Microlaser à anneau pour la génération de fréquences THz

G. Leo1, S. Mariani1, A. Andronico1, I. Favero1, S. Ducci1, Y. Todorov1, C. Sirtori1, M. Kamp2, J. Claudon3, J. M. Gérard3

1 Paris Diderot University, Sorbonne Paris Cité, Laboratoire MPQ, Paris, France 2 Technische Physik, University of Würzburg, Würzburg, Germany 3 CEA, INAC, SP2M, Grenoble, France

http://www.treasure-project.eu

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Outline

• Motivation

• Design

• Fabrication & characterization of passive samples

• Active device

• Far-field engineering

• Perspectives and conclusion

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State of the art and motivation

Photomixing: Pmax ≈ 100 nW at 1 THz, 1 nW at 2 THz QCLs: Low-temperature operation

Main THz CW sources today

2020 worldwide market predictions:

THz technology increase from today’s annual volume of ≈80 M$ to ≈500 M$.

GOAL:

Provide a CW electrically pumped THz emitter operating at 300K

• µW range • 1-4 THz custom emission • power up-scaling

Driving emerging applications:

Security & screening, biomedical, non-destructive evaluation & test, wireless comm.

(BCC Research)

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THz NL sources on GaAs chip Vodopyanov-Fejer-Marandi Optics-to-THz conversion In metallic waveguides

OPEX 16, 10427 (2008) OPEX 17, 13502 (2009)

Belkin-Capasso Intracavity THz DFG in mid-IR QCL: 300 nW at RT

NATURE PHOTON. 1, 288 (2007) APL 92, 201101 (2008)

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Cherenkov DFG at 300K in mid-IR QCLs Belkin Longer coherence length Low-loss, undoped substrate: 0.5 µW, h = 70µW/W2

APL 100, 251104 (2012)

Razeghi Optimized QCL design, Dual-L DFB for spectral purification, ⇒ single mode from 1.0 to 4.6 THz: 65 µW, h = 45µW/W2

APL 101, 251121 (2012) OPEX 21, 968 (2013)

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An alternative approach: DFG in a QD laser

4 mm diam. pillar

T=14K

Y.-R. Nowicki et al., OPEX 15, 17291 (2007)

A. Andronico et al., OL 33, 2026-2028 (2008)

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• No mode competition • Lower laser threshold • Simpler processing

1) Automatic QPM in (100) GaAs WGMs

 

ceff

2( ) µ cos 2q( )

WGM DFG : c(2) and phase matching

w3 TM w1 w2 TE

QD laser pumps THz DFG field

x

y

z

x

y

z

(100) GaAs: 2 TE and 1 TM fields

1 10 1003.0

3.3

3.6

3.9

Wavelength (mm)

Re

sts

trah

len

ba

nd

Re

fra

ctive

in

dex

2) Anomalous dispersion

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w3

= w1-w

2

m1- m

2- m

3= ±2

Dummy passive micropillars Near–IR characterization

Q = 3 103

FSR = 4.7 nm

S. Mariani et al., IEEE Trans. THz Sci. Technol. PP (99), 1-7 (2013) 8/19

Dummy passive micropillars THz Characterization

Normal incidence

Bolometer

Dry-air flux

FTIR

Globar lamp

45o incidence

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S. Mariani et al., IEEE Trans. THz Sci. Technol. PP (99), 1-7 (2013)

From a micropillar to a microring

Internal radius: a useful degree of freedom for: - DFG tuning - maximizing NL overlap and DFG efficiency

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The active microring Optical-electrical-thermal design

undoped Al0.4Ga0.6As

Graded AlGaAs

Graded AlGaAs

n+-GaAs (1019 cm-3)

p+-GaAs (1019 cm-3)

Pt Au

Pt Au

500 nm 50 nm 10 nm

2690 nm

50 nm

• 40% to 80% Al grading

• 5 1016 cm-3 doping QD layer (5 nm)

• gold-on gold bonding • p-side down

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Rext = 18.91 mm, Rint = 16.27 mm l1 = 1251 nm, l2 = 1267 nm, l3 = 98.8 mm (n3 = 3.04 THz) m1 = 289, m2 = 285, m3 = 2

Expected cw performance Optical-electrical-thermal design

Pump Q = 5 105

• Near IR power: 2 x 10 mW

• THz power ≈ 5 nW

• h ≈ 50 µW/W2

• Bias 9.5 V

• Current 26 mA

• Internal temperature 335 K

• Dissipated power : 0.23 W

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1220 1230 1240 1250 1260 1270 1280 1290

-30

-20

-10

0

No

rm. in

tensity [dB

]

Wavelength [nm]

40-1µm ring

I = 1mA

T = 20°C

QD laser performances @ 1.25µm

Emission spectrum of a 40-1 µm ring

laser at a drive current of 1 mA Threshold current versus active area

for 40 and 80 µm diameter ring lasers

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Mode selection mechanism m1 - m2 = 4

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Final device

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• Only pulsed operation • Three dominating laser modes

No normal emission for the phase-matched quadrupolar THz mode

THz out-coupling

K. Iwaszczuk et al., IEEE Trans. TST 3, 192 (2013)

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Far-field engineering Enabling quadrupole THz mode to radiate normally

Concentric grating

l/2 phase shift

K. Iwaszczuk et al., IEEE Trans. TST 3, 192 (2013)

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Reflectivity test on passive sample

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m = 2 THz resonance for the parallel polarization of the incident field

Multi-spectral emission Phased-array geometries

… Coherent detection schemes

Strong points: Compact size, low current threshold, RT operation, scalable output power. CW emission frequency from 1 to 4 THz.

Key issues: TPA, FCA in the THz.

Under way: Fabrication of the active DFG device

Conclusion and perspectives

Tuning

A. Andronico et al., OPEX 20, 17678 (2012)

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