Fig. 2: Cryogenic MO modulator, design and optimization.
From: An integrated magneto-optic modulator for cryogenic applications
a, Magnetic field generated by the electric current in the metal coil (electromagnet). The streamlines of the current are highlighted in red, whereas the intensity of the in-plane radial magnetic field is shown in the Ce:YIG plane. On the same plane, the arrows indicate the direction of the magnetic field. b, Magnetic-field distribution in the device cross-section for a current of 110 mA. c, Profile of the transverse-magnetic optical mode (the main magnetic-field component) computed assuming a 10-nm-thick silica layer between the silicon and Ce:YIG layers. d, Calculated redshifted and blueshifted spectral response of the device when the current is +110 mA (dashed pointed red curve) and −110 mA (solid blue curve), respectively. As a reference, the spectral response when no current is injected is also plotted (dashed grey curve). These curves refer to a microring resonator with a full-width at half-maximum ΛFWHM = 97 pm, such that the loaded Q = λ/ΛFWHM equals 16,000. The input laser wavelength is shown (λtbm, green dashed line) along with the ER and MO shift (±ΔλMO). e, ER as a function of modulation current for several microring-based modulators with different coupling coefficients (K) to the waveguide. The dot refers to the DUT, where the coupling coefficient (K = 0.11) and the round-trip loss (γ = 0.063) are computed from the measured ER and FWHM of the spectral response. f, Modelled energy consumption per bit as a function of the modulation current at different temperatures for a modulation rate of 2 Gbps (the experimental values of gold conductivity at 300, 77 and 4 K are considered). In the case of a superconducting (SC) magnet, the power dissipated in the resistance of the coil vanishes, leaving only the LI2/2 component of dissipation. The dot refers to the DUT. g, Energy per bit as a function of ER in the undercoupled, critically coupled and overcoupled conditions. The simulations refer to the case of gold contacts, at a temperature of 4 K, with a modulation rate of 2 Gbps. The dot refers to the DUT.
