A test method for half-wave voltage and modulation efficiency of Mach-Zehnder modulator

Abstract

The present invention relates to the technical field of optical modulators, in particular to a method for testing the half-wave voltage and modulation efficiency of a Mach-Zehnder modulator, comprising: controlling the input optical power from a beam splitter to be a fixed value, adjusting the output optical power of the Mach-Zehnder modulator to half of the maximum value of the output optical power; applying voltage values ​​and to an upper modulation arm and a lower modulation arm respectively; linearly fitting the relationship between the electro-optical phase shift and the voltage value generated by the upper modulation arm, and the relationship between the electro-optical phase shift and the voltage value generated by the lower modulation arm, to obtain a fitting coefficient; calculating the half-wave voltage of the upper modulation arm and the half-wave voltage of the lower modulation arm based on the fitting coefficient; and calculating the half-wave voltage of the Mach-Zehnder modulator. The present invention facilitates testing the half-wave voltage and modulation efficiency of a Mach-Zehnder modulator.

Description

Technical Field

[0001] The invention relates to the technical field of optical modulators, and in particular to a method for testing half-wave voltage and modulation efficiency of a Mach-Zehnder modulator. Background Art

[0002] The electro-optic modulator is the core component of the optical communication system. Its main function is to complete the conversion of signals from the circuit to the optical path, and to achieve high-capacity and high-speed data transmission by taking advantage of the low loss and large bandwidth of optical signals in the channel. The Mach-Zehnder modulator is a common electro-optic modulator, which consists of a beam splitter, a modulation arm, a beam combiner, metal electrodes and other parts. It usually has a large optical bandwidth, good process tolerance and low temperature sensitivity, and has been widely used in electro-optic modulators such as silicon-based modulators and thin-film lithium niobate modulators. The modulation efficiency of the Mach-Zehnder modulator can usually be expressed as a half-wave voltage With modulation length L The product of To characterize. Half-wave voltage It means that the modulator generates a modulation voltage corresponding to a π phase shift change.

[0003] For common high-speed silicon-based Mach-Zehnder modulators, in order to avoid the reflection of RF signals, a terminal resistor with a specific resistance is connected to the end of the metal electrode to absorb the RF signal. In the range of 3V-10V, at such a voltage, the terminal resistor will produce a non-negligible thermal effect. Due to the thermo-optical properties of silicon materials, the phase shift of the modulator at this time includes the thermo-optical phase shift, which affects the accurate test of the electro-optical modulation efficiency. Therefore, a common method is to make a modulator with the same parameters but without the terminal resistor for testing. Obviously, such a method will increase a certain amount of redundant area, which is not conducive to reducing the chip size; at the same time, this method can only indirectly represent the modulation efficiency of the modulator actually integrated in the silicon photonic chip, and its error will depend on the consistency of device manufacturing. Summary of the invention

[0004] Therefore, in response to the above problems, the present invention proposes a test method for the half-wave voltage and modulation efficiency of a Mach-Zehnder modulator, which can effectively solve the influence of the thermal effect of the terminal resistance on the phase shift and facilitate the testing of the half-wave voltage and modulation efficiency of the Mach-Zehnder modulator.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for testing the half-wave voltage of a Mach-Zehnder modulator, wherein the Mach-Zehnder modulator comprises a beam splitter, an upper modulation arm, a first terminal resistor, a first phase shifter, a lower modulation arm, a second terminal resistor, a second phase shifter and a beam combiner; a first output end of the beam splitter is electrically connected to a first input end of the beam combiner through the upper modulation arm and the first phase shifter in sequence, and a second output end of the beam splitter is electrically connected to a second input end of the beam combiner through the lower modulation arm and the second phase shifter in sequence; the upper modulation arm is electrically connected to the first terminal resistor, the lower modulation arm is electrically connected to the second terminal resistor, and the first terminal resistor is electrically connected to the second terminal resistor. The method for testing the half-wave voltage comprises the following steps:

[0007] Step 1: Control the input optical power from the beam splitter is a fixed value, and the output optical power of the Mach-Zehnder modulator is adjusted to half of the maximum output optical power by adjusting the first phase shifter and / or the second phase shifter;

[0008] Step 2 includes the following sub-steps:

[0009] 2.1, apply voltage values ​​to the upper modulation arm and the lower modulation arm respectively and ;

[0010] At this time, the electro-optical phase shift generated by the upper modulation arm and voltage value relationship, and the electro-optical phase shift produced by the lower modulation arm and voltage value The relationship is expressed as follows:

[0011] ;

[0012] and are the electro-optic phase shift coefficients of the upper modulation arm and the lower modulation arm respectively;

[0013] 2.2 Calculation and The value of each voltage adjustment or The output optical power of the Mach-Zehnder modulator is measured at the same time and recorded as P ;

[0014] , multiple groups of output optical powers are fitted by polynomials to obtain and The value of

[0015] in, t is the thermo-optical coefficient of the first terminal resistor and the second terminal resistor, The electro-optic phase shift generated by the upper modulation arm The electro-optic phase shift produced by the lower modulation arm The phase difference, The phase difference between the upper modulation arm and the lower modulation arm due to process factors;

[0016] Half-wave voltage of upper modulation arm , ; Half-wave voltage of the lower modulation arm , ;

[0017] Step 3: Calculate the half-wave voltage of the Mach-Zehnder modulator :

[0018] .

[0019] Further, the upper modulation arm includes a first ground electrode, a first signal electrode, and a first waveguide arranged between the first ground electrode and the first signal electrode, the first output end of the beam splitter is connected to the first input end of the beam combiner through the first waveguide and the first phase shifter in sequence, and the first signal electrode is electrically connected to the first terminal resistor;

[0020] The lower modulation arm includes a second ground electrode, a second signal electrode, and a second waveguide arranged between the second ground electrode and the second signal electrode. The second output end of the beam splitter is connected to the second input end of the combiner through the second waveguide and the second phase shifter in sequence, and the second signal electrode is electrically connected to the second terminal resistor.

[0021] Furthermore, the first terminal resistor and the second terminal resistor have the same resistance value.

[0022] Based on the same inventive concept, a method for testing the modulation efficiency of a Mach-Zehnder modulator is also proposed. The Mach-Zehnder modulator half-wave voltage is calculated by using the above-mentioned method for testing the half-wave voltage of the Mach-Zehnder modulator. ;

[0023] The modulation efficiency of the Mach-Zehnder modulator is calculated as ,in L is the modulation length of the Mach-Zehnder modulator.

[0024] By adopting the above technical solution, the beneficial effects of the present invention are:

[0025] (1) No need to add an additional modulator to remove the terminal resistors (first terminal resistor and second terminal resistor) for testing, reducing the test complexity;

[0026] (2) Directly test the half-wave voltage of the Mach-Zehnder modulator, the result is accurate and not affected by the manufacturing consistency of the device;

[0027] (3) At the same time, the modulation efficiency of the Mach-Zehnder modulator can be tested. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the structure of a Mach-Zehnder modulator according to an embodiment of the present invention.

[0029] Figure 2 It is a set of test data of the embodiment of the present invention.

[0030] Figure 3 is another set of test data of the embodiment of the present invention.

[0031] Description of reference numerals:

[0032] 1. Beam splitter; 21. First ground electrode; 22. Second ground electrode; 31. First signal electrode; 32. Second signal electrode; 41. First terminal resistor; 42. Second terminal resistor; 51. First phase shifter; 52. Second phase shifter; 6. Beam combiner. DETAILED DESCRIPTION

[0033] The present invention will now be further described with reference to the accompanying drawings and specific implementation methods.

[0034] refer to Figure 1 Figure 2 and Figure 3 , this embodiment provides a method for testing the half-wave voltage of a Mach-Zehnder modulator.

[0035] like Figure 1 As shown, the Mach-Zehnder modulator is composed of the following parts, including a beam splitter 1, a first ground electrode 21, a first signal electrode 31, a first terminal resistor 41, a first phase shifter 51, a second ground electrode 22, a second signal electrode 32, a second terminal resistor 42, a second phase shifter 52, and a combiner 6.

[0036] Among them, the first ground electrode 21, the first signal electrode 31, and the first waveguide (not marked in the figure) controlled between the first ground electrode 21 and the first signal electrode 31 constitute an upper modulation arm, and the first output end of the beam splitter 1 is connected to the first input end of the combiner 6 through the first waveguide and the first phase shifter 51 in sequence, and the first signal electrode 31 is electrically connected to the first terminal resistor 41 for absorbing electrical signals.

[0037] Among them, the second ground electrode 22, the second signal electrode 32, and the second waveguide (not marked in the figure) controlled between the second ground electrode 22 and the second signal electrode 32 constitute a lower modulation arm, and the second output end of the beam splitter 1 is connected to the second input end of the combiner 6 through the second waveguide and the second phase shifter 52 in sequence, and the second signal electrode 32 is electrically connected to the second terminal resistor 42 for absorbing electrical signals.

[0038] The first signal electrode 31 is electrically connected to the second terminal resistor 42. Preferably, the first signal electrode 31 and the second terminal resistor 42 have the same resistance value.

[0039] The above-mentioned electronic components are existing equipment and will not be described in detail here.

[0040] In this scheme, the test method of the half-wave voltage of the Mach-Zehnder modulator is specifically as follows:

[0041] Step 1: Control the input optical power from beam splitter 1 is a fixed value, and the output optical power of the Mach-Zehnder modulator is adjusted to the orthogonal bias point by adjusting the first phase shifter 51 and / or the second phase shifter 52, that is, the output optical power of the Mach-Zehnder modulator is adjusted to half of the maximum value;

[0042] Apply voltage values ​​to the upper modulation arm and the lower modulation arm respectively and ;

[0043] At this time, the electro-optical phase shift generated by the upper modulation arm and voltage value relationship, and the electro-optical phase shift produced by the lower modulation arm and voltage value The relationship is expressed as follows:

[0044] ;

[0045] and are the electro-optic phase shift coefficients of the upper modulation arm and the lower modulation arm, respectively.

[0046] Refractive index change due to thermo-optic effect in silicon waveguides (i.e., first waveguide and second waveguide) Proportional to the change in temperature At the same time, in the terminal resistor (i.e., the first terminal resistor 41 and the second terminal resistor 42) and the silicon waveguide near them, the specific heat is constant; and the heating of the terminal resistor conforms to Joule's law, then With fever Proportional to the phase difference caused by the thermo-optical effect Proportional to the change in the square of the voltage across the terminal resistance ,Right now ;

[0047] Therefore, assuming that the thermo-optical coefficients of the first terminal resistor 41 and the second terminal resistor 42 are the same and t The first terminal resistor 41 and the second terminal resistor 42 generate a thermal optical phase shift due to the heat generated by the applied voltage. and It can be written as:

[0048] ;

[0049] In addition, the phase difference between the upper modulation arm and the lower modulation arm due to process or other factors is recorded as , then the phase difference between the upper modulation arm and the lower modulation arm is It can be written as:

[0050] ;

[0051] by represents the input optical power of the Mach-Zehnder modulator. According to the relationship between the output optical power of the Mach-Zehnder modulator and the input optical power and the phase difference between the upper modulation arm and the lower modulation arm, the output optical power P The bias voltage of the upper and lower modulation arms and The relationship can be written as:

[0052] ;

[0053] At the same time, according to the definition of half-wave voltage, the half-wave voltage of the upper modulation arm With coefficient The relationship between the lower modulation arm and the half-wave voltage With coefficient The relationship is:

[0054] ;

[0055] Therefore, we get and The value of the half-wave voltage of the upper modulation arm can be obtained The half-wave voltage of the lower modulation arm .

[0056] In order to get and , you can perform the following test steps:

[0057] 1. Maintain input optical power A bias voltage is applied to the upper and lower modulation arms. and .

[0058] Adjust the voltage of the upper modulation arm and the lower modulation arm so that and ,in represents the bias voltage, Represents the voltage difference between the upper modulation arm and the lower modulation arm. At this time, the phase difference between the upper modulation arm and the lower modulation arm is recorded as , the output optical power is recorded as , then we can get:

[0059] ;

[0060] First control =0, and by adjusting the first phase shifter 51 and the second phase shifter 52, the output optical power of the Mach-Zehnder modulator is adjusted to the orthogonal bias point, that is, satisfying .

[0061] Then control It is a series of smaller voltage values, such as 0 to 1V, with an interval of 0.1V. At this time, the phase difference between the two arms is And the output optical power Only with Related, that is:

[0062] ;

[0063] In each A corresponding value, we can get a series of . Combined with known The values ​​of these Can be converted to ,Right now:

[0064] ;

[0065] Then at this time and The fitting coefficients A, B and C can be obtained by polynomial fitting, that is:

[0066] ;

[0067] but and t It can be calculated by the fitting coefficient, namely:

[0068] ;

[0069] 2. Similarly, adjust the voltage of the upper modulation arm and the lower modulation arm to make and , first control =0, and by adjusting the first phase shifter 51 and the second phase shifter 52, the Mach-Zehnder modulator is adjusted to the orthogonal point, that is, ; then control is a series of smaller voltage values, such as 0 to 1V, with an interval of 0.1V. At this time, the phase difference between the upper modulation arm and the lower modulation arm is recorded as , the output optical power is recorded as , we can get:

[0070] ;

[0071] Likewise, each The corresponding Convert to , fitting yields:

[0072] ;

[0073] Can get The value of .

[0074] 3. According to and Calculate the half-wave voltage of the upper modulation arm and the lower modulation arm and .

[0075] 4. Then the average value can be calculated to obtain the half-wave voltage of the Mach-Zehnder modulator . The harmonic mean can be used to calculate , that is:

[0076] .

[0077] Further, based on the above-mentioned test method for the half-wave voltage of the Mach-Zehnder modulator, the half-wave voltage of the Mach-Zehnder modulator is calculated. ; Calculate the modulation efficiency of the Mach-Zehnder modulator as ,in L is the modulation length of the Mach-Zehnder modulator.

[0078] Figure 2 is a set of test data of the present invention, each data point corresponds to a The ratio of the output optical power to the input optical power of the Mach-Zehnder modulator measured under V, modulation length L=0.3cm.

[0079] Figure 3 Yes Figure 2 After further processing of the test data, the vertical axis is transformed into and , the dotted line represents the fitting curve obtained by polynomial fitting.

[0080] The results of polynomial fitting are:

[0081] y=-0.0084x2-0.608x+1.5559 and y=-0.0217x2+0.5674x+1.5574;

[0082] We can get:

[0083] ;

[0084] V;

[0085] ;

[0086] V;

[0087] V;

[0088] The modulation efficiency of the Mach-Zehnder modulator is V·cm.

[0089] Although the present invention has been specifically shown and described in conjunction with the preferred embodiments, it should be understood by those skilled in the art that various changes may be made to the present invention in form and details without departing from the spirit and scope of the present invention as defined by the appended claims, all of which are within the scope of protection of the present invention.

Claims

1. A method for testing the half-wave voltage of a Mach-Zehnder modulator, the Mach-Zehnder modulator comprising a beam splitter (1), an upper modulation arm, a first terminal resistor (41), a first phase shifter (51), a lower modulation arm, a second terminal resistor (42), a second phase shifter (52) and a beam combiner (6); a first output end of the beam splitter (1) is electrically connected to a first input end of the beam combiner (6) through the upper modulation arm and the first phase shifter (51) in sequence, and a second output end of the beam splitter (1) is electrically connected to a second input end of the beam combiner (6) through the lower modulation arm and the second phase shifter (52) in sequence; the upper modulation arm is electrically connected to the first terminal resistor (41), the lower modulation arm is electrically connected to the second terminal resistor (42), and the first terminal resistor (41) is electrically connected to the second terminal resistor (42), characterized in that: The half-wave voltage testing method comprises the following steps: Step 1: Control the input optical power from the beam splitter (1) is a fixed value, and the output optical power of the Mach-Zehnder modulator is adjusted to half of the maximum value of the output optical power by adjusting the first phase shifter (51) and / or the second phase shifter (52); Step 2 includes the following sub-steps: 2.1, apply voltage values ​​to the upper modulation arm and the lower modulation arm respectively and ; At this time, the electro-optical phase shift generated by the upper modulation arm and voltage value relationship, and the electro-optical phase shift produced by the lower modulation arm and voltage value The relationship is expressed as follows: ； and are the electro-optic phase shift coefficients of the upper modulation arm and the lower modulation arm respectively; 2.2 Calculation and The value of each voltage adjustment or The output optical power of the Mach-Zehnder modulator is measured at the same time and recorded as P ; , multiple groups of output optical powers are fitted by polynomials to obtain and The value of in, t is the thermo-optical coefficient of the first terminal resistor (41) and the second terminal resistor (42), The electro-optic phase shift generated by the upper modulation arm The electro-optic phase shift produced by the lower modulation arm The phase difference, The phase difference between the upper modulation arm and the lower modulation arm due to process factors; Half-wave voltage of upper modulation arm , ; Half-wave voltage of lower modulation arm , ; Step 3: Calculate the half-wave voltage of the Mach-Zehnder modulator : 。 2. The method for testing the half-wave voltage of a Mach-Zehnder modulator according to claim 1, characterized in that: The upper modulation arm comprises a first ground electrode (21), a first signal electrode (31), and a first waveguide arranged between the first ground electrode (21) and the first signal electrode (31); a first output end of the beam splitter (1) is connected to a first input end of the beam combiner (6) via the first waveguide and a first phase shifter (51) in sequence; and the first signal electrode (31) is electrically connected to a first terminal resistor (41); The lower modulation arm comprises a second ground electrode (22), a second signal electrode (32), and a second waveguide arranged between the second ground electrode (22) and the second signal electrode (32); the second output end of the beam splitter (1) is connected to the second input end of the beam combiner (6) via the second waveguide and the second phase shifter (52) in sequence; and the second signal electrode (32) is electrically connected to a second terminal resistor (42).

3. The method for testing the half-wave voltage of a Mach-Zehnder modulator according to claim 1, characterized in that: The first terminal resistor (41) and the second terminal resistor (42) have the same resistance value.

4. A method for testing the modulation efficiency of a Mach-Zehnder modulator, characterized in that: The Mach-Zehnder modulator half-wave voltage is calculated by using the test method of the Mach-Zehnder modulator half-wave voltage according to claim 1, 2 or 3. ; The modulation efficiency of the Mach-Zehnder modulator is calculated as ,in L is the modulation length of the Mach-Zehnder modulator.

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