Design and fabrication of DR1/PC-based electro-optic switch

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 present the design of a 2&times;2 photonic switch operating at 1.55-&mu;m wavelength using electro-optic (EO) polymer waveguides. A Mach-Zehnder interferometer (MZI) is used to implement the proposed switch in which two identical 2&times;2 multimode interference (MMI) couplers are connected by two identical parallel single mode waveguides (two MZI arms). These two single-mode waveguides with electrodes allow modulating the phase difference between the two MZI arms based on the EO effect. In the proposed switch, the EO polymer, IPC-E/polysulfone, is used for the core layer of optical waveguides. UV15 and NOA61 are employed for the lower and upper cladding layers, respectively. The singlemode waveguide structure and 2&times;2 MMI coupler have been designed and analyzed for the EO switch. Device performance has been simulated using the beam propagation method. It is found that the switch performance is most sensitive to the MMI width and less sensitive to the MMI length. Optimized structure has been obtained for the 2&times;2 polymeric EO switch, which has a crosstalk level better than -25 dB and insertion loss lower than -1.8 dB. This performance makes the switch a potential candidate for practical use in photonic systems.

High-speed electro-optic switch based on nonlinear polymer-clad waveguide incorporated with quasi-in-plane coplanar waveguide electrodes

Material processing and device fabrication of many different electro-optic (EO) polymers developed at USC are reviewed. Detailed discussion is given to guest-host CLD/APCs, crosslinking perfluorocyclobutane (PFCB) polymer CX1, and thermally stable side-chain polymers CX2 and CX3. Excellent EO performance (1.4V at 1.31 &mu;m, 2.1 V at 1.55 &mu;m) was achieved in CLD/APC Mach-Zehnder modulators (2-cm, push-pull). CLD/APCs also possess low optical losses (1.2 dB/cm in slab waveguides and in thick core channel waveguides). However, the guest-host materials only have limited thermal stability (110-132 &deg;C in short term, <60 &deg;C in long term) and require special techniques in device fabrication. The crosslinking polymer CX1 was able to provide long-term stability at 85 oC when fully cured. It also has a low optical loss (comparable to CLD/APCs) before curing and decent EO coefficient when poled at 180 &deg;C. However, after the films were poled at the crosslinking temperatures (200 &deg;C or above), the transmissions of the waveguides and EO activity became very poor due to poling-induced chromophore degradation. By judicial molecular design of both chromophore and monomer structures to suppress thermal motion of polymer segments, we were able to realize the same or even better thermal stability in side-chain polymers CX2 and CX3. Since no curing is needed, devices can be poled at their optimal poling temperatures, and all good properties can be obtained simultaneously. Despite the excellent solubility in chlorinated solvents, these side-chain polymers are resistant to some other organic solvents or solutions such as acetone, photoresist and various UV-curable liquids.

Silicon photonic switches are widely considered as a cost-effective solution for addressing the ever-growing data traffic in datacenter networks, as they offer unique advantages such as low power consumption, low latency, small footprint and high bandwidth. Despite extensive research efforts, crosstalk in large-scale photonic circuits still poses a threat to signal integrity. In this paper, we present two designs of silicon Mach-Zehnder Interferometer (MZI) switches achieving ultra-low-crosstalk, driven thermally and electrically. Each switch fabric is optimized at both the device and circuit level to suppress crosstalk and reduce system complexity. Notably, for the first time to the best of our knowledge, we harness the inherent self-heating effect in a carrier-injection-based MZI switch to create a pair of phase shifters that offers arbitrary phase differences. Such a pair of phase shifters induces matched insertion loss at each arm, thus minimizing crosstalk. Experimentally, an ultra-low crosstalk ratio below −40 dB is demonstrated for both thermo-optic (T-O) and electro-optic (E-O) switches. The T-O switch exhibits an on-chip loss of less than 5 dB with a switching time of 500 µs, whereas the E-O switch achieves an on-chip loss as low as 8.5 dB with a switching time of under 100 ns. In addition, data transmission of a 50 Gb/s on–off keying signal is demonstrated with high fidelity on the E-O switch, showing the great potential of the proposed switch designs.

Data communication around the whole globe has seen an enormous increase in the exchange of data across the networks. This has urged the need of optical communication systems that can provide the desired bandwidth. This paper is a step to the path of building such optical processing elements. The paper presents optical designs of a 3-bit incrementer and a 3- bit decrementer logic function. The two optical circuits increment or decrement each 3-bit input binary number by unity. The optical designs have been implemented using the LiNbO₃ based Mach-Zehnder Interferometer (LNMZI) electrooptical switches. The incrementer circuit has employed just five LNMZIs and the decrementer circuit has only six LNMZIs. The optical circuits have been designed and tested using beam propagation method (BPM). A critical analysis of the two designs has been performed by calculation of the important performance metric parameters like extinction ratio (ER), contrast ratio (CR), insertion loss (IL). The incrementer/decrementer shows best values of ER, CR and IL as 31.43 dB, 35.71 dB and 0.95 dB respectively. The calculated parameters have been found within the acceptable limits which support the feasibility of the design.

Aluminum nitride has advantages ranging from a large transparency window to its high thermal and chemical resistance, piezoelectric effect, electro-optic property, and compatibility with the complementary metal-oxide-semiconductor fabrication process. We propose a hybrid aluminum nitride and silicon platform for integrated photonics. Hybrid aluminum nitride-silicon basic photonic devices, including the multimode interferometer, Mach-Zehnder interferometer, and micro-ring resonator, are designed and fabricated. The measured extinction ratio is > 22 dB and the insertion loss is < 1 dB in a wavelength range of 40 nm for the Mach-Zehnder interferometer. The extinction ratio and intrinsic quality factor of the fabricated micro-ring resonator are > 16 dB and 43,300, respectively. The demonstrated hybrid integrated photonic platform is promising for realizing ultralow-power optical switching and electro-optic modulation based on the piezoelectric and electro-optic effects of aluminum nitride thin films.

We demonstrate a broadband 2×2 electro-optic switch based on a Mach-Zehnder interferometer with counter-tapered directional couplers (DCs). The counter-tapered DC is introduced here to replace the conventional one formed with uniform waveguides so that a splitting ratio of 50%∶50% is much easier to be realized over a wide wavelength range and, hence, increase bandwidth of the switch. The proposed switch is fabricated with x-cut lithium niobate by the annealed proton exchange process. A comparison of several experimental devices, fabricated on the same chip with the conventional and different counter-tapered DCs, respectively, confirms the increase of the bandwidth and the improvement of the fabrication tolerance by using the counter-tapered DC. Our fabricated best device, which has a length of ∼22 mm, exhibits an ∼85 nm bandwidth for an extinction ratio (ER) higher than 15dB and a maximum ER of ∼35 dB at 1563nm at a driving voltage of 6.0V. The insertion losses are less than 8.5dB for all channels. Our proposed optical switch could find applications in wavelength-division-multiplexing optical communication systems.

In mode-locked fiber lasers and optical sensors, in-line filters are essential components. Fiber-core Mach–Zehnder interferometer (MZI) technology has garnered a lot of research interest for the several manufacturing techniques for in-line MZI filters. Although multi-line inscription is frequently needed in existing methods to attain enough waveguide width, this approach adds complexity to production and may result in compromised waveguide quality. In this work, we present an improved single-line direct-writing method that attains similar MZI filtering results to multi-line scan. Additionally, the MZI filter created with the modified single-line direct-writing technique has a smaller insertion loss and requires less direct-writing energy than the previous single-line direct-writing technique. A 516 μm long MZI-based in-line filter was successfully constructed. The results of the characterization showed a central loss dip at 1089.82 nm, a free-spectral range (FSR) of 141.36 nm, an extinction ratio of 19.69 dB, and an insertion loss of 1.122 dB. This method decreased the insertion loss by a factor of 2.7 for an identical extinction ratio and improved the direct-writing efficiency by a factor of 9 for an equivalent FSR with multi-line scan. There was consistency between the experimental and simulation results. We also took measurements of the MZI’s temperature sensitivity. This work shows notable improvements in waveguide quality and ease of manufacture. This accomplishment lays the groundwork for further advancements in integrated mode-locked fiber laser technology.

We report our recent progress on high-throughput 16×16 silicon non-blocking optical switches based on Mach- Zehnder interferometers (MZIs) and dual-ring assisted MZIs (DR-MZIs). TiN microheaters and p-i-n diodes are both integrated in each switch element for thermo-optic phase error correction and GHz-speed electro-optic switching, respectively. The MZI switch exhibits a broad optical bandwidth and low crosstalk. The DR-MZI switch exhibits low electrical switching power but with a narrower optical bandwidth. The two types of switches are designed to have a chip size of 12.1 mm × 4.6 mm mainly restricted by the chip package requirement. The DR-MZI chip can potentially have a smaller footprint due to its much more compact switch element, suitable for high-density on-chip optical data exchange.

We report the demonstrations of two Mach-Zehnder based 2 × 2 electro-optical switches with low crosstalk. One is with assist of variable optical attenuator and the other is based on cascaded Mach-Zehnder interferometer.

We demonstrate an electro-optic switch and a variable attenuator for telecommunication applications at λ=1550nm by employing the ferroelectric and electroclinic properties of an organosiloxane liquid crystal. In the ferroelectric SmC* phase an optical switch has been realised with an extinction ratio of 36dB between crossed polarisers. The switching time was ~200microseconds. In the SmA* phase the analogue nature of the electroclinic effect was employed to obtain a variable attenuator. The maximum attenuation range between crossed polarisers was 35dB for an applied electric field of +-9V/micron. The response time of the device was about 100microseconds, independent of the applied electric field. Both devices where demonstrated in the same 21.5micron thick cell which provided a retardance of λ/2 at λ=1550nm.

An all-fiber Mach-Zehnder interferometer (MZI) interleaver using one planar 3×3 fiber coupler, one 2×2 fiber coupler and one 8-shaped fiber ring resonator is developed by the new configuration. Based on its structure, the output spectrum expression is established and described by using the principle of fiber transmission and the matrix transfer function. The results of numerical simulation indicate that when the length difference of interference arms and the coupling coefficients of the couplers are some certain values, it obtains a uniform flat-top passband and similar to rectangular output spectrum. Compared with the traditional MZI interleaver, the isolation in stopband and the rolloff in transition band are strengthen, the 25dB stopband bandwidth and 0.5dB passband bandwidth are simultaneously remarkably improved. Compared with the asymmetrical ring resonator MZI interleaver, the influence of transmission loss on extinction ratio can be effectively reduced. The device has a certain ability to resist the deviation, which reduces the difficulties in fabricating it. The experiment results agree with the theoretical analysis well. The interleaver designed by the proposed approach has favorable performance, which has the potential application value in optical fiber communication system.

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <?Pub Dtl=""?>Generation of optical millimeter-wave (mm-wave) signal using a Mach–Zehnder modulator (MZM) based on double-sideband (DSB), single-sideband (SSB), and double-sideband with carrier suppression (DSBCS) modulation schemes have been demonstrated for various applications, such as broadband wireless signals or optical up-conversion for wavelength-division-multiplexing (WDM) radio-over-fiber (RoF) network, wideband surveillance, spread spectrum, and software-defined radio. Among these schemes, DSBCS modulation offers the best receiver sensitivity, lowest spectral occupancy, the least stringent requirement of electrical bandwidth, and the smallest receiving power penalty after long transmission distance. Nonetheless, the inherent nonlinear E/O (electrical/optical) conversion response of a MZM is such that the signal quality of the optical mm-wave suffers. Fabrication tolerances make a balanced 50/50 splitting ratio of the MZM's y-splitter particularly difficult to achieve. As a result, imbalanced MZMs have a finite extinction ratio (ER) and degrade the optical carrier suppression ratio (OCSR) using DSBCS modulation. In this paper, the effect of the MZM nonlinearity and imbalanced y-splitter on optical mm-wave generation by DSBCS modulation is theoretically and experimentally investigated. A novel approach with better performance and greater cost-effectiveness than dual-electrode MZM (DD-MZM) is presented to realize a DSBCS modulation scheme based on a single-electrode MZM (SD-MZM). </para>

In the presented structure, the performance of the all-optical XOR logic gate (AO-XOR-LG) is investigated. The XOR-LG is designed and simulated using a photonic crystal semiconductor optical amplifier (PC-SOA) based on Mach–Zehnder interferometer (MZI) and cross-phase modulation (XPM) nonlinear mechanism. The input optical pulse train used in this simulation is the type of RZ (Return-to-Zero). The finite difference method (FDM) has been used to solve the rate and propagation equations. The effect of input signal energy, bias current, and group refractive index on the output signal and gain of the XOR-LG is studied. The optimal mode is obtained for the XOR-LG with a bit rate of 80 Gbps. Furthermore, for the first time, the effects of quality factor (QF), conversion efficiency (CE), extinction ratio (ER), pattern effect (PE), and gain recovery are simultaneously analyzed in the simulation to increase PC-SOA performance. According to the results, PC-SOA has a more reasonable logic performance than conventional SOA, and due to its much shorter length than SOA, it can be a much better choice for integrated optical circuits.