Low distortion all-optical threshold device

Apparatus responsive to an applied optical digital input signal having a first level and a second level, for developing an output signal with a reduced noise level relative to the noise level of said input signal, comprising:

• a non-linear loop interferometer exhibiting an input/output transfer function which relates said output signal to said input signal that is sigmoid in an initial region thereof, having a lower saturation region at said first level of said optical digital signal and a higher saturation region straddling said second level of said optical digital signal.

An optical digital noise reducer having an input and an output, comprising:

• a non-linear loop interferometer exhibiting an input/output transfer function that is sigmoid in an initial region thereof, with a lower saturation region at one level of input signals applied to said interferometer and a higher saturation region at another level of input signals applied to said interferometer, and
• information bearing digital signals applied to said interferometer having a low level signal in the lower saturation region of said interferometer and a high level signal in the higher saturation region of said interferometer.

An optical digital noise reducer having an input and an output, comprising:

• a non-linear loop interferometer having an input/output transfer function that exhibits a sigmoid input/output transfer function in a region thereof, with a lower saturation region at one level of input signal and a higher saturation region at another level of input signal, and
• a bandpass filter at the output of the interferometer.

An optical digital noise reducer responsive to an input signal having a first level and a second level, comprising:

• a non-linear loop interferometer with an input/output transfer function having at least two of regions with a derivative (dP.sub.out /dP.sub.in) of magnitude less than 1, and a third region interposed between said two regions and having a derivative of magnitude greater than 1;
• where said input signal is arranged to have its first level at one of said two regions and its second level at the other of said two regions.

An optical digital noise reducer responsive to an input signal having a first level and a second level, comprising:

• a non-linear loop interferometer with an input/output transfer function having at least two of regions with a normalized derivative 1/K (dP.sub.out /dP.sub.in) of magnitude significantly less than 1, and a third region interposed between said two regions and having an average derivative of magnitude K;
• where said input signal is arranged to have its first level at one of said two regions and its second level at the other of said two regions.

An optical digital noise reducer responsive to an input signal having a first level and a second level, comprising:

• a non-linear loop interferometer with an input/output transfer function having at least two of regions with a normalized derivative ##EQU1## of magnitude less than 1, and a third region interposed between said two regions;
• where said input signal is arranged to have its first level at one of said two regions and its second level at the other of said two regions.

An optical digital noise reducer responsive to an input signal having a first level and a second level, comprising:

• a non-linear loop interferometer with an input/output transfer function having a first region spanning from zero input power to a first input power level, a second region spanning from said first input power level to a second power level, and a third region spanning from said second power level to a third power level, where the normalized derivative in said first and third regions is of magnitude significantly less than 1, and
• where said input signal is arranged to have its first level within said first region, and its second level substantially at the center of said third region.

An optical digital amplifier comprising:

• optical signal amplification means for developing an amplified signal having a first level and a second level;
• a non-linear loop interferometer exhibiting a sigmoid input/output transfer function, having one saturation region in the neighborhood of said first level and another saturation region in the neighborhood of said second level.