KR102624704B1 - A method for simulating a multi-mode fiber - Google Patents

Abstract

splitting the input optical signal into a plurality of optical streams; apply delays to each optical stream; combine multiple delayed optical streams; decomposing the combined optical signal into an x-polarization signal and a y-polarization signal; to calculate the power of the combined optical signal and further obtain its reciprocal; Obtain the product of the reciprocal and the input optical signal; Calculate the square root of the product; Multiply the x-polarization signal and the y-polarization signal by the square root of the product, respectively; A method is provided to simulate a multimode fiber including combining the multiplied x-polarization signal and y-polarization signal to obtain an output optical signal. The solution provided by the present invention simulates MMF in the optical domain which will be closer to real conditions. Furthermore, the bone preserves the phase information of the transmitted optical signal.

Description

{A METHOD FOR SIMULATING A MULTI-MODE FIBER}

The present invention relates to the field of computer-aided design and in particular to the simulation of multi-mode fibers.

Multimode fiber (MMF) can transmit high bandwidth signals at high speeds over medium distances. Common MMF core diameters are 50, 62.5 and 100 μm.

The launch condition is important for increasing the bandwidth of MMF transmission and it characterizes the spatial and angular content of the light source. The center launch condition (CL) may stimulate fewer modes compared to the overfield condition, which may stimulate almost all modes of the MMF. An introduction to excitation modes in MMF can be found in “The Impact of Limited Excitation Modes on the Bandwidth of Multimode Fiber Links,” IEEE Photonics Lets, 10(4), 534-536.

However, building a network will cost hundreds or thousands of dollars, and building and testing a new network architecture on a case-by-case basis is cost-inefficient. An attractive and cost-effective solution is to use computer-aided design.

Currently, MMF modules are mainly simulated in the electrical domain, and the phase information of optical signals is almost lost.

The purpose of the present invention is to design a simulated MMF for MMF learning and research.

According to the present invention, splitting an input optical signal into a plurality of optical streams; Applying different delays to each optical stream to obtain a plurality of delayed optical signals; combining a plurality of delayed optical streams to obtain a combined optical signal; decomposing the combined optical signal into an x-polarization signal and a y-polarization signal; Calculate the power of the combined optical signal and further obtain its reciprocal; Obtain the product of the reciprocal and the power of the input optical signal; Calculate the square root of the product; Multiply the x-polarization signal and the y-polarization signal by the square root of the product, respectively; Combine the multiplied x-polarization signal and y-polarization signal to obtain an output optical signal; For overfield launch conditions of multimode fiber, delay times, in seconds, include 540e-12, 729e-12, 1006e-12, 1408e-12, 1798e-12 and 2001e-12.

Compared to a typical simulation of MMF, where the signal processing part is performed in the electrical domain, the solution provided by the present invention simulates the MMF in the optical domain, which will be closer to the actual conditions. Furthermore, the bone preserves the phase information of the transmitted optical signal.

Figure 1 shows a flow chart of the method according to the invention.
Figure 2 shows a block diagram of a system according to the invention.
Figures 3A-3C show eye diagrams of the received signal for different transmission distances in a simulated MMF.

The present disclosure will be described in more detail below in conjunction with several embodiments. It should be understood that the specific embodiments described herein are merely for illustrating the present disclosure and do not limit the present disclosure.

Figure 1 shows a flow chart of the method according to the invention, and Figure 2 shows a block diagram of the system according to the invention.

As shown in Figure 1, according to one aspect of the present invention, the method includes splitting the input optical signal into a plurality of optical streams in step S110. That step may be performed at splitter 210 shown in FIG. 2. Although splitter 210 has three output paths, those skilled in the art may have more or fewer output paths, for example five outputs.

It is worth mentioning that the word “input optical signal” is a data module capable of simulating a light source, for example a laser or LED source. Light sources are used in a variety of optical simulation tools, such as the commercially available simulation software VPI Transmission Maker.

The split optical signal represents and simulates the various modes excited in the MMF. The present invention uses six dominant modes and other modes are omitted. The six dominant modes may include one propagating close to the center of the MMF, and other modes reflected within the MMF. The dominant modes can significantly affect the transmission quality of optical power. Other modes, after the median distance of propagation, have less influence on the transmission, and simulations of these modes are omitted.

Then, in step S120, different delays are applied to each optical stream to obtain a plurality of delayed optical streams. That step may be performed in delayer 220 shown in FIG. 2.

Each mode may travel and transmit different paths in the MMF, and may induce different time delays. The present invention uses an MMF with a length of 500 meters. The time delays of the six modes are 540e-12, 729e-12, 1006e-12, 1408e-12, 1798e-12 and 2001e-12 seconds, respectively. Those skilled in the art will understand that other delay values may also be applied in some specific MMFs.

After time delay is applied to the optical streams, in step S130, the plurality of delayed optical streams are combined to obtain a combined optical signal. That step may be performed at adder 230 shown in FIG. 2.

The combined optical signal will act as a single optical signal, but contains various delay information of each mode, and the various delay information is different from the original input optical signal.

Next, in step S140, the combined optical signal is decomposed into an x-polarized signal and a y-polarized signal. In other words, the combined optical signal can be expressed as Emid _x + jEmid _y , where Emid _x represents the x-direction polarization of the optical signal, Emid _y represents the y-direction polarization of the optical signal, and j is a complex value indicates a sign. The “mid” designation means that the optical signal is at an intermediate stage compared to the input signal and output signal. Therefore, the input optical signal can be expressed as Ein _x +jEin _y . That step may be performed in unpacker 240 shown in FIG. 2.

Decomposing the coupled optical signal is advantageous in that the phase information of each mode can be maintained, and those skilled in this technique can also analyze the phase changes in the optical signal caused by MMF transmission.

Next, in step S150, the power of the combined optical signal is calculated and further its reciprocal is obtained. The power of the above-mentioned optical signal is Pmid=Emid _x ² +Emid _y ² and its reciprocal is 1/(Emid _x ² +Emid _y ² ). That step can be performed at the power meter 250 and reciprocal operator 255 shown in FIG. 2.

Next, in step S160, the reciprocal 1/(Emid _x ² +Emid _y ² ) obtained in step S150 and the power of the input optical signal are converted to (Ein _x ² +Emid _y ² )/(Emid _x ² +jEmid _y ² ) are multiplied, and in step S170, the square root of the aforementioned product is calculated. That step can be performed in the multiplier 260 and square root operator 270 shown in FIG. 2.

Next, in step S180, the square root of the product is multiplied by the x-polarization signal and the y-polarization signal, respectively. That step can be performed in the two multipliers 280 shown in FIG. 2. As a result, the output optical signal can be expressed as below.

Pout=Emid _x * +

jEmid _y *

From the above equation, we can see that the output optical signal is not significantly attenuated or amplified in the MMF module, and the power of the output signal is quite at the same level as the input signal. In other words, simulation of MMF according to the present invention will mitigate or eliminate the effects on signal transmission caused by fiber weakening. Alternatively, if the weakening of the fibers must be taken into account when the MMF transmission system is simulated, an external weakening module can be easily placed within the system. The present invention provides great flexibility in simulating MMF transmission systems.

Finally, in step S190, the multiplied x-polarization signal and y-polarization signal are combined to obtain the output optical signal. That final step is necessary because the raw data must be packaged into a "real" optical signal. That step may be performed in packer 290 shown in FIG. 2.

Furthermore, to further simulate the different attenuation of each mode, it is preferred to apply different gains to the plurality of delayed optical streams, as the modes may have different amplitudes. The step of applying the gain may be performed at amplifier 410 shown in FIG. 2.

According to the present invention, for overfield launch conditions, the gains of the amplifications applied to each delayed optical stream are -1 dB, -2.766 dB, -13.01 dB, -20.8 dB, -22.5 dB and -28.1 dB. Please note that the above gains are illustrative and illustrative only. For other specific MMFs, other gains may also be used.

Furthermore, in order to remove distortions caused by other harmonic components, it is also desirable to filter these distortions. According to the invention, the method includes applying a plurality of Gaussian band-pass filtering to each of the amplified optical signals. That step may be performed in filter 420 shown in FIG. 2.

For overfield launch conditions, the bandwidth of band-pass filtering is 1.737e9 Hz; Includes 1.727e9 Hz, 3.45e9 Hz, 3.9e9 Hz, 3.34e9 Hz and 3.61e9. Please note that the above bandwidths are illustrative and illustrative only. For other specific MMFs, other bandwidths may also be used.

Figures 3a-3c show eye diagrams of the received signal for different transmission distances (500m, 800m and 1100m respectively) in the simulated MMF.

As shown in Figures 3A-3C, after 500m transmission, the eye diagram of the signal is wide open and the bit error rate is at a relatively low level. Next, after 800m transmission (the time delay is for example 8/5 times the predetermined delay value), the eye diagram becomes worse and more distortion occurs. Finally, in Figure 3c, after 1100 m transmission, the eye diagram is almost closed.

From the above results, the MMF module according to the present invention can theoretically simulate multimode fiber in the optical domain, which will be closer to actual conditions. Furthermore, the bone preserves the phase information of the transmitted optical signal. Additionally, the results are very close to real-world MMF and are therefore suitable for MMF-related learning and research.

It should be understood by those skilled in the art that the present disclosure is not limited to the specific embodiments described herein. Various obvious changes, adjustments and alternatives may be made by those skilled in the art without departing from the scope of protection of the present disclosure.

Claims (5)

Splitting the input optical signal into a plurality of optical streams,
Applying a different delay to each said optical stream to obtain a plurality of delayed optical streams;
combining the plurality of delayed optical streams to obtain a combined optical signal;
Decomposing the combined optical signal into an x-polarization signal and a y-polarization signal,
Calculate the power of the combined optical signal and further calculate its reciprocal,
Obtain the product of the reciprocal and the power of the input optical signal,
Calculate the square root of the product,
multiplying the x-polarization signal and the y-polarization signal by the square root of the product, respectively,
Combining the multiplied x-polarization signal and y-polarization signal to obtain an output optical signal,
For overfield launch conditions of multimode fiber, latency, in seconds, simulates multimode fiber including 540e-12, 729e-12, 1006e-12, 1408e-12, 1798e-12, and 2001e-12. How to.
According to paragraph 1,
Applying a plurality of amplification to each of the plurality of delayed optical streams,
For overfield launch conditions, the gains of the amplification include -1, -2.766, -13.01, -20.8, -22.5 and -28.1 in dB.
According to paragraph 2,
Applying a plurality of Gaussian band-pass filtering to each of the amplified optical signals,
In overfield launch conditions, the bandwidth of the band-pass filtering is 1.737e9 in Hz; How to simulate multimode fiber including 1.727e9, 3.45e9, 3.9e9, 3.34e9, and 3.61e9.
According to any one of claims 1 to 3,
A method of simulating a multimode fiber where the combined optical signal is expressed by the following equation:
<expression>
Emid _x +jEmid _y
In Eq.
1) Emid _x is the x-direction polarization of the optical signal,
2) Emid _y is the y-direction polarization of the optical signal,
3) j represents a complex value.
a first unit that decomposes an input optical signal into a plurality of optical streams;
a second unit for applying a different delay to each optical stream to obtain a plurality of delayed optical streams;
a third unit combining the plurality of delayed optical streams to obtain a combined optical signal;
a fourth unit decomposing the combined optical signal into an x-polarization signal and a y-polarization signal;
a fifth unit for calculating the power of the combined optical signal and further obtaining its reciprocal;
a sixth unit that obtains the product of the reciprocal and the power of the input optical signal;
a seventh unit calculating the square root of the product;
an eighth unit for multiplying the x-polarization signal and the y-polarization signal, respectively, by the square root of the product;
a ninth unit combining the multiplied x-polarization signal and y-polarization signal to obtain an output optical signal;
In overfield launch conditions, the latency, in seconds, includes 540e-12, 729e-12, 1006e-12, 1408e-12, 1798e-12 and 2001e-12.

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