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Fast, externally triggered, digital phase controller for an optical lattice
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Image of FIG. 1.
FIG. 1.

Experimental setup. The frequency/phase controller (FPC), which sets the two direct digital synthesis (DDS) devices, is programmed by the personal computer (PC) and triggered by the same pulses from the pulse generator (PG) as are used to gate the RF signal at the RF switch (RFS). After the RF switch, the RF signal is amplified and frequency doubled (AMP, Fx2) and sent to the acousto-optic modulators (AOM) which control the amplitude, frequency, and relative phase of the two beams which make the standing wave. Pulses of the standing wave are often referred to as “kicks” and so we label the source laser diode as the KICK LD. Light from this source is split by a beam splitter (BS) before being sent to the two AOMs, so the two beams have a well defined phase.

Image of FIG. 2.
FIG. 2.

Detailed schematic diagram of the triggered phase controller circuit. Note that the schematic of the micro-controller is simplified. Pins of the AD9851 without connections were unconnected in the actual circuit.

Image of FIG. 3.
FIG. 3.

Interferometer measurements demonstrating the triggering function and the accuracy of the phase changing mechanism. (a) A raw oscilloscope trace in which the upper line shows the pulses being sent to gate the AOM output. This same pulse sequence is also fed to the trigger input of the phase controller. The lower line shows the voltage across a photodiode which is measuring a fringe formed by interference between the first order light of the two AOMs. In this case, the phase pattern has been set to 32 values from π/32 to 2π. In (b), the phase pattern has been set to five values {0, π/2, 0, π/2, 0}, with the upper and lower curves showing the same measurements as in (a). (Note that the exact starting point in the phase sequence depends on the number of pulses previously applied to the phase controller. In (b) the phase counter was at the end of the sequence when the oscilloscope trace started so it starts with two “0” phases, the first of which is from the end of the sequence. Of course, the phase controller can be reset after each experiment to avoid ambiguity about the initial phase, but this was not required for the test here). Finally, in (c) the averaged photodiode measurements from the experiment in (a) along with error bars showing the standard deviation of photodiode measurements for each pulse are shown. The solid line shows a sinusoidal fit to the data.


Generic image for table
Table I.

Pseudocode for micro-controller phase control application.


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Scitation: Fast, externally triggered, digital phase controller for an optical lattice