Lasers were realized on silicon by flip-chip bonding of indium phosphide (InP) devices containing total internal reflection turning mirrors for surface emission. Light is coupled to the silicon waveguides through surface grating couplers. With this technique, InP lasers were integrated on silicon. Laser cavities were also formed by coupling InP reflective semiconductor optical amplifiers to microring resonator filters and distributed Bragg reflector mirrors. Single-mode continuous wave lasing was demonstrated with a side mode suppression ratio of 30 dB. Up to 2 mW of optical power was coupled to the silicon waveguide. Thermal simulations were also performed to evaluate the low thermal impedance afforded by this architecture and potential for high wall-plug efficiency.

As datacenters continue to scale in size, energy efficiency for short reach (<2 km) links is a major factor for networks that may connect hundreds of thousands of servers. We demonstrate that links based on analog coherent detection (ACD) offer a promising path to simultaneously achieving significantly larger link budgets and improved link energy efficiency. A complete analysis is presented that considers the power consumption of all the photonic and electronic components necessary to realize an ACD link architecture based on 50 Gbaud (GBd) quadrature phase-shift keying (QPSK) signaling combined with polarization multiplexing to achieve 200 Gb/s/λ. These links utilize receivers that incorporate an optical phase-locked loop (OPLL) to frequency- and phase-lock the local oscillator (LO) laser to the incoming signal. QPSK modulation offers compelling advantages both in achievable link budget and in energy efficiency. Indeed, low-complexity electronics based on limiting amplifiers can be used as opposed to the linear front-ends, A/D converters, and digital signal processing (DSP) required for higher-order QAM or PAM formats. Our analysis indicates that links with 13 dB of unallocated budget operating at error rates of <10 ⁻¹² can be achieved and is compatible with higher error rates that require forward error correction (FEC). We present a comparison of silicon and InP platforms and evaluate both traveling-wave and segmented modulator designs, providing an illustration of the wide design space before converging on the most promising architectures that maximize energy efficiency and minimize laser power. We establish the theoretical potential to achieve picojoule-per-bit energy efficiency targets.

We present a photonic integrated circuit (PIC) transceiver for frequency modulated continuous wave (FMCW) LiDAR applications. The transmitter consists of a widely tunable sampled grating distributed Bragg reflector laser (SGDBR) and a frequency discriminator which combines multimode interference couplers, a tunable asymmetric Mach-Zehnder Interferometer (a-MZI), and balanced photodiodes. The frequency discriminator converts frequency fluctuations of the laser to amplitude fluctuations of the photodiode currents. This provides an error signal for feedback into the laser cavity for frequency stabilization. Frequency modulation is obtained by a phase shifter in the a-MZI which tunes the quadrature point of the filter and the frequency where the error is zero. An on-chip receiver couples power from the transmitter to self-heterodyne with the time-delayed echo of a distance object. The generated beat frequency of the self-heterodyne measurement gives the echo signals time-of-flight to obtain the distance and velocity of the reflecting object. The theory of the components is described, and characterization of the transmitter and receiver are presented.

In this paper, we present a coherent receiver based on an optical phase-locked loop (PLL) for linear phase demodulation. The receiver concept is demonstrated at low frequency. For high-frequency operation, monolithic and hybrid integrated versions of the receiver have been developed and experimentally verified in an analog link. The receiver has a bandwidth of 1.45 GHz. At 300 MHz, a spurious free dynamic range (SFDR) of 125 dB ldr Hz^2/3 is measured.

Three-ORR based integrated ultra-low loss silicon nitride 1 × 4 optical beamforming networks (OBFNs) for millimeter-wave (mmW) beamsteering are reported. The group delay ripple of multi-ORR delay line was theoretically optimized and quantitatively studied by applying a genetic algorithm. The optimized 3-ORR delay true time delay (TTD) responses were experimentally achieved with 208.7 ps and 172.4 ps of delay tuning range for a bandwidth of 6.3 GHz and 8.7 GHz, corresponding to a phase shift of 17.1π and 14.1π for a 41 GHz mmW signal. The TTD performance of the 3-ORR delay line was also verified by control the delay of a 3 Gbps data stream. A 22 deg beamsteering angle equivalent OBFN delay distribution was achieved for a 41 GHz half-wavelength dipole antenna array. Both the theoretical analysis and experiments exhibit that the topology with one ring shared could balance the system complexity and TTD bandwidth well. Using heterodyne upconversion technology and a single delay path, 41 GHz mmW signal with 3 Gbps OOK NRZ data modulation was generated and delayed.

Heteroepitaxy of III–V compound semiconductors on industry standard (001) silicon (Si) substrates is highly desirable for large-scale electronic and photonic integrated circuits. Challenges of this approach relate primarily to lattice, polarity, and coefficient of thermal expansion mismatch, which ultimately generate a high density of defects and limit the reliability of active devices. Ongoing efforts to monolithically integrate lasers in silicon photonics include leveraging quantum dots for reduced sensitivity to defects and the ability to enable 1310 nm lasers with gallium arsenide (GaAs) and related compounds. In this work, to extend the operation window to the widely used 1550 nm telecommunications region, we have demonstrated continuous-wave (CW) electrically pumped indium phosphide (InP)-based quantum well lasers on complementary metal-oxide-semiconductor (CMOS)-compatible (001) Si. Heteroepitaxy of InP and related compounds on Si poses additional challenges because the lattice mismatch is significantly larger compared to GaAs. Key to our approach is the development of a low dislocation density InP-on-Si template by metalorganic chemical vapor deposition (MOCVD). Following an InP buffer with a surface defect density of ${1.15} \times {{10}^8}/{{\rm cm}^2}$, a seven-layer indium gallium arsenide phosphide (InGaAsP) multi-quantum well laser diode structure was grown. Fabry–Perot ridge waveguide lasers were then fabricated. A 20-µm wide and 1000-µm long laser demonstrates a room temperature continuous-wave (CW) lasing threshold current density of ${2.05}\;{{\rm kA}/{\rm cm}^2}$ and a maximum output power of 18 mW per facet without facet coating. CW lasing up to 65°C and pulsed lasing greater than 105°C were achieved. This MOCVD-based heteroepitaxy approach offers a practical path toward monolithic integration of InP lasers in silicon photonics.