Optical module is a connection module for photoelectric conversion, in which the sender converts electrical signals into optical signals, and the receiver converts optical signals into electrical signals after transmission through optical fibers.

The optical module is composed of optoelectronic devices, functional circuits and optical interfaces. Optoelectronic devices include transmitting and receiving parts.

Transmitting part: after the signal input a certain code rate is processed by the internal driver chip, it drives the semiconductor laser (LD) or light-emitting diode (LED) to emit the corresponding rate of modulation optical signal, and its internal optical power automatic control circuit (APC), so that the output optical signal power remains stable.

Receiving part: after the optical signal with a certain code rate is input into the module, it is converted into an electrical signal by the optical detection diode, and the electrical signal with the corresponding code rate is output through the preamplifier. Next, etu-link will introduce the indicators to measure the performance of optical modules?

Transmitter

1. Average transmit power

The average emitted optical power refers to the optical power output by the emitting light source of an optical module under normal working conditions. It can be regarded as the optical intensity.

The transmitted optical power is related to the proportion of “1” in the transmitted data signal. The more “1”, the greater the optical power.

When the transmitter sends the pseudo random sequence signal, “1” and “0” are roughly equal in half, then the power obtained by the test is the average transmitted optical power, in dBm.

2. Extinction ratio

Extinction ratio refers to the minimum value of the ratio of the average optical power of the laser transmitting all “1” code to the average optical power of the laser transmitting all “0” code under the condition of full modulation, in the unit of dB.

When converting electrical signals into optical signals, the laser transmitting part of the optical module converts them into optical signals according to the code rate of the input electrical signals.

All “1” yards when the average optical power indicates that the average power of laser light, full “0” means the average optical power of the laser light of average power and extinction ratio of characterization of 0 1 signal difference ability, therefore the extinction ratio can be regarded as a kind of laser efficiency measure of extinction than a typical range of the minimum value of 8.2 dB to 10 dB.

3. The central wavelength of the optical signal

In the emission spectrum, different types of lasers or two lasers of the same type will have different central wavelengths corresponding to the midpoint of the 50% maximum value line segment due to production process and other reasons. Even the same laser may have different central wavelengths under different conditions.

Generally, manufacturers of optical devices and optical modules provide users with a parameter, namely, the central wavelength (for example, 850nm), which is generally in a range. Currently, there are three common central wavelengths of optical modules :850nm band 1310nm band and 1550nm band.

Receiver

1. Overload optical power

Overload optical power, also known as saturation optical power, refers to the maximum average input optical power that can be received by the receiving component of an optical module at a certain bit error rate (BIT error rate), in dBm.

It should be noted that photocurrent saturation phenomenon will occur in the light detector under strong light. When this phenomenon occurs, the detector needs a certain time to recover. At this time, the receiving sensitivity will decrease, and the received signal may misjudge and cause error code phenomenon.

Simply put, if the input optical power exceeds the overload optical power, it may cause damage to the equipment. In operation, avoid strong light as far as possible to avoid exceeding the overload optical power.

2. Receiving sensitivity

The receiving sensitivity refers to the minimum average input optical power that an optical module can receive at a certain bit error rate. If the transmitting optical power refers to the optical intensity of the transmitting end, the receiving sensitivity refers to the optical intensity that an optical module can detect in dBm.

In general, the higher the rate, the worse the reception sensitivity, that is, the greater the minimum received optical power, and the higher the requirements for the receiving devices of the optical module.

3. Receiving optical power

The received optical power refers to the average optical power range that can be received by the receiving component of an optical module at a certain bit error rate, in dBm. The upper limit of the received optical power is the overload optical power, and the lower limit is the maximum receiving sensitivity.

Generally speaking, when the received optical power is less than the received sensitivity, the signal may not be properly received because the optical power is too weak. When the received optical power is greater than the overload optical power, the signal may not be properly received because of the error code phenomenon.

The performance indexes affecting the optical transceiver mainly include average transmitted optical power, extinction ratio, optical signal center wavelength, overload optical power, receiving sensitivity and received optical power. The performance of the optical module can be judged by detecting whether these values are within the normal range.