Based on a high power InGAsP distributed feedback (DFB) semiconductor laser coupling with an ultra-high-Q silicon nitride microring, we proposed a hybrid integration semiconductor laser scheme for realizing high power and narrow linewidth. For such a scheme, the high power DFB laser serves as the light source, whose output is efficiently coupled into the input waveguide port of ultra-high-Q silicon nitride microring through a silicon lens. Under the optical feedback provided by the Rayleigh scattering in the inhomogeneity silicon nitride microring, the laser may be driven into the self-injected locking state, under which the lasing linewidth can be obviously narrowed. The experimental results demonstrate that, adopting such a hybrid integration scheme, the lasing linewidth can be narrowed to 10 kHz and meanwhile the output power is maintained at the level of 20 mW. The hybrid integration semiconductor lasers have application prospects in some fields simultaneously requiring high coherence and high power, such as LiDAR and long-distance coherence communication.
We proposed an integrated semiconductor laser scheme that combines an ultra-high Q silicon nitride microresonator with a DBR semiconductor laser, resulting in a tunable ultra-narrow linewidth laser. The experiment achieves tuning within the wavelength range of 1554.2-1557.15nm (about 370GHz), being almost ten times larger than that of reported DFB scheme. Moreover, the sidemode suppression ratio is low to 52dB with a ultra-narrow linewidth about 6.6kHz. It needs the joint adjustment of DBR operating current, coupling of the high-Q silicon nitride external cavity. These results can be applied in fields such as dense wavelength division multiplexing systems and integration LiDAR System.
An optoelectronic feedback structure is introduced to a distributed Bragg reflector mode-locked laser diode (DBR-MLLD) to improve its phase noise performance. Optical pulses with a repetition rate of 40 GHz, a pulse width of 5.2 ps, and a center wavelength tuning range of 4.3 nm are demonstrated. The phase noise of the hybrid mode-locked DBR-MLLD has been reduced by 44 dB to a level of -97 dBc/Hz at a 10 kHz frequency offset from the carrier frequency comparing to the passive mode-locked state.
We propose a new waveguide loss measurement method based on the reflected interferometric pattern from the waveguide. The loss of the waveguide is obtained by analyzing the fineness of the reflected interferometric pattern from the Fabry-Perot (F-P) cavity formed by the facets of a single-mode waveguide. In this method, a single mode lensed fiber and a circulator is used to direct the tunable laser into the waveguide under test and collect the reflected spectrum pattern through a photodetector. Comparing to the traditional transmission F-P interferometric method relying on double end fiber coupling, the proposed method requires only a single end coupling, considerably simplifying the coupling difficulty and the measurement system complexity. The fineness measurement is also free from the influence of background noise level, and reduces the coupling accuracy requirement. This method is low-cost, easy-to-operate and reliable, which can serve as an alternative method to measure the waveguide loss.
A novel design of two-mode (DE)MUX based on multimode interference (MMI) couplers on InP substrate is proposed. A phase shifting section based on the thickness variation of the core layer is introduced in the (DE)MUX to realize a 100% mode conversion efficiency and multiplexing. The total length of the structure is only 549 μm, much shorter than other InP based mode (DE)MUXs. Simulations show that, the device crosstalk is below -20 dB and the insertion loss is lower than 1 dB for both of the fundamental mode and the first order mode within the whole C band. This new structure can be potentially integrated with other devices based on InP substrate to serve as a monolithic few-mode transmitter/receiver.
All-optical clock recovery (AOCR) for 100 Gb/s RZ-OOK signal is demonstrated by using a dualmode beating DBR laser. Based on the injection-locking of the DBR (distributed Bragg reflector) laser, a 100-GHz optical clock is recovered. Timing jitter (<1 ps) derived from both phase noise and power fluctuation is measured by an optical sampling oscilloscope (OSO). Furthermore, clock recovery is also realized for the 100 Gb/s signal after 25 km transmission. After the 25-km SMF (5- dB loss) transmission, the signal-to-noise ratio (SNR) of the signal drops from 18 dB to 5.2 dB. The dependence of the timing jitter on the input power is investigated. The lowest timing jitter of 665 fs is realized when the input power is 3 dBm.
A comprehensive design optimization of 1.55-μm high power InGaAsP/InP board area lasers is performed aiming at
increasing the internal quantum efficiency (IQE) while maintaing a low internal loss of the device as well. The P-doping
profile and separate confinement heterostructure (SCH) layer band gap are optimized respectively with commercial
software Crosslight. Analysis of lasers with different p-doping profiles shows that, although heavy doping in P-cladding
layer increases the internal loss of the device, it ensures a high IQE because higher energy barrier at the SCH/P-cladding
interface as a result of heavy doping helps reduce the carrier leakage from the waveguide to the InP-cladding layer. The
band gap of the SCH layer are also optimized for high slope efficiency. Smaller band gap helps reduce the vertical
carrier leakage from the waveguide to the P-cladding layer, but the corresponding higher carrier concentration in SCH
layer will cause some radiative recombination, thus influencing the IQE. And as the injection current increases, the
carrier concentration increases faster with smaller band gap, therefore, the output power saturates sooner. An optimized
band gap in SCH layer of approximately 1.127eV and heavy doping up to 1e18/cm3 at the SCH/P-cladding interface are
identified for our high power laser design, and we achieved a high IQE of 94% and internal loss of 2.99/cm for our design.
High power single-mode ridge waveguide 1060-nm semiconductor lasers are reported. The lasers consist of
compressively strained double InGaAs/GaAs quantum wells and a GaAs/AlGaAs separate confinement vertical structure.
A super large vertical optical cavity is employed to have a low internal loss, large optical spot size and low vertical
optical divergence angle. The material composition and thickness of waveguide layers and claddings layer are optimized
systematically. The active layer is detuned from center of the waveguide and thickness of cladding layers is optimized to
guaranty single mode lasing of the large optical cavity. The large vertical cavity laser structure with thickness of 4 μm
allows the lasers have a low internal loss of less than 0.6 /cm, a large optical spot size about 1μm and a vertical
divergence angle about 20 degree. For lateral optical confinement, a double trench ridge waveguide is employed to
maintain single-lateral-mode operation. Based on the optimization, 1.5 W continue wave optical power is achieved for
broad area lasers with 1mm longitude cavity length. Narrow stripe ridge waveguide lasers of 1mm cavity length with
single mode current and optical power of 700 mA and 340 mW is obtained. Suggestions for further improvements in
terms of single mode power and applications of the high power semiconductors are discussed.
We have investigated 1.3-μm InGaAsP strained multi-quantum-well (MQW) lasers on InP substrate for direct
modulation applications using the commercial laser simulator PIC3D. The physical mechanisms affecting the laser
dynamic characteristics such as nonradiative recombination losses and vertical electron leakage effect are considered in
our simulation. The number of wells is optimized because increasing the number of QWs can decrease the nonradiative
recombination losses and increase the modal differential gain, nevertheless, the carrier distribution between wells
become more non-uniform with too many QWs numbers resulting in uneven simulated recombination rate and
increasing Auger recombination. The influence of barrier height is analyzed and a tradeoff has to be determined because
too high barriers results in more nonuniform carrier distribution in the active regions, increasing the Auger
recombination rate severely while the vertical current leakage outside the QWs will increase dramatically at lower barrier
height. The 1.3-μm FP laser with the MQWs of 6 wells, 1.15 Q barriers bandgap and 8 wells, 1.1 Q barrier bandgaps is
fabricated and characterized. The FP laser with MQWs structures composed of 8 compressive strain quantum wells and 9
barriers with the optimized bandgap 1.1 Q shows better properties. The threshold current is around 19 mA and the
resonance frequency of 9.5 GHz and 3-dB bandwidth in excess of 13.3 GHz at 120 mA injection current. This
modulation frequency is suitable for 10 Gbits/s optical data transmission.
We report systematic modelling of 1310 nm InGaAsP/InP electroabsorption modulators. The modulator is a reverse
biased p-i-n diode, in which the MQW structure is composed of several InGaAsP/InGaAsP quantum wells. By a 3D
finite element software PICS3D, we have comprehensively investigated the internal physical mechanism of the
modulator, which includes the red shift of the absorption edge with the reverse bias and the absorption intensity, which
could be derived from the normalized overlap integral between the energy levels for the electrons and the holes. The
absorption spectrum on wavelength and the reverse bias voltage is analyzed, which provide us with both the extinction
ratio and the transimision loss for a special operating wavelength. Key design parameters such as barrier height and
quantum well width are optimized for extinction ratio, and confirmed by parallel experimental studies. What’s more, the
RF performance has been investigated in detail. The junction capacitance, the series resistance and the parasitic
capacitance (mostly the bonding pad) are studied systematically. A ridge structure model is analyzed for high speed
performance, in which the important parameters, such as the ridge width, the cavity length, the area of the bonding pad
and the thickness of polyimide (or BCB) under the bonding pad, are optimized for over 20GHz 3dB bandwidth. The
cavity length is optimized by making compromise between the extinction ratio and the RF performance. In conclusion,
the design parameter space of the 1310nm InGaAsP/InP EAM have been systematically explored. Our work should
provide a firm basis for 1310nm InGaAsP/InP EAM device design optimization for optical datacom applications.
A novel 4 × 4 multimode interference couplers based phase-shifted photonic quantization scheme using multiwavelength mode locked pulse lasers as sampling source for all-optical analog-to-digital converter is proposed. Numerical analysis indicates that 8-bit quantization resolution operating at 40 GHz bandwidth could be achieved with an incident average optical power of 1.932 mW to each photodiode. The whole scheme can be integrated on a InP-based chip.
A high power single-lateral-mode double-trench ridge waveguide semiconductor laser is reported. The laser has a compressively strained double quantum-well (DQW) and an GaAs/AlGaAs separate confinement structure. The ridge waveguide is defined by two trenches of finite width on either side of the ridge, which will result mode radiation towards outside of the trenches. The relationship between the leakage loss and the waveguide geometry of the each lateral mode is studied with effective index method. The relationship under different bias condition is evaluated. Based on the simulation, lasers with various trench width, trench depth and ridge width are fabricated and tested. With optimized geometry parameters, a laser of 1.5-mm cavity length with a maximum single-lateral-mode operation current of 550 mA is obtained. The threshold current and the slope efficiency of the laser is 30 mA and 0.72 W/A, respectively. The maximum single-lateral-mode power is up to 340 mW.
A novel mode-beating DBR laser with dual-mode lasing is fabricated. The DBR laser has four parts, a front gain section, a phase section, a DBR grating section, and a rear gain section. When the current of the front gain section is above the threshold, the device is working in single-mode. Dual-mode lasing can be obtained by adjusting the current of the rear gain section. The power difference between the two modes can be less than 1 dB. An optical down-conversion technique was used to measure the beating frequency. The mode-beating frequency of the two modes is about 93 GHz, and the 3- dB linewidth of the mode-beating RF spectrum of the laser when free-running is about 5 MHz. Moreover, the wavelength of the dual-mode can be tuned synchronously when the current injected into the DBR grating section is adjusted. The wavelength tuning range of the device is at least 3 nm.
We propose and demonstrate a simple and robust short pulse source based on chirp compression scheme and Mamyshev
2R regenerator. Pedestal-free optical pulse with repetition rate of 25 GHz, FWHM of 1.33 ps and RMS timing jitter of
112.81fs (100-Hz~10-MHz) is generated experimentally. Moreover, it is successfully applied to a 200-Gbit/s OTDM
system by multiplexing in time domain.
The performance of DPSK and DQPSK with NRZ, 33% RZ and CSRZ formats are numerically compared and investigated
for 160 Gbit/s single channel transmission system. The impairments caused by chromatic dispersion (CD), higher-order
chromatic dispersion, nonlinearity and accumulated noise are considered. The primary limitation for those modulation
formats in 160 Gbit/s transmission system is investigated.
Factors influencing the birefringence property of double cladding fiber (DCF) are numerically investigated for
DCF with rectangular and D-shape inner cladding. Research shows that the choices of inner cladding shape,
outer cladding material and cooling temperature have considerable influence on thermal induced birefringence
in the core of DCF. Birefringence increases with the increase of Young's Modulus, thermal expansion coefficient,
thickness of outer cladding, and the ellipticity of inner cladding.
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