High-speed electro-optical silicon modulators based on photonic crystal waveguides

Electro-optic Mach-Zehnder interferometric (MZI) modulators have been fabricated by proton exchange in LiTaO₃. Electro-optic efficiency of these modulators has been found to be depending on phase composition of H_xLi_1-xTaO₃ waveguide in full accordance with the data of Raman scattering spectroscopy on microscopic contributions in electro-optic effect for the different H_xLi_1-xTaO₃ phases. These spectroscopy data were used to found an appropriate phase composition and, thus, optimize MZI modulators. The experimental samples of MZI modulator fabricated at the optimal technological conditions exhibit the improved electro-optical efficiency with far superior photorefractive resistance compared to the LiNbO₃ waveguides and modulators.

A novel all-fiber Mach-Zehnder modal interferometer (MZMI) for temperature and strain measurements is demonstrated. The interference between the core and the cladding modes in the single mode fiber (SMF) is utilized. To excite the cladding modes, a microcavity is embedded in the SMF. After propagating a distance in the cladding, the cladding modes will couple back to the core mode at the other point fabricated by core-offset splicing. The MZMI exhibits a high temperature sensitivity (<0.1nm/ °C) in the range of 200-600 (°C). The strain response of the MZMI is also investigated. This compact, simple and cost-effective MZMI owns potential applications in temperature and strain measurements.

We investigate the phase sensitivity of the SU(1,1) interfereometer [SU(1,1)I] and the modified Mach–Zehnder interferometer (MMZI) with the entangled coherent states (ECS) as inputs. We consider the ideal case and the situations in which the photon losses are taken into account. We find that, under ideal conditions, the phase sensitivity of both the MMZI and the SU(1,1)I can beat the shot-noise limit (SNL) and approach the Heisenberg limit (HL). In the presence of photon losses, the ECS can beat the coherent and squeezed states as inputs in the SU(1,1)I, and the MMZI is more robust against internal photon losses than the SU(1,1)I.

This chapter focuses on the fundamental and high-speed characteristics of small-footprint integrated optical modulators designed and fabricated on the basis of the silicon-photonic platform to assess their key performance factors in applications related to high-capacity energy-efficient optical networks transmitting data in various modulation formats. The design and characteristics of high-speed silicon rib-waveguide phase shifters, which are most essential in the high-speed optical modulators, are described. A low-loss quasi-single-mode silicon rib-waveguide phase shifter with reduced RC delay is highlighted along with its design features and fundamental performances in terms of optical loss and on/off dynamic response. Free-carrier plasma dispersion is reviewed as a physical process for performing optical modulation, which allows a reduction in thermal drift and frequency chirping. The plasma dispersion has a unique property in that signal distortion due to residual intensity modulation cancels with the nonlinear voltage dependence of the optical phase, thereby being useful for zero-chirp optical modulators to eliminate transmission impairments. The on-off keying performance of a silicon optical modulator using a single Mach–Zehnder interferometer waveguide is described in the first example of optical network applications with emphasis on a 10-Gb/s dispersion tolerance comparable to that of a commercial lithium niobate modulator. The advantage of silicon-photonic integration is remarkable, in particular, for the ultrasmall-footprint silicon optical modulator consisting of a pair of IQ nested Mach–Zehnder interferometers for two orthogonal polarization components and a polarization multiplexer monolithically integrated on a silicon chip. Such a chip is presented with respect to applications in digital coherent communication in optical-fiber links up to 1000 km long at a bit rate as high as 128 Gb/s.

We propose a novel system for synchronous measurement of out-of-plane deformation and two orthogonal slopes using a single camera. The linearly polarized reference beam introduced by an optical fiber interferes with the unpolarized object beam to measure the out-of-plane deformation. A modified Mach–Zehnder interferometer is used to measure the two orthogonal slopes of the out-of-plane deformation. One of the object beams of the Mach–Zehnder interferometer is an unpolarized beam, and the other object beam is split into two orthogonal linearly polarized object beams by a polarizing prism. The two beams are orthogonally polarized. Hence, they will not interfere with each other. The two polarized beams respectively interfere with the unpolarized beam to simultaneously measure the two orthogonal slopes of the out-of-plane deformation. In addition, the imaging lens and apertures are respectively placed in three optical paths to independently control the carrier frequencies and shearing amounts. The effectiveness of this method can be proved by measuring two pressure-loaded circular plates.

Lithium niobate LiNbO/sub 3/ (LN) Mach-Zehnder interferometer (MZI) modulators are a key in high-speed optical communication systems. The optimization of integrated Mach-Zehnder interferometer modulator is discussed in this paper. We have extensively characterized the drift phenomena in a typical MZI modulator as a function of time, temperature and optical power. We have carried out optical and electrical measurements of the characteristics of the passive component and the active component as well. We also took into account of other physical properties such as pyroelectric effect, photovoltaic effect and photoconductivity. The electrical characteristics of the wafer and component were investigated and reported here. We present here the first results of the simulations which were obtained in this frame. These predictions are then compared with the effective electric field in the different layers and its time behavior.

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.

We report the measurement of quadratic electro-optical coefficients of head-to-tail poly(3-dodecylthiophene) using a modified Mach-Zehnder interferometer at 633 nm. We find s1133 = 3.7×10-20 m2/V2 and s3333 = 4. 1×10-20 m2/V2.

We describe ultra wideband frequency control of millimetre-wave and lightwave signals using optical single-sideband modulation. Precise and rapid frequency control can be achieved by digital arbitrary waveform generation and high-speed electro-optic modulation. Frequency multiplication in optical modulators also plays important roles. Ultra-wideband frequency chirp signals from 9.6 GHz to 16 GHz, which were generated by using a computer controlled arbitrary waveform generator and a wideband frequency multiplier, were fed to an optical single-sideband modulator consisting of two sub Mach-Zehnder interferometers.

In silicon photonics, the carrier depletion scheme has been the most commonly used mechanism for demonstrating high-speed electro-optic modulation. However, in terms of phase modulation efficiency, carrier-accumulation-based devices potentially offer almost an order of magnitude improvement over those based on carrier depletion. Previously reported accumulation modulator designs only considered vertical metal-oxide-semiconductor (MOS) capacitors, which imposes serious restrictions on the design flexibility and integratability with other photonic components. In this work, for the first time to our knowledge, we report experimental demonstration of an all-silicon accumulation phase modulator based on a lateral MOS capacitor. Using a Mach–Zehnder interferometer modulator with a 500-μm-long phase shifter, we demonstrate high-speed modulation up to 25 Gbit/s with a modulation efficiency (VπLπ) of 1.53 V·cm.

Balloon-like angle and micro-displacement sensor based on bent single-mode fiber

We discuss three ways to combine two laser beams with equal linear polarizations and very closely spaced frequencies into a single output beam containing up to 100% of the input power of each beam. One setup, a modified Mach–Zehnder interferometer, is examined in detail; it allows to adjust the combined output power electronically with the help of a simple servo loop. With off-the-shelf optical components we obtained a 98% efficiency.

A microlens of numerical aperture (NA) 0.85 a small-form-factor optical pickup, following the specifications of the Blu-ray disc (BD), was designed, fabricated and evaluated. To avoid difficulties in the fabrication of a high-NA objective lens and to obtain a low chromatic aberration, a new hybrid lens unit was designed to have a refractive lens and a diffractive lens. The micro-plano-aspheric refractive lens was fabricated using glass molding technology, and the diffractive lens was fabricated in a two-dimensional array using the electron beam mastering and consecutive UV embossing process. For the evaluation of the developed lens unit, diffraction efficiency was measured with the proposed diffraction efficiency measurement method, and the wavefront error of the lens unit was evaluated using a modified Mach–Zehnder interferometer. The measured average efficiency of the diffractive lens was approximately 85% and the RMS wavefront error of the lens unit was 0.0376 λrms.

We describe an optoacoustic imaging technique based on time-resolved measurements of laser-induced thermoelastic expansion. Tomographic images of tissue phantoms are formed using such measurements made at several locations following irradiation with a Q-switched Nd:YAG (λ=1064nm) laser pulse. Our system is based on a modified Mach–Zehnder interferometer that measures surface displacement with a temporal resolution of 4ns and a displacement sensitivity of 0.3nm. Images formed from data sets acquired from several highly scattering tissue phantoms provide better than 200μm resolution and show great promise for high-resolution noninvasive imaging of heterogeneous tissues at depths approaching 1cm.

We present photonics technology based on a bulk-Si substrate for cost-sensitive dynamic random-access memory (DRAM) optical interface application. We summarize the progress on passive and active photonic devices using a local-crystallized Si waveguide fabricated by solid phase epitaxy or laser-induced epitaxial growth on bulk-Si substrate. The process of integration of a photonic integrated circuit (IC) with an electronic IC is demonstrated using a 65 nm DRAM periphery process on 300 mm wafers to prove the possibility of seamless integration with various complementary metal-oxide-semiconductor devices. Using the bulk-Si photonic devices, we show the feasibility of high-speed multidrop interface: the Mach–Zehnder interferometer modulators and commercial photodetectors are used to demonstrate four-drop link operation at 10 Gb/s, and the transceiver chips with photonic die and electronic die work for the DDR3 DRAM interface at 1.6 Gb/s under a 1∶4 multidrop configuration.