Self-aligning analog laser transmitter

Claim 2

Apparatus for aligning an analog laser transmitter to provide proper modulation of a signal for fiber optic communication, comprising: a laser; means for monitoring the magnitude of a communication signal coupled to modulate said laser; means coupled to said laser for determining operational characteristics thereof; means for deriving, from the determined operational characteristics, the level required of said communication signal to properly modulate said laser for communication across an optical fiber; and means for adjusting the magnitude of said communication signal to said level.

Claim 3

The apparatus of claim 1 wherein said operational characteristics comprise the slope efficiency of the laser.

Claim 4

The apparatus of claim 1 or 2 wherein said operational characteristics comprise the rated output power of said laser.

Claim 5

The apparatus of claim 2 or 3 wherein said laser requires an input bias current to produce an output, and said determining means comprises: means for measuring the bias current I₁ of said laser at one output power level P₁ and for measuring the bias current I₂ of said laser at another output power level P₂; and means for computing the slope efficiency SE from the relationship:

Claim 6

The apparatus of claim 4 wherein said laser has a rated output power P nom and an input impedance R, and wherein said deriving means comprises: means for calculating said level L for a desired modulation index M from the relationship: L = ½ * (P nom /SE)² * R * M²

Claim 11

A self aligning analog laser transmitter comprising: a computer processor; an input terminal for receiving a communication signal; a laser module having an input coupled to receive said communication signal and an output for transmitting a laser signal modulated by said communication signal over an optical fiber; means operatively associated with said computer processor for determining operational characteristics of said laser module; means operatively associated with said computer processor for deriving, on the basis of said characteristics, the power required of said communication signal to modulate said laser at a desired level; and means responsive to said computer processor for adjusting the power of said communication signal to said required power.

Claim 12

A self aligning analog laser transmitter comprising: a computer processor; an input terminal for receiving a communication signal; a laser module having an input coupled to receive said communication signal and an output for transmitting a laser signal modulated by said communication signal over an optical fiber; means operatively associated with said computer processor for determining operational characteristics of said laser module; means operatively associated with said computer processor for deriving, on the basis of said characteristics, the power required of said communication signal to modulate said laser at a desired level; and means responsive to said computer processor for adjusting the power of said communication signal to said required power.

Claim 13

The laser transmitter of claim 10 further comprising: means for applying an input bias current to said laser module to cause said laser module to produce a laser output; and means for measuring the power of said laser output; wherein said determining means obtains a set of bias current and output power characteristics for said laser module, said set including a bias current I₁, that produces an output power P₁, and a bias current I₂ that produces an output power P₂, to determine the slope efficiency SE of said laser module according to the relationship:

Claim 14

The laser transmitter of claim 11 wherein said laser module has a rated output power P nom and an input impedance R, and said deriving means derives the required power L for a desired modulation index M from the relationship: L = ½ * (P nom /SE)² * R * M²

Claim 15

The laser transmitter of claim 12 further comprising: means for computing a nominal laser bias current to be applied to said laser module when communicating over an optical fiber; and means for applying the computed current to the laser module during a fiber optic communication.

Claim 16

The laser transmitter of claim 13 wherein said nominal laser bias current I bias is computed according to the formula:

Claim 17

The laser transmitter according to one of claims 10 to 14 further comprising: means for applying an input bias current to said laser module to cause said laser to produce a laser output; and wherein said determining means comprises: means for applying a test tone to said input terminal; means for gradually increasing the power of said test tone from a relatively low power to a higher power; means for monitoring said input bias current during the application of said test tone to the input terminal; means coupled to said monitoring means for detecting a change in said bias current due to overmodulation of said laser by the test tone; and means for determining the test tone power when said detecting means detects a change in said bias current; wherein the magnitude of the determined test tone power is an operational characteristic indicative of the power required to operate said laser module at 100% modulation, and is used by said deriving means to derive the power required of said communication signal.

Claim 20

The method of claim 16 wherein the slope efficiency SE of said laser is determined at said determining step, and said power level L is calculated at said deriving step in accordance with the relationship: L = ½ * (P nom /SE)² * R * M² where P nom is the rated output power of said laser, R is the input impedance of said laser, and M is a desired modulation index.

Claim 21

The method of claim 16 or 17 wherein the magnitude of a communication signal required to operate said laser at 100% modulation is determined at said determining step, and the power level derived at said deriving step is computed from said determined magnitude.