Three-photon-excited upconversion luminescence of Ce3+: YAP crystal by femtosecond laser irradiation

Infrared to ultraviolet and visible upconversion luminescence was demonstrated in trivalent cerium doped YAlO3 crystal (Ce3+: YAP) under focused infrared femtosecond laser irradiation. The fluorescence spectra show that the upconverted luminescence comes from the 5d-4f transitions of trivalent cerium ions. The dependence of luminescence intensity of trivalent cerium on infrared pumping power reveals that the conversion of infrared radiation is dominated by three-photon excitation process. It is suggested that the simultaneous absorption of three infrared photons pumps the Ce3+ ion into upper 5d level, which quickly nonradiatively relax to lowest 5d level. Thereafter, the ions radiatively return to the ground states, leading to the characteristic emission of Ce3+. (c) 2005 Optical Society of America.

Photoreduction of Ag+ in aluminoborate glasses induced by irradiation of a femtosecond laser

We report on photoreduction of Ag+ in aluminoborate glasses induced by irradiation of a femtosecond laser. Novel fluorescence was observed in the femtosecond laser irradiated glass when excited by a 365 nm ultraviolet lamp. Optical absorption, emission, and electron spin resonance spectra of the glass samples demonstrated that after the laser irradiation, portions of silver ions near the focused part of the laser beam inside the glass were reduced to silver atoms, which resulted in the formation of the characteristic fluorescence. The observed phenomenon may have promising applications in the fabrication of functional optical devices.

High quantum fluorescence yield of Er3+ at 1.5 mu m in an Yb3+, Ce3+-codoped CaF2 crystal

For the first time, a quaternary doping system of Er3+, Yb3+, Ce3+, Na+:CaF2 single crystal was demonstrated to have high fluorescence yield in the eye-safe 1.5 mu m region under 980 nm laser diode pumping, with relatively broad and flat gain curves. A simplified model was established to illustrate the effect of Ce3+ on the branching ratio for the Er3+4I11/2 -> I-4(13/2) transition. With 0.2-at.% Er3+ and 2.0-at.% Ce3+ in the quaternary-doped CaF2 crystal, the branching ratio was estimated to be improved more than 40 times by the deactivating effect of Ce3+ on the Er3+ 4I11/2 level. The quaternary-doped CaF2, system shows great potential to achieve high laser performance in the 1.5 mu m region. (c) 2006 Elsevier B.V. All rights reserved.

Judd-Ofelt analysis of spectra and experimental evaluation of laser performance of Tm3+ doped Lu2SiO5 crystal

This paper reports that the TM3+:Lu2SiO5 (Tm:LSO) crystal is grown by Czochralski technique. The room-temperature absorption spectra of Tm:LSO crystal are measured on a b-cut sample with 4 at.% thulium. According to the obtained Judd-Ofelt intensity parameters Omega(2)=9.3155 x 10(-20) cm(2), Omega(4)=8.4103 x 10(-20) cm(2), Omega(6)=1.5908 x 10(-20) cm(2), the fluorescence lifetime is calculated to be 2.03 ms for F-3(4) -> H-3(6) transition, and the integrated emission cross section is 5.81 x 10(-18) cm(2). Room-temperature laser action near 2 mu m under diode pumping is experimentally evaluated in Tm:LSO. An optical-optical conversion efficiency of 9.1% and a slope efficiency of 16.2% are obtained with continuous-wave maximum output power of 0.67 W. The emission wavelengths of Tm:LSO laser are centred around 2.06 mu m with spectral bandwidth of similar to 13.6 nm.

Judd-Oflet analysis of spectrum and laser performance of Ho:YAP crystal end-pumped by 1.91-mu m Tm:YLF laser

The Ho:YAP crystal is grown by the Czochralski technique. The room-temperature polarized absorption spectra of Ho:YAP crystal was measured on a c-cut sample with 1 at% holmium. According to the obtained Judd-Ofelt intensity parameters Omega(2) = 1.42 x 10(-20) cm(2), Omega(4) = 2.92 x 10(-20) cm(2), and Omega(6) = 1.71 x 10(-20) cm(2), this paper calculated the fluorescence lifetime to be 6 ms for I-5(7) -> I-5(8) transition, and the integrated emission cross section to be 2.24 x 10(-18) cm(2). It investigates the room-temperature Ho:YAP laser end-pumped by a 1.91-mu m Tm:YLF laser. The maximum output power was 4.1 W when the incident 1.91-mu m pump power was 14.4W. The slope efficiency is 40.8%, corresponding to an optical-to-optical conversion efficiency of 28.4%. The Ho:YAP output wavelength was centred at 2118 nm with full width at half maximum of about 0.8 nm.

A Single-Fundamental-Mode Photonic Crystal Vertical Cavity Surface Emitting Laser

Single-fundamental-mode photonic crystal (PhC) vertical cavity surface emitting lasers (VCSEL) are produced and their single-fundamental-mode performances are investigated and demonstrated. A two-dimensional PhC with single-point-defect structure is fabricated using UV photolithography and inductive coupled plasma reactive ion etching on the surface of the VCSEL's top distributed Bragg-reflector. The PhC VCSEL maintains single-fundamental-mode operating with output power 1.7 mW and threshold current 2.5 mA. The full width half maximum of the lasing spectrum is less than 0.1 nm, the far field divergence angle is less than 10 degrees and the side mode suppression ratio is over 35 dB. The device characteristics are analyzed based on the effective index model of the photonic crystal fiber. The experimental results agree well with the theoretical expectation.

Application of sampled grating to control the lasing wavelength in complex-coupled DFB laser

This paper reports that the complex-coupled distributed feedback laser with the sampled grating has been designed and fabricated. The +1st order reflection of the sampled grating is utilized for laser single mode operation, which is 1.5387 mu m in the experiment. The typical threshold current of the device is 30 mA, and the optical output power is about 10 mW at the injection current of 100 mA.

40-Gb/s Low Chirp Electroabsorption Modulator Integrated With DFB Laser

A 40-Gb/s monolithically integrated transmitter containing an InGaAsP multiple-quantum-well electroabsorption modulator (EAM) with lumped electrode and a distributed-feedback semiconductor laser is demonstrated. Superior characteristics are exhibited for the device, such as low threshold current of 20 mA, over 40-dB sidemode suppression ratio at 1550 nm, and more than 30-dB dc extinction ratio when coupled into a single-mode fiber. By adopting a deep ridge waveguide and planar electrode structures combined with buried benzocyclobutene, the capacitance of the EAM is reduced to 0.18 pF and the small-signal modulation bandwidth exceeds 33 GHz. Negative chirp operation is also realized when the bias voltage is beyond 1.6 V.

Fabrication and performance of an index-coupled DFB laser with sampled grating

An index-coupled DFB laser with a sampled grating has been designed and fabricated. The key concept of the approaches is to utilize the +1st-order reflection of the sampled grating for laser operation, and use a conventional holographic exposure combined with the usual photolithography to form the sampled grating. The typical threshold current of the sampled grating DFB laser is 25 mA, and the optical output is about 10 mW at the injected current of 100 mA. The lasing wavelength of the device is 1.5314 mu m, which is the +1st-order peak of the sampled grating.

Control of the lasing wavelength by a sampled grating in a complex-coupled DFB laser

The lasing wavelength of a complex-coupled DFB laser is controlled by a sampled grating. The key concepts of the approach are to utilize the -1st order (negative first order) reflection of a sampled grating for laser single mode operation, and use conventional holographic exposure combined with the usual photolithography to fabricate the sampled grating. The typical threshold current of the sampled grating based DFB laser is 32 mA, and the optical output is about 10 mW at an injected current of 100 mA. The lasing wavelength of the device is 1.5356 mu m, which is the -1st order wavelength of the sampled grating.

Two-photon excited fluorescence from CdSe quantum dots on SiN photonic crystals

Two-photon excited fluorescence from CdSe quantum dots on a two-dimensional SiN photonic crystal surface is investigated by using a femtosecond laser. By using a photonic crystal, a 90-fold enhancement in the two-photon excited fluorescence in the vertical direction is achieved. This is the highest enhancement achieved so far in the two-photon excited fluorescence in the vertical direction. The mechanism of the enhancement for two-photon excited fluorescence from quantum dots on photonic crystals is analyzed.

Diode-pumped self-starting mode-locked Nd : YVO4 laser with semiconductor saturable absorber output coupler

By using a semiconductor saturable-absorber output coupler as a mode-locking device, we experimentally realized the operation of a diode-pumped passively mode-locked Nd:YVO4 laser. Stable laser pulses with duration of 2.3 ps were generated at the output power of about 1 W. With increasing the pump power to 9 W, the maximum mode-locked power of 1.7 W was obtained, which corresponds to a slope conversion efficiency of 44% and optical-to-optical conversion efficiency of 19%.

MOVPE growth of grade-strained bulk InGaAs/InP for broad-band optoelectronic device applications

In this paper we present a novel growth of grade-strained bulk InGaAs/InP by linearly changing group-III TMGa source flow during low-pressure metalorganic vapor-phase epitaxy (LP-MOVPE). The high-resolution X-ray diffraction (HRXRD) measurements showed that much different strain was simultaneously introduced into the fabricated bulk InGaAs/InP by utilizing this novel growth method. We experimentally demonstrated the utility and simplicity of the growth method by fabricating common laser diodes. As a first step, under the injection current of 100 mA, a more flat gain curve which has a spectral full-width at half-maximum (FWHM) of about 120 nm was achieved by using the presented growth technique. Our experimental results show that the simple and new growth method is very suitable for fabricating broad-band semiconductor optoelectronic devices. (C) 2003 Elsevier B.V. All rights reserved.

10 Gbit s(-1) electroabsorption-modulated laser light-source module using selective area MOVPE

A distributed-feedback (DFB) laser and a high-speed electroabsorption (EA) modulator are integrated, on the basis of the selective area MOVPE growth (SAG) technique and the ridge waveguide structure, for a 10 Gbit s(-1) optical transmission system. The integrated DFB laser/EA modulator device is packaged in a compact module with a 20% optical coupling efficiency to the single-mode fibre. The typical threshold current is 15 mA, and the side-mode suppression ratio is over 40 dB with the single-mode operation at 1550 nm. The module exhibits 1.2 mW fibre output power at a laser gain current of 70 mA and a modulator bias voltage of 0 V. The 3 dB bandwidth is 12 GHz. A dynamic extinction ratio of over 10 dB has been successfully achieved under 10 Gbit s(-1) non-return to zero (NRZ) operation, and a clearly open eye diagram is obtained.

8 mu m strain-compensated quantum cascade laser operating at room temperature

We report on the material growth and device performance characterization of a strain-compensated In0.54Ga0.46As/In0.51Al0.49As quantum cascade laser at lambda similar to 8 mu m. For 2 mu s pulse at a 5 kHz repetition rate, laser action is achieved up to room temperature (30 degrees C). The tuning coefficient d lambda/dT is 1.37 nm K-1 between 83 K and 163 K and 0.60 nm K-1 in the range from 183 K to 303 K. The peak output power is reported to be similar to 11.3 mW per facet at 293 K and the corresponding threshold current density is 5.69 kA cm(-2).