-
[show abstract]
[hide abstract]
ABSTRACT: We discuss the origins and the suppression of the large frequency jitter on the carrier-envelope offset frequency (fceo) of fiber-laser frequency combs. While this frequency noise appears most prominently on fceo, its effects are felt across the frequency comb and it is a potential limiting factor in applications of fiber-laser frequency
combs. Here we show that its origin lies in the white amplitude noise of the pump laser output. We dramatically reduce this
noise by operating the pump laser in a lower-noise state, i.e. at higher pump current, and by more aggressively feeding back
to the pump current with an optimal feedback network. We demonstrate instrument-limited fceo linewidths and an integrated fceo phase jitter of 1rad.
Applied Physics B 04/2012; 86(2):219-227. · 2.19 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The authors report on a thermal beam optical frequency reference with a fractional frequency instability of 9.2×10<sup>-14</sup> at 1 s reducing to 2.0×10<sup>-14</sup> at 64 s before slowly rising. The <sup>1</sup>S<sub>0</sub>↔<sup>3</sup>P<sub>1</sub> intercombination line in neutral <sup>40</sup> C a is used as a frequency discriminator. A diode laser at 423 nm probes the ground state population after a Ramsey–Bordé sequence of 657 nm light-field interactions on the atoms. The measured fractional frequency instability is an order of magnitude improvement on previously reported thermal beam optical clocks. The photon shot-noise of the read-out produces a limiting square root Λ -variance of 7×10<sup>-14</sup>/ √ τ .
Applied Physics Letters 08/2009; · 3.84 Impact Factor
-
J J McFerran
[show abstract]
[hide abstract]
ABSTRACT: Details for constructing an astronomical frequency comb suitable as a wavelength reference for échelle spectrographs associated with optical telescopes are outlined. The source laser for the frequency comb is a harmonically mode-locked fiber laser with a central wavelength of 1.56 microm. The means of producing a repetition rate greater than 7 GHz and a peak optical power of approximately 8 kW are discussed. Conversion of the oscillator light into the visible can occur through a two-step process of (i) nonlinear conversion in periodically poled lithium niobate and (ii) spectral broadening in photonic crystal fiber. While not necessarily octave spanning in spectral range to permit the use of an f -to- 2f interferometer for offset frequency control, the frequency comb can be granted accuracy by linking the mode spacing and a comb tooth to separate frequency references. The design avoids the use of a Fabry-Perot cavity to increase the mode spacing of the frequency comb; however, the level of supermode suppression and sideband asymmetry in the fiber oscillator and in the subsequent frequency conversion stages are aspects that need to be experimentally tested.
Applied Optics 06/2009; 48(14):2752-9. · 1.41 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We have used an optical frequency comb referenced to coordinated universal time (UTC) to perform spectroscopic measurements of the D1 transition in laser-cooled 85Rb and 87Rb. Our measurements of the optical frequencies have uncertainties of 28 kHz for 85Rb and 79 kHz for 87Rb. These measurements were used to calculate the magnetic dipole constant A(2P1/2) for 85Rb and 87Rb with similar ranges of uncertainty. Previously, A(2P1/2) for these isotopes was determined with a stated 7–15 kHz uncertainty level; however, there is a large discrepancy, 140 kHz for 85Rb and 2.2 MHz for 87Rb, between the two apparently most precise measurements. Our transition frequency measurements, which avoid saturated absorption spectroscopy and transfer resonator systematics, help resolve this disagreement.
Phys. Rev. A. 03/2008; 77(3).
-
[show abstract]
[hide abstract]
ABSTRACT: We demonstrate a fundamentally mode-locked fiber laser with a repetition frequency in excess of 2 GHz at a central wavelength of 1.535 mum. Co-doped ytterbium-erbium fiber provides the gain medium for the laser, affording high gain per unit length, while a semiconductor saturable absorber mirror (SAM) provides the pulse shaping mechanism in a standing wave cavity. Results are shown confirming cw mode-locking for 1 GHz and 2 GHz repetition frequency systems. The response of the frequency comb output to pump power variations is shown to follow a single pole response. The timing jitter of a 540MHz repetition-rate laser has been suppressed to below 100 fs through phase-lead compensated feedback to the pump power. Alternatively, a single comb line of a 850MHz repetition-rate laser has been phase-locked to a narrow linewidth cw laser with an in-loop phase jitter of 0.06 rad(2). The laser design is compatible with low-noise oscillator applications.
Optics Express 11/2007; 15(20):13155-66. · 3.59 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The most common time-domain measure of frequency stability, the Allan variance, is typically estimated using a frequency counter. Close examination of the operation of modern high-resolution frequency counters shows that they do not make measurements in the way commonly assumed. The consequence is that the results typically reported by many laboratories using these counters are not, in fact, the Allan variance, but a distorted representation. We elucidate the action of these counters by consideration of their operation in the Fourier domain, and demonstrate that the difference between the actual Allan variance and that delivered by these counters can be very significant for some types of oscillators. We also discuss ways to avoid, or account for, a distorted estimation of Allan variance
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 06/2007; · 1.69 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We discuss various aspects of high resolution measurements of phase fluctuations at microwave frequencies. This includes methods to achieve thermal noise limited sensitivity, along with the improved immunity to oscillator amplitude noise. A few prototype measurement systems were developed to measure phase fluctuations of microwave signals extracted from the optical pulse trains generated by femtosecond lasers. This enabled first reliable measurements of the excess phase noise associated with optical-to-microwave frequency division. The spectral density of the excess phase noise was found to be -140 dBc/Hz at 100 Hz offset from the 10 GHz carrier which was almost 40 dB better than that of a high quality microwave synthesizer
IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control 05/2007; · 1.69 Impact Factor
-
W C Swann, J J McFerran,
I Coddington,
N R Newbury,
I Hartl,
M E Fermann,
P S Westbrook,
J W Nicholson,
K S Feder,
C Langrock,
M M Fejer
[show abstract]
[hide abstract]
ABSTRACT: We investigate the comb linewidths of self-referenced, fiber-laser-based frequency combs by measuring the heterodyne beat signal between two independent frequency combs that are phase locked to a common cw optical reference. We demonstrate that the optical comb lines can exhibit instrument-limited, subhertz relative linewidths across the comb spectra from 1200 to 1720 nm with a residual integrated optical phase jitter of approximately 1 rad in a 60 mHz to 500 kHz bandwidth. The projected relative pulse timing jitter is approximately 1 fs. This performance approaches that of Ti:sapphire frequency combs.
Optics Letters 11/2006; 31(20):3046-8. · 3.40 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Optical frequency combs generated by femtosecond fiber lasers typically exhibit significant frequency noise that causes broad optical linewidths, particularly in the comb wings and in the carrier-envelope offset frequency (f(ceo)) signal. We show these broad linewidths are mainly a result of white amplitude noise on the pump diode laser that leads to a breathing-like motion of the comb about a central fixed frequency. By a combination of passive noise reduction and active feedback using phase-lead compensation, this noise source is eliminated, thereby reducing the f(ceo) linewidth from 250 kHz to <1 Hz. The in-loop carrier-envelope offset phase jitter, integrated to 100 kHz, is 1.3 rad.
Optics Letters 07/2006; 31(13):1997-9. · 3.40 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We demonstrate an optical frequency comb with fractional frequency instability of </=2x10(-14) at measurement times near 1 s, when the 10th harmonic of the comb spacing is controlled by a liquid helium cooled microwave sapphire oscillator. The frequency instability of the comb is estimated by comparing it to a cavity-stabilized optical oscillator. The less conventional approach of synthesizing low-noise optical signals from a microwave source is relevant when a laboratory has microwave sources with frequency stability superior to their optical counterparts. We describe the influence of high frequency environmental noise and how it impacts the phase-stabilized frequency comb performance at integration times less than 1 s.
Optics Express 05/2006; 14(10):4316-27. · 3.59 Impact Factor
-
V. Gerginov,
K. Calkins,
C. E. Tanner, J. J. McFerran,
S. Diddams,
A. Bartels,
L. Hollberg,
School of Physics, University of Western Australia, Stirling Highway, Nedlands,
[show abstract]
[hide abstract]
ABSTRACT: High resolution laser spectroscopy of the 6s {sup 2}S{sub 1/2}{yields}6p {sup 2}P{sub 1/2} transition (D{sub 1} line) in neutral {sup 133}Cs is performed in a highly collimated thermal atomic beam by use of a femtosecond laser frequency comb and narrow-linewidth diode laser. The diode laser is offset locked to a single frequency component of the femtosecond laser frequency comb and probes the optical transitions between selected pairs of ground-state and excited-state hyperfine components. A photodiode detects the excited-state decay fluorescence, and a computerized data acquisition system records the signal. The Doppler shift is eliminated by orienting the laser beam in a direction perpendicular to the atomic beam to within a precision of 5x10{sup -6} rad. Optical frequencies for all four pairs of hyperfine components are measured independently, from which the D{sub 1} line centroid and excited-state hyperfine splitting are obtained by least-squares minimization with the ground-state splitting as a fixed constraint. We find the D{sub 1} line centroid to be f{sub D{sub 1}}=335 116 048 748.1(2.4) kHz, and the 6p {sup 2}P{sub 1/2} state hyperfine splitting to be 1 167 723.6(4.8) kHz. These results, in combination with the results of an atom interferometry experiment by Wicht et al. [Phys. Scripta T 102, 82 (2002)], are used to calculate a new value for the fine-structure constant.
Physical Review. A. 03/2006; 73(3).
-
[show abstract]
[hide abstract]
ABSTRACT: Optical frequency references achieve the best frequency stability of any oscillators by taking advantage of high Q = v<sub>0</sub>/Δv optical resonances. These systems are beginning to run into fundamental and technical limitations which are discussed.
LEOS Summer Topical Meetings, 2005 Digest of the; 08/2005
-
[show abstract]
[hide abstract]
ABSTRACT: An efficient means of isolating and detecting the carrier-envelope offset frequency signal in an optical frequency synthesizer is demonstrated. The technique uses spliced and connectorized fiber for comb broadening, a periodically poled KTP crystal for doubling 1064-nm light in the supercontinuum, and a laser-line filter at 532nm for comb-section selection. The technique produces an offset frequency with a 40-dB signal-to-noise ratio in a resolution bandwidth of 100kHz with as little as 55GW/cm2 of peak pulse intensity inside the fiber. The strong signal-to-noise ratio helps realize an offset frequency signal with frequency instability of 1mHz at 1s when controlled through feedback to the optical power driving the femtosecond laser.
Applied Physics B 06/2004; 79(1):39-44. · 2.19 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Uniform oscillations of supercontinua, generated with microstructured fibre, have been observed and investigated. The oscillations are uniform in the sense that the optical power through the fibre changes with a regular and periodic waveform and the spectral bandwidth of the transmitted light changes correspondingly. The oscillations are continuous over periods of hours and the spectral width ranges from the octave-spanning condition (310-THz wide at 20dB below the maximum) to zero broadening of the input light. The corresponding contrast ratio of the fluctuating output light signal is as high as 0.75. Silica photonic crystal fibre with hexagonal air-hole structure and core diameter of 2.0m was used for the supercontinuum generation. The oscillations are produced when at least 15mm of fibre is allowed to extend from the mount of the fibre launcher. Arguments in terms of thermal behaviour are used in an attempt to explain the fluctuations of light through the microstructured fibre. This appears to be the first occasion in which such behaviour has been reported.
Applied Physics B 01/2003; 77(2):259-264. · 2.19 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: We have demonstrated two continuous-wave nonlinear processes: third-harmonic generation (THG) of 1064-nm radiation with a lithium triborate (LBO) crystal, and second-harmonic generation of 696-nm radiation in deuterated rubidium dihydrogen arsenate. With 34 mW of 1064-nm and 25 mW of 532-nm radiation incident upon the LBO crystal, as much as 60 nW of third-harmonic power has been produced. We present the characteristics that optimize the production of nonlinear power in this sum-frequency generation process. In the second experiment, 15 nW of radiation at 348 nm was produced with 9 mW of 696-nm incident radiation. Both processes will play an important role in the new generation of optical synthesis techniques.
Applied Optics 07/2000; 39(18):3115-9. · 1.41 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The UWA research group is developing a coherent microwave-to-optical frequency chain beginning with a series of frequency interval bisection stages. The first stage requires a transfer oscillator at a wavelength of 709 nm. Two such oscillators have been constructed from broad area laser diodes (BALs) and a beat signal between the two has been generated with a fast linewidth less than 100 kHz
Precision Electromagnetic Measurements Digest, 2000 Conference on; 02/2000
-
[show abstract]
[hide abstract]
ABSTRACT: This paper reports on the development of a second generation
coherent optical-to-microwave frequency chain based on the
frequency-interval bisection method. We report successful operation of
all three key elements of such a frequency chain: efficient nonlinear
radiation production, reliable and accurate laser diode phase locking,
as well as wide-span optical frequency comb generation. An analysis of
the expected frequency stability of a synthesizer based on this type of
frequency chain shows that it should be capable of transferring
frequency stabilities at the level of 1.3×10<sup>-15</sup>/τ
IEEE Transactions on Instrumentation and Measurement 05/1999; · 1.21 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Reports on progress towards the creation of an optical
synthesizer. We consider the noise contributions of the two key elements
of the new generation of frequency synthesisers: frequency interval
dividers and frequency comb generators. We demonstrate that a synthesis
resolution of 1 part in 10<sup>15</sup> over a few seconds of
integration time is feasible using these elements
Frequency and Time Forum, 1999 and the IEEE International Frequency Control Symposium, 1999., Proceedings of the 1999 Joint Meeting of the European; 02/1999
-
[show abstract]
[hide abstract]
ABSTRACT: The linewidth of single modes in fibre-laser mode-locked laser is typically substantially higher than those derived from bulk solid-state mode-locked lasers. Active frequency stabilization of fibre combs has been hampered by the long lifetime of the population inversion in the fibre that prevents high bandwidth control of dispersion fluctuations. We present the means for external stabilization of the comb using an acousto-optic modulator.
Frequency Control Symposium, 2007 Joint with the 21st European Frequency and Time Forum. IEEE International;
-
Opt. Express. 14(10):4316-4327.
