Fiber Bragg Grating (FBG)

A fiber Bragg grating (FBG) is a type of distributed Bragg reflector constructed in a short segment of optical fiber that reflects particular wavelengths of light and transmits all others. This is achieved by creating a periodic variation in the refractive index of the fiber core, which generates a wavelength-specific dielectric mirror. A fiber Bragg grating can therefore be used as an inline optical filter to block certain wavelengths, or as a wavelength-specific reflector. Raysung is capable of manufacturing various FBGs, including Uniform FBG, Apodized FBG, Double-Clad FBG as well as Chirped FBG.

Uniform FBG

Uniform FBG can reflect the light of a certain wavelength in the incident light, and the reflection bandwidth is narrow. In the laser field, it can be used to make low-power Narrow-linewidth Fiber Lasers or the narrow-linewidth laser output at the laser end. In the sensor field, it can be used to make temperature, strain and other sensors. In the optical communications field, it can be used to make filters, add/drop multiplexers and demultiplexers for WDM.

Product applications: Pumping laser wavelength locking, fiber sensor, fiber filter

Apodized FBG

For uniform FBG, there are a series of peaks aside the main reflection peak, which are called side modes or side lobes. For certain applications, such as DWDM, the side lobes will be a disadvantage and affect the channel isolation of an optical device. By using function to modulate the refractive index modulation amplitude, the side modes of a grating could be effectively suppressed, which is called apodization. Apodized gratings offer significant improvement in side-mode suppression while maintaining reflectivity and a narrow bandwidth. The side mode suppression ratio (SMSR) is an indicator of how much the side modes is suppressed.

Product applications: Pumping laser wavelength locking, fiber sensor, fiber filter

Chirped FBG

The refractive index profile of the grating may be modified to add other features, such as a linear variation in the grating period, called a chirp. The reflected wavelength changes with the grating period, broadening the reflected spectrum. A grating possessing a chirp has the property of adding dispersion—namely, different wavelengths reflected from the grating will be subject to different delays. This property has been used in the development of phased-array antenna systems and polarization mode dispersion compensation, as well.

Product applications: FTTH reflector, gain flattening filter, fiber sensor, fiber filter, dispersion compensation module

Double Clad FBG

Double clad FBGs are referred to writing gratings on the passive double clad fiber. For fiber laser application, the doped double clad fiber is used as active medium, and double clad FBGs on matching passive fiber are used as cavity mirrors, which play an irreplaceable role for fiber laser.

Product applications: Fiber laser, pump lockers, fiber sensor

Pump Laser Wavelength Locker

The fiber lens is used to couple light from the laser diode, and with good matching between the divergence of laser chip and fiber lens, coupling efficiency as high as 90% could be achieved. The FBG is used to form an external feedback structure, which will stablize the output laser around the center wavelength of the FBG, and meanwhile narrow the laser output spectrum. Besides, due to the low thermal dependence of FBG, the thermal stability of the laser output is also greatly improved. Therefore, high pumping efficiency as well as good pumping stability of the pump laser could be achieved.

Product applications: EDFA and Raman pumping application, a fiber pigtail that integrates a 9xx/14xxnm FBG and a fiber lens is commonly used in the pump laser.

FBG for Ultrafast Lasers

The traditional small-chirped FBG is limited by its chirp coefficient, it has a small bandwidth and large dispersion rate, thus it cannot generally be used as a broadband filter device. However, the large chirped FBG has a wide bandwidth and a small amount of dispersion, it can be conveniently used in broadband filtering, amplifier noise suppression, gain flatness, fiber sensing and etc.

The application of CFBG in dispersion compensation has attracted more and more attention. The use of CFBG for dispersion compensation (pulse broadening/compression) is one of the core technologies in the field of ultrafast lasers, and has become an important application direction of large chirped FBG.

Product applications: High-Power Ultrafast Lasers

FBG Mirrors for High Power Fiber Lasers

For fiber laser, double clad fiber is commonly used, as the fiber core is very small, which will limit just a few laser modes, and therefore can easily achieve high power density; also, by cladding mode pumping, the inner clad structure will allow high power laser diode pumping, which could improve the pumping efficiency, and then achieve high gain in the active fiber.

Currently, a high power fiber laser cavity is usually consisted with a Yb-doped double clad fiber as the active fiber, and a pair of high reflector (HR) and output coupler (OC) fiber bragg gratings, which have the same geometry as the active fiber in order to have good matching.

Based on the Double-Clad FBG writting technique, Raysung developed high power FBG mirrors, specifically for the application of fiber laser. The wavelength matching between HR and OC could be controlled <0.2 nm. Also, with particular heat management technique, these FBGs are built to handle as high as kW pumping power, so that they could meet the highest standard of reliability and performance. Product applications: kW power fiber laser FBG

OTDR FBG Reflector

Raysung OTDR FBG reflector uses FBG technology to reflect OTDR test signal (1645~1655nm or 1615~1635nm). With wide bandwidth and low insertion loss, Raysung FBG reflectors are ideal to create high reflectance at the termination of a passive optical network (PON) without disturbing traffic. Comparing with the traditional reflector with thin film technology, FBG reflector has the advantage of very high reflectance at the test signal, very low insertion loss at the traffic signal very sharp reflection bandwidth edge, and very long lifetime. Raysung FBG reflector can be embeded into an adaptor or a connector with pigtail with the option of SC/APC, LC/APC, etc.

Athermal FBG filter

With the development of DWDM systems, high isolation channel is necessary to avoid crosstalk. Based on Raysung’s FBG, our athermal DWDM FBG filter features for flat top response and a steep roll down spectral range, which is available in an individual package or combined with multiple filters to form a complete add/drop module. The specifications for Raysung’s Athermal DWDM FBG filter are listed in the tables below.

Applications: DWDM system 50/100/200 GHz in fiber narrowband signal filtering, OADM module, mux/demux, wavelength selection or rejection filter

Lensed fiber

Lensed fiber, also called fiber lens, is a piece of fiber which forms a lens shape at the end face, and is used to change the optical path, or coupling light in the optical fiber systems. Based on the specific requirement of different applications, there are tapered, wedged, angle wedged, beveled, and spherical lens, etc. Raysung applies the most advanced mechanical processing method in the world for manufacturing lensed fiber. The company’s cutting-edge technology holds independent intellectual property protection. Raysung is capable of manufacturing lensed fiber into different shapes. The geometrical parameters can be well controlled in order to reach the best performance. AR Coating and metallization are also available.

Applications: DLB coupling, pump laser coupling, SLD laser coupling, high speed receive device

FBG + Lensed Fiber Turn-Key

The fiber lens is used to couple light from the laser diode, and with good matching between the divergence of laser chip and fiber lens, coupling efficiency as high as 90% could be achieved. The FBG is used to form an external feedback structure, which will stabilize the output laser around the center wavelength of the FBG, and meanwhile narrow the laser output spectrum. Besides, due to the low thermal dependence of FBG, the thermal stability of the laser output is also greatly improved. Therefore, high pumping efficiency as well as good pumping stability of the pump laser could be achieved. Raysung is one of the only manufacturers in the world who have the capacity to manufacture the type of optical fiber which incorporates FBG and lensed fiber. The minimum distance between the lensed fiber and FBG can be controlled within 1.5mm. This type of fiber can be used as cavity resonator in the application of fiber laser and also stabilizator for pump laser.

FBG + Lensed Fiber Turn-Key

As a special optical fiber, polarization-maintaining fiber patchcord transmit polarized light signals, which can ensure that the direction of linear polarization is unchanged, improve the coherent signal-to-noise ratio, and achieve high-precision measurement. Raysung adopts PANDA-type polarization-maintaining fiber and provides different fiber types and selects imported, high-precision optional connectors and ceramic ferrules. Each polarization-maintaining fiber patchcord is carefully manufactured using the most stringent process to ensure high return loss and high polarization extinction ratio, meets the industry’s highest quality standards. Also, we provide customized services to customize patchcord products that meet various application needs from customers.

Applications: Coherent communication, high-speed fiber optic communication, fiber laser, fiber amplifiers, test equipment, interference sensing