98 research outputs found
High repetition rate fiber lasers
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 117-121).This thesis reports work in high repetition rate femtosecond fiber lasers. Driven by the applications including optical arbitrary waveform generation, high speed optical sampling, frequency metrology, and timing and frequency distribution via fiber links, low noise fiber laser sources operating at multi-gigahertz repetition rates are developed systematically. A 200 MHz fundamentally mode-locked soliton laser and a 200 MHz fundamentally mode-locked similariton laser are first developed. Intra-cavity soliton formation is recognized as the optimum route towards achieving high fundamental repetition rates compact lasers, under the limitation of realistically available pump power. A 3 GHz fundamentally mode-locked femtosecond fiber laser is developed and verifies the soliton formation theory. Techniques in external cavity repetition rate multiplications are also discussed. A theoretical model that relates the repetition rate of the soliton laser and its other physical measurable parameters is developed to guide further high repetition rate laser development.by Jian Chen.Ph.D
Sub-100 fs watt-level Kerr-lens mode-locked Yb:CaYAlO4 laser with a gigahertz repetition rate
We report a 1.04Â GHz high-power Kerr-lens mode-locked Yb:CaYAlO4 laser pumped by a single-mode fiber laser at 976Â nm. Based on a bow-tie cavity, stable unidirectional mode-locked operation is obtained with an output coupler of 1.6%. The oscillator delivers pulses with an average power of 1.46Â W and with the pulse duration of 99Â fs, which, to the best of our knowledge, is the first gigahertz-level Kerr-lens mode-locked laser based on the Yb:CaYAlO4 gain medium. We believe that the watt-level solid-state femtosecond laser at GHz would be an excellent source for developing time-resolved broadband dual-comb spectroscopy
Carrier-Envelope Offset Stabilized Ultrafast Diode-Pumped Solid-State Lasers
Optical frequency combs have been revolutionizing many research areas and are finding a growing number of real-world applications. While initially dominated by Ti:Sapphire and fiber lasers, optical frequency combs from modelocked diode-pumped solid-state lasers (DPSSLs) have become an attractive alternative with state-of-the-art performance. In this article, we review the main achievements in ultrafast DPSSLs for frequency combs. We present the current status of carrier-envelope offset (CEO) frequency-stabilized DPSSLs based on various approaches and operating in different wavelength regimes. Feedback to the pump current provides a reliable scheme for frequency comb CEO stabilization, but also other methods with faster feedback not limited by the lifetime of the gain material have been applied. Pumping DPSSLs with high power multi-transverse-mode diodes enabled a new class of high power oscillators and gigahertz repetition rate lasers, which were initially not believed to be suitable for CEO stabilization due to the pump noise. However, this challenge has been overcome, and recently both high power and gigahertz DPSSL combs have been demonstrated. Thin disk lasers have demonstrated the highest pulse energy and average power emitted from any ultrafast oscillator and present a high potential for the future generation of stabilized frequency combs with hundreds of watts average output power
Versatile silicon-waveguide supercontinuum for coherent mid-infrared spectroscopy
Infrared spectroscopy is a powerful tool for basic and applied science. The
molecular spectral fingerprints in the 3 um to 20 um region provide a means to
uniquely identify molecular structure for fundamental spectroscopy, atmospheric
chemistry, trace and hazardous gas detection, and biological microscopy. Driven
by such applications, the development of low-noise, coherent laser sources with
broad, tunable coverage is a topic of great interest. Laser frequency combs
possess a unique combination of precisely defined spectral lines and broad
bandwidth that can enable the above-mentioned applications. Here, we leverage
robust fabrication and geometrical dispersion engineering of silicon
nanophotonic waveguides for coherent frequency comb generation spanning 70 THz
in the mid-infrared (2.5 um to 6.2 um). Precise waveguide fabrication provides
significant spectral broadening and engineered spectra targeted at specific
mid-infrared bands. We use this coherent light source for dual-comb
spectroscopy at 5 um.Comment: 26 pages, 5 figure
High-repetition-rate Yb-doped lasers for frequency comb generation
The research presented in this thesis addresses the development of directly diode
pumped Yb3+:KY(WO4)2 and Yb: bre lasers, operating at several-hundred-MHz
repetition frequencies and investigates their suitability as the basis of high-e ciency,
convenient, low-cost and moderate precision optical frequency combs.
The design, construction, and characterisation of a 1042-nm 1-GHz Yb3+:KY(WO4)2
femtosecond laser is presented, achieving pulses with an average power output of 770
mW, bandwidths of 3.8 nm, and durations of 278 fs. The laser achieved an opticalto-
optical conversion e ciency and slope e ciency of 61% and 69%, respectively, and
the relative intensity noise was <0.1%. Spectral broadening of the output pulses
in a photonic crystal bre with a negative dispersion wavelength of 975 nm and a
core diameter of 3.7 m resulted in a supercontinuum with a bandwidth of 400 nm,
which was insu cient to enable f-2f referencing.
A re-designed Yb:KYW laser was demonstrated, operating at a pulse repetition
frequency of 666 MHz and producing pulses with reduced durations of 220 fs and
increased bandwidths of 5 nm, while maintaining an average output power of >700
mW. Repetition-frequency locking was implemented on this laser and had the e ect
of reducing its relative intensity noise from 1.1% to 0.5%, with limitations on the
locking stability being traced to cantilever-like vibrational modes of the mirrormount
assemblies.
A fully stabilised 1030-nm Yb: bre frequency comb operating at a pulse repetition
frequency of 375 MHz was developed. The comb spacing was referenced to
a Rb-stabilised microwave synthesiser and the comb o set was stabilised by generating
a supercontinuum containing a coherent component at 780.2 nm, which was
heterodyned with a 87Rb-stabilised external cavity diode laser to produce a radiofrequency
beat used to actuate the carrier-envelope o set frequency of the Yb: bre
laser. The two-sample frequency deviation of the locked comb was 235 kHz for an
averaging time of 50 seconds, and the comb remained locked for over 60 minutes
with a root mean squared deviation of 236 kHz
Novel optical fibre based laser sources for spectral and temporal versatility
As laser amplifiers and oscillators continue to see widespread use in all branches of science and engineering, they continue to develop in terms of operating parameters to keep pace with their applications. Importantly, the temporal and spectral characteristics of laser systems must be carefully tailored to match application requirements. This thesis reports advances in the development of laser systems, based upon optical fibre technology, which demonstrate the flexibility of optical fibre and fibre integrated devices to cover a wide range of temporal and spectral characteristics.
First, the principle of spectrally masked phase modulation for short pulse generation is explored. Here, a phase modulator is used to generate a time dependent optical frequency shift, which can be turned into an effective amplitude modulation by the introduction of an optical band pass filter. This method is combined with nonlinear compression techniques based on solitonic propagation in optical fibre to generate optical pulses with duration of a few hundreds of femtoseconds and repetition rates of tens of gigahertz.
Increasing the range of wavelengths over with doped fibre amplifier systems will operate requires the development of laser/amplifier systems based on new active dopants. To this end amplifier systems based upon bismuth activated alumosilicate fibre were evaluated. The amplifier stages were then incorporated into a master oscillator power fibre amplifier (MOPFA) scheme, demonstrating the applicability of bismuth doped silica fibre to advanced laser configurations.
Finally, the development of a novel laser source for use in fluorescent microscopy is detailed. The source was based on a gain switched diode which is amplified in a two stage Raman fibre amplifier system, subsequently frequency doubled in a periodically poled lithium tantalate crystal. Nonlinearity and optical filtering are exploited to re-shape the output pulse's temporal profile.Open Acces
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Ultra-Low Phase Noise Microwaves from Optical Signals
Continuous-wave lasers locked to high-finesse optical reference cavities are oscillators that produce ~500 THz optical signals with unprecedented stability. Indeed, sub-femtosecond fractional frequency instability at one second averaging can now be achieved. A self-referenced femtosecond laser frequency comb (FLFC) is used as a frequency divider to provide a phase-coherent link between optical and microwave domains, dividing the frequency down to the gigahertz range while also transferring the stability of the original signal. Photodetectors then convert the optical pulses into electronic signals. The resultant 10 GHz microwave signals have ultra-low phase noise below -100 dBc/Hz at 1 Hz offset, surpassing that of traditional microwave oscillators. This new approach offers significant improvement for many applications that rely on stable microwave signals, and may even create new measurement technologies otherwise unachievable with current signal sources. In reality, fundamental and technical sources of noise in each stage of the optical-to-microwave generation process limit the ultimate achievable stability of the signal. Optical reference cavities are limited by environmental effects and thermal fluctuations, and FLFC dividers suffer from intrinsic timing jitter, amplitude noise, and limited stabilization servo bandwidth. However, it is the seemingly straightforward photodetection of optical pulses that proves to be the limiting factor in the ultimate noise floor of these signals. In this thesis, I describe the noise limitations of each part of the optical-to-microwave scheme, particularly focusing on the noise limitations of photodetection. I will give a basic representation of these photodetection noise phenomena in terms of the physical behavior of optically-generated electrons in semiconductor photodiodes. The two main photodetection noise phenomena--shot noise and amplitude-to-phase conversion--will be thoroughly characterized in the context of generation of 10 GHz low phase noise signals. Finally, I will use this characterization of photodetector noise to choose optimal photodetectors and operating conditions to realize unprecedentedly low phase noise signals with a variety of optical-to-microwave generation schemes
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