Detachable interface toward a low-loss reflow-compatible fiber coupling for co-packaged optics (CPO).

High-density reflow-compatible fiber I/O is one of the challenges for co-packaged optics (CPO). This paper developed a detachable coupling interface based on expanded beam edge coupling, which can be applied for optical coupling between lasers, PICs, and fibers, seamlessly supporting many channels with high efficiency. It comprises a removable fiber connector and a permanent chip/device connector, in which microlens/lens arrays are used for waveguide mode expansion and MT-like connectors are used for position registration. An effective alignment scheme based on beam detection was developed and implemented in an assembly station for building the removable fiber connectors, while the permanent chip/device connector was assembled by active alignment to a pre-made fiber connector mated with a registration connector. Promising results were obtained from the proof-of-concept demonstrations of the coupling from SiP PIC and III/V lasers to fibers using the off-the-shelf lenses and modified MT registration connectors. In both cases, less than 1 dB coupling loss was achieved with an expanded beam size of 160 µm in diameter. Even with a relatively large lens offset of ∼35 µm, the detachable fiber array connectors showed good interchangeability. Such a coupling interface is expected to be solder-reflow compatible by replacing the plastic registration connectors with ceramic ones, making it a promising candidate for the solution to CPO fiber I/O.

Modulation properties enhancement in a monolithic integrated two-section DFB laser utilizing side-mode injection locking method.

A monolithic optical injection-locked (MOIL) DFB laser with large stable injection locking range is experimentally demonstrated using the side-mode injection locking technique. The low-frequency roll-off in the MOIL DFB laser is suppressed significantly. The relaxation oscillation frequency is measured to be 26.84 GHz and the intrinsic 3-dB response bandwidth is more than 30 GHz, which is about 20 GHz higher than that of the free running DFB laser. The nonlinear distortions, including the 1-dB compression point, second harmonic distortion (2HD) and third-order intermodulation distortion (IMD3), are also suppressed significantly. A simple radio-over-fiber system transmitting 40 Msymbol/s 32-QAM signal with 6 GHz carrier is achieved using the MOIL DFB laser. After 50 km transmission, the average error vector magnitude (EVM) of the whole link is 2.94% in injection locked state, while the EVM in free running DFB laser is 5.25% as a comparison. To our knowledge, this is the first time that the MOIL DFB laser is realized utilizing the side-mode injection locking method.