Volume 5, Issue 2

An automatic linewidth control loop which provides stable optimum linewidth reduction and single cavity mode operation of an external cavity semiconductor laser is presented. Stable linewidth reduction from 70 MHz to below 2 MHz is obtained for a 1.3 μm BH-laser, whereas simultaneous mean frequency stabilization to within 1 kHz and linewidth reduction from 17 MHz to 1.6 MHz is demonstrated for an 830 nm CSP-laser.

A new detection method has been realized for laser wavelength and power control. A single detector scheme gives simultaneous response of occuring changes in the two laser output parameters of interest. Experimental results showing a wavelength and power stabilization of 10 -9 and 10 -3 , respectively, are presented.

The wavelength of a GaAlAs semiconductor laser has been locked for the first time to an integrated-optic LiNbO 3 Fabry-Perot-Interferometer. By use of a feedback loop to the injection current, the laser wavelength was stabilized to within a value of the order of 10 -9 by an integration time of 30 ms.

A frequency stabilization system for semiconductor lasers is described which makes use of a Fiber-Fabry-Perot (FFP) as frequency reference element. The FFP is fabricated from a 3 cm length piece of monomode fiber thus allowing for a compact “all fiber” packaging of the optical part of the system. The electronics includes laser diode and FFP temperature stabilization (± 1 mK) as well as a laser current modulation technique with phase sensitive detection and current control in order to stabilize the laser wavelength to the peak of the FFP transmission curve. Stability of 500 kHz (peak to peak) with respect to the FFP reference is demonstrated as well as insensitivity of this stabilization against substantial variations of the optical intensity coupled into the system.

A numerical technique based on finite differences is used for solving the vectorial wave equation in circular multimode fibers presenting an arbitrary index profile. This method provides fast and accurate results on the fiber bandwidth in analysis as well as in synthesis of optimum index profiles.

This article reports the dependence of baseband response amplitude of spliced-fiber links, as far as the baseband response of individual fibers included in each particular link is concerned. The measurements are made in frequency domain and the bandwidth reproducibilities are evaluated from the amplitude response measurements. As a main conclusion, it seems not to be necessary to measure the baseband response characteristics of spliced fiber links in the field, if measurements are previously carried out on individual fibers.