Daryl T. Spencer

Electrically-pumped compact hybrid silicon microring lasers for optical interconnects

We demonstrate an electrically-pumped hybrid silicon microring laser fabricated by a self-aligned process. The compact structure (D = 50 microm) and small electrical and optical losses result in lasing threshold as low as 5.4 mA and up to 65 degrees C operation temperature in continuous-wave (cw) mode. The spectrum is single mode with large extinction ratio and small linewidth observed. Application as on-chip optical interconnects is discussed from a system perspective.

Ultra-high quality factor planar Si 3 N 4 ring resonators on Si substrates

We demonstrate planar Si3N4 ring resonators with ultra-high quality factors (Q) of 19 million, 28 million, and 7 million at 1060 nm, 1310 nm, and 1550 nm, respectively. By integrating the ultra-low-loss Si3N4 ring resonators with laterally offset planar waveguide directional couplers, optical add-drop and notch filters are demonstrated to have ultra-narrow bandwidths of 16 MHz, 38 MHz, and 300 MHz at 1060 nm, 1310 nm, and 1550 nm, respectively. These are the highest Qs reported for ring resonators with planar directional couplers, and ultra-narrowband microwave photonic filters can be realized based on these high-Q ring resonators.

An Integrated Hybrid Silicon Multiwavelength AWG Laser

The first integrated multiwavelength laser based on an arrayed waveguide grating (AWG) fabricated on a silicon-on-insulator wafer is presented. It consists of Fabry-Perot cavities integrated with hybrid silicon amplifiers and an intracavity filter in the form of an AWG with a channel spacing of 360 GHz. Four-channel lasing operation is shown. Single-sided fiber-coupled output powers as high as 35 μW are measured. The device shows subnanosecond rise and fall times, and direct modulation at 1 GHz gives an open eye with an extinction ratio of 7.7 dB.

Teardrop Reflector-Assisted Unidirectional Hybrid Silicon Microring Lasers

We study directional bistability in hybrid silicon microring lasers and demonstrate a unidirectional laser. Unidirectional emission is achieved by integrating a passive reflector that feeds laser emission back into the laser cavity to introduce an extra unidirectional gain. We show that the length of the passive reflector is a critical parameter in determining the lasing behavior.

An optical-frequency synthesizer using integrated photonics.

Integrated-photonics microchips now enable a range of advanced functionalities for high-coherence applications such as data transmission, highly optimized physical sensors, and harnessing quantum states, but with cost, efficiency, and portability much beyond tabletop experiments. Through high-volume semiconductor processing built around advanced materials there exists an opportunity for integrated devices to impact applications cutting across disciplines of basic science and technology. Here we show how to synthesize the absolute frequency of a lightwave signal, using integrated photonics to implement lasers, system interconnects, and nonlinear frequency comb generation. The laser frequency output of our synthesizer is programmed by a microwave clock across 4 THz near 1550 nm with 1 Hz resolution and traceability to the SI second. This is accomplished with a heterogeneously integrated III/V-Si tunable laser, which is guided by dual dissipative-Kerr-soliton frequency combs fabricated on silicon chips. Through out-of-loop measurements of the phase-coherent, microwave-to-optical link, we verify that the fractional-frequency instability of the integrated photonics synthesizer matches the 7.0x10^(−13) reference-clock instability for a 1 second acquisition, and constrain any synthesis error to 7.7x10^(−15) while stepping the synthesizer across the telecommunication C band. Any application of an optical frequency source would be enabled by the precision optical synthesis presented here. Building on the ubiquitous capability in the microwave domain, our results demonstrate a first path to synthesis with integrated photonics, leveraging low-cost, low-power, and compact features that will be critical for its widespread use.Optical-frequency synthesizers, which generate frequency-stable light from a single microwave-frequency reference, are revolutionizing ultrafast science and metrology, but their size, power requirement and cost need to be reduced if they are to be more widely used. Integrated-photonics microchips can be used in high-coherence applications, such as data transmission1, highly optimized physical sensors2 and harnessing quantum states3, to lower cost and increase efficiency and portability. Here we describe a method for synthesizing the absolute frequency of a lightwave signal, using integrated photonics to create a phase-coherent microwave-to-optical link. We use a heterogeneously integrated III–V/silicon tunable laser, which is guided by nonlinear frequency combs fabricated on separate silicon chips and pumped by off-chip lasers. The laser frequency output of our optical-frequency synthesizer can be programmed by a microwave clock across 4 terahertz near 1,550 nanometres (the telecommunications C-band) with 1 hertz resolution. Our measurements verify that the output of the synthesizer is exceptionally stable across this region (synthesis error of 7.7 × 10−15 or below). Any application of an optical-frequency source could benefit from the high-precision optical synthesis presented here. Leveraging high-volume semiconductor processing built around advanced materials could allow such low-cost, low-power and compact integrated-photonics devices to be widely used.An optical-frequency synthesizer based on stabilized frequency combs has been developed utilizing chip-scale devices as key components, in a move towards using integrated photonics technology for ultrafast science and metrology.

Continuous wave-pumped wavelength conversion in low-loss silicon nitride waveguides

In this Letter we introduce a complementary metal-oxide semiconductor (CMOS)-compatible low-loss Si3N4 waveguide platform for nonlinear integrated optics. The waveguide has a moderate nonlinear coefficient of 285  W/km, but the achieved propagation loss of only 0.06  dB/cm and the ability to handle high optical power facilitate an optimal waveguide length for wavelength conversion. We observe a constant quadratic dependence of the four-wave mixing (FWM) process on the continuous-wave (CW) pump when operating in the C-band, which indicates that the waveguide has negligible high-power constraints owing to nonlinear losses. We achieve a conversion efficiency of -26.1  dB and idler power generation of -19.6  dBm. With these characteristics, we present for the first time, to the best of our knowledge, CW-pumped data conversion in a non-resonant Si3N4 waveguide.

Coupled-Ring-Resonator-Mirror-Based Heterogeneous III–V Silicon Tunable Laser

We show theoretical and experimental results from a tunable laser, with its center wavelength in the C-band, designed using coupled-ring resonator mirrors. The effective cavity length enhancement and negative optical feedback obtained from the resonators helps to narrow the laser linewidth in a small form factor. We report a linewidth of 160 kHz and a side-mode suppression ratio of > 40 dB over the full tuning range.

Integrated hybrid Si/InGaAs 50 Gb/s DQPSK receiver

A monolithic 25 Gbaud DQPSK receiver based on delay interferometers and balanced detection has been designed and fabricated on the hybrid Si/InGaAs platform. The integrated 30 µm long InGaAs p-i-n photodetectors have a responsivity of 0.64 A/W at 1550 nm and a 3dB bandwidth higher than 25 GHz. The delay interferometer shows a delay time of 39.2 ps and an extinction ratio higher than 20 dB. The demodulation of a 25 Gb/s DPSK signal by a single branch of the receiver demonstrates its correct working principle.

An Ultra-Low Phase-Noise 20-GHz PLL Utilizing an Optoelectronic Voltage-Controlled Oscillator

This paper describes a novel phase-locked loop (PLL) architecture utilizing an optoelectronic oscillator (OEO) as a voltage-controlled oscillator (VCO). The OEO demonstrates excellent far-out phase-noise performance while the PLL reduces the close-in phase noise. The nonmonotonic VCO characteristics of the OEO placed stringent demands on the loop filter electronics and startup conditions. The crystal reference, prescalar, frequency synthesizer, and loop filter were all implemented with discrete high-performance components. The resulting frequency synthesizer yields a -10-dBm output at 20 GHz with phase noise of -80 dBc/Hz at 100-Hz offset, and -134 dBc/Hz at 10-kHz offset. These results are far superior to PLL synthesizers utilizing only an electronic VCO and illustrate the power of optoelectronic integration.

Realization of a Novel

The first experimental demonstration of a novel ring resonator-based 1 × N optical power splitter is reported. We fabricate the device on a Si3N4 waveguide platform utilizing a bonded thermal oxide upper cladding. Fiber coupling and near-held-imaging experiments at 1550 nm show that a 1 × 16 power splitter achieves very low excess loss of 0.9 dB in addition to excellent uniformity of 0.4 dB. The resonances of the device show a loaded quality factor of 6 million and hnesse of 100. The device is promising for high-port-count power splitters without the need for cascaded stages. We also discuss applications requiring the wavelength selectivity of the device.