Narrow-linewidth Semiconductor Laser Research Articles

Frequency Noise Characterization of Narrow-Linewidth Semiconductor Lasers: A Bayesian Approach

Frequency Noise Characterization of Narrow-Linewidth Semiconductor Lasers: A Bayesian Approach

Narrow linewidth laser based on a sidewall grating active distributed Bragg reflector.

We demonstrated a narrow linewidth semiconductor laser based on a deep-etched sidewall grating active distributed Bragg reflector (SG-ADBR). The coupling coefficients and reflectance were numerically simulated for deep-etched fifth-order SG-ADBR, and a reflectance of 0.86 with a bandwidth of 1.04 nm was obtained by the finite element method for a 500-period SG-ADBR. Then the fifth-order SG-ADBR lasers were fabricated using projection i-line lithography processes. Single-mode lasing at 1537.9 nm was obtained with a high side-mode suppression ratio (SMSR) of 65 dB, and a continuous tuning range of 10.3 nm was verified with SMSRs greater than 53 dB. Furthermore, the frequency noise power spectral density was characterized, from which a Lorentzian linewidth of 288 kHz was obtained.

Characterization of Tunable Narrow-Linewidth Semiconductor Lasers with Micro-Ring-Based External Cavities

Characterization of Tunable Narrow-Linewidth Semiconductor Lasers with Micro-Ring-Based External Cavities

High Brightness Narrow-linewidth Semiconductor Laser Based on Beam Waist Splitting Polarization Combining

High Brightness Narrow-linewidth Semiconductor Laser Based on Beam Waist Splitting Polarization Combining

Hybrid integrated narrow-linewidth semiconductor lasers.

Integrated narrow-linewidth lasers are the key devices in compact coherent optical systems of metrology, sensing, and optical microwave generation. Here, we demonstrate a hybrid integrated laser based on an optical negative feedback scheme. The laser is composed of a commercial distributed feedback (DFB) laser diode and an on-chip micro-resonator with a Q-factor of 0.815 million. The feedback optical field is coupled back to the laser cavity through the back facet. Therefore, the laser can maintain the lasing efficiency of the DFB laser diode. The linewidth of the DFB laser diode is compressed from 2MHz to 6kHz, corresponding to the linewidth reduction factor of 25.2dB. The theoretical result shows that the laser performance still has a huge improvement margin through precise control of the detuning between laser frequency and the micro-resonator, as well as the phase delay of the feedback optical field. The hybrid narrow-linewidth laser diode has wide application prospects in coherent optical systems benefitting from the low cost and volume productivity.

Narrow linewidth semiconductor multi-wavelength DFB laser array simultaneously self-injection locked to a single microring resonator.

We experimentally demonstrate a narrow linewidth semiconductor multi-wavelength distributed feedback (DFB) laser array by simultaneously injection locking each laser to the corresponding resonance of a single on-chip microring resonator. The white frequency noises of all the DFB lasers is reduced by more than 40 dB once they are simultaneously injection locked to a single microring resonator with a quality factor (Q-factor) of 2.38 million. Correspondingly, the instantaneous linewidths of all the DFB lasers are narrowed by a factor of 104. In addition, frequency combs originating from non-degenerate four-wave mixing (FWM) between the locked DFB lasers are also observed. Simultaneously injection locking multi-wavelength lasers to a single on-chip resonator may enable the possibilities of integrating a narrow-linewidth semiconductor laser array on a single chip and having multiple microcombs in a single resonator, which are in high demand in wavelength division multiplexing coherent optical communication systems and metrological applications.

Narrow linewidth semiconductor laser with a multi-period-delayed feedback photonic circuit.

A multi-period-delayed feedback (MPDF) photonic circuit constructed by a Sagnac ring and two coupled rings was designed. By coupling a distributed feedback (DFB) laser diode (LD) with the MPDF, a narrow linewidth semiconductor laser was demonstrated. The linewidth of the DFB-LD with MPDF was narrowed to be around 2 kHz, which is reduced by three orders of magnitude, and the linewidth reduction capability could be maintained when the wavelength of the DFB-LD was tuned in a range wider than 3 nm. The laser frequency stability can also be improved using the proposed technique, and the frequency fluctuation was reduced for nearly 8 times in comparison with the DFB-LD.

Narrow Linewidth Semiconductor Laser Based on Anti-Symmetric Bragg Grating

We present a new configuration of narrow linewidth semiconductor lasers (NLSLs) based on a novel narrow-band reflector (NBR) with π phase-shifted anti-symmetric Bragg grating (π-ASBG). Based on this configuration, two specific laser structures are theoretically analyzed. The effective length of Bragg grating is highly increased due to the double hybrid-mode resonances between the fundamental transverse electric (TE0) mode and first-order transverse electric (TE1) mode in the π-ASBG with the aid of a uniform grating reflector. The narrowest linewidth of ∼2.4 kHz is obtained of the proposed NLSLs, which is much lower than the traditional NLSLs with external uniform Bragg grating in the case of the same grating length.

Research progress of high power semiconductor laser pump source

High power semiconductor lasers are the main pump source for solid-state lasers and fiber lasers. The improvement in the performance of laser pump sources directly promotes the development of solid-state lasers, fiber lasers and other lasers. The article introduces the latest research progress of 8xx nm and 9xx nm semiconductor laser pump sources. The output power research level of 8xx nm single-emitter laser has reached 18.8 W@95 µm, the output power research level of 8xx nm laser bar has reached 1.8 kW(QCW), the output power research level of 9xx nm single-emitter laser has reached 35 W@100 µm, the output power research level of 9xx nm laser bar has reached 1.98 kW(QCW). The output power of a narrow linewidth semiconductor laser with a linewidth ＜1 nm can reach 14 W. The development trend of semiconductor laser pump source in the future is forecasted.

Waveguide external cavity narrow linewidth semiconductor lasers

Narrow linewidth light source is a prerequisite for high-performance coherent optical communication and sensing. Waveguide-based external cavity narrow linewidth semiconductor lasers (WEC-NLSLs) have become a competitive and attractive candidate for many coherent applications due to their small size, volume, low energy consumption, low cost and the ability to integrate with other optical components. In this paper, we present an overview of WEC-NLSLs from their required technologies to the state-of-the-art progress. Moreover, we highlight the common problems occurring to current WEC-NLSLs and show the possible approaches to resolving the issues. Finally, we present the possible development directions for the next phase and hope this review will be beneficial to the advancements of WEC-NLSLs.

(Invited) Temperature Stable III-V/Si/Si3N4 Heterogeneous Integrated Laser

Silicon nitride (Si3N4) is a widely used complementary metal–oxide–semiconductor (CMOS) compatible material in modern IC industry and recent years have witnessed tremendous development of Si3N4 in photonics. The benefits of Si3N4 in photonics include low loss, low thermo optic coefficient and negligible nonlinear absorption at telecom wavelengths. Devices based on Si3N4 waveguides innovates in the field of nonlinear photonics, sensing, microwave photonics and so on. However, they are all dependent on the excellent passive properties of Si3N4. There are no successful demonstrations of fully integrated laser with Si3N4 yet.For an external cavity laser design, it is beneficial to have a low loss waveguide. A low loss waveguide platform can enable a long optical cavity which can greatly reduce the laser phase noise. Butt-coupled hybrid integrated lasers are extensively studied using Si3N4 cavity, but they are based on separate chips and are not scalable for large volume integration.Heterogeneous integration of III-V material and Si has achieved great success in the past years, offering the silicon photonics industry with low-cost, high-performance silicon photonic integrated circuits fully integrated with lasers. For the heterogeneous integration of III-V material with Si3N4, the biggest challenge is the large index mismatch. Typical III-V epi used for heterogeneous lasers is about 2 μm thick and extreme tapering cannot facilitate a high coupling efficiency between the III-V layer and Si3N4 layer.In this work, we used an intermediate Si layer to bridge the index mismatch between the III-V and Si3N4 layer. By using multilayer heterogeneous integration shown in Fig.1 (a), we enable a III-V/Si/Si3N4 structure to efficiently couple the mode between III-V/Si and Si/Si3N4. Based on this structure, we designed the III-V/Si/Si3N4 laser using an external Si3N4 spiral grating as the feedback cavity. This spiral grating provides the narrow-band optical feedback and determines the laser wavelength. The laser configuration is shown in Fig. 1(b).The laser performance is summarized in Fig. 1 (c)-(e). The lasing wavelength is at 1546 nm and the laser has over 58 dB side mode suppression ratio (SMSR). This shows the excellent mode selectivity from the 20 mm long Si3N4 spiral grating. We measured the frequency noise of the laser. With optimized loop mirror reflectivity, the laser fundamental linewidth is about 4 KHz. This linewidth can be further improved by lowering the Si3N4 waveguide loss. We anticipate the laser fundamental linewidth can be reduced to below 100 Hz using this design.Another advantage of integrating Si3N4 into the laser cavity is to have much higher temperature stability. By comparison, III-V/Si/Si3N4 laser wavelength shifts by only 0.47 nm for 45 oC change, while for a III-V/Si DBR laser this wavelength shift is 3.3 nm. This is over 7x difference and is a result of the low thermo-optic coefficient of Si3N4. When combined with Si3N4 based arrayed waveguide gratings, our laser can be potentially used in dense wavelength-division-multiplexing (DWDM) systems.The successful demonstration of this multilayer heterogeneous integration will enable a whole new class of devices that require low loss waveguides and are presently not integrated. This is a key step in fully exploiting the capabilities of wafer-bonding technologies. We anticipate this platform can take narrow-linewidth semiconductor laser performance to a new level. Figure 1

On-chip optical narrowband reflector based on anti-symmetric Bragg grating.

We propose an on-chip optical narrowband reflector (NBR) based on two cascaded Bragg gratings (BGs). A π phase shifted anti-symmetric Bragg grating (π-PS-ASBG) and a rear uniform Bragg grating (UBG), are in-line connected. The π-PS-ASBG provides a hybrid mode resonance between the even- and odd TE (TE0 and TE1) modes, while the UBG is used as a rear reflector to reflect the TE0 mode that transmitted from the π-PS-ASBG. Different from traditional UBG, the reflection bandwidth decreases when the coupling coefficient increases. The calculated 3-dB bandwidth is 0.16 nm when the whole grating length is 400 µm. The proposed NBR can be applied in the cases requiring narrow reflection such as narrow linewidth semiconductor lasers.

Ring-Resonator Based Widely-Tunable Narrow-Linewidth Si/InP Integrated Lasers

This paper presents recent results on widely-tunable narrow-linewidth semiconductor lasers using a ring-resonator based mirror as the extended cavity. Two generations of lasers on the heterogeneous Si/InP photonic platform are presented. The first-generation lasers, with a total footprint smaller than 0.81 mm2, showed an intrinsic linewidth of ∼2 kHz over a 40 nm wavelength tuning range across C+L bands. The second-generation lasers using ultra-low loss silicon waveguides and a novel cavity design achieved an intrinsic linewidth below 220 Hz. The lasers also possess an ultrawide wavelength tuning range of 110 nm across three optical communication bands (S+C+L). These are records among all fully integrated semiconductor lasers reported in the literature.

Narrow linewidth DBR laser based on high order Bragg grating defined by i-line lithography

In order to obtain narrow linewidth semiconductor laser around 1564 nm, we design a distributed Bragg reflector (DBR) laser with high-order Bragg gratings (HOBGs) using butterfly encapsulation. The DBR laser is fabricated only by i-line lithography technology with grating period of 4. 84μm, groove width of 1. 5μm and grating length of 72μm on a strip width of 4μm. The 1mm-long devices achieved an output power of 9.9 mW and a side mode suppression ratio (SMSR) more than 30 dB without facet coating at an injection current of 80 mA. The lasers showed ultra-narrow Lorentz linewidth of 70 kHz. This paper provides a simple method for large-scale production of narrow linewidth semiconductor lasers.

Thermal design and optimization of narrow linewidth semiconductor lasers

Thermal design and optimization of narrow linewidth semiconductor lasers

Compact narrow-linewidth optical negative feedback laser with Si optical filter

A compact narrow-linewidth semiconductor laser is demonstrated by hybridly integrating an optical filter constructed from Si waveguides with a single-mode semiconductor laser, whose spectral linewidth is narrowed through optical negative feedback. We design the optimum structure of a reflective ring filter for an optical negative feedback laser, and a narrow spectral linewidth of 160 kHz is realized by the hybridly integrated laser source whose effective device length is less than 1.5 mm.

A newly designed high-spectral-resolution Rayleigh temperature lidar based on two-stage Fabry–Perot interferometer

A two-stage Fabry–Perot interferometer (FPI)-based high-spectral-resolution (HSR) Rayleigh temperature lidar technology is proposed that is capable of simultaneously detecting tropospheric temperature and aerosol optical properties with high-precision. The system structure is designed and the measurement principle is analysed. A two-channel integrated FPI used forming a two-stage FPI ensures the relative stability of the two FPI spectrums. The first-stage FPI with high spectral resolution can effectively separate Mie and Rayleigh signals to derive the signal components. Two adjacent-order transmission spectrums of the second-stage FPI are just located in the two wings of Rayleigh–Brillouin (R–B) scattering spectrum to measure temperature. Two multimode polarization insensitive optical circulators used in receiver system can achieve high-efficiency utilization of signals. A narrow linewidth semiconductor laser at 852 nm is used as light source. Using the selected and optimized system parameters, the lidar performance simulation results show that in the sunny weather conditions for 0.15WSr–1 m–2 nm–1 sky brightness, with 0.3 W laser power, a 30 cm diameter telescope, 60 m range resolution and 30 min observation time, the temperature measurement errors are below 0.4 K in night-time and below 1.6 K in daytime; the relative measurement errors of backscatter ratio are below 0.04% in night-time and below 0.13% in daytime respectively up to 6 km height. Compared with the traditional FPI-based HSR technique, the technique we proposed can improve the detection accuracy of temperature by 2.5 times and can also significantly improve the detection accuracy of backscatter ratio.

3-kHz Spectral Linewidth Laser Assembly With Coherent Optical Negative Feedback

We demonstrate the stable operation of a narrow-linewidth semiconductor laser source based on a coherent optical negative feedback system. The linewidth was reduced to 3 kHz from 13.5 MHz. The power spectral density of frequency modulation (FM) noise was reduced by 35 dB, while the relative intensity noise was low enough for a light source for optical communications (less than -140 dB/Hz). Additionally, the system showed stable operation more than an hour. Our results indicate that the instability of a laser system is caused by fluctuations in the feedback loop length due to the mechanical vibrations, which can be suppressed by the robust integration of the system.

A recirculating delayed self-heterodyne method using a Mach–Zehnder modulator for kHz-linewidth measurement

Abstract A laser linewidth measurement method which uses a Mach–Zehnder electro-optic modulator (MZM) is proposed in a loss-compensated recirculating delayed self-heterodyne interferometer (LC-RDSHI). Compared with the traditional acousto-optic modulator (AOM), the electro-optic modulator has the merits of broader bandwidth, lower insertion loss, higher extinction ratio and thus, a wider application. A theoretical analysis shows that the power spectrum curve of the novel measurement system is a Lorentzian line, which fits well with experiment. The linewidth is measured to be 137 ± 7 kHz at a frequency shift of 4 GHz. Measurement of a distributed feedback Bragg (DFB) laser has manifested that the linewidth broadens from 98.5 kHz to 137.4 kHz as the operating temperature changes by 16 °C. This work will allow investigation of narrow linewidth semiconductor and fiber laser stability.

Stable and Efficient Generation of High Repetition Rate ($>$160 GHz) Subpicosecond Optical Pulses

A stable optical beat-signal with frequency >; 160 GHz is produced by injection-locking two narrow-linewidth semiconductor lasers emitting at frequencies spaced by the beat-frequency to a low-jitter 10-GHz optical comb. The generated beat-signal with broadband noise suppression of >; 75 dB is temporally compressed by factors of up to four in a high stimulated Brillouin scattering threshold aluminosilicate highly nonlinear fiber. The generated subpicosecond pulses have a root mean square (rms) timing jitter below 150 fs measured over 1 s.