On August 18, Ciena fell 4.89% in regular trading, trading at $421.02/share, with turnover of $115 million. The optical communication sector came under broad selling pressure as global long-term bond yields surged to multi-year highs and AI infrastructure financing concerns intensified.

On the news front, the U.S. 30-year Treasury yield rose to 5.327%, its highest since 2007, while the optical communication sector entered a profit-taking phase following a brief rebound driven by Lumentum's strong Q4 results. Industry analysts noted that high-beta optical communication stocks are undergoing a pricing standard shift from rewarding growth to demanding sustained earnings beats and profit delivery, compressing sector valuations. Additionally, prominent investors warned that over $500 billion in AI infrastructure financing could signal a cyclical peak in AI spending enthusiasm.

Within the Communication Equipment sector, Lumentum fell 4.28%, Applied Optoelectronics fell 6.84%, Nokia fell 3.11%, and Cisco fell 0.91%, reflecting broad sector weakness.

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