The Pound-Drever-Hall (PDH) technique is a powerful method for laser frequency stabilization, and a PDH loop can also act as a single-channel sensor with high resolution and fast response speed. In ...this work, we expand the PDH technique into a time-domain distributed form, accomplishing a fast Brillouin optical time domain analysis (BOTDA) scheme which measures the distribution of Brillouin frequency shifts along optical fiber without frequency scanning. Approaches of phase modulated probe light, synchronous demodulation for PDH error, arbitrarily accessing in single interrogation, and distributed form feedback control are employed in the system. The scheme achieves fast measurement speed and large dynamic range at the same time, as well as good response linearity and high tolerance to optical power fluctuation. In the demonstration experiment, sensing resolution of 0.4 MHz and measurement range of 300 MHz are realized, under the condition of 25 km single mode communication fiber, 5 m spatial resolution and 0.24 s measurement time (400 times of averaging).
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 nε-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.
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.
A Pound-Drever-Hall laser frequency-locking scheme is developed based on the principle of orthogonal demodulation. In the orthogonal demodulation Pound-Drever-Hall system, three sine signals are ...generated simultaneously using a direct digital synthesizer. A 0° phase sine signal is used to drive an electro-optic modulator to produce the phase sidebands, and 180° and 270° phase sine signals are used as reference signals for phase demodulation. The phase-modulated laser beam is coupled with a reference Fabry–Pérot cavity, and the reflected beam is sent into a photo-detector whose output is mixed with two orthogonal reference signals to obtain in-phase and orthogonal components of the error signal. An analog switch is used to eliminate the offset of the analog demodulator and channel mismatch. Using an analog-to-digital converter, the two orthogonal components are processed using orthogonal phase sensitive detection to obtain the error signal and PI controlled to acquire the correction signal on a host computer. To increase the resolution and SNR of analog-to-digital conversions, oversampling and averaging is utilized. The Pound-Drever-Hall laser frequency discrimination and tracking system is established and investigated experimentally using the orthogonal demodulation method. A frequency discrimination curve is obtained, and it is observed that the resonant frequency of the Fabry–Pérot cavity can automatically track laser frequency variation.
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.
We report on a novel optical microcavity sensing scheme by using the orthogonal demodulation Pound-Drever-Hall (PDH) technique. We found that larger sensitivity in a broad range of cavity quality ...factor (Q) could be obtained. Taking microbubble resonator (MBR) pressure sensing as an example, a lower detection limit than the conventional wavelength shift detection method was achieved. When the MBR cavity Q is about 10
-10
, the technique can decrease the detection limit by one or two orders of magnitude. The pressure-frequency sensitivity is 11.6 GHz/bar at wavelength of 850 nm, and its detection limit can approach 0.0515 mbar. This technique can also be applied to other kinds of microcavity sensors to improve sensing performance.
A laser and acoustooptic frequency shifter jointed Pound-Drever-Hall technique is designed to lock the resonant optical gyroscope. Utilizing direct digital synthesizer (DDS) technology and ...temperature control in the driver, the frequency-shift precision of the acoustooptic frequency shifter higher than 1 Hz is obtained. Experiments show that compared with locking by tuning the laser only, the zero-bias stability of the gyroscope is improved. In this locking scheme, there are few additional devices, the tuning of the laser and the acoustooptic frequency shifter share a common Pound-Drever-Hall locking system, and the demodulation and the locking algorithms are simple.
We have proposed a new scheme for the realization of an excellent active optical frequency standard by utilizing fast and slow twice cavity-locking technique in dual-wavelength active optical clock. ...The performance is expected to achieve the short term stability of 3.8\times 10^{-16} at 1 s and long-term stability of 10 −18 magnitude. Also, the linewidth is expected to reach the quantum limited linewidth with the frequency shift of 7.1\times 10^{-5} \text{Hz}/\mathrm{s} . The system includes four main technologies: dual-wavelength active optical clock, Pound-Drever-Hall technique, phase-stabilized femtosecond laser comb and high speed feedback technique. The cavity length is relocked through slow and fast feedback to two piezoelectric translators of the main-cavity. Therefore, the residual cavity-pulling effect influencing the long-term frequency stability in four-level active optical clock can be suppressed by square times of the bad-cavity coefficient. The frequency stability and the frequency shift of the active optical frequency standard are expected to be two orders and four orders of magnitude better than the ultra-stable reference cavity laser, respectively.
We have achieved a four-wave mixing process in a high-finesse highly nonlinear fiber Fabry–Perot resonator, where the amplified signal and idler were enhanced in transmission by 6
dB and 10
dB ...respectively comparing with those in a single fiber. We used a 6
m long low-loss Fabry–Perot resonator with two high-reflectivity fiber Bragg gratings written directly into a highly nonlinear fiber provided by Sumitomo Electric Inc., where the minimised intracavity loss resulted in the finesse in excess of 100. The resonator length was locked for 30
min by means of a modified Pound–Drever–Hall technique. The maximum intracavity power was increased by 14.3
dB by increasing the stimulated Brillouin scattering threshold with periodic phase modulation by a pseudo-random bit sequence, with length matching that of the cavity.
High frequency stability, narrow-linewidth lasers have been long dreamed of since the invention of the laser. They have recently developed dramatically due to the advent of optical clocks. ...State-of-the-art narrow-linewidth lasers have been constructed by using the Pound-Drever-Hall (PDH) technique to lock the laser frequencies to the resonance of ultra-stable external optical cavities with high finesse. This paper introduces the developments of narrow-linewidth lasers, with a focus on the improvements of length stability of optical reference cavities, including optical cavity designs of vibration insensitivity and low thermal noise. Future trends and alternative methods for narrow-linewidth lasers are also discussed.
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