LED Modulation

Since the light ouput from an LED has a region where it is linearly proportional to the forward current through the diode, it is useful for producing a light level which is proportional to some signal. That signal can then be send through a fiber optic cable and detected on the other end. The basic need for modulation is then a device which produces a current proportional to the input voltage of the applied signal. This can be done with an op-amp arranged as a voltage-to-current converter. 由于LED的光输出在某个区域与二极管的正向电流成线性比例关系，因此它可用于产生与某个信号成比例的光强。该信号可以通过光纤电缆传输并在另一端检测。因此，调制的基本需求是产生一个电流，该电流与输入信号的电压成比例。这可以通过将运算放大器配置为电压-电流转换器来实现。 Detailed Modulation Circuit 详细调制电路

LED Modulation Circuit

This op-amp application is a summing amplifier where the signal input has a gain of -1 and the 12V supply is amplified by -3/7 to provide enough voltage to turn on the LED to get it into its linear range. The change in light output is then proportional to the signal voltage.

Modulation of an LED is one common way of getting a signal into a fiber optic transmission line.

LED Characteristics

When an LED is forward biased to the threshold of conduction, its current increases rapidly and must be controlled to prevent destruction of the device. The light output is quite linearly proportional to the current within its active region, so the light output can be precisely modulated to send an undistorted signal through a fiber optic cable.

LED Radiation Patterns

An LED is a directional light source, with the maximum emitted power in the direction perpendicular to the emitting surface. The typical radiation pattern shows that most of the energy is emitted within 20¡ of the direction of maximum light. Some packages for LEDs include plastic lenses to spread the light for a greater angle of visibility. LED是一种定向光源，其最大发射功率垂直于发射表面方向。典型的辐射模式显示，大部分能量在最大光方向的20°范围内发射。一些LED封装包括塑料透镜，用于扩展光的覆盖角度，以提高可见性。

Light Emitting Diodes