Polarization Dependent Isolator vs Polarization Independent Isolator

Connectors and other types of optical devices on the output of the transmitter may cause reflection, absorption, or scattering of the optical signal. These effects on the light beam may cause light energy to be reflected back at the source and interfere with source operation. In order to reduce the effects of the interference, an optical isolator is usually used. Optical isolator allows a beam of light to stream through a single one way direction. At the same time, it prevents the light from going back in the opposite direction. According to the polarization characteristics, optical isolators can be divided into two types, including polarization dependent isolator and polarization independent isolator. The polarizer-based module makes a polarization dependent isolator, and the birefringent crystal-based structure makes a polarization independent isolator. You may be very confused about them as you find that there is only a little difference via their names. So, what are they and what are the differences between them? This paper will give you the answer.

Polarization Dependent Isolator

The polarization dependent isolator consists of three parts, an input polarizer , a Faraday rotator, and an output polarizer. Light traveling in the forward direction becomes polarized vertically by the input polarizer. The Faraday rotator will rotate the polarization by 45°. The analyser then enables the light to be transmitted through the isolator.

Light traveling in the backward direction becomes polarized at 45° by the analyser. The Faraday rotator will again rotate the polarization by 45°. This means the light is polarized horizontally. Since the polarizer is vertically aligned, the light will be extinguished.

The picture shows us a Faraday rotator with an input polarizer, and an output analyser. For a polarization dependent isolator, the angle between the polarizer and the analyser, is set to 45°. The Faraday rotator is chosen to give a 45° rotation.

Because the polarization of the source is typically maintained by the system, polarization dependent isolator is widely used in free space optical systems.

Polarization Independent Isolator

The polarization independent isolator also consists of three parts, an input birefringent wedge, a Faraday rotator, and an output birefringent wedge. Light traveling in the forward direction is split by the input birefringent wedge into its vertical (0°) and horizontal (90°) components, called the ordinary ray (o-ray) and the extraordinary ray (e-ray) respectively. The Faraday rotator rotates both the o-ray and e-ray by 45°. This means the o-ray is now at 45°, and the e-ray is at −45°. The output birefringent wedge then recombines the two components.

Light traveling in the backward direction is separated into the o-ray at 45, and the e-ray at −45° by the birefringent wedge. The Faraday Rotator again rotates both the rays by 45°. Now the o-ray is at 90°, and the e-ray is at 0°. Instead of being focused by the second birefringent wedge, the rays diverge. The picture shows the propagation of light through a polarization independent isolator.

While polarization dependent isolator allows only the light polarized in a specific direction, polarization independent isolator transmit all polarized light. So it is usually widely used in optical fiber amplifier.

Comparison of Polarization Dependent Isolator and Polarization Independent Isolator

In fact, you have already understood these two types of isolators according to the contents above. We can see their similarities and differences through the comparison of their definition, working principle and applications. Both of them consist of three parts and have a same principle based on Faraday effect. However, to overcome the limitation of polarization dependent isolator, polarization independent isolator has been developed. Regardless of the polarization state of the input beam, the beam will propagate through the isolator to the output fiber and the reflected beam will be isolated from the optical source. If the extinction ratio is important, a polarization dependent isolator should be used with either polarization maintaining fibers or even regular single-mode fibers. If the system has no polarization dependence, a polarization independent isolator will be the obvious choice.

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DK Photonics – www.dkphotonics.com specializes in designing and manufacturing of high quality optical passive components mainly for fiber laser applications such as 1064nm high power isolator, Cladding Power Stripper, Multimode High Power Isolator, pump combiner,1064nm Band-pass Filter,(6+1)X1 Pump and Signal Combiner, PM Circulator, PM Isolator, optical Coupler. More information, please contact us.

Large Mode Area Fibers

Optical fibers with relatively large mode areas and a single transverse mode or only a few modes.

For some applications, it is desirable to use optical fibers with a large mode area (LMA fibers) – often with single-mode guidance. Due to the reduced optical intensities, such fibers effectively have lower nonlinearities and a higher damage threshold, which makes them suitable for example for the Amplification of intense Pulses or single-frequency signals in Fiber amplifiers, or in case of passive fibers for delivery of such light. While standard single-mode fibers have an Effective Mode Area below 100 μm2, large mode area fibers reach values of hundreds or even thousands of μm2.

Pump and signal combiner for bi-directional pumping of all-fiber lasers and amplifiers(7)

Pump and signal combiner for bi-directional pumping of all-fiber lasers and amplifiers(7)

5. Simulations and results for a multi pump port configuration

So far, the modeling results consider a TF with only a single pump port. However, for monolithic high power fiber laser and amplifier systems, it is often required to provide multiple pump ports due to the limited output power of available fiber coupled pump diodes and the efforts to develop laser systems with redundancy. Thus, in this section, we investigate the impact of multiple pump ports on the coupling efficiency and the loss mechanism. The setup of each pump combiner is identical to the description in Section 2 (see Fig. 1), but with several additional ports placed around the cladding of the TF, leading to a fiber bundle. A schematic of a fiber combiner with multiple pump ports is shown in Fig. 7

Pump and signal combiner for bi-directional pumping of all-fiber lasers and amplifiers(7)

Fig. 7 Fiber combiner with multiple pump ports, PFF: pump feeding fiber with a piece of coreless intermediate fiber (IF) as described in Fig. 1, TF: target fiber, TP: transmitted power.

5.1 Simulations of the pump coupling efficiency

The experiments and simulations in Section 4 showed that for a pump combiner with a single pump port, a TL of 20 mm and a TR of 6 yields an excellent coupling efficiency in the range of 95%. In comparison, for a fiber band pass filter with multiple pump ports, the simulations for a TL of 20 mm (Fig. 8(a)

Pump and signal combiner for bi-directional pumping of all-fiber lasers and amplifiers(7)-2

Fig. 8 Simulated coupling efficiency for a pump combiner with up to 6 pump ports for (a) a TL of 20 mm and (b) a TL of 10 mm for a pump light input NA of 0.22.

) revealed that the pump coupling efficiency of the combined pump power depends on the number of pump ports and significantly on the choice of the TR. In the simulations the input pump light NA of the PFFs was 0.22. In general, it can be seen that the pump coupling efficiency decreases with each additional pump port. A lower TR yields a greater decrease of the pump coupling efficiency with each additional pump port than a higher TR. In the case of a TL of 20 mm and a TR of 2.5, the theoretically obtainable pump coupling efficiency of almost 90% decreases to 73%, if the number of pump ports increases from 1 to 6. However, as already mentioned, the increasing losses due to additional pump ports can be reduced with increasing TR. In Fig. 8(a) it can be clearly observed that for 6 pump ports and a TR of 6, a pump coupling efficiency of 90.2% can be achieved. For a TR higher than 6, it is not possible to achieve a significant improvement in pump coupling efficiency for multiple pump ports by increasing of the TR.

For a single pump port configuration it is already known that the pump coupling efficiency decreases with shorter TLs at constant TRs (Fig. 2(a)). However, for multiple pump ports a reduction of the TL leads to the advantage that the pump coupling efficiency of the combined pump power decreases less with each additional pump port, especially at lower TRs. The simulation results for a TL of 10 mm instead of a TL of 20 mm are presented in Fig. 8(b). A comparison of Fig. 8(a) and 8(b) shows: If the number of pump ports is increased from 1 to 6 at a TR of 2.5, the pump coupling efficiency experiences a decrease of 16.9 and 11.2% for a TL of 20 and 10 mm, respectively. Although the total power losses for a TL of 10 mm are higher than for a TL of 20 mm, the example reveals, that the decrease of the pump coupling efficiency due to additional pump ports can be reduced by using shorter TLs.

Besides having less available combined pump power, the additional pump power losses generated in comparison to a fiber combiner with a single pump port, corresponds to an enhanced risk of damaging the component due to additional thermal load. Hence, the loss mechanism for a fiber combiner with multiple pump ports needs to be investigated in more detail.

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Optical Filters: Filter stacks transmit wide-angle incident light without shifting wavelength(3)

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

Rugged, no coating degradation

Advantages of using a filter stack rather than a thin-film-coated optical element include wide-angle performance (see Fig. 2) and high durability. Because the glass itself performs the blocking, there is no concern of coating degradation due to extreme environmental shifts, contamination, or mishandling. Filter stacks are as durable as the glass they are made from, surviving aggressive cleaning methods, severe abrasion, salt/fog testing, humidity, and temperature cycling per durability standards of MIL-PRF-13830B, MIL-C-48497A, and MIL-C-675C.

Because all filter glass types have approximately the same index of refraction, there is no Fresnel loss as light propagates from one internal layer to another. However, as with any glass, the air-to-substrate interfaces will incur an ~8% total Fresnel loss for the component.

The addition of a broadband antireflection (BBAR) coating on each air-to-substrate surface can mostly eliminate this loss. The spectral range of the BBAR is designed to be much wider than the active spectral region of the 100G DWDM filter, so the stability of the transmission band will not be affected by changes in the angle of the filter. Blocking coatings can also be added if it is necessary to create steeper edges for in-band performance; however, doing so can affect the wide-angle performance at the edge wavelengths.

ColorLock filter stacks can be designed for spectral ranges from ultraviolet to near-infrared, with transmission exceeding 60% at the specified design wavelength. This transmission may not be as high as with dielectric filters, but is sufficient for applications with controlled and stable illumination, such as for machine vision, in which the consistency of wavelengths from wider incident angles is more important than transmission.

Having overcome considerable design challenges, we believe that these filter stacks can be used as an innovative solution in applications that demand consistent wavelengths from incident angles that are wide enough that dielectric filters would not be sufficient, and where the higher transmission that is afforded by dielectric filters is less important.

Industrial Fiber Laser Introduction and Global Market Forecast –DK Photonics

The Global Industrial Fiber Laser market to grow at a CAGR of 21.4% over the period 2013-2018

Fiber lasers contain the active gain medium, which is an optical fiber integrated with rare earth elements such as erbium and ytterbium. Unlike conventional gas lasers, a fiber laser uses part of the fiber as the resonating cavity, where the laser action takes place to generate laser beams , Fiber lasers are preferred over other lasers such as CO2 lasers and excimer lasers, primarily because they are more reliable, efficient, robust, and portable, and easier to operate than other lasers.

Fiber lasers used for industrial applications such as cutting, welding, marking, and engraving in the Manufacturing, Semiconductor, and Automotive industries are referred to as industrial fiber lasers. Moreover, due to their superior performance, compact size, high output power, low cost of ownership, durability, and eco-friendly attributes, industrial fiber lasers are being adopted at a significant rate. They also eliminate the mechanical adjustments and high maintenance costs that are necessary with other lasers.

Increased R&D spending by vendors to gain a competitive advantage over other players in the market is one key trend in this market. Vendors are increasingly investing in their R&D division to provide better functionality and to meet the unsatisfied requirements of consumers. R&D investments have enabled vendors to capture a significant market share and gain a competitive edge over other vendors in the Global Industrial Fiber Laser market.

According to the report, one major driver of the market is the increased adoption of fiber lasers because of their superior attributes. These lasers used for industrial applications are gaining more significance because they exhibit excellent light properties.

Further, the report states that one of the key challenges that the market faces is the uncertainty regarding the lifespan of fiber lasers. Despite their existence in the industry for more than 10 years, the lifespan fiber lasers are not definite.

Pump and signal combiner for bi-directional pumping of all-fiber lasers and amplifiers(6)

Pump and signal combiner for bi-directional pumping of all-fiber lasers and amplifiers(6)

4.4 Experimental results

In order to verify the simulations, two fiber combiners with a single pump port based on the setup described in Section 2 were developed. For the first combiner an IF with a low TR of 2.6 and a short TL of 9.5 mm was fabricated. In the case of the second combiner the TR and the TL were increased to 6.7 and 18 mm, respectively. For both combiners the geometrical dimensions of the obtained tapered IFs were measured with an optical microscope. After completion of the fabrication, both combiners were optically characterized. Therefore, each PFF (pump port) with a NA of 0.15 was connected to a pump diode (Oclaro BMU25) with a pigtail fiber delivering a maximum output power of ~25 W at a wavelength of 976 nm. The delivery fiber of the pump diode had parameters identical to the PFF.

The experimental results for the first fiber combiner are shown in Fig. 6(a)

getImage

Fig. 6 Coupled and transmitted power measured for a fiber combiner with one pump port with (a) a TL of 9.5 mm (TR of 2.6) and (b) a TL of 18 mm (TR 6.7), * ratio of coupled or transmitted power to total diode power in percent.

. Due to the low TR of 2.6, an experimental pump coupling efficiency of only 74% was achieved. The residual pump power was almost completely measured as TP, with a power fraction of 25.3%. The simulations for the coupled as well as the TP show good agreement with the experimental results, and confirm that in the case of a low TR of 2.6, the pump power is only divided into coupled power and TP. In Fig. 6(a) it can be seen that in the simulations the sum of the coupled and TP is 99.9%, corresponding to 0.1% of pump light rays not detected in the simulations. This can be treated as a simulation error. That the measured sum of coupled pump power and TP is only 99.3% can be explained by measurement uncertainties, marginal splice losses and additional power losses in the fiber component caused by dust particles. Since the thermal load of this fiber combiner design is negligible it would be feasible to couple several kW of pump power, but with the disadvantage of a moderate coupling efficiency of about 75% and consequently a undesirable overall efficiency for high power laser system.

For the second fiber combiner, depicted in Fig. 6(b), a higher pump coupling efficiency of 95.2% (96.0% in simulation) was measured as compared to the first combiner presented in Fig. 6(a) due to the increase in TR and TL. Following the simulations the residual pump power of 4% can be divided into TP, PCT and PAA with 2.4%, 0.6% and 0.9%, respectively. Again, the missing pump power of 0.1% was associated with an error owing to undetected power in the simulations. For the TP a fraction of 2.3% was measured and shows very good agreement with the simulation (2.4%), i.e. more than 50% of the total power loss was TP. This fraction of power represents no risk for damage to the fiber component. Due to the excellent agreement between simulation and experiment, the simulated PCT-fraction of only 0.6% is a good value for an estimate of the thermal load of the coating of the TF. Based on the simulations and experiments an error of less than 1% of the pump input power can be assumed for the PCT-fraction.

Unfortunately, the power fractions PAA and PCT are difficult to measure and therefore could not be experimentally determined. In future work an indirect measurement of PCT will be realized by measuring the coating temperature of the CWDM Module. In summary, the simulations describe the coupling efficiency as well as the fraction of TP very well, and thus, serve as a very good estimation for the fraction of PCT and PAA.

DK Photonics – www.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.

Fiber Optics Sensors Provide Early Warning for Landslides-DK Photonics

CASERTA, Italy, Sept. 29, 2014 — Fiber optic sensors could warn people of imminent landslides, potentially saving lives and reducing destruction.

A team at the Second University of Naples is developing sensor technology that could detect and monitor both large landslides and slow slope movements. The researchers hope to mitigate the effects of these major natural disasters, similar to the way hurricane tracking can prompt coastal evacuations.

Optical fiber sensors embedded in shallow trenches within slopes would detect small shifts in the soil, the researchers said. Landslides are always preceded by various types of pre-failure strains, they said.

While the magnitude of pre-failure strains depends on the rock or soil involved — ranging from fractured rock debris and pyroclastic flows to fine-grained soils — they are measurable. Electrical sensors have long been used for monitoring landslides, but that type of sensor can be easily damaged, the researchers said. Optical fiber is more robust, economical and sensitive.

“Distributed optical fiber sensors can act as a ‘nervous system’ of slopes by measuring the tensile strain of the soil they’re embedded within,” said professor Dr. Luigi Zeni.

The researchers are also combining several types of optical fiber sensors into a plastic tube that twists and moves under the forces of the pre-failure strains. This will allow them to monitor the movement and bending of the optical fiber remotely to determine if a landslide is imminent.

The use of fiber optic sensors “allows us to overcome some limitations of traditional inclinometers, because fiber-based ones have no moving parts and can withstand larger soil deformations,” Zeni said.

He added that such sensors can be used to cover several square kilometers and monitored continuously to pinpoint critical zones.

The team will present their research at Frontiers in Optics in Tucson, Ariz., next month.

Ovum: Optical components market to grow 8% in 2014 from $6.8 bn in 2013

The global optical components (OC) market is expected to grow 8 percent in 2014 from $6.8 billion in 2013, said Ovum.

In 2013, the OC market increased 3 percent from 2012. Ovum said main growth drivers in 2013 were data communication sales driven by large data centers, 100G coherent demand, and unexpected growth in sales of transceivers for fiber-to-the-antenna applications for 4G build-outs.

“Demand for 100G metro–optimized transmission gear will begin shipments and ramp in 2015. Multiple component vendors introduced components and pluggable optics for 100GHz DWDM in anticipation. Opportunities are also emerging in the data center for high-speed interconnects,” said Daryl Inniss, practice leader for Telecoms Components at Ovum.

In the first quarter of 2014, the optical components market declined 1 percent sequentially and grew 7 percent compared to the year-ago period. New lower telecom prices were one of the main reasons for the marginal growth in OC on quarter-on-quarter basis.

Ovm said demand for 100G components for coherent transmission in WAN, datacom transceivers at 10 and 40G, and fiber-to-the-antenna transceivers is expected to continue. Traffic continues to increase, and high-speed optics being used in new applications are helping to drive the market forward.

The WAN OC segment, which includes components in telecom carriers’ core and metro networks, the largest segment, will grow at a compound annual growth rate (CAGR) of 11 percent to $7 billion in 2019. Demand for 100G components and modules is a big driver for growth in WAN. Ovum expects strong demand for pluggable coherent transceivers in 2015.

Datacom will be expanding at a 16 percent CAGR to reach $4.2 billion in 2019 — led by demand for 10 and 40G components in the early years and then 100G in the later years driven by the availability of server ports supporting data rates greater than 10G.

Access — including CATV, FTTx and transceivers for the fiber-to-the-antenna application — will decline at 2 percent CAGR to $1.1 billion in 2019. The decline will be driven by the FTTx application, where volumes are nearly constant through the forecast period but price declines are projected to pull down revenues.

Fiber Media Converters in Private Datacom Market Forecast (March 2014)

Fiber Media Converters in Private DatacomMarket Forecast (March 2014)

According to ElectroniCast, the global use of fiber media converters in private datacom networks is expected to reach $1.29 billion in 2014…

Aptos, CA (USA) – March 20, 2014 —ElectroniCast Consultants, a leader in fiber optic market research, announced the release of a new market analysis of the worldwide use of fiber optic / Fiber media converters in private data communications. A fiber media converter is a networking device that makes it possible to connect two dissimilar media types such as copper with fiber optic cabling, as well as (different) fiber-to-fiber (F2F), such as multimode to single mode optical fiber.

The worldwide value for selected fiber media converters used in private datacom networks reached $1.07 billion in 2013. The consumption value is forecast increase with strongly rising quantity growth partially offset by declining average prices.

The EMEA and the APAC regions are forecast for double-digit consumption value growth during the timeline covered in this study (2013-2018); however, the American region’s growth is forecast to “flatten” and eventually turn to negative. The worldwide use of private datacom fiber media converters, which are specified in the ElectroniCast market study, is forecast to peak at $1.646 billion in 2017, before slipping to $1.628 billion in 2018.

“The fiber media converters researched in this market study are typically used within an existing Private Enterprise Data Centers (DCs) and Local Area Networks (LANs), as well as other non-public data communication links. They are often used to connect newer 100-Mbps, Gigabit Ethernet, 10G, or other equipment in existing networks, which are generally (copper-based) 10BASE-T, 100BASE-T, or a mixture of both,” stated Stephen Montgomery, Director of the Fiber Optics Components group at ElectroniCast Consultants.

“Several factors make the conversion from copper to optical fiber a good choice, such as – longer link lengths in campuses and industrial plants; resistance to electromagnetic and radio-frequency interference (EMI/RFI) may be necessary; and wider bandwidth capability, just to point-out a few examples,” Montgomery added.

The strong user demand for greater bandwidth and increased interconnectivity to the desktop, throughout the buildings, campuses, from LAN-to-LAN (Metropolitan Area Network – MAN) continues in 2014.

This is matched by rapidly growing demand for global broadband interconnectivity. Interactive multimedia terminals, triple play (voice, video and data), quadruple-play (adding mobility as a communications function to the network), and numerous other dynamics/ applications, continuing bring rapid access to massive databases, which increase productivity while providing rapid ROI (return on investment).

Such expanded capability, however, must often be obtained without making the current network elements obsolete. Local area network (LAN) applications illustrate this trend. LANs are becoming larger and more complex. Reconfiguration, relocation, and extension of LANs are occurring more frequently, due to organization restructuring, advances in computer usage, and the trend toward decentralized computing.

These changes to LAN cabling represent a major ongoing operational expense and a disruption of work for many companies (enterprises). For example, adding capabilities often requires that network administrators upgrade their existing LANs to another media type: for example, copper-to-fiber, multimode-to-singlemode fiber, or even singlemode –to- different types of singlemode optical fiber (note: copper-to-copper conversion is not covered in the study). By using media converters, the network administrator can achieve these upgrades inexpensively.

According to ElectroniCast, the global use of fiber media converters in private datacom reached $1.07 billion in 2013 and is forecast to peak at $1.646 billion in 2017, before slipping to $1.628 billion in 2018.

Private Datacom Fiber Media Converter Global Market Forecast,
(Value Basis, $ Million) – Source: ElectroniCast Consultants

Note: Market forecast data in this study report refers to consumption (use) for a particular calendar year; therefore, this data is not cumulative data.

Where can WDM-PON go next? — DK Photonics

Where can WDM-PON go next?

The current generation of commercial WDM-PON/ 100GHz DWDM systems based on reflective ONU technology is optimized for applications up to 20 km, 40 channels, and 1 Gbps per customer. Current research focuses on how to scale WDM-PON toward higher bit rates and longer reach. Forward error correction is a key technology for scaling the current generation of WDM-PON technology to higher bit rates, longer reach, tighter channel spacing, or a combination thereof. An important challenge is to package the technology in an MSA form-factor pluggable module to maintain its benefits in cost and compatibility with third-party equipment.

A typical requirement for next generation metro/access systems is to enable node consolidation. That means operators can reduce opex by closing down portions of their central offices; at the same time, this goal requires the optical signals to bridge longer distances than what is typical of the access networks of today. Thus, when routing WDM-PON / 1064nm high power isolator signals through the metro part of the network, it becomes necessary to support ring architectures as an alternative to the basic tree structure.

In a ring structure, cascaded filters may decrease the effective channel passband. Since the spectral width of the WDM-PON signal is wider than the signals from a normal DFB source, such filtering effects may affect transmission.

In a recent evaluation project, a partnership between Transmode and Deutsche Telekom Hochschule für Telekommunikation of Leipzig, Germany, achieved 140-km long reach WDM-PON transmission over a ring-based access-network architecture. The partnership investigated the effects of using WDM-PON based on ASE-seeded wavelength-locked transmitters in a ring-based network architecture with cascaded CWDM OADM nodes. Transmission at 1.25 Gbps over 140-km singlemode fiber was demonstrated using an EDFA and dispersion compensation.

The results were first published at ECOC 2013 (In de Betou, Bunge, Åhlfeldt, and Olson, “140km Long-reach WDM-PON Test for Ring-based Access Network Architecture”). This partnership has investigated what opportunities could be provided by WDM-PON technology in such network topologies by studying experimentally the influence of narrow filtering and maximum reach.

The experimental testbed (in Leipzig) was built around Transmode’s TM-Series iWDM-PON system to create an optical line terminal (OLT) (see Figure 2). The OLT has a transponder line card that hosts pluggable wavelength-locked Fabry-Perot transceivers, ASE seed light sources, dual circulators for up- and downstream, and a 40-channel multiplexer based on an AWG.

To reach distances beyond 100 km, amplifiers dispersion compensation, and remote ASE seed sources were used. While an experimental field trial today, it shows that WDM-PON may well continue to evolve to support longer reach and more sophisticated network architectures in the future supporting a broader range of deployment scenarios.

DK Photonics – www.dkphotonics.com specializes in designing and manufacturing of high quality optical passive components mainly for telecommunication, fiber sensor and fiber laser applications,such as High Power Isolator,1064nm Components,PM Components,Pump Combiner,Pump Laser Protector,which using for fiber laser applications.Also have Mini-size CWDM, Optical Circulator, PM Circulator,PM Isolator, Fused Coupler,Mini Size Fused WDM.More information,please contact us.