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Reconfigurable photonic integrated devices and circuits are very important for many applications. Among various mechanisms for realizing reconfigurability, thermo-optic effect is popular because of the availability for many materials, the design simplicity and the fabrication ease. In particular, silicon has a large thermo-optic coefficient as well as a high heat conductivity, and thus it is promising to realize efficient thermally-reconfigurable silicon photonic integrated devices and circuits. Recent progress is reviewed in this paper. First, thermally-tunable silicon photonic filters based on different structures are summarized, including microring resonators (MRRs) and MRRs-assisted Mach-Zehnder interferometers (MZIs). Second, silicon photonic switches based on MZIs and MRRs are reviewed. Finally, a review is given for thermally-reconfigurable silicon photonic integrated circuits developed for the applications in quantum photonics, microwave photonics, and optical interconnects.

Integrated photonics have experienced a rapid advance in the past few decades, and various materials/platforms for integrated photonic devices and circuits have been developed successfully, such as silicon-on-insulator, silicon nitride, and indium phosphide. The realization of on-chip polarization rotators (PRs) is often challenging as a planar optical waveguide usually has a very good ability of polarization maintaining. Waveguide gratings have attracted intensive attention because of the possibility of enabling the free spectral range-free optical filtering. The development of reconfigurable photonic integrated devices and circuits is important for making optical networks intelligent so that the bandwidth/channels can be utilized optimally and flexibly. MEMS-based silicon photonic devices also provide a good option for achieving ultra-low power consumption. It is also possible to develop some non-volatile silicon photonic devices with the help of phase-change materials. Therefore, in order to develop powerful silicon PICs in the future, it is useful to introduce other functional materials “X” and versatile structures on silicon.

Phase change material G e 2 S b 2 T e 5 (GST) has recently emerged as a highly promising candidate for photonic device applications owing to its high optical contrast, self-holding bi-stability, and fast material response. Here, we propose and analyze a 1 × 2 tunable switch using a GST embedded silicon microring resonator exploiting high optical contrast during GST phase change and a high thermo-optic coefficient of amorphous phase GST. Our device exhibits high extinction ratios of 25.57 dB and 18.75 dB at through and drop ports, respectively, with just a 1 µm long GST layer. The two states of the switch are realizable by electrically inducing phase change in GST. For post phase change from amorphous to crystalline and vice versa, the fall time down the 80% of phase transition temperature is ∼ 66 n s and ∼ 45 n s , respectively. The resonance wavelength shift per unit active length is 0.661 nm/µm, and the tuning efficiency is 1.16 nm/mW. The large wavelength tunability (4.63 nm) of the proposed switch makes it an attractive option for reconfigurable photonic integrated circuits.

Silicon photonics is recognized as one of the most promising platforms for on-chip optical interconnects. In order to further enhance the on-chip optical-interconnect link capacity, silicon photonic devices for advanced multiplexing technologies have been widely investigated, including wavelength-division-multiplexing (WDM), mode-divisionmultiplexing (MDM), as well as the hybrid multiplexing. This paper gives a review for our recent progresses in the development of silicon-based on-chip wavelength/mode-division-multiplexers.

A dual-polarization waveguide superlattice is designed and realized by using 340 nm-thick silicon photonic waveguides. The silicon waveguide superlattices are formed with periodically arranged waveguides. Each period consists of five optical waveguides with core-widths designed optimally for minimizing the crosstalk among the optical waveguides. The optimized core-widths are 390 nm, 320 nm, 260 nm, 360 nm, and 300 nm when the separation between two adjacent waveguides is as small as 0.8 µm. With this design, the silicon waveguide superlattice works with low crosstalk (nearly –18 dB or less) for both polarizations within the range of 1530 nm to 1560 nm, which agrees well with the theoretical analysis.

Based on first-principles calculations, we have studied the crystal, electronic structure and optical properties in both wurtzite and zinc blend structure of AlN doped with rare-earth element Er. T...

We present a silicon racetrack-resonator based on a modified Euler curve for high-performance microwave photonic filters. It has a high Q-factor of 7×105, free spectral range of 0.73 nm, and tuning range of 92 GHz. © 2020 The Author(s)

An ultrahigh-Q silicon racetrack resonator is proposed and demonstrated with uniform multimode silicon photonic waveguides. It consists of two multimode straight waveguides connected by two multimode waveguide bends (MWBs). In particular, the MWBs are based on modified Euler curves, and a bent directional coupler is used to achieve the selective mode coupling for the fundamental mode and not exciting the higher-order mode in the racetrack. In this way, the fundamental mode is excited and propagates in the multimode racetrack resonator with ultralow loss and low intermode coupling. Meanwhile, it helps achieve a compact 180° bend to make a compact resonator with a maximized free spectral range (FSR). In this paper, for the chosen 1.6 μm wide silicon photonic waveguide, the effective radius R eff of the designed 180° bend is as small as 29 μm. The corresponding FSR is about 0.9 nm when choosing 260 μm long straight waveguides in the racetrack. The present high-Q resonator is realized with a simple standard single-etching process provided by a multiproject wafer foundry. The fabricated device, which has a measured intrinsic Q-factor as high as 2.3 × 10 6 , is the smallest silicon resonator with a > 10 6 Q-factor.

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.