Shaoqi Feng

Elastic optical networking by dynamic optical arbitrary waveform generation and measurement

This paper discusses elastic optical networking (EON) by dynamic optical arbitrary waveform generation and measurement (DOAWG/DOAWM) technologies for flexible and agile bandwidth-variable transponders. The ability to generate and measure flexible bandwidth signals with arbitrary modulation formats and subwave-length granularity, as well as superchannels, makes DOAWG/DOAWM an attractive technology for EON. We introduce the DOAWG/DOAWM concept and its application to EON, and we discuss the use and advantages of DOAWG/DOAWM as the technology for a sliceable bandwidth variable transponder (SBV-T). Then we report our most recent experimental demonstration of a two-spectral-slice OAWG-SBV-T experiment to generate a single-carrier 60 Gbaud channel with dual-polarization quadrature phase-shift keying and dual-polarization 16 quadrature amplitude modulation formats. Finally, we discuss our current progress on the development of a chip-scale DOAWG on a heterogeneous Si3N4-InP integration platform.

Athermal silicon ring resonators clad with titanium dioxide for 1.3µm wavelength operation

We investigate the athermal characteristics of silicon waveguides clad with TiO(2) designed for 1.3 µm wavelength operation. Using CMOS-compatible fabrication processes, we realize and experimentally demonstrate silicon photonic ring resonators with resonant wavelengths that vary by less than 6 pm/°C at 1.3 µm. The measured ring resonance wavelengths across the 20-50°C temperature range show nearly complete cancellation of the first-order thermo-optical effects and exhibit second-order thermo-optical effects expected from the combination of TiO(2) and Si.

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.

Uniform emission, constant wavevector silicon grating surface emitter for beam steering with ultra-sharp instantaneous field-of-view

We report on uniform emission intensity profile, uniform propagation constant silicon gratings for beam steering application with ultra-sharp instantaneous field-of-view (IFOV). To achieve uniform emission intensity across relatively long emission length, we designed a custom grating with varying Si3N4 width and duty cycle while maintaining a uniform propagation constant for relatively narrow divergence emission pattern. We designed and fabricated the custom Si3N4/Si grating with the varying Si3N4 width/duty cycle together with the reference Si3N4/Si grating with a constant 50:50 duty cycle. The custom grating demonstrated the beam steering angle value of 6.6° by sweeping wavelength between 1530 nm and 1575 nm with the emission length over 1 mm. The measured IFOV based on the 3-dB beamwidth values of the far field patterns for the TE polarization are 0.10° and 0.75° for the custom grating and for the reference grating, respectively. The custom grating also indicates mode-selective behavior due to the perturbation of propagation constant for input modes other than TE polarization. The measured TE-mode to TM-mode suppression ratio for the custom grating is approximately 8.2 dB peak-to-peak measured at far field.

Hybrid integration of modified uni-traveling carrier photodiodes on a multi-layer silicon nitride platform using total reflection mirrors

We demonstrate hybrid integration of modified uni-traveling carrier photodiodes on a multi-layer silicon nitride platform using total reflection mirrors etched by focused ion beam. The hybrid photodetectors show external responsivity of 0.15 A/W and bandwidth of 3.5 GHz for devices with a diameter of 80 µm. The insertion loss of the waveguide is 3 dB and the coupling efficiency of the total reflection mirror is -3 dB. The highest RF output power is -0.5 dBm measured at 3 GHz with 9 mA photocurrent and -9 V bias.

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.

Dynamic and Static Optical Arbitrary Waveform Generation from Chip-Scale Heterogeneously Integrated InP/Si3N4 Module

We demonstrate static and dynamic optical arbitrary waveform generation in a heterogeneously integrated Si₃N₄ AWG-InP modulator array-Si₃N₄ AWG chip-scale module. High contrast Si₃N₄ AWGs and nearly pure phase InP modulation provided high fidelity OAWG.