Increase In Optical Power Research Articles

A long single-span dispersion-decreasing-like fiber transmission system

We propose a novel unrepeated long single-span front-haul transmission system based on dispersion-decreasing-like fibers (DDLF). The modulation format is 160Gbps and PM-16QAM. The system transmission performance is effectively improved due to the balance of dispersion and nonlinear effects by using the DDLF, the balance of Raman amplification power and input optical power induced by equalization amplification between Raman amplifier and EDFA. The proposed system can effectively avoid the time delay of signal because of low dispersion of the DDLF system, and compensate the transmission attenuation impairment by employing the first-order Raman amplification at lower input power. The bit error rate (BER) of the system is better than 7% hard-decision forward error correction (FEC) threshold value of 3.8 × 10−3 in a wide range of input optical power. This system can be used in the long single-span front-haul transmission in special application scenarios. At higher input optical power, the nonlinear effect of the DDLF is the dominant factor affecting the performance of the transmission system, and nonlinear effect of the DDLF is increased with the increase of input optical power and Raman pump power, resulting in the system performance deterioration.

A dispersion flattened fiber front-haul transmission system with high bitrate signal at low input optical power

We propose a dispersion flattened fiber (DFF) front-haul transmission system with high bitrate, polarization multiplexing (PM) and quadrature amplitude modulation (QAM) signal at low input optical power. The modulation format of the system is PM-16QAM, and the bitrate is 256 Gbit/s. The transmission characteristics over DFF link system are experimentally studied, which are compared with those over non-zero dispersion shifted fiber (NZDSF) link and standard single mode fiber (SSMF) link. The experimental results show that the error vector magnitude (EVM) of 256 Gbit/s and PM-16QAM signal over 25 km DFF link is 0.75% better than that over 25 km NZDSF link at least, and the bit error rate (BER) and Q-factor are much better than those of NZDSF. Their EVM and BER are both decreased with the increase of input optical power, and the Q-factor is increased. Those characteristics over 25 km SSMF are the worst at the same case. The larger the dispersion is, the more the constellation points are deviated from their respective centers and the worse the constellation characteristics are. The greater the attenuation of the DFF is, the smaller the input power of the DFF is, the more the constellation points are deviated from their centers and the worse the constellation characteristics are. This study provides a new idea and experimental support for long span front-haul propagation in mobile communication.

Nonlinear dynamic analysis of a photonic crystal nanocavity resonator

A nonlinear dynamic model of a one-dimensional photonic crystal nanocavity resonator is presented. It considers the internal tensile stress and the geometric characteristics of a photonic crystal with rectangular (and circular) holes. The solution of the dynamic model shows that the internal tensile stress can suppress the hardening and softening behaviors of the resonator. However, the stress can reduce the amplitude, which is not conducive to an improvement of the sensitivity of the sensor. It is demonstrated that with an optimized beam length, the normalized frequency drift of the beam can be stabilized within 1% when the optical power increases from 2 mW to 6 mW. When the hole size of the resonator beam is close to the beam width, its increase can lead to a sharp rise of the resonant frequency and the promotion of hardening behavior. Moreover, the increase in the optical power initially leads to the softening behavior of the resonator followed by an intensification of the hardening behavior. These theoretical and numerical results are helpful in understanding the intrinsic mechanism of the nonlinear response of an optomechanical resonator, with the objective of avoiding the nonlinear phenomena by optimizing key parameters.

Research on photoresponse characteristics of bilayer molybdenum disulfide field effect transistors

The field-effect transistors (FETs) have attracted much attention because of the unique properties of the layered MoS2 nanosheet as an ideal channel material. The phototransistors based on the MoS2 FET have advantages of high photoresponsivity, rapid and stable response. This paper is concerned with the fabrication of bilayer MoS2 based FET and the research on the photoelectric characteristics of the devices. The effect of the optical power and gate voltage on the photoelectric properties of the device was researched through the contrast experiments. It has been achieved that the photocurrent increases with the increase of optical power at the same gate voltage and drain voltage. The photoresponsivity also been enhanced with the gate voltage increased. And the photoresponsivity of bilayer MoS2 FET was enhanced more than 100 folds by using MoS2/MoO3 as the channel material. The results indicated that the MoS2/MoO3 nanosheets can be a promising heterostructure material to offer a compelling case for application in enhancing the photoresponse characteristics of MoS2 transistors. These unique properties make the bilayer MoS2 based FET to be a great potential candidate of the next generation optoelectronic devices, which have the trend of miniaturization and integration.

Nonlinear Metasurface Based on Giant Optical Kerr Response of Gold Quantum Wells

A nonlinear metasurface is demonstrated numerically based on the recently developed quantum-sized gold film. The active functionality of the metasurface is realized by varying the incident optical power through the ultrahigh Kerr nonlinearity of the quantum-sized gold films. In the low power region, the device acts as a normal reflecting surface, while it becomes a phase grating with most energy in the ±1 diffraction modes when the optical power increases and the nonlinear effect plays a dominating role. Unlike previously demonstrated nonlinear metasurfaces focusing on nonlinear frequency generation, the functionality of our device may be modulated by the power of incident light. As the first nonlinear metasurface that is based on optical Kerr nonlinearity, our design may lead to various applications, such as optical limiters and tunable phase gratings.

Low loss GaN waveguides at the visible spectral wavelengths for integrated photonics applications.

We perform comprehensive studies on the fundamental loss mechanisms in III-nitride waveguides in the visible spectral region. Theoretical analysis shows that free carrier loss dominates for GaN under low photon power injection. When optical power increases, the two photon absorption loss becomes important and eventually dominates when photon energy above half-bandgap of GaN. When the dimensions of the waveguides reduce, the sidewall scattering loss will start to dominate. To verify the theoretical results, a high performance GaN-on-sapphire waveguide was fabricated and characterized. Experimental results are consistent with the theoretical findings, showing that under high power injection the optical loss changed significantly for GaN waveguides. A low optical loss ~2 dB/cm was achieved on the GaN waveguide, which is the lowest value ever reported for the visible spectral range. The results and fabrication processes developed in this work pave the way for the development of III-nitride integrated photonics in the visible and potentially ultraviolet spectral range for nonlinear optics and quantum photonics applications.

6-mW Single-Mode High-Speed 1550-nm Wafer-Fused VCSELs for DWDM Application

This paper presents data on wafer-fused 1550-nm vertical-cavity surface-emitting lasers (VCSELs) based on the active region and distributed Bragg reflectors (DBRs) grown by molecular beam epitaxy. VCSELs with a tunnel junction aperture diameter of 8 μm show lasing at a threshold current density j th <; 3 kA/cm 2 , an output optical power of ~4 mW, and a -3 dB bandwidth of approximately 7 GHz at a 10-mA bias current. The devices demonstrate single-mode continuous wave operation with the transverse side-mode suppression ratio (SMSR) varying in the range of 40-45 dB up to roll-over currents. The increase in mirror losses due to the etching of the top DBR makes the output optical power increase to 6 mW and causes the wallplug efficiency value to reach 20%, but SMSR remains in the range of 40-45 dB. This also makes it possible to reduce both the photon lifetime and, as a result, the effect of damping and increase the modulation bandwidth to 9 GHz. The observed open and clear eye diagrams indicate that non-return-to-zero operation is possible at bit rates of up to 30 Gbps without equalization or forward error correction. The high-output optical power and modulation performance pave the way for the dense wavelength division multiplexing application of wafer-fused 1550-nm VCSELs.

Power scaling and experimentally fitted model for broad area quantum cascade lasers in continuous wave operation

Experimental and model results for 15-stage broad area quantum cascade lasers (QCLs) are presented. Continuous wave (CW) power scaling from 1.62 to 2.34 W has been experimentally demonstrated for 3.15-mm long, high reflection-coated QCLs for an active region width increased from 10 to 20 μm. A semiempirical model for broad area devices operating in CW mode is presented. The model uses measured pulsed transparency current, injection efficiency, waveguide losses, and differential gain as input parameters. It also takes into account active region self-heating and sublinearity of pulsed power versus current laser characteristic. The model predicts that an 11% improvement in maximum CW power and increased wall-plug efficiency can be achieved from 3.15 mm×25 μm devices with 21 stages of the same design, but half doping in the active region. For a 16-stage design with a reduced stage thickness of 300 A, pulsed rollover current density of 6 kA/cm2, and InGaAs waveguide layers, an optical power increase of 41% is projected. Finally, the model projects that power level can be increased to ∼4.5 W from 3.15 mm×31 μm devices with the baseline configuration with T0 increased from 140 K for the present design to 250 K.

Optical wireless communication using positive real-valued orthogonal frequency-division multiplexing and optical beamforming

The relatively unsatisfactory performance of optical wireless communication (OWC) with respect to WiFi and millimeter-wave communications has formed a key issue preventing its commercialization. We experimentally demonstrate an OWC technology using a combination of positive real-valued orthogonal frequency-division multiplexing (OFDM) and optical beamforming (OB). Due to the intensity-modulation and direct-detection aspects of OWC systems, a positive real-valued OFDM signal can be suitably utilized to maximize the OWC data rate. Further, the OB technique, which can focus laser light on a desired target, can be utilized to increase the OWC data rate and transmission distance. Our experimental results show that the received optical signal power and electrical signal increase by up to 42 and 25 dB, respectively. Further, the data rate increases by a factor of 200 with OB over the conventional approach.

Ultrasonic modulation of tissue optical properties in ex vivo porcine skin to improve transmitted transdermal laser intensity.

Applications of light-based energy devices involving optical targets within the dermis frequently experience negative side-effects resultant from surface scattering and excess optical absorption by epidermal melanin. As a broadband optical absorber, melanin decreases the efficacy of light-based treatments throughout the ultraviolet, visible, and near-infrared spectra while also generating additional heat within the surface tissue that can lead to inflammation or tissue damage. Consequently, procedures may be performed using greater energy densities to ensure that the target receives a clinically relevant dose of light; however, such practices are limited, as doing so tends to exacerbate the detrimental complications resulting from melanin absorption of treatment light. The technique presented herein represents an alternative method of operation aimed at increasing epidermal energy fluence while mitigating excess absorption by unintended chromophores. The approach involves the application of continuously pulsed ultrasound to modulate the tissue's optical properties and thereby improve light transmission through the epidermis. To demonstrate the change in optical properties, pulsed light at a wavelength of 532 nm from a Q-switched Nd:YAG laser was transmitted into 4 mm thick samples of porcine skin, comprised of both epidermal and dermal tissue. The light was transmitted using an optical waveguide, which allowed for an ultrasonic transducer to be incorporated for simultaneous paraxial pulsation in parallel with laser operation. Light transmitted through the tissue was measured by a photodiode attached to an integrating sphere. Increasing the driving voltage of ultrasonic pulsation resulted in an increase in mean transmitted optical power of up to a factor of 1.742 ± 0.0526 times the control, wherein no ultrasound was applied, after which the optical power increase plateaued to an average amplification factor of 1.733 ± 0.549 times the control. The increase implies a reduction in light either back-scattered or absorbed within the tissue, which would allow for a greater proportion of incident energy to be delivered to the clinical target, thereby improving procedural efficacy and potentially reducing the severity of detrimental side-effects. Apparatus Lasers Surg. Med. 49:666-674, 2017. © 2017 Wiley Periodicals, Inc.

Room temperature direct-bandgap electroluminescence from a horizontal Ge ridge waveguide on Si**Project supported by the National Basic Research Program of China (Grant No. 2013CB632103), the National Natural Science Foundation of China (Grant Nos. 61176013 and 61036003), and the Science Fund from Beijing Science and Technology Commission, China (Grant No. Z151100003315019).

We report a lateral Ge-on-Si ridge waveguide light emitting diode (LED) grown by ultrahigh vacuum chemical vapor deposition (UHV-CVD). Direct-bandgap electroluminescence (EL) of Ge waveguide under continuous current is observed at room temperature. The heat-enhancing luminescence and thermal radiation-induced superlinear increase of edge output optical power are found. The spontaneous emission and thermal radiation based on the generalized Planck radiation law are calculated and fit very well to the experimental results. The Ge waveguides with different lengths are studied and the shorter one shows stronger EL intensity.

Bi-directional dual color mid-IR light emitting diodes

We demonstrate a two-contact, bi-directional, dual color light emitting diode with superlattice active regions operated at wavelengths near 4 μm and 8 μm. The operational wavelength of the device is controlled by the bias polarity. A modification of the long wavelength superlattice facilitated hole transport into the corresponding active region and lead to a more than fourfold increase in output optical power.

Optical Power Control in GMPLS Control Plane

The exponential traffic growth in optical networks has triggered the evolution from fixed-grid to flex-grid technology. This evolution allows better spectral efficiency and spectrum usage over current optical networks in order to facilitate huge dynamic traffic demands. The promise of flex-grid technology in terms of increasing the number of optical channels established over optical links, however, may not be sustainable because of the associated increase in optical amplification power. In this work, we detail a power control process that takes advantage of link optical power and channel optical signal-to-noise ratio (OSNR) margins to allow network operators to support this optical power increase while maintaining the use of legacy optical amplifiers. New generalized multiprotocol label switching (GMPLS) protocol extensions are proposed on which to integrate the optical power control process in the control plane. The performance of the process is evaluated in terms of the blocking ratio and network throughput over fixed-grid and flex-grid networks. Results show that controlling optical power benefits from the flex-grid technology in terms of spectrum and capacity gain and reduces optical connection blocking.

Improvement of thermal management in the composite Yb:YAG/YAG thin-disk laser

To improve the thermal management in the composite Yb:YAG/YAG thin-disk laser a new design of laser head is developed. Thermal-induced phase distortions, small signal gain and lasing in the upgraded laser head are investigated and compared with previously published results. A substantial decrease of the thermal lens optical power and phase aberrations and increase of the laser slope efficiency are observed. A continuous-wave laser with 440 W average power and 44% slope efficiency is constructed.

Active Maintenance of the Gradient of Refractive Index Is Required to Sustain the Optical Properties of the Lens.

To determine whether the cellular physiology of the lens actively maintains the optical properties of the lens and whether inhibition of lens transport affects overall visual quality. One lens from a pair of bovine lenses was cultured in artificial aqueous humor (AAH), while the other was cultured in either AAH-High-K+ or AAH + 0.1 mM ouabain for 4 hours. Lens pairs or whole enucleated eyes were then imaged in 4.7 Tesla (T) high-field small animal magnet. Lens surface curvatures, T1 measurements of water content, and T2 measurements of water/protein ratios were extracted from cultured lenses, while the geometrical parameters that define the optical pathway were obtained from whole eyes. Gradients of refractive index (GRIN), calculated from T2 measurements, and the extracted geometric parameters were inputted into optical models of the isolated lens and the whole bovine eye. Inhibiting circulating fluxes by inhibiting the Na/K-ATPase with ouabain or depolarization of the lens potential by High K+ caused changes to lens water content, the water/protein ratio (GRIN) and surface geometry that manifested as an increase in optical power and a decrease in negative spherical aberration in cultured lenses. Changes to optical properties of the lens resulted in a myopic shift that impaired vision quality in the optical model of the bovine eye. The cellular physiology of the lens actively maintains its optical properties and inhibiting the Na/K/ATPase induces a myopic shift in vision similar to that observed clinically in patients who go on to develop cataract.

Epitaxial growth and solar-blind photoelectric properties of corundum-structured α-Ga2O3 thin films

Corundum-structured α-Ga2O3 thin films have been employed to deposit on m-plane (300) α-Al2O3 substrates under different temperature, oxygen pressure, pulse laser energy and frequency by laser molecular beam epitaxy method. (300)-oriented α-Ga2O3 epitaxial thin film can be obtained under the appropriate growth parameters. The prepared α-Ga2O3 thin film shows a band gap of 5.15eV which is larger than that of β-Ga2O3, exhibiting an excellent solar-blind ultraviolet (UV) characteristic. The α-Ga2O3 thin film exhibits obvious photoresponse under 254nm UV light irradiation, and it increases in photocurrent with both the increase of optical input power and applied bias. However, it is not sensitive to 365nm light. The results suggest that α-Ga2O3 thin film is a promising candidate for use in solar-blind photodetectors.

Integrated Extended-Cavity 1.5-μm Semiconductor Laser Switchable Between Self- and Anti-Colliding Pulse Passive Mode-Locking Configuration

We present the first integrated linear extended-cavity passively mode-locked (PML) semiconductor laser in which the operating mode can be switched electrically between two configurations. The first configuration is where the saturable absorber (SA) is located next to the output coupler, the so-called anti-colliding pulse mode-locking (ACPML) scheme. The second is where the SA is next to the high reflectance mirror, the self-colliding pulse mode-locking (SCPML) scheme. The 7.5-GHz PML was used to demonstrate experimentally the theoretical prediction that placing the SA next to the output coupler leads to a significant improvement in the laser stability and quality of the optical pulses. The experimental results show that the ACPML scheme allows for more deeply saturated SA due to the increase of optical power in the SA. The measurements of the RF spectra and autocorrelation traces confirm the superiority of the ACPML design in terms of pulse stability and width over the SCPML design for a wide range of operating conditions. The linewidth of the beat tone at the repetition rate was reduced by more than 60 times, the measured minimal autocorrelation width improved from 22 to 7.5 ps and a 3 dB increase in average output power was achieved.

Miniaturized Photoacoustic Trace Gas Sensing Using a Raman Fiber Amplifier

This paper presents the development of a Raman fiber amplifier optical source with a maximum output power of 1.1 W centered around 1651 nm, and its application in miniaturized 3D printed photoacoustic spectroscopy (PAS) trace gas sensing of methane. The Raman amplifier has been constructed using 4.5 km of dispersion shifted fiber, a 1651 nm DFB seed laser and a commercial 4W EDFA pump. The suppression of stimulated Brillouin scattering (SBS) using a high frequency modulation of the seed laser is investigated for a range of frequencies, leading to an increase in optical output power of the amplifier and reduction of its noise content. The amplifier output was used as the source for a miniature PAS sensor by applying a second modulation to the seed laser at the resonant frequency of 15.2 kHz of the miniature 3D printed gas cell. For the targeted methane absorption line at 6057 cm-1 the sensor system performance and influence of the SBS suppression is characterized, leading to a detection limit (1σ) of 17 ppb methane for a signal acquisition time of 130 s, with a normalized noise equivalent absorption coefficient of 4.1•10-9 cm-1 W Hz-1/2 for the system.

Wide Optical Bandwidth and High Output Power Superluminescent Diode Covering C and L Band

We report on the development of a novel superluminescent diode (SLD) design with high output power and a wide optical bandwidth operation. The SLD combines an asymmetrical cladding structure for reduced internal losses and thick quantum wells to obtain emission from both the fundamental level and the first excited level. The <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${-}{\rm 3}~{\rm dB}$</tex></formula> optical bandwidth is equal to 135 nm for a 2-mm long device. For longer devices, the optical bandwidth is slightly reduced but the optical output power increases. By reinjecting a part of the optical power using an external reflector we obtain 27 mW of output power.

Electronic liquid crystal contact lenses for the correction of presbyopia

Presbyopia, the age-related reduction in near vision acuity, is one of the leading issues facing the contact lens industry due to an increasingly ageing population and limitations associated with existing designs. A plastic-based liquid crystal contact lens is described which is designed to allow switchable vision correction. The device is characterized by low operating voltages (<5V(rms)) and has curvatures suitable for placement upon the cornea. Imaging and Point Spread Function analysis confirm that the lens provides an increase in optical power of + 2.00 ± 0.25 D when activated, ideal for presbyopia correction.