l ,m ,n
m* N (Байду номын сангаас) 2 Lz
H ( E El )
l
2 m* N (E) 2Lz Lx
H ( E Elm )
l ,m
1 / 2
N (E)
(E E
lmn
)
2017/7/17
4
Broadband high gain amplification
2017/7/17
10
Loss decreases with optical intensity
Subpicosecond pulses directly from a QD laser
2017/7/17
11
Performance of QDMLLs
2017/7/17
12
Applications & challenges
2017/7/17
6
Mode-locking techniques
2017/7/17
7
2017/7/17
8
Three main forms of mode-locking
Direct modulation of the gain section with a frequency equal to the repetition frequency of the cavity.
Optical communication systems
A
Optical clocks for computer motherboards Biophotonics applications
Deploying a higher number of QD layers in the active region Using colliding-pulse mode-locking
2017/7/17
5
Ultrafast carrier dynamics — QD lasers
• Requiring low current to initiate lasing • Insensitive to temperature changes • Routinely grown on GaAs substrates • Strongly suppressed carrier diffusion • Exploiting GS and ES bands
Application: QD-SOA • Small size • High gain (> 18 dB) • Ultrashort pulses • Broad spectral range • High repetition rates (distortion-free)
[1]Rafailov E U, Loza-Alvarez P, Sibbett W, et al. Amplification of femtosecond pulses over by 18 dB in a quantum-dot semiconductor optical amplifier[J]. Photonics Technology Letters IEEE, 2003, 15(8):1023-1025. [2]Rafailov E U, Cataluna M A, Sibbett W. Mode-locked quantum-dot lasers[J]. Nature Photonics, 2007, 1(1):395-401.
C
High repetition rates
2017/7/17
13
Thank you!
2017/7/17 14
Mode-locked quantum-dot lasers
2017/7/17
1
Outline
Introduction of quantum dots Application of quantum dots Introduction of mode-locking Passive mode-locking lasers Performance of QDMLLs Applications of QDMLLs
2017/7/17
3
Quantum confinement
Step-like density of states
2 2 2 2l 2 2 k x2 k y El * 2m* L2 2 m 2m* z
Spiked decaying density of states
El ,m
2 2 2 2l 2 2 2 m 2 k y * 2 * 2 2m Lz 2m Lx 2 m*
Delta function density of states
El ,m ,n 2 2l 2 2 2 m 2 2 2 n 2 * 2 * 2 2m* L2 2 m L 2 m Ly z x 2 Lx L y Lz
Using a saturable absorber incorporated into the laser, and providing the shortest pulses of all three techniques. Pulse generation is driven by an RF current imposed on the gain or absorber section, whereas further shaping and shortening is assisted by a saturable absorber.
• Broadband high gain amplification • Ultrafast carrier dynamics
2017/7/17
2
Quantum dots
• Zero-dimensional; • Nanoparticles/structures, size: ~2-10nm • Composed of groups II-VI, III-V, and IV-VI materials
2017/7/17
9
Passive mode-locking of lasers diodes
• A saturable absorber is incorporated into the laser cavity • In practical terms, it can be monolithically integrated into a semiconductor laser, by electrically isolating one section of the device