Integrated Bragg gratings (IBGs) developed on the silicon-on-insulator (SOI) platform, owning to their high spectral flexibility, are showing great potential for many optical applications such as optical telecommunications and optical signal processing. In this tutorial, we describe how to design SOI-based IBGs to achieve arbitrary, complex, spectral responses. The overall design flow of IBGs is first introduced, followed by detailed elaborations of each individual step of the design and implementation process. Then, design examples of two SOI IBG-based, advanced optical devices, which are a multichannel photonic Hilbert transformer and a flattop, dispersion-compensating filter, are described, to further illustrate the design methodology. Finally, a conclusion of this tutorial and an outlook of the future work are given.

Multichannel photonic Hilbert transformers (MPHTs) are reported. The devices are based on single compact spiral integrated Bragg gratings on silicon with coupling coefficients precisely modulated by the phase of each grating period. MPHTs with up to nine wavelength channels and a single-channel bandwidth of up to similar to 625 GHz are achieved. The potential of the devices for multichannel singlesideband signal generation is suggested. The work offers a new possibility of utilizing wavelength as an extra degree of freedom in designing radio-frequency photonic signal processors. Such multichannel processors are expected to possess improved capacities and a potential to greatly benefit current widespread wavelength division multiplexed systems. (C) 2018 Optical Society of America

Precise and reliable apodization of silicon integrated Bragg gratings (IBGs) is the key to realizing their spectral tailoring for many optical applications such as optical signal processing and wavelength-division multiplexing systems. However, apodization in a silicon IBG that is typically realized by modifying the physical waveguide grating structure can also introduce unwanted grating phase variations that can affect the grating response. In this paper, we present a model to characterize apodized silicon IBGs which can take such apodization phase noise (APN) into account, based on direct synthesis of the physical grating structure. The model is used to characterize a set of different silicon IBGs apodized by lateral misalignment ($\mathrm{\Delta }L$) and duty-cycle (DC) modulations and designed with different responses, and the results show that the APN can greatly distort the complex responses of the gratings. Then, we develop a methodology to compensate the APN and thus to correct the distorted grating responses. The designed silicon IBGs were fabricated and tested experimentally. The accuracy of the model is examined by comparing the measured grating spectra with those predicted by the model. Spectral corrections are then demonstrated in Gaussian-apodized gratings based on $\mathrm{\Delta }L$- and DC-modulated silicon IBGs and a square-shaped filter developed on a $\mathrm{\Delta }L$-modulated IBG. Finally, a complex spectral correction of a photonic Hilbert transformer developed on a $\mathrm{\Delta }L$-modulated silicon IBG is achieved.

Ultracompact channel add-drop filter consisting of a single nanobeam photonic crystal cavity is proposed, designed and demonstrated. Transversely anti-symmetric multimode nanobeam photonic crystal cavity is employed in the design to implement degenerate resonant modes that are indispensable for achieving complete channel dropping function. The experimental results on the silicon-on-insulator show that the insertion losses of drop port, the crosstalk of add port of the filter are -1 dB and -14 dB, respectively. Typical modal volume and footprint of the involved nanobeam photonic crystal cavity are small as 1.2(/n)³ and 20 m² respectively, indicating huge potentials in developing low-power consumption tunable devices for future VLSI on-chip photonic applications.

Integrated-optic cavity resonators, such as Fabry–Perot microcavities and microrings, are key building blocks of photonics integrated circuits and are used extensively in applications such as optical communications and microwave photonics. For a single, conventional, optical-cavity resonator, resonance peaks appear periodically in frequency and have Lorentzian shapes in nature, which generally cannot be broken. Here, we report on fully tailorable, integrated-optic resonators that allow for independent control of individual resonance or spectral peaks as regards their presence, linewidths and extinction ratios, resonant wavelengths, and shapes and bandwidths. The response shapes can be set to be Lorentzian, Gaussian-like, or square. The resonators are based on chirped waveguide Moiré gratings developed on a silicon-on-insulator platform. We also demonstrate that they can be implemented on compact Archimedean spiral shapes to have sizes comparable to microring and microdisk resonators, with no spectral degradation. The unprecedented spectral flexibility of these resonators makes them attractive for a variety of fields and will enable new avenues for exploration in relevant areas such as optical waveform synthesis and microwave photonics.