CN102193140B - Optical fiber and optical communication system comprising the same - Google Patents

Abstract

The invention relates to an optical fiber and the like, which are applied in an optical communication system carrying out Raman amplification, improve an OSNR (Optical Signal to Noise Ratio) and restrain bending loss simultaneously. The optical fiber is the quartz optical fiber which has a depressed refractive index curve, an effective sectional area Aeff and an optical fiber cut-off wavelength lambda C, wherein the depressed refractive index curve consists of a fiber core, an inside covering with low refractive index and an outside covering; the effective sectional area Aeff is not less than 110mum2 when the wavelength is below 1550nm; and the optical fiber cut-off wavelength lambda C is not less than 1.3mum and not more than 1.53mum. The depressed refractive index curve is designed in such a manner that the ratio Ra (equivalent to 2b/2a) of the inside covering diameter to the fiber core diameter is not less than 2.5 and not more than 3.5; and the relative refractive index delta- of the inside covering relative to the outside covering is not less than the relative refractive index delta-min with smallest bending loss when using the wavelength and not more than delta-min+0.06%.

Description

Optical fiber and comprise the optical communication system of optical fiber

Technical field

The present invention relates to a kind of optical fiber and use the optical communication system of above-mentioned optical fiber, it in the optical WDM communication system of long repeater span using Raman amplifiction, can improve Optical Signal To Noise Ratio (hereinafter referred to as OSNR:Optical Signal-to-Noise Ratio).

Background technology

In optical communication system, in recent years, as with digital coherent reception technique for representative, utilize the technology development that digital signal processing (DSP) compensates the waveform distortion produced due to dispersion in the receiver.Accompany therewith, compared with the dispersion values improved in light transmission path, increasing fast is required to the improvement of OSNR.Under the state that repeater interval is in a communications system fixing, in order to make transmission speed high speed not make signal quality worsen, OSNR must be increased.Such as, in order to transmission speed is turned to 2 times at a high speed, need OSNR is increased to 2 times (increasing 3dB).In addition, when repeater span is elongated under the state maintaining transmission speed, also OSNR must be increased.Such as, in order to repeater interval is increased 5km, need to make OSNR increase 1dB.

For the OSNR increasing optical communication system, increase the net sectional area A of transmission medium and optical fiber _eff, and the loss that reduces this optical fiber be effective.By increasing net sectional area A _effeven if carry powerful flashlight in a fiber, the generation of nonlinear optical phenomena also can be suppressed fully.Thus, net sectional area A is increased _effoptical fiber can allow larger incoming signal luminous power.If because incoming signal luminous power is comparatively large, then correspondingly Received signal strength luminous power is also comparatively large, so OSNR can be made to increase.

In addition, if loss is lower, even if then incoming signal luminous power is identical, also larger signal light power can be received at receiving end.Also OSNR can be made in this case to increase.

In Jap.P. No. 4293156 publication (document 1), disclose a kind of optical fiber, it has and is more than or equal to 110 μm ²net sectional area A _eff, loss is less than or equal to 0.180dB/km.This optical fiber has depressed cladding (depressed clad) type refractive index curve, is made up of in turn from optical axis center fibre core, inner side covering, outside covering.Core diameter 2a is 11.5 ~ 23.0 μm, and inner side covering is 1.1 ~ 7 relative to the diameter of fibre core than 2b/2a, and fibre core is relative to the refractive index contrast Δ of outside covering ⁺be 0.15% ~ 0.30%, inner side covering is relative to the refractive index contrast Δ of outside covering ^-for-0.15% ~-0.01%.

At M.Bigot-Astruc et al.; " Trench-Assisted Profiles for Large-Effective-Area Single Mode Fibers ", in Mo.4.B.1, ECOC2008 (document 2); disclose a kind of optical fiber, its net sectional area A _effit is 120 μm ², loss is 0.183dB/km.This optical fiber has grooved refractive index curve.

Summary of the invention

Inventor studies above-mentioned prior art, found that problem as described below.That is, in the optical communication system of reality, the two ends of transmission optical fiber and repeater or send/receive the equipment connections such as device.The two ends of equipment are made up of optical fiber such as general single-mode fiber (hereinafter referred to as SMF:Single-Mode Optical Fiber) or non-zero dispersion displacement optical fibers (hereinafter referred to as NZDSF:Non-Zero Dispersion-Shifted Optical Fiber), and above-mentioned optical fiber utilizes welding or by connector connection etc. and transmission Fiber connection.Or transmission optical fiber is at the midway of transmission path and other transmission Fiber connection different types of sometimes.If the net sectional area A of transmission optical fiber _effexcessive compared with the optical fiber at equipment two ends or other transmission optical fiber, then junction loss becomes large, and therefore, the OSNR of this optical communication system entirety worsens.

In addition, in long distance optical communication systems, distributed Raman is often used to amplify, if but the net sectional area A of transmission optical fiber _effcomparatively large, then Raman amplifiction efficiency declines.Thus, in order to obtain expected gain, need huge pumping light power.Accordingly, the net sectional area A of transmission optical fiber _effbe not be the bigger the better, must optimal value be set as.In the above prior art, do not report and junction loss is also taken into account and makes net sectional area A in the mode can improving OSNR _effoptimized optical fiber.

Usually, the net sectional area A in optical fiber _effincrease along with the increase of bending loss.In the optical fiber disclosed in above-mentioned document 1, in order to suppress bending loss, adopting depressed cladding type refractive index curve, but in this curve, must be noted that to produce the patten's design curve that basic mode ends the leakage loss caused.Above-mentioned document 1 records following content, that is, " at the refractive index contrast Δ n of fibre core relative to outside covering ⁺and inner side covering is relative to the refractive index contrast Δ n of outside covering ^-when respective absolute value is equal to each other, do not transmit basic mode light in a fiber " (the paragraph sequence number " 0047 " with reference to above-mentioned document 1).But this is only to basic mode be caused to end under use wavelength.In fact, under wavelength short compared with fundamental mode cutoff wavelength, basic mode conveying light starts to leak, and loss increases.Need in whole use wave band (1530nm ~ 1625nm), suppress the leakage loss because basic mode cut-off produces.

The present invention proposes to solve above-mentioned problem, its object is to provide a kind of optical communication system and operable optical fiber thereof, and this optical communication system has and the connecting structure of equipment with the Fiber connection of other kind, and carries out Raman amplifiction.Especially, target optical fiber is the optical fiber had for realizing the structure that OSNR improves, and has depressed cladding type refractive index curve, can suppress bending loss while avoiding the leakage loss due to basic mode cut-off generation.In addition, overall as this optical communication system, use the technology that digital coherent reception technique etc. is compensated the waveform distortion that dispersion causes by receiver, thus without the need to considering the improvement of fibre-optical dispersion value.

Optical fiber involved in the present invention is quartzy type optical fiber, its have as optical characteristics under wavelength 1550nm, be less than or equal to 0.19dB/km loss, under wavelength 1550nm, be more than or equal to 110 μm ²net sectional area A _eff, and be more than or equal to 1.3 μm and be less than or equal to the fiber cut off wavelength λ of 1.53 μm _c.In addition, in order to realize depressed cladding type refractive index curve, this optical fiber has: the fibre core be made up of pure quartz, it has refractive index n ₁, diameter 2a; Inner side covering, it is arranged on the periphery of fibre core, and has refractive index n ₂, diameter 2b; And outside covering, it is arranged on the periphery of inner side covering, and has refractive index n ₃.

In optical fiber involved in the present invention, preferred index n ₃meet n ₁> n ₃> n ₂(condition 1).Preferred inner side covering is relative to the refractive index contrast Δ of outside covering ^-(=100 × (n ₂-n ₃)/n ₃) meet-0.12%≤Δ ^-≤-0.06% (condition 2).In addition, preferably inner side cladding diameter meets 2.5≤Ra≤3.5 (condition 3) relative to the ratio Ra (=2b/2a) of core diameter.

In addition, optical fiber involved in the present invention can be applied in for carrying wavelength to be less than or equal in the medium of the light of 1625nm.This optical fiber has low-loss pure silica core, and has the outstanding depressed cladding type refractive index curve in bending loss aspect.For this optical fiber, by by fundamental mode cutoff wavelength λ _fCbe set greater than or equal 2400nm, thus realizing leakage loss reduction.

Optical fiber involved in the present invention also while having above-mentioned optical characteristics and depressed cladding type refractive index curve, can meet following 2 conditions except above-mentioned condition 1 and condition 3.That is, λ is set at the fundamental mode cutoff wavelength started when leaking by the basic mode used under the wavelength upper limit _fCuptime, by fundamental mode cutoff wavelength λ _fCbe set greater than λ _fCupwavelength (condition 4).In addition, for the refractive index contrast Δ of inner side covering relative to outside covering ^-(=100 × (n ₂-n ₃)/n ₃), the bending loss used under wavelength is being become minimum Δ ^-be set to Δ ^-during min, by Δ ^-be designed to be more than or equal to Δ ^- _minand be less than or equal to Δ ^- _min+ 0.006% (condition 5).

In addition, in optical fiber involved in the present invention, the net sectional area A under wavelength 1550nm can also be made _effbe less than or equal to 150 μm ², can carry out the transmission till 1625nm as upper limit wavelength.In the relaying span of optical communication system using this optical fiber, imagine and connect being at least more than or equal to 2 positions, and imagination carries out Raman amplifiction in this relaying span, in this optical communication system entirety, guarantee that the OSNR being more than or equal to 1dB improves.In addition, in order to ensure better OSNR, the net sectional area A under wavelength 1550nm also can be made _effbe more than or equal to 120 μm ²and be less than or equal to 140 μm ².

Optical communication system involved in the present invention has the optical fiber (optical fiber involved in the present invention) forming above-mentioned structure.In addition, this optical communication system carries out Raman amplifiction to conveying light in this optical fiber.In this case, as the condition making the exciting light of Raman amplifiction carry out single mode transport, preferred fiber has the fiber cut off wavelength being less than or equal to 1.45 μm.

Optical communication system involved in the present invention, utilizes multiple 1st optical fiber and multiple 2nd optical fiber, forms the optical communication system with the relaying span (long relaying span) being more than or equal to 80km.In this case, multiple 1st optical fibre frame is located to be more than or equal to and is more than or equal to 2 positions in the relaying span of 80km.Multiple 2nd optical fiber is more than or equal to 4 positions and the 1st Fiber connection in relaying span.In addition, multiple 2nd optical fiber has separately be less than or equal to 85 μm under wavelength 1550nm ²net sectional area A _eff.At least any one two ends being erected at relaying span or the position be erected in relaying span in multiple 2nd optical fiber.That is, in this optical communication system, imagination the 1st optical fiber is less than or equal to 85 μm being more than or equal to 4 positions with having ²less net sectional area A _effthe 2nd Fiber connection, because the 1st optical fiber has 110 μm ²~ 150 μm ²larger net sectional area A _{e ff}, so the input of more high-power Raman amplifiction exciting light can be carried out, on the other hand, because the 1st optical fiber has the low transmission loss being less than or equal to 0.19dB/km under wavelength 1550nm, thus the optical transport of long relaying span can be carried out.Its result, in this optical communication system entirety, the OSNR that can realize being more than or equal to 1dB improves.

Preferably the 1st optical fiber have separately under wavelength 1550nm, be less than or equal to 0.19dB/km loss, under wavelength 1550nm, be more than or equal to 110 μm ²and be less than or equal to 150 μm ²net sectional area A _eff, and be more than or equal to 1.3 μm and be less than or equal to the fiber cut off wavelength λ of 1.45 μm _c.In this case, this optical communication system carries out Raman amplifiction to transmission light in each the 1st optical fiber.

In order to realize depressed cladding type refractive index curve, each the 1st optical fiber also can have: the fibre core be made up of pure quartz, it has refractive index n ₁, diameter 2a; Inner side covering, it is arranged on the periphery of described fibre core, and has refractive index n ₂, diameter 2b; And outside covering, it is arranged on the periphery of described inner side covering, and has refractive index n ₃.In addition, preferred index n ₃meet above-mentioned condition 1.Preferred inner side cladding diameter meets above-mentioned condition 3 relative to the ratio Ra of core diameter.Further, preferably each the 1st optical fiber meets above-mentioned condition 4 and condition 5 simultaneously.

And, for each the 1st optical fiber used in optical communication system involved in the present invention, preferably it is the medium for carrying wavelength to be less than or equal to the light of 1625nm, has above-mentioned depressed cladding type refractive index curve, meets above-mentioned condition 1, condition 2 and condition 3.In this case, preferred the 1st optical fiber net sectional area A separately _effbe more than or equal to 120 μm ²and be less than or equal to 140 μm ².

Accompanying drawing explanation

Fig. 1 represents net sectional area A _effwith the figure of the relation of OSNR improving amount.

Fig. 2 A and 2B is figure and the refractive index curve thereof of the profile construction of the embodiment representing optical fiber involved in the present invention.

Fig. 3 represents the curve map starting the relation produced between the wavelength of leakage loss and fundamental mode cutoff wavelength.

Fig. 4 is the curve map of the relation represented between bending loss under diameter 20mm and fundamental mode cutoff wavelength.

Fig. 5 is the table that the constructing variable of the optical fiber (embodiment 1 ~ 15) involved by present embodiment and the optical fiber involved by comparative example and optical characteristics are carried out gathering and obtained.

Fig. 6 is the multiple samples for the optical fiber involved by present embodiment, by resin-coated Young modulus and net sectional area A _effthe table that microbending loss during change carries out gathering and obtains.

Fig. 7 A ~ 7C utilizes net sectional area A _effwith the relation of loss, represent the figure of the OSNR improving amount relative to single-mode fiber (SMF) caused by the difference of the connection status in relaying span.

Fig. 8 is the process flow diagram determining action for illustration of the structure of the optical fiber involved by present embodiment.

Fig. 9 A and 9B is the figure of the structure of each embodiment representing optical communication system involved in the present invention.

Embodiment

Below, utilize Fig. 1,2A ~ 2B, 3 ~ 6,7A ~ 7C, 8 and 9A ~ 9B, describe each embodiment of optical fiber involved in the present invention and optical communication system in detail.In addition, in the description of the drawings, identical label is marked for identical element, omit repeat specification.

First, the net sectional area A of that can be applied to the transmission optical fiber of optical communication system, involved by present embodiment optical fiber is described _effoptimal value.That is, from the angle of the characteristic of optical fiber, OSNR can be represented by following formula (1) approx.

OSNR(dB)∝10log Aeff×α(1/km))-α _sp(dB)×N-α(dB/km)×L(km) (1)

Here, A _efffor the net sectional area of the optical fiber under signal light wavelength, α is the loss under signal light wavelength, α _sPfor junction loss, N is the link position quantity of every 1 relaying span, and L is the fiber lengths of every 1 relaying span.

The Section 1 of above-mentioned formula (1), allows that incident optical power corresponding when the nonlinear phase side-play amount produced is fixed with one of nonlinear optical phenomena making to produce in a fiber i.e. Self-phase modulation (SPM:Self-Phase Modulation).Nonlinear phase side-play amount Φ _sPMobtain according to following formula (2).

${\mathrm{\φ}}_{\mathrm{SPM}}=\frac{2\mathrm{\π}}{\mathrm{\λ}}\frac{n_2}{A_{\mathrm{eff}}}\·L_{\mathrm{eff}}\·P_{\mathrm{in}}---\left(2\right)$

Here, λ is signal light wavelength, n ₂for the nonlinear refractive index of optical fiber, L _efffor the effective length of optical fiber, P _infor incident optical power.

As long as fiber lengths is fully long, such as, be more than or equal to 50km, then effective length L _effcan be approximated to be according to above-mentioned formula (2), make nonlinear refractive index n ₂fixing, nonlinear phase side-play amount Φ _sPMincident power is allowed, with A time fixing _eff(μm ²) × α (1/km) proportionally increases.

The Section 2 of above-mentioned formula (1) is corresponding with the junction loss of optical fiber, if only consider not mating of mode field diameter (hereinafter referred to as the MFD:Mode Field Diameter) between two kinds of optical fiber being connected, then junction loss (dB) can be estimated according to following formula (3).

${\mathrm{\α}}_{\mathrm{sp}}\left(\mathrm{dB}\right)=10\log \left[{\left(\frac{{2W}_1{W}_2}{W_1^2+W_2^2}\right)}^2\right]---\left(3\right)$

Here, W ₁the MFD of the optical fiber involved by present embodiment, W ₂for the optical fiber at equipment two ends or the MFD of other transmission optical fiber.

As the transmission optical fiber of other kind, such as, A under wavelength 1550nm is used in _{ef f}=80 μm ², the single-mode fiber (SMF:Single Mode Fiber) of MFD=10.1 μm or A _eff=50 ~ 70 μm ², the dispersion shifted optical fiber (DSF:Dispersion-Shifted Fiber) of MFD=8 ~ 10 μm and non-zero dispersion displacement optical fiber (NZDSF:Non-Zero Dispersion-Shifted Fiber).According to the Section 2 of above-mentioned formula (1), if A _efflarge compared with the optical fiber at equipment two ends or other transmission optical fiber, then MFD does not mate and becomes large, and junction loss becomes large.In addition, the Section 3 of above-mentioned formula (1) represents the loss of optical fiber.Below, for the characteristic depending on wavelength, when specifically not going out wavelength, be set to the characteristic under wavelength 1550nm.

Fig. 1 represents net sectional area A _effwith the figure of the relation of OSNR improving amount.In addition, in FIG, the link position quantity N illustrating in expression 1 relaying span is the curve map of the OSNR of each syndeton of 0,2,4.In FIG, the longitudinal axis represents and use SMF (A _eff=80 μm ², loss=0.190dB/km) and as the improving amount of the relative OSNR of the situation of transmission optical fiber.In addition, in FIG, in order to evaluate net sectional area A _{ef f}on the impact that OSNR improving amount applies, make loss all identical with SMF.In addition, the W of above-mentioned formula (3) ₂for the MFD of SMF, specifically 10.1 μm.

According to Fig. 1, when there is not link position (N=0), net sectional area A _effmore OSNR can be improved more greatly.Then, when the two ends of 1 relaying span exist 2 link positions (N=2), be equivalent to and the state of the Fiber connection in the equipment such as the repeater at transmission optical fiber two ends (with reference to Fig. 9 A).In this case, net sectional area A _{e ff}be more than or equal to 150 μm ²time, OSNR improving amount is roughly saturated.Thus, even if continue to increase net sectional area A _eff, it is also less that OSNR improves effect.In addition, the pumping light power in order to distributed Raman be amplified suppresses in the scope of practicality, (to be less than or equal to several watts), net sectional area A _eff150 μm must be less than or equal to ².Thus, in order to make OSNR improving amount be more than or equal to 1dB, as long as net sectional area A _effdrop on 110 ~ 150 μm ²scope in.Link position in 1 relaying span exists 4, be equivalent to there is this transmission optical fiber and another kind of transmission situation (with reference to Fig. 9 B) connected between optical fiber to stop at 2 positions further in relaying span.In this case, OSNR improving amount is at net sectional area A _effit is 135 μm ²shi Chengwei maximal value.In addition, the condition making OSNR improving amount be more than or equal to 1dB is, net sectional area A _effdrop on 110 ~ 150 μm ²scope in.It drops on and makes the pumping light power of Raman amplifiction be in the scope of realistic scale.

Fig. 2 A and 2B is figure and the refractive index curve thereof of the profile construction of the embodiment representing optical fiber involved in the present invention.Optical fiber 100 involved by present embodiment as shown in Figure 2 A, has: fibre core 110, and it extends along regulation axle, has refractive index n ₁, diameter 2a; Inner side covering 120, it is arranged on the periphery of fibre core 110, has refractive index n ₂(< n ₁), diameter 2b; Outside covering 130, it is arranged on the periphery of inner side covering 120, has refractive index n ₃(< n ₁, > n ₂); And resin-coated 140, it is arranged on the periphery of outside covering 130.In addition, resin-coated 140 by being arranged on first resin-coated 141 of covering 140 periphery, outside and being arranged on second resin-coated 142 of the first resin-coated 141 peripheries and forming.

In addition, in fig. 2b, the refractive index curve 150 of the glassy zone in the optical fiber 100 shown in illustrating in fig. 2.In this refractive index curve 150, region 151 represents the refractive index of fibre core 110, and region 152 represents the refractive index of inner side covering 120, and region 153 represents the refractive index of outside covering 130.

As the feature of above-mentioned refractive index curve 150, for having identical net sectional area A _{e ff}optical fiber between, bending loss, compared with having the optical fiber of Stepped-index curve, can suppress lower by the optical fiber with refractive index curve 150.But in the optical fiber with refractive index curve 150, if known wavelength is longer, then basic mode light starts to leak from fibre core to covering, causes basic mode to end under certain wavelength.In addition, in the optical fiber with Stepped-index curve, there is not basic mode cut-off, but bending loss is larger.

Fig. 3 represents the wavelength X starting to produce leakage loss _lKand fundamental mode cutoff wavelength λ (nm) _fC(nm) curve map of the relation between.Here, wavelength X _lKbe defined as, basic mode leakage loss with there is Stepped-index curve and central core essence is compared with the loss in the optical fiber of pure silicon dioxide, be more than or equal to its 20% time wavelength.(wavelength X is made in order to make not produce leakage loss in the whole wavestrip of the C wavestrip ~ L wavestrip (1530 ~ 1625nm: the wave band used in the optical communication system involved by present embodiment) utilized in optical communication _lKbe more than or equal to 1625nm), according to Fig. 3, need to make fundamental mode cutoff wavelength λ _fCat least be more than or equal to 2400nm.In addition, #1 shown in Figure 3 represents the comparative example shown in the table 1 of aftermentioned Fig. 5.

Fig. 4 is the curve map of bending loss under diameter 20mm and the relation between fundamental mode cutoff wavelength.Specifically, illustrate at the refractive index contrast Δ of inner side covering 120 relative to outside covering 130 ^-, inner side covering 120 diameter when changing relative to the diameter ratio (2b/2a) of fibre core 110, fundamental mode cutoff wavelength λ _fC(nm) relation between the bending loss and under diameter 20mm.In this Fig. 4, by the refractive index contrast Δ of fibre core 110 relative to inner side covering 120 ⁺and the diameter 2a of fibre core 110 is adjusted to, and makes net sectional area A _effit is 135 μm ², cutoff wavelength λ in LP11 mould _cfor 1350nm.

When Raman amplifiction, in order to also realize single mode when incentive optical wavelength, preferred fiber cutoff wavelength is less than or equal to 1.45 μm.Bending loss is minimum when ratio 2b/2a is 3.0, identical with SMF or be less than or equal to 20dB below, namely in order to be suppressed by bending loss, need to make ratio 2b/2a be 2.5 ~ 3.5, makes refractive index contrast Δ ^-be less than or equal to-0.06%.In addition, in order to make fundamental mode cutoff wavelength λ _fCbe more than or equal to 2400nm, need when ratio 2b/2a is 3.0, refractive index contrast Δ ^-be more than or equal to-0.12%.

Fig. 5 is the table that the constructing variable of the optical fiber (embodiment 1 ~ 15) involved by present embodiment and the optical fiber involved by comparative example and optical characteristics are carried out gathering and obtained.In the comparative example shown in the table of this Fig. 5, fundamental mode cutoff wavelength λ _fCfor 2263nm, longer compared with signal light wavelength, leakage loss is from 1441nm (=λ _lK) start to produce, the loss under wavelength 1550nm is 0.32dB/km, also higher.On the other hand, embodiment 1 ~ 15 does not all produce leakage loss in optical communication wavestrip.In addition, the net sectional area A of embodiment 1 _{ef f}it is 134 μm ², bending loss is 8.0dB/m, is good.Other embodiment 2 ~ 15 also has the bending loss more excellent than comparative example.

In addition, at increase net sectional area A _efftime also along with the increase of microbending loss.Fig. 6 is the multiple samples for the optical fiber involved by present embodiment, by resin-coated Young modulus and net sectional area A _effthe table that microbending loss during change carries out gathering and obtains.In this Fig. 6, illustrate with glass diameter (diameter of outside covering 130), first resin-coated 141 Young modulus and diameter, second resin-coated 142 Young modulus and diameter, optical fiber A _eff, λ _crelative microbending loss.Here, loss recruitment when optical fibre winding is on the bobbin of diameter 400mm represents by with tension force 80g by microbending loss, and this spool surface is covered by the wire gauze at diameter 50 μm, 100 μm, interval.

Sample 1 ~ 3 according to Fig. 6 and the comparison between sample 4 ~ 6, known by making the Young modulus of first resin-coated 141 reduce, there is identical net sectional area A _effoptical fiber between, the optical fiber of sample 4 ~ 6 can reduce microbending loss.In addition, per sample 5 and the comparison of sample 7, known by the Young modulus of second resin-coated 142 is become large, between the optical fiber with identical net sectional area Aeff, the optical fiber of sample 7 can reduce microbending loss.

Usually, the lower and optical fiber that second resin-coated 142 Young modulus is higher of the Young modulus of first resin-coated 141, microbending loss is lower.Specifically, preferably the Young modulus of first resin-coated 141 is set in the scope of 0.3 ~ 0.6MPa, and the Young modulus of second resin-coated 142 is set in the scope of 700 ~ 1500MPa.

As the method reducing microbending loss, also there is method glass diameter or the diameter of resin-coated 140 (comprising first resin-coated 141 and second resin-coated 142) increased, but due to normally used optical fiber (glass diameter: 125 μm, coated diameter: 245 μm) between difference become large, so impracticable.Thus, in the optical fiber involved by present embodiment, be set as 125 ± 1 μm as glass diameter, be set as 240 ~ 250 μm as the diameter of second resin-coated 142.

Fig. 7 A ~ 7C utilizes net sectional area A _effwith the relation of loss, represent the figure of the OSNR improving amount relative to SMF caused by the difference of the connection status in relaying span.Especially, Fig. 7 A utilizes net sectional area A _eff(μm ²) and the relation of loss (dB/km), represent that relative to the OSNR improving amount of SMF, Fig. 7 B utilizes net sectional area A in the relaying span structure of the 80km be made up of the transmission optical fiber of the link position not having to be connected between SMF _eff(μm ²) and the relation of loss (dB/km), represent and comprise in the 80km relaying span structure of the transmission optical fiber be connected on 2 positions with SMF, relative to the OSNR improving amount of SMF, Fig. 7 C utilizes net sectional area A _eff(μm ²) and the relation of loss (dB/km), represent and comprise in the 80km relaying span structure of the transmission optical fiber be connected on 4 positions with SMF, relative to the OSNR improving amount of SMF.

In addition, as noted above, Fig. 7 A ~ 7C is for net sectional area A _effwith loss and represent in 1 relaying span with level line, the curve map of the OSNR improving amount when transmission optical fiber involved by present embodiment and the link position between SMF exist 0,2,4.The length of 1 relaying span is 80km, as the W of above-mentioned formula (3) ₂, the MFD of SMF is 10.1 μm.In addition, OSNR improving amount is to use SMF as the situation of conveying optical fiber as benchmark.

According to Fig. 7 A ~ 7C, if known net sectional area A _effit is 110 ~ 150 μm ², loss is less than or equal to 0.19dB/km, even if the link position then in 1 relaying span exists 0 ~ 4, OSNR improving amount also can be made for being more than or equal to 1dB.Further, if net sectional area A _effit is 120 ~ 140 μm ², loss is 0.18dB/km, then, the link position in 1 relaying span exists 0 or 2, OSNR improving amount can be made for being more than or equal to 2dB.Further, if net sectional area A _effit is 120 ~ 140 μm ², loss is less than or equal to 0.17dB/km, even if then link position exists 4 in 1 relaying span, OSNR improving amount also can be made for being more than or equal to 2dB.

In addition, preferred fiber cutoff wavelength λ _cdrop in the scope of 1.3 ~ 1.53 μm.If lower than this scope, then bending loss becomes large.On the contrary, if higher than this scope, then, in C wavestrip (1530 ~ 1565nm), flashlight cannot become single mode.Further, more preferably fiber cut off wavelength λ _cbe less than or equal to 1450nm.Its reason is, because the wavelength of the pump light used in distributed Raman amplification is 1450nm degree, so pump light becomes single mode, its result, can not make launching efficiency worsen.

In the optical fiber 100 involved by present embodiment, by making the fibre core 110 transmitted most signal light power be pure silicon dioxide free from foreign meter in fact, transport loss can be reduced, therefore more preferably.But, the micro-additive of the degree that can not increase loss also can be contained in fibre core 110.Such as, also can containing micro-halogen or alkali metal in fibre core 110.Specifically, fibre core 110 also can containing be less than or equal to 2mol% chlorine Cl, be less than or equal to the fluorine F of 1mol%, be less than or equal to the potassium K of 0.1mol%.

In addition, there is the optical fiber of pure silicon dioxide fibre core, nonlinear refractive index n ₂lower, nonlinear phase side-play amount Φ can be made _sPMallow that incident power increases further time fixing.Thus, OSNR can be made to increase further.In addition, in fibre core 110, be added with the nonlinear refractive index n of the SMF of Ge ₂be 2.35 × 10 ^-20(m ²/ W), on the other hand, there is the nonlinear refractive index n of the optical fiber of pure silicon dioxide fibre core ₂be 2.20 × 10 ^-20(m ²/ W).

, utilize Fig. 8 below, the structure describing the optical fiber involved by present embodiment in detail determines action.In addition, Fig. 8 is the process flow diagram determining action for illustration of the structure of the optical fiber involved by present embodiment.

In the structure of optical fiber 100 is determined, first, the material (step ST1) of fibre core 110 is determined.More preferably essence is the fibre core of pure silicon dioxide.Inner side covering 120 and outside covering 130 preferably add fluorine, and (in pure silicon dioxide fibre core, loss reduces less, nonlinear refractive index n ₂also lower).

In step ST2, according to above-mentioned formula (1) and formula (2), determine the net sectional area A improving the OSNR expected _eff.In addition, in step ST3, to form single mode and the mode that bending loss can not increase determines λ in use wavestrip _c.In step ST4, to the refractive index contrast Δ of fibre core 110 relative to inner side covering 120 ⁺and the diameter 2a of fibre core 110 determines, to obtain above-mentioned determined A _effand λ _c.

On the other hand, in step ST5, to make λ in figure 3 _lKmode longer compared with use wavestrip determines λ _fC.In addition, in step ST6, determine the bending loss as target.In step ST7, determine the refractive index contrast Δ of inner side covering 120 relative to outside covering 130 according to Fig. 4 ^-and ratio 2b/2a, to obtain above-mentioned determined λ _fC, bending loss, in addition, in step ST8, determine first resin-coated 141 and second resin-coated 142, suppressing lower by microbending loss.

Fig. 9 A and 9B is the figure of the structure of each embodiment representing optical communication system involved in the present invention.In addition, Fig. 9 A represents that the link position in 1 relaying span and between SMF exists the structure of the optical transmission system of 2.In addition, Fig. 9 B represents that the link position in 1 relaying span and between SMF exists the structure of the optical transmission system of 4.

Specifically, the optical communication system 200A shown in Fig. 9 A has the output signal transmitter 210 of light and the receiver 220 of Received signal strength light, and the transmission path between these transmitter 210 and receivers 220 is configured with multiple repeater 230A, 230B.Relaying span is between the optical transmission region between these repeaters 230A, 230B, and in this optical communication system 200A, this relaying span comprises 1 transmission optical fiber 100 (optical fiber involved by present embodiment).This transmission two ends of optical fiber 100 are connected with the another kind transmission optical fiber (not shown) of repeater 230A, 230B end respectively, in the optical communication system 200A of this Fig. 9 A, in 1 relaying span, there are 2 link positions A1, A2.

On the other hand, the optical communication system 200B shown in Fig. 9 B also has the output signal transmitter 210 of light and the receiver 220 of Received signal strength light, and the transmission path between these transmitter 210 and receivers 220 is configured with multiple repeater 230A, 230B.Relaying span is between the optical transmission region between these repeaters 230A, 230B, in this optical communication system 200B, further, this relaying span comprises two transmission optical fiber 100 (optical fiber involved by present embodiment) and another kind of transmission optical fiber 300.This relaying span comprises link position B1, B4 between repeater 230A, 230B end, has 4 link position B1 ~ B4.That is, in the optical communication system 200B of Fig. 9 B, in 1 relaying span, there are 4 link position B1 ~ B4.

In addition, in any one optical communication system 200A, 200B, the optical fiber 231 at repeater 230A, 230B two ends is the SMF of standard (usually, net sectional area A under wavelength 1550nm _effit is 80 μm ², but be sometimes also 85 μm ²).The another kind of transmission net sectional area A of optical fiber 300 _effwith the net sectional area A of the SMF of standard _eff(such as 85 μm ²) compare little.

As mentioned above, according to the present invention, the OSNR in the optical communication system of carrying out Raman amplifiction can be improved, and the leakage loss that can realize avoiding Yin Jimo to end and cause and suppress taking into account of both bending losss.Namely, overall as optical communication system, performance along with light-receiving device improves and becomes the impact not being vulnerable to increase as the dispersion values of the optical fiber self of light transmission path, not to improve for the purpose of dispersion values but the special optical fiber involved in the present invention for the improvement of OSNR and the suppression of bending loss becomes effective.

Claims (6)

1. an optical fiber, it is quartzy type optical fiber, have under wavelength 1550nm, be less than or equal to 0.19dB/km loss, under wavelength 1550nm, be more than or equal to 120 μm ²and be less than or equal to 150 μm ²net sectional area A _eff, and be more than or equal to 1.3 μm and be less than or equal to the fiber cut off wavelength λ of 1.53 μm _c,

It is characterized in that having:

A fibre core that () is made up of pure quartz, it has refractive index n ₁, diameter 2a;

B () inner side covering, it is arranged on the periphery of described fibre core, and has refractive index n ₂, diameter 2b; And

C () outside covering, it is arranged on the periphery of described inner side covering, and has refractive index n ₃,

(d) described refractive index n ₃be less than described refractive index n ₁and be greater than described refractive index n ₂,

E the diameter of () described inner side covering is more than or equal to 2.5 relative to the diameter ratio Ra of described fibre core and is less than or equal to 3.5, wherein, and Ra=2b/2a,

F fundamental mode cutoff wavelength that the basic mode used under the wavelength upper limit is starting when leaking by () is set to λ _fCuptime, by fundamental mode cutoff wavelength λ _fCbe set greater than λ _fCupwavelength,

G () described inner side covering is relative to the refractive index contrast Δ of described outside covering ^-be more than or equal to-0.12% and be less than or equal to-0.06%, wherein, Δ ^-=100 × (n ₂-n ₃)/n ₃.

2. optical fiber according to claim 1, is characterized in that,

Net sectional area A under wavelength 1550nm _effbe less than or equal to 140 μm ².

3. optical fiber according to claim 2, is characterized in that,

Described optical fiber has the fiber cut off wavelength being less than or equal to 1.45 μm.

4. an optical communication system, in this optical communication system, the transmission path as relaying span has the optical fiber described in claim 1 or 2, and the feature of this optical communication system is,

Use digital coherent reception technique, this digital coherent reception technique, by receiver acknowledge(ment) signal light, uses the digital signal processing in receiver, compensates the waveform distortion of the flashlight that dispersion causes.

5. optical communication system according to claim 4, is characterized in that,

In described optical fiber, conveying light is by Raman amplifiction.

6. an optical communication system, it has:

Multiple 1st optical fiber, it is erected to be more than or equal to and is more than or equal to 2 positions in the relaying span of 80km, has the structure identical with the optical fiber of claim 3 respectively; And

Multiple 2nd optical fiber, it is more than or equal to 4 positions and described 1st Fiber connection in described relaying span and two ends thereof, has respectively and be less than or equal to 85 μm under wavelength 1550nm ²net sectional area A _eff, and one of them of described multiple 2nd optical fiber is erected at the two ends of described relaying span, or be erected at 1 position in described relaying span.