Optical Modulation Enhancement Through CW Injection Locking of a Sinusoidally Modulated Fabry-Perot Laser Diode

Abstract

This paper reports an interesting phenomenon of optical modulation enhancement produced by CW optical sideband injection locking of a directly modulated Fabry-Perot Laser Diode (FPLD) lasing at 1557.1 nm wavelength, the modulation being sinusoidal in nature and effected at 300 kHz and 3 MHz. This investigation is carried out for direct modulation of the FPLD effected in the RF region at 300 kHz and 3 MHz in contradistinction to earlier studies being conducted with the modulation in the microwave frequency band. A nonlinear analysis has been carried out which corroborates experimental observation on modulation enhancement. At low level of optical Intensity Modulation (IM) index, not exceeding 20 %, typical modulation enhancement of 2 % at 300 kHz and 11 % at 3 MHz modulation frequency have been observed. Larger modulation enhancement is expected at higher values of IM indices of the slave FPLD and for medium to high power laser diodes. This circuit can have direct application in Wavelength Division Multiplexed-Passive Optical Network (WDM-PON).

Post-detection modulating signal power reduction due to optical feedback

“…Figure 4 shows detected signal power reduction variation for various values of R 2 . Observing the signal power (20) = 20 log 10 k 2 1 +…”

“…IN fiber-optic communication, IM-DD is, by far, the simplest and cost-effective scheme. In IM-DD communication [1][2][3][4][5][6][7], nonlinear signal distortion [1][2][3][4][5][6] is detrimental on one hand while undesired circuit reflection is an adverse effect on the other hand. Reflection in optical circuits often plays a detrimental role in the process of reception of an IM-DD fiber optic link.…”

Total Harmonic Modulation Distortion of an Injection-Locked Fabry-Perot Laser Diode Directly Modulated by a Multi-harmonic RF Signal

“…The basic scheme of modulation and detection in optical communication is the intensity modulation (IM) and direct detection (DD) in a photodiode. Some workers have studied theoretically the phenomenon of nonlinear distortion reduction [3][4][5] in a laser diode (LD) by high power lightwave injection into the modulated LD. This distortion is generated internally in the LD itself due to its nonlinearity in the light output vs. bias current characteristics.…”