Arshad K. Mairaj

Nonsilica glasses for holey fibers

The authors of this paper investigated the thermal properties and optical properties of typical nonsilica glasses, including viscosity, surface tension, thermal conductivity, transmission, linear and nonlinear refractive index, and fiber attenuation in order to judge the feasibility of using nonsilica glasses as the background material of holey fibers (HFs). Novel techniques were presented to fabricate the nonsilica glass microstructured fiber preforms. Examples of fabricated nonsilica glass HFs with various promising optical applications were finally exhibited.

Development of channel waveguide lasers in Nd3+-doped chalcogenide (Ga:La:S) glass through photoinduced material modification

We report the development of a waveguide laser source in a neodymium-doped chalcogenide (Ga:La:S) glass. Channel waveguide structures were directly written via above band gap (=244 nm) illumination provided by a focused UV-laser beam with fluencies 1.5–150 J/cm2. Effects of photoinduced material modification in the form of surface compaction and photodensification were evident. Characterization revealed a low threshold waveguide laser with emission at 1075 nm and slope efficiency of 17%. The active device was spatially single mode and exhibited laser operation with 8.6 mW peak power and attenuation <0.5 dB cm–1.

Laser performance and spectroscopic analysis of optically written channel waveguides in neodymium-doped gallium lanthanum sulphide glass

We present a spectroscopic analysis and laser characterization of optically written waveguides in neodymium-doped gallium lanthanum sulphide (Nd/sup 3+/-Ga:La:S) chalcogenide glass. Uniform channel waveguides were fabricated in Nd/sup 3+/-Ga:La:S by exposure to radiation from a focused UV-laser beam (/spl lambda/=244 nm), producing a refractive index change /spl utri/n/spl ap/+10/sup -3/. The observed laser performance and fluorescence decay were in good agreement with values calculated from a spectroscopic analysis of 85 /spl mu/s for the /sup 4/F/sub 3/2/ lifetime and 5.9/spl times/10/sup -20/ cm/sup 2/ for the emission cross section at 1075 nm. Low threshold laser operation with emission at 1075 nm and a slope efficiency of 17% is demonstrated. The active device is spatially single mode and exhibits up to 8.6 mW of output power and propagation losses of <0.5 dBcm/sup -1/. Waveguide fabrication, photoinduced effects, and optical characterization in terms of spectroscopy, laser performance, and device attenuation are discussed.

Fabrication and characterization of continuous wave direct UV (/spl lambda/=244 nm) written channel waveguides in chalcogenide (Ga:La:S) glass

Gallium lanthanum sulphide (Ga:La:S) optical glass is an interesting material for both fiber and planar technologies, as it offers possibilities for a wide array of devices suitable for use in both nonlinear applications and as IR lasers. Direct laser writing into this glass has yielded low-loss single-mode channel waveguides. Samples were exposed to above-bandgap illumination of focused UV (/spl lambda/=244 nm) light at varying intensities (I/sub UV/=1.5-90 kW/cm/sup 2/) and scan velocities (V/sub SCAN/=0.005-0.067 m/s). The exposed regions were evaluated through atomic force microscopy (AFM), and surface compaction (0.3-3.6 /spl mu/m) was observed. Sample topography was examined using a scanning electron microscope (SEM) with analysis of chemical changes within the exposed regions performed with energy-dispersive X-ray microscopy (EDAX). Waveguide attenuation was measured to be 0.2/spl plusmn/0.1 dB/cm at 1.3 /spl mu/m with a positive change in refractive index (/spl Delta/n=10/sup -3/). The chemical mechanism for these photo-induced changes with resulting photodensification has been correlated with a relative increase in the lanthanum content within the waveguide core.

Inverted deposition and high-velocity spinning to develop buried planar chalcogenide glass waveguides for highly nonlinear integrated optics

We report on buried planar waveguides in a highly nonlinear infrared transmitting chalcogenide glass, fabricated using a combination of inverted deposition of the molten glass phase and high-velocity spinning. Films of gallium lanthanum sulphide (Ga:La:S) glass were deposited onto an expansion coefficient matched Ga:La:S cladding substrate. These amorphous films, with an optimized composition designed to be resistant against crystallization, were observed to have an excellent interface quality and uniformity. The designed planar chip had a buried core, 6μm thick in the vertical direction, in single-mode operation at 1.064μm and a measured propagation loss of <0.2dBcm−1. Through this technique waveguides from Ga:La:S glass, a highly versatile optical semiconductor material, can potentially be used in nonlinear applications as well as provide passive and active integrated optic functionality into the infrared beyond 5μm.

Advances in gallium lanthanum sulphide glass for optical fiber and devices

The advantages of gallium lanthanum sulphide (GLS) based glass over other competing glasses for active and infrared applications are evident through its low-phonon energy, high rare-earth solubility, high transition temperature and non-toxicity. However this glass often devitrifies during fibre drawing due to a small separation between the crystallisation and fibre thawing temperatures. Improving GLS fabrication technology may hold the key to achieving practical optical waveguide devices. In this paper, we describe the cunent GLS research status, methods ofimproving glass purity and our directions toward alternatives to traditional fibre technology, in particular planar channel waveguides and holey or microstructured fibres.

Channel waveguide lasers in a lead silicate glass fashionedusing the extrusion technique

We report the use of extrusion for the development of planar buried channel waveguide lasers in a neodymium-doped lead-silicate glass host. The extrusion process was performed at a constant die temperature of 555±10°C, an applied pressure of 1850Ncm−2 and a viscosity of 107.8–107.2P, respectively. A planar substrate, 10mm in length cut from the extruded product, had four buried waveguides each with a core size of 8 by 2.5μm in the horizontal and vertical directions. Optical characterization of this waveguide revealed single-mode laser operation at 1058nm with a slope efficiency of 40% for an absorbed power of 59.3mW. The measured device propagation loss was ∼0.3dBcm−1.

Extruded channel waveguides in a neodymium-doped lead-silicate glass for integrated optic applications

We report on the development of channel waveguides in a lead–silicate glass through the extrusion technique. An extruded glass slab with four imbedded fibers each with core size of 8 by 2.5 μm in the horizontal and vertical directions was manufactured. These neodymium-doped channel waveguides were in single-mode operation at 808 nm and had attenuation of 0.1 dB cm−1 at 1.06 μm. The measured 4F3/2 lifetime of 488 μs and emission cross section of 2.5×10−20 cm2 were in good agreement with reported values. The integration of multiple glass variants into a single compact platform is presented as a manufacturing route for complex integrated optical waveguides.

Using the extrusion technique to fashion amorphous channel waveguide lasers

We report the first neodymium-doped amorphous channel waveguide laser through extrusion. Single-mode operation was observed at 1058 nm for a 10 mm long channel waveguide. An output power of 13.3 mW with 36% slope efficiency was measured.

Toward compact optical waveguide devices for active infrared applications

The infrared (IR) spectrum is of significant importance in many defence applications including free-space communication, thermal imaging and chemical sensing. The materials used in these applications must exhibit a number of suitable properties including mid-IR transparency, rare-earth solubility and low optical loss. When moving towards miniaturised optical devices one tends to adopt the concepts introduced by integrated optics; multiple devices operating harmoniously on a single photonic chip. Our work focuses on the use of a laser to directly write into a novel chalcogenide glass to engineer optical waveguide devices. Our material of choice is gallium lanthanum sulphide (Ga:La:S) glass, an exceptional vitreous chalcogenide material possessing these aforementioned properties as well as a broad range of other properties. These Ga:La:S glasses have a wide transmission window between 0.5 to 10 μm. Furthermore, these low-phonon energy glasses have a high transition temperature (Tg = 560°C), high refractive index, the highest reported non-linearity in a glass, excellent rare-earth solubility with well documented near-mid IR spectroscopic properties. We report on low loss single-mode active channel waveguides in Ga:La:S glass engineered through direct laser writing (λ= 244 nm). We discuss laser operation at 1.075 µm (neodymium) and IR emission at 1.55, 2.02 and 2.74 µm (erbium) from these waveguides.