We present a frequency-domain method for measuring various types of optical fibers primarily using a vector network analyzer (VNA). Through proper E-O conversion to launch frequency sweeping signals into the fiber and O-E conversion at the receiving side, the VNA measures the complex transfer function (CTF) of the fiber transmission for a given launch condition. The group delay information can be calculated from the inverse Fourier transform of the CTF. Due to the long fiber length relative to the number of points used by VNA for frequency sampling, the measured CTF is under-sampled and aliased. With proper de-aliasing procedures, the aliased CTF can be transformed into a modified CTF in the local time frame. The output pulses can then be recovered with the full group delay information obtained. The group delay and dispersion of different modes or different cores can be obtained from the CTF over a range of wavelengths. For single mode fibers, we can obtain the group delay and chromatic dispersion from the wavelength dependence. For fibers with multiple modes, cores or polarization maintaining fibers with two distinct polarization modes, the group delay of each mode or core can be obtained simultaneously. For multimode fibers, we have developed a thorough procedure to conduct differential mode delay measurements and calculate modal bandwidth, equivalent to the time domain method defined by the standard. Overall, the VNA based frequency domain method can measure various types of optical fibers from short lengths of a few hundred meters to long lengths of many kilometers at different wavelengths. The technique is unique among fiber measurement techniques in that it can determine the group delay, dispersion, modal and bandwidth properties across different fiber types, not limited to just single mode fibers.
The data center interconnect is moving toward 1.6 Tbit/s, which is posing challenges for reaching a solution that is cost effective and technically feasible. Intensity modulation and direct detection (IM/DD) transmission over O-Band using standard single-mode fiber is a potential low-cost solution. However, limitations imposed by chromatic dispersion and four-wave-mixing (FWM) needs to be understood, such as in the case when operating at 8 x 100 GBaud PAM4 in LWDM configuration. In this paper, a statistical approach has been adopted to evaluate the probability of outage by considering practical link parameter fluctuations such as wavelength variation and drift, polarization variation and the natural variation of the fibers zero dispersion wavelength. Numerical modeling shows that IM/DD can be used up to distances of 5 km if transmission power is maintained under 0 dBm. Coherent transmission can extend the distance beyond 5 km due to its signal processing capabilities. However, it is desirable to reduce its complexity for cost effective and power efficient data center applications. Using dual wavelength transmission and DP-16 QAM transceivers, which share similar components to the IM/DD counterpart, the feasibility of simplifying this architecture is studied. The analysis shows that the complexity of the coherent approach can be reduced without significant penalties for distances up to 10 km.
Recently it has been shown that standard single-mode fibers, which support two LP modes around 850 nm, can yield high modal bandwidth with graded-index profile design. A transmission system using such fibers along with 850 nm single mode VCSEL transceivers offers a potentially cost-effective high-bandwidth solution for data center applications and future high-speed short distance communications. The system reach highly depends on the modal bandwidth of the fiber. In this context, it is of interest to explore the characterization method of the modal bandwidth of two-mode and few-mode fibers, especially if the method can be simpler than traditional methods used for 50-μm core multimode fiber. To address this issue, we propose a simple and robust method for two-mode and few-mode fiber modal delay and bandwidth measurements using frequency domain method. An analytical transfer function model was formulated and achieved excellent agreement with experimental results. The model allows one to extract the modal delay based on one single measurement, regardless of the launch condition. The transfer function and hence modal bandwidth with arbitrary launch condition can be calculated, from which we define a worst-case modal bandwidth that can gauge the fiber modal bandwidth under general conditions. The analytical model is also generalized to consider higher-order modes and additional bandwidth degradation effects. Through the detailed study, we show that the simple frequency domain measurement method as facilitated by the analytical model can deliver a full set of modal delay and modal bandwidth information that otherwise requires more complex method like differential mode delay measurements.
In this paper, we present an optical fiber that is single-mode at 1310 nm window and few-mode at 850 nm window with high bandwidth. The fiber is compatible with standard single-mode fiber at 1310 nm, which can meet long reach requirements for hyper-scale data centers. In addition, the fiber can be used for few-mode transmission at 850 nm using single-mode or few-mode VCSELs, providing low-cost solutions for short links. We discuss fiber design considerations and present fiber properties and 25 Gb/s transmission results at 850 nm.
In this paper, we present a new type of optical fiber, called universal fiber, which can be used for both multimode and single mode transmissions. The fiber is a multimode fiber that has an LP01 mode field diameter approximately matched to that of standard single mode fiber. First, we will present the universal fiber design concept and discuss design tradeoffs for both single mode and multimode operations. Then we will show characterizations of a preliminary experimental fiber and present system testing results with 110 m, 150 m and 2700 m system reach using 100G SR4, 40G sWDM multimode and 100G CWDM4 single mode transceivers, respectively, which demonstrate both multimode and single mode transmission capabilities of universal fiber.
40G BiDi is a commercial WDM transceiver with duplex LC connectivity for transmissions over multimode fibers. In
this paper, we evaluate the transmission performance of 40G BiDi over OM4 fibers. We have carefully selected OM4
fibers with the lowest and highest peak wavelengths around 850 nm to evaluate the reach capability for 40G BiDi
transmission. We demonstrated that the OM4 fiber with the lowest peak wavelength can transmit error free over 325 m
while the OM4 fiber with the highest peak wavelength can transmit up to 350-390 m. In both cases, the maximum
lengths are much longer than 150 m and 200 m specified for OM4 and wideband MMF transmissions, respectively. We
also measured the transceiver encircled flux and found that it was tighter than the encircled flux standard, which may be
a factor favoring long system reach at 900 nm.
We show that for coherent 112 Gbps PDM-QPSK systems employing inline
dispersion management, and for a wide range of birefringence parameters, spinning
reduces the benefit of local birefringence in the mitigation of nonlinear impairments.
Rare-earth doped fibers for high power fiber amplifiers normally have a small refractive index difference between the
core and inner cladding, but have a larger core diameter than conventional telecom fibers. We take advantage of this
feature as well as the difference between the optical and acoustic waveguides and proposed several fiber designs to
mitigate Stimulated Brillouin Scattering (SBS) to produce higher output powers. The numerical modeling showed that
an increase in SBS threshold by 3-5 dB can be achieved using Ge-codopant while maintaining diffraction limited beam
quality. The study also highlights the need to take into account the effects of minor refractive index profile variation in
evaluating SBS performance.
Over the past decades, discrete or distributed Fiber Optic Sensing (FOS) applications have seen an increased acceptance
in many areas. High level optical and mechanical reliability of optical fiber is necessary to guarantee reliable
performance of FOS. In this paper, we review recent research and development activities on new specialty fibers. The
main approaches to enhancing fiber attributes include new refractive index profile design and fiber coating
modification.
We present a novel fiber design using both stress rods and air holes for making wide band single polarization fibers as
well as polarization maintaining fibers. The key factor that makes the fiber design possible is that the stress-induced
birefringence from the stress rods and the form birefringence from air holes are added constructively, which increases
the total birefringence and allows more flexible choice of fiber parameters. We established a finite element model that is
capable to study both the stress-optic effect and the wave-guide effect. Through the detailed modeling, we
systematically explore the role of each major parameter. Different aspects of the fiber properties related to the
fundamental mode cutoff, fiber birefringence and effective area are revealed. As a result, fibers with very large single
polarization bandwidth as well as larger effective area are identified.
Suppressing nonlinear effects such as stimulated Brillouin scattering (SBS), stimulated Raman scattering (SRS) in high
power fiber amplifiers and lasers is crucial for scaling up output power well beyond kW levels. The paper uses a
sophisticated model to analyze many different fiber amplifier designs and compare their performance. The systematic
modeling reveals many interesting results and shows that a co-pumped amplifier can be optimized by carefully choosing
fiber lengths and applying additional heating to the fiber. It also explains why the amplifier configuration can make
great impacts on SBS characteristics. In addition, a single-polarized fiber having an effective area of 206 μm2 and cutoff
wavelength of 1100 nm is designed to suppress SRS and provide better polarization properties. The systematic
modeling concludes that in general a counter-pumped fiber amplifier has the lowest nonlinear effects and is less sensitive
to the fiber length comparing with the co-pumped amplifiers. However, the co-pumped amplifier is easy to integrate
with an all-fiber-based pump combiner without risking LD damage and it can be heated to increase SBS threshold by a
factor of 1.7.
Over the last several years, Fiber Optic Sensor (FOS) applications have seen an increased acceptance in many areas
including oil & gas production monitoring, gyroscopes, current sensors, structural sensing and monitoring, and
aerospace applications. High level optical and mechanical reliability of optical fiber is necessary to guarantee reliable
performance of FOS. In this paper, we review recent research and development activities on new specialty fibers. We
discuss fiber design concepts and present both modeling and experimental results. The main approaches to enhancing
fiber attributes include new index profile design and fiber coating modification.
High power fiber lasers have been recently demonstrated at the kilowatt level. The
spectral linewidths of these lasers oscillators can exceed 20 nm. Whereas, such broad
spectra are fine for many applications, such as materials processing where raw power is
the primary requirement, other applications, including coherent beam combination,
harmonic generation, or gravitational wave detection, require high powers beams with
much narrower linewidths. Amplification of narrow linewidth signals in optical fibers is
limited by stimulated Brillouin scattering (SBS). We discuss novel fiber designs that limit
SBS allowing the amplification of narrow linewidth signals to kilowatt power levels.
This paper reviews different fiber design approaches for high power lasers. First, we discuss the conventional step index
profile design and methods for achieving single mode operation in high power lasers such as bending, helical core fibers
and Yb dopant profile designs. Then we present new design approaches for reducing the SBS through profile and glass
composition designs. Finally, we describe fiber designs to achieve single polarization and at the same time to mitigate
the SRS effect.
This paper outlines recent work at Corning Incorporated on fiber composition design and fabrication of a SBS-managed, large-mode-area (LMA), Yb-doped double-clad fiber for high-power, narrow-linewidth fiber laser applications. Through a detailed theoretical analysis for the SBS threshold in optical fibers, an Aluminum/Germanium (Al/Ge) counter-graded fiber-core composition profile has been proposed and demonstrated for reducing the SBS effect, via the reduced-overlap between optical and acoustic modes in the fiber design. Such Al/Ge counter-graded-composition-profile design overcomes the limitation in a multilayer fiber-core approach, in terms of the low-loss fiber fabrication. The new compositionally SBS-managed, LMA Yb-doped double-clad laser fiber fabricated through the new design, has shown more than ~7 dB improvement in SBS threshold over the conventional LMA fiber design. The new fiber offers exceptionally low passive-loss characteristics, and has been demonstrated with uncompromised high laser efficiency for high-power, narrow-linewidth fiber laser applications.
This paper reviews recent progress and experiment and modeled results on dual air hole-assisted polarizing fibers which can act as either Single Polarization (SP) fiber or Polarization Maintaining (PM) fiber. Dual air hole-assisted fiber design provides both SP and PM characteristics for the same fiber at different wavelength range. SP operating windows centered at wavelength from 980 nm to 1550 nm with bandwidth ranging from 24 nm to 63 nm are demonstrated. Various properties of the fibers are studied. We explored bend and length dependence of SP window which enables fining tuning in actual device application. We also investigated SP and PM characteristics over wide range of temperature, such as fundamental cutoff wavelength, extinction ratio and birefringence. It was found that hole-assisted polarizing fiber provides less temperature sensitivity compared to stress member-assisted polarizing fiber. Lastly, Ytterbium (Yb) doped SP fiber, which combines gain medium and polarizer into single element was realized. Significant benefits can be achieved by using Yb-doped SP fiber in application such as fiber laser or amplifier, which requires linearly polarized output.
Single transverse mode fiber lasers have recently achieved output powers at the kilowatt level. These breakthroughs can be attributed to the maturation of high power diode pump technology at 980 nm and the use of large mode area (LMA) fibers. In the continous wave (cw) operation regime, LMA fibers, through their reduction of device length and increase of the effective area, have been effective in the reduction of deleterious nonlinear optical effects such as stimulated Raman scattering (SRS). The use of LMA fiber has been less effective in the suppression of stimulated Brillouin scattering (SBS), for which the threshold can be several orders of magnitude lower than for SRS. In this work we use refractive index profiles and index modifying dopant distributions for the mitigation of SBS. Our theoretical and modeling efforts led to an experimentally demonstrated increase in SBS threshold of 2.5 dB for single mode fiber and 6 dB for LMA amplifier fiber. We discuss the use of this SBS-suppressive fiber in the demonstration of a high-power,
narrow linewidth fiber amplifier.
This paper reviews and presents the recent specialty fiber research and development conducted at Corning Incorporated
towards high-power and high-brightness fiber lasers. These include the fabrication of all glass-composition, high-NA,
Yb-doped double-clad laser fibers, and also of double-clad single-polarization laser fibers for further improved
brightness in laser beam quality through innovative fiber designs. These have led to the 1st all-glass, high NA, Yb-doped
high-power double-clad fiber made by an all-vapor-phase fiber-preform process in the world, and also the highbrightness,
single-polarization double-clad high power laser fiber.
Fiber spinning has been widely used in reducing polarization mode dispersion of optical transmission fibers in the past decade. It also affects the polarization evolution in fibers, which has measurable effects. This paper reviews and reports the progress in understanding the properties of polarization evolution in spun fibers in both of the cases with and without the influence of external factors. Theoretical formalism is constructed and various properties of the polarization evolution are revealed through numerical modeling. Some aspects of the features have been experimentally explored.
We have demonstrated high power, linearly polarized output from an
all-fiber laser using an integrated polarizing fiber. In this
paper, we will detail the design, fabrication and operation of the
single polarization fiber as well as the fiber laser experiments.
This paper reviews recent progress and presents new designs and experimental results on single polarization (SP) fibers. The design concept for achieving SP propagation and approaches using either stress induced birefringence or hole-assisted geometrical birefringence for realizing single polarization fibers are described. Designs of hole-assisted SP fibers with either dual holes or a central hole are discussed in details. Effects of fiber parameters on SP fiber performance such as bandwidth, cutoff wavelength, mode field area are analyzed. Results on fabrication and characterization of dual-hole-assisted SP fibers are presented. SP operating windows centered at wavelength from 900 to 1600 mm with bandwidths from 18 to 55 nm are realized. Applications of SP fibers for single mode fiber lasers to produce linear polarized laser output are demonstrated with extinction ratio of 17-20 dB.
We review current work on fiber laser systems at Corning. In particular, we describe design and performance of all-glass double-clad laser fibers, broad-area laser pumps, and pump coupling optics. We discuss our approaches using single-polarization fiber and low-nonlinearity photonic band gap fiber as technologies for developing the next generation of high-power fiber lasers.
This paper surveys recent progress in fiber spinning technology for reducing polarization mode dispersion with the focus on theoretical understanding of fiber spinning mechanism and features of spun fibers, as well as their applications in fiber spin profiles designs. First, a brief introduction to the requirements of fiber PMD for high-speed optical fiber communications systems is given. Further discussion covers several spin technologies, including preform spinning and fiber spinning. Different theoretical approaches for modeling fiber spinning are reviewed with the emphasis on the coupled-mode formalism. The coupled-mode theory is then applied to different fiber spin profile designs, including constant, sinusoidal and frequency and amplitude modulated spin profiles. Main features of these spin profiles, such as PMD reduction dependence on fiber beatlength and sensitivity to spin parameters, are compared. Scaling properties of spun fibers, which show different behaviors from unspun fibers, are also discussed.
Smart structure has become an increasingly common term describing a structure embedded or bonded with a large number of lightweight active electro-mechanical sensors and actuators. In this paper, we consider the modeling and control issues related to smart structures bonded with piezoelectric sensors and actuators from the passivity viewpoint. We show that when a piezoelectric patch is used both as an actuator and a sensor, the mapping from the voltage input to current output is passive, which implies that any strictly passive feedback controllers are stabilizing. Issues related to the design of the passive feedback controller with performance optimization and controller order reduction are investigated.
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