Basic Optical Components of Integrated Photonics

As an example of an important branch of optics that includes some of disciplines is the field of integrated optics or, in other words, integrated photonics. Integrated photonics is represented by the combining  of waveguide technology with other disciplines, such as electro-optics, acoustooptics, nonlinear optics, and optoelectronics.  
The term “integrated photonics” means the fabrication and integration of several photonic components on a common planar substrate. These components include beam splitting means, gratings, couplers, polarizers, interferometers, sources, and detectors. Along with,then these can  be used as components for fabricating more complex planar devices which can accomplish a different range of functions with applications in optical communication systems, CATV, instrumentation, and sensors.
A photonic integrated circuit (PIC) or integrated optical circuit is a device that includes multiple (at least two) photonic functions and as such is similar to electronic integrated circuit. The major difference between the two is that a photonic integrated circuit provides functions for information signals impressed on optical wavelengths mostly in the visible spectrum or near infrared 850 nm-1650 nm.
The first examples of photonic integrated circuits were 2 section distributed Bragg reflector (DBR) lasers. It was consist of two independently controlled device sections – a gain section and a DBR mirror section. As a result, all modern monolithic tunable lasers, widely tunable lasers, externally modulated lasers and transmitters, integrated receivers, etc. are examples of photonic integrated circuits. The primary application for photonic integrated circuits is in the area of fiber-optic communication through applications in other fields.
The optical multiplexers in wavelength division multiplexed (WDM) fiber-optic communication systems are an example of a photonic integrated circuit. These devices are capable of multiplexing a large number of wavelengths into a single optical fiber, thereby increasing the transmission capacity of optical networks considerably.
The main goal of integrated photonics is the miniaturization of optical systems. It became possible thanks to the small wavelength of the light, which allow the fabrication of photonic devices with sizes of the order of microns. The multiple functions  integration within a planar optical structure  can be achieved by means of planar lithographic production.
The basic concept in an optical integrated circuit is the same as that which operates in optical fiber: the confinement of light. A medium that possesses a certain refractive index, surrounded by media with lower refractive indices,can act as a light trap, where the rays cannot escape from the structure due to the phenomena of total internal reflection at the interfaces.