| CPC G02F 1/3528 (2021.01) [G02B 6/02328 (2013.01); G02F 1/365 (2013.01); G03F 9/7034 (2013.01); G06F 30/392 (2020.01); G06F 30/398 (2020.01); H01S 3/06741 (2013.01); G06F 2119/18 (2020.01)] | 20 Claims |

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1. A broadband radiation source device comprising a hollow-core photonic crystal fiber (HC-PCF) to generate broadband output radiation upon receipt of pump radiation therein, the HC-PCF comprising at least one structurally varied portion, wherein the at least one structurally varied portion is configured to have radiation pass therethrough and has at least one structural parameter of the HC-PCF varied with respect to one or more main portions of the HC-PCF so as to narrow or widen a hollow core region through which radiation passes.
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