Nazanin Hoghooghi

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.

A Semiconductor-Based 10-GHz Optical Comb Source With Sub 3-fs Shot-Noise-Limited Timing Jitter and

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 <150 kHz over 30 s.

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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.

500-Hz Comb Linewidth

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.

Low Noise Optically Tunable Opto-Electronic Oscillator With Fabry–Perot Etalon

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.

Resonant cavity linear interferometric intensity modulator

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.

Optoelectronic loop design with 1000 finesse Fabry-Perot etalon

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-Pérot 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.

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

We characterize an Er:fiber laser frequency comb that is passively carrier envelope phase-stabilized via difference frequency generation at a wavelength of 1550 nm. A generic method to measure the comb linewidth at different wavelengths is demonstrated. By transferring the properties of a comb line to a cw external cavity diode laser, the phase noise is subsequently measured by tracking the delayed self-heterodyne beat note. This relatively simple characterization method is suitable for a broad range of optical frequencies. Here, it is used to characterize our difference frequency generation (DFG) comb over nearly an optical octave. With repetition-rate stabilization, a radiofrequency reference oscillator limited linewidth is achieved. A lock to an optical reference shows out-of-loop linewidths of the comb at the hertz level. The phase noise measurements are in excellent agreement with the elastic tape model with a fix point at zero frequency.

Optical Frequency Stability Measurement Using an Etalon-Based Optoelectronic Oscillator

Detection of phase-modulated optical signals without the use of an externally generated local oscillator is demonstrated using an injection-locked vertical-cavity surface-emitting laser. When it is used in a multichannel system, this technique is also capable of actively filtering out one of the phase-modulated optical carriers. The experimental results of the proposed receiver performance in a three-channel optical system are presented here. A signal-to-noise ratio of 75 dBc/Hz is obtained.

Characterization of a DFG comb showing quadratic scaling of the phase noise with frequency

We demonstrate line-by-line pulse shaping of optical comb lines separated by 6.25 GHz. An array of injection-locked VCSELs independently modulate four optical comb lines at frequencies up to 3.125 GHz, updating the pulse shape on the time scale of the pulse period.