CN1745322A - Method for compensating modal dispersion in multimode optical fiber transmission path - Google Patents

Abstract

In an optical transmission line consisting of a multimode optical fiber, the mode dispersion of the optical transmission line is reduced in order to permit a wide-band optical signal to be transmitted at high speed, over a long distance and at low costs. When a plurality of multimode optical fibers are connected together to form a transmission line for the purpose of reducing a mode dispersion, length ratios between the respective multimode optical fibers that can maximize the band of this optical transmission are determined, and they are connected together at the length ratios. In addition, a multimode optical fiber having a specific refractive index profile is used as a mode dispersion compensating fiber. Also, a compensated fiber and a compensating fiber each having a specific length are connected together.

Description

Modal dispersion compensation method in the multimode optical fiber transmission lines

Technical field

The present invention relates to method that the modal dispersion that utilizes in the optical transmission line that multimode optical fiber constructs is compensated, it can reduce the modal dispersion of this optical transmission line, and obtains wide transmission band.

Background technology

In general, connect by optical transmission line among the LAN (LAN) etc. of computing machine and associate device thereof at FA (factory automation) and OA (office automation) etc., in this optical transmission line, extensively employing can realize the heavy caliberization of sensitive surface, and can easily carry out the multimode optical fiber with the binding operation of luminous infrared rays receiver.

In this multimode optical fiber, graded index type optical fiber (hereinafter referred to as GI optical fiber) is as following optical fiber that the index distribution of fibre core forms refractive index and reduces gradually along with the increase of radius, and reaches consistent the time of arrival of each pattern of flashlight, modal dispersion reduces, and can obtain broadband.For obtaining broadband, this GI optical fiber is used for optical transmission lines such as LAN, can realize the high speed of transfer rate thus.

In recent years, in the Ethernet (registered trademark) of the international standards of LAN, determined that a kind of transfer rate is the Ethernet (registered trademark) (to call 10GbE in the following text) of 10Gb/s, and its practicability that waits in expectation.For realizing this 10GbE, as described in following document, require in its optical transmission line, modal dispersion is suppressed to lowlyer as far as possible, and can stably obtain wide transmission band.

" IEC 60793-2-10 fiber section 2-10: product specification-sub specification Al multimode optical fiber classification (Optical fibers-Part 2-10:Product specifications-Sectionalspecification for category Al multimode fibres) ", International Electrotechnical Commission (IEC) (International Electrotechnical Commission), in March, 2002, p.3-30

In addition, because the transmission band of GI optical fiber is decided by index distribution, thereby for realizing desired broadband among this 10GbE, be necessary according to having largest refractive index at core centre, and, come extremely critically to form the index distribution of fibre core along with the shape that the increase refractive index of radius reduces gradually.

Like this, the error permissible range of GI Refractive Index Profile o is just minimum, is difficult to carry out the good manufacturing of qualification rate, and causes manufacturing cost to improve.In addition, because the error permissible range of index distribution is narrow and small, thereby is difficult to stably form certain index distribution, and be difficult to make the GI optical fiber of long size.

In addition, because the error permissible range of index distribution is narrow and small, thereby is difficult to stably form certain index distribution, and be difficult to obtain being made as the broadband of target.In addition, because it is different because of the signal light wavelength to obtain the index distribution of maximum band, thereby adopted the optical transmission line of existing GI optical fiber in utilization, and transmit under the occasion of flashlight of the wavelength band different with the specification of this optical transmission line, then can not obtain broadband.

But, index distribution at GI optical fiber does not become the shape that is made as purpose, and can not obtain under the wide band occasion, known to the described technology of following document, that is: will have the GI optical fiber that distributes with this GI optical fiber (by compensated optical fiber) different refractivity as the modal dispersion compensated optical fiber, and be connected in by compensated optical fiber, come the compensation model chromatic dispersion thus.

Yet the document does not clearly illustrate concrete modal dispersion compensation condition, and does not have to propose such as compensating by the optimum value of the index distribution of the required modal dispersion compensated optical fiber of the modal dispersion of compensated optical fiber well for efficient etc.

W.F. granny rag (W.F.Love) is outstanding, the pre-original text collected works (Proceedings of European Conference on Optical Communication ' 81) in optical communication international conference ' 81, Europe, (Denmark), electromagnetism institute of Technical University Of Denmark, (Electromagnetics Institute, TechnicalUniversity of Denmark), 1981, the 4th volume, p.4-1-4-4

In addition, in Japanese Unexamined Patent Application Publication 2001-52205 communique, a kind of following technology has been proposed, that is: utilizing the modal dispersion compensated optical fiber to compensate under the occasion of modal dispersion of GI type optical fiber, by following method, calculate the modal dispersion compensated optical fiber of connection with by the length of compensated optical fiber ratio.

In the method that this motion relates to, at first by following formula (1), come the index distribution of approximate treatment modal dispersion compensated optical fiber and, and calculate each index distribution exponential α by the index distribution of compensated optical fiber.

$n\left(r\right)=\left\{\begin{array}{cc}{n}_1[1-2\mathrm{\&Delta;}{(r/a)}^{\mathrm{\&alpha;}}{]}^{1/2}& (0\&le;r\&le;a)\\ n_1{[1-2\mathrm{\&Delta;}]}^{1/2}& (a<r)\end{array}\right.---\left(1\right)$

Wherein, about the refractive index at a distance of fiber core centre distance r place, n ₁The refractive index of expression core centre, Δ ₁The expression core centre is poor to the specific refractivity of coating, and a represents fiber core radius, and α represents the index distribution exponential.

Then, utilize each index distribution exponential α, according to the modal dispersion compensated optical fiber with satisfied the mode of following formula (2) by the length of compensated optical fiber ratio, decide the length of modal dispersion compensated optical fiber.

L _comp/L _target＝(α _target-α _opt)/(α _opt-α _comp) (2)

Wherein, L _CompThe length of expression modal dispersion compensated optical fiber, L _TargetExpression is by the length of compensated optical fiber, α _CompThe index distribution exponential of expression modal dispersion compensated optical fiber, α _TargetExpression is by the index distribution exponential of compensated optical fiber, α _OptExpression can obtain the index distribution exponential in the index distribution of maximum band in the provision wavelengths.

The length calculation method of existing modal dispersion compensated optical fiber is based on thumb rule, and error is bigger.In addition, be necessary with aforementioned formula (1), come approximate treatment modal dispersion compensated optical fiber with by the index distribution of compensated optical fiber, thereby be easier to produce error.Therefore, can not compensate fully, such as being difficult to obtain the broadband corresponding with the high speed transfer rate to modal dispersion.

In addition, also proposed a kind of following method, that is: resolved by electromagnetic field, calculated at the modal dispersion compensated optical fiber and the group velocity of the flashlight that transmits in by compensated optical fiber, and, calculate the modal dispersion compensated optical fiber and compared L by the length of compensated optical fiber by simulation based on this value of calculating _Comp/ L _TargetOptimum value.

Yet this method need be carried out complicated calculating, is not easy to weave into the electronics Program for Calculation.And the calculating that is used to simulate needs the long period, such as not being used for scene of laying optical transmission line etc.

Summary of the invention

Therefore, even have the method for wide band optical transmission line and have broadband and can realize high speed transfer rate that 10GbE is such and optical transmission line and light LAN that long distance also can form easily at an easy rate even problem of the present invention is to provide a kind of GI of utilization optical fiber to come also easily to form with cheap and long distance.

In addition, problem is to provide a kind of and can carries out the modal dispersion compensation method of the compensation that efficient is good and precision is good and almost do not have modal dispersion and have wide band optical transmission line and light LAN modal dispersion.

For solving aforementioned problems, the application provides following three groups of invention groups.

The first invention group

What claim 1 related to is a kind of optical transmission line formation method, wherein, connect a plurality of multimode optical fibers and form optical transmission line, the method is characterized in that: the frequency band of obtaining this optical transmission line becomes the length ratio of each maximum multimode optical fiber, and recently connects a plurality of multimode optical fibers with this length.

The invention that claim 2 relates to is a kind of optical transmission line, has a plurality of multimode optical fibers, it is characterized in that: the frequency band according to this optical transmission line becomes maximum mode, and the length ratio of each multi-mode optical fiber is adjusted.

The invention that claim 3 relates to is an optical transmission line according to claim 2, it is characterized in that having: in the flashlight that transmits in multimode optical fiber with a plurality of transmission modes, the time of arrival of high power pattern is early than the multimode optical fiber of low power pattern; Be later than the multimode optical fiber of low power pattern the time of arrival of high power pattern.

The invention that claim 4 relates to is according to claim 2 or 3 described optical transmission lines, it is characterized in that: be the optical transmission line that transmits 0.85 μ m band and/or 1.3 μ m band signal light.

The invention that claim 5 relates to is a kind of smooth LAN, it is characterized in that: utilize the described optical transmission line of the invention described above to form.

The second invention group

The invention that claim 6 relates to is a kind of modal dispersion compensation method, it is characterized in that:

Form by multimode optical fiber by compensated optical fiber on the connection mode dispersion compensating fiber, compensate by the modal dispersion of compensated optical fiber, when desiring to make when in provision wavelengths, obtaining maximum band, adopt have the index distribution that satisfies following formula (3) by compensated optical fiber and modal dispersion compensated optical fiber

Δ _comp(r)＝Δ _opt(r)+k{Δ _opt(r)-Δ _target(r)} (3)

Wherein, Δ _Comp(r) expression is poor apart from the specific refractivity at r place at a distance of modal dispersion compensated optical fiber core centre, Δ _Target(r) expression is poor apart from the specific refractivity at r place by the compensated optical fiber core centre apart, Δ _Opt(r) expression is at a distance of connecting by compensated optical fiber and modal dispersion compensated optical fiber, and it is poor apart from the specific refractivity at r place to obtain the optical fiber integrally core centre of maximum band in provision wavelengths, and k represents proportionality constant.

The invention that claim 7 relates to is a kind of modal dispersion compensation method according to claim 6, it is characterized in that: become maximum length ratio with frequency band, connect previous mode dispersion compensating fiber and aforementioned by compensated optical fiber.

The invention that claim 8 relates to, be a kind of modal dispersion compensated optical fiber, its be connected in by multimode optical fiber form by compensated optical fiber, and compensate this by the modal dispersion of compensated optical fiber, thereby can obtain maximum band in provision wavelengths, it is characterized in that: index distribution satisfies above-mentioned formula (3).

The invention that claim 9 relates to is a kind of optical transmission line, it is characterized in that: the modal dispersion compensated optical fiber that is satisfied above-mentioned formula (3) by compensated optical fiber and index distribution that is formed by multimode optical fiber becomes maximum length with frequency band and recently connects and constitute.

The invention that claim 10 relates to is an optical transmission line according to claim 9, it is characterized in that: it is the optical transmission line that transmits 0.85 μ m band and/or 1.3 μ m band signal light.

The invention that claim 11 relates to is a kind of smooth LAN, it is characterized in that: adopt claim 9 or 10 described optical transmission lines to form.

The 3rd invention group

The invention that claim 12 relates to is a kind of modal dispersion compensation method, it is characterized in that:

Form by multimode optical fiber by compensated optical fiber on the connection mode dispersion compensating fiber, compensate by the modal dispersion of compensated optical fiber, when desiring to make when in provision wavelengths, obtaining maximum band, with the length that satisfies following formula (4) recently the connection mode dispersion compensating fiber with by compensated optical fiber

$L_{\mathrm{comp}}/L_{t\arg \mathrm{et}}=\frac{{\&Integral;}_0^{a_{t\arg \mathrm{et}}}\{{\mathrm{\&Delta;}}_{t\arg \mathrm{et}}\left(r\right)-{\mathrm{\&Delta;}}_{\mathrm{opt}}\left(r\right)\}\mathrm{dr}}{{\&Integral;}_0^{a_{\mathrm{comp}}}\{{\mathrm{\&Delta;}}_{\mathrm{opt}}\left(r\right)-{\mathrm{\&Delta;}}_{\mathrm{comp}}\left(r\right)\}\mathrm{dr}}---\left(4\right)$

Wherein, L _CompThe length of expression modal dispersion compensated optical fiber, L _TargetExpression is by the length of compensated optical fiber, a _CompThe fiber core radius of expression modal dispersion compensated optical fiber, a _TargetExpression is by the fiber core radius of compensated optical fiber, Δ _Comp(r) expression is poor apart from the specific refractivity at r place at a distance of the core centre of modal dispersion compensated optical fiber, Δ _Target(r) expression is poor apart from the specific refractivity at r place by the core centre of compensated optical fiber apart, Δ _Opt(r) expression is at a distance of connecting by compensated optical fiber and modal dispersion compensated optical fiber, and it is poor apart from the specific refractivity at r place to obtain the core centre of optical fiber integrally of maximum band in provision wavelengths.

The invention that claim 13 relates to is a kind of modal dispersion compensation method, it is characterized in that:

Form by multimode optical fiber by compensated optical fiber on the connection mode dispersion compensating fiber, compensate by the modal dispersion of compensated optical fiber, when desiring to make when in provision wavelengths, obtaining maximum band, employing have the index distribution that satisfies following formula (5) by compensated optical fiber and modal dispersion compensated optical fiber, to satisfy the length ratio of following formula (6), come the connection mode dispersion compensating fiber and by compensated optical fiber.

$n\left(r\right)=\left\{\begin{array}{cc}{n}_1{\{1-2{\mathrm{\&Delta;}}_1{(r/a)}^{\mathrm{\&alpha;}}\}}^{1/2}& (0\&le;r\&le;a)\\ n_1\{1-2{\mathrm{\&Delta;}}_1{\}}^{1/2}& (a<r)\end{array}\right.---\left(5\right)$

Wherein, n (r) expression is at a distance of the core centre of the optical fiber index distribution apart from the fiber core radius direction at r place, n ₁The refractive index of expression core centre, Δ ₁The specific refractivity of the relative coating of expression core centre is poor, and a represents fiber core radius, and α represents the index distribution exponential.

$L_{\mathrm{comp}}/L_{t\arg \mathrm{et}}=\left(\frac{{\mathrm{\&alpha;}}_{t\arg \mathrm{et}}-{\mathrm{\&alpha;}}_{\mathrm{opt}}}{{\mathrm{\&alpha;}}_{\mathrm{opt}}-{\mathrm{\&alpha;}}_{\mathrm{comp}}}\right)\&times;\left(\frac{1+{\mathrm{\&alpha;}}_{\mathrm{<figure-callout\; id="1"\; label="comp"\; filenames="A20048000336000571.png,A20048000336000572.png"\; state="\{\{state\}\}">comp</figure-callout>}}}{1+{\mathrm{\&alpha;}}_{t\arg \mathrm{et}}}\right)---\left(6\right)$

Wherein, L _CompThe length of expression modal dispersion compensated optical fiber, L _TargetExpression is by the length of compensated optical fiber, α _CompThe index distribution exponential of expression modal dispersion compensated optical fiber, α _TargetExpression is by the index distribution exponential of compensated optical fiber, α _OptExpression connects by compensated optical fiber and modal dispersion compensated optical fiber and can obtain the index distribution exponential of the optical fiber integrally of maximum band in provision wavelengths.

The invention that claim 14 relates to is a kind of optical transmission line, it is characterized in that: by multimode optical fiber form by compensated optical fiber and modal dispersion compensated optical fiber, be connected with the length ratio that satisfies above-mentioned formula (4).

The invention that claim 15 relates to, it is a kind of optical transmission line, connection by multimode optical fiber form by compensated optical fiber and modal dispersion compensated optical fiber and constitute, it is characterized in that: the modal dispersion compensated optical fiber with by compensated optical fiber, have the index distribution that satisfies above-mentioned formula (5), and be connected with the length ratio that satisfies above-mentioned formula (6).

The invention that claim 16 relates to is an optical transmission line according to claim 4, it is characterized in that: previous mode dispersion compensating fiber and aforementioned by in the compensated optical fiber, index distribution exponential α _Comp, α _TargetMore than or equal to 0.5, the specific refractivity difference Δ of the relative coating of core centre _1comp, Δ _1targetBe 0.005～0.025, fiber core radius a _Comp, a _Target Be 5～50 μ m.

The invention that claim 17 relates to is according to any described optical transmission line of claim 14 to 16, it is characterized in that: be the optical transmission line that transmits 0.85 μ m band or 1.3 μ m band signal light.

The invention that claim 18 relates to is a kind of smooth LAN, it is characterized in that: adopt the described optical transmission line of the invention described above to form.

Description of drawings

Fig. 1 be expression GI optical fiber index distribution, with the summary mode chart of the transmission path of each transmission mode.

Fig. 2 is the summary mode chart of an example of expression optical transmission line of the present invention.

Fig. 3 is the accompanying drawing of the DMD characteristic of GI optical fiber 1,2 in the presentation graphs 2 and optical transmission line.

Fig. 4 is the figure of frequency band of the optical transmission line of presentation graphs 2.

Fig. 5 is the figure of Inner/Outer DMD of the optical transmission line of presentation graphs 2.

Fig. 6 is that expression index distribution exponential is optimum value α ₀The figure of DMD characteristic of GI optical fiber.

Fig. 7 is the figure of the DMD characteristic of expression when path length is made as 0.3km.

Fig. 8 is the figure that expression is made as the link position of GI optical fiber on the frequency band of opposite optical transmission line.

Fig. 9 is the figure that expression is made as the link position of GI optical fiber the Inner/Outer DMD characteristic of opposite optical transmission line.

Figure 10 is the figure of the frequency band of optical transmission line among the expression concrete example 1-1.

Figure 11 is the figure of the Inner/Outer DMD of optical transmission line among the expression concrete example 1-1.

Figure 12 is the figure of the DMD characteristic of GI optical fiber 1,2 and optical transmission line among the expression concrete example 1-1.

Figure 13 is the figure of the frequency band of optical transmission line among the expression concrete example 1-2.

Figure 14 is the figure of the Inner/Outer DMD of optical transmission line among the expression concrete example 1-2.

Figure 15 is the figure of the DMD characteristic of GI optical fiber 1,2 and optical transmission line among the expression concrete example 1-2.

Figure 16 is the figure of the frequency band of optical transmission line among the expression concrete example 1-3.

Figure 17 is the figure of the Inner/Outer DMD of optical transmission line among the expression concrete example 1-3.

Figure 18 is the figure of the DMD characteristic of GI optical fiber 1,2 and optical transmission line among the expression concrete example 1-3.

Figure 19 is the figure of the frequency band of optical transmission line among the expression concrete example 1-4.

Figure 20 is the figure of the Inner/Outer DMD of optical transmission line among the expression concrete example 1-4.

Figure 21 is the figure of the frequency band of optical transmission line among the expression concrete example 1-5.

Figure 22 is the figure of the Inner/Outer DMD of optical transmission line among the expression concrete example 1-5.

Figure 23 is the figure of the DMD characteristic of GI optical fiber 1,2 and optical transmission line among the expression concrete example 1-5.

Figure 24 is the figure of the index distribution of GI optical fiber 1,2 among the expression concrete example 1-6.

Figure 25 is the figure of the frequency band of optical transmission line among the expression concrete example 1-6.

Figure 26 is the figure of the Inner/Outer DMD of optical transmission line among the expression concrete example 1-6.

Figure 27 is the figure of the DMD characteristic of GI optical fiber 1,2 and optical transmission line among the expression concrete example 1-6.

Figure 28 is the summary mode chart of the transmission path of the index distribution of expression GI optical fiber and each transmission mode.

Figure 29 is expression is obtained index distribution one example of maximum band in the index distribution of compensated optical fiber and modal dispersion compensated optical fiber and the used signal light wavelength a skeleton diagram.

Figure 30 is the summary pie graph of expression optical transmission line one example of the present invention.

Figure 31 is the figure that can be obtained the index distribution of maximum band among the expression concrete example 2-1 in the index distribution of compensated optical fiber and modal dispersion compensated optical fiber and the used signal light wavelength.

Figure 32 is the figure of relation of the length of the frequency band of optical transmission line among the expression concrete example 2-1 and modal dispersion compensated optical fiber.

Figure 33 is the figure of relation of the length of the Inner/Outer DMD of optical transmission line among the expression concrete example 2-1 and modal dispersion compensated optical fiber.

Figure 34 is that (a) reached (b) figure of the DMD characteristic of optical transmission line by compensated optical fiber among the expression concrete example 2-1.

Figure 35 is the figure of the frequency band of optical transmission line among the expression concrete example 2-2.

Figure 36 is that (a) reached (b) figure of the DMD characteristic of optical transmission line by compensated optical fiber among the expression concrete example 2-2.

Figure 37 is the figure of the frequency band of optical transmission line among the expression concrete example 2-3.

Figure 38 is that (a) reached (b) figure of the DMD characteristic of optical transmission line by compensated optical fiber among the expression concrete example 2-3.

Figure 39 is the figure of the frequency band of optical transmission line among the expression concrete example 2-4.

Figure 40 is that (a) reached (b) figure of the DMD characteristic of optical transmission line by compensated optical fiber among the expression concrete example 2-4.

Figure 41 is the figure of the frequency band of optical transmission line among the expression concrete example 2-5.

Figure 42 is that (a) reached (b) figure of the DMD characteristic of optical transmission line by compensated optical fiber among the expression concrete example 2-5.

Figure 43 is the figure of the frequency band of optical transmission line among the expression concrete example 2-6.

Figure 44 is that (a) reached (b) figure of the DMD characteristic of optical transmission line by compensated optical fiber among the expression concrete example 2-6.

Figure 45 is the figure of the frequency band of optical transmission line among the expression concrete example 2-7.

Figure 46 is that (a) reached (b) figure of the DMD characteristic of optical transmission line by compensated optical fiber among the expression concrete example 2-7.

Figure 47 is a modal dispersion compensated optical fiber and the figure that can be obtained the index distribution of maximum band in the index distribution of compensated optical fiber and the used signal light wavelength that has made among the expression concrete example 2-8.

Figure 48 is the figure of the frequency band of optical transmission line among the expression concrete example 2-8.

Figure 49 is that (a) reached (b) figure of the DMD characteristic of optical transmission line by compensated optical fiber among the expression concrete example 2-8.

Figure 50 is the figure of the frequency band of optical transmission line among the expression concrete example 2-9.

Figure 51 is that (a) reached (b) figure of the DMD characteristic of optical transmission line by compensated optical fiber among the expression concrete example 2-9.

Figure 52 is illustrated in the length of calculating among the concrete example 3-1 to compare L _Comp/ L _TargetWith α _CompThe figure of relation.

Figure 53 is that (a) compared L by compensated optical fiber, (b) by the length of calculating with existing method among the expression concrete example 3-1 _Comp/ L _TargetThe optical transmission line that constitutes, (c) compare L by the length of calculating with the inventive method _Comp/ L _TargetThe figure of the DMD characteristic of the optical transmission line that constitutes.

Figure 54 is illustrated in the length of calculating among the concrete example 3-2 to compare L _Comp/ L _TargetWith α _CompThe figure of relation.

Figure 55 is that (a) compared L by compensated optical fiber, (b) by the length of calculating with existing method among the expression concrete example 3-2 _Comp/ L _TargetThe optical transmission line that constitutes, (c) compare L by the length of calculating with the inventive method _Comp/ L _TargetThe figure of the DMD characteristic of the optical transmission line that constitutes.

Figure 56 is illustrated in the length of calculating among the concrete example 3-3 to compare L _Comp/ L _TargetWith α _CompThe figure of relation.

Figure 57 is that (a) compared L by compensated optical fiber, (b) by the length of calculating with existing method among the expression concrete example 3-3 _Comp/ L _TargetThe optical transmission line that constitutes, (c) compare L by the length of calculating with the inventive method _Comp/ L _TargetThe figure of the DMD characteristic of the optical transmission line that constitutes.

Figure 58 is illustrated in the length of calculating among the concrete example 3-4 to compare L _Comp/ L _TargetWith α _CompThe figure of relation.

Figure 59 is that (a) compared L by compensated optical fiber, (b) by the length of calculating with existing method among the expression concrete example 3-4 _Comp/ L _TargetThe optical transmission line that constitutes, (c) compare L by the length of calculating with the inventive method _Comp/ L _TargetThe figure of the DMD characteristic of the optical transmission line that constitutes.

Figure 60 is illustrated in the length of calculating among the concrete example 3-5 to compare L _Comp/ L _TargetWith α _CompThe figure of relation.

Figure 61 is that (a) compared L by compensated optical fiber, (b) by the length of calculating with existing method among the expression concrete example 3-5 _Comp/ L _TargetThe optical transmission line that constitutes, (c) compare L by the length of calculating with the inventive method _Comp/ L _TargetThe figure of the DMD characteristic of the optical transmission line that constitutes.

Figure 62 is illustrated in the length of calculating among the concrete example 3-6 to compare L _Comp/ L _TargetWith α _CompThe figure of relation.

Figure 63 is that (a) compared L by compensated optical fiber, (b) by the length of calculating with existing method among the expression concrete example 3-6 _Comp/ L _TargetThe optical transmission line that constitutes, (c) compare L by the length of calculating with the inventive method _Comp/ L _TargetThe figure of the DMD characteristic of the optical transmission line that constitutes.

Figure 64 be made among the expression concrete example 3-7 by the figure of the index distribution of compensated optical fiber.

Figure 65 is illustrated in the length of calculating among the concrete example 3-7 to compare L _Comp/ L _TargetWith α _CompThe figure of relation.

Figure 66 is that (a) compared L by compensated optical fiber, (b) by the length of calculating with existing method among the expression concrete example 3-7 _Comp/ L _TargetThe optical transmission line that constitutes, (c) compare L by the length of calculating with the inventive method _Comp/ L _TargetThe figure of the DMD characteristic of the optical transmission line that constitutes.

Figure 67 is illustrated in the length of calculating among the concrete example 3-8 to compare L _Comp/ L _TargetWith α _CompThe figure of relation.

Figure 68 is that (a) compared L by compensated optical fiber, (b) by the length of calculating with existing method among the expression concrete example 3-8 _Comp/ L _TargetThe optical transmission line that constitutes, (c) compare L by the length of calculating with the inventive method _Comp/ L _TargetThe figure of the DMD characteristic of the optical transmission line that constitutes.

Figure 69 is illustrated in the length of calculating among the concrete example 3-9 to compare L _Comp/ L _TargetWith α _CompThe figure of relation.

Figure 70 is that (a) compared L by compensated optical fiber, (b) by the length of calculating with existing method among the expression concrete example 3-9 _Comp/ L _TargetThe optical transmission line that constitutes, (c) compare L by the length of calculating with the inventive method _Comp/ L _TargetThe figure of the DMD characteristic of the optical transmission line that constitutes.

The figure of the frequency band of Figure 71 optical transmission line that to be expression calculate with the electromagnetic field analytic simulation of existing method and the relation of modal dispersion compensated optical fiber length.

Figure 72 connects Inner/Outer DMD when being formed optical transmission line by compensated optical fiber and modal dispersion compensated optical fiber, and the figure of the relation of modal dispersion compensated optical fiber length in the existing method of expression.

Embodiment

Below, the present invention is elaborated.

At first, describe the first invention group in detail.

[the formation method of optical transmission line, optical transmission line]

Incide the flashlight of multimode optical fibers such as GI optical fiber, transmit with a plurality of transmission modes.The difference of the time that arrives output terminal at flashlight because of each transmission mode produces under the occasion of difference, the flashlight that is transmitted since this time of arrival difference difference, and chromatic dispersion (hereinafter referred to as modal dispersion) can take place.

Under the bigger occasion of modal dispersion, the flashlight that the transmission capacity is high (flashlight that pulse width is narrow) is after transmission, and its pulse width will enlarge because of modal dispersion, and flashlight can overlap each other, thereby can't detect.As, the transfer rate of the flashlight that can transmit is restricted because of modal dispersion, the ultimate value of this flashlight that can transmit is called the frequency band of this optical fiber.

The transfer rate of flashlight in the optical fiber, be subjected to the signal light frequency that can transmit about, thereby it is decided by the frequency band of this optical fiber.Reach consistent by the time that makes flashlight under each transmission mode arrive output terminal, can make that modal dispersion is most of to disappear, the frequency band of optical fiber is broadened, and can improve the transfer rate of flashlight.

Fig. 1 is the mode chart of transmission path of each transmission mode of the index distribution of expression GI optical fiber and the flashlight that transmits in this GI optical fiber with multiple transmission mode.

The index distribution n of this GI optical fiber (r) is the shape that has largest refractive index at core centre, and comes approximate treatment by following formula (7).Wherein, in the formula (7), n1 represents the refractive index of core centre, Δ ₁The expression specific refractivity is poor, and a represents fiber core radius, and r represents the distance at a distance of core centre, and α represents the index distribution exponential.

$n\left(r\right)=\left\{\begin{array}{cc}{n}_1{\{1-2{\mathrm{\&Delta;}}_1{(r/a)}^{\mathrm{\&alpha;}}\}}^{1/2}& (0\&le;r\&le;a)\\ n_1\{1-2{\mathrm{\&Delta;}}_1{\}}^{1/2}& (a<r)\end{array}\right.---\left(7\right)$

Low power pattern in the transmission mode reaches maximum mode according to the light intensity at the core centre place, propagates near core centre.Relative therewith, in the high power pattern, then reach maximum mode and propagate leaving the core centre place, thereby in boundary portion total reflection and propagation with wide-angle of fibre core and coating, so compare with low power pattern, transmission path can extend according to light intensity distributions.

As mentioned above, the index distribution of GI optical fiber has following shape, has largest refractive index at core centre that is:, and refractive index reduces gradually along with the increasing of radius, thereby with the flashlight of low power mode transfer, though transmission path shorten, with transmission at a slow speed.Relative therewith, with the flashlight of high power mode transfer, though transmission path is longer, refractive index is little in fibre core periphery vicinity, and with high-speed transfer.

The shape of the index distribution of GI optical fiber is that α decides by the index distribution exponential in aforementioned formula (7).Therefore, can be by adjusting this index distribution exponential α, the time that makes the flashlight that transmits with each transmission mode arrive output terminal reaches consistent.At this moment, it is minimum that modal dispersion reaches in theory, can realize broadband.The index distribution exponential of this moment is made as optimum value α ₀

In addition, behind the increase index distribution exponential α, index distribution just becomes following shape, that is: the core at fibre core slowly changes, and sharply reduces in the periphery refractive index of fibre core.Therefore, at refractive index profile shape α greater than optimum value α ₀Occasion under, the time that arrives output terminal with the flashlight of high power mode transfer will postpone.Otherwise if reduce α, then the time that arrives output terminal with the flashlight of high power mode transfer will be done sth. in advance.

Fig. 2 represents optical transmission line one example of the present invention.In this optical transmission line, with index distribution exponential α less than optimum value α ₀GI optical fiber 1, with index distribution exponential α greater than optimum value α ₀GI optical fiber 2 be connected.

About these GI optical fiber, can adopt the optical fiber made from known method.In addition, index distribution exponential α is greater than still less than optimum value α ₀All can, needn't tightly adjust index distribution exponential α and make GI optical fiber.

The GI optical fiber 1,2 among Fig. 2 that the (a) and (b) of Fig. 3, (c) represent to calculate by simulation and the DMD characteristic (delay of DMD:Differential Mode Delay/ differential mode) of optical transmission line.This DMD characteristic is when making the misalignment GI fiber optic hub of pulse type incident light, encourages each transmission mode, and describe the curve of output waveform in time zone, and it represents the transmission time difference between each pattern.In addition, so-called biasing, the radial direction distance of expression incoming signal light center and core centre.

Depart to radial direction more than core centre at the center of incoming signal light, and flashlight is just more with higher power mode transfer.Therefore, being biased to 0 waveform is the more flashlight that contains low power pattern, and biasing is big more, then represents the waveform with the flashlight of higher power mode transfer.

The index distribution exponential α of GI optical fiber 1 is 1.94, and the index distribution exponential α of GI optical fiber 2 is 2.14, the index distribution exponential optimum value α of GI optical fiber 1,2 ₀Be 2.04.In addition, the radius of GI optical fiber 1,2 is 62.5 μ m, and fiber core radius is 25 μ m, and specific refractivity difference Δ is 0.01, and total length is 1km.

In addition, the optical transmission line in this example, the GI optical fiber 1 of 0.48km is connected with the GI optical fiber 2 of 0.52km to be constituted.

In addition, the centre wavelength of flashlight is 0.85 μ m, and the frequency spectrum half width is 0.25nm, and pulse half-width is 0.08ns.

Refractive index distribution exponential α is less than optimum value α ₀GI optical fiber 1, shown in Fig. 3 (a), high power pattern is just arrive exit end more early.Therefore, if will with time of arrival of the flashlight of minimum power mode transfer as benchmark, just then become negative value with the relative value of time of arrival of the flashlight of high power mode transfer.

Relative therewith, refractive index distribution exponential α is greater than optimum value α ₀GI optical fiber 2, shown in Fig. 3 (b), high power pattern postpones more just arrive exit end.Therefore, if will with time of arrival of the flashlight of minimum power mode transfer as benchmark, just then with the relative value of time of arrival of the flashlight of high power mode transfer become on the occasion of.

In this optical transmission line, this GI optical fiber 1 is connected with GI optical fiber 2, and can compensates the negative relative value of the high power pattern time of arrival that in GI optical fiber 1, produces with the positive relative value of high power pattern time of arrival of GI optical fiber 2.

In addition, the relative value with time of arrival of the flashlight of this high power mode transfer increases with the length of GI optical fiber is proportional.Therefore, for this optical transmission line, adjust the length ratio of GI optical fiber 1 and GI optical fiber 2, make in this GI optical fiber 1 the high power pattern that produces time of arrival relative value, reach consistent with the relative value of the time of arrival of the high power pattern of generation in GI optical fiber 2, and shown in Fig. 3 (c), for all transmission modes, make reach consistent the time of arrival of the flashlight that is transferred to exit end.

This GI optical fiber 1 is obtained by following method with the length ratio of GI optical fiber 2.

At first, measure the index distribution of each GI optical fiber 1,2, and utilize the measured value of this index distribution, calculate the transmission speed of the flashlight in each transmission mode by simulation.Here, as analogy method, such as adopting L.Raddtz, et., al, J, Lightwave Technol., Vol.16, disclosed method in (1998) p.324-331, the power of calculating each pattern that is energized from incident light.In addition, distribute, calculate from the mode excitation of GI optical fiber 1 to GI optical fiber 2 by the electromagnetic field of the transmission mode of correspondence.

Next, utilize K.Okamoto, Appl.Opt., vol.18, disclosed method in (1979) is p.2199-2206 calculated the transmission speed of each transmission mode in GI optical fiber 1 and the GI optical fiber 2.

Utilize this theoretical calculation, calculate the frequency band that connects the optical transmission line that 2 GI optical fiber 1,2 form with all lengths ratio by simulation.At this moment, suppose to transmit the flashlight that in a GI optical fiber, transmits with each transmission mode that another GI optical fiber can transmit.

In addition, for the frequency band of optical transmission line, output signal light is carried out the conversion of Fuli's leaf, and form frequency spectrum, and the amplitude of this frequency spectrum is obtained as half the following frequency band that becomes the zero frequency amplitude.

Fig. 4 calculates all mode excitation states of aforementioned lights transmission lines (hereinafter referred to as OFL by simulation.OFL:Over-filled Launch) frequency band, and with the length ratio L of GI optical fiber 1 ₁The curve map of describing.Can find out that therefrom the frequency band of optical transmission line is the length ratio L with respect to GI optical fiber 1 ₁The curve that raises up, and have maximal value.Here, the frequency band maximal value among Fig. 4 betides the length ratio L that works as with respect to the GI optical fiber 1 of optical transmission line ₁Be in 0.48.

As mentioned above, form the length ratio of the GI optical fiber 1,2 of this optical transmission line, be to calculate with all lengths ratio to connect this GI optical fiber 1,2 and the frequency band of the optical transmission line that forms, and the length ratio of each the GI optical fiber when becoming maximum as this frequency band is obtained.

Fig. 5 calculates with all lengths ratio by simulation to connect in the optical transmission line that this GI optical fiber 1,2 forms, be transferred to various transmission modes in time of arrival of flashlight of exit end, time of arrival and earliest arrival time is poor at the latest, and with the length ratio L of GI optical fiber 1 ₁The curve map of describing.Among Fig. 5, Inner DMD is be biased to the time of arrival at the latest of 5～18 μ m and earliest arrival time poor, and Outer DMD is be biased to the time of arrival at the latest of 0～23 μ m and earliest arrival time poor.

Therefrom can find out, when the frequency band of optical transmission line becomes length ratio L in the optical transmission line of maximum GI optical fiber 1 ₁Be 0.48 o'clock, Inner DMD and Outer DMD all become minimum, and almost consistent.

Fig. 6 is that to calculate the index distribution exponential be optimum value α by simulation ₀The figure of DMD characteristic of GI optical fiber.

As Fig. 3 (c) and shown in Figure 6, when the mode that becomes maximum according to frequency band is adjusted the length ratio of GI optical fiber 1,2 and connected into optical transmission line, just can obtain reaching optimum value α with the index distribution exponential ₀GI optical fiber DMD characteristic much at one.

Like this, as shown in Figure 4, calculate with all lengths ratio and connect index distribution exponential α less than optimum value α ₀GI optical fiber 1, with index distribution exponential α greater than optimum value α ₀GI optical fiber 2 and the frequency band of the optical transmission line that forms, and the length ratio of each the GI optical fiber when obtaining this frequency band and becoming maximum.Then, with this length ratio of calculating, each GI optical fiber is connected and the formation optical transmission line.Like this, shown in Fig. 3 (c),, reach consistent the time of arrival of the flashlight of exit end, can realize having wide band optical transmission line thus just be transferred to for all transmission modes.

DMD characteristic when Fig. 7 represents that transmission lines length is made as 0.3km, Fig. 7 (a) expression GI optical fiber 1, Fig. 7 (b) expression GI optical fiber 2, Fig. 7 (c) represents to be connected the optical fiber that GI optical fiber 1,2 forms with same length ratio shown in Figure 3.Even transmission lines is long different, if but length ratio is identical, and then for all transmission modes, the time of arrival that is transferred to the flashlight of exit end also can be consistent.

Fig. 8 is the length ratio L with the GI optical fiber 2 of incident end one side ₂, the curve map of the frequency band under the OFL of the optical transmission line when describing that GI optical fiber 1 is set to exit end one side and GI optical fiber 2 being set to incident end one side, Fig. 9 is the length ratio L with GI optical fiber 2 ₂Describe the curve map of the Inner/Outer DMD of this optical transmission line.

Length ratio L when GI optical fiber 2 ₂Be 0.52 o'clock, it is maximum that the frequency band of optical transmission line just reaches, and Inner DMD all reaches minimum with Outer DMD, and unanimity almost.At this moment, the length ratio L of GI optical fiber 1 ₁Be 0.48, by with the order of connection of GI optical fiber 1,2 irrespectively, come length ratio is carried out optimization, thereby, can make reach consistent the time of arrival of the flashlight that is transferred to exit end for all transmission modes.

In addition, in this optical transmission line, do not need to form closely the GI optical fiber of index distribution, can adopt the optical fiber made from known method.Therefore, can make employed GI optical fiber in the optical transmission line, can form optical transmission line at an easy rate thus with high finished product rate.

In addition, for the GI optical fiber of optional refractive index distribution, can calculate to form and have the required optimum length ratio of wide band optical transmission line and used, and can effectively utilize the GI optical fiber that has produced.Such as, also can on the GI optical fiber that has laid, connect the GI optical fiber that length ratio obtains adjusting in addition, form wide band optical transmission line thus.Owing to also can so use the GI optical fiber that has laid, thereby can effectively utilize existing GI optical fiber.

[light LAN]

Smooth LAN of the present invention adopts aforesaid optical transmission line.Other formation is not particularly limited, applicable known product.Such as, can enumerate product that connects computing machine and auxiliary device thereof with the aforementioned lights transmission lines etc.

As mentioned above, the frequency band broad of aforementioned lights transmission lines can be realized the high speed of transfer rate thus.Like this, can realize that the transfer rate such as this class of 10GbE is the Ethernet (registered trademark) of 10Gb/s.

Below represent concrete example of the present invention.Utilization has the GI optical fiber of the index distribution exponential shown in the table 1, has formed optical transmission line of the present invention.When the signal light wavelength is 0.85 μ m, the optimum value α of index distribution exponential ₀Be 2.04.

Table 1

Concrete example	The index distribution exponential of GI optical fiber 1	The index distribution exponential of GI optical fiber 2	Signal light wavelength (μ m)	The length ratio (value of calculating) of GI optical fiber 1
					/-1	1.94	2.06	0.85	0.16
/-2	2.02	2.14	0.85	0.83
					/-3	2.02	2.06	0.85	0.51
/-4	1.94	2.02	0.85	0
					/-5	1.84	2.04	1.3	0.48
/-6	-	-	0.85	0.43

Figure 10 calculates with all lengths ratio by simulation to connect frequency band under the OFL of the optical transmission line that the GI optical fiber of concrete example 1-1 forms, and with the length ratio L of GI optical fiber 1 ₁The curve map of describing, Figure 11 are the length ratio L with GI optical fiber 1 ₁Describe the curve map of the Inner/Outer DMD of this optical transmission line.

As can be seen from Figure, as the length ratio L of GI optical fiber 1 ₁Be 0.16 o'clock, it is maximum that the frequency band of optical transmission line reaches, and Inner DMD all reaches minimum with Outer DMD, and almost reach unanimity.In concrete example 1-1, according to the length ratio L of GI optical fiber 1 ₁Become 0.16 mode, connect GI optical fiber 1,2 and formed optical transmission line.

Figure 12 represents the DMD characteristic by the concrete example 1-1 that calculates of simulation, Figure 12 (a) expression GI optical fiber 1, and Figure 12 (b) expression GI optical fiber 2, Figure 12 (c) expression connects with aforementioned length ratio and characteristic when forming light path.

Shown in this Figure 12 (c), obtaining frequency band becomes maximum length ratio, and connects GI optical fiber 1,2 with this length ratio, thus, for all transmission modes, can make reach consistent the time of arrival of the flashlight that is transferred to exit end.

Figure 13 calculates with all lengths ratio by simulation to connect frequency band under the OFL of the optical transmission line that the GI optical fiber of concrete example 1-2 forms, and with the length ratio L of GI optical fiber 1 ₁The curve map of describing, Figure 14 are the curve maps of describing the Inner/Outer DMD of this optical transmission line with the length ratio of GI optical fiber.

As can be seen from Figure, as the length ratio L of GI optical fiber 1 ₁Be 0.83 o'clock, it is maximum that the frequency band of optical transmission line reaches, and Inner DMD all reaches minimum with Outer DMD, and unanimity almost.In concrete example 1-2, according to the length ratio L of GI optical fiber 1 ₁Become 0.83 mode, connect GI optical fiber 1,2 and form optical transmission line.

Figure 15 represents by simulating the DMD characteristic of the concrete example 1-2 that calculates, Figure 15 (a) expression GI optical fiber 1, Figure 15 (b) expression GI optical fiber 2, the characteristic when Figure 15 (c) expression is formed by connecting light path with aforementioned length ratio.

Shown in this Figure 15 (c), obtaining frequency band becomes maximum length ratio, and connects GI optical fiber 1,2 with this length ratio, thus, for all transmission modes, can make reach consistent the time of arrival of the flashlight that is transferred to exit end.

Figure 16 calculates with all lengths ratio by simulation to connect frequency band under the OFL of the optical transmission line that the GI optical fiber of concrete example 1-3 forms, and with the length ratio L of GI optical fiber 1 ₁The curve map of describing, Figure 17 are the curve maps of describing the Inner/Outer DMD of this optical transmission line with the length ratio of GI optical fiber.

As can be seen from Figure, as the length ratio L of GI optical fiber 1 ₁Be 0.51 o'clock, it is maximum that the frequency band of optical transmission line reaches, and Inner DMD all reaches minimum with Outer DMD, and unanimity almost.In concrete example 1-3, according to the length ratio L of GI optical fiber 1 ₁Become 0.51 mode, connect GI optical fiber 1,2 and form optical transmission line.

Figure 18 represents the DMD characteristic by the concrete example 1-3 that calculates of simulation, Figure 18 (a) expression GI optical fiber 1, and Figure 18 (b) expression GI optical fiber 2, Figure 18 (c) expression connects with aforementioned length ratio and characteristic when forming optical transmission line.

Even the index distribution exponential at GI optical fiber 1,2 approaches under the occasion of optimum value 2.04, shown in Figure 18 (c), become maximum length ratio by obtaining frequency band, and connect GI optical fiber 1,2 with this length ratio, thus for all transmission modes, also can precision make well to reach consistent the time of arrival of the flashlight that is transferred to exit end.

Figure 19 calculates with all lengths ratio by simulation to connect frequency band under the OFL of the optical transmission line that the GI optical fiber of concrete example 1-4 forms, and with the length ratio L of GI optical fiber 1 ₁The curve map of describing, Figure 20 are the curve maps of describing the Inner/Outer DMD of this optical transmission line with the length ratio of GI optical fiber.

Because the index distribution exponential of GI optical fiber 1,2, all less than the optimum value 2.04 of index distribution exponential, even thereby connect this GI optical fiber 1,2 and form optical transmission line, can not compensate the deviation of the time of arrival that causes by transmission mode that in GI optical fiber 1, produces by GI optical fiber 2.Therefore, as shown in figure 19, the frequency band of optical transmission line does not become the curve that raises up.

Length ratio L when GI optical fiber 1 ₁Be 0 o'clock, the frequency band of optical transmission line becomes maximum, and Inner DMD and Outer DMD all become minimum.Therefore, in concrete example 1-4, do not adopt GI optical fiber 1, and only adopt GI optical fiber 2 to form optical transmission line, can obtain wideer frequency band thus.So can judge, calculate the frequency band of optical transmission line in advance by simulation, be thus connected 2 GI optical fiber and form optical transmission line, thereby can obtain broadband.

Figure 21 calculates with all lengths ratio by simulation to connect frequency band under the OFL of the optical transmission line that the GI optical fiber of concrete example 1-5 forms, and with the length ratio L of GI optical fiber 1 ₁The curve map of describing, Figure 22 are the curve maps of describing the Inner/Outer DMD of this optical transmission line with the length ratio of GI optical fiber.In this concrete example 1-5, for flashlight, wavelength is 1.3 μ m, and the frequency spectrum half width is 1.0nm, and pulse half-width is 0.05ns, the optimum value α of the index distribution exponential of the GI optical fiber of this moment ₀Be 1.94.

Length ratio L when GI optical fiber 1 ₁Be 0.48 o'clock, the frequency band of optical transmission line becomes maximum, and Inner DMD and Outer DMD all become minimum, and almost consistent.In concrete example 1-5, according to the length ratio L of GI optical fiber 1 ₁Become 0.48 mode, connect GI optical fiber 1,2 and the formation optical transmission line.

Figure 23 represents the DMD characteristic by the concrete example 1-5 that calculates of simulation, Figure 23 (a) expression GI optical fiber 1, and Figure 23 (b) expression GI optical fiber 2, Figure 23 (c) expression connects with aforementioned length ratio and characteristic when forming light path.

Shown in Figure 23 (c), obtaining frequency band becomes maximum length ratio, and connects GI optical fiber 1,2 with this length ratio, thus, for all transmission modes, can make reach consistent the time of arrival of the flashlight that is transferred to exit end.

Figure 24 represents the measurement result of the index distribution of GI optical fiber among the concrete example 1-6, Figure 24 (a) expression GI optical fiber 1, Figure 24 (b) expression GI optical fiber 2.Specific refractivity difference Δ (r) is defined as follows.

Δ (r)=(n ₁ ²(r)-n ₂ ²)/2n ₁ ²(r) (wherein, n ₁Be the refractive index of fibre core, n ₂It is the refractive index of coating.)

Figure 25 is a measurement result of utilizing this index distribution, calculates with all lengths ratio by simulation to connect frequency band under the OFL of the optical transmission line that GI optical fiber 1,2 forms, and with the length ratio L of GI optical fiber 1 ₁The curve map of describing, Figure 26 are the curve maps of describing the Inner/Outer DMD of this optical transmission line with the length ratio of GI optical fiber.In this concrete example 1-6, the path length of optical transmission line is 4km.In addition, for flashlight, wavelength is 0.85 μ m, and the frequency spectrum half width is 0.25nm, and pulse half-width is 0.08ns, the optimum value α of the index distribution exponential of the GI optical fiber of this moment ₀Be 2.04.

The length ratio L that works as GI optical fiber 1 as can be known ₁Be 0.43 o'clock, the frequency band of optical transmission line becomes maximum, and Inner DMD and Outer DMD all become minimum, and almost consistent.

Figure 27 represents the DMD characteristic of practical measurement among the concrete example 1-6, and Figure 27 (a) only represents that path length is the GI optical fiber 1 of 2km, and Figure 27 (b) only represents that path length is the GI optical fiber 2 of 2.22km.In addition, Figure 27 (c) expression connects the GI optical fiber 1,2 shown in Figure 27 (a) and Figure 27 (b) and the light path of formation.In the middle optical transmission line of this Figure 27 (c), the length ratio L of GI optical fiber 1 ₁Be 0.47, and become the length ratio L of maximum GI optical fiber 1 with frequency band by the simulation optical transmission line of calculating ₁It is 0.43 o'clock length ratio much at one.

Therefore, shown in Figure 27 (c),, can make the time of arrival of the flashlight that is transferred to exit end almost consistent for all transmission modes.

As mentioned above, for the GI optical fiber of optional refractive index distribution, can calculate and be used to form optimum length ratio with wide band optical transmission line.Form optical transmission line by connecting GI optical fiber, thereby can realize, make the optical transmission line that reaches unanimity time of arrival of the flashlight that is transferred to exit end for all transmission modes with this length ratio.At this moment, the deviation and the modal dispersion that produces can realize broadband time of arrival that does not almost not cause by basic transmission mode.

As mentioned above,, all can make reach consistent the time of arrival of the flashlight that is transferred to exit end, can realize having wide band optical transmission line thus for all transmission modes.In addition, the GI optical fiber that forms index distribution closely needn't be adopted, the optical fiber made from known method can be adopted.Therefore, can make employed GI optical fiber in the optical transmission line with high finished product rate, and can form optical transmission line at an easy rate thus.In addition owing to needn't adopt the GI optical fiber that forms index distribution closely, even thereby the optical transmission line of long distance also can form easily.

And then, for the GI optical fiber of optional refractive index distribution, can calculate to form and have the required optimum length ratio of wide band optical transmission line and used, and can effectively utilize the GI optical fiber that has produced.

In addition, can realize having wide band optical transmission line easily at an easy rate, can improve the transfer rate of flashlight.

Next, the second invention group is elaborated.

At first, to graded index type optical fiber (hereinafter referred to as GI optical fiber.) index distribution and be explained the time of arrival under the various transmission modes of the flashlight that in this GI optical fiber, transmits.

Figure 28 be the index distribution of expression GI optical fiber and in this GI optical fiber with the mode chart of the transmission path under each transmission mode of the flashlight of multiple transmission mode transmission.

In the low power pattern in the transmission mode, reach maximum mode, near core centre, propagate according to the light intensity at core centre place.Relative therewith, in the high power pattern, then reach maximum mode and transmit leaving the core centre place, thereby come total reflection with low-angle and transmit in the boundary portion of fibre core and coating according to light intensity distributions, so compare with low power pattern, transmission path can extend.

Because the index distribution of GI optical fiber has following shape, has largest refractive index at the core centre place that is:, and the shape that reduces gradually along with the increasing of radius of refractive index, thereby, to hang down the flashlight that the power pattern is transmitted, though transmission path is shorter, to transmit at a slow speed.Relative therewith, with the flashlight that high power pattern is transmitted, though transmission path is longer, refractive index is less in fibre core periphery vicinity, and to transmit at a high speed.

Therefore, can be by adjusting index distribution, the time that makes the flashlight that transmits with each transmission mode arrive output terminal reaches consistent.At this moment, modal dispersion becomes minimum in theory, can realize the maximum band in the signal light wavelength.

Under the index distribution occasion different with the index distribution that in the signal light wavelength, can obtain maximum band, with the flashlight of low power mode transfer, with time with the flashlight arrival output terminal of high power mode transfer between, to produce difference by the difference of this index distribution, thus can the emergence pattern chromatic dispersion.

In the present invention, the optical fiber conduct that will have the index distribution different with the index distribution that can obtain maximum band in the signal light wavelength is by compensated optical fiber, this is connected with the modal dispersion compensated optical fiber of the index distribution with regulation by compensated optical fiber, and to being compensated, thereby obtain broadband by the modal dispersion of compensated optical fiber.Below the index distribution of this modal dispersion compensated optical fiber is explained.

Figure 29 is that expression is by the index distribution of compensated optical fiber and modal dispersion compensated optical fiber and the skeleton diagram that can obtain index distribution one example of maximum band in used signal light wavelength.Here, will be at a distance of being called Δ apart from the specific refractivity difference at r place by the compensated optical fiber core centre _Target(r), will be called Δ apart from the specific refractivity difference at r place at a distance of modal dispersion compensated optical fiber core centre _Comp(r).In addition, will be called Δ apart from the specific refractivity difference at r place at a distance of the core centre on the index distribution that in the signal light wavelength, can obtain maximum band _Opt(r).This Δ _Opt(r) be the calculated value of calculating by simulation.

As mentioned above, because Δ _Target(r) and Δ _Opt(r) difference δ differs and make to produce on time of arrival of the high power pattern of the flashlight that transmits in by compensated optical fiber and low power pattern.Should low power pattern and relative mistake time of arrival of high power pattern, for the roughly proportional value of value of delta.

Here, will have Δ _Comp(r) optical fiber is used as the modal dispersion compensated optical fiber, wherein, and Δ _Comp(r) and Δ _Opt(r) difference is with respect to Δ _Target(r) and Δ _Opt(r) difference opposite in sign, and absolute value satisfies proportionate relationship.Thus, the low power pattern of the flashlight that transmits in the modal dispersion compensated optical fiber and the relative mistake of the time of arrival of high power pattern just become and Δ _Comp(r) and Δ _Opt(r) the proportional value of difference k δ.

Such Δ _Comp(r), use Δ _Target(r) and Δ _Opt(r) and by following formula (8) represent.

Δ _comp(r)＝Δ _opt(r)+k{Δ _opt(r)-Δ _target(r)} (8)

Next, as shown in figure 30, according to the length L of modal dispersion compensated optical fiber _CompWith by the length L of compensated optical fiber _TargetRatio L _Comp/ L _TargetBecome the mode of 1/k, the connection mode dispersion compensating fiber with formed optical transmission line by compensated optical fiber.

Because the relative mistake of the low power pattern of flashlight and the time of arrival of high power pattern is also proportional with the length of Transmission Fibers, thereby according to L _Comp/ L _TargetBecome the mode of 1/k, the connection mode dispersion compensating fiber with formed optical waveguide by compensated optical fiber, thus, can be used in the relative mistake of the time of arrival of the low power pattern of the flashlight that transmits in the path of modal dispersion compensated optical fiber and high power pattern, compensate the relative mistake of the time of arrival of the low power pattern of the flashlight that in by the path of compensated optical fiber, transmits and high power pattern.

In the aforementioned lights transmission lines, the core centre apart of this transmission lines integral body becomes Δ apart from the specific refractivity difference at r place _Opt(r), almost reach consistent the time of arrival that is transferred to the flashlight of exit end with each transmission mode, can obtain broadband.

Here, can determine Δ by the mode that becomes big value according to constant k _Comp, shorten the L that is connected _Comp

Utilize each index distribution Δ shown in Figure 29 _Target(r), Δ _Opt(r), Δ _Comp(r), specify aforesaid compensation principle.

With Δ _Opt(r) compare Δ _Target(r) have the less shape of refractive index of fibre core periphery, in the flashlight that transmits in by compensated optical fiber, high power pattern, its transmission speed are just fast more, and the time that arrives output terminal just more early.The relative mistake of the low power pattern of the flashlight that therefore, transmits in by compensated optical fiber and the time of arrival of high power pattern just becomes negative value.

Be somebody's turn to do the absolute value of the relative mistake of the time of arrival of hanging down power pattern and high power pattern, be and Δ _Target(r) and Δ _Opt(r) the proportional value of difference δ.

Relative therewith, Δ _Comp(r) satisfy following formula (8), with Δ _Opt(r) compare, the refractive index of fibre core periphery is big, and in the flashlight that is transmitted, high power pattern arrives exit end and just postpones more.Therefore, the relative mistake of the time of arrival of the low power pattern of the flashlight that transmits in by compensated optical fiber at the modal dispersion compensated optical fiber and high power pattern just become on the occasion of.

Be somebody's turn to do the absolute value of the relative mistake of the time of arrival of hanging down power pattern and high power pattern, be and Δ _Comp(r) and Δ _Opt(r) the proportional value of difference k δ.

Because the relative mistake of the time of arrival of low power pattern and high power pattern is also proportional with the fiber lengths that is transmitted, thereby compare L according to length _Comp/ L _TargetBecome the mode of 1/k, the connection mode dispersion compensating fiber with formed optical transmission line by compensated optical fiber.

Like this, can be with the low power pattern of modal dispersion compensated optical fiber positive relative mistake with the time of arrival of high power pattern, low power pattern that almost entirely compensates in to be produced and the relative mistake of bearing of the time of arrival of high power pattern by compensated optical fiber.

As mentioned above, in the present invention, the optical fiber that will have the represented index distribution of formula (8) is as the modal dispersion compensated optical fiber.By this modal dispersion compensated optical fiber is formed optical transmission line with being connected by compensated optical fiber, can come efficient to compensate well by this modal dispersion compensated optical fiber, and can realize having wide band optical transmission line by the modal dispersion of compensated optical fiber.

By on this optical transmission line, connecting computing machine and associate device thereof etc., can form light LAN.Because the aforementioned lights transmission lines has broadband, thereby can realize that the transfer rate high speed becomes possible light LAN.Thus, can realize that the communication speed such as 10GbE and so on reaches the Ethernet of 10Gb/s.

Next, utilize concrete example to be described in more detail.

[concrete example 2-1]

Figure 31 represents among the concrete example 2-1 by the index distribution of compensated optical fiber and modal dispersion compensated optical fiber and the index distribution that can obtain maximum band in used signal light wavelength.

By compensated optical fiber, be at a distance of the refractive index n of its core centre apart from the r place _Target(r) come approximate calculating to form with following formula (9).

Wherein, n (r) expression is at a distance of the refractive index at fiber core centre distance r place, n ₁The refractive index at expression core centre place, Δ ₁The specific refractivity of the relative coating of expression core centre is poor, and a represents fiber core radius, and α represents the index distribution exponential.

$n\left(r\right)=\left\{\begin{array}{cc}{n}_1{\{1-2{\mathrm{\&Delta;}}_1{(r/a)}^{\mathrm{\&alpha;}}\}}^{1/2}& (0\&le;r\&le;a)\\ n_1\{1-2{\mathrm{\&Delta;}}_1{\}}^{1/2}& (a<r)\end{array}\right.---\left(9\right)$

By coming approximate treatment n with following formula (9) _Target(r) the index distribution exponential α that obtains _TargetBe 1.90.In addition, the specific refractivity difference Δ of the relative coating of core centre _1targetBe 0.01, fiber core radius a is 25 μ m.

In addition, for flashlight, centre wavelength is 0.85 μ m, and the frequency spectrum half width is 0.16nm, and pulse half-width is 0.09ns.Δ under this signal light wavelength 0.85 μ m _Opt(r) be 2.04 corresponding to index distribution exponential α in the aforementioned formula (9).

Utilize Δ shown in Figure 31 _TargetAnd Δ _Opt, calculate Δ by aforementioned formula (8) _Comp(r).Among Figure 31, constant k in the formula (8) be shown be 1,5,10 figure.The specific refractivity difference Δ of the coating of the relative modal dispersion compensated optical fiber of core centre _1compAnd fiber core radius a, with identical by compensated optical fiber.

Next, obtain connection and have the Δ of calculating by preceding method _CompThe modal dispersion compensated optical fiber, with the optimum value of aforementioned length ratio during by compensated optical fiber.

Figure 32 be by simulation calculate connect previous mode dispersion compensating fiber and the optical transmission line that is constituted by compensated optical fiber all mode excitation states (hereinafter referred to as OFL.OFL:Over-filled Launch) frequency band, and with the length L of modal dispersion compensated optical fiber _CompThe curve map of describing.By the length L of compensated optical fiber _TargetBe 1km.

The frequency band of all mode excitation states of this optical transmission line is meant, consider the situation that input signal light is transmitted by all transmission modes that can evenly transmit, and be made as frequency spectrum to carry out Fuli's leaf conversion from the output signal light of being obtained by the index distribution of compensated optical fiber and modal dispersion compensated optical fiber, and calculate less than half frequency band of zero frequency power as the power of this frequency spectrum.

The frequency band of optical transmission line is the length L with respect to the modal dispersion compensated optical fiber as can be known _CompAnd the curve that raises up, and has maximal value.This is because of the relative mistake of the time of arrival of low power pattern and high power pattern and fiber lengths is proportional increases, relative mistake when time of arrival of low power pattern that in by compensated optical fiber, produces and high power pattern, when reaching consistent with the relative mistake of time of arrival of low power pattern that produces and high power pattern in the modal dispersion compensated optical fiber, the frequency band of optical transmission line becomes maximum.The length of this moment compares L _Comp/ L _TargetApproximately become 1/k.

Such as, the constant k that has a formula (8) in employing is 2 Δ _CompThe occasion of modal dispersion compensated optical fiber under, according to Figure 32, when the length L of modal dispersion compensated optical fiber _CompDuring for 0.54km, it is maximum that the frequency band of optical transmission line reaches.

As mentioned above, utilize by the index distribution of compensated optical fiber and modal dispersion compensated optical fiber, and by simulating the length L of calculating with the modal dispersion compensated optical fiber _CompDescribe to connect the curve of the frequency band of the optical transmission line that is constituted by compensated optical fiber and modal dispersion compensated optical fiber, and obtain the length L that this frequency band becomes maximum modal dispersion compensated optical fiber _Comp

Like this, compare L with obtaining according to length _Comp/ L _TargetBecome the length L of the modal dispersion compensated optical fiber that the mode of 1/k connects _CompMethod compare, can more correctly obtain the length L of the modal dispersion compensated optical fiber that can obtain maximum band _Comp

Then, with this modal dispersion compensated optical fiber length L _CompConnect by compensated optical fiber and modal dispersion compensated optical fiber.

Figure 33 is with modal dispersion compensated optical fiber length L _CompDescribe the InnerDMD of optical transmission line and the curve map of Outer DMD.Inner DMD is to have calculated in the time of arrival of the flashlight that transmits with low power pattern, at the latest the value of the difference of time of arrival and earliest arrival time.In addition, Outer DMD is to have calculated with each transmission mode that also comprises high power pattern to be transferred in time of arrival of flashlight of exit end, at the latest the value of the difference of time of arrival and earliest arrival time.

This is calculated by following method.At first, calculate departing from core centre to come incoming signal light and come the transmission signals light time with specific transmission mode thus, be transferred to the time of arrival of the flashlight of exit end by simulation.

At the center of the flashlight that incides optical fiber and the distance of core centre (hereinafter referred to as biasing) is under the situation of 5～18 μ m, calculate with each transmission mode and be transferred in time of arrival of flashlight of exit end, time of arrival and earliest arrival time is poor at the latest, and will deduct the value of input pulse width as Inner DMD from this value.Because biasing is more little, just comes transmission signals light with low more power pattern, thereby by this Inner DMD, can find out whether reach consistent time of arrival with the flashlight of low power mode transfer.

In addition, under the situation that is biased to 0～23 μ m, calculate with each transmission mode and be transferred in time of arrival of flashlight of exit end, time of arrival and earliest arrival time is poor at the latest, and will deduct the value of input pulse width as Outer DMD from this value.To also comprising the transmission mode of high power pattern, can find out by this Outer DMD whether the time of arrival of flashlight is consistent.

Inner DMD and Outer DMD as can be known, the length that becomes maximum modal dispersion compensated optical fiber at the frequency band of optical transmission line is L _CompThe time, all become minimum value, and almost reach the time of arrival that is transferred to the flashlight of exit end with each transmission mode consistent.

Figure 34 represent by the simulation calculate by the DMD characteristic of compensated optical fiber and optical transmission line (delay of DMD:Differential Mode Delay/ differential mode).The DMD characteristic is to calculate the center of departing from fibre core by simulation to come the incoming signal light time to the waveform of the flashlight of exit end transmission.

The incoming signal light center departs from core centre more, and flashlight just transmits with high more power pattern.Therefore, this DMD characteristic is to have described with the light intensity of the flashlight of each transmission mode transmission with the relative mistake of time of arrival.Be biased to 0 waveform and be the flashlight with low power mode transfer, the expression biasing is defecated more with the waveform of the flashlight of high more power mode transfer.

Figure 34 (a) expression is by compensated optical fiber, and Figure 34 (b) is illustrated in this by on the compensated optical fiber 1km, connects the modal dispersion compensated optical fiber of the index distribution with k=2 of 0.54km, and forms the occasion of optical transmission line.

As can be known by compensated optical fiber shown in Figure 34 (a), with the flashlight of high power mode transfer, just first more arrival exit end, and flashlight is inconsistent between each transmission mode.Relative therewith, the length L of the modal dispersion compensated optical fiber when becoming maximum by frequency band with optical transmission line _Comp, will have the Δ that satisfies aforementioned formula (8) _Comp(r) modal dispersion compensated optical fiber is connected in aforementioned by compensated optical fiber, thereby shown in Figure 34 (b), can make reach consistent time of arrival with the flashlight of each mode transfer.

In addition, although the constant k in the aforementioned formula (8) can be got arbitrary value, to being compensated by the wavelength dispersion of compensated optical fiber, and decision can form the Δ of the modal dispersion compensated optical fiber with wide band optical transmission line for more effectively _Comp(r), also can adopt method shown below.

Shown in figure 32, represent Δ as can be known _CompThe constant k of formula (r) (8) is big more, the length L of the modal dispersion compensated optical fiber the when frequency band of optical transmission line becomes maximum _CompJust short more, but the frequency band maximal value of this optical transmission line will diminish.

For this reason, at first various constant k are calculated Δ _Comp(r), for each modal dispersion compensated optical fiber, shown in figure 32, calculate the length L of the frequency band and the modal dispersion compensated optical fiber of optical transmission line by simulation _CompRelation.Thus, to each constant k, the length L of the modal dispersion compensated optical fiber the when frequency band of obtaining optical transmission line becomes maximum _Comp, and the maximal value of frequency band.

In the frequency band maximal value of this optical transmission line, obtain the scope of the constant k of the modal dispersion compensated optical fiber that can obtain desired desired value and higher value, in this scope, the length L of the modal dispersion compensated optical fiber when frequency band is become maximum _CompFor the shortest constant k is made as optimum value.

Such as, in Figure 32, as can be known, express Δ _Comp(r) constant k in the formula (8) is big more, and the maximal value of frequency band is just more little, but constant k be below 2 after, the maximal value of frequency band just no longer significantly diminishes, but almost certain.For this reason, adopting the constant k with formula (8) is 2 Δ _Comp(r) modal dispersion compensated optical fiber is with the length L of 0.54km _CompBe connected in by compensated optical fiber, and as optical transmission line.Thus, can realize effectively obtaining wide band optical transmission line with the shortest length.

As mentioned above, at first various constant k are obtained Δ _Comp(r), and calculate the optical transmission line that connects this modal dispersion compensated optical fiber and form frequency band, with the length L of modal dispersion compensated optical fiber _CompRelation.Length L when then, preferably obtaining frequency band and become maximum _CompWith the maximal value of this frequency band, and consider this length L _CompWith the maximal value of this frequency band, and obtain Δ _Comp(r) and length L _CompOptimum value.

Like this, such as obtaining Δ according to the mode of the frequency band that obtains to be made as purpose with the shortest length _Comp(r) and length L _Comp

[concrete example 2-2]

Utilization have the index distribution exponential shown in the table 2 by compensated optical fiber and modal dispersion compensated optical fiber, similarly form optical transmission line with concrete example 2-1.When the signal light wavelength is 0.85 μ m, can obtain the index distribution exponential α of the index distribution of maximum band _OptBe 2.04.

Table 2

Concrete example	Signal light wavelength (μ m)	By the index distribution exponential α of compensated optical fiber target	The index distribution constant k of modal dispersion compensated optical fiber	The length L of modal dispersion compensated optical fiber comp(km)
					2-2	0.85	1.90	2	0.162
2-3	0.85	2.00	10	0.11
					2-4	0.85	2.03	20	0.05
2-5	0.85	2.05	20	0.05
					2-6	0.85	2.10	10	0.09
2-7	0.85	2.20	2	0.47
					2-8	0.85	-	10	0.11
2-9	1.3	1.84	5	0.22

Figure 35 calculates by simulation to have adopted among the concrete example 2-2 by the OFL frequency band of the optical transmission line of compensated optical fiber, and with the length L of modal dispersion compensated optical fiber _CompThe curve map of describing.

Be with the difference of concrete example 2-1, by the length L of compensated optical fiber _TargetBe 0.3km.Be under the occasion of modal dispersion compensated optical fiber of 2 index distribution, in the constant k that connection has a formula (8) when the length L of modal dispersion compensated optical fiber _CompDuring=0.162km, frequency band becomes maximum.

When the frequency band of aforementioned lights transmission lines becomes maximum, the modal dispersion compensated optical fiber with compared L by the length of compensated optical fiber _Comp/ L _TargetBe 0.164/0.3=0.54, identical with concrete example 2-1 shown in Figure 32, even as can be known by the length L of compensated optical fiber _TargetChange, the modal dispersion compensated optical fiber the when frequency band of optical transmission line becomes maximum with compared L by the length of compensated optical fiber _Comp/ L _TargetAlso identical.

Figure 36 represent by the simulation calculate by the DMD characteristic of compensated optical fiber and optical transmission line.Figure 36 (a) expression is by compensated optical fiber, Figure 36 (b) be illustrated in this 0.3km by on the compensated optical fiber, connect the modal dispersion compensated optical fiber of the index distribution of 0.164km, and form the occasion of optical transmission line with k=2.Shown in Figure 36 (b), reach consistent time of arrival with the flashlight of each mode transfer as can be known.

As mentioned above, such as prolonging down by compensated optical fiber occasion etc., the modal dispersion compensated optical fiber when becoming maximum according to the frequency band of optical transmission line with compared L by the length of compensated optical fiber _Comp/ L _TargetReach identical mode, the modal dispersion compensated optical fiber is further connected get final product.

[concrete example 2-3]

Figure 37 calculates by simulation to have utilized among the concrete example 2-3 by the frequency band of the OFL of the optical transmission line of compensated optical fiber, and with the length L of modal dispersion compensated optical fiber _CompThe curve map of describing.Be with the difference of concrete example 2-1, by the index distribution exponential α of compensated optical fiber _TargetBe 2.00.

Although have the expression Δ as can be known _Comp(r) constant k in the formula (8) is big more, the tendency that the maximal value of frequency band is just more little, but constant k be below 10 after, the maximal value of the frequency band tendency that descends is just not remarkable, but almost keeps certain.

Therefore, under the occasion that the modal dispersion by compensated optical fiber to concrete example 2-3 compensates, adopting the constant k with formula (8) is 10 Δ _Comp(r) modal dispersion compensated optical fiber, the length L of the modal dispersion compensated optical fiber when becoming maximum with frequency band _Comp=0.11km is connected in by compensated optical fiber, and forms optical transmission line.

Figure 38 represent by the simulation calculate by the DMD characteristic of compensated optical fiber and optical transmission line.Figure 38 (a) expression is by compensated optical fiber, Figure 38 (b) be illustrated in this 1km by on the compensated optical fiber, connect the modal dispersion compensated optical fiber of the index distribution of 0.11km, and form the occasion of optical transmission line with k=10.Shown in Figure 38 (b), reach consistent time of arrival with the flashlight of each mode transfer as can be known.

Thus, can realize to obtain effectively the optical transmission line of big frequency band with the shortest length.

[concrete example 2-4]

Figure 39 be by simulation calculate utilized concrete example 2-4 by the frequency band of the OFL of the optical transmission line of compensated optical fiber, and with the length L of modal dispersion compensated optical fiber _CompThe curve map of describing.Be with the difference of concrete example 2-1, by the index distribution exponential α of compensated optical fiber _TargetBe 2.03.

Has the expression Δ _Comp(r) constant k in the formula (8) is big more, the tendency that the maximal value of frequency band just increases more.This is that the specific refractivity that is in close proximity to the optical fiber that can obtain maximum band is poor because poor by the specific refractivity of compensated optical fiber, and the frequency band of optical transmission line is mainly about the length by the modal dispersion compensated optical fiber.

Therefore, under the occasion that the modal dispersion by compensated optical fiber to concrete example 2-4 compensates, adopting the constant k with formula (8) is 20 Δ _Comp(r) modal dispersion compensated optical fiber, the length L when becoming maximum with frequency band _Comp=0.05km is connected in by compensated optical fiber, and forms optical transmission line.

Figure 40 represent by the simulation calculate by the DMD characteristic of compensated optical fiber and optical transmission line.Figure 40 (a) expression is by compensated optical fiber, Figure 40 (b) be illustrated in this 1km by on the compensated optical fiber, connect the modal dispersion compensated optical fiber of the index distribution of 0.05km, and become optical transmission line with k=20.Shown in Figure 40 (b), reach consistent time of arrival with the flashlight of each mode transfer as can be known.

Thus, can realize to obtain effectively the optical transmission line of big frequency band with the shortest length.

[concrete example 2-5]

Figure 41 be by simulation calculate utilized concrete example 2-5 by the frequency band of the OFL of the optical transmission line of compensated optical fiber, and with the length L of modal dispersion compensated optical fiber _CompThe curve map of describing.Be with the difference of concrete example 2-1, by the index distribution exponential α of compensated optical fiber _TargetBe 2.05.

2-4 is same with concrete example, has the expression Δ _Comp(r) constant k in the formula (8) is big more, the tendency that the maximal value of frequency band just increases more.This also is that the specific refractivity that is in close proximity to the optical fiber that can obtain maximum band is poor because poor by the specific refractivity of compensated optical fiber, and the frequency band of optical transmission line is mainly about the length by the modal dispersion compensated optical fiber.

Therefore, under the occasion that the modal dispersion by compensated optical fiber to concrete example 2-5 compensates, adopting the constant k with formula (8) is 20 Δ _Comp(r) modal dispersion compensated optical fiber, the length L of the modal dispersion compensated optical fiber when becoming maximum with frequency band _Comp=0.05km is connected in by compensated optical fiber, and forms optical transmission line.

Figure 42 represent by the simulation calculate by the DMD characteristic of compensated optical fiber and optical transmission line.Figure 42 (a) expression is by compensated optical fiber, Figure 42 (b) be illustrated in this 1km by on the compensated optical fiber, connect the modal dispersion compensated optical fiber of the index distribution of 0.05km, and become optical transmission line with k=20.Shown in Figure 42 (b), reach consistent time of arrival with the flashlight of each mode transfer as can be known.

Thus, can realize to obtain effectively the optical transmission line of big frequency band with the shortest length.

[concrete example 2-6]

Figure 43 be by simulation calculate utilized concrete example 2-6 by the frequency band of the OFL of the optical transmission line of compensated optical fiber, and with the length L of modal dispersion compensated optical fiber _CompThe curve map of describing.Be with the difference of concrete example 2-1, by the index distribution exponential α of compensated optical fiber _TargetBe 2.10.

Same with concrete example 2-3 as can be known, although express Δ _Comp(r) constant k in the formula (8) is big more, and the maximal value of frequency band is just more little, but constant k be below 10 after, the maximal value of the frequency band tendency that descends is just not remarkable, but almost keeps certain.

Therefore, under the occasion that the modal dispersion by compensated optical fiber to concrete example 2-6 compensates, adopting the constant k with formula (8) is 10 Δ _Comp(r) modal dispersion compensated optical fiber, the length L of the modal dispersion compensated optical fiber when becoming maximum with frequency band _Comp=0.09km is connected in by compensated optical fiber, and forms optical transmission line.

Figure 44 represent by the simulation calculate by the DMD characteristic of compensated optical fiber and optical transmission line.Figure 44 (a) expression is by compensated optical fiber, Figure 44 (b) be illustrated in this 1km by on the compensated optical fiber, connect the modal dispersion compensated optical fiber of the index distribution of 0.09km, and become optical transmission line with k=10.Shown in Figure 44 (b), reach consistent time of arrival with the flashlight of each mode transfer as can be known.

Thus, can realize to obtain effectively the optical transmission line of big frequency band with the shortest length.

[concrete example 2-7]

Figure 45 be by simulation calculate utilized concrete example 2-7 by the frequency band of the OFL of the optical transmission line of compensated optical fiber, and with the length L of modal dispersion compensated optical fiber _CompThe curve map of describing.Be with the difference of concrete example 2-1, by the index distribution exponential α of compensated optical fiber _TargetBe 2.20.

Same with concrete example 2-2 as can be known, although express Δ _Comp(r) constant k in the formula (8) is big more, and the maximal value of frequency band is just more little, but constant k be below 2 after, the maximal value of the frequency band tendency that descends is just not remarkable, but almost keeps certain.

Therefore, under the occasion that the modal dispersion by compensated optical fiber to concrete example 2-7 compensates, adopting the constant k with formula (8) is 2 Δ _Comp(r) modal dispersion compensated optical fiber, the length L of modal dispersion compensated optical fiber when becoming maximum with frequency band _Comp=0.47km is connected in by compensated optical fiber, and forms optical transmission line.

Figure 46 represent by the simulation calculate by the DMD characteristic of compensated optical fiber and optical transmission line.Figure 46 (a) expression is by compensated optical fiber, Figure 46 (b) be illustrated in this 1km by on the compensated optical fiber, connect the modal dispersion compensated optical fiber of the index distribution of 0.47km, and become optical transmission line with k=2.Shown in Figure 46 (b), reach consistent time of arrival with the flashlight of each mode transfer as can be known.

Thus, can realize to obtain effectively the optical transmission line of big frequency band with the shortest length.

[concrete example 2-8]

Concrete example 2-8, be with the optical fiber made as by compensated optical fiber, this by compensated optical fiber on the connection mode dispersion compensating fiber, and form the occasion of optical transmission line.

Figure 47 represent concrete example 2-8 the modal dispersion compensated optical fiber, made by the index distribution of compensated optical fiber and the index distribution that in used signal light wavelength, can obtain maximum band.By the index distribution of compensated optical fiber is that measurement result is carried out curve after level and smooth.

Figure 48 be by simulation calculate utilized concrete example 2-8 by the frequency band of the OFL of the optical transmission line of compensated optical fiber, and with the length L of modal dispersion compensated optical fiber _CompThe curve map of describing.

Same with concrete example 2-3 as can be known, although have the expression Δ _Comp(r) constant k in the formula (8) is big more, the tendency that the maximal value of frequency band just reduces more, but constant k be below 10 after, the maximal value of the frequency band tendency that descends is just not remarkable, but almost keeps certain.

Therefore, under the occasion that the modal dispersion by compensated optical fiber to concrete example 2-8 compensates, adopting the constant k with formula (8) is 10 Δ _Comp(r) modal dispersion compensated optical fiber, the length L of the modal dispersion compensated optical fiber when becoming maximum with frequency band _Comp=0.11km is connected in by compensated optical fiber, and forms optical transmission line.

Figure 49 represent by the simulation calculate by the DMD characteristic of compensated optical fiber and optical transmission line.Figure 49 (a) expression is by compensated optical fiber, Figure 49 (b) be illustrated in this 1km by on the compensated optical fiber, connect the modal dispersion compensated optical fiber of the index distribution of 0.11km, and become optical transmission line with k=10.Shown in Figure 49 (b), reach consistent time of arrival with the flashlight of each mode transfer as can be known.

Thus, even under the occasion that adopts existing GI optical fiber, also can realize to obtain effectively the optical transmission line of big frequency band with the shortest length.

[concrete example 2-9]

Concrete example 2-9, being to use centre wavelength is that 1.3 μ m, frequency spectrum half width are that 1.0nm, pulse half-width are the occasion of the flashlight of 0.05ns.Can obtain the optical fiber of maximum band when the signal light wavelength is 1.3 μ m, be index distribution exponential α _OptBe 1.94 optical fiber.In addition, be with the difference of concrete example 2-1, by the index distribution exponential α of compensated optical fiber _TargetBe 1.84.

Figure 50 be by simulation calculate utilized concrete example 2-9 by the frequency band of the OFL of the optical transmission line of compensated optical fiber, and with the length L of modal dispersion compensated optical fiber _CompThe curve map of describing.

Although have the expression Δ _Comp(r) constant k in the formula (8) is big more, the tendency that the maximal value of frequency band just reduces more, but constant k be below 5 after, the maximal value of the frequency band tendency that descends is just not remarkable, but almost keeps certain.

Therefore, under the occasion that the modal dispersion by compensated optical fiber to concrete example 2-9 compensates, adopting the constant k with formula (8) is 5 Δ _Comp(r) modal dispersion compensated optical fiber, the length L of the modal dispersion compensated optical fiber when becoming maximum with frequency band _Comp=0.22km is connected in by compensated optical fiber, and forms optical transmission line.

Figure 51 represent by the simulation calculate by the DMD characteristic of compensated optical fiber and optical transmission line.Figure 51 (a) expression is by compensated optical fiber, Figure 51 (b) be illustrated in this 1km by on the compensated optical fiber, connect the modal dispersion compensated optical fiber of the index distribution of 0.22km, and become optical transmission line with k=5.Shown in Figure 51 (b), reach consistent time of arrival with the flashlight of each mode transfer as can be known.

Thus, can realize to obtain effectively the optical transmission line of big frequency band with the shortest length.

Shown in concrete example, by on by compensated optical fiber, connecting aforesaid modal dispersion compensated optical fiber, can be to being undertaken by the modal dispersion of compensated optical fiber effectively and the good compensation of precision, especially be the optical transmission line of the flashlight of 0.85 μ m or 1.3 μ m as center transmission wavelength, can realize broadband.

In addition, even such as Δ _Target(r) can not by aforementioned formula (9) precision approximate well by compensated optical fiber, also can be by adopting by aforementioned formula (8) expression Δ _Comp(r) modal dispersion compensated optical fiber comes being compensated by the modal dispersion of compensated optical fiber equally with present embodiment.

As mentioned above, by adopting by formula (8) expression Δ _Comp(r) modal dispersion compensated optical fiber, can be effectively to being compensated by the modal dispersion of compensated optical fiber, and can realize having wide band optical transmission line.In addition, by adopting this optical transmission line, can realize to obtain broadband and can be corresponding to the light LAN of high-speed communication.

Next, the 3rd invention group is elaborated.

In the present invention, the optical fiber that will have an index distribution different with can obtain the index distribution of maximum band in the signal light wavelength is as by compensated optical fiber, this by compensated optical fiber on, with the regulation length than connection mode dispersion compensating fiber, to being compensated, and can obtain broadband by the modal dispersion of compensated optical fiber.Below to the modal dispersion compensated optical fiber that connected with likened to explanation by the length of compensated optical fiber.

Figure 29 is expression by the index distribution of compensated optical fiber and modal dispersion compensated optical fiber and the skeleton diagram of an example that can obtain the index distribution of maximum band in used signal light wavelength.Here, will be at a distance of being called Δ apart from the specific refractivity difference at r place by the core centre of compensated optical fiber _Target(r), will be called Δ apart from the specific refractivity difference at r place at a distance of the core centre of modal dispersion compensated optical fiber _Comp(r).In addition, will in the signal light wavelength, can obtain being called Δ at a distance of core centre apart from the specific refractivity difference at r place on the index distribution of maximum band _Opt(r).This Δ _Opt(r) be the calculated value of calculating by simulation.

As mentioned above, because Δ _Target(r) and Δ _Opt(r) poor produces time of arrival of the high power pattern of the flashlight that transmits and low power pattern difference and make in by compensated optical fiber.Should hang down the relative mistake of the time of arrival of power pattern and high power pattern, with Δ _Target(r) and Δ _Opt(r) difference is proportional.

Here, will have Δ _Comp(r) and Δ _Opt(r) difference is to Δ _Target(r) and Δ _OptThe Δ of its opposite in sign of difference (r) _Comp(r) optical fiber is as the modal dispersion compensated optical fiber.Therefore, the symbol of the relative mistake of the low power pattern of the flashlight that transmits in the modal dispersion compensated optical fiber and the time of arrival of high power pattern is just with the opposite in sign of the relative mistake of time of arrival of the low power pattern of the flashlight that transmits in by compensated optical fiber and high power pattern.

Next, as shown in figure 30, according to the length L of modal dispersion compensated optical fiber _CompWith by the length L of compensated optical fiber _TargetRatio L _Comp/ L _TargetSatisfy the mode of following formula (10), the connection mode dispersion compensating fiber with formed optical transmission line by compensated optical fiber.

In the formula (10), a _CompThe fiber core radius of expression modal dispersion compensated optical fiber, a _TargetExpression is by the fiber core radius of compensated optical fiber.

$L_{\mathrm{comp}}/L_{t\arg \mathrm{et}}=\frac{{\&Integral;}_0^{a_{t\arg \mathrm{et}}}\{{\mathrm{\&Delta;}}_{t\arg \mathrm{et}}\left(r\right)-{\mathrm{\&Delta;}}_{\mathrm{opt}}\left(r\right)\}\mathrm{dr}}{{\&Integral;}_0^{a_{\mathrm{comp}}}\{{\mathrm{\&Delta;}}_{\mathrm{opt}}\left(r\right)-{\mathrm{\&Delta;}}_{\mathrm{comp}}\left(r\right)\}\mathrm{dr}}---\left(10\right)$

The relative mistake of the low power pattern of flashlight and the time of arrival of high power pattern, also proportional with the length of institute Transmission Fibers.Therefore, relative mistake and the following product of the time of arrival of this low power pattern and high power pattern are proportional, and this product is specific refractivity difference and the Δ at a distance of fiber core centre distance r place _Opt(r) poor, long-pending with fiber lengths.

Therefore, when comparing L according to length _Comp/ L _TargetThe mode that satisfies aforementioned formula (10) come the connection mode dispersion compensating fiber with by compensated optical fiber, and when forming optical waveguide, the low power pattern of the flashlight that in by compensated optical fiber, transmits and high power pattern time of arrival relative mistake absolute value, with the low power pattern of the flashlight that in the modal dispersion compensated optical fiber, transmits and high power pattern time of arrival relative mistake absolute value reach consistent, and can compensate by the modal dispersion of compensated optical fiber, can realize broadband.

The aforementioned lights transmission lines is Δ at a distance of core centre apart from the specific refractivity difference at r place in this whole transmission lines _Opt(r), the time of arrival of flashlight that is transferred to exit end with each transmission mode is almost consistent, can obtain broadband.

Here, come under the approximate occasion by following formula (11) by the index distribution n (r) of the core centre apart of compensated optical fiber and modal dispersion compensated optical fiber apart from the r place, aforementioned formula (10) can be out of shape by the following calculating formula of carrying out.

In the formula (11), n (r) expression is at a distance of the index distribution of the fiber core radius direction at fiber core centre distance r place, n ₁The refractive index at expression core centre place, Δ ₁The specific refractivity of the relative coating of expression core centre is poor, and a represents fiber core radius, and α represents the index distribution exponential.

$n\left(r\right)=\left\{\begin{array}{cc}{n}_1{\{1-2{\mathrm{\&Delta;}}_1{(r/a)}^{\mathrm{\&alpha;}}\}}^{1/2}& (0\&le;r\&le;a)\\ n_1\{1-2{\mathrm{\&Delta;}}_1{\}}^{1/2}& (a<r)\end{array}\right.---\left(11\right)$

At this moment, be similar to by following formula (13) apart from the specific refractivity difference Δ (r) at r place by the core centre apart of compensated optical fiber and modal dispersion compensated optical fiber.

$\mathrm{\&Delta;}\left(r\right)=\frac{n^2\left(r\right)-n^2\left(a\right)}{2n^2\left(r\right)}\&ap;{\mathrm{\&Delta;}}_1\{1-{(r/a)}^{\mathrm{\&alpha;}}\}---\left(13\right)$

Since with at a distance of core centre come Δ (r) to aforementioned formula (13) to carry out integration apart from r the time, just become following formula (14), thereby aforementioned formula (10) just becomes following formula (12).

${\&Integral;}_0^a\mathrm{\&Delta;}\left(r\right)\mathrm{dr}\&ap;a{\mathrm{\&Delta;}}_1\frac{\mathrm{\&alpha;}}{1+\mathrm{\&alpha;}}---\left(14\right)$

$L_{\mathrm{comp}}/L_{t\arg \mathrm{et}}=\left(\frac{{\mathrm{\&alpha;}}_{t\arg \mathrm{et}}-{\mathrm{\&alpha;}}_{\mathrm{opt}}}{{\mathrm{\&alpha;}}_{\mathrm{opt}}-{\mathrm{\&alpha;}}_{\mathrm{comp}}}\right)\&times;\left(\frac{1+{\mathrm{\&alpha;}}_{\mathrm{<figure-callout\; id="1"\; label="comp"\; filenames="A20048000336000571.png,A20048000336000572.png"\; state="\{\{state\}\}">comp</figure-callout>}}}{1+{\mathrm{\&alpha;}}_{t\arg \mathrm{et}}}\right)---\left(12\right)$

From the above mentioned, being similar under the occasion of aforementioned formula (11), compare L according to length by the index distribution n (r) of the core centre apart of compensated optical fiber and modal dispersion compensated optical fiber apart from the r place _Comp/ L _TargetSatisfy the mode of formula (12), the connection mode dispersion compensating fiber with formed optical transmission line by compensated optical fiber.

Therefore, the low power pattern of the flashlight that in by the path of compensated optical fiber, transmits and high power pattern time of arrival relative mistake absolute value, with the low power pattern of the flashlight that in the path of modal dispersion compensated optical fiber, transmits and high power pattern time of arrival relative mistake absolute value reach consistent, can compensate by the modal dispersion of compensated optical fiber, can realize broadband.

By on this optical transmission line, connecting computing machine and associate device thereof etc., can form light LAN.Because the frequency band broad of this optical transmission line, thereby can realize the light LAN of transfer rate high speed.Can realize that thus the communication speed such as 10GbE and so on is the Ethernet of 10Gb/s.

Next, utilize concrete example to elaborate.

[concrete example 3-1]

Utilization have the index distribution exponential shown in the table 3 by compensated optical fiber and modal dispersion compensated optical fiber, by as follows, form optical transmission line.

(following blank)

Table 3

Concrete example	Signal light wavelength (μ m)	By the index distribution exponential α of compensated optical fiber target	The index distribution constant k α of modal dispersion compensated optical fiber target	The length L of modal dispersion compensated optical fiber comp(km)
					3-1	0.85	1.90	3.00	0.201
3-2	0.85	2.00	2.60	0.086
					3-3	0.85	2.03	2.20	0.066
3-4	0.85	2.05	1.90	0.068
					3-5	0.85	2.10	1.00	0.037
3-6	0.85	2.20	1.40	0.187
					3-7	0.85	-	1.50	0.092
3-8	0.85	1.90	2.30	0.494
					3-9	1.3	1.84	2.80	0.156

For by compensated optical fiber, at a distance of the refractive index n of its core centre apart from the r place _Target(r) be similar to aforementioned formula (12), and its index distribution exponential α _TargetBe 1.90.In addition, the specific refractivity difference Δ of the relative coating of core centre _1targetBe 0.01, fiber core radius a is 25 μ m.

Employed flashlight, its centre wavelength are 0.85 μ m, and the frequency spectrum half width is 0.16nm, and pulse half-width is 0.09ns.In this signal light wavelength 0.85 μ m, can obtain the index distribution exponential α of the optical fiber of maximum band _OptBe 2.04.

Therefore, with Δ _Opt(r) compare Δ _Target(r) become in the less shape of fibre core periphery refractive index, the low power pattern of the flashlight that is transmitted and relative mistake time of arrival of high power pattern become negative value.

The modal dispersion compensated optical fiber, with same by compensated optical fiber, its index distribution is come approximate treatment, α with formula (12) _TargetValue greater than α _Opt, with Δ _Opt(r) compare Δ _Target(r) become in the bigger shape of fibre core periphery refractive index.Thus, relative mistake time of arrival of the low power pattern of the flashlight that in the modal dispersion compensated optical fiber, transmits and high power pattern become on the occasion of.

Thus, can be used on the low power pattern of the flashlight that transmits in the path of modal dispersion compensated optical fiber and relative mistake time of arrival of high power pattern, compensate the low power pattern of the flashlight that in by compensated optical fiber, transmits and relative mistake time of arrival of high power pattern.

Here, the specific refractivity difference Δ of the relative coating of core centre _1compAnd fiber core radius a, with identical by compensated optical fiber.

Like this, compare L according to length _Comp/ L _TargetSatisfy the mode of aforementioned formula (12), the connection mode dispersion compensating fiber with formed optical transmission line by compensated optical fiber.

Figure 52 is with α _CompBe depicted in the condition (α of input concrete example 3-1 in the aforementioned formula (12) _Target=1.90, α _Opt=2.04) length that obtains compares L _Comp/ L _TargetCurve map.

In addition, in Figure 52,,, drawn curve map to utilizing value of calculating based on existing empirical method and the value of calculating by the method that has adopted the electromagnetic field analytic simulation for comparing.

So-called method based on existing empirical method is the method for being calculated by following formula (15).

L _comp/L _target＝(α _target-α _opt)/(α _opt-α _comp) (15)

In addition, below expression is obtained the modal dispersion compensated optical fiber that utilizes existing electromagnetic field analytic simulation to come to obtain maximum band and is compared L by the length of compensated optical fiber _Comp/ L _TargetMethod.

Figure 71 utilizes the electromagnetic field analytic simulation to calculate the frequency band of connection mode dispersion compensating fiber and the syntype foment of the optical transmission line that constituted by compensated optical fiber, and with length L _CompThe curve map of describing.Length L _TargetBe 1km.

Utilize the frequency band and the length L of the optical transmission line shown in this Figure 71 _CompRelation, obtaining frequency band becomes maximum length and compares L _Comp/ L _Target

Figure 72 is the length L with the modal dispersion compensated optical fiber _CompDescribe the InnerDMD of optical transmission line and the curve map of Outer DMD.Inner DMD is following value, that is: be under the situation of 5～18 μ m in the center of the flashlight that incides optical fiber and the distance of core centre (hereinafter referred to as biasing), calculate flashlight difference of time of arrival and earliest arrival time at the latest in time of arrival, and deducted the value of input pulse width from this value of calculating.In addition, Outer DMD is following value, under the situation that is biased to 0～23 μ m, calculates flashlight time of arrival and earliest arrival time poor at the latest in time of arrival that is:, and has deducted the value of input pulse width from this value of calculating.

Here, being transferred to time of arrival of the flashlight of exit end with each transmission mode, is as by departing from the time of arrival that core centre incoming signal light comes to be transferred to the specific transmission mode transmission signals light time exit end, and the value of calculating by simulation.

Can find out that from Figure 71 the length that becomes maximum modal dispersion compensated optical fiber when the frequency band of optical transmission line is L _CompThe time, it is minimum that the Inner DMD of Figure 24 and Outer DMD all reach, and almost reach consistent the time of arrival that is transferred to the flashlight of exit end with each transmission mode.

Like this, in the method for having utilized existing electromagnetic field analytic simulation method, almost reach the time of arrival that can calculate flashlight unanimity and modal dispersion by full remuneration the length of optical transmission line compare L _Comp/ L _Target

In following concrete example, will compare L by the length that the method for having utilized aforementioned existing electromagnetic field analytic simulation is calculated _Comp/ L _TargetAs theoretical analytic value, compare L with the length that in concrete example, obtains _Comp/ L _TargetCompare.

Shown in Figure 53, the length of calculating in concrete example 3-1 compares L as can be known _Comp/ L _Target, be and aforesaid theoretical analytic value value much at one.In contrast to this, by the value of calculating based on existing empirical method, bigger difference is arranged with theoretical analytic value.

As an example, connect on illustrating in concrete example 3-1 by compensated optical fiber and have α _CompThe modal dispersion compensated optical fiber of=2.60 index distribution exponential, and the occasion of formation optical transmission line.

Utilizing aforementioned formula (12), obtaining the length that is connected and compare L _Comp/ L _TargetAfter, length compares L _Comp/ L _TargetJust become 0.201.It also can compare L by the length of Figure 52 _Comp/ L _TargetWith α _CompRelation, as α _Comp=2.60 o'clock length compares L _Comp/ L _TargetObtain.

With this length the modal dispersion compensated optical fiber is connected in by compensated optical fiber, and forms optical transmission line.

Figure 53 represent by the simulation calculate by the DMD of compensated optical fiber and optical transmission line.The DMD characteristic is that a kind of having calculated by simulation departed from the characteristic of waveform that core centre comes the flashlight that is transferred to exit end of incoming signal light time.

Core centre is departed from the center of incoming signal light more, and flashlight just transmits with high more power pattern.Therefore, this DMD characteristic just becomes with the relative mistake of time of arrival and describes curve with the light intensity of the flashlight of each transmission mode transmission.When the distance of flashlight center and core centre (hereinafter referred to as biasing) hour, flashlight transmits with low power pattern, and when biasing greatly the time, then transmits with high power pattern.Therefore, it is big more to setover, the waveform of the flashlight that expression is transmitted with high more power pattern.

Figure 53 (a) expression is by compensated optical fiber.Figure 53 (b), (c) are illustrated in this and are gone up the aforementioned α of connection by compensated optical fiber 1km _Comp=3.00 modal dispersion compensated optical fiber and the optical transmission line that constitutes, Figure 53 (b) expression is compared L by the length of calculating with existing method _Comp/ L _Target=0.146 occasion that connects, Figure 53 (c) expression is compared L by the length of calculating among the concrete example 3-1 _Comp/ L _Target=0.201 occasion that connects.

The length of calculating in by concrete example 3-1 compares L _Comp/ L _TargetUnder=0.201 occasion that connects, almost completely consistent with the time of arrival of the flashlight of each mode transfer as can be known shown in Figure 53 (c), and be compensated by the modal dispersion of compensated optical fiber.Relative therewith, comparing L by the length of calculating with existing method _Comp/ L _TargetUnder=0.146 occasion that connects, shown in Figure 53 (b), time of arrival of the flashlight of each mode transfer not reach in full accord.

Like this, with by using the length of calculating based on existing empirical method to compare L _Comp/ L _Target=0.146 connects and the occasion that forms optical transmission line is compared, by comparing L by the length of calculating among the concrete example 3-1 _Comp/ L _Target=0.201 connects, and make with the time of arrival of the flashlight of each mode transfer almost completely consistent, but and precision compensate well by the modal dispersion of compensated optical fiber.Therefore, can realize having wide band optical transmission line.

In addition, calculate the length of modal dispersion compensated optical fiber by utilizing aforementioned formula (13), can obtain and the theoretical analytic value value of calculating by the electromagnetic field analytic simulation much at one, and needn't as the electromagnetic field analytic simulation, need complicated calculating, can calculate easily.Therefore, compensation model chromatic dispersion easily.

[concrete example 3-2]

Figure 54 be the modal dispersion compensated optical fiber is connected in the concrete example 3-2 shown in the table 3 by the occasion of compensated optical fiber under, with α _CompDescribe to compare L by the length that formula (12) is calculated _Comp/ L _TargetCurve map.The length of calculating with this formula (12) compares L _Comp/ L _Target, be and the theoretical analytic value value of calculating with the method that has adopted the electromagnetic field analytic simulation much at one.

To have α as an example explanation _CompThe modal dispersion compensated optical fiber of=2.60 index distribution exponential is connected among the concrete example 3-2 by compensated optical fiber, and forms the occasion of optical transmission line.

Utilizing aforementioned formula (12), obtaining the length that is connected and compare L _Comp/ L _TargetThe time, length compares L _Comp/ L _TargetJust become 0.086.With this length the modal dispersion compensated optical fiber is connected in by compensated optical fiber, and forms optical transmission line.

Figure 55 represent by the simulation calculate by the DMD characteristic of compensated optical fiber and optical transmission line.Figure 55 (a) expression is by compensated optical fiber.Figure 55 (b), (c) represent the previous mode dispersion compensating fiber is connected in this optical transmission line that is constituted by compensated optical fiber of 1km, and Figure 55 (b) is for comparing L by the length of calculating with existing method _Comp/ L _Target=0.071 occasion that connects, Figure 55 (c) is for to compare L by the length of calculating among the concrete example 3-2 _Comp/ L _Target=0.086 occasion that connects.

Comparing L by the length of calculating with this method _Comp/ L _TargetUnder the occasion that connects, almost completely consistent with the time of arrival of the flashlight of each mode transfer shown in Figure 55 (c), but precision compensates well by the modal dispersion of compensated optical fiber.

[concrete example 3-3]

Figure 56 be the modal dispersion compensated optical fiber is connected in the concrete example 3-3 shown in the table 3 by the occasion of compensated optical fiber under, with α _CompDescribe to compare L by the length that formula (12) is calculated _Comp/ L _TargetCurve map.The length of using this formula (12) to calculate as can be known compares L _Comp/ L _TargetBe and theoretical analytic value value much at one.

To have α as an example explanation _CompThe modal dispersion compensated optical fiber of=2.20 index distribution exponential is connected among the concrete example 3-3 by compensated optical fiber, and forms the occasion of optical transmission line.

Utilizing aforementioned formula (12), obtaining the length that is connected and compare L _Comp/ L _TargetThe time, length compares L _Comp/ L _TargetJust become 0.066.With this length the modal dispersion compensated optical fiber is connected in by compensated optical fiber, and forms optical transmission line.

Figure 57 represent by the simulation calculate by the DMD characteristic of compensated optical fiber and optical transmission line.Figure 57 (a) expression is by compensated optical fiber.Figure 57 (b), (c) represent the previous mode dispersion compensating fiber is connected in this optical transmission line that is constituted by compensated optical fiber of 1km, and Figure 57 (b) expression is compared L by the length of calculating with existing method _Comp/ L _Target=0.063 occasion that connects, Figure 57 (c) represents by the L that calculates among the concrete example 3-3 _Comp/ L _Target=0.066 occasion that connects.

Comparing L by the length of calculating with this method _Comp/ L _TargetUnder the occasion that connects, almost completely consistent with the time of arrival of the flashlight of each mode transfer shown in Figure 57 (c), but precision compensates well by the modal dispersion of compensated optical fiber.

[concrete example 3-4]

Figure 58 be the modal dispersion compensated optical fiber is connected in the concrete example 3-4 shown in the table 3 by the occasion of compensated optical fiber under, with α _CompDescribe to compare L by the length that formula (12) is calculated _Comp/ L _TargetCurve map.The length of using this formula (12) to calculate as can be known compares L _Comp/ L _TargetBe and theoretical analytic value value much at one.

To have α as an example explanation _CompThe modal dispersion compensated optical fiber of=1.90 index distribution exponential is connected among the concrete example 3-4 by compensated optical fiber, and forms the occasion of optical transmission line.

Utilizing aforementioned formula (12), obtaining the length that is connected and compare L _Comp/ L _TargetThe time, length compares L _Comp/ L _TargetJust become 0.068.With this length the modal dispersion compensated optical fiber is connected in by compensated optical fiber, and forms optical transmission line.

Figure 59 represent by the simulation calculate by the DMD characteristic of compensated optical fiber and optical transmission line.Figure 59 (a) expression is by compensated optical fiber.Figure 59 (b), (c) represent the previous mode dispersion compensating fiber is connected in this optical transmission line that is constituted by compensated optical fiber of 1km, and Figure 59 (b) is for comparing L by the length of calculating with existing method _Comp/ L _Target=0.071 occasion that connects, Figure 59 (c) is for to compare L by the length of calculating among the concrete example 3-4 _Comp/ L _Target=0.068 occasion that connects.

Comparing L by the length of calculating with this method _Comp/ L _TargetUnder the occasion that connects, the time of arrival of the flashlight that transmits with each pattern is almost completely consistent, but precision compensates well by the modal dispersion of compensated optical fiber.

[concrete example 3-5]

Figure 60 be the modal dispersion compensated optical fiber is connected in the concrete example 3-5 shown in the table 3 by the occasion of compensated optical fiber under, with α _CompDescribe to compare L by the length that formula (12) is calculated _Comp/ L _TargetCurve map.The length of using this formula (12) to calculate as can be known compares L _Comp/ L _TargetBe and theoretical analytic value value much at one.

To have A as an example explanation _CompThe modal dispersion compensated optical fiber of=1.00 index distribution exponential is connected among the concrete example 3-5 by compensated optical fiber, and forms the occasion of optical transmission line.

Utilizing aforementioned formula (12), obtaining the length that is connected and compare L _Comp/ L _TargetThe time, length compares L _Comp/ L _TargetJust become 0.037.With this length the modal dispersion compensated optical fiber is connected in by compensated optical fiber, and forms optical transmission line.

Figure 61 represent by the simulation calculate by the DMD characteristic of compensated optical fiber and optical transmission line.Figure 61 (a) expression is by compensated optical fiber.Figure 61 (b), (c) represent the previous mode dispersion compensating fiber is connected in this optical transmission line that is constituted by compensated optical fiber of 1km, and Figure 61 (b) is for comparing L by the length of calculating with existing method _Comp/ L _Target=0.058 occasion that connects, Figure 61 (c) is for to compare L by the length of calculating among the concrete example 3-5 _Comp/ L _Target=0.037 occasion that connects.

Comparing L by the length of calculating with this method _Comp/ L _TargetUnder the occasion that connects, almost completely consistent with the time of arrival of the flashlight of each mode transfer shown in Figure 61 (c), but precision compensates well by the modal dispersion of compensated optical fiber.Compare L with the length of calculating by the existing method of usefulness _Comp/ L _TargetThe occasion that connects and constitute optical transmission line is compared, and can obtain obviously better frequency band.

[concrete example 3-6]

Figure 62 be the modal dispersion compensated optical fiber is connected in the concrete example 3-6 shown in the table 3 by the occasion of compensated optical fiber under, with α _CompDescribe to compare L by the length that formula (12) is calculated _Comp/ L _TargetCurve map.The length of using this formula (12) to calculate as can be known compares L _Comp/ L _TargetBe and theoretical analytic value value much at one.

To have α as an example explanation _CompThe modal dispersion compensated optical fiber of=1.40 index distribution exponential is connected among the concrete example 3-6 by compensated optical fiber, and forms the occasion of optical transmission line.

Utilizing aforementioned formula (12), obtaining the length that is connected and compare L _Comp/ L _TargetThe time, length compares L _Comp/ L _TargetJust become 0.187.With this length the modal dispersion compensated optical fiber is connected in by compensated optical fiber, and forms optical transmission line.

Figure 63 represent by the simulation calculate by the DMD characteristic of compensated optical fiber and optical transmission line.Figure 63 (a) expression is by compensated optical fiber.Figure 63 (b), (c) represent the previous mode dispersion compensating fiber is connected in this optical transmission line that is constituted by compensated optical fiber of 1km, and Figure 63 (b) is for comparing L by the length of calculating with existing method _Comp/ L _Target=0.250 occasion that connects, Figure 63 (c) is for to compare L by the length of calculating among the concrete example 3-6 _Comp/ L _Target=0.187 occasion that connects.

Comparing L by the length of calculating with this method _Comp/ L _TargetUnder the occasion that connects, shown in Figure 63 (c), the time of arrival of the flashlight that transmits with each pattern is almost completely consistent, but precision compensates well by the modal dispersion of compensated optical fiber.Compare L with the length of calculating by the existing method of usefulness _Comp/ L _TargetThe occasion that connects and constitute optical transmission line is compared, and can obtain obviously better frequency band.

[concrete example 3-7]

Concrete example 3-7 is the optical fiber that will make as by compensated optical fiber, and this by compensated optical fiber on the connection mode dispersion compensating fiber, and form the occasion of optical transmission line.

Figure 64 be illustrated among the concrete example 3-7 to made by the specific refractivity difference Δ of compensated optical fiber _CompMeasured value carried out curve after level and smooth.

Figure 65 be the modal dispersion compensated optical fiber is connected in aforementioned by the occasion of compensated optical fiber under, with α _CompDescribe to compare L by the length that formula (12) is calculated _Comp/ L _TargetCurve map.The length of using this formula (12) to calculate as can be known compares L _Comp/ L _TargetBe and theoretical analytic value value much at one.

To have α as an example explanation _CompThe modal dispersion compensated optical fiber of=1.50 index distribution exponential is connected among the concrete example 3-7 by compensated optical fiber, and forms the occasion of optical transmission line.

Compare L utilizing aforementioned formula (12) to obtain the length that is connected _Comp/ L _TargetThe time, length compares L _Comp/ L _TargetJust become 0.092.With this length the modal dispersion compensated optical fiber is connected in by compensated optical fiber, and forms optical transmission line.

Figure 66 represent by the simulation calculate by the DMD characteristic of compensated optical fiber and optical transmission line.Figure 66 (a) expression is by compensated optical fiber.Figure 66 (b), (c) expression previous mode dispersion compensating fiber are connected in this optical transmission line that is constituted by compensated optical fiber of 1km, and Figure 66 (b) expression is compared L by the length of calculating with existing method _Comp/ L _Target=0.115 occasion that connects, Figure 66 (c) represents by the L that calculates among the concrete example 3-7 _Comp/ L _Target=0.092 occasion that connects.

As mentioned above, even under the occasion that has adopted existing GI optical fiber, comparing L by the length of calculating with this method _Comp/ L _TargetUnder the occasion that connects, almost completely consistent with the time of arrival of the flashlight of each mode transfer shown in Figure 66 (c), but precision compensates well by the modal dispersion of compensated optical fiber.Compare L with the length of calculating by the existing method of usefulness _Comp/ L _TargetThe occasion that connects and constitute optical transmission line is compared, and can obtain better frequency band.

[concrete example 3-8]

Concrete example 3-8 by in the compensated optical fiber, the specific refractivity difference Δ of the relative coating of core centre ₁Be 0.02, fiber core radius a is 31.25 μ m.Therefore, under signal light wavelength 0.85 μ m, can obtain the index distribution exponential α of the index distribution of maximum band _OptBe 2.02.

Figure 67 be the modal dispersion compensated optical fiber is connected in the concrete example 3-8 shown in the table 3 by the occasion of compensated optical fiber under, with α _CompDescribe to compare L by the length that formula (12) is calculated _Comp/ L _TargetCurve map.The length of using this formula (12) to calculate as can be known compares L _Comp/ L _TargetBe and theoretical analytic value value much at one.

To have α as an example explanation _CompThe modal dispersion compensated optical fiber of=2.30 index distribution exponential is connected among the concrete example 3-8 by compensated optical fiber, and forms the occasion of optical transmission line.

Utilizing aforementioned formula (12), obtaining the length that is connected and compare L _Comp/ L _TargetThe time, length compares L _Comp/ L _TargetJust become 0.494.With this length the modal dispersion compensated optical fiber is connected in by compensated optical fiber, and forms optical transmission line.

Figure 68 represent by the simulation calculate by the DMD characteristic of compensated optical fiber and optical transmission line.Figure 66 (a) expression is by compensated optical fiber.Figure 68 (b), (c) represent the previous mode dispersion compensating fiber is connected in this optical transmission line that is constituted by compensated optical fiber of 1km, and Figure 68 (b) is for comparing L by the length of calculating with existing method _Comp/ L _Target=0.434 occasion that connects, Figure 68 (c) is for to compare L by the length of calculating among the concrete example 3-3 _Comp/ L _Target=0.494 occasion that connects.

Comparing L by the length of calculating with this method _Comp/ L _TargetUnder the occasion that connects, almost completely consistent with the time of arrival of the flashlight of each mode transfer shown in Figure 68 (c), but precision compensates well by the modal dispersion of compensated optical fiber.Compare L with the length of calculating by the existing method of usefulness _Comp/ L _TargetConnect the occasion that constitutes optical transmission line and compare, can obtain obviously better frequency band.

[concrete example 3-9]

Among the concrete example 3-9, adopting centre wavelength is 1.3 μ m, and the frequency spectrum half width is 1.0nm, and pulse half-width is the flashlight of 0.05ns.In the signal light wavelength index distribution exponential α that can obtain the index distribution of maximum band under the situation of 1.3 μ m _OptBe 1.94.

Figure 69 be the modal dispersion compensated optical fiber is connected in the concrete example 3-9 shown in the table 3 by the occasion of compensated optical fiber under, with α _CompDescribe to compare L by the length that formula (12) is calculated _Comp/ L _TargetCurve map.The length of using this formula (12) to calculate as can be known compares L _Comp/ L _TargetBe and theoretical analytic value value much at one.

To have α as an example explanation _CompThe modal dispersion compensated optical fiber of=2.80 index distribution exponential is connected among the concrete example 3-9 by compensated optical fiber, and forms the occasion of optical transmission line.

Utilizing aforementioned formula (12), obtaining the length that is connected and compare L _Comp/ L _TargetThe time, length compares L _Comp/ L _TargetJust become 0.156.With this length the modal dispersion compensated optical fiber is connected in by compensated optical fiber, and forms optical transmission line.

Figure 70 represent by the simulation calculate by the DMD characteristic of compensated optical fiber and optical transmission line.Figure 70 (a) expression is by compensated optical fiber.Figure 70 (b), (c) represent the previous mode dispersion compensating fiber is connected in this optical transmission line that is constituted by compensated optical fiber of 1km, and Figure 70 (b) is for comparing L by the length of calculating with existing method _Comp/ L _Target=0.116 occasion that connects, Figure 70 (c) is for to compare L by the length of calculating among the concrete example 3-9 _Comp/ L _Target=0.156 occasion that connects.

Comparing L by the length of calculating with this method _Comp/ L _TargetUnder the occasion that connects, almost completely consistent with the time of arrival of the flashlight of each mode transfer shown in Figure 70 (c), but precision compensates well by the modal dispersion of compensated optical fiber.Compare L with the length of calculating by the existing method of usefulness _Comp/ L _TargetThe occasion that connects and constitute optical transmission line is compared, and can obtain obviously better frequency band.

Like this, by employing formula (12), can calculate the length that is connected easily and compare L _Comp/ L _TargetBy recently connecting with this length by compensated optical fiber and modal dispersion compensated optical fiber, can compensate well and precision effective by the modal dispersion of compensated optical fiber, be the optical transmission line of the flashlight of 0.85 μ m or 1.3 μ m as center transmission wavelength especially, can realize broadband.

In addition, for the modal dispersion compensated optical fiber in these concrete examples and by compensated optical fiber, index distribution exponential α _Comp, α _TargetFor more than or equal to 0.5, the specific refractivity difference Δ of the relative coating of core centre _1comp, Δ _1targetBe 0.005～0.025, fiber core radius a _Comp, a _Target Be 5～50 μ m, at this moment, can be effectively and precision well to being compensated by the modal dispersion of compensated optical fiber, can realize having wide band optical transmission line.

In addition, for by compensated optical fiber and modal dispersion compensated optical fiber, even can not come under the approximate well occasion of precision also applicable the present invention in its index distribution by aforementioned formula (12).Under this occasion, obtain modal dispersion compensated optical fiber and the length that is satisfied the modal dispersion compensated optical fiber of aforementioned formula (11) by the length of compensated optical fiber ratio, and the modal dispersion compensated optical fiber is connected in by compensated optical fiber by this length.Like this, can almost entirely compensate, can realize having wide band optical transmission line by the modal dispersion of compensated optical fiber.

As mentioned above, by employing formula (10) or formula (12), can calculate the length that is connected easily and compare L by compensated optical fiber and modal dispersion compensated optical fiber _Comp/ L _Target, by recently connecting by this length by compensated optical fiber and modal dispersion compensated optical fiber, can be effectively and precision well to being compensated by the modal dispersion of compensated optical fiber, can realize having wide band optical transmission line.

By adopting this optical transmission line, can realize having broadband and corresponding to the light LAN of high-speed communication.

Utilize the field on the industry

The present invention can be used for adopting the optical transmission lines such as LAN of multimode fibre, applicable to set up at a high speed, the system of the transmission lines of wide band flashlight etc.

Claims (18)

1. an optical transmission line formation method wherein, connects a plurality of multimode optical fibers and forms optical transmission line, the method is characterized in that:

The frequency band of obtaining this optical transmission line becomes the length ratio of each maximum multimode optical fiber, and recently connects a plurality of multimode optical fibers with this length.

2. an optical transmission line has a plurality of multimode optical fibers, it is characterized in that:

Frequency band according to this optical transmission line becomes maximum mode, and the length ratio of each multimode optical fiber is adjusted.

3. optical transmission line according to claim 2 is characterized in that having:

In the flashlight that transmits in multimode optical fiber with a plurality of transmission modes, the time of arrival of high power pattern is early than the multimode optical fiber of low power pattern; Be later than the multimode optical fiber of low power pattern the time of arrival of high power pattern.

4. according to claim 2 or 3 described optical transmission lines, it is characterized in that:

It is the optical transmission line that transmits 0.85 μ m band and/or 1.3 μ m band signal light.

5. light LAN is characterized in that:

Utilize any described optical transmission line of claim 2 to 4 to form.

6. modal dispersion compensation method is characterized in that:

Form by multimode optical fiber by compensated optical fiber on the connection mode dispersion compensating fiber, compensate by the modal dispersion of compensated optical fiber, when desiring to make when in provision wavelengths, obtaining maximum band, adopt have the index distribution that satisfies following formula (1) by compensated optical fiber and modal dispersion compensated optical fiber

Δ _comp(r)＝Δ _opt(r)+k{Δ _opt(r)-Δ _target(r)}(1)

Wherein, Δ _Comp(r) expression is poor at a distance of the specific refractivity apart from the r place of the core centre of modal dispersion compensated optical fiber, Δ _Target(r) expression is poor by the specific refractivity apart from the r place of the core centre of compensated optical fiber apart, Δ _Opt(r) expression is at a distance of connecting by compensated optical fiber and modal dispersion compensated optical fiber, and it is poor apart from the specific refractivity at r place to obtain the core centre of optical fiber integrally of maximum band in provision wavelengths, and k represents proportionality constant.

7. modal dispersion compensation method according to claim 6 is characterized in that:

Become maximum length ratio with frequency band, connect previous mode dispersion compensating fiber and aforementioned by compensated optical fiber.

8. modal dispersion compensated optical fiber, its be connected in by multimode optical fiber form by compensated optical fiber, and compensate this, thereby in provision wavelengths, can obtain maximum band by the modal dispersion of compensated optical fiber, this modal dispersion compensated optical fiber is characterised in that:

Index distribution satisfies above-mentioned formula (1).

9. optical transmission line is characterized in that:

By multimode optical fiber form by compensated optical fiber, satisfy the modal dispersion compensated optical fiber of above-mentioned formula (1) with index distribution, become maximum length than connecting and constituting with frequency band.

10. optical transmission line according to claim 9 is characterized in that:

It is the optical transmission line that transmits 0.85 μ m band and/or 1.3 μ m band signal light.

11. a light LAN is characterized in that:

Adopt claim 9 or 10 described optical transmission lines to form.

12. a modal dispersion compensation method is characterized in that:

Form by multimode optical fiber by compensated optical fiber on the connection mode dispersion compensating fiber, compensate by the modal dispersion of compensated optical fiber, when desiring to make when in provision wavelengths, obtaining maximum band, with the length that satisfies following formula (2) recently the connection mode dispersion compensating fiber with by compensated optical fiber

$L_{\mathrm{comp}}/L_{t\arg \mathrm{et}}=\frac{{\&Integral;}_0^{a_{t\arg \mathrm{et}}}\{{\mathrm{\&Delta;}}_{t\arg \mathrm{et}}\left(r\right)-{\mathrm{\&Delta;}}_{\mathrm{opt}}\left(r\right)\}\mathrm{dr}}{{\&Integral;}_0^{a_{\mathrm{comp}}}\{{\mathrm{\&Delta;}}_{\mathrm{opt}}\left(r\right)-{\mathrm{\&Delta;}}_{\mathrm{comp}}\left(r\right)\}\mathrm{dr}}---\left(2\right)$

Wherein, L _CompThe length of expression modal dispersion compensated optical fiber, L _TargetExpression is by the length of compensated optical fiber, a _CompThe fiber core radius of expression modal dispersion compensated optical fiber, a _TargetExpression is by the fiber core radius of compensated optical fiber, Δ _Comp(r) expression is poor apart from the specific refractivity at r place at a distance of the core centre of modal dispersion compensated optical fiber, Δ _Target(r) expression is poor apart from the specific refractivity at r place by the core centre of compensated optical fiber apart, Δ _Opt(r) expression is at a distance of connecting by compensated optical fiber and modal dispersion compensated optical fiber and can to obtain the core centre of optical fiber integrally of maximum band in provision wavelengths poor apart from the specific refractivity at r place.

13. a modal dispersion compensation method is characterized in that:

Form by multimode optical fiber by compensated optical fiber on the connection mode dispersion compensating fiber, compensate by the modal dispersion of compensated optical fiber, when desiring to make when in provision wavelengths, obtaining maximum band, employing have the index distribution that satisfies following formula (3) by compensated optical fiber and modal dispersion compensated optical fiber, and to satisfy the length ratio of following formula (4), come the connection mode dispersion compensating fiber with by compensated optical fiber

$n\left(r\right)=\left\{\begin{array}{cc}{n}_1{\{1-2{\mathrm{\&Delta;}}_1{(r/a)}^{\mathrm{\&alpha;}}\}}^{1/2}& (0\&le;r\&le;a)\\ n_1{\{1-2{\mathrm{\&Delta;}}_1\}}^{1/2}& (a<r)\end{array}\right.---\left(3\right)$

Wherein, n (r) expression is at a distance of the core centre of the optical fiber index distribution apart from the fiber core radius direction at r place, n ₁The refractive index of expression core centre, Δ ₁The specific refractivity of the relative coating of expression core centre is poor, and a represents fiber core radius, and α represents the index distribution exponential.

$L_{\mathrm{comp}}/L_{t\arg \mathrm{et}}=\left(\frac{{\mathrm{\&alpha;}}_{l\arg \mathrm{et}}-{\mathrm{\&alpha;}}_{\mathrm{opt}}}{{\mathrm{\&alpha;}}_{\mathrm{opt}}-{\mathrm{\&alpha;}}_{\mathrm{comp}}}\right)\&times;\left(\frac{1+{\mathrm{\&alpha;}}_{\mathrm{comp}}}{1+{\mathrm{\&alpha;}}_{t\arg \mathrm{et}}}\right)---\left(4\right)$

Wherein, L _CompThe length of expression modal dispersion compensated optical fiber, L _TargetExpression is by the length of compensated optical fiber, α _CompThe index distribution exponential of expression modal dispersion compensated optical fiber, α _TargetExpression is by the index distribution exponential of compensated optical fiber, α _OptExpression connects by compensated optical fiber and modal dispersion compensated optical fiber and can obtain the index distribution exponential of the optical fiber integrally of maximum band in provision wavelengths.

14. an optical transmission line is characterized in that:

By multimode optical fiber form by compensated optical fiber and modal dispersion compensated optical fiber, be connected with the length ratio that satisfies above-mentioned formula (2).

15. an optical transmission line connects by being constituted by compensated optical fiber and modal dispersion compensated optical fiber that multimode optical fiber forms, it is characterized in that:

The modal dispersion compensated optical fiber with by compensated optical fiber, have the index distribution that satisfies above-mentioned formula (3), and be connected with the length ratio that satisfies above-mentioned formula (4).

16. optical transmission line according to claim 15 is characterized in that:

Previous mode dispersion compensating fiber and aforementioned by in the compensated optical fiber, index distribution exponential α _Comp, α _TargetFor more than or equal to 0.5, the specific refractivity difference Δ of the relative coating of core centre _1comp, Δ _1targetBe 0.005～0.025, fiber core radius a _Comp, a _TargetBe 5～50 μ m.

17. any described optical transmission line according to claim 14 to 16 is characterized in that:

It is the optical transmission line that transmits the flashlight of 0.85 μ m band and/or 1.3 μ m band.

18. a light LAN is characterized in that:

Adopt any described optical transmission line of claim 14 to 17 to form.

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