WO2017118153A1

WO2017118153A1 - Long-distance passive optical network system based on chirp grating and dispersion compensation method

Info

Publication number: WO2017118153A1
Application number: PCT/CN2016/102819
Authority: WO
Inventors: 王素椅; 义理林; 李正璇; 王晓东
Original assignee: 烽火通信科技股份有限公司
Priority date: 2016-01-05
Filing date: 2016-10-21
Publication date: 2017-07-13
Also published as: CN105553559B; CN105553559A

Abstract

Disclosed are a long-distance passive optical network system based on a chirp grating and a dispersion compensation method. The system comprises an optical line terminal (OLT), an optical transmission unit (ODN) and an optical network unit (ONU). The OLT is in network connection with the ONU via the ODN. The OLT comprises a downlink signal transmitting means, an uplink signal receiving means, a chirp grating, a first optical circulator and an optical amplifier. Pin 1 of the first optical circulator is connected to the transmitting end of the uplink signal receiving means via the chirp grating; pin 2 of the first optical circulator is connected to the transmitting end of the downlink signal transmitting means; and pin 3 of the first optical circulator is connected to the ODN via the optical amplifier. In the present invention, a chirp grating is accessed at an OLT end, through which chirp grating a fixed negative dispersion compensation amount is given to a directly modulated signal, so that not only the chirp of the directly modulated signal can be compensated for, but also the accumulated dispersion of an ordinary single mode optical fibre can be compensated for; in addition, since the directly modulated signal has a positive chirp characteristic, which has a greater tolerance range for dispersion, the overall management for both can realize the long-distance transmission of a high-speed signal.

Description

Long-distance passive optical network system based on chirped grating and dispersion compensation method

Technical field

The present invention relates to the field of optical communication technologies, and in particular to a long-distance passive optical network system based on chirped gratings and a dispersion compensation method.

Background technique

With the rapid development of China's economy, the demand for user communication bandwidth is growing rapidly. Among various broadband access technologies, passive optical networks become popular technologies with their large capacity, long transmission distance, low cost, and full service support. .

Compared with the traditional optical transmission network, the optical access network has the lower cost, especially in the optical network unit (ONU), which generally uses a relatively low-cost direct-adjusting laser; in addition, the number of central offices is reduced to facilitate management and Reduce the cost, so that the coverage of a single optical line terminal (OLT) is gradually increased; however, due to the simultaneous occurrence of the direct modulation laser and the abnormal dispersion of the optical fiber, the direct modulation signal rapidly deteriorates during transmission, so the dispersion compensation becomes long. Essential measures for passive optical access networks. The current dispersion compensation schemes are mainly as follows:

(1) Realized by a helium management laser (CML).

D. Mahigerefteh et al. presented at the Optical Fiber Communication Conference (OFC) conference in 2006 (Chirp Managed Laser (CML): A compact transmitter for dispersion tolerant 10Gbps networking applications] (啁啾Management Laser: a compact 10Gbps signal transmitter network application module)). Its proposed 啁啾-managed laser can achieve 10km without dispersion compensation transmission. The specific solution is to add behind the direct modulation laser. Add a suitable narrow-band filter to filter the sidebands, thereby compressing the spectrum of the signal and increasing the signal transmission distance. The disadvantage of this scheme is that the shaping filter after the direct-tuning laser is relatively expensive, which is not suitable for cost. Sensitive passive optical access network.

(2) It is realized by improving the spectrum utilization rate.

N.Cheng et al. presented "10Gb/s Upstream Transmission in TWDM PON UsingDuobinary and PAM-4Modulations with Directly Modulated Tunable DBR Laser" at the Communications and Photonics Conference (ACP) in 2013 (in TWDM-PON) In the uplink, a direct modulation laser is used to transmit a 10 Gbps signal using a dual binary and four-level pulse amplitude modulation format signal. The scheme uses a dual binary and four-level pulse amplitude modulation format to transmit 10Gbps signals, and successfully realizes the transmission of 20km signals. The disadvantage of this scheme is that the signal degradation is particularly severe when the signal is transmitted to 40 km.

In view of this, there is an urgent need to provide a low-cost, high-performance way to complete high-quality, long-distance transmission of uplink signals.

Summary of the invention

The technical problem to be solved by the present invention is to realize a problem of high-power transmission of a high-speed uplink signal of 10 Gbps or more and a speed of 40 km or more using a simple and low-cost device.

In order to solve the above technical problem, the 啁啾-grating-based long-distance passive optical network system used in the present invention includes an OLT (Optical Line Terminal), an ODN (Optical Transmission Unit), and an ONU (Optical Network Unit);

The OLT is connected to the ONU network by using the ODN; the OLT includes a downlink signal transmitting device, an uplink signal receiving device, a chirped grating, a first optical circulator, and an optical amplifier; and a pin of the first optical circulator Connected to the transmitting end of the uplink signal receiving device by the chirped grating, the pin of the first optical circulator is connected to the line signal At the transmitting end of the transmitting device, the 3 pin of the first optical circulator is connected to the ODN through the optical amplifier.

The ODN includes a beam splitter and a single film fiber connected to the beam splitter, a single film fiber is connected to the OLT, and the beam splitter is connected to the ONU;

The ONU includes a second optical circulator, a tunable optical filter, a downlink signal receiving optical device, and an uplink signal transmitting device; a pin of the second optical circulator is connected to a transmitting end of the uplink signal transmitting device, 2 feet of the second optical circulator are connected to the input end of the downlink signal receiving optical device through the tunable optical filter, and the 3 legs of the second optical circulator are connected to the ONU;

The uplink signal transmitting device transmits the uplink signal to the second optical circulator, then enters the optical splitter in reverse, and then transmits the optical fiber into the OLT through the single-film optical fiber, and the uplink direct-adjusting signal is amplified by the optical amplifier and transmitted to the first optical circulator, and then After the 啁啾 raster enters the uplink signal receiving device, the uplink signal transmission is completed.

In the above solution, the downlink signal transmitting device is a 10 Gbps 啁啾 management laser or DFB+MZM.

In the above solution, the uplink signal receiving device is a 10G APD.

In the above solution, the dispersion compensation amount of the chirped grating is set to compensate for the dispersion accumulated by the single film fiber 40 km.

In the above solution, the amplifier is a common commercial EDFA with a gain bandwidth of 1510 nm to 1560 nm, a maximum output power of 23 dBm, and a maximum gain multiple of 35 dB.

In the above solution, the tunable optical filter is a commercial optical filter, and has an output power of 3 dBm and a gain bandwidth of 1530 nm to 1610 nm.

In the above solution, the uplink signal transmitting device is a direct-adjusting DFB laser having a center wavelength of 1543 nm, a maximum output power of 10 dBm, a pulse signal generator (PPG) generating a signal rate of 10 Gbps, and a pseudo-random sequence length of 2 used. ~31.

The invention also provides a dispersion compensation method for a long-distance passive optical network system based on a chirped grating, comprising the following steps:

A chirped grating is connected between the upstream signal receiving device RX and the optical circulator WDM, and the chirped grating can generate a fixed dispersion compensation amount to compensate the received signal;

The direct-modulated laser signal from the ONU, that is, the uplink signal, is transmitted through the single-mode fiber and enters the chirped grating in the OLT. Different wavelengths of light pass through different paths in the chirped grating, thereby generating different delays and realizing the laser. The compensation of 啁啾 and fiber dispersion completes the high-quality transmission of the uplink signal.

The invention accesses a chirped grating at the OLT end, and gives a fixed negative dispersion compensation amount to the direct modulation signal through the chirped grating, which not only compensates for the chirp of the direct modulation signal, but also compensates for the cumulative dispersion of the ordinary single mode fiber; Complete high-quality transmission of the uplink signal; and because the direct-adjustment signal has a positive-negative characteristic, it has a greater tolerance range for dispersion. In the experiment, it is found that the tolerance limit for the 10 Gbps signal is as high as -200 ps/nm to 2,450 ps/nm. Manage both to achieve long-distance transmission of high-speed signals.

DRAWINGS

1 is a block diagram of a long-distance passive optical network system based on a chirped grating in the present invention;

2 is a schematic diagram of a chirped grating fiber in the present invention;

3 is a schematic diagram of a long-distance passive optical network system based on a chirped grating in the present invention;

FIG. 4 is an eye diagram of a 10 Gbps uplink signal transmitted at different distances according to the present invention.

detailed description

The present invention will be described in detail below in conjunction with the specific embodiments and the accompanying drawings.

As shown in FIG. 1 , it is a block diagram of a chromatic dispersion compensation passive optical network system, which is composed of an OLT (optical line terminal), an ODN (optical transmission unit), and an ONU (optical network unit). The OLT and the ONU are connected through the ODN, and the device of the RN node in the ODN may be an optical power splitter, a wavelength router, or a combination of the two.

The system is connected with a chirped grating between the upstream signal receiving device RX of the OLT (optical line terminal) and the optical circulator WDM, and the chirped grating can generate a fixed dispersion compensation amount to compensate the received signal; The principle is shown in Figure 2. The grating is periodically changed by a certain technique on a common fiber. When the optical signal enters the grating, the light with twice the wavelength of the grating will be reflected, and the light of different wavelengths is in the chirped grating. The positions of the reflection points are different, so different wavelengths in the wavelength of the incident light pass through different paths in the grating, thereby generating different delays for the purpose of dispersion compensation.

In the system, the uplink signal is from the direct modulation laser signal of the ONU (optical network unit), and the direct modulation optical signal is transmitted through the optical fiber and enters the chirped grating in the OLT (optical line terminal), since the direct modulation signal has a positive Moreover, the optical signal is transmitted through the G.652 fiber to generate anomalous dispersion, so that the dispersion of the signal is further increased. The 啁啾 grating of the OLT (optical line terminal) generates a large fixed dispersion, and after the optical signal passes through the 啁啾 grating, the compensation of the laser 啁啾 and the optical fiber dispersion can be realized, and the high-quality transmission of the uplink signal is completed. Because the signal has 啁啾 characteristics, it has a greater tolerance to dispersion. In the experiment, it is found that the tolerance of 10Gbps signal can reach -200ps/nm~2450ps/nm, and the management of both can achieve high-speed signal length. Distance transfer.

As shown in FIG. 3, the 啁啾-grating-based long-distance passive optical network system provided by the present invention includes an OLT (Optical Line Terminal) 101, an ODN (Optical Transmission Unit) 102, an ONU (Optical Network Unit) 103, and an OLT ( 101) Connect to the ONU (103) network through the ODN (102).

The OLT (101) includes a downlink signal transmitting device 1, an uplink signal receiving device 2, a chirped grating 3, a first optical circulator 4, and an optical amplifier 5; a pin 1 of the first optical circulator 4 receives the uplink signal through the chirped grating 3 The transmitting end of the device 2 is connected, the 2 pin of the first optical circulator 4 is connected to the transmitting end of the downlink signal transmitting device 1, and the 3 legs of the first optical circulator 4 pass The optical amplifier 5 is connected to the ODN (102).

The downlink signal transmitting apparatus 1 described above may be a 10 Gbps Helium Management Laser (CML) or a DFB + MZM.

The above uplink signal receiving device 2 is a 10G APD.

The above-mentioned chirped grating has a dispersion compensation amount that can compensate for the dispersion accumulated by a single film fiber (G.652) of 40 km, which is equivalent to -680 ps/nm.

The optical amplifier 5 is a general commercial EDFA with a gain bandwidth of 1510 nm to 1560 nm, a maximum output power of 23 dBm, and a maximum gain multiple of 35 dB, which is used to improve the power of the downlink signal injected into the optical fiber and improve the uplink signal receiving sensitivity.

ODN (102) includes a common single-film optical fiber (G.652) 6 connected to a splitter (Splitter) 7;

The ONU (103) includes a second optical circulator 8, a tunable optical filter 9, a downlink signal receiving optical device 10, and an uplink signal transmitting device 11;

One end of the ODN (102) is connected to the OLT (101) through the single-film optical fiber 6, and the other end is connected to the 3rd leg of the second optical circulator 8 in the ONU (103) through the optical splitter 7, and the 1st pin of the second optical circulator 8 is The transmitting end of the upstream signal transmitting device 11 is connected, and the second leg of the second optical circulator 8 is connected to the input end of the downstream signal receiving optical device 10 through the tunable optical filter 9.

The splitter 7 mainly sends the downlink data signals to the respective ONUs connected thereto, and the uplink data of different wavelengths of different ONUs are coupled by the optical splitter 7, and the coupled uplink data is uploaded to the OLT through the single-film optical fiber 6 (101). ) for processing.

The above single film fiber 6 is a common commercial single film fiber.

The above spectroscope 7 is a general commercial spectroscope.

The tunable optical filter described above is a commercial tunable optical filter having an output power of 3 dBm and a gain bandwidth of 1530 nm to 1610 nm.

The above-described downlink signal light receiving device 10 is a 10G PIN.

The above-mentioned uplink signal transmitting device 11 is a modulated direct modulation laser having a center wavelength of 1543 nm, a maximum output power of 10 dBm, a pulse signal generator (PPG) generating a signal rate of 10 Gbps, and a pseudo random sequence (PRBS) length of 2^. 31.

The working principle of the system in this embodiment is specifically described below. Since the embodiment focuses on the management of the upstream chromatic dispersion, the downlink is not specifically explained in detail.

First, the downlink signal transmitting device 1 sends a downlink signal, enters the optical amplifier 5 through the first optical circulator 4, and after the signal is amplified, enters the single-film optical fiber 6, and then enters the optical splitter 7, and the optical splitter 7 distributes the downlink signal to different ONUs ( 103), the downlink signal entering the ONU (103) enters the tunable filter 9 via the second optical circulator 8, selects the desired wavelength signal, and transmits it to the downlink signal receiving device 10 to complete the downlink signal transmission; the uplink signal The transmitting device 11 transmits the uplink signal to the second optical circulator 8, that is, the direct modulation signal is transmitted to the second optical circulator 8, and then enters the optical multiplexer 7 in reverse, and the optical splitter 7 realizes the combination of the uplink signals and is coupled. The film fiber 6 is transmitted into the OLT (101), and the up-regulated signal is amplified by the optical amplifier 5, transmitted to the first optical circulator 4, and then passed through the 啁啾 grating 3. At this time, the 啁啾 grating 3 gives a fixed negative dispersion compensation signal. The quantity can not only compensate the flaw of the direct modulation signal, but also compensate the accumulated dispersion of the ordinary single mode fiber. Finally, the signal is received by the uplink signal receiving device 2 to complete the uplink signal transmission.

A chirped grating is connected between the upstream signal receiving device 2 and the first optical ring 4 (WDM), and the chirped grating can generate a fixed dispersion compensation amount to compensate the received signal;

The basis of this dispersion compensation method is:

Make full use of the characteristics of the direct modulation signal and the single-fiber 6-fiber dispersion, and manage the two to achieve full-range coverage dispersion compensation from 0 to 40km. Specifically, the signal emitted by the modulated direct-tuning laser itself has a large positive-negative characteristic (the rising edge of the pulse, that is, the frequency of the leading edge is higher than the falling edge, that is, the frequency of the trailing edge), and the ordinary single-mode fiber is an anomalous dispersion fiber (ie, The dispersion coefficient D is greater than zero, that is to say, in a single-film fiber, the high-frequency component of the signal is transmitted faster than the low-frequency component of the signal. Therefore, when the direct-modulated signal is transmitted in a common single-mode fiber, the pulse front is longer than the pulse trailing edge. Running fast, which causes the signal pulse to rapidly broaden during transmission; and if it is in a normal dispersion fiber (ie, the dispersion coefficient D is less than zero, that is, the signal is transmitted in a normal dispersion fiber, the high frequency component of the signal is transmitted in a specific signal The low-frequency component is slow, the signal pulse front runs slower than the signal pulse trailing edge, and the signal pulse is first compressed and then broadened, which causes the signal quality to become better first and then change. difference.

Therefore, before the receiving end (OLT) decides, a large negative dispersion compensation amount is given by the chirped grating, which not only compensates for the chirp of the direct modulation signal, but also compensates for the dispersion accumulation of the single mode fiber 6. The effect is equivalent to The modulated signal is transmitted in the normal dispersion fiber, that is, the signal quality first becomes better and then worsened; since in the optical access network, the power budget required for the near-end user is relatively low; and the remote user demand is large. The power budget compensates for the attenuation of the fiber; thus, the point with the best signal quality can be placed at 40km by a certain optimization, so that the full coverage of 0-40km is achieved, and the signal power budget is gradually increased with the transmission distance, thereby achieving maximum The power budget value.

As shown in FIG. 4, the eye diagram of the uplink signal under different transmission distances can be seen. As the transmission distance increases, the quality of the signal gradually increases. It can be clearly seen from the specific implementation effect of the embodiment. The overall management scheme of direct modulation signal and fiber dispersion based on chirped grating can better realize the full range of high power budget transmission of signals from 0 to 40 km.

The present invention is not limited to the above-described preferred embodiments, and any one skilled in the art should be aware of the structural changes made in the light of the present invention. Any technical solutions having the same or similar to the present invention fall within the protection scope of the present invention.

Claims

A long-distance passive optical network system based on a chirped grating includes: an OLT and an ONU connected by an ODN, and is characterized by:

The OLT includes a downlink signal transmitting device, an uplink signal receiving device, a chirped grating, a first optical circulator, and an optical amplifier; a pin of the first optical circulator passes through the chirped grating and the uplink signal receiving device a transmitting end is connected, a pin 2 of the first optical circulator is connected to a transmitting end of the downlink signal transmitting device, and a pin 3 of the first optical circulator is connected to the ODN through the optical amplifier;

The ODN includes a beam splitter and a single film fiber connected to the beam splitter, a single film fiber is connected to the OLT, and the beam splitter is connected to the ONU;

The ONU includes a second optical circulator, a tunable optical filter, a downlink signal receiving optical device, and an uplink signal transmitting device; a pin of the second optical circulator is connected to a transmitting end of the uplink signal transmitting device, 2 feet of the second optical circulator are connected to the input end of the downlink signal receiving optical device through the tunable optical filter, and the 3 legs of the second optical circulator are connected to the ONU;

The uplink signal transmitting device transmits the uplink signal to the second optical circulator, then enters the optical splitter in reverse, and then transmits the optical fiber into the OLT through the single-film optical fiber, and the uplink direct-adjusting signal is amplified by the optical amplifier and transmitted to the first optical circulator, and then After the 啁啾 raster enters the uplink signal receiving device, the uplink signal transmission is completed.
The 啁啾 grating-based long-distance passive optical network system according to claim 1, wherein the downlink signal transmitting device is a 10 Gbps 啁啾 management laser or DFB+MZM.
The 啁啾-grating-based long-distance passive optical network system according to claim 1, wherein the uplink signal receiving device is a 10G APD.
The 啁啾grating-based long-distance passive optical network system according to claim 1, It is characterized in that the amount of dispersion compensation of the chirped grating is set to compensate for the dispersion accumulated by the single film fiber 40 km.
The 啁啾 grating-based long-distance passive optical network system according to claim 1, wherein the amplifier is a general commercial EDFA, and the gain bandwidth is 1510 nm to 1560 nm, and the maximum output power is 23 dBm, and the maximum gain multiple is 35dB.
The 啁啾 grating-based long-distance passive optical network system according to claim 1, wherein the tunable optical filter is a commercial optical filter, and the output power is 3 dBm, and the gain bandwidth is 1530 nm to 1610 nm. .
The 啁啾 grating-based long-distance passive optical network system according to claim 1, wherein the uplink signal transmitting device is a direct-adjusting DFB laser having a center wavelength of 1543 nm and a maximum output power of 10 dBm, and a pulse signal. The generator (PPG) generates a signal rate of 10 Gbps and uses a pseudo-random sequence length of 2 to 31.
A dispersion compensation method for long-distance passive optical network systems based on chirped gratings, comprising the following steps:

A chirped grating is connected between the upstream signal receiving device RX and the optical circulator WDM, and the chirped grating can generate a fixed dispersion compensation amount to compensate the received signal;

The direct-modulated laser signal from the ONU is transmitted through the single-mode fiber and enters the chirped grating in the OLT. Different wavelengths of light pass through different paths in the chirped grating, resulting in different delays, achieving laser chirp and fiber dispersion. The compensation completes the high-quality transmission of the uplink signal.