Zhao Zhou

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.

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.

A Tunable Encoder/Decoder Based on Polarization Modulation for the SAC-OCDMA PON

We propose a tunable encoder/decoder based on polarization modulation for the spectrum amplitude coded-optical code-division multiple access (SAC-OCDMA) passive optical network (PON) and experimentally demonstrate its coding/decoding performance for the first time. The experiment result verifies that the encoder/decoder with 40-dB blocking ratio can fully suppress the unwanted spectral slices and performs good coding/decoding capability. Code length of 45 and code weight of 9 are demonstrated for proof-of-concept.

Self-interference cancellation using dual-drive Mach-Zehnder modulator for in-band full-duplex radio-over-fiber system

In this paper, we design a self-interference cancellation (SIC) scheme for in-band full-duplex (IBFD) radio-over-fiber (RoF) systems based on wavelength division multiplexing passive optical network (WDM-PON) architectures. By using a single dual-drive Mach-Zehnder modulator (DDMZM), over various bands up to 25 GHz, this proposed SIC system can simultaneously cancel the in-band downlink (DL) self-interference and modulate the recovered uplink (UL) radio frequency (RF) signal. OFDM-RF signals are used to study the cancellation performances of optical SIC system for the first time. Experimental results show more than 32-dB cancellation depth over 250-MHz bandwidth within 1-GHz RF band, as well as 300-MHz within 2.4-GHz and 400-MHz within 5-GHz band. As for 2.4-GHz RF band, 390.63-Mbps 16-QAM OFDM UL signal buried by strong in-band DL OFDM signal is well recovered. For broadband applications, more than 27-dB cancellation depth is achieved over 10 MHz~25 GHz wideband, so that up to 25 GHz RF band can be expanded for this IBFD WDM-RoF system.

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.

Directly modulated laser-based optical radio frequency self-interference cancellation system

Abstract. We propose a microwave photonics system for radio frequency self-interference cancellation using optical techniques. With a simple structure, this system employs two low-cost directly modulated lasers and a balanced photodetector to subtract the strong self-interference signal from a corrupted received signal. For commonly used wireless applications, 40-dB cancellation within 900-MHz band and 33-dB cancellation within 2.4-GHz band are experimentally obtained, both over 400-MHz bandwidth. Moreover, for ultra-wideband cancellation, this system achieves more than 27-dB cancellation over 6-GHz bandwidth. The experimental results show good recovery of the weak signal of interest buried by strong self-interference after the cancellation.

A new symbol timing synchronization scheme for direct modulation optical OFDM PON

A new symbol timing synchronization scheme based on a tailored training sequence is proposed and implemented in direct modulation and direct detection optical OFDM PON (DM-DD OFDM PON) systems. This tailored training sequence is added in front of OFDM data symbols. By using the received signal correlation operation, receiver calculates the peak value of metrics to achieve accurate symbol timing synchronization. The performance of this new timing synchronization scheme is presented by simulation and experiment. The results show that the proposed scheme has high synchronization accuracy and is suit for DM-DD OFDM PON system.

25-GHz-Spaced DWDM-PON With Mitigated Rayleigh Backscattering and Back-Reflection Effects

A novel 25-GHz-spaced dense wavelength-division multiplexing passive optical network (DWDM-PON) is proposed to improve the utilization of wavelength resource and mitigate the Rayleigh backscattering (RB) and back-reflection effects. A colorless optical network unit (ONU) is realized by remodulating the downstream (DS) signal via a gain-saturated reflective semiconductor optical amplifier (RSOA). Due to the simple interconnecting architecture at the remote node (RN), the DS and upstream (US) signals in each feed fiber (FF) are carried on different channels. Therefore, the RB and back-reflection effects are significantly reduced. The feasibility and merits of the proposed system are experimentally demonstrated with the error-free transmission of 10-Gb/s DS and 1.25-Gb/s US signals over a 25-km single-mode fiber.

Survivable wavelength-division multiplexing passive optical network system with centralized protection routing scheme and efficient wavelength utilization

Abstract. A survivable wavelength-division multiplexing passive optical network (WDM-PON) with centralized protection scheme and colorless optical network units is proposed. The sideband channels generated via optical carrier suppression technique are used to carry both the downstream (DS) and the upstream (US) remodulated signals for two neighboring sub-PONs. By employing alternate path routing of sideband channels, the centralized protection scheme can provide reliable protection against any failure in feed fibers, remote node, and distribution fibers. The number of extra fibers is greatly reduced, and efficient utilization of wavelength resource is achieved. The feasibility of the proposed system is verified by 10-Gb/s DS and 1.25-Gb/s US signals over 25-km single-mode fiber transmission in both working and protection modes.

A greedy scheduling algorithm for resource assignment in OFDMA-PON

We design a greedy scheduling algorithm for resource assignment in OFDMA-PON, which makes one of the best choices at every step. The proposed algorithm demonstrates high channel utilization and less Total Grant Time.