Compact PIN-Diode-Based Silicon Modulator Using Side-Wall-Grating Waveguide

Abstract

We developed PIN-diode-based silicon Mach-Zehnder modulators, which have side-wall-gratings in the phaseshifter sections. Such passive waveguides with gratings were fabricated using ArF immersion lithography, which showed a small scattering loss of 0.4 dB/mm. We extensively investigated the forwardbiased operation of the modulators by using equivalent circuit analysis and the measurement of the fabricated devices. We argue carrier recombination time only plays a minor role for the overall performance of the modulator. Dependences of the modulation efficiency on other various critical parameters are discussed. In particular, if we use relatively short phase shifter, the forwardbiased operation provides smaller V π L than reversed one even at high frequency of 20 GHz, at the expense of the narrow bandwidth. Our approach enables high-speed operation up to 50 Gb/s, by using phase shifter as short as 250 μm and preemphasis signals. For 12.5-Gb/s operation, the modulator cell size was only 300 μm × 50 μm, which was suitable for the applications of high-density optical interconnects.

Wide Spectral Characteristics of Si Photonic Crystal Mach-Zehnder Modulator Fabricated by Complementary Metal-Oxide-Semiconductor Process

“…It is well suited for the development of components and subsystems for optical interconnects in data centers and high-performance computers. For these cases, optical modulators are key [1][2][3][4][5][6] and a wide working spectrum and wide working temperature range are particularly required in optical interconnects, in addition to small size, low loss, low drive voltage and high speed.…”

High-speed and efficient silicon modulator based on forward-biased pin diodes

“…When ωρc >> 1 above the cut-off frequency, FOM becomes proportional to the product of αQ π ρ, as shown at the rightmost side in the last equation. Forward-bias operation provides more efficient operation than the reverse [25,26] by using suitable frequency compensation.…”

“…Figure 5 has schematic views of the device we used in the experiments [23][24][25][26]. Modulators based on an asymmetric MZ interferometer [25] and a ring resonator [24] were respectively used in the experiment to extract the parameters and achieve high-speed large signal modulation. These experiments are described in the sections that follow in series.…”

“…Further, we embedded the phase shifter into a ring resonator to increase the effective optical interaction length, as Figure 5B shows. We used pre-emphasis signals to compensate for the frequency response of the modulator in forward-biased mode, which were generated by a finite-impulse-response (FIR) filter from standard non-return-to-zero (NRZ) signals in a pseudo-random bit sequence (PRBS) of 2 7 -1 [21,23,25]. The rate of the preemphasis signals was 56 Gb/s and their amplitude was about 2 V pp .…”

“…These modulators need electric capacitors, which can dynamically store and release electrons and/or holes at the waveguide core. Thus, far, forward [20][21][22][23][24][25][26] and reverse-biased [20,[27][28][29][30][31][32][33][34] pn diodes, and MOS capacitors operated in accumulation mode [35][36][37][38] have been implemented, and such devices have all demonstrated high-speed operations above 40 Gb/s with reasonably small driving voltages and footprints. Modulators that are superior in terms of fundamental performance should be chosen to meet the requirements of continuously increasing data rates of transceivers.…”