Abstract

Wavelength-division (WD) and time-division (TD) hybrid switching networks are expected to be one of the strong candidates for future broadband ISDN (B-ISDN) H₄ signal (around 150 Mbps) STM switching networks[1]. In these switching networks, high-speed wavelength switching operation of tunable wavelength filters is necessary. Recently, to confirm the feasibility of an 8 WD and 4 TD hybrid switching network to cater for 100 Mbps signals, a wavelength switching experiment was demonstrated with a TD multiplexed signal in a byte-interleaved signal form with 6.7-nsec guard-time. Wavelength switching within the guard-time was accomplished[2], by using a phase-shift-controlled DFB LD tunable wavelength filter[3]. However, a bit-interleaved signal form is more suitable for the hybrid switching network than that of a byte-interleaved signal form, because of the amount of hardware required for the time switch, used for the hybrid switching networks. To employ the bit-interleaved signal form, improvement in the wavelength switching time is required for tunable wavelength filters. Wavelength switching in times of 1 nsec has been reported, using a DFB LD tunable filter[4]. However, this type of filter with wavelength tuning principles based on the effective refractive index change due to the carrier injection effect, lacks the possibility of achieving less than 1-nsec wavelength switching time. This is mainly due to the value of the carrier life time.

© 1991 Optical Society of America