Jens Engholm Pedersen

PECVD grown multiple core planar waveguides with extremely low interface reflections and losses

A novel and generic method for fabricating silica-on-silicon planar lightwave circuits with cores composed of two or more different types of glasses is described. The basic process technologies used are silane/germane/nitrous-oxide based plasma enhanced chemical vapor deposition and fluorine based reactive ion etching. Very high-quality interfaces between the different core glasses are obtained with interface losses as low as 0.022/spl plusmn/0.012 dB and reflection levels below -80 dB. This technique adds flexibility and ease to the design of complex silica planar waveguide components, allowing, e.g., independent optimization of amplifying and passive sections in lossless devices based on erbium-doped planar waveguides.

Continuous anneal method for characterizing the thermal stability of ultraviolet Bragg gratings

We present a new method for determining the long-term stability of UV-induced fiber Bragg gratings. We use a continuous temperature ramp method in which systematic variation of the ramp speed probes both the short- and long-term stability. Results are obtained both for gratings written in D2 loaded and nonloaded fibers. The results for the nonloaded fibers are in good agreement with those previously obtained. Precise predictions of the grating decay were made. We find good agreement with a broad trap energy distribution where the defects with the lowest energy decay first. For the D2 loaded fiber grating we resolve two separate energy distributions, suggesting that two different defects are involved. The experiments show that complicated decays originating from various energy distributions can be analyzed with this continuous isochronal anneal method. The results have both practical applications in determining the long-term stability of fiber gratings and fundamental importance since they can be used to d...

Fiber laser optical frequency standard at 1.54 μm

A 32 mW fiber laser is stabilized to the (13)C(2)H(2) P(16) (ν1 + ν3) transition at 1542 nm using saturated absorption. The short-term shot-noise limited fractional frequency instability is 5.0 × 10(-13)(τ/s)-½ for averaging times τ up to about 100 s. The relative lock-point repeatability over 2½ month is 4.3 × 10(-13) corresponding to 83 Hz. The simple setup includes a 21 cm long gas cell, but it does not require an enhancement cavity or external modulators. The spectroscopic lineshape is analyzed with respect to optical power and acetylene pressure. Narrow linewidths of 300 kHz FWHM are observed with a signal to noise ratio of 35 dB in a 9 Hz bandwidth.

UV-written Y-splitter in Ge-doped silica

A three-layer silica structure was grown on a 4-inch silicon wafer using plasma enhanced chemical vapor deposition. The 2.5 micrometers thick core layer is surrounded by 12 micrometers thick buffer and cladding layers. An aluminum layer, deposited on the cladding glass and patterned with the desired waveguide structures, serves as a mask for the UV exposure. An excimer laser operating on ArF giving an energy of 60 mJ/pulse was used to expose the sample to the total fluence of 4800 J/cm2 of 193 nm light. The rise in refractive index is estimated to be around 3 - 10-3 without hydrogen loading or any other kind of sensitization. The Y-splitters were evaluated on an automatic alignment setup using a semiconductor laser operating at 1542 nm. The splitting ratio was measured to be 1:1 at 1542 nm and 1:0.95 at 1310 nm. We measured the loss in the splitter to be 5 dB (fiber to fiberneglecting the splitting). The minimum coupling loss from fiber to waveguide was theoretically calculated to be 1.1 dB, leaving the propagation loss to be smaller than 2.8 dB/cm. The same value was measured for straight waveguides next to the couplers, indicating no measurable excess loss induced by the Y-splitters.

Strong Bragg gratings in nonsensitized low-loss planar waveguides as building blocks for WDM network components

The performance of WDM networks is highly dependent on the wavelength selective components within the network. When using Bragg gratings as wavelength selective elements they have to fulfill a number of criteria such as low loss, high reflectivity, nearly square filter function and high background rejection. Highly photosensitive germanium doped silica-on-silicon planar waveguides have been produced by plasma enhanced chemical vapor deposition (PECVD). Total insertion losses (including fiber to waveguide coupling losses) down to 1 dB for a 5.1 cm long waveguide have been measured at 1541 nm. A germanium content of 8.6 mol% in the core combined with the PECVD process insures high photosensitivity towards 193 nm. Twenty mm long Bragg gratings have been induced by illuminating the waveguides with 193 nm light through a phase mask. The induced gratings show up to 99.98 percent reflectivity and a background rejection better than 22 dB at plus or minus 1 nm from the Bragg wavelength. No hydrogen loading or any other kind of sensitization was necessary to produce these gratings. The spectral flatness (3 dB reflection bandwidth: 0.55 nm and 1 dB reflection bandwidth: 0.47 nm) around the Bragg wavelength and the high background rejection make these gratings well suited building blocks for multi-wavelength network components.

Optimum placement of filters in 1300 nm Nd-fibre amplifiers

Abstract A general procedure for determining the optimum placement of filters in Nd 3+ -doped ZBLANP fibres is presented. Extra gain of 5 dB per filter is predicted for the first four filters, yielding 20 dB of gain with 125 mW of pump power using three filters.

Ultra-Low Noise Fiber Lasers for Optical Fiber Sensor Systems

Fiber lasers provide a combination of low noise, potential for high power, small size, ease of use and high reliability, and as such present an attractive candidate for a number of fiber optic sensing applications.