An internal combustion engine having a combustion heater is constructed to prevent a thermal damage to the structure of an intake system due to combustion heat emitted from the combustion heater. All light within the optical bandwidth of operation is first coupled from the core mode of an optical fiber to a specific cladding mode by a chirped broadband cladding mode coupler. The invention further relates to processes for making such thermoplastic and polyareneazole pulp.