Sergey S. Sarkisov

Single-arm double-mode double-order planar waveguide interferometric sensor

A sensor is described for which interference measurements of the phase delay between two propagating modes of different orders in a slab thin-film waveguide are used as the sensing technique. The basic building block of the sensor is a polymer film doped with an indicator dye such as Bromocresol Purple. The modes of two orders such as TM(0) and TM(1) are simultaneously excited in the light-guiding film with a focusing optics and a prism coupler. The modes are decoupled from the film and recombined to produce an interference pattern in the face of an output optical fiber. The sensitivity of the sensor to the ambient temperature change is 1.5 degrees C, and the sensitivity to NH(3) is 200 parts in 10(6) for one full oscillation of the signal.

Optical branching in dye-doped polymeric waveguide

We demonstrate theoretically and experimentally that a single optical beam splits into multiple beams (branches) as a result of light induced permanent refractive index decrease in a dye-doped polymeric slab waveguide upon its upconverted photobleaching. The input Gaussian beam initially splits into two primary branches that grow in time moving out of the central axis and eventually collapse into numerous secondary branches. The proposed theoretical model is nonlocal in time and is based on a Shrodinger-type nonlinear propagation equation complemented by a rate equation for the decrease of the refractive index.

Optical channel waveguides formed by upconverted photobleaching of dye-doped polymer film in regime of dark spatial soliton

We demonstrate theoretically and experimentally that an initially Gaussian optical beam (633 nm wavelength) sent through a π-step phase mask and launched into a thin film of polymer poly(methyl methacrylate) doped with laser dye 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)4H-pyran known as DCM evolves into a spatial structure similar to a dark spatial soliton. This takes place due to nonlinear mechanism of upconverted photobleaching of the dye-doped polymer. The result of beam structuring is the formation of a permanent pattern of the refractive index of the film that acts as a channel waveguide trapping a weak Gaussian probe beam coaxial with the main beam. The proposed theoretical model is nonlocal in time and is based on a Schrodinger-type nonlinear propagation equation for the main beam and a linear propagation equation for the probe beam complemented by a rate equation for the light-induced decrease of the refractive index.

Dark spatial solitons in photopolymer films for optical interconnections

We demonstrate theoretically and experimentally that an initially Gaussian red light beam sent through a ?step phase mask and launched into a thin film of polymer poly(methyl methacrylate) doped with laser dye 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)4H- pyran known as DCM evolves into a spatial structure similar to a dark spatial soliton. This takes place due to the Kerr-type time-delayed nonlinearity associated with the mechanism of up-converted photobleaching of the dye-doped polymer. The proposed theoretical model is nonlocal in time and is based on the Shrodinger-type nonlinear equation for the amplitude of the propagating beam complemented by the rate equation for the light-induced decrease of the refractive index. The result of the structuring of the beam is the formation of a permanent pattern of the refractive index of the film that acts as a channel waveguide, trapping a weak Gaussian probe beam close to it. The probe beam can propagate along or against the soliton. We also demonstrate the tolerance of trapping to a possible shift or tilt of the probe beam with respect to the soliton. This makes the proposed approach potentially useful for interconnections between individual fibers, fiber ribbons, bundles, and multicore fibers as well as between fibers and planar integrated optical devices.

Statistical analysis of cloud-cover mitigation of optical turbulence in the boundary layer

One atmospheric phenomenon that adversely affects laser propagation is optical turbulence. From ten months of observation, the refractive index structure constant in the atmospheric boundary layer was found to be significantly reduced under widespread cloudy conditions. The refractive index structure constant (C(n) (2)) depends upon the turbulent flux of momentum, sensible and latent heat. The intensity of a propagating laser beam will not be degraded nearly as much as would be expected under clear or lightly scattered cloud conditions. New experimental data are presented that support this hypothesis. The refractive index structure constant was measured for various cloud-cover conditions.

Planar optical waveguide sensor of ammonia

We describe a novel sensor of ammonia based on a planar optical waveguide made of a thin film of polymer polyimide doped with indicator dye bromocresol purple. The film of dye-doped polyimide demonstrated reversible increase of absorption with a peak near 600 nm in response to presence of ammonia in ambient air. Coupling of input and output optic fibers with the waveguide was done by means of coupling prisms or coupling grooves. The latter configuration has the advantage of low cost, less sensitivity to temperature variation, and the possibility of coupling from both sides of the waveguide. Special experimental setup was built to test the sensor. It included test gas chamber with sealed optic fiber feed-throughs, gas filling line, laser source, photodetector, and signal processing hardware and software. The sensor was capable of detecting 100 ppm of ammonia in air within 8 seconds. Further increase of sensitivity can be achieved by adding more dye dopant to the polymer, increase of the length of the waveguide, and suppression of noise. Overexposure of the sensor to more than 5000 ppm of ammonia led to the saturation of the polymer film and, as a result, significant decrease of sensitivity and increase of the response time. The sensor can be used as low cost component of a distributed optical network of chemical sensors for monitoring presence of hazardous industrial pollutants in air.

Thin film electro-optic modulator based on single crystal of N-(4-nitrophenyl)-(L)-prolinol (NPP) grown from melt by the modified Bridgman method

We discuss the plate-guiding method of growing micrometer- thick single crystal films of electro-optic organic material N-(4- nitrophenyl)-(L)-prolinol. This approach has the advantages of full control over the thickness of the film and selection of a proper seed for initial crystal growth. Characterization of the electro-optic properties of the films is performed using the intensity modulation technique with a low (of the order of 10 V) alternating driving voltage. Both the fundamental and double-frequency responses are used for the characterization. The electro-optic effect is pseudolongitudinal since the configuration of the experiment is that of a longitudinal intensity modulator. The main contri- bution to the effect originated from the transverse component of the ex- ternal electric field. By purely electro-optic means we determine the ori- entation of the dielectric axes and measure the half-wave voltage, the figure of merit, and electro-optic coefficientsr 12 and r 22 to be 3.24 kV and 99.2, 461, and 154 pm/V, respectively. We also find that electro-optic coefficientsr 61 and r 63 are two orders of magnitude less than r 12 and r 22 .

Light-driven polymer actuators for propulsion and light control

New light-driven actuators based on films of polymer polyvinylidene fluoride are described. The actuators employ the photomechanical bending of the polymer film caused by low power (10 mW and less) laser radiation. The photomechanical effect combines various physical mechanisms, such as anisotropic thermal expansion, converse piezoelectric mechanism along with photovoltaic and pyroelectric ones, while the mechanism of thermal expansion is dominant for slow motion. Mechanical vibrations of the strips of the photomechanical polymer were observed with periodic pulsed laser excitation. The resonance frequency is inversely proportional to the square of the length of the strip, in full agreement with the theory. Resonance frequency measurements were used to determine the modulus of elasticity of the films, which was close to 3.0×109 Pa. Two possible applications were discussed: optical fiber switch and adaptive mirror propelled by the proposed actuators. The actuators have a potential of being used as the components of future light-driven micro/nano systems.

All -Optical Smart Structure Based on Thin Film Chemical Sensor/Actuator

The design of two of the components which comprise a smart structure is described. A smart structure is a system that has a sensor, control, and actuator. The two aspects that are discussed are the sensor and actuator. There have been numerous changes made to the basic design of the smart structure components to improve their simplicity and cost efficiency. The novel design of the sensor of ammonia based on a planar optical waveguide made of thin fi lm of polymer polyimide doped with indicat or dye bromocresol purple is explained . This particular sensor is designed to detect the presence of ammonia in ambient air. The film of dye -doped polyimide demonstrated reversible increase of absorption with a pea k near 600 nm in response to presence of ammonia in ambient air. Two advantages of the polymer is that it works at elevated temperatures as high as 300 o C and it can be saturated with water vapor in such a way that our sensor will not be affected by the cha nge in humidity of ambient air. To improve the sensitivity of the sensor the concentration of dye dopant was increased. This gave more than a ten times better sensitivity (1 ppm) . The coupling of input and output optic fibers with the waveguide was done by means of coupling prisms or coupling grooves. The latter configuration has the advantage of low cost, less sensitivity to temperature variation, and the possibility of coupling from both sides of the waveguide . Exposing the sensor to more than 5000 ppm of ammonia led to saturation of the sensitive film which causes an increase in response time and a decrease in sensitivity. Also a description of an actuator that uses the principle of the photomechanical effect in polyvinylidene fluoride is detailed. To ach ieve the photothermal bending of strips of polyvinylidene fluoride a laser beam with a few milliwatts of power was used. The force generated by the bending strip of polymer was 10 -4 N, which propelled a 1 g oscillating wheel of a mechanical clock. The freq uency of photomechanical resonance at pulsed illumination was inversely proportional to the length of the strip.

Chemical Sensor based on Thin Film Optical Planar Waveguide

We describe novel sensor of ammonia based on a planar optical waveguide made of thin film of polymer polyimide doped with indicator dye bromocresol purple. The film of dyedoped polyimide demonstrated reversible increase of absorption with a peak near 600 nm in response to presence of ammonia in ambient air. Coupling of input and output optic fibers with the waveguide was done by means of coupling prisms or coupling grooves. The latter configuration has the advantage of low cost, less sensitivity to temperature variation, and the possibility of coupling from both sides of the waveguide. Special experimental setup was built to test the sensor. It included test gas chamber with sealed optic fiber feedthroughs, gas filling line, laser source, photodetector, and signal processing hardware and software. The sensitivity of the sensor was evaluated to be close to 100 ppm of ammonia in air and the time response was about 8 seconds. Further increase of sensitivity can be achieved by adding more dye dopant to the polymer, increase of the length of the waveguide, and suppression of the noise. Overexposure of the sensor to more than 5000 ppm of ammonia led to the saturation of the sensitive film and, as a result, significant decrease of its sensitivity and increase of the response time. The sensor can be used as low cost component of a distributed optical network of chemical sensors for monitoring presence of hazardous air pollutants in the exhaust of aircraft/spacecraft propulsion systems.