We demonstrate an optical filter using multistage of second-order microring resonators (2nd-order MRRs) for a box-like filter response. All stages have identical structure parameters elaborately designed to obtain a flat-top spectrum. The maximally flat condition is deduced in consideration of loss and compared with those reported in literature. We present the insertion loss, extinction ratio, bandwidth and roll-off rate of the maximally flat response. We find that for the flat response of a 2nd-order MRR, the product of bandwidth and roll-off rate is constant. We compare the cascading 2nd-order MRRs with single-stage high-order filters with the same number of ring cavities. We find that the cascading structure has comparable performances in the aspects of insertion loss and roll-off rate for small radius. This cascading structure relaxes the fabrication tolerance and mitigates the difficulty of electrical wiring difficulty since there are only two ring cavities in each stage. As a proof of concept, we fabricate this kind of optical filter with ten stages on silicon-on-insulator platform, with each ring cavity tunable and each stage measurable. We obtain five flat-top responses corresponding to one to five cascading stages. The five-stage filter response has a 3dB bandwidth of $\sim$ 17 GHz, a roll-off rate of $\sim -5$ dB/GHz at -3dB point, and an on-chip insertion loss of $\sim$ -6 dB.

In this paper, we design and experimentally demonstrate an eight-channel cascaded Mach–Zehnder interferometer (MZI) based Local Area Network (LAN) Wavelength Division Multiplexing (WDM) (de)multiplexerwith channel spacing of 800 GHz on a silicon-on-insulator. By cascading a three-stage MZI, eight target wavelengths are (de)multiplexed. The length difference of the third-stage MZI delay arms is adjusted so that the output channels skip the guard band. In order to keep the central wavelength of each channel from shifting, we utilize a wide waveguide for the phase delay arm in MZI to achieve large fabrication tolerance, and the multi-mode interference (MMI) couplers as power splitters with weak dispersions. The measurement results of the fabricated device show the precise wavelength alignment over the whole working wavelength range.

The application of the inverse design method and free-form geometrical optimization in photonic devices endows them with highly tunable functionality and an ultra-compact footprint. In this paper, we implemented this platform to silicon photonic guided-mode manipulation and demonstrated a guided mode-based signal switching architecture. The passive signal switching mechanism is utilized so that no power consumption is needed for routing state maintenance. To solve the explosive increasing design cost in such mechanism when the switching scale is expanded, we illustrate that only a small number of mode switching devices need to be designed as the switching basis. In theory, arbitrary signal routing states can be constructed by cascading some selected basis. The required switching devices can be decreased from factorial N to N - 1 for the N channels switching. For proof of concept, we design and experimentally demonstrate the three-mode cases and the cascade method to combine any three mode-based switching devices. Experiments show that the insertion losses of TE₀ - TE₁ mode switching unit (U₁), TE₁ - TE₂ mode switching units (U₂), and TE₀ - TE₂ mode switching unit (U₃) are less than 2.8 dB, 3.1 dB, and 2.3 dB, respectively. The demonstrated architecture has both arbitrary signal switching capability and ultra-compact footprint, which is promising in the application of mode-division multiplexing communication systems.

An ultra-small arrayed-waveguide grating (AWG) router with microbends based on silicon-on-insulator nanowires is demonstrated experimentally. The presented AWG router has 15 input/output channels and the channel spacing is 400 GHz. The device size is only 163×147 µm. The thermal-tunability of the presented ultra-small AWG router is also characterised.

In order to increase the communication capacity of optical links, hybrid multiplexing technology has attracted a lot of interest. In this letter, we have proposed and experimentally demonstrated a polarization-independent silicon hybrid multiplexer with two-mode channels and four-wavelength channels based on an active polarization control scheme. It consists of eight on- chip polarization controllers, one $8\times $ 8 arrayed waveguide grating multiplexer, and one mode switch. Experimental results show that the polarization-dependent loss is about 0.6 dB. And the crosstalk is less than −18 dB for an arbitrarily polarized light. At the same time, this device also features a signal exchange function between the TE0 and TE1 modes for the aggregated throughput of wavelength channels.