Method and apparatus for converting phase-modulated light to amplitude-modulated light and communication method and apparatus employing the same

A communications system comprising:

• a transmitter station including light modulator means for generating phase-modulated light corresponding to a first oscillatory electrical signal;
• said light modulator means comprising at least one liquid crystal cell comprising two parallel transparent plates;
• a transparent electrical conductive layer applied to the confronting surfaces of the said two plates;
• each said conductive layer having parallel surface alignment, the said alignment of the two adjoining surfaces being parallel;
• a continuous layer of nematic liquid crystal having positive dielectric anisotropy between the two electrical conducting coatings;
• means for applying an electrical bias to the two said electrical conducting coatings;
• means for applying an electrical signal of varying amplitude having a frequency greater than 10 hertz across the said continuous layer;
• a source of polarized light directed through the said two transparent plates;
• whereby the light which passes through the said two transparent plates is a phase modulated light which is distinguishable from the light from said source in a manner which corresponds to said electrical signal of varying amplitude;
• a receiver station for demodulating the said phase-modulated light comprising:
• a linear polarizer for converting the said phase-modulated light to amplitude-modulated light;
• a light detector for generating an electrical signal corresponding to the said amplitude-modulated light;
• a demodulator for demodulating the said electrical signal from the said light detector to generate a second electrical signal of varying amplitude corresponding to the said first electrical signal of varying amplitude.

A method for generating amplitude-modulated light corresponding to a first oscillatory electrical signal comprising:

• polarizing light from a light source in a first linear polarizer to generate a first polarized light beam;
• passing said polarized light beam through an electrically biased, liquid crystal cell to develop a phase-modulated light beam;
• applying an electrical bias to the said electrically biased, liquid crystal cell;
• applying said first oscillatory electrical signal modulated with a carrier wave to said first electrically biased, liquid crystal cell whereby the said phase-modulated light corresponds to the said first oscillatory electrical signal;
• passing the said phase-modulated light through a second linear polarizer to convert the said phase-modulated light to amplitude-modulated light.

The method of delivering a first electrical signal of varying amplitude from a transmitter station to a receiving station which comprises

• generating in said transmitter station a phase-modulated light beam corresponding to said first electrical signal of varying amplitude by the following means;
• directing a beam of linearly polarized light through a liquid crystal cell formed from two parallel transparent plates and having a transparent electric conductive layer applied to the confronting surfaces of the said two plates wherein each said conductive layer has parallel surface alignment and wherein the alignment of the two adjoining surfaces is parallel and having a continuous layer of nematic liquid crystal with positive dielectric anisotropy between the two said electrical conductor coatings;
• applying an electrical bias to the two said electrical conducting coatings;
• applying said electrical signal of varying amplitude having a frequency greater than 10 hertz to the said electrical conducting coatings;
• whereby the said phase modulated light beam is distinguishable from the said polarized light source in manner which corresponds to the said electrical signal of varying amplitude;
• delivering said phase-modulated light to said receiving station including a light detector for generating an electrical signal corresponding to an amplitude-modulated light;
• a demodulator for demodulating the said electrical signal from the said light detector to generate a second electrical signal of varying amplitude corresponding to said first electrical signal of varying amplitude;
• interposing a linear polarizer in the optical path of said phase-modulated light beam between said transmitter station and said receiving station.

An apparatus for modulating light comprising

• means for polarizing incident light;
• at least one liquid crystal cell comprising two parallel transparent plates;
• a transparent electrical conductive layer applied to the confronting surfaces of the said two plates;
• each said conductive layer having parallel surface alignment, the said alignment of the two adjoining surfaces being parallel;
• a continuous layer of nematic liquid crystal having positive dielectric anisotropy between the two electrical conductive coatings;
• means for applying an electrical bias to the two said electrical conductive coatings;
• means for applying an electrical signal of varying amplitude to the said electrical conductive coatings;
• whereby the said nematic liquid crystal is affected by said electrical signal solely at the interfacing surface with at least one of said electrical conducting coatings, thereby permitting rapid response of the said nematic liquid crystal layer to the applied electrical signal having frequencies of 10 hertz to 500 kilohertz;
• a source of polarized light directed through the said two transparent plates;
• whereby the light which passes through the said two transparent plates is a phase shifted beam which is distinguishable from the said source in a manner which corresponds to the said electrical signal.

A method for generating intensity modulated light corresponding to a first electrical signal of varying amplitude comprising:

• passing polarized light through a liquid crystal film containing nematic liquid crystals having positive anisotropy;
• orienting the liquid crystal structure perpendicular to said film;
• applying said first electrical signal of varying amplitude to a surface of said liquid crystal film in its oriented condition, whereby light leaving said liquid crystal film corresponds in phase to the said first electrical signal;
• polarizing the leaving light to convert the output light to intensity modulated light.