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Optical modulators are vital for many applications, including telecommunication, data communication, optical computing, and microwave photonic links. A compact modulator with low voltage drive requirement, low power, high speed, and compatibility with CMOS foundry process is highly desirable. Current modulator technologies in Si suffer from trade-offs that constrain their power, performance (speed, drive voltage), and area. The introduction of additional materials to the silicon platform for efficient phase shift promises alternatives to relax those trade-offs. Si-organic-hybrid (SOH) devices demonstrate large modulation bandwidth leveraging the electro-optic (EO) effect and smaller drive voltage or footprint owing to a strong EO coefficient. In this study, we review various SOH modulators and describe their path towards integration to silicon, including their challenges associated with aging and temperature. We also briefly discuss other high-performance modulators such as plasmonic-organic-hybrid (POH), photonic-crystal-assisted SOH, and LiNbO3.

Integrating photonics with CMOS electronics in silicon is essential to enable chip-scale, electronic-photonic systems that will revolutionize classical and quantum communication and computing systems. However, the lack of an on-silicon isolator, capable of blocking unwanted back reflections and ensuring the stable operation of the laser, precluded many previous demonstrations from providing single-chip solutions. For most optical systems employing a laser, magneto-optic isolators have been indispensable, but such isolators are incompatible with silicon. To stabilize on-chip lasers, reflections-cancellation circuits were proposed as a way to reduce the reflections going back to the laser. Yet, a stable laser against time-varying back reflections was never demonstrated. Here we demonstrate a stable quantum well-distributed feedback (QWDFB) laser against slowly time-varying reflections using a reflections-cancellation circuit (RCC) on a foundry-produced, silicon-photonic (SiP) chip. The optical spectrum and the relative intensity noise (RIN) of the laser when the RCC was running is comparable to when an isolator was used. By accurately locking the laser in a stable optical feedback regime, the RCC further enhances the QWDFB laser performance by reducing its linewidth by a factor of 100, down to 3 kHz. Both results are enabled using novel techniques in the design, calibration, tuning, and control of the proposed SiP RCC. The optical insertion loss of the RCC is less than 1.5 dB for reflections smaller than −20 dB and can yield isolation ranges of up to 64 dB. Our device paves the way towards the mass production of fully integrated, low-cost electronic-photonic silicon chips without attaching magneto-optic isolators between the laser and the SiP chip.

An ultra-narrow slot waveguide is fabricated for use in highly-efficient, electro-optic-polymer-based, integrated-optic modulators. Measurement results indicate that $V_\pi L$'s below 1.2 V.mm are possible for balanced Mach-Zehnder modulators using this ultra-narrow slot waveguide on a silicon-organic hybrid platform. Simulated $V_\pi L$'s of 0.35 V.mm have also been obtained. In addition to adapting standard recipes, we developed two novel fabrication processes for achieving miniaturized devices with high modulation sensitivity. To boost compactness and decrease the overall footprint, we use a fabrication approach based on air bridge interconnects on thick, thermally-reflowed, MaN 2410 E-beam resist protected by an alumina layer. To overcome the challenges of high currents and imperfect infiltration of polymers into ultra-narrow slots, we use a carefully designed, atomically-thin layer of TiO$_2$ as a carrier-barrier to enhance the polling efficiency of our electro-optic polymers. Additionally, finite-difference time-domain simulations are employed to optimize the effect of the thin layer of TiO$_2$. As compared to other, non-optimized, cases, our peak measured current is reduced by a factor of 3; scanning electron microscopy images also demonstrate that we achieve almost perfect infiltration. The anticipated increase in total capacitance due to the TiO$_2$ layer is shown to be negligible. In fact, applying our TiO$_2$ surface treatment to our ultra-narrow slot, allows us to obtain an improved phase shift efficiency ($\partial n / \partial V$) of $\sim$94% for a 10 nm TiO$_2$ layer., Comment: 16 pages, 13 figures, Optics Express

We demonstrate a method to predict the photolithography effects of a 193 nm deep ultraviolet (DUV) process, and we build a lithography model using physical measurements on a fabricated test pattern. Our model accurately predicts the proximity and smoothing effects that are characteristic of DUV lithography. We verify the accuracy of the model by visually inspecting the fabricated test patterns and comparing them to the predicted ones. Additionally, using predicted shapes, we compare experimental measurements on a benchmark device (the contra-directional coupler) against those of our predicted, computed responses. Our predictions show good agreement with the fabricated results using both verification methods. Lastly, we illustrate the design-for-manufacturability enabled by our model by demonstrating a design correction method for the contra-directional coupler that improves its compatibility with the DUV process.

We demonstrate automated adaptation, and stabilization of a silicon photonic wavelength-division multiplexing (WDM), polarization-independent receiver. A two-channel, tunable WDM polarization-independent receiver is designed, and used to demonstrate automated WDM polarization control. Using a control algorithm based on Barzilai, and Borwein's two-point step size gradient descent method, we realize automated polarization adaptation, and wavelength stabilization for two arbitrarily polarized input data streams. 10 Gb/s on-off keying, and 20 Gb/s pulse-amplitude modulation 4-level formats are generated as the high-speed input data streams. In addition, we implement a long-duration experiment, in which we measure the bit-error-ratio for continuously varying polarization states, and changing chip temperatures. The experimental results show that, with the automated control, the WDM polarization-independent receiver can adapt, stabilize, and track the arbitrary input polarization states from a standard optical fiber into the transverse electric mode of a silicon waveguide, and simultaneously stabilize the transmitted wavelength channels at various chip temperatures. We also show how the presented WDM polarization-independent receiver scales with N channels, and propose an improved design for large-scale WDM applications.

We propose and demonstrate a cost-effective, microring-based, silicon photonic sensor that uses doped silicon detectors and a broadband source. Shifts in the sensing microring resonances are electrically tracked by a doped second microring, which acts as both a tracking element and a photodetector. By tracking the power supplied to this second ring, as the sensing ring’s resonance shifts, the effective refractive index change caused by the analyte is determined. This design reduces the cost of the system by eliminating high-cost, high-resolution tunable lasers, and is fully compatible with high-temperature fabrication processes. We report a bulk sensitivity of 61.8 nm/RIU and a system limit of detection of 9.8x10-4 RIU.

We demonstrate a method to emulate the optical performance of silicon photonic devices fabricated using advanced deep-ultraviolet lithography (DUV) processes on a rapid-prototyping electron-beam lithography process. The method is enabled by a computational lithography predictive model generated by processing SEM image data of the DUV lithography process. We experimentally demonstrate the emulation method’s accuracy on integrated silicon Bragg grating waveguides and grating-based, add-drop filter devices, two devices that are particularly susceptible to DUV lithography effects. The emulation method allows silicon photonic device and system designers to experimentally observe the effects of DUV lithography on device performance in a low-cost, rapid-prototyping, electron-beam lithography process to enable a first-time-right design flow.

A successful design, fabrication and test of silicon photonic circuits requires design tools, process design kits (PDKs), foundries for fabrication, and test facilities. This paper describes the complete design flow of photonic circuits using rapid-prototyping multiproject wafer foundry processes available in the SiEPIC program. The focus of this paper is on rapid prototyping based on electron beam lithography as an alternative and complementary to what is available via deep-UV lithography-based foundries. We describe in detail the PDK and the use of open-source and commercial tools for the design of optical filters, sensors, neuromorphic photonic processors, optical switches, and discuss test and packaging approaches for these designs. We demonstrate that a “germanium less” process can be used to build small systems featuring photoconductive detectors, electronics, and phase shifters.

The goal of SiEPICfab is to conduct research in the fabrication of silicon photonic devices and photonic integrated circuits, and to make leading-edge silicon photonic manufacturing accessible to Canadian and international academics and industry. SiEPICfab builds on the success of the Silicon Electronic Photonic Integrated Circuits (SiEPIC) program, which has been offering research training workshops since 2008, by adding a fabrication facility “fab”. We have developed a rapid prototyping facility to support a complete ecosystem of companies involved in silicon photonics product development, including modelling, design, library development, fabrication, test, and packaging of silicon photonics. SiEPICfab allows designers to rapidly complete design-fabricate-test cycles, with technologies such as sub-wavelength sensors, PN junction ring modulators, silicon defect-based detectors, single photon detectors, single photon sources, and photonic wire bond integration of lasers and optical fibres.

We demonstrate a method for measuring on-chip waveguide losses using a single microring resonator with a tunable coupler. By tuning the power coupling to the microring and measuring the microring’s through-port transmission at each power coupling, one can separate the waveguide propagation loss and the effects of the coupling to the microring. This method is tolerant of fiber-chip coupling/alignment errors and does not require the use of expensive instruments for phase response measurements. In addition, this method offers a compact solution for measuring waveguide propagation losses, only using a single microring (230 µm×190 µm, including the metal pads). We demonstrate this method by measuring the propagation losses of silicon-on-insulator rib waveguides, yielding propagation losses of 3.1-1.3 dB/cm for core widths varying from 400-600 nm.

In this work, we experimentally demonstrate a FSR-free, MRR-based, coupling modulator that integrates a bent, grating-based contra-directional-coupler (contra-DC) into a microring cavity to achieve an FSR-free response at its through port. Our modulator suppresses the amplitude response at all but one resonance, operating mode (hence, has an FSR-free response). In our modulator, coupling modulation is used and is achieved by modulating a relatively short, 210 μm long, p-n junction phase-shifter in a two-point coupler (which forms the drop-port coupler of the MRR). We demonstrate open eyes at 2.5 Gbps and discuss how the effects of DUV lithography on the contra-DC limited the electro-optic bandwidth of the fabricated modulator to 2.6 GHz. In these proceedings, we also cover details of the device design and the small and large signal characterization of the device, including an analysis of the effect of lithography on the “as-fabricated" device performance. We also discuss how to significantly improve the electro-optic bandwidth in future implementations by accounting for these lithographic effects in the device design flow and layout.

We demonstrate a silicon photonic, two-channel, tunable WDM-polarization receiver with automated polarization and wavelength control. Using a gradient descent-based control algorithm, we realize automated polarization adaptation and wavelength sta-bilization for two arbitrarily polarized inputs.

We present a four-channel, silicon-photonic, wavelength multiplexer-demultiplexer made using cascaded contra-directional couplers with adjacent and nonadjacent channel isolations of at least 37 dB and 45 dB, respectively. The device’s maximum insertion-loss is 0.72 dB.

We present a compact, single microring resonator with a tunable coupler to measure waveguide losses. The method is demonstrated by extracting the propagation losses of 550 nm and 600 nm wide SOI rib waveguides.

Coupled silicon ring resonator filters offer high-order spectral features such as steep roll-offs, high extinction ratios, and wide pass-bands, which are attractive to many applications in telecommunications and quantum computing systems. However, so far, their sensitivity to fabrication and temperature variations have limited the usability of such filters in practical applications. Here, by using in-resonator photoconductive heaters (IRPHs) to both sense and tune the resonance conditions of ring resonators, we demonstrate automatic configuration and wavelength locking of multiring resonator filters to an input laser's wavelength. We demonstrate the automatic configuration of a four-ring Vernier filter across a 36.7-nm wavelength range spanning the entire C-band and the wavelength locking of the same filter to counteract a practical chip temperature variation of 65 ${^\circ }$ C. As IRPHs do not require additional material depositions, photodetectors, or power taps and use the same contact pads for both the sense and the tune operations, these results are achieved without compromising the cost or area of the devices. Furthermore, by localizing the feedback loops to only rely on the resonance conditions of adjacent rings, we present a tuning algorithm in which the number of iterations scales linearly with the number of coupled rings in the system. As this method does not rely on the output spectral shape of the system, it is, in general, applicable to a wide range of coupled resonator systems. Our results pave a path toward practical deployment of high-order and large-scale silicon ring resonator systems.

We demonstrate an apodization technique by tapering the corrugations of spiral Bragg grating waveguides on the silicon-on-insulator platform, for the fundamental transverse magnetic mode. The transmission and reflection responses of uniform and apodized spiral Bragg grating waveguides are experimentally compared to show higher sidelobe suppression ratios by the proposed apodization scheme. We also present an apodized, period-chirped spiral Bragg grating waveguide, and the group delay of the proposed device has been measured; the results show an efficient suppression in the ripples of the group delay response.

This publisher’s note contains corrections to Opt. Lett. 46, 2738 (2021)OPLEDP0146-959210.1364/OL.423745.

High coincidence-to-accidental ratio (CAR) is crucial for photon-pair sources (PPSs) integrated with pump reject filters (PRFs) in silicon, but CAR values currently reported for integrated PPS/PRF chips still fall short of those achieved using stand-alone sources with external PRFs. Here we report measured and modelled CAR values for a micro-ring resonator PPS integrated with a PRF consisting of a three-stage, cascaded (via their through ports), contra-directional coupler (CDC) that compare favorably even with some stand-alone sources. CDC-based PRFs provide the benefits of compact area and wide reject bands without a need for tuning, in comparison to prior-art implementations.

Fabrication errors currently hold back the large-scale adoption of silicon micro-ring modulators (MRMs). The ability to correct their spectral features post-fabrication is required to enable their commercialization. Here, we report and demonstrate an MRM that uses a tunable two-point coupling scheme, which maintains the MRM’s compact footprint (60 µm×45 µm) and allows one to tune the MRM’s operating wavelength and adjust the optical bandwidth (and/or extinction ratio). This means that one can compensate for fabrication errors and thereby improve the yields. We confirm the modulator’s operation by showing NRZ and PAM-4 modulation, up to 28 Gb/s and 19.9 Gb/s, respectively. Also, the proposed tunable MRM maintains the microring’s free-spectral range (FSR), which proves its compatibility for configurable and high-bandwidth DWDM applications.

We report on broadband, flat-top, optical add–drop filters using apodized, sub-wavelength grating contradirectional couplers (SWG CDCs) on a silicon-on-insulator platform. In our device, two asymmetric SWG waveguides, having corrugation-apodized Bragg gratings, are used to couple light contradirectionally between the fundamental and next higher-order transverse electric modes of a two-waveguide system. We demonstrate an apodized, SWG CDC that has a flat-top, drop-port response with a 3 dB bandwidth of 32.6 nm, a sidelobe suppression ratio of 19 dB, and a low excess loss of 0.26 dB. We also demonstrate series-cascaded, apodized, SWG CDCs that have square-shaped, drop-port responses with 3 dB bandwidths >30 nm, sidelobe suppressions >50 dB, and low excess losses

We demonstrate how lithography smoothing and proximity effects affect the performance of silicon-on-insulator devices that include grating-based, contra-directional couplers (contra-DCs). Using lithography models developed for CMOS-compatible, deep ultraviolet lithography processes, we predict and verify the spectral responses of fabricated contra-DC test structures. These verified models are then used to simulate and analyze the effects of lithography on the performance of a microring resonator with an integrated contra-DC, as regards the device 3-dB bandwidth (BW), insertion loss (IL), and adjacent side mode suppression ratio (SMSR). We demonstrate how the corrugation profile of the contra-DC is affected by smoothing and the inner and outer corrugation depths are reduced due to proximity effects. We show that, if the effects of lithography are not taken in account during device design flow, large discrepancies result between the predicted "as-fabricated" and "as-designed" device performance. Specifically, we demonstrate how the BW is reduced from 47 GHz to 21 GHz, how the IL is increased from 0.5 dB to 5.8 dB, and how the adjacent SMSR is reduced to 26 dB. We also establish that it is possible to use the lithography models to compensate for lithographic effects during device design flow and layout and to design a contra-DC in which the as-fabricated device performance metrics matches the target/expected as-designed performance metrics.

We propose and demonstrate compact, add-drop filters using cladding-modulated, sub-wavelength grating (SWG), contra-directional couplers (CDCs) on a silicon-on-insulator platform. In our device, two asymmetric SWG waveguides, integrated with periodically loaded Bragg segments along the sides of the waveguides, are used to achieve contra-directional coupling between the fundamental and next higher-order transverse electric modes of the two-SWG-waveguide system. We present results for a 286.8-µm-long CDC that has a 3 dB bandwidth of 13.4 nm at the drop-port with a low excess loss of 0.8 dB. This device also has an 11.5-nm region at the through-port over which the extinction ratio is greater than 40 dB.

Contra-directional couplers are proposed as optical pump reject filters with the potential to achieve over 100 dB extinction ratios for on chip photon-pair sources. A scheme for these filters to enable reusing the pump laser for multiple microring resonator, photon-pair sources is presented.

We present a wideband, flat-top, optical add-drop filter using an apodized sub-wavelength-grating contra-directional coupler on a silicon-on-insulator platform. Our device achieves a >30 nm wide, flat-top drop-port response, centered at 1545 nm, with an extinction ratio >20 dB.

We demonstrate an optical add-drop multiplexer on the silicon-on-insulator platform with a 3 dB bandwidth of 6.3 nm, an ultra-high adjacent channel isolation of 58 dB, an insertion loss of 0.8 dB, and a footprint of only 1882 μm2.

Vernier effect, series-coupled microring resonators (MRRs) are used to extend the free-spectral-range (FSR) of MRRs. In this work we demonstrate integrating two MRRs in a compact Vernier configuration (compact as compared to previously demonstrated Vernier effect devices). our design was realized by using two waveguide crossings to form a major, outer ring that was coupled to a minor ring nested within the major ring. The ratio of the path length of the major ring to the path length of minor ring was 5:2. The spectral response of the device had an FSR of 27.94 nm, a drop port 3 dB bandwidth of 0.87 nm, a minimum extinction ratio of 16.1 dB, a minimum interstitial peak suppression of 10.6 dB, and a footprint of only 540 μm2 .

We report on a narrow-band, polarization-independent, transmission filter using phase-shifted, polarization-rotating Bragg gratings (PRBGs) in a silicon-on-insulator strip waveguide. In our device, phase-shifted PRBGs provide narrow transmission peaks for the transverse electric (TE) and transverse magnetic (TM) modes, both at the same wavelength. We present results for a 330.6 μm long device that has transmission peaks centered at 1556.36 nm, 3 dB bandwidths of 0.26 nm, and extinction ratios of 19 dB for both TE and TM modes. We also integrated a heater onto our device and obtained a wavelength tuning efficiency of 0.028 nm/mW for both TE and TM modes.

We present the designs, theory, and experimental demonstrations of ultra-broadband, optical add–drop filters on the silicon-on-insulator platform, realized using period-chirped contra-directional couplers. Our fabricated devices have ultra-broad 3 dB bandwidths of up to 11 THz (88.1 nm), with flat-top responses at their drop ports. All of our devices were fabricated using a commercial, CMOS-compatible, 193 nm deep-ultraviolet lithography process. By using lithography-prediction models, the measured bandwidths, insertion losses, central wavelengths, and extinction ratios of our devices are all in good agreement with our predicted, simulated results. Such filters are necessary for photonic integrated circuits to operate over multiple optical bands.