Subnanosecond timekeeper system

Abstract

A timing device for keeping time by marking the time boundaries between contiguous time periods. Time is measured by measuring charging voltage on a pair of capacitances where each capacitance is charged and discharge in successive cycles. Detection of a preset value of potential on each one of the capacitances is used to initiate commencement of charge on the other capacitance and detection of another preset value on the other capacitor is used to record measurement of potential at a full scale potential point on the one capacitor. By this means “dynamic” measurements of potential are made by which is meant that the potentials are measured while the potential is changing, rather than when the potential has reached a target end point. This technique eliminates errors arising from unstable conditions at the capacitor due to, for example, dielectric hysteresis, a requirement to measure a charging or discharging step simultaneous with a measuring step, etc. Among the various applications of the invention, there is adaptation to a real time clock, calibrated pulses, etc., all involving measurement requiring a high resolution as provided with this invention. In many instances, the resolution required is less than a nanosecond.

I claim:  
     
         24 . A calibration device for a time keeping system which comprises: 
 (a) a pair of light guide tubes, positioned in line, one end of one tube facing an end of said other tube with a space between said ends;    (b) one tube being longer than said another tube by difference of length , L;    (c) a light source positioned in said space;    (d) one photodetecter positioned facing an end of one tube opposite said space and another photodetecter positioned facing an end of said other tube opposite said space;    (e) means for causing said light source to emit a pulse of light through both tubes whereby said one photodetector emits a signal at one instant which is later than a pulse emitted by said another photodetecter by a time period equal to said difference, L, divided by the velocity of light.    
     
     
         25 . A high frequency signal generator which comprises: 
 (a) a pair of light guide tubes, positioned in line, one end of one tube facing an end of said other tube with a space between said ends;    (b) one tube being longer than said another tube by difference of length, L;    (c) a light source positioned in said space:    (d) one photodetecter positioned facing an end of one tube opposite said space and another photodetecter positioned facing an end of said other tube opposite said space;    (e) means for causing said light source to emit a pulse of light through both tubes whereby said one photodetector emits a signal at one instant which is later than a pulse emitted by said another photodetecter by a first time period equal to said difference, L, divided by the velocity of light; and    (f) means connected to said one photodetecter and responsive to said one photodetecter for stimulating said light source to emit a pulse of light whereby said device generates a series of pulses, each pulse separated in time on one side by a period equal to said first pulse and on another side by a time required by light to traverse said another tube.    
     
     
         26 . A time base generator which comprises: 
 (a) a pair of light guide tubes, positioned in line, one end of one tube facing an end of said other tube with a space between said ends;    (b) one tube being longer than said another tube by difference of length, L;    (c) a light source positioned in said space;    (d) one photodetecter positioned facing an end of one tube opposite said space and another photodetecter positioned facing an end of said other tube opposite said space;    (e) means for causing said light source to emit a pulse of light through both tubes whereby    said one photodetector emits a signal at one instant which is later than a pulse emitted by said another photodetecter by a first time period equal to said difference, L, divided by the velocity of light; and    (f) means connected to said one photodetecter and responsive to said one photodetecter for stimulating said light source to emit a pulse of light whereby said device generates a series of pulse pairs, each pulse pair separated in time by neighboring pulse pairs by a period required by light to traverse said another tube and each pulse separated from its pair member by a time equal to L divided by the velocity of light.    
     
     
         29 . A method for generating a start pulse followed by a stop pulse for display on a scope which includes the steps in operable order: 
 (a) positioning a tubular waveguide in line and end to end with another tubular wave guide wherein said one wave guide is longer than said another wave guide by a length, L and wherein a space is positioned between said waveguides;    (b) positioning a light source in said space;    (c) positioning one photodector at one end of one wave guide opposite said light source and another photodetector at an end of said another waveguide opposite said light source;    (d) connecting each said detector to a scope for displaying said pulses generated in said scope;    (e) stimulating said light source to generating a light pulse that travels down said wavguide tubes to both photodetectors; and    (f) measuring the different time positions of the pulse displayed on the scope of the two pulses and set this time represented as distance on the scope as beng equal to the difference in length of the two tubes dividd by the velocity of light in the tubes.    
     
     
         30 . A method for measuring refractive index of a material that includes the steps: 
 (a) providing two tubes of equal length and filling one tube with the medium to be measured;    (b) positioning a tubular waveguide in line and end to end with another tubular wave guide wherein said one wave guide is longer than said another wave guide by a length, L and wherein a space is positioned between said waveguides;    (c) positioning a light source in said space;    (d) positioning one photodector at one end of one wave guide opposite said light source and another photodetector at an end of said another waveguide opposite said light source;    e) positioning a third photodetecter adjacent the source of light;    (f) connecting each said detector to a scope for displaying said pulses generated in said scope by said three photodetectors;    g) stimulating said light source to generating a light pulse that travels down said wave guide tubes to both photodetectors;    (h) measuring the time positions of the three pulses displayed on the scope;    (i) set the optical length of each tube as being eqal to time that the pulse travels through both tubes as measured with the scope.    set the index of refraction as being equal to the ratio of the opfijal lengths of the tubes.