Commercial high-speed silicon (Si) Mach-Zehnder modulator (MZM) required to be active around the quadrature bias point (linear transmission area) with low power consumption, small footprint, and small drive voltage. The bias controlling is done by an optical phase-shifter (PS). However, the accuracy is limited by the drive voltage, laser thermal drift, and fabrication errors. To overcome these problems, we propose in this paper the study and analysis of Si PIN diode PS under forward biasing at 1550 nm wavelength using the standard 220 nm substrate silicon-on-insulator (SOI) rib waveguide technology. Numerical investigations were carried out on the key geometrical parameters, doping concentration, doping locations, operating wavelength, biasing level. Results show that the optimal design can be operated with a lower voltage (Vπ = 1.629 v), lower attenuation (α = 28.985 dB/cm), and short device length with an extremely small voltage-length product VπL = 0.815 vmm. Thus, this PS can be used for designing an efficiency high-speed MZM and to obtain better performances in the optical commutation system.

Optimizations of Si PIN diode phase-shifter for controlling MZM quadrature bias point using SOI rib waveguide technology

Junction-less optical phase shifter loaded silicon Mach-Zehnder modulator

Performance analysis of an electrostatic doping assisted silicon microring modulator

Nonlinear performance and small signal model of junction-less microring modulator

The use of electrical precompensation for high-speed operation of lumped MZMs is demonstrated for 50 Gb/s PAM4 modulation through experiment and simulation. An accurate equivalent circuit model is fitted to S11 measurements and then used to analyse design trade-offs in terms of system performance, energy consumption and drive voltage requirements. If precompensation is not used, careful selection of source resistance with respect to electrode and packaging inductance is shown to be crucial for high-speed modulation. Increasing the electrode inductance is shown to be beneficial as it introduces inductive peaking, which allows optimum performance with a higher source impedance. Furthermore, combining precompensation with a slight inductive peaking and optimised source resistance is demonstrated to reduce drive voltage requirements and further reduce the energy dissipated in the equivalent circuit.

Predistortion for High-Speed Lumped Silicon Photonic Mach-Zehnder Modulators

. We present the design of a single-drive Mach-Zehnder modulator for amplitude modulation in silicon-on-insulator technology with 250 nm active layer thickness. The applied RF signal modulates the carrier density in a reverse biased lateral pn-junction. The free carrier plasma dispersion effect in silicon leads to a change in the refractive index. The modulation efficiency and the optical loss due to free carriers are analyzed for different doping configurations. The intrinsic electrical parameters of the pn-junction of the phase shifter like resistance and capacitance and the corresponding RC-limit are studied. A first prototype in this technology fabricated at the IMS CHIPS Stuttgart is successfully measured. The structure has a modulation efficiency of VπL = 3.1 V ⋅ cm at 2 V reverse bias. The on-chip insertion loss is 4.2 dB. The structure exhibits an extinction ratio of around 32 dB. The length of the phase shifter is 0.5 mm. The cutoff frequency of the entire modulator is 30 GHz at 2 V. Finally, an optimization of the doping structure is presented to reduce the optical loss and to improve the modulation efficiency. The optimized silicon optical modulator shows a theoretical modulation efficiency of VπL = 1.8 V ⋅ cm at 6 V bias and a maximum optical loss due to the free carrier absorption of around 3.1 dB cm−1. An ultra-low fiber-to-fiber loss of approximately 4.8 dB is expected using the state of the art optical components in the used technology.

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Design of a carrier-depletion Mach-Zehnder modulator in 250 nm silicon-on-insulator technology

An improved phase detection scheme for Mach-Zehnder and bimodal interferometers is presented. By using a 90° hybrid, always two outputs operate at a highly sensitive point and the phase-shift-unambiguousness is extended to a range of 2π. The phase detection is independent of mode attenuations and input power fluctuations.

Improved Phase Detection in On-Chip Refractometers

A broadband integrated notch filter, using the silicon nitride (Si 3 N 4 ) platform, is presented. It achieves an extinction ratio (ER) of 60 dB and a full width at half maximum (FWHM) of 10 nm at the central wavelength (CW) 785 nm. The main filter components are Bragg gratings (BGs). For separating the occurring reflections from the input waveguide, two identical BGs are combined with a directional coupler (DC) acting as optical circulator. The 3-dB bandwidth of the passband (790 nm to 1200 nm) is more than 400 nm.

Design of a Broadband Integrated Notch Filter in Silicon Nitride

A switch-fabric for the channel routing is presented which combines the wavelength-separation-ability of arrayed waveguide gratings (AWGs) with the tunability of generalized Mach-Zehnder interferometers (GMZIs). The resulting tunable filter allows to maximize and shift a desired spectral transmission-window, whereby the window-bandwidth is defined by waveguide-length-offsets.

Enhanced Generalized Mach-Zehnder Interferometer for Tunable Channel Routing

In photonic integrated circuits grating couplers are commonly used to establish an efficient and stable fiber-to-chip link. However, the actual coupling efficiency of a fiber-to-chip interface depends strongly on the used wavelength and exhibits a maximum at a distinct target wavelength, determined by grating design parameters. In this paper, an enhancement of the optical bandwidth of silicon grating couplers by adding integrated dispersive structures is discussed. These are realized by single layers, prism-like geometries and additional silicon nitride gratings. Theoretical considerations for a bandwidth-enhancement by dispersive layers are performed and applied to an existing grating coupler design. A simulated 1dB-bandwidth of up to 90 nm at a maximum efficiency of − 0.65 dB in the C-band could be achieved, which is an enhancement to a factor of about 2 compared with the original coupler design.

https://link.springer.com/content/pdf/10.1007/s11082-020-2194-0.pdf

Raik Elster

Papers

Design of a carrier-depletion Mach-Zehnder modulator in 250 nm silicon-on-insulator technology

Improved Phase Detection in On-Chip Refractometers

Design of a Broadband Integrated Notch Filter in Silicon Nitride

Enhanced Generalized Mach-Zehnder Interferometer for Tunable Channel Routing

Integrated dispersive structures for bandwidth-enhancement of silicon grating couplers