Patent Application
20060095216
1. Field of the Invention
The present invention is generally in the field of fiber-optics. More specifically, the invention is in the field of fiber-optic module calibration.
2. Background Art
Conventional approaches to fiber-optic (or simply optic) module calibration have involved the calibration of parameters such as transmit power, extinction ratio control, and received power over temperature and voltage using specialized test systems. The cost of a single specialized test system can be on the order of tens or hundreds of thousands of dollars.
Referring to
Programmable optic attenuator 126 is coupled between transmitter 118, BERT 120, and PC 112. Programmable optic attenuator 128 is coupled between reference receiver 116 and BERT 120. PC 112 is also coupled to BERT 120 and module under calibration 114 on test station 110. Specialized test system 100 typically includes an oscilloscope 121 and a power meter, among other devices.
In use, in a first step, reference module under calibration 114 is powered up and the transmit power of transmitter 118 is adjusted, via PC 112, to the middle of a target specification range. Typically this range is from about −1 dbm to about −3 dbm (decibels relative to 1 milliwatt). The transmit power is adjusted by adjusting the modulation current and bias current via PC 112, while at the same time keeping the extinction ratio above the target minimum. Typically the target minimum for the extinction ratio is in the range of about 6 to about 8 dB. The extinction ratio is the ratio of the zero level to the one level of the optic signal. These various values are measured by specialized test system 100 and stored as calibrated values.
In a second step, in order to calibrate reference receiver 116 of module under calibration 114, reference receiver 116 is starved of signal until the bit error rate (BER) exceeds a target value. The value of the power received by reference receiver 116 is stored as a calibrated value of input power.
In a third step, the value of received power at reference receiver 116 is measured by module under calibration 114 and compared to the known applied value of power. A correction factor and the received power level are recorded.
In a fourth step, loss-of-signal (LOS) hysteresis are measured and recorded. These four steps are repeated over various voltages and temperatures.
Module under calibration 114 can be calibrated manually, such as by adjusting a potentiometer for example, or automatically. This time-consuming and expensive process is typically repeated for a plurality of modules to be calibrated.
Thus, it is seen that there is need in the art for an improved system and method for calibrating an optic module. The system and method should allow for relatively inexpensive calibration.
The present invention is directed to optic module calibration. The invention overcomes the need in the art for an improved system and method for calibrating an optic module and allows for relatively inexpensive calibration.
According to one embodiment of the invention, a system is provided for calibrating a production module having a production module transmitter, a production module receiver, a production module controller, a production module optical device driver, and at least one of a production module post-amplifier, a production module retimer, a production module equalizer and a production module wakeup function. The system comprises a calibrated reference module having a calibrated reference module transmitter, and a calibrated reference module receiver, a calibrated reference module controller, a calibrated reference module optical device driver, and at least one of a calibrated reference module post-amplifier, a calibrated reference module retinier, a calibrated reference module equalizer and a calibrated reference module wakeup function, wherein the calibrated reference module is calibrated using test equipment. The system further comprises a first pulse generator coupled to the calibrated reference module; a second pulse generator coupled to the production module; a first attenuator coupled between the calibrated reference module receiver and the production module transmitter; and a second attenuator coupled between the production module receiver and the calibrated reference module transmitter. The system uses the calibrated reference module to calibrate at least one of the calibrated reference module post-amplifier, the calibrated reference module retimer, the calibrated reference module equalizer and the calibrated reference module wakeup function using a respective one of the at least one of the calibrated reference module post-amplifier, the calibrated reference module retimer, the calibrated reference module equalizer and the calibrated reference module wakeup function.
In a further aspect, the calibrated reference module controller controls the at least one of the calibrated reference module post-amplifier, the calibrated reference module retimer, the calibrated reference module equalizer and the calibrated reference module wakeup function for calibrating the production module.
In another aspect, the calibrated reference module includes the calibrated reference module equalizer, and wherein the calibrated reference module controller controls input equalizer settings of the calibrated reference module optical device driver for controlling the calibrated reference module equalizer.
In yet another aspect, the calibrated reference module includes the calibrated reference module equalizer, and wherein the calibrated reference module controller controls the calibrated reference module equalizer via internal registers of the calibrated reference module controller. Further, in the calibrated reference module, the calibrated reference module controller controls input equalizer settings of the calibrated reference module optical device driver for controlling the calibrated reference module equalizer.
Other features and advantages of the present invention will become more readily apparent to those of ordinary skill in the art after reviewing the following detailed description and accompanying drawings.
The present invention is directed to optic module calibration. Although the invention is described with respect to specific embodiments, the principles of the invention, as defined by the claims appended herein, can obviously be applied beyond the specifically described embodiments of the invention described herein. Moreover, in the description of the present invention, certain details have been left out in order to not obscure the inventive aspects of the invention. The details left out are within the knowledge of a person of ordinary skill in the art.
The drawings in the present application and their accompanying detailed description are directed to merely example embodiments of the invention. To maintain brevity, other embodiments of the invention which use the principles of the present invention are not specifically described in the present application and are not specifically illustrated by the present drawings.
At step 210, a calibrated reference module is installed on a test board. This module corresponds to module under calibration 114 of
In one embodiment, the calibration of the reference module can be performed in a manner similar to the calibration of module under calibration 114 discussed with reference to
At step 220, calibration constants are read from the calibrated reference module, and at step 230, a production module is installed on a reference board on which the calibrated reference module (golden module) is installed. Once a golden module has been obtained, modules (which are referred to as silver modules for purposes of this application) can be achieved by calibrating production modules with respect to the single golden module without the use of specialized test equipment.
At step 240, the production module is calibrated using the calibrated reference module or the golden module, thus producing a silver module. Advantageously, expensive specialized test equipment does not need to be used once the calibrated reference module or the golden module is obtained. Thus, a large number of production modules can be calibrated from a single calibrated reference module.
Referring to
Calibrated reference module 314 is plugged into test station 311. Calibrated reference module 314 comprises receiver 316 and transmitter 318. Calibrated reference module 314 is coupled to simple pulse generator 320, which is also on test station 311. Simple pulse generator 320 is coupled to calibrated reference module 314 via transmit line 324. In one embodiment, simple pulse generator 320 can be a pattern generator. Calibrated reference module 314 and production module 304 both include an integrated controller and an optical device driver in one embodiment. The optical device driver may be a laser driver, an LED driver or a modulator driver.
Production module 304 is plugged into test station 311. Production module 304 comprises receiver 330 and transmitter 332. Production module 304 is coupled to simple pulse generator 334, which is also on test station 311. Simple pulse generator 334 is coupled to production module 304 via transmit line 328. It is envisioned that simple pulse generators 320 and 334 can be replaced with a single pulse generator having one output driving calibrated reference module 314 and another output driving production module 304.
Fixed optic attenuator 326 is coupled between receiver 316 of calibrated reference module 314 and transmitter 332 of production module 304. Fixed optic attenuator 328 is coupled between receiver 330 of production module 304 and transmitter 318 of calibrated reference module 314. It is noted that fixed optic attenuator 326 can be replaced with a programmable optic attenuator. PC 312 is coupled to production module 304 and calibrated reference module 314. PC 312 can also be coupled to simple pulse generators 320 and 334.
In use, calibrated reference module 314 is instructed, via PC 312, to transmit a known optic power that has a known extinction ratio from transmitter 318 of calibrated reference module 314. A laser bias current is set to achieve the desired output power, as measured by calibrated reference module 314. Fixed optic attenuators 326 and 328 can be switched in to provide some loss. Fixed optic attenuators 326 and 328 can each comprise a length of optic fiber (e.g. 10, 20, or 80 kilometers in length) in one illustrative embodiment. Fixed optic attenuators 326 and 328 help duplicate the real effects of optic fiber over long distances,-introducing delays and phase shifts.
After the signal from transmitter 318 gets attenuated by fixed optic attenuator 328, the signal is received by receiver 330 of production module 304. A mapping is performed of the laser's power/current characteristics. The extinction ratio and the power level of the transient signal from transmitter 318 can be determined by interrogating calibrated reference module 314. Thus, from this extinction ratio, and the link loss between calibrated reference module 314 and production module 304, it can be determined what the received power should be at receiver 330.
Subsequently, production module 304 is interrogated to determine that production module 304 measures the received power from receiver 330, and a correction is applied for any discrepancy. Using the results of the laser mapping, modulation and bias currents are set to achieve a desired extinction ratio. The transmit power level is calibrated based on the optic power measurement at calibrated reference module 314. The receive power level is calibrated from the signal provided by calibrated reference module 314. Various warnings, alarm levels, and registers are then loaded in a memory of production module 304 for reference during actual usage.
Referring to
Production module 304 is plugged into test station 311. Production module 304 comprises receiver 330 and transmitter 332. Production module 304 is coupled to CDR with BER counter and pattern generator 362, which is also on test station 311. CDR with BER counter and pattern generator 362 is coupled to production module 304 via receive line 336 and transmit line 338. CDR with BER counter and pattern generators 362 and 364 generally can represent any suitable set of integrated circuits (ICs) that can be used to generate test signals and to measure the quality of the return signal (e.g. jitter and other parameters), in one embodiment. As is known in the art, a pattern generator simply generates a test signal, and a BER counter is a device that measures the BER.
In keeping with some embodiments of the invention, fixed optic attenuator 326 is coupled between transmitter 332 of production module 304 and receiver 316 of calibrated reference module 314. Programmable optic attenuator 360 is coupled between receiver 330 of production module 304 and transmitter 318 of calibrated reference module 314. PC 312 is coupled to production module 304 and calibrated reference module 314. PC 312 can also be coupled to CDR with BER counter and pattern generators 362 and 364.
In use, an optical device driver configuration, desired optic output power, and extinction ratio are downloaded into production module 304. The laser bias current is set to achieve the desired output power, as measured at receiver 316 of calibrated reference module 314. A mapping of the laser's power/current characteristics is performed.
Using the results of the mapping, the modulation current is set to achieve a desired extinction ratio. The transmit power level is calibrated based on the optic power measurement from calibrated reference module 314. The receive power level of production module 304 is calibrated based on the optic power level from calibrated reference module 314, and various warnings, alarm levels, and registers are then loaded. It is noteworthy that additional attenuation can be introduced, either automatically using programmable optic attenuator 360 or manually, until production module 304 is starved of signal to the point where the sensitivity threshold for a given BER can be determined.
When calibrating transmitter 332 of production module 304, transmitter 332 is instructed to output a transmit signal. Receiver 316 of calibrated reference module 314 is used to measure the transmitted power from transmitter 332 of production module 304 in addition to the extinction ratio. In some cases, little or no attenuation may be required. However, some attenuation may be introduced, via fixed optic attenuator 326 for example, to ensure that receiver 316 of calibrated reference module 314 is not damaged.
One advantage of the present system is that calibrated reference module 314 can be used as a specification with respect to which a plurality of other optic modules are calibrated. Once module under calibration 314 has been calibrated to achieve calibrated reference module 314, expensive specialized test equipment need no longer be used. Advantageously, calibration of large volumes of optic modules can thus be achieved at a relatively low cost. Conventional implementations required repeated use of expensive specialized test equipment and did not allow for a single optic module to be a reference for subsequently calibrating a plurality of other optic modules.
Another advantage of the present invention is that production module 304 and calibrated reference module 314 each include a microprocessor-based controller and state machine in one embodiment. Alternative embodiments may contain only a state machine, microcontroller (microprocessor) or both. The controller and or state machine can be configured to default to various modes as needed (e.g. a calibration and setup mode, a reference module mode, etc.). In one embodiment, the microprocessor(s) and/or state machine may comprise a Digital Diagnostic Monitoring Interface (DDMI) chip and run special firmware that places production module 304 into a reference mode, for example. The DDMI chip(s) allow PC 312 to control production module 304 and calibrated reference module 314, and to set various values for the optic modules.
An additional advantage is that the present system can use external ICs in order to achieve reduced cost. The external ICs generate test patterns at different bit rates and receive patterns, in lieu of using expensive specialized test equipment. The external ICs also measure the received electrical performance (e.g. BER, rise/fall time, jitter, and the like).
It is noteworthy that module-to-module communication in the present system can be performed via an external loop-back connection in addition to the fiber-optic connections. Alternatively, a fiber-optic data signaling link can be used alone as described in U.S. Patent Application titled “Module to Module Signaling Utilizing Amplitude Modulation”, filed Aug. 10, 2004, having Ser. No. 10/916,216, assigned to the assignee of the present application, which is hereby fully incorporated by reference. Thus calibration can be performed with a minimum of connections. In one embodiment, intra-system communication is performed via an I2C interface.
An additional benefit achieved by the present system involves changing the transmit parameters over time to compensate for the degradation of optic components such as lasers after a module containing such an enabled device with associated firmware has been placed into service. Conventional approaches do not accomplish the foregoing without the help of a host system or supervisory controller. Conventional systems do not allow modules to communicate with each other, and did not optimize optic link performance without the intervention of a supervisory device or system.
Therefore, another advantage achieved includes providing the ability to change the operating characteristics of the optic modules in the field remotely, without local intervention. In devices enabled with the necessary hardware and firmware, the need for a separate supervisory system to perform the foregoing duty is not mandated, allowing implementation in relatively low-cost links. The present system further allows for simpler and quicker troubleshooting than conventional methods, and is less error prone. To this end, the invention of the present application can utilize a low-frequency side channel, which is also known as out-of-band communication, as described in U.S. patent application Ser. No. 10/916,216, filed Aug. 10, 2004, entitled “Module to Module Signaling.”
In one embodiment, in addition to a controller and a optical device driver, production module 404 and calibrated reference module 414 may include post-amplifier 411 and post-amplifier 420, respectively, where the controllers would control the operation of post-amplifier 411 and post amplifier 420 and would measure signals from post-amplifier 411 and post-amplifier 420. In one example, post amplifier 410 and 420 may have variable bandwidth, where calibrated reference module 414 measure such bandwidth and calibrate production module 404 accordingly, to make production module 404 the same as calibrated reference module 414. In one embodiment, post-amplifier 410 and post amplifier 420 can be a part of receivers 430 and 416, respectively.
In another embodiment, in addition to a controller and an optical device driver, production module 404 and calibrated reference module 414 may include modules for conditioning the incoming and outgoing high-speed signals, such as retimers 411 and 421, respectively. In this case, the controllers would control the operation of retimers 411 and 421, and measure signals from retimers 411 and 421, and calibrated reference module 414 would calibrate production module 404 accordingly, to make production module 404 the same as calibrated reference module 414. In one embodiment, retimer 411 and retimer 421 can be a part of receivers 430 and 416, respectively.
In yet another embodiment, in addition to a controller and an optical device driver, production module 404 and calibrated reference module 414 may include modules for conditioning the incoming and outgoing high-speed signals, such as equalizers 412 and 422, respectively. In this case, controller would control the operation of the input equalizer settings of the optical device driver via internal registers, and measure signals from equalizers 412 and 422, and calibrated reference module 414 would calibrate production module 404 accordingly, to make production module 404 the same as calibrated reference module 414. In one embodiment, equalizer 412 and equalizer 422 can be a part of transmitters 432 and 418, respectively. According to one aspect, internal registers are used to control the optical device driver, rather than the controller directly controlling the optical device driver. This approach is advantageous, because in the event that the controller is corrupted or non-operational, register settings remain intact. Although the controller still controls the optical device driver, but such control is performed by loading values into the internal registers, which control the optical device driver. As a result, the optical device driver may update the internal register settings, which the controller can read at a much higher data rate, and the controller can read the internal register settings when time permits. Therefore, this approach offers superior speed advantage and data integrity compared to conventional approaches.
In a further embodiment, in addition to a controller and an optical device driver, production module 404 and calibrated reference module 414 may include wakeup functions 413 and 423 for waking up respective modules after a pre-determined sequence of light pulses are input to respective receivers 330 and 316, drawing current from a current source specifically intended to detect such a sequence of events. In this case, the controller would detect the current from the pre-determined sequence of light pulses, which have been input to respective receivers 330 and 316, to wake up respective production module 404 and calibrated reference module 414. In one embodiment, wakeup function 413 and wakeup function 423 can be a part of receivers 430 and 416, respectively.
From the above description of the invention it is manifest that various techniques can be used for implementing the concepts of the present invention without departing from its scope. Moreover, while the invention has been described with specific reference to certain embodiments, a person of ordinary skill in the art would recognize that changes can be made in form and detail without departing from the spirit and the scope of the invention. The described embodiments are to be considered in all respects as illustrative and not restrictive. It should also be understood that the invention is not limited to the particular embodiments described herein, but is capable of many rearrangements, modifications, and substitutions without departing from the scope of the invention. For example, although the systems and methods have been described with respect to optic modules and optic attenuators, it is contemplated that other types of modules and attenuators might be used in conjunction with embodiments according to the present invention.
The present application is a Continuation-In-Part of U.S. patent application Ser. No. 10/981,027, filed Nov. 4, 2004.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10981027 | Nov 2004 | US |
| Child | 11156878 | Jun 2005 | US |
