Modeling of generating ultra-high frequency oscillations in VCSEL integrated with cascaded transverse coupled cavities
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Modeling of generating ultra‑high frequency oscillations in VCSEL integrated with cascaded transverse coupled cavities Moustafa Ahmed1,2 Received: 6 March 2020 / Accepted: 17 September 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract We report on the design and modeling of vertical-cavity surface-emitting laser (VCSEL) integrated in the lateral direction with a cascade of multiple passive cavities. The scheme is proposed to increase the bandwidth of the VCSEL in the mmwaveband to generate ultra-high-frequency oscillations with low-frequency chirp. The model treats the transverse feedback induced by the cascaded transverse coupled cavities (TTCs) as time delay of the transverse slow light due to round trips in these cavities. The simulation is based on numerical integration of the modified time-delay rate equations of the intensity and phase of the electric field. The simulation results are used to optimize the TCCs parameters, including the coupling ratio and TCC length, for generating ultra-high-frequency signals with high intensity, low chirping and low distortion. The obtained results show that the proposed structure could achieve 300% enhancement of the modulation bandwidth of the C-VCSEL due to either extended carrier-photon resonance (CPR) frequencies of photon–photon resonance (PPR). Signals with frequencies as high as (40–49 GHz) with second-harmonic distortion lower than − 30 dB are presented.
1 Introduction Semiconductor laser is an integral part of high-speed telecommunications. The next-generation optical networks require optical transmitters to operate in tens of GHz modulation speed [1]. A commonly used directly modulated laser has fundamental speed limits, due to the CPR effect and displays severe wavelength chirp [2–4]. The principal attraction of the direct modulation technique is its simplicity and low cost. With the laser biased above threshold and a modulation signal superimposed on the drive current, the output optical power of the laser is an analog of the modulation waveform. The intrinsic response is set mainly by the differential gain, and much effort has been put into increasing this value. Strained quantum well long-wavelength semiconductor lasers have achieved modulation bandwidths of 25 GHz for DFB structures [5, 6]. However, the frequency chirping of DFB laser is also directly related to the differential gain, with higher values producing lower chirp. One way to reduce * Moustafa Ahmed [email protected]; [email protected] 1
Department of Physics, Faculty of Science, King Abdulaziz University, 80203, Jeddah 21589, Saudi Arabia
Department of Physics, Faculty of Science, Minia University, Minia 61519, Egypt
2
the wavelength chirp is to use an external modulator based on a Mach–Zehnder interferometer in a material showing strong electro-optic effect, such as LiNbO [7–9]. However, such an external modulator is very expensive and cannot be integrated with III–V semiconductor lasers. On the other hand, the vertical-cavity surface-emitting laser
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