We show that controlling the phase difference among the various tones of a multitone phase modulator can substantially increase the stimulated Brillouin scattering (SBS) threshold during optical fiber transmission. We present detailed modeling and experimental validation of the effect. This result should be especially useful for optical networks requiring high signal launch power.
In this paper, we studied SC generation in fiber lasers and in optical fibers pumped by different
light sources which include fs and ps pulse sources, and continuous-wave (CW) amplified spontaneous
emission (ASE) light sources. First, we demonstrated SC generation with a 10dB spectral bandwidth of
430nm in a fiber ring laser with conventional nonlinear fiber. Second, we proposed and demonstrated a
new and efficient approach to generation of a CW SC in optical fibers pumped by a CW ASE light. A
bandwidth of 268nm (at -15dB level) with an average spectral density of 2.7mW/nm was
demonstrated. Various approaches to flattening the spectrum and increasing the spectral width were
also studied. The application of this SC source in WDM passive optical access networks (WDM-PONs)
was investigated. Third, the approach of SC generation in a fiber combination of standard SMF
and nonlinear DSF pumped by an all-fiber fs pulse Master Oscillator Power Amplifier (MOPA) system
was developed. A spectral bandwidth of over 1000nm was demonstrated. Finally, the generation of
broad comb-like-spectral light based on the pulse compression of 40GHz optical pulses in a new
nonlinear dispersion-decreasing fiber with high SBS threshold was studied. A continuum light source
with over 125 channels and a channel spacing of 40 GHz was achieved. The use of this continuum light
source as WDM source in WDM-PONs was investigated.
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.
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.
The design of optical communication networks with network switching elements operating in the optical domain requires careful system analysis and potentially stringent component requirements. We consider here network elements such as transparent optical cross-connects that demultiplex WDM signals, optically switch individual channels, and then multiplex the wavelengths together again before transmission into the next span. Network element optical impairments that can degrade signal quality are in-band (same wavelength) crosstalk, out-of-band crosstalk, and signal distortion from filter concatenation effects. These impairments can limit the transmission distance of a signal before regeneration is required. We examine the trade-offs between crosstalk and filter distortion in the context of the optical filters used in the optical multiplexers and demultiplexers in the network elements. We demonstrate the balance that must be struck between these impairment types in the design of the filters and network system. We study a 10 Gb/s network with 50 GHz channel spacing, examining both NRZ and RZ modulation formats. In both cases, we find optimal filter bandwidths that minimize the total signal degradation measured in terms of Q penalty. The total penalty suffered by RZ signals is higher than that of NRZ signals and must be considered when estimating system reach.