Low optical loss electrical isolation for multi-section monolithic GaSb-based photonic circuits

Monolithic photonic integrated circuit (PIC) platforms exploiting III–V materials combine passive and active waveguide structures in multi-section optoelectronic device architectures. Their operation requires high electrical isolation between adjacent functional sections without compromising the optical signal. This fundamental requirement is addressed for GaSb-based waveguides, which are known to exhibit high conductivity of p-type layers, reducing the electrical isolation capability. To this end, a co-designed electrical–optical isolation strategy based on using deeply etched strip waveguides combined with adiabatic ridge-to-strip waveguide tapers in GaSb-based multiple-quantum well heterostructures is proposed. While deep etching alone enables isolation resistances of up to 40 kΩ, it severely degrades optical propagation. By introducing optimized adiabatic tapers, we demonstrate good optical performance as single mode continuous-wave lasing in a two-section device with integrated absorber, while maintaining an isolation resistance of 17.3 kΩ; this corresponds to an approximately 17-fold improvement over previously reported GaSb two-section devices. The approach establishes a critical building block for the development of monolithic GaSb-based PICs operating above 2 μm.