Eric Donkor

Silicon-Layer Guided-Mode Resonance Polarizer With 40-nm Bandwidth

Fabrication and characterization of a guided-mode resonance-based polarizer is presented. This polarizer is made by electron-beam patterning a single layer of amorphous silicon on a glass substrate. The fabricated device has high and low transmittance for transverse-electric and transverse-magnetic polarizations, respectively, over a ~ 40-nm wavelength range for normally incident light. Its experimental extinction ratio is ~ 97:1 at a central wavelength of 1510 nm.

Experimental multiuser quantum key distribution network using a wavelength-addressed bus architecture

A six-user quantum key distribution network implemented on a bus topology is experimentally demonstrated. The network employs the BB84 protocol to transmit cryptographic keys encoded unto the phase states of highly attenuated laser light to distances of up to 31 km in a standard telecommunication-grade fiber. Each user on the network is assigned a unique wavelength for communication with the network server at a time. The measured quantum bit error rate and sifted key rate compare favorably with theoretical results

All-optical Lyot-filter-assisted flip-flop operation using a semiconductor optical amplifier

All-optical flip-flop operation using external optical control is demonstrated in a single semiconductor optical amplifier (SOA)-based fiber ring laser with an intracavity Lyot filter. Its operation is based on the principle of cross-gain saturation in the SOA. A unique feature of this flip-flop is its ability to be set and reset at multiple wavelength pairs of an auxiliary continuous wave control light that is injected into the fiber ring cavity; this, together with the wide wavelength tunability of the Lyot filter makes the flip-flop potentially useful in wavelength-division multiplexing applications. Bistable output at 1571 nm with a contrast ratio of 20 dB between the two output power states of the flip-flop using -3 dBm power of the external optical control is demonstrated

Optoelectronics Encoder for a 12-bit 1.28-GSPS Analog-to-Digital Converter

In this letter, a novel 1.28-gigasamples/s (GSPS) 12-bit optoelectronics analog-to-digital converter (ADC) system is presented. The ADC architecture encodes and multiplexes four 320-megasamples/s 12-bit time-interleaved quantized data into an aggregated 1.28-GSPS 12-bit digital signal in real time. All clock signals at frequencies of 1.28 GHz, and 640 and 320 MHz are generated from a single 320-MHz femtosecond laser source, thereby eliminating the need for external synchronization and control signals. A spurious-free dynamic range of value 80.6 dB, signal-to-noise and distortion ratio of value 54.33 dB, full-scale and zero-scale offset errors of value 2 least significant bits, and an effective number of bits of value 8.8 bits were all measured for the system.

Demonstration of a Self-Synchronized Polyphase Sampling and Demultiplexing Scheme for Radio-Frequency Analog Signals

A novel self-synchronizing optoelectronics polyphase scheme for sampling and demultiplexing radio-frequency (RF) signals is demonstrated. One unique feature of this approach is that the optically sampled RF signal always remains in the electrical domain and thus eliminates the need for electrical-to-optical and back to electrical conversions. Furthermore, the simplicity and ease of construction of the scheme readily allows it to be scaled to obtain high sampling rates. As a proof of concept, a 100-MHz RF electrical signal sampled at the rate of 1.28 GS/s and then demultiplexed into four 320-MHz signals was experimentally demonstrated.

Bit-Resolution Improvement of an Optically Sampled Time-Interleaved Analog-to-Digital Converter Based on Data Averaging

In this paper, we present an experimental method demonstrating an improvement in the resolution of optically sampled time-interleaved analog-to-digital converters (ADCs) by applying a data averaging technique. We implemented two experiments for oversampling four times the bandwidth of an analog input signal using a multichannel time-interleaved arrangement. The sampling rate for each experiment was 2.08 gigasamples per second. In the first experiment, the optically sampled signal of each channel is digitized by a single ADC, whereas in the second, the signal is simultaneously digitized by four ADCs, and thereafter, the four digitized samples are averaged. A 20-dBm white-noise signal was superimposed on the input analog signal to test the implemented ADC systems. An improvement in the signal-to-noise-and-distortion ratio from 55.58 to 61.44 dB was achieved with averaging. Likewise, an improvement in the effective number of bits from 8.94 to 9.91 was achieved with averaging.

Terahertz Optical Frequency Comb Generation by Spectral Filtering of Broadband Spontaneous Amplified Emissions From a Semiconductor Optical Amplifier

In this paper, we describe a fiber-optics-based system for the generation of optical frequency comb using amplified spontaneous emissions from a semiconductor optical amplifier (SOA) as signal source. The continuous-wave (CW) spectrum from the SOA ranges from 1480 nm to 1680 nm. A Solc-Sagnac birefringent interferometer filters the CW into a comb of discrete spectral lines with line spacing of 600 GHz, producing comb signals than span 182-230 THz.

Demonstration of a six-user quantum key distribution network on a bus architecture

A six-user quantum key distribution over a bus network spanning a total distance 30km of standard telecommunication-grade fiber is demonstrated. Each user on the network has one unique address wavelength channel for establishing secure quantum cryptographic keys with a central network server. The address wavelengths are all in the C-band region of between 1553 nm and 1557 nm, making the system compatible with present fiber-optic communication network infrastructures. The quantum bit error rate measurements made on the network agree favorably with theoretically calculated values.

A 2.5 Gb/s flash all-optical analog-to-digital converter

We present the design and demonstration of an 8-bit flash all-optical A/D converter whose attractive features include 1) direct optical sampling of the input RF signal, 2) optical quantization, 3) flash architecture allowing for post electronic signal processing, and 4) low-power consumption.

Passively Modelocked Laser With Tunable Pulse Repetition Frequency in a Semiconductor Optical Amplifier

We present the experimental demonstration of a pulse repetition frequency tunable passively mode-locked laser using semiconductor optical amplifier as the gain medium. The laser is designed for the 1550-nm telecommunication applications. The mode-locking mechanism is explained in terms of normal mode splitting of the continuous-wave spontaneous emission signal from the semiconductor optical amplifier. The splitting arises from the coupling between a quantum cavity, represented by the semiconductor gain medium, and an optical cavity comprised of a high-birefringence fiber in line with a Faraday mirror. Experimental results are presented for pulse repetition frequency tunability ranging between 93 and 1400 MHz, as well as for the pulse width which is measured to be 343 ps. These results are shown to compare favorably with theoretical calculations.