Weihong Shen

Due to the resonant nature and silicon’s strong optical nonlinearity, the system’s performance of silicon micro-ring modulators can be seriously affected by the input optical power. In this Letter, we proposed and experimentally demonstrated a multi-mode silicon micro-ring modulator to mitigate its optical nonlinear effects by operating in the TE₁ mode. The TE₁ mode features a high nonlinear threshold compared with the TE₀ mode because of its larger waveguide loss and larger mode effective area. Under the condition of 10 mW optical input power, the resonance spectrum maintains a good symmetric Lorentz shape. The resonant wavelength shifts less than one resonance linewidth, showing an improved robustness to optical nonlinearity compared with regular silicon micro-ring modulators.

Nonlinear distortion for single-sideband (SSB) signals will significantly reduce the performance of Kramers–Kronig (KK) receiver-based optical transmission. In this work, we present a proof-of-concept study of stimulated Brillouin scattering (SBS)-induced nonlinear distortion for 10 Gbaud and 28 Gbaud SSB QAM16 transmission over 80 km standard single mode fiber (SSMF) based on a KK receiver. Significantly reduced bit error rate (BER) has been experimentally observed due to the SBS and the threshold of SBS at about 7 dBm is detected for such an 80 km SSMF link. With left sideband (LSB) modulation of SSB, together with optical filtering, reduced SBS nonlinear distortion has been achieved with ~2 dB power tolerance improvement. The results reveal an important issue of SBS-induced nonlinear distortion, which would be of great significance for KK receiver-based optical transmission applications.

Due to the difficulty of controlling the waveguide loss in the doping region, high-speed silicon micro-ring modulators usually have limited extinction ratio. In this work, we present a mode-division-multiplexing (MDM) resonance-enhanced silicon micro-ring modulator with an ultrahigh extinction ratio. We used a two-mode micro-ring resonator and a mode conversion circular structure to trap the light twice within a single micro-ring resonator. Proof-of-concept high extinction ratio up to 55 dB was obtained. 30 Gb/s PAM-8 and 50 Gb/s PAM-4 signaling with a bit error rate below the hard-decision forward error correction (HD-FEC) threshold were demonstrated with the fabricated modulator, indicating great potential for high-order pulse amplitude modulation (PAM).

Germanium (Ge) ion implantation into silicon waveguides will induce lattice defects in the silicon, which can eventually change the crystal silicon into amorphous silicon and increase the refractive index from 3.48 to 3.96. A subsequent annealing process, either by using an external laser or integrated thermal heaters can partially or completely remove those lattice defects and gradually change the amorphous silicon back into the crystalline form and, therefore, reduce the material’s refractive index. Utilising this change in optical properties, we successfully demonstrated various erasable photonic devices. Those devices can be used to implement a flexible and commercially viable wafer-scale testing method for a silicon photonics fabrication line, which is a key technology to reduce the cost and increase the yield in production. In addition, Ge ion implantation and annealing are also demonstrated to enable post-fabrication trimming of ring resonators and Mach–Zehnder interferometers and to implement nonvolatile programmable photonic circuits.

Recently, significantly raised interests have emerged for the 2 µm waveband as an extended new window for fiber optic communication. Much research progress has been made on the photonic integrated circuits for the 2 µm waveband, especially on the CMOS-compatible silicon-on-insulator wafer. In this work, a silicon integrated microring modulator (MRM) with record high-speed performances at the 2 µm waveband was demonstrated. An L-shaped PN junction was specially designed for 2 µm to achieve a high modulation efficiency with V π L of 0.85   V · cm . The measured 3 dB bandwidth is 18 GHz, supporting up to 50 Gbps signaling at 2 µm. Additionally, optical bistability induced by the thermo-optical effect and nonlinear effects was analyzed theoretically and observed experimentally in the 2 µm MRM for the first time to our knowledge. Nonlinear coupled mode theory and the Runge–Kutta method were used to simulate the behaviors of bistability in the 2 µm MRM. The simulation and experimental results indicate that, when the MRM is launched by a high optical power, the distorted resonant spectrum under an optical bistable state deteriorates the modulation efficiency and signal performances. This work breaks the record of high-speed silicon MRM at 2 µm, drawing a promising prospect for the silicon photonic integration and high-speed interconnection at the 2 µm waveband, and it provides the referenceable analysis of optical bistability, which guides the design and experimental investigation of 2 µm MRM.

Silicon micro-ring modulator assisted by MDM resonance is experimentally demonstrated. Ultrahigh ER up to 55 dB was obtained for supporting 50 Gb/s PAM4 signaling with 0.79-V∙cm V_πL, indicating promising performance for advanced modulation formats.

Optical signaling without a high voltage driver for electric-optic modulation is in high demand to reduce power consumption, packaging complexity, and cost. In this work, we propose and experimentally demonstrate a silicon mode-loop Mach–Zehnder modulator (ML-MZM) with record-high modulation efficiency. We used a mode-loop structure to recycle light twice in the phase shifter. With an L-shaped PN junction, a comparably large overlap between the PN junction and optical modes of both TE 0 and TE 1 was achieved to lower the driving voltage or decrease the photonic device size. Proof-of-concept high-efficiency modulation with low V π L of 0.37    V · cm was obtained. Subvoltage V π can be realized with a millimeter’s length phase shifter by this scheme, which makes the realization of CMOS-compatible driverless modulation highly possible. 40 Gb/s signaling with a bit error rate below the 7% forward-error-correction threshold was then demonstrated with the fabricated ML-MZM, indicating great potential for high-speed optical communication.

In this work, mode-division multiplexing (MDM) phase-sensitive amplification (PSA) for all-optical mode selective and mode equalized phase regeneration is presented and investigated. MDM PSA relies on reasonable phase-matching conditions, which makes intramode four-wave mixing in the fiber much stronger than that of cross-mode. It enables multimode signals to interact mainly with the same spatial mode pumps and idlers. Thus, MDM signals can obtain synchronous phase regeneration and avoid cross talk with different mode signals. To achieve this, we designed an appropriate few-mode fiber by an inverse design method based on a neural network for obtaining the desired phase mismatch and low modal dispersion. The results show that effective phase regeneration can be achieved for the degraded 40 Gbit/s binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK) signals. For BPSK signals, error vector magnitudes (EVMs) of the regenerated signal on two modes are reduced from − 8.013 d B and − 8.068 d B to − 24.867 d B , and − 26.090 d B , respectively. For QPSK signals, the EVMs are reduced from − 16.767 d B and − 16.583 d B to − 24.867 d B and − 24.822 d B , respectively.

Chromatic dispersion engineering of photonic waveguide is of great importance for Photonic Integrated Circuit in broad applications, including on-chip CD compensation, supercontinuum generation, Kerr-comb generation, micro resonator and mode-locked laser. Linear propagation behavior and nonlinear effects of the light wave can be manipulated by engineering CD, in order to manipulate the temporal shape and frequency spectrum. Therefore, agile shapes of dispersion profiles, including typically wideband flat dispersion, are highly desired among various applications. In this study, we demonstrate a novel method for agile dispersion engineering of integrated photonic waveguide. Based on a horizontal double-slot structure, we obtained agile dispersion shapes, including broadband low dispersion, constant dispersion and slope-maintained linear dispersion. The proposed inverse design method is objectively-motivated and automation-supported. Dispersion in the range of 0–1.5 ps/(nm·km) for 861-nm bandwidth has been achieved, which shows superior performance for broadband low dispersion. Numerical simulation of the Kerr frequency comb was carried out utilizing the obtained dispersion shapes and a comb spectrum for 1068-nm bandwidth with a 20-dB power variation was generated. Significant potential for integrated photonic design automation can be expected.

In this work, we designed and fabricated a dual-mode switch based on triple-waveguide couplers and two thermal phase shifters, and demonstrated the first silicon-integrated mode division multiplexing (MDM) switching network for $2-\mu \text{m}$ waveband. The proposed dual-mode switch shows < 2.6 dB insertion loss, <−20 dB inter-mode crosstalk at 1960 nm, with broadband operation over 100 nm. The experimental results of dynamic switching at 10 kHz presents 9.2- $\mu \text{s}$ rising time and $13.2-\mu \text{s}$ falling time, with switching power of 19.2 mW. High speed on-chip MDM routing of $2\times 60$ Gbps signal was experimentally demonstrated using the proposed 2- $\mu \text{m}$ MDM switching network, drawing the promising prospect for the future photonic integration and high-speed MDM networking at 2- $\mu \text{m}$ waveband.