Mao-Teng Hsu

Silicon Optical Modulators in Silicon-on-Insulator Substrate Based on the p–i–n Waveguide Structure

We report the fabrication and characterization of the P–P-–N optical waveguide modulators fabricated on silicon-on-insulator (SOI) substrate. The modulation scheme was achieved via the carrier injection, or plasma dispersion effect. The corresponding P and N regions were defined in both types of SOI substrates (P-type SOI and highly resistive N-type SOI substrates with respective resistivities of ρ~7–10 Ω cm and ρ~7000–10000 Ω cm) using the spin-on-dopant (SOD) technique conducted at 900–1000 °C in a nitrogen ambient. The resultant dopant concentrations and diffusion depths were found to be critically dependent on the diffusion time/temperature and the resistivity of SOI substrate used. For the modulators fabricated with various waveguide widths and electrode lengths, the corresponding modulation index was enhanced in response to an increase in the electrode (or modulation) length and/or a decrease in waveguide width. The highest modulation index of ~4.15% was successfully achieved for a silicon P–P-–N waveguide modulator with 5-µm-wide waveguide and 7-mm-long modulation electrode.

Silicon Electro-Optic Modulator Fabricated on Silicon Substrate Utilizing the Three-Terminal Transistor Waveguide Structure

The fabrication and characterization of the three-terminal transistor-based optical waveguide modulators fabricated on silicon substrate are reported. The modulation scheme was achieved via the carrier injection, or plasma dispersion effect. The spin-on-dopant (SOD) method was conducted at 1000 °C in a mixture of nitrogen/oxygen ambient to separately pattern the heavily-doped source (n+), gate (p+), and drain (n+) regions. The corresponding p- and n-type dopant profiles were determined using the spreading resistance probe (SRP) technique, of which the highest surface concentrations of ~2.09×1020 and ~3.53×1020 cm-3 were respectively achieved. The resultant dopant concentrations and diffusion depths were found to be critically dependent on the diffusion time and temperature. The results of our experiments revealed that there are virtually little or no dependencies of the modulation depth on the gate current and modulation length. Finally, the modulators thus fabricated showed an ultra-sensitivity on the drain–source voltage (VDS), with a modulation depth close to 100% at VDS~±5 V when a 5 mA gate current was applied.

Silicon Optical Modulators in Silicon-on-Insulator (SOI) Substrate Based on the p-i-n Waveguide Structure

Silicon has already been demonstrated as a viable material for passive and active optoelectronic device applications in the infrared regime (λ > 1.2 μm) of the electromagnetic spectrum. Over these years, silicon’s role in integrated optics has been successfully transformed from substrate material to guiding material. In fact, a lot of works in the past have shown that the silicon planar and rib waveguides can be fabricated with low losses, and hence they can easily be adapted into the designs of many passive and active silicon-based devices. One structure that exhibits a strong confinement of light is silicon-on-insulator (SOI). The ability of SOI to confine the propagating light in two dimensions is actually due to the large refractive index difference between the silicon guiding region (n = 3.5) and the two cladding regions, air (n = 1.0) and SiO2 (n = 1.46). SOI-based rib waveguides have been reported to show losses of typically 0.4 dB/cm [1] at a wavelength of λ = 1.5 μm. Until recently the majority of work in the field of silicon optical phase modulators has been based on modulators with silicon surface layers on the order of several microns thick [2]. Optical modulation can be achieved either via the thermal-optical effect [3] or the plasma dispersion effect [4]. In terms of device operating speed, however, the plasma dispersion effect has a fast response whereas the thermal-optical effect is a rather slow process. Free-carrier plasma dispersion has been demonstrated in silicon waveguides as a technique of modulating refractive index [5], and the carrier density within waveguides can be modulated using a forward biased p-i-n junction which brings about changes in the refractive index [6]. This work describes the fabrication and characterization of single mode optical waveguide modulators based on the plasma dispersion effect using SOI as the substrate. The single mode waveguide condition is to be achieved based on a rib waveguide structure with large cross-section [7-8] and the pertinent waveguide dimensions (rib width/height and the neighboring slab waveguide thickness) are to be decided based on the simulation results of Beam Propagation Method (BPM).

Multimode interference (MMI) waveguides-based photonic modulators integrated on SOI substrates

Multimode interference (MMI) waveguides-based photonic modulators integrated on silicon-on-insulator (SOI) substrates are designed, fabricated and evaluated. With 100% modulation depth achieved, the lowest rise and fall times were respectively measured to be 52 and 48 ns. The highest 3 dB bandwidth in the excess of 6.5 MHz was determined from the corresponding devices.

Mach-Zehnder Electro-Optic Modulator Fabricated on Silicon-on-Insulator (SOI) Substrate Based on the Multimode Interference (MMI) Effect

Substrate Based on the Multimode Interference (MMI) Effect Ricky W. Chuang, Mao-Teng Hsu, Yu-Chun Chang, Shen-Horng Chou, and Yao-Jen Lee Institute of Microelectronics, Department of Electrical Engineering, Advanced Optoelectronic Technology Center (AOTC), and Center for Micro/Nano Science and Technology, National Cheng Kung University, Tainan 70101, Taiwan, R.O.C. National Nano Device Laboratories, Hsinchu City 30078, Taiwan, R.O.C. National Nano Device Laboratories, Tainan 74147, Taiwan, R.O.C. Corresponding Author’s Phone and Email: +886-6-2757575 ext. 62397 and rwchuang@mail.ncku.edu.tw

2 x 2 Thermooptic Silicon Oxynitride Optical Switch Incorporating the Cascaded Multimode Interference Waveguides

Cascaded Multimode Interference Waveguides Ricky W. Chuang, Mao-Teng Hsu, and Zhen-Liang Liao 1 Institute of Microelectronics, Department of Electrical Engineering, Advanced Optoelectronic Technology Center, and Center for Micro/Nano Science and Technology, National Cheng Kung University, Tainan City 70101, Taiwan, R.O.C. 2 National Nano Device Laboratories, Tainan County 74147, Taiwan, R.O.C. Corresponding Author’s Phone and Email: +886-6-2757575 ext. 62397 and rwchuang@mail.ncku.edu.tw

Silicon p-i-n optical waveguide modulators fabricated on the silicon and silicon-on-insulator substrates

The fabrication and characterization of the p-i-n optical waveguide modulators on silicon-on-insulator (SOI) substrate were demonstrated. The modulation was based on the mechanism of carrier injection, or plasma dispersion effect. The corresponding p and n regions were defined in both types of silicon substrates (conventional p-doped and highly resistive SOI substrates with respective resistivities of &rgr;~7-10&OHgr;-cm and &rgr;~7000-10000&OHgr;-cm) using the spin-on-dopant (SOD) technique. The SOD diffusion process was conducted at 900-1000°C in nitrogen ambient. The diffusion time and temperature, and the resistivity of SOI substrate used were the primary parameters dictating the resultant dopant concentrations and diffusion depths. For the modulators fabricated with various waveguide widths and electrode lengths, the corresponding modulation index was enhanced in response to an increase in the electrode (or modulation) length and/or a decrease in waveguide width. The highest modulation index of ~4.15% was successfully achieved for a silicon p-i-n waveguide modulator with 5&mgr;m,wide waveguide and 7mm-long modulation electrode.