used to eliminate the mutual interference between the bidirectional signals. There is a feature that can be transmitted by almost matching the wavelength band of the up and down signal.

Example 4

Referring to FIG. 5, each of the central base station and the local base station has an optical multiplexer having a periodic transmission characteristic, a demultiplexer having a periodic transmission characteristic, and a multiplexer and demultiplexer in each station. The circulator is installed. The central base station includes first transmitters connected to the multiplexer and receivers connected to the demultiplexer. The pressurized cluster is provided with a transmitter optically connected to the multiplexer of the local base station and a receiver connected to the demultiplexer of the local base station. Then, the optical circulator installed in the central base station and the optical circulator installed in the local base station are connected through the optical fiber.

Comparing the bidirectional WDM-PON according to the fourth embodiment with the bidirectional WDM-PON according to the third embodiment, although the optical circulator is removed from the subscriber end, the subscriber end is more economically configured, but the local base station and the subscriber end use a transmitter and a receiver. It is characterized by the fact that two strands of fiber are connected to each other. However, according to the third embodiment or the fourth embodiment, since the insertion loss in the bidirectional WDM-PON is the same, the performance of the signal according to the third embodiment and the fourth embodiment is the same.

Example 5

Referring to FIG. 6, the configuration of the bidirectional WDM-PON is the same as that of the third embodiment, but includes at least one downlink transmitter selected from among the first transmitters (hereinafter, referred to as downlink transmitters) connected to the multiplexer of the central base station. The DPCC described in Embodiment 2 was added, and at least one downlink transmitter selected from the downlink transmitters was added with an FEC encoder and a DPCC, respectively, and a first receiver connected to the demultiplexer of the central base station (hereinafter referred to as an uplink receiver). The FEC decoder is added to at least one uplink receiver selected from the above. A second transmitter (hereinafter referred to as an uplink transmitter) and a second receiver (hereinafter referred to as a downlink receiver) of at least one subscriber station selected from subscriber stations connected to the multiplexer / demultiplexer of the local base station are included. We added FEC encoder and FEC decoder respectively.

The downlink transmitters are directly modulated by changing the driving current of the SLD according to the input electrical signal to output a high speed data signal of 622Mbps. In this case, the transmitters for the long-distance subscribers output the optical signal by directly modulating the SLD after the electrical signal is converted through the DPCC, or simultaneously through the FEC and the DPCC. For example, a subscriber with a transmission distance of 10 km or more and 20 km or less drives a transmitter to which a DPCC is added. In addition, subscribers with a transmission distance of more than 20 km are coded for transmission signals using FEC technology, predistorted using DPCC, and directly modulated SLD to produce high-speed modulated optical output at speeds of 622Mbps or more.

The multiplexer of the central base station receives and transmits each of the optical signals output from the downlink transmitter. The transmitted downlink signal passes through the optical circulator and passes through the low-dispersion optical fiber with small chromatic dispersion value in the corresponding wavelength band, and then demultiplexed by the multiplexer / demultiplexer at the local base station, and the channels of each wavelength are transmitted to different subscribers. do. In this case, the devices used as the multiplexer of the central base station, the multiplexer / demultiplexer of the local base station, and the demultiplexer of the central base station are multi-light having multiple optical signals in the wavelength region, in which the spectrum is divided by the periodic output characteristics as in the AWG of the embodiment It provides an output. As a result, in the process of multiplexing and demultiplexing the optical outputs from the N transmitters by AWG having periodic transmission characteristics, each channel is automatically spectrum-spectrally divided. Unlike the prior art, the method using the multiple light outputs has an excellent effect in terms of optical power margin and power penalty due to bit noise, as can be seen in Equations 1 and 2 described above. Each demultiplexed signal delivered to each subscriber enters a downlink receiver including the APD through an optical cycle and is converted into an electrical signal. On the other hand, for short distance subscribers less than 20km, only the 622Mbps signal APD receiver is sufficient, and for long distance subscribers over 20km, the signal converted into an electrical signal by the 622Mbps signal APD receiver passes through an FEC decode that can be reverse coded. The correction function will be performed.

On the other hand, the uplink signal transmitted from each subscriber end to the central base station via the local base station is transmitted in a symmetrical structure with the downlink signal. However, unlike the downlink signal, the transmitter for the uplink signal directly modulates a general LED having a smaller light output than the SLD and transmits a high speed light output. The transmission rate in the embodiment is 155 Mbps, and the current signal applied to the LED is directly converted into the light output. And, for long distance subscribers over 20km, FEC technology is introduced to improve reception sensitivity of upstream receivers. That is, the FEC encoder is installed in the uplink transmitter, and the signal received from the central base station performs the error correction function through the FEC decoder. This serves to verify the technical spirit of the present invention mentioned in the first embodiment. The signals of the uplink transmitter of each subscriber end are multiplexed by the same periodic multiplexer / demultiplexer used for downlink transmission from the local base station via the optical circulator, and are transmitted upward through the optical fiber. The uplink signal arriving at the central base station is demultiplexed by the demultiplexer installed in the central base station and is incident on the uplink receiver corresponding to each channel. The upstream receiver is an APD receiver for 155Mbps, and the optical signal is restored to an electrical signal by the upstream receiver. For subscribers over 20km, the upstream receiver is decoded into an original signal through an FEC decoder installed behind the APD receiver. Therefore, unlike the prior art, since the uplink signal uses multiple light outputs in the spectral segmentation transmission, it is possible to perform high-speed transmission of 155Mbps or more while implementing economical bidirectional WDM-PON using a general low-power LED. In addition, by directly modulating the light source, there is no need for a separate optical device for modulation, and by using an optical fiber with a small chromatic dispersion value in the corresponding wavelength band, an additional optical filter such as OBPF is also unnecessary, and the optical power margin increases due to multiple light outputs. This eliminates the need for expensive optical devices such as optical amplifiers.

In the present embodiment, since the center wavelength of the SLD and the LED used as the transmitter are in the 1295 nm band, the zero-dispersion wavelength uses a similar commercially available SMF as a transmission medium. At this time, the loss of the optical fiber was 0.35dB / km, the zero dispersion wavelength was 1315nm, the chromatic dispersion slope was 0.083ps ² / nm ² / km, and the performance experiment was performed as described below while changing the distance of the optical fiber.

FIG. 7 is a graph showing the output light spectrum of SLD and LED used as transmitter in Example 5. FIG.

In FIG. 7, SLD and LED have line widths of 45.5 nm and 49 nm, respectively, and the center wavelengths are 1290 nm and 1295 nm, respectively. 7 (a) and 7 (b) show spectral divisions after demultiplexing of one channel when the channel spacing is 100 GHz, the FSR is 1.63 THz, and the wide bandwidth is 28.4 GHz. 7 (c) and (d) show spectral divisions in the case of using 1 × 40 AWG having a channel interval of 120 GHz, an FSR of 8 THz, and a wide bandwidth of 99.9 GHz.

Referring to (a) to (d) of FIG. 7, the measured spectrum is for one channel for one subscriber, but the spectrum of the other channel shows a spectrum division in which an integer multiple of the channel interval is located. The overall shape of the subscriber's light output has the appearance of the spectral characteristics of the SLD and LED. In this case, the number of multiple light outputs shown may be represented by the ratio of the line width of the SLD or LED and the FSR of the AWG used, as shown in Equation 1 above.

FIG. 8 is an eye diagram before transmission (back-to-back, hereinafter referred to as BTB) and after transmission when the length of the SMF is 10 km in Example 5. FIG. (A) and (b) of FIG. 8 are eye diagrams before and after transmission when the downlink signal directly modulates the SLD at 622 Mbps. FIG. 8 (c) and (d) show the uplink signal of 155 Mbps. This is the eye diagram before and after transmission in case of direct modulation.

Referring to (a) to (d) of Figure 8, the extinction ratio before transmission (extinction ratio) was 12dB, 15dB, respectively, it was confirmed that the child is open even after transmitting 10km.

FIG. 9 is a graph illustrating BER measured by transmitting a signal as shown in FIG. 8. In this case, 1 × 16 AWG used in (a) and (b) of FIG. 7 was used as the AWG. In the graph on the left in FIG. 9, the BER curve graphs are for the uplink transmitted 16 channel 155 Mbps signal, and the linear graph is for the BER before transmission. In the graph at the right, the BER curve graphs are for the downlink transmitted 16 channel 622 Mbps signal. The linear graph shows the BER before transmission.

Referring to the graph curve and a straight line graph to the left in Fig. 9, the minimum optical power for obtaining a reception sensitivity (Sensitivity), i.e. 10 ^-9 BER to obtain 10 ^-9 BER is -45.5 dBm, the power of the channel 16 The penalties were all within 0.1 dB.

Referring to the straight line and the curve graphs located on the right side in FIG. 9, the reception sensitivity before transmission is -37.5dBm, but the reception sensitivity after transmission is -35.5dBm. Therefore, it can be seen that 16 downlink signals can be transmitted within a power penalty of 2 dB. The power penalty generated in this case is divided into a 0.5 dB bit noise penalty caused by bit noise and a 1.7 dB dispersion penalty caused by pulse broadening of optical signals due to color dispersion of the optical fiber. According to the prior art, when only one output is selected from among the multiple light outputs, a bit noise penalty of 4 dB or more is generated, whereas in the case of the present invention, it can be understood that this is greatly alleviated by using the multiple light outputs. In the case of using the multiple light outputs, the splitting loss, which is the loss of the optical power generated by the spectral splitting, can be suppressed. In the case of the fifth embodiment, about 7 dB is improved.

FIG. 10 is a graph illustrating BER measured by transmitting a signal as shown in FIG. 8. In this case, 1 × 40 AWG used in (c) and (d) of FIG. 7 was used as the AWG.

Referring to FIG. 10, it can be seen that all 40 channels can be transmitted within a power penalty within 0.1 dB. On the other hand, the downward 40 channels show a power penalty of 1.5 dB to 3.5 dB. As described above, the main cause of the power penalty is the color dispersion of the optical fiber, and as shown in FIG. 7, when the light spectrum is sparse, the power penalty is different because the effect of color dispersion is different depending on the channel.

FIG. 11 is a graph showing an experimental configuration for quantifying chromatic dispersion affecting a spectral division WDM-PON using multiple optical outputs and frequency response characteristics measured using the experimental configuration. to be.

Referring to FIG. 11, a sinusoidal wave was applied to the SLD, and the output electrical power was measured compared to the input electrical power while constantly increasing the frequency. The measurement result shows that attenuation is less than 10dB when there is no optical fiber at 1GHz, but it shows a big attenuation of 20dB after passing 10km SMF and 25dB after passing 20km SMF. Therefore, when the distance is 0km, the frequency response characteristic by the modulation characteristics of the SLD itself is shown, and it can be seen that the graph is relatively gentle in the frequency band for the digital video service. However, as the frequency increases, the frequency response becomes worse as the distance increases, which makes it difficult to achieve high-speed transmission.

FIG. 12 is a graph showing a power penalty measured with varying transmission distances when the bidirectional WDM-PON according to the fifth embodiment is deteriorated due to color dispersion as shown in FIG.

Referring to FIG. 12, when directly modulating the SLD and the LED as in Embodiment 5, the transmission distance is limited to 30 km for the uplink signal and 10 km for the downlink signal.

The limitation of the transmission distance can be improved by reducing the amount of color dispersion that is fundamentally caused, by using an SLD having a center wavelength consistent with the zero dispersion wavelength of the optical fiber, or by reducing the line width of the SLD.

On the other hand, as shown in Figure 12, the frequency response characteristic of the bidirectional WDM-PON is attenuated linearly with respect to frequency, which can be improved by using a DPCC inverted the frequency characteristic as shown in FIG.

13 shows the BER performance of the up-down signal when the optical fiber length is 20 km in the bidirectional WDM-PON according to the fifth embodiment, the DPCC added to the 622 Mbps downlink signal, and the BTC (128,120) ² to the 155 Mbps uplink signal. This is a graph measuring BER performance.

First, referring to FIG. 9, when the 622 Mbps signal is directly modulated and transmitted to the SLD, even if the signal is distorted due to color dispersion and the optical power is increased, the BER does not fall below 10 ⁻⁷ . Has occurred. However, referring to FIG. 13, after passing the DPCC, a BER of 10 ⁻⁹ or less was obtained within a 4 dB penalty. The power penalty at this time was caused by the noise characteristics of the fabricated DPCC and can be improved to within 1dB in theory. Based on the results of using the DPCC, the WDM-PON according to the fifth embodiment can be improved by introducing a DPCC to the transmitter of the central base station and reducing the slope of the frequency response of the DPCC even for a transmission distance of 20 km or less. Increasing the slope of the frequency response can accommodate subscribers over 20 km in distance.

On the other hand, when the distance increases or the number of subscribers increases and the loss inside the WDM-PON increases, it is necessary to secure sufficient optical power margin for reliable operation of the WDM-PON. To this end, additional FEC techniques can be introduced as described in Example 5. In the embodiment of the present invention, a two-dimensional BTC that recovers an original signal by correcting an error by using an encoder at a transmitting end to block code an uplink 155 Mbps signal using an encoder at a transmitting end and using a soft-decision at a receiving end. (128, 120) ² (Block turbo coding, hereinafter referred to as BTC) was used. The code used has 12% redundancy and theoretically has a gain of 7dB at 10 ^-9 BER. As a result, the left BER curve in FIG. 13 shows the BER characteristics with and without BTC in the 155Mbps uplink signal when the distance of the WDM-PON is 20km. Contrary to the theory, about 5dB of coding gain was obtained at 10 ^-9 BER. Since the performance of the BTC is independent of the transmission rate, it is expected that a coding gain of 5 dB or more can be obtained even when applied to a downlink signal. Based on these results, even when FEC is applied in a conventional WDM-PON, it is determined that the performance of the WDM-PON can be improved as much as the reception sensitivity is improved.

FIG. 14 shows the bidirectional WDM-PON according to the fifth embodiment when the channel interval of the AWG is 100 GHz, the transmission speed of the downlink signal is 622 Mbps, the output optical power of the SLD is 2 dBm, and the reception sensitivity of the receiver is -37 dBm. It is a graph showing the optical power margin of the downlink signal. At this time, the length of the transmission optical fiber is 10km, the line width of the SLD is 45.5nm.

In theory, when the channel spacing between subscribers is 100 GHz, the minimum FSR should increase as the number of channels increases. Therefore, as shown in Equation 1, the splitting loss is greatly increased, and as shown in Equation 2, the power penalty due to bit noise is also gradually increased.

Referring to FIG. 14, when the wide bandwidth (B _o ) of the AWG increases from 30 GHz to 80 GHz, the division loss is reduced by 4.3 dB, thereby improving performance, and improving the center wavelength (λ ₁ ) of the SLD and the zero dispersion of the optical fiber. Matching the wavelength λ ₀ can suppress a 1.5 dB chromatic dispersion penalty, further improving performance. As a result, assuming that the margin margin of WDM-PON is 2dB, 80 channels can be accommodated when the FSR of AWG is 8THz.

FIG. 15 shows the bidirectional WDM-PON according to the fifth embodiment when the channel interval of the AWG is 50 GHz, the transmission speed of the downlink signal is 622 Mbps, the output optical power of the SLD is 2 dBm, and the reception sensitivity of the receiver is -37 dBm. It is a graph showing the optical power margin of the downlink signal. At this time, the length of the transmission optical fiber is 10km, the line width of the SLD is 45.5nm.

Referring to FIG. 15, when the FSR of the AWG is 4THz, it is determined that 80 channels can be accommodated even when the center wavelength of the SLD and the zero dispersion wavelength of the optical fiber are separated by 15 nm or more.

FIG. 16 is a graph illustrating a spectrum of a subcarrier multiplexed optical signal when a digital broadcasting service is provided using a wavelength division multiplex bidirectional WDM-PON using a spectrum division scheme according to the fifth embodiment.

In the first and second embodiments, the transmitter N and the receiver N are configured to provide a broadcast signal such as digital video. In the present invention, since the SLD of the transmitting end of the central base station has the frequency response characteristic as shown in FIG. 11, the subcarrier multiplexing technique can be additionally provided to the frequency band not used by the digital signal.

Looking at the multiplexed signal in the electrical frequency domain with reference to Figure 16, the 155Mbps high-speed data (NRZ) signal or 622Mbps high-speed data signal is present in the band below 600MHz, digital video signal is present in the 900 ~ 1.5GHz band. At this time, the digital video signal in the experiment is composed of a digital video signal received from the actual Mugunghwa satellite and a noise source for simulating more video channels. From the experimental results, it is determined that the digital video signal of 80 channels or more can be transmitted and serviced in the bidirectional WDM-PON according to the present invention.

As described above, according to the wavelength division multiplexing passive optical subscriber network according to the present invention, since the structure of the network is simple and the non-interfering light source can be directly modulated, a multiplexer and an inverse multiplexer having economical and periodic transmission characteristics can be used. By using all of the spectral-divided multiplexed light outputs by the multiplexer, it is possible to reduce optical power loss due to power components, to suppress the effects of bit noise, and to improve reception sensitivity by applying FEC.

In addition, by using the wavelength of the zero-dispersion band of the optical fiber, the distortion of the optical signal can be reduced, the error is prevented, the transmission distance can be more than 10km, and if the additional distributed predistortion circuit is used, the transmission distance is 20km. This can be done.

Furthermore, it is excellent in scalability to accommodate more than 80 subscribers and can provide a digital broadcasting service by modifying a simple transceiver.

It is apparent that many modifications are possible by those skilled in the art within the technical idea of the present invention.

Claims (12)

In the wavelength division multiplex passive optical subscriber network using spectral division, At least one transmitter includes an error correcting code encoder, each of the transmitter to directly modulate the non-interfering light source to output an optical signal, and a passive wavelength division multiplexer for multiplexing the optical signals output from the transmitters; ; A passive wavelength division demultiplexer for demultiplexing the multiplexed signal, and at least one receiver includes an error correcting code decoder corresponding to the error correcting code encoder and receives the demultiplexed optical signal and converts the demultiplexed optical signal into an electrical signal Receiving end consisting of; And a wavelength division multiplexing passive optical subscriber network comprising an optical fiber connecting the wavelength division multiplexer and the wavelength division multiplexer. In the wavelength division multiplex passive optical subscriber network using spectral division, A transmitter comprising a transmitter for directly modulating a non-interfering light source and outputting an optical signal, and a passive wavelength division multiplexer having a periodic transmission characteristic and multiplexing the optical signals output from the transmitters; A receiver comprising a passive wavelength division demultiplexer having a periodic transmission characteristic and demultiplexing the multiplexed signal, and a receiver for receiving the demultiplexed optical signal and converting the demultiplexed optical signal into an electrical signal; And a wavelength division multiplexing passive optical subscriber network comprising an optical fiber connecting the wavelength division multiplexer and the wavelength division multiplexer. 3. The wavelength division multiplex passive optical subscriber network according to claim 2, wherein the transmitter comprises an error correcting encoder and the receiver comprises an error correcting decoder corresponding to the error correcting encoder. 4. The wavelength division multiplex passive optical subscriber network according to any one of claims 1 to 3, wherein the light source is an LED, SLD or semiconductor optical amplifier. The wavelength division multiplex passive optical subscriber network according to any one of claims 1 to 3, wherein the central wavelength band of the non-interfering light source of the transmitting end is 1290 to 1310 nm, and the optical fiber is a single mode optical fiber. . 4. The wavelength division of any one of claims 1 to 3, wherein the central wavelength band of the non-interfering light source of the transmitting end is 1510 to 1610 nm, and the optical fiber is a dispersion transition optical fiber or a non-zero dispersion transition optical fiber. Multi-passive passive subscriber network. 4. The wavelength division multiplexing passive optical subscriber network according to claim 2 or 3, wherein the wavelength division multiplexer and the wavelength division multiplexer are waveguide type diffraction gratings. 4. The wavelength division multiplex passive optical subscriber network according to any one of claims 1 to 3, wherein at least one selected from the transmitters is configured by applying a distributed predistortion circuit. The central base station includes: a plurality of first transmitters for directly modulating a non-interfering light source and outputting an optical signal; A passive wavelength division multiplexer having a periodic transmission characteristic and multiplexing optical signals output from the first transmitters; A passive wavelength division multiplexer having periodic transmission characteristics and demultiplexing the multiplexed signal; First receivers for receiving the demultiplexed optical signal and converting the optical signal into an electrical signal; A first optical cycler optically connected to the wavelength division multiplexer and the wavelength division multiplexer, The local base station is provided with a multiplexer / demultiplexer optically connected to the first optical circulator via an optical fiber, Each of the pressurized clusters; A second optical cycler optically coupled to the multiplexer / demultiplexer; A second transmitter optically coupled to the second optical circulator and outputting an optical signal by directly modulating a non-interfering light source; And a second receiver optically connected to the second optical circulator and configured to receive the demultiplexed optical signal and convert the optical signal into an electrical signal. Bidirectional wavelength division multiplexing passive subscriber network. The central base station includes: a plurality of first transmitters for directly modulating a non-interfering light source and outputting an optical signal; A passive first wavelength division multiplexer having a periodic transmission characteristic and multiplexing optical signals output from the first transmitters; A passive first wavelength division multiplexer having a periodic transmission characteristic and demultiplexing the multiplexed signal; First receivers for receiving the demultiplexed optical signal and converting the optical signal into an electrical signal; A first optical cycler optically connected to the wavelength division multiplexer and the first wavelength division multiplexer; The local base station includes: a passive second wavelength division multiplexer having periodic transmission characteristics and receiving and multiplexing optical signals; A passive second wavelength division multiplexer having periodic transmission characteristics and demultiplexing the multiplexed signal; A second optical cycler optically connected to the second wavelength division multiplexer and the second wavelength division multiplexer and optically connected to the first optical cycler, Each of the pressurized clusters; A second transmitter optically coupled to the second multiplexer and directly modulating a non-interfering light source to output an optical signal; And a second receiver optically connected to the second demultiplexer and receiving a demultiplexed optical signal and converting the optical signal into an electrical signal. Bidirectional wavelength division multiplexing passive subscriber network. The at least one first transmitters selected from the first transmitters and the at least one second transmitters selected from the second transmitters comprise an error correcting code encoder. Become; At least one first receiver selected from the first receivers and at least one second receiver selected from the second receivers include an error correcting decoder corresponding to the error correcting encoder. By Bidirectional wavelength division multiplexing passive subscriber network. 11. A method according to claim 9 or 10, wherein at least one of the first transmitters selected from the first transmitters comprises a distributed predistortion circuit. Bidirectional wavelength division multiplexing passive subscriber network.

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