InP Platform Research Articles

Optimization of Balanced Detector for Coherent Receiver on Generic InP Platform by Particle Swarm Optimization

Optimization of Balanced Detector for Coherent Receiver on Generic InP Platform by Particle Swarm Optimization

Scaling photonic integrated circuits with InP technology: A perspective

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.

Heterogeneous integration of single InAs/InP quantum dots with the SOI chip using direct bonding.

Quantum information processing with photons in small-footprint and highly integrated silicon-based photonic chips requires incorporating non-classical light sources. In this respect, self-assembled III-V semiconductor quantum dots (QDs) are an attractive solution, however, they must be combined with the silicon platform. Here, by utilizing the large-area direct bonding technique, we demonstrate the hybridization of InP and SOI chips, which allows for coupling single photons to the SOI chip interior, offering cost-effective scalability in setting up a multi-source environment for quantum photonic chips. We fabricate devices consisting of self-assembled InAs QDs embedded in the tapered InP waveguide (WG) positioned over the SOI-defined Si WG. Focusing on devices generating light in the telecom C-band compatible with the low-loss optical fiber networks, we demonstrate the light coupling between InP and SOI platforms by observing photons outcoupled at the InP-made circular Bragg grating outcoupler fabricated at the end of an 80 µm-long Si WG, and at the cleaved edge of the Si WG. Finally, for a device with suppressed multi-photon generation events exhibiting 80% single photon generation purity, we measure the photon number outcoupled at the cleaved facet of the Si WG. We estimate the directional on-chip photon coupling between the source and the Si WG to 5.1%.

Graphene-based hybrid plasmonic optical electro-absorption modulator on InP platform

Graphene-based hybrid plasmonic optical electro-absorption modulator on InP platform

A Hybrid-Integrated Photonic Spiking Neural Network Framework Based on an MZI Array and VCSELs-SA

We propose an inferencing framework of a hybrid-integrated photonic spiking neural network (PSNN) to perform pattern recognition tasks, where the linear computation is realized based on a 4 × 4 silicon photonic Mach-Zehnder interferometer (MZI) array, and the nonlinear computation is performed by an InP-based spiking neuron array based on vertical-cavity surface-emitting lasers with an embedded saturable absorber (VCSELs-SA). With the modified Tempotron-like remote supervised method (ReSuMe) training algorithm, we realize two pattern recognition tasks, the recognition of numbers “0-3” and optical character recognition (OCR). The phase shifts in the MZI array are accurately configured to represent the weight matrix according to the decomposition procedure of a 4 × 4 triangular MZI mesh. Besides, the effects of the phase shift error and quantization precision of phase shifters (PSs) on the recognition performance are analyzed. For the OCR task, the 400 × 10 PSNN is realized by multiplexing the 4 × 4 MZI array based on the matrix blocking and the reconfigurability of the MZI array. This work provides a systematic computational model of the hybrid-integrated PSNN based on the silicon photonics and InP platforms, enabling the co-design and optimization of hardware architecture and algorithm, which contributes one step forward toward the construction of a hybrid-integrated PSNN hardware system.

Long term experimental verification of a single chip quantum random number generator fabricated on the InP platform

This work presents the results from the experimental evaluation of a quantum random number generator circuit over a period of 300 minutes based on a single chip fabricated on the InP platform. The circuit layout contains a gain switched laser diode (LD), followed by a balanced Mach Zehnder Interferometer for proper light power distribution to the two arms of an unbalanced MZI incorporating a 65.4 mm long spiral waveguide that translates the random phase fluctuations to power variations. The LD was gain-switched at 1.3 GHz and the chip delivered a min-entropy of 0.5875 per bit after removal of the classical noise, resulting a total aggregate bit rate of 6.11 Gbps. The recoded data set successfully passed the 15-battery test NIST statistical test suite for all data sets.

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.

Design and Fabrication of Low Polarization Dependent Bulk SOA Co-Integrated With Passive Waveguides for Optical Network Systems

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.

Mid-infrared microring resonators and optical waveguides on an InP platform

We demonstrate mid-infrared ring resonators fabricated in an In0.53Ga0.47As/InP materials platform operating at a wavelength of approximately 5.2 μm with quality factors over 120 000. We also perform broadband characterization of optical losses in passive In0.53Ga0.47As/InP ridge waveguides in the 5–11 μm wavelength range with waveguide losses ranging from below 0.5 dB/cm at shorter wavelengths to 4–5 dB/cm at longer wavelengths of this spectral range. Our results establish In0.53Ga0.47As/InP as a low-loss waveguiding platform for mid-infrared photonic integrated circuits that are fully integrable with InGaAs/AlInAs/InP quantum cascade lasers and detectors.

Design of a resonator-bus-resonator anti-parity-time-symmetric integrated optical gyroscope

Integrated optical gyroscopes are urgently required in different fields where space occupation and weight need to be minimized. However, in the state-of-the-art ring-based optical gyroscopes, Sagnac resonance splitting is proportional to the radius of the resonator, making it impossible to design an integrated gyroscope for high-resolution requirements. The enhancement of the sensitivity and the improvement in the limit of detection enabled by exceptional points has been already experimentally proved for parity-time-symmetric gyroscopes. Anti-parity-time-symmetric gyroscopes have been demonstrated to show even better performance, exhibiting a real eigenfrequency splitting, that can be easily measured. Here we present, for the first time, a resonator-bus-resonator anti-parity-time-symmetric integrated optical gyroscope designed on InP platform. This completely new architecture critically reduces the fabrication tolerance problems. The proposed configuration makes the gyroscope robust against the external perturbations that would make previous designs exit from the anti-PT-symmetric condition. Moreover, this new architecture enables an electrical fine-tuning method for setting the system at the exceptional point. Finally, a time domain analysis is performed in this work, using the Fast Fourier Transform, to demonstrate the ease of its readout.

AlGaInAs Multi-Quantum Well Lasers on Silicon-on-Insulator Photonic Integrated Circuits Based on InP-Seed-Bonding and Epitaxial Regrowth

The tremendous demand for low-cost, low-consumption and high-capacity optical transmitters in data centers challenges the current InP-photonics platform. The use of silicon (Si) photonics platform to fabricate photonic integrated circuits (PICs) is a promising approach for low-cost large-scale fabrication considering the CMOS-technology maturity and scalability. However, Si itself cannot provide an efficient emitting light source due to its indirect bandgap. Therefore, the integration of III-V semiconductors on Si wafers allows us to benefit from the III-V emitting properties combined with benefits offered by the Si photonics platform. Direct epitaxy of InP-based materials on 300 mm Si wafers is the most promising approach to reduce the costs. However, the differences between InP and Si in terms of lattice mismatch, thermal coefficients and polarity inducing defects are challenging issues to overcome. III-V/Si hetero-integration platform by wafer-bonding is the most mature integration scheme. However, no additional epitaxial regrowth steps are implemented after the bonding step. Considering the much larger epitaxial toolkit available in the conventional monolithic InP platform, where several epitaxial steps are often implemented, this represents a significant limitation. In this paper, we review an advanced integration scheme of AlGaInAs-based laser sources on Si wafers by bonding a thin InP seed on which further regrowth steps are implemented. A 3 µm-thick AlGaInAs-based MutiQuantum Wells (MQW) laser structure was grown onto on InP-SiO2/Si (InPoSi) wafer and compared to the same structure grown on InP wafer as a reference. The 400 ppm thermal strain on the structure grown on InPoSi, induced by the difference of coefficient of thermal expansion between InP and Si, was assessed at growth temperature. We also showed that this structure demonstrates laser performance similar to the ones obtained for the same structure grown on InP. Therefore, no material degradation was observed in spite of the thermal strain. Then, we developed the Selective Area Growth (SAG) technique to grow multi-wavelength laser sources from a single growth step on InPoSi. A 155 nm-wide spectral range from 1515 nm to 1670 nm was achieved. Furthermore, an AlGaInAs MQW-based laser source was successfully grown on InP-SOI wafers and efficiently coupled to Si-photonic DBR cavities. Altogether, the regrowth on InP-SOI wafers holds great promises to combine the best from the III-V monolithic platform combined with the possibilities offered by the Si photonics circuitry via efficient light-coupling.

Integrated InP optical unitary converter with compact half-integer multimode interferometers

Integrated optical unitary converters (OUCs) are vital devices for various emerging applications such as mode-multiplexed optical communication, optical neural networks, and quantum computing. In order to realize large-scale OUCs in a limited footprint, the number of elements, as well as the size of each element, is important. In this work, we present a novel type of OUC using half-integer multimode interferometers (MMIs) based on the multi-plane light conversion (MPLC) concept. A half-integer MMI enables unitary coupling among the multiple input and output ports, while requiring only half the length of a conventional uniform MMI. Although the splitting ratio is not uniform across the ports, we show both numerically and experimentally that arbitrary unitary operation can still be achieved with comparable performance. We fabricate 4×4 OUC with half-integer MMIs on the monolithic InP platform and experimentally demonstrate reconfigurable 4-mode sorting and switching with a significantly reduced footprint compared with the conventional OUCs using uniform MMIs.

Increasing Integration Density of Photonic Integrated Circuits by Employing Optimized Dielectric Metamaterial Structures

All-dielectric metamaterial structures in the role of the cladding of optical waveguides (WGs) in photonic integrated circuits (PICs) are investigated and optimized by means of numerical simulations to increase the integration density of PICs. First the role of the refractive index (material platform) on the effects of metamaterial cladding is studied. The results of a quantitative analysis show that only material platforms with a high refractive index contrast (such as existing Si or membrane InP platform) can noticeably benefit from optimized metamaterial cladding in terms of integration density. Furthermore, we perform a comprehensive optimization of the geometry of metamaterial claddings in Si platform to achieve the lowest possible gap width between cores of two adjacent WGs, while keeping the cross-talk bellow the targeted limit of −30 dB at the length of 2 mm. By doing this we can, for the first time, explicitly show how much the integration density of a PIC can be increased. We demonstrate that a metamaterial cladding can, in best case, reduce the gap width by 60% compared to Si WGs with normal cladding in case of 450 nm wide core. The wavelength dependence and sensitivity to fabrication variability are also studied, revealing a trade-off between the lowest possible integration density and usable wavelength range. We show that a sizable decrease in gap width at a wide usable wavelength range is possible, demonstrating that waveguides with metamaterial cladding have the potential to be utilized in future applications requiring a high integration density of PICs.

Monolithically Integrated InP Bistable Photonic Waveguide Memory

In this article, we experimentally demonstrate, for the first time, an all-optical bistable monolithically integrated photonic waveguide memory of distinctive simplicity, relying on two travelling waveguide Semiconductor Optical Amplifiers with Cross Gain modulation (SOA-XGM) phenomena. Experimental proof-of-principle memory operation and wavelength switching operation are demonstrated at 5Gb/s, featuring an Extinction Ratio of 6 dB and a 4.6 dB BER penalty, in the case of the memory operation, as well as a power penalty of 3.5 dB at 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−9</sup> BER value, in the case of the wavelength switching. Being entirely designed and fabricated using standard library-based components, the proposed photonic memory fits within a 3.5 mm waveguide configuration of a generic monolithic InP platform, while its overall footprint is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.5\times 2$ </tex-math></inline-formula> mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> demonstrating a footprint reduction of 40% compared to previous hybrid SOA-MZI SR-FF architectures, holding the credentials for a fast photonic memory unit.

Fabrication and error analysis of a InGaAsP/InP polarization beam splitter based on an asymmetric Mach-Zehnder interferometer

A polarization beam splitter (PBS) based on an asymmetrical Mach-Zehnder interferometer (MZI) is experimentally demonstrated on a InP platform. The experimental results show that the polarization extinction ratios (PERs) are 8 dB and 14 dB for transverse-electric (TE) and transverse-magnetic (TM) polarization at 1550 nm, respectively. The PER is greater than 5 dB/12 dB for TE/TM polarization over the full C band wavelength range. Fabrication errors including the waveguide width, arm length, film thickness, and sidewall are analyzed using the beam propagation method. The width and sidewall are the most sensitive factors that affect the performances of this type of PBS. This analysis will improve the fabrication tolerance of the PBS.

Hybrid integrated mode-locked laser diodes with a silicon nitride extended cavity

Integrated semiconductor mode-locked lasers have shown promise in many applications and are readily fabricated using generic InP photonic integration platforms. However, the passive waveguides offered in such platforms have relatively high linear and nonlinear losses that limit the performance of these lasers. By extending such lasers with, for example, an external cavity, the performance can be increased considerably. In this paper, we demonstrate for the first time that a high-performance mode-locked laser can be achieved with a butt-coupling integration technique using chip scale silicon nitride waveguides. A platform-independent SiN/SU8 coupler design is used to couple between the silicon nitride external cavity and the III/V active chip. Mode-locked lasers at 2.18 GHz and 15.5 GHz repetition rates are demonstrated with Lorentzian RF linewidths several orders of magnitude smaller than what has been demonstrated on monolithic InP platforms. The RF linewidth was 31 Hz for the 2.18 GHz laser.

Efficient InGaAsP MQW-based polarization controller without active-passive integration.

Carrier-injection-based efficient polarization controller with a strained InGaAsP multiple-quantum-well (MQW) layer is demonstrated on a regrowth-free InP platform. We employ a straight-line device configuration by cascading an asymmetric polarization rotator (PR) to provide a fixed polarization conversion and a polarization-dependent phase shifter (PD-PS) to enable tunable polarization rotation. Based on a novel design concept, both the PR and PD-PS sections are integrated monolithically without active-passive integration. Using the fabricated device, we experimentally demonstrate efficient polarization conversion over the entire Poincaré sphere with a total current of less than 40 mA. With the capability of monolithically integrating other InP-based active components, the demonstrated scheme should be attractive for various applications, such-as low-cost coherent communication, microwave photonics, and quantum key distribution.

GaAsBi Quantum Dots for 1.55 μm Laser Diode

Bi incorporations can reduce the bandgap of GaAs1-xBix. With a Bi content of 10.5%, GaAsBi is predicted to emit light at 1.55 μm. However, high Bi incorporation is difficult for material growth and deteriorates the optical property of GaAsBi. In this work, a GaAsBi quantum dot (QD)/InAlAs structure on InP platform is proposed to fabricate 1.55 μm laser diodes. Strain distributions and band structures are calculated with different Bi contents and QD sizes using finite element method. High Bi contents and large QD sizes are beneficial for achieving long wavelengths. GaAsBi QD/InAlAs structures with a low Bi content of 5.6% and proper QD sizes, such as a diameter of 30 nm and a height of 6 nm, can emit light at 1.55 μm. The proposed structure can be realized by migration enhanced epitaxy and droplet epitaxy and provides a feasible way for fabricating GaAsBi based 1.55 μm laser diodes applied in fiber-optic communications. The emission wavelength of GaAsBi QDs with different sizes and Bi contents

Integrated dual-polarization coherent receiver without a polarization splitter-rotator.

We propose and demonstrate a simple integrated dual-polarization (DP) coherent receiver that does not require a polarization splitter-rotator (PSR). Based on a novel concept, a DP coherent signal is mixed with the local-oscillator (LO) waves inside a single interferometer and detected by five single-ended photodetectors. The signal-signal and LO-LO beat noises are eliminated through differential detection. We design and fabricate a proof-of-concept device on InP and experimentally demonstrate complete retrieval of DP quadrature phase-shift keyed signals. Requiring minimal number of optical components without a PSR, the demonstrated scheme would be attractive particularly for the InP and thick-silicon photonic platforms due to its significantly reduced footprint and ease of fabrication.

Analog Coherent Detection for Energy Efficient Intra-Data Center Links at 200 Gbps Per Wavelength

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 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-12</sup> 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.