Frequency Domain Equalization Method

Abstract

The present invention discloses a frequency domain equalization method, including transmitting an optical signal transmitted over a long distance to a dispersion compensation device, and performing dispersion compensation and equalization processing on the optical signal through the dispersion compensation device. The present invention utilizes the compensation effect of a single dispersion compensation device to realize dispersion compensation and frequency equalization on the optical signal, reducing the bandwidth requirements for the devices at the emitting and receiving ends, allows the directly modulated laser to still support long-distance fiber transmission in the case of high-speed signal modulation, and greatly reduces the system cost. In addition, transmissions over different distances can be supported by changing the value for the dispersion amount, so that the distance can be adjusted flexibly according to the requirements in the data center or other application scenarios.

Claims

1. A frequency domain equalization method, comprising transmitting an optical signal transmitted over a long distance to a dispersion compensation device, and performing dispersion compensation and equalization processing on the optical signal through the dispersion compensation device.

2. The frequency domain equalization method according to claim 1, wherein the compensation amount of the dispersion compensation device is the sum of a compensation value for an optical fiber dispersion amount and an over-compensated dispersion amount.

3. The frequency domain equalization method according to claim 2, wherein the compensation value for the fiber dispersion amount is 2720 ps/nm, and the over-compensated dispersion amount is 100-200 ps/nm.

4. The frequency domain equalization method according to claim 1, wherein the dispersion compensation device is a dispersion compensation device capable of performing dispersion compensation on the transmitted signal band.

5. The frequency domain equalization method according to claim 1, wherein the dispersion compensation device is a dispersion compensation device with a fixed dispersion value.

6. The frequency domain equalization method according to claim 1, wherein the number of the dispersion compensation devices is one.

7. The frequency domain equalization method according to claim 1, wherein the frequency domain equalization method further comprises performing, by a signal emitter, optical modulation on a high-speed signal to obtain a modulated optical signal, and the modulated optical signal will be transmitted over the long distance.

8. The frequency domain equalization method according to claim 7, wherein the signal emitter realizes the optical modulation of the high-speed signal by current modulation.

9. The frequency domain equalization method according to claim 8, wherein the signal emitter is a narrowband device or a broadband device.

10. The frequency domain equalization method according to claim 8, wherein the signal emitter is a directly modulated laser.

11. The frequency domain equalization method according to claim 10, wherein the bandwidth of the directly modulated laser is 10 GHz.

12. The frequency domain equalization method according to claim 8, wherein the high-speed signal loaded on the directly modulated laser is a binary signal at a rate of 25 Gb/s.

13. The frequency domain equalization method according to claim 1, wherein the transmission over a long distance refers to a transmission through optical fiber.

14. The frequency domain equalization method according to claim 13, wherein the optical fiber is a single mode fiber, the dispersion coefficient of the optical fiber in the C-band is 17 ps/nm/km, and the length of the optical fiber is 160 km.

15. The frequency domain equalization method according to claim 1, wherein the frequency domain equalization method further comprises receiving, by a signal receiver, a dispersion compensated and equalization processed optical signal.

16. The frequency domain equalization method according to claim 15, wherein the signal receiver is a photoelectric detector with a bandwidth of 10 GHz.

17. The frequency domain equalization method according to claim 15, wherein the signal receiver is a narrowband device or a broadband device.

18. A frequency domain equalization method, comprising steps as follows: step 1, performing, by a signal emitter, optical modulation on a high-speed signal to obtain a modulated optical signal; step 2, transmitting, through an optical fiber, the modulated optical signal to a dispersion compensation device, and performing dispersion compensation and equalization processing to obtain a compensated and equalized optical signal, the compensation amount of the dispersion compensation device is the sum of a compensation value for an optical fiber dispersion amount and an over-compensated dispersion amount; step 3: receiving, by a signal receiver, the compensated and equalized optical signal.

19. The frequency domain equalization method according to claim 18, wherein the compensation value for the fiber dispersion amount is 2720 ps/nm, and the over-compensated dispersion amount is 100-200 ps/nm.

20. The frequency domain equalization method according to claim 18, wherein the dispersion compensation device is a dispersion compensation device capable of performing dispersion compensation on the transmitted signal band.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] FIG. 1 is a flow chart of a frequency domain equalization method according to a preferred embodiment of the present invention;

[0047] FIG. 2 is a graph of the error rates obtained by keeping the received power constant and changing the over-compensated dispersion value in the cases of BTB, 100 km, and 160 km according to a preferred embodiment of the present invention;

[0048] FIG. 3 is a graph of the frequency response of the system before and after dispersion compensation for a direct optical signal which is not transmitted through optical fiber according to Embodiment 1 of the present invention;

[0049] FIG. 4 is a graph of the frequency response of the system before and after dispersion compensation for the optical signal which is transmitted over 160 km optical fiber according to Embodiment 1 of the present invention;

[0050] FIG. 5 is an eye diagram corresponding to the directly modulated optical signal before dispersion compensation according to Embodiment 1 of the present invention;

[0051] FIG. 6 is an eye diagram corresponding to the directly modulated optical signal after dispersion compensation according to Embodiment 1 of the present invention;

[0052] FIG. 7 is an eye diagram corresponding to the optical signal which is not subjected to dispersion compensation after transmission over 160 km optical fiber according to Embodiment 1 of the present invention; and

[0053] FIG. 8 is an eye diagram corresponding to the optical signal which is subjected to dispersion compensation after transmission over 160 km optical fiber according to Embodiment 1 of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0054] The present invention is described in further detail below in conjunction with the accompanying drawings and with reference to the data. It is to be understood that the implementations are merely illustrative of the present invention and are not intended to limit the scope of the invention in any way.

[0055] As shown in FIG. 1, a preferred embodiment of the present invention provides a frequency domain equalization method based on dispersion over-compensation, including the steps as follows.

[0056] Step 1: performing, by a signal emitting means 10, optical modulation on a high-speed signal to obtain a modulated optical signal.

[0057] In a preferred embodiment, the signal emitting means 10 is a directly modulated laser with a bandwidth of 10 GHz, and the high-speed signal loaded on the directly modulated laser is a binary signal at a rate of 25 Gb/s, the directly modulated laser realizes modulation of the signal by current modulation.

[0058] Step 2: transmitting, through an optical fiber 20, the modulated optical signal to a dispersion compensation device 30 capable of performing dispersion compensation on the transmitted signal band, and performing dispersion compensation and equalization processing, and the compensated and equalized optical signal is obtained.

[0059] In a specific embodiment, the dispersion compensation device 30 is a dispersion compensation device with a fixed dispersion value. The amount of compensation of the dispersion compensation device 30 is the sum of the compensation value for the fiber dispersion amount and the over-compensated dispersion amount. In a preferred embodiment, the optical fiber 20 is a single mode fiber, the dispersion coefficient thereof in the C-band is 17 ps/nm/km, and the length thereof is 160 km.

[0060] Step 3: receiving, by a signal receiving means 40, the compensated and equalized optical signal.

[0061] In a preferred embodiment, the signal receiving means is a photoelectric detector with a bandwidth of 10 GHz.

[0062] Unlike the existing technologies such as high-order modulation and electrical dispersion compensation, the working principle of the present embodiment is: [0063] in terms of frequency equalization, since the narrowband device has a good response to low frequency and a weak response to high frequency, the high frequency spectrum components will be greatly attenuated when the high-speed signal modulation is performed by it, so that the spectrum components of the modulated signal are changed, and thus good modulation effect cannot be obtained, and therefore, this embodiment proposes to use the high-frequency boosting effect of the single dispersion compensation device in the case of dispersion over-compensation so that the high and low frequency components of the signal are equalized, thereby improving the modulation effect.

[0064] The spectrum components of the dispersion over-compensated optical signal are changed, so that the characteristics of the signal is changed and the high frequency of the signal is boosted, thereby realizing the high-speed modulation and long-distance transmission of the narrowband device, on the condition that the dispersion compensation device 30 can realize dispersion compensation for the signal in the transmission band without other performance requirements.

[0065] In order to confirm the feasibility of the technology, it will be described in connection with specific embodiments:

Embodiment 1

[0066] In this embodiment, the signal emitting means 10 is a directly modulated laser (DML), the bandwidth of the directly modulated laser is 10 GHz, the signal loaded on the laser is a binary signal at a rate of 25 Gb/s, and the modulation of the signal can be realized by current modulation.

[0067] The optical fiber 20 is an ordinary single mode fiber, the dispersion coefficient thereof in the C-band is 17 ps/nm/km, and the length thereof is 160 km.

[0068] The dispersion compensation device 30 is a dispersion compensation fiber (DCF) in which the compensation range includes the C-band and the dispersion amount is fixed, and the amount of compensation of the dispersion compensation device 30 is the sum of the compensation value for the fiber dispersion amount of 2720 ps/nm and the over-compensated dispersion amount of 150 ps/nm, totaling 2870 ps/nm. The compensation value for the fiber dispersion amount is the compensation value calculated from the transmission distance, and the optimal over-compensated dispersion value is achieved by ensuring the power at the receiving end constant in the cases of BTB, 100 km, and 160 km, changing the over-compensated dispersion amount in the range of 0 ps/nm to 500 ps/nm after compensating the dispersion of the optical fiber, recording the error codes in each case, and finding the corresponding dispersion over-compensated value when the error code is a minimum, which is the optimal over-compensated dispersion value. As shown in FIG. 2, the experiments found that although the compensation values for the fiber dispersion amount under various transmission distances are not consistent, the optimal value for the over-compensated dispersion amount of 150 ps/nm remains unchanged, and there is a good compensation effect in the case of 100-200 ps/nm, thus having a certain dispersion capacity.

[0069] In this embodiment, the signal receiving means 40 is a photoelectric detector with a bandwidth of 10 GHz.

[0070] The transmission path of the high-speed signal is that: the high-speed NRZ signal at a rate of 25 Gb/s is firstly modulated onto the signal emitting means 10, the modulated optical signal enters into the optical fiber 20 for long-distance transmission, then is subjected to dispersion compensation and equalization processing by the dispersion compensation device 30 connected to the other end of the optical fiber 20, and finally is subjected to signal detection by the signal receiving means 40 connected to the dispersion compensation device 30.

[0071] FIG. 3 is a graph of the frequency response of the system before and after dispersion compensation for a direct optical signal which is not transmitted through optical fiber according to this embodiment. Since the frequency domain equalization caused by the dispersion compensation boosts the high frequency components of the signal, the magnitude of the boosting of the high frequency is associated with the dispersion value for over-compensation. Therefore, the best boosting effect is found by setting different dispersion compensation values.

[0072] FIG. 4 is a graph of the frequency response of the system before and after dispersion compensation for the optical signal which is transmitted over 160 km optical fiber according to this embodiment. It can be seen from FIG. 4 that the high frequency of the system after compensation is boosted, reducing the signal quality fading caused by the narrowband device at the emitting and receiving ends.

[0073] FIG. 5 and FIG. 6 are eye diagrams corresponding to the directly modulated optical signal before and after dispersion compensation, respectively. It can be seen, by comparison, that after the original high-speed signal is modulated onto the narrowband device and is detected via a narrowband receiver, the high frequency components of the optical signal are very low, and the middle eyes are not very clear (FIG. 5). The deteriorated high-frequency components of the compensated optical signal are improved, achieving the effect of frequency equalization, so that the middle eyes are open (FIG. 6). It can be seen from FIG. 5 and FIG. 6 that the middle eyes in the eye diagram after over-compensation become significantly larger and clearer, so that the decision at the receiving end is more accurate.

[0074] FIG. 7 is an eye diagram corresponding to the optical signal which is not subjected to dispersion compensation after transmission over 160 km optical fiber according to this embodiment. It can be seen that after the high-speed directly modulated optical signal is transmitted over the long-distance optical fiber, a decidable eye diagram cannot be obtained due to dispersion. FIG. 8 is an eye diagram corresponding to the optical signal which is subjected to dispersion compensation after transmission over 160 km optical fiber according to this embodiment. It can be seen that after the long-distance transmission, the dispersion over-compensation scheme can obtain a decidable eye diagram. In summary, the optical dispersion over-compensation cannot only realize dispersion compensation, but also has the effect of frequency equalization.

[0075] This embodiment utilizes the compensation effect of a single dispersion compensation device to realize dispersion compensation and frequency equalization on the optical signal, reduces the bandwidth requirements for the devices at the emitting and receiving ends, allows the directly modulated laser to still support long-distance fiber transmission in the case of high-speed signal modulation, and greatly reduces the system cost. In addition, transmissions over different distances can be supported by changing the value for the dispersion amount, so that the distance can be adjusted flexibly according to the requirements in the data center or other application scenarios.

[0076] The preferred specific embodiments of the present invention have been described in detail above. It is to be understood that numerous modifications and variations can be made by those ordinary skilled in the art in accordance with the concepts of the present invention without any inventive effort. Hence, the technical solutions that can be derived by those skilled in the art according to the concepts of the present invention on the basis of the prior art through logical analysis, reasoning and limited experiments should be within the scope of protection defined by the claims.