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.
Compared with the optical modulator based on 1310 nm and 1550 nm wavelength band, the silicon-based modulator at 2 μm band has a higher absorption loss, since the free carrier effect is more significant in the 2 μm band. In this paper, we demonstrate an optical modulator at 2 μm wavelength band, using a doping compensation method. We reduce absorption loss and keep the modulation extinction ratio at a high level through optimizing waveguide width, PN junction offset and compensated area. With doping compensation, the modulator has an absorption loss by PN junction of 2.8 dB/cm at 0 V and an extinction ratio of 14.2 dB at bitrates of 40 Gb/s.
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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