Discrete Mode Laser Diodes emitting at l~689 and 780nm for Optical Atomic clock applications.

Transcription

1 Discrete Mode Laser Diodes emitting at l~689 and 780nm for Optical Atomic clock applications. Richard Phelan*, M. Gleeson, J. O'Carroll, D. Byrne, L. Maigyte, R. Lennox, K. Carney. J. Somers and B.Kelly Eblana Photonics Ltd, Unit 32, Trinity Technology and Enterprise Campus, Dublin 2, Ireland Workshop on "Laser Diodes for Space Applications 4:00 PM, November 24 th 2015 III-V Lab, Palaiseau Cedex, France. 1

2 Talk Outline Eblana Company background Discrete mode laser diode technology overview Sr Optical clock transitions & laser requirements Characteristics Laser diode at l~689nm Characteristics Laser diode at l~780nm Narrow linewidth laser designs and results Summary 2

3 Company Background Eblana established 2001 with the core technology developed at Tyndall Institute (Cork) and Trinity College Dublin Technology to deliver low cost, easy to manufacture single mode laser diodes for Fibre Optic Communications Market IP protection with over 15 patents Staff 15 and located in Dublin, Ireland. Market prominence established in Taiwan and China Eblana building volume shipments to 200,000 laser units per month Launched Specialty Laser business 2011 (lasers for Sensing applications) Supplying laser diodes at wavelengths from l~690, 760,780, 1877, 2004, 2051, 2300, 2400, 3300nm EU (FP7, Horizon 2020) / ESA / EI programs funding R&D activities

4 Laser Diode Packages Bare Die TOSA TO-56 Coaxial Module TO-9 Butterfly Module 4

5 Discrete Mode Technology Overview 5

6 Discrete Mode Laser Diode Overview Etched features select 1 Fabry Perot mode 1mm 2mm R 6

7 Discrete Mode Laser Diode ~ 689nm ESA contract /14/NL/CBi/fk 7

8 Optical clock Overview Optical Atomic Clock (OAC) block diagram Ultra narrow linewidth Laser An absorbing medium atoms, ions which has to be laser cooled and trapped Detection & Electronics to lock the laser to the transition Frequency comb to transfer to RF Ref Space Optical Clocks (SOC2) ( ) ( 8

9 Sr Levels Relevant to the Clock ESA motivation ~Optical clock in space Emphasize on and low-power consumption Use advanced miniature laser technologies and avoid frequency doubling (SHG) stages. Implement light propagation in optical fibers Key laser parameters: 1. Wavelength 2. Power 3. Linewidth Laser Sub-system Wavelength Linewidth Power Sr Optical Lattice 1 st Stage Cooling Laser 461 nm < 1MHz 150mW 2 nd Stage Cooling 689 nm < 1kHz 20mW Repumper Laser No nm < 100 MHz 10mW Repumper Laser No nm < 100 MHz 10mW Clock Laser 698 nm < 1 Hz 10mW 9

10 Laser emission at l=689nm [Al(x)Ga]In(y)P material 4 x (+1%) 8 nm-thick In60GaP QW 5 x (-0.2%) 5 nm thick [AlGa]InP B 2 x 40 nm-thick [AlGa]InP SCH 2 x [AlGa]InP cladding layers 1um thick 10

11 Grating Design d MQWs 11

12 Laser Manufacture 1. Epitaxy 2. Processing Wafers are grown by MOCVD on 3 GaAs substrates 3. Cleave and Facet coating 4. Test and Packaging 600µm 12

13 FP Laser Characteristics LD 600um Rf=20% Rb=95% Butterfly module contains TEC, thermistor. No micro-isolators!! Threshold current ~40mA SE ~0.25 W/A 40% coupling efficiency to PM fibre 13

14 DM Laser Characteristics l~677nm l~687nm l~689nm l~692nm 14

15 DM Laser Characteristics 15

16 Discrete Mode Laser Diode at 780nm ESA contract 22472/09/CO 16

17 Laser emission at l=780nm AlGaAs material 2 x 8 nm-thick Al12GaAs QW 3 x 6 nm-thick Al40GaAs B 2 x 40 nm-thick Al50GaAs SCH 2 x Al50GaAs cladding 2um thick 17

18 780nm DM Laser Characteristics

19 Design for Narrow linewidth operation Laser diode Intrinsic linewidth is governed by the Modified Schawlow-Townes-Henry expression : h 2 res 2 0 ~ (1 H lpout Design rules for low linewidth devices : Decreasing the α-factor Achieved Strained MQW Increasing the power in the cavity P Reducing internal losses α i Increasing the laser cavity length ) vg 1 1 ln( ) res i 2 2L R 1 R2 resonator linewidth Laser Cavity Engineering 19

20 Delayed Self-Heterodyne Method. PD isolator AO Modulator Laser diode 20

21 Linewidth v Laser Cavity Length 2500um 3000um l=1550nm 2000um 1200um 1500um 700um 21

22 PSD of freq noise S (f) (Hz 2 /Hz,SS) Ultra low linewidth performance Normalized power (W) Measured Power Spectral Density of Frequency Noise PSD of freq noise 10 9 Free-running (Linewidth = 198 khz) 10 8 Locked (Linewidth = 4.9 khz) MHz FWHM Normalized power at spectrum analyser (W), Tobs=1.0 ms Locked Free-running Fourier frequency (Hz) Optical frequency - x (Hz) Using external feedback orders of magnitude linewidth reduction achieved 5 khz!!!

23 Summary Overview of DM laser diode technology DM lasers operating in the 689nm region DM lasers operating in the 780nm region Narrow linewidth lasers ~5kHz demonstrated 23

24 Thank you! E!8598 HICOLA 24