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A compact fiber-optic diode-laser sensor system for measuring relative humidity is studied. In such a system, a distributed feedback laser lasing near 1877 nm is used as light source while a high-precision Pt resistance as temperature sensor, an accuracy of 0.1% relative-humidity can be achieved. The laser sensor system is able to lock to the absorption peak and calculate the density of water vapor without any additional reference measurements. Using programs built in to the microcontroller unit, the laser system can switch functions between direct measurement at high density and second-harmonic detection at low density. The system can switch between the two modes automatically and work in a wide dynamic range. [ABSTRACT FROM AUTHOR]

We present a means to optically tune the emission of an organic laser reversibly over a range of 14 nm. This is enabled by incorporating a photochromic spiropyran (10,30-dihydro-10,30,30-trimethyl-6-nitrospiro[2H-1-benzopyran-2,20-(2H)-indole]) into the gain medium formed by the laser dye Rhodamine 700 in poly(methyl methacrylate). This is structured by nanoimprinting to form a distributed feedback resonator. Exposure of the device to ultraviolet and visible light leads to a reversible refractive index change of the photochromic additive and the gain medium, which enables the continuous shift of the laser wavelength. This is possible without compromising the optical gain properties of the device. [ABSTRACT FROM AUTHOR]

NH3 absorption lines due to vibration-rotation transitions are observed at 1.50-1.54 μm by using an InGaAsP superluminescent diode. A 1.5-μm InGaAsP distributed feedback (DFB) laser is frequency stabilized to an NH3 linear absorption line at 15196 Å. Frequency stability of σ(2,τ)=8×10-11τ-1 is achieved for an averaging time range of 10 ms≤τ≤1 s. Such an absolute frequency-stabilized DFB laser is useful for coherent optical system applications, since it is free from the longitudinal mode jumping which results from a wide range of temperature changes and long-term device degradation. [ABSTRACT FROM AUTHOR]

The first generation of bandwidth-limited, single-mode ultrashort optical pulses with excellent coherency from a distributed feedback InGaAsP diode laser at 1.3 μm by the method of strong rf modulation superimposed on the dc bias current is reported. It was realized only by the laser diode itself with no requirement of any other optical elements or external cavity or careful optical control. The measurement of time-bandwidth product of the generated coherent picosecond pulses at 500-MHz modulation gave the value of 0.38 for Lorentzian pulse shape with a full width at half-maximum of nearly 34 ps, which proved definitely the Fourier-transform-limited character. By changing the dc bias current from positive to negative, the pulse width was demonstrated to be continuously controllable over a range of approximately twice to three times depending upon the modulation frequency. [ABSTRACT FROM AUTHOR]