Khurram Karim Qureshi

High-pressure and high-temperature characteristics of a Fabry–Perot interferometer based on photonic crystal fiber

A fiber-optic Fabry-Perot interferometer was constructed by splicing a short length of photonic crystal fiber to a standard single-mode fiber. The photonic crystal fiber functions as a Fabry-Perot cavity and serves as a direct sensing probe without any additional components. Its pressure and temperature responses in the range of 0-40 MPa and 25°C-700°C were experimentally studied. The proposed sensor is easy to fabricate, potentially low-cost, and compact in size, which makes it very attractive for high-pressure and high-temperature sensing applications.

All-optical bit-error monitoring system using cascaded inverted wavelength converter and optical NOR gate

A novel all-optical bit-error monitoring system is demonstrated by cascading two all-optical logic gates: an inverted wavelength converter and an optical NOR gate which are realized using injection-locked laser diodes operating at different thresholds. Real-time optical monitoring signal is generated which indicates the positions and duration of both bit and burst errors in 10-Gb/s nonreturn-to-zero signals.

Multiwavelength laser source using linear optical amplifier

We propose and demonstrate a high-performance multiwavelength ring laser based on a linear optical amplifier (LOA) for potential applications in dense wavelength-division-multiplexing communication systems. Experimental results indicate that the inhomogeneous gain medium provided by the LOA reduces the gain competition and leads to stable multiwavelength lasing. Thirty-eight wavelengths covering C+L-band with 0.8-nm channel spacing are generated at room temperature. Simultaneous tuning of multiwavelengths is demonstrated and a stability test shows a power fluctuation of less than 0.2 dB during a 3-h test.

Chromatic Dispersion Monitoring for DPSK Systems Using RF Power Spectrum

We have demonstrated a method for dispersion monitoring of differential phase-shift keying (DPSK) signals by measuring the power of its wide bandwidth radio frequency (RF) spectral components. In particular, the RF spectrum is found to increase with the increase of chromatic dispersion. The proposed method is investigated in detail both analytically and experimentally and results are in close agreement with each other.

Towards sensor array materials: can failure be delayed?

Abstract Further to prior development in enhancing structural health using smart materials, an innovative class of materials characterized by the ability to feel senses like humans, i.e. ‘nervous materials’, is discussed. Designed at all scales, these materials will enhance personnel and public safety, and secure greater reliability of products. Materials may fail suddenly, but any system wishes that failure is known in good time and delayed until safe conditions are reached. Nervous materials are expected to be the solution to this statement. This new class of materials is based on the novel concept of materials capable of feeling multiple structural and external stimuli, e.g. stress, force, pressure and temperature, while feeding information back to a controller for appropriate real-time action. The strain–stress state is developed in real time with the identified and characterized source of stimulus, with optimized time response to retrieve initial specified conditions, e.g. shape and strength. Sensors are volumetrically embedded and distributed, emulating the human nervous system. Immediate applications are in aircraft, cars, nuclear energy and robotics. Such materials will reduce maintenance costs, detect initial failures and delay them with self-healing. This article reviews the common aspects and challenges surrounding this new class of materials with types of sensors to be embedded seamlessly or inherently, including appropriate embedding manufacturing techniques with modeling and simulation methods.

Gain Control of Semiconductor Optical Amplifier Using a Bandpass Filter in a Feedback Loop

The authors present a simple configuration of a gain-clamped semiconductor optical amplifier (GC-SOA) based on automatic intensity control of a feedback light generated by amplified spontaneous emission, using a narrow bandwidth thin-film-tunable filter. Experimental results show that the proposed amplifier has good gain clamping characteristics and the feedback light dramatically reduces steady and transient gain variations. The feedback light operates satisfactorily with the channels add-drop frequency up to 20.9 kHz. We also examined the performance of the GC-SOA by employing the feedback light at different wavelengths.

Single-longitudinal-mode lanthanum-codoped bismuth-based erbium doped fiber ring laser

We propose and demonstrate a stable single-longitudinal-mode lanthanum-codoped bismuth oxide-based erbium doped fiber ring laser. The combination of a free-space thin-film filter and a Lyot filter enable single longitudinal mode efficiency.

Signed frequency offset measurement for direct detection DPSK system with a chromatic dispersion offset

We demonstrated a method for the measurement of signed frequency offset between optical source and delay interferometer (DI) for 10 Gb/s DPSK signals based on asynchronous delay-tap sampling technique with a chromatic dispersion (CD) offset. The demodulated DPSK signals show asymmetrical property and amplitude shoulder appears on the waveforms with frequency offset and a fixed CD offset together. The delay-tap sampling scatter plots also show the asymmetry related to the asymmetrical signal distortion. Our proposed method cannot only realize the measurement of the magnitude of frequency offset but also the polarity. The measurement range is from -2 GHz to +2 GHz and the sensitivity can reach ±100MHz. The simulation and experimental results are demonstrated and in good agreement.

All optical on-off switching using bismuth-based highly nonlinear fiber

We have demonstrated all-optical on-off switching at 10 Gbit/s using four-wave mixing in only 1.9 m of bismuth-based highly nonlinear fiber. The all-optical on-off switch has a fast response time and high ON/OFF switching ratio.

A broadly tunable fiber ring laser employing a gain-clamped semiconductor optical amplifier

A widely tunable fiber ring laser is demonstrated experimentally using a specially designed gain-clamped semiconductor optical amplifier (GC-SOA). The 3 dB bandwidth of the generated amplified spontaneous emission is increased by 10 nm using the GC-SOA. The lasing wavelength is continuously tunable in a range from 1522 nm to almost 1600 nm using a thin-film Fabry–Perot tunable filter. A side-mode-suppression ratio of greater than 55 dB is achieved over the entire tuning range.