Mode Theory vs Ray Theory of Light
Mode theory and ray theory are two concepts involved in transmission of light or other electromagnetic waves. These theories are very important in understanding fields such as radio transmission, data communication, fiber optics, and LASERs. Prominent scientists like Sir Isaac Newton and James Clarke Maxwell did an outstanding contribution to the study of light and other electromagnetic waves. These theories help us understand how light works and the nature of light to a very good extent.
A ray is usually known as a narrow beam of light. It is known as the classical theory of light or geometrical optics. This ray theory only describes limited amount of properties of light such as refraction and reflection. A light ray can be defined as the line or curve perpendicular to the wavefronts of light. This definition of light ray makes it actually collinear to the wave vector. The refraction of a light can be described using rays. A fundamental property of rays is that it bends in the interface of two media. The refractive indices of these media determine the angle of the bend. Most of the simple calculation like magnification and distance of the image of optical systems such as telescopes, microscopes or simple lens systems are carried out using ray theory of light.
Mode theory of light propagation plays a vital role when it comes to fiber optics. To understand the mode theory of light one must first understand the term mode. Mode is a term used in the study of standing wave. A standing wave is produced when two waves with the same frequency and amplitude moving in the opposite direction interfere. A standing wave has no net energy transfer in any direction. The mode of the standing wave is given by the number of loops within the standing wave. In the field of fiber optics, modes are created by waves bouncing from the two sides of the fiber cylinder. If a standing wave is created this causes a signal loss. Therefore, the number of modes that can be inside an optical fiber is limited, thereby, limiting the number of frequencies that can be sent through the optical fiber. This is known as the bandwidth of the channel. Mode theory uses wave theory of light to describe itself, phenomena like diffraction and interference.
Difference between Mode theory and Ray theory of light
Ray theory is a theory that is connected with the geometric optics. It does not assume light as either a wave or a particle. The mode theory of light assumes light as a wave. The mode theory of light is used to calculate quantities such as bandwidth but the ray theory is used to calculate properties like magnification or distance to the object or image in an optical system.