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Tilted EML package in TO Can

The traditional EML TO Can package places the chip on the base patch line and the lens on the TO Cap. The lens is a single lens that focuses on the line. To improve coupling efficiency and create more parallel light, a combination of two lenses is required. The collimator lens converts the divergent light of the laser. The size of the parallel light spot is related to the distance between the lens and the chips.

To reduce the light spot and improve coupling efficiency, we can move the lens closer to the chip. There are two solutions to achieve this goal. One is to move the chip closer to the lens, and the other is to move the TO Cap closer to the lens.

EML packages can be in a vertical or horizontal orientation. The vertical EML package requires an L-type ceramic submount, and for high-power chips, Direct Plating Copper (DPC) can be used for the best heat dissipation and better power output. The horizontal EML package provides good heat dissipation but has a long distance between the chip and the lens, resulting in decreased coupling efficiency.

To optimize these two options, a tilt substrate for EML is a compromise solution. The traditional EML's COC is shown in the picture below. The tilt substrate solution has two approaches to achieve the goal. One is to use a special tilt TEC, as shown in the picture below. This structure allows the EML to be horizontally welded on the TEC while the lens remains in place. The other approach is to use the traditional TEC with an angle pad.

The transition substrate of GSG modulation signal is also made beveled, which reduces the length of gold wire bonding and increases bandwidth. The parallel light path formed can slightly reduce the light spot and improve coupling efficiency.

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