DK Photonics got a successful exhibition on OFC2013

Shenzhen, China, Apr. 10, 2013 -- DK Photonics Technology Co., Limited, one of the leading companies in designing and manufacturing of high quality optical passive components mainly for telecommunication, fiber sensor and fiber laser applications, announced that the Company got a successful show on OFC2013 in Anaheim. DK Photonics took two weeks to attend OFC2013 in Anaheim and visit customers in USA, and then came back last Monday with successful achievement.

On the exhibition, DK Photonics showed our traditional products such as PLC Splitter, WDM, FWDM, CWDM, DWDM, OADM, Optical Circulator, Optical Isolator, PM Circulator, PM Isolator, Fused Coupler, Fused WDM, Polarization Maintaining Components, Pump Combiner, High power Isolator, Patch Cord. At the same time, we took some innovative products such as 2000nm passive components to the show.

Through the OFC2013, customers got a deeper understanding to DK Photonics, such as products portfolio, inner management system, quality system and some research plan. Here we hope to express our salute to customers and DK Photonics would continue to give customers’ good service and quality products.

About DK Photonics

DK Photonics Technology Co., Limited is one of the leading companies in designing and manufacturing of high quality optical passive components mainly for telecommunication, fiber sensor and fiber laser applications. Headquartered and factory are located in Shenzhen of China.

DK Photonics have a group who has more than eight years working experience experts in the field of optical components and optical fiber laser; they formed a professional high-end R&D team. Our products are widely used in modern fiber lasers, amplifier, telecommunications, scientific research and other high-tech field of optical communication.

For more information about DK Photonics, please visit: http://www.dkphotonics.com/ , or email: info@dkphotonics.com

What Is an Optical Attenuator?

An optical attenuator decreases the strength of an optical signal passing through it to a fiber optic cable or open air. The intensity of the signal is described in decibels over a specific distance the signal travels. It is the strength, or amplitude of the signal that changes and not the overall waveform or frequency, so the optical signal remains undistorted for use in the desired application. Optical attenuators are often used in optical communication systems, in which the attenuation, also called transmission loss, helps with the long-distance transmission of digital signals. The most common optical attenuator types include fixed and continuously variable attenuators.

Application of fiber optic high power isolator and some mutual problems about its production process

1 introduction

Semiconductor lasers, optical amplifiers and optical fiber lasers from the connector, fusion point, filter the reflection light is very sensitive, and may cause performance deterioration and even damaged, requiring a optical isolator to prevent the reflection of light. The optical isolator is permitted only light along one direction through and in the opposite direction blocks light through the optical passive devices. In the optical fiber communication, optical fiber reflection light through the optical isolator can be a good isolation. In the fiber laser applications, optical isolators are usually used in the optical path to avoid the light path of the light source, the echo on the pumping source and other light emitting device causes interference and damage. Isolators’s isolation represents the optical isolator to echo the isolation (blocking) ability.

2 optical isolator principle

Optical isolator using magnetic optical crystal Faraday effect ( also known as the Faraday effect ). In 1845, Faraday first observed with optical material under the action of magnetic field to make the material in the direction of polarization rotation, therefore often called the Faraday effect. In Faraday effect, the rotation of the polarization direction direction and magnetic field, and the orientation of the light transmitting is independent of the forward and reverse, and we usually in the index of refraction, reflection phenomena seen in the reversibility of optical path difference. Along the magnetic field direction of transmission line polarized, the polarization direction rotating angle θand magnetic field strength of B and L is proportional to the product of the length of the material, the proportion coefficient is what we often say that the Wilde constant. Optical isolator based on polarization characteristics can be divided into polarization-independent and polarization dependent type. These two kinds of isolators are used with the Faraday effect in magneto-optic crystal, Faraday magnetic medium in 1~2μ m wavelength range usually adopts the optical loss low yttrium iron garnet ( YIG ) single crystals. Model of input and output of the fiber optical isolator has fairly good performance, the minimum insertion loss of approximately 0.5 dB, the isolation of up to 35～ 60 dB, a maximum of 70 dB.   The optical isolator using most still is polarization independent type, its principle is shown in Figure 1, using the forward and reverse transmission optical path is inconsistent, it is this time signal transmission is not reversible, thereby forming isolation. The typical structure of only four major components: the magnetic ring, a Faraday rotator, two pieces of LiNbO3 wedge angle piece, with a pair of fiber collimator, can be made into an in-line optical isolators.      

Positive transmission: the parallel light beam from the collimator, into the first wedge angle piece P1, beam is divided into o light and e light, the polarization direction perpendicular to the propagation direction, forming an included angle. When they pass through 45o Faraday rotator, emitted by the o light and e light polarizing surfaces of respective to the same direction of rotation 45o, because the second wedge-shaped plate P2 crystal axis relative to the first wedge angle piece is just in a 45o angle, so o light and e light is refracted into a small space, synthesis. Parallel light, and then by another collimator is coupled to the optical fiber core. In this case, the input optical power only a very small fraction of outage, this loss is called isolator insertion loss.

Reverse transmission: when a beam of parallel light reverse transmission, first with a P2 crystal, divided into the polarization direction and P1 crystal axis respectively in 45o angle o light and E light. Due to the Faraday effect non reciprocity, O Light and e light through the Faraday rotator, the polarization direction to the same direction of rotation 45 °, so the original o light and e light in the second wedge-shaped plate ( P1 ) later became e and O light. Because the refractive index differences, the two light beam in the P1 no longer possible synthesis of a parallel beam of light, but in different directions to the refraction of light, e and o are further separated from a larger perspective, even after a GRIN lens coupling, can not enter the fiber core to, from and achieved reverse isolation purposes. The transmission loss is bigger, this loss is called isolators isolation.

3 main technical parameters of optical isolator

The optical isolator, the main technical indicators have insertion loss, reverse isolation, return loss, polarization dependent loss, polarization mode dispersion.

(1) insertion loss ( Insertion Loss ): isolator core mainly comprises a Faraday rotator and a two piece of LN wedge angle piece, a Faraday rotator extinction ratio higher, lower reflectivity, absorption coefficient is smaller, insertion loss is smaller, general Faraday rotator loss is about 0.02～ 0.06dB. Parallel light pass through the isolator core, will be divided into o, e beams of parallel light. Due to the inherent characteristics of birefringent crystals, O Light and e light can not fully converge, which may cause additional insertion loss.

(2) reverse isolation ( Isolation ): reverse isolation isolator is one of the most important indicators, which characterizes the isolator on the reverse transmission attenuation ability. Effect of isolator isolation of many factors : 1 ) the isolation and polarizer from the Faraday rotator is related to the distance; 2) isolation and optical element surface reflectance relationship. Isolator optical element surface reflectance is bigger, the isolation degree is worse. The practical technology that R must be less than 0.25%, to ensure the isolation degree is greater than 40 dB; 3) isolation of polarimeter and wedge angle, spacing. Double refraction crystal yttrium vanadate ( YVO4 ) of the optical isolator, when the wedge angle of less than 2°, isolation with the perspective of the increase, when the wedge angle is greater than 2°, change is much smaller, approximately stable at about 43.8 dB. Optical isolation with the increase of the distance between the change range is not big, because isolation depends mainly on the reverse output light and the angle between the optical axis; 4) isolation and crystal axis angular relationship relative. The two polarizers and rotator crystal axis relative angle to the isolation effect is maximum, when the angle is greater than the difference between the 0.3o isolation will not be greater than 40 dB; 5) the two polarizer extinction ratio, crystal thickness on isolation effect; 6) the influence of temperature and magnet. In Faraday effect, Verdet constant is a function of temperature, so the Faraday rotation angle will change with the temperature, and the temperature will be on permanent magnet performance impact, so it is one of important factors.

(3) return loss ( Return Loss ): optical return loss refers to the positive incident to the isolator optical power and along the input path to return to the isolator input port of the optical power ratio, this is one of the important indicators, because the echo intensity, isolation would be affected by. Isolator echo loss by each element and the air refractive index mismatch caused by the reflection. The generally planar element caused by echo return loss is controlled in 14 dB, through antireflective film and surface polishing can make the return loss reached more than 60 dB. Optical return loss mainly from the collimated light path (i.e., collimator parts), through the theoretical calculation when the slant angle 8 °, return loss is greater than 65 dB.

(4) the polarization-dependent loss ( Polarization Dependent Loss, PDL ) :PDL and insertion loss is different, it is a when the input light polarization state changes and other parameters unchanged, the insertion loss of maximum variation, is a measure of device insertion loss by effect of polarization degree index. The polarization-independent optical isolator, the device has some may cause polarization components, impossible to achieve PDL is zero, a generally accepted PDL is less than 0.2 dB.

(5) the polarization mode dispersion ( Polarization Mode Dispersion, PMD ) :PMD is defined through the device of the signal light with different polarization states of the phase delay between, in high speed optical communication system is very important in PMD. In optical passive devices, different polarization modes have different propagation paths and different propagation speed, produce corresponding polarization mode dispersion. At the same time, because the light source spectrum lines have a certain bandwidth, can also cause certain dispersion. In a polarization-independent optical isolator, birefringent crystal to produce two beams linearly polarized light in different phase velocity and group velocity of transmission, which is PMD, its main source is used for separation and convergence o light and e light of birefringent crystal. It can be made of two linearly polarized optical path differenceΔ L approximation. PMD is mainly affected by E and O optical refractive index difference, therefore also has great relationship with wavelength.

4 key technologies of high power isolator

Compared with the common optical fiber communication system in the use of low power optical isolator is compared, in the high power laser, optical isolator design and production also exhibit differences, it is also in high power device is designed to solve the main problems in the development of.

(1) the optical element at a high power density laser radiation damage problems. Not only is this problem in a high power optical isolator in existence, is the other high power optical device design process is also to face. In order to solve this problem, first of all need to products in the production and testing process to ensure good environmental cleanliness and selects the damage threshold of high optical device and optical thin films, of course it is cost constraint. Because the air in the tiny particles if adhesion in optical surface will greatly reduce the laser damage threshold of optical surface, these tiny particles on laser absorption is relatively large, easily lead to particle near the energy is concentrated, resulting in optical surface film damage even surface damage, the element surface pitting and even small pit to device failure. Secondly, because in most cases within the optical element damage threshold than the surface laser damage threshold is much higher, so the surface of the laser power density is determined by the whole device resisting laser damage ability, especially in the pulse work situation is even more so. This can be through optical transform method to make optical element surface spot area expansion method to increase the damage threshold, such as expanded core fiber and beam expanding lens optical method is the use of the principle of work, or by changing the laser pulse stretching method to reduce the power density of laser, laser energy in space and by avoiding time of concentration can effectively improve product for resisting laser damage properties.

(2) the high power device for thermal effects and thermal design. Because of the high power device to work in a higher power, and low power devices compared, easy fever, inevitably subjected to temperature rise, so the device performance by the thermal characteristics and thermal design to compare the effects of severe. Usually the optically active crystal optical rotation characteristic of easily affected by temperature, if the device is operating due to the absorption of laser energy accumulation and lead to internal temperature appears bigger rise, will make the optically active crystal on light polarization plane rotation angle deviations from normal values and lead to significant performance loss, serious and even lead to damaged devices; in addition, the permanent magnet at work under high temperature but also more prone to field weakening and demagnetization phenomenon, appear even the magnetic field of the irreversible loss, so the high temperature to the permanent magnet steady work is negative; and, in case of high optical power, optical element temperature will appear bigger rise, due to heat from the inside to the conveying surface, its internal the temperature is above its surface temperature, so that it will in the optical component internal temperature gradient and thermal stress, causing the beam cross-sectional internal center of the refractive index and the edge of the refractive index change in different extent, appear thereby the refractive index difference, also is the emergence of lens effect, it will change the beam propagation characteristics, leading to beam quality drops badly, seriously affect the normal work and even cause damage to device. Therefore, we must take effective measures to reduce the absorption of laser radiation and effective. To reduce the absorption of laser selected absorption coefficient smaller optical materials, Ko Hikaru in the components inside the transmission distance, reasonable structure design, effective heat dissipation requirements may arise in heat accumulation place provides effective heat transfer path and heat dissipation, according to the size of power can adopt a passive or active heat radiation method. The million kilowatts level optical isolation design on the use of the lath shape of the optically active crystal to improve device cooling temperature control ability.

(3) the magnetic field design for high power isolator. High power optical isolator design another key is the magnetic field and magnet design and selection. In general, the optical isolator is the use of magnetic rotation effect work, so must the optically active crystal with proper magnetic field. In order to energy saving and convenient use, generally by the strong permanent magnetic material to produce a desired magnetic field, the magnetic field and magnet selection and design is very important, on device performance and the cost of. Under normal circumstances required in the optically active crystal space to provide a strong homogeneous magnetic field, so it can reduce the optically active crystal size, high ratio of performance to price, so the requirement in without significantly increasing the device volume in the case of the design of suitable magnet to obtain a strong homogeneous magnetic field. In specific design, through the choice of magnetic strong magnets, and adopt suitable shape and volume, to obtain the required magnetic field.

(4) High power optical isolator assembly process. High power optical isolator can work stably for a long time in bad environment, this device structure and assembly process raised very tall requirement. Design of the structure and assembly technology can effectively reduce the optical components of the internal stress, thereby improving the product performance and stability, allows the device to long-term stable and reliable work. Isolator structure design mainly need to solve two problems, first is the optical components of the assembly, stable and reliable heat dissipation requirements, can effectively control; second is firm and reliable assembly of strong permanent magnet, with the magnet design and manufacturing capabilities, devices may use more complex shape of the magnet pieces combined to provide a strong homogeneous magnetic field, between the magnets and strong magnetic requires the design of suitable assembly method and reliable assembly magnet, and required in the assembly process causes no damage or the magnet demagnetization. These need to be accumulated in practice and improve.

Above only briefly in the high power optical isolator design process often encounter some problems, along with applications to expand and deepen, may be needed for isolator corresponding improvement or design to meet the technical and market development, in this process may occur early in the design of possibly unforeseen problems, this requires us to according to the specific circumstances to provide the corresponding solutions, only in this way can we continue to design excellent performance to meet the application needs of the high power optical isolator.

Application of optical communication is still broad prospects

Once the Nortel global leader in fiber optic communications during the Internet bubble in 2000, the money in the acquisition of a large number of optical communications research and the production of small and medium enterprises, the industry has been criticized in the subsequent bankruptcy of Nortel. In fact, Nortel grasp of technology trends, the direction is right, unfortunately, Nortel too hasty, global demand for optical communication was not to such an extent.

But now the situation is very different compared with around 2000. The rapid development of mobile Internet and the widespread popularity of smart mobile terminal equipment, being a huge challenge to the global telecommunications network capacity, transmission speed. The era of “data flood peak to optical communication technology has always been known by the transmission bit of new development opportunities and a huge space. Optical communication technology not only did not fall behind, the contrary, the optical communication industry chain, from fiber optic cable system equipment, terminal equipment to optical devices, a critical period in the comprehensive technology upgrade.

The field of optical communication is a noteworthy event, the National Development and Reform Commission recently organizing the preparation of strategic emerging industries key products and services Guidance Catalogue, which in conjunction with the relevant departments, the optical communication technology and product responsibility and selected emerging industries of strategic focus products.

In fiber optics, including FTTx G.657 optical fiber, broadband long-distance high speed large capacity optical fiber transmission with G.656 optical fiber, photonic crystal fiber, rare earth doped fiber (including ytterbium doped fiber, erbium doped fiber and thulium doped fiber, etc.) the laser energy transmission fiber, and has some special properties of new optical fiber, plastic optical fiber, polymer optical fiber is fully finalists. The upgrade of the fiber optic technology, will bring the data transmission capacity, distance, quality leap.

In the field of fiber access equipment, passive optical network (PON), wavelength division multiplexer (WDM),OLT and ONU on the list. Optical transmission equipment, especially the line rate of 40 Gbit/s, 100Gbit/s large capacity (1.6Tb/s and abobe) DWDM equipment, reconfigurable optical bifurcation Multiplexer (ROADM) wavelength division multiplexing system ran cross-connect (OXC) equipment, large-capacity high-speed OTN optical transport network equipment as well as packetized enhanced OTN equipment, PTN packet transport network equipment also impressively. These products are “broadband China” works to promote a powerful weapon; both long-distance backbone network, metropolitan area network or access network even close to the user’s “last mile” of these products will come in handy.

The major products are classified as strategic emerging industries in the field of optical devices, high-speed optical components (active and passive). This is the core and foundation of the field of optical communication technology, device development, the improvement of integration, function enhancement can bring significantly reduce the cost of system equipment and provide a performance boost.

At the same time, the annual OFC / NFOEC (fiber-optic communications exhibition) will be held in late March in California. This event will showcase the latest technology and research progress of the global optical component modules, systems, networks and fiber optic products, represents a new trend of development of optical communication technology.

100G for ultra-high-speed network technology is the current OFC hot one. 2012 100G technology on a global scale backbone network level scale application of 100G optical network applications will rapidly expand with the 100G device further mature. In the same time, the industry has also increased efforts to develop the 100G optical modules, silicon photonics technology pluggable multi-source agreement 100G CFP MSA CPAK optical module has been available. Outside the backbone network, 100G MAN application is the current one of OFC discussion topic.

The rise of cloud computing brings data center construction boom, 100G technology in the data center is a popular data center for high-speed pluggable optical devices is also a hot topic. Experts believe that photonic technology has a key role to play in the large enterprise data centers, but this is only a start, the size of the new cloud computing data center such as a warehouse, with more than 100,000 servers carrying the computing and storage resources, the required network bandwidth than PB level. These data centers only optical communications technology in order to achieve VCSEL (vertical cavity surface emitting lasers) and multi-mode fiber has played an important role, and will continue to introduce new fiber optic communication technology.

Relationship Between The Optical Coupler And PLC Splitter

In fact, splitter is named for the function of the device, coulper named for its working principle, splitter may be based coupler, and may be based on the waveguide or the separating element, coupler can be done either the splitter, but also can be done WDM, attenuator.

Optical coupler either split optical signals into multiple paths or combines multiple signals on one path. Optical signals are more complex than electrical signals, making optical couplers trickier to design than their electrical counterparts. Like electrical currents, a flow of signal carriers, in this case photons, comprise the optical signal. However, an optical signal does not flow through the receiver to the ground. Rather, at the receiver, a detector absorbs the signal flow. Multiple receivers, connected in a series, would receive no signal past the first receiver which would absorb the entire signal. Thus, multiple parallel optical output ports must divide the signal between the ports, reducing its magnitude. The number of input and output ports, expressed as an N x M configuration, characterizes a coupler. The letter N represents the number of input fibers, and M represents the number of output fibers. Fused couplers can be made in any configuration, but they commonly use multiples of two (2 x 2, 4 x 4, 8 x 8, etc.).

PLC Splitter is a device that split the fiber optic light into several parts by a certain ratio. The simplest couplers are PLC Splitters. These devices possess at least three ports but may have more than 32 for more complex devices.PLC Splitters are important passive components used in FTTX networks. But two kinds of fiber splitters are popular used, one is the traditional fused type PLC Splitter (FBT splitter), which features competitive prices; the other is PLC PLC Splitter, which is compact size and suit for density applications. Both of them have its advantages to suit for different requirement.

PLC Splitter typical parameter include input and output part cable length, splitting ratio, working wavelength and with what kind of fiber optic connectors. Just like fiber patch cable, fiber splitters are usually with 0.9mm, 2mm or 3mm cables. 0.9mm outer diameter cable is mostly used in stainless steel tube package PLC Splitters, while 2mm and 3mm cables are mostly used in box type package fiber splitters. Based on working wavelength difference there are single window and dual window PLC Splitters. And there are single mode fiber splitter and multimode fiber splitter. Typical connectors installed on the PLC Splitters are FC or SC type.

Optical coupler or PLC splitters are available in a selection of styles and sizes to separate or combine light with minimal loss. All couplers are produced employing a proprietary procedure that produces reliable, low-cost devices. They’re rugged and impervious to common high operating temperatures. Couplers can be fabricated with custom fiber lengths or with terminations of any type.