Optics for multi-pass optical channel monitor

Abstract

The optical device can include a dispersive element. The optical device can include a reflective optical device to reflect the light beam with a fixed offset from a dispersion direction of the dispersive element and a negative offset from the dispersion direction of the dispersive element. The reflective optical device can be aligned with the dispersive element to offset the light beam relative to the dispersive element and pass the light beam through the dispersive element in multiple passes, each offsetting the light beam.

Description

[0001] Cross-reference to related applications

[0002] This patent application claims priority to U.S. Provisional Patent Application No. 63 / 131,181, filed December 28, 2020, entitled “MULTI-PASS HIGH RESOLUTION SPECTROMETER”, the disclosure of which is considered part of this patent application and is incorporated herein by reference. Technical Field

[0003] The present invention generally relates to a reflective optical device and an optical apparatus comprising a reflective optical device aligned with a dispersive element and a microelectromechanical system (MEMS) element such that a light beam passes through the dispersive element and the MEMS element in multiple passes, the light beam having a fixed vertical offset applied in the dispersive direction of the dispersive element and a spectral reversal applied in each of the multiple passes. Background Technology

[0004] An optical channel monitor (OCM) is a device capable of measuring the optical power in a wavelength channel of an optical signal. An OCM can be connected to a point in an optical network to measure, for example, the power, frequency, and other characteristics of the optical channel at that point. In some cases, an OCM can scan multiple wavelength channels to measure the optical power in multiple channels (e.g., within a wavelength range). For example, an OCM can be used to monitor channels in wavelength division multiplexing (WDM) systems, where wavelength channels are multiplexed into a common carrier signal for transmission over an optical network (e.g., dense wavelength division multiplexing (DWDM) systems where wavelength channels are spaced at frequencies of 50 GHz, and other examples). Summary of the Invention

[0005] According to some embodiments, the optical device may include a dispersive element. The optical device may include reflective optics for reflecting a light beam having a fixed offset perpendicular to the dispersion direction of the dispersive element and a negative offset in the dispersion direction of the dispersive element. The reflective optics may be aligned with the dispersive element to deflect the light beam relative to the dispersive element and to allow the light beam to pass through the dispersive element multiple times, deflecting the light beam at each of the multiple passes.

[0006] According to some embodiments, a method may include: receiving a light beam at an input port of an optical channel monitor; guiding the light beam multiple times through a dispersive element of the optical channel monitor by a reflecting optics of the optical channel monitor, wherein each pass is deflected according to a fixed vertical offset of the reflecting optics; and determining the characteristics of the light beam by the optical channel monitor based on guiding the light beam multiple times through the dispersive element.

[0007] According to some embodiments, the reflective optics may include a plurality of prism surfaces. The plurality of prism surfaces may be angled relative to each other to produce a fixed vertical offset in at least one optical path passing through the reflective optics relative to at least another optical path passing through the reflective optics. The plurality of prism surfaces may be angled relative to each other to induce spectral inversion in at least one optical path. Attached Figure Description

[0008] Figure 1A-1C This is a schematic diagram of the example optical device described in this article.

[0009] Figure 2A and 2B This is a schematic diagram of the example optical device described in this article.

[0010] Figures 3A-3C This is a schematic diagram of the example optical path described in this article.

[0011] Figure 4 This is a flowchart of an example process related to guiding a light beam through the optical device described herein. Detailed Implementation

[0012] The following detailed description of the exemplary embodiments is taken with reference to the accompanying drawings. The same reference numerals in different drawings may identify the same or similar elements.

[0013] As mentioned above, an optical channel monitor (OCM), or spectrometer, can be used to measure the characteristics of a light beam. The spectral resolution of an OCM can be expressed as the frequency width ΔF, which has a spectral shape with a single measured frequency, for example, when measuring a laser. A narrower measured frequency corresponds to a higher spectral resolution. Spectral resolution can be defined as F / ΔF based on the measured frequency (F). A conventional OCM can be used to cover the C-band from approximately 191 terahertz (THz) to 196 THz, which can produce a desired spectral range of approximately 5000 gigahertz (GHz). Given a frequency width, for a conventional OCM of approximately 20 GHz, a conventional OCM can resolve approximately 250 different frequencies within the covered C-band.

[0014] Therefore, the tuning element, which can be a microelectromechanical system (MEMS) component, such as a MEMS mirror of an OCM, will have a size and tilt angle selected to resolve 250 different beam positions. To achieve this range for the tuning element, the product of the mirror size and the tilt angle must be greater than 250λ / 2, where λ is the wavelength of light in the C-band. For example, a mirror size of 1000 micrometers (μm) and a wavelength of 1.55 μm (approximately 193 THz at the center of the C-band) result in a tilt angle of at least 11 degrees (or + / - 5.5 degrees for a mirror that can tilt to both positive and negative angles). For OCMs covering larger bands, such as those covering the C-band (191 THz to 196 THz) and the L-band (184 THz to 191 THz), the tuning element may require a larger tilt angle and / or mirror size. Increasing the tilt angle and the size of the mirror can lead to manufacturing difficulties. Furthermore, as communication density increases, miniaturization may prevent the use of optical devices with relatively large mirrors or components to achieve increased tilt angles. Therefore, it may be desirable to achieve high spectral resolution with optical devices that have a small form factor.

[0015] Some embodiments described herein enable OCMs or spectrometers to have compact form factors and high spectral resolution. For example, the optical device may include a reflective element to reflect the beam through a diffractive element and a MEMS mirror in multiple passes, separating the beam by an offset each time. By reflecting the beam multiple times through the diffractive element and MEMS mirror, the optical device achieves increased spectral resolution without increasing the size of the reflective element and / or the achievable tilt angle of the reflective element. Similarly, a given spectral resolution can be achieved using a smaller reflective element and / or a reflective element with a reduced achievable tilt angle. Similarly, a given spectral resolution or frequency range for a given size can be increased by using multiple passes, as described herein. The optical device can reflect the beam with a fixed offset and spectral inversion perpendicular to the dispersion direction of the dispersive element, thereby enabling separation between the output and input light within the optical device. As a result, among other examples, the optical device can achieve increased spectral resolution or a reduced form factor.

[0016] Figure 1A-1C This is a schematic diagram of an example optical device 100. (As shown) Figure 1A As shown, the example optical device 100 includes a reflective optics 110, a lens 120, a diffraction grating 130, and a MEMS mirror 140.

[0017] The reflecting optics 110 may include one or more components to reflect a light beam through the diffraction grating 130 and the MEMS mirror 140. For example, the reflecting optics 110 may include a reflector array (e.g., a retroreflector array), a cube reflector or retroreflector, a prism (e.g., having a reflective surface), a retroreflection prism, a set of retroreflection prisms, a refractor (e.g., a prism having a refractive surface), a refractor array, or a mirror, etc. The reflecting optics 110 may receive the incident light beam on its first pass and reflect the incident light beam with a lateral offset and a reversal of the beam spectrum. In some embodiments, the lateral offset may be a fixed vertical offset. For example, the reflecting optics 110 may reflect the incident light beam multiple times, such that the reflecting optics offset the incident light beam by a fixed amount in a direction perpendicular to the dispersion direction of the diffraction grating 130. In this way, the output light (relative to the reflecting optics 110) can be separated from the input light (relative to the reflecting optics 110). In some implementations, spectral inversion can be a negative offset of the beam applied at each reflection of the reflective optics 110 (corresponding to each pass through the diffraction grating 130 and the MEMS mirror 140). In this way, light on different paths is prevented from being refolded into a single point as it passes through the diffraction grating 130 (e.g., this might occur in a wavelength-selective switch where no spectral inversion occurs between beams on different paths passing through the diffraction grating). Furthermore, in this way, the reflective optics 110 doubles the dispersion at each pass, thereby achieving similar dispersion levels by eliminating the need for multiple beam expander optics, thus increasing spectral resolution and / or enabling miniaturization for a given spectral resolution level.

[0018] Lens 120 may be an optical element configured to align reflective optics 110 with diffraction grating 130 and MEMS mirror 140. For example, lens 120 may be a collimating lens, etc. In some embodiments, reflective optics 110 and lens 120 may form a single unit that is co-aligned with diffraction grating 130 and MEMS mirror 140. In some embodiments, optical device 100 may include another type of optical element to align reflective optics 110 with diffraction grating 130 and MEMS mirror 140. For example, optical device 100 may include a mirror to reflect a light beam between reflective optics 110 and diffraction grating 130 (instead of lens 120). Additionally or alternatively, optical device 100 may include a combination of optical elements, such as lens 120 and one or more additional optical elements, to align reflective optics 110 with diffraction grating 130.

[0019] Diffraction grating 130 is an example of a dispersive element included in optical device 100. For example, diffraction grating 130 can separate and diffract a light beam into multiple component optical beams, enabling the measurement of one or more optical properties of each component beam. In some embodiments, optical device 100 may include different types of dispersive elements. For example, optical device 100 may include prisms or mirrors that act as dispersive elements aligned with reflective optics 110 and MEMS mirror 140 to enable beam measurement. Based on the alignment with reflective optics 110 to receive multiple passes of the beam, diffraction grating 130 can achieve a smaller size than other diffraction gratings at a specific spectral resolution. The spectral resolution of a diffraction grating can be based on the number of grating lines N and the diffraction order m, such that F / ΔF = πmN. As a result, a reduction in beam size, for example, by a factor of 4, will result in a decrease in spectral resolution by a factor of 4 in this example. However, by using the reflective optics 110 to make the beam pass through the diffraction grating 4 times in 4 passes, the diffraction grating 130 can achieve the same spectral resolution as another diffraction optics, which is 4 times the size of the diffraction grating 130.

[0020] MEMS mirror 140 is an example of a tuning element in optical device 100. For example, MEMS mirror 140 may include a set of tilting mirrors to reflect component beams (e.g., different channels of the beam) at different angles, thereby enabling measurement of the component beams. In some embodiments, optical device 100 may include different types of tuning elements to achieve the reflection of component beams. In some embodiments, MEMS mirror 140 may be aligned with diffraction grating 130 without any beam expander / compressor optics (or with reduced beam expander optics relative to other OCMs). For example, based on reducing the size of the beam passing through diffraction grating 130 (and as described above, compensated by having the beam pass through multiple times to maintain spectral resolution), the beam can directly illuminate MEMS mirror 140 without the intervention of beam expander / compressor optics. In some embodiments, diffraction grating 130 may be directly disposed on the surface of MEMS mirror 140. For example, diffraction grating 130 may be fabricated on the surface of MEMS mirror 140, forming a single integrated component. In this way, the use of multiple pass-through and reflection optics 110 reduces the number of optics in optical device 100, thereby reducing size, cost, and complexity, and improving durability relative to other optical devices. In some cases, the number of pass-throughs of optics 100 can be based on the size of MEMS mirror 140. For example, optical device 100 can be configured with a specific number of pass-throughs to ensure a specific level of spectral resolution while keeping the beam size below a threshold. In this case, the threshold is based on the size of MEMS mirror 140 (e.g., the threshold is the size that enables direct illumination without beam expander / compressor optics or with beam expander / compressor optics of less than the threshold amount or size).

[0021] like Figure 1B As shown, the reflective optics 110 may include an input port 150 and an output port 152. The input port 150 receives a light beam for multiple passes through the diffraction grating 130 and the MEMS mirror 140, and the output port 152 outputs the light beam after multiple passes through the diffraction grating 130 and the MEMS mirror 140. For example, the reflective optics 110 may (as described above, via lens 120) guide the light beam through the diffraction grating 130 and the MEMS mirror 140 for the first pass and receive the reflection of the light beam at the end of the first pass. Subsequently, the reflective optics 110 may (e.g., as described herein with respect to...) Figure 2AAfter internal reflection, the beam is guided back to the diffraction grating 130 and MEMS mirror 140 (e.g., via lens 120), and then passes through the diffraction grating 130 and MEMS mirror 140 one or more times (e.g., a second, third, or fourth pass). In this example, after the fourth pass through the diffraction grating 130 and MEMS mirror 140, the reflecting optics 110 can guide the beam to the output port 152 for output. In some embodiments, the optical device 100 may include different configurations. For example, instead of including the input port 150 and / or the output port 152 in the reflecting optics 110, the optical device 100 may include input and / or output ports separate from the reflecting optics 110. In this case, the lens 120, diffraction grating 130, and / or MEMS mirror 140 may be configured to receive the beam from the input port and / or output port and / or guide the beam to the input port and / or output port, respectively, without the reflecting optics 110.

[0022] like Figure 1CAs shown, the reflective optics 110 may include a set of component reflective optics 160 to allow the light beam to pass through the diffraction grating 130 and the MEMS mirror 140 multiple times. For example, after the first pass (e.g., from the input port 150 through the lens 120, diffraction grating 130, and MEMS mirror 140, and then back through the diffraction grating 130 and lens 120), the reflective optics 110 may receive the light beam at the first component reflective optics 160-1. In this case, the first component reflective optics 160-1 may cause a spectral inversion and a fixed vertical offset of the light beam, and guide the light beam through the diffraction grating 130 and MEMS mirror 140 (e.g., through the lens 120) for a second pass. Similarly, after the second pass, component reflective optics 160-2 may reflect the light beam for a third pass, and after the third pass, component reflective optics 160-3 may reflect the light beam for a fourth pass. In this case, after the fourth pass, the light beam is incident on the output port 152 for output. In some embodiments, each component reflective optic 160 is a discrete optical element. For example, reflective optic 110 may include a plurality of discrete prisms forming component reflective optics 160. Additionally or alternatively, a single optical element may form multiple component reflective optics 160. For example, a single prism may include multiple possible paths through the single prism, and for example, a first path may form a first component reflective optic, and a second path may form a second component reflective optic. Although some embodiments have been described with respect to a particular number of passes, number of component reflective optics 160, or arrangement of component reflective optics 160 and ports, other embodiments with different numbers of passes, numbers of component reflective optics 160, or arrangements of component reflective optics 160 and ports are also contemplated.

[0023] As mentioned above, Figure 1A-1C This is provided as an example. Other examples may differ from those provided for this purpose. Figure 1A-1C As described.

[0024] Figure 2A and 2B This is a schematic diagram of an example embodiment 200 / 200' of an optical device, such as a reflective optical device 110 and / or its component reflective optical device 160.

[0025] like Figure 2AAs shown, a set of light rays can be incident on the surface of reflector 210, which is configured to reflect the light beam in an optical device such as optical device 100. In some embodiments, reflector 210 may be a prism made of a glass material, plastic material, or semiconductor material. In some embodiments, reflector 210 may be similar to a corner cube reflector, but the prism facet angle is chosen to induce additional total internal reflection on the front surface of reflector 210, thereby achieving fixed separation in the vertical direction, as described in more detail below. For example, reflector 210 is configured to induce internal reflection of the set of light rays such that the output light ray position has a fixed offset from the input light ray position in a direction perpendicular to the dispersion direction of the dispersive element (e.g., in the vertical direction). In other words, reflector 210 has a prism facet with a constituent angle (e.g., 30 degrees (30°) (and the two prism facets are perpendicular to each other, as shown)) such that the first input light ray is incident at a first position on the surface of reflector 210 and exits from a second position, such that the first position and the second position are offset by a specific amount. Additionally or alternatively, the set of prisms can be angled so that the second input light ray is incident at a third position and outputs from a fourth position, which is different from the first and second positions, such that the third and fourth positions are also separated by a specific amount. This contrasts with other corner cube reflectors, where the interval between the incident and output positions is based on the location of the incident position rather than being fixed. In some embodiments, reflector 210 is configured to cause a spectral reversal relative to the dispersion direction.

[0026] like Figure 2B As shown, a set of light rays can be incident on the surface of a refractor 210', which is configured to reflect the light beam in an optical device such as optical device 100. In this case, the refractor 210' is configured to cause the reflection of the set of light rays such that the position of the output light ray has a fixed offset from the position of the input light ray in a direction perpendicular to the dispersion direction of the dispersive element (e.g., in the vertical direction). In some embodiments, the refractor 210' can be formed of a prism having a refractive surface capable of producing a vertical offset, as shown. In some embodiments, a particular type or configuration of the refractor 210' can be selected to minimize chromatic aberration associated with the refractive surface of the refractor 210'. In some embodiments, the refractor 210' is configured to cause a spectral inversion relative to the dispersion direction.

[0027] As mentioned above, Figure 2A and 2B This is provided as one or more examples. Other examples may be related to... Figure 2A and 2B The descriptions are different.

[0028] Figures 3A-3C This is a schematic diagram of an example optical path. Figure 3A Example 300 illustrates a first set of optical paths (e.g., a set of positions that can be aligned on a dispersive element) in an optical device (e.g., optical device 100) described herein when a reflector (e.g., reflective optics 110 or reflector 210) described herein is aligned with a set of optical fibers. Figure 3B Example 310 illustrates a second set of optical paths when another type of reflector is not aligned with the set of optical fibers, and the reflector is not configured for a fixed vertical offset. Figure 3C Example 320 illustrates a third optical path when the reflector described herein (e.g., reflective optics 110 or reflector 210) does not coincide with this set of optical fibers. Figure 3B In this context, the offset caused by the rotation of the MEMS mirror in the vertical direction results in an optical axis offset in the first direction at reference numeral 311. At reference numeral 312, the offset in the first direction relative to the optical axis causes an offset in the first direction at the position where the beam enters the optical reflector. An optical reflector with single internal reflection causes an offset in the second direction at the position where the beam leaves the optical reflector (at reference numeral 313). At reference numeral 314, the offset in the second direction causes an offset in the beam's pointing position in the first direction, resulting in the beam missing the output fiber. In this case, a reflector not configured to fix the vertical offset, when misaligned with a set of fibers, causes the output beam to fail to reach the output fiber of that set of fibers. This is a result of having a vertical offset based on the incident position, as described above regarding... Figure 2A and 2B As stated above. In contrast, as... Figure 3C As shown in Example 320, when misaligned with a set of optical fibers, a reflector configured to fix a vertical offset causes the output beam to continue reaching the output fiber of that set of fibers. For example, as indicated by reference numeral 321, the optical axis is offset in a first direction due to the offset caused by the rotation of the MEMS mirror in the vertical direction. At reference numeral 322, the offset in the first direction relative to the optical axis results in an offset in the first direction at the location where the beam enters the optical reflector. An optical reflector with a fixed vertical offset causes an offset in the first direction at the location where the beam leaves the optical reflector (reference numeral 323). This is a result of having a fixed vertical offset independent of the incident position, thus causing the beam to still reach the output fiber.

[0029] In this way, by using reflective optics with a fixed vertical offset, such as reflective optics 110 or reflector 210, the possibility of poor optical performance due to misalignment of components of the optics can be reduced. For example, ensuring that the alignment of the optical path to the output fiber is independent of the alignment of the optical path to the input fiber avoids the amplification effect that may occur when the optical device is used multiple times. In other words, if the beam is reflected four times by a misaligned MEMS mirror (e.g., MEMS mirror 140), the output beam offset is multiplied by a factor of four. Due to insertion loss, this could increase the power level error by a factor of 16. However, by using, as Figure 3A and 3C The reflected optical device shown (and) Figure 2A and Figure 2B The refractive optical device shown is relative to the reflective optical device. Figure 3B The reflective optics shown have additional internal reflections, eliminating alignment errors, thus enabling misaligned MEMS mirrors to be used multiple times with corresponding reflections without amplifying output beam offset and associated power level errors.

[0030] As mentioned above, providing Figures 3A-3C As an example. Other examples can be found related to... Figures 3A-3C The descriptions are different.

[0031] Figure 4 This is a flowchart of an example process 400 associated with an optical device used for a multi-channel optical channel monitor. In some embodiments, Figure 4 One or more process blocks may be composed of optical devices or components thereof (e.g., optical device 100 or components thereof, reflector 210, etc.). Figure 3A and 3C (Reflectors and other examples) are used to perform this. In some implementations, Figure 4 One or more process blocks can be executed by another device or a group of devices that are separate from or include the optical device.

[0032] like Figure 4 As shown, process 400 may include receiving a light beam at the input port of an optical channel monitor (box 410). For example, as described above, an optical device may receive a light beam at the input port of an optical channel monitor.

[0033] like Figure 4 As further shown, process 400 may include guiding the light beam multiple times through the dispersive element of the optical channel monitor, wherein each pass is deflected according to a fixed vertical offset of the reflecting optics (box 420). For example, the optical device may guide the light beam multiple times through the dispersive element of the optical channel monitor, wherein each pass is deflected according to a fixed vertical offset of the reflecting optics, as described above.

[0034] like Figure 4 As further shown, process 400 may include determining the characteristics of the beam based on the multiple passes of the guide beam through the dispersive element (box 430). For example, as described above, the optical device may determine the characteristics of the beam based on the multiple passes of the guide beam through the dispersive element.

[0035] Process 400 may include additional implementations, such as any single implementation or any combination of implementations of one or more other processes described below and / or elsewhere herein.

[0036] In a first embodiment, guiding the beam through the dispersive element includes guiding the beam through the dispersive element during the first pass of multiple passes, reflecting the beam with a fixed vertical offset using reflective optics based on guiding the beam through the dispersive element during the first pass, and guiding the beam through the dispersive element during the second pass of multiple passes based on reflecting the beam with the fixed vertical offset. In some embodiments, the beam offset in the vertical direction is canceled out during successive reflections.

[0037] In the second embodiment, alone or in combination with the first embodiment, the reflective optics include multiple component reflective optics corresponding to multiple passes.

[0038] In the third embodiment, guiding the light beam through the dispersive element, either alone or in combination with one or more of the first and second embodiments, includes reflecting the light beam with a fixed vertical offset using a first component of a plurality of component reflective optics for a first pass in a plurality of passes, and reflecting the light beam with a fixed vertical offset using a second component of a plurality of component reflective optics for a second pass in a plurality of passes.

[0039] In the fourth embodiment, guiding the light beam through the dispersive element, alone or in combination with one or more of the first to third embodiments, includes causing the spectrum of the light beam to be reversed during the second pass of the dispersive element in a series of passes, relative to the first pass of the light beam.

[0040] although Figure 4 An example box of process 400 is shown, but in some implementations, process 400 may include... Figure 4 The boxes shown are compared to additional boxes, fewer boxes, different boxes, or boxes with different arrangements. Additionally or alternatively, two or more boxes of process 400 can be executed in parallel.

[0041] The foregoing disclosure provides illustrations and descriptions, but is not intended to be exhaustive or to limit the implementation to the precise forms disclosed. Modifications and variations can be made based on the foregoing disclosure, or can be derived from the practice of implementation. Furthermore, any implementation described herein can be combined unless the foregoing disclosure expressly provides reasons why one or more implementations cannot be combined.

[0042] As used here, depending on the context, satisfying the threshold can refer to a value that is greater than the threshold, greater than or equal to the threshold, less than the threshold, less than or equal to the threshold, equal to the threshold, not equal to the threshold, etc.

[0043] Even if a particular combination of features is referenced in the claims and / or disclosed in the specification, these combinations are not intended to limit the disclosure of various implementations. In fact, many of these features can be combined in ways not specifically stated in the claims and / or not disclosed in the specification. Although each dependent claim listed below may directly depend on only one claim, the disclosure of various embodiments includes each dependent claim as well as every other claim in the claim set. As used herein, the phrase “at least one” in the list of items refers to any combination of those items, including a single member. For example, “at least one of a, b, or c” is intended to cover any combination of a, b, c, ab, ac, bc, and abc, as well as a plurality of the same items.

[0044] Unless explicitly stated otherwise, the elements, actions, or instructions used herein should not be construed as critical or necessary. 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 one or more items associated with the article “the” and may be used interchangeably with “the one or more.” Furthermore, as used herein, the term “group” is intended to include one or more items (e.g., related items, unrelated items, or a combination of related and unrelated items) and may be used interchangeably with “one or more.” When only one item is intended to be used, the phrase “only one” or similar language is used. Furthermore, as used herein, the terms “having” and the like are intended to be open-ended terms. Furthermore, the phrase “based on” is intended to mean “at least partially based on” unless explicitly stated otherwise. Furthermore, as used herein, the term “or” is intended to be included when used in series and may be used interchangeably with “and / or” unless explicitly stated otherwise (e.g., if used in conjunction with “any” or “only one of them”). Furthermore, for ease of description, spatially relative terms such as “below,” “down,” “up,” “above,” etc., may be used here to describe the relationship of one element or feature to another element or feature shown in the figure. In addition to the orientations shown in the figure, spatially related terms are intended to include different orientations of the equipment, apparatus, and / or element in use or operation. The equipment may be oriented in other ways (rotated 90 degrees or in other orientations), and the spatially relative descriptors used herein may be interpreted accordingly.

Claims

1. An optical device for guiding a light beam, comprising: Dispersive element; A reflective optical device for reflecting the light beam with a fixed offset perpendicular to the dispersion direction of the dispersive element and a negative offset in the dispersion direction of the dispersive element. The reflecting optics are aligned with the dispersive element to deflect the beam relative to the dispersive element, and the beam passes through the dispersive element multiple times, being deflected at each of the multiple passes; and A reflective tuning element for receiving the light beam from the dispersive element and reflecting the light beam back to the dispersive element.

2. The optical device according to claim 1, wherein, The negative offset in the dispersion direction is configured to cause spectral inversion.

3. The optical device according to claim 1, wherein the optical device is an optical channel monitor or a spectrometer.

4. The optical device according to claim 1, wherein the dispersive element comprises a diffraction grating.

5. The optical device according to claim 1, wherein, The reflection tuning element is a microelectromechanical system tilting mirror.

6. The optical device according to claim 1, wherein the reflective optical element comprises a reflective prism.

7. The optical device according to claim 1, wherein the reflective optical element comprises a plurality of reflective prisms.

8. The optical device according to claim 1, wherein the reflective optical element comprises a prism having a refractive surface.

9. The optical device according to claim 1, further comprising: A lens in the optical path between a dispersive element and a reflective optics device.

10. The optical device according to claim 1, wherein, The reflective optics are configured such that beam deflection in the vertical direction is canceled out in continuous reflections of the reflective optics, wherein the vertical direction is perpendicular to the dispersion direction of the dispersive element.

11. A method for guiding a light beam, comprising: The beam is received at the input port of the optical channel monitor; The light beam is guided by the reflective optics of the optical channel monitor to pass multiple times through the dispersive element and the reflective tuning element of the optical channel monitor, wherein each pass is deflected according to a fixed vertical offset of the reflective optics, wherein the fixed vertical offset is perpendicular to the dispersion direction of the dispersive element. and The characteristics of the light beam are determined by the optical channel monitor based on guiding the light beam through the dispersive element multiple times.

12. The method of claim 11, wherein guiding the beam through the dispersive element and the reflection tuning element comprises: During the first pass of multiple passes, the beam is guided through the dispersive element and the reflection tuning element; Based on guiding the beam through a dispersive element and a reflection tuning element on the first pass, a reflective optics is used to reflect the beam with a fixed vertical offset; and Based on reflecting the beam with a fixed vertical offset, the beam is guided through the dispersive element and the reflection tuning element during the second pass of multiple passes.

13. The method of claim 11, wherein the reflective optics comprises a plurality of component reflective optics, wherein each of the plurality of component reflective optics corresponds to a corresponding first pass in the plurality of passes.

14. The method of claim 13, wherein guiding the beam through the dispersive element and the reflection tuning element comprises: For the first pass in a series of passes, the first component of the multi-component reflecting optics is used to fix the vertical offset of the reflected beam; and For the second pass in a series of passes, the second component of the multi-component reflective optics is used to reflect the beam with a fixed vertical offset.

15. The method of claim 11, wherein guiding the beam through the dispersive element and the reflection tuning element comprises: The spectrum of the beam that passes through the dispersive element and the reflection tuning element a second time in a series of multiple passes is inverted, relative to the first pass of the beam in the series of multiple passes.

16. The method of claim 11, wherein the reflective tuning element is a microelectromechanical system (MEMS) reflector.

17. A reflective optical device, comprising: Multiple prism surfaces, The plurality of prism surfaces are angled relative to each other to produce a fixed vertical offset relative to at least one other optical path passing through the reflecting optics in at least one optical path passing through the reflecting optics. The magnitude of the fixed vertical offset is independent of the incident position of the light beam on one of the plurality of prism surfaces, and Multiple prism surfaces are angled relative to each other to induce spectral inversion in at least one optical path.

18. The reflective optics of claim 17, wherein the at least one optical path through the reflective optics includes at least one internal reflection within the reflective optics.

19. The reflective optical device of claim 17, wherein the plurality of prism surfaces are formed of at least one of a glass material, a plastic material, or a semiconductor material.

20. The reflective optical device of claim 17, wherein the at least one optical path comprises a plurality of optical paths alignable to a plurality of positions on the dispersive element.

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