Coupled Mach-Zehnder Interferometer Research Articles

Asymmetric Mach-Zehnder prism interferometer coupler-based combined fiber ring resonator system for a Brillouin gyroscope.

Brillouin fiber-optic gyroscope (BFOG) is a fiber ring resonator (FRR)-based ring laser gyroscope with a large dynamic range and high sensitivity. Previous BFOGs operated under simultaneous resonance of the pump and Brillouin laser light in the FRR, resulting in complex control systems. This article introduces an asymmetric prism Mach-Zehnder interferometer coupler (APMZIC)-based FRR system, in which the coupling ratio of pump light is large, while the Brillouin laser resonates in the cavity with a negligible coupling loss, resulting in a simple control system. We analyzed the characteristics of the APMZIC and its combined resonator system both theoretically and experimentally and verified the feasibility of connecting the APMZIC with the resonant cavity of a Brillouin laser. This coupler system is compact, easy to fabricate, highly stable, and exhibits good repeatability, which are necessary for miniaturizing lasers and gyroscopes.

Optical Spectral Shaping Based on Reconfigurable Integrated Microring Resonator-Coupled Fabry–Perot Cavity

We demonstrate a multifunctional optical spectral shaper on a silicon photonic chip. The proposed structure is composed of a tunable microring resonator (MRR) and three tunable Sagnac loop mirrors (SLMs), which can be regarded as a large SLM incorporating an MRR-coupled Fabry–Perot (FP) cavity. To realize flexible tuning, thermo-optically tunable Mach-Zehnder interferometer (MZI) couplers are used to replace conventional directional couplers with fixed coupling coefficients. By controlling the tunable MZI couplers, the proposed structure can be reconfigured as various functional structures including an all-pass MRR with tunable coupling regime, a tunable FP cavity, an SLM incorporating FP cavity, and an MRR-coupled FP cavity. This flexible reconfiguration allows for multifunctional optical spectral shaping including tunable comb filtering, Fano and EIT-like resonances. In particular, the complementary flat-top comb filtering responses can be theoretically obtained in the two ports of this device with same free spectral range (FSR) value, which enable the (de)interleaver operation. The experimental results show that the implemented all-pass MRR has a maximum extinction ratio (ER) of 38.9 dB and the corresponding quality factor is 6.5×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> . The comb filter based on configured FP cavity can be switched from narrowband response (0.06 nm) to wideband flat-top response (0.23 nm), with ERs up to 10.6 dB and 22 dB, respectively. Moreover, a dynamic conversion between Lorentz, EIT, and Fano resonance line shapes based on the coupled resonant system can be realized. The demonstrated integrated device holds great potential for various applications such as filtering and switching in optical wavelength-division multiplexing (WDM) communication networks.

Simple reconfigurable multiport photonic temporal N-differentiator and integrator based on dual-ring coupled Mach–Zehnder interferometer

At present, a high-order, reconfigurable photonic signal processor is very difficult to implement. A simple, reconfigurable photonic N-differentiator and integrator based on a unit of the dual-ring coupled Mach–Zehnder interferometer (DRMZI) is proposed first. The reconfigurability is achieved only by controlling the thermo-optic phase shifter (TO-PS) on the two improved micro-ring resonators. The device presents a wide fine-tunable differentiation order range from 0.2 ≤ N ≤ 1.7 reconfigured as a 2 × 2 differentiator after being optimized the TO-PS and the tunable couplers (TC). If it is reconfigured as an integrator, a first-order photonic temporal integrator with 16.1 GHz 3-dB bandwidth and integration time window 38.4 ps is achieved in our design. The 4 × 4 port DRMZI differential unit can be cascaded into k-stage to realize 0.2 × k ≤ N ≤ 1.7 × k order differential function, theoretically approaching any large order. At the same time, the differential signals can be successfully routed to different output ports by reconfiguring the optical path in the structure. The simulation results have shown that a two-stage 4 × 4 photonic temporal differentiator can perform more than two order differential operations, e.g., N = 2.4. Our research can provide a reference for chip-level large-scale integrated photonic processors.

Compact High Resolution Speckle Spectrometer by Using Linear Coherent Integrated Network on Silicon Nitride Platform at 776 nm

AbstractMotivated by applications in mobile optical sensing, ultracompact high‐resolution integrated spectrometers have attracted much interest. Here, a high‐resolution integrated speckle spectrometer, comprising a linear coherent network formed by mutually coupled Mach–Zehnder interferometers and nonidentical microring resonators, is proposed and demonstrated. Deep‐etched grating lines used as mirrors on the edges of the coherent network increase the effective optical path lengths. The speckle spectrometer is realized on a silicon nitride platform, operating at 776 nm central wavelength. The eight‐in−eight‐out linear coherent network provides 64 physical channels. Fine spectral lines separated by 20 pm are experimentally resolved within a device footprint of 520 µm × 220 µm. Compressive sensing is achieved for sparse spectra over a wide optical bandwidth. Up to 600 distinctive wavelength channels can be reconstructed from the 64 physical channels, giving 12 nm operating bandwidth. Both sparse spectra and continuous spectra are well reconstructed experimentally. The integrated speckle spectrometer has great potential for use in future biosensing and bioimaging applications where high spectral resolution is desired.

Monolithic InP optical unitary converter based on multi-plane light conversion.

Integrated reconfigurable optical unitary converters (OUCs) are crucial in realizing all-optical spatial mode demultiplexing for mode-division-multiplexed transmission systems and programmable photonic processing for optical neural networks. In this work, we present the first experimental demonstration of 4×4 OUC monolithically integrated on InP. To avoid the difficulty of integrating a large number of Mach-Zehnder interferometer couplers on the InP platform, we apply the concept of multi-plane light conversion and use cascaded stages of 4-port multimode interference couplers, which are more scalable and easier to fabricate on InP. By optimizing the phase shifters, we demonstrate reconfigurable 4-mode sorting as well as error-free switching of 40-Gbit/s signal.

A Stopband and Passband Switchable Microwave Photonic Filter Based on Integrated Dual Ring Coupled Mach–Zehnder Interferometer

A stopband and passband switchable microwave photonic filter based on the integrated tunable dual ring coupled Mach–Zehnder interferometer has been demonstrated. By using the optical single sideband modulation, the switchable stopband and passband optical responses of the optical filter are one-to-one mapping to the RF spectra. The center frequency and bandwidth of the switchable microwave photonic filter are both reconfigurable. A frequency tuning range of 4–25 GHz is obtained, and the bandwidth tuning ranges of the passband and stopband MPFs are 4.54–9.72 GHz and 3.65–6.35 GHz, respectively. In addition, a RF rejection ratio about 20 dB is achieved. Compared with the switchable MPFs implemented by nonintegrated devices, the proposed switchable MPF provides a simple and low cost method to process radiofrequency signals.

Reconfigurable and tunable compact comb filter and (de)interleaver on silicon platform

We propose and demonstrate a reconfigurable and tunable chip-scale comb filter and (de)interleaver on a silicon platform. The silicon-based photonic integrated device is formed by Sagnac loop mirrors (SLMs) with directional couplers replaced by multi-mode interference (MMI) assisted tunable Mach-Zehnder interferometer (MZI) couplers. The device can be regarded as a large SLM incorporating two small SLMs which form a Fabry-Perot (FP) cavity. By appropriately adjusting the micro-heaters in tunable MZI couplers and cavity, switchable operation between comb filter and (de)interleaver and extinction ratio and wavelength tunable operations of comb filter and (de)interleaver are achievable by thermo-optic tuning. Reconfigurable comb filter and (de)interleaver is demonstrated in the experiment. The central wavelength shifts of comb filter and (de)interleaver are demonstrated with wavelength tuning efficiencies of ~0.0224 nm/mW and ~0.0193 nm/mW, respectively. The 3-dB bandwidth of the comb filter is ~0.032 nm. The 3-dB and 20-dB bandwidths of the (de)interleaver passband are ~0.225 nm and ~0.326 nm. The obtained results indicate that the designed and fabricated device provides switchable comb filtering and interleaving functions together with extinction ratio and wavelength tunabilities. Reconfigurable and tunable silicon-based comb filter and (de)interleaver may find potential applications in robust wavelength-division multiplexing (WDM) optical communication systems.

Microwave frequency upconversion employing a coupling-modulated ring resonator

We present a method to generate a frequency-doubled microwave signal by employing a coupling-modulated ring resonator. Critical coupling is achieved when the resonator intrinsic loss is perfectly balanced by the external coupling enabled by a Mach–Zehnder interferometer coupler. The high suppression of the carrier leads to a clean two-tone optical signal with the frequency interval two times larger than that of the input microwave frequency. The beating of the two-tone signal at a photodiode generates the frequency upconverted microwave signal. A theoretical model is established to analyze the modulation process and the microwave signal generation. Experimental results show that the electrical harmonic suppression ratio is around ∼20 dB (29 dB) for an input microwave signal with 5 dBm (10 dBm) power.

Silicon ring resonator-coupled Mach-Zehnder interferometers for the Fano resonance in the mid-IR.

We present ring resonator (RR)-coupled Mach-Zehnder interferometers (MZIs) based on silicon-on-insulator rib waveguides, operating around the mid-IR wavelength of 3.8μm. A number of different photonic integrated devices have been designed and fabricated experimentally to obtain the asymmetric Fano resonances in the mid-IR. We have investigated the influence of the coupling efficiency between the RR and the MZI as well as the phase shift between the two arms of the MZI on the Fano-type resonance spectral features, in agreement with theoretical predictions. Finally, wavelength-dependent Fano transmittances have been successfully measured with insertion losses up to ∼1 dB and extinction ratios of ∼20 dB. A slope of sharp Fano resonances as high as -574.6/μm has been achieved and estimated to be 35.5% higher than the slope of single RR Lorentzian-type resonances.

Application of SOI microring coupling modulation in microwave photonic phase shifters

Phase shifter is one of the key devices in microwave photonics. We report a silicon microring resonator with coupling modulation to realize microwave phase shift. With coupling tuning of the Mach-Zehnder interferometer (MZI) coupler to change the resonator from under-coupling to over-coupling, the device can realize a π phase shift on the incoming microwave signal with a frequency up to 25 GHz. The device can also realize 2.5π continuous phase tuning by manipulating the three DC bias voltages applied on the MZI coupler.

Wavelength and bandwidth-tunable silicon comb filter based on Sagnac loop mirrors with Mach-Zehnder interferometer couplers.

We propose and experimentally demonstrate a wavelength and bandwidth-tunable comb filter based on silicon Sagnac loop mirrors (SLMs) with Mach-Zehnder interferometer (MZI) couplers. By thermally tuning the MZI couplers in common and differential modes, the phase shift and reflectivity of the SLMs can be changed, respectively, leading to tunable wavelength and bandwidth of the comb filter. The fabricated comb filter has 93 comb lines in the wavelength range from 1535 nm to 1565 nm spaced by ~0.322 nm. The central wavelength can be red-shifted by ~0.462 nm with a tuning efficiency of ~0.019 nm/mW. A continuously tunable bandwidth from 5.88 GHz to 24.89 GHz is also achieved with a differential heating power ranging from 0.00 mW to 0.53 mW.

Low-voltage high-speed coupling modulation in silicon racetrack ring resonators.

We demonstrate a low-voltage high-speed modulator based on a silicon racetrack resonator with a tunable Mach-Zehnder interferometer coupler. Both static measurement and dynamic modulation experiment are carried out. The 3-dB electro-optic bandwidth is measured to be >30 GHz beyond the limit by the cavity photon lifetime. A 32 Gb/s on-off keying (OOK) modulation is realized under a peak-to-peak drive voltage as low as 0.4 V, and a 28 Gb/s binary phase-shift-keying (BPSK) modulation is realized with a drive voltage of 3 V. The low drive voltages results in low energy consumptions of ~13.3 fJ/bit and ~1.2 pJ/bit for OOK and BPSK modulations, respectively.

An interleaver with tunable bandwidth ratio based on microring resonator coupled Mach–Zehnder interferometer

A fundamental structure of a passive interleaver based on microring resonator coupled Mach–Zehnder interferometer is proposed in this paper. The most conspicuous advantage is the simplicity, compactness of the structure and the flatness of the passband top. Then we propose two methods of realizing a bandwidth tunability in this structure. A further analysis shows that both methods have their own strengths. We expect the compact and flexible interleaver can provide some potential and important implications for upgrading a hybrid Dense Wavelength Division Multiplexing (DWDM) system.

Binary phase-shift keying by coupling modulation of microrings.

We propose a coupling-modulated microring in an add-drop configuration for binary phase-shift keying (BPSK), where data is encoded as 0 and π radian phase-shifts on the optical carrier. The device uses the π radian phase-flip across the zero coupling point in a 2 × 2 Mach-Zehnder interferometer coupler to produce the modulation. The coupling-modulated microring combines the drive power reduction of resonant modulators with the digital phase response of Mach-Zehnder BPSK modulators. A proof-of-concept device was demonstrated in silicon-on-insulator, showing differential binary phase-shift keying operation at 5 and 10 Gb/s.

A Photonic Temporal Integrator With an Ultra-Long Integration Time Window Based on an InP-InGaAsP Integrated Ring Resonator

A photonic temporal integrator with an ultra-wide integration time window implemented based on a photonic integrated circuit (PIC) in an InP-InGaAsP material system consisting of semiconductor optical amplifiers (SOAs) and current-injection phase modulators (PMs) is proposed and experimentally demonstrated. The proposed photonic integrated integrator employs a ring structure coupled with two bypass waveguides. The tunable coupling between the ring and the waveguides is realized by a multi-mode interference (MMI) Mach-Zehnder interferometer coupler. Within the ring, two SOAs are incorporated to compensate for the insertion loss. In addition, there is a current injection PM in the ring for wavelength tuning. The use of the device provides a photonic temporal integrator with an ultra-wide integration time window and a tunable operation wavelength in a single PIC. The proposed integrator is fabricated and experimentally verified. The integration time window as wide as 6331 ps is achieved, which is an order of magnitude longer than that provided by the previously reported photonic integrators.

A NEW STRUCTURE FOR ALL-OPTICAL THREE-INPUT XOR LOGIC GATE BASED ON SEMICONDUCTOR OPTICAL AMPLIFIER MACH–ZEHNDER INTERFEROMETER

In this paper the design and simulation of an all-optical three-input exclusive-OR (XOR) gate based on semiconductor optical amplifier-Mach–Zehnder interferometer (SOA-MZI) configuration is presented. This gate is constructed of three semiconductor optical amplifiers placed at the arms of the two coupled Mach–Zehnder interferometers. The outputs of these two MZIs are combined at the output port to form the final signal. The proposed scheme does not need a continuous wave (CW) laser for its operation and is designed so that the minimum number SOAs are employed. Theoretical analyses and simulations show that this structure acts as an all-optical three-input XOR logic gate which has many applications in optical data communications.

Investigation of Coupling Tuning in Self-Coupled Optical Waveguide Resonators

We investigate the influence of coupling strength on self-coupled optical waveguide (SCOW) resonators. Experimental results reveal that the SCOW resonator transmission spectrum can exhibit single-channel or dual-channel stopbands with the band splitting level determined by the two coupling coefficients. Electrically tunable SCOW resonators comprising 2×2 Mach-Zehnder interferometer couplers are also demonstrated, which shows a similar change trend upon coupling tuning.

Reversible Fano resonance by transition from fast light to slow light in a coupled-resonator-induced transparency structure

We theoretically propose and experimentally perform a novel dispersion tuning scheme to realize a tunable Fano resonance in a coupled-resonator-induced transparency (CRIT) structure coupled Mach-Zehnder interferometer. We reveal that the profile of the Fano resonance in the resonator coupled Mach-Zehnder interferometers (RCMZI) is determined not only by the phase shift difference between the two arms of the RCMZI but also by the dispersion (group delay) of the CRIT structure. Furthermore, it is theoretically predicted and experimentally demonstrated that the slope and the asymmetry parameter (q) describing the Fano resonance spectral line shape of the RCMZI experience a sign reversal when the dispersion of the CRIT structure is tuned from abnormal dispersion (fast light) to normal dispersion (slow light). These theoretical and experimental results indicate that the reversible Fano resonance which holds significant implications for some attractive device applications such as highly sensitive biochemical sensors, ultrafast optical switches and routers can be realized by the dispersion tuning scheme in the RCMZI.

Nested fiber ring resonator enhanced Mach–Zehnder interferometer for temperature sensing

We numerically investigate the properties of the nested fiber ring resonator coupled Mach-Zehnder interferometer as a sensor. By introducing the phase bias of 0.5π in the reference arm, the two output intensities exhibit sharp asymmetric line shapes around the resonance wavelength. Utilizing the intensity interrogation, we analyze the effect of parameters on the sensitivity and the detection limit. For the 30 dB signal-noise system, the sensitivity and the detection limit can achieve 4.0866/°C and 7.341×10(-3)°C, respectively; the results indicate that this structure is suitable for high-sensitivity measurements.

Characteristics of Microring Resonators With Waveguide-Resonator Coupling Modulation

The general output characteristics of high quality factor microring resonators with modulated coupling strengths are derived. The results are applied to the case of a microring integrated with a Mach-Zehnder interferometer coupler to investigate the amplitude, linearity, distortion, and chirp of the output. These modulators can be designed to give low-distortion, high extinction ratio, chirp-free outputs at modulation rates only limited by the maximum modulation rate of the coupler or the free spectral range frequency of the resonator.