Side-lobe Level Reduction of an Optical Phased Array Using Amplitude and Phase Modulation of Array Elements Based on Optically Injection-Locked Semiconductor Lasers

Abstract

The side-lobe level (SLL) in optical phased array (OPA) systems should be reduced to ensure their high performance. We investigate theoretically the performance of an OPA based on optically injection-locked (OIL) semiconductor lasers. The phase and amplitude of the OIL laser are modulated by controlling the injection-locking parameters to reduce the SLL as well as to achieve beam steering. We successfully achieved an SLL reduction of >16 dB when compared with the uniform amplitude profile based on the application of the Taylor window function profile to the injection-locked OPA elements. The reduced SLL and high power efficiency achieved in this study can expedite the use of OPA in real field applications, such as free-space communication, imaging, and light detection and ranging (LIDAR).

Theoretical Demonstration of Security Improvement of Optical Phased Array Based on Optically Injection-Locked Lasers

“…The far-field radiation pattern is formed by combining the array outputs radiated from the OPA elements. Electrical beam steering and shaping can be achieved by the PM and AM of the OPA elements [41]. The optical signal of the ML with amplitude A ML , phase φ ML , and frequency f ML is injected into the SLs to achieve injection locking between the ML and each SL.…”

“…The amplitude and phase of an SL can be modulated by controlling the injection-locking parameters when the SL operates within a stable locking range. AM and PM can be achieved by adjusting the bias current of the SL [33,41].…”

“…This is realized by modulating the bias current of the SL array. In real application, the look-up tables for each OIL-OPA element, which determine the relationship between the injection locking parameters and the amount of PM/AM of the injection-locked SL, should be experimentally obtained [33,41]. When the OIL laser array is used as the OPA elements, the beam shaping and steering of the OPA signal are realized by the AM and PM of the optical signal.…”

“…When the OIL laser array is used as the OPA elements, the beam shaping and steering of the OPA signal are realized by the AM and PM of the optical signal. The optical field of the OIL-based OPA Tx of the OWC system can be expressed as [41]  The colored areas depict the stable locking regions. Figure 4a,b show the output amplitude and phase of the OIL lasers as functions of the injection-locking parameters, respectively.…”

Modulation Performance Enhancement of Directly Modulated Injection-Locked Semiconductor Lasers Using an Equivalent Electrical Circuit

“…Although the rate equations based on photon number have been widely used in the optical simulation of lasers including OIL lasers [5], we modify the photon-based equations into electric field-based equation and rearrange the rate equations as ( 5)- (7). Electrical-field-based rate equations can be utilized, such as an optical phased array [23] and optical advanced modulation [24], which should consider optical interference. Moreover, we show that these field-based equations are suitable for the inclusion of optoelectronic device models in a SPICE-based electrical simulation framework [25,26].…”