Josue Davila-Rodriguez

Advanced Ultrafast Technologies Based on Optical Frequency Combs

This paper presents recent results in the development of novel ultrafast technologies based on the generation and application of stabilized optical frequency combs. By using novel active resonant cavity injection locking techniques, filtering, modulation and detection can be performed directly on individual components of the frequency comb enabling new approaches to optical waveform synthesis, waveform detection and matched filtering, with effective signal processing bandwidths in excess of 1 THz.

Resonant cavity linear interferometric intensity modulator

We propose an intensity modulator based on injection locking of a resonant cavity with gain that has a linear transfer function, multigigahertz bandwidth, possible optical gain, and very low V(pi). The arcsine phase response of the injection-locked resonant cavity placed in one arm of a Mach-Zehnder interferometer is the key to the true linear performance of this modulator. The first (to our knowledge) demonstration of this modulator with 5 GHz bandwidth, V(pi) of approximately 2.6 mV, and 95 dB spur-free dynamic range is reported here.

Millimeter-Wave Generation in an Optoelectronic Oscillator Using an Ultrahigh Finesse Etalon as a Photonic Filter

A Fabry-Perot etalon with a finesse of 100 000 is used as a photonic filter in a single loop optoelectronic oscillator. The etalon provides narrow bandwidth microwave filtering at harmonics of its 1.5 GHz free spectral range for oscillation in the range of 6 to 60 GHz. Fiber delays as long as 2 km are added to the loop with no spurious modes visible above the noise floor. The environmental stability of the etalon makes it suitable as a secondary reference for feedback to the optical frequency which contributes to the reduction of phase noise and long term frequency drift.

Multiheterodyne Detection for Spectral Compression and Downconversion of Arbitrary Periodic Optical Signals

Optical frequency combs are used as local oscillators for the measurement and analysis of unknown optical waveforms with periodic time domain structures. Experimental results obtained by heterodyning pulsed and phase-modulated laser sources are presented. The analysis is then extended to the heterodyning and sampling of bandlimited incoherent light sources. It is shown theoretically and experimentally that the correlations between photodetected white light at different times can generate RF interference that is sensitive to the optical phase.

Dynamic line-by-line pulse shaping with GHz update rate

We introduce a novel scheme for dynamic line-by-line pulse shaping with GHz update rates. Four lines of an optical frequency comb source are used to injection-lock four individual VCSEL, which are subsequently electrically modulated at 0.4 to 1 GHz through current modulation. This concept could be considered a completely new way of pulse shaping as the light is not simply modified, but rather regenerated with the desired properties. We also discuss an important drawback of line-by-line pulse shapers that ultimately limits the modulation speed capability.

Noise Characterization of an Injection-Locked COEO With Long-Term Stabilization

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.

Measurement of carrier envelope offset frequency for a 10 GHz etalon-stabilized semiconductor optical frequency comb

We report Carrier Envelope Offset (CEO) frequency measurements of a 10 GHz harmonically mode-locked, Fabry-Perot etalon-stabilized, semiconductor optical frequency comb source. A modified multi-heterodyne mixing technique with a reference frequency comb was utilized for the measurement. Also, preliminary results from an attempt at f-2f self-referencing measurement are presented. The CEO frequency was found to be ~1.47 GHz for the particular etalon that was used.

Frequency stability of a 10 GHz optical frequency comb from a semiconductor-based mode-locked laser with an intracavity 10,000 finesse etalon.

An optical frequency comb is constructed using a semiconductor gain medium with a fiber-coupled external cavity and stabilized to an intracavity 10,000 finesse etalon, which is temperature stabilized and held in a vacuum chamber at 10(-6)  Torr. Optical frequency stability measurements show that the comb has a reduced sensitivity to environmental fluctuations. An upper limit on the optical frequency variation of 100 kHz over >12  min of continuous operation is measured using a real-time spectrum analyzer. This measurement is limited by the linewidth of the reference source, and further measurements with a frequency counter show a fractional deviation of 2×10(-11) at 50 ms. Furthermore, out-of-band ASE rejection is shown to be >36  dB, a tenfold improvement over that of a laser with a 1000 finesse FPE.

Characterization of Semiconductor-Based Optical Frequency Comb Sources Using Generalized Multiheterodyne Detection

A spectrally efficient multiheterodyne scheme is applied for the independent measurement of the spectral phase profiles of three distinct semiconductor frequency combs. The amount of quadratic and cubic phase is quantified for each source, providing insight on the dispersive properties of the semiconductor gain and the fiberized laser cavity. This information is vital for the optimization and expansion of the spectral bandwidth of such sources.

Ultralow Noise, Etalon Stabilized, 10-GHz Optical Frequency Comb Based on an SCOW Amplifier

A slab-coupled optical waveguide amplifier (SCOWA) is used to construct a 10-GHz harmonically modelocked laser with an intra-cavity etalon that serves as a high-finesse spectral filter. The laser output is a frequency comb that is actively stabilized to the transmission peaks of the etalon through a Pound-Drever-Hall scheme. The linewidth of the individual comb-lines is ~1 kHz and the frequency instability <;300 kHz over 60 s. The output power exceeds 20 mW due to the high saturation power of the SCOWA. The residual timing jitter of the pulse-train is ~1.9 fs (1 Hz to 100 MHz). A much broader comb (~10 nm) is generated after dispersion compensation of the cavity and the output pulses are compressible to <;1 ps. A comparison of the timing jitter of the all-anomalous dispersion and dispersion compensated cavities is presented along with a previous result with a similar architecture.