Zhengxuan Li

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.

Compatible TDM/WDM PON Using a Single Tunable Optical Filter for Both Downstream Wavelength Selection and Upstream Wavelength Generation

We propose a hybrid time-division multiplexing/wavelength-division multiplexing passive optical network (TDM/WDM-PON) architecture compatible with the traditional TDM-PON configuration using a power splitter in the remote node. A tunable optical filter (TOF) is used to select the downstream wavelength in each optical network unit. Meanwhile, the TOF plays a second role of seeding a reflective semiconductor optical amplifier (RSOA) so as to construct a tunable fiber-ring laser as colorless upstream source. A stable performance is observed for the upstream laser source tuned from 1535 to 1565 nm and with a modulation data rate of 1.25 Gb/s. The upstream wavelength has a offset with the central wavelength of the TOF when the RSOA is biased at its saturation region, which mitigates the Rayleigh backscattering and back reflection-induced crosstalk in single-fiber bidirectional PON systems.

28 Gb/s duobinary signal transmission over 40 km based on 10 GHz DML and PIN for 100 Gb/s PON

In this paper, we demonstrate the direct modulation and direct detection of 28-Gb/s duobinary signal for the future downstream capacity upgrade in next generation passive optical network (PON). Commercial 10-GHz directly modulated laser (DML) and PIN with a combined modulation bandwidth of ~7 GHz are used as transmitter and receiver respectively. In order to mitigate the chromatic dispersion induced signal distortion, an optical delay interferometer (DI) is employed to narrow down the signal spectrum, thereby realizing 40-km single mode fiber (SMF) transmission in C-band. Besides, the chirp-induced spectral broadening of the directly modulated signal enables a higher launch power than external modulation schemes, which increases the loss budget of the system. As a result, 31-dB loss budget is achieved, supporting 64 users with 40-km reach. Also, as the transceivers in both optical line terminal (OLT) and optical network unit (ONU) are commercial l0-GHz devices, the proposed scheme is compatible with 40-Gb/s time and wavelength division multiplexing passive optical network (TWDM-PON) systems, providing a cost-efficient alternative for the development of 100G PON.

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.

100-Gb/s TWDM-PON based on 10G optical devices.

High speed data modulation based on bandwidth limited devices has been considered as a cost-effective way to upgrade 10G-EPON to the next generation 100G-EPON. In this paper, we experimentally demonstrate the modulation, fiber transmission and reception of 25-Gb/s signal based on directly modulated laser and photo-detector both operating at 10 GHz. Instead of digital signal processing, the chirp management, dispersion compensation and frequency equalization in our scheme are realized in optical domain using a single delay interferometer. Three popular formats are investigated, including NRZ-OOK, PAM-4 and duobinary. According to the experimental results, the NRZ-OOK format shows its superiority in both launch power and receiver sensitivity, which provides a cost-effective solution for the construction of 100-Gb/s TWDM-PON.

Upstream capacity upgrade in TDM-PON using RSOA based tunable fiber ring laser

An upstream multi-wavelength shared (UMWS) time division multiplexing passive optical network (TDM-PON) is presented by using a reflective semiconductor amplifier (RSOA) and tunable optical filter (TOF) based directly modulated fiber ring laser as upstream laser source. The stable laser operation is easily achieved no matter what the bandwidth and shape of the TOF is and it can be directly modulated when the RSOA is driven at its saturation region. In this UMWS TDM-PON system, an individual wavelength can be assigned to the user who has a high bandwidth demand by tuning the central wavelength of the TOF in its upgraded optical network unit (ONU), while others maintain their traditional ONU structure and share the bandwidth via time slots, which greatly and dynamically upgrades the upstream capacity. We experimentally demonstrated the bidirectional transmission of downstream data at 10-Gb/s and upstream data at 1.25-Gb/s per wavelength over 25-km single mode fiber (SMF) with almost no power penalty at both ends. A stable performance is observed for the upstream wavelength tuned from 1530 nm to 1595 nm. Moreover, due to the high extinction ratio (ER) of the upstream signal, the burst-mode transmitting is successfully presented and a better time-division multiplexing performance can be obtained by turning off the unused lasers thanks to the rapid formation of the laser in the fiber ring.

Symmetric 40-Gb/s TWDM-PON with 51-dB loss budget by using a single SOA as preamplifier, booster and format converter in ONU.

In this paper, we propose to use a semiconductor optical amplifier (SOA) in the optical network unit (ONU) to improve the loss budget in time and wavelength division multiplexed-passive optical network (TWDM-PON) systems. The SOA boosts the upstream signal to increase the output power of the electro-absorption modulated laser (EML) and simultaneously pre-amplifies the downstream signal for sensitivity improvement. The penalty caused by cross gain modulation (XGM) effect is negligible due to the low extinction ratio (ER) of upstream signal and the large wavelength difference between upstream and downstream links. In order to achieve a higher output power, the SOA is driven into its saturation region, where the self-phase modulation (SPM) effect converts the intensity into phase information and realizes on-off-keying (OOK) to phase-shifted-keying (PSK) format conversion. In this way, the pattern effect is eliminated, which releases the requirement of gain-clamping on SOA. To further improve the loss budget of upstream link, an Erbium doped fiber amplifier (EDFA) is used in the optical line terminal (OLT) to pre-amplify the received signal. For the downstream direction, directly modulated laser (DML) is used as the laser source. Taking advantage of its carrier-less characteristic, directly modulated signal shows high tolerance to fiber nonlinearity, which could support a downstream launch power as high as + 16 dBm per channel. In addition, the signal is pre-amplified by the SOA in ONU before being detected, so the sensitivity limitation for downstream link is also removed. As a result, a truly passive symmetric 40-Gb/s TWDM-PON was demonstrated, achieving a link loss budget of 51 dB.

Upstream dispersion management supporting 100 km differential reach in TWDM-PON.

An optical dispersion compensator (ODC) with negative dispersion value in optical line terminal (OLT) is proposed to manage the chromatic dispersion of 10 Gb/s upstream directly-modulated signals from users with 100 km differential distances, achieving a maximal 51.9 dB loss budget thanks to the positive chirp of the directly-modulated signals and the characteristics of access networks that lower loss budget is required for the users at shorter transmission distance. The optimal dispersion value of the ODC is determined by the maximal distance of the users and the objective is to guarantee the loss budget monotonically improved with the increase of reach, therefore supporting differential reach. Experimental results show that it is a potential solution for practical implementation of long-reach and high splitting-ratio time and wavelength division multiplexed passive optical network (TWDM-PON).

Mitigation of reflection-induced crosstalk in multi-wavelength TDM-PON using spectral red-shifted, tunable fiber ring laser based upstream source

We proposed a gain-saturated RSOA and TOF based spectral red-shifted, directly-modulated tunable fiber ring laser as upstream laser source to suppress the reflection-induced crosstalk in a single-fiber bidirectional multi-wavelength TDM-PON system.