A compact plasmonic tunable filter using elasto-optic effects

We report on the theoretical concept of the design of a compact plasmonic tunable filter made of a metal–dielectric–metal waveguide and using elasto-optic effects. The proposed device is designed in a nanoring resonator structure and numerically studied by means of 3D-FEM simulations. We obtained an optimized nanoring resonator that has a radius R=390 nm and resonances at the telecommunication wavelength of 1.58 μm. Simulations using elasto-optic material as the dielectric layer and top and bottom Ag layers as electrodes indicate that the output can be tuned in the telecommunication wavelength range with an applied field. Further, using the proposed device, optical switching phenomenon is also found to be possible. This tunable ring resonator filter with ultra-small radii is considered valuable for photonic integrated systems.     

Compact resonantly intra-cavity pumped tunable Ho:Sc2SiO5 laser

A compact intra-cavity pumped low threshold continuous-wave Ho:Sc₂SiO₅ laser is reported. The characteristics of output wavelength tuning are investigated by use a intra-cavity briefringent (BF) filter. A wavelength tunable range of 140 nm from 2020 to 2160 nm is achieved. For the free-running mode, the laser slope efficiency is 24.8%, when the output central wavelength is 2110 nm. The laser threshold is about 820 mW of incident pump power. With the BF filter, a maximum output power of 870 mW is obtained at the incident pump power of 5 W, corresponding to a slope efficiency of 20.3%. The characteristics of output wavelength verse the crystal temperature are also investigated.     

Widely tunable compact erbium-doped fiber ring laser for fiber-optic sensing applications

A compact erbium-doped ring-shaped fiber laser suitable for fiber-optic sensing applications has been developed. The fiber laser utilized a tunable fiber Fabry–Perot filter as the tuning element and had a moderate milli-Watt level power output over almost the whole tuning range from 1530 to 1595 nm with a power fluctuation of 0.15 dB. High repetition rate scanning of laser operation over the whole tuning range was achieved at rates of up to 200 Hz. Moreover, the performance of the ring-shaped fiber laser configured with a high-concentration erbium-doped fiber was investigated for its larger wavelength tunability of over 100 nm. Output power characteristics of this ring-shaped fiber laser were also investigated when it worked in a scanning mode. A distorted power wavelength dependence, as well as some pulsing phenomenon were observed in scanning mode.     

Analysis and applications of nanocavity structures used as tunable filters and sensors

This paper reports on a novel design for a tunable filter and plasmonic sensor based on the metal–insulator–metal waveguide with a nanocavity resonator. Simulation results show that as a one-channel filter, the resonance wavelengths show a linear red-shift with an increase in nanocavity length with a slope of 1742 nm/μm and a nonlinear blue-shift with an increase in nanocavity width, respectively. A two-channel filter can be realized using two nanocavities and the arrangement of the two nanocavities with respect to the waveguide and the value of the distance between the nanocavities has only a marginal effect on the filter notch wavelength. Finally, both in-slit and out-slit refractive index plasmonic sensors are investigated with a sensitivity of 710 nm/RIU and 250 nm/RIU, respectively.     

Numerical analysis of a direct UV-written 1 × 8 double smooth octagon microrings resonant wavelength demulti/multiplexer

A microring resonant wavelength demulti/multiplexer (MRRWDM) based on UV-written technology is designed. By using a double smooth octagon microrings structure, a 1 × 8 device around the central wavelength of 1550.918 nm with the wavelength spacing of 1.4 nm is presented. Analytical results based on coupled mode theory show that the 3 dB bandwidth is about 0.22 nm, the insertion loss is less than 0.7 dB, and the crosstalk is below ?47 dB for every output channel of the designed device without tolerances.     

Comprehensive electro-optical analysis of long wavelength GaInNAs edge-emitting laser diode

Comprehensive analysis of GaInNAs edge-emitting laser operating near 1300 nm wavelength are made to underline the behavioural features of the proposed laser device, in view of the analytical investigation for various material and device electrical-optical parameters analysis such as band diagram, material gain, quantum well emission wavelength, optical wave and mode profiles, light-current-voltage characteristic, output mode spectrum, current distribution and far-field profile. The material analysis indicates that a high quality GaInNAs active region is designed, where high material gain and photoluminescence wavelength near 1.3 μm are achieved. The device obtains low threshold current operation with lasing emission around 1.285 μm.     

Tunable single-longitudinal-mode operation of a sandwich-type YAG/Ho:YAG/YAG ceramic laser

We present a 2.09 μm single-longitudinal-mode sandwich-type YAG/Ho:YAG/YAG ceramic laser pumped by a Tm-doped fiber laser for the first time. A pair of F-P etalons was used to achieve tunable single-longitudinal-mode operation. The maximum single-longitudinal-mode output power of 530 mW at 2091.4 nm was obtained with an absorbed pump power of 8.06 W, corresponding to an optical conversion efficiency of 6.6% and a slope efficiency of 12.7%. Wavelength tunable was achieved by tuning the angle of etalons and the wavelength could be tuned from 2091.1 nm to 2092.1 nm, corresponding to a tuning frequency of 68 GHz. The M² factor was measured to be 1.23.     

Dual-wavelength narrow-linewidth fiber laser based on F-P fiber ring filter

A dual-wavelength fiber laser with a narrow-linewidth, based on a P-F fiber filter has been proposed. Polarization-maintaining fiber Bragg grating (PM-FBG) and a F-P fiber filter are introduced based on the traditional fiber laser. PM-FBG is used as the wavelength selection device. The fiber F-P filter consists of two optical couplers and a section of un-pumped erbium-doped fiber (EDF). Due to the delay of cavity and the loss generated by the EDF, the filter has comb spectral response. The incorporation of the fiber F-P filter leads to the suppression of undesirable modes. At the room temperature, under 980 nm LD pumped, the maximum output of the two wavelengths is respectively ?2.259 dBm and 0.568 dBm, with the 3-dB bandwidth separately 0.1 nm and 0.14 nm, realizing the narrow linewidth and dual-wavelength output.     

Er/Yb co-doped fiber amplifier with wavelength-tuned Yb-band ring resonator

Erbium-ytterbium co-doped fiber amplifier with wavelength-tuned Yb-band loop resonator is presented. The amplified spontaneous emission (ASE) from Yb ions is utilized to stimulate a laser emission at several wavelengths from the 1 μm band in the 1550 nm amplifier. The wavelength of this lasing is tuned by introducing a fiber Bragg grating (FBG). The results show, that the overall efficiency of the amplifier at nominal 1550 nm wavelength can be increased by introducing a feedback loop with 1040 nm and 1050 nm FBG. This loop also protects the Er/Yb amplifier from parasitic lasing at 1 μm and allows significant output power scaling without risk of self-pulsing.     

Tunable dual-wavelength erbium-doped fiber ring laser covering both C-band and L-band for high-speed communications

A simple, continuously tunable dual-wavelength erbium-doped fiber ring laser (TDEDFL) structure for applications in high-speed communication systems is proposed and experimentally demonstrated. The dual-wavelength tuning range is 58 nm covering both the C-band and L-band from 1547 to 1605 nm. We can not only obtain a 45% improvement over previously reported tuning ranges, but also tune the wavelength of each lasing output independently. The power equalization of the dual-wavelength outputs is less than 1.5 dB. We obtain extremely stable power variation and wavelength fluctuation at room temperature. Using this fiber laser, a 10-Gb/s data transmission over a 25-km single-mode fiber (SMF) can be made available with a power penalty of 0.5 dB is demonstrated with this laser.     

Fabrication and characterization on an organic/inorganic 2 × 2 Mach–Zehnder interferometer thermo-optic switch

An organic/inorganic hybrid 2 × 2 directional coupler (DC) Mach–Zehnder interferometer (MZI) thermo-optic (TO) switch was successfully designed and fabricated using simple direct ultraviolet photolithography process. The hybrid organic/inorganic waveguide structure includes poly-methyl-methacrylate-glycidyl-methacrylate (P(MMA-GMA)), SU-8 2005 and silica as core, upper cladding and under cladding, respectively. Device optimization and simulation were performed to decrease radiation loss and leakage loss, quicken response time and cut down power consumption. Measurements of the fabricated devices at 1550 nm wavelength result in a switching power of 7.2 mW, a response time of ∼100 μs, and crosstalk of −22.8 and −26.5 dB under cross state and bar state, respectively. Besides, the driving-noise-tolerance characteristics of this device were experimentally investigated by directly imposing a generated tunable noise on the pure driving signal (4 V_pp) and the minimum extinction ratio is larger than 18 dB under a noise level of 2.5 V_pp. The effect of noise on extinction ratio was found decreased with the increase of noise frequency.     

A tunable and single-longitudinal-mode Ho:YLF laser

A 1.94 μm Tm-doped fiber laser pumped tunable single-longitudinal-mode Ho:YLF laser with double etalons was reported for the first time. The maximum single-longitudinal-mode output power of 345 mW at 2051.6 nm was achieved at the absorbed pump power of 11.9 W, corresponding to a slope efficiency of 5.5% and an optical conversion efficiency of 2.9%. By regulating the angle of the F–P etalons, the output wavelength of the laser can be tuned from 2051.6 nm to 2063.3 nm. The single-longitude-mode Ho:YLF laser operating at 2 μm can be used as the seed laser source of coherent Doppler lidar, differential absorption lidar and so on.     

Generation of tunable and narrow linewidth continuous-wave yellow laser by sum–frequency mixing of diode-pumped solid-state Nd:YAG ring lasers

We report a tunable, narrow linewidth and high beam quality continuous-wave (CW) yellow laser system at 589 nm. The system is an all solid-state design employing single-pass sum–frequency generation in a KTP crystal by mixing the 1064 nm with 1319 nm lines of two side-pumped Nd:YAG enforcing unidirectional ring lasers. With this method, a CW yellow laser at 589.159 nm with an output power of 0.8 W, a linewidth less than 1.5 GHz and a beam quality M² = 1.29 is obtained. The wavelength of the laser also can be precisely tuned from 589.112 to 589.181 nm in step-length of about 0.22 pm.     

Laser diode end-pumped passively Q-switched Tm,Ho:YLF laser with Cr:ZnS as a saturable absorber

Output performance of a continuous-wave (CW) laser diode end-pumped passively Q-switched Tm,Ho:YLF laser is demonstrated with a Cr:ZnS crystal as the saturable absorber. We particularly investigate the influence of saturable absorber's position in the resonator when the Cr:ZnS crystal is placed close to and far from the laser beam waist. We compare the experimental results at the two different positions, and find that the laser shows unusual output characteristics when the Cr:ZnS saturable absorber is placed close to the beam waist. The pulse width and the pulse energy almost keep constant, measured about 1.25 μs and 4 μJ respectively, when the pump power is changed in the range of 1–1.9 W. Moreover, the pulse repetition frequency can be tuned between 1.3 kHz and 2.6 kHz by changing the pump power. The output wavelength of the passively Q-switched laser shifts to 2053 nm from 2067 nm in CW operation.     

Tunable single-longitudinal-mode Ytterbium all fiber laser with saturable-absorber-based auto-tracking filter

A broadband tunable, single-longitudinal-mode (SLM) Ytterbium fiber laser with unpumped Ytterbium-doped Sagnac loop is proposed and demonstrated experimentally. The unpumped Ytterbium-doped Sagnac loop is employed as a saturable absorber based auto-tracking filter to ensure single-longitudinal-mode oscillation. And a tunable band pass optical filter with large tuning range is applied to achieve broadband tuning ability. With 1-m Ytterbium-doped fiber as the gain medium, the SLM operation is achieved with over 60-nm wavelength tuning range at 160-mW pump power. The laser is very stable with output power of about 3 dBm and optical signal to noise ratio of higher than 50 dB in all the 60-nm tuning range.     

High power Nd:YAG lasers operating at 1.3 μm wave band

The laser properties of 1.3 μm spectral region in Nd:YAG crystal and their simultaneous dual wavelength threshold condition are investigated. Three types of high power 1.3-μm Nd:YAG quasi continuous wave (QCW) lasers, which operate at 1.319 μm or 1.338 μm single wavelength, 1.319 μm and 1.338 μm simultaneous dual wavelength, are achieved with a maximum average output power of 138 W, 132 W and 120 W, respectively.     

Integrated polymers (PVCi/PMATRIFE) microring resonators for low power tunable filters

In this paper we present optical and thermo-optical characterization results of integrated filters based on micro-ring resonators fabricated with a couple of polymers “PVCI/PMATRIFE”. Their high index contrast (Δn～0.15 at the wavelength of 1550 nm) allows to make small size waveguides with cross sections of 1.5×1.5 μm². The study of the impact of different gaps on the extinction ratio and FWHM (full width at half maximum) of filters leads to a better design. First experiments of thermal tunability of the microring filter using a thermo-electric cooler (TEC) are also reported giving a 5 nm shift of the dropped wavelength for a temperature change of 40 K. The fabrication of gold electrodes on microrings is reported and the electrical power required for the tuning of the drop wavelength of 0.0055 nm/1 mW show that with an optimized electrode design the consumption will be low.     

60 W yellow laser at 561 nm by intracavity frequency doubling of a diode-pumped Q-switched Nd:YAG laser

A high-power yellow laser was achieved by intracavity frequency doubling of a diode-pumped Nd:YAG rod laser. A solid etalon was inserted into the resonator to implement efficient operation of the low-gain single line at 1123 nm transition. By using a LBO crystal inside the cavity as the frequency doubler, the maximum output power of the 561 nm yellow laser was obtained to be as high as 60.3 W with a pulse repetition frequency of 6 kHz, corresponding to an optical-to-optical conversion efficiency of about 6.1%. The output power fluctuation of the yellow laser was measured to be better than 3% in half an hour.     

Tunable dual-wavelength fiber laser based on an opto-VLSI processor and four-wave mixing in a photonic crystal fiber

A stable wavelength and wavelength spacing tunable dual-wavelength fiber laser based on an Opto-very-large-scale-integration (Opto-VLSI) processor and four-wave mixing (FWM) in a high-nonlinear photonic crystal fiber is experimentally demonstrated. The results show that the line width of the tunable dual-wavelength fiber laser is 0.02 nm, and the wavelength spacing can be tuned from 0.8 nm to 4 nm with a 0.15 nm step. Under the influence of the FWM, the uniformity is below 0.6 dB and the measured side mode suppression ratio (SMSR) is above 45 dB.     

Tunable multi-wavelength fiber laser based on a polarization-maintaining erbium-doped fiber and a polarization controller

A stable and tunable multi-wavelength fiber laser with a polarization-maintaining erbium-doped fiber (PM-EDF) and a polarization controller (PC) is proposed and demonstrated. A homemade PM-EDF incorporated in the ring cavity is used as the gain medium. Simultaneous multi-wavelength oscillation is achieved at room temperature. The theory of the PM-EDF and PC to suppress the wavelength competition is described in detail. The 3 dB bandwidth is less than 0.01 nm. The power fluctuation and wavelength shift are measured to be less than 0.5 dB and 0.05 nm over 32 min. The wavelength tuning between single-, double-, triple-, and four-wavelength is realized.