Power balancing effect on the performance of IMPACC modulator under critical coupling (CC), over coupling (OC), and under coupling (UC) conditions at high frequency

Abstract

IMPACC (Interferometric Modulator with Phase-modulating and Cavity-modulating Components) is ultralinear optical consisting of a phase modulator and a ring resonator on different arms of a Mach Zehnder interferometer (MZI). External control of the RF power split ratio from an input radio frequency (RF) signal into the two separate arms of the interferometer has been shown to add (1) design flexibility, (2) the ability to achieve high spurious free dynamic range (SFDR) of more than 130 dB, when compared to the single-ring RAMZI (Resonator-assisted MZI) and (3) compensate parameter deviation due to manufacturing imperfection. Our previous reports have assumed that the Optical power split ratio of the input optical signal into the two arm of MZI is balanced with a 50:50 split ratio due to the optical splitter or optical coupler. Here, we investigate three issues. First, we report the negative effect of unbalanced power of the input optical signal on the SFDR performance of IMPACC. Second, we utilize the inherent compensate technique of IMPACC to counteract this effect. Third, the power unbalanced effect is reported at high RF modulation frequency (23GHz) for three different conditions of the ring resonator (RR) namely, critical coupling (CC), over coupling (OC), and under coupling (UC). Lastly, we compare the performance of IMPACC to the single-ring RAMZI with travelingwave electrode design under sub-octave operations.

Adaptive High Linearity Intensity Modulator for Advanced Microwave Photonic Links

“…Here, we set the other RF phase shift, ξ MRR equal to 0, for simplicity. Using again these two external parameters, we show that IMPACC can also extend its SFDR-vs-modulation bandwidth capability beyond that of RAMZI [91,[106][107][108]110]. Overall, the adaptive mode of IMPACC allows the link design to be flexible with excellent results.…”

“…Accordingly, the corresponding phase response, Θ MRR and group-delay (GD) [95] response of MRR can be derived as [110,111]:…”

“…(14) and (16) will be handy in the analysis of the new modulator that we discuss in Section 4. The relationship between the magnitude of the bus waveguide-to-MRR transmission coupling coefficient (τ) and the RR waveguide loss factor (α) defines the three different coupling conditions of MRR [73,85,91,[110][111][112]. Figure 10(a) shows the typical MRR while Figure 10(b) depicts its three different operating coupling conditions known as (1) critical-coupled (CC) when α = τ, (2) over-coupled (OC) when α>τ, and (3) under-coupled (UC)whenα<τ.…”

“…This section studies the effect on nonideal, unbalanced split ratios of the optical splitter (OS) or optical combiner (OC) on the SFDR performance of IMPACC for three different MRR operating conditions (OC, UC, CC) [110]. To simplify the analysis, we limit our study to unbalanced OS by maintaining OC to have 50:50 power split ratio.…”

“…This unique ability of IMPACC overcomes the negative effect of the intrinsic insertion loss due to MRR. This feature is not feasible in RAMZI or any In this section, we highlight IMPACC's ability to compensate the negative effect due to unbalanced optical splitter performance [110,113]. This is emphasized in Figure 20(a) where the original drop of 6 dB in the SFDR performance, when the optical splitter is nonideal (55:45), can be compensated to return to SFDR value equal to 129 dB by adjusting the external parameters, F and ξ PM to 0.2003 and 1.307π, respectively.…”