Oliver Hadeler

The emission characteristics of liquid-crystal lasers

— Liquid-crystal lasers exhibit narrow linewidth, large coherence area, and low threshold laser emission. Moreover, the wavelength of the laser line can be readily tuned using a variety of different external stimuli, including electric fields. These combined features make them particularly attractive as compact tunable laser light sources. Recent experimental results with regards to the emission characteristics of chiral nematic photonic band-edge lasers are discussed. This type of liquid-crystal laser consists of a self-organizing one-dimensional photonic band structure and a gain medium in the form of a laser dye. Some of the generic features that are observed for these lasers are discussed, including the typical emission linewidth of the laser line, the change in emission energy of the laser for high excitation energies and high pump repetition rates, and the dependence of the excitation threshold and slope efficiency on the cell thickness. In addition, how the performance changes when either the molecular structure of the chiral nematic host or the gain medium is varied is considered. To conclude, results are presented on the laser emission for a wide-temperature-range blue phase I band-edge laser which consists of a self-organizing three-dimensional photonic band structure.

Electro-optic Telecommunication Devices at 1550 nm Employing Electroclinic and Ferroelectric Switching of an Organosiloxane Liquid Crystal

ABSTRACT We demonstrate three electro-optic telecommunication devices operating at a wavelength λ = 1550 nm: an optical switch or modulator, a variable attenuator, and a rotatable waveplate. These devices make use of the electroclinic and ferroelectric properties of a chiral smectic organosiloxane liquid crystal. Under moderate electric fields of ≤23 V/μm we observed an optical power modulation of up to 38 dB and a switching time of ∼100 μs. The waveplate could be continuously rotated over 38°. We also present birefringence data of this liquid crystal at λ = 1550 nm as a function of temperature and the implications on the development of liquid crystal telecommunication devices.

Ferroelectric Liquid Crystal Mixture Integrated Into Optical Waveguides

We report an on-chip integrated ferroelectric liquid crystal (FLC) waveguide structure suitable for telecommunication applications. Single gaps with different widths of 5, 10, and 20 μ m inside individual silica waveguides were filled with an FLC mixture. The waveguide devices operate as a binary switch or an attenuator in a temperature range from 30 ° C to 60 ° C. The FLC mixture exhibited a good alignment quality in these gaps without alignment layers. A good extinction ratio of up to 33.9 dB and a low insertion loss of <; 4.3 dB at λ = 1550 nm were observed. Switching times of <; 100 μs were obtained for the low electric fields applied in this experiment.

Novel electroclinic organosiloxane materials for optoelectronic devices

The paper describes an enhancement of the electroclinic characteristics of low molar mass dimeric organosiloxane liquid crystals. The degree of polymerisation of the siloxane core unit was varied in order to study the effect on phase transitions and electro-optic properties. It was found that the SmA*-SmC* phase transition temperature could be moved to any position in the range from 50°C to 10°C if we varied the number of SiMe2 groups in the flexible linkage of the dimeric molecule. More importantly, because the organosiloxane liquid crystal material had some distribution of the number of SiMe2 groups, it showed a rather broad SmA*-SmC* phase transition in contrast to the sharp phase transition of conventional electroclinic materials. The electroclinic coefficient reached the maximum value of 8 degrees/V/μm and was at least 1 degree/V/μm over a temperature range as broad as 10°C. The induced electroclinic tilt angle was as high as 22-23 degrees with good linearity and moderate applied electric fields.

Fast electro-optic liquid crystal switch and attenuator with large extinction ratio at 1550 nm

We demonstrate an electro-optic switch and a variable attenuator for telecommunication applications at λ=1550nm by employing the ferroelectric and electroclinic properties of an organosiloxane liquid crystal. In the ferroelectric SmC* phase an optical switch has been realised with an extinction ratio of 36dB between crossed polarisers. The switching time was ~200microseconds. In the SmA* phase the analogue nature of the electroclinic effect was employed to obtain a variable attenuator. The maximum attenuation range between crossed polarisers was 35dB for an applied electric field of +-9V/micron. The response time of the device was about 100microseconds, independent of the applied electric field. Both devices where demonstrated in the same 21.5micron thick cell which provided a retardance of λ/2 at λ=1550nm.

Development of an open technology sensor suite for assisted living: a student-led research project.

Many countries have a rapidly ageing population, placing strain on health services and creating a growing market for assistive technology for older people. We have, through a student-led, 12-week project for 10 students from a variety of science and engineering backgrounds, developed an integrated sensor system to enable older people, or those at risk, to live independently in their own homes for longer, while providing reassurance for their family and carers. We provide details on the design procedure and performance of our sensor system and the management and execution of a short-term, student-led research project. Detailed information on the design and use of our devices, including a door sensor, power monitor, fall detector, general in-house sensor unit and easy-to-use location-aware communications device, is given, with our open designs being contrasted with closed proprietary systems. A case study is presented for the use of our devices in a real-world context, along with a comparison with commercially available systems. We discuss how the system could lead to improvements in the quality of life of older users and increase the effectiveness of their associated care network. We reflect on how recent developments in open source technology and rapid prototyping increase the scope and potential for the development of powerful sensor systems and, finally, conclude with a student perspective on this team effort and highlight learning outcomes, arguing that open technologies will revolutionize the way in which technology will be deployed in academic research in the future.

Electro-optic integration of liquid crystal cladding switch with multimode passive polymer waveguides on PCB

Optical switching functionality is demonstrated in PCB integrated multimode passive polymer waveguides using a localised liquid-crystal cladding structure. Waveguide switching contrast of 15 dB is achieved with only 0.5 dB of on-state excess loss.

Introduction to ‘Sensors in technology and nature’

Welcome to this compendium of articles that reviews sensor research in all its facets, ranging from the physical and chemical nature of sensing at the molecular level, to the monitoring of buildings and human behaviour. The theme of this issue, ‘Sensors in technology and nature’, was the theme

Low Molar Mass Organosiloxane Liquid Crystals for Telecommunication Applications

Mixtures of two proprietary low molar mass organosiloxane liquid crystals were studied in order to improve their alignment and optimize their electro-optic properties for telecommunication applications. Over a certain concentration range, mixtures exhibited an isotropic-chiral smectic A-chiral smectic C (Iso-SmA*-SmC*) phase sequence leading to exceptionally good alignment. At room temperature, the spontaneous polarization of these samples was reduced from 225 nC cm-2 in the pure SmC* liquid crystal to as low as 75 nC cm-2 in the mixture. Within this concentration range, the ferroelectric tilt angle could be varied between 35° and 15° , while the rise time decreased by 69.4%. The rise times were <;45 μs for moderate electric fields of ±10 V μm-1 in the SmC* phase and ∼4 μs, independent of electric field, in the SmA* phase. At λ = 1550 nm, these mixtures exhibited very large extinction ratios of ~60 dB for binary switching in the SmC* phase and ~55 dB continuous variable attenuation in the SmA* phase.

Correction to "High Optical Contrast Liquid Crystal Switch and Analogue Response Attenuator at 1550 nm" (Nov. 15, 2011 1655-1657]

In the above paper (ibid., vol. 23, no. 22, pp. 1655-1657, Nov. 15, 2011), the second authors name was spelled incorrectly. The correct spelling is Oliver Hadeler. The financial acknowledgement on page 1655 should read as follows: The work of O. Hadeler and H. J. Coles was supported by Dow Corning Inc., Midland, MI, USA.