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We have developed a Mach-Zehnder interferometric all-optical switch employing intersubband transition in an InGaAs∕AlAs∕AlAsSb-coupled double quantum well waveguide. The recently discovered cross-phase modulation phenomenon was utilized as the switching mechanism; the nonlinear index of refraction for transverse electric polarized light is induced by intersubband optical excitation using transverse magnetic pump light. We demonstrate the demultiplexing operation of 160Gbit∕s data signals to 10Gbit∕s using this switch. At the input control pulse energy of 8pJ, the demultiplexed signals showed an extinction ratio better than 10dB, and an error-free demultiplexing was achieved.

Vertical correlation of highly organized exciton complex at ZnSe / BeTe typeII asymmetric superlattices AIP Conf. Proc. 772, 967 (2005); 10.1063/1.1994431Structural study of (CdS/ZnSe)/BeTe superlattices for λ=1.55 μm intersubband transition

Articles you may be interested inMagnetic properties of heavily Mn-doped quaternary alloy ferromagnetic semiconductor (InGaMn)As grown on InP Appl. Phys. Lett. 83, 2175 (2003); 10.1063/1.1610788 Magnetic and transport properties of III-V based magnetic semiconductor (GaMn)As: Growth condition dependence Appl. Phys. Lett. 74, 398 (1999); 10.1063/1.123082Epitaxial growth and properties of III-V magnetic semiconductor (GaMn)As and its heterostructures

Ultrafast all-optical switching at an optical communication wavelength has been investigated by utilizing an intersubband transition (ISBT) of II–VI-based multiple quantum wells (MQWs) fabricated in high-mesa waveguide devices. The waveguide structure consists of a CdS∕ZnSe∕BeTe MQW core layer and two top and bottom ZnMgBeSe quaternary cladding layers grown by molecular beam epitaxy on a (001) GaAs substrate. A marked increase in waveguide transmittance was observed only for transverse-magnetic-polarized subpicosecond pulse with increasing incident pulse energy at λ=1.57μm, indicative of the ISBT absorption saturation. The pulse energy necessary for a 10dB transmittance increase is as low as 13.3pJ for a waveguide device with 2.7μm mesa, and the saturation pulse energy can be even further reduced by employing a narrower mesa structure. Ultrafast gate switching within a time window of 0.56ps was also demonstrated with pump pulse at λ=1.57μm and probe pulse at λ=1.63μm in this waveguide device.

We have grown laser diode structures using highly strained BeZnCdSe quantum wells by molecular beam epitaxy and successfully obtained continuous-wave lasing in the green-to-yellow spectral region (543–570 nm) at room temperature. The green-to-yellow lasing color was tuned by simply varying the Cd content of the quaternary BeZnCdSe quantum well. The threshold current densities of 20-µm-wide lasers were found to be sufficiently low (less than 0.85 kA/cm2). This result demonstrates that BeZnCdSe is a promising material for use as the active layer in high-performance green-to-yellow laser diodes.

We investigated the carrier spin dynamics in diluted magnetic semiconductor quantum wells, CdTe/Cd 1Ϫx Mn x Te (xϷ0.35), using femtosecond time-resolved circular dichroic spectroscopy. When the heavy-hole exciton was resonantly excited by the circularly polarized laser pulse, the positive and negative circular dichroism appeared at the heavy-hole-and the light-hole-exciton energy, respectively. They decay with different time constants, from which we succeeded in determining the spin dynamics of electrons separately from that of holes. Furthermore, we found that the electron-spin-relaxation time decreases dramatically with decreasing the well width, while the heavy-hole-spin relaxation is relatively insensitive to the variation of the well width. This strongly suggests that the electron-spin-relaxation process is governed by the s-d exchange interaction in the magnetic barrier layer, while the heavy-hole-spin relaxation by p-d exchange interaction is regulated by the degree of the mixing between the heavy-and light-hole subbands.

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