Figure 6
From: Ultra-stable clock laser system development towards space applications
(a)Drawing of the external cavity diode laser (ECDL) with an interference filter (FI) for wavelength selection. (DL–laser diode, LC–collimating lens, L1–focusing lens, OC–output coupler, PZT–piezo-electric transducer, L2–re-collimating lens). (b) Overview of the distribution module. Light from the ECDL is coupled into a fibre for spatial mode filtering and split at the output for three different beams. One beam after double-passing an acousto optical modulator (AOM1) is sent through a fibre-coupled electro optical modulator (EOM) to provide frequency modulation sidebands for the Pound-Drever-Hall (PDH) locking. The second beam passes through AOM2 and is coupled into a fibre for reference with an optical frequency comb (OFC). The third beam passes through AOM3 and is coupled into a fibre that will transfer light into the atomic package. After both fibres there are half-reflecting mirrors that couple part of the light back into the fibres. Photo diodes (PD2 and PD3) are used to detect the beat note of the reflected light with the original beam before the AOM’s. The beat note signal is sent to frequency length stabilisation (FLS) servo that compensates for phase fluctuations in the fibre link with an AOM.
