Er3+Ylif4 Continuous Wave Cascade Laser Operation At 1620 And 2810 Nm At Room-Temperature

For the first time cw, cascade lasing was demonstrated in 1% Er doped yttrium lithium fluoride (YLF) at room temperature at both 1620 and 2810 nm. In addition, cw lasing in Er[1%]:YLF at 1640 nm and in Er[5%]:YLF at 2810 nm at room temperature is reported for the first time in material of such low concentration

Wavelength tuning of fiber lasers using multimode interference effects

We report on a novel scheme to fabricate a simple, cheap, and compact tunable fiber laser. The tuning is realized by splicing a piece of single-mode fiber to one end of an active double-clad fiber, while the other end of the single-mode fiber is spliced to a 15 mm long section of 105/125 multimode fiber. The fluorescence signal entering into the multimode fiber will be reproduced as single images at periodic intervals along the propagation direction of the fiber. The length of the multimode fiber is chosen to be slightly shorter than the first re-imaging point, such that the signal coming out from the single mode fiber is obtained in free space, where a broadband mirror retroreflects the fluorescence signal. Since the position of the re-imaging point is wavelength dependent, different wavelengths will be imaged at different positions. Therefore, wavelength tuning is easily obtained by adjusting the distance between the broadband mirror and the multimode fiber facet end. Using this principle, the tunable fiber laser revealed a tunability of 8 nm, ranging from 1088-1097 nm, and an output power of 500 mW. The simplicity of the setup makes this a very cost-effective tunable fiber laser

Widely tunable erbium-doped fiber laser based on multimode interference effect

A widely tunable erbium-doped all-fiber laser has been demonstrated. The tunable mechanism is based on a novel tunable filter using multimode interference effects (MMI). The tunable MMI filter was applied to fabricate a tunable erbium-doped fiber laser via a standard ring cavity. A tuning range of 60 nm was obtained, ranging from 1549 nm to 1609 nm, with a signal to noise ratio of 40 dB. The tunable MMI filter mechanism is very simple and inexpensive, but also quite efficient as a wavelength tunable filter

2 × 2 Quantum Dot Based Switching Device Employing Multimode Interference Effects

An integrated 2 × 2 multimode interference switching device was fabricated with InAs/In 0.15Ga 0.85As quantum dots as the active medium. The device, when probed with a 1.31 μm wavelength laser beam, showed similar responses for TE and TM polarization with initial power splitting ratios of 1:29 (TE) and 1:52 (TM) that were continuously adjustable to 49:1 (TE) and 38:1 (TM) when a change in current of 24 mA was applied through one of the electrodes. This is equivalent to achieving channel-to-channel crosstalk values of better than -15 dB for both polarizations. A 50:50 split ratio was reached at a current of 17 mA. We also present the preliminary results from an integrated variable power splitter that is based on a half-length multimode interference structure. ©2009 SPIE

Enhanced Control Over Selective-Area Intermixing Of In 0.15Ga0.85As/Gaas Quantum Dots Through Post-Growth Exposure To Radio-Frequency Plasma

Post-growth treatment with a low pressure, CF4-plasma is demonstrated to reliably inhibit the interdiffusion of In and Ga atoms in In0.15Ga0.85As/GaAs self-assembled quantum dot wafer structures subjected to rapid thermal annealing temperatures between 700 °C and 800 °C for a duration of 20 s. Comparative studies of the effects of rapid thermal annealing were made on plasma treated samples and samples that were capped with either 200 nm of plasma enhanced chemical vapor deposited SiO2 or 220 nm of thermally deposited TiO2 prior to plasma exposure, as well as to uncapped, untreated control samples. Room-temperature photoluminescence spectra were acquired using a Ti-Sapphire laser operating at 742 nm as the excitation source. A bandgap differential of 84 meV (94 nm) was measured across a wafer sample annealed at 775 °C, when contrasting sections that were uncapped and treated with the CF4-plasma versus sections that were annealed without any treatment to the surface. This was comparable to a sample that was capped with the TiO2 film, which produced a 73.5 meV (82 nm) variance from the raw, annealed-only sample. © 2010 Elsevier B.V. All rights reserved

Quasi-CW self-guided optical beams in GaAs-AlGaAs double heterostructure slab waveguides

Self-guiding of an optical beam at energies close to and below the bandgap has been demonstrated in an active semiconductor optical amplifier under quasi CW conditions with a laser intensity of ∼ 1.1 MW/cm2. A second beam at a 60nm longer wavelength was guided and steered by the self-guided beam

Reconfigurable 1×4 Inp-Based Optical Switch

An integrated 1×4 InP-based optical switch is reported. The device is quite simple and full device operation is achieved by injecting electrical currents to two electrodes. Since the operation of the switch relies on current spreading, using the carrier-induced refractive index change in InGaAsP multiple quantum wells, an area-selective zinc in-diffusion process is used to regulate the current spreading and optimize device performance. As a result, the fabricated 1×4 switch exhibits a -14 dB crosstalk between channels over a wavelength range of 30 nm, while maintaining low electrical power consumption and allowing the switch to be operated uncooled and under d.c. current conditions. © 2007 Elsevier Ltd. All rights reserved

Tunable Multimode Interference Devices

A tunable multimode interference (MMI) coupler that operates by modifying the phase of the multiple images that are formed around the midpoint of the MMI section is demonstrated. The phase change is achieved by current injection, and therefore minimizing current spreading is crucial for optimal operation. A zinc in-diffusion process has been implemented to selectively define p-i-n regions and effectively regulate the current spreading by controlling the depth of the zinc doping. Using this process a tunable 3-dB MMI coupler has been fabricated. Our initial results show that the device can be easily tuned all the way from a 90:10 to a 30:70 splitting ratio of the optical power transmitted through the two output ports. We believe that further improvement on the device fabrication will lead to a more symmetric tuning response of the device. Nevertheless, the initial results are very encouraging since, to our knowledge, this degree of tuning has never been experimentally demonstrated in similar MMI devices. Furthermore, this device processing technique can easily be applied to a wide variety of semiconductor photonic switches that operate on MMI effects

Time-domain depolarization of waves retroreflected from dense colloidal media

We report on depolarization measurements of femtosecond pulses retroreflected from dense suspensions of silica microspheres with solid loads increasing from 5% to 54%. Backscattered pulse shapes compare well with predictions of the diffusion theory for all volume fractions, and the inferred values of the transport mean free path agree with independent measurements of enhanced backscattering. The measured degree of polarization decays exponentially with temporal rates that scale with the solid load. It is newly found that, for all solid loads, depolarization sets in for path lengths longer than approximately five transport mean free paths. © 1997 Optical Society of America

An Integrated 1x3 InP Photonic Switch

An integrated 1×3 optical switch that operates using the principle of carrier-induced refractive index change in InGaAsP multiple quantum wells is demonstrated. The device is very simple, only requiring currents to be applied to two electrodes for complete operational control. An area-selective zinc in-diffusion process is used to channel the currents into the multiple quantum wells, thereby enhancing the efficiency of the carrier-induced effects. This results in a low electrical power consumption, allowing the switch to be operated uncooled and under d.c. current conditions. The crosstalk between channels is better than -17 dB over a range of 50 nm centered at 1565 nm. © 2006 IEEE