A versatile digital GHz phase lock for external cavity diode lasers

Appel, J.; MacRae, Andrew; Lvovsky, A. I.

doi:10.1088/0957-0233/20/5/055302

Cited by 62 publications

(56 citation statements)

References 13 publications

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“…For much longer times we expect that electronic instabilities such as drift of voltage reference will cause the trend to collapse. At small averaging times the −1 trend discontinues due to internal frequency characteristics of the laser, such as white or flicker frequency noise [13,18,28]. This kind of noise dominates in the case of unlocked laser.…”

Section: Performancementioning

confidence: 99%

“…Nevertheless, one of the most commonly used solutions is the optical phase locked loop (OPLL) [12][13][14][15]. In a generic OPLL the master laser (ML) and the slave laser (SL) are combined and the beat note is measured on a fast photodiode (PD), compared with a reference value and then the difference is fed through the loop filter and used to tune SL by employing a fast current modulator.…”

mentioning

confidence: 99%

“…We address these issues by employing a method that yields excellent phase stabilization [13] to the regime of long-term frequency stabilization of broad-line lasers, such as DFB laser diodes applicable in harsh environmental conditions [2,9]. Additionally, a compact design is achieved using an integrated PFD chip.…”

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

2017

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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]. In a generic OPLL the master laser (ML) and the slave laser (SL) are combined and the beat note is measured on a fast photodiode (PD), compared with a reference value and then the difference is fed through the loop filter and used to tune SL by employing a fast current modulator. However, phase difference has to be kept within tight margins for OPLLs to work, rendering them impractical for broad-line lasers.If the OPLL is constructed to ensure only the frequency drift stabilization and not the phase coherence, it constitutes an optical frequency locked loop (OFLL). Such approach has been presented previously in Ref.[16]; however, it was applied to narrow-line external cavity diodes lasers (ECDL) and was based on a frequency voltage converter, allowing only up to 8 MHz offsets between SL and ML. OPLL setups involving phase-frequency detectors (PFD) have been presented in Refs. [17] or [18] but for frequency offsets only up to 7 GHz. Both works were concerned with phase coherence requiring complicated loop filters and either field programmable gate array (FPGA) implementation or two parallel proportional-integral (PI) controllers. Ivanov et. al. [18] apply their setup to DFB lasers albeit of narrower line (1 MHz) than in our case. They also present a detailed analysis of OPLL performance in the presence of frequency dividers.Here we present an OFLL designed for the stabilization of the long-term (>100 μs) frequency drift. Our setup is based on an integrated PFD chip that compares the beat note signal of ML and SL with low-frequency reference. The PD and PFD are specifically matched to provide the simplicity of setup construction and usage. AbstractWe present an experimental realization of the optical frequency locked loop applied to long-term frequency difference stabilization of broad-line DFB lasers along with a new independent method to characterize relative phase fluctuations of two lasers. The presented design is based on a fast photodiode matched with an integrated phase-frequency detector chip. The locking setup is digitally tunable in real time, insensitive to environmental perturbations and compatible with commercially available laser current control modules. We present a simple model and a quick method to optimize the loop for a given hardware relying exclusively on simple measurements in time domain.Step response of the system as well as phase characteristics closely agree with the theoretical model. Finally, frequency stabilization for offsets within 4-15 GHz working range achieving <0.1 Hz long-term stability of the beat note frequency for 500 s averaging time period is demonstrated. For these measurements we employ an I/Q mixer that allows us to precisely and independently measure the full phase tr...

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Section: Performancementioning

confidence: 99%

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

2017

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“…The Raman light is supplied from a standard extended cavity diode laser, beatnote-locked to our MOT repump laser [20]. This leads to a flexible choice of carrier detuning, typically 4.5 GHz above the center of the transition from the jF 4i to the jF 0 2…5i manifold.…”

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confidence: 99%

Dipole force free optical control and cooling of nanofiber trapped atoms

et al. 2017

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The evanescent field surrounding nanoscale optical waveguides offers an efficient interface between light and mesoscopic ensembles of neutral atoms. However, the thermal motion of trapped atoms, combined with the strong radial gradients of the guided light, leads to a time-modulated coupling between atoms and the light mode, thus giving rise to additional noise and motional dephasing of collective states. Here, we present a dipole force free scheme for coupling of the radial motional states, utilizing the strong intensity gradient of the guided mode and demonstrate all-optical coupling of the cesium hyperfine ground states and motional sideband transitions. We utilize this to prolong the trap lifetime of an atomic ensemble by Raman sideband cooling of the radial motion which, to the best of our knowledge, has not been demonstrated in nano-optical structures previously. This Letter points towards full and independent control of internal and external atomic degrees of freedom using guided light modes only. Light guided by nano-optical waveguide and resonator structures propagates partly as an evanescent wave; its tight subwavelength confinement allows for strong interactions between guided light and single atoms [1][2][3][4][5] or atomic ensembles [6][7][8][9][10][11][12][13] trapped within the confined field.The inherent intensity gradients of evanescent modes are a necessity for the realization of dipole traps close to the surface of the structure. However, if the atoms are probed or manipulated also by evanescent modes, the gradients lead to detrimental effects, such as time-dependent coupling for moving atoms, additional quantum partition noise in probing atomic ensembles, and motional dephasing of collective internal quantum states. As strong gradients imply strong dipole forces for any Stark shift induced by guided light [14], a scheme for optical manipulation of the internal degrees of freedom without perturbation of the motional state is desirable.Additionally, any non-zero temperature above the motional quantum ground state potentially decreases the average interaction of atoms with the guided light mode, reducing the single atom optical depth.Previous results for addressing these challenges in the nanofiber platform [15] include microwave cooling of the azimuthal degree of freedom [16] by exploiting the state dependency of the trapping potentials for different Zeeman sub-states [17], as well as polarization gradient cooling [7].In this Letter, we present a Raman coupling scheme that allows us to drive coherent transfers on the hyperfine transition in cesium (Cs), as well as radial motional sideband transitions, while canceling all quadratic ac-Stark shifts and, thus, dipole forces. By driving Raman transitions with a single beam propagating through the waveguide, we implement a cooling protocol that relies on the gradient of the coupling strength, rather than its phase [18].A key ingredient in our experimental implementation is the Stark shift canceling the Raman coupling scheme presented in Fig. 1(a): w...

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“…The master laser (ML) is locked to a stable reference, and the slave laser (SL) uses optical phase locked loops (OPLL) to synchronize its phase to the ML. The different frequency and highly stable laser can be easily obtained by adjusting the local oscillator [5,6] . In this letter, we demonstrate a compact and robust laser frequency stabilizing system based on PoundDrever-Hall (PDH) [7−9] method and OPLL.…”

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Seed laser frequency stabilization for Doppler wind lidar

Bian¹,

Huang²,

Chen³

et al. 2012

中国光学快报

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We demonstrate a tunable wavelength-locked seed laser source with high-frequency stability to realize the precise measurements of global atmospheric wind field. An Nd:YAG laser at 1 064 nm is used as the master laser (ML). Its frequency is locked to a confocal Fabry-Perot interferometer by using the Pound-DreverHall method, which ensures the peak-to-peak value of its frequency drifts less than 180 kHz over 2 h. Another Nd:YAG laser at 1 064 nm, as the slave laser, is offset-locked to the above ML using optical phase locked loop, retaining virtually the same absolute frequency stability as the ML. The tunable ranges of the frequency differences between two lasers are up to 3 GHz, and the tuning step length was an arbitrary integral multiple of 200 kHz. The researched seed laser source is compact and robust, which can well satisfy the requirement of the Doppler wind lidar.OCIS Wind field, as an important parameter of the atmospheric dynamics and climate variability, can be used to obtain the rule and tendency of atmospheric changes. Doppler wind lidar (DWL) is not only able to obtain the wind field distribution information, but can also measure cloud top height, vertical distribution of cloud, aerosol properties, and changes of the wind field. Currently, DWL is the only tool appropriate for realizing the direct measurements of global three-dimensional (3D) wind profile [1,2] . According to the principle of detection, DWL can be divided into two kinds: coherent DWL, which uses the heterodyne method to detect the aerosol backscatter spectrum, and incoherent DWL, which directly detects both aerosol and molecular backscatter spectra. Very low aerosol concentrations are present in the free troposphere over the mid-oceanic regions and large regions of the southern hemisphere. Consequently, incoherent DWL has incomparable advantages relative to coherent DWL. Meanwhile, the wind profiles over large parts of the tropics, as well as the major oceans, are difficult to measure using ground-based DWL. Therefore, space-borne incoherent DWL is required to measure the whole global wind field. In the system of the space-borne incoherent DWL, the detection unit will falsely treat the frequency jitters of the laser source as the Doppler shifts caused by wind. The speed of spacecraft can also bring the Doppler shifts into the DWL, thereby seriously affecting the measuring accuracy of wind speed [3,4] . As a result, the laser source in space-borne incoherent DWL must have high-frequency stability and large tuning range.The most common approach for laser stabilization is to use a single laser locked to a stable external reference, and then directly diffracting it with an acousto-optic modulator (AOM) or an electro-optic modulator (EOM). However, this method is not feasible when the tuning range goes up to several gigahertz or higher. In order to solve the above problem, the approach of using two individual lasers to separate the requirements of frequency stability and large tuning range is introduced. The master laser (ML) is locked to...

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A versatile digital GHz phase lock for external cavity diode lasers

Cited by 62 publications

References 13 publications

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

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

Dipole force free optical control and cooling of nanofiber trapped atoms

Seed laser frequency stabilization for Doppler wind lidar

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