Application of Superluminescent Diode in White Light Interferometer

White light interferometry using superluminescent diode is a well-developed and very old technique for optical analysis. Combining it with modern electronics, computers, and software has resulted in extremely powerful measurement methods.

Currently, the most popular light source for interferometry is a laser. The primary explanation for this is that laser light has a long coherence duration, making interference fringes simple to obtain, and interferometer path lengths do not need to be balanced as they do when using a white light source with a short coherence length.

The principle of White Light Interferometer

To be a true white light interferometer, a superluminescent diode interferometer must meet these two states. First, the zero-order interference fringe's position must be independent of wavelength. Next, the distance between interference fringes must not be related to wavelength.

The inherent difference between the two beams is typically associated when light is split into two beams from a source, and the beams are said to be entirely or partially coherent based on the current correlation. The phase functions of light beams from two different sources are typically uncorrelated, and such beams are referred to as incoherent beams. 

Coherent waves create noticeable interference effects as they superpose because their amplitudes will combine, whereas incoherent waves' intensities combine. In a superluminescent diode interferometer, incoherent wave interference varies too quickly in time to be observed in practice.

As two mutually coherent beams pass through a point, there is interference between the wavefronts. At that point, the combined effect of the two vibrations is applied to the medium, and under some circumstances, this superposition results in interference fringes, which are stationary waves.

Advantages of Using Superluminescent Diode White Light Source

Because of their long coherence range, superluminescent diodes, or lasers are commonly used as the light source for interferometer systems because interference fringes are simple to acquire regardless of the direction difference between the two interfering beams. On the other hand, using white light as the source in superluminescent diodes Interferometer optical topographers have a range of advantages.

The first benefit is that noise from spurious interference fringes is avoided because white light has very limited coherence duration, and interference can only be achieved when the path length is a few microns or less. As a result, even though spurious reflections occur in the white light interferometer or superluminescent diode interferometer, they do not create fringes that can contribute to noise.

It is important for an optical topographer to have the sample in focus, or else the measurements would be inaccurate. Due to the lack of structures, determining the focus on a smooth surface is extremely difficult. The presence of interference fringes, which specifically determines concentration, is a major benefit when using a white light source or superluminescent diodes. Only when the path lengths are precisely balanced, you get the best contrast fringes.

Inphenix, headquartered in the United States, is a company that produces high-quality amplifiers and other light sources. In addition to light sources, the company also deals with lasers, driver boards, superluminescent diodes, semiconductor optical amplifiers, and O-band optical amplifiers.