When it comes to the use of optical transceivers, we know that optics need to be maintained to ensure that they can operate well during their lifespan. Then do you know what fiber optic testing standards are performed during the manufacturing of the transceiver module? Indeed, to ensure the stability and reliability of optics, manufacturers often implement multiple optical transceiver testing processes to make their parameters within industry standards. Since transceiver testing methods are vast and specific procedures may varied vendor to vendor, we will talk about the most basic fiber testing levels that a high-quality transceiver should pass.
Before the SFP test, prepare testing equipment and tools, such as an optical attenuator, optical power meter, bit error meter (adjust optical power and sensitivity by rate), eye diagram meter, fiber end face detector, fiber optic cleaning pen, etc.
Incoming Quality Control (IQC)
The transceiver test should begin with a pre-assembly inspection to make sure the rare materials used for manufacturing are qualified. Specifically, two key components of the transceiver are analyzed: receivers and transmitters. The receiver optical sub-assembly (ROSA) includes the optical connector, photodiode, etc. The transmitter optical sub-assembly (TOSA) covers the electrical interface and laser diodes, etc. The ROSA and TOSA together are called a bi-directional optical sub-assembly (BOSA), which will also be inspected before assembly.
Average Output Optical Power Test
Output optical power is an important parameter that defines the transceiver’s transmission distance and quality. Operators often use an optical power meter to test the average output optical power of the transmitting end.
Extinction Ratio Measurement
Extinction ratio, one of the parameters to measure the quality of transceivers, is to measure the ratio of two optical power levels of a digital signal generated by an optical source. Defining P1 as the optical power level when the light source is on, and P0 as the power level when the light source is off. Then the ratio of optical power at the high level full “1” code to the low level full “0” code the laser outputs is the extinction ratio. Extinction ratio = P1/P0.
The value of the parameter indicates whether the laser operates at the optimal bias point and modulation efficiency. The bigger the Extinction Ratio, the stronger the capability to receive and identify the optical signal, and the higher the receiving sensitivity. The extinction ratio is inversely proportional to the input optical power. The test result shows the larger the extinction ratio, the smaller the emitted optical power.
Optical Modulation Amplitude Test
Similar to extinction ratio, Optical modulation amplitude (OMA) is to calculate the difference between two optical power levels of a digital signal generated by an optical source. Then OMA = P1 - P0.
Bit Error Rate & Receiving Sensitivity Test
The bit error rate is the ratio of the number of bit error symbols received after optical-to-electrical conversion by the receiving end to the symbol provided by the transmitting end within a specific period of time. It is a parameter to measure the functionality of transceivers to transmit symbols correctly.
Use a bit error meter to test the bit error rate and receiving sensitivity. Usually, transceivers with higher data rates have poorer receiving sensitivity.
Eye Pattern Test
The eye pattern results from multiple acquisitions and superimposed displays on the digital signals by an oscilloscope, which reflects whether the measured signals are lost, or transmitted in good condition. By observing the eye diagram height, width, Jitter, and duty cycle, operators can identify its performance. The bigger the eye, the smaller the intersymbol interference, and the better the performance.
Given that two devices communicate when the optical modules used at both ends are working at the same wavelength. Before shipment, manufacturers should test the transceiver's wavelength to ensure it is within the deviation range.
The optical spectrum analyzer is a typical testing device for measuring the central wavelength of the optics. In real testing results, it is common that there to be a deviation of the central wavelength to the standard wavelength. However, the wavelength test will pass if the deviation value is within a reference range.
Usually, different optics types are offered with different deviation values. For example, a deviation of ±50nm is eligible for SFP-1G-LX that works at a central wavelenght of 1310nm and ±10nm is acceptable for the multimode 850nm SFP-1G-SX transceiver. Otherwise, the transceiver will be viewed as a defective product.
High and Low-Temperature Aging Test
A qualified transceiver should adjust its working temperature to adapt to the application environment. To measure whether the performance is reliable in extreme environments, optical transceivers should be placed in the aging test chamber for high and low-temperature aging tests. For instance, to test an industrial-grade transceiver module, QSFPTEK sets the temperature to 85°C and places the optic in the chamber for 4 hours to measure its tolerance to high temperature.
For third-party transceivers, compatibility tests must be performed on brand system equipment to ensure optic-to-device interoperation. The most common tested bed equipment is the switch. Compatible transceiver manufacturers often code the optic to a specific brand and plug it into target switches to check whether the connectivity is normal.
While manufacturing and testing transceivers, dust and scratches are inevitable. After each testing step, transceivers must be inspected under a Fiber End Face Detector microscope to check whether there are any stains. If there are, then use optical fiber pen cleaner to clean the connector. If there are scratches, then the transceiver should be rejected and returned to the production line for reassembling. When plugging fiber into the module or unplugging it from the module, the optical connector can be easily contaminated. Cleaning the optical end-face is a way to prevent link failure brought by the contaminated end face.
Though transceiver modules are not data communication equipment, they play a vital role in data transmission. Its quality directly affects signal quality and transmission stability. Low-quality optics may lead to network crush and cause huge economic losses in large data centers. Fiber Optic Testing before shipment is key to guaranteeing transmission performance.
SFP module manufacturers that emphasize quality should have a comprehensive transceiver testing system. A series of performance tests, compatibility tests, and end-face inspection are the most important and fundamental optical transceiver testing levels every operator should perform.
QSFPTEK R&D specialists have built a transceiver testing program, which strictly defined the testing process of optics. Each module must undergo the listed SFP testing steps to be qualified for shipment. Please contact firstname.lastname@example.org for test reports.