Comments on `Fundamental error of recent coupled mode formulations´ [and reply]

For the original article see ibid., vol.23, no.20, p.1097-8 (1987). In a recent letter Snyder, Ankiewicz and Altintas stated, without justification according to the commenter, that the recent coupled mode theory of Hardy and Streifer (see J. Lightwave Technol., vol.LT-3, no.5, p.1135-46, 1985) (hereafter H-S) is fundamentally in error, and claimed that the prior theory is superior. To support this contention they published two misleading graphs, which on more careful scrutiny indicate that the H-S theory is in fact more accurate than the prior theory. In reply the original authors show that the H-S full perturbation result is consistently less accurate than the standard first-order result for describing polarisation phenomena, and also show how this is corrected