# Two Polarization Comb Dynamics in VCSELs Subject to Optical Injection  
[PERSON]  
1 Laboratoire Materiaux Optiques Photonique et Systemes (LMOPS), Chaire Photonique, CentraleSupelec, 2 Rue [PERSON], 57220 Metz, France; [EMAIL_ADDRESS] (D.W.); [EMAIL_ADDRESS] (M.S.) [PERSON]  
1 Laboratoire Materiaux Optiques Photonique et Systemes (LMOPS), Chaire Photonique, CentraleSupelec, 2 Rue [PERSON], 57220 Metz, France; [EMAIL_ADDRESS] (D.W.); [EMAIL_ADDRESS] (M.S.) [PERSON]  
3 Brussels Photonics Group (B-PHOT), Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium; [EMAIL_ADDRESS]  
[PERSON]  
1 Laboratoire Materiaux Optiques Photonique et Systemes (LMOPS), Chaire Photonique, CentraleSupelec, 2 Rue [PERSON], 57220 Metz, France; [EMAIL_ADDRESS] (D.W.); [EMAIL_ADDRESS] (M.S.) the VCSELs between the two polarization modes [5; 6; 7]. Polarization switching has been first observed in the free-running operation when varying the injection current [8]. More recently, optical injections have been demonstrated as a powerful tool to induce PS in VCSELs [6; 9; 10]. Depending on the injected power and detuning frequency, the PS has been found to bifurcate to more complex dynamics including periodic dynamics, complex dynamics and chaos [6]. Interestingly, a very recent study has shown that VCSEL output can exhibit complex chaotic dynamics even in free-running [11]. These rich nonlinear polarization dynamics in VCSELs have found several applications such as optical frequency comb generation [12]. Optical frequency combs have been in recent years the focus of intense scientific research from the fundamental viewpoint, as well as from the technological perspectives [13; 14; 15]. These works have unveiled several physical systems generating optical frequency combs such as mode-locked lasers [14; 16], electro-optic modulator and optically pumped nonlinear microresonators [17]. The development of semiconductor laser based frequency combs has been widely motivated by their numerous properties such as low energy consumption, low size and possibility of mass production and on-chip integration. The semiconductor lasers employed for optical comb generation by mode locking include multisection lasers, Vertical Extended-Cavity Surface-Emitting Lasers (VECSELs) [16; 18], quantum cascade lasers [19; 20] and quantum dot lasers [21; 22]. Unfortunately, the repetition rate of the combs based on these systems depend intrinsically of their cavity properties including cavity length and temperature inside the cavity. Frequency combs with large comb spacing have been proposed using the above systems but achieving a low and stable comb spacing remains a challenge because of the change in the cavity due to temperature variations. For example, 6-millimeter-long devices correspond to a comb spacing of \(\approx\)7.5 GHz [23] and require an active stabilization by acting on the cavity temperature for practical implementations such as dual comb spectroscopy. The comb generation system based on the electro-optic modulators has been adopted to overcome the limitations of the mode-locked lasers-based frequency combs. Optical comb generation using electro-optic modulators is relatively simple because the comb is obtained by directly modulating the output of a single-frequency CW laser. The physical phenomena underlying these comb generation systems are linked to the electro-optic effect. Electro-optic modulator based-optical combs have shown several limitations including fluctuation in the amplitude of the comb lines and low bandwidth. Insertions of the electro-optic modulator inside an optical resonator and cascade electro-optic modulator have been adopted as alternatives to improve comb bandwidth and flatness. Recent works have controlled the comb properties by injecting a narrow comb into semiconductor lasers [24; 25; 26; 27].