陳偉,袁健,賀作為,宋君

(江蘇亨通光纖科技有限公司,江蘇蘇州 215200)

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400Gbit/s骨干網(wǎng)用超低損耗超大有效面積光纖的開(kāi)發(fā)

陳偉,袁健,賀作為,宋君

(江蘇亨通光纖科技有限公司,江蘇蘇州 215200)

摘要:損耗和非線性是影響超100 Gbit/s高速光通信系統(tǒng)性能最為關(guān)鍵的因子。文章設(shè)計(jì)并研制了一種適合400 Gbit/s高速傳輸用的新型單模光纖,該光纖具備超低損耗與超大有效面積特性,在1550nm波長(zhǎng)處衰減為0.165dB/km,在1625nm波長(zhǎng)處衰減為0.179dB/km;在1550nm波長(zhǎng)的模場(chǎng)直徑為13.96μm,有效面積為153μm2。該光纖具備優(yōu)良的抗彎曲性能,其關(guān)鍵技術(shù)指標(biāo)優(yōu)于當(dāng)前國(guó)際技術(shù)水平,可為下一代高速光纖通信提供關(guān)鍵基礎(chǔ)材料支撐。

關(guān)鍵詞:400Gbit/s系統(tǒng);高速光通信;超低損耗光纖;大有效面積光纖;大容量

0　引 言

隨著大數(shù)據(jù)與云計(jì)算的迅速發(fā)展,人們對(duì)光纖通信的帶寬與速率需求迅速提高。我國(guó)的光纖通信系統(tǒng)從10 Gbit/s跨過(guò)40 Gbit/s中間階段直接構(gòu)建100 Gbit/s,乃至400 Gbit/s高速光纖通信網(wǎng)絡(luò)。而高速光纖通信的編碼方式從傳統(tǒng)的RZ(歸零)碼和NRZ(非歸零)碼發(fā)展到100 Gbit/s采用QPSK(正交相移鍵控)[1-2],400 Gbit/s采用QAM(正交幅度調(diào)制)或DP-QPSK(雙偏振正交相移鍵控)的方式[3-4]。調(diào)制方式的變化對(duì)光纖的波長(zhǎng)色散和偏振模色散冗余度較大,對(duì)光纖的損耗卻要求極高。光纖的損耗和非線性成為限制高速大容量光纖通信系統(tǒng)OSNR(光信噪比)的關(guān)鍵因素。

國(guó)內(nèi)外科學(xué)工作者開(kāi)展了光纖的低損耗制作技術(shù)和有效面積提升技術(shù)的研究[5-12],但是未能很好地解決有效面積增大與彎曲損耗增加的矛盾,目前的低損耗大有效面積單模光纖在1 550 nm波長(zhǎng)損耗為0.185 d B/km,有效面積為110μm2,難以滿足400 Gbit/s高速光纖通信的技術(shù)需求。本文分析了400 Gbit/s通信系統(tǒng)對(duì)光纖的要求和實(shí)現(xiàn)途徑,設(shè)計(jì)了一種新型超低損耗超大有效面積單模光纖的波導(dǎo)結(jié)構(gòu),并研制開(kāi)發(fā)出該新型光纖,以滿足我國(guó)高速大容量光纖通信系統(tǒng)對(duì)光纖的新需求。

1　400 Gbit/s通信系統(tǒng)對(duì)光纖的要求

100 Gbit/s光纖通信系統(tǒng)采用DP-QPSK編碼調(diào)制格式[13-14],系統(tǒng)的背靠背OSNR要求在9.8～ 12.2 dB之間,光纖在1 550 nm波長(zhǎng)的衰減系數(shù)小于0.21 dB/km;400 Gbit/s系統(tǒng)采用DP-QPSK、DP-16QAM和DP-256QAM調(diào)制技術(shù)[15-16],相對(duì)于100 Gbit/s系統(tǒng),OSNR代價(jià)分別為6、10和20 dB以上,這些增加的OSNR代價(jià)需要從光端機(jī)的注入光功率或光纖鏈路損耗兩個(gè)方面進(jìn)行解決。因此, 400 Gbit/s通信系統(tǒng)對(duì)光纖的要求主要體現(xiàn)在兩個(gè)方面:較低的衰減系數(shù)和非線性系數(shù)[17-18]。

可以看出,影響通信系統(tǒng)FOM的光纖參數(shù)有:光纖的有效面積Aeff、光纖的衰減系數(shù)αdB/km和光纖的非線性長(zhǎng)度Leff。

我們以80 km長(zhǎng)度的跨段進(jìn)行通信鏈路FOM研究,重點(diǎn)研究αdB/km、Leff和Aeff對(duì)FOM的影響。圖1所示為光纖衰減對(duì)鏈路FOM的影響。由圖可知,當(dāng)αdB/km分別為0.185、0.175和0.165 dB/km 時(shí),鏈路FOM分別為1.2、2.0和2.8 d B,可見(jiàn)降低αdB/km對(duì)通信系統(tǒng)鏈路的FOM貢獻(xiàn)非常顯著。但光纖衰減的降低隨之帶來(lái)光纖的非線性效應(yīng)增強(qiáng), 而Leff增大對(duì)通信鏈路的FOM會(huì)產(chǎn)生負(fù)面貢獻(xiàn),如圖2所示。當(dāng)αdB/km為0.175 dB/km時(shí),Leff為23.83 km,80 km的通信跨段將產(chǎn)生0.651 dB的負(fù)貢獻(xiàn);當(dāng)αdB/km為0.165 dB/km時(shí),Leff為25.06 km的通信跨段將產(chǎn)生0.661 dB的負(fù)貢獻(xiàn)。

圖1　光纖衰減對(duì)通信鏈路FOM的影響

圖2　光纖非線性長(zhǎng)度對(duì)通信鏈路FOM的影響

為了降低光纖非線性導(dǎo)致通信鏈路FOM值降低與OSNR的惡化,需要提升Aeff。圖3所示為Aeff對(duì)鏈路FOM的影響。當(dāng)Aeff增加20%達(dá)到96μm2時(shí),通信系統(tǒng)入纖功率可增大0.792 d Bm,對(duì)鏈路FOM貢獻(xiàn)0.792 dB,等效于降低光纖衰減0.009 9 dB/km;當(dāng)Aeff增加40%達(dá)到110μm2時(shí),通信系統(tǒng)入纖功率可增大1.461 dBm,等效于降低光纖衰減0.018 3 dB/km,鏈路FOM貢獻(xiàn)1.46 dB; 當(dāng)Aeff增加70%達(dá)到135μm2時(shí),通信系統(tǒng)入纖功率可增大2.3 dBm,等效于降低光纖衰減0.028 8 d B/km,鏈路FOM貢獻(xiàn)2.3 d B。

圖3　有效面積Aeff對(duì)通信鏈路FOM的影響

光纖的光學(xué)衰減系數(shù)、非線性效應(yīng)和有效面積這3個(gè)關(guān)鍵參數(shù)對(duì)光纖等效衰減的影響如圖4所示。當(dāng)αdB/km為0.165 d B/km、Aeff為110μm2時(shí),光纖的等效衰減系數(shù)為0.155 dB/km;當(dāng)αdB/km為0.165 dB/km、Aeff為135μm2時(shí),光纖的等效衰減系數(shù)為0.144 d B/km。因此,超100 Gbit/s及400 Gbit/s高速大容量通信系統(tǒng)要求光纖具備較低的衰減和較大的有效面積。

圖4　光纖參數(shù)對(duì)等效衰減的影響

2　超低損耗超大有效面積單模光纖的設(shè)計(jì)與制備

光纖的波導(dǎo)結(jié)構(gòu)不僅決定光纖的損耗特性,而且直接決定其有效面積Aeff,因此光纖波導(dǎo)結(jié)構(gòu)的設(shè)計(jì)對(duì)于超低損耗超大有效面積光纖的綜合性能至關(guān)重要。光纖屬于圓形對(duì)稱波導(dǎo),在弱導(dǎo)近似下, Ψ(R)滿足標(biāo)量波動(dòng)方程[21]:

和邊界條件:

式中,k0為真空波數(shù),R=r/a為光纖歸一化半徑,r為徑向坐標(biāo),a為纖芯半徑,n(R)為徑向折射率分布,β為軸向傳播常數(shù),Ψcore(R)為光纖芯區(qū)的基模場(chǎng)分布,Ψcl(R)為包層的基模場(chǎng)分布。對(duì)于任意折射率剖面光纖,只要計(jì)算出Ψ(R),便可代入式(2)計(jì)算出Aeff[21]:

本項(xiàng)目設(shè)計(jì)的超低損耗超大有效面積單模光纖的折射率剖面結(jié)構(gòu)如圖5所示。圖6所示為Aeff隨波長(zhǎng)變化關(guān)系曲線圖。該折射率結(jié)構(gòu)不僅可以獲得超大有效面積,其在1 550 nm波長(zhǎng)的Aeff為150μm2,而且該結(jié)構(gòu)還可以降低光纖的二氧化鍺含量,優(yōu)化界面材料的粘度匹配,大幅度降低光纖的光損耗。同時(shí)在芯周邊引入折射率下凹的結(jié)構(gòu)可以有效調(diào)節(jié)基模模場(chǎng)分布,大大提高了大有效面積光纖的抗彎曲損耗。

圖5　超低損耗超大有效面積光纖的折射率剖面設(shè)計(jì)

圖6　有效面積Aeff隨波長(zhǎng)變化關(guān)系曲線

3　光纖性能測(cè)試與試驗(yàn)結(jié)果分析

按照上述波導(dǎo)結(jié)構(gòu),我們采用CCVD(連續(xù)化學(xué)氣相沉積)工藝完成了光纖預(yù)制棒的制造,在2 120℃的高溫拉絲塔上,將光纖預(yù)制棒拉制成石英包層直徑為125μm、涂層直徑為245μm的石英玻璃光纖。該光纖的測(cè)試數(shù)據(jù)如表1所示。該光纖不僅損耗低于國(guó)際水平,而且Aeff大于當(dāng)前國(guó)際商用水平的130μm2。同時(shí),該光纖具備良好的抗彎曲能力,將光纖繞在彎曲半徑為30 mm的芯軸上,彎曲100圈,測(cè)得光纖在1 550 nm的彎曲附加損耗為0.032 d B,在1 625 nm的彎曲附加損耗為0.093 dB,二者均優(yōu)于當(dāng)前國(guó)際技術(shù)水平。

表1　研制的光纖樣品關(guān)鍵性能指標(biāo)測(cè)試值

4　結(jié)束語(yǔ)

本文分析了400 Gbit/s通信系統(tǒng)調(diào)制格式及其對(duì)光纖的要求,得出損耗和非線性是影響未來(lái)高速光通信系統(tǒng)最為關(guān)鍵的因素的結(jié)論,然后設(shè)計(jì)了具備低損耗和大有效面積的光纖折射率剖面結(jié)構(gòu)。采用CCVD工藝技術(shù)研制了超低損耗超大有效面積光纖,該光纖在1 550 nm波長(zhǎng)的模場(chǎng)直徑為13.96μm,有效面積為153μm2,1 550 nm波長(zhǎng)的衰減為0.165 d B/km,1 625 nm波長(zhǎng)的衰減為0.179 dB/km,并且具備優(yōu)良的抗彎曲性能,關(guān)鍵技術(shù)指標(biāo)優(yōu)于當(dāng)前國(guó)際技術(shù)水平。該新型光纖技術(shù)可望滿足“寬帶中國(guó)戰(zhàn)略”基礎(chǔ)設(shè)施建設(shè)對(duì)光纖的需求,為我國(guó)下一代高速光通信“提網(wǎng)速、降網(wǎng)費(fèi)”提供關(guān)鍵的基礎(chǔ)材料。

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光纖光纜技術(shù)與應(yīng)用

Development of the Ultra-Low-Loss Super-Large-Area Optical Fibers for 400 Gbit/s Backbone Networks

CHEN Wei,YUAN Jian,HE Zuo-wei,Song Jun (Jiangsu Heng Tong Optical Fiber Technologies Co.Ltd.,Suzhou 215200,China)

Abstract:Loss and nonlinearity are the most critical factors affecting the performances of 100 Gbit/s optical communication systems.This letter designs and develops a novel single-mode fiber for 400 Gbit/s high-rate transmissions.With ultra-low-loss and super-large effective area characteristics,its attenuation coefficients are reduced to 0.165 dB/km at 1 550 nm and 0.179 dB/km at 1 625 nm respectively.The mode-field-diameter is 13.96μm at 1 550 nm,and the effective area is 153μm2. Moreover,this fiber has outstanding anti-bending performance and its key technological specifications are superior to the current international technological level and can provide the key fundamental material support to the next generation high-rate fiber-optic communications.

Key words:400 Gbit/s system;high-rate communication;ultra-low-loss optical fiber;large effective area fiber;large capacity

中圖分類號(hào):TN818

文獻(xiàn)標(biāo)志碼:A

文章編號(hào):1005-8788(2016)01-0025-04

收稿日期:2015-10-13

基金項(xiàng)目:江蘇省重點(diǎn)研發(fā)基金資助項(xiàng)目(BE2015078);姑蘇創(chuàng)新基金資助項(xiàng)目(ZXL2014107)

作者簡(jiǎn)介:陳偉(1976-),男,湖北大悟人。教授級(jí)高工,博士,主要研究方向?yàn)楣饫w通信及光電子材料的研究與開(kāi)發(fā)。

doi:10.13756/j.gtxyj.2016.01.008