M. D. H. Bhuiyan

Synthesis, Structural and Nonlinear Optical Properties of 2-(3-Cyano-4-{5-[1-(2-Hydroxyethyl)- 3,3-Dimethyl-1,3-Dihydro-Indol-2-ylidene]-Penta-1,3-dienyl}-5,5-Dimethyl-5H-Furan-2-ylidene)-Malononitrile

A chromophore for nonlinear optics with extended conjugation has been synthesized, and its structure determined from X-ray diffraction data. The compound crystallizes in the monoclinic system with the space group P21/n and Z = 4. The unit cell parameters are a = 10.7826(4) Å, b = 14.5943(5) Å, c = 15.3792(5) Å and beta = 96.213(2)°. A thin film containing 5% of the chromophore in amorphous polycarbonate when poled at 180°C and 60 V/μm yields a maximum r33 value of 206 pm/V. This is seven times higher than the value found for the archetypical inorganic material, lithium niobate.

Investigation of polyimide coated fibre Bragg gratings for relative humidity sensing

This paper reports the development of a polyimide coated fibre Bragg grating for relative humidity sensing. The humidity response was measured for several polyimide coatings including P84 and P84 HT. The P84 HT polyimide coating proved the most promising with a large coefficient of moisture expansion measured at 73.8 ppm/%rh. The effect of coating thickness and optical fibre diameter were also investigated.

Development of fibre Bragg grating based strain/temperature sensing system

We have characterised a strain and temperature sensing system being developed by Southern Photonics that uses a new Optical Interrogator and fibre Bragg gratings. We have determined the key strain and temperature coefficients, and shown that strain and temperature can be measured simultaneously. The experimental uncertainty is 5.2 pm when using the 1540 nm fibre Bragg grating, which corresponds to an experimental uncertainty in measuring the temperature of 0.54 ºC and in measuring the strain of 3.4 με. Simulations predict that a Bragg reflection of more than 90% can be achieved for Bragg Gratings in polymer thin films containing chromophores for grating lengths as small as 200 μm. A small Bragg grating length means that it should be possible to create waveguides and four Bragg gratings for strain tensor and temperature measurements within an area as small as 5×5 mm2.

Photoluminescence and optical studies of photodegradation in nonlinear optical organic chromophores

Photostability measurements have been made on host-guest films containing amorphous polycarbonate and an organic chromophore with a high 2nd order nonlinear optical figure of merit. We find that the rate of photodegradation strongly depends on the oxygen partial pressure. At very low oxygen partial pressures (1.4×10-5 bar) the average number of photons required to photodegrade a chromophore is as high as 1×109 at 655 nm. Encapsulation leads to an initial rapid decrease in the photodegradation rate due to the trapped oxygen and a gradual photodegradation where 2×109 photons are required to photodegrade a chromophore. There is an anomalous increase and then decrease in the photoluminescence intensity during ultraviolet irradiation.

PHOTOSTABILITY ENHANCEMENT STUDIES ON ZWITTERIONIC CHROMOPHORES FOR NONLINEAR OPTICS

Optical and photostability measurements have been made on nonlinear optical films containing amorphous polycarbonate and an organic chromophore that has a high 2nd order nonlinear optical figure of merit. We show that the decrease in the photodegradation quantum efficiency with increasing optical intensity can be modelled in terms of oxygen depletion by oxygen-mediated chomophore photodegradation. The addition of a known singlet oxygen quencher, beta carotene, leads to a 1100% decrease in the photodegradation quantum efficiency.

Polyimide coated fibre Bragg grating based moisture sensor development

The humidity and temperature characteristics of a 53 μm polyimide coated fibre Bragg grating (FBG) were investigated. The humidity response was 7.09 pm / %rh resulting in a coefficient of moisture expansion of 74.3 ppm /%rh. The temperature response was 12.8 pm / °C.

Photostability study of structurally modified electro-optic chromophores and the effect of singlet oxygen quenchers

The addition of structural modifications to enhance the temporal stability of the electro-optic (EO) chromophore, PYR-3, have not adversely affected the photostability. We find that the photostability can be enhanced by the addition of singlet oxygen quenchers.