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What is CPO (co-packaged optics)?

Technology that mounts the optical transceiver parts (optical engines) in the same package as a switch IC or similar. Shorter electrical connections lower the energy per bit, but the optics cannot be swapped out by unplugging, so testing before assembly and the use of external laser sources become important.

Japanese name: CPO(コパッケージドオプティクス)

CPO (co-packaged optics) appears in 7 practice questions across 3 topics, including Silicon photonics, Compound semiconductors, Advanced packaging (3D and chiplets).

Field: Silicon photonics

Try it: questions about CPO (co-packaged optics)

Which is a correct challenge of CPO (Co-Packaged Optics), which mounts the optical transmit/receive components in the same package as the switch IC?

  1. AFailed optical components cannot be replaced as modules, so high reliability and thorough pre-assembly testing are required
  2. BThe electrical path between the switch IC and the optical components becomes longer, increasing power consumption compared with pluggables
  3. CThe step of attaching optical fiber to the package is eliminated, but communication reach is limited to a few cm
Show answer and explanation

Answer: A. Failed optical components cannot be replaced as modules, so high reliability and thorough pre-assembly testing are required

In CPO, the optical engines sit right next to the switch IC, so the electrical paths are short, lowering energy per bit and allowing many optical links to be packed densely. On the other hand, a failed optical component cannot be swapped out by unplugging it from the front panel, and the failure affects the entire package. Therefore, testing at the wafer or chip level before assembly and using only good parts, and moving the failure-prone lasers outside the package, become important. Operating optical components near the hot switch IC and precisely connecting many fibers are also challenges.

In CPO, an external laser source—placing the laser outside the switch IC package and supplying only light via fiber—is often considered. What is the main reason?

  1. ALasers tend to lose efficiency and lifetime at high temperatures, so they are kept away from the hot switch IC and made easier to replace
  2. BPlacing the laser outside the package completely eliminates coupling loss when carrying the light through fiber
  3. CSilicon modulators can generate light from electrical signals alone, without laser light
Show answer and explanation

Answer: A. Lasers tend to lose efficiency and lifetime at high temperatures, so they are kept away from the hot switch IC and made easier to replace

As temperature rises, a semiconductor laser's threshold current increases, its efficiency drops and degradation accelerates. In CPO, the optical engines are placed right next to a switch IC consuming several hundred W, so a laser inside the package would have to operate at harsh temperatures. An external laser source can run in a relatively cool location and can be replaced by plugging and unplugging, for example from the front panel. In exchange, the coupling loss of guiding the laser light to the optical engine through fiber increases, and the laser output must be raised accordingly. Modulators do not generate light.

CPO (co-packaged optics) in the explanations

Questions that mention CPO (co-packaged optics) (7)

  1. Which is a correct challenge of CPO (Co-Packaged Optics), which mounts the optical transmit/receive components in the same package as the switch IC?
  2. In CPO, an external laser source—placing the laser outside the switch IC package and supplying only light via fiber—is often considered. What is the main reason?
  3. In CPO, which integrates optical components with a switch IC and others in one package, why is it especially important to test optical characteristics at the wafer level before assembly?
  4. In silicon photonics, why are compound semiconductors combined with silicon for the laser light source?
  5. Which is a correct advantage of pluggable optical transceivers inserted into a switch's front panel?
  6. For a switch with a total bandwidth of 51.2 Tb/s, if all optical links operate at 5 pJ per bit, which is closest to the power consumption of the optical links?
  7. What is the technology called that mounts optical transceiver components close to switch ICs and the like in the same package, shortening electrical wiring to reduce power?

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