Extending the Offset Frequency Range of the D2-135 Offset Phase Lock Servo by “Indirect” Locking

The Vescent Photonics D2-135 Offset Phase Lock Servo is normally used to phase lock a pair of lasers with a user-adjustable frequency offset between 250 MHz and ≥9.5 GHz.  It features a full PID loop filter transfer function with adjustable poles and gain with bandwidth from DC to10 MHz.  Because it employs a phase-frequency detector a true phase lock with the capture range of a frequency lock is possible.  It features a feed forward input that allows for frequency jumps of the slave laser in as little as 35 µs.  It has an on-board VCO to provide the offset reference frequency or will accept an external frequency reference.  The lock range is normally sufficient for many applications including cooling of atomic Cesium which requires an offset on the order of 9.2 GHz.[1]  But some work requires the two lasers to be locked with larger offsets than this.  In this application note we demonstrate a method for achieving offsets of at least 43 GHz with indications that with the proper equipment the offset could be extended to 100 GHz or more.

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[1] http://steck.us/alkalidata/cesiumnumbers.1.6.pdf