Low-loss Ti:LiNbO3waveguide bends at λ = 1.3 µm

Low-loss waveguide bends are necessary for many proposed integrated optical circuits. The bend loss associated with anS-shaped transition connecting offset 6 μm wide titanium-indiffused lithium niobate strip waveguides has been measured as a function of transition length and initial Ti metal thickness for 1.3 μm wavelength. Losses as low as 0.2 ± 0.2 dB have been achieved for a transition between offset parallel waveguides with a 0.1 mm lateral and 3.25 mm longitudinal separation. The bend loss is shown to be strongly dependent on the mode confinement and less sensitive to the shape of the transition curve.     

Minimum-mode-size low-loss Ti: LiNbO3channel waveguides for efficient modulator operation at 1.3 µm

Efficient operation of Ti-diffused LiNbO3modulators and switches requires small, tightly guiding channel waveguide modes which effectively overlap the applied modulating field. This in turn requires Ti:LiNbO3channel waveguides with minimum mode size. The small-mode-size waveguides are obtained inz-cut crystals by optimizing the fabrication parameters to achieve maximum index change in the wave-guiding region and the optimum diffusion depth and width. For 6 h diffusion at 1025°C, and Ti strip thickness of 800 Å and strip width of 4 μm, the TM mode has a1/eintensity full width of 3.9 μm and full depth of 2.8 μm. This is by far the smallest mode size atlambda = 1.32 mum presented to date for Ti:LiNbO3waveguides. Since these waveguides have small mode size, largeDelta n, and low propagation loss (0.2 dB/cm) atlambda = 1.32 mum, it should be possible to fabricate modulators and switches with small voltage-length products and optical circuits that incorporate small bending radii curves, thus decreasing the total device length.     

Influence of temperature and initial titanium dimensions of fiber-Ti:LiNbO3waveguide insertion loss at λ = 1.3 µm

This paper describes the influence of fabrication parameters on fiber-Ti:LiNbO3waveguide-fiber insertion loss measured atlambda = 1.32 mum inc-cut LiNbO3. We present a systematic study of the influence of titanium thickness on insertion loss. Within the range examined, diffusion of 950 Å thick 6 μm wide strip of Ti at 1050°C for 6 h produced the minimum loss of 2.0 dB in a 2 cm long waveguide for both TE and TM modes. An analysis of fiber-waveguide coupling for the particular case of an asymmetric diffused waveguide is presented. In general, we find that coupling loss due to modal mismatch between the fiber and waveguide and propagation loss in the waveguide contribute approximately equally to total insertion loss.     

Traveling wave optical modulator using a directional coupler LiNbO3waveguide

Fabrication methods for low drive voltage and broad-band LiNbO3waveguide directional coupler optical modulator are described. Optical waveguides were prepared by conventionaly Ti in-diffusion into LiNbO3c-cut plate. To obtain wide-band frequency response, traveling wave electrodes were used. Electrode characteristic impedance measured by time domain reflectometry method coincided well with the calculated value by conformal mapping. Measured electrode conductor losses followed square root of frequency. To reduce electrode conductor losses, asymmetric and 3-μm thick Al electrodes were used. Directional coupler optical modulator frequency response was analyzed, using the phase difference average value along the propagation directions. Calculated value by this method coincided well with measured value obtained by a swept frequency technique. The characteristics of this modulator at the 1.317-μm wavelength are as follows: 100 percent modulation voltage is 4 V, extinction ratio is 17 dB, optical insertion loss is 5.4 dB, 3-dB bandwidth is 3.6 GHz, and rise time is about 400ps.     

High-efficiency, high-power difference-frequency generation at 2-4 µm in LiNbO3

High-efficiency generation of high-peak power and high-average power difference-frequency radiation, continuously tunable over the range of 2 to 4 μm, has been achieved by mixing the Nd:YAG laser radiation with the output of a near-infrared dye laser pumped by the second harmonic of the same Nd:YAG laser in LiNbO3. A peak power as high as 1.6 MW with an average power of 130 mW was obtained near 2.3 μm.     

New laser lines with wavelengths from λ = 61.7 µm down to λ = 27.7 µm in optically pumped CH3OH and CD3OH

25 new CW far infrared laser lines have been observed with wavelengths fromlambda = 61.7 mum down tolambda = 27.7 mum. We have significantly increased the number of known short wavelength laser lines and extended the laser line spectrum to the 30 μm region by using a BaF2outcoupling system.     

High-speed traveling-wave directional coupler switch/modulator for λ = 1.32 µm

We have designed and fabricated a Ti:LiNbO3waveguide traveling-wave directional coupler switch/modulator operating atlambda = 1.32 mum that exhibits a 3 dB modulation bandwidth of 7.2 GHz, a switching voltage of 4.5 V, and power per unit bandwidth of 7.6 mw/ GHz. Using short drive pulses, optical pulsewidths as short as 58 ps have been generated and directly measured with a high-speed InGaAs/InP p-i-n photodiode. Thick (sim 2.8 mum) electroplated gold has been used to produce a small gap (5 μm) and low-loss coplanar strip electrode. The 1.5 cm long, 15 μm wide electrode has a dc resistance of 7 Ω and a total microwave power loss of ∼4dB at 5 GHz.     

LiNbO3traveling-wave light modulator/switch with an etched groove

A Ti dffused lithium niobate traveling-wave interferometric light modulator/switch with a groove excavated at the electrode gap has been fabricated and tested at microwave frequency. The groove suppresses the undesirable light coupling between the two parallel waveguides for the phase shifting section so that the drive voltage is decreased by reducing the separation of the parallel waveguides, or of the electrodes. In addition, the groove decreases the effective index for the modulating wave to reduce the velocity mismatch between light wave and microwave so that the bandwidth is broadened. The modulation experiment was carried out from dc to 15 GHz at 633 nm light wavelength. For the modulator with the electrodes 6 mm long and 10 μm apart, the half-wave or switching voltage was 3 V, the extinction ratio was 18 dB, the 3 dB bandwidth was 12 GHz and aP/Delta fof 1.5 mW/GHz was obtained.     

A novel Ti:LiNbO3ridge waveguide linear mode confinement modulator fabricated by reactive ion-beam etching

In this paper we report the realization of a ridge waveguide linear mode confinement modulator using reactive ion-beam etching (RIBE). With the help of a design analysis, the modulation characteristics are predicted. Along with the measured modulation characteristics, preliminary results of the calibration of ion-beam etching inZ-cut LiNbO3by Ar and a mixture of Ar and CHF3are presented. Differential etching rates between photoresist and LiNbO3of as high as 7 are obtained. Using the proposed design of a ridge waveguide linear modulator, a linear modulation of over 67 percent is measured.     

0.15 µm Channel-length MOSFET's fabricated using e-beam lithography

We have fabricated MOSFET's with channel lengths as short as 0.1 µm by a modified NMOS process. The devices have been designed according to parameters obtained from numerical simulation. Electron-beam lithography has been used to define patterns at all levels with the negative resist GMC in a tri-level configuration. Heat treatments have been as short as possible to preserve very shallow source-drain junction depths (<0.1µm). We observe quasi-long channel behavior for low bias voltages. Measured values for the transconductance are among the highest ever reported. For a channel lengthL = 0.14µm, we obtaing_{m} = 180mS/mm for a gate oxide thickness of 160Å.     

Optimum cut for a LiNbO3transverse light modulator

The most general expression for the half-wave voltage of a LiNbO3transverse light modulator has been studied. As a result, a novel cut with a minimum half-wave voltage of 1440 V for amplitude modulation is proposed. A preliminary experimental verification confirms the promising theoretical results.     

Continuous wave 16 µm CF4laser

A 16 μm CF4laser oscillator has operated continuous wave in a cooled static cell. Pump powers required from the low-pressure continuous wave CO2laser were approximately 3 W. The laser cavity was a multiple-pass off-axis-path two-mirror ring resonator. Unidirectional CF4laser power at 615 cm^-1exceeded 2 mW. Rate equations were used to estimate scaling of this laser source. For modest pump powers (40 W) approximately 1 W of emission power is predicted from this small and simple system.     

12 µm Raman lasers in NH3pumped by low-power CO2laser pulses

We report the operation of optically pumped 12 μm lasers in NH3using peak pumping powers as low as 2 W. These low pumping powers represent a 1-2 order-of-magnitude improvement over previously published threshold values. Measurements of the lasing offset frequency clearly demonstrate that a two-photon Raman process is responsible for optical gain at 12 μm. In light of our results, we discuss the feasibility of an optically pumped CW 12 μm laser.     

10 GHz bandwidth traveling-wave LiNbO3optical waveguide modulator

A broad-band traveling-wave electrooptic modulator of Ti-diffused LiNbO3optical waveguide was designed, constructed, and tested at 0.63 μm over a bandwidth of 10.5 GHz. Using a novel asymmetric electrode configuration as a microwave waveguide, practically smooth frequency response of the modulator was obtained. For 300 mW drive power, the phase modulation index was 1 rad at 2 GHz and 0.53 rad at 10 GHz, while the intensity modulation index was 64 and 34 percent, respectively.     

1.6 µm wavelength GaInAsP/InP lasers prepared by two-phase solution technique

Reduction of the threshold current of GaInAsP lasers with an antimeltback layer was studied in the wavelength range1.50-1.65 mun. The two-phase solution growth technique was applied using a relatively low temperature and a slow cooling rate of 0.17°C/min to reduce the active layer thickness. The antimeltback layer with a bandgap wavelength of 1.35 μm resulted in a flat active layer and eliminated the melt-back problem completely. From experiments and calculations we found that both the carrier and the optical confinement of this structure, having an antimeltback layer, were almost the same as those for the conventional InP cladding structure. A threshold eurrent density as low as 1.2 kA/cm²and an active layer thickness of 0.20μm were obtained at these wavelengths. The lattice-match condition of low-temperature growth was studied. In the low-temperature growth, the longer wavelength lasers were grown with the same amount of InAs.J_{th}/dwas independent of the growth condition (T_{S}, T_{G}) and had a value of 5-6 kA/cm². μm.     

Amplifying medium characteristics in optimized 190 µm/195 µm DCN waveguide lasers

Extensive study of the CW, dischaxge-pumped, DCN laser operating on the (22⁰0-09¹0) 190 and 195 μm lines has been undertaken in order to develop a new source of radiation suitable for plasma diagnostics. The optimum values of the parameters of the discharge, the unsaturated gain, and the saturation intensity are given as a function of the tube diameter. Scaling laws predicting the maximum output power as a function of the tube dimensions and of the cavity loss are established. Such lasers compare favorably with optically pumped submillimeter lasers, since 250 mW are available from a 3 m long, 5 cm diameter waveguide DCN laser.     

A 10.6 µm scan laser with programmable VO2mirror

A scan laser controlled by the variable reflectance of a VO2film on a CRT faceplate has been demonstrated at 10.6 μm. The cavity is a flat field conjugate resonator with an active medium of axially flowing CO2-N2-He gas mixture. The output beam has been scanned in a circular pattern at 20 Hz. Output modulation has been observed at a raster frame rate of 45 Hz (100 percent) and at a raster line rate of 4.44 kHz (< 100 percent).     

High-power difference-frequency generation at 4.4-5.7 µm in LiIO3

Efficient generation of high-power difference-frequency radiation, continuously tunable over the range of4.4-5.7 mum, has been achieved by mixing the Nd :YAG laser and Nd :YAG pumped infrared dye-laser outputs in LiIO3. Peak pulse powers as high as 550 kW with an average power output of 45 mW were obtained around 4.9μm.     

Continuous-wave CH3F waveguide laser at 496 µm: Theory and experiment

The kinetic processes controlling the conversion of CO2pump radiation into far-infrared (FIR) radiation in optically pumped waveguide lasers are discussed. It is found that pump saturation and excited-state FIR absorption play major roles in limiting the conversion. Good agreement between theory and experiment was obtained over a wide range of pump powers, gas pressures, and mirror reflectivities. For a well-optimized system, power-conversion efficiencies of 0.2-0.6 percent can be realistically achieved for CH3F.