Drever Hall Technique Research Articles

High-Resolution Two-Degree-of-Freedom Displacement Measurement Based on Fiber Fabry–Perot Interferometer and Pound–Drever–Hall Technique

High-Resolution Two-Degree-of-Freedom Displacement Measurement Based on Fiber Fabry–Perot Interferometer and Pound–Drever–Hall Technique

Stability of silicon resonator temperature sensors with the Pound-Drever-Hall technique.

In this paper, we research the temperature stability of silicon-based ring resonator thermometers utilizing the Pound-Drever-Hall (PDH) technique. A slight temperature fluctuation of 12.2 mK in 200 s was experimentally detected by immersing the sensor in the triple point of water (TPW) system with ultrahigh precision. Additionally, factors that affect temperature stability, including fundamental thermal noise, laser frequency drift, and power fluctuation were analyzed and calculated theoretically. This shows high consistency with experimental results. Moreover, it is proved that the laser drift can be suppressed from 11.3 pm to 0.013 pm with the developed experimental system based on the PDH technique. The silicon-based ring resonator as a potential platform for precise temperature monitoring is proved based on this work.

A new method for spatial mode shifting of stabilized optical cavities for the generation of dual-color X-rays

We propose an innovative method to shift the transversal position of the focal point of an optical cavity keeping it actively frequency stabilized. Our cavity is a 4 mirrors bow-tie cavity and the spatial shift of the resonant mode is obtained by properly rotating the two curved mirrors by piezo actuators. This method allows us to move the transversal position of the cavity focal point of 135µm in a time of 50ms, keeping the resonance condition of the cavity by means of the Pound–Drever–Hall technique. We propose to use this technique for the generation of 2-color X-rays via Inverse Compton Scattering (ICS). This technique exploits the large average power stored in the high finesse cavity by shifting the laser beam with respect to the electron beam trajectory, hence controlling the spatial superposition of the electron and photon beams in the interaction region. Arranging two cavities assembled one on top of the other, with different collision angle with the electron beam, allows the generation of X-ray bursts of different energies just by swiftly moving the two cavities, switching the two focal points onto the electron beam trajectory, thus activating in sequence two different ICS spectral lines.

Broadening the dynamic range of the Pound–Drever–Hall frequency stabilization technique

The Pound–Drever–Hall technique is widely used for laser frequency or optical cavity length stabilization. We propose a method to broaden its dynamic range. The conventional error signal divided by the transmission power serves as the new error signal, which increases the dynamic range in the linear regime. The use of an extended Kalman filter improves the resilience to noise when the transmitted power is low. This expands the dynamic range into the nonlinear regime and achieves a deterministic auto-lock even in the presence of a large disturbance. Such a nonlinear extension is, however, limited to an auto-lock for a previously locked state because the extended Kalman filter requires accurate prior knowledge of the initial state. For demonstration purposes, we simulate the implementation of this method for locking a ten-meter scale cavity with a single-stage suspension.

Linear cavity tapered fiber sensor using amplified phase-shift cavity ring-down spectroscopy

Phase-shift cavity ring-down spectroscopy (PS-CRDS) enables the measurement of minute fluctuations in optical loss encountered by an intensity modulated laser beam via lock-in demodulation of the accumulated signal phase as the laser beam propagates through the cavity. A linear fiber cavity containing two highly reflective fiber Bragg gratings (FBGs) and a tapered fiber is a favorable cavity geometry for sensor applications due to its compact nature and wide availability of its components at telecom wavelengths. However, due to the optical absorption of water, usage of telecom wavelengths for sensing of aqueous solutions degrades the sensitivity. This problem can be worked around via an optical amplifier placed inside the fiber cavity, compensating for intrinsic cavity losses. In this work, we demonstrate amplified PS-CRDS using such a linear cavity tapered fiber sensor utilizing an optical amplifier that enables the use of thinner tapered fibers, thus achieving higher sensitivities. We also employ continuous laser wavelength sweeps and analyze peak-to-peak PSs of individual cavity modes instead of using laser-cavity mode locking with the Pound–Drever–Hall technique. This enables further simplification of the experimental arrangement without compromising sensor performance. To test the performance of the reported sensor, solutions of varying sucrose concentrations in deionized water were measured systematically by tracking the average peak-to-peak PS ⟨ ϕ pp ⟩ of the cavity modes. Tapered fibers with waist diameters ( D t a p e r ) around 2.2 µm were used during the experiment and limit of detection (LOD) values were measured down to 2.7 µM, corresponding to 1.01 × 10 − 7 R I U . The reported LOD values can be further improved by mechanical stabilization and thermal control of the device by the use of FBGs with higher reflectivity, by applying automatic optical gain control, and by spectral filtering to remove errors caused by amplified spontaneous emission. The presented concentration sensing device can be suitable for developing compact and highly sensitive, label-free optofluidic sensors.

Highly Sensitive Complicated Spectrum Analysis in Micro-Bubble Resonators Using the Orthogonal Demodulation Pound–Drever–Hall Technique

Whispering gallery mode micro-bubble optical cavities are asymmetrical ellipsoids in experimental settings, which makes their modes nondegenerate. A complicated dense spectrum is thus generated. Overlapping and coupled resonances exist in this dense spectrum. In this study, we determined that the orthogonal demodulation Pound-Drever-Hall technique can be used to analyze complicated resonances. Using this method, overlapping weak and strong coupling resonances can be analyzed. Compared to spectrum simplification and the ab initio theory of Fano resonances, this method is repeatable, simple, sensitive, and accurate. The method can increase the measurement range of differential resonance sensing, thus allowing the differential sensing of overlapped resonances.

Single-frequency Q-switched Er:YAG laser with high frequency and energy stability via the Pound-Drever-Hall locking method.

We present an injection-seeding Q-switched 1645 nm Er:YAG ceramic laser with high frequency stability and energy stability by combining the injection-seeding technique and Pound-Drever-Hall technique. 10.31 mJ single-frequency pulses with optimal frequency stability (525 kHz) and relative energy stability (0.52%) at a high pulse repetition rate of 1 kHz are obtained. To the best of our knowledge, this is the highest frequency stability and energy stability so far in a high pulse repetition frequency, large pulse energy, single-frequency Q-switched Er-doped solid laser. This single frequency laser with high stability provides an excellent light source for a coherent lidar system.

Steady-state frequency-tracking distortion in the digital Pound-Drever-Hall technique.

We present here a general method for evaluating the steady-state frequency-tracking distortion in the digital Pound-Drever-Hall technique with modulation harmonic distortion. The theoretical tracking distortion model is established based on the multi-beam interference theory. The effects of the additional harmonic phase shift and the relative distortion ratio changes in the model are simulated by the Runge-Kutta method. Moreover, we demonstrate the steady-state frequency-tracking distortion caused by the modulation harmonic distortion in a resonant frequency tracking system with a 35 mm Si3N4 waveguide ring resonator. According to the measured and simulated results, we obtain the optimal modulation frequency and depth with minimal frequency-tracking distortion, which are 11.49 MHz and 3.96, respectively.

Stabilization of Transverse Modes for a High Finesse Near-Unstable Cavity

We develop a method to lock a high-finesse near-unstable Fabry–Perot (FP) cavity (F = 7330) to a frequency stable dye laser operating at 605.78 nm using the Pound–Drever–Hall technique. The experimental results show the feasibility of locking this cavity to different transverse modes. This method links the external FP cavity to the dye laser cavity, and a 379 kHz final linewidth of the FP cavity is achieved. Such a near-unstable cavity is potentially useful for cavity-enhanced spontaneous parametric down-conversion to generate narrow-band single photon or photon pairs in different transverse modes.

An ultrastable laser system at 689 nm for cooling and trapping of strontium

We present a 689-nm cavity-based laser system for cooling and trapping strontium atoms. The laser is stabilized to a high-finesse cavity by the Pound–Drever–Hall technique, exhibiting a frequency stability in the $$10^{-14}$$ range for averaging times up to 100 s. A cavity drift of 8 kHz per day is mapped out and compensated. At short times, the laser exhibits a linewidth of a few kilohertz. With this laser system, we realize a magneto-optical trap of strontium operated on the narrow inter-combination transition yielding sub-microkelvin temperatures, and demonstrate absorption spectroscopy on the strontium inter-combination line.

Accurate optical vector network analyzer based on optical double-sideband suppressed carrier modulation

A high-accuracy optical vector network analysis (OVNA) based on optical suppressed carrier double-sideband (DSB) modulation and the Pound Drever Hall (PDH) technique is proposed and demonstrated. The accurate and stable frequency responses can be achieved by transmitting the optical carrier suppressed DSB modulation signals through the DUT, and then detecting the reflected signals. Compared with the traditional DSB-based OVNA, the measurement accuracy is improved by eliminating the errors caused by the even-order sidebands. Furthermore, the stability of the OVNA system can be kept by using the PDH feedback loop. An experiment is accomplished. The frequency responses of the FP interferometer are achieved with little measurement error induced by high-order sidebands, and no repeated frequency response appears even when the test time reaches up to 30 min. This novel method is simple and accurate, and would be used for charactering the symmetric ultra-high Q optical devices.

P<inline-formula> <tex-math notation="LaTeX">$\varepsilon$ </tex-math> </inline-formula>-Resolution Fiber Grating Sensor With Adjustable Measurement Range and Ultralow Probe Power

A novel active fiber grating sensor system based on injection-locking and Pound–Drever–Hall techniques is presented. In demonstrational experiments, $\text{p}\boldsymbol {\varepsilon }$ -level strain resolution is achieved with a very low probe power down to −70 dBm, which is at least 50 dB lower compared with the classical Pound–Drever–Hall technique. Besides, the measurement range of the sensor can be adjusted over a large scale up to 17 dB by changing the injection ratio. With the ultrahigh resolution, ultralow probe power, and adjustable measurement range, the proposed sensor has great potential in high-resolution and large-scale sensor networks.

Long-term measurement of high Q optical resonators based on optical vector network analysis with Pound Drever Hall technique.

An optical vector network analysis (OVNA) based on double sidebands (DSB) modulation and the Pound Drever Hall (PDH) technique is proposed and demonstrated. The frequency responses measurement of the high Q optical device with high stability are achieved by transmitting the DSB modulation signals through the device. The high stability can be realized by using the PDH feedback loop. Compared with the conventional DSB-based OVNA, the proposed scheme with only one step measurement avoids the complex post-processing. Moreover, the long-term measurement with high stability can also be realized. A proof-of-concept experiment is carried out, which achieves the magnitude and phase responses of the Fabry-Perot interferometer, and there is no frequency response shift even though the test time is up to 90 minutes. The proposed method is simple and stable, which can be potentially applied in characterization and fabrication of high Q optical devices.

Frequency locking of multiple lasers to an optical cavity

We demonstrate the locking of multiple lasers to an ultralow expansion cavity using a single fiber electro-optical modulator. We use this modulator to lock the frequency of one of the sidebands to the cavity resonance using an extension of the Pound–Drever–Hall technique. The frequency of the carrier can be tuned by changing the sidebands’ separation. We distinguish the signal coming from different lasers by their modulation frequency in the demodulation. The scheme is scalable to a large number of lasers without requiring extra optical components.

Short fiber resonant optic gyroscope using the high-frequency Pound-Drever-Hall technique.

Optical gyros are attractive angular rotation sensors based on the Sagnac effect. The phase modulation technique is adopted to detect the weak resonant frequency shift induced by the Sagnac effect, which determines the detection sensitivity of the gyros. The Pound-Drever-Hall (PDH) modulation is a mature laser frequency stabilization technique that is widely recognized. A resonant optic gyro equipped with a short and high-finesse fiber ring resonator employing the high-frequency PDH modulation technique is proposed and demonstrated. The modulation index and frequency are optimized to maximize the slope of the demodulation curve. Compared with the low-frequency modulation, the high-frequency PDH modulation increases the slope of the demodulation curve by a factor of 1.23 and achieves an extra 15.8dB of laser frequency noise suppression. The bias stability of the gyro output is improved from 9.6°/h to 8°/h, and the equivalent lock-in frequency accuracy increases 12dB.

Frequency stabilization of multiple lasers on a single medium-finesse cavity

We present a simple, compact, and robust frequency stabilization system of three lasers operating at 649, 759, and 770 nm, respectively. These lasers are applied in experiments on ytterbium optical lattice clocks, for which each laser needs to have a linewidth of a few hundred or tens of kilohertz while maintaining a favorable long-term stability. Here, a single medium-finesse cavity is adopted as the frequency reference and the standard Pound–Drever–Hall technique is used to stabilize the laser frequencies. Based on the independent phase modulation, multiple-laser locking is demonstrated without mutual intervention. The locked lasers are measured to have a linewidth of 100 kHz and the residual frequency drift is about 78.5 Hz s−1. This kind of setup provides a construction that is much simpler than that in previous work.

Coherent Pound–Drever–Hall Technique for High Resolution Fiber-Optic Sensors at Low Probe Power

The Pound–Drever–Hall (PDH) technique has been widely adopted in high-resolution fiber-optic sensors, but its performance degenerates as the probe power drops. In this work, we develop a coherent PDH technique for detection of very weak probe light, in which the probe beam is coherent detected with a strong local oscillator. Assisted with an analog frequency doubler and a band-pass filter, the configuration of proposed coherent PDH technique is highly compatible with classical PDH technique. The influence of fiber dispersion is also assessed. In the demonstrational experiments, the signal-to-noise ratio of the extracted PDH signal is dramatically improved compared with classical PDH technique, especially under weak probe power. Using a π-phase shifted fiber Bragg grating as the sensing element, a ne-order strain resolution is achieved at a low probe power down to –43 dBm, which is about 15-dB lower compared with classical PDH technique. The proposed technique has great potentials in high-resolution large-scale fiber sensor networks.

Ultrahigh Resolution Fiber Bragg Grating Sensors for Quasi-Static Crustal Deformation Measurement

Recently developed ultrahigh resolution optical fiber grating sensors provide powerful tools for crustal deformation monitoring thanks to their unique advantages such as high resolution, low cost, easy deployment, and capability of remote and multiplexed sensing. This paper reviews the development of several types of fiber-optic sensors with ultrahigh resolution in quasi-static domain, including a fiber Bragg grating sensor interrogated with a narrow-linewidth wavelength-sweeping laser, a fiber grating based Fabry–Perot interferometer sensor by using Pound–Drever–Hall technique, sensors interrogated with sideband interrogation method, and the realization of time division multiplexed ultrahigh resolution fiber sensors. The implementation of fiber grating sensors for in situ measurement of crustal deformation are also introduced.

Laser frequency stabilization using folded cavity and mirror reflectivity tuning

A new method of laser frequency stabilization using polarization property of an optical cavity is proposed. In a standard Fabry–Perot cavity, the coating layers thickness of cavity mirrors is calculated to obtain the same phase shift for s- and p-wave but a slight detuning from the nominal thickness can produce s- and p-wave phase detuning. As a result, each wave accumulates a different round-trip phase shift and resonates at a different frequency. Using this polarization property, an error signal is generated by a simple setup consisting of a quarter wave-plate rotated at 45°, a polarizing beam splitter and two photodiodes. This method exhibits similar error signal as the Pound–Drever–Hall technique but without need for any frequency modulation. Lock theory and experimental results are presented in this paper.

A Hertz-Linewidth Ultrastable Diode Laser System for Clock Transition Detection of Strontium Atoms

The frequencies of two 698 nm external cavity diode lasers (ECDLs) are locked separately to two independently located ultrahigh finesse optical resonant cavities with the Pound—Drever—Hall technique. The linewidth of each ECDL is measured to be ∼4.6 Hz by their beating and the fractional frequency stability below 5 × 10−15 between 1 s to 10 s averaging time. Another 698 nm laser diode is injection locked to one of the cavity-stabilized ECDLs with a fixed frequency offset for power amplification while maintaining its linewidth and frequency characteristics. The frequency drift is ∼1 Hz/s measured by a femtosecond optical frequency comb based on erbium fiber. The output of the injection slave laser is delivered to the magneto-optical trap of a Sr optical clock through a 10-m-long single mode polarization maintaining fiber with an active fiber noise cancelation technique to detect the clock transition of Sr atoms.