TWI608270B - Method of fabricating and operating an optical modulator - Google Patents

Description

Method for manufacturing and operating an optical modulator References for related applications

This application is part of a continuation of U.S. Patent Application Serial No. 13/831,334, filed on March 14, 2013.

The present invention relates to an optical transmission system for analog or digital radio frequency (RF) signals using an externally modulated solid state laser, and in particular to an optical modulator coupled to the laser.

An optical telecommunication system transmits information from one location to another via an optical carrier, the frequency of which is typically in the visible or near infrared region of the electromagnetic spectrum. A carrier having such a high frequency is sometimes referred to as an optical signal, an optical carrier, a light beam, or a light wave signal. An optical telecommunication system includes a plurality of optical fibers, and each optical fiber includes a plurality of channels. A channel is a frequency band defined by one of the electromagnetic signals and is sometimes referred to as a wavelength. The use of multiple channels (referred to as dense wavelength division multiplexing (DWDM)) in the same fiber utilizes the high capacity (ie, bandwidth) provided by the fiber. Basically, each channel has its own wavelength and all wavelengths are sufficiently separated to prevent overlap. The International Telecommunications Union (ITU) standard currently determines channel separation.

A link of an optical telecommunication system typically has a transmitter, an optical fiber, and a receiver. An optical transmitter has an electrical signal converted into an optical signal and transmitted to an optical fiber One of the lasers. The fiber carries the optical signal to the receiver. The receiver converts the optical signal back into an electrical signal.

An optical transmitter for transmitting analog or digital radio frequency (RF) signals over an optical fiber can use a direct modulated laser or a continuous wave (CW) laser coupled to an external modulator.

The ability to directly modulate the intensity of a light-emitting diode (LED) or semiconductor laser by means of an electrical signal is considered to be among the simplest methods known in the prior art for transmitting analog signals, such as voice and video signals, via optical fibers. . While such analog transmission techniques have advantages over digital transmissions (such as digital pulse modulation modulation) or bandwidth requirements that are substantially smaller than analog or pulse frequency modulation, the use of amplitude modulation typically affects the noise and distortion characteristics of the transmitter. Have more stringent requirements. One of the limiting factors in such a link may be second order distortion due to optical frequency modulation or a combination of chirp and fiber dispersion.

For these reasons, direct modulation techniques have typically been used in conjunction with 1310 nm lasers, where the application employs short transmission links with low dispersion fiber links. It is also possible to use direct modulation of a 1550 nm laser, but in this case, one of the predistorters for a particular fiber length setting must be used to eliminate distortion due to chirp and dispersion. In some cases, such as when a signal must be transmitted to more than one location or through a redundant fiber link of varying length, such a programmable predistorter may be undesirable.

In order to avoid distortion problems associated with enthalpy and dispersion at 1550 nm by means of direct modulation, low-level external optical modulators are typically used in analog optical fiber communication systems (such as CATV signal distribution) to have a message or content. The optical carrier of one of the signals (such as audio, video or data signals) is amplitude modulated.

There are two general types of external optical modulators known in the prior art that are implemented as semiconductor devices: Mach Zehnder modulators and electroabsorption modulators. A Mach-Zehnder modulator splits the beam into two arms or paths on a semiconductor device, one of which incorporates a phase modulator. The beams are then recombined, which results in interference of the two wavefronts, thereby varying with the modulated bias signal applied to the phase modulated arm The resulting beam is amplitude modulated. An electroabsorption modulator is implemented as a waveguide in a semiconductor device in which the absorption spectrum in the waveguide is modulated by an applied electrical bias field that changes the semiconductor The band gap energy in the region, thereby modulating the amplitude or intensity of the beam across the waveguide.

The object of the invention

One object of the present invention is to provide an improved optical transmission system that uses an externally modulated laser.

Another object of the present invention is to provide an electro-optical modulator for use in an externally modulated 1550 nm optical transmission system having a high power and good linearity using a modulated semiconductor saturable absorber.

Yet another object of the present invention is to provide a high linearity optical suitable for long-distance dispersion optical fiber media using an externally modulated laser having one of a predetermined bias and an optical modulator having a lower electrical bias. Transmission system.

Yet another object of the present invention is to provide an optical modulator having a waveguide region adapted to operate in a positive voltage, negative current characteristic region for use in an analog optical transmission system using long-range dispersion fiber media.

It is also an object of the present invention to provide a semiconductor waveguide region for biasing a thermo-optical modulator in a broadband analog optical transmission system such that the carrier is excited into a conductive strip and is self-conducted by an electric field. The method of extraction.

It is also an object of the present invention to provide a method for fabricating an optical modulator by evaluating a gain peak wavelength of a semiconductor material; and fabricating the modulator with a material composition of one of the quantum well regions such that The modulator has an operating wavelength that is lower than an operating wavelength of the gain peak wavelength of the semiconductor material.

It is also an object of the present invention to provide a method for fabricating an optical modulator by determining a material composition of a quantum well region such that the modulator is at a predetermined ratio One of the predetermined wavelengths of the wavelength is transparent at the peak wavelength of the gain.

It is also an object of the present invention to provide a method for fabricating an optical modulator by determining a material composition of a quantum well region using an electroluminescence measurement prior to fabricating a laser grating.

It is also an object of the present invention to provide a method for fabricating an integrated laser and optical modulator that is fabricated from the laser grating such that the gain associated with the modulator portion of the structure is achieved. The peak wavelength is at least 10 nm less than the wavelength of the beam from the laser.

Certain embodiments or embodiments may achieve less than all of the foregoing objectives.

Features of the invention

Briefly and broadly, the present invention provides a method of operating an optical modulator comprising a semiconductor device, the semiconductor device having: an optical input for receiving a continuous wave coherent beam having a predetermined power; a waveguide for transmitting the beam; an electrode coupled to an RF signal input and a bias potential to form an electric field in the waveguide and optically modulating the beam as the beam traverses the waveguide; And an optical output coupled to the waveguide for transmitting the modulated optical signal, the method comprising: applying a continuous wave (cw) coherent beam to the optical input; and applying a bias voltage to the electrode such that The coherent beam is optically modulated by a signal that modulates the absorption characteristics of the semiconductor device such that the waveguide operates in the absorption region at a wavelength less than the peak wavelength of the gain.

In some embodiments, the modulator generates a current from a photovoltaic effect that is extracted or extracted from the modulator.

In some embodiments, the carrier density along the length of the semiconductor modulator in the direction of the beam is modulated, thereby optically modulating the continuous wave beam entering the modulator.

In some embodiments, the optical signal varies with wavelength to the peak wavelength of the gain. It is at least 10 nm larger than the wavelength of the continuous wave beam.

In some embodiments, the semiconductor device is operated in a negative current region of the I-V characteristic.

In some embodiments, the gain peak wavelength associated with the modulator is between 20 nm and 40 nm greater than the wavelength of light applied to the modulator.

In some embodiments, the bias voltage is in the range of 0.6 volts to 1.0 volts with the coherent beam applied to the optical input.

In some embodiments, the bias voltage is in the range of 0.7 volts to 0.9 volts with the coherent beam applied to the optical input.

In some embodiments, the modulator junction voltage without the net current extraction injection is in the range of 0.7 volts to 0.9 volts with the coherent beam applied to the optical input.

In some embodiments, the modulator junction voltage that does not have a net current extraction injection is 0.8 volts when the coherent beam is applied to the optical input.

In another aspect, the present invention provides a method of fabricating an optical modulator comprising a semiconductor device, the semiconductor device having: an optical input for receiving a continuous wave coherent beam having a predetermined power; a waveguide layer for transmitting the light beam; an electrode coupled to an RF signal input and a bias potential to form an electric field in the waveguide and optically modulating the beam as the beam traverses the waveguide And an optical output coupled to the waveguide to transmit the modulated optical signal, the method comprising: determining a wavelength of the continuous wave coherent beam to be applied to the modulator; for various predetermined compositions of the waveguide layer, Determining the gain of an optical signal as a function of wavelength; and fabricating the waveguide layer with a particular composition such that the gain peak of an optical signal as a function of wavelength is greater than the continuous wave coherent beam to be applied to the modulator The predetermined wavelength.

In some embodiments, the gain peak of one of the optical signals in the waveguide layer is between 20 nm and 40 nm greater than the wavelength of the continuous wave coherent beam to be applied to the modulator.

In another aspect, the present invention provides a method of fabricating a laser transmitter for optical communication comprising a semiconductor device, the semiconductor device comprising: (a) a first semiconductor region for responding to a current Injecting to produce a dimming output; and (b) a second semiconductor region disposed adjacent to the first semiconductor region and separated therefrom by a channel, the second semiconductor region having an optical coupling thereto Receiving, by a semiconductor region, an optical input of the same dimming output and connecting to the second semiconductor region to transmit an optical output of the modulated optical signal, the method comprising: forming a laser resonator in the first semiconductor region such that Operating at an optical output wavelength; forming a semiconductor waveguide structure in the second semiconductor region to transmit the same dimming output from the first semiconductor region beam; forming an optical modulator in the semiconductor waveguide structure, the optical modulation The device includes an active layer having a quantum well region and an electrode connected to an RF signal input and a bias potential at the Forming an electric field in the guiding structure such that the dimming output is optically modulated as the beam traverses the waveguide; determining a material composition of the quantum well region such that the modulator is output at a ratio of the laser resonator The wavelength is greater than a predetermined amount of the gain peak wavelength is transparent; and the modulator is fabricated using the determined material composition.

In some embodiments, the gain peak wavelength associated with the modulator is between 20 nm and 40 nm greater than the output wavelength of light applied to the modulator.

In another aspect, the invention provides a method of performing an electroluminescence measurement on a waveguide structure.

In some embodiments, the electroluminescence measurement of the waveguide structure is made prior to fabrication of the laser resonator.

In some embodiments, the optical output wavelength of the laser resonator is determined by one of the laser resonators and the grating is formed such that a gain peak wavelength ratio modulator region associated with the laser resonator The gain peak wavelength below which is transparent is between 20 nm and 40 nm.

In another aspect, the present invention provides an electro-optic device including a semiconductor device The semiconductor device includes: (a) a first semiconductor region including one of the laser resonators operable to generate a dimming output in response to current injection; and (b) a second semiconductor region adjacent to Arranging in the first semiconductor region and separated therefrom by a channel having a composition identical to the first semiconductor region and comprising optically coupled to the first semiconductor region for receiving from the first semiconductor region An optical input of the same dimming output, the second semiconductor region being energized and biased by a second bias potential lower than the first semiconductor region and electrically coupled to a signal source containing radio frequency information, such that in the second A current is generated in the semiconductor region and current is extracted therefrom, while the coherent beam is optically modulated by the signal.

In some embodiments, the first bias potential is positively biased and the second bias voltage is in the range of 0.7 volts to 0.9 volts with the same dimming output applied to the optical input.

In some embodiments, the semiconductor region comprises an InP semiconductor waveguide structure.

In some embodiments, the first semiconductor region includes an InP semiconductor gain structure having one of a mirrored first end region and a second end region disposed adjacent to the modulator.

In some embodiments, the semiconductor device includes a first electrode disposed over the InP semiconductor gain structure and a second electrode disposed over the InP semiconductor waveguide structure.

In some embodiments, the bias applied to the second electrode is zero.

In some embodiments, the bias applied to the second electrode is from a current-free injection or extraction of the electrode that will be pumped by the source laser and self-coupled to the modulator. The value of the voltage that occurs below is plus or minus 0.1 volts.

In another aspect, the present invention provides a method of fabricating an optical modulator comprising a semiconductor device, the semiconductor device having: an optical input for receiving a continuous wave coherent beam having a predetermined power; a waveguide in the semiconductor device for transmitting the light beam; an electrode disposed on the semiconductor device and coupled to an RF signal input and a bias potential to form an electric field in the waveguide and traversing the beam The waveguide pair The beam is optically modulated; and an optical output is coupled to the waveguide in the semiconductor device to transmit the modulated optical signal, the method comprising the steps of: defining the continuous wave coherent beam to be applied to the modulator a wavelength for determining a wavelength-dependent gain of an optical signal in the waveguide for each predetermined composition of the waveguide; and fabricating the waveguide with a particular composition such that a wavelength of the optical signal varies with wavelength The predetermined wavelength of the continuous wave coherent light beam to be applied to the modulator is greater than 10 nm.

In another aspect, the present invention provides a method of fabricating an optical modulator comprising a semiconductor device, the semiconductor device having: an optical input for receiving a continuous wave coherent beam having a predetermined power; a waveguide in the semiconductor device for transmitting the light beam; an electrode disposed on the semiconductor device and coupled to an RF signal input and a bias potential to form an electric field in the waveguide and traversing the beam Optically modulating the beam when the waveguide is; and an optical output coupled to the waveguide in the semiconductor device to transmit the modulated optical signal, the method comprising the steps of: specifying the to be applied to the modulator a wavelength of a continuous wave coherent beam; an electroluminescence measurement is performed on the modulator under an open circuit condition to determine a wavelength-dependent gain of an optical signal in the waveguide; the waveguide is fabricated using a particular composition The gain peak of an optical signal as a function of wavelength is greater than the specified wavelength of the continuous wave coherent beam to be applied to the modulator by more than 10 nm.

In another aspect, the present invention provides a method of fabricating a laser transmitter for optical communication comprising a semiconductor device, the semiconductor device comprising: (a) a first semiconductor region for responding to a current Injecting to produce a dimming output; and (b) a second semiconductor region disposed adjacent to the first semiconductor region and separated therefrom by a channel, the second semiconductor region having an optical coupling thereto Receiving, by a semiconductor region, an optical input of the same dimming output and connecting to the second semiconductor region to transmit an optical output of the modulated optical signal, the method comprising: providing the transmitter to be designed to operate underneath one of the predetermined a wavelength value; forming a laser resonator in the first semiconductor region; Forming a semiconductor waveguide structure in the second semiconductor region to transmit the same dimming output from the first semiconductor region beam; forming an optical modulator in the semiconductor waveguide structure, the optical modulator comprising a quantum well region An active layer and an electrode coupled to an RF signal input and a bias potential to form an electric field in the waveguide structure such that the dimming output is optically modulated as the beam traverses the waveguide And determining an electroluminescence measurement of the modulator under an open circuit condition to determine a gain of the optical signal in the waveguide as a function of wavelength; determining a material composition of the quantum well region such that the modulation The transducer is optically transparent to the dimming output at a gain peak wavelength that is greater than a predetermined wavelength by a predetermined amount; and the modulator is fabricated from the determined material composition.

In certain embodiments, the predetermined amount of wavelength difference is greater than 10 nm but less than 50 nm.

In another aspect, the invention provides an electro-optical arrangement comprising a semiconductor device, the semiconductor device comprising: (a) a first semiconductor region operative to respond to current injection at a specified wavelength Generating a laser resonator of a continuous wave and a dimming output; and (b) a second semiconductor region disposed adjacent to the first semiconductor region and separated therefrom by a channel, the second semiconductor region having a first semiconductor region of the same composition and comprising optically coupled to the first semiconductor region to receive an optical input of the same dimming output from the first semiconductor region, the second semiconductor region being lower than the first semiconductor region by a second The bias potential is energized and electrically coupled to a signal source containing radio frequency information such that a current is generated in the second semiconductor region and current is extracted therefrom while being transmitted in the second semiconductor region by the signal pair The coherent beam is optically modulated such that the gain peak of the optical signal varies with wavelength than the specified wave of the continuous wave coherent beam applied to the modulator A large 10nm or more.

In another aspect, the present invention provides a method of fabricating an optical modulator comprising: an RF signal input containing information; a semiconductor device having optical for receiving and optically connecting one of the coherent beams The RF signal is input and has one of the modulated bias potential electrodes, such that a current is generated in the semiconductor device and current is extracted therefrom. A particular composition fabricates a waveguide such that the coherent beam is optically modulated by a signal such that the gain peak of the optical signal as a function of wavelength is greater than the specified wavelength of the continuous wave coherent beam applied to the modulator by 10 nm the above.

In another aspect, the present invention provides an optical modulator comprising: a radio frequency signal input containing information; a semiconductor device having optical means for receiving an optical input of the coherent beam and connecting to The RF signal is input and has an electrode of a modulated bias potential, such that a current is generated in the semiconductor device and a current is extracted therefrom, and the coherent beam is optically modulated by the signal, so that the optical signal has a wavelength The varying gain peak is greater than the specified wavelength of the continuous wave coherent beam applied to the modulator by more than 10 nm.

In another aspect, the present invention provides an electro-optic arrangement comprising a semiconductor device, the semiconductor device comprising: a first semiconductor region comprising a laser operable to generate a dimming output in response to current injection a resonator; and a second semiconductor region disposed adjacent to the first semiconductor region and separated therefrom by a channel, the second semiconductor region having optical coupling thereto to receive the same dimming output from the first semiconductor region An optical input, the second semiconductor region being energized and biased by a second bias potential lower than the first semiconductor region and electrically coupled to a signal source comprising radio frequency information such that a second semiconductor region is generated The current is drawn from the current and the homology beam is optically modulated such that the gain peak of the optical signal as a function of wavelength is greater than the specified wavelength of the continuous wave coherent beam applied to the modulator by more than 10 nm.

In another aspect, the present invention provides a laser transmitter for optical communication, comprising: a first semiconductor device operative to generate a response to current injection at a first bias potential a laser resonator having a dimming output; a second semiconductor device disposed adjacent to the first semiconductor device and having an optical input optically coupled thereto for receiving the same dimming output, the second semiconductor device being One of the second lower bias potentials of the first semiconductor device is electrically biased and electrically coupled to a signal source containing radio frequency information, such that A current is generated in the second semiconductor device and current is extracted therefrom, and the coherent beam is optically modulated such that the gain peak of the optical signal varies with wavelength than the continuous wave coherent beam applied to the modulator The predetermined wavelength is 10 nm or more.

In another aspect, the present invention provides a method of fabricating a laser transmitter for optical communication, the laser transmitter comprising: a first semiconductor device operative to operate at a first bias voltage Positioning a laser resonator in response to current injection to produce a dimming output; a second semiconductor device disposed adjacent to the first semiconductor device and having an optical input optically coupled thereto for receiving the same dimming output The second semiconductor device is electrically biased and electrically coupled to a signal source containing radio frequency information at a second bias potential lower than the first semiconductor device, such that a current is generated in the second semiconductor device. At the same time, the coherent beam is optically modulated such that the gain peak of the optical signal as a function of wavelength is greater than the specified wavelength of the continuous wave coherent beam applied to the modulator by more than 10 nm.

In another aspect, the present invention provides a method of operating an optical modulator comprising a semiconductor device, the semiconductor device having: an optical input for receiving a continuous wave coherent beam having a predetermined power; a waveguide layer for transmitting the light beam; an electrode coupled to an RF signal input and a bias potential to form an electric field in the waveguide and optically modulating the beam as the beam traverses the waveguide And an optical output coupled to the waveguide for transmitting the modulated optical signal, the method comprising: applying a continuous wave coherent beam to the optical input; and applying a bias voltage to the electrode such that the coherence The beam is optically modulated and the gain peak of the optical signal as a function of wavelength is greater than the specified wavelength of the continuous wave coherent beam applied to the modulator by more than 30 nm.

In another aspect, the present invention provides a method of fabricating an optical modulator by determining a material composition of a quantum well region in a waveguide portion of the modulator such that the modulator is at a predetermined ratio The wavelength is greater than a predetermined amount of the gain peak wavelength is transparent; and the modulator is fabricated using the determined material composition.

In some embodiments, the modulator operates at wavelengths from 1540 nm to 1550 Between nm.

In some embodiments, the gain peak of an optical signal as a function of wavelength is greater than the specified wavelength of the continuous wave coherent beam to be applied to the modulator by more than 20 nm.

In some embodiments, the gain peak of an optical signal varies with wavelength by more than 30 nm greater than the specified wavelength of the continuous wave coherent beam to be applied to the modulator.

In some embodiments, the operating wavelength of the modulator is at least 30 nm lower than the gain peak wavelength.

In some embodiments, the operating wavelength of the modulator is 30 nm to 40 nm lower than the gain peak wavelength.

In some embodiments, the operating wavelength of the modulator is 40 nm below the gain peak wavelength.

In some embodiments, the laser is integrated with the modulator on a single semiconductor substrate.

In another aspect, the bias potential applied to the laser is less than the bias potential applied to the modulator.

In some embodiments, the external electrical bias potential applied to the modulator is plus or minus 0.1 volts.

In some embodiments, the modulator is optically pumped to a level of 0.8 volts by a beam from the laser.

In another aspect, the modulator generates a current from the photovoltaic effect in operation, the current being drawn from the modulator.

In another aspect, the carrier density along the length of the semiconductor modulator in the direction of the beam is modulated, thereby optically modulating the continuous wave beam entering the modulator.

In another aspect, the modulator includes an InP semiconductor waveguide structure.

In another aspect, the laser includes a mirror image having a placement adjacent to the modulator An InP semiconductor gain structure of one of the first end region and the second end region.

In another aspect, the laser includes a first electrode disposed over the InP semiconductor gain structure.

In another aspect, the modulator includes a second electrode disposed over the InP semiconductor waveguide structure.

In another aspect, the laser and the modulator are integrated on a single semiconductor substrate and extend approximately one micron into a vertical gap in the substrate to electrically separate the laser from the modulator. The laser is optically coupled to the modulator by a common optical waveguide.

Additional objects, advantages and novel features of the invention are apparent from the <RTIgt; Although the invention is described below with reference to the preferred embodiments, it should be understood that the invention is not limited thereto. Those skilled in the art who have read the teachings herein will recognize additional applications, modifications, and embodiments in other fields, and such additional applications, modifications, and other embodiments in the field are disclosed and claimed herein. Within the scope of the invention, and with regard to it, the invention may have utility.

10‧‧‧Transmitter

11‧‧‧Semiconductor laser/laser

12‧‧‧ fiber

13‧‧‧Transformer

14‧‧‧Information/information

15‧‧‧Broadband RF signals

16‧‧‧Electric bias

17‧‧‧Amplifier/Doped Fiber Amplifier

20‧‧‧Fiber path/fiber link/fiber transmission link

30‧‧‧Remote Receiver/Receiver

31‧‧‧RF signal

32‧‧‧Terminal/Monitor

50‧‧‧ fiber

51‧‧‧External modulator/modulator

53‧‧‧ RF signals/RF signals with information

55‧‧‧ Output fiber

100‧‧‧Semiconductor device / laser resonator

102‧‧‧Ground electrode

103‧‧‧First semiconductor region/region/InP semiconductor gain structure region/InP semiconductor gain structure/first semiconductor device/source laser

104‧‧‧Second semiconductor region/InP semiconductor waveguide structure

105‧‧‧ channel

106‧‧‧External electric bias potential

107‧‧‧electrode/first electrode

108‧‧‧ bias potential

109‧‧‧electrode/second electrode

110‧‧‧RF input signal

112‧‧‧ Optical output

These and other features and advantages of the present invention will be more fully understood and appreciated from the <RTIgt; An example of a modulated optical transmission system; FIG. 2 is a first embodiment of an external modulator coupled to a laser in accordance with the present invention; and FIG. 3 is coupled to one of the lasers in accordance with the present invention. A second embodiment of a modulator; FIG. 4 is a graph of current versus voltage operating characteristics of an electro-optical modulator of one of various input powers in accordance with the present invention and in accordance with the present invention; FIG. 5 is a diagram illustrating A plot of modulator output power versus modulator input power at various current operating levels; Figure 6 illustrates the various operating levels of a Mach-Zehnder or EA modulator as known in the prior art. a plot of the output power of the modulator to the input power of the modulator; Figure 7 is a graph showing one of the modal gain versus wavelength for a given composition of the modulator for a given modulator; 8 series painted in a given Modal gain for one of the wavelengths of the flow chart. The gain peak wavelength is indicated by λ ₀ , and one of the potential operating wavelength ranges for a modulator waveguide design is from λ ₁ to λ ₂ ; Figure 9 is a graph showing modal gain vs. wavelength. For a given composition of one of the modulator waveguides, the gain peak wavelength is indicated by λ ₀ , a potential operating wavelength range is from λ ₁ to λ ₂ , and a selected operating wavelength is indicated by λ ₃ ; A graph of modal gain vs. wavelength for one of the electroluminescence measurements of a sample test modulator at various modulator current values; and Figure 11 shows the same pair of current values from various modulators A test chart of one of the gain peak wavelength versus current for one of the electroluminescence measurements.

Additional objects, advantages and novel features of the invention are apparent from the <RTIgt; Although the invention is described below with reference to the preferred embodiments, it should be understood that the invention is not limited thereto. Those skilled in the art who have read the teachings herein will recognize additional applications, modifications, and embodiments in other fields, and such additional applications, modifications, and other embodiments in the field are disclosed and claimed herein. Within the scope of the invention, and with regard to it, the invention may have utility.

The details of the invention, including its illustrative aspects and embodiments, are now set forth. The same element symbols are used to identify the same or functionally similar elements, and are intended to illustrate the main features of the exemplary embodiments in a highly simplified illustration. In addition, the drawings are not intended to depict each feature of the actual embodiments and the The dimensions are not drawn to scale.

A reference to "an embodiment" or "an embodiment" in this specification 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 an embodiment" or "in an embodiment" Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.

1 is a block diagram of a prior art optical transmission system in which information or "content" (such as audio, video, data files, databases, or other materials) is transmitted by an optical transmitter to a remote end via a fiber optic link. The information content is copied, displayed, executed, implemented, or otherwise utilized. An optical transmitter can be shown, for example, in U.S. Patent No. 5,699,179, the disclosure of which is incorporated herein. A transmitter (generally shown at 10) transmits an optical signal to a remote receiver 30 via a fiber path 20. Transmitter 10 includes a semiconductor laser 11 that produces a continuous wave (CW) output. A typical example of such a laser is a distributed feedback (DFB) laser or a Fabry-Perot laser that produces an output beam at one of the wavelengths of 1,550 nm. The unmodulated optical signal from the laser is coupled to a modulator 13 by an optical fiber 12. The modulator 13 can be a single modulator (such as a Mach-Zehnder modulator), a cascade MZ modulator, or more than one modulator (such as in a feedforward linearizer).

Information or content-containing signals 14 (such as audio, video or data) are initially converted into a wideband RF signal (such as an amplitude modulated vestigial sideband (AM-SDB) cable television (CATV) or video signal in a suitable transmission channel or frequency band. Or represent a digital signal (such as a Quadrature Amplitude Modulation (QAM) symbol) in a digital format. The wideband RF signal 15 is applied to the modulator 13 via one of the terminals or electrodes on its surface. An electrical bias 16 is also applied to the modulator 13.

In some embodiments, the modulated optical signal carrying video data can be coupled to an amplifier 17, which in turn is coupled to a fiber optic link 20. Amplifier 17 is typically a doped fiber amplifier (FDFA). The amplified optical signal is transmitted via the fiber optic transmission link 20 To the receiver 30. The fiber optic transmission link 20 can be a long distance link extending up to 100 km. In this case, a line amplifier (such as EDFA 17) may be provided at spaced intervals along the line to boost the signal to the desired level. At the receiver 30, an amplifier (not shown) may also be provided to boost the incoming optical signal. The boosted signal is then applied to a photodetector and demodulated at the receiver 30 to become an RF electrical signal 31 that is applied to a terminal or display 32 where the original audio is copied at the remote location , video or data signal.

2 is a first embodiment of an optical transmitter including an external modulator coupled to one of the lasers in accordance with the present invention. A semiconductor laser 11 that produces a continuous wave (CW) output is shown. The laser 11 operates under an electrical bias expressed as one of the bias voltages (1). The unmodulated beam from the laser is coupled to an external modulator 51 by fiber 50 or by free space propagation. The modulator 51 is configured to have one of the electrodes coupled thereto and operated under an electrical bias expressed as one of the bias voltages (2), the bias voltage (2) being less than the bias voltage (1). In some embodiments, the bias voltage (2) can be 0.8 volts and the bias voltage (1) can be 1.2 volts. In some embodiments, the bias voltage (2) can be derived from the value of the voltage that would occur if the modulator was pumped by the source laser and self-coupled to the electrode of the modulator without current injection or extraction. Or minus 0.1 volts. In some embodiments, the bias voltage (2) can range from 0.7 volts to 0.9 volts. In some embodiments, the bias voltage (2) can range from 0.6 volts to 01.0 volts.

The information-containing RF signal 53 is also applied to the electrodes of the modulator 51 such that during modulation, the electrical bias applied to the modulator remains less than the bias (1). The electrical bias applied to the modulator 51 determines the amount of continuous wave beam from the laser 11 that is absorbed by the modulator 51. In this way, the continuous wave beam entering the modulator is modified or modulated by the RF signal 53. An optical output is provided to deliver the modulated beam to an output fiber 55.

3 is a second embodiment of one of the external modulators coupled to a laser in accordance with the present invention. The design and operation of the apparatus of Figure 3 is similar to the design and operation of the apparatus of Figure 2 except that the laser and modulator are implemented on a single integral semiconductor device. More specifically, the semiconductor device 100 includes one of the following: a first semiconductor region 103, which includes A laser resonator that produces a dimming output in response to current injection; and a second semiconductor region 104 disposed adjacent to the first semiconductor region and separated therefrom by a channel 105. The second semiconductor region 104 has an optical input optically coupled thereto for receiving a dimming output that is emitted from the first semiconductor region 103 and traverses the channel 105.

The first semiconductor region 103 is electrically biased by an electrode 107 on the top surface that is coupled to an external electrical bias potential 106 to inject current into the region 103. The second semiconductor region includes: a waveguide layer for transmitting a light beam from the optical input; an electrode 109 coupled to a RF signal input 110 and a bias potential 108 to form an electric field in the waveguide and in the beam transverse direction The beam is optically modulated as it passes through the waveguide. The second semiconductor region further includes an optical output 112 coupled to the waveguide to transmit the modulated optical signal to an external optical fiber or other optical component. The bias voltage applied to the electrode 109 is suitably selected such that the coherent beam in the waveguide is optically modulated by the applied RF signal by modifying or modulating the absorption characteristics in the semiconductor device while extracting from the semiconductor device due to continuous The light of the wave coherent beam absorbs the current generated in the waveguide. The resulting RF and DC currents are drawn by the RF source and DC bias, respectively.

In some embodiments, the laser and modulator comprise a single wafer InP semiconductor device. The laser can include an InP semiconductor gain structure region 103 having one of a mirrored first end region and a second end region disposed adjacent to the modulator. The first electrode 107 is disposed over the InP semiconductor gain structure 103, and the second electrode 109 is disposed over the InP semiconductor waveguide structure 104, and a ground electrode 102 is provided to extend over the bottom surface of the entire semiconductor structure.

In embodiments in which the laser and modulator are integrated on a single semiconductor substrate, extending about 1 micron into one of the vertical gaps in the substrate, the laser and modulator or first semiconductor region 103 and second semiconductor Region 104 is electrically separated.

In other embodiments, the laser and modulator are implemented on two adjacent discrete semiconductor devices, such as depicted in FIG. In some embodiments, having a width of less than 1 micron One of the air gaps separates the laser from the modulator device.

The first semiconductor region 103 is electrically biased by an electrode 107 on the top surface that is coupled to an external electrical bias potential 106. The second semiconductor region 104 is biased with a second bias potential that is lower than the first semiconductor region 103. The particular bias voltage of the second semiconductor region 104 and the operating current versus voltage characteristics of the device will be explained in more detail with reference to FIG.

4 is a graph of current versus voltage operating characteristics of one of the electro-optical modulators of the various input powers (ie, 10 mW, 20 mW, 30 mW, and 40 mW) for the continuous wave beam in the prior art and in accordance with the present invention. In the prior art, in an electroabsorption modulator, the waveguide is biased to operate in a negative voltage, positive current region as shown by the dashed line region labeled "Prior Art EA Operating Range." In a modulator according to the present invention, the waveguide is biased to operate in a positive voltage, higher negative current region as shown by the dashed line region labeled "Proposed Operating Range."

In the absence of any applied bias signal, a small number of continuous wave beams are absorbed in the modulator and this causes a steady state carrier density to accumulate in the modulator. These carriers are recombined with a typical lifetime of approximately one nanosecond. An equalization level is reached when the number of carriers generated by optical absorption is balanced by the number of losses lost by recombination. In one embodiment, the absorption is high when the carrier level is low; and the absorption is low when the carrier density is high. The self-modulator extracts the carrier when a bias signal is applied. This reduces the carrier density and thus increases the absorption of the modulator. In particular, if the self-modulator extracts one of the currents of -10 mA, the absorption increases by one amount required to produce a current of -10 mA. Similarly, if the self-modulator extracts one of the currents of -20 mA, the absorption increases by one amount required to produce a current of -20 mA. Another way of describing the operation is that the carrier generated by the continuous wave beam in the semiconductor waveguide is excited into a conductive strip and extracted from the semiconductor region by an applied electrical bias field.

Figure 5 shows a plot of output power versus input power of a modulator in accordance with the present invention, wherein the parameters are currents drawn from the modulator. Since the proposed modulator has a low RF impedance, it may be modulated in a manner close to one of the current source modulations (at least As low as the output power is close to zero). As can be seen from Figure 5, this actually modulates the saturation power of the device. When operating at a fixed input power of, for example, 30 mW, the net effect is modulated by one of the optical output powers. The operation is similar to an optical power reduction device in which one of the light amounts corresponding to one of the extracted currents is absorbed from the input continuous wave beam. In fact, the absorption mechanism is saturated after absorbing the amount of light corresponding to the extracted current.

The operation of the modulator of Figure 5 should be compared to a conventional modulator in which the modulated optical transmission factor is one. Figure 6 shows what happens with an MZ or EA type modulator. The parameters in this Figure 6 are transmitted through the modulator. For one of the fixed input powers of 30 mW, a modulated output similar to one of the outputs of the proposed modulator is produced. However, the change in output optical power and input optical power by a fixed bias signal is substantially linear compared to the saturation type variation of the proposed modulator. This reflects the fundamentally different modulation mechanisms involved in the proposed modulator.

Figure 7 is a graph showing one of modal gain versus wavelength for a given modulator current value for a given one of the modulator waveguides. It should be noted that there are different maximum or peak modal gain values for different current values through the modulator.

Figure 8 is a graph showing one of modal gain versus wavelength for a given current. The gain peak wavelength is indicated by λ ₀ and one of the potential operating wavelength ranges for a modulator waveguide design is from λ ₁ to λ ₂ .

Figure 9 is a graph showing one of modal gain versus wavelength. For a given composition of one of the modulator waveguides, the gain peak wavelength is indicated by λ ₀ , a potential operating wavelength range is from λ ₁ to λ ₂ , and a selected operating wavelength is indicated by λ ₃ .

In the proposed arrangement according to the invention, the material in the modulator section 104 is primarily pumped by light from a source laser 103 that operates DC. In a test environment, the modulator can be evaluated under open circuit conditions in which neither DC current is injected nor DC current is extracted from the modulator. Under this open circuit condition, the material in the modulator section 104 is pumped to give a carrier density that is only below the level at which the material becomes optically transparent or has no net absorption or gain. degree. Under this condition, the modulator junction is at a voltage corresponding to a forward bias of approximately 0.8 volts (similar to the open circuit voltage of a solar cell).

The modulator does not have to be used with an open circuit bias condition. The modulator can be biased by injecting current, in which case the material will move towards the optical gain or the extraction current, in which case the absorption is increased compared to the open circuit bias conditions. The current values in the curves plotted in Figure 7 are intended to be nominal or representative only for typical gain peak wavelengths at different current values, since the data presented are derived from electro-pump only One prototype test structure, which differs from the proposed modulator that will be used in practice and will be primarily optically pumped. Although it is experimentally impossible to directly measure the optical gain curve for the passion of the optical pump, the data is suggestive and believed to be similar to the curve plotted in Figure 7 for the electrically pumped test structure, for the optical pump passion The corresponding curve moves upwards and to the left for the increased current.

The present invention does not specify the signal wavelength relative to the modulator gain curve, as it may depend on other product design specifications and the customer application environment. However, one aspect of the present invention is directed to the design of an optical modulator and how to specify the wavelength of the material for a given operational specification or requirement. Both methods are reasonable and are embodiments of the invention. One method is to determine the photoluminescence (PL) peak wavelength. In this case, the material is optically pumped and the spectrum of the light emitted from the material is measured by a commercially available photoluminescent apparatus. This measurement of the photoluminescence (PL) peak wavelength is different from the measurement of the gain curve, but it is correlated. For example, the material used for the gain profile presented in Figure 10 has a PL peak wavelength of 1574 nm. A second method would specify the peak of the gain curve for a particular pumping condition. All pumping is a good experimental method for specifying a gain peak because there is no gain peak, and absorption only steadily increases as the wavelength decreases. Pumping the modulator until there is a gain peak at a particular level is another way of trying to dictate this, but is believed to be well defined as the PL peak. An embodiment of the present invention thus provides a method of making a PL measurement and using a PL wavelength, thus determining one of the characterization materials. In terms of operation, It would be desirable to have the signal wavelength be below the PL peak, which is different from the design of the semiconductor material in the EA modulator, where the signal wavelength in the EA modulator is typically much larger than the peak PL wavelength. An embodiment of the invention thus provides a choice or specification of operating wavelengths that are at least 10 nm lower than the PL peak. In some embodiments, the selection or specification of the operating wavelength is an operating wavelength that is 30 nm lower than the PL peak.

Figure 10 is a graph showing one of modal gain versus wavelength for one of the electroluminescence (EL) measurements of a sample test modulator at various modulator current values. In one embodiment of the invention, the peak wavelength of the zero current is presumed to characterize one of the materials in an appropriate and precise manner. In the case illustrated in Figure 10, the peak wavelength is about 1589 nm. This is different from the PL characteristic, which is 1574 nm for the same test wafer. In terms of the operating wavelength to be used with this material, in one embodiment of the invention, the suitable wavelength will be in the range of 1540 nm to 1550 nm. In another embodiment of the invention, the operating wavelength will be at least 30 nm below the gain peak wavelength. In another embodiment of the invention, the operating wavelength will be in the range of 40 nm to 30 nm below the gain peak wavelength.

Figure 11 is a graph showing one of gain peak wavelength versus current from one of the sample test modulators at various modulator current values.

Based on the foregoing characteristics of the material, in one embodiment of the present invention, the present invention provides a method of fabricating a laser transmitter for optical communication comprising a semiconductor device, the semiconductor device comprising: (a) a first a semiconductor region for generating a dimming output in response to current injection; and (b) a second semiconductor region disposed adjacent to the first semiconductor region and separated therefrom by a channel, the second semiconductor region Having optical input optically coupled thereto for receiving one of the coherent light output from the first semiconductor region and for connecting to the second semiconductor region to transmit an optical output of the modulated optical signal, the method comprising the steps of: providing the transmission The device is designed to operate a predetermined wavelength value therein; forming a laser resonator in the first semiconductor region; forming a semiconductor waveguide structure in the second semiconductor region to transmit the light beam from the first semiconductor region Same dimming Forming an optical modulator in the semiconductor waveguide structure, the optical modulator comprising an active layer having a quantum well region and an electrode connected to an RF signal input and a bias potential to Forming an electric field in the waveguide structure such that the dimming output is optically modulated as the beam traverses the waveguide; and determining a material composition of the quantum well region such that the modulator is greater than a predetermined wavelength One of the amounts is transparent at a peak wavelength; and the modulator is fabricated from the determined material composition.

While the invention has been described with respect to the specific embodiments of the present invention, the embodiments of the invention are intended to be illustrative and not intended to limit the scope of the invention. It is to be understood that the above embodiments may be modified without departing from the scope and spirit of the invention as defined by the appended claims.

11‧‧‧Semiconductor laser/laser

16‧‧‧Electric bias

50‧‧‧ fiber

51‧‧‧External modulator/modulator

53‧‧‧ RF signals/RF signals with information

55‧‧‧ Output fiber

Claims (15)

A method of operating an optical modulator comprising a modulator optical waveguide formed on a substrate, the method comprising: (a) launching a continuous wave input optical signal to follow a modulator optical waveguide propagation, the input optical signal being characterized by an input optical power level and an optical signal wavelength; and (b) applying an electrically modulated signal to the optical waveguide of the modulator a semiconductor modulator is disposed on one of the modulator electrodes to modulate an optical transmission level of the input optical signal via the modulator, thereby causing a result in the modulation One of the emitted (emitted) modulated output optical signals, wherein: (c) the electrically modulated signal is applied with a positive voltage; (d) causing the carrier to be injected into one of the modulator layers The signal level produces an increment of the optical transmission level relative to the optical transmission level having a positive modulator bias voltage level applied to one of the modulator electrodes, which causes the carrier to be The input optical signal is transmitted along the optical waveguide of the modulator In which case the modulator is not implanted and is not extracted by the modulator active layer; and (e) causing the carrier to extract an electrical modulation signal level from the modulator active layer to produce the optical Decrease of a transmission level relative to having the optical transmission level applied to the modulator electrode, which causes the carrier to not propagate as the input optical signal propagates along the modulator optical waveguide The positive modulator bias voltage level that is injected into the modulator active layer is also not extracted by the modulator active layer. The method of claim 1, wherein the modulator active layer is characterized by an estimated optical gain peak wavelength, and the optical signal wavelength is shorter than the evaluated optical gain peak wavelength. The method of claim 2, wherein the optical signal wavelength (i) is shorter than the evaluated optical gain peak wavelength by about 10 nm, or (ii) is between about 20 nm and about 40 nm shorter than the evaluated optical gain peak wavelength. The method of claim 2 or 3, wherein the evaluated optical gain peak wavelength is one of peak wavelengths of an electroluminescence spectrum of one of the modulator active layers. The method of any one of claims 1 to 3, wherein the electrical modulation signal comprises a substantially constant modulator bias voltage and one of the modulator electrodes is applied to carry information RF modulation The sum of one of the signals. The method of claim 5, wherein the modulator bias voltage is within ±0.1 volts of a voltage, the input optical signal present at the input optical power level and not present in the RF modulated signal A negligible carrier is injected into or extracted from the active layer. The method of claim 5, wherein the modulator bias voltage is applied and the RF modulation signal is generated on a portion of one of the negative current regions of the carrier extracted from one of the IV characteristics of the modulator (over) the modulator active layer. The method of any one of claims 1 to 3, further comprising generating the continuous wave input optical signal from a semiconductor laser by applying a substantially constant electrical laser bias voltage to a laser electrode The laser electrode is disposed on a semiconductor laser action region of one of the laser optical waveguides formed on the substrate, wherein the laser electrode and the modulator waveguide are disposed such that at least the optical output of the semiconductor laser is A portion is transmitted along the modulator optical waveguide to propagate the input optical signal. The method of claim 8, wherein the laser optical waveguide comprises a grating region having a grating period that produces a wavelength of the optical signal that is shorter than the evaluated optical gain peak wavelength. The method of claim 8, wherein (i) the laser electrode and the modulator electrode are electrically isolated by a vertical gap formed in the semiconductor material between the electrodes, or (ii) the laser waveguide And the modulator optical waveguide is a distinct portion of the shared optical waveguide formed on the substrate. The method of claim 8, wherein the laser bias voltage is greater than the modulator bias voltage. The method of claim 8, wherein the laser optical waveguide comprises a reflective first end region and a second end region adjacent to one of the modulator optical waveguides. The method of claim 8, wherein the semiconductor laser comprises InP. The method of any one of claims 1 to 3, wherein the optical modulator comprises InP or the modulator active region comprises a semiconductor multi-quantum-well structure. The method of any one of claims 1 to 3, wherein the optical signal wavelength is between about 1540 nm and about 1550 nm.