The LC Variable Phase Retarder

The liquid crystal variable phase retarder (or phase shifter) is a transmissive element with an electrically tunable optical phase retardance. Optical retardation is often obtained with piezoelectric mirrors. However this option is not ideal if robust and compact design is necessary. This product offer an interesting alternative especially when working with polarized light (which is often the case when working with lasers). The Arcoptix phase shifter is a thin transmissive element causing minimal losses and can be simply placed within the optical path of our system. The more, its optical retardation is electrically tunable with the LC driver of ARCoptix (but it can also be driven with simple labor alternative power supply). It can also be used as optical valve (for a narrow wavelength range) or as polarization State controller. To summarize :

• Compact and robust device • Transmissive element • No moving parts • Electrically Tunable • Needs polarized light • Weak absorption in VIS • Optical valve (with extra polarizer) • Polarization state controller
	Arcoptix scientific grade LC variable phase retarder with its 1'' housing

The liquid crystal variable phase shifter can be compared to a variable waveplate. By addressing it with the right voltage, it is able to provide any phase shift from zero to several times the light wavelength. They can be used throughout the visible and the near infrared region (400nm to 1800nm) without losses higher than 15%. Thanks to the use of thick substrate (scientific grade) and a special liquid crystal bend were are capable to offer robust equipment with minimal wavefront distortion and power absorption.

Driver (optional)

The Variable phase retarder can be driven with a standard labor function generators but it can also be driven by the USB ARCoptix LC Driver.
The Arcoptix LC (Liquid Crystal) driver is a USB computer controlled electrical power supply optimized for driving one or two phase retarders.

The LC driver has two independent outputs (Lemo connectors). They are controlled via a simple windows compatible software. The output has a variable square amplitude with polarity inversion and a frequency of 1.6 KHz. This guarantees a homogenous variation of the LC layer inside the cell. An external trigger input can be provided on demand .

Retarder type selection

In functions of your needs you can select essentially between three categories of products:

Retarder Type	Specificities	Applications	Price
Industrial grade	• Spacer (few microns) over the aperture • Large aperture • Thin substrates • Phase distortions (spherical) • Low beam deviation	• Polarization manag. • Polarization vision	**
Scientific grade	• Low phase distortions • No beam deviation • No spacers over the aperture • Aperture 10 mm • Thick substrates • Broadband AR coating	• Interferometry • Metrology • Use in an imaging plane • colimated laser beam	***
Custom	• Larger apertures. • High switching speeds. • Large quantities/low price. • Zero phase shift	•Custom adapted cells for industrial applications • Specific scientific applications	* / ****

For more details please download the description file here below

DOWNLOAD detailed description of the phase shifter

DOWNLOAD detailed description of LC Driver

Prices

Devices	Price
Industrial grade (23mm ap. without housing)	390 Euro
Industrial grade (larger ap. without housing)	Ask
Scientific grade (10mm ap.with housing)	890 Euro
Scientific grade (20mm ap.with housing)	1290 Euro
USB LC Driver (2 outputs)	590 Euro

For custom models please contact info@arcoptix.com for quotation.

Specifications

The table below summarizes the principal characteristics for the industrial grade and scientific grade cells:

Phase shift range	50-2300 nm (more on demand)
wavelength range	350-1800 nm
Active area	scientific grade: 10 mm (diam.) Industrial grade: 22 mm (square)
Transmission	About 85% (VIS)
Retarder material	Nematic Liquid-Crystal Dn=0.14
Substrates	Glass (2x3mm)
wavefront distortion	scientific grade: < l/4 (over 10 mm) Industrial grade: < 2l (over 23 mm)
temperature range	15°-35°
Retardance temperature dependency	About 0.5%/°C (wavelength dependent)
Phase shift adjustment precision	10nm
Maximum modulation frequency of the phase shift	< 10Hz
Phase shift stability (with arcoptix LC driver and at thermal equilibrium)	Better than 10 nm.
Save operating limit	500 W/cm2 CW 300 mJ/cm2 10 ns, visible 200 mJ/cm2 10 ns, 1064 nm
Anti-reflection coating (scientific grade only)	Broadband for VIS.
Total size (with housing)	Scientific grade: 25mm diameter, 16mm long Industrial grade: 31mmx25mmx2.2mm (without housing).

Principle

The Arcoptix variable phase retarders are manufactured with standard liquid crystal technology. As depicted in figure 1, they are principally made of a liquid crystal layer sandwiched between two flat glass plates coated with a transparent electrode (ITO) and an alignment layer. The two glass plates are precisely spaced apart with a matrix of glass fibers. The cavity formed by these plates is filled with a special blend of liquid crystals optimized for high birefringence, small temperature dependence and high stability. The cell is hermetically sealed with a polymer frame. The alignment layer is a gently rubbed polyimide layer necessary for the alignment of the LC molecules. The electric field that can be induced by applying a voltage on the transparent ITO electrodes (0-7V) modifies the alignment of the LC molecules and by the same way the apparent retardance of the cell. Figure (a) shows the alignment of the LC molecules when no voltage is applied. In this case the molecules are aligned along the glass plates and the retardance (along the optical axis) is maximum. Figure (c) shows the other extreme case where a “high” voltage (7V) is applied and the electric field forces the LC molecules to align perpendicularly to the glass plates (parallel to the electric field). Figure (b) shows an intermediate state where we apply a small voltage of about 3V. In this case the molecules have an oblique orientation and the apparent retardation is somewhere in between the maximum retardation (several times the wavelength) and the minimum retardation (almost zero).