We present our work on photonic crystal membrane devices exploiting Fano resonance between a line-defect waveguide and a side coupled nanocavity. Experimental demonstration of fast and compact all-optical switches for wavelength-conversion is reported. It is shown how the use of an asymmetric structure in combination with cavity-enhanced nonlinearity can be used to realize non-reciprocal transmission at ultra-low power and with large bandwidth. A novel type of laser structure, denoted a Fano laser, is discussed in which one of the mirrors is based on a Fano resonance. Finally, the design, fabrication and characterization of grating couplers for efficient light coupling in and out of the indium phosphide photonic crystal platform is discussed.
We experimentally demonstrated 10 GHz frequency comb spectral broadening in an AlGaAsOI nano-waveguide with the peak power of only several watts. The spectral broadened 10 GHz frequency comb has high optical signal to noise ratio (OSNR) at the output of the nano-waveguide. As far as we know, it is the first photonic chip based frequency comb, relying on spectral broadening of a 10 GHz mode-locked laser comb in an AlGaAsOI nano-waveguide, with a sufficient comb output power to support several hundred Tbit/s optical data.
This paper presents a new optical circuit that performs both pulse compression and frame synchronization and retiming.
Our design aims at directly multiplexing several 10G Ethernet data packets (frames) to a high-speed OTDM link. This
scheme is optically transparent and does not require clock recovery, resulting in a potentially very efficient solution. The
scheme uses a time-lens, implemented through a sinusoidally driven optical phase modulation, combined with a linear
dispersion element. As time-lenses are also used for pulse compression, we design the circuit also to perform pulse
compression, as well. The overall design is: (1) Pulses are converted from NRZ to RZ; (2) pulses are synchronized,
retimed and further compressed at the specially designed time-lens; and (3) with adequate optical delays, frames from
different input interfaces are added, with a simple optical coupler, completing the OTDM signal generation. We
demonstrate the effectiveness of the design by laboratory experiments.
A time- and wavelength-interleaved optical pulse source, which is based on spectral slicing and dispersion management, is proposed and experimentally demonstrated. The pulse source has a simple configuration, and both the repetition rate and the wavelength channels can be tuned easily.
A time- and wavelength-interleaved optical pulse source, which is based on spectral slicing and dispersion management,
is proposed and experimentally demonstrated. The pulse source has a simple configuration, and both the repetition rate
and the wavelength channels can be tuned easily.
Short locking and unlocking time is essepecially important in the packet clock recovery, as it determines the network
resource utilization. This paper presents a novel 10-GHz all-optical packet clock extractor with ultrafast locking and
unlocking time via self-phase modulation (SPM) effect of the semiconductor optical amplifier (SOA). Low finesse
Fabry-Perot (F-P) filter and a saturated SOA, in cascade, are used to directly extract the packet clock from the data
stream. An optical bandpass filter(OBPF) is used to filter out the red-shifted parts of the packet clock in order to reduce
the locking and unlocking time. We analytically investigate the impact of the locking and unlocking time thanks to the
self-gain modulation (SGM) effect and self-phase modulation(SPM) effect induced by the SOA, and demonstrate 10GHz
clock extraction with the establishing time of 200ps and vanishing time of 600ps experimentally.
We demonstrate a novel 40-Gb/s all-optical serial to parallel converter (AOSPC), which can convert 40-Gb/s serial
optical signals to 4-channel 10-Gb/s parallel optical signals. Moreover, based on the sequential multi-wavelength
conversion the AOSPC shows the regeneration ability.
A novel 10Gbit/s all-optical packet clock extractor, which comprises a Fabry-Perot (F-P) filter and a semiconductor
optical amplifier (SOA), is proposed in this paper. Low Finesse Fabry-Perot (F-P) filter was used to directly extract the
packet clock from the data packet stream, which ensures that the clock locks fast and vanishes quickly. The clock,
amplitude modulated as a result of low-Q filter, then goes into SOA to reduce the low-frequency amplitude noise. The
impact of F-P filter and SOA on the locking and unlocking time of the packet clock is theoretically analyzed. The result
shows that the locking time is reduced while the unlocking time is increased, due to the self-gain modulation (SGM)
effect. We demonstrate instantaneous 10.075GHz clock extraction experimentally with the establishing time of about 8
code-periods and vanishing time of about 22 code-periods.
We experimentally demonstrate a 4×10-Gb/s optical multicast scheme using a semiconductor optical amplifier (SOA)
and a single optical source, which produce a 10-GHz multi-wavelength pulse-trains used as the probe light of the SOA.
The multicast principle is based on the multi-wavelength conversion (MWC) by means of the interaction of both cross
gain modulation (XGM) and transient cross phase modulation (T-XPM) of the SOA. Because of the nonlinear
amplification of SOA, the 4 output copies are regenerated with respect to the input degraded signal. This scheme is very
simple and allows photonic integration.
We present a compact short pulses source, in which the pulses generated by large-signal directly modulated laser diode
are phase-modulated, and it can compress the pulse from 30ps to 5.3ps with 184fs timing jitter.
PMD vectors can be described by Stokes vectors pointing to the direction of slow PSP with a length equal to DGD. Measuring DOP is a way of obtaining DGD information and the direction of PSP can be characterized by scrambling at the transmitter. When totally polarized optical signals (DOP=1) transmit a distance, DOP decreases due to the influence of PMD. However, if the input SOP is aligned to the direction of the PSP, DOP of optical signals remains unchanged. Placing a scrambler at the transmitter, SOP of input signals covers Poincare sphere at a certain frequency. The effect of PMD on SOPs in different directions changes with transmission, and the output DOP is described and shown. SOPs of two extreme points in the main axis are just two PSPs. After one time scrambling, 3500 SOPs are distributed equally in the Poincare sphere. The DOP of all SOPs can be calculated under the condition that splitting ratio is 0.5, with two SOPs at maximum DOP being two PSPs and two SOPs at minimum DOP being the SOP. Since the whole information of first-order PMD vector can be acquired, feed-forward PMD compensation will be feasible and fast.
A phase-modulator-based optoelectronic oscillator (OEO) is utilized to implement a self-starting optical pulse and microwave signal source. This system is able to simultaneously generate a 9.8-GHz optical pulse stream with 141-fs (over 100 Hz to 1 MHz) timing jitter and 6.5-ps pulse width, along with a high spectral purity electrical signal that is locked to the repetition rate of the optical pulses. The measured phase noise is −112 dBc/Hz at 10 kHz away from carrier, and the side modes are perfectly suppressed.
KEYWORDS: Dispersion, Microwave radiation, Telecommunications, Signal processing, Digital signal processing, Signal detection, Sensors, Transmitters, Fiber optic communications, Optical amplifiers
A feasible and cost-effective online chromatic dispersion (CD) monitoring scheme for high speed optical communication system is demonstrated in this paper. Based on the formerly verified theoretical model, the output electrical power of a specific frequency band is tested to reflect the residual chromatic dispersion online. Thus the microwave devices are selected to form the electrical power detecting circuit, which consists of a PIN photodiode, a microwave power filter and a power detector in tandem. In the experiments, frequency band center were chosen at 5 GHz for the 10 Gbit/s system and 12 GHz for the 40 Gbit/s system. Then the output voltage of the detector was processed and converted to digital signal and the signal was processed to obtain the amount of the chromatic dispersion of the tested systems. For the 40 Gbit/s system, the maximum detectable chromatic dispersion was around 130-ps/nm and a resolution of 5-ps/nm/db was achieved at the chosen frequency band centered at 12 GHz. Performance of the microwave devices and comparison of the experimental results at different frequency bands are also discussed, which verified that the chosen center frequency was suitable for detection of CD in optical communication system beyong 10 Gbit/s speed.
KEYWORDS: Polarization, Feedback signals, Polarization control, Signal processing, Polarimetry, Detection and tracking algorithms, Beam splitters, Signal detection, Control systems, Optoelectronics
Polarization mode dispersion compensation for fiber communications systems of higher rate is of great importance. Key elements in polarization mode dispersion compensation are polarization controllers and differential group delay lines. Usual ways of compensation for PMD is to control both elements with the same feedback signals, which are processed with an algorithm for control of these elements. Algorithms should be designed for both the controller and delay line with an input signal and give out controlling signals for both elements alternatively. This may cause aimless action of DGD line or polarization state controlling. This paper gives a method of controlling these compensating elements, the polarization controller and the variable differential delay line, with different feedback signals, i.e., to control compensation elements for PMD Compensation separately. It uses Stocks parameters to control polarization controller and uses degree of polarization (DOP) to a variable delay line.
KEYWORDS: Polarization, Digital signal processing, Polarimetry, Telecommunications, Eye, Gaussian pulse, Process control, Optoelectronics, Fiber optic communications, Signal processing
We firstly derive the mathematical expression of degree of polarization (DOP) for Gauss pulse sequence, then analysis theoretically the relationship between DOP and differential group delay (DGD). The relevant experiments well demonstrate the relationship of DOP-DGD. We get the conclusions that the DOP-DGD curve is independent of fibre dispersion, line chip, and bit rate, and are affected by the width of optical spectrum and splitting ratio. Based on the theory, we successfully complete an automatic PMD compensation system for first-order PMD, which can compensate PMD in the optical link in real-time. The response time of compensation system can reach several milliseconds.
Based on the assumption of a quasi-monochromatic wave for light in fibres and 2□2 coherency matrix, a relationship of DO P with several parameters as well as DGD is derived from the common definition of DOP. A normalized coherent coefficient, showing the degree of correlation of optical signals in both principal states of polarization (PSPs), is derived theoretically. The value of this parameter indicates directly the degree of polarization of optical signals within the communications fibers. The correlation is also the straightforward express of differential group delay between two PSPs. With a pulse shape of Gaussian, we give a useful expression of DOP with power splitting ratio and differential group delay. Two curves of calculations are also given. When DGD becomes bigger, the coherent coefficient is smaller, meaning that the DOP is lower. DOP is one of feedback control signals for dynamic PMD compensation.
Theoretical calculations are made on the basis of relationship between electrical power and differential group delay (DGD). Curves are given representing the change of electrical power with DGD, central frequency of electrical signal and power ratio γ between principal states of polarization (PSPs). Experimental results confirming the theoretical calculations are also presented for voltage V changing with DGD. Factors affecting the feedback signals are proposed and means are given to make the fluctuations smaller. Eye patterns show the effectiveness of a PMD compensation prototype for a 10Gbit/s pseudo random sequence. Receiver sensitivity under 3 different bit error rates are also measured using BER measuring equipment. Comparisons of results under different conditions are also made, confirming the results and deterioration caused by the simulator is well compensated for by using the compensation system.
This paper presents a method of splitting signals from fast and slow axes of polarization maintaining fibers by using a polarization splitter. The new scheme includes a turning connector and a polarization splitter. The polarization splitter will split signals from a fiber and give two separated outputs. It gives some theoretical calculations and the relations between the turning angle and output power from the splitter. It also analyzes the relationship of electrical power spectrum versus differential group delay and relative angles between the axis of a fiber and direction of a polarization splitter. Preliminary experiments are also given in this paper. The scheme has a great potential of becoming an effective method of solving polarization mode dispersion (PMD) problem.
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