Application of high precision digital source meter in optical module test

Optical module is an optoelectronic device that performs photoelectric and electro-optical conversion. To be precise, optical module is a collective concept, which includes multiple internal component modules, including: optical receiving module, optical transmitting module, optical transceiver module and optical forwarding module. Nowadays, the optical module we usually refer to generally refers to the optical transceiver module, which is used to convert optical signals into electrical signals and electrical signals into optical signals. It is widely used in video surveillance, radio and television, medical equipment and other fields.
The optical transceiver module usually includes BOSA (laser transmitting device TOSA), ROSA (including photodetector), other functional circuits and optical (electrical) interfaces. At the transmitting end, the driver chip processes the original electrical signal and then drives the semiconductor laser (LD) or light emitting diode (LED) to emit a modulated optical signal; at the receiving end, after the optical signal comes in, it is converted into an electrical signal by the photodetector diode, and then outputs the electrical signal after the preamplifier.
The structural diagram of the optical module is as follows:

● Test for BOSA

In order to ensure the accuracy and stability of the operation of the optical transceiver module, its key component BOSA will undergo strict testing and quality inspection procedures before shipment. Among them, the test of the core components LD and PD-TIA in BOSA is particularly important.
The threshold current of LD is the current at which the laser tube starts to generate laser oscillation. For general low-power laser tubes, its value is about tens of milliamperes. The threshold current of the laser tube with a strained multi-quantum well structure can be as low as 10mA or less. PD converts the optical signal into current, which is then converted into a voltage signal through a transimpedance amplifier (TIA).
The schematic diagram of the operating structure of the BOSA device is as follows:

● Test indicators of key characteristics of BOSA

●Response current Ip
●Responsivity R, R=Ip/Pi, where Ip represents the photocurrent generated by the photodetector, and Pi represents the optical power input to the photodetector.
●Dark current Id, the current generated under a specified reverse voltage when there is no light incident.
●Reverse breakdown voltage VBR, the reverse voltage at which the reverse current reaches a predetermined value when there is no light irradiation.
NGI N2600 series high-precision digital source meter integrates high-precision power supply and high-performance DMM in one instrument. It can output ultra-high-precision voltage source and current source and provide high-precision I/V/R measurement function. It can meet the needs of optical module devices for high-precision index testing with a small number of devices.
The test diagram of N2600 series source meter is as follows: