Are Polarization Optical Isolators Essential for Fiber Optic Systems? 

Fiber optic systems play a crucial role in modern telecommunications, offering high-speed data transmission and reliable connectivity. Within these systems, maintaining signal integrity and minimizing signal loss is paramount. Polarization-maintaining optical isolators (PMIs) are essential components that help achieve these objectives by managing the polarization state of light within the fiber optic system. In this blog, we’ll explore the importance of PMIs in fiber optic systems, their key features, and how they enhance performance. 

Understanding Polarization Maintaining Optical Isolators 

What are Polarization Maintaining Optical Isolators? 

Polarization-maintaining optical isolators are devices designed to control the transmission of light within fiber optic systems while preserving the polarization state of the light. They are made up of specific optical components that selectively permit light to travel through one direction while obstructing light from returning in the other. In the fiber optic system, this unidirectional transmission ensures effective light propagation and prevents signal degradation. 

Importance of Polarization Maintaining Optical Isolators in Fiber Optic Systems 

1. Minimizing Signal Degradation 

In fiber optic systems, signal degradation can occur due to back reflections, polarization fluctuations, and other sources of optical interference. PMIs play a crucial role in minimizing signal degradation by isolating the transmitted signal from reflected light and maintaining the polarization state of the transmitted light. This ensures consistent signal quality and reliability in data transmission. 

2. Protecting Sensitive Components 

Fiber optic systems often include sensitive components such as lasers, detectors, and modulators, which are susceptible to damage from back reflections and optical feedback. By incorporating PMIs into the system, these sensitive components are protected from harmful effects caused by unwanted reflections, ensuring their optimal performance and longevity. 

3. Enhancing System Performance 

PMIs enhance the overall performance of fiber optic systems by optimizing signal integrity, reducing signal noise, and improving system stability. By mitigating polarization-related issues and maintaining signal coherence, PMIs enable more efficient data transmission, higher data rates, and greater system reliability, ultimately leading to enhanced system performance and user experience. 

Applications of Polarization Maintaining Optical Isolators 

1. Telecommunications 

In telecommunications networks, PMIs are used to manage signal polarization and prevent signal degradation caused by reflections and optical feedback. They are employed in optical amplifiers, wavelength division multiplexing (WDM) systems, and other critical components to ensure reliable data transmission over long distances. 

2. Fiber Optic Sensing 

PMIs are utilized in fiber optic sensing applications, such as distributed temperature sensing (DTS) and distributed acoustic sensing (DAS), to maintain signal integrity and accuracy. They enable precise measurement and detection of physical parameters, such as temperature, strain, and pressure, in various industrial and environmental monitoring applications. 

3. Optical Instrumentation 

PMIs find use in optical instrumentation and measurement systems, where accurate polarization control is essential for precise optical measurements and analysis. They are employed in spectroscopy, interferometry, and other optical characterization techniques to optimize signal quality and measurement accuracy. 

Conclusion 

Polarization-maintaining optical isolators are indispensable components in fiber optic systems, offering crucial benefits such as signal isolation, polarization control, and enhanced system performance. With their versatile applications and advanced features, PMIs play a vital role in enabling reliable and efficient data transmission across various industries and applications.

Features and Applications of 780nm Optical Isolators

The high-power dual-stage optical isolator 780nm is a polarization-independent fiber element that enables all polarized light to propagate in one direction while blocking it in the opposite direction.

It is not possible to adjust the polarization of input light in many applications. In such instances, a polarization-independent optical fiber isolator with a wavelength of 780nm is required. 780nm optical fiber is a critical component that protects lasers, amplifiers, and ASE sources from instabilities caused by spurious back-reflected light.

Overview of the 780nm Optical Isolators

Low-power lasers benefit from the flexibility, convenience, and performance of the I-780-LM compact designs. I-780-LM covers the wavelength range of 770 to 790nm. A Faraday rotator constructed of LPE film is included in this design.

Due to the absorption of the Faraday rotator material, this type is only advised for low-power applications. For OEM requirements, metal-bonded or hermetic construction alternatives are available. I-780-LM has a standard wavelength of optimization of 780nm.

Applications

  • Semiconductor Laser Modules
  • Tunable Laser Modules
  • Small Form Factor Laser Modules

Features

  • Low Insertion Loss
  • High Isolation
  • Micro-Miniature Size
  • Broad Bandwidth
  • Wide temperature range
  • Polarization alignment

Single Mode / Single Frequency Laser Diode, 780nm DFB, 4mW

The DFB laser is made with discrete-mode (DM) technology, which results in a low-cost laser diode with mode-hop-free tuneability, high SMSR, and a narrow linewidth.

These laser diodes come in a variety of wavelengths ranging from 776 to 784nm, making them ideal for Rb-based atomic clocks, Rubidium sensing, and interferometry applications.

The fiber-coupled butterfly package includes a TEC and a thermistor for precise temperature and wavelength control.

780nm for Rubidium-Based Atomic Clocks

These 780nm lasers operate reliably and without mode hop over a broad wavelength tuning range. These Rubidium-based atomic clocks and spectrometer lasers have a single longitudinal mode. The low linewidth output is ideal for high-performance applications in a variety of environments.

Polarization-Independent Dual-Stage Optical Isolator Fundamentals

The polarization dependence of dual-stage optical isolators using polarizers and a Faraday rotator is a severe problem. The insertion loss will rise as a result of this problem. As a result, optical isolators that are not polarization-dependent are particularly appealing for transmission systems.

By replacing the polarizers with polarizing splitters combiners, it is possible to achieve a polarization-independent design: they divide the input light into two orthogonal states of polarization that run through the Faraday cell separately to experience isolation and are recombined at the output.

Many applications in fiber optic systems necessitate high-power polarization-independent dual-stage optical isolators, which allow inputs with any polarization direction to flow through without PDLs while isolating back reflections (return lights).

The high-power dual-stage optical isolator is a vital component in optical systems. High-power dual-stage optical fiber isolators are used to ensure that laser transmitters and amplifiers are stabilized, and that transmission performance is maintained.

Introduction of Fiber Optic Coupler with its Benefits & Classification

A fiber optic coupler is an indispensable part of the world of electrical devices. Without these no signals would be transmitted or converted from inputs to outputs. This is the reason these are so important thereby this article discussed about these, introduction, classification and benefits in detail.

Fiber Optic Coupler is an optical cog that is capable of connecting single or multiple fiber ends in order to permit the broadcast of light waves in manifold paths. This optical device is also capable of coalescing two or more inputs into a single output while dividing a single input into two or more outputs. In comparison to a connector or a splice, the signals may be even more attenuated by FOC i.e. Fiber Optic Couplers; this is due to the division of input signal amongst the output ports.

Types of Fiber Optic Coupler

Fiber Optic Couplers are broadly classified into two, the active or passive devices. For the operation of active fiber coupler an external power source is required, conversely no power is needed when it comes to operate the passive fiber optic couplers.

Fiber Optic Couplers can be of different types for instance X couplers, PM Fiber Couplers, combiners, stars, splitters and trees etc. Let’s discuss the function of each of the type of the Fiber Optic Couplers:

Combiners: This type of Fiber Optic Coupler combines two signals and yields single output.

Splitters: These supply multiple (two) outputs by using the single optical signal. The splitters can be categorized into T couplers and Y couplers, with the former having an irregular power distribution and latter with equal power allocation.

Tree Couplers: The Tree couplers execute both the functions of combiners as well as splitters in just one device. This categorization is typically based upon the number of inputs and outputs ports. These are either single input with a multi-output or multi-input with a single output.

PM Coupler: This stands for Polarization Maintaining Fiber Coupler. It is a device which either coalesces the luminosity signals from two PM fibers into a one PM fiber, or splits the light rays from the input PM fiber into multiple output PM fibers. Its applications include PM fiber interferometers, signal monitoring in its systems, and also power sharing in polarization sensitive systems etc.

Star Coupler: The role of star coupler is to distribute power from the inputs to the outputs.

Benefits of Fiber Optical Couplers

There are several benefits of using fiber optic couplers. Such as:

  • Low excess loss,
  • High reliability,
  • High stability,
  • Dual operating window,
  • Low polarization dependent loss,
  • High directivity and Stumpy insertion loss.

The listed benefits of Fiber Optical Couplers make them ideal for many applications for instance community antenna networks, optical communication systems and fiber-to-home technology etc.

Optical Filters: Filter stacks transmit wide-angle incident light without shifting wavelength(2)

To avoid the problem of color change versus incidence angle in an optical system, thin-film-coated filter elements can be replaced by a filter consisting of a stack of different filter glasses.

JASON KECK

Wide-angle filter stack apps

There is a multitude of applications for this type of filter. In the field of digital imaging, colorimeters-which take wideband spectral energy readings-are used to profile and calibrate display devices, verifying that pixel color and intensity at the edge of a display matches the performance of pixels in the center of the display.

In astronomy, biomedical or fluorescence imaging, and mineralogy, hyperspectral imaging has many important applications. It is essential that the incident light undergo as little iridescence as possible. Also, when precision imaging instruments are expensively launched into orbit, the filters must be robust enough to withstand extreme environmental operating conditions.

In agriculture, the color of crops or food products reveals vital information. The use of Earth-observing satellites to measure the “vegetation index” of crops (a measurement of green hue) is nothing new, but the affordability of aerial drones has brought new possibilities. A drone can be programmed with GPS data to fly on a fixed pattern over a designated crop area and take wide-angle images at regular intervals, building up a picture of the vegetation index of crops. If the images used in such applications provide accurate spectral data that is as free as possible from iridescent distortion, it can give farmers precise control over fertilizer application rates and greatly improve efficiency and productivity. This is a considerable cost saving over low-resolution, narrowband satellite imagery and conventional aerial photography using manned aircraft.

Design hurdles

There are three complicating factors in the design of such filter stacks. The first is the limited choice in filter glass, limited not only by manufacturer availability but also by physics. Filter glass with an ideal edge cut-on or cut-off wavelength for an application is not always easy to find, or may be impossible to precisely manufacture. Where it is available, the designer is then limited by what the manufacturer can deliver in a reasonable time, as melts may be scheduled as infrequently as once every several years, depending on demand.

The second factor is that, while the perfect filter glass for a particular application may not exist, there are hundreds of other glass types from numerous vendors that can be combined to achieve a close approximation of the requirement.

The third complicating factor is that the design of ColorLock filters is a massively multidimensional, nonsmooth optimization challenge. Physical manufacturing requirements restrict the thickness of all combined individual layers to not exceed the overall thickness requirement of the resulting optical component, further putting restrictions on the selection of specific CWDM filter glass types.

Reynard streamlined this complex design process by developing in-house software into which all of the system requirements are fed. The software produces a manufacturable design for a filter in which the necessary materials are combined at the correct thickness in each layer. The design is then manufactured and validated for performance.

About DK Photonics

DK Photonics – www.dkphotonics.com  specializes in designing and manufacturing of high quality optical passive components such as 8CH CWDM Module,100GHz 8CH DWDM,200GHz DWDM,Mini-size CWDM,compact CWDM,Athermal AWG DWDM Module,100GHz AWG,Thermal AWG DWDM Module,1310/1490/1550nm FWDM, PLC Splitter, Optical Circulator,Optical Isolator,Fused Coupler,Mini Size Fused WDM.

Optical Filters: Filter stacks transmit wide-angle incident light without shifting wavelength(1)

To avoid the problem of color change versus incidence angle in an optical system, thin-film-coated filter elements can be replaced by a filter consisting of a stack of different filter glasses.

JASON KECK

Wide-angle imaging systems have to overcome numerous problems. Distortion of the shape of objects in the scene is the predominant issue, recognizable as the “fish-eye lens” look that is often corrected in software. However, lens distortion is not the only problem.

Iridescence, or the change in transmitted or reflected color of light viewed from different angles, is a phenomenon that can be found both in nature and in artificial light-detecting systems with precise color requirements, where it can cause many problems.

Wide-angle color-sensing applications commonly require that a CWDM wavelength must be detectable regardless of the incident angle. Iridescence through a thin-film-coated optical element can cause problems in this situation by distorting the spectral transmission of light coming from peripheral objects.

Maximizing light transmission in a thin-film WDM coating’s passband while blocking out-of-band light is a requirement for coated optical components such as dielectric filters; however, the wavelength’s transition commonly only remains steady within relatively narrow cone angles. Beyond angles of 5°, such filters are susceptible to iridescence, observable as a change of color, or “blueshift.” As the angle of light entering the filter increases, the light propagates through more of each thin-film stack layer, altering the apparent overall thickness of the optical-filter stack and affecting the performance of the original intended design. This can make such filters unsuitable for wide-angle imaging applications with bright illumination and where higher standards of consistency are required of the wavelength of all incident light.

One of the more convoluted wide-angle imaging solutions is the use of a cluster of cameras or a polycamera, pointing in various directions like the compound eye of an insect; the resulting multiple pictures are then assembled into one image in software. Although the light entering each camera thus fills only a narrow cone angle, the complexity and resultant high expense of such a system is obvious.

Engineers at Reynard have addressed this problem in a single optical device with a system in which two or more layers of filter glass are combined into a stacked configuration. These ColorLock filter stacks eliminate the wavelength shift as incident angle increases and are customized to meet specific system needs.

Software is used to determine the exact composition and thickness of the layers in these filters; the software determines a merit function that best estimates the filter requirements and allows filter stacks to be designed for band pass, short-wave pass, long-wave pass, or user-specified functions. Incident angles can be as high as 50° without any shift in the transmitted wavelength, while more traditional coated filters with the same conditions would see a significant shift toward shorter wavelengths.

 

About DK Photonics

DK Photonics – www.dkphotonics.com  specializes in designing and manufacturing of high quality optical passive components such as 8CH CWDM Module,100GHz 8CH DWDM,200GHz DWDM,Mini-size CWDM,compact CWDM,Athermal AWG DWDM Module,100GHz AWG,Thermal AWG DWDM Module,1310/1490/1550nm FWDM, PLC Splitter, Optical Circulator,Optical Isolator,Fused Coupler,Mini Size Fused WDM.

Optical Isolators Global Market Forecast

According to ElectroniCast, the Asia Pacific Region leads in the use of optical isolators…

ElectroniCast Consultants, a leading market research & technology forecast consultancy addressing the fiber optics communications industry, today announced the release of a new market forecast of the global consumption of optical isolators in optical communication and specialty applications.

According to ElectroniCast, the Asia Pacific region (APAC), region held the lead in terms of relative market share consumption volume (quantity/number of units) of optical isolators in 2012, with 47 percent; however the Asia Pacific region (APAC), pushed along by the telecommunication category in the People’s Republic of China. The consumption of optical isolators in the APAC region is forecast to nearly triple (3x) during the 2012-2017 time frame.

Optical isolators are passive devices that allow light to be transmitted in only one direction. They are most often used to prevent any light from reflecting back down the optical fiber, as this light would enter the source and cause backscattering and feedback problems. This is especially important for high data rate transceivers and transponders, or those devices requiring long span lengths between transceiver pairs.

Optical isolators are used in many applications in commercial, industrial, and laboratory settings.  They are reliable devices when used in conjunction with fiber optic amplifiers, fiber optic ring lasers, fiber optic links in cable TV/multimedia applications, and high-speed/ DWDM and coherent fiber optic telecommunication communication systems, laboratory R&D, sensors, gyro-systems, test/instrumentation measurement quality assurance applications in automation of manufacturing processes and several others.

ElectroniCast estimates that the Telecommunication applications held 85% of the relative market share of the worldwide consumption volume of optical isolators in 2012.

According to ElectroniCast, 13.4 million optical isolators were used in 2012…

2012 – Optical Isolator Global Volume (Quantity) Market Share (%),

By Region, 13.4 Million Units

optical isolator

DK Photonicswww.dkphotonics.com  specializes in designing and manufacturing of high quality optical passive components mainly for telecommunication, fiber sensor and fiber laser applications,such as PLC Splitter, WDM, FWDM, CWDM, DWDM, OADM,Optical Circulator, Isolator, PM Circulator, PM Isolator, Fused Coupler, Fused WDM, Collimator, Optical Switch and Polarization Maintaining Components, Pump Combiner, High power isolator, Patch Cord and all kinds of connectors.

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.