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.
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.
Monolithically integrated electroabsorption modulated lasers (EML) are widely being used in the optical fiber communication systems, due to their low chip, compact size and good compatible with the current communication systems. In this paper, we investigated the effect of Zinc diffusion on extinction ratio of electroabsorption modulator (EAM) integrated with distributed feedback laser (DFB). EML was fabricated by selective area growth (SAG) technology. The MQW structure of different quantum energy levels was grown on n-type InP buffer layer with 150nm thick SiO2 parallel stripes mask by selective area metal-organic chemical vapor deposition (MOCVD). A 35nm photoluminescence wavelength variation was observed between the laser area (λPL=1535nm) and modulator area (λPL=1500nm) by adjusting the dimension of parallel stripes. The grating (λ=1550nm) was fabricated in the selective area. The device was mesa ridge structure, which was constituted of the DFB laser, isolation gap and modulator. The length of every part is 300μm, 50μm, and 150μm respectively. Two samples were fabricated with the same structure and different p-type Zn-doped concentration, the extinction ratio of heavy Zn-doped device is 12.5dB at -6V. In contrast, the extinction ratio of light Zn-doped device is 20dB at -6V, that was improved for approximate 60%. The different Zn diffusion depth into the MQW absorption layer was observed by Secondary ion mass spectrometer (SIMS). The heavy Zn-doped device diffused into absorption layer deeper than the light Zn-doped device, which caused the large non-uniformity of the electric field in the MQW layer. So the extinction ratio characteristics can be improved by optimizing the Zn-doped concentration of p-type layer.
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.
Based on side-port multimode interference coupler, a novel design of 1.31/1.55-μm wavelength multiplexer/demutiplexer on SOI platform with conventional channel waveguides is proposed and analyzed by using wide-angle beam propagation method. With a 25.9μm long ultra-short MMI section, nearly an order of magnitude shorter than that of the previously reported 1.31/1.55-μm wavelength MMI splitters on SOI, simulation results exhibit contrasts of 28dB and 25dB at wavelength 1.31 and 1.55 μm, respectively, and the insertion losses are both below 0.55dB. Meanwhile, the analysis shows that the proposed structure has larger fabrication tolerances than restricted MMI based structures and the present design methodology also applies to split other wavelengths and in different material platforms, such as InP, GaAs and PLC guides, etc.
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.
A 1.65μm three-section Distributed Bragg Reflective (DBR) laser for CH4 gas sensor was reported. Wide tunable range
covering R3 and R4 methane absorption line manifolds. Wavelength tunable properties and temperature stability were
characterized and analyzed. Several advantages were demonstrated compared with traditional DFB laser in harmonic
detection method.
KEYWORDS: Clocks, Optical clocks, Modulation, Semiconductor lasers, Interference (communication), Single sideband modulation, Single mode fibers, Laser optics, Binary data, Signal to noise ratio
We demonstrate 40 Gb/s all-optical clock recovery by using a monolithic integrated amplified-feedback laser (AFL) with
coherent injection-locked method. The AFL consists of a gain-coupled DFB laser and an optical amplified feedback
external cavity. With proper design and operation of AFL, the device can work at self-pulsation state that resulted from
the beating between two lasing modes. The self-pulsation can be injection-locked to the optical clock embedded in input
data streams. Due to different work mechanisms, there are two all-optical clock recovery operation modes: incoherent
injection-locked and coherent injection-locked. It's predicted that the coherent injection method has various advantages:
1) requiring low injection power recovery, 2) independent of the bit rate and 3) introducing little timing jitter to the
recovered clock. The robustness of coherent clock recovery is confirmed by our experimental results. We set up a return-to-
zero (RZ) pseudorandom binary sequence (PRBS) data streams all-optical clock recovery system. This coherent
injection-locked based clock recovery method is optical signal noise ratio (OSNR) and chromatic dispersion (CD)
degeneration tolerant, and has low timing jitter and high sensitivity.
A dual-depletion-region lumped electroabsorption modulator (DDR-LEAM) based on InP at 1550nm is designed and
fabricated. The measurement results reveal that the dual depletion region structure can reduce the device capacitance
significantly without any degradation of extinction ratio. The simulation results show that the highly doped charge layer
can concentrate almost all of the external applied voltage in MQW region and thus contribute to the identical extinction
ratio curves. The expected 3-dB bandwidth of the DDR-LEAMs using an equivalent circuit model is more than twice
lager than that of the conventional LEAM.
This paper will introduce the fabrication methods of electro-absorption modulated lasers (EMLs) and the latest
results of EMLs fabricated by a novel technology named selective area growth double-stack active layer
(SAG-DSAL) developed by the authors.
More than 11mW output powers for all wavelengths from the fiber and over 49 nm range tuning in sampled
grating distributed Bragg reflector laser with an integrated semiconductor optical amplifier which is enabling
access to 110 ITU 50GHz channels is demonstrated. Tilted amplifier and anti-reflection facet coating are
used to suppress reflection.
In this paper, a simple wavelength-locking scheme for a tunable distributed Bragg reflector laser is presented. A 1*2
wide band fiber coupler as the function of beam splitter forms two optical paths with evenly separated power, one for
wavelength monitoring and the other for power reference. For wavelength monitoring, two single mode fiber
collimators- one as a transmitter and the other as a receiver-form a collimated light path for laser beam and a highly
stable air-paced Etalon inserted between them is used as an optical frequency discriminator to lock the laser wavelengths
to several ITU channels maintain 100GHz or 0.8 nm channel spacing in C band. Meanwhile, a photodetector connected
with receiving collimator by a FC/PC connector turns the optical signal into electronic signal. For power reference, one
of the coupler output pots is directly connected with a similar photodetector. Then wavelength shifting signal
proportional to the power differences between two optical paths could be feed backed to the phase region or DBR region
for stabilizing the laser output wavelength.
A novel EAM/PD monolithically-integrated optical logic element is presented. 5Gb/s optical logic AND gate operations
at about -2 V for non-return-to-zero (NRZ) signals with8.4dB extinction ratio and16mW absorbed optical power was
demonstrated.
All-optical clock recovery is a key technology in all-optical 3R signal regeneration (Re-amplification, Retiming, and Reshaping) process. In this paper, a monolithic integrated three-section amplified feedback semiconductor laser (AFL) is demonstrated as an all optical clock regenerator. We fabricated a three-section AFL using quantum well intermixing process without regrowth instead of butt-joint process. The tunable characteristics of three-section AFL were investigated, and all optical clock recovery for 40Gb/s return to zero (RZ) 231-1 pseudorandom binary sequence (PRBS) is demonstrated experimentally using AFL with time jitter about 689.2fs.
A partly gain-coupled ridge varied two-section DFB self-pulsation laser for optical microwave generating
has been fabricated. It produces microwave with a wide tuning range of more than 135GHz. A successful
locked to the microwave frequencies of 30GHz, 40GHz, 50GHz, 60GHz are demonstrated and a timing
jitter below 300fs is detected.
We present fabrication and characterization of 1.3-μm InAs quantum dot (QD) vertical cavity surface emitting lasers
(VCSELs) and QD-VCSEL arrays. The continuous-wave (CW) output power of single QD-VCSEL of 1.2 mW with
lasing wavelength of 1.28 μm is obtained at room temperature (RT) at a bias current of 15 mA without power saturation.
The low threshold current of 1.1 mA can be achieved for the single mode device. We investigate the 3-dB modulation
bandwidth of QD-VCSELs with oxide aperture size of 5-μm, 10-μm and 15-μm in the small signal frequency response
measurements. Modulation bandwidth of 2.65 GHz is achieved for single-mode QD-VCSEL with oxide aperture size of
5 μm at a bias current of 4.5 mA. The maximum modulation bandwidth of 2.5 GHz can be obtained for multimode QD-VCSEL
with oxide aperture size of 10 μm at a bias current of 7 mA. The 61 QD-VCSELs array is also investigated at
RT without optimization. Maximum CW output power of 28 mW and pulsed output power of 18 mW are demonstrated
for 2-D QD-VCSEL array with threshold current of 50 mA. The far field pattern beam angle of QD-VCSEL arrays at
two perpendicular directions are about 18 degree.
A complex-coupled DFB Laser with the sampled grating has been designed and fabricated. The +1st order reflection of
the sampled grating is utilized for laser single mode operation, which is 1.5387μm in the experiment. The typical
threshold current of the device is 30mA, and the optical output power is about 10mW at the injected current of 100mA.
We present the 1.3-μm InAs quantum dot (QD) vertical cavity surface emitting lasers (VCSELs) with novel planar
electrodes configuration. The lasing wavelength is around 1274 nm. The lowest threshold current of wafer level device is
~1 mA, which corresponds to a low threshold current density of ~1.3 kA/cm2 or 76 A/cm2 per QD layer. The maximum
output power of 1 mW can be obtained at room temperature. High temperature stability can be seen in temperature
dependence L-I characteristics of InAs QD VCSEL 3-dB modulation frequency response of 1.7 GHz can be obtained in
the small signal response measurements.
The linear electro-optic (Pockels) effect of wurtzite gallium nitride (GaN) films and six-period GaN/AlxGa1-xN
superlattices with different quantum structures were demonstrated by a polarization-maintaining fiber-optical Mach-Zehnder interferometer system with an incident light wavelength of 1.55μm. The samples were prepared on (0001)
sapphire substrate by low-temperature metalorganic chemical vapor deposition (MOCVD). The measured coefficients of
the GaN/AlxGa1-xN superlattices are much larger than those of bulk material. Taking advantage of the strong field
localization due to resonances, GaN/AlxGa1-xN SL can be proposed to engineer the nonlinear responses.
Wavelength tunable electro-absorption modulated distributed Bragg reflector lasers (TEMLs) are promising light source
in dense wavelength division multiplexing (DWDM) optical fiber communication system due to high modulation speed,
small chirp, low drive voltage, compactness and fast wavelength tuning ability. Thus, increased the transmission capacity,
the functionality and the flexibility are provided. Materials with bandgap difference as large as 250nm have been
integrated on the same wafer by a combined technique of selective area growth (SAG) and quantum well intermixing
(QWI), which supplies a flexible and controllable platform for the need of photonic integrated circuits (PIC). A TEML
has been fabricated by this technique for the first time. The component has superior characteristics as following:
threshold current of 37mA, output power of 3.5mW at 100mA injection and 0V modulator bias voltage, extinction ratio
of more than 20 dB with modulator reverse voltage from 0V to 2V when coupled into a single mode fiber, and
wavelength tuning range of 4.4nm covering 6 100-GHz WDM channels. A clearly open eye diagram is observed when
the integrated EAM is driven with a 10-Gb/s electrical NRZ signal. A good transmission characteristic is exhibited
with power penalties less than 2.2 dB at a bit error ratio (BER) of 10-10 after 44.4 km standard fiber transmission.
High performance InGaAsP/InGaAsP strained compensated multiple-quantum-well (MQW) electroabsorption
modulators (EAM) monolithically integrated with a DFB laser diode have been designed and realized by ultra low
metal-organic vapor phase epitaxy (MOVPE) based on a novel butt-joint scheme. The optimization thickness of upper
SCH layer for DFB and EAM was obtained of the proposed MQW structure of the EAM through numerical simulation
and experiment. The device containing 250μm DFB and 170μm EAM shows good material quality and exhibits a
threshold current of 17mA, an extinction ratio of higher than 30 dB and a very high modulation efficiency (12dB/V)
from 0V to 1V. By adopting a high-mesa ridge waveguide and buried polyimide, the capacitance of the modulator is
reduced to about 0.30 pF corresponding to a 3dB bandwidth more than 20GHz.
The narrow stripe selective growth of the InGaAlAs bulk waveguides and InGaAlAs MQW waveguides was first investigated. Flat and clear interfaces were obtained for the selectively grown InGaAlAs waveguides under optimized growth conditions. These selectively grown InGaAlAs waveguides were covered by specific InP layers, which can keep the waveguides from being oxidized during the fabrication of devices. PL peak wavelength shifts of 70 nm for the InGaAlAs bulk waveguides and 73 nm for the InGaAlAs MQW waveguides were obtained with a small mask stripe width varying from 0 to 40 μm, and were interpreted in considering both the migration effect from the masked region (MMR) and the lateral vapor diffusion effect (LVD). The quality of the selectively grown InGaAlAs MQW waveguides was confirmed by the PL peak intensity and the PL FWHM. Using the narrow stripe selectively grown InGaAlAs MQW waveguides, then the buried heterostructure (BH) lasers were fabricated by a developed unselective regrowth method, instead of conventional selective regrowth. The InGaAlAs MQW BH lasers exhibit good performance characteristics, with a high internal differential quantum efficiency of about 85% and an internal loss of 6.7 cm-1.
Unselective regrowth for fabricating 1.5-µm InGaAsP multiple-quantum well (MQW) distributed-feedback (DFB) buried heterostructure (BH) lasers is developed. The experimental results exhibit superior characteristics, such as a low threshold of 8.5 mA, high slope efficiency of 0.55 mW/mA, circular-like far-field patterns, the narrow linewidth of 2.5 MHz, etc. The high performance of the devices effectively proves the feasibility of the new method to fabricate buried heterostructure lasers.
Width varied quantum wells show a more flat and wide gain spectrum (about 115nm) than that of identical miltiple quantum well. A new fabricating method was demonstrated in this paper to realize two different Bragg grating in an identical chip using traditional holographic exposure. A wavelength selectable DFB laser based on this material grown by MOVPE was presented. Two stable distinct single longitudinal mode of 1510nm and 1530nm with SMSR of 45 dB were realized.
Optoelectronic packaging has become a most important factor that influences the final performance and cost of the module. In this paper, low microwave loss coplanar waveguide(CPW) on high resistivity silicon(HRS) and precise V groove in silicon substrate were successfully fabricated. The microwave attenuation of the CPW made on HRS with the simple process is lower than 2 dB/cm in the frequency range of 0~26GHz, and V groove has the accuracy in micro level and smooth surface.These two techniques built a good foundation for high frequency packaging and passive coupling of the optoelectronic devices. Based on these two techniques, a simple high resistivity silicon substrate that integrated V groove and CPW for flip-chip packaging of lasers was completed. It set a good example for more complicate optoelectronic packaging.
A novel wideband polarization-insensitive semiconductor optical amplifier (SOA) gate containing compressively strained InGaAs quantum wells and tensile-strained InGaAs quasi-bulk layers is developed. The fabricated SOA gates have a wide 3-dB optical bandwidth of 102 nm, less than 0.8-dB polarization sensitivity, more than 50-dB extinction ratio, and less than 75-mA fiber-to-fiber lossless operating current.
1.3 micrometers and 1.55 micrometers InGaAsP/InP quantum well (QW) light emitting diodes (LEDs) with narrow beam divergence grown by low pressure metal organic chemical vapor deposition are reported in this paper. 1.3 micrometers and 1.55 micrometers QW LEDs with beam divergence of 30 - 45 degree, chip output power of more than 300 (mu) W and 200 (mu) W, and single mode fiber output power of 60 (mu) W and 40 (mu) W were obtained by optimizing the device structure parameters.
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