Showing papers by "Jong H. Chow published in 2005"

Demonstration of a passive subpicostrain fiber strain sensor.

Abstract: We demonstrate a fiber Fabry–Perot (FFP) sensor that is capable of detecting subpicostrain signals, from 100 Hz and extending beyond 100 kHz, using the Pound–Drever–Hall (PDH) frequency locking technique. A low-power diode laser at 1550 nm is locked to a free-space reference cavity to suppress its free-running frequency noise, thereby stabilizing the laser. The stabilized laser is then used to interrogate a FFP sensor whose PDH error signal yields the instantaneous fiber strain.

Phase-sensitive interrogation of fiber Bragg grating resonators for sensing applications

Abstract: This paper discusses a phase-sensitive technique for remote interrogation of passive Bragg grating Fabry-Pe/spl acute/rot resonators. It is based on Pound-Drever-Hall (PDH) laser frequency locking, using radio-frequency phase modulation sidebands to derive an error signal from the complex optical response, near resonance, of a Fabry-Pe/spl acute/rot interferometer. We examine how modulation frequency and resonance bandwidth affect this error signal. Experimental results are presented that demonstrate, when the laser is locked, this method detects differential phase shifts in the optical carrier relative to its sidebands, due to minute fiber optical path displacements.

Demonstration of a passive sub-picostrain fiber strain sensor

Abstract: We demonstrate a fiber Fabry-Perot (FFP) sensor capable of detecting sub-picostrain signals, from 100 Hz and extending beyond 100 kHz, using the Pound-Drever-Hall frequency locking technique. A low power diode laser at 1550 nm is locked to a free-space reference cavity to suppress its free-running frequency noise, thereby stabilizing the laser. The stabilized laser is then used to interrogate a FFP where the PDH error signal yields the instantaneous fiber strain.

Photothermal effects in passive fiber Bragg grating resonators.

Abstract: This research was supported by the Australian Research Council under the auspices of the Australian Consortium for Interferometric Gravitational Astronomy, with partial assistance from the Centre for Ultrahigh Bandwidth Devices for Optical Systems.

Experimental demonstration of in-loop intracavity intensity-noise suppression

Abstract: Experimental results for intracavity-laser intensity-noise suppression, or "squashing," manifested as reduced fluctuations on the transmitted field photodetector voltage are presented. It is experimentally demonstrated that a rigid optical cavity within the feedback loop is compatible with squashing. The observed closed loop detector noise floor is approximately 16 nV/sub rms///spl radic/Hz in the acoustic frequency range (/spl sim/100 Hz), well below the quantum limit due to shot noise of 148 nV/sub rms///spl radic/Hz. This corresponds to 19 dB of observed noise suppression below the quantum limit and is consistent with the measured disturbance suppression function of the feedback loop. We also present measurements demonstrating the orthogonality of the squashing and frequency-locking control loops.

Alignment locking to suspended Fabry-Perot cavity

Abstract: In this paper we report on the alignment locking of an in vacuum 77 m long suspended mirror Fabry-Perot cavity. Lock was achieved by mode-matching a 500 mW Nd:YAG NPRO onto a pre-mode cleaner, the output of which was then mode-matched to the suspended cavity. The longitudinal locking was achieved by feeding back to the laser frequency actuator to follow the cavity resonance. Subsequent implementation of a hybrid auto-alignment system enhanced the stability of the circulating power inside the cavity. Preliminary results are presented.

Technology developments for ACIGA high power test facility for advanced interferometry

Abstract: The High Optical Power Test Facility for Advanced Interferometry has been built by the Australian Consortium for Interferometric Gravitational Astronomy north of Perth in Western Australia. An 80 m suspended cavity has been prepared in collaboration with LIGO, where a set of experiments to test suspension control and thermal compensation will soon take place. Future experiments will investigate radiation pressure instabilities and optical spring effects in a high power optical cavity with ~200 kW circulating power. The facility combines research and development undertaken by all consortium members, whose latest results are presented.

Automatic alignment of a rigid spacer cavity

Abstract: A bench-top auto-alignment system employing an invariant Gouy phase telescope is described in this paper. Our system uses external galvanometer-actuated mirrors for the tilt and offset control of a laser beam onto a rigid spacer cavity. Wavefront sensing diagnostics which accurately decouple tilt and offset er-rors are employed, and corresponding orthogonal corrections are enabled with the aid of electronic nulling. The closed loop system achieves an alignment fluctua-tion suppression of 50.4 dB for angular tilt and 58.3 dB for lateral offset at 1 Hz, with a unity gain bandwidth in excess of 115 Hz.

Interrogation of a passive fiber Bragg grating resonator sensor by current modulation of a diode laser

Abstract: In this paper, experimental results for a current modulation frequency locking scheme in a single feedback control loop are presented, and are compared with the Pound-Drever-Hall (PDH) topology. This experiment provides confidence that with proper pre-stabilization of the diode laser in a more sophisticated two-loop control scheme, current modulation may well attain similar ultra-resolution strain sensitivities as those achieved using the PDH technique.

Ultra-high resolution strain sensing by phase-sensitive interrogation of a passive fiber Bragg resonator

Abstract: We demonstrate and compare two similar pico-strain sensing techniques by laser frequency locking to a passive Bragg grating Fabry-Perot resonator. One technique uses auxiliary phase modulation while the other employs current modulation of the diode laser source. The former is based on the Pound-Drever-Hall locking technique, while the latter is its variant, as current modulation introduces both amplitude and frequency modulation. The two modulation schemes utilize radio-frequency sidebands to derive error signals from the complex optical response of the fiber Bragg resonator. Experimental results are presented that demonstrate when the laser is locked, these methods detect differential phase shift between the optical carrier and the sidebands, due to minute fiber optical path displacements.

Sub-picostrain sensing by laser frequency locking to a passive fiber Bragg resonator

Abstract: We demonstrate, for the first time, a sensing architecture capable of detecting broadband dynamic strain beyond picostrain resolution, with signal frequencies extending from 100 Hz to beyond 100 kHz. The system uses a pre-stabilized external cavity diode laser to interrogate a passive fiber Bragg resonator, using the Pound-Drever-Hall frequency locking technique. The low-loss resonator comprises of a Bragg grating pair written in standard SMF-28 fiber.

Dynamic photothermal resonance push-pull in a fiber Bragg grating Fabry-Perot

Abstract: The dynamic photothermal behavior of a passive fiber Bragg grating Fabry-Perot (FFP) is investigated, when it is interrogated with a tunable laser. This photothermal effect needs to be taken into account when an FFP is used as a wavelength demultiplexer, as it can be a source of filter instability; while as a sensor, this effect can also translate into phase noise. Finally, the photothermal push-pull should be considered in the characterization of passive fiber resonators, as it can distort the reflectivity and transmissivity scans of the FFP.

Ultra-Sensitive Remote Fiber Sensing by Radio-Frequency Current Modulation of a Diode Laser

Abstract: We present long-range interferometric remote fiber sensing, demonstrating unprecedented picostrain sensitivity over a broad acoustic frequency range, by simultaneously overcoming several well-known limitations, such as Rayleigh backscatter, laser coherence length, and down fiber noise.

Ultra-sensitive dynamic strain detection by phase-sensitive laser frequency locking to a passive Bragg grating resonator

Abstract: We demonstrate a pico-strain sensing technique by remote interrogation of passive Bragg grating Fabry-Perot resonators, based on the Pound-Drever-Hall technique, used for laser frequency locking and signal extraction. It employs radio-frequency phase modulation to derive error signals.