The number of photonic components integrated into the same circuit is approaching one million, but so far, this has been without the large-scale integration of active components: lasers, amplifiers, and high-speed modulators. Emerging applications in communication, sensing, and computing sectors will benefit from the functionality gained with high-density active–passive integration. Indium phosphide offers the richest possible combinations of active components, but in the past decade, their pace of integration scaling has not kept up with passive components realized in silicon. In this work, we offer a perspective for functional scaling of photonic integrated circuits with actives and passives on InP platforms, in the axes of component miniaturization, areal optimization, and wafer size scaling.

Optical beam steerers on InP integrated photonics have not been able to offer high angular resolution, due to the technological challenges in realizing a large emission aperture. In this paper, we propose the creation of waveguide-based grating antennas fabricated in SiO2 super-cladding on InP membrane on silicon (IMOS) to achieve simultaneously high resolution and good compatibility with InP-based active devices. By exploiting the high dry etch selectivity between SiO2 and InP, a tolerant fabrication process is proposed and demonstrated, allowing for high controllability in the process. Device parameters including buffer thickness and pitch have been explored to obtain an optimized design. A 2-mm long grating antenna is fabricated and shows a record narrow full-width-half-maximum angular beam width of 0.05° and a high spatial resolution of more than 250 points when the wavelength is tuned over a range of 100 nm.

Energy-efficient electro-optic phase shifters have been widely adopted in the InP material system, but their lengths have been in millimeter scales. The strong thermo-optic effect of InP ( $dn/dT = 2.0 \times 10^{-4}~\textrm {K}^{-1}$ ) can potentially enable compact devices, but it has been hindered by the large heat capacity of the bulky waveguide and inefficient heat transfer to the optical mode. By moving to a sub-micron-thick InP membrane, where the optical modes are more exposed and heat capacity minimized, we report here, to the best of our knowledge, first ultra-compact ( $97~\mu \textrm {m}^{2}$ footprint)m efficient ( $2.26~\textrm {mW}/\pi$ ) and broadband (100 nm) thermo-optic microheaters in the InP material system. An epitaxially grown layer as part of the waveguide is used as the heating element, enabling maximum heat transfer efficiency. The epitaxial layer structure is designed to be compatible with the membrane photonics platform that includes monolithic amplifiers and lasers. This work could contribute to the further miniturization of monolithic photonic integrated circuits (PIC) that involves phase shifters and amplifiers, and facilitate applications such as optical computing, switching, and sensing.

We present waveguide photonic crystal reflectors on the InP-membrane-on-silicon (IMOS) platform, and a method to accurately measure the reflectivity of those reflectors. The photonic crystal holes are patterned on a waveguide using electron-beam lithography and etched through the waveguiding layer to create a broadband distributed Bragg reflector. We show simulations of these reflectors and experimental results of fabricated devices, both showing a high, free-to-choose reflectivity, and high quality factor Fabry-Pérot cavities. We experimentally show reflectivities higher than 95% for the reflectors and a quality factor as high as 15,911±511 for a Fabry-Pérot cavity, using reflectors with a length of only 4 microns. For the first time, to our knowledge, two methods for measuring the reflectivity are used for characterization of on-chip reflectors to accurately determine the reflection. The first method is based on analysis of the transmission through a Fabry-Pérot cavity, the second is based on a direct four-port measurement of the reflector. A systematic error is made in both methods, resulting in an upper and lower boundary for the actual reflection coefficient.

Semiconductor optical amplifiers (SOAs) are a fundamental building block for many photonic systems. However, their power inefficiency has been setting back operational cost reduction, circuit miniaturization, and the realization of more complex photonic functions such as large-scale switches and optical phased arrays. In this work, we demonstrate significant gain and efficiency enhancement using an extra degree of freedom of light—the mode space. This is done without changing the SOA’s material design, and therefore high versatility and compatibility can be obtained. Light is multiplexed in different guided modes and reinjected into the same gain section twice without introducing resonance, doubling the interaction length in a broadband manner. Up to 87% higher gain and 300% higher wall-plug efficiency are obtained in a double-pass SOA compared to a conventional single-pass SOA, at the same operating current, in the wavelength range of 1560–1580 nm.