Transistor laser could change communications
The researchers fabricated several hundred transistor lasers and characterized them. From the test results, they developed circuit models of the device's performance. Tests involved using a photodetector to receive the optical signal, from which the researchers measured three-port S-parameters (s11, s12, s21, s22, s31, and s32) with an Agilent Technologies N5230 parametric network analyzer (s13, s23, and s33 represent the parameters of the optical port that were not used in this work). The DC and S-parameter measurements let the researchers obtain values for the device's I-V and L-I characteristics as well as resistance, capacitance, and inductance of the device's junctions (Ref. 1).They also measured eye diagrams at data rates up to 13 Gbps with an Agilent 86100A sampling oscilloscope using a 27 PRBS (pseudorandom bit sequence) data stream. From the models, the researchers have demonstrated the performance of the transistor lasers at data rates up to 40 Gbps.
At first glance, the transistor laser appears to defy Kirchhoff's current law, which states that the charge that enters a node must exit it (charge conservation). In a typical transistor, IEMITTER = IBASE + ICOLLECTOR, but with the transistor laser, the equation needs an additional term for energy conservation, ISTIM, which represents an additional base-charging current for photon continuity and energy conservation.
1. Then, H.W., Milton Feng, and Nick Holonyak, Jr., "Microwave circuit model of the three-port transistor laser," Journal of Applied Physics, May 10, 2010. American Institute of Physics, jap.aip.org.