HK1139236B - Integrated wavelength selectable photodiode using tunable thin-film filters - Google Patents

Description

Integrated wavelength selectable photodiode using tunable thin film filters

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

Related applications section

This application claims priority to U.S. provisional patent application serial No. 60/891,647, entitled "Integrated wavelet selective telephonic use a flexible Filter", on 26.2.2007. This application claims priority to U.S. provisional patent application serial No. 60/971,247, entitled "wavelet selective photo diode Using a Tunable Filter", on 10.9.2007. The entire specification of U.S. provisional patent application serial No. 60/891,647 and U.S. provisional patent application serial No. 60/971,247 are incorporated herein by reference.

Technical Field

The demand for bandwidth has prompted the spread of optical transmission systems to all types of homes and businesses. Single wavelength fiber systems can support substantial data rates. However, services such as HDTV, video-on-demand TV programming, internet telephony, and telepresence (telepresence) require bandwidth beyond the capabilities of many existing networks. The present invention relates to integrated wavelength selectable photodiodes and their application to fiber-to-x (fttx) traffic. fiber-to-X service refers to the expansion of optical data transmission into areas traditionally served by electrical communication systems, such as homes and small and medium-sized businesses. Examples of FTTX systems are fiber-to-home (FTTH), fiber-to-street (FTTC), and fiber-to-building. FTTX architectures are also used for certain highly reliable optical communication links, such as radar tower interfaces.

Drawings

Aspects of the invention may be better understood by referring to the following description in conjunction with the accompanying drawings. The same or similar elements in the drawings may be designated by the same reference numerals. Detailed descriptions about these similar elements may not be repeated. The drawings are not necessarily to scale. The skilled artisan will appreciate that the drawings described below are for illustration purposes only. The drawings are not intended to limit the scope of the present teachings in any way.

Fig. 1A illustrates a block diagram of an integrated wavelength selectable photodiode according to the present invention.

Fig. 1B illustrates a block diagram of an integrated wavelength selectable photodiode with an integrated transmitter 131 in accordance with the present invention.

Fig. 1C illustrates a schematic diagram of an integrated wavelength selectable photodiode according to the present invention that includes a thermally tunable filter that has been installed in a configuration in which reduced thermal noise and increased signal-to-noise ratio are obtained at the detector.

FIG. 1D illustrates a schematic diagram of another embodiment of an integrated wavelength selectable photodiode according to the present invention that includes a thermally tunable filter with reduced thermal noise and increased signal-to-noise ratio.

FIG. 2A illustrates a perspective view of a relatively low cost package for a wavelength selectable photodiode including molded reflective optics in accordance with the present invention.

FIG. 2B illustrates the fiber holder/mirror element in the low cost package shown in FIG. 2A.

FIG. 2B-1 illustrates a cross-sectional view of the fiber optic holder/mirror element of FIG. 2B showing a V-groove configuration that securely holds the fiber optic/mirror element in place.

Fig. 2B-2 shows a top cross-sectional view of the fiber/mirror element of fig. 2B.

Fig. 2B-3 show side cross-sectional views of the fiber/mirror element of fig. 2B.

Fig. 2C illustrates a cross-sectional view of a spacer element that may be used with the low-cost package shown in fig. 2A.

Fig. 2C-1 shows a cross-sectional view through line a-a of the spacer element shown in fig. 2C.

Fig. 2D illustrates a cross-sectional view of an integrated filter chip that may be used with the low-cost package shown in fig. 2A.

Fig. 2D-1 illustrates a cross-sectional view of the integrated filter chip shown in fig. 2D along line a-a.

Fig. 2D-2 illustrates a cross-sectional view of the integrated filter chip shown in fig. 2D along line B-B.

Fig. 2E illustrates a cross-sectional view of an electronic device housing that may be used with a low-cost package.

Figure 3 illustrates a block diagram of an embodiment of an optical network unit that can provide premium services to subscribers including a wavelength selectable photodiode according to the present invention.

Figure 4 illustrates a block diagram of another embodiment of an optical network unit that includes a wavelength selectable photodiode according to the present invention that can provide an upgrade port to upgrade a subscriber's services.

Figure 5 illustrates a block diagram of another embodiment of an optical network unit that may be configured as a symmetric point-to-point link including a wavelength selectable photodiode according to the present invention.

Figure 6 illustrates an embodiment of an optical network unit that provides subscribers with an optional personalized High Definition (HD) video channel in addition to a standard broadcast channel.

Fig. 7 illustrates a tunable-receiver multiplexer including an integrated wavelength selectable photodiode according to the present invention.

Figure 8 illustrates a tunable diplexer comprising an integrated wavelength selectable photodiode according to the present invention.

Detailed Description

Reference in the specification to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment.

It should be understood that the steps of the methods of the present invention may be performed in any order and/or simultaneously as long as the invention remains operable. Further, it should be understood that the apparatus and methods of the present invention can include any number or all of the described embodiments, so long as the invention remains operable.

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

Those of skill in the art having access to the present 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, while the integrated wavelength selectable photodiode is described in connection with fiber-to-x (fttx) traffic, it should be understood that the integrated wavelength selectable photodiode according to the present invention may be used in any application.

The emerging service demands, such as HDTV, on-demand programming and telepresence services, have led data service providers and system manufacturers to introduce PON architectures using DWDM to keep up with the demands in FTTX applications. Unfortunately, the currently available wavelength-agile technologies for DWDM backbone networks do not meet the stringent cost constraints of the end-user market. Thus, the change to multi-wavelength systems in FTTX has not until now focused on DWDM-PON systems where all wavelengths are broadcast to all receivers and static filters are used to select the appropriate channel. See, for example, M.Abrams et al, "FTTPDeployments in the United States and Japan-Equipment Christesses and service Provider improvements," Journal of Lightwave technology, vol.23, No.1, pp.236-246, month 1 2005.

However, in order to fully realize the operational advantages of such DWDM-PON systems, the ability to dynamically specify wavelengths at the ONUs and ONTs is required. Tunable filters for receivers 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 hSense Random Access (λ -RA) for Power-Splitter-Based WDM-PON", ECOC 2006, Paper We3. P.157. One aspect of the invention relates to a dynamically reconfigurable receiver based on tunable filters.

Recent standards promulgated by the International Telecommunications Union (ITU) standards organization establish "enhanced frequency bands" which are a range of wavelengths between 1550 and 1560nm 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 to limit the scope of the present invention to function only within the aforementioned wavelength range.

One aspect of the present invention relates to a low cost, reliable and manufacturable hardware solution for allowing flexibility in FTTX networks. In some embodiments, these hardware solutions utilize the enhancement band. The opto-electronic component according to the invention allows a flexible high bandwidth network architecture. In some embodiments, an optoelectronic assembly in accordance with the present invention can be used to allow wavelength control at or near an end user node at minimal cost.

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

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

Fig. 1A illustrates a block diagram of an integrated wavelength selectable photodiode 100 in accordance with the present invention. A light source 101 is shown which generates a light beam 102 in the direction of a wavelength selectable photodiode 100. In certain embodiments, light source 101 comprises a single mode or multimode optical fiber that directs a light beam through the end of the optical fiber. In these embodiments, the optical fiber may be combined with a lens, or other beam shaping optical element 103, located near the end of the optical fiber. Alternatively, the optical fiber may be incorporated into a single lens fiber tip. In other embodiments, the light source is a free space light source suitable for use with a point-to-point free space optical communication link.

The wavelength selectable photodiode 100 also includes an optical element 103 that shapes and orients (steer) the light beam. In various embodiments, the optical element 103 may be located inside and/or outside the package 109. The optical element 103 shapes the light beam into a collimated light beam 104. In one embodiment, the optical element 103 is a low cost molded reflective (mirror) or refractive (lens) optic. In some embodiments, the optical element 103 and the component package are molded as one integrated unit. Also, in certain embodiments, the optical element 103 includes a plurality of individual lens elements. An optical isolator may be located between the light source 101 and the optical element 103 to reduce the intensity of the reflection coupled back into the light source.

The wavelength selectable photodiode 100 also includes a tunable optical bandpass filter 105 located in the optical path of the collimated beam 104. The optical element 103 directs the collimated beam to the input of the tunable optical bandpass filter 105. The filter 105 is tuned (set) to a selected signal wavelength such that only the desired optical signal passes through the filter 105 while other signals having wavelengths outside its pass band are blocked. The filter may be operated in such a way that it remains fixed (held) at the set wavelength. The tunable optical bandpass filter 105 transmits a filtered optical signal 106.

The tunable optical bandpass filter 105 may be constructed in a variety of ways. In one embodiment, the tunable optical bandpass filter 105 is a thin film filter formed of a semiconductor film such as amorphous silicon and silicon nitride thin films. Such films may be fabricated using Plasma Enhanced Chemical Vapor Deposition (PECVD). One advantage of using PECVD is that the resulting thin film can have a relatively low stress and defect density, which makes the film highly stable and reliable.

The tunable optical bandpass filter 105 is wavelength tunable. In one embodiment, the tunable optical bandpass filter is thermally tuned. In this embodiment, the tunable optical bandpass filter 105 may include an integrated heater element, such as a thin plate heater. The peak transmission wavelength of the tunable bandpass filter is changed by changing the current applied to the integrated heater element. There are many ways to fabricate the tunable optical bandpass filter 105. The geometry of the substrate and thin film structures may utilize island structures, as well as other known geometries having thermal management properties that improve filter performance and/or lifetime.

There are a number of ways to construct tunable filter stacks to optimize the shape of the filter bandpass and 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 multi-cavity structure. The use of a multi-cavity structure provides substantial flexibility in optimizing the filter bandpass shape and performance for a particular application.

The wavelength selectable photodiode 100 also includes a high speed photodiode 107 configured to receive the filtered optical signal 106 at an input. The high-speed photodiode 107 converts the filtered optical signal into a corresponding electrical signal. The high speed photodiode 107 is selected to respond in the wavelength range of interest. For example, indium gallium arsenide photodiodes may be used in DWDM telecommunications applications where optical wavelengths in the range of 1.5-1.6 μm must be detected.

For applications requiring electrical bandwidths greater than a few hundred MHz, the high speed photodiode 107 can be operated with a reverse bias to minimize capacitance and maximize frequency response. In certain embodiments, electrical conditioning and/or electrical amplification circuitry is used to process the signal generated by the high speed photodiode 107 to improve signal integrity. The electrical conditioning and/or electrical amplification circuitry may be integrated on the same die as the photodiode 107.

In certain embodiments, the high-speed photodiode 107 is configured to minimize the amount of thermal radiation from the tunable optical bandpass filter 105 that is incident on the high-speed photodiode 107. For example, in one particular embodiment where the tunable optical bandpass filter 105 includes a filter element and a thin plate heater, the filter element may be located between the high speed photodiode 107 and the thin plate heater.

In some embodiments, the package 109 houses various components of the wavelength selectable photodiode 101. The package 109 protects these components. Also, the package 109 may provide an interface to a Printed Circuit Board Assembly (PCBA) 108. The PCBA 108 can redirect electrical signals from the component package to the motherboard where the output of the high speed detector 107 is processed for data content and the output of the high speed detector 107 is monitored for feedback control of the tunable filter. The PCBA 108 may be designed to minimize noise and electrical attenuation at high frequencies. The amplification and conditioning circuitry may be incorporated into the PCBA 108.

The component package 109 must provide optical and electrical access to the device while providing protection from contaminants. The assembly package 109 may be hermetically sealed to maximize protection for the active sub-assemblies. Molded plastic and/or ceramic, and chip-scale packaging (chip-scale packaging) may be used to allow low cost mass production. See, for example, U.S. patent application No. 6,985,281, assigned to the present assignee. The finished wavelength selectable photodiode can be relatively small in size and relatively low cost because thousands of tunable filters are fabricated simultaneously on a single wafer.

In one embodiment, the component package 109 is a standard TO46 package widely used in the industry. Such a package is relatively small and inexpensive. In various other embodiments, the component package 109 is smaller than the TO46 package. One aspect of the present invention is that the thermally tunable filter and detector may be integrated into a relatively small package. Prior art devices including mechanically tunable filters are too large to fit into such packages. Mechanically tunable filters are typically much larger than thermally tunable thin film filters.

A wavelength selectable photodiode having 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 including various types of semiconductor thin 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. The isolated optical signal may then be detected by a high frequency detector.

In operation, the light source 101 provides a light beam to the input of the optical element 103. The optical element 103 collimates and directs the optical beam to the input of the tunable filter 105. The tunable filter 105 is tuned to a desired wavelength to pass a desired optical bandwidth. The high speed detector 107 detects the desired beam.

In some embodiments, the tunable filter 105 is a set-and-hold type (set-and-hold) filter. In this embodiment, tunable filter 105 may 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 filter 105 may then be held at the set wavelength.

In some embodiments, tunable filter 105 may be locked to the wavelength of interest using a feedback control loop that monitors the DC power level of the signal, or by using any of a number of other servo locking techniques known in the art. For example, the tunable filter can be locked to any channel within a certain range by adjusting the drive power up and down in stages and monitoring the signal strength sent by the tunable filter to the photodetector (dither control). The thermally tunable filter works well in channel lock applications. In contrast, mechanical structures are not ideal for dithering applications where they may age quickly due to repeated cycling.

In other embodiments, tunable filter 105 operates in a mode in which it scans across the spectrum of interest to determine which channels are present and measures the power in each channel. A tunable filter manufactured by Aegis Lightwave, the assignee of the present invention, may be used in this mode of operation.

The wavelength selectable photodiode of the present invention is well suited for applications using a multi-wavelength transmission architecture for transmitting analog and/or digital signals. One particular application is to provide multiple data streams, propagating on a single wavelength, to a home. In this application, the wavelength selectable photodiode of the present invention can be used to select from the plurality of data streams.

Fig. 1B illustrates a block diagram of an integrated wavelength selectable photodiode 120 with an integrated transmitter 131 in accordance with the present invention. The integrated wavelength selectable photodiode 120 is similar to the integrated wavelength selectable photodiode 100 described with respect to fig. 1A. However, a splitter/combiner 130 and a transmitter 131 are included. In various embodiments, transmitter 131 may be a fixed wavelength transmitter or a tunable transmitter.

Fig. 1C illustrates a schematic diagram of another embodiment of an integrated wavelength selectable photodiode 150 in accordance with the present invention that includes a thermally tunable filter 152 with reduced thermal noise and increased signal-to-noise ratio. The integrated wavelength selectable photodiode 150 includes a thermally tunable filter 152 having a support substrate 154 and a filter stack 156, the filter stack 156 including various thin film material layers that form an optical filter. In addition, the thermally tunable filter 152 includes a heater layer 158 that controls the temperature, and thus the transmission characteristics, of the filter stack 156. In one embodiment, the thermally tunable filter 152 is a set-and-hold type filter. The integrated wavelength selectable photodiode 150 also includes a photodiode detector 160 that detects the filtered optical signal.

In operation, the incident optical signal 162 is filtered by the filter stack 156, and only the desired center wavelength and bandwidth of the thermally tunable filter 152 passes through the filter stack 156. The temperature generated by the heater layer 158 defines the desired center wavelength and bandwidth. The filtered optical signal 164 having the desired center wavelength and bandwidth is then sent to the photodiode detector 160.

By positioning the thermally tunable filter 152 between the heater layer 158 and the photodiode detector 160, the amount of thermal radiation reaching the photodiode detector 160 is reduced. The above configuration substantially reduces the noise generated compared to a configuration in which a transparent substrate is present between the heater layer 158 and the photodiode detector 160. When the heater layer 158 is at operating temperature, it emits black body radiation according to Planck's law. The black body radiation has two effects on the photodiode detector 160. First, because there is typically some emission in the wavelength range sensed by the photodiode detector 160, black body radiation is superimposed on the background noise level of the optical signal. Second, the blackbody radiation causes the temperature of the photodiode detector 160 to rise, resulting in increased thermal (Johnson) noise.

FIG. 1D illustrates a schematic diagram of another embodiment of an integrated wavelength selectable photodiode 180 in accordance with the present invention that includes a thermally tunable filter with reduced thermal noise and increased signal-to-noise ratio. The integrated wavelength selectable photodiode 180 is similar to the integrated wavelength selectable photodiode 150 described in connection with fig. 1C.

The integrated wavelength selectable photodiode 180 includes a thermally tunable filter 182 having a support substrate 184 and a filter stack 186, the filter stack 186 including various thin film material layers that form an optical filter. In addition, the thermally tunable filter 182 includes a heater layer 188 that controls the temperature, and thus the transmission characteristics, of the filter stack 186. In one embodiment, the thermally tunable filter 182 is a set-and-hold type filter. The integrated wavelength selectable photodiode 180 also includes a photodiode detector 190 that detects the filtered optical signal.

In addition, the integrated wavelength selectable photodiode 180 includes a blocking material 192 that shields the edges of the heater layer 188 from the photodiode detector 190. The blocking material 192 further reduces the amount of unfiltered radiation reaching the photodiode detector 190. The blocking material 192 may be any material that provides a thermal barrier in the wavelength range sensed by the photodiode detector 190 and also absorbs optical radiation. The blocking material 192 reduces the amount of black body radiation from the heater layer 188 that is incident on the photodiode detector 190.

The operation of the integrated wavelength selectable photodiode 180 is similar to the operation of the integrated wavelength selectable photodiode 150 shown in fig. 1C. The incident optical signal 194 is filtered by the filter stack 186 and only the desired center wavelength and bandwidth of the thermally tunable filter 182 passes through the filter stack 186. The temperature generated by the heater layer 188 defines the desired center wavelength and bandwidth. The filtered optical signal 196 having the desired center wavelength and bandwidth is then sent to the photodiode detector 160.

Fig. 2A illustrates a perspective view of a relatively low cost package 250 for a wavelength selectable photodiode including molded reflective optics in accordance with the present invention. The package 250 can be used in place of an existing manufactured component housing and circuit board assembly, which is more expensive to manufacture.

The package 250 includes a fiber support/lens element 252. FIG. 2B illustrates the fiber holder/mirror element 252 in the low cost package shown in FIG. 2A. FIG. 2B-1 illustrates a cross-sectional view of the fiber holder/mirror element of FIG. 2B showing a V-groove configuration that securely holds the fiber/lens element in place. Fig. 2B-2 shows a top cross-sectional view of the fiber/mirror element of fig. 2B. Fig. 2B-3 show side cross-sectional views of the fiber/mirror element of fig. 2B. The fiber holder/mirror element 252 may be formed from metallized plastic, ceramic, micromachined silicon (or glass), or any combination of these materials. For example, in one embodiment, the fiber optic holder/mirror element 252 is fabricated from a low cost molded plastic. The area at the front face of the fiber optic is metallized to provide optimal performance when orienting and shaping the beam.

In certain embodiments, a separate spacer element 254 is used to isolate the fiber holder/mirror element 252. In other embodiments, the spacer element 254 is integrated into the fiber support/lens element 252 or into some other structure, such as a filter. Fig. 2C illustrates a cross-sectional view of a spacer element 254 that may be used with the low-cost package 250 shown in fig. 2A. Fig. 2C-1 shows a cross-sectional view through line a-a of the spacer element 254 shown in fig. 2C.

The package 250 also includes an integrated filter chip 256. In one embodiment, the integrated filter chip 256 is a film structure that includes optical filters. Fig. 2D illustrates a cross-sectional view of an integrated filter chip 256 that may be used with the low-cost package 250 shown in fig. 2A. The integrated filter chip 256 shown in fig. 2D includes conductive paths that allow current to pass directly through the filter chip 256. Fig. 2D-1 illustrates a cross-sectional view of the integrated filter chip 256 shown in fig. 2D along line a-a. The top surface includes an unsupported thin film filter membrane that remains after the substrate has been etched away under the filter. Fig. 2D-2 illustrates a cross-sectional view of the integrated filter chip 256 shown in fig. 2D along line B-B.

In addition, the low cost package 250 includes an electronics enclosure that supports electronics (such as amplification and filtering circuitry). Also, the electronics enclosure includes the required signal routing transmission lines connected to the tunable filter. Fig. 2E illustrates a cross-sectional view of an electronic device housing 258 that may be used with the low-cost package 250 shown in fig. 2A.

Fig. 3 illustrates a block diagram of an embodiment of an optical network unit that can provide premium services to subscribers including a wavelength selectable photodiode according to the present invention. Fig. 3 illustrates a block diagram of a DWDM PON Optical Network Unit (ONU)300 comprising a wavelength selectable photodiode 302 according to the present invention. ONU 300 includes an enhanced bandpass filter 301 that directs light at wavelengths outside the enhanced band to a first receiver 303, which first receiver 303 may be included in a duplexer 308 with a transmitter 306 in some embodiments. Duplexers are well known devices that process signals having different wavelengths. Wavelengths within the enhancement band are directed to the wavelength selectable photodiode 302. Tunable filter 304 passes only the desired wavelengths within the enhancement band to second receiver 305.

In one embodiment of the optical network unit 300, the transmitter 306 is included in the package as part of the duplexer 308. Many types of transmitters may be used. In some embodiments, transmitter 306 is a fixed wavelength transmitter. In other embodiments, transmitter 306 is a wavelength tunable transmitter. Using a tunable wavelength transmitter improves the flexibility of the optical network unit 300.

The wavelength splitter/combiner 309 is used to couple the transmitter 306 to the optical fiber 307 in an optical network unit propagating transmit and receive signals having different wavelengths outside the enhancement band. In optical network units where the transmit and receive signals outside the enhancement band are at the same wavelength, a simple power splitter/combiner may be used instead of the wavelength splitter/combiner 309. In a particular embodiment, in addition to wavelengths within the enhanced frequency band, the optical network unit 300 transmits a downstream signal wavelength near 1490nm and an upstream signal wavelength near 1310 nm.

In one embodiment, these components are used in a Central Office (Central Office) configuration. In a central office configuration, return signals from a plurality of ONUs are received by one or more Optical Line Terminals (OLTs). This embodiment is useful for applications requiring symmetric (peer-to-peer transmission and reception) bandwidth.

In another mode of operation, the diplexer 308 sends a signal to the optical line terminal at the service provider's central office requesting a DWDM wavelength. The wavelength selectable photodiode 302 is then tuned to the wavelength specified by the optical line termination. An on-demand download or other premium service is then sent by the optical line terminal and received by the wavelength selectable photodiode 302 at the location of delivery to the receiver 305. For example, a large movie file may be downloaded to a computer or DVR system. The diplexer 308 then notifies the optical line terminal to release the wavelength after the download is complete.

This architecture allows the receiver 403 to operate at full speed. Thus, the architecture presented herein with the wavelength selectable photodiode 305 makes more efficient use of the receiver bandwidth than prior art architectures that only provide an amount of time slots for downloading or other premium services. In other words, this architecture provides full bandwidth download to subscribers. Also, the architecture presented herein with the wavelength selectable photodiode 305 provides for efficient utilization of optical line terminations so fewer optical line terminations may be used and/or optical line terminations may be made available or eliminated as needed. In another embodiment, the optical network unit shown in fig. 3 may be configured to provide access to shared high bandwidth fast download wavelengths on demand.

Figure 4 illustrates a block diagram of another embodiment of an optical network unit 400 that can provide premium services to subscribers including a wavelength selectable photodiode 402 in accordance with the present invention. The optical network unit 400 includes an enhanced bandpass filter 401 with a passive splitter connected to an upgrade port 407. The enhancement band-pass filter 401 passes a predetermined frequency band of the incoming optical signal to the upgrade port 407. If the user has purchased a premium service, the premium service signal is coupled via an optical connection (in some embodiments an optical fiber) to the wavelength selectable photodiode 402 and then to the receiver 403.

In addition, the optical network unit 400 includes a duplexer 406. In various embodiments, the optical network unit 400 is electrically connected to a wavelength selectable photodiode 402. Duplexers are well known devices that process signals having different wavelengths. In the embodiment shown in fig. 4, a 1490nm optical signal is received from the optical network and passed by the enhancement band pass filter 401 to the diplexer 406. The 1490nm optical signal can be used for control and monitoring functions as well as for basic video and data services. An optical signal of 1310nm is generated by a transmitter in the diplexer 406 and then passes from the diplexer 406 through the enhancement band pass filter 401 and then back through the optical network to the Optical Line Terminal (OLT), which may be located at a central office.

In one embodiment, the optical network unit 400 is used in a passive optical network architecture. Such passive optical network architectures use unpowered components to enable a single fiber to serve multiple subscribers. The diplexer 406 enables the optical network unit 400 to communicate with optical line terminals at the service provider's central office. These PON network architectures reduce the amount of fiber and central office equipment required compared to point-to-point architectures.

Figure 5 illustrates a block diagram of another embodiment of an optical network unit 500 that may be configured as a symmetric point-to-point link that includes a wavelength selectable photodiode 502 in accordance with the present invention. The optical network unit 500 may further comprise an enhancement band-pass filter 501 similar to the enhancement band-pass filter 401 described in connection with fig. 4. The enhancement band-pass filter 501 passes a predetermined frequency band of the incoming optical signal to a wavelength selectable photodiode 502, where it is filtered by a tunable filter 504, and then to a receiver 503.

In embodiments using an enhanced bandpass filter, the optical network unit 500 further includes a duplexer 506 as shown in fig. 3 and 4. The diplexer 506 may provide a signal that is sent back to an optical line terminal located at the service provider's central office to request certain transmissions or certain services. However, the duplexer 506 is not necessary in the embodiment shown in fig. 5.

In addition, the optical network unit 500 includes a tunable transmitter 508 that transmits signals back to the optical line terminal at the service provider's central office. Tunable transmitter 508 is a dedicated transmitter that provides a way to transmit high bandwidth signals back to the service provider's central office. There are a number of applications that require a dedicated transmitter, such as transmitter 508. Such a transmitter may provide a symmetric bandwidth for enterprise applications. In some applications, such dedicated transmitters include a Reflective Silicon Optical Amplifier (RSOA) that receives incoming signals from a service provider and amplifies and remodulates them before returning them to the service provider's optical line terminal. This allows the tunable transmitter/receiver module 510 to operate without an internal light source. In some applications, the signal sent back to the service provider's central office is then retransmitted to a third party. For example, the optical network unit 500 may be used for teleconferencing or high bandwidth telepresence applications. Applications such as teleconferencing and telepresence may have symmetric bandwidth requirements.

Figure 6 illustrates an embodiment of an optical network unit that provides subscribers with an optional personalized High Definition (HD) video channel in addition to a standard broadcast channel. The optical network unit 600 consists of an enhanced band splitter 601, a diplexer 606 and a wavelength selectable photodiode 602 with an integrated tunable filter 603 and receiver 604. The signal from the receiver 604 may be output via a coaxial connection 605.

One method of operation of the embodiment of the optical network unit shown in figure 6 allows sharing of one wavelength among all subscribers comprising a standard encapsulation of the broadcast channel. In the example shown in fig. 6, each of the 32 subscribers can select up to 3 personalized video channels, which requires only one wavelength. More than 3 personalized channels per subscriber require an increase in wavelength 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. This configuration allows highly personalized video content to be dynamically selected by and delivered to the subscriber.

Fig. 7 illustrates a tunable-receiver multiplexer 700 including an integrated wavelength selectable photodiode according to the present invention. The tunable multiplexer 700 includes an input/output port 706 and a first dichroic beam splitter 701 that splits an input optical beam into two wavelength ranges. In addition, the tunable multiplexer 700 includes a second beam splitter 705 that passes the input optical signal and transmits the output optical signal.

Further in accordance with the present invention, the tunable-receiver multiplexer 700 includes a first 702 and a second integrated wavelength selectable photodiode 703. These integrated wavelength selectable photodiodes 702, 703 replace the static receivers in many known multiplexers. In addition, the tunable-receiver multiplexer 700 includes a transmitter 704. The tunable-receiver multiplexer 700 is commonly known as a triplexer because it processes three signals. However, those skilled in the art will recognize that any number of signals may be processed by a tunable-receiver multiplexer according to the present invention.

Fig. 8 illustrates a tunable diplexer 800 including an integrated wavelength selectable photodiode according to the present invention. The duplexer 800 is one embodiment of the tunable-receiver multiplexer 700 described with respect to fig. 7. The duplexer includes an input-output port 802 and a beam splitter 804. In addition, the diplexer includes an integrated wavelength selectable photodiode 806 and a transmitter optically coupled to a respective port of the beam splitter 804.

Such a tunable diplexer 800 is well suited for FTTX applications and can directly replace a known static diplexer to allow service provision from the network (network provisioning). Because the integrated wavelength selectable photodiode 806 can be fabricated in a standard TO46 package, it can be a replacement for the static reception of the prior art. Equivalents while the present teachings are described in conjunction with various embodiments and examples, the present teachings are not intended to be limited to such embodiments. On the contrary, the present teachings encompass various alternatives, modifications, and equivalents, as will be recognized by those skilled in the art, may be made therein without departing from the spirit and scope of the invention.

Claims (25)

1. An integrated wavelength selectable photodiode for receiving data, comprising:

a. a device package having an input for receiving an optical signal;

b. a set-and-hold, thermally tunable thin-film filter located in the device package, the set-and-hold, thermally tunable thin-film filter having an input optically coupled to the input of the device package, the set-and-hold, thermally tunable thin-film filter being locked to a single optical channel and passing only the single optical channel to which the set-and-hold, thermally tunable thin-film filter is set to an output, while blocking other optical channels;

c. an optical element that collimates a light beam incident on an input end of the set-and-hold type thermally tunable thin-film filter; and

d. a detector in the device package and having an input optically coupled directly to an output of the set-and-hold, thermally tunable thin-film filter, the detector detecting data modulated on the single optical channel through the thermally tunable thin-film filter.

2. The integrated wavelength selectable photodiode of claim 1 wherein the device package comprises a TO46 package.

3. The integrated wavelength selectable photodiode of claim 1 wherein a size of the device package is less than or equal TO a size of the TO46 package.

4. The integrated wavelength selectable photodiode of claim 1 wherein the set-and-hold, thermally tunable thin-film filter operates in a locked mode and a dither control is utilized to lock the transmission wavelength of the filter.

5. The integrated wavelength selectable photodiode of claim 1 wherein the thermally tunable thin-film filter operates in a scan mode that scans a predetermined spectral range to determine a wavelength at which an optical signal is present.

6. The integrated wavelength selectable photodiode of claim 1 wherein the set-and-hold, thermally tunable thin-film filter comprises a filter element located between a heating element and a detector.

7. The integrated wavelength selectable photodiode of claim 1 wherein the set-and-hold, thermally tunable thin-film filter has an insertion loss of less than 3.5 dB.

8. The integrated wavelength selectable photodiode of claim 1 wherein the optical element comprises a single lens or mirror.

9. The integrated wavelength selectable photodiode of claim 1 wherein the optical element is located in the device package proximate to an input of the set-and-hold, thermally tunable thin-film filter.

10. The integrated wavelength selectable photodiode of claim 1 wherein the optical element is located outside the device package proximate to the input end of the device package.

11. An integrated wavelength selectable photodiode for receiving data, comprising:

a. a device package having an input for receiving an optical signal;

b. a set-and-hold, thermally tunable thin-film filter including a filter element and a heater in the device package and having an input optically coupled to the input of the device package, the set-and-hold, thermally tunable thin-film filter being locked to a single optical channel and passing only the single optical channel to which the set-and-hold, thermally tunable thin-film filter is set to an output while blocking other optical channels; and

c. a detector having an input optically coupled directly to an output of the set-and-hold, thermally tunable thin-film filter, the detector being located in the device package proximate to the filter element to reduce thermal coupling to the heater to minimize the generation of thermal noise when detecting data modulated on the single optical channel through the thermally tunable thin-film filter.

12. The integrated wavelength selectable photodiode of claim 11 further comprising an optical element to collimate a light beam incident on an input of the set-and-hold, thermally tunable thin-film filter.

13. The integrated wavelength selectable photodiode of claim 12 wherein the optical element is located in the device package proximate to the input of the set-and-hold, thermally tunable thin-film filter.

14. The integrated wavelength selectable photodiode of claim 12 wherein the optical element is located outside the device package proximate to the input end of the device package.

15. The integrated wavelength selectable photodiode of claim 11 wherein a size of the device package is less than or equal TO a size of the TO46 package.

16. The integrated wavelength selectable photodiode of claim 11 wherein the set-and-hold, thermally tunable thin-film filter operates in a locked mode and a dither control is utilized to lock the transmission wavelength of the filter.

17. The integrated wavelength selectable photodiode of claim 11 wherein the thermally tunable thin-film filter operates in a scan mode that scans a predetermined spectral range to determine a wavelength at which an optical signal is present.

18. A method of receiving a single channel optical signal, the method comprising:

a. collimating an optical signal input into the set-and-hold, thermally tunable thin-film filter;

b. adjusting the temperature of the set-and-hold, thermally tunable thin-film filter such that the filter passes only a single channel to which the filter is set to the output, while blocking optical signals on other channels;

c. locking the set-and-hold, thermally tunable thin-film filter to the single channel;

d. coupling the filtered optical signal directly to a photodetector integrated in a device package with a set-and-hold, thermally tunable thin-film filter; and

e. detecting the filtered optical data signal modulated on the single channel with a light detector arranged to reduce a detected amount of thermal radiation and spectral noise generated by the thermally tunable thin-film filter.

19. The method of claim 18, wherein the step of adjusting the temperature of the set-and-hold, thermally tunable thin-film filter comprises locking the set-and-hold, thermally tunable thin-film filter at a center wavelength that maximizes the amount of light from the single channel passing through the set-and-hold, thermally tunable thin-film filter.

20. The method of claim 18, wherein adjusting the temperature of the set-and-hold, thermally tunable thin-film filter comprises sweeping the temperature of the set-and-hold, thermally tunable thin-film filter to change the center wavelength of the tunable thin-film filter.

21. A tunable-receiver multiplexer, comprising:

a. a first beam splitter having a first port to receive and transmit optical signals into and out of the multiplexer;

b. an integrated wavelength selectable photodiode having an input optically coupled to the second port of the first beam splitter, the integrated wavelength selectable photodiode comprising a set-and-hold, thermally tunable thin-film filter that passes a predetermined center wavelength at an output, and a detector having an input optically coupled directly to the output of the set-and-hold, thermally tunable thin-film filter;

c. a second beam splitter having a first port optically coupled to the third port of the first beam splitter; and

d. an optical transmitter having an output optically coupled to the second port of the second beam splitter.

22. The tunable-receiver multiplexer of claim 21 wherein the integrated wavelength selectable photodiode is located within a device package having a size less than or equal TO the size of a TO46 package.

23. The tunable-receiver multiplexer of claim 21 further comprising a second integrated wavelength selectable photodiode having an input optically coupled to the second port of the second beam splitter, the second integrated wavelength selectable photodiode comprising a set-and-hold, thermally tunable thin-film filter passing a second predetermined center wavelength at an output; and a detector having an input optically coupled directly to the output of the set-and-hold, thermally tunable thin-film filter.

24. The tunable-receiver multiplexer of claim 21 wherein the tunable-receiver multiplexer comprises a duplexer.

25. The tunable-receiver multiplexer of claim 21 wherein the tunable-receiver multiplexer comprises a triplexer.