Читать книгу VCSEL Industry - Babu Dayal Padullaparthi - Страница 19

Semiconductor lasers can be categorized into several types depending on:

1 Emission wavelength and materials;

2 Resonant cavity configuration;

3 Single mode or multi‐mode;

4 Direction of emitted light;

5 Direct modulation speed;

6 Power output;

7 Footprint of device;

8 Beam form and connectivity to optics such as optical fibers;

9 Price of device;

10 Manufacture volume;

11 1D or 2D array; and so on.

A simple category is outlined in Table 1.1. In this case, we categorized into two types on the basis of cavity configuration, i.e., edge‐ and surface‐emitting cavities. This book is focused on the research, development, and industrial sectors to demonstrate the impact of VCSEL.

A schematic of an edge‐emitting laser (EEL) is shown in Figure 1.2a. In edge‐emitting lasers, the light emits through the edges of the wafer that is in‐plane with the substrate and the optical cavity is horizontal for laser resonance. On the other hand, the structure of VCSEL is illustrated in Figure 1.2b. The resonance of light is vertical to the substrate and taken from the surface. The laser structure is formed on the substrate in just one manufacturing process.

Table 1.1 Categorization of semiconductor lasers.

Source: Table by K. Iga [copyright reserved by author].

Type of cavity	Edge‐emitting laser	Surface‐emitting laser
Single Mode
Transverse	narrow stripe	narrow aperture
Wavelength	DFB, DBR	Fabry‐Pérot
Multi‐Mode
Transverse	broad area	wide aperture
Wavelength	Fabry‐Pérot	Fabry‐Pérot
Array	one‐dimensional	two‐dimensional

Figure 1.2 Schematic of semiconductor lasers (a) Edge‐emitting laser (EEL). (b) Vertical‐cavity surface‐emitting laser (VCSEL).

Source: Figure by B. D. Padullaparthi [copyright reserved by authors].

In both cases, the emission and amplification of light in semiconductor lasers is due to the recombination of electrons and holes that exist in the active region. This is what most of the standard textbooks on optical properties of semiconductors teach. Later, we will show the readers a different explanation.