For no overlapping of light pulses down on an optical fiber link, the digital bit rate BT must be . . . . . . . .

The correct answer is: A. Less than the reciprocal of broadened pulse duration.

The broadened pulse duration is the time it takes for a light pulse to spread out after it has been launched into an optical fiber. The digital bit rate is the number of bits that can be transmitted per second. In order to avoid overlapping of light pulses, the digital bit rate must be less than the reciprocal of the broadened pulse duration. This is because if the digital bit rate is too high, the light pulses will overlap and cause errors in the transmitted data.

Here is a more detailed explanation of each option:

• Option A: Less than the reciprocal of broadened pulse duration. This is the correct answer because it ensures that the light pulses do not overlap.
• Option B: More than the reciprocal of broadened pulse duration. This is incorrect because it would cause the light pulses to overlap.
• Option C: Same as that of than the reciprocal of broadened pulse duration. This is incorrect because it would not ensure that the light pulses do not overlap.
• Option D: Negligible. This is incorrect because it would not ensure that the light pulses do not overlap.