Skip to main content

Evanescent wave coupling

In optics, evanescent wave coupling is a process by which electromagnetic waves are transmitted from one medium to another by means of the evanescent, exponentially decaying electromagnetic field.

Coupling is usually accomplished by placing two or more electromagnetic elements such as optical waveguides close together so that the evanescent field generated by one element does not decay much before it reaches the other element. With waveguides, if the receiving waveguide can support modes of the appropriate frequency, the evanescent field gives rise to propagating wave modes, thereby connecting (or coupling) the wave from one waveguide to the next.

Evanescent wave coupling is fundamentally identical to near field interaction in electromagnetic field theory. Depending on the impedance of the radiating source element, the evanescent wave is either predominantly electric (capacitive) or magnetic (inductive), unlike in the far field where these components of the wave eventually reach the ratio of the impedance of free space and the wave propagates radiatively. The evanescent wave coupling takes place in the non-radiative field near each medium and as such is always associated with matter, i.e. with the induced currents and charges within a partially reflecting surface. This coupling is directly analogous to the coupling between the primary and secondary coils of a transformer, or between the two plates of a capacitor. Mathematically, the process is the same as that of quantum tunneling, except with electromagnetic waves instead of quantum-mechanical wavefunctions.
Labels:

Comments

Post a Comment

Popular posts from this blog

Characteristics of Mass Communication

Five characteristics of mass communication have been identified by Cambridge University's John Thompson. Firstly, it "comprises both technical and institutional methods of production and distribution". This is evident throughout the history of the media, from print to the Internet, each suitable for commercial utility. Secondly, it involves the "commodification of symbolic forms",as the production of materials relies on its ability to manufacture and sell large quantities of the work. Just as radio stations rely on its time sold to advertisements, newspapers rely for the same reasons on its space. Mass communication's third characteristic is the "separate contexts between the production and reception of information", while the fourth is in its "reach to those 'far removed' in time and space, in comparison to the producers". Mass communication, which involves "information distribution". This is a "one to many" f...
2 comments
Read more

Conclusion

Open communication climates encourage employees through supporting them, through allowing them to participate in decision making, and, through trusting them, which assures the integrity of information channels. Ultimately, the openness of any communication climate depends upon the character of the participants. Openness often demands courage because the communicator operates with lowered or eliminated defensive barriers, even when standing up to verbal assault. Because open communicators have to articulate their positions in meetings, public arenas, and in print, they must be secure individuals, confident in their own positions, ability, and authority. Yet, while open communication climate may make formidable personal demands, such openness ultimately rewards both the individual and the organization in providing an environment where people thrive and enterprise flourishes.
4 comments
Read more

Trusting Environments

All parties in information exchange must tell the truth as they perceive it. They must also ensure that information is correct. Credibility is any employee's greatest asset. A reputation for carelessness, lying, deceit, or manipulation undercuts all future messages. The result of credibility is trust; it underpins all human relationships. Employees have to believe their information sources. If, for example, at weekly meetings, the staff hears contradictory information about project plans, decisions, or salary, they will dis­miss all information because they cannot confidently choose which to believe. If one week they are told the start-up date is November 14, the next week November 20, and following week November 7, they will understandably dismiss all the information as not credible. Repeated instances of passing such contradictory information will corrupt the integrity of the communication channel. People quickly dismiss information sources that prove to be wrong or untrustworthy...
Post a Comment
Read more