Grating periods

Figure 9. Cross-section of a refractive index sensor based on a quasi one-dimensional photonic crystal with grating period A = 190 nm. The top cladding over the grating is formed by a fluid contained in a cuvette that is sealed to the sensor chip.

The system Alq3 DCM was successfully incorporated into a DFB structure by different research groups and optically pumped [194, 195]. The materials were deposited on embossed flexible substrates with grating periods for second-and third-order coupling (400-600 nm). By varying the him thickness, the wavelength of the lasers can be tuned over 44 nm [196]. 

The initial step is to layout the waveguide pattern using the AutoCAD software. The waveguide pattern is segmented, with the period of the segmentation equal to the required QPM period for SHG (e.g. for conversion of 850 nm the grating period is 4 pm). 

While periodically-poled materials are typically characterized by very narrow spectral acceptance bandwidths (< 1 nm), aperiodically-poled structures (characterized by a linear gradient in grating period) have the advantage of providing sufficiently broad spectral acceptance bandwidths to utilize more of the spectrum associated with picosecond and femtosecond" pulses. They can also simultaneously provide some pulse compression of sufficiently pre-chirped incident pulses ... 

The bulk appKTP crystal was 4 mm in length, and was not AR-coated. The grating periods varied from 4.1 pm to 4.3 pm in order to provide a fundamental bandwidth of 7 nm, for SHG at room temperature centered at 851 nm. With an experimentally-optimized focusing lens (f= 15 mm w =... 

It is readily apparent that a mask consisting of equal lines and spaces constitutes a diffraction grating and when uniformly illuminated will produce a diffraction pattern similar to that just discussed with an intensity profile depending on the grating period ( ), the wavelength (X) and the position of the image plane. This will be discussed in more detail later. 

Figure 9.12 Seed scattering at refractive index modulations induced by localized internal random fields via the electro-optic effect. The internal fields are also responsible for the formation of a rich ferroelectric domain structure. Here, a periodic sequence of domains with lengths A d is shown. Note, that the grating period of the refractive index modulation As is equal to the lengths of the ferroelectric domains.

As illustrated in Fig. 9 and described in Sect. 3.1.2, prior to sputtering deposition of the layers, two surface relief gratings (period of A = 400 nm) were fabricated on the glass slide for input and output coupling of the optical beam. A calculation based on the theory developed in Sect. 2.2 gave an electric field profile for the TE mode as shown in Fig. 10. 

SLM) imaged onto the sample surface in order to generate SAWs, the frequency and wavefront of which are controlled by the SLM. When the grating period matches the surface acoustic wavelength, the surface wave is strongly excited, so the wavelength, and hence the phase velocity, can be readily determined [38]. 

---