A highly digital optical phase-locked loop (OPLL) is designed and implemented to generate phase-coherent lasers in quantum optics. All the controlling circuit in this OPLL are implemented in a single field programmable gate array (FPGA) chip. Pipeline and parallelism technology have been adapted in PID controller. Especially, an equivalent 3.5 GHz high speed clock and twisted ring counter have been integrated in the most crucial part. This OPLL has the narrow beat note line width below 1 Hz, residual mean-square phase error of 0.05 rad2and transition time of 100 μs under 10 MHz frequency step.
A highly digital optical phase-locked loop (OPLL) is designed and implemented to generate phase-coherent lasers in quantum optics. All the controlling circuit in this OPLL are implemented in a single field programmable gate array (FPGA) chip. Pipeline and parallelism technology have been adapted in PID controller. Especially, an equivalent 3.5 GHz high speed clock and twisted ring counter have been integrated in the most crucial part. This OPLL has the narrow beat note line width below 1 Hz, residual mean-square phase error of 0.05 rad2and transition time of 100 μs under 10 MHz frequency step.
Abstract Among the existing techniques for Raman laser preparation, optical phase-locked loops (OPLLs) are widely used in quantum precision measurements due to their high regulation accuracy and low phase noise. Aiming at the problems of limited adjustment range and insufficient stability of the current OPLL, this paper designs an OPLL by optimizing the operating points with a bias voltage. Performance tests show that, the tuning range of the optimized OPLL is 2 GHz to 9 GHz. This wide frequency cover can produce Raman laser for both 87Rb and 85Rb atomic gravimeters. It can also be used to simplify the optical path in experiments to test the equivalence principle. The optimized OPLL has a long-term phase-locking capability. For integration times of 1 s and 1000 s, the relative Allan’s variance is 1.6 × 10−11 and 5.2 × 10−13, respectively.
With the optical phase lock loop (OPLL) we made, we can achieve phase locking at frequency differences ranging from 0.5GHz to 7.5 GHz. This OPLL is fully applicable in atomic physics experiments, mostly in coherent lasers frequency locking. Two kinds of modulation modes were brought to ensure the frequency range and precision: the fast feedback current as the injection current and the slow feedback current to adjust the piezo-electric transducer. This device has been put into an optical lattice platform to lock a laser used for cooling and trapping atoms. The beat signal has a -3dB band width of 1Hz at 6.834GHz, corresponding to the hyperfine splitting of the ground state 87Rb atom.
This paper presents a synthesizable FPGA hardware architecture for real-time laser phase noise suppression in quantum optical and precision timing applications under the Zulfiqar Frequency-Stabilization (ZFS) framework. Utilizing a dual-actuator path combining a fast Acousto-Optic Modulator (AOM) and a high-dynamic-range Piezoelectric Transducer (PZT), the proposed architecture implements a fixed-point DSP multiplication pipeline to achieve deterministic phase correction. By integrating a calibrated fractional scaling factor within a 32-bit Q-format structure, the ZFS core compensates for high-frequency phase fluctuations while bounded by a localized phase noise floor Φdec≈10−22rad2/Hz. Post-synthesis timing simulation demonstrates robust phase-lock loop stability across a 100MHz control clock, providing an efficient hardware foundation for atomic clocks and optical interferometry.
Lasers are imperative in quantum simulation experiments to trap and cool atoms. With the growing complexity of experimental setups, precise control and stability of the position and exotic shape of lasers have become essential for high-fidelity operations. However, disturbances such as temperature fluctuations, mechanical vibrations, deformation of materials, and acoustic noise pose challenges to fulfill these requirements. In this paper, we propose and evaluate the first system for stabilizing the laser's beam position using two high-resolution cameras with high frame-rates, and image processing in a field-programmable gate array (FPGA) with low latency and subsequent in-loop feedback to the laser control. The proposed image processing hardware extracts the Gaussian beam distribution from two 5 MP cameras at 47 fps and 435 ns latency. These are fed to four proportional-integral-derivative (PID) controllers implemented on the FPGA. The PID modules provide feedback through parallel digital-to-analog converter (DAC) channels for steering mirrors to stabilize the beam within 5 µm accuracy. Using two cameras at distinct sample distances on the optical axis allows for controlling the incidence angle of the laser beam onto the image planes. The current system is a building block for future extensions allowing real-time phase-feedback on optical lattices, stabilization of independent optical tweezers in an array, and focus position stabilization of transverse electromagnetic (e.g. TEM01) modes enabling large-scale quantum simulations.
Abstract This paper presents a new method for implementing an All-Digital Phase-Locked Loop (ADPLL) using rapid single flux quantum (RSFQ) circuit technology. The ADPLL consists of a digitally controlled oscillator (DCO), a time-to-digital converter (TDC), a proportional-differential (PD) controller, a DCO controller, and a frequency divider. The DCO is based on a ring oscillator with newly designed tunable delay Josephson transmission line (TDJTL) cells in series. Verilog simulations of the ADPLL demonstrate improved performance with the integration of the TDC and PD controller. In comparison with the configuration without the TDC, the new ADPLL configuration realizes a 54% reduction in the variation of the DCO oscillation period. This reduction in frequency variation makes the ADPLL particularly well-suited for applications requiring highly accurate frequency sources, such as transmon qubit control.
Quantum technologies using laser-cooled atoms, such as cold atom interferometersand atomic clocks, have revealed their potential in ground-based instruments. Un-doubtedly, space-based quantum devices could provide orders of improvement undermicro-gravity environments. However, current instruments, including both terrestrialand space-based, rely on complex laser systems, resulting in a high Size, Weight, andPower (SWaP) and high-cost design. Overcoming this bottleneck could enable quantumtechnologies for low-cost experiments and missions using small satellites. This wouldopen the door to new types of scientific experiments and missions, such as constella-tions of quantum sensors, deep space optical communication networks, and cold atomgyroscopes.This research develops the Software Defined Laser (SDL), a compact laser systemarchitecture that applies Software Defined Radio (SDR) concepts to optical frequencycontrol. By combining reconfigurable Field-Programmable Gate Array (FPGA)-basedelectronics with Radio Frequency (RF) techniques and optical modulators, SDL reducesthe number of seed lasers and optical components while maintaining the performancerequired for quantum applications. We derive quantitative requirements for SDL byanalysing existing ground-based and space-based quantum instruments and develop ahighly configurable system-on-chip firmware to support diverse missions.A Python-based SDL model is developed to evaluate RF technologies, frequency-tuning topologies, and noise performance. Comprehensive noise analysis shows that allinvestigated RF sources contribute less than 100 Hz to laser linewidth, satisfying Ramanand optical clock requirements. A novel frequency-tuning method is proposed, main-taining sub-1 kHz linewidth while reducing tuning dead time from 5.8 ms to 200 µs.To improve robustness beyond conventional PID control, SDL enables a multiple-input multiple-output (MIMO) laser controller synthesised using H2 robust control.Both single-input single-output (SISO) and MIMO controllers are evaluated under re-alistic disturbances. The MIMO controller maintains laser frequency noise below 1 kHzand achieves 0.02 % power stability under 17.5 K temperature variations over 6000 s,outperforming state-of-the-art systems. To enable autonomous adaptation, an FPGA-accelerated H2 synthesis module is developed, reducing optimisation time by 30 % andenabling real-time controller reconfiguration during operation.