The use of optical fibers in low earth orbiting (LEO) satellites is a source of concern due to the radiation environment in which these satellites operate and the reliability of devices based on these fibers. Although radiation induced damage in optical fibers cannot be avoided, it can certainly be minimized by intelligent engineering. Qualifying fibers for use in space is both time consuming and expensive, and manufacturers of satellites and their payloads have started to ask for radiation performance data from optical fiber vendors. Over time, Nufern has developed fiber designs, compositions and processes to make radiation hard fibers. Radiation performance data of a variety of fibers that find application in space radiation environment are presented.
With the use of fiber lasers pervading diverse applications and environmental conditions, the long-term reliability of low index (LI) polymer coated double-clad (DC) fibers used for this purpose is significant. Mechanical reliability standards for 125um fibers are well established by Telcordia GR-20-CORE requirements and some work1 has been published investigating optical reliability of DC fibers with specially engineered coatings with respect to accelerated temperature and humidity aging. While these are helpful in providing a figure of merit to the optical reliability of LI fluoroacrylate coatings, it becomes important to decouple the effects of temperature and humidity in order to understand the underlying degradation mechanisms of LI polymers in various storage and operating environments. This paper identifies the effects of temperature and humidity on the spectral attenuation of DC fibers and presents a reliability model capable of predicting lifetimes under prolonged exposure to typical temperature and humidity conditions experienced during storage and operation of fiber lasers.
The reliability of low-index polymer coated double-clad (DC) fibers used in the manufacture of fiber lasers and amplifiers has not received adequate attention. This paper evaluates the mechanical reliability of fibers, using standard fiber optic test procedures, and compares the performance of the DC fibers to the GR-20-CORE standard adopted by the industry. An 85 °C hot water soak test is proposed as an accelerated test to evaluate a low-index polymer coated DC fiber performance with prolonged exposure to temperature and humidity conditions experienced during storage and operation of fiber lasers. The test is used to evaluate DC fibers with three different coatings, including a specially engineered coating, and benchmark fibers from competitors. The data in this paper demonstrate that a dual acrylate coated DC fiber, using the specially engineered coating, has median failure stress values of over 700 kpsi and an average stress corrosion parameter of 21, well exceeding the recommended industry minimum values of 550 kpsi and 18, respectively. The accelerated temperature and humidity aging test clearly demonstrates that DC fibers with specially engineered coatings have 2 to 3 orders of magnitude better optical reliability. Such remarkable optical and mechanical performance significantly alleviates long term reliability concerns of fiber lasers and amplifiers.
Being the new frontier of science and technology, as the near earth space begins to attract attention, low cost and rapidly
deployable earth observation satellites are becoming more important. Among other things these satellites are expected
to carry out missions in the general areas of science and technology, remote sensing, national defense and
telecommunications. Except for critical missions, constraints of time and money practically mandate the use of
commercial-off-the-shelf (COTS) components as the only viable option. The near earth space environment (~50-50000
miles) is relatively hostile and among other things components/devices/systems are exposed to ionizing radiation.
Photonic devices/systems are and will continue to be an integral part of satellites and their payloads. The ability of such
devices/systems to withstand ionizing radiation is of extreme importance. Qualification of such devices/systems is time
consuming and very expensive. As a result, manufacturers of satellites and their payloads have started to ask for
radiation performance data on components from the individual vendors. As an independent manufacturer of both
passive and active specialty silica optical fibers, Nufern is beginning to address this issue. Over the years, Nufern has
developed fiber designs, compositions and processes to make radiation hard fibers. Radiation performance data (both
gamma and proton) of a variety of singlemode (SM), multimode (MM), polarization maintaining (PM) and rare-earth
doped (RED) fibers that find applications in space environment are presented.
Although fiber amplifiers have been employed in communications systems for many years, until very recently the fiber laser was little more than a scientific curiosity. However the fiber laser format has a number of intrinsic advantages over lamp and diode pumped YAG lasers including size, reliability, wavelength selectivity, heat dissipation, wallplug efficiency and operational cost; and with kiloWatt output powers now possible fiber lasers are beginning to replace lamp and diode pumped YAG lasers in many industrial applications. In this paper we review the recent and ongoing advances in fiber design that have facilitated this revolution.
The advent of double clad fiber technology has made high power lasers and amplifiers possible. However, the scalability of output powers can be limited by amplified spontaneous emission and nonlinear processes such as stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS). These limitations can be overcome by using low numerical apertures (NAs), large-mode areas (LMAs), novel index profiles and high dopant concentrations. This paper discusses advances made in design and fabrication of highly efficient, large-mode area double clad fibers. Experimental and modeling results pertaining to changes in mode area, resultant power density and nonlinear threshold with changing core size are discussed. In addition, the mechanical reliability of the LMA fibers is discussed.
For intrinsic fiber optic sensors such as interferometric fiber optic gyroscopes that use polarization maintaining fibers, performance of the fibers that constitute the sensing coils is a key issue. In general, requirements include small form-factor, good bend performance, tight tolerances on fiber geometry and ability to maintain a single polarization state. Currently, bow-tie or elliptical clad type high birefringence fibers are used in such sensors. This paper deals with the development and characterization of small form-factor (80 μm) PANDA style high birefringence fibers for sensing applications at different wavelengths of interest. The rationale and advantages of the new design are discussed along with geometrical and optical characteristics of one new fiber. Performance data of the fiber in terms of cross-talk variation in the -55 to + 85°C temperature range are presented.