1. Optoelectronics Group Electronics Department University of Pavia Operating Regimes And Modelling Of Single Mode Monolithic Semiconductor Ring Lasers G. Giuliani, R. Miglierina, S. Donati, University of Pavia, Italy M. Sorel, P. J. R. Laybourn, University of Glasgow, UK A. Sciré, IMEDEA, Palma de Mallorca, Spain

2. Semiconductor Ring Laser (SRL) MOTIVATION Easy integration devices (no mirrors or Bragg gratings are required)  Possible applications: Gyroscopy, Filters, Wavelength Converters, MUX/DEMUX  Application in OEICs (Opto-Electronic Integrated Circuits): Optical Gating, Optical Memories 

3. SRL Structure R L PD1PD2 PD3 MODE 2 MODE 1 MATERIAL:AlGaAs/GaAs InP/InGaAsP RING RADIUS:1mm PD1,2 LENGTH:1mm PD3 LENGTH:50-200μm FABRICATION LAS = 860nm Single Longitudinal Mode

4. Dynamics: Experimental Results P-I CHARACTERISATION BIDIRECTIONAL CW BIDIRECTIONAL HO B: BIDIRECTIONAL C: UNIDIRECTIONAL UNIDIRECTIONAL Photocurrent PD1 Photocurrent PD2 Frequency: 80-100MHz

5. Dynamics: Theoretical Model SLOWLY VARYING AMPLITUDE MEAN FIELD NORMALIZED RATE EQUATIONS S, C = SELF/CROSS SATURATION COEFFICIENTS EXPLICIT COUPLING BETWEEN THE TWO MODES (H. A. Haus, IEEE JQE, 1985) K D = DISSIPATIVE COUPLING K C = CONSERVATIVE COUPLING IMPORTANT TO UNDERSTAND SRL DYNAMICS

6. Dynamics: Simulations Results K D AND K C COEFFICIENTS CAN BE ADJUSTED TO FIT THE MODE OSCILLATION FREQUENCY OBSERVED IN THE EXPERIMENTS Time [s] Power of the two modes [a. u.]

7. Experiment-Model Comparison  S =1ns  P =20ps S=0.0335 C=0.037 K D =0.00035 K C =0.0079  =3.5

8. SRL Regimes Interpretation NEW RESULT IN SEMICONDUCTOR LASERS K C = LOCALISED REFLECTION IN THE CAVITY K D = LOCALISED LOSS IN THE CAVITY IT FAVOURS HARMONIC OSCILLATIONS IT FAVOURS UNIDIRECTIONALITY

9. Previous Results DYE LASERF. C. Cheng, Phys. Rev. A, 1992 GAS LASERR. J. C. Spreew et al., Phys. Rev. A, 1990 HARMONIC OSCILLATION INSTABILITY: He-Ne LASER: R. J. C. Spreew et al., Phys. Rev. A, 1990

10. Coherence Length Measurement Linewidth Measurement: Experimental Setup Low power coupled in SM fiber (~ 50-100nW) Contrast Measurement Technique (non-conventional)

11. Linewidth Measurement: Results LINEWIDTH ESTIMATION Linewidth ~ doubling in Bi-HO regime Bi-CW 110 MHz UNI 38 MHz Mode power halving Schawlow-Townes limit Bi-CW UNI

12. Conclusions Experimental characterisation of semiconductor ring lasers (AlGaAs - InGaAsP) SRL theoretical model realisation and computer simulations Experiment-Model Fitting SUCCESSFUL Linewidth first-time measurement in UNI and Bi-CW regimes (40-100MHz)

13. Optical Spectrum Measures Scale: 21.6 GHz/div MODE SPACING MEASUREMENT 13.6 GHz 

14. SRL Structure RIDGE STRUCTURE SINGLE TRANSVERSAL MODE

15. SRL Structure

16. Linewidth Measurement: Mode Cross-Correlation Cross-Correlation Measurement

17. Linewidth Measurement: Mode Cross-Correlation Interferometric Signal (Oscilloscope Trace) Cross-Correlation Vs. Autocorrelation