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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.

We propose a strategy to improve sensing performance of sub-wavelength-grating (SWG) waveguide-based sensors by introducing a substrate-overetch (SOE) geometry. The proposed SOE-SWG waveguide shows enhanced analyte interaction and a reduced group index, which improves the sensitivity of resonator-based sensors. The SiO2 overetch process was realized in Ar/C4F8/O2 plasma for 40 sec with a SiO2/Si selectivity of 10:1, obtaining a 285-nm anisotropic overetch in the SiO2 layer. Sensor performance of the SOE-SWG architecture is characterized by using isopropyl alcohol solutions, indicating an enhanced bulk sensitivity up to 575 nm/RIU (479 nm/RIU before the SOE), and a maximum waveguide mode sensitivity larger than one.

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

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 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.

A silicon-on-insulator (SOI), bandwidth (BW)-tunable, free-spectral-range (FSR)-free, microring resonator (MRR)-based filter is experimentally demonstrated. The device achieves an FSR-free response at its through and drop ports by using a grating-assisted coupler in one coupling region of the MRR and achieves a non-adjacent channel isolation, (nAi), for 400 GHz WDM, greater than 26.7 dB. A thermally tunable Mach–Zehnder Interferometer-based coupling scheme is also utilized to compensate for fabrication variations and enable the BW tunability of the filter. The BW of the filter can be continuously tuned from 25 to 60 GHz while maintaining an nAi greater than 26.7 dB.

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.

We design and demonstrate a compact broadband polarization beam splitter (PBS) using a symmetric directional coupler with sinusoidal bends on a silicon-on-insulator platform. The sinusoidal bends in our PBS suppress the power exchange between two parallel symmetric strip waveguides for the transverse-electric (TE) mode, while allowing for the maximum power transfer to the adjacent waveguide for the transverse-magnetic (TM) mode. Our PBS has a nominal coupler length of 8.55 μm, and it has an average extinction ratio (ER) of 12.0 dB for the TE mode, an average ER of 20.1 dB for the TM mode, an average polarization isolation (PI) of 20.6 dB for the through port, and an average PI of 11.5 dB for the cross port, all over a bandwidth of 100 nm.

In this work, we present optical add/drop multiplexer (OADM) filters for coarse wavelength-division-multiplexing (CWDM) systems with high sidelobe suppressions that result in high adjacent channel isolations (A i ). The filters are realized by using a compact, series-cascaded configuration of apodized, contradirectional-coupling-based filters. We experimentally demonstrate a device with a measured A i of 53 dB (these devices hold the promise of achieving even higher A i s). While having large A i s, our devices have the wide bandwidths and low insertion losses required for CWDM applications. In addition, our demonstrated OADM has a nearly constant group delay, which results in low dispersion in the passband.

It is shown that an apodization profile to realize a specific spectral response for a silicon integrated Bragg grating (IBG) can be amplified/scaled-up greatly by an order of magnitude by introducing phase delays between the two sides of the apodized gratings. This amplification brings about significant improvements in the apodization dynamic range and resolution/precision, thereby facilitating the spectral tailoring of the IBGs. The concept is first exploited in corrugation width-modulated Gaussian-apodized silicon IBGs, and then in phase-modulated silicon IBGs to achieve a five-channel dispersionless square-shaped filter. Significant spectral performance improvements brought by the amplification are demonstrated in both cases.

We experimentally demonstrate high-performance integer and fractional-order photonic Hilbert transformers based on laterally apodized Bragg gratings in a silicon-on-insulator technology platform. The sub-millimeter-long gratings have been fabricated using single-etch electron beam lithography, and the resulting HT devices offer operation bandwidths approaching the THz range, with time-bandwidth products between 10 and 20.

We report on a compact, broadband, 2×2 adiabatic 3 dB coupler using sub-wavelength gratings (SWGs) for silicon-on-insulator waveguides. In our device, two SWG waveguides that support two transverse electric modes and have tapered waveguide widths were used to achieve an adiabatic mode evolution of the two-waveguide system for broadband 3 dB power splitting. We present results for a SWG adiabatic 3 dB coupler that has an overall coupler length of 50 μm and achieves broadband power splitting over a 130 nm wavelength range with an imbalance of no greater than ±0.3 dB and with low excess losses of less than 0.5 dB.

We demonstrate large-area silicon-on-insulator ring resonators with Q values of about 2×10sup6/supat critical coupling and 3.6×10sup6/supfor heavily undercoupled conditions. A model has been developed to understand the impact of waveguide backscattering and subcomponent imperfections on the spectral response of our devices. The model predicts the appearance of signals at ports that would not have them under backscattering-free, ideal-power-splitting conditions. The predictions of our model are shown to match the phenomena observed in our measurements.

We report on a compact, ultra-broadband, 2×2 adiabatic 3 dB coupler using silicon-on-insulator (SOI) strip waveguides assisted by sub-wavelength gratings (SWGs). In our device, two tapered SWG-assisted SOI strip waveguides achieve an adiabatic mode evolution of the two lowest-order transverse electric modes, in a two-waveguide system, for broadband 3 dB power splitting. Theory predicts that the proposed coupler will operate from 1200 nm to 1700 nm. We have been able to measure the performance of a device with a 15 μm long mode evolution region that achieves even, broadband power splitting over the 185 nm wavelength range of our tunable laser with an imbalance of less than ±0.3 dB and with low average excess losses of

Multichannel photonic Hilbert transformers (MPHTs) are reported. The devices are based on single compact spiral integrated Bragg gratings on silicon with coupling coefficients precisely modulated by the phase of each grating period. MPHTs with up to nine wavelength channels and a single-channel bandwidth of up to ∼625 GHz are achieved. The potential of the devices for multichannel single-sideband signal generation is suggested. The work offers a new possibility of utilizing wavelength as an extra degree of freedom in designing radio-frequency photonic signal processors. Such multichannel processors are expected to possess improved capacities and a potential to greatly benefit current widespread wavelength division multiplexed systems.

We have experimentally demonstrated, in silicon, a double microring resonator with Mach–Zehnder interferometer-based coupling that meets many commercial specifications. Our device has a ripple of 0.5 dB, an adjacent channel isolation of at least 41.0 dB, a nonadjacent channel isolation of at least 38.6 dB, an interstitial peak suppression of at least 37.5 dB, an express channel isolation of 10.0 dB, and a free spectral range greater than the span of the C-band of 37.23 nm.

We proposed and experimentally demonstrated an ultra-broadband on-chip microwave photonic processor that can operate both as RF phase shifter (PS) and true-time-delay (TTD) line, with continuous tuning. The processor is based on a silicon dual-phase-shifted waveguide Bragg grating (DPS-WBG) realized with a CMOS compatible process. We experimentally demonstrated the generation of delay up to 19.4 ps over 10 GHz instantaneous bandwidth and a phase shift of approximately 160° over the bandwidth 22–29 GHz. The available RF measurement setup ultimately limits the phase shifting demonstration as the device is capable of providing up to 300° phase shift for RF frequencies over a record bandwidth approaching 1 THz.

We propose and experimentally demonstrate the first THz bandwidth on-chip photonic fractional Hilbert transformer. The reported design uses a novel approach, based on a uniform and nonapodized single phase-shifted integrated waveguide Bragg grating on silicon, where the fractional order P can be engineered by simply varying the effective index modulation δn. Experimental results for P=1.5 show very low processing error for a broad range of pulse bandwidths between 77 GHz and 2.07 THz, corresponding to a time-bandwidth product as high as 27.

We demonstrate an apodization technique using tapered coupler gaps in grating-assisted asymmetric couplers, which circumvents the need for tapered waveguide perturbations and enables a higher tolerance to fabrication errors. A high sidelobe suppression ratio of 30 dB has been obtained on the submicrometer silicon-on-insulator platform using a CMOS-compatible photonics process with 193 nm lithography.

The spectral responses of series-coupled racetrack resonators exhibiting the Vernier effect have many attractive features as compared to the spectral responses of identical series-coupled racetrack resonators, such as free spectral range (FSR) extension and enhanced wavelength tunability. Here we present experimental results of a thermally tunable quadruple series-coupled silicon racetrack resonator exhibiting the Vernier effect. We thermally tune two of the four racetrack resonators to enable discrete switching of the major peak by 15.54 nm. Also, our device has an interstitial peak suppression of 35.4 dB, a 3 dB bandwidth of 0.45 nm, and an extended FSR of 37.66 nm.

We demonstrate record performance of series-coupled silicon racetrack resonators exhibiting the Vernier effect. Our device has an interstitial peak suppression (IPS) of 25.5 dB, which is 14.5 dB larger than previously reported results. We also demonstrate the relationship between the inter-ring gap distance and the IPS as well as the 3 dB bandwidth (BW) both theoretically and experimentally. Namely, we show that as the inter-ring gap distance increases, the IPS increases and the 3 dB BW decreases.

We demonstrate contradirectional couplers in silicon-on-insulator rib waveguides using a CMOS compatible technology, in which a periodic dielectric perturbation is introduced in the coupling region between two different-sized rib waveguides. This structure enables high fabrication tolerances for narrow-bandwidth add-drop filters, using commercially available deep-ultraviolet lithography, that do not suffer from having a free spectral range. The simulation using coupled-mode theory and mode-profile calculations shows good agreement with experiment. A narrow bandwidth of 0.35 nm and a low loss of less than 1 dB have been achieved experimentally.

We present a novel design of a wavelength-selective reflector using a microring resonator integrated with a low-loss, low-crosstalk waveguide crossing. Functioning as a reflective notch filter, it can be used for optical communications and for sensor applications. The device is simulated using the transfer-matrix method combined with a two-dimensional finite-difference mode solver and is fabricated by a CMOS-compatible silicon-on-insulator technology. The measurement shows an extinction ratio greater than 25 dB and a resonance-wavelength temperature dependence of 0.09 nm/K.

We report on a wavelength-selective, polarization-rotating filter using a partially etched asymmetric Bragg grating on a compact single-mode, silicon-on-insulator (SOI) strip waveguide. The asymmetric Bragg grating rotates and reflects the fundamental transverse electric (TE) and transverse magnetic (TM) modes at selected wavelengths. Our device offers wavelength-selective, polarization-rotating reflection at its reflection port and wavelength-selective, polarization-independent notch filtering at its through port. The device is fabricated using a CMOS-compatible process with 193 nm-deep ultraviolet lithography on an SOI platform. We present results for a 294.4 μm long device that has a 3 dB bandwidth of 2.63 nm and a low-excess loss of less than 1 dB. This device also has a maximum polarization-extinction-ratio of greater than 27 dB.

We present a methodology to design broadband grating couplers using one-dimensional subwavelength gratings. Using the presented method, we design subwavelength grating couplers (SWGCs) with 1-dB bandwidths ranging from 50 to 90 nm. Our designed SWGCs have competitive coupling efficiency, as high as -3.8 dB for the fundamental TE mode, and state-of-the-art back reflections, as low as -23 dB.

We present waveguide Bragg gratings with misaligned sidewall corrugations on a silicon-on-insulator platform. The grating strength can be tuned by varying the misalignment between the corrugations on the two sidewalls. This approach allows for a wide range of grating coupling coefficients to be achieved with precise control, and substantially reduces the effects of quantization error due to the finite mask grid size. The experimental results are in very good agreement with simulations using the finite-difference time-domain (FDTD) method.