Equally important for the LISA noise performance are the photodiode preamplifiers, for which we have developed a circuit with discrete transistors which outperforms the op-amp designs used elsewhere. A quadrant version is under development.
All components for the clock-noise transfer via GHz sidebands have been tested and suitable components have been identified, including RF cables, electro-optical modulators and frequency multipliers/dividers.
An important ancillary function of the laser link is the measurement of absolute spacecraft distances to sub-meter accuracy (ranging) and the transfer of data (roughly 10 kbits/s). In an optical experiment we have implemented a weak phase modulation of the carrier with pseudo-random codes (PRN spread-spectrum). We have shown that the required performance can indeed be achieved both for ranging and data rate. A non-standard feature of this scheme is that one data bit is shorter than one PRN code. Since the usual shift-register codes of length 2n-1 are awkward to subdivide into data bits and moreover have a non-zero average, we developed codes of length 2n by numerical optimization.