This PDF file contains the front matter associated with SPIE Proceedings Volume 9267, including the Title Page, Copyright information, Table of Contents, Authors, and Conference Committee listing.

In this paper, we demonstrate a novel InGaAlAs/InGaAlAs quantum well multimode-interferometer-Fabry-Perot laser diode (MMI-FP LD) in which a 1x3 multimode interferometer is inserted into the conventional FP laser waveguide to generate single wavelength emission. The designed and fabricated laser diode shows a single longitudinal mode lasing with side mode suppression ratio (SMSR) of 25dBm at a wavelength of 1567nm with driving current of 170mA and can be tuned over a certain range by adjusting the driving current. A laser diode incorporating a 1x3 MMI and three single mode waveguide outputs is also proposed which could be potentially used to generate a 3-channel single longitudinal mode coherent source using injection locking. The simple structure of this single longitudinal mode laser significantly eases the fabrication processing enabling an increase in the yield and a reduction in the cost compared with the traditional single mode lasers.

Nonlinear dynamics associated with polarization switching (PS) in a 1550 nm vertical-cavity surface-emitting laser (VCSEL) with orthogonal optical injection is investigated theoretically by scanning the injected power. The results show that, adjusting injected powers may induce complex variation of dynamical state of each polarization mode and PS. When the PS happens, its dynamical states can be located at an injection locking state or not, which depends on the frequency detuning between the injected field and the VCSEL. Detailed mappings of polarization-resolved nonlinear dynamical states are calculated to unveil a rich variety of dynamical scenarios for different scanning routes of injected power in the parameter space of injected power and frequency detuning, and show that the dynamical states and PS are critically dependent on the scanning routes of the injected power under the case of larger current.

We design photonic crystal (PC) array surface emitting lasers with large-area coherence. The structure has six-fold rotational symmetry. By finite-difference time-domain method, we investigate the far-field characteristics of the individual element and the array. We demonstrate theoretically that the coherent PC array has lower far-field divergence angles and higher power compared to those of individual elements. Our PC array exhibits strong leaky coupling which has high mode stability and high intermodal discrimination. Thus, the coherent PC array shows great potential for high power low divergence in-phase surface laser emitting.

We numerically and experimentally investigate and compare the performance of a Fabry-Perot laser diode (FP-LD) under both strong- and weak-injection in detail. The numerical simulation results prove that the optically injection-locked semiconductor laser will become stable in the injection-locking region under the above two conditions. Nonetheless, the former can achieve stability faster than the latter whatever the frequency detuning is. The dynamic injection-locking map and the property of side-mode suppression ratio (SMSR) for the optically injection-locked FP-LD are experimentally obtained, and associated experiment phenomena are observed and qualitatively discussed for both conditions. Our experiments show that quite different dynamics occur in the two conditions, with weak-injection arrangement offering overall benefits in terms of more complicated dynamics and potential application.

This paper presents the results revealing the influence of the nonlinear gain on the stability limit of a semiconductor laser (SL) with external optical feedback (EOF). A new system determinant is derived from the original Lang and Kobayashi (L-K) equations. By making analysis on the locus of the roots of the system determinant, the stability limit of the system is obtained, from which a number of important and interesting phenomenon revealed by the nonlinear gain is uncovered. The correctness of results is verified by numerical simulations.

High side-mode suppression ratio (SMSR) and higher optical power output of frequency converted lightwave is successfully realized by single side band injection locking of distributed feedback laser (DFB). This method is of great potential in the application of fast optical frequency sweep signal generation. Compared to that acquired from direct carrier suppressed single sideband (CS-SSB), the SMSR of the injection locked slave laser by single sideband injection locking is much higher (32.5dB to 12dB at best), and the power of the injection locked slave laser output is 11dB higher (-22dBm to -33.5dBm) than converting directly from CS-SSB. The variation of SMSR and locking bandwidth of the slave laser as optical injection ratio changes is also researched.

In this paper, we investigate the dynamics of a BAL with lateral-mode selected external feedback experimentally by measuring the far-field profile, intensity noise spectrum and time series of the output beam. The mode-selection is achieved by adjusting a stripe mirror at the pseudo far-field plane. Different dynamic behaviors are observed when different lateral modes are selected. When the mirror is aligned correctly and high-order modes are selected, in most of the cases periodic dynamics of the output power corresponding to a single roundtrip external-cavity loop is observed, but the dynamic behavior disappears in some case; when the zero-order mode is selected, periodic dynamics corresponding to a double roundtrip external-cavity loop is observed. When the stripe mirror is not aligned perfectly, a dynamic behavior like pulse-package oscillations is observed: a periodic oscillated output with a frequency of the single roundtrip external-cavity loop modulated by periodic low-frequency fluctuation. This is the first observation of pulse-package oscillation in a diode laser with long-cavity feedback, to our knowledge.

Position localization has drawn great attention due to its wide applications in radars, sonars, electronic warfare, wireless communications and so on. Photonic approaches to realize position localization can achieve high-resolution, which also provides the possibility to move the signal processing from each sensor node to the central station, thanks to the low loss, immunity to electromagnetic interference (EMI) and broad bandwidth brought by the photonic technologies. In this paper, we present a review on the recent works of position localization based on photonic technologies. A fiber-connected ultra-wideband (UWB) sensor network using optical time-division multiplexing (OTDM) is proposed to realize high-resolution localization and moving the signal processing to the central station. A 3.9-cm high spatial resolution is achieved. A wavelength-division multiplexed (WDM) fiber-connected sensor network is also demonstrated to realize location which is independent of the received signal format.

Pulse compression is widely used to increase the range resolution for modern radars. To enlarge the pulse compression ratio, a phase-modulated microwave signal is usually involved. In this paper, we review recent progress of our group on the generation of phase-modulated microwave signals. These techniques features outstanding performances, wide bandwidth, and flexible tunability.

We investigate the phase modulation to intensity modulation conversion in dispersive fibers for measuring frequency responses of electro-optic phase modulators, and demonstrate two typical measurements with cascade path and fold-back path. The measured results achieve an uncertainty of less than 2.8% within 20 GHz. Our measurements show stable and repeatable results because the optical carrier and its phase-modulated sidebands are affected by the same fiber impairments. The proposed method requires only dispersive fibers and works without any small-signal assumption, which is applicable for swept frequency measurement at different driving levels and operating wavelengths.

The envisioned C-RAN concept in wireless communication sector replies on distributed antenna systems (DAS) which consist of a central unit (CU), multiple remote antenna units (RAUs) and the fronthaul links between them. As the legacy and emerging wireless communication standards will coexist for a long time, the fronthaul links are preferred to carry multi-band multi-standard wireless signals. Directly-modulated radio-over-fiber (ROF) links can serve as a lowcost option to make fronthaul connections conveying multi-band wireless signals. However, directly-modulated radioover- fiber (ROF) systems often suffer from inherent nonlinearities from directly-modulated lasers. Unlike ROF systems working at the single-band mode, the modulation nonlinearities in multi-band ROF systems can result in both in-band and cross-band nonlinear distortions. In order to address this issue, we have recently investigated the multi-band nonlinear behavior of directly-modulated DFB lasers based on multi-dimensional memory polynomial model. Based on this model, an efficient multi-dimensional baseband digital predistortion technique was developed and experimentally demonstrated for linearization of multi-band directly-modulated ROF systems.

Super-Nyquist, also known as Fast-than-Nyquist (FTN), signal generation based on optical or electrical spectrum shaping methods has been demonstrated to be an efficient scheme for future high-capacity transmission systems. Super- Nyquist signal demodulations based on maximum a posteriori (MAP) or maximum likelihood sequence estimation (MLSE) on receiver side have been demonstrated in 100G, 200G and 400G systems, which enables PDM-QPSK transmission with 4bit/s/Hz net spectral efficiency (SE) at lower OSNR requirement and longer transmission distance. Further studies also show the highly filtering-tolerant advantage of the super-Nyquist signal when using the 9-QAMbased multi-modulus equalization. This feature is quite useful for signals transmission under the aggressive optical filtering in multiple reconfigurable optical add-drop multiplexers (ROADMs) transmission link. In this paper, we review the newly reported super-Nyquist experiments using the optical super-Nyquist filtering 9-QAM like signals based on multi-modulus equalization (MMEQ). We directly recover the Nyquist filtered QPSK to a 9-QAM like signal. We first successfully transmitted 100-GHz-grid, 20 channels single-carrier 440-Gb/s super-Nyquist 9-QAM-like signal over 3600-km ultra-large effective-area fiber (ULAF) at record a net SE of 4b/s/Hz (after excluding the 7% hard-decision FEC overhead). The highly filtering-tolerant performance of the 9-QAM liked super-Nyquist signal is also experimentally demonstrated. Using this scheme, we then successfully transmit 10 channels 440-Gb/s signal over 3000- km ULAF and 10 cascaded ROADMs with 100-GHz-grid based on the single-carrier ETDM 110-GBaud QPSK. It is the highest baud rate of all-ETDM signal reported with the highest net SE at this baud rate for PDM-QPSK signal.

We fabricated a narrow linewidth 1.55μm directly-modulated distributed-feedback (DFB) laser. The laser exhibits an output power of 14mW at 100mA, flat frequency response with -3 dB bandwidth of 18 GHz, the third-order intermodulation distortion (IMD3) with 39.8dBm, narrow optical linewidth with 181kHz, and RIN below -135.7dB/Hz in the 0.1-10GHz range along with the high side-mode suppression ratio (<52dB). We also experimentally verified the modulation bandwidth, linearity, and linewidth is related to the bias current. The characteristics of the laser, namely sufficient modulation bandwidth, high linearity, low relative intensity noise (RIN) and narrow linewidth, make it the perfect candidates for high dynamic directly modulated analog optical link.

An ultra wideband optical frequency comb (OFC) generator based on semiconductor Quantum dot F-P cavity is packaged by our group. The free spectral rage (FSR) of the OFC can be tunable from 97GHz to 100GHz and the pulse width of the 100GHz OFC is 1.2ps.The full span of the OFC spectra is 80nm with a Gaussian shaped, and in span of 10nm, the flatness of the OFC can be limited to 1.7dB. The OFC has the advantages of small volume, simple and compact structure, low power dissipation, and has an ultra-wide bandwidth and flat spectrum, which can be used in the field of arbitrary waveform generation, channel information processing, and optical frequency division multiplexing.

Mid-infrared pulsed fiber laser with centered wavelength from 2 to 5 μm have attracted substantial attention owing to their potential applications in defence, laser microsurgery, material processing, nonlinear frequency conversion, etc. We demonstrated our recent achievements at 3 μm pulsed fiber lasers by utilizing Q-switching method. Firstly, a cascaded dual wavelength actively Q-switched Ho3+-doped ZBLAN fiber was reported by inserting an external electrically driven acoustic-optical modulator (AOM) into the cavity. The 3.0 μm and 2.07 μm pulse trains were achieved with a μs level time delay corresponding to the pulse energy of 29 μJ and 7 μJ, pulse duration of 380 ns and 260 ns, respectively. The narrower pulse width in this case compared to that in passively Q-switched fiber lasers can be attributed to the much higher modulation depth of AOM. Using a reversely designed semiconductor saturable mirror (SESAM) as the saturable absorber (SA), we presented a passively Q-switched Ho³⁺-doped ZBLAN fiber laser operating at ~2971 nm, the obtained maximum pulse energy of 6.65 μJ only limited by the maximum pump power was also the highest level from passively Q-switched fiber lasers at this wavelength range, and corresponding pulse repetition rate and duration were 47.6 kHz and 1.68 μs, respectively. Then using a Fe²⁺: ZnSe crystal with an initial transmission of 69 % as the SA, a passively Q-switched Ho³⁺-doped ZBLAN fiber laser operating at 2970.3 nm was also achieved. The obtained pulse duration and repetition rate were 1.92 μs and 62.74 kHz, respectively with an output power of 266 mW and a pulse energy of 4.24 μJ. The further performance improvements were possible because they were just limited by the maximum pump power. To sum up, the above achievements would be beneficial for further development of mid-infrared pulsed fiber lasers.

We report the first demonstration of blue shift of optical pumping photonic crystal (PhC) laser. A femtosecond laser was used to pump the InGaAsP based two dimensional photonic crystal laser at room temperature. Linear dependence of the resonance wavelength with respect to the pump power is observed: dλ/dP=-1.5×10^-2 nm/μW . Blue shift of overall 1.1nm was obtained with the increase power of pump laser. These results are in agreement with theoretical expectation while the carrier-induced index change is introduced into the PhC semiconductor laser. It shows a possibility that by proper wafer design and careful optimization, we may obtain wavelength stable photonic crystal laser, which is important in photonic integration.

Self-mixing interferometry (SMI) is considered both efficient and accurate for alpha factor measurement. In this work, a high-performance filtering method and effective data processing algorithms are combined to optimise the measurement accuracy on the frequency-domain based alpha measurement method. In order to achieve fast real-time measurement, FPGA (Field Programmable Gate Arrays) is employed for the implementation of the proposed algorithms. The FPGA design includes noise reduction, SMI signal normalisation, phase signal detection, spectrum calculation and alpha estimation. The results show that the FPGA based design can achieve fast and reliable alpha factor measurement.

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.

High-resolution absorption measurements of H₂O using direct absorption spectroscopy technology were made to acquire the spectroscopic parameters of High Resolution Transmission Molecular Absorption Database (HITRAN database). The most important spectral parameters frequently used in the researchers and study, was calculated from the integrated absorbance area of H₂O at the different temperature from 296K to 923K of the spectrum near 1397nm based on the distributed feedback laser. From the result of experiment, the calculated spectral parameters was compared with the literature values from HITRAN database. The method and results of the measurement obtained from this paper are expected to be helpful in the supply of the sufficient accuracy spectral parameters in the practical measurement.

This paper has established a thermal model of Vertical-external-cavity surface-emitting semiconductor laser (VECSELs) with water-cooled heatsink, calculated the distribution of temperature field with finite element method, and studied the effects of pumping light, heat transfer coefficient, and heatsink characteristics on the maximum temperature of the quantum well. Calculations show that there is an optimal heat transfer coefficient value interval, thermal conductivity of the VECSELs heatsink will have a significant impact on the maximum temperature of the quantum well, and increasing area of cooler heatsink would help to improve heat dissipation performance. It also shows that the maximum temperature of the quantum well has a linear relationship with pump power, and a nearly inverse relationship with the spot size. Due to thermal diffusion of water-cooled heatsink for VECSELs point heat source, the maximum temperature of quantum well is not sensitive to thickness and area of the heatsink, heat dissipation performance which uses a diamond heatsink is about 1.7 times the oxygen-free copper heatsink.

We investigated the etching process especially for the integrated InGaAs/InP multiquantum-well laser. Two different ways of etching process were demonstrated, which are RIE followed by selective wet etching and selective wet etching only. The latter one showed ideal interface between active region and passive waveguide after regrowth. This etching process is simpler and more effective than the first one. Using this process, we also fabricated a 1.79-μm DBR laser with 350-μm active region and 400-μm passive waveguide. The output power and threshold current and were demonstrated as a function of temperature. The wavelength tuning characters were investigated with current and temperature changes. It is demonstrated that this etching process can be successfully used to fabricate integrated photonic devices with InGaAs/InP materials and the DBR laser can be a candidate for gas sensing system due to the single mode and large tuning range.

2.X μm InGa(As)Sb/AlGaAsSb compressively strained quantum wells laser has been grown and fabricated. Antimonide laser with 1.5mm*90μm without AR/HR emitted 550mW of continuous wave output power at 2μm.And 2.4μm laser without AR/HR output 195mW at room temperature.

A method for measuring blood oxygenation and blood flow rate using a single widely tunable semiconductor laser is proposed and investigated. It is shown that a 700-nm-band tunable laser gives the highest sensitivity for blood oxygen measurement. The corresponding tunable laser is designed using the V-coupled cavity structure. The wavelength tuning range can reach 8 nm, which is sufficient for the blood oxygenation measurement in the 700-nm-band by using the Beer- Lambert law. In contrast to conventional blood oxygenation measurement method based on two LEDs, the laser can be used at the same time to measure the blood flow rate based on the Doppler principle.

An asymmetric sampled Bragg grating (SBG) semiconductor laser, which consists of two sections with same length but different sampling duty cycle, can be introduced an arbitrary equivalent-phase-shift (EPS) into its center. At the same time, to adjust the sampling duty cycles in the two sections as different magnitude, the studied laser can output more lasing power from its one facet than that from the other one. That is to say, this method can be used to design and fabricate the EPS SBG semiconductor laser with higher output efficiency.

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 (λ_PL=1535nm) and modulator area (λ_PL=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.

We present a 1560-nm-band digitally wavelength tunable V-coupled-cavity semiconductor laser monolithically integrated with two waveguides based monitoring photodiodes (MPD) through deeply etched reflective trenches. The reflective trenches are designed to be 1.16μm wide, about three quarters of the wavelength, and are deeply etched through the waveguide with a depth larger than 4μm. Due to the high reflectivity of the etched trenches, a low threshold current of 19mA is achieved. Using a single electrode control, wavelength tuning of 22 channels at 100GHz spacing with SMSR above 35 dB is obtained. The relationship between the photocurrents of the two MPD at the two waveguide branches and the laser output power from the coupler side is investigated as a function of the wavelength. Since the integrated tunable laser with MPDs is very compact and does not involve any grating or epitaxial regrowth, it is suitable for low-cost multifunctional photonic applications for access and data center networks.

Edge-emitting laser diodes operating at 900 nm are designed and fabricated with an epitaxial one-dimensional photonic crystal (PC). PC structure consists of a p-waveguide layer, an active quantum region, and an n-waveguide layer. The p-cladding totally reflects one tilted optical mode. The PC with a particular band structure confines the optical mode with a certain tilted angle. Meanwhile mode extends vertically due to the photonic band modulation at the direction perpendicular to the interface. Then we obtain the broad-area lasers with a narrow vertical far-field divergence of 10°, and a small thermal shift (dλ/dT~-0.06 nm/K) in continuous wave operation.