Enhanced Optical Fiber for Distributed Acoustic Sensing beyond the Limits of Rayleigh Backscattering.

We report on engineered fibers with enhanced optical backscattering that exceeds Rayleigh scattering limits by more than one order of magnitude. We measure attenuation less than 0.5 dB/km from 1,300 to 1,650 nm. By controlling the enhanced backscatter over a 1.5-km length, we compensate for this attenuation, resulting in a higher backscatter signal at the end of the fiber. We demonstrate that the scattering strength may be stabilized for operation at temperatures above 200°C for at least 3 weeks. We show that the deleterious signal distortion due to the Kerr nonlinearity is within 10% of standard fiber. We then report on the use of these fibers in distributed acoustic sensing (DAS) measurements. A significant increase in acoustic signal-to-noise ratio leads to the possibility of improved spatial resolution in the enhanced fiber DAS system.

Transmission of single-carrier 400G signals (515.2-Gb/s) based on 128.8-GBaud PDM QPSK over 10,130- and 6,078 km terrestrial fiber links.

We experimentally demonstrate the coherent transmission system with the highest ETDM-based symbol rate of 128.8-GBaud over record breaking distances. We successfully transmitted single-carrier 515.2-Gb/s PDM-QPSK/9-QAM signals over 10,130km/6,078-km, respectively, over 100km spans of TeraWave SLA + fiber. To the best of our knowledge, it is the highest ETDM-based symbol rate reported so far, and the longest WDM transmission distance with single-carrier 400G signals. For the first time, the 515.2-Gb/s single-carrier PDM-QPSK signals in 200-GHz-grid are successfully transmitted over distance above 10,000km in terrestrial transmission environment. We have also demonstrated the transmission of single carrier 128.8-GBaud filtered QPSK signals in 100-GHz-grid over 6,078-km, which has the line spectral efficiency (SE) of 5.152 (b/s/Hz).

Time-division-multiplexed few-mode passive optical network.

We demonstrate the first few-mode-fiber based passive optical network, effectively utilizing mode multiplexing to eliminate combining loss for upstream traffic. Error-free performance has been achieved for 20-km low-crosstalk 3-mode transmission in a commercial GPON system carrying live Ethernet traffic. The alternative approach of low modal group delay is also analyzed with simulation results over 10 modes.

Comparison of 80 × 112-Gb/s PDM-QPSK system performance over large effective area fiber and standard SMF with Raman amplification.

We experimentally investigate the transmission performance of 80 × 112-Gb/s polarization-division-multiplexed quadrature phase shift keying (PDM-QPSK) signals over large effective area fiber and standard single mode fiber (SSMF) links with Raman amplification. The large effective area fiber offers higher optimum launch power and longer reach than SSMF. The maximum reach of 5200-km is obtained using large effective area fiber. The Gaussian noise (GN) model is explored to fit with experimental data for optimum power.

Seven-core erbium-doped double-clad fiber amplifier pumped simultaneously by side-coupled multimode fiber.

We demonstrate a seven-core erbium-doped fiber amplifier in which all the cores were pumped simultaneously by a side-coupled tapered multimode fiber. The amplifier has multicore (MC) MC inputs and MC outputs, which can be readily spliced to MC transmission fiber for amplifying space division multiplexed signals. Gain over 25 dB was obtained in each of the cores over a 40-nm bandwidth covering the C-band.

High-power broadband Yb-free clad-pumped EDFA for L-band DWDM applications.

We demonstrated high-power broadband Yb-free clad-pumped erbium-doped fiber amplifier (EDFA) using commercial available low-cost 976 nm multimode diodes. An output power +33 dBm with less than ±1 dB natural gain flatness over a gain bandwidth of 33 nm (1570.3-1603.3 nm) was obtained using a new double-clad erbium-doped fiber which has a large core diameter of 17 µm and low NA of 0.11. The saturated output power, net gain, noise figure, and optical power conversion efficiency of the clad-pumped EDFA were characterized, and system impact of LP11 mode and four-wave-mixing nonlinearity were also evaluated.

Entirely passive coexisting 10G-PON and GPON compatible reach extender using Raman amplification.

This paper describe a truly-passive coexistence of 10G-PON and GPON compatible reach extension system with a novel optical configuration, by using laser pumps to provide reverse-pumped distributed Raman gain for both 1270 nm 10G-PON and 1310 nm GPON upstream (US) signals, and using semiconductor optical amplifiers (SOA) as boosters to improve the loss budgets for both 1577 nm 10G-PON and 1490 nm GPON downstream (DS) signals. The Raman interaction between laser pumps and the two US signals is investigated, and the system transmission penalties of US signals due to Raman ASE noises is measured. The transmission impairments of 1490 nm DS signals due to pattern-dependent distortion caused by gain dynamics of the SOA is discussed in this paper. Finally, we present experimental demonstration of coexisting 10G-PON and GPON bi-directional transmission over 50-km of AllWave(TM) fiber with entirely passive fiber plant and a total 1:96 split, accommodating link loss budget more than 39-dB for both 10G-PON and GPON US signals.

Crosstalk in multicore fibers with randomness: gradual drift vs. short-length variations.

Random perturbations play an important role in the crosstalk of multicore fibers, and can be captured by statistical coupled-mode calculations. In this approach, phase matching contributes a multiplicative factor to the average crosstalk, depending on the perturbation statistics and any intentional heterogeneity of neighboring cores. The impact of perturbations is shown to be qualitatively different depending on whether they are gradually varying, or have short-length (centimeter-scale) variations. This insight implies a novel crosstalk suppression strategy: fast modulation of a bend perturbation by spinning the fiber can disrupt the bend-induced phase matching.

Colorless coherent receiver using 3x3 coupler hybrids and single-ended detection.

We demonstrate a single-ended colorless coherent receiver using symmetric 3x3 couplers for optical hybrids. We show that the receiver can achieve colorless reception of fifty-five 112-Gb/s polarization-division-multiplexed quadrature-phase-shift-keyed (PDM-QPSK) channels with less than 1-dB penalty in the back-to-back operation. The receiver also works well in a long-haul wavelength-division-multiplexed (WDM) transmission system over 2560-km TrueWave® REACH fiber.

Entirely passive reach extended GPON using Raman amplification.

In previous investigation of extended GPON system, we employed 1240 nm and 1427 nm dual pumps within optical line terminal (OLT) equipments at central office (CO) to provide distributed Raman gains of upstream 1310 nm and downstream 1490 nm signals. These pump wavelengths were selected to ensure compatibility with the standard GPON wavelengths and reduce the unwanted pump-to-signal interactions. In this paper, we propose a new system scheme for an entirely-passive extended reach GPON to further enhance the system performance by eliminating the pump-to-signal interactions. In this scheme, a 1240 nm laser is employed to provide counter-pumping distributed Raman amplification of the upstream 1310 nm signal, and a discrete Raman amplifier is integrated with the 1490 nm transmitter to booster the downstream signal power and to improve the link loss budget. An operation over 60-km of zero-water-peak Allwave® fiber with a 1:128 way splitter is experimentally demonstrated at 2.5 Gbit/s. The system performance of such purely passive GPON extender is investigated in the paper. The system transmission limitation of upstream signal due to Raman ASE noises is discussed, and the non-linear impairment on downstream signal due to high launch power into feeder fiber is also examined.

Long distance transmission in few-mode fibers.

Using multimode fibers for long-haul transmission is proposed and demonstrated experimentally. In particular few-mode fibers (FMFs) are demonstrated as a good compromise since they are sufficiently resistant to mode coupling compared to standard multimode fibers but they still can have large core diameters compared to single-mode fibers. As a result these fibers can have significantly less nonlinearity and at the same time they can have the same performance as single-mode fibers in terms of dispersion and loss. In the absence of mode coupling it is possible to use these fibers in the single-mode operation where all the data is carried in only one of the spatial modes throughout the fiber. It is shown experimentally that the single-mode operation is achieved simply by splicing single-mode fibers to both ends of a 35-km-long dual-mode fiber at 1310 nm. After 35 km of transmission, no modal dispersion or excess loss was observed. Finally the same fiber is placed in a recirculating loop and 3 WDM channels each carrying 6 Gb/s BPSK data were transmitted through 1050 km of the few-mode fiber without modal dispersion.

Statistics of crosstalk in bent multicore fibers.

A statistical theory for crosstalk in multicore fibers is derived from coupled-mode equations including bend-induced perturbations. Bends are shown to play a crucial role in crosstalk, explaining large disagreement between experiments and previous calculations. The average crosstalk of a fiber segment is related to the statistics of the bend radius and orientation, including spinning along the fiber length. This framework allows efficient and accurate estimates of cross-talk for realistic telecommunications links.