Hitless Wavelength Switching of Semiconductor Optical Amplifier-integrated Reflection-type Transversal Filter Laser with Suppressed Frequency Error

A spurious wavelength (spurious) from a tunable laser during tuning is an issue in optical systems based on dynamically controlled laser wavelengths.Output shuttering synchronized with tunable-laser tuning is promising way to suppress spurious.A semiconductor optical amplifier (SOA) is an ideal shutter for laser outputs with spurious in terms of lowwavelength-independent extinction ratio.We developed an electro-optically tunable reflection-type transversal filter (RTF) laser monolithically integrated with an SOA.Thanks to the nanosecond scale tuning speed of the RTF laser, the required shuttering time of the integrated SOA is also a corresponding nanosecond scale, which leads to little temperature change in the laser cavity.As a result, the laser frequency drift after turning off/on the SOA is suppressed to within +/-2.5 GHz without any additional laser control algorithm to compensate for the thermal crosstalk from the SOA.Using the laser, we demonstrated a "hitless" wavelength-switching subsystem based on a coherent format.Namely, outputs from an SOA-RTF laser coded with 32-GBd dual-polarization quadrature phase-shift keying (128 Gbps) are dynamically switched with spurious eliminated by SOA shuttering.In addition to practical bit error rates (BERs) of wavelength channels from the SOA-RTF laser, we observe no interference with the BER of a wavelength channel from another monitor laser in the wavelength-switching subsystem.