Two Polarization Comb Dynamics in VCSELs Subject to Optical Injection

Abstract

Optical frequency comb technologies have received intense attention due to their numerous promising applications ranging from optical communications to optical comb spectroscopy. In this study, we experimentally demonstrate a new approach of broadband comb generation based on the polarization mode competition in single-mode VCSELs. More specifically, we analyze nonlinear dynamics and polarization properties in VCSELs when subject of optical injection from a frequency comb. When varying injection parameters (injection strength and detuning frequency) and comb properties (comb spacing), we unveil several bifurcation sequences enabling the excitation of free-running depressed polarization mode. Interestingly, for some injection parameters, the polarization mode competition induces a single or a two polarization comb with controllable properties (repetition rate and power per line). We also show that the performance of the two polarization combs depends crucially on the injection current and on the injected comb spacing. We explain our experimental findings by utilizing the spin-flip VCSEL model (SFM) supplemented with terms for parallel optical injection of frequency comb. We provide a comparison between parallel and orthogonal optical injection in the VCSEL when varying injection parameters and SFM parameters. We show that orthogonal comb dynamics can be observed in a wide range of parameters, as for example dichroism linear dichroism (γa=−0.1 ns−1 to γa=−0.8 ns−1), injection current (μ=2.29 to μ=5.29) and spin-flip relaxation rate (γs=50 ns−1 to γs=2300 ns−1).

Polarization dynamics in VCSELs subject to optical frequency comb injection

“…Figure 2 is measured for injected comb spacing of Ω = 2 GHz. As we have learned from our previous manuscript, [40][41][42][43] injection of a narrow optical frequency comb with parallel or orthogonal polarization can sustain a two polarization comb dynamics in a singlemode VCSEL. For fixed injection parameters, i.e., detuning frequency of ∆ν = −17 GHz and injected power of P inj = 248.8 µW, we analyzed the impact of the polarization of the injected comb on the two polarization comb dynamics.…”

“…Figure 1 (c) is obtained for injection current of 6 mA. Our previous publications 40,41 provide more details on the characteristic of the VCSEL. The frequency detuning ∆ν is measured from the frequency position of the central injected comb line to the frequency of dominant polarization mode (X-PM) of the VCSEL, i.e., ∆ν = ν 0 − ν x , where ν 0 and ν x are the frequencies of the central injected comb line and the X-polarization mode (X-PM) of VCSEL, respectively.…”

“…Our previous publications provide more details on the acquisition systems. 40,41 Figure 1 (b), shows the optical spectrum of the injected comb for injected comb spacing of Ω = 2 GHz. The difference, in dB, between the power of the central frequency line and the others frequency lines is around 12 dB.…”

“…The injected comb is a narrow optical comb with three frequencies line. To realistically model our experimental configuration in, [40][41][42][43] we consider that the difference between the amplitudes of the injected comb lines is 12 dB. Figure 3 shows the polarization-resolved optical spectra of Xpolarization mode (X-PM) and Y-polarization mode (Y-PM), respectively.…”

“…38,39 Some recent works have taken advantage of the polarization properties in VCSEL to control the injection locking and the injected comb properties. 40,41 It is also shown that parallel or orthogonal optical injection in single-mode VCSEL can enable two polarization comb dynamics. The comparison between the polarization comb dynamics induced by parallel and orthogonal optical in VCSEL is lacking.…”