Integration Of Optical Systems Research Articles

Mode Controlling of Surface Plasmon Polaritons by Geometric Phases

Metasurfaces are made of two-dimensional arrays of subwavelength nanostructures that form a spatially varying optical response, to control the wave fronts of optical waves. As the feature size of its constituent materials is nanoscale, investigation of the light-nanostructure interactions in the near field is critical for understanding the novel properties of metasurfaces. Here, we used a scanning near-field optical microscope (SNOM) to observe the near-field distribution of surface plasmon polaritons (SPPs) from a ring-shaped metasurface under illumination of circularly polarized light. It was found that with an additional degree of freedom of the geometric phase provided by the regularly arranged metamolecules, control over the near-field interference of the SPPs can be achieved, which is governed by the metasurface geometric symmetry that can be tuned by its topological charge. Meanwhile, the planar chiral character of the metamolecules exerts a deep influence on the near-field interference patterns. Our results can pave the way for active control of SPP propagation in near fields and have potential applications in highly integrated optical communication systems.

Generation of vortex beams with multi topological charges, high purity and operating on broadband using a simple silver metasurface

We propose a simple approach to generate vortex beam based on silver metasurface under the incidence of circularly polarized light. The topological charge and purity of result beam is from -4 to 4 and more than 95% respectively, furthermore, it can operate on broadband (800∼1800 nm) including telecom wavelengths. The designed metasurface is composed of ten concentric rings, where each ring is composed of sub-wavelength rectangular apertures with circular array distribution. These rectangular apertures act as localized space-variant linear polarizers and space-variant polarization manipulation can introduce Pancharatnam–Berry (PB) phase. Simulation results show that this design is logically coincidence. The designed metasurface has the advantage of high fabrication tolerance and may be a potential candidate in future integrated optical communication system.

Integrated broadband Ce:YIG/Si Mach-Zehnder optical isolators with over 100 nm tuning range.

We demonstrate integrated optical isolators with broadband behavior for the standard silicon-on-insulator platform. We achieve over 20dB of optical isolation across 18nm of optical bandwidth. The isolator is completely electrically controlled and does not require a permanent magnet. Furthermore, we demonstrate the ability to tune the central operating wavelength of the isolator across 100nm, which covers the entire S + C telecom bands. These devices show promise for integration in optical systems in which broadband isolation is needed such as wavelength multiplexed systems or optical sensors.

Two-dimensional switchable blue phase gratings manufactured by nanosphere lithography.

Switchable two dimensional liquid crystal diffraction gratings are promising candidates in beam steering devices, multiplexers and holographic displays. For these areas of applications a high degree of integration in optical systems is much sought-after. In the context of diffraction gratings this means that the angle of diffraction should be rather high, which typically poses a problem as the fabrication of small grating periods is challenging. In this paper, we propose the use of nanosphere lithography (NSL) for the fabrication of two-dimensionally structured electrodes with a periodicity of a few micrometers. NSL is based on the self-assembly of micro- or nanometer sized spheres into monolayers. It allows for easy substrate structuring on wafer scale. The manufactured electrode is combined with a liquid crystalline polymer-stabilized blue phase, which facilitates sub-millisecond electrical switching of the diffraction efficiency at a diffraction angle of 21.4°.

Compact integrated optical system for a tip-enhanced Raman spectrometer.

A compact integrated optical system is presented to overcome the low optical efficiency, poor coordination, bulk size, and high cost of a traditional tip-enhanced Raman spectroscopy (TERS) instrument. In this optical system, the excitation and collection optics are integrated with white light illumination and micro-imaging optics and Raman spectrometer optics. The optics are simplified, the optical path is decreased, and the Raman spectrometer structure is improved. The integrated optical system has high optical efficiency, high resolving power, and compact size; it is designed to couple with a specific homemade STM head and cooperative control circuit to develop a small integrated TERS instrument.

Flexible and broadband graphene polarizer based on surface silicon-core microfiber

A graphene-coated polarizer based on the surface silicon-core microfiber has been proposed and numerically analyzed. The numerical discussion shows that our proposed polarizer serves alternatively as TM-pass or TE-pass polarizers depending on the change of the radius of the silicon core. Their polarization extinction ratios can be adjusted by the structure parameters of the ellipticity, the major and minor diameter of the microfiber, and the thickness of the graphene film. When the length of the graphene film is 1.5 mm, extinction ratios of ~30 and ~32 dB can be respectively achieved at the wavelength of 1.55 μm for TM-pass and TE-pass polarizers. The operation wavelength range of the TM- and TE-pass polarizer could cover ~400 and ~1000 nm, respectively. Our proposed polarizer provides a flexible way to manipulate the polarization of the light in the fiber and highly integrated optical fiber system.

Material platforms for integrated quantum photonics

On-chip integration of quantum optical systems could be a major factor enabling photonic quantum technologies. Unlike the case of electronics, where the essential device is the transistor and the dominant material is silicon, the toolbox of elementary devices required for both classical and quantum photonic integrated circuits is vast. While III-V materials have been shown to host most quantum photonic components, the issues of their intercompatibility, scalability and performance are far from being solved. Therefore, many material platforms are being examined to host the future quantum photonic computers and network nodes. We discuss the pros and cons of several platforms for realizing various elementary devices, compare the current degrees of integration achieved in each platform and review several composite platform approaches.

Robust subwavelength focusing of surface plasmons on graphene

Graphene plays a substantial role in nano-scale optical engineering and miniature information signal processing systems gradually. In this letter, we propose a pipe-like substrate scheme to achieve the properly designed inhomogeneous, nonuniform conductivity distribution on a single sheet of graphene. The transverse-magnetic surface plasmon polariton wave supported by graphene will oscillate like water running in an inclined pipe and focus onto one point in a deep-subwavelength scale in the graphene sheet. Importantly, we find that this focusing behavior is robust and insensitive to the variance of background Fermi energy and incident frequency based on the analytic analysis. We verify our scheme by exploiting Hamiltonian optics and numerical calculation. This nano-scale optical manipulation will lead to the development of miniature optical system integration on a 1-atom-thick structure.

Writing of 3D optical integrated circuits with ultrashort laser pulses in the presence of strong spherical aberration

A novel technique was proposed for 3D femtosecond writing of waveguides and optical integrated circuits in the presence of strong spherical aberration, caused by inscription at significantly different depth under the surface of optical glasses and crystals. Strong negative effect of spherical aberration and related asymmetry of created structures was reduced due to transition to the cumulative thermal regime of femtosecond interaction with the material. The differences in the influence of spherical aberration effect in a broad depth range (larger than 200 µm) was compensated by dynamic adjustment of laser pulse energy during the process of waveguides recording. The presented approach has been experimentally implemented in fused silica. Obtained results can be used in production of a broad class of femtosecond written three-dimensional integrated optical systems, inscripted at non-optimal (for focusing lens) optical depth or in significantly extended range of depths.

Simultaneous generation and focus of radially polarized light with metal-dielectric grating metasurface

Simultaneous manipulation of light polarization and phase possesses great significance for modern optical technologies. Here we propose metal-dielectric gratings capable of tailoring the polarization and phase of light based on polarization filtering with the polarization extinction ratio exceeding 10dB and the transmittance higher than 65%. The standard radially polarized (RP) light with axially symmetric polarization distribution can be generated by using arrayed grating with gradient phase under the illumination of circularly polarized (CP) light. Besides, a RP metasurface lens with high numerical aperture is presented, which can convert the CP light into the focused radially polarized light at wavelength of 632.8nm. This compact and efficient approach would have potential applications in beam manipulation, super-resolution imaging and integrated optics system.

Smart electro-optical iris diaphragm based on liquid crystal film coating with photoconductive polymer of poly(N-vinylcarbazole).

This study develops a light shutter whose transmittance can be tuned electro-optically. The liquid crystal (LC) film applies the photoconductive material of poly(N-vinylcarbazole) (PVK) based on twisted nematic (TN) liquid crystals (LCs). The hole-transport layer of PVK could reduce the built-in electric field of the LC film under the exposure of UV light. The driving voltage is considerably decreased with the aid of UV light exposure. The repeating optical switching is performed under sunlight illumination with an external bias of electric field ∼5 V. Further, it could be operated under a parallel/cross-polarizer to change the light beam/ring as an iris and used to automatically block the UV light to protect an optical integrated system.

Monolithic Low-Power 6-Gb/s Optical Transmitter for a Silicon HBT-Based Carrier Injection Electroabsorption Modulator

Photonic devices monolithically integrated with nanoscale electronic signal processing circuitry in silicon are emerging as a disruptive technology to reduce cost and improve optical system integration and performance. Silicon heterojunction bipolar transistor (HBT)-based carrier injection electroabsorption modulators (EAMs) implemented in a commercial silicon process have several merits, including high speed, low power, low driving voltage, small footprint, and high modulation efficiency. A low-power high-speed optical transmitter driver module has been realized in a 130-nm SiGe BiCMOS process for an HBT-based carrier-injection-type modulator. The transmitter consists of a monolithic $2^{7}-1$ pseudorandom bit sequence generator and a driver circuit with digitally tuned preemphasis strength. With 1.5-V power supply, the transmitter circuit consumes 44.5 mW at an operating speed of 6 Gb/s.

A Coaxial and Off-axial Integrated Three-mirror Optical System with High Resolution and Large Field of View

A novel optical design for high resolution, large field of view (FOV) and multispectral remote sensing is presented. An f/7.3 Korsch and two f/17.9 Cook three-mirror optical systems are integrated by sharing the primary and secondary mirrors, bias of the FOV, decentering of the apertures and reasonable structure arrangement. The aperture stop of the Korsch system is located on the primary mirror, while those of the Cook systems are on the exit pupils. High resolution image with spectral coverage from visible to near-infrared (NIR) can be acquired through the Korsch system with a focal length of 14 m, while wide-field imaging is accomplished by the two Cook systems whose focal lengths are both 13.24 m. The full FOV is 4°×0.13°, a coverage width of 34.9 km at the altitude of 500 km can then be acquired by push-broom imaging. To facilitate controlling the stray light, the intermediate images and the real exit pupils are spatially available. After optimization, a near diffraction-limited performance and a compact optical package are achieved. The sharing of the on-axis primary and secondary mirrors reduces the cost of fabrication, test, and manufacture effectively. Besides, the two tertiary mirrors of the Cook systems possess the same parameters, further cutting down the cost.

Monolithic Integration of a Silicon-Based Photonic Transceiver in a CMOS Process

This work presents the design, fabrication, and characterization of a monolithic and complementary-metal–oxide–semiconductor (CMOS)-based integrated optical system, including the light emitter working in the visible range, waveguide, and photodetector. The presented system aims to be applied for the development of optochemical sensors. The work presents the proposed concept and the integration strategy, as well as the fabrication process. The individual elements of the system are theoretically evaluated to assure compatibility among them. Then, the fabrication and studies to the complete system are presented. The response of the light sensor is shown to be caused by optical stimulation of light originated in the integrated light source and transmitted through a dielectric waveguide, thus validating the integration procedure.

大视场可见红外一体化光学系统设计

大视场可见红外一体化光学系统设计

大视场可见红外一体化光学系统设计

大视场可见红外一体化光学系统设计

Metasurface wave in planar nano-photonics

Development of optical systems is toward smaller sizes, more new functions and improved device performance. However, traditional optical systems face many fundamental limits. For example, the Abbe’s diffraction limit sets a minimal value at which the optical microscopy, telescopy and lithography resolution can be achieved. On the other hand, the Snell’s law states that one can only change the shape or materials of optical elements to realize different optical functionalities. Recently, metasurfaces based on artificially structured thin films with unique optical properties are thought to be a promising alternative to traditional optical materials. The thickness of these structures is far smaller than light wavelength, allowing the miniaturization and integration of several optical components and systems together. But there is still not a universal theory available for the understanding and design of metasurface-based devices. Luo et al. [1] systematically brought forward a new concept of metasurface wave (M-wave), which is quite different from the traditional bulk electromagnetic wave. The M-wave is a special electromagnetic excitation, either propagating along the surface or tunneling through the surface with abrupt phase and amplitude changes, which provides a general theory to describe the principles of ‘‘planar nanophotonics’’. They used the M-wave to extend the traditional laws of diffraction, refraction, reflection and absorption. In particular, they revealed that the M-wave has three unique optical properties: extremely short wavelength, locally tunable phase shift and tunable chromatic dispersion. Based on these three characteristics, several important theories and laws to further elaborate the M-wave theory have been presented, such as the metasurface-assisted diffraction theory (MDT), metasurface-assisted law of refraction and reflection (MLRR), metasurface-assisted law of polarization conversion (MLPC) and metasurface-assisted absorption theory (MAT). These theories would pave the way in the design of novel electromagnetic devices with various improved performance [2–6]. On the basis of the extremely short wavelength property and the MDT which emerged through the M-wave, the authors proposed a plasmonic lithography technique. It was shown that a sub-22 nm resolution can be achieved by using a light source at 365 nm. These results demonstrated that both the Abbe’s diffraction limit and the near-field diffraction limit can be surpassed. Unlike the super-resolved fluorescence microscopy (The Nobel Prize in Chemistry 2014), which only applies well to fluorescence samples, this new technique does not rely on any fluorescent materials and thus has no limitation to applications, in principle. With the locally tunable phase shift property and the MLRR, Luo et al. [1] demonstrated a set of flat optical devices, including lenses, prisms, axicons and spiral phase plates. The author extended the super-resolution ability to far-field imaging systems. It was shown that a 10-m metasurface-based telescope can achieve the performance of a normal 16-m one. This is also a big improvement and contributes to revise the text book of Optics. For instance, Born and Wolf [2] have written in their Principle of Optics that the primary diffraction-limited images of an objective lens would not be observed in more detail by the following eyepiece. On the contrary, the new results show that deep sub-diffraction features absent in the diffraction-limited images of objective lens can be optically restored in the relayed system by taking advantage of the exotic properties M. Hong (&) Department of Electrical and Computer Engineering, National University of Singapore, Singapore, Singapore e-mail: elehmh@nus.edu.sg

Topography Measurement for Monitoring Manufacturing Processes in Harsh Conditions

High precision manufacturing, e.g. milling and grinding, which have manufacturing tolerances in the range of <10 μm require microscopic measurement techniques for the inspection of the manufactured components. These measurement techniques are very sensitive to cooling liquids and lubricants which are essential for many manufacturing processes. Therefore, the measurement of the components is usually conducted in separate and clean laboratories and not directly in the manufacturing machine. This approach has some major drawbacks, e.g. high time consumption and no possibility for online process monitoring. In this article, a novel concept for the integration of high precision optical topography measurement systems into the manufacturing machine is introduced and compared to other concepts. The introduced concept uses a reservoir with cooling liquid in which the measurement object is immersed during the measurement. Thereby, measurement disturbance by splashing cooling liquids and lubricants can effectively be avoided.

Realizing Broadband and Invertible Linear-to-circular Polarization Converter with Ultrathin Single-layer Metasurface.

The arbitrary control of the polarization states of light has attracted the interest of the scientific community because of the wide range of modern optical applications that such control can afford. However, conventional polarization control setups are bulky and very often operate only within a narrow wavelength range, thereby resisting optical system miniaturization and integration. Here, we present the basic theory, simulated demonstration, and in-depth analysis of a high-performance broadband and invertible linear-to-circular (LTC) polarization converter composed of a single-layer gold nanorod array with a total thickness of ~λ/70 for the near-infrared regime. This setup can transform a circularly polarized wave into a linearly polarized one or a linearly polarized wave with a wavelength-dependent electric field polarization angle into a circularly polarized one in the transmission mode. The broadband and invertible LTC polarization conversion can be attributed to the tailoring of the light interference at the subwavelength scale via the induction of the anisotropic optical resonance mode. This ultrathin single-layer metasurface relaxes the high-precision requirements of the structure parameters in general metasurfaces while retaining the polarization conversion performance. Our findings open up intriguing possibilities towards the realization of novel integrated metasurface-based photonics devices for polarization manipulation, modulation, and phase retardation.

Impact of deposition and laser densification of Silicalite-1 films on their optical characteristics

Although the field of integrated optics has advanced tremendously in the past two decades, the state-of-the-art still lags behind its electronic counterpart, particularly in the development and integration of new optical materials systems. Nanostructured materials, and in particular, porous, nanostructured materials, often have unique and complex relationships between their structure and their resulting optoelectronic properties. These relationships may be tailored during or after synthesis or deposition, leading to potentially intriguing new material systems suitable for various applications in integrated optics (tunable lasers, waveguides, transmitters, etc.) in the visible or near infrared regions. Zeolites represent a unique example of this material class; with their uniform microporosity and structural symmetry, their physicochemical and optoelectronic properties may be tailored to present a broad range of structures, compositions, surface areas, chemical and thermal stabilities, refractive index, dielectric constants, etc. Here, we synthesize a model zeolite system, silicalite-1 (MFI), in film form and characterize the resulting films both before and after partial laser densification to evaluate its potential for integrated optics. We use scanning electron microscopy, X-ray diffraction, and ellipsometry to determine the crystallinity, film thickness, surface coverage, crystal size, and crystal habit of the MFI films. We explore the fundamental optical properties of these films, such as index of refraction, and absorption and transparency windows, as a function of deposition method and film orientation. Within these parameters, we discuss their potential versatility and how slight structural changes induced via CO2 laser-assisted densification impact their resulting IR and Raman characteristics. The resulting randomly- and b-oriented films of thickness 94.32–510.31 nm showed the ability to reach a range of refractive indices (1.327–1.678), depending on film orientation, deposition technique, and crystallization time. The intensities of their IR (1400–400 cm−1) and relative Raman (1500–600 cm−1) absorption regions indicate an increase in crystallinity with laser irradiation from 10 to 20% power, however, crystallinity then decreases above 30% laser irradiation. These changes are all possible without changes in the overall composition. Determining these fundamental optical properties will allow us to explore the functionality of these materials for a wider array of applications in optics and electronics, where nanostructured materials can make a significant difference in scale, cost, efficiency, and overall performance. The results of this study will help determine the suitability of zeolites for optoelectronic materials, and will broaden their usage in optical computing, signal processing, and a new generation of optical components.