A method of manufacturing a hollow core optical fiber including (a) a consolidated tube presenting step including presenting a consolidated cladding tube including a consolidated cladding first end, a consolidated cladding second end, a consolidated cladding longitudinal axis, and a consolidated cladding inner surface, the consolidated cladding inner surface defining a consolidated cladding interior and including consolidated cladding recesses (i) positioned around the consolidated cladding longitudinal axis and (ii) extending from the consolidated first end to the consolidated second end; and (b) a capillary tube coupling step comprising coupling preform capillary tubes to the consolidated cladding inner surface within the consolidated cladding recesses thus creating an optical fiber preform, each of the preform capillary tubes disposed within a different one of the consolidated cladding recesses.

A hollow core optical fiber preform including a seal at least partially sealing one or more of a cladding opening of a cladding tube and a capillary opening of each or some of one or more capillary tubes within a cladding interior of the cladding tube. The hollow core optical fiber preform includes a seal glass composition exhibiting a seal coefficient of thermal expansion that is within 10% of a coefficient of thermal expansion of the cladding or a coefficient of thermal expansion of the one or more capillaries. The hollow core optical fiber perform can further include one or more metal tubes extending through the seal. The metal tubes can be placed in fluid communication with one or more sources of a gas to control gas pressure within the one or more capillary tubes and the cladding interior during a draw step to control the dimensions thereof.

The invention relates to the production of an anti-resonant hollow-core fiber consisting of a capillary blank and a sleeve tube. The capillary blank comprises an external capillary and a nested internal capillary, and is stretched to a maximum external diameter ODARE_cap and a maximum wall thickness WTARE_caP. The blank is mounted on the inside of the sleeve tube. In order to retain the advantages of the pre-produced capillary blank with respect to ease of assembly and precision, while keeping the associated drawbacks owing to ovality low and predictable, it is proposed that the geometric internal diameter and external diameter of the external capillary and of the internal capillary, as well as ODARE_cap and WTARE_caP, are aligned in relation to one another in such a way that the ARE-external capillary of the capillary blank has a degree of ovality of less than 1.025.