Patrick LiKamWa

Fiber-optic sensor for liquid level measurement

A novel (to the best of our knowledge) liquid level sensor based on multimode interference (MMI) effects is proposed and demonstrated. By using a multimode fiber (MMF) without cladding, known as no-core fiber, liquids around the MMF modify the self-imaging properties of the MMI device and the liquid level can be detected. We show that the sensor exhibits a highly linear response with the sensing range and multiplexed operations easily controlled by just modifying the length of the no-core fiber. At the same time, we can measure the refractive index of the liquid based on the maximum peak wavelength shift. We can also use the sensor for continuous and discrete liquid level sensing applications, thus providing a liquid level sensor that is inexpensive with a very simple fabrication process.

Tunable multimode-interference bandpass fiber filter

We report on a wavelength-tunable filter based on multimode interference (MMI) effects. A typical MMI filter consists of a multimode fiber (MMF) spliced between two single-mode fibers (SMF). The peak wavelength response of the filter exhibits a linear dependence when the length of the MMF is modified. Therefore a capillary tube filled with refractive-index-matching liquid is used to effectively increase the length of the MMF, and thus wavelength tuning is achieved. Using this filter a ring-based tunable erbium-doped fiber laser is demonstrated with a tunability of 30 nm, covering the full C-band.

Multicore fiber sensor for high-temperature applications up to 1000°C

A novel high temperature sensor based on customized multicore fiber (MCF) is proposed and experimentally demonstrated. The sensor consists of a short, few-centimeter-long segment of MCF spliced between two standard single-mode fibers. Due to interference effects, the transmission spectrum through this fiber chain features sharp and deep notches. Exposing the MCF segment to increasing temperatures of up to 1000°C results in a shift of the transmission notches toward longer wavelengths with a slope of approximately 29  pm/°C at lower temperatures and 52  pm/°C at higher temperatures, enabling temperature measurements with high sensitivity and accuracy. Due to its compact size and mechanical rigidity, the MCF sensor can be subjected to harsh environments. The fabrication of the MCF sensor is straightforward and reproducible, making it an inexpensive fiber device.

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.

Generation of 150-fs tunable pulses in Cr:LiSrAlF6.

We report ultrashort-pulse generation in a Cr:LiSrAlF6 solid-state laser. The 15-mm crystal was pumped by 1 W of red light from a cw krypton laser and actively mode locked at an 82-MHz repetition frequency using an acousto-optic modulator. Wavelength tuning was demonstrated over the range 800–880 nm, limited by the bandwidth of the optical components. By including intracavity dispersion compensation, pulse widths of 150 fs were obtained with evidence that self-phase modulation contributes to spectral broadening and pulse shortening.

130 PS RECOVERY OF ALL-OPTICAL SWITCHING IN A GAAS MULTIQUANTUM WELL DIRECTIONAL COUPLER

A significantly improved recovery time of 130 ps has been achieved in an all‐optical zero‐gap directional coupler containing multiple quantum wells. The mechanism for the all‐optical switching is due to free‐carrier induced refractive nonlinearities at near‐band‐gap resonant frequencies. The large reduction in the switch recovery time was obtained by the application of an external dc bias which sweeps out the carriers from the quantum wells. From our experimental results on the laser pulse width limited switch‐up time of 2 ps, we deduce that the contribution of self‐electro‐optic effect nonlinearity is negligible in this case.

180-GHz clock recovery using a multisection gain-coupled distributed feedback laser

All-optical clock recovery from 180-Gb/s data streams has been demonstrated using a self-pulsing multisection gain-coupled distributed feedback laser. The laser produces self-pulsations with a tuning range of more than 230 GHz. The recovered clock has a jitter of less than 410 fs over a dynamic range of 7 dB.

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.

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.

Self-mode-locked Cr3+:LiCaAlF6 laser.

A cw-pumped Cr3+:LiCaAlF6 laser has been configured to produce chirp-free, self-mode-locked pulses of 170-fs duration. The prism-dispersion-compensated cavity contained no active or passive mode-locking device. Mode locking was accomplished through self-focusing in the LiCaAlF6 crystal with 2.5 W of red light from a cw krypton laser. Rocking of the output coupler initiated the ultrashort-pulse formation.