Third-order optical nonlinearity in optical fibers has many attractive applications to all-optical signal processing that will be employed in future large-capacity photonic networks. After reviewing the third-order nonlinear optical property of optical fibers, we describe our recent experimental results on all-optical signal processing functions such as wideband wavelength conversion, ultrafast gate switching, and ultrafast pulse reshaping. These functions are based on self-phase modulation (SPM), cross-phase modulation (XPM), and four-wave mixing (FWM) in nonlinear fibers.
Long period fiber gratings (LPGs) have been fabricated in photosensitive fiber by use of point to point exposure method. The fiber is mounted on a constantly moving stage with a highly precise positioning function while a frequency-doubled Argon ion laser (244 nm) is switched on/off by an acousto-optic modulator (AOM). The development of transmission spectrum (HE1,5) and resonant wavelength of the LPGs as a function of laser exposure time is obtained. We present a thermal processing technique to stabilize the LPGs characteristics. The influence of hydrogen diffusion and temperature factor on the resonance wavelength and transmission peak loss is analyzed detailedly.
Third-order optical nonlinearity in optical fibers has attractive applications to all-optical signal processing that will be employed in future photonic networks. After reviewing the third-order nonlinear optical property of optical fibers, we describe some examples of all-optical signal processing devices, focussing on self-phase modulation (SPM), cross-phase modulation (XPM), and four-wave mixing (FWM).
Bismuth oxide based highly nonlinear fiber (Bi-NLF) enabled by glass composition and small core fiber design was successfully fabricated. There's much expectation for the development of high nonlinearity optical devices along with the large volumetric and speed increase of the information traffic in recent years. In order to achieve higher nonlinearity, it is necessary to enlarge the nonlinear refractive index n2 and make the effective core area Aeff smaller, as g is γ=2πn2/(λAeff). Much effort has been put into the development of small-Aeff holey fiber, as its high nonlinearity and dispersion can be controlled to a certain extent. However, holey fiber has issues such as large propagation loss, high connection loss with silica single-mode-fiber (SMF) because of their particular structure, and higher fabrication cost. We performed the fabrication of a conventional step-index-type SMF with high nonlinearity and low propagation loss using Bi2O3-based glass. First, we fabricated Bi2O3-based glass with high refractive index of >2.2 at 1550 nm by a conventional melting method. This glass exhibited extreme thermal stability for fiber drawing. Then in order to make Aeff smaller, cladding glass composition was designed so that the difference with the refractive index of the core glass must be large. Finally the core diameter was controlled to satisfy the single mode condition, and fiber drawing was performed. Typical Aeff of this fiber is less than 5 um2. The nonlinearity g of the fiber can be estimated to be >600 W-1km-1, as large as the value reported in holey fibers using non-silica glass. Bi-NLF with step-index-type structure would become the best candidate for short length and highly nonlinear optical devices.
Thin-film (TF) based dispersion compensators are of necessity some form of allpass filter. Whether these allpass filters are cast in the form of a coupled or a cascaded cavity structure, they can provide compact, low-loss, and highly stable dispersion compensation thereby having the potential of becoming important future components in both optical time-division multiplexing (OTDM) and wavelength division multiplexing (WDM) systems. In this paper, the salient points in the development of these devices are discussed up to the present state of the technology. Particular emphasis is placed on TF coupled cavity allpass (CCAP) filters as devices that provide only third-order dispersion compensation (TODC), having a group delay response that is purely quadratic. These CCAP filters are shown to have evolved over a number of important steps, from a hybrid two-cavity device, to a completely TF two-cavity single-surface filter, and finally to a dual-surface multi-reflection four-cavity device. The adjustable hybrid coupled cavity allpass filter provides TODC between 2.0 and 15.5 ps3 over a bandwidth between 3.6 and 1.2 nm respectively with a center wavelength tunable over an 8 nm range and the four-cavity multi-reflection completely TF device offers TODC between 0.37 ps3 and 3.2 ps3 over a 10 nm bandwidth with a center wavelength tunable over a 10 nm range. Important issues, such as the need to increase the TODC figure of merit, which is directly proportional to the number of cavities and the number of surface reflections, of these devices without incurring large loss penalties are discussed in the context of some of the important technological challenges that need to be addressed and solved before TF dispersion compensators can be effectively employed in optical systems as well as successfully compete with other existing dispersion-compensation technologies.
Conference Committee Involvement (3)
Optical Transmission Systems and Equipment for WDM Networking IV
25 October 2005 | Boston, MA, United States
Optical Transmission Systems and Equipment for WDM Networking III
25 October 2004 | Philadelphia, Pennsylvania, United States
Optical Transmission Systems and Equipment for WDM Networking II
8 September 2003 | Orlando, Florida, United States
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