Pan Cao

A High-Speed Second-Order Photonic Differentiator Based on Two-Stage Silicon Self-Coupled Optical Waveguide

In this paper, we propose and demonstrate an all-optical second-order differentiator based on a two-stage self-coupled optical waveguide on a silicon-on-insulator platform. The transmission spectrum of the fabricated device has a parabola-like filtering notch with a 3-dB bandwidth of up to ~ 100 GHz and a depth of ~ 12 dB. Experiments are carried out for 10-, 20-, and 40-Gb/s optical time-domain multiplexing (OTDM) picosecond pulse trains, and the second-order differentiations are achieved using the fabricated device.

Energy-efficient WDM-OFDM-PON employing shared OFDM modulation modules in optical line terminal

We propose and experimentally demonstrate a scheme to improve the energy efficiency of wavelength division multiplexing - orthogonal frequency division multiplexing - passive optical networks (WDM-OFDM-PONs). By using an N × M opto-mechanic switch in optical line terminal (OLT), an OFDM modulation module is shared by several channels to deliver data to multiple users with low traffic demands during non-peak hours of the day, thus greatly reducing the number of operating devices and minimizing the energy consumption of the OLT. An experiment utilizing one OFDM modulation module to serve three optical network units (ONUs) in a WDM-OFDM-PON is performed to verify the feasibility of our proposal. Theoretical analysis and numerical calculation show that the proposed scheme can achieve a saving of 23.6% in the energy consumption of the OFDM modulation modules compared to conventional WDM-OFDM-PON.

Simultaneous generation of independent wired and 60-GHz wireless signals in an integrated WDM-PON-RoF system based on frequency-sextupling and OCS-DPSK modulation

We propose a simple and cost-effective scheme to integrate a wavelength division multiplexed-passive optical network (WDM-PON) with a 60-GHz radio-over-fiber (RoF) system. In optical line terminal/central station (OLT/CS), 10-GHz electronic devices and single-drive Mach-Zehnder modulators (MZMs) are used to generate 60-GHz wireless signals based on frequency-sextupling and optical carrier suppression-differential phase shift keying (OCS-DPSK) modulation. By designing a new architecture, only N + 1 single-drive MZMs are required for an N-channel WDM-PON-RoF converged system. The proposed scheme is experimentally demonstrated with 1.25-Gb/s independent wired, wireless and upstream data. Error-free performances are achieved for all these signals after transmission of 25-km single mode fiber (SMF).

Compact tunable silicon photonic differential-equation solver for general linear time-invariant systems

We propose and experimentally demonstrate an all-optical temporal differential-equation solver that can be used to solve ordinary differential equations (ODEs) characterizing general linear time-invariant (LTI) systems. The photonic device implemented by an add-drop microring resonator (MRR) with two tunable interferometric couplers is monolithically integrated on a silicon-on-insulator (SOI) wafer with a compact footprint of ~60 μm × 120 μm. By thermally tuning the phase shifts along the bus arms of the two interferometric couplers, the proposed device is capable of solving first-order ODEs with two variable coefficients. The operation principle is theoretically analyzed, and system testing of solving ODE with tunable coefficients is carried out for 10-Gb/s optical Gaussian-like pulses. The experimental results verify the effectiveness of the fabricated device as a tunable photonic ODE solver.

Generation and transmission of multiband and multi-gigabit 60-GHz MMW signals in an RoF system with frequency quintupling technique.

We propose and experimentally demonstrate a cost-effective radio-over-fiber (RoF) system to simultaneously generate and transmit multiband and multi-gigabit 60-GHz millimeter wave (MMW) signals using frequency quintupling technique. Multiband signals at 56-GHz and 60-GHz are realized with two cascaded single-drive Mach-Zehnder modulators (MZMs), where phase control is not required. Furthermore, only low-frequency (≤12GHz) optical and electrical devices are used in the central station (CS), which enable a cost-effective system. At the user-terminal, two-stage down-conversions are employed by envelope detection (ED) and intermediate frequency (IF) mixing, eliminating expensive high-speed synthesizer and critical phase control components. Error-free performances are achieved for the multiband MMW signals after 50-km single-mode fiber (SMF) and 10-ft wireless link transmissions.

Compact on-chip 1 × 2 wavelength selective switch based on silicon microring resonator with nested pairs of subrings

We propose and experimentally demonstrate compact on-chip 1×2 wavelength selective switches (WSSs) based on silicon microring resonators (MRRs) with nested pairs of subrings (NPSs). Owing to the resonance splitting induced by the inner NPSs, the proposed devices are capable of performing selective channel routing at certain resonance wavelengths of the outer MRRs. System demonstration of dynamic channel routing using fabricated devices with one and two NPSs is carried out for 10  Gb/s non-return-to-zero signal. The experimental results verify the effectiveness of the fabricated devices as compact on-chip WSSs.

Reconfigurable and Scalable All-Optical VPN in WDM PON

In this letter, we propose and experimentally demonstrate an all-optical virtual private network (VPN) structure in a wavelength-division-multiplexed (WDM) passive optical network (PON). The scheme utilizes a semiconductor optical amplifier (SOA) in optical line terminal (OLT) to transfer optical VPN data among different optical network units (ONUs) based on the cross-gain-modulation (XGM) effect. By dynamically copying the optical VPN signal onto different wavelengths, the optical VPN can be reconfigured.

Energy-efficient optical network units for OFDM PON based on time-domain interleaved OFDM technique.

We propose and experimentally demonstrate a new scheme to reduce the energy consumption of optical network units (ONUs) in orthogonal frequency division multiplexing passive optical networks (OFDM PONs) by using time-domain interleaved OFDM (TI-OFDM) technique. In a conventional OFDM PON, each ONU has to process the complete downstream broadcast OFDM signal with a high sampling rate and a large FFT size to retrieve its required data, even if it employs a portion of OFDM subcarriers. However, in our scheme, the ONU only needs to sample and process one data group from the downlink TI-OFDM signal, effectively reducing the sampling rate and the FFT size of the ONU. Thus, the energy efficiency of ONUs in OFDM PONs can be greatly improved. A proof-of-concept experiment is conducted to verify the feasibility of the proposed scheme. Compared to the conventional OFDM PON, our proposal can save 17.1% and 26.7% energy consumption of ONUs by halving and quartering the sampling rate and the FFT size of ONUs with the use of the TI-OFDM technology.

Flexible and Concurrent All-Optical VPN in OFDMA PON

We propose and experimentally demonstrate a new scheme to support an all-optical virtual private network (VPN) in orthogonal frequency-division multiple-access passive optical networks (OFDMA PONs). In our scheme, VPN communications among optical network units (ONUs) are concurrent, where each ONU can simultaneously transmit/receive different VPN traffic to/from other ONUs. Therefore, VPN communications between any two ONUs can be achieved at any time. The bit rates of VPN traffic can be also flexibly adjusted by using dynamic OFDM subcarrier-allocation technique. The proposed scheme is experimentally demonstrated with 5-Gb/s downlink, 2-Gb/s uplink, and 2-Gb/s VPN OFDM signals. Error-free performances are obtained for all these signals after 25-km standard single-mode fiber (SSMF) transmission.

A bidirectional radio over fiber system with multiband-signal generation using one single-drive MZM

We propose and experimentally demonstrate a simple and cost-effective bidirectional radio-over-fiber (RoF) system for transmission of downstream multiband signals and upstream data. At the central station (CS), the multiband data consisting of baseband, micro-wave (MW) and millimeter-wave (MMW) signals are generated using only one single-drive x-cut Mach-Zehnder modulator (MZM), which is driven by a clock signal at radio frequency (RF) port and an electrical data at bias port. Upstream data transmission is realized by re-modulation of filtered frequency-shift-keying (FSK) signal, selected from the multiband signals.