The term "optical transceiver" is now so widely known that even everyday people can chat about it. Its massive popularity boils down to the explosive global buildup of AI infrastructure. As a core component in this buildup, optical transceivers are incredibly hot both on the industry front line and in the secondary market. In particular, the latest 1.6T and 800G products not only command high prices but also frequently face supply shortages.
In this issue, EEFocus plans to directly teardown an optical transceiver to see what it looks like inside. Of course, with a limited budget, we cannot afford to teardown the 1.6T and 800G models just yet, so we chose a 400G optical transceiver from Eoptolink. At least in the domestic market, this is still a mainstream product and holds more practical reference value.
Based on the nameplate information, it can be inferred that this 400G optical transceiver from Eoptolink is primarily used for data centers. The product model contains key information: "DR4+ 2km". DR4 stands for 4-lane parallel transmission over single-mode fiber, with each lane operating at 100Gbps, totaling 400Gbps; the "2km" indicates it is specifically designed for a 2-kilometer transmission distance.
Teardown
Having understood the specifications of this optical transceiver, let's directly open it up to examine the internal hardware solution.
First of all, it must be said that you get what you pay for. This metal enclosure is far beyond what is found in typical consumer electronics. The all-metal housing not only shields against electromagnetic interference but also features abundant thermal grease distributed inside, adhering to the inner metal shell to effectively enable passive cooling for the chips. The only regret is that during the teardown of this optical transceiver, we accidentally broke the cover glass at the fiber optic coupling point, making it impossible to restore. What a pity.
Let's first look at the overall functions of this optical transceiver. Starting with the receiving circuit, the optical signal enters through the MPO optical interface and then reaches the PD (Photodiode), where the optical signal is converted into a weak current signal. Next, it goes to the TIA (Transimpedance Amplifier), which converts the weak current signal into a voltage signal. After that, it is sent to the DSP (Digital Signal Processor), and finally, the signal processed by the DSP is transmitted to the server via the gold finger interface.
The transmission path for the transmitting circuit is the reverse. Data from the AI server passes through the gold finger interface to the DSP for processing, and is then sent to the EML (Electro-absorption Modulated Laser). Through its internal electro-absorption modulator, the electrical signal is loaded onto the optical carrier wave and transmitted out via the optical fiber.
The specific chips involved in the circuit of this optical transceiver include:
Inphi's low-power PAM-4 DSP chip, model IN010C50-MD02. In current optical transceiver solutions, the cost of this chip accounts for the absolute majority. Currently, Inphi has been acquired by Marvell.
ADI's TEC (Thermoelectric Cooler) driver, model ADN8833. Its core role in the optical transceiver is to precisely control the operating temperature of the laser, ensuring the stability of its wavelength and output power.
The chips on the back of the optical transceiver PCB (Printed Circuit Board) include:
- ADI's precision analog microcontroller, model ADUCM320BBCZ, responsible for the system management and precision monitoring of the entire optical transceiver
- Two ADI synchronous step-down converters, model LTC3309A
- ADI's 12-bit digital-to-analog converter, model MAX5825AWP+T
In addition, it is rumored that this EML laser uses Broadcom's 100G product, though the truth remains unverified for now. Overall, this 400G optical transceiver from Eoptolink mainly adopts a solution combining Marvell, ADI, and Broadcom. The core chips heavily rely on US imports, and the proportion of domestic chips is not high, which makes it highly susceptible to supply chain chokepoints—this is also a common issue faced by the entire industry.
Summary
The above is the teardown of Eoptolink's 400G optical transceiver, which basically represents the mainstream technical direction of current 400G data center interconnects. From the perspective of the hardware solution, although the core chips still heavily rely on imports, domestic substitution is accelerating—silicon photonics chips have seen breakthroughs, and some driver and amplifier chips can be domestically produced, while DSP chips remain the most critical chokepoint at present. We look forward to seeing more domestic chips on the motherboard when we teardown the next-generation optical transceivers in the near future.