The Nonlinear and Ultrafast Fiber Optics Laboratory specialize in nonlinear optics and photonic crystal fibers, and their use for infrared frequency metrology. This year we have made significant contributions to these fields. In addition, we have started a new project to develop a molecular gas laser in a hollow core photonic crystal fiber.
Mid-infrared gas filled photonic crystal fiber laser based on population inversion
We demonstrate for the first time an optically pumped gas laser based on population inversion using a hollow core photonic crystal fiber (HC-PCF). The HC-PCF filled with 12C2H2 gas is pumped with ~ 5 ns pulses at 1.52 μm and lases at 3.12 μm and 3.16 μm in the mid-infrared spectral region. The maximum measured laser pulse energy of ~ 6 nJ was obtained at a gas pressure of 7 torr with a fiber with 20 dB/m loss near the lasing wavelengths. While the measured slope efficiencies of this prototype did not exceed a few percent due mainly to linear losses of the fiber at the laser wavelengths, 25% slope efficiency and pulse energies of a few mJ are the predicted limits of this laser. Simulations of the laser’s behavior agree qualitatively with experimental observations.
Phase-stabilized 167 MHz Repetition Frequency Carbon Nanotube Fiber Laser Frequency Comb
A frequency comb generated by a 167 MHz repetition frequency erbium-doped fiber ring laser using a carbon nanotube saturable absorber is phase-stabilized for the first time. Measurements of the in-loop phase noise show an integrated phase error of 0.35 radians, which is a factor of three larger than that of another fiber frequency comb based on a figure-eight laser. For further investigation of stability, we heterodyned the carbon nanotube laser comb with a 1532 nm CW laser stabilized to a ν1+ν3 overtone transition of an acetylene-filled kagome photonic crystal fiber reference. These measurements resulted in an upper limit on the comb stability of 1.2x10-11 in 1 s. The carbon nanotube laser frequency comb offers much promise as a robust and inexpensive all-fiber frequency comb with further potential for scaling to higher repetition frequencies.
10 kHz accuracy of an optical frequency reference based on 12C2H2-filled large-core kagome photonic crystal fibers
Saturated absorption spectroscopy reveals the narrowest features so far in molecular-gas-filled hollow-core photonic crystal fiber. The 48 - 68 μm core diameter of the kagome-structured fiber used here allows for 8 MHz full-width half-maximum sub-Doppler features, and its wavelength-insensitive transmission is suitable for high-accuracy frequency measurements. A fiber laser is locked to the 12C2H2 n1+n3 P(13) transition inside kagome fiber, and compared with frequency combs based on both a carbon nanotube fiber laser and a Cr:forsterite laser, each of which are referenced to a GPS-disciplined Rb oscillator. The absolute frequency of the measured line center agrees with those measured in power build-up cavities to within 9.3 kHz (the 1 σ error bar). The fractional stability is less than 1.2´10-11 at 1 s averaging time.
Parabolic Pulse Compression in a Low-Dispersion Slope Photonic Bandgap Fiber
Sub-33 fs, 1 nJ pulses are generated in a Er-doped fiber amplifier composed of a normal dispersion gain fiber, a low dispersion slope photonic crystal fiber, and a highly nonlinear fiber.
A gas lasing medium offers advantages over solid-state materials for high power laser applications that require high electrical-to-optical power efficiency. Gas lasers offer higher power efficiency due to, in part, the higher quantum efficiency of the gas. In addition, gas lasers have superior heat management properties that facilitate demonstrations of continuous wave powers in the megawatts. Unfortunately, the drawbacks of a gas medium are in containment, efficiently pumping the lasing transition, and the small gain per unit length. These drawbacks have lead to commercial systems that favor solid-state lasers, which have tended to supplant gas lasers in many research and industrial applications. A prime example is the replacement of bulky, power-consuming argon ion lasers by small semiconductor-pumped solid-state green lasers for many scientific and industrial applications. Currently, solid state lasers offer a more compact and reliable laser at the sacrifice of lower quantum efficiency.
We wish to create a new class of lasers through the amalgamation of hollow-fiber and optically-pumped-gas technologies. The new laser will have a molecular gas lasing medium in a hollow fiber that will be optically pumped using a fiber-coupled laser diode or a fiber laser. This novel laser will have the advantages of quantum efficiency of a gas medium with laser cavity that is compatible with fiber-coupled laser diodes and fiber components. Applications for lasers that that exhibit efficient electrical-to-optical power transfer are in laser ranging and missile defense. This program will also help to develop new technology for possible industrial applications such as precision machining and cutting. The results from this research will help develop high-power gas lasers in the infrared atmospheric transmission windows (3.5 to 4.1 mm).
Stability of Optical Frequency References Based on Acetylene-filled Kagome-structured Hollow Core Fiber
A continuous-wave laser has been stabilized to an acetylene transition inside kagome photonic crystal fiber. Stability as measured with a carbon nanotube fiber laser frequency comb to is better than 1x10-11 at 10 s.
Pulse Compression Using Hollow Core Photonic Bandgap Fiber
Infrared frequency combs based on mode-locked erbium-doped fiber lasers typically require an external amplifier since the pulses directly from the laser have insufficient peak power to generate an octave-spanning supercontinuum for self-referencing. Here we implement a unique, all-fiber erbium-doped fiber amplifier that uses hollow-core photonic bandgap fiber for pulse compression. Through a combination of experiment and numerical simulations we have demonstrated temporal compression in the hollow-core photonic bandgap fiber, thus increasing the pulse’s peak power.
Electric Arc Splicing Hollow Hollow Core Photonic Bandgap Fiber to Single Mode Fiber
The difficulty of fusion splicing hollow-core photonic bandgap fiber (PBGF) to conventional step index single mode fiber (SMF) has severely limited the implementation of PBGFs. To make PBGFs more functional we have developed a method for splicing a hollow-core PBGF to a SMF using a commercial arc splicer. A repeatable, robust, low-loss splice between the PBGF and SMF is demonstrated. By filling one end of the PBGF spliced to SMF with acetylene gas and performing saturation spectroscopy, we determine that this splice is useful for a PBGF cell.
Phase Stabilization of a Cr:Forsterite Mode-Locked Laser
The frequency comb from a prism-based Cr:forsterite laser has been frequency stabilized using intracavity prism insertion and pump power modulation. Absolute frequency measurements of a CW fiber laser stabilized to the P(13) transition of acetylene demonstrate a fractional instability of ~2×10-11 at a 1 second gate time, limited by a commercial GPS disciplined rubidium oscillator. Additionally, absolute frequency measurements made simultaneously using a second frequency comb indicate relative instabilities of 3×10-12 for both combs for a 1 second gate time. Estimations of the carrier envelope offset frequency linewidth based on relative intensity noise and the response dynamics of the carrier envelope offset to pump power changes confirm the observed linewidths.
Work as a Postdoctoral Researcher at the National Institute of Standards and Technology (NIST) in Boulder, Colorado
Work as a Graduate Student for Dr. Stephen Ralph (ECE) at Georgia Institute of Technology
|This site was last updated 01/04/11.|