Amplitude Modulation Response and Linearity Improvement of Directly Modulated Lasers Using Ultra-Strong Injection-Locked Gain-Lever Distributed Bragg Reflector Lasers

Abstract

Directly modulated fiber-optic links generally suffer higher link loss and larger signal distortion than externally modulated links. These result from the electron-photon conversion loss and laser modulation dynamics. As a method to overcome the drawbacks, we have experimentally demonstrated the RF performance of directly modulated, ultra-strong injection-locked gain-lever distributed Bragg reflector (DBR) lasers. The free-running DBR lasers exhibit an improved amplitude modulation efficiency of 12.4 dB under gain-lever modulation at the expense of linearity. By combining gain-lever modulation with ultra-strong optical injection locking, we can gain the benefits of both improved modulation efficiency from the gain-lever effect, plus improved linearity from injection locking. Using an injection ratio of R=11 dB, a 23.4-dB improvement in amplitude response and an 18-dB improvement in spurious-free dynamic range have been achieved.

Analysis of the effect of optical confinement factor on the distortion performance of gain lever laser diode

“…Improvement in optical modulation depth is also observed in such devices due to gain lever effect [7][8][9][10][11][12][13][14][15]. The inherent nonlinearity of the two section gain lever laser diode also produces harmonic and intermodulation distortion.…”

“…A sublinear relation between optical gain and carrier density is obtained. Hence a small amount of increase in carrier density N g , results in modulation depth improvement in such multi section laser diodes [8][9][10][11][12]. The two sections of laser diode are shorted together as shown in Fig.…”

A novel distortion reduction scheme for multiple quantum well gain lever laser diodes

“…However, the distortion in such devices may significantly affect the link performance. The gain lever effect is an approach by which modulation efficiency can be improved in two-section MQW laser diodes [3][4][5][6][7][8][9]. Two-section laser diodes can exhibit bistability and a self-pulsation phenomenon, as well as the gain lever effect [10,11].…”

“…Westbrook [5] reports the intermodulation free dynamic range of InGaAs/InP gain lever lasers in a 900 MHz analog fiber optic link, where the effect of the short section bias current with a constant section ratio is analyzed. Recently, reduction in harmonic distortion (2HD) and third-order intermodulation distortion (IMD3) in a gain lever DBR laser diode by the optical injection locking method was reported by Sung et al [8]. In this method, a number of devices are used in the optical transmitter, thereby increasing its complexity.…”

Modulation Effects in Multi-Section Semiconductor Lasers (Postprint)

“…As a consequence of the bandwidth enhancement and other beneficial characteristics offered by this approach, it has been the focus of over a hundred studies including Refs. [32][33][34][35][36][37][38][39][40][41][42][43][44][45][46] and is still attracting interest today as higher bandwidths are sought and new gain platforms explored [47].…”