CN117470366A - Low noise optical assembly - Google Patents

Abstract

In some embodiments, the optical assembly comprises: an optical power monitor for receiving a portion of the light beam and measuring the portion of the light beam; an optical tap for tapping the light beam and providing a portion of the light beam; and an optical element allowing the portion of the light beam from the optical tap to propagate toward the optical power monitor, wherein the optical element includes an absorptive material to absorb light other than the portion of the light beam propagating toward the optical power monitor.

Description

Low noise optical assembly

Technical Field

The present disclosure relates generally to optical assemblies and optical assemblies for implementing low noise optical power monitoring.

Background

An Optical Power Monitor (OPM) may measure the power of an optical signal or beam. For example, an optical power monitor may tap a portion of a light beam in an optical communication system and measure the tapped portion of the light beam. The optical power monitor may provide feedback information regarding the power of the optical beam to enable control of the optical communication system. For example, based on the feedback information, the controller may change the current level, the output optical power level, the attenuation level, the amplification level, the laser wavelength, or an adjustable filter, etc.

Disclosure of Invention

In some embodiments, the optical assembly comprises: an optical power monitor for receiving a portion of the light beam and measuring the portion of the light beam; an optical tap for tapping the light beam and providing a portion of the light beam; and an optical element allowing the portion of the light beam from the optical tap to propagate toward the optical power monitor, wherein the optical element includes an absorptive material to absorb light other than the portion of the light beam propagating toward the optical power monitor.

In some embodiments, the optical assembly comprises: at least one optical power monitor for receiving a portion of the light beam and measuring said portion of the light beam; an optical tap for tapping the light beam and providing a portion of the light beam; and an optical element for directing a portion of the light beam from the optical tap to the at least one optical power monitor, wherein the optical tap, the optical element, and the optical power monitor are separated by free space, and wherein the optical element comprises an absorptive material that absorbs light other than the portion of the light beam and a reflective material that reflects the portion of the light beam toward the optical power monitor.

In some embodiments, the optical system includes: an optical emitter for emitting a light beam; an optical power monitor that receives a portion of the light beam; and an optical element for directing the portion of the light beam to the optical power monitor, wherein the optical element comprises an absorptive material that absorbs light other than the portion of the light beam and a reflector that reflects the portion of the light beam to the optical power monitor.

Brief Description of Drawings

FIG. 1 is a diagram of an exemplary embodiment of a low noise optical assembly.

Fig. 2A-2B are diagrams of exemplary embodiments of low noise optical components.

Fig. 3A-3B are diagrams of exemplary embodiments of low noise optical components.

Detailed Description

The following detailed description of exemplary embodiments refers to the accompanying drawings. The same reference numbers in different drawings may identify the same or similar elements.

The optical power monitor may be implemented in free-space optics. For example, an optical tap that taps a portion of the beam for monitoring may be aligned with the optical power monitor and separated by free space. In other words, for at least a portion of the optical path between the optical tap and the optical power monitor, the tapped portion of the light beam may pass through a free space medium (e.g., air). The optical path may also include other free-space optical elements, such as lenses, filters, or mirrors, to direct a portion of the tapped-off light beam to the optical power monitor.

However, when implementing optical power monitors and optical tap systems using free-space optics, scattered light, reflected light, or other spurious light (typically "unwanted light") may also be incident on the optical power monitor. In other words, unwanted light may be combined with the tapped portion of the optical signal and may not be needed at the optical power monitor. Unwanted light may be a form of noise that reduces the accuracy of the measurement of the optical power monitor. For example, when the optical power monitor determines the optical power of the tapped portion of the light beam, the optical power may include contributions from unwanted light, resulting in a measured optical power that is higher than the optical power actually present in the tapped portion of the light beam. Furthermore, unwanted light may change over time, resulting in a change in measured optical power over time when the tap portion is constant over time.

A housing may be provided around the entire free space optical assembly (e.g., optical tap and optical power monitor) to reduce the presence of unwanted light. Such a housing may include an input opening and an output opening to receive and output the light beam to be tapped. However, it may be difficult and/or inaccurate to use an opening that is approximately equal in size to the light beam (e.g., to minimize unwanted light entering through the opening) and to align the opening with the light beam. Thus, the housing may interfere with the light beam, negatively affecting the performance of an optical system (e.g., an optical communication system, an optical measurement system, a Mach-Zehnder interferometer, or a Michelson interferometer, etc.) using the light beam. It is therefore desirable to reduce the impact of unwanted light on optical power measurements without enclosing the free space optical tap and optical power monitor assembly within a housing.

Some embodiments described herein enable optical power monitoring in free-space optics while reducing noise and without enclosing the free-space optics in a housing. For example, an optical element may be provided that is configured to block unwanted light directed to the optical power monitor. In this case, the optical element may be a reflector with an absorptive housing. The reflector may direct the tapped portion of the light beam toward the optical power monitor and the absorptive housing may absorb unwanted light (rather than the unwanted light being incident on the optical power monitor). In this way, the optical power monitor may perform measurements of the tapped portion of the light beam with reduced noise (e.g., from reduced amounts of unwanted incident light) relative to other optical component configurations.

Fig. 1 is a diagram of an exemplary embodiment 100 of a low noise optical component. As shown in fig. 1, exemplary embodiment 100 includes an optical tap 110, an optical element 120, and an optical power monitor 130. As shown in fig. 1, optical tap 110, optical element 120, and optical power monitor 130 are implemented as free space optics.

Optical tap 110 may include components configured to tap a portion of the light beam. For example, the optical path 150 may direct a light beam from a light source to the optical tap 110, the optical tap 110 may tap off a portion of the light beam, and direct the light beam from the optical tap 110 to an optical destination. In some embodiments, optical tap 110 may be a beam splitter that splits an incident beam into two parts. For example, optical tap 110 may be a cube beam splitter comprising two triangular glass prisms. Additionally or alternatively, the optical tap 110 may be a waveguide tap that splits a portion of a light beam transmitted via a waveguide into different waveguides or optical paths.

The optical tap 110 may be an optical device that splits a light beam into a first portion and a second portion. The first portion may remain along optical path 150 and the second portion may be directed to optical element 120 and optical power monitor 130 via optical paths 160 and 170, respectively. The relative amounts of light directed into each optical path (e.g., a first percentage of light in the first portion and a second percentage of light in the second portion) may be controlled by the composition of the optical tap 110. For example, optical tap 110 may be configured for use with 50:50 separate the incident light beam (e.g., 50% of the light beam is directed to light path 150, 50% of the light beam is directed to light paths 160 and 170). Other separations are also possible, such as a 90:10 separation (e.g., 90% of the light beam is directed to optical path 150, 10% of the light beam is directed to optical paths 160 and 170), a 95:5 separation, a 99:1 separation, or any other separation ratio.

In some embodiments, the optical assembly or optical system may omit the optical tap 110. For example, the optical power monitor 130 may be configured to absorb only a first portion of the light beam and reflect or pass a second portion of the light beam. In this case, the optical power monitor 130 may be used as an optical tap for such an optical component or optical system. Similarly, the optical element 120 may be configured to direct a first portion of the light beam and reflect or pass a second portion of the light beam in one direction. In this case, the optical element 120 may be used as an optical tap of such an optical assembly or optical system.

The optical element 120 may be an optical element configured to block unwanted light from being incident on the optical power monitor 130. For example, the optical element 120 may be an absorbing optical component having a reflector 122 (e.g., a mirror). In this case, reflector 122 reflects the tapped portion of the light beam from optical path 160 and optical tap 110 and directs the tapped portion of the light beam along optical path 170 to optical power monitor 130. In some embodiments, the optical element 120 may omit the reflector 122, as shown in fig. 1. For example, the optical element 120 may be configured to allow the tapped portion of the light beam from the optical tap 110 to propagate (e.g., without reflection) toward the optical power monitor 130.

In some embodiments, the optical element 120 may include a particular material as an absorptive material or a reflective material. Furthermore, the optical element 120 may comprise a metal layer reflector or a dielectric mirror stack reflector for the reflector 122. Additionally or alternatively, the absorptive material of the optical element 120 may be formed of a filter glass material. For example, a filter glass that filters light in the wavelength range of optical power monitor 130 may be used to ensure that light in the wavelength range of optical power monitor 130 is blocked from being incident on optical power monitor 130.

In some implementations, the optical element 120 may have one or more structures to block unwanted light from being incident on the optical power monitor 130 (e.g., without impeding the optical path 160 and the tapped portion of the beam). For example, the optical element 120 may have a set of wings 124 or other surfaces (e.g., extending in a direction different from the reflector 122 and the back of the optical element 120, such as extending in an orthogonal direction in other examples) that provide openings for the optical path 160 incident on the reflector of the optical element 120 and the optical path 170 incident on the optical power monitor 130, but that are absorptive to block unwanted light from being incident on the optical power monitor 130, as described in more detail herein.

In one example, as shown, the optical element 120 may form a cube shape and have a first absorption side 151 (e.g., corresponding to the wing 124) and a second absorption side 152 (e.g., corresponding to the wing 124) surrounding the optical power monitor 130, and a third absorption side 154 and a fourth absorption side 156 associated with a reflector surface disposed on the absorption structure. Further, the optical element 120 may have a fifth side (e.g., a front side) that is open to allow the tapped portion of the light beam to be directed to the reflector 122 and the optical power monitor 130. In this case, the sixth side (e.g., bottom) may be formed of a substrate (not shown) that absorbs light to prevent light from being incident on the optical power monitor 130. In another example without reflector 122, optical power monitor 130 may be disposed against third absorption side 154 (e.g., at least partially disposed within optical element 120 such that the absorptive material of optical element 120 at least partially surrounds optical power monitor 130, but allows a portion of the light beam to propagate toward optical power monitor 130) to be directly aligned with optical path 160 (e.g., without reflection).

The optical power monitor 130 may be a component configured to measure a portion of a light beam directed at the optical power monitor 130. For example, the optical power monitor 130 may be a photodiode. In some implementations, the optical power monitor 130 may be configured to measure optical power associated with a particular wavelength range. For example, the optical power monitor 130 may be configured to monitor and measure a portion of a light beam in the range of 800 nanometers (nm) to 1700nm or sub-ranges thereof. In this case, the absorptive material of the optical element 120 may be configured to be absorptive within the range that the optical power monitor 130 is configured to monitor and measure, thereby avoiding unwanted light from affecting the measurement of the optical power monitor 130. Similarly, the reflector of the optical element 120 may be configured to be reflective over a range of wavelengths that the optical power monitor 130 is configured to monitor and measure. In some embodiments, the reflector may be transmissive or absorptive in another wavelength range to ensure that light incident on the optical power monitor 130 is within a selected wavelength range for a particular measurement, rather than, for example, any wavelength range in which the optical power monitor 130 is configured.

Although optical tap 110, optical element 120, and optical power monitor 130 are depicted as being implemented in free-space optics, it is contemplated that one or more components of the embodiments described herein may be implemented in non-free-space optics, such as a first portion of optical path 160 between optical tap 110 and optical element 120 being implemented in a waveguide, and a second portion of optical path 160 being implemented in free-space optics. Alternatively, additional components may be present in one or more embodiments described herein, which may or may not be implemented in free space optics. For example, two or more components (e.g., optical tap 110, optical element 120, optical power monitor 130, or other components) may be implemented as free-space optics, and/or two or more components (e.g., optical tap 110, optical element 120, optical power monitor 130, or other components) may be implemented as non-free-space optics (e.g., integrated into a solid, packaged, or monolithic assembly of one or more parts).

As mentioned above, fig. 1 is provided as an example. Other examples may differ from that described with respect to fig. 1. The number and arrangement of devices shown in fig. 1 are provided as examples. In practice, there may be more devices, fewer devices, different devices, or different arrangements of devices than shown in FIG. 1. For example, the optical system may include an optical transmitter (e.g., an edge-emitting laser, a Vertical Cavity Surface Emitting Laser (VCSEL), or a Light Emitting Diode (LED), etc.), a controller (e.g., controlling the optical transmitter based on measurements performed by the optical power monitor 130), or an optical receiver (e.g., using measurements performed by the optical power monitor 130 to effect reception, decoding, or noise removal, etc.). Furthermore, two or more devices shown in fig. 1 may be implemented within a single device, or a single device shown in fig. 1 may be implemented as multiple distributed devices. Additionally or alternatively, a group of devices (e.g., one or more devices) shown in fig. 1 may perform one or more functions described as being performed by another group of devices shown in fig. 1.

Fig. 2A-2B are diagrams of an exemplary embodiment 200 of a low noise optical assembly. As shown in fig. 2A and side view 210, in a first configuration (e.g., a non-low noise optical component), optical power monitor 130 is disposed on substrate 212. An optical element 214 that does not include a side barrier (e.g., a structure that at least partially surrounds the optical power monitor 130 to block unwanted light) or a back barrier (e.g., an absorptive material that blocks the optical path 216 as shown) is disposed in the optical path 160 to reflect light toward the optical path 170 and the optical power monitor 130.

In contrast, as shown in cross-section 220, in a second configuration, optical power monitor 130 is disposed on substrate 212 and aligned with optical element 222, which optical element 222 may correspond to optical element 120. In this case, the optical element 222 includes a back stop. For example, the optical element 222 may be of an absorptive material (e.g., absorb unwanted light) and the reflector is configured to reflect a portion of the light beam from the optical path 160 to the optical path 170 and toward the optical power monitor 130. As shown, the optical path 216 is blocked based on having an absorptive material, thereby preventing unwanted light from passing through the optical element 222 and being incident on the optical power monitor 130.

In a third configuration, as shown in fig. 2B and side view 230, another optical element 232 may have a back stop to reduce unwanted light incident on optical power monitor 130. In this case, the optical element 232 may be at least partially absorptive to achieve a back stop. In a fourth configuration, as shown in cross-section 240, the other optical element 242 may also have side and back stops to reduce unwanted light incident on the optical power monitor 130. With respect to the third configuration and the fourth configuration, as shown, different shapes of optical elements are possible, such as an open cube-shaped optical element (e.g., optical element 232) or an open non-cube-shaped optical element (e.g., optical element 242).

As described above, fig. 2A to 2B are provided as examples. Other examples may differ from those described with respect to fig. 2A-2B.

Fig. 3A-3B are diagrams of an exemplary embodiment 300 of a low noise optical assembly. As shown in fig. 3A, an optical element 310, which may correspond to optical element 120, may have a reflector surface 320, a set of side blocking structures 330, and a back blocking structure 340. The side blocking structure 330 and the back blocking structure 340 may partially surround or enclose an optical power monitor (not shown) to block unwanted light from being incident on the optical power monitor. The side blocking structure 330 and the back blocking structure 340 may leave an area for transmitting the tapped portion of the light beam from the optical tap (not shown) along the optical path 160 and along the optical path 170 to the optical power monitor.

In some embodiments, reflector surface 320 may form a plurality of reflector facets or reflector portions. For example, the reflector surface 320 may have a single continuous face that is split into a first portion that reflects a first light beam (e.g., to a first optical power monitor) and a second portion that reflects a second light beam (e.g., to a second optical power monitor). In this case, the first and second portions of the reflector surface 320 may be arranged side-by-side, or otherwise. Additionally or alternatively, the reflector surface 320 may be divided into a plurality of discrete facets. For example, a first side of the reflector surface 320 may have a first characteristic, such as reflecting the light beam in a first direction or at a first wavelength, and a second side of the reflector surface 320 may have a second characteristic, such as reflecting the light beam in a second direction or at a second wavelength.

In some embodiments, the reflector surface 320 may have a particular shape. For example, the reflector surface 320 may have a planar surface, a curved surface, or a surface having multiple facets. Additionally or alternatively, the reflector surface 320 may perform an optical function, such as by focusing light. For example, the reflector surface 320 may form a lens or a set of lenses to focus the light beam onto the optical power monitor. Additionally or alternatively, the reflector surface 320 may form a grating or filter to filter or otherwise modify the light beam incident thereon. In some embodiments, other optical elements may be formed on the reflector surface 320 or in the optical path, as described herein, such as filters, lenses, gratings, or the like.

Fig. 3B shows a plan view of an optical element 310, the optical element 310 having a plurality of facets for reflecting light along a plurality of light paths. Although components such as the optical element 310, the substrate 360, and the optical power monitor 130 are shown as separate in plan view, it is contemplated that these components may be provided in an assembly (e.g., the optical element 310 is attached to the substrate 360 and at least partially surrounds the optical power monitor 130 and/or the etalon 350).

As shown, the optical element 310 includes a first reflector 320-1 that reflects a first portion of the tap beam from the optical path 160 toward the first optical power monitor 130-1 via a first optical path 170-1. Additionally or alternatively, the optical element 310 includes a second reflector 320-2 that reflects a second portion of the tapped beam from the optical path 160 toward the second optical power monitor 130-2 via the second optical path 170-2. Although some embodiments are described in terms of one or two optical power monitors and one or more optical paths (e.g., one or two portions that reflect off of an optical element), it is contemplated that different numbers of optical power monitors, optical paths, and optical element portions or facets are possible, such as three or more optical power monitors. Other beam splitting configurations are also contemplated, such as beam 170-1 being split to form beam 170-2, rather than beam 170-2 being formed from the second split of beam 160.

As shown, in some embodiments, the first optical power monitor 130-1 and the second optical power monitor 130-2 may be disposed on a common substrate 360. Additionally or alternatively, an etalon 350 may be disposed in one of the light paths 170, as shown. The etalon 350 may be a Fabry-Perot (Fabry-Perot) etalon. Although a fabry-perot etalon is described, it is contemplated that the exemplary embodiment 300 may be used with or in conjunction with a filter, mach-Zehnder interferometer, michelson interferometer, or the like.

An etalon 350 may be disposed in the optical path 170-2. In this case, a controller (not shown) may compare a first measurement of optical power monitor 130-1 (e.g., no etalon is located in optical path 170-1) with a second measurement of optical power monitor 130-2 (e.g., etalon 350 is located in optical path 170-2) to perform wavelength locking. As shown, in some embodiments, the reflector surfaces may be arranged back and forth. For example, a first portion of the tap beam is reflected by the first reflector 320-1 and a second portion of the tap beam passes through the first reflector 320-1 to the second reflector 320-2 as shown. In another example, multiple reflector surfaces may be arranged side-by-side, rather than front-to-back. In this case, the reflector 320-1 and the reflector 320-2 may be disposed on the same side of the optical element 310 and may, for example, receive a first portion of the tap beam via the first optical path 160 and a second portion of the tap beam via the second optical path 160, respectively. It is contemplated that other shapes of optical elements may also reduce the amount of unwanted light incident on one or more optical power monitors, and that there may be other numbers of reflectors on a single optical element (or on multiple optical elements included in a common assembly or system).

As described above, fig. 3A to 3B are provided as examples. Other examples may differ from those described with respect to fig. 3A-3B.

The foregoing disclosure provides illustration and description, but is not intended to be exhaustive or to limit the embodiments to the precise form disclosed. Modifications and variations are possible in light of the above disclosure or may be acquired from practice of the implementations. Furthermore, any of the embodiments described herein can be combined unless the foregoing disclosure explicitly provides a reason that one or more embodiments may not be combined.

As used herein, satisfying a threshold may refer to a value greater than a threshold, greater than or equal to a threshold, less than or equal to a threshold, not equal to a threshold, etc., depending on the context.

Even though particular combinations of features are recited in the claims and/or disclosed in the specification, these combinations are not intended to limit the disclosure of the various embodiments. Indeed, many of these features may be combined in ways not specifically set forth in the claims and/or disclosed in the specification. Although each of the dependent claims listed below may depend directly on only one claim, the disclosure of various embodiments includes a combination of each dependent claim with each other claim in the claim set. As used herein, a phrase referring to "at least one" of a series of items refers to any combination of those items, including individual members. For example, "at least one of a, b, or c" is intended to encompass a, b, c, a-b, a-c, b-c, and a-b-c, as well as any combination of a plurality of like items.

No element, act, or instruction used herein should be construed as critical or essential unless explicitly described as such. Furthermore, as used herein, the article "a" is intended to include one or more items and may be used interchangeably with "one or more". Furthermore, as used herein, the article "the" is intended to include, and be used interchangeably with, one or more items associated with the article "the. Furthermore, as used herein, the term "set" is intended to include one or more items (e.g., related items, unrelated items, or a combination of related and unrelated items), and can be used interchangeably with "one or more". If only one item is referred to, the phrase "only one" or similar language is used. Furthermore, as used herein, the terms "having," "having," and the like are intended to be open ended terms. Furthermore, the phrase "based on" is intended to mean "based, at least in part, on" unless explicitly stated otherwise. Furthermore, as used herein, the term "or" is inclusive in a series of uses and may be used interchangeably with "and/or" unless otherwise specifically indicated (e.g., if used in conjunction with "either" or "only one"). Further, spatially relative terms, such as "lower," "upper," and the like, may be used herein for ease of description to describe one element or feature's relationship to another element or feature's illustrated in the figures. Spatially relative terms are intended to encompass different orientations of the device, apparatus and/or element in use or operation in addition to the orientation depicted in the figures. The device may be otherwise oriented (rotated 90 degrees or other directions) and the spatially relative descriptors used herein interpreted accordingly.

Cross Reference to Related Applications

This patent application claims priority from U.S. provisional patent application 63/369,866 entitled "Low noise optical Power monitor," filed on 7/29, 2022. The disclosure of this prior application is considered to be part of the present patent application and is incorporated by reference.

Claims (20)

1. An optical assembly, comprising:

an optical power monitor that receives a portion of the light beam and measures the portion of the light beam;

an optical tap that taps the light beam and provides the portion of the light beam; and

an optical element allowing the portion of the light beam from the optical tap to propagate toward the optical power monitor,

wherein the optical element comprises an absorptive material to absorb light other than the portion of the light beam propagating towards the optical power monitor.

2. The optical assembly of claim 1, wherein the optical element comprises a reflective material for reflecting the portion of the light beam toward the optical power monitor.

3. The optical assembly of claim 1, wherein the optical power monitor is disposed at least partially within the optical element and is located in a non-reflective path of the portion of the light beam.

4. The optical assembly of claim 1, wherein two or more of the optical tap, optical element, and optical power monitor are separated by free space.

5. The optical assembly of claim 1, wherein two or more of the optical tap, optical element, and optical power monitor are integrated into a solid assembly of one or more components.

6. The optical assembly of claim 1, wherein the optical tap is a beam splitter or waveguide tap.

7. The optical assembly of claim 1, wherein the absorptive material absorbs at least light in a wavelength range that the optical power monitor is configured to monitor.

8. The optical assembly of claim 7, wherein the optical power monitor is configured to monitor a wavelength range from 800 nanometers (nm) to 1700 nanometers (nm).

9. An optical assembly, comprising:

at least one optical power monitor for receiving a portion of the light beam and measuring said portion of the light beam;

an optical tap for tapping the light beam and providing said portion of the light beam; and

an optical element for directing the portion of the light beam from the optical tap to at least one optical power monitor,

wherein the optical tap, the optical element and the optical power monitor are separated by a free space, and

wherein the optical element comprises an absorptive material that absorbs light other than the portion of the light beam and a reflective material that reflects the portion of the light beam toward the optical power monitor.

10. The optical assembly of claim 9, wherein the absorptive material includes a first portion that absorbs a first light other than the portion of the light beam and a second portion that absorbs a second light other than the portion of the light beam,

wherein the first portion extends in a first direction relative to the reflective material and the second portion extends in a second direction different from the first direction relative to the reflective material.

11. The optical assembly of claim 9, wherein the absorptive material at least partially surrounds the optical power monitor without blocking the portion of the light beam.

12. The optical assembly of claim 9, wherein the at least one optical power monitor comprises a first optical power monitor and a second optical power monitor, and

wherein the reflective material includes a first reflector face portion aligned with the first optical power monitor and a second reflector face portion aligned with the second optical power monitor.

13. The optical assembly of claim 12, wherein the first and second reflector face portions are disposed in a side-by-side or front-to-back arrangement.

14. The optical assembly of claim 9, further comprising:

one or more etalons disposed in one or more optical paths of one or more optical power monitors of the at least one optical power monitor.

15. An optical system, comprising:

an optical emitter for emitting a light beam;

an optical power monitor that receives a portion of the light beam; and

an optical element directing the portion of the light beam to an optical power monitor,

wherein the optical element comprises an absorptive material that absorbs light other than the portion of the light beam and a reflector that reflects the portion of the light beam toward the optical power monitor.

16. The optical system of claim 15, wherein the reflector is associated with at least one of a planar surface, a curved surface, or a surface having a plurality of facets.

17. The optical system of claim 15, wherein the reflector is a metal layer reflector or a dielectric mirror stack reflector.

18. The optical system of claim 15, wherein the absorptive material is a filter glass material.

19. The optical system of claim 15, wherein the reflector is configured to focus the portion of the light beam onto the optical power monitor.

20. The optical system of claim 15, further comprising:

a controller configured to control the optical emitter based on the measurement of the portion of the light beam by the optical power monitor.