File Name: mid-infrared photonics in silicon and germanium creator.zip
In this paper, a review of the state of the art of silicon nitride strip waveguide platforms is provided, alongside the experimental results on the development of a versatile nm guiding film height silicon nitride platform.
Other material systems and technology platforms, including silicon-on-silicon nitride, germanium-on-silicon, germanium-on-SOI, germanium-on-silicon nitride, sapphire-on-silicon, SiGe alloy-on-silicon, and aluminum nitride-on-insulator are explored as well in order to realize low-loss waveguide devices for different MIR wavelengths.
In this paper, we will comprehensively review silicon photonics for MIR applications, with regard to the state-of-the-art achievements from various device demonstrations in different material platforms by various groups. Meanwhile, we will discuss the integration schemes along with remaining challenges in devices e. A few application-oriented examples will be examined to illustrate the issues needing a critical solution toward the final production path e.
Finally, we will provide our assessment of the outlook of potential future research topics and engineering challenges along with opportunities. Silicon photonics, mainly referred to at the near-infrared NIR wavelength, have attracted great research interest in the past decade because they are a potential candidate to meet the increasing demands for high data transmission capacity in communication systems.
One key driving force of silicon photonics is the fabrication compatibility with the matured CMOS technology, which has the ability to provide low-cost photonic integrated circuits PIC for a high volume of production.
Due to the worldwide efforts fueled by researchers in the past years, silicon photonic technology working at NIR wavelength range around 1. In fact, the NIR is not only the wavelength range where silicon photonics have an impact. As shown in Fig. Some other toxic gases such as HF and H 2 S also have the absorption peaks within this range 2. The real-time monitoring of these gases in the environment and during the industrial process demands low cost and compact sensors.
Silicon photonics stands out as a promising candidate for such application because it can provide an on-chip solution, which is cost effective and highly compact. Through the appropriate design of the optical waveguide cross-section, the evanescent field of the optical mode could overlap with the surrounding materials and consequently induce absorption loss of the light. The gas concentration can be then extracted from the output optical power detected at the end of the waveguide.
In general, microring resonators MRRs are employed to improve the sensitivity and reduce the footprint. The light transmits in the ring with several rounds, thus essentially increasing the effective interaction lengths between the light and the detected materials. The Vernier effect, which is constructed by MRRs for further improvement of the sensor performance at the NIR wavelength [ 15 , 16 ], has transferred to the MIR range by scaling up the device dimension [ 17 , 18 ].
Compared with the visible light and NIR waveguides, the large MIR waveguide dimension helps to improve the phase array performance used in the LIDAR system [ 19 — 23 ] because it alleviates the requirement of the fabrication precision as well as the phase error induced by the sidewall roughness.
Moreover, the MIR lasers are safer for humans compared with their counterparts at the visible light range, as the MIR light is unable to penetrate cornea and skin tissues [ 24 ]. In addition, in the MIR range of 2—6. On the other hand, higher optical power density in the waveguides or cavities benefits nonlinearity phenomenon generation [ 25 , 26 ], which is utilized to explore the MIR nonlinearity devices on a silicon platform, such as the wavelength conversion [ 27 ], parametric oscillator [ 28 , 29 ], amplifier [ 30 ], and frequency comb generator [ 31 ].
The fabrication technology of these platforms is compatible with that of silicon photonics, while most of them use the silicon as cladding or core layers for the waveguides.
Thus, in the following discussion, we consider they are silicon photonics technology in a broad sense. Material absorption characteristic in the MIR range [ 1 , 3 ]. Gray region represents the optical transparency; black area denotes the high loss. Absorption peaks of some detected gases and the fingerprint region are marked. These pioneering works open the way to MIR photonic integration. Besides the passive devices, the active devices, i.
In the reported work, the free carrier dispersion effect FCDE and Pockels electro-optic effect are employed to implement the modulators at short MIR wavelengths [ 61 — 67 ].
However, the device performance is far away from its counterparts working at NIR wavelengths. Meanwhile, because of the inherent limitation of the materials used in the aforementioned platforms, the MIR lasing and detection remain as challenges for the silicon photonics.
The detection spectral range covers the short- and middle-wave infrared. Inspired by the success of silicon photonics at NIR, a silicon platform is considered as the most attractive solution for MIR photonics because it has potential to provide the hybrid integration system with low cost by the CMOS pilot lines.
The material limitation and choice of integration platform are discussed in this section as well. Finally, we provide our perspective on potential future research topics and engineering challenges. In pursuit of the optical waveguide with low propagation loss, various platforms and geometric structures were demonstrated. According to the low-loss MIR waveguides demonstrated in Refs.
Because these wafers are the commercially available products, they may become the standard platforms for the two interesting wavelengths. However, silicon has a large thermal-optic coefficient that causes the device performance sensitive to the temperature fluctuation. In their following work, the rapid thermal annealing process was used to reduce the loss [ 35 ]. Apart from a germanium-based platform, due to the wide transparent range of 1. However, the measured loss is not as low as expected.
The authors state that the loss can be further reduced by improving the sidewall quality with advanced processes [ 37 ]. But there are not obvious merits compared with other platforms, in aspects of the low loss range and the fabrication compatibility.
Another attractive platform is the SiGe alloy on silicon substrate. Table 1. The edge coupling scheme requires a more complicated alignment system.
One typical setup is to use a CCD camera to capture the input optical mode of the fiber and judge whether it is launched into the waveguide, while an alternative is to employ a visible laser to visualize the light coupling into the waveguide.
However, currently, the lack of the lensed MIR fiber limits the light coupling efficiency between the fiber and the chip. In contrary, the fiber-to-chip grating couplers provide an easier way for the light coupling. The coupling loss of 3. A suspended structure on SOI platforms is considered as one of the solutions to reduce the propagation loss caused by the BOX absorption.
The measured coupling efficiency at the wavelength of 2. The uniform grating coupler with SOS platform also was experimentally demonstrated by the same group at the wavelength of 2. For longer wavelength at 3. Though the coupling efficiency of 7. But, for the practical application in products, the coupling loss needs to be further reduced. In this case, the grating couplers are not the best choice.
Other coupling schemes, such as the suspended edge coupler, may be an alternative solution. It is an important and basic building block in the photonic circuit. The device adopted the undercut structure and was characterized at the wavelength of Their measured insertion loss is 0.
The design approach of these commonly used components is easily transferred from those at the NIR. However, there is still a large room for improvement of their performance. The versatile applications of MRRs in optical filters, routers, de multiplexers, and modulators make them the most thoroughly studied passive photonic devices. The ER increases with the stronger coupling between the bus and ring waveguides but at the sacrifice of the decreasing of Q -factors.
Another type of microresonators frequently reported are PhC cavities. The Q -factor of 13, was obtained but without ER presented. Generally, compared with PhC cavities, MRRs are easier to design and have less stringent requirements of the fabrication process. Thus, MRRs are more practical for the photonic circuit integration. Table 2. The de multiplexers are widely used in the wavelength-division multiplexing WDM system to increase the data transmission bandwidth, the function of which is the optical signal multiplexing and routing between different channels.
In particular, the de multiplexers are used in the spectrometers as the core elements. The eight-port PCGs also was reported in the paper, with the insertion loss and crosstalk of 1.
Silicon photonics face polarization problems caused by birefringence, which results in the control of polarizations in silicon photonics devices, are of great importance. A large amount of work has been done and reported on these two kinds of devices. However, most of the demonstrated devices are working at the NIR range. The proposed PSR utilize a partially etched grating-assisted coupler on the SOI platform to realize the polarization splitting and rotation in the contra direction.
The device shows a conversion efficiency of A modulator plays a key role in PICs. To date, only a few works on MIR modulators have been reported. However, the modulation speed is neither measured nor comparable with modulators working at the telecom wavelengths [ 66 , 67 ]. The FCDE accompanies with large absorption loss, while the wavelength is beyond 2. In order to realize the modulators working at longer wavelengths, the Pockels electro-optic effect in lithium-niobate LiNbO 3 and AlN are employed.
Chiles and Fathpour implemented the modulators working at 3. Unfortunately both the modulation frequency and the efficiency are quite low. However, in terms of the construction of the NIR photonic systems, the all-optical modulation is found to be seldom used. Silicon and germanium are inefficient material for optical light generation due to their indirect band gap.
More recently, some pioneer work of the MIR laser integration with the waveguides also have been reported [ 78 — 80 ].
At the short-wave infrared range, the GeSn alloy attracts a lot of interest to build up the detectors due to its widely tunable bandgap.
The devices can work at the wavelength up to 2. However, the low cost and high yield approach to integrate these III—V components, including the lasers and PDs, with silicon photonic platform remains a challenge.
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The system can't perform the operation now. Try again later. Citations per year. Duplicate citations. The following articles are merged in Scholar. Their combined citations are counted only for the first article. Merged citations.
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With the increasing bandwidth requirement in computing and signal processing, the inherent limitations in metallic interconnection are seriously threatening the future of traditional IC industry. Silicon photonics can provide a low-cost approach to overcome the bottleneck of the high data rate transmission by replacing the original electronic integrated circuits with photonic integrated circuits. Although the commercial promise has not been realized, this perspective gives huge impetus to the development of silicon photonics these years. This paper provides an overview of the progress and the state of the art of each component in silicon photonics, including waveguides, filters, modulators, detectors, and lasers, mainly in the last five years. Silicon Si has been the mainstay of the electronics industry for more than 40 years and once revolutionized the way the world operates.
For instance, mid-IR optical components are made from germanium, However, unlike near-IR silicon photonics for telecom, which relies on fiber/silicon photonic wire short-wave infrared wavelength converter/amplifier (Accessed August 14, , at mydowntownsmyrna.org).
The emergence of silicon photonics over the past two decades has established silicon as a preferred substrate platform for photonic integration. In this review, we offer our perspective on the burgeoning field of mid-IR integrated photonics on silicon. A comprehensive survey on the state-of-the-art of key photonic devices such as waveguides, light sources, modulators, and detectors is presented. Furthermore, on-chip spectroscopic chemical sensing is quantitatively analyzed as an example of mid-IR photonic system integration based on these basic building blocks, and the constituent component choices are discussed and contrasted in the context of system performance and integration technologies.
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