電子電氣自動化通信外文翻譯--光纖的布線對光學(xué)偏振模色散的影響（英文）

1、Optical Fiber Technology 14 (2008) 149–153www.elsevier.com/locate/yofteEffect of cabling on polarization mode dispersion in optical fiber ribbon cablesKunihiro Toge ?, Kazuo HogariNTT Access Service System Laboratories,

2、NTT Corporation, 1-7-1, Hanabatake, Tsukuba-city, Ibaraki 305-0805, JapanReceived 5 April 2007; revised 27 July 2007Available online 3 December 2007AbstractThis paper theoretically and experimentally investigates an effe

3、ct of cabling on polarization mode dispersion (PMD) in ribbon fibers helically stranded in optical fiber ribbon cables aimed at designing low PMD ribbon cables. Based on the birefringence model focused on the change in t

4、he birefringence when ribbon fibers are cabled, the helical pitch of optical fiber ribbon cables is designed to minimize the maximum PMD in the cables. A low PMD characteristic is confirmed in optical fiber ribbon cable

5、with approximately the optimal helical pitch.© 2007 Elsevier Inc. All rights reserved.Keywords: Optical fiber cable; Optical fiber ribbon; Polarization mode dispersion1. IntroductionThe demand for greater transmissi

6、on capacity is growing rapidly as a result of the increase in the number of broadband services provided by the Internet and the bit-rate has been in- creasing to meet this demand. As the bit-rate has increased, polarizat

7、ion mode dispersion (PMD) has become a major fac- tor limiting the transmission length and has attracted increasing attention [1]. Optical fiber ribbon cables are widely used in both access and trunk networks because of

8、their high-count compactness, ease of fiber identification and capacity for mass splicing. Sev- eral studies have investigated the PMD in optical fiber ribbons and cables [2–5]. It has been reported that the inner pair o

9、f fibers in 4-fiber ribbons has a high PMD. A finite element analy- sis has also been performed to model the stress distribution in optical fiber ribbons, and induced birefringence was found to be high for the inner fibe

10、rs in the ribbons as a result of the ribbon coating [2]. Such a high PMD has also been found in cables. However, this high PMD has often appeared in the outer fibers in ribbons [3,4]. These results lead us to believe tha

11、t the change in the birefringence induced by cabling would signifi-* Corresponding author. Fax: +81 298 52 6142. E-mail address: toge@ansl.ntt.co.jp (K. Toge).cantly affect the PMD, and would depend strongly on the cable

12、 structure. However, the change in the birefringence induced by cabling has remained unclear. In order to achieve low PMD ca- bles, it is important to design the structure of optical fiber ribbon cables taking the effect

13、 of cabling on the birefringence in opti- cal fiber ribbons into consideration. In this paper, we investigate the effect of cabling on PMD in optical fiber ribbon cables with helically stranded ribbons the- oretically an

14、d experimentally. First, we compare numerically calculated and measured results to confirm the model. In the numerical calculation, we use a birefringence model focused on the change in the birefringence in ribbon fibers

15、 induced by tension, bending and twisting when ribbon fibers are cabled. Then, we discuss the effect of cable structure on the PMD in optical fiber ribbon cables, and point out that the helical pitch of cables can be opt

16、imized to minimize the maximum PMD in optical fiber ribbon cables. We also measure the PMD in opti- cal fiber ribbon cables with approximately the optimal helical pitch to reveal the validity of the design and report the

17、 result.2. Theoretical background2.1. Birefringence caused by cablingWe considered two types of optical fiber ribbon cable com- posed of 4-fiber ribbons as shown in Fig. 1. One was 100-fiber1068-5200/$ – see front matter

18、 © 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.yofte.2007.09.010K. Toge, K. Hogari / Optical Fiber Technology 14 (2008) 149–153 151Table 1 Dimensions of optical fiber ribbons and cables used in the experim

19、ents and calculationsCable A Cable BFiber (ribbon) count 100 (25) 40 (10) Pitch radius a 2.5 mm 0 mm Helical pitch P 500 mm 350 mm Fiber diameter 2r 125 µm 125 µm Ribbon width 1.1 mm 1.1 mm Ribbon thickness 0.3

20、 mm 0.3 mmFig. 2. Polarization-sensitive optical time domain reflectometry setup used to measure beat length.Table 1 summarizes the typical dimensions of the ribbons and the cables we used.3.2. PMD and beat length measur

21、ementThe PMD was measured for ribbon fibers and cabled ribbon fibers by the Jones matrix eigenanalysis method in the 1520– 1630 nm wavelength range. The beat length LB was measured with a polarization-sensitive optical t

22、ime domain reflectometry (P-OTDR) technique [13,14]. Figure 2 shows the measurement setup. A distributed feedback laser diode (DFB-LD) with a nar- row linewidth of 160 MHz was used to avoid depolarization in wavelength [

23、15]. We operated the DFB-LD at 1550 nm, and varied the wavelength on a range of 1 nm during averaging in order to reduce the coherence noise [13]. The DFB-LD was externally modulated by a LiNbO3(LN) modulator. The pulse

24、width was set at 10 ns, which corresponds to a spatial resolu- tion of 1 m. To obtain an optical pulse with a high peak power, we used an optical amplifier and eliminated amplified noise by using an acousto-optic modulat

25、or. A linear polarizer was used in front of the fiber input end. The Rayleigh backscattering light that passed through the polarizer was detected and then averaged. We analyzed its power fluctuation to obtain the beat le

26、ngth. The beat length was calculated from the peak Fourier frequency of the power spectrum of the fluctuation as described in [14]. The coupling length LC in cables can be estimated from the measured PMD and beat length

27、in cables. The strain differ- ence between ribbon fibers and cabled ribbon fibers ?ε was measured by using a Brillouin OTDR [16].4. Results and discussion4.1. Comparison of calculated and measured PMDFigure 3 compares th

28、e PMD reduction factors (PMDRFs) obtained by measurement and calculation, where the PMDRFsFig. 3. Comparison of calculated and measured PMD reduction factors (PM- DRFs) for cables A and B. The open and closed symbols sho

29、w the PMDRFs for the outer and inner fibers in ribbons, respectively.Table 2 Measured beat lengths and PMD in optical fiber ribbonsBeat length LB (m) PMD in ribbons (ps/rkm)Outer fibers Max. 26 0.16 Mean 17 0.10 Min. 2 0

30、.05Inner fibers Max. 17 0.35 Mean 6 0.23 Min. 2 0.11Note. Number of measured fibers is 10 for each.Fig. 4. Calculated PMD as a function of the helical pitch and lateral stress.are defined by the PMD in cabled ribbon fibe

31、rs which is normal- ized by the measured PMD in ribbon fibers. Since the PMD in the long length regime exhibits a Maxwell distribution owing to random mode coupling, we defined the calculated PMD as the mean PMD obtained

32、 from the calculation of 100 instances. The beat length in ribbon fibers and the strain difference we used for the calculation are based on measured results. We found that the calculated and measured results agreed well,

33、 which in- dicates that the birefringence change caused by cabling can be modeled as described in the previous section.4.2. Effects of cabling on PMD in optical fiber ribbonsTable 2 shows the measured beat lengths and PM