Here is a TOSA composed of EML TO Can
Placing a lens on the TO cap.
The lens of the TO cap is put into the interior TO. The previous traditional lens is changed to collimated light field. TO is made as a flat window for hermetic protection. In addition, a lens is added near the core for focusing.
One of the inside structures is to place collimating lenses, Glens and Clens inside TO can. C lens is the low-cost option.
In the position of the metal welding ring, a lens can be embedded. It is used to focus parallel light and coupled to the optical fiber.
Another solution use two lenses to improve the coupling efficiency of the fiber and increase the output optical power of the optical module.
In the long optical structure, you can avoid the excessive divergence of the light, shorten the spot diameter with parallel light, and improves the efficiency.
Some other manufacture use the concave and convex crescent to changes the incident angle of the light path. Thereby the coupling efficiency is improved. This lens is embedded into the TO cap. The crescent lens can be used in many applications. For example, it can be used in the 800G coherent module package. The modulator and ICR of 800G need a better signal-to-noise ratio. Improving the coupling efficiency to increase the energy of the signal so as to enhance of high signal-to-noise ratio under wide bandwidth.
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