CA2287134A1 - Top contact vcsel with monitor - Google Patents
Top contact vcsel with monitor Download PDFInfo
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- CA2287134A1 CA2287134A1 CA002287134A CA2287134A CA2287134A1 CA 2287134 A1 CA2287134 A1 CA 2287134A1 CA 002287134 A CA002287134 A CA 002287134A CA 2287134 A CA2287134 A CA 2287134A CA 2287134 A1 CA2287134 A1 CA 2287134A1
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- vcsel
- chip
- assembly
- monitor
- package
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/02—Structural details or components not essential to laser action
- H01S5/022—Mountings; Housings
- H01S5/0225—Out-coupling of light
- H01S5/02257—Out-coupling of light using windows, e.g. specially adapted for back-reflecting light to a detector inside the housing
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
- H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
- H01L2224/42—Wire connectors; Manufacturing methods related thereto
- H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
- H01L2224/48—Structure, shape, material or disposition of the wire connectors after the connecting process of an individual wire connector
- H01L2224/4805—Shape
- H01L2224/4809—Loop shape
- H01L2224/48091—Arched
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L2924/00—Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
- H01L2924/19—Details of hybrid assemblies other than the semiconductor or other solid state devices to be connected
- H01L2924/191—Disposition
- H01L2924/19101—Disposition of discrete passive components
- H01L2924/19107—Disposition of discrete passive components off-chip wires
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/02—Structural details or components not essential to laser action
- H01S5/0201—Separation of the wafer into individual elements, e.g. by dicing, cleaving, etching or directly during growth
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/02—Structural details or components not essential to laser action
- H01S5/022—Mountings; Housings
- H01S5/023—Mount members, e.g. sub-mount members
- H01S5/02325—Mechanically integrated components on mount members or optical micro-benches
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/02—Structural details or components not essential to laser action
- H01S5/022—Mountings; Housings
- H01S5/0233—Mounting configuration of laser chips
- H01S5/02345—Wire-bonding
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/02—Structural details or components not essential to laser action
- H01S5/022—Mountings; Housings
- H01S5/0235—Method for mounting laser chips
- H01S5/02355—Fixing laser chips on mounts
- H01S5/0237—Fixing laser chips on mounts by soldering
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/04—Processes or apparatus for excitation, e.g. pumping, e.g. by electron beams
- H01S5/042—Electrical excitation ; Circuits therefor
- H01S5/0421—Electrical excitation ; Circuits therefor characterised by the semiconducting contacting layers
- H01S5/0422—Electrical excitation ; Circuits therefor characterised by the semiconducting contacting layers with n- and p-contacts on the same side of the active layer
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
- H01S5/062—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium by varying the potential of the electrodes
- H01S5/06226—Modulation at ultra-high frequencies
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/06—Arrangements for controlling the laser output parameters, e.g. by operating on the active medium
- H01S5/068—Stabilisation of laser output parameters
- H01S5/0683—Stabilisation of laser output parameters by monitoring the optical output parameters
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
- H01S5/00—Semiconductor lasers
- H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
- H01S5/18—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities
- H01S5/183—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
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- Physics & Mathematics (AREA)
- Condensed Matter Physics & Semiconductors (AREA)
- General Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Optics & Photonics (AREA)
- Semiconductor Lasers (AREA)
Abstract
A vertical cavity surface emitting laser (VCSEL) and monitoring diode combination having reduced parasitic capacitance for use in high bandwidth communications systems. The VCSEL has both p-type and n-type contacts on the same face. This allows the VCSEL to be mounted on a monitor chip or diode without using a metal contact layer. In an embodiment wherein the VCSEL is soldered to the monitor chip for mechanical stability only a small metal pad no larger than the VCSEL
is used.
The reduction in metallisation results in a lower parasitic capacitance that io turn results in higher potential operational speeds,
is used.
The reduction in metallisation results in a lower parasitic capacitance that io turn results in higher potential operational speeds,
Description
Field of the Tnvention This invention relates to a vertical cavity surface emitting laser (VCSEL) with associated output monitoring device and more particularly to such a combination for use in high bandwidth applications.
Back ~r~, ound of the Invention Lasers, and in particular semiconductor lasers, sucli as tliose formed of ILI-V
compounds, are commonly employed as the transmitter in digital comn~.uaication systems. Lasers of this type arc particularly well suited for optical fiber based systems l0 wherein the optical output of the laser is modulated in accordance with an electrical input to the device. The modulated optical signal can be transferred over relatively long distances using current optical fiber transmission systems.
Early lasers used in such applications included edge emitting lasers wherein the cleaved edges of the device provided the reflecting faces of the Fabry-Perrot cavity. Bdge ccnitting Lasers, however, have certain limitations with respect to pre-assembly testing aztd mounting techniques for efficient coupling to small diameter optical fibers.
Surface emitting lasers and in pazt7cular vertical cavity surface emitting lasers (VCSELs) have been developed recently and provide an improvement over edge ~~nittiug devices for use in optical fiber communication applications. The VCSEL which has its 2 o active region located between two reflecting layers, such as Bragg mirrors, emits in a plane normal to one of the two major surface of the laser device. As is known such devices include material of a first conductivity type, for example n-type, for one of the Bragg ntirrors and material of a second conductivity type, namely p-type, for the other Bragg min-or.. The intermediate active region or layer may include a cladding layer adjacent each of the Bragg mirrors. The Bragg mirrors are iypically formed of alternate layers of 111-V senticonduetor material each layer having a different reflectivity eharaeteristic_ Each alternate layer typically has a thickness equal to one quarter wavelength based on the enussion wavelength of the active material.
In this stricture, and in particular top emitting YCSELs, the back or bottom surface of the device is usually attached to a mounting substrate and the Laser output is c~itted through the top or front face of the device. An emitting aperture, which may be defined by one of the device contacts, is typically configured to allow alignment witli an optical fiber. Such devices are fabricated using well established processing techniques l0 and provide reliable lasers which may be coavectiently assembled into optical hansmitter tmits_ The nature of VCSfiI.s, and indeed semiconductor lasers in general, is that the electrical and optical characteristics between each device may vary slightly.
The optical output taken as a function of input current daring lasing action represents a steep slope and minor variations in the operating environment can result in significant output changes. For this reason, it is common to include a moruitoxing diode or rttonitor chip with a VCSEL, wherein the monitor chip is arranged to receive a representative portion of the optical output. This representative output can be used to calibrate eacli laser device or it can be used in a feedback mode to control the optical output of the laser.
Control tnay 2 o be required to ensure that the optical output of the laser falls within a preset liatit such as might be required by "eye safe" regulations prescribed by Standards Agencies.
Typically the monitoring diode will be a phototzaasistor such as a PIN device having a sensitivity curve geaerally matched to the wavelength output of the laser_ Laser/monitor cotxibiuarions are frequently mounted in a specially designed package such as a TO-46 eau which has a mounting base with insulated connector leads and a sealed cover. Tlie cover has a window of glass or other suitable transparent material over a central portion of the top such that the window is aligned with ti.~e emitting aperture of the lacing device_ One such combination is described in US Patent 5,812,58?
which issued September 22, 1998 to Gilliland et al. In the 5,812,582 patent the photodiode is mounted on an insulated substrate that is positioned within in a TO-46 can, or the Iike. A large portion, of the top surface of the photodiodc is covered with a metal layer oc mask. A VCSIrL is electrically attached to the mask by solder or conductive 1 o epoxy and one of the contacts to the VCSEL, i.e. the back contact, is made by way of the mask. The top or emitting surface contact is through a wire bond to one of the isolated connectors in the TO-46 can.
The bandwidth capacity of cturent optical fibers far ekceeds the bandwidth utilixed by present day communication systems. Accordingly, there is a continuing effort, to increase the data rate of communication systems ui order to make better usage of optical fiber capabilities. Since the laser transmitter represents an important aspect of dte complete communication system it is important that the switching rate ofthe laser be as high as possible_ One factor which effects the switching rate in high speed devices is the parasitic capacitance of the VCSEL, die monitoring chip and the mounting configuration.
2 0 A further important eonsiderat~iota, of course i.s the cost of the optical transmitter or laser/monitor assembly_ Tltis cost includes the material processing costs as well as the cost of assembling the devices and in accurately aligning the device in relation to an optical fiber.
It is, accordingly, an object of the present invention to provide a low cost VCSEL/monitor device with reduced parasitic capacitance for high bandwidth applications.
Sununar~of the Invention In a preferred embodiment of the present i.nvcntion there is provided a VCSELlmoni.tor assembly in which the VCSEL has both p-type and n-type corLtacts on the top or emitting face and is mounted on a monitoring diode utilizing little or no metallisatiozr in the mounting technique.
Therefore, in accordance with a fu-st aspect of the present invention there is provided a vertical cavity surface emitting laser (VCSEL) and photo detecting monitor assembly comprising: a photo detecting moutor chip having a first photo detecting face and a second fact parallel thereto; a top emitting VCSEL, mounted on the first face of the monitor chip, the VCSEL having both. p-type and u-type contacts on a top surface.thercof;
and means associated with the assembly to direct a portion of the VCSEL
emission to the fast face of the monitor chip.
In accordance with a second aspect of the present invention there is provided a method of assembling a top emitting vertical cavity surface emitting laser (VCSEL) and photo detecting optical output monitoring chip pair comprising. providing a mouitoruig chip having a photo detecting surface; attaching a top emitting VCSEL to the detecting 2 0 surface, the VCSEL having p-type and n-type contacts on the top surface;
and providing means to contact the monitoring chip and the VCSEL.
Brief Description of the Drawings the invention will now be described in greater detail with reference to the attached drawings wherei.a:
Figucc 1 is a top view of a monitoc chip;
Figure 2 is a top view of a top emitting VCSEL having both contacts ou the emitting face;
Figure 3 is a cross-sectional view of a VCSfiL mounted on a monitor chip according to the present invention;
Figure 4 is a cross-sectional view of the assembly in a mounting case including a receptacle or sleeve for use in the connection to an optical fiber; and Figure 5 is a bandwidtlx curve showing modulation response as a function of fiequency.
~7etailed Description of the Tnvention Figure 1 repcesents one example of a monitor chip 10 for use in the present invention. The monitor is a photodiode, PIN, avalanche diode etc. In operation, surface 12 will be impinged with optical energy of an appropriate wavelength and this will result in an electrical output across contacts on the device. The electrical output will be dependent on the intensity of the oprical energy (from the laser in this application)~which is received by the photo detecting or monitor chip. One electrical contact is provided on the back surface (not shown) and it may be connected to a lead wire or mounted directly onto a substrate by well known means. Sinularly, a contact to the top or front face can be made by way of wire bonds to one or both of contact pads 14. Alternatively, the monitor diode may have both contacts on the same side and the electrical connections made by bonding to the puss, for contacts on top side, or by means of patterned electrodes on the 2 0 photodiode carrier for contacts on the bottom side.
As shown in Figure I, centrally positioned on the top surface of the monitor chip is an alignment mark 16. This may be a square, or substantial square, as shown is Figure 1 and correspond to the shape or outline of a VCSEL, to be described later.
Alternatively the alignment mark 16 may represent a small poirtion of the VC.S6L outline.
The alignment mark can be formed of an appropriate metal in order to allow the VCSEL to be soldered in an accurately aligned relationship with respect to the photodiode.
This alit' ent is important in relation to system packaging as will be described later.
Altemativcly, the alignment mark may be of a non-metallic layer as long as it provides a stable surface while providing a suitable alignment mark. It is, of course, possible in certain assembly techniques to position the VCSEL accurately on the monitor chip without the aid of a special alignment mark. For example, the contact pattern or chip edge can be utilized for alignment purposes.
As shou~tt in Figure 2, the VCSEL 20 according to the present invention has both 1.0 p and n-type contacts on the top surface. An emitting aperture 22 will typically be defined by one of the contacts 24 (for example p-type) which will be connected to the p-type Bragg mirror of the VCSEL structure. A second contact 26, n-type in this cxaunplc, will be connected to the a-type Bragg mirror as is known in ~c art. A current aperture is typically provided in the active region (not shown) in order to confine the injection current to the desired region of the stntcture. Contact pads 24 and 26 are formed of suitable material for accepting wire bonds or the like for connection to a suitable input source.
VCSEL 20 is shown. in Figure 2 as being substantially square while it is to be understood that other shapes and sizes of devices can be used in the present invention.
2 0 The alignment mark 16 on the monitor chip will, of course, need to be modified to correspond generally to the shape and size of the VCSEL chip if other configurations are used.
It is also within the scope of the present invention to use a bottom erui.ttiug VCSEL having both p-h~pe and n-type contacts on the bottom face.
Figure 3 shows a cross section of a VCSEL 20 stacked or mounted on the monitor chip 10. If the alignment mark is foamed of metal the back face of the VCSEL
chip wil I
have a suitable ntetallisation to allow the VCSEL to be attaclted to the monitor chip by soldering. In this case the VCSEL will be self aligned to the alignment mark by the soldering process. It is to be understood that the aligncnent mark can be restricted to some portion of the size of the VCSEL and still result in a good mechanical connection and be suitably aligned.
The VGSEL can also be attached to the monitor chip by a suitable epoxy, many of which are available for such purposes. The alignment mark in this case will preferably not be metal bur some other material such as a dielectric again having a pattern designed to assist an operator in the proper location of the VCSEL in relation to the monitor chip. As previously discussed certain assembly techniques will allow an operator to position the VCSEI. on the monitoring chip without the use of anj~ special alignment marks.
, .
Figure 4 is a cross sectional view of the assembly of Figure 3 mounted in a package such as a conventional TO-46 can. As shown the can includes posts or connectors 32 wltich are normally isolated but one may be non isolated for use in providing electrical input to the VCSEL and for monitoring the optical output of the VCSEL by way of the electrical signal generated across the monitor chip. The cover 42 includes a reflective surface 4.~ which cnay be a window or lens. The material for the 2 o reflective surface may be glass, plastic epoxy or other material at least partially transparent to the wavelength of the VCSEL. A portion of the Laser output will be reflected by the window 44 back inside the cover and will impinge on monitor chip surface 12 thus providing a signal which is proportional to the VCSEL output.
As will be apparent the positioning of the emitting aperture of the VCSEL with respect to an optical fiber coupled to the arrangement is critical.
Positioning the sub assembly, which rnay be a TO-46 can, a TO-56 can, a MT connector or other sub assembly, in relation to the fiber can be fixed by way of a receptacle or sleeve. It is therefore important that the VCSEL and hence the emitting aperture is well positioned with respect to the base of the TO-4.6 can The alignment mark oa the monitor chip assists in the positioning of the VCSEL with respect to the monitor chip and the positioning of the monitor chip with respect to the package can be arranged through other means. As shown in Figure 4 the central axis of the emitting apedure is aligned with the center of window 44 and the longitudinal axis of an optical fiber (not shown).
By reducing the amount of metal in the VCSELmonitor assembly of the present invention the parasitic capacitance is correspondingly reduced. The prior art device as described in US Patent 5,812,582 utilizes a metal mask or layer on top of the monitor cliip. Tlus mask in combination with the substrate oa which the chip is mounted act as a plate capacitor and the parasitic capacitance produced by it can introduce a delay which affects high speed operation. Similarly, the VCSEL contacts, being on opposed faces, create another plate capacitor which also adds to the parasitic capacitance of the combination. In the present invention both VCSEL contacts are on the top or emitting face thereby reducing parasitic capacitance. Additionally, the metal mask on the monitor 2 0 chip of the prior art device is not required by the present invention since no back face electrical connection is made.
The graphs in Figure ~ compare the frequency response of devices made by the present invention. (curve A) with devices made by prior art techniques (curves B and C).
As shown the output of devices made in accordance with the present invention s remains substantially constant up to 1_7 GHz, even when the package is a TO-46 can, which is not optimized for high frequencies. Applications for devices of the present invention include low and high speed data communications, for example 100Mbps Ethernct, Gigabit Etliernet, Fiber Channel, and ATM or SD'Cd and IEEE.
Applications also include non-fiber applications like medical and chemical where the conceot~ation of a substance is mcasttred by means of its interaction with photons at the emitted wavelength.
'hi fact, the invention pertains to any application where a monitor diode is needed for the feedback of optical power.
While particular embodiments of the invention have been described and 1 o illustrated it will be apparent to ore skilled in the art that numerous variations can be effected without departing firom the basic concept of the present invention.
For example the shape and size of the VCS EL and monitor diode can be selected according to the application. The conductivity type of the VCSEL and~monitor diode ~is not affected by the mounting technique, i_e_ a VCSEL having a n-type substrate can be mounted oa a p-type, an n-type or an isolating part of the monitor ctup. The same is true of a VCSEL grown on a p-type substrate. It is to be understood, however, that such variations will fall within the full scope of the invention as defined by the appended claims.
Back ~r~, ound of the Invention Lasers, and in particular semiconductor lasers, sucli as tliose formed of ILI-V
compounds, are commonly employed as the transmitter in digital comn~.uaication systems. Lasers of this type arc particularly well suited for optical fiber based systems l0 wherein the optical output of the laser is modulated in accordance with an electrical input to the device. The modulated optical signal can be transferred over relatively long distances using current optical fiber transmission systems.
Early lasers used in such applications included edge emitting lasers wherein the cleaved edges of the device provided the reflecting faces of the Fabry-Perrot cavity. Bdge ccnitting Lasers, however, have certain limitations with respect to pre-assembly testing aztd mounting techniques for efficient coupling to small diameter optical fibers.
Surface emitting lasers and in pazt7cular vertical cavity surface emitting lasers (VCSELs) have been developed recently and provide an improvement over edge ~~nittiug devices for use in optical fiber communication applications. The VCSEL which has its 2 o active region located between two reflecting layers, such as Bragg mirrors, emits in a plane normal to one of the two major surface of the laser device. As is known such devices include material of a first conductivity type, for example n-type, for one of the Bragg ntirrors and material of a second conductivity type, namely p-type, for the other Bragg min-or.. The intermediate active region or layer may include a cladding layer adjacent each of the Bragg mirrors. The Bragg mirrors are iypically formed of alternate layers of 111-V senticonduetor material each layer having a different reflectivity eharaeteristic_ Each alternate layer typically has a thickness equal to one quarter wavelength based on the enussion wavelength of the active material.
In this stricture, and in particular top emitting YCSELs, the back or bottom surface of the device is usually attached to a mounting substrate and the Laser output is c~itted through the top or front face of the device. An emitting aperture, which may be defined by one of the device contacts, is typically configured to allow alignment witli an optical fiber. Such devices are fabricated using well established processing techniques l0 and provide reliable lasers which may be coavectiently assembled into optical hansmitter tmits_ The nature of VCSfiI.s, and indeed semiconductor lasers in general, is that the electrical and optical characteristics between each device may vary slightly.
The optical output taken as a function of input current daring lasing action represents a steep slope and minor variations in the operating environment can result in significant output changes. For this reason, it is common to include a moruitoxing diode or rttonitor chip with a VCSEL, wherein the monitor chip is arranged to receive a representative portion of the optical output. This representative output can be used to calibrate eacli laser device or it can be used in a feedback mode to control the optical output of the laser.
Control tnay 2 o be required to ensure that the optical output of the laser falls within a preset liatit such as might be required by "eye safe" regulations prescribed by Standards Agencies.
Typically the monitoring diode will be a phototzaasistor such as a PIN device having a sensitivity curve geaerally matched to the wavelength output of the laser_ Laser/monitor cotxibiuarions are frequently mounted in a specially designed package such as a TO-46 eau which has a mounting base with insulated connector leads and a sealed cover. Tlie cover has a window of glass or other suitable transparent material over a central portion of the top such that the window is aligned with ti.~e emitting aperture of the lacing device_ One such combination is described in US Patent 5,812,58?
which issued September 22, 1998 to Gilliland et al. In the 5,812,582 patent the photodiode is mounted on an insulated substrate that is positioned within in a TO-46 can, or the Iike. A large portion, of the top surface of the photodiodc is covered with a metal layer oc mask. A VCSIrL is electrically attached to the mask by solder or conductive 1 o epoxy and one of the contacts to the VCSEL, i.e. the back contact, is made by way of the mask. The top or emitting surface contact is through a wire bond to one of the isolated connectors in the TO-46 can.
The bandwidth capacity of cturent optical fibers far ekceeds the bandwidth utilixed by present day communication systems. Accordingly, there is a continuing effort, to increase the data rate of communication systems ui order to make better usage of optical fiber capabilities. Since the laser transmitter represents an important aspect of dte complete communication system it is important that the switching rate ofthe laser be as high as possible_ One factor which effects the switching rate in high speed devices is the parasitic capacitance of the VCSEL, die monitoring chip and the mounting configuration.
2 0 A further important eonsiderat~iota, of course i.s the cost of the optical transmitter or laser/monitor assembly_ Tltis cost includes the material processing costs as well as the cost of assembling the devices and in accurately aligning the device in relation to an optical fiber.
It is, accordingly, an object of the present invention to provide a low cost VCSEL/monitor device with reduced parasitic capacitance for high bandwidth applications.
Sununar~of the Invention In a preferred embodiment of the present i.nvcntion there is provided a VCSELlmoni.tor assembly in which the VCSEL has both p-type and n-type corLtacts on the top or emitting face and is mounted on a monitoring diode utilizing little or no metallisatiozr in the mounting technique.
Therefore, in accordance with a fu-st aspect of the present invention there is provided a vertical cavity surface emitting laser (VCSEL) and photo detecting monitor assembly comprising: a photo detecting moutor chip having a first photo detecting face and a second fact parallel thereto; a top emitting VCSEL, mounted on the first face of the monitor chip, the VCSEL having both. p-type and u-type contacts on a top surface.thercof;
and means associated with the assembly to direct a portion of the VCSEL
emission to the fast face of the monitor chip.
In accordance with a second aspect of the present invention there is provided a method of assembling a top emitting vertical cavity surface emitting laser (VCSEL) and photo detecting optical output monitoring chip pair comprising. providing a mouitoruig chip having a photo detecting surface; attaching a top emitting VCSEL to the detecting 2 0 surface, the VCSEL having p-type and n-type contacts on the top surface;
and providing means to contact the monitoring chip and the VCSEL.
Brief Description of the Drawings the invention will now be described in greater detail with reference to the attached drawings wherei.a:
Figucc 1 is a top view of a monitoc chip;
Figure 2 is a top view of a top emitting VCSEL having both contacts ou the emitting face;
Figure 3 is a cross-sectional view of a VCSfiL mounted on a monitor chip according to the present invention;
Figure 4 is a cross-sectional view of the assembly in a mounting case including a receptacle or sleeve for use in the connection to an optical fiber; and Figure 5 is a bandwidtlx curve showing modulation response as a function of fiequency.
~7etailed Description of the Tnvention Figure 1 repcesents one example of a monitor chip 10 for use in the present invention. The monitor is a photodiode, PIN, avalanche diode etc. In operation, surface 12 will be impinged with optical energy of an appropriate wavelength and this will result in an electrical output across contacts on the device. The electrical output will be dependent on the intensity of the oprical energy (from the laser in this application)~which is received by the photo detecting or monitor chip. One electrical contact is provided on the back surface (not shown) and it may be connected to a lead wire or mounted directly onto a substrate by well known means. Sinularly, a contact to the top or front face can be made by way of wire bonds to one or both of contact pads 14. Alternatively, the monitor diode may have both contacts on the same side and the electrical connections made by bonding to the puss, for contacts on top side, or by means of patterned electrodes on the 2 0 photodiode carrier for contacts on the bottom side.
As shown in Figure I, centrally positioned on the top surface of the monitor chip is an alignment mark 16. This may be a square, or substantial square, as shown is Figure 1 and correspond to the shape or outline of a VCSEL, to be described later.
Alternatively the alignment mark 16 may represent a small poirtion of the VC.S6L outline.
The alignment mark can be formed of an appropriate metal in order to allow the VCSEL to be soldered in an accurately aligned relationship with respect to the photodiode.
This alit' ent is important in relation to system packaging as will be described later.
Altemativcly, the alignment mark may be of a non-metallic layer as long as it provides a stable surface while providing a suitable alignment mark. It is, of course, possible in certain assembly techniques to position the VCSEL accurately on the monitor chip without the aid of a special alignment mark. For example, the contact pattern or chip edge can be utilized for alignment purposes.
As shou~tt in Figure 2, the VCSEL 20 according to the present invention has both 1.0 p and n-type contacts on the top surface. An emitting aperture 22 will typically be defined by one of the contacts 24 (for example p-type) which will be connected to the p-type Bragg mirror of the VCSEL structure. A second contact 26, n-type in this cxaunplc, will be connected to the a-type Bragg mirror as is known in ~c art. A current aperture is typically provided in the active region (not shown) in order to confine the injection current to the desired region of the stntcture. Contact pads 24 and 26 are formed of suitable material for accepting wire bonds or the like for connection to a suitable input source.
VCSEL 20 is shown. in Figure 2 as being substantially square while it is to be understood that other shapes and sizes of devices can be used in the present invention.
2 0 The alignment mark 16 on the monitor chip will, of course, need to be modified to correspond generally to the shape and size of the VCSEL chip if other configurations are used.
It is also within the scope of the present invention to use a bottom erui.ttiug VCSEL having both p-h~pe and n-type contacts on the bottom face.
Figure 3 shows a cross section of a VCSEL 20 stacked or mounted on the monitor chip 10. If the alignment mark is foamed of metal the back face of the VCSEL
chip wil I
have a suitable ntetallisation to allow the VCSEL to be attaclted to the monitor chip by soldering. In this case the VCSEL will be self aligned to the alignment mark by the soldering process. It is to be understood that the aligncnent mark can be restricted to some portion of the size of the VCSEL and still result in a good mechanical connection and be suitably aligned.
The VGSEL can also be attached to the monitor chip by a suitable epoxy, many of which are available for such purposes. The alignment mark in this case will preferably not be metal bur some other material such as a dielectric again having a pattern designed to assist an operator in the proper location of the VCSEL in relation to the monitor chip. As previously discussed certain assembly techniques will allow an operator to position the VCSEI. on the monitoring chip without the use of anj~ special alignment marks.
, .
Figure 4 is a cross sectional view of the assembly of Figure 3 mounted in a package such as a conventional TO-46 can. As shown the can includes posts or connectors 32 wltich are normally isolated but one may be non isolated for use in providing electrical input to the VCSEL and for monitoring the optical output of the VCSEL by way of the electrical signal generated across the monitor chip. The cover 42 includes a reflective surface 4.~ which cnay be a window or lens. The material for the 2 o reflective surface may be glass, plastic epoxy or other material at least partially transparent to the wavelength of the VCSEL. A portion of the Laser output will be reflected by the window 44 back inside the cover and will impinge on monitor chip surface 12 thus providing a signal which is proportional to the VCSEL output.
As will be apparent the positioning of the emitting aperture of the VCSEL with respect to an optical fiber coupled to the arrangement is critical.
Positioning the sub assembly, which rnay be a TO-46 can, a TO-56 can, a MT connector or other sub assembly, in relation to the fiber can be fixed by way of a receptacle or sleeve. It is therefore important that the VCSEL and hence the emitting aperture is well positioned with respect to the base of the TO-4.6 can The alignment mark oa the monitor chip assists in the positioning of the VCSEL with respect to the monitor chip and the positioning of the monitor chip with respect to the package can be arranged through other means. As shown in Figure 4 the central axis of the emitting apedure is aligned with the center of window 44 and the longitudinal axis of an optical fiber (not shown).
By reducing the amount of metal in the VCSELmonitor assembly of the present invention the parasitic capacitance is correspondingly reduced. The prior art device as described in US Patent 5,812,582 utilizes a metal mask or layer on top of the monitor cliip. Tlus mask in combination with the substrate oa which the chip is mounted act as a plate capacitor and the parasitic capacitance produced by it can introduce a delay which affects high speed operation. Similarly, the VCSEL contacts, being on opposed faces, create another plate capacitor which also adds to the parasitic capacitance of the combination. In the present invention both VCSEL contacts are on the top or emitting face thereby reducing parasitic capacitance. Additionally, the metal mask on the monitor 2 0 chip of the prior art device is not required by the present invention since no back face electrical connection is made.
The graphs in Figure ~ compare the frequency response of devices made by the present invention. (curve A) with devices made by prior art techniques (curves B and C).
As shown the output of devices made in accordance with the present invention s remains substantially constant up to 1_7 GHz, even when the package is a TO-46 can, which is not optimized for high frequencies. Applications for devices of the present invention include low and high speed data communications, for example 100Mbps Ethernct, Gigabit Etliernet, Fiber Channel, and ATM or SD'Cd and IEEE.
Applications also include non-fiber applications like medical and chemical where the conceot~ation of a substance is mcasttred by means of its interaction with photons at the emitted wavelength.
'hi fact, the invention pertains to any application where a monitor diode is needed for the feedback of optical power.
While particular embodiments of the invention have been described and 1 o illustrated it will be apparent to ore skilled in the art that numerous variations can be effected without departing firom the basic concept of the present invention.
For example the shape and size of the VCS EL and monitor diode can be selected according to the application. The conductivity type of the VCSEL and~monitor diode ~is not affected by the mounting technique, i_e_ a VCSEL having a n-type substrate can be mounted oa a p-type, an n-type or an isolating part of the monitor ctup. The same is true of a VCSEL grown on a p-type substrate. It is to be understood, however, that such variations will fall within the full scope of the invention as defined by the appended claims.
Claims (19)
1. A vertical cavity surface emitting laser (VCSEL) and photo detecting monitor assembly comprising: a photo detecting monitor chip having a first photo detecting face and a second face parallel thereto; a top emitting VCSEL, mounted on said first face of said monitor chip, said VCSEL having both p-type and n-type contacts on a top surface thereof, and means associated with said assembly to direct a portion of the VCSEL emission to said first face of said monitor chip.
2. An assembly as defined in claim 1 wherein said VCSEL is bottom emitting and said p-type and n-type contacts are on the bottom side.
3. An assembly as defined in claims 1 or 2 wherein said photo detecting monitor chip has a responsive wavelength range which includes the wavelength of the emission of said VCSEL.
4. An assembly as defined in claim 3 arranged in a package which provides access to external connections for said monitoring chip and said VCSEL.
5. An assembly as defined in claim 4 wherein said package has a cover which includes an at least partly transparent window substantially in line with an emitting region of said VCSEL.
6. An assembly as defined in claim 4 wherein said package has a cover which includes an at least partly transparent lens, substantially in line with an emitting region of said VCSEL.
7. An assembly as defined in claims 5 or 6 wherein said window or lens includes a reflective portion which directs a portion of the emission from said VCSEL to said monitoring chip.
8. An assembly as defined in claim 7 wherein said monitoring chip includes on said first face alignment marks for use in aligning said VCSEL to said monitoring chip.
9. An assembly as defined in claim 8 wherein said alignment marks represent a shape substantially the same as the shape of said VCSEL.
10. An assembly as defined in claim 8 wherein said alignment marks are metallised for use in soldering said VCSEL to said monitoring chip.
11. An assembly as defined in claim 9 wherein said alignment marks represent a portion of the shape of said VCSEL and is metallised for use in soldering said VCSEL co said monitoring chip.
12. An assembly as defined in claim 8 further including receptacle means for receiving said package and for aligning said emitting portion of said VCSEL
with an optical fiber.
with an optical fiber.
13. A method of assembling a top emitting vertical cavity surface emitting laser (VCSEL) and photo detecting optical output monitoring chip pair comprising;
providing a monitoring chip having a photon detecting surface; attaching a top emitting VCSEL to said detecting surface, said VCSEL having p-type and n-type contacts on said top surface; and providing means to contact said monitoring chip and said VCSEL.
providing a monitoring chip having a photon detecting surface; attaching a top emitting VCSEL to said detecting surface, said VCSEL having p-type and n-type contacts on said top surface; and providing means to contact said monitoring chip and said VCSEL.
14. A method as defined in claim 13 wherein said detecting surface of said monitoring chip is provided with an alignment mark for use in aligning said VCSEL to said chip.
15. A method as defined in claim 14 wherein said alignment mark is metallised to allow said VCSEL to be attached to said monitor chip by soldering.
16. A method as defined in claims 13 or 14 wherein said monitor chip and VCSEL
combination is mounted in a package having a window such that emission from said VCSEL exits said package aria said window.
combination is mounted in a package having a window such that emission from said VCSEL exits said package aria said window.
17. A method as defined in claim 16 wherein a portion of said emission is reflected by said window onto said monitor chip.
18. A method as defined in claims 13 or 14 wherein said monitor chip and VCSEL
combination is mounted in a package having a lens such that emission from said VCSEL exits said package via said lens.
combination is mounted in a package having a lens such that emission from said VCSEL exits said package via said lens.
19. A method as defined io claim 18 wherein a portion of said emission is reflected by said lens onto said monitor chip.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB9910202A GB2349740A (en) | 1999-05-05 | 1999-05-05 | Vertical cavity surface emitting laser with monitoring diode |
| GB9910202.2 | 1999-05-05 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2287134A1 true CA2287134A1 (en) | 2000-11-05 |
Family
ID=10852713
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002287134A Abandoned CA2287134A1 (en) | 1999-05-05 | 1999-10-19 | Top contact vcsel with monitor |
Country Status (5)
| Country | Link |
|---|---|
| JP (1) | JP2000323791A (en) |
| CA (1) | CA2287134A1 (en) |
| DE (1) | DE19947817A1 (en) |
| GB (1) | GB2349740A (en) |
| SE (1) | SE9903888L (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE10012869C2 (en) | 2000-03-16 | 2002-05-29 | Infineon Technologies Ag | Vertical resonator laser diode with coplanar electrical connection contacts and process for their production |
| JP4058633B2 (en) | 2003-07-10 | 2008-03-12 | セイコーエプソン株式会社 | Surface-emitting light emitting device, optical module, optical transmission device |
| JP2005085942A (en) | 2003-09-08 | 2005-03-31 | Seiko Epson Corp | Optical module and optical transmitter |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR100259490B1 (en) * | 1995-04-28 | 2000-06-15 | 윤종용 | Vertical cavity surface emitting laser |
| US5812582A (en) * | 1995-10-03 | 1998-09-22 | Methode Electronics, Inc. | Vertical cavity surface emitting laser feedback system and method |
| US5724376A (en) * | 1995-11-30 | 1998-03-03 | Hewlett-Packard Company | Transparent substrate vertical cavity surface emitting lasers fabricated by semiconductor wafer bonding |
-
1999
- 1999-05-05 GB GB9910202A patent/GB2349740A/en not_active Withdrawn
- 1999-10-05 DE DE19947817A patent/DE19947817A1/en not_active Withdrawn
- 1999-10-19 CA CA002287134A patent/CA2287134A1/en not_active Abandoned
- 1999-10-28 SE SE9903888A patent/SE9903888L/en not_active Application Discontinuation
- 1999-11-09 JP JP11318214A patent/JP2000323791A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| SE9903888L (en) | 2000-11-06 |
| SE9903888D0 (en) | 1999-10-28 |
| DE19947817A1 (en) | 2000-11-09 |
| GB9910202D0 (en) | 1999-06-30 |
| GB2349740A (en) | 2000-11-08 |
| JP2000323791A (en) | 2000-11-24 |
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