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1、 Optical Fiber evanescent field components an overlooked technology? Dr Ian Giles Article published in Fiberoptic Product News April 2004 Article published Fiberoptic Product News April 2004 pages18 - 21 Page 2 of 11 Optical Fiber evanescent field components an overlooked technology? Manipulation of
2、 the optical signal by components in fiber networks is generally accomplished by breaking the fiber path and applying the required functionality in an alternative media, either planar waveguide or free space. There are notable all-fiber exceptions, such as fiber amplifiers, Bragg grating filters and
3、 fused biconical couplers. In general however, all-fiber solutions are difficult to integrate into more complex multi- functional modules and are limited in the functionality they can offer. A less commercially exploited all-fiber technology is the fiber evanescent field approach to component manufa
4、cture. These devices utilize the optical fiber waveguide by building the optical circuit directly onto the fiber without breaking into the fiber core. Significant potential benefits can be derived from such a minimally invasive technology is this an overlooked technology? Guided wave optical systems
5、, whether for communication networks or sensors, in general utilize Silica based optical fibers to provide a passive, low loss transmission medium, offering relative immunity from the surrounding environment for the propagating wave. The optical energy is tightly bound within the core region of the
6、fiber making it ideal for transmission, but making it difficult to modify the characteristics of the propagating wave in the fiber itself. Therefore functionality is generally applied in optical fiber networks by breaking the fiber and introducing an alternative medium either guided or free space. A
7、dvantages from the use of alternative media for optical components are apparent in the capability to provide complex functionality over multi-channels in a compact, low cost format. Progression of such integration is analogous to the development of electronic integrated circuits from discrete compon
8、ent beginnings. The argument is clear when there is no alternative fiber based integratable technology, but if an all-fiber technology with the potential to provide integrated complex functionality was available would the argument for non-fiber components be as compelling? System functionality Syste
9、m designers require optical modules to perform specific functions or complex combinations of functions. Qualifying technology platforms should be able to produce a majority of the functional requirements. Such requirements can be divided into essentially three general groups which facilitate full co
10、ntrol of the optical signal: Power, wavelength and polarization, control. The table below identifies specific functions within each area which have families of components with specific parameters associated Power control Wavelength control Polarization control Generation sources Detection photodiode
11、s Power splitting Switching Modulation Amplification Attenuation Power monitoring Filtering Mux./Demux. Dispersion compensation State of polarization control Polarizing Depolarizing PMD compensation Stokes parameter measurement Article published Fiberoptic Product News April 2004 pages18 - 21 Page 3
12、 of 11 All-fiber components All fiber components are directly compatible with the transmission medium, without the necessity for precision alignment and fixing to different materials therefore not incurring the mismatches associated with alternative approaches. In general this provides four major be
13、nefits, reduced reflection, low insertion loss, minimized PDL and similar effective operational bandwidth. Drawing on the inherent advantages of incorporating all-fiber components several all-fiber technologies are currently utilized in systems to provide specific functions: Fiber doping to give amp
14、lification properties Fused taper couplers for power splitting, wavelength and polarization differentiation Bragg gratings for filtering, dispersion compensation Discrete fiber evanescent field devices are also currently used, primarily for polarizers, VOAs and power monitors, however this particula
15、r technology platform has the potential to extend beyond simple discrete components to offer benefits normally assigned to planar waveguide and similar technologies. The rationale for this is that the evanescent field device is constructed on a fiber waveguide substrate. Evanescent field devices To
16、satisfy Maxwell s equations for a dielectric waveguide the field of a propagating wave contained within the central core extends beyond the core cladding interface decaying exponentially from the interface into the cladding. The magnitude of the field in the cladding is dependent on the characteristics of the waveguide and the wavelength of the wave. Optical fibers are circular cross section dielectric waveguides and
