Читать книгу VCSEL Industry - Babu Dayal Padullaparthi - Страница 46

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)	hours	high	high
Manufacture	Array scaling	dimension	2D	1D
Wafer diameter	inch(mm)	4″ (100 mm) & 6″ (15O mm) ready	4″ (100 mm) to be ready
Assembly and packaging	complexity	simple and easy	complex
Growth and processing	complexity	monolithic/standard CMOS	regrowth/facet coating needed
Cost	amount	low	high

Table 1.4 Attributes of VCSEL in datacom, sensing, and manufacturing.

Source: [Table by B. D. Padullaparthi and K. Iga] [copyright reserved by authors].

Datacom	Sensing	Manufacturing	Others (Performance)
high fiber coupling efficiency	high peak pulse powers	vertical integration	low threshold currents
high bandwidths	high PCE and SE	array scalability and small footprint	circular beam (Low divergence)
high modulation speed	high rise and fall time (integration time)	easy alignment and packaging	narrow linewidth
low power consumption (energy efficient in data centers)	low power consumption (long battery operating times consumer)	monolithic process handling (epi‐growth and wafer fabrication)	operation in single‐mode and multi‐mode
wavelength tunability (WDM)	high beam quality	low cost and high yield	high reliability (auto grade)
low thermal impedance (efficient heat dissipation)	on‐wafer testing	wavelength stability

Table 1.5 Mode dependent VCSEL applications.

Source: [Arranged by K. Iga and B. D. Padullaparthi] [copyright reserved by authors].

	Optical Communications	Optical Sensing	Others
Single mode	mid distance transceiver	optical mouse	printers
		gas sensing	displays
		OCT	atomic clock
		bio sensing
		motion sensing
Multi‐Mode	LAN
	short‐reach transceiver	face recognition	manufacturing
	interconnects	illumination	heating
		LiDAR
		robotics

Using high performance VCSELs with sufficient output power, low‐loss optical fibers, and efficient high‐speed detectors, data can be transmitted at speeds of 25–100 Gb/s over 300 m at temperatures well over 85°C [56]. The details of multi‐mode VCSELs for data communications/data‐center applications are discussed in Chapter 4.