It has been twenty years since the first fused fiber optic coupler was made and remarkable progress has been achieved during this period on the production, performance, and reliability of these devices. Several million fused couplers have now been produced and placed into service. Applications have included test instrumentation, both outside plant and central office telephony applications, cable TV systems, sensors, optical amplifiers, DWDM systems, and submarine repeaters, to mention a few. To meet the increased production requirements, significant work has been done to make the process more flexible and thereby more amenable to automation and computerization. Modern fused coupler operations are highly automated and can make a large variety of products by simply changing a computer file. Similar improvements have also been made in high volume testing so that sophisticated tests of a number of parameters can be performed in a matter of minutes. As the volume and variety of the products have increased over the years, so has the performance. Improvements have been made in reducing excess loss, polarization effects, and wavelength dependence. In addition, higher port count devices (1 X 3, 1 X 4, etc.) have been developed. Numerous studies have been conducted over the years to determine the reliability of these devices. The introduction of glass-to-glass sealing techniques to isolate the fused region by bonding the fibers directly to the quartz substrate significantly improved the stability and long term reliability of these devices. The state-of-the-art production, performance, and reliability of fused coupler technology will be reviewed in this paper.
Tap couplers with small coupling ratios (1-10%) play a critical role in monitoring optical fiber systems such as optical amplifiers. They are often used in a feedback control loop and hence must exhibit extreme stability. Very small changes in the operating characteristics of the taps can be interpreted as changes in laser power giving rise to instability in the amplifier gain. Tap couplers made by the fused biconical taper (FBT) process are inherently stable with regard to temperature and, thus, this is usually not a concern. Of much greater significance are the wavelength dependence and polarizastion sensitivity of the tap ratio. Wavelength dependence can be minimized by introducing a mismatch in the propagation constants between the two fibers, but it is also influenced to a lesser extent by the coalescence of the fibers. On the other hand, polarization sensitivity is primarily dependent on coalescence and only somewhat dependent on propagation constant mismatch. As a consequence, it is necessary, in practice, to trade off wavelength dependence against polarization sensitivity in order to optimize the overall stability of the tap coupler. We report here the results of such an optimization study, consistently yielding taps with less than 0.5 dB total change in the insertion loss of the tap leg due to all effects.
Refinement and new product development of splitters made by the fused biconical taper process are discussed relative to the emerging technologies of optical fiber amplifiers and practical fiber to the curb telecommunication systems.
In the fused biconical taper process (FBT) the mode diameter of the optical fields within the fibers are spread to the extent that the surrounding medium acts as the fiber cladding. Usually this medium is air whose optical properties are benign resulting in stable devices. However, if the coupler is recladded with a material other than air, the optical fields spread further into the cladding region and the behavior of the coupler becomes substantially more sensitive to variations in the refractive index of the cladding material. In this paper we report the results of a study of recladded FBT couplers. Experimental results will be presented and compared to the predictions of a model previously used to describe the coupling characteristics of FBT couplers.
In this paper, fused biconical taper (FBT) hard clad silica (HCSR) couplers of varying port configurations will be characterized with respect to the parameters most important to system designers. Port insertion loss, uniformity, back reflection, launch conditions and the effects of environmental conditions will be addressed.
The fused biconical taper process has been the technology of choice for fabricating a variety of passive fiber optic couplers. These couplers exhibit excellent optical and environmental characteristics. Most recently, this process has been used to fabricate tree and star couplers of various configurations: 1x3, 3x3, 1x4, 4x4 and 1x7 for both local loop and sensing applications. In this paper we report the development of broadband 1x3 and 1x4 couplers for applications requiring simultaneous transmission in both the 1300 and 1550 nm wavelength regions. The wavelength response, insertion loss and optical uniformity of these broadband couplers will be discussed. Their environmental performance will also be presented.
Over the last several years, fiber optic couplers manufactured via the fused biconical taper (FBT) process have been extensively used in a variety of fiber optic systems and instrumentation. However, because of the rapid development and deployment of this technology, there is only limited field data available regarding the long term performance and reliability of these components. In this paper some recent results of a such a study on FBT couplers will be reported. The test program consisted of accelerated heat and humidity tests, repetitive temperature cycling, mechanical shock and vibration tests as well as long term shelf tests. A review of the test data will be presented along with an estimate of component lifetimes.
The interferornetric properties of an abrupt nonadiabatic taper in an optical fiber can be used to create an all fiber wavelength filter. To date the maximum attenuation possible from a single taper has typically been 4 to 5 dB. In this paper we report the realization of single taper filters with significantly unproved performance. Typical optical properties for 1300/1550 nm filters include as much as 30 dB attenuation at the stop wavelength and less than 0. 5 dB insertion loss at the pass wavelength. Similar filters have been built for other wavelength combinations including 980/1550 and 1480/1550 mu. The operation performance and application of these high isolation single taper filters will be presented and discussed in this paper.
Over the last few years the fused biconical taper (FBT) process has been the technology of choice for fabricating passive fiber optic couplers. The FBT couplers can be made with a wide variety of fiber types and exhibit excellent optical and envirornnental characteristics. Recently much attention has been given to the fabrication of compact MxN singlemode star couplers for future local subscriber loop applications. Some of the systems being considered utilize passive star architectures which require singlemnode star couplers to split the light to a multiple number of ports or residences. In this paper we report the fabrication of true lxN and MxN singlemnode tree and star couplers using the fused biconical taper techniques. In addition to good optical uniformity and insertion loss the fused couplers offer the same environmental stability and long term reliability that are characteristic of standard FBT couplers. A discussion of the optical and environmental data will be presented.