Experimental and theoretical investigations of coherent optical-frequency-domain reflectometry using semiconductor laser sources are presented. Good agreement was found between the analysis of the signal-to-noise ratio due to the phase noise and the experimental results. The sensitivity limit due to the quantum noise is also described. Limitations due to the nonlinearity in the optical frequency sweep produced by the thermal-response time of the laser and mode hopping are investigated and compared with experimental results. Two interferometric methods to characterize the thermal-response time of the laser and their implementations are described. The effects of mode hopping in the optical-frequency sweep are compared to numerical simulations. A simple formula to predict the position of spurious peaks due to mode hopping are presented. A spatial resolution of 400 /spl mu/m over 10 cm was obtained by correcting the nonlinearity in the optical-frequency sweep by using an auxiliary interferometer. The Rayleigh backscattering was observed for the first time over more than 400 m of fiber using a DFB laser coupled to an external cavity. >

Experimental and theoretical investigations of coherent OFDR with semiconductor laser sources

Part I. An Introduction to Gravitational Waves and Methods for their Detection: 1. Gravitational waves in general relativity D. G. Blair 2. Sources of gravitational waves D. G. Blair 3. Gravitational wave detectors D. G. Blair Part II. Gravitational Wave Detectors: 4. Resonant-bar detectors D. G. Blair 5. Gravity wave dewars W. O. Hamilton 6. Internal friction in high Q materials J. Ferreirinko 7. Motion amplifiers and passive transducers J. P. Richard 8. Parametric transducers P. J. Veitch 9. Detection of continuous waves K. Tsubono 10. Data analysis and algorithms for gravitational wave-antennas G. V. Paalottino Part III. Laser Interferometer Antennas: 11. A Michelson interferometer using delay lines W. Winkler 12. Fabry-Perot cavity gravity-wave detectors R. W. P. Drever 13. The stabilisation of lasers for interferometric gravitational wave detectors J. Hough 14. Vibration isolation for the test masses in interferometric gravitational wave detectors N. A. Robertson 15. Advanced techniques A. Brillet 16. Data processing, analysis and storage for interferometric antennas B. F. Schutz 17. Gravitational wave detection at low and very low frequencies R. W. Hellings.

The Detection of Gravitational Waves

We demonstrate the generation of broadband continuous-wave optical squeezing from 280 Hz-100 kHz using a below-threshold optical parametric oscillator (OPO). The squeezed state phase was controlled using a noise locking technique. We show that low frequency noise sources, such as seed noise, pump noise, and detuning fluctuations, present in optical parametric amplifiers, have negligible effect on squeezing produced by a below-threshold OPO. This low frequency squeezing is ideal for improving the sensitivity of audio frequency measuring devices such as gravitational-wave detectors.

Squeezing in the audio gravitational-wave detection band.

We demonstrate a new heterodyne Michelson interferometer design for displacement measurements capable of fringe interpolation accuracy of one part in 36 000. Key to this level of accuracy are the use of two acousto-optic modulators for heterodyne frequency generation and digital signal processing demodulation electronics. We make a direct comparison of our interferometer to a commercial interferometer based on a Zeeman-stabilized laser, and show that the residual periodic errors in ours are two orders of magnitude lower than those in the commercial unit. We discuss electronically induced optical cross talk and optical feedback as sources of periodic error. Our new interferometer is simple, robust, and readily implemented.

Michelson Interferometry With 10 PM Accuracy

Recently, the design of a white-light cavity has been proposed using negative dispersion in an intracavity medium to make the cavity resonate over a large range of frequencies and still maintain a high cavity buildup. This Letter presents the first demonstration of this effect in a free-space cavity. The negative dispersion of the intracavity medium is caused by bifrequency Raman gain in an atomic vapor cell. A significantly broad cavity response over a bandwidth greater than 20 MHz has been observed. A key application of this device would be in enhancing the sensitivity-bandwidth product of the next generation gravitational wave detectors that make use of the so-called signal-recycling mirror.

Demonstration of a tunable-bandwidth white-light interferometer using anomalous dispersion in atomic vapor.

Two schemes for interferometric optical phase measurement, with sensitivity limited only by quantum noise in the light, are analyzed. Direct detection is applicable to signals at modulation frequencies away from the technical noise of the light, so that quantum noise dominates the measurement. Alternatively signals otherwise obscured by classical optical noise may be recovered with a phase-modulation technique that shifts the signals to a quantum-noise-limited region of the photocurrent spectrum. The analysis is tested experimentally by using a polarimetric electric-field sensor. In the direct-detection scheme quantum-noise-limited performance produced a phase sensitivity of 0.25 μrad. The indirect scheme allowed subkilohertz signals to be extracted from classical noise 67 dB greater with sensitivity approaching the quantum noise limit.

Quantum-noise-limited interferometric phase measurements

The theory is given for polarizing beam splitters made from polished-type directional couplers using anisotropic core material. A comparison is made between these beam splitters and those of the fused, biconical type.

Polished-type couplers acting as polarizing beam splitters

We present experimental data on the frequency response of both broadband and tuned signal recycling with a benchtop Michelson interferometer. These data are in excellent agreement with our simple theoretical model. We use in-line modulation to give a control system that provides a high degree of orthogonality between the two servo loops.

Broadband and tuned signal recycling with a simple Michelson interferometer

We report on experimental demodulation of nonstationary shot noise, which is associated with strongly modulated light. For sinusoidal modulation and demodulation, measurements confirm theoretical predictions of 1.8-dB excess noise in the modulation quadrature and 3-dB noise reduction in the opposite quadrature, relative to the standard quantum limit. Demodulation with a third harmonic produces noise correlated with that which is due to the fundamental. Reducing excess noise by 0.8 dB in the modulation quadrature, by combining the fundamental and third harmonics in a 2:1 ratio, is shown to be feasible.

Harmonic demodulation of nonstationary shot noise.

We analyze and test a laboratory benchtop version of a compound interferometric phase sensor, a Michelson interferometer whose output is combined coherently with a phase-modulated local oscillator beam tapped off the Michelson input beam This configuration models a whole class of external-modulation interferometers designed to shift signals, obscured by low-frequency intensity noise of the light source, into a shot-noise-limited region of the photocurrent spectrum We find analytically that the shot-noise-limited sensitivity achievable with this system is comparable with that obtained by using internal phase modulation, with both schemes suffering (for different reasons) approximately a 22% sensitivity penalty compared with ideal shot-noise-limited direct detection Experimentally we achieve true shot-noise-limited sensitivity, and we investigate trade-offs necessitated by commonly encountered nonideal features in any external-modulation system Our analytic model, which specifically accounts for Michelson fringe contrast, electronic receiver noise, phase-modulation depth, and the local oscillator tap-off fraction, is sufficiently accurate to predict the absolute sensitivity of our benchtop instrument to within 05 dB

Andrew J. Stevenson

Papers

Quantum-noise-limited interferometric phase measurements

Polished-type couplers acting as polarizing beam splitters

Broadband and tuned signal recycling with a simple Michelson interferometer

Harmonic demodulation of nonstationary shot noise.

External phase-modulation interferometry