40 Gbit/s low-loss silicon optical modulator based on a pipin diode

Abstract

40 Gbit/s low-loss silicon optical modulators are demonstrated. The devices are based on the carrier depletion effect in a pipin diode to generate a good compromise between high efficiency, speed and low optical loss. The diode is embedded in a Mach-Zehnder interferometer, and a self-aligned fabrication process was used to obtain precise localization of the active p-doped region in the middle of the waveguide. Using a 4.7 mm (resp. 0.95 mm) long phase shifter, the modulator exhibits an extinction ratio of 6.6 dB (resp. 3.2 dB), simultaneously with an optical loss of 6 dB (resp. 4.5 dB) at the same operating point.

Recent breakthroughs in carrier depletion based silicon optical modulators

“…A loss of 1 dB/mm occurred in this case with a phase efficiency of 3.5 V.cm. The authors were also able to demonstrate 40 Gbit/s modulation [43]. In a similar concept Tu et al [35] used a doping compensation method to reduce the concentration of free carriers in the upper sides of the rib (as depicted in the bottom image of Figure 4).…”

“…Devices with operation in excess of 40 Gbit/s [25,33,41,45,48], phase efficiencies below 1 V.cm [50], power consumption down to 2 fJ/bit [51] and loss at 1 dB/mm and below [35,43,45] have been demonstrated although not with all these parameters together. Continual improvements in the device performance are still regularly being reported.…”

“…Recently other research groups have also used the same self-aligned angled ion implantation approach [42]. Furthermore it was also later reported that the device of Marris-Morini et al could also be formed using a self-aligned process [43]. The device of Gardes et al is a slightly different category of device which combines different pn junction types, in this case the vertical and horizontal pn junctions.…”

Silicon Mach-Zehnder modulator using low-loss phase shifter with bottom PN junction formed by restricted-depth doping

“…Various types of silicon MZMs have therefore been widely studied. Some of them have even achieved 40-Gbps on-off-keying (OOK) by operating in carrier depletion mode [2,3,4,5,6,7]. For long-distance optical communications, signal qualities such as extinction ratio (ER) and chirp characteristics are important.…”

“…The high modulation efficiency was realized using strong optical confinement in the thick silicon waveguide of 340-nm height instead of 220-nm height widely used for silicon waveguide devices. Optimization of a dopant profiles in 220-nm height waveguides [10] and an improved PN junction design [6] are also reported respectively. The doping profiles are fabricated using complicated fabrication steps in comparison with the conventional PN junction.…”