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.
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.
We report the demonstration of Si-based waveguide Ge1-xSnx photodetector (PD) at L-band (1565-1625 nm), U-band (1625-1675 nm), and 2μm light detection, optical and electrical properties are studied by using simulation models. With introduction of 4.5% Sn into Ge, the GeSn waveguide PD with evanescent coupling exhibits a high responsivity of 1.25 A/W, dark current is lower than 12 nA. This work provides a new choice for future infrared detection, beneficial to needs of broadband spectrum communication, and compatible with CMOS circuits.
A compact and broadband optical 90° hybrid based on a 2×4 multimode interference (MMI) coupler using the Si3N4 technology is proposed. The effects of MMI length, width, and wavelength on optical power transmission are investigated. With the length of 217 μm for the 2×4 MMI coupler, this optical 90° hybrid shows a maximum phase error of 5°, an excess loss of 1 dB, and a transmission imbalance of 1 dB over a 75-nm-wide wavelength range.
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