High Side-mode Suppression Ratio Research Articles

Full C-Band Tunable V-Cavity-Laser Based TOSA and SFP Transceiver Modules

We report the latest development in tunable transmitter optical sub-assembly (TOSA) and small form-factor pluggable (SFP) transceivers based on simple and compact V-cavity laser (VCL), aiming for low-cost deployment in metro, access, and data center networks. The VCL employs a half-wave coupler to achieve high side-mode suppression ratio (SMSR) and the Vernier effect to achieve a wide wavelength tuning range. Full C-band tuning from 1529.55- to 1566.31-nm with SMSR above 36 dB is demonstrated. Since the laser does not involve any grating or epitaxial regrowth, and has a simple tuning algorithm, it allows simpler processes for fabrication and testing as compared with other widely tunable laser structures. Compact TOSAs and SFP transceiver modules have been developed for full C-band tuning with up to 93 channels at 50 GHz spacing. Transmission experiments are carried out for direct modulation with data rates from 2.5 to 8.5 Gbps. The results of reliability tests of the modules are also presented.

Plasmon enhancement for Vernier coupled single-mode lasing from ZnO/Pt hybrid microcavities

It is essential to develop a single mode operation and improve the performance of lasing in order to ensure practical applicability of microlasers and nanolasers. In this paper, two hexagonal microteeth with varied nanoscaled air-gaps of a ZnO microcomb are used to construct coupled whispering-gallery cavities. This is done to achieve a stable single mode lasing based on Vernier effect without requiring any complicated or sophisticated manipulation to achieve positioning with nanoscale precision. Optical gain and the corresponding ultraviolet lasing performance were improved greatly through coupling with localized surface plasmons of Pt nanoparticles. The ZnO/Pt hybrid microcavities achieved a seven-fold enhancement of intensity of single mode lasing with higher side-mode suppression ratio and lower threshold. The mechanism that led to this enhancement has been described in detail.

High power, high SMSR and wide tuning range silicon micro-ring tunable laser.

An external cavity tunable laser, which is based on a silicon hybrid micro-ring resonator, is demonstrated. The heat isolate grooves around the rings effectively cuts off temperature crosstalk. Experimental results have shown that the output power of this device can reach 15.5dBm, with a linewidth less than 130 kHz. The tuning range is more than 57nm in C-band with 60 dB side mode suppression ratio (SMSR).

Spectral Characteristics of Narrow-Linewidth High-Power 1180 nm DBR Laser With Surface Gratings

We report narrow-linewidth 1180-nm GaInNAs/GaAs distributed Bragg reflector lasers reaching up to ~500-mW continuous-wave output power at room temperature. The lasers employ surface gratings, which avoided the problematic regrowth and enabled a high side-mode suppression ratio over a relatively large mode-hop-free tuning range. The wavelength tuning rates of 0.1 nm/°C and 1 pm/mA were obtained by changing the mount temperature and the drive current, respectively. The lasers exhibit a narrow emission linewidth (<250 kHz) even at high output power levels. The side-mode suppression ratio is relatively independent of the power level and remains higher than 50 dB even in the vicinity of the roll-off point. An outstanding temperature stability is provided by good carrier confinement in the GaInNAs/GaAs quantum well. A 2000 h burn-in with constant 1.5 A bias at 20 °C improved the output characteristics slightly and did not reveal any failure among the tested components.

Simultaneous Triangular Waveform Signal and Microwave Signal Generation Based on Dual-Loop Optoelectronic Oscillator

A self-starting triangular waveform and microwave signal generator based on a dual-loop optoelectronic oscillator (OEO) is proposed. In this scheme, two continuous waves (CWs) with different wavelength are emitted from two laser diodes (LDs) to form two feedback loops in an OEO system. When the oscillation is established and the modulation index of the Mach–Zehnder modulator (MZM) is set to be 0.752, a triangular waveform could be generated by the superposition of the two oscillation signal envelopes on photodetector with appropriate time delay between two wavelength channels. Although the proposed system is similar to a traditional dual-loop OEO and no more devices are required, it is not only a microwave signal source with high side-mode suppression ratio (SMSR) but a triangular waveform generator simultaneously as well. The operation principle is theoretically analyzed and stimulated. In experimental demonstration, the full-duty-cycle triangular waveform signal and high-quality microwave signal at 5 GHz can be achieved simultaneously. In addition, the experiment result shows that the variety of the modulation depth for triangular waveform generation does not influence the quality of the generated microwave signal.

Wide tuning range fiber laser source using new double linear cavity techniques

A wide range fiber laser source is experimentally reported in this paper. The fiber laser source is constructed from two branches splitted by coupler band splitter to form broader laser source. The double linear topology is used either for wide lasing source or generation of two simultaneous wavelengths tuned independently. The achieved crucial results are mainly based on the use of the new techniques which called double linear cavity laser. A wide range of 80nm spectrum is tuned from 1525nm to 1605nm, with maximum output power of 13.21dBm. An average high side mode suppression ratio (SMSR) of about 68dB is recorded for the whole tuning spectrum.

2004-nm Ridge-Waveguide Distributed Feedback Lasers With InGaAs Multi-Quantum Wells

Fabrication and characteristics of 2004-nm wavelength InP-based ridge-waveguide distributed feedback lasers with InGaAs multi-quantum wells are described. By means of a relatively simple fabrication process, the device can operate stably in a single mode without any mode hopping. A high side-mode suppression ratio of 49 dB is achieved. The emission wavelength can be finely controlled from 2000 to 2008 nm with a current-tuning rate of 0.0047 nm/mA and a temperature-tuning rate of 0.127 nm/K. In addition, the influence of facet coating conditions on the single-mode property of these distributed feedback lasers was investigated.

Low-threshold external-cavity quantum cascade laser around 7.2 μ m

Room-temperature continuous wave (CW) operation of a tunable external-cavity quantum cascade laser (EC-QCL) at center wavelength around 7.2 μm is presented. The EC-QCL was implemented in a Littrow configuration. The gain chip is based on a diagonal bound-to-continuum design with a high-reflection coating on the back facet. A two-layer antireflection (AR) coating consisting of Al2O3 and ZnSe was designed and deposited on the front facet of the chip to suppress the Fabry–Perot modes. With this AR coating, single-mode tuning range of 128 cm−1 was achieved, from 1346.7 to 1475.3 cm−1 (6.78 to 7.43 μm). High side-mode suppression ratio over 30 dB was achieved near the center gain region. A very low-threshold current density of 0.89 kA/cm2 and a high output power of 50 mW were obtained when the EC-QCL was operated in CW mode at 20°C.

Magnetic Field Sensor Using Fiber Ring Cavity Laser Based on Magnetic Fluid

A magnetic field sensor using fiber ring cavity laser based on magnetic fluid (MF) is proposed and experimentally demonstrated. MF-coated single-mode—no-core—single-mode fiber structure is inserted in the fiber ring laser cavity, which acts as a bandpass filter and the magnetic field sensing component simultaneously. The excellent bandpass filtering with a high side-mode suppression ratio (14 dB) and small insert loss of around (−1.03 dB) is caused by the self-imaging effect. The experimental results show that the lasing wavelength shifts to blue side with the increase of external magnetic field. The magnetic field sensing sensitivity of 12.05 pm/Oe is achieved within the range of 15.9–222.32 Oe. This configuration exhibits obvious advantages in term of high visibility ( $\sim 40$ dB) and relative narrow 3-dB bandwidth ( $\sim 0.19$ nm) of the lasing output spectrum. Therefore, its $Q$ value is more than 10 times larger than those of other reported magnetic field sensing structures.

Study on Two-Section DFB Lasers and Laser Arrays Based on the Reconstruction Equivalent Chirp Technique and Their Application in Radio-Over-Fiber Systems

Two-section distributed feedback (TS-DFB) semiconductor lasers based on the reconstruction equivalent chirp technique is proposed. A four-channel TS-DFB laser array (TS-DFB-LA) is theoretically studied and experimentally demonstrated. Compared with the conventional one-section DFB lasers, the proposed TS-DFB lasers have much higher output efficiency and higher side-mode suppression ratio (SMSR) when both the facets of the laser cavity are coated with antireflection coatings. About 39% increase in output efficiency, more than 10 mA decrease in threshold current, and about 5 dB increase in SMSR have been achieved experimentally. Furthermore, experimental results show that the wavelength spacing accuracy of the four-channel TS-DFB-LA can be improved by tuning the injection current of one of the two sections. Using the two-section structure, the dynamic characteristics including small-signal frequency response, relative intensity noise, and spurious-free dynamic range are also improved significantly. A radio-over-fiber link utilizing the TS-DFB laser as directly modulated light source was experimentally achieved. About 50 MSymbol/s 64-QAM signal with 10 GHz carrier was transmitted from the TS-DFB laser. After 40 km transmission in single-mode fiber, the average error vector magnitude of the whole link is 2.97%.

Single-mode Fabry-Perot laser with deeply etched slanted double trenches

This work proposed and demonstrated a single-mode Fabry-Perot (FP) laser structure with a pair of deeply etched slanted trenches inside the cavity. We implemented the proposed mode selection scheme in conventional 1310 nm InAlGaAs/InP strained-layer multiple-quantum-well ridge waveguide FP laser diodes and obtained single-mode operation with a side-mode suppression ratio (SMSR) as high as 35 dB. The single-mode yield was approximately 55%, and other device performance measures such as the threshold and the slope efficiency were not greatly affected. Additionally, temperature cycling and aging tests show no exceptional disadvantages when compared with the performance of conventional FP lasers. Fiber-optic transmission tests show that the proposed device can send directly modulated 2.5 Gbps and 6.25 Gbps optical signals for distances of over 50 km in standard single-mode fiber. Thus, as a cost-effective solution, this device is promising as a replacement for conventional distributed feedback laser diodes in specific applications where single-mode operation is indispensable but precise control of the lasing wavelength and/or very high SMSR (e.g., &amp;gt;40 dB) are not required.

Development of stable, narrow spectral line-width, fiber delivered laser source for spin exchange optical pumping

We developed a stable, narrow spectral line-width, fiber delivered laser source for spin exchange optical pumping. An optimized external cavity equipped with an off-the-shelf volume holographic grating narrowed the spectral line-width of a 100 W high-power diode laser and stabilized the laser spectrum. The laser spectrum showed a high side mode suppression ratio of >30 dB and good long-term stability (center wavelength drifting within ±0.002 nm during 220 h of operation). Our laser is delivered by a multimode fiber with power ~70 W, center wavelength of 794.77 nm, and spectral bandwidth of ~0.12 nm.

A tunable optical frequency comb generator using a single dual parallel Mach–Zehnder modulator

Abstract A scheme of generating optical frequency combs (OFC) utilizing a single dual parallel Mach–Zehnder modulator (DPMZM) is detailedly investigated. Both the theoretical analysis and experimental results show that the generator is power efficient. Gaussian-shaped OFC and flat OFC with a tunable spacing, flexible line-number and high side mode suppression ratio (SMSR) are experimentally generated with relatively lower RF power.

Hybrid vertical‐cavity laser with lateral emission into a silicon waveguide

We experimentally demonstrate an optically-pumped III-V/Si vertical-cavity laser with lateral emission into a silicon waveguide. This on-chip hybrid laser comprises a distributed Bragg reflector, a III-V active layer, and a high-contrast grating reflector, which simultaneously funnels light into the waveguide integrated with the laser. This laser has the advantages of long-wavelength vertical-cavity surface-emitting lasers, such as low threshold and high side-mode suppression ratio, while allowing integration with silicon photonic circuits, and is fabricated using CMOS compatible processes. It has the potential for ultrahigh-speed operation beyond 100 Gbit/s and features a novel mechanism for transverse mode control.

1310 nm hybrid InP/InGaAsP on silicon distributed feedback laser with high side-mode suppression ratio.

We report on the design, fabrication and performance of a hetero-integrated III-V on silicon distributed feedback lasers (DFB) at 1310 nm based on direct bonding and adiabatic coupling. The continuous wave (CW) regime is achieved up to 55 °C as well as mode-hop-free operation with side-mode suppression ratio (SMSR) above 55 dB. At room temperature, the current threshold is 36 mA and the maximum coupled power in the silicon waveguide is 22 mW.

Laser Tuning Performance Testing and Optimization in TDLAS Oxygen Measuring Systems

TDLAS (tunable diode laser absorption spectroscopy) technology, with its unmatched advantages such as high selectivity molecular spectra, fast response, high sensitivity, non-contact measuring, become the preferred scheme for combustion process diagnosis, and can be effectively used for oxygen measuring. DFB (distributed feedback) laser diode with its small size, low power consumption, long service life, narrow linewidth, tunable wavelength has become the main choice of the TDLAS system. Performance of laser tuning characteristics is a key factor restricting TDLAS's measuring performance. According to TDLAS oxygen measuring system's working requirements, a simple experimental method was used to test and analyze tuning characteristics such as wavelength current, power current and wavelength temperature of a 764 nm DFB laser diode in the system. Nonlinear distortion of tuning curves was obvious, which affects oxygen measuring accuracy. The laser spectra's characteristics such as narrow linewidth, high side mode suppression ratio and wide wavelength tuning range are obvious, while its wavelength-current tuning curve with a tuning rate of about 0.023 nm x mA(-1) is not strictly linear. The higher the temperature the greater the threshold current, the PI curve is not strictly linear either. Temperature tuning curve is of good linearity, temperature-wave-length tuning rate keeps constant of about 0.056 nm/DEG C. Temperature tuning nonlinearity can be improved by high temperature control accuracy, and current power nonlinearity can be improved by setting the reference light path. In order to solve the wavelength current tuning nonlinear problems, the method of DA controlling injection current was considered to compensate for non-linear wavelength current tuning according to DFB laser diode tuning mechanism and polynomial fitting of test results. In view of different type of lasers, this method needs only one polynomial fitting process before the system's initial work. The compensation scheme is reasonable and the realization is simple, what's more, it does not affect the measuring process. The experiments prove that XI curve's linear fit residuals are less than 1 μm after compensation, far less than those of before compensation 22 pm, the compensation effect is obvious, which provided a basis for various oxygen parameters' TDLAS measuring and inversion.

980 nm fiber grating external cavity semiconductor lasers with high side mode suppression ratio and high stable frequency

The coupling cavity theory is used to analyze the impact of high side mode suppression ratio (SMSR) on fiber grating external cavity semiconductor lasers (FGECSL). The high SMSR and high stable frequency FGECSLs were obtained by experiment. The center wavelength is 974 nm, SMSR is 45 dB, the center wavelength change rate reaches 3.08 ppm/°C in the temperature range of −20 to 80 °C.

Narrow linewidth two-electrode 1560 nm laterally coupled distributed feedback lasers with third-order surface etched gratings.

We report on the design and characterization of a re-growth free InGaAsP/InP multiple quantum well two-electrode laterally coupled distributed feedback (LC-DFB) lasers. Third-order surface etched gratings have been defined on the ridge sidewalls along the laser cavity by means of stepper lithography. The lasers oscillate in single-mode around 1560 nm with high side mode suppression ratios (>52 dB), a wavelength tuning (≥ 3nm), an output power (≥ 6 mW), and narrow linewidth (<170 kHz) under various current injection ranges at room temperature. A minimum linewidth of 94 kHz has been recorded for 1500 µm-long two-electrode LC-DFB laser while providing non-uniform current injection through the two electrodes. The effect of the width of the inter-electrode gap on these different performance measures is also studied.

Narrow Linewidth 1550 nm Corrugated Ridge Waveguide DFB Lasers

We report on the design and characterization of InP-based multiple quantum well corrugated ridge waveguide distributed feedback diode lasers operating at 1550 nm. Third-order gratings have been etched along the sidewalls of the ridge waveguide using the standard I-line stepper lithography technique with an inductively coupled reactive ion etching process. An as-cleaved 1500-μm-long laser diode shows stable continuous wave single-mode operation at 1550 nm with high side-mode suppression ratios (>50 dB), a temperature-dependent wavelength shift dλ/dT ~0.095 nm/°C, and output powers ≥7 mW at 25 °C. Linewidth determination has been carried using the delayed self-heterodyne interferometric technique. Narrow linewidths (≤250 kHz) have been observed for a wide range of current injection, with a minimum of 184 kHz at 300 mA.

Mode-hop-free photonic crystal laser fabricated by holographic exposure technology.

A mode-hop-free single-mode laser with a two-dimensional photonic crystal was demonstrated. In the device, the photonic crystal was realized by double holographic exposure technology. This novel procedure simplifies the fabrication of such structures greatly. The design of a reverse junction in the photonic crystal layer induces a partial gain coupling into the laser, which could break the symmetry of the transmission spectrum and realize stable single-mode lasing of the laser. The fabricated device has a high single-mode stability and side-mode suppression ratio of over 45dB without mode hop at a relatively wide injected current range. The measurement results indicate that the laser with a simple fabrication process is promising as a stable single-mode and high-power light source in optical communication systems.