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

Чувствительность приема относится к минимальной средней входной оптической мощности, которую оптический модуль может принимать при определенной частоте битовых ошибок. Если оптическая мощность передачи относится к оптической силе передающего конца, то чувствительность приема относится к оптической силе, которую оптический модуль может обнаружить в дБм.

В общем, чем выше скорость, тем хуже чувствительность приема, то есть больше минимальная принимаемая оптическая мощность, и тем выше требования к приемным устройствам оптического модуля.

3.  Получение оптической мощности

Принятая оптическая мощность относится к среднему диапазону оптической мощности, который может быть принят приемным компонентом оптического модуля при определенной частоте битовых ошибок, в дБм. Верхним пределом принимаемой оптической мощности является оптическая мощность перегрузки, а нижним пределом — максимальная чувствительность приема.

Вообще говоря, когда принимаемая оптическая мощность меньше принятой чувствительности, сигнал может быть принят неправильно, поскольку оптическая мощность слишком слабая. Когда принимаемая оптическая мощность превышает оптическую мощность перегрузки, сигнал может быть принят неправильно из-за явления кода ошибки.

Показатели производительности, влияющие на  оптический  приемопередатчик  , в основном включают  среднюю передаваемую оптическую мощность, коэффициент ослабления, центральную длину волны оптического сигнала, оптическую мощность перегрузки, приемную чувствительность и принимаемую оптическую мощность . О производительности оптического модуля можно судить, определяя, находятся ли эти значения в пределах нормы.