Silicon nitride tri-layer vertical Y-junction and 3D couplers with arbitrary splitting ratio for photonic integrated circuits.

We designed and demonstrated a tri-layer Si3N4/SiO2 photonic integrated circuit capable of vertical interlayer coupling with arbitrary splitting ratios. Based on this multilayer photonic integrated circuit platform with each layer thicknesses of 150 nm, 50 nm, and 150 nm, we designed and simulated the vertical Y-junctions and 3D couplers with arbitrary power splitting ratios between 1:10 and 10:1 and with negligible(< -50 dB) reflection. Based on the design, we fabricated and demonstrated tri-layer vertical Y-junctions with the splitting ratios of 1:1 and 3:2 with excess optical losses of 0.230 dB. Further, we fabricated and demonstrated the 1 × 3 3D couplers with the splitting ratio of 1:1:4 for symmetric structures and variable splitting ratio for asymmetric structures.

Rapidly reconfigurable high-fidelity optical arbitrary waveform generation in heterogeneous photonic integrated circuits.

This paper demonstrates rapidly reconfigurable, high-fidelity optical arbitrary waveform generation (OAWG) in a heterogeneous photonic integrated circuit (PIC). The heterogeneous PIC combines advantages of high-speed indium phosphide (InP) modulators and low-loss, high-contrast silicon nitride (Si3N4) arrayed waveguide gratings (AWGs) so that high-fidelity optical waveform syntheses with rapid waveform updates are possible. The generated optical waveforms spanned a 160 GHz spectral bandwidth starting from an optical frequency comb consisting of eight comb lines separated by 20 GHz channel spacing. The Error Vector Magnitude (EVM) values of the generated waveforms were approximately 16.4%. The OAWG module can rapidly and arbitrarily reconfigure waveforms upon every pulse arriving at 2 ns repetition time. The result of this work indicates the feasibility of truly dynamic optical arbitrary waveform generation where the reconfiguration rate or the modulator bandwidth must exceed the channel spacing of the AWG and the optical frequency comb.

Low-loss compact multilayer silicon nitride platform for 3D photonic integrated circuits.

We design, fabricate, and demonstrate a silicon nitride (Si(3)N(4)) multilayer platform optimized for low-loss and compact multilayer photonic integrated circuits. The designed platform, with 200 nm thick waveguide core and 700 nm interlayer gap, is compatible for active thermal tuning and applicable to realizing compact photonic devices such as arrayed waveguide gratings (AWGs). We achieve ultra-low loss vertical couplers with 0.01 dB coupling loss, multilayer crossing loss of 0.167 dB at 90° crossing angle, 50 µm bending radius, 100 × 2 µm(2) footprint, lateral misalignment tolerance up to 400 nm, and less than -52 dB interlayer crosstalk at 1550 nm wavelength. Based on the designed platform, we demonstrate a 27 × 32 × 2 multilayer star coupler.

Design trade-offs for silicon-on-insulator-based AWGs for (de)multiplexer applications.

We demonstrate compact silicon-on-insulator-based arrayed waveguide gratings (AWGs) for (de)multiplexing applications with a large free spectral range (FSR). The large FSR is obtained by reducing the arm aperture pitch without changing the device footprint. We demonstrate 4 × 100 GHz, 8 × 250 GHz, and 12 × 400 GHz AWGs with FSRs of 6.9, 24.8, and 69.8, respectively. We measured an insertion loss from -2.45 dB for high to -0.53 dB for low-resolution AWGs. The crosstalk varies between 17.12 and 21.37 dB. The bandwidth remains nearly constant, and the nonuniformity between the center wavelength channel and the outer wavelength channel improves with larger FSR values.

Athermal arrayed waveguide gratings in silicon-on-insulator by overlaying a polymer cladding on narrowed arrayed waveguides.

Athermal arrayed waveguide gratings (AWGs) in silicon-on-insulator (SOI) are experimentally demonstrated for the first time to our knowledge. By using narrowed arrayed waveguides, and then overlaying a polymer layer, the wavelength temperature dependence of the AWGs is successfully reduced to -1.5 pm/°C, which is more than 1 order of magnitude less than that of normal SOI AWGs. The athermal behavior of the AWGs is obtained with little degradation of their performance. For the central channel, the cross talk is less than -15 dB and the insertion loss is around 2.6 dB. Good characteristics can be maintained with temperatures up to 75 °C. The total size of the device is 350 µm × 250 µm.