Materials and Processing Requirements for Efficient Fiber Optic Nonlinear Devices
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MATERIALS AND
R.H.
PROCESSING REQUIREMENTS FOR EFFICIENT FIBER OPTIC NONLINEAR DEVICES
Stolen
AT&T Bell Laboratories Holmdel,
NJ 07733
ABSTRACT Materials and structures for efficient nonlinear devices are discussed in terms of Raman amplification, nonlinear switching, and self-organized gratings.
INTRODUCTION Nonlinear optics in an optical fiber can be used to make a variety of devices for the amplification or control of light. What keeps these devices out of the realm of practical application is the need for new materials and improvements in the guiding geometry itself.[l] Nonlinear optics involves the mixing of optical beams over some interaction length. It is this interaction length which can be increased by several orders of magnitude when the nonlinear interactions occur in an optical fiber. The problem is that even this sort of enhancement does not bring the power requirements down to the 1-100 mW range desired for compatibility with semiconductor laser sources. The most obvious approach is to try to replace the fused silica of the optical fiber core with a glass of large nonlinear response. This has proved to be difficult because improvements in nonlinear response seem to go along with linear loss, processing problems, and optical damage. The second approach which is now receiving more attention, is to try to modify the properties of the guide itself both to increase the efficiency of the interaction and to optimize the fiber for the specific nonlinear device. Here we pick out three nonlinear effects of potential practical application and examine possible improvements from new materials and modifications in guide structure. These three effects are Raman amplification, nonlinear optical switching, and self-organized gratings.
Mat. Res. Soc. Symp. Proc. Vol. 172.
o1990 Materials Research Society
304
RAMAN GAIN Raman gain comes from coupling of light to high-frequency vibrational modes of the medium. Raman gain in fibers has been investigated both for amplification in optical communications systems and for fiber Raman lasers. [2] A fiber Raman amplifier is illustrated schematically in Fig.la. The energy source is a strong optical wave called the "pump". By tuning the Raman signal wavelength the gain can be measured as a function of wavelength. The gain spectrum is a characteristic of the material. The gain spectrum of a silicacore fiber is shown in Fig. lb.[3]
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