ABSTRACT
We discuss the design, modelling, fabrication and characterisation of an integrated tuneable birefringent waveguide for quantum cascade lasers. We have fabricated quantum cascade lasers operating at wavelengths around 4450 nm that include polarisation mode converters and a differential phase shift section. We employed below laser threshold electroluminescence to investigate the single pass operation of the integrated device. We use a theory based on the electro-optic properties of birefringence in quantum cascade laser waveguides combined with a Jones matrix based description to gain an understanding of the electroluminescence results. With the quantum cascade lasers operating above threshold we demonstrated polarisation control of the output.
ABSTRACT
Laser-cooled atoms are central to modern precision measurements. They are also increasingly important as an enabling technology for experimental cavity quantum electrodynamics, quantum information processing and matter-wave interferometry. Although significant progress has been made in miniaturizing atomic metrological devices, these are limited in accuracy by their use of hot atomic ensembles and buffer gases. Advances have also been made in producing portable apparatus that benefits from the advantages of atoms in the microkelvin regime. However, simplifying atomic cooling and loading using microfabrication technology has proved difficult. In this Letter we address this problem, realizing an atom chip that enables the integration of laser cooling and trapping into a compact apparatus. Our source delivers ten thousand times more atoms than previous magneto-optical traps with microfabricated optics and, for the first time, can reach sub-Doppler temperatures. Moreover, the same chip design offers a simple way to form stable optical lattices. These features, combined with simplicity of fabrication and ease of operation, make these new traps a key advance in the development of cold-atom technology for high-accuracy, portable measurement devices.
ABSTRACT
We discuss the design, fabrication and characterization of waveguide polarization mode converters for quantum cascade lasers operating at 4.6 µm. We have fabricated a quantum cascade laser with integrated polarization mode converter that emits light of 69% Transverse Electrical (TE) polarization from one facet and 100% Transverse Magnetic (TM) polarization from the other facet.
ABSTRACT
All-optical switching by using a nondegenerate cascaded second-order nonlinearity is described wherein a phase shift is induced at one frequency owing to the presence of intense light at a different frequency. A Mach-Zehnder waveguide device is proposed to take advantage of this process and has applications for all-optical switching and demultiplexing, potentially at power levels near 10 W by using quasi-phase matching in semiconductor waveguides.
ABSTRACT
Refractive and absorptive optical nonlinearity can be distinguished using a pump-probe interferometric technique with picosecond time resolution. The method is applied to both resonant and nonresonant nonlinearities in optical fibers and reveals marked differences between the relaxation behavior of the refractive and absorptive nonlinearity in certain cases. A monomode fiber doped with CdS(x)Se(1-x) semiconductor nanocrystals exhibits a large optically induced phase shift with ~10-psec relaxation time, which is many orders faster than the relaxation of the absorptive nonlinearity under identical conditions.
ABSTRACT
An interferometric technique for measuring with picosecond resolution the time evolution of the real and imaginary components of optical nonlinearities in channel waveguides is described. Characteristics of the technique are illustrated with measurements of band-filling optical nonlinearities in CdS(x)Se(1-x)-doped glass channel waveguides.
