Meihua Bi

Symmetric 40-Gb/s TWDM-PON With 39-dB Power Budget

Time- and wavelength-division multiplexed passive optical network (TWDM-PON) has been selected by full service access networks as a primary solution for next generation PON stage 2 in April 2012. In this letter, we propose and demonstrate a symmetric 40-Gb/s TWDM-PON with 39-dB power budget. A reflective semiconductor optical amplifier is used in optical network unit as a pre-amplifier to enhance the sensitivity of downstream signals. For the upstream direction, a thermally-tuned directly modulated laser with 10-Gb/s modulation rate is used as upstream colorless source, and a chirp management filter is employed in optical line terminal to mitigate chromatic dispersion therefore enabling fiber transmission. Symmetric 40-Gb/s TWDM-PON is experimentally demonstrated with a power budget of 39 dB, which could support 25-km fiber transmission and 1:1000 splitting ratio.

A Sensitivity-Enhanced Refractive Index Sensor Using a Single-Mode Thin-Core Fiber Incorporating an Abrupt Taper

A sensitivity-enhanced fiber-optic refractive index (RI) sensor based on a tapered single-mode thin-core diameter fiber is proposed and experimentally demonstrated. The sensor head is formed by splicing a section of tapered thin-core diameter fiber (TCF) between two sections of single-mode fibers (SMFs). The cladding modes are excited at the first SMF-TCF interface, and then interfere with the core mode at the second interface, thus forming an inter-modal interferometer (IMI). An abrupt taper (tens of micrometers long) made by the electric-arc-heating method is utilized, and plays an important role in improving sensing sensitivity. The whole manufacture process only involves fiber splicing and tapering, and all the fabrication process can be achieved by a commercial fiber fusion splicer. Using glycerol and water mixture solution as an example, the experimental results show that the refractive index sensitivity is measured to be 0.591 nm for 1% change of surrounding RI. The proposed sensor structure features simple structure, low cost, easy fabrication, and high sensitivity.

Experimental Demonstration of Symmetric 100-Gb/s DML-Based TWDM-PON System

In this letter, first, the symmetric 100-Gb/s time and wavelength-division-multiplexed passive optical network system is experimentally demonstrated, based on the directly modulated lasers (DMLs) modulated by 25-Gb/s none-return-to-zero signals. A bypass delay interferometer (DI) is deployed in the optical line terminal to mitigate the signal distortion caused by the DML chirp and fiber chromatic dispersion. The experimental results show that with the DI, error free transmission is achieved over 25-km single mode fiber with a power budget of 42 dB, which could support 1:1024 splitting ratio. Moreover, the transmission performance of differential fiber length and burst-mode operation is also investigated.

Simultaneous DPSK demodulation and chirp management using delay interferometer in symmetric 40-Gb/s capability TWDM-PON system.

We propose a symmetric 40-Gb/s aggregate rate time and wavelength division multiplexed passive optical network (TWDM-PON) system with the capability of simultaneous downstream differential phase shift keying (DPSK) signal demodulation and upstream signal chirp management based on delay interferometer (DI). With the bi-pass characteristic of DI, we experimentally demonstrate the bidirectional transmission of signals at 10-Gb/s per wavelength, and achieve negligible power penalties after 50-km single mode fiber (SMF). For the uplink transmission with DI, a ~11-dB optical power budget improvement at a bit error ratio of 1e-3 is obtained and the extinction ratio (ER) of signal is also improved from 3.4 dB to 13.75 dB. Owing to this high ER, the upstream burst-mode transmitting is successfully presented in term of time-division multiplexing. Moreover, in our experiment, a ~38-dB power budget is obtained to support 256 users with 50-km SMF transmission.

Symmetric 40-Gb/s, 100-km Passive Reach TWDM-PON with 53-dB Loss Budget

A truly passive long-reach, symmetric 40-Gb/s time and wavelength division multiplexed passive optical network (TWDM-PON) with a high loss budget is demonstrated, using direct modulation and direct detection in both upstream and downstream directions. Thermally tuned directly modulated lasers (DMLs) are employed to serve as both upstream and downstream transmitters, not only owing to their low cost, but also, as a carrier-less modulation method, where the signal generated by direct modulation is demonstrated to be more robust to high launch power induced fiber nonlinearities compared with external intensity modulation formats with strong carrier power. Therefore, DML is suitable for applying in TWDM-PON to achieve a high loss budget. Moreover, the frequency chirp induced dispersion of directly-modulated signal is managed thanks to the combination of optical spectral reshaping and dispersion supported transmission effects, which makes it possible for the directly-modulated signal to reach a distance of 100 km and still with a good quality. As a result, a system loss budget of 53 dB is achieved, supporting more than 1000 users with 100-km purely passive reach, which is the first demonstration of high loss budget, long reach TWDM-PONs to our best knowledge.

An upstream multi-wavelength shared PON based on tunable self-seeding Fabry-Pérot laser diode for upstream capacity upgrade and wavelength multiplexing

We proposed an Upstream Multi-Wavelength Shared (UMWS) PON architecture based on a tunable self-seeding Fabry-Perot laser diode (FP-LD) at ONU. The performances of the wavelength and power stability, side-mode suppression ratio (SMSR), tuning range for the proposed tunable self-seeding laser module at ONU are experimentally investigated. The BER is measured with direct modulation on FP-LD of 1.25 Gbps upstream data. The extensive simulations not only evaluate the enhanced performance from the upstream wavelength-sharing, but also for the first time investigate the impact of channel Switch Latency (SL) on the network performance.

Performance Analysis of Space-Diversity Free-Space Optical Links Over Exponentiated Weibull Channels

We propose a simple analytical method for evaluating the average bit-error rate (BER) performance of multiple input multiple output (MIMO) free-space optical (FSO) communication systems over independent exponentiated Weibull (EW) channels. We first present an accurate approximation to the probability density function (PDF) of the sum of independent EW random variables corresponding to the EW-distributed FSO channel fading. Then, a closed-form expression for the BER of MIMO FSO systems using ON-OFF keying is derived based on the obtained PDF. The proposed method is validated through comparing the BER results obtained by the analytical calculation and the Monte Carlo simulation.

Single LED Beacon-Based 3-D Indoor Positioning Using Off-the-Shelf Devices

In this paper, we demonstrate a single light-emitting diode (LED) beacon-based 3-D indoor positioning scheme by experiment and theoretical derivation, which can overcome the limitation of multiple LED beacons involved in one positioning process. Only off-the-shelf devices are employed in this scheme, such as an image sensor, a gyroscope, and a photodiode, which have been integrated in most of commercial available smartphones so that it is compatible with most of mobile terminals. Moreover, with these simple devices, we estimate the 3-D position by using the received-signal-strength (RSS) and angle-of-arrival (AoA)-based hybrid positioning algorithm. The performance of this scheme is investigated in scenarios of the ceiling-mounted and the wall-mounted LED. The corresponding results show that, by using this scheme, 7.3 cm and 67.2 cm mean positioning errors are achieved in the ceiling and the wall LED cases, respectively. Therefore, this scheme may be considered as one of the competitive indoor positioning candidates in the future.

Cladding-Mode Backward-Recoupling-Based Displacement Sensor Incorporating Fiber Up Taper and Bragg Grating

A temperature-insensitive fiber-optic displacement sensing scheme by cascading the fiber up taper and Bragg grating is experimentally demonstrated. The strength-robust up taper, which is fabricated by excessively splicing the Bragg grating to the interrogation fiber, functions as the bridge between the core mode and the cladding modes. This cascading structure realizes the cladding-mode backward recoupling, and displacement information can be directly read out by measuring the power of the highly bending sensitive recoupled cladding modes. Two sensing configurations that respectively utilize the normal fiber Bragg grating (FBG) and the uniform chirped FBG (CFBG) for the cladding-mode backward recoupling have been studied contrastively, in which the tunability of the up taper is fully validated to support a better dynamic range of the measurement. Aiming to improve the low reflection power and enhance the sensing sensitivity, the CFBG is used, and the reflection power is increased by more than 200 times and reaches 176 μW, which lowers the precision requirement for the optical power meter and potentially reduces the cost of the sensing system.

Suppression of SRS induced crosstalk in RF-video overlay TWDM-PON system using dicode coding

In this paper, we investigate the nonlinear Raman crosstalk in RF-video overlay time and wavelength division multiplexed passive optical network (TWDM-PON), and propose a novel spectrum-reshaping method based on dicode coding to mitigate this crosstalk. The dicode coding features ultra-low power spectral density in the low frequency region, which can reduce the nonlinear Raman crosstalk on the RF-video signal effectively. Experimental results show that, compared with traditional non-return-to-zero on-off keying (NRZ-OOK) signals, the crosstalk on RF-video signal can be reduced by 10 ~14 dB when the launch power per TWDM-PON channel varies from 10-dBm to 15-dBm. The transmission of 10-Gb/s dicode signal over 20-km standard single mode fiber (SSMF) is also demonstrated with the receiver sensitivity of -31 dBm at bit error ratio (BER) of 3.8e-3.