Slow light with interleaved p-n junction to enhance performance of integrated Mach-Zehnder silicon modulators

Abstract

Slow light is a very important concept in nanophotonics, especially in the context of photonic crystals. In this work, we apply our previous design of band-edge slow light in silicon waveguide gratings [M. Passoni et al, Opt. Express 26, 8470 (2018)] to Mach-Zehnder modulators based on the plasma dispersion effect. The key idea is to employ an interleaved p-n junction with the same periodicity as the grating, in order to achieve optimal matching between the electromagnetic field profile and the depletion regions of the p-n junction. The resulting modulation efficiency is strongly improved as compared to common modulators based on normal rib waveguides, even in a bandwidth of 20-30 nm near the band edge, while the total insertion loss due to free carriers is not increased. The present concept is promising in view of realizing slow-light modulators for silicon photonics with reduced energy dissipation.

Compact and Energy-Efficient Forward-Biased PN Silicon Mach-Zehnder Modulator

“…The refractive index of silicon can be varied by changing the concentration of the carriers inside the material, which can be performed in two ways [5,6]. The first is to deplete the carriers (by utilizing reverse-bias configuration) [7,8], and the second way is to inject carriers (by a forward-bias configuration) [9][10][11][12]. The number of reverse-biased MZMs manufactured by the silicon industry every year is far more than the number of forward-biased MZMs as they are suitable for various applications that require high BW, high speed, etc.…”

Comparison of lithium niobate and silicon substrate on phase shift and efficiency performance for mach-zehnder interferometer modulator

“…This means that the slow light is due to the large firstorder dispersion dk/dω. Furthermore, the slow light is limited by the delay-bandwidth product written as ng(Δω/ω)=ng(Δλ/λ)=Δn, where Δω and Δλ are the frequency and wavelength bandwidth of slow light, respectively and Δn is the effective refractive index change in material or structure within the bandwidth [28,29]. This relationship implies that, one cannot expect a large ng independently of the bandwidth.…”

Recent Progress in Silicon-Based Slow-Light Electro-Optic Modulators

“…The research illustrates the trade-off between modulation rate, loss, and energy consumption. However, the optimization of the device was not enough, and further optimization should be able to get better results [72]. Furthermore, they developed the full simulation of the silicon slow-light modulator with interleaved PN junction along the waveguide axis, as in Figure 15B.…”

“…However, in general, although the modulation efficiency and footprint of the modulator have both achieved ideal values, the EO bandwidth of the modulator is still not large enough and the high-speed performance is limited, while the optical bandwidth also has a certain space for optimization for a more stable working condition [74]. [72]. (B) Schematic of the slow-light waveguide with interleaved PN junctions [73].…”

“…According to the simulation results, the modulation efficiency was improved compared to the conventional silicon modulator, with 0.1–0.5 V·cm over a bandwidth of 20–30 nm, as shown in Figure 15 C. The research illustrates the trade-off between modulation rate, loss, and energy consumption. However, the optimization of the device was not enough, and further optimization should be able to get better results [ 72 ]. Furthermore, they developed the full simulation of the silicon slow-light modulator with interleaved PN junction along the waveguide axis, as in Figure 15 B.…”