This study describes the basic principles of optical waveguide refractive index sensing and the various design structures of refractive index sensors. These waveguides generate different optical resonances, which cause changes in the sensing refractive index and temperature and are subsequently used to detect the concentration in the analyses. First, the structural characteristics and performance indices of the microring sensor and interferometer are studied based on the refractive index of the optical waveguide. Second, the principle and sensing detection mechanism of the two types of refractive index sensing employed in these sensors are analyzed. Then, the two sensors are classified and discussed from the perspective of the waveguide materials and structures, as well as the substances to be measured. Simultaneously, performance indicators such as sensitivity and detection range are compared and summarized. The comparison results show that there is a compromise between the sensitivity and quality factor of the optical waveguide refractive index sensor. Finally, applications of refractive index sensing in the biochemical field for material detection are discussed, showing that the optical waveguide refractive index sensor has significant advantages over other types of biochemical optical sensors.

Tunable semiconductor lasers have many important applications such as wavelength division multiplexing, light detection and ranging, and gas detection. The increased interest in silicon photonics has led to the rapid development of miniaturized on‐chip tunable semiconductor lasers. However, silicon has poor light‐emitting properties. Therefore, realizing high‐performance tunable semiconductor lasers requires the integration of light sources with silicon. In this study, we review silicon‐based light source integration methods and the development of silicon‐based integrated tunable semiconductor lasers. Considering that narrow‐linewidth performance greatly expands the applications of tunable semiconductor lasers, methods for reducing the linewidth of tunable lasers are summarized. Finally, the development trends and prospects for silicon‐based integrated light sources and silicon‐based integrated tunable lasers are analyzed and discussed.

The 1550 nm band semiconductor optical amplifier (SOA) has great potential for applications such as optical communication. Its wide-gain bandwidth is helpful in expanding the bandwidth resources of optical communication, thereby increasing total capacity transmitted over the fiber. Its relatively low cost and ease of integration also make it a high-performance amplifier of choice for LiDAR applications. In recent years, with the rapid development of quantum-well (QW) material systems, SOAs have gradually overcome the shortcomings of polarization sensitivity and high noise. The research on quantum-dot (QD) materials has further improved the noise characteristics and transmission loss of SOAs. The design of special waveguide structures—such as plate-coupled optical waveguide amplifiers and tapered amplifiers—has also increased the saturation output power of SOAs. The maximum gain of the SOA has been reported to be more than 21 dB. The maximum saturation output power has been reported to be more than 34.7 dBm. The maximum 3 dB gain bandwidth has been reported to be more than 120 nm, the lowest noise figure has been reported to be less than 4 dB, and the lowest polarization-dependent gain has been reported to be 0.1 dB. This study focuses on the improvement and enhancement of the main performance parameters of high-power SOAs in the 1550 nm band and introduces the performance parameters, the research progress of high-power SOAs in the 1550 nm band, and the development and application status of SOAs. Finally, the development trends and prospects of high-power SOAs in the 1550 nm band are summarized.

The paper presents a wide-bandwidth, low-polarization semiconductor optical amplifier (SOA) based on strained quantum wells. By enhancing the material gain of quantum wells for TM modes, we have extended the gain bandwidth of the SOA while reducing its polarization sensitivity. Through a combination of tilted waveguide design and cavity surface optical thin film design, we have effectively reduced the cavity surface reflectance of the SOA, thus decreasing device transmission losses and noise figure. At a wavelength of 1550 nm and a drive current of 1.4 A, the output power can reach 188 mW, with a small signal gain of 36.4 dB and a 3 dB gain bandwidth of 128 nm. The linewidth broadening is only 1.032 times. The polarization-dependent gain of the SOA is below 1.4 dB, and the noise figure is below 5.5 dB. The device employs only I-line lithography technology, offering simple fabrication processes and low costs yet delivering outstanding and stable performance. The designed SOA achieves wide gain bandwidth, high gain, low polarization sensitivity, low linewidth broadening, and low noise, promising significant applications in the wide-bandwidth optical communication field across the S + C + L bands.

Lasers used for space communication, lidar, and laser detection in space-air-ground integration applications typically use a traditional 1550 nm band tunable distributed-feedback Bragg (DFB) semiconductor laser. This has low output power, complex fabrication process, and high fabrication cost. In this paper, we present a gain-coupled surface grating-based 1550 nm DFB semiconductor laser that can be fabricated without the use of secondary epitaxial growth techniques or high-precision lithography. The periodic electrical injection is used to achieve a gain coupling effect. A tapered waveguide is added to achieve a high output power, and the use of AlGaInAs multiple quantum wells in the active region reduces the linewidth of the laser. A continuous-wave (CW)output power of 401.5 mW is achieved at 20 °C, the maximum side mode rejection ratio exceeds 55 dB, the measured 3 dB linewidth is 18.86 MHz, and the stable single-mode output with a quasi-continuous tuning range of 6.156 nm near 1550 nm from 10 °C to 50 °C. This simple preparation method, low cost, excellent performance, and stable tunable laser have extremely high commercial value in applications such as space communication, lidar, and laser detection.