In this paper, we present a flip-chip bonding concept for InP die on SiN-based TriPleX carrier using laser soldering. The InP die and SiN-based TriPleX carrier include the metalization patterns for commonly used photonic integrated circuit reference designs. Two laser soldering schemes were investigated: (1) using a laser wavelength where silicon is highly transmissive (through-silicon laser soldering) and (2) using a laser wavelength where silicon is not transmissive (heat-conduction laser soldering). We demonstrated a 4.0 mm $\times $ 4.6 mm InP die with 58 electrical connections flip-chip bonded on a 16.0 mm $\times $ 8.0 mm SiN-based TriPleX carrier. Comparison experiments were carried out including solder reflow and shear force tests. Both schemes showed reliable electrical interconnects that meet MIL-STD 883 standards. Especially, the through-silicon soldering showed faster soldering time, lower power for solder reflows, and less thermal impact which is therefore preferred over heat-conduction soldering. This concept is promising for a high-density, reliable interconnect of hybrid packaging of InP on SiN-based photonic integrated circuits, in particular large photonic dies.

We present our hybrid InP to SiN TriPleX integration interface with a novel alignment technique and its application to complex photonic integrated circuits. The integration interface comprises vertical alignment stops, which simplify the alignment process and allow for array integration with the same simplicity as for single dies. Horizontal alignment is carried out by utilizing optical backscatter reflectometry to get an active feedback signal without the need to operate the chip. Thus, typical contacting limitations of active flip-chip alignment are overcome. By using this method, we demonstrate the integration of InP DFB lasers with more than 60 mW of optical power coupled to a SiN waveguide with an averaged coupling loss of -2.1 dB. The hybrid integration process is demonstrated for single dies as well as full arrays. We evaluate the feasibility of the assembly process for complex photonic integrated circuits by integrating an InP gain chip to a SiN TriPleX external cavity. The process proves to be well suited and allows monitoring chip quality during assembly. A fully functional hybrid integrated tunable laser is fabricated, which is capable of full C-band tuning with optical output power of up to 60 mW.

We propose and experimentally demonstrate a photonic integrated circuit (PIC) that operates as an optical equalizer (OE) with multi-rate and multi-channel capability. The OE has the structure of a 3-tap direct form finite impulse response (FIR) filter and is based on the use of micro-ring resonators (MRRs) for the tuning of its delay lines. The PIC is fabricated on TriPleX platform and has 17 reconfigurable elements in total including nine MRRs, five optical couplers and three standalone phase shifters. Using this OE in an on-off keying system with bandwidth limitations we achieve an eye-diagram opening improvement more than 14 dB working with signals at 4.67 and 5.84 Gbaud both in single- and dual-channel operation. Extension to higher modulation formats is direct. Extension to higher symbol rates is also possible via the use of smaller MRRs.

Wafer-level probing of photonic integrated circuits is key to reliable process control and efficient performance assessment in advanced production workflows. In recent years, optical probing of surface-coupled devices such as vertical-cavity lasers, top-illuminated photodiodes, or silicon photonic circuits with surface-emitting grating couplers has seen great progress. In contrast to that, wafer-level probing of edge-emitting devices with hard-to-access vertical facets at the sidewalls of deep-etched dicing trenches still represents a major challenge. In this paper, we address this challenge by introducing a novel concept of optical probes based on 3D-printed freeform coupling elements that fit into deep-etched dicing trenches on the wafer surface. Exploiting the design freedom and the precision of two-photon laser lithography, the coupling elements can be adapted to a wide variety of mode-field sizes. We experimentally demonstrate the viability of the approach by coupling light to edge-emitting waveguides on different integration platforms such as silicon photonics (SiP), silicon nitride (TriPleX), and indium phosphide (InP). Achieving losses down to 1.9 dB per coupling interface, we believe that 3D-printed coupling elements represent a key step towards highly reproducible wafer-level testing of edge-coupled photonic integrated circuits.

We present an interface for hybrid flip-chip integration of InP-based laser sources to silicon-nitride-based photonic platforms. The design enables efficient high optical power coupling over a wide temperature range. The optical modes of laser and SiN chip are expanded using integrated tapers allowing for high alignment tolerance. The chips comprise physical alignment stops for vertical alignment. In the horizontal direction, the integration interface is optimized for active and/or visual alignment with high precision using precise visual alignment marks. The hybrid integrated chip shows a waveguide coupled optical power of more than 40 mW and can operate at elevated temperatures up to 85 degrees C.

Photonic Integrated Circuit (PIC) technology is becoming more and more mature and the three main platforms that offer Multi Project Wafer runs (Indium Phosphide (InP), Silicon on Insulator (SOI) and the silicon nitride based TriPleX platform) each have their own unique selling points. New disruptive PIC based modules are enabled by combinations of the different platforms complementing each other in performance. In particular the InP-TriPleX combination are two very complementary technologies. Combining them together yields for instance tunable ultra-narrow linewidth lasers extremely suitable for telecom and sensing applications. Also microwave photonics modules for Optical Beam Forming Networks and 5G communication can, and have been realized with this combination. Important part of this combination is the integration of the different platforms in modules via cost effective assembly techniques. This talk will present the combination of both technologies, the interconnection issues faced in the assembly process and latest measurement results on these hybrid integrated devices.

We present our hybrid III-V/SiN integration interface with a novel active alignment technique overcoming contacting limitations in flip-chip assembly. The interface allows for integration of single chips and full arrays. An average coupling loss of −2.1dB and a record coupled power exceeding 60mW is achieved.

A low-loss, broadband and high fabrication tolerant optical coupler is significantly required for the integration of various optical modules into a compact cost-effective device. However, its performance usually changes originating from fabrication uncertainties. Here, a tolerance investigation of various design parameters is carried out for the couplers between the Si3N4 and various polymer materials. Low-loss operation is experimentally verified at both 976 nm and 1460–1635 nm wavelengths. Measured losses per coupler are found to be as low as 0.12 dB and 0.14 dB at 976 nm and 1550 nm respectively, paving the way for the integration of various active materials onto the Si3N4 platform.

Technology integration of liquid crystal cells for electro-optic modulation has been implemented on the commercial TriPleX photonic platform. Design and fabrication procedure have been optimized for fulfilling the low insertion loss criterion for applications such as space communication and enabling the implementation of compact liquid crystal tuning elements for achieving high integration density. First performance testing of this concept has confirmed low-power consumption switching with 2π phase tuning being obtained within a voltage range of 2.5 V.

An overview of the most recent developments and improvements to the low-loss TriPleX Si3N4 waveguide technology is presented in this paper. The TriPleX platform provides a suite of waveguide geometries (box, double stripe, symmetric single stripe, and asymmetric double stripe) that can be combined to design complex functional circuits, but more important are manufactured in a single monolithic process flow to create a compact photonic integrated circuit. All functionalities of the integrated circuit are constructed using standard basic building blocks, namely straight and bent waveguides, splitters/combiners and couplers, spot size converters, and phase tuning elements. The basic functionalities that have been realized are: ring resonators and Mach–Zehnder interferometer filters, tunable delay elements, and waveguide switches. Combination of these basic functionalities evolves into more complex functions such as higher order filters, beamforming networks, and fully programmable architectures. Introduction of the active InP chip platform in a combination with the TriPleX will introduce light generation, modulation, and detection to the low-loss platform. This hybrid integration strategy enables fabrication of tunable lasers, fully integrated filters, and optical beamforming networks.

A low-loss, broadband and high fabrication tolerant optical coupler for the monolithic integration of Si3N4 and polymer waveguides is designed and experimentally demonstrated. The coupler is based on the adiabatic vertical tapering of the Si3N4 waveguides. Low-loss operation is experimentally verified at both 976 and 1460-1635 nm wavelengths. Measured losses per coupler are as low as 0.12 and 0.14 dB at 976 and 1550 nm, respectively, and below 0.2 dB at both wavelengths for lateral misalignments between the Si3N4 and polymer waveguides up to 1.0 μm.

We demonstrate an integrated optical probe including an on-chip microlens for a common-path swept-source optical coherence tomography system. This common-path design uses the end facet of the silicon oxynitride waveguide as the reference plane, thus eliminating the need of a space-consuming and dispersive on-chip loop reference arm, thereby obviating the need for dispersion compensation. The on-chip micro-ball lens eliminates the need of external optical elements for coupling the light between the chip and the sample. The use of this lens leads to a signal enhancement up to 37 dB compared to the chip without a lens. The light source, the common-path arm and the detector are connected by a symmetric Y junction having a wavelength independent splitting ratio (50/50) over a much larger bandwidth than can be obtained with a directional coupler. The signal-to-noise ratio of the system was measured to be 71 dB with 2.6 mW of power on a mirror sample at a distance of 0.3 mm from the waveguide end facet. Cross-sectional OCT images of a layered optical phantom sample are demonstrated with our system. A method, based on an extended Fourier-domain OCT model, for suppressing ghost images caused by additional parasitic reference planes is experimentally demonstrated.

This paper proposes and tests a design of electro-thermal bimorph actuators for alignment of flexible photonic waveguides fabricated in 16 µm thick SiO2. The actuators are for use in a novel alignment concept for multi-port photonic integrated circuits (PICs), in which the fine alignment is taken care of by positioning of suspended, mechanically flexible waveguide beams on one or more of the PICs. The design parameters of the bimorph actuator allow to tune both the initial relative position of the waveguide end-facets, and the motion range of the actuators. Bimorph actuators have been fabricated and characterized. The maximum out-of-plane deflection of the bimorph actuator (with 720 μm-long poly-Si) can reach 18:5 μm with 126:42mW, sufficient for the proposed application.

In this letter, low-loss and highly fabrication-tolerant flip-chip bonded vertical couplers under single-mode condition are demonstrated for the integration of a polymer waveguide chip onto the Si3N4/SiO2 passive platform. The passively aligned vertical couplers have a lateral misalignment between polymer and Si3N4 waveguide cores of +/- 1.25 mu m. Low-loss operation has been experimentally demonstrated over a wide spectral window of 1480-1560 nm, with measured coupler losses below 0.8 dB for Si3N4 taper angles below 1.2 degrees, in good agreement with the calculated values. Furthermore, thermal shock test results show less than 0.1 dB degradation, indicating a robust coupling performance.

Fully automated, high precision, cost-effective assembly technology for photonic packages remains one of the main challenges in photonic component manufacturing. Next to the cost aspect the most demanding assembly task for multiport photonic integrated circuits (PICs) is the high-precision (±0.1 μm) alignment and fixing required for optical I/O in InP PICs, even with waveguide spot size conversion. In a European research initiative – PHASTFlex - we develop and investigate an innovative, novel assembly concept, in which the waveguides in a matching TriPleX interposer PIC are released during fabrication to make them movable. After assembly of both chips by flip-chip bonding on a common carrier, TriPleX based actuators and clamping functions position and fix the flexible waveguides with the required accuracy.

Reduction of the divergence angle of a beam coupled out from an optical waveguide is desired in many applications. Collimation in one dimension has been demonstrated, see e.g. [1-3] However, for some applications such as on-chip optical coherence tomography (OCT) or Raman spectroscopy [4,5], it is necessary to produce a light beam that is collimated in two dimensions in order to increase the efficiency of chip-sample coupling. In our previous work [6], we have designed a fabrication procedure of a direct on-chip reflowed polymer micro-ball lens to enable light collimation in both, horizontal and vertical directions. In this work, we realized the complete design, optical characterization and demonstrate the feasibility of mass production.

We demonstrate a fabrication procedure for the direct integration of micro-ball lenses on planar integrated optical channel waveguide chips with the aim to reduce the divergence of light that arises from the waveguide in both horizontal and vertical directions. Fabrication of the lenses is based on photoresist reflow which is a procedure that allows for the use of photolithography for careful alignment of the lenses with respect to the waveguides and enables mass production. We present in detail the design and fabrication procedures. Optical characterization of the fabricated micro-ball lenses demonstrates a good performance in terms of beam-size reduction and beam shape. The beam half divergence angle of 1544 nm light is reduced from 12.4 ° to 1.85 °.

Spiral-waveguide amplifiers in erbium-doped amorphous aluminum oxide are fabricated by RF reactive co-sputtering of 1-μm-thick layers onto a thermally-oxidized silicon wafer and chlorine-based reactive ion etching. The samples are overgrown by a SiO2 cladding. Spirals with several lengths ranging from 13 cm to 42 cm and four different erbium concentrations between 0.5−3.0×1020 cm-3 are experimentally characterized. A maximum internal net gain of 20 dB in the small-signal-gain regime is measured at the peak emission wavelength of 1532 nm for two sample configurations with waveguide lengths of 13 cm and 24 cm and erbium concentrations of 2×1020 cm-3 and 1×1020 cm-3, respectively. The obtained gain improves previous results by van den Hoven et al. in this host material by a factor of 9. Gain saturation as a result of increasing signal power is investigated. Positive net gain is measured in the saturated-gain regime up to ~100 μW of signal power, but extension to the mW regime seems feasible. The experimental results are compared to a rate-equation model that takes into account migration-accelerated energy-transfer upconversion (ETU) and a fast quenching process affecting a fraction of the erbium ions. Without these two detrimental processes, several tens of dB/cm of internal net gain per unit length would be achievable. Whereas ETU limits the gain per unit length to 8 dB/cm, the fast quenching process further reduces it to 2 dB/cm. The fast quenching process strongly deteriorates the amplifier performance of the Al2O3:Er3+ waveguide amplifiers. This effect is accentuated for concentrations higher than 2×1020 cm-3.

Photonic applications based on planar wave-guide technology impose stringent requirements on properties such as optical propagation losses, light coupling to optical fibers, integration density, as well as on reliability and reproducibility. The latter is correlated to a high level of control of the refractive index and waveguide geometry. In this paper, we review a versatile dielectric waveguide platform, called TriPleX, which is based on alternating silicon nitride and silicon dioxide films. Fabrication with CMOS-compatible equipment based on low-pressure chemical vapor deposition enables the realization of stable material compositions being a prerequisite to the control of waveguide properties and modal shape. The transparency window of both materials allows for the realization of low-loss waveguides over a wide wavelength range (400 nm-2.35 mu m). Propagation losses as low as 5 x 10(-4) dB/cm are reported. Three basic geometries (box shell, double stripe, and filled box) can be distinguished. A specific tapering technology is developed for on-chip, low-loss (< 0.1 dB) spotsize convertors, allowing for combining efficient fiber to chip coupling with high-contrast waveguides required for increased functional complexity as well as for hybrid integration with other photonic platforms such as InP and SOI. The functionality of the TriPleX platform is captured by verified basic building blocks. The corresponding library and associated design kit is available for multi-project wafer (MPW) runs. Several applications of this platform technology in communications, biomedicine, sensing, as well as a few special fields of photonics are treated in more detail.

Spiral-waveguide amplifiers in erbium-doped aluminum oxide on a silicon wafer are fabricated and characterized.Spirals of several lengths and four different erbium concentrations are studied experimentally and theoretically.A maximum internal net gain of 20 dB in the smallsignal-gain regime is measured at the peak emission wavelength of 1532 nm for two sample configurations with waveguide lengths of 12.9 cm and 24.4 cm and concentrations of 1.92 × 10 20 cm -3 and 0.95 × 10 20 cm -3 , respectively.The noise figures of these samples are reported.Gain saturation as a result of increasing signal power and the temperature dependence of gain are studied.