and multi‐mode VCSELs categorized in Section 1.2.1 show decisive advantages as optical components in communication and sensing as shown in Table 1.5.
1 Single or 1D VCSEL emitters are used as light source in active optical cable (AOC) or optical interconnects for data communication.
2 2D VCSEL arrays found high volume applications as printer and time of flight (ToF) or structured light sources in 3D sensing. Proximity illumination in Face Recognition (FR), Gesture Recognition (GR). Time‐of‐Flight (ToF), Phase shift, FMCW light sources in 3D ranging. They are also used for scanning mode or flash mode LiDARs for automotive, surveillance/night vision ranging, robotics, and drones.
3 Large scale VCSEL arrays in industrial heating etc.
All these items will be discussed in detail in Chapters 4–9 as classified in Table 1.5.
1.4.5 VCSELs in Optical Communication and Sensing
1.4.5.1 The Concept of VCSEL Communication and Sensing
As depicted in Figure 1.16, in most of the applications, VCSELs are used either as light transmitters for communication or light sources for sensors. Data transmission in optical communication systems requires a light transmitter and a receiver together with a transmission media such as optical fibers or air. Along with these core components, driver/receiver ICs with connecting optics are incorporated.
Similarly, in an optical sensing system, a VCSEL light source illuminates 2D/3D objects, and a receiver is used to capture the reflected rays from the objects. Figure 1.17 shows the concepts of optical communication and sensing that are required to understand Chapters 4–9.
1.4.5.2 VCSELs in Optical Communications
The two‐way communication concept described in Figure 1.16(a) is used in optical transceivers made from VCSELs, such as pluggable transceiver, active optical cable (AOC), HDMI‐AOC, active direct attach copper (DAC), and USB‐3 or USB‐C. These are high‐volume applications especially in 100 and 400 Gb/s networks in data centers with ranges from <3 m to >100 m. Normally, multi‐mode fibers are used for short‐reach (<100 m) applications, and single‐mode fibers are employed for long‐reach (2–10 km) applications.
Table 1.3 Differences between VCSEL and edge‐emitting lasers (EEL).
Source: [Table by B. D. Padullaparthi and K. Iga] [copyright reserved by authors].
| Structure/Parameter | Units | VCSEL | Edge‐Emitting Lasers | ||||
|---|---|---|---|---|---|---|---|
| Single Mode | Multi‐Mode | Multi‐Mode Array | DFB/DBR | Fabry‐Pérot | |||
| Electro‐Optical | Operating current | mA | 6 mA | depends on the numbers of emitters | 30 mA | ||
| Threshold current | mA | <1 mA | 25 mA | ||||
| Series resistance | ohm | 50 Ω | 3 Ω | ||||
| PCE/WPE | % | 35–40% | >40% | >50% | >55% | ||
| Slope efficiency | Watt/Amp | 0.4–0.7 W/A | >0.45 W/A | 0.3 W/A | |||
| Output power | mW | 1–10 mW | >1000 mW | <120 mW | |||
| Rise and fall time | nano sec | <1 ns | 5–10 ns | ||||
| Modulation speed | Gbit/s | >40 Gb/s | >200 Gb/s | not reported | >200 Gb/s | >25 Gb/s | |
| 3 dB down S 21 bandwidth | GHz | >20 GHz | >40 GHz | not reported | > ~ 100 GHz | >30 GHz | |
| Spectrum | Linewidth | nm | <0.1 nm | 0.2–0.6 nm | 1–3 nm | <1 nm | 1–2 nm |
| Beam divergence (angle)/quality | degree | symmetric (2–20°)/no astigmatism | elliptical (15/40°)/astigmatism | ||||
| Speckle | looking | high | low | moderate | high | ||
| Single/multi‐mode behavior | looking | pure single | multi‐transverse | quasi‐single/multi‐longitudinal | |||
| Thermal | Wavelength stability (shift) | nm/Kelvin | 0.06 nm/K | 0.3 nm/K | 0.3 | ||
| Reliability (lifetime) |
| ||||||
