Method for independent and continuous tuning of N lasers phase-locked to the same frequency comb

Abstract

We present a method of phase-locking any number of continuous-wave lasers to an optical frequency comb (OFC) that enables independent frequency positioning and control of each laser while still maintaining lock to the OFC. The scheme employs an acousto-optic modulator (AOM) in a double pass configuration added to each laser before its light is compared by optical heterodyne with the comb. The only requirement is that the tuning bandwidth of the double pass AOM setup be larger than half the OFC repetition rate. We demonstrate this scheme and achieve an arbitrary frequency tuning precision, a tuning rate of 200 MHz/s and a readout precision at the 1 kHz level.Modern experiments often require multiple lasers, differing in frequencies by tens of THz and referenced to atomic transitions or stable cavities. For example, optical clocks based on 88 Sr + utilize stabilized coherent sources at 422 nm, 674 nm, 1033 nm and 1092 nm [1,2]. For applications in spectroscopy and related experiments aiming at production of ultracold ground state molecules [3][4][5][6][7], an additional technical difficulty arises from the need to vary the frequency of these stabilized lasers over hundreds to thousands of MHz to characterize a priori unknown molecular levels.Since the development of the self-referenced optical frequency combs (OFC) [8,9] it has been possible to frequency stabilize lasers to the resulting "frequency ruler" by stabilizing the heterodyne beatnote between the laser and the OFC. Using the broadened spectrum of the OFC provides a wide bandwidth for locking, typically corresponding to the 500 -1100 nm range for titanium sapphire based systems [8]. Moreover, non-linear optical processes (including frequency doubling the OFC output when the CW frequency is higher or frequency mixing the OFC output with the CW source itself when the CW frequency is lower) can be used to reliably lock the CW laser even when its frequency has no overlap with the OFC's output spectrum [10,11]. It is worth noting that coherent sources at wavelengths below 500 nm are often based on frequency doubling [13] or frequency sum generation [14], and therefore their stabilization can be done by referencing the seed lasers before nonlinear mixing.The frequency f L of a laser frequency locked to an OFC by stabilizing the beatnote produced in an optical heterodyne with the OFC can be expressed as f L = f CEO + n × f rep ± f beat , where f CEO is the carrier envelope frequency, f rep is the repetition rate of the comb and ±f beat refers to the heterodyne beatnote between the laser frequency and the comb tooth to which the laser is locked.The most straightforward method to simultaneously achieve absolute frequency stability and wide tunability of a CW laser referenced to an OFC relies on the change of f rep [11,15,16], which is multiplied by the mode number n (on the order of 10 6 ) of the comb element to which the laser is referenced. This allows for scanning ranges of many GHz, typically limited by the mode-hop-free tuning range of a laser. This method, ho...

Fast, precise, and widely tunable frequency control of an optical parametric oscillator referenced to a frequency comb

“…Demonstrated solutions to this problem include sudden jumps to a beat note of opposite sign via a sudden step of a control voltage 14 or the use of an acousto-optic modulator 12,15 to avoid such regions of the spectrum. In both cases, a lock to the OFC was maintained during frequency tuning 12,14,15 possibly limiting the speed. Our frequency tracking approach allows for fast ramping to a target frequency independent of the locking electronics.…”

“…A number of methods have been developed to achieve both absolute frequency stability and large tunability over many comb modes of a continuouswave (cw) laser or OPO referenced to an OFC. For tuning, the comb 9,10 , the cw laser [11][12][13][14][15] , or both 16 can be scanned. Tuning over 10 GHz without changing the frequency lock has been demonstrated by adding an external electro-optic modulator 17 .…”

Optical frequency locked loop for long-term stabilization of broad-line DFB laser frequency difference

“…Applications range from quantum optics, cold atomic physics and off-resonant light-atom interfaces [1][2][3][4][5], through frequency comb stabilization [6][7][8][9] to precision spectroscopy and sensing [10,11].…”

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In multiple applications, phase coherence of the two laser fields locked at a frequency offset is not required [2][3][4][5][6][7][8][9][10][11] and a mere frequency lock is a sufficient solution. Nevertheless, one of the most commonly used solutions is the optical phase locked loop (OPLL) [12][13][14][15].

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Optical frequency synthesizer for precision spectroscopy of Rydberg states of Rb atoms

“…[1][2][3][4][5][6][7] Such optical frequency synthesizers have been used for optical clocks. 8) Recently, Rydberg atoms, highly excited states of atoms with a large principal quantum number, have become attractive because quantum entanglement between nearby atoms is relatively simple to realize by using the long-range interaction between Rydberg atoms.…”