Silicon photonics has attracted considerable attention in datacom and telecom due to its Complementary- Metal-Oxide-Semiconductor (CMOS) compatibility, high integration, and low transmission loss. Optical splitter can be widely used as a building block in large-scale photonic integration chips, such as wave-division-multiplexing (WDM), optical modulating and optical switching. Suffering from waveguide dispersion, the power splitter exhibits high wavelength sensitivity. This imposes a huge impact on the overall performance of large-scale photonic integration. In order to achieve a significant optical response, we need to implement a beam splitter with large operating bandwidth and small footprint, as well as the ability to achieve arbitrary power-splitting-ratios. Enabled by inverse design, we propose broadband, compact arbitrary-ratio power splitters based on curved directional coupler (CDC). The enhanced particle swarm optimization (EPSO) algorithm is used to engineer the coupling region of the CDCs, greatly reducing the device footprint and improving the device optimization efficiency. The simulation results show that the proposed CDCs based on EPSO can achieve 80 nm operating bandwidth from 1260 nm to 1340 nm. The device coupling footprint can be reduced to 7.15 μm, with an excess loss of less than 0.01 dB. Inverse design allows for the reduction of the considerable time and labor required for manual adjustments. In addition, the optimization room of device footprint and operating bandwidth can be further exploited. With the comprehensive performance metrics, our proposed CDCs can be widely used in high-density photonic systems.
Silicon modulators play an important role in silicon photonics for efficient modulation and transmission of optical signals. Enhancing the performance of silicon modulators has largely relied on optimizing doping profiles. However, in recent years, progress in finding superior solutions to optimize performance has faced obstacles. To address this challenge, the concept of inverse design, which has gained popularity in passive photonic devices, can be applied to silicon active devices by dividing the doping region into segments and adjusting each segment based on feedback from the results. Consequently, we introduce the inverse design method into modulator doping profile optimization by utilizing the particle swarm optimization (PSO) algorithm, resulting in the attainment of a G-shaped doping profile for the modulator. The proposed modulator demonstrates the superior VπL of 0.48 V·cm and the low loss of 13.5 dB/cm. The small-signal frequency response suggests a reliable operation range under reverse biases of 1 V to approximately 3 V with the bandwidth over 26 GHz. The G-shaped silicon modulator exhibits impressive modulation efficiency and minimal loss, indicating its high potential for use in microwave front-end applications. The utilization of inverse design holds immense promise in advancing active silicon photonic devices for faster, higher-capacity and more reliable data communication systems.
We propose an ultra-broadband, compact size and low loss 3-dB adiabatic subwavelength grating-based power splitter based on the silicon-on-insulator platform. Simulation results show that our proposed device has an operating bandwidth of 250 nm, covering the wavelength range from 1400 to 1650 nm, while the device size is reduced to 11 μm and the excess loss is as low as 0.22 dB. Compatible with mature CMOS process, our proposed subwavelength grating-based power splitter shows excellent potential for large-scale photonic integrated circuits.
KEYWORDS: Modulation, Doping, Silicon, Design and modelling, Capacitance, Resistance, Waveguides, Silicon photonics, Data communications, Monte Carlo methods
In order to achieve effective modulation, researchers have studied various doping profiles within silicon modulators, but optimization has so far mainly been carried out in the cross-section or solely in the propagation direction. Generating 3D doping profile can add more optimizing dimensions to the modulator design. This work proposes a modulator based on U-shaped and L-shaped junctions by the 3D effective Monte-Carlo method. The simulation results show that the modulation efficiency is 0.67 V·cm, and the loss is 25.7 dB/cm, with the bandwidth more than 36.3 GHz. This work demonstrates the benefits of 3D modulator design as the direction of light propagation is utilized to transport carriers, and provides a modulator solution for high-speed datacom.
As a widely studied fundamental block in photonic integrated circuits, multimode interferometer (MMI) is excellent in coupling of multiple light sources with equal intensity. However, unacceptable excess loss occurs if phase-matching is not satisfied at any input port. In this paper, we proceed direct binary search (DBS) algorithm to optimize an inverse designed 3 × 1 MMI coupler with nano-pixel structure and realize high-efficiency coupling of equal input (intensity and phase) sources of 1550 nm fundamental TE mode, with a compact footprint of 2.5 × 2.5 μm2 and low excess loss of 0.04dB. We also investigated the possibility of inverse design method to handle the coupling of multiple input sources with arbitrary phase difference among different ports.
Interleaved modulators enable more optimized doping profiles for higher modulation efficiency and lower loss. Nevertheless, as far as we know, complex doping for interleaved modulators has hardly been studied. Hence this work proposes a modulator based on interleaved vertical and U-shaped junctions using the Monte-Carlo simulation. The results illustrate that the modulation efficiency of the designed interleaved period is 0.57 V·cm, while the loss is 15.5 dB/cm. This high-efficiency design verifies the benefits of interleaved 3D modulator design as significantly increasing modulation efficiency with low loss, showing great potential for high-speed application.
We propose and experimentally demonstrate the ultra-compact on-chip silicon mode (de)multiplexers [(De)MUXs] based on a tapered bent asymmetric direction coupler. By combining the advantages of tapered asymmetric directional coupler and bent directional coupler, low loss, broad bandwidth, and good robustness against fabrication variations can be obtained within ultra-compact coupling length. The coupling length of the proposed TE1-TE0 and TE2-TE0mode (de)multiplexers is less than 8.7 µm. Experimental results reveal that, over the wavelength range from 1.534 μm to 1.6 μm, the insertion loss is lower than 1.4 dB and 1.55 dB for the TE1-TE0 and TE2-TE0 mode multiplexing, respectively, and the crosstalk is lower than -10dB.
We designed an ultra-broadband, compact, CMOS compatible, arbitrary ratio power splitter based on 220-nm-thick silicon-on-insulator (SOI) platform. The geometry of power splitter was digitalized into 20 parameters. For each different power splitting ratio (PSR), these 20 parameters were optimized to achieve low excess loss, using variational finite difference time domain (varFDTD) simulation and adjoint shape optimization. After many iterations of optimization, the structure was finally determined. The simulated excess loss was optimized to a low value, which was below 0.13dB. The PSR variation was limited to less than 0.459dB over 500 nm, across the O band and C band, showing that the PSR of the device was wavelength independent. An order of magnitude smaller than other kind of typical power splitters, the footprint of the proposed device is only about 1.2 μm × 2 μm, ensuring the compactness of the photonic integrated circuits (PICs). Simultaneously, it is easy to fabrication since the boundaries are smooth with a fairly large feature size.
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