Quantum Dot Distributed Feedback Lasers Research Articles

Design of high power evanescent quantum dot distributed feedback lasers on Si

Great advancements in III–V/Si epitaxy have pushed quantum dot lasers to the forefront of silicon photonics. In this work, we designed the structures of evanescent coupled quantum dot distributed feedback lasers with asymmetric gratings, which made significant improvement in on-chip output power while maintaining single-longitudinal-mode stability. The optimal λ/4 phase-shift position (the ratio of the grating length from the rear-end of λ/4 phase-shift to the total grating length) from conventional position of 0.50 to 0.64 allows the ratio of the output power at both sides of silicon waveguide to be increased from 1.0 to 5.9. Moreover, the optimal duty cycle at one side of the phase-shift from 0.50 to 0.8 allows the ratio to be increased from 1.0 to 3.7. Meanwhile, the ratio could be dramatically improved from 1.0 to 9.2 by changed the duty cycle at one side of phase-shift to 0.7 while maintaining the phase-shift position of 0.64. With those designed structures, evanescent coupled quantum dot lasers could challenge the state-of-the-art bonded quantum well lasers and may eventually become ubiquitous and affordable for future commercial production.

Impact of external carrier noise on the linewidth enhancement factor of a quantum dot distributed feedback laser.

This paper demonstrates that the linewidth enhancement factor of quantum dot lasers is influenced by the external carrier transport issued from different external current sources. A model combining the rate equation and semi-classical carrier noise is used to investigate the different mechanisms leading to the above phenomenon in the context of a quantum dot distributed feedback laser. Meanwhile, the linewidth enhancement factor extracted from the optical phase modulation method shows dramatic differences when the quantum dot laser is driven by different noise-level pumps. Furthermore, the influence of external carrier noise on the frequency noise in the vicinity of the laser's threshold current directly affects the magnitude of the linewidth enhancement factor. Simulations also investigate how the external carrier transport impacts the frequency noise and the spectral linewidth of the QD laser. Overall, we believe that these results are of paramount importance for the development of on-chip integrated ultra-low noise oscillators producing light at or below the shot-noise level.

A self-locking structure for quantum dot DFB and FP lasers based on optical feedback

This paper presents a self-coherent optical feedback system that achieves resonance between the external cavity mode and the relaxation oscillation frequency of distributed feedback (DFB) laser and the repetition frequency of Fabry–Perot (FP) laser, all in an effort to achieve optical feedback self-locking. Results using this system show that for FP lasers, feedback is able to reduce the 3 dB radio frequency linewidth from 2 MHz to 600 kHz. In the case of DFB lasers, an electric frequency comb with an external cavity repetition rate of 17.25 MHz is achieved. This research presents a significant step toward the improvement of the performance of quantum dot lasers in optical communication systems.

High‐Power, Narrow‐Linewidth, and Low‐Noise Quantum Dot Distributed Feedback Lasers

AbstractSingle‐frequency semiconductor lasers represent a critical role in optical communications, light detection and ranging systems, photonics integrated circuits, etc. Here, combining atom‐like quantum dot (QD) materials and advanced lateral gratings, a high‐power, ultra‐low‐noise 1.3 µm InAs/GaAs QD distributed feedback laser is demonstrated. Stable single‐longitudinal‐mode output power of 100 mW from 25 ℃ to 85 ℃ is achieved with a maximum side mode suppression ratio of 62.6 dB, and the variations of threshold current and slope efficiency over the temperature range are slight, indicting a high temperature stability. A record‐narrow intrinsic linewidth of 1.62 kHz is achieved at 55 ℃ with a white noise level of merely 515 Hz2 Hz–1, and a minimum averaged relative intensity noise of only –166 dB/Hz between 0.1 GHz and 20 GHz is obtained at 25 ℃. Furthermore, a strong tolerance to external optical feedback (〉 –14 dB) is demonstrated in the range from 25 ℃ to 85 ℃, with a maximum value of –8 dB at 85 ℃. This high‐quality single‐frequency laser fabricated with simplified processes and compact size paves the way for its future large‐scale applications such as high‐capacity optical communication, high‐precision optical detection, high‐speed optical interconnections, etc.

1550 nm‐Band InAs/InGaAlAs Quantum Dot Distributed Feedback Lasers Grown on InP(311)B Substrate with Side‐Wall Gratings Simultaneously Fabricated with a Ridge Waveguide

A 1550 nm‐band InAs/InGaAlAs quantum dot (QD) distributed feedback (DFB) laser is fabricated, in which the side‐wall grating is formed in a simultaneous process with the ridge waveguide, and room‐temperature continuous‐wave single‐mode oscillation is achieved. A rather low‐threshold current density of about 2.2 kA cm−2 is obtained. Side‐mode suppression ratios (SMSRs) are 28 dB just above the threshold current Ith and 44 dB at I/Ith = 2.0. Antireflection (AR) coating suppresses the amplified spontaneous emission (ASE) and increases the slope efficiency by a factor of 1.3.

Dynamic performance and reflection sensitivity of quantum dot distributed feedback lasers with large optical mismatch

This work reports on a high-efficiency InAs/GaAs distributed feedback quantum dot laser. The large optical wavelength detuning at room temperature between the lasing peak and the gain peak causes the static, dynamic, and nonlinear intrinsic properties to all improve with temperature, including the lasing efficiency, the modulation dynamics, the linewidth enhancement factor, and consequently the reflection insensitivity. Results reported show an optimum operating temperature at 75°C, highlighting the potential of the large optical mismatch assisted single-frequency laser for the development of uncooled and isolator-free high-speed photonic integrated circuits.

High-performance quantum-dot distributed feedback laser on silicon for high-speed modulations

We report a 1310 nm heterogeneous quantum-dot distributed feedback laser on silicon with high efficiency and modulation capability and demonstrate isolator-free external modulation at 25 Gb/s using a metal-oxide semiconductor capacitor microring modulator.

1.3 μm InAs/GaAs quantum dot DFB laser integrated on a Si waveguide circuit by means of adhesive die-to-wafer bonding.

In this paper we report a single mode InAs/GaAs quantum dot distributed feedback laser at 1.3 μm wavelength heterogeneously integrated on a Si photonics waveguide circuit. Single mode lasing around 1300 nm with a side-mode suppression ratio higher than 40 dB is demonstrated. High temperature operation with continuous wave lasing up to 100°C is obtained. Threshold current densities as low as 205 A/cm2 were measured. These devices are attractive candidates to use in uncooled silicon photonic transceivers in data centers.

Narrow spectral linewidth in InAs/InP quantum dot distributed feedback lasers

This paper reports on the spectral linewidth of InAs/InP quantum dot distributed feedback lasers. Owing to a low inversion factor and a low linewidth enhancement factor, a narrow spectral linewidth of 160 kHz (80 kHz intrinsic linewidth) with a low sensitivity to temperature is demonstrated. When using anti-reflection coatings on both facets, narrow linewidth operation is extended to high powers, believed to be due to a reduction in the longitudinal spatial hole burning. These results confirm the high potential of quantum dot lasers for increasing transmission capacity in future coherent communication systems.

Tunable colloidal quantum dot distributed feedback lasers integrated on a continuously chirped surface grating.

We report a colloidal quantum dot (CQD) distributed feedback (DFB) laser structure containing a chirped grating. The device exhibits single-mode DFB lasing, of which the wavelength is spatially dispersed in a single chip. A period-chirped surface grating is fabricated using a modified Lloyd-type laser interference lithography setup, where a flat Lloyd's mirror is replaced with a concave one. A dense red-emitting CdSe/CdS/ZnS CQD film is prepared on a temporary substrate by spin-coating, which is subsequently released and wet-transferred onto a period-chirped quartz surface grating. Upon optical excitation, the fabricated DFB laser device lases in a single mode at a laser threshold of ∼400 μJ cm-2, with its lasing wavelength shifted linearly (in proportion to the grating pitch) along the chirp direction from 613.4 nm to 623.2 nm over a distance of ∼5.6 mm.

15 Gb/s index-coupled distributed-feedback lasers based on 1.3 μm InGaAs quantum dots

The static properties and large-signal modulation capabilities of directly modulated p-doped quantum-dot distributed-feedback lasers are presented. Based on pure index gratings the devices exhibit a side-mode-suppression ratio of 58 dB and optical output powers up to 34 mW. Assisted by a broad gain spectrum, which is typical for quantum-dot material, emission wavelengths from 1290 nm to 1310 nm are covered by the transversal and longitudinal single-mode lasers fabricated from the same single wafer. Thus, these lasers are ideal devices for on-chip wavelength division multiplexing within the original-band according to the IEEE802.3ba standard. 10 Gb/s data transmission across 30 km of single mode fiber is demonstrated. The maximum error-free data rate is found to be 15 Gb/s.

Generation of Tunable Millimeter-Wave and THz Signals With an Optically Injected Quantum Dot Distributed Feedback Laser

Generation of tunable millimeter-wave (MMW) and terahertz (THz) signals is experimentally demonstrated with an optically injected 1310-nm quantum dot distributed feedback (QD DFB) laser. A novel technique for MMW and THz signal generation is proposed, which is based on the dual-mode laser operation and the four-wave mixing induced in the QD DFB under single-beam optical injection into one of its residual Fabry-Perot modes. Coarse and fine tunability of the MMW and THz signals from 117 to 954 GHz is also demonstrated by injecting the external light into different residual modes of the QD laser and by controlling the injection strength and the initial frequency detuning.

Two-Wavelength Switching With a 1310-nm Quantum Dot Distributed Feedback Laser

Two-wavelength switching operation and bistability is reported for the first time with a 1310-nm quantum-dot (QD) distributed feedback (DFB) laser. We demonstrate experimentally the switching of the lasing mode of the QD laser under external optical injection into one of the residual Fabry-Perot (FP) modes of the device. Clockwise switching and bistability occurs for both the lasing and the injected subsidiary modes of the QD DFB laser as the injection strength is increased. Moreover, very high ON-OFF contrast ratio is measured for the switching transition of the lasing mode of the device. We have also analyzed experimentally the influence of two important system parameters, namely the initial wavelength detuning and the applied bias current. The variety of switching behaviors obtained with a 1310-nm QD DFB laser added to the theoretically superior properties of nanostructure lasers offers exciting prospects for novel uses of these devices in all-optical logic and all-optical switching/routing applications in present and future optical telecommunication networks.

1.3-µm Quantum Dot Distributed Feedback Laser with Half-Etched Mesa Vertical Grating Fabricated by Cl2 Dry Etching

We propose a quantum dot (QD) laser with the half-etched mesa distributed feedback (HEM DFB) structure fabricated by single-step dry etching. The HEM DFB structure provides several advantages, such as low scattering loss and wavelength stability. In this study, we demonstrated a low threshold current of 23 mA and a high thermal stability of 0.077 nm/K for 1.3 µm ground state emission. We also improved the performance of the slope efficiency of HEM DFB lasers by using Cl2 dry etching.

Dual-mode lasing in a 1310-nm quantum dot distributed feedback laser induced by single-beam optical injection

Tunable dual-mode lasing is experimentally demonstrated in a 1310-nm quantum dot (QD) distributed-feedback (DFB) laser under single-beam optical injection. The wavelength spacing between the two lasing modes is controlled by injecting the external optical signal into different residual Fabry-Perot modes of the QD DFB laser. The influence of important parameters, i.e., injection strength and bias current, is also analyzed. The simple experimental configuration used to achieve tunable dual-mode lasing and the theoretically superior properties of the QD laser offer exciting prospects for the use of these devices in microwave signal generation and radio-over-fiber applications for future mobile communication networks.

High-performance 1.52 µm InAs/InP quantum dot distributed feedback laser

A high performance ridge-waveguide InAs/InP quantum dot distributed feedback laser around 1.52 µm with a cavity length of 1 mm and a stripe width of 3 µm is demonstrated. In continuous-wave operation singlemode output power was up to 18.5 mW and its sidemode suppression ratio was greater than 62 dB. The relative intensity noise was measured to be less than −154 dB/Hz from 10 MHz to 10 GHz, and the optical linewidth smaller than 150 kHz when the injection current was 200 mA at room temperature of 18°C.

Wide-temperature-range 10.3 Gbit/s operations of 1.3 [micro sign]m high-density quantum-dot DFB lasers

Wide-temperature-range 10.3 Gbit/s operations of 1.3 µm distributed feedback (DFB) lasers using high-density quantum dots are presented. Clearly opened eye diagrams are obtained from −40 to 80°C with extinction ratios of more than 5.2 dB.

Two-color multi-section quantum dot distributed feedback laser

A dual-wavelength emission source is realized by asymmetrically pumping a two-section quantum-dot distributed feedback laser. It is found that under asymmetric bias conditions, the powers between the ground-state and excited-state modes of the two-section device can be equalized, which is mainly attributed to the unique carrier dynamics of the quantum-dot gain medium. As a result, a two-color emission with an 8-THz frequency difference is realized that has potential as a compact THz source. It is also shown that the combination of significant inhomogeneous broadening and excited-state coupled mode operation allows the manipulation of the quantum-dot states through external optical stabilization.

Frequency-Dependent Linewidth Enhancement Factor of Quantum-Dot Lasers

We present detailed measurements of the linewidth enhancement factor (LEF) of a quantum-dot distributed-feedback laser emitting around 1.3 mum above and below threshold. The above threshold method is based on the measurement of the frequency modulation and amplitude modulation response of the laser and shows significant dependence on modulation frequency. Drive current dependent measurements with both methods yield LEF values between 1 well below and 3 well above threshold, converging around 2 close to threshold.

1.55 $\mu$m InAs/InAlGaAs Quantum Dot DFB Lasers

For the fabrication of quantum dot (QD) distributed feedback (DFB) lasers, self-assembled InAs/InAlGaAs QDs were grown on the InP/InGaAs grating structures by a molecular beam epitaxy. Ridge-waveguide QD DFB lasers with a stripe width of 3 mum were fabricated. Single-mode lasing operation around the wavelength of 1.56 mum was successfully achieved under the pulsed and continuous-wave (CW) modes at room temperature. The lasing operation was also observed up to 70 degC under pulsed mode, which is the first observation on the single-mode lasing around 1.55 mum. The characteristic temperatures calculated from the temperature dependence of the threshold current density were 121.8 K from room temperature to 45 degC, which was reduced to 74.2 K from 45 degC to 70 degC.