Transistor Laser Research Articles

Influence of Franz Keldysh effect on the modulation depth and distortion characteristics of transistor laser

Influence of Franz Keldysh effect on the modulation depth and distortion characteristics of transistor laser

Effect of shorter section length on the performance of bisection gain lever transistor laser

Effect of shorter section length on the performance of bisection gain lever transistor laser

Effects of base and quantum wells widths variations on technical characteristics of tunneling injection transistor laser

Effects of base and quantum wells widths variations on technical characteristics of tunneling injection transistor laser

Investigations on the effect of separate confinement heterostructure width on the distortion performance of tunnel injection based transistor laser

Investigations on the effect of separate confinement heterostructure width on the distortion performance of tunnel injection based transistor laser

A Hybrid Optical-Electrical Analog Deep Learning Accelerator Using Incoherent Optical Signals

Optical deep learning (DL) accelerators have attracted significant interests due to their latency and power advantages. In this article, we focus on incoherent optical designs. A significant challenge is that there is no known solution to perform single-wavelength accumulation (a key operation required for DL workloads) using incoherent optical signals efficiently. Therefore, we devise a hybrid approach, where accumulation is done in the electrical domain, and multiplication is performed in the optical domain. The key technology enabler of our design is the transistor laser, which performs electrical-to-optical and optical-to-electrical conversions efficiently. Through detailed design and evaluation of our design, along with a comprehensive benchmarking study against state-of-the-art RRAM-based designs, we derive the following key results: (1) For a four-layer multilayer perceptron network, our design achieves 115× and 17.11× improvements in latency and energy, respectively, compared to the RRAM-based design. We can take full advantage of the speed and energy benefits of the optical technology because the inference task can be entirely mapped onto our design. (2) For a complex workload (Resnet50), weight reprogramming is needed, and intermediate results need to be stored/re-fetched to/from memories. In this case, for the same area, our design still outperforms the RRAM-based design by 15.92× in inference latency, and 8.99× in energy.

Effect of quantum well thickness and temperature on electrical and optical characteristics of transistor laser using group-IV material

Effect of quantum well thickness and temperature on electrical and optical characteristics of transistor laser using group-IV material

Dynamic performance analysis of lasing mode optical integrated device

In this paper, the dynamic response of the optical gain of optical integrated device composed of a heterojunction bipolar transistor (HBT) and a laser diode (LD) has been numerically analyzed. This type of optical integrated device is called transistor laser (TL). First, the rate equation of LD has been solved to obtain its transfer function. Second, the overall transfer function of the whole structure has been analyzed numerically. The effect of HBT cutoff frequency on the amplitude and phase frequency response has been studied. The obtained results show that HBT has a strong influence on the device performance. In particular, higher values of HBT cutoff frequency result in lower amplitudes and higher phase values in the low-frequency range. The device is stable and has a fast response and high optical gain at higher frequencies. Therefore, it can be used as an optical amplifier or optical switch in high-speed optical systems.

Modulation Characteristics of High-Speed Transistor Lasers

The spontaneous emission recombination lifetime of carriers in the active region of transistor lasers (TLs) is significantly reduced due to the accelerated carrier transport in the base region under the collector bias. Thus, it has the potential for use as a high-speed optical fiber communication light source. The unique three-electrode structure of TL notably enriches the modulation methods of the light source. As an important parameter to measure the data transfer rate, the modulation bandwidth of TL has been studied extensively. This paper briefly analyzes the inherent characteristics and advantages of TL and then discusses the progress in the research on TL modulation characteristics. Currently, the common methods to increase the modulation rate include optimizing the device structure, intracavity photon-assisted tunneling, and adding external auxiliary circuits. Through these techniques, single quantum well GaAs- based TL can achieve error-free transmission of 22 Gb/s, and simulation data show that for InP- based TL, this can reach 40 Gb/s. Finally, the challenges faced by TL in the area of optical fiber communication are elucidated.

Numerical simulation and analysis of dual base transistor laser

AbstractIn this work, characteristics of dual base transistor laser are numerically analyzed for the first time. Active base region of the transistor laser is split into two unequal regions composing of shorter and longer sections, which are biased separately. Static characteristics of transistor laser are evaluated using a rate equation model, which reveals switching action in output optical power for a longer section base current of 9.2 mA with unpumped shorter section. Hysteresis behavior in the optical output is observed for the longer section input current till 1.6 mA. Optical bistable characteristics are studied for various values of gain (longer) and absorber (shorter) section currents. Further slope efficiency is evaluated using P‐I characteristics, before the onset of bistability, for gain lever features under common emitter (CE) configuration. A maximum gain lever of 4.5 dB is observed with the longer section bias current of 1.3 mA.

Transistor Laser Antenna: Electromagnetic Model in Transmit and Receive Modes

Transistor laser can drive recent innovative technologies like optical antennas and rectennas. To this end, this semiconductor device requires an accurate electromagnetic model capable of determining the antenna characteristics like radiation pattern, directivity, gain, bandwidth, and polarization. Nonetheless, the current semiconductor models of transistor laser describe the absorption and emission of light mainly by simplified expressions and circuit models. These models usually overlook the actual physical geometry and full-wave light-emitting analysis of the device. In this article, a comprehensive computational electromagnetic modeling and characterization is presented for transistor laser. The existing semiconductor and electromagnetic equations are reorganized in a systematic fashion, coupled, and solved numerically to get the electromagnetic field components emitted or absorbed by the device. These fields determine the radiation pattern, directivity, gain, bandwidth, and polarization of transistor laser in transmit and receive modes. The equations involved in the above electromagnetic model are the Poisson and continuity equations incorporating radiative and non-radiative recombination rates, the vector magnetic potential equation interacting with the Hamiltonian operator of electrons in valance and conduction bands, the equation of the dielectric properties fluctuations of semiconductor layers, and the Poynting vector determining the power flow. The constructed model demonstrates agreement with the general performance of the device in experimental reports.

Analytical Modeling of Tunnel-Junction Transistor Lasers

Compared with transistor lasers (TLs), tunnel-junction transistor lasers (TJTLs) are more easily modulated with the voltage across base-collector (BC) junction. In this work, the charge-control model and modified rate equation of TJTLs which includes the Franz-Keldysh effect and direct tunneling is developed. We conduct DC and AC analysis with our model and show that the doping concentration in the BC junction plays a key role in the capability to voltage modulate TJTLs since it affects the junction field. A trade-off between the optical power and capability of the voltage modulation emerges as a concern for designing the doping concentration. We also study the effect of the quantum well (QW) position. The result shows that the QW closer to the BC junction can obtain a higher confinement factor to achieve better output power and modulation bandwidth.

Effect of number of quantum wells on modulation and distortion characteristics of transistor laser

Numerical analysis on the effect of number of quantum wells (QW) on the modulation and distortion characteristics of 1300 nm Transistor Laser (TL) is reported. The terminal currents are found by using triangular charge model in the base region. The parameters such as threshold current and optical power are analyzed from the DC characteristics for different number of quantum wells. Modulation depth, frequency response are determined by providing an ac input signal with dc bias offset. It is found that the modulation depth decreases for increasing the number of quantum wells and input bias current under CE and CB configuration respectively. From this analysis, the Transistor Laser bandwidth, resonance frequency are estimated for different number of quantum wells and a maximum bandwidth of 27.5 GHz and 44.3 GHz for 25Ith are observed under CE and CB configurations respectively. Further, the distortion characteristics such as second harmonic and intermodulation products are analyzed at 2.4 GHz band for Radio over Fiber applications. The magnitude of 2HD and IMD3 components are found to decrease for increase in number of quantum wells and bias current under both CE and CB configurations. A minimum value of magnitude of 2HD components is obtained as −27.58 dBc at 25IBth and −17.82 dBc at 1.8IEth under CE and CB configuration respectively for six quantum wells in the transistor laser. Similarly, minimum value of IMD3 magnitude is obtained as − 40.47 dBc at 25IBth and − 36.91 dBc at 1.8IEth under CE and CB configuration respectively. A maximum Spurious Free Dynamic Range of 58.85 dB-Hz2/3 is predicted at 10IEth for four number of quantum wells under CE configuration.

Numerical design and frequency response of MQW transistor lasers based entirely on group IV alloys

A theoretical model is developed for n–p–n mid-infrared transistor lasers (TLs) with a strain-balanced Ge0.85Sn0.15 multiple quantum well (MQW) structure in their base. The variation of the optical confinement factor, the modal gain, and the threshold current density is rigorously investigated for different numbers (N) of QWs in the MQW structure. The results show that overall the optical confinement factor and the modal gain increase with N. The frequency response of the MQWTL in the common-base (CB) configuration is estimated from the small-signal relationship between the photon density and the emitter current density by solving the laser rate equation and the continuity equation, considering the virtual states as a conversion mechanism. Increasing N causes the modulation bandwidth first to increase then to decrease with N. This reveals a shift in the nature of the device for higher values of N. The results also suggest that judicious selection of N will enable the proposed device to become a viable monolithic light source.

Design and novel turn-off mechanism in transistor lasers

We provide a quantitative analysis of the spontaneous recombination time in the quantum well (QW) of a transistor laser (TL) that shows that owing to the heavy doping in the base of the transistor, Auger recombination is responsible for the short carrier lifetime and low quantum efficiency of the device. By taking advantage of the QW location close to the collector in the TL three-terminal configuration, we devise a new turn-off mechanism that results in quick electron tunneling through the QW barrier by applying a high base-collector reverse bias to deplete the QW and suppress further recombination. For practical base-collector reverse bias, tunneling time from the QW is on the order of 10th of picosecond, which with a lighter base doping density would simultaneously achieve a fast TL turn-off response, while reducing Auger recombination.

Analysis of distortion reduction in 1.3 μm transistor laser using Schottky diode based predistortion network

A Schottky diode based linearization network is investigated for distortion reduction in 1.3 μm Transistor Laser for the first time. Second harmonic and third order intermodulation distortion (IMD3) are numerically analyzed in transistor laser using single and dual Schottky diode based predistortion techniques. An improvement of 13.56 dB and 15.53 dB are obtained for IMD3 under single and dual Schottky diode predistortion techniques respectively. Further, an enhancement in SFDR of 60.54 dB Hz2/3 and 62.92 dB Hz2/3 are observed for the above schemes. Moreover, the bandwidth is improved to 12 GHz and 13.8 GHz for single and dual Schottky diode predistortion techniques, whereas it is only 10.96 GHz without predistortion, under similar bias conditions.

Effect of Collector Voltage on the Large and Small Signal Modulation Characteristics of 980 nm Transistor Laser

Theoretical analysis of Transistor Laser is carried out and the static and frequency responses for different collector voltages, under common emitter configuration are determined. The threshold current (Ith) is observed as 33mA and it increases linearly with reverse collector to base voltage (VCB). Meanwhile, the output optical power is found to decrease proportionately when VCB is increased. A maximum of 18.7GHz modulation bandwidth is observed when an input base current of 95 mA is applied at a fixed value of VCB (1V). The modulation bandwidth is found to decrease with increase in reverse VCB. The turn on delay increases with collector voltage. However, it decreases with increase in base current.

Effect of Franz–Keldysh absorption on the short optical pulse generation in Transistor Laser

In this work, the effect of Franz–Keldysh (FK) absorption on the short optical pulse generation in Transistor Laser (TL) is analyzed. Franz–Keldysh (F–K) Absorption coefficient is incorporated in the rate equations and solved numerically by fourth order Runge–Kutta (R–K) method. Short optical pulses are generated for various values of collector to base voltage. The output optical power is found to decrease with increasing reverse collector to base voltage. The magnitude of peak optical power and full width half maximum (FWHM) are predicted for various values of VCB. The collector base reverse bias voltage is varied from 0 V to 3 V. The peak optical pulse power is found to decrease with increasing reverse collector to base voltage. Full width half maximum is found to increase with increasing reverse collector to base voltage (VCB). The maximum peak optical power of 156.2 mW and minimum FWHM of 17.97 ps are predicted for the unbiased VCB at the base current amplitude of 128 mA. The optimum value of peak optical pulse power of 45.89 mW and full wave half maximum of 24.21 ps are obtained for the VCB value of 1.5 V at the base current amplitude of 96 mA.

Chirp-free optical-signal generation using dual-and-direct current-voltage modulation of transistor lasers.

Transistor lasers (TLs) can be current-modulated as a diode laser or voltage-modulated as a Franz-Keldysh electro-absorption modulator. These two modulation schemes result in opposite frequency shifts that can cancel each other. In this work, we present the principle of generating optical signals with minimal frequency chirps using TLs. With the proper setting of pulse shapes for the current and voltage inputs, optical signals that are robust against distortions can be directly output from TLs for the medium-distance or long-distance optical fiber communication.

Large signal analysis of multiple quantum well transistor laser: Investigation of imbalanced carrier and photon density distribution

In this paper, we present a large-signal and switching analysis for the Heterojunction Bipolar Transistor Laser (HBTL) to reveal its optical and electrical behavior under high current injection conditions. Utilizing appropriate models for carrier transport, nonlinear optical gain, and optical confinement factor, we have simulated the large-signal response of the HBTL in relatively low and high modulation frequencies. Our results predict that for multiple quantum well (MQW) structures at low frequencies, there should not be a difference in either the carrier density or the photon density. However, the carrier concentration can be differently distributed between subsequent wells in the case of a high speed yet large-signal input. This leads to increased linewidth instead as it depends on ΔNqw. We show the effect of different structural parameters on the switching behavior by performing a switching analysis of the single quantum well and MQW structures using computationally efficient numerical methods. A set of coupled rate equations are solved to investigate the large-signal and switching behavior of MQW-HBTL. Finally, to have a comprehensive judgment about this optoelectronic device, we introduce a relative performance factor taking into account all the optoelectronic characteristics such as the output power, ac current gain, modulation bandwidth, and base threshold current, as well as turn-on time in order to design a suitable TL for optoelectronic integrated circuits.

Continuous-wave operation of a 1.3 μm wavelength npn AlGaInAs/InP transistor laser up to 90 °C

A transistor laser (TL) is a device that operates at a high-speed with multiple functions such as output control with low wavelength shift and signal mixing. By adopting a high heat dissipation structure with a high-speed compatible wide electrode pad and thick Au plating in TLs, improvement of temperature performance in 1.3 μm wavelength npn AlGaInAs/InP TL was demonstrated. As a result, continuous-wave operation of a 1.3 μm TL up to 90 °C was achieved. The thermal resistance was estimated to be 25 K W−1, based on the spectrum behavior, which is at least four times lower than the previously observed value.