Showing papers on "Comb generator published in 2009"

Phase-stabilized, 15 W frequency comb at 28–48 μm

Abstract: We present a high-power optical-parametric-oscillator (OPO) based frequency comb in the mid-IR wavelength region. The system employs periodically poled lithium niobate and is singly resonant for the signal. It is synchronously pumped by a 10 W femtosecond Yb:fiber laser centered at 1.07 microm. The idler (signal) wavelength can be continuously tuned from 2.8 to 4.8 microm (1.76 to 1.37 microm) with a simultaneous bandwidth as high as 0.3 microm and a maximum average idler output power of 1.50 W. We also demonstrate the performance of the stabilized comb by recording the heterodyne beat with a narrow-linewidth diode laser. This OPO is an ideal source for frequency comb spectroscopy in the mid-IR.

Improved signal-to-noise ratio of 10 GHz microwave signals generated with a mode-filtered femtosecond laser frequency comb.

Abstract: We use a Fabry-Perot cavity to optically filter the output of a Ti:sapphire frequency comb to integer multiples of the original 1 GHz mode spacing. This effectively increases the pulse repetition rate, which is useful for several applications. In the case of low-noise microwave signal generation, such filtering leads to improved linearity of the high-speed photodiodes that detect the mode-locked laser pulse train. The result is significantly improved signal-to-noise ratio at the 10 GHz harmonic with the potential for a shot-noise limited single sideband phase noise floor near -168 dBc/Hz.

Brillouin-enhanced hyperparametric generation of an optical frequency comb in a monolithic highly nonlinear fiber cavity pumped by a cw laser.

Abstract: Introduction.—The ability to create a simple, coherent optical frequency comb has potential applications in precision measurement, short-pulse generation, microwave production, arbitrary optical and rf waveform engineering, and astronomy. In particular, generation of an optical comb with modes spaced by tens of gigahertz is especially useful because the resulting comb may be easily divided into its constituents for access and control of individual modes, and the coherent connection to radio frequencies enables low-phase-noise electronic signals. Historically, frequency combs were generated through electro-optic phase modulation of a laser [1,2] or by use of the output of a modelocked laser where the net gain is higher for a train of short pulses than for cw operation. Recent interest, however, has centered on comb generation in compact monolithic resonators. The combination of small mode volume and high quality factors (Q) makes monolithic resonators with nonlinear gain an ideal medium for efficient nonlinear optical processes. Previous work on nonlinear optics in monolithic resonators focuses on whispering-gallery modes and includes generation of frequency combs in microtoroids [3], four-wave mixing in microspheres [4] and microrings [5], and coherent backscattering and oscillation in LiNiO3 and CaF2 gain-based resonators [6]. Here, we report a substantially different monolithic

Phase and frequency control of a radio frequency generator from an external source

Abstract: Controlling a phase and/or a frequency of a RF generator. The RF generator includes a power source, a sensor, and a sensor signal processing unit. The sensor signal processing unit is coupled to the power source and to the sensor. The sensor signal processing unit controls the phase and/or the frequency of a RF generator.

High-performance, vibration-immune, fiber-laser frequency comb

Abstract: We demonstrate an environmentally robust optical frequency comb based on a polarization-maintaining, all-fiber, figure-eight laser. The comb is phase locked to a cavity-stabilized cw laser by use of an intracavity electro-optic phase modulator yielding 1.6 MHz feedback bandwidth. This high bandwidth provides close to shot-noise-limited residual phase noise between the comb and cw reference laser of -94 dBc/Hz from 20 Hz to 200 kHz and an integrated in-loop phase noise of 32 mrad from 1 Hz to 1 MHz. Moreover, the comb remains phase locked under significant mechanical vibrations of over 1 g. This level of environmental robustness is an important step toward a fieldable fiber frequency comb.

Absolute length measurement with the frequency comb of a femtosecond laser

Abstract: We report exploiting the frequency comb of a femtosecond laser as a means of realizing the time-based SI definition of the meter for length metrology. Specifically, an external-cavity diode laser is continuously tuned to a stabilized frequency comb, and its output frequency is modulated over an extensive range to measure the absolute value of a given length by means of multi-wavelength optical interferometry. This approach could find applications in establishing practical length standards with a small amount of uncertainty directly traceable to time standards.

Simple-Design Low-Noise NLTL-Based Frequency Synthesizers for a CPT Cs Clock

Abstract: This paper presents simple-architecture low-noise frequency synthesis chains generating a 9-GHz signal. These devices are based on the use of a nonlinear transmission line (NLTL) used as a comb generator. The residual phase noise spectra of the key components are reported. The residual phase noise performance of the chains at 9 GHz is measured to be less than -80 dBrad2/Hz at 1-Hz offset frequency. The measured fractional frequency stability of the chains is 1 times 10-14 at 1 s and better than 4 times 10-17 at one day. The contributions of these chains to phase lock two extended cavity diode lasers (ECDLs) involved in a coherent-population-trapping (CPT) Cs clock experiment are evaluated and measured.

Optical frequency stabilization of a 10 GHz Ti:sapphire frequency comb by saturated absorption spectroscopy in 87rubidium

Abstract: The high power per mode of a recently developed 10 GHz femtosecond Ti:sapphire frequency comb permits nonlinear Doppler-free saturation spectroscopy in 87 Rb with a single mode of the comb. We use this access to the natural linewidth of the rubidium D2 line to effectively stabilize the optical frequencies of the comb with an instability of 7 10 �12 in 1so faveraging. The repetition rate is stabilized to a microwave reference leading to a stabilized and atomically referenced comb. The frequency stability of the 10 GHz comb is characterized using optical heterodyne with an independent self-referenced 1 GHz comb. In addition, we present alternative stabilization approaches for high repetition rate frequency combs and evaluate their expected stabilities.

A phase-stabilized carbon nanotube fiber laser frequency comb.

Abstract: A frequency comb generated by a 167 MHz repetition frequency erbium-doped fiber ring laser using a carbon nanotube saturable absorber is phase-stabilized for the first time. Measurements of the in-loop phase noise show an integrated phase error on the carrier envelope offset frequency of 0.35 radians. The carbon nanotube fiber laser comb is compared with a CW laser near 1533 nm stabilized to the ν1 + ν3 overtone transition in an acetylene-filled kagome photonic crystal fiber reference, while the CW laser is simultaneously compared to another frequency comb based on a Cr:Forsterite laser. These measurements demonstrate that the stability of a GPS-disciplined Rb clock is transferred to the comb, resulting in an upper limit on the locked comb’s frequency instability of 1.2 × 10-11 in 1 s, and a relative instability of <3 × 10-12 in 1 s. The carbon nanotube laser frequency comb offers much promise as a robust and inexpensive all-fiber frequency comb with potential for scaling to higher repetition frequencies.

A deep-UV optical frequency comb at 205 nm

Abstract: By frequency quadrupling a picosecond pulse train from a Ti:sapphire laser at 820 nm we generate a frequency comb at 205 nm with nearly bandwidth-limited pulses. The nonlinear frequency conversion is accomplished by two successive frequency doubling stages that take place in resonant cavities that are matched to the pulse repetition rate of 82 MHz. This allows for an overall efficiency of 4.5 % and produces an output power of up to 70 mW for a few minutes and 25 mW with continuous operation for hours. Such a deep UV frequency comb may be employed for direct frequency comb spectroscopy in cases where it is less efficient to convert to these short wavelengths with continuous wave lasers.

Optical frequency comb generation based on repeated frequency shifting using two Mach-Zehnder modulators and an asymmetric Mach-Zehnder interferometer.

Abstract: A novel approach to generating an optical frequency comb based on repeated frequency shifting is proposed and experimentally demonstrated. The frequency shifting is implemented via optical carrier suppression and single-sideband modulation using two Mach-Zehnder modulators in conjunction with a bidirectional asymmetric Mach-Zehnder interferometer with wavelength-shifted transmission spectra along the opposite directions. A theoretical analysis is performed, which is confirmed by a proof-of-concept experiment. A stable optical comb covering a spectral range of 0.18 THz is generated.

All in fiber optical frequency metrology by selective Brillouin amplification of single peak in an optical comb

Abstract: Suitable use of stimulated Brillouin amplification (SBA) effect for selective single peak amplification in an optical frequency comb is demonstrated to provide high accuracy in optical frequency metrology. A pump wave generated by a tunable laser source (TLS) is used to stimulate SBA of such optical comb along an optical fiber and selectively amplify only one single peak of the comb. Nature of SBA preserves both linewidth and absolute wavelength position of the selected comb peak. All of these features result in a simple, robust and compact all in fiber system. Relative optical frequency accuracy in the order of Hz is confirmed.

Er-doped fiber frequency comb with mHz relative linewidth.

Abstract: A low-noise fiber frequency comb is demonstrated to improve the frequency accuracy and linewidth by suppressing the phase noise caused by the nonlinear self-phase modulation as well as the amplified spontaneous emission within the Er-doped fiber amplifier The linewidth of the carrier-envelop-offset signal measures less than 19 mHz and the frequency stability well follows the reference Rb clock This achievement will facilitate the use of the fiber frequency comb for industrial applications to precision near-infrared spectroscopy, frequency calibration, optical clocks and length metrology

Low-noise RF oscillation and optical comb generation based on nonlinear optical resonator

Abstract: Techniques and devices based on optical resonators made of nonlinear optical materials and nonlinear wave mixing to generate RF or microwave oscillations and optical comb signals.

High-accuracy displacement metrology and control using a dual Fabry-Perot cavity with an optical frequency comb generator

Abstract: A displacement metrology and control system using an optical frequency comb generator and a dual Fabry-Perot cavity is developed with sub-nm accuracy. The optical frequency comb generator has expanded the displacement measurement range and the dual cavity system has suppressed the environmental fluctuation. We evaluated the absolute uncertainty of the developed displacement measurement system to be approximately 190 pm for the displacement of 14 μm and the accurate displacement control using a phase-locked loop was demonstrated with a resolution of approximately 24 pm.

Échelle spectrograph calibration with a frequency comb based on a harmonically mode-locked fiber laser: a proposal

Abstract: Details for constructing an astronomical frequency comb suitable as a wavelength reference for echelle 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 μm. The means of producing a repetition rate greater than 7 GHz and a peak optical power of ~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.

Method and device for generating a self-referenced optical frequency comb

Abstract: The invention relates to a method and to a device (1) by which a train (2, 2) of short laser pulses of a mode-coupled laser (3) is compensated with respect to the carrier envelope offset frequency of the individual lines contained in the associated frequency comb. The aim of the invention is to determine the carrier envelope offset frequency and to utilize said frequency to operate an acousto-optical frequency shifter (13). In said shifter, the uncompensated train of temporally equidistantly short laser pulses is diffracted in a first order such that the individual lines of the frequency comb are shifted by the carrier envelope offset frequency. The resulting compensated train of short laser pulses has a frequency comb, the individual lines of which are integral multiples of the repetition frequency of the individual light pulses in the train of short laser pulses.

Sinusoid signal generator for on-chip impedance spectroscopy

Abstract: Compact signal generators are a necessary component for many biomedical and chemical sensor microsystems. This paper presents a signal generator with precise digital frequency control that is 62% smaller the previous designs. The signal generator can produce analog sine waves and digital cosine waves from 4.8 Hz to 39 kHz with a SFDR greater than 99 dB. In a 0.5 µm CMOS process the total signal generator area is 361µm × 1048µm.

Optical Under-Sampling And Reconstruction Of Sparse Multiband Signals

Abstract: A scheme for reconstructing multiband signals that occupy a small part of a given broad frequency range under the constraint of a small number of sampling channels. The multirate sampling scheme (MRS) entails gathering samples at several different rates whose sum is significantly lower than the Nyquist sampling rate. The number of channels does not depend on any characteristics of a signal. The reconstruction method may or may not rely on the synchronization between different sampling channels. The scheme can be implemented easily with optical sampling systems. The optical pulses required for the under-sampling are generated by a combination of an electrical comb generator and an electro-absorption optical modulator

Low-noise synthesis of microwave and millimetre-wave signals with optical frequency comb generator

Abstract: The phase noise of a 20 GHz picosecond optical pulse train generated by a modulator-based optical frequency comb generator is analysed. The residual timing jitter is≤10 fs for Fourier frequencies from 10 Hz to 10 MHz. Photodetection of the optical pulse train provides millimetre-wave signals with similarly low residual jitter at 40, 60, and 80 GHz with applicable powers of −7.5, −10.5, and −13 dBm, respectively.

Push-pull spread spectrum clock signal generator

Abstract: A spread spectrum clock signal generator modulates a reference clock signal based on a spread spectrum frequency profile and includes a phase-lock loop for generating a spread spectrum clock signal by aligning a phase of the modulated reference clock signal with a phase of the spread spectrum clock signal. The spread spectrum clock signal generator also includes a loop modulator for modulating the spread spectrum clock signal based on the spread spectrum frequency profile. Because the spread spectrum clock signal generator modulates both the reference clock signal and the spread spectrum clock signal based on the spread spectrum frequency profile, the spread spectrum clock signal has a non-distorted frequency profile and low phase jitter.

Optical Under-Sampling and Reconstruction of Several Bandwidth-Limited Signals

Abstract: We demonstrate experimentally an optical system for under-sampling several bandwidth-limited signals with carrier frequencies that are not known apriori and can be located anywhere within a very broad frequency region between 0-18 GHz. The system is based on under-sampling asynchronously at three different sampling rates. The optical pulses required for the under-sampling are generated by a combination of an electrical comb generator and an electro-absorption optical modulator. To reduce loss and improve performance the implementation of the optical system is based on a wavelength division multiplexing technique. An accurate reconstruction of both the phase and the amplitude was obtained when two chirped signals each with a bandwidth of about 150 MHz were sampled.

Generation of a 20 GHz train of subpicosecond pulses with a stabilized optical-frequency-comb generator.

Abstract: With a modulator-based 10 GHz optical-frequency-comb generator at 1.55 μm, we report a 20 GHz repetitive train of optical pulses as short as 450 fs. The timing stability of the 20 GHz pulses, in addition to the phase for optical-comb modes, shows a strong dependence on the relative frequency detuning between the comb generator's cavity and the seed cw laser. With a new and simple scheme, the comb generator's cavity resonance was locked to a narrow-linewidth seed laser within an estimated optical-frequency range ⩽6 MHz, enabling high-fidelity 20 GHz subpicosecond pulses and stable optical-frequency-comb generation for indefinite periods.

Interferometer with frequency combs and synchronisation scheme

Abstract: The invention relates to an interferometer comprising: 1 ) a first frequency comb 2) a second frequency comb adapted to interact with the first frequency comb in order to produce interferences. 3) means for isolating the beating signal between a subset of frequency components among the frequency components of the two combs. This subset of frequency components is preferably but not necessarily a single line of the first frequency comb and a single line of the second frequency comb. 4) means for monitoring this beating signal and using it as a trigger or as a clock for the acquisition unit device recording the beating interference signal between the entire frequency components of the first and the second frequency combs.

Analog variable-frequency controller and switching converter therewith

Abstract: An analog variable-frequency controller includes a first current generator, a second current generator, a clock generator and a light/heavy load selector. The first and second current generator receive a load current signal and then output a first voltage signal and a second voltage signal, respectively. The clock generator generates a corresponding switching frequency according to the first voltage signal or the second voltage signal. The light/heavy load selector, connected with the first current generator, the second current generator and the clock generator, receives a control signal for controlling the clock generator to receive the first voltage signal or the second voltage signal. The abovementioned controller is implemented by an analog circuit, which has a lower circuit complexity, lower cost and is easy to be integrated into a switching converter.

Ultra-broad absolute-frequency tunable light source locked to a fiber-based frequency comb

Abstract: A phase-locked 110-GHz continuously-tunable optical-single-frequency generator is developed based on a phase-stabilized fiber-based comb. Stability of the optical frequencies at 1s are 3.0 and 31×10−12 at scanning speeds of 0.17 and 1 GHz/s, respectively.

An optical frequency comb generator as a broadband pulse source

Abstract: We demonstrate the generation of wavelength tunable, 0.62 ps, near transform-limited pulses at a repetition rate of 20 GHz by combining an ultra-stable optical frequency comb generator with a delay line interferometer.

Laser diode comb spectrum amplification preserving low RIN for WDM applications

Abstract: Quantum dot-based diode comb lasers enable a single multi-channel-laser source for short-reach, high-speed WDM interconnects. In this paper, we demonstrate for the first time a 15 channel low RIN comb laser with 80 GHz channel spacing. We show that all the FP modes can be simultaneously directly modulated simply by modulating the pump current at 3.2 Gb/s, which indicates that the comb laser may be an ideal broadband light source in WDM-PON applications.We demonstrate that the whole comb laser spectrum can be amplified by a quantum dot SOA without increasing the relative intensity noise (RIN). Small signal amplification factor was measured as high as 30 dB and the saturated output power was as high as 15 dBm.

Integrated optical comb source system and method

Abstract: The present invention provides a system and method for creating a coherent optical comb comprising a plurality of lasers, each laser providing an optical output channel; means for combining each optical channel output; a modulator for modulating the combined optical channel outputs, to provide a modulated signal; means for feeding back said modulated signal to said plurality of lasers, such that each laser output channel is phase and/or frequency locked with respect to at least one other of said plurality of lasers. A discrete optical comb is obtained without the need for excessively high power laser outputs and only employs a single (optional) wavelength locker for all channels.