Transmission properties of some hollow glass waveguides at 10.6 mu m wavelength

The CO/sub 2/ laser transmission properties of two hollow glass waveguides of different composition are reported. The results for both straight and bent guide clearly demonstrate the reductions in waveguide loss with a glass of refractive index of less than unity at 10.6 mu m wavelength.<>     

Erbium-doped composite glass waveguide amplifier

Optical amplification at 1.523 mu m wavelength is demonstrated in an erbium-doped glass waveguide. More than 10 dB amplification is achieved in a 4.7 mm long waveguide with about 30 mW guided pump power of 0.9734 mu m wavelength.<>     

Erbium-doped silica-based planar waveguide amplifier pumped by 0.98 mu m laser diodes

A 0.98 mu m laser-diode-pumped waveguide amplifier is successfully realised by using an Er-doped silica-based planar lightwave circuit. The highest signal gain of 9.4 dB is achieved at a signal wavelength of 1.533 mu m with a pump power of 99 mW, using a highly efficient erbium-doped waveguide and high power laser diodes.<>     

Large modulation depth, single-moded quantum well waveguide modulator operating around 1.57 mu m

The performance of long wavelength single-mode waveguide modulators suitable for monolithic integration with a quantum well laser is reported. The device operated between 1.560 mu m and 1.570 mu m. The guiding layer was formed by a 0.27 mu m quaternary layer at the centre of which were four 50 AA In/sub 0.53/Ga/sub 0.47/As quantum wells separated by 100 AA InP barrier layers. Lateral confinement was obtained by etching ridges in the top InP contact layer. For devices of 500 mu m length, a modulation depth of 19 dB was obtained at a wavelength of 1.568 mu m with a reverse bias voltage of only 3 V and an internal loss of 2.5 dB.<>     

Germania-based core optical fibers

Germania-glass-based core silica glass cladding single-mode fibers (/spl Delta/n up to 0.143) with a minimum loss of 20 dB/km at 1.9 /spl mu/m were fabricated by the modified chemical vapor deposition (MCVD) method. The fibers exhibit strong photorefractivity with the type-IIa-induced refractive-index modulation of 2/spl times/10/sup -3/. The Raman gain of 300 to 59 dB/(km/spl middot/W) was determined at 1.07 to 1.6 /spl mu/m, respectively, in a 75 mol.% GeO/sub 2/ core fiber. Only 3 m of such fibers are enough for the creation of a 10-W Raman laser at 1.12 /spl mu/m with a 13-W pump at 1.07 /spl mu/m. Raman generation in optical fiber at a wavelength of 2.2 /spl mu/m was obtained for the first time.     

Silica-clad neodymium-doped lanthanum phosphate fibers and fiber lasers

We have fabricated a neodymium-doped phosphate glass fiber with a silica cladding and used it to form a fiber laser. Phosphate and silicate glasses have considerably different glass transition temperatures and softening points making it hard to draw a fiber from these two glasses. A bulk phosphate glass of composition (Nd/sub 2/O/sub 3/)/sub 0.011/(La/sub 2/O/sub 3/)/sub 0.259/(P/sub 2/O/sub 5/)/sub 0.725/(Al/sub 2/O/sub 3/)/sub 0.005/ was prepared and the resultant material was transparent, free from bubbles and visibly homogeneous. The bulk phosphate glass was drawn to a fiber while being jacketed with silica and the resultant structure was of good optical quality, free from air bubbles and major defects. The attenuation at a wavelength of 1.06 /spl mu/m was 0.05 dB/cm and the refractive index of the core and cladding at the pump wavelength of 488 nm was 1.56 and 1.46, respectively. The fibers were mechanically strong enough to allow for ease of handling and could be spliced to conventional silica fiber. The fibers were used to demonstrate lasing at the /sup 4/F/sub 3/2/-/sup 4/I/sub 11/2/ (1.06 /spl mu/m) transition. Our work demonstrates the potential to form silica clad optical fibers with phosphate cores doped with very high levels of rare-earth ions (27-mol % rare-earth oxide).     

Design and performance of an erbium-doped silicon waveguide detector operating at 1.5 /spl mu/m

A new concept for an infrared waveguide detector based on silicon is introduced. It is fabricated using silicon-on-insulator material, and consists of an erbium-doped p-n junction located in the core of a silicon ridge waveguide. The detection scheme relies on the optical absorption of 1.5-/spl mu/m light by Er/sup 3+/ ions in the waveguide core, followed by electron-hole pair generation by the excited Er and subsequent carrier separation by the electric field of the p-n junction. By performing optical mode calculations and including realistic doping profiles, we show that an external quantum efficiency of 10/sup -3/ can be achieved in a 4-cm-long waveguide detector fabricated using standard silicon processing. It is found that the quantum efficiency of the detector is mainly limited by free carrier absorption in the waveguide core, and may be further enhanced by optimizing the electrical doping profiles. Preliminary photocurrent measurements on an erbium-doped Si waveguide detector at room temperature show a clear erbium related photocurrent at 1.5 /spl mu/m.     

Highly efficient Er-doped fibre amplifiers pumped in 660 nm band

High gain coefficient in an erbium-doped fibre amplifier, 3.8 dB/mW at 1.536 mu m and 2.3 dB/mW at 1.552 mu m, is achieved for a pump wavelength of 664 nm by using an erbium-doped fibre with a high numerical aperture of 0.285 and thermally-diffused expanded core fibre ends. The gain at 1.536 mu m reaches 30 and 35 dB for launched pump powers of 10 and 15 mW, respectively.<>     

Continuous-wave operation of GaInAsSb-GaSb type-II ridge waveguide lasers emitting at 2.8 /spl mu/m

We have realized compressively strained GaInAsSb-GaSb type-II double quantum-well lasers with an emission wavelength of 2.8 /spl mu/m. Using broad area devices, an internal absorption of 9.8 cm/sup -1/ and an internal quantum efficiency of 0.57 is determined. For the increase of the threshold current with temperature, a T/sub 0/ of 44 K is obtained. Narrow ridge waveguide lasers show continuous-wave laser operation at temperatures up to 45 /spl deg/C, with room-temperature (RT) threshold current of 37 mA. At RT, the maximum optical output power per facet of an uncoated 800/spl times/7 /spl mu/m/sup 2/ ridge waveguide laser exceeds 8 mW.     

Low-loss, high- Delta , single-mode channel waveguides for high-density integrated optical devices

Low-loss, high- Delta , single-mode channel waveguides having cores of SiO/sub 2/-Ta/sub 2/O/sub 5/ mixture film are successfully fabricated using sputtering and reactive ion-beam etching. Propagation loss is less than 0.6 dB/cm, and no bending loss for 500 mu m curvature radius at 1.3 mu m wavelength is achieved for an optical waveguide having a relative index difference of 5.6%.<>     

Propagation-mode-controlled fabrication of self-written waveguide in photosensitive polyimide for single-mode operation

We have developed a new fabrication method of single-mode self-written waveguide by controlling the propagation mode in an optical fiber. This method is very appropriate for repeatable fabrication of the single-mode self-written waveguide. Since a Gaussian-like near-field pattern is required for the fabrication of a tiny and uniform waveguide core, the propagation mode in a conventional optical communication fiber was controlled by coupling with an optical fiber having 3-/spl mu/m core, which shows a single-mode operation at visible wavelength region. Single-mode propagation at optical communication wavelength was confirmed for the fabricated self-written waveguide. The evaluated core diameter of the self-written waveguide was /spl sim/9.5 /spl mu/m.     

Highly efficient 40 GHz waveguide InGaAs p-i-n photodiode employing multimode waveguide structure

The authors describe the design procedure of a highly efficient waveguide p-i-n photodiode. The efficiency of the waveguide InP/InGaAsP ( lambda /sub g/=1.3 mu m)/InGaAs/InGaAsP ( lambda /sub g/=1.3 mu m)/InP p-i-n photodiode is calculated using the step-segment method and overlap-integral between the optical field of a fiber and that of the photodiode. A remarkably high coupling efficiency to a fiber can be obtained by using a multimode waveguide structure. The fabricated device has an external quantum efficiency of 68% as well as 3 dB bandwidth of higher than 40 GHz at a 1.55 mu m wavelength.<>     

Second harmonic generation in GeO/sub 2/ ridge waveguide

Reports the first observation of 'seeded' second harmonic generation in a GeO/sub 2/ and P/sub 2/O/sub 5/ codoped silica ridge waveguide from a pump wavelength at 1.064 mu m. A 200-fold increase over the background signal has been measured.<>     

Polarisation-insensitive Si/sub 3/N/sub 4/ strip-loaded BaTiO/sub 3/ thin-film waveguide with low propagation losses

A low-loss and polarisation-insensitive singlemode BaTiO/sub 3/ thin-film waveguide is reported. Polarisation-dependent loss as low as 0.1 dB/cm at a wavelength of 1.55 /spl mu/m has been achieved by a novel Si/sub 3/N/sub 4/ strip-loaded BaTiO/sub 3/ waveguide structure. Propagation loss of less than 0.9 dB/cm for both TE and TM polarisations was measured     

Photopumped lasing at 1.25 /spl mu/m of GaInNAs-GaAs multiple-quantum-well vertical-cavity surface-emitting lasers

We report room-temperature (RT) continuous-wave (CW) photopumped operation of long-wavelength vertical-cavity surface-emitting lasers (VCSELs) employing a Ga/sub 0.7/In/sub 0.3/N/sub 0.007/As/sub 0.993/-GaAs multiple-quantum-well (MQW) active layer grown directly on a GaAs-AlAs distributed Bragg reflector (DBR). Evidence for laser oscillation includes spectral linewidth narrowing, clamping of spontaneous emission, and a distinct increase in slope efficiency at threshold. By taking advantage of lateral growth rate nonuniformity, we obtained laser emission over an extremely broad 110-nm wavelength range, from 1.146-1.256 /spl mu/m. Equivalent threshold current density over this range was estimated at 3.3-10 kA/cm/sup 2/.     

Characterization of new FIR laser lines from CHD/sub 2/OH

In this work, we report new optically pumped far-infrared (FIR) laser lines from CHD/sub 2/OH. A waveguide CO/sub 2/ laser of wide tunability (290 MHz) was used as pump source, and a Fabry-Pe/spl acute/rot open cavity was used as a FIR laser resonator. Optoacoustic absorption spectra were used as a guide to search for new FIR laser lines. We could observe 15 new laser lines in the range from 116.4 to 401.4 /spl mu/m. The lines were characterized according to wavelength, relative polarization, relative intensity, and optimum working pressure. The transferred Lamb-dip technique was used to measure the frequency absorption transition both for the new and previously reported laser lines.     

Large nonlinear optical effect in an InGaAs/InAlAs multiquantum well waveguide

All-optical refractive nonlinearity in a passive InGaAs/InAlAs multiquantum well waveguide is evaluated for TE and TM modes at 1.55 mu m wavelength and room temperature. A quarter wavelength change in the optical path length is observed at an input pump light power of 6.5 mW for 1.47 mu m wavelength in a 960 mu m long device. Nonlinear refractive index n/sub 2/ is evaluated to be -1.2*10/sup 6/ and -0.5*10-6cm/sup 2//W for the TE and the TM modes, respectively.<>     

Two-step laterally tapered spot-size converter 1.55-/spl mu/m DFB laser diode having a high slope efficiency

We demonstrate a two-step lateral tapered 1.55-/spl mu/m spot-size converter distributed feedback laser diode (SSC DFB LD) having slope efficiencies as high as 0.457 and 0.319 mW/mA measured at 25 /spl deg/C and 85 /spl deg/C, respectively. The SSC DFB LD fabricated by using a nonselective grating process has a double core waveguide structure including a planar buried heterostructure type active waveguide and a ridge type passive waveguide. The fabricated SSC DFB LD operates at 1.553-/spl mu/m wavelength and shows a far-field pattern in horizontal and vertical directions of 7.3/spl deg/ and 11.6/spl deg/, respectively.     

Monolithic integration of an InGaAsP-InP MQW laser/waveguide using a twin-guide structure with a mode selection layer

We demonstrate a monolithically integrated 1.55-/spl mu/m wavelength InGaAsP-InP multiple-quantum-well (MQW) laser with a passive Y-branch waveguide in a vertical twin-waveguide structure. To reduce the sensitivity of the device performance characteristics to laser cavity length and variations in the layer structure, we introduce an In/sub 0.53/Ga/sub 0.47/As absorption, or "loss" layer. This layer eliminates the propagation of the even mode, while having minimal effect on the odd mode. The threshold current densities and differential efficiencies of the devices are unaffected by the loss layer. A record high coupling efficiency of 45% from the laser to the external passive waveguide is obtained.     

Wavelength trimming by photoabsorption-included disordering for multiple-wavelength distributed-feedback laser arrays

In this letter, we describe a simple method to adjust the oscillation wavelength of distributed-feedback (DFB) lasers after the device fabrication without using any external active tuning. The method utilizes a permanent change of refractive index in the quantum well active layer induced by external laser beam irradiation. We have demonstrated 0.36 nm adjustment in a 1.55-/spl mu/m ridge waveguide DFB laser.