Distributed Feedback Laser Research Articles

Stepped-height ridge waveguide MQW polarization mode converter monolithically integrated with sidewall grating DFB laser.

We report, to the best of our knowledge, the first demonstration of a 1555-nm stepped-height ridge waveguide polarization mode converter monolithically integrated with a sidewall grating distributed-feedback (DFB) laser using the identical epitaxial layer scheme. The device shows stable single longitudinal mode (SLM) operation with the output light converted from TE to TM polarization with an efficiency of >94% over a wide range of DFB injection currents (IDFB) from 140 mA to 190 mA. The highest TM mode purity of 98.2% was obtained at IDFB = 180 mA. A particular advantage of this device is that only a single step of metalorganic vapor-phase epitaxy and two steps of III-V material dry etching are required for the whole integrated device fabrication, significantly reducing complexity and cost.

Low-cost automated spin coater and thermal annealer for additive prototyping of multilayer Bragg reflectors

We present and implement a design for an automated system that fabricates multilayer photonic crystal structures. The device is constructed with low-cost materials. A polystyrene/cellulose acetate multilayer Bragg reflector was fabricated to confirm the device's capability. A distributed feedback laser was also fabricated and characterized. The system has also been used to fabricate microlasers for a Modern Physics laboratory assignment in which students measure fluorescence, amplified spontaneous emission, lasing from one-dimensional Bragg reflectors, and lasing from scattering media.

Laser-induced periodic surface structures as optical resonators for organic thin-film distributed feedback lasers

Laser-induced periodic surface structures (LIPSS) have received considerable attention due to their potential for micro-and nanostructuring and surface functionalization of various materials. We present a novel application of LIPSS on a glass substrate as distributed feedback (DFB) laser resonators, capable of providing sufficient positive optical feedback to achieve lasing in thin-film waveguides with organic small molecules as a gain medium. The direct femtosecond micromachining allows for easy variation of the periodicity across a broad range of values, including those required to reach 1st Bragg order DFB operation. We investigate several small molecule organic thin-film systems and observe lasing in strong accordance with the underlying periodicities of all photonic structures involved. These results demonstrate the effectiveness of LIPSS as DFB laser resonators and suggest that they could facilitate the integration of organic thin-film media-based lasers and other photonic devices into various integrated photonic systems.

Wideband tunable REC-DFB laser array using thin-film heaters on the submount

A wideband wavelength-tunable 4×5 distributed feedback (DFB) semiconductor laser array based on the reconstruction-equivalent-chirp (REC) technique using a simple tuning scheme is demonstrated. It consists of 20 DFB lasers with 4×5 matrix interleaving distributions, two-level cascaded Y-branch optical combiners, and one active semiconductor optical amplifier (SOA), all in-series integrated on one chip. Unlike the traditional thermal-electric cooler (TEC)-based wavelength-tuning scheme, the tunable 4×5 REC-DFB laser array achieves a faster and broader continuous wavelength-tuning range using TaN thin-film heaters integrated on the AlN submount. By changing the injection current of the TaN resistor from 0 to 190 mA, the proposed tunable laser achieves a wavelength-tuning range of ∼2.5 nm per channel and a total tuning of over 50 nm. This study opens up new avenues for realizing cost-effective and wide-tuning-range semiconductor lasers.

InAs/GaAs quantum dot laterally coupled distributed feedback lasers at 1.3 μm

We report the InAs/GaAs quantum dot laterally coupled distributed feedback (LC-DFB) lasers operating at room temperature in the wavelength range of 1.31 µm. First-order chromium Bragg gratings were fabricated alongside the ridge waveguide to obtain the maximum coupling coefficient with the optical field. Stable continuous-wave single-frequency operation has been achieved with output power above 5 mW/facet and side mode suppression ratio exceeding 52 dB. Moreover, a single chip integrating three LC-DFB lasers was tentatively explored. The three LC-DFB lasers on the chip can operate in single mode at room temperature, covering the wavelength span of 35.6 nm.

A Width Measurement Method of Line Shape Based on Second Harmonic Peak and Modulation Amplitude.

The line width of different line shapes is a very important parameter in absorption spectroscopy sensing techniques. Based on the high sensitivity and low noise properties of wavelength modulation spectroscopy, we report a novel line width measurement method. After theoretically proving the relationship between line width, modulation amplitude and the amplitude of the second harmonic at the center frequency, the absorption lines of CH4 near 6046.96 cm-1 and CO2 4989.97 cm-1 were chosen for simulation, and the relative errors of the line width between our method and theoretical data were kept at about 1%. A distributed feedback laser diode operating near 1653 nm with three different concentrations of CH4 was used for experimental validation, and the results were consistent with the numerical simulation. Additionally, since only the peaks of second harmonic need to be measured, the advantages of wavelength modulation can be utilized while reducing the difficulty of data acquisition.

High-Output-Power 1358-nm-Wavelength SOA-Integrated EADFB Laser (AXEL) for 25-Gbit/s 100-km Transmissions

We developed a 1358-nm-wavelength semiconductor optical amplifier (SOA)-assisted extended-reach electroabsorption modulator integrated distributed feedback laser (AXEL) as a high-power light source for 25G-class passive optical networks (PONs) to ensure sufficient power margin in the transmitter and extend the transmission reach to 100 km. We investigated the effect of the integrated SOA length on the light output power and modulation performance of the AXEL. We found that there was no significant degradation in modulation performance at 25 Gbit/s even for an AXEL with a 175-μm-long SOA. Using this AXEL chip, we fabricated a transmitter by using a commercially available package. The transmitter attained sufficient modulated light output power of 10. 5 dBm and had a high-quality eye diagram for 25-Gbit/s operation. In addition, we found that the measured chirp parameter of the AXEL transmitter was almost 0. This alleviates the transmission distance limitation due to chromatic dispersion and enables the transmission distance to be extended. The loss budget for 20-km transmission, as determined from the measured bit error rate, was 38.4 dB, which is much larger than the value specified for 25G-EPONs. Moreover, the transmission reach was extended to 100 km for the first time, thanks to the AXEL transmitter's high output power. Finally, the possibility of incorporating the AXEL in 100-Gbit/s-ZR4 (80 km) applications using four wavelength channels was considered. The estimated power penalties using the measured chirp parameter were significantly smaller than the measured penalty for 1358 nm. This suggests that the AXEL can also be used for 100-Gbit/s over 80-km transmissions using four channels in a LAN-WDM grid.

Active waveguide Bragg lasers via conformal contact PDMS stamps

Lasing is observed in Bragg lasers formed through conformal contact of a patterned PDMS stamp with a plain active film, spincoated on glass. The thresholds, output efficiencies and spectral characteristics are compared to standard substrate patterned gratings and is discussed in relation to the coupling coefficient upkappa . The reported thresholds are highly sensitive in distributed feedback (DFB) lasers to grating duty cycles, for both PDMS-air and substrate–film lasers. Overall, laser thresholds of PDMS-air (PA) DFB lasers are found to be significantly higher than substrate–film (SF) lasers, which is attributed to an approximate three-fold reduction of optical-confinement in the grating region. Slope output efficiencies are found to be comparatively higher in PA lasers relative to SF lasers for both DFB and DBR configurations and is attributed to several competing factors. The PDMS can be removed from the surface of the active film repeatedly and conformal contact is limited mainly by the particle build up on the PDMS surface. The proposed PA system is expected to be useful in rapid laser metrology of new gain materials and in practical applications of optically pumped lasers.

Flexible, Stretchable, Tunable, and Switchable DFB Laser

We are reporting on easily-made, flexible, wearable, and stretchable holographic gratings for tunable distributed-feedback lasers. The laser device is formed by the integration of a reflection volume phase grating in a flexible substrate. The grating is recorded in a photopolymerizable mixture by using optical holography. The photopolymerizing material is a new compound derived from a recently developed mixture which is based largely on haloalkanes and acrylates. An appropriate choice of photoinitiators promotes the photoactivation of the monomers at the writing wavelength of 460 nm. The laser device has a low emission threshold due to the high efficiency of the photopolymerization process at 460 nm. Finally, the amplified spontaneous emission of the device can be continuously tuned by simply bending the film. This peculiarity is promising for the manufacturing of optical pumped tunable organic lasers and flexible displays.

Ultra-wideband discrete Raman amplifier optimization for single-span S-C-L-band coherent transmission systems.

We experimentally compare the performance of two key ultra-wideband discrete Raman amplifier structures, a cascaded dual-stage structure and an in-parallel dual-band structure, in fully loaded S-C-L band coherent transmission systems over 70 km of single-mode fiber. Our results show that dual-band discrete Raman amplifier with minimized backreflections can effectively avoid unstable random distributed feedback lasing, reduce the noise figure, and therefore improve the transmission performance for signals at shorter wavelengths, versus the cascaded dual-stage structure. The average noise figure for S-band signals is 6.8 dB and 7.2 dB for the dual-band structure and cascaded dual-stage structure, respectively, while the average S-band Q2 factor is similarly improved by 0.6 dB. Moreover, the cascaded dual-stage discrete Raman amplifier requires guard bands around the 1485-nm and 1508-nm pumps as the signal and pump wavelengths overlap, which results in a bandwidth loss of ∼10 nm and reduces the potential net data throughput to 28.6 Tb/s for 30-GBaud DP-16QAM signals. However, the dual-band structure can utilize the bandwidth more effectively, which leads to a higher estimated net data throughput of 31.2 Tb/s.

High power 1.55 µm buried heterojunction distributed feedback laser with a linewidth less than 200 kHz.

With the rapid development of coherent optical communication systems, lasers are required to have higher power and narrower linewidths. In this paper, a process method using buried heterojunction is proposed. By comparing the optoelectronic properties of lasers with different mesa widths and different cavity lengths, the laser with a 1000 µm cavity length and a mesa width of 2.4 µm can reach 133.7 mW at 25°C at 300 mA, and a side mode suppression ratio (SMSR) greater than 50 dB. This laser also exhibits low relative intensity noise (<-150d B/H z at 260 mA) and narrow linewidth (<200k H z).

Grating index difference (GID) and order based distributed feedback laser effects on coarse wavelength division multiplexing optical fiber systems

Abstract The study has outlined grating index difference (GID) and grating order based distributed feedback laser effects on coarse wavelength division multiplexing optical fiber systems. Signal amplitude level (SPL), noise signal level are measured accurately based on various grating order of distributed feedback laser. Max. signal power (MSP), noise signal power (NSP) are also measured along the variations of frequency spectrum related to spectral wavelength and bit period time versus GID variations. The optimum signal power level and minimum noise power level, maximum SPL, minimum SPL are achieved with 0.1% GID and grating order of unity.

High-stability and high-beam-quality single-frequency nanosecond 589 nm laser based on sum-frequency generation

A high repetition rate, high peak power, narrow linewidth nanosecond 589 nm laser based on sum-frequency generation (SFG) of 1064 nm and 1319 nm laser is demonstrated. A 1064 nm single-frequency distributed-feedback laser diode (DFB-LD) externally modulated by an acousto-optic modulator (AOM) and amplified by a fiber-solid hybrid amplifier with three-stage fiber amplifier and six-stage solid-state end-pump Nd:YVO4/Nd:YAG amplifier, a high beam quality laser output with pulse energy of 20 mJ at repetition rate of 500 Hz is achieved, which pulse duration and waveform are adjustable and editable. The ramp–hold–fire detection and dual piezoelectric ceramic (PZT) feedback compensation are employed in the 1319 nm oscillator to achieve high stability and low jitter laser. Then the 1319 nm laser pulse is amplified to 12.2 mJ by three-stage end-pumped Nd:YAG amplifier, with pulse duration of 70 ns. By sum-frequency of the 1064 nm and 1319 nm lasers, finally, 589.1595 nm laser with pulse energy of 10.4 mJ and pulse duration of 62 ns is generated efficiently, the laser beam quality factor M2 is less than 1.3. With the ability of switching frequencies quickly and the characteristic of compatible frequency-stabilized, this laser is believed to be a very potential solution for sodium Doppler lidar.

Phase Noise Modeling and Experimental Demonstration of Single and Dual-Loop Direct Modulation Optoelectronic Oscillator

A single and dual loop direct modulation Opto-Electronic Oscillator (DMOEO) phase noise model for generation of low phase noise signal operating in Radio Frequency (RF) and microwave frequency range is proposed and experimentally demonstrated. The distribute feedback (DFB) laser diode is used in the proposed design to perform the RF to optical conversion by exploiting its non-linear transfer function characteristics, in contrast to external modulator in conventional OEO designs. We presented the theoretical phase noise model for single and multi-loop DMOEO deign with all possible noise contributions. Also, simulation scenarios have been demonstrated to show the impact of different noise source on the overall phase noise performance of the OEO. A single and dual loop DMOEO with phase noise of −112 dBc/Hz and −110 dBc/Hz at 10 kHz offset from 2.4 GHz carrier respectively is designed and the side mode suppression better than 50 dB is achieved for the generated signal with 11 dBm output power.

1.3 μm InGaAlAs/InP DFB Laser Integrated With SSC Having Reverse Mesa Ridge Waveguide

We report the fabrication of a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.3~\mu \text{m}$ </tex-math></inline-formula> InGaAlAs/InP multi-quantum well (MQW) distributed feedback (DFB) laser integrated with a laterally tapered spot size converter (SSC) having a reverse mesa ridge waveguide. Because the top waveguide width of the reverse mesa waveguide is notably larger than the bottom width, a narrow SSC tip width, which is key for high quality SSC, can be fabricated by using conventional photolithography easily, helping to lower the device cost. At 25 °C, the emission wavelength is around 1314 nm and side mode suppression ratio larger than 45 dB can be obtained when the current is larger than 100 mA. The lateral and vertical divergence angles measured from the SSC facet of the laser are 11.8 and 13.2, respectively, which helps to ease the outcoupling of the light power.

Measurement and characterization of microwave interaction between integrated distributed feedback laser diode and electro-absorption modulator

Integrated electro-absorption-modulated distributed feedback laser diodes (EMLs) are attracting much interest in optical communications for the advantages of a compact structure, low power consumption, and high-speed modulation. In integrated EML, the microwave interaction between the distributed feedback laser diode (DFB-LD) and the electro-absorption modulator (EAM) has a nonnegligible influence on the modulation performance, especially at the high-frequency region. In this paper, integrated EML was investigated as a three-port network with two electrical inputs and a single optical output, where the scattering matrix of the integrated device was theoretically deduced and experimentally measured. Based on the theoretical model and the measured data, the microwave equivalent circuit model of the integrated device was established, from which the microwave interaction between DFB-LD and EAM was successfully extracted. The results reveal that the microwave interaction within integrated EML contains both the electrical isolation and optical coupling. The electrical isolation is bidirectional while the optical coupling is directional, which aggravates the microwave interaction in the direction from DFB-LD to EAM.

On the Technology of a Laterally Coupled Bragg Grating of Single-Mode Distributed Feedback Laser Diodes

On the Technology of a Laterally Coupled Bragg Grating of Single-Mode Distributed Feedback Laser Diodes

Bidirectional WDM Multi-Nodes Analog Radio-Over-Fiber Mobile Fronthaul Link Enhanced by Photonic Integrated Devices

A bidirectional wavelength division multiplexing (WDM) analog radio-over-fiber (A-RoF) mobile fronthaul (MFH) link is enhanced using photonic integrated devices. Two key photonic integrated devices are combined in the A-RoF link: an 8-channel InP directly modulated laser (DML) transmitter and a 32×100-GHz silicon array waveguide grating (AWG). The DML transmitter has 8 parallel monolithically integrated distributed feedback lasers, enabling cooperative and reconfigurable downlink analog transmission. Moreover, the 32×100-GHz AWG is featured by low insertion loss (<4.5-dB) and low crosstalk (<−20.4-dB), to achieve a high-density WDM system. In the distributed field experiments, we have successfully demonstrated a bidirectional A-RoF MFH over 10-km standard single mode fiber, providing an 8×5-Gbit/s 4-quadrature amplitude modulation (QAM) orthogonal frequency division modulation (OFDM) downlink transmission and a 3×12-Gbit/s 16-QAM uplink transmission.

Dual-Wavelength Differential Detection of FBGs Using a Frequency-Scanning Pulsed Laser

The dual-wavelength differential detection of fiber Bragg gratings is reported. A directly modulated distributed-feedback laser array is used as a frequency-scanning pulsed light source. Trains of four 100-ns pulses with a frequency drift of 6.5 GHz and the same intensity are generated. Interrogating two serially connected Bragg gratings using the pulse trains, we show the selectivity of the high-sensitivity measurement and the wide measurement range, and the possibility of expansion to time-division multiplexing systems with a simple setup.

DFB laser array based on four phase-shifted sampled Bragg gratings with precise wavelength control.

A four-laser array based on sampled Bragg grating distributed feedback (DFB) lasers in which each sampled period contains four phase-shift sections is proposed, fabricated, and experimentally demonstrated. The wavelength spacing between adjacent lasers is accurately controlled to 0.8 nm ± 0.026 nm and the lasers have single mode suppression ratios larger than 50 dB. Using an integrated semiconductor optical amplifier, the output power can reach 33 mW and the optical linewidth of the DFB lasers can be as narrow as 64 kHz. This laser array uses a ridge waveguide with sidewall gratings and needs only one metalorganic vapor-phase epitaxy (MOVPE) step and one III-V material etching process, simplifying the whole device fabrication process, and meeting the requirements of dense wavelength division multiplexing systems.