Waveguide structures are spatially inhomogeneous structures which can guide waves. For light propagating in a waveguide, the self-consistency condition for a mode is more strict than for free-space modes: the shape of the complex amplitude profile in the transverse dimensions must remain exactly constant. Any re-scaling is not allowed, only an overall phase change (described by the propagation constant) and a loss or gain of total optical power. The phase change per unit length is called the propagation constant, and is generally different for different modes.
A waveguide has only a finite number of guided propagation modes, the intensity distributions of which have a finite extent around the waveguide core. The number of guided modes, their transverse amplitude profiles and their propagation constants depend on the details of the waveguide structure and on the optical frequency. A single-mode waveguide (e.g. a single-mode fiber) has only a single guided mode per polarization direction. As an example of a multimode waveguide, Figure 3 shows the transverse profiles of all the modes of a multimode fiber.
modes of a fiber
Figure 3: Electric field amplitude profiles for all the guided modes of a fiber with a top-hat refractive index profile (→ step index fiber). The two colors indicate different signs of electric field values.
A waveguide also has cladding modes, the intensity distributions of which essentially fill the whole cladding (and core) region. Optical fibers (even single-mode fibers) have a large number of cladding modes, which often exhibit substantial propagation losses at the outer interface of the cladding.作者: badan 时间: 2009-7-17 08:10
这里还有个计算光线模式的matlab程序。 Fiber modes.zip(12.15 KB, 下载次数: 48)
Fiber modes.zip
(12.15 KB, 下载次数: 48)
