Jacques M. Laniel

Nonreciprocal waveguide Bragg gratings.

The use of a complex short-period (Bragg) grating which combines matched periodic modulations of refractive index and loss/gain allows asymmetrical mode coupling within a contra-directional waveguide coupler. Such a complex Bragg grating exhibits a different behavior (e.g. in terms of the reflection and transmission spectra) when probed from opposite ends. More specifically, the grating has a single reflection peak when used from one end, but it is transparent (zero reflection) when used from the opposite end. In this paper, we conduct a systematic analytical and numerical analysis of this new class of Bragg gratings. The spectral performance of these, so-called nonreciprocal gratings, is first investigated in detail and the influence of device parameters on the transmission spectra of these devices is also analyzed. Our studies reveal that in addition to the nonreciprocal behavior, a nonreciprocal Bragg grating exhibits a strong amplification at the resonance wavelength (even with zero net-gain level in the waveguide) while simultaneously providing higher wavelength selectivity than the equivalent index Bragg grating. However, it is also shown that in order to achieve non-reciprocity in the device, a very careful adjustment of the parameters corresponding to the index and gain/loss gratings is required.

Photosensitivity of As2S3 chalcogenide thin films at 1.5 microm.

Chalcogenide glasses are promising candidates for all-optical switching and various nonlinear applications. However, we show that As2S3 thin films are photosensitive at wavelengths in the 1.5-microm telecommunication window. This sensitivity is evidenced by the formation of self-written waveguides in slabs, where channels as narrow as 1 microm are created. We also show the detrimental effects of such photosensitivity in ridge waveguides. This photosensitivity seems to occur only in thin-film form and not in bulk samples or fibers.

Trapping light in a ring resonator using a grating-assisted coupler with asymmetric transmission

A recently proposed concept suggests that a matched periodic modulation of both the refractive index and the gain/loss of the media breaks the coupling symmetry of the two co-propagating modes and allows only a unidirectional coupling from the i-th mode to j-the mode but not the opposite. This concept has been used to design a ring resonator coupled through a complex grating composed of both real (index) and imaginary (loss/gain) parts according to Euler relation: n = n0 exp(-jkx) = n0 (cos(kx) - j sin(kx)). Such asymmetrical coupling allows light to be coupled into the ring without letting it out. We present a detailed theoretical analysis of the ring resonator in the linear regime, and we investigate its linear temporal dynamics. Three possible states of the complex grating leads to the possibility of developing a dynamic optical memory cell where, for example, a data modulated train of optical pulses can be stored. This data can be accessed without destroying it, and can also be erased thus permitting the storage of a new bit. Finally, the ring can be used for pulse retiming.

Refractive index measurements of planar chalcogenide thin film

Abstract We report on the measurements of the refractive index of As–S–Se chalcogenide glasses near 1.55 μm. The measurements were made on annealed and non-annealed samples of thermally evaporated thin films. The data for two different series of glasses are presented: the compositions As40S60−xSex and the compositions AsxS(100−x)/2Se(100−x)/2 where the ratio of sulfur to selenium is kept constant (1:1). It has been found that replacing sulfur by selenium in the first series increases the refractive index from 2.4 to 2.8 and increasing the arsenic content in the second series increases the refractive index. In all cases, it has been found that annealing the samples increase the refractive index. The accuracy in the refractive index measurement is ±0.2%.

A shallow-etched multilayer grating-based wavelength demultiplexer in SOI

A very shallow multilayer etched-grating is proposed as a wavelength demultiplexer. Two different configurations are compared for diffraction efficiency and resolution. Single-step-etch fabrication designs are presented and modeled for their grating efficiency and overall performance

Creation of microchannels in a photosensitive As 2 S 3 slab waveguide

We report the creation of microchannels in a photosensitive material, the arsenic trisulfide As2S3. We show that microchannels are created through the process of self-writing and are highly sensitive to the photosensitivity of the material as well as the quality of the incident wave front. The very high photosensitivity of As2S3 allows the self-written waveguide to become much smaller than the incident beam. We present a numerical analysis based on the nonlinear Schrodinger equation that accounts well for the diversity of the microchannels that were experimentally observed and shows that they can actually guide light.

Refractive index measurements of planar chalcogenide waveguide

We report results from a systematic study of the linear refractive index of thin films made of As-S-Se glasses which are part of the chalcogenide family. We have studied eight different compositions. The refractive index are measured by the mean of a grating coupling experiment. The measurements are performed around 1.5μm for both annealed and non-annealed glasses. We observe that annealing the samples increases their refractive index. We also note that the increase of Selenium concentration increases the refractive index and the decrease of Arsenic concentration decreases the refractive index.

Polarization instability in a long period grating of χ (3)

We present a novel type of mode coupling phase matched by a long period grating of chi(3) with no coupling due to the linear grating. We demonstrate its use for polarization switching.

Stationary Solutions in Bragg Grating of χ (3)

Bragg gratings produced by a longitudinal modulation of χ(3)support a novel type of stationary solutions. Simple analytical solutions are found under the assumption of no detuning and no linear grating.

A Shallow-Etched Distributed-Grating Wavelength Demultiplexer in SOI

A shallow-etched, distributed grating is proposed as a wavelength demultiplexer. Modeling results predict up to 94% efficiency over a 120nm wavelength range. Early fabrication results, using electron-beam lithography and electron-cyclotron-resonance single-step etching, are presented.