CN102713703A

CN102713703A - Waveguide optically pre-amplified detector with passband wavelength filtering

Info

Publication number: CN102713703A
Application number: CN200980163274XA
Authority: CN
Inventors: 瓦莱里·托希凯恩; 吴芳; 克里斯多夫·沃特森; 龙利·隆格维; 基里尔·皮梅诺夫
Original assignee: Onechip Photonics Inc
Current assignee: Onechip Photonics Inc
Priority date: 2009-12-10
Filing date: 2009-12-10
Publication date: 2012-10-03
Also published as: CA2783710A1; WO2011069225A1; EP2510390A1; EP2510390A4

Abstract

The invention describes an integrated-photonics arrangement, implementable in a multi-guide vertical integration (MGVI) structure composed from III-V semiconductors and grown in one epitaxial growth run, allowing for the integration of semiconductor optical amplifier (SOA) and PIN photodetector (PIN) structures within a common wavelength-designated waveguide of the plurality of the vertically integrated wavelength-designated waveguides forming the MGVI structure. The integration includes a wavelength filter integrated between the SOA and PIN to reduce noise within the PIN arising from ASE generated by the SOA. In exemplary embodiments of the invention, the wavelength filter is integrated into MGVI structure either within a common wavelength designated waveguide or within the wavelength- designated waveguide. Further in other embodiments the wavelength filter is provided by a thin- film filter abutting a facet of the integrated-photonics arrangement wherein optical signals are coupled by optical waveguides and/or additional optical elements such as a multimode interference device.

Description

Waveguide optical pre-amplification detector with passband wavelength filtering

Technical Field

The present invention relates to waveguide photonic devices and photonic integrated circuits, and more particularly to waveguide optical pre-amplification detectors in III-V semiconductor materials.

Background

Deep penetration of optical fibers into access networks requires non-parallel large-scale deployment of optical interface devices that push traffic to and from subscribers. For example, an optical transceiver that receives downstream signals on one wavelength and transmits upstream signals on another wavelength (both wavelengths share the same fiber) must be deployed at each Optical Line Terminal (OLT)/Optical Network Unit (ONU). Thus, cost-efficiency and mass scalability in manufacturing such components are becoming more and more of a major issue. It is widely accepted in the telecommunications industry that optical access solutions do not become a commodity service until the mass production of optical transceivers and other large-scale deployed optical components reaches the cost-effective and scalability level of consumer products.

In the framework of current optical assembly manufacturing models, which are based primarily on bulk optical component assembly (OSA) from off-the-shelf discrete passive and active photonic devices, the root cause of the problem is labor-intensive optical alignment and high cost of packaging in large quantities. They not only limit cost effectiveness, but also greatly limit the ability of manufacturers to increase production volume and provide scalability in manufacturing. The solution is to reduce the optical alignment and packaging content in the OSA and eventually to replace the optical assembly with Photonic Integrated Circuit (PIC) technology, where all functional elements of the optical circuit are monolithically integrated onto the same substrate. The manually performed active optical alignment is then replaced by an automated passive alignment defined by lithography and the multi-component packaging is completely eliminated, enabling automated and volume scalable mass production of complex optical components based on existing planar and semiconductor wafer fabrication technologies.

In the context of applications, the materials of choice for monolithic PICs for use in optical transmission systems are still indium phosphide (InP) and its related III-V semiconductors, as they uniquely allow active and passive devices operating in the spectral range of interest for optical telecommunications to be bonded to the same InP substrate. In particular, InP PICs may be a cost-effective and volume-scalable solution to most large-scale deployment components: optical transceivers operating in the 1.3 μm and 1.5 μm wavelength ranges for accessing passive Optical Networks, see, for example, v.tolstin ("Integrated Photonics: Integrated Optical components technologies for Next Generation Access Networks", proc.asia Optical fiber Communication & Optical amplification & reference, 10 months 2007).

Within each optical transceiver is an optical photodetector that converts a received optical signal into an electrical signal, allowing this received signal to be provided to an electrical device connected to a telecommunications network, such as with a Voice Over IP (VOIP) phone, computer, or digital television set top box. Such photodetectors are designed as PIN diodes with low reverse voltage bias, with lightly doped "near" intrinsic semiconductor regions between the p-type and n-type semiconductor regions, or as Avalanche Photodiodes (APDs) with high reverse voltage bias. The compatibility of PIN diodes with standard CMOS electronics, the typical reverse bias of a few volts rather than tens of volts with APDs, low capacitance and high bandwidth operation, has made PIN diodes the preferred choice in network deployments.

As previously mentioned, PIC is the most promising cost-effective and volume-scalable solution needed to implement access network transceivers. In monolithic PICs, PIN diodes are implemented in a waveguide structure, resulting in Waveguide Photodetectors (WPDs) that are compatible with the passive waveguide circuitry of the PICs, and thereby facilitate monolithic integration of the photodetectors with passive wavelength demultiplexing and routing elements. Accordingly, the requirements for a PIC compatible, high performance and still inexpensive PIN WPD are further developed and are essential for such fiber penetration to the subscriber customer base and the resulting PIC penetration to the access communication system.

While drivers for implementing such PIN WPDs are particularly apparent in access networks, it should be understood that they are particularly attractive general-purpose devices at high bit rates, where surface-illuminated detectors are limited by carrier-transit time absorption efficiency trade-offs and limited in PICs, and where any non-waveguide device is difficult to integrate.

One key performance parameter of any photodetector is the responsivity of the induced photocurrent, defined with respect to incident optical power. It is measured in amperes/watt (A/W) and can be expressed as

Wherein R is the total quantum efficiency, e is the electronic charge, andis the photon energy. However, the η values in on-chip PIN WPDs, which are mainly dependent on device design, can reach a considerable 70%, see e.g. "One-Step grown Optical transmitter PICs in InP" by v.tolstikhin (proc.ecoc 2009, 20-24 months 2009, Paper 8.6.2), which is still always less than One, and thus the response rate of any PIN detector is substantially lower than that of any PIN detector

Meanwhile, a clear trend in the development of optical networks today is the requirement of higher and higher responsivity at the receiver end. For example, in the case of access PONs, the constant goal driven by network operators is towards higher split ratios and longer extension architectures, as this reduces the central office equipment and operating costs per subscriber, thereby enabling it to offer lower prices to the end customers. Thus, some PON standards, such as GPON B + (ITU-T G.984.2), have required that the detector responsivity be higher than for any conceivable transimpedance amplifier (TIA)

The photodetector pair is typically loaded into the receiver circuitry. Obviously, this requirement cannot be met with any PIN photodetector, even PIN WPD alone, which generally has higher insertion loss and therefore slightly lower quantum efficiency than its surface-illuminated counterpart.

To achieve a total quantum efficiency η >1, some form of gain must be added between the incoming signal from the optical fiber and the receiver circuit. There are three on-chip solutions to this:

a) electrical gain after detection, for example by using phototransistors, where the signal is amplified while in the electrical domain, is not entirely a waveguide-based PIC compatible solution and in fact requires that photonic integrated circuits (active and passive waveguide-based photonic devices integrated onto the same substrate) be upgraded to optoelectronic integrated circuits (electronic devices integrated onto the same substrate with active and passive waveguide-based photonic devices) at the expense of substantially more complex and expensive manufacturing processes;

b) for example, by utilizing electrical gain in the detection process of Avalanche Photodiodes (APDs), where the signal is amplified while being transformed from light to the electrical domain, is substantially limited in gain bandwidth product, particularly in its waveguide-based implementation, and is therefore not well suited for integration into PICs for most network applications; and

c) optical gain prior to detection, for example in a Semiconductor Optical Amplifier (SOA), where the signal is amplified without leaving the optical domain, a waveguide-based solution compatible with the rest of the PIC design and fabrication process; referred to hereinafter as an optical pre-amplification detector (OPAD).

OPAD appears to be higher than that of the waveguide-based PIC architecture and manufacturing process due to its compatibility

A suitable PIC solution for fiber coupled responsiveness is defined as the current delivered by the PIC into the receiver circuitry versus the optical power delivered by the optical signal to the PIC. This solution has no specific speed limit (unless the SOA is in saturation and its optical gain is affected by the amplified optical signal) and can provide an end-to-end gain of tens of, thus achieving a good gain-bandwidth product. For these reasons, the design of high-function PIC-compatible OPAD devices has attracted considerable attention in recent years.

Any integrated OPAD is generally a waveguide-based device that combines a gain waveguide section (where optical amplification occurs) and a detection waveguide section (where optical conversion to the electrical domain occurs) that are optically connected through a passive waveguide that passes optical signals to/from the two elements of the OPAD. Monolithic integration of multiple waveguide devices, such as Optical Amplifiers (OA) and Photodetectors (PD) required for OPAD, with different waveguide core regions made of different semiconductor materials can be achieved essentially by one of three ways:

1. direct butt coupling; this takes advantage of the ability to perform multiple steps of epitaxial growth, including selective area etching and regrowth, to provide multiple semiconductor materials spatially horizontally distinct from a common vertical plane across the PIC die, and different semiconductor materials are grown horizontally adjacent, such that waveguides are formed in each direct interface with one another to form a transition from one material to another;

2. modifying butt coupling; this utilizes selective area post-growth modification of the semiconductor material, for example by quantum well intermixing techniques, rather than etching and regrowth, to form areas of the desired semiconductor material that are in turn spatially differentiated in a common plane across the vertical orientation of the PIC die; and

3. coupling evanescent fields; wherein vertically separated but still optically coupled waveguides featuring different semiconductor materials of the core region are used to provide the required material differences without additional growth steps, so that it is now distinguished in a common vertical stack of PIC dies.

Examples of prior art can be found in each of these three categories. Integrated OPAD devices using direct butt coupling are reported, for example, by Haleman et al in U.S. Pat. No. 5029297 "Optical-Amplifier-Photometer Device", by W.Rideout et al in U.S. Pat. No. 5299057 "monolithic Integrated Optical Amplifier and Photometer Tap", and by J.Walker et al in U.S. Pat. No. 6909536 "Optical Receiver index A Linear Semiconductor Optical Amplifier". An example of a modified docking coupling is presented by m.aoki et al in us patent 5574289 "Semiconductor Optical Integrated Device and Light Receiver Using Said Device". Finally, an Integrated OPAD based on evanescent field coupling in a vertical twin waveguide structure is reported by s.forrest et al in us patent 7343061 entitled "Integrated Photonic Amplifier and Detector".

Each of these design solutions has its benefits and disadvantages. Considering direct butt-coupling, this allows planar integration with minimal vertical topology, which is an advantage from a planar technology point of view, since no or minimal planarization is required in handling the PIC during fabrication. However, direct butt-coupling requires multiple epitaxial steps to provide multiple semiconductor materials, which not only poses difficulties in managing optical reflections from these material interfaces, but also significantly affects manufacturing yield and thereby significantly increases the cost of the final PIC device. Modifying butt-coupling potentially enables the removal of extra epitaxial steps and in this way improves manufacturing yield, but with possible semiconductor material modifications involved, its ability is limited: in general, only the bandgap of the quantum well layer can be blue shifted up to 100nm, while the other layers, e.g. the heavily doped contact layers, which are required in the active waveguide section but are highly undesirable in the passive waveguide section due to the propagation losses they generate, remain unchanged. Evanescent field coupling, by contrast, does not have the drawbacks of the butt-coupling approach described above, but, since it is based on vertical rather than planar integration, it is based on a slightly more complex fabrication process of planar technology, by requiring multiple etching steps at different vertical levels and creating an increased vertical topology.

Evanescent field coupling is therefore the only practical way to be able to achieve in one step epitaxial growth without any post-growth modification of the semiconductor material, and thus offers the possibility of the highest manufacturing yield in combination with a cost-effective manufacturing process, and accordingly the lowest possible cost of PIC devices. It also provides a direct solution to the integrated OPAD design based on a twin waveguide structure, where the lower of the two vertically coupled waveguides is a passive waveguide with a core layer bandgap that is much higher than the photonic energy of the optical signal intended for the OPAD, allowing low loss propagation, while the upper of the two vertically coupled waveguides is a passive waveguide with an intrinsic material bandgap close to the spectral range of the optical signal to be processed by the OPADAnd (6) PIN structure. This upper waveguide is an active waveguide with the ability to optically amplify (under forward bias) or detect (under reverse bias) for the spectral range of interest. Optical coupling between the two waveguides can be achieved with a selectable transverse taper to promote smooth and controllable vertical transition of the guided optical signal. In this way, with appropriate waveguide and transverse taper design, the optical signal can be adiabatically transferred from the amplifying waveguide segment to the detecting waveguide segment via the passive waveguide segment therebetween, in which case the passive waveguide segment in the absence of the intrinsic active layer and the upper contact layer but in the presence of the lower contact layer also serves as electrical insulation between the forward (amplifying) and reverse (detecting) bias segments of the waveguide PIN. This is reported, for example, by K.T. Shiu et al in "A Simple monolithic Integrated Optical receiver coupling of an Optical Pre-amplifier and p-i-n Photodate" (photon. Technol. Lett., Vol.18, page 956 & 958, month 4 2006) and V.Tolstikhin et al in "Optical Pre-Amplified Detectors for Multi-guided vertical Integration InP" (Proc. Ind. phosphor and related materials, 2009, page 155 & 158, Newport Beach Beach, 2009). Tolstikhin et al report ratios

A 10 times greater fiber coupling responsivity with polarization sensitivity less than 0.4dB for a 50nm wavelength bandwidth, with approximately 150mA of injection current in an OPAD operating at room temperature around 1490 nm.

The twin guided integration of active and passive waveguides is the simplest and most common example of vertical integration based on evanescent fields, and can be implemented in various forms, for example based on conventional Directional Couplers (DC) (see e.g. "Integrated Twin-Guide AlGaAs Laser with multistage electronic structure" (IEEE j.quantum electron, vol.11, p. 457. 460, p. 1975, p. 7) by y.suematsu et al) or DC enhanced by Coupling Impedance Matching layers between optical waveguides (see e.g. "Impedance Matching for enhanced Waveguide/photonic Integration" (applied. phys.lett., vol.55, p. 2712. 2714, p. 1989, p. 12) by r.j.driri et al) or DC with transverse taper assisted Coupling between Twin waveguides see e.g. "effect Coupling in Integrated Coupling-Coupling, p. v. stenu kov et al" (see e.g. phase Matching, p. 10911. moisture Matching, p. 10911. moisture).

Multi-guided vertical integration (MGVI) is an extension of this approach towards multifunctional PICs, in which optical waveguides with different functions are vertically stacked in ascending order of the mutually coupled evanescent field and waveguide bandgap wavelength, the adiabatic transition between vertically disposed waveguides is affected by lateral tapers defined at the necessary vertically oriented stages and acting in relation to each other, see, for example, "ceramic-Coupled DFB filters for One-Step grown Photonic Integration in InP" (IEEE photon. technique. Lett., Vol.21, p. 621. 623, 5.2009) by V.Tolstikhin et al, "optical Pre-Amplified Detectors for Multi-Guide Integration in InP" (Proc.Ind. phosphor and modified Materials 2009 Conference, p. 155. 158, Newport Beach, 2009) by V.Tolstikhin et al and also "Integrated-Optics Arrangement for Multi-Guide Integration in InP" (Proc.Ind. phosphor and modified Materials 2009 Conference, P. 155. 158, Newport Beach, 2009) by V.Tolstikhin et al.

One key feature of the MGVI approach that distinguishes it from the aforementioned prior art continuous twin guided integration in the same multi-guided vertical stack is the ability of the optical signal in a multi-functional PIC with more than two overlapping stacked and evanescent field coupled optical waveguides to be adiabatically transferred between these waveguides by means of a transverse taper defined in at least a portion of the vertically guided stages and acting in relation to each other in use. This may be suitable for parallel adiabatic transfer, as opposed to serial adiabatic transfer, where no more than two vertical stacked guides are simultaneously coupled through the evanescent field, and if the PIC structure has more than two functions and thus more than two guided vertical stages, the transition of the optical signal between them is achieved by a continuous transition between two adjacent waveguides, excluding all other guiding layers in the process. Examples of such parallel and serial approaches to evanescent field based integration in a multi-guided Vertical stack are given by v.tolstin et al in us patent 7532784 entitled "Integrated Vertical wavelentth (De) multiplexer" and s.forrest et al in us patent 6795622 entitled "Photonic Integrated Circuits", respectively.

Regardless of the particular active-passive waveguide integration technique (i.e., planar butt coupling or vertical evanescent field coupling) or its particular implementation (e.g., parallel or serial approach based on vertical integration of evanescent field coupling), any OPAD device should provide substantially gain-enhanced responsivity without significant degradation of signal-to-noise ratio. In other respects, as a component to be used for signal transfer from the optical to the electrical domain in a receiver, the OPAD should ideally combine high gain with low noise. The main noise source that OPAD specifically adds to other than general noise sources (e.g. thermal and shot noise in the receiver circuit) is Amplified Spontaneous Emission (ASE) generated in the amplification section of the OPAD. Intrinsic ASE in optical amplifiers, independent of monolithic design, such as OPAD, hybrid or fiber-based, such as Erbium Doped Fiber Amplifiers (EDFAs). In case the ASE-dependent noise becomes a major contributor to receiver noise, the optical signal amplification provided by the OPAD does not help much, since it makes the signal-to-noise ratio worse and eventually the receiver sensitivity worse, although increasing its responsivity. This aspect of OPAD performance is critical for device applications, particularly in extended extension/add-split ratio PONs, but has not been adequately addressed in prior art OPAD designs.

In order to better understand the effect ASE can have on receiver sensitivity and the way it is reduced, it is beneficial to consider current fluctuations in the receiver circuit that are generated by ASE. Neglecting estimates of the current mean square of the induced photocurrent for all noise sources except thermal noise (typically determined by the equivalent input noise of the transimpedance amplifier to which the detector is loaded), we write as follows (1):

wherein i_DIs the RMS noise current in the receiver circuit generated by a device with a similar PIN detector but without an optical amplifier, and the second term on the right illustrates the excessive ASE-related noise generated by the optical preamplifier, which results from the combination of spontaneous-spontaneous and spontaneous-signal beat frequencies represented by the first and second terms in parentheses on the right of this equation, respectively (e.g.n.a. ollson, j.lightwave technol., vol.7, page 1071 and 1082, month 1991 and 7). In this connection, it is possible to use,

is the response rate with respect to the optical power in front of the detection section, E_ASEIs the spectral density of the ASE power at the input of the detection section, B_eIs the receiver circuit bandwidth, B_o≈(cΔλ_PBF)/λ²Is equivalent to the optical wavelength passband DeltaLambda in the transition from amplification to detection waveguide segment_PBFG is the waveguide-reduced (waveguide-referred) aggregate gain, and P is the time-averaged waveguide-coupled optical power of the signal.

If the receiver noise is mainly determined by sources other than ASE, i.e., the first term of equation 1 is dominant, the waveguide coupling sensitivity is estimated as shown in equation (2) below:

where Q is the Q factor under the following assumptions: the noise is Gaussian; the receiver decision circuit threshold is set to give equal error probability for either 1 or 0 bits of the data signal (see "Fiber-optical communication Systems" of g. agrawal, second revision, Wiley, 1997) and the average power P in 1 bit₁Than P in 0 bit₀The height of the tube is much higher, i.e.,

in other cases, when the second term of equation (1) dominates, i.e., in the ASE noise limiting case, the waveguide-coupled receiver sensitivity can be approximated as shown in equation (3) below, in order to approximate the minimum optical power

<math> <mrow> <mover> <msub> <mi>P</mi> <mi>min</mi> </msub> <mo>&OverBar;</mo> </mover> <mo>≈</mo> <mi>hν</mi> <mo>·</mo> <msub> <mi>B</mi> <mi>e</mi> </msub> <mo>·</mo> <msub> <mi>F</mi> <mi>g</mi> </msub> <mo>·</mo> <mi>Q</mi> <mo>·</mo> <mrow> <mo>(</mo> <mi>Q</mi> <mo>+</mo> <msqrt> <mfrac> <msub> <mi>B</mi> <mi>o</mi> </msub> <msub> <mi>B</mi> <mi>e</mi> </msub> </mfrac> </msqrt> <mo>)</mo> </mrow> <mo>,</mo> <mo>-</mo> <mo>-</mo> <mo>-</mo> <mrow> <mo>(</mo> <mn>3</mn> <mo>)</mo> </mrow> </mrow> </math>

Wherein h v is photon energy, and F_gIs the noise factor of the OPAD amplification segment (see "Sensitivity of optical amplified Receivers with optical filtering" by R.C. Steele et al (IEEE photon. Technol. Lett., Vol.3, p. 545. 547, 6 months 1991).

Equations (1) to (3) provide a useful understanding of the limits of OPAD performance and optimization. First, as long as the receiver noise is determined by other factors than ASE, i.e., when the aggregate gain is relatively low, the increase in gain decreases

As can be seen from equation (2), and thereby improve receiver performance. Secondly, in the ASE noise limited case, i.e. when the aggregate gain becomes high, further increase of the gain has no beneficial effect, since this causes

As can be seen from equation (3). Third, at least a portion of the ASE noise associated with the spontaneous-spontaneous beat frequency can be suppressed by inserting a wavelength filter between the amplification and detection sections of the OPAD section, such that the passband of the filter is wide enough to allow passage of all signal wavelengths, but at the same time is narrower than the spontaneous-spontaneous beat frequency bandwidth.

Thus, optical signals in a predetermined narrow wavelength range pass through and are detected in the photodetector section, while ASE noise does not. It can be re-routed away from the detection segment of the OPAD, or absorbed in an intermediate PIC circuit preceding the detection segment, or both, so that the ASE-related OPAD noise is limited to the expected wavelength range of the received signal.

Accordingly, the present invention provides improvements in OPAD by providing MGVI-compatible design solutions that feature passband filtering between amplification and detection of the received optical signal. In this way, performance improvements are combined with the capabilities and advantages of the one-step epitaxial growth MGVI technique, thereby providing a high-functionality and low-cost PIC solution for large-scale deployed OPAD-based receivers, e.g. in extended extension/increased shunt ratio PONs

Object of the Invention

The object of the present invention is an integrated OPAD design compatible with MGVI platforms by providing on-chip ASE filtering outside the signal wavelength range and thus reducing the effect of ASE-dependent noise on the sensitivity of the OPAD-based receiver while providing more than oneReceiver responsivity to enhance device performance. ASE Filter OPThe AD is formed in the MGVI platform such that, in use, the amplifying and detecting waveguide segments are formed in the same waveguide designated active waveguide layer, while the passive waveguide segments and elements of the waveguide circuit are defined in passive waveguide layers positioned below the active waveguide layers in the multi-guiding vertical stack, which may also include other waveguide designated active and passive waveguide layers. All elements of the MGVI photonic circuit are implemented in one epitaxial growth step and monolithically integrated on one substrate. The passband Wavelength filter may be implemented either inside the MGVI structure or outside the MGVI structure, according to MGVI design principles, see U.S. patent 7532784 entitled "Integrated Vertical Wavelength (De) Multiplexer" to v.tolstin et al and 7444055 entitled "Integrated optical reflection for Wavelength (De) Multiplexing in a Multi-Guide Vertical stack".

Disclosure of Invention

It is an object of the present invention to obviate or mitigate at least one disadvantage of the prior art.

According to another embodiment of the present invention, there is provided a photonic component including:

a) an epitaxial semiconductor structure grown in a III-V semiconductor material system in a single growth step when the substrate includes a common designated waveguide for supporting propagation of optical signals in a predetermined first wavelength range and at least one of a plurality of wavelength designated waveguides vertically arranged in order of increasing wavelength bandgap, wherein each of the plurality of wavelength designated waveguides supports a predetermined second wavelength range, each of the predetermined second wavelength ranges being in the predetermined first wavelength range;

b) an optical input port for receiving an optical signal in a first wavelength range;

c) a first filter comprising at least a first output port and a second output port and characterized by at least a first pass-band width, the filter being optically coupled to an optical input port for receiving optical signals in a first wavelength range and for providing a first predetermined portion of the received optical signals to the first output port, the first predetermined portion of the received optical signals being determined based at least on the first pass-band width;

d) an optical amplifier including at least a gain section formed in one of the plurality of wavelength-specific waveguides, a first contact for forward-biasing the optical amplifier, and a third output port, the optical amplifier optically coupled to the first output port for receiving a first predetermined portion of the received optical signal and providing an amplified filtered optical signal to the third output port;

e) a second filter comprising at least a fourth output port and a fifth output port and characterized by at least a second passband width, the filter being optically coupled to the third output port of the optical amplifier and being for providing a first predetermined portion of the amplified filtered optical signal to the fourth output port and a second predetermined portion of the amplified filtered optical signal to the fifth output port, the first and second predetermined portions of the amplified filtered optical signal being determined at least in accordance with the second passband width;

f) a first photodetector optically including at least a second contact for reverse biasing the first photodetector, the first photodetector coupled to a fourth output port of the second filter for receiving the first predetermined portion of the amplified filtered optical signal;

g) a second photodetector optically coupled to a fifth output port of the second filter for receiving the amplified, filtered optical signal; and

h) a third photodetector optically coupled to the second output port of the first filter for receiving a predetermined portion of the optical signal propagating from the optical amplifier to the first filter, the predetermined portion of the optical signal determined based at least on the first pass-band width; wherein,

the first contact and the second contact are formed on the same layer of the epitaxial semiconductor structure, but are electrically isolated from each other.

According to another embodiment of the present invention, there is provided

A photonic component comprising:

a) an epitaxial semiconductor structure grown in a III-V semiconductor material system grown in a single growth step, wherein each of the plurality of wavelength-designated waveguides supports a predetermined second wavelength range, each of the predetermined second wavelength range being in the predetermined first wavelength range, when the substrate includes a common designated waveguide for supporting propagation of optical signals in the predetermined first wavelength range and at least one of the plurality of wavelength-designated waveguides vertically arranged in order of increasing wavelength bandgap;

c) an optical amplifier including at least a gain section formed in one of the plurality of wavelength-specific waveguides, a first contact for forward-biasing the optical amplifier, and a first output port, the optical amplifier optically coupled to an optical input port for receiving an optical signal and providing an amplified optical signal to the first output port;

d) a first filter including at least a second output port and characterized by at least a first pass-band width, the filter being optically coupled to the first output port of the optical amplifier and for providing a first predetermined portion of the amplified optical signal to the second output port, the first predetermined portion of the amplified optical signal being determined based at least on the first pass-band width;

e) a first photodetector optically including at least a second contact for reverse biasing the first photodetector, the first photodetector coupled to a second output port of the first filter for receiving a first predetermined portion of the amplified optical signal; wherein

Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.

Drawings

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1A shows a prior art OPAD according to "optical Pre-amplification detectors for Multi-Guide Vertical Integration in InP" by Tolstikhin et al (Proc. IPRM 2009);

FIG. 1B shows a schematic diagram of the functionality provided by the prior art of Tolstikhin with respect to OPAD;

FIG. 2 shows Q-factor versus optical gain with varying filter bandwidth for an OPAD receiver;

FIG. 3 shows a schematic diagram of the functionality provided by the present invention;

FIG. 4A shows an OPAD in which wavelength filtering is achieved by a thin film filter with reflective interfaces and waveguide interfaces at the edges of the circuit, according to one embodiment of the invention;

FIG. 4B shows an OPAD in which wavelength filtering is achieved by a reflective interface and a thin film filter in combination with a multimode interference coupler, according to one embodiment of the invention;

FIG. 4C shows an OPAD in which wavelength filtering is achieved by a reflective interface and a thin film filter with waveguide horns, according to one embodiment of the invention;

FIG. 5 illustrates an OPAD in accordance with one embodiment of the invention, in which wavelength filtering is achieved by a multi-mode interference filter employed in a passive waveguide layer;

FIG. 6 illustrates an OPAD in accordance with an embodiment of the invention in which wavelength filtering is achieved by a grating assisted laterally directional coupler formed in a passive waveguide layer; and

figure 7 shows an OPAD according to one embodiment of the invention in which wavelength filtering between the optical amplifier and the photodetector is achieved by a grating assisted coupling structure and a second grating assisted coupling structure couples a corresponding filtered broadband noise signal from the front facet of the optical amplifier to the monitoring photodetector.

Detailed Description

The present invention is directed to an integrated optical pre-amp detector (OPAD) having a bandpass wavelength filter between the amplification and detection sections of the device that is intended to reduce the effect of amplified spontaneous emissions generated in the amplification section of the device on broadband noise generated in the detection section of the device, thereby enhancing the signal-to-noise ratio and improving the performance of an optical receiver characterized by the optical pre-amp detector.

Reference will now be made to specific elements that are numbered in accordance with the accompanying drawings. The following discussion is to be construed as exemplary in nature and not as limiting the scope of the present invention. The scope of the invention is defined in the claims and should not be construed as being limited to the implementation details described below, which can be modified by a person skilled in the art by substituting equivalent functional elements.

The optical waveguide is typically referenced by reference to an etched rib waveguide structure and is identified by a rib element in the uppermost layer of each etched rib waveguide structure. Such reference is intended to simplify the description and not to represent any element of the optical waveguide as including only the identified upper etched ridge elements. Those skilled in the art will appreciate that the scope of the present invention is therefore not intended to be limited to such etched rib waveguides as they represent only a portion of the possible embodiments.

Referring to fig. 1A, there is shown a prior art integrated OPAD 100A according to "optical available pre-Amplified Detectors for Multi-Guide Vertical Integration in InP" by v.tolstimkhin et al (proc.iprm 2009). OPAD 100A includes passive and active waveguides, shown by structures 110 and 120, respectively, that are vertically stacked relative to each other such that passive waveguide 110 is below and designed to be transparent in the specified wavelength range of upper active waveguide 120. Laterally, the waveguide is defined by etching the shallow ridge of the passive waveguide 110 and the deep ridge of the active waveguide 120. The terms "shallow" and "deep" ridge are used hereinafter to identify ridge waveguide designs in which the etch stop is above and through the guiding layer, respectively. The deep etch active waveguide 120 actually forms a mesa where the N contact 130 to the waveguide PIN structure is deposited on the top surface of the passive waveguide 110 in addition to the mesa. A P-contact is formed on the top surface of the mesa as the upper surface of the active waveguide 120. Thus, electrical isolation between the amplification and detection sections 140, 150 of the respectively forward and reverse biased active waveguide PIN sharing a common ground, i.e., N contact, is achieved by etching away the material of the mesa between the two sections. A similar design as previously described is reported by s.forrest et al in U.S. patent 6795622 entitled "photonics integrated Circuits".

Although a simple isolation trench between the two PIN structures provides this electrical isolation, it also abruptly interrupts the active waveguide, thereby causing undesirable light loss for the transition from amplification to detection section. Not only is such a loss undesirable because it must be compensated for with a greater gain that will produce greater ASE dependent noise, but when it relates to the PIC environment, excessive light scattering at the output of the amplification stage will also cause optical crosstalk to other optical circuit elements. Therefore, a low insertion loss transition between the amplifying and detecting segments of the active waveguide via an adiabatic transition from the amplifying segment to the passive waveguide segment and then from the passive waveguide segment to the detecting segment is a more preferred solution. This still provides electrical isolation between the two oppositely biased active waveguide segments. In practice, this adiabatic transition is achieved by a suitable taper of the active waveguide and possibly a passive waveguide in the transition region, as shown in fig. 1, but not explicitly identified.

Transverse tapered assisted adiabatic vertical transitions of optical signals between the active waveguide 120 and the passive waveguide 110, or vice versa, are a design solution that can reduce the insertion loss between the electrically insulating amplification section 140 and the detection section 150 to between 1dB and 2dB (see "optical Pre-Amplified Detectors for Multi-Guide vertical integration in InP" by v.tolstin et al (proc.iprm 2009, page 155-.

Thus, the effective circuit configuration is illustrated in FIG. 1B by circuit 100B, which includes optical gain block 180 and photodetector 190. At a wavelength λ_sIs fed into the circuit 100B from the optical input 170 and is coupled to the optical gain block 180. From the optical gain block 180 at wavelength λ_sPropagates forward via transition block 185 to photodetector 190, which represents the effect of two optical transitions between active and passive waveguides. Also coupled from the optical gain block 180 are forward and reverse propagating ASE signals having a wavelength spectrum λ, to the optical input 170 and the photodetector 190, respectively_ASE. The forward-propagating ASE signal propagates through both optical transitions between the active and passive waveguides essentially unaffected with respect to the wavelength spectrum, but with reduced optical power (typically 0.5db1.0db) due to the insertion loss of these interfaces, each as reported by v.tolstin et al in "optical Pre-Amplified Detectors for multi-Guide Vertical Integration in InP" (proc.iprm 2009, page 155, Newport beacon, 2009).

The effect of ASE on receiver signal-to-noise ratio is illustrated by the calculations shown in FIG. 2, where the Q factor is calculated as having a varying ASE filter spectral width Δ λ_PBFIs given as a function of the net gain of the signal and is provided based on the analysis shown previously. With reference to the application of OPADs in fiber-optic home optical access,the optical (transmitter relative intensity noise, shot and thermal noise in waveguide detectors) and electrical (by equivalent input noise i in front-end amplifier) of the receiver are considered according to the GPON ITU standard (ITU-T g.984.2)² _EINRepresented) is shown) is detected. It can be seen from fig. 2 that while the Q factor tends to saturate as a function of net gain, the noise factor F when the gain section is active_gHigher (i.e., F)_g=7), saturation occurs at lower Q and net optical gain. Reducing the gain section noise factor (i.e., F)_g=5) and/or limit the optical passband of the ASE (i.e. filter out the passband Δ λ_PBFExternal ASE) to increase the achievable Q factor. Input noise i of the front-end amplifier_EINIs set to a value

I.e. an optical pass band delta lambda of 50nm or less_PBFReaches a value corresponding to a bit error rate of 10 when the value of commercially available TIA used in these calculations of (a) is reached^-12Values of Q of more than 7 are feasible. The calculations in fig. 2 are performed for an electrical bandwidth of 1.8GHz at a center wavelength of 1490nm suitable for 2.5Gb/s transmission. As shown, the first to third curves 210 to 230 represent performance curves of gain segment noise factors Fg =7 for bandwidths of 20nm, 30nm and 50nm, respectively. Fourth to sixth 240 to 260 represent gain section noise factors F of bandwidths of 20nm, 30nm and 50nm, respectively_gPerformance curve of = 7.

In order for the optical passband filter to have a positive effect on receiver sensitivity, the filter passband DeltaLambda is reduced by reducing ASE-ASE beat frequency noise_PBFShould be larger than the ASE spectral width lambda under operating conditions_ASEIs narrow but wider than or equal to the wavelength range width lambda of the pre-amplified optical signal_s. In a typical waveguide semiconductor optical amplifier featuring a large number or quantum well active layer and providing a net gain of-5 dB 7dB, the ASE spectral width is wider than 50nm and may exceed 100nm, while the signal wavelength range width is typically narrower, e.g. 20nn in the case of an EPON or GPON ONU data receiver or 10nm in the case of a GPON ONU video receiver, leaving the designer to pass through appropriatelyWhen the pass band width of the filter is selected to be in the inequality lambda_S≤λ_PBF≤λ_ASEInto a certain space. In such a passband, both the signal and the ASE will pass from the amplification into the detection section of the OPAD, while all wavelengths outside the passband will be rejected and will therefore not contribute to receiver noise.

It is therefore apparent from fig. 2 that it is an improvement of the integrated OPAD design if passband wavelength filtering is also provided to reduce the effect of ASE generated in the amplification section on the total received noise while keeping within the framework of a solution that achieves electrical isolation between the amplification and detection sections of the active waveguide with minimal optical loss. It would be further advantageous to make this or such a solution compatible with the MGVI platform and, accordingly, to make the integrated OPAD not only a high-function device, but also an important building block for cost-effective PIC receivers and transceivers.

Referring to fig. 3, there is a schematic diagram illustrating an OPAD300 in accordance with an embodiment of the invention in which pass-band filtering elements are employed between the optical amplification and detection sections of the OPAD300 and between the lead optical circuit or network and the optical amplification section of the OPAD 300. The former is necessary for any embodiment of the invention, while the latter is optional and therefore serves to prevent unwanted ASE light from entering the leading optical circuit or network.

Wavelength range λ in the case of optical filters employed on both the front and back sides of the amplification section of OPAD300_sEnters OPAD300 at source 310 and is coupled to front Pass Band Filter (PBF) 320. Front PBF 320 has a wavelength passband width Δ λ^F _PBFSuch that it includes all signal wavelengths and thereby passes the incoming optical signal into the amplification section (gain element) 330. Pass band range delta lambda^F _PBFExternal wavelengths are rejected and rerouted to absorber 350 where the optical signals they carry are absorbed and thereby prevented from propagating further into OPAD 300. Since front PBF 320 must transmit all incoming optical signals to detector element 360, Δ λ^F _PBFShould include all signalsThe wavelength of the light emitted by the light source, i.e.,

at the same time, ideally, it should not include the signal wavelength range λ_sAll external wavelengths, indicated in a properly designed deviceWithout the provision of the front PBF 320 and, correspondingly, the absorber 350 on the front side of the amplification section, the incoming optical signal passes directly from the source 310 into the gain element 330.

In either case, the incoming optical signals are amplified in gain element 330 and then forward coupled to post-PBF 350 where they follow their pass band Δ λ^B _PBFFiltered such that wavelengths in this pass band propagate further to the detection section of OPAD300, i.e. detector element 360, while wavelengths outside this pass band range are rejected and optionally routed to a monitoring element 370, e.g. another photo detector, thereby providing a feedback signal allowing control of the net gain in the amplification section (gain element 330). Since the back PBF 360 must pass all incoming optical signals to the detector element 370, Δ λ^B _PBFShould include all signal wavelengths, i.e.And preferably does not include the signal wavelength range lambda_sAll wavelengths outside, i.e. in the optimum design

In addition to providing the required amplification of the incoming optical signal prior to its detection in the detector element 360, the gain element 330 also generates an unwanted ASE, which is represented by the addition of an ASE element 380 in parallel with the gain element 330 in the block diagram shown in figure 3. This ASE is characterized by a wavelength range λ_ASEWhich is substantially equal to the net gain range lambda of the gain element 330_GOverlap and from OPADThe ASE element 340 in 300 propagates forward and backward.

The signal wavelength range λ would be in the presence of the front PBF 320 and in the absence of the front BPF 320_sBackward propagating ASE λ in (1)_ASEInto a lead optical circuit or network (schematically represented by source 310). However, with pre-PBF 320, the signal wavelength range λ is_sExternal signals can be rejected by the front PBF 320 and then absorbed in the absorber element 340, thereby reducing ASE penetration into the leading circuit or network.

Signal wavelength range lambda_sIs transmitted by the back PBF 360 into the detector element 360 along with the pre-amplified incoming signal. However, the signal wavelength range λ_sThe external ASE signal is rejected in all embodiments of the invention. Optionally, these rejected signals are rerouted to and detected in monitoring element 370 to provide control of gain element 330, or otherwise absorbed, dissipated, or routed.

The effect of the post-PBF 350 on receiver noise is estimated as ASE-ASE beat contribution to the broadband noise reduction factor, according to equation (3) above

If Δ λ_ASE＞＞Δλ_SFor example, in devices with a wide gain spectrum and a narrow signal wavelength range, it may be significant, thereby improving OPAD300 performance, but if Δ λ_ASE≤λ_SASE filtering does not actually improve OPAD performance and is therefore meaningless.

Accordingly, the block diagram of the OPAD300 with ASE filtering as presented in fig. 3 represents the most common solution and approach to this problem, and is not limited to any particular OPAD design, nor is it dependent on the design of the PBF elements and rerouting waveguide elements. The embodiments shown below with respect to fig. 4-7 represent some specific designs of the back PBF 360 elements previously described with respect to OPAD300 of fig. 3. These are achievable using a range of optical waveguide circuit elements and arrangements. These waveguide circuits and arrangements are merely examples for ease of explanation and do not represent all potential embodiments that fall within the scope of the claims.

Referring to fig. 4A-4C, an embodiment of the present invention is shown in which a Thin Film Filter (TFF) provides the desired passband filtering in an OPAD. With the functionality described above with respect to fig. 3, the TFF is designed for a signal wavelength range λ_sAnd a transmission filter for the ASE wavelength outside this range, lambda_ASE≤λ_{PBF Lower}And λ_ASE≥λ_{PBF_Upper}Wherein λ is_{PBF_Lower}And λ_{PBF_Upper}Denotes the lower and upper wavelength limits of the PBF provided by the TFF, which can be set to the signal wavelength range λ_sOr tolerances may be determined to allow for environmental influences such as temperature. TFFs employ, for example, a multilayer dielectric stack design (see, e.g., JDS UniphaseInterference Filter hnadwood, revision 2, 2007).

The basic idea of an embodiment comprising a TFF (i.e. a post-PBF 360) as a filtering element between the amplification and detection sections is illustrated in fig. 4A by a schematic diagram of an OPAD 400A. Accordingly, OPAD 400A includes an optical substrate 410 upon which the MGVI waveguide structure has been grown and patterned, not explicitly shown for clarity. Accordingly, the first passive waveguide 411 receives the amplified optical signal from the amplification section 412 of the passive and waveguide layers that includes the MGVI that receives the incoming signal from the second passive waveguide 410. The enlarged segment 412 is shown schematically and is not intended to reflect the actual active-passive waveguide integration in the MGVI platform as would be apparent to one skilled in the art. Thus, respectively at the wavelength λ_sAnd λ_ASEThe incoming optical signal and the forward propagating ASE propagate towards the back end face 416 of the device where they are incident on the TFF 413. Predetermined wavelength range lambda_sReflects from the TFF 413 and is then coupled to a third passive waveguide 414, the third passive waveguide 414 being optically connected to the detection section 415 of the OPAD 400A. As with the amplification section 412, the detection section 415 is shown schematically, rather than to reflect the actual active-passive waveguide integration in the MGVI platform. Predetermined wavelength rangeλ_sAll external wavelengths are transmitted through TFF 413 and accordingly out of the PIC including OPAD 400A.

It will be apparent to those skilled in the art that optionally a photodetector (not shown in this schematic for clarity) may be provided behind the TFF 413 to measure transmitted light outside the signal wavelength range as forward ASE light, thereby providing gain control of the amplification section of the OPAD 400A in accordance with the previous block diagram of the OPAD300 in fig. 3.

The design of the TFF 413 at the rear end face 416 of the OPAD 400A should be adjusted to the angle of incidence of the first passive waveguide 411 such that the target wavelength range λ_sIs coupled into the second passive waveguide 414 after being reflected by the TFF 413. Unlike conventional TFF designs intended for near normal (i.e., 0 degree) incidence, such as those outlined by D.H. Cushing in U.S. Pat. No. 6011652 entitled "Multi-Layer Thin Film Dielectric Bandpass Filter" and P.J. Gasoli in U.S. Pat. No. 5179468 entitled "spacing of silicon Thin Film Stacks for Producing optical interference Coatings", TFF 413 will be designed to operate at larger angles of incidence, but still remain less than or equal to a predetermined wavelength range λ_sAngle corresponding to the total internal reflection angle in the outer wavelengths.

In contrast to the design simplicity of the embodiment depicted in fig. 4A, the practical implementation is rather tricky, for example, it partly requires an accurate splitting of the end face coated with TFF 413 at a position predetermined by the layout of the first and second

passive waveguides

411, 414, respectively. If accurate splitting on the micron scale, such as is the case with typical shallow etched ridge waveguides in InP-based materials operating in the 1.3 μm or 1.5 μm wavelength range, is not an option, within tolerances comparable to waveguide width, certain design modifications can be implemented to mitigate splitting tolerances.

One such modification is shown in fig. 4B, which shows another embodiment according to the present invention of an OPAD400B comprising TFF425 of the device end face, where the mitigation of the split tolerance is achieved by adding more ports respectivelyA mode interferometer (MMI)421 is inserted between the first and second passive waveguides 422,423 and the device end face 424 with TFF 425. A first passive waveguide 422 couples signals from the amplification section 426 to the MMI 421 and a second passive waveguide 423 couples filtered signals from the MMI 421 to the detection section 427. For a predetermined signal wavelength range λ reflected by TFF425 into the PIC chip_sAlthough wavelengths outside this range pass through the TFF425 and are transmitted from the PIC chip, the performance of an MMI 421 containing an input port 421A and an output port 421B of the same end face 421 is equivalent to the performance of a double-length MMI having an MMI 421 with input and output ports of the opposite end face (such a transmissive MMI is not shown in fig. 4B). Design techniques that utilize MMI 421 to thereby achieve increased tolerance of the two-port MMI to the length of MMI 421 are well known and are actually reduced to provide a flat top passband in the port-port transmission spectrum, see, for example, l.soldano et al, "Optical Multi-Mode interference device Based on Self-Imaging: Principles and Applications" (j.lightwave tech., vol., 13, No.4, p.615 + 627, p.1995-4).

Thus, the deviations in TFF425 and back facet position (i.e., device facet 424 relative to the front facet of MMI 421) that are equivalent to wavelength deviations are less pronounced in their effect on port-to-port transmission, thereby mitigating the impact of splitting tolerances on device performance. As an additional benefit, MMI-assisted back facet TFF solutions allow the use of conventional TFF designs intended for normal incidence, such as described by d.h. cushing in U.S. patent 6011652 entitled "Multi-Layer Thin Film Dielectric Bandpass Filter" and p.j. gasoli in U.S. patent 5179468 entitled "Interleaving of Thin-Film stacks for Producing Optical Interference Coatings". One skilled in the art will appreciate that MMI 421 may also be designed to provide at least some aspect of wavelength filtering to function in conjunction with TFF 424.

It will also be apparent to those skilled in the art that TFF425 may be provided as a separate TFF element bonded to the device end face 424, or it may be deposited onto the deviceAnd an end face 424. Optionally, a third output optical port may also be added to MMI 421 and, accordingly, a third passive waveguide provided leading to a second sensing section, in use, acts as a monitor, such as monitoring element 380 of figure 3 described above, to provide a gain control loop to the amplification section of OPAD400B, which elements are not shown in figure 4B for clarity. In this case, the equivalent optical circuit of the resulting PIC reproduces the back end of the generic OPAD300 given in fig. 3 above, with TFF425 and optionally MMI 421 serving as the back PBF 360 and the two detection segments of the active waveguide serving as the detector element 370 and the monitor element 380. In order for this functionality to be feasible, the tree port MMI must now transmit the wavelength range λ to the output passive waveguide connected to the first detection segment of the active waveguide (i.e. detection segment 427 acting as detection element 370)_sAnd wavelength range λ_sThe ASE light in the external wavelength is coupled to another passive waveguide segment leading to the second detection segment of the active waveguide (operating as a monitoring element 380).

Another design solution is shown in fig. 4C by OPAD400C, which allows to mitigate the effect of the splitting tolerance on the OPAD performance characterized by the back facet TFF of the PBF between the amplification and detection sections of the device. Here, first and second passive waveguides 431, 432, which couple the Optical signal from the amplification section and are directed to the detection section and are not shown for the sake of clarity, respectively, are provided with planar focusing elements 433, 434, as described for example in "Optical wave guide parallel Coupling Horns" by w.k.burns et al (appli.phys.lett.vol.30, pages 28-30, 1/1977). These planar focusing elements 433 and 434 are intended to provide parallel beams into the slab waveguide 435 at the exit of the rib waveguide, thereby reducing beam divergence in the plane of the waveguide core. The slab waveguide terminates at the end of the device on which the TFF440 is bonded or deposited. Thus, the predetermined signal range λ_sThe wavelengths in (b) will be reflected into the chip by the TFF440 at the end facet, while the reflected beam in the slab waveguide will remain nearly parallel regardless of the exact position of the split end facet relative to the passive waveguide. The planar focusing elements 433 and 434 need not be identical, but insteadIt is fully conceivable that they have different shapes, e.g. at the end of the first passive waveguide 431, the emission plane focusing element 433 cascaded to the amplification section of the OPAD400C and not shown in fig. 4C can be designed to provide parallel beams at small angles of incidence, while at the beginning of the second passive waveguide 432, the collection plane focusing element 434 leading to the detection section of the OPAD400C and similarly not shown in fig. 4C can be optimized for coupling a wider and diverging two-dimensional light beam, i.e. in a direction perpendicular to the plane of fig. 4C, the light rays are confined in and around the passive waveguide core.

It will be apparent to those skilled in the art that in each of the embodiments described above with respect to fig. 4A to 4C, ASE light propagating through the TFFs as

TFFs

413, 425, 440, respectively, may optionally be monitored by a detector placed behind the TFFs, thereby allowing control of the gain in the amplification section of the OPAD. This additional TFF may be provided externally to the MGVI structure, or alternatively where the TFF is provided in a recess formed in the MGVI structure, it may be provided externally with the waveguide interconnect (e.g., planar waveguide structure), or in an additional feature implemented in the MGVI structure.

It will also be apparent to those skilled in the art that the previously illustrated embodiments employ reflective TFFs, in which the optical signal λ in the pass band of the filter_sAnd λ_ASEIs reflected and coupled to the photodetector, and alternatively a transmissive TFF filter may be employed, such that the optical signal λ in the pass band of the filter_sAnd λ_ASETransmitted and reflected outside the pass band. Such a transmissive TFF element may be realized in embodiments according to the invention by a suitable arrangement of detector elements 370, the detector elements 370 being associated with transmissive TFFs with or without planar waveguide elements in between with or without monitoring elements 380.

Finally, it is also apparent that other waveguide elements and structures may be used in combination with the TFF for achieving the predetermined signal wavelength range λ_sWavelength filtering of external ASE, see, e.g., U.S. Pat. No. T. Augustsson, entitled "Device and Method for Optical Add/Drop MultiplexingNational patent 7423658 and U.S. patent 5596661 entitled "Monolithic Optical waveform filters based on Fourier Expansion" to C.H.Henry et al.

Referring now to fig. 5, a schematic diagram of an OPAD 500 according to an embodiment of the present invention is shown, as previously shown in the schematic diagram of fig. 3, comprising an amplification section 510 (gain element 330 in fig. 3) and a detection section 520 (detector element 360 in fig. 3). ASE filtering is achieved by inserting an MMI 530 with associated first and second passive waveguides 530 and 540, acting as a rear PBF 360, between the active waveguide segments 515 and 525, respectively, thereby providing an amplification segment 510 and a detection segment 520. Like other embodiments of the present invention, this integrated component OPAD 500 includes a substrate 505 on which MGVI structures are grown and processed, not explicitly identified for clarity. MGVI structures and guided optical signal propagation therein (e.g., lateral taper assisted Vertical switching between passive and active waveguides) are similar to those reported by v.tolstin et al in "optical pre-Amplified Detectors for Multi-Guide Vertical Integration in InP" (proc. index and Related Materials 2009 Conference, page 155-158, Newport beacon, 2009).

It will be apparent that the OPAD 500 differs from this prior art in that at this point the MMI 530 has been incorporated into a section of the passive waveguide between the amplifying and detecting sections 510 and 520, respectively, of the active waveguide, where the MMI 530 is defined on the same vertical layer as the passive waveguide, as shown in figure 5. The two-port MMI 530 is designed to operate as an optical pass-band filter in accordance with the general description of the invention with reference to figure 3. It receives a predetermined wavelength range lambda_sTogether with a general specific signal range lambda_sWavelength range λ to be broad_ASEMiddle ASE light. However, it only transmits the signal wavelength range λ_sUniform range lambda_PBFSuch that they are vertically transferred into the active waveguide 525 by first propagating into the second passive waveguide 550 between the MMI 530 and the detection segment 520, and second passing into the OPAD 5 by means of a vertical taper defined at the passive and active waveguide levels00 and its active waveguide segment 525.

The design Principles of MMI 530 with the intended wavelength filtering are well known, for example, as described in "Optical Multi-Mode Interference Devices Based on Self-Imaging: Principles and Applications" (J.Lightwave Tech., Vol.13, No.4, p.615 + 627, 4. 1995) and in U.S. Pat. No. 5428698 "Optical Routing Device" by L.Soldano et al. It should be apparent to those skilled in the art that the passive waveguide layers in the MGVI optimized for efficient and controllable passive-active vertical coupling are also suitable for the desired MMI passband filtering by appropriate selection of MMI shape and size, and adjustment of the layout of the passive waveguides entering and exiting the MMI filter.

Optionally, a second output optical port may be added to the MMI 560 and, accordingly, a second passive waveguide provided leading to the second sensing section acts in use as the monitoring element 308 to provide a gain control loop to the amplification section of the OPAD, not shown in figure 5 for clarity. In this case, the equivalent optical circuit of the integrated assembly reproduces the back-end of the generic OPAD shown in FIG. 3, where the MMI 530 serves as the back PBF 350 and the two sensing segments of the active waveguide serve as the detector element 360 and the monitor 370, respectively. In order for this functionality to be feasible, the tree port MMI must now transmit the wavelength range λ to the output passive waveguide connected to the first detection segment of the active waveguide acting as detector element 360_sOf the optical signal, and a wavelength range λ_sThe ASE light in the external wavelength is directed to a passive waveguide operating as a monitor 370 to the second detection segment of the active waveguide.

Referring now to fig. 6, a schematic diagram of an OPAD 600 according to an embodiment of the present invention is shown, as previously shown in the schematic diagram of fig. 3, comprising an amplification section 610 (gain element 330 in fig. 3) and a detection section 620 (detector element 360 in fig. 3). ASE filtering is achieved by inserting a grating assisted directional coupler 650 with associated first and second coupler waveguides 630, 640 acting as a back PBF 360 between the amplification section 610 and the detection section 620, respectively. The first and second coupler waveguides 630, 640 each form first and second gratings 635, 645, respectively, on their upper surfaces, such that the entire combination acts as a grating assisted directional coupler 650. As with other embodiments of the invention, this integrated assembly OPAD 600 includes a substrate 605 on which MGVI structures are grown and processed, not explicitly identified for clarity. MGVI structures and guided optical signal propagation therein, such as transverse taper assisted vertical switching between passive and active waveguides, are similar to those reported by v.tolstin et al in "optical Pre-Amplified Detectors for Multi-guided vertical Integration in InP" (proc. index and related materials 2009 Conference, page 155-158, near beacon, 2009).

It is apparent that the OPAD 600 differs from this prior art in that at this point the grating assisted directional coupler 650 has been incorporated into the segment of the passive waveguide between the amplification and detection segments 610, 620, respectively, of the active waveguide, with the grating assisted directional coupler 650 being defined on the same vertical layer as the passive waveguide, as shown in fig. 6. The grating assisted directional coupler 650 is designed to operate as an optical pass-band filter as generally described in the present invention with reference to figure 3. It receives a predetermined wavelength range lambda_sTogether with a general specific signal range lambda_sWavelength range λ to be broad_ASEMiddle ASE light. It transmits and signals in a wavelength range lambda_sUniform range lambda_PBFSuch that they enter the detection section 620 of the OPAD 600 and its active waveguide section 625 by first propagating in the first coupler waveguide 630 and second coupling into the second coupler waveguide 640 before passing vertically into the active waveguide 625 by means of the vertical taper defined at the passive and active waveguide stages. λ at the output of the grating assisted directional coupler 650_PBFThe external signals are in the first coupler waveguides 630 in which they are disposed.

The design principles of Grating assisted directional coupler 650 with the desired wavelength filtering are well known, for example, as described in U.S. Pat. No. 6549707, "Grating-Type optical Filter with Apodistributed Spectral Response" to A.Carenco et al and "coupling Coefficient Modulation of waveform shaping using Sample grading" (IEEEP. Tech., Lett., Vol.6, pp.1222-1224, 1994 to Y.Shibata et al. It should be apparent to those skilled in the art that the passive and active waveguide layers in the MGVI optimized for efficient and controllable passive-active vertical coupling are also suitable for the desired grating-assisted directional coupler filtering by appropriate selection of the grating structure, directional coupler waveguides, coupler transfer characteristics, and appropriate design and adjustment of the layout of any passive waveguide segments disposed between the grating-assisted directional coupler 650 and the amplification and detection segments 610 and 620, such passive waveguide segments not being shown in fig. 6.

Optionally, a second output passive optical waveguide may be added to the output of the first coupler waveguide 630 and accordingly acts in use as a monitoring element 308 when appropriately arranged leading to the second detection section, so as to provide a gain control loop to the amplification section of the OPAD, not shown in fig. 6 for clarity. In this case, the equivalent optical circuit of the integrated assembly reproduces the back-end of the generic OPAD shown in fig. 3, with the grating assisted directional coupler 650 serving as the back PBF 350 and the two detection segments of the active waveguide serving as the detector element 360 and the monitor 370, respectively. In order for this functionality to be viable, the three-port directional coupler must now deliver the wavelength range λ to the output passive waveguide connected to the first detection segment of the active waveguide acting as detector element 360_sOf the optical signal, and a wavelength range λ_sASE light in the external wavelength is directed to a passive waveguide operating as monitor 370 to a second detection segment of the active waveguide

Referring now to fig. 7, a schematic diagram of an OPAD700 is shown, according to one embodiment of the present invention, which, as previously shown in the schematic diagram of fig. 3, includes an amplification section 730 (gain element 330 in fig. 3), a detection section 750 (detector element 360 in fig. 3), and a monitoring section 745. ASE filtering for the detection segment 750 is achieved by inserting a first grating auxiliary coupler 740 acting as the back PBF 360, while ASE filtering back into the optical network to which the OPAD700 is connected is achieved by inserting a second grating auxiliary coupler 725 acting as the current PBF 320. As with the other embodiments of the invention described above with respect to fig. 4A-6, this fully integrated implementation of OPAD700 includes substrate 705 on which MGVI structures have been grown and processed, not explicitly identified for clarity. MGVI structures and guided optical signal propagation therein, such as lateral taper assisted Vertical switching between passive and active waveguides, are similar to those reported by v.tolstin et al in "optical pre-Amplified Detectors for Multi-Guide Vertical Integration in InP" (proc. index and Related Materials 2009 Conference, page 155-158, Newport beacon, 2009).

It is apparent that the OPAD700 differs from this prior art in that now a second grating auxiliary coupler 725 combines the input 710 and amplification section 730 in a section of the passive waveguide, and a first grating auxiliary coupler 740 is inserted between the amplification and

detection sections

730 and 750, respectively, of the active waveguide, wherein the first and second grating

auxiliary couplers

740 and 725, respectively, are defined on the same vertical layer as the passive waveguide, as shown in fig. 7. Each of the first and second grating

auxiliary couplers

740 and 725, respectively, are designed to operate as optical pass-band filters as generally described in the present invention with reference to fig. 3. Consider a first grating auxiliary coupler 740 that receives a predetermined wavelength range λ_sIntermediate amplified optical signal together with wavelength range lambda_ASEOf the amplification section 730, which is generally larger than the signal range λ from the amplification section 730_sIs wider. However, it only transmits the signal wavelength range λ to the first output port_sUniform range lambda_PBFSuch that they enter the detection section 750 of OPAD700 and its active waveguide section, which are not explicitly identified for clarity. Range lambda_PBFFirst propagates in the passive waveguide between the first grating auxiliary coupler 740 and the detection section 750, before being vertically transferred into the active waveguide of the detection section 750 by means of a vertical taper defined at the passive and active waveguide levels.

Similarly, the range λ_PBFExternal optical informationThe signals are passed to the second output port of the first grating auxiliary coupler 740 so that they enter the monitoring segment 745 of the OPAD700 and its active waveguide segment, which are not explicitly identified for clarity. Range lambda_PBFThese external optical signals first propagate in the passive waveguide between the first grating auxiliary coupler 740 and the monitoring segment 745, before being vertically transferred into the active waveguide of the monitoring segment 745 by means of a vertical taper defined at the passive and active waveguide levels.

Considering now the optical signals entering the OPAD700, they are coupled at the input 710 to the input passive waveguide 715 and then coupled into the second grating auxiliary coupler 725 which has been incorporated between the input passive waveguide 715 and the amplification section 730. Thus, the second grating auxiliary coupler 725 receives the predetermined wavelength range λ from the front light guiding network_sAlong with any out-of-band signals. However, it only transmits the signal wavelength range λ to the first output port_sUniform range lambda_PBFSuch that they enter the amplification section 730 of OPAD700 and its active waveguide section, which are not explicitly identified for clarity. Any signal received from the front optical guide network is coupled to the other output of the second grating auxiliary coupler 725 and not to the amplification section 730.

As previously described, the amplification section 730 emits ASE bi-directionally, and accordingly, if the optical input 710 is directly connected to the amplification section 730, this ASE is re-coupled directly into the leading optical network where it may or may not be filtered and attenuated before being emitted into the primary optical telecommunications network. However, the OPAD700 as described above includes a second grating auxiliary coupler 725. Accordingly, it correspondingly transmits to the input passive waveguide 715 a wavelength in the wavelength range λ_PBFWavelength range lambda of the neutralization signal_sThat portion of the coherent ASE such that these wavelengths enter the input passive waveguide 715 and then couple into the leading optical network. Lambda [ alpha ]_PBFThe external ASE is coupled to the other output of the second grating auxiliary coupler 725 and to the reverse monitoring segment 735. Accordingly, OPAD700 provides a monolithic implementation of the general description of the invention of fig. 3. The signal from the reverse monitoring segment 735 may be combined with the signal from the monitoring segment 745 to provide control of the individual amplification segments 730 or of the entire OPAD 700.

It will be apparent to those skilled in the art that the first and second grating

auxiliary couplers

725 and 740 are shown as having the same passband, i.e., λ, as previously described with respect to fig. 7_PBF. However, depending on the performance requirements of the entire OPAD700 and its receiver path elements (i.e., amplification section 730 and detection section 750), it may be advantageous to design these things with different performance characteristics, which may include bandpass width, isolation, etc. It is also apparent that the design of the OPAD700 shown has an input passive waveguide 710, an amplification section 730, and a detection section 750 formed in the same continuous passive waveguide. Alternatively, the design may be adjusted such that λ_PBFOf the expected optical signal λ_sIn a cross-over, so-called cross-over, state of each directional coupler, and not in a through, so-called through, state. Alternatively, one directional coupler may be designed to be in a through state while the other directional coupler is in a cross state. In each case, detection and

monitoring segments

750 and 745, respectively, are juxtaposed as needed.

Furthermore, in the previous fig. 6 and 7, the grating auxiliary couplers are shown as co-propagating directional couplers, such that the optical signal propagates from one end of the directional coupler to the other. Alternatively, the design can be implemented as a counter-propagating directional coupler by means of a grating-assisted directional coupler, so that the filtered optical signals are not only coupled to the other arm of the directional coupler, but also reflected so that they are coupled from the end of the same directional coupler as the input. In such designs, the outputs at the other end of the directional coupler each contain unwanted signals and each may be coupled to a separate photodetector, i.e., either the repeated monitoring segment 745 or the inverted monitoring segment 735, or a single large photodetector coupled to both. The position of the detection segment 750 is also adjusted if implemented in the first grating auxiliary coupler 740.

It is obvious that in the embodiments shown in the foregoing, the wavelength filtering element, the grating assisted directional coupler and the MMI represent only two of the possible embodiments of wavelength filtering elements possible in the PIC. Alternatively, the wavelength filtering may include other structures including, but not limited to, Mach-Zehnder interferometers (MZIs), echelle gratings, directional couplers, and arrayed waveguide gratings (AGWs). Furthermore, it will be apparent to those skilled in the art that while the previously illustrated embodiments employ transmissive waveguide filter elements, such as MMI 530 and grating assisted directional coupler 670, alternative design options exist, including reflective filter elements that can be used with equivalent arrangements of detector elements and the like.

Alternatively, different structures may be implemented for the front PBF 320 and the back PBF 350 in a fully monolithic waveguide solution, or a monolithic waveguide solution of one of these PBFs may be used in conjunction with a TFF solution of the other. Alternatively, both PBFs may be implemented using a single TFF or dual TFFs. Specific implementations are determined, for example, by including but not limited to the following factors: the standards with which the OPAD operates or the wavelength filtering requirements of the system, performance limitations of other PIC functions in the PIC of which the OPAD forms a part, cost, footprint, performance, etc. are expected.

In addition, alternative embodiments of the OPAD are possible without departing from the scope of the invention, including, for example, providing multiple detector elements coupled from a single amplification section of wavelength division multiplexed PONs, local area networks, metropolitan area networks, and long range applications, and providing wavelength filtering from a cascade of two or more elements.

The above-described embodiments of the present invention are intended to be examples only. Alterations, modifications and variations may be effected to the particular embodiments by those of skill in the art without departing from the scope of the invention, which is defined solely by the claims appended hereto.

Claims

1. A photonic component comprising:

b) an optical input port for receiving optical signals in the first wavelength range;

c) a first filter comprising at least a first output port and a second output port and characterized by at least a first pass-band width, the filter being optically coupled to an optical input port for receiving optical signals in the first wavelength range and for providing a first predetermined portion of the received optical signals to the first output port, the first predetermined portion of the received optical signals being determined at least in accordance with the first pass-band width;

d) an optical amplifier including at least a gain section formed in one of the plurality of wavelength-specific waveguides, a first contact for forward-biasing the optical amplifier, and a third output port, the optical amplifier optically coupled to the first output port for receiving the first predetermined portion of the received optical signal and providing an amplified filtered optical signal to the third output port;

f) a first photodetector optically including at least a second contact for reverse biasing the first photodetector, the first photodetector coupled to the fourth output port of the second filter for receiving a first predetermined portion of the amplified filtered optical signal;

g) a second photodetector optically coupled to a fifth output port of the second filter for receiving a second predetermined portion of the amplified filtered optical signal; and

h) a third photodetector optically coupled to a second output port of the first filter for receiving a predetermined portion of the optical signal propagating from the optical amplifier to the first filter, the predetermined portion of the optical signal determined based at least on the first pass-band width; wherein,

2. The photonic component of claim 1, wherein:

at least one of the first photodetector, the second photodetector, the third photodetector, and the optical amplifier includes a vertical element for coupling optical signals in a predetermined second wavelength range from one of a plurality of wavelength-designated waveguides of a common designated waveguide to the one of the plurality of wavelength-designated waveguides, the vertical element including at least one lateral taper formed by at least one semiconductor etching process in each of the common designated waveguide, the one of the plurality of wavelength-designated waveguides, and any intermediate waveguide of the plurality of wavelength-designated waveguides between the common designated waveguide and the one of the plurality of wavelength-designated waveguides.

3. The photonic component of claim 1, wherein,

at least one of the first and second filters comprises at least one of a thin film filter and a waveguide filter implemented in the epitaxial semiconductor structure.

4. The photonic component of claim 3, wherein,

when the at least one is a thin film filter, it is at least one of: abutting an end face of the epitaxial semiconductor structure, depositing on the end face of the epitaxial semiconductor structure, and disposing in a feature formed in a surface of the epitaxial semiconductor structure.

5. The photonic component of claim 3, wherein,

when said at least one is a waveguide filter, it comprises at least a first element selected from the group consisting of a multimode interference filter, a directional coupler, a Mach-Zehnder interferometer, an arrayed waveguide grating, an echelle grating, a bragg grating and a ring resonator.

6. The photonic component of claim 3, wherein,

when the at least one is a waveguide filter, the first predetermined portion of the waveguide filter is implemented in one of the common designated waveguide and another one of the plurality of wavelength designated waveguides, the one being adjacent to the one of the plurality of wavelength designated waveguides.

7. A photonic component comprising:

a) an epitaxial semiconductor structure grown in a III-V semiconductor material system grown in a single growth step when the substrate includes a common designated waveguide for supporting propagation of optical signals in a predetermined first wavelength range and at least one of a plurality of wavelength designated waveguides vertically arranged in order of increasing wavelength bandgap, wherein each of the plurality of wavelength designated waveguides supports a predetermined second wavelength range, each of the predetermined second wavelength ranges being in the predetermined first wavelength range;

c) an optical amplifier including at least a gain section formed in one of the plurality of wavelength-specific waveguides, a first contact for forward-biasing the optical amplifier, and a first output port, the optical amplifier optically coupled to an optical input port for receiving the optical signal and providing an amplified optical signal to the first output port;

d) a first filter comprising at least a second output port and characterized by at least a first pass-band width, the filter being optically coupled to the first output port of the optical amplifier and for providing a first predetermined portion of the amplified optical signal to the second output port, the first predetermined portion of the amplified optical signal being determined based at least on the first pass-band width;

8. The photonic component of claim 7, wherein,

at least one of the optical amplifier, the first filter, and the first photodetector further comprises a vertical element for coupling optical signals in the predetermined second wavelength range from and to at least one of the commonly-designated waveguides and to and from at least one of the plurality of wavelength-designated waveguides between the at least one of the plurality of wavelength-designated waveguides, the vertical element comprising at least one lateral taper formed in each of the commonly-designated waveguides, one of the plurality of wavelength-designated waveguides, and any intermediate waveguide of the plurality of wavelength-designated waveguides between the commonly-designated waveguide and the one of the plurality of wavelength-designated waveguides by at least one semiconductor etching process.

9. The photonic component of claim 7, further comprising:

f) a second photodetector optically connected to the first filter and configured to receive a second predetermined portion of the amplified optical signal, the second predetermined portion of the amplified optical signal determined based at least on the first pass-band width.

10. The photonic component of claim 7, further comprising:

f) a second filter disposed between the input port and the optical amplifier and characterized by at least a second passband width, the filter for providing one of a third predetermined portion of the received optical signal to the optical amplifier and a first predetermined portion of the noise generated by the optical discharger to the input port, at least one of the third predetermined portion of at least one of the received optical signals and the first predetermined portion of the noise generated by the optical discharger being determined at least in accordance with the second passband width.

11. The photonic component of claim 9, further comprising:

g) a third photodetector optically connected to the second filter and configured to receive a second predetermined portion of the noise generated by the optical amplifier, the second predetermined portion of the noise generated by the optical amplifier determined based at least on the second passband width.

12. The photonic component of claim 7, wherein,

the first filter includes at least one of a thin film filter and a waveguide filter implemented in the epitaxial semiconductor structure.

13. The photonic component of claim 10, wherein,

the second filter includes at least one of a thin film filter and a waveguide filter implemented in the epitaxial semiconductor structure.

14. The photonic component of claim 12, wherein,

when the at least one is a thin film filter, it is at least one of: abutting an end face of the epitaxial semiconductor structure, depositing on the end face of the epitaxial semiconductor structure, and disposing in a feature in a surface of the epitaxial semiconductor structure.

15. The photonic component of claim 13, wherein,

16. The photonic component of claim 12, wherein,

when the at least one is a waveguide filter, it comprises at least one of: a first predetermined portion of said waveguide filter implemented in one of said common designated waveguides and another of said plurality of wavelength designated waveguides, said one adjacent to one of said plurality of wavelength designated waveguides, and at least one first element selected from the group consisting of a multimode interference filter, a directional coupler, a Mach-Zehnder interferometer, an arrayed waveguide grating, an echelle grating, a bragg grating, and a ring resonator.

17. The photonic component of claim 13, wherein,

when the at least one is a waveguide filter, it comprises at least one of: a first predetermined portion of said waveguide filter implemented in one of said common designated waveguide and another of said plurality of wavelength designated waveguides, said one adjacent to one of said plurality of wavelength designated waveguides, and at least one first element selected from the group consisting of a multimode interference filter, a directional coupler, a Mach-Zehnder interferometer, an arrayed waveguide grating, an echelle grating, a bragg grating, and a ring resonator.

18. The photonic component of claim 7, further comprising:

f) at least one optical element of a plurality of optical elements disposed between the optical amplifier and the first filter and at least one of the first filter and the first photodetector, the optical element including at least one of a waveguide filter element, a predetermined portion of a multimode interference waveguide element, a predetermined portion of a directional coupler, a predetermined portion of a Mach-Zehnder interferometer, a parabolic waveguide element, a planar waveguide, and a lens.

19. The photonic component of claim 11, further comprising:

h) at least one optical element of a plurality of optical elements disposed between at least one of the optical amplifier and the second filter, the input port and the second filter, and the second filter and a third photodetector, the optical element including at least one of a waveguide filter element, a predetermined portion of a multimode interference waveguide element, a predetermined portion of a directional coupler, a predetermined portion of a Mach-Zehnder interferometer, a parabolic waveguide element, a planar waveguide, and a lens.