Fiber optic coupler array

An assembly includes optical fibers each having a waveguide core, a photonic integrated circuit (IC) that includes in-plane waveguides corresponding to the optical fibers, and a substrate bonded to the photonic IC with grooves that support the optical fibers. The substrate and photonic IC can have metal bumps that cooperate to provide mechanical bonding and electrical connections between the substrate and photonic IC. Portions of the optical fibers supported by the substrate grooves can define flat surfaces spaced from the optical fiber cores. The photonic IC can include passive waveguide structures with a first coupling section that interfaces to the flat surface of a corresponding optical fiber (for evanescent coupling of optical signals) and a second coupling section that interfaces to a corresponding in-plane waveguide (for adiabatic spot-size conversion of optical signals).

BACKGROUND

The present application is related to waveguide input and output couplers for optical integrated circuits.

2. State of the Art

Waveguide input and output couplers have always been an important issue in optical integrated circuit design. Various coupling schemes have been proposed or demonstrated to overcome the low coupling efficiency between the optical fiber and the waveguides on the chip. Based on the direction at which light is coupled in or out of the waveguides, these schemes fall into one of two categories: vertical coupling (out of plane) and lateral coupling (in plane).

Vertical coupling is typically accomplished with diffractive gratings incorporated into a waveguide layer to provide a conversion between the optical mode in the single-mode fiber (SMF) and the waveguide. The vertical coupling scheme typically requires the fiber to be positioned at some angle to the wafer. Multiple fiber I/O is possible. The drawbacks are that the diffractive nature of this approach relies on interferometric behavior applicable only to a limited wavelength range and therefore may not be suitable for large-spectral bandwidth optical coupling. It also has strong polarization dependence.

In lateral coupling, light is coupled in and out of an exposed cross-section of the waveguide in the lateral direction and this has always been reported in a butt coupling configuration. Typically a lens or a spot-size converter (SSC) is needed for the mode conversion between the fiber and the waveguide. Multichannel coupling of waveguide to fiber arrays has been demonstrated. While the lateral coupling has weak polarization dependence and is insensitive to the input bandwidth, it puts a stringent demand on the alignment of the fiber both vertically and laterally. Also, SSC designs require excellent control of the critical dimensions and lensed fiber or special fiber are often needed for nano-waveguides especially when implemented for short wavelength, which adds to the cost and complicates the fabrication and packaging of the integrated circuits.

SUMMARY OF THE INVENTION

An optical fiber coupler array assembly includes a plurality of optical fiber waveguides each having a waveguide core, a photonic integrated circuit (IC) that includes a plurality of in-plane waveguide structures corresponding to the plurality of optical fiber waveguides, and a substrate that is bonded to the photonic ICt. The substrate includes a plurality of grooves that support the optical fiber waveguides. The substrate and the photonic IC can both have metal bump bonds that cooperate to provide mechanical bonding and electrical connections between the substrate and the photonic IC.

Portions of the optical fiber waveguides that are supported by the grooves of the substrate can define a corresponding plurality of flat surfaces that are spaced from the waveguide cores of the optical fiber waveguides, and the photonic IC can include a plurality of passive waveguide structures that correspond to both the plurality of in-plane waveguide structures of the photonic IC and the plurality of optical fiber waveguides. Each passive waveguide structure can include a first coupling section that interfaces to the flat surface of the corresponding optical fiber waveguide and a second coupling section that interfaces to the corresponding in-plane waveguide structure of the photonic IC. The first coupling section can be configured to provide for evanescent coupling of optical signals into or from the corresponding optical fiber waveguide, and the second coupling section can be configured to provide for adiabatic spot-size conversion of optical signals between the first coupling section and the corresponding in-plane waveguide structure of the photonic IC.

In one embodiment, the waveguide cores of the optical fiber waveguides are realized from a material with a first refractive index, and the first coupling section and the second coupling section of the passive waveguide structures of the photonic IC are realized from a material with a second refractive index that matches the first refractive index.

In another embodiment, the waveguide cores of the optical fiber waveguides are realized from silicon dioxide, and the first coupling section and the second coupling section of the passive waveguide structures of the photonic IC are also realized silicon dioxide.

In yet another embodiment, the first coupling section of each respective passive waveguide structure has a square cross section with a size that corresponds to size of the optical mode of the corresponding optical fiber waveguide.

In still another embodiment, the second coupling section of each respective passive waveguide structure defines a number of distinct levels that overlap one another vertically along the length of the second coupling section, wherein each level has opposed sidewalls that taper laterally in width. In one exemplary configuration, the second coupling section includes bottom, intermediate and top levels that extend along the length of the second coupling section, wherein the top level has a height that corresponds to height of the first coupling section and opposed sidewalls that taper laterally from a width WIthat corresponds to width of the first coupling section to a width W1, wherein the second level has a portion that extends beyond the top level with opposed sidewalls that taper laterally from a width WMto a width W2adjacent the corresponding in-plane waveguide structure, wherein the third level has a portion that extends beyond the top level with opposed sides that taper laterally from the width WMto a width W0, and wherein W2<W1<WM<WIand W0<WM.

The photonic IC can be realized with a material system of group III-V materials. The photonic IC can also be realized from an epitaxial layer structure that includes an n-type modulation doped quantum well interface offset vertically from a p-type modulation doped quantum well interface.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1illustrates a fiber optic coupler array100according to the present application. The coupler array100includes two parts: a wafer101that mechanically supports a plurality of single-mode optical fibers (SMFs)103; and a photonic integrated circuit (IC)105with active electro-optical components that are operably coupled to the SMFs103supported by the wafer101. The SMFs103can extend beyond the periphery of the wafer101for connection to other network components as needed. The photonic IC105is configured in an inverted configuration (with the substrate107up) with on-chip passive semiconductor waveguides (PG)109integral to its top surface111(opposite the substrate107). Each PG109is configured such that is in intimate contact with a corresponding SMF103in which the fiber cross-section has been suitably modified to provide evanescent-wave coupling between the SMF103and the PG109. As best shown inFIGS. 3 and 6, each PG109includes an evanescent coupling guide (ECG) section113and a spot-size converter (SSC) section115. The ECG section113interfaces to the SMF103and provides evanescent-wave coupling to the SMF103. The SSC section115interfaces to a rib waveguide117that is integral to the top surface111of the photonic IC105and provides low-loss adiabatic spot-size conversion of optical signals between the rib waveguide117and the evanescent coupling guide (ECG) section113. There is one rib waveguide117corresponding to a particular SMF103with a corresponding PG109(ECG section113and SSC section115) coupled therebetween. The ECG section113and SSC section115of the respective PG109provide optical coupling and mode conversion of optical signals between the SMF103and the RW117of the corresponding SMF/RW pair.

This design has the following advantages. First, it is naturally suitable for a multiple fiber-waveguide interface to achieve low cost. Second, the alignment for both vertical and lateral directions can be well controlled. Third, it can be fabricated using standard techniques so that high demands on critical dimensions can be relaxed. Although the design has been performed for photonic integrated circuits based on Planar Opto-electronic Technology as noted below, it can be readily adapted to photonic integrated circuits utilizing any semiconductor waveguide.

According to one embodiment of the present application, the wafer101is prepared to hold the SMFs103as shown inFIG. 2. First, a set of grooves119(which can have a V-shaped cross-section) are formed on one surface of the wafer101(i.e., the top surface121ofFIG. 2) using standard techniques. The grooves119can extend parallel to one another as shown. There is one groove119for each SMF103. The SMFs103are placed into the grooves119and mechanically fixed therein by the injection of an index-matching gel (not shown inFIG. 2). The SMFs103each have a core123that is surrounded by cladding material that traps the light in the core123using an optical technique called total internal reflection. The cladding material of each SMF103can be coated by a buffer (not shown) that protects the cladding and core from moisture and physical damage. The depth of the grooves119are configured by lithography (such as by the fixed etch angle for the grooves) so that the cores123of the SMFs103lie about 1 μm below the surface121of the wafer101as best shown inFIG. 3. Then, with the SMFs103positioned in the grooves119, portions of the SMFs103supported in the grooves119(particularly, the top cladding material of supported portions of the SMFs103) are removed by polishing down to the surface121of the wafer101to define flat surfaces122of the SMFs103that are approximately 1 μm radially above the respective cores123of the SMFs103. The flat surfaces122of the SMFs103also extend parallel to the respective cores123along the lengthwise dimension of the SMFs103as best shown inFIGS. 2 and 3. The surface121of the wafer101also includes a predetermined number of metal bumps125(for example, eight shown) and a predetermined number of alignment marks127(for example, four shown). The metal bumps125are preferably disposed about the periphery of the surface121of the wafer101as shown. The alignment marks127are preferably disposed about the periphery of the surface121of the wafer101, for example adjacent the four corners of the surface121as shown. The metal bumps125of the wafer101are positioned to contact and bond to corresponding metal bumps129disposed on the top surface111of the photonic IC105as best shown inFIG. 1. The alignment marks127are used to align the wafer101to the photonic IC105such that the corresponding metal bumps contact one another for bonding purposes. The wafer101can be silicon or other suitable substrate. The metal bumps125can be realized from Indium. The metal bumps125of wafer101connect to through-substrate metal vias (TSVs, not shown) that extend through the wafer101to the opposed back surface. The back surface of the wafer101is mounted to a printed circuit board (PCB, not shown). The TSVs are electrically coupled to metal traces on the PCB by suitable surface mount packaging technology (such as a pin grid array or ball grid array package) for off-chip electrical I/O. Other ICs can be mounted on the PCB.

The surface111of the photonic IC105(depicted as the bottom surface of the inverted configuration ofFIGS. 1 and 3) includes rib waveguides (RW)117that guide optical signals in the plane of the photonic IC105. There is one RW117for each SMF103. The RW117can be part of a passive optical device (e.g., passive waveguide) or an active optoelectronic device (e.g., a laser, detector or coupler switch) realized as part of the photonic IC105. The surface111of the photonic IC105also includes a predetermined number of metal bumps129(for example, eight shown). The metal bumps129are preferably realized from Indium. The metal bumps129are preferably disposed about the periphery of the surface111of the photonic IC105as shown. The metal bumps129are positioned to contact and bond to the corresponding metal bumps125of the wafer101. The surface111of the photonic IC105also includes alignment marks (not shown), which are used to align the photonic IC105to the wafer101such that the corresponding metal bumps125/129contact one another for bonding purposes. The metal bumps129of the photonic IC105are electrically coupled to electro-optical components (or electrical components) of the photonic IC105by vias and/or other metal/conductor interconnect schemes for electrical I/O.

The photonic IC105is flipped upside down (substrate up) and bonded to the wafer101with the help of the alignment marks on both parts. The bonding is performed with the use of the corresponding metal bumps125,129, which are also utilized at the same time to perform electrical connections to the bump bonds129around the edge of the photonic IC105. In this way, the electrical connections are performed simultaneously with the optical connections. More specifically, when the metal bumps129of the photonic IC105are bonded to the corresponding metal bumps125of the wafer101, the TSVs and back side packaging technology of the wafer101are electrically coupled to the electro-optical components (or electrical components) of the photonic IC105to provide for electrical I/O over the metal traces of the PCB with the electro-optical components (or electrical components) of the photonic IC.

With the photonic IC105bonded to the wafer101, the bottom surface of the ECG section113of each respective PG109interfaces to the polished surface122of the corresponding SMF103and provides evanescent-wave coupling to the SMF103. Specifically, the optical signal in each SMF103is coupled into the ECG section113of the corresponding PG109(or vice versa) by evanescent coupling between the core123of the SMF103(which is disposed under the polished surface122of the SMF102) and the ECG section113of the PG109(which is positioned above the core123of the SMF103) as best shown inFIG. 3. Evanescent coupling is a process by which electromagnetic waves are transmitted from one medium to another by means of an evanescent, exponentially decaying electromagnetic field. Such evanescent coupling can be examined in BeamPROP, a commercial 3D photonic simulation tool based on BPM method. It was found that the refractive index of the material of the ECG section113(as well as the refractive index of the material of the SSC section115) should be the same as that of the material of the core123of the SMF103for maximum power transfer efficiency. Therefore, in the event that the core of the SMF103is realized from SiO2, then SiO2can be used to form the corresponding ECG section113and the SSC section115of the photonic IC105.

In one embodiment, the cross section of the ECG section113can be a square shape as shown inFIG. 6, with an edge length Widetermined to be ˜6 μm to obtain a mode comparable in size to a standard SMF at a wavelength of 980 nm. For the case where the spacing G between the ECG section113and the core123of the SMF103as shown inFIG. 3is 1 μm, the length L0of the ECG section113can be ˜550 μm. This configuration can maximize power transfer between the SMF103and the ECG section113of the PG109as evident fromFIG. 4. The length L0of the ECG section113(in this example, ˜550 μm) is also selected to establish a stable propagating mode in the ECG section113. The efficiency of the optical power transferred from the SMF103to the ECG section113peaks at 87% which corresponds to a loss of ˜0.6 dB. Such loss can be attributed to the portion of the SMF103polished away to provide the interface surface122of the SMF103. The optical mode coupled into the ECG section113(or vice versa) has a mode field diameter (MFD) that matches the MFD of the SMF103, which is ˜5 μm.

An exemplary embodiment of the rib waveguides117of the photonic IC105into which the optical signal is coupled (or vice versa) is shown in cross-section inFIG. 5A. The profile of the fundamental (TE) mode of the RW117is shown inFIG. 5B, with an effective index of ˜3.356. Since the size of this mode is smaller than the one in the ECG section113, the SSC section115is needed to perform adiabatic spot-size conversion between the MFD of the ECG section113(e.g., ˜5 μm) and the smaller MFD of the RW117of the photonic IC105.

An exemplary configuration of the SSC section115suitable for 980 nm is shown inFIG. 6and was characterized using BeamPROP to determine its minimum length. It can also be formed by depositing and patterning SiO2on the top surface111of the photonic IC105. It has three levels (over its height from top to bottom) that each perform adiabatic conversion of the optical mode. The first (top) level has a height of 1.9 μm, and has opposed sidewalls that taper laterally along the length L1of 300 μm from an initial width Wi of 6 μm (the same width as the ECG) to a width w1of 1 μm. The second (intermediate) level, which is disposed under the first level, has a height of 3 μm. For the section under the first level (corresponding to the length L1), the second level has opposed sidewalls that taper laterally from an initial width Wi of 6 μm (the same width as the ECG) to a width Wm of 5 μm. The second level continues with opposed sidewalls that taper laterally along the length L2of 200 μm from the width Wm of 5 μm to a width w2of 1 μm. The width Wm can vary and is preferably larger than 4 μm. The exemplary design employs a width Wm of 5 μm to achieve a linear lateral profile. The third (bottom) level, which is disposed under both the first and second level, has a height Ho of 1.1 μm. For the section under the first and second level (corresponding to the length L1), the third level has opposed sidewalls that taper laterally from an initial width Wi of 6 μm (the same width as the ECG) to a width Wm of 5 μm. It continues under the second section (corresponding to the length L2) with opposed sidewalls that taper laterally from the width Wm of 5 μm to a width Wo of 4 μm. These dimensions can be easily achieved by using standard lithographic techniques.

For optical signals entering the SSC section115from the ECG section113, the lateral taper of the first level of the SSC section115narrows the width of the optical mode exiting the ECG section113. The first level of the SSC section115also narrows the height of the optical mode exiting the ECG section113and couples it to the second level of the SSC section115disposed thereunder. The lateral taper of the second level of the SSC section115further narrows the width of optical mode. The second level of the SSC section115also further narrows the height of the optical mode and couples it to the third level disposed thereunder. The third level of the SSC section115further narrows the width and height of optical mode such that its size is compatible the size of the RW117.

For optical signals entering the SSC section115from the RW117, the operations are reversed to expand (widen) the optical mode in width and height such that its size is compatible with the ECG section113and the SMF103coupled thereto by evanescent coupling.

The performance of the SSC section115can be modeled by the BeamPROP simulation and the results for the overlap integral with the mode of the RW117(shown inFIG. 5B) and the mode of the ECG section113vs. propagation distance shown inFIG. 7. The efficiency of the SSC section115can be read from the figure as 96%, corresponding to a loss of only 0.18 dB, which can even further reduced if techniques capable of creating submicron features such as E-beam are used.

The SSC section115as described above can be formed by deposition of SiO2on the top surface111of the photonic IC105after a section of the RW117is etched away. To avoid the formation of a gap between the SSC section115and the RW117, extra SiO2will be deposited on the RW structure117as shown inFIG. 8.

Additional loss can occur at the interface between the SSC section and the RW section117. The first additional loss is the reflection between the SSC section115and the RW117caused by different effective indices. Such reflection can be calculated as:

-10⁢log⁡(1-R)=-10⁢log⁡[1-(n1-n2n1+n2)2]=-10⁢log⁡[1-(3.356-1.453.356+1.45)2]=0.74⁢⁢dB(1)
in which R is the reflectivity at the interface and n1and n2are the effective indices for the local mode at the end of the SSC section115and that of the RW117, respectively. The second additional loss is the diffraction loss caused by the rise of the SiO2layer adjacent the RW117as shown inFIG. 8, which can be estimated by simulation in BeamPROP to be ˜0.15 dB. Based on the calculations above, the overall insertion loss of the coupler can be obtained as
IL=/LSMF-ECG+ILSSG+ILSSC-RW=0.6+0.18+(0.74+0.15)=1.77 dB  (2)
The total length of each respective PG is ˜1 mm.

The performance of the fiber optic coupler array100as described herein can be modeled assuming perfect conditions assumed. In reality, there are misalignment issues which should be considered when evaluating the coupler performance. First, the spacing G between the polished surface122of the SMF103and the ECG section113shown inFIG. 3determines the coupling coefficient between them and therefore the length of the ECG section113. Moreover, when creating the grooves119on the wafer101and polishing the portions of the SMFs103down to the wafer surface, this spacing can be different from the designed value.FIG. 9shows the transfer efficiency between a SMF103and ECG section113vs. spacing between them when the length of the ECG is 550 μm. When the spacing deviates −0.5 μm from the design value of 1 μm, the transfer efficiency changes from 86% to 66%; when the spacing is increased to 1.5 μm, the transfer efficiency changes to 76%.

Second, mask misalignment is expected when standard lithography techniques are used. In terms of misalignment as shown inFIG. 10A, conversion efficiency is more sensitive to the second level misalignment than to the first level due to the fact that the overlap efficiency at the first interface is larger than that at the second. This is verified by the simulation results shown inFIG. 10bin which 1 μm misalignments of mask layers for the first and second level are introduced. While the misalignment at the first level has little effect on the conversion efficiency, the misalignment at the second level causes a loss of ˜1.1 dB.

The design of the fiber optic coupler array100as described herein has a major advantage in that it is suited for manufacturing due to its inherently low cost.

The photonic IC105can include photonic devices that carry out one or more of a wide variety of active photonic functions, such as laser transmission, optical-to-electrical conversion, bidirectional transmission and optical-to-electrical conversion of optical signals, optical amplification, optical modulation, optical coupling and cross-connection, and other optical processing functions. The photonic devices of the photonic IC can also carry out a passive photonic function, such as passive optical waveguiding.

The photonic IC105can be preferably realized from a multilayer structure of group III-V materials that provides for monolithic integration of high speed transistor functionality, such as high-speed complementary HFET transistors and/or high-speed complementary bipolar transistors. In one embodiment, the photonic IC employs Planar Optoelectronic Technology (POET) that provides for the realization of a variety of devices (optoelectronic devices, logic circuits and/or signal processing circuits) utilizing inversion quantum-well channel device structures as described in detail in U.S. Pat. No. 6,031,243; U.S. patent application Ser. No. 09/556,285, filed on Apr. 24, 2000; U.S. patent application Ser. No. 09/798,316, filed on Mar. 2, 2001; International Application No. PCT/US02/06802 filed on Mar. 4, 2002; U.S. patent application Ser. No. 08/949,504, filed on Oct. 14, 1997, U.S. patent application Ser. No. 10/200,967, filed on Jul. 23, 2002; U.S. application Ser. No. 09/710,217, filed on Nov. 10, 2000; U.S. Patent Application No. 60/376,238, filed on Apr. 26, 2002; U.S. patent application Ser. No. 10/323,390, filed on Dec. 19, 2002; U.S. patent application Ser. No. 10/280,892, filed on Oct. 25, 2002; U.S. patent application Ser. No. 10/323,390, filed on Dec. 19, 2002; U.S. patent application Ser. No. 10/323,513, filed on Dec. 19, 2002; U.S. patent application Ser. No. 10/323,389, filed on Dec. 19, 2002; U.S. patent application Ser. No. 10/323,388, filed on Dec. 19, 2002; U.S. patent application Ser. No. 10/340,942, filed on Jan. 13, 2003; all of which are hereby incorporated by reference in their entireties. These device structures are built from an epitaxial layer structure and associated fabrication sequence that can be used to make the devices on a common substrate. In other words, n type and p type contacts, critical etches, etc. can be used to realize one or more of the devices simultaneously on a common substrate. Features of the epitaxial structure include 1) a bottom n-type layer structure, 2) a top p-type layer structure, and 3) an n-type modulation doped quantum well interface and a p-type modulation doped quantum well interface disposed between the bottom n-type layer structure and the top p-type layer structure. N-type and p-type ion implants are used to contact the n-type and p-type modulation doped quantum well interfaces, respectively. N-type metal contacts to the n-type ion implants and the bottom n-type layer structure. P-type metal contacts to the p-type ion implants and the top p-type layer structure. The epitaxial layer structure can be realized with a material system of group III-V materials (such as a GaAs/AlGaAs). The n-type modulation doped quantum well interface includes a relatively thin layer of highly doped n-type material (referred to herein as an “n+ charge sheet”) spaced from one or more quantum wells by an undoped spacer layer. The p-type modulation doped quantum well interface includes a relatively thin layer of highly doped p-type material (referred to herein as a “p+ charge sheet”) spaced from one or more quantum wells by an undoped spacer layer. The n+ charge sheet is disposed above the quantum well(s) of the n-type modulation doped quantum well interface adjacent the top p-type layer structure. The p+ charge sheet is disposed below the quantum well(s) of the p-type modulation doped quantum well interface adjacent the bottom n-type layer structure. One or more spacer layers are disposed between the quantum well(s) of the n-type modulation doped quantum well interface and the one or more quantum well(s) of the p-type modulation doped quantum well interface. A bottom dielectric distributed bragg reflector (DBR) mirror can be formed below the bottom n-type layer structure. The bottom DBR mirror can be formed from alternating layers of AlAs and GaAs. The AlAs layers are subjected to high temperature steam oxidation to produce the compound AlxOyso as to form the bottom DBR mirror. A top dielectric mirror can be formed above the top p-type layer structure. The top dielectric mirror can be formed from alternating layers of SiO2and a high refractive index material such as silicon. The bottom and top mirrors provide for vertical confinement of light. The top dielectric mirror can cover the sidewalls of the device structure to provide for lateral confinement of light as needed.

POET can be used to construct a variety of high performance transistor devices, such as complementary NHFET and PHFET unipolar devices as well as n-type and p-type HBT bipolar devices. POET can also be used to construct a variety of optoelectronic devices which include:a thyristor VCSEL laser;an NHFET laser;an PHFET laser;a thyristor optical detector;an NHFET optical detector;a PHFET optical detector;a semiconductor optical amplifier (SOA) or a linear optical amplifier (LOA) based on either one (or both) of the n-type and p-type quantum well interfaces;an absorption (intensity) optical modulators based on either one (or both) of the n-type and p-type quantum well interfaces;a phase modulator based on either one (or both) of the n-type and p-type quantum well interfaces;a waveguide switch; anda passive waveguide.

It is worth noting that the approach described above couples SMFs to in-plane waveguides that guide optical signals in the plane of the photonic IC105, but it can be used equally as well for a multi-mode fiber optic (MMF). For the case of coupling to an MMF, an additional fiber element is required such as a photonic lantern which adiabatically converts the MMF signal to a SMF signal. The additional fiber element interfaces by evanescent coupling to the ECG section113of the photonic IC105as described above.

There have been described and illustrated herein several embodiments of a fiber optic coupler array and corresponding methods of fabrication. While particular embodiments of the invention have been described, it is not intended that the invention be limited thereto, as it is intended that the invention be as broad in scope as the art will allow and that the specification be read likewise. Thus, while particular configurations of the ECG and SSC sections of the coupler waveguides have been disclosed, it will be appreciated that other configurations of the ECG and SSC sections of the coupler waveguides can be used as well. In addition, while particular types of photonic integrated circuits have been disclosed, it will be understood that other photonic circuits can be used. Also, while particular bump bonding and packaging configurations have been disclosed, it will be recognized that other wafer level bonding and packaging configurations could be used as well. It will therefore be appreciated by those skilled in the art that yet other modifications could be made to the provided invention without deviating from its spirit and scope as claimed.