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In this paper, compact optical subassemblies are demonstrated based on a novel silicon interposer, which is designed and fabricated in a wafer scale process. The interposer includes the design of optical and electrical connections. A low-cost fabrication method, wet etching, is used to define light inputs and outputs as well as create the required recesses in the interposer to embed the chips into the silicon wafer at the same time. Impedance matched traces, for the high speed signals of the CMOS and opto-electronic ICs, are designed using advanced design system software and transferred onto the interposer by photolithography and electro-plating, which are accomplished on the deeply etched topology. The whole process flow of the silicon interposer patterning is designed and demonstrated, and the challenges are discussed. After the process, the optoelectronic dies and their complimentary CMOS parts are flipped and bonded on the interposer in close proximity, and a mechanical optical interface (MOI) is mounted for light coupling. Both transmitter and receiver subassemblies provide 12 parallel optical interconnections, and are scaled down to an area measuring 6 by 8 mm. Signal integrity testing is performed on a probe station for 10 Gb/s data signal delivering clear eye patterns for all channels (in both Rx and Tx subassemblies). The performance is further characterized using bit error rate (BER) testing. Both transmitter and receiver assemblies outperform a reference SFP+, with receiver sensitivity of-10 dBm at a BER lower than 10-12 after compensating for the MOI insertion loss. Finally, we also test the assemblies for crosstalk and demonstrate that the current design has a maximal additional penalty lower than 0.2 and 0.8 dB for transmitter and receiver, respectively.

Integrated polarization converters (PCs) with high (>99%) conversion efficiency open up many new possibilities in an InP-based photonic integrated circuit. In this paper, we describe how such a PC can be added to a circuit containing semiconductor optical amplifiers (SOAs), in order to obtain polarization independent amplification. Polarization independence is obtained by placing the PC halfway between two identical SOA sections. This approach has the advantage that no compromises in design and fabrication are needed. The polarization conversion is found to be very high, above 99.5%, when using a tolerant two-section PC. The extra insertion loss due to the converter is below 0.5 dB. The polarization-dependent gain (PDG) of the SOA reduces from 17 dB to only 0.3 dB by the inclusion of the PC. This is comparable to the best PDG values found in the literature with other techniques. The reduction is achieved over the whole C-band and for varying pump currents.

Low polarization-dependent semiconductor optical amplifiers (SOA) co-integrated with passive circuits via an easy fabrication process are highly demanded in optical communication systems. However, despite several SOAs have been reported, co-integration of polarization-independent bulk SOA with passive waveguides in the InP platform to generate complex systems remains an issue. In this work, we design, simulate, fabricate and characterize a low polarization-dependent SOA based on a bulk active layer that is co-integrated with passive waveguides and exhibits its potential application to realize photonic integrated circuits. Simulation results are in good agreement with the experimental results. Based on the simulation results, the designed SOAs with the length of 300 μm, 750 μm, and 1500 μm cover broadband with 3-dB bandwidth of around 65 nm, 40 nm, and 37 nm, respectively. Characterization of SOAs with different lengths between 300 μm and 1500 μm co-integrated with passive waveguide has been performed. Broadband gain and polarization-dependent gain (PDG) less than 2 dB is measured for 300 μm SOA. Also, at 1550 nm, output saturation power of 12.8 dBm is achieved at the current density of 11.6 kA/cm2. For the longest SOA with 1500 μm length, the higher gain of 16 dB with PDG lower than 2.5 dB and saturation power of 7.4 dBm at the wavelength of 1588 nm and current density of 4.1 kA/cm2 are achievable. Thus, one could design SOA based photonic circuits with higher gain and saturation power and low PDG by exploiting different SOA lengths and design at the wavelength of interest, opening to potential application in photonic integrated circuits like low-loss and polarization-insensitive switches.