Low loss optical fiber designs and methods for their manufacture

Abstract

The specification describes an improved optical fiber produced by a hybrid VAD / MCVD process. The core of the fiber is produced using VAD and the inner cladding layer has a depressed index and is produced using MCVD. In preferred embodiments, the optical power envelope is essentially entirely contained in VAD produced core material and the MCVD produced depressed index cladding material. Optical loss is minimized by confining most of the optical power to the VAD core where OH presence is low, as well as by maximizing the optical power in the un-doped silica region. The MCVD substrate tube material is essentially devoid of optical power.

Description

FIELD OF THE INVENTION [0001] This invention relates to a family of designs for optical fibers and methods for producing optical fibers employing those designs having improved optical transmission characteristics. More specifically it relates to a hybrid production method wherein optical fiber preforms are fabricated using a combination of MCVD and VAD techniques, wherein the VAD-MCVD interface is inside the waveguide-forming region of the refractive index profile design. BACKGROUND OF THE INVENTION [0002] A wide variety of methods have been proposed and explored for producing optical fibers. As optical fiber technology has matured, three main production methods, MCVD, VAD, and OVD have emerged. All involve the deposition of glass particulates (frequently referred to as “soot”) on a starting substrate, then consolidating the particulates into a solid glass body. The techniques involve producing the particulates using an in situ vapor phase reaction. The vapor phase reaction is induc...

AI Technical Summary

Benefits of technology

[0011] We have designed a set of optical fiber index profiles that reduce the level of dopant related excess scattering loss, and have developed a hybrid method for producing optical fibers using a combination of MCVD and VAD that significantly advance the prior art in terms of loss and high productivity. The hybrid method combines the desirable features of each processing technique. We have also noted the loss characteristics of optical fiber produced using these methods. Recognizing that the loss characteristics are different, we have combined the MCVD and VAD techniques to optimize the composite loss characteristic. The profile design can be optimized to distribute the optical power so as to reduce Rayleigh scattering, while achieving nearly zero water peak 1385 nm loss performance and maintaining good macrobending performance. In the preferred embodiment of the invention a VAD method is used to produce a core rod, with an up-doped inner core and a less heavily doped, or undoped, outer core. An MCVD method is used to produce a cladding with one or more depressed index regions. Using this basic preform fabrication approach, we adapt the profile and the optical power envelope such that essentially all of the optical power is contained in either the VAD material and the MCVD material, and most of the power envelope is contained in the VAD material, with for example typically 60% of the power contained in the VAD inner core, which has Ge-doping levels that are typically less than 60% of that found in standard single mode fiber cores, and with for example 20-40% of the power contained in the undoped or lightly doped VAD outer core.

Problems solved by technology

We have also noted the loss characteristics of optical fiber produced using these methods.

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