Methods and apparatuses for forming optical preforms from silica glass soot are disclosed. According to one embodiment, a method for forming an optical preform may include loading silica glass soot in a mold cavity of a mold body. The mold body may be rotated at a rotational speed sufficient to force the silica glass soot towards an inner wall of the mold body. Thereafter the silica glass soot is compressed in an inward radial direction as the mold body is rotated to form a soot compact layer.

Provided is a manufacturing method of an optical fiber preform, comprising: depositing SiO.sub.2 fine particles by adhesion onto a starting preform formed of quartz glass to obtain a soot preform, the starting preform including a core having a high refractive index and a cladding having a lower refractive index than the core; sintering the soot preform to dehydrate and vitrify it sequentially from one end in a dehydration gas atmosphere; and prior to the sintering, preheating at least a vicinity of a sintering-process-start end of the soot preform. Provided is an optical fiber preform formed of quartz glass and including a core having a high refractive index and a cladding having a lower refractive index than the core, wherein an average of OH concentrations in a radial direction of the optical fiber preform is 25 ppm or less throughout a section of 90% or more in a longitudinal direction.

A preform for multicore optical fiber is described. The preform includes an assembly of core canes arranged in a desired configuration. The core canes are placed in mutual contact with each other to define a series of contact zones between contacting pairs of core canes. The core canes are fused at selected locations within the contact zones to secure the core canes to form a preform from which a multicore optical fiber can be formed. The preform maintains good alignment of core canes and minimizes deformation of core canes during the fiber draw process. Multicore fibers having excellent uniformity in core diameter are produced from the preforms in conventional fiber draw processes.

A method of fabricating an optical fibre preform is disclosed comprising using a subtractive process on an optical monolith to define therein at least a transverse section of the optical fibre preform, wherein the transverse section comprises at least two regions with different refractive indexes. An optical fibre preform fabricated in accordance with the method is also disclosed along with a method of assembling optical components using a subtractive process to define a first interconnecting feature in or for use with a first optical component; using a subtractive process to define a second interconnecting feature in or for use with a second optical component; and coupling the first and second components together using the first and second interconnecting features such that the coupling dictates a passive alignment of the first and second components.