Sarper Ozharar

Optical frequency combs from semiconductor lasers and applications in ultrawideband signal processing and communications

Modelocked semiconductor lasers are used to generate a set of phase-locked optical frequencies on a periodic grid. The periodic and phase coherent nature of the optical frequency combs makes it possible for the realization of high-performance optical and RF arbitrary-waveform synthesis. In addition, the resulting optical frequency components can be used for communication applications relying on direct detection, dense wavelength division multiplexing (WDM), coherent-detection WDM, optical time-division multiplexing, and optical code division multiple access. This paper highlights the recent results in the use of optical frequency combs generated from semiconductors for ultrawideband signal processing and communication applications.

Ultraflat Optical Comb Generation by Phase-Only Modulation of Continuous-Wave Light

We propose a theory and experimentally verify ultraflat comb generation by dual-sine-wave phase-only modulation. This novel approach requires a single optical element and is very practical and efficient in terms of both power budget and bandwidth. Using this approach, we have generated two optical spectra, one with 11 comb lines and 1.9-dB flatness and the other with 9 comb lines and 0.8-dB flatness.

Simultaneous optical comb frequency stabilization and super-mode noise suppression of harmonically mode-locked semiconductor ring laser using an intracavity etalon

Using an intracavity Pound-Drever-Hall technique, simultaneous optical frequency comb stabilization within /spl plusmn/3-MHz range and super-mode phase noise suppression were demonstrated for a 10-GHz harmonically mode-locked semiconductor ring laser. Together with an additional phase-lock loop, timing jitter integrated from 10 Hz to 10 MHz (5 GHz) was 63.5 fs (161 fs).

Harmonically mode-locked semiconductor-based lasers as high repetition rate ultralow noise pulse train and optical frequency comb sources

Recent experimental work on semiconductor-based harmonically mode-locked lasers geared toward low noise applications is reviewed. Active, harmonic mode-locking of semiconductor-based lasers has proven to be an excellent way to generate 10 GHz repetition rate pulse trains with pulse-to-pulse timing jitter of only a few femtoseconds without requiring active feedback stabilization. This level of timing jitter is achieved in long fiberized ring cavities and relies upon such factors as low noise rf sources as mode-lockers, high optical power, intracavity dispersion management and intracavity phase modulation. When a high finesse etalon is placed within the optical cavity, semiconductor-based harmonically mode-locked lasers can be used as optical frequency comb sources with 10 GHz mode spacing. When active mode-locking is replaced with regenerative mode-locking, a completely self-contained comb source is created, referenced to the intracavity etalon.

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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Noise characteristics are studied for a self-stabilized laser utilizing the interplay between the intracavity dispersion and the optical frequency shift. The noise suppression bandwidth of this scheme is from 0 to ~100 KHz and showed the reduction of residual timing jitter (integrated from 0.9 Hz to 1 MHz) from 2.2fs to 660 attosecond which represents, to our knowledge, the lowest timing jitter reported for an actively mode-locked laser

500-Hz Comb Linewidth

A coupled optoelectronic oscillator (COEO) based on a laser with a high finesse intracavity etalon is presented. Unlike a conventional COEO, the incorporation of the etalon produces a 10.24-GHz spaced optical frequency comb by selecting a single optical supermode. The same etalon serves as a reference for active stabilization of the optical frequencies and the pulse repetition rate via the Pound-Drever-Hall stabilization method. This results in 160 to 190 comb lines with sub-1-MHz drift and sub-10-kHz linewidth, as well as subpicosecond pulses and 350-Hz maximum deviation of the pulse repetition rate over 10 min. The completely self-contained source allows the COEO utility to extend to a host of new coherent communication and signal processing applications.

Self-Stabilization of an Actively Mode-Locked Semiconductor-Based Fiber-Ring Laser for Ultralow Jitter

We report a semiconductor-based, low-noise, 10.24 GHz actively mode-locked laser with 4.65 fs of relative timing jitter and a 0.0365% amplitude fluctuation (1 Hz to 100 MHz) of the optical pulse train. The keys to obtaining this result were the lasers high optical power and the low phase noise of the rf source used to mode lock the laser. The low phase noise of the rf source not only improves the absolute and relative timing jitter of the laser, but also prevents coupling of the rf source phase noise to the pulse amplitude fluctuations by the mode-locked laser.

Self-Stabilization of the Optical Frequencies and the Pulse Repetition Rate in a Coupled Optoelectronic Oscillator

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.

Ultralow-jitter and -amplitude-noise semiconductor-based actively mode-locked laser

We report the generation of optical pulse trains with 8.5 fs timing jitter (10 Hz to 10 MHz) from a mode-locked semiconductor laser, with a slab coupled optical waveguide amplifier used as the gain element. This is, to our knowledge, the lowest residual timing jitter reported to date from an actively mode-locked laser.