Nonlinear Optical Crystals: A Complete Survey

Micro-combs: A novel generation of optical sources

Femtosecond-laser micromachining (also known as inscription or writing) has been developed as one of the most efficient techniques for direct three-dimensional microfabrication of transparent optical materials. In integrated photonics, by using direct writing of femtosecond/ultrafast laser pulses, optical waveguides can be produced in a wide variety of optical materials. With diverse parameters, the formed waveguides may possess different configurations. This paper focuses on crystalline dielectric materials, and is a review of the state-of-the-art in the fabrication, characterization and applications of femtosecond-laser micromachined waveguiding structures in optical crystals and ceramics. A brief outlook is presented by focusing on a few potential spotlights.

Optical waveguides in crystalline dielectric materials produced by femtosecond-laser micromachining

Ultrashort pulsed lasers, operating through the phenomenon of mode-locking, have had a significant role in many facets of our society for 50 years, for example, in the way we exchange information, measure and diagnose diseases, process materials, and in many other applications. Recently, high-quality resonators have been exploited to demonstrate optical combs. The ability to phase-lock their modes would allow mode-locked lasers to benefit from their high optical spectral quality, helping to realize novel sources such as precision optical clocks for applications in metrology, telecommunication, microchip-computing, and many other areas. Here we demonstrate the first mode-locked laser based on a microcavity resonator. It operates via a new mode-locking method, which we term filter-driven four-wave mixing, and is based on a CMOS-compatible high quality factor microring resonator. It achieves stable self-starting oscillation with negligible amplitude noise at ultrahigh repetition rates, and spectral linewidths well below 130 kHz.

https://researchbank.swinburne.edu.au/file/d731e9cd-3ae6-4564-9d82-af7ed13acc76/1/2012_peccianti_demonstration of a stable.pdf

Demonstration of a stable ultrafast laser based on a nonlinear microcavity

Silicon photonics has offered a versatile platform for the recent development of integrated optomechanical circuits However, silicon is limited to wavelengths above 1100 nm and does not allow device operation in the visible spectrum range where low noise lasers are conveniently available The narrow band gap of silicon also makes silicon optomechanical devices susceptible to strong two-photon absorption and free carrier absorption, which often introduce strong thermal effect that limit the devices' stability and cooling performance Further, silicon also does not provide the desired lowest order optical nonlinearity for interfacing with other active electrical components on a chip On the other hand, aluminum nitride (AlN) is a wideband semiconductor widely used in micromechanical resonators due to its low mechanical loss and high electromechanical coupling strength Here we report the development of AlN-on-silicon platform for low loss, wideband optical guiding, as well as its use for achieving simultaneous high optical quality and mechanical quality optomechanical devices Exploiting AlN's inherent second order nonlinearity we further demonstrate electro-optic modulation and efficient second-harmonic generation in AlN photonic circuits Our results suggest that low cost AlN-on-silicon photonic circuits are excellent substitutes for CMOS-compatible photonic circuits for building new functional optomechanical devices that are free from carrier effects

Aluminum nitride as a new material for chip-scale optomechanics and nonlinear optics

Based on fiber Bragg gratings (FBGs) and high nonlinear photonic crystal fiber (HN-PCF), a novel dual-wavelength erbium-doped fiber (EDF) laser is proposed and demonstrated. Experimental results show that, owing to the contributions of two degenerate four-wave mixings in the HN-PCF, the proposed fiber laser is quite stable and two output signals are uniform at room temperature. With adjustment of the attenuator, our fiber laser can selectively realize one wavelength lasing.

Stable and uniform dual-wavelength erbium-doped fiber laser based on fiber Bragg gratings and photonic crystal fiber.

We propose and demonstrate a novel room-temperature multiwavelength erbium-doped fiber laser (EDFL) with a 0.8-nm wavelength spacing based on four-wave mixing (FWM) in a length of high-nonlinear photonic crystal fiber and sampled-fiber Bragg grating. The FWM processes suppress the wavelength competition of the EDFL and increase the number of lasing wavelength. By adjusting the FWM efficiency, the number of the concurrent lasing wavelengths can be changed, and the peak power differences among the main oscillation wavelengths are less than 2.0 dB.

Multiwavelength erbium-doped fiber laser with 0.8-nm spacing using sampled Bragg grating and photonic crystal fiber

We report the passive mode-locking at harmonics of the free spectral range (FSR) of the intracavity multi-channel filter in a fiber ring laser. The laser uses a sampled fiber Bragg grating (SFBG) with a free spectral range (FSR) of 0.8 nm, or 99 GHz at 1555 nm, and a length of highly nonlinear photonic crystal fiber with low and flat dispersion. Stable picosecond soliton pulse trains with twofold to sevenfold enhancement in the repetition rate, relative to the FSR of the SFBG, have been achieved. The passive mode-locking mechanism that is at play in this laser relies on a dissipative four-wave mixing process and switching of repetition rate is realized simply by adjustment of the intracavity polarization controllers.

Passive mode locking at harmonics of the free spectral range of the intracavity filter in a fiber ring laser

A cw laser-diode-pumped Yb-doped double-clad fiber laser operating in a hybrid Q-switched regime was demonstrated. The output pulses had a duration as short as 4.2 ns, a tunable wavelength range from 1080.8 to 1142.7 nm, and a linewidth of less than 0.05 nm. Maximum peak power of ∼175 kW and single-pulse energy of 1.57 mJ were obtained.

Tunable high-peak-power, high-energy hybrid Q-switched double-clad fiber laser

A laser-diode-pumped Yb-doped double-clad fiber laser operating in a hybrid Q-switched regime has been demonstrated. With pulsed pump light and stimulated Brillouin scattering of the gain fiber as the Q-switching mechanisms, the laser generated nanosecond pulses with a stable repetition rate. A single-pulse energy of as much as 143.1 µJ with a peak power of 28.6 kW was obtained. Use of an external-cavity diffraction grating in the Littman configuration permitted tuning of the laser wavelength over a 15.7-THz range from 1080 to 1140 nm, and a linewidth of 0.04 nm over the whole tuning range was achieved.

Fuyun Lu

Papers

Stable and uniform dual-wavelength erbium-doped fiber laser based on fiber Bragg gratings and photonic crystal fiber.

Multiwavelength erbium-doped fiber laser with 0.8-nm spacing using sampled Bragg grating and photonic crystal fiber

Passive mode locking at harmonics of the free spectral range of the intracavity filter in a fiber ring laser

Tunable high-peak-power, high-energy hybrid Q-switched double-clad fiber laser

Narrow-linewidth widely tunable hybrid Q-switched double-clad fiber laser.