The main parameters of the transmitting end are reflected from the eye map, including the rate-bit Rate of the modulating signal of the optical module; Eye height reflecting the output power of the signal at the transmitting end Eye Ampl; Signal peak-to-peak jitter (Jitter_P-P) and root-mean-square jitter (Jitter_RMS); Measure the percentage of eye cross between signals "1" and "0"; The average transition time and rise and fall time of level conversion; Optical modulation amplitude (OMA) of the difference between the "1" signal and the "0" signal; Total modulation optical Power and Average optical Power; Laser power in logic "1" power and in logic "0" power ratio extinction ratio (ER).

The main parameter of the receiving end is the receiving sensitivity of PD, the higher the sensitivity, the smaller the received optical power can be, and the design transmission distance of the entire transmission system can be farther.

In module production, the optical power received under BER=10-12 is generally characterized.

When the bit error rate received by the module reaches the threshold (BER≥10-3), the optical module enters the LOS state and signals are lost, that is, LOS Assert. The signal from loss to recovery indicates LOS Dessert; LOS Hysteresis Indicates the power difference between signal loss and signal recovery.

Test system

The test system of optical module needs to integrate optical oscilloscope, error meter, optical switch, optical attenuator, optical power meter, etc.

Based on the sensitivity test of the ROSA end of the device under test, BERT is used to drive a standard optical module single-ended to generate a reference optical signal, and input the multi-channel attenuator through WDM split-wave. The attenuator simulates the link loss and sends the attenuator to the ROSA end of the module under test. After photoelectric conversion, the bit error meter compares the bit error rate under different link loss. Finally, the module sensitivity index is quickly obtained by fitting method.

For the TOSA optical index test, BERT single-ended drive to be measured optical module is also used, and multiple signals are sent to the oscilloscope through the WDM device for eye diagram test.

According to the number of optical port channels of the eye diagram test, optical switches can also be used for serial testing of multi-channel eye diagram.

Classic parallel test scheme diagram

In order to achieve fast and efficient testing of optical modules, in addition to the selection of high speed test instruments, the basic parallel test module is essential.

In large-scale production line testing, it is also common to use typical measurement values to estimate the actual value that needs to be measured over a long period of time.

Improving efficiency

For multi-channel optical modules, corresponding parallel test equipment is needed to improve efficiency. From the perspective of the whole test system link, the use of multi-channel error meter, multi-channel optical attenuator and DCA instrument supporting multi-channel eye map will be the best efficiency scheme regardless of cost.

After the parallel high-speed electrical signal is converted into optical signal, it is also necessary to simulate the link loss for each channel. The multi-channel attenuator with power monitoring power can simplify the test system and monitor the power status of the module online in real time while meeting the needs of fast detection module sensitivity.

In the process of eye image testing, using multi-channel optical port DCA for parallel eye image testing can greatly save test time, replace optical switch for channel switching, and avoid eye image distortion caused by crosstalk between channels or redundant link nodes.

The sensitivity of the receiver is tested by curve fitting

The sensitivity test of optical module needs to observe the bit error rate by adjusting the optical attenuator, but in the case of low bit error rate, the test time is often relatively long. In large-scale production, it is not advisable for each module to detect the actual sensitivity value. Generally, several typical bit error rate points can be tested under high bit error rate, and the average optical power obtained under low bit error rate (BRT=10-12) can be derived by fitting the received optical power-bit error rate curve of the module by least square method. This method can especially reflect its superiority in large-scale testing process of the production line.

The transmitter and receiver are tested simultaneously at the same station

The test of sensitivity and eye pattern is arranged in the same station, which requires the error meter to drive a standard light source module and the optical module to be measured at the same time. The choice of more channels of error meter or the choice of high-quality single-end drive error meter can make the system connection more concise. In terms of device connection, a standard optical module can be driven by a bit error meter differential positive extreme as a standard optical signal source, and the module to be tested can be driven by a negative end to detect the eye image quality at the transmitting end.

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