Binary Phase Modulation

Pseudostochastic random binary sequences are noise-like time patterns. They are defined at times n A t and assume only two different values, corresponding to the grating amplitudes -1 and +1, if 180°-phase modulation is used for switching off the optical grating. Only software modifications, and no changes in the hardware of the TDFRS setup, are necessary in order to utilize pseudostochastic excitation sequences. The timing for heterodyne/homodyne separation is identical to the one already described for pulsed excitation. 

The first evidence for incommensurate smectic modulations was obtained by Leadbetter and coworkers in the smectic E phase of n-alkyl cyanoterphenyls [181, 182]. Subsequent studies presented evidence for fluid SmAi SmA2,i c and SmAinc soliton phases in binary mixtures [183-185]. However, more recent high resolution X-ray studies have contradicted these latter findings and have found that the apparently incommensurate phases are actually coexistence regions between various smectic phases (e.g. SmAi-bSmA SmA2 + SmAd) [24, 186-189]. These authors have recently claimed to have found a true incommensurate ordered smectic phase in mixtures of TBBA and DB6 [190]. Evidence has also been presented for two soli-ton-type incommensurate SmA phases (one... 

From this analysis it is possible to see why FLC SLMs form a vital part in optical systems. The liquid crystal modulation allows the display of information into coherent optical systems as both intensity and phase images. The nature of the FLC molecular interaction makes it fast and this ideally suits nondisplay applications. Even the restriction of binary modulation does not limit the usefulnes of FLC SLMs, although fast grey scale and multilevel phase modulation would be desirable. In fact, for some applications, binary modulation is a bonus and enhances performance. 

The use of SLMs in matched filters has been proposed on several occasions, but has always been limited by the availability to suitable SLM technologies. The first use of SLMs in a BPOMF was done with a magneto-optic SLM [24] and proved to be the first step in the development of the BPOMF. The choice of binary phase modulation allows us to use FLC SLMs to display the information in an all-optical system. The availability of high quality transmissive FLC SLMs [25, 26] has opened the door to the possibility of practically implementing... 

With binary phase modulation (T g [+1, -1]), the pixel in the center of the replay field can be defined by the structure of the hologram. A drawback of both these binary modulation schemes is that the hologram will always be a real function, which means that the FT of the hologram is the same as the FT of the hologram rotated about the origin... 

Figure 31. Binary intensity versus binary phase modulation.

If we use the CGH in Fig. 34 as a binary phase image displayed on an FLC SLM, then it is possible to route light to several fibers in the replay field. We are limited however, by the binary phase modulation of the FLC SLM, which means that a symmetric copy of the desired replay field always ap-... 

Due to the binary phase modulation, the distribution of the background power is not uniform and there tend to be small peaks of intensity which may occur at fiber positions. This becomes less of a problem with large numbers of CGH pixels and careful CGH design. 

The filter was tested in an experimental bench setup and used to filter the amplified spontaneous emission of an erbium-doped fiber amplifier (EDFA). The SLM was a 128x128 2-D device with a cell thickness optimized for use at a wavelength of 1550 nm and was used with constant row data and columns set with the hologram data. The SLM was used as a binary phase modulator without polarizers to reduce the... 

Mobile phases employed for the separations are housed in a cartridge and delivered to the LC columns through a set of binary HPLC pumps (Shimadzu Corporation), as shown in Figure 6.2. The pumps provide a flow rate accuracy of 2% or 2 fiL (whichever is greater) in constant flow pumping mode, with a flow rate precision of 0.3%. A degasser (two channels internal volume of 195 /.d. /channel) is also housed in the pump module employed to minimize the occurrence of air bubbles. 

Reversed-phase chromatography employs a nonpolar stationary phase and a polar aqueous-organic mobile phase. The stationary phase may be a nonpolar ligand, such as an alkyl hydrocarbon, bonded to a support matrix such as microparticulate silica, or it may be a microparticulate polymeric resin such as cross-linked polystyrene-divinylbenzene. The mobile phase is typically a binary mixture of a weak solvent, such as water or an aqueous buffer, and a strong solvent such as acetonitrile or a short-chain alcohol. Retention is modulated by changing the relative proportion of the weak and strong solvents. Additives may be incorporated into the mobile phase to modulate chromatographic selectivity, to suppress undesirable interactions of the analyte with the matrix, or to promote analyte solubility or stability. 

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