New Scheme of MEMS-Based LiDAR by Synchronized Dual-Laser Beams for Detection Range Enhancement.

A new scheme presents MEMS-based LiDAR with synchronized dual-laser beams for detection range enhancement and precise point-cloud data without using higher laser power. The novel MEMS-based LiDAR module uses the principal laser light to build point-cloud data. In addition, an auxiliary laser light amplifies the single-noise ratio to enhance the detection range. This LiDAR module exhibits the field of view (FOV), angular resolution, and maximum detection distance of 45° (H) × 25° (V), 0.11° (H) × 0.11° (V), and 124 m, respectively. The maximum detection distance is enhanced by 16% from 107 m to 124 m with a laser power of 1 W and an additional auxiliary laser power of 0.355 W. Furthermore, the simulation results show that the maximum detection distance can be up to 300 m with laser power of 8 W and only 6 W if the auxiliary laser light of 2.84 W is used, which is 35.5% of the laser power. This result indicates that the synchronized dual-laser beams can achieve long detection distance and reduce laser power 30%, hence saving on the overall laser system costs. Therefore, the proposed LiDAR module can be applied for a long detection range in autonomous vehicles without requiring higher laser power if it utilizes an auxiliary laser light.

Microlens array device for laser light shaping in laser scanning smart headlights.

We present, what we believe to be, a novel microlens array (MLA) scheme for laser light shaping in laser scanning smart headlight. The laser spot has a Gaussian distribution that may reach a high peak power density in the central part, which is called hot spot. When the laser beam is applied to a phosphor plate for luminous conversion, the hot spot of Gaussian beam causes thermal quench and decreases luminous efficacy. To avoid this effect, an MLA is used, so as to achieve a uniform energy distribution. In this study, we propose a laser scanning smart headlight fabricated by a new MLA structure, with an arrangement providing both light uniformity and shaping. The novel MLA is designed by two-dimensional micro-concave lens array yielding a flat-top beam. The flexible fabrication process employs laser drilling to shape the micro-hole array on the glass substrate surface and then etch it to form MLA without requiring any mask lithography process. The full-width half maximum (FWHM) of light output distribution can be adjusted by the glass etching parameters, and the light distribution could be controlled by the arranged layout of the array. Thus, beams with FWHM divergence ranging from 5° to 34° has been fabricated and characterized. The typical pixel shape is a rectangle with two different FWHMs in two orthogonal directions, and the fabrication method achieves this goal as well. This novel design and unique maskless process of the MLAs is a promising tool for development the next generation laser scanning smart headlight.

Laser-assisted LED for adaptive-driving-beam headlights employing ultra-reliable single crystal phosphor for autonomous vehicles.

A novel laser-assisted LED for adaptive-driving-beam (ADB) headlights employing an ultra-reliable Ce3+: YAG-based single crystal phosphor (SCP)-converter layer for use in autonomous vehicles is demonstrated. The SCP fabricated at a high-temperature of 1,940°C exhibited better thermal stability than other phosphor-converter materials, evidenced by a thermal aging test. The high-beam pattern of the ADB is measured at a luminous intensity of 88,436 cd at 0°, 69,393 cd at ± 2.5°, and 42,942 cd at ± 5°, which well satisfies the ECE R112 class B regulation. The advantage of introducing the laser-assisted LED system employing the highly reliable SCP is to produce the high intensity for the ADB, which enables the increase of the field of view by 20% and the brightness by 28% for the ADB headlight and results in improving the visibility from ± 7° to ± 8.5° and the illumination distance up to 200 m. This proposed advance ADB headlight with the ultra-reliable SCP and the novel laser-assisted LED is favorable as one of the most promising ADB light source candidates for use in the next-generation autonomous vehicle applications.

High color rendering index of 94 in white LEDs employing novel CaAlSiN3: Eu2+ and Lu3Al5O12: Ce3+ co-doped phosphor-in-glass.

High color rendering index (CRI) and wide correlated color temperatures (CCTs) white LEDs (WLEDs) employing CaAlSiN3: Eu2+ and Lu3Al5O12: Ce3+ co-doped phosphor-in-glass (PiG) are demonstrated. Through fabrication using a low sintering temperature of 620°C to minimize inter-diffusion between the red phosphor and glass, and adjusting thickness of 0.5-0.7 mm to obtain the chromaticity tailorable co-doped PiG, the WLEDs exhibit high CRI of 94 and wide CCTs of 3900 K to 5300 K. This CRI is the highest yet reported for the co-doped PiG. The proposed of the co-doped PiG with good thermal stability fabricated by using a low sintering temperature may provide a novel technique to achieve high-performance WLEDs with high CRI for use in many high-quality of indoor lighting applications, especially in color inspection, clinical inspection, and gallery lighting.

New scheme of LiDAR-embedded smart laser headlight for autonomous vehicles.

A new scheme of LiDAR-embedded smart laser headlight module (LHM) for autonomous vehicles is proposed and demonstrated. The LiDAR sensor was fabricated by LeddarTech with the wavelength of 905-nm, whereas the LHM was fabricated by a highly reliable glass phosphor material that exhibited excellent thermal stability. The LHM consisted of two blue laser diodes, two blue LEDs, a yellow glass phosphor-converter layer with a copper thermal dissipation substrate, and a parabolic reflector to reflect the blue light and the yellow phosphor light combined into white light. The LHM exhibited a total output optical power of 9.5 W, a luminous flux of 4,000 lm, a relative color temperature of 4,300 K, and an efficiency of 421 lm/W. The high-beam patterns of the LHMs were measured to be 180,000 luminous intensity (cd) at 0° (center), 84,000 cd at ± 2.5°, and 29,600 cd at ± 5°, which met the ECE R112 class B regulation. The low-beam patterns also satisfied the ECE R112 class B regulation as well. Integrating the signals received from the Lidar detection and CCD image by a smart algorithm, we demonstrated the generation of smart on/off signals for controlling the laser headlights. The recognition rate of the objects was evaluated to be more than 86%. This novel LiDAR-embedded smart LHM with the unique highly reliable glass phosphor-converter layer is favorable as one of the most promising candidates for use in the next-generation high-performance autonomous vehicle applications.

An advanced laser headlight module employing highly reliable glass phosphor.

An advanced laser headlight module (LHM) employing highly reliable glass phosphor is demonstrated. The novel glass-based YAG phosphor-converter layers fabricated by low-temperature of 750°C exhibited better thermal stability. The LHM consisted of a 5 × 1 blue laser diode array, an aspherical lens, a glass phosphor-converter layer with an aluminum thermal dissipation substrate, and a dichroic filter to allow pass blue light and reflect yellow phosphor light. The 5 × 1 blue laser array was packaged with five blue lasers having optical power of 1.2 W per laser. The LHM exhibited total output optical power of 6 W, luminous flux of 1860 lm, relative color temperature of 4100 K, and efficiency of more than 310 lm/W. The high-beam patterns of the LHMs were measured to be 45,000 luminous intensity (cd) at 0°, 31,000 cd at ± 2.5°, and 12,500 cd at ± 5°, which were well satisfied the ECE R112 class B regulation. The proposed high-performance LHM with highly reliable glass-based phosphor-converter layer fabricated by low temperature is favorable as one of the promising LHM candidates for use in the next-generation automobile headlight applications.

Micro-hyperboloid lensed fibers for efficient coupling from laser chips.

A novel technique is presented for producing micro-hyperboloid lensed fibers for efficient coupling to semiconductor laser chips. A three-step process including a precision mechanical grinding, a spin-on-glass (SOG) coating and an electrostatic pulling process is used to form the hyperboloid lens structure on a flat-end single mold fiber (SMF) with the core diameter of 6.6 µm. Micro-hyperboloid lensed fibers with tunable radii of curvature around 4.18 - 4.83 µm can be formed on the SMF end face. A high average coupling efficiency around 80% and low coupling variation of 0.116 ± 0.044% are obtained for the produced fibers. The developed method is efficient to produce micro-hyperboloid lensed fibers for high-performance light coupling between the SMF and the semiconductor diode lasers.

Comparison of single-/few-/multi-mode 850 nm VCSELs for optical OFDM transmission.

For high-speed optical OFDM transmission applications, a comprehensive comparison of the homemade multi-/few-/single-transverse mode (MM/FM/SM) vertical cavity surface emitting laser (VCSEL) chips is performed. With microwave probe, the direct encoding of pre-leveled 16-QAM OFDM data and transmission over 100-m-long OM4 multi-mode-fiber (MMF) are demonstrated for intra-datacenter applications. The MM VCSEL chip with the largest emission aperture of 11 µm reveals the highest differential quantum efficiency which provides the highest optical power of 8.67 mW but exhibits the lowest encodable bandwidth of 21 GHz. In contrast, the SM VCSEL chip fabricated with the smallest emission aperture of only 3 µm provides the highest 3-dB encoding bandwidth up to 23 GHz at a cost of slight heat accumulation. After optimization, with the trade-off set between the receiving signal-to-noise ratio (SNR) and bandwidth, the FM VCSEL chip guarantees the highest optical OFDM transmission bit rate of 96 Gbit/s under back-to-back case with its strongest throughput. Among three VCSEL chips, the SM VCSEL chip with nearly modal-dispersion free feature is treated as the best candidate for carrying the pre-leveled 16-QAM OFDM data over 100-m OM4-MMF with same material structure but exhibits different oxide-layer confined gain cross-sections with one another at 80-Gbit/s with the smallest receiving power penalty of 1.77 dB.

Efficient Heat Dissipation of Uncooled 400-Gbps (16×25-Gbps) Optical Transceiver Employing Multimode VCSEL and PD Arrays.

An effective heat dissipation of uncooled 400-Gbps (16×25-Gbps) form-factor pluggable (CDFP) optical transceiver module employing chip-on-board multimode 25-Gbps vertical-surface-emitting-laser (VCSEL) and 25-Gbps photodiode (PD) arrays mounted on a brass metal core embedded within a printed circuit board (PCB) is proposed and demonstrated. This new scheme of the hollow PCB filling with thermally-dissipated brass metal core was simulated and used for high temperature and long term stability operation of the proposed 400-Gbps CDFP transceiver. During one-hour testing, a red-shift of central wavelength by 0.4-nm corresponding temperature increment of 6.7 °C was observed with the brass core assisted cooler module. Such a temperature change was significantly lower than that of 28.3 °C for the optical transceiver driven with conventional circuit board. After 100-m distance transmission over a multimode fiber (OM4), the 400-Gbps CDFP transceiver exhibited dispersion penalty of 2.6-dB, power budget of ≧ 3-dB, link loss of ≦ 0.63-dB, mask margin of 20%, and bit error rate (BER) of <10-12 with maintained stability more than one hour. The developed 400-Gbps CDFP transceiver module employing low-power consumption VCSEL and PD arrays, effective coupling lens arrays, and well thermal-dissipation brass metal core is suitable for use in the low-cost and high-performance data center applications.

Broadband Ce/Cr-doped crystal fibers for high axial resolution OCT light source.

The fabrication and characteristics of Ce/Cr-doped crystal fibers employing drawing tower technique are reported. The fluorescence spectrum of the Ce/Cr fibers at the core diameter ranging from 10 to 21 µm exhibited a 200-nm near-Gaussian broadband emission which enabled to provide an axial resolution of 1.8-µm and a power density of 79.1 nW/nm. The proposed broadband Ce/Cr-doped crystal fibers may be provided as a high-resolution light source for the use in optical coherence tomography system as well as industrial inspection and biomedical imaging applications.

Chromaticity tailorable glass-based phosphor-converted white light-emitting diodes with high color rendering index.

In this paper, Lu3Al5O12:Ce3+ and CaAlSiN3: Eu2+ co-doped glass are presented as color conversion materials for white light-emitting diodes (WLEDs). Through adjusting the thickness of the glass phosphors, the chromaticity and CCT of the WLEDs follows the Planckian locus well. The WLEDs show CCT ranging from ~4000K to ~7000K with high CRI ranging from 83 to 90 due to the wide emission spectrum from the proposed glass phosphors. The glass phosphors provide an effective way to achieve chromaticity-tailorable WLEDs with high color quality for indoor lighting applications.

Novel broadband glass phosphors for high CRI WLEDs.

New broadband glass phosphors with excellent thermal stability were proposed and experimentally demonstrated for white light-emitting-diodes (WLEDs). The novel glass phosphors were realized through dispersing multiple phosphors into SiO2 based glass (SiO2-Na2O-Al2O3-CaO) at 680°C. Y3Al5O12:Ce³âº (YAG), Lu3Al5O12:Ce³âº (LuAG), and CaAlSiN3: Eu²âº (nitride) phosphor crystals were chosen respectively as the yellow, green, and red emitters of the glass phosphors. The effect of sintering temperature on inter-diffusion reduction between phosphor crystals and amorphous SiO2 in nitride-doped glass phosphors was studied and evidenced by the aid of high-resolution transmission electron microscopy (HRTEM). Broadband glass phosphors with high quantum-yield of 55.6% were thus successfully realized through the implementation of low sintering temperature. Proof-of-concept devices utilizing the novel broadband phosphors were developed to generate high-quality cool-white light with trisstimulus coordinates (x, y) = (0.358, 0.288), color-rending index (CRI) = 85, and correlated color temperature (CCT) = 3923K. The novel broadband glass phosphors with excellent thermal stability are essentially beneficial to the applications for next-generation solid-state indoor lighting, especially in the area where high power and absolute reliability are required.

Fluorescence enhancement in broadband Cr-doped fibers fabricated by drawing tower.

The fluorescence enhancement in broadband Cr-doped fibers (CDFs) fabricated by a drawing tower with a redrawn powder-in-tube preform is proposed and demonstrated. The CDFs after heat treatment exhibited Cr4⁺ emission enhancement with spectral density of 200 pW/nm, verified by the formation of α-Mg2SiO4 nanocrystalline structures in the core of CDFs. The high fluorescence achievement in the CDFs is essential to develop a broadband CDF amplifier for next-generation optical communication systems.

Stable mode-locked fiber laser based on CVD fabricated graphene saturable absorber.

A stable mode-locked fiber laser (MLFL) employing multi-layer graphene as saturable absorber (SA) is presented. The multi-layer graphene were grown by chemical vapor deposition (CVD) on Ni close to A-A stacking. Linear absorbance spectrum of multi-layer graphene was observed without absorption peak from 400 to 2000 nm. Optical nonlinearities of different atomic-layers (7-, 11-, 14-, and 21- layers) graphene based SA are investigated and compared. The results found that the thicker 21-layer graphene based SA exhibited a smaller modulation depth (MD) value of 2.93% due to more available density of states in the band structure of multi-layer graphene and favored SA nonlinearity. A stable MLFL of 21-layer graphene based SA showed a pulsewidth of 432.47 fs, a bandwidth of 6.16 nm, and a time-bandwidth product (TBP) of 0.323 at fundamental soliton-like operation. This study demonstrates that the atomic-layer structure of graphene from CVD process may provide a reliable graphene based SA for stable soliton-like pulse formation of the MLFL.

Liquid crystal modified photonic crystal fiber (LC-PCF) fabricated with an un-cured SU-8 photoresist sealing technique for electrical flux measurement.

The optical transmission properties of photonic crystal fibers (PCFs) can be manipulated by modifying the pattern arrangement of the air channels within them. This paper presents a novel MEMS-based technique for modifying the optical transmission properties of commercial photonic-crystal fiber (PCF) by selectively filling the voids within the fiber structure with liquid crystals. In the proposed approach, an un-cured SU-8 ring pattern with a thickness of 5 µm is fabricated using a novel stamping method. The PCF is then brought into contact with the SU-8 pattern and an infra-red (IR) laser beam is passed through the fiber in order to soften the SU-8 surface; thereby selectively sealing some of the air channels with molten SU-8. Liquid crystals (LCs) are then infiltrated into the un-sealed holes in the PCF via capillary effects in order to modify the transmission properties of the PCF. Two selectively-filled PCFs are fabricated, namely an inner-ring LC-PCF and a single-line LC-PCF, respectively. It is shown that the two LC-PCFs exhibit significantly different optical behaviors. The practical applicability of the proposed selective-filling approach is demonstrated by fabricating an electric field sensor. The experimental results show that the sensor has the ability to measure electric fields with an intensity of up to 40 kV/cm.

Pulse shortening mode-locked fiber laser by thickness and concentration product of carbon nanotube based saturable absorber.

The dependence of thickness and concentration product (TCP) of single-wall carbon nanotubes saturable absorber (SWCNTs SA) on stabilizing and shortening pulsewidth in mode-locked fiber lasers (MLFLs) was investigated. We found that an optimized TCP for pulse energy and nonlinear self-phase modulation (SPM) enabled to determine the shorter pulsewidth and broader 3-dB spectral linewidth of the MLFLs. The shortest MLFL pulsewidth of 418 fs and broad spectral linewidth of 6 nm were obtained as the optimized TCP was 70.93 (µm•wt%), which was in good agreement with the area theorem prediction. This significant effect of TCP on pulse energy, SPM, pulsewidth, and spectral linewidth of MLFLs suggests that the TCP represents the total amount of SWCNTs in SA, which can be used as one of important and key parameters for characterizing the passive MLFL pulsewidth.

Direct near-field phase measurement of laser diodes employing a single-mode fiber interferometer.

A method of direct measurement of near-field phase and intensity distribution of laser diodes employing a single-mode fiber interferometer is proposed and demonstrated. The phase and intensity of the output beam of the laser in the vicinity of the output facet are measured directly via interferometry. Using a 980 nm laser diode as an example, we obtained a beam width of 0.9 and 3.6 µm at the output facet in the vertical and horizontal axes, respectively. In addition, the phase information of the output beam was also obtained by using interferometry. This technique is particularly useful for laser diodes whose near-field phases are difficult to measure directly. The measured vertical and horizontal wavefront radius of curvatures of a laser diode are in good agreement with the calculation from Gaussian beam theory. Detailed understanding and measurement of the near-field phase and intensity distributions of light sources and optical components are essential for micro-optic designs with better mode matching to minimize the insertion loss.

Concentration effect of carbon nanotube based saturable absorber on stabilizing and shortening mode-locked pulse.

We comprehensively investigated the concentration effect of dispersed single-walled carbon nanotubes (SWCNTs) in polymer films for being a saturable absorber (SA) to stabilize the mode locking performance of the erbium-doped fiber laser (EDFL) pulse through the diagnosis of its nonlinear properties of SA. The measured modulation depth was from 1 to 4.5% as the thickness increased 18 to 265 microm. The full-width half-maximum (FWHM) of the stable mode-locked EDFL (MLEDFL) pulse decreased from 3.43 to 2.02 ps as the concentrations of SWCNTs SA increased 0.125 to 0.5 wt%. At constant concentration of 0.125 wt%, the similar pulse shortening effect of the MLEDFL was also observed when the FWHM decreased from 3.43 to 1.85 ps as the thickness of SWCNTs SA increased 8 to 100 microm. With an erbium-doped fiber length of 80 cm, the shortest pulse width of 1.85 ps were achieved at 1.56 microm with a repetition rate of 11.1 MHz and 0.2 mW of the output power under an output coupling ratio of 5%. An in-depth study on the stable mode-locked pulse formation employing SWCNTs SA, it is possible to fabricate the SWCNT films for use in high performance MLEDFL and utilization of many other low-cost nanodevices.

Photo and electrical tunable effects in photonic liquid crystal fiber.

This work demonstrates photo alignment and electrical tuning effects in photonic liquid crystal fiber (PLCF). Applying voltages of 0 approximately 130V and 250 approximately 400V shifts the short and long wavelength edges of the transmission bands by about 45 nm and 74 nm toward longer wavelengths, respectively. An electro-tunable notch filter is formed in the PLCF without the use of gratings. The range of tunability of the notch filter is around 180 nm with an applied voltage of 140 approximately 240 V. This photo-induced alignment yields a permanently tilted LC structure in PCF, which reduces the threshold voltage, and can be further modulated by electric fields. The polarization dependent loss and fast response time of photo-aligned PLCF is also demonstrated. The finite-difference frequency-domain method is adopted to analyze the shift of the transmission bandgap, and the simulation results are found to correlate well with experimental data.

Fabrication and Performance of MEMS-Based Pressure Sensor Packages Using Patterned Ultra-Thick Photoresists.

A novel plastic packaging of a piezoresistive pressure sensor using a patterned ultra-thick photoresist is experimentally and theoretically investigated. Two pressure sensor packages of the sacrifice-replacement and dam-ring type were used in this study. The characteristics of the packaged pressure sensors were investigated by using a finite-element (FE) model and experimental measurements. The results show that the thermal signal drift of the packaged pressure sensor with a small sensing-channel opening or with a thin silicon membrane for the dam-ring approach had a high packaging induced thermal stress, leading to a high temperature coefficient of span (TCO) response of -0.19% span/°C. The results also show that the thermal signal drift of the packaged pressure sensors with a large sensing-channel opening for sacrifice-replacement approach significantly reduced packaging induced thermal stress, and hence a low TCO response of -0.065% span/°C. However, the packaged pressure sensors of both the sacrifice-replacement and dam-ring type still met the specification -0.2% span/°C of the unpackaged pressure sensor. In addition, the size of proposed packages was 4 × 4 × 1.5 mm(3) which was about seven times less than the commercialized packages. With the same packaging requirement, the proposed packaging approaches may provide an adequate solution for use in other open-cavity sensors, such as gas sensors, image sensors, and humidity sensors.