Abstract: In one aspect, the invention relates to a waveguide structure for differential transmission lines. The waveguide structure includes a first ground structure, a first signal line, a second ground structure, a second signal line, a third ground structure. The first signal line is typically positioned adjacent and substantially parallel to the first ground structure. The second ground structure has a first separation distance from the first ground structure and is typically positioned adjacent and substantially parallel to the first signal line. The first signal line is typically positioned between both the first and second ground structures. The second signal line typically a has a second separation distance from the first signal line and is positioned adjacent and substantially parallel to the second ground structure. The second ground structure is typically positioned between both the first and second signal lines.

Abstract: In one aspect, the invention relates to a waveguide structure for differential transmission lines. The waveguide structure includes a first ground structure, a first signal line, a second ground structure, a second signal line, a third ground structure. The first signal line is typically positioned adjacent and substantially parallel to the first ground structure. The second ground structure has a first separation distance from the first ground structure and is typically positioned adjacent and substantially parallel to the first signal line. The first signal line is typically positioned between both the first and second ground structures. The second signal line typically has a second separation distance from the first signal line and is positioned adjacent and substantially parallel to the second ground structure. The second ground structure is typically positioned between both the first and second signal lines.

Abstract: A preamplifier for use with currents developed by a photodetecting diode is disclosed wherein the currents are coupled to the base of an NPN transistor connected as a common emitter stage and a feedback resistor is connected by way of a buffer amplifier to the base to provide a standard transimpedance configuration. A control loop monitors the signal level by integrating the output of the buffer amplifier, and upon the detection of large signals the control loop causes a MOSFET in parallel with the feedback resistor to decrease the transimpedance and thereby increase the signal handling capability of the preamplifier. The control loop is also connected to a second MOSFET in parallel with the collector load resistor of said NPN transistor to decrease the effective collector load impedance for large signal levels.

Abstract: Apparatus and method are disclosed for controlling the tone spacing (2.omega..sub.d) and output power level in an FSK lightwave transmitter. An arrangement is utilized which splits a tapped-off portion of the output data stream into two essentially equal components. A first component is then delayed and scrambled (polarization state) with respect to the second component. Self-heterodyning of the two signals results in forming a signal at the beat frequency, or tone spacing value. By comparing this beat frequency with a predetermined tone spacing value, adjustments may be made to the transmitter to maintain the desired tone spacing value. The self-heterodyned signal will also contain a component indicative of the data signal power level and may be utilized to adjust the transmitting device so as to maintain a constant power.

Abstract: A test apparatus and method is disclosed for determining the absolute noise figure of an optical amplifier. The apparatus comprises an optical receiver and functions to measure the output power of a test noise source, such as a lamp or LED. A plot of input power versus output power yields a linear relationship, with a y-intercept at the test apparatus (first) noise floor (N.sub.0). An optical amplifier to be tested is then inserted in the signal path between the noise source and the receiver. A new plot is generated and a second system noise floor value is determined (N.sub.1). The difference between the two noise floor values (N.sub.1 -N.sub.0) is then defined as the amplifier absolute noise figure (N.sub.A). The inventive technique is equally applicable to semiconductor and fiber optical amplifiers.