Distributed Bragg Reflector Laser Diode Research Articles

Photonic-assisted wideband microwave frequency measurement based on optical heterodyne detection

Photonic-assisted wideband microwave frequency measurement based on optical heterodyne detection

Photonic generation of a tunable multi-band linearly frequency-modulated waveform

A photonic-assisted tunable multi-band linearly frequency-modulated (LFM) waveform generator based on optical heterodyne detection is proposed and experimentally demonstrated. The multi-band LFM waveform is generated from a photodetector (PD), where a broadband LFM optical pulse and a multi-wavelength optical signal with the same magnitude at different wavelengths are heterodyne-detected. The LFM optical pulse is generated from a three-electrode distributed Bragg reflector laser diode (DBR-LD). The multi-wavelength optical signal is produced through a Mach-Zehnder modulator (MZM), in which a light wave from an optical fiber laser (OFL) is nonlinearly intensity-modulated by a radio frequency (RF) signal. By tuning the wavelength of the LFM optical pulse lower than that of the multi-wavelength optical signal, a multi-band LFM waveform is generated at the PD. The center frequency of the generated LFM waveform can be adjusted by manipulating the wavelength of the OFL. The versatility in the bandwidth and temporal duration of the LFM waveform is attained through the precise tuning of the LFM optical pulse. The tuning of the center frequency difference between frequency bands is performed by altering the frequency of the RF signal. Experimental results have corroborated the realization of a tunable multi-band LFM waveform generator. The bandwidth and temporal duration of each band and the center frequency difference between frequency bands have tuning ranges from 0.7 to 6.7 GHz, 1 to 50 μs, and 2 to 6.7 GHz, respectively. The demonstration shows new avenues to implement high-performance multi-band LFM waveform generators for applications in multi-functional modern radar systems.

Wide-wavelength-tunable distributed Bragg reflector laser diode with high thermal efficiency.

We proposed a thermally-tuned distributed Bragg reflector (DBR) laser diode that has a high tuning efficiency over a wide wavelength tuning range. The laser diode is composed of a gain, a phase control (PC), and a DBR region, and its wavelength is tuned coarsely and finely by the micro-heaters on the DBR and PC regions, respectively. To improve the tuning efficiency, we developed a technique for fabricating a thermal isolation structure through a reverse mesa etching process, replacing the complex process that uses an InGaAs sacrificial layer. The DBR laser diodes (DBR-LD) fabricated using this method effectively confines heat generated by the heater, resulting in an approximate tuning range of 40 nm. This technology, which has achieved nearly four times larger wavelength tuning range than the thermally-tuned DBR-LDs without a thermal isolation structure, is considered suitable for the cost-effective development of wide-wavelength-tuning DBR-LD light sources.

A low-magnetic packaging for a distributed Bragg reflector laser diode chip for atomic sensor applications

We implement a distributed Bragg reflector (DBR) laser diode (LD) package with low-magnetic field generation. The package consists of a commercial 795 nm DBR LD chip, a thermo-electric cooler (TEC), a thermistor, a flexible printed circuit board (FPCB) which cancels the magnetic field emitted by the TEC current flow, and a non-magnetic aluminum case. We confirm that the magnetic dipole moment of our low-magnetic package body is about three orders of magnitude smaller than that of a commercial DBR laser package. Moreover, it is shown that our compensating FPCB, the effectiveness of which is supported by computer simulations, reduces the magnetic field magnitude by a factor of 2.2. The FPCB also reduces the magnetic field gradient emitted by the TEC current flow so that gradient-induced spin relaxations are suppressed in applications. A portable optically pumped atomic magnetometer (OPAM) utilizing two low-magnetic packages as light sources is reported as an application of the package and shows a 0.30 pT/Hz1/2 level magnetic sensitivity at a 69 μT external magnetic field; in contrast, the OPAM utilizing the commercial packages showed a magnetic sensitivity of 0.87 pT/Hz1/2.

Monolithically Integrated Tunable Three- Section All-Active DBR Laser Diodes With 30 nm Tuning Range

We present a monolithically integrated three-section all-active AlGaInAs/InP tunable distributed Bragg reflector (DBR) ridge waveguide laser diode that uses thermal tuning mechanism and mode-hopping tuning principle to achieve wide-range wavelength tuning. It is similar to the traditional three-section DBR laser structure, including a gain section, a phase section, and a DBR grating section. The difference is that the phase section and the DBR section incorporate the same active quantum well structure as the gain section. In this case, weak effective refractive index changes of the three active sections affected by the current injection will occur since the carrier density is clamped by the threshold gain condition of the DBR laser diode. Despite this limitation, a noncontinuous tuning up to ∼30 nm (1564–1594 nm) can be observed using only current injection at a constant temperature of 25 °C. Significant thermal effects occurred during the tuning process. In addition, a discontinuity is introduced in the tuning because it does not contain a passive region for phase adjustment. However, the device still provides a stable single longitudinal mode output with nine channels, a wavelength spacing of about 4 nm, and a side mode suppression ratio (SMSR) of more than 30 dB. Furthermore, the DBR laser diode can be easily fabricated utilizing the conventional distributed feedback laser diode fabrication process without secondary epitaxy and heater metal. The all-active DBR laser diode will be expected to be applied in the coarse wavelength division multiplexing (CWDM) systems with the advantage of low cost.

Photonic Generation of a Tunable Dual-Chirp Microwave Waveform

A photonic-assisted tunable dual-chirp microwave waveform generator based on optical heterodyne detection is proposed and experimentally demonstrated. In the proposed scheme, a three-electrode distributed Bragg reflector laser diode (DBR-LD) is used to generate a broadband frequency-chirped optical pulse. A stable optical fiber laser and a Mach-Zehnder modulator (MZM) are used to perform a double-sideband suppressed carrier (DSB-SC) signal. The frequency difference between the two sidebands of the DSB-SC signal is larger than the frequency chirp range of the optical pulse. By tuning the center frequency of the optical pulse equals that of the DSB-SC signal and beating the optical pulse and the DSB-SC signal at a photodetector (PD), a dual-chirp microwave waveform is generated. The center frequency of the generated waveform is tuned by adjusting the modulated frequency of the DSB-SC signal. The tunability of the bandwidth and the temporal duration are achieved by tuning the optical pulse. Experimental results show that the center frequency, the bandwidth, and the temporal duration have tuning ranges from 7 to 13 GHz, 13 to 17 GHz, and 500 ns to 50 μs, respectively. Chirp rates up to ±26 GHz/μs for the up- and down-chirp waveforms are measured in the experimental demonstration, respectively. The demonstration shows new avenues to implement high-performance dual-chirp microwave waveform generators for applications in modern radar systems with improved range-Doppler resolution.

Electroabsorption modulator‐integrated distributed Bragg reflector laser diode for C‐band WDM‐based networks

AbstractWe report an electroabsorption modulator (EAM)‐integrated distributed Bragg reflector laser diode (DBR‐LD) capable of supporting a high data rate and a wide wavelength tuning. The DBR‐LD contains two tuning elements, plasma and heater tunings, both of which are implemented in the DBR section, which have blue‐shift and red‐shift in the Bragg wavelength through a current injection, respectively. The light created from the DBR‐LD is intensity‐modulated through the EAM voltage, which is integrated monolithically with the DBR‐LD using a butt–joint coupling method. The fabricated chip shows a threshold current of approximately 8 mA, tuning range of greater than 30 nm, and static extinction ratio of higher than 20 dB while maintaining a side mode suppression ratio of greater than 40 dB under a window of 1550 nm. To evaluate its modulation properties, the chip was bonded onto a mount including a radiofrequency line and a load resistor showing clear eye openings at data rates of 25 Gb/s nonreturn‐to‐zero and 50 Gb/s pulse amplitude modulation 4‐level, respectively.

Lateral characteristics improvements of DBR laser diode with tapered Bragg grating

Broad area semiconductor laser (BAL) has poor lateral beam quality due to lateral mode competition, which limits its application as a high-power optical source. In this work, the distributed Bragg reflector laser diode with tapered grating (TDBR-LD) is studied. By changing the lateral width, the tapered grating increases the loss of high-order lateral modes, thus improving the lateral characteristics of the laser diode. The measuring results show that the TDBR-LD can achieve a single-lobe output under 0.9 A. In contrast to the straight distributed Bragg reflector laser diode (SDBR-LD), the lateral far field divergence of TDBR-LD is measured to be 5.23° at 1 A, representing a 17% decline. The linewidth of TDBR-LD is 0.4 nm at 0.2 A, which is reduced by nearly 43% in comparison with that of SDBR-LD. Meanwhile, both of the devices have a maximum output power value of approximate 470 mW.

Continuous-wave operation of 405 nm distributed Bragg reflector laser diodes based on GaN using 10th-order surface gratings

Single longitudinal mode continuous-wave operation of GaN-based distributed Bragg reflector (DBR) laser diodes with 10th-order surface gratings is demonstrated. The DBR consists of periodic V-shaped grooves on a 2 μm wide ridge waveguide fabricated by using electron-beam lithography and plasma etching. The effect of different lengths of the DBR section and the gain section on the device performance has been studied. Periodic mode hops to the adjacent longitudinal Fabry–Perot resonator mode at shorter wavelength have been observed when increasing the operation current. Between the mode hops, single longitudinal mode emission at around 405 nm is achieved with a full width at half-maximum of 0.03 nm. A linear redshift of the emission wavelength with increasing temperature of 0.019 nm/K was derived.

Ten emitter dual-wavelength Y-branch DBR laser diode array emitting 1 W at 785 nm with a spectral emission width below 60 pm

We present a 5 mm wide ten emitter dual-wavelength Y-branch DBR laser diode array emitting at 785 nm with an output power of 1 W at both wavelengths. The two emission wavelengths are individually addressable. The emitters are spectrally stabilized by deeply etched 10th order Distributed Bragg Reflector (DBR) gratings, realized by e-beam lithography. The wavelengths at 1 W output power are 784.0 nm and 784.6 nm. The spectral width of the emission of the individual emitters is below 20 pm. The spectral width of the array at 1 W is less than 60 pm caused by a variation in emission wavelength of about 40 pm of the individual emitters operating at one wavelength. The ten individual emitters reach an optical output power of 100 mW with minor variation of only 5 mW.

Feedback Sensitivity of DBR-Type Laser Diodes

It is shown theoretically that the feedback sensitivity of Distributed Bragg Reflector laser diodes with low-loss Bragg section decreases with the length of the Bragg section and also can be decreased by detuning from the Bragg peak. The effect of detuning is not only due to a change in effective linewidth enhancement factor, but also due to a change of the effective cavity length. The results can be applied also to laser diodes coupled on one side to one or more ring resonators Such lasers can have very weak feedback sensitivity.

A 1.6-[formula omitted]m widely tunable distributed Bragg reflector laser diode based on InGaAs/InGaAsP quantum-wells material

We demonstrate a widely tunable InGaAs quantum-wells (QWs) distributed Bragg reflector (DBR) laser, in which the DBR section was realized by using butt-jointed InGaAsP (λ=1.46μm) material. In the device process, we explored an optimal chemical etchant applied in the butt-jointed active–passive integration technology. A wide tuning range of 10.7 nm with 19 consecutive channels is obtained with a single tuning current at room temperature (RT). With the help of the heat sink temperature, the tuning range is expanded to 16 nm. A side mode suppression ratio (SMSR) of higher than 34 dB is obtained for all channels at 5 °C to 45 °C. A six-wavelength laser array that can cover a wavelength tuning range of 41.6 nm at 20 °C with a side mode suppression ratio higher than 37 dB in all channels is demonstrated by varying the grating periods. It is a promising light source for methane or multispecies gas detection.

16-channel tunable and 25-Gb/s EAM-integrated DBR-LD for WDM-based mobile front-haul networks.

We report a tunable distributed Bragg reflector-laser diode (DBR-LD) integrated with an electro-absorption-modulator (EAM) at an operating wavelength of 1.3 µm. This LD consists of gain, phase control (PC), DBR, and EAM sections, realized by using a butt-coupling technique in monolithically integrating the multiple quantum wells (MQWs) with the passive core and by applying an etched-mesa buried hetero-structure (EMBH) to the resonance cavity (i.e., gain to DBR section) and a deep-ridge type to the EAM section in fabricating the waveguide structure. Wavelength tuning of the LD is achieved by both applying a voltage to the heater metal of DBR section (coarse tuning) and injecting a current to the ohmic metal of PC section (fine tuning). From the work, the fabricated chips show a threshold current of about 13 mA, a side mode suppression ratio (SMSR) of more than 35 dB, and a tuning range of 15 nm within a heater voltage of 2 V. Dynamic tests for the EAM-integrated LD show the 3 dB bandwidth of more than 20 GHz and clear 25 Gb/s eye openings with a dynamic extinction ratio (DER) of over 7 dB for 16 channels spaced at the wavelength interval of 0.55 nm. Based on these results, we conclude that the EAM-integrated DBR-LD is capable of providing 16 channel operation at a data rate of 25 Gb/s and can be used as an effective light source for WDM-based mobile front-haul networks.

High-Power 1.5 μm Tapered Distributed Bragg Reflector Laser Diodes for Eye-Safe LIDAR

A high-power InAlGaAs/InP tapered distributed Bragg reflector laser diode with narrow linewidth emission at $1.5~\mu \text{m}$ is reported. The laser has a monolithic waveguide architecture comprising a third-order grating section for longitudinal mode selection, an index-guided gain section for lateral mode filtering, and a gain-guided tapered section for power scaling. An output power of 770 mW is reported for continuous wave operation at room temperature. In pulsed mode, the laser delivered a peak power of 4.6 W with a full width at half-maximum spectral linewidth of only 250 pm. In addition to the narrow linewidth and high-power features, the emission wavelength exhibits a temperature dependent shift of only 0.1 nm/°C. The parameters achieved suggest that these laser diodes would enable the realization of compact LIDAR systems with improved signal-to-noise ratio, owing to the high output power and the possibility to use narrow passband filters at receiver side, which is enabled by the narrow and temperature-stable emission spectrum. The wavelength range around $1.5~\mu \text{m}$ also enables LIDAR systems with high output powers while maintaining eye safety, ultimately leading to improved system performance.

Vertical GaN MISFET for chip‐on‐chip high speed laser driving applications

In this work, the authors developed vertical gallium nitride metal-insulator-semiconductor field-effect transistors (GaN MISFETs) for direct chip-on-chip assembly with gallium arsenide-based broad area distributed Bragg reflector diode laser. The intention of this work had been to provide a high-speed driver solution having extremely small parasitic inductive loops. It is shown that devices manufactured on ammonothermal substrates have large conduction current density above 1.7 kA/cm2, specific on-state resistance as low as 2.1 mΩ·cm2 and on-state sheet resistance of 18.6 Ω·mm. It is further shown that scaling these devices to large gate periphery chips is possible. Finally, a low inductance vertical GaN MISFET on laser diode integration assembly is realised on an AlN ceramic board using a transistor chip with 142 mm gate width and 305 mΩ on-state resistance. The arrangement enables 3.6 ns laser pulses at an emission wavelength at 904 nm and a peak optical power of 4 W.

Compact diode laser based light source with alternating dual-wavelength emission at 532\xa0nm

Compact nonlinear frequency conversion of a Y-branch distributed Bragg reflector (DBR) diode laser for alternating dual-wavelength laser emission at 532 nm is presented for the very first time. The developed light source, realized on a 5 × 25 mm2 micro-optical bench, is based on single-pass second harmonic generation of a 1064 nm Y-branch DBR diode laser in a periodically poled lithium niobate waveguide crystal with superimposed poling periods. Phase-matching is obtained by intrinsic wavelength stabilization of the laser and wavelength tuning by implemented heater elements above the DBR gratings. Obtained optical output powers of 5.6 mW at 532.45 nm and 6.7 mW at 531.85 nm are limited by central lobe power contents of 52% available for waveguide coupling. With a spectral performance showing narrowband emission with spectral widths of 0.01 nm (0.4 cm−1) limited by the spectral resolution of the spectrum analyzer and a spectral spacing of 0.6 nm (20 cm−1), the developed light source is suitable for applications such as Raman spectroscopy and shifted excitation Raman difference spectroscopy (SERDS). Separate electrical contacts of the Y-branch diode laser enable alternating operation at both wavelengths.

Continuous Wave THz System Based on an Electrically Tunable Monolithic Dual Wavelength Y-Branch DBR Diode Laser

We analyse the use of a tunable dual wavelength Y-branch DBR laser diode for THz applications. The laser generates electrically tunable THz difference frequencies in the range between 100 and 300 GHz. The optical beats are tuned via current injection into a micro-resistor heater integrated on top of one of the distributed Bragg reflector (DBR) section of the diode. The laser is integrated in a homodyne THz system employing fiber coupled ion-implanted LT-GaAs log spiral antennas. The applicability of the developed system in THz spectroscopy is demonstrated by evaluating the spectral resonances of a THz filter as well as in THz metrology in thickness determination of a polyethylene sample.

Wavelength-stabilized DBR high-power diode laser

This paper reports a wavelength-stabilized high-power diode laser emitting up to 14 W CW in the 9xx nm range. Wavelength stabilization is achieved by a distributed Bragg reflector (DBR) monolithically integrated in the diode laser chip. Key features are identical layer epitaxy (ILE) and the use of a multiple-order electron beam lithography (EBL) optical confining grating. ILE avoids any regrowth or complex technology processes, while EBL multiple-order grating allows narrow-band back reflection and effective lateral optical confinement, and makes it possible to stabilize multiple wavelengths on the same wafer using a manufacturable and reliable technology. DBR diode lasers with different pitches, whose wavelengths were 3 nm spaced, were fabricated and high spectral purity (95% optical power within about 0.6 nm) and wavelength stability were measured. Moreover, the high uniformity of performances across the wafer with different emitted wavelengths demonstrates the maturity of the proposed technology for high-yield, high-volume laser diode production for wavelength-stabilized applications. A multi-emitter module, including ten DBR diode lasers, collimating and focusing optics, showed 100 W CW wavelength-stabilized output power at 14 A in a 135 μm core optical fiber within 0.17 NA. Single diode lasers, or multi-emitter modules, can be used to combine high-power optical beams by wavelength division multiplexing (WDM) using dichroic optics, scaling up beam power to the kW range and maintaining optical beam quality.

Modulation transfer spectroscopy for frequency stabilization of 852 nm DBR diode lasers

We report on the realization of modulation transfer spectroscopy on the D2 transition of 133Cs for frequency stabilization of the 852 nm distributed Bragg reflector diode lasers. Proper modulation frequency, optimal pump and probe beam power are investigated according to the peak-to-peak amplitude and the slope of the modulation transfer spectroscopy signals. The laser frequency can be locked robustly for more than one day. The beat signal between two independent lasers has a frequency drift of 716 kHz at 5000 s. The result shows that the fractional frequency instability of the locked laser falls below 5 × 10−11 at 1000 s averaging time.

1.3-µm and 10-Gbps tunable DBR-LD for low-cost application of WDM-based mobile front haul networks.

We report a 1.3-µm and 10-Gbps tunable distributed Bragg reflector laser diode (DBR-LD) for the low-cost application of a wavelength division multiplex based mobile front-haul network. The device consists of gain, phase control, and DBR sections, implemented using a butt-coupling method through a monolithic integration and through the introduction of an etched mesa planar buried hetero-structure in a waveguide structure. From the work, a 560-µm long DBR-LD with a 220-µm long micro-heater DBR section has a threshold current of 10 mA ± 1 mA and a tuning range of more than 15 nm within a heater injection current of ∼100 mA. Spectral and dynamic tests for this LD show 16 channels spaced a wavelength grid of 0.8 nm with a side mode suppression ratio of greater 40 dB and clear eye openings with a dynamic extinction ratio of over 5.4 dB at an operating current of 60 mA.