Thermal stability of bias point of packaged linear modulators in lithium niobate

The thermal stability of the bias point of packaged, passively biased, X-cut LiNbO/sub 3/ interferometric modulators is described. Absolute stability is assessed and a comparison is made of stability before and after laser ablation adjustment used to tune the bias point to linear operation (90/spl deg/ phase angle). Ablation is shown to be successful in setting the bias angle to /spl plusmn/1/spl deg/ of the desired value. The angle remained stable to a total variation of <5/spl deg/ over -25-+42/spl deg/C both before and after ablation. All the observed angular changes with temperature were in the range 0.02-0.09 deg//spl deg/C. The effect of humidity in the package on modulator stability is characterized and then minimized for the actual devices.