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Sinc-shaped Nyquist pulses have wide applications in optical communications and microwave photonics. The quality of the generated Nyquist pulses has a significant effect on the overall performance of the communication system and the signal processing system. Generating high-quality Nyquist pulses with integrated silicon modulators is however still challenging due to the highly nonlinear response and fabrication-induced discrepancies of the device. We present a model for a silicon dual-parallel modulator with which the best possible quality of the generated optical frequency comb (OFC) and sinc-shaped Nyquist pulses can be obtained. In the model, the phase and amplitude deviations are taken into consideration. Device induced waveform and spectrum distortion can be well described. Based on the guidance of the model, a root-mean-square error of 2.8% is obtained between the experimentally generated signals and the ideal pulses, which proves the high accuracy of the model and its importance for high-quality Nyquist pulse generation.

Silicon nitride (Si3N4) has a higher nonlinear threshold compared to silicon, which reduces the effect of two-photon absorption. However, the low thermo-optic coefficient and the reduced refractive index contrast of thin Si3N4 waveguides lead to a low thermal tuning speed and low thermal efficiency. This paper demonstrates a widely tunable III-V/Si3N4 hybrid-integrated external cavity laser with a relatively faster switching time. The Si3N4 external feedback circuit is based on 800-nm-thick Si3N4 waveguides with an optical confinement factor of 87%. It allows the reduction of the oxide under-cladding layer thickness to 4 μm and the oxide upper-cladding layer to 1.7 μm without additional loss. The switching time between two non-adjacent lasing wavelengths is 60.7 μs. The maximum output power is 34 mW under 500 mA injection current. The side mode suppression ratio is more than 70 dB over the tuning range of 58.5 nm. The laser intrinsic linewidth is 2.5 kHz.

We experimentally demonstrate optical frequency-modulated continuous-wave (FMCW) signal generation utilizing a silicon dual-parallel Mach-Zehnder modulator (DP-MZM). The sideband suppression ratio (SSR) and the sideband-to-carrier suppression ratio (SCSR) of the single-sideband suppressed carrier (SSB-SC) modulation are higher than 15 dB when RF frequency is lower than 20 GHz. With the generated triangular modulated FMCW signal, we demonstrate simultaneous ranging and velocimetry. The chirp bandwidth is 10 GHz and the chirp period is $1~\mu \text{s}$ , corresponding to a ranging resolution of 13 mm and a velocimetry resolution of 0.5 m/s, consistent with the theoretical calculation. These results show that wideband FMCW signal generation by a silicon DP-MZM is promising for high-resolution light detection and ranging.

In this paper, we demonstrate a method to generate a low-chirp ultra-wideband pulse (UWB) signal based on a silicon single-drive push-pull segmented Mach-Zehnder modulator (SMZM). The concept is analyzed theoretically and demonstrated experimentally. We get positive monocycle pulses with different relative time delays between the two driving signals. The center frequency and fractional bandwidth of the generated positive monocycle pulse is 5.97 GHz and 161% with a relative time delay of 56 ps. By changing the operating point of the SMZM, we can get negative monocycle pulses. We modulate the UWB signals with on-off keying and pulse position formats by properly coding the driving signal. As far as we know, this is the first time to realize low-chirp UWB signals using only one silicon modulator. The successful generation of UWB signals poses a significant step in realizing a compact low-cost and low-chirp UWB generator on the silicon photonics platform.

We demonstrate nine-line optical frequency comb (OFC) and sinc-shaped Nyquist pulse generation based on two cascaded silicon Mach–Zehnder modulators. The OFC has a flatness of 1.83 dB, a frequency spacing of 5 GHz, and a corresponding Nyquist pulsewidth of ∼22 ps. Moreover, multi-wavelength operation and repetition rate tunability have also been demonstrated, which indicates the potential of our work to generate an on-chip high-speed pulse train demanded in optical communications and microwave photonics applications.

We demonstrate novel phase-coded microwave signal generation based on a two-segment single-drive push–pull silicon Mach–Zehnder modulator. The coding signal and the microwave frequency are each applied to one of the separate segments. The phase-coded microwave signal is generated by properly setting the working point of the modulator. The precise π phase shift is determined by the sign of the coding signal. Both theoretical analysis and experimental demonstration are performed to verify the concept. The modulator successfully generates a 10-GHz (20-GHz) phase-coded microwave signal with a 5-Gb/s (10-Gb/s) coding data rate and the measured pulse compression ratio is 133.0 (156.8).

We demonstrate a high-efficiency silicon Mach-Zehnder modulator with U-shaped PN junctions. The depletion region of the U-shaped PN junction has a large overlap with the waveguide optical mode, leading to a low drive voltage. The calculated modulation efficiency is 0.33 V·cm at 0 V bias and 0.55 V·cm at −2 V bias. On-off keying (OOK) modulation and four-level pulse amplitude modulation (PAM-4) are achieved at 32 Gb/s and 64 Gb/s data rates under 2 V drive voltage, respectively. The bit error rate for the PAM-4 modulation is below the hard-decision forward error correction threshold of 3.8 × 10−3.

In this paper, we reported an integrated method to generate ultra-wideband (UWB) pulses of different orders based on a reconfigurable silicon micro-ring resonator-coupled Mach-Zehnder interferometer. Under proper operating conditions, the device can produce Fano resonances with a peak-to-valley extinction ratio of above 20 dB. UWB monocycle and doublet signals with picosecond pulse widths are produced when the microring resonator is modulated by square and Gaussian electrical pulses, respectively. With our Fano resonance modulator on silicon photonics, it is promising to foresee versatile on-chip microwave signal generation. [Image: see text]

We report a reconfigurable optical filter chip based on the Si3N4 waveguide platform. Microwave filtering is realized using a device with optical-to-electrical mapping. The filter chip is based on a lattice structure with the dual-ring-coupled Mach-Zehnder interferometers (DR-MZIs) as the basic elements. Both the lattice and ring couplers are tunable, making the chip reconfigurable to various filter functions. A theoretical model is developed to analyze its optical filtering performance. Measurement reveals that the filter passband can reach hundreds of megahertz in the lower limit and several gigahertz in the upper limit. Various orders of infinite impulse response filters are implemented with a tailorable passband. The flexibility in tuning filter center frequency and passband makes it suitable in high-resolution adaptable microwave signal front-end processing.

Cloudlet deployment and resource allocation for mobile users (MUs) have been extensively studied in existing works for computation resource scarcity. However, most of them failed to jointly consider the two techniques together, and the selfishness of cloudlet and access point (AP) are ignored. Inspired by the group-buying mechanism, this paper proposes three-stage auction schemes by combining cloudlet placement and resource assignment, to improve the social welfare subject to the economic properties. We first divide all MUs into some small groups according to the associated APs. Then the MUs in same group can trade with cloudlets in a group-buying way through the APs. Finally, the MUs pay for the cloudlets if they are the winners in the auction scheme. We prove that our auction schemes can work in polynomial time. We also provide the proofs for economic properties in theory. For the purpose of performance comparison, we compare the proposed schemes with HAF, which is a centralized cloudlet placement scheme without auction. Numerical results confirm the correctness and efficiency of the proposed schemes., 22 pages,12 figures, Accepted by Wireless Networks

We report an 8-channel wavelength-mode optical pulse interleaver on a silicon photonic chip. Wavelength- and mode-division multiplexing techniques are combined to increase the repetition rate of the pulses without adding the complexity of a single dimension. The interleaver uses a cascaded Mach–Zehnder interferometer architecture as a wavelength-division (de)multiplexer, an asymmetric directional coupler as a mode (de)multiplexer, and various lengths of silicon waveguides as delay lines. A pulse sequence with a time interval of 125 ps is implemented with the repetition rate being eight times that of the initial one. The demonstrated wavelength-mode multiplexing approach opens a new route for the generation of high-speed optical pulses.