Spin Laser Local Oscillators for Homodyne Detection in Coherent Optical Communications

Abstract

We numerically investigate spin-controlled vertical-cavity surface-emitting lasers (spin-VCSELs) for local oscillators, which are based on an injection locking technique used in coherent optical communications. Under the spin polarization modulation of an injection-locked spin-VCSEL, frequency-shifted and phase-correlated optical sidebands are generated with an orthogonal polarization against the injection light, and one of the sidebands is resonantly enhanced due to the linear birefringence in the spin-VCSEL. We determine that the peak strength and peak frequency in the spin polarization modulation sensitivity of the injection-locked spin-VCSEL depend on detuning frequency and injection ratio conditions. As a proof of concept, 25-Gbaud and 16-ary quadrature amplitude modulation optical data signals and a pilot tone are generated, and the pilot tone is used for the injection locking of a spin-VCSEL. An orthogonally-polarized modulation sideband generated from the injection-locked spin-VCSEL is used as a frequency-shifted local oscillator (LO). We verify that the frequency-shifted LO can be used for the homodyne detection of optical data signals with no degradation. Our findings suggest a novel application of spin-VCSELs for coherent optical communications.

Injection-locked spin-VCSELs for coherent optical communications

“…The modulation sidebands were generated at ±50 GHz, and polarization of the carrier component and the sidebands were orthogonal each other as previously mentioned in Ref. 34. The conversion loss was defined as the highest sideband power compared to the carrier component.…”

“…33 In Ref. 34, generation of an orthogonally polarized modulation sideband using the injection-locked spin-VCSEL was confirmed to be useful as the frequency-shifted local oscillator. Effect of birefringence in the spin-VCSEL was also confirmed to be important to efficiently generate the modulation sideband.…”

“…33 We previously proposed and confirmed that a frequencyshifted local oscillator for the homodyne detection in the coherent optical communication system can be composed of a spin-VCSEL. 34 As shown in Fig. 1, a pilot tone and data signal are generated and transmitted in the system, then the pilot tone is used as a master laser light for injection locking of the spin-VCSEL which corresponds to low noise amplification of the pilot tone.…”

Observation of spin polarization modulation responses of injection-locked vertical-cavity surface-emitting lasers

“…These features made a spin-controlled VCSEL attractive as a light source for high-speed optical communications and computing [24,25,26,27]. To further explore possible applications of spin-controlled VCSELs, we suggested the combination of a spin-controlled VCSEL and an optical injectionlocking technique [28,29,30]. Previous researches about spin-controlled VCSELs were focused on a free-running operation which means that spin-controlled VCSELs were assumed to be used alone.…”

Linear gain anisotropy and mode profile asymmetry in spin-VCSELs: extended spin-flip models

“…1,2 It has been soon understood, that optically or electrically controlled spin injection 3,4 leads to threshold reduction 5,6 and polarization control. 7 Since then, several other applications of spin-VCSELs have been proposed or demonstrated, such as spin-amplification, 8 homodyne detection in optical communications, 9 neuro-inspired computing based on spin-laser 10 or generation of coherent THz radiation. 11 The residual cavity anisotropy of VCSEL is not viewed as beneficial for many of aforementioned applications.…”