Asymmetric Mach-Zehnder Interferometer Research Articles

Low‐loss and broadband InP mirror‐based out‐of‐plane optical coupler

The authors developed a mirror-based out-of-plane optical coupler (MOOC) for InP photonic integrated circuits (PICs). The coupler has the coupling loss and alignment tolerance comparable to those of a conventional edge coupler. An asymmetric Mach–Zehnder interferometer (a-MZI) with the MOOC exhibits little wavelength-dependent loss (WDL) and a high extinction ratio (ER) of >20 dB over 100-nm wavelength bandwidth. In addition, the temperature-independent transmittance spectra were obtained. Finally, the authors fabricated a 4-ch MOOC array with the pitch of 40 μm, which corresponds to the core pitch of practical multi-core fibre (MCF).

Integrated Optical Electric Field Sensor Based on Asymmetric Mach-Zehnder Interferometer With Straight Waveguide Arms

In this paper, an asymmetric Mach-Zehnder interferometer with straight waveguide arms based integrated optical electric field sensor is proposed. Compared with the present reported integrated optical electric field sensors, the proposed sensor has relatively lower transmission loss, higher extinction ratio, much larger linear measurable range, and better thermal stability. The transmission loss of the device is demonstrated to be as low as 6 dB and the extinction ratio is as high as 35 dB. Moreover, the sensor has a linear measurable range of approximately 34 dB and the minimal detectable electric field strength of 10 V/m is achieved in the experiments. Combining the wavelength tuning technique, the thermal variations in the sensor bias have fallen from around 120 degrees down to be 2 degrees with the temperature ranging from 24°C to 70°C. These results are very encouraging toward the development of integrated optical electric field sensing systems in the practical applications.

Performance Analysis of Scalable Optical Circuit Switch Employing Fast-Tunable AMZI Filters for Coherent Detection

High-port-count optical switches are expected to resolve the envisaged bandwidth and power crunch in intra-data center networks stemming from the slowdown of Moore's Law. This paper briefly reviews electrical switching technologies in current intra-data centers and discusses requirements for optical circuit switches in future data centers. We highlight an optical switch architecture that combines the two independent dimensions of space and wavelength to realize large port counts and fast switching. Wavelength routing is implementable with receiver-side channel selection using wavelength tunable filters (TFs). Coherent detection necessitates a fast-tunable local oscillator (LO) at the receiver. It can be cost-effectively realized using an LO bank that consists of fixed-wavelength laser sources and Silicon-photonic asymmetric Mach-Zehnder interferometer (AMZI) filters. Colorless detection that removes a TF at the front of the receiver is possible when the number of wavelength-division multiplexing (WDM) channels is small, however, as the number exceeds a certain limit the TF is needed to prevent power saturation of the receiver. We present an effective cooperative filtering scheme for transmission signals and LO channels sourced from an LO bank; it can detect C-band WDM coherent signals while easing the receiver's power limitation. The scheme is analyzed to clarify receiver performance and the switch port-count bounds under various operating conditions. We demonstrate that the cooperative filtering scheme effectively works from 60 (typical of coherent receivers) to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$ &gt; $</tex-math></inline-formula> 116 wavelength channels, which is verified by experiments for 1,856 × 1,856 optical switching with the short switching time of 3.2 μs.

Frequency-selectable microwave generation based on on-chip switchable spectral shaping and wavelength-to-time mapping.

We propose and experimentally demonstrate a scheme for the photonic generation of pulsed microwave signals with selectable frequency based on spectral shaping and wavelength-to-time mapping (WTTM) technique. The frequency selectivity is realized by channel switching on an integrated silicon-on-insulator (SOI) spectral shaping chip. The incident signal is spectrally shaped by the asymmetric Mach-Zehnder interferometer (MZI) in the selected channel, and an optical spectrum with uniform free spectral range (FSR) can be generated in a broad bandwidth up to dozens of nanometers, implying large microwave signal duration after WTTM if a pulse light source with matched bandwidth is available. Microwave pulses of frequency from 3.6 GHz to 28.4 GHz with a fixed interval are experimentally generated respectively. The realization of eight microwave frequencies selectable with only one shared dispersive element (DE) required indicates high expansibility in the frequency cover range of our scheme by tuning the dispersion value in WTTM.

Reconfigurable optical filter based on microring resonator assisted by tunable Sagnac reflector

To meet the demands for various applications in optical filtering and microwave signal processing, integrated silicon photonic filters are required to be multifunctional, reconfigurable and tunable. In this work, an integrated multi-functional optical filter is proposed, which is designed based on a tunable Sagnac loop reflector and a microring resonator. The through port and drop port of an add-drop microring resonator are connected with the two ports of a tunable reflector. By controlling the thermal phase shifters in different scenarios, the device can be reconfigured into a reflective-type asymmetric Mach-Zehnder interferometer filter, a reflective-type all-pass microring resonator filter and self-interference microring resonator filters. An analytical model is established based on the transfer matrix. The simulation results show that the device can achieve the following functions: sinusoidal spectral filtering with four different free spectral ranges, Lorentzian spectral filtering toggling between band pass and band stop, and spectral reconfigurations of Fano resonance, electromagnetically induced transparency, and electromagnetically induced absorption. Each spectrum mentioned above can be tuned fast and widely. Reflection provides a new degree of freedom in design, breaks through the inherent footprint limit, and achieves a wide range of free spectral ranges. Our proposed tunable Sagnac loop reflector assisted microring resonator provides a new scheme for realizing flexible, tunable and multi-functional reconfigurable integrated photonic filters, and has broad applications in the integrated photonic analog signal processing and microwave photonics.

Optical Temperature Sensor Based on Polysilicon Waveguides

Traditional temperature detection has limitations in terms of sensing accuracy and response time, while chip-level photoelectric sensors based on the thermo-optic effect can improve measurement sensitivity and reduce costs. This paper presents on-chip temperature sensors based on polysilicon (p-Si) waveguides. Dual-microring resonator (MRR) and asymmetric Mach-Zehnder interferometer (AMZI) sensors are demonstrated. The experimental results show that the sensitivities of the sensors based on AMZI and MRR are 86.6 pm/K and 85.7 pm/K, respectively. The temperature sensors proposed in this paper are compatible with the complementary metal-oxide-semiconductor (CMOS) fabrication technique. Benefitting from high sensitivity and a compact footprint, these sensors show great potential in the field of photonic-electronic applications.

A modulated positioning scheme for asymmetric vibration sensor using high-frequency carrier

The asymmetric dual Mach-Zehnder interferometer can be used in the vibration sensing system for the long-distance monitoring. It can effectively suppress the backscattering noises of the system. However, it will also seriously deteriorate the positioning accuracy because of the asymmetry of the interferometer. In this paper, a modulated asymmetric dual Mach Zehnder interferometer (ADMZI) system using a high-frequency carrier scheme has been theoretically proposed and experimentally demonstrated. Field trials have been carried out to verify the effectiveness. Our experimental results show that the standard deviation of the proposed scheme is less than 60 m for a sensing length of 51 km, with an average processing time of 106 ms. Compared to traditional methods, the proposed approach can also be applied to weak signals with low frequencies and small amplitudes. This indicates that the proposed scheme can significantly improve the applicability of the asymmetry based distributed sensing systems.

Temperature characterizations of silica asymmetric Mach-Zehnder interferometer chip for quantum key distribution

Quantum key distribution (QKD) system based on passive silica planar lightwave circuit (PLC) asymmetric Mach–Zehnder interferometers (AMZI) is characterized with thermal stability, low loss and sufficient integration scalability. However, waveguide stresses, both intrinsic and temperature-induced stresses, have significant impacts on the stable operation of the system. We have designed silica AMZI chips of 400 ps delay, with bend waveguides length equalized for both long and short arms to balance the stresses thereof. The temperature characteristics of the silica PLC AMZI chip are studied. The interference visibility at the single photon level is kept higher than 95% over a wide temperature range of 12 °C. The delay time change is 0.321 ps within a temperature change of 40 °C. The spectral shift is 0.0011~nm/0.1 °C. Temperature-induced delay time and peak wavelength variations do not affect the interference visibility. The experiment results demonstrate the advantage of being tolerant to chip temperature fluctuations.

Fabrication tolerant and wavelength independent arbitrary power splitters on a monolithic silicon photonics platform.

We experimentally demonstrate wavelength-independent couplers based on an asymmetric Mach-Zehnder interferometer on a monolithic silicon-photonics platform in a state-of-the-art CMOS foundry. The devices are also designed to exhibit fabrication tolerant performance for arbitrary splitting ratios. We have developed a semi-analytical model to optimize the device response and the reliability of the model is benchmarked against 3D-FDTD simulations. Experimental results are consistent with the simulation results obtained by the model and show uniform performance across different wafer sites with a standard deviation for the splitting ratio of only 0.6% at 1310 nm wavelength. The maximum spectral deviation of the splitting ratio (3-dB splitter) is measured to be 1.2% over a wavelength range of at least 80 nm and the insertion loss ranges from 0.08 to 0.38 dB. The wavelength-independent coupler has a compact footprint of 60 × 40 μ m 2.

Pulse amplitude modulation wireless communication in the 300 GHz-band employing an integrated-optic interferometer-based signal emulator

Wireless communication using a pulse amplitude modulation signal was carried out in the 300 GHz-band. In this investigation, the used THz-wave signal was generated with a silica waveguide-type optical signal emulator and high-speed photo-mixing. The optical signal emulator consisting of a tunable asymmetric Mach-Zehnder interferometer produces an optical pulse amplitude modulation signal from an optical on-off keying signal by partly adopting lightwave interference. 25 Gsymbol/s three and four-level pulse amplitude modulation signals in the 300 GHz-band were generated and used for the wireless communication. Bit error rates of received signals were evaluated with off-line processing, and the bit error rates were estimated to be 1.9 × 10−4 and 8.0 × 10−3 in the communications using the three and four-level signals, respectively.

Asymmetric Mach-Zehnder Interferometric Biosensing for Quantitative and Sensitive Multiplex Detection of Anti-SARS-CoV-2 Antibodies in Human Plasma.

The Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) pandemic has once more emphasized the urgent need for accurate and fast point-of-care (POC) diagnostics for outbreak control and prevention. The main challenge in the development of POC in vitro diagnostics (IVD) is to combine a short time to result with a high sensitivity, and to keep the testing cost-effective. In this respect, sensors based on photonic integrated circuits (PICs) may offer advantages as they have features such as a high analytical sensitivity, capability for multiplexing, ease of miniaturization, and the potential for high-volume manufacturing. One special type of PIC sensor is the asymmetric Mach–Zehnder Interferometer (aMZI), which is characterized by a high and tunable analytical sensitivity. The current work describes the application of an aMZI-based biosensor platform for sensitive and multiplex detection of anti-SARS-CoV-2 antibodies in human plasma samples using the spike protein (SP), the receptor-binding domain (RBD), and the nucleocapsid protein (NP) as target antigens. The results are in good agreement with several CE-IVD marked reference methods and demonstrate the potential of the aMZI biosensor technology for further development into a photonic IVD platform.

On-Chip RF Signal Shaping by Coherent Control of Optically Driven Acoustic Wave Interference

Photonic–phononic systems that mix photons and acoustic waves have been actively investigated for the development of next-generation integrated photonics for signal processing. Here, we propose a new method of arbitrary RF signal shaping using active control of optically driven acoustic-wave interference, offering new photonic–phononic–microwave signal processing schemes with MHz linewidths at GHz carrier frequencies. The demonstrated system consists of two suspended optical waveguides and an asymmetric Mach–Zehnder interferometer. The two waveguides generate acoustic waves at a 3.03 GHz carrier frequency with a 3.3 MHz bandwidth, and one of the paths of the asymmetric interferometer experiences phase modulation induced by the acoustic waves. Then, the interferometer converts the phase information to RF signals of complicated shapes using a linear combination of multiple optical envelopes. This RF signal-shaping method will open new applications of optomechanical systems for microwave photonics.

Monolithic mode separator for the first-order spatial mode of light field.

We propose a monolithic mode separator (MS) for the first-order spatial mode of a light field. The principle of the MS is an asymmetric Mach-Zehnder interferometer, which consists of two non-polarizing beam splitters, a right-angle prism, and a pentagonal prism. These optics are glued together as a monolithic one. The phase difference between the two light paths inside the interferometer is temperature controlled. The separation efficiency for two first-order orthogonal Hermite Gaussian (HG) modes, i.e., HG01 and HG10, is 97.5%, and the overall transmission is 77%. The device is intrinsically stable and convenient to be adopted in various experiments.

Modelling, characterization, and applications of silicon on insulator loop terminated asymmetric Mach Zehnder interferometer

This work presents a loop terminated asymmetric Mach–Zehnder interferometer (LT-aMZI) structure based on the widespread silicon-on-insulator (SOI) platform. Four different path length differences of the LT-aMZI, which correspond to free spectral ranges (FSR) from 0.8 to 6.4 nm, are designed. These designs are compared to the common asymmetric Mach–Zehnder interferometer (C-aMZI) and are shown to be more compact. These devices are suitable for optical filtering as well as wavelength demultiplexing (WDM) applications. A compact analytical model is derived that accurately describe the operation of the LT-MZI devices. The designs are then fabricated using Electron Beam Lithography (EBL) and characterized. The experimental data show good agreement when compared to the simulation results. To our knowledge, this is the first time LT-aMZI fabrication and characterization. Moreover, the LT-MZI spectrum can be tuned not only by the interferometer arms phase difference like C-MZI, but also by using its directional couplers coefficients, forming a spectral tunable filter. Finally, we determine the performance parameters of optical sensors and modulators and show that our proposed LT-MZI structure will enhance the sensor figure of merit (FOM) and modulator speed, power consumption and Vπ × L compared to C-MZI. A comparison between symmetric and asymmetric MZI sensors and the advantage of the latter is also mentioned.

Ultra-power-efficient heterogeneous III–V/Si MOSCAP (de-)interleavers for DWDM optical links

We discuss the design and demonstration of various III–V/Si asymmetric Mach–Zehnder interferometer (AMZI) and ring-assisted AMZI (de-)interleavers operating at O-band wavelengths with 65 GHz channel spacing. The wafer-bonded III–V/Si metal-oxide-semiconductor capacitor (MOSCAP) structure facilitates ultra-low-power phase tuning on a heterogeneous platform that allows for complete monolithic transceiver photonic integration. The second- and third-order MOSCAP AMZI (de-)interleavers exhibit cross-talk (XT) levels down to − 22 dB and − 32 dB with tuning powers of 83.0 nW and 53.0 nW, respectively. The one-, two-, and three-ring-assisted MOSCAP AMZI (de-)interleavers have XT levels down to − 27 dB, − 22 dB, and − 20 dB for tuning powers of 10.0 nW, 7220.0 nW, and 33.6 nW, respectively. The leakage current density is measured to be in the range of 1.6 – 27 μA / cm 2 . To the best of our knowledge, we have demonstrated for the first time, athermal III–V/Si MOSCAP (de-)interleavers with the lowest XT and reconfiguration power consumption on a silicon platform.

All-Optical Tunable Plasmonic Biosensor Made of Graphene and Metamaterial

We demonstrate a novel, label-free and real-time tunable infrared biosensor by employing surface-plasmon polaritons in asymmetric Mach–Zehnder interferometer. The waveguides cladding in the Mach–Zehnder interferometer are made of lossy media with positive and negative electromagnetic susceptibilities, including metamaterial, metal and graphene. The core consists of dielectric media. We introduce two configurations for our biosensor structure. First configuration is an open-path structure and the second one consists of a sample housing made of a silicon layer around the structure. We also present a tunable biosensor by applying a gate voltage to the graphene in the structure. We employ three different cancerous cells, including cervical, breast and basal, as samples to examine the capabilities of the biosensor. Our biosensor structure is highly sensitive, compared to the existing biosensors in the literature, with the sensitivity for basal cancer cell of 1034THz/RIU. The proposed biosensor structure is compact and easy to fabricate with applications in biomedical sensing and environmental control to detect water pollutants.

Demonstration of a 17 × 25 Gb/s Heterogeneous III-V/Si DWDM Transmitter based on (De-) Interleaved Quantum Dot Optical Frequency Combs

We discuss the design and demonstration of a space and dense wavelength division multiplexed heterogeneous III-V&#x002F;Si transmitter based on a single multi-wavelength quantum dot laser source and ultra-power-efficient metal-oxide-semiconductor capacitor (MOSCAP) (de-)interleaver. This paper begins by introducing a transceiver architecture capable of &gt; 1 Tb&#x002F;s transmission with &lt; 1.5 pJ&#x002F;bit power consumption, followed by a detailed discussion of the heterogeneous laser source and (de-)interleaver. The O-band quantum dot laser, based on a compound cavity design, has a FSR &#x223C; 64 GHz with a 1&#x03C3; variation of &#x223C; 1.08 GHz and a measured relative intensity noise (RIN) of &#x223C; -144 dB&#x002F;Hz for the largest comb peak. The single-ring-assisted asymmetric Mach-Zehnder interferometer (1-RAMZI) MOSCAP (de-)interleaver exhibit cross-talk (XT) levels down to -27 dB for tuning powers of 10.0 nW. Finally, to the best of our knowledge, we have demonstrated for the first time, a simultaneous wavelength and space division multiplexed transmitter fabricated on a heterogeneous III-V-on-silicon platform. Experiments show (de-)interleaved 17 optical comb lines, each modulated at 25 Gb&#x002F;s non-return-to-zero (NRZ) for an aggregate bandwidth of 425 Gb&#x002F;s.

Highly sensitive and stable fiber-laser pressure-sensing system based on an unequal-arm Mach-Zehnder cascaded with a Sagnac structure

We propose, analyze, and experimentally demonstrate a highly sensitive and stable fiber-laser pressure-sensing system based on an unequal-arm Mach-Zehnder interferometer (MZI) merged with a Sagnac interferometer (SI). The unequal-arm MZI structure consists essentially of two single-mode fibers of different lengths, and the SI structure uses a section of polarization-maintaining fiber, which acts as a sensing head. Moreover, in the proposed sensing system, the MZI and SI structures both act as a cascade filter. Given the asymmetric MZI and cascade filter structure laser mode hopping is effectively suppressed, so minor variations in environmental parameters cause a stable shift of the interference spectrum. The experimental results show that the proposed system can be used to make accurate pressure measurements. The −3 dB linewidth of the reflection interference peak produced by the proposed system is less than 0.02 nm, and the signal-to-noise ratio (SNR) can exceed 45 dB. With a 1-m-long sensor head, the proposed system provides a pressure sensitivity of 29.275 nm/MPa, and the interference spectrum of the sensing system fluctuates less than ±0.02 nm over 1 h. The proposed sensing system thus offers the attractive characteristics of good sensing linearity and stability, high SNR, and high sensitivity.

Quantum key distribution transmitter chip based on hybrid-integration of silica and lithium niobates

A quantum key distribution transmitter chip based on hybrid-integration of silica planar light-wave circuit (PLC) and lithium niobates (LN) modulator PLC is presented. The silica part consists of a tunable directional coupler and 400-ps delay line, and the LN part is made up of a Y-branch, with electro-optic modulators on both arms. The two parts are facet-coupled to form an asymmetric Mach–Zehnder interferometer. We successfully encode and decode four BB84 states at 156.25-MHz repetition rate. Fast phase-encoding of 0 or π is achieved, with interference fringe visibilities 78.53% and 82.68% for states |+〉 and |–〉, respectively. With the aid of an extra off-chip LN intensity modulator, two time-bin states are prepared and the extinction ratios are 18.65 dB and 15.46 dB for states |0〉 and |1〉, respectively.

Realization of high interference visibility based on silica-on-silicon planar lightwave circuit

Quantum key distribution can realize unconditional security of communication. Here, a quantum decoding chip based on silica-on-silicon planar lightwave circuit (PLC) platform, which is compatible for multiprotocol has been demonstrated. PLC technology provides stability, high integration, and practicality for the chip, whereas silica-on-silicon material makes it low loss and low cost. The chip is integrated with three variable optical splitters, two asymmetric Mach–Zehnder interferometers, and four variable directional couplers. The interference visibility is investigated by self-interfering method, and the results showed it is high to 98.2% under temperature control. The extinction ratio for the phase states is kept between 23 and 25 dB for 6 h without active phase correction.