In this article, a high-efficiency grating coupler based on a lithium niobate platform is presented. To enhance the coupling efficiency, a silicon nitride strip waveguide grating is introduced beneath the lithium niobate grating. Through the optimization of grating period, duty cycle, and other parameters using a particle swarm optimization (PSO) algorithm, a TE-polarized grating coupler with high coupling efficiency is achieved, resulting in a simulated peak coupling efficiency of approximately -2.19 dB. To further improve the performance of the grating coupler, a chirped design of the grating etch slots is implemented. A double-layer design with inversely linear variation in duty cycle is adopted, and the variation coefficients are optimized using the PSO algorithm, achieving a simulated peak coupling efficiency of approximately -1.72 dB with a 1 dB bandwidth of approximately 42 nm. Process tolerance simulations are also performed on the key parameters of the double-layer grating coupler, demonstrating good process tolerance of this design.
Applying various functional materials to silicon to enhance the functionality of silicon photonics is a potential solution for silicon photonics platform under the requirement of CMOS compatibility. In this paper, two LN heterogeneous integration platforms have been proposed. One is the integration of LN film with a 220 nm top silicon SOI platform, in which the simulated results demonstrate that the designed modulator has a low half wave-voltage length product of 2.27 V·cm. And the other is the integration of LN film with a 400 nm top silicon nitride on insulator platform, in which the the proposed device achieves a VpiL of 2.58 V·cm and a 3-dB bandwidth of ~130 GHz with 7-mm long modulation region is verified by simulation.
High-quality factor(Q) waveguide ring resonators (WRRs) are essential components of the resonator-integrated optical gyroscope (RIOG). The single-mode and multimode silicon oxynitride (SION) WRRs are investigated in this paper. The optical, resonance, and polarization properties are characterized. The intrinsic Q of single-mode WRR is 8.25×105 . And the multimode WRR achieves an intrinsic Q of 1.02×106 , corresponding to the waveguide propagation loss of 0.3 dB/cm. The designed multimode SION WRRs can be used as a critical sensing element to enhance RIOG performance further. Keywords: High Q ring resonators, Multi-mode SION waveguide, Integrated optics.
A polarization-insensitive four-channel wavelength-division multiplexing (WDM) (de)multiplexer based on Mach-Zehnder interferometers is proposed and demonstrated. Polarization insensitivity can be achieved by utilizing the square waveguides and bend directional couplers (bend DCs) based on silicon oxynitride (SiON) waveguides. The WDM (de)multiplexer has an 800GHz spacing for LAN-WDM application. Two stages of cascaded MZIs are utilized to achieve a four-channel spectral response. For the realized WDM (de)multiplexer with Gaussian-like passbands, the polarization-dependent losses (PDL) are less than 0.7dB for all 1-dB passbands. The insertion losses are <~ 3dB and the crosstalk is <~ -12dB for both TE and TM polarizations at channel central wavelengths.
Since carrier dispersion and carrier absorption exist at the same time when the phase shifter is under phase modulation, decrease in extinction ratio is inevitable for silicon-based MZI modulator based plasma dispersion effect. In this paper, we demonstrate an optical modulator at 1550 nm wavelength band, using a cascaded compensation method. We balance the optical intensity in the two phase shifters of the MZI structure during modulation. With cascaded compensation method, the modulator has an extinction ratio of 51 dB and a dynamic extinction ratio of 10 dB at bitrates of 40 Gb/s.
A high efficient cantilever-type mode size converter applied at 800 nm wavelength is proposed and analyzed in this letter. The converter can compress and couple the light spot from a single mode fiber into the Silicon nitride waveguide effectively and smoothly. The core of the entire structure is supported by the SiO2 cantilever beam to make the device suspended, which can effectively prevent the light leaking from the substrate to cause great coupling loss. A Gaussian light source with a diameter of 4.5 μm and wavelength of 800nm is used for the coupling test. The coupling loss of the device with both TE and TM mode are greater than 0.54 dB. The alignment tolerances for 1-dB excess loss are both ± 0.8 μm in horizontal and vertical directions.
The 3D photonic integrated structure can increase the integration density of the device on a limited chip area, so that the chip has a higher optical interconnection capability. A polarization beam splitter (PBS) is one of the key components for manipulating different polarization states in the areas of optical interconnection and communication. In this paper, a novel interlayer PBS based on an asymmetrical directional coupler (DC) was proposed, which consists of a silicon rib waveguide (WG) and a silicon nitride (Si3N4) strip WG with a gap of 850 nm. By carefully adjusting the geometric parameters of the DC, the phase matching condition between these two WGs can be satisfied for the TM polarization, while the coupling efficiency of the TE polarization is frustrated due to the large phase mismatch. By adding a filter to the thru port the performance of the proposed PBS is improved. The device with a 220 nm Silicon-On-Insulator (SOI) WG and a 700 nm × 400 nm Si3N4 WG operates in a broadband width of 100 nm, with an extinction ratio (ER) <20 dB. The insertion losses (ILs) are <0.22 dB for both TE and TM polarizations at a wavelength of 1550 nm. At the same time, our design parameters conform to the Multi Project Wafer (MPW) process conditions, and the device is highly implementable. The device is potential to use for the on-chip 3D optical interconnect in the future.
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