Planar Lightwave Circuits (PLCs) Market Trends

By Stephen Montgomery, ElectroniCast

This article provides a market overview of Planar Lightwave Circuits (PLCs), also known as Planar Waveguide Circuits (PWCs) consumed in selected devices for optical communication applications. As shown in Table 1, several product categories are discussed, including discrete (single function) devices, such as: arrayed waveguide gratings (AWGs); switches; variable optical attenuators (VOAs);optical couplers/splitters; Lithium Niobate Modulators; Interconnect Waveguides; Other Discrete; as well as PLCs used in devices that are capable of two or more functions (Integrated Multifunction Devices).

Table 1
Hierarchy of Selected PWC-Based Devices
Source: ElectroniCast

TOTAL PWC CONSUMPTION

Discrete PWC Devices

Array Waveguides (AWGs)

Switches

Variable Optical Attenuators (VOAs)

Coupler/Splitter

Lithium Niobate Modulators

Interconnect Waveguides

Other Discrete PWCs

Integrated Multifunction PWC Devices

Reducing size, Weight, and Cost with Multiple Functions                     The planar waveguide substrate enables optical signal processing between components, providing one or more functions. The optical waveguides are typically fabricated in polymer or in glass films deposited on silicon - so-called silica-on-silicon technology. The majority of optical functions, such as couplers/splitters, variable optical attenuators (VOAs) and array waveguides (AWGs) are currently developed and implemented forming discrete (single function/monolithic) component integration. The combination of the packaging and integrated optics aspects of PWC technology provides for an attractive and powerful technology for devices/modules, which will hold multiple (two or more) functions (integrated multifunction devices); thereby, reducing size, weight, and cost versus larger, bulkier discrete devices/modules.

Planar Lightwave Circuits (PLCs/PWCs), largely driven by Fiber-to-the-Home (FTTH), are emerging as a popular solution for integration and large-scale commodity manufacturing of selected optical communication components.  As the demand for larger quantities of optical communication components evolve, technologies, which are friendly to automation assembly processes, will have a competitive manufacturing/cost advantage.  Use of silicon wafers, for example, draws extensively on the mass-production techniques of the commercial integrated circuit (IC) production whelm, since the fabrication of PWCs incorporates many of the same pieces of equipment and processes.

Rise of Integrated Multifunction Optics              FTTH passive optical network (PON) integrated PLCs, with multiple functions, have promise for a sizable market. The biplexer (bi-directional/Bi-Di), an all-in-one transponder that includes the two wavelengths, 1310nm upstream and 1490nm downstream, is one end-use modules based on planar waveguide technology that is required for PON. And some networks will use a 1550nm wavelength for a cable TV overlay, creating the need for triplexers.

Smaller and less expensive                   The planar waveguide technology approach in PONs can win market share against the traditional fiber optic discrete devices because the parts are smaller and less expensive.  Planar waveguide technology aims to do for photonics what integrated circuits (ICs) did for electronics: take the market away from the bulky groups of circuitry and replace-it with products that are easy to replicate in mass quantities. The fact that PLCs can be inexpensive is particularly important given that cost has been a roadblock to past PON deployments. Planar technology allows a much tighter density of components given that all functions are performed on a single chip. The end result is a much smaller device and smaller footprint for the OEM manufacturer's equipment. This is a key metric for new systems as Central Office Space is in short supply.

Regional Overview: PWC Consumption Value          The global consumption value of planar waveguide circuits (PWCs) used in the production of selected packaged optical communication devices was $47.6 million in 2005 and is forecasted to reach $99.8 million in 2010 and $141.2 million in 2015.  North America will maintain its market share lead throughout the forecast period (2005-2015), growing in value from $19.6 million, or a relative market share of 41 percent, in 2005 to $60.5 million (41 percent) in year 2015, as shown in Figure 1.  The Japan/Pacific Rim region, with a consumption value of $19.2 million in 2005 and forecasted to reach $56.9 million in 2015 will remain a close second in relative market share throughout the forecast period. Europe will remain in a distant third place in relative market share with the Rest of World region as very distance last place in global PWC (PLC) market share.

Figure 1
PWC Global Consumption Market Forecast,
By Region (Value Basis, $ Million)
Source: ElectroniCast

PWC Global Market to Reach $141.2 Million in 2015           The worldwide consumption value of planar waveguide circuits (PWCs) used in optical communications was $47.6 million in 2005.  These PWCs, also known as planar lightwave circuits (PLCs) are forecasted to increase to $99.8 million in 2010 and $141.2 million in 2015.  PWCs are used in discrete devices (devices with one function only) or in integrated devices, which provide several functions (multifunction).  Initially, the discrete devices category leads in consumption value; however in year 2010, PWCs used in integrated multifunction devices takes the leading market share position, as shown in Figure 2.  PWCs used for planar coupler/splitter led the discrete device category with a consumption value of $18 million in 2005, followed by PWCs for variable optical attenuators (VOAs) with a consumption value of $11 million.  PWCs used for the manufacturing of devices that incorporate two or more functions (integrated multifunction devices) will eventually lead the PWC marketplace.

Figure 2
Planar Waveguide Circuits Global Consumption Value,
Discrete Devices & Integrated Multifunctional Devices ($, Million)
Source: ElectroniCast

Bell Labs, Lucent, developed a planar optical grating (array waveguide-AWG) for dense WDM.  This was developed under the leadership of Dr. C. Dragone, at the Crawford Hill, New Jersey Bell Laboratory, and accordingly designated the Dragone router.  Fabrication is by deposition of a layer of silica (glass), followed by masking and etching to form optical waveguides on a silicon wafer substrate.  The Dragone router provides for lower cost production, in large quantities, compared to other filter technologies.  Also, unlike gcascadedh multistage filters such as thin film and Bragg fiber gratings, the per-channel insertion loss does not increase greatly as the number of channels accommodated is increased. However, in common with all planar optical waveguide devices, it had cost and performance concerns related to interfacing the singlemode fibers to the substrate waveguides.

The strong growth in the use of DWDM techniques was substantially driven by AT&T's decision to upgrade their US terrestrial network by an order of magnitude capacity expansion through DWDM.

More than a decade ago, Bell Laboratories committed to the "silicon mount" as the base for precision optical assemblies.  They carried this into multifiber connectors, parallel optical interconnect components (the OETC consortium) and multichip module packaging.  They extended this to DWDM filters, in a design invented by Dr. C. Dragone.  This design formed a DWDM grating by precision deposition of silica (glass) to form optical waveguides on a silicon substrate. 

The array waveguide grating, as a filter, is a concept, which reportedly evolved from the gstarh optical coupler concept, invented by Will Hicks, an American Optical Corporation alumnus. (The star coupler patent was part of the intellectual property subsequently acquired by Polaroid Corporation.)  By interconnecting two star couplers via a number of optical waveguides of different lengths, the numerous wavelengths that are combined on the incoming fiber can be separated at the outputs of the second star coupler.

Figure 3:  AWG DWDM Filter
             Source: ElectroniCast


Optical Power Splitters                            Passive Optical Networks (PONs) connects one transceiver at the Telecommunications Central Office (CO) or the CATV Head-end to multiple end users through the distribution segment of the network infrastructure (optical distribution network/ODN) using optical power splitters. The optical line terminal (OLT), and the other end is an optical network unit (ONU), if the fiber is terminated directly at the end user. The ODN can use either a single fiber or separate fibers for upstream (1310 nm) and downstream transmission (1490 nm, which leaves the EDFA window from 1535 nm to 1560 nm). Industry standards mandate single-fiber networks with 1 ~ 32 splits. Single-fiber PONs use Time Division Multiplexing (TDM) broadcast mode for downstream and Time Division Multiple Access (TDMA) for upstream transmission.

The conventional way to achieve an optical power split is to fuse to fibers together. The technology is simple and offers acceptable results for low split counts like 1 ~ 2 or 1 ~ 4 or where insertion loss and uniformity are not an issue. In the emerging FTTPH architectures based on PON IL, PDL and uniformity are key parameters because they translate directly into system performance and network cost. In PLC-based power splitters, the cascaded fused fiber segments are replaced by a single PLC device.   For higher split counts like 1 ~ 8, 1 ~ 16, and 1 ~ 32, only PLC-based splitters meet the stringent performance objectives for FTTH networks.

The several process technologies for PLC splitters differ in their key parameters of insertion loss, uniformity, reliability and volume production cost. Certain network architectures require a second input port (2 ~ N configuration) to insert an overlay signal into a PON, for example, to combine a video overlay signal on the drop fiber to the customer location. PLC devices allow both 1 ~ N and 2 ~ N configurations.

PONs does not have active components in the outside plant. Therefore, power splitters have to maintain their performance and reliability over the entire industrial grade temperature range of ? 40‹ C to +85‹ C.   A common set of compliance tests that are used around the world are specified in Telcordia GR-1209/1221.  Both FSAN and IEEE provide detailed optical specifications for their respective FTTP transceiver categories.  FSAN specifications can be found in ITU-T G983.3 and G984.2 for BPON and GPON, respectively, and the IEEE specifications are listed in 802.3ah EFM.

The isolation level between the different transmission windows of a triplexer defines its performance in terms of physical reach and data rates, as well as BER and SNR ratios for digital and analog signals, respectively. The functional elements of a triplexer include one laser diode, two photo diodes, and one or several filter and focusing elements plus a fiber pigtail. Assembling a device out of that many discrete components represents a sizable challenge for low-cost manufacturing. Therefore, it is not surprising that the triplexer currently (2006) represents the most expensive component of the residential ONT.