Publications by authors named "Michel J F Digonnet"

27 Publications

  • Page 1 of 1

Radiation-Balanced Silica Fiber Amplifier.

Phys Rev Lett 2021 Jul;127(1):013903

Edward L. Ginzton Laboratory, Stanford University, Stanford, California 94305, USA.

We report what we believe to be the first radiation-balanced fiber amplifier-a device that provides optical gain while experiencing no temperature rise. The gain medium is a silica fiber with a 21-μm-diameter core highly doped with Yb^{3+} (2.52 wt. %) and codoped with 2.00 wt. % Al to reduce concentration quenching. The amplifier is core pumped with 1040-nm light to create anti-Stokes fluorescence cooling and gain in the core at 1064 nm. Using a custom slow-light fiber Bragg grating sensor with mK resolution, temperature measurements are performed at multiple locations along the amplifier fiber. A 4.35-m fiber pumped with 2.62 W produced 17 dB of gain, while the average fiber temperature remained slightly below room temperature. This advancement is a fundamental step toward the creation of ultrastable lasers necessary to many applications, especially low-noise sensing and high-precision metrology.
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http://dx.doi.org/10.1103/PhysRevLett.127.013903DOI Listing
July 2021

Rotation sensitivity and shot-noise-limited detection in an exceptional-point coupled-ring gyroscope.

Opt Lett 2021 Jun;46(12):2936-2939

A theoretical study is performed of the sensitivity and quantum-noise limit of a passive coupled-ring optical gyroscope operated at and detuned from its exceptional point (EP) and interrogated with a practical conventional readout system. When tuned to its EP, the Sagnac frequency splitting is proportional to the square root of the applied rotation rate, but the signal generated by the sensor is shown to be proportional to the applied rotation rate. The sensitivity is never larger, and the minimum detectable rotation rate in the quantum-noise limit never lower, than that of a standard single-ring gyro of the same radius and loss, even when the coupled-ring gyro is tuned exactly to its EP. As pointed out elsewhere for other EP sensors, in this particular passive sensor at least, there is no sensitivity or resolution benefit in operating at an EP.
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http://dx.doi.org/10.1364/OL.423700DOI Listing
June 2021

Enhanced rotation sensing and exceptional points in a parity-time-symmetric coupled-ring gyroscope.

Opt Lett 2020 Dec;45(23):6538-6541

Enhancement in rotation sensitivity is achieved in a parity-time-symmetric gyroscope consisting of a ring with gain coupled to a lossy ring, operated below laser threshold and in the vicinity of its exceptional point (EP). An external laser and a conventional readout system are used to measure the large rotation-induced shifts in resonance frequency known to occur in this device. A complete model of the rotation sensitivity is derived that accounts for gain saturation caused by the large circulating power. Compared to a single-ring gyro, the sensitivity is enhanced by a factor of ∼300 when the inter-ring coupling is tuned to its EP value , and ∼2400 when it is decreased from , even though the Sagnac frequency shift is then much smaller. ∼40 of this 2400-fold enhancement is assigned to a new sensing mechanism where rotation alters the gain saturation. These results show that this compact gyro has a far greater sensitivity than a conventional ring gyro, and that this improvement arises mostly from the gain compensating the loss, as opposed to the enhanced Sagnac frequency shift from the EP. This gyro is also shown to be much more stable against gain fluctuations than a single-ring gyro with gain.
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http://dx.doi.org/10.1364/OL.399985DOI Listing
December 2020

Experimental comparison of silica fibers for laser cooling.

Opt Lett 2020 Jul;45(14):4020-4023

Laser cooling in silica has recently been demonstrated, but there is still a lack of understanding on how fiber composition, core size, and contamination influence cooling performance. In this work, six Yb-doped silica fibers were studied to illuminate the influence of these parameters. The best fiber cooled by -70 with only 170 mW/m of absorbed pump power at 1040 nm, which corresponds to twice as much heat extracted per unit length compared to the first reported laser cooling in silica. This new fiber has an extremely low loss and a higher Al concentration (2.0 wt.% Al), permitting a high Yb concentration (2.52 wt.% Yb) without incurring significant quenching. Strong correlations were found between the absorptive loss responsible for heating and the loss measured at 1380 nm due to absorption by .
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http://dx.doi.org/10.1364/OL.395513DOI Listing
July 2020

Compact diaphragm-based optical accelerometers with µg/√Hz resolution.

Opt Lett 2020 Jul;45(14):3933-3936

A compact fiber accelerometer that meets the resolution requirement for aircraft navigation is reported. It detects extremely weak acceleration-induced vibrations of a spring-loaded diaphragm using a two-wave interferometer with a /2 biasing step micro-fabricated on the diaphragm. A single-mode fiber provides a laser beam that interrogates the interferometer. This sensor has a measured flat-band sensitivity with a bandwidth of 10.7 kHz, and a resolution limited by thermo-mechanical noise of 13µ/√ at 100 Torr, and 712/√ at 20 mTorr.
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http://dx.doi.org/10.1364/OL.395737DOI Listing
July 2020

Loss-compensated slow-light fiber Bragg grating with 22-km/s group velocity.

Opt Lett 2020 Jun;45(11):3179-3182

This Letter reports the behavior of the slow-light resonances of a strong apodized fiber Bragg grating (FBG) in which the intrinsic loss is compensated for by a small internal gain. The 6.5-mm FBG, written with a femtosecond laser in an Er-doped single-mode fiber, was pumped at ∼1475 just below the lasing threshold to offset most of its intrinsic loss, thereby narrowing its resonances. The fundamental slow-light resonance was measured to have a linewidth of 8.5 fm, or a record group velocity of ∼22/, and a peak transmission near unity (-0.2). The measured dependencies of the linewidth and peak transmission on pump power agree well with a new model that predicts the transmission spectrum of loss-compensated FBGs in the presence of pump and signal saturation.
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http://dx.doi.org/10.1364/OL.392808DOI Listing
June 2020

Laser cooling in a silica optical fiber at atmospheric pressure.

Opt Lett 2020 Mar;45(5):1092-1095

For the first time, to the best of our knowledge, laser cooling is reported in a silica optical fiber. The fiber has a 21-µm diameter core doped with 2.06 wt.% ${{\rm Yb}^{3 + }}$Yb and co-doped with ${{\rm Al}_2}{{\rm O}_3}$AlO and ${{\rm F}^ - }$F to increase the critical quenching concentration by a factor of 16 over the largest reported values for the Yb-doped silica. Using a custom slow-light fiber Bragg grating sensor, temperature changes up to $ - {50}\;{\rm mK}$-50mK were measured with 0.33 W/m of absorbed pump power per unit length at 1040 nm. The measured dependencies of the temperature change on the pump power and the pump wavelength are in excellent agreement with predictions from an existing model, and they reflect the fiber's groundbreaking quality for the radiation-balanced fiber lasers.
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http://dx.doi.org/10.1364/OL.384658DOI Listing
March 2020

Demonstration of anti-Stokes cooling in Yb-doped ZBLAN fibers at atmospheric pressure.

Opt Lett 2019 May;44(9):2338-2341

For the first time, to the best of our knowledge, optical cooling is demonstrated in a fiber at atmospheric pressure. Using a specialized slow-light fiber Bragg grating temperature sensor, -5.2  mK and -0.65  K were measured in a single-mode (1% YbF) and multimode (3% YbF) ZBLAN fiber with respective cooling efficiencies of 2.2% and 0.90%. Fitting a recently reported quantitative model of optical cooling in fibers to the measured temperature change dependence on the pump power per unit length validates the model and allows us to infer the fibers' absorptive loss and quenching lifetime, key parameters that are scarce in literature. These values are necessary for accurate cooling predictions and will aid in the development of fibers for application in optical coolers and radiation-balanced lasers.
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http://dx.doi.org/10.1364/OL.44.002338DOI Listing
May 2019

High-resolution slow-light fiber Bragg grating temperature sensor with phase-sensitive detection.

Opt Lett 2018 Jul;43(14):3337-3340

This Letter reports a slow-light fiber Bragg grating (FBG) temperature sensor with a record temperature resolution of ∼0.3  m°C/√Hz, a drift of only ∼1  m°C over the typical duration of a measurement (∼30  s), and negligible self-heating. This sensor is particularly useful for applications requiring the detection of very small temperature changes, such as radiation-balanced lasers and the measurement of small absorptive losses using calorimetry. The sensor performance is demonstrated by measuring the heat generated in a pumped Yb-doped fiber. The sensor is also used to measure the slow-light FBG's very weak internal absorption loss (0.02  m), which is found to be only ∼2% of the total loss.
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http://dx.doi.org/10.1364/OL.43.003337DOI Listing
July 2018

Photonics sensing at the thermodynamic limit.

Opt Lett 2017 May;42(10):2018-2021

We report a slow-light fiber Bragg grating strain sensor with a resolution limited by the extremely low thermodynamic phase fluctuations of the fiber. This was accomplished by using a short grating (4.5 mm) to enhance the thermal phase noise, an ultra-stable interrogation laser to lower the laser frequency noise, and a slow-light mode with a high group index (∼533) to suppress all other noise sources. We demonstrate that in a similar but longer grating (21 mm), the phase noise is suppressed in inverse proportion to the square root of the length, in accordance with theory, leading to a strain resolution as low as 130  fε/√Hz and a minimum detectable length of ∼3×10-15  m at 1.5 kHz.
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http://dx.doi.org/10.1364/OL.42.002018DOI Listing
May 2017

Aircraft-navigation-grade laser-driven FOG with Gaussian-noise phase modulation.

Opt Lett 2017 Apr;42(8):1600-1603

A laser-driven fiber optic gyroscope (FOG) is demonstrated with an angular random walk noise of 5.5×10-4  deg/√h, a drift of 6.8×10-3  deg/h, and an inferred scale-factor stability of 0.15 ppm, making it, to the best of our knowledge, the first laser-driven FOG to satisfy the performance requirements for inertial navigation of commercial aircraft. This is achieved using Gaussian white noise phase modulation to broaden the linewidth of the source laser and to strongly suppress the narrow-linewidth optical carrier. The performance of this laser-driven FOG is shown to have better noise and only slightly higher drift than the same FOG driven by a conventional superfluorescent fiber source. This result is validated for two lasers with widely different intrinsic coherence.
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http://dx.doi.org/10.1364/OL.42.001600DOI Listing
April 2017

Pseudo-random-bit-sequence phase modulation for reduced errors in a fiber optic gyroscope.

Opt Lett 2016 Dec;41(24):5664-5667

Low noise and drift in a laser-driven fiber optic gyroscope (FOG) are demonstrated by interrogating the sensor with a low-coherence laser. The laser coherence was reduced by broadening its optical spectrum using an external electro-optic phase modulator driven by either a sinusoidal or a pseudo-random bit sequence (PRBS) waveform. The noise reduction measured in a FOG driven by a modulated laser agrees with the calculations based on the broadened laser spectrum. Using PRBS modulation, the linewidth of a laser was broadened from 10 MHz to more than 10 GHz, leading to a measured FOG noise of only 0.00073  deg/√h and a drift of 0.023  deg/h. To the best of our knowledge, these are the lowest noise and drift reported in a laser-driven FOG, and this noise is below the requirement for the inertial navigation of aircraft.
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http://dx.doi.org/10.1364/OL.41.005664DOI Listing
December 2016

Fiber-feedback optical parametric oscillator for half-harmonic generation of sub-100-fs frequency combs around 2 μm.

Opt Lett 2015 Sep;40(18):4368-71

We demonstrate a femtosecond fiber-feedback optical parametric oscillator (OPO) at degeneracy. The OPO cavity comprises an 80-cm-long fiber composed of a combination of normal and anomalous dispersion sections that provide a net intracavity group delay dispersion close to zero. By using a mode-locked, Yb-doped fiber laser as the pump, we achieved half-harmonic generation of 250-MHz, 1.2-nJ nearly transform-limited 97-fs pulses centered at 2090 nm with a total conversion efficiency of 36%.
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http://dx.doi.org/10.1364/OL.40.004368DOI Listing
September 2015

High Purcell factor in fiber Bragg gratings utilizing the fundamental slow-light mode.

Opt Lett 2015 Aug;40(15):3440-3

We demonstrate through numerical simulations that the slow-light resonances that exist in strong, apodized fiber Bragg gratings (FBGs) fabricated with femtosecond pulses in deuterium-loaded fibers can exhibit very large intensity enhancements and Purcell factors with the proper optimization of their length. This potential is illustrated with two saturated FBGs that are less than 5 mm long and have been annealed to reduce their internal loss. The first one exhibits the largest measured Purcell factor in an all-fiber device (38.7), and the second one exhibits the largest intensity enhancement (1525). These devices are anticipated to have significant applications in quantum-dot lasers, nonlinear fiber devices, and cavity quantum-electrodynamics experiments.
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http://dx.doi.org/10.1364/OL.40.003440DOI Listing
August 2015

Slowing down light to 300  km/s in a deuterium-loaded fiber Bragg grating.

Opt Lett 2015 Apr;40(7):1524-7

We report light propagation with a group velocity of only 300  km/s, a group index of 1010, and a group delay of 42 ns, in a strong apodized fiber Bragg grating 12.5 mm in length. The grating was fabricated in a deuterium-loaded fiber using a femtosecond laser and a phase mask, followed by annealing to reduce residual losses. Data analysis indicates a strong index modulation of 1.98×10(-3) and an ultra-low single-pass power loss of 0.010 dB.
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http://dx.doi.org/10.1364/OL.40.001524DOI Listing
April 2015

Piconewton force measurement using a nanometric photonic crystal diaphragm.

Opt Lett 2014 Aug;39(15):4533-6

A compact force fiber sensor capable of measuring forces at the piconewton level is reported. It consists of a miniature Fabry-Perot cavity fabricated at the tip a single-mode fiber, in which the external reflector is a compliant photonic-crystal diaphragm that deflects when subjected to a force. In the laboratory environment, this sensor was able to detect a force of only ∼4  pN generated by the radiation pressure of a laser beam. Its measured minimum detectable force (MDF) at 3 kHz was as weak as 1.3  pN/√Hz. In a quiet environment, the measured noise was ∼16 times lower, and the MDF predicted to be ∼76  fN/√Hz.
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http://dx.doi.org/10.1364/OL.39.004533DOI Listing
August 2014

Observation of ~20 ns group delay in a low-loss apodized fiber Bragg grating.

Opt Lett 2014 Jul;39(13):3978-81

We report a record group delay of 19.5 ns (an equivalent group index of 292) measured in a strongly apodized, 2 cm long, femtosecond fiber Bragg grating (FBG). This significant (~4-fold) improvement over the previous record results from the presence of a Fabry-Perot arising from the apodization. The measured group-index spectrum is well explained by a model that accounts for the apodized profiles of the index modulation, propagation loss, and birefringence of the grating. The peak power loss inferred from this model is only ~0.12  m⁻¹, which is one of the lowest values reported for an FBG.
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http://dx.doi.org/10.1364/OL.39.003978DOI Listing
July 2014

Miniature photonic-crystal hydrophone optimized for ocean acoustics.

J Acoust Soc Am 2011 Apr;129(4):1837-50

EL Ginzton Laboratory, Stanford University, 348 Via Pueblo Mall, Stanford, California 94305, USA.

This work reports on an optical hydrophone that is insensitive to hydrostatic pressure, yet capable of measuring acoustic pressures as low as the background noise in the ocean in a frequency range of 1 Hz to 100 kHz. The miniature hydrophone consists of a Fabry-Perot interferometer made of a photonic-crystal reflector interrogated with a single-mode fiber and is compatible with existing fiber-optic technologies. Three sensors with different acoustic power ranges placed within a sub-wavelength sized hydrophone head allow a high dynamic range in the excess of 160 dB with a low harmonic distortion of better than -30 dB. A method for suppressing cross-coupling between sensors in the same hydrophone head is also proposed. A prototype was fabricated, assembled, and tested. The sensitivity was measured from 100 Hz to 100 kHz, demonstrating a sound-pressure-equivalent noise spectral density down to 12 μPa/Hz(1/2), a flatband wider than 10 kHz, and very low distortion.
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http://dx.doi.org/10.1121/1.3543949DOI Listing
April 2011

Optimization of the splice loss between photonic-bandgap fibers and conventional single-mode fibers.

Opt Lett 2010 Jun;35(12):1938-40

Edward L. Ginzton Laboratory, Stanford University, 450 Via Palou Mall, Stanford, California 94305, USA.

To understand the loss limitations of a splice between a hollow-core fiber and a conventional fiber, we use a numerical model to calculate the expected coupling loss between the NKT Photonics' HC-1550-02 fiber and a single-mode fiber (SMF) of arbitrary step-index profile. When the SMF parameters are optimized, the splice loss is predicted to be as low as approximately 0.6 dB. This minimum is believed to be largely due to mode-shape mismatch. These predictions are confirmed experimentally by optimizing the splice loss between this photonic-bandgap fiber and five SMFs with different mode-field diameters (MFDs) and V numbers. With the SMF-28 fiber, the measured loss is 1.3 dB, in excellent agreement with theory. Using a SMF with parameters close to the optimum values (MFD=7.2 microm and V=2.16), this loss was reduced to a new record value of 0.79 dB.
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http://dx.doi.org/10.1364/OL.35.001938DOI Listing
June 2010

Measurement of reduced backscattering noise in laser-driven fiber optic gyroscopes.

Opt Lett 2010 Jan;35(2):121-3

Edward L. Ginzton Laboratory, Stanford University, Stanford, California 94305, USA.

We report what we believe to be the first demonstration of a laser-driven fiber optic gyroscope (FOG) built with an air-core fiber. Its phase noise is measured to be 130 murad/ radicalHz. When the sensing fiber is replaced with a conventional fiber, this figure drops to 12 murad/ radicalHz. Comparison between these values suggests that the air-core fiber gyro is most likely not limited solely by backscattering noise but by reflections at the solid-core/air-core interface. By minimizing additional noise sources and reducing the air-core fiber loss to its theoretical limit (approximately 0.1 dB/km), we predict that the backscattering noise of the laser-driven air-core FOG will drop below the level of current FOGs. Compared with commercial FOGs, this FOG will exhibit a lower noise, improved thermal and mean-wavelength stability, and reduced magnetic-field sensitivity.
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http://dx.doi.org/10.1364/OL.35.000121DOI Listing
January 2010

Ring-coupled Mach-Zehnder interferometer optimized for sensing.

Appl Opt 2009 Sep;48(26):4874-9

Edward L. Ginzton Laboratory, Stanford University, Stanford, California 94305, USA.

We demonstrate numerically that the theoretical maximum sensitivity of a ring-coupled Mach-Zehnder interferometer (MZI) optimized as a sensor is about 30% greater than the optimized sensitivity of a conventional single-bus ring sensor with an identical ring perimeter and loss. The ring-coupled MZI sensor also achieves its greater sensitivity with a 25% lower circulating power, which is useful for the suppression of undesirable nonlinear effects.
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http://dx.doi.org/10.1364/AO.48.004874DOI Listing
September 2009

Laser-driven photonic-bandgap fiber optic gyroscope with negligible Kerr-induced drift.

Opt Lett 2009 Apr;34(7):875-7

Edward L. Ginzton Laboratory, Stanford University, Stanford, CA 94305-4085, USA.

We predict theoretically and confirm experimentally that the Kerr-induced phase drift of a fiber optic gyroscope (FOG) operated with a laser instead of a broadband source is virtually eliminated when the sensing coil is made of an air-core photonic-bandgap fiber. This is the first demonstration of a laser-driven FOG with a Kerr-induced drift low enough to meet the inertial navigation requirement for a 10-h transcontinental flight.
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http://dx.doi.org/10.1364/ol.34.000875DOI Listing
April 2009

Linearly polarized, 3.35 W narrow-linewidth, 1150 nm fiber master oscillator power amplifier for frequency doubling to the yellow.

Opt Lett 2007 Jun;32(11):1530-2

Edward L. Ginzton Laboratory, Stanford University, Stanford, California 94305-4085, USA.

A high-power linearly polarized Yb-doped silica fiber master oscillator power amplifier at 1150 nm is reported. It produced 3.35 W cw and 2.33 W of average power in 1 micros pulses at a 100 kHz repetition rate, both with 8 pm linewidth. This is the first report, to the best of our knowledge, of a high-power Yb-doped fiber amplifier at a wavelength longer than 1135 nm. The pulsed output was frequency doubled in a bulk periodically poled near-stoichiometric LiTaO(3) chip to generate 976 mW of average power at 575 nm with an overall system optical-to-optical efficiency of 9.8% with respect to launched pump power.
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http://dx.doi.org/10.1364/ol.32.001530DOI Listing
June 2007

Polarization controller for hollow-core fiber.

Opt Lett 2007 Jun;32(11):1524-6

Edward L. Ginzton Laboratory, Stanford University, Stanford, California 94305, USA.

We demonstrate a universal polarization controller for hollow-core fibers, a simple device consisting of three twisted fiber sections that makes use of the inherent birefringence of the air-core fiber. The device 5% bandwidth at 1550 nm is calculated from measured data to be approximately 13 nm.
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http://dx.doi.org/10.1364/ol.32.001524DOI Listing
June 2007

A fast and accurate numerical tool to model the modal properties of photonic-bandgap fibers.

Opt Express 2006 Apr;14(7):2979-93

We describe a finite-difference numerical method that allows us to simulate the modes of air-core photonic-bandgap fibers (PBF) of any geometry in minutes on a standard PC. The modes' effective indices and fields are found by solving a vectorial transverse magnetic-field equation in a matrix form, which can be done quickly because this matrix is sparse and because we reduce its bandwidth by rearranging its elements. The Stanford Photonic-Bandgap Fiber code, which is based on this method, takes about 4 minutes to model 20 modes of a typical PBF on a PC. Other advantages include easy coding, faithful modeling of the abrupt discontinuities in the index profile, high accuracy, and applicability to waveguides of arbitrarily complex profile.
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http://dx.doi.org/10.1364/oe.14.002979DOI Listing
April 2006

Efficient yellow-light generation by frequency doubling a narrow-linewidth 1150 nm ytterbium fiber oscillator.

Opt Lett 2006 Feb;31(3):347-9

Edward L Ginzton Laboratory, Stanford University, California 94305-4085, USA.

A linearly polarized, narrow-linewidth, diode-pumped, Yb-doped silica-fiber oscillator operating at 1150 nm was frequency doubled to produce 40 mW of 575 nm radiation. The oscillator generated 89 mW of cw linearly polarized output power and was tunable over 0.80 nm. The laser output was coupled to a periodically poled LiNbO3 waveguide that converted 67% of the coupled power to the yellow. The system was fully integrated, with no free-space optics, and had an overall optical-to-optical efficiency of 7.0% with respect to the incident diode-laser pump power.
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http://dx.doi.org/10.1364/ol.31.000347DOI Listing
February 2006

Demonstration of a folded Sagnac sensor array immune to polarization-induced signal fading.

Appl Opt 2003 Dec;42(36):7132-6

Edward L. Ginzton Laboratory, Stanford University, 450 Via Palou, Stanford, California 94305-4085, USA.

We demonstrate a new folded Sagnac sensor array design that combines a Faraday rotator mirror and a polarization beam splitter to eliminate the optical noise pulses otherwise generated in a folded Sagnac sensor array. A depolarization scheme compatible with this configuration is also proposed and demonstrated experimentally. It is shown that this new configuration passively eliminates polarization-induced signal fading on every sensor in the array. The minimum detectable phase was measured to be approximately 1.1 microrad/square root of Hz, in agreement with theory.
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http://dx.doi.org/10.1364/ao.42.007132DOI Listing
December 2003
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