Constant modulation index technique for measuring the derivatives of device parameters
AssigneeBell Telephone Laboratories, Incorporated
InventorRichard Wayne Dixon
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Abstract
Described is a technique for generating directly certain derivatives of device parameters by measuring the device response to ac modulation under conditions of constant modulation index. In particular, the technique as it applies to measuring directly idF/di and i.sup.2 d.sup.2 F/di.sup.2 for AlGaAs DH p-n junction lasers is described for two cases: where the generalized function F equals either voltage V across the laser or the light intensity output L of the laser, and i equals current through the laser. For p-n junction lasers this technique permits measurement of the series resistance R.sub.s, lasing current threshold i.sub.th and the exponential factor .beta. = q/nkT.
Claims10
A method for generating a product of an n.sup.th order derivative of a device parameter F with respect to current flowing through the device times the n.sup.th power of the current comprising the steps of:
- a. applying to said device a variable current which has both a d.c. component i and an a.c. component .DELTA.i which oscillates at a frequency .OMEGA.,
- b. maintaining substantially constant the ratio i/.DELTA.i,
- c. detecting a signal produced in response to the flow of said current through said device, and
- d. extracting from said signal the frequency component thereof which corresponds to the desired current-derivative product.
Dependencies are inferred from the claim text.