Research Area 6. Electronics: Low noise Energy Efficient Micro-cavity Transistor Laser for 50 Gb/s direct modulation
Abstract
We have accomplished the layout design and process development for a highly efficient vertical-cavity transistor laser (VCTL) with lateral oxidation confinement. The VCTL demonstrates a threshold current of 1.6 mA and optical power greater than 200 ?W, and provides us with a reference design that we shall refine in the next phase in order to demonstrate high-speed operation. We have also fabricated a high speed edge-emitting transistor laser capable of room temperature 20 Gb/s data transmission via collector voltage modulation. The relative intensity noise (RIN) of an edge-emitting transistor laser and a diode laser are determined, showing that a transistor laser has a lower RIN (~28 dB) than a diode laser. By varying the bias conditions, the transistor laser switches from ground state to the excited state, showing higher bandwidth and lower RIN because of higher differential gain and faster recombination. To further lower the power consumption of the VCTLs, we have developed a low operating VCTL through reduction of collector offset voltage VCE with external dielectric (SiO2/TiO2) top distributed Bragg reflector (DBR) mirror. The external top DBR helps reduce the emitter resistance, but it also has a lower cavity Q which leads to a higher threshold current. We also have fabricated a high speed edge-emitting transistor laser which showed error-free data transmission at 13.5Gb/s data rate. Microcavity lasers show high modulation bandwidth and low threshold current for high speed and energy efficient operation. We fabricated an 85 0nm vertical cavity surface-emitting laser (VCSEL) which demonstrated 40Gb/s error-free data transmission with an Energy/Data efficiency of 556 fJ/bit. Also, with smaller cavity dimensions, microcavity VCSELs showed not only low threshold current but also lower RIN as a consequence of reduced mode competition. Furthermore, we fabricated another 850 nm VCSEL with improved material layer design. The active region is reduced to 0.5 ? with 5 InGaAs quantum wells for higher speed operation and stronger light output. The bottom n-DBR mirror includes AlAs layers for better thermal conductivity to improve the thermal-limited bandwidth. In the top p-DBR, there are secondary AlGaAs oxidation layers to help reduce the parasitic capacitance. The 850 nm VCSEL showed a 29.2 GHz bandwidth and passed BER for error-free transmission at 57 Gb/s which is the highest error-free data rate demonstrated without external equalization circuits. Also, the device showed 50 Gb/s error-free at 85 ¡C which is the highest error-free data rate demonstrated.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jun 25, 2021
- Source ID
- W911NF1210394
Entities
People
- Milton Feng
Organizations
- Army Contracting Command
- United States Army
- University of Illinois Urbana–Champaign