Investigation On Optical Frequency Comb Generation Based On A Current-modulated 1550 Nm-VCSEL Subject To Optical Injection

Optical Frequency Comb?OFC?,which consists of a series of discrete and equally spaced frequency components,can provides several to dozens of different frequency components in a band at the same time.OFC has many advantages,such as a large number of spectral lines,balanced spacing and large frequency coverage,which has attracted great attention of researchers in many optical research fields,such as spectroscopy,microwave photonics,optical communication,metrology,and optical arbitrary waveform generation.At present,the commonly used methods to acquire OFC mainly include mode-locking,photoelectric modulation and gain switching.The OFC generated by gain switching semiconductor laser has attracted much attention due to its advantages of simple structure,easy control and low harmonic loss due to its repeatable frequency.Vertical-cavity surface-emitting laser?VCSEL?are a new type of semiconductor lasers,which have been used in many fields due to their low production cost,easy integration,low threshold current,high fiber coupling efficiency and low energy consumption.By directly superimposing the orthogonal OFC of two polarization outputs of the optical injection gain switch VCSEL,a wide-band wide OFC can be obtained.However,since the OFC essentially comes from the OFC of two orthogonal polarizations,it obviously has great limitations in related practical applications of polarization sensitivity.This paper presents and numerically studies an OFC scheme based on current modulation 1550nm-VCSEL under optical injection to obtain broadband width and consistent polarization direction.In this scheme,a 1550nm-VCSEL is firstly modulated by the large modulation signal current with the modulation frequency f_m=f₀/n?f₀ is the frequency interval of two orthogonal polarization components in 1550nm-VCSEL,and n is an integer?,so that the main oscillation mode in the 1550nm-VCSEL--Y polarization component outputs OFC,while X polarization component is in the suppressed state.Furthermore,by introducing linearly polarized optical injection,OFC output can be achieved for both polarization components in the laser?the spectral peak ratio is less than 15 dB?.With the aid of a polarizer,the two polarization components are guided to the transmittance direction of the polarizer to achieve spectral splicing,so as to obtain broadband OFC.Based on the spin reversal model,the OFC characteristics are numerically studied.The simulation results show that:under the given parameter conditions,when the bias of a free-running 1550nm-VCSEL?threshold current 2.6mA?is 11.5mA,Y polarization components are dominant and X polarization components are inhibited?the main peak ratio of spectrum is greater than 30 dB?.Under the action of current modulation with large modulation depth,the laser only outputs OFC in Y polarization component.Then,the linearly polarized optical is introduced into the current-modulated laser and the OFC output can be achieved by properly adjusting the direction of linearly polarized optical.Finally,a polarizer is used to guide X and Y polarization components to the transmittance direction of the polarizer to achieve spectral splicing.Finally,an OFC with bandwidth over 80 GHz can be obtained.