Theory and experiments of a tunable wavelength-selective photodetector based on a taper cavity

We demonstrate a wavelength-selective photodetector that combines a Fabry-Perot filtering cavity (FPC) with a taper absorption cavity (TAC). The taper cavity shows a nonresonant effect but exhibits an absorption enhancement effect, so that high speed, high quantum efficiency, wide tuning range, and an ultranarrow spectral linewidth can be achieved simultaneously. Device performance was theoretically investigated by including key factors such as taper angle, finite-size diffracting-beam input, and lateral walk-off in the taper cavity. The device was fabricated by bonding a GaAs-based FPC, which can be tuned via thermal-optic effect, with an InP-based TAC. An integrated device with a spectral linewidth of 0.6 nm (FWHM), a wavelength tuning range of 10.2 nm(1518.0-1528.2 nm), a 3 dB bandwidth of 12 GHz, and a quantum efficiency of approximately 70% was demonstrated, and the absorption layer thickness is only 0.3 microm.     

Pump efficiency improvement of a C-band tunable fiber laser using optical circulator and tunable fiber gratings

We propose and demonstrate a tunable fiber laser based on an optical circulator (OC) and two tunable fiber Bragg gratings (TFBGs). The OC acts as a pump power router to improve the pumping efficiency, and a 4% increase in overall conversion efficiency has been observed. The combined tuning spectra range of two TFBGs could cover the entire C-band spectrum from 1530 to 1560 nm. Stable laser output power above 10 dBm is obtained using 1.9 m of erbium-doped fiber and TFBGs with 50% reflectivity. With power equalization by using variable optical attenuators, the power variation is less than 0.1 dB in the whole C band with narrow linewidth of 0.05 nm. A signal-to-noise ratio of 60 dB and a continuous tuning resolution of 0.5 nm have been achieved. The TFBG-based tunable fiber laser can be a promising light source for WDM transmission and fiber sensor applications.     

Theory and experiments of a three-cavity wavelength-selective photodetector

We propose a novel wavelength-selective photodetector with three subcavities, i.e., a filtering cavity, a spacer cavity, and an absorption cavity, for obtaining a narrow spectral response linewidth and a high quantum efficiency simultaneously. A theoretical prediction has been made that a less than 1-nm linewidth and a quantum efficiency as high as 90% are possible. We discuss the effects of the key factors on the performance of this type of photodetector that has been designed and fabricated. A spectral response linewidth of approximately 1.4 nm (FWHM) and an external quantum efficiency higher than 50% have been achieved experimentally. Such devices are promising for wavelength-division multiplexing applications.     

Hybrid integrated photodetector with flat-top steep-edge spectral response

Hybrid integrated photodetectors with flat-top steep-edge spectral responses that consist of an Si-based multicavity Fabry-Perot (F-P) filter and an InP-based p-i-n absorption structure (with a 0.2?μm In_0.53Ga_0.47As absorption layer), have been designed and fabricated. The performance of the hybrid integrated photodetectors is theoretically investigated by including key factors such as the thickness of each cavity, the pairs of each reflecting mirror, and the thickness of the benzocyclobutene bonding layer. The device is fabricated by bonding an Si-based multicavity F-P filter with an InP-based p-i-n absorption structure. A hybrid integrated photodetector with a peak quantum efficiency of 55% around 1549.2?nm, the -0.5 dB band of 0.43?nm, the 25?dB band of 1.06?nm, and 3?dB bandwidth more than 16?GHz, is simultaneously obtained. Based on multicavity F-P structure, this device has good flat-top steep-edge spectral response.     

Highly integrated coupled cavity photonic crystal laser with on-chip power control on the AlGaIn/AsSb material system

We present a multi-segment photonic crystal coupled cavity laser device on GaSb with a microstructured internal photodiode. This monolithically integrated power monitor is added as a third segment to a coupled cavity laser and is separated from the active device by six rows of two-dimensional photonic crystals, acting as highly reflecting mirrors. There is no additional fabrication step needed to integrate this feature into the coupled cavity laser, resulting in a highly integrated laser device of only 800?μm length. The device with lasing wavelength around 1955?nm shows single mode emission over a tuning range of as large as 16?nm and exhibits output powers of up to 9?mW.     

Purely axial compression of fiber Bragg gratings embedded in a highly deformable polymer

We demonstrate a tuning device for fiber Bragg gratings with a wavelength tuning range in excess of 65 nm. A purely axial tuning technique using a highly deformable polymer molded in a cylinder shape is used to embed a fiber Bragg grating and to achieve a wavelength tuning range from 1551.7 to 1485.5 nm. The tuning curve is highly linear with a tuning rate of 9.6 nm for every percent of applied strain. The insertion losses of the device, the variations of the full width at half maximum, and the stability of the Bragg wavelength over a working day have been studied and shown to be less than 0.02 dB, 0.14, and 0.2 nm, respectively.     

Replicated arrays of hybrid elements for application in a low-cost micro-spectrometer array

Abstract

We report on the fabrication and characterization of replicated hybrid elements for low-cost micro-spectrometer array applications. An array of hybrid elements, where one surface combines the fairly large dimensions of refractive microlenses with the submicron features of a diffraction grating, was successfully replicated by hot embossing. The parameters are: lens diameter=990 μm, height=60 μm, grating period=1 μm, linewidth=300 nm and grating depth=2 μm. These replicated spectrometer elements showed a maximum resolution of 2.25 nm and a stray-light suppression better than 30 dB.     

Increasing the output of a Littman-type laser by use of an intracavity Faraday rotator

We present a method of external-cavity diode-laser grating stabilization that combines the high output power of the Littrow design with the fixed output pointing of the Littman-Metcalf design. Our new approach utilizes a Faraday-effect optical isolator inside the external cavity. Experimental testing and a model that describes the tuning range and optimal tuning parameters of the laser are described. Preliminary testing of this design has resulted in a short-term linewidth of 360 KHz and a side-mode suppression of 37 dB. The laser tunes mode hop free over 7 GHz, and we predict that much larger tuning ranges are possible.     

Improved nanofabrication through guided transient liquefaction

A challenge in nanofabrication is to overcome the limitations of various fabrication methods, including defects, line-edge roughness and the minimum size for the feature linewidth. Here we demonstrate a new approach that can remove fabrication defects and improve nanostructures post-fabrication. This method, which we call self-perfection by liquefaction, can significantly reduce the line-edge roughness and, by using a flat plate to guide the process, increase the sidewall slope, flatten the top surface and narrow the width while increasing the height. The technique involves selectively melting nanostructures for a short period of time (hundreds of nanoseconds) while applying a set of boundary conditions to guide the flow of the molten material into the desired geometry before solidification. Using this method we reduced the 3sigma line-edge roughness of 70-nm-wide chromium grating lines from 8.4 nm to less than 1.5 nm, which is well below the 'red-zone limit' of 3 nm discussed in the International Technology Roadmap for Semiconductors. We also reduced the width of a silicon line from 285 nm to 175 nm, while increasing its height from 50 nm to 90 nm. Self-perfection by liquefaction can also be extended to other metals and semiconductors, dielectrics and large-area wafers.     

InGaAs/GaAs Quantum-Dot Superluminescent Diode for Optical Sensor and Imaging

We report on the design and fabrication of a novel wideband superluminescent diode (SLD) based on InGaAs/GaAs quantum-dot structure. In this device, we monolithically integrate a photon absorber section to suppress lasing action and optical feedback oscillation. The fabricated SLDs produce a close-to-Gaussian shaped spectrum centered at 1210 nm with a bandwidth of 135 nm. Spectral ripple as low as 0.3 dB has been measured     

Locally oxidized silicon surface-plasmon Schottky detector for telecom regime

We experimentally demonstrate an on-chip nanoscale silicon surface-plasmon Schottky photodetector based on internal photoemission process and operating at telecom wavelengths. The device is fabricated using a self-aligned approach of local-oxidation of silicon (LOCOS) on silicon on insulator substrate, which provides compatibility with standard complementary metal-oxide semiconductor technology and enables the realization of the photodetector and low-loss bus photonic waveguide at the same fabrication step. Additionally, LOCOS technique allows avoiding lateral misalignment between the silicon surface and the metal layer to form a nanoscale Schottky contact. The fabricated devices showed enhanced detection capability for shorter wavelengths that is attributed to increased probability of the internal photoemission process. We found the responsivity of the nanodetector to be 0.25 and 13.3 mA/W for incident optical wavelengths of 1.55 and 1.31 μm, respectively. The presented device can be integrated with other nanophotonic and nanoplasmonic structures for the realization of monolithic opto-electronic circuitry on-chip.     

Design of a high-efficiency grating coupler based on a silicon nitride overlay for silicon-on-insulator waveguides

A waveguide grating coupler based on a silicon nitride overlay at 1.55 μm for TE polarization is designed with no experimental demonstration. Its coupling efficiency for a fiber is 76%, the 1 dB bandwidth is 75 nm, and the coupling angle is 10°. The effects of different device parameters on the coupling performance for the grating coupler are discussed. The coupling efficiency of our grating coupler is almost equal, yet the 1 dB spectral bandwidth is around 25 nm broader, as compared with the grating coupler design based on a poly-silicon overlay. The coupling performance of our coupling device could still be further improved. The grating coupler presented in this paper is applicable to the optical coupling in nanophotonic integrated circuits.     

熔锥型光纤声光可变衰减器

利用耦合模理论对光纤熔锥声光器件进行了数值模拟,得到了全光纤声光衰减器传输谱和可调谐性。分析了带宽与声波长、耦合长度的关系。数值分析结果表明,声波在光纤熔锥中引起的轴向电介质微扰、耦合长度和工作波长都会对器件的传输谱产生影响,选择合适的设计参数可以制作较为理想的声光衰减器。实验上获得了损耗小于0．2dB,带宽大于200nm,动态范围为20dB的单模光纤熔锥可变衰减器,所得结果与理论分析相符合。这种器件可用于光纤通信及光纤传感。     

Broadband,continuous, and fine-tune properties of external-cavity thermoelectric-stabilized mid-infrared quantum-cascade lasers

Continuous, broad, and single-mode wavelength tuning of thermoelectrically cooled short-pulse quantum-cascade lasers is demonstrated with a combination of coarse grating tuning and fine phase tuning of the gain element. This approach overcomes the problem of a poor facet antireflection coating of the gain chip by shifting a Fabry-Perot longitudinal mode to coincide with the desired grating-selected wavelength. The 9-microm laser was tested with NH3 gas absorption and showed fine frequency tuning at a rate of 31 MHz/step and a time-averaged linewidth of 500-750 MHz. The total tuning range was 9.08-9.36 microm and was limited only by the intrinsic gain of the device.     

In Situ Growth of Graphene Catalyzed by a Phase-Change Material at 400 °C for Wafer-Scale Optoelectronic Device Application

The use of metal foil catalysts in the chemical vapor deposition of graphene films makes graphene transfer an ineluctable part of graphene device fabrication, which greatly limits industrialization. Here, an oxide phase-change material (V₂O₅) is found to have the same catalytic effect on graphene growth as conventional metals. A uniform large-area graphene film can be obtained on a 10 nm V₂O₅ film. Density functional theory is used to quantitatively analyze the catalytic effect of V₂O₅. Due to the high resistance property of V₂O₅ at room temperature, the obtained graphene can be directly used in devices with V₂O₅ as an intercalation layer. A wafer-scale graphene-V₂O₅-Si (GVS) Schottky photodetector array is successfully fabricated. When illuminated by a 792 nm laser, the responsivity of the photodetector can reach 266 mA W⁻¹ at 0 V bias and 420 mA W⁻¹ at 2 V. The transfer-free device fabrication process enables high feasibility for industrialization.     

Tunable microcavity based on InP/air Bragg mirrors

A tunable Fabry–Perot filter based on InP/air Bragg mirrors has been studied. We have measured a resonance linewidth of 0.6 nm and a tuning range of 62 nm. The linewidth is kept below 1 nm over a 40 nm tuning range. The relation between the bending of the suspended layers during the actuation and the optical properties of the filter are analysed.     

Laser-textured silicon photodiode with broadband spectral response

A femtosecond-laser-textured Si photodetector is reported. Broadband spectral optical response is detected from UV to NIR. A quantum efficiency of greater than 80% from 490 nm to 780 nm has been achieved. The quantum efficiency at 245 nm is 62%, which is comparable to UV-enhanced Si photodiodes. The bandwidth of a 250-μm-diameter device is 60 MHz.     

Tm3+-doped fiber master oscillator power amplifier with broad tunability in pulse duration using an acousto-optic external modulator

ABSTRACT

We demonstrate a pulse-duration tunable Tm³⁺-doped pulsed all-fiber master oscillator power amplifier (MOPA) operating at a central wavelength of 1908 nm. By using acousto-optic(AO) external modulation, the amplified laser pulse shows a tuning range having pulse durations from 66.5 ns to 8.0 μs and a repetition rate of 100 kHz-2 MHz. The laser achieved a maximum average power of 28.1 W and a corresponding energy of 28.1 μJ at 1MHz with a 3 dB linewidth of 0.63 nm and a beam quality factor of M_x²=1.25 and M_y²=1.32. The ASE suppression ratio is 50 dB and the corresponding total amplifier gain is 27.5 dB. To the best of our knowledge, it is the highest average output power and slope efficiency (～51.0%) achieved using AO external modulation in a Tm³⁺-doped pulsed fiber amplifier.     

Low loss, low refractive index fluorinated self-crosslinking polymer waveguides for optical applications

Synthesis and optical applications of low loss methacrylate-based fluorinated polymers are described. The synthesis of well defined self-crosslinking fluorinated polymers has been carried out in order to tune refractive index in the range of 1.390 < n < 1.450. After thermal crosslinking, one single lithographic step followed by reactive ion etching is necessary to monomode optical waveguide fabrication on silicon substrates. Optical losses lower than 1 dB/cm at 1300 nm and 2 dB/cm at 1550 nm were measured for highly confined modes. Efficient chip coupling to lensed optical fibers was obtained. Using waveguides with an effective index close to that of bulk silica, a significant coupling interaction between the guided modes and the whispering gallery modes of a silica microsphere was evidenced thus opening the way for new device applications.     

Tunable and Sensitive Biophotonic Waveguides Based on Photonic-Bandgap Microcavities

This paper presents a theoretical study of the single-mode and birefriengence condition of the silicon photonic wires using the imaginary distance beam propagation method. The photonic wires are suitable for integration with active one-dimensional silicon photonic bandgap waveguides. This inherently will reduce the propagation loss caused by the scattering factors within the photonic bandgap structure itself. To the best of our knowledge, we provide for the first time, a systematic study of the various physical parameters that can affect the$Q$-factor and transmission properties in such waveguides. In order to make this technology viable, the waveguides must be tunable, have low attenuation, possess high$Q$-factor, and can be switched. Can these be achieved simultaneously without changing the device width and height dimensions? Furthermore, can we meet these aims without placing unrealistic demands in fabrication? The electrical switching of this device is implemented using a p-i-n optical diode. The diode is predicted to require an on state power of 81 nW with rise and fall times of 0.2 and 0.043 ns, respectively. The length of the microcavity and the diameter of the air holes are finely tuned with reference to the$Q$-factor and transmission. It will be shown that for certain desired resonant wavelength, the$Q$-factor and transmission properties can be optimized by tuning the length of the cavity and the diameter of the two inner most air holes. This method allows ease of fabrication by not having to vary the waveguide width and height to obtain the tuning effects. Optical simulation was performed using the three-dimensional finite-difference time-domain simulation method.