High Side-mode Suppression Ratio Research Articles

High Side-Mode Suppression Ratio Optical Pulses Generated From a Self-Seeded Fabry–Perot Laser Diode Locked by a Linear Erbium-Doped Fiber Laser

A new configuration of self-seeding scheme has been developed for wavelength-tunable optical pulse generation. In the system, an erbium-doped fiber laser is used to provide a strong wavelength seeding power and as a result, an extremely high side- mode suppression ratio of larger than 50 dB over the whole wavelength-tuning range of 13 nm can be obtained, with good pulse stability. When compared with other erbium-doped fiber amplifier configurations reported previously, the developed system exhibits higher pump efficiency and signal amplification capability. The system is simple, robust, and of low cost.

Tunable Erbium-Doped Fiber Lasers Using Various Inline Fiber Filters

Several high-performance and tunable erbium-doped fiber lasers are reviewed. They are constructed by using fiber Bragg gratings (FBGs) or short-wavelength-pass filters (SWPFs) as wavelength tunable components inside the laser cavity. Broadband wavelength tuning range including C- and/or S-band was achieved, and tunable laser output with high slope efficiency, high side-mode suppression ratio was obtained. These fiber lasers can find vast applications in lightwave transmission, optical test instrument, fiber-optic gyros, spectroscopy, material processing, biophotonic imaging, and fiber sensor technologies.

Tunable Erbium-Doped Fiber Lasers Using Various Inline Fiber Filters

Several high-performance and tunable erbium-doped fiber lasers are reviewed. They are constructed by using fiber Bragg gratings (FBGs) or short-wavelength-pass filters (SWPFs) as wavelength tunable components inside the laser cavity. Broadband wavelength tuning range including C- and/or S-band was achieved, and tunable laser output with high slope efficiency, high side-mode suppression ratio was obtained. These fiber lasers can find vast applications in lightwave transmission, optical test instrument, fiber-optic gyros, spectroscopy, material processing, biophotonic imaging, and fiber sensor technologies.

A single-mode laser based on asymmetric Bragg reflection waveguides

A single oscillation-mode laser employing the asymmetric waveguide structure is designed and analyzed. The mode selection mechanism is realized by using an asymmetric Bragg reflection waveguide (BRW) and shown to be effective to achieve high side-mode suppression ratio (SMSR). As an example, a silicon-based quasi-one-dimensional BRW with Er-doped Si-nanocrystal in the silicon oxide core is considered and illustrated for the laser structure. Guidance properties and threshold conditions are examined to verify the design procedure and performance feasibility for the single oscillation mode laser.

Wide temperature operational range of a 1310 nm AlGaInAs MQW-DFB laser with silicon oxynitride as a facet coating

We successfully fabricated 1310 nm AlGaInAs MQW–DFB laser diodes with silicon oxynitride (SiON) as an AR facet coating. In this report, the low reflectivity of the single layer SiON film on the facet of the 1310 nm DFB LD is achieved, with the result that the FP mode can be effectively suppressed over a wide temperature range. The AlGaInAs MQWs is also adopted in order to achieve a good temperature performance of the 1310 nm DFB LD. We demonstrate that these devices have high slope efficiency, low threshold current, and high SMSR characteristics over the temperature range of −40 °C to 95 °C. Less than 1 dB degradation of slope efficiency was obtained when the temperature increased from 25 °C up to 95 °C. The side mode suppression ratio (SMSR) above 37 dB and clear openings of eye diagrams at 2.5 G modulation were maintained within the temperature range of −40 °C to 95 °C. These superior characteristics over the very wide temperature range of 1310 nm DFB laser diodes were achieved by the combination of AlGaInAs MQW and silicon oxynitride AR coating deposited on the facet.

Design of wavelength adjustable lasers with photonic crystal based Fabry-Perot etalon for applications in optical network units of wavelength-division-multiplexed passive optical network systems

We propose a novel wavelength adjustable laser (WAL) with a photonic crystal based Fabry-Perot (FP) etalon. This laser will be a promising light source for optical network units (ONUs) of conventional wavelength-division-multiplexed passive optical network (WDM-PON) systems for up-stream transmission. It has the merits of a relatively simple fabrication and operation, wide process tolerance, low-cost, high side-mode suppression ratio, and wavelength-tunable characteristics. The optimization of the device structure and the implementation methods for this type of laser are discussed. Although the WALs in WDM-PON systems are not colorless, each laser can cover several wavelengths. Thus, the required number of different ONUs can be reduced. This approach may be necessary for 10 Gbps upstream transmission in next-generation optical access networks because the 10 Gbps data rate is difficult to achieve by using current colorless schemes.

Discrete mode lasers for communication applications

The authors present a novel, low cost laser transmitter for telecommunication systems. This device, called discrete mode (DM) laser, is basically a ridge waveguide Fabry-Perot (FP) laser, whose wavelength spectra has been modified to obtain a single mode operation. This is achieved by perturbing the effective refractive index of the guided mode along very small sections of the laser cavity, by etching features into the ridge waveguide. Suitable positioning of these interfaces allows the mirror loss spectrum of an FP laser to be manipulated in order to achieve single longitudinal mode emission. The waveguide structure requires only a single growth stage and uses optical lithography to realise the ridge. In addition, the fabrication process is re-growth free. Despite this simple and low cost fabrication process, the DM lasers portray many advantages over the distributed feedback and distributed Bragg reflector lasers, such as very high side mode suppression ratio, stable operation over a large temperature range, narrow linewidth and low sensitivity to optical feedback.

Spectral Linewidth Reduction in Widely Wavelength Tunable DFB Laser Array

We have developed an L-band tunable distributed feedback laser array (TLA) with a new design to reduce the spectral linewidth. A wide wavelength tuning range of ~ 40 nm is obtained with a high fiber output power of 20 mW and a high side-mode suppression ratio of >50 dB in the TLA module. A narrow linewidth of less than 580 kHz is achieved over the entire tuning range. Furthermore, we investigated the causes of linewidth variation. We found that a TLA with a longer cavity is more tolerant to external feedback, which reduces the variation in linewidth.

Wavelength-tunable optical short pulses with high sidemode suppression ratio generated by use of Bi-EDFA

A bidirectional erbium-doped fiber amplifier (Bi-EDFA) has been used in a self-seeding scheme for wavelength-tunable optical short pulse generation. The pulse wavelength is selected and purified by use of two tunable Fabry-Perot (FP) optical filters with bandwidth of 0.11 nm and 99 pm respectively, while a constant repetition frequency of 1.045 GHz is maintained. The sidemode suppression ratio (SMSR) of the output pulses achieved is better than 40 dB over the wavelength tuning range of 33 nm. The system is simple and efficient, and a continuous wavelength tuning can be readily achieved.

Injection Locking and Switching Operations of a Novel Retro-Reflector-Cavity-Based Semiconductor Micro-Ring Laser

Injection locking and switching characteristics are investigated in the novel retro-reflector-cavitiy-based semiconductor ring laser with equivalent circular radius of 26 mum. The allowed detuning range is up to ~3 GHz wide and the highest side mode suppression ratio of ~43.7 dB can be achieved. A fast response speed of ~70 ps to the cavity is achieved, which indicates that this device can be utilized as an all optical switch at a data rate of 10 Gb/s or higher.

$C$- and $L$-Band External Cavity Wavelength Tunable Lasers Utilizing a Wideband SOA With Coupled Quantum Well Active Layer

We have developed a wideband semiconductor optical amplifier as a gain chip for a $C$ - and $L$ -band external cavity tunable laser. We introduced a coupled quantum well structure to obtain gain spectrum covering both bands. Low threshold current deviation, over 13-dBm fiber coupled power, and high sidemode suppression ratio were demonstrated across a 77-nm tuning range.

1550 nm GaInNAsSb distributed feedback laser diodes on GaAs

Singlemode laser diodes on GaAs substrates were developed using GaInNAsSb double quantum well active regions grown by molecular beam epitaxy. The distributed feedback devices were fabricated using a regrowth-free process in which lateral Cr gratings were deposited adjacent to a dry-etched narrow ridge waveguide. In continuous-wave (CW) operation the devices exhibit a lasing wavelength of 1550 nm at 10°C with a very high sidemode suppression ratio of >50 dB throughout most of the operational range, and output power up to 15 mW.

Low Threshold Distributed Feedback Quantum Cascade Lasers withWidely Spaced Emission Wavelengths

We report lasing properties of distributed feedback quantum cascadelasers (DFB QCLs) including a double-phonon-resonance active region,at wavelength of about 8.4 μm. A broad gain spectrum isgenerated due to the coupling between the lower laser level in theactive region and the levels in the injector, and is demonstrated bythe lasing spectrum of the corresponding Fabry–Pérot QCLs whose widthis 0.5 μm at 1.5 times of the threshold current. As a result, the DFBQCLs employing different grating periods exhibit a wavelength span of0.18 μm at room temperature and total wavelength coverage of0.28 μm at various heat sink temperatures. A high side modesuppression ratio of about 30 dB and a low threshold current density of1.78 kA/cm2 are achieved as the lasers operate at room temperaturein pulsed mode.

Lasing Actions of Octagonal Quasi-Periodic Photonic Crystal Microcavities

Lasing actions are obtained from well-fabricated octagonal quasi-periodic photonic crystal (OQPC) microcavities. The defect modes in OQPC microcavities are investigated and compared with the calculation results obtained using the finite-difference time-domain (FDTD) method. A large single-mode lasing wavelength range over 200 nm without mode hopping and a high side-mode suppression ratio (SMSR) of over 30 dB are observed, which result from the mode dependence suppression mechanism on the cavity geometry.

Room temperature, low-threshold distributed feedback quantum cascade lasers at ∼8.4 and ∼7.7 μm

We report on pulsed single-mode operation of mid-infrared distributed feedback quantum cascade lasers with a very low-threshold current density at room temperature. The lasers exploited a three-well vertical transition active region and a low-doped injector as the active layers. A novel waveguide and grating structure was proposed to achieve a sufficient coupling coefficient and low waveguide loss simultaneously. For the λ∼8.4 μm lasers, a low-threshold current density ( J th) of 1.78 kA/cm 2 and a peak output power ( P out) of 4 mW are achieved at room temperature. For the λ∼7.7 μm lasers, J th is as low as 970 A/cm 2 at room temperature and the corresponding P out reaches 75 mW. Both kinds of the lasers show single-mode emission with a high side-mode suppression ratio of ∼30 dB.

Selective-area MOVPE growth for 10 Gbit/s electroabsorption modulator integrated with a tunable DBR laser

We have designed and fabricated electroabsorption modulator integrated monolithically with a distributed Bragg reflector laser using selective area growth (SAG) by metalorganic vapor phase epitaxy (MOVPE). Through the bandgap engineering due to the growth rate enhancement and compositional variation from the difference of migration and/or diffusion length of species by various SAG mask pattern, we have achieved the photoluminescence peak wavelengths of active layer in the laser, modulator, and Bragg grating regions to 1.557, 1.503, and 1.442 μm, respectively. The electroabsorption modulator-integrated laser shows a good performance including threshold current of below 6 mA, output power of 5 mW for 45 mA current injected in the active region, and high side-mode suppression ratio over 45 dB with the 3-dB modulation bandwidth over 11 GHz.

Performance analysis of a wavelength-locked Fabry-Perot laser diode by light injection of an external spectrally sliced Fabry-Perot laser diode

We have analyzed and experimentally demonstrated the performance of a wavelength-locked Fabry-Perot laser diode (FP-LD) with a spectrally sliced FP-LD as an external-injection optical source. A high side-mode suppression ratio exceeding 30 dB was obtained, and the noise characteristic of the wavelength-locked FP-LD was analyzed in terms of both mode partition noise and interferometric noise. The measured relative intensity noise had a minimum value of -140 dB/Hz. We also investigated the transmission characteristics such as the Q factor and extinction ratio for a 622 Mbits/s and 2.5 Gbits/s baseband digital signal.

Uncooled 1.3-/spl mu/m complex-coupled DFB BH laser diodes with the Fe-doped InGaAsP-InP hybrid current-blocking grating

We proposed an alternate method by using the Fe-doped InGaAsP-InP hybrid grating layers to fabricate the 1.3-μm current-blocking-grating complex-coupled distributed-feedback (CBG CC-DFB) laser diodes (LDs) grown by metal-organic chemical vapor deposition (MOCVD). By combining the Fe-doped InGaAsP-InP grating layers, the CBG CC-DFB LDs can provide high optical DFB coupling coefficient and high current confining ability. Moreover, the current aperture in the lateral direction can be easily controlled by the self-aligned MOCVD regrowth process. Therefore, the manufacture of CBG CC-DFB buried heterostructure LDs is easy as the ridge-waveguide LDs. The LDs exhibit a low threshold current of 5.3 mA, a high slope efficiency of 0.42 mW/mA, and a stable single mode with a high sidemode suppression ratio of /spl sim/42 dB at two times the threshold (10.5 mA). Even at high temperatures, these LDs still have an extremely low threshold current of 15.8 mA at 90/spl deg/ and a small variation in slope efficient of only -1 dB at the temperatures between 20/spl deg/ and 80/spl deg/. Furthermore, these LDs show a high-speed characteristic of more than 11.8 GHz at 20/spl deg/, which are suitable for 10-Gb/s Ethernet and OC-192 applications.

Simple system for optical short-pulse generation in both active mode-locking and self-seeding schemes

A simple system that simultaneously supports active mode-locking and self-seeding schemes for wavelength-tunable optical short-pulse generation is proposed. The system consists of a gain-switched Fabry-Perot laser diode, an erbium-doped fiber amplifier, a tunable optical filter, and two circulators. The mode-locked optical pulses exhibit good stability, a high side-mode suppression ratio of more than 31 dB over a wide wavelength tuning range of 42 nm, and a pulse width of around 35 ps at a repetition frequency of approximately 2.8 GHz.

Highly linear-polarized external cavity lasers hybrid integrated on planar lightwave circuit platform

We propose and demonstrate, for the first time, a highly linear-polarized external cavity laser (ECL) integrated on planar lightwave circuit (PLC) with an in-PLC polarizer designed to improve polarization extinction ratio (PER). The in-PLC polarizer based on a 45deg-tilted grating was simply formed in the laser cavity composed of a Fabry-Peacuterot laser diode and a Bragg grating. The proposed ECL exhibited a PER value as high as 30 dB and single longitudinal mode oscillation with a high sidemode suppression ratio of 50 dB at 1310 nm