This paper highlights micro-transfer printing (MTP) as a promising scalable approach to heterogeneous integration for silicon photonics. MTP uniquely achieves high integration density, high throughput, and high material efficiency through a low-temperature, back-end integration process. Current demonstrations, including integrated III-V lasers and thin-film electro-optic modulators, confirm MTP's potential. Industrial adoption requires resolving challenges related to final integration yield and throughput, device reliability, and supply chain maturity.

In this work, we investigate the impact of contact annealing on the device performance of C-band laser diodes micro-transfer printed onto a silicon photonics platform. Annealing allows reducing the contact resistance of the devices but can also have an impact on the diffusion of dopants towards the active region, decreasing the quantum efficiency of the laser. This trade-off is studied in this paper. Through capacitance deep-level transient spectroscopy (C-DLTS) analysis, the decrease in performance upon annealing is associated with zinc impurities. These defects are believed to diffuse toward the active region, and as a result, act as non-radiative recombination centers. To eliminate the influence of the micro-transfer printing step, two sets of devices were compared. Both were fabricated from the same epitaxial wafer and underwent identical processing, except that one set was characterized before transfer-printing on the native substrate, whereas the other was measured after being transfer-printed onto silicon. C-DLTS measurements confirmed that the same process occurs on native InP substrates. Once the device contacts are annealed, constant current stress testing does not introduce further substantial threshold current variations.

We present an optical transmitter consisting of a SiGe BiCMOS driver amplifier heterogeneously integrated through micro-transfer printing onto a silicon photonic chip that contains a Mach-Zehnder modulator (MZM) and optical couplers. The driver has a footprint of only 200 µm × 300 µm, and features small bond pads of 20 µm × 20 µm. It was fabricated using a modified SiGe BiCMOS on SOI process to enable the release process prior to micro-transfer printing. The post-print metallization process to contact the EIC with the PIC consists of spin coating a layer of divinylsiloxane-bis-benzocyclobutene (DVS-BCB) to create a ramp to overcome the 20 µm step height, after which a gold metal layer is deposited to connect the driver to the MZM. To verify the operation of the optical transmitter, a high-speed measurement setup is used to capture eye diagrams. The 3D-integrated transmitter achieves 56 Gb∕s non-return to zero (NRZ) with a 5-tap feed-forward equalizer (FFE) and 28 GBd 4-level pulse amplitude modulation (PAM-4) with a 5-tap FFE and nonlinearity pre-compensation, both at a total transmitter power efficiency of 9.1 pJ∕bit. Integration through micro-transfer printing offers the possibility of greatly increasing scalability and fabrication throughput of short-reach optical transceivers for data centers.

We demonstrate micro-transfer printing (mu TP) and post-printing metallization of thin electronic chiplets on silicon, with a view to heterogeneously integrate electronic integrated circuits (EICs) with photonic integrated circuits (PICs). (mu TP) decouples the fabrication of EICs and PICs, and simultaneously enables their tight integration with high-throughput, small form-factor and on wafer-scale. In this study, we successfully established the process flow for releasing and printing 300 mu m & times; 200 mu m SiGe BiCMOS electronic driver chiplets and electrically connecting these chiplets using a polymer ramp to overcome the 20-mu m chiplet thickness, providing a gain of 14 dB and bandwidth of over 35 GHz with low-parasitic interconnections. The proposed methodology provides a practical and mass-producible solution to realize the stacking of EICs on silicon photonic wafers for emerging applications such as co-packaged optics (CPO).

Meeting the escalating demands of data transmission and computing, driven by artificial intelligence (AI), requires not only faster optical transceivers but also advanced integration technologies that can seamlessly combine photonic and electronic components. Traditional approaches struggle to overcome the parasitic limitations arising from fabricating those components using different processes. Here, we report a novel 3D heterogeneously integrated optical receiver based on micro-transfer printing (μTP), enabling the co-integration of a compact bipolar CMOS (BiCMOS) electronic chiplet (0.06 mm2) directly onto a silicon photonic integrated circuit (SiPIC). While previous μTP demonstrations have focused primarily on photonic integration, our work pioneers the direct integration of electronics and photonics, significantly enhancing performance and scalability. The resulting optical receiver achieves 224 Gb/s four-level pulse amplitude modulation (PAM-4) operation, delivering -5.2 dBm optical modulation amplitude(OMA) sensitivity at a bit-error rate (BER) of 2.4 x 10-4, a record-small footprint, and an excellent power efficiency of 0.51 pJ/b. This demonstration not only showcases the potential of μTP for high-density, cost-efficient integration but also represents a critical step toward next-generation optical interconnects in the AI era.

We realized low-ohmic, high-speed interconnects to transfer-printed, 20 mu m thick electronic chiplets with small (20 mu mx20 mu m) pads. Spray-coated divinylsiloxane-bis-benzocyclobuten (DVS-BCB) ramps were created, onto which a lithographically defined metal redistribution layer including vias was fabricated. This approach facilitates short (low parasitic) interconnects between electronics and photonics.

We experimentally demonstrate the use of a micro-transfer-printed on-chip distributed Bragg reflector laser to interrogate an opto-mechanical ultrasound sensor. By eliminating the need for an external tunable laser source, this work presents a scalable pathway toward an all-on-chip photonic platform for high-performance acoustic sensing and imaging.

The feedback sensitivity of a tunable laser with a highly wavelength-selective reflector using a high-Q Vernier-effect based ring resonator structure is examined through both experimental and simulation work. The study demonstrates that by properly tuning the amplitude and phase of the reflector, the laser exhibits reduced feedback sensitivity, leading to improved laser performance under external optical feedback. The onset of deterioration in the quantum-well-based laser due to optical feedback, characterized by excess relative intensity noise (RIN), is suppressed through red detuning to a feedback level above -13 dB, over 5 dB higher than for the non-detuned laser state. The study further characterizes the high-speed data transmission performance of the laser, showing that the red-detuned ring resonator based tunable laser offers enhanced stability against feedback. Simulation results confirm that the phase-detuned tunable laser, with its lower feedback coefficient, outperforms traditional distributed Bragg reflector (DBR) lasers, particularly under detuning conditions.

A laser source that is both narrow-linewidth and frequency-agile is essential for FMCW applications, such as LIDAR or distributed optical fiber sensing (DOFS). In this work, we present the design and characterization of a laser architecture based on the heterogeneous integration of III-V gain material on a SiN photonic circuit that meets these specifications. By incorporating a dual-ring resonator mirror in the cavity, we achieved a linewidth of 2.4 kHz and a large frequency excursion. We obtained chirps with an amplitude of 20 GHz, with residual nonlinearities of less than 1%. A preliminary DOFS measurement was carried out, demonstrating the excellent performance of the laser.

Leveraging its superior waveguide properties,silicon-nitride(Si3N4)photonics is emerging to expand the appli-cations of photonic integrated circuits to optical systems where bulk optics and fibers today still dominate.In order to fully leverage its advantages,heterogeneous integration of Ⅲ-Ⅴ gain elements on Si3N4 is one of the most critical steps.In this paper,we demonstrate a Ⅲ-Ⅴ-on-Si3N4 widely tunable narrow-linewidth laser based on micro-transfer printing.Detailed design considerations of the tolerant Ⅲ-Ⅴ-to-Si3N4 vertical coupler,Si3N4-based micro-ring resonators(MRRs),and micro-heaters are discussed.By introducing the dispersion of Si3N4 waveguide in the design,the proposed Vernier MRRs enable an extended tuning range over multiple Vernier periods.The laser shows a wavelength tuning range of 54 nm in C and L bands with intrinsic linewidth less than 25 kHz.Within the tuning range,the side mode suppression ratio is larger than 40 dB and the output power in the Si3N4 waveguide reaches 6.3 mW.The integration process allows for the fabrication and quality control of both the Si3N4 circuits and Ⅲ-Ⅴ devices in its own foundry,which greatly enhances the integration yield and paves the way for large-scale integration.

We present an approach for integrating pre-fabricated III-V chiplets onto Si/Si 3 N 4 PICs through micro-transfer printing. It allows completion of III-V and Si/Si 3 N 4 processes on their native substrate, while enabling simple integration of multiple III-V functions.

We present the current state of the art in micro-transfer printing for heterogeneously integrated silicon photonic integrated circuits. The versatility of the technology is highlighted, as is the way ahead to make this technology a key enabler for next-generation photonic systems-on-chip.

A fabrication-tolerant and low-loss III-V-to-Si3N4 adiabatic coupling structure is designed and experimentally demonstrated. The simulation shows an excess loss less than -0.3-dB at +/-1-um lateral misalignment with the DVS-BCB bonding layer thickness varying from 10 to 70 nm. A micro-transfer printed III-V-to-Si3N4 coupler was measured to have a similar to -0.7 dB loss per coupler over a 1510 nm to 1610 nm wavelength range.

Tunable lasers and photonic integrated circuits are a promising technology to provide compact and high performance solutions for coherent remote sensing applications such as Lidar, and distributed acoustic fiber sensing (DAS). A hybrid tunable laser was fabricated within the EU funded INSPIRE project, based on the micro-transfer printing of a pre-fabricated InP gain section on the IMEC low-loss silicon nitride platform. By simultaneously modulating the laser SOA current and Vernier ring resonators, we demonstrate a 20 GHz chirp amplitude, while maintaining a <5 kHz linewidth. DAS measurement with this laser are presented.

SiN photonic integrated circuit (PIC) technology has emerged as an attractive platform for a variety of sensing, LIDAR, and communication uses.[1] In comparison to Si and InP photonics, SiN offers a wide transparency window, negligible nonlinear losses (i.e. two photon absorption), and possesses a low refractive index and a low thermal coefficient. Thus, ultralow loss SiN waveguides have been achieved which are less susceptible to thermal fluctuations.[2] Driving out hydrogen content in SiN via high temperature anneal is critical during processing to minimize optical losses in the C-band (1550nm) wavelength.[3] Here, we discuss possible reasons for increased losses observed in our devices including; 1) cladding oxide, 2) SiN impurities and 3) proximity of a-Si, see process in Fig. 1(a). Note the stack indicated in the scheme illustrates the cross-section at spiral test structure sites only (Fig. 1b). An a-Si intermediate layer is also introduced to mitigate the large index difference between SiN and III-V materials for light amplification or detection purposes. Pan et al. used the same stack to demonstrate a narrow-linewidth laser post III-V gain medium micro transfer printing.[4] Exemplar SEM images are shown in Fig. 1(b) of a SiN waveguide with $1\mu \mathrm{m}$ oxide top cladding (left image) and an a-Si waveguide layer close to the SiN waveguide (right image). The distance between the a-Si waveguide layer and SiN is 100 nm (nominal, see blue arrows in Fig. 1(b). We will outline the SiN waveguides losses as were measured using the cut-back method of varying spiral lengths at process steps 1, 3 and 4.

We demonstrate a narrow-linewidth tunable laser through micro-transfer printing a prefabricated III-V gain section on imec’s 200-mm Si/SiN platform. Lasing in distinct bands in the C+L band is demonstrated, with linewidth down to 2.87-kHz.

Silicon photonics (SiPh) is a disruptive technology in the field of integrated photonics and has experienced rapid development over the past two decades. Various high-performance Si and Ge/Si-based components have been developed on this platform that allow for complex photonic integrated circuits (PICs) with small footprint. These PICs have found use in a wide range of applications. Nevertheless, some non-native functions are still desired, despite the versatility of Si, to improve the overall performance of Si PICs and at the same time cut the cost of the eventual Si photonic system-on-chip. Heterogeneous integration is verified as an effective solution to address this issue, e.g. through die-wafer-bonding and flip-chip. In this paper, we discuss another technology, micro-transfer printing, for the integration of non-native material films/opto-electronic components on SiPh-based platforms. This technology allows for efficient use of non-native materials and enables the (co-)integration of a wide range of materials/devices on wafer scale in a massively parallel way. In this paper we review some of the recent developments in the integration of non-native optical functions on Si photonic platforms using micro-transfer printing.

A single-wavelength single-polarization 35GHz-class (112Gbps-class) commercial EML-based IM/DD 214Gbps PAM4 signal transmission is experimentally demonstrated. By using advanced MLSE with low complexity and power consumption, the BER is below standard KP4-FEC requirement of 2×10−4.

A linearly chirped microwave waveform (LCMW) generator based on a monolithically integrated dual-mode amplified feedback laser (AFL) is demonstrated. The proposed LCMW generator is very simple, only consisting of an AFL, an arbitrary waveform generator, and a photodetector. By applying a sweeping signal to the amplifier section of the AFL, the beating frequency of the AFL's output can be changed in a chirped manner. LCMW is experimentally demonstrated using a heterodyne-beating technique. The measured microwave waveform has a pulse duration of 1 mu s, a bandwidth of 3.3 GHz (ranging from 31.5 to 34.8 GHz), corresponding to a time-bandwidth product of 3.3 x 10(3) and a compression ratio of 2.6 x 10(3).

We experimentally demonstrate a compact, long-range, high-resolution chaotic correlation optical time-domain reflectometry based on a monolithic integrated chaotic laser (MICL). The MICL can directly generate a broadband chaotic signal covering a RF frequency range of over 40 GHz. Multi-reflection events can be precisely located in a detection range of ∼47  km with a range-independent resolution of 2.6 mm.