We demonstrate optical signal amplification in a solid-state dye-doped polymer with a rib waveguide structure. The device consists of a 1μm x 120μm poly(methyl methacrylate) (PMMA) waveguide, doped with 1% by weight Rhodamine 640 dye, spin coated onto a silica substrate. A 625nm pulsed signal and a co-linear 575nm pump are facet coupled into the waveguide and optical amplification of the signal is demonstrated.
Depending on the signal intensity, a maximum internal gain in the 21-26dB range at 625nm is achieved using a 1.2cm long waveguide. The device exhibits a promising signal-to-noise ratio in the 9-16dB range and has the potential for tuning in a 40-50nm wavelength window with the same dye, and throughout the visible spectrum using other dyes. The wavelength operating range of this device is also analyzed.
We therefore present a compact, easy to fabricate, high gain block suitable for use in conjunction with plastic optical fibers, which have a low-loss window at around 640nm. Since most of the optical amplification takes place in a short region (<10μm), an even more compact device geometry can be envisaged using a shorter waveguide.
We describe a photonic bandgap polarization selector based on a photonic crystal placed at junction of two 90° intersecting waveguides to form an ultra-compact device. The photonic crystal consists of 7 layers of a triangular lattice with a radius to pitch ratio (r/a) of 0.24 and a lattice constant of 0.386μm. The PBG is orientated so that the light is incident and collected at 45° to the Γ-K crystallographic direction. Modeling of the PBG shows that TM polarized light is strongly reflected while TE light passes largely into the crystal. Measurements of the fibre-to-fibre transmitted power of the device for each polarization show that the TM collected power is ~6dB higher than the TE light for equal input polarization powers. Further evidence of the strong reflection of TM light comes from an equivalent sample without a 2-D lattice at the waveguide junction. In these samples, no TM light is detected at the output. Furthermore, by taking into account the TE and TM gains within the active waveguides, the TM to TE polarization selection of the PBG is estimated to be up to 22dB.
A novel low cost, non-contact optical vibration sensor requiring only a single optoelectronic component has been developed. It consists of a CW semiconductor laser operating with external optical feedback. The laser beam reflected from a target generates a series of lasing modes set by the external cavity length. Beating of the modes produces an RF signal and this signal is detected as a variation in the junction voltage. Any change in the external cavity length induces corresponding beat frequency variations in the RF signal, which are transformed into amplitude variations using a simple edge-detection filter system. Using this sensor, low amplitude vibrations have been measured at frequencies of up to 600 Hz. Successful results have been achieved with target reflectivities lower than 5%. When calibrated, the sensor demonstrates satisfactory output for submicron vibration amplitudes. Maximum amplitudes of 1 mm have been measured with an accuracy of 0.2%.