Engineering trade-offs at 2.1µm: SWIR detector-limited performance and hybrid receiver integration beyond NIR

The Short-Wave InfraRed (SWIR) spectral region is emerging as a promising operating band for next-generation active sensing, laser range finding, and countermeasure receivers, offering lower scattering losses, enhanced eye safety, and improved atmospheric transmission. However, the performance of detectors operating in this transitional region between extended-InGaAs and InGaAsSb remains limited by increased dark current, junction capacitance, and lack of high-efficiency avalanche gain. This paper highlights the limitations of available detectors operating in this wavelength range and the performance that can still be achieved when assembled in CMC Electronics’ products.

Hybrid integration with ultra-low noise transimpedance amplifier (TIA) achieves noise-equivalent power (NEP) values as low as 0.8 pW/√Hz at 10 MHz for small-area detectors, and below 6 pW/√Hz for 270 pF devices at 10 MHz, at room temperature. Simulations show a 3–4× NEP advantage of the CMC hybrid over conventional PCB-mounted COTS TIA designs, translating directly into a corresponding 3.75× reduction in the required transmitter peak power for equal detection range.

This transmitter power leverage is the central finding of this work: at 2.1 μm, where pulsed laser sources are significantly less mature and lower in power than their 1.55 μm Er:fiber counterparts, the hybrid receiver architecture compensates for the unavoidable transmitter power penalty even without internal gain of an avalanche photodiode (APD) and with the higher dark currents. Ranging performance modelling under realistic laser assumptions shows that with today’s available Ho:YAG transmitters (around 100 kW class), the CMC hybrid PIN receiver achieves about 35 km range under clear-sky conditions, compared to about 23 km with COTS electronics, while a future Ho:fiber MOPA at equal power would match the 1.55 μm baseline. The results establish that optimized receiver design is a necessary condition for a complete 2.1 μm laser rangefinders (LRFs) system, which also requires maturation of compact 2.1 μm laser source technology.