Integrated wavelength selectable photodiode using tunable thin film filters

An integrated wavelength selectable photodiode includes a device package having an input that receives an optical signal. A set-and-hold, thermally tunable thin-film filter is positioned in the device package and includes an input that is optically coupled to the input of the device package. The set-and-hold, thermally tunable thin-film filter passes light with a predetermined optical bandwidth to an output. An optical element collimates an incident optical beam onto the input of the set-and-hold, thermally tunable thin-film filter. A detector is positioned in the device package and includes an input that is optically coupled to the output of the set-and-hold, thermally tunable thin-film filter. The detector detects data received by the integrated wavelength selectable photodiode.

The section headings used herein are for organizational purposes only and should not be construed as limiting the subject matter described in the present application.

BACKGROUND OF THE INVENTION

Demand for bandwidth is driving the expansion of optical transmission systems into homes and businesses of all sizes. Single wavelength fiber optic systems can support substantial data rates. However, services such as HDTV, on-demand TV programming, internet telephony, and telepresence are bandwidth intensive beyond the capabilities of many traditional networks. The present invention relates to integrated wavelength selectable photodiodes and their application to Fiber-To-The-X (FTTX) services. Fiber-To-The-X services refer to the extension of optical data transport into areas traditionally served by electrical communications systems, such as homes and small and medium sized businesses. Examples of FTTX systems are Fiber-To-The Home (FTTH), Fiber-To-The Curb (FTTC) and Fiber-To-The-Premises. FTTX architectures are also used for some highly secure optical communications links, such as radar tower interfaces.

DETAILED DESCRIPTION

The present teachings will now be described in more detail with reference to exemplary embodiments thereof as shown in the accompanying drawings. While the present teachings are described in conjunction with various embodiments and examples, it is not intended that the present teachings be limited to such embodiments. On the contrary, the present teachings encompass various alternatives, modifications and equivalents, as will be appreciated by those of skill in the art.

Those of ordinary skill in the art having access to the teachings herein will recognize additional implementations, modifications, and embodiments, as well as other fields of use, which are within the scope of the present disclosure as described herein. For example, although the integrated wavelength selectable photodiodes are described in connection Fiber-To-The-X (FTTX) services, it should be understood that the integrated wavelength selectable photodiodes according to the present invention can be used for any application.

Emerging demand for services, such as HDTV, on-demand programming, and telepresence services, has led data-service providers and system manufacturers to introduce PON architectures using DWDM to keep pace with demand in FTTX applications. Unfortunately, presently available wavelength-agile technologies used in DWDM backbone networks are not able to meet the severe cost constraints of an end-user market. Therefore, migration to multi-wavelength systems in FTTX has until now focused on DWDM-PON systems in which all wavelengths are broadcast to all receivers and a static filter is used to select the appropriate channel. See, for example, M. Abrams, et al., “FTTP Deployments in the United States and Japan—Equipment Choices and Service Provider Imperatives”, Journal of Lightwave Technology, vol. 23, no. 1, pp. 236-246, January 2005.

However, in order to fully realize the operational benefits of such DWDM-PON systems, the ability to dynamically provision wavelengths at both the ONU and ONT is needed. Tunable filters at the receiver have been identified as a possible solution to this challenge. See, for example, H. Suzuki, et al., “A Remote Wavelength Setting Procedure based on Wavelength Sense Random Access (λ-RA) for Power-Splitter-Based WDM-PON”, ECOC 2006, Paper We3.P.157. One aspect of the present invention relates to a dynamically reconfigurable receiver based on a tunable filter.

Recent standards issued by the International Telecommunications Union (ITU) standards organization have established the “enhancement band,” which is a range of wavelengths between 1550 and 1560 nm for use in DWDM PON systems. The use of the term “enhancement band” refers to any wavelength that may be used with the present invention to increase transmission bandwidth and should not be construed as limiting the scope of present invention to function within only the aforementioned wavelength range.

One aspect of the present invention relates to low-cost, reliable and manufacturable hardware solutions for enabling flexibility in FTTX networks. In some embodiments, these hardware solutions make use of this enhancement band. Optoelectronic components according to the present invention enable flexible high-bandwidth network architectures. In some embodiments, optoelectronic components according to the present invention are available to enable wavelength control at or near the end user node with minimal cost.

More specifically, a system according to the present invention is capable of selecting a single wavelength from an optical fiber carrying a plurality of wavelengths. In addition, the detector also detects data carried in the optical signal and converts the data to electrical signals. The electrical signals can then be routed to network devices in a desired manner. For example, the electrical signals can be routed to network devices within a home or can be routed to a larger distribution point upstream in the network. In many embodiments, the detector can be manufactured for very low cost.

An integrated wavelength selectable photodiode according to the present invention can achieve a sufficient dynamic selection of wavelengths for many applications, with relatively small size and at a relatively low cost by using tunable thin-film filters. In many applications, these tunable thin-film filters are formed of semiconductor materials, such as hydrogenated amorphous silicon.

FIG. 1Aillustrates a block diagram of an integrated wavelength selectable photodiode100according to the present invention. An optical source101is shown that generates an optical beam102in the direction of the wavelength selectable photodiode100. In some embodiments, the optical source101includes a single or multimode optical fiber that guides an optical beam through an end of the optical fiber. In these embodiments, the optical fiber may be combined with the lens, or other beam-shaping optical element103that is positioned near the end of the optical fiber. Alternatively the optical fiber can be incorporated into a monolithic lensed fiber tip. In other embodiments, the optical source is a free-space optical source that is suitable for use in point-point free-space optical communications links.

The wavelength selectable photodiode100also includes an optical element103that shapes and steers the optical beam. In various embodiments, the optical element103can be positioned inside and/or outside the package109. The optical element103shapes the optical beam into a collimated optical beam104. In one embodiment, the optical element103is a low-cost molded reflective (mirror) or refractive (lens) optical device. In some embodiments, the optical element103and the component package are molded as one integrated unit. Also, in some embodiments, the optical element103includes a plurality of individual lens elements. An optical isolator can be positioned between the optical source101and the optical element103to reduce the intensity of reflections that are coupled back into the optical source.

The wavelength selectable photodiode100also includes a tunable optical bandpass filter105that is positioned in the optical path of the collimated optical beam104. The optical element103directs the collimated optical beam to the input of the tunable optical bandpass filter105. The filter105is tuned (set) to the chosen signal wavelength so that only the desired optical signal passes through the filter105, while other signals with wavelengths outside its passband are blocked. The filter may be operated in a manner such that it remains fixed (held) at the set wavelength. The tunable optical bandpass filter105transmits a filtered optical signal106.

The tunable optical bandpass filter105can be constructed in many ways. In one embodiment, the tunable optical bandpass filter105is a thin film filter formed of semiconductor films, such as amorphous silicon and silicon nitride thin films. Such films can be manufactured using Plasma Enhanced Chemical Vapor Deposition (PECVD). One advantage of using PECVD is that the resulting films can have relatively low stress and defect density which make the films highly stable and reliable.

The tunable optical bandpass filter105is tunable in wavelength. In one embodiment, the tunable optical bandpass filter is tuned thermally. In this embodiment, the tunable optical bandpass filter105can include an integrated heater element, such as a sheet heater. The peak transmission wavelength of a tunable bandpass filter is changed by changing the current applied to the integrated heater element. There are numerous ways of making the tunable optical bandpass filter105. The geometry of the substrate and film structure may make use of, island structures, and other known geometries which have thermal management properties that improve filter performance and/or lifetime.

There are numerous ways to construct the tunable filter stack in order to optimize the shape of the filter bandpass and the filter performance parameters, such as insertion loss. In some embodiments, the filter includes only one cavity. In other embodiments, the tunable filter stack is a multiple-cavity structure. Using multiple-cavity structures provide substantial flexibility to optimize the filter bandpass shape and performance for particular applications.

The wavelength selectable photodiode100also includes a high-speed photodiode107that is positioned to receive the filtered optical signal106at an input. The high-speed photodiode107converts the filtered optical signal into a corresponding electrical signal. The high-speed photodiode107is chosen to respond in the wavelength range of interest. For example, an indium gallium arsenide photodiode can be used for DWDM telecommunications applications where optical wavelengths in the range of 1.5-1.6 μm must be detected.

The high-speed photodiode107can be operated with a reverse bias voltage in order to minimize capacitance and maximize frequency response for applications that require electrical bandwidths which are greater than a few hundred MHz. In some embodiments, electrical conditioning and/or electrical amplification circuitry are used to process the signals generated by the high-speed photodiode107in order to improve signal integrity. The electrical conditioning and/or electrical amplification circuitry can be integrated on the same die as the photodiode107.

In some embodiments, the high-speed photodiode107is positioned to minimize the amount of thermal radiation from the tunable optical bandpass filter105that is incident on the high-speed photodiode107. For example, in one specific embodiment where the tunable optical bandpass filter105comprises a filter element and a sheet heater, the filter element can be positioned between the high-speed photodiode107and the sheet heater.

In some embodiments, a package109houses the various components of the wavelength selectable photodiode101. The package109protects the components. Also, the package109can provide an interface to a printed circuit board assembly (PCBA)108. The PCBA108can redirect electrical signals from the component package to a host board where the output of the high-speed detector107is processed for data content and monitored for feedback control of the tunable filter. The PCBA108can be designed to minimize noise and electrical attenuation at high frequencies. Amplification and conditioning circuitry may be incorporated into the PCBA108.

The component package109must provide both optical and electrical access to the devices while offering protection from contaminants. The component package109may be hermetically sealed to maximize protection for the active subcomponents. To enable low-cost, high-volume manufacturing, molded plastic and/or ceramics may be used, as well as chip-scale packaging. For example, see U.S. Pat. No. 6,985,281, which is assigned to the present assignee. The complete wavelength selectable photodiode can be relatively small in size and relatively low-cost because thousands of tunable filters are simultaneously fabricated on a single wafer.

In one embodiment, the component package109is a standard TO46 package, which is widely used in the industry. Such a package is relatively small and inexpensive. In various other embodiments, the component package109is smaller than a TO46 package. One aspect of the present invention is that a thermally tunable filter and a detector can be integrated into a relatively small package. Prior art devices that include mechanically tunable filters are too large to fit into such packages. Mechanically tunable filters are typically much larger than thermally tunable thin-film filters.

The wavelength selectable photodiode with a tunable, thin-film filter according to the present invention can detect data propagating in a single optical channel by using a thermally tunable, thin-film filter comprising various types of semiconductor films, such as silicon films, and/or various types of dielectric films, such as silicon nitride. The thermally tunable, thin-film filter isolates the spectral region of interest from optical signals or noise at other wavelengths. This isolated optical signal can then be detected by a high-frequency detector.

In operation, the optical source101provides an optical beam to the input of the optical element103. The optical element103collimates and directs the optical beam to the input of the tunable filter105. The tunable filter105is adjusted to the desired wavelength so as to pass the desired optical bandwidth. The high-speed detector107detects the desired optical beam.

In some embodiments, the tunable filter105is a set-and-hold type filter. In this embodiment, the tunable filter105can be set to any wavelength within a range defined by its starting wavelength and the maximum reliable operating temperature for its constituent materials. The tunable filter105may then be held at the set wavelength.

In some embodiments, the tunable filter105may be locked to the wavelength of interest using a feedback control loop which monitors the DC power level of the signal, or by using any one of numerous other servo-locking techniques known in the art. For example, a tunable filter can be locked to any channel within a range by stepping the drive power up and down and monitoring the signal intensity transmitted by the tunable filter to the photodetector (dither control). Thermally tunable filters work well in channel-locking applications. In contrast, mechanical structures are not ideal for dithering applications where they may rapidly age from repeated cycling.

In other embodiments, the tunable filter105is operated in a mode where it is scanned across the optical spectrum of interest to determine which channels are present, and to measure the power in each channel. A tunable filter manufactured by Aegis Lightwave, the assignee of the present invention, can be used in such a mode of operation.

The wavelength selectable photodiode of the present invention is well suited for applications that use multi-wavelength transmission architectures to transmit analog and/or digital signals. One particular application is where multiple data streams propagating on a single wavelength are provided to homes. In this application, the wavelength selectable photodiode of the present invention can be used to select from among these multiple data streams.

FIG. 1Billustrates a block diagram of an integrated wavelength selectable photodiode120according to the present invention with an integrated transmitter131. The integrated wavelength selectable photodiode120is similar to the integrated wavelength selectable photodiode100described in connection withFIG. 1A. However, the splitter/combiner130and a transmitter131are included. In various embodiments, the transmitter131can be a fixed wavelength transmitter or a tunable transmitter.

FIG. 1Cillustrates a schematic diagram of an integrated wavelength selectable photodiode150according to the present invention that includes a thermally tunable filter152which has reduced thermal noise and an increased signal-to-noise ratio. The integrated wavelength selectable photodiode150includes a thermally tunable filter152having a supporting substrate154and a filter stack156that includes various layers of thin film material that form an optical filter. In addition, the thermally tunable filter152includes a heater layer158that controls the temperature and, therefore, the transmission properties of the filter stack156. In one embodiment, the thermally tunable filter152is a set-and-hold filter. The integrated wavelength selectable photodiode150also includes a photodiode detector160that detects the filtered optical signal.

In operation, the incident optical signal162is filtered by the filter stack156and only the desired center wavelength and bandwidth of the thermally tunable filter152is passed through the filter stack156. The temperature generated by the heater layer158defines the desired center wavelength and bandwidth. The filtered optical signal164with the desired center wavelength and bandwidth is then transmitted to the photodiode detector160.

By positioning the thermally tunable filter152between the heater layer158and the photodiode detector160, the amount of thermal radiation reaching the photodiode detector160is reduced. This configuration reduces the resulting noise substantially compared to a configuration where there is a transparent substrate between the heater layer158and the photodiode detector160. When the heater layer158is at operating temperature, it emits blackbody radiation according to Planck's law. The blackbody radiation has two effects on the photodiode detector160. First, the blackbody radiation adds to the background noise level of the optical signal because there is usually some emission in the wavelength range where the photodiode detector160is sensitive. Second, the blackbody radiation causes the temperature of the photodiode detector160to rise, resulting in increased thermal (Johnson) noise.

FIG. 1Dillustrates a schematic diagram of another embodiment of an integrated wavelength selectable photodiode180according to the present invention that includes a thermally tunable filter which has reduced thermal noise and an increased signal-to-noise ratio. The integrated wavelength selectable photodiode180is similar to the integrated wavelength selectable photodiode150that was described in connection withFIG. 1C.

The integrated wavelength selectable photodiode180includes a thermally tunable filter182having a supporting substrate184and a filter stack186that includes various layers of thin film material that form an optical filter. In addition, the thermally tunable filter182includes a heater layer188that control the temperature and, therefore, the transmission properties of the filter stack186. In one embodiment, the thermally tunable filter182is a set-and-hold filter. The integrated wavelength selectable photodiode180also includes a photodiode detector190that detects the filtered optical signal.

In addition, the integrated wavelength selectable photodiode180includes a blocking material192that masks the edges of the heater layer188from the photodiode detector190. The blocking material192further reduces the amount of unfiltered radiation that reaches the photodiode detector190. The blocking material192could be any material that provides a thermal barrier and which also absorbs optical radiation in the wavelength range where the photodiode detector190is sensitive. The blocking material192reduces the amount of black body radiation from the heater layer188that is incident on the photodiode detector190.

The operation of the integrated wavelength selectable photodiode180is similar to the operation of the integrated wavelength selectable photodiode150shown inFIG. 1C. The incident optical signal194is filtered by the filter stack186and only the desired center wavelength and bandwidth of the thermally tunable filter182is passed through the filter stack186. The temperature generated by the heater layer188defines the desired center wavelength and bandwidth. The filtered optical signal196with the desired center wavelength and bandwidth is then transmitted to the photodiode detector160.

FIG. 2Aillustrates a perspective view of a relatively low-cost package250for a wavelength selectable photodiode according to the present invention that includes molded reflective optics. The package250can be used instead of a conventional manufactured component housing and circuit board assembly, which is much more expensive to manufacture.

The package250includes a fiber holder/lens element252.FIG. 2Billustrates the fiber holder/mirror element252in the low-cost package shown inFIG. 2A.FIG. 2B-1illustrates a cross-sectional view of the fiber holder/mirror element252ofFIG. 2Bthat shows a V-groove structure that holds the fiber/lens element securely in place.FIG. 2B-2shows a top cross-sectional view of the fiber/mirror element ofFIG. 2B.FIG. 2B-3shows a side cross-sectional view of the fiber/mirror element ofFIG. 2B. The fiber holder/mirror element252can be formed of metallized plastic, ceramic, micro-machined silicon (or glass) or any combination of these materials. For example, in one embodiment, the fiber holder/mirror element252is fabricated from low-cost, molded plastic. The area in front of the fiber optic is metallized to provide optimal performance when steering and shaping the optical beam.

In some embodiments, a separate spacer element254is used to isolate the fiber holder/mirror element252. In other embodiments, the spacer element254is integrated into the fiber holder/lens element252or integrated into some other structure, such as the filter.FIG. 2Cillustrates a cross-sectional view of a spacer element254that can be used with the low-cost package250shown inFIG. 2A.FIG. 2C-1shows a cross-sectional view of line A-A through the spacer element254shown inFIG. 2C.

The package250also includes an integrated filter chip256. In one embodiment, the integrated filter chip256is a membrane structure comprising an optical filter.FIG. 2Dillustrates a cross-sectional view of an integrated filter chip256that can be used with the low-cost package250shown inFIG. 2A. The integrated filter chip256shown inFIG. 2Dincludes electrically conductive vias that pass current directly through the filter chip256.FIG. 2D-1illustrates a cross-sectional view of the integrated filter chip256shown inFIG. 2D, along line A-A. The top surface comprises the free-standing, thin-film filter membrane which remains after the substrate has been etched away beneath the filter.FIG. 2D-2illustrates a cross-sectional view of the integrated filter chip256shown inFIG. 2Dalong line B-B.

In addition, the low-cost package250includes an electronics enclosure that supports electronic devices, such as amplification and filtering circuitry. Also, the electronics enclosure includes the necessary signal routing transmission lines to connect to the tunable filter.FIG. 2Eillustrates a cross-sectional view of an electronics enclosure258that can be used with the low-cost package250shown inFIG. 2A.

FIG. 3illustrates a block diagram of an embodiment of an optical network unit that includes a wavelength selectable photodiode according to the present invention that can provide premium services to a subscriber.FIG. 3illustrates a block diagram of a DWDM PON optical network unit (ONU)300which includes a wavelength selectable photodiode302according to the present invention. The ONU300includes an enhancement-band filter301that directs wavelengths of light outside of the enhancement band to a first receiver303which in some embodiments may be contained in a diplexer308along with a transmitter306. A diplexer is a well known device that processes signals having different wavelengths. The wavelengths within the enhancement band are directed to the wavelength selectable photodiode302. The tunable filter304passes only the desired wavelength from within the enhancement band to a second receiver305.

In one embodiment of the optical network unit300, a transmitter306is included in the package as part of the diplexer308. Numerous types of transmitters can be used. In some embodiments, the transmitter306is a fixed-wavelength transmitter. In other embodiments, the transmitter306is a tunable-wavelength transmitter. Using a tunable-wavelength transmitter improves the flexibility of the optical network unit300.

A wavelength splitter/combiner309is used to couple the transmitter306to the optical fiber307in optical network units that propagate transmit and receive signals which have different wavelengths outside of the enhancement band. In optical network units where transmit and receive signals outside of the enhancement band are at the same wavelength, a simple power splitter/combiner may be used in place of the wavelength splitter/combiner309. In one particular embodiment, the optical network unit300propagates downstream signal wavelengths near 1490 nm and upstream signal wavelengths near 1310 nm in addition to the wavelengths within the enhancement band.

In one embodiment, these components are used in a central office configuration. In the central office configuration, return signals from multiple ONUs are received by one or more Optical Line Terminations (OLTs). This embodiment is useful for applications requiring symmetric (equal transmit and receive) bandwidths.

In another mode of operation, the diplexer308sends signals to the optical line terminal at the service provider's central office to request a DWDM wavelength. The wavelength selectable photodiode302is then tuned to the wavelength designated by the optical line terminal. An on-demand download or other premium service is then transmitted by the optical line terminal and is received by the wavelength selectable photodiode302where it is passed to the receiver305. For example, large movie files can be downloaded to a computer or DVR system. The diplexer308then signals the optical line terminal to release the wavelength after the download is complete.

Such architectures allow the receiver403to operate at full speed. Therefore, the architecture presented herein with the wavelength selectable photodiode305more efficiently uses the receiver bandwidth compared with prior art architectures that provide only a slotted amount of time for downloads or other premium services. In other words, such architectures provide the subscriber with full bandwidth downloads. Also, the architecture presented herein with the wavelength selectable photodiode305provides efficient use of optical line terminals so fewer optical line terminals can be used and/or optical line terminals can be brought on-line and taken off line as necessary. In another embodiment, the optical network unit shown inFIG. 3can be configured to provide access to a shared high-bandwidth express download wavelength on demand.

FIG. 4illustrates a block diagram of another embodiment of the optical network unit400which includes a wavelength selectable photodiode402according to the present invention that can provide premium services to subscribers. The optical network unit400includes an enhancement band filter401with a passive splitter that is connected to an upgrade port407. The enhancement band filter401passes a predetermined band of incoming optical signals to the upgrade port407. If the subscriber has purchased a premium service, the premium service signals are coupled via an optical connection, which in some embodiments is an optical fiber, to a wavelength selectable photodiode402and then to a receiver403.

In addition, the optical network unit400includes a diplexer406. In various embodiments, the optical network unit400is electrically connected to the wavelength selectable photodiode402. A diplexer is a well-known device that processes signals having different wavelengths. In the embodiment shown inFIG. 4, the 1490 nm optical signal is received from the optical network and is passed by the enhancement band filter401to the diplexer406. The 1490 nm optical signal can be used for control and monitoring functions as well as for basic video and data services. The 1310 nm optical signal is generated by a transmitter in the diplexer406and then passed from the diplexer406through the enhancement band filter401and then back through the optical network to an optical line terminal (OLT) which may be located at a central office.

In one embodiment, the optical network unit400is used in a passive optical network architecture. Such passive optical network architectures use un-powered components to enable a single optical fiber to serve multiple subscribers. The diplexer406enables the optical network unit400to communicate with an optical line terminal at the service provider's central office. These PON network architectures reduce the amount of fiber and central office equipment required compared with point-to-point architectures.

FIG. 5illustrates a block diagram of another embodiment of the optical network unit500which includes a wavelength selectable photodiode502according to the present invention that can be configured as a symmetric point-to-point link. The optical network unit500may also include an enhancement-band filter501similar to the enhancement-band filter401described in connection withFIG. 4. The enhancement-band filter501passes a predetermined band of incoming optical signals to the wavelength selectable photodiode502where they are filtered by the tunable filter504and then passed to the receiver503.

In embodiments where an enhancement band filter is used, the optical network unit500also includes the diplexer506that was shown inFIGS. 3 and 4. The diplexer506can provide signals that are transmitted back to the optical line terminal at the service provider's central office to request certain transmissions or certain services. However, the diplexer506is not necessary in the embodiment shown inFIG. 5.

In addition, the optical network unit500includes a tunable transmitter508that transmits signals back to the optical line terminal at the service provider's central office. The tunable transmitter508is a dedicated transmitter that provides a way to transmit high-bandwidth signals back to the service provider's central office. There are many applications which require a dedicated transmitter, such as the transmitter508. Such transmitters can provide symmetric bandwidth for enterprise applications. In some applications, such dedicated transmitters include a Reflective Silicon Optical Amplifier (RSOA) that receives incoming signals from the service provider and amplifies and re-modulates them before returning them to the service provider's optical line terminal. This allows the tunable transmit/receiver module510to operate without an internal optical source. In some applications, the signals transmitted back to the service provider's central office are then re-transmitted to a third party. For example, the optical network unit500can be used for teleconferencing or high bandwidth telepresence applications. Applications, such as teleconferencing and telepresence, can have symmetric bandwidth requirements.

FIG. 6shows an embodiment of an optical network unit that provides subscribers with optional personalized high-definition (HD) video channels in addition to standard broadcast channels. The optical network unit600consists of an enhancement band splitter601, a diplexer606and a wavelength selectable photodiode602with integrated tunable filter603and receiver604. Signals from the receiver604may be output via a coaxial connection605.

One method of operation for the embodiment of the optical network unit shown inFIG. 6allows one wavelength to be shared among all subscribers that contains a standard package of broadcast channels. In the example shown inFIG. 6, each of 32 subscribers may choose up to 3 channels of personalized video, which requires only one wavelength. More than 3 personalized channels per subscriber will require the addition of wavelengths to provide sufficient bandwidth as shown in this example. The diplexer is used to handle standard data services as well as configuration and OLT communication tasks. Such a configuration allows highly personalized video content to be dynamically selected by and delivered to subscribers.

FIG. 7illustrates a tunable-receiver multiplexer700comprising integrated wavelength selectable photodiodes according to the present invention. The tunable multiplexer700includes an input/output port706and first dichroic beam splitter701that splits the input optical beam into two wavelength ranges. In addition, the tunable multiplexer700includes a second beam splitter705that passes the input optical signal and transmits an output optical signal.

In addition, the tunable-receiver multiplexer700includes a first702and a second integrated wavelength selectable photodiode703according to the present invention. These integrated wavelength selectable photodiodes702,703replace static receivers in many known multiplexers. In addition, the tunable-receiver multiplexer700includes a transmitter704. The tunable-receiver multiplexer700is commonly known as a triplexer because it processes three signals. However, one skilled in the art will appreciate that a tunable-receiver multiplexer according to the present invention can process any number of signals.

FIG. 8illustrates a tunable diplexer800comprising an integrated wavelength selectable photodiode according to the present invention. The diplexer800is one embodiment of the tunable-receiver multiplexer700that was described in connection withFIG. 7. The diplexer includes an input output port802and a beam splitter804. In addition, the diplexer includes an integrated wavelength selectable photodiode806and a transmitter that are optically coupled to respective ports of the beam splitter804.

Such a tunable diplexer800is well suited for FTTX applications and can directly replace known static diplexers to allow network provisioning. Because the integrated wavelength selectable photodiode806can be manufactured in a standard TO46 package, it can be drop-in replacement for prior art static receives.

EQUIVALENTS

While the present teachings are described in conjunction with various embodiments and examples, it is not intended that the present teachings be limited to such embodiments. On the contrary, the present teachings encompass various alternatives, modifications and equivalents, as will be appreciated by those of skill in the art, may be made therein without departing from the spirit and scope of the invention.