Ea Evgeni Patent

All-optical switching due to state filling in quantum dots

We report all-optical switching due to state filling in quantum dots (QDs) within a Mach–Zehnder interferometric switch (MZI). The MZI was fabricated using InGaAsP/InP waveguides containing a single layer of InAs/InP QDs. A 1530–1570 nm probe beam is switched by optical excitation of one MZI arm. By exciting below the InGaAsP band gap, we prove that the refractive index nonlinearity is entirely due to the QDs. The switching efficiency is 5 rad/(μW absorbed power), corresponding to a 6 fJ switching energy. Probe wavelength insensitivity was obtained using a broad size distribution of QDs.

Self-switching in Mach-Zehnder interferometers with SOA phase shifters

A self-switching mechanism in Mach-Zehnder interferometers (MZIs) is described. The input light signal is distributed unequally over the interferometer arms using an multimode interference (MMI) coupler. In the arms, semiconductor optical amplifiers are placed as nonlinear phase shifters. Unequal intensities yield a nonlinear phase shift. The signals from the two arms are then recombined in an output MMI coupler. If an obtained nonlinear phase shift in the arms can compensate the coupler-induced phase difference between the arms, the signals are in phase at the output port. Choosing an appropriate output coupler, 2/spl times/1 and 2/spl times/2 devices can be obtained. The 2/spl times/2 and 2/spl times/1 MZIs can be used as pattern effect compensators and 2R-regenerators or low-loss combiner circuits, respectively. An active-passive integration technique is applied in order to realize the interferometric structures. Fabrication, simulation, and characterization of these devices are presented in this letter.

Modeling of optical nonlinearities based on engineering the semiconductor band

A simplified model is used to describe the nonlinear optical behaviors of absorption and refractive index change of semiconductors. Based on engineering the semiconductor band, the optical absorption spectrum and the dispersion of the refractive index change are calculated by means of the density-matrix theory. The dependence of absorption coefficient and refractive index change on the optical intensity is shown. The numerical results show that near the bandgap the change in refractive index is remarkable. A trade-off of optical absorption and index change should be taken for the practical nonlinear optical devices.

Photonic switching in InAs/InP quantum dots

We report all-optical switching due to state-filling in quantum dots (QDs). The switching energy is as low as 6 fJ since state-filling requires only 2 electron-hole pairs per QD. The single layer of InAs/InP QDs is inserted within a InGaAsP/InP waveguide which are processed into a Mach-Zehnder interferometric switch (MZI). A 1530-1570 nm probe beam is switched by optical excitation of one MZI-arm from above. By exciting below the InGaAsP bandgap, we prove that the refractive index nonlinearity is entirely due to state-filling in the QDs.

First integrated combiner based on self-switching in quantum dots

We demonstrate all-optical switching in quantum dots (QDs). The switching is studied in an integrated optical combiner circuit. This is a Mach-Zehnder interferometer with an unequal power distribution over the branches. The refractive index is intensity dependent in the branches due to the QDs. Large all-optical nonlinearities are measured. This device is aimed to avoid an unwanted 3-dB loss, fundamental in passive optical splitters.

Effect of the first-order mode in access waveguides on the performance of unbalanced MMI couplers

This study demonstrates that the excitation of the first-order mode in access waveguides can significantly deteriorate the coupling ratio of unbalanced MMI couplers and increase the excess losses. Care, therefore, should be taken in coupling light into the access waveguides, as well as in the circuit design to avoid this effect. Another option for this, as measurement results suggest, is controlling the relative phase difference.