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This paper presents recent results in the development of novel ultrafast technologies based on the generation and application of extremely chirped optical pulses. Linearly frequency-swept mode-locked optical pulses of ns durations are generated, at the infrared telecommunications wavelength of 1.55 μm, by using chirped fiber Bragg gratings. The swept pulses appear as continuous wave signals, which completely fill the mode-locked pulse period which enables the implementation of semiconductor optical amplifying systems that completely circumvent the conventional limitation imposed by short pulse gain saturation. The use of these technologies is exemplified in a laser radar application that exploits the two characteristic coherent lengths in a chirped-pulse mode-locked laser, corresponding to the linewidth and the full lasing bandwidth, resulting in sub-mm resolution at the horizon. Finally, we show how stretched pulses can be used in a pulse shaping scheme to avoid detrimental nonlinearities associated with high power, optical pulse generation.

A hybrid mode-locked Erbium-doped fiber laser that provides very short pulse-widths while achieving high repetition rates is proposed and experimentally demonstrated. This hybrid configuration is realized by using a thin film of polydimethylsiloxane (PDMS) doped with single wall carbon nanotubes (SWCNT). This PDMS/SWCNT composite acts as a saturable absorber and is inserted within an active mode-locked laser system using angled connectors. Therefore, the effect of the PDMS/SWCNT composite is to effectively narrow the width of the pulses generated by the active system without modifying its repetition rate. A pulse-width of 730 fs was generated at a repetition rate of 4 GHz, while achieving an average output power of 4 mW. A reduction in the noise of the photodetected RF spectrum was also observed in the hybrid system.

Extensive noise analysis is presented of a semiconductor-based coupled opto-electronic oscillator using continuous-wave optical injection for the generation of an optical frequency comb with 10.24 GHz spacing. The suppression of unwanted optical axial mode groups arising from the harmonic nature of mode locking is achieved via gain competition. Amplitude noise measurements show a marked reduction in noise due to optical injection for multiple injection powers. Supermode noise spur suppression is shown to be greater than 15 dB in absolute phase noise measurements, taken using the frequency discriminator technique. Allan deviation measurements are also shown for both the free-running and injection-locked states.

A novel method of measuring the optical frequency stability of a continuous-wave (CW) laser by using an etalon-based optoelectronic oscillator is demonstrated. A 1000 finesse Fabry-Perot etalon is used as a reference which eliminates the need of using an independent optical source as a frequency reference. Using this technique, the optical frequency stability of a CW laser is measured with ~3.5-kHz optical frequency resolution at update rates of 90 Hz.

In this work, we demonstrate mode partition noise in the radio-frequency spectra of periodic signals generated using electrical pattern generators that are often used in digital optical communications and error testing. This effect makes the measurement of the amplitude modulation noise of the repetitive signal through its single sideband (SSB) power spectral density (PSD) at its fundamental frequency inaccurate. This is demonstrated for a square wave, where the dependence of the SSB PSD on the duty cycle of the signal is experimentally shown. To alleviate this ambiguity, we propose and experimentally demonstrate a photonic up-convert and down-convert method that results in invariant SSB power spectra at the signal's fundamental frequency.

In this work, a 10.287-GHz semiconductor-based harmonically mode-locked laser with 1000 finesse intracavity etalon is demonstrated. The timing jitter integrated from 1 Hz to 100 MHz (Nyquist) is 3 fs (14 fs). The optical linewidth is ~500 Hz and the optical frequency stability is

In this letter, a feedforward system is developed for control of a quasi-continuous-wave (CW) chirped source. The goal of this study is to improve the uniformity of the temporal profile of a quasi-CW chirped laser source. The chirped spectrum input to the system is dynamically flattened using a feedforward scheme having bandwidth in excess of 1 GHz, resulting in more than three times reduction on the contrast of the input spectrum. A uniform chirped spectrum laser source can be used in time-stretched photonic analog-to-digital conversion, as part of laser radar system, or for optical coherence tomography.

In this letter, we introduce a novel interferometric method for dynamic extinction ratio measurement of temporally demultiplexed pulses. A high extinction intensity modulator is used in order to temporally demultiplex the pulse train. The resulting extinction ratio is measured to be 44 dB. Our method has a dynamic range of ~60 dB. To our knowledge, this is the highest dynamic extinction ratio measurement method reported to date for high-speed optical modulators.

The RF stability of a COEO subject to external optical injection is measured as a function of injection frequency instability. Allan Deviation measurements show a distinct dependence of RF output on injection frequency.

We compare the performance of two optical frequency comb sources containing intra-cavity Fabry-Perot etalons but differing gain media. Both 10 GHz harmonically mode-locked, fiberized lasers are stabilized via the etalon and active feedback.

Self-phase modulation in fiber amplifiers can significantly degrade the quality of compressed pulses in chirped pulse amplification systems. Parabolic pulses with linear frequency chirp are suitable for suppressing nonlinearities, and to achieve high peak power pulses after compression. In this paper, we present an active time domain technique to generate parabolic pulses for chirped pulse amplification applications. Pulses from a mode-locked laser are temporally stretched and launched into an amplitude modulator, where the drive voltage is designed using the spectral shape of the input pulse and the transfer function of the modulator, resulting in the generation of parabolic pulses. Experimental results of pulse shaping with a pulse train from a mode-locked laser are presented, with a residual error of less than 5%. Moreover, an extinction ratio of 27 dB is achieved, which is ideal for chirped pulse amplification applications.

This work presents an extensive investigation of the performance characteristics of a semiconductor-based Theta cavity design laser with an intra-cavity Fabry-Perot etalon operating at 100 MHz repetition rate. The Theta laser being an external cavity harmonically mode-locked semiconductor laser exhibits supermode noise that impairs its performance. A fiberized Fabry-Perot periodic filter inserted within the Theta laser cavity mitigates the contribution of the supermode noise to the pulse-to-pulse energy variance by 20 times. The laser has both a compressed output with picosecond pulse duration and a uniform intensity quasi-CW linearly chirped pulse output with 10 nm bandwidth. Long-term stability is attained by referencing the cavity length to the etalon using an intra-cavity Hansch-Couillaud locking scheme.

A CW injection locked Coupled Opto-Electronic Oscillator (COEO) is presented with a 10.24 GHz spaced optical frequency comb output as well as a low noise RF output. A modified Pound-Drever-Hall scheme is employed to ensure long-term stability of the injection lock, feeding back into the cavity length to compensate for cavity resonance drifts relative to the injection seed frequency. Error signal comparison to an actively mode-locked injection locked laser is presented. High optical signal-to-noise ratio of ~35 dB is demonstrated with >20 comblines of useable bandwidth. The optical linewidth, in agreement with injection locking theory, reduces to that of the injection seed frequency

An optical comb source based on a slab-coupled optical waveguide amplifier (SCOWA) is presented. The laser is harmonically mode-locked at 10.287 GHz repetition rate and stabilized to an intra-cavity Fabry-Perot etalon via Pound- Drever-Hall locking. The Fabry-Perot etalon serves as a reference for the optical frequency of the comb-lines and suppresses the fiber cavity modes to allow only a single longitudinal mode-set to oscillate, generating a frequency comb spaced by the repetition rate. The pulse-to-pulse timing jitter and energy fluctuations are < 2 fs and < 0.03%, respectively (integrated from 1Hz to 100 MHz). Fundamental to this result is the incorporation of the SCOW amplifier as the gain medium and the use of an ultra-low noise sapphire-loaded cavity oscillator to mode-lock the laser. The SCOWA has higher saturation power than commercially available gain media, permitting higher intra-cavity power as well as available power at the output, increasing the power of the photodetected RF tones which increases their signal-to-noise ratio. A high visibility optical frequency comb is observed spanning ~3 nm (at -10 dB), with optical SNR > 60 dB for a cavity with no dispersion compensation. Initial results of a dispersion compensated cavity are presented. A spectral width of ~7.6 nm (-10 dB) was obtained for this case and the pulses can be compressed to near the transform limit at ~930 fs.

We report the fabrication of a saturable absorber made of a novel polymer SU8 doped with Single Wall Carbon Nanotubes (SWCNTs). A passive mode-locked ring cavity fiber laser was built with a 100 μm thick SU8/SWCNT film inserted between two FC/APC connectors. Self-starting passively mode-locked lasing operation was observed at 1572.04 nm, with a FWHM of 3.26 nm. The autocorrelation trace was 1.536 ps corresponding to a pulse-width of 871 fs. The time-bandwidth product was 0.344, which is close enough to transform-limited sech squared pulses. The repetition rate was 21.27 MHz, and a maximum average output power of 1 mW was also measured.

This work discusses the development of a frequency chirped, low repetition rate, semiconductor based mode-locked laser having reduced noise over previous demonstrations. Specifically, we present a major upgrade on the 100 MHz harmonically mode-locked Theta (Θ) laser cavity design in the form of the introduction of an intra-cavity fiberized Fabry-Perot etalon. The initial demonstration of the Theta cavity design offered improved energy per pulse and a linearly chirped pulse output compared to conventional cavity designs. Nonetheless, it suffered from pulse-to-pulse timing and energy noise. The noisy operation arises from the harmonic nature of the laser. To mitigate this effect we have inserted a fiberized etalon within the laser cavity. The intra-cavity etalon stores and inter-mixes the pulses of the harmonically mode-locked laser, as well as enforces lasing on a single optical mode-set from the multiple interleaved sets supported by the mode-locked laser due to its harmonic nature. This leads to the generation of a stable optical frequency comb with 100 MHz spacing and the suppression of the RF super-mode noise spurs, which results in a reduction of the laser noise. Due to fiber length drift in both the fiberized laser cavity and the fiberized etalon, a long-term stabilization scheme is necessary. An intra-cavity Hansch - Couillaud scheme is employed. The laser outputs chirped pulses with 10 nm of bandwidth. This work provides an in depth analysis of both the development of the Theta cavity with the intra-cavity etalon and the performance of the developed laser system.

A hybrid mode-locked fiber laser was built by using a PDMS/SWCNTs film as a saturable absorber. The system allows for a high repetition rate of 4 GHz, while achieving pulse widths of 730 fs.

A 10 GHz mode-locked laser based on a Slab-Coupled Optical Waveguide Amplifier with an intra-cavity etalon is presented. The timing jitter is ∼2.3 fs (10 Hz to 100 MHz), the lowest reported to our knowledge.

A novel temporal pulse shaping technique for chirped pulses is presented. Parabolic pulses with residual error of less than 5% and signal to noise ratio of 27dB is achieved, ideal for chirped pulse amplification applications.

We present a semiconductor-based laser cavity operating in the extreme chirped pulse amplification regime using a 100 MHz fiberized Fabry-Perot etalon. An intra-cavity modified Hansch-Couillaud scheme ensures long-term operation. The laser exhibits supermode noise spur suppression and a semiconductor-based optical frequency comb is generated.

A low noise optically tunable optoelectronic oscillator (OEO) scheme which uses a 1000 finesse Fabry-Perot etalon as the mode selector is demonstrated. The dependency of input optical frequency on RF frequency is theoretically analyzed and experimentally shown. The etalon-based OEO is compared with the standard OEO with RF filter and the results show higher RF frequency stability and lower phase noise. A single optical side band modulation technique is also used to improve the spectral purity and the results are compared with the double side band modulation technique. Low noise operation of an optically tunable OEO is achieved by using optical single side band modulation.

An optically tunable optoelectronic oscillator(OEO) scheme with 1000 finesse intracavity Fabry-Perot etalon is demonstrated at 10GHz. Optical single side band modulation is implemented and resulted in 10–20dB higher SNR than standard dual side band modulation.

We characterize the properties of a 100 MHz fiberized etalon. Sub-Hz (10−8) precision is attained for the FSR measurement for both polarization eigenstates. The finesse is measured with 3 % precision and the acoustic noise frequency response of the etalon is experimentally measured.

In this work a narrow linewidth (1 kHz) laser source is used to measure the free spectral range of a fiberized Fabry-Perot etalon with sub-Hz accuracy (10(-8)). A previously demonstrated technique based on the Pound-Drever-Hall error signal is improved in accuracy by the use of a narrow linewidth laser swept in frequency via an acousto-optic modulator, or single sideband generation. The sub-Hz (10(-8)) accuracy attained enables the characterization of both the long-term drift and the polarization dependence of the free spectral range of the fiberized etalon.

The generation of optical pulses with parabolic time intensity profiles is experimentally demonstrated. A Mode Locked Laser (MLL) that generates near transform limited pulses with a gaussian optical spectrum are temporally stretched using a linearly chirped fiber Bragg grating. The temporal intensity profile of the stretched pulses matches the optical spectrum of the laser due to frequency-to-time mapping. An amplitude modulator is driven by a carefully designed voltage signal to result in parabolic pulses. Experimental results of pulse shaping with a MLL input source are presented, and show good agreement with modeling results. Parabolic pulse generation using a CW laser source is also demonstrated and a deviation of less than 3% from an ideal parabola is observed.

A lidar technique employing temporally stretched, frequency chirped pulses from a 20 MHz mode locked laser is presented. Sub-millimeter resolution at a target range of 10.1 km (in fiber) is observed. A pulse tagging scheme based on phase modulation is demonstrated for range resolved measurements. A carrier to noise ratio of 30 dB is observed at an unambiguous target distance of 30 meters in fiber.

A Fabry-Perot etalon is inserted into a semiconductor-based laser cavity operating at the chirped pulse amplification regime. The laser output exhibits supermode noise spur suppression and a semiconductor-based optical frequency comb is generated.

Measurement of the FSR of an etalon having finesse of 1000 with 7 digits of accuracy or 2.5 kHz. A modified PDH technique is used in conjunction with a frequency swept, narrow-linewidth CW laser.

We measure the AM Noise of periodic electrical signals in the frequency domain. Mode partition noise is found to be detrimental and dependent on the signal's duration. A photonic technique is presented alleviating this ambiguity.

A 10.287 GHz optoelectronic oscillator is demonstrated which uses a 1000 finesse Fabry-Perot etalon as the mode selector instead of an RF filter. The new OEO has higher RF frequency stability and lower phase noise.

A low noise, frequency stabilized, semiconductor based, 10.287 GHz actively mode-locked laser is reported with optical linewidth ≪1 kHz, optical frequency instability of ∼150 kHz and integrated timing jitter (1Hz–100MHz) of 3fs.

A lidar system with a resolution of 400um and a range of 10 km in fiber is demonstrated using temporally stretched, frequency chirped pulses from a mode-locked laser.

An optical frequency stabilized, coupled optoelectronic oscillator(COEO) with 1000 finesse intracavity etalon is presented with 10.287 GHz optical comb separation, ≪1kHz optical linewidth and ≫121dBc/Hz RF supermode noise spur suppression.

In this work we present a method for improving the uniformity of the optical spectrum or the temporal intensity profile of a quasi-CW, linearly chirped laser source covering the time interval between subsequent pulses. A novel laser cavity design, referred to as the Theta (Θ) cavity, provides linearly chirped pulses directly from the laser oscillator that having non-uniform optical spectrum, that is mapped into the temporal intensity profile of the pulse, due to the frequency-to-time mapping nature of this cavity design. The system developed in this work has been designed to improve the spectral and temporal intensity profile of lasers for photonic signal processing. A fiberized feed-forward system is implemented to reduce variations in the temporal intensity profile, or the optical spectrum due to the time-to-frequency mapping, input to the system. In the feedforward scheme presented, the quasi-CW pulse train generated from the laser is split and part of it is photodetected, while the electrical signal generated alters the transmittance of the second part of the input as it goes through an amplitude modulator, resulting in increase in the uniformity of the signal. The contrast of the optical spectrum of a chirped pulse at input to the system is improved from 51% to 16%, or 3.1 times.

Mode-locked lasers have applications in signal processing and communications such as analog to digital conversion, arbitrary waveform generation and wavelength division multiplexing. For such applications low noise and phase coherent frequency stabilized optical combs are needed. In this work we report a low noise, Pound-Drever Hall frequency stabilized, semiconductor mode-locked laser at 10.287GHz centered at 1550nm with 1000-Finesse sealed, ultralow insertion loss intracavity etalon. The output optical power of the mode locked laser is ~5mW.

A semiconductor based, optically injection-locked coupled optoelectronic oscillator with long term feedback stabilization, operating at 10.24 GHz is presented. Optical supermode suppression, RF supermode noise spur suppression by 11 dB, and linewidth reduction is observed.

A chirped fiber Bragg grating with a dispersion of 1651ps/nm is used to generate temporally stretched, frequency chirped pulses from a passively mode locked fiber laser that generates pulses of ~1ps (FWHM) duration at a repetition rate of 20MHz with 3.5mW average power (peak power of 175W). The use of a chirped fiber Bragg grating enables the generation of temporally stretched pulses with low peak power so that non-linear effects in the fiber can be avoided. A fiber based interferometeric arrangement is used for interfering a reference signal with the reflected signal from the target to realize a coherent heterodyne detection scheme. In the RF domain, the detected heterodyne beat frequency shifts as the target distance is changed. A round trip target distance of 14km in air is simulated using 9.3km of optical fiber and a resolution of less than a millimeter is observed.

A temporally stretched, frequency chirped pulsed lidar system employing a phase modulation heterodyne scheme for range resolved measurements with sub-millimeter resolution at a range of 4.65km with 30dB dynamic range is demonstrated.

We report a low noise, frequency stabilized, semiconductor based, 10.287 GHz actively mode-locked laser with 1000 finesse intracavity etalon, with a timing jitter (1Hz - 100MHz) of 3 fs and optical linewidth

A semiconductor low-noise, sub-100MHz repetition rate laser source is developed by time demultiplexing a harmonically mode-locked 2.56GHz, SCOWA-based mode-locked laser to the cavity fundamental frequency. The laser source is suitable for time-stretched photonic ADC.

A feedforward system is developed for the control of a quasi continuous wave chirped source developed for photonic analog-to-digital conversion. The input chirped spectrum is dynamically flattened by the feedforward system having 1.4 GHz bandwidth.

An eXtreme Chirped Pulse Oscillator (XCPO) implemented with a Theta cavity and based on a semiconductor optical amplifier (SOA) is presented for generating 10 ns frequency-swept pulses and 3.6 ps compressed pulses directly from the oscillator. In this experiment, we show the two distinct characteristics of the XCPO which are the scalability of the output energy and the mode-locked spectrum. By using these characteristics, we obtain a pulse energy of 58.4 pJ from the stretched pulse and a mode-locked optical bandwidth of 14.6 nm (10 dB) directly from the oscillator. The laser cavity design allows for low repetition rate operation100 MHz, as well. The cavity, significantly, reduces nonlinear carrier dynamics, integrated self phase modulation (SPM), and fast gain recovery in an SOA. Due to the laser's ability to generate directly frequency-swept pulses from the oscillator, this oscillator can be used for high speed frequency-swept optical coherence tomography (OCT) and time-stretched photonic analog to digital converters (P-ADC).

An alternative to the sub-100 MHz repetition rate laser source is explored. A low noise SCOWA-based harmonically mode-locked laser is developed and temporally demultiplexed to twice the cavity fundamental resulting in a 40 MHz pulse train.

An eXtreme Chirped Pulse Oscillator (XCPO) implemented with a Theta cavity and based on a semiconductor optical amplifier (SOA) is presented for generating 10ns frequency-swept pulses and 3.6ps compressed pulses directly from the oscillator. In this experiment, we show the two distinct characteristics of the XCPO which are the scalability of the output energy and the mode-locked spectrum. The laser cavity design allows for low repetition rate operation

We demonstrate an XCPO with 10 ns stretched pulse duration. Because the pulse duration is longer than the carrier life time of SOA, the pulse energy is linearly proportional to the stretch ratio.

The development of a TEA HF (SF6:C3H8:He) oscillator-double amplifier laser system with one common switching element and one common power supply unit is presented. All three cavities employ the conventional charge transfer excitation circuit and the surface corona discharge preionization scheme. For each amplifier the small signal gain coefficient go and the saturation energy density Es are determined and their dependence on the charging voltage and the active gas concentrations is investigated. The performance characteristics of the laser system i.e. maximum output energy, pulse duration, spectral and beam profile evolution through all three stages of the system are given. Additionally, beam propagation measurements through a 150cm long, 250μm core diameter GeO2 mid-IR fiber are presented.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We report the fabrication of a saturable absorber based on SU8 single wall carbon nanotube (SWCNT) composite material. Thin films with a controllable thickness can be fabricated using a simple and reliable process. These films can be inserted between two FC/APC connectors in order to have an inline saturable absorber. A passive mode-locked laser was built by interleaving the fiberized saturable absorber in an erbium-doped fiber (L-band) ring cavity laser. The laser produces 871 fs pulses with a repetition rate of 21.27 MHz and a maximum average power of 1 mW.

A semiconductor-based mode-locked laser source with low repetition rate, ultralow amplitude, and phase noise is introduced. A harmonically mode-locked semiconductor-based ring laser is time demultiplexed at a frequency equal to the cavity fundamental frequency (80MHz), resulting in a low repetition rate pulse train having ultralow amplitude and phase noise, properties usually attributed to multigigahertz repetition rate lasers. The effect of time demultiplexing on the phase noise of harmonically mode-locked lasers is analyzed and experimentally verified.

A 10.287 GHz optoelectronic oscillator is experimentally demonstrated that uses a 1000 finesse Fabry-Perot etalon as the mode selector instead of an rf filter. The results are compared with a standard optoelectronic loop with an rf filter. The substitution of the rf filter with the optical filter results in a higher rf stability and lower phase noise.