A polarization-insensitive mode-order converting power splitter using a pixelated region is presented and investigated in this paper. As TE₀ and TM₀ modes are injected into the input port, they are converted into TE₁ and TM₁ modes, which evenly come out from the two output ports. The finite-difference time-domain method and direct-binary-search optimization algorithm are utilized to optimize structural parameters of the pixelated region to attain small insertion loss, low crosstalk, wide bandwidth, excellent power uniformity, polarization-insensitive property, and compact size. Experimental results reveal that the insertion loss, crosstalk, and power uniformity of the fabricated device at 1550 nm are 0.57, -19.67, and 0.094 dB in the case of TE polarization, while in the TM polarization, the relevant insertion loss, crosstalk, and power uniformity are 0.57, -19.40, and 0.11 dB. Within a wavelength range from 1520 to 1600 nm, for the fabricated device working at TE polarization, the insertion loss, crosstalk, and power uniformity are lower than 1.39, -17.64, and 0.14 dB. In the case of TM polarization, we achieved an insertion loss, crosstalk, and power uniformity less than 1.23, -17.62, and 0.14 dB.

A flexible-grid 1×(2×3) mode- and wavelength-selective switch which comprises counter-tapered couplers and silicon microring resonators has been proposed, optimized, and demonstrated experimentally in this work. By carefully thermally tuning phase shifters and silicon microring resonators, mode and wavelength signals can be independently and flexibly conveyed to any one of the output ports, and different bandwidths can be generated as desired. The particle swarm optimization algorithm and finite difference time-domain method are employed to optimize structural parameters of the two-mode (de)multiplexer and crossing waveguide. The bandwidth-tunable wavelength-selective optical router composed of 12 microring resonators is studied by taking advantage of the transfer matrix method. Measurement results show that, for the fabricated module, cross talk less than -10.18dB, an extinction ratio larger than 17.41 dB, an in-band ripple lower than 0.79 dB, and a 3-dB bandwidth changing from 0.38 to 1.05 nm are obtained, as the wavelength-channel spacing is 0.40 nm. The corresponding response time is measured to be 13.64 µs.

Optical neural networks (ONNs), enabling low latency and high parallel data processing without electromagnetic interference, have become a viable player for fast and energy-efficient processing and calculation to meet the increasing demand for hash rate. Photonic memories employing nonvolatile phase-change materials could achieve zero static power consumption, low thermal cross talk, large-scale, and high-energy-efficient photonic neural networks. Nevertheless, the switching speed and dynamic energy consumption of phase-change material-based photonic memories make them inapplicable for in situ training. Here, by integrating a patch of phase change thin film with a PIN-diode-embedded microring resonator, a bifunctional photonic memory enabling both 5-bit storage and nanoseconds volatile modulation was demonstrated. For the first time, a concept is presented for electrically programmable phase-change material-driven photonic memory integrated with nanosecond modulation to allow fast in situ training and zero static power consumption data processing in ONNs. ONNs with an optical convolution kernel constructed by our photonic memory theoretically achieved an accuracy of predictions higher than 95% when tested by the MNIST handwritten digit database. This provides a feasible solution to constructing large-scale nonvolatile ONNs with high-speed in situ training capability.

We demonstrate a single-chip silicon optical single sideband (OSSB) modulator composed of a radio frequency (RF) branch line coupler (BLC) and a silicon dual-parallel Mach–Zehnder modulator (DP-MZM). A co-design between the BLC and the DP-MZM is implemented to improve the sideband suppression ratio (SSR). The modulator has a modulation efficiency of VπLπ∼1.75V·cm and a 3 dB electro-optical (EO) bandwidth of 48.7 GHz. The BLC can generate a pair of RF signals with equal amplitudes and orthogonal phases at the optimal frequency of 21 GHz. We prove through theoretical calculation and experiment that, although the BLC’s performance in terms of power balance and phase orthogonality deteriorates in a wider frequency range, high SSRs can be realized by adjusting relevant bias phases of the DP-MZM. With this technique, the undesired sidebands are completely suppressed below the noise floor in the frequency range from 15 GHz to 30 GHz when the chip operates in the full carrier OSSB (FC-OSSB) mode. In addition, an SSR >35dB and an carrier suppression ratio (CSR) >42dB are demonstrated at 21 GHz in the suppressed carrier OSSB (SC-OSSB) mode.

We demonstrate a high responsivity all-silicon in-line optical power monitor by using the thermal effect to enhance the quantum efficiency of defect-mediated absorption at 1550 nm. The doping compensation technique is utilized to increase the density of lattice defects responsible for the sub-bandgap absorption and suppress the detrimental free carrier absorption. The 200-μm-long device presents a propagation loss as low as 2.9 dB/cm. Its responsivity is enhanced from 12.1 mA/W to 112 mA/W at -9V bias by heating the optical absorption region. With this device, we build an optical power monitoring system that operates in the sampling mode. The minimal detectable optical power of the system is below -22.8dBm, while the average power consumption is less than 1 mW at a sampling frequency of 10 Hz. Advantages of this scheme in terms of high responsivity, low insertion loss, and low power consumption lend itself to implement the feedback control of advanced large-scale silicon photonic integrated circuits.

We propose and demonstrate an ultrasensitive integrated photonic current sensor that incorporates a silicon-based single-mode-multimode-single-mode waveguide (SMSW) structure. This kind of SMSW structure is placed over a direct current carrying power resistor, which produces Joule’s heat to change the temperature of the SMSW and further results in the change of the effective refractive index between different propagating modes. Interference occurs when the modes recombine at the second single mode waveguide. Finally, the current variation is measured by monitoring the shift in the output spectrum of the multimode interferometer. In low current, the wavelength shift has almost linear dependence: Δλ∝Ic. This effect can be used as a current sensor with a slope efficiency of 4.24 nm/A in the range of 0–200 mA.

In this Letter, we study the characteristics of a selectively buried glass waveguide that is fabricated by the backside masking method. The results show that the surface region appears when the width of the backside mask is larger than 7 mm. Here, the glass substrate is 1.5 mm thick. It is also found that the buried depth evolution of the transition region remains almost unchanged and is independent of the width of the backside mask. The loss of the transition region is only 0.28 dB at the wavelength of 1.55 μm if the surface condition is good enough.