Tunable impedance microwave matching of laser diodes

Three types of an impedance matching circuits (MC) namely resistive, reactive and tunable reactive MC (TRMC) are analyzed to estimate the advisability of their application for directly modulated lasers (DML) in microwave (MW) photonic systems. Return loss (|S11|) and insertion loss (|S21|) frequency dependencies for MCs loaded by a DML are calculated for X-band broadly used in radar systems. Analysis of the TRMC characteristics is carried out taking into account the microwave parameters of tunable elements of different classes (semiconductor, ferroelectric and micro-electromechanical (MEM) elements). It is shown that in the instantaneous frequency band (Δfi ∼ 1 GHz) the TRMC in comparison with the resistive MC provides more than 10 dB increase of the MW power delivered to an active region of the DML. Proposed TRMC demonstrate ∼ 2.5 times increase of the total frequency operating bandwidth (Δfop ∼ 5 GHz) due to a frequency scan possibility for the instantaneous band in contrast with the non-tunable reactive MC.