Laser inscribed waveguide optical isolators in iron-doped lithium niobate.

There is a growing need for optical isolators that do not require a magnetic field, especially for uses such as on-chip optical devices and cold atom physics. As one approach, we propose using waveguides in photorefractive materials, such as Fe:LiNbO3, as optical isolator devices due to their unique asymmetric transmission properties that allow low loss transmission in one crystal orientation and attenuation in the flipped orientation. We utilize ultrafast laser inscription to fabricate photorefractive depressed cladding waveguides in Fe:LiNbO3 along the crystal c axis to demonstrate the operation of Fe:LiNbO3 waveguide optical isolators. We show the ability to write transmission and reflection gratings into these waveguides that provide an isolation ratio of approximately 5000:1 per cm of path length.

Continuous wave Fe2+:ZnSe mid-IR optical fiber lasers.

Today fiber lasers in the visible to near-infrared region of the spectrum are well known, however mid-infrared fiber lasers have only recently approached the same commercial availability and power output. There has been a push to fabricate optical fiber lasers out of crystalline materials which have superior mid-IR performance and the ability to directly generate mid-IR light. However, these materials cannot currently be fabricated into an optical fiber via traditional means. We have used high pressure chemical vapor deposition (HPCVD) to deposit Fe2+:ZnSe into a silica optical fiber template. These deposited structures have been found to exhibit laser threshold behavior and emit CW mid-IR laser light with a central wavelength of 4.12 µm. This is the first reported solid state fiber laser with direct laser emission generated beyond 4 µm and represents a new frontier of possibility in mid-IR laser development.

Rapidly tunable HIP treated Cr:ZnSe narrow-linewidth laser.

A narrow - linewidth, hot isostatic treated Cr:ZnSe laser was non - mechanically tuned over a total wavelength range of 195 nm by a novel organic liquid crystal etalon. The narrow - linewidth laser was continuously tuned by applying a 1 kHz square wave signal of 1 - 5 Vpp to the intracavity 9 THz nominal free spectral range liquid crystal etalon. The maximum and minimum lasing wavelengths were 2650 nm and 2455 nm, respectively, and a maximum average output power of 475 mW was recorded at 2503 nm. This work demonstrated continuous tuning, while maintaining an intrinsic narrow-linewidth ≤ 900 MHz. The results presented in this work are attributed to the low insertion loss of the liquid crystal etalon at ≤ 5%. It is believed that this is the first demonstration of purely electronic tuning of a mid-IR laser by an organic liquid crystal etalon.

Path to doubling the efficiency of mid-IR erbium lasers.

It has been experimentally shown that a Cr:ZnSe optical amplifier can be successfully used for self-amplification of the cascade Er:Y2O3 laser. This is to our best knowledge the first demonstration of an optical amplifier where both signal and pump are delivered from a single laser source. Absorption and emission spectra of the Cr:ZnSe are perfectly positioned to amplify the output of the cascade Er:Y2O3 laser, when the 1.6 µm emission of the cascade laser serves as a pump, while 2.7 µm as a signal. We have also shown that this concept is valid for any bulk or fiber cascade erbium laser.

Lasing of surface-polished polycrystalline Ho: YAG (yttrium aluminum garnet) fiber.

A polycrystalline 1.5% Ho: YAG fiber with a diameter of 31 µm was prepared. Surface roughness from grain boundary grooving was reduced by polishing, which decreased the fiber scattering coefficient from 76 m-1 to 35 m-1. Lasing tests were done on this fiber with a SF57 Schott glass cladding. Lasing was confirmed by spectrum narrowing with threshold pump power lower than 500 mW and a slope efficiency of 7%. To our knowledge, this is the first lasing demonstration from a small diameter polycrystalline ceramic fiber.

Power scaling of ultrafast laser inscribed waveguide lasers in chromium and iron doped zinc selenide.

We report demonstration of Watt level waveguide lasers fabricated using Ultrafast Laser Inscription (ULI). The waveguides were fabricated in bulk chromium and iron doped zinc selenide crystals with a chirped pulse Yb fiber laser. The depressed cladding structure in Fe:ZnSe produced output powers of 1 W with a threshold of 50 mW and a slope efficiency of 58%, while a similar structure produced 5.1 W of output in Cr:ZnSe with a laser threshold of 350 mW and a slope efficiency of 41%. These results represent the current state-of-the-art for ULI waveguides in zinc based chalcogenides.