High Side-mode Suppression Ratio Research Articles

1550 nm external cavity diode laser with enhanced SMSR based on polarization mismatch by grating rotation.

A tunable external cavity diode laser (ECDL) with high side-mode suppression ratio (SMSR) is demonstrated. The ECDL is operated at both strong and weak feedback steady states with single longitudinal mode. Compared with the strong feedback mode, the SMSR of the weak feedback mode is significantly enhanced by rotating the grating along the axis of the incident beam, which changes the polarization orientation versus the grating grooves. The highest SMSR of the weak feedback mode is 54dB at the injection current of 300mA. The tunable range of the ECDL with weak feedback mode reaches 130.9nm.

Research on Multi-wavelength Fiber Laser Based on Nonlinear Effect

A multi-wavelength erbium-doped fiber laser (MWEDFL) is introduced, which uses highly erbium-doped fiber (EDF) as the gain medium and uses the nonlinear effect of the single mode fiber to suppress the mode competition. In order to obtain higher side mode suppression ratio and flatness, a nonlinear fiber loop mirror is added to the structure. The results show that a stable multi-wavelength laser with 16 lasing wavelengths and a side mode suppression ratio (SMSR) higher than 30dB is obtained.

4–λ hybrid InGaAsP-Si evanescent laser array with low power consumption for on-chip optical interconnects

A 4–λ hybrid InGaAsP-Si evanescent laser array is obtained by bonding III–V distributed feedback lasers to a silicon on insulator (SOI) substrate using a selective area metal bonding technique. Multiple wavelengths are realized by varying the width of the III–V ridge waveguide. The threshold current is less than 10 mA for all wavelength channels under continuous-wave (CW) operation at room temperature, and the lowest threshold current density is 0.76 kA/cm2. The side mode suppression ratio (SMSR) is higher than 40 dB for all wavelength channels when the injection current is between 20 mA and 70 mA at room temperature, and the highest SMSR is up to 51 dB. A characteristic temperature of 51 K and thermal impedance of 144°C/W are achieved on average. The 4–λ hybrid InGaAsP-Si evanescent laser array exhibits a low threshold and high SMSR under CW operation at room temperature. The low power consumption of this device makes it very attractive for on-chip optical interconnects.

Dual-wavelength thulium/holmium-doped fiber laser generation in 2 μm region with high side-mode suppression ratio

We demonstrate a dual-wavelength laser with emission in the 2 μm wavelength region using a thulium/holmium co-doped fiber and a non-adiabatic tapered fiber as a comb filter. The configuration employed a backward pumping scheme and dual-wavelength laser was generated at 2023.53 and 2032.82 nm. The side-mode suppression ratio (SMSR) is more than 44 dB with overall good stability performance. The proposed configuration presents a simple yet practical scheme of generating 2 μm dual-wavelength laser with good SMSR. This investigation may offer a more efficient yet eye safe dual-wavelength related applications for end users.

990 nm High-Power High-Beam-Quality DFB Laser With Narrow Linewidth Controlled by Gain-Coupled Effect

High-power single-longitudinal-mode regrowth-free gain-coupled distributed feedback laser diode based on ridge waveguide with periodic current injection is achieved at 990 nm. Our device is fabricated only by standard i-line lithography with micron-scale precision, obtains an excellent performance at high injection current. A continuous-wave power of over 0.681 W is achieved at 3 A. The maximum continuous-wave power at single-longitudinal-mode operation is up to 0.303 W at 1.4 A. Narrow linewidth emission has been reached with a 3 dB spectrum width less than 1.41 pm. The high side mode suppression ratio is over 35 dB. The lateral far field divergence angle is only 15.05°, the beam quality factor M 2 is 1.245, achieving a laterally near-diffraction-limit emission. It is more beneficial for single-mode fiber coupling as pumping sources and other applications which require high beam quality at high power with easy fabrication technique.

Visible astro-comb filtered by a passively stabilized Fabry-Perot cavity.

We demonstrate a compact 29.3 GHz visible astro-comb covering the spectrum from 560 nm to 700 nm. A 837 MHz Yb:fiber laser frequency comb phase locked to a Rb clock served as the seed comb to ensure the frequency stability and high side mode suppression ratio. After the visible super-continuum generation, a Fabry-Perot cavity based on ultra-low expansion glass was utilized to filter the comb teeth. The mirrors were home-made complementary chirped mirrors pair with zero net-dispersion and high reflection to guarantee no mode skipping. Those filtered comb teeth were clearly resolved in an astronomical spectrograph of 49 000 resolution, exhibiting sharp line shape, zero noise floor, and uniform exposure amplitude.

Opto-electronic oscillator mediated by acoustic wave in a photonic crystal fiber stimulated in 1 μm band.

An opto-electronic oscillator based on guided acoustic wave Brillouin scattering in a photonic crystal fiber (PCF) stimulated by a light wave in 1μm band is proposed and demonstrated. A short length of a homemade PCF stimulated by relatively low pump power leads to strong coupling between the pump and probe waves. The oscillation is realized in a feedback loop, in which the acoustic wave bridges the pump and probe. Oscillation is achieved at 1.237GHz, which matches the resonance of the acoustic mode, in a single-longitudinal-mode operation of the hybrid cavity. It has a high side mode suppression ratio of over 60dB.

A Single-Mode Laser Based on Parity-Time-Symmetry Structured Vertical Bragg Reflection Waveguide

A parity-time symmetric vertical Bragg reflection waveguide structure is proposed and analyzed for realizing single-mode operation of a laser diode. Impact of the key design parameters on laser performance are investigated for the purpose of achieving high side-mode suppression ratio and high injection slope efficiency. Our studies indicate that an electrically pumped edge-emitting single-mode laser is possible with proper design. Such lasers exhibit a number of highly desirable and in some cases unique characteristics, such as high-modulation bandwidth, high transverse gain, and high confinement of optical field in the low-effective index Fabry–Perot cavity.

Application of optical frequency comb generation with controlled delay circuit for managing the high capacity network system

The generation of optical frequency comb (OFC) with novel controlled delay circuit is presented in this study. The proposed OFC is based on a single laser source which is cascadingly connected with three modulators; all the modulators are tailored by RF signal while incorporating no phase shifter or electrical/optical amplifier. The proposed OFC is used as a source at optical line terminal (OLT) of WDM-PON setup, which serves multiple users with a single laser source making OLT side very cost effective. 41 comb lines with over 40 dB tone to noise ratio and high side mode suppression ratio, least amplitude difference of under 0.3 dB, with cost effective setup is an attractive source for WDM-PON system. The frequency spacing is 32 GHz between OFCG lines which provides enough bandwidth for data transmission, the overall bandwidth provided by this scheme is 1.2 THz. Using DPSK modulation technique across each frequency of OFCG, the controlled delay circuit increases the capacity by factor two, whereas by deploying DQPSK modulation technique, it quadrupled the overall capacity in downlink transmission. Thus, the system offers four times increased capacity ∼1.6 Tbps by deploying state of the art technique for modulation and generating OFC with controlled delay. The average power penalty in the downlink and uplink transmission is 2.5 dBm and 3.13 dBm.

Wavelength stability in a hybrid photonic crystal laser through controlled nonlinear absorptive heating in the reflector

The need for miniaturized, fully integrated semiconductor lasers has stimulated significant research efforts into realizing unconventional configurations that can meet the performance requirements of a large spectrum of applications, ranging from communication systems to sensing. We demonstrate a hybrid, silicon photonics-compatible photonic crystal (PhC) laser architecture that can be used to implement cost-effective, high-capacity light sources, with high side-mode suppression ratio and milliwatt output output powers. The emitted wavelength is set and controlled by a silicon PhC cavity-based reflective filter with the gain provided by a III–V-based reflective semiconductor optical amplifier (RSOA). The high power density in the laser cavity results in a significant enhancement of the nonlinear absorption in silicon in the high Q-factor PhC resonator. The heat generated in this manner creates a tuning effect in the wavelength-selective element, which can be used to offset external temperature fluctuations without the use of active cooling. Our approach is fully compatible with existing fabrication and integration technologies, providing a practical route to integrated lasing in wavelength-sensitive schemes.

Optical frequency comb generation based on dual-parallel Mach–Zehnder modulator and intensity modulator with RF frequency multiplication circuit

A new method of generating optical frequency comb by cascading a single dual-parallel Mach–Zehnder modulator and two intensity modulators is proposed. The intensity modulators are modulated by a frequency multiplication circuit of radio frequency. Theoretical model of the system is derived, and optical frequency comb with ultra-flatness and high side-mode suppression ratio can be obtained. The study results show that 72-line optical frequency comb with spectrum power variation of 0.26 dB, SMSR of 21 dB and frequency space of 4 GHz is gotten easily by adjusting the amplitude of radio frequency signal and the direct current bias of the modulators. The simulation result is in good agreement with the theoretical analysis model.

Narrow-Strip Single-Longitudinal-Mode Laser Based on Periodic Anodes Defined by i-Line Lithography

A low-cost regrowth-free narrow-strip single-longitudinal-mode diode laser, based on periodic anodes defined only by i-line lithography is proposed. With the periodic anodes separated by surface insulated grooves acting as a 44th-order gain grating, a high gain contrast is achieved without introducing effective index coupling. The CW output power of the device without facet coatings is up to 100.9 mW/facet at 980.63 nm in single-longitudinal-mode operation with a single facet having a power conversion efficiency of up to 18.6% and a slope efficiency of 0.53 W/A. The highest side-mode suppression ratio is 45 dB with a linewidth below 889 MHz, at 350 mA. The beam parameter product, M ${\,}^{2}$ , in the slow axis is 1.85, achieving a near diffraction-limited beam quality. A novel method for easy surface gratings fabrication is first presented, wherein, 4-μm-width periodic surface grooves, acting as waveguide ridges, are defined once by i-line lithography only without regrowth, nanoscale gratings fabrication, or facet coating. Owing to the low-cost fabrication methods and good performances, our single-longitudinal-mode devices can be used for widespread practical applications.

High-Power, Ultra-Low Noise Hybrid Lasers for Microwave Photonics and Optical Sensing

This paper describes the design, fabrication, and excellent performance achieved with prototype hybrid lasers incorporating a high performance gain chip coupled into a fiber external cavity including a novel fiber Bragg grating (FBG) reflector. Packaged ultra-low noise (ULN) hybrid lasers operating at 1550 nm and at 1319 nm with high output power, >100 mW, and extremely low relative intensity noise (RIN) are described. Devices provide extremely stable singlemode output with high side-mode suppression ratio (SMSR), typically above 70 dB, with worst case measured RIN at microwave frequencies (1–20 GHz) being below –165 dBc/Hz. Operation of these high power, low RIN devices within an analog optical link demonstrates a Spurious Free Dynamic Range as high as 114.6 dB.Hz 2/3. In addition to high power and very low RIN, the ULN hybrid lasers provide extremely small low frequency phase noise, with Lorentzian linewidths down to 15 Hz, enabling key Microwave Photonics and Optical Sensing applications. A comparison of the phase noise and Lorentzian linewidth of ULN lasers with different FBG designs / external cavity lengths is described, demonstrating the novel hybrid approach for achieving extremely low phase noise lasers.

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

<span lang="EN-US">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-nm 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 to 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 Gbps to 8.5 Gbps. The results of reliability tests of the modules are also presented.</span>

Photonic Integrated Circuit Based on Hybrid III–V/Silicon Integration

This paper summarizes the recent advances of integrated hybrid InP/SOI lasers and transmitters based on edge coupling. First, we review the different integration methods between III–V material and silicon. Then, we focus on using an external III–V chip coupled via edge coupling to our silicon photonic integrated circuit. The paper reports on the results of wavelength tunable lasers containing one or two ring resonators as well as an integrated reflectivity tunable mirror. We demonstrate that a wide thermal tuning range, exceeding the C band, with a high side mode suppression ratio above 35 dB can be achieved. Design of external silicon cavities enables the realization of a broad range of on-chip functionalities as well as advanced hybrid transmitters. Parallel wavelength tunable cavities and compact variable optical attenuator-controlled arrayed waveguide gratings on silicon are integrated with a reflective semiconductor optical amplifiers, creating fast wavelength switching lasers. Furthermore, integrated transmitters that combine silicon modulators with tunable hybrid III–V/Si lasers are reported. The integrated transmitter for on–off keying signal generation exhibits more than 30 nm wavelength tunability and excellent bit-error-rate performance up to 40 Gb/s. A multichannel integrated transmitter is then reported with combined silicon-based arrayed waveguide gratings laser cavity and multiple ring modulators. Finally, an advanced wavelength-tunable hybrid III–V/Si transmitter with two microring modulators nested in a Mach–Zehnder interferometer is demonstrated for quadrature phase-shift keying generation where a BPSK signal is generated by each ring.

Optical frequency comb generation for DWDM transmission over 25- to 50-km standard single-mode fiber

Dense wavelength division multiplexed (DWDM) transmission equal to 1.2 Tbps over 25 to 50 km across standard single-mode fiber (SSMF) in the C band is performed based on an optical frequency comb generator. Sixty-one flattened optical frequency tones were realized with 30-GHz frequency spacing, high side-mode suppression ratio over 35 dB, and minimum amplitude difference was realized using amplitude modulator for first time in cascade mode with two Mach–Zehnder modulators (MZMs) where all the modulators were tailored by RF signals. 20×61 Gbps DWDM-based differential quadrature phase shift keying modulated signals were successfully transmitted over SSMF and analyze its transmission capability for range of 25 to 50 km with acceptable power penalties and bit error rates.

Flattened Optical Multicarrier Generation Technique for Optical Line Terminal Side in Next Generation WDM-PON Supporting High Data Rate Transmission

A novel and cost effective optical multicarrier (OMC) generator is introduced in this article. OMC is generated by connecting three modulators in cascade with laser source, where laser is connected with one amplitude modulator and two Mach-Zehnder modulators (MZMs) in cascade. The amplitude modulator is used for the first time in cascade configurations for the generation of OMC signal. All the modulators are driven by RF signal of 30 GHz where specially tailored or fiber-Bragg gratings are not required. The generated OMC is very flat due to the proper DC biasing of MZMs and being related to the optimum ratio of DC bias and half wave voltage of MZMs. OMC offers 61 comb lines with minimum excursions in its comb lines, having tone-to-noise ratio greater than 40 dB, frequency spacing equal to 30 GHz, and high side mode suppression ratio over 35 dB. In this configuration, no optical phase shifter, amplifier, or attenuator is used. Second, optical line terminal (OLT) costs of conventional wavelength division multiplexed passive optical network (WDM-PON) system are reduced by introducing the proposed OMC source at OLT side of WDM-PON system for large capacity WDM-PON that supports numerous users. At OLT side, each out of 61 carriers is capable of supporting 10 Gb/s differential phase shift keying based data in downlink transmission. In the uplink transmission, half power splitters are deployed at optical network unit (ONU) side, where half power of the downlink signal is utilized for uplink transmission based on intensity-modulated on-offkeying resulting in colorless ONUs. The detailed power budget is discussed for the validity of results. Bit error rate (BER), eye patterns, and power penalties lie in the metrics encountered for the analysis in full duplex PON’s transmission. Minimum power penalties at specific BERs of different channels show the applicability of the proposed model.

Experimental Demonstration of the Distributed Feedback Semiconductor Laser With S-Bent Waveguide and Sampled Grating

A distributed feedback (DFB) semiconductor laser based on s-bent waveguide and sampled grating is theoretically studied and experimentally demonstrated. The proposed laser operates with a high side mode suppression ratio (SMSR) when the bias current is changed from 50 to 130 mA. When the bias current is fixed at 130 mA, the SMSR is larger than 55 dB, which is benefit from the suppressed spatial hole burning, while the SMSR of the equivalent phase shifted DFB laser decreases to 39 dB. The wavelength spacing error between two proposed DFB lasers is measured to be 0.089 nm compared with the designed value. When temperature is increased from 20 °C to 42 °C, the presented DFB laser achieves stable single longitudinal mode (SLM) operation with SMSR >51 dB and the wavelength varies from 1562.24 to 1564.6 nm with a slope of 0.11 nm/°C. The s-bent waveguide and sampled grating can be fabricated simply by the common holography exposure and photolithograph technique resulting in a low cost. Besides, the wavelength accuracy and SLM yield can be improved significantly, which is very beneficial for the multiwavelength DFB laser array.

Erbium-doped fiber ring laser with wavelength selective filter based on non-linear photonic crystal fiber Mach–Zehnder interferometer

A high output power, stable wavelength spacing and switchable multi-wavelength erbium-doped fiber laser has been demonstrated experimentally using a combination of non-linear photonic crystal fiber Mach–Zehnder (MZI) interferometer with polarization dependent loss effect. This MZI functions together with a polarization controller (PC) as a wave selecting filter (WSF). Adjusting the PC within the WSF part gives rise to three emissions as single, dual and triple wavelengths. Multi-wavelength laser with maximum spacing of 1.6 nm was achieved by controlling the polarization state in a ring cavity. Such stable wavelength spacing aroused interest in wavelength-division-multiplexer systems. Output power around −3 dB at 1550 nm wavelength, with small power fluctuation for each line, was recorded at room temperature. The measured 3-dB laser line-width was 0.03 nm, with a high side-mode suppression ratio of 48 dB.

Widely tunable semiconductor lasers with three interferometric arms.

We present a comprehensive study for a new three-branch widely tunable semiconductor laser based on a self-imaging, lossless multi-mode interference (MMI) coupler. We have developed a general theoretical framework that is applicable to all types of interferometric lasers. Our analysis showed that the three-branch laser offers high side-mode suppression ratios (SMSRs) while maintaining a wide tuning range and a low threshold modal gain of the lasing mode. We also present the design rules for tuning over the dense-wavelength division multiplexing grid over the C-band.