Simin Chen

1-Tb/s single-channel coherent optical OFDM transmission over 600-km SSMF fiber with subwavelength bandwidth access

A 1-Tb/s single-channel coherent optical OFDM (CO-OFDM) signal consisting of continuous 4,104 spectrally-overlapped subcarriers is generated using a novel device of recirculating frequency shifter (RFS). The RFS produces 320.6-GHz wide spectrum using a single laser with superior flatness and tone-to-noise ratio (TNR). The 1-Tb/s CO-OFDM signal is comprised of 36 uncorrelated orthogonal bands achieved by adjusting the delay of the RFS to an integer number of OFDM symbol periods. The 1- Tb/s CO-OFDM signal with a spectral efficiency of 3.3 bit/s/Hz is successfully received after transmission over 600-km SSMF fiber without either Raman amplification or dispersion compensation.

1-Tb/s Single-Channel Coherent Optical OFDM Transmission With Orthogonal-Band Multiplexing and Subwavelength Bandwidth Access

A 1-Tb/s single-channel coherent optical OFDM (CO-OFDM) signal consisting of continuous 4104 spectrally-overlapped subcarriers is generated using a recirculating frequency shifter (RFS). Theoretical and experimental analysis of the RFS is performed to study its effectiveness in extending OFDM bandwidth. In particular, the RFS produces a 320.6-GHz wide frequency comb from a single laser with superior flatness and tone-to-noise ratio (TNR). The 1-Tb/s CO-OFDM signal is consisted of 36 uncorrelated orthogonal bands achieved by adjusting the delay of the RFS to an integer number of OFDM symbol periods. The 1-Tb/s CO-OFDM signal with a spectral efficiency of 3.3 bit/s/Hz is successfully received after transmission over 600-km SSMF fiber without either Raman amplification or dispersion compensation.

1-Tb/s per channel coherent optical OFDM transmission with subwavelength bandwidth access

1-Tb/s per channel coherent optical OFDM transmission over 600-km SSMF fiber is demonstrated assisted with a recirculating frequency shifter. Record spectral efficiency and transmission reach is achieved at 1-Tb/s channel rate without Raman amplification.

Dual-LP 11 mode 4x4 MIMO-OFDM transmission over a two-mode fiber

We report successful transmission of dual-LP(11) mode (LP(11a) and LP(11b)), dual polarization coherent optical orthogonal frequency-division multiplexing (CO-OFDM) signals over two-mode fibers (TMF) using all-fiber mode converters. Mode converters based on mechanically induced long-period grating with better than 20 dB extinction ratios are realized and used for interfacing single-mode fiber transmitter and receivers to the TMF. We demonstrate that by using 4×4 MIMO-OFDM processing, the random coupling of the two LP(11) spatial modes can be successfully tracked and equalized with a one-tap frequency-domain equalizer. We achieve successful transmission of 35.3 Gb/s over 26-km two-mode fiber with less than 3 dB penalty.

Real-time reception of multi-gigabit coherent optical OFDM signals.

Coherent Optical OFDM (CO-OFDM) has been demonstrated for delivering superior performance in spectral efficiency, receiver sensitivity, and polarization-dispersion resilience. Fueled by the rapid advancement in semiconductor technology, high-speed field-programmable gate arrays (FPGA) and analogue-to-digital-converters/digital-to-analogue converters (ADC/DACs) have been increasingly adopted for digital signal processing in optical communications. In this paper, we report the first FPGA-based real-time implementation of coherent optical OFDM (CO-OFDM) receiver with a transmission rate up to 3.1 Gb/s. Several basic aspects of CO-OFDM signal processing are described in detail, and the BER sensitivity performance are evaluated in real-time. To the best of our knowledge, we have achieved the record real-time reception date rate for a single-input single-output (SISO) coherent OFDM signal, in either RF domain or optical domain.

Reception of Dual-Spatial-Mode CO-OFDM Signal Over a Two-Mode Fiber

We demonstrate the use of mechanical grating based mode converters to achieve two forms of dual-spatial-mode transmission: LP₀₁ and LP₁₁, and dual LP₀₁ modes. High modal extinction ratio (>; 20 dB) is shown for the mode converter within a 10-nm wavelength range. We first present 107-Gb/s coherent optical OFDM (CO-OFDM) transmission over a 4.5-km two-mode fiber using LP₀₁ and LP₁₁ modes where the mode separation is performed optically. We then show 58.8-Gb/s CO-OFDM transmission using dual LP₁₁ modes where the mode separation is achieved via 4 × 4 electronic MIMO processing.

Real-Time Multi-Gigabit Receiver for Coherent Optical MIMO-OFDM Signals

In this paper we implement a first multi-gigabit real-time dual-polarization CO-OFDM receiver in a 2 times 2 multiple-input multiple-output (MIMO) configuration. The experimental setup consists of four 1.5 Giga samples per second (GS/s) high-speed analog-to-digital converters (ADC) and one Stratix III field-programmable gate array (FPGA). The signal streams are processed in real-time mode, and the data rates of 3.33 Gb/s and 6.67 Gb/s are realized for 4-QAM and 16-QAM, respectively.

Statistical moments-based OSNR monitoring for coherent optical systems

We present a novel statistical moments-based method for optical signal-to-noise ratio (OSNR) monitoring in polarization-multiplexed (pol-mux) coherent optical systems. This technique only requires the knowledge of the envelope of the equalized signal before phase correction, which can be achieved by using any two arbitrary statistical moments, and it is suitable for both constant and non-constant modulus modulation formats. The proposed estimation method is experimentally demonstrated for 10-Gbaud pol-mux coherent systems using QPSK and 16-QAM. Additionally, numerical simulations are carried out to demonstrate 20-Gbaud systems using 16-QAM and 64-QAM. The results show that the OSNR can be estimated accurately over a wide range of values for QPSK, 16-QAM or 64-QAM systems up to 1920-km long and with up to 50-ps all-order polarization mode dispersion. By setting a proper reference value for calibration, the proposed algorithm also shows good tolerance when the received signal is not well compensated.

Data-Aided Chromatic Dispersion Estimation for Polarization Multiplexed Optical Systems

We propose a full transmission link chromatic dispersion (CD) estimation technique for polarization-multiplexed coherent optical single carrier system using data-aided channel estimation and least square quadratic fit. New training sequences based on Chu sequence and Golay complementary pair are designed and compared for estimation performance against the ideal full-level Chu sequence for both QPSK and 16-QAM systems. The proposed technique is demonstrated in a 40-Gb/s coherent polarization multiplexed optical system over 2080-km fiber transmission for QPSK format and 80-Gb/s system over 1800-km fiber for 16-QAM format to verify its accurate and robust estimation performance.

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Owing to its low transmitter complexity and low sensitivity to nonlinear impairments, phase noise, and frequency offset, the single carrier system with frequency domain equalization (SC-FDE) is of interest for high-bit-rate optical transmission. In this letter, we experimentally demonstrate a 8×40-Gb/s optical coherent polarization-multiplexed SC-FDE over 2080-km fiber transmission using novel training sequences. The sequences are designed based on Chu and Golay complementary sequences to have binary levels and are fully compatible with the commercial quadrature phase-shift keying (QPSK) systems. The use of these training sequences helps achieve accurate channel estimation and equalization in full-system demonstration.