Multifunctional Optical Filter Using Direct-Coupled and Cross-Coupled All-Pass Filters

Electro-optic Mach-Zehnder interferometer (MZI) switches are well known devices in optical systems for their high speed of operation. In next generation optical network, such switches have wide applications due to their high switching capability and great reliability. In this paper we have investigated the enhanced performance of an electro-optic switch made by titanium diffused lithium niobate (Ti:LiNbO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ) functioned as waveguide medium based on integrated Mach-Zehnder interferometer (MZI) at 1.55 μm wavelength. The performance of the switch is optimized for low switching voltage, low insertion loss, high extinction ratio. This is done by varying the strip thickness of titanium, interferometer arm length, arm gap, waveguide width, gap in the coupling region of the 3 dB couplers, and center position of second electrode deposited on integrated Mach-zehnder Interferometer arm with respect to the original axis of the switch. The designed switch gives lowest insertion loss of 0.00881dB and highest extinction ratio of 33.581 dB at 8.8 V.

We propose and fabricate an ultrafast and high extinction ratio 1×4 optical switch based on a cascade, dual-output Mach–Zehnder interferometer (MZI) on the lithium niobate platform. The optical switch consists of cascaded, identical, dual-output MZI structures, and each of them includes a Y-branch waveguide, two parallel interference arms (electrode action area), and a 3 dB directional coupler. Four output optical paths can be switched through three groups of electrode hierarchical modulation. The test results of the fabricated device show that the insertion loss of each port is less than 7.1 dB and that the maximum extinction ratio is higher than 39.3 dB. The optical switch can achieve a high extinction ratio greater than 20 dB within the 50 nm wavelength range. The measured half-wave voltage is less than 4.13 V, and the minimum switching rise and fall times reach 125 ps and 250 ps, respectively. This result shows that the proposed and fabricated 1×4 integrated optical switch on a lithium niobate platform has the advantages of a fast response rate, high extinction ratio, and low switching voltage.

Linewidth and Ranging Characterization of a Vernier-Tuned Distributed Bragg Reflector (VT-DBR) All-Semiconductor Tunable Swept Laser System for Lidar in Autonomous Applications Taewan Kim Linewidth and ranging experiments of a Insight packaged Vernier-Tuned Distributed Bragg Reflector (VT-DBR) laser across its wavelength output range of 1522.13 to 1566.18 nm is done in this work to characterize it for lidar applications. The purpose of this paper is to investigate the laser’s potential to combine the advantages of lidar and FMCW radar for autonomous systems. Linewidth measurements were done by using a Mach-Zehnder interferometer to set up a delayed self-homodyne measurement. The laser was set to output at a fixed wavelength across a range of 1523 to 1566 nm in 1 nm increments, and linewidth was captured each of these increments. For each of the linewidths, coherence time and length along with laser currents were associated. The minimum linewidth found in this test was found to be 50 MHz, leading to a maximum coherence time of 6.366 ns and a maximum coherence length of 129.92 cm. There was a somewhat linear, albeit low correlation, area of low linewidths depending on the front mirror and back mirror currents across the wavelength range. Initial ranging experiments were performed using interference fringes caused by variable stationary path length differences introduced into a homemade Mach-Zehnder interferometer around the coherence lengths found in the linewidth test. The experimental path length differences indicated by the interference fringes seem to be accurate at very small ruler measured path length differences, but starts to stray away from the ruler measured as the path length differences get larger. Data taken suggests that there is a mathematical relationship in the error between the ruler measured and experimental path length differences leading to the belief that this error can be compensated for. Keywords: Vernier-Tuned Distributed Bragg Reflector, VT-DBR, FMCW, linewidth, coherence, self-homodyne, Mach-Zehnder Interferometer, interference fringes

We experimentally demonstrate two types of silicon-on-insulator microring devices: 1) a slotted conventional microring resonator (MRR) using a multimode interferometer (MMI) coupler as the coupling element; and 2) an MMI-coupled slotted Mach-Zehnder interferometer (MZI) racetrack microring. We achieved a high bandwidth of 1.1 nm and a quality factor Q of ~ 1300 at the wavelength of 1510 nm for the conventional MRRs with a radius of 20 μm. A high extinction ratio (17-25 dB) is exhibited over a wavelength range from 1490 to 1520 nm. At the 1515-nm resonance wavelength, the MMI-coupled MZI racetrack microring demonstrates a quasi-free spectral range of 22.6 nm with a high extinction ratio of 25 dB. The demonstrated devices have many applications such as biochemical and gas sensing and modulation in communication systems.

We demonstrate a multiwavelength semiconductor optical amplifier (SOA) fiber ring laser with a dual- pass Mach- Zehnder interferometer (MZI) filter. Two SOAs provide enough gain and wider gain spectrum for more wavelength lasing. The dual-pass MZI with a high extinction ratio (ER) serves as comb filter. 82 wavelengths within a power deviation of 5 dB with the signal-to-noise ratio of 30 dB oscillate simultaneously.

In this paper, we proposed high speed 8PSK optical modulator using silicon/electro-optic polymer hybrid coupled ring resonators (Si/EO-PHCRR). The design comprises of two coupled ring resonator (CRRs) that has a primary and secondary rings and a single ring resonator (SRR), which acts as a delay line. The two CRRs are arranged in parallel within the two branches of the Mach–Zehnder interferometer (MZI), collectively producing a quadrature phase shift keying (QPSK) at the output terminal of MZI. The SRR is also configured in series with MZI and functions as an angle modulator, essentially serving as a π/4 phase shift modulator that operates based on the bit pattern applied to it. The CRR ensures a high energy storing capability that enhances the modulation efficiency and enables relatively high extinction ratio with better design flexibility and negligible losses. Thus, in this system, a 3 dB modulation bandwidth f 3dB = 51.14 GHz is realized with the moderate quality factor of Q = 3,839 and tunability of the modulator is found to be 723.65 pm/V with an extinction ratio of 29 dB. Also, the performance analysis of the modulator have be done at the bit rate of 150 Gbps and resulted in a high optical signal to noise ratio (OSNR) of 17.98 dB with a BER of 10−9 at the span of 100 Km dispersion shifted fiber.

In future wavelength-division multiplexed (WDM) reconfigurable networks, the ability to shift a signal from one wavelength to another may be an essential function due to a limited number of available wavelengths. The Mach-Zehnder interferometer (MZI) has sparked the interest of the WDM community because ofits ability to wavelength convert signals at high speed, in both inverting and noninverting configurations with a high output extinction ratio, and with low chirp. In this paper, we assess the stability of the extinction ratio of the MZI with variations in the SOA bias currents, as well as with the wavelength and the power of the pump and probe. We characterize the operating point stability of the MZI and find ranges for the bias currents and for the input parameters, in order to minimize the sensitivity of the extinction ratio (ER).

Differential Phase Shift Keying (DPSK) modulation format has been shown as a robust solution for next-generation optical transmission systems. One key device enabling such systems is a delay interferometer, converting the phase modulation signal into the intensity modulation signal to be detected by the photodiodes. Usually, a standard Mach-Zehnder interferometer (MZI) is used for demodulating a DPSK signal. In this paper, we develop an MZI which is based on all-fiber Multimode Interference (MI) structure: a multimode fiber (MMF) with a central dip, located between two single-mode fibers (SMFs) without any transition zones. The MI based MZI (MI-MZI) is more stable than the standard MZI as the two arms share the same MMF, reducing the impact of the external effects, such as temperature and others. Performance of this MI-MZI is analyzed theoretically and experimentally from transmission spectrum. Experimental results shows that high interference extinction ratio is obtained, which is far higher than that obtained from a normal graded-index based MI-MZI. Finally, by software simulation, we demonstrate that our proposed MI-MZI can be used for demodulating a 40 Gbps DPSK signal. The performance of the MI-MZI based DPSK receiver is analyzed from the sensitivity. Simulation results show that sensitivity of the proposed receiver is about −22.3 dBm for a BER of 10−15 and about −23.8 dBm for a BER of 10−9.

Filters are key devices in optical systems and are usually applied to signal suppression or selection based on their amplitude frequency responses. Different from amplitude filtering, an all-pass filter (APF) is a unique type of filter that exhibits a uniform amplitude and variable phase in the frequency response. Traditionally, an APF is designed to be ideal and waveguide loss as well as coupling loss are omitted, which is impossible in practice. Here we demonstrate a method of realizing an APF even when waveguide loss and coupling loss exist, and a feasible structure for realizing the APF with waveguide loss and coupling loss is proposed. The method indicates that an APF can be realized by introducing self-compensation of loss to the structure of an ideal single-stage APF, and further, an APF based on silicon-on-insulator foundry is fabricated and demonstrated. The method of self-compensation of loss can also be used to realize APFs in the electrical domain. We anticipate that our work will inspire realizations of more APF-related devices that once seemed impossible in practice, as well as loss related devices or structures.

Development of modern optical fiber networks puts an increasing demand on the optical hardware. All-optical signal processing components enable the highest switching rates and allow all-optical regeneration of pulse streams without converting the optical signal into electrical current. The subject of our research is self-switching in a Mach-Zehnder interferometer (MZI) and its applications in optical telecommunication networks. In this device, light injected in one of the input ports is unequally distributed over the two interferometer arms. Due to the intensity dependent refractive index in the interferometer arms, there can be a nonlinear phase shift induced between the optical signals of unequal intensities. The two signals therefore interfere destructively or constructively depending on the input power: in this way we obtain nonlinear self-switching. Two mechanisms of nonlinear phase shifting were considered: active, based on semiconductor optical amplifiers (SOAs), and passive, based on quantum dots (QDs). Interferometers of two types were developed: 2-to-2 (two input ports and two output ports) and 2-to-1 (two input ports and one output port). The 2-to-2 SOA-MZIs based on self-switching have been investigated for two applications. One of them is the pattern effect compensator. If SOAs are employed for all-optical signal amplification, e.g. in optical access networks, an unwanted pulse distortion (known also as the pattern effect) takes place, as a result of the SOA gain saturation. Our component allows pattern-free amplification of the optical signals at bitrates up to 20 Gb/s. At 10 Gb/s it shows an extended input power range (up to 7 dB improvement) and comparable gain, which makes it suitable to be used as an optical amplifier. Another application of the 2-to-2 SOA-MZI is a 2R-regenerator. Optical amplifiers used in long distance optical links add noise to the optical signal, causing signal degradation. The signal can be regenerated by passing it through an optical gate with a nonlinear transfer function. The 2-to-2 SOA-MZI has such a nonlinear transfer function. The regeneration capabilities were demonstrated at 2.5 Gb/s by an improvement of the receiver sensitivity of about 2.5 dB. The dynamic characterization of the chips was carried out in a close cooperation with the research group COM at the Technical University of Denmark within the ePIXnet "network of excellence". The 2-to-1 MZI based on self-switching can be used as a low-loss optical combiner. An essential function in optical fiber networks is the combining of optical signals. A serious disadvantage of the conventional type of combiners used in the networks is that they let only half of the power (3 dB) through. In order to compensate for this loss, passive optical combiners are often used in combination with an in-line SOA. The first realization of the low-loss optical combiner uses SOAs as active phase shifters. Such an active low-loss combiner shows an improvement of transmission of over 2 dB compared to a conventional combiner with an in-line SOA. It is therefore expected that the output optical signal-to-noise ratio of the self-switching SOA-MZI is more than 2 dB better than that of a conventional combiner with an in-line SOA. While for the pattern effect compensator and the 2R-regenerator SOAs are used not only for inducing the nonlinear phase shift, but also for sufficient amplification, for the low-loss optical combiner the preferred nonlinear effects should be passive: combination of the signal is a passive function. Therefore, the second realization is based on a novel material, quantum dots. QDs provide improved all-optical nonlinearities resulting in a very small switching energy and large refractive index changes. Such a passive 2-to-1 QD-MZI based on self-switching showed an improvement up to 1.7 dB with respect to a conventional combiner. These improvements have a huge effect on e.g. the power budget in passive optical networks, where a large number of splitting stages are required. The Mach-Zehnder interferometers were realized in the InP/InGaAsP semiconductor material system, which is perfectly suitable for the integration of the photonic integrated circuits for the telecommunication applications. In order to realize both active components (such as e.g. SOAs) and passive components (such as e.g. waveguides, couplers), an active-passive integration technique was applied. This integration was realized in a close cooperation between JDS Uniphase Eindhoven and the COBRA Research Institute. It employs a three-step metal-organic vapor-phase epitaxy regrowth process. The quantum dot material was grown within the COBRA Research Institute. Our MZIs use a ridge waveguide design, for which a reactive ion etching process was developed in the COBRA cleanroom. As a result of photonic integration our integrated Mach-Zehnder interferometers have very small dimensions: less than a square millimeter.

We propose and experimentally demonstrate a silicon photonic independently tunable dual-passband microwave photonic filter (MPF) based on cascaded high-Q silicon micro-disk resonators (MDRs). The MPF integrates a micro-ring resonator modulator (MRM), two thermally tunable MDRs, and a Mach-Zehnder interferometer (MZI) on a single chip. The MRM and MDRs are placed in one arm of the MZI to map the spectral response via single-sideband modulation and carrier beating. Independent tunability of dual-passband center frequencies is achieved through voltage-controlled thermal actuation of micro-heaters monolithically integrated atop the MDRs. Experimental results demonstrate that the proposed MPF chip has dual passbands with bandwidths of 325 MHz and 425 MHz, extinction ratios of 23 dB and 25 dB, and a continuously tunable center frequency spanning 3-31 GHz. Featuring narrow passband, high extinction ratio, flexible frequency tunability and high integration degree, the proposed dual-passband MPF is suitable for multi-functional photonic-assisted microwave processing systems.

The authors have proposed, simulated, and experimentally demonstrated all-optical multiple logic gates using two parallel semiconductor optical amplifier (SOA)-Mach-Zehnder interferometer (MZI) structures that enable simultaneous operations of various logic functions of XOR, NOR, OR, and NAND. The proposed scheme, which is optimized by adjusting the optical gain and phase differences in SOA-MZI structures with creative and systematic method, has great merits to achieve the reshaped output pulses with high extinction ratio and enable the high-speed operation at over 10 Gb/s through performance enhancement of SOAs. Its validity is confirmed through simulation and experiments at 2.5 and 10 Gb/s, respectively

A compact high-temperature fiber-optic sensor is demonstrated by fusion splicing a 3.25mm-long two-mode fiber (TMF) between two single mode fibers (SMFs) to form an all-fiber Mach-Zehnder interferometer (MZI). Under optimized splicing conditions, a strong interference is achieved with high extinction ratio (~10dB). Two methods are applied to detect temperature changes from temperature induced wavelength shift and intensity change of a probing light source. Experimental results show the device is capable of monitoring temperature change from 25degC to 425degC with temperature sensitivity of 58pm/degC and 0.45muW/degC with 360muW of input power, respectively, and a theoretical temperature range from 25degC up to 1000degC

An overview of the advanced Indium Phosphide (InP) Electro-Optic Mach-Zehnder (MZ) Modulator technology which enables small form factor pluggable transceivers for coherent transmission is presented here. A highly efficient IQ-Modulator with a low insertion loss (IL), low V&#960;, high extinction ratio and high electro-optic bandwidth is demonstrated. The modulator described here is very well suited for pluggable 100G/200G coherent transceivers with stringent electrical power consumption requirements. Additional functions already implemented on the mature InP photonic integration platform are expected to add further functionality to the InP IQ Modulator and finally result in a monolithic InP coherent transmitter.

Evanescent waves are central to many technologies such as near-field imaging that beats the diffraction limit and plasmonic devices. Frustrated total internal reflection (FTIR) is an experimental method commonly used to study evanescent waves. In this paper, we shape the incident beam of the FTIR process with a Mach–Zehnder interferometer and measure light transmittance while varying the path length difference and interferometric visibility. Our results show that the transmittance varies with the path length difference and, thus, the intensity distribution of the shaped beam. Experiment and finite element method simulation produce results that agree. We also show, through simulations, that the transmittance can be controlled via other methods of beam shaping. Our work provides a proof-of-concept demonstration of the coherent control of the FTIR process, which could lead to advancements in numerous applications of evanescent waves and FTIR.