Intra-cavity coherent combining of DBR lasers on an InP generic foundry platform

We report an intra-cavity coherent combining of two distributed Bragg reflector (DBR) lasers with a combining efficiency of ∼84% on an InP generic foundry platform. The on-chip power of the intra-cavity combined DBR lasers is ∼9.5 mW at the injection current of 42 mA in both gain sections simultaneously. The combined DBR laser operates in a single-mode regime with a side-mode suppression ratio of 38 dB. This monolithic approach paves the way toward high-power and compact lasers, which is useful in scaling integrated photonic technologies.

Integration of GaAs waveguides on a silicon substrate for quantum photonic circuits

We report a method for integrating GaAs waveguide circuits containing self-assembled quantum dots on a Si/SiO₂ wafer, using die-to-wafer bonding. The large refractive-index contrast between GaAs and SiO₂ enables fabricating single-mode waveguides without compromising the photon-emitter coupling. Anti-bunched emission from individual quantum dots is observed, along with a waveguide propagation loss <7 dB/mm, which is comparable with the performance of suspended GaAs circuits. These results enable the integration of quantum emitters with different material platforms, towards the realization of scalable quantum photonic integrated circuits.

Ultralow-linewidth ring laser using hybrid integration and generic foundry platforms

Two photonic integrated circuits (PICs) are coupled to form a hybridly integrated semiconductor ring laser in the telecom C band with an intrinsic linewidth of (158±21) Hz. This is, to the best of our knowledge, the first time an InP active-passive platform is used in conjunction with an integrated low-loss resonator to obtain a narrow-linewidth laser implemented using generic foundry platforms. The presented results pave the way for a hybrid integrated platform for microwave photonics (MWP), as the demonstrated device includes multiple active-passive components, and its narrow optical linewidth can potentially be translated to a narrow-linewidth microwave signal. Furthermore, as the laser is based on hybrid integration of two PICs from generic foundry platforms, there is a path to reproducible and low-cost devices.

A 10-kHz intrinsic linewidth coupled extended-cavity DBR laser monolithically integrated on an InP platform

We report a monolithically integrated coupled extended-cavity distributed Bragg reflector laser with, to our knowledge, the lowest reported intrinsic linewidth of ∼10 kHz, which is extracted from a corresponding frequency-noise level of ∼3200 Hz²/Hz, realized on an InP generic foundry platform. Using the delayed self-heterodyne method, the experimentally measured linewidth was 45 kHz. The laser has an on-chip optical output power of 18 mW around 1550 nm at an injection current of 95 mA. The laser operates in a single-mode regime with a side-mode suppression ratio of 54 dB. Our monolithic approach paves the way toward further integration, such as integrated quantum key distribution transceivers.

Fully integrated 45-GHz harmonically mode-locked ring laser with an intra-cavity Mach-Zehnder filter

Wavelength division multiplexing (WDM) systems can utilize the full capacity of a single optical fiber and thereby keep up with the increasing demand for higher bandwidths within datacenters. A single mode-locked laser diode emits a comb of wavelengths and can thus, in principle, be used to generate all the channels of a WDM system. However, achieving a large channel spacing of much more than 20-30 GHz can be troublesome, since this depends directly on making the cavity smaller. To circumvent this, harmonic mode-locking can be utilized, as this increases the channel spacing while keeping the cavity size fixed. In this work, we show that a monolithically integrated 45-GHz harmonically mode-locked ring laser based on an intra-cavity Mach-Zehnder filter is feasible on a generic integration platform. True harmonic mode-locking was achieved with no measurable RF peak at the fundamental frequency. The pulse train exhibits an autocorrelation trace width of ∼2.5ps FWHM, RF linewidth of ∼0.44MHz, and 3-dB comb bandwidth of ∼240GHz.

Feasibility of Telecom-Wavelength Photonic Integrated Circuits for Gas Sensors

To be of commercial interest, gas sensors must optimise, among others, sensitivity, selectivity, longevity, cost and measurement speed. Using the example of ammonia, we establish that integrated optical sensors provide means to maintain the benefits of optical detection set-ups at, in principle, a lower cost and smaller footprint than currently available commercial products. Photonic integrated circuits (PICs) can be used in environmental and agricultural monitoring. The small footprint and great cost scaling of PICs allow for sensor networks with multiple devices. We show, that Indium Phosphide based commercial foundries reached the technological maturity to enable ammonia detection levels at less than 100 ppb. The current unavailability of portable, low cost ammonia sensors with such detection levels prevents emission monitoring, for example, in pig farms. The feasibility of these sensors is investigated by applying the common noise figures of the multiproject wafer platforms operating around 1550 nm to a model for an absorption measurement. The analysis is extended to other relevant gas species with absorption features near telecom-wavelengths.

Unidirectional hybrid silicon ring laser with an intracavity S-bend

We demonstrate a hybrid silicon ring laser with an internal amplifying S-bend that couples a fraction of the counter-clockwise circulating light into the the clockwise direction. The device supported single-mode, unidirectional laser oscillation at certain bias conditions. A spatial field distribution model is derived to describe the unidirectional operation. A unidirectional clockwise laser output with a suppression ratio up to 18.6 dB over the counter-clockwise mode was achieved.

Multi-octave spectral beam combiner on ultra-broadband photonic integrated circuit platform

We present the design of a novel platform that is able to combine optical frequency bands spanning 4.2 octaves from ultraviolet to mid-wave infrared into a single, low M2 output waveguide. We present the design and realization of a key component in this platform that combines the wavelength bands of 350 nm - 1500 nm and 1500 nm - 6500 nm with demonstrated efficiency greater than 90% in near-infrared and mid-wave infrared. The multi-octave spectral beam combiner concept is realized using an integrated platform with silicon nitride waveguides and silicon waveguides. Simulated bandwidth is shown to be over four octaves, and measured bandwidth is shown over two octaves, limited by the availability of sources.

Heterogeneously integrated 2.0 μm CW hybrid silicon lasers at room temperature

Here we experimentally demonstrate room temperature, continuous-wave (CW), 2.0 μm wavelength lasers heterogeneously integrated on silicon. Molecular wafer bonding of InP to Si is employed. These hybrid silicon lasers operate CW up to 35°C and emit up to 4.2 mW of single-facet CW power at room temperature. III-V tapers transfer light from a hybrid III-V/silicon optical mode into a Si waveguide mode. These lasers enable the realization of a number of sensing and detection applications in compact silicon photonic systems.

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.

Fully integrated hybrid silicon two dimensional beam scanner

In this work we present the first fully-integrated free-space beam-steering chip using the hybrid silicon platform. The photonic integrated circuit (PIC) consists of 164 optical components including lasers, amplifiers, photodiodes, phase tuners, grating couplers, splitters, and a photonic crystal lens. The PIC exhibited steering over 23° x 3.6° with beam widths of 1° x 0.6°.

Heterogeneous lasers and coupling to Si₃N₄ near 1060 nm

A III-V/Si₃N₄ platform on silicon is presented capable of broad-spectral performance with initial heterogeneous lasers near 1060 nm. Continuous wave Fabry-Perot laser results for heterogeneous InGaAs/GaAs multiple quantum well (MQW) laser with output power approaching 0.25 mW on Si is demonstrated. Taper transmission loss measurements from III-V to Si₃N₄ are measured to be 2.5±0.75  dB.

Heterogeneously integrated III-V-on-silicon multibandgap superluminescent light-emitting diode with 290 nm optical bandwidth

A broadband superluminescent III-V-on-silicon light-emitting diode (LED) was realized. To achieve the large bandwidth, quantum well intermixing and multiple die bonding of InP on a silicon photonic waveguide circuit were combined for the first time, to the best of our knowledge. The device consists of four sections with different bandgaps, centered around 1300, 1380, 1460, and 1540 nm. The fabricated LEDs were connected on-chip in a serial way, where the light generated in the smaller bandgap sections travels through the larger bandgap sections. By balancing the pump current in the four LEDs, we achieved 292 nm of 3 dB bandwidth and an on-chip power of -8  dBm.

Low threshold and high speed short cavity distributed feedback hybrid silicon lasers

In this paper we investigate reducing threshold and improving the efficiency and speed of distributed feedback hybrid silicon lasers. A low threshold current of 8.8 mA was achieved for a 200 μm cavity at 20 °C. A 3 dB bandwidth of 9.5 GHz as well as 12.5 Gb/s direct modulation of DFB laser diode was achieved on the hybrid silicon platform for the first time.

Fano resonances in a multimode waveguide coupled to a high-Q silicon nitride ring resonator

Silicon nitride (Si3N4) optical ring resonators provide exceptional opportunities for low-loss integrated optics. Here we study the transmission through a multimode waveguide coupled to a Si3N4 ring resonator. By coupling single-mode fibers to both input and output ports of the waveguide we selectively excite and probe combinations of modes in the waveguide. Strong asymmetric Fano resonances are observed and the degree of asymmetry can be tuned through the positions of the input and output fibers. The Fano resonance results from the interference between modes of the waveguide and light that couples resonantly to the ring resonator. We develop a theoretical model based on the coupled mode theory to describe the experimental results. The large extension of the optical modes out of the Si3N4 core makes this system promising for sensing applications.

Sidewall gratings in ultra-low-loss Si3N4 planar waveguides

We demonstrate sidewall gratings in an ultra-low-loss Si3N4 planar waveguide platform. Through proper geometrical design we can achieve coupling constant values between 13 and 310 cm(-1). The TE waveguide propagation loss over the range of 1540 to 1570 nm is below 5.5 dB/m.

Silicon on ultra-low-loss waveguide photonic integration platform

We demonstrate a novel integrated silicon and ultra-low-loss Si3N4 waveguide platform. Coupling between layers is achieved with (0.4 ± 0.2) dB of loss per transition and a 20 nm 3-dB bandwidth for one tapered coupler design and with (0.8 ± 0.2) dB of loss per transition and a 100 nm 3-dB bandwidth for another. The minimum propagation loss measured in the ultra-low-loss waveguides is 1.2 dB/m in the 1590 nm wavelength regime.

Hybrid III/V silicon photonic source with integrated 1D free-space beam steering

A chip-scale optical source with integrated beam steering is demonstrated. The chip was fabricated using the hybrid silicon platform and incorporates an on-chip laser, waveguide splitter, amplifiers, phase modulators, and surface gratings to comprise an optical phased array with beam steering across a 12° field of view in one axis. Tuning of the phased array is used to achieve 1.8°(steered axis)×0.6°(nonsteered axis) beam width with 7 dB background suppression for arbitrary beam direction within the field of view.

Dual-wavelength passive and hybrid mode-locking of 3, 4.5 and 10 GHz InAs/InP(100) quantum dot lasers

We present an investigation of passive and hybrid mode-locking in Fabry-Pérot type two-section InAs/InP(100) quantum dot lasers that show dual wavelength operation. Over the whole current and voltage range for mode-locking of these lasers, the optical output spectra show two distinct lobes. The two lobes provide a coherent bandwidth and are verified to lead to two synchronized optical pulses. The generated optical pulses are elongated in time due to a chirp which shows opposite signs over the two spectral lobes. Self-induced mode-locking in the single-section laser shows that the dual-wavelength spectra correspond to emission from ground state. In the hybrid mode-locking regime, a map of locking range is presented by measuring the values of timing jitter for several values of power and frequency of the external electrical modulating signal. An overview of the systematic behavior of InAs/InP(100) quantum dot mode-locked lasers is presented as conclusion.

Planar waveguides with less than 0.1 dB/m propagation loss fabricated with wafer bonding

We demonstrate a wafer-bonded silica-on-silicon planar waveguide platform with record low total propagation loss of (0.045 ± 0.04) dB/m near the free space wavelength of 1580 nm. Using coherent optical frequency domain reflectometry, we characterize the group index, fiber-to-chip coupling loss, critical bend radius, and propagation loss of these waveguides.

Two-dimensional free-space beam steering with an optical phased array on silicon-on-insulator

We demonstrate a 16-channel, independently tuned waveguide surface grating optical phased array in silicon for two dimensional beam steering with a total field of view of 20° x 14°, beam width of 0.6° x 1.6°, and full-window background peak suppression of 10 dB.

Low-loss Si3N4 arrayed-waveguide grating (de)multiplexer using nano-core optical waveguides

A 16-channel 200 GHz arrayed-waveguide grating (AWG) (de)-multiplexer is demonstrated experimentally by utilizing Si3N4 buried optical waveguides, which have 50 nm-thick Si3N4 cores and a 15 μm-thick SiO2 cladding. The structure with an ultra-thin core layer helps to reduce the scattering due to the sidewall roughness and consequently shows very low loss of about 0.4~0.8 dB/m. When using this type of optical waveguide for an AWG (de)multiplexer, there is no problem associated with gap refill using the upper-cladding material even when choosing a small (e.g., 1.0 μm) gap between adjacent arrayed waveguides, which helps to reduce the transition loss between the FPR (free-propagation region) and the arrayed waveguides. Therefore, the demonstrated AWG (de)multiplexer based on the present Si3N4 buried optical waveguides has a low on-chip loss. The fabricated AWG (de)multiplexer is characterized in two wavelength ranges around 1310 nm and 1550 nm, respectively. It shows that the crosstalk from adjacent and non-adjacent channels are about -30 dB, and -40 dB, respectively, at the wavelength range of 1310 nm. The Si3N4 AWG (de)multiplexer has a temperature dependence of about 0.011 nm/°C, which is close to that of a pure SiO2 AWG device.

Ultra-high quality factor planar Si3N4 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.

Ultra-low-loss high-aspect-ratio Si3N4 waveguides

We characterize an approach to make ultra-low-loss waveguides using stable and reproducible stoichiometric Si3N4 deposited with low-pressure chemical vapor deposition. Using a high-aspect-ratio core geometry, record low losses of 8-9 dB/m for a 0.5 mm bend radius down to 3 dB/m for a 2 mm bend radius are measured with ring resonator and optical frequency domain reflectometry techniques. From a waveguide loss model that agrees well with experimental results, we project that 0.1 dB/m total propagation loss is achievable at a 7 mm bend radius with this approach.

Ultra-low loss Si3N4 waveguides with low nonlinearity and high power handling capability

We investigate the nonlinearity of ultra-low loss Si3N4-core and SiO2-cladding rectangular waveguides. The nonlinearity is modeled using Maxwell's wave equation with a small amount of refractive index perturbation. Effective n2 is used to describe the third-order nonlinearity, which is linearly proportional to the optical intensity. The effective n2 measured using continuous-wave self-phase modulation shows agreement with the theoretical calculation. The waveguide with 2.8-μm wide and 80-nm thick Si3N4 core has low loss and high power handling capability, with an effective n2 of about 9×10(-16) cm2/W.

Analysis of hybrid mode-locking of two-section quantum dot lasers operating at 1.5 microm

For the first time a detailed study of hybrid mode-locking in two-section InAs/InP quantum dot Fabry-Pérot-type lasers is presented. The output pulses have a typical upchirp of approximately 8 ps/nm, leading to very elongated pulses. The mechanism leading to this typical pulse shape and the phase noise is investigated by detailed radio-frequency and optical spectral studies as well as time-domain studies. The pulse shaping mechanism in these lasers is found to be fundamentally different than the mechanism observed in conventional mode-locked laser diodes, based on quantum well gain or bulk material.

Observation of Q-switching and mode-locking in two-section InAs/InP (100) quantum dot lasers around 1.55 mum

First observation of passive mode-locking in two-section quantum-dot lasers operating at wavelengths around 1.55 mum is reported. Pulse generation at 4.6 GHz from a 9 mm long device is verified by background-free autocorrelation, RF-spectra and real-time oscilloscope traces. The output pulses are stretched in time and heavily up-chirped with a value of 20 ps/nm, contrary to what is normally observed in passively mode-locked semiconductor lasers. The complete output spectrum is shown to be coherent over 10 nm. From a 7 mm long device Q-switching is observed over a large operating regime. The lasers have been realized using a fabrication technology that is compatible with further photonic integration. This makes the laser a promising candidate for e.g. a mode-comb generator in a complex photonic chip.

Characterization of a 15 GHz integrated bulk InGaAsP passively modelocked ring laser at 1.53microm

We report on an extensive characterization of a 15GHz integrated bulk InGaAsP passively modelocked ring laser at 1530 nm. The laser is modelocked for a wide range of amplifier currents and reverse bias voltages on the saturable absorber. We have measured a timing jitter of 7.1 ps (20 kHz - 80 MHz), which is low for an all-active device using bulk material and due to the ring configuration. Measured output pulses are highly chirped, a FWHM bandwidth is obtained of up to 4.5 nm. Such lasers with high bandwidth pulses and compatible with active-passive integration are of great interest for OCDMA applications.