Effective thermo-optical enhanced cross-ring resonator MZI interleavers on SOI

Electro-optical tunable interleaver in hybrid silicon and lithium niobate thin films

The interleaver was one of the key devices in dense wavelength division multiplexing (DWDM) applications. In this study, an interleaver with an asymmetrical Mach-Zehnder interferometer structure was designed, fabricated, and characterized in hybrid silicon and lithium niobate thin films (Si-LNOI). The interleaver based on Si-LNOI could be fabricated by mature processing technology of Si photonic, and it was capable of the electro-optical (E-O) tuning function by using the E-O effect of LN. In the range of 1530-1620 nm, the interleaver achieved a channel spacing of 55 GHz and an extinction ratio of 12-28 dB. Due to the large refractive index of Si, the Si loading strip waveguide based on Si-LNOI had a compact optical mode area, which allowed a small electrode gap to improve the E-O modulation efficiency of the interleaver. For an E-O interaction length of 1 mm, the E-O modulation efficiency was 26 pm/V. The interleaver will have potential applications in DWDM systems, optical switches, and filters.

Programmable wavelength filter with double ring loaded MZI

We propose a novel filter circuit that incorporates a double ring resonator with a balanced Mach–Zehnder interferometer (MZI). The circuit has a response equivalent to a conventional ring loaded MZI filter, but with added flexibility in terms of configurability. The second-order filter can also be cascaded to realize higher-order filters. The circuit incorporates a two-stage input and output coupler to further reduce the effect of dispersion. A combination of local and global optimization strategies to program the filter, using tailored objective functions, have been tested in simulation and experiments. To our best knowledge, this is the first time a global optimization strategy is directly used in ARMA filter synthesis and simulation without any additional requirement. We further extend the optimization strategy into experiments and demonstrated its use in practical case for programmable filter circuits.

Passive silicon ring-assisted Mach-Zehnder interleavers operating in the broadband spectral range

We propose and experimentally demonstrate a passive and compact interleaver on a silicon on insulator (SOI) platform using a ring-assisted asymmetrical Mach-Zehnder interferometer configuration. The wavelength-insensitive couplers, i.e., multimode interference couplers and adiabatic 3-dB couplers, are introduced to eliminate the effect of an unequal splitting ratio and wavelength on crosstalk and the operating spectral range. In addition, there exists an inherent phase shift between the two couplers; the device can be fully passive and works well without additional thermal tuning. In the calculation, the influence of wavelength sensitivity of self-coupling coefficients and couplers on the performance of the interleaver is considered. The experiment shows that, by employing wavelength-insensitive couplers, the operating spectral range of the proposed interleavers was extended to be >140nm for all sorts of channel spacing and channel count. The measured free spectral range is 4.6 nm, and the crosstalk is as low as -46.6dB for the best case.

Compact silicon photonic interleaver based on a self-coupled optical waveguide

We propose and experimentally demonstrate a new scheme to realize an on-chip silicon photonic interleaver by using a self-coupled optical waveguide (SCOW). Benefiting from the high-order filtering property of a multistage SCOW resonator, the device has a smaller footprint and higher extinction ratio compared to conventional ring-assisted Mach-Zehnder interferometer interleavers. Its high fabrication tolerance is also demonstrated in this paper. The operation principle of the proposed interleaver is theoretically analyzed. The designed device is fabricated on a silicon-on-insulator wafer under standard complementary metal oxide semiconductor compatible fabrication processes. Experimental results show that 20 dB extinction ratio and about 8 dB insertion loss can be achieved in the entire C-band without any thermo-optic tuning, verifying the effectiveness of the proposed device as an on-chip interleaver with a compact footprint and high extinction ratio.

Slot waveguide ring resonators coated by an atomic layer deposited organic/inorganic nanolaminate

In this study, slot waveguide ring resonators patterned on a silicon-on-insulator (SOI) wafer and coated with an atomic layer deposited nanolaminate consisting of alternating layers of tantalum pentoxide and polyimide were fabricated and characterized. To the best of our knowledge, this is the first demonstration of atomic layer deposition (ALD) of organic materials in waveguiding applications. In our nanolaminate ring resonators, the optical power is not only confined in the narrow central air slot but also in several parallel sub-10 nm wide vertical polyimide slots. This indicates that the mode profiles in the silicon slot waveguide can be accurately tuned by the ALD method. Our results show that ALD of organic and inorganic materials can be combined with conventional silicon waveguide fabrication techniques to create slot waveguide ring resonators with varying mode profiles. This can potentially open new possibilities for various photonic applications, such as optical sensing and all-optical signal processing.

Microring resonator photodetector for enhancement in L-band performance

We proposed a microring resonator (MRR) enhanced photodetector (PD) structure. Resonance wavelength enhanced by the MRR amplifies the PD response. At L-band wavelengths, responsivity was doubled for an ultra-short germanium PD of 4 µm employing the MRR structure. Data rates of up to 40 Gb/s were also demonstrated at 1600 nm.

On-chip quasi-digital optical switch using silicon microring resonator-coupled Mach-Zehnder interferometer

In this work, we demonstrate thermo-optical quasi-digital optical switch (q-DOS) using silicon microring resonator-coupled Mach-Zehnder interferometer. The optical transmission spectra show box-like response with 1-dB and 3-dB bandwidths of ~1.3 nm and ~1.6 nm, respectively. Such broadband flat-top optical response improves the tolerance to the light source wavelength fluctuation of ± 6 Å and temperature variation of ± 6 °C. Dynamic characterizations show the device with switching power of ~37 mW, switching time of ~7 μs, and on/off ratio of > 30 dB. For performance comparison, we also demonstrate a carrier injection-based electro-optical q-DOS by integrating lateral P-i-N junction with the microring resonator, which significantly reduces power consumption to ~12 mW and switching time to ~0.7 ns only.

Integrated in-band optical signal-to-noise ratio monitor implemented on SOI platform

Based on different coherence properties of signal and noise, we measured the in-band optical signal-to-noise ratio using an integrated thermally tunable Mach-Zehnder optical delay interferometer on SOI platform. The experimental results exhibit errors smaller than 1 dB for signals with bit rate <40 Gbps over an OSNR range of 9~30 dB. The effects of the extinction ratio, noise equivalent bandwidth and arm length difference on the implementation of measurement are analyzed.

Low-loss silicon slot waveguides and couplers fabricated with optical lithography and atomic layer deposition

We demonstrate low-loss silicon slot waveguides patterned with 248 nm deep-UV lithography and filled with atomic layer deposited aluminum oxide. Propagation losses less than 5 dB/cm are achieved with the waveguides. The devices are fabricated using low-temperature CMOS compatible processes. We also demonstrate simple, compact and efficient strip-to-slot waveguide couplers. With a coupler as short as 10 µm, coupling loss is less than 0.15 dB. The low-index and low-nonlinearity filling material allows nonlinearities nearly two orders of magnitude smaller than in silicon waveguides. Therefore, these waveguides are a good candidate for linear photonic devices on the silicon platform, and for distortion-free signal transmission channels between different parts of a silicon all-optical chip. The low-nonlinearity slot waveguides and robust couplers also facilitate a 50-fold local change of the waveguide nonlinearity within the chip by a simple mask design.

Thermo-optical tunable planar ridge microdisk resonator in silicon-on-insulator

In this work, we design and demonstrate planar ridge microdisk resonators in silicon-on-insulator, which assemble the advantages of microring and microdisk resonators. The dependences of resonator optical modes on the slab thickness and the waveguide-to-resonator coupling gap are investigated. The highest Q-factor obtained is ~4 × 10(5). Using the thermo-optical effect, we attain a resonance wavelength tuning efficiency of ~66.5 pm/mW. We also compare the transmission spectra measured by using wavelength-scanning method and voltage-scanning method and show potential application for the adopted voltage-scanning method.

Thermally-efficient reconfigurable narrowband RF-photonic filter

We present the design and fabrication of thermally-efficient tuning structures integrated into a narrowband reconfigurable radio-frequency (RF)-photonics filter using silicon-on-insulator waveguide optical delay lines. By introducing thermal isolation trenching, we are able to achieve IIR, FIR or arbitrary mixed response with less than 120 mW average tuning power in a single RF-photonic unit cell filter.

High bandwidth on-chip silicon photonic interleaver

We demonstrate a 120 GHz 3-dB bandwidth on-chip silicon photonic interleaver with a flat passband over a broad spectral range of 70 nm. The structure of the interleaver is based on an asymmetric Mach-Zehnder interferometer (MZI) with 3 ring resonators coupled to the arms of the MZI. The transmission spectra of this device depict a rapid roll-off on the band edges, where the 20-dB bandwidth is measured to be 142 GHz. This device is optimized for operation in the C-band with a channel crosstalk as low as -20 dB. The device also has full reconfiguration capability to compensate for fabrication imperfections.

Fano-resonance-based Mach-Zehnder optical switch employing dual-bus coupled ring resonator as two-beam interferometer

A kind of Mach-Zehnder optical switch with a dual-bus coupled ring resonator as a two-beam interferometer is proposed and investigated. The analysis based on the transfer matrix method shows that a sharp asymmetric Fano line shape can be generated in the transmission spectra of such a configuration, which can be used to significantly reduce the phase change required for switching. Meanwhile, it can also be found that complete extinctions can be achieved in both switching states if the structural parameters are carefully chosen and the phase bias is properly set. Through tuning the phase difference between the arms of the Mach-Zehnder interferometer, complete extinction can be easily kept within a large range of the ring-bus coupling ratios in the OFF state. By properly modulating the phase change in the ring waveguide, the shift of the resonant frequency and the asymmetry of the transmission spectra can be controlled to finally enable optical switching with a high extinction ratio, even complete extinction, in the ON state. The switching functionality is verified by the finite-difference time-domain simulation.