Hamed Pishvai Bazargani

Ultrashort Flat-Top Pulse Generation Using On-Chip CMOS-Compatible Mach–Zehnder Interferometers

Reshaping of an ultrashort Gaussian-like pulse into a flat-top pulse is demonstrated using an integrated Mach-Zehnder interferometer (MZI). The 7.8-ps Gaussian-like pulses are reshaped into nearly chirp-free 17.1-ps and 20.0-ps flat-top-pulses based on two different linear filtering schemes. In addition, the capability of this integrated MZI to generate a Hermite-Gaussian pulse with duration of a few picoseconds is demonstrated.

Experimental demonstration of sub-picosecond optical pulse shaping in silicon based on discrete space-to-time mapping

We experimentally demonstrate on-chip optical pulse shaping based on discrete space-to-time mapping in cascaded co-directional couplers. The demonstrated shapers validate a recent design methodology that exploits the direct relationship between the discrete complex spatial apodization profile of a structure of cascaded couplers and the time-domain impulse response of the device. In this design, the amplitude and phase of the apodization profile can be controlled through the coupling strength of each coupler and the relative time delay between the waveguides connecting consecutive couplers, respectively. This design methodology has been successfully used to demonstrate direct synthesis of high-quality flat-top and phase-coded pulse trains with resolutions down to the sub-picosecond range using passive devices in a silicon-on-insulator platform.

Optical pulse shaping based on discrete space-to-time mapping in cascaded co-directional couplers

We propose and numerically validate a new design concept for on-chip optical pulse shaping based on discrete space-to-time mapping in cascaded co-directional couplers. We show that under weak-coupling conditions, the amplitude and phase of the discrete complex apodization profile of the device can be directly mapped into its temporal impulse response. In this scheme, the amplitude and phase of the apodization profile can be controlled by tuning the coupling strength and relative time delay between the couplers, respectively. The proposed concept enables direct synthesis of the target temporal waveforms over a very broad range of time-resolution, from the femtosecond to the sub-nanosecond regime, using readily feasible integrated waveguide technologies. Moreover, the device offers compactness and the potential for reconfigurability.

Photonic Hilbert transformers based on laterally apodized integrated waveguide Bragg gratings on a SOI wafer

We experimentally demonstrate high-performance integer and fractional-order photonic Hilbert transformers based on laterally apodized Bragg gratings in a silicon-on-insulator technology platform. The sub-millimeter-long gratings have been fabricated using single-etch electron beam lithography, and the resulting HT devices offer operation bandwidths approaching the THz range, with time-bandwidth products between 10 and 20.

Tunable, nondispersive optical filter using photonic Hilbert transformation

We propose and numerically demonstrate a new design concept for implementing nondispersive complementary (band-pass/band-reject) optical filters with a wide range of bandwidth tunability. The device consists of two photonic Hilbert transformers (PHTs) incorporated into a Michelson interferometer (MI). By controlling the central frequency of PHTs with respect to each other, both the central frequency and the spectral width of the rejection/pass bands of the filter are proved to be tunable. Bandwidth tuning from 260 MHz to 60 GHz is numerically demonstrated using two readily feasible fiber Bragg grating-based PHTs. The designed filter offers a high extinction ratio between the pass band and rejection band (>20  dB in the narrow-band filtering case) with a very sharp transition with a slope of 170  dB/GHz from rejection to pass band.

Long-Duration Optical Pulse Shaping and Complex Coding on SOI

This paper evaluates novel design strategies to enhance the performance of a recently proposed waveguide-based pulse-shaping method, i.e., discrete space-to-time mapping (D-STM), demonstrating the capability of the method to shape pulse waveforms with duration periods in the tens of picoseconds regime. In particular, we experimentally synthesize 70-ps high-quality flat-top pulses and a 40-ps-long 200-GBd 16-quadrature amplitude modulation (16-QAM) data sequence using D-STM in concatenated co-directional couplers. Our proposed devices have been fabricated on a silicon-on-insulator (SOI) technology platform using ultraviolet and single-etch electron-beam lithography processes. The fabricated devices are all-passive, functioning without needing post-fabrication tuning, which further proves the robust performance of the proposed scheme.

Integer and fractional-order photonic Hilbert transformer on SOI

High-performance photonic integer and fractional-order Hilbert transformers, with processing bandwidths above 350 GHz, are experimentally realized using laterally-apodized Bragg gratings in SOI wafers.

On-chip optical pulse shaping based on discrete space-to-time mapping in concatenated co-directional couplers

We introduce a simple and practical design approach for on-chip optical pulse shaping based on concatenated co-directional couplers, and demonstrate synthesis of high-quality flat-top and phase-coded pulse trains with (sub-)picosecond resolutions in a SOI platform.

Frequency agile microwave photonics notch filter based on a waveguide Bragg grating on silicon

We propose and experimentally demonstrate a broadband, frequency agile RF-photonic notch filter based on a waveguide Bragg grating on silicon, realized with CMOS compatible process via a multi-project wafer (MPW) run. The resulting RF filter shows a seamless tuning over 20 GHz of the central RF frequency of the notch, without changes in the shape of the filter response.

On-Chip, Single-Shot Characterization of GHz-Rate Complex Optical Signals

Phase reconstruction based on optical ultrafast differentiation is implemented using an integrated-waveguide Mach-Zehnder interferometer to demonstrate self-referenced phase characterization of gigahertz-rate complex modulated signals (e.g., quadrature phase shift keying and amplitude phase shift keying modulation formats), through a single-shot and real-time technique. This method is transparent to both modulation format and bit rate, limited only by the bandwidth capabilities of the temporal intensity measurement instrumentation.