Engineers in many enterprises will ask what the laser diode pd means and what the relationship between it and LD looks like. Let's give you a brief introduction in the following small series.

Laser Diode (LD) is the most commonly used core light source in laser optoelectronic devices. From the appearance, many laser diodes not only have positive and negative electrodes, but also have an extra PD pin.

Combining the principle and application, this paper will give you a comprehensive interpretation of the significance of PD foot and the close relationship between LD and PD.

1. What is the PD pin of a laser diode?

In the structure of laser diode, PD(Photodiode) is usually integrated on the back of LD chip to monitor the luminous intensity of laser in real time.

PD pin: It is the output pin of the photodiode, which will convert the monitored optical signal into a current signal for output.

Function: The driving circuit can judge the luminous power of LD by reading the signal of PD pin, and adjust the driving current in real time, thus ensuring the stability of laser output.

Second, why do laser diodes need PD?

Compared with ordinary LED, laser diode has two remarkable features:

1. Extremely sensitive to current: a slight overcurrent may lead to power out of control and even damage the device.

2. The output stability is extremely demanding: many applications (communication, ranging, medical treatment) require accurate and long-term stability of optical power.

In this case, it is not enough to provide a constant current to LD, because the laser output will fluctuate due to factors such as temperature, driving power supply and device aging. So we must cooperate with a PD to do feedback monitoring.

Third, the relationship between LD and PD in laser diode

1. Physical relationship

LD is the light-emitting body, which is responsible for generating laser.

PD is located on the back of LD and used to receive a small amount of reflected or transmitted light.

Both of them are integrated in the same device to form a closed-loop control system.

2. Electrical relations

LD generates laser by forward current driving;

PD converts the received optical signal into current and feeds it back to the driving circuit;

The drive circuit adjusts the LD drive according to the PD current, thus forming an APC (Automatic Power Control) loop.

3. Application relationship

Without PD, the output of LD may fluctuate with the environment and it is difficult to maintain stability;

With PD, the output power of LD can be accurately controlled, which meets the requirements of communication, medical care, ranging and other applications with high accuracy.

Fourth, typical application scenarios

1. Optical communication:

PD ensures that each laser pulse is within the set power range, avoids signal distortion and improves communication quality.

2. Laser ranging:

PD ensures the laser output power to be stable and consistent, which makes the echo signal more accurate and the ranging accuracy higher.

3. Medical and beauty laser:

PD feedback mechanism can prevent LD output from being too strong or too weak, ensure accurate energy control and ensure treatment safety.

4. Industrial processing:

High-power LD array needs PD monitoring to prevent overload and improve system reliability and life.

PD pin: refers to the output end of the photodiode inside the laser diode, which is used to monitor the laser power.

Relationship between LD and PD: LD is responsible for light emission, PD is responsible for detection, and the driving circuit adjusts the LD current through PD signal to form a stable closed-loop control.

It is this LD+PD cooperative design that makes the laser diode stable, accurate and long-lived in various complex environments.

When choosing laser diode, PD function is often one of the important standards to measure its quality and application level. Almost all high-end laser devices are equipped with PD to meet the strict stability requirements of industrial, scientific and medical applications.