Asymmetric Mach-Zehnder Interferometer Research Articles

Ultracompact Photonic-Waveguide Circuits in Si-Pillar Photonic-Crystal Structures for Integrated Nanophotonic Switches

Highly integrated optical device technology based on square-lattice Si-pillar photonic-crystal-(PC) waveguides is described. The Si-pillar PC waveguides are now ready to use, since efficient optical coupling structures to Si-wire waveguides have been devised. Nanophotonic switches using the Si-pillar-PC waveguides were experimentally demonstrated. The nanophotonic switches make use of two of the features of Si-pillar photonic crystal waveguides. One is the property of slow-light and the other is the usability of zero-radius 90 degrees bends, both of which enable waveguide-based optical devices to be greatly miniaturized. Even apart from the cut-off wavelength, the group index of the pillar-PC waveguides was about 7.8, which was about twice that of a Si-wire waveguide for the entire C-band of telecommunications wavelengths. The 3-dB couplers we fabricated were only 3.2-microm long thanks to the 90 degrees sharp bends, and they operated throughout the entire C-band. Waveguide-cross operation was also demonstrated in the entire C-band. Asymmetric Mach-Zehnder interferometers (MZIs) were configured by using the 3-dB couplers in an area of 13.2 x 37.2 microm. An MZI with a Si-wire heater successfully operated with an extinction ratio of about 20 dB at a heating power of 17 mW. It is strongly suggested that Si-pillar PC photonic-waveguide technology should help us to achieve densely integrated optical-matrix switches demanded for future photonic-telecommunication systems.

The influence of the time delay through long trunk fiber on the phase-coding quantum key distribution system

Optical pulse will reach the receiver not at exact time instance due to the transmission through the long trunk fiber, and this phenomenon will effect on the bits error rate in the Quantum key distribution (QKD) system to some extend. The time jitter based on the differential phase shift quantum key distribution system and two asymmetric Mach-Zehnder interferometers is measured outdoors in different transmission distance and the physical model of the relationship between the time jitter and the quantum bit error rate is proposed. According to this relationship, the quantum bit error rate can be estimated for some optical pulse shape and some statistical distribution function.

Performance of hybrid entanglement photon pair source for quantum key distribution

We report on the experimental demonstration of a source of hybrid entanglement pairs between two different degrees of freedom, a 1550 nm time-bin qubit and an 810 nm polarization qubit. The polarization qubit at 810 nm is transformed by an asymmetric Mach–Zehnder interferometer consisted of a Glan laser prism and a polarization-maintaining fiber. We obtained visibilities of 95.8% and 88% with tolerance ±0.2% and ±1% along Z-Z and X-X axes on the Poincare sphere, respectively, with a coincidence count rate of more than 800 c/s after entanglement format transformation. These values are well above the threshold of 70.7% needed to violate a Bell inequality and allow distilling a secure key in the quantum key distribution.

Optical frequency comb generation based on repeated frequency shifting using two Mach-Zehnder modulators and an asymmetric Mach-Zehnder interferometer

A novel approach to generating an optical frequency comb based on repeated frequency shifting is proposed and experimentally demonstrated. The frequency shifting is implemented via optical carrier suppression and single-sideband modulation using two Mach-Zehnder modulators in conjunction with a bidirectional asymmetric Mach-Zehnder interferometer with wavelength-shifted transmission spectra along the opposite directions. A theoretical analysis is performed, which is confirmed by a proof-of-concept experiment. A stable optical comb covering a spectral range of 0.18 THz is generated.

DQPSK: When Is a Narrow Filter Receiver Good Enough?

In this paper, we investigate experimentally and via simulation the pros and cons of a narrow filter receiver for differential quadrature phase-shift keying based on a single optical filter and eschewing the conventional asymmetrical Mach-Zehnder interferometer structure. We quantify the performance differences between the two receivers, allowing system designers and operators to determine when the less complex narrow filter receiver might be the appropriate choice. We numerically optimize the 3-dB bandwidth and center frequency of the narrow filter and show it is more robust to carrier frequency detuning than the conventional solution. We show that the narrow filter receiver is more tolerant to chromatic dispersion (CD) than the conventional one, and equally tolerant to first-order polarization-mode dispersion. We show the impact of the 3-dB bandwidth on the receiver performance when CD accumulates. Finally, we show via experiments and simulations that the 3 dB advantage of the conventional receiver vanishes when the nonlinear impairments are fiber nonlinearities; comparing the two receivers at the optimum launch power for a 25 times 80 km system, the difference in optical SNR margin is reduced to ~1.6 dB. Experiments are conducted at 42 Gb/s using a commercially available narrow filter for reception.

A Photonic UWB Generator Reconfigurable for Multiple Modulation Formats

In this letter, we propose and demonstrate a simple and flexible optical ultra-wideband (UWB) pulse generator that can be reconfigured for pulse-position modulation, biphase modulation, and pulse-shape modulation. The system is implemented using a dual-drive Mach-Zehnder modulator and an electrically reconfigurable asymmetric Mach-Zehnder interferometer (AMZI). The AMZI consists of a polarization modulator (PolM), a polarization controller (PC), a section of polarization-maintaining fiber, and an optical polarizer. By adjusting the PC and the drive voltage to the PolM, the system is reconfigured to generate UWB signals with different modulation formats. An experiment is performed, which verifies the proposed technique.

Polarization-Insensitive Phase Trimming of Silica-Based Waveguide Using 193- and 244-nm UV Irradiation

In this paper, we describe polarization-insensitive phase trimming of silica-based waveguides with both 193- and 244-nm ultraviolet (UV) light and the trimming of both phase error and polarization dependence. A wide beam of 193-nm UV light from an ArF excimer laser is useful for phase trimming multiple waveguides. We utilize stress-release grooves to control birefringence generation while phase trimming, and we reduce the birefringence change during refractive index change by 95%. At the same time, we found that this grooved structure enhances the refractive index increase with UV light. We also utilize 244-nm UV light from a frequency doubled Ar ion laser with high space coherence, which is suitable for trimming the phase error of a single waveguide. We control UV-induced birefringence by controlling the size of the 244-nm laser beam light, and we reduce the birefringence change during phase trimming by 98%. In addition, we investigate the change in the refractive index and stress distribution of our waveguide when UV light is irradiated, and discuss the differences of polarization-insensitive phase trimming between 193- and 244-nm UV light. Finally, we utilize these techniques to eliminate the polarization-dependent phase error of an asymmetric Mach-Zehnder interferometer. We successfully demonstrate the individual trimming of the center wavelength and its polarization dependence.

Recent Progress in High-Speed Silicon-Based Optical Modulators

The evolution of silicon optical modulators is recalled, from the first effect demonstrations to the characterization of high-performance devices integrated in optical waveguides. Among possibilities to achieve optical modulation in silicon-based materials, the carrier depletion effect has demonstrated good capacities. Carrier depletion in Si and SiGe/Si structures has been theoretically and experimentally investigated. Large phase modulation efficiency, low optical loss, and large cutoff frequency are obtained by considering simultaneously optical and electrical structure performances. Integrated Mach-Zehnder interferometers and resonators are compared to convert phase modulation into intensity modulation. Finally, recent results on high-speed and low-loss silicon optical modulator using an asymmetric Mach-Zehnder interferometer are presented. It is based on a p-doped slit embedded in the intrinsic region of a lateral pin diode integrated in a silicon-on-insulator waveguide. This design allows a good overlap between the optical mode and carrier density variations. An insertion loss of 5 dB has been measured with a -3 dB bandwidth of 15 GHz.

Optical generation of polarity- and shape-switchable ultrawideband pulses using a chirped intensity modulator and a first-order asymmetric Mach–Zehnder interferometer

We propose and demonstrate a simple method to generate ultrawideband (UWB) pulses in the optical domain using a chirped intensity modulator and an asymmetric Mach-Zehnder interferometer (AMZI). Polarity- and shape-switchable UWB Gaussian monocycle, doublet, and triplet pulses with fractional bandwidths of 158%, 134%, and 100% and center frequencies of 6.52, 9.78, and 10.1 GHz are experimentally generated by controlling the dc bias of the intensity modulator and adjusting the polarization controller in the AMZI.

Optimization design of all-fiber 3 × 3 multiplexer based on an asymmetrical Mach–Zehnder interferometer

All-fiber 3 × 3 multiplexer based on an asymmetrical Mach–Zehnder Interferometer has been analyzed theoretically, which is made of a fused planar 3 × 3 and a fused triangular 3 × 3 single mode fiber coupler. The mathematical description is provided. The variation in the channel crosstalk at the output port due to the lateral deviation of the splitting ratios of the couplers are studied. Comparing with the three-fiber 3 × 3 multiplexer using two the triangular 3 × 3 fiber coupler, the reduced sidelobe level of channel of the proposed device is more than 13.6 dB, and the proposed device has better crosstalk characteristics when the same lateral deviation of the power splitting ratio is introduced. Analysis and experiment show that there is a relative high success rate of fabricating an all-fiber 3 × 3 multiplexer by using proposed configuration and design approach. The experiment results are in good agreement with the analytical ones. The result shows that the measured sidelobe level is about −34.6 dB, the insertion loss is less than 1.0 dB and channel isolation is higher than 30 dB, respectively.

Differential-quadrature-phase-shift quantum key distribution

This paper presents a quantum key distribution (QKD) protocol named differential-quadrature-phase-shift (DQPS) QKD. A transmitter sends a coherent pulse train in which each pulse is phase modulated by ${0,\ensuremath{\pi}}$ ${\ensuremath{\pi}/2,3\ensuremath{\pi}/2}$, and a receiver measures it with either one of two asymmetric Mach-Zehnder interferometers having phase biases of 0 and $\ensuremath{\pi}/2$, respectively. This scheme is devised such that the idea of the conventional Bennett-Brassard 1984 protocol (BB84) is introduced to differential-phase-shift (DPS) QKD. Simulations show that the proposed scheme is robust against a sequential attack that is crucial eavesdropping to DPS-QKD.

Switchable UWB pulse generation using a phase modulator and a reconfigurable asymmetric Mach-Zehnder interferometer

We propose a new scheme to generate polarity-switchable ultrawideband (UWB) Gaussian pulses in the optical domain by use of a phase modulator and a reconfigurable asymmetric Mach-Zehnder interferometer (AMZI). In the proposed system, an optical carrier is phase modulated by a Gaussian pulse train and then sent to a first-or second-order AMZI. The system is equivalent to a first- or second-order differentiator for the production of Gaussian UWB monocycle or doublet pulses. The polarity of the generated UWB pulses can be switched by adjusting the phase difference between the two interference components in the AMZI. An experiment is performed. Gaussian monocycle and doublet pulses with fractional bandwidths of about 177% and 140% are generated. The polarity switchability of generated UWB pulses is also experimentally confirmed.

A Monolithic Wideband Wavelength-Tunable Laser Diode Integrated With a Ring/MZI Loop Filter

We propose a widely tunable and low insertion loss loop filter incorporating two ring resonators and an asymmetric Mach-Zehnder interferometer. A semiconductor optical amplifier, phase control section, and loop filter are monolithically integrated on one chip in the InP-InGaAsP material system. The tuning range of 39 nm with side-mode suppression ratio of over 30 dB was demonstrated. The maximum of the total heater power over the tuning range was 84 mW.

Performance evaluation and assessment of receiver impairments of a novel PolSK transceiver based on differential demodulation

We present a novel transceiver setup for Polarization Shift Keying (PolSK) modulation using a simple transmitter and a receiver based on differential demodulation. The transmitter is made up of a LiNbO(3) phase modulator with the input fiber pigtailed at 45 degrees with respect to the principal axes of the modulator. The receiver is composed of an asymmetric Mach-Zehnder Interferometer (AMZI) and a couple of balanced photodetectors (BPD), as usually employed for receiving DPSK. To our knowledge, it is the first time such receiver structure is applied to PolSK. In order to fully assess the system performance of the proposed setup, we have carried out numerical simulations using a semi-analytical technique for bit-error-rate evaluation and performed experimental measurements at 10 Gbit/s. After having optimized transceiver performances, we evaluated the resilience to receiver impairments to verify the viability of a realistic implementation. Surprisingly, PolSK shows a better sensitivity using a single-end receiver (with the AMZI tuned at the minimum transmittance point) than using a balanced one. Another improvement has been obtained optimizing the driving voltage at the transmitter: this leads to a "non-ideal" PolSK modulation with non-orthogonal symbols, which shows an enhanced performance thanks to a synchronous phase modulation.

Electronic dispersion compensation using full optical-field reconstruction in 10Gbit/s OOK based systems

We investigate the design of electronic dispersion compensation (EDC) using full optical-field reconstruction in 10Gbit/s on-off keyed transmission systems limited by optical signal-to-noise ratio (OSNR). By effectively suppressing the impairment due to low-frequency component amplification in phase reconstruction, properly designing the transmission system configuration to combat fiber nonlinearity, and successfully reducing the vulnerability to thermal noise, a 4.8dB OSNR margin can be achieved for 2160km single-mode fiber transmission without any optical dispersion compensation. We also investigate the performance sensitivity of the scheme to various system parameters, and propose a novel method to greatly enhance the tolerance to differential phase misalignment of the asymmetric Mach-Zehnder interferometer. This numerical study provides important design guidelines which will enable full optical-field EDC to become a cost-effective dispersion compensation solution for future transparent optical networks.

Dephasing in the electronic Mach-Zehnder interferometer at filling factorν=2

We propose a simple physical model which describes dephasing in the electronic Mach-Zehnder interferometer at filling factor $\ensuremath{\nu}=2$. This model explains very recent experimental results, such as the unusual lobe-type structure in the visibility of Aharonov-Bohm oscillations, phase rigidity, and the asymmetry of the visibility as a function of transparencies of quantum point contacts. According to our model, dephasing in the interferometer originates from strong Coulomb interaction at the edge of two-dimensional electron gas. The long-range character of the interaction leads to a separation of the spectrum of edge excitations on slow and fast mode. These modes are excited by electron tunneling and carry away the phase information. The new energy scale associated with the slow mode determines the temperature dependence of the visibility and the period of its oscillations as a function of voltage bias. Moreover, the variation of the lobe structure from one experiment to another is explained by specific charging effects, which are different in all experiments. We propose to use a strongly asymmetric Mach-Zehnder interferometer with one arm being much shorter than the other for the spectroscopy of quantum Hall edge states.

Quantum encoder and decoder for practical quantum key distribution using a planar lightwave circuit

To launch quantum key distribution (QKD) into the commercial market, it is important to develop a system that is simpler and more reliable using current technology. This report proposes quantum encoders and decoders using a passive planar lightwave circuit (PLC) that is useful for implementing optical-fiber-based QKD systems. Our encoders and decoders are based on an asymmetric Mach–Zehnder interferometer and allow us to prepare and analyze various photonic time-bin qubits reliably. The system can be stable and polarization-insensitive merely by stabilizing and controlling the device temperature. Our PLC-based devices enables us to simplify the QKD system and increase its reliability.

Integrated optofluidic Mach–Zehnder interferometer based on liquid core waveguides

We report the fabrication and the characterization of an integrated optofluidic Mach–Zehnder interferometer based on liquid core waveguides. The light is confined inside a low refractive index liquid core by antiresonant reflecting optical waveguide. Several asymmetric Mach–Zehnder interferometers have been realized with standard silicon technology. An optical characterization of the devices has been carried out by measuring the spectrum of optical transmitted intensity from two different Mach–Zehnder configurations. The results show that interferometers with a good visibility can be achieved in good agreement with the theoretical results.

Silicon-on-insulator eight-channel optical multiplexer based on a cascade of asymmetric Mach-Zehnder interferometers

A monolithically integrated eight-channel optical multiplexer (Mux) with a 400 GHz channel spacing ~1550 nm is presented based on a silicon-on-insulator rib waveguide and an asymmetric Mach-Zehnder interferometer. All channels were optimized independently with integrated heaters. The fully tuned Mux shows an adjacent channel isolation of ~13 dB, an excess loss of ~2.6 dB, and a channel uniformity of ~1.5 dB over a 25 nm wavelength span. In addition, the phase tuning efficiency for different interlevel dielectric layer thicknesses and thermal crosstalk were investigated.

Coherence Multiplexing System Based on Asymmetric Mach–Zehnder Interferometers for Faraday Sensors

An optical coherence multiplexing system for Faraday sensors is proposed. With an asymmetric Mach-Zehnder (M-Z) interferometer, the linearly polarized light from a Faraday sensor is decomposed into two orthogonal modes, which are interrogated by a path-scanning Michelson interferometer at different path positions. The variations in the intensities of these two modes are utilized to deduce the rotation of the polarization plane, which is related to the measurand tested by the Faraday sensor. By employing multiple asymmetric M-Z interferometers with arm-lengths carefully controlled, the sensing signals of the multiplexed Faraday sensors are obtained and well separated in one scan of the Michelson interferometer.