CN114323586A - Waveguide loss measurement method based on dual-channel detection - Google Patents
Waveguide loss measurement method based on dual-channel detection Download PDFInfo
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- CN114323586A CN114323586A CN202111628057.2A CN202111628057A CN114323586A CN 114323586 A CN114323586 A CN 114323586A CN 202111628057 A CN202111628057 A CN 202111628057A CN 114323586 A CN114323586 A CN 114323586A
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Abstract
The invention provides a waveguide loss measuring method based on double-channel detection, which comprises the following steps: the output light of the narrow linewidth tunable laser is divided into two paths through the optical fiber coupler: one path of the laser beam is used as reference light and directly enters a first power meter probe to monitor and record laser power change in real time; the other path of light is guided into the tapered optical fiber through the optical fiber connector and focused into the waveguide, and light emitted by the waveguide is collimated by the collecting objective lens and then enters the second power meter probe; and changing the output wavelength of the tunable laser, reading the optical power recorded by the first power meter probe and the second power meter probe by the dual-channel power meter, and calculating the waveguide loss. The method and the device can effectively eliminate measurement errors caused by factors such as the change of the light source power along with the wavelength, the instability of the light source power along with the time and the like, and can obtain a free spectral range FSR curve and waveguide loss of the waveguide resonant cavity more accurately.
Description
Technical Field
The invention belongs to the field of waveguides, and particularly relates to a waveguide loss measuring method based on dual-channel detection.
Background
The transmission loss in the waveguide is an important parameter for measuring the quality of the waveguide, and the measurement of the transmission loss of the waveguide is an important prerequisite for the application of the waveguide in an integrated photoelectric chip. The existing methods for measuring the waveguide mainly include (1) measuring the scattered light along the propagation direction of the waveguide, (2) directly measuring and comparing the input and output optical powers of the waveguide, and (3) a "truncation method", that is, simultaneously measuring and comparing the transmitted optical powers of a plurality of waveguides with different lengths. The three methods described above tend to have great limitations in practical applications: the method (1) measures the scattered light along the waveguide light transmission direction, and calculates the waveguide loss value by comparing the change of the scattered light measured from the top of the chip along with the transmission length, so that the top surface of the chip is required to have no other structures influencing the light scattering and the like, and the requirement on the quality of a wafer is high; the method (2) calculates the waveguide loss by comparing the optical power of the waveguide input end and the optical power of the waveguide output end, so that the optical power of the waveguide input end needs to be known in advance, and the input coupling efficiency of different waveguides in actual operation is greatly different and is difficult to know, so that the method is also limited; the method (3) calculates the waveguide loss by comparing the output light intensities of the same waveguide with different lengths, but requires that the unit length loss and the coupling efficiency of different waveguides are kept consistent, and is difficult to realize in actual operation.
Disclosure of Invention
The embodiment of the application provides a waveguide loss measurement method based on dual-channel detection, which can effectively eliminate the influence caused by factors such as the change of light source power along with wavelength, the instability of the light source power along with time and the like, and can obtain a more accurate FSR curve and waveguide loss of a waveguide resonant cavity.
The embodiment of the application provides a waveguide loss measurement method based on dual-channel detection, which comprises the following steps:
the output light of the narrow linewidth tunable laser is divided into two paths through the optical fiber coupler:
one path of the laser beam is used as reference light and directly enters a first power meter probe to monitor and record laser power change in real time;
the other path of light is guided into the tapered optical fiber through the optical fiber connector and focused into the waveguide, and light emitted by the waveguide is collimated by the collecting objective lens and then enters the second power meter probe;
and changing the output wavelength of the tunable laser, reading the optical power recorded by the first power meter probe and the second power meter probe by the dual-channel power meter, and calculating the waveguide loss.
The output light of the narrow linewidth tunable laser is divided into two paths through the optical fiber coupler, wherein one path of the output light is used as reference light to directly enter the first power meter probe, and the laser power change is monitored and recorded in real time, and the method comprises the following steps:
laser with a certain wavelength output by the narrow-linewidth tunable laser is divided into two paths through the optical fiber coupler, wherein one path directly enters the first power meter probe, and the recording power is Pref (lambda).
The ratio of the power Pref (lambda) recorded by the first power meter probe to the output power of the light source is constant and depends on the splitting ratio of the optical fiber coupler.
Wherein, the conical fiber of other way process fiber connector leading-in to inside the focusing to the waveguide, the light that the waveguide was emergent incides the second power meter probe after collecting the objective collimation, include:
and the other path of light enters the tapered optical fiber through the optical fiber connector, is focused and coupled into the optical waveguide, and enters the second power meter probe after being collected by the objective lens, and records the power value Pout (lambda).
Wherein, changing the output wavelength of tunable laser, the optical power that the dual-channel power meter read first power meter probe and second power meter probe record, calculate the waveguide loss, include:
the first power meter probe and the second power meter probe are simultaneously connected with the dual-channel power meter, and simultaneously record the values of Pref (lambda) and Pout (lambda), and T (lambda) is Pout (lambda)/Pref (lambda); changing the output wavelength of the tunable laser to obtain a curve of T (lambda) along with the change of the wavelength; by recording the maximum value Tmax and the minimum value Tmin in each period of the curve, the waveguide loss α is obtained by calculation with the following formula:
where lwg is the waveguide length, R is the end face reflectivity, and Tmax and Tmin are the maximum and minimum values of the interference pattern, respectively.
The waveguide loss measuring method based on the dual-channel detection has the following beneficial effects:
the waveguide loss measuring method based on the dual-channel detection comprises the following steps: the output light of the narrow linewidth tunable laser is divided into two paths through the optical fiber coupler: one path of the laser beam is used as reference light and directly enters a first power meter probe to monitor and record laser power change in real time; the other path of light is guided into the tapered optical fiber through the optical fiber connector and focused into the waveguide, and light emitted by the waveguide is collimated by the collecting objective lens and then enters the second power meter probe; and changing the output wavelength of the tunable laser, reading the optical power recorded by the first power meter probe and the second power meter probe by the dual-channel power meter, and calculating the waveguide loss. The method and the device can effectively eliminate measurement errors caused by factors such as the change of the light source power along with the wavelength, the instability of the light source power along with the time and the like, and can obtain a free spectral range FSR curve and waveguide loss of the waveguide resonant cavity more accurately.
Drawings
Fig. 1 is a schematic flow chart of a waveguide loss measurement method based on dual-channel detection according to an embodiment of the present application;
FIG. 2 is a schematic structural diagram of a waveguide loss measurement system based on dual-channel detection according to an embodiment of the present application;
FIG. 3 is a graph of T (λ) as a function of source wavelength.
Detailed Description
The present application is further described with reference to the following figures and examples.
In the following description, the terms "first" and "second" are used for descriptive purposes only and are not intended to indicate or imply relative importance. The following description provides embodiments of the invention, which may be combined or substituted for various embodiments, and this application is therefore intended to cover all possible combinations of the same and/or different embodiments described. Thus, if one embodiment includes feature A, B, C and another embodiment includes feature B, D, then this application should also be considered to include an embodiment that includes one or more of all other possible combinations of A, B, C, D, even though this embodiment may not be explicitly recited in text below.
The following description provides examples, and does not limit the scope, applicability, or examples set forth in the claims. Changes may be made in the function and arrangement of elements described without departing from the scope of the disclosure. Various examples may omit, substitute, or add various procedures or components as appropriate. For example, the described methods may be performed in an order different than the order described, and various steps may be added, omitted, or combined. Furthermore, features described with respect to some examples may be combined into other examples.
At present, a Fabry-Perot (Fabry-Perot) resonant cavity (also called F-P cavity) method is commonly adopted to test waveguide light transmission loss, the method utilizes the F-P cavity formed by a waveguide incident surface and a waveguide emergent surface, and the end surface of the cavity is strictly vertical to the light transmission direction of a waveguide. After the narrow-linewidth light source is coupled into the waveguide, interference is formed by reflection of the end face of the F-P cavity; an interference pattern can be formed at the emergent end by changing the wavelength of the light source, and the waveguide loss can be calculated by the following formula according to the difference between the peak value and the valley value in the interference pattern:
wherein lwgIs the waveguide length, R is the end face reflectivity, TminAnd TmaxRespectively, the peak and valley of the interference pattern. However, when the waveguide transmission loss is measured using the F-P cavity method, light sources of different wavelengths are required to keep the power constant in order to obtain accurate measurement results. In practical operation, a narrow linewidth tunable laser is usually used as an incident light source, and when the wavelength is tuned, the outputs of different wavelengths are difficult to keep consistent, so that the measured curve error is large. Therefore, the invention provides a waveguide loss measuring method based on dual-channel detection, and the signal-to-noise ratio of the test is greatly improved by introducing a reference beam.
As shown in fig. 1, the waveguide loss measurement method based on dual-channel detection of the present application includes: s101, dividing output light of the narrow linewidth tunable laser into two paths through an optical fiber coupler: one path of the laser beam is used as reference light and directly enters a first power meter probe to monitor and record laser power change in real time; the other path of light is guided into the tapered optical fiber through the optical fiber connector and focused into the waveguide, and light emitted by the waveguide is collimated by the collecting objective lens and then enters the second power meter probe; s103, changing the output wavelength of the tunable laser, reading the optical power recorded by the first power meter probe and the second power meter probe by the dual-channel power meter, and calculating the waveguide loss.
As shown in fig. 1-2, the waveguide loss measurement method based on dual channel detection uses a waveguide loss measurement system, and the waveguide loss measurement system includes a narrow linewidth tunable laser 1, an optical fiber coupler 2, an optical fiber connector 3, a tapered optical fiber 4, a waveguide to be measured 5, a collection objective 6, a second power meter probe 7, a first power meter probe 8, and a dual channel power meter 9.
The output light of the narrow linewidth tunable laser 1 is divided into two beams by the optical fiber coupler 2: one beam of the laser beam is used as reference light to directly enter a probe of the power meter, and the change of the laser power is monitored and recorded in real time; and the other beam is guided into the tapered optical fiber 4 through the optical fiber connector 3 and focused into the waveguide 5, light emitted by the waveguide 5 is collimated by the collecting objective lens 6 and then enters the first power meter probe 7, and the power recorded by the power meter probe changes along with the change of the wavelength of the laser. The dual-channel power meter 9 is used for reading the optical power recorded by the first power meter probe 7 and the second power meter probe 8, and the influence of the self power change of the laser on the output power change of the waveguide can be eliminated through comparison.
In the application, laser with a certain wavelength output by a narrow linewidth tunable laser 1 is divided into two paths through an optical fiber coupler 2, wherein one path directly enters a first power meter probe 8, and the recording power is Pref(lambda). The power P recorded by the first power meter probe 8refThe ratio of (lambda) to the output power of the light source is constant and depends on the splitting ratio of the fiber coupler 2. The other path of light enters the tapered optical fiber 4 through the optical fiber connector 3, is focused and coupled into the optical waveguide 5, and the laser output from the optical waveguide enters the second power meter probe 7 after being collected by the objective lens 6 and records the power value Pout(lambda). The first power meter probe 7 and the second power meter probe 8 are simultaneously connected with the dual-channel power meter 9, and can simultaneously record Pref(lambda) and PoutA value of (λ), and T (λ) ═ Pout(λ)/Pref(lambda). By changing the output wavelength of the narrow linewidth tunable laser 1, a curve of T (λ) with wavelength (i.e., the free spectral range FSR curve in the waveguide resonator shown in fig. 3) can be obtained. By recording the maximum value T in each cycle of the curvemaxAnd a minimum value TminThe waveguide loss α can be calculated by the following formula:
wherein lwgIs the waveguide length, R is the end face reflectivity, TmaxAnd TminRespectively, the maximum and minimum of the interference pattern.
As can be seen from FIG. 3, although the laser source power varies greatly with wavelength, the source output power P can be recorded simultaneously using a dual channel detection methodref(lambda) and waveguide output power Pout(λ), so that in calculating T (λ) ═ Pout(λ)/PrefAnd (lambda) can effectively eliminate the influence caused by factors such as the change of the light source power along with the wavelength, the instability of the light source power along with the time and the like, and can obtain a more accurate FSR curve and waveguide loss.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (5)
1. A waveguide loss measurement method based on dual-channel detection is characterized by comprising the following steps:
the output light of the narrow linewidth tunable laser is divided into two paths through the optical fiber coupler:
one path of the laser beam is used as reference light and directly enters a first power meter probe to monitor and record laser power change in real time;
the other path of light is guided into the tapered optical fiber through the optical fiber connector and focused into the waveguide, and light emitted by the waveguide is collimated by the collecting objective lens and then enters the second power meter probe;
and changing the output wavelength of the tunable laser, reading the optical power recorded by the first power meter probe and the second power meter probe by the dual-channel power meter, and calculating the waveguide loss.
2. The waveguide loss measurement method based on dual-channel detection as claimed in claim 1, wherein the output light of the narrow linewidth tunable laser is divided into two paths by the optical fiber coupler, wherein one path directly enters the first power meter probe as reference light to monitor and record the laser power change in real time, and the method comprises:
laser with a certain wavelength output by the narrow linewidth tunable laser is divided into two paths through the optical fiber coupler, wherein one path directly enters the first power meter probe, and the recording power is Pref(λ)。
3. Waveguide loss measurement method based on dual channel detection according to claim 1 or 2, characterized in that the power P recorded by the first power meter proberefThe ratio of (lambda) to the output power of the light source is constant and depends on the splitting ratio of the fiber coupler.
4. The waveguide loss measurement method based on the dual-channel detection according to any one of claims 1 to 3, wherein the other path is guided into the tapered optical fiber through the optical fiber connector and focused into the waveguide, and light emitted from the waveguide is collimated by the collecting objective lens and then enters the second power meter probe, and the method comprises the following steps:
the other path of light enters the tapered optical fiber through the optical fiber connector, is focused and coupled into the optical waveguide, and the laser output from the optical waveguide enters the second power meter probe after being collected by the objective lens and records the power value Pout(λ)。
5. The waveguide loss measurement method based on the dual-channel detection according to any one of claims 1 to 4, wherein the output wavelength of the tunable laser is changed, the dual-channel power meter reads the optical power recorded by the first power meter probe and the second power meter probe, and the waveguide loss is calculated, and the method comprises the following steps:
the first power meter probe and the second power meter probe are simultaneously connected with the dual-channel power meter and simultaneously record Pref(lambda) and PoutA value of (λ), and T (λ) ═ Pout(λ)/Pref(λ); changing the output wavelength of the tunable laser to obtain a curve of T (lambda) along with the change of the wavelength; by recording the maximum value T in each cycle of the curvemaxAnd a minimum value TminThe waveguide loss α is obtained by calculation using the following formula:
wherein lwgIs the waveguide length, R is the end face reflectivity, TmaxAnd TminRespectively, the maximum and minimum of the interference pattern.
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