Showing papers by "Leimeng Zhuang published in 2017"
TL;DR: In this article, the use of a low-loss, high-index-contrast stoichiometric silicon nitride waveguide is presented as a practical material platform for realizing high-performance optical signal processors and points toward photonic RF filters with digital signal processing level flexibility, hundreds-GHz bandwidth, MHz-band frequency selectivity, and full system integration on a chip scale.
Abstract: Integrated optical signal processors have been identified as a powerful engine for optical processing of microwave signals. They enable wideband and stable signal processing operations on miniaturized chips with ultimate control precision. As a promising application, such processors enables photonic implementations of reconfigurable radio frequency (RF) filters with wide design flexibility, large bandwidth, and high-frequency selectivity. This is a key technology for photonic-assisted RF front ends that opens a path to overcoming the bandwidth limitation of current digital electronics. Here, the recent progress of integrated optical signal processors for implementing such RF filters is reviewed. We highlight the use of a low-loss, high-index-contrast stoichiometric silicon nitride waveguide which promises to serve as a practical material platform for realizing high-performance optical signal processors and points toward photonic RF filters with digital signal processing (DSP)-level flexibility, hundreds-GHz bandwidth, MHz-band frequency selectivity, and full system integration on a chip scale.
45 citations
TL;DR: It is shown that the logic resource occupation of L/E-ACO-OFDM transmitter is almost the same as that of DC-biased OFDM transmitter when they achieve the same spectral efficiency, proving its great potential to be used in a real-time short-haul optical transmission link.
Abstract: Layered/enhanced ACO-OFDM is a promising candidate for intensity modulation and direct-detection based short-haul fiber-optic links due to its both power and spectral efficiency. In this paper, we firstly demonstrate a hardware-efficient real-time 9.375 Gb/s QPSK-encoded layered/enhanced asymmetrical clipped optical OFDM (L/E-ACO-OFDM) transmitter using a Virtex-6 FPGA. This L/E-ACO-OFDM signal is successfully transmitted over 20-km uncompensated standard single-mode fiber (S-SMF) using a directly modulated laser. Several methods are explored to reduce the FPGA’s logic resource utilization by taking advantage of the L/E-ACO-OFDM’s signal characteristics. We show that the logic resource occupation of L/E-ACO-OFDM transmitter is almost the same as that of DC-biased OFDM transmitter when they achieve the same spectral efficiency, proving its great potential to be used in a real-time short-haul optical transmission link.
20 citations
TL;DR: In this article, the importance of the order of components such as modulators, delays, and filters within these circuits is stressed, as simple changes to the circuit topology have significant impacts on the spectra of the signals, and the required bandwidths of the modulators.
Abstract: Photonic circuits are the key to advanced functionality in future optical systems, as they efficiently process terabit/s data streams. This paper reviews how photonic circuit topologies have evolved to support high-spectral efficiency modulation formats, including: all-optical optical frequency division multiplexing (AO-OFDM), discrete Fourier transform spread OFDM (DFT-S-OFDM), Nyquist wavelength division multiplexing, (NWDM), orthogonal time division multiplexing (OrthTDM, OTDM), chirped-OFDM, and quasi-Nyquist signals. The importance of the order of components such as modulators, delays, and filters within these circuits is stressed, as simple changes to the circuit topology have significant impacts on the spectra of the signals, and the required bandwidths of the modulators.
15 citations
TL;DR: This work addresses comb spectrum processing on an integrated platform, pointing towards a device-compact solution for optical clock multipliers (frequency comb filters) which have diverse applications ranging from photonic-based RF spectrum scanners and photonic radars to GHz-granularity WDM switches and LIDARs.
Abstract: We report a photonic integrated circuit implementation of an optical clock multiplier, or equivalently an optical frequency comb filter. The circuit comprises a novel topology of a ring-resonator-assisted asymmetrical Mach-Zehnder interferometer in a Sagnac loop, providing a reconfigurable comb filter with sub-GHz selectivity and low complexity. A proof-of-concept device is fabricated in a high-index-contrast stoichiometric silicon nitride (Si3N4/SiO2) waveguide, featuring low loss, small size, and large bandwidth. In the experiment, we show a very narrow passband for filters of this kind, i.e. a −3-dB bandwidth of 0.6 GHz and a −20-dB passband of 1.2 GHz at a frequency interval of 12.5 GHz. As an application example, this particular filter shape enables successful demonstrations of five-fold repetition rate multiplication of optical clock signals, i.e. from 2.5 Gpulses/s to 12.5 Gpulses/s and from 10 Gpulses/s to 50 Gpulses/s. This work addresses comb spectrum processing on an integrated platform, pointing towards a device-compact solution for optical clock multipliers (frequency comb filters) which have diverse applications ranging from photonic-based RF spectrum scanners and photonic radars to GHz-granularity WDM switches and LIDARs.
14 citations
TL;DR: An integrated tunable delay line is reported that overcomes the delay-dependent loss, and simultaneously allows for independent manipulation of group delay and amplitude responses, serving as a novel building block for creating chip-scale programmable optical signal processors.
Abstract: Optical delay lines implemented in photonic integrated circuits (PICs) are essential for creating robust and low-cost optical signal processors on miniaturized chips. In particular, tunable delay lines enable a key feature of programmability for the on-chip processing functions. However, the previously investigated tunable delay lines are plagued by a severe drawback of delay-dependent loss due to the propagation loss in the constituent waveguides. In principle, a serial-connected amplifier can be used to compensate such losses or perform additional amplitude manipulation. However, this solution is generally unpractical as it introduces additional burden on chip area and power consumption, particularly for large-scale integrated PICs. Here, we report an integrated tunable delay line that overcomes the delay-dependent loss, and simultaneously allows for independent manipulation of group delay and amplitude responses. It uses a ring resonator with a tunable coupler and a semiconductor optical amplifier in the feedback path. A proof-of-concept device with a free spectral range of 11.5 GHz and a delay bandwidth in the order of 200 MHz is discussed in the context of microwave photonics and is experimentally demonstrated to be able to provide a lossless delay up to 1.1 to a 5 ns Gaussian pulse. The proposed device can be designed for different frequency scales with potential for applications across many other areas such as telecommunications, LIDAR, and spectroscopy, serving as a novel building block for creating chip-scale programmable optical signal processors.
13 citations
TL;DR: This letter proposes using pairwise coding within each layer to improve the bit error rate in layered/enhanced asymmetrically clipped optical OFDM (ACO-OFDM), and finds a 3.6-dB improvement in the $Q^{2}$ -factor.
Abstract: Dispersion-induced power fading in intensity modulated direct-detection systems degrades the higher frequency subcarriers’ signal qualities. In layered/enhanced asymmetrically clipped optical OFDM (ACO-OFDM), which is a spectrally efficient version of ACO-OFDM, the error propagation in the iterative decoding can further degrade the performance, especially when a low bias current is used for the directly modulated laser. In this letter, we propose using pairwise coding within each layer to improve the bit error rate. We transmitted ~5-GBb 16-QAM OFDM signals over a 19.8-km single mode fiber, and found a 3.6-dB improvement in the $Q^{2}$ -factor.
13 citations
TL;DR: Although the ASE-DMT transmitter requires multiple IFFTs, it is shown how these can be mapped onto a single IFFT, by using both the real and imaginary outputs of the IffT and by extracting some signals from within the IFTT's structure.
Abstract: Increasing the power and spectral efficiency in intensity-modulated direct-detection short-haul fiber-optic links enables higher data rates in power- and bandwidth-limited optical communication systems. Augmented spectral efficiency discrete multi-tone (ASE-DMT) can improve the spectral efficiency of pulse-amplitude-modulated DMT while maintaining its power advantage over dc-biased DMT, whose transmitter requires only one inverse fast Fourier transform (IFFT) with Hermitian symmetric inputs. Although the ASE-DMT transmitter requires multiple IFFTs, we show how these can be mapped onto a single IFFT, by using both the real and imaginary outputs of the IFFT and by extracting some signals from within the IFFT's structure. Using only one IFFT, we first demonstrate a real-time PAM4-encoded optical ASE-DMT transmitter with a net data rate of 18.4 Gb/s. When implemented in a FPGA, using a single IFFT saves 30% of logic resources, compared with a four-IFFT ASE-DMT transmitter. Finally, a 1550-nm directly modulated laser is used to evaluate its optical transmission performance with offline signal processing in the receiver. Without using any optical amplifiers, the ASE-DMT signal can be successfully transmitted over 10-km standard single-mode fiber (SSMF), but fails over 20-km SSMF due to the influence of fiber dispersion and laser chirp.
6 citations
TL;DR: An integrated microwave photonic method of a binary-phase-coded millimeter-wave signal generation with potential for full integration and low cost fabrication is presented, which points to the realization of a chip-scale flexible millimeter -wave signal generator.
Abstract: Phase-coded radio frequency (RF) pulses are widely adopted for radar systems as an effective signal format to enable high-range resolution. However, generating such signals conventionally requires high-speed electronics and complex RF circuitry that impose burdens on the system cost and power consumption. In particular, modern radar systems desire features such as high frequencies, e.g., in the millimeter-wave region, high compactness, and high system flexibility, which pose great challenges for the conventional all-electronics solutions. In contrast, integrated microwave photonics opens a way to solutions that are able to provide those features simultaneously, together with potential for full integration and low cost fabrication. Here, we present an integrated microwave photonic method of a binary-phase-coded millimeter-wave signal generation. The core device is a silicon microring modulator with a device size of 0.13 mm×0.32 mm and a modulation bandwidth of 23 GHz. Using RF seed frequencies of 17.5 GHz and 20 GHz, respectively, we experimentally demonstrated the generation of binary-phase-coded signals at 35 GHz and 40 GHz using our proposed approach, the performance of which was verified by a pulse compression ratio of 94 and 106, respectively. The result of this work points to the realization of a chip-scale flexible millimeter-wave signal generator.
6 citations
19 Mar 2017
TL;DR: With optical pre-sampling, 4-dB sensitivity improvement at the 7% hard FEC limit is experimentally demonstrated and this method is proposed to improve a system degraded by a low receiver electrical bandwidth.
Abstract: We propose a novel method to improve a system degraded by a low receiver electrical bandwidth. With optical pre-sampling, 4-dB sensitivity improvement at the 7% hard FEC limit is experimentally demonstrated.
4 citations
21 Jul 2017
TL;DR: An FPGA-based QPSK-encoded 9.375 Gb/s layered/enhanced ACO-OFDM transmitter giving a high spectral efficiency and the measured Q-factor is greater than 13 dB after 20km standard single-mode fiber transmission.
Abstract: We present an FPGA-based QPSK-encoded 9.375 Gb/s layered/enhanced ACO-OFDM transmitter giving a high spectral efficiency. The measured Q-factor is greater than 13 dB after 20km standard single-mode fiber transmission.
3 citations
19 Mar 2017
TL;DR: An integrated silicon 4×5 Gb/s OFDM transmitter PIC with four modulators and an optical Fourier transform is characterized with a channel spacing of 5 GHz and an 80-GHz free spectral range.
Abstract: We characterize an integrated silicon 4×5 Gb/s OFDM transmitter PIC (2.1×4.8 mm2) with four modulators and an optical Fourier transform. This PIC features a channel spacing of 5 GHz and an 80-GHz free spectral range.
21 Sep 2017
TL;DR: The computational load for ASE-DMT can be reduced to that of DCO-OFDM by mapping of the inverse fast Fourier transform's (IFFTs) inputs and extraction of signals from within the IFFT.
Abstract: The computational load for ASE-DMT can be reduced to that of DCO-OFDM by mapping of the inverse fast Fourier transform's (IFFTs) inputs and extraction of signals from within the IFFT. A realtime transmitter enables 9.2 Gbit/s over 20-km SSMF.
19 Mar 2017
TL;DR: It is shown that N-WDM super-channel multiplexing with zero guard-band, 12.5-GHz spacing, 0.08 roll-off, and a Q fluctuation <0.3-dB across C-band can be done with a Nyquist-filtering interleaver.
Abstract: We experimentally demonstrate full C-band coverage of a Nyquist-filtering interleaver for super-channel multiplexing. We show N-WDM super-channel multiplexing with zero guard-band, 12.5-GHz spacing, 0.08 roll-off, and a Q fluctuation <0.3-dB across C-band.
TL;DR: In this paper, a commercial travelling-wave Mach-Zehnder modulator is demonstrated to be able to function as an electro-optical temporal integrator with an integration window twice as long as its propagation delay.
Abstract: This letter demonstrates that a commercial travelling-wave Mach–Zehnder modulator is a versatile device. Next to being a modulator, it is also able to function as an electro-optical temporal integrator with an integration window twice as long as its propagation delay. Using the similar principle and being driven by a periodic RF frequency, the modulator is able to perform as an optical time-gate isolator that blocks any reverse-travelling lightwave, but simultaneously allows forward-travelling periodically-pulsed optical signals to pass. In the experiment, sub-nanosecond forward-travelling time gates and reverse-travelling optical power extinction >20 dB are successfully demonstrated.
21 Sep 2017
TL;DR: In this paper, a 3.8-THz wide superchannel was generated using a photonic-chip-based filter for sub-channel definition, which was able to shape and aggregate 304× NRZ-32-QAM sub-channels with an effective data-rate of 24.79 Tb/s.
Abstract: We demonstrate the all-optical generation of a 3.8-THz wide superchannel, using a photonic-chip-based filter for sub-channel definition. The photonic chip is able to shape and aggregate 304× NRZ-32-QAM sub-channels, carrying 10-Gbd data, with an effective data-rate of 24.79 Tb/s.
01 Jul 2017
TL;DR: In this paper, the authors review the recent works in this area that pave the path towards realizing microwave photonic filters with DSP-level flexibility, MHz-level frequency selectivity, and very importantly, full function integration on a chip scale.
Abstract: Programmable optical chips are a key technology for integrated microwave photonics. They enable flexible and stable signal processing operations on miniaturized chips with ultimate control precision and potential for low-cost fabrication. Integrated microwave photonic filters are an important function for photonic-assisted RF front-ends which opens a path to overcome the bandwidth limitation of the current digital electronics. Programmable optical chips enable such filters with high function flexibility, continuous tunability, and sharp frequency selectivity, which facilitate innovations of a wide range of new applications. Here, we review the recent works in this area that pave the path towards realizing microwave photonic filters with DSP-level flexibility, MHz-level frequency selectivity, and very importantly, full function integration on a chip scale.
01 Jul 2017
TL;DR: In this article, the authors present four functions on a single active photonic integrated circuit (4.5 mm × 4 mm) for a single-input single-output (SISO) configuration.
Abstract: Active photonic circuits use combinations of active semiconductor devices and passive elements to support many applications. We present four functions on a single active photonic integrated circuit (4.5 mm × 4 mm).
01 Jul 2017
TL;DR: The recent research outputs at Monash Electro-Photonics Laboratory in a new field: electro-photonics, where the best of the electronic and photonic technologies are combined to increase the capacity, flexibility and energy efficiency of optical communications systems and networks.
Abstract: We review the recent research outputs at Monash Electro-Photonics Laboratory in a new field: electro-photonics, where the best of the electronic and photonic technologies are combined to increase the capacity, flexibility and energy efficiency of optical communications systems and networks.