A Mach-Zehnder optical modulator with the tunable multimode interference coupler was fabricated using Ti-diffused LiNbO3. The modulation extinction ratio could be voltage controlled to maximize up to 50 dB by tuning the coupler. Optical single-sideband modulation was also achieved with a sideband suppression ratio of more than 30 dB.

A technique for improving the input power dynamic range and extinction ratio of wavelength converters based on cross-gain modulation in a semiconductor optical amplifier is presented.

To enhance the extinction ratio (ER) of NRZ-to-inverted-RZ converter based on cross-gain compression of a semiconductor optical amplifier (SOA), a modified terahertz optical asymmetric demultiplexer (TOAD) is cascaded. ER is improved from 1.6-6.7 dB to 5.4-14.5 dB, depending on the intensity of input optical NRZ signal. The proposed NRZ-to-inverted-RZ converter enhances and regulates ER to a high value (14.5 dB) for very wide optical NRZ signal intensity range.

To enhance the extinction ratio (ER) of NRZ-to-inverted-RZ converter based on cross-gain compression of a semiconductor optical amplifier (SOA), a modified terahertz optical asymmetric demultiplexer (TOAD) is cascaded. ER is improved from 1.6-6.7 dB to 5.4-14.5 dB, depending on the intensity of input optical NRZ signal. The proposed NRZ-to-inverted-RZ converter enhances and regulates ER to a high value (14.5 dB) for very wide optical NRZ signal intensity range.

We have developed a multiple quantum well (MQW) electroabsorption (EA) modulator for wavelength-division multiplexing (WDM) switching systems. The fabricated MQW EA gate has low polarization and wavelength-dependent loss and high extinction ratio within the wavelength range of 1545 to 1560 nm. And by using this gate ultra-high-speed switching is achieved for WDM signals. Moreover, we optimize the EA gate for the full gain-band of an erbium-doped fiber amplifier (EDFA)(1535 to 1560 nm). This EA gate provides low polarization-dependent loss, higher extinction ratio, and high saturation input power in the wider wavelength range. These MQW EA gates will play an important role in future WDM switching systems.