504 research outputs found
Chirped-grating output couplers in dielectric waveguides
This paper reports on the method of fabrication and first experiments of chirped (variable period) gratings in a dielectric waveguide. Such gratings, which are proposed as a new optical building block, are used in this work as focusing output couplers
Operating injection lasers by fast square current pulses of variable amplitude
A simple solid state circuit was used to drive GaAs injection lasers by fast (âŒ100 nsec) square pulses of variable amplitude (0â25 A). The amplitudes of the current pulses and the corresponding emitted light pulses were measured by a dual peak detector circuit. Using these circuits we were able to plot automatically the current vs light curve and determine the threshold current of the laser diodes
Fast, high current, high repetition rate pulse generator for injection lasers
The circuit described is capable of generating highâcurrent (2â50 A), fastâriseâtime (10 nsec), squareâwave pulses into a 50âΩ load. This circuit may be used for driving injection lasers at high repetition rates (up to 1.5 kHz) when connected to coaxial cables
Chirped gratings in integrated optics
Gratings with variable periods (chirped gratings) have been fabricated by recording the interference pattern of a collimated laser beam with a converging beam generated by a cylindrical lens. An analysis is presented for the behavior of the chirped gratings as a function of wavelength, the angle between the illuminating beams, the F number of the lens, and its position. To calculate the power radiated into air, the coupled-mode equations are solved for the case of a waveguide with chirped surface corrugation. Experimentally, chirped gratings have been etched on the surface of an optical waveguide and used to couple light out of the waveguide. It was found that the light was focused outside the waveguide, and the fraction of the power radiated into air compared favorably with the theoretical calculation. The focal point outside the waveguide was found to move by about 1 cm when the wavelength was changed by 500 Ă
-in agreement with theoretical estimates
Linearity and enhanced sensitivity of the Shipley AZ-1350B photoresist
The properties of the Shipley AZ-1350B positive photoresist used with the Shipley AZ-303A developer were investigated. It was found that the use of AZ-303A developer results in a significant improvement of the sensitivity and the linearity of the photoresist. The unexposed etch rate of the photoresist was 35 Ă
± 5 Ă
/sec. Gratings of high efficiency have been successfully fabricated using the above combination of photoresist and developer
Room-temperature operation of GaAs Bragg-mirror lasers
Room-temperature operation of GaAs distributed Bragg reflector lasers is reported. The diodes are fabricated from conventional double heterostructures involving only a single step of liquid-phase epitaxy. For gratings with a period of 3700 Ă
, the diodes lased at 8770 Ă
, which corresponds to the high-absorption side of the spontaneous emission spectrum. Thresholds as low as 6 kA/cm^2 have been realized
Broad-band grating filters for thin-film optical waveguides
Broad-band grating filters have been fabricated on glass thin-film waveguides and evaluated with a tunable dye laser. Measured and calculated filter responses were found to be in good agreement. Grating filters with bandwidths of 300 and 150 Ă
, and reflectivities of 18 and 40%, respectively, are reported
GaAs-GaAlAs distributed-feedback diode lasers with separate optical and carrier confinement
Remarkable reduction of the threshold current density is achieved in GaAs-GaAlAs distributed-feedback diode lasers by adopting a separate-confinement heterostructure. The diodes are lased successfully at temperatures up to 340 °K under pulsed operation. The lowest threshold current density is 3 kA/cm^2 at 300 °K
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