Abstract: The invention relates to processes for the extraction of products from titanium-bearing minerals. In particular embodiments the invention relates to methods of recycling sulphuric acid used in a titanium dioxide extraction process. The invention also relates to methods for minimising chromophore contamination in calcined titanium dioxide. The process may also comprise steps for removing contaminants from recycled acid or desirable products.

Abstract: The present application provides an optical comb source in which the comb is produced by seeding a gain switched Fabry-Pérot laser with light from a single mode laser, while at the same time driving the Fabry-Pérot laser with a DC bias and RF signal.

Abstract: The present application relates to comb frequency generator devices generally and more particularly to the use of comb generators for use in fibre optic communications. More particularly, the application provides a frequency comb generator device. The device comprises a laser (30), a biasing circuit for providing a DC bias current (26), an RF circuit (22) providing a RF signal and a drive circuit (28) for combining the RF signal with the DC bias current to provide a drive current to the laser (30). With the DC bias current below threshold of the laser diode and RF bias with a frequence close to the relaxation ascillation frequency of the laser diode, a periodic pulse train is emitted with constant phase.

Abstract: The invention provides a bacterium with an increased tolerance to butyric acids, such as 2-hydroxybutyric acid (2-HIBA). In particular, the invention provides a bacterium that tolerates at least 2.5 g/L of butyric acid. The bacterium may be derived, for example, from genus Clostridium, Moorella, Oxobacter, Peptostreptococcus, Acetobacterium, Eubacterium, or Butyribacterium.

Abstract: The present application provides an optical comb source in which the comb is produced by seeding a gain switched Fabry-Pérot laser with light from a single mode laser, whilst at the same time driving the Fabry-Pérot laser with a DC bias and RF signal.

Abstract: The present application is directed to the measurement of the intensity and phase of high speed optical signals. The present application uses a tunable optical local oscillator, an optical coupler, a photodiode and RF electronics. The tunable laser enables successive measurements to be taken across the optical spectrum allowing the system to measure extremely high bandwidth signals. The signal generated by the local oscillator comprises a component at a frequency between two adjacent modes of the periodic optical signal to be measured. The local oscillator and said periodic signal are optically mixed and sent to a photodiode, the measurement of the phase being based on isolating the resulting beat frequencies. This approach offers a significant improvement over existing time resolved approaches which are limited to the bandwidth of the photodiode (˜50 GHz).

Abstract: In wavelength switching optical networks, the optical data being transmitted may be routed to different end points by switching the operating frequency of the laser. However, the phase noise of the laser source increases following a switching event. This increased phase noise can prevent the successful transmission of phase modulation formats which are sensitive to it. Accordingly, it is generally necessary to wait a short period before transmitting data. However, the period may be as long as the data packet being transmitted (e.g. 3 ?S), which is a limiting factor. The present application obviates this problem by including a radio frequency pilot tone with the data prior to modulation onto the optical carrier.

Abstract: According to the invention there is provided a tunable laser system for use in an optical communication system, said tunable laser system comprising a multi-section laser separated by at least two slots to define a plurality of sections, each section adapted to provide an optical gain. Each section comprises a separate control means to provide an adjustable optical gain in each section. The tunable laser system and method of the present invention provides a wide tuning range, narrow linewidth and fast switching times.

Abstract: The present application relates to comb frequency generator devices generally and more particularly to the use of comb generators for use in fibre optic communications. More particularly, the application provides a frequency comb generator device. The device comprises a laser (30), a biasing circuit for providing a DC bias current (26), an RF circuit (22) providing a RF signal and a drive circuit (28) for combining the RF signal with the DC bias current to provide a drive current to the laser (30). With the DC bias current below threshold of the laser diode and RF bias with a frequence close to the relaxation ascillation frequency of the laser diode, a periodic pulse train is emitted with constant phase.

Abstract: The invention relates to an apparatus and method for providing an improved optical pulse source suitable for use in high-speed optical communication systems. The optical pulse source can output spectrally pure pulses in a high capacity optical communication system. An optical pulse source in accordance with the invention comprises; at least one gain switched laser diode; and at least one non-linearly chirped optical processing element adapted to enhance the spectral purity of the output pulses generated from the laser diode.

Abstract: A semiconductor photodetector (1) for detecting short duration laser light pulses of predetermined wavelength in a light signal (2) comprises a micro-resonator (3) of vertical Fabry-Perot construction having a Bragg mirror pair, namely, a front mirror (5) and a rear mirror (6) with an active region (8) located between the front and rear mirrors (5,6). An N-type substrate (11) supports the rear mirror (6). The light signal (2) is directed into the active region (8) through the front mirror (5) while a pump beam (17) is directed into the active region (8) at an end (18) thereof. The spacing between the front and rear mirrors (5,6) is such as to cause light of the predetermined wavelength to resonate between the mirrors (5,6).

Abstract: A demultiplexer and method for a high speed time division multiplex optical communication system uses an opto-electronic device in which two photon absorption can occur configured in circuit. The received optical multi-channel signal and a control optical signal at the repetition rate of and synchronized to the selected channel to be detected are applied to the device, which is configured in circuit as to generate by non-linear two photon absorption effect a current similar to the original signal.