Low-cost PCB-integrated polymer waveguide sensor for gas detection

An optical waveguide sensor formed directly on low-cost PCB substrates is presented for the first time. The device integrates polymer waveguides functionalized with chemical dyes, photonic and electronic components and allows multiple-gas detection. © 2011 OSA.

First demonstration of two photon absorption in a semiconductor waveguide pumped by a diode laser

For the first time, lasers have been used to induce a fast all-optical nonresonant nonlinearity at wavelengths well beyond the band edge in a GaAs/GaAlAs multiquantum well waveguide. Using a Q-switched diode laser, which gave optical pulses of 3.5 ps duration and 7 W peak power, an intensity-dependent transmission was recorded that was consistent with the presence of two photon absorption in the waveguide. The measured two photon absorption coefficient was 11 ± 2cm/GW.

Bias-dependent recovery time of all-optical resonant nonlinearity in InGaAsP/InGaAsP MQW waveguide

We have investigated a resonant refractive nonlinearity in a semiconductor waveguide by measuring intensity dependent phase shifts and bias-dependent recovery times. The measurements were performed on an optimized 750-μm-long AR coated buried heterostructure MQW p-i-n waveguide with a bandedge at 1.48 μm. Figure 1 shows the experimental arrangement. The mode-locked color center laser was tuned to 50 meV beyond the bandedge and 8 ps pulses with peak incident power up to 57 W were coupled into the waveguide. Some residual bandtail absorption remains at this wavelength and this is sufficient to cause carriers to be photogenerated and these give rise to a refractive nonlinearity, predominantly by plasma and bandfilling effects. A Fabry-Perot interferometer is used to measure the spectrum of the light which exits the waveguide. The nonlinearity within the guide causes self phase modulation (SPM) of the light and a study of the spectrum allows information to be recovered on the magnitude and recovery time of the nonlinear phase shift with a reasonable degree of accuracy. SPM spectra were recorded for a variety of pulse energies coupled into he unbiased waveguide. Figure 2 shows the resultant phase shift measured from the SPM spectra as a function of pulse energy. The relationship is a linear one, indicating that no saturation of the nonlinearity occurs for coupled pulse energies up to 230 pJ. A π phase shift, the minimum necessary for an all-optical switch, is obtained for a coupled pulse energy of 57 pJ while the maximum phase shift, 4 π, was measured for 230 pJ. The SPM spectra were highly asymmetric with pulse energy shifted to higher frequencies. Such spectra are characteristic of a slow, negative nonlinearity. This relatively slow speed is expected for the unbiased guide as the recovery time will be of the order of the recombination time of the photogenerated electrons, about 1 ns for InGaAsP material. In order to reduce the recovery time of the nonlinearity, it is necessary to remove the photogenerated carriers from the waveguide by a process other than recombination. One such technique is to apply a reverse bias to the waveguide in order to sweep the carriers out. Figure 3 shows the effect on the recovery time of the nonlinearity of applying reverse bias to the waveguide for 230 pJ coupled power. The recovery time was reduced from one much longer than the length of the pulse, estimated to be about 1 ns, at zero bias to 18 ± 3 ps for a bias voltage greater than -4 V. This compares with a value of 24 ps obtained in a bulk waveguide.

Low power all-optical switch in a passive InGaAsP multiple quantum well waveguide

We demonstrate the use of resonant bandfilling nonlinearity in an InGaAsP/InGaAsP Multiple Quantum Well (MQW) waveguide due to photogenerated carriers to obtain switching at pulse powers, which can readily be obtained from an erbium amplified diode laser source. In order to produce gating a polarisation rotation gate was used, which relies on an asymmetry in the nonlinear refraction on the principle axes of the waveguide.

Gain-switched dynamics of tapered waveguide bow-tie lasers

The use of tapered waveguide lasers and amplifiers for enhanced picosecond pulse generation has led to order-of-magnitude peak power and pulse energy improvements. Monolithic pulse generation schemes have so far relied on a double-tapered bow-tie structure. The modeling of tapered lasers has so far been limited to steady-state operation or has lacked experimental comparison. This paper considers both experimentally and theoretically the gain-switched performance of bow-tie lasers of various taper angles. The role of transverse-mode spatial hole burning in tapered waveguide lasers is thereby investigated.

Beam propagation modelling of tapered waveguide lasers

A dynamic beam propagation model allows design optimization of high power low divergence tapered waveguide lasers. The model is extended to include spatially-resolved temperature profiles and a temperature dependent gain. Using this model, design parameters such as the optimum facet reflectivity, taper angle, and waveguide dimension can be calculated for low far-field divergence and high continuous wave power.

Design of high power tapered waveguide semiconductor lasers

An advanced beam propagation model was developed to show that the far field narrows with good suppression of higher order modes for an appropriate temperature rise, without significant power penalty. To verify the accuracy of the model, the dependence of far field pattern on bias conditions were assessed both experimentally and theoretically, initially under pulsed conditions to reduce thermal effects. The results highlight the optimum taper angle and the role of local heating effects.