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This paper presents a novel approach to counterbalance free-carrier-absorption (FCA) in electro-optic (E-O) Mach-Zehnder interferometer (MZI) cells by harnessing self-heating effect. We show insights on crosstalk limitations in MZIs with direct carrier-injection and provide a detailed design methodology on a differential phase shifter pair. Leveraging both free-carrier dispersion (FCD) and self-heating effects, our design enables arbitrary phase tuning with balanced FCA loss in the pair of arms, eliminating the need for additional phase corrections and creating ultralow crosstalk MZI elements. This neat design disengages from the commonly used nested structure and thus provides an opportunity of embedding tunable couplers for correcting imperfect splitting ratios given that only two of which are needed. We show that with the use of tunable direction couplers (DCs), a standard ±10 nm process variation is tolerated, whilst achieving below -40dB crosstalk ratio. By direct carrier injection in both arms, the proposed device operates at nanosecond scales and can bring about a breakthrough in the scalability of E-O switch fabrics, as well as other silicon integrated circuits that have stringent requirements on crosstalk leakage.

Ring resonators are a vital element for filters, optical delay lines, or sensors in silicon photonics. However, reconfigurable ring resonators with low-power consumption are not available in foundries today. We demonstrate an add-drop ring resonator with the independent tuning of round-trip phase and coupling using low-power microelectromechanical (MEMS) actuation. At a wavelength of 1540 nm and for a maximum voltage of 40 V, the phase shifters provide a resonance wavelength tuning of 0.15 nm, while the tunable couplers can tune the optical resonance extinction ratio at the through port from 0 to 30 dB. The optical resonance displays a passive quality factor of 29 000, which can be increased to almost 50 000 with actuation. The MEMS rings are individually vacuum-sealed on wafer scale, enabling reliable and long-term protection from the environment. We cycled the mechanical actuators for more than 4 x 109 cycles at 100 kHz, and did not observe degradation in their response curves. On mechanical resonance, we demonstrate a modulation increase of up to 15 dB, with a voltage bias of 4 V and a peak drive amplitude as low as 20 mV.(c) 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

We present our work in the European project MORPHIC to extend an established silicon photonics platform with low-power and non-volatile micro-electromechanical (MEMS) actuators to demonstrate large-scale programmable photonic integrated circuits (PICs).

We present our work to extend silicon photonics with MEMS actuators to enable low-power, large scale programmable photonic circuits. For this, we start from the existing iSiPP50G silicon photonics platform of IMEC, where we add free-standing movable waveguides using a few post-processing steps. This allows us to implement phase shifters and tunable couplers using electrostatically actuated MEMS, while at the same time maintaining all the original functionality of the silicon photonics platform. The MEMS devices are protected using a wafer-level sealing approach and interfaced with custom multi-channel driver and readout electronics.

Silicon photonic circuits are rapidly growing in complexity and spreading to new applications. However, programmable circuits consume much power and require active electrical interfaces. For the first time, we demonstrate a nonvolatile photonic MEMS pi-phase switch using dual comb-drive actuation and adhesion forces, implemented in a silicon photonics foundry. Both nonvolatile states are low-loss, display low dispersion, could be cycled through over 100 times, and have retention times over 12 hours. We believe that the demonstrated nonvolatility combined with excellent optical performance can enable a new generation of programmable photonic chips that do not consume any electrical power once (re)configured.

Programmable photonic chips allow flexible reconfiguration of on-chip optical connections, controlled through electronics and software. We will present the recent progress of such complex photonic circuits powered by silicon photonic MEMS actuators.

Orthogonal chirp-division multiplexing is deployed as a novel waveform in an optical/millimeter-wave system. Enhanced channel estimation gives a 5-dB receiver sensitivity improvement over a conventional OFDM implementation, and compatibility with 256-QAM at 60-GHz is experimentally demonstrated.

Orthogonal chirp-division multiplexing (OCDM) has recently been proposed as an attractive modulation technique for high-speed fiber-optic systems in virtue of its resilience against system impairments. In this paper, we propose an iterative block (IB) decision feedback equalization (DFE) algorithm for the intensity-modulation and direct-detection (IM/DD) based OCDM system to effectively mitigate the chromatic-dispersion (CD) induced power fading in the fiber. An efficient algorithm is derived to simplify the IB-DFE at the receiver. Analysis is provided to show that the fading effect is compensated by recovering the noisy signals in the vicinity of frequency notches. Simulations were carried out to study the performance of the proposed system. The results show that the proposed system with IB-DFE is able to compensate severe fading effects and improves the bit error rate (BER) by several orders of magnitude. An experiment was implemented to realize 30.3-Gb/s IM/DD-OCDM signal over 50-km fiber, in which power fading due to CD over 20 dB was observed. The experiment results show that the proposed system further reduced the required optical signal-to-noise ratio by 8 dB to achieve a BER of 3 × 10−5.

Dynamically reconfigurable passive optical networks (PONs) using time-division multiplexing and dense wavelength division multiplexing will require low-cost, high-performance customer premises equipment to be economically viable. In particular, substantial cost savings can be achieved through the use of efficient re-growth free, foundry-compatible fabrication techniques. Using this strategy, this paper presents the first detailed characterization of a monolithically integrated transmitter comprised of a discretely tunable slotted Fabry–Pérot ridge waveguide laser, an absorptive modulator and a semiconductor optical amplifier (SOA) produced using a standard off-the-shelf AlInGaAs/InP multiple quantum well epitaxial structure. This first generation device demonstrates a discrete single-mode tuning range of approximately 12 nm between 1551nm and 1563 nm with a side-mode suppression ratio ≥30 dB. Moreover, the integrated modulator section is shown to support transmission at 10 Gb/s using non-return to zero on-off keying with an extinction ratio in excess of 8 dB. Furthermore, using a time-resolved chirp measurement technique to examine dynamic deviations in the set carrier frequency, the modulator section exhibits a chirp contribution of

Orthogonal chirp-division multiplexing (OCDM) was recently proposed as a promising modulation technique for high-speed fiber-optic communications due to its resilience to transmission impairments. By exploiting the pulse-compression property of the chirped waveforms, in this paper we propose a channel estimation algorithm compatible with the coherent optical (CO) OCDM system. In the proposed algorithm, a chirp from the orthogonal basis of the Fresnel transform is employed as the pilot signal. At the receiver, noise-rejection windowing is adopted in the Fresnel domain to remove the excessive noise after pulse compression, and then dispersions can be effectively compensated by efficient single-tap equalizers. It is shown that the proposed estimator is unbiased as long as the width of the noise-rejection window is wider than the maximum excess delay of the system. Moreover, the optimal window function achieving the minimum mean square error is derived in closed form. With these desired properties, it is shown that the proposed estimator outperforms conventional estimators, such as the intrasymbol frequency-domain average estimator, especially when the dispersion is severe. Finally, numerical results are provided to confirm the advantages of the CO-OCDM system with the proposed channel estimation algorithm.

We present a silicon photonics technology extended with low-power MEMS scalable to large circuits. This enables us to make photonic waveguide meshes that can be reconfigured using electronics and software.

Programmable photonic circuits electronically reconfigure the flow of light on a chip. This requires hundreds or thousands of phase shifters and tunable couplers. Silicon photonic MEMS offer both high integration density and low power consumption.

In the European project MORPHIC we develop a platform for programmable silicon photonic circuits enabled by waveguide-integrated micro-electro-mechanical systems (MEMS). MEMS can add compact, and low-power phase shifters and couplers to an established silicon photonics platform with high-speed modulators and detectors. This MEMS technology is used for a new class of programmable photonic circuits, that can be reconfigured using electronics and software, consisting of large interconnected meshes of phase shifters and couplers. MORPHIC is also developing the packaging and driver electronics interfacing schemes for such large circuits, creating a supply chain for rapid prototyping new photonic chip concepts. These will be demonstrated in different applications, such as switching, beamforming and microwave photonics.

The physical layout of cables and nodes in many of today’s passive optical networks (s) still dates back to the early days of copper loop installations, with customer to exchange node distances limited to a few kilometers largely by the transmission distance of analogue telephony over the copper pairs. However, modern optical communication technologies can enable much longer transmission distances, and through the use of optical amplification can effectively integrate the access and metro portions of the network into a single all-optical communication system, which is commonly referred to as “Long-reach PON” () or “Amplified PON”. LR-PONs offer several advantages in terms of infrastructure sharing, network node consolidation and core network delayering.

Hierarchical PAM4 modulation in passive optical network downstream channels is experimentally demonstrated as a way to redistribute power margin between users with different path losses due to unequal fiber distribution and split losses. Using hierarchical PAM4 modulation the most-significant bit (MSB) and less-significant bit (LSB) can be assigned to two different optical network units (ONU) groups, whose receiver sensitivity can be optimized to increase the power budget of the ONUs with higher path losses, effectively redistributing power margin of the ONUs with lower losses. A single-threshold receiver is sufficient for the MSB ONU type and a dual-threshold receiver coupled with an and logic gate for the LSB ONU type, both of which are simpler than a full PAM4 receiver with three thresholds. Sensitivity improvement in a 25 Gb/s system is achieved using unequal signal level spacing and separate detection of the binary tributary streams of the PAM4 channel. Power budget increase of up to 3.5 dB is reported with respect to a standard PAM4 transmission. Higher chromatic dispersion tolerance is also measured for the higher sensitivity ONU group, enabling transmission over up to 40 km of single-mode fiber for the MSB ONUs with no chromatic dispersion compensation.

Orthogonal chirp-division multiplexing (OCDM) has been recently proposed as an attractive modulation technique for realizing high-speed coherent lightwave systems in virtue of its resilience against system impairments. However, the complex-valued OCDM signal is not directly viable for optical intensity modulation and direct detection (IM/DD) systems. In this paper, a double-sideband (DSB)-modulated OCDM scheme is proposed for short-reach, high-speed IM/DD systems. In the proposed scheme, the real-valued OCDM signal is generated by a simple digital up-conversion technique, which converts the complex-baseband signal to a passband to avoid the aliasing for DSB modulation. At the receiver, inverse operations revert the signal back to the baseband for demodulation. Experiments were carried out to validate the feasibility and advantages of the proposed scheme, and OCDM signals with data rates up to 174.5 Gbit/s were successfully demonstrated. The results confirm that the proposed IM/DD-OCDM system is more robust to impairments and thus achieves better performance than a discrete multi-tone system.