Current communication networks needs to keep up with the exponential growth of today’s internet traffic, and telecommunications industry is looking for radically new integrated photonics components for new generation optical networks. We at National Research Council (NRC) Canada have successfully developed nanostructure InAs/InP quantum dot (QD) coherence comb lasers (CCLs) around 1.55 m. Unlike uniform semiconductor layers in most telecommunication lasers, in these QD CCLs light is emitted and amplified by millions of semiconductor QDs less than 60 nm in diameter. Each QD acts like an isolated light source acting independently of its neighbours, and each QD emits light at its own unique wavelength. The end result is a QD CCL is more stable and has ultra-low timing jitter. But most importantly, a single QD CCL can simultaneously produce 50 or more separate laser beams at distinct wavelengths over the telecommunications C-band. Utilizing those unique properties we have put considerable effort well to design, grow and fabricate InAs/InP QD gain materials. After our integrated packaging and using electrical feedback-loop control systems, we have successfully demonstrated ultra-low intensity and phase noise, frequency-stabilized integrated QD CCLs with the repetition rates from 10 GHz to 100 GHz and the total output power up to 60 mW at room temperature. We have investigated their relative intensity noises, phase noises, RF beating signals and other performance of both filtered individual channel and the whole CCLs. Those highly phase-coherence comb lasers are the promising candidates for flexible bandwidth terabit coherent optical networks and signal processing applications.
The gain media of the quantum dot lasers consist of InAs QDs in an InGaAsP matrix on an InP substrate. The
quantum dot lasers have different free spacing ranges (FSRs) corresponding to Fabry-Pérot (F-P) cavity lengths. A
silicon ring resonator and a QD laser have been combined to form comb laser. The output characteristics of the
combined comb laser were investigated. The measured FSR was about 2.8nm and the extinction ratio was about
10(dB) when the FSR of the QD laser was about 0.4nm and the FSR of the ring resonator was about 0.47nm. The
experimental results show that the ring resonator had a strong control on the FSR and extinction ratio of the comb
Linewidth enhancement factor (LEF) of InAs/InP quantum dot (QD) multi-wavelength lasers (MWL) emitting at 1.53 μm
are investigated both above and below threshold. Above threshold, LEFs at three different wavelengths around the gain
peak by injection locking technique are obtained to be 1.63, 1.37 and 1.59, respectively. Then by Hakki-Paoli method LEF
is found to decrease with increased current and shows a value of less than 1 below threshold. These small LEF values have
confirmed our InAs/InP QDs are perfect gain materials for laser devices around 1.5 μm.
We have designed and fabricated a quantum dot (QD) gain medium which consists of InAs QDs in an InGaAsP matrix
on an InP substrate. By using these InAs/InP QD layers, we have generated femtosecond (fs) pulses with pulse duration
of 295 fs from a single-section monolithic Fabry-Perot (F-P) cavity at the repetition rate of 50 GHz around 1560 nm
wavelength range without any external pulse compression. The average output power is 40.1 mW at the injection current
of 200 mA. Optical signal-to-noise ratio (OSNR) of the proposed QD mode-locked laser (QD-MLL) is up to 50 dB. The
lasing threshold current and the external differential quantum efficiency are 23 mA and 30 %, respectively. And the
mode beating linewidth was measured to be less than 20 KHz. We have interpreted that several nonlinear optical effects
related to interaction of QD excitons with intracavity laser fields could create nonlinear dispersion to compensate
intracavity linear dispersion. So total dispersion is minimized and four-wave mixing (FWM) is dramatically enhanced
within QD F-P cavity. If spectral bandwidth is broad enough, tens or hundreds of longitudinal modes would lase and
their phases would be locked together through FWM process. Eventually a train of fs pulses with a repetition rate
corresponding to cavity round-trip time is generated.
We have demonstrated femtosecond pulses from a passive single-section monolithic InAs/InP quantum-dot (QD)
semiconductor laser with the active length of 456 µm and the ridge width of 2.5 µm in the C-band wavelength range
from 1528 nm to 1565 nm. The transform-limited Gaussian-pulses are generated at the 92-GHz repetition rate with the
312-fs pulse duration without any pulse compression scheme. The average output power is larger than 13.2 mW for the
injection current of 60 mA. And the lasing threshold current and external differential quantum efficiency are 17.2 mA
and 38%, respectively. The mode-beating linewidth of the proposed QD mode-locked laser (MLL) was measured less
than 20 KHz. We have interpreted that four-wave-mixing (FWM) process and other nonlinear effects within the QD
waveguide gain materials make the major contributions to lock the phase the longitudinal modes of the QD Fabry-Perot
cavity together to achieve this strong self-pulsation process.
We have demonstrated a novel approach to achieve a stable multi-wavelength laser system (MWLS) which is making
use of a quantum dot semiconductor optical amplifier (QD SOA) as a highly birefringence material and an optical
polarizer at the same time. Both the channel frequency spacing and the central lasing wavelength of the QD MWLS can
be accurately set by using the desired-designed QD SOA with the certain operation conditions and by setting the
polarization controller properly. The detailed working principles and the experimental results have been reported in this
paper. The proposed QD MWLS technology can be used for characterizing the intrinsic properties of the QD
semiconductor waveguide materials that could also be used for spectral narrowing of a laser system. We have
experimentally confirmed that the QD SOA is highly inhomogeneous gain material as compared with QW SOA.
We demonstrated an ultra-broadband wavelength converter based on co-polarized dual-pumping four-wave mixing
technique in a dispersion-flattened photonic crystal fiber. Over 380-nm wavelength conversion range from 1260 nm to
1640 nm has been achieved. By sweeping the wavelengths of the second pump laser, we have obtained the relationship
between the wavelength conversion efficiency and the converted data signals, which are consistant with our theoretical
analysis. The OSNR of the converted data signals are up to 30 dB.
We have demonstrated a continuum-wave (CW) supercontinuum (SC) fiber light source with over 1000 nm bandwidth
based on a low-cost erbium/ytterbium co-doped double-cladding fiber ring cavity laser. Based on the observation to the
SC evolvement, we have experimentally analyzed the detailed contributions of several nonlinear effects within highly
nonlinear dispersion-shifted fiber (HNLF). Our experimental results have clearly indicated that four-wave mixing (FWM)
and stimulated Raman scattering (SRS) play key roles in CW-pumped SC generation. At the same time, self-phase
modulation (SPM) mainly contributes to generate new frequency components near the peaks that appear in the form of
the spectra broadening while cross-phase modulation (XPM) enhances the broadening of peaks.
We have designed, fabricated and characterized self-assembled InAs/InGaAsP QD-waveguide devices around 1.55 μm.
In order to obtain optimal performance, we have investigated several QD-based semiconductor optical amplifiers
(SOAs) / lasers with different core geometry and doped profiles. To make the fair comparison between QD-SOA and
QW-SOA, InAs/InGaAsP QW-SOAs with the same structure and the doped profiles have been designed and
characterized. The experimental results indicate the QD-SOA is much better than QW-SOA in term of optical spectral
bandwidth, temperature sensitivity and output power stability. The
3-dB and 10-dB bandwidths of the amplified
spontaneous emission (ASE) spectra of the QD-SOA are 150 nm and 300 nm around 1520 nm. By using CW pump and
probe signals we have demonstrated a non-degenerated four-wave mixing (ND-FWM) process and the experimental
results indicate that the asymmetry of the FWM conversion efficiencies is eliminated by using the QD-SOA. To make
use of the inhomogeneous broadening which is one of the specific properties of QD waveguide devices, we have
designed and investigated the QD-based multi-wavelength semiconductor laser. A stable multi-wavelength laser output
with a 93-channel multi-wavelength laser with maximum channel intensity non-uniformity of 3-dB were demonstrated
on the basis of a single InAs/InGaAsP QD F-P cavity chip. All channels were ultra-stable because of the inhomogeneous
gain broadening due to statistically distributed sizes and geometries of self-assembled QDs.
Optical fiber sensors have shown great potentials for aerospace applications. But two issues need to be addressed before
these applications can be realized. One is how to reliably implement optical sensors in the air vehicles. The other is the
need of compact, low weight sensor interrogation systems. We propose to use planar lightwave circuits (PLC) to address
the second issue. In this article, we report some of our results on the development of both echelle diffractive gratings
based sensor interrogator and arrayed waveguide gratings based sensor interrogators. Both approaches offer miniaturized
solutions for the development of optical fiber sensor interrogation systems.
Using an arrayed waveguide gratings (AWG) based demultiplexer, a simple channel gain equalizer can be designed. The gain equalization and blocking functions are realized by the hybrid waveguide based variable optical attenuators fabricated on the output waveguides of the demultiplexer. This paper discusses the operation principle of the design and presents some simulation results.
Quantum operator algebra related to Jaynes-Cummings model is developed to design multi-reflector resonant bandpass filters for the first time. Transmittance and reflectance spectra of these filters are givens with analytic expressions. The results are found in agreement with those based on the existing filter design method. By selecting parameters such as r and N, designed filters can achieve a target spectrum profile with flat-top, large bandwidth, and minor ripples.
By using two orthogonally-polarized pump beams, an ultrabroad tunable wavelength converter is demonstrated with uniform efficiency and equalized signal-to-noise ratio (SNR) through four-wave mixing (FWM) in an 1500-nm semiconductor optical amplifier (SOA). This device allows the conversion of the input data signal to lower or higher frequencies with nearly-constant conversion efficiency and SNR over a 10.66 THz tuning range. This result is a significant improvement of both the conversion efficiency and the SNR as compared with the conventional FWM-based wavelength converters. We have also investigated the effect of parameters of both input power and wavelength of pump P2 on conversion efficiency and SNR of the wavelength-converted signals.
A widely tunable, narrow-linewidth, simultaneous triple-wavelength oscillation erbium-doped fiber ring laser (EDFRL) has been developed. The EDFRL can produce double-wavelength oscillations with the same linear-polarization output, as well as another widely tunable wavelength oscillation with orthogonal linear-polarization from 1522.2 nm to 1595.9 nm. The long-term stability of the triple-wavelength output was observed with a high signal-to-noise ratio of larger than 40 dB. By using this EDFRL in combination with a 1550-nm semiconductor optical amplifier (SOA), an ultrabroad tunable wavelength converter is demonstrated with uniform efficiency and equalized optical signal-to-noise ratio (OSNR) over a 9.1 THz tuning range through four-wave mixing (FWM) in a SOA. This result is a significant improvement of both the conversion efficiency and the SNR as compared with the conventional FWM-based wavelength converters. We have also investigated the effect of both input power and wavelength of pump P2 on conversion efficiency and OSNR of the wavelength-converted signals
We present a simple method to generate a stable high-power (> 30 dBm) multi-wavelength ytterbium/erbium co-doped double-cladding fiber ring laser source at room temperature. This method is based a wavelength-dependent filter through spatial mode beating between the LP01 and LP11 modes within the multimode fiber section. We also investigate the relationship between the lasing wavelengths and the length of the ytterbium/erbium fibers (YEFs), the number of lasing wavelength lines dependent on the total pumping power level and the polarization states, and the characteristics of both the wavelength switching operation and the total output power. Eight simultaneous lasing wavelengths with 0.78 nm spacing were generated at room temperature.
We have described a high-power hybrid fiber amplifier, which comprising an erbium / ytterbium co-doped double-cladding fiber amplifier (EYCDFA) as a post-amplifier and a conventional erbium-doped fiber amplifier (EDFA) as a pre-amplifier. At the signal wavelength of 1550 nm, the signal gains of up to 71 dB and the maximum output powers of 36.4 dBm or 4.37 W have been demonstrated when the total pump laser power was 12.3 W.
We have developed a widely tunable, narrow-linewidth, simultaneous triple-wavelength oscillation erbium-doped fiber ring laser (EDFRL), which can produce double-wavelength oscillations with the same polarization output, as well as another widely tunable wavelength oscillation with orthogonal polarization from 1522.2 nm to 1595.9 nm. By using this EDFRL along with a method of measuring polarization-mode dispersion (PMD) in optical fibers based on a broad-band orthogonal-pump four-wave mixing in a semiconductor optical amplifier (SOA), we have measured the PMD values of optical fibers, which are in good agreement with values measured by means of commercial PMD testing equipment. We have also proposed several novel devices for in-field PMD measurement and monitoring on dense wavelength-division multiplexed (DWDM) traffic-carrying links, which will significantly reduce the cost and time of the PMD testing in the running DWMD networking systems.
A novel polarization scrambling optical signal-to-noise ratio (OSNR) monitor has been proposed and demonstrated. The OSNR monitor consists of a polarization scrambler, a polarizer and a photodetector. When the channel signal input to the polarizer is a linear polarization state aligned parallel (orthogonal) to the polarizer the output reaches its maximum (minimum). The OSNR can be obtained from the measured maximum and minimum of the output power if the sampling time is long enough to ensure a good coverage on Poincare sphere. The new OSNR monitor is polarization mode dispersion insensitive. The effect of polarizer extinction ratio and sampling time on the accuracy has been discussed.
We present a focal plane terahertz (THz) ray imaging system through use of a big-size <100> oriented ZnTe electro- optic crystal plate. Some concealed living insects and moving objects have been directly imaged and the dynamic processes of the THz field distributions are clearly displayed, both in real-time model. We also discuss the maximum and minimum sizes of the available imaging objects in this THz imaging system, and give ways to improve them.
Recently several THz sampling detection systems have been used to characterize the temporal and spatial distribution of free- space broadband, pulsed electromagnetic radiation (THz beams). Free-space sampling systems use electro-optic or magneto-optic sensors and a femtosecond laser system, to provide diffraction-limited spatial resolution, picosecond temporal resolution, and DC-THz spectral bandwidth. In this paper, we review recent progress and preliminary applications of free- space electro-optic and magneto-optic sensors.
An ultra-wideband, nonperturbing, electric-field sensor is being developed that uses the linear electro-optic effect and is packaged in a suitcase-sized optical configuration. The methodology has been demonstrated on the optical bench with ZnTe and used to measure an applied electric field. The immediate goal is to demonstrate the sensor up to 5 GHz and apply it to unknown fields in a configuration that uses DAST crystals, which are significantly more sensitive than ZnTe. This sensor eventually will be applied to the measurement of electromagnetic pulses, preserving the amplitude, polarization, and phase content of the detected signal. Preliminary measurements reported here verify the crystal sensitivity and response linearity. Variations in optical configurations are compared on the basis of sensitivity.