Temperature-stable lithium niobate electro-optic Q-switch for improved cold performance

We investigate the influence of Zinc diffusion on the modulation efficiency and optical insertion loss of InP-based MZI modulators. By analyzing the electric-optical field distribution and free-carrier absorption loss of three types of Zinc diffusion profiles, the mechanisms between Zn diffusion and modulation efficiency and optical insertion loss inside MZI modulators are systematically studied. We show that InP-based MZI modulator modulation efficiency is limited by electro-optic field distribution overlap and optical mode interacts with p-type dopant increases device insertion loss when Zn diffuses during MOCVD epitaxial process.

Integrated Microwave Photonics (IMWP), which aims at the incorporation of MWP components/ subsystems in photonic circuits, is crucial for the implementation of both low-cost and advanced analog optical front-ends, thus has attracted great interest. In this research, we introduced a four-channel direct-modulated electronic-opto convertor module modulated based on Optoelectronic assembling and Packaging Technology, which integrated function blocks, i.e. RF amplifier, RF equalizer, semiconductor high-speed laser, optical lens, MCU, AD/DA, etc. in a 25-pin compact package with external SMPM and optical fiber pigtail connection. The coupling of supervision/control signals are coupled to RF/Optical components by wire-bonding and pin insulator. The implementation of internal connection methods, compared with traditional fibers and RF cables, will bring much benefit including smaller size and lower cost. Based on test results, we realized 18GHz electronic-opto modulation bandwidth with 5 dB insertion loss and <2.5 VSWR; and each channel is working at single mode status with wavelength interval around 5nm, and single mode suppression ratio better than 55 dBc. The relation between link noise figure and optical insertion loss is also analyzed.

Realization of sub 1 V polymeric EO modulators through systematic definition of material structure/function relationships

Optical insertion losses in embedded strip waveguides fabricated in LiNbO3 by Ti diffusion have been examined at a 0.633-μm wavelength, taking into account resultant near-field patterns. It is confirmed that the main factors influencing optical insertion losses are radiation loss by the deficient refractive-index change of a waveguide, scattering loss by insufficient diffused residual titanium oxide film on a waveguide, and coupling loss between a waveguide and a fiber. A diffusion condition for making a low-loss waveguide is presented, although suppression of lateral diffusion is necessary to achieve further insertion-loss reduction.

An optical crossconnect (OXC) using drawbridge micromirrors

Summary form only given. Silicon photonic integrated circuits (PICs) combine dense optical system integration with industrial scalability by adopting well-established CMOS fabrication processes [1]. An electro-optic phaseshifter (EOP) represents a basic building unit of several PICs applications [1], including datacom optical switches [3], PIC-FPGAs [4], and beam steering [5]. In-situ resistive-heaters in close vicinity of waveguides [2], or free-carrier injection/depletion in doped junctions [3], are common methods to build EOPs. Literature reports thermal shifters consuming 24.7 mW to achieve DC large signal π-phaseshift [2], power consumption of injection PIN implementations [5] and depletion PN modulators [6] of 10 mW and ≈ 0 mW respectively. A thermal EOP naturally avoids carrier-induced optical insertion losses (IL), in contrast to a PIN/PN modulator. Thus, thermal and PIN/PN methods trade-off IL with electrical power rather than minimizing both [2,3]. An EOP of low optical losses and low electrical power is highly desired in large-signal, and low-speed applications [5, 7]. In this work, we propose a novel low-loss depletion type EOP. The device (Fig. 1A) utilizes a doping cross section, resembling a bi-junction transistor with both junctions reverse biased, in a rib-waveguide. While introducing implants in a waveguide adds IL, their depletion using applied voltage induces phaseshift and decreases IL [3]. Hence, using bi-junctions to increase overlapping area of the optical mode with variable depletion regions, increases induced phaseshift efficiency relative to IL, by minimizing the number of non-depleted implants overlapping with the optical mode. Figure 1B depicts 25 % increase of such overlap in the bi-junction approach relative to a conventional PN modulator under the same implant conditions. Inserting intrinsic regions between central doped area and peripheral ones leverages such higher efficiency to achieve IL of 3 dB less than a conventional NP modulator at a maximum power consumption of 0.3 nW thus preserving desired low power consumption of depletion type modulators and achieving full n-phaseshift at 4.7V. Table 1 lists simulated IL of the proposed devices using Silvaco AtlasTM and Lumerical ModeTM, as well as measurement of a conventional PN junction modulator to verify the model.

Lithium niobate (LiNbO<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf>) remains the most common <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\chi^{2}$</tex>-material for electro-optic devices due to its physical properties and commercial availability [1]. With the development of thin-film lithium niobate-on-insulator (LNOI) the material started to be used for photonic integrated circuits with ultimate performance in respect to the conventional bulk lithium niobate photonics [2]–[4]. However, modern integrated lithium niobate photonic solutions lack some of the features routinely achieved in other platforms such as silicon or silicon nitride [5]. We present our recent advances in heterogeneously integrated lithium niobate photonics, combining thin-film LNOI with the photonic Damascene silicon nitride technology [6]. The platform retains low optical propagation losses (<0.1 dB/cm) as well as fiber-to-chip insertion losses (<2.5 dB/facet) of the underlying silicon nitride waveguides. The lithographic precision of the underlying silicon nitride waveguides fabrication helps to achieve 3-dB splitters/couplers with <1 dB insertion loss using silicon nitride inverse tapers.

A reflow step and an improved burial procedure are demonstrated for channel waveguides formed in sol-gel glass on silicon substrates. Thick sol-gel films are deposited by repetitive spin coating and rapid thermal annealing, and etched to form ridge waveguides. Furnace heating is then used to melt both core and buffer layers simultaneously, providing a smooth surface for burial by further spin-coat deposition. Results are presented for typical core shapes, surface profiles after planarization, and optical insertion losses. >

Self-phase modulation and spectral broadening in millimeter long self-written polymer waveguide integrated with single mode fibers

A high-performance monolithic integrated wavelength division multiplexing silicon (Si) photonics receiver chip is fabricated on a silicon-on-insulator platform. The receiver chip has a 25-channel Si nanowire-arrayed waveguide grating, and each channel is integrated with a high-speed waveguide Ge-on-Si photodetector. The central wavelength, optical insertion loss, and cross talk of the array waveguide grating are 1550.6 nm, 5–8 dB, and −12–−15 dB, respectively. The photodetectors show low dark current density of 16.9 mA/cm2 at −1 V and a high responsivity of 0.82 A/W at 1550 nm. High bandwidths of 23 and 29 GHz are achieved at 0 and −1 V, respectively. Each channel can operate at 50 Gbps with low input optical power even under zero bias, which realizes an aggregate data rate of 1.25 Tbps.

A circuit design approach using cascaded structures for integrated optic modulators and switches with high extinction ratios is described and analyzed. The extinction ratios are improved by a multiplication effect and can be exceeding 30 dB for polarization independent devices with no individual voltage tuning. The trade-offs are more chip area consumption, more optical insertion loss, and a slower device response speed. These trade-offs can be minor for nonhigh speed applications, such as photonic cross-connect systems, where the switch control and crosstalk are more important issues.

Traditional EO polymer modulators employ a Mach-Zehnder interferometer architecture with only one arm modulated under a microstrip line electrode. The V/sub /spl pi// of such modulator can be expressed as, V/sub /spl pi//=/spl lambda/h/n/sup 3/r/sub 33/L/spl Gamma/ (Eq. 1) where /spl lambda/ is the optical wavelength, h is the gap between electrodes, n is the index of refraction, r/sub 33/ is the EO coefficient of the polymer waveguide layer, L is the interaction length, and /spl Gamma/ is a modal overlap integral. Low V/sub /spl pi// can be achieved by adjusting one or several parameters in Eq. 1. However, many factors such as reducing the gap distance or increasing the interaction length are limited by optical insertion loss and modulation frequency requirements. The most effective approach for low V, is to increase the EO coefficient r/sub 33/, and recent work at the University of Southern California has demonstrated some limits to increasing the doping density of the nonlinear chromophores.

A new approach for attaching optical fibers to LiNbO/sub 3/ integrated optic devices is described. The all-solder approach, which uses no organic adhesives, is fast, robust, and low cost. A three-port fiberoptic gyro chip was pigtailed, and temperature cycled from 20 to 100/spl deg/C with only +//spl minus/0.5-dB change in optical insertion loss. >

Some of the most promising transmitter linearization techniques for high performance radio over fiber systems are reviewed and compared through simulation tests. Comparison is focused on Mach-Zehnder modulator (MZM) operated at low bias; MZM conventionally biased at quadrature, driven with low modulation depth and cascaded with a notch optical filter; optical single sideband and double sideband plus carrier (SSB/DSB + C); and carrier suppressed plus carrier (CS + C) methods. These transmitters are evaluated through carrier to interference ratio, optical insertion losses, and RF power penalty. The robustness to deviation from ideal transmitter settings is also assessed.

The influences of waveguide materials, fabrication conditions, and packaging substrates on the optical waveguide properties of electrical-optical circuit boards have been investigated by systematic variation of these conditions. Pt catalyst in polydimethysiloxane, casting mould sidewall roughness, interlay thickness, and packaging substrates show sensitive impact on optical waveguide insertion loss and in terms of defined target of optical loss, the basic quality criteria can be defined before production.