Testing Optical Transceiver: Different Testing Parameters and Methods Discussed

Optical transceivers are an integral part of fiber optic networks. Owing to the growing demand and quality requirements of the optical transceivers, most times manufacturers and suppliers ensure that each individual device has been tested properly. Thus, testing their performance is important. Fiber optics is a multi-parameter technology, so several factors must be considered while testing the optical transceivers. This is why multiple tests are performed by industry experts to inspect and analyze the quality and performance efficiency of optical transceivers. This post discusses different parameters and introduces testing methods of fiber optic transceivers. An optical transceiver features a transmitter and a receiver, so it is important to test this equipment for individual functionality.

Different Techniques of Transmitter Testing and Receiver Testing

Let us focus on different methods and parameters of transmitter and receiver testing.
Testing Transmitter
When it comes to transmitter testing, the following factors must be tested on a priority basis.  
  • Transmitter Signal Strength: The transmitter signal strength impacts the overall performance of an optical transceiver. To test the transmitter signal strength, the following tests are performed.
  • Jitter Test: This test helps analyze the signal strength and scope for signal fluctuations. The fluctuating signal strength might result in loss of signal, attenuation, insertion losses and reflective losses, therefore, the test is one of the essential activities for testing transmitters.
  • Eye Mask Test: This test helps analyze the optical waveform and overall performance of a transmitter. The parameters of optical waveforms include amplitudes, wavelength, etc.
  • Optical Metrics: The optical metrics such as transmitter output is tested in the following ways:
  • Optical Modulation Amplitude (OMA): This test calculates the difference between optical powers of two wavelengths. This helps in analyzing the sustainable operating optical power of the transmitter.
  • Extinction Ratio Test: This test detects the optimal bias point and optimal modulation efficiency of the transmitter.
Testing Receiver
The receiver of an optical transceiver features an optoelectronic photodiode. This photodiode converts optical signals to electronic pulses decoding the optical signals into electronic bits. The following tests are conducted on the receiver to analyze its efficiencies.   
  • Optical Power Measurement Test:  This test helps analyze the signal delivering strength of the receiver. The poor signal strength affects the signal decoding capacity of the receiver. Thus, this test is performed to ensure the signal strength is within the expected range.
  • Bit Error Ratio: The poor performance of the receiver may result in bit decoding errors. This test is performed in order to calculate the frequency of the bit error and analyze its impact on the overall performance of the transceiver. 
Although all these methods of testing optical transceivers are utilized for testing transmitters and receivers, the optical transceiver has several other factors that impact the performance. There are additional methods of testing transceivers. Different pre-and post-assembly tests performed while installing these optical transceivers in the fiber optics network. which are covered further in this blog.
Pre and Post Assembly Techniques for Testing Optical Transceivers
In general, the optical transceivers are tested pre-assembly and post-assembly in order to test the component performance and overall assembly. Let us discuss the methods of testing optical transceivers before and after the assembly.
  • Pre-Assembly Testing Optical Transceivers
The following are the techniques adopted for preassembly testing optical transceivers.
  • Incoming Quality Control (IQC): The incoming quality control (IQC) test is performed to analyze the quality of components before surface-mounting. In this test, the quality of fiber optic cables, transmitters, and receivers are analyzed. The components of transmitters such as laser diodes, electrical interfaces, etc are tested as transmitter optical sub-assembly (TOSA). The components of the receiver such as a photodiode, optical interface, etc are tested as receiver optical sub-assembly (ROSA). TOSA and ROSA together form a bi-directional optical sub-assembly (BOSA) which is also collectively tested for performance before the surface mount assembly.
Once the pre-assembly tests are done, the fiber optic transceivers are assembled as tested using post-assembly testing techniques.
  • Post-Assembly Testing Optical Transceivers
The following post-assembly techniques are used for testing optical transceivers.
  • Optical Power (Average Output) Measurement: In order to perform this test, the device called optical power meter is utilized. On connecting with a fiber optic transceiver, the optical power meter indicates the optical power at the transmitter’s end. In the case of long-distance transmission requirement, the transmitter’s optical power is expected to be higher than the maximum input optical power. It is an essential step in transmitter testing
  • Extinction Ratio Test: The extinction power indicates the ratio of the highest optical power to the lowest optical power. This test is performed to analyze the strength of the optical signal which should be in a significant range of optimal bias point so that optimal modulation efficiency is achieved. The higher the extinction ratio, the higher is the strength of the optical signal.
  • Optical Modulation Amplitude Test: This test is performed to calculate the difference between the optical power at the source and delivering end. This difference defines the load on the receiver.
  • Receiving Sensitivity and Bit Error Test (BER): The receiving capability or the sensitivity of the receiver is an essential factor in the communication ability of a transceiver. The receiving capacity is tested through the bit error test (BER). In this test, the ability of a receiver to decode the optical signals into electrical bits is tested. If the receiver sensitivity is less, the decoding from the optical pulses to bits will be delayed. The delay results in bit error and delayed communication.
  • Eye Mask/Pattern Test: The eye pattern test is essential to analyze the performance of a transceiver. In this test, the waveform is analyzed by using an oscilloscope. In this test, the wavelength, waveform, wave amplitudes, jitters, duty cycles, etc of the optical waveform eye pattern are tested. Multi-Source Agreement (MSA) has defined a standard eye pattern so that during eye pattern test, the results can be matched in compliance with MSA.
  • Wavelength Analysis: The wavelength of the fiber optic transceiver should remain consistent from the transmitter to the receiver. To ensure the same, the wavelength analysis is performed by checking the wavelength and signal strength at multiple nodes during the transmission. Factors like deviation, wavelength depletion, the dispersion can be tested via this test.
Along with these above-mentioned techniques of testing optical transceivers, a few additional techniques are performed to ensure the durability and compatibility of the device.

Additional Tests Performed On Optical Transceivers
The following additional tests are performed on the optical transceivers.
  • Aging Test: Based on the results of the above-mentioned performance tests, the life expectancy of the transmitter, receiver, and overall transceiver assembly are tested.
  • Compatibility Test: Since there is a wide variety of fiber optic products, the transceivers must be compatible with the third-party devices in the network. This is ensured by the compatibility test.
  • End-Face Inspection: In this test, the optical transceiver is observed under a microscope to check any dirt or dust in the path of optical signal transmission.
Now that all the methods of testing fiber optic transceivers are discussed, you must buy the transceivers that pass all these tests. In order to ensure the quality, one must go for MSA compliant devices from reliable suppliers like VERSITRON. The company offers high-quality fiber optic devices for various industrial communication and data transmission requirements.

Rich Tull

R.W. Tull is the President of Versitron Inc. He works closely with clients to review layout diagrams and drawings in order to ensure that the best fiber optic solution is achieved for a particular project.

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