ABSTRACT
In this paper, a design for a high extinction ratio Mach-Zehnder optical modulator is proposed. The switchable refractive index of the germanium-antimony-selenium-tellurium (GSST) phase change material is employed to induce destructive interference between the waves passing through Mach-Zehnder interferometer (MZI) arms and to realize amplitude modulation. A novel, to the best of our knowledge, asymmetric input splitter is designed for the MZI to compensate for unwanted amplitude differences between MZI arms and increase the modulator performance. Three-dimensional finite-difference-time-domain simulations show a very high extinction ratio (ER) and low insertion loss (IL) of 45 and 2 dB, respectively, for the designed modulator at the wavelength of 1550 nm. Moreover, the ER is above 22 dB, and the IL is below 3.5 dB in the wavelength range of 1500-1600 nm. The thermal excitation process of GSST is also simulated using the finite-element method, and the speed and energy consumption of the modulator are estimated.
ABSTRACT
A high-performance electro-optic Mach-Zehnder modulator (MZM) with outstanding characteristics is proposed. The MZM is in a push-pull configuration that is constructed using an ITO/graphene-based silicon waveguide. A novel idea for engineering of the plasma dispersion effect in an ITO/graphene-based waveguide is proposed so that the modulation characteristics of the MZM are highly improved. Plasma dispersion effects of ITO and graphene layers are tailored in such a way that a large difference between real parts of guided mode effective index of the two arms is achieved while their corresponding imaginary parts are equal. As a result, a very low [Formula: see text] of [Formula: see text] is achieved. To the best of our knowledge, this is one of the lowest [Formula: see text] reported for an electro-optic modulator. In addition, the proposed modulator exhibits a very high extinction ratio of more than 30 dB, low insertion loss of 2.8 dB and energy consumption of as low as 10 fJ/bit, which are all promising for optical communication and processing systems.
ABSTRACT
A design for a CMOS-compatible active waveguide is proposed in which the epsilon-near-zero (ENZ) property of the indium-tin-oxide (ITO) is used to induce large variations in the real and imaginary parts of the waveguide effective index. The proposed waveguide comprises a TiN/HfO2/ITO metal-oxide-semiconductor (MOS) structure where the speed and power consumption are significantly improved by the application of the TiN and realization of double accumulation layers in the ITO. Simulations show the insertion loss (IL) of 0.38 dB/µm, extinction ratio (ER) of 11 dB/µm, the energy consumption of 11.87fJ/bit and electrical bandwidth of 280 GHz when the designed waveguide is used as an electro-absorption modulator. The waveguide is then used in an MZI structure to design binary and quadrature-amplitude-modulator (QAM) modulators. For binary modulator, the IL, ER, and VπLπ figures of merit are found to be 1.24 dB, 54 dB, and 6.4 V µm, respectively, which show substantial improvement over previous ITO-based designs. In the QAM design, the symmetry in the real and imaginary parts of the waveguide effective index is employed to obviate the need for additional phase shift elements. This considerably reduces the overall length of the proposed QAM modulator and improves efficiency. Simulations show the energy consumption and bit rate, of 2fJ/bit and 560 Gbps, respectively in a 4-QAM modulator with the overall length of 6.2 µm. The symmetry properties of the proposed waveguide can be further exploited to realize quadrature-phase-shift-keying (QPSK) modulators which here is used in combination with the 4-QAM to propose a design for the more advanced modulation scheme of 16-QAM. The design of ITO-based QAM modulators is here reported for the first time and the abovementioned performance parameters show the unique properties of these modulators in terms of footprint, energy consumption and modulation-speed.
