Single longitudinal mode operation in phase-shifted DFB laser diodes

✍ Scribed by C. Ferreira Fernandes

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 165 KB
• Volume: 22
• Category: Article
• ISSN: 0895-2477
• DOI: 10.1002/(sici)1098-2760(19990805)22:3<171::aid-mop7>3.0.co;2-n

✦ Synopsis

and three modes corresponding to s 1. In Figure 3, which is a plot of the LHS of the cutoff condition for the second Ž . case Case II: a s 20 m and b s 30 m , we get four cutoff ␤-values corresponding to s 0 and another four cutoff ␤-values corresponding to s 1. Again, in Figure 4, Ž . when a s 10 m and b s 30 m Case III , there are only three cutoff ␤-values corresponding to s 0; and for s 1, there are as many as ten cutoff values for ␤. The cutoff ␤-values are tabulated in Table 1 for the three different cases.

It is found that the number of sustained guided modes increases with the increase of the azimuthal index marginally when a and b are not very large. But for large values of b, the number of modes increases significantly as is increased if the value of a is kept at a comparatively small value. This means that, when the thickness of the guiding region increases, the number of guided modes increases. Also, when the thickness is kept fixed and the curvature of the annular structure is decreased, the number of guided modes increases marginally.

CONCLUSION

In the above discussion, a simple numerical analysis of an annular waveguide with a truncated parabolically decaying refractive-index profile has been presented with respect to its cutoff behavior of the modes. All relevant information regarding the cutoff ␤-values for the different modes can be Ž . obtained from Eq. 7 . The numerical values for the cutoff ␤-values have been computed for some lower order modes. Although we cannot obtain a complete behavior of the guided modes from this analysis, the cutoff behavior of various modes can be obtained, and is presented here. It is found that the thickness and curvature of the annular guided region affect the number of guided modes, at least near cutoff.