There are five very important parameters for the optical module. Only when these parameters meet the relevant standards can the optical module perform best. The important parameters of the HTF optical module are introduced as follows.
1. Average Optical Power (POWER)
The average value of instantaneous optical power in a period is called "average optical power", which can be understood as the unit of light intensity in mW or dBm. In communications, dBm is commonly used to indicate optical power.
1W (watt) = 1000mW (milliwatt), 1mW = 1000ηW (microwatt), 1ηW = 1000nW (nW)
2. Bias current IBIAS (BIAS)
In order to make the laser LD high-speed switch work normally, it must be added to the DC bias current IBIAS slightly larger than the threshold current ITH, directly expressed by BIAS. Excessive BIAS conference accelerates the aging of devices,The BIAS laser is too small to work properly.
BIAS is proportional to optical power, that is, the greater the optical power, the greater the bias current BIAS required. BIAS value is also to judge the laser LD
An important indicator of good and bad performance, the smaller the BIAS required for the laser to reach the optical power, the better the performance. The laser will increase with the use of time, the BIAS current required will become larger and larger.
When the bias current BIAS reaches the maximum limit of the rated range, it is also the limit of the service life of the laser.
3. Extinction ratio (EXT)
The extinction ratio refers to the ratio of the optical power (P1) sent by the laser when the code is full "l" to the optical power (Po) emitted when the code is full "0", in dB. The extinction ratio is inversely proportional to the optical power during the commissioning process.
You will find that the extinction ratio will become smaller when the optical power is increased, and the extinction ratio will become larger when the optical power is reduced. The extinction ratio reflects the relative amplitude of the "1" level and "0" level of the optical signal.
The greater the degree, the stronger the discriminating ability of the acceptable part of the optical signal, and the sensitivity will be improved.
4. Saturated optical power
Saturated optical power value refers to the maximum detectable optical power at the receiving end of the optical module, and can also be referred to as overload. When the received optical power is greater than the saturated optical power, it will also cause errors
Code generation. Therefore, for optical modules with high transmit optical power without attenuation loopback, bit errors will occur.
5. Sensitivity (SEN)
The minimum optical power that can be received by the receiving part. The longer the transmission distance of the optical signal in the transmission process, the greater the power loss. The longer the transmission distance, the higher the sensitivity requirements.
For example, the sensitivity is -33dB,Then, comparing with the above table, the receiver (ROSA) can receive the optical power of 0.5nW at the minimum.
The effect of adjustable parameters on the sensitivity has
① extinction ratio, too small extinction ratio will lead to low sensitivity.
② light Power, optical power is too large, the sensitivity will be low.
③ Among them, the APD voltage of the avalanche diode is too low and the sensitivity will be low.
In addition, choose different "wavelength", "transmission rate" and "Signal pattern" also affects sensitivity.
